Polymerizable Liquid-Crystal Medium for Reliable VA Display Response
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Solution Overview
Problem
Existing LC media with negative dielectric anisotropy in VA and FFS displays suffer from reduced reliability, high viscosity, slow response times, and image sticking due to interactions with alignment layers and UV exposure, and polymerizable compounds used in PSA displays face incomplete polymerization and tilt angle instability.
Innovation Solution
Development of LC media with specific polymerizable compounds and additives that enable complete polymerization at longer UV wavelengths, improving reliability, response times, and reducing image sticking, while maintaining suitable dielectric anisotropy and birefringence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LC media with negative dielectric anisotropy are used in VA and FFS displays, then the director orientation has less tilt and more twist orientation resulting in higher transmission, but the reliability is significantly lower due to ion extraction from alignment layers
Solution Approach 1:
The patent modifies the chemical composition parameters of the LC medium by incorporating specific compounds (cyclohexyl benzoates, phenyl benzoates, cyclohexyl phenyl ethers, and phenyl phenyl ethers with specific molecular structures and ratios) to change the interaction parameters with alignment layers, thereby reducing ion extraction while maintaining the negative dielectric anisotropy and transmission characteristics
Solution Approach 2:
The patent creates a composite LC medium formulation by combining multiple specific compound classes (cyclohexyl benzoates, phenyl benzoates, cyclohexyl phenyl ethers, phenyl phenyl ethers) in defined proportions to achieve synergistic effects that simultaneously improve reliability through reduced ion extraction and maintain high transmission performance
2Stability of the object's composition
If polymerizable compounds are added to LC media for PSA displays, then the tilt angle can be stabilized, but incomplete polymerization occurs and tilt angle instability remains
Solution Approach 1:
The patent optimizes the polymerization process parameters by selecting specific UV wavelengths and controlling exposure conditions to achieve complete polymerization of the added compounds (0.1-5 wt%) while maintaining stable tilt angles, preventing both incomplete polymerization and over-polymerization effects
Solution Approach 2:
The patent enables the LC medium to self-stabilize its tilt angle through in-situ polymerization of added compounds under UV exposure, where the medium itself provides the necessary conditions for complete polymerization and subsequent tilt angle stabilization without requiring external intervention during operation
3Ease of manufacture
If conventional LC media are used, then the manufacturing process is simple, but the response times are slow due to high viscosity
Solution Approach 1:
The patent changes the molecular structure parameters of the LC compounds by incorporating specific cyclic structures (cyclohexyl rings) and functional groups (benzoates, phenyl ethers) that reduce rotational viscosity while maintaining liquid crystalline properties, thereby achieving faster response times without complicating the manufacturing process
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 LC media exhibit enhanced VHR, high specific resistance, fast response times, and reduced image sticking, with complete polymerization and stable tilt angles, even under UV exposure, and are suitable for VA, IPS, and FFS displays.
Implementation Method 1
the LC medium usually has a negative value of the dielectric anisotropy (Δε). 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 a voltage to the two electrodes, a realignment of the LC molecules parallel to the electrode surfaces takes place.
Implementation Method 2
FFS displays usually contain an LC medium with positive dielectric anisotropy, and an alignment layer, usually of polyimide, which provides planar alignment to the molecules of the LC medium.
Implementation Method 3
which have good UV absorption properties, in particular at wavelengths of more than 340 nm, very preferably in the range from 350 to 400 nm, and which enable a quick and complete polymerization
Data Source
AI summary
The present invention relates to a liquid-crystal (LC) medium (as a subcategory of liquid crystal material), based on a mixture of polar compounds, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the vertically aligned mode, to an LC display of the vertically aligned mode comprising the LC medium, especially an energy-saving LC display and to a process of manufacturing the LC display.