Kapton

Kapton® is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -269 °C to +400 °C (4 K - 673 K). Kapton is used in, among other things, flexible printed circuits (flexible electronics) and Thermal Micrometeoroid Garments, the outside layer of space suits.

The chemical name for Kapton H and HN is poly(4,4'-oxydiphenylene-pyromellitimide). It is produced from the condensation of pyromellitic dianhydride and 4,4'-oxydiphenylamine. Kapton synthesis is an example of the use of a dianhydride in step polymerization. The intermediate polymer, known as a "poly(amic acid)," is soluble because of strong hydrogen bonds to the polar solvents usually employed in the reaction. The ring closure is carried out at high temperatures (200–300 °C, 473-573 K).

Kapton insulated wiring has been widely used in civil and military avionics (electrical wiring for aircraft) because of its very light weight compared to other insulator types as well as good insulating and temperature characteristics. However it was soon found to have very poor resistance to mechanical wear, mainly abrasion within cable harnesses due to aircraft movement. Many aircraft models have had to undergo extensive rewiring modifications, sometimes completely replacing all the Kapton-insulated wiring, because of short circuits caused by the faulty insulation.

According to a NASA internal report, Space Shuttle "wires were coated with an insulator known as Kapton that tended to break down over time, causing short circuits and, potentially, fires. [http://www.nytimes.com/2005/07/25/science/space/25shuttle.html] " The NASA Jet Propulsion Laboratory has considered Kapton as a good plastic support for solar sails because of its long duration in the space environment (J. L. Wright, "Space Sailing", Gordon and Breach, 1992).

Kapton is also commonly used as a material for windows of all kinds at x-ray sources (synchrotron beam-lines and x-ray tubes) and x-ray detectors. Its high mechanical and thermal stability as well as its high transmittance to x-rays make it the preferred material. It also does not suffer from radiation damage [cite journal
author = Janez Megusar
year = 1997
title = Low temperature fast-neutron and gamma irradiation of Kapton polyimide films
journal = Journal of Nuclear Materials
volume = 245
pages = 185–190
doi = 10.1016/S0022-3115(97)00012-3 ] . Another prominent material for these purposes is beryllium.

The thermal conductivity of Kapton in temperatures from 0.5 to 5 Kelvins is rather high κ = 4.638×10⁻³ "T"^0.5678 W·m^-1·K. [cite journal
author = Jason Lawrence, A. B. Patel and J. G. Brisson
year = 2000
title = The thermal conductivity of Kapton HN between 0.5 and 5 K
journal = Cryogenics
volume = 40
pages = 203–207
doi = 10.1016/S0011-2275(00)00028-X ] This together with its good dielectric qualities and its availability as thin sheets have made it a favorite material in cryogenics (devices working in temperatures down to absolute zero, -273 °C or 0 K).

Kapton is also regularly used as an insulator in ultra-high vacuum environments as it has a low outgassing rate.

References

External links

* [http://www.dupont.com/kapton/ DuPont Kapton]
* [http://www.caplinq.com/blog/?p=7/ How Polyimide (generic version of DuPont's Kapton) Tape is Made]