Highly robust and transparent flexible cover window films based on UV-curable polysilsesquioxane nano sol

Abstract

Flexible cover window films based on the ultraviolet-curable polysilsesquioxane are prepared to have enhanced mechanical, optical properties, and bending performance. To figure out the factors determining those properties, post-treatment conditions are varied into the light source, temperature, and relative humidity. Then, the effect of such variables is examined in respect of surface hardness, yellow index (YI), and bending cycle reliability of flexible hard coating. Also, the effect of photoinitiator type in terms of their chemical structure is also investigated. Notably, the relative humidity and thermal treatment are more effective to enhance the mechanical properties rather than light exposure. Indeed, compared to that of reference condition, the cover windows treated with 99% relative humidity and thermal aging at 85 degrees C exhibit improved surface hardness by 24.4 and 19.5%, respectively. However, only the relative humidity is rather effective to enhance the optical properties such as the YI by lowering to the most 2.6. The YI is also improved by varying the chemical structure of the photoinitiator. By virtue of post-treatment and a different photoinitiator, we could achieve flexible cover window films with bending reliability at bending radius of 3 mm for 100,000 cycles, showing good mechanical and optical properties simultaneously.