Discoloration Improvement of Window Black-Matrix by Control of Polymer Crosslink-Density for Mobile Phones

Abstract

Black Matrix (BM) patterned on window glass is essentially used for shielding out direct light exposure to the inactive peripheral areas of displays of mobile phones. However, during the mobile phone display-module manufacturing process, discoloration of the BM frequently occurs, mainly caused by swelling effect that is due to the penetration of monomers of UV-curable resin into the BM ink after window lamination. To solve the BM discoloration problem, in this paper, the direct correlation between the discoloration and the crosslink density of BM was investigated. In addition, highly-crosslinked BM ink was fabricated by employing methyl methacrylate (MMA) as an acrylate monomer and 3-methacryloxy propyl trimethoxy-silane (MPTS) as a silicone monomer. The backbone of an MMA-co-MPTS polymer was generated from double bonds of MMA and MPTS, and the trimethoxysilane of MPTS played the role of a reactive site to the increase the crosslink density of the copolymer. The crosslink densities with various fractional weights of MPTS in copolymer were confirmed by XPS experiments, and the surface roughness and surface energy were evaluated by AFM and contact angle measurements. The analysis of the degree of swelling was performed using SEM measurements. By comparing the theoretical crosslink densities with the swelling degree for different amounts of MPTS, the optimal MPTS content was verified to be 28.6 wt%. Consequently, we have reached the conclusion that the discoloration of mobile-device window BM can be drastically improved by increasing the crosslink density of the polymer against the monomer of the uncured UV resin.