uv-screen technology basics-00-gb
TRANSCRIPT
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UVUV--screen printingscreen printingseminarseminar
by
Gerhard Lffler
For
Screenprint Co. MultiNr, Romania on 19. 1. 2005
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Contents
1.0 Preface
2.0 Chemical structure3.0 Process of polymerisation
4.0 UV-curing-systems
5.0 Printquality-check
6.0 Safety
7.0 Trouble-Shooting
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1.0 Preface
New development in the early 70`ies
Research of chemicals to reduce or eliminatesolvents in printing inks
R&D of first row-materials for UV-printing inks
legal requirements by law/safety ofemployees
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Regarding
First UV-printing-inks in the early 80`ies
Marabu present their first UV-Screen-printing-inks in 1988.
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1.1 UV-screen-printing-inksfirst applications
Container printing Labels
Highgloss laquers
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2.0Chemical structureTechnical specfications
Curing in millisecounds
= high productionrates compact and small UV-curing-stations
= development of full-color-machines
with an low requirement of space
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2.0Chemical structureTechnical specfications
very high chemical and mechanicresistance
print-ready adjustment =ready for use
perfect mesh opening
perfect color stable
high block resistance
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High glossgrade
In-line-processing No solvents = no pollution of the
working-area-air
= no air-pollution-problems with thelaws for enviremental-protections
2.0Chemical structureTechnical specfications
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2.0Chemical structureTechnical specfications
lower risk for the health
clean process economical advantages
UV- technology in all industrial printing
processes but complex technology
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2.1Basics UV-radiati
on
What is UV-radiation ?
Spectrum of electromagnetic wave-lengths
UV infra-redX-rays
UV-AUV-BUV-C
100 nm 1400 nm
100 nm - 280 nm -315nm ---------420nm
visible light
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2.2Chemical stucture
on UV- inks
UV-ink conventionellsolvent ink
pigments/extender
monomers
photo-initiators
oligomers/
prepolymers
additives
resins
hardener
pigments/extender
solvents
additives
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2.3Ch
emical structures
all chemical structures will be
completley fixed printed inkfilm are the same as the
cured inkfilm
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2.3Ch
emisch
e Grundlagen Curing of the printed ink film
substrate substratesubstrate
UV
~ 12 m ~ 12 m
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2.3 Chemische Grundlagen
composing of a UV-Screen-printing-ink
UV-Screen-printing-ink
prepolymers/oligomers
pigments/extender/mattpastes
UV-photo-initiatorssynergists
monomers
inhibitors/additves
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3.0Curingprocess on
UV-Screen printing inks
UV-exposure have the energy to startup the reaction
Forming on free radicals
Chain reaction begins
Polymerization of the inkfilm
Complex chemical reaction finished,
strong chemical network
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UV-C
uring printedinkfilm
monomers
photo-initiators
R prepolymersRRRR
RR
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UV-curing
monomers
photo-initiators
R prepolymers
free radicals
RRRR
RR
yUV-ligth excites inkfilm
yphoto-initiators break off
yand forming off
free radicals
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v
monomers
photoinitiators
R prepolymeres
free radicals
RRRR
RR
UV-curing polymerization
yChainreaction starts up
y Polymerization off the
ink film
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UV-curing
v
UV Monomer
Photoinitiator
R Prpolymere
RRRR
RR
ychemical reactionfinished
y strong chemical
network
y pure adhesive ink-adhesion
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3.0UV-curing pr
ocess
Qualtiy off UV-curing are directlyresponsible for the complex process of
curing
cured inkfilm are a complete newchemical structure
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3.1Po
st-curing effect
period of time to finish thepolymerization after the UV-exposure
without the influence of UV-light
Depends on UV-ink-system
Varition on raw materials, monomers,substrate applications and
characteristics on the inkfilm
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Process are normally completedafter 12-24 hours
chemical und mechanic stressresistances should be tested afterthis period
3.2Po
st-curing effect
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4.0UV-curingsystems
Reflectorsystems
Focus, halffocus, multifocus, diffus,Dichroid
UV-Lamps
80-300 W/cm, medium-pressure-
Mercury-Vapour Lamps
coolingsystems
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4.1 UV-curingsystems focus-system: focuspoint 25 mm
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4.2 UV-curingsystems
halffocus-system: focuspoint 37 mm
temp. - 20 %
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4.3 UV-curingsystems Multifocus-system: more focuspoints
temp. - 40 %
low power
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4.4 UV-curingsystems not focussed (nitrogen dryer)
no focuspoint
low temperature
.
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4.5 UV-curingsystems
Focus-System with IR absorption
Dichroic reflector system
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4.6 UV-Curingsystems
Coolingsystems
Air-cooling-system(inside or outside of the reflector)
Water-cooling-system(inside or outside of the refelctor)
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4.7 UV-curing-systems
Heat production must be controlledControlled, but not eliminated
Chemical reactions are general accelerated byheat
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5.0Control of the printing quality
3 main variables in UV-screen printing
UV-curing system UV-screen printing ink
substrate
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5.1Control of the printing quality
UV-curing systemLamps (1 or 2 UV-Lamps)
power consumption (in Watt/cm)
counter for run-hours
( in general about 1000 hours, vary from
maintence and cleaning, reflectorsystem- andtype, manufactorer and quality, cooling system
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5.2Control of the printing quality
ink application
condition: even and regular ink applicationscreen frame: form und profil/wallstrengthness, select for high screen tension(>18 N/cm)
Slope-profile reduces delay of frame
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5.3Control of the printing quality
screencondition:
High-tech screens with 140 up to 180threads/cm for high screen tensions
(>18 N/cm) S- (small) threads facilitate a
optimized easy ink-flow2/2 coatings with IR-drying
or Direct/Indirectsystem
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5.4Control of the printing quality
print-squeegee
condition:hardness between 75oand 85
oShore A
squeegee degree ca. 70o
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5.5Control of the printing quality
squeegee pressurecondition:
princip of kiss-printing
in general; less pressure as possible and
just enough for a perfect printresult
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5.6Co
ntro
lo
f th
e printing quality
Substrate:
big influence for the print result:depending from
kind of material (PE, PP, PC)
thickness/flexibility/sensitivness
color/surface
Pre-treatment/printing-machine
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6.0 Test methods at the ink film
Adhesion and scratch resistencegenerall diffrences
Tackniness of the ink film*
Fingernail - scratch test*
Adhesive tape test with Scotch- or tape
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6.1 Safety when working with UV
screen printing inks
UV-inks only cure under the exposure ofUV-lightPrecautions; wear impermeable gloves,aprons or working coats, wash seperatly
Personal hygiene; never wash your hands
with screen cleaning agents, use only soapand water
wear glasses when cleaning screens
Spilled ink should be removed immediately
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7.0 Trouble-Shooting
Adhesion and scratch-resistance
Pre-treatment on critical substrates
Over-curing/color scale
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Expierences
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Marabu
Th
ank Yo
u