Liquid-Crystal Medium Polymerization Stability
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Solution Overview
Problem
Current liquid-crystal (LC) displays face challenges in achieving high specific resistance, short response times, low threshold voltage, high birefringence, and stability at low temperatures, while maintaining reliability and preventing issues like 'image sticking' and 'ODF mura', especially when using polymerizable mesogenic compounds that react with UV light, particularly at shorter wavelengths.
Innovation Solution
Development of an LC medium comprising specific polymerizable compounds and mesogenic compounds that allow for high specific resistance, rapid polymerization, and stability, even at longer UV wavelengths, with a formulation that includes compounds of formulas IA, IB, and IC, which enable quick and complete polymerization and reduce tilt angle generation, while minimizing residues and enhancing tilt stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If shorter UV wavelengths are used to polymerize RMs, then polymerization efficiency is improved, but reliability decreases due to reaction with polyimide alignment layer
Solution Approach 1:
The patent changes the UV wavelength parameter from shorter wavelengths (e.g., 300-320nm) to longer wavelengths (340-380nm, preferably 365nm). This parameter change allows efficient polymerization of RMs while avoiding the harmful reaction with polyimide alignment layer that occurs at shorter wavelengths, thus resolving the contradiction between polymerization efficiency and reliability
Solution Approach 2:
The patent introduces alternative compounds (compounds of formulae IA, IB, IC) that can serve as substitutes for traditional alkenyl compounds. These compounds enable polymerization at longer UV wavelengths, effectively replacing the problematic shorter wavelength UV light source and eliminating the reliability issue while maintaining polymerization efficiency
2Speed
If alkenyl compounds are used to reduce response times, then response time is improved, but reliability decreases due to UV light reaction
Solution Approach 1:
The patent replaces alkenyl compounds with compounds of formulae IA, IB, and IC that do not react with UV light at 340-380nm wavelengths. This substitution maintains the fast response time benefit while eliminating the reliability problem caused by UV-induced reactions, effectively resolving the contradiction
3Reliability
If UV intensity is reduced to prevent harmful reactions, then reliability is improved, but polymerization completeness worsens
Solution Approach 1:
The patent changes the UV wavelength parameter to 340-380nm (preferably 365nm) where the compounds of formulae IA, IB, and IC have appropriate absorption characteristics. This allows using higher UV intensity for complete polymerization without causing the harmful reactions that occur at shorter wavelengths, thus resolving the contradiction between reliability and polymerization completeness
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 LC medium exhibits high transmittance, contrast ratio, reduced image sticking and ODF mura, fast response times, and strong tilt generation with minimal polymerization residues, ensuring high reliability and stability across various temperature conditions.
Implementation Method 1
After filling the LC medium into the display the RMs are then polymerized in situ by UV photopolymerization
Data Source
AI summary
The present invention relates to a liquid-crystal (LC) medium comprising polymerizable compounds, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the PSA (polymer sustained alignment) or SA (self-aligning) mode, to an LC display of the PSA or SA mode comprising the LC medium, and to a process of manufacturing the LC display.