Liquid-Crystal Medium for Polymer Sustained Alignment Displays
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Solution Overview
Problem
Current liquid crystal (LC) media for polymer sustained alignment (PSA) displays face issues such as inadequate pretilt angles, high rotational viscosity, voltage holding ratio (VHR) concerns, image sticking, and limited solubility, which affect display performance and reliability, especially in outdoor applications where durability and broad temperature range are required.
Innovation Solution
A liquid crystal medium comprising a polymerisable component and a liquid-crystalline host mixture with specific compounds selected from formulae C, P, and T, which enables quick and complete polymerisation, stable pretilt angles, reduced viscosity, and high VHR, even under UV exposure, while allowing for low threshold voltages and broad viewing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional LC media are used in PSA displays, then the display can operate, but the response times are slow due to high rotational viscosity
Solution Approach 1:
The patent modifies the chemical composition parameters of the LC medium by incorporating specific compounds (cyclohexane carboxylic acid derivatives with fluorine substitution) to change the rotational viscosity parameter, thereby achieving faster response times while maintaining other display performance characteristics
2Stability of the object's composition
If polymerisation is performed to stabilise alignment, then pretilt angle is generated, but the polymerisable component may crystallise out of the mixture
Solution Approach 1:
The patent adjusts the compositional parameters of the LC medium by selecting specific host mixture components and ratios that maintain the polymerisable compound in solution throughout the operating temperature range, preventing crystallisation while enabling effective polymerisation for alignment stabilisation
Solution Approach 2:
The patent creates a composite LC medium system combining the host mixture with specifically selected polymerisable compounds that have complementary solubility characteristics, ensuring homogeneous mixing and preventing phase separation or crystallisation during storage and operation
3Loss of time
If UV photopolymerisation is used to speed up polymerisation, then production time is reduced, but the LC medium must remain stable under UV exposure
Solution Approach 1:
The patent selects polymerisable compounds with specific molecular structures that exhibit inherent UV stability, allowing rapid photopolymerisation to proceed while the remaining monomer and host mixture maintain stability under UV exposure conditions, thus achieving both fast processing and long-term reliability
4Adaptability or versatility
If the LC medium is to work in outdoor applications, then broad temperature range and UV stability are required, but conventional media lack durability
Solution Approach 1:
The patent develops a composite LC medium formulation combining host mixture components and polymerisable compounds selected for their thermal stability and UV resistance, creating a material system that maintains performance across broad temperature ranges and withstands outdoor environmental conditions
Solution Approach 2:
The patent optimizes the compositional parameters including the selection of fluorinated compounds and specific molecular weight ratios to broaden the liquid crystal phase temperature range while incorporating UV-stable components to enhance durability for outdoor applications
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 LC medium achieves high specific resistance, quick response times, reduced image sticking, and improved reliability, making it suitable for outdoor applications with enhanced UV stability and birefringence, thus addressing the limitations of prior art in PSA displays.
Implementation Method 1
The polymerisable compound (A) is comprised of one or more polymerisable compounds... which enables quick and complete polymerisation... The polymerisable compound undergoes photopolymerisation upon UV exposure
Implementation Method 2
enhanced UV stability and birefringence... The liquid crystal medium exhibits birefringence to modulate light transmission based on molecular orientation
Implementation Method 3
PSA displays an LC medium is used that contains an LC mixture... a pretilt angle of the LC molecules is generated... Upon application of a voltage to the interdigital electrodes, which create an electrical field that is substantially parallel to the layer of the LC medium, the LC molecules are switched to an orientation substantially parallel to the substrates
Data Source
AI summary
The present invention relates to a liquid crystal (LC) medium comprising a polymerisable compound, 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.