Fluorinated Polyimide Film for Low-Hysteresis Humidity Sensing
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Solution Overview
Problem
Capacitance-type humidity sensors experience high hysteresis during moisture absorption and desorption processes, leading to inaccurate humidity detection.
Innovation Solution
A moisture-sensitive film is developed using a resin composition with a fluorinated polyimide resin containing a phthalimide ring and a benzene ring, where the mass fraction of the benzene ring to the phthalimide ring satisfies a specific ratio, reducing hysteresis by promoting molecular packing and minimizing dimensional changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional polyimide is used as a moisture-sensitive film, then the film can detect humidity changes, but it exhibits high hysteresis between moisture absorption and desorption processes
Solution Approach 1:
The patent changes the chemical composition parameters of the polyimide by introducing fluorinated groups and controlling the ratio of phthalimide rings to benzene rings. Specifically, the polyimide resin is designed with a phthalimide ring content of 20-80 mass% and a specific mass fraction ratio W(PhI)/W(Be) of 1.2 or more, which fundamentally alters the molecular structure to reduce hysteresis while maintaining humidity sensitivity
Solution Approach 2:
The patent creates a composite polyimide structure combining fluorinated polyimide with specific ring structures (phthalimide and benzene rings in controlled ratios). This composite molecular architecture leverages the complementary properties of different structural elements: fluorinated groups for moisture sensitivity, phthalimide rings for dimensional stability, and benzene rings for structural framework, achieving low hysteresis performance
2Measurement precision
If the polyimide structure is modified to reduce hysteresis, then measurement accuracy improves, but the complexity of resin composition control increases
Solution Approach 1:
The patent establishes clear quantitative parameters to simplify the complexity: fluorinated polyimide with 20-80 mass% phthalimide ring content and a mass fraction ratio W(PhI)/W(Be) of 1.2 or more. By defining specific numerical ranges and ratios, the invention transforms a complex material design problem into a controllable parameter optimization problem with clear target values
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 solution effectively reduces hysteresis in the moisture-sensitive film, enabling more accurate humidity detection and minimizing film deterioration by allowing moisture to absorb and desorb without significant dimensional changes.
Implementation Method 1
reducing hysteresis by promoting molecular packing and minimizing dimensional changes
Implementation Method 2
environmental humidity is detected by detecting changes in the dielectric constant of the moisture-sensitive film based on change in the capacitance between the electrodes
Implementation Method 3
detecting changes in the dielectric constant of the moisture-sensitive film
Data Source
AI summary
A moisture-sensitive film formed from a resin composition and containing a polyimide resin component. The polyimide resin component comprises a fluorinated polyimide resin. The polyimide resin component comprises a phthalimide ring and a benzene ring different from a benzene ring included in the phthalimide ring. Based on a total amount of the polyimide resin component, the benzene ring different from the benzene ring included in the phthalimide ring has a mass fraction W (Be) and the phthalimide ring has a mass fraction W (PhI) satisfying the following formula: W (PhI)/W (Be)≥1.2.