Low Birefringence Polyimide Substrate for Flexible Displays
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Solution Overview
Problem
High birefringence in polyimide substrates used in flat panel displays leads to reduced black and white contrast and increased color shift at wide viewing angles, making them unsuitable for large and flexible displays.
Innovation Solution
A transparent polyimide substrate with a birefringence below 0.005 is developed by synthesizing polyimide using diamine monomers with sulfonyl functionality and dianhydride monomers, such as bis[4-(3-aminophenoxy)phenyl]sulfonyl and 3,3′,4,4′-diphenylsulfonyl tetracarboxylic dianhydride, through polycondensation routes that include thermal or chemical imidization, resulting in a material suitable for flexible flat panel displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional polyimide substrates are used for flexible flat panel displays, then mechanical strength and heat resistance are improved, but birefringence increases causing reduced contrast and color shift
Solution Approach 1:
The patent changes the chemical structure parameters of polyimide by introducing specific aromatic groups (terephthalyl, isophthalyl, trimellitic anhydride units) to achieve a birefringence value of 0.005 or less while maintaining mechanical strength and heat resistance properties
Solution Approach 2:
The patent creates a composite polyimide structure combining multiple aromatic acid anhydride units (terephthalyl, isophthalyl, trimellitic anhydride) with diamine monomers to achieve both low birefringence and high mechanical strength through the synergistic effect of different structural components
2Strength
If glass substrates are used for large flat panel displays, then mechanical strength and stability are improved, but weight and cost increase
Solution Approach 1:
The patent replaces expensive and heavy glass substrates with lighter plastic polyimide substrates that can be processed more economically, achieving comparable mechanical stability through optimized molecular structure while reducing weight and manufacturing cost
Solution Approach 2:
The patent changes the material parameter from glass to specifically designed polyimide with controlled aromatic group composition, achieving the necessary mechanical stability for display substrates while obtaining the weight reduction benefits of plastic materials
3Strength
If polyimide with high birefringence is used, then mechanical strength is improved, but display quality deteriorates due to reduced contrast and increased color shift
Solution Approach 1:
The patent optimizes the chemical structure parameters of polyimide by controlling the types and ratios of aromatic acid anhydride units to achieve birefringence of 0.005 or less, which directly improves the contrast ratio and reduces color shift in display applications while maintaining adequate mechanical strength
Data Source
AI summary
The invention relates to a transparent substrate with low birefringence. The transparent substrate comprises polyimide having a repeat unit of formula (I) and has a birefringence below 0.005:wherein each A of the repeat unit, being the same or different, represents an aromatic or aliphatic group, and at least one A is an aromatic or aliphatic group containing sulfonyl functionality; each B of the repeated unit, being the same or different, represents an aromatic or cycloaliphatic group; and n is an integer greater than one.