Weathering performance of thermoset and photoset acrylate coatings

Thermosetting and photosetting acrylate polymers have been tested for their resistance to accelerated weathering. The chemical changes occurring both upon curing and upon photoaging have been followed by infrared spectroscopy. In the photodegraded polymers some functional groups are lost (ether, amide, CH groups) and oxidation products are formed (carbonyl and hydroxyl groups). The UV-cured polyurethane-acrylate coatings were found to be more resistant to accelerated weathering than the melamine/acrylate thermosets currently used as automotive finishes. The light stability of both thermoset and photoset acrylate clearcoats was substantially increased by the addition of a hydroxy-phenyltriazine UV-absorber and a HALS radical scavenger. The weathering resistance of painted metallic panels has been markedly enhanced by means of properly stabilized UV-cured acrylic coatings. Département de Photochimie Générade (UMR-CNRS No. 7525), 3, rue Werner - 68200 Mulhouse (France). Additives Division, BU Imaging and Coating Additives, CH-4002 Basle, Switzerland.