16-paper-Industrial PVD for Continuous Strip Coati

IndustrialPVDforContinuousStripCoatingChallengesandSolutionsSEYFERTUlf,DEUSCarsten,GOTTSMANNLutzVONARDENNEANLAGENTECHNIKGMBHPlattleite19/29,D-01324Dresden,GermanyAbstract:Duringthelastfewyearsthethinfilmapplicationsinthemetallurgicalindustrieshavebeenextendedwidely.Besidestheaimofcorrosionprotectionofstripsteelalotofcoatingtasksbecameanurgentissue,i.e.opticalcoatings,catalyticcoatings,protectioncoatingsandotherfunctionalcoatingsonvariousmetalstripsasstainlessorcarbonsteelstrips,copperstripsandaluminiumstrips.ThispapergivesanoverviewofdifferentindustrialscaledPVD-techniquesbylargeareaprocessesforhighlyproductivecoatinglines.Thecoatingprocessesarediscussedfacingtheirapplicationbackground.SpecialattentionwillbegiventotechnologicalanddesignrequestsregardingsuitablePVDcoatingprocessesforpilotandproductionlineconcepts.Industriallyrelevantproductivesolutionswillbepresented.Keywords:PVD-Processes,Thinfilmcoating,Evaporation,Sputtering,Corrosionprotection1.INTRODUCTIONIndustrialPVD(PhysicalVapourDeposition)ofmetalstripsbeganmorethan30yearsagobasedonelectronbeamevaporationprocesses.Inthistimethemainobjectivewasthedepositionofcorrosionprotectivecoatingsonstripsteel[1].Theevaporantsthenusedweremetalsasaluminum,copperortitanium.ProductivityrequirementsofthesteelproductioncompaniesleadtothedevelopmentoflargeareacoatinglineswhichmadepossiblelongtermstablehighrateElectronBeam(EB)-evaporationprocessesusinghighpowerEBgunsandlargecrucibleswithfeedingsystems(Figure1).Fig.1:EB-coaterforAlcoating,installed1981Howevertheapplicationbackgroundofthisstartsituationwasrathernarrowandonlyreferredtocorrosionprotectionofstripsteel,andeventhiswasasubstitutiontaskconcerningapredominantconventionalfinishingtechnology.Thetraditionalalternativetechnologiesgenerallyretainedtheirpositionintheanti-corrosivefinishingtechnologiesbecausetheyrequiredlowerinvestmentcostsandalesssophisticatedprocessmanagementasEB-PVD.TheinsignificantnichesituationoflargeareaPVDofmetalstripsforabouttwodecadeschangedwhenotherdepositiontasksemergedwhichcouldnotbesolvedbythetraditionalalternativetechnologies.Inthelastfewyearsthevarietyofmetalstripsubstrateshasbeenenlargedespeciallybyaluminum,copperandstainlesssteelstripsaswellasbysimilaralloys[2].Surfacecoatedsteelsheetranksamongstthekeymaterialsforagreatnumberofapplications,inparticularintheautomotive,buildingandrenewableenergyindustries.Nowadaysthemanufacturersarefacedtoincreasinglycomplexprofilesofusersrequirementsonmetalsheet.Inadditiontosufficientcorrosionprotectionimprovedprocessingsuchasforming,joiningorpaintingisrequired.Moreover,functionalanddecorativefinishaspectsascolorandstructureanddefinedsurfacepropertiese.g.scratchresistanceoranti-fingerprintorhighsolarabsorptionpropertiesareofincreasingimportance.2.PRINCIPLESANDPROCESSES2.1.PLASMAPRETREATMENTTheadhesionproblemofasubstrate-layer-systemrequiresusefulpretreatmenttechnologiesofthemetalstripstobecoated.Aproperlydesignedwet-chemicalsurfacecleaningschemeisusuallysufficientforsubsequentwet-chemicalcoatingortreatmentsteps,e.g.electro-galvanizingorphosphatizing.Thesemethodshadonlyalimitedapplicabilitybecausetheycouldnotremoveseveraltypesofsurfacecovering.Forthisreasonplasmacleaningandactivationprocesseseffectingadirectsubstratebombardmentbeforethecoatinghavebecomemoreandmoreimportant.Theaimofinvestigationhasbeenthematchingofplasmaprocessessuitableforcleaningseveralkindsofmetalstripsatspeedsashighaspossible[].Regardingaluminumstrips,DC-aswellasMF-glowdischargeprocessesareeffectivepretreatmentmethods.Consistingofasubstratebombardmentwithelectronstheytakeintoaccountthataluminumsurfacesarecoveredeitherbyoxidefromtheanodizingprocessorbylacquers.Asfarasofmagneticsteel,stainlesssteel,copperandzincstripsisconcerned,electronbombardmentisnotasufficientsurfacepretreatmenttoguaranteegoodadhesionofEB-PVDcoatings.Inthesecasesofconductivesubstratematerialsamoreeffectivearrangementistousethestripascathodeofthedischarge.Insuchasputteretchingmodulebasedonthemagnetronprinciplethesubstrateisbombardedbyions.Figure2showstheschemeofsuchapretreatmentstation.Fig.2:SchemeofPlasmaPretreatmentunit2.2.ELECTRONBEAMEVAPORATIONDuetoitsabilitytoevaporatealargevarietyofmaterialsathighrates,EB-PVDhasbecomeacoatingtechnologythatoffersnewfieldsofapplication.Substrateshapes,requiredlayerproperties,requirementswithregardtotheproductivityandenergeticefficiencyaswellastheaccuracyofdepositionorspecificplantconceptsdemandformanyspecialsolutions.WithEBevaporation,thesurfaceoftheevaporantisdirectlyheatedbytheimpingingelectrons,whichpresentsasignificantadvantageincomparisontoconventionalheatingmethods.Theevaporationofreactiveandrefractorymaterialsanddepositionofhighpuritylayersathighratesbecomespossible.Figure3givestheschematicsetupofanEBevaporationfacility.Withevaporation,facilitiesforkeepingtheevaporantandmovingtheworkpiecestobecoatedmustbeprovided.Theseprerequisitessubstantiallydeterminetheoveralldesignoftheplant.Figure3:PrinciplesetupofElectronBeamEvaporationunitMoreandmorecoatingtasksrefertothedepositionof