Light-weighting of vehicle is now strongly required for reducing gasoline consumption and CO2 emission. In this study, F2 laser was irradiated to the surface of hard silicone resin, coated by dip coating method onto the film of acrylic resin on a polycarbonate substrate. The surface part of the silicone resin was photo-chemically modified into SiO2. One of two types of aperture mask, 3×3 mm2 and 50×50 μm2, was set on the sample surface. The single pulse fluence was varied from 4 to 14 mJ/cm2, pulse repetition frequency was set to 10 Hz, and irradiation time was changed from 30 to 120 s. N2 gas was induced around the surface of the sample. After modification, SiO2 modified layer was etched by HF 1% diluted solution, and the etched depth was measured by a stylus-type surface profilometer. As a result of experiments, stress in the SiO2 modified layer increased by increasing of F2 laser irradiation time. In case of using aperture mask of 3×3 mm2, cracks were generated only on the irradiated area for longer irradiation time than 60 s. It is considered that the tensile stress in the modified layer exceeded the tensile fracture strength of 48 MPa of typical SiO2. When a mesh mask of 50×50 μm2 aperture was used, no crack generated even for a long irradiation of 200 s. We found, the tensile stress in SiO2 modified film can be reduced remarkably with using smaller aperture size of mesh mask, and it is very effective to prevent cracking.
Hidetoshi Nojiri and Masayuki Okoshi, "Crack suppression of SiO2 thin film formed by 157 nm F2 laser induced photochemical surface modification of hard silicone coating film on polycarbonate (Conference Presentation)," Proc. SPIE 10091, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXII, 1009107 (Presented at SPIE LASE: January 30, 2017; Published: 21 April 2017); https://doi.org/10.1117/12.2250124.5389784790001.
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