Curing and photostabilization of thermoset and photoset acrylate polymers

The light-stability of thermosetting acrylate and UV-cured acrylate polymers has been tested in an accelerated QUV weatherometer. Infrared spectroscopy was used to monitor in situ the chemical changes occurring upon both curing and photoageing of 35 mum thick clearcoats. The curing was shown to proceed more extensively in photoset than in thermoset acrylate polymers which contain 6 and 20% unreacted functional groups, respectively. During photoageing, the loss of the binder oxistructural groups is accompanied by the production of oxidation products (carbonyl and hydroxyl groups). The UV-cured polyurethane-acrylate coating was shown to be more resistant to accelerated weathering than the melamine/acrylate thermoset currently used as automotive finishes. The addition of a hydroxyphenyltriazine UV-absorber and a hindered amine light stabilizer (HALS) radical scavenger was found to increase substantially the light stability of acrylate clearcoats.