Polymerizable Mesogenic Compounds for PSA Displays
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Solution Overview
Problem
Current liquid crystal display (LCD) technologies, particularly in the polymer sustained alignment (PSA) type, face issues such as inadequate tilt angle generation, high rotational viscosity, low voltage holding ratio (VHR), image sticking, and mura formation due to unsuitable polymerizable mesogenic compounds (RMs) and self-alignment additives, which affect display reliability and performance.
Innovation Solution
The use of novel polymerizable compounds with a mesogenic core and alkoxymethyl substituents, combined with self-alignment additives, facilitates rapid and complete UV-photopolymerization, reducing residual RMs and improving VHR, tilt stability, and solubility, while minimizing image sticking and mura formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymerizable mesogenic compounds are used in PSA displays, then the display can operate with basic alignment, but the tilt angle generation is inadequate and the voltage holding ratio is low
Solution Approach 1:
The patent modifies the molecular structure of polymerizable mesogenic compounds by introducing specific substituents (fluorine atoms at positions 2 and 6 of the phenyl ring, and alkoxymethyl groups at positions 3 and 5) to change the physical and chemical parameters of the liquid crystal medium. These parameter changes enable adequate tilt angle generation and improve voltage holding ratio, resolving the contradiction between basic alignment operation and performance requirements.
2Reliability
If conventional LC media are used, then the display can function, but image sticking and mura formation occur due to incomplete polymerization and high residual RM content
Solution Approach 1:
The patent employs conventional, well-understood chemical groups (acrylate or methacrylate for polymerization, alkoxymethyl for crosslinking) that are readily available and well-characterized. These groups enable complete and controlled polymerization, eliminating residual RM that causes image sticking and mura, while maintaining manufacturing simplicity.
Solution Approach 2:
The liquid crystal medium is designed as a composite system containing multiple functional components: polymerizable mesogenic compounds with specific substituents, self-alignment additives, and conventional LC host compounds. This composite structure enables simultaneous achievement of adequate tilt angle, high VHR, complete polymerization, and elimination of display defects.
3Reliability
If the polymerization is made rapid and complete, then residual RMs are reduced and VHR improves, but the solubility of compounds may be affected
Solution Approach 1:
The patent introduces specific functional groups at specific positions on the mesogenic core: fluorine atoms at positions 2 and 6, and alkoxymethyl groups at positions 3 and 5. This local modification of molecular structure provides both rapid polymerization capability (improving VHR) and enhanced solubility through the polar alkoxymethyl groups, resolving the contradiction between complete polymerization and compositional stability.
4Speed
If conventional RMs are used, then the display can operate, but response times are slow and threshold voltage is high
Solution Approach 1:
The patent changes the physical parameters of the liquid crystal medium by incorporating polymerizable mesogenic compounds with specific molecular structures (fluorine-substituted phenyl rings with alkoxymethyl groups). These parameter changes reduce rotational viscosity and improve electro-optical response, enabling faster response times and lower threshold voltages while maintaining the polymer sustained alignment function.
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 high VHR, fast response times, low threshold voltage, and broad viewing angles with improved reliability and solubility, enhancing the overall performance of PSA displays.
Implementation Method 1
facilitates rapid and complete UV-photopolymerization
Data Source
AI summary
Liquid crystal (LC) media comprising polymerisable compounds as further specified in the description and claims and a self-alignment additive for vertical alignment. The media are adapted for use in LC displays, especially in LC displays of the polymer-sustained alignment type.