Failure Analysis of Paints and Coatings

Revised Edition

Dwight G. WeldonWeldon Laboratories, Inc, Imperial, PA, USA

A John Wiley & Sons, Ltd., Publication

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Failure Analysis of Paints and Coatings

Revised Edition

Failure Analysis of Paints and Coatings

Revised Edition

Dwight G. WeldonWeldon Laboratories, Inc, Imperial, PA, USA

A John Wiley & Sons, Ltd., Publication

This edition fi rst published 2009 2009 John Wiley and Sons, Ltd

Registered offi ceJohn Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom

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Library of Congress Cataloging-in-Publication Data

Weldon, Dwight G. Failure analysis of paints and coatings / Dwight G. Weldon. Rev. ed. p. cm. Includes bibliographical references and index. ISBN 978-0-470-69753-5 (pbk.) 1. PaintTesting. 2. CoatingsTesting. I. Title. TP936.5.W45 2009 667.90287 dc22 2009005620

A catalogue record for this book is available from the British Library.

ISBN: 978-0-470-69753-5 (Cloth)

Set in 10 on 12 pt Times by SNP Best-set Typesetter Ltd., Hong KongPrinted and bound in Great Britain by TJ International, Padstow, Cornwall

www.wiley.comwww.wiley.com

To my son Andy, who can still make me smile.

Contents

Preface to the Revised Edition xiii

Preface to the First Edition xv

Acknowledgements xvii

1 General Principles of Coating Formulation 11.1 Introduction 11.2 Binders 21.3 Pigments 41.4 Solvents 51.5 Additives 51.6 Formulation Concepts: Pigment-to-Binder Ratio 61.7 Formulation Concepts: Pigment-Volume Concentration 61.8 Formulation Concepts: Density, Weight Solids and

Volume Solids 7References 8

2 Why Coatings Work and Why They Fail 92.1 Why Coatings Work 9

2.1.1 Adhesion 92.1.2 Wetting 102.1.3 Surface Preparation 142.1.4 Cohesive Strength 232.1.5 Permeability 23

2.2 Why Coatings Fail 242.2.1 Mechanical Stress 252.2.2 Internal Stress 292.2.3 Chemical Attack 312.2.4 Weathering Stress 33

viii CONTENTS

2.2.5 Osmotic Blistering 342.2.6 Electroendosmotic Blistering 35References 36

3 Pigments 393.1 Inorganic Pigments 39

3.1.1 Inorganic Colour Pigments White 393.1.2 Inorganic Colour Pigments Yellow 403.1.3 Inorganic Colour Pigments Orange 403.1.4 Inorganic Colour Pigments Red 413.1.5 Inorganic Colour Pigments Blue 413.1.6 Inorganic Colour Pigments Green 41

3.2 Extender Pigments 413.2.l Silica/Silicates 423.2.2 Calcium Carbonate 423.2.3 Barytes 43

3.3 Corrosion-Resistant Pigments 433.4 Organic Pigments 46

3.4.1 Organic Red Pigments 473.4.2 Organic Yellow Pigments 483.4.3 Organic Blue Pigments 493.4.4 Organic Green Pigments 50References 50

4 Additives and Solvents 514.1 Additives 51

4.1.1 Anti-settling Agents 514.1.2 Viscosity Modifi ers 524.1.3 Surfactants and Emulsifying Agents 534.1.4 De-foaming and Anti-foaming Agents 544.1.5 Driers 544.1.6 Plasticizers 544.1.7 Ultraviolet Stabilizers 554.1.8 Anti-skinning Agents 554.1.9 Biocides 564.1.10 Flow-Modifying Agents 56

4.2 Solvents 57References 64

5 Coating Types and Common Failure Modes 655.1 Natural Resins and Oils 65

5.1.1 Natural Resins 665.1.2 Oils 68

CONTENTS ix

5.2 Alkyds and Epoxy Esters 705.2.1 Alkyds 705.2.2 Epoxy Esters 74

5.3 Epoxies 755.3.1 Amine and Amide Curing Agents for Epoxy Resins 765.3.2 Epoxy Failure Modes 80

5.4 Modifi ed Epoxies 845.4.1 Acrylic Epoxies 845.4.2 Coal Tar Epoxies 855.4.3 Epoxy Phenolics 85

5.5 Phenolics 865.5.1 Resole Phenolics 865.5.2 Novolac Phenolics 875.5.3 Phenolic Failure Modes 87

5.6 Amino Resins 885.7 Acrylics 90

5.7.1 Solution Acrylics 915.7.2 Acrylic Latex Coatings 925.7.3 Thermoset Acrylics 95

5.8 Polyesters 965.8.1 Saturated Polyesters 975.8.2 Unsaturated Polyesters 100

5.9 Polyurethanes 1015.9.1 Two-Component Polyisocyanate/Polyol Coatings 1035.9.2 Urealkyds 1065.9.3 Moisture-Cured Polyurethanes 1075.9.4 Polyurethane Lacquers and Dispersions 1085.9.5 Two-Component Water-Borne Polyurethanes 108

5.10 Vinyls 1095.10.1 Solution Vinyls 1095.10.2 Plastisols and Organosols 1105.10.3 Vinyl Fluorides 1105.10.4 Poly(vinyl butyral) 1115.10.5 Vinyl Latexes 111

5.11 Bituminous Coatings 1125.12 Inorganic and Silicone-Modifi ed Coatings 114

5.12.1 Silicone Coatings 1145.12.2 Silicate Coatings 1165.12.3 Polysiloxane Coatings 118

5.13 Polyureas 1205.13.1 Polyaspartic Polyurea Coatings 121

5.14 Powder Coatings 122References 124

x CONTENTS

6 Application-Related Problems 1256.1 Brush and Roller 1256.2 Spray Applications 126

6.2.1 Air (Conventional) Spray 1266.2.2 Airless Spray 1266.2.3 Plural Spray 1276.2.4 Electrostatic Spray 127

6.3 Flow Coating 1276.4 Roll Coating 1286.5 Powder Coating 1286.6 Coating Failures Related to Application Problems 129

References 134

7 Field Methods 135

8 Analytical Methods 1418.1 Light Microscopy 1418.2 Infrared Spectroscopy 152

8.2.1 Theory 1528.2.2 Instrumentation 1668.2.3 Sample Handling 1698.2.4 Applications 177

8.3 Gas Chromatography (GC) 2028.3.1 Theory of GC 2028.3.2 Instrumentation 2088.3.3 Pyrolysis-GC 2168.3.4 Application of GC 217

8.4 Gel Permeation Chromatography (GPC) 2218.4.1 Theory 2228.4.2 Instrumentation 2268.4.3 Applications 227

8.5 Ion Chromatography 2328.5.1 Theory 2328.5.2 Applications 237

8.6 Scanning Electron Microscopy 2388.6.1 Imaging Theory 2398.6.2 Elemental Analysis by X-ray Spectroscopy 2418.6.3 Sample Preparation 2448.6.4 Applications of SEM-EDS 244

8.7 Differential Scanning Calorimetry (DSC) 2478.7.1 Theory 2478.7.2 Calibration and Sample Preparation 2508.7.3 Applications of DSC 252

8.8 Miscellaneous Methods of Analysis 258References 259

CONTENTS xi

9 Physical Methods 2619.1 Adhesion 2619.2 Flexibility and Impact Resistance 2639.3 Solvent Resistance 2659.4 Weathering Resistance 2659.5 Chemical Resistance 2669.6 FreezeThaw 2699.7 Application Variables 269

References 273

10 Examples of Coating Failures 27510.1 Urethane Topcoat Disbonding from Epoxy 27510.2 Blistering of an Epoxy Tank Coating 27910.3 Cracking and Delamination of Epoxy Coating Systems on

Masonry Walls 28210.4 Discolouration of Coil-Coated Aluminium Siding 28510.5 Discolouration and Delamination of Plastisol 28810.6 Delamination of Floor Coating 29310.7 Delamination of Dry-Fall Alkyd 29610.8 Coal Tar Epoxy Failure 30010.9 Splitting of Inorganic Zinc-Rich Primer 30410.10 Defects on Electro-Coated Panels 30910.11 Failure of Coated Light Poles 30910.12 Blistering of Coating on Concrete Floor, Number 1 31410.13 Blistering of Coating on Concrete Floor, Number 2 31810.14 Peeling of Paint from Metal Chairs 32210.15 Failure of Railroad Car Liner 32710.16 Failure of Calcium Sulfonate Modifi ed Alkyd Topcoat from

a Bridge 33110.17 Discolouration of Furniture Lacquer 33310.18 Failure of Tank Car Lining 337

References 345

11 The Repair of Coating Failures 347

Index 351

Preface to the Revised Edition

It has been over 8 years since the fi rst edition of Failure Analysis of Paints and Coatings was published. During this period, many coating types have remained the same, and a few new ones have been introduced, or at least have been more heavily marketed. Advances have been made in surface preparation technology, and more opportunities for training and education have been made available than ever before. However, in spite of all of this, the coatings industry still experiences its fair share of failures.

A coating failure does not just involve the cost of some paint. Repair of an existing structure can be extremely expensive, perhaps even entailing lost produc-tion time if the facility has to be shut down for repairs. If a coating lining a process vessel or a railroad tank car fails, large amounts of product may become unmar-ketable and may have to be disposed of. Reputations can be damaged. The cost of a paint failure is seldom cheap.

The fi rst edition of this book introduced some basic concepts in paint formula-tion and chemistry. This has been updated in the second edition to include some additional types of coatings, such as polyureas, polysiloxanes and powder coat-ings. Some additional discussion has been included concerning surface prepara-tion, the mechanism of blistering and the chemistry of amine blush. Analytical techniques such as gas chromatography mass spectroscopy and differential scan-ning calorimetry have been discussed in more detail. However, as with the fi rst edition, the subjects of coatings chemistry and analytical chemistry are presented at the introductory level. Although essential to conducting a failure analysis, many thorough texts already exist on these subjects.

As pointed out in the preface to the fi rst edition, the failure analysis of paints and coatings is all about problem solving. Problem solving is a diffi cult subject to teach, and probably relies on curiosity and experience more than anything else. Therefore, in addition to the basics of coatings science and analytical chemistry, which form the foundation upon which curiosity and experience can build, this book contains numerous practical examples of solving real - world coating failures. Indeed, the biggest difference between the fi rst and second editions is