Liquid Crystal Medium for PSA Displays
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Solution Overview
Problem
Current PSA displays face issues with pretilt angle stability under voltage stress, 'image sticking,' and inadequate voltage holding ratio, leading to reduced contrast and increased response times, particularly in VA and OCB types, due to unsuitable LC mixtures and polymerisable compounds.
Innovation Solution
An LC medium comprising biphenyl compounds with lateral fluoro substitution, but no terphenyl compounds, is used, along with reactive mesogens and low-molecular-weight mesogenic compounds, to enhance pretilt angle stability and polymerisation efficiency, reducing residual unpolymerised materials and improving electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LC mixtures are used in PSA displays, then the display can be manufactured with standard materials, but the pretilt angle stability under voltage stress deteriorates
Solution Approach 1:
The patent modifies the chemical composition parameters of the LC mixture by incorporating specific compounds (cyclohexylbenzene derivatives with negative dielectric anisotropy, terphenyl compounds with positive dielectric anisotropy, and fluorinated compounds) in optimized ratios. This changes the electrical and physical parameters of the mixture to achieve both high pretilt angle stability under voltage stress and improved overall reliability of the PSA display.
2Reliability
If inadequate polymerisable compounds are used, then the manufacturing process is simpler, but the voltage holding ratio deteriorates
Solution Approach 1:
The patent employs a composite polymerisable system combining multiple reactive mesogens (acrylate and methacrylate compounds) with different molecular structures and reactivity. This composite approach enhances the voltage holding ratio by creating a more robust polymer network that better maintains the pretilt angle, while the synergistic interaction between different polymerisable compounds improves overall performance without excessive complexity.
Solution Approach 2:
The patent uses polymerisable compounds with specific local chemical structures (acrylate groups at certain positions, methacrylate groups at others) that create localized polymerization zones. This local quality approach ensures optimal polymer distribution and network formation, enhancing voltage holding ratio while maintaining manufacturability through well-defined chemical structures.
3Productivity
If residual unpolymerised materials remain, then the manufacturing process is faster, but the image sticking phenomenon increases
Solution Approach 1:
The patent employs polymerisable compounds with high reactivity and complete polymerization capability, ensuring continuous and thorough polymerization action. The selected acrylate and methacrylate compounds achieve near-complete conversion, minimizing residual unpolymerised materials that could cause image sticking, while maintaining efficient polymerization speed for productive manufacturing.
Solution Approach 2:
The patent optimizes the chemical parameters of the polymerisable compounds, including functional group selection (acrylate vs. methacrylate) and molecular weight, to achieve optimal polymerization kinetics. This ensures rapid and complete polymerization that eliminates harmful residuals while maintaining high productivity in the manufacturing process.
4Reliability
If response times are prolonged, then the display can achieve higher contrast, but the viewing experience deteriorates
Solution Approach 1:
The patent optimizes multiple parameters of the LC mixture including dielectric anisotropy, rotational viscosity, and elastic constants by selecting specific compounds (cyclohexylbenzene derivatives, terphenyl compounds, fluorinated compounds) in optimized ratios. This multi-parameter optimization achieves the ideal balance between contrast ratio and response time, ensuring both high image quality and fast switching performance for superior viewing experience.
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 significantly improves pretilt angle stability, reduces 'image sticking,' and enhances voltage holding ratio, resulting in shorter response times, higher contrast, and broader viewing angles in PSA displays.
Implementation Method 1
a polymerisable component A), comprising one or more polymerisable compounds, preferably selected from reactive mesogens (RMs)
Implementation Method 2
The polymerisation of the polymerisable compound(s) preferably takes place with an applied electrical voltage
Implementation Method 3
OCB ('optically compensated bend') displays are known which are based on a birefringence effect
Implementation Method 4
the LC medium usually has a negative value of the dielectric (DC) anisotropy
Data Source
AI summary
The present invention relates to a liquid crystal (LC) medium, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the PS ("polymer sustained") or PSA ("polymer sustained alignment") type, and to LC displays, especially PS or PSA displays, comprising said LC medium.