Crack Filling of Cover Glasses by Sol-Gel Coatings

Abstract

Strengthening of glass sheets through the process of ion exchange have been widely used in thinner cover glass for smart phone. The compressive stress improves the ability of the glass surface to withstand damage from mechanical impact. However, the presence of the damage resistant layer makes conventional mechanical and laser cutting of the ion-exchanged glass difficult. Normally, the cutting process will lead to spontaneous glass sheet breakage or shattering. Even successful in some samples, the underlying central tension is exposed on the edge, and the mechanical strength and durability of this edge is degraded. The repair of edge cracks becomes an extremely important issue for the development of single glass based smart phone. The ion exchanged glass plates (Corning IOX-FS) with a thickness of 0.7 mm were selected as the substrate materials. After cutting ion exchanged glass by high penetration diamond scribing wheels, the edge of glass plates can be protected or strengthened with silica sol using roll coating process. It was observed that the strength could be improved achieving 210 % compared to the strength of uncoated glass sheets. The sol-gel coating could improve the strength of the glass mainly by the mechanisms of filling in edge flaws or blunting crack tips. The effects of silica sol and processing parameters of roll coating process on the cracks filling effects were investigated.

Strengthening mechanism of cover glass by Sol‐Gel SiO2 coating

“…Coatings that meet the above requirements can be specifically divided into two categories: (a) organic films, such as epoxy resin film 22 , and (b) inorganic film, such as silica film. 17,18 The chemical bonding on the interface between SiO 2 coating and glass substrate is strong and anti-aging, since the chemical composition of SiO 2 coating is consistent with the principal component of electronic cover glass. The preparation of SiO 2 coating by the sol-gel method also has other advantages, such as simple process and low cost.…”

“…Generally, coating process needs to meet the following basic requirements: (a) The curing temperature of coating shall not exceed 290°C, to avoid stress relaxation at high temperature and (b) the coating shall be transparent, hard enough, and cohesive to the glass surface to minimize interface defects. Coatings that meet the above requirements can be specifically divided into two categories: (a) organic films, such as epoxy resin film, and (b) inorganic film, such as silica film . The chemical bonding on the interface between SiO 2 coating and glass substrate is strong and anti‐aging, since the chemical composition of SiO 2 coating is consistent with the principal component of electronic cover glass.…”

“…14,15 At present, for chemically tempered glass, surface coating approach is an effective method to fill and repair surface microcracks, so it attracts much scientific interests. [17][18][19][20][21] Generally, coating process needs to meet the following basic requirements: (a) The curing temperature of coating shall not exceed 290°C, to avoid stress relaxation at high temperature 15,16 and (b) the coating shall be transparent, hard enough, and cohesive to the glass surface to minimize interface defects. Coatings that meet the above requirements can be specifically divided into two categories: (a) organic films, such as epoxy resin film 22 , and (b) inorganic film, such as silica film.…”

Improving the Transparency of a MgAl2O4 Spinel Damaged by Sandblasting through a SiO2-ZrO2 Coating

“…A hardness of 22 GPa and a Young's modulus of 193 GPa were achieved for 100% ZrO 2 . In general, the deposition of a sol-gel coating can improve the mechanical properties by healing the superficial defects [18], filling flaws or crack tips [19]. The incorporation of ZrO 2 in the composition of the coatings is beneficial because ZrO 2 offers mechanical resistance, good surface properties and good biocompatibility and biological properties [17,20], making it a beneficial material for reinforcement.…”