Block Copolymer Alignment Layer for LCD Stability
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Solution Overview
Problem
In liquid crystal displays (LCDs), the immiscibility of polyimide and polyamic acid in the alignment layer leads to weak Van der Waals forces, causing fragments to detach and become impurities in the liquid crystal layer, resulting in alignment defects and stained images.
Innovation Solution
A block copolymer alignment layer is formed using polyamic acid and polyimide moieties with a dianhydride structure, where the two components are covalently bonded, creating distinct regions that remain intact even under mechanical stress, preventing detachment and impurity formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide and polyamic acid are mixed in the alignment layer, then the alignment layer can be formed, but the immiscibility causes weak Van der Waals forces leading to fragment detachment
Solution Approach 1:
The patent creates a block copolymer composite material where polyimide blocks and polyamic acid blocks are covalently bonded together. This composite structure combines the benefits of both materials while eliminating the immiscibility problem through covalent bonding, resulting in an alignment layer that maintains both stability and adhesiveness
Solution Approach 2:
The block copolymer structure creates local regions with distinct properties: polyimide blocks provide thermal stability and structural integrity, while polyamic acid blocks provide adhesiveness and alignment characteristics. Each block performs its specific function locally while being covalently connected to prevent detachment
2Reliability
If polyimide alignment layer is used, then chemical resistance is excellent, but fragment detachment occurs under mechanical force such as rubbing
Solution Approach 1:
The block copolymer combines polyimide's chemical resistance with polyamic acid's cohesive bonding capability. The covalent bonds between blocks prevent fragment detachment during rubbing while maintaining the chemical resistance properties of the polyimide segments
Solution Approach 2:
The polyamic acid blocks act as intermediary elements that covalently connect polyimide blocks to each other and to the substrate. This intermediary bonding mechanism prevents fragment detachment while allowing the polyimide segments to maintain their chemical resistance
3Strength
If fragments detach from alignment layer, then mechanical stress is relieved, but impurities form in the liquid crystal layer causing stained images
Solution Approach 1:
The block copolymer structure with covalently bonded blocks creates a mechanically durable alignment layer that does not produce fragments under stress. The covalent bonds ensure that the entire structure moves as one unit, preventing fragment detachment and subsequent impurity formation in the liquid crystal layer
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 covalent bonding between polyimide and polyamic acid moieties in the alignment layer enhances the stability and adhesiveness, reducing detachment and impurity issues, thereby improving the alignment of liquid crystal molecules and preventing image defects in LCDs.
Implementation Method 1
the polyamic acid moieties and the polyimide moieties form a block copolymer
Implementation Method 2
Since the only force existing between polyimide and polyamic acid is the Van der Waals force, which is a weak attractive force between certain molecules
Data Source
AI summary
A liquid crystal display includes; a first and a second display panel facing each other, an alignment layer formed on at least one of the first and the second display panels and including a polyamic acid moieties and a polyimide moieties which form a block copolymer, and a liquid crystal layer interposed between the first display panel and the second display panel.