真空卷材涂料的热模拟Thermalmodelingofvacuumwebcoating

ThermalmodelingofvacuumwebcoatingG.Cominia,*,S.Savinoa,N.Magriotisb,S.MuratoribaUniversityofUdine,DepartmentofEnergyandFluidMachinery,ViadelleScienze208,33100Udine,ItalybArcotronicsTechnologiesSrl,ViaS.Lorenzo19,40037SassoMarconi(BO),ItalyReceived3February2006;accepted26May2006Availableonline12July2006AbstractThepaperpresentsananalyticalmodelforthepredictionofthesubstratetemperatureinvacuumwebcoaters.Themodelisbasedonthetheoryofheattransferbetweenacontinuouslymovingworkpieceandastationarysource,orsink,ofenergy.Theinvestigationcon-cernsthePhysicalVaporDeposition(PVD)ofametallayeronapolymerfilmbymeansofthermalevaporation,butmanyaspectsapplyequallywelltosputteringandelectronbeamevaporation.Thecontributionstothespecificheatloadonthewebarequantified,andtheinfluenceoftheheatexchangebetweenthefilmandthecoolingdrumisdiscussedindetail.Aftersatisfactorilycomparingthepredictionswithavailableliteratureresults,themodelisusedasaguidelineforaseriesofexperimentaltestsaimedatdeterminingtheinfluenceoftheoperatingconditionsonthefinalqualityoftheproductsobtainedfromvacuumdepositionofthickmetallayersonthinpolymersub-strates.Theexperimentalresultsdemonstratetheinfluenceofthemechanicaltractionofthewebonthethermalconductancebetweenthefilmandthecoolingdrum.2006ElsevierLtd.Allrightsreserved.Keywords:Vacuumcoating;Webcoating;Thermalmodeling;Thermalevaporation;Movingworkpieces;Webtension1.IntroductionPolymerwebs.i.e.thinpolymersubstrateswithconsid-erableflexibility,whencoatedwithmetallayersoffercon-sumersthecombinedadvantagesofmetalandplasticfilms.Thelistofsubstratesincludes,butisnotlimitedto:PE(polyethilene),PET(polyethyleneterephtalate),PP(polypropylene),CPP(castpolypropylene),BOPP(biaxi-allyorientedpolypropylene).Thelistofcoatingmaterialsincludes,butisbyfarnotlimitedto:aluminum,copper,sil-ver,nickel,cobalt,zinc[1].Themetallizedpolymerwebshaveelectrical,opticalandgasbarrierpropertiessimilartometalfoils,butcanbethinnerthanmanyavailablemetalfoils.Thereforeitisnotsurprisingthatmetallizedpolymerwebsareusedinacontinuouslygrowingnumberofsituationswherehighelectricconductivity,highbarrierpropertiesor,simply,strikingappearancearerequired.Applicationsinclude,forexample,•electriccapacitors,•gas,lightandUVbarriersforflexiblefoodpackagings,•thermalradiationscreensforbuildingenvelopes,•reflectivecoatingsand•decorativewrappings.PhysicalVaporDeposition(PVD)isthemostreliabletechnologyforthedepositionofmetalcoatingsonthinsubstrates,andthePVDprocessbasedonthermalevapo-rationisthemosteconomicalchoiceforseverallargescaleproductions[1].Theprocesstakesplace,atoperatingpres-suresoftheorderof4·102Pa,inelectricallyheatedcera-miccrucibles,continuouslyfedbyawireofpuremetal.Inthecrucibles,themeltingbathisbroughttoatemperaturehighenoughtoensurethedesignrateofmetalevaporation.Thevaporstreams,emergingfromthecrucibles,aredirec-tedtowardsthemovingwebwherethecondensationpro-cesstakesplace.Inmanyinstancesthekeytothesuccessofaproductisthepossibilityofdepositingarelativelythicklayerofahighlyconductivemetalonathinfilm(see,forexample,Ref.[2]).Thetaskisachallengingone,1359-4311/$-seefrontmatter2006ElsevierLtd.Allrightsreserved.doi:10.1016/j.applthermaleng.2006.05.026*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](G.Comini).(2007)611–618becauseahighrateofcoatingimpliesthatahighlatentheatfluxisassociatedwiththecondensationofthemetal.Toavoidthermaldamagesthelatentheatflux,increasedbythethermalradiationfluxcomingfromthecrucibles,mustbeeffectivelybalancedbyacorrespondingheatfluxfromthewebtoacoolingdrum.Polymersubstrates,infact,areverysensitivetothermallyinducedstresses,whichmaycausevariousdamages,rangingfromtheformationofwrinklestorecrystallization(see,forexample,Refs.[3–5]).Thepredictionofsubstratetemperaturedistributionsinvacuumwebcoatingprocessesisavaluabledesigntool,whichcanhelpassessingthefeasibilityofnewplantsandreducingheat-relateddefectsinexistingplants.Thepaperpresentsananalyticalmodelforthepredictionofwebtem-peraturedistributionsinPVDprocessesbasedonthermalevaporation,butmanyaspectsoftheanalysisapplyequallywelltosputteringandelectronbeamevaporation[6,7].Themainfeatureofthemodelistheincorporationofthesim-plifyingassumptionssuggestedbythevacuumcoatinglit-erature[6–10]inthegeneraltheoryofheattransferbetweenacontinuouslymovingworkpieceandastationarysource,orsink,ofenergy[11].Themajordifferencewiththemodelsemployedinthevacuumcoatingliterature,infact,istheadoptionoftheEulerianpointofview,typicalofastationaryobserver,insteadofthestandardLagrang-ianpointofview,movingwiththeweb.Temperaturevalues,predictedbytheproposedmodel,werefirstcomparedsatisfactorilywithliteratureresults[6,8].Themodelwasthenusedasaguidelineforaseriesofexperimentaltestsaimedatdeterminingtheinfluenceoftheoperatingconditionsonthefinalqualityoftheprod-uctsobtainedfromvacuumdepositionofthickmetallayersonthinpolymersubstrates.Thetestswerecarriedoutinavacuumrollcoater,espe-ciallybuiltforthedevelopmentofnewproducts.Measuredquan