ASSESSMENT OF PHOTOOXIDATION IN MULTILAYER COATING SYSTEMS BY TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been use d to assess the formation of O-18-labeled photooxidation products in t wo multi-layer coating systems held in 20% O-18(2)/80% nitrogen atmosp here during brief Xenon are weatherometer exposure. A four-layer model coating system without hindered amine light stabilizer or ultraviolet light absorber additives was examined first. The model was exposed fo r 8 days in the weatherometer, and then its TOF-SIMS-O-18(-) response was recorded. This response tracks the known photooxidation resistance of the coating layers used to prepare the model system. Next, the tec hnique was extended to a fully formulated six-layer 'repair' paint pan el that had been weathered for 4 years in Florida prior to 10 addition al days of weatherometer exposure in 20% O-18(2)/80% nitrogen atmosphe re. The TOF-SIMS-O-18(-) response observed clearly suggests that the T OF-SIMS-O-18(-) technique can be used to assess the relative photooxid ation rates of individual coating layers in fully formulated, multi-la yer coating systems.