Radicals are generated in paint films by UV-irradiation.
In order to investigate whether bisphenol A/epichlorohydrin type epoxy resin is able to be the radical trapping agent, the clear films prepared as the mixtures of the epoxy resin and polyester/melamine resin were exposed under ultra-high pressure mercury arc lamp (Main wave length, 365 nm) at room temperature and the relative concentrations of phenoxyl radical generated were measured by ESR spectrometer.
It was clarified that the epoxy resin was able to be adopted as a suitable radical trapping agent of paint films.
Using the epoxy resin as the radical trapping agent, the relative concentrations of phenoxyl radical for seven clear films, i.e, four kind of silicone modified polyesters (modified quantity; 50%, 35%, 20% and unmodified) and three kinds of acrylic resin, fluoro carbon resin and acrylic resin/fluorocarbon resin were tested with the same method as that mentioned above.
For comparison, gloss retentions and color differences of these paint films were measured after outdoor exposure at Omaezaki, Shizuoka, Japan for 6 to 24 months.
The relative concentrations of the phenoxyl radical estimated by ESR spectrometer, and gloss retentions and color differences of exposed paint films were nicely correlated one another, which shows that the ESR method has a high potential to determine quickly the photodegradation of paint films.