| Summary: | 博士 === 國立交通大學 === 材料科學與工程學系所 === 103 === In this study, we combine the stress measurement using bending beam technique with static thermal-dependent and transient time-dependent three-dimensional (3D) finite element analysis (FEA) analysis to examine the light leakage variation of the thin-film transistor liquid-crystal display (TFT-LCD) panel. The objective is to understand the effects of material properties of key components, temperature, and humidity under hygrothermal reliability test on the light leakage phenomena. The shrinkage stress in stretched poly(vinyl alcohol) (PVA) film and stress relaxation ability of pressure-sensitive adhesives (PSA) layers are found to be the key factors determining the stress distribution and out-of-plane displacement of a polarizer stack. For hard-type PSA, its polarizer stack generates the highest bending curvature with maximum out-of-plane displacement but minimum in-plane displacement, leading to anisotropic stress distribution with high stress around the edges. On the other hand, polarizer stack with soft-type PSA yields the maximum in-plane displacement but the minimum out-of-plane displacement, resulting in isotropic stress distribution.
3D FEA shows that a strong correlation exists between light leakage and retardation difference induced by stress on triacetyl cellulose (TAC) films. For hard-type PSA, the area of higher principal stress difference is relatively small and localized on the edges of the panel, thus indicating low dimensional variations. In contrast, funnel-type light leakage and greater polarizer shrinkage are found for soft-type PSA. Moreover, the magnitude of hygroscopic stress in the simulated analysis is found to be significantly higher than that of thermal stress. This can be attributed to moisture’s plasticizing effect on the hydrophilic polymers such as PVA and PSA layers, leading to enhanced stress relaxation and degradation of the display image quality. An increase in Young’s modulus of PSA brings in lower relaxation ability and better resistance to shrinkage in polarizer stack, making it an effective solution to minimize the light leakage. The other effective solution is to develop a TAC film with lower Young’s modulus and/or lower coefficient of thermal expansion (CTE).
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