Fluorene Polyimide Film Composition for Low-Expansion Transparency
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Solution Overview
Problem
Polyimide films lack sufficient heat resistance and optical transparency, particularly in display applications, due to high thermal expansion coefficients and inherent coloration issues, which are not adequately addressed by existing materials like KAPTON.
Innovation Solution
A polyimide precursor solution is developed with a fluorene structure integrated into the rigid polyimide chain, using specific tetracarboxylic dianhydrides and diamines in an organic solvent with a positive LogP value, allowing for enhanced heat resistance and optical properties through controlled thermal expansion and reduced thickness retardation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polyimide is used to ensure mechanical strength and thermal stability, then the film maintains structural integrity, but the thermal expansion coefficient remains too high and optical clarity is insufficient
Solution Approach 1:
The patent modifies the chemical structure parameters of polyimide by introducing specific substituents (fluorene groups, cyclo-olefin structures) and adjusting the molecular composition ratio of diamine and tetracarboxylic dianhydride components. These parameter changes reduce the thermal expansion coefficient while maintaining thermal stability, achieving a balance between structural integrity and thermal performance.
Solution Approach 2:
The patent creates a composite polyimide structure by combining different functional units: rigid aromatic rings for thermal stability, fluorene groups for reduced thermal expansion, and cyclo-olefin structures for optical clarity. This composite approach integrates multiple benefits into a single polymer system that simultaneously achieves low thermal expansion and high reliability.
2Strength
If aromatic polyimide structure is used to ensure mechanical strength, then the film maintains durability, but the inherent color (dark brown) reduces optical clarity
Solution Approach 1:
The patent applies local quality modification by introducing specific functional groups (fluorene, cyclo-olefin) at strategic positions within the polyimide chain. These localized structural modifications affect optical properties without compromising the overall mechanical strength provided by the aromatic backbone, achieving colorless transparency while maintaining durability.
Solution Approach 2:
The patent directly addresses the color issue by replacing chromophoric aromatic structures with non-chromophoric fluorene and cyclo-olefin groups. This chemical modification changes the color from dark brown to colorless, improving optical clarity while the rigid backbone structure maintains mechanical strength.
3Ease of manufacture
If conventional polyimide synthesis is used to ensure process simplicity, then the manufacturing process remains straightforward, but heat resistance and optical properties are insufficient
Solution Approach 1:
The patent employs preliminary action by pre-synthesizing the specific diamine and tetracarboxylic dianhydride monomers with the required functional groups before polymerization. This allows the complex molecular structure to be built step-by-step through standard polycondensation reactions, maintaining process simplicity while achieving enhanced heat resistance and optical properties in the final product.
4Adaptability or versatility
If flexible display requirements are met with low thermal expansion, then the film adapts to bending applications, but heat resistance at high temperature processes is reduced
Solution Approach 1:
The patent creates a composite polyimide structure that combines flexible segments (introduced through specific diamine structures) with rigid heat-resistant units (aromatic rings, fluorene groups). This composite architecture provides both flexibility for bending applications and sufficient heat resistance for high-temperature processing, resolving the contradiction between adaptability and temperature stability.
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 heat resistance, transparency, and mechanical strength, suitable for flexible displays and high-temperature applications, with a coefficient of thermal expansion between 0 ppm/°C and 25 ppm/°C, and haze of 2 or less, optimizing thermal stability and visual sensitivity.
Implementation Method 1
reacting polymerization ingredients, which comprises: tetracarboxylic dianhydrides of Chemical Formula 1 and Chemical Formula 2; and a diamine of Chemical Formula 3, in an organic solvent
Implementation Method 2
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 3
the polyimide absorbs light of the wavelength below 400 nm to 500 nm of visible light region
Implementation Method 4
the thermal expansion coefficient should be further lowered. For example, KAPTON sold by Dupont has a low thermal coefficient of about 30 ppm/°C
Implementation Method 5
a method for manufacturing the polyimide film by using the polyimide precursor solution
Data Source
AI summary
The present invention provides a polyimide film which, by having a fluorine structure adopted into a rigid polyamide chain structure, exhibits not only superb heat resistance but also enhanced optical properties. Additionally, the polyimide according to the present invention, by having the particular structure, exhibits excellent transparency, heat-resistance, mechanical strength and flexibility, and thus can be utilized in a variety of functions such as an element substrate, display cover substrate, optical film, integrated circuit (IC) package, adhesive film, multilayered flexible printed circuit (FPC), tape, touch panel, and protective film for optical disks.