Kapton
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Structure of poly-oxydiphenylene-pyromellitimide Kapton insulating pads for mounting electronic parts on a heat sink Kapton is a polyimide film used in flexible printed circuits (
flexible electronics Flexible electronics, also known as ''flex circuits'', is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additi ...
) and
space blanket A space blanket (also known as a Mylar blanket, emergency blanket, first aid blanket, safety blanket, thermal blanket, weather blanket, heat sheet, foil blanket, or shock blanket) is an especially low-weight, low-bulk blanket made of heat-refle ...
s, which are used on spacecraft, satellites, and various space instruments. Invented by the
DuPont Corporation DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
in the 1960s, Kapton remains stable (in isolation) across a wide range of temperatures, from .


History

Kapton was invented by the
DuPont Corporation DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
in the 1960s. The name ''Kapton'' is a registered trademark of E. I. du Pont de Nemours and Company.


Chemistry and variants

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 solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...
s usually employed in the reaction. The
ring closure A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...
is carried out at high temperatures of . The chemical name for Kapton K and HN is ''poly (4,4'-oxydiphenylene-pyromellitimide)''. It is produced from the condensation of pyromellitic dianhydride (PMDA) and 4,4'-oxydiphenylamine (ODA). Kapton E is a mix of two dianhydrides, PMDA and biphenyltetracarboxylic acid dianhydride (BPDA), and two diamines, ODA and
p-phenylenediamine ''p''-Phenylenediamine (PPD) is an organic compound with the formula C6H4(NH2)2. This derivative of aniline is a white solid, but samples can darken due to air oxidation. It is mainly used as a component of engineering polymers and composites lik ...
(PPD). The BPDA component adds greater dimensional stability and flatness in flexible circuitry applications. Kapton E offers reduced
coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kineti ...
(CTE), reduced moisture absorption, and reduced coefficient of
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substan ...
expansion (CHE) compared to Kapton H.


Characteristics

Kapton remains stable (in isolation) across a wide range of temperatures, from . The thermal conductivity of Kapton at temperatures from 0.5 to 5 Kelvin is rather high for such low temperatures, κ = 4.638×10−3 ''T''0.5678 W·m−1·K−1. Kapton insulation ages poorly: an FAA study shows degradation in hot, humid environments or in the presence of seawater. 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. According to a
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...
internal report,
Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program ...
"wires were coated with an insulator known as Kapton that tended to break down over time, causing short circuits and, potentially, fires."


Usage

Kapton tapes, three rolls of different widths


Electronics manufacturing

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 the final consumer product.


Spacecraft

Aluminized Kapton thermal cover was used on the Ultra Heavy Cosmic Ray Experiment 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 Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ...
Kapton foil to provide thermal insulation. During the return journey from the Moon,
Apollo 11 Apollo 11 (July 16–24, 1969) was the American spaceflight that first landed humans on the Moon. Commander Neil Armstrong and lunar module pilot Buzz Aldrin landed the Apollo Lunar Module ''Eagle'' on July 20, 1969, at 20:17 UTC, ...
astronaut Neil Armstrong commented that during the launch of the Lunar Module ''Eagle'' ascent stage, he could see "Kapton and other parts on the LM staging scattering all around the area for great distances." The NASA
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
has considered Kapton as a good plastic support for solar sails because of its durability in the space environment. NASA's '' New Horizons'' spacecraft used Kapton in an innovative "
Thermos bottle A vacuum flask (also known as a Dewar flask, Dewar bottle or thermos) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Sir James Dew ...
" insulation design to keep the craft operating between throughout its more than nine-year, journey to rendezvous with the dwarf planet Pluto on 14 July 2015. The main body is covered in lightweight, gold-colored, multilayered thermal insulation which holds in heat from operating electronics to keep the spacecraft warm. The thermal blanketing of 18 layers of
Dacron Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foo ...
mesh cloth sandwiched between aluminized
Mylar BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and a ...
and Kapton film also helped to protect the craft from
micrometeorites A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. T ...
. The James Webb Space Telescope sunshield is made of five Kapton E sheets coated with aluminum and
doped silicon In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic se ...
to reflect heat away from the spacecraft body. The crew aboard the
International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ( ...
used Kapton tape to temporarily repair a slow leak in a
Soyuz Soyuz is a transliteration of the Cyrillic text Союз ( Russian and Ukrainian, 'Union'). It can refer to any union, such as a trade union (''profsoyuz'') or the Union of Soviet Socialist Republics (Сою́з Сове́тских Социалис ...
spacecraft attached to the Russian segment of the orbital complex in August 2018. It was used again in October 2020 to temporarily seal a leak in the transfer chamber of the Zvezda Service Module of the ISS.


X-rays

Kapton is also commonly used as a material for windows used with all kinds of
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
sources ( synchrotron beam-lines and
X-ray tube An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contrast ...
s) and X-ray detectors. Its high mechanical and thermal stability as well as high transmittance of X-rays make it the preferred material. It is also relatively insensitive to
radiation damage Radiation damage is the effect of ionizing radiation on physical objects including non-living structural materials. It can be either detrimental or beneficial for materials. Radiobiology is the study of the action of ionizing radiation on livin ...
.


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 printer 3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
s. Kapton is laid down on a flat surface and the ABS is extruded onto 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. A more durable alternative is to use a
polyetherimide Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK. When comparing PEI to PEEK, the former is cheaper but has lower impact strength and a tighter temperature range. D ...
surface. Researchers have devised a method to 3D-print polyimide material including Kapton. The polyamic acid precursor to Kapton is mixed with an acrylate cross linker and photoinitiator that can form a gel when exposed to ultraviolet light during 3D printing. Subsequent heating of the 3D printed part up to 400 °C removes the sacrificial crosslinks and imidizes the part forming Kapton with a 3D printed geometry.


Others

Kapton's relatively high thermal conductivity at very low temperatures, together with its good dielectric qualities and its availability as thin sheets, have made it a favorite material in
cryogenics In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
, 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 Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...
rate. 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.


See also

*
Mylar BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and a ...


References


External links


Polyimide Films
at DuPont {{DuPont Aerospace materials Dielectrics Flexible electronics