Polyimide Photo-Alignment Agent for LCD Afterimage Reduction
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Solution Overview
Problem
Conventional liquid crystal photo-alignment methods, such as the rubbing method and photo-alignment method, face issues with dust contamination, electrical discharge, poor structural and thermal stability, and afterimage generation, which affect the uniformity and contrast ratio of liquid crystal displays.
Innovation Solution
A liquid crystal photo-alignment agent comprising a polyimide copolymer with specific structure units is applied to a substrate, followed by a primary bake and exposure process, and a secondary bake, to enhance alignment and film hardness, minimizing afterimages and improving AC and DC alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rubbing method is used to align liquid crystals, then alignment can be achieved, but fine dust or electrical discharge occurs causing manufacturing problems
Solution Approach 1:
The patent replaces the mechanical rubbing method with a photo-alignment method using UV irradiation. The polyimide copolymer film is exposed to UV light to induce photo-alignment, eliminating the need for physical contact with fibers that generate dust and electrical discharge. This substitution resolves the contradiction by maintaining alignment capability while removing harmful mechanical effects.
Solution Approach 2:
The patent modifies the chemical structure of the polyimide polymer by incorporating specific cyclic carbonate structure units (Formula 1) and carboxyl structure units (Formula 2) in controlled ratios. This parameter change in molecular structure enables the material to achieve proper photo-alignment properties and thermal stability without requiring mechanical rubbing, thus eliminating dust and discharge issues while maintaining alignment precision.
2Manufacturing precision
If conventional photo-alignment polymer is used, then alignment can be achieved, but structural and thermal stability are poor causing afterimages
Solution Approach 1:
The patent creates a composite polyimide copolymer structure combining cyclic carbonate units (Formula 1) and carboxyl units (Formula 2) in specific proportions (70-95 mol% and 5-30 mol% respectively). This composite structure leverages the complementary properties of both units: the cyclic carbonate provides photo-alignment capability while the carboxyl groups enhance thermal stability and structural rigidity, preventing afterimages while maintaining alignment quality.
Solution Approach 2:
The patent optimizes the molecular composition parameters by controlling the ratio of cyclic carbonate to carboxyl structure units. This parameter optimization ensures the polymer achieves the critical balance between photo-reactivity for alignment and thermal/structural stability for afterimage prevention, resolving the contradiction between alignment capability and material stability.
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 improved afterimage resistance, film hardness, and uniform alignment, leading to enhanced electro-optic properties and reliability in liquid crystal displays.
Implementation Method 1
linearly polarized UV is radiated on the alignment layer to cause a photo-reaction. As a result, the photo-alignment in which main chains of the photo-alignment polymer are arranged in a set direction occurs
Implementation Method 2
The liquid crystal display may generate electric fields in a liquid crystal layer by applying voltage to the field-generating electrodes, and may change the direction of liquid crystal molecules of the liquid crystal layer according to the generated electric field, thereby controlling polarization of incident light
Implementation Method 3
a photo-alignment method in which anisotropy is induced to the polymer film by light radiation instead of friction thereby arranging the liquid crystals using anisotropy
Data Source
AI summary
A liquid crystal photo-alignment agent includes a polyimide copolymer including a first structure unit represented by the described Chemical Formula 1 and a second structure unit represented by the described Chemical Formula 2, and, based on a 100 mole % sum total of the first structure unit and the second structure unit, the first structure unit is included in an amount of 70 to 95 mole % and the second structure unit is included in an amount of 5 to 30 mole %. A liquid crystal photo-alignment film may be manufactured using the same, and a liquid crystal display may include the liquid crystal photo-alignment film.