Polyimide Coating Composition with COOH Capping Groups
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Solution Overview
Problem
Current polyimide (PI) materials face challenges in achieving a balance between physical properties such as chemical resistance, thermal stability, and operability, with issues like excessive molecular weight leading to poor leveling and internal stress during coating, and cyclized SPIs becoming brittle and prone to yellowing during thermosetting.
Innovation Solution
A polyimide with two —COOH capping groups at each end, combined with a hardening agent having 2 to 6 functional groups capable of reacting with —COOH, forming a coating composition that undergoes net-like cross-linking, resulting in excellent chemical resistance, thermal properties, and resistance to yellowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the molecular weight of PAA is excessively high, then the chemical resistance and thermal stability are improved, but the viscosity becomes too high resulting in poor operability and poor leveling property during coating
Solution Approach 1:
The patent changes the molecular weight parameter of PAA to an optimal range (10,000-100,000) to simultaneously achieve good chemical resistance and acceptable viscosity for coating operations. This parameter optimization resolves the contradiction between high molecular weight benefits and processing difficulties.
Solution Approach 2:
The patent uses a composite system combining PAA with specific diamine monomers to create a polyimide coating that achieves both high chemical resistance and good operability. The composite approach allows tuning of properties through monomer selection while maintaining processability.
2Reliability
If the molecular weight of PAA is excessively high, then the chemical resistance is improved, but unleveling phenomena such as convex center and thick edges occur during spin coating
Solution Approach 1:
The patent optimizes the molecular weight parameter of PAA to balance chemical resistance with coating uniformity. By controlling molecular weight within a specific range, the patent prevents excessive viscosity that would cause spin coating defects while maintaining protective film performance.
3Reliability
If the molecular weight of PAA is excessively high, then the chemical resistance is improved, but an extremely large internal stress is generated during imidization causing the coated substrate to bend and deform
Solution Approach 1:
The patent controls the molecular weight parameter of PAA to reduce internal stress during imidization. By avoiding excessively high molecular weights, the patent prevents severe chain entanglement and bond shortening that would generate large internal stresses, thereby preventing substrate deformation while maintaining chemical resistance.
4Temperature
If cyclized SPI is used, then the thermosetting temperature is reduced, but a rigid structure is formed making the SPI brittle during thermosetting
Solution Approach 1:
The patent modifies the chemical structure of SPI by introducing flexible spacer groups between rigid aromatic rings. This structural parameter change allows the material to maintain low thermosetting temperature while avoiding excessive rigidity and brittleness, achieving a balance between processing temperature and mechanical flexibility.
5Temperature
If cyclized SPI is used, then the thermosetting temperature is reduced, but the SPI becomes prone to yellowing after cross-linking
Solution Approach 1:
The patent changes the chemical composition parameters of SPI by selecting specific monomer combinations and introducing stabilizing groups that resist oxidation and yellowing. This allows maintenance of low thermosetting temperature while improving color stability through compositional optimization.
6Ease of operation
If the cross-linking density is low, then the flexibility is improved, but the chemical resistance is poor
Solution Approach 1:
The patent uses a composite cross-linking system combining multiple cross-linking mechanisms and monomer types to achieve both flexibility and chemical resistance. The composite approach creates a nuanced network structure that provides adequate cross-linking for chemical resistance while maintaining spacing and flexibility through appropriate monomer selection.
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 provides a PI film with enhanced chemical resistance, thermal stability, and transparency, suitable for protective materials, replacing glass, and applicable in flexible electronic devices without yellowing or brittleness.
Implementation Method 1
Next, imidization of the PAA is carried out through heating, and after condensation, dehydration, and cyclization, the PAA is converted into the PI
Implementation Method 2
A coating composition which contains the aforementioned PI and a hardening agent having 2 to 6 functional groups capable of reacting with —COOH. A PI coating layer or PI film formed by the coating composition of the present invention has excellent chemical resistance and thermal properties
Data Source
AI summary
A polyimide (PI) having two —COOH capping groups at each end is provided. A coating composition is further provided, which contains the PI and a hardening agent having 2 to 6 functional groups capable of reacting with —COOH. A PI coating layer and PI film formed by the coating composition of the present invention possess excellent chemical resistance and coefficient of thermal expansion (CTE), which makes them applicable in fabrication of protective materials for active/passive devices, optical materials, touch panels, copper foil substrates, soft flexible electronic materials or integrated circuit elements, or film substrate for glass film touch panels.