Non-Aromatic Polymerizable Compounds for PSA Liquid Crystal Displays
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Solution Overview
Problem
Current liquid crystal display (LCD) technologies, particularly in polymer-sustained alignment (PSA) mode, face issues such as inadequate tilt angle generation, high rotational viscosity, low voltage-holding ratio (VHR), image sticking, and mura formation due to residual unpolymerized reactive mesogens (RMs), which affect display reliability and performance.
Innovation Solution
The use of non-aromatic polymerizable compounds with mesogenic cores and self-alignment additives that facilitate quick and complete UV-photopolymerization, reducing residual RM amounts and improving VHR, tilt stability, and solubility, while minimizing image sticking and mura occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymerisable compounds are used in PSA displays, then alignment is sustained, but incomplete polymerisation occurs leading to residual RMs causing image sticking and mura formation
Solution Approach 1:
The patent changes the chemical parameters of the polymerisable compounds by selecting specific structures (cyclohexane rings with acrylate/methacrylate groups, bicyclic structures) that have optimized reactivity and solubility characteristics, enabling more complete polymerisation and reducing residual RMs that cause image sticking and mura
Solution Approach 2:
The patent uses composite LC media containing multiple components: polymerisable compounds (5-20 wt%), non-polymerisable LC compounds (80-95 wt%), and self-alignment additives (0.1-5 wt%). This composite approach ensures complete polymerisation while maintaining proper alignment and reducing harmful residuals
2Productivity
If aromatic polymerisable compounds are used, then polymerisation occurs, but solubility in LC host mixture is limited and crystallisation tendency increases
Solution Approach 1:
The patent changes the structural parameters of the polymerisable compounds by replacing aromatic rings with alicyclic structures (cyclohexane, bicyclic rings). This structural modification improves solubility in the LC host mixture, reduces crystallisation tendency, and maintains adequate polymerisation speed through proper functional group selection (acrylate, methacrylate)
Solution Approach 2:
The patent introduces specific local structural features (cyclohexyl rings, bicyclic structures with specific bridge configurations) that locally modify the molecular properties to enhance solubility and prevent crystallisation while maintaining the polymerisable functional groups for adequate reactivity
3Shape
If high concentration of polymerisable compounds is used, then tilt angle generation improves, but rotational viscosity increases leading to slower response times
Solution Approach 1:
The patent optimizes the concentration parameter of polymerisable compounds (5-20 wt%) to achieve adequate tilt angle generation while minimizing viscosity increase. The specific molecular structure of the polymerisable compounds (cyclohexane-based with appropriate spacer lengths) is selected to balance tilt generation efficiency with minimal impact on rotational viscosity
Solution Approach 2:
The patent uses specific local molecular structures (cyclohexane rings with controlled spacer groups) that provide efficient tilt angle generation at lower concentrations, thereby avoiding the need for high polymerisable compound concentrations that would increase rotational viscosity and slow response times
4Productivity
If standard UV polymerisation is used, then polymerisation occurs, but polymerisation completeness is insufficient leaving residual RMs
Solution Approach 1:
The patent changes the UV irradiation parameters (wavelength, intensity, exposure time) and selects polymerisable compounds with appropriate absorption characteristics to achieve complete polymerisation. The cyclohexane-based structures with acrylate/methacrylate groups are designed to absorb UV effectively and polymerise completely under standard display manufacturing conditions
Solution Approach 2:
The patent introduces self-alignment additives that also serve as UV absorbers and polymerisation promoters, facilitating complete polymerisation of the main polymerisable compounds while ensuring proper alignment. These additives act as intermediaries that enhance the overall polymerisation completeness
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
This approach enables high VHR, fast response times, low threshold voltage, and high birefringence, along with improved stability and reduced image sticking and mura formation, enhancing the overall performance of PSA displays.
Implementation Method 1
The use of non-aromatic polymerizable compounds with mesogenic cores and self-alignment additives that facilitate quick and complete UV-photopolymerization
Data Source
AI summary
The present invention relates to liquid crystal (LC) media comprising one or more polymerisable compounds as further specified in the description or 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.