Light Stabilizers for Coatings

Almost twenty years after the first edition of this book, the editor was asked by colleagues in the coating industry whether it would be possible to publish an up-dated second edition. When the editor asked us whether we would be interested in working on such a second edition, we agreed with great pleasure. Although some time has passed since the first edition, the problems facing the industry are still the same: paint flaking off an object remains a serious concern. The object has lost its protection and is exposed to the elements. It has lost the colour that made it attractive. It has become insignificant and unnoticed.The purpose of this book is to explain the underlying principles of paint degradation, demonstrate, with the help of numerous examples, how paint films can be protected and serve as a practical guide for formulators when selecting light stabilizers for their paint formulation.For a more precise analysis of the mechanism of paint degradation and its prevention, the reader is referred to the extensive bibliography at the end of the book, which covers the subject comprehensively.Hermann Hesse wrote "Blue, yellow, white, red and green - what wonderful colours" [1]. When properly stabilized, colourful finishes ARE wonderful.We would like to take this opportunity to thank our colleagues from the former Ciba Specialty Inc. and BASF Switzerland AG. Without their collaboration and support it would have never been possible to carry out the research, over a period of more than two decades, on which this book is based. We would also to thank Dr. Godwin Berner and Hans-Jürgen Berger who pioneered, built-up and led this successful business for so many years. Special thanks goes to Allan Cunningham for his great support editing our English text.Basle, Switzerland June 2016Andreas Valet and Adalbert Braig

1Introduction 112Light and photo-oxidative degradation 132.1Light 132.1.1Photo-physical processes 152.2Photo-chemical degradation processes 163Stabilization options 213.1UV absorbent pigments 223.2UV absorbers 233.2.1UV absorber classes 243.2.2Mode of action of UV absorbers 273.2.2.1Phenolic UV absorbers 283.2.2.2Non-phenolic UV absorbers 303.2.3Examples of UV absorbers 303.3Free-radical scavengers 363.3.1Antioxidants 363.3.2Sterically hindered amines 383.3.2.1Mode of action of HALS 423.4Quenchers 453.5Peroxide decomposing agents 464Stabilization of coatings 494.1Automotive coatings 514.2Light stabilization of automotive coatings 524.2.1Two-coat systems 534.2.2Specific requirements of UV absorbers in coatings 554.2.2.1Solubility and compatibility of UV absorbers 564.2.2.2Volatility of UV absorbers 594.2.2.3Reactable UV absorbers 614.2.2.4Effect of UV absorbers on coating colour 634.2.2.5Unwelcome side reactions 644.2.2.6UV absorbers and photoinitiators 674.2.3Specific requirements on HALS in coatings 714.2.3.1Solubility and compatibility of HALS 714.2.3.2Volatility of HALS 744.2.3.3Reactable HALS 754.2.3.4Effect of HALS on coating colour 764.2.3.5Unwelcome side reactions 774.2.4Weathering results for two-coat systems 794.2.4.1Weathering tests 794.2.4.2Results for solvent-borne clear coats 864.2.4.3Results for water-borne clear coats 974.2.4.4Results for powder clear coats 1004.2.4.5Results for UV-curable clear coats 1034.2.4.6Coatings on plastic substrates 1064.2.4.7UV protection of epoxy-based fibre reinforced plastics 1114.2.4.8Effect of additional basecoat stabilization 1144.2.4.9Exposure results for one-coat finishes 1174.3Light stabilization of industrial coatings 1214.3.1Stabilization of paints for metal substrates 1224.3.2Stabilization of clear wood coatings 1254.4Stability of light stabilizers 1284.4.1Photo-chemical stability of UV absorbers 1284.4.2Long-term stability of HALS 1375Conclusions 1416References 143Authors 151Index 153