Liquid-Crystal Medium Polymerization UV Wavelength Optimization
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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 birefringence, and stability at low temperatures, while also requiring effective polymerization at longer UV wavelengths to minimize energy consumption and prevent issues like 'image sticking' and 'ODF mura'.
Innovation Solution
The development of an LC medium comprising polymerizable compounds with specific chemical structures that allow for efficient polymerization at UV wavelengths between 340 to 380 nm, providing high voltage-holding ratios, tilt stability, and solubility in a broad temperature range, suitable for use in PSA or SA displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If UV-LED lamps with higher wavelength emission (365nm) are used for polymerization, then energy consumption is reduced and lifetime is extended, but polymerization efficiency at longer wavelengths decreases
Solution Approach 1:
The patent modifies the chemical structure of the mesogenic compound by introducing specific functional groups (acrylate, methacrylate, oxetane, epoxide) that are highly responsive to UV irradiation at wavelengths of 340-380nm. This parameter change in molecular structure enables efficient polymerization using UV-LED lamps with 365nm emission, resolving the contradiction between energy consumption and polymerization efficiency
Solution Approach 2:
The patent uses photopolymerization initiators as intermediaries that absorb UV light at 365nm and transfer the energy to initiate polymerization of the mesogenic compound. This intermediary mechanism enables efficient energy transfer from the UV-LED lamp to the polymerizable groups, maintaining high polymerization efficiency while using energy-efficient 365nm UV-LED lamps
2Speed
If alkenyl compounds are used to reduce response times in LC media, then response time is shortened, but reliability decreases due to reaction with polyimide alignment layer under UV light
Solution Approach 1:
The patent extracts the problematic alkenyl group from the LC medium composition and replaces it with polymerizable functional groups (acrylate, methacrylate, oxetane, epoxide) that do not react with polyimide alignment layers. This substitution maintains fast response time performance while eliminating the harmful reaction that compromised reliability
Solution Approach 2:
The patent converts the potential harm of UV light causing unwanted reactions into a beneficial effect by using UV-initiated polymerization to create the desired tilt angle stabilization. The UV light that previously caused harmful reactions with alkenyl compounds and polyimide is now harnessed to initiate controlled polymerization of the mesogenic compound, creating a beneficial crosslinked structure for tilt stability
3Productivity
If shorter UV wavelengths (<320nm) are used for polymerization, then polymerization speed increases, but reliability decreases due to reaction with alignment layer
Solution Approach 1:
The patent optimizes the UV wavelength parameter to the range of 340-380nm, which provides sufficient polymerization speed while avoiding the harmful reactions that occur at wavelengths below 320nm. This parameter optimization balances polymerization efficiency with reliability by staying above the absorption threshold of the polyimide alignment layer
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 enables quick and complete polymerization, maintains high performance parameters, and reduces production costs by minimizing residual effects on LC mixture performance, ensuring stability and reliability across a wide temperature range.
Implementation Method 1
After filling the LC medium into the display the RMs are then polymerized in situ by UV photopolymerization
Data Source
AI summary
The present invention relates to a liquid-crystal (LC) medium comprising polymerizable compounds comprising a thioalkyl group, 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.