Transparent Polyimide Film Composition With Low Haze and Thermal Expansion
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Solution Overview
Problem
Current polyimide films used as substrates for flexible electronic devices face challenges in achieving high heat resistance, low thermal expansion, and transparency due to trade-offs between these properties, with existing solutions either compromising on thermal expansion or haze levels.
Innovation Solution
A polyamic acid solution is developed using 2,2′-bistrifluoromethylbenzidine as a diamine component and 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 9,9′-(3,4′-dicarboxyphenyl)fluorenic dianhydride, with optional pyromellitic anhydride, which is imidized to form a polyimide film with a glass transition temperature of 380°C or higher, a coefficient of thermal expansion of 100 ppm/K or less, and high transparency, reducing haze and maintaining thermal dimensional stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If polyimide is made transparent by shortening the absorption wavelength through molecular design, then high visible light transmittance is achieved, but film-shaped polyimide has large haze and poor suitability as substrate material
Solution Approach 1:
The patent changes the molecular structure parameters of polyimide by incorporating specific rigid cyclic structures (naphthalene, fluorene, pyromellitic anhydride units) to shorten the absorption wavelength and achieve high visible light transmittance while controlling the polymerization parameters to maintain low haze through proper molecular weight and chain conformation
2Illumination intensity
If transparency of polyimide is enhanced, then high visible light transmittance is achieved, but the coefficient of thermal expansion tends to increase
Solution Approach 1:
The patent creates a composite molecular structure within the polyimide chain by combining multiple rigid cyclic units (naphthalene, fluorene, pyromellitic anhydride) that work synergistically to provide both optical transparency and thermal expansion control, effectively creating a multi-functional polymer composite structure
3Weight of moving object
If a plastic film substrate is used instead of glass substrate to achieve thin and lightweight electronic devices, then flexibility and weight reduction are achieved, but heat resistance and thermal expansion control become problematic
Solution Approach 1:
The patent fundamentally changes the thermal parameters of plastic film substrates by developing a polyimide with exceptionally high glass transition temperature (above 380°C) and controlled thermal expansion coefficient, transforming it from a typical heat-sensitive plastic into a high-temperature resistant substrate material suitable for electronic device fabrication
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 exhibits excellent thermal dimensional stability, high transparency, and low haze, making it suitable for flexible electronic devices, while maintaining high heat resistance and low thermal expansion, addressing the trade-offs in existing solutions.
Implementation Method 1
a polyimide precursor is applied onto the release layer, and imidized by heating to prepare a polyimide film substrate
Data Source
AI summary
A polyamic acid that is a polyaddition reaction product of a diamine and a tetracarboxylic dianhydrides, according to one or more embodiments of the present invention. The polyamic acid contains 2′-bistrifluoromethylbenzidine as a diamine component in addition to 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 9,9′-(3,4′-dicarboxyphenyl)fluorenic dianhydride as tetracarboxylic dianhydride components. The polyamic acid may include 9,9′-(3,4′-dicarboxyphenyl)fluorenic dianhydride in an amount ranging from 0.5 mol % or more to 10 mol % or less based on total amount of the tetracarboxylic anhydride.