Liquid-Crystal Medium Polymerizable Compounds PSA Alignment
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Solution Overview
Problem
Current liquid-crystal (LC) displays face challenges in achieving high specific resistance, short response times, low threshold voltage, high tilt stability, and broad viewing angles while maintaining reliability and low melting points, especially at low temperatures, and require materials that can polymerize effectively at longer UV wavelengths to reduce image sticking and 'ODF mura' issues.
Innovation Solution
Development of an LC medium comprising specific polymerizable compounds, such as those of formulas IA and IB, which exhibit negative dielectric anisotropy, allowing for high specific resistance, rapid polymerization, and stability, even at low temperatures, and enabling efficient UV photopolymerization with low threshold voltage and reduced rotational viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If alkenyl compounds are used to reduce response times, then response time is improved, but reliability decreases due to reaction with polyimide alignment layer
Solution Approach 1:
The patent removes alkenyl compounds from the LC host mixture to eliminate the harmful reaction with polyimide alignment layer. Instead, it uses a specialized polymerizable compound (compound 1) with specific molecular structure that does not contain reactive alkenyl groups, thereby extracting the problematic component while maintaining the desired fast response performance through alternative mechanisms.
Solution Approach 2:
The patent employs a polymerizable compound that undergoes controlled polymerization to form a stable polymer network. This polymer network acts as a temporary scaffold during the alignment process and then stabilizes the liquid crystal orientation, providing reliable performance without the harmful side reactions of alkenyl compounds.
2Productivity
If shorter UV wavelengths are used for polymerization, then polymerization efficiency is improved, but harmful reactions with alignment layer increase
Solution Approach 1:
The patent changes the UV wavelength parameter from shorter wavelengths (which cause harmful reactions) to longer wavelengths in the range of 365-380 nm. This parameter change allows efficient polymerization of the specialized compound (1) while avoiding the harmful reactions with the polyimide alignment layer, thus resolving the contradiction between polymerization efficiency and harmful effects.
3Speed
If highly polar LC compounds are used to reduce response times, then response time is improved, but reliability decreases
Solution Approach 1:
The patent introduces compound (1) with specific local molecular characteristics that provide fast response locally without compromising overall reliability. The compound has a molecular structure designed to interact favorably with the polymer network formed during PSA process, creating localized regions of fast response while maintaining bulk material reliability.
Solution Approach 2:
The patent creates a composite system combining the LC host mixture with polymerizable compound (1) and polymerized RMs. This composite material structure allows the liquid crystal phase to maintain its reliability while the polymer network provides the fast response characteristics, effectively combining the advantages of both components.
4Stability of the object's composition
If polymerizable compounds are added to achieve PSA mode, then tilt stability is improved, but melting point increases
Solution Approach 1:
The patent modifies the molecular structure parameters of the polymerizable compound (1) to optimize the balance between tilt stability and melting point. By adjusting the molecular weight, functional groups, and structural parameters of compound (1), the patent achieves sufficient tilt stability through polymer network formation while keeping the melting point below 0°C for practical display applications.
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 LC medium demonstrates improved transmittance, contrast ratio, reduced image sticking and 'ODF mura', fast response times, and energy-efficient operation with minimal residual polymerization residues, maintaining high reliability and tilt stability across various temperatures.
Implementation Method 1
After filling the LC medium into the display the RMs are then polymerized in situ by UV photopolymerization, while a voltage is applied to the electrodes of the display.
Implementation Method 2
Development of an LC medium comprising specific polymerizable compounds, such as those of formulas IA and IB, which exhibit negative dielectric anisotropy, allowing for high specific resistance, rapid polymerization, and stability
Implementation Method 3
a small amount, typically 0.1 to 2.5%, of a self alignment (SA) additive is added to the LC medium, which induces the desired alignment, for example homeotropic or planar alignment, in situ by a self assembling mechanism
Data Source
AI summary
The present invention relates to a liquid-crystal (LC) medium comprising polymerizable compounds, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the PSA (polymer sustained alignment) or SA (self-aligning) mode, to an LC display of the PSA or SA mode comprising the LC medium, and to a process of manufacturing the LC display.