VA Mode LCD Retardation Compensation for Viewing Angle
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Solution Overview
Problem
Liquid crystal displays face challenges in achieving a wide viewing angle and minimizing color shift at the black state, particularly in VA mode, where existing solutions fail to adequately compensate for oblique light incidence and maintain contrast ratio.
Innovation Solution
A liquid crystal display configuration with specific relationships between the in-plane retardation (Re) and thickness-direction retardation (Rth) of protective films and the liquid crystal cell's birefringence (Δnd), along with optimized polarizer arrangements and backlight color temperature, ensures wide viewing angles and reduced color shift at the black state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional optical compensation sheet (stretched birefringent film or liquid crystal coated film) is applied to a TN mode liquid crystal cell, then the viewing angle is expanded, but the contrast ratio deteriorates at oblique viewing angles and color shift occurs at the black state
Solution Approach 1:
The patent changes the liquid crystal display mode from TN to VA mode, which fundamentally alters the liquid crystal molecule alignment parameters. In VA mode, molecules are vertically aligned at the black state, creating different optical properties that inherently provide better contrast ratio at oblique angles while maintaining wide viewing angle capability
Solution Approach 2:
The patent employs a composite structure combining VA mode liquid crystal cell with specifically designed optical compensation sheets. The optical compensation sheets use cellulose acylate films with controlled retardation values (Re: 30-200 nm, Rth: 70-400 nm) that work synergistically with the VA mode liquid crystal to eliminate coloration and maintain contrast ratio across wide viewing angles
2Stability of the object's composition
If synthetic polymer films (polycarbonate or polysulfone) with high retardation values are used for optical compensation sheets, then optical anisotropy is achieved, but the film complexity and manufacturing difficulty increase
Solution Approach 1:
The patent changes the material parameter from synthetic polymers to cellulose acylate films, which can be processed more easily while achieving the required optical anisotropy through controlled stretching and orientation processes. The cellulose acylate films require lower processing temperatures and simpler handling procedures
Solution Approach 2:
The patent applies local quality by using cellulose acylate films with specifically controlled retardation parameters (Re: 30-200 nm, Rth: 70-400 nm) tailored for VA mode liquid crystal displays. This localized optimization of optical properties in the compensation sheet enables easier manufacturing while maintaining the required optical anisotropy
3Ease of manufacture
If cellulose acylate films are used for optical compensation, then manufacturing ease is improved, but the retardation value is insufficient for VA mode requirements
Solution Approach 1:
The patent changes the physical and optical parameters of cellulose acylate films through controlled stretching ratios, orientation treatments, and film thickness adjustments. By optimizing these parameters, the films achieve the required high retardation values (Re: 30-200 nm, Rth: 70-400 nm) while maintaining ease of manufacture and processing simplicity
Solution Approach 2:
The patent applies preliminary action by pre-orienting the cellulose acylate film molecules during film production through controlled stretching and heat treatment. This preliminary orientation establishes the required optical anisotropy and retardation values before the film is assembled into the liquid crystal display, simplifying subsequent manufacturing steps
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 configuration significantly enhances contrast ratio and eliminates coloration issues at oblique viewing angles, providing a more stable and vivid display experience.
Implementation Method 1
The optical compensation sheet is used to eliminate undesirable coloring of image or expand the viewing angle. As such an optical compensation sheet there is used a stretched birefringent film
Implementation Method 2
Liquid crystal displays have been widely used for monitor for personal computer and cellular phone, television, etc. because they are advantageous in that they can operate at low voltage with low power consumption
Data Source
AI summary
A liquid crystal display is provided and includes: a liquid crystal cell; a pair of polarizing plates disposed in cross-Nicol arrangement and sandwiching the liquid crystal cell. One of the pair of the polarizing plates has a protective film A for polarizer, disposed on the liquid crystal cell side, and the other of the pair has a protective film B for polarizer, disposed on a liquid crystal cell side. ReA(λ) and RthA(λ) of the protective film A, RthB(λ) of the protective film B and Δnd(λ) of the liquid crystal cell satisfy expressions (I) and (II) at a wavelength of 400 nm to 700 nm:0.74×(Δnd(λ)−RthB(λ))≦RthA(λ)≦0.97×(Δnd(λ)−RthB(λ)) (I)0.018×λ2/(Δnd(λ)−RthB(λ))+0.032×λ≦ReA(λ)≦0.036×λ2/(Δnd(λ)−RthB(λ))+0.032×λ (II).