1 Introduction 11 2 Light and photo-oxidative degradation 13 2.1 Light 13 2.1.1 Photo-physical processes 15 2.2 Photo-chemical degradation processes 16 3 Stabilization options 21 3.1 UV absorbent pigments 22 3.2 UV absorbers 23 3.2.1 UV absorber classes 24 3.2.2 Mode of action of UV absorbers 27 3.2.2.1 Phenolic UV absorbers 28 3.2.2.2 Non-phenolic UV absorbers 30 3.2.3 Examples of UV absorbers 30 3.3 Free-radical scavengers 36 3.3.1 Antioxidants 36 3.3.2 Sterically hindered amines 38 3.3.2.1 Mode of action of HALS 42 3.4 Quenchers 45 3.5 Peroxide decomposing agents 46 4 Stabilization of coatings 49 4.1 Automotive coatings 51 4.2 Light stabilization of automotive coatings 52 4.2.1 Two-coat systems 53 4.2.2 Specific requirements of UV absorbers in coatings 55 4.2.2.1 Solubility and compatibility of UV absorbers 56 4.2.2.2 Volatility of UV absorbers 59 4.2.2.3 Reactable UV absorbers 61 4.2.2.4 Effect of UV absorbers on coating colour 63 4.2.2.5 Unwelcome side reactions 64 4.2.2.6 UV absorbers and photoinitiators 67 4.2.3 Specific requirements on HALS in coatings 71 4.2.3.1 Solubility and compatibility of HALS 71 4.2.3.2 Volatility of HALS 74 4.2.3.3 Reactable HALS 75 4.2.3.4 Effect of HALS on coating colour 76 4.2.3.5 Unwelcome side reactions 77 4.2.4 Weathering results for two-coat systems 79 4.2.4.1 Weathering tests 79 4.2.4.2 Results for solvent-borne clear coats 86 4.2.4.3 Results for water-borne clear coats 97 4.2.4.4 Results for powder clear coats 100 4.2.4.5 Results for UV-curable clear coats 103 4.2.4.6 Coatings on plastic substrates 106 4.2.4.7 UV protection of epoxy-based fibre reinforced plastics 111 4.2.4.8 Effect of additional basecoat stabilization 114 4.2.4.9 Exposure results for one-coat finishes 117 4.3 Light stabilization of industrial coatings 121 4.3.1 Stabilization of paints for metal substrates 122 4.3.2 Stabilization of clear wood coatings 125 4.4 Stability of light stabilizers 128 4.4.1 Photo-chemical stability of UV absorbers 128 4.4.2 Long-term stability of HALS 137 5 Conclusions 141 6 References 143 Authors 151 Index 153