What is the high temperature resistance of polyimide film
Polyimide film (PI film) is one of the known polymer materials with excellent high temperature resistance. Its high temperature resistance is not only reflected in the long-term use temperature range, but also includes short-term extreme high temperature resistance, thermal stability, and thermal oxidation resistance. The following provides a detailed analysis from the aspects of material structur
Polyimide film (PI film) is one of the known polymer materials with excellent high temperature resistance. Its high temperature resistance is not only reflected in the long-term use temperature range, but also includes short-term extreme high temperature resistance, thermal stability, and thermal oxidation resistance. The following provides a detailed analysis from the aspects of material structure, performance data, and application scenarios:
1、 Core indicators and mechanisms of high temperature resistance performance
Molecular structure determines thermal stability
Aromatic cyclic structure: Polyimide molecular chains are covalently connected by benzene rings and imide rings (- CO-N-CO -), forming a rigid planar structure with bond energies as high as 335-590 kJ/mol (such as C-N bond energy of 305 kJ/mol and C=O bond energy of 745 kJ/mol), and are not easily broken at high temperatures.
Conjugated π - electron system: The benzene ring in the molecular chain forms a large π - bond conjugated system with the imide ring, resulting in a high degree of electron cloud delocalization and difficulty in breaking its chemical structure due to thermal vibration. This is the essential reason for the high temperature resistance of PI thin films.
2、 Specific manifestations of high temperature resistance performance
1. Stability under long-term high temperature environment
Continuous use in air at 200-280 ℃: mechanical properties (tensile strength, elastic modulus) retention rate ≥ 80%, size change rate<1%, no melting or significant degradation (e.g. DuPont Kapton) ® PI film can be used for over 10000 hours at 260 ℃.
Resistant to high and low temperature cycling: Repeatedly subjected to cold and hot shocks from -269 ℃ (liquid helium temperature) to 280 ℃, the film is not easily cracked or delaminated, making it suitable for scenarios with severe temperature differences such as aerospace.
2. Resistance to damage under extreme high temperatures
Short term tolerance above 400 ℃: exposed to an environment of 400-500 ℃ for several hours, only the surface is slightly carbonized, and the internal structure remains intact (such as the PI film used for NASA spacecraft insulation can withstand the high temperature of 480 ℃ during re-entry into the atmosphere).
Non flammability and low smoke toxicity: oxygen index (LOI) ≥ 35% (belonging to flame retardant materials), almost no toxic gases are produced during combustion (only a small amount of CO2 and water vapor are released), meeting UL94 V-0 flame retardant standards, superior to most plastics (such as PVC, which releases HCl during combustion).
3. Thermal oxidation and thermal aging resistance
Anti oxygen corrosion: In high-temperature aerobic environments, the imide ring is not easily oxidized and broken, and the oxidation induction time (OIT) is greater than 1000 hours (200 ℃ air atmosphere), while the OIT of PET is only about 50 hours.
Radiation aging resistance: Under the dual effects of high temperature and high-energy radiation (such as gamma rays and X-rays), the performance degradation rate of PI film is much lower than other polymers, making it suitable for the nuclear industry and space radiation environment.
3、 Application scenarios for high temperature resistance performance
1. Electrical and electronic field
High temperature motor insulation: used as a slot insulation layer for new energy vehicle drive motors (working temperature 180-220 ℃) and industrial servo motors, replacing traditional polyester film to avoid insulation failure caused by high temperature.
Flexible Circuit Board (FPC) substrate: In semiconductor packaging and 5G high-frequency circuits, PI film can withstand the high temperature of 260 ℃ during soldering process, and maintain circuit stability even when working in an environment of 150-200 ℃ for a long time.
2. Aerospace and Defense
Spacecraft thermal control material: As a multi-layer thermal insulation component (MLI) on the surface of the satellite, it is resistant to temperature difference impact in the space environment from -270 ℃ to+120 ℃, and also serves as a corrosion-resistant coating near the rocket engine (300-400 ℃).
Thermal insulation layer of missile warhead: PI foam and film composite structure can withstand 500 ℃ aerodynamic heating during re-entry into the atmosphere to protect internal electronic equipment.
3. Industrial and energy sectors
High temperature filter material: Used for flue gas filter bags in thermal power plants and waste incinerators, it can resist dust wear and acid-base corrosion at high temperatures of 250-280 ℃ (traditional PTFE filter bags have a temperature resistance of ≤ 230 ℃).
New energy battery separator: During fast charging of lithium batteries, the temperature can reach 120-150 ℃. The separator coated with PI coating can improve thermal stability and avoid short circuits caused by shrinkage at high temperatures (ordinary PP/PE separators begin to melt at 130 ℃).
4. Special environmental equipment
High temperature sensor packaging: Sensors used in oil drilling, metallurgical furnaces, and other scenarios can work stably in an environment of 200-300 ℃ after being wrapped with PI film (ordinary polymer packaging materials will soften at this temperature).
Firefighting and high-temperature protective clothing: Protective clothing made of PI fiber and film composite, which can resist flames above 300 ℃ while maintaining flexibility (aramid fiber protective clothing has a temperature resistance of ≤ 260 ℃).
4、 Factors and optimization directions affecting high temperature resistance performance
1. Molecular structure design
Introducing fluorine atoms or silicon oxygen bonds: For example, fluorinated PI thin films (FPI) can increase the long-term use temperature to 300 ℃, and the thermal decomposition temperature of siloxane modified PI exceeds 550 ℃, further enhancing thermal stability.
Crosslinking density control: By chemical crosslinking or irradiation crosslinking, a three-dimensional network structure is formed to reduce molecular chain slip at high temperatures. For example, the upper temperature limit of cross-linked PI films can be increased by 20-30 ℃.
2. Composite reinforcement process
Composite with inorganic fillers: Adding nano silica (SiO ?), graphene, etc. can prevent the thermal expansion of PI thin films at high temperatures (reducing the thermal expansion coefficient from 50ppm/℃ to 20ppm/℃), while improving their resistance to thermal oxidation.
Multi layer structure design: such as PI film and ceramic coating composite, forming a ceramic protective layer at a high temperature of 500 ℃ to prevent further internal decomposition (similar to the insulation tile principle of space shuttles).
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