uv-screen technology basics-00-gb

8/7/2019 UV-Screen Technology Basics-00-GB

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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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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



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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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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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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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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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print-squeegee

condition:hardness between 75oand 85

oShore A

squeegee degree ca. 70o


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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

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