INTERNAL-STRESSES IN UV-CURED EPOXIDE-RESIN COATINGS

Internal stresses of UV-cured epoxide resin coatings were determined by measuring the deflection of the coated substrate with a laser displacement detector. In this method, we could measure precisely the internal stresses generated in both the curing and cooling processes of the coatings. The internal stresses of coatings decreased for smaller increments of coating temperature during UV-irradiation. This phenomenon is due to the decrease in the shrinkage of coatings during the cooling process. The internal stresses also decreased as the coating thickness was increased. This behavior of the internal stress was based on lack of uniformity of the degree of curing and the coating temperature in the curing and cooling processes. In the curing process, the curing shrikage of the surface layer is relaxed by the ductile deformations of the inner layer which is not still cured completely, while in the cooling process, the cooling shrinkage of the inner layer is suppressed by the surface layer which was cooled earlier and thus has a higher modulus. © 1990, The Society of Polymer Science, Japan. All rights reserved.