The polyimide film is a heat-resistant film developed by DuPont Co., Ltd. as early as in the mid-1960s under the trade name of Kapton. It is soft, tough, transparent, amber, has excellent dielectric, mechanical strength, and chemical resistance. It is especially excellent in moisture resistance and can be used in a wide temperature range from -269°C to 400°C.
DuPont’s Kapton film is mainly of two types: one is an HN film, which is the most popular Kapton film. The standard thickness is 7.5, 12.5, 25, 50, 75, and 125um. This film is mainly used for the coil to the ground. Insulation; the other type is FN type film, which is made by coating polyvinyl fluoride-propylene polymer (Teflon FEP) on one side or both sides of HN type film, which can bond well when heated, while keeping Polyimide film has excellent performance. The fluoropolymer coating on one or both sides of the film and its thickness can be selected according to the application requirements. This kind of film is mainly used to wrap the electromagnetic wire, and after being wrapped, the film is sintered to make the film firmly adhere to the copper wire to obtain a wire with thin insulation and high electromechanical strength. In recent years, in order to meet the requirements of special applications, DuPont has also developed many new Kapton film types, 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 main heat-resistant film insulation material in the current traction motor manufacturing. It can greatly reduce the size and weight of the motor and significantly increase the working life and operational reliability of the motor. The Kapton film has been used in traction motors for more than 20 years. It is trusted by manufacturers and used more and more widely. It can be used not only for magnet wire and interturn insulation, but also for armature insulation slot liner and ground insulation. In May 1990, the French high-speed rail car with the world record of 515.3km per hour, the Japanese super Hikari 300 series Shinkansen, and the German express trains and London metro vehicles all used polyimide films. The traction motor produced by American GE’s Yili plant has a large output, and its armature coil manufacturing can be said to be a polyimide film, starting from a bare copper wire wrapped with a polyimide film (FN type), after the coil is formed, Insulation between padding and insulation, cross-formed insulation made of polyimide film is continuously manufactured by a special machine; the coil-to-ground insulation is made of polyimide film wrap insulation. The special machine rolls into a square sleeve and then fits into the straight part of the coil. Others such as fixing the coil lead, nose and corner, use polyimide film pressure sensitive tape. Therefore, the wide use of the polyimide film can not only reduce the thickness of the insulation, but also facilitate the mechanized continuous production, simplify the production process, and improve the coil manufacturing efficiency.
Japan’s Hitachi Motors ZQl30 metro vehicle motor and the Soviet Union’s motor vehicle HB-515 traction motor armature coils are all insulated with polyimide film, but between the polyimide film and the outer glass ribbon, stacking Polytetrafluoroethylene is coated with a layer of PTFE. This is due to the fact that PTFE has a high elongation (200% to 300%) and is tightly packed. At the same time, it can also prevent solvent-free paint from entering during VPI loss during baking and curing.