Polarizing Plate Retardation Control for LCD Iridescent Unevenness
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Solution Overview
Problem
Liquid crystal displays (LCDs) face issues with iridescent unevenness due to the high birefringence of polyester films used as polarizer-protective films, which affects visibility, especially as brightness and color purity increase, and existing solutions to mitigate this issue are insufficient.
Innovation Solution
A liquid crystal display design that incorporates a first polarizing plate with a protective film having specific optical properties, including an in-plane retardation of 0 nm to 3000 nm, a thickness direction retardation greater than 2500 nm, and a refractive index ratio that minimizes birefringence-induced polarization changes, using aromatic polyester films like polyethylene terephthalate or polyethylene naphthalate, to prevent iridescent unevenness without compromising mechanical or chemical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyester film is used as a polarizer-protective film, then mechanical properties and chemical resistance are improved, but iridescent unevenness occurs due to high birefringence
Solution Approach 1:
The patent applies parameter changes by precisely controlling the in-plane retardation (Re) and thickness direction retardation (Rth) values of the protective film. By setting Re within 0-3000 nm and Rth > 2500 nm, the patent modifies the optical parameters of the polyester film to reduce birefringence effects while maintaining mechanical strength, thereby eliminating iridescent unevenness without sacrificing mechanical properties.
2Strength
If a polyester film with high birefringence is used, then mechanical strength is improved, but polarization is distorted between the polarizer and liquid crystal cell
Solution Approach 1:
The patent modifies the optical parameters of the protective film by controlling the in-plane retardation (Re) and thickness direction retardation (Rth) to specific ranges. This parameter optimization reduces the birefringence effect that causes polarization distortion, while maintaining the mechanical strength benefits of polyester films.
3Object-affected harmful factors
If a light scattering layer is provided on the surface of the protective film, then iridescent unevenness becomes less visible, but sufficient visibility cannot be obtained when brightness and color purity increase
Solution Approach 1:
Instead of using a light scattering layer to mask the iridescent unevenness, the patent converts the harmful birefringence effect into a beneficial outcome by precisely controlling the retardation parameters. By setting Re within 0-3000 nm and Rth > 2500 nm, the patent eliminates the root cause of iridescent unevenness, allowing high brightness and color purity displays to maintain sufficient visibility without requiring light scattering layers.
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 effectively prevents iridescent unevenness in LCDs, enhancing visibility and maintaining the mechanical and chemical resistance properties of the polarizer-protective films, even under harsh environments.
Implementation Method 1
the polyester film has high birefringence in the in-plane direction and the thickness direction, because its intrinsic birefringence is high and is highly stretched
Implementation Method 2
it is proposed that a light scattering layer should be provided on the surface of a polarizer-protective-film
Data Source
AI summary
Provided is a liquid crystal display in which occurrence of iridescent unevenness is suppressed, even when a film with high level of mechanical properties, chemical resistance and water-barrier properties is used as a polarizer-protective-film. Also, disclosed is a polarizing plate to be used in the liquid crystal display. The liquid crystal display includes a liquid crystal cell, a light source, a first polarizing plate placed between the liquid crystal cell and the light source, and a second polarizing plate placed on a viewer side of the liquid crystal cell. The first polarizing plate includes a polarizer and a first protective film placed on a light source side principal surface of the first protective film, and the first protective film satisfies following relations: (i) 0 nm≦Re1≦3000 nm; (ii) Nz1≧5; and (iii) Rth1>2500 nm.