IN-SITU GENERATION OF LIGHT-STABILIZERS UPON PHOTOAGING OF THERMOSET OR UV CURED-ACRYLATE COATINGS

A 2-hydroxy phenylbenzotriazole (HBTA) light-stabilizer was generated by photolysis of the 2-acetate derivative (ABTA) in an acrylate coating. The ABTA disappearance upon QUV aging was monitored by UV spectroscopy and shown to follow a single exponential law, with an initial quantum yield of 5.7 x 10(-3) mol einstein(-1). A good correlation was found between the first order rate constants of ABTA photolysis and HBTA formation. The distribution profile of the photoproduct within the irradiated film exhibits a sharp decrease from the UV-exposed face toward the deep lying layers, due to a strong internal filter effect. In-situ photogeneration of UV absorber proved to be a technique particularly well suited to stabilization of UV-cured coatings, since the ABTA precursor has only a minor effect on the cure speed. The HBTA photoproduct formed upon QUV aging acts as an efficient UV absorber and to a large extent prevents the photodegradation of the polymeric support.