Optical Compensation Sheet for VA Mode LCDs
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Solution Overview
Problem
Existing optical compensation films for VA mode liquid crystal displays are insufficient in reducing viewing-angle dependence of hue and fail to maintain high-quality images when viewed from oblique directions.
Innovation Solution
An optical compensation sheet comprising a cellulose acylate film with specific optical anisotropy and an optically anisotropic layer, where the retardations are controlled to ensure ideal wavelength dispersion characteristics, reducing hue changes when viewed from different angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical compensation films are used, then contrast improvement is achieved, but viewing-angle dependence of hue is not reduced
Solution Approach 1:
The patent changes the optical parameters of the compensation film by precisely controlling the wavelength dispersion characteristics of retardation. Specifically, it sets the in-plane retardation Re and thickness-direction retardation Rth to satisfy specific relationships at different wavelengths (446nm, 590nm, 749nm), thereby reducing hue changes when viewed from oblique directions while maintaining contrast improvement
Solution Approach 2:
The patent uses a composite structure combining cellulose acylate film with specific optical anisotropy and an optically anisotropic layer. This composite material design allows simultaneous achievement of contrast improvement and reduced viewing-angle dependence of hue by coordinating the optical properties of different layers
2Manufacturing precision
If stretching method with retardation developing agent is used, then in-plane retardation is controlled, but range of retardation control is limited
Solution Approach 1:
The patent extends the range of retardation control by changing multiple optical parameters simultaneously - controlling both in-plane retardation Re and thickness-direction retardation Rth to satisfy specific wavelength dispersion relationships. This approach overcomes the limitations of conventional single-parameter control methods
Solution Approach 2:
The patent adds the dimension of thickness-direction retardation control to the conventional in-plane retardation control. By controlling both Re and Rth with specific wavelength dispersion characteristics, it achieves broader retardation control range and reduced viewing-angle dependence of hue
3Measurement precision
If polymer film with wavelength dispersion control is used, then contrast is improved, but hue changes by viewing angles are not reduced
Solution Approach 1:
The patent changes the wavelength dispersion parameters of retardation by setting specific relationships between Re and Rth at different wavelengths. The key innovation is making Re smaller on the short-wavelength side than on the long-wavelength side, which reduces hue changes by viewing angles while maintaining contrast improvement
Solution Approach 2:
The patent inverts the conventional approach to wavelength dispersion control. Instead of making Re larger on the short-wavelength side, it makes Re smaller on the short-wavelength side by controlling the relationship between in-plane and thickness-direction retardation, thereby reducing viewing-angle dependence of hue
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 solution ensures high-quality images with minimal hue changes when viewed from oblique directions by controlling the wavelength dispersion of retardation, improving contrast and viewing-angle dependence in liquid crystal displays.
Implementation Method 1
a cellulose acylate film having optical anisotropy
Implementation Method 2
the birefringent films whose in-plane retardation and thickness-direction retardation are controlled
Implementation Method 3
the change in hue is ascribable to a change in wavelength dispersion
Data Source
AI summary
An optical compensation sheet is provided and includes: a cellulose acylate film having optical anisotropy and meeting all of requirements represented by the following expressions (1) to (3); and an optically anisotropic layer having a slow axis orthogonal to a slow axis of the cellulose acylate film.2.6≦X+Y<3.0 Expression (1)0≦X≦1.8 Expression (2)1.0≦Y<3.0 Expression (3)X represents a substitution degree of acetyl group and Y represents a total sum of substitution degrees of propionyl, butanoyl, pentanoyl and hexanoyl groups.