Liquid-Crystal Media for IPS Displays with Low Viscosity
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Solution Overview
Problem
Liquid-crystal displays, particularly those using in-plane switching (IPS) and fringe-field switching (FFS) modes, face challenges with long addressing times, high operating voltages, inadequate resistivity, and poor stability under thermal, light, and UV exposure, necessitating the development of liquid-crystalline media with improved dielectric anisotropy, viscosity, and nematic phase range.
Innovation Solution
The use of specific compounds, such as those represented by formulae S1 and S2, in combination with other dielectrically positive and neutral compounds, to create liquid-crystal media with enhanced dielectric anisotropy, reduced viscosity, and improved thermal and light stability, optimizing the nematic phase range for efficient display performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional liquid-crystal compositions are used, then the nematic phase range and birefringence are adequate, but the rotational viscosity is too high resulting in long addressing times
Solution Approach 1:
The patent modifies the chemical composition parameters of the liquid-crystal medium by incorporating specific compounds (cyclohexyl compounds with cyanobiphenyl or phenylpyridine moieties) to change the rotational viscosity parameter while maintaining other critical parameters like dielectric anisotropy and nematic phase range
Solution Approach 2:
The patent creates a composite liquid-crystal composition by combining multiple components including the novel cyclohexyl compounds of formula (I), compounds of formulae (II) and (III), and compounds of formula (IV), where each component contributes different properties to achieve the desired balance of low viscosity and high dielectric anisotropy
2Use of energy by moving object
If liquid-crystalline media with high dielectric anisotropy are used, then operating voltage can be reduced, but the resistivity becomes insufficient
Solution Approach 1:
The patent optimizes the dielectric anisotropy parameter to a specific range (>2 and preferably >3 but <20 and particularly <17) that balances the competing requirements of low operating voltage and high resistivity, achieved through careful selection and concentration of compounds with different dielectric properties
Solution Approach 2:
The patent combines compounds with different dielectric characteristics in a composite formulation, where the cyclohexyl compounds of formula (I) provide high dielectric anisotropy while compounds of formulae (II), (III), and (IV) contribute to maintaining appropriate resistivity levels
3Reliability
If existing liquid-crystal compositions are used, then the basic display function is achieved, but the stability under thermal, light, and UV exposure is insufficient
Solution Approach 1:
The patent incorporates small amounts (0.01-5% by weight) of stabilizer compounds that act as sacrificial protective agents, consuming degradation effects through their chemical structure design to protect the main liquid-crystal components over extended periods
Solution Approach 2:
The patent creates a multi-component composite system where compounds of formulae (I), (II), (III), and (IV) work synergistically to provide thermal stability, while the inclusion of stabilizer compounds provides additional protection against light and UV degradation
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 liquid-crystal media exhibit significantly reduced voltage holding ratio degradation under UV exposure and improved thermal stability, along with shorter addressing times and lower operating voltages, enhancing the overall performance and lifespan of liquid-crystal displays.
Implementation Method 1
liquid-crystalline media having improved properties are required... the dielectric anisotropy (Δε) should be sufficiently high to allow a fairly low operating voltage
Implementation Method 2
an appropriate birefringence (Δn)... These modes utilise an electric field which is substantially perpendicular to the substrates or the liquid-crystal layer
Data Source
AI summary
The present invention relates to dielectrically positive liquid-crystalline media comprising one or more compounds of the formulae S1 and S2, and one or more compounds selected from the group of the compounds of the formulae II and III and/or IV and/or VIII, in which the parameters have the respective meanings indicated in the specification, and optionally one or more further dielectrically positive compounds and optionally one or more further dielectrically neutral compounds, and to liquid-crystal displays, especially active-matrix displays and in particular TN, IPS and FFS displays, containing these media.