陜科大包裝技術(shù)基礎(chǔ)雙語(yǔ)課件11包裝印刷

Lesson11PackagePrinting

第11課包裝印刷IntroductionTheobjectiveofpackageprintinganddecoratingistocreateavisiblyidentifiableimage,consistently,foralargenumberofimpressions.thesehavebeendividedintotwogroups:"Printing"inthecontextofthisdiscussionreferstoflexography,lithographyandgravure--themethodsthataccountforthevastmajorityofallpackaginggraphicart.Eachofthesemethodshasanumberofvariations."Decorating"isusedtodescribeanumberofspecialmethodssuchasscreenprinting,hotfoilstamping,embossing,andpadprinting.PrintingMethods

Printinganimagerequirestheabilitytotransferfluidinkoranothermarkingmediumontothesubstrateinthedesiredpattern.Therearedozensofwaysofdoingthis,butthebulkofpackageprintingcanbegroupedinthreebasiccategoriesbasedonthefundamentalgeometryoftheprintingplate:Relief:Variationsareflexography(commonlyreferredtoasflexo),letterpress,andoffsetletterpress(commonlyreferredtoasdryoffset)PrintingMethodsPlanographic:Theprocessisknownasoffsetlithographyandcommonlyreferredtoaslithography,offsetorlithoGravure:Theprocessisrotogravure,sometimescalledrotoandoccasionallyreferredtoasintaglioPrintingpresseshavethefollowingfeaturesincommonregard1essoftheactualprintingmethodused:Anaccuratematerialfeedsystemthatwillpresentsubstratetotheprintingstationinpreciseregister.Aninkreservoirorinkfountainandamethodofintroducinginkintotheprintingtrain.PrintingMethodsAmeansofmeteringinksothattheamountappliedisconsistentovertheprintrun.Awayofconfiguringtheinktotherequiredpattern.Thisisdonebytheprintingplates,oneforeachcolor.Ameansoftransferringinktothesubstratebypressingthesubstratebetweentheink-bearingsurfaceandanimpressionroll.Sinceinksareappliedasfluids,ameansofdryingor]solidifyingthem.PrintingMethodsPrintingpressesarevariouslyconfigured,dependingontheprintmethodandonwhetherthemachineissheetfedorwebfed.Lightmaterialsandthosethatareextensibleorhavepoordimensionalstabilitymustbewebfed;thematerialissuppliedfromarollandisusuallyrewoundintoarollafteritisprinted.Web-fedmachinestypicallyrunfaster,andlargerunsmaybebetteronaweb-fedmachine.Sometypesoffillingmachinesmustbesuppliedwithpackagingmaterialfromaroll.PrintingMethodsMostpaperscanbeeitherweborsheetfed,inwhichcaseotherfactorsmustbeconsidered.Forinstance,corrugatedboardandotherstifforrigidmaterialsthatcannotwraparoundfeedrollsmustbesheetfed.Whileinprinciplemostartcanbeprintedwithfourstations,printingpresseswitheightormoreprintingstationsarenotunusual.Theaddedstationsallowtheprintermoreoptionsandflexibilityonhowtoproduceexactingdesignsofthehighestquality.Theaddedstationshavemanyuses,includingtheseprintingsituations:PrintingMethodsFluorescentandmetalliccolorsthatcannotbeprintedwithstandardCMYKinksLineart,orprocessartcombinedwithlineart,thatrequiresalargenumberofPMScolors.DoubleapplicationsofthesamecolorneededtodevelopdesireddepthCorporatecolorsthatareoftenspecifiedPMSorproprietaryformulationsProtectiveordecorativecoatingssuchashigh-glosslacquersorvarnishes·FluorescentandmetalliccolorsthatcannotbeprintedwithstandardCMYKinksPrintingMethodsDifficulttoduplicatecolorssuchasorange,darkbrownsandsomegreensExceptionallybrightcolor,ifneededLargesolid(lineart)areasPattern-appliedadhesives.Theprintingprocessthatisselectedforaparticulartaskisdependentonmanyfactors:Thevolumeornumberofimpressionsdesired(10,000or10millionimpressions)PrintingMethodsThearttypeanddesiredeffect(lineart,processcolor,vignettes,metallicsheen)Thesubstrate(paper,plasticfilm,surfacequality,colored,porous,flexible,rigid)Thephysicalshapeofthesubstrate(rollstock,sheets,discreteitems,round,irregularshape)Specialpackageprocessoruseconditions(chemicalresistance,thermalresistance)ReliefPrinting

PlateProduction.Modernreliefprintingplatesaremadefromrubber,photopolymeroroccasionallymetal,dependingontheapplication.Platesaremodestincostandcanbemadequickly.Nearlyallaremadebyphotographicallyimposingtheimagerecordedonaphotonegativeontoalight-sensitivematerial.Inthecaseofphotopolymers,thepolymerhardenswhereexposedtoultraviolet(UV)lightandremainsfluidwhereunexposed.Theunexposedpartisthendissolvedaway.(SeeFigure11.1)ReliefPrintingFigure11.1UVlightprojectedthroughtheimagephotonegativewillcurephotopolymer.Uncuredpolymercanbewashedaway,leavingtheraisedimageareasReliefPrintingFlexographyInatypicalflexographicprintingstation(seeFigure11.2)excessinkisappliedtoanengravedtransfer,oranilox

roll.Theengravingsontheaniloxrollmeterthecorrectamountofink,dependingontheengravinggeometryanddepth.Theinkistransferredtotheraisedsurfacesoftheprintingplateattachedtotheplatecylinder.Lineartprintingplateshaveasolid,smoothsurface.Halftoneandprocessprintingplatesurfacesarecomposedofsmalldotsstandingoutinrelief.Thesubstrateispassedbetweentheplatecylinderandtheimpressioncylindertoachieveinktransfer.ReliefPrinting

Figure11.2Atypicalflexographicprintdeck.Achambereddoctorbladeinkfountainappliesinktotheaniloxroll.Inothersystems,inkisappliedwithrollsrotatingintheinkfountainReliefPrintingFlexographicpressstationscanbearrangedinseveralways.(SeeFigure11.3)Thestackpresshasindividualcolorstationsstackedoneabovetheother,withdryingzonesbetweenthestations.Eachplatecylinderhasitsownimpressioncylinder.Thecentralimpression(CI)presshasprintingstationsgroupedaroundasinglelargecentralimpressiondrum.ExtensiblewebssuchaspolyethylenearebestprintedonaCIpress,becausethecentralimpressiondrumkeepswebdistortiontoaminimum.ReliefPrintingFigure11.3Asix-colorflexographicstackpress(left)andasix-colorflexographiccentralimpression(CI)press(right)

ReliefPrintingLetterpressandOffsetLetterpress(DryOffset).Letterpressreferstoreliefprintingprocessesthatusehardplasticorsometimesmetalprintingplates.Whereflexographicprintinginksarefairlyfluidandcanbemeteredwithengravedrolls,letterpressinksareheavypastessimilartolitho-graphicinks,andmustbemeteredbyacomplicatedseriesofrollers.Cylindricalobjectssuchastwo-piecemetalcanshavenocircumferentialregisterpointagainstwhichtoregisterprintingstations.Thisproblemisresolvedbyaprocessmodificationvariouslyknownasoffsetletterpress,dryoffset,orletterset.(SeeFigure11.4)ReliefPrintingFigure11.4Offsetletterpress(dryoffset)assemblestheentireimageonablanketrollandtransferstheimagetoaroundcontainerinonerotationofthecontainerReliefPrintingInoffsetletterpresstheinkedimagesfromtheletterpressprintingplatesaretransferredontoanintermediateresilientrubberblanketroll,whereallthecolorscanbeassembledincompleteregister.Theheavypastenatureofletterpressinkspreventsthemfromrunningorspreadingwhiletheimageisbeingassembled.Theblanketrollisthenrolledagainsttheroundobject,andallthecolorsthatmakeuptheimagearetransferredatonetimeandincompleteregister.Thecolorsappliedtotheblanketarewetandmuststaywetuntiltransferredtothecontainer.Lithography

Lithographyisaplanographicprocess,meaningthatprintingandnonprintingareasareallonthesameplane.Unlikeareliefplate,alithographicprintingplateisfiatandsmooth.Themutuallyexclusivenatureofoilandwaterformsthebasisofmodernlithography.Lithographicinkisbydefinitionalwaysoilbased.Itisaheavypasteandismeteredtotheplatecylinderbyatrainofinkingrollers.Anothergroupofrollersappliesathinfilmofwatertothewater-receptiveareas.(SeeFigure11.5)LithographyFigure11.5Alithographicprintingstation

Lithography

Mostlithographicpressesforpackagingapplicationsaresheetfed,althoughtherearesomeweb-fedpresses.Theplanographicnatureoftheprocessrequiresthatthesubstratesurfacebereasonablysmoothinordertogetgoodinktransfer.Lithographicplatescanbemadewith200-lineandfinerscreens,although133and150aremorecommoninpackaging.Accordingly,thelithographicimageissharpandhasexcellentdetail.Theedgesoflineartaresharpandstraight.Auniqueadvantageoflithographynotavailablewiththeothermethodsisthatsomecoloradjustmentcanbemadeon-press.GravurePrinting

Gravureprintingusesengravedcopper-platedsteelcylinderstomeasureandapplypatternsofinktotheSubstrate(SeeFigure11.6).Inthemostcommonprocess,astyluscontrolleddirectlybydigitalinformationengravesthedesiredcellpatternintothecylinder’ssoftcoppersurface.Thecylinderisthenchromeplatedtogiveitahardwear-resistantsurface.GravurePrinting

Figure11.6Agravurecylindermayhavemillionsoftinycells,orwells,whosevolumecanbecontrolledtocarrydifferentamountsofink

GravurePrinting

Normalgravureprintingisalwaysdonefromrollsandinwebform.Theentiresurfaceofthegravurecylinderisfloodedwithalow-viscosityinkandthenwipedcleanwithastraight-edgedmetaldoctorblade.Afterthecylinderhasbeenwiped,onlytheinkinsidetherecessedcellpatternremainsonthecylinder.(SeeFigure11.7).Gravureprintinggivessuperiorprintqualityandunmatchedcontroloverlongproductionruns.Make-readyissimple.Sincethereisnoplatejointonagravurecylinder,itispossibletoprintcontinuouspatterns.

ComparingFlexography,Lithography,andGravure

Thequalityofprintedimagesvarieswidelyamongflexography,lithography,andgravure.Itiseasytodistinguishbetweenthethreeprocesseswhentheprintingisnotdonetothehighestofstandards(seeFigure11.8),buttheprocessisidentifiableonlybycarefulexaminationwithamagnifyingglasswhentheprintingisofthefirstquality.TheUPCcodeisusuallythebestlinearttoexamineforprintIdentification.ComparingFlexography,Lithography,andGravureElexoprinting“halo”effectLithoprintingsmoothedgesGravureprintingsawtoothedgesFigure11.8TheprintingmethodcanoftenbedeterminedbyexaminingtheedgesoflineartundermagnificationComparingFlexography,Lithography,andGravureGravureprintingpressesarealwayswebfedandareusedprimarilyforlarge-volumerunsonanysmooth-surfacedstock.Therearealimitednumberofcombinationpressesavailablethatcombinelithographyandgravureorflexographyandgravureinordertotakeadvantageofthestrengthsoftwoprocesses.OtherPackageDecorationTechniques

Notallpackagedecoratingandmarkingrequirementscanbemetwithflexography,lithography,orgravure.Fordistinctiveeffects,specialsubstrates,orirregularshapes,anumberofadditionalprocessesandvariationscanbecalledintouse.StencilorScreenPrinting.Theterm"silkscreen",whilecommonlyused,istechnicallyincorrectsincemodernscreenprintingusesfinemetalorplasticscreens.OtherPackageDecorationTechniquesThescreenismaskedoffintoapatternthatleavesporousscreenareaswhereinkisdesiredandsealedareaswherenoinktransferisindicated.Thescreenisplacedagainstthesurfacetobeprinted,andawiperblademovesaninkpuddleacrossthescreen.(SeeFigure11.9)Wherethescreenhasbeenleftporous,theinkdropsthroughontothesubstrate.Stencilscreenareeasilyandeconomicallymadebyexposingascreencoatedwithphotosensitivematerialinamannersimilartothatusedinlithographyandflexography.OtherPackageDecorationTechniquesFigure11.9Screenprintingcanbedoneonflatorroundobjects.OtherPackageDecorationTechniquesReflectiveMetallics.Onlyanintactmetalsurfacecanprovideareflectiveglossymetallicsheen.Inpackagingthisisdonebyprintingonaluminummetalfoiloraluminummetallized

surfaces.Thegraphicwillhaveahard,glossysurfaceeveninthoseareasprintedwithopaqueink.Allglossyreflectivemetallicsarebasedonaluminum.

Metallizingisafull-webprocess;metallizeddesignsandpatternsarenotpractical.OtherPackageDecorationTechniquesHeat-TransferandHot-StampPrinting.Heat-transferandhot-stampprintingaresimilarinthattheybothuseheattotransferimagesfromacarrierwebtothesubstratetobedecorated.Theyarebothcleanprocessessincetherearenoinkstodry.Bothprocessesrequireasubstratethatisreasonablyheattolerant.(SeeFigure11.10)

OtherPackageDecorationTechniquesFigure11.10Hotstampprintingusesaheateddiethathastheimageengravedintoitssurface

OtherPackageDecorationTechniques

Metallicdecorationistheprincipalhot-stampapplication.Toprovidethemetallicsheen,thedecorativecoatingiscreatedwithavacuummetallized

aluminumlayer.PadPrinting.

Padprintingisarelativeofgravureprinting.Theinkedimageiscreatedonanetchedflatplate(thecliché)inamannersimilartogravure.Alarge,resilientsiliconerubberpillowispressedagainsttheinkedcliché.Theinkpatternistransferredtothepad,whichissubsequentlypressedagainstthesubstrate.(SeeFigure11.11).OtherPackageDecorationTechniquesFigure11.11Padprintingisusedtodecorateirregularlyshapedobjects.ThepadisfirstpressedagainsttheinkedclichéandthenmovedoverandpressedagainsttheobjecttobeprintedOtherPackageDecorationTechniquesEmbossing.Embossingisthepracticeofpressingasubstrate,usuallypaper,sothatadesignstandsoutinrelief.Akeyrequirementofembossingisthatthesubstratebecapableofdeformingunderpressureandofholdingthenewlycreatedcontour.Embossingdiesaremadebydirectengravingorbycastingfromamasterengraving.Mostembossingisdoneinregisterwithaprintedpatternalreadylaiddowninprevioussteps.Webstockcanbeembossedcontinuouslybyembossingrollstoimpartanoveralltexturetothesubstrate.OtherPackageDecorationTechniquesOtherDecoratingandMarkingMethods.Otherimportantdecoratingandmarkingmethods