Polyimide film is a kind of heat-resistant film developed by Dupont Company of the United States in the mid-1960s under the trade name of Kapton. It is soft, tough, transparent, and amber-colored. It has excellent dielectric, mechanical strength, and chemical resistance, especially excellent moisture resistance. It can be used in a wide temperature range of -269 ℃ to 400 ℃.
There are two main types of Kapton films from DuPont: one is HN film, which is the most common Kapton film, and the standard thickness is 7.5, 12.5, 25, 50, 75, and 125um. This film is mainly used for coil to ground Insulation; the other is FN-type film, which is made by coating one or both sides of HN-type film with a polyvinyl fluoride-propylene polymer (Teflon FEP from DuPont), which can adhere well after being heated while maintaining The excellent properties of polyimide film. Fluoropolymer coating on one or both sides of the film and its thickness can be selected according to application requirements. This film is mainly used for wrapping electromagnetic wires. After being wrapped, it is sintered to make the film firmly adhere to the copper wire to obtain a thin insulating wire and a high electrical mechanical strength wire. In recent years, in order to meet the requirements of special applications, DuPont has also developed many new Kapton film varieties, such as XP type (with better hot melt), XHS type (with heat shrinkability), XT type (with good Thermal conductivity) and XC type (with conductivity).
Polyimide film is the most important heat-resistant film insulation material in the current traction motor manufacturing. It can greatly reduce the size and weight of the motor, and significantly improve the motor's working life and operating reliability. Kapton film has been used in traction motors for more than 20 years. It has been trusted by manufacturers and is widely used. It can be used for both electromagnetic wire and turn-to-turn insulation, as well as armature insulation slot liner and ground insulation. In May 1990, the French high-speed trains, which set the world record speed of 515.3km per hour, the Japanese Super Hikari300 series Shinkansen, as well as the German express trains and London Underground vehicles, all used polyimide films. The traction motor produced by the US company's Yili plant has a large output. The armature coil manufacturing can be said to be polyimide film. Starting from bare copper wire wrapped polyimide film (FN type), after the coil is formed, With pad-to-turn insulation, the cross-shaped insulation made of polyimide film is continuously manufactured by a special machine; the coil to ground insulation is insulated with polyimide film rolls, which is firstly made by a The special machine is rolled into a square sleeve, and then it is put into the linear part of the coil. For other coil leads, noses and corners, polyimide film pressure-sensitive tape is used. Therefore, the widespread use of polyimide films can not only reduce the insulation thickness, but also facilitate the realization of mechanized continuous production, simplify the production process, and improve the efficiency of coil manufacturing.
Japan ’s Hitachi ZQl30 metro vehicle motor and former Soviet Union motor HB-515 traction motor armature coils are wrapped with polyimide film insulation, but between the polyimide film and the outer glass ribbon, increase the stack Cover the Teflon tape with 1 layer. This is to take into consideration that the Teflon tape has a large elongation (200% ~ 300%), and the packing is tightly adhered. At the same time, it can prevent the solvent-free paint entered during VPI from losing during baking and curing .
