High-irradiance laboratory weathering testing of coatings

 
Accelerated laboratory weathering testing is used to evaluate the effects of sunlight, heat, and water on materials exposed to outdoor environments. Acceleration is only possible up to a certain extent, after which laboratory phenomena may not match outdoor results. However, for some light-induced behavior acceleration may be possible using irradiance levels higher than those typically used in laboratory testing. This work compares results from several high-irradiance accelerated test protocols, including natural sunlight concentrators, xenon arc instruments, and UV fluorescent apparatus. Testing in UV fluorescent apparatus at very high "3-sun" type irradiances, as well as xenon arc testing at irradiance values 50% higher than in common test standards. Higher temperatures in xenon arc testing are also considered to increase water absorption rates. Test results are presented for colour change and gloss loss of aluminum specimens with field-applied protective coatings. Results indicate that good rank-order correlation in colour change and gloss loss can be achieved between outdoor and high-irradiance laboratory testing, for some coatings.