Journal of Chemical Engineering of Japan, Vol.48, No.4, 300-306, 2015
Preparation of the Diffuser Films Using a 1,700 mm Wide Reverse Mode Gravure Coating System
Diffuser fillms are key components in the backlight unit of a liquid crystal display and function as the light unifier. A heterogeneous coating solution containing solid poly(methyl methacrylate) beads, liquid acrylic resin and methylethyl-ketone (MEK) is coated on the poly(ethylene terephthalate) substrate using a 1,700 mm wide reverse mode gravure coater and the diffuser films are thereafter prepared after drying. Depending on the bead concentration and size distribution in the coating solution, the resulting films are appropriate as the top diffuser films, the bottom diffuser films and the spacing films. The results show that with a coating width of 1,700 mm, a varying and narrow range of stable web-to-roll speed ratios is found for the reverse mode gravure heterogeneous coating system. While streaking defects are observed at high web-to-roll speed ratios, cascading defects occur at low web-to-roll speed ratios. When the viscosity of the coating solution decreases from 21 to 8 mPa.s, the gravure cell pick-out fraction decreases from 0.75 to 0.25. An empirical equation is developed to predict the stable operating web-to-roll speed ratio.