Alignment Film Copolymer for Liquid Crystal Display Thermal Stability
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Solution Overview
Problem
Conventional liquid crystal display devices using polyimide-based alignment films suffer from display defects like image sticking and stain, especially in high-temperature environments, due to the dissolution of low-molecular-weight compounds into the liquid crystal layer, which affects their thermal stability and reliability.
Innovation Solution
A copolymer with a repeating structural unit formed by cyclocondensation of tetraamine and dicarboxylic acid is used to create an alignment film with improved stiffness, preventing the dissolution of low-molecular-weight components into the liquid crystal layer and enhancing the film's thermal stability and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide-based alignment film is used, then good physical properties (heat resistance, affinity, mechanical strength) are achieved, but display defects (image sticking, stain) occur in high-temperature environments
Solution Approach 1:
The patent changes the chemical composition parameters of the alignment film by using polybenzoxazole, polybenzothiazole, or polybenzimidazole base polymers instead of conventional polyimide. These alternative polymers have different thermal and chemical properties that prevent dissolution into the liquid crystal layer while maintaining good alignment performance and heat resistance.
Solution Approach 2:
The patent creates a composite alignment film system by combining the base polymer (polybenzoxazole/polybenzothiazole/polybenzimidazole) with specific additives and photo-active groups. This composite structure achieves both thermal stability and prevention of display defects through synergistic effects of the components.
2Temperature
If thermal stability is improved by using polybenzoxazole-, polybenzothiazole-, or polybenzimidazole-based alignment film, then heat resistance is enhanced, but sufficient thermal stability is still not achieved in high-temperature environments
Solution Approach 1:
The patent optimizes the thermal stability by carefully selecting and adjusting the base polymer type (polybenzoxazole, polybenzothiazole, or polybenzimidazole), molecular weight, and compositional ratios. These parameter changes enable the alignment film to maintain dimensional stability and prevent dissolution even at elevated temperatures.
Solution Approach 2:
The patent introduces specific additives as intermediaries that enhance the thermal stability of the alignment film. These additives fill gaps in the polymer structure and strengthen intermolecular interactions, preventing film degradation and dissolution into the liquid crystal layer at high temperatures.
3Strength
If low-molecular-weight additive is introduced to improve cross-linking density, then hardness and compactness are improved, but unreacted additive dissolves into liquid crystal layer causing image sticking and stain
Solution Approach 1:
The patent changes the molecular weight parameters of the crosslinking additive to ensure complete reaction. By using low-molecular-weight additives with appropriate reactivity and stoichiometry, the patent achieves full cross-linking without leaving unreacted residues that could dissolve into the liquid crystal layer.
Solution Approach 2:
The patent eliminates the harmful effect by completely reacting and consuming the low-molecular-weight additive through controlled cross-linking reactions. The additive is fully integrated into the polymer network structure, leaving no free unreacted molecules that could migrate into the liquid crystal layer.
4Ease of manufacture
If conventional alignment film is used, then manufacturing is straightforward, but dissolution of low-molecular-weight compounds into liquid crystal layer occurs in high-temperature environments
Solution Approach 1:
The patent uses composite material systems with well-established solution processing methods. The alignment film composition includes base polymers and additives that can be dissolved in common solvents, allowing conventional coating and curing processes to be used while achieving superior thermal stability.
Solution Approach 2:
The patent maintains ease of manufacture by keeping the processing parameters (solvent selection, coating conditions, curing temperature and time) within conventional ranges. The chemical composition parameters are optimized for thermal stability while preserving compatibility with standard manufacturing equipment and processes.
Data Source
AI summary
An alignment film includes a copolymer containing a repeating structural unit represented by the following formula (1), wherein X1 and X2 may be the same as or different from each other and are each represented by any one of several formulas; and Y is represented by any one of several formulas