Optical Laminate Birefringence Control for LCD Viewing Angle
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Solution Overview
Problem
Existing liquid crystal display devices face challenges in maintaining sufficient contrast when viewed from oblique angles due to uneven optical compensation, particularly with films exhibiting birefringence, which are prone to breaking during stretching and result in fluctuated phase contrast.
Innovation Solution
An optical laminate comprising a layer with negative intrinsic birefringence and a transparent resin layer with no orientation, where the in-plane retardation of the negative birefringence layer is greater than that of the transparent resin layer, and satisfying specific refractive index and glass transition temperature conditions, is used to enhance optical compensation and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a film exhibiting birefringence is used for optical compensation, then the contrast can be improved, but the film is prone to breaking during stretching and results in fluctuated phase contrast
Solution Approach 1:
The patent uses a composite optical laminate structure comprising a biaxially stretched film (first film) and a uniaxially stretched film (second film) with different birefringence characteristics. The biaxially stretched film provides isotropic optical compensation, while the uniaxially stretched film provides anisotropic compensation. This composite structure achieves the desired phase contrast without requiring high-stretching ratios that would cause film breaking, thereby resolving the contradiction between contrast improvement and film strength.
2Reliability
If the transmission axes of two polarizer plates are arranged perpendicular to each other, then sufficient contrast can be obtained in horizontal and vertical directions, but the contrast decreases when viewed from oblique directions
Solution Approach 1:
The patent applies different optical compensation characteristics to different regions and directions by combining biaxial stretching (affecting both horizontal and vertical directions equally) with uniaxial stretching (affecting specific directions). This allows the optical laminate to provide tailored phase compensation for different viewing angles, maintaining contrast performance across wide viewing angles while preserving the perpendicular polarizer configuration.
3Reliability
If a shrinking film is adhered to resin film to form laminate and stretched under heating, then birefringence can be achieved, but the production process becomes complicated
Solution Approach 1:
The patent achieves the desired birefringence by controlling the stretching ratios and temperatures during the stretching process, rather than relying on complex multi-step processes involving shrinking films. By optimizing the stretching parameters (ratio, temperature, humidity), the patent obtains films with controlled birefringence values that satisfy the optical compensation requirements, thereby simplifying the production process while maintaining optical performance.
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 provides a stable and uniform phase contrast with minimal brightness unevenness across various viewing angles, improving the contrast and field angle of liquid crystal display devices, particularly in the in-plane switching mode.
Implementation Method 1
an optical laminate which enables optical compensation in accordance with the mode of the liquid crystal display by the three dimensional control of the refractive index
Data Source
AI summary
An optical laminate having layer A having a resin having a negative intrinsic birefringence and at least one layer B having a transparent resin, having substantially no orientation and laminated at least on one face of layer A and satisfies a relation |Re(A)|>|Re(B)|, wherein Re(A) and Re(B) represent in-plane retardations of layer A and layer B, respectively, measured with light having a wavelength of 400 to 700 nm, an optical element having a laminate of the optical laminate and a polarizer plate, and a liquid crystal display device using at least one sheet of the optical laminate. In the liquid crystal display device, optical compensation can be made in accordance with the mode of the liquid crystal display by the three dimensional control of the refractive index, and the liquid crystal display device provides an image display with liquid crystals exhibiting small change in the phase contrast depending on the viewing angle.