In order to elucidate the photodegradation process of methacrylate resin/butylated melamine resin paint films, four kinds of methacrylate resins have been synthesized from methyl methacrylate (MMA), hydroxyethyl methacrylate (HEMA), and styrene (ST) (ST conts. : 0, 20, 40, 60% by wt. in the resin).
Their photodegradation processes have investigated by using ESR and FT-IR spectroscopies.
It has been found from these measurements that in the photodegradation process of methacrylate paint films, hydrogen, methacrylate, and methyl radicals are generated, followed by the formations of dimer acid and benzyl compounds.
The use of an anthrapyridine pigment to the resins resulted in the formation of a stable anthraquinone radical (g=2.0042), when the resins were irradiated by ultra-low pressure and ultra-high pressure mercury arc lamps at room temperature.
The concentration of the radical increased as the styrene content increased.
The relationships between the concentration of the anthraquinone radical and gloss retention and color difference of the painted panels exposed under ultra-low pressure mercury arc lamp and sunshine weather meter were also examined, which leads to the useful application of the ESR measurements to determine the degree of degradation of resins.
Finally the degradation mechanism of the resins are discussed based on the results.
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