Water sealing problem with epoxy and PVC

[DogPAnt]

I hope I'm in the appropriate forum.

I'm potting some electronics in epoxy (BEEP 6112).
I'm having water ingress problems and suspect it is due to a weak bond to the PVC sheathed wires going into the potted part.
I think water is leaking in along the interface between the PVC sheath and the epoxy.
The water works its way in over a few days.


Is there a simple way to improve this bond?

I've been trying to find a readily available compound to work as an intermediary that bonds well to epoxy AND PVC. Hopefully something that I can simply paint onto the wire sheath.

I'm only looking at up to say 10m depths.

Any ideas?

Thanks

 

[btrueblood]

You might be right. But you might be getting leakage down the wire, between insulation and wire strand(s). We had similar issues, and found that one way to really waterproof a populated circuit board is to send it out for parylene coating. Costs a few bucks, but is wildly better at sealing the electronics from water intrusion than anything else (multi-seal paths, various sealers and coatings).

 

[TugboatEng]

Getting a strong bond between PVC and epoxy is going to be a challenge. There are acrylic epoxies that are better suited for bonding low surface energy plastics.

https://www.permabond.com/materials_bonded/how-to-bond-pvc/

Is this individual wires or a cable? Are you forced to use PVC? Wire and cable are both available with rubber insulation. Polyurethane, neoprene, and EPDM rubber will be much easier to bond to.

I would also suggest using a more flexible potting compound.

 

[IRstuff]

There are reasons why connectors are often preferred at interfaces. Better sealing with the potting material, and no strain relief issues at the potting compound/wire interface.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[3DDave]

I second connectors/feed-thru features.

 

[DogPAnt]

Blueblood - thanks. With these units I'm certain its not following the copper down as the sheath is new. I've had that happen in the past with damaged cables though.

Unfortunately Parylene coating is not going to happen with this one.


TugboatEng - thanks. We are stuck with the cable. The epoxy we are using is also used in another product successfully. It's just this one design that's causing grief at the moment. Thanks for the link.


IRStuff / 3DDave - yes a connector would be a nice solution but this is a low cost product which rules that out unfortunately.



I'm looking at the Sika 215 Primer, the data sheet suggests it may work ok as an intermediary between epoxy and PVC.