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Old 16th June 2007, 07:00 PM   #1
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Default Thermal Conductivity of Kapton Compared To Aluminum?

What is the Thermal Conductivity of Kapton compared to aluminum?

I have seen thermal conductivity charts where aluminum is about 250, but Kapton is not listed.

I have looked up Kapton and gives a number, 4.3 or thereabouts, but I am not sure if the units used are exactly the same as those used to measure aluminum.

For instance, in some loudspeaker specs, diaphragm mass is given in grams. In other specs, in kilograms. In the same way, I don't know if the specs I get for Kapton are measured in the same units as those which produced 250 for aluminum.

Does anyone know?


PS: While we are at it, are there any other common plastics with a thermal conductivity nearly equal to or perhaps greater than Kapton?
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Old 17th June 2007, 04:32 AM   #2
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Kapton 0.12 to 0.37 W/m_K - variation based upon percentage of absorbed water Dupont Datasheet

Aluminum 240 W/m_K Materials Handbook
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Old 17th June 2007, 08:43 AM   #3
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Hi,

Quote:
While we are at it, are there any other common plastics with a thermal conductivity nearly equal to or perhaps greater than Kapton?
AFAIK, Kapton has no significant thermal conductivity, but a good thermal stability.

Cheers.
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Old 19th June 2007, 02:22 AM   #4
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Hmmm, I was under the impression that Kapton was used in voice coils because it had good thermal conductivity for a plastic. Guess not, although it does seem to be more thermally conductive than many other plastics.

Are there any plastics which could loosely be called thermal conductors instead of insulators? I realize it is unlikely any plastic would have a thermal conductivity to rival metal, but is there a plastic with a rating of 4 or so?
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Old 19th June 2007, 11:28 AM   #5
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I'd wonder why. Where should the voice coil former conduct the heat to - there's no sink.

Conductivity would stress the glue joints between coil former and cone, but not spread the heat farther away.

AFAIK, the heat is ventilated (into the air gap) and radiated (and sunk into the pole plate). That's why ventings and heat spreaders on magnets and baskets are commonly found on professional speakers, particularly on neodymium drivers...

Cheers,
Sebastian.

PS: I guess you need the plastic heat conductivity for something other than voice coils. I'm afraid I can't answer your original question...
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Old 19th June 2007, 12:00 PM   #6
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I figured that if the voice coil former was thermally conductive, it would act like a heat sink and conduct the heat into the air gap. It might make only a small difference, but every little bit helps, I thought.

But you are correct, I did have a different application in mind.

As it turned out, there is at least one manufacturer of thermally conductive plastics, (both electrically conductive and non electrically conductive), with a rating between 1 and 20 W/m_K.

Source

Although what this actual substance is, I don't know.
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Old 19th June 2007, 12:29 PM   #7
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Like sek said, the choice of Kapton (or similar polyimides like Upilex) is because of the thermal stability, unusually high for a plastic. One sacrifices thermal conductivity and specific heat for low mass. Thermally conducting plastics generally are made by loading up a conventional plastic with a thermally conductive filler (like BeO), and are much heavier, not to mention less thermally stable.

edit: The site you linked to lists the thermal conductivities of several materials. The filled polymers have thermal conductivities 10 to 200 times lower than aluminum.
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Old 20th June 2007, 06:23 AM   #8
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The small disadvantage regarding thermal conductivity is well worth having. A lighter voice-coil leads to better efficiency and therefore smaller thermal losses.

Regards

Charles
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