Liquid Crystal Medium for PSA Displays with Low Rotational Viscosity
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Solution Overview
Problem
Current liquid crystal mixtures for PSA displays, particularly IPS and FFS types, face challenges such as inadequate Voltage Holding Ratio (VHR), high rotational viscosity, and limited viewing angle range, which affect switching times and contrast performance.
Innovation Solution
Development of new liquid crystalline media with specific compounds that offer high dielectric anisotropy, low rotational viscosity, and improved optical properties, allowing for faster switching times and enhanced display performance without the need for photoinitiators, and enabling polymerization within the display without external electric or magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional liquid crystal mixtures are used in PSA displays, then the display can be manufactured with standard materials, but the switching times are slow due to high rotational viscosity
Solution Approach 1:
The patent changes the chemical composition parameters of the liquid crystal mixture by incorporating specific compounds (cyclic carbonate compounds, compounds with specific molecular structures) to reduce rotational viscosity. This allows the liquid crystal molecules to reorient faster in response to electric fields, directly improving switching times while maintaining other display performance characteristics.
Solution Approach 2:
The patent creates a composite liquid crystal mixture by combining multiple compounds with specific properties - cyclic carbonate compounds, compounds with particular molecular structures, and other liquid crystal materials. This composite approach allows the mixture to achieve low rotational viscosity while maintaining appropriate dielectric anisotropy and other critical properties for PSA display operation.
2Stability of the object's composition
If polymerizable compounds are added to stabilize liquid crystal orientation, then the alignment is improved, but the Voltage Holding Ratio decreases
Solution Approach 1:
The patent optimizes the concentration parameter of polymerizable compounds in the liquid crystal mixture, maintaining them within a specific range (0.1-10 wt%) to achieve sufficient orientation stability while minimizing the negative impact on Voltage Holding Ratio. This parameter optimization balances the competing requirements of alignment stability and electrical performance.
Solution Approach 2:
The patent introduces compounds with specific local molecular structures and properties that provide orientation stabilization through localized interactions rather than bulk polymerization. This allows stabilization at the molecular level while preserving the overall electrical properties and VHR of the liquid crystal mixture.
3Speed
If liquid crystal mixtures with high dielectric anisotropy are used, then the switching response is improved, but the viewing angle range is limited
Solution Approach 1:
The patent combines multiple liquid crystal compounds with different optical and dielectric properties in a composite mixture. This allows the mixture to achieve high overall dielectric anisotropy for fast switching response while the specific combination of compounds provides broader viewing angle characteristics that compensate for the narrow viewing angles of individual high-Δε components.
Solution Approach 2:
The patent uses compounds with specific local molecular structures that contribute to dielectric anisotropy through their electronic properties while their spatial arrangement and optical properties provide broader viewing angles. The local molecular characteristics are optimized to achieve both fast response and wide viewing angle performance.
4Stability of the object's composition
If photoinitiators are added to enable polymerization, then the PSA effect is achieved, but the material complexity and potential harmful residues increase
Solution Approach 1:
The patent extracts or eliminates the photoinitiator component from the liquid crystal mixture while maintaining the polymerizable compounds. This allows the PSA effect to be achieved through direct polymerization of the liquid crystal molecules themselves or through alternative initiation methods, reducing material complexity and eliminating potential harmful residues from photoinitiator decomposition.
Solution Approach 2:
The patent enables the liquid crystal mixture to self-polymerize or self-stabilize without requiring external photoinitiators. The mixture contains polymerizable compounds that can undergo polymerization through applied electric fields, thermal energy, or other conditions, making the system self-sufficient and eliminating the need for additional chemical initiators.
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 new liquid crystalline media provide improved switching times, high VHR, and reduced threshold voltage, maintaining performance across a wide temperature range and viewing angles, thus addressing the limitations of existing materials.
Implementation Method 1
the liquid crystalline medium typically exhibiting a negative value of dielectric (DC) anisotropy (Δε). When an electrical voltage is applied to the electrodes, the liquid crystal molecules reorient themselves parallel to the electrode surfaces
Implementation Method 2
this compound is polymerized or crosslinked in situ when an electrical voltage is applied between the electrodes, usually by UV photopolymerization
Data Source
AI summary
The present invention relates to dielectrically positive, preferably nematic media comprising one or more polymerizable compounds, to polymer-stabilized media obtained therefrom, to the use thereof in liquid crystal displays, and to said displays, in particular PSA-IPS, PSA-FFS and PSA-Posi-VA displays.