Liquid Crystal Medium for IPS FFS Displays
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Solution Overview
Problem
Existing liquid-crystal compositions for FFS and IPS displays suffer from long addressing times, inadequate resistivity, and the need for high operating voltages, which limits their performance and shelf life.
Innovation Solution
A liquid-crystalline medium with positive dielectric anisotropy, comprising specific compounds of formulas I, II, and III, which balances dielectric anisotropy, rotational viscosity, and elastic constants to achieve high brightness, fast response times, and improved contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional liquid-crystal compositions are used in FFS and IPS displays, then the displays can be manufactured with existing materials, but the displays suffer from long addressing times and inadequate resistivity
Solution Approach 1:
The patent modifies the chemical composition parameters of the liquid-crystal medium by incorporating specific compounds (cyclic carbonates, cyclic carboxylic acid esters, and compounds with formula I) in controlled proportions. This changes the physical parameters of the mixture to achieve both fast addressing times (γ1/K11 ≤ 4.0 ms/nN) and adequate resistivity (ρ ≥ 1.0×10^12 Ω·cm at 20°C), resolving the contradiction between speed and reliability.
2Use of energy by moving object
If liquid-crystal compositions with higher dielectric anisotropy are used, then the operating voltage can be reduced, but the rotational viscosity increases leading to slower response times
Solution Approach 1:
The patent optimizes the dielectric anisotropy parameter (Δε) to a specific range (+2.0 to +6.0 at 20°C) and balances it with rotational viscosity (γ1 ≤ 80 mPa·s) and elastic constant (K11 ≥ 10.0 pN) through careful selection of liquid-crystal compounds. This parameter optimization allows the display to operate at reduced voltages while maintaining fast response times, resolving the contradiction between energy efficiency and speed.
Solution Approach 2:
The patent creates a composite liquid-crystal medium by combining multiple types of compounds: cyclic carbonates (5-20 wt%), cyclic carboxylic acid esters (10-30 wt%), and compounds of formula I (30-60 wt%), along with optional additives. This composite approach allows the system to achieve balanced properties including low rotational viscosity, appropriate dielectric anisotropy, and fast response times simultaneously.
3Speed
If the liquid-crystal medium is optimized for fast response times, then the addressing time decreases, but the brightness and transmission are reduced
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: birefringence (Δn = 0.090-0.110), elastic constant (K11 ≥ 10.0 pN), and rotational viscosity (γ1 ≤ 80 mPa·s) to achieve the optimal balance between response time (γ1/K11 ≤ 4.0 ms/nN) and optical performance. The specific compound selection and proportions ensure both fast switching and high brightness/transmission characteristics.
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 medium enables liquid-crystal displays with high brightness and transmission, fast response times, and improved contrast, while maintaining low rotational viscosity and elastic constants, thus addressing the limitations of existing compositions.
Implementation Method 1
Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 195 28 104. Furthermore, so-called 'fringe-field switching' (FFS) displays have been reported... which contain an LC medium with positive dielectric anisotropy
Implementation Method 2
On application of a voltage to the electrodes an electric field with a significant component parallel to the LC layer is generated between them. This causes realignment of the LC molecules in the layer plane
Data Source
AI summary
The present invention relates to liquid-crystalline (LC) media having positive dielectric anisotropy and to liquid-crystal displays (LCDs) containing these media, especially to displays addressed by an active matrix and in particular to LC displays of the TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS, XB-FFS, PS-FFS, SA-HB-FFS, SA-XB-FFS, polymer stabilised SA-HB-FFS, polymer stabilised SA-XB-FFS, positive VA or positive PS-VA type.