Neoprene or Nitrile... and how to weld/fuse/join either of them

[Jamie Buxton]

Why do you keep talking about rubber? Isn't your problem just to waterproof the magnet? If so, just focus on that. Encapsulate it with something that can be rigid, like epoxy or some other plastic.

[Stan Calow]

Permatex? or maybe that Flex Seal stuff they show on TV? I don't think nitrile will hold up under dishwashing.

[dustin wassner]

when I say rubber I mean the neoprene. The item I am trying to design is two laminated pieces and it needs to be thin and flat and have small flat magnets between it in specific places. If the magnets fall out the item is useless. Waterproofing the magnets is not really the concern, keeping the joint between the two pieces of rubber is so that the magnets don't fall out.

The ideal scenario would be to injection mold a flat thin piece of neoprene with an encapsulated magnet but that just ins't feasible...

I have read of using contact cement with MEK to reactivate the surface of the rubber... this might allow the joint to retain the elasticity/flexibility that the neoprene normally has

hope that all makes sense

[Andrew Joiner]

I have used solvent based contact cement to patch neoprene wet-suits for years. On wet-suits in cold or warm water it lasts a year or more. In your application use 2 coats and test it on a sample in the dishwasher.

[dustin wassner]

thanks, Andrew. Can you suggest a brand name that you have used?

[Grant Wilkinson]

I've had good results on my dive and kayak wetsuits with this

https://www.amazon.com/3M-1300-Neopr...SIN=B0012IYOH4

[Mark Bolton]

3M Scotch Weld would be my choice for Nitrile.

[dustin wassner]

thanks Grant. If you were to try to pull apart a repair on your wetsuit with this, could you eventually work it loose? Does it require a large bead of the adhesive on the repaired spot in order to be strong enough?

[Andrew Joiner]

thanks, Andrew. Can you suggest a brand name that you have used?

Dap 00272 Weldwood

[Dave Anderson NH]

Neoprene and nitrile (Buna-N, NBR) are thermoset materials meaning that once cured they can' be softened or reshaped like thermoplastic materials. Adhesive bonding layers together is a fine interim approach but won't stand up to multiple dishwasher cycles IF there is any flex. Additionally neither material is injection moldable except by liquid injection molding. As an alternative consider using a thermoplastic elastomer (TPE,TPR) such as Kraton or Santoprene. These are readily injection moldable on standard plastic molding machinery.

[dustin wassner]

thanks, Dave that is very informative. I actually really don't care if it is neoprene. I just need something that is as close to gum rubber as possible - doesn't need to be as elastic but needs to be grippy. I was going to order a 1/32" silicone 12"x12" sheet from ebay or find a supplier that could send a sample.

Are Kraton or santoprene going to give at least somewhat similar grippy-ness and elasticity as gum rubber?

DW

[Dave Anderson NH]

Grippiness or coefficient of friction is somewhat a function of surface finish and also the particular polymer. Elasticity is normally expressed as a percentage of elongation to break. Nothing will have the elasticity of pure gum rubber (rubber band material) which is around 400% to break. Silicone (polysiloxane) comes about as close as anything in the lower durometer hardnesses and thin cross sections. Stay way from pure gum and natural rubber since they have poor heat aging characteristics. Silicone will be unaffected by ozone, UV, and has a useful service life beyond 20 years from -75F to + 500F

[dustin wassner]

the issue I have with silicone is that when I called several local mold shops they all said they could not do silicone. Like literally, all of them said no. I was surprised at that. But if nothing else will work then I guess it is worth a shot...

Is silicone a thermoplastic, and if so, is there a solvent I could use to fuse the two pieces together?

thank you.

[Kev Williams]

What about food-grade silicone?

[Dave Anderson NH]

Silicone like all non-thermoplastic rubbers can not be solvent bonded or welded. It can be bonded with a silicone pressure sensitive adhesive. For molding you need to go to a rubber molder who has very different equipment than a plastic molder. Generally the only rubber materials a plastic molder can process are TPE/TPRs. Quantity is key here since the cost of tooling is prohibitive for very small quantities. I might be worthwhile to investigate the TPRs since they an be ultrasonically welded.