Polyimide Precursor with Thermally-Leaving Group for Adhesion
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Solution Overview
Problem
The challenge is to enhance the adhesion of polyimide liquid crystal alignment films to sealing agents in liquid crystal display devices, as polyimides lack polar groups, leading to insufficient bonding, and to efficiently remove decomposed products from photo-alignment methods using polarized ultraviolet rays.
Innovation Solution
A liquid crystal aligning agent containing specific polyimide precursors and imidized polymers with thermally-leaving groups, which form amino groups upon heating, improving adhesion and solubility of decomposed products in aqueous washing solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyimide liquid crystal alignment film is used, then liquid crystal alignment performance is achieved, but adhesion to sealing agent is insufficient due to lack of polar groups
Solution Approach 1:
The patent changes the chemical parameters of the polyimide alignment film by introducing polar groups (carboxyl, hydroxyl, or amine groups) through specific chemical structures in the polyimide precursor. This allows the film to form covalent bonds with sealing agents, fundamentally changing the bonding mechanism from physical adhesion to chemical bonding.
Solution Approach 2:
The patent creates a composite polyimide structure that combines the original polyimide backbone with additional polar functional groups. This composite structure maintains the liquid crystal alignment properties of polyimide while adding the bonding capability of polar groups, achieving both alignment performance and improved adhesion.
2Reliability
If photo-alignment method is used to impart liquid crystal alignment performance, then alignment is achieved, but decomposed products remain on the film surface
Solution Approach 1:
The patent changes the chemical composition of the polyimide film by incorporating polar groups that enhance solubility in aqueous washing solutions. This allows decomposed products from photo-alignment to be effectively removed through washing, as the polar groups increase the polarity and water solubility of the film material and its decomposition products.
3Productivity
If picture frame area is reduced to broaden effective pixel area, then device efficiency is improved, but adhesion between substrates becomes insufficient
Solution Approach 1:
The patent introduces polar functional groups (carboxyl, hydroxyl, or amine groups) into the polyimide alignment film structure, fundamentally changing the surface chemistry from non-polar to polar. This enables covalent bonding with sealing agents, ensuring reliable adhesion even when picture frame areas are minimized for higher pixel density.
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 results in improved adhesion between the liquid crystal alignment film and sealing agents, enhancing the reliability of liquid crystal display devices, and facilitates efficient removal of decomposed products, thereby improving display quality and reducing residual images.
Implementation Method 1
a polyimide precursor having a bond represented by the following formula (1) in its main chain, wherein D is a protecting group to be replaced with a hydrogen atom by heat
Implementation Method 2
one utilizing photoisomerization reaction, one utilizing photocrosslinking reaction, one utilizing photodecomposition reaction
Implementation Method 3
since a polyimide has no polar group, no covalent bond is formed between the sealing agent and the surface of the liquid crystal alignment film
Data Source
AI summary
To provide a liquid crystal aligning agent to obtain a liquid crystal alignment film which is excellent in the adhesion to a sealing agent and a substrate of a liquid crystal display device, and of which a decomposed product formed after irradiation with ultraviolet rays will easily be removed.A liquid crystal aligning agent containing at least one polymer selected from the group consisting of a polyimide precursor having a bond represented by the following formula (1) in its main chain and an imidized polymer of the polyimide precursor:wherein each of R1, R2, R3 and R4 which are independent of one another, is a hydrogen atom or a C1-20 monovalent hydrocarbon group which may have a substituent, and D is a protecting group to be replaced with a hydrogen atom by heat.