Liquid-Crystalline Medium for Fast Response and Low Threshold Voltage
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Solution Overview
Problem
Liquid-crystal displays face challenges with high specific resistance, broad temperature range, short response times, low threshold voltage, and image sticking issues due to limitations in existing liquid-crystal materials, particularly in TN and STN cells, which affect display performance and longevity.
Innovation Solution
Incorporating specific liquid-crystalline compounds with negative dielectric anisotropy, such as those of formulas IA, IB, IC, ID, and IE, into TN-TFT mixtures to achieve low rotational viscosities, fast response times, high dielectric anisotropy, and reduced image sticking, while maintaining high clearing points and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional liquid-crystal materials are used in TN and STN cells, then the displays can operate at standard temperatures, but the specific resistance is insufficiently high leading to contrast deterioration and after-image elimination problems
Solution Approach 1:
The patent combines cyano-phenylcyclohexane compounds (providing high specific resistance and positive dielectric anisotropy) with phenylpyrimidine or phenylcyclohexane compounds (providing nematic phase stability and low viscosity) to create a composite liquid-crystal mixture that achieves very high specific resistance while maintaining good electro-optical properties and compatibility with TN/TFT displays
2Power
If liquid-crystal materials with high dielectric anisotropy are used to reduce threshold voltage, then the operating voltage decreases, but the rotational viscosity increases leading to slower response times
Solution Approach 1:
The patent carefully balances the molecular structures and proportions of components to achieve optimal parameter combinations - using cyano-phenylcyclohexane compounds with specific substituent patterns (X1, X2 = F, Cl, CHF2, CF3, OCHF2, or OCF3) that provide high dielectric anisotropy while the phenylpyrimidine/phenylcyclohexane components contribute low rotational viscosity, resulting in threshold voltages ≤2.0V and response times ≤5.0ms
3Speed
If liquid-crystal materials with low viscosity are used to achieve fast response times, then the addressing speed increases, but the clearing point decreases reducing the working temperature range
Solution Approach 1:
The patent creates a composite mixture where phenylpyrimidine compounds (providing low rotational viscosity and fast response) are combined with phenylcyclohexane compounds (providing high clearing points and broad nematic phase ranges), achieving response times ≤5.0ms while maintaining clearing points ≥70°C and nematic phase ranges ≥90°
4Reliability
If conventional liquid-crystal mixtures are used, then the initial specific resistance can be adequate, but the resistance drops over the life of the display due to interaction with interior surfaces
Solution Approach 1:
The patent modifies the chemical composition by incorporating fluorinated and chlorinated substituents (X1, X2 = F, Cl, CHF2, CF3, OCHF2, or OCF3) on the phenyl rings of cyano-phenylcyclohexane compounds, which increase the initial specific resistance to ≥1.0×10^12 Ω·cm and reduce the rate of resistance degradation over time through improved chemical stability and reduced interaction with interior surfaces
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 use of these compounds results in liquid-crystal media with improved properties, including low rotational viscosities, fast response times, high dielectric anisotropy, and reduced image sticking, enhancing the performance and longevity of TN, STN, and IPS displays.
Implementation Method 1
at least one compound selected from the group of the compounds of the formulae IA to IE... compounds with negative dielectric anisotropy... high dielectric anisotropy
Implementation Method 2
low rotational viscosities... fast response times
Implementation Method 3
relatively low birefringence... optical anisotropy
Data Source
AI summary
The invention relates to a liquid-crystalline medium containing one or more compounds of the formula Iand one or more compounds selected from the group of the compounds of the formula IA to IEin which R0, R1, R2, X0, X1, X2, A1, Z1, m, p, q, v have the meanings indicated in Claim 1, and to the use thereof in electro-optical liquid-crystal displays.