Biaryl Polymerizable Compounds for PSA Liquid Crystal Displays
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Solution Overview
Problem
Current PSA displays, particularly VA and OCB types, face challenges with limited selection criteria for suitable polymerizable compounds, high switching times, low threshold voltages, and reduced viewing angle independence of contrast and grayscale, especially when using UV light without photoinitiators.
Innovation Solution
Incorporating a racemate of chiral polymerizable compounds with a biaryl structural element into the liquid crystal medium, which allows for pretilt angle setting without photoinitiators, enhancing specific resistance, switching times, and voltage holding ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional VA displays with uniform orientation are used, then the FK molecules can be uniformly oriented, but the viewing angle independence of contrast and grayscale is limited and additional surface treatment (rubbing) is necessary
Solution Approach 1:
The invention changes the physical-chemical parameters of the FK medium by introducing polymerizable compounds with specific molecular structures (rigid core, flexible spacer, polymerizable group) and controlling their concentration (0.1-10 wt%). This enables the medium to form polymer networks that sustain alignment without requiring additional surface treatment, thereby improving viewing angle independence while simplifying manufacturing
Solution Approach 2:
The invention creates a composite FK medium by combining low-molecular-weight liquid crystal compounds with polymerizable compounds. This composite system forms a polymer network within the FK medium that provides both the liquid crystalline properties and the alignment stabilization function, eliminating the need for separate surface treatment steps
2Reliability
If MVA displays with protrusions on both electrodes are used, then controlled switching and viewing angle improvement are achieved, but light transmission is reduced
Solution Approach 1:
The invention changes the electrical and optical parameters of the FK medium through the addition of polymerizable compounds. The polymer network formed adjusts the dielectric anisotropy and viscosity, enabling controlled switching with reduced electrode structuring, which in turn improves light transmission while maintaining viewing angle performance
3Illumination intensity
If the distances between slits and protrusions are increased to improve light transmission, then light transmission improves, but switching times increase
Solution Approach 1:
The invention changes the viscosity and dielectric properties of the FK medium by incorporating polymerizable compounds at optimized concentrations. This allows for larger electrode pitch distances that improve light transmission while the modified medium properties maintain fast switching speeds through reduced rotational viscosity and optimized dielectric anisotropy
4Reliability
If PSA displays with polymerizable compounds are used, then pretilt angle control and alignment stability are improved, but the selection criteria for suitable compounds are limited and UV polymerization requires photoinitiators
Solution Approach 1:
The invention defines specific parameter ranges for polymerizable compounds including molecular structure (rigid core + flexible spacer + polymerizable group), concentration (0.1-10 wt%), and glass transition temperature (-50 to 50°C). These parameter specifications expand the selection of suitable compounds while ensuring reliable alignment stability and pretilt control
Solution Approach 2:
The invention enables the FK medium to perform its own polymerization function by incorporating compounds that can polymerize under UV light. The polymerizable compounds within the medium itself serve as the polymerizing agents, eliminating the need for separate photoinitiator additives and enabling direct UV crosslinking for alignment stabilization
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 use of biaryl-based polymerizable compounds improves the display's performance by reducing switching times, increasing contrast and luminance, and providing a wide viewing angle with stable performance after UV exposure.
Implementation Method 1
Incorporating a racemate of chiral polymerizable compounds with a biaryl structural element into the liquid crystal medium, which allows for pretilt angle setting without photoinitiators
Implementation Method 2
PSA (polymer sustained alignment) type
Data Source
AI summary
Polymerizable compounds (II) comprising polymerizable groups bonded to a biaryl structure (I), either directly or via an organic group or spacer group, are new. Polymerizable compounds comprising polymerizable groups bonded to a biaryl structure of formula (I), either directly or via an organic group or spacer group, are new. A, B : optionally substituted aromatic or at least partially saturated rings in which CH groups can be replaced by N and CH 2 groups can be replaced by O or S. Independent claims are also included for: (1) liquid crystal medium comprising a polymerized compound (II); (2) liquid crystal display of the polymer sustained alignment type comprising a liquid crystal medium as above in a cell between two substrates, including a transparent substrate and a substrate with an electrode layer, where the compound (II) is polymerized within the cell by applying an electrical voltage. [Image].