Hardening process and surface structure of lacquer films studied by x-ray photoelectron spectroscopy

The changes of the composition ratios and chemical binding states of the component elements in the surfaces of four varieties of lacquer films during the hardening process were studied by x-ray photoelectron spectroscopy (XPS). Additionally, the relationship between the surface structure and hardening process of lacquer films was studied by the pencil hardness testing method. The relative oxygen contents and the existence ratios among the COO, C=O, C-O-C, C-OOH, C-N and N=O functional groups in the surfaces of the lacquer films increased significantly with the progress of hardening. In addition, it was revealed that a lacquer film with a faster hardening rate showed a higher relative oxygen content and a larger existence ratio among these functional groups in the surface. The increases support the progress of the following three phenomena in the surface of lacquer film during the hardening process, i.e. the concentration of gummy substances and nitrogen-containing compounds, laccase-catalysed oxidative polymerization and autoxidative polymerization.