Evaluation of ASTM D7869-13 method for premium architectural finishes-II

Abstract

In recent studies comparing the outdoor weathering of poly(vinylidene fluoride) (PVDF)-based coatings against several accelerated weathering test cycles, including ASTM D7869-13, we found all the cycles accurately reproduced Florida rank order gloss and color retention trends for PVDF-based coatings made with single (non-TiO₂) pigments. However, none of the cycles accurately predicted the rank order of rutile TiO₂ grades for Florida gloss retention, nor the magnitude and direction of color fade in organic pigment/inorganic pigment blends. This paper follows up on these earlier studies, to examine whether the ASTM D7869 cycle might nevertheless have some utility for industry standard or specification purposes, across resin lines. We report for the first time the results of two recent studies comparing ASTM D7869 and South Florida weathering, for a range of weatherable binder chemistries commonly used in industrial coatings, and specifically examining color-matched, non-white colors. The data suggest that ASTM D7869 testing for 5000–6000 h might be a promising way to gauge the weatherability of coatings intended to meet 5-year South Florida weathering requirements. At the same time, the data also suggest that the ASTM D7869 cycle would be unreliable for predicting the weatherability of coatings intended to last 10 years or even much longer, within a 6–12-month timeframe, due to issues with false positives. For this reason, in the new SSPC Paint 47 fluoropolymer topcoat standard, a more aggressive UVB-313 fluorescent cabinet cycle was chosen, due to its ability to give results in 6 months, with a very low level of false positives.