TPU and PBT bonding in overmold 4

[Chitahua]

I've got a project that will be underwater. it needs a hard shell for rigidity (PBT). and a low pressure material (TPU?) to seal/enclose some electronics. we designed it such that, even if there is separation between plastics, the circuits are -almost- completely enclosed within the TPU but I'd like to know if another low pressure material is better for bonding with PBT.
this is going into a harsh chemical environment and we've had success with PBT so I'd like to stick with that as my outer shell.

 

[Pud]

I would surmise a guess that a polyester elastomer might be a better bet for bonding onto another polyester. (e.g. Hytrel, Arnitel, and others)

H

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Harry is spot on.

The elastomer/hard resin pairs that are compatible are:-

PET or PBT and polyester block copolymers like Hytrel and Arnitel.
Nylon and polyurethane.
PP and Santoprene.

Regards
Pat
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[Pud]

Cheers Pat - it really was a guess! (sorta educated one though!)

Don't forget the obvious that polyesters are aggressively hygroscopic and the part to be overmoulded needs to be "polyester dry".

H

http://www.tynevalleyplastics.co.uk

 

[patprimmer]

Harry

You mould the polyester over the Hytrel as the higher melting point resin goes in last.

And of course the polyester and the Hytrel both need to be very well dried with very good dryers.

Regards
Pat
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[Chitahua]

Thanks for the inputs. particularly the hard / elastomeric compatibility. I'll try to marry those couples whenever I can.
I found a claim on a website that plasma treated PTU will have excellent bond with PBT. It's an obvious sales pitch, so I'm not sure how much to believe it.

 

[btrueblood]

If it's truly an underwater part and needs to provide a moisture barrier over a long time period, I'd lean towards PP and Santoprene. But listen to Pud and Pat on the materials combos.

 

[patprimmer]

btrue.

Good point.

Water permeability can be a problem with submerged parts made of nylon or polyurethane or even Hytrel types, depending on the make up of the elastomer block in the particular grade.

Regards
Pat
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[btrueblood]

Pat,

Musta learned it here.