Polyimide is the molecular structure contains an aromatic heterocyclic polymer compounds of polyimide-based chain links, the English name Polyimide (PI for short), can be divided into benzene-type PI, soluble PI, polyamide-imide (PAI) and polyetherimide (PEI) four categories.
PI is currently one of the best varieties of engineering plastics heat resistance, some varieties can withstand long-term 290 ℃ high temperature for a short period of time to withstand a high temperature of 490 ℃, but also very low temperature, such as in the -269 ℃ liquid helium will not be brittle. In addition, mechanical properties, fatigue resistance, flame retardant, dimensional stability, electrical properties are good, molding shrinkage is small, resistant to oil, general acids and organic solvents, not alkali resistance, excellent friction resistance, abrasion properties. And PI is non-toxic, can be used to manufacture tableware and medical equipment, and withstand thousands of times disinfection.
PI moulding methods include compression moulding, impregnation, injection moulding, extrusion, die-casting, coating, casting, laminating, foaming and transfer moulding. PI has applications in aerospace, automotive, electronic and electrical appliances, industrial machinery, etc. It can be used as engine combustion system parts, jet engine components, compressor and generator parts, fasteners, spline joints and electronic contacts, as well as automotive engine parts, bearings, piston bushings, timing gears, printed wiring boards, insulating materials, heat-resistant cables, terminal blocks, sockets in the electronics industry, high temperature resistant self-lubricating bearings, and sockets in the machinery industry. High-temperature self-lubricating bearings, compressor blades and piston machine, sealing rings, equipment heat shield, thrust washers, bushings, etc..
Polyetherimide has excellent mechanical properties, electrical insulation properties, irradiation resistance, high and low temperature resistance and abrasion resistance, self-extinguishing, good melt flow, the shrinkage rate of the moulding is only 0.5 % ~ 0.7 %. PEI can be injection and extrusion moulding, post-processing is easier, can be adhesive or a variety of welding method and other materials, PEI in the electronics and electrical appliances, aerospace, automotive, medical equipment and other industries have been widely used. GE is the world’s largest producer of PEI, there are some engineering plastics modification company to provide PEI alloys and other modified products. The trend of development is the introduction of p-phenylenediamine structure or with other special engineering plastics alloy to improve its heat resistance; or with PC, PA and other engineering plastics alloy to improve its mechanical strength.
Polyamide-imide strength is currently the highest in the non-reinforced plastics, the colour of the material tensile strength of 190MPa, bending strength of 250MPa. 1.8MPa load heat deflection temperature of 274 ℃. PAI has good ablation resistance and high temperature, high frequency under the electromagnetic properties of metals and other materials have good adhesive properties. Mainly used for gears, rollers, bearings and copier separation claws, etc., but also for aircraft ablative materials, magnetic permeability and structural materials.PAI by Amoco company was the first to develop a successful and commercialised, in addition to Amoco, Japan’s Toray can also provide moulding plastics. Its development direction is to enhance the modification, and alloy with other plastics.
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