This document discusses the importance of process controls and instrumentation in the printing industry. It notes that without quantitative measurement of processes, it is difficult to effectively manage processes to meet customer expectations. The use of process controls can help minimize customer rejections and reprints by basing acceptability on measured data rather than subjective opinions. When controls are lacking, it can lead to inconsistencies, longer makereadies, decreased efficiency, and increased waste. The document also provides an overview of standards for color measurement devices and examples of how process controls helped identify and address specific issues for customers.

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Theuseofprocesscontrolsandinstrumentationiscoretoasuccessful
qualityprintoperation.Itunderpinstheproductionlifecycleandprovides
thebasisforproducingaccurate,consistent,andrepeatableprintsfor
customers.Itisdifficult,ifnotimpossible,toeffectivelymanagethepro-
cesstomeetcustomerexpectationswithoutmeasurementtoquantify
theprocess.
Therearemanyreasonstoemployprocesscontrols;themostobviousis
toavoidcustomerrejectionsandrerunsofexistingjobs.Wecomeface
tofacewiththisinourlabwhenwereviewprintingjobsthatcustomers
haverejectedduetocolorvariation.Thisunhappinesscanbeminimized
ifthecontractdocumentscustomerexpectationsandtheacceptabilityof
colorcanbebasedonmeasureddataandnotdifferingopinionsofwhat
iscommerciallyacceptable.Theabsenceofprocesscontrolswillleadto
inconsistenciesinthecolorandincreasedworkandinterventionfrom
thepressoperatorstomaintainquality.Thiscreateslongermakereadies,
therebydecreasingtheoverallefficiencyoftheequipmentwhileincreas-
ingwaste.
Whenconsideringprocesscontrols,itisimportanttounderstand
themagnitudeofthecolormeasurementendeavorandwherethechal-
lengeslay.Ithasbeenestimatedthatahumancandistinguishbetween
10millioncolors;thisputsintoperspectivethechallengeinusingan
instrumenttomeasurecolorwithmoreaccuracythenwecanseevisu-
ally.Theinstrumentshaveimprovedsignificantlyovertheyearsinboth
theirqualityandaffordability.Measurementswithdifferentinstrument
configurations,suchasdensitystandard,observerangle,ormeasure-
mentaperturewillproducedifferentresults.Usingdifferentinstruments
withinthesameinstrumentfamily,betweeninstrumentfamilies,and
betweenmanufacturerswillalsoproducedifferentresults.Itisimportant
tonotethattherearestandardsthatdefinetheinstrument’sconfigura-
tion,andthemostrecentversionsincludecapabilitiesfordealingwith
opticalbrighteningagentsandfluorescents.Thesearesummarizedas:
M0—Alllegacymeasurementdevicesfallintothiscategory.The
UVcontentisnotdefined,anditnotrecommendedwithfluores-
cence.Itisusedformostcurrentstandards,e.g.,GRACoL2006.
M1(D50)—Thisisforusewithsubstratesthatcontainoptical
brighteningagentssotheusergetsabettermatchbetween
measurementsandvisualobservations.Itisusedinnewstandards,
(e.g.,GRACoL2013).Therearetwospecificpartstothis,withpart2
usedonlywithopticallybrightenedpapersandnotcolorantsthat
fluoresce.
M2(formerly:UVcut)—InM2,theUVcomponentofalight
sourceiscut,andthefiltercharacteristicsfortungstenlightsources
aredefinedforthefirsttime.
M3(formerly:Polarizationfilter)—Thisshouldbeusedwhere
firstsurfacereflectionsneedtobeeliminatedusingpolarization.
ThisalsousestheUVfilterindicatedintheM2definition.
Itisnotonlythepresswhereprocesscontrolsshouldbeappliedbutalso
onalloftheincomingmaterials,plates,andproofs.Thiscanbedonewith
instrumentation,targets,andincertainapplications,avisualcheckwith
atarget.Withoutconsistentinputtothepress,additionalcostsintime
andmaterialswillbeincurred.
Twoexamplescometomind,thefirstbeingwithincomingproofs.Inthis
exampletheproductionjobwassentbythecustomeralongwithaproof
andcolormanagedtoaparticularprintspecification.Theprintercolor
managedthefilescorrectly,butthepressoperatorhadsignificantissues
ingettingacolormatch.Thiswasaconsistentproblemwithonecus-
tomeronlyandresultedinadditionalcostsandlessprofitfortheprinter.
Whenthecustomer-providedproofswerechecked,theywereidentified
asbeingincorrect.Thecustomerwashappywiththeirproofs,sothesolu-
tionwasmadeinprepressforthenewcolortarget.Theproblemcould
havebeenavoidediftheincomingproofshadbeenqualitychecked.
Asecondexamplewaswithinkbeingrejectedattheflexopressfor
beingtooweak.Uponinvestigationitwasidentifiedthecausewasthe
operatingproceduresonpressasthewater-basedinkwasbeingreduced.
Therewerenocontrolsormeasurementsinplace,andtheoperatorswere
addingtoomuchwaterandthenrejectingtheink.
Platesneedtobecheckedanditisimportantthat,whenpossible,the
instrumentsareconnectedtoacomputerthatautomaticallysavesand
analyzesthedata.Therearemanysystemsthatdothis,andtheycan
eliminateproblemsbeforetheyoccuronpress.Inoneassignmentwe
Dr. Mark Bohan and Jim Workman, Printing Industries of America

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werebroughtintosolvemakereadyissuesonpress.Operatorshadto
alterpressconditionstogetacolormatch,andattimesplatesneeded
toberemade.Uponinvestigationitwasdeterminedthatprepresswas
taskedwithmeasuringtheplates,butsincetheywereconsistentoverthe
firstcoupleofweeks,theyhadstartedtomarkthecontrolchartswithout
measuringthem.Hadtheprepresspersonnelproperlymeasuredthe
plates,theywouldhaveidentifiedtheissue.
Controloftheprintedproductonpresscanbecarriedoutbydiffer-
entmeans,andeachhastheirownadvantagesanddisadvantages.
Traditionalprocesscontroliscarriedoutbymeasuringthedensity,tone
valueincrease(TVI),andtrappingcharacteristics.Thenaturalvariation
inanyprocessneedstobeunderstoodbeforetolerancesareputinplace.
Themeasurementscanalsobeusedtohelpidentifyissueswiththe
pressitself.Thiscanoccurregardlessoftheprocess—onadigitaldevice
recentlyweidentifiedissueswiththetransferbeltandreplacedthisprior
toacolormanagementexercise.Inanothercaseacolorvariationwas
identifiedasonlyoccurringoncertainjobswiththecolorshiftsbeing
visibleonsequentialsignatures.Analysisofthedensitydatashowedthe
problemoccurredonallthejobs,butthatyoucouldonlyseeitsomeof
thetimedependentupontheimagecomposition.Astheconditionsof
thepresschangedensity,TVIandtrappingcanbeusedtoidentifythe
changesandthepropercorrectiveaction.
Thereisincreaseduseofneutraldensityorgraybalancecontrolonpress
tocalibrateandthenmaintaincolor.Theneutraltonesaresome
ofthefirstinwhichhumanswillseeacolorshiftandcanbeusedinpro-
ductioneitherasavisualguideorwithinstrumentation.Itisimportant
whenusingtheneutraltonesforcontrolthatthereisagoodunderstand-
ingofwhytherehasbeenacolorshift.Thereproductionofsolids,tones,
overprintingandregistershouldbeinvestigatedpriortoanychanges.
WehaveseenamovetowardtheuseofCIEL*a*b*colorspaceinprocess
controlswithmanycontrolpatchesenablingitsuse.Inaddition,the
modernstandardsandspecificationshavemovedawayfromdensityto
definingthecolorofthepatches/overprintsandsettingtolerancesusing
CIEL*a*b*.Thisprovidesoneofthemostcompleteformsofprocess
controlsandcanbeusedbothwithcontrolbars,spotcolors,andwithin
theimageitselftoensurethatoptimalreproductionisasachieved.When
changesareidentified,itisthenagainsteppingbackandlookingateach
ofthecomponentsthatmakeuptheimagetoidentifythetruecauseof
thecolorchange.
Processcontrolisfundamentaltoobtainpredictableandconsistentprint.
Theuseofinstrumentationprovidesthemetricsandthefoundationofa
well-designedcontrolsystem.