Foam adhesives, chemical off-gassing with long-term microphone storage

[klem]

Surprised this hasn’t been specifically addressed as a topic, but I’ve searched and searched… I’ve been looking for cases for microphone systems (e.g., including PSU, shock mount etc.). I’m using a lot of Pelican cases or equivalents with ‘pick and pluck’ layers of foam. Most cases have multiple layers of this foam, and will be far less fragile if, once cut into their final shapes, are bonded both to each other and to the outer case. However, if I had to choose between just bonding the layers of foam together or bonding the outer layers to the case, I’d definitely prioritize bonding the foam layers together.

I am concerned, of course, about any chemical reactions between the foams, case, and any adhesive that could cause damage to the capsule. I am no chemist, but I bet someone one here is. Can anyone recommend a glue, tape, spray etc. adhesive that is known to be compatible in long term (gaseous) contact with mic capsules?

Pelican has a tech bulletin for welding parts to its outer case / shell made of polypropylene (PP), but no such bulletin for their Pick N Pluck™ foam, which is described as an “ester” foam and polyurethane based.

I called Pelican, and a CSR stated they can’t give an official endorsement of a product or compatible chemical, but have heard from many users that 3M Super 77 works well for bonding the foam to itself and the case, and seems to be recommended on lots of other forums, along with Foam Fast 74. I’ve linked the SDSs for the 3M products. Note both of these are the low VOC version of the product, which I ASSume has less chance of creating compounds / gases that adversely affect capsules.

Are either of these products (see SDS sheets) safe for long term coexistence with foam and capsules?
3M Super 77 SDS

3M Foam Fast 74 SDS

A couple of semi-related threads:
https://groupdiy.com/threads/microphone-cases.58354/
https://groupdiy.com/threads/this-is-why-you-line-you-mic-boxes-with-silk.43042/

Appreciate any insight or links to overlooked threads.

 

[klem]

I know there are people here that understand the chemical properties better than I do, and there are surely people that have experimented with adhesives for layers of polyurethane foam. Can anyone share any experiences or insights, including any disaster stories of ruined capsules in storage cases?

I'm starting to think it's better to use a liquid adhesive to avoid the additional chemical ingredients that are in aerosolized / spray adhesives. But that's mainly just an effort to minimize the number of independent variables for any potentially chemical reactions. I've damaged a capsule with solder fumes before I knew better, I don't want to create similar outcomes due to building storage cases with the wrong adhesives!

Gorilla glue?

 

[sahib]

Part of my business used to be in architectural, engineering and marine modelmaking. So we have used every conceivable type of glue you can think off. This is probably why I never needed to touch drugs.

For sticking polyurethane together or to a case any contact adhesive will do . On this application key is to use it in small strips rather than slapping it to the entire surface. In fact even in reasonable size dots. Leave it for a couple of days to dry and de-gass completely.

If the case is made of timber you can also use wood glue (Gorilla Glue is a good make). It will take a couple of days to completely dry but it is safe.

Or hot glue. Instant.

Or Industrial double sided tape.

 

[klem]

much obliged.
to be clear, i'm not as concerned about the performance of the adhesive, more of any chemical reactions / off-gassing (after it stabilizes a week or so out of the case) that could slowly build up and causes corrosion or damage otherwise to the microphone capsules. and i trust that's what you mean by saying wood glues or gorilla glue is 'safe'?

as for drugs, understood. how i wish i worked outside or some proper ventilation when i built model cars with various 'Testors' glues and paints as a child...

 

[sahib]

Even in large quantity it will eventually de-gass. It is a matter of time. Give it a weak if you have the time. But as I mentioned before for this type of application all you need to do is to apply in very small quantities.

 

[k brown]

Safest probably neutral pH PVA glue, like:

https://www.amazon.com/Lineco-Adhesive-Acid-Free-Flexible-Projects/dp/B001I6FEHE?th=1

As long as you wait long enough for all the water to evap out before storing mics.