一,Introduction to polyimide
Polyimide (PI) is a molecular structure containing imide-based chain links of aromatic heterocyclic polymer compounds, is currently one of the best varieties of engineering plastics heat resistance, widely used in aviation, aerospace, microelectronics, nano, liquid crystal, laser and other fields.
Recently, all countries are including the research, development and use of PI in the 21st century, one of the focuses of the development of new chemical materials. Polyimide, due to its outstanding features in performance and synthesis, has great application prospects, whether as a structural material or as a functional material.
Polyimide is known as the top of the pyramid of polymer materials, also known as the "problem solver", and even some industry insiders believe that "no polyimide will not have today's microelectronics technology".
二,Polyimide classification and application
Polyimides can be used in a wide range of applications due to their excellent properties and can be classified into a variety of types, including engineering plastics, fibres, photosensitive polyimides, foams, coatings, adhesives, films, aerogels, composites and more.
Among many polymers, polyimide is the only one that has a wide range of applications and shows outstanding performance in each of them. Below, I'll take you through the main uses of each variety of polyimide.
1.Engineering plastic
Polyimide engineering plastic has thermosetting and thermoplastic, that can be divided into poly tetramethylene tetracarbimide (PMMI), polyetherimide (PEI), polyamide an imide (PAI), etc., have their own uses in different fields.
PMMI in 1.8MPa load heat distortion temperature of 360 ℃, excellent electrical properties, can be used for special conditions of precision parts, high temperature self-lubricating bearings, seals, blower impellers, etc., can also be used in contact with liquid ammonia valve parts, jet engine fuel supply system parts.
PEI has excellent mechanical properties, electrical insulation properties, irradiation resistance, high temperature resistance and abrasion resistance, good melt fluidity, moulding shrinkage rate of 0.5% to 0.7%, available for injection and extrusion moulding, post-processing is relatively easy, can also be used for welding method and other materials combined in the electronics and electrical appliances, aviation, automobiles, medical equipment and other industries are widely used.
The strength of PAI is the highest among the current non-reinforced plastics, the tensile strength is 190MPa, the bending strength is 250MPa, and the heat distortion temperature is as high as 274℃ under the load of 1.8MPa. PAI has good resistance to ablation and electromagnetism under high temperature and high frequency, and it has good adhesive properties to metals and other materials, mainly used for gears, bearings and separating claws of photocopiers, etc., and it can be also used for It is mainly used for gears, bearings and separating claws of photocopiers, etc. It can also be used for ablative materials, magnetically permeable materials and structural materials of aircraft.
2.Polyimide fibre
Polyimide fibre is an important high-performance fibre, its high temperature polyimide fibre is currently one of the highest temperature of organic synthetic fibres, can be used at 250~350 ℃. In the light resistance, water absorption, heat resistance and other aspects of aramid and polyphenylene sulfide fibres are more superior compared to the high-performance polyimide fibre strength than the aramid is about one times higher than the current mechanical performance of one of the best organic synthetic fibres. It is one of the best organic synthetic fibres in terms of mechanical properties.
With the continuous development of high-tech fields, the physical and chemical properties of PI products are increasingly demanding. The traditional PI materials in mechanics, thermal and optical, electrical, magnetic and other aspects of the performance has been unable to meet the modern scientific and technological fields of the special requirements of the material. PI high-performance fibres with its superior mechanical properties, heat stability, irradiation and other characteristics will become the next generation of high-performance fibers typical representative.
At present, the domestic PI fibre industry is mainly engaged in Asxc, Hipolyking, Aieplastics, Jsshino and so on.Among them, Hipolyking has become an important base for polyimide research, development and production in China. Jsshino a high-performance organic fibre with completely independent intellectual property rights passed the appraisal of scientific and technological achievements in 2016, and at the same time took the lead in completing the formulation of the national standard of "high-strength and high-modulus polyimide filament" in 2020.
3.Photosensitive polyimide (PSPI)
Photosensitive polyimide (PSPI) is a class of polymer chain both in the imide ring and photosensitive genes, set of excellent thermal stability, good mechanical properties, chemical and photographic properties of organic materials.
PSPI in the field of electronics, mainly photoresist and electronic packaging two major roles, in the photosensitive polyimide added to the sensitiser, stabilizer, etc. can be obtained "polyimide photoresist". Compared with the traditional photoresist, because the polyimide itself has good dielectric properties, so when used without the need to coat the role of the working medium of the light barrier agent, can greatly shorten the process and improve production efficiency.
PSPI production technology is mainly controlled by U.S. and Japanese companies, of which Toray is one of the world's most successful enterprises in the market of positive PSPI products, and its positive products are used in microelectronics packaging, optoelectronics encapsulation and other fields.
Restricted by the backwardness of production technology, China's polyimide industry is still to film and other low-end products to stabilise, photosensitive polyimide production is less, the market demand depends on imports. In the 《Made in China 2025》 policy support, China's industrial, mechanical, electronic and other fields are entering the domestic substitution stage, domestic enterprises for PSPI continue to deepen, some companies have mastered the production technology.
Currently, the layout of the PSPI R & D, production of local enterprises have Rayitek, MINSEOA Advanced Material, Guofeng New Materials, Dragon-chen, etc., the future of the field of domestic substitution of space.
4.Polyimide foam
Polyimide foam is a type of polyimide material, first developed in the 1970s by NASA Langley Research Centre in cooperation with Unitika America, used on the Space Shuttle, and is now widely used in aircraft, ships, trains, automobiles and other fields. It with intrinsic flame retardant, heat-resistant, lightweight and environmentally friendly non-toxic features, and can be used for a long time under ultra-high temperature, ultra-low temperature, high salt spray, strong noise, strong corrosion, strong radiation and other extreme conditions of service.
Polyimide foam can be divided into three categories:
As the same of in general polyimide, foam materials with an mide as the main chain, with an operating temperature of 300°C or more (PI foam).
Foam materials in which the mide ring exists as a side group (PMI foam).
Nano-foam materials obtained by introducing thermally unstable fatty chain segments into polyimide and cracking them at high temperatures.
Polyimide foam material belongs to advanced functional materials, has been increasingly used in aerospace, ocean transportation, national defence and microelectronics and other high-tech fields in the heat insulation, vibration and noise reduction and insulation and other key materials.
The most important application of PI foam is heat insulation and noise reduction material for ships. PI foam as the first choice of heat insulation and noise reduction material in new warships is rapidly increasing.
PMI foam is a new type of high molecular structure foam material with the best comprehensive performance, which is a high-performance composite foam core material with high specific strength, high specific modulus, high closure rate and high heat resistance, and has the characteristics of light weight, high strength and high/low temperature resistance. In addition, as the most excellent structural foam core material, PMI foam is widely used in fan blades, helicopter blades, aerospace and other fields, and its substitution trend for PET foam is clear, with a wide market space.
PI foam is heat-resistant, flame-retardant, does not produce harmful gases, easy to install, is widely used in heat insulation and noise reduction materials. At present, the U.S. Navy has used PI foam as the thermal and acoustic insulation material for all surface ships and submarines, and the SOLIMIDE foam produced by INSPEC has been used by more than 15 countries to develop the thermal and acoustic insulation system for naval vessels. In addition, PI foam is also widely used in civilian ships, such as luxury cruise ships, speedboats and liquefied natural gas ships.
Similar to PI foam, the application of PMI foam is also very wide.Typical applications of PMI foam include:
(1) Structural foam core material: excellent resistance to high-temperature compression, so that it is widely used as a core material for fan blades, aviation, aerospace, ships, sports equipment, medical equipment and other fields;
(2) Broadband wave-transparent 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, tyres, audio and so on.
Since the 21st century, the number of units involved in the research of polyimide foam in China has grown significantly, and the industry has made significant technological breakthroughs. At present, the main domestic manufacturers of polyimide foam are Qingdao Ouc, Shkdchem and Tschina, Zgzts and AMMT. Among them, Ningbo Institute of Materials Tachnology ＆ Engineeing, CAS has built a polyimide microfoam particles pilot equipment, Qingdao Ouc and Shkdchem polyimide products passed the military test.
5.Polyimide coating
The use of polyimide in the preparation of coatings is one of its earliest applications, and this type of substance is mainly used as an insulating coating for enamelled wires in coatings. Enamelled wire insulating coatings are mainly dip-coated round wire, flat wire and other types of wire diameter bare copper wire, alloy wire and glass wire wrapped wire outer layer, improve and stabilise the outer layer of the enamelled wire.
One of the important indexes of insulating coatings is heat-resistant grade, according to the 1954 International Electrotechnical Association ICE-85 motor and electrical insulating materials in the use of thermal stability grading standards, insulating materials are divided into seven heat-resistant grade.
To meet the requirements of industrial technology development of insulation materials is characterised by the insulation system should be able to 180-200 ℃ its to higher temperatures for long-term work, but no significant weight loss and electrical strength reduction, and maintain a good elasticity, moisture, ozone, arc resistance and other properties. Polyimide materials can be very good to meet the requirements of this use, to prepare F-class and above heat-resistant grade insulation coating, polyimide can be used as an insulating varnish for the electromagnetic wire, or as a high-temperature coatings used.