PI heating film principle and characteristics

One of the key challenges in PI heating film production is maintaining a consistent and stable output pressure of the polyimide resin. PI heating films can be classified into aliphatic polyimides, semi-aromatic polyimides, and aromatic polyimides based on the chemical structure of their repeating units. Based on the intermolecular forces between chains, they can be divided into cross-linked and non-cross-linked types. Polyimide is one of the organic polymer materials with excellent comprehensive properties. It can withstand temperatures above 400℃, with a long-term operating temperature range of -200 ~ 300℃. Some parts have no obvious melting point, high insulation performance, a dielectric constant of 4.0 at 103 Hz, and dielectric loss of only 0.004 ~ 0.007, belonging to F to h. PI heating films are widely used in heating applications and can achieve high temperature control accuracy. To ensure stable resin delivery, a high-precision gear metering pump can be installed.

PI heating film

A liquid metering pump is a high-precision gear pump with only three moving parts (driving gear, driven gear, and drive shaft). The gears are driven by a high-precision drive system. A commonly used gear pump is one with two externally meshing gears. When the gears mesh and separate, the gear meshing creates a free space, forming the inlet side of the pump. The resin is forced into the meshing area of the pump body by the gears, and the high-pressure liquid in this area can only be pressed into the discharge pipe, not the inlet area. The gear metering pump is a positive displacement metering pump that, through actual operation, is in good working condition. The injection volume of the metering pump depends on the gear backlash and pump speed. The output of each cycle of material is constant, and the pump speed can be controlled through the drive system of the variable frequency motor.

PI heating film

During the gear pump metering process, the instantaneous liquid delivery volume changes from small to large, and then from large to small, i.e., there are periodic small fluctuations. The fluctuations are related to gear parameters such as the number of teeth, tip height coefficient, gear meshing angle, and overlap coefficient, etc., but these small fluctuations can be absorbed during resin delivery.

PI heating film

To further improve measurement accuracy, a three-stage metering pump can also be used. The oil injection fluctuation of a three-stage metering pump is smaller than that of a two-stage metering pump. In actual production and use, this system has high resistance and can play a buffering role. Therefore, a two-stage gear pump can basically meet the production requirements.

The PI heating film produced by the biaxial orientation method has the following characteristics:

1. The PI heating film is not a single polymer physical processing technology before rewinding. As the chemical reaction proceeds from start to finish, not only must the necessary procedures for heating the film be completed, but also the physical processing and chemical reactions can be carried out synchronously and strictly to more thoroughly complete these reactions. PI heating film has been successfully applied to the Fengyun series satellites, Long March series launch vehicles, Dongfeng and Hongqi series missiles, and gyroscopes, accelerometers, and fire control radars of aircraft, ships, tanks, and artillery. Polyimide is one of the organic polymer materials with excellent comprehensive properties. It can withstand temperatures above 400℃, with a long-term operating temperature range of -200 ~ 300℃. Some parts have no obvious melting point, high insulation performance, a dielectric constant of 4.0 at 103 Hz, and dielectric loss of only 0.004 ~ 0.007, belonging to F to h. PI heating films are widely used in heating applications and can achieve high temperature control accuracy.

PI heating film

2. During the entire production process, a large amount of gas is obviously harmful to human health. Therefore, production must be carried out in a closed system with negative internal pressure; the emitted gas has a significant corrosive effect on carbon steel and most non-ferrous metals. Therefore, the components of PI heating film production equipment should be made of corrosion-resistant materials.

PI heating film

3. The casting machine cannot be very long. Machines with a general perimeter of 3-10 meters are large-scale equipment, so the speed of the entire production line is generally 3-10 minutes.

PI heating film

4. Due to the slow speed and considering the corrosion resistance of the parts, these moving parts operate at high temperatures around 300°C, and the moving parts usually use self-lubricating stainless steel materials.

PI heating film

5. In the post-treatment furnace, although using pure high-temperature hot air circulation heating is technically feasible, it is economically expensive. Therefore, in the high-temperature zone, especially the imidization zone, infrared heating elements or other electromagnetic radiation heaters should be used for heating to obtain the required high temperature; the temperature, length, and speed of the configured equipment are very important. Ensuring the coordination of post-treatment equipment and chemical reactions is a necessary condition, otherwise it will lead to PI heating film breakage or poor product performance.

PI heating film

6. The gases generated during casting and post-treatment should be collected. On the one hand, a large amount of solvent can be recovered to reduce costs. More importantly, to prevent toxic gases from being discharged into the atmosphere and polluting the environment.