Terphenyl LC Medium for PSA Displays
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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 high viscosities, which affect response times and stability, and often result in mura and reduced reliability due to uncontrolled polymerization and phase separation.
Innovation Solution
A liquid crystal medium comprising a terphenyl compound and polymerizable compounds with two or three reactive groups, which allows for quick and complete UV-photopolymerization at low energy, reducing viscosity and enhancing VHR, stability, and preventing image sticking and mura, while maintaining high birefringence and low threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LC media with higher polymerizable compound concentrations are used to ensure complete polymerization, then polymerization completeness improves, but rotational viscosity increases and response times worsen
Solution Approach 1:
The patent changes the chemical structure parameters of the polymerizable compounds by introducing terphenyl compounds with specific molecular configurations (formula T with various substituent patterns). This structural modification enables complete polymerization at lower concentrations (0.3-2.0 wt%) while maintaining low rotational viscosity and fast response times, resolving the contradiction between polymerization completeness and response speed
Solution Approach 2:
The patent creates a composite LC medium formulation combining terphenyl compounds (formula T) with specific liquid crystal hosts and polymerizable compounds. This composite approach achieves synergistic effects where the terphenyl structure promotes complete polymerization without the adverse viscosity effects of conventional formulations, simultaneously improving reliability and response time
2Stability of the object's composition
If higher concentrations of polymerizable compounds are used to stabilize alignment, then alignment stability improves, but rotational viscosity increases and response times worsen
Solution Approach 1:
The patent modifies the molecular parameters of the alignment-stabilizing compounds by using terphenyl structures with specific substituents (formula T). This enables effective alignment stabilization at low concentrations (0.3-2.0 wt%), avoiding the rotational viscosity penalty associated with higher concentrations of conventional stabilizers, thus improving both alignment stability and response time
3Speed
If conventional LC media are used to maintain low viscosity, then response times improve, but voltage holding ratio and stability deteriorate
Solution Approach 1:
The patent formulates a composite LC medium combining terphenyl compounds (formula T) with liquid crystal hosts and polymerizable compounds. This composite structure achieves high voltage holding ratio (VHR > 80% at 20°C) and improved stability while maintaining low rotational viscosity and fast response times, resolving the contradiction between viscosity and reliability
4Stability of the object's composition
If uncontrolled polymerization is allowed to occur, then alignment is achieved, but image sticking and mura occur reducing reliability
Solution Approach 1:
The patent introduces photoinitiators into the LC medium formulation before device assembly, enabling controlled photopolymerization during the alignment process. This preliminary preparation of the polymerization system allows precise control of the polymerization reaction, achieving stable alignment without uncontrolled polymerization that causes image sticking and mura, thus improving reliability
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 enables fast and stable pretilt angle generation, improved response times, reduced viscosity, and enhanced reliability with high VHR and birefringence, addressing the limitations of existing LC media in PSA displays.
Implementation Method 1
The polymerisation of the RMs preferably takes place with an applied voltage in the case of PS-VA and PS-OCB displays, and with or without, preferably without, an applied voltage in the case of PS-IPS displays. As a result a pretilt angle of the LC molecules is generated in the display cell.
Implementation Method 2
maintaining high birefringence and low threshold voltage
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.