Polymerizable LC Medium for Long-Wavelength PSA Polymerization
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Solution Overview
Problem
Existing LC displays face issues with incomplete polymerization of reactive mesogens (RMs) during production, leading to residual unpolymerized RMs that cause image sticking and tilt angle instability, especially when using UV wavelengths below 320 nm, and result in decreased reliability and contrast.
Innovation Solution
The use of LC media comprising polymerizable compounds with specific structures, such as formula I and II, that enable complete polymerization at longer UV wavelengths (340 to 380 nm) using UV-LED lamps, minimizing residual RMs and enhancing tilt angle stability and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If UV wavelengths below 320 nm are used for polymerization, then polymerization efficiency is improved, but reliability decreases due to reaction with alignment layer polyimide
Solution Approach 1:
The patent changes the UV wavelength parameter from below 320 nm to 340-380 nm range, which reduces the harmful reaction with polyimide alignment layers while maintaining adequate polymerization efficiency through optimized initiator systems and extended exposure protocols
2Loss of energy
If UV intensity is reduced, then energy consumption decreases, but polymerization completeness worsens
Solution Approach 1:
The patent employs periodic UV irradiation with optimized duty cycles, using pulsed or intermittent exposure patterns that allow thermal management and prevent initiator depletion, thereby achieving complete polymerization at lower average power levels
Solution Approach 2:
The patent extends the total polymerization time through continuous or near-continuous low-intensity UV exposure, ensuring complete conversion of reactive mesogens while maintaining low energy consumption through efficient LED sources
3Speed
If alkenyl compounds are used to reduce response times, then response speed is improved, but reliability decreases due to reaction with polyimide
Solution Approach 1:
The patent introduces spatial or temporal differentiation in the LC composition, using alkenyl compounds only in specific regions or time periods during operation, or employing gradient concentrations that minimize harmful reactions while maintaining fast response in critical areas
Solution Approach 2:
The patent uses small, controlled amounts of alkenyl compounds that are intentionally designed to be consumed or deactivated during the polymerization process, sacrificing these components to achieve fast response times without compromising long-term reliability
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 quick and complete polymerization of RMs, reducing image sticking and improving display reliability with high VHR values, tilt stability, and low threshold voltages, suitable for PSA and SA displays.
Implementation Method 1
the RMs are then polymerized in situ by UV photopolymerization
Implementation Method 2
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
A liquid crystal (LC) medium comprising one or more polymerizable compounds, 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. Also, an LC display of the PSA or SA mode comprising the LC medium, and a process of manufacturing the LC display using the LC medium, especially an energy-saving LC display and energy-saving LC display production process.