Liquid Crystal Panel Optical Compensation Layers
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Solution Overview
Problem
Conventional liquid crystal panels in VA-mode or OCB-mode suffer from light leakage due to birefringence and axis displacement of polarizing plates, leading to inadequate screen contrast, significant color shift, and display unevenness.
Innovation Solution
A liquid crystal panel design incorporating a first and second optical compensation layer with specific refractive index profiles and photoelastic coefficients, placed between polarizers, to enhance screen contrast and reduce color shift and display unevenness without complex additions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If biaxial optical compensation plates with nx>ny>nz are used to compensate for light leakage, then light leakage from polarizing plates is reduced, but screen contrast enhancement, color shift reduction, and display unevenness suppression remain insufficient
Solution Approach 1:
The optical compensation function is divided into two separate layers: a first optical compensation layer with nx>ny>nz to compensate for polarizing plate axis displacement, and a second optical compensation layer with nx=ny>nz to compensate for liquid crystal birefringence. This segmentation allows each layer to specialize in compensating for specific optical defects, achieving superior overall performance compared to using a single biaxial compensation plate.
Solution Approach 2:
The invention uses composite optical compensation structures combining two different types of optical compensation layers with distinct refractive index characteristics. The first layer uses materials with biaxial optical properties (nx>nymaximum in-plane retardation of 90 nm or more and minimum in-plane retardation of 30 nm or less at 550 nm wavelength), while the second layer uses materials with uniaxial optical properties (nx=nymaximum in-plane retardation of 90 nm or more and thickness direction retardation Rth greater than 5 nm at 550 nm wavelength). This composite approach enables simultaneous compensation for both polarizing plate axis displacement and liquid crystal birefringence effects.
2Device complexity
If conventional single optical compensation layer designs are used, then device complexity is low, but display unevenness and color shift occur under oblique viewing conditions
Solution Approach 1:
The invention applies different optical compensation characteristics to different locations in the optical path. The first optical compensation layer is positioned on the viewer side with specific biaxial properties (nx>nymaximum in-plane retardation of 90 nm or more and minimum in-plane retardation of 30 nm or less at 550 nm), while the second optical compensation layer is positioned on the backlight side with uniaxial properties (nx=nymaximum in-plane retardation of 90 nm or more and thickness direction retardation Rth greater than 5 nm at 550 nm). This local differentiation of optical properties enables effective compensation for viewing angle-dependent display defects without requiring overly complex overall structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed design significantly enhances screen contrast, minimizes color shift, and suppresses display unevenness by optimizing the optical compensation layers' properties, resulting in improved performance without adding intricate mechanisms.
Implementation Method 1
the polarization state of light from the oblique direction changes due to the birefringence of liquid crystal, which generates light leakage from polarizing plates
Implementation Method 2
The first optical compensation layer has an absolute value of a photoelastic coefficient of 40×10−12 (m2/N) or less
Data Source
AI summary
There are provided a liquid crystal panel and a liquid crystal display apparatus each having an excellent screen contrast, a small color shift, and small display unevenness. The liquid crystal panel includes a liquid crystal cell, a first polarizer, a second polarizer, a protective layer, a first optical compensation layer and a second optical compensation layer. The protective layer has relationships of 0 nm≦Δnd (550)≦10 nm and 0 nm≦Rth(550)≦20 nm. The first optical compensation layer has an absolute value of a photoelastic coefficient of 40×10−12 (m2/N) or less, and has relationships of Δnd(380)<Δnd(550)<Δnd(780), nx>ny≧nz and 90 nm≦Δnd(550)≦200 nm. The second optical compensation layer has relationships of Rth(380)>Rth(550)>Rth(780) and nx=ny>nz.