A study of the effect of water-pick up of UV curable offset ink on its curing time and its end use properties

Rochester Institute of Technology

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1-1993

A study of the effect of water-pick up of UV curable

offset ink on its curing time and its end use

properties

Ike Siti Fatnasari

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A STUDY OF THE EFFECT OF WATER-PICK UP OF

UVCURABLEOFFSET INK ON ITS CURING TIME AND ITS END USE PROPERTIES

by

Ike S. Fatnasari

A thesissubmittedin partialfulfillmentofthe

requirementsforthedegreeofMasterofScience in the School of

Printing

Management andSciences intheCollege

of

Imaging

ArtsandSciencesofthe RochesterInstituteof

Technology

May

1993

School of Printing Management and Sciences

Rochester Institute of Technology

Rochester, New York

Certificate of Approval

Master's Thesis

This is to certify that the Master's Thesis of

Ike Siti Fatnasari

With a major in Printing Technology

has been approved by the Thesis Committee as satisfactory

for the thesis requirement for the Master of Science degree

at the convocation of

May, 1993

date

Thesis Committee:

Chester J. Daniels

Thesis Advisor

Joseph L. Noga

Graduate Program Coordinator

Title of thesis A Study of The Effect Of Water pick up of UV Curable

Offset Ink on its Curing Time and its End Use Properties

I, Ike Siti Fatnasari , hereby

grant permission

to the Wallace Memorial

Library of the Rochester Institute of Technology to reproduce my thesis in

whole or in part. Any reproduction will not be for commercial use or profit.

Ike S. Fatnasa ri

IK..e'

s .

:fM""t-IAfA-it-I

Date: May 1993

Signature of Author:

ACKNOWLEDGMENTS

The author would like to express a

deep

gratitude to Perum Percetakan

Uang

Republik Indonesia for the _opportunity that

they

have provided to _study at Rochester

Institute of Technology. Theirtrustand support were extendedthrough the period ofthe

studyand_preparingthisthesis.

This thesis could not have come about without the assistance of the Thesis

Committee in the School of

Printing

management andScience at Rochester Institute of

Technology.

A very special note of appreciation is extended toMr. Chester J. Daniels for his

enthusiasm for the subject, his extra time and efforts in technical guidance and for his

permission to use the equipment in the Ink and Paper

Laboratory

of the Technical and Education Centerof the Graphic Arts. The author also thanks Mr. Ching-Yih Chen for

his adviceand technical guidance. Gratitudeis also extended toProf. Sam Hoff for his

permissiontouseArgon UVTrix

Curing

unit.

Theauthoris also gratefultoProf. Charles A. LayneandProf Cliff Frazier. Their

comments and advice minimized error and add to the completeness ofthis thesis. The

authorisalso thankfultoProf. J. Noga for hisadviceand encouragementthroughout the

durationofthe _studyatRochester InstituteofTechnology.

TABLE OF CONTENTS

Page

LISTOFTABLES vi

LIST OFFIGURES viii

Abstract ix

Chapter 1 Introduction 1

Endnotes forChapter 1 5

Chapter 2-Theoretical Basesofthe

Study

6

Endnotes for Chapter 2 12

Chapter 3 ReviewofLiterature 14

Endnotesfor Chapter 3 17

Chapter 4- Hypotheses 18

Chapter5

-Methodology

/ Design

Study

20

1. Thewater_pickupcharacteristics 20

2. Tack 21

3.

Curing

rate 22

4. Enduse Properties 23

4.1 Film Hardness 23

4.2 Abrasionresistance 24

TABLEOF CONTENTS

(CONTINUED)

Page

4.3 Adhesion resistance 27

Chapter6- The Results 30

1. Water_pickupcharacteristics 30

2.

Curing

time 35

3. Resistance Properties 42

3.1 Film Hardness 42

3.2 Abrasionresistance 43

3.3 Adhesionresistance 45

3.4 Resistanceproperties ofdifferentsubstrates 47

4. Other Findings 49

4.1 Tack 49

4.2 Different

Curing

Stages 52

Chapter7

-Summary

andConclusions 54

Bibliography

57

AppendixA Material Data 61

AppendixB EquipmentData 66

Appendix CMeasurementResult 70

LIST OF TABLES

Table Page

1 Water_pickuptests 21

2 _{Water pickup}rate offourcolors processUV inks 31

3 Anovatablewater_pickuprate 35

4

Curing

timeoftheUV inks 37

5

Curing

timeofUVinkswith neutral

density

38

6 Anovaof_curingtime 39

7 Substratesproperties 40

8

Curing

timeforovercoat varnish ondifferentsubstrates 40

9

Oneway

anovafor differentsubstrates 41

10 Film hardnessoffourcolor processUVinks 42

11 Analysis of varianceforscratch resistance/filmhardness 43

12 Abrasionresistance ofUV inks 44

13 Anovaforabrasionresistance 45

14 AdhesionresistanceoffourcolorsUVinks 46

15 Anova foradhesion resistance 46

16 ResistancepropertiesofUVvarnish ondifferentsubstrates 47

17

Oneway

anovaforresistanceproperties 48

18 Tackvalue ofthefourcolorprocessUVinks 50

19 Abrasionranksfordifferent_curingstages 53

20

Summary

ofhypotheses

testing

55

LIST OF TABLES

(Continued)

Table Page

21 _{Water pickup}ofUV inkswithFountain Solution 1 71

22 Water_pickupofUV inkswithFountain Solution 2 73

23 Water_pickupofUV inks withDistilled Water 75

24 TackoftheUVinksatlowerspeed 77

25 TackoftheUVinksathigherspeed 79

26

Curing

timedata 81

27 Beltspeeddata 82

28

Curing

timecalibrationtable 83

29 Scratchresistancedata 84

30 Abrasionresistancedata 85

31 Adhesionresistancedata 86

LIST OF FIGURES

Figure _Page

1 Cureratefor differentinkcolor ₈

2 UV TransmissionofInkpigments 9

3 Typicalemulsificationcurves 15

4 The Gardco/Hoffman Tester 24

5 Panel holders 25

6 Themovement ofGACAT Comprehensive Abrasion Tester 26

7 _{The cutting}patternforadhesiontest 27

8 Classificationof adhesiontestresults 28

9 _{Water pickup}as afunctionoftheink 32

10 _{Water pickup}rate as afunctionoffountainsolutionforeachink 33

11 Theprint withblue laminated film 38

12 TackofUV inks comparedtoconventional ink 51

13 _{Three different curing} stages 52

14 Calibrationcurvefor curing unit speed 82

ABSTRACT

The curingtime and theend usepropertiesare asimportantas _{printing quality}for

theprinter. Shorter_curingtime equals morejobsandhigher productivityeachweek. The latest available

technology

for

decreasing

_curing time_{is Ultraviolet curing} technology.

This

technology

uses ultraviolet radiation as the_energysource toexcitetheactive site of

the monomerin the ink to start thepolymerization process. The desiredresult is a hard

polymerizedinkfilm. Anotheradvantage of_{Ultraviolet curing}

technology

is that theink

is solventless. The screen _printing process has the advantage of

being

a single-fluid

printing process. Ink is the _only chemical compound to be considered in this _printing process.

Lithography

requires _{compatibility between ink}and fountain solution. Extensive

research has been done to betterunderstand the _{relationship between fountain} solution

and

ink,

_primarily with conventional ink. The water _pickup characteristics of

conventional ink is mainly studied fortheeffect ofwateronthe _printing quality. Dueto the nature of Ultraviolet

ink,

the water-ink relation is more complicated. The water

pickup

by

the ink is thoughttohavean effect on the curingprocess. This thesis studies

the effect of water _pickup of ultraviolet inkon_curing time and end use properties. The

water _pickup of the ink was varied

by

_using three levels of _{acidity for} the fountain

solution. To simulate the actual _{printing condition, the} fountain solutions used were those _commonlyused on press. Threeresistance properties

including

film

hardness,

abrasion resistance and adhesion resistance were measured in this _{study for} responses

relating toend use. The effect ofthesubstrate _absorptivity on the_curing time was also reviewed.

This _study indicates that the higher water _pickup of the Ultraviolet ink needed

longer_curing time. There is a significant effect of_acidity offountain solution on water

pickupofthe ink.

Curing

time _{is considerably}affected

by

the color ofthe inkor

by

the transmission properties of the pigment. Cyan acts like a neutral

density

filter on the

printed_{film. Increased absorptivity}ofthesubstratehelps shortenthe_curingtime.

Water pickup of the UV inks affects its film hardness. High water _pickup

decreased film hardness. On the other

hand,

theeffect of water _pickup of the ink with

regard toabrasion resistance and adhesion resistanceisinsignificant.

Tackas a rheological _propertyofthe inkand the _curing stages are also reviewed

Chapter 1

Introduction

Quality

of a printed product consists ofits physical _quality

(meeting

customer's

specification),price and

delivery

time. Themethod requiredtoachieve a product ofhigh

quality will _{vary according} to _printing process. For the Lithographic process, one important requiredfactor toproduce a good result is the so-called "water-ink balance".

Water or fountain solution in this process is responsible to

keep

the non-image area

clean. Braun * reported thatthe behavior ofLithographic ink is primarily governed

by

the amount of water _pickup

by

the

ink,

the position of the ink/water equilibrium, the

nature of the emulsion and the

drop

size distribution. Fountain solution is not _purely

water, italso consists of several additives to meet the requirements ofthe process. The chemicals in fountainsolutioninfluencethewater-ink_relationshipoftheprocess.

Drying

timeisalso a_qualityattribute. Shorter

drying

timereducesturnaroundtime

and

drying

related problems such as set-off. The Environmental Protection

Agency

regulationsinusageof volatile solvents make radiation_curingtechniques seem tobethe betterchoice over conventional

drying

mechanisms. Radiation curing techniquesinvolve

polymerization ofmonomers and low molecular weight polymers initiated

by

radiation

energy. This technique eliminates the needfor _spray powder. Radiation _{curing inks} are

in their _{implementation. Radiation curing} processes are classified _according tothe type

of _energy source applied. Three processes _currently available are Electron

Beam(EB),

Infrared(IR)

and _{Ultraviolet(UV). UV curing has} the largest volume of the specialized

radiation curable ink and varnish market. It offers faster

drying

rate with more simple

equipment thanother radiation_curing techniques. The final ink film properties ofthe

printing issuperiorto thatof conventionalink.

Theink contains a photoinitiatorthatacts as a catalysttoinitiatethereaction. As

withother chemical_processes, polymerization will beinfluenced

by

suchfactors such as

the concentration of the reactive sites and the irradiationenergy. The reaction could be

inhibited

by

the presence of other chemicals and the impurities from a _variety of

sources.

The purpose of this _study was to investigate the effect of the water _pickup

characteristic of UV curable offset inks on its _curing rate and end use properties.

Considering

thepriceand the_complexityofUV curing_equipment, theinvestigation was

conducted

by

_{comparing different UV} offset inks in laboratory/process simulation. Thereforethe behaviorofUV curable inkonthe press is beyondthescope ofthis study.

This study was further limited

by

the fact that most ink formulations are _proprietary,

therefore the _study of formulation was not_specifically addressed butwill _{probably be} inferred on theBasis ofMaterial

Safety

data sheets and whateverthemanufacturer_may

was _willingtoshare. The informationonthe_curingunit wasalsolimitedto that whichis

availableinthemanufacturer's datasheet

The result of the

testing

will be useful for the printer that intends to use UV

curing

technology

since

implementing

a new

technology

requires a thorough

lithographic printers to decide the best

technology

to be used for them. On the other

hand,

the ink

industry

_may find theresult ofthis _study useful for the improvementof UVcurableink.

Definitions :

Radiation is the term to describea passage of_{energy from} a

transmitting

source to an

absorbing

body

withoutinteractionwith_any

intervening

matter.^

UVoffsetinks are solvent-freelithographic inks which

dry by

polymerization of mono

mers and molecular weightpolymersinitiated

by

theabsorption of ultravioletlight.-* Ultraviolet_curing isaconversionof a_coatingfrom itsapplication statetoits final state

by

means of a mechanism initiated

by

ultraviolet radiation generated

by

equipment

designedforthatpurpose.

Conventional inks are solventbased lithographic inks and

dry by

_absorption, oxidation

or evaporation. Sometime it isalso calledoleoresinousink.

Water Pick upcharacteristic is thedegreeofthewater picked _up

by

theink. Since water

pickup of the ink is measured over cumulative period of _time, the water _pickup characteristicinthisexperimentis statedintermsofwater_pickuprate.

Tack is a rheological parameter indicative of internal cohesion of the fluid and is

defined as a function of the force required to split athin fluid film of a_{printing ink} or

vehicle betweentwo_{rapidly separating}surfaces.

Resistance Properties are theinkcharacteristics toresistcertain forms of chemical and

physical attack

during

their life span. In this _study three resistance properties will be

measured.These includethe

following

:

- Film Hardness : the

Two end points defined are the force required to _slightly mark the film and the force

requiredtoscratchthefilm intothesubstrate.

- Abrasion

resistance: the_abilityofafilmtoresist

being

worn _away andto maintain its

original appearance andstructurewhen subjectedtorubbing,_scrapingor wear. 4

- Adhesion

: the _property

denoting

the _ability of a material to resist delamination or

separationinto twoor more layers. Delaminationisseparation of onecoat orlayerfrom another coatorlayerorfromthe substrate.-*

Curing

rate is howfasttheinkcouldbe dried

by

the_curingprocess. Inthisexperiment,

Endnotes forChapter 1

1.

Braun,

E,

"Studieson offsetinks- Effect

of pigments ontheformationofemulsions",

AmericanInk

Maker, 1985,

p. 26

2.

Chatterjee,

P.C. and

Ramaswamy, R.,

"UltraViolet Radiation

Drying

of

inks",

The

BritishInk Maker,

February

1977,

p.76

3. R. H. Leach

(ed.),

The

Printing

Ink

Manual,

4thed., Van Nostrand Reinhold

(International),

London,

1989,

p. 516

4. Paint-Test forFormulatedProductsandApplied

Coatings,

AnnualBookofASTM

Standards,

Volume

06.01, ASTM,

Philadelphia,

1991

Chapter 2

Theoretical Basesofthe

Study

Ultravioletcurableinks ingeneral havethe

following

composition *

Pigment 15- 20 %

Prepolymers 35- 25

%

Monomers

(including

_oligomers) 10- 25%

Photoinitiatorpackage 5- 10%

Additives 1 5%

100%

The low viscosity monomer, usually referred as

diluent,

acts like the solvent in

oleoresinousink. Itwets thepigmentanddeterminesthe _rheologyoftheUV ink.

Being

a

monomer, diluent in UV inks are chosen from

difunctionality

species which will also

chemically reactwith each other andtherest oftheinktoformpolymer. Prepolymeracts

as a hardresin portion oftheinkand contributes toits

hardness,

_{gloss, adhesion,}strength

and

flexibility

of the ink. The radiation sensitive material in the ink is called

photoinitiator. Itcatalyzes the polymerizationreaction. A small part ofitwill beused_up

in the reaction but the rest will be left unbound in the cured polymer. ^ This residual

Curing

process willinvolvethree stages:

(1)

Initiation

(2)

Polymerchainpropagation

(3)

Termination

Initiation is the firststage ofthe reaction where the free radicals needed in thereaction

are generated. Photoinitiatorsare effective sources of_{photochemically}generatedradicals

to start the polymerization. The photoinitiators are broken-down to free radicals

by

exposure to UV radiation in the 200-400 nm waveband. The concentration and the

reactivityofthe photoinitiatorinfluence theaverage molecular weight and the technical properties of the polymer. The most common chemicals used as photoinitiators in UV

inks are the carbonyl function. The Initiation reactions _{usually follows} the

following

form3 :

1. AB

^

AB*

Energy

absorption

by

a photoinitiator andexcitation

2. AB* AB

Fluorescenceand phosphorescence

3.AB* ₊AB AB₊AB*

Energy

transfer

4. AB* A ₊ B

Formationoffreeradicals

The freeradicals react withdouble bonds in UV curable resin to_{form propagating}

chain species. The free radicals begin to open the double bond in the monomer and

oligomer and theparts begintohookontoeach other

forming

a _{cross-linking}chain. The furtherreactions of_propagating chain species form polymer chains are similarto those

8

and _stop to react. Ultimate termination occurs as the rate of polymerizationdecreaseto

zero

by

a _{decrease in free} radicals or molecular _mobilityas the _viscosity ofthe system

increases . Certain materials_can interfere inthe _propagation

step causing the reaction

terminatebeforeitiscompleted.

The overall reactions are more complicated since some ofthe pigments in theink

compete with thephotoinitiator to absorb UVradiation. _{The absorbancy property}of the

pigmentto UV irradiation determines the_efficiency ofthe _curing process. The pigment

thatabsorbed ahighportion ofUV lightwill retardthe_curingrate oftheinks. Otsubo ^

reported thatfor thesame _{film thickness,} magentainkshows the_{fastest curing} rate and

followed

by

_yellow,cyan andblack. Theresearchconducted

by

Bassemiret al "alsoled

tothesame conclusion as shownin figure 1.

2

s

U

450 4001 300

200.

100 K7 ?fc-V

1 :TF : Tack Free

2 :TTF: Thumbtwistfree

[image:20.546.100.433.313.615.2]

m

a: ess

m

f&! 2 3 xtct sua

m

m

0

M

Figure 1

They

definedthecure state

by

twodifferentmethods, as thumbtwistfree

(TTF)

and tack

free (TF). Thethumb twistfreemethodinvolved the applicationof5 kgs pressure while

a _rotary

twisting

_{motion is applied to the film with the thumb. Tack free method is}

definedas theabsenceofstickinessorinktransferwhenthefilmis touchedor comeinto

contact withanother surface. Since TTFmethodismore severe thanTF_method, thecure rate ofTTF is slowerthanTF. Magentaappears tohave the fastestcure rate_among the

four color process. The unit of cure is expressed in f/m/1

(ft/min/lamp)

to provide the

information for_scaling purposes from

laboratory

test toactual press condition at given

speed.

Further, they

measured the UV transmission of a set of process colorants

dispersed ina non-absorbant oil.Theresultisshownin Figure 2.

4> (J G es

a

c CO C

t

a* 60 50 40 30 20 10 n Magenta

f

^

/

/

Yellow

^'

^ B,ack

"*"~-Cyan

230 260 270 300 330 350

[image:21.546.91.476.290.506.2]

Wavelength

(nanometers)

Figure 2

UV TransmissionofInkPigments."

Thecolorantcharacteristicsmaybe explained

by

the differenceofthecurerate

by

10

which is the casein Figure 1. Metallic pigments reflect most ofthe UV irradiation and

should reduce the amount ofUV _energy absorbed

by

the film to form polymer. 7 This

characteristic willinfluencethe_curingrateoftheinks. Thechoice of pigments shouldbe

suitable forthephotoinitiator. As anexample, an_epoxysystem photoinitiatorhas acidic

active species which should not bemixedwith basicpigments.

They

will neutralizethe

activityofthephotoinitiator.This photoinitiatorwithacidic pigmentswillalsoshortenits

shelf-life and lead to gellation

during

storage. >* Some pigments _commonly used in

conventional inkare not suitable for UV ink formulation since some resin available for

UV ink has poor_{pigment-wetting}characteristics.

In the lithographic process the image and non image areais separated

by

_applying

fountain solution onto _printing plate. The ink-water balance is crucial in this type of

process. Water-miscible resins whichare morepopularin UV screen_{printing ink} should

be avoided for _{UV litho ink. A study}

by

Mac Phee and others10

indicates that the

fountain solution on press _{is mostly}carried

by

the ink. Someofthefountain solutionis

transferred to the substrate and is absorbed and the rest evaporates from the

inking

system. In both cases the fountain solution deposits impurities in the ink. The water

soluble impurities can reactwith thefree radicals

thereby

_preventing particle generation

and

inhibiting

polymerization processes. There is always a risk that the photoinitiator

will leach into the fountain solution with a subsequent reduction in cure efficiency.

Acidity

of the fountain solution will also be very critical _regarding the active site of

photoinitiators. It also defines the amount of the water _picked-up

by

the ink.1 * The NPIRI Task force on Water

Pick-up

reported that the fountain solutions provide lower

water _pick-up than distilled water. Lower pickup characteristic of the ink performs

better on the press and reducethe effectof waterin

drying

time. Surland l3 concluded

11

thepH and

conductivity

ofthe

dampening

solution, andtoparticularinkand

dampening

solutionconstants".

The ultraviolet system ofink

drying

utilizes radiantUV-light energyas the

driving

force toconvert afluid ink intoa

dry

abrasion-resistantink inafractionof asecond.The

energy requiredin the processis generated

by

_mercuryvapor quartz lamps. To cure the

ink _completely, UV irradiation must reach the bottom of the film and must generate

sufficientfree radicals throughout thefilm. Therefore forthesamelevel of_{energy used,}

the thicknessofthefilmwilldeterminethe_curing time. Thepolymerization process can

be retarded or terminated in the presence of oxygen. An incomplete polymerization process will influencethe resistance propertiesof the

dry

film. Therub resistanceofthe

film and theoverall adhesion might alsobe affected. The rub resistance testis used to

Endnotes for Chapter 2

1. R.H. Leach

(ed.),

The

Printing

Ink

Manual,

4thed., Van Nostrand Reinhold

(International), London,

1989,

p.525

2.

Ibid,

p. 526

3. Dr. R. Holman B.Sc. Ph.D. & Dr. P.

Oldring

Ph. D. BA

(ed.),

UV & EB

Curing

Formulation for

Printing

Inks Coatings &

Paints,

SITA-Technology,

London, 1988,

p. 10

4. R.H. Leach

(ed),

The

Printing

Ink

Manual,

4thed.,Van Nostrand Reinhold

(International), London, 1989,

p. 534

5.

Otsubo, Y,

et. _al., "Rheological MeasurementsofCure RateofUV

Inks",

Journal_of

Applied Polymer

Science,

Vol.

31,

John

Wiley

&

Sons,

Inc.,

1986,

p. 2099

6.

Bassemir,

R.W and

Bean, A.J.,

"Parametersof ultraviolet_printing

inks",

TAGA

Proceedings,

191

A,

p. 133

7.

Chatterjee,

PC. and

Ramaswamy,

R.,

"UltraViolet Radiation

Drying

of

Inks",

The

British Ink Maker,

February

1977,

p. 76

8. A. A.

Gamble,

"RadiationCurable Offset Inks : ATechnical and

Marketing

Overview",

Radiation

Curing

_{of Polymer} , Royal

Society

of

Chemistry, London,

1987,

p58.

9.

Bisset, D.,

"A Review ofAccelerated

Drying",

The British Ink

Maker,

February

1977,

p.69

13

10.

MacPhee, J.,

"Further insightintothelithographicprocess- _with

specialemphasis

on wherethewater_goes",TAGA

Proceedings,

1985,

p.297

11.

Koniecki,

J.et. _al., "Ink/Paper/Fountain Solution

Interactions",

TAGA

Proceedings,

1983,

p. 258

12.NPIRI Task Forceon waterpick-up, "Effectofinkwater_pick-upon_{printability in}a

highspeed lithographicpress", TAGA

Proceedings, 1990,

p. 226

13.

Surland,

Aage,

"Factors

determining

the_efficiencyoflithographic

inks",

TAGA

Chapter 3

Review ofLiterature

Ink formulation has a great influence on its properties. The combination of

pigments, varnish, solvent and additives are formulated to meet certain properties for

each_printing process. Solvent in conventional inkacts as _viscosityreducerto

help

flow.

It physically interactswiththevehicle components. Onthe other

hand,

_viscosity reducer

in UV ink is adiluent (low _{viscositymonomer)}and "... will_{ultimately form}a part ofthe

cured polymer matrix.Thusthechoice ofmaterial_used, not_{only influences} the_rheology

ofthe ink or _varnish, butcan have a profound effect onthe characteristics ofthe cured

product."*

The _complexity of the interaction ofdiluent in UV ink formulation makes

the choice of material more difficult. Increased

functionality

of the diluent leads to a

faster cure, but this is often at the expense of adhesion and scuff resistance.^ The

resistance of UV-cured coatings to water vapor and chemicals depend on the type of

prepolymer and reactivediluentselected.D

K. Nate and T Kobayashi 4 investigated the adhesive characteristics of

Ultraviolet Radiation Curable resins. The UV curable resin was applied to aluminium

oxide substrate/plate _usingscreen _printingtechnique.

They

mentionedthat photoinitiator

andUV radiation condition(time and

distance)

would not affect theadhesive strength.

They

also mentioned that : "

Tensile strengths of the UV resins decreased

by

water

15

absorption in all cases". There is a significant effect of the additive on the tensile

adhesive strength oftheresin_especiallydueto thepresenceof

boiling

water.

Golovoy

-*

reportedthatwaterabsorption

by

thepolymer reducesitsmechanicalproperties.

Mostwater_pickupcharacteristics ofthelithographicinks were studiedinrelation to

ink rheology andpress perfomance. Surland^ reported that the emulsification curve of

[image:27.546.74.457.204.587.2]

the

ink/dampening

solutioncanbe usedtopredictpress perfomance as shown

by

Figure 3.

G

V)

2

Oft

O

o Vi Oft c

'3

(A

3

2

O

01 23 456789 10

Time,

minutes

Figure3

16

He also mentioned that the addition of isopropil alcohol to the

dampening

solution

improves emulsification characteristics. In the case of UV curable lithographic

ink,

Tasker pointed outthat twoofthethreeUV inks used weredifficulttorun. Mostofthe

constituents of these UV inks were soluble in isopropanol. These are extracted

by

isopropanol in the fountain solution. This _studyalso indicated that _{inks emulsify} water

by

first-orderreaction andhavealimitontheamountof water

they

can emulsify.

Water-ink balance is also a problem with UV ink. Some lithographic processes use propanol

solution in place of propanol substitute and problems have been experienced with UV

Endnotes for Chapter 3

1. Dr. R. Holman

B.Sc.Ph.D,

andDr. P.

Oldring

Ph.D.BA

(ed.),

UV&EB

Curing

Formulationfor

Printing

Inks Coatings &

Paints, London,

SITA-Technology,

1988,

p. 162

2.

Ibid,

p. 163

3.

Decker,

C,

"EffectofUV Radiationon

Polymers",

_{Handbook ofPolymer Science} and

Technology,

Vol.

3,

Marcel

Dekker,

Inc.,

New

York,

p.541

4.

Lieng-Huang

Lee

(ed.),

"Adhesive CharacteristicsofUltraviolet Curable

Resins",

Adhesionand_{Adsorption of}

Polymers,

Volume

12B,

Plenum

Press,

New

York,

1980,

p. 551-561

5.

Golovoy,

A. and

Cheung,M.E,

"Waterabsorption anditseffect on _{polyacrylate",}

Journal ofApplied Polymer

Science,

Vol.

35,

John

Wiley

&

Sons, 1988,

p. 1511

6.

Surland, Aage,

"Factors

determining

the_efficiencyoflithographic

inks",

TAGA

Proceedings, 1983,

p. 191

7.

Tasker,

W. et.al, "Water pick-uptestfor lithographic

inks",

TAGA

Proceedings, 1983,

p. 176

8. J.B.

Emerson,

"A User's ViewoftheApplicationofRadiation Curable

Materials",

Radiation

Curing

_of

Polymers,

TheRoyal

Society

of

Chemistry, London,

1987,

p.39

Chapter 4

Hypotheses

The water_pick-upcharacteristic ofUV curable inksand its effecton_curing rate

and end use propertiesisthesubject ofthis study.Thequestions answered are :

1. Relatedtowater_pickupand_curingtime

1.1 Do differentcolor ofUV inks differinwater_pickuprate ?

1.2 Doesthewater_pickupoftheUVcurable inkaffectits curingrate?

1.3 Doesthe_acidityoffountainsolution affectthewater_pickuprate oftheink ?

1.4 Do differentsubstratesinfluence the_curingrate?

2. Relatedto theend use properties

Does thewater pick_upaffect film

hardness,

abrasion resistance and adhesion

resistanceofthe end product?

Hypotheses

There were sevenhypothesesformulated fromtheseresearch questions :

1. Relatedtowater_pickupand_curingtime

1.1 DifferentcolorofUV inks havesimilarwater_pickuprate

19

1.2 Waterpicked_up

by

theink doesnotaffectthe_curing rateoftheink

1.3 The_acidityof

fountain

_solutiondoesnot affectthe water_pick-upcharacteristicofthe

ink

1.4 _{The curing}rate willbesimilarfordifferentsubstrates.

2. Relatedto theend useproperties:

2.1 Water_pick-upoftheUV curableink doesnot affect film hardness.

2.2 Water_pick-upoftheUVcurableink doesnot affect abrasion resistance.

2.3 Water_pickupoftheUVcurableink doesnot affect adhesion resistance

Ifthenull hypothesesare rejectedatthe95%confidence levelthealternate hypothesis

is then inferred. To test the above hypotheses the regression analysis and analysis of

variance were applied. Theregression analysis was used tofind the _{relationship between}

variables. The oneway analysis of variance andcrossed designanalysis of variance were

Chapter 5

Methodology

The studyto test thehypotheseswas conducted as follows:

1.The water_pick-upcharacteristics.

Water pickup characteristic of several UV inks were determined using the Duke

Ink-Water Emulsification Tester. The testprocedure followedthe method specifiedin ASTM

D4942-89 test method B. One set of measurements in a ten minute period required 50

grams of the ink and 100 ml of fountain solution. The clean

bowl,

mixer and spatula

were weighed before and aftertheaddition of 50 grams ofink. 20 ml Water/Fountain

solution was added to the ink and were mixed for one minute at 90 rpm. After each

mixing period, the free water was returned to the beaker glass _containing the unused

water. The ink with the spatula and the mixer were weighed. For the next _mixing

interval,

the returned and unused water was mixedbefore itwas addedto the ink. These

steps were repeated until the cumulative mixing time total was 10 minutes. The water

picked _up

by

the inkafter each _mixing periodwas determined

gravimetrically

_using the

following

equation :

21

P=(W-S)xl00/S,

where :

P : water_pickup,%or mlwater/

lOOg

ink.

W : weightofthespecimenplus waterpicked_upafter each_mixing

interval,

_g,and

S : weight ofinitial_specimen, g.

Condition of the

instrument,

water and ink sample was kept constant in room

temperature. Distilled water and twokind ofRosos fountain solution were used in this

experiment. Each measurement was repeated 3 times (ASTM specified two

measurements).The designoftheexperimentisshownin Table 1.

Table 1

Water pickuptests.

Inks Fountain Solution

Distilledwater Rosos RV 1000 Rosos G-C #1

pH =6.6 _pH =3.4 _pH=7.1

Yellow

(Y)

Y-6.6 Y-3.4 Y-7.1

Magenta

(M)

M-6.6 M-3.4 M-7.1

Cyan

(C)

C-6.6 C-3.4 C-7.1

Black

(K)

K-6.6 K-3.4 K-7.1

2. Tack

The tack of the ink was measured _using the LTFInkometer from

Thwing

Albert

Instrument Company. The Inkometer is connected with an electronic readout. The

measurement procedure followed the ASTM Standard Method D4361-89. The

cooling

waterwassetat90

F.

Thevolumeoftheinkwas 1.32mL(thickness 12.3 urn). 800rpm

22

rollers of the _{Inkometer. The Inkometer} and a stopwatch were started simultaneously.

The_{first reading}was_takenat20seconds afterInkometeroperated andthen_everyminute

foratotal period oftenminutes. Themeasurementwas repeated three timesforeachink

at each speed.

3.

Curing

rate

The UV Trix_curing unitforscreen _printing was used tocure theink in thisstudy. This

apparatus is Manufactured

by

Argon Industrie Meccaniche Italy. The radiation source

and the speed of the belt in this _curing unit can be varied. In this experiment, the

intensity

ofthe radiation source was keptconstantforall inksand the timerequired for

the _curing process was measured

by

_varying the speed ofthe belt. The speed displayed

by

the machine was calibrated

by

_passingpaperthrough theunit anddeterminedthe time

required forthepapertopassthrough the_curing unit. A stopwatchwas used. _{The safety}

feature of the machine will shut down the whole unit if the _{heat build up} exceed a

specified temperature(75-85 C). The heat_{build up is}determined

by

the

intensity

ofthe

lamp

and speed of the belt. The full

intensity

at the slow speed can shut down the

machine. Forthis study, thespeed ofthe machine was maintained above25ft/min. Ifthe

ink was not cured at the slowest _speed, it was passed through the _curing unit several

times. Since thelengthof_curingunitis

known,

the_curingtimewill be:

t=

l/s*60*f,

where: t: _curingtimeinsecond

1 : lengthofthe_curingunit=2250_mm

s : beltspeedinm/minute

23

The degree ofthedrynessoftheink filmwas tested_using a_rubbingtestor set off

test as standardized in ASTM D3732-82 (Reapproved 1989). One sample was put in

contact with a sheet of paper

immediately

aftercuring.Theothermethod usedwas

dry

to

the touch. Thedegreeofsetoff will define thedryness oftheink. All theUV inkswere

printed on coated paper. To find the effect of different substrates on the _curing rate, a

clear overcoat varnish was usedtopreparethesample andwas appliedto:

1. Conventional inkprintedonmylar/plastic

2. Conventional inkprinted on coated paper

3. Conventional inkprinted on uncoated paper

For this experiment,the overcoatvarnishwas applied _using wire-woundrod #3 and the

inkwas printed _usingtheLittle Joe Proof Press. The inkused was metered _usinga metal

adjustable clearance applicator. The volume ofthe ink for each clearance stripe was

approximately 0. 1mL. Thevolume oftheinkusedinthis _studywas0.1 mL.

4.End Use Properties

Theend use properties testedwerefilm

hardness,

abrasion resistance anddelamination.

4.1 FilmHardness

The film hardness was tested_using theGardco/ Hoffman S.A.M. Tester. As specifiedin

ASTM STP

500,

5.1.2.5,

to determine scratch resistance, the low range of the tester

shouldbe used. The low range includea force from 20 grams to250 grams. The tested

filmwas placed on afirm horizontal surface. Theforceofthe testerwas setto thelowest

24

away from operator)andpushed away. Ifthefilmwas not marked atthelowest

force,

the

force was increased until the film was marked. The force required to _slightly mark the

film was defined as the lower end. The force was _continuously increased until the ink

film was scratch through to the substrate. This force was defined as the upper end of

scratchresistance. Theseprocedureswere repeatedfor fivedifferentprints.

r

d

e b

c

JL

JA

a :

Locking

nut on reverse side

c : Load Control dial

e : Hoffmancutter

b:Fulcrumselection on reverse side

d:Pull Direction

Figure 4

The Gardco/ Hoffman tester.

4.2Abrasion Resistance

Tosimulate actual resistance to

handling

moreaccurately, the abrasion resistance ofthe

25

specified in ASTM standard method no. D5181-91. The tested printed sheet and a

receptorpaper were puttogetherface toface.Twopieces offoam sheeting were used as

a

backing

for the specimen and the receptor to provide uniform pressure over the test

surface and prevent the particles from

imbedding

into the sensitive surface of panel

holder. This sandwich was clamped in the panel holder of the GA CAT with a known

force and were made toslide over each otherat a known

frequency

and at adetermined

timeperiod(this arrangementisshownin

Fig

5).

a : Spacerpanels

c: Protectivefoamsheets

e:Test Print

L:Left

d

e

b: Testpanels

d: Receptor

[image:37.546.104.430.253.561.2]

R: Right

Figure 5

26

Forthis measurement, the

following

conditionswereapplied :

Sidepressure : 20psi

Top

pressure :40psi

Span : 1.0inch

Frequency

:2.0 Hz.

Time : 120sec.

Threetypesofreceptors availableare :

CI ,

Glossy

coated paper suitablefor lowest_qualitygraphics(leastabrasive).

- A-0

toA-5for intermediateabrasivenessand

A-6,

trimite600 (mostabrasive).

- B2-2 to

B3-3,

for_evaluatingtheabrasivenessof another printed panel.

Thisexperiment usedtheA-0toA-5typereceptors which are imperial

lapping

filmwith

aluminium oxide abrasive particles of different sizes

(3,

9,

12,

30 and 40 um, [image:38.546.93.482.359.624.2]

respectively).

Figure 6

27

4.3 Adhesion Resistance

The delamination of the film was tested _using the peel offtest or Scotch tape test as

specified in Standard Method ASTM D3359-90 method B. Figure 7 shows the cut

pattern appliedto the ink film. Thecut shouldbethrough theink film intothesubstrate.

There are6cuts 2mm apartasillustratedinFigure 7. Aftercutting,thefilmsurface and

[image:39.546.194.359.236.368.2]

cuttingedgewas smoothened

by

a softbrushtoremoveflakes.

Figure 7

The cuttingpatternforadhesiontest

A three inches (75 mm)

long

size of tape was placed _smoothly and

firmly

over the cut

ink film. Within 90+/-_{30 seconds application,the} tape was removed_rapidly

by

_pulling

it off at as closeto an angle of 180 as possible. The tape used was 0.75 inch (19 _mm)

wide semitransparent pressure-sensitive Scotch tape no. 519 and transparent

pressure-sensitive Scotch tape no. 600 from 3M. ASTM recommend to use tape from the same

28

Classifications SurfaceofCross-cutareafrom

whichthe

flaking

hasoccurred

5B None

4B

]""

3B _zx:HI

-*

-I:

i

2B Z'.'.Z

IB

Ii

[image:40.546.93.368.85.563.2]

OB Greaterthan65 %

Figure 8

ClassificationofAdhesionTest Result.

29

Thefilm surface aftertape testwillbeclassifiedtothe

following

scale :

5B Theedges ofthecuts are_{completelysmooth;}none ofthesquaresofthe

lattice is detached.

4B Small flakesofthe_coatingaredetachedat

intersections,

lessthan5%ofthe

areaisaffected.

3B Smallflakes ofthe_coatingaredetached_alongedges and atintersectionsof

cuts. Thearea affectedis 5to 15%ofthelattice.

2B The_{coatinghas flaked along}theedges andonpartsofthesquares.

Theareaaffectedis 15to35% ofthelattice.

IB _{The coating has flaked along}theedges of cutsin largeribbons and whole

squareshave detached. Theareaaffectedis 35to65%ofthelattice.

Chapter6

The Results

1. _{Water pick-up}characteristics.

The ink used for this project was Ultraviolet Ink manufactured

by

Tjemani Toka

Indonesia under licensed

by

Toka

Shikisho,

Japan. The set consisted of four color

process

inks,

i.e. yellow, magenta, cyan and black. Two Rosos fountain solutions and

commercial distilled water were used to test the water _pickup rate of the inks. The

fountain solution was used tosimulatethe actual condition on the press. Distilledwater

isconsidered a standard solution for many

laboratory

procedures was usedin

laboratory

measurements of water pickup. The _acidity offountain solutions were chosen between

acid and neutral asthepH range and thatwhich is normally found inthepress room. The

completedataoftheseinksandfountainsolutions are shownin Appendix A. Theresults

ofthe water _pickup rate test is shown on Table 2. Each numberis the average of three

measurements asdisplayed inAppendix C. % Water pickuptends to increase overtime

for all these inks in three fountain solutions.

However,

these rates are lower than the

water _pickup of conventional offset ink. The data were also plotted against time and

classified _according to the pH and to the ink color. The water _pickup rate of the inks

usingeachfountainsolution are shownin Figure 9.

31 tfi >

2

Q. o c<

S

t-S 3 o

2

3 *EL u

5

5

Si

a

COCO

&

s

3

3

5

co C i-H ON CN CN CN

a

CO CN CO CN

?S

m CN CN e

cn

a

fc

o

CN

8

o

CN

S

8

$

>

D

i>

u

^

o<N CM CN

a

VO CN CN VO CN

55

ON CN 8 c cj in

88

00

CN

88

CN

00

. t

3

CN

S

CO

CO

ii

D.

01

>n ON CN CN

CN

CN CN

a

S

in CN

^

vO CN CJ _IS o cn co 00

8

co CO CO

in

3

$

&

O

CN

O-O

<L> in 1_t CN 00 CN On CN o CO CN CO CN CO CN CO CO CQ CN

$

.-H

ON

IB

CO CN CO

00

CO in

O

O

in i-H

CN

a

a

VO

CN CN

VO

CN CN

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S

On

r-ON

in

8

CN

o

3

i-H

8

CN vO

8

CN o 3 o CL VO

O

2;

CN

in

CN

r-CN c^

8

On CN o CO CO 8 a CJ ON CO cn

a

CN

X

CN

in ON 00

s?

On CO CN in II zc O-ou cs lO r ₁ cn CN CN CN in CN in CN VO CN VO

CN CN CN

3

o

8

ON COCN

3

CO CO CO ON CN vo ON CN a *<

"3

2;

o

cn CN

CN

?]

CN

?i

S

in CN in CN in CN

S

in(N 00

CO CN

CN

m

3

8

<n

CO

5

2

o (NCN

?]

a

in CN VO CN vo CN CN

S

3

O

S

00

a

8

CN

CO

8

^

c CJ a CD

>

u I 1

o

cn

a

CN

in CN VO CN 00 CN ON CN On CN o CO cL

CO c co

CO

a

mCN

CN in On 00

8

On CO CN in II ZC D. OX

CS m CN_CN

a

in_CN inCN

VO

CN

vo

CN

J5

o m.I

s

$

s

S

3

9

s

VO

CN

13 >

00

r _{1 CM}

a

_{CO CO}

CO

CO CO CO

m

CO CO

s CM CO ^r m VO r _{00 On} o

H

32

G

3

2

OC

2 4 6 8 10 12

Time,

minutes

pH=3.4

Yy=19.6+17.64Log(x)

RA2=0.977 R=0.988

Cy=15.14+15.64Log(x)

RA2=0.985 R=0.992

My=16.8+ 11.61

Log(x)

RA2=0.953 R=0.976

Ky=15.92+ 12.3

lLog(x)

RA2=0.983 R=0.991

pH=6.6

Yy=_{17.55 +17.45Log(x)}

RA2=0.944 R=0.971 Cy=_{16.49 +15.07Log(x)}

RA2=0.960 R=0.979

Ky= 17.16+ 11.

47Log(x)

RA2=0.916 R=0.957

My=16.4+

9.93Log(x)

RA2=0.933 R=0.966

pH=_7.1

Yy=_{16.27 +18.47Log(x)}

RA2=0.986 R=0.992

Cy=15.53 +

13.58Log(x)

RA2=0.964 R=0.981

My=_{16.32 +10.09Log(x)}

RA2=0.948 R=0.974

Ky=_{16.54 +8.97Log(x)}

[image:44.546.59.491.48.527.2]

RA2=0.923 R=0.961

Figure 9

Water_pickupwithdifferent fountainsolution as afunctionoftheink.

Theyellow ink appearedto have the highestwater_pickuprate ofthe tested inks ineach

33

solution. The data point fitted the logarithmic equation and yielded high coefficient

correlation

(R)

foreachinkandfountain solution.

To more _clearly show the effect of pH to each

ink,

the above curves were

classified_accordingto thecolor as shown

by

Figure 10.

50

JX 20

c ^

3

10

GS U

Oft

^H

50

U

O

GS 40

#

30

20

10

50

2 4 6

YellowInk

8 10

0 2 4 6 8 10

Magenta Ink

50

I ' -T"

0 2 4 6 8 10

Cyan Ink

0 2 4 6 8 10

Black Ink

[image:45.546.57.492.157.562.2]

Time,

minutes

Figure 10

34

Yellow,

magenta and black inks showed the same tendency. The rate is higher at the

lower pH. The rates of pH=6.6 and pH=7.1 for yellow and magenta are close to each

other. The solution with the _acidityof6.6 was distilled water. Although distilled water

and fountain solution with the _acidity of7. 1 are _{chemically very} different and have

different formulationand _{conductivity,} theeffect of_acidity appears to be important for

theseinks. The narrow pH range between these two solution did not have a significant

differenceinthe water_{pickup for}yellow and magenta inks. Ontheother

hand,

thecyan

ink behaved differently. The highestwater _pickup rate for the inks tested was reached

when the inks were emulsified with distilled water. Distilled water had the lowest

conductivity among all the solutions used in this experiment. Even though lower pH

yielded ahigherwater_pickuprate,the_conductivityappears tohave alargereffect onthe

water_pickuprateforcyan ink.

The overall effect of _acidity and different inks to the water _pickup rate were

tested _using ANOVA forcrossed design. The purpose of this significance test was to

draw verbal conclusions about this _study

by

_using a numerical test. The calculated F

value is compared to the F critical value from the table. The rejection of the null

hypothesis implies a difference between the subjects of the test The critical F value

from the table is denoted

by

F(a,v^,V2)

where a representthe

risk,

vj

is the degreeof

freedomofthenumerator(the subjectofthe

test)

and

i^

isthedegree offreedom ofthe

denominator (residual orerror). ANOVA calculationforthis _studywas performed_using

Minitab,

the statistical package intheRIT-VAXsystem. Theresult of this calculation is

35

Table 3

ANOVA Tableofwater_pickuprate.

Source DF SS MS F P

PH 2 184.710 92.086 56.51 0.000

Time 9 6188.135 687.571 421.92 0.000

Ink 3 2131.396 710.465 435.97 0.000

pH*Time 18 37.217 2.068 1.27 0.209

pH*Ink 6 126.509 21.085 12.94 0.000

Time*

Ink 27 313.821 11.623 7.13 0.000

pH*Time*Ink 54 37.241 0.690 0.42 1.000

Error 240 391.112 1.630

Total 359 9409.603

Thecritical Fvaluefortheinkat 95 %confidence level is

F(0.053,240)

= 2.60. From

Table

3,

the calculated F for ink is higher than 2.6 . Therefore hypothesis 1.1 which

stated thatdifferentinks havesimilar water_{pickup is} rejectedat95 %confidence level.

Different UV inks performed differentwater_pickupcharacteristics. Since thecalculated

F of pH is also higher than

F(0.05,2,240)

=

3.00,

hypothesis 1.3 which stated that the

acidity offountain solutiondoes not affectthewater_pick-upcharacteristicofthe

ink,

is

also rejected at95 %confidencelevel. The acidityoffountainsolutionaffectedthewater

pickupcharacteristicoftheUV inks.

2.

Curing

time

The curing timeofthe inkwere measured through several steps. The Argon

Curing

unit

36

curing unit remains unknown

because

of the lack of calibration equipment _namely a

radiometer.Thetechnical sheet ofthemanual didnot state_{anyinformation regarding}the

intensity

ofthe

lamp,

the unit of absorbed doseand theunit ofthe belt speed. The belt

speed ofthe_curing unit was calibrated_usinga stopwatch. The lengthofthe _curing unit

was statedinthemanual. TherearefourUV

lamps,

twoofthem are300 W/inchand the

other are200 W/inch.Two meters measuredtheabsorption

dose,

oneforeach side. The

full capacity of the lamps will turn both absorption meters to 35 (70 in total). Half

capacityof each side will turn theabsorption meter

halfway

(15-18). In total, therewere

four

lamp

_capacitysettings available. The first experiment used full capacity for both

side. In the middle of the experiment, the left

lamp

control burnt down. All

measurements were repeated _using one _setting, i.e. one fourth of the overall capacity.

The printed sheet was positioned in same spot in the _curing unit to ensure a similar

curingpattern forall thesamples.

The _curing system was used at the slowest speed. If the sample is _completely

dry,

the speed is increased forthe next fresh sample until the speed with a _slightly wet

sample was found. Several samples were passedthrough the_curing unit_usingthefastest

dry

speed andthe _slightlywet speed. Iftheinkwas still wet_usingthe slowest_{speed, the}

sample was passed through the unit several times with the similar speed until it dried.

The procedure was repeated forothersamples of each color. Magenta inkappeared to

dry

withthe fastestspeed. Thereweredifferentrates dueto the differentpHforthesame

ink. Cyan appeared to be the mostdifficult inkto dry. The _curing speed was slower at

low pHforyellow,magentaandblack. Thisresultledto theconclusionthathigherwater

pickup (lower pH) for yellow, magenta and black reduced the _curing speed. This

conclusion was also validforcyaninksince the slowest_curingrate forcyan occurred at

37

The difference in time needed to

dry

the ink between cyan and the other color

was considerable. The

summary

of the result of this experiment is shown in the

following

table.

Table 4

Curing

timeoftheUV inksatdifferent fountain solution.

Inks

Curing

time,seconds

pH=3.4 pH=6.6 pH=7.1

UV-Yellow 10.21 5.52 5.15

UV-Magenta 4.27 4.04 3.81

UV-Cyan 1 14.77 122.29 106.03

UV-Black 27.81 25.52 24.54

The cyan pigment appeared to act like a neutral

density

filter for the UV radiation.

Referredto fig.

2,

there isa _possibility thatthe cyan pigment inthis ink had lowerUV

radiationtransmittance thantheblackcolorantorthewavelengthoftheUV_{energy from}

the Argon

Curing

Unit was longer than 300 nm. Therefore the

drying

process of the

cyan inkwasinhibited.

Toprovethe firstassumption, the magenta, yellow andblackprintswere covered

by

theblue laminated film and clearfilm. Theclearfilmprolonged the

drying

process of

the magenta,yellow andblack inks. The blue laminatedfilm inhibitedthe

drying

process

to somelarge extent. Thequantitative effect ofthis neutral

density

itself is differentfor

38

Figure 11

[image:50.546.105.366.58.294.2]

Theprint withblue laminated film.

Table 5

Curing

timeofUV inkswith neutraldensity.

Inks

Curing

time,seconds

pH=6.6 Clearfilm Blue film

UV-Yellow 5.52 18.20 54.60

UV-Magenta 4.04 18.20 36.40

39

The hypothesis 1.2 stated that water picked _up

by

the ink does not change the

curing rate of the inks. This

hypothesis

was tested _using crossed design ANOVA in

Minitab forthe completedataas shownin Appendix B. The calculated Fin Table 6 is

higherthan

F(0.05,2,48)=3.23.

Therefore hypothesis 1.2 is rejected at95 % confidence

level. _{Water pickup} ofthe UV inks changed the _curing rate of the inks. Table 6 also

shows that the calculated F value for the ink is _{considerably higher} than

F(0.053,48)=2.84which supporttheexperiment conducted

by

Bassemirand others.

Table 6

ANOVAof_curingtime.

Source DF SS MS F P

PH 2 261 130 24.94 0.000

Inks 3 121394 40465 7739.82 0.000

pH*Inks 6 510 85 16.27 0.000

Error 48 251 5

Total 59 122416

The effectof the substrates were studied

by

_applying conventional ink to three

differentsubstrates and _overcoatingthe ink film

by

theUV varnish. Dueto the UV inks'

tack, it was impossible to print the UV ink on the uncoated paper. Three different

substrates were chosen

including

coated paper, uncoated paper and mylar film.

Thickness,

porosity, roughness andoil _absorptivityofthesesubstrates were measured as

40

Table7

Substrates properties.

Substrates Thickness

Porosity

Roughness % K&N Oil

per1000th inch mL/min um absorptivity

Domtar 50#offset 3.68 424 6.65 68.00

(Uncoated)

MOffset Austria 80# 7.13 1 1.33 25.96

(Coated)

Mylarplastic 2.75 0 1.90 9.46

The samples generated were cured andtested forresistance properties. The results were

as follows :

Table 8

Curing

timeforovercoat varnish ondifferent substrates.

Substrates

Curing

time, seconds

Uncoated paper 12.17

Coated paper 22.6

41

Table 8 revealsthe_curingtimefortheovercoat varnish ondifferentsubstrates.Uncoated

paper is the most absorbent substrate used in this experiment and produced the fastest

curing rate. Someofthevarnish applied totheprinted uncoated paper was absorbed

by

thepaper whichhelpedthe_curingprocess.

The mylar plastic used is classified as a non absorbent substrate. It is the most

difficulttocure. Eventhoughthesample passedthe_{rubbing test,}thevarnishonthemylar

plastic was still _slightly wet to the touch. To find out if this result is _{significantly}

differentone _{to another,} a

Oneway

ANOVA was usedto test the dataand produced the

following

table:

Table 9

Oneway

ANOVA for differentsubstrates.

Source DF SS MS F P

Substrates 2 342.2 171.1 15.13 0.005

Error 6 67.8 11.3

Total 8 410.0

The calculated F value is higher than F(0.05,2,6)=5. 14 which means substrates have

significant effect on the _curing time. Hypothesis 1.4 states that the _curing rate will be

42

3.

Resistance Properties

3.1 FilmHardness

Film hardness was measured at twodifferent levelsof scratch severity. Table 10 shows

the force required to scratchthe ink film. Foreach _color, the required force to _slightly

markthe_{film is nearly}alike.Therequired forcetoscratchthefilm downto thesubstrate

are _{different for different pH with eachink. For}

yellow, magenta and

black,

the highest

scratchresistance propertieswere produced at pH=6.6(Distilledwater).AtpH=6.6these

inks generatedthe lowestwater _pick-uprate. Thehighestresistance properties forcyan

was _{reached at pH=7.1} which had the lowest water _pick-up rate for cyan. This

phenomenon led to the conclusion that the lowest water _pickup will give the highest

scratch resistance.

Table 10

Filmhardnessoffourcolor processUV inks.

Apparatus: Gardco/HoffmanTester

Position : Lowrange,20

-250grams

Required force to scratch the

film,

in grams

Inks pH=3.4 pH=6.6 pH=7.1

lower upper lower upper _{lower upper}

Yellow 35 208 30 246 35 210

Magenta 30 170 36 192 30 ₁₉₀

Cyan 33 182 32 188 34 198

!

43

Hypothesis 2.1 was tested_using the MINITAB program as summarized in table

11.The calculatedFvalue forpH was higherthan F(0.05,2,96)=3.10which means that

hypothesis 2.1 was rejected at 95 % confidence level. Water pickup of the UV inks

affectedthefilm hardnessofthecuredfilm.ThecalculatedF valuefor ink isalso higher

than F(0.05,3,96)=2.7 which shows the significant effect of different ink to the film

hardness.

Table 11

Anova forscratch resistance/filmhardness.

Source DF SS MS F P

PH 2 5075 2538 25.83 0.000

Setting

1 890963 890963 9070.25 0.000

Ink 3 14862 4954 50.43 0.000

pH*

Setting

2 3870 1935 19.7 0.000

pH*Ink 6 2810 468 4.77 0.000

Setting*Ink 3 10065 3355 34.15 0.000

pH*Set*Ink 6 2861 477 4.85 0.000

Error 96 9430 98

Total 119 939937

3.2.Abrasion Resistance

Abrasionresistance was measured _using the GA CAT Comprehensive Abrasion Tester.

44

displayed here were _using receptor A-5 to ensure comparability. The result was

compared to the _{Rank Book from GAVARTI. The higher the number, the} poorer the

abrasion resistance ofthesamples. Table 12shows therankoftheabrasion resistancefor

each color and each pH. Therewere no significant_{difference among}pHs ofeach color.

Table 13 is the _{ANOVA summary}tableof abrasion resistance to test hypothesis

2.2. The calculated F value for pH was less than F(0.05,2,24)=3.40 . Therefore

hypothesis 2.2 which stated that water _pickup of UV inks does not affect abrasion

resistance ofthe curedfilm isaccepted at95%confidencelevel. On theother

hand,

the

calculatedFvalue for inkwashigher than F(0.053,24)=3.01 which indicated that there

wassignificant effectofdifferentinkstoabrasionproperties ofthecuredfilm.

Table 12

Abrasionresistance ofUV inks.

Apparatus: GA CAT Comprehensive Abrasion Tester

Receptor : A-5

PH Abrassionranks

3.4 6.6 7.1

Inks

UV-Yellow 4 5 4

UV Magenta 5 5 6

UV-Cyan 5 5 5

Table 13

AnovaforAbrasionresistance.

3.3. Adhesion Resistance

45

Source DF SS MS F P

PH _{2 5.0556 2.5278 3.37 0.051}

Inks 3 18.0833 6.0278 8.04 0.001

pH*Inks 6 11.1667 1.8611 2.48 0.052

Error 24 18.0000 0.7500

Total 35 52.3056

Adhesion testforthe samples was done using twodifferent Scotch tapes from 3M. The

pressure sensitive transparent tapecode no. 600 is more whitethan thepressure sensitive

tape code no. 519. Forall colorinks and _pHs, these tapes yielded a similarresult. The rank ofthe adhesion properties of the samples wasjudged

by

_counting the flakedarea

and compared them toFigure 8 (ASTM Standard D3359). Theresultis shown in table

14. The highernumber, thebetteradhesion resistance ofthesamples.

The adhesion resistance was similar for each pH and ink's color. There was

difference among colors at similar pH. The result indicated that water _{pickup had} no significant effect on theadhesion properties ofthe curedfilm. The ANOVA calculation

totesthypothesis2.3 isshownintable 15.

The calculated F value forthe pHwas _only0.50 which was

considerably

lower

46

UV inks does not affect the adhesion resistance of the cured film is accepted at 95%

confidence level. The calculated F value for the ink was _{significantly} higher than

F(0.05,3,12)=3.49.

The null hypothesis is rejected

indicating

that the different inks

significantly have differentadhesionproperties ofthecuredfilm.

Table 14

AdhesionresistanceoffourcolorsUV ink.

Adhesion rank of the ink film

Inks pH=3.4 pH=6.6 pFi[=7.1

600 519 600 519 600 519

Yellow OB OB 4B OB 4B OB

Magenta OB OB OB OB OB OB

Cyan 4B 4B 4B 4B 4B 4B

Black 4B 4B 4B 4B 4B 4B

Table 15

Anovaforadhesion resistance.

Source DF SS MS F P

PH 2 1.333 0.667 0.50 0.619

Inks __ 3

72.000 24.000 18.00 0.000

pH*Inks 6 4.000 0.667 0.50 0.797

Error 12 16.000 1.333

47

3.4 Resistanceproperties_ofdifferentsubstrates

The

testing

methods to measure resistance properties of these samples were similar to

thoseforUV inks'

samples.Table 16 showstheresult ofthesemeasurements.

Table 16

ResistancepropertiesofUVvarnish ondifferentsubstrates.

Resistance properties of the varnish + ink film Substrates Abrasion Adhesion Scratchresistance

lower upper

Uncoated 5 OB 30 166

Coated 7 4B 60 176

Mylar 3 5B 30 65

Different substrates gave different resistance properties. Coated paper had the lowest

resistancetoabrasionbutresisteddelaminationand scratch.Mylarhadgood resistanceto

abrasion and

delamination,

but easily scratched. Uncoated paper _poorly resisted

delamination. The flaked formed was between the first layerto the substrate (between

inkand substrate). Forall the samples, therewas no apparent

flaking

between first layer

(ink)

and secondlayer(Varnish).

Table 17 shows the_{oneway ANOVA} tableforthesemeasurements. ANOVA had

[image:60.546.79.472.110.462.2]

Table 17

Oneway

ANOVA forthe resistanceproperties.

48

AnalysisofVarianceonabrasion

Source DF SS MS F P

Substrates 2 24.89 12.44 4.67 0.060

Error 6 16.00 2.67

Total 8 40.89

Analysis ofVarianceonScratchtest

AnalysisofVarianceon adhesion resistance

Source DF SS MS F P

Substrates 2 28302 14151 4.64 0.019

Error 27 82383 3051

Total 29 110684

Source DF SS MS F P

Substrates 2 45.17 22.58 17.30 0.001

Error 9 11.75 1.31

Total 11 56.92

For abrasion resistance, the calculated F value is lower than F(0.05,2,6)=5.14

which means substrateshaveinsignificanteffect on abrasion resistance ofthecuredfilm.

F(0.05,2,27)=5.45 is higher than calculated F value for scratch resistance which also

indicatesthatsubstrates have insignificant effecton scratch resistance. ThecalculatedF

value for adhesion resistance is higher than F(0.05,2,9)=8.02.

Among

these three

resistance properties, only adhesion resistance was _{significantly} affected

by

the

49

4. OtherFindings.

4.1 Tack

In_conducting thewater_{pickupmeasurements,} itwas foundthatthe UV inks were more

difficultto workthan theconventional

ink,

therefore tackmeasurementwas performed.

Thetack was measured attwo_{different rotating} speeds suchas 800rpm and 1200rpm.

The result is shown in table 18. The tack ofthe inks are _{significantly higher} than the

conventional ink which _{is usually less}than 25. Figure 12 shows the tackcurves derived

from table compared to the conventional ink. The conventional ink used was process

black ink RS-01 10-445. Magenta ink hada

flying(

misting) problem atthehigherspeed.

Tacksofthe UV inks werehighat the

beginning

oftheprocess, afterthree minutes,the

curves tend to flattenout. The shape ofthe curves might be interpreted to