Emmanouil Spyrou

Powder Coatings Chemistry and Technology3rd Revised Edition

European CoatingsSymposium

European CoatingsTech Files

Jörg Sander

Coil Coating

Ulrich Poth • Autom

otive Coatings Formulation

Jörg Sander · Coil Coating

The Mission: To know everything about coil coatings and how they can be used successfully, from the basic principle underlying the coil coating process to substrate preparation, selection of raw materials, coil coating line equipment, perfor-mance testing and research topics through to standardisation. To provide a solid grounding in all the important principles of coil coatings – essential for the successful development of can and coil coatings.

The Audience: Formulators seeking to stay abreast of the latest developments in can and coil coatings as well as immersing themselves in the topic, along with experts looking for detailed information about surface preparation, materials, application, standardisation and test methods. Anyone involved in the coil coating manufacturing process who needs a full understanding of the relationships involved.

The Value: At last, a highly topical technical book in English on the subject of coil coatings. This comprehensive book covers every aspect of the topic in a format that the reader can understand. In addition to detailing the technological basics of can and coil coatings, the book features a detailed chapter on standardisation and test methods.

ISBN 978-3-86630-834-3

European CoatingsSymposium

European CoatingsTech Files

eBook

Jörg Sander: Coil Coating© Copyright 2014 by Vincentz Network, Hanover, GermanyISBN: 978-3-86630-651-6

Jörg Sander

Coil Coating

Jörg SanderCoil CoatingHanover: Vincentz Network, 2014 EuropEan Coatings tECh FilEs

ISBN 3-86630-651-2ISBN 978-3-86630-651-6

© 2014 Vincentz Network GmbH & Co. KG, Hanover Vincentz Network, Plathnerstr. 4c, 30175 Hanover, GermanyThis work is copyrighted, including the individual contributions and figures.Any usage outside the strict limits of copyright law without the consent of the publisher is prohibited and punish-able by law. This especially pertains to reproduction, translation, microfilming and the storage and processing in electronic systems.The information on formulations is based on testing performed to the best of our knowledge.The appearance of commercial names, product designations and trade names in this book should not be taken as an indication that these can be used at will by anybody. They are often registered names which can only be used under certain conditions.

Please ask for our book catalogueVincentz Network, Plathnerstr. 4c, 30175 Hanover, GermanyT +49 511 9910-033, F +49 511 9910-029books@european-coatings.com, www.european-coatings.com

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ISBN 3-86630-651-2ISBN 978-3-86630-651-6

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EuropEan Coatings tECh FilEs

Jörg Sander

Coil Coating

Jörg Sander: Coil Coating© Copyright 2014 by Vincentz Network, Hanover, GermanyISBN: 978-3-86630-651-6

European Coatings Handbook“Comprehensive“ and “based on practice“ sum up the aims of the European Coatings Handbook. The book covers the full spectrum of coatings formulation in a single vol-ume. Topics range from the underlying chemistry to process engineering, from safety to quality control, as well as the regulatory issues involved in the manufacture and application of coatings. The book contains the latest information on all aspects in all parts of coatings composition, application methodology, quality assurance, industrial health, and safety is highly useful.

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European Coatings Tech Files

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Another interesting book hint...

Also as eBook!

ForewordDuring my entire business career, I have seen many industrial applications of paints and coatings to metal, be it on extruded profi les, bicycle frames, escalator steps, car bodies, wheel rims and automotive trim parts, or beverage cans, to name a few. The most appealing application for me, however, has always been the continuous coating of metal coils.

Coil coating provides fascinating ways of producing coated metal goods. Highly sophisti-cated processes and the profi cient and sustainable use of elaborate process chemicals and materials bring about durable, high-quality painted products. These can be processed to create a wide range of articles with an abundance of uses, technical features, shapes, and surface aspects.

This present book is based on the manuscript of a tutorial I held during the European Coat-ings Conference Coil and Can Coating that was organised by Vincentz Network in Berlin in October 2011. It is the fi rst comprehensive English-language description of the coil coating technology available to the public in years. To make the book attractive for the insiders of the coil coating community and instructive for newcomers to this exciting technology alike, a good deal of elaboration was needed beyond the conference script. Thus the book embraces both: A synopsis, maybe also a useful look at the bigger picture for those already conversant with the subject, and an in-depth introduction for those who want to familiarise with it. In particular, students of process and equipment engineering, surface science, pretreatment and paint technologies, but also of architecture and metal design shall fi nd detailed, and, I hope, popular descriptions, explanations, and interesting connections demonstrated.

I am grateful to many colleagues in the business who helped in discussions and by provid-ing detail information about their specialist subjects. A particular pleasure was meeting Dr. Bernd Meuthen, Past President of the ECCA, long-standing President and Honorary President of the German ECCA Group, and lead author of a German standard publication on the topic, during my very early days in the business. I have been very much indebted to Bernd for sharing his profound knowledge and his enthusiasm for coil coating that I have always admired. The compilation on standards, one of his very particular interests, is based on his earlier work. Sadly, Bernd Meuthen died on October 24, 2013. And so I feel it fi tting to dedicate this work to his memory. I hope it helps to inspire and enthuse future coil coating chemists and engineers as Bernd was able to do.

Velbert, Germany, October 2013

Jörg Sander

Jörg Sander: Coil Coating© Copyright 2014 by Vincentz Network, Hanover, GermanyISBN: 978-3-86630-651-6

Contents 7

Jörg Sander: Coil Coating© Copyright 2014 by Vincentz Network, Hanover, GermanyISBN: 978-3-86630-651-6

Contents

1 Coil coating – principle, market and applications ...................................... 13

1.1 Introduction ............................................................................................................................ 131.2 Coil coating process .............................................................................................................. 141.3 Metalworking with precoated coil ..................................................................................... 181.4 Inherent benefits of coil coating ........................................................................................ 191.5 Coil coating market in Europe ............................................................................................ 201.6 Applications of precoated metal......................................................................................... 221.6.1 Overview ................................................................................................................................. 221.6.2 Building applications ............................................................................................................ 221.6.3 Transport applications ......................................................................................................... 241.6.4 Applications in appliance and general industries ......................................................... 251.6.5 Packaging applications ........................................................................................................ 261.7 European Coil Coating Association, ECCA ...................................................................... 261.8 History of coil coating .......................................................................................................... 28

2 Corrosion protection ..................................................................................... 31

2.1 Principles of function ........................................................................................................... 312.1.1 Corrosion phenomena .......................................................................................................... 312.1.2 Strategies for corrosion inhibition ..................................................................................... 332.1.3 Metal oxide formation, passivation and conversion coating ........................................ 342.1.4 Cathodic protection ............................................................................................................... 352.2 Design of organic coating systems .................................................................................... 352.2.1 Diffusion barriers .................................................................................................................. 352.2.2 Pigments ................................................................................................................................. 352.3 Function of individual coating layers ............................................................................... 36

3 Industrial cleaning ........................................................................................ 39

3.1 Introduction ............................................................................................................................ 393.2 Why cleaning? ........................................................................................................................ 393.2.1 Contaminations ...................................................................................................................... 393.2.2 Cleanliness and surface tension ........................................................................................ 403.2.3 Paint adhesion ................................................................................................................................................... 413.3 Aqueous cleaning .................................................................................................................. 413.3.1 Overview ................................................................................................................................. 413.3.2 Alkaline cleaners ................................................................................................................... 423.3.3 Mechanism of alkaline cleaning, bath age and control ............................................... 423.3.4 Surfactants .............................................................................................................................. 443.4 Cleaning physics ................................................................................................................... 463.4.1 Influence factors .................................................................................................................... 463.4.2 Rinsing and maintenance .................................................................................................... 46

Contents8

4 Pretreatment .................................................................................................. 49

4.1 Introduction ............................................................................................................................ 494.2 Substrates ............................................................................................................................... 494.2.1 Overview: Particular substrates for coil coating............................................................. 494.2.2 Steel .......................................................................................................................................... 504.2.2.1 Blast furnace process ........................................................................................................... 504.2.2.2 Steel making and refining ................................................................................................... 514.2.2.3 Galvanised steel .................................................................................................................... 514.2.3 Aluminium .............................................................................................................................. 534.2.3.1 Bauxite refining and Al electrolysis .................................................................................. 534.2.3.2 Properties of aluminium and its alloys ............................................................................. 544.3 Basics of pretreatment technology ................................................................................... 554.4 Pretreatments for coil coating ............................................................................................ 554.4.1 Alkaline passivation ............................................................................................................. 554.4.2 Iron phosphating ................................................................................................................... 564.4.3 Chromating ............................................................................................................................ 564.4.3.1 Yellow chromating (chromium chromating) ................................................................... 564.4.3.2 Green chromating ................................................................................................................. 574.4.4 [Ti,Zr]F6

2- based processes: Chromium-free pretreatment ........................................... 584.4.4.1 Basics ....................................................................................................................................... 584.4.4.2 Chemistry ............................................................................................................................... 584.4.4.3 Conversion layer composition ............................................................................................ 584.4.4.4 Performance ........................................................................................................................... 594.4.4.5 Architectural application ..................................................................................................... 614.4.5 Synopsis: State-of-the-art coil coating pretreatments ................................................... 614.5 Recent pretreatment development .................................................................................... 624.5.1 Pre-commercial processes .................................................................................................. 624.5.2 Primer-pretreatment ............................................................................................................ 634.6 Application.............................................................................................................................. 644.6.1 Immersion and spray processes ........................................................................................ 644.6.2 Alternative application processes ..................................................................................... 644.7 Environmental considerations............................................................................................ 654.7.1 Legislation............................................................................................................................... 654.7.2 Environment: Labelling and emissions ............................................................................ 664.7.3 Waste Treatment ................................................................................................................... 66

5 Coil coating paints ........................................................................................ 69

5.1 Definition ................................................................................................................................ 695.2 Ingredients: Carrier media .................................................................................................. 695.3 Drying and curing mechanisms ......................................................................................... 695.3.1 Physical drying ...................................................................................................................... 695.3.2 Chemical curing, crosslinking ........................................................................................... 705.3.3 Radiation curing systems ................................................................................................... 715.4 Powder paints ........................................................................................................................ 725.5 Binder resins .......................................................................................................................... 725.5.1 Introduction ............................................................................................................................ 725.5.2 Polyvinyl chloride, PVC ....................................................................................................... 735.5.3 Polyvinylidene difluoride, PVdF ........................................................................................ 745.5.4 Epoxy resins ........................................................................................................................... 755.5.5 Polyester resins ..................................................................................................................... 76

Contents 9

5.5.5.1 Raw materials for polyester resins .................................................................................... 765.5.5.2 Crosslinking of polyesters with melamines .................................................................... 785.5.5.3 Crosslinking of polyesters with polyisocyanates ........................................................... 805.5.6 Polyurethanes ........................................................................................................................ 805.5.7 Acrylic resins ......................................................................................................................... 815.5.8 Binder resins: Comparison and uses ................................................................................ 825.6 Coil coating paints statistics ............................................................................................... 835.7 Roles and classes of pigments ............................................................................................ 835.7.1 Introduction ............................................................................................................................ 835.7.2 Anticorrosive pigment ......................................................................................................... 835.7.2.1 Overview ................................................................................................................................. 835.7.2.2 Active pigments – lead and chromate pigments ............................................................ 845.7.2.3 Active pigments – phosphate pigments ........................................................................... 845.7.2.4 Other active anticorrosive pigments ................................................................................. 855.7.3 Barrier and sacrificial pigments ........................................................................................ 855.7.4 Colouring and extender pigments ..................................................................................... 865.8 Auxiliaries............................................................................................................................... 87

6 Coil coating line equipment .......................................................................... 91

6.1 Cleaning and pretreatment installations ......................................................................... 916.1.1 Cleaning .................................................................................................................................. 916.1.2 Pretreatment application ..................................................................................................... 936.1.3 Advances in plasma technology for cleaning and pretreatment ................................ 946.2 Strip travel and planarity control ...................................................................................... 946.3 Coater technology ................................................................................................................. 966.3.1 Roll-coaters ............................................................................................................................. 966.3.1.1 Roll-coater operation ............................................................................................................ 966.3.1.2 Coater rolls ............................................................................................................................. 976.3.1.3 Control of the roll-coating process .................................................................................... 986.3.1.4 Auxiliary equipment ........................................................................................................... 996.3.2 Other paint application techniques ................................................................................... 1006.4 Curing and oven technologies ............................................................................................ 1056.4.1 Thermal curing ...................................................................................................................... 1056.4.1.1 Convection ovens .................................................................................................................. 1056.4.1.2 Infrared and near-infrared curing ..................................................................................... 1066.4.1.3 Induction curing .................................................................................................................... 1086.4.1.4 Comparison of thermal curing techniques ...................................................................... 1096.4.2 Radiation curing .................................................................................................................... 1106.4.3 Cooling and exhaust management .................................................................................... 1116.5 Examples of modern coil coating installations ............................................................... 112

7 Performance testing ...................................................................................... 117

7.1 Introduction ............................................................................................................................ 1177.2 Coating thickness .................................................................................................................. 1177.3 Adhesion testing ................................................................................................................... 1187.3.1 Overview ................................................................................................................................. 1187.3.2 Application tests .................................................................................................................... 1187.3.2.1 Tests involving deformation ............................................................................................... 1187.3.2.2 Other adhesion tests ............................................................................................................. 1207.3.3 Laboratory methods .............................................................................................................. 120

Contents10

7.3.3.1 Atomic force microscopy ..................................................................................................... 1207.3.3.2 Dynamic mechanical analysis ............................................................................................ 1217.4 Corrosion testing ................................................................................................................... 1227.4.1 Outdoor exposure tests ........................................................................................................ 1227.4.2 Accelerated corrosion tests ................................................................................................. 1237.4.2.1 Overview ................................................................................................................................. 1237.4.2.2 Salt spray test ........................................................................................................................ 1247.4.2.3 Constant climate humidity .................................................................................................. 1257.4.2.4 Condensation.......................................................................................................................... 1267.4.2.5 Water soak and boiling tests ............................................................................................... 1267.4.2.6 Filiform corrosion .................................................................................................................. 1267.4.2.7 Cyclic humidity...................................................................................................................... 1277.4.2.8 Prohesion ................................................................................................................................ 1277.4.2.9 VDA test .................................................................................................................................. 1277.4.2.10 UV test and weathering ....................................................................................................... 1287.5 Electrochemical testing ....................................................................................................... 1297.5.1 General remarks .................................................................................................................... 1297.5.2 Electrochemical potential .................................................................................................... 1307.5.2.1 Standard potential ................................................................................................................ 1307.5.2.2 Corrosion potential/current monitoring .......................................................................... 1307.5.3 Electrochemical impedance spectroscopy ....................................................................... 1317.5.4 Electrochemical techniques with high spatial resolution ............................................ 1327.5.4.1 Scanning vibrating electrode .............................................................................................. 1327.5.4.2 Height-regulated scanning Kelvin probe ......................................................................... 134

8 Research topics .............................................................................................. 139

8.1 Introduction ............................................................................................................................ 1398.2 Recycling and renewable materials .................................................................................. 1398.3 Functional coatings ............................................................................................................... 1408.4 Nanotechnology ..................................................................................................................... 1418.5 Academic and institutional research lines ...................................................................... 143

9 Can coating .................................................................................................... 147

9.1 Introduction: Precoated metal for packaging .................................................................. 1479.2 Substrates and market ......................................................................................................... 1479.3 Pretreatment and base coating .......................................................................................... 1479.4 Can coatings ........................................................................................................................... 1489.5 Coil and sheet lines ............................................................................................................... 1499.6 Specified tests ........................................................................................................................ 150

10 Standardisation ............................................................................................. 153

10.1 Introduction ............................................................................................................................ 15310.2 Creation of standards by CEN ............................................................................................ 15410.2.1 CEN .......................................................................................................................................... 15410.2.2 Standardisation procedure .................................................................................................. 15410.2.2.1 Proposal stage ........................................................................................................................ 15410.2.2.2 Working stage ........................................................................................................................ 15410.2.2.3 Enquiry stage ......................................................................................................................... 15410.2.2.4 Approval stage ....................................................................................................................... 155

Contents 11

10.2.2.5 Implementation stage........................................................................................................... 15510.3 ECISS, ISO and ASTM ......................................................................................................... 15510.4 General standards and regulations ................................................................................... 15610.4.1 Relevant standardisation bodies ........................................................................................ 15610.4.2 Coil coated metal: Terminology and definitions ............................................................. 15710.4.3 Coil coated metal: Product standards ............................................................................... 16010.5 Substrate and test standards .............................................................................................. 16010.5.1 Overview ................................................................................................................................. 16010.5.2 Coil coated aluminium ......................................................................................................... 16010.5.3 Coil coated steel ..................................................................................................................... 16110.5.3.1 General provisions ................................................................................................................ 16110.5.3.2 Cold rolled steel substrates ................................................................................................. 16110.5.3.3 Metallic-coated steel substrates (except packaging sheet) ......................................... 16210.5.3.4 Further cold rolled and metallic coated steel substrates – packaging sheet ........... 16210.5.3.5 Hot rolled steel substrates................................................................................................... 16210.5.3.6 Electrical steel ........................................................................................................................ 16310.5.3.7 Stainless steels ...................................................................................................................... 16310.5.4 Coil treatment lines: Standards and regulations ............................................................ 16310.5.5 Test methods .......................................................................................................................... 16410.5.5.1 Overview ................................................................................................................................. 16410.5.5.2 EN standardisation body in charge ................................................................................... 16510.5.5.3 EN testing standards ............................................................................................................ 16510.5.5.4 Test methods: Further standards ....................................................................................... 16610.5.6 Terms and words of art for coatings, coating materials and plastics, and country codes: Standards .................................................................................................... 17110.5.7 Building components: Standards on products and test methods ............................... 17110.5.7.1 CEN bodies in charge ........................................................................................................... 17110.5.7.2 Building components standards ........................................................................................ 17110.5.7.3 Special test standards and features for fire protection ................................................. 17210.5.8 Quality management and environmental management systems: Standards .......... 17310.5.9 Selected European organisations ....................................................................................... 174

Author...... ....................................................................................................................... 177

Index ............................................................................................................................... 178

13Introduction

1 Coil coating – principle, market and applications

1.1 IntroductionCoil coating makes use of a simple, but effective principle, i.e. to clean, pretreat and coat flat coils or sheets of steel or aluminium in a continuous operation, before other stages of industrial manufacture [1–4]. The slogan for this concept is: Finish first – fabricate later!

A conventional process sequence in coil coating consists of:

• Cleaning

• Conversion treatment (including optional post-rinse)

• Drying

• Primer coating

• Top coating

• Foil lamination (optional)

An overview of a large coil coating line is depicted in Figure 1.1.

Jörg Sander: Coil Coating© Copyright 2014 by Vincentz Network, Hanover, GermanyISBN: 978-3-86630-651-6

Figure 1.1: Schematic of a steel coil coating line Source: Voestalpine

Coil coating – principle, market and applications14

The official definition of the coil coating process is codified in the European Standard EN 10169-1: 2003. It states that coil coating is

• “a method in which an organic coating material is applied on rolled metal strip in a contin-uous process. This process includes cleaning if necessary and chemical pre-treatment of the metal surface and either one side or two side, single or multiple application of (liquid) paints or coating powders which are subsequently cured or laminated with plastic films”.

1.2 Coil coating processMetal coils are fed into a coil coating line from an entry station, where the coils are reeled off an uncoiler (Figure 1.2), and the beginning of one coil fixed to the end of the preced-

ing coil by welding or stitching. The uncoiler station is usually duplicated, or equipped with twin reels, in order to allow for faster coil changes. The metal strip then enters the active section of the line through a loop accumula-tor. The large accumulator shown in Figure 1.3a has been emptied during the change of a coil, while feeding the strip length that was stored in it to the continuously running process. It waits to be filled up again to be ready for the next coil change.

The active section comprises a degreasing stage, with a brushing section and rinses; one or more pretreatment stages in either immersion or spray technique, followed by another rinse cas-cade, and a water dryer. In case of so-called no-rinse pretreat-ment processes, the strip needs to be dried beforehand, and the treatment solution is applied by a roll-coater (chem-coater), before reacting off and evaporating the water in the dryer. The pretreated strip then enters the primer stage with its roll-coater unit and cur-ing oven, followed by a water quench cooler. Afterwards, the finish coater section is passed which again comprises the roll-coater units and curing oven with subsequent cooling. The finish (topcoat) section often has two coater installations that allow

Figure 1.2: Coil reel Source: ThyssenKrupp Steel Europe

Figure 1.3: a) Entry accumulator; b) Loop pit Source: a) ThyssenKrupp Steel Europe; b) Alcoa Inc.