Based on these results, it is apparent that the used
HPT chromophores significantly outperform all the
modified BTZ in terms of photopermanence. After
2000 h of exposure, both HPT-DW types show with
90% of UVA retention a far superior performance of
HPT vs BTZ. These findings have been reported
earlier and are an intrinsic property of the HPT
chemistry. BTZs show very different retention levels
depending on product forms. The better photopermanence
is the most important advantage of the HPT
chemistry. It was confirmed earlier that improved
weathering performance is always related to the higher
UVA photopermanence in coating films.