The long-term weathering behavior of UV curable clearcoats I. Bulk chemical and physical analysis

The long-term weathering behavior of two UV cure clearcoat systems, one a monocure, the other a dual cure system, was studied by infrared spectroscopy, UV spectroscopy, Raman spectroscopy, dynamic mechanical thermal analysis (DMTA), and fracture energy measurements. The photooxidation rate and consumption of residual acrylate double bonds during weathering was highly dependant on the presence of hindered amine light stabilizers (HALS) for both systems. Ultraviolet light absorbers (UVA) had little effect on the photooxidation rate or rate of consumption of acrylate double bonds during weathering. Changes in fracture energy (brittleness) of the clearcoats mirrored the changes found in the consumption of residual acrylate double bonds. DMTA analysis of both clearcoats indicated no increase in crosslink density as weathering progressed, suggesting the acrylate double bonds were not reacting to form additional crosslinks. (C) 2003 Elsevier Science Ltd. All rights reserved.