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°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.

Enhanced Polymerization and Surface Hardness of Colloidal Siloxane Films via Electron Beam Irradiation

“…The OH and Si–H bonds disappear with the formation of Si–Si bonds because the EB breaks the Si–H bonds and converts them into free radical states. The suspended silicon atoms then recombine into Si–Si bonds. − The other change in the silicon-containing functional groups after EB curing is the change in the Si–OH bonds to Si–O–Si bonds . Moreover, it can be seen in Figure c,d that the EB-cured colloidal siloxane coating layer further affects carbon-containing groups.…”

“…These curing methods enhance the hardness of coating materials, yielding better folding performance. Traditional thermal curing increases the hardness by changing the distribution of Si–O and Si–H bonds via chemical changes in the material . However, long curing times, high energy consumption, complicated processes, and insufficient heat penetration depths restrict the application of thermal curing for hard coating.…”

Thermal Insulating Property of Silsesquioxane Hybrid Film Induced by Intramolecular Void Spaces

“…When a polysilsesquioxane solution is coated on a substrate and then cured, a cross-linked gel film is formed. By taking advantage of their excellent mechanical and thermal stability and transparency, polysilsesquioxanes have been applied as a scratch-resistant coating, , barrier coating, , optical film, , and low dielectric film. − Additionally, owing to their thermal stability and nonflammable property, the cross-linked gel film of polysilsesquioxanes may be utilized as thermal barrier coating under high-temperature conditions. Polysilsesquioxane also exhibits good processability for coating, which could be exploited for the fabrication of thermal barrier coating on various substrates and materials by spin coating, dip coating, or spray coating.…”

Hard Coating Materials Based on Photo-Reactive Silsesquioxane for Flexible Application: Improvement of Flexible and Hardness Properties by High Molecular Weight

“…In general, acid-catalyzed reactions are used to synthesize linear polymers and branched polysiloxanes, and base and heating reactions are widely used to synthesize cubes and ladder-like silsesquioxanes (LPSQs) [ 21 ]. Recently, silsesquioxane structure based on 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ECTMS), which has high thermal stability and good mechanical properties, has been widely studied [ 39 , 40 , 41 , 42 ].…”

“…In addition, a siloxane hybrid structure was synthesized using ECTMS by Bae et al that showed a 9H pencil hardness at a load of 9.8 N (coating thickness of 50 μm) and an 88.5% elastic recovery value [ 40 ]. Jeong et al reported that polysilsesquioxane with ECTMS was flexible even in a folding test repeated 100,000 times at a radius of curvature of 3 mm [ 41 ].…”