Liquid-Crystal Medium for PSA Displays with Fluorine Substitution
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Solution Overview
Problem
Liquid crystal media for polymer sustained alignment (PSA) displays face challenges with high viscosities leading to long switching times and reduced reliability, especially when exposed to UV radiation, which affects the voltage holding ratio (VHR), and there is a demand for materials with improved properties such as low threshold voltage, high birefringence, and broad viewing angles.
Innovation Solution
The development of liquid crystal media comprising specific compounds with formula IA and P, which exhibit low rotational viscosity and high clearing temperatures, allowing for fast switching times and improved stability, along with the use of polymerizable compounds for polymer stabilization in PSA displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid crystal media with high dielectric anisotropy are used in PSA displays, then voltage holding ratio (reliability) is improved, but rotational viscosity increases leading to longer switching times
Solution Approach 1:
The patent modifies the molecular structure of liquid crystal compounds by changing parameters such as introducing fluorine atoms at specific positions (e.g., position 2' of the phenyl ring) and adjusting chain lengths (e.g., propyl vs. butyl groups). These structural parameter changes optimize the balance between dielectric anisotropy and rotational viscosity, achieving fast switching times while maintaining adequate voltage holding ratio.
Solution Approach 2:
The patent employs composite liquid crystal media formulated by combining multiple compounds with different molecular structures and properties. The composition includes compounds with various chain lengths and fluorine substitution patterns, creating a synergistic effect that achieves both fast switching and acceptable voltage holding ratio that cannot be obtained from single compounds.
2Speed
If liquid crystal media are used in PSA displays requiring fast switching, then switching time is reduced, but reliability under UV radiation exposure deteriorates
Solution Approach 1:
The patent introduces fluorine atoms at specific positions in the molecular structure (e.g., position 2' of the phenyl ring in compounds of formula I) to modify the electronic properties and enhance UV stability. This parameter change in the molecular structure allows the medium to maintain fast switching while improving resistance to UV-induced degradation and maintaining voltage holding ratio over time.
3Speed
If liquid crystal media with low rotational viscosity are used, then switching time is reduced, but clearing temperature decreases affecting operational stability
Solution Approach 1:
The patent optimizes the balance between rotational viscosity and clearing temperature by carefully selecting and adjusting molecular parameters. Compounds with fluorine substitution and specific chain lengths (propyl or butyl groups) are used to achieve low rotational viscosity for fast switching while maintaining adequate clearing temperature for operational stability across a wide temperature range.
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 media achieve low rotational viscosity, high voltage holding ratio, and excellent low-temperature stability, enabling displays with broad operating temperature ranges and fast switching times while maintaining reliability even under UV exposure.
Implementation Method 1
The LC cell of a VA display contains a layer of an LC medium between two transparent electrodes, where the LC medium usually has a negative dielectric anisotropy. 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 an electrical 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
the use of polymerizable compounds for polymer stabilization in PSA displays
Data Source
AI summary
The invention relates to a liquid-crystalline medium comprising one or more compounds of the formula lA, and one or more compounds selected from the following formulae: wherein R11 and R12 have the meanings indicated in claim 1, and to an LC display comprising said medium.