Plastic Materials: Kapton within Plastic Fasteners

kaptonHigh-quality fasteners are needed in a wide variety of applications, especially when those applications involve extreme temperatures, high stress levels, or other challenging circumstances. Choosing the right fastener is a must. Kapton within you plastic fasteners may be a potential choice.

Kapton fasteners are often a good choice because Kapton products utilize a unique polyimide film. This film offers excellent physical, electrical, and mechanical properties over a wide range of temperatures. In addition, it has excellent chemical resistance, and adhesives are available that allow Kapton products to bond to other Kapton products, as well as various paper types and other films.

Physical and thermal properties

Kapton polyimide film is able to maintain its physical properties, even in extreme temperatures. Temperatures can range from as low as –269°C (–452°F) to as high as 400°C (752°F) before the film is compromised. With a UL-94 flammability rating of V-0, it does not melt or burn easily.
However, the polyimide film is affected by water, since it is created as a result of a condensate reaction. Boiling water can reduce the film’s properties, but sufficient tensile and elongation remain, ensuring high-quality mechanical performance. Low temperature water reduces the rate of property reduction and higher water temperatures increase property reduction.
Thermal expansion and residual stress can also affect the Kapton polyimide film. During manufacturing, residual stressed is placed on the film, which causes it to shrink when it is first exposed to extreme high temperatures. However, once exposed, normal levels of stability can be expected.

Temperature and oxygen concentration affect the life of the film. However, the tensile strength can be expected to remain strong at 234 MPa (34,000 psi), with an elongation of 67 percent at temperatures up to 325°C (617°F). The life of the film can be extended when utilized in low-oxygen environments.

Electrical properties

The electrical properties of polyimide film depend on the type of film being utilized. However, they are all affected by humidity, temperature, and frequency.

Humidity levels can cause dielectric strength to drop from 8,600 V/mil at zero percent humidity to 6,800 V/mil at 100 percent humidity. As mentioned earlier, extreme temperatures have very little effect on the film. Frequency can affect the dielectric constant and dissipation factor as well.

Because Kapton polyimide film is made out of organic materials, it will fail when continuously exposed to corona discharge. However, with moderate exposure, devices and fasteners that are insulated with Kapton can survive up to 3,000 h. Just how well the device that’s utilizing Kapton fasteners can withstand corona discharge depends on the insulation thickness, air gap thickness, and device shape.

Chemical properties

Kapton fasteners have chemical resistant properties that allow them to work well with isopropyl alcohol, toluene, 2 N hydrochloric acid, and more. They allow for moisture absorption and gas permeability for carbon dioxide, oxygen, hydrogen, and helium. The material is also resistant to radiation.

Industries that utilize Kapton fasteners

Because Kapton polyimide film has so much to offer, it is occasionally used within a fastener. It is used in many industries and applications that include:

  • Thermal management in the United States space program
  • Solar arrays
  • Automotive switches and applications
  • Hard disk drives and other electronics
  • Insulation for traction motors
  • Voice coils
  • Automotive switches
  • Barcode labels on PC boards and flexible circuitry

Kapton polyimide film is also used in electrical applications which include:

  • Wire and cable tapes
  • Formed coil insulation
  • Motor slot liners
  • Magnet wire insulation
  • Transformer and capacitor insulation

Types of Kapton film

Kapton Type HN is an all-polyimide film. It functions at temperatures as low as –269°C (– 452°F) and as high as 400°C (752°F). It can be laminated, metalized, punched, formed, and coated with adhesive.

Film sizes available include:
7.5 μm (0.3 mil)
12.5 μm (0.5 mil)
19 μm (0.75 mil)
25 μm (1 mil)
50 μm (2 mil)
75 μm (3 mil)
125 μm (5 mil)

Kapton Type VN is an all-polyimide film that includes all of the properties of HN. However, it also provides dimensional stability.

Film sizes available include
12.5 μm (0.5 mil)
19 μm (0.75 mil)
25 μm (1 mil)
50 μm (2 mil)
75 μm (3 mil)
125 μm (5 mil)

Kapton Type FN is technically the HN film, but it has been coated on one or both sides with Teflon® FEP fluoropolymer resin. This resin can seal against heat, and it provides a moisture barrier while enhancing chemical resistance. It is available in numerous combinations of polyimide and Teflon® FEP thicknesses.

In addition to these film types, other standard and specialty film types can be ordered.

Safety and application

Kapton fasteners are fairly easy and safe to use. When soldering, Kapton film rarely produces off-gasses that are hazardous. Welding arcs can destroy Kapton film, so it’s best to remove it before welding begins, or to apply it after all welding is finished. If the film cannot be removed, or if it’s being applied in high temperature situations, make sure there is plenty of ventilation.
Basic incineration techniques can be used on the film, but it is recommended that scrap film be disposed of in the landfill, since it is so difficult to burn.

The film isn’t likely to exacerbate a fire, but care should be taken to discharge static electricity, as it can build many thousands of volts, depending on the application and situation.

Summary

Every application is a little different. Although Kapton polyimide film fasteners have a lot to offer in the way of heat and chemical resistance, they aren’t ideal in every situation. If you’d like to learn more about everything that Kapton fasteners have to offer, or to learn more about whether they’re right for your application, contact us. We’re always happy to answer your questions.

Sources:

* http://www.dupont.com/content/dam/dupont/products-and-services/membranes-and-films/polyimde-films/documents/DEC-Kapton-general-specs.pdf
* http://www.dupont.com/products-and-services/membranes-films/polyimide-films/brands/kapton-polyimide-film.html