Accelerated testing of waterborne coatings

We report here effects of weathering on waterborne coatings. Three styrene-acrylate waterborne paint systems containing various types of inorganic pigments were studied on steel substrate; salt spray, humidity chamber and field exposure tests were carried out on them. The accelerated laboratory tests were performed both on coatings after 2 weeks of coating preparation (“fresh” coating) and on naturally aged ones, i.e. after field exposures of various durations ranging from 3 months to 2.5 years. We found that-for a certain time-the longer the exposure period, the better are the results of salt spray and humidity chamber tests. Additional experiments were carried out on samples with different pretreatments: in some cases the results of the accelerated tests after cyclic dry-wet or heat pretreatments are better than that of “fresh” coatings.