Fluorinated Polyimide Film for Flexible Display Substrates
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Solution Overview
Problem
Current polyimide films used in flexible displays face challenges such as thermal decomposition during high-temperature processes, poor mechanical and optical properties, and increased risk of tearing during rolling processes due to high residual stress and low modulus, which affect the reliability and performance of flexible displays.
Innovation Solution
A polyimide film with a thickness of 5 to 10 µm, a modulus of 3 to 8 GPa, and a strain of 10% or less at 100 MPa, incorporating fluorine-containing substituents in the acid dianhydride and diamine, which provides improved heat resistance, reduced retardation, and minimized residual stress, thereby enhancing the flexibility and reliability of the film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If polyimide film is used for flexible substrate, then lightness and flexibility are improved, but thermal decomposition occurs during high temperature process
Solution Approach 1:
The patent modifies the chemical structure of polyimide by introducing fluorine-containing substituents at specific positions (using compounds of formulas 1-6 with fluorine atoms replacing hydrogen atoms). This chemical parameter change enhances the polymer's thermal stability and heat resistance, allowing the flexible substrate to withstand high-temperature processes without decomposition while maintaining its lightweight properties.
Solution Approach 2:
The patent creates a composite polyimide structure by combining fluorinated aromatic compounds with specific molecular architectures. The resulting polyimide film integrates the lightweight characteristics of plastic materials with enhanced thermal stability through the fluorinated composite structure, resolving the contradiction between lightness and heat resistance.
2Strength
If polyimide film with high modulus is used, then mechanical strength is improved, but residual stress increases causing tearing during rolling process
Solution Approach 1:
The patent optimizes the molecular structure parameters of polyimide by selecting specific fluorinated compounds (formulas 1-6) with controlled rigidity and flexibility. This parameter optimization achieves a balanced mechanical property profile where the film has sufficient strength to prevent tearing but maintains low residual stress through appropriate molecular chain flexibility introduced by the fluorinated structure.
Solution Approach 2:
The patent introduces fluorine atoms at specific local positions within the polyimide molecular structure (using compounds of formulas 1-6 with fluorine substituents at various positions). This local structural modification creates regions of enhanced strength while maintaining overall flexibility, preventing stress concentration that would lead to tearing during rolling processes.
3Illumination intensity
If polyimide film with low retardation is used, then visual sensibility is improved, but optical anisotropy increases affecting display quality
Solution Approach 1:
The patent controls the optical parameters of polyimide by selecting fluorinated compounds with specific molecular orientations and symmetries (formulas 1-6). This parameter control achieves low retardation values that enhance visual sensibility and display quality while maintaining optical isotropy through the symmetric fluorinated molecular structure, preventing unwanted optical anisotropy effects.
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 polyimide film exhibits improved mechanical and optical properties, reducing the risk of tearing and current drop during TFT driving, while maintaining high transparency and visual sensibility, thus enhancing the process reliability and performance of flexible displays.
Implementation Method 1
curing by heat treatment
Implementation Method 2
applying to a surface of the polyimide film a predetermined direct current voltage by corona discharge to accumulate static charges
Data Source
Figure 1~2
AI summary
According to the present invention, damage such as film tearing during a rolling process can be reduced by using, as a substrate for a flexible display, a polyimide film having the thickness of 5-10 µm, modulus of 3-8 GPa, the absolute value of out-of-plane retardation (Rth) of 200-600 nm, and a strain, at a tensile force of 100 MPa, of 10% or less. In addition, since the polyimide film has low residual stress with respect to inorganic substrates, the occurrence of defects during a TFT process is reduced. As a result, processing reliability for a flexible display can be improved. In addition, the saturated static electricity half-life of the polyimide film is controlled to be 250 seconds or more so as to minimize the voltage loss ratio of saturated static electricity and reduce the current drop during a TFT operation, and, as a result, enables a display having improved luminosity to be provided.