Discoloration mechanism of UV-curable polymer/metal hybrid coating

The purpose of this study is to conduct an in-depth analysis of the discoloration mechanism of UV-curable polymer/metal hybrid coating. A variety of technical approaches, including microscopic, spectroscopic, and chromatographic analysis techniques, were used to investigate the nature of discoloration and the root cause. The hybrid coating has a typical multilayered structure consisting of a base coat, a vacuum deposited metal layer, and a top coat. The results obtained by microscopic and spectroscopic analyses demonstrated that the discoloration of the hybrid coating stemmed from yellowing of the top coat. Deterioration or degradation of the metal component in the vacuum deposited metal layer was not confirmed. The results of an analysis of additives in the discolored top coat showed that there is a small quantity of unreacted photoinitiators remaining in the top coat. From the results of solvent extraction and gel content measurement, it is believed that an excessive amount of photoinitiators was used in the resin of the top coat and one of the residual unreacted photoinitiators caused yellowing of the top coat.