KITECH, based on new flexible hard-coating materials
Successful independent development of cover window manufacturing technology


On the 7th, the Korea Institute of Industrial Technology independently developed a new flexible hard-coating material applicable to foldable displays and succeeded in manufacturing a cover window with a composite structure using it.

Most displays on various IT devices, such as smartphones, are equipped with a 'cover window' made of glass. This component protects the display substrate from external impacts, contamination, and fingerprints, and is an essential part of the display manufacturing process.

Tempered glass has been primarily used for IT devices that frequently utilize touch functions. On the other hand, foldable phones are applying 'Colorless Polyimide (CPI),' a plastic material with excellent flexibility that allows them to be folded and unfolded, instead of conventional glass materials.

Cover windows made of CPI have high light transmittance, do not break, and are durable enough to withstand hundreds of thousands of folds. However, it is more susceptible to scratches than glass material, and there is a high possibility of deformation, such as wrinkles, occurring in the hinge part that acts as a joint when folding or unfolding.

The industry is pushing for the development of Ultra Thin Glass (UTG), a foldable ultra-thin tempered glass, but is facing difficulties in mass production due to a lack of technology to make the glass thin and low yields.

A research team led by Dr. Yong-Cheol Jeong of the Micro-Nano Process Group at the Institute of Science and Technology launched research in 2015 to address the shortcomings of these materials, and after five years of effort, developed a new flexible hard-coating material capable of simultaneously achieving glass-level hardness and plastic-level flexibility.

The newly developed material is a type of glass material that allows for free molding and processing; it is a nanostructure artificially formed to possess properties intermediate between silicate (SiO2), which is close to ceramic, and silicon oil (SiO).

By controlling the connection structure and ratio between silicon (Si) and oxygen (O), desired properties ranging from hard to soft, such as ceramics, rubber, and oil, can be easily produced, and in particular, conflicting properties such as hardness and flexibility can be realized on a single sheet.

The research team succeeded in fabricating a cover window in the form of a composite structure (Rigid-Soft-Rigid; RSR) in which the flat sides of the foldable phone are rigid but the hinge area is flexible by controlling the physical properties of this new material.

The hardness of the manufactured cover window is high at the 9H level, which is close to that of tempered glass, so it does not get scratched even if it is scratched hard multiple times with a car key or similar object. In addition, it does not break even when bent up to a radius of curvature of 1R, possessing flexibility equivalent to CPI material, and maintains durability even after approximately 200,000 repeated uses. Among foldable methods, it is possible to apply both in-folding (folding inward) and out-folding (folding outward), making it highly versatile.

In addition, the research team verified the feasibility of mass production based on a roll-to-roll process by successfully producing cover windows continuously using a self-developed slot coater.

Dr. Jeong Yong-cheol predicted, “In addition to foldable phones, the application range of new flexible materials will be extensive, including secondary battery separators, optical module coatings, automotive curved foam molding, and the construction and furniture sectors.”

Meanwhile, market research firm Counterpoint Research projected that foldable phone sales would surge from 400,000 units in 2019 to 36.8 million units in 2023.