| Polyimide | |
|---|---|
 |
|
| Density | 1430 kg/m3 |
| Young's modulus(E) | 3200 MPa |
| Tensile strength(t) | 75-90 MPa |
| Elongation @ break | 4-8% |
| notch test | 4-8 kJ/m |
| Glass temperature | >400 °C |
| melting point | none |
| Vicat B | 220(?) °C[1] |
| heat transfer coefficient () | 0.52 W/m.K |
| linear expansion coefficient () | 5.5 10-5 /K |
| Specific heat (c) | 1.15 kJ/kg.K |
| Water absorption (ASTM) | 0.32 |
| Dielectric constant (Dk) at 1MHz | 3.5 |
Polyimide (sometimes abbreviated PI) is a polymer of imide monomers. The structure of imide is as shown. Thermosetting 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 and Kaptrex. Polyimide parts and shapes include Meldin, Vespel and Plavis. Polyimides have been in mass production since 1955.
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Properties
Thermosetting polyimides are known for temperature stability, good chemical resistance, and for their excellent mechanical properties. Polyimides compounded with graphite or glass 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 high tensile strength. These properties are maintained during continuous use to temperatures of 450oF (232oC) and for short excursions, as high as 900oF (482oC). Molded polyimide parts and laminates have very good heat resistance. Normal operating temperatures for such parts and laminates range from cryogenic to those exceeding 500oF (260oC). Polyimides are also inherently resistant to flame combustion and do not usually need to be mixed with flame retardants. Most carry a UL rating of VTM-0. Polyimide laminates have a flexural strength half life at 480oF (249oC) of 400 hours Polyimide parts are not affected by most commonly used solvents and oils — including such ones as hydrocarbons, esters, ethers, alcohols and freons. They also resist weak acids but are not recommended for use in environments that contains alkalis or inorganic acids.
Application
Polyimide is often used in the electronics industry for flexible cables and as an insulating film on magnet wire. 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.
References
- Modern Plastic Mid-October Encyclopedia Issue, Polyimide, thermoset, page:146
Notes
- ^ Deformation temperature at 10kN needle load, source: A.K. vam der Vegt & L.E. Govaert, Polymeren,van keten tot kunstof, ISBN 90-407-2388-5
See also: Polyamide
