Polyimide heating film is an excellent insulating material with excellent high and low temperature resistance, excellent mechanical and insulating properties, chemical stability and heat radiation resistance, and the molecular structure of polyimide heating film. The silicone rubber heater makes it widely applicable to the heating field and can obtain quite high temperature control accuracy. According to the chemical structure of the repeating unit, the pi heating film can be divided into three types: aliphatic, semi-aromatic and aromatic polyimides. According to the interaction force between chains, it can be divided into cross-linked type and non-cross-linked type. The polyimide heating film is made of polyimide film as the outer insulator, and metal foil and wire as the inner conductive heating element, which is formed by high temperature and high pressure heat bonding. The content of N element in the medium is greater than 7N, self-extinguishing when burning.
(1) Excellent high and low temperature resistance. Aromatic polyimide heating film has high heat resistance, its thermal decomposition temperature is 450-600℃, glass transition temperature (Tg) is usually higher than 380℃, even as high as 400℃ or higher. This industry is usually used for long-term use above 180°C (or even 250°C); at the same time, it has excellent low temperature resistance, and its mechanical properties will not be greatly affected when used in a low temperature environment. It is not fragile when bent into a radius of 1.0 mm.
(2) Excellent mechanical properties. Due to its aromatic molecular structure, the polyimide heating film has a tensile strength greater than 115 MPa and an elongation at break greater than 40%. For example, the tensile strength of the Kapton H heating film is 170 MPa, the Upilex heating film is 400 MPa, and the elastic modulus is 2 to 4 GPa.
(3) Excellent electrical insulation performance. The volume resistance of the polyimine heating film is 1014-1015m, and the surface resistance is 1013-1014. Generally, the dielectric constant is about 3.5. If fluorine atoms are introduced into the molecular chain to improve the molecular structure, or coated with F46 resin, the dielectric constant can be reduced to about 2.8. Stable dielectric properties are maintained in a wide temperature range and frequency range.
(4) Good chemical stability and heat resistance. Polyacetamide heating film is usually insoluble in organic solvents and resistant to corrosion and hydrolysis. For example, Kapton's various heating membranes can boil at high temperatures at 120°C, which is stable to low-concentration acidic media. In addition, polyimide heating film has a low coefficient of thermal expansion (CTE), usually between (10-5 and 10-6) ℃), which is essential for reducing the internal stress of the material. For example, Kapton V-type heating film has a KTE of less than 2×10 -5°C-1, which is close to the CTE of metallic copper.
(5) Good radiation resistance: After being irradiated at 5109 rad, the mechanical strength of the polyimide film remains above 86%. It can be used for electrical, electrical and electronic equipment in airplanes, nuclear power plants, nuclear submarines and other places. As a high-performance insulating material, polyimide thermal film is more and more widely used in the motor, electrical and electronic industries, and is particularly eye-catching.