TFT LCD 背光模組之薄型化平板導光板射出成形研究

Abstract

現行市面筆記型電腦，隨應用需求，朝更輕、更薄做發展；組件當中之TFT LCD顯示器模組，發光機制為架構內之背光模組提供光源，而背光模組內之零件¬¬¬-導光板，也隨趨勢而由楔形板變為薄平板架構；但因薄平板導光板之面積與厚度尺寸差異值過大，因此在成形條件較其它射出工件不同，除需搭配高速成形機進行外，另需考慮薄平板工件之品質及穩定度；因此在許多操作特性上須參考現有理論，對高速成形下之各項問題做考量。

本研究為在高速成形機台架構下，搭配現行導光板使用之光學級壓克力PMMA材料，主要針對翹曲問題，以控制不同製程因子，利用田口實驗計畫方法，安排各製程因子之實驗條件組合並做成形，再進行高溫環測實驗；後續依導光板量測翹曲量結果，求得影響翹曲在穩健及準確特性上，最佳控制條件及主要作用因子；並針對主要作用因子建立其操作視窗。本實驗架構結果顯示，影響翹曲穩健性 之主要作用因子，為充填速度及保壓壓力影醒最大，而影響準確性 之主要作用因子，為充填速度及模具溫度影醒最大。其中高充填速度主要利用材料在高剪切率下，黏度下降的剪切稀薄特性，模穴內的壓力分佈與溫度分佈會較均勻，也減少了薄平板導光板工件內的殘留應力所造成之翹曲。在保壓壓力部分，過高之壓力則使工件過於飽和使體積收縮率不均，造成翹曲。準確特性上，在模具溫度部分，冷卻行為在成形中是一直在進行的，若產品沒有均勻的冷卻，則會有不均勻的收縮行為發生，因此成形品容易造成翹曲之缺陷。

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.