TFT LCD 背光模組之薄型化平板導光板射出成形研究

Abstract

Due to application needs, the trend of notebook development is toward lighter and slimmer. Backlight units in a TFT-LCD provide a suitable lighting mechanism. The light-guide plate - a component in the backlight unit is necessary to change formation from wedge type to flat type. However, the area and thickness of a flat type Light-guide plate are greatly different in dimension, and therefore require different injection conditions than other injection workpieces. Not only is a high speed injection machine needed, but the quality and stability of flat type LGP must be controlled. Therefore, reference on existing theory of operation is necessary, and other issues of high speed injection must be considered. The purpose of this study is to study warp of LGP under different process factor. This is achieved using the Taguchi Methods /Design of Experiments approach. Each experimental condition in this study uses different process factors and high speed injection machine with optical PMMA material. The main influencing factor and best condition for robust character & accuracy can be determined by measuring the amount of warp after RA test. Further, the operation window of the main factor can be built up. The results of this study show that the main factors affecting the robust character of S/N are the fill-in speed and packing pressure. The main factors affecting accuracy are the fill-in speed and mold temperature. A high fill-in speed produces a high shear rate (shear thinning), reduced viscosity, and a more uniform pressure and temperature inside the mold. These factors reduce the residual stress on a flat-type LGP, and hence, produce less warp. Setting the packing pressure too high will produce uneven contraction, which results in warp. In terms of accuracy, mold temperature is always affected be cooling behavior, if the workpiece cools down unevenly, there will be uneven contraction, which will result in warp.