/2..-
`
`RESEARCH & TECHNOLOGY
`
`AN INVESTIGATION INTO THE EFFECT OF
`PROCESS PARAMETERS ON THE INK SUPPLY
`CHARACTERISTICS TO A ROLLER TRAIN IN AN
`OFFSET PRINTING PRESS
`
`Mark F3. Bohan. Tim C. Claypole and David T. Gethin, Welsh Centre for Printing and Coating, Department of Mechanical
`£ngineering, University of Wales, Swansea
`
`ABS’I’I~CT
`
`This paper describes an experimental investigation into the effect of process parameters on product quality in web offset print-
`ing. A production printing unit, part of an eight-station press, was instrumented to record strategic temperatures and speeds. A
`series oforthogonal array experiments were carried out to investigate the sensitivity of the process to changes in important
`press parameters, The changes in product quality were measured using densitometr7 in the test strip, The speeds of certain
`rolls and press temperatures were found to dominate. The response of the press to ink temperature changes was non-linear and
`interacted with the image coverage. This was shown experimentally and by a numerical model that was used m provide the
`phystca] insight to this interaction.
`
`NOMENCLATURE
`
`Ink specific heat capacity
`C
`Blade length for analysis
`L
`Flow rate
`Q
`Temperature
`T
`U~ Sliding sp~ed
`a,b Wahher equatio.n coefficients
`h
`Film thickness
`Ink key/duct rail tilm thickness
`h,
`kr Film thermal conductivity
`Blade thermal conductivity
`k,
`p
`Pressure
`u,v,w Velocity components
`x,y,z Coordinate directions
`Film convergence angle
`a
`p
`Ink dynamic viscosity
`ink density
`r
`Ink kinematic viscosity
`u
`
`INTRODUCTION
`
`High quality printing is a complex manufactunng process hav-
`ing a high hourly operating cost, so the experimental tzmc for
`the investigation of parameter effects needed to be minimized
`and the results obtamed maximized. Onhogonal array tech-
`niques were utilized for ~he experimental programme as they
`have several advantages over other methods including the reduc-
`tion in the nuroher of tests to evaluate the effects of process
`parameters and the ability to investigate interactions between
`parameters. This allows the time and cost ofexpenmcnts to be
`minimized. This is of Importance as the trials were carried out
`
`Journal of Prepress and Printing Technolog3" page J
`
`on a production web offset printing press which was subject to a
`multitude of production constraints inc[uding, for example, job
`scheduling and time to good copy.
`
`The optimization of an existing process necessitates the identifi-
`cation of the important parameters rn the process. It is necessary
`to identify those parameter~ that will significantly affect the
`product quality, and also those which do not affect the process
`but arc generally perceived as being important and for which an
`appropriate control system is in operation. Traditional methods
`include: full factorial trials; the adoption of an elimination
`approach; or the use of experience to optimize the system. The
`full factorial approach requires a large number o f experiments to
`be completed. For example, to evaluate completely eight vari-
`ables at two levels only (infernng a linear behaviour) requires 2s
`(256) tests, if three levels are investigated this will increase to
`6561. This number of tests can not be carried out on a commer-
`cial printing press. Therefore, a technique that reduces the total
`number of tests, from the full factorial, is required.
`
`A second technique which can be used to reduce the number of
`experiments is an elimination approach. This involves holding
`every parameter constant except one and then optimizing for the
`one parameter. This is repeated for all the parameters which are
`believed to be important. The elimination approach is a random
`subset of the fu!l factorial trials, Two assumptions are made dur-
`ing the elimination process which can lead to significant errors
`in the results, First, it assumes there is no variability in the
`process and that identical trials lead to identical results, In the
`best case, a near optimal sening can be achieved, however, this
`is by coioctdence and it is not easy to validalc because the way it
`was achieved is not defined. The most dangerous assumption,
`
`FAST FELT 2006, pg. 1
`Owens Corning v. Fast Felt
`IPR2015-00650
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`

`
`however, is that none of the parameter~ interact which is not the
`case in many processes.
`
`The third wadkional approach is to optimize the process using
`experience. The set ofparameters fi-om the furl factorial trial is
`reviewed and reduced in number until a full factorial is practica-
`ble. tn processes such as printing where the detailed physics is
`not well understood, this can lead to the elimination of signifi-
`cant parameters.
`
`Orthogonal arrays allow the detailed investigation and evalua-
`tion of all the parameters effectively and systematically in ~he
`minimum number otr tests. Onhogona! arrays are balarmed sub-
`sets of the full factorial. No two experiments are either repeats
`or mirror images of each other and each variable setting occurs
`the same number of times. The use of these arrays allows the
`number of runs per experiment to be minimized and the possible
`interactions between the parameters to be investigated. In addi-
`tion, it is possible to compound ~he interactions allowing a larger
`number of parameters to be investigated (for example, seven
`parameters at three levels and one parameter at two levels in 18
`tests).
`
`The Le onhognnal array# were utilized for the majority of the
`trials. These allow four parameters at two levels to be evaluated
`simultaneously with three possible interactions occurring,
`Changes in the process were evaluated using a quality charac-
`teristic, in this case either the print density or the CIE colour
`space values, Although analysis of the results will r,.vea] the
`dominant parameters along with interactions, knowledge of’the
`process is an advant~ige. The design of the experiments will then
`allow the parameters to be identified and the interactions to be
`easily detected.
`
`In the following sections, the orthogonal array techniques used
`in the experimental programme are discussed in detail. This is
`followed by a description of the background theory used in the
`modelling of the ink keylduc~ rot! junction. The significant find.
`ings from the orthogonal array investigation are presented and
`discussed, with the numerical results being used to explain the
`
`Black Cyan MagemaYellow
`Unttl Unit2 Unit3 UnK4
`
`Infeed
`
`Press 2
`
`Un!tS Untt6 Unit7 Unit8
`Bla:k Cyan Magenta Yellow
`
`Press 1
`
`RESEARCH & TECHNOLOGY
`
`physical phenomena that are present in the experimental ~als.
`Finally, conclusions are drawn highlighting the imporvant find-
`ings f-rom the work.
`
`EXPERIMENTAL METHODOLOGY
`
`Parameter selection
`
`Printing is a complex process with a large number ofdifferem
`parameters affecting the quality oi~ the printed productz, An ini-
`tial list exceeding eighty parameters was generated. It was not
`practical to investigate all or’these on a commercial press and
`therefore the effect of some of these were investigated by instru-
`menting and comroBing strategic variables on a single test unit.
`This allowed the investigation of some parameters, together with
`the provision of boundary conditions, to be used in numerical
`modelling teghniques3.’=.
`
`The remaining parameters selected were divided into those relat-
`ing to control and process stability. The control paramcte~ were
`those which could normally be adjusted by the print crew to
`achieve and maintain colour on the press. The process stability
`parameters were those that varied through or between print jobs
`and over which the press operators had no control.
`
`Strategic approach to the experimental
`programme
`
`The experimental programme was carried out using a commer-
`cial eight-unit printing press, with no toss of production.
`Initially, a monitoring exercise was carried out ~ prior to the
`invasive oahogonal array experimental programme. This moni-
`toring was used to determine the process variability and the nat-
`ura! fluctuations present in the product coMur and was
`completed without loss of product.
`
`To the dryer
`
`Lower web
`
`A single unit was fully insrngmcnted for the measurement of"
`temperaturvs and roller speeds. The top roJ]er train on magenta
`unit seven was chosen for this purpose (Figure I), This unit was
`selected because any chan~ ~es in magenta have a sigrtificant
`impact in the image, and also
`because it was located near to the
`dryer. The measurements on the
`printed copy were taken on the
`magenta printed on the upper side
`of the web and analysed using den-
`sitometry. Samples were not col-
`lected until the press had stabilized
`following parameter changes, the
`total time being dependent on the
`parameter that was altered. In all
`circumstances, a minimum time of
`five minutes was aHowod once a
`change had been implemented.
`
`Research & /echnoloKt" INK SUPPLY OIARAc’rEt~’TIG; page 5
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`FAST FELT 2006, pg. 2
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`

`
`RESEARCH IE TECHNOLOGY
`
`Table ! List of orthogonal array experiments
`
`Orthogonal array
`
`Parameters investigated
`
`Army ! A (18 array)
`
`Array I B (Two L4 arrays)
`
`Ar~y I C (L4 array)
`
`Army i D (L4 array)
`
`Array I E (L4 array)
`
`Array l F (L9 array)
`
`Ink key se~ing, duct roll speed,
`pan roll speed
`
`Pa~ roll speed, CUIM rotl speed,
`temperature of ink in duct, tem-
`perature of fount in pan
`
`Temperature of ink in duct, tem-
`perature of fount in pan, tempera-
`ture of the copper roll cooling
`water
`
`Temperature of ink in duct, tem-
`perature of fount in pan
`
`Temperature of ink in duct, tern-
`perature of fount in pan
`
`Temperature of ink in duct, tem-
`perature of the copper toil cool-
`ing water
`
`Array l G (L2 array)
`
`Temperature of ink in duct
`
`The monitoring exercise showed ~hat there are large thermal
`transients in the printing press during the star~÷up period. For
`example, the temperature~ of the ink in the ducz took approxi-
`mately two hours to stabilize. The press needed to be stable
`before any quantitative assessment of the process could take
`place. These temperatures were monitored throughout the entire
`experimental programme and the orthogonal array nlals did not
`¯ proceed until they had reached equilibrium.
`
`To perform analysis of the printed copy, measurements were
`carried out on a test strip printed as par~ of the job. Sequential
`copy analysiss has shown that the ink densities vatv between
`samples throughout the complete run and that these variations
`are cyclical. Four, or analysis was used to calculate the frequency
`of the density variation. Based on this work, it was identified
`that 32 sequent, al samples were required for each test condition
`investigated during the onhogonal array trials,
`
`Roll
`
`h2
`
`Blade
`
`Figure 2 Schematic of the ink key/duc~ rol[juncttOn
`
`JournM of Prepress and Printing Technology page 6
`
`A large number ofonhogonai array experiments were ca~ed
`out to investigate control and process parameters and these are
`summarized in Table 1. By experience, it was found that the
`largest practical array was an L9 (three levels). This was due to
`the rime constraints caused by the requirement to obtain thermal
`stabilily, a pass to be achieved, together with unforeseen press
`stops (web breaks etc). Generally, however, experiments were
`based on the L8 array and were designed such that when termi-
`nal problems occurred, the first four runs could be analysed as
`an L4 formal
`
`The physical experimental ~ta from the press unit seven was
`recorded primarily on computer using a data acquisition system¯
`Thermocouples were mounted in the ink ducts and at strategic
`positions on and around the units to be measured along and
`across the press. The coolant supplies to and fi~m the press were
`also reconied. The temperature ofthe ink in the duct and on the
`rollers was monitored using an infra-red thermometer. The
`insw.~nent was calibrated to ensure the measurements were of
`the ink on the roller surface and not the roLLer surface itselP.
`Inductive probes with slotted discs were used to measure the
`roller speeds.
`
`A numerical model will be used to establish the insight into the
`processes taking place. It is appropriate to summarize this model
`here as it wi|l be applied later in .the analysis of the printing trial
`results.
`
`NUMERICAL MODEL THEORY
`
`The flow of ink through the ink key/duct roll junction controls
`the quantity of ink passing to the ink roller train. A schematic of
`the junctinn local to the end of the key is shown in Figure 2 and
`a hydrodynamic wedge exists in which there wiJ] be an increase
`in pressure through the junction. The shearing of the film will
`generate heat, whzch is convected through the ink and conducted
`through the ink key and duct roll.
`
`The assumption that ink is a Newtonian fluid has been made in
`this work -- this assumption has also been made in much of the
`published datum.? analysing printing, Printing inks are well
`known to be non-No.ionian and this will
`affect the details of the flow characteristics.
`However, for the purpose of physical insight,
`good qualitative unde~tanding can be
`achieved by modelling the ink assuming a
`New~ooian behaviour. At the junction
`between the ink key and duct roll, the hydro-
`dynamic behaviour can be approximated by
`the generalized pressure equations. For a two
`dimensional 61m this is given by
`
`Z
`
`(!)
`
`FAST FELT 2006, pg. 3
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`
`

`
`RESEARCH & TECHNOLOGY
`
`where
`
`Ioglo [Iogwo (v + 0"6}] = ~,log~0 T+ b
`
`This equation aJlows f‘or the inclusion of the cross film variation
`o1’ viscosity 0 either with respect to temperature or non-
`Newtonian behaviour. In this work, it will be restricted to tem-
`perature only.
`
`In describing the thermal behaviour the ink key and duct roller
`need to be considered. In the ink film the physics is described by
`the balance ofconvection, conduction and generation and is
`expressed in the following differential equation.
`
`with the heat generation term wri~en as
`
`The heat is transferred by conduction only in the blade and the
`mechanism is described by the following equation
`
`~, ~ ~_-~÷--r - u
`
`{3)
`
`Closure of’these equations requires a description of the film
`thickness profile and the relationship between ~he viscosity and
`the temperature. At the ink keylduct roll interface the film thick-
`ness can be approximated by the following equation
`
`Assuming the ink is a Newtonian fluid the temperature depen-
`dence on the kinematic viscosity can be described using the
`Walther equation
`
`where Tis expressed in Kelvin and a and b are constants
`obtained by curve+fi~ng equation (5) at two temperatures. The
`solution of’equations (1) to (5) was accomplished using numeri-
`cal techniques and, in ~his application, the finite element method
`was employed.
`
`Thus. having explained the strategy of the experimental pro-
`gramme together with the applicable modelling ~ols, their use
`in the analysis of the pfindng behaviour will be illustrated in the
`following sections.
`
`RESULTS AND DISCUSSION
`
`The om~ogonal array experiments were pert’on’ned during nor-
`mal production with minimal loss of (cid:128)opy or production time.
`The experimental results have been grouped and presented to
`depict the significant variables. The associated results, in order
`of discussion, are the ink temperatm’e in the duct, the ink key
`sc~ng, the duct roll speed and the CUIM roll spee~L These para-
`meters were all shown to affect the printed ink density. No sig-
`nificant interactions, where the combined effect of two
`parameters is different E’om the sum of the independent effects,
`were found between the parameters investigated. A numbe¢ of
`repeat investigations of certain parameters, principally tempera-
`tutes, occur in the orthogona] arrays (see Table 1). This was
`mainly dependent on the results, some of" which at the time
`appeared to be conflicting.
`
`Temperature of the ink in the duct
`
`The effect of changes in the ink duct temperature was investi-
`gated in six or~ogonal array experiments. This was due to the
`differing results obtained both within the tests and between tests.
`The changes detected were in both magnitude and ~irection and
`are summarized in Table 2. The "are~’ represem a number of
`measurement positions taken across the width of the web.
`
`In each case. the temperatures of the press flame, the ambient
`and the fount were similar in each experiment. In addition, the
`paper used in each case wa~ ofa similax
`type. However, the coverage varied signifi-
`candy both whhin some of the individual
`prinQobs and between.jobs. These varied
`fTom a Low coverage of~% up to high coy-
`erage of 35%, Following extensive analysis
`to capture thermal effects (cid:128)learly, the rela-
`tionship between the scanned coverage and
`a modified density response, IL[-L2), per
`10°C is shown in Figure 3. This shows an
`approximately linear response. The modi-
`fied density response, ill-L21, represents
`~he difference between d~e levels, L] and
`
`Table 2 Ink density changes for orthogonal array ~rpenment~ with respect to
`changes in the i~k temperalure.
`
`Experiment Array
`
`Area I
`
`Area 2
`Area 3
`Asea 4
`Area .5
`
`IB
`
`0-10
`
`0.02
`0.00
`0,06
`
`IC
`
`-0-05
`
`0.41
`-0.06
`0-2’;
`0-20
`
`ID
`
`-&0l
`
`0.43
`0,01
`
`IE
`0.00
`
`0"33
`-0’03
`0.22
`
`IF
`-0-14
`-0" 15
`-0. [ l
`-0.14
`-0-19
`
`I G
`
`-0-08
`
`-0-i6
`
`Rcse,~rch & ~echnolo~" INK SUPPLY CHAg~CI"EIItSTI(~; page 7
`
`FAST FELT 2006, pg. 4
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`RESEARCH & TECHNOLOGY
`
`Table 3 The effect of the minimum f!lra thJc "knes$ and rein-
`peratur¢ on Ihe global parameler$o Uj= 10’0
`TD Pressure
`T FlowQ
`Gap hs
`(K)
`(K)
`(US)
`(ram)
`(N)
`
`0"08
`0"08
`0-32
`0"32
`
`303
`313
`303
`313
`
`1048
`766
`300
`209
`
`315"I
`320"0
`306’9
`315"0
`
`0"034
`0"025
`0"096
`0"101
`
`L2, used in the orzhogonal array programme. Experimentally,
`the temperature change between these levels varied, depending
`on the individua! trial, and the responses were scaled linearly to
`compensate, This allowed the experiments to be compared
`directly. For areas of low coverage, ;he printed ink density
`decreased as the ink temperature was increased, while in high
`
`0.4
`
`03
`
`-02 ~
`
`Coverage
`+Array IA o~ray i8 ~ray ~C ~AffaylO ~ray ~E ~ray ~G
`
`Figu re 3 Relationship be~’een ~canned co~rage and ink dens~ for a IO~C
`~empermur¢ change
`
`005,
`
`00~4
`
`00~4
`0’03
`
`_ 0 ~0s
`
`¯ =, 1o3
`
`¯ 0 I0! ~
`
`¯ 0099 ~
`
`¯ o O97
`
`Ga~, ¯ 0 08
`
`Ga~ - 0 32
`
`Figure 4 Relationship between ink flo~ ra~e and lempera~ure for di~’erent mk
`~y/duct roller gap$.
`
`Journal of Preprezs and Prmang ~’eChlJOtO~l p(.l~e 8
`
`coverage areas the printed ink density increased. Therefore,
`linking this to practice, when the temperatures are not controlled
`in the mk duct, the operators will need to adjust the press con-
`trois in different directions to achieve a pass copy dependent on
`the print coverage level. Once the pass has been attained, any
`further temperature changes will again result in changes in the
`product quality and clearly the change in ink density is depen-
`dent on the coverage of the individual print job,
`
`To establish an under, tending of the phenomenon that is present
`required the application of the model described in the previous
`section. A parametric study of the conditions at the ink key/duct
`roll interface was carried out focussing on the minimum film
`thickness (h=) and the duct temperature (T). Model output com-
`prised blade load, nominal film temperature in the junction and
`the flow rate. The results are presented in Figure 4 and Table 3.
`These show that for the same i O°C tempera-
`ture increase the flow rate decreases for the
`smaller gap while increasing with the I~gar.
`
`o
`
`’=
`
`This occurs since the flow at the ink key gap
`comprises both roller rotation and pressure
`induced components and this is further com-
`plicated by the temperature changes ~hat
`occur at the ink key/duct roll junction. For
`the thinner gap, the pressure levels induced
`at the junction are high and so this compo-
`nent of flow is important. This is also
`markedly affected by the viscosity that
`varies most extremely in the case of lower
`duct temperatures combined with the higher
`temperatures generated in the junction. The
`net effect is a small decrease in nip flow as
`the temperature is increased. For the larger
`gap, the roller rotation induced flow is more
`dominant and as the duct temperature
`increases, so the pressure component
`becomes a smaller contribution. In this case,
`the ne~ result is an increase in the flow
`through the junction,
`
`In the printing application, the deflection of
`the keys in the segmented blade is also an
`important issue that is excluded in the ther-
`mohydrodynamic model explained previo
`ously. However, by referring to Table 3 the
`pressures generated in the junction for the
`smaller gap are largest. This high pressure
`will result in a more significant deflection of
`the ink key due to hydrodynamic action. The
`shearing action in the ink in the narrower
`gap is also reflected in a larger increases in
`the hulk film temperature (T), through the
`(cid:128)ontac~ (Table 3), (cid:128)ontr,buting to the warm-
`
`FAST FELT 2006, pg. 5
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`RESEARCH &: TECHNOLOGY
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`between the change in tempera-
`ture and the change in ink den-
`sity. As the temperature
`increases with equal increment,
`there is a small but discernible
`increase in the rate of change of"
`ink density. This reflects the
`mechanism discussed above. A~
`the ink temperature increases so
`the pressure generated in the
`ink key/duet roll junction will
`decrease and the hydrodynamic
`deflection of the ink key will also reduce, leading to a closure of
`the ink key gap. The rate of increase may be atmbutabte to a
`disproportionate increase in the ink temperature at the ink
`key/duct roll junction as the film thiclmess reduces. This mecha-
`nism requires further detailed investigation to confirm this
`understanding.
`
`Figure 5 $ckematic of ink key/duct roll interface for low coverage area~
`
`ing action in the duct+ When the temperature of the ink is
`increased, the viscosity is lowered. This results in a reduction in
`pressure in the contact region (Table 3) and a movement in the
`ink key system to a new gap hb, where hb < ha. The smaller gap
`will then result in a decrease in the ink flow and this is reflecled
`in a lower printed ink density. The mechanism is shown
`schematically in Figure 5.
`
`At the large ink key/duct roll gap the load, and hence pressures
`generated, are [owcr (Table 3). This wilt result in very tinle
`deflection of the ink key due to the hydrodynamic mechanism. In
`this case, the increase in temperature causes a thinning of the ink
`and a subsequent increase in the ink flow since the pressure com-
`ponent of flow, which reduces flow through the nip, has Jess
`irnpacl. This will be reflected in an increase in the printed ink
`density.
`
`The linearity of the influence of ink temperature change on the
`¯ printed ink density v,;as investigated in Army i F, which features
`an L9 onhogonal array invesrigatmn. The ink temperature set
`points selected were 22°C, 30°C and 38°C. The responses at
`each level for five positions across the web are shown m Figure
`6. The image coverage was low and varied from 5% to 10%
`across the web. The resul~ show a non-linear relationship
`
`1.6
`
`1.7
`
`1.6
`
`I.S
`
`1.4
`
`1.3
`
`1.2
`2S
`
`30 35
`
`Figure 6 Change in mk den$i~. . ith duct roll temperalure
`
`These results have shown large changes in pnnted ink density
`with respect to variations in the ink temperature. There is a clear
`interaction in this relationship betweed the ink key opening and
`temperature change, with the ink density increasing in the high
`coverage areas and decreasing in the low coverage areas for the
`same temperature increase. The important factors are the ink
`viscosity and the hydrodynamic forces that are generated in the
`contact region that cause a deflection of the ink key interacting
`with the ink temperature.
`
`The large changes in ink density in both magnitude and direc-
`tion with respect to the ink temperature in the duct wilt cause
`problems for the consistency of printed copy and repeatability
`between pdnt jobs. To overcome this variation the control of the
`ink temperature entering the miler train becomes an important
`factor in stable printing, This can be achieved by utilizing the
`flow channels incorporated into many duct rollers. The supply of
`water through these channels fi’om
`a temperature control system
`co~!d be used to ensure stable ink
`temperature in the duct. This
`could be achieved both within a
`single print nm and between simi-
`lar jobs pdnmd months apart. The
`consistent feed temperature would
`then minimize colour changes
`detected on the printed copy.
`Systems employed further down
`the inking train, as used in some
`waterless applications on vibrating
`rollers++ would not provide the
`same level of stability as they do
`nol control ~he temperature of the
`ink in the duct, but ~ther in the
`inkmg train+
`
`Re~earch & technolo~, INK SUPPLY (cid:128)]~,R.AC’T1E$~S’I1CS page 9
`
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`
`RESEARCH & TECHNOLOGY
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`Ink key setting
`
`Table 4 Variation in ink density widt respect to a ~-increment increase of ~e ink key setting
`
`Solid Solid Grey balance Grey balance 40% halftone
`
`Ink key setting 30
`+0.14
`Density change
`
`16
`+0-23
`
`32
`+0,07
`
`17
`+0.08
`
`17
`+ 0.04
`
`Table 5 Variation in ink density with respect to alterations of the duct roll speed
`
`Solid
`
`Ink key setting 30
`+0. I0
`Density change
`
`Solid
`
`Grey balance Grey balance
`
`40% halftone
`
`16
`+0-06
`
`32
`+0,05
`
`17
`+0-03
`
`17
`+0.03
`
`Table 6 Variation in ink densi~ with respect to alterations of the CUIM roll speed
`
`Density change
`
`Solid Solid Solid Solid 80% halftone
`0-29 0-22 0.27 0.22
`0-22
`
`40% halftone
`0.06
`
`This represents one of~e pri-
`mary control parameters used in
`the process and was assessed
`during the initial investigations,
`Array I A. The blade fitted on
`the press was a segmented type.
`The ink key setlings used were
`those set at the slan of’the
`experiment, level one, ~nd all
`the ink keys were increased by
`two steps on the ink key con-
`troller, corresponding to level
`two. This level of adjustment
`was limited by the requirement
`to produce acceptable cop)’.
`However, this method minimizes any disturbances associated
`with local adjustments where there will be some interaction
`between adjacent blades.
`
`"l~e chang~ in ink key se~ing produced a significanz change in
`the ink density, with an average of 0.19 in the solid patches.
`Measurements w~re carried out using solid, halftone and grey
`balance patches across the width of the web and these showed
`significant variations (Table 4). The results for the halftone and
`grey balance patches show similar wends to the solids, and as
`such the analysis of these patches was minimized in the subse-
`quent arrays. The small changes in ink key sorting produced
`large density changes, with those made on the lower ink key set-
`~ings having a much l~rger eft’eeL This infers a non-linear opera-
`tion of the ink key with respect to coverage. These results reflect
`the mechanism that the hydrodynamic forces generated at the
`ink key/duct roll junction is most sensitive to film thickness
`change for thinner films, which are present in the case of the low
`coverage areas.
`
`Duct roll speed
`
`The duct roll is another primary control parameter used in the
`printing process, which was assessed during the minal ~nvestiga-
`tions, A.rray IA. The duct roll speed was increased from 38 rev-
`olutions per minute (rpm) at level one up to 41 rpm, at level two.
`
`The increase in the duct roll speed increases the ink flow
`through the duct and hence the printed ink density (Table 5).
`The changes detected are not as large as those for the ink key
`se~ng, but again they display a non-linear response w~th respect
`to the coverage. In ",his instance, as the duct roll speed is
`increased the changes of ink density are largest in areas of high
`coverage.
`
`This result is again explained by the ink key model, where the
`duct roll speed and the temperature of the ink m the duct ,nteract
`
`Jo,rnal of Prepress ,and Prinling Technolo~" page 10
`
`non-lin~rly. As the duct roll speed increases the fluid entrain-
`ment will also increase since the relative size of the pressure
`component ofthe flow will be decreased. This results in a
`greater ink flow through the ink key/duct roll junction. This
`reflects the interaction that is present at-high coverage that has
`been discussed earlier.
`
`However, the influence ofthe duct roll speed is different ~rom
`the ink key setting with respect to printed ink density. The
`changes in the duct roll speed have a more significant effect on
`the high coverage areas whereas the changes in the ink key set-
`ling have a more significant effecx on the low coverage areas.
`Therefore, global changes in these will have different effects
`dependent on the coverage being printed, and in images of vary-
`ing coverage, the changes witl be more apparent.
`
`CUIM roll speed
`
`The influence of the CUIM roll on the printed in density was
`analysed using speeds of 57 rpm and 85 rpm, Array lB. The
`CU IM is not normally altered during production although the
`printers do have this control facility. In this study, it was
`assessed as a control parameter to meter the flow through the ink
`train.
`
`The results show an increase in ink density with an increase in
`the CUIM roll speed (Table 6). Measurements were carried out
`for bolh solid and halftone patches across the web, There is
`some variation in solid density across the width of the web,
`although the scanned coverage for all the measurement zones
`were similar varying between 15% and 19%, There is no (cid:128)orre-
`lation between the scanned coverage and the magnitude of the
`density changes. The results indicate strongly that the CUIM roll
`could be used as an effective metenng system since the density
`change appears to be relatively independent of other parameters,
`although further investigations are required to confirm this.
`
`FAST FELT 2006, pg. 7
`Owens Corning v. Fast Felt
`IPR2015-00650
`
`

`
`RESEARCH & TECHNOLOGY
`
`CONCLUSIONS
`
`REFERENCES
`
`I
`
`Phadke, M S "Quality engineering using robust design’
`Prentice Hall Int. Edit. 0989)
`
`Saleh, A G ’The analysis of the dot gain problems and its
`effect on colour reproduction’, TAGA Proc. (1982)
`pp 497-517
`
`Bobnn, M F J, IAm, C H, Korochkina, T V, Claypole, T
`C, Gethin, D T and Roylanee, B J ’An investigation of the
`hydrodynamic and mechanical behaviour of a soft nip in
`rOlling contact’ Proc. IM¢chE parr J Engineering Tribology
`Vol 211 NoJl (1997) pp 37-$0
`
`4
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`Bohan, M F J, Claypole, T C, Gethin, D T and Basri,
`S B ’Application of boundary element modelling to soft
`nips in roiling contrast’ TAGA Conf Proc. (1997)
`
`Bohan, M F J, CIaypole, T C and Gethin, D T "An evalu-
`ation of print to print variation in web offset, sheet offset
`and gravure printing’ 14th Int. Syrup. on Graphic Art$
`Zagreb, Croatia (6-8 Novexnbcr 1996)
`
`6 Lira, C H "An elastohydrodynamic behaviour of a soft
`printing roller nip’ PhD thesis University of Wales,
`Swansea (1995)
`
`MnePhee, J, Shieh, J and Hamrock, B J ’The Application
`of Elastohydrodynamic Lubrication Theory to the
`Prediction of Conditions Existing in Lithographic Printing
`Press Roller Nips’ Advances in Printing Science and
`Technology. Vol 21 (1992) pp 242-276
`
`8 Dowson, D ’A Generalised Reynolds Equation for Fluid
`Film Lubrication’ International Journal of Mechanical
`Engineering Sciences Vol 4 (1962) pp 159-170
`
`9 MacPhee, J ’Fundamentals of lithographic printing’ GATF
`(1998)
`
`An experimental programme investigating both control and
`process parameters has been carried out on a commercial press
`with no loss of production. Orthognnal arrays have been used
`which have facilitated the investigation of multiple parameters
`simultaneously with the minimum of’ press time and associated
`costs while maximizing data yield. The investigations bitve
`highlighted the significant parameters affecting the printed ink
`density of those e~luated and it has been found that their effects
`are non-linear.
`
`The printed ink density is significantly affected by changes in
`the temperature of the ink. The relationship is complex wi