包装材料专业英语78讲 package printing.docx

包装材料专业英语78讲 package printing.docx

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包装材料专业英语78讲packageprinting

Lesson11packageprinting

Introduction

Theobjectiveofpackageprintinganddecoratingistocreateavisiblyidentifiableimage,consistently,foralargenumberofimpressions.Printingordecoratingrequirestheabilitytoseparateimageandnonimageareas.Thisisdonewithaprintingplate,andthevariousprintingordecoratingmethodsarenamedafterthenatureoftheprintingplate.Manytechniquesandvariationshavebeendevelopedforthispurpose,andforthesakeofthisdiscussion,thesehavebeendividedintotwogroups:

“Printing”inthecontextofthisdiscussionreferstoflexography,lithographyandgravure——themethodsthataccountforthevastmajorityofallpackaginggraphicart.Eachofthesemethodshasanumberofvariations.

“Decorating”isusedtodescribeanumberofspecialmethodssuchasscreenprinting,hotfoilstamping,embossing,andpadprinting.Involume,thesemethodsaccountforasmallproportionofpackaginggraphicart.However,eachisabletocreatedecorativevaluesnotavailablebythemain-linemethodsorisabletodecoratesubstratesnotreadilydecoratedbyothermeans.

PrintingMethods

Printinganimagerequirestheabilitytotransferfluidinkoranothermarkingmediumontothesubstrateinthedesiredpattern.Thesearedozensofwaysofdoingthis,butthebulkofpackageprintingcanbegroupedinthreebasiccategoriesbasedonthefundamentalgeometryoftheprintingplate:

Relief:

variationsareflexography,letterpress,andoffsetletterpress（commonlyreferredtoasdryoffset）.

Planographic:

Theprocessisknownasoffsetlithographyandcommonlyreferredtoaslithography,offsetorlitho.

Gravure:

theprocessisrotogravure,sometimescalledrotoandoccasionallyreferredtoasintaglio.

Eachmethodhasadifferentwayofcreating,carrying,andtransferringinkpatternsontoasubstrate,butregardlessoftheprintingmethod,thedeviceusedtocreatetheinkpatternisgenerallycalledaprintingplate.Intheinstanceofflexographyandlithography,theplatearemadeintheflatbutthenattachedtoroundrollsinsidetheprintingpress.Theprintimageforgravureisengraveddirectlyintothesurfaceofaroundmetalrollorcylinder.

Printingpresseshavethefollowingfeaturesincommonregardlessoftheactualprintingmethodused:

Anaccuratematerialfeedsystemthatwillpresentsubstratetotheprintingstationinpreciseregister.

Aninkreservoirorinkfountainandamethodofintroducinginkintotheprintingtrain.

Ameansofmeteringinksothattheamountappliedisconsistentovertheprintingtrain.

Awayofconfiguringtheinktotherequiredpattern.Thisisdonebytheprintingplates,oneforeachcolor.

Ameansoftransferringinktothesubstratebypressingthesubstratebetweentheink-bearingsurfaceandanimpressionroll.

Sinceinksareappliedasfluids,ameansofdryingorsolidifyingthem.

Printingpressesarevariouslyconfigured,dependingontheprintmethodandonwhetherthemachineissheetfedorweb.Lightmaterialsandthosethatareextensible（verystretchy）orhavepoordimensionalstability（textiles,forexample）mustbewebfed;thematerialissuppliedfromarollafteritisprinted.Web-fedmachinestypicallyrunfaster,andlargerunsmaybebetteronaweb-fedmachine.

Sometypesoffillingmachines（forexample,form-fill-and-sealmachines）mustbesuppliedwithpackagingmaterialfromaroll.Bydefinitionthesematerialsmustbeprintedonaweb-fedmachine.Thesematerialswillusuallyrequireregistration,or“eye”,marks,indicatingcuttingorsealingpoints.

Mostpaperscanbeeitherweborsheetfed,inwhichcaseotherfactorsmustbeconsidered.Forinstance,corrugatedboardandotherstifforrigidmaterialsthatcannotwraparoundfeedrollsmustbesheetfed.

In-linepresses,typicaloflithographyandgravureapplications,arrangetheindividualprintingstationsinastraightline.Stackpresses,moretypicalofflexography,clusterprintingstationsonverticalframes.

Whileinprinciplemostartcanbeprintedwithfourstations,printingpresswitheightormoreprintingstationsarenotunusual.Theaddedstationsallowtheprintermoreoptionsandflexibilityonhowtoproduceexactingdesignsofthehighestquantity.Theaddedstationshavemanyuses,includingtheseprintingsituations:

●FluorescentandmetalliccolorsthatcannotbeprintedwithstandardCMYKinks.

●Lineart,orprocessartcombinedwithlineart,thatrequiresalargenumberofPMScolors.

●Doubleapplicationsofthesamecolorneededtodevelopdesireddepth.

●CorporatecolorsthatareoftenspecifiedPMSorproprietyformulations.

●Protectiveordecorativecoatingssuchashigh-glosslacquersorvarnishes.

●Difficulttoduplicatecolorssuchasorange,darkbrownsandsomegreens.

●Exceptionallybrightcolor,ifneeded.

●Largesolid（lineart）areas.

●Pattern-appliedadhesives.

Theprintingprocessthatisselectedforaparticulartaskisdependentonmanyfactors:

●Thevolumeornumberofimpressionsdesired（10000ormillionimpressions）.

●Thesubstrate（paper,plasticfilm,surfacequality,colored,porous,flexible,rigid）.

●Thephysicalshapeofthesubstrate（rollstock,sheets,discreteitems,round,irregularshape）.

●Specialpackageprocessoruseconditions（chemicalresistance,thermalresistance）.

ReliefPrinting

Reliefprinting,theearliestprintingmethod,usesaraisedsurface（onethatstandsoutinrelief）toholdtheink.Theraisedsurfaceisinkedbypassinganinkedrolleroveritorbypressingtheplateagainstaninkingpad.Thesimpleofficerubberstampisanexampleofreliefprinting.Thefirstreliefplateswerehand-carvedfromwood.Laterversionswereengravedintometaltype.

Modernreliefprintingplatesaremadefromrubber,photopolymeroroccasionallymetal,dependingontheapplication.Platesaremodestincostandcanbemadequickly.Nearlyallaremadebyphotographicallyimposingtheimagerecordedonaphotonegativeontoalight-sensitivematerial.Inthecaseofphotopolymers,thepolymerhardenswhereexposedtoultravioletlightandremainsfluidwhereunexposed.Theunexposedpartisthendissolvedaway.

Rubberprintingplatesaretheoldestoftheflexographicplatetechnologiesandtheiruseisslowlydeclining.Rubberprintingplateproductionstartswithamagnesiummetalplatecoatedwithalight-sensitivecoating.Themetalplateisexposedtolightshiningthroughtheimagenegative,andtheunexposedpartsarethenchemicallyetchedaway.Uncuredphenolicmoldingcompoundispressedintothemastermetalplatetomakeaphenolicmatrixmold.Soft,uncuredrubberispressedintothephenolicmatrixsurfaceandheat-cured.

Photopolymerplatesareabletoholdasmallerscreenthanrubberplatesandgenerallyproducebetterprocessartimages.However,photopolymermaterialissignificantlymoreexpensive.Productionoftheinitialrubberplateistime-consuming,butoncethephenolicmatrixhasbeenmade,additionalprintingplatesorreplacementscanbemadequickly.

Newertechnologyusingdigitalcomputer-to-plateprocessingisreplacingtraditionalphotonegative-basedimageimposition.Ablationtechnologyusesconventionalphotopolymerexceptthatthesurfaceofthephotopolymersheetiscoatedwithanopaque,carbon-basedblackcoating.Alaser“ablates”orburnsawaythecarbonfollowingdigitaldesigninformation.Ineffect,anultrathinphotonegativeiscreatedattachedthephotopolymer.ThesheetisthenexposedtoUVlight,andtheuncuredphotopolymerremovedintheusualway.

Flexography

Inatypicalflexographicprintingstation,excessinkisappliedtoanengravedtransfer,oraniloxroll.Theengravesontheaniloxrollmeterthecorrectamountofink,dependingontheengravinggeometryanddepth.Theinkistransferredtotheraisedsurfacesoftheprintingplateattachedtotheplatecylinder.Lineartprintingplateshaveasolid,smoothsurface.Halftoneandprocessprintingplatesurfacesarecomposedofsmalldotsstandingoutinrelief.Thesubstrateispassedbetweentheplatecylinderandtheimpressioncylindertoachieveinktransfer.

Flexographybydefinitionusesaflexibleprintingplateandpressuretocreateanimage.Accordingly,flexographytendstobesensitivetosmallpressurechanges,whichcancauseimagestospread,or“gain”.Pressurevariationsappearascolorvariationsinfinishedwork.Flexographicpressoperationispossiblymoreofanartthanotherprintingprocesses.

Theflexibleplatematerialusedinflexographylimitsthescreenthatcanbeusedforprocessprintingandthereproductionoffinelines.Flexographicscreensarenormallybetween60and120dpi.Inksqueeze-out,producingalight“halo”effectalongsolidedges（lineart）,isacommoncharacteristicofflexographyandletterpress.

Finescreensorfinecopyandblocksofsolidcoloronthesameplateshouldbeavoidedwhendesigningpackagestobeprintedwithflexography.Thepressureneededtoprintthesolidwillsqueezeanddistortthefinescreensandlines.Vignettes（imagesinwhichcolorgraduallyfadestothepaper）,soft-focusedimages,andsubtle,moodysubjectmatterarealsodifficulttoreproduceusingflexographybecauseofdotsizelimitationsandpressuredifferencesbetweendarkandhighlightedareas.

Flexography’srubberstampnature,beingmoreforgivingofsurfaceirregularities,makesittheprocessofchoiceforroughortexturedsurfaces.Mostcorrugatedfiberboardandkraftlinerboardisprintedwithflexography.Flexographyisusuallythechoiceforprintingflexibleplasticwebrollstockintendedforpackage-formingmachines,pressure-sensitiveadhesivelabelsandwrapperstock.Thesoftpolymerink