Liquid Crystal Medium for PSA Displays
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current liquid crystal (LC) media for polymer sustained alignment (PSA) displays face issues such as inadequate tilt angles, high rotational viscosity, voltage holding ratio (VHR) limitations, image sticking, and increased production costs due to incomplete polymerization and residual unpolymerized reactive mesogens (RMs), leading to suboptimal display performance and stability.
Innovation Solution
A liquid crystal medium comprising a host mixture without terphenyl compounds, incorporating polymerizable compounds with two or three reactive groups, which enables quick and complete UV-photopolymerization at lower energy, reducing viscosity and enhancing VHR, while minimizing residual RMs and image sticking, and improving pretilt angle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional LC media with terphenyl compounds and single-reactive-group RMs are used, then the LC medium can be formulated with standard components, but polymerization is incomplete requiring high energy UV irradiation which causes image sticking and mura effects
Solution Approach 1:
The patent changes the chemical structure parameters of RMs from single-reactive-group to multi-reactive-group (two or three reactive groups per molecule), which fundamentally alters the polymerization kinetics and completeness, enabling rapid and complete polymerization at lower UV energy levels without causing image sticking or mura effects
Solution Approach 2:
The patent creates a composite LC medium formulation combining host mixture without terphenyl compounds with multi-reactive-group RMs, achieving synergistic effects that improve polymerization completeness while reducing harmful side effects through the specific composition ratio and component selection
2Reliability
If high energy UV irradiation is applied to ensure complete polymerization, then polymerization completeness improves, but image sticking and mura effects increase
Solution Approach 1:
The patent changes the reactive group multiplicity parameter of RMs, which modifies the polymerization reaction pathway and kinetics, allowing complete polymerization to occur at lower UV energy levels, thereby eliminating the need for high energy irradiation that causes image sticking
3Ease of manufacture
If terphenyl compounds are included in the host mixture, then standard LC formulations can be used, but viscosity increases and response times slow down
Solution Approach 1:
The patent extracts/removes terphenyl compounds from the host mixture formulation, eliminating their detrimental effect on viscosity and response time while maintaining formulation effectiveness through the use of alternative host compounds and multi-reactive-group RMs
4Device complexity
If conventional RMs with one reactive group are used, then formulation is simpler, but polymerization is incomplete and residual RMs cause instability
Solution Approach 1:
The patent changes the reactive group count parameter from one to two or three per RM molecule, which fundamentally improves polymerization completeness and display stability. The increased complexity in reactive group structure is offset by the elimination of formulation adjustments needed for incomplete polymerization
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 achieves reduced viscosity, high VHR, fast response times, low threshold voltage, and improved pretilt angle stability, reducing image sticking and mura effects, thus enhancing the reliability and performance of PSA displays.
Implementation Method 1
enables quick and complete UV-photopolymerization at lower energy
Data Source
AI summary
The present invention relates to a liquid crystal (LC) medium comprising a terphenyl compound and at least two polymerisable compounds, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in an LC display of the polymer sustained alignment (PSA) type, and to an LC display, especially a PSA display, comprising it.