Aromatic Polyimide Substrate for Optical Displays
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Solution Overview
Problem
Existing methods struggle to produce a flexible polyimide film substrate with excellent mechanical, optical, and thermal properties using a solution with high solids content and low viscosity, suitable for use during the manufacture of displays.
Innovation Solution
A method involving the application of a solution containing an aromatic tetracarboxylic acid or derivative and a low molecular weight polyamic acid on a solid support, followed by heating to 425-450°C to produce a polyimide film with enhanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a classic preparation process uses high molecular weight polyamic acid solutions, then the film has good mechanical properties, but the solution viscosity becomes too high for easy film fabrication
Solution Approach 1:
The patent changes the molecular weight parameter of the polyamic acid from high to low (specifically <10,000 g/mol), which simultaneously reduces solution viscosity to acceptable levels for film fabrication while maintaining adequate mechanical properties through optimized composition and processing conditions
Solution Approach 2:
The patent creates a composite system combining low molecular weight polyamic acid with specific additives and controlling the ratio of monomers (BPDA:PMDA:p-PDA), achieving both low viscosity and good mechanical properties through the synergistic effect of multiple components working together
2Ease of manufacture
If the polyamic acid molecular weight is lowered to reduce viscosity, then the solution becomes easier to process, but the film performance particularly elongation is reduced
Solution Approach 1:
The patent compensates for the reduced elongation from low molecular weight polyamic acid by creating a composite formulation with optimized monomer ratios (BPDA:PMDA:p-PDA) and controlled composition, achieving a balance where both viscosity and mechanical properties are acceptable
Solution Approach 2:
The patent optimizes multiple parameters simultaneously including molecular weight (<10,000 g/mol), monomer ratios, and processing conditions (temperature, time, atmosphere) to achieve the desired balance between processability and mechanical performance
3Ease of manufacture
If end-capping with mono-anhydrides is used to lower molecular weight, then viscosity decreases, but amine volatile production increases causing haze and color changes
Solution Approach 1:
The patent removes the problematic end-capping step entirely, avoiding the source of amine volatile production. Instead, it achieves low viscosity through direct use of low molecular weight polyamic acid prepared from controlled monomer polymerization, eliminating the harmful byproducts while maintaining processability
Solution Approach 2:
The patent converts the potential harm of low molecular weight (reduced elongation) into a benefit by using it to achieve low viscosity and fast processing, then compensates for the elongation loss through optimized composite formulation rather than through problematic end-capping chemistry
4Reliability
If glass substrate is used to withstand high deposition temperatures, then TFT characteristics are excellent, but the substrate becomes thick, heavy, and fragile
Solution Approach 1:
The patent replaces thick rigid glass substrate with a thin flexible polyimide film substrate that can be processed at lower temperatures, eliminating the weight and fragility problems while maintaining adequate performance through optimized film composition and structure
Solution Approach 2:
The patent changes the substrate material from inorganic glass to organic polyimide, fundamentally altering the temperature requirements and enabling flexible display applications while reducing weight and improving manufacturability
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 elongation at break greater than 30%, modulus greater than 8 GPa, maximum stress at break greater than 400 MPa, and a yellowness factor b*<25, while maintaining a softening temperature above 450°C.
Implementation Method 1
heating to high temperatures a solution of a tetracarboxylic acid or a tetracarboxylic acid derivative and a polyamic acid that has been cast on a solid substrate
Implementation Method 2
an aromatic dianhydride and an aromatic diamine are polymerized in a solvent to form a soluble precursor polyamic acid
Data Source
AI summary
Disclosed herein is a method for the preparation of an aromatic polyimide substrate for optical displays that can be carried out during the manufacture of the display, The process includes the steps of applying a solution of an aromatic tetracarboxylic acid or an aromatic tetracarboxylic acid derivative and a low molecular weight polyamic acid on a solid support and heating to 425° C. to 450° C. The polyamic acid is prepared from non-stoichiometric amounts of BPDA and PDA. The tetracarboxylic acid is BPTA or PMA. The solution has a solids content of 15 to 25 wt % and an apparent viscosity of 2,000 to 10,000 cPs. The substrate has an elongation to break of greater than 30%, a modulus greater than 8 GPa, a maximum stress to break greater than 400 MPa, and a yellowness factor b*<25. For display manufacturing, the substrate has a softening temperature above 450° C.