Deterioration of surface structure of lacquer films due to ultraviolet irradiation

The mechanism of deterioration due to ultraviolet irradiation of black (with iron ion) and kurome (translucent) lacquer films that had been dried at 15–20 °C in 60–70% relative humidity environment was revealed. The lacquer film changes were evaluated by observations of the surface by microscopy, IR, and XPS. A particulate material and toroidal shapes appeared in the black lacquer film during UV irradiation within 48 h, but they did not appear in the kurome lacquer film under UV irradiation before 240 h. The IR peak at ～3445 cm^?1 increased owing to the hydroxyl group, and the C 1s peak decreased and O 1s increased in the XPS spectra as the UV irradiation time increased, implying that a chemical reaction occurred on the surface of the lacquer film. On the top surface of the coating film, many toroidal shapes were observed in the black lacquer film, which showed that the black lacquer film deteriorated more quickly than the kurome lacquer film. In addition, the structural changes in the black lacquer film are also discussed in detail, on the basis of the results of the Py‐GC/MS measurement. Copyright © 2006 John Wiley & Sons, Ltd.