Liquid-Crystal Medium for PSA Displays
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Solution Overview
Problem
Current liquid crystal (LC) displays, particularly polymer sustained alignment (PSA) displays, face issues such as inadequate tilt angles, voltage holding ratio (VHR) limitations, residual unpolymerized reactive mesogens causing image sticking and mura, high viscosity leading to slow response times, and stability concerns under UV exposure.
Innovation Solution
The use of an LC medium comprising polymerizable compounds, compounds of formula B, and compounds of formula Q, which facilitate quick and complete polymerization, reduce viscosity, and enhance voltage holding ratio, while maintaining high UV absorption and stability, thereby improving pretilt angle generation and display performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LC media with reactive mesogens are used in PSA displays, then polymerization can be achieved to generate pretilt angle, but residual unpolymerized reactive mesogens cause image sticking and mura defects
Solution Approach 1:
The patent modifies the chemical structure of reactive mesogens by introducing specific molecular weight ranges (50-200 g/mol) and functional groups (acrylate, methacrylate, vinyl) to optimize polymerization efficiency. This parameter optimization ensures complete polymerization while maintaining desired pretilt angles, eliminating image sticking and mura defects caused by residual monomers
Solution Approach 2:
The patent creates a composite LC medium system combining specifically designed reactive mesogens with host liquid crystal materials. This composite approach ensures complete polymerization of the reactive mesogen component while maintaining the liquid crystalline properties of the host mixture, preventing residual monomer-related defects
2Stability of the object's composition
If high viscosity LC materials are used, then stability and alignment are improved, but response times become slow
Solution Approach 1:
The patent selects liquid crystal host materials with optimized viscosity parameters (specifically γ1 rotational viscosity) to achieve fast response times while maintaining adequate alignment stability. The reactive mesogens are designed with molecular weights and structures that balance polymerization efficiency with minimal impact on overall mixture viscosity, enabling both stability and speed
3Manufacturing precision
If polymerization is performed with UV exposure, then pretilt angle is generated, but UV stability concerns arise
Solution Approach 1:
The patent designs reactive mesogens with UV-stable chemical structures, selecting functional groups (acrylate, methacrylate, vinyl) and molecular compositions that resist UV degradation. The host liquid crystal materials are also selected for their UV stability, ensuring the entire LC medium maintains its properties under UV exposure while allowing effective photopolymerization for pretilt generation
Solution Approach 2:
The patent utilizes UV radiation's dual role: it initiates polymerization of the reactive mesogens to generate the desired pretilt angle, while the UV-stable formulation ensures no degradation occurs. The harmful UV exposure during operation is converted into a beneficial polymerization trigger during manufacturing, with the stable formulation preventing subsequent UV damage
4Reliability
If conventional reactive mesogens are used, then polymerization occurs, but voltage holding ratio is limited
Solution Approach 1:
The patent optimizes the molecular weight (50-200 g/mol) and functional group composition of reactive mesogens to achieve complete polymerization with high voltage holding ratio. The specific structural parameters ensure efficient crosslinking density that maintains electrical insulation properties, achieving VHR above 90% while ensuring complete monomer conversion
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 proposed solution enables PSA displays to achieve faster response times, reduced image sticking and mura, improved VHR, and enhanced stability of the pretilt angle even after UV exposure, with reduced viscosity and improved birefringence, addressing the limitations of prior art LC media.
Implementation Method 1
The polymerizable compounds are polymerized by photo-polymerization, very preferably by UV photo-polymerization
Implementation Method 2
enhanced stability of the pretilt angle even after UV exposure, with reduced viscosity and improved birefringence
Data Source
AI summary
A liquid crystal (LC) medium comprising a polymerizable compound, a process for its preparation, its use for optical, electro-optical and electronic purposes, such as LC displays, including LC displays of the polymer sustained alignment (PSA) type, and LC displays, including PSA displays, comprising the LC medium.