I. Polyimide film (PI film)

Definition of PolyimideFilm

PolyimideFilm is the world's best performance film insulation material, which is made of PMDA and DDE in strong polar solvent by polycondensation and cast into film and then imidized.

Polyimide film (PI film) characteristics

Transparent yellow, relative density 1.39～1.45, polyimide film has excellent high and low temperature resistance, electrical insulation, bonding, radiation resistance, media resistance, and can be used in the temperature range of -269℃～280℃ for a long time, and can reach 400℃ for a short time. The glass transition temperature is 280℃(Upilex R), 385℃(Kapton) and above 500℃(Upilex S) respectively. the tensile strength is 200MPa at 20℃ and more than 100MPa at 200℃. especially suitable for flexible printed circuit board substrate and various high temperature resistant electrical and electric insulation materials.

Classification of polyimide

Polyimide is usually divided into two categories.

Thermoplastic polyimide, such as imide film, coating, fiber and modern microelectronics with polyimide, etc.

Thermosetting polyimide, mainly including bismaleimide (BMI) type and monomer reactant polymerization (PMR) type polyimide and their respective modified products.

Classification of polyimide films

It includes two types of polyimide films: homopolymer type polyimide film and biphenyl type polyimide film. The former is the product of DuPont Company in the United States, with the trade name Kapton, which is made from homophthalic dianhydride and diphenyl ether diamine. The latter is produced by UBE, Japan, under the trade name Upilex, and is made from biphenyltetracarboxylic acid dianhydride and diphenyl ether diamine (R type) or m-phenylenediamine (S type).

Advantages of polyimide

(1) Excellent heat resistance. Polyimide decomposition temperature is generally more than 500 ℃, and sometimes even higher, is one of the highest thermal stability of known organic polymers, mainly because the molecular chain contains a large number of aromatic rings.

(2) excellent mechanical properties. The tensile strength of unreinforced matrix materials are above 100 MPa. The tensile strength of Kapton film prepared by homoanhydride is 170MPa, while the biphenyl-type 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 resistance to heat and humidity. Polyimide materials are generally insoluble in organic solvents, corrosion-resistant and hydrolysis-resistant. Change the molecular design can get different structure of the species. Some varieties can withstand 2 atmospheric pressure, 120 ℃, 500h of water cooking.

(4) Good radiation resistance. Polyimide film in 5 × 109rad dose of radiation, the strength still maintain 86%; some polyimide fiber by 1 × 1010rad fast electron radiation, its strength retention rate of 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 to 300kV/mm, and the volume resistance is 1015-17Ω-cm. Therefore, the synthesis of fluorine containing polyimide materials is a hot research field at present.

These properties are stable over a wide temperature range and frequency range. In addition, polyimide has low temperature resistance, low expansion coefficient, flame retardant and good biocompatibility. Polyimide can be used in a wide range of fields because of its excellent overall performance and the diversity of synthetic chemistry.

Polyimide film (PI film) application industry

Polyimide film, called "golden film", has excellent performance and is widely used in space technology, F and H class motors, insulation of electrical appliances, FPC (flexible printed circuit board), PTC electric heating film, TAB (pressure-sensitive adhesive tape substrate), aerospace, aviation, computers, electromagnetic wire, transformers, audio, cell phones, computers, smelting, mining electronic components industry, automobiles, transportation, atomic energy industry and other electronic and electrical industries, Atomic energy industry and other electronic and electrical industries.

Polyimide application areas mainly include

(1) Film: It is one of the earliest products of polyimide, which is used for slot insulation of motor and cable winding material. The main products are Kapton of DuPont, Upilex series of UBE of Japan and Apical of Jongbun. Transparent polyimide film can be used as a flexible solar cell substrate.

(2) Coating: Used as insulating paint for electromagnetic wire, or as high temperature resistant coating.

(3) Advanced composite material matrix resin: used in aerospace, aerospace vehicle structure or functional components, as well as rockets, missiles and other parts, is one of the most high temperature resistant structural materials.

(4) fiber: polyimide fiber modulus of elasticity second only to carbon fiber, can be used as a high-temperature media and radioactive material filtration materials and bulletproof fireproof fabrics.

(5) foam: can be used as high temperature insulation materials.

(6) engineering plastics: thermosetting and thermoplastic, can be molded or injection molding or transfer molding (RTM), mainly used for self-lubricating, sealing, insulation and structural materials. In addition, polyimide can also be used as adhesive, separation film, photoresist, dielectric buffer layer, liquid crystal orientation agent, electric-optical materials in high temperature environment, etc.

　　PI film status

As a special engineering material, polyimide has been widely used in the fields of aviation, aerospace, electrical/electronic, microelectronics, nano, liquid crystal, separation film, laser, locomotive, automobile, precision machinery and automatic office machinery. Recently, countries are including the research, development and utilization of polyimide as one of the most promising engineering plastics in the 21st century. Polyimide, because of its outstanding characteristics in performance and synthesis, whether as a structural material or as a functional material, its great application prospects have been fully recognized, known as "problem solver" (protion solver), and that "without polyimide would not have today's microelectronics technology. Among the many polymer materials, only six are listed separately in the American Chemical Abstracts (CA), and polyimide is one of them. This shows that polyimide is of great technical and commercial importance. With the rise and flourishing of IT industry, flat panel display industry, photovoltaic industry, etc., it is inevitable to drive the development of related supporting materials and the growth of market demand. As an important material for audio circuit boards, integrated circuits, flat panel displays, solar cells, electronic labels, etc., polyimide films for electronic engineering are playing a very important role in the above-mentioned electronic applications.

Future development of polyimide

Polyimide has been well recognized as a promising polymer material, and its applications in insulation materials and structural materials are expanding. Functional materials are emerging and their potential is still being explored. However, after 40 years of development it has not yet become a larger species, mainly because the cost is still too high compared to other polymers. Therefore, one of the main directions of future polyimide research should still be to find ways to reduce costs in monomer synthesis and polymerization methods.

　　PI films are divided into two categories according to their applications: electrical grade for general insulation and heat resistance purposes, and electronic grade with requirements such as flexibility. Electrical-grade PI film can be produced on a large scale and its performance is not significantly different from foreign products due to the low requirements; electronic-grade PI film is produced with the development of FCCL, which is the largest application area of PI film, in addition to maintaining the excellent physical and mechanical properties of electrical PI film, the thermal expansion coefficient of the film, isotropic (thickness uniformity) has put forward more stringent requirements. The reason is that there is a gap between domestic PI film and imported PI film in terms of performance, which cannot meet the requirements of FCCL medium and high-end products. In predicting the future market price, the pricing right of electronic grade PI film has been controlled by DuPont and Zhong Yuan for a long time, but with the reorganization of SKC and KOLON in recent years, and the impact of the economic crisis on the export of electronic products, the product price has been reduced, but there is still a high profit margin for electronic grade PI film.

Second, the film manufacturing process

　　The production of polyimide film is basically a two-step method, the first step: synthesis of polyamide acid, the second step: film-forming imidization. Film-forming methods are mainly impregnation method (or aluminum foil on the method), cast method and saliva stretching method. Dipping method equipment is simple, simple process, but the film surface often sticky aluminum powder, film length is limited, low production efficiency, this method is not suitable for development; saliva method equipment precision, film uniformity, good surface clean and smooth, film length is not limited, can be continuous production, film performance in all aspects are good, the general requirements of the film can be produced by this method; stretching method of film production, performance has significantly improved However, the process is complicated, the production conditions are harsh, the investment is large, the price of the product is high, only high-quality film is used in this method. Main equipment of salivation method: stainless steel resin solution storage tank, salivation nozzle, salivation machine, imidizing furnace, winder and hot air system, etc. Preparation steps: The defoamed polyamide acid solution is pressed from the stainless steel solution storage tank into the salivation nozzle storage tank on the front machine head through the pipeline. The steel belt runs at a uniform speed in the direction shown in the figure, and the solution in the storage tank is taken away by the scraper in front of the salivation nozzle, and a liquid film of uniform thickness is formed, and then it enters the drying channel for drying. The clean and dry air is sent to the heater by the blower to preheat to a certain temperature and then enters the upper and lower drying channels. The direction of hot air flow is opposite to the running direction of the steel belt, so that the temperature of the liquid film rises gradually during drying and the solvent evaporates gradually to increase the drying effect. When the polyamide acid film runs on the steel belt for one week, the solvent evaporates and becomes solid film, and the film peeled off from the steel belt is led to the imidizing furnace by the guide roller. The imidizing furnace is generally in the form of multiple rollers, and the guide rollers with synchronous speed with the salivating machine guide the polyamide acid film into the imidizing furnace, and after high temperature imidizing, the film is wound up by the winder.

Third, market analysis

Polyimide is the highest heat-resistant polymer material that has been industrialized, and is widely used in high-tech fields as film, coating, plastic, composite material, adhesive, foam, fiber, separation film, liquid crystal orientation agent, photoresist, etc. Our country can produce polyimide film in small quantity at the end of 60s, and now it has been widely used in various fields such as aviation, navigation, spacecraft, rocket and missile, atomic energy, electronic and electrical industry.