Nematic Liquid Crystal Composition for Fast Response and Defect Suppression
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Solution Overview
Problem
Liquid crystal display devices face challenges with stability to heat and light, leading to display defects such as image sticking and dropping marks, while requiring low viscosity, wide temperature range, and high resistivity and voltage holding ratios.
Innovation Solution
A nematic liquid crystal composition containing specific compounds with a polar group-containing biphenyl moiety, which provides negative dielectric anisotropy, low viscosity, and stability to heat and light, used in VA-mode or PSVA-mode liquid crystal display devices to minimize display defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If liquid crystal compounds with large Δn are used to achieve fast response and low cell gap, then response speed is improved, but stability to light and heat deteriorates
Solution Approach 1:
The patent uses composite liquid crystal compositions containing multiple compounds including fluorinated cyclohexylbenzene compounds, biphenyl compounds, and cycloaliphatic compounds. This composite approach allows achieving Δn≥0.13 for fast response while selecting compounds with high photostability and thermal stability to prevent display defects like image sticking and dropping marks.
Solution Approach 2:
The patent optimizes specific physical parameters of the liquid crystal composition: Δn≥0.13 for fast response, η≤25 mPa·s for low viscosity, and γ1≤150 mPa·s for fast response. By carefully controlling these parameters within specific ranges, the patent achieves fast response while maintaining stability through proper parameter balancing.
2Speed
If monomer is added and cured by ultraviolet light irradiation to form pre-tilt angle and achieve fast response, then response speed is improved, but display defects such as dropping marks and image sticking occur
Solution Approach 1:
The patent removes or minimizes the use of photopolymerizable monomers that cause display defects when cured by UV light. Instead, the patent achieves pre-tilt angle and fast response through alternative means using specifically selected liquid crystal compounds that inherently provide the required properties without requiring photopolymerization, thereby eliminating dropping marks and image sticking.
Solution Approach 2:
The patent replaces long-lived photopolymerizable monomers with short-lived liquid crystal compounds that achieve the desired pre-tilt angle and response characteristics temporarily through their molecular structure, without requiring permanent polymerization. This approach avoids the harmful effects of UV curing while maintaining performance.
3Speed
If viscosity is decreased to achieve fast response, then response speed is improved, but dielectric anisotropy and refractive index anisotropy become difficult to optimize
Solution Approach 1:
The patent simultaneously optimizes multiple parameters: η≤25 mPa·s for fast response, Δε within -3.0 to -7.0 for proper voltage control, and Δn≥0.13 for fast response. By selecting compounds with specific molecular structures (fluorinated cyclohexylbenzene, biphenyl, cycloaliphatic compounds), the patent achieves this multi-parameter optimization without excessive complexity.
Solution Approach 2:
The patent uses composite compositions of fluorinated cyclohexylbenzene compounds (5-50 wt%), biphenyl compounds (20-60 wt%), and cycloaliphatic compounds (5-30 wt%). This composite approach allows balancing viscosity, dielectric anisotropy, and refractive index anisotropy by combining compounds with complementary properties, making optimization more manageable.
4Speed
If cell gap is decreased to achieve fast response, then response speed is improved, but voltage holding ratio and resistivity become compromised
Solution Approach 1:
The patent optimizes the product Δn×d (refractive index anisotropy times cell gap) to achieve fast response while maintaining proper voltage holding ratio and resistivity. By controlling Δn≥0.13 and selecting appropriate cell gap d, the patent balances response speed with electrical stability, ensuring VHR≥90% and resistivity≥1×10^12 Ω·cm.
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 composition achieves fast response and suppresses display defects, ensuring high practicality and quality in liquid crystal display devices by maintaining stability and performance.
Implementation Method 1
a liquid crystal composition having negative Δε
Implementation Method 2
exhibit a liquid crystal phase within as wide a temperature range as possible including room temperature as a center
Data Source
AI summary
A liquid crystal composition having negative dielectric anisotropy, large refractive index anisotropy, and low viscosity and containing as a first component, one or two or more compounds represented by general formula (I) and, as a second component, one or two or more compounds represented by general formula (II), wherein dielectric anisotropy (Δε) at 25° C. is −2.0 or less. Also, a liquid crystal display device having high contrast, fast response, and excellent display quality without causing image sticking and display defects.