Liquid Crystal Display Alignment Film Stabilization
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Solution Overview
Problem
Liquid crystal displays with vertical alignment mode experience a decrease in voltage retention rate over time when using a liquid crystal composition containing an alkenyl compound, leading to degraded response characteristics.
Innovation Solution
Incorporating a liquid crystal composition with alkenyl compounds and crosslinkable polymer compounds in the alignment films, where the alkenyl compounds are represented by a specific general formula, and applying pretilt to the liquid crystal molecules using crosslinked or deformed polymer compounds to stabilize their orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a liquid crystal composition containing an alkenyl compound is used to achieve high-speed response, then response speed is improved, but voltage retention rate decreases over time
Solution Approach 1:
The patent uses a composite alignment film structure combining a polyimide layer and a crosslinked polymer layer. The polyimide layer provides initial vertical alignment, while the crosslinked polymer layer (formed from polymer compounds with crosslinkable functional groups) stabilizes the alignment and prevents degradation over time. This composite structure allows the liquid crystal composition to contain alkenyl compounds for high-speed response while maintaining voltage retention through the stabilizing crosslinked layer.
Solution Approach 2:
The alignment films are prepared in advance with specific properties before the liquid crystal composition is sealed. The crosslinked polymer layer is formed prior to sealing, creating a pre-established alignment structure that prevents future degradation. This preliminary preparation ensures that when the alkenyl-containing liquid crystal composition is sealed between the alignment films, it maintains both high-speed response and stable voltage retention without requiring additional treatment after sealing.
2Adaptability or versatility
If vertical alignment mode is used to achieve wider viewing angle, then viewing angle is improved, but response characteristics are degraded due to disordered molecular alignment
Solution Approach 1:
The patent applies different alignment properties to different layers of the alignment film structure. The polyimide layer provides vertical alignment for wide viewing angle, while the crosslinked polymer layer provides localized stabilization that induces a uniform tilt direction. This local differentiation allows the liquid crystal molecules to maintain vertical alignment for wide viewing angle while having a predetermined tilt direction for improved response characteristics, resolving the contradiction between viewing angle and response speed.
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 configuration enhances the response speed and maintains excellent display properties by setting the long axis direction of liquid crystal molecules in a predetermined direction, preventing the decrease in voltage retention rate and improving response characteristics.
Implementation Method 1
pretilt is applied to the liquid crystal molecules by the crosslinked compound
Implementation Method 2
the liquid crystal molecules have negative dielectric anisotropy, that is, a property for obtaining a smaller dielectric constant of the liquid molecules in a long axis direction compared to that in a short axis direction
Data Source
AI summary
There is provided a liquid crystal display including: a liquid crystal display element which includes a pair of alignment films which are provided on facing surface sides of a pair of substrates, and a liquid crystal layer which is provided between the pair of alignment films and is configured to have a liquid crystal composition containing liquid crystal molecules having negative dielectric anisotropy, in which at least one of the pair of alignment films contains a compound obtained by crosslinking polymer compounds each including a first side chain which interacts with the liquid crystal molecules and a crosslinkable functional group as a second side chain, with each other, the liquid crystal composition configuring the liquid crystal layer contains at least one kind of an alkenyl compound represented by the following general formula (AN-1), and pretilt is applied to the liquid crystal molecules by the crosslinked compound.