Study on Thermal Stress Cleavage of Chemically Strengthened Glass by CO2 Laser Beam

This study deals with the thermal stress cleavage of chemically strengthened glass by CO2 laser beam irradiation. In order to prevent breakage from external stress, the surface of chemically strengthened glass is load with compressive stress by ion-exchanging methods. Generally, thermal stress cleavage occurs because of tensile stress on the brittle material. This stress is induced by laser beam irradiation. Therefore, the compressive stress on the surface of chemically strengthened glass renders the thermal stress cleavage difficult to create. It is also difficult to introduce an initial crack on the surface. In this study, cleavage characteristics of chemically strengthened glass with a thickness of 0.7 mm are investigated experimentally. The depth of compressive stress from the surface is 33 μm. The laser used is a continuous CO2 laser beam with a wavelength of 10.6 μm. This laser is also applied to the introduction of the initial crack at the edge of the chemically strengthened glass. Additionally, the influence of laser power and energy density on the introduction of the initial crack and the thermal stress cleavage are evaluated. From these results, in order to propagate the initial crack, the depth of the initial crack needs to exceed the depth of the compressive stress layer from the surface. The depth of the initial crack tends to increase with increasing energy density. When an initial crack is introduced along the cleaving line, the quality of the cleaved surface is poor. The quality of cleavage was improved by the introduction of an initial crack at the edge of the glass.