Localization of the core materials of foldable phones that Japan blocked exports

New materials have been localized to solve the wrinkles of foldable displays. In 2019, it is a fluorine-based polyimide film, one of the three semiconductor and display materials that Japan regulated exports to Korea.

The Korea Institute of Industrial Technology (Director Lee Nak-kyu) announced on the 10th that Dr. Sung-Woo Hong, a research team at the research section of eco-friendly convergence materials, has developed a high-intensity transparent flexible optical film with reliability of flexion while maintaining the light characteristics of existing glass-based materials.

When the display is folded, the compression force inside the inside and the tensile force on the outside can result in repeatedly folding the display, and the surface can be broken or cracked, and the wrinkles can occur.

The polyimide optical film used for foldable displays form a unique structure called a charge-dong-dong complex (CTC), and has good mechanical properties. The resilience is good, shocked, and can be made in a thin film through the continuous unveiling process. That’s why you can create a light and flexible display.

On the other hand, due to the structural characteristics of the CTC that easily absorbs the light of the lower wavelength, there is a disadvantage of the film yellow. The optical characteristics and mechanical properties of the polyimide film show the ‘trade-off’ phenomenon that is inversely proportional to each other.

Dr. Sung-Woo Hong succeeded in developing fluorine-based polyimide films that use both optical and mechanical characteristics. Introducing a bulky fluoride with a bulky carbonization in the polyimide, the CTC has reduced the distance between the polyimide chains, which is strongly combined, to ensure the light characteristics.

In addition, in order to solve the problem of decreasing mechanical physical properties in proportion to controlling physical distances, the polyimide chain between hydrogen binding and metal ion binding is increased. This amplified the interaction of the CTC to overcome the trade-off phenomenon.

The polyimide film developed by the researchers showed more than 8 ㎬ of elasticity, 90%of the total transmittance, and less than 3 yellow index. Even if you folded more than 200,000 times, there was no break, cracking, and wrinkles.

Dr. Hong Sung-woo said, We have noticed the fluorine polyimide in that it is a key material for the development of next-generation displays and urgent materials for localization. I will focus on the development of materials.

This study was published in the International Materials, an international journal of materials.