Automotive Paints and CoatingsEdited byHans-Joachim Streitbergerand Karl-Friedrich D osselFurther ReadingH. Lipowsky, E. ArpaciCopper in the Automotive Industry2007ISBN: 978-3-527-31769-1G. Pfaff (Ed.)Encyclopedia of Applied Color2009ISBN: 978-3-527-31551-2G. Buxbaum, G. Pfaff (Eds.)Industrial Inorganic PigmentsThird, Completely Revised and Extended Edition2005ISBN: 978-3-527-30363-2E. B. Faulkner, R. J. Schwartz (Eds.)High Performance PigmentsSecond, Completely Revised and Extended Edition2008ISBN: 978-3-527-31405-8S. K. Ghosh (Ed.)Functional Coatingsby Polymer Microencapsulation2006ISBN: 978-3-527-31296-2Automotive Paints and CoatingsEdited byHans-Joachim Streitbergerand Karl-Friedrich D osselSecond, Completely Revised and Extended EditionThe EditorsDr. Hans-Joachim StreitbergerMarket & ManagementSustainability in BusinessPatronatsstr. 1348165 M unsterGermanyDr. Karl-Friedrich DosselDupont Performance CoatingsChristbusch 2542285 WuppertalGermany1. Edition 19952. Completely Revised and Extended Edition2008All books published by Wiley-VCH are care-fully produced. Nevertheless, authors, editors,and publisher do not warrant the informa-tion contained in these books, including thisbook, to be free of errors. Readers are ad-vised to keep in mind that statements, data,illustrations, procedural details or other itemsmay inadvertently be inaccurate.Library of Congress Card No.:applied forBritish Library Cataloguing-in-Publication DataA catalogue record for this book is availablefrom the British Library.Bibliographic information published by theDeutsche NationalbibliothekDie Deutsche Nationalbibliothek lists thispublication in the Deutsche Nationalbibli-ograe; detailed bibliographic data are avail-able in the Internet at. 2008 WILEY-VCH Verlag GmbH & Co.KGaA, WeinheimAll rights reserved (including those of trans-lation into other languages). No part of thisbook may be reproduced in any form byphotoprinting, microlm, or any othermeans nor transmitted or translated intoa machine language without written permis-sion from the publishers. Registered names,trademarks, etc. used in this book, evenwhen not specically marked as such, are notto be considered unprotected by law.Typesetting Laserwords Private Limited,Chennai, IndiaPrinting Strauss GmbH, M orlenbachBinding Litges & Dopf GmbH, HeppenheimCover Design Grak-Design Schulz,Fug onheimPrinted in the Federal Republic of GermanyPrinted on acid-free paperISBN: 978-3-527-30971-9VContentsPreface XVIIAbbreviations XIXList of Contributors XXIII1 Introduction 1Hans-Joachim Streitberger1.1 Historic Development 11.2 Legislation 71.3 Automotive and Automotive Paint Market 92 Materials and Concepts in Body Construction 13Klaus Werner Thomer2.1 Introduction 132.2 Methods of Body Construction 152.2.1 Monocoque Design 152.2.2 Space Frame 182.2.3 Hybrid Type of Construction 192.2.4 Modular Way of Construction 192.3 Principles of Design 202.3.1 Conventional Design 202.3.2 Design Under Consideration of Light-Weight Construction 222.3.3 Bionics 232.4 Materials 262.4.1 Steel 262.4.1.1 General Remarks 262.4.1.2 Low-Carbon Deep Drawing Steels 292.4.1.3 Higher-Strength Steels 292.4.1.4 High-Strength Steels 312.4.1.5 High-Grade (Stainless) Steels 322.4.1.6 ManganeseBoron Steels 322.4.1.7 Light-Construction Steel with Induced Plasticity (TWIP Steel) 332.4.2 Aluminum 34Automotive Paints and Coatings. Edited by H.-J. Streitberger and K.-F. D osselCopyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-30971-9VI Contents2.4.2.1 General Remark 342.4.2.2 Further Treatment 352.4.2.3 Aluminum Alloys 382.4.2.4 Aluminum as Light-Weight Construction Material 392.4.3 Magnesium 402.4.4 Titanium 422.4.5 Nonmetallic Parts Fiber Composites 432.5 Manufacturing Methods 472.5.1 Tailored Products 472.5.1.1 General Remarks 472.5.1.2 Tailored Blanks 472.5.1.3 Tailored Tubes 482.5.1.4 Tailored Strips 482.5.1.5 Patchwork Blanks 482.5.1.6 Future 492.5.2 Hydroforming 492.5.3 Press Hardening 502.5.4 Metal Foam 502.5.5 Sandwich Structures 512.5.6 Roll Forming to Shape 522.6 Joining Methods 522.6.1 Bonding 532.6.2 Laser Welding 542.6.3 Others 552.6.3.1 Clinching 552.6.3.2 Riveting 562.6.3.3 Roller Hemming 562.7 Outlook 572.8 Surface Protection 592.8.1 Precoating of Sheets 592.8.2 Corrosion Prevention in the Design Phase 593 Pretreatment of Multimetal Car Bodies 61Horst Gehmecker3.1 Introduction 613.2 Car Body Construction Materials 613.2.1 Sheet Materials 613.2.2 Surface Conditions/Contaminations 633.3 Pretreatment Process 653.3.1 Sequence of Treatment 653.3.2 Degreasing 653.3.3 Activation 693.3.4 Zinc Phosphating 703.3.5 Passivation 753.3.6 Pretreatment of Aluminum Steel Structures 75Contents VII3.3.7 Pretreatment of Magnesium 763.3.8 Pretreatment of Plastic Parts 773.4 Car Body Pretreatment Lines 773.4.1 Spray Lines 803.4.2 Continuous Horizontal Spray/Dip Line 803.4.3 RoDip3 Line 803.4.4 Vario Shuttle Line 813.4.5 Other Types of Lines 823.4.6 Construction Materials 823.4.7 Details on Process Stages 823.4.7.1 Precleaning Stage 823.4.7.2 Spray degrease 833.4.7.3 Dip Degrease 833.4.7.4 Rinsing 843.4.7.5 Activation 843.4.7.6 Phosphating 843.4.7.7 Rinsing 853.4.7.8 Passivation 853.4.7.9 Deionized water rinsing 853.4.7.10 Entering the Electrocoat Line 853.5 Properties and Specications of Zinc Phosphate Conversion Layers 853.6 Environmental Legislations 863.7 Outlook 864 Electrodeposition Coatings 89Hans-Joachim Streitberger4.1 History and Introduction 894.2 Physico-chemical Basics of the Deposition Process 904.3 Data for Quality Control 954.3.1 Voltage, Current Density, Bath Temperature, and BathConductivity 964.3.2 Wet Film Conductivity 964.3.3 Solid Content, Solvent Content, and pH 974.4 Resins and Formulation Principles 984.4.1 General Remarks 984.4.2 Anodic Electrodeposition Paints 994.4.3 Cathodic Electrodeposition Paints 994.5 Film Performance of Cathodic Electrocoatings 1014.5.1 Physical Film Data 1014.5.2 Corrosion Protection 1024.5.3 Chip Resistance 1044.5.4 Surface Smoothness and Appearance 1054.6 Design of Cathodic Electrocoating Lines 1064.6.1 Integration into the Coating Process of Cars and Trucks 1064.6.2 Pretreatment 107VIII Contents4.6.3 General Functions and Equipment of an Electrocoat Line 1074.6.4 Tanks, Filters, Heat Exchanger, and Power Supply 1084.6.5 Replenishment and Anode Cells 1114.6.6 Ultraltration and Rinsing Zones 1144.6.7 Baking Oven 1184.7 Defects During Application and their Prevention 1194.7.1 Dirt 1194.7.2 Craters 1204.7.3 Surface Roughness 1214.7.4 Film Thickness/Throwing Power 1224.7.5 Other Defects 1234.8 Electrocoating and Similar Processes Used in Automotive SupplyIndustry 1244.9 Outlook 1255 Primer Surfacer 129Heinrich Wonnemann5.1 Introduction 1295.2 Requirement Prole 1325.2.1 Legislative Requirement 1325.2.2 Technological Requirements 1335.2.2.1 Film Properties 1335.2.2.2 Product Specications 1365.2.2.3 Application 1365.3 Raw Materials 1385.3.1 Resin Components 1395.3.2 Pigments and Extenders 1415.3.2.1 Titanium Dioxide 1435.3.2.2 Barium Sulfate 1445.3.2.3 Talc 1445.3.2.4 Silicon Dioxide 1455.3.2.5 Feldspar 1465.3.2.6 Carbon Blacks 1465.3.3 Additives 1465.3.3.1 Pigment Wetting and Dispersion Additives 1485.3.3.2 Defoaming and Deaerating Agents 1485.3.3.3 Surfactants and Additives for Substrate Wetting 1495.3.3.4 Rheology Additives 1495.3.4 Solvents 1505.3.4.1 Aromatic Hydrocarbons: Diluents/Thinners 1515.3.4.2 Alcohols, Cellosolves, and Esters: Solvents 1515.3.4.3 Tetralin or Pine Oil: Very High Boiling Additive Diluents 152Contents IX5.4 Liquid Primers 1525.4.1 Formula Principles 1525.4.1.1 Application 1525.4.1.2 Rheology 1535.4.2 Manufacturing Process 1565.4.3 Application 1585.5 Powder Primer Surfacers 1605.5.1 Formula Principles 1605.5.2 Manufacturing Process 1625.5.3 Application 1665.6 Process Sequence 1705.7 Summary and Future Outlook 1716 Top Coats 175Karl-Friedrich D ossel6.1 Introduction 1756.2 Pigments and Color 1756.3 Single-Stage Top Coats (Monocoats) 1806.4 Base Coats 1816.4.1 Base Coat Rheology 1846.4.2 Low and Medium Solids Base Coat 1856.4.3 High Solids (HS) Base Coats 1866.4.4 Waterborne Base Coats 1866.4.5 Global Conversion to Waterborne Base Coat Technology 1876.4.6 Drying of Base Coats 1896.5 Clear Coat 1896.5.1 Market 1896.5.2 Liquid Clear Coats 1906.5.2.1 One-Component (1K) Acrylic Melamine Clear Coat 1906.5.2.2 Acrylic Melamine Silane 1926.5.2.3 Carbamate-Melamine-Based 1K Clear coat 1926.5.2.4 One-Component Polyurethane (PUR) Clear Coat 1926.5.2.5 One- (and Two-) Component Epoxy Acid Clear Coat 1926.5.2.6 Two-Component (2K) Polyurethane Clear Coat 1936.5.2.7 Waterborne Clear Coat 1946.5.3 Powder Clear Coat 1956.5.4 Top Coat Performance 1986.5.4.1 Enviromental Etch 1986.5.4.2 UV Durability of Clear Coats 1996.5.4.3 Scratch Resistant Clear Coats 2016.5.4.4 Application Properties 2046.5.5 Future Developments: UV Curing 206X Contents6.6 Integrated Paint Processes (IPP) for Top Coat Application 2086.6.1 Wet-On-Wet-On-Wet Application (3 Coat 1 Bake) of PrimerSurfacerBase CoatClear Coat 2086.6.2 Primerless Coating Process 2097 Polymeric Engineering for Automotive Coating Applications 211Heinz-Peter Rink7.1 General Introduction 2117.2 Polyacrylic Resins for Coating Materials in the AutomotiveIndustry 2147.2.1 Managing the Property Prole of the Polyacrylic Resins 2147.2.2 Manufacturing Polyacrylic Resins 2187.2.2.1 Manufacturing Polyacrylic Resins by Means of SolutionPolymerization 2187.2.2.2 Polymerization in an Aqueous Environment 2227.2.2.3 Mass Polymerization 2247.3 Polyester for Coating Materials for the Automotive Industry 2247.3.1 Managing the Property Prole of Polyesters 2247.3.2 Manufacturing Polyesters 2287.4 Polyurethane Dispersions in Coating Materials for the AutomotiveIndustry 2317.4.1 Managing the Property Prole of Polyurethane Resins andPolyurethane Resin Dispersions 2327.4.2 Manufacturing Polyurethane Resin Dispersions 2347.5 Polyurethane Polyacrylic Polymers in Coating Materials for theAutomotive Industry 2387.5.1 Introduction 2387.5.2 Managing the Property Prole of Polyurethane PolyacrylicPolymers 2397.5.3 Manufacturing Polyurethane Polyacrylic Polymers 2407.6 Epoxy Resins 2417.6.1 Managing the Property Prole 2427.6.2 Manufacturing Polyepoxy Resins 2437.7 Cross-Linking Agents and Network-Forming Resins 2447.7.1 Introduction 2447.7.2 Cross-Linking Agents for Liquid Coating Materials 2457.7.2.1 Melamine and Benzoguanamine Resins 2457.7.2.2 Tris(Alkoxycarbonylamino)-1,3,5-Triazine 2487.7.2.3 Polyisocyanates and Blocked Polyisocyanates 2497.7.2.4 Other Cross-Linking Agents for Liquid Coating Materials 2527.7.3 Cross-Linking Agents for Powder Coatings in the AutomotiveIndustry 252Contents XI8 Paint Shop Design and Quality Concepts 259Pavel Svejda8.1 Introduction 2598.2 Coating Process Steps 2608.2.1 Pretreatment 2618.2.2 Electrocoating (EC) 2618.2.3 Sealing and Underbody Protection 2628.2.4 Paint Application 2638.2.4.1 Function Layer and Primerless Processes 2638.2.4.2 Powder 2648.2.5 Cavity Preservation 2658.3 General Layout 2668.4 Coating Facilities 2688.4.1 Process Technology 2688.4.2 Automation in the Paint Application 2698.4.2.1 Painting Robot 2708.4.3 Application Technology 2718.4.3.1 Atomizer 2728.4.3.2 Paint Color Changer 2758.4.3.3 Paint Dosing Technology for Liquid Paints 2778.4.3.4 Paint Dosing Technology for Powder Paints 2788.4.4 Paint-Material Supply 2798.4.4.1 Paint Supply Systems for the Industrial Sector 2808.4.4.2 Paint Mix Room 2808.4.4.3 Container Group 2808.4.4.4 Circulation Line System 2828.4.4.5 Basic Principles for the Design of the Pipe Width for CirculationLines 2828.4.4.6 Paint Supply Systems for Small Consumption Quantities and FrequentColor Change 2838.4.4.7 Small Circulation Systems 2838.4.4.8 Supply Systems for Special Colors 2848.4.4.9 Voltage Block Systems 2858.4.4.10 Voltage Block Systems with Color-Change Possibility 2858.4.4.11 Installations for the High Viscosity Material Supply 2868.4.5 Conveyor Equipment 2878.5 Paint Drying 2888.6 Quality Aspects 2908.6.1 Control Technology 2908.6.1.1 Process Monitoring and Regulation 2928.6.2 Automated Quality Assurance 2938.6.2.1 Process Optimization in Automatic Painting Installations 296XII Contents8.7 Economic Aspects 2988.7.1 Overall Layout 2988.7.2 Full Automation in Vehicle Painting 2988.7.3 Exterior Application of Metallic Base Coats with 100% ESTAHigh-Speed Rotation 3008.7.4 Robot Interior Painting with High-Speed Rotation 3019 Coatings for Plastic Parts 3059.1 Exterior Plastics 305Guido Wilke9.1.1 Introduction 3059.1.1.1 Ecological Aspects 3059.1.1.2 Technical and Design Aspects 3069.1.1.3 Economical Aspects 3079.1.2 Process Denitions 3079.1.2.1 Ofine, Inline, and Online Painting 3079.1.2.2 Process-Related Issues, Advantages, and Disadvantages 3079.1.3 Exterior Plastic Substrates and Parts 3109.1.3.1 Overview 3109.1.3.2 Basic Physical Characteristics 3119.1.3.3 Part Processing and Inuence on Coating Performance 3159.1.4 Pretreatment 3159.1.5 Plastic-Coating Materials 3189.1.5.1 Basic Technical Principles of Raw-Material Selection 3189.1.5.2 Car-Body Color 3209.1.5.3 Contrast Color and Clear Coat on Plastic Systems 3249.1.6 Technical Demands and Testing 3249.1.6.1 Basic Considerations 3249.1.6.2 Key Characteristics and Test Methods 3259.1.7 Trends, Challenges, and Limitations 3299.1.7.1 Substrates and Parts 3299.1.7.2 Paint Materials 3309.1.7.3 Processes 3329.2 Interior Plastics 334Stefan Jacob9.2.1 Introduction: the Interior Concept 3349.2.2 Surfaces and Effects 3359.2.3 Laser Coatings 3379.2.3.1 Substrate Requirements 3399.2.3.2 Requirements to Be Fullled by the Paint Systems and Coating 3399.2.3.3 Demands Expected by the Inscription Technique 3409.2.4 Performances of Interior Coatings 3419.2.4.1 Mechanical and Technological Demands 3419.2.4.2 Substrates and Mechanical Adhesion 3429.2.4.3 Ecological and Economical Requirements 343Contents XIII9.2.4.4 Equipment for the Application of Interior Paint Systems 3449.2.5 Raw-Material Basis of Interior Paints 3469.2.6 Summary/Outlook 34710 Adhesive Bonding a Universal Joining Technology 351Peter W. Merz, Bernd Burchardt and Dobrivoje Jovanovic10.1 Introduction 35110.2 Fundamentals 35110.2.1 Basic Principles of Bonding and Material Performances 35110.2.1.1 Types of Adhesives 35110.2.1.2 Adhesives are Process Materials 35510.2.1.3 Advantages of Bonding 35610.2.1.4 Application 35910.2.2 Surface Preparation 35910.2.2.1 Substrates 36110.2.2.2 Adhesion 36110.2.2.3 Durability and Aging of Bonded System 36210.3 Bonding in Car Production 36610.3.1 Body Shop Bonding 36710.3.1.1 Antiutter Adhesives 36710.3.1.2 Hem-Flange Bonding 36810.3.1.3 Spot-Weld Bonding 36910.3.1.4 Crash-Resistant Adhesives/Bonding 36910.3.2 Paint Shop 37010.3.3 Trim Shop 37110.3.3.1 Special Aspects of Structural Bonding in the Trim Shop 37110.3.3.2 Direct Glazing 37110.3.3.3 Modular Design 37210.3.3.4 Other Trim Part Bondings 37210.4 Summary 37411 In-plant Repairs 377Karl-Friedrich D ossel11.1 Repair After Pretreatment and Electrocoat Application 37711.2 Repair After the Primer Surfacer Process 37811.3 Top-Coat Repairs 37811.4 End-of-Line Repairs 38012 Specications and Testing 38112.1 Color and Appearance 381Gabi Kiegle-B ockler12.1.1 Visual Evaluation of Appearance 38112.1.1.1 Specular Gloss Measurement 38212.1.1.2 Visual Evaluation of Distinctness-of-Image (DOI) 38512.1.1.3 Measurement of Distinctness-of-Image 385XIV Contents12.1.1.4 Visual Evaluation of Orange Peel 38612.1.1.5 Instrumental Measurement of Waviness (Orange Peel) 38812.1.1.6 The Structure Spectrum and its Visual Impressions 39012.1.1.7 Outlook of Appearance Measurement Techniques 39212.1.2 Visual Evaluation of Color 39312.1.2.1 Solid Colors 39312.1.2.2 Metallic and Interference Colors 39712.1.2.3 Color Measurement of Solid Colors 39812.1.2.4 Color Measurement of Metallic and Interference Coatings 40112.1.2.5 Typical Applications of Color Control in the Automotive Industry 40212.1.2.6 Color Measurement Outlook 40312.2 Weathering Resistance of Automotive Coatings 405Gerhard Pausch and J org Schwarz12.2.1 Introduction 40512.2.2 Environmental Impact on Coatings 40612.2.2.1 Natural Weathering 40812.2.2.2 Articial Weathering 41412.2.2.3 New Developments 42112.2.3 Standards for Conducting and Evaluating Weathering Tests 42312.2.4 Correlation Between Articial and Natural Weathering Results 42612.3 Corrosion Protection 427Hans-Joachim Streitberger12.3.1 Introduction 42712.3.2 General Tests for Surface Protection 42912.3.3 Special Tests for Edge Protection, Contact Corrosion, and Inner PartProtection 43212.3.4 Total Body Testing in Proving Grounds 43312.4 Mechanical Properties 434Gerhard Wagner12.4.1 General Remarks 43412.4.2 Hardness 43512.4.2.1 Pendulum Damping 43512.4.2.2 Indentation Hardness 43612.4.2.3 Scratch Hardness 43912.4.3 Adhesion and Flexibility 44112.4.3.1 Pull-Off Testing 44112.4.3.2 Cross Cut 44112.4.3.3 Steam Jet 44412.4.3.4 Bending 44512.4.3.5 Cupping 44612.4.3.6 Impact Testing by Falling Weight 44812.4.4 Stone-Chip Resistance 44912.4.4.1 Standardized Multi-Impact Test Methods 45012.4.4.2 Single-Impact Test Methods 45112.4.5 Abrasion 454Contents XV12.4.5.1 Taber Abraser 45412.4.5.2 Abrasion Test by Falling Abrasive Sand 45512.4.6 Scratch Resistance 45612.4.6.1 Crockmeter Test 45612.4.6.2 Wet-Scrub Abrasion Test 45712.4.6.3 Simulation of Car Wash 45812.4.6.4 Nanoscratch Test 46012.4.7 Bibliography, Standards 46213 Supply Concepts 467Hans-Joachim Streitberger and Karl-Friedrich D ossel13.1 Quality Assurance (QA) 46713.2 Supply Chain 46813.2.1 Basic Concepts and Realizations 46813.2.2 Requirements and Limitations of a System Supply Concept 47314 Outlook 475Hans-Joachim Streitberger and Karl-Friedrich D ossel14.1 Status and Public Awareness of the Automotive Coating Process 47514.2 Regulatory Trends 47614.3 Customer Expectations 47814.4 Innovative Equipments and Processes 47914.5 New Business Ideas 481Index 483XVIIPrefaceIt isnowover 10yearssincetherst publicationof AutomotivePaintsandCoatings in1996. Theoriginal publicationwasmadepossiblethanks totheuntiringeffort of GordonFettis tobringout abookdedicatedtoautomotiveOEMcoatings. Inachangingbusiness environment,theautomotive industry isalwaysreevaluatingitscorecompetenciesandhastransferredmanytechnicaldevelopments and manufacturing tasks to the supplier industry. Painting, so far,hasremainedoneof itscorecompetenciesandisavalueadded processinthe car manufacturing industry. This fact underlines the necessity for a new andcompletely revised edition of the book. We thank Mr. Fettis for taking this up, andgiving us the opportunity to publish this book. We also thank all the contributors fortheir articles that demonstrate the expertise of each of them in his respective eld.Thebook covers thepaintingprocess ofpassenger carsandlighttrucks,astheyarecalledbytheAmericanautomotiveindustry. Thesevehiclesaremassmanufactured and therefore their coating requirements in terms of processing andcoating performance are similar in nature.The key performance drivers inautomotive coatings are quality, cost, andenvironmental compliance. Quality, in this context, relates to corrosion protectionandlonglastingappearance. Qualityandcost areaddressedbymoreefcientcoating processes and a higher degree of automatization. This has led to reduceduseofpaintandlesserwasteperbody. Withthewidespreaduseofhighsolid,waterborne,andpowdercoatings,solvent emission frompaintshops havebeenreduced by more than 50% over the last ten years.We are proud to contribute to this development by publishing the second editionof Automotive Paints and Coatings, in which we try to describe the state-of-the-arttechnology of automotive coating processes and the paint materials used in theseprocesses.Automotivecoatingprocessesrepresent thecuttingedgeof applicationtech-nology andpaintformulations. Theyarethemost advancedprocesses inregardtovolumehandling, sophisticatedbodygeometriesandspeedinmassproduc-tion. Colored coatings offer mass customization and product differentiation at anaffordable cost.Automotive Paints and Coatings. Edited by H.-J. Streitberger and K.-F. D osselCopyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-30971-9XVIII PrefaceThis secondeditionmay helpmany readers tounderstandthesehigh-performancecoating processes and the related materials, and also appreciate the scope for newideas and innovations.Thecontentsandthemainfocusofthiseditiondifferfromthoseintherstedition. Processes, technology, and paint formulations have been weighted equally,reecting that legislation and cost were the driving forces of the past.We hopethatnotonly experts butalsotechnicallyinterested readerswillndthis book useful.M unster and Wuppertal, Germany Dr. Hans-Joachim StreitbergerDecember 2007 Dr. Karl-Friedrich D osselXIXAbbreviations1K 1-component2K 2-componentABS Acrylonitrile-Butadiene-StyreneAED Anodic Electro DepositionAFM Atomic Force MicroscopyAPEO AlkylPhenolEthOxylateASTM American Society for Testing and MaterialsATRP Atom Transfer Radical PolymerizationBAT Best Available TechnologyBSC Balanced Score CardBMC Blow Molding CompoundBPA BisPhenol-ACASS Copper Accelerated Salt Spray testCCT Cyclic Corrosion TestCED Cathodic Electro DepositionCIE Comite International dEclairageCMC Critical Micelle ConcentrationCPO Chlorinated PolyOlenesCPU Cost Per UnitCSM Centre Suisse delectronique et de MicrotechniqueCTE Coefcient of Thermic ExtensionDBP Di-ButylPhtalatDDDA DoDecane-Di-AcidDDF Digital Dichtstrom F orderung (digital dense ow transporation)DIN Deutsche IndustrieNorm (German industrial normation ofce)DMPA DiMethylol-Propronic AcidDOI Distinctness Of ImageDOS DiOctylSebacateDPE DiPhenylEthaneEDT Electro Discharge TexturingEDTA Ethylene Diamino Tetra AcidEEVC European Enhanced Vehicle safety CommitteeAutomotive Paints and Coatings. Edited by H.-J. Streitberger and K.-F. D osselCopyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-30971-9XX AbbreviationsEINECS European Inventory of Existing commercial Chemical SubstancesEIS Electrochemical Impedance SpectroscopyEN European NormsEO EthOxyEP EPoxyEPA Environmental Protection AgencyEPDM Ethylene-Propylene-Diene-MonomerERP Enterprise Resource PlanningESCA Electron Spectroscopy for Chemical AnalysisESTA ElectroSTatic ApplicationFEM Finite Element MethodFMVSS Federal Motor Vehicle Safety Standards (USA)GMA GlycidylMethAcrylatHALS Hindered Amine Light StabilizerHAPS Hazardous Air Polluting SubstancesHDI 1.6-HexamethyleneDiIsocanateHDI HexamethyleneDiIsocanateHLB Hydrophilic Lipophilic BalanceHMMM HexaMethoxyMethylMelamineHVLP High Volume Low PressureICEA IsoCyanatoEthyl(meth)AcrylateIPDI IsoPhoronDiIsocyanateIPN InterPenetrating NetworkIPP Integrated Paint ProcessISO International Standard OrganisationKPI Key Performance IndicatorLEPC Low Emission Paint ConsortiumMCC Mercedes Compact CarMDI Diphenyl-Methan-DiIsocyanateMDF Medium Density FibreboardNMMO N-MethylMorpholine-n-OxidNAFTA NorthAmerican Free Trade AgreementNTA NitroloTriAceticacidOEM Original Equipment ManufacturerPA PolyAmidePA-GF Glas Fiber reinforced PolyAmidePBT PolyButyleneterephtalatePC PolyCarbonatePFO Paint Facility OwnershipPMMA PolymethylmethAcrylatePO ProprOxyPP PolyPropylenePPE Poly Phenylene EtherPUR PolyURethaneAbbreviations XXIPVC PolyVinylChlorideQC Quality ControlQA Quality AssuranceQUV Tradename for test chambers (Q-Lab)RAFT Reversible Addition Fragmentation chain TransferRCA Rheology Contol AgentRRIM Reinforced Rejection InMoldRT Room TemperatureR-TPU Reinforced ThermoPlastic PolyurethaneSAE Society of Automotive Engineers (USA)SCA Sag Control AgentSCM Supply Chain ManagementSDAT Short safe Drive Away TimeSEA South East AsiaSMC Sheet Molding CompoundSNIBS Sodium NItroBenzeneSulfonateTACT Tris(AlkoxyCarbonylamino)-1.3.5-TriazineTDI Toluylene DiIsocaynateTEM Transmission Electron MicroscopyTEMPO TEtraMethylPiperidin-n-OxidTGIC TriGlycidylIsoCyanuratm-TMI 3-isoporpenyl-dimethylbenzyl-isocyanateTMXDI Tetra-Methyl-Xylylene-DiIsocyanateToF-SIMS Time of Flight Secondary Ion Mass SpectroscopyTPO ThermoPlastic OlenesUP Unsaturated PolyesterUV UltraVioletteUVA UV-AbsorberVDA Verband der Deutschen Automobilindustrie (German association ofcar manufactureres)VOC Volatile Organic CompoundsXXIIIList of ContributorsBernd BurchardtSika Schweiz AGOEM Adhesives & SealantsT uffenwies 168048 Z urichSwitzerlandKarl-Friedrich DosselDupont Performance CoatingsChristbusch 2542285 WuppertalGermanyHorst GehmeckerChemetall GmbHTrakehnerstr. 360407 FrankfurtGermanyStefan JacobMankiewicz Gebr. & Co.Georg-Wilhelm-Str. 18921107 HamburgGermanyDobrivoje JovanovicSika Schweiz AGOEM Adhesives & SealantsT uffenwies 168048 Z urichSwitzerlandGabi Kiegle-BocklerBYK-Gardner GmbHLausitzerstr. 882538 GeretsriedGermanyPeter W. MerzSika Schweiz AGOEM Adhesives & SealantsT uffenwies 168048 Z urichSwitzerlandGerhard PauschPausch Messtechnik GmbHNordstr. 5342781 HaanGermanyHeinz-Peter RinkBASF Coatings AGCTS Trailers, Trucks & ACEAutomotive Renish / CommercialTransport Coatings SolutionsGlasuritstr. 148165 M unster-HiltrupGermanyJorg SchwarzDaimler AGWerk Sindelngen B 430 PWT/VBT71059 SindelngenGermanyAutomotive Paints and Coatings. Edited by H.-J. Streitberger and K.-F. D osselCopyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-30971-9XXIV List of ContributorsHans-Joachim StreitbergerMarkt & ManagementPatronatsstr. 1348165 M unsterGermanyPavel SvejdaD urr Systems GmbHApplication TechnologyVertrieb/SalesRosenstr. 3974321 Bietigheim-BissingenGermanyKlaus Werner ThomerAdam Opel AGITDC/MEFriedrich-Lutzmann-Ring65423 R usselsheimGermanyGerhard WagnerDupont Performance CoatingsQualit atspr ufungChristbusch 2542285 WuppertalGermanyGuido WilkeHochschule EsslingenUniversity of Applied SciencesLabor PolymerwerkstoffeKanalstr. 3373728 EsslingenGermanyHeinrich WonnemannBASF Coatings AGCO/XEH B32548165 M unsterGermany11IntroductionHans-JoachimStreitberger1.1Historic DevelopmentThe car painting industry has undergone incredible changes by way of materials andprocesses development following the general progress of manufacturing technologyfrom the start of the twentieth century until today. Early coating processes, that is,during the rst half of the twentieth century, involved the use of air drying paints,sanding of each layer and polishing, all of which needed weeks for completion. Allthe coating steps were executed manually (Figure 1.1).Different drivingforces behindthedevelopment of better andmore efcientprocesses have brought in dramatic changes over the last 100 years. Introduction ofmass production requiring faster curing paints, better lm performance in termsof corrosion and durability of colors, improved environmental compatibility, andfullyautomatedprocessesforbetterreliabilitycharacterizethemostimportantmilestones in this eld (Table 1.1).The status of mass production of cars during the 1940s required new coatingsproviding faster drying and curing: the result the birth of enamels! At the sametime, owingtotheirlimitedavailability, thenatural rawmaterialsusedinthemanufacture of the paints had to give way to synthetic chemicals. Crosslinkingof paints became state of the art. The coating process could be reduced to a dayincluding all necessary preparation time for the car body like cleaning, sanding,repairing, and so on.The number of applied coatings had been reduced to four or ve layers, all handsprayed this time (Figure 1.2). The function of these layers were corrosion protec-tionfor the primers, smoothness andchipresistance for the primer surfacers (whichare often applied at the front ends and exposed areas in two layers), and color andweather resistance for the nal top-coat layer. In the 1950s the process of applyingthe primer changed to dip coating, a more automated process, but a hazardousoneowingtothesolventemissionofthesolvent-bornepaints. Explosionsandre hazards then forced automotive manufacturers to introduce either waterbornepaints or electrodeposition paints. The latter, which were introduced during theAutomotive Paints and Coatings. Edited by H.-J. Streitberger and K.-F. D osselCopyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-30971-92 1IntroductionFig. 1.1Painting of cars in the 1920s and 1930s.Table 1.1Milestones and driving forces in the car coating processYear Topics/Driving forces Aspects1920 Manual painting Time-consuming process : weeks1940 Mass production Enamels/oven/time : day1970 Improved lm performance CED/2-layer top coat/new materials1980 Environmental compliance Waterborne coatings/powder/transferefciency2000 Automated processes First time capability/time : hoursClear coatCED-primerPrimersurfacerSubstrateBase coat40m15m30m20m1mPretreatmentFig. 1.2Scheme of the multilayer coating of cars.1.1Historic Development 3late 1960s, are more efcient interms of material transfer as well as throwingpower that is necessary for improved corrosion protection of the inner parts of thecar body.Inthe 1970s the anodic depositioncoatings, mostly basedonmaleinizedpolybutadiene resins, quickly gave way to cathodic ones owing to better corrosionprotectionby their modied epoxy resinbackbones and reactive polyurethane-basedcrosslinkers, increased throwing power, and higher process reliability. At the sametime, thesinglelayertopcoatsweregraduallyreplacedbytwo-layertopcoatsconsisting of a thin base coat and a thicker clear coat applied wet-on-wet. The basecoats are responsible for color and special effects (for example, metallic nish),whereas the clear coats provide improved durability using specially designed resinsandformulaingredientslikeUV-absorberandradical scavengers. Today, mostclear coats in Europe are based on two-component (2K-) formulation consisting ofan acrylic resin with OH-functions and a reactive polyurethane crosslinker. Therest of the world still prefers the one-component technology based on acrylic resinsand melamine crosslinkers. An interesting one-component technology based oncarbamate functionality has been recently introduced in the United States [1].All these developments contributed to an improved lm performance resultingin better corrosion protection and longer top-coat durability for example, glossretention for up to 57 years was observed in Florida.Furthermore, raw material development in the pigment section, with improvedake pigments based on aluminum and new interference pigments that changecolor depending on the angle in which they are viewed, has resulted in enhancedbrilliance and color effects of automotive coatings [2].Along with this development of coating and paint technology, spray applicationtechniques also underwent signicant improvements. Starting with simple pneu-matic guns and pressure pots for paint supply, today, craftsmanship in painting isno longer needed. Several factors have contributed to the development of coatingmachines and robots and the state of automation that is present today. The rstfactor was the health risk to the painters who were exposed to solvent emissionfrom paints in the spray booth and the investment in safety equipment, which wasoften unsuitable for them. The second factor was the hazards of the electrostaticapplicationtechnique. Yet anotherfactorwasthelackofuniformqualityinamanual painting job.Because of the latest developments in wet-on-wet coating technology, coatingmachines, automated cleaning processes, and modern paints, the time taken todayfor the coating process, including pretreatment, can be as short as 8 hours for a carbody leaving the body shop and entering the assembly line (Figure 1.3) [3].Together with the continuous improvements of the application technology, newwater-basedmaterialsweredeveloped tocontributetowardthelegallyenforcedenvironmental compliance of the processes. The rst water-based base coats wereintroducedat Opel inGermanyinthe1980s, followedbywater-basedprimersurfacers in the 1990s.Investments in modern paint shops vary from 200 up to 600 million for coat-ing 1000 units a day. Today, painting technology for the car industry has been more4 1IntroductionWasherBody-in-whitePretreatment CED Baking ovenSanding SealingSounddampersDryingCleaning Baking oven Primer surfacer applicationBaking oven Clear coat Flash off Basecoat CleaningSpotrepairRepair Inspection WaxingTo AssemblylineBacktoCleaning before primersurfacerapplicationFig. 1.3Process steps in modern automotive paint shops.or less standardized all over the world. Inorganic pretreatment, cathodic electrode-position, liquid or powder primer surfacer, liquid base coats, and one-componentor two-component solvent-borne clear coats are mostly used today. This is a resultof the consolidation of the engineering and coating line manufacturers and paintproducers into just a handful of major players. In 2002, 70% of the car coatingmarket was in the hands of Dupont, PPG, and BASF.Asof today, thetechnologyof powdercoatingshasreachedapoint wheremanycarmanufacturershavedecidedtointroduceenvironmentallycomplianttechnology more aggressively. Today, powder is established as the primer surfacerin North America: at Chrylser in all actual running plants, at GM for their truckplants, and in all new paint shops. In Europe, in a number of plants at BMW,powder is also used as a clear coat. [4].Over the same period of time, body construction materials have also changedsignicantly. Starting with pure steel bodies, today the share of aluminum andmagnesium, as well as plastic, as raw materials for specic car components orhang-on parts can account for about 30% of the weight of the car. On an average,half of this is plastic. The main focus is on weight reduction, design variability, andcost (Figure 1.4).Starting with bumpers in the 1970s, and moving on to fenders and hoods, manyof the exterior parts are nowmade of specially designed plastics. The coating processis predominantly outsourced for these parts, even though some car manufacturersassemble the parts in the coating line and apply the original base coatclear coattechnology on these parts to overcome color match problems.1.1Historic Development 5Steel60.7Iron11.8Plastics 8.6Rubber5.0Glass3.3Copper/Brass1.6Al8.7Zinc0.4Fig. 1.4Share ( % )of different material classes for carmanufacturing ( source : Ward s Communications, Facts &Figures 2002) .Interior parts made of plastic materials were introduced in the 1960s and aretoday increasingly being coated by specially formulated paints for providing the softfeel touch that gives the plastic an improved acceptance by the customers. Theseparts were mostly painted by the part manufacturers and supplied to the automotiveindustry as complete modules to the assembly line. Special laser coatings havebeen developed to inscribe symbols of functions on coated dash board or otherunits in the interior of a car.Another increasing application of coatings is connected with the modern designof head lamps made of blowmolding compounds(BMC) for the head lamp reectorscovered by a polycarbonate lens. Both parts are coated dominantly by UV coatings.Manyotherexterior partslikehoodsandtrunklids, aswell asother bodysegments, areincreasinglymadeof aluminumor sheet moldingcompounds(SMC). Inadditiontotheaspectofcareful constructioninrespectofbuildinggalvanic elements, pretreatment chemicals and the process of multimetal bodieshad to be developed. This was a demanding task that needed avoidance of anyharmful heavymetal ionslikechromic-VI. Thecompletealuminumbodystillremains a niche product.Connected with an increased share of multicomponent parts of different sub-strates, the welding process for manufacturing cars has been partially replaced byother assembling techniques like clinching and riveting. Glewing, a technologyknown from the air transportation industry, has become very important. This tech-nique is based on surface treatment and product application similar to coatings.On the basis of the use of interface with coating layers like gluing back-windowsonelectrocoat layers andits increasingapplication, this will bedescribedinChapter 10.The performance requirements for an OEM (Original Equipment Manufacturer)coating of passenger cars are many and diverse. They can be attributed to corrosionprotection, durability, including stone chip resistance, and appearance. One shouldbearinmindtheextentofextremestressthatcarsareexposedtothroughouttheirlifespan. Hightemperaturesupto70

CondarkcolorsinFloridaandsimilar regions, as well as low temperatures of 50 C in polar regions, permanent6 1Introductiontemperature uctuation of 1020

C daily, stone chip attacks on unpaved roads,highloadsofsalt incoastal regions, aswell asinwintertime, highultravioletradiation in combination with dry and humid periods, the action of acid or alkalineair pollutants frommany sources, and the physical and mechanical stress in vehiclewashing installations are the most important among the many factors. Recently,the gloss, appearance, and effect coatings became important factors for selling carsby underlining the image and personality of the car and its driver.Because of the fact that many resources have been directed to the environmentalimprovement of paint application as well as toxic aspects of the paint formulas,the performance of automotive coatings has increased signicantly. Even the lmthickness of a car coating today is only 100140m, which needs, in most coatingprocesses, about 916 Kg deposited paint per car; the corrosion protection andthe long time durability of color and gloss is about two times higher than whatit was 25 years ago. Three main factors have contributed to this: new substrates,introduction of cathodic electrodeposition paints, and the two-layer top-coat systemwith a special designed clear coat for long term durability. The life time of a car isno longer related to the corrosion or durability of the coating and color.The color of cars has become a very important design tool, signicantly support-ing the purchasing habits of customers. For this reason, color trends are beingobserved by the paint and automotive industry together to develop trendy colorsfor the right cars.The color variability has been increased at the same time. Todays customers, es-pecially in the premium car level, can demand whichever colors they want at a cost.Newcolor effects like color op, whichis a coating providing different color impres-sions to the customer depending on the angle of vision, have entered the scene [5].The latest signicant milestone in the history of the development of car paintingis the combination of highly efcient application techniques like high rotationalmini- ormicro-bellsandthepaintingrobots(Figure1.5). Thishasleadtothehighest degree of transfer efciency and reliability, resulting in an efciency of90% and more of defect free coatings in modern paint shops [6].The application of sealants, sound deadeners and underbody protection is veryoften a part of the coating process. These materials need to be dried. In an efciencymove, the primer baking ovens are mostly used for this process.Shorter cycle time of car models requires faster planning and realization periodsfordesigningnewpaint shops. Additionally, globallycompetitivebusinesshasbrought into the focus of car manufacturers not only the respective investmentcosts, but also the running cost of a coating line [7].At the end of the paint line, the application of transport coatings, wrap up ofcoated cars for company design on a commercial eet, as well as safety measures,all become part of the coating processes connected with the manufacture of cars [8].Qualityassurancehasreachedanewdimensionforautomotive OEMpaintsand coatings. While time-consuming batch-to-batch approvals of the customersspecications has been the order of the day, supporting-system approaches, forexample, audit-management systems accordingtoDIN-ISO9001and14001,ISO/TS 16949, QS 9000 or VDA 6.1, have become mandatory for the paint industry1.2Legislation 7Fig. 1.5Paint robot withelectrostatic bell (source: BASF Coatings).tobeapprovedas asupplier totheautomotiveindustry. So, right fromthebeginning, the development of new products has to be quality oriented to zerodefect levels through all the steps leading up to the delivery status.At the same time, the testing and physical methods of describing the performanceof paint and coatings have become much more precise and value based not onlyfor the performance of the lms, but also the performance during the applicationand lm forming processes. In top-coat color specications and in general physicalcolor matching, especially, colorimetric data will replace visual inspections, whichhave reliability problems. The so-called nger print methods have been developedto improve the performance of paints during the application processes [9]. Filmperformances like durability andcorrosionprotection, andmechanical performancelike scratch, mar, and gravel resistance are very predictable in short term testingprocedures today.1.2LegislationAnother driving force for nding new coating formulas is the passing of legislativeacts all over the world calling for a ban on toxic components in all the formulae8 1Introductionto the maximum possible extent [10]. So lead- and chrome-free paint formulas aretoday state of the art. Also, the emission of volatile organic compounds (VOC) hasbeen restricted, especially in Europe and the NAFTA (North American Free TradeAgreement) region for the last 20 years, to numbers that are dened in variousways and controlled in NAFTA and Europe, and are about ve to ten times lowerthan what they were 30 years ago. This was reached by simultaneous material andprocess development as described herein. The industry has to deal with movingtargets set by the authorities according to the best available technology. In general,the emission of any type of greenhouse gases is in worldwide focus based on theKyoto protocol. Life cycle assessments are gaining awareness [11].Owing to the fact that the most important application processes of automotivepaints release solvents and that the composition of coatings can have more than15ingredients, togetherwiththeglobal agreementsonenvironmental targets,the politicalscenario inNorthAmerica andEurope wasto focus rst onpaintconsumers and manufacturers for improved environmentally compatible productsand application processes.The response in the 1980s in North America was to increase the solid contentsanddecreasethesolventsoftheactual solvent-bornepaint formulations. Newresinshadtobedevelopedandformulationaswell asapplicationconditionshad to be optimized in the direction of sagging resistance and surface and lmproperties. The relative increase of solids by about 20% generated a completely newtechnology. The legislation controlled the progress by measuring the solvent inputin the factories.In Europe the resources for research and development were directed towaterborne coatings rst, resulting in the introduction of waterborne base coats.Solvent-borne base coats were the paints providing the highest amount of solventemission owingto theverylowsolid contentof 1218%atthattime. Laterinthe 1990s waterborne primer surfacer and some waterborne clear coats were in-troduced. The legislation inGermany supported abatement technology to meetits requirements. The new European approach of the VOC directive of 1999 nowcombines after-treatment with the pragmatic approach of North America, mostlythe United States.Bothpaint development directions resulted inrather different paint formulations,creating problems for the South East Asia (SEA) region, which still has to decidewhichwaytogo. Signalsandrecent decisionsofToyota, Honda, Nissan, andMitsubishi favor the waterborne products.Safetystandardsforthehandlingof paintsinthepaint kitchenaswell asapplicationbooths are quite uniformaroundthe world. The personal safetyequipment in spray booths now mostly consists of complete overall, mask, andrespiratory systems protecting the worker fromany contamination. A greater use ofrobots keeps workers out of the paint booth. They become engineers who programand run the robots and look into other booth parameters.Harmful chemicals and additives have been tested comprehensively during thelast 30 years. Many products have been abandoned either by the car manufacturersthemselves or by legislation. Among these are lead, inelectrocoatings and pigments,1.3Automotive and Automotive Paint Market 9chromium, in primers and electrocoatings, cadmium, in pigments, many solventsqualiedasHAPS(HazardousAirPollutingSubstances), andmonomerslikeacrylonitrile, acrylamide, andsoon, whichbelongtothe cmr (carcinogenic,mutagenic, reproduction toxic) products. Special awareness has been created withrespect to the biozides in Europe [12]. Other VOCs may contribute to the generationof ozone in the lower atmosphere and so they have been limited by legislation, stepby step, leading up to the best state-of-the-art technology of the paint applicationprocess [13] as well as paint product development. Signicant steps have been madein this respect by the introduction of waterborne base coats, waterborne primer,and the slurry-clear coat. Further reduction in VOC can be achieved by powderprimer surface and powder clear coat [14].Inrecent years, legislationinEurope focuses onthe harmful and environmentallysignicant impact of chemicals. Thiswill alsoleadtofurtherreplacement ofingredients and components in paint formulation [15].1.3Automotive and Automotive Paint MarketIn 2004, car manufacturers, worldwide, produced about 58 million cars and lighttrucks (vans, mini-vans, pickups). Europe, North America, and Japan are tradition-ally the largest producing regions, accounting for about 78% of all cars (Figure 1.6).SEA including Korea, China, and India, is gaining importance as a consumermarket aswellas aproducing region. Thisis achangefrom the past andwillchange in the future owing to two main reasons:1. Todays quality concepts in manufacturing as well aspainting cars allow car manufacturers to produce whereverworkforce is available. This drives most of them to regionswith low labor costs.2. Most car manufacturers produce world class cars, which canbe exported and brought into all market places around theworld.Europe34%Nafta33%Japan11%SEA14%SouthAmerica4%Others4%58 Mio cars and trucksFig. 1.6Contribution of the regions to world light vehiclecar manufacturing ( Automobilprod.Juni/2004) .10 1IntroductionPrintinginks4Refinishing3%AutomotiveOEM4Generalindustry29Architectural6024.8Mio t Fig. 1.7Volume of the worldwide paint market as of 2002.Among the limiting factors are the supply bases of components and hang-onparts, especiallywhenit comestojust-in-timedeliveries. Thisleadstocertainregions where the car manufacturers would prefer to settle in the future like NorthCarolina, South Korea, Eastern Europe, and Shanghai, for example.Since the 1980s, the outsourcing of manufacturing components and integratedmodules like headlamps, fenders, bumpers, doors, and roof elements for direct de-livery to the assembly line represents the global trend in worldwide car manufactur-ing so that the value added is transferred to the automotive supplier industry. Since2000, the supplier industry, which has a 40% share of the worldwide productionvalue in the car industry and which includes more of design work, is increasinglyfocusing on innovation efforts and is consolidating to become a global industry.Theworldwidemarket volumeof carpaintsof about 1.0Miot consistsofelectrodeposition coatings, primer surfacers, base coats, and clear coats, as well asspeciality coatings consumed in the automotive coating lines and in the supplierindustry, onlycountsforabout 4%of thetotal paint market (seeFigure1.7).Thebiggest sharecontributestothearchitectural market, followedbygeneralindustry (OEM market), which, in other statistics, like in North America, includesthe contribution of car paints. From a technological standpoint, car paints as wellas their coating processes are valued as the most advanced technologies both bycoating performance, and the efciency and reliability of the coating process. Thesehigh standards and requirements forced many players out of business, resultinginthefact that todayjust threemainpaint suppliersdominatetheworldwideautomotive OEM paint market. Regional paint manufacturers exist mostly in Japanand SEA.Inrecent years, themethodof conductingbusinessactivitieshasbeguntochange signicantly. With the single sourcing concept in which one paint supplierdelivers all products and takes responsibility for all paint-related problems of thecoating process, the business arrangements between paint manufacturers and theautomotive industry has reached a point where the responsibility of running paintlines as well as cost targets have been taken over by the paint supplier [16]. Theso-called Tier 1 suppliers manage the various degrees and levels of cooperationwith1.3Automotive and Automotive Paint Market 110100200300400500g m

Fig. 1.8Reduction potential of volatile organic compound( VOC)emission of the automotive coating process in gramper square meter bodysurface based on paint and processdevelopment ( best available technology ) .the customer. Tier 2 suppliers manage the total paint shops including engineering,logistics, auxiliaries, quality control, and stafng [17].Targeting the cost per unit and not cost per paint, together with new processes[18], modernapplicationtechniques, andpaint formulationshas brought theefciency and environmental compliance of the coating processes in terms of VOCto a level that could not have been imagined 30 years ago (Figure 1.8). This hashappened with an increased performance level of coatings in terms of corrosionprotection, the top coats long-term durability in respect to chip resistance, andcolor and gloss retention.References1 Green, M.L. (2001)Journal of Coat-ings Technology, 73 (981), 55.2 Rochard, S. (2001)Modern Paintand Coatings, 91 (9), 28.3Anonymous, Automobilproduktion(12/2000) 38.4 K onneke, E. (2002)Journal f urOber achentechnik, 42 (3), 64.5 Cramer, W.R., Gabel, P.W.(78/2001)EuropeanCoatings Jour-nal, 34.6 Hoffmann, A. (2002)Journal f urOber achentechnik, 42 (3), 54.7 Gruschwitz, B. (2004)Metallober ache58 (6), 22.8 Vaughn-Lee, D. (2004)Polymers PaintColour Journal, 194 (4478), 24.9 Voye, C. (2000)Farbe Lack, 106 (10),34.10 Shaw, A. (2001)Modern Paintand Coatings, 91 (2), 13.11 Papasauva, S., Kia, S., Claya, J.,G unther, R., (2002),Journal of Coat-ings Technology, 74 (925), 65.12 Hagerty, B. (2002)Polymers PaintColour Journal, 192 (4451), 13.13 Drexler, H.J., Snell, J. (04/2002)EuropeanCoatings Journal, 24.14 Klemm, S., Svejda, P. (2002)Journalf ur Ober achentechnik, 42 (9), 18.15 Scott, A. (2007)Chemical Work, 169(11), 17.16 Esposito, C.C. (2004)Coatings World,9 (3), 21.17 (a) Cramer, W.R. (2005)Fahrz. +Kaross., 58 (5), 34. (b) Bloser, F.(2004)Coatings Yearbook, Vincentz,Hannover.18 Wegener, E. (2004)Coatings World, 9(10), 44.894Electrodeposition CoatingsHans-Joachim Streitberger4.1History and IntroductionTheautomotive industry in the 1960s initiatedthe commercialization andintro-ductionofthiscoatingtechnologydrivenbymanyfactors. Underthemsafety,environmental, and processing aspects were the most important ones. The water-borne or solvent-borne dip tanks that were used till then were either dangerous interms of re hazards owing to high solvent emission even in the case of waterborneproducts or had a lot of processing problems e.g. cavities caused by boiling out andaccuracy issues due to lm thickness.OneofthedrivingcompanieswasFordwhichsupportedthedevelopmentofpaintsandthecoatingsprocessheavily[1]. Therst tankswerelledinUSAfollowedbyEuropeinthemid1960s. Until 1977theanodicprocesshadbeenusedwidelyinautomotivebodyprimingthroughouttheworld,whichwasthenalmost completely changed to the cathodic process, further implemented to nearly100% today. Reasons for this complete change were improved corrosion protectionby better resinchemistry, passivationof thesubstrates insteadof dissolutionduring the deposition process, and a more robust application process provided bya predispersed 2-component feed technology.Thisimpressive penetration of theelectrocoating process intothemarket wasboosted further by the introduction of the ultraltration process, which enhancedthe material usage to nearly 100% [2].Todaythelmthicknessandmaterialusageperbodyhasbeenoptimizedto2022 montheoutsideandabout3 kgsolidcontentper100 m2surfacearea,respectively. The solvent level in the electrocoat tanks is below 0.5%, so that thenal rinsingwithd.i. (deionized) water inthemultistagecleaningstepisnotnecessary any more. The reliability of the process has led to the fact that in mostpaint shops of the automotive industry only one electrocoat tank feeds all top-coatlines, coating sometimes more than 1500 units a day.Automotive Paints and Coatings. Edited by H.-J. Streitberger and K.-F. D osselCopyright 2008 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimISBN: 978-3-527-30971-990 4Electrodeposition CoatingsTable 4.1 History of dominant electrodeposition technology for the automotive industryTime frame Technology Chemistry Film thicknessa(m)19641972 Anodic Maleinized natural oils 2519721976 Anodic Maleinized oligobutadienes 2519761984 Cathodic Epoxy-polyurethanes 1819841992 Cathodic Epoxy-polyurethanes 351992today Cathodic Epoxy-polyurethanes 20a Cured lm.4.2Physico-chemical Basics of the Deposition ProcessElectrocoat paints are aqueous dispersions consisting of typical paint ingredientslike lmforming agents (resins), pigments, extenders, additives, and some solvents.The dispersionhas to be stabilized by electrostatic forces. Negatively charged paints,normally called anodic electrocoatings or anodic electrodeposition (AED) coatingsare deposited at the anode, positively charged paints, called cathodic electrocoatingsor cathodic electrodeposition (CED) coatings at the cathode. To enable the paint tobe deposited, the object must be immersed in a tank lled with the electrocoat andconnected to a rectier as the corresponding electrode. The counterelectrode mustbe immersed at the same time and a direct charge must be provided by applyingsufcient voltage of more than 300 V on the technical scale.Under these suitable conditions the water is split at the electrodes into hydrogenand oxygen according to Equation (1):H2O = H2 + 1/2 O2. (1)The particular reactions at the anode and cathode are as follows:cathode reaction: 2H2O + 2e= H2 + 2OH, (2)anode reaction: H2O 2e= 1/2 O2 + 2 H+. (3)From Equations (2) and (3) it becomes evident that double the volume of gas isbeing generated at the cathode in comparison to the anode. But the most importantfactor in the electrocoating process is the change of pH in the diffusion-controlledlayer at theelectrode. Thethickness of this layer canvary between080 mdependingonthespeedofapplicationoftheelectrocoatmaterialatthesurfaceof the electrode relative to the specimen to be coated. This has been explored byBeck [3] and has been established as the basic reaction for the electrocoat processat the anode (see Figure 4.1) and the cathode.ThepHorC+H- andCOH -concentrationat theelectrodescanbecalculatedbased on Faraday- and Fick-law respectively. According to the Sand or Cottrell [4]4.2Physico-chemical Basics of the Deposition Process 91xCCathodesurfaceDiffusion-controlledlayerdCs(OH)Co(OH)Electrocoat bathFig. 4.1ProleofOH-concentrationatelectrodesduringcathodicelectrodeposition.Equation(4) forOHandpotentiostaticapplicationconditionswhichusesthediffusion constants of H+or OHand the electrical current density:COH= 2j/F (t/ D) 1/2, (4)wherej isthecurrentdensityinAcm 2, DthediffusionconstantofOH-ionin cm2s 1and F the Faraday constant. Without considering the inuence of theelectrocoat migrating and diffusing into the diffusion-controlled layer, this resultsin pH of 12 at the cathodes and 2 at the anodes. In the presence of the electrocoatthepH-proleinthediffusionlayer differsfromtheideal conditionsof purewater decomposition. The reason for this is the fact that the electrocoat materialcoagulates according to the pH-depending equilibrium of the carboxylate-ions inthecaseofananodicdepositableelectrocoatinthediffusionlayeraccordingtoEquation (5) and for a cathodic one according to Equation (6):at the anode: RCOO+ H+(dispersible)(insoluable) RCOOH, (5)at the cathode: R3N+H + OH(dispersible)(insoluable) R3N + H2O. (6)92 4Electrodeposition CoatingsThatthediffusionandmigrationofthedispersionparticleintothediffusionlayerplaysanimportantroleinthedepositionprocesshasbeendemonstratedinexperimentsbyBeck[5]; heusedrotatingdiscelectrodes, at acertainspeedof thediscsthereisnobuildupof thepH-proleandnodepositionoccurs.Inthoseexperimentsit wasalsofoundthat buildingupthepH-proletakessometimesothat depositionstartsafteracertaininductiontime , whentheOHorH+-ionconcentrationhasreachedthelevel tostartcoagulationoftheelectrocoating. This critical ion-concentration is dependent on the applied voltageor the current density at the electrode and the charge of the electrocoating material.Under specic conditions the critical H+or OHion concentration is related tothe current density which is called the minimum current density jm. This value isabout 0.15 mA cm 2. It could be shown that will be reduced by increasing j2. Theproduct of j12is a characteristic value for each coating material [6]. The necessarytimeforstartingthedepositionprocessislessthanasecondunderindustrialapplication conditions [7].The following lm growth after the start of the deposition process takes about24 minunder industrial applicationconditions. It denes the nal thickness of thelmand the throwing power. The throwing power for the coating of inner segmentsis a result of the dynamics and resistivity build up of the lmduring deposition.Thisdynamics of lmgrowth can be described by potentiostatic experiments [8, 9] whichreect the normal industrial electrodeposition conditions.Applying voltage to a standardized electrodeposition tank, with dened electrodeareas and electrode distances, increases the current A or current density A cm 2toa certain level after which the current decreases. The increase is connected to thebuild up to the critical level of ion-concentration, the decrease to the resistivity ofthe lm. The current will not go down to zero (see Figure 4.2.). During the appliedTimeCurrentFilm thicknessFig. 4.2CurrentversustimecurvesinpotentiostaticexperimentsofCED.4.2Physico-chemical Basics of the Deposition Process 9317 C 21 C 24 CFig. 4.3Morphologyofcathodical depositedcoatingsatdifferentbathtemperatures.voltage the dispersion particles of the electrocoat paint migrate as charge carriersto the electrical eld of the diffusion-controlled layer as a result of the interactionof the forces of electrical attraction and retarding friction at a constant rate of about10 410 5m s 1[10]. This generates up to 20 m lm thickness in one minute.It has also been shown that the build up of the thickness of the lm is correlatedto the viscous behavior during the deposition process [8] and to the Tgof the lm[11]. The viscosity again is dependent on the type of resin and the temperature ofthe bath.Inside the deposited lm the increased electrical eld up to approximately 105Vcm 1generates electro-osmotic pressure to remove water from the electrode andmakesthedepositedlmmoredense.After24minutesthelmstickstothesubstrateandhasonly510%waterandcannotbewashedoff. Thelmhasacharacteristic morphology due to the fact that hydrogen and oxygen also develop atthe electrodes (see Figure 4.3). The gases form bubble-type structures in the highviscous deposited lm depending on the bath temperature which needs to be ownout during baking and cross-linking [8].The lm growth d can approximately be described according to Equation (7)[8]: d = 1/E c (jt jm) t, (7)where d is the lm thickness after curing of a given system, t is the time, c is a paintspecic constant and jt the current density in Acm 2at the time t, jm the minimumcurrent density for depositing the electrocoat dispersion and E the electrochemicalequivalent in C cm 3. If the current density jt falls below jm due to the increasingresistanceofthedepositedlm(seeabove),nofurtherdeposition processtakesplace (Equation 8). d/ t = 0 at jt< jm(8)94 4Electrodeposition CoatingsThe current density at the time t also can be expressed according to the Ohmslaw:jt = (kF)t(9)wherekisthespecicconductivityofthesystemandFtheeldstrengthinVcm 1. CombiningEquations(7)and(9)weobtainthegeneralformulaforlmgrowth, Equation (10):d/t = 1/E c ((kF)t jm) (10)Two distinct factors contribute to k:k = kwet + kbath(11)kwet is the conductivity of the freshly deposited wet lm and kbath is the conductivityof thetank. Duetothefact that kwetdecreasesduringtheapplicationprocessEquation (10) gives only the rst approximation for lm growth. The dynamics ofkwet can be measured by experiments.Anotherimportant factorforcontrollingtheelectrodepositionprocessisthetemperature, T4.6Design of Cathodic Electrocoating lines 109Fig. 4.9Carbodyenteringtheelectrocoattankonaskid(BASFCoatings).used will differ to a large extent. The most common systemis an overhead conveyorsystem, which will be changed to ground based conveyors for the following sprayapplication station. The trends is to use special skid conveyors which x the bodybetter to the conveyor system and do not have to be changed for the subsequentsprayapplicationstations.Newdevelopments arealreadybeingevaluatedonanindustrial scalewhichcanprovideabetterimmersingprocessintheformofrotational moves during the dipping step similar to the technique used for batchtanks[31]. Thisallowsafasterdippingprocessforasmallertankdesignandprotects horizontal surfaces against settling because during most of the depositionprocess the body moves on top through the tank. The paint should not have anyfoamon topoftheliquidsurface especially intheentry zone.Otherwiseseveremarkings appear on the hoods entering rst into the tank.The tanks are built as reinforced steel construction and are isolated at least insidewith an epoxy coating. The coating is carefully applied in many layers to avoid anyleakage and provides a perfect isolation. Bare steel spots are coated (see below) andcreated by the coagulants and dirt. At the end of the tank is an overow from wherethe different circuits start the heat exchange, the feed to the ultraltration units,the feeding system, and sometimes a separate circuit for the heat exchanger. Thegeneration of heat is caused by the many pumps and the deposition process itself.Thebathtemperatureisdesignedtobeashighaspossiblethatis35Csothatcooling is signicantly provided by the rinsing zones and the temperature in themanufacturing hall.For cleaning up and repair work often a dumping tank is under the body tank totake the entire volume of the electrocoat.All the paint circuits are designed to maintain a constant ow of more than 0.3 ms 1but less than 3.0 m s 1of thecoatingmaterial in thestainless steel orPVC(polyvinylchloride) pipes as well as in the tank. As a basic number these circuits110 4Electrodeposition Coatingsmove the total tank volume ve times per hour. There are two reasons for the owlimits: rst to avoid settling of the material, second to provide enough movementon the surface of the body to establish sufcient heat transfer from the depositionprocess to the bath material. Too high ow can affect the deposition process, forexample, by lowering the lm build.The paint circuits are entering the tank on the ground in a direction against themovement of the bodies and the ow is enforced normally by Venturi nozzles. Atthe entry zone the ow will be directed back at the top of the tank. This guaranteesno settling as well as the necessary movement all over the tank. The body movesinthesamedirectionasthepaint at theupperpart of thetankbut at higherspeed.The commontype of pumps usedfor all paint circuits has double sealedpackings. The sealing uid is an ultraltrate of the respective paint and pumpedunder pressure between the two packings. These types have the advantage of notgenerating coagulants and foam.Impurities from various sources can contaminate the electrocoat. Those are entrainment of dirt by the body dirt from the periphery of the CED system via air, abrasion and dirt from the conveyor system, dried-on paint from the hanger, coagulation and deposits from the electrocoat paint, contaminated d.i. water, coagulants generated by electrical breakthrough and highpeak voltage.To further avoid any settling on horizontal surfaces by dirt particles or coagulantsall paint circuitsarenormallyltered. Standardltertypesarebaglterswithparticleretentionof greaterthan25or50 m. Thepreferredltermaterial ispolypropylene ina needle-felt nish. Thelter bags areplaced in a special steelbasket and these are placed in steel lter vessels holding two to eight such baskets.Theelectrocoat owsfromtoptobottomunderpressurewhichismaintainedas low as possible for best ltering effect. Every week the lters are ushed andcleaned.Anotherpaintcircuitmayfeedtheheatexchanger. Excessheatbasedonthedeposition process and the corresponding electrical resistance of the tank and lmwill be detracted and the paint cooled down to the operational temperature. Thistemperature can be between 28 and 35C for the actual cathodic electrocoating duetotheirhighthermalstability. Temperaturevariationshouldnotexceed0.5C,otherwise the lm build will vary too much. Higher temperatures normally meanincreased lm build.It may be necessary to increase the ow in the entry area to avoid markings onthe hood of the body. The so-called entry marks depend on the wetting propertiesof the electrocoat formulation and on the heat generation and heat transfer in thisof the tank. The reason for the high heat generation in this area is reason that most4.6Design of Cathodic Electrocoating lines 111Rectifier1Rectifier2Conveyor(+) ( ) (+) ( )GroundAnodes in anolyte boxesFig. 4.10Principlesofelectriccircuitsforcontinuousconveyorcathodicelectrocoattankswithtworectiers.current is running in the entry area generating the highest current density (ampereper square meter) during the electrodeposition process.Powersupplyiscarriedoutbydirectcurrentwhichisnormallygeneratedbythyristor rectiers fromanindirect current. The remaining ripple should not exceed5% otherwise the smoothness of the deposited electrocoat will deteriorate.For stationary tanks one rectier is sufcient which can be programmed in termsof a voltage-versus-time-program. This is necessary to avoid high current densitiesat the beginning of the deposition process. Too high voltages create rupture effectsof the deposited lm by heat and gas generation supported by low ow and lowheat transfer of the electrocoat bath.In the case of the continuous conveyer mode at least two rectiers are mandatory.The rst supplies the entry zone, the second the main and exit zone. Often a thirdrectier is in place to supply specic voltage to the exit zone alone (see Figure 4.9).The voltages are between 300 and 450 V depending on the electrode distances,surfaceareaandrequestedthrowingpower.Thecoatingtimeismorethantwominutes, for bigger bodies it can reach four minutes. Based on the differences inthe electrochemical equivalence per type of paint and the coating time the practicalelectrical energyfortheelectrodepositionprocessofanaveragecarof70 m2isbetween 5 and 8 kW h.4.6.5Replenishment and Anode CellsTokeeptheprocessparameterconstanttheelectrocoatbathmustbekeptinaconstant composition. In other words, the deposited material and the removed parts(i.e. solidcontent)mustbereplacedappropriately.Itmustberememberedthatnot only the solid paint but also the neutralizing agent will be discharged duringcurrent ows. There are two principle ways of replenishing electrocoat tanks. They112 4Electrodeposition Coatingsareconnectedwiththeequilibriumofthedepositedandremovedmaterial andtherespectiveneutralizationagent.Thelattercannotberemovedfromthetankwithout special equipment.In the anodic deposition process this excess neutralizing agent generated by theapplication of the electrocoat between the feeding steps is used to help dispersingthe partially, and in any case, underneutralized feeding material (see Figure 4.10a).Thiswasdoneinaseparatetankinwhichthefeedmaterial wasmixedandpredispersedwiththetankmaterialandthenafteracertaintimepumpedwithspecial pumps into the body tank. This step is not easy to control for appropriategeneration and stability of the dispersion. Furthermore it was not a continuous stepresulting in quality uctuations of the respective electrocoat tank. The advantageis that only one component material with a rather high solid content of more than60% could be used with the disadvantage of a high solvent content of up to 50%based on solids.For improved processability andlow solvent materialsof less than10% basedon solids the second way of using fully neutralized feed material is the better one(seeFigure4.10b)andhasgainedthemostfrequentapplication. Thespeciedand approveddispersions, mostly as two components inthe formof a lowsolvent-containingresindispersionandapastedispersion, aresimplypumpedinto the tank. One of the paint circulation lines is normally used for replenishingor feeding these components. The ratio of these components vary for the differentkinds of paints and can be between three and ve parts of resin dispersion to onepart of pastedispersion. Theratiomay beused for trouble shooting thevariousdefectsforthesamepaint(seeSection4.7). Inveryrarecasessolventandacidadditionsmayalsobenecessarytobringthebathcomponentsintotheproperoperational values.Usingcurrent consumptionandthe correspondingcorrelationfor materialconsumption or the daily measurement of car bodies and solid content of the bathas controls the necessary amount of electrocoat feed material is often continuouslypumped into the respective feed line [32]. For this feeding technique as mentionedoneneedstoremovetheneutralizingagentfromthetank, otherwiseanexcesswill be generated andproblems of lm build and too high voltages or other notacceptable changes of the application parameter will arise.For the cathodic electrocoating process, anolyte cells (see Figure 4.12) are used toremove the excess acid. The standard cells consist of a plastic box with the stainlesssteel anode in it and are covered by an anionic exchange membrane, which allowsacid to enter the cell during the deposition process but not to return back to thetank. Anionic exchange membranes have cationic charges, which are xed to themembranepolymermaterial sothatcationscannotpass. Togenerateaowofanionsthecurrent must owbetweentheanodeinsidethecell andtheparts.The acid level in the separate circuit of the cell will continue to increase until theconductivity of the anolyte uid reaches a preset level. Deionized water is fed intothe circuit and an overow is sent to waste pretreatment.4.6Design of Cathodic Electrocoating lines 113+ Polymer-N+HR2Polymer-NR2+ CH3COOHPolymer-NR2+ CH3COOHCH3COO(a)(b)+ Polymer-N+HR2 CH3COOFeedmaterialRemovedby objectFeedmaterialRemovedby objectDepositionDispersionDepositionDispersionRemovedby anolytecircuitFig. 4.11Acid-base-balanceofthetwotypesofreplenishingprocessesofCED. (a)underneutralized, (b)fullyneutralized.The anode material is high grade stainless steel with alloys resistant to chlorineanionslike1-4404, 1-4429, or1-4439accordingtotheDINnomenclature. Thelifetime is dependent on the current passing through the anode area.Exceeding the concentration of chlorine-ions of 50 mg l 1in the anolyte causespitting corrosion and reduces the lifetime drastically. Anodes in the entry area oftheelectrocoattankmaybechangedeveryhalfayeareveryotheryear.Iridiumcoveredtitaniumanodepanelsarealsoused. Costversus lifetimewereoften infavor for these costly anode materials.For control and monitoring of the acid removal the conductivity of the anolyteisused. Theconductivitysensor maybepresetbetween 700and1400 Scm 1.When the upper limit is reached a valve will be opened to let deionized water owinto the system. When the lower value is reached it closes the valve. Depending onthe turn over of the tank the limits have to be adjusted.Tokeepthesystemrunningsmoothlytheowoftheanolytecircuitmustbesufcient at the minimum of 4 l min 1and cell. The ow should be monitored byvisual inspections and ow meters. Leakage of the membranes must be avoided,otherwise the inner side of the membrane will be coated and blocked for acid ow.Insome casesmold canbegeneratedespecially whenaceticacidisused astheneutralizing agent. Fungicides have then to be added to the anolyte circuit.The type of cells has changed from boxes in the early days to tube cells which canbe better maintained, more easily replaced and more variably located [33]. Becauseof the low pH value of the anolyte liquid, the materials of a circuit system are made114 4Electrodeposition CoatingsCarrierframeformembraneAnolyte tankDeionized WaterConductivitymeterFlow meterValveAnolyteboxAnolyte outletIonexchangemembraneCross section(a) (b)Anolyte inletFig. 4.12Anolytecells(b)andanolytecircuit(a).Table 4.7 Typical data of an anolyte uid compared to cathodic electrocoatProperty Units Anolyte circuit Cathodic electrocoatpH 2.22.8 57Conductivity (20 C) S cm 17001400 12001800Solid content % 4 bar) normally lead to coagulants on the membrane surfaceand to the reduced life time of the membranes.The rate at which the permeate is generated is called the ux. There are severalfactors inuencing the ux and the lifetime of the membrane surface, including the1. ow rate of the electrocoat at the membrane surface,2. area of membrane surface,3. fouling of the membrane surface,4. pressure of the electrocoat,5. stability of the electrocoat.The most important factor is the owrate of the electrocoat material. Incombination with the membrane conguration (pipe, at membrane etc.) it denesthe diffusion layer at the membrane surface. At high ow rates the diffusion layerwill be thinner compared to low ow rates and the danger of a material build upon the membrane surface will be reduced.Membrane fouling can occur when between the diffusion layer and the mem-brane surface either bacteria or other material like dirt, unstable resins andpolymers, or other retained components are xed and neither permeate throughthe membrane nor diffuse back into the bulk stream of the electrocoat. Build up ofa fouling layer can be a lengthy process and soon becomes irreversible. It then canonly be removed by mechanical or chemical cleaning processes.116 4Electrodeposition CoatingsExperienceshowsthat thehighpressureof theelectrocoat isdetrimental tothelifetimeofthemembranes. Thebasicformulationincombinationwiththechemical and physical stability of the distinct electrocoat materials have also someinuence on the ux and lifetime of the membranes.The semipermeable membranes mostly used for this process must be resistanttothe constituents of the electrocoat that is solvents, acids, andelectrolytes.The preparationof the membrane material is oftencarried out by ushingthemembraneswithaspecial solution. Thissolutioncleansthesurfaceofthemembranes andushes out all depositedmaterials but alsomay x cationiccharges at the membrane surface. These charges help avoid the dispersion fromconcentrating and coagulating on the membrane surface.There are two main congurations of ultraltration membranes, which currentlynd application in the electrocoating industry. These are spiral wound and plateand frame modules. These types of modules have outperformed the old tubular andhollow ber modules due to the fact that high membrane areas can be constructedonthesmallest spacecontributingtothefact that highuxratesaremostlydetermined by the membrane area.The spiral wound conguration is structured as a at sheet of membrane foldedon bothsides ofasheetof porous material.Themembraneissealedalongtwoedges to form an envelope with the porous media protruding from the opening.Theporous media isthenattachedtoaperforated tubeandtheentireenvelopeassemblywithfeedspacermaterialiswrappedaroundtheperforatedtube.Theassembly is covered with a berglass outer layer (see Figure 4.14).The electrocoat is pumped to one end of the spiral wound assembly and owsinto the open space created by the feed spacer, ows through the entire membraneand exits at the other end. Ultraltrate is collected in the porous media inside theenvelope and ows in a spiral pattern toward the perforated tube and then into thestorage tank. As many tubes as necessary for the required ux are connected to anal ultraltration unit.Antitelescoping devicePerforated collection tubeFeed solutionFeed solutionFeed flowacross feedchannel spacerPermeate flowCovering and controlled bypass spacerConcentrateConcentrateMembraneCarrierMaterialMembraneFeed channelspacerPermeateFig. 4.14Congurationofspiral woundmembraneforultraltrationunitsofCED.4.6Design of Cathodic Electrocoating lines 117From ultrafiltratestorage tankRinse tank IIRinse tank IFinal spray rinseFirst spray rinseTo EC-tankFig. 4.15Rinsingzoneswithtwodippingtanks.This type of membrane conguration provides a rather high membrane surfacearea at low space requirements.This also accounts for the second type of the plate and frame conguration. Paintows along the membranes xed in frames and stacked to packages of differentsizes. Standardunitshavemeasuresof1 1.8 1.0 mforsizeandgenerate700 l h 1at input paint pressure of about three bars.Forsometimereverseosmosiswasusedasanadditionalpuricationsteptogenerate from the ultraltrate rather pure d.i. water to further increase the materialefciency. Due to the fact that energy cost has become too high and the modernpaint formulations have much lower solvents and less low-molecular fractions ofthe resins, those units have become obsolete.AsseeninFigure4.8andalreadymentioned, thepermeategeneratedbytheultraltration units is feeding the closed-loop rinsing zones which are necessaryto purge the deposited electrocoat surface from the adhering electrocoat material.Noncleaned surfaces will not be smooth after the baking process. After exiting theelectrocoat tank the body must be kept wet by a small rinsing station 50 secondslater followed by a rst rinsing zone and a second one. Final rinse can be d.i. wateror pure permeate.Today most of the rinsing zones consist of two dipping tanks (see Figure 4.15).The former rinsing stations with many crowns were cheaper by way of investmentbut less efcient in rinsing the inner parts and cavities of the car body. Furthermorethe large surface of the recirculated spray dust was detrimental to many electrocoatproducts due to increased oxygen attack of the resin backbone. The solid contentsof the two tanks vary between 12% for the rst tank after exit from the CED tankup to 0.51% in the second tank.The nal d.i. water rinse can improve the smoothness of the lm, but in moderncathodic electrocoatings the nal ultraltrate rinse is sufcient, so that the wastegenerated by a nal d.i. water rinse can be eliminated. Under these circumstancestheCEDprocess is almost freeof emissionconsideringthat thelowsolventemission of the tank will be conducted to the baking oven and incinerated there.118 4Electrodeposition Coatings4.6.7Baking OvenAlmostdirectlyafterthenal rinsingstepintherinsingzonethebodyentersthe baking oven. Some ovens use multistages in continuous lines. They consist ofan IR (Infra Red)-heating zone and two or three stages of convection zones withcirculating air. Some only have circulating air stages. Even the convection ovens ingeneral are not very energy efcient compared to IR-ovens, but are mandatory forthe baking process because of the complex shape of a car body.The state-of-the-artovens are called A-ovens characterizingthe shape of theoven in which the body is moved up to a certain height in the entry area, conductedthroughtheovenandmoveddownbacktothestartinglevel at theexit oftheoven.Theadvantageofthisshapeissignicantlyreducedlossofenergyduetothefact that warmairmovestothetopof theoven, inotherwordsit cannotleavetheoven easily.TheIR-zonealsohelpstosaveenergy becauseitheatsupthe outside of the body very rapidly, so that the circulation zones can concentratetheir air ow specically on the critical parts of the body. Those are the inner partsand the parts with high masses of steel like rocker panels or the B-columns. Thisis provided by air fans in conjunction with ow apertures and corresponding airspeeds of 25 m s 1or higher for special tasks. Nevertheless measurements fromthetemperature/timecurvesshowdifferencesdependingonthelocationofthebodies (see Figure 4.16).Toguaranteethespeciedlmperformanceitismandatorytocontrol thesedata on a regular basis. The minimum metal temperature has to be reached at allpoints for example 10 minutes over 170C. Sensitivity to overbake has also to beconsidered while this is not such a critical factor compared to underbake. Owing tothe already mentioned fact that cathodic electrocoats based on their chemistry splitchemical components the air owalso has to manage this material load. Dependingon the zone the share of recirculating air changes in the different stages.The last stage can have higher recirculating air compared to the rst and middleones in case of a three stage oven. Considering the weight loss of between 8 and0:00:00020406080Temperature100120140160180MaxMidMinC0:10:00 0:20:00 0:30:00 0:40:00Time0:50:00 1:00:00 1:10:00 1:20:00 1Fig. 4.16Temperature/timecurvesondifferentlocationsofabodyinaconvectionovenduringelectrocoatcuring.4.7Defects During Application and their Prevention 11918%formostelectrocoatmaterialsbasedonthetypeofcoatingsandairdrieddeposited lms this results in the concentration of organic emissions in the ovenair of several grams per cubic meter. This is well above the value limits speciedin the regulations of most countries in the world. Therefore the waste air, that isreplaced by preheated fresh air, normally goes into an incineration unit to fulllthe VOC-emission regulations. Other methods like adsorption on activated carbonbeds are used rarely. Because the thermal energy generated in the incinerators canalso be used for heating air, thermal incineration systems are often an integral partof the oven system.Gas- oroil-red-boilersarenormallyusedforheat generation, whichisthentransferred by a heat exchanger to the recirculating oven air. If natural gas is usedthe heat exchanger can be dispensed and the hot fuel gases can go directly into theoven. In some cases this can lead to lm performance deciencies like adhesionfailures to the primer surfacer [27].4.7Defects During Application and their PreventionAs is usual in the coating technology processes, paints have to blend together toprovide a stress- and defect-free coating result. If defects occur it is not always easyto identify the source of the problem immediately as related to the process or to thepaint. This especially accounts for dirt, craters, throwing power, and lm thicknessof electrocoatings. In case of defects or insufcient coating result it is mandatory tocollect all the data of the paint batches and the actual data of the process parameterofthepretreatmentstep,theelectrocoatapplication, andthebakingconditions.Reviewingallthedatamayhelptheoperatortomakeabetterapproachforthetrouble shooting.4.7.1DirtDirt is one of the most common recurring problems of coating processes, howeverthis is not the case for electrocoats. As mentioned already the 100% ltering of allcircuits and a careful handling of the conveyor systems as well as the cleanliness ofthe body contributes to this fact.If dirt appears it may be caused by insufcient cleaning cycles of the conveyor,dirt or other particles in the car body, broken lters, or paint stability.Conveyors for the electrocoat process are normally so constructed that dirt fromabrasionorothersourcescannotfalldirectlyintothetank. Butincasesofbadmaintenance, excess dirt can contaminate the liquid electrocoat material as well asthe freshly cured lm in the oven area. The highest danger is generated here by theaccumulated cured electrocoat lms reaching so high a lm build that they easilybreak and fall onto the body from the overhead conveyors.120 4Electrodeposition CoatingsTypical particlesfromthebodyshopareweldingpearlswhentheyarenotcompletely removed fromthebody bythecleaningandpretreatmentprocesses.They easily can be identied by microscopic evaluation like most of the other dirtparticles that is mainly paint splits or rust.Broken lters can be identied by monitoring the pressure differences betweenthe input and output of the lter cartridges. In these cases the dirt will decrease,but the cartridge has to be switched off and the lter bags completely replaced. Incases of heavy dirt load the lter bags should be replaced to coarser mesh-size thatis >100 m (see Section 4.6.3).4.7.2CratersCratersinamorphouslmsarecausedbysurfacetensiondifferencesof inho-mogenic particleswithvery lowsurface tensions(