Introduction of polyimide film

  1. Definition of Polyimide Film

Polyimide film (PolyimideFilm) is a thin-film insulating material, which is made of pyromellitic dianhydride (PMDA) and diamine diphenyl ether (DDE) in a strong polar solvent by polycondensation and casting to form a film, and then sub-processed. Aminated.

  1. Polyimide film (PI film) characteristics

It is yellow and transparent, with a relative density of 1.39 to 1.45. The polyimide film has excellent high and low temperature resistance, electrical insulation, adhesion, radiation resistance, and medium resistance. It can be used for a long time, and it can reach a high temperature of 400 ℃ in a short time. The glass transition temperatures were 280°C (Upilex R), 385°C (Kapton) and above 500°C (Upilex S), respectively. The tensile strength at 20°C is 200MPa, and it is greater than 100MPa at 200°C. It is especially suitable for use as flexible printed circuit board substrate and various high temperature resistant electrical and electrical insulation materials.

  1. Polyimide classification

Polyimides are generally divided into two categories:

Thermoplastic polyimides, such as imide films, coatings, fibers and polyimides for modern microelectronics.

Thermosetting polyimides mainly include bismaleimide (BMI) type and monomer reactant polymerization (PMR) type polyimides and their respective modified products. BMI is easy to process but more brittle.

  1. Polyimide film classification

There are two types of polyimide films including homophenylene type polyimide film and biphenyl type polyimide film. The former is a product of DuPont in the United States, with the trade name Kapton, which is prepared from pyromellitic dianhydride and diphenyl ether diamine. The latter is produced by Japan’s Ube Industries Co., Ltd. under the trade name Upilex, which is prepared from biphenyltetracarboxylic dianhydride and diphenyl ether diamine (R type) or m-phenylenediamine (S type).

  1. Advantages of polyimide

(1) Excellent heat resistance. The decomposition temperature of polyimide generally exceeds 500 ℃, sometimes even higher, and it is one of the most thermally stable varieties of organic polymers known at present, mainly because the molecular chain contains a large number of aromatic rings.

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

(3) Good chemical stability and heat and humidity resistance. Polyimide materials are generally insoluble in organic solvents, resistant to corrosion and hydrolysis. Varieties of different structures can be obtained by changing the molecular design. Some varieties can withstand 2 atmospheres, 120 ℃, 500h boiling.

(4) Good radiation resistance. The strength of the polyimide film remains 86% after being irradiated with a dose of 5×109rad; the strength retention rate of some polyimide fibers is 90% after being irradiated by 1×1010rad fast electrons.

(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 to 300kV/mm, and the volume resistance is 1015-17Ω·cm. Therefore, the synthesis of fluorine-containing polyimide materials is currently a hot research field.

The above properties are stable over a wide temperature and frequency range. In addition, polyimide also has the characteristics of low temperature resistance, low expansion coefficient, flame retardant and good biocompatibility. Due to the excellent comprehensive properties and the diversity of synthetic chemistry, polyimide can be widely used in various fields.

  1. Polyimide film (PI film) application industry

The polyimide film known as “gold film” has excellent performance, it is widely used in space technology, F, H class motor, electrical insulation, FPC (flexible printed circuit board), PTC electric heating film, TAB (Pressure-sensitive tape substrate), aerospace, aviation, computer, magnet wire, transformer, audio, mobile phone, computer, smelting, mining, electronic components industry, automobile, transportation, atomic energy industry and other electronic and electrical industries.

  1. The application fields of polyimide mainly include

(1) Film: It is one of the earliest products of polyimide and is used for slot insulation of motors and cable wrapping materials. The main products are DuPont’s Kapton, Japan’s Ube Industries’ Upilex series and Zhongyuan’s Apical. Transparent polyimide film can be used as a flexible solar cell backplane;

(2) Paint: used as insulating paint for magnet wire, or as high temperature resistant paint;

(3) Matrix resin of advanced composite materials: It is one of the high-temperature-resistant structural materials used for aerospace, aerospace vehicle structural or functional components, as well as rockets, bombs and other components;

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

(5) Foamed plastic: can be used as high temperature heat insulation material;

(6) Engineering plastics: There are thermosetting and thermoplastic, which can be molded or injection molded or transfer molding (RTM), mainly used for self-lubricating, sealing, insulating and structural materials. In addition, polyimide can also be used as adhesives, separation films, photoresists, dielectric buffer layers, liquid crystal aligning agents, electro-optical materials, etc. in high temperature environments.