Meta-Bonded Polymerizable Mesogens for PS LC Displays
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Solution Overview
Problem
Current liquid crystal (LC) displays, particularly in PS(A) types, face challenges such as limited viewing angle independence of contrast, high melting points, and solubility issues with existing polymerizable mesogenic compounds, leading to difficulties in achieving high stability, short switching times, and low threshold voltages.
Innovation Solution
The use of polymerizable mesogenic compounds with a 'kinked' molecular structure, featuring meta-bonds instead of the traditional para-bonded ring systems, which allows for improved solubility and lower melting points, enabling effective pretilt angle control and polymerization without photoinitiators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If polymerizable mesogenic compounds with traditional para-bonded ring systems are used, then the LC display achieves stable molecular orientation, but the melting point is high and solubility is poor
Solution Approach 1:
The patent changes the bonding parameter from traditional para-position (1,4-) to meta-position (1,3-) in the mesogenic compound structure. This structural parameter change reduces the melting point and improves solubility while maintaining the liquid crystalline properties and molecular orientation stability needed for LC display operation.
Solution Approach 2:
The patent creates a composite FK medium by combining the novel meta-bonded polymerizable mesogenic compounds with conventional liquid crystal host materials. This composite approach allows the unique properties of the meta-bonded compounds (lower melting point, improved solubility) to complement the established performance of conventional LC hosts, achieving both processability and display performance.
2Stability of the object's composition
If polymerizable mesogenic compounds with traditional para-bonded ring systems are used, then the LC display achieves stable molecular orientation, but solubility in FK medium is poor
Solution Approach 1:
The patent changes the bonding parameter from traditional para-position (1,4-) to meta-position (1,3-) in the mesogenic compound structure. This structural parameter change improves solubility in the FK medium while maintaining the liquid crystalline properties and molecular orientation stability needed for LC display operation.
3Reliability
If protrusions are added to electrodes to achieve controlled switching in MVA displays, then viewing angle independence is improved, but light transmission is reduced
Solution Approach 1:
The patent extracts the function of controlled switching from the electrode protrusions and transfers it to the meta-bonded polymerizable mesogenic compounds. By removing the protrusion structure, light transmission is improved while the meta-bonded compounds maintain the controlled switching capability through their inherent molecular properties and polymerization behavior.
4Illumination intensity
If distances between slits and protrusions are increased to improve light transmission, then light transmission is improved, but switching times increase
Solution Approach 1:
The patent removes the protrusion structure entirely, eliminating the need to optimize distances between slits and protrusions. The meta-bonded polymerizable mesogenic compounds provide controlled switching through their molecular structure and polymerization kinetics, maintaining fast switching times while allowing optimized slit geometry for maximum light transmission.
Solution Approach 2:
The patent changes the switching mechanism parameter from geometric control (protrusion distance) to molecular control (polymerization kinetics of meta-bonded compounds). This allows independent optimization of both light transmission (through slit geometry) and switching speed (through polymerization rate), resolving the trade-off between these two parameters.
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
This approach results in LC displays with enhanced stability, reduced switching times, and improved viewing angle independence of contrast and grayscale, while maintaining high voltage holding ratios and low threshold voltages.
Implementation Method 1
a layer of an FK medium located between the substrates containing a polymerized component and a low molecular weight component, the polymerized component being obtainable by polymerizing one or more polymerizable compounds between the substrates of the FK cell in the FK medium
Implementation Method 2
the FK medium typically has a negative value of dielectric (DK) anisotropy. When switched off, the molecules of the FK layer are oriented perpendicular to the electrode surfaces (homeotropic) or tilted homeotropically. When an electrical voltage is applied to the electrodes, the FK molecules are reoriented parallel to the electrode surfaces.
Implementation Method 3
OCB displays (optically compensated bend) are known, which are based on a birefringence effect and have an FK layer with a so-called 'bend' orientation and usually positive (DK) anisotropy. When an electrical voltage is applied, the FK molecules are reoriented perpendicular to the electrode surfaces.
Implementation Method 4
when a voltage is applied, an electric field is generated which has a significant component parallel to the FK layer. This causes a reorientation of the FK molecules in the layer plane.
Implementation Method 5
only one of which is designed as a structured (comb-shaped) electrode and the other electrode is unstructured. This creates a strong so-called 'fringe field’, i.e. a strong electric field close to the edge of the electrodes and an electric field in the entire cell, which has both a strong vertical and a strong horizontal component.
Implementation Method 6
OCB displays typically contain one or more birefringent optical retardation films to avoid unwanted light transmission of the 'bend' cell in the dark state.
Data Source
AI summary
The invention relates to a PS (polymer stabilized) or PSA (polymer sustained alignment) liquid crystal (FK) display, and to polymerizable compounds and liquid crystal (FK) means for use in PS (polymer stabilized) and PSA displays.