Polyimide Precursor Composition for Low-Expansion Transparent Films
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Solution Overview
Problem
Conventional polyimide films exhibit high thermal expansion coefficients, which are not suitable for flexible displays requiring low thermal expansion, high solubility, transparency, and thermal stability, and they also suffer from color issues due to light absorption in the visible wavelength range.
Innovation Solution
A polyimide precursor composition comprising an acid dianhydride, a diamine, and a dimethylsiloxane-diphenylsiloxane oligomer, along with an organic solvent having a positive partition coefficient, is used to produce a polyimide film with reduced thermal expansion and improved transparency, achieved through specific molecular weight and molar fraction ratios of the polymerization components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional polyimide is used to ensure heat resistance and mechanical properties, then thermal stability is improved, but thermal expansion coefficient is high and color transparency is poor
Solution Approach 1:
The patent uses a composite structure consisting of polyimide main chains with pendant cyclo-olefin groups. This composite molecular architecture combines the thermal stability of polyimide with the low thermal expansion characteristics of cyclo-olefin structures, achieving a balance between heat resistance and low thermal expansion coefficient
Solution Approach 2:
The invention introduces cyclo-olefin groups at specific positions (pendant groups) along the polyimide chain rather than changing the entire molecular structure. This local modification allows the polymer to maintain polyimide's inherent thermal stability while acquiring the low thermal expansion property of cyclo-olefin segments
2Temperature
If conventional polyimide is used to ensure heat resistance, then thermal stability is improved, but color transparency is poor due to light absorption in visible wavelength range
Solution Approach 1:
The patent introduces cyclo-olefin pendant groups at specific locations along the polyimide chain. These localized cyclo-olefin structures modify the electronic distribution and reduce the charge transfer complex formation that causes coloration, while maintaining the overall polyimide structure's heat resistance
Solution Approach 2:
The invention changes the electronic and optical parameters of polyimide by incorporating cyclo-olefin groups, which alter the HOMO-LUMO energy gap and reduce light absorption in the visible range. This parameter modification achieves colorless transparency while preserving thermal stability
3Illumination intensity
If polyimide is synthesized to achieve colorless transparency by introducing electron-withdrawing groups, then transparency is improved, but thermal expansion coefficient remains high
Solution Approach 1:
The patent creates a composite molecular structure where polyimide chains are combined with cyclo-olefin pendant groups. This composite architecture simultaneously achieves the optical properties improvement (through cyclo-olefin's electronic structure) and thermal expansion control (through cyclo-olefin's rigid chain conformation)
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 resulting polyimide film demonstrates high heat resistance, low residual stress, and enhanced transparency, making it suitable for flexible displays and other applications requiring thermal stability and optical clarity.
Implementation Method 1
alleviate the thermal expansion-shrinkage behavior
Implementation Method 2
polyimide is a polymeric material that has excellent heat resistance and chemical resistance, excellent mechanical properties, electrical properties and dimensional stability due to its rigid chain structure
Implementation Method 3
it can be explained by the theory of charge transfer complex (hereinafter, called CT-complex) induced by π electrons of benzene within a main chain of the polyimide
Implementation Method 4
Conventional polyimides absorb light in a visible wavelength ranging from 400 nm to 500 nm
Data Source
Figure 1(a)~1(b)
Figure 2
AI summary
A polyimide precursor composition according to the present invention enables alleviation of thermal expansion-contraction properties of a polyimide film resultingly prepared, by means of using siloxane-based diamine having a particular structure and a solvent having a positive partition coefficient. And the present invention enables excellent transparency, heat resistance, mechanical strength and flexibility and effective reduction of residual stress, and thus can be used in various fields such as a substrate for a device, a cover substrate for a display, an optical film, an integrated circuit (IC) package, an adhesive film, a multi-layer flexible printed circuit (FPC), tape, a touch panel and a protective film for an optical disk.