11:15 AM - 11:30 AM
[14a-C31-7] Crack suppression of silica glass film formed by F2 laser induced photochemical surface modification of hard silicone coating film on polycarbonate
Keywords:F2 laser, SiO2, modification
Light-weighting of vehicle is now strongly required for reducing gasoline consumption and CO2 emission. Previously, we have been found that the surface of silicone rubber was photo-chemically modified into carbon-free silica (SiO2) by irradiation of a 157 nm F2 laser. We switched silicone rubber to silicone resin-for advanced coating applications and have focused on whether the resin can be modified into SiO2 as same as the case in the rubber. In this study, F2 laser was irradiated to the surface of hard silicone resin. The silicone resin was coated by dip coating method onto the film of acrylic resin on a polycarbonate substrate. The thickness of silicone resin was about 4 µm. The surface part of the silicone resin was modified to SiO2, maximum thickness was approximately 1.3µm. 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. Then the SiO2 modified layer of samples were etched by HF 1% diluted solution. After etching, the etched depth was measured by a stylus-type surface profilometer.
The results of above experiments, it was found that the tensile stress in the SiO2 modified layer increased by increasing of F2 laser irradiation time. In the 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 exceeds the tensile fracture strength of 48MPa of typical SiO2. When a mesh mask of 50×50 µm2 was used, no crack generates on the irradiated areas even for a long irradiation of 200 s. The volumetric shrinkage might cause a tensile stress in the SiO2 modified layer and its thickness reduction works to release the strain in the lateral direction. We estimated the tensile stress by calculation. The result of considerations, we found that the tensile stress can be reduced remarkably by using smaller aperture size of mesh mask, and it is very effective to prevent cracking. On the basis of zoning the laser-irradiated area in micron size, the thicker film of SiO2 1µm and over was successfully formed without cracking.
The results of above experiments, it was found that the tensile stress in the SiO2 modified layer increased by increasing of F2 laser irradiation time. In the 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 exceeds the tensile fracture strength of 48MPa of typical SiO2. When a mesh mask of 50×50 µm2 was used, no crack generates on the irradiated areas even for a long irradiation of 200 s. The volumetric shrinkage might cause a tensile stress in the SiO2 modified layer and its thickness reduction works to release the strain in the lateral direction. We estimated the tensile stress by calculation. The result of considerations, we found that the tensile stress can be reduced remarkably by using smaller aperture size of mesh mask, and it is very effective to prevent cracking. On the basis of zoning the laser-irradiated area in micron size, the thicker film of SiO2 1µm and over was successfully formed without cracking.