偏光板元件之熱機械性質與黏彈特性對TFT-LCD漏光現象之探討

Abstract

偏光板漏光 (polarizer light leakage) 是指在液晶顯示器 (LCD)面板上亮度不均勻的瑕疵。 主要原因為經過了溼熱穩定度測試或是一般面板製程後，偏光板中的polyvinyl alcohol (PVA)層會收縮，造成整體偏光板的位移和應力集中。隨著面板尺寸增大將使得偏光板漏光更加嚴重，如何改善偏光板材料以增加其可靠度是目前研發工作的主要課題。 本論文利用微拉力機(MTS)、熱機械分析儀(TMA)、動態機械分析儀 (DMA)與光學彎曲測定儀(bending beam system)，實際量測偏光板中各主要材料的熱機械與黏彈性質，結合商業模擬軟體ANSYSTM以有限元素分析法(FEM)，建立三維的數值模型來計算LCD面板在經過溼熱穩定測試之後所產生的應力與應變，研究其與漏光現象的相關性，並且探討偏光板所引起漏光現象的成因。接著研究TAC與PSA層之熱機械與黏彈特性對於偏光板漏光現象的影響。 根據實驗與模擬計算的結果，發現偏光板中TAC層的應力分佈和漏光現象有高度的相關性。根據分析結果，濕熱穩定度測試所產生的應力，造成TAC層的光位相差效應為偏光板漏光的根本原因。另一方面，PSA膠的應力釋放能力(stress relaxation)為偏光板漏光隨著穩定度測試時間改變的主要原因。根據模擬計算結果，藉由增加PSA的楊氏係數可以有效減少偏光板的收縮，並且減少面板中央的漏光現象。而降低TAC層的熱膨脹係數或楊氏係數可以有效改善偏光板的漏光程度。最後本論文根據數值分析的結果，提出使用低吸水率與低應力釋放的PSA膠可以改善偏光板的漏光現象。

Polarizer light leakage occurred on LCD panel after thermal and/or moisture reliability test, since the shrinkage of the PVA film induced stress and strain generated in the polarizer. Light leakage deteriorated as larger panels were introduced for better visual quality. Therefore, how to improve the material properties of polarizer components is one of the critical tasks in current research. In this study, 3-D finite element analysis models using ANASYSTM was first established to examine the stress and deformation of the polarizer after the reliability test in order to explore their correlation with the light leakage phenomenon. In addition to have the accurate result, MTS, TMA, DMA and home made bending beam system were used for measuring the thermomechanical and viscoelastic properties of polarizer components for simulation input. Specifically, the root cause of polarizer light leakage was examined and proposed. Then, the impact of thermomechanical and viscoelastic properties of PSA and TAC was investigated. Based on experimental data and numerical analysis, a strong relationship among light leakage and stress distribution on the TAC film has been established. Beside, the root cause of polarizer light leakage is proposed. The polarizer light leakage appeared due to the retardation difference in the TAC film induced by thermal and/or moisture shrinkage of the polarizer. Moreover, the stress relaxation behavior of PSA has been found to be the critical factor for affecting the time-dependent polarizer light leakage variation. Numerical modeling was also utilized to analyze the material design direction on polarizer light leakage improvement. Increasing the Young’s modulus of the PSA layer can effectively reduce the shrinkage of polarizer and also diminish center light leakage of the panel, and an effective solution can be achieved with low modulus and/or low CTE TAC film. Finally, using low stress relaxes ability and low moisture absorbability PSA layer can provide stable display quality.