Application of Polyimide

Application of Polyimide

• Introduction of PI

Polyimide (PI) is an aromatic heterocyclic polymer compound with imide-based chain. It is currently one of the best heat-resistant varieties in engineering plastics, and widely used in aviation, aerospace, microelectronics, and Nanometer, liquid crystal, laser fields.

Recently, Most of countries have performanced the research, development and application of PI which is listeds as the most  priorities of new chemical materials in the 21st century. Polyimide, because of its outstanding characteristics in performance and synthesis, has great application prospects whether it is used as a structural material or as a functional material.

Polyimide is known as the top material of the polymer material pyramid, and is also known as the "problem-solving expert". Some people in the industry even believe that "without polyimide, there would be no today's microelectronics technology.

• Classfication and Application of PI

Due to its excellent performance, polyimide can be used in many fields, and can also be divided into many types, including engineering plastics, fibers, photosensitive polyimides, foam materials, coatings, adhesives, films, aerogels, and composites Materials, etc.

Among the many polymers, polyimide is the only polymer that has a wide range of applications and shows outstanding performance in every application area.

1. Engineering Plastics

Polyimide engineering plastics can be divided into both thermosetting and thermoplastic, and can be divided into polypyromellitic imide (PMMI), polyetherimide (PEI), polyamide-imide (PAI), etc. They have their own uses in different fields.

PMMI has a thermal deformation temperature of 360°C under a load of 1.8MPa, and has excellent electrical properties. It can be used for precision parts under special conditions, high temperature resistant self-lubricating bearings, sealing rings, blower impellers, etc., and also used for valve parts in contact with liquid ammonia , Jet engine fuel supply system parts.

PEI has excellent mechanical properties, electrical insulation properties, radiation resistance, high temperature resistance and abrasion resistance, good melt fluidity, molding shrinkage rate of 0.5% to 0.7%, injection and extrusion molding can be used, and post-processing is relatively easy. It can also be combined with other materials by welding, and is widely used in industries such as electronics, aviation, automobiles, and medical equipment.

The strength of PAI is the highest among current non-reinforced plastics, with a tensile strength of 190MPa, a bending strength of 250MPa, and a thermal deformation temperature of 274°C under a load of 1.8MPa. PAI has good ablation resistance and electromagnetic properties under high temperature and high frequency. It has good adhesion to metals and other materials. It is mainly used for gears, bearings and copier separation claws. It can also be used for ablation of aircraft Materials, magnetically permeable materials and structural materials.

2. Polyimide fiber

Polyimide fiber is an important high-performance fiber. Its high temperature resistant polyimide fiber is one of the highest temperature organic synthetic fibers at present. It can be used at 250~350℃. Compared with aramid fiber and polyphenylene sulfide fiber in terms of thermal properties, the strength of high-performance polyimide fiber is about 1 times higher than that of aramid fiber. It is one of the organic synthetic fibers with the best mechanical properties. .

With the continuous development of the high-tech field, its requirements for the physical and chemical properties of PI products are getting higher and higher. The properties of traditional PI materials in mechanics, heat, light, electricity, and magnetism can no longer meet the special materials of modern science and technology. Requirement, PI high-performance fiber will become a typical representative of the next generation of high-performance fiber with its superior mechanical properties, heat stability, radiation resistance and other characteristics.

3. Photosensitive polyimide (PSPI)

Photosensitive polyimide (PSPI) is a kind of organic material with imine ring and photosensitive gene in the polymer chain, which integrates excellent thermal stability, good mechanical properties, chemical and photosensitive properties.

In the electronic field, photosensitive polyimide mainly has two functions: photoresist and electronic packaging. Adding sensitizers and stabilizers to photosensitive polyimide can obtain "polyimide photoresist". Compared with traditional photoresist, polyimide itself has very good dielectric properties, so there is no need to coat a photo-blocking agent acting as a working medium during use, which can greatly shorten the process and improve production efficiency.

4. Polyimide foam

Polyimide foam is a type of polyimide material. It was first developed by NASA Langley Research Center in cooperation with Unitika America in the 1970s. It is used on space shuttles and is now widely used in aircraft and ships. , Trains, automobiles and other fields, it has the characteristics of intrinsic flame retardancy, strong heat resistance, light weight, environmental protection and non-toxicity, and can be used in extreme conditions such as ultra-high temperature, ultra-low temperature, high salt spray, strong noise, strong corrosion, and strong radiation for a long time. Under service.

Polyimide foam can be divided into three categories:

(1) Same as general polyimide, the foam material with imide as the main chain, the use temperature reaches 300℃ or higher (PI foam)

(2) Foam material with imide ring as side groups (PMI foam)

(3) A nano-foam material obtained by introducing thermally unstable aliphatic segments into polyimide and pyrolyzing at high temperature.

Polyimide foam materials are advanced functional materials and have been increasingly used in key materials such as heat insulation, shock absorption, noise reduction, and insulation in high-tech fields such as aerospace, ocean transportation, national defense, and microelectronics.

PI foam has strong heat resistance, good flame retardancy, does not generate harmful gases, and is easy to install. It is a widely used heat insulation and noise reduction material. The most important application of PI foam is heat insulation and noise reduction materials for ships.

Polymethacrylimide foam (PMI) is a new type of polymer structure foam material with the best comprehensive performance at present. It is a kind of high specific strength, high specific modulus, high closed cell rate and high heat resistance. Performance composite foam core material has the characteristics of light weight, high strength, high/low temperature resistance and so on. In addition, as the most excellent structural foam core material, PMI foam is widely used in wind turbine blades, helicopter blades, aerospace and other fields. Its replacement trend for PET foam is clear and the market space is broad.

Similar to PI foam, PMI foam is also widely used. Typical applications of PMI foam include:

(1) Structural foam core material: excellent resistance to high temperature compression, making it widely used as a core material in fan blades, aviation, aerospace, ships, sports equipment, medical equipment and other fields;

(2) Broadband wave-transmitting materials: low dielectric constant and loss make it widely used in radar, antenna and other fields;

(3) Heat and sound insulation materials: high-speed locomotives, tires, audio, etc.

5. Polyimide coating

The use of polyimide in the preparation of coatings is one of its earliest applications. Such substances are mainly used as insulating coatings for enameled wires in coatings. Enameled wire insulation coating is mainly dip coated with round wire, flat wire and other types of wire diameter naked copper wire, alloy wire and glass wire outer layer to improve and stabilize the outer layer of enameled wire.

One of the important indicators of insulating coatings is the heat resistance grade. According to the ICE-85 classification standard for thermal stability of electrical and mechanical insulation materials in use established by the International Electrotechnical Association in 1954, insulating materials are divided into 7 heat resistance grades.

The characteristics of insulation materials that meet the requirements of industrial technology development are that the insulation system should be able to work for a long time at a temperature of 180-200 ℃ or higher, but without significant weight loss and electrical strength reduction, and maintain good elasticity, moisture resistance, and Ozone resistance, arc resistance and other properties. Polyimide materials can meet this requirement well to prepare insulating coatings of F and above heat resistance grades. Polyimide can be used as insulating varnish for magnet wires or as high temperature resistant coatings.

6. Polyimide adhesive

PI (polyimide) adhesive is a kind of organic heterocyclic adhesive containing imide cyclic structure in the main chain. It has excellent high temperature mechanical properties, dielectric properties and radiation resistance. The disadvantage is that it is easy to Hydrolysis has been widely used in high-tech fields such as aerospace, precision electronic machinery, etc., and has solved the problem of lower upper limit heat resistance temperature of other organic adhesives.

7. Polyimide film

In addition to being used as the "coat" of spacecraft and military applications, polyimide film can be seen in the fields of microelectronics, nanometer, liquid crystal, separation membrane, laser, and new energy. For example, transparent polyimide film can be used as a flexible solar cell bottom plate; PI can be used as a next-generation lithium-ion battery separator material and so on.

In recent years, with the development of the electronics industry, high-performance polyimide film has become a key material for microelectronics manufacturing and packaging. It is widely used in the manufacture of ultra-large-scale integrated circuits, automatic bonding carrier tape, flexible packaging substrates, and flexible connecting tapes. Line and other aspects.

In addition, polyimide is an ideal material for high temperature resistant gas separation membranes because of its high heat resistance and good overall performance. At present, a very small number of polyimides are used in high-temperature gas separation membrane materials for the separation of various gas pairs (such as hydrogen/nitrogen, nitrogen/oxygen, carbon dioxide/nitrogen, carbon dioxide/methane, etc.). It can also be used as pervaporation membrane and ultrafiltration membrane to remove water from hydrocarbon feed gas and alcohol. However, conventional polyimide resins are difficult to dissolve and melt, which limits the possibility of their industrial wide application.

8. Polyimide aerogel

Polyimide aerogel (PIA) is a cross-linked three-dimensional porous material composed of polymer molecular chains. It combines the excellent properties of polyimide and aerogel. It not only has the excellent properties of polyimide, but also Moreover, it has the outstanding characteristics of aerogels such as light weight and ultra-low density, high specific surface area, low thermal conductivity, low acoustic impedance, environmental durability and low dielectric constant. These special properties make polyimide aerogel materials in Thermal, electrical, mechanics, acoustics and other fields have excellent application prospects.

In addition to the aerospace field, polyimide aerogel materials have good application prospects in the fields of electronic communications, heat insulation and flame retardant materials, adsorption cleaning, sound insulation and sound absorption, catalytic carriers, and wire/cable insulation layers.

9. Polyimide-based composite materials

Fiber-reinforced composite materials are a new generation of lightweight materials after magnesium-aluminum alloys. Polyimide-based composite materials have excellent high temperature resistance and tensile properties, and are widely used. Polyimide resin-based composite material has the characteristics of polyimide high heat resistance, excellent mechanical properties, dielectric properties, and solvent resistance. It is currently the highest temperature resin-based composite material. It is used in aviation (especially aviation). Engines), aerospace and other fields have been widely used.

After nearly 40 years of development, polyimide high temperature resistant resin-based composite materials have developed four generations of composite materials, and the use temperature has been continuously improved. At present, the most advanced fourth-generation polyimide resin-based composite materials can reach 450 ℃, an d use for a long time.