Response of Resin Coating Films Containing Fine Metal Particles to Ultrashort Laser Pulses

Resin coating films are extensively used for aesthetic improvement and preventing deterioration of metal surfaces. Some of the films contain fine metal particles for the purpose of coloring. For such films, surface waviness with millimeter-scale wavelength is a significant problem because it induces visible irregularities on the surface. Conventionally, man-powered polishing has been used to planarize the waviness. However, it is labor-intensive and leads to other problems such as waste slurry disposal and embedment of abrasive grains in the film. Hence, a new method is required to eliminate the surface waviness. In this study, ultrashort pulsed laser irradiation on resin coating films is proposed. By controlling the focal position and/or scanning speed of the laser beam along the surface, protrusions are preferentially removed. Firstly, the effects of pulse width, laser fluence, and scanning speed on surface morphology were clarified. Next, the material removal mechanism was examined by elemental analysis of the surface and its cross section after irradiation. Finally, as a preliminary result of surface flattening, the arithmetic mean waviness in the wavelength range of 2.4–5.0 mm was reduced by 45.3%. This study demonstrated the feasibility of selectively removing and flattening of resin coating films by substituting laser processing for man-powered polishing.