Polymerizable Compounds for Stable Pretilt Angles in LC Media
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Solution Overview
Problem
Current liquid crystal (LC) displays, particularly those using the polymer-sustained alignment (PSA) mode, face issues such as inadequate tilt angles, high rotational viscosity, low voltage-holding ratio (VHR), image sticking, and sensitivity to UV radiation, which affect display reliability and performance.
Innovation Solution
The use of specific polymerizable compounds, such as those of formulas I and II, in combination with self-alignment additives, enables quick and complete UV-photopolymerization, reducing residual unpolymerized materials and improving pretilt angle stability, while also allowing for UV processing without photoinitiators, thus enhancing VHR and reducing image sticking and mura occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymerizable compounds are used in PSA mode, then the display can achieve vertical alignment, but the tilt angle is inadequate and rotational viscosity is high
Solution Approach 1:
The patent modifies the chemical structure of polymerizable compounds by introducing specific functional groups (cyanoacrylate, acrylate, methacrylate) and adjusting molecular parameters (melting point below 50°C, specific molecular weight ranges) to optimize the balance between alignment quality and response time performance
Solution Approach 2:
The invention uses composite LC media comprising multiple components: cyclic carbonate compounds (5-30 wt%), polymerizable compounds (1-10 wt%), and liquid crystal compounds, creating a synergistic material system that achieves both adequate tilt angles and reduced rotational viscosity
2Reliability
If conventional polymerizable compounds are used, then polymerization can occur, but VHR is low and image sticking occurs
Solution Approach 1:
The patent employs transient radical initiators that decompose completely during polymerization, leaving no harmful residues that would cause image sticking or reduce VHR, thus eliminating long-term degradation effects
Solution Approach 2:
The invention optimizes polymerization parameters by selecting specific initiators (peroxide, azo compound, photopolymerizer) and controlling polymerization conditions (temperature, time, UV exposure) to achieve complete polymerization without residual effects that would harm display performance
3Productivity
If UV processing is performed with photoinitiators, then polymerization is efficient, but sensitivity to UV radiation increases
Solution Approach 1:
The patent removes photoinitiators from the LC medium composition, eliminating the source of UV sensitivity while maintaining polymerization capability through alternative initiators that do not require photoinitiator addition
Solution Approach 2:
The LC medium performs self-initiation of polymerization through built-in initiators or radical generation mechanisms that activate without external photoinitiator addition, making the system self-sufficient and eliminating UV sensitivity issues
4Reliability
If residual unpolymerized materials remain, then polymerization is incomplete, but pretilt angle stability deteriorates
Solution Approach 1:
The patent implements multi-stage polymerization processes including pre-polymerization, main polymerization, and post-curing steps that continuously drive the reaction to completion, ensuring all polymerizable compounds are fully converted to stable polymers
Solution Approach 2:
The invention optimizes polymerization parameters by adjusting temperature profiles, time durations, UV intensity, and initiator concentrations to achieve complete conversion while maintaining pretilt angle stability and eliminating residual materials
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
This approach results in improved VHR, reduced image sticking and mura, faster response times, and increased reliability, with the ability to use longer UV wavelengths for polymerization, leading to more efficient and cost-effective display production.
Implementation Method 1
The use of specific polymerizable compounds, such as those of formulas I and II, in combination with self-alignment additives, enables quick and complete UV-photopolymerization
Data Source
AI summary
The present invention relates to liquid crystal (LC) media comprising several polymerizable compounds and an additive for vertical alignment as further specified in the description or claims. The media are adapted for use in LC displays, especially in LC displays of the polymer-sustained alignment type while omitting one or both of the conventional alignment layers.