Kapton

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 in the late 1960s[1] that remains stable across a wide range of temperatures, from −269 to +400 °C (−452 to 752 °F; 4–673 K).[2] Kapton is used in, among other things, flexible printed circuits (flexible electronics) and thermal blankets used on spacecraft, satellites, and various space instruments.

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

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.[3] 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.[4]

Aircraft

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.[5]

However, Kapton insulation ages poorly: an FAA study shows degradation in under 100 hours in a hot, humid environment.[6] 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. Kapton-wire degradation and chafing due to vibration and heat has been implicated in multiple crashes of both fixed wing and rotary wing aircraft, with loss of life.[7]

Spacecraft

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." [8]

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."[9] 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.[10]

NASA's New Horizons spacecraft used Kapton in an innovative "Thermos bottle" insulation design to keep the craft operating between 10–30 °C (50–86 °F) throughout its more than nine-year, 3 billion mile journey to rendezvous with the dwarf planet Pluto on July 14, 2015.[11] The main body is covered in lightweight, gold-colored, multilayered thermal insulation – like a survival camping blanket – which holds in heat from operating electronics to keep the spacecraft warm. The thermal blanketing – 18 layers of Dacron mesh cloth sandwiched between aluminized Mylar and Kapton film – also helped to protect the craft from micrometeorites.[12]

X-rays

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.[13]

Electronic manufacturing

Blue Kapton tape in a smartphone.

Due to its large range of temperature stability, and its electrical isolation ability, Kapton tape is usually used in electronic manufacturing as an insulation and protection layer on electrostatic sensitive and fragile components. As it can sustain the temperature needed for a reflow soldering operation, its protection is available throughout the whole production process, and Kapton is often still present in final consumer product.

3D printing

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. The ABS part being printed will not detach from the build platform as it cools and shrinks, a common cause of print failure by warping of the part.

Kapton tape is also commonly used to secure components such as thermocouples to the hot end of the plastic extruder. This helps to prevent detachment of the thermocouples, which can lead to runaway overheating of the nozzle, and fires.

Trademark

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

References

  1. ↑ "DuPont Circuit & Packaging Materials Awarded U.S. Patents for Matte Black Film and Coverlay". November 15, 2013. Retrieved 2015-05-28. DuPont invented Kapton® polyimide film over 45 years ago
  2. ↑ 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.
  3. ↑ 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.
  4. ↑ Peter Kittel (30 September 1998). Advances in Cryogenic Engineering. Birkhäuser. pp. 1366–. ISBN 978-0-306-45807-1. Retrieved 29 April 2012.
  5. ↑ Nasa description of the JWST sunshield. Ngst.gsfc.nasa.gov. Retrieved on 2012-04-28.
  6. ↑ FAA insulation aging test results. DOT/FAA Tech Report AR-08/2, January 2008. Retrieved on 2013-08-23
  7. ↑ Fatal helicopter crash caused by Kapton wiring www.military.com Retrieved 2015-02-17.
  8. ↑ Apollo 11 Flight Journal – Day 6 part 4: Trans-Earth Injection. History.nasa.gov (2011-03-15). Retrieved on 2012-04-28.
  9. ↑ High Tech in the 1970s, Shuttles Feel Their Age. New York Times (2005-07-25)
  10. ↑ Jerome L. Wright (1 January 1992). Space Sailing. Taylor & Francis US. pp. 100–. ISBN 978-2-88124-842-9. Retrieved 28 April 2012.
  11. ↑ NASA New Horizons Pluto Mission, Mission Design Retrieved April 23, 2015
  12. ↑ NASA, New Horizons Mission, Thermal Control
  13. ↑ 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.
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