Polymerisable Compounds for PSA Liquid-Crystal Displays
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Solution Overview
Problem
Current liquid-crystal (LC) mixtures and reactive mesogens (RMs) for Polymer-Sustained Alignment (PSA) displays face challenges such as difficulty in achieving desired pretilt angles, high rotational viscosity, and inadequate voltage holding ratio, leading to issues like image sticking and prolonged response times, especially in VA and OCB types.
Innovation Solution
The use of novel polymerisable compounds with specific chemical structures, allowing for low pretilt angles to be established quickly without photoinitiators, which facilitate faster polymerisation and improved electrical properties, thereby reducing image sticking and enhancing display performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional polymerisable compounds are used in PSA displays, then pretilt angle can be established, but the establishment process is slow and requires photoinitiators, leading to prolonged response times
Solution Approach 1:
The patent removes photoinitiators from the polymerisation system by using polymerisable compounds that can polymerise autonomously under UV irradiation without requiring external initiators. This extraction of the photoinitiator component eliminates the delay associated with initiator decomposition and enables direct polymerisation, significantly reducing response time.
Solution Approach 2:
The patent modifies the chemical structure of polymerisable compounds by introducing specific functional groups (carboxyl, hydroxyl, or amino groups) that enable autonomous polymerisation. This parameter change in molecular structure allows the compounds to undergo polymerisation directly upon UV exposure without waiting for photoinitiator activation, thereby accelerating the polymerisation process and reducing response time.
2Reliability
If higher pretilt angles are achieved using conventional RMs, then alignment is improved, but image sticking occurs and voltage holding ratio deteriorates
Solution Approach 1:
The patent changes the chemical parameters of polymerisable compounds by incorporating specific functional groups (carboxyl, hydroxyl, or amino groups) that create optimal interactions with LC molecules. This parameter change enables the formation of stable alignment layers with appropriate pretilt angles while preventing the harmful effect of image sticking and maintaining high voltage holding ratio.
Solution Approach 2:
The patent uses composite polymerisable compounds that combine mesogenic units with specific functional groups (carboxyl, hydroxyl, or amino groups). This composite structure allows the material to simultaneously achieve good alignment quality through molecular interactions and prevent image sticking through controlled polymerisation characteristics, resolving the contradiction between alignment quality and image sticking.
3Ease of manufacture
If conventional LC mixtures are used, then display can be manufactured, but rotational viscosity is high leading to slow response times
Solution Approach 1:
The patent modifies the composition parameters of the LC mixture by incorporating polymerisable compounds with specific functional groups that reduce rotational viscosity. This parameter change in mixture composition maintains manufacturability while significantly improving response time by reducing the resistance to molecular reorientation under electric field.
4Illumination intensity
If slitted electrodes are used to improve transparency, then light transmission increases, but response time lengthens
Solution Approach 1:
The patent changes the polymerisation kinetics parameters by using compounds that polymerise rapidly under UV irradiation without photoinitiators. This parameter change in polymerisation speed compensates for the reduced light transmission caused by slitted electrodes, enabling fast response times despite the electrode structure that improves transparency.
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
These compounds enable the rapid establishment of low pretilt angles, improve voltage holding ratio, and reduce image sticking, resulting in shorter response times and better display stability, particularly at low temperatures, while maintaining high contrast and viewing angles.
Implementation Method 1
novel polymerisable compounds with specific chemical structures, allowing for low pretilt angles to be established quickly without photoinitiators, which facilitate faster polymerisation
Implementation Method 2
the LC medium usually has a negative value of the dielectric (DC) anisotropy. In the switched-off state, the molecules of the LC layer are aligned perpendicular to the electrode surfaces (homeotropically) or have a tilted homeotropic alignment. On application of an electrical voltage to the electrodes, a realignment of the LC molecules parallel to the electrode surfaces takes place.
Data Source
AI summary
The present invention relates to polymerizable compounds, to processes and intermediates for the preparation thereof, and to the use thereof for optical, electro-optical and electronic purposes, in particular in liquid-crystal (LC) media and LC displays, especially in LC displays of the PS (polymer-stabilized) and PSA (polymer-sustained alignment) type.