Accelerated testing of waterborne coatings

Abstract

According to environmental regulations, many of the traditionally used organic solventborne coatings should be replaced by low-toxicity and environmentally friendly alternatives (e.g. by waterborne paints). 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.