Optical Compensation Polarizing Plate for IPS LCD Viewing Angles
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Solution Overview
Problem
Liquid crystal display units, particularly in the IPS mode, face challenges with narrow viewing angles due to light leakage and unignorable phase contrast caused by polarizing plates and protective films, which are unstable under temperature and humidity changes, leading to poor display performance.
Innovation Solution
An optical compensation polarizing plate is developed with a polarizer and an optical compensation layer laminated on transparent cellulose acylate films, where the films' retardation values and Nz factor are specifically optimized to minimize optical anisotropy and maintain stability across varying conditions, enhancing viewing angles and contrast without degrading frontal contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If an optical compensation sheet is provided between the polarizer and the liquid crystal cell to improve viewing angle characteristics, then the viewing angle is enlarged to a certain extent, but the display contrast and stability under environmental changes deteriorate
Solution Approach 1:
The patent merges the protective film and optical compensation sheet into a single integrated layer. The cellulose acylate film serves dual functions: protecting the polarizer while providing optical compensation. This eliminates the interface between separate components, ensuring uniform stress distribution and maintaining optical compensation effectiveness under environmental changes.
Solution Approach 2:
The patent uses cellulose acylate as a composite material that combines protective properties with optical compensation capabilities. By selecting specific cellulose acylate films with controlled retardation values (Re ≤ 10 nm, Rth ≤ 25 nm) and matching them with appropriate optical compensation layers, the system achieves both protection and optical performance stability.
2Strength
If a protective film is directly laminated on the polarizer to protect it from dimensional changes, then the polarizer is protected, but the phase contrast of the optical compensation sheet deteriorates due to deformation
Solution Approach 1:
The protective film and optical compensation sheet are merged into a single cellulose acylate layer, eliminating the deformation interface. This integrated structure ensures that stress is distributed uniformly throughout the film, preventing local deformation that would compromise optical compensation while maintaining protection against environmental factors.
3Reliability
If a TAC film is used as the protective film to avoid stress on the optical compensation sheet, then the phase contrast stability is improved, but the TAC film itself causes unignorable phase contrast that makes optical compensation design difficult
Solution Approach 1:
The patent changes the material parameter from TAC film to cellulose acylate film with specifically controlled optical properties. By selecting cellulose acylate films with retardation values satisfying Re ≤ 10 nm and Rth ≤ 25 nm, the system achieves both low phase contrast and stable optical compensation without the design complexities associated with TAC films.
4Manufacturing precision
If synthetic resin films are used as protective films to reduce phase contrast, then the phase contrast is lowered, but the adhesion to the polarizer deteriorates due to hydrophobic nature causing peeling
Solution Approach 1:
The patent changes the material from synthetic resin to cellulose acylate, which has different surface properties. Cellulose acylate provides sufficient adhesion to the polarizer while maintaining low phase contrast characteristics when properly selected (Re ≤ 10 nm, Rth ≤ 25 nm), avoiding the peeling problem of hydrophobic synthetic resins.
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 improved display contrast and viewing angle characteristics, achieving a wide viewing angle and high contrast ratio while maintaining stability under environmental changes, effectively addressing the limitations of existing IPS mode liquid crystal display units.
Implementation Method 1
an optical compensation layer having an Nz factor of 0.45 or more and an in-plane phase contrast Re1 of 100 nm or more is laminated on one side of the polarizing plate
Implementation Method 2
unignorable phase contrast caused by the homogeneously oriented liquid crystals and the transparent protective films
Implementation Method 3
at least one of the transparent protective films is a cellulose acylate film the retardation value in plane Re (expressed in nm) and the retardation value in the film thickness direction Rth (expressed in nm) of which fulfill the following formulae (I) and (II)
Data Source
AI summary
An optical compensation polarizing plate comprising: a first transparent protective film; a polarizer; a second transparent protective film; and an optical compensation layer in this order, wherein at least one of the first and second transparent protective films is a cellulose acylate film having a retardation value in plane Re (nm) and a retardation value in film thickness direction Rth (nm) which fulfill the following formulae (I) and (II), and Nz and Re1 defined by the following formulae (III) and (IV), of the optical compensation layer fulfill the following formulae (V) and (VI):(I) |Re|≦10, (II) |Rth|≦25, (III) Nz=(nx1−nz1)/(nx1−ny1), (IV) Re1=(nx1−ny1)×d1, (V) 0.4≦Nz≦0.6 (VI) 100≦Re1≦350, wherein Re1 is a retardation value in plane (nm) at a wavelength of 590 nm; Nz is an Nz factor at a wavelength of 590 nm; nx1 is a refractive index along a slow axis in a film plane; ny1 is a refractive index along a direction perpendicular to the slow axis in a film plane; nz1 is a refractive index along a thickness direction of the film; and d1 is a thickness of the film (nm).