Liquid Crystal Alignment Film Composition for Dust-Free Photo-Alignment
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Solution Overview
Problem
Conventional liquid crystal display technologies face challenges in achieving uniform luminance and high contrast ratios due to issues with the rubbing method, such as dust and electrostatic discharge, and the photo-alignment method requires high energy and additional heat treatments, leading to productivity and alignment stability problems. Additionally, polyimide-based alignment agents struggle with high film strength and electrical characteristics, especially at low frequencies and high temperatures.
Innovation Solution
A liquid crystal alignment agent composition comprising a copolymer with specific repeating units and a crosslinker compound, which includes silicon-containing functional groups, is used to form a liquid crystal alignment film. This composition is coated, dried, and then subjected to light irradiation or rubbing for alignment, followed by heat treatment to enhance alignment stability and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rubbing method is used to align liquid crystals, then liquid crystal alignment is achieved, but dust and electrostatic discharge occur during manufacturing
Solution Approach 1:
The patent replaces the mechanical rubbing method with a photo-alignment method using UV irradiation. The copolymer composition contains photoreactive groups that undergo photo-induced alignment when exposed to UV light, eliminating the need for physical contact with fibers that cause dust and electrostatic discharge. This substitution of mechanical alignment with optical alignment resolves the contradiction between achieving liquid crystal alignment and avoiding harmful manufacturing byproducts.
2Reliability
If polyimide is used for photo-alignment, then liquid crystal alignment property is improved, but high energy consumption and additional heat treatment are required
Solution Approach 1:
The patent modifies the chemical structure of the alignment agent by using a copolymer containing both imide groups and carboxylic acid groups, rather than conventional polyimide. This compositional parameter change enables the material to achieve effective liquid crystal alignment with lower UV energy exposure, reducing the energy consumption contradiction while maintaining alignment quality.
Solution Approach 2:
The patent employs a copolymer composition combining imide units and carboxylic acid units in a specific ratio (70:30 to 90:10). This composite structure leverages the alignment properties of imide groups while the carboxylic acid groups enhance photo-reactivity, allowing effective alignment at lower energy levels and reducing the need for additional high-temperature heat treatment processes.
3Strength
If crosslinker is added to enhance film strength, then film strength is improved, but electrical characteristics deteriorate at high temperatures and low frequencies
Solution Approach 1:
The patent carefully controls the crosslinker content parameter within a specific range (0.1-5 wt%) and optimizes the imide-to-carboxylic acid unit ratio (70:30 to 90:10). This parameter optimization achieves sufficient film strength through controlled crosslinking while preventing excessive crosslinking that would cause electrical property deterioration at high temperatures and low frequencies, thus resolving the contradiction between film strength and 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 solution provides a liquid crystal alignment film with improved alignment stability, high voltage holding ratio, reduced afterimage, and enhanced electrical characteristics, while maintaining film strength and shielding power through increased film density.
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
a copolymer for a liquid crystal alignment agent containing a first repeating unit including at least one selected from the group consisting of a repeating unit represented by Chemical Formula 1, a repeating unit represented by Chemical Formula 2, and a repeating unit represented by Chemical Formula 3, and a second repeating unit including at least one selected from the group consisting of a repeating unit represented by Chemical Formula 4, a repeating unit represented by Chemical Formula 5 and a repeating unit represented by Chemical Formula 6
Data Source
AI summary
The present invention relates to a liquid crystal alignment agent composition including a copolymer for liquid crystal alignment agent containing two types of repeating units classified according to the types of diamine-derived functional groups, and a crosslinker compound in which the protecting group having a specific structure was introduced, a method for preparing a liquid crystal alignment film using the same, and a liquid crystal alignment film and a liquid crystal display device using the same.