| Résumé : |
The durability of high gloss industrial and automotive coatings, their service life, is usually predicted from gloss retention data. Because of time pressures, business decisions are often based on data of an early phase of exposure. Evidence and conclusions are presented that show that initial gloss retention results of coatings pigmented with TiO2 involve phenomena of film formation rather than weathering. We show that film formation of automotive finishes continues after cars leave the baking ovens, albeit on a time scale of months rather than the minutes for which the paint film is baked. Later in the service life of a paint film, weathering sets in. Oxidation of the polymeric binder takes place involving the combined actions of UV light, water, and oxygen. As a result, the film surface erodes and its gloss degrades far beyond effects of film formation. According to our hypothesis, high gloss rather than good durability of the TiO2 pigment in the coating makes for good initial gloss retention. Eventually, of course, the durability of the TiO2 pigment, that is, the inhibition of its surface catalytic activity, becomes important for film performance. |
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Durability and gloss in JOURNAL OF COATINGS TECHNOLOGY (JCT), Vol. 67, N° 851 (12/1995)
