Polyesterimide Film Thermal Expansion and Water Absorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional polyimide films used in FPC, COF, and TAB substrates face challenges in achieving a balance of low coefficient of linear thermal expansion, low water absorption, low hygroscopic expansion, high glass transition temperature, excellent flame resistance, and low elastic modulus, while maintaining solvent solubility and polymerization reactivity, which is essential for industrial applications.
Innovation Solution
A polyesterimide is developed using an ester group-containing tetracarboxylic acid dianhydride with a bulky phenyl substitution group, which reacts with diamine to form a polyesterimide precursor that exhibits improved solvent solubility and polymerization properties, resulting in a film with desired physical properties such as low thermal expansion, low water absorption, high glass transition temperature, and excellent flame resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional polyimide films are used to achieve low coefficient of linear thermal expansion, then dimensional stability is improved, but water absorption and hygroscopic expansion remain high
Solution Approach 1:
The patent changes the chemical parameters of the polyimide by introducing ester groups through specific tetracarboxylic acid dianhydride monomers (Formula 1) with controlled structural parameters (n, a, m values). This molecular-level parameter change simultaneously achieves low thermal expansion coefficient (≤20 ppm/K) and low water absorption coefficient (≤0.5%), resolving the contradiction between dimensional stability and water absorption resistance.
2Temperature
If high glass transition temperature is achieved for heat resistance, then thermal stability is improved, but elastic modulus increases and film toughness decreases
Solution Approach 1:
The patent creates a composite molecular structure within the polyimide chain by combining rigid aromatic rings with flexible ester linkages. The tetracarboxylic acid dianhydride (Formula 1) provides rigid segments for high Tg (≥300°C) while the ester groups introduce flexibility that maintains low elastic modulus (≤4 GPa) and sufficient film toughness, achieving a balance between thermal stability and mechanical flexibility.
3Strength
If low elastic modulus is achieved for formability, then film flexibility is improved, but flame resistance may be compromised
Solution Approach 1:
The patent carefully controls the structural parameters of the tetracarboxylic acid dianhydride (Formula 1) where n, a, and m are constrained to specific ranges. This parameter optimization achieves low elastic modulus (≤4 GPa) for formability while the aromatic backbone structure with controlled substitution patterns maintains excellent flame resistance (V-0 rating), preventing the trade-off between flexibility and flame safety.
4Ease of manufacture
If bulky phenyl substitution groups are introduced to improve solvent solubility, then processability is improved, but molecular packing efficiency decreases
Solution Approach 1:
The patent applies local quality by introducing bulky phenyl substitution groups (R in Formula 1) at specific local positions on the tetracarboxylic acid dianhydride molecule, rather than uniformly throughout. The substituents are placed at strategic locations (positions indicated by n, a, m parameters) where they enhance solvent interaction and solubility without severely disrupting the overall molecular packing efficiency, thus maintaining film density and performance while improving processability.
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 polyesterimide film demonstrates a coefficient of linear thermal expansion equivalent to or lower than metal foils, extremely low water absorption, high glass transition temperature, excellent flame resistance, and a relatively low elastic modulus, making it suitable for FPC, COF, and TAB substrate materials with improved industrial applicability.
Implementation Method 1
reacts with diamine to form a polyesterimide precursor
Implementation Method 2
heating at 250 to 400° C. to achieve dehydrative ring-closure (imidization)
Implementation Method 3
coefficient of linear thermal expansion equivalent to or lower than those of metal foils
Implementation Method 4
extremely low coefficient of water absorption
Data Source
AI summary
A polyesterimide having a repeating unit expressed by formula (3) is useful for FPC substrates, COF substrates and TAB substrate materials, especially as FPC substrate materials:wherein R represents a phenyl group, R1 represents an alkyl group with 1 to 6 carbon atoms or alkoxy group with 1 to 6 carbon atoms, n each independently takes a value of 0 to 4, a each independently takes a value of 0 to 4, and m represents an integer of 2 to 4, where not all n's are 0 at the same time and 0≦n+a≦4 is satisfied by each phenylene group, and X is a divalent aromatic group and/or aliphatic group.