- Polyimide
Polyimide (sometimes abbreviated PI) is a
polymer ofimide monomers. The structure of imide is as shown.Thermoset ting polyimides are commercially available as uncured resins, stock shapes, thin sheets, laminates and machines parts.Thermoplastic polyimides are very often called "pseudothermoplastic". There are two general types of polyimides. One type, so-called linear polyimides, are made by combining imides into long chains. Aromatic heterocyclic polyimides are the other usual kind, where R′ and R″ are two carbon atoms of an aromatic ring. Examples of polyimide films include Apical,Kapton , Norton TH andKaptrex . Polyimide parts and shapes includeMeldin ,Vespel andPlavis . Polyimides have been in mass production since1955 .Properties
Thermosetting polyimides are known for thermal stability, good chemical resistance, excellent mechanical properties, and characteristic orange/yellow color. Polyimides compounded with
graphite orglass fiber reinforements have flexural strengths of up to 50,000 p.s.i. and flexural moduli of 3 million p.s.i. Thermoset polyimides exhibit very low creep and hightensile strength . These properties are maintained during continuous use to temperatures of 450°F (232°C) and for short excursions, as high as 900°F (482°C). Molded polyimide parts and laminates have very good heat resistance. Normal operating temperatures for such parts and laminates range from cryogenic to those exceeding 500°F (260°C). Polyimides are also inherently resistant to flame combustion and do not usually need to be mixed withflame retardant s. Most carry a UL rating of VTM-0. Polyimide laminates have a flexural strength half life at 480°F (249°C) of 400 hours.Typical polyimide parts are not affected by commonly used solvents and oils — including hydrocarbons, esters, ethers, alcohols and
freon s. They also resist weak acids but are not recommended for use in environments that contains alkalis or inorganic acids. Some polyimides, such as CP1 and CORIN XLS, are solvent-soluble and exhibit high optical clarity. The solubility properties lend them towards spray and low temperature cure applications.Application
Polyimide is often used in the electronics industry for flexible cables, as an insulating film on
magnet wire and for [http://www.accellent.com/solutions/component_manufacturing.shtml medical tubing] . For example, in a laptop computer, the cable that connects the main logic board to the display (which must flex every time the laptop is opened or closed) is often a polyimide base with copper conductors. The semiconductor industry uses polyimide as a high-temperature adhesive; it is also used as a mechanical stress buffer. Some polyimide can be used like aphotoresist ; both "positive" and "negative" types of photoresist-like polyimide exist in the market.References
*Modern Plastic Mid-October Encyclopedia Issue, Polyimide, thermoset, page 146.
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Polyamide
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