Industrial Photoinitiators

The most important radical photoinitiators applications and relevant topics

Jean-Luc Birbaum

Consortium Meeting Mainz 15102019

Prologue

J-L Birbaum 2

ldquoLightacts chemically on substances [hellip]

It is absorbed it combines with themhellip it even solidifies

them and makes them more or less insoluble according to

the duration or the intensity of its action This is in short the

principle of my discoveryrdquo

JN Nieacutepce Notice sur lrsquoHeacuteliographie

1829

The same year the German chemist August Kekuleacute is born

He will identify the chemical structure of benzene in 36 years

Photopolymerization vision of a

new technology

The invention of photolithography

J-L Birbaum 3

The worldrsquos oldest lsquophotocopyrsquo

obtained by Nieacutepce in 1825

Bought for euro 450rsquo000 by the French National

Library in 2002

Sunlight

Bitumen of Judea the first photoresist

Copper plate

Exposure

through mask

Development

by lavender oil

Etching

by acid

crosslinked

bitumen

Modern restart of radiation curing

4J-L Birbaum

After 100 years Sleeping Beauty woke up

in the 1940rsquos with the first photoinitiator patents

Illustration by G Doreacute (1867)

US 2rsquo406rsquo878 (1946) Interchemical Co

first UV-curable printing ink

US 2rsquo423rsquo520 (1947) DuPont

solution photopolymerization of styrene MMA etc

Attractive features of radiation curing

5J-L Birbaum

Time

Vis

cosity

Thermally curable formulation

shelf life few days at RT

UV-curable formulation

several months in the dark

UV light

Long shelf life in the dark

No light no viscosity increase

Fast cure after UV irradiation

Spatial control by imaging

through mask

No light no curing

Cure on demand control of time and space

Photoresist for printed circuit

boards

Added bonus no VOC

Contents

6

1 Basic photochemistry

Types of photoinitiators

Excited states and the generation of active radicals

2 Most important radical initiators

Spectral characteristics pros and cons uses

3 Selected topics of interest

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration emissions and the law

Water soluble photoinitiators

4 Conclusion

J-L Birbaum

times Cationic photoinitiators

times Photolatent bases

times Radical specialties for microelectronics

Out of scopeOslash

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Prologue

J-L Birbaum 2

ldquoLightacts chemically on substances [hellip]

It is absorbed it combines with themhellip it even solidifies

them and makes them more or less insoluble according to

the duration or the intensity of its action This is in short the

principle of my discoveryrdquo

JN Nieacutepce Notice sur lrsquoHeacuteliographie

1829

The same year the German chemist August Kekuleacute is born

He will identify the chemical structure of benzene in 36 years

Photopolymerization vision of a

new technology

The invention of photolithography

J-L Birbaum 3

The worldrsquos oldest lsquophotocopyrsquo

obtained by Nieacutepce in 1825

Bought for euro 450rsquo000 by the French National

Library in 2002

Sunlight

Bitumen of Judea the first photoresist

Copper plate

Exposure

through mask

Development

by lavender oil

Etching

by acid

crosslinked

bitumen

Modern restart of radiation curing

4J-L Birbaum

After 100 years Sleeping Beauty woke up

in the 1940rsquos with the first photoinitiator patents

Illustration by G Doreacute (1867)

US 2rsquo406rsquo878 (1946) Interchemical Co

first UV-curable printing ink

US 2rsquo423rsquo520 (1947) DuPont

solution photopolymerization of styrene MMA etc

Attractive features of radiation curing

5J-L Birbaum

Time

Vis

cosity

Thermally curable formulation

shelf life few days at RT

UV-curable formulation

several months in the dark

UV light

Long shelf life in the dark

No light no viscosity increase

Fast cure after UV irradiation

Spatial control by imaging

through mask

No light no curing

Cure on demand control of time and space

Photoresist for printed circuit

boards

Added bonus no VOC

Contents

6

1 Basic photochemistry

Types of photoinitiators

Excited states and the generation of active radicals

2 Most important radical initiators

Spectral characteristics pros and cons uses

3 Selected topics of interest

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration emissions and the law

Water soluble photoinitiators

4 Conclusion

J-L Birbaum

times Cationic photoinitiators

times Photolatent bases

times Radical specialties for microelectronics

Out of scopeOslash

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

The invention of photolithography

J-L Birbaum 3

The worldrsquos oldest lsquophotocopyrsquo

obtained by Nieacutepce in 1825

Bought for euro 450rsquo000 by the French National

Library in 2002

Sunlight

Bitumen of Judea the first photoresist

Copper plate

Exposure

through mask

Development

by lavender oil

Etching

by acid

crosslinked

bitumen

Modern restart of radiation curing

4J-L Birbaum

After 100 years Sleeping Beauty woke up

in the 1940rsquos with the first photoinitiator patents

Illustration by G Doreacute (1867)

US 2rsquo406rsquo878 (1946) Interchemical Co

first UV-curable printing ink

US 2rsquo423rsquo520 (1947) DuPont

solution photopolymerization of styrene MMA etc

Attractive features of radiation curing

5J-L Birbaum

Time

Vis

cosity

Thermally curable formulation

shelf life few days at RT

UV-curable formulation

several months in the dark

UV light

Long shelf life in the dark

No light no viscosity increase

Fast cure after UV irradiation

Spatial control by imaging

through mask

No light no curing

Cure on demand control of time and space

Photoresist for printed circuit

boards

Added bonus no VOC

Contents

6

1 Basic photochemistry

Types of photoinitiators

Excited states and the generation of active radicals

2 Most important radical initiators

Spectral characteristics pros and cons uses

3 Selected topics of interest

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration emissions and the law

Water soluble photoinitiators

4 Conclusion

J-L Birbaum

times Cationic photoinitiators

times Photolatent bases

times Radical specialties for microelectronics

Out of scopeOslash

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Modern restart of radiation curing

4J-L Birbaum

After 100 years Sleeping Beauty woke up

in the 1940rsquos with the first photoinitiator patents

Illustration by G Doreacute (1867)

US 2rsquo406rsquo878 (1946) Interchemical Co

first UV-curable printing ink

US 2rsquo423rsquo520 (1947) DuPont

solution photopolymerization of styrene MMA etc

Attractive features of radiation curing

5J-L Birbaum

Time

Vis

cosity

Thermally curable formulation

shelf life few days at RT

UV-curable formulation

several months in the dark

UV light

Long shelf life in the dark

No light no viscosity increase

Fast cure after UV irradiation

Spatial control by imaging

through mask

No light no curing

Cure on demand control of time and space

Photoresist for printed circuit

boards

Added bonus no VOC

Contents

6

1 Basic photochemistry

Types of photoinitiators

Excited states and the generation of active radicals

2 Most important radical initiators

Spectral characteristics pros and cons uses

3 Selected topics of interest

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration emissions and the law

Water soluble photoinitiators

4 Conclusion

J-L Birbaum

times Cationic photoinitiators

times Photolatent bases

times Radical specialties for microelectronics

Out of scopeOslash

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Attractive features of radiation curing

5J-L Birbaum

Time

Vis

cosity

Thermally curable formulation

shelf life few days at RT

UV-curable formulation

several months in the dark

UV light

Long shelf life in the dark

No light no viscosity increase

Fast cure after UV irradiation

Spatial control by imaging

through mask

No light no curing

Cure on demand control of time and space

Photoresist for printed circuit

boards

Added bonus no VOC

Contents

6

1 Basic photochemistry

Types of photoinitiators

Excited states and the generation of active radicals

2 Most important radical initiators

Spectral characteristics pros and cons uses

3 Selected topics of interest

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration emissions and the law

Water soluble photoinitiators

4 Conclusion

J-L Birbaum

times Cationic photoinitiators

times Photolatent bases

times Radical specialties for microelectronics

Out of scopeOslash

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Contents

6

1 Basic photochemistry

Types of photoinitiators

Excited states and the generation of active radicals

2 Most important radical initiators

Spectral characteristics pros and cons uses

3 Selected topics of interest

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration emissions and the law

Water soluble photoinitiators

4 Conclusion

J-L Birbaum

times Cationic photoinitiators

times Photolatent bases

times Radical specialties for microelectronics

Out of scopeOslash

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

7J-L Birbaum

Basic photochemistry

1

Two main types of photoinitiators

Excited states and the generation of active radicals

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Basic Photochemistry type I

8J-L Birbaum

RC

OC

O

RRC

O

+

T

excited photoinitiator

UV light

2 initiating free radicals

Type I = Cleavage type unimolecular bond cleavage upon

irradiation

Main mechanism is cleavage of a-bond (next to C=O)

Minor mechanism is cleavage of b-bond

S C

O

N O

S C

O

C N O

S C O

C N O

+

GA Rist et al Macromolecules 1992 25 4182

O

Cl

Cl

Cl

Important for

a-haloketones

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Fast photocleavage from the triplet state

9J-L Birbaum

IC Internal Conversion (non radiative)

ISC Inter-System Crossing

Flu

ore

sce

nce

Energy

kISC

ISCkIC

S0

S1

T1Initiating radicals via

C-C bond cleavagekcleavage

The same triplet state T1 (np or pp) is populated and the same triplet photochemistry

takes place independently of the excitation wavelength

The rate constants kisc and kcleavage are very fast and compete efficiently with fluorescence

phosphorescence and radiationless deactivation in typical photoinitiators

Example for BAPO kisc = 8 times109 s-1 and kcleavage = 1010 s-1 (J Am Chem Soc 2002 124 14952)

Polymer

reaction with O2

disproportionation

recombination

rearrangement

Quenching(by O2 or monomer)

By-products

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Basic Photochemistry type II

10J-L Birbaum

Type II = Abstraction type bimolecular reaction of excited

photoinitiator with coinitiator needed for radical generation

Two mechanisms

With tertiary amines electron transfer followed by hydrogen transfer

With other H-donors direct hydrogen transfer

1 initiating

free radical

inactive

charge transfer

exciplex

H-

transferUV light

inactive

(dimerizes)

electron

transfer

no cleavage

C

O

OC

N

H

R

R

R

COH N

R

R

R

N

H

R

R

R

CO

T

+ +

T

C O H

Donorketyl

radical +

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Special case of type IIPhenylglyoxylates

11J-L Birbaum

C

O

C

O

O

H

C

O

C

O

O CH3

O

H

C

OH

C

O

O CH3

O

- CH2O

- CO

C

O

C

O

O CH3

C

OH

C

O

O CH3

C

O

C

O

O CH2

C

C

O

OHCH

2O

T

C

O

C

O

O

CH2

H

C

O

h

H-donor(eg ether acrylate)

+

dimerization

+

+

initiation

dimerization initiation

initiation

(at high initiator conc)

-Habstraction

Some benzoyl radicals formed

but not by direct a-cleavage

DCNeckers et al Macromolecules 2000 33 4030

Norrish II

Darocur MBF

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

The efficiency of a photoinitiator is the result of a chain of events

12J-L Birbaum

A high absorption in the near UV (good match with the emission spectrum of the light

source is desirable

For a given chromophore substituent effects (electron donating or withdrawing) can tune

the absorption spectrum of the photoinitiator

However red-shifting can affect the spectroscopic nature of the triplet state (for instance

from np to pp) and reduce the efficiency of photocleavage

Efficiency of

light absorption

Overall

efficiency of

photoinitiator

Efficiency of

radical generation

Reactivity of

generated radical=

Absorbance

extinction molar

coefficient e at l

Quantum yield of triplet

formation and photocleavage

fISC fcleavage

Addition constant to

monomer kA

Not independent from each other

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

A red-shifted absorption is not always beneficial

13J-L Birbaum

photoinitiatorlmax

(nm)t T (ns) F cleavage

triplet

naturekadd (M-1∙ s -1)n-butylacrylate

Darocur 1173

243 037 038 np 27∙105

Darocur 2959

273 12 029 nppp 35∙105

302 7rsquo000 001 pp 55∙105

335 12rsquo000 003 pp(41∙105)4-morpholino

S Jokusch F Landis N Turro Macromolecules 2001 34 1619

C S Colley et al J Am Chem Soc 2002 124 14952

13∙107

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

14J-L Birbaum

Most important radical

photoinitiators

2

Spectral characteristics pros and cons uses

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Absorption range of main classes of photoinitiators

15J-L Birbaum

Absorbance

c = 01 in acetonitrile

0

02

04

06

08

1

12

14

16

300 350 400 450 500 550Wavelength (nm)

a-Aminoketones

Acylphosphine oxides

Titanocenes and specialties

a-Hydroxyketones

Clear formulations and surface cure

Pigmented formulations

Pigmented and white formulations

Type II Initiators(benzophenones and thioxanthones)

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Spectral overview of commercial Type I products

16J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

c = 0001 in acetonitrile

C

O

OH

OHO C

O

O H

S C

O

N O

N C

O

NO

C

O

P

O

C

O

BAPO

Irgacure 369

Irgacure 907

Daroccur 2959

Daroccur 1173

c = 001

N

F

F

N

F

F

Ti

Irgacure 784

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Main photoinitiatorsfor clear coats and surface cure (1)a-Hydroxyketones phenylglyoxylate benzilketal

17J-L Birbaum

Compound Darocur 1173 Irgacure 184 Irgacure 2959 Darocur MBF Irgacure 651

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 7473-98-5 947-19-3 106797-53-9 15206-55-0 24650-42-8

Properties liquid good solvent

properties good for

blends with other

photoinitiators

efficient surface cure

Volatile

low yellowing

medium volatility

highly efficient

surface cure

low yellowing low

odor low volatility

low migration FDA

approval for indirect

food contact

(adhesives)

(type II initiator)

liquid good surface

cure low emission

low residual odor

low yellowing after

cure

extremely short tT

yellowing after

curing

Applications clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal and

plastics co-initiator

in pigmented

systems

clear top-coats for

paper metal

plastics also in

waterbased

UV dispersions

floor coatings wood

parquets furniture

plastic metal

coatings

flexo printing

plates fillers and

topcoats based on

UPESstyrene

C

O

OHOH

O C

O

O H

OOH

O

O

OOO

O

200 250 300 350 400 200 250 300 350 4000

05

1

15

200 250 300 350 400 200 250 300 350 400 200 250 300 350 400

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Main photoinitiatorsfor clear coats and surface cure (2)Dimeric a-Hydroxyketones phenylglyoxylate

18J-L Birbaum

Compound Irgacure 127 Esacure ONE Esacure KIP 160 Irgacure 754

Structure

+30 monoester

Spectrum

005

0001

in CH3CN

CAS Regno 474510-57-1 163702-01-0 71868-15-0211510-16-6

442536-99-4

Properties high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

after curing

high reactivity low

sensitivity to

oxygen inhibition

low

emissionmigration

after curing

high reactivity low

sensitivity to oxygen

inhibition low

emissionmigration

can show some

yellowing after cure

very good surface

cure low emission

low residual odor

lowest yellowing

after cure

Applications pigmented UV-inks

thin clear lacquers

food packaging

thin clear lacquers

food packaging

pigmented UV-inks

thin clear lacquers

food packaging

clear coats PVC

floors wood

parquetsfurniture

O

OH

O

OH

0

05

1

15

200 250 300 350 400

C

O

OH

C

O

OH

200 250 300 350 400 200 250 300 350 400

O

OH

O

OH

O

O

O

O

O

O

O

O

200 250 300 350 400

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Main photoinitiators for pigmented systemsa-Aminoketones

19J-L Birbaum

Compound Irgacure Omnirad 907 Irgacure Omnirad 369 Irgacure Omnirad 379

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 71868-10-5 119313-12-1 119344-86-4

Properties White to light beige powder

rel high volatility

toxicity labeling H360

light yellow powder limited

solubility

Good through-cure of

pigmented formulations

light yellow powder much

better solubility than lsquo369rsquo

Good through-cure of

pigmented formulations

Applications for pigmented systems

photoresists (printed circuit

boards)

for pigmented systems

photoresists and printing

plates

for pigmented systems

photoresists and printing

plates

N C

O

NO N C

O

NO

S C

O

N O

200 250 300 350 400 450200 250 300 350 400 4500

05

1

15

200 250 300 350 400 450

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Main photoinitiatorsfor white and pigmented systems Acylphosphinoxides (MAPO and BAPO)

20J-L Birbaum

Compound Lucirin Omnirad TPO Lucirin Omnirad TPO-L Irgacure Omnirad 819

Structure

Spectrum

005

0001

in CH3CN

CAS Regno 75980-60-8 84434-11-7 162881-26-7

Properties low yellowing low odor

good solubility lower through-

cure performance thanrsquo819rsquo

bleaching high O2 sensitivity

liquid easy to incorporate

low yellowing bleaching

good through-cure high O2

sensitivity

low odor low volatility

photosensitivity at longer l

bleaching excellent through-

cure high O2 sensitivity

Applications Pigmented systems white

systems fibre-reinforced

coatings LED curing

White systems LED curing Pigmented systems white

systems fibre-reinforced

coatings LED curing

PC

OOPO

OO

P

O

C

O

C

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Main Type II PhotoinitiatorsBenzophenones thioxanthones etc

21J-L Birbaum

Compound Benzophenone Camphorquinone ITX CPTX Esacure 1001

Structure

Spectrum

005

0001

in CH3CN(MeOH for

CPTX)

CAS Regno 119-61-9 10373-78-1 5495-84-1 142770-42-1 272460-97-6

Properties very good surface

cure

Banned from food

packaging by Nestleacute

Absorbs in the

visible range direct

abstraction of H

from amines

Through-cure

sensitizer for Type I

PI Banned from

food pack by Nestleacute

Absorption into the

visible Sensitizer

Cl radicals formed

by photocleavage

Mixed Type II and I

(b-cleavage)

Through-cure and

surface cure

Applications General low cost in

combination with

amine synergists

Dental applications Printing inks resists

LED cure

cationics banned

from food packaging

Photoresists

cationic formulations

Pigmented

systems

O

O

O

0

05

1

15

200 250 300 350 400 450 200 250 300 350 400 450 200 250 300 350 400 450

S

O

S

OCl

O S

O

S

O

O

O

200 250 300 350 400 450

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

22J-L Birbaum

Selected topics

3

Absorption vs penetration surface cure and through-cure

laquoBleachingraquo photoinitiators conventional lamps vs LED

Photocleavage products migration polymeric photoinitiators

Water solubility of photoinitiators

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Light absorption in solutionLambert-Beer law

23J-L Birbaum

c e

II0

lI = I0 10-e c l

Absorbance A = e c l = -log II0

Transmission T = I I0

A = -log T

Absorbed light = Ia = I0 ndash I = I0 middot(1-10-e c l)

e depends on the wavelength e = e(l)

e(l) is characteristic of the electronic and optical properties

of the chromophore

Assumptions no reflection no scattering diluted solution

e molar extinction coefficient of the

dissolved substance (L mol-1 cm-1)

c concentration of the solution (mol L)

l path length (cm)

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Absorption spectrum of Irgacure 369 and overlap with emission of Hg lamp

24J-L Birbaum

0

02

04

06

08

1

200 250 300 350 400 450 500

Irgacure 369

N C

O

N

CH3

CH3

CH3

O

313 nm 366 nm

e (313nm) = 19900

e (366nm) = 1100

A

wavelength (nm)

c = 0001 = 273 x 10-5 molL

l = 1 cm

emission spectrum of medium pressure Hg lamp (arbitrary units)

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Through-cure and surface cure with a single photoinitiator at two wavelengths

25J-L Birbaum

The photoinitiator has large differences of e at main wavelengths of Hg lamp

Since light penetration varies with wavelength production of radicals also varies with depth

Concentration of radicals ~ fRmiddotIa

At 313nm good surface cure

At the same time good throughcureat 366 nm

In practice a mixture of several photoinitiators may be superior to a single one at the same overall loading 0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

e (313nm) = 19900

e (366nm) = 1100

Ra

dic

al co

nce

ntr

ation

(a

rbitra

ry u

nits)

2 Irgacure 369

0

02

04

06

08

1

200 250 300 350 400 450 500

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

0 20 40 60 80 100

Effect of concentrationon light penetration at single wavelength

26J-L Birbaum

0

50

mm

25

0

50

mm

25

0

50

mm

25

2

02

1

Example Irgacure 369 at 313 nm in a 50 mm clear coat

conc

Good surface cure no bottom cure1 absorbed

by bottom half

68 absorbed

by top 5 mm

total absorption

682

11 absorbed

by top 5 mm

5 absorbed

by bottom half

44 absorbed

by top 5 mm

Fair surface cure poor bottom cure

Poor surface cure good bottom cure

Relative absorption ()

Assuming no competitive absorption from formulation and e = 19900 at 313 nm

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

The challenge of through-cure under LED light Bleaching photoinitiators

27J-L Birbaum

0

20

40

60

80

100

5 10 15 20 25 30 35 40 45 50

coating depth (mm)

313 nm

366 nm

Rad

ical co

nce

ntr

ation 2 Irgacure 369

medium pressure Hg lamp

0

02

04

06

08

1

200 250 300 350 400 450 500

LED UV-A Nichia NSHU550E

Emax 375 nm

wavelength (nm)

Irg 369

A good balance of surface cure and through-cure

requires in principle differential absorbance at 2

wavelengths (polychromatic light)

LED have a narrow emission spectrum therefore

little differential absorbance over the range

overlapping with the photoinitiator sensitivity

Option I use a combination of LED of 2 different wavelengths (eg 365 and 395 nm)

Option II use a bleaching photoinitiator

The chromophore of a bleaching photoinitiator is destroyed during radical generation

this results in an absorbance loss and allows light penetration in the deeper layers

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Bleaching photoinitiatorsBAPO under irradiation

28J-L Birbaum

0

02

04

06

08

325 350 375 400 425 450

Wavelength (nm)

Ab

so

rban

ce

CM

O

P MM

O

PM C

OO

O

CO R

C M

O

C

O

P C

OO

O

CO R

h

m

h

n n o p+ +

( m + n ) ( o + p )

The chromophore of a bleaching

photoinitiator is destroyed during

radical generation this results in

a decrease of absorbance with

time and allows light penetration

in the deeper layers

Curing in the presence of white

colored pigments or UV absorber

Curing of glass fiber reinforced

coatings and thick layers

Wavelength-dependent photo-

chemistry allows synthesis of

diblock copolymers

h lt410nm

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Use of bleaching photoinitiators in pigmented formulations

29J-L Birbaum

0

02

04

06

08

1

12

240 280 320 360 400 440 480

0001

TiO2

005

Ab

so

rban

ce

Irgacure 819

Lucirin TPO

In pigmented formulations (especially white) most of the UV light is

absorbed by the pigment The only light available is in the visible

range

However photoinitiators absorbing blue light are necessary yellow

The solution is to use a yellow photoinitiator that will bleach after

doing the job

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Present options for LED curing

30J-L Birbaum

Acylphosphine oxidesPros Cons

PC

OO

C

O

P

O

C

O

PO

OO

Thioxanthones

Excellent through-cure

Good spectral overlap

with 385 and 395 nm

LED

Photobleaching low YI

Slow surface cure

High oxygen inhibition

S

O

S

O

S

O

O

Cl

TPO TPO-L BAPO

ITX DETX CPTX Acceptable surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Ban in food packaging

O

NN

Benzophenones

O

NN

Michlerrsquos ketone EMK Excellent surface cure

Good spectral overlap

with 385 and 395 nm

LED

Limited through-cure

No photobleaching

high YI

Human carcinogens

Typical surface cure photoinitiators a-hydroxyketones have poor spectral overlap with LED

Poor surface cure not only impacts mechanical and chemical resistance but also causes migration

and odor problems due to incomplete crosslinking

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Other bleaching chromophoressuitable for LED curing

31J-L Birbaum

SP h C

O

R

N O

OP h

SP h C

O

R

N O P h

O

SP h C O

Oxime esters (Irgacure OXE01)

Commercially available only for electronic applications but several patents

filed by Agfa for LED UV printing (captive use)

J Finter et al Makromol Chem

Makromol Symp 1989 24177

+ CO2 +RCN + Ph

Titanocenes (Irgacure 784)

Visible photoinitiator must be

handled under red light

N

F

F

N

F

F

Ti

Arylglyoxylates (MBF Irgacure 754)

Bleaching expected but not well investigated

Several patent applications on derivatives

suitable for LED curing

O

O

OR

R

C O

R

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Neutral by-products of photocleavage cause unwanted emissions

32J-L Birbaum

Example Irgacure 184

polymerization

OOH

C O

OR

O

OR

O

O

OR

O

OR

O

OR

O

OR

OOH

OR

OOH

OOR

O

H

O

C

C

C

C

OR

O

O

ORO

OH

C

polymerization

volatility of unreacted initiator

Benzaldehyde

Cyclohexanone

Desired chemistry Main by-products

High mw (unproblematic)

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Emission migration and set-off

33J-L Birbaum

Mobile

soluble

neutral

breakdown

products from

photoinitiator

Volatile

Set-off

Transfer by contact

Emission Release into air

Printing amp Packaging

photoinitiator Migration Contamination

of food by diffusion through

substrate

Furniture amp Flooring

Food

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Legislation pressure on photoinitiators for sensitive applications is growing

34J-L Birbaum

Emissions of some photocleavage products are regulated

France Regulation 2011-321

(introduced 01012012)

Limit values for 10 VOC released

by construction materials

Germany Introduction of LCI (Lowest

Concentration of Interest) as the

maximum permissible emission of a

given volatile organic compound (2010)

In addition IKEA guidelines forthcoming EU legislation etc hellip

Migration (Printed substrates)

EU Commission Regulation 102011Only food packaging legislation in Europe with a detailed description of migration test conditions

how to determine OML and SML values In principle only for plastics

Swiss Ordinance SR 81702321First legislation in Europe regulating ingredients of food packaging inks as non-plastic food

contact materials Inventory list (appendix 10) consisting of part A (complete risk assessment

data available) and part B (incomplete data migration limit 001 mgkg)

Exclusion list based on Swiss OrdinanceEuropean Printing Association

Positive list based on Swiss Ordinance

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Why waterborne formulations

35J-L Birbaum

In dispersions the viscosity is independent of the molecular weight of

the resin only governed by particle size and particle concentration

Thinning with water lowers viscosity enough for spraying applications

and UV curing removes the drawbacks of traditional dispersions

poor chemical and blocking resistance

Applying thin low-weight coatings onto metal or plastics by spraying

or dipping become possible

But water must be removed from coatings prior to UV cure and

therefore photoinitiators must be non steam-volatile

So does adding an extra drying step makes sense

mw

viscosity

polymer solution

dispersion

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Industrial applications of waterborne formulations

36J-L Birbaum

Wood coatings first market to adopt waterborne PUD

‒ laquo100 solidsraquo UV formulations can soak into the wood Uncured components

can migrate during lifetime of substrate

‒ Mat varnishes work best with some volumetric shrinkage

Coating with matting agent

Dried and cured good matting

Evaporation

(H2O)

only slight shrinkage more gloss

UVdrying

+ UV

Metal and plastic coatings applied by spraying or dipping

‒ Viscosity of 100 systems too high

Digital water-based UV inkjet

‒ Viscosity very important But water-soluble photoinitiators for pigmented inks

are needed

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Comparison of photoinitiators in aqueous emulsions and dispersions

37J-L Birbaum

UV cure (Hg lamp) after drying at 80degC The uncured films (20 mm) are clear

Higher conversions from lsquoemulsionsrsquo due to greater molecular mobility in the soft low-

modulus polymer formed lsquoDispersionsrsquo yield harder polymers with lower conversion

C Decker and I Lorinczova JCT Research 2004 1 247

D-1173 Esa KIP I-2959 TPO-L I-819DW

D-1 70 80 84 68 68

D-2 49 52 52 50 56

D-3 32 42 40 45 40

E-1 100 99 100 100 98

E-2 78 73 81 77 79

Acrylate conversion () after one pass 5mmin

Dis

pe

rsio

ns

Em

uls

ions

D-1 Laromer 8949

D-2 Laromer 8983

D-3 Laromer 9005

E-1 Laromer PE55W

E-2 Laromer PE-22WN

Esacure KIPEM-1

water-dispersed

[photoinitiator] = 1

D-1

-1

RTIR profiles for UV curing of water-based

acrylate resins at 80degC

[ICU 819 DW] = 1 wt I = 200 mW cmndash2

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Water-based formulations and the solubility of photoinitiators

38J-L Birbaum

Irgacure 2959 has the highest solubility among usual photoinitiators

but still somewhat limited to ca 1

Low mw oil soluble photoinitiators can be incorporated using high

speed stirring Liquids respond much better than solids Omnirad 1000 (mixture of D-1173 and ICU-184

Speedcure BEM (mixture BP and MBP)

Irgacure 754 Darocur MBF

Irgacure 2100 (Mix TPO-LBAPO)

Examples

But water-soluble (~ 5) photoinitiators would be preferred

especially for UV inkjet where water-dispersed photoinitiators

are not adequate

S

N+

OH

O

Cl

Type II initiator solubility ca 20 (Great Lakes)

formerly commercial but not successful

Quantacure QTX

There is a need for mid-UV high speed photoinitiators that are

compatible with WB formulations

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Coming soon Water soluble BAPO derivatives

39J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P C

OO

CO

O

O

N a+

h

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Coming soon Water soluble BAPO derivatives

40J-L Birbaum

Chemistry developed at Ciba BASF ETH

Will it be commercialized by IGM

Polymerization of styrene in a continuous flow reactor snowballing

radical generation leads to ultrahigh mw polymers

C P C

OO

CO

O H

O

C

O

P

O

C

O

OH

C P

O

C

OOO

N a+

BAPO-AA BAPO-POH BAPO-PONa

acceptable solubility in H2O high solubility in H2O

C P

O

CO

O

O

styrene

h

styrene

styrene

P Laurino et al Macromol Rapid Commun 2012 1770

head to head

P

O

O

O

n

C O

+

P

O

O

O

O

n

n

+P

O

O

O

On

m

n

P

O

O

O

m

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

New photochemistry of BAPO derivatives in aqueous media

41J-L Birbaum M Schmallegger et al Chem Eur J 2019 25 8982

Photolysis of BAPOs in the presence of water or alcohols generates a new delocalized p-radical

which does not participate in the polymerization It either converts into a MAPO acting as a

secondary photoactive species or works as a one-electron reducing agent

C P O

R

OC

O C4

H9

O

C P

O

R

O

C P

O

R

O H

O R

C N

N C

N C

C N

C P

O

R

O

O R C P

O

R

O

O R

C O

P O

R

R O

R O Hm o n o m e r

( B A )

- e- H +

T C E -+

n ( B A )

h h

+

- H

polymerization

secondary

polymerization

electron transfer manifold

radical manifold

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

42J-L Birbaum

Summary

4

Conclusion

Bibliography

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Conclusion

43J-L Birbaum

High curing performance requires the careful match of all components

of the system the formulation the photoinitiator and the light source

But this is not enough low emission migration and sustainability

become increasingly important

Safety

vs

Sustainability

UV curing

=

Low VOC

Cure speed

vs

Migration

Environment Society

Industry

New products must show an advantage to succeed Creativity is plentiful

Commercialization is difficult The costs of a complex regulatory system

are a high hurdle for innovation

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4

Bibliography

44J-L Birbaum

WA Green (2010) Industrial Photoinitiators a Technical Guide

CRC Press Boca Raton FL

JV Crivello and K Dietliker (1998) Photoinitiators for Free Radical

Cationic amp Anionic Photopolymerization vol 3 of G Bradley (ed)

Chemistry amp Technology of UV amp EB Formulation for Coatings Inks

and Paints 2nd Ed Wiley SITA London

ldquoThree months in the laboratory can save a

couple of hours in the libraryldquo

Nick Turro The Spectrum 2004 17 4