Effects of Inorganic Acid and Light Stabilizer on Whitening of Melamine-cured Coating Film
Kentaro WATANABE*,Tatsuya ISHIHARA and Masahiko YAMANAKA
Material Development Department, NISSAN Motor Co. Ltd.; 560-2, Okatsukoku, Atsugi-shi 243-0192 Japan
Effect of inorganic acid and light stabilizer on whitening of melamine-cured coating film was clarified. Based on the IR spectra of the whitening section, it was found that amounts of ether bond and triazine ring decreased and that of secondary amine increased compared to the initial material. In the whitening section stabilizer contained in the polypropylene substrate was also detected by gas chromatography. The relation between the dipping time in aqueous H2SO4 solution to lead whitening and the composition and the preparation conditions of the films shows that whitening occurred by the penetration of water to the coating film. Whitening occurred easily on the coating film having lower cross-linking density and/or containing light stabilizer. It was thought that the light stabilizer in the coating film caused the high osmotic pressure through amine salt formation with inorganic acid. The acceleration of whitening in the film by the elevation of drying temperature was interpreted that the rate of penetration of water was enhanced through the lowering the cross-linking density of the film.