A model for non-image area of offset lithographic process

Rochester Institute of Technology

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2-1-1988

A model for non-image area of offset lithographic

process

Vinay Chhajlani

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Certificate of Approval -- Master's Thesis

School of Printing and 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

Vinay Chhajlani name of student

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

February 1988 date

Thesis committee : Julius Silver

-:T,....h-e-s-::i-s-A-d-v-i~s-o...r

-Joseph L. Noga

~du~~ pz~gram C~orAinator Miles Southworth

A MODEL FOR NON-IMAGE AREA OF OFFSET LITHOGRAPHIC PROCESS

by

Vinay Chhajlani

A thesis submitted in partial fulfillment of the

requirements for the degree of Master of Science in the

School of _Printing Management and Sciences in the College of Graphic Arts and _Photography of the

Rochester Institute of _Technology

February, 1988

Title of Thesis:

A MODEL FOR NON-IMAGE AREA OF OFFSET LITHOGRAPHIC PROCESS

I, vinay Chhajlani, hereby grant permission to the Wallace Memorial Library, of RIT, to reproduce my thesis in whole or in part. Any reproduction will not be for commercial use or profit.

ACKNOWLEDGEMENTS

I am _very thankful to _my advisor Dr. J. L. Silver for his

help and guidance in _completing this thesis. I am also

thankful to Prof. J. L. Noga for for his advise and

Mr. Frank Cost for _being on _my thesis committee and his

support on the subject matter I chose. I am grateful to _my

wife for her constant support _during the entire period of _my

thesis work.

TABLE OF CONTENTS

LIST OF FIGURES IV

ABSTRACT _v

1. INTRODUCTION ₁

2. NEED FOR A MODEL ₃

3. THE PHYSICAL MODEL ₉

4. DEVELOPING THE MODEL ₁₆

5. CONCLUSION ₂₅

6. RECOMMENDATIONS ₂₈

APPENDIX A ₃₁

APPENDIX B ₃₂

LIST OF FIGURES

Figure 2.1: Model of water flow in an offset unit

Figure 3.1: Diagram _showing the plate surface and

the various films present at the plate inking form roller nip.

Figure 4.1: Diagram _showing a three phase interface

with respective interfacial tension and contact angle.

Figure 4.2: Diagram _showing a three phase interface

with respective interfacial tension and

contact angles where one phase is solid.

Figure A.l: Graphical determination of tolerance range

for the surface properties of the fountain

solution based on Griffith's surface _energy

for fracture.

ABSTRACT

Lithography is the most common _printing process. _However,

very little is known about the _theory of lithography.

Pressroom practices have evolved more out of experience than

on the basis of _any theory. The objective of this paper is

to develope a mathematical model for the non-image area of

the offset lithographic plate. A model of this kind would

provide a rationalization for the observed behavior in

lithographic process.

The _study concentrates on the various materials and the

phenomenons involved. Properties of aluminum oxide surface

and gum arabic that make them suitable for the process have

been presented. Rheological properties of ink have been

discussed to show their effect on the print quality. Most

importantly the subject of surface energetics has been used

to explain the interfacial behavior of the three phases

involed

-ink, fountain solution and plate surface.

The _study of the interfacial behavior helps in _arriving at

the final model. There are several phenomenon _taking place

in _making lithography work. Adsorption of gum _arabic,

wetting of the plate _by fountain solution and film _splitting

at the _nip exit are explained and the interrelationship

between them derived. Surface energetic equations and

Griffith's free _energy for fracture have been usedto present

the final model for the system.

The model as proposed in this paper gives a deeper insight

into the lithographic process and helps- in understanding the

reasons for the _printing abberations. There is a need to

model other aspects of the process and design methods to

test them so as to _help in development of better equipment

and standard practices for lithography.

CHAPTER I

INTRODUCTION

Lithographic offset _printing is the most _commonly used

printing process. It is different from the other printing

processes in that the _printing plate is planar. There is no

mechanical separation between the image and the non-image

areas instead their delineation is achieved chemically.

Lithography, to a _layman, means a process _involving two

liquids, ink and fountain solution, that do not mix and two

different surfaces

-1. hydrophilic and oleophobic 2.

hydrophobic and oleophilic. The ink _being solvent based gets

attracted to the oleophilic image area and the fountain

solution _being an aqueous solution gets attracted to the

hydrophilic non-image areas. This is a _very simple

explanation for the theory of _lithography but it is not

accurate.

The _theory of lithographic offset _printing is not well

understood. In the past not much work has been done to

explain the process. In recent years with the growth of the

industry there is a _growing interest in the _theory of

The lack of _theory and well developed mechanisms means that

there is no well marked approach to press room practices.

There is also no set procedure to _correcting printing

abberations. Press room practices have evolved more out of

experience than based on _any theory. Researchers are now

attempting to explain the mechanism.

The purpose of this thesis is to develope a model for the

non-image area of the plate and the process of _keeping the

non image clean. A _study and a model of this kind would aid

CHAPTER II

THE NEED FOR A MODEL

The lithographic process is _very complex and involves

several variables and mechanisms. Studies have been

conducted to _study different aspects of the process. In

order to get a _{understanding} of the process it is _very

necessary to understand all the mechanisms and their role in

the process. Theories have been proposed for:

1. Ink transfer mechanism

2. Fountain solution transfer

3. Ink and fountain solution transfer

4. Ink water emulsification

The above mentioned theories are discussed in brief in this

paper. The main mechanism dealt in each is explained _along

with the significance and how it helps in understanding

lithography

-INK TRANSFER MECHANISM

Several models have been proposed to calculate ink film

thickness through the various rollers in the _{inking system,}

plate, blanket and the image area on the paper. These models

reasons for ink transfer related problems like ghosting.

There have been studies _{by Bradford1, Hull2,} Mill3

addressing the issue of ink distribution. Guerrette4

has

proposed a model for calculating steady state ink film thickness throughout the _inking system.

The method uses inversion of a matrix _representing volume

continuity of ink within a roller distribution. It is based on an ink split at each _nip and incorporates the effect of

plate coverage on the transfer. _Along with the thickness

distribution, the amount of ink contributed to the plate _by

each form roller and principal ghost magnitude have been

calculated. It has been shown that thickness distribution on

rollers and contribution _by each roller is _highly dependent

on the image coverage.

This model based on volume _continuity is useful in

understanding ink transfer mechanism. However it gives no

insight to what causes the ink to transfer to the image

areas and not transfer to the non image areas.

FOUNTAIN SOLUTION TRANSFER

Fountain solution flow model has been proposed _by Kartunnen

and Lindqvist5. This model gives water flow schematically

only. It does not represent ink and water interaction. The

continuous as a function of time. It also assumes that water

flow is even and equal in all image and non image areas

respectively.

Figure 2. 1 below shows the water flow as proposed by the

authors. Variable Io is the water _feed, K]_, _K3 , K5, K8, K10

are the evaporation factors in the process and _K2, K4, K6,

K7, K9, _K^ are the _splitting coefficients. X and Y are the

transfer parameters.

Non-image area io

y'o

IN_KER_

W

kil_3M

k,I_A1!

U=R\

Image area 12

Plate kfil_6'2

kcl

t t=

Blanket

kinl/.

Paper 3

Scale

0 1 2 3 U um

Fig. 2.1 Model of water flow in an offset unit

The model also proposes that the most important criterion

for the print quality are the amounts of water transferred

to the image and the non image areas. If too much water is

transferred to the image areas it would result in water

areas it would cause scumming. It _{is very important}

therefore that a proper water feed level be maintained to

ensure good print quality.

A simulation program was developed based on the model which

can be used to calculate tolerance limits of water feed

based on relative _printing area and interaction parameters.

This model does not however deal with the factors that

affect the water and ink transfer.

INK AND FOUNTAIN SOLUTION TRANSFER

This model also proposed _by Kartunnen and Lindqvist6 is a

composite model. It discusses both ink and fountain solution

transfer. An offset unit simulator has been proposed based

on both ink and water transfer. Presence and the effect of

surface water and emulsified water have proposed.

The models described in this chapter provide a _{understanding}

of the quantitative flow. However a _study of the factors

that cause this flow is required. The _theory of lithographic

printing process is _very incomplete. _Many press subsystems

like _dampening and _inking systems designs have evolved over

the years and have been improvised _by experience. There is

very little theoretical basis for many designs. Press room

practices have been developed mofe out of experience than

certain _operating conditions on the print _quality but there

is not much work done to understand the mechanisms. A better

understanding of the mechanism would explain the reason for

the effects of certain conditions on print quality.

The main objective of this thesis is to _develop a model for

the lithographic plate non image area at the _dampening form

roller

-plate _nip and at the _inking form roller

-plate

nip. Various phenomena _taking place at these two nips are

described in detail. A _relationship is developed between

these phenomena which would lead to the model.

This thesis is focused on a conventional lithographic

grained aluminum plate surface, a conventional _dampening

References for Chapter II

1. _Bradford, Dr. J. R. , 'Lithographic Press Ink Distribution Studies _by Radio Tracer Techniques'

, TAGA Proceedings

(1954) , p.279.

2. _Hull, H. H. , 'The Theoretical Analysis and Practical Evaluation of Roller Ink Distribution _Systems', TAGA

Proceedings (19₆₈₎ .

3. _Mill, C. _C, 'An Experimental Test of a _Theory of Ink

Distribution', Advances in _Printing Sciences and

Technology, Vol. 1 _(1961), Ed. _by Banks.

4. _Guerrette, D. _J., 'A _Steady State _Inking System Model for _Predicting Ink Film Thickness _{Distribution',} TAGA Proceedings , p. 404

5. _{Karttunen, S., Lindqvist,} U. _, 'Water Flow and Surfactant Effects in Offset Litho _Printing', Advances in _Printing Science and _Technology, Vol. 15, Ed. W. H. Banks

CHAPTER III

THE PHYSICAL MODEL

In _{lithography, keeping the non image area free of ink is}

very critical to the _quality of printing. The non image area

is kept clean chemically. In order to arrive at a

mathematical model it is _necessary to start with a simple

descriptive model. As a _starting point a simple model is

being assumed.

This model assumes that when the plate is "gummed"

before

running the press the porous non image area made of a

grained aluminum surface adsorbs gum arabic. When the

dampening form roller passes over the non image area a water

film is left on it. This happens because the gum arabic

molecules attract the water dipole and hence reduce the

surface tension and so the water spreads on the non image

area. When the _inking form roller passes over the image area

there are three different films at the nip. These films are:

1. Water film

2. Ink film

10

At the _nip exit a cleavage takes place. The film _requiring the minimum force will split. In order to get a clean non

image _area, the water film should split. This will happen only when the ink film thickness is such that it requires a

larger force to split than the water film. The composite

film should _backtrap onto the ink film on the form roller

and the interfacial tension between the composite film and

water film should be so that there is no split at this

interface.

INK RLrf

XrlAC-,6 A*EA

^ |M|

f

^e^RE*

GRAIHED AUUniHurn

SURFACE

Figure 3. 1 Diagram showing the plate surface and

the various films present at the plate

inking form roller nip.

In order to _develop a mathematical model for the non image

area it would be necessary to understand the various

phenomena _taking place at the non

image1

areas. It is also

necessary to know the materials involved and their physical,

chemical and interfacial properties. One of the most

11

This chapter concentrates on _{the materials,} their

interaction and the surface phenomena that make _lithography

work. The actual mathematical relationships would be derived

based on surface energetics.

ALUMINUM PLATE SURFACE

The conventional lithographic plate is made of anodized

aluminum and has a grained surface. The plate is grained to

give it a large surface area and porosity. The grains serve

two important _{functions, they help} hold the image area

coating in place and the grained surface serves as the non

image area.

Chemical and physical structures of an anodized aluminum

plate have been described in detail _by Salgo1. _Chemically,

the aluminum plate surface is covered _by solid A1203.H20 and

the _top layer consists of gamma _A1203 crystal grains. The

oxide layer thickness ranges from 5 to 4 0 microns.

When wetted with water, the water content of this oxide

hydrogel depends on the condition under which it was

manufactured. _Physically the oxide layer is cellular and

porous2- Its properties depend on the _following variables:

pore dimension, cell wall _{thickness, boundary} layer

thickness at the cell bottom, nature of oxide formed and

pore sealing. This microstructure makes the plate surface

12

The _wettability of water to this aluminum oxide surface is

increased _by adsorption of gum arabic. The type of

adsorption and the factors _affecting it are discussed later

in this chapter.

GUM ARABIC ADSORPTION

Gum arabic plays a _very important role in _keeping the non

image area of a lithographic plate clean. When _using

conventional _lithography, the plate is _usually "gummed"

before _starting the press. Gum is also a component of the

fountain solution.

Gum arabic is a natural product obtained from acacia trees.

Chemically it consists of the mixed magnesium and calcium

salts of complex polymeric hydroxiacid3. It has a mean

molecular weight of about 250000. In solution it behaves as

a typical colloidal electrolyte and the free _acid, arabic

acid, can be obtained _{by using} an ion exchange column to

remove the cations.

The free acid has an equivalent weight of about 1250. It has

about 2 00 carboxyl groups present per molecule. This means

at _very low pH gum arabic solution could cause active

corrosion or dissolution of a metal _by the free acids.

The gum arabic molecules are adsorbed _by the grained

aluminum. Since gum arabic in solution is a _highly hydrated

anion with multiplicity of carboxyl group the sorption would

13

A monolayer of gum arabic adsorbed is enough to make the non

image area _{hydrophilic i.e.} it reduces the surface tension

for the formation of the water film. Contact angle studies

as reported _by Adams4

prove that adsorption rates depend on

the concentration and pH of the solution. Contact angle is a

good measure of _wettability of a surface _by a liquid.

FILM SPLITTING AT NIP EXIT

When the non image area passes under the _dampening form

roller a water film forms on it. At the _inking form roller

-plate _nip there are at least three films _{present, ink,} ink

& water and water film. At the _nip exit one of the films or

an interface has to cleave. The force _necessary to split a

film between two surfaces is expressed _by Stefan's equation:

F = _CuVA/t

Where F = _{force required} to _split the film

C = _constant

u =

viscosity V =

velocity at which parted A = _{surface area}

t = _film thickness

If there are two more films then the film _requiring the

lesser force will cleave at the cavitation nuclei4.

It can be seen _by the above discussions that it is _very

important to have a proper plate surface, desired level of

gum adsorption, proper water film thickness, and proper ink

14

There is a need to understand these procedures and their

operating limits.

The main objective in this thesis is to establish the

relationship between these practices and explain the need

for each from a theoretical stand point. These relationships

would be used to derive at a model that would rationalize

15

References for Chapter III

1. _{Salgo, V.,} Theoretical principles of the application of

aluminum oxide layers in the _printing industry' , APST

Vol.2 ₍₁₉₆₂₎ ed. _W.Banks, p.235.

2. _{Severn, I.D., Burring, S.L.,} 'The _wetting properties of litho _printing surfaces. 'London:Academic _Press(1978)

3. _{Mantell, C.L.,} 'Water soluble gums' ,reinhold (1947)

4. _Adams, R. A. C. Sorption of Gum arabic from aqueous

solution onto _{aluminum', Printing technology, Vol.15,}

No._{2, (1971) ,} p.24.

5. _{McPhee, J.,} 'An engineers analysis of the lithographic

16

CHAPTER IV

Chapter 4: DEVELOPING THE MODEL

Two fields are _{very important in} the _study of the _theory of

lithography, they are _Rheology and Surface energetics.

Rheology helps _{in understanding} the properties and behavior

of ink and surface energetics gives an insight to the

interfacial behavior in the process.

RHEOLOGICAL PROPERTIES OF THE INK

Ink is a non newtonian fluid. It is a solid in liquid

dispersion. The solid is the pigment and the liquid is the

solvent. One of the most important rheological _property of

the ink is the tack. Tack of ink is a function of _elasticity

and viscosity of the ink. It is _very important for the

working of the lithographic process that the ink and the

fountain solution be insoluble in each other but be miscible

with each other.

*-Water take _up of ink has been a subject of _study in several

experiments. There has been work on water take up of ink

with time and its effect on print quality. Lindqvist has

determined that the emulsification _tendency of ink depends

on its viscosity and interfacial tension. A higher viscosity

17

interfacial tension also reduces the total water content,

evidently by _decreasing the amount of surface water on the

form rollers2.

The tack of ink-water emulsion is less than that of the ink

on the form rollers. This is also _very important because a

low tack ink would _trap onto a high tack ink. At the plate

inking form roller _nip, water film on the plate comes in

contact with the ink on the form roller. The interfacial

tension should be such that the ink and water are able to

mix to form an emulsion. This emulsion would _backtrap onto

the ink on the form roller which is _necessary so that no ink

is left on the non image area.3

Ink and water surface

properties are also critical to the process. The next

section concentrates on the surface properties of these two

and the interfacial phenomenon in _lithography

-SURFACE ENERGETICS OF LITHOGRAPHY

The most important subjects required to understand the

relationship between the three phase _{namely plate,} ink and

water are surface _chemistry and surface energetics. Concepts

of interfacial _tension, surface tension and contact angle

should be well understood.

Surface chemistry or the physical _chemistry of surfaces is a

science that deals with the _study of two or more phases at

their interface. The phases could be

18

liquid, a liquid and a _solid, a liquid and a vapor _, a

vapor and a solid.

When two phases are brought together so that one would

dissolve in the other _they would form a composite single

phase called a _solution, an example is when salt is mixed

with water a saline solution is formed. When the two phases

do not form a solution but can be mixed with one phase

finely divided and dispersed in the other, it forms a

dispersion.

In _lithography, there are three phases in the non image

area, the plate surface, the fountain solution and the ink.

It is desired that the fountain solution has a greater

affinity for the solid phase as compared to the ink. One of

the measures of _affinity is the contact angle between two

surfaces.

Contact angle is the angle that a phase makes with another

at the interface. The contact angle is a good measure of

wettability of a solid phase _by a liquid phase. The

properties that determine the contact angle are interfacial

tension and interfacial free energy- Surface tension is

defined as the energy required (work _done) to create a unit

area of additional surface. If there are two liquid phases

19

would have more _affinity for the solid phase. For example,

when _something is _greasy water will not stick to it because

water has a greater surface tension than the oil. But whenl

detergent is mixed with water it wets the surface and

replaces the oil because the solid is preferentially wet _by

the detergent solution as compared to oil or grease.

When more than one phase come in contact _they form contact

angles that are related to their surface tension. Consider

figure 4.1 with three phases _1, 2 and 3 with _{#13, ^23'} ^12

and !, ₂' ^3 as tne contact angles. Y12

23

Fig. 4.1: diagram showing a three phase interface with respective interfacial tension and

contact angle.

When the phases are in a state of equilibrium the three

forces balance themselves.

At the _inking form roller

-plate _nip the lithographic

process is a special case of this where phase 1 is _ink,

20

surface. This is a case with one solid phase. The schematic

diagram of the three phase interface is shown in figure 4.2.

*12

Fig.4. 2: diagram _showing a three phase interface

with respective interfacial tension and contact angles where one phase is solid.

In this situation the contact angle 03 is equal to 180

degrees due to solid constraint. This schematic will be used

to derive at a model for the non image area of lithographic

plate. In this three phase situation the horizontal forces

balance as:

^

13 =

*

23 +

^12

where Y = interfacial _tension Q = _{contact angle}

There are no direct ways of _measuring the interfacial

tensions. However, equations to calculate interfacial

tension between two phases, i and _j have been proposed _by

Kaeble, Dynes and Pav4.

21

where <*= _{square root}

of that part of interfacial

tension due to dispersion type _(London)

bonding forces

^<- = _square

root of that part of interfacial

tension due to polar type _(Keesom)

bonding forces

This equation can be used to calculate the forces _knowing

the measurable material properties which are the dispersion

and polar type _bonding forces. Appendix A shows calculated

interfacial tension for some common lithographic material

based on equation 2.

Of special interest to _lithography is the application of

Griffith fracture theory. _Using the theory of fracture the

criteria for failure _by crack can be expressed as:

J-c- J-""' TT rt-~

equation 3

where dc= the critical crack propagation stress

c = _{length of the crack}

E =

Young' s modulus

3e> = _{Griffith's free}

energy for fracture

The adhesion of ink and fountain solution to the image or

non image area of the plate is related _by the Griffith's

free energy which is defined as follows:

$ = _-S2/2 = R2 - Rq2

equation 4

where _S2 =

z

22

S2 is the _spreading coefficient of the fountain solution.

The _{spreading coefficient provides a criteria for describing}

spontaneous mechanism of _bonding and _debonding between

phases. If the value of S is greater than or equal to zero

then one phase would bond with the other. Constants R and _R0

are derived from the values of =k and > . This _relationship

is given _by equation 5.

^ ^ 2- ^

Equation 5

Equation 4 defines a circle in the ~6_{g, <'2, >2} cartesian

space. It can be seen that if R < RO then the _spreading

coefficient _S2 > 0 which means that phase 2 would debond

phase 1 from phase 3. This is the conditions desired in the

non image area of the lithographic plate. This models the

non image area and describes the properties required in the

three _phases, the interaction between the three phase and

the actual process at the _inking form roller

-plate nip.

The image area is also described _by the same equation when

the _spreading coefficient S2 < 0. The circles defined _by

equation 4 which give a graphic representation of the

interfacial phenomenon are shown in Appendix II.

A relationship between measurable surface properties of the

23

established with the _help of equations 1 to 5. This model

helps in _{understanding} the surface interactions that come

into _play in the _{lithographic printing} process. _They also

help in _{graphically establishing} a criteria and surface

property tolerance for the ink and fountain solution in the

process.

The discussions and derivations in this chapter have shown

how each phenomenon is important to the success of good

lithographic printing. The _study of _rheology of ink and the

surface properties of the phases involved lead to the final

model for the process. Studies _addressing Gum Arabic

adsorption and contact angle as a measure of _wettability and

Griffith _theory of fracture _by propagation of crack have

24

References for Chapter IV

1. _{Silver, J.,} Course Lecture notes from _Ink, Color and

Substrates, Spring 86.

2. _Lindqvist, U. , 'Ink Emulsification and its Effect on

Print _Quality in Offset_',Graphic Arts in _Finland,

Vol. _5, No. 1 ₍₁₉₇₆₎

3. _{Silver, J.,} Course Lecture notes from _Ink, Color and

Substrates, Spring 86.

4. _Kaelbel, D. H. , Dynes, P. J., and Pav, D. E. , 'Surface

Energetics Analysis of _{Lithography',} Adhesion Science

25

CHAPTER V

CONCLUSION

A model has been proposed in this paper that takes into

account the materials involved and the phenomenon that take

place in the plate

-dampening form roller _nip and the plate

-ink form roller nip. emphasis has been placed on the

surface properties of the phase involved. The model was

aimed at _giving a better insight into the _theory of

lithography.

The model has not been proved through an experiment designed

to test it. The author has _instead, in the _following

sections, supported the model _by the conditions often

reported _by the pressmen from their experience of the

lithographic process. Conditions reported _by other

researchers in _lithography have also been used for this

purpose. These are presented in the appendix section. The

model also provides an explanation for the _commonly reported

printing abberations.

One of the most common problems in lithography is scumming.

The causes for scumming could be several as can be seen from

the model. _Scumming could result if there is not an optimum

26

area as this would cause the ink film to split at the _nip

exit hence _{causing ink transfer in the non image areas.}

Wearing out of gum arabic from the plate surface can also

cause scumming. If the gum wears out it results in increased

interfacial tension between the fountain solution and plate

surface thus _affecting the _debonding of ink from the non

image area _by propagation of crack. This also results in

scumming.

The common practice to start _{up printing} also supports the

model. When a press is _started, the _dampening form roller is

always dropped onto the plate first and the _inking form

roller is dropped _only after a film of fountain solution is

formed on the plate surface. If the pressman makes a mistake

and drops the ink roller _first, the entire plate surface

gets covered _by an ink film. But when the _dampening form

roller is dropped the plate starts to clear from the non

image area. This is consistent with the model. This happens

because the non image area has a positive _spreading

coefficient for the fountain solution so even if the area is

covered with ink the fountain solution will _{spontaneously}

debond ink from the non image area.

Critical to _running of the process is the ink water balance.

The need for this balance also arises from the phenomenon

27

solution _{necessary for keeping the non image} area clean.

There is also a maximum limit on fountain solution feed

above which water mark _up of the image area would appear.

The model explains the observed press behavior

qualitatively. A quantitative proof would require the use of

measuring techniques that would enable _measuring the values

of _key variables on a _running press. An _{understanding} of

materials and mechanisms involved and their inter

relationships presented as a mathematical model provides a

rational for the behavior of the non image area in

28

CHAPTER VI

RECOMMENDATIONS

The non image area of a conventional lithographic plate has

been studied _{in this thesis. There} are several other

mechanisms involved in this process. Ther is a need to

understand all of these in greater detail to provide a

complete _theory for lithography- Research needs to be done

to develope models for the other mechanisms involved.

Another area of interest is the developement of

instrumentation to aid in verification of the models. A

major _difficulty involved in the design of proper _measuring

device is the non newtonian nature of ink and its behavior

at high speeds. There is a need for _measuring film

thicknesses, ink properties and interfacial properties on a

running press. The dynamic measurements would represent the

true value for the process.

There is a need for a better _way to explain the _relationship

between ink viscocity, elasticity and the ink tack, limits

on ink tack that would aid in _keeping the non image area

29

The model desribed _{in this} paper is specific to a grained

aluminum plate and a conventional _dampening system. There

are several other types of _plates, fountain solutions and

dampening system in use. Each has its unique properties.

Each of these have to be studied _individually to explain the

principles _{underlying them.}

A thechnique that can be _very useful in _testing the various

models is simulation. A computer program could be designed

to test the model under various conditions _{by using} assumed

realistic values of variables.

Developing models for all the mechanisms and _having

techniques to test them would _greatly aid in the design of

equipment and would lead to more controlled process. It

would also enable the standardization of press room

30

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