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Where to find such material?
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Old 17th July 2017, 05:05 PM   #1
gentlevoice is offline gentlevoice  Denmark
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Where to find such material?
Default Where to find such material?

Hi All,

I have for some time now been looking for a low dielectric constant (<= 2.2), low diffraction factor (as low as possible), frequency-linear material that has a viscosity similar to the silicone that is used e.g. for lining the tiles in a bedroom. And which also solidifies (sets almost as hard as teflon) e.g. in 24 hours (but the solidifying time is not that important).

I will be using it to seal some cables and a source of inspiration could e.g. be TARA Labs' "aerospace polyethylene", however, I don't know where to find such material - and also not in small amounts ...

Any of you know where to buy such material?

Cheers,

Jesper
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Last edited by gentlevoice; 17th July 2017 at 05:22 PM.
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Old 17th July 2017, 11:41 PM   #2
phase is offline phase  United States
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I would say 3m DP820, but I'm not sure if the electrical properties are what you want...
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Old 17th July 2017, 11:56 PM   #3
Monte McGuire is offline Monte McGuire
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Where to find such material?
Silicones are very very good, and there are a few that are designed for electronics that have relatively low K and extremely low dissipation factor. However, they are generally difficult to purchase in small quantities.

I looked around a year or two ago, and the best I could come up with was this two part silicone from Momentive, sold to folks who maintain aircraft: Momentive RTV615 Clear Silicone Rubber Compound - A/B Kit - 1 lb Kit at SkyGeek.com

It has a very low dissipation factor (0.0006 IIRC), its dielectric constant is 2.7, and since it's a two part (resin and catalyst) system, you can use it for 'deep sections', since it does not need atmospheric moisture to cure, as do the single part silicones.

It's pricey, but hey, good stuff is sometimes not cheap! :-) I've never used these products, but I was planning to do so somewhat soon for an electronics potting application, and the Momentive 615P seemed very nice, even if it wasn't the absolute best. Here's the data sheet: https://www.momentive.com/en-US/products/tds/RTV615/

The Skygeek.com site has a number of other silicones and sealants for various uses. Check what's available and go to the Dow or Momentive sites to see the full specs, so you can see which makes the most sense for your application. Best of luck!
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Old 18th July 2017, 12:16 AM   #4
sq225917 is offline sq225917  United Kingdom
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Send a message via MSN to sq225917 Where to find such material?
Sugru?
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Old 18th July 2017, 06:43 AM   #5
gentlevoice is offline gentlevoice  Denmark
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Where to find such material?
Hi All,

- & thanks for your suggestions & ideas. I've looked into the various products you suggest - and it looks interesting - but my "feel" is that I should stay with my specifications for DK, i.e. lower than ~2.2. When TARA Labs (likely) can find such a material then it's out there and I just would like to find something similar (have no need to directly copy them).

@sq225917: Sugru also looks interesting but their datasheet doesn't specify neither the Dk or DF - so I would guess that it's not something that is special for this compound.

Thanks again for considering and replying ;-)

Jesper
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Old 18th July 2017, 02:46 PM   #6
Monte McGuire is offline Monte McGuire
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Where to find such material?
I found a list of dielectric constants for plastics, and it seems that PTFE is one of the few with K = 2.2. However, low density polyethylene might be able to be melted and cast, has only slightly higher dissipation, and lower dissipation than silicones.

Another trick people use is to foam a dielectric so that there's a predictable amount of air in the dielectric. That could get you below K = 2.2, and a lower K is usually never bad. That could be mechanically tough to do at home though.

Good luck on your search!
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Old 19th July 2017, 07:39 AM   #7
gentlevoice is offline gentlevoice  Denmark
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Where to find such material?
Hi Monte,

Thanks again for considering my question & search ...

Quote:
However, low density polyethylene might be able to be melted and cast, has only slightly higher dissipation, and lower dissipation than silicones.
... Actually, I think that glue guns in many cases may use PE so that might be a feasible way to go. I would need to find out about the electrical specifications for the specific glues - which may not be that simple - but possibly it could be an option.

Regarding air-filled material I've actually considered this myself - also as a microsphere filled substance. The "only issue" is that the viscous material itself - which will be in immediate contact with the conductor in question - will not be air-filled (I hope you can visualize this). So I'm less inclined to go that way although it could be interesting.

Anyway, I just made an internet search and it seems that both PE and PP hot melts are available. Possibly even an PTFE-like material! So I think I have enough information now to progress ...

Cheers & thanks ;-)

Jesper
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