1. 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 have included the research, development and utilization of PI in the 21st century as one of the development focuses 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.
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Pyramid of polymer materials
2. polyimide classification and application
Polyimide can be used in a variety of fields due to its excellent performance, and can also be divided into a variety of types, including engineering plastics, fibers, photosensitive polyimide, foams, coatings, adhesives, films, aerogels, composites and so on.
Polyimide is widely used
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 plastics
Polyimide engineering plastics can be divided into both thermosetting and thermoplastic, can be divided into poly(tetramethylene tetraimide) (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 and abrasion resistance, good melt fluidity, molding shrinkage of 0.5% to 0.7%, available for injection and extrusion molding, post-processing is easier, can also be used for welding method and other materials combined in the electronics and electrical appliances, aerospace, automotive, 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 at 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 used for the ablation materials of aircraft, transmittance materials, and other materials, and can be used in the production of electronic devices. It is mainly used for gears, bearings and separator claws of copiers, etc. It can also be used for ablative materials, magnetically permeable materials and structural materials of aircraft.
Polyimide for high performance parts
(2). Polyimide fiber
Polyimide fiber is an important high-performance fibers, its high temperature polyimide fiber is currently one of the highest temperature of organic synthetic fibers, can be used at 250 ~ 350 ℃, in the light resistance, water absorption, heat resistance and other aspects of aramid and polyphenylene sulfide fibers compared to the superiority of high-performance polyimide fibers than the strength of the aramid is about one times higher than the current mechanical performance of the best organic It is one of the best organic synthetic fibers in terms of mechanical properties.
With the continuous development of high-tech fields, its 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 fibers with its superior mechanical properties, thermal stability, irradiation and other characteristics of the next generation of high-performance fibers will become a typical representative of the fiber.
At present, the domestic PI fiber industry is mainly engaged in Jiangsu Aoshen, Changchun Gaoqi, Kejiu New Material, Jiangsu Xiannuo and so on. Among them, Changchun Gaoqi has become an important base for polyimide research, development and production in China, and a high-performance organic fiber with completely independent intellectual property rights of Jiangsu ceno passed the scientific and technological achievements appraisal in 2016, and also took the lead in 2020 to complete the development of national standards of "high-strength and high-modulus polyimide filament".
Polyimide Fiber
(3). Photosensitive polyimide (PSPI)
Photosensitive polyimide (PSPI) is a class of polymer chain both the imide ring as well as photosensitive genes, set of excellent thermal stability, good mechanical properties, chemical and photographic properties of organic materials.
Photosensitive polyimide in the field of electronics, mainly photoresist and electronic packaging two major roles, in the photosensitive polyimide added to the sensitizer, stabilizer, etc. can be obtained "polyimide photoresist". Compared with traditional photoresists, polyimide itself has good dielectric properties, so it is not necessary to coat the working medium when using the role of light barrier, which can greatly shorten the process and improve production efficiency.
Photosensitive polyimide (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 stable, 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 are Rui Huatai, Ming Shi new materials, national wind plastic industry, Dinglong Technology, etc., the future of the field of domestic substitution of space.
Polyimide for photoresist
(4). Polyimide Foam
Polyimide foam is a type of polyimide material, first developed in the 1970s by NASA Langley Research Center in cooperation with Unitika America, used in the space shuttle, is now widely used in aircraft, ships, trains, automobiles and other fields, with the nature of flame retardant, heat-resistant, lightweight, and environmentally friendly non-toxic, can be a long period in the 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:
(a) The same as the general polyimide, the imide as the main chain of the foam material, the use of temperature reaches more than 300 ℃ (PI foam)
(b) Foam materials in which the imide ring exists as a side group (PMI foam)
(c) Nano-foam materials obtained by introducing thermally unstable fatty chain segments into polyimide and cracking them at high temperatures.
Polyimide foam materials belong to the advanced functional materials, has been increasingly used in aerospace, ocean transportation, national defense and microelectronics and other high-tech fields such as heat insulation, vibration and noise reduction and insulation and other key materials.
PI foam is currently the most important application for ships with heat insulation and noise reduction materials, China's navy is currently in the third shipbuilding climax, PI foam as a new type of warships in the first choice of heat insulation and noise reduction materials, the demand is rapidly rising.
Poly(methacrylimide) foam (PMI for short) is a new type of high molecular structure foam material with optimal 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 is characterized by light weight, high strength and high/low temperature resistance, etc. In addition, PMI foam, as the most excellent thermal insulation and noise reduction material for ships, has a rapidly increasing demand. In addition, PMI foam as the most excellent structural foam core material, widely used in fan blades, helicopter blades, aerospace and other fields, its substitution trend for PET foam is clear, the market space is vast.
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 in more than 15 countries for the development of thermal and acoustic insulation systems 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.
Polyimide Foam
Similar to PI foam, the application of PMI foam is also very wide.Typical applications of PMI foam include:
(a) 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;
(b) Broadband wave-transparent materials: low dielectric constant and loss make it widely used in radar, antenna and other fields;
(c) heat and sound insulation materials: high-speed locomotives, tires, audio and so on.
Since the 21st century, the number of units involved in polyimide foam research in China has grown significantly, and the industry has made significant technological breakthroughs, and at present, the main domestic manufacturers of polyimide foam are Qingdao Ocean, Kanda New Material and Tiansheng New Material, Zigong Zhongtiansheng, Qingdao Ocean New Material and so on. Among them, Ningbo Institute of Materials, Chinese Academy of Sciences has built a polyimide microfoam particles pilot equipment, Qingdao Ocean and Kangda New Material polyimide products passed the military test.
(5). Polyimide coatings
Polyimide for the preparation of coatings is one of its earliest applications, the substances in the coating is mainly used as an enameled wire insulation coating. Enameled wire insulation coating is 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 stabilize the outer layer of enameled 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 characterized by the insulation system should be able to 180-200 ℃ its to higher temperatures under 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.
To be continued
Source "China Composites Industry Association official website".