Improvement of Surface Hardness of Transparent Poly(amide-imide) Films Using Fumed Silica Nanoparticles

초록

A hard coating is generally applied to transparent polymer films in flexible displays to protect the surface from scratching and abrasion. The degree of improvement of the surface hardness of a polymer film after a hard coating can be increased, further improving the surface hardness of the polymer film first. This study evaluated the applicability of fumed silica nanoparticles (FSNs) and mesoporous silica nanoparticles (MSNs) to improve the surface hardness of colorless and transparent poly(amide-imide)s (CPAIs) films. CPAIs were prepared using monomers with electron-withdrawing trifluoromethyl groups. CPAI-5 refers to CPAI with an amide linkage content of 50 mol%. The 3H pencil hardness of the CPAI-5 film was increased to 4H by adding 1 % of FSNs without sacrificing their transparency and mechanical properties. The FSNs diffused to the surface of the CPAI-5 films because of their low density and improved surface hardness. On the other hand, when MSNs were added to CPAI-5, the optical transmittance of the CPAI-5 films decreased dramatically. The pencil hardness of the CPAI-5 film was 6H after a hard coating of ladder-like structured poly(2-(3,4-epoxycyclohexyl) ethylsilsesquioxane) (LPESQ). By contrast, the LPESQ hard coating increased the pencil hardness of the FSNs/CPAI-5 composite films to 8H. By improving the surface hardness of the CPAI films first by adding small amounts of FSNs, the final surface hardness of the CPAI films after a hard coating could be improved further.

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