Low-temperature insulation materials can be classified into polymer materials, composite materials, and ceramic materials. For the application of the superconducting force device, the low-temperature insulating material is mainly applied in the form of a thin film, an adhesive, and a structural material.
In order to reduce the insulation duty, it is necessary to use an insulating material in the form of a thin film with excellent mechanical properties. The higher tensile strength at break can also reduce the thickness of the film and reduce the number of layers, thereby further reducing the space occupied by the insulation. As mentioned in the previous chapter, currently used superconducting insulator films include: polyimide film (PI), polytetrafluoroethylene film (PTFE), polypropylene film (PP), polyester film (PET), polynaphthalene Ester film (PEN), polyethylene film (PE) and so on. The PI film is the most ideal low-temperature insulation film material because of its excellent mechanical properties, high and low temperature resistance, high electrical breakdown strength, and good chemical stability.
Among polymer insulating films, PI films and PTFE films have been widely used in low temperature technologies such as superconductivity, low temperature engineering, and low temperature physics because of their excellent electrical properties and chemical stability at low temperatures. PTFE film can work in the range of -250 ~ 250 °C, the dielectric loss is small, in the wide temperature range within a wide range of changes, not in the arc under the effect of carbonization; at high temperature tensile strength, elongation increased, low temperature The lower tensile strength increases and the elongation decreases. However, the obvious disadvantage of PTFE films is their low mechanical properties and anisotropy, which makes them difficult to bond at low temperatures. The PI film not only possesses most of the advantages of PTFE film, but also maintains flexibility under liquid nitrogen and liquid helium temperature, is resistant to almost all organic solvents and acids, and has good abrasion resistance, arc resistance, and high energy radiation resistance. Other characteristics. The PI film can maintain good tensile strength and elongation after being irradiated with 1010 erg/g gamma rays. PI film also has features such as strong design, easy processing and modification. These characteristics make the PI film the most used film in the superconducting work-insulation material, especially the high-temperature superconductivity around 77 K and the low-temperature superconductivity under 4.2 K have been more and more applied.
Polyimide film products are mainly used by Kapton series films of DuPont Co., Ltd., Upilex series of Japan Ube Kogyo Co., Ltd., and Apical series films of Kyungwon. Institute of Physics and Chemistry, Chinese Academy of Sciences and Institute of Chemistry have developed nano-particle-modified polyimide films for high-temperature superconducting current limiter insulation materials, and their mechanical properties at low temperature and dielectric properties have been significantly improved.