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 used to assess the formation of O-18-labeled photooxidation products in two multi-layer coating systems held in 20% O-18(2)/80% nitrogen atmosphere 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 for 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 technique was extended to a fully formulated six-layer 'repair' paint panel that had been weathered for 4 years in Florida prior to 10 additional days of weatherometer exposure in 20% O-18(2)/80% nitrogen atmosphere. The TOF-SIMS-O-18(-) response observed clearly suggests that the TOF-SIMS-O-18(-) technique can be used to assess the relative photooxidation rates of individual coating layers in fully formulated, multi-layer coating systems.