射出成型參數對導光板之光學特性影響研究

Influences of the Injection Process Parameters of Light Guide Plate on the Optical Characteristics of the LCD Backlight Module

陳孝用(Hsiao-Yung Chen)

指導教授 ： 陳永樹

元智大學/工程學院/機械工程學系/碩士(2009年)

摘要

摘 要
進年來平面顯示科技不斷進步，從早期陰極射線管顯示器(Cathode Ray Tube Display-CRT)，至目前市面上以液晶顯示(Liquid Crystal Display- LCD)為主流，LCD具有體積輕薄短小，低耗電及低幅射等特性，成為顯示器市場主流。由於LCD本身為非發光的裝置，必須藉由背光模組(Back Light Module)提供光源。背光模組光學元件包括導光板、反射片、擴散片、綾鏡片等及機構元件(Housing、Frame)，其中導光板是最主要的關鍵零件之一。導光板主要的功能是線光源(冷陰極管CCFL)或點光源(LED)透過導光板將其光源導引行進方向並轉為均勻且高亮度的光源。
對導光板而言，高輝度、高均齊性及高轉寫性是判定品質良窳的重要關鍵。因為高輝度及高均齊性導光板將使光得使用效率提高，甚至減少LED使用數量，可直接降低背光模組成本。本研究將以2.83吋導光板(62.94mm x 46.64mm x 0.45mm)為例，討論導光板在四種不同成型參數下如模溫、料溫、射度、保壓對模組輝度變化及影響，首先利用田口實驗方法中的直交表進行實驗，經S/N因子反應圖及變異數分析結果發現，模溫與料溫對導光板輝度及均勻性影響最大，在均勻度方面，模溫與料溫的影響卻呈現相反的趨勢，當模溫與塑料溫度越高時均勻性及中央輝度都會降低。
基於傳統的田口分析法主要解決單一品質特性，影響光學品質問題經常是包含多重影響性的評估，故本研究結合灰關聯分析改善射出成型製程多重目標品質特性最佳化的問題。首先利用田口參數設計降低實驗次數及時間的優點，再配合灰關聯分析得到多重品質特性的最佳組合，確認在95%信心區間內，證明輝度實驗的再現性是可信賴的。

關鍵詞：背光模組、導光板、田口方法、灰關聯分析

關鍵字

背光模組；導光板；田口方法；灰關聯分析

並列摘要

ABSTRACT

With the technology advances, the CRT(Cathode Ray Tube) display has been replaced by the Liquid Crystal Display-LCD in recent years. LCD displays are generally light, thin and small both in the weight and volume. Besides, all these features plus the low power consumption and low radiation have driven it as the mainstream in the displays’ market. However, the LCD itself is not a light emitting device; it has to rely on the back light module to provide the light source. The back light module, as the core component in LCD display, consists of light guide plate, reflector, diffuser, prism sheet as well as the housing and frame. It functions in guiding line-light source (either Cold cathode fluorescent lamp -CCFL or Light emitting diode-LED) to propagate through the whole LCD display area and to turn into homogeneous and bright light.

The luminance, homogeneity, and high transfer rate are all indices in quality excellence of light guide plates. For example, those with high luminance and homogeneity always means high light efficiency and require fewer LED use whereby reducing the cost. The study investigates a variety of process parameters, such as mold temperature, material temperature, injection speed, and retaining pressure, in affecting the illumination of the light guide plate. The typical 2.83 inch light guide plates (62.94mm x 46.64mm x 0.45mm) are used as the test vehicle. First, the orthogonal array in the Taguchi method is used as the guide for the test arrangement. It is then found though the factorial response and variation analyses that mold temperature and material temperature dominate in influencing the illumination and homogeneity of the light guide plate. However, these two factors have opposite effects on homogeneity. Also, the homogeneity and illumination at central areas of LCD become worse with higher mold and material temperature.

The normal Taguchi method is mainly used for solving single characteristic of quality. Nevertheless, the optical performance of light guide plate is affected by multiple factors. It then incorporates the grey relational analysis technique to optimize multiple process parameters in the injection of light guide plate. It is known that the Taguchi method has advantage of reducing the number of test and thus also saving the corresponding test time. The test results out of it are analyzed further through the grey relational analysis for obtaining the best combinations of those processing parameters. The corresponding results for illumination are even proved to be repeatable within a confidence interval of 95%.

Keywords: backlight module, grey relational analysis, light guide plate, Taguchi method

並列關鍵字

backlight module ； grey relational analysis ； light guide plate ； Taguchi method

參考文獻

17. 張自恭、林奇鋒、方育斌，「背光模組光學設計」，光連雙月刊，49期，pp.39-47, 2004。

7. N. Chang, I. Choi, and H. Shim, “DLS: Dynamic Backlight Luminance Scaling of Liquid Crystal Display,” IEEE Tran. VLSI, Vol. 12, No. 8, pp. 837-846, 2004.

8. T. Okumura, A. Tagaya, and Y Koike, “Highly-efficient backlight for liquid crystal display having no optical films,” Appl. Phys. Lett, Vol. 83, pp. 2515-2517, 2003.

9. D. Feng, Y. Yan, X. Yang, G. Jin, and S. Fan, “Novel integrated light-guide plate for liquid crystal display backlight ” Pure and Applied Optics,2005.

10. A. Funamoto and S. Aoyama, “LED backlight system with double prism,” Society of Iinformation Display, pp. 1045-1050, 2006.