advancements in shorter wavelength led technology and … · · 2017-11-07ebecryl 3700 (epoxy...

Advancements in shorter wavelength LED technology and its impact on UV curing applications.

P.K. Swain, D. Leonhardt, B. Skinner, D. Skinner : Heraeus Noblelight America LLC

RadTech Europe 2017, October 2017,

Agenda

Overview

Experimental set up

Clear Coat chemistries

▪ Irg184, Irg 819

▪ TPO dependence

▪ Peak Irradiance vs. Total Dose vs. multiple narrow bands

▪ LED vs. Broadband

▪ LED vs. ‘Long-wavelength’ Broadband

Recap of prior research

Results and discussions

Summary/Conclusion

P.K. Swain | RadTech | October 2017

Overview/Background


INTRODUCTION

UV Curing has been used for many diverse applications

Until recently, Hg based UV lamps have primarily been utilized

Key Advantages of Hg based lamps:

▪ Mature technology

▪ Fast process speed (higher UV output)

▪ Low cost of ownership

Drawbacks:

▪ High electrical power consumption

▪ Ozone formation

▪ Presence of “Hg”

Status of UV LED Technology


INTRODUCTION

White light LED manufacturing technology has made steady progress

over the past decade

Associated manufacturing technology for UV LEDs have benefited

Some key benefits of LED technology are:

▪ Instant on-off

▪ Hg free

▪ Longer life

▪ Possible lower cost of ownership

UV LEDs have shown significant potential for UV curing applications

Until now, mostly UV-A LEDs have been used for curing applications

Recent emergence of UVC LEDs are expected to bring further

innovation

Basis of Current Research - I


INTRODUCTION

UVLED systems with higher output and flexible working

distance have emerged in the market

Until now, most existing formulations are optimized for

broad band illumination (for Hg based lamps)

Since broad band LED sources are not imminent, special

formulations, optimized for LED output and wavelength

needs to be developed for specific applications

Basis of Current Research - II


INTRODUCTION

Additionally, exact interactions between LED wavelength,

intensity, total dose, formulation’s photo-absorption

property, curing speed etc. need to be carefully considered

for optimum performance

In this paper, we would present the curing effect as a

function of:

▪ (i) LED intensity

▪ (ii) process speed

▪ (iii) total dose

▪ (iv) LED wavelength

Experimental Set Up - LED Lamp

Wavelength, Intensity and Optics

▪ 395 nm

▪ High density LED packaging

▪ High peak irradiance (> 10 W/cm2)

▪ Longer working distance


EXPERIMENTAL

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 120

5

10

15

20

25

30

UV

A2

IR

RA

DIA

NC

E (

W/c

m2)

POSITION (mm)

WORKING

DISTANCE

5mm

7mm

10mm

15mm

25mm

35mm

45mm

55mm

LED LAMP OUTPUT IRRADIANCE

Experimental Set Up - LED Lamp

Wavelength, Intensity and Optics

▪ 275 nm

▪ Low density LED packaging

▪ Low peak irradiance

▪ Short working distance

▪ Higher driving voltages


EXPERIMENTAL

LED LAMP OUTPUT IRRADIANCE Vs. CURRENT

4 cm

Experimental Set Up - Hg based Lamp

Broadband source (LightHammer® 6)

▪ Microwave driven electrode-less

▪ Standard D bulb

▪ Cold reflector (dichroic)

▪ 4 - 6 W/cm2

Standard conveyor (NO N2 inerting)

Substrates

▪ Black and White Leneta cards


EXPERIMENTAL

Experimental Set Up - Lamps

Comparison of custom LED lamp to

high power microwave lamp

(LightHammer® 6)

▪ UVA LED: higher peak irradiance over

smaller area

▪ UVC LED not shown (low scale)

▪ 4 cm spatial width

▪ Microwave lamp: broader spatial

distribution


EXPERIMENTAL

-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 300

5

10

15

20

25

30

UV

A2 IR

RA

DIA

NC

E (

W/c

m2)

POSITION (mm)

LED at focus

LH10 at focus

(13mm bulb)

LH10 at focus

(9mm bulb)

Review – Some Previous Findings (Radtech India 2016)


DATA & ANALYSIS: CLEAR COATS

Significantly different performance

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

60

70

80

90

100

365 nm

385 nm

405 nm

DO

UB

LE

BO

ND

CO

NV

ER

SIO

N (

%)

AVERAGE POWER at substrate (W/cm2)

July2011 data summary.opj - Irg819 comparison

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

60

70

80

90

100

365 nm

385 nm

405 nm

DO

UB

LE B

ON

D C

ON

VE

RS

ION

(%

)

AVERAGE POWER at substrate (W/cm2)

July2011 data summary.opj - Irg184 comparison

Double bond conversion vs. average power

Irg 819 Irg 184Urethane acrylates



200 250 300 350 400 450 500

Irg 819 (4%)

Irg 184 (4%)

385 n

m

405 n

m

385 n

m

PhI A

BS

OR

BA

NC

E (

abs.)

& L

ED

EM

ISS

ION

(re

l.)

WAVELENGTH (nm)

365 n

m

• This can be explained by

photoinitiator curves and

LED spectrum

• Even for 4% Irg 184, only a

small overlap occurs for 365

and 385, but none for 405

nm

• On the other hand, Irg 819

(4%) has good overlap for all

LED wavelengths

• Wavelength and Shape of

the LED emissions curves

matter!





Photon Management is Crucial – for Monochromaic Radiation

Exposure Time

Inte

nsi

ty (

arb

. u

nit

)

Optimum beam Profile

Photo-initiation

Photo-finishing

Photo-initiation

Photo-finishing

0,00

0,25

0,50

0,75

1,00

200 300 400 500 600 700 800In

ten

sit

y,

a.u

.

l, nmSurface cure

Review – RadTech 2015



UVA LED v Broadband Lamp

▪ Higher concentrations of TPO

generally results in better cure when

judged by surface tackiness

▪ Higher viscosity urethanes cured

better with high intensity (25 W/cm2)

LED lamps performed better than the

broad band Hg lamps with lower

intensity (4-6 W/cm2) @ 5% TPO

2 4 6 8 100

5

10

15

20

25

30

35

40

MA

XIM

UM

CU

RE

SP

EE

D (

mete

rs/m

in)

TPO (%)

MAXIMUM CURE SPEED v. %TPO

Tacky

Tack Free

Double bond conversion (via FTIR) showed NO correlation with the physical surface tack and therefore only surface tack was considered as a measure of final cure.

Review – RadTech 2015



UVA LED v Broadband Lamp

▪ Inconsistent TPO consumption was

observed at lower viscosity, possibly

due to increased diffusion and

monomers

▪ Increased absorption at shorter

wavelength indicated formations of

reaction intermediate (carbonyl

containing group)

▪ More thorough investigation needs to be

conducted for further understanding

320 340 360 380 400 420 4400.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

2000 mJ

100 mJ

WAVELENGTH (nm)

initial LOW VISCOSITY

UVA LED

0.10

0.15

0.20

0.25

0.30

0.35

0.40

LOW VISCOSITY

BROADBAND

1200mJ

100mJ

initial

AB

SO

RB

AN

CE

Experimental Set Up – Clear Coat Chemistry 1 & 2

CHEM 1 Urethane acrylates

▪ EBECRYL 3700 (epoxy acrylate)

▪ 1800-2800 cP (Low viscosity)

▪ EBECRYL 85 (polyether acrylate)

CHEM 2

▪ EBECRYL 221 (urethane acrylate)

▪ 28500 cP (High viscosity)

Photoinitiator

▪ 5% BASF Lucerin® TPO OR Irgacure 184

▪ Synergist: EBECRYL P115

12 micron films on white and black cards


EXPERIMENTAL

Maximum cure speed – UVA + UVC LED at CHEM 1 (TPO)



Maximum cure speed determined by

presence of surface tack.

▪ UVA LED at various peak irradiances

▪ UVC LED at 6 mW/cm2

▪ Multiple 60 mJ exposures

▪ Cure strongly influenced on BLACK

card with UVC exposure (solid line)

▪ Cure on WHITE card less affected

(Empty Circles)

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200

MA

XIM

UM

CU

RE

SP

EE

D (

M/M

IN)

UVC EXPOSURE (mJ/cm2)

CHEM 1 (5% TPO)

UVA 6 W/cm2

UVA 10 W/cm2

UVA 20 W/cm2

Max Cure Speed per prior

work with UVA alone

Maximum cure speed – UVA + UVC LED at CHEM 2 (TPO)



Maximum cure speed determined by

presence of surface tack.

▪ UVA LED at various peak irradiances

▪ UVC LED at 6 mW/cm2

▪ Multiple 60 mJ exposures

▪ Cure strongly influenced on BLACK

card with UVC exposure (solid line)

▪ Cure on WHITE card less affected

(Empty Circles)

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200

MA

XIM

UM

CU

RE

SP

EE

D (

M/M

IN)

UVC EXPOSURE (mJ/cm2)

CHEM 2 (5% TPO)

UVA 6 W/cm2

UVA 10 W/cm2

UVA 20 W/cm2

NOTE: 20 & 10 W/cm2 DATA FOR WHITE CARD IS THE SAME VALUE

Maximum cure speed – UVA + UVC LED using Irg184



CHEM 1 UVC only

(mJ)

UVC (mJ) +

UVA

BLACK card 720 (2) 540 (2)

WHITE card 1080 (1) 360 (2)

CHEM 2 UVC only

(mJ)

UVC (mJ) +

UVA

BLACK card 360 (4) 360 (4)

WHITE card 360 (4) 360 (4)

UVA: single pass11 W/cm2

1.6 J/cm2

UVC: multiple exposures(# in parens)6 mW/cm2

Improving cure – UVA + UVC LED with PhI mixtures

CHEM 1 only (Black Card)

2.5% TPO & 2.5% Irg 184 allowed curing with

120 mJ UVC (+ UVA)

1% TPO & 4% Irg 184 allowed curing with

180 mJ UVC (+ UVA)


UVA: single pass11 W/cm2

1.6 J/cm2

UVC: multiple exposures(# in parens)6 mW/cm2

CHEM 1 UVC only

(mJ)

UVC (mJ) +

UVA

BLACK card 720 (2) 540 (2)

WHITE card 1080 (1) 360 (2)

5.0% Irg 184 (11 W/cm2 UVA)

Photo Initiator Vs. UVC exposure – A possible Tradeoff!!:

At 20 M/MIN Line Speed


0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10 12 14

TPO Concentration (%)

UV

C (

mJ

/cm

2)

Summary of UVA + UVC LED

LED wavelength matters as much as total energy

Multiple low exposure performs better than one single high energy exposure

TPO

▪ Curing benefited greatly from low power UVC

▪ TPO samples require the lowest total power

Irg 184

▪ Irg184 samples could be fully cured with low power UVC

For the TPO:Irg184 ratios (1:1 and 1:4) showed marginal improvement

Generally,

▪ A little UVC (275 nm, 6mW/cm2) goes a long way

▪ Full power dependencies (esp. UVC) still need much work

▪ Multiple short exposures had better performance than one long exposure


THANK YOU.

P.K. Swain | RadTech | October 2017 23

advancements in shorter wavelength led technology and … · · 2017-11-07ebecryl 3700 (epoxy...

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