Strengthening mechanism of cover glass by Sol‐Gel SiO ₂ coating

Abstract Strengthening is a huge challenge of ultrathin cover glass in mobile electronic devices. In this paper, a transparent sol‐gel silica coating has been sprayed on the surface of chemically strengthened cover glass, and three different coatings (identified as thickness/curing temperature: 3 μm/80°C, 5 μm/80°C, and 3 μm/180°C) have been prepared. Characterized by four‐point bending experiment, the strengthening effects of three coatings, representing by the increases of strength of the coated glass, are 47 MPa, 98 MPa, and 58 MPa for 3 μm/80°C, 5 μm/80°C, and 3 μm/180°C, respectively. Based on finite element simulation and experimental data of four‐point bending, the influence of four parameters of surface coating (elastic modulus, residual stress, filling ratio, and thickness) on glass strengthening has been investigated. Simulation analysis shows that the increase of elastic modulus, residual stress, and filling ratio of the SiO ₂ coating facilitates the increase of bending strength of cover glass, and the coating thickness has less influence on the glass strength. However, the experimental results demonstrate that the coating thickness has a significant impact on the strength of glass: when the layer thickness of sample cured at 80°C increases from 3μm to 5μm, the bending strength of glass can improve by 51MPa. Since greater coating thickness induces greater filling ratio, which is the main contributor to the strengthening effect of increased coating thickness, so, elastic modulus, residual stress, and filling ratio of the coating are the three key factors of the cover glass strengthening.