Polyimide film (PI film)

Polyimides are usually divided into two categories:

Thermoplastic polyimide, such as polyimide film, coating, fiber and polyimide used in modern microelectronics.

Thermosetting polyimide mainly includes bismaleimide (body mass index) and monomer reactant polymerization (PMR) polyimide and its modified products. Body mass index is easy to process, but fragile. (1) excellent heat resistance. The decomposition temperature of polyimide is generally above 500℃, sometimes even higher. It is one of the organic polymers with the best thermal stability at present, mainly because there are a large number of aromatic rings in the molecular chain.

(2) Excellent mechanical properties. The tensile strength of unreinforced matrix materials is above 100MPa. The tensile strength of Kapton film prepared by anhydride is 170MPa, while the tensile strength of biphenyl polyimide (Upilex S) can reach 400MPa. The elastic modulus of polyimide fiber can reach 500MPa, which is second only to carbon fiber.

(3) Good chemical stability and moisture resistance. Polyimide materials are usually insoluble in organic solvents, and are resistant to corrosion and hydrolysis. Variants with different structures can be obtained by changing the molecular design. Some varieties can withstand the boiling of water at120℃ for 500 hours.

(4) Good radiation resistance. After 5× 109rad radiation, the strength of polyimide film still remains at 86%. The strength retention rate of some polyimide fibers after 1× 10 10rad fast electron irradiation reaches 90%.

(5) Good dielectric properties. The dielectric constant is less than 3.5. If fluorine atoms are introduced into the molecular chain, the dielectric constant can be reduced to about 2.5, the dielectric loss is 10, the dielectric strength is 100 ~ 300kv/mm, and the volume resistance is1015-17 ω cm. Therefore, the synthesis of fluorine-containing polyimide materials is a research hotspot at present.

The above performance is stable in a wide temperature range and frequency range. In addition, polyimide has the characteristics of low temperature resistance, low expansion coefficient, flame retardancy and good biocompatibility. Polyimide has excellent comprehensive properties and diversity of synthetic chemistry, and can be widely used in many fields. (1) film: It is one of the earliest products of polyimide, which is used for slot insulation of motors and cable wrapping materials. The main products are Kapton of DuPont, Upilex series of Ube of Japan and Apical of Zhongyuan Company. Transparent polyimide film can be used as the bottom plate of soft solar cells;

(2) Paint: used as insulating paint or high temperature resistant paint for electromagnetic wires;

(3) Matrix resin of advanced composite materials: it is used in aerospace, aircraft structural or functional parts, rocket and missile parts, and is one of the most high-temperature resistant structural materials;

(4) Fiber: The elastic modulus of polyimide fiber is second only to that of carbon fiber, which can be used as a filter material for high-temperature media and radioactive substances and as a bulletproof and fireproof fabric;

(5) Foam plastic: it can be used as heat insulation material and has high temperature resistance;

(6) Engineering plastics: both thermosetting and thermoplastic, which can be molded, injected or RTM, are mainly used for self-lubrication, sealing, insulation and structural materials. In addition, polyimide can also be used as PI film, such as adhesive, separation film, photoresist, dielectric buffer layer, liquid crystal alignment agent, electro-optical material and so on. In a high temperature environment. According to the application, polyimide can be divided into two categories: electrical grade with general insulation and heat resistance and electronic grade with flexible requirements. Electrical grade PI film can be produced on a large scale in China because of its low requirements, and its performance is not obviously different from that of foreign products. Electronic polyimide film is produced with the development of FCCL, which is the largest application field of polyimide film. In addition to maintaining the excellent physical and mechanical properties of electrical PI films, stricter requirements are put forward for the thermal expansion coefficient and in-plane isotropy (thickness uniformity) of the films. In the future, a large number of electronic-grade PI films will still be imported, because there is a certain gap in performance between domestic PI films and imported PI films, which cannot meet the requirements of high-end products of FCCL. In predicting the future market price, the pricing power of electronic-grade PI films has long been controlled by DuPont and Zhongyuan. However, with the reorganization of SKC and Kelon in South Korea in recent years and the impact of the economic crisis on the export of electronic products, the price of products has also declined, but there is still a high profit margin for electronic-grade PI films.