Liquid Crystal Medium Composition for Fast, UV-Stable PSA Displays
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Solution Overview
Problem
Existing liquid-crystal displays, particularly PSA displays, face issues such as high viscosity leading to long switching times, reduced reliability due to UV exposure during polymerization, occurrence of ODF mura, and a need for improved response times, contrast, and luminance, especially in mobile applications.
Innovation Solution
Development of liquid crystalline media with high negative dielectric anisotropy, suitable phase range, and low rotational viscosity, comprising specific compounds of formula I and II, which are polymerized in situ to stabilize the alignment of liquid crystals, reducing ODF mura and enhancing display performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional liquid crystal media are used in PSA displays, then the display can be manufactured with standard materials, but the viscosity is high leading to long switching times and reduced reliability
Solution Approach 1:
The patent changes the chemical composition parameters of the liquid crystal medium by incorporating specific compounds (formula I and II) with optimized molecular structures. This modifies the viscosity and dielectric anisotropy parameters to achieve fast switching times while maintaining reliability. The specific compounds provide negative dielectric anisotropy and controlled phase behavior that resolves the contradiction between reliability and switching speed.
Solution Approach 2:
The patent creates a composite liquid crystal medium by combining multiple components: compounds of formula I and II, chiral dopants, and polymerizable compounds. This composite approach allows optimization of individual material properties to achieve both high reliability and fast switching, with each component contributing specific characteristics to the overall medium performance.
2Reliability
If UV exposure is applied during polymerization to stabilize alignment, then the LC medium reliability improves, but the LC medium degrades due to UV exposure
Solution Approach 1:
The patent incorporates polymerizable compounds into the liquid crystal medium before filling the display cell. These compounds undergo photopolymerization during the manufacturing process to form a stabilizing network that prevents molecular reorientation and maintains alignment. This preliminary preparation allows the medium to gain UV resistance and stability during manufacturing without requiring post-manufacturing UV exposure that would cause degradation.
Solution Approach 2:
The polymerizable compounds act as intermediaries between the liquid crystal molecules and the UV radiation. During photopolymerization, these compounds absorb UV energy and form cross-linked structures that stabilize the liquid crystal alignment. This intermediary mechanism allows the system to utilize UV exposure for beneficial stabilization while protecting the main liquid crystal material from direct UV damage through the formed polymer network.
3Manufacturing precision
If standard liquid crystal media are used, then the manufacturing process is simple, but ODF mura occurs and contrast is reduced
Solution Approach 1:
The patent modifies the liquid crystal medium composition by incorporating specific compounds (formula I and II) with optimized molecular structures that reduce optical anisotropy variations. This changes the optical and rheological parameters to minimize ODF mura formation during manufacturing while improving contrast. The specific compounds provide more uniform optical properties across the cell, resolving the contradiction between manufacturing simplicity and display quality.
4Speed
If high dielectric anisotropy is used to improve switching speed, then response time improves, but the phase range becomes unsuitable for display applications
Solution Approach 1:
The patent carefully selects and combines compounds with specific dielectric anisotropy values and phase behavior characteristics. By optimizing the composition ratio and molecular structures, the patent achieves high dielectric anisotropy for fast switching while maintaining an appropriate phase range for display operation. The specific compounds (formula I and II) are designed to provide the right balance between switching speed and phase stability.
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 new liquid crystalline media provide improved contrast, transmission, low-temperature stability, high voltage-holding ratio, fast switching, and stability against UV exposure, while minimizing ODF mura and reducing switching times, suitable for displays like VA, IPS, and FFS types.
Implementation Method 1
comprising specific compounds of formula I and II, which are polymerized in situ to stabilize the alignment of liquid crystals
Implementation Method 2
The LC medium usually has a negative dielectric anisotropy... FFS displays usually contain an LC medium with positive dielectric anisotropy
Implementation Method 3
In the switched-off state, the molecules of the LC layer are aligned perpendicular to the electrode surfaces (homeotropically)
Implementation Method 4
On application of an electrical voltage to the two electrodes, a realignment of the LC molecules parallel to the electrode surfaces takes place
Data Source
AI summary
The present invention relates to liquid-crystal (LC) media as defined in claim 1, to the use thereof for optical, electro-optical and electronic purposes, in particular in LC displays, and to LC displays containing said LC media. The invention in particular relates to LC media with improved response time that enable energy saving displays.