Effects of Affinity with 2-Methylheptane of Melamine Resin on Cracking of Melamine-cured Coating Film

Abstract

Effect of affinity with 2-methylheptane of melamine resin on cracking on melamine-cured coating film was clarified by mineral spirits tolerance (MST). It was found that cracking occurred easily on the coating film having higher MST in exposure test. The coating film having higher MST led to remarkable changes in glass transition temperature, cross-linking density, tensile strength and ultimate elongation. It was also found that the coating film having higher MST had lower initial cross-linking density.
Based on the IR spectra of the coating film after exposure test, it was found that the amounts of alkyl-group and melamine decreased and they were more in the coating film having higher MST.
The cracking of melamine-cured coating film was affected by MST of melamine resin, and the coating film having higher MST occurred the cracking at short time compared to lower ones. It was thought that higher penetration of water to coating film caused by the initial lower cross-linking density led to the hydrolysis of the film and the cracking occurred by falling of physical properties of the film.