Liquid Crystal Aligning Agent Composition for Film Strength and Electrical Reliability
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Solution Overview
Problem
Conventional liquid crystal display devices face challenges in achieving high electrical characteristics and film strength due to limitations in the rubbing method and solubility issues with polyimide materials, which affect alignment stability and reliability.
Innovation Solution
A liquid crystal aligning agent composition containing polyamic acid repeating units and a urea-based compound with specific chemical structures is used, allowing for crosslinking between polyimide main chains, enhancing mechanical strength and reducing reactivity, thereby improving electrical characteristics and film strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rubbing method using fibers is used to align liquid crystals, then liquid crystal alignment is achieved, but fine dust and electrostatic discharge occur during manufacturing
Solution Approach 1:
The patent replaces the mechanical rubbing method with a photo-alignment method using light irradiation. Instead of using fibers to mechanically rub the polymer film surface, the invention uses polarized light to induce anisotropy in the polymer film, thereby aligning liquid crystals without contact. This substitution eliminates the generation of fine dust and electrostatic discharge while maintaining effective liquid crystal alignment.
Solution Approach 2:
The patent changes the alignment mechanism from mechanical contact to optical parameter control. By using polarized light with specific wavelength and intensity parameters, the polymer film's molecular orientation is controlled through photo-induced anisotropy, achieving liquid crystal alignment without mechanical rubbing and its associated harmful effects.
2Reliability
If polyimide is used as the alignment material, then superior alignment performance is achieved, but solubility in solvent is poor making direct coating difficult
Solution Approach 1:
The patent uses a solubilizing group as an intermediary component attached to the polyimide molecule. This solubilizing group acts as a mediator that enables the polyimide to dissolve in appropriate solvents while the polyimide backbone maintains its alignment performance. After coating and curing, the solubilizing group can be removed or remains as a benign residue, achieving both manufacturability and performance.
Solution Approach 2:
The patent creates a composite polyimide structure combining the polyimide backbone (providing alignment performance) with solubilizing side groups (providing solvent compatibility). This composite molecular structure allows the material to exhibit both good solubility for easy coating and superior liquid crystal alignment properties after curing.
3Strength
If high heat treatment temperature (200-230°C) is applied to form polyimide, then film strength is improved, but electrical characteristics deteriorate
Solution Approach 1:
The patent changes the heat treatment parameter from high temperature (200-230°C) to low temperature (80-150°C) curing process. By using a low-temperature curing regime with extended time, the polyimide film achieves sufficient crosslinking and mechanical strength without the thermal degradation that harms electrical characteristics. This parameter optimization resolves the contradiction between film strength and electrical performance.
Solution Approach 2:
The patent performs preliminary molecular design by incorporating crosslinkable functional groups into the polyimide structure before coating. This preliminary structural preparation enables the film to achieve adequate strength through low-temperature curing, avoiding the need for high-temperature treatment that would degrade electrical characteristics.
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 composition achieves high voltage holding ratios, low residual DC content, and improved film strength, leading to enhanced reliability and performance in liquid crystal display devices.
Implementation Method 1
a photo-alignment method for inducing anisotropy in a polymer film by light irradiation rather than the rubbing, and aligning liquid crystals using anisotropy
Implementation Method 2
heat-treating and curing the alignment-treated coating film
Data Source
AI summary
Provided is a liquid crystal aligning agent composition including a urea-based compound that contains two or more urea functional groups and has a structure in which a hydroxyalkyl group is substituted for a terminal amino group of a urea functional group, together with polyimide and its precursor polymer.