Kapton

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Structure of poly-oxydiphenylene-pyromellitimide
Kapton insulating pads for mounting electronic parts on a heat sink
Aluminized Kapton thermal cover was used on the Ultra Heavy Cosmic Ray Experiment.
Kapton tapes, three rolls of different widths

Kapton is a polyimide film developed by DuPont that remains stable across a wide range of temperatures, from −269 to +400 °C (−452 – 752 °F / 4 – 673 K).[1] 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 K 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).

Usage[edit]

The thermal conductivity of Kapton at temperatures from 0.5 to 5 kelvins is rather high for such low temperatures, κ = 4.638×10−3 T0.5678 W·m−1·K−1.[2] This, together with its good dielectric qualities and its availability as thin sheets have made it a favorite material in cryogenics, as it provides electrical insulation at low thermal gradients. Kapton is regularly used as an insulator in ultra-high vacuum environments due to its low outgassing rate.[3]

Aircraft[edit]

Kapton-insulated electrical wiring has been widely used in civil and military aircraft because it is lighter than other insulators and has good insulating and temperature characteristics. For these reasons, the sunshield of the James Webb Space Telescope will be made of it.[4]

However, Kapton insulation ages poorly: an FAA study shows degradation in under 100 hours in a hot, humid environment.[5] It was 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.

Spacecraft[edit]

The descent stage of the Apollo Lunar Module, and the bottom of the ascent stage surrounding the ascent engine, were covered in blankets of aluminized Kapton foil to provide thermal insulation. During the return journey from the Moon, Apollo 11 astronaut Neil Armstrong commented that during the launch of the Lunar Module ascent stage, he could see "Kapton and other parts on the LM staging scattering all around the area for great distances." [6]

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."[7] 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.[8]

X-rays[edit]

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 and high transmittance to X-rays make it the preferred material. It is also relatively insensitive to radiation damage.[9]

3D printing[edit]

Kapton and ABS adhere to each other very well which has led to widespread use of Kapton as a build surface for 3D printers. Kapton is laid down on a flat surface and the ABS is extruded on to the Kapton surface. Since Kapton and ABS strongly adhere to each other the ABS will not detach from the build platform as the ABS cools and shrinks. This is a common cause of 3d print failures as well as warping in parts.[citation needed]

Kapton tape is also commonly used to secure components such as thermocouples to the hot-end of 3D printer extruders. Care must be used, as insufficiently attached thermocouples can detach, leading to runaway overheating of the nozzle, and fires.

Trademark[edit]

Kapton is a registered trademark of E. I. du Pont de Nemours and Company.

References[edit]

  1. ^ Navick, X.-F.; Carty, M.; Chapellier, M.; Chardin, G.; Goldbach, C.; Granelli, R.; Hervé, S.; Karolak, M.; Nollez, G.; Nizery, F.; Riccio, C.; Starzynski, P.; Villar, V. (2004). "Fabrication of ultra-low radioactivity detector holders for Edelweiss-II". NIM A 520: 189–192. doi:10.1016/j.nima.2003.11.290. 
  2. ^ Jason Lawrence, A. B. Patel and J. G. Brisson (2000). "The thermal conductivity of Kapton HN between 0.5 and 5 K". Cryogenics 40 (3): 203–207. doi:10.1016/S0011-2275(00)00028-X. 
  3. ^ Peter Kittel (30 September 1998). Advances in Cryogenic Engineering. Birkhäuser. pp. 1366–. ISBN 978-0-306-45807-1. Retrieved 29 April 2012. 
  4. ^ Nasa description of the JWST sunshield. Ngst.gsfc.nasa.gov. Retrieved on 2012-04-28.
  5. ^ FAA insulation aging test results. DOT/FAA Tech Report AR-08/2, January 2008. Retrieved on 2013-08-23
  6. ^ Apollo 11 Flight Journal – Day 6 part 4: Trans-Earth Injection. History.nasa.gov (2011-03-15). Retrieved on 2012-04-28.
  7. ^ High Tech in the 1970s, Shuttles Feel Their Age. New York Times (2005-07-25)
  8. ^ Jerome L. Wright (1 January 1992). Space Sailing. Taylor & Francis US. pp. 100–. ISBN 978-2-88124-842-9. Retrieved 28 April 2012. 
  9. ^ Janez Megusar (1997). "Low temperature fast-neutron and gamma irradiation of Kapton polyimide films". Journal of Nuclear Materials 245 (2–3): 185–190. doi:10.1016/S0022-3115(97)00012-3.