Polyimide Precursor Low Thermal Expansion Flexible Displays
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Solution Overview
Problem
Semi-alicyclic polyimides with alicyclic tetracarboxylic dianhydride and aromatic diamine components face challenges in maintaining low coefficient of linear thermal expansion both at low and high temperatures, affecting their suitability for forming fine circuits and flexible display substrates.
Innovation Solution
A polyimide precursor with specific repeating units, such as norbornane-spiro-cyclopentane tetracarboxylic acid and aromatic diamines, is used to produce a polyimide with a coefficient of linear thermal expansion of 100 ppm/K or less from 50°C to 400°C, ensuring high transparency and bending resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If semi-alicyclic polyimide is used to achieve transparency and bending resistance, then transparency and flexibility are improved, but coefficient of linear thermal expansion becomes too high (50 ppm/K or more)
Solution Approach 1:
The patent changes the chemical structure parameters of the polyimide by using specific alicyclic tetracarboxylic dianhydrides with constrained ring structures (norbornane, bicyclo[2.2.2]octane, adamantane frameworks) to reduce thermal expansion while maintaining transparency. This structural parameter change achieves coefficient of linear thermal expansion below 50 ppm/K while preserving the transparency and flexibility required for flexible displays
Solution Approach 2:
The patent creates a composite molecular structure by combining alicyclic tetracarboxylic dianhydride components with specific aromatic diamine components. This composite approach at the molecular level achieves both transparency (from the alicyclic structure) and low thermal expansion (from the constrained ring framework), resolving the contradiction between these two properties
2Strength
If semi-alicyclic polyimide is used for flexible substrates, then bending resistance is improved, but warpage occurs during circuit board formation due to high thermal expansion
Solution Approach 1:
The patent modifies the molecular structure parameters by incorporating constrained alicyclic ring systems (norbornane, bicyclo[2.2.2]octane, adamantane) into the polyimide backbone. This structural change reduces the coefficient of linear thermal expansion to below 50 ppm/K, preventing warpage during circuit board formation while maintaining the bending resistance needed for flexible substrates
3Temperature
If conventional polyimide is used to achieve heat resistance, then high temperature stability is improved, but transparency deteriorates due to yellowish-brown coloration
Solution Approach 1:
The patent changes the chemical structure by using alicyclic tetracarboxylic dianhydrides with constrained ring structures instead of conventional aromatic tetracarboxylic dianhydrides. This structural parameter change eliminates the intramolecular conjugation that causes yellowish-brown coloration, achieving high transparency while maintaining heat resistance through the stable alicyclic framework
Data Source
AI summary
A polyimide precursor including at least one repeating unit represented by the following chemical formula (1):in which A is an arylene group; and X1 and X2 are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms, and a polyimide obtained from the polyimide precursor has a coefficient of linear thermal expansion from 50° C. to 400° C. of 100 ppm/K or less.