Cinnamic Acid Derivatives Photoalignment for Liquid Crystal Displays
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Solution Overview
Problem
Conventional liquid crystal displays face challenges with strong viewing-angle dependence of contrast, high production costs due to rubbing processes for polyimide alignment layers, and limitations in achieving high voltage holding ratios without using polyimide layers.
Innovation Solution
A liquid crystal mixture comprising self-assembling photoalignment agents and polymerizable compounds is used, where the mixture is photoaligned with linearly polarized light and cured with UV light to achieve homogeneous alignment within the LC display, eliminating the need for polyimide layers and enabling short response times and good viewing-angle dependence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polyimide alignment layers with rubbing processes are used, then homogeneous alignment of liquid crystals is achieved, but production costs increase and process complexity increases
Solution Approach 1:
The patent replaces the mechanical rubbing process with a photoalignment mechanism. Instead of using mechanical contact between a rubbing cloth and the polyimide layer to achieve molecular orientation, the invention uses linearly polarized light to induce photoalignment of liquid crystal molecules through photoreactive groups in the alignment layer, thereby eliminating the need for mechanical rubbing while maintaining alignment homogeneity
Solution Approach 2:
The patent introduces photoreactive groups (such as cinnamate, styrene, or vinyl groups) into the alignment layer material structure. These photoreactive groups undergo photochemical reactions when exposed to linearly polarized light, changing the molecular orientation parameters of the alignment layer and enabling photoinduced alignment without mechanical rubbing
2Manufacturing precision
If polyimide alignment layers are used, then homogeneous alignment is achieved, but response time increases
Solution Approach 1:
The patent incorporates photoreactive functional groups (cinnamate, styrene, vinyl) into the alignment layer polymer structure. These groups enable photoinduced molecular reorientation that creates a more effective alignment field, improving the speed and efficiency of liquid crystal molecule reorientation during switching operations, thereby reducing response time while maintaining alignment homogeneity
3Reliability
If polyimide layers are used to achieve high voltage holding ratio, then voltage holding performance is improved, but device complexity and production cost increase
Solution Approach 1:
The patent creates an alignment layer that simultaneously performs multiple functions: (1) provides homogeneous alignment through photoinduced molecular orientation, (2) achieves high voltage holding ratio through the formation of a dense polymer network structure from photopolymerization, and (3) enables photoalignment without mechanical rubbing. This multi-functional alignment layer eliminates the need for separate polyimide layers and rubbing processes, reducing device complexity while maintaining or improving voltage holding performance
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 method simplifies the production process, reduces costs, and maintains high contrast and short response times, achieving stable and irreversible homogeneous alignment of liquid crystals without the use of polyimide layers.
Implementation Method 1
N.A. Clark et al., Langmuir 2010, 26(22), 17482-17488 have shown that it is possible to self assemble a compound of the following structure onto a substrate to give a monolayer that is able to be photoaligned
Implementation Method 2
irradiating the liquid crystal mixture with linearly polarised light causing photoalignment of the liquid crystal; and curing the polymerisable compound in the liquid crystal mixture by irradiation with ultraviolet light
Data Source
AI summary
The invention relates to cinnamic acid derivatives of formula (S) wherein the radicals have the meaning indicated in claim1, to a process for their preparation and their use as self assembling photoalignment agent in liquid crystal mixtures. The invention further relates to a process for the fabrication of a liquid crystal (LC) display device with homogeneous alignment by photoaligning a liquid crystal mixture with positive or negative dielectric anisotropy comprising one or more compounds of formula S and optionally a polymerisable compound, to the liquid crystal mixture comprising the self assembling photoaligning agent and optionally the polymerisable compound and to the LC display produced by said process.