PSA Liquid Crystal Display Polymer Alignment Control
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Solution Overview
Problem
PSA-mode liquid crystal display devices face challenges in achieving uniform pre-tilt angles and alignment stability, leading to display defects and unsatisfactory response speeds due to non-uniform pre-tilt angles and the influence of low-response-speed liquid crystal molecules far from projecting structures.
Innovation Solution
A liquid crystal display device with a polymer that regulates the alignment direction of liquid crystal molecules, featuring a number-average molecular weight of 50,000 or more, and a liquid crystal composition containing specific compounds, which are polymerized between substrates to control pre-tilt angles and ensure uniform alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a PSA-mode liquid crystal display device is used to improve viewing angle characteristics, then viewing angle is improved, but response speed becomes non-uniform and overall response speed decreases
Solution Approach 1:
The patent introduces a polymer as an intermediary substance that mediates between the liquid crystal molecules and the substrate. This polymer forms an alignment layer that uniformly controls the pre-tilt angle of liquid crystal molecules across the entire pixel area, including regions far from projecting structures. The polymer acts as a mediator that transmits alignment information uniformly, resolving the response speed non-uniformity while preserving the viewing angle improvements of PSA-mode displays.
2Productivity
If a polymerizable compound with low molecular weight is used to achieve fast polymerization, then polymerization speed is improved, but alignment stability deteriorates
Solution Approach 1:
The patent optimizes the molecular weight parameter of the polymerizable compound to a specific range (5,000-50,000) to simultaneously achieve fast polymerization and good alignment stability. This parameter optimization balances the competing requirements: lower molecular weight enables faster polymerization while the minimum threshold ensures sufficient alignment stability. The patent also optimizes the polymerizable compound content (0.01-5 wt%) to achieve this balance.
Solution Approach 2:
The patent creates a composite liquid crystal composition that combines the polymerizable compound with specific liquid crystal compounds (having negative dielectric anisotropy and specific molecular structures). This composite formulation ensures that the polymerizable compound polymerizes rapidly while the resulting polymer network provides stable alignment. The specific liquid crystal compounds enhance both the polymerization kinetics and the final alignment stability.
3Manufacturing precision
If reactive monomer is added to liquid crystal composition to form PSA structure, then pre-tilt angle control is improved, but unreacted monomers cause adverse effects on display device
Solution Approach 1:
The patent optimizes the concentration parameter of the polymerizable compound within a specific range (0.01-5 wt%) to ensure sufficient polymerization while minimizing unreacted monomers. This parameter control ensures that enough polymerizable compound is present to form the alignment structure, but not so much that excessive unreacted monomers remain to cause display defects. The patent also controls polymerization conditions (irradiation dose, temperature) to maximize conversion.
Solution Approach 2:
The patent employs rapid polymerization by optimizing the polymerization process conditions, including using appropriate photoinitiators and controlling irradiation intensity. This allows the polymerization to proceed quickly and completely, minimizing the time that unreacted monomers remain in the system and reducing their opportunity to cause adverse effects such as display defects or stability issues.
4Manufacturing precision
If polymer with low molecular weight is used to achieve uniform alignment, then alignment uniformity is improved, but pre-tilt angle stability deteriorates
Solution Approach 1:
The patent identifies and optimizes the molecular weight parameter of the polymer to a specific range (5,000-50,000) that balances alignment uniformity and pre-tilt angle stability. Polymers with molecular weights in this range provide sufficient chain length to maintain stable pre-tilt angles while remaining small enough to distribute uniformly throughout the liquid crystal composition. This parameter optimization resolves the contradiction between uniformity and stability.
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 solution achieves stable and uniform pre-tilt angles, improving display quality and response speed, and suppressing display defects, making it suitable for high-quality liquid crystal TV and monitor applications.
Implementation Method 1
polymerizing the polymerizable compound by irradiation with active energy rays
Implementation Method 2
controls the alignment direction of liquid crystal molecules in the liquid crystal composition layer to be substantially vertical to the first substrate and the second substrate on the sides adjacent to the liquid crystal composition layer when a voltage is applied between the common electrode and the pixel electrodes
Data Source
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AI summary
The present invention relates to a PSA-mode liquid crystal display device including a polymer produced by polymerizing a polymerizable compound by energy ray irradiation in a state in which a mixture of the polymerizable compound and a liquid crystal composition is held between the first substrate and the second substrate, the polymer having a number-average molecular weight of 50,000 or more in terms of polystyrene. In a PSA-mode display device in which alignment of liquid crystal molecules substantially vertically aligned between the substrates is controlled by applying a voltage, a pre-tilt angle can be properly given without being inhibited. Therefore, the present invention provides a PSA-mode display device with good alignment stability, uniform alignment within the substrates, and no or suppressed display defects and a method for producing the same. The liquid crystal display device is useful for VA-mode and PSVA-mode liquid crystal display devices for active matrix driving and can be applied to liquid crystal display devices of liquid crystal TV, monitors, cellular phones, smart phones, etc.