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 of. 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.

 

[klem]

Update, I used the Lineco adhesive @k brown linked to above. I used scraps of the 'pick and pluck' polyurethane ester foam to test with various amounts of the glue (after being brought to room temp for 48 hrs post delivery - that's evidently an issue with this product in some of the user reviews. It appears fully dried now, so here are my findings:

I have no way to evaluate any chemical off-gassing, but don't see any degradation of the foam itself, dissolving etc. However, the nature of the foam sheets I'm bonding to one another required a significant amount of glue in a given area. For the sheets that I tried small amounts on, it simply sank into the open spaces in the foam, and the subsequent bond was easily separated, comparable force to saw pulling a mic box out of a snug multi-layer foam cut out. So, the more saturated areas of the samples were the only ones that bonded effectively. Despite the product's claim of maintaining flexibility after curing, in this application, it is marginal at best. You can bend the bonded foam maybe 5-10 degrees, after that, it will snap. Since this is science, or something, I bent one sample to break up the bond and see how it responded. The sheets are still bonded well enough together. The only issue I see is that for glue that has reached the edge (and I imagine in some areas that are fractured in the 'field' of the foam, the glue can chip off with some friction (my finger), and therefore separate. So it's worth keeping an eye on, especially if you don't have any additional covering (from ziplock bag to wooden presentation case).

hope this helps someone. this may be as good as it gets, but i'm open to trying out other adhesives. one note, @sahib , hot glue seems dicey at best, at least without the qualifications of specifying a specific type of glue, and one that is a low temperature melt. when using a glue stick supposed equivalent to Super 77, the temp at 350F IIRC, melted some of the PU. maybe obvious for some, but figured it's worth mentioning for anyone that may take that suggestion without this caveat. thanks again to both of you for weighing in.

 

[k brown]

Would be interesting to compare the Lineco with a less watery form of PVA, like original white Elmer's Glue-All.

I was imagining a 2-step process of 'priming' the surface of the foam with a coat that is allowed to dry, then gluing in place with fresh glue.

There are also even thicker PVA glues sold under various names ( Mod Podge, etc.) in craft stores.

________

This stuff claims to be non-toxic, but I don't what that means regarding off-gassing exactly:

https://www.amazon.com/Beacon-Hold-Foam-Styrofoam-2-Ounce/dp/B000YQDXJ0?th=1

 

[DaveDC]

I’ve been using 3M Super 77 but I give it several days to dry. I figure the outgassing from it is no worse than from the foam itself. I have also had very good results making custom cutouts using layers of foam sheet cut using a DIY hot wire cutter and sheet metal templates. I then glue the layers with Super 77.

 

[klem]

I think for applications like @DaveDC the chemistry is less critical. Yes, for whatever adhesive/glue is used, let it fully cure and then give it another 1-2 weeks minimum. But for a 421 case or similar, there's more air that can enter and leave, whereas a pelican case can only equalize pressure but is more of a chamber. It's that chamber that, when left unopened for a decade or so, I worry about. May sound silly, but life takes turns and I'm best laid plans to do enjoyable endeavors like recording get side-tracked by immediate responsibilities. Regardless, doesn't seem like a bad idea to try to strive to the most inert storage situation to do the least harm.
Anyhow, I appreciate the ongoing discussion. I have a few Elmer's products to also try out on separate prototype projects with semi-rigid fiberglass, among them I ordered this Elmer's E430. Similar experience to the Lineco. Will try the two step process suggested by @k brown next week.

 

[k brown]

FWIW, I've never stored mics in any kind of foam; it's fine for protection during shipping, but my mics never see the stuff again after that.

Between uses my mics live in light canvas door hung shoe storage pockets; similar to: https://www.amazon.com/Fentec-Door-...x=door+hung+shoe+storage,aps,166&sr=8-24&th=1

I transport them to locations in heay cloth / light canvas drawstring banker's bags bought on eBay over the years and/or DIY leather drawstring bags, then into equipment cart drawers.

In nearly 30 years, never had a mic damaged, scratched or had one misbhave due to dust or moisture.

 

[k brown]

Many top pros use this stuff in their cases and swear that it's safe for mics:

https://www.kaizensource.com/

 

[soliloqueen]

i think kaizen is EPE foam? should be mic safe. any closed cell foam that won't deteriorate should be mic safe. Chief among these would be XLPE, EPE, etc.

 

[klem]

Thank you all for the suggestions and info. I'm currently working with kaizen as the base material for a wooden microphone 'presentation' box that will then go into the Pelican case. From what I've read and a few cuts yesterday, it does seem to offer a lot of advantages over the more crumbly PU foam. It also has the advantage of being more physically robust so hopefully smaller amounts of adhesive will be needed to bond multiple sheets together. So, will probably go with kaizen for both mic box and lining of the larger Perlican case that will also have shock mounts, PSUs, cablings in addition to the mic box.

For shock absorption and a bit of base traction of the wood mic boxes in and of themselves (that will also go into the Pelican case storage),

I'm considering putting a thin layer of rubber material (thinking EPDM or neoprene) on the exterior bottom base of the wooden mic case. I realize the chemicals in any pressure sensitive adhesive PSA on the rubber could be of issue as well, for now I'll set aside both this as well as all of the physics related to shock absorption, i.e., durometer, loading / deflection, F, etc. I also realize there's only so much mechanical shock that can be absorbed from a thin sheet of rubber if some jackal (or me, not mutually exclusive) were to drop the wood mic box 3 feet to the floor. But, all that being said...

How (chemically) compatible are EPDM and neoprene and capsules?
EPDM's composition is in the name: ethylene, propylene, and a diene monomer.
Neoprene is made from chloroprene
Sorbothane is made from FU / cost-prohibitive stuff


Long post as is, so putting this slightly smaller font:
A member recently gave me a perspective I hadn't considered re: how offering knowledge here could sort of backfire on them, so here's my attempt at a bit of caution and disclaimer for anyone coming across this thread now or years from now:
Anything mentioned by myself or by anyone contributing to this thread should be taken with a grain of salt. I'm just trying to get some insight as to any chemicals that would negatively affect microphone capsules. By no means should this thread be thought of as an exhaustive list, much less as an endorsement by anyone of what will or will not harm a capsule over years of exposure. No one here can account for things like the purity of chemicals in the many materials that can, and are, used in a DIY build by someone else. Also, everyone posting here is offering up their own insight, and that's very much appreciated for someone like me who was never great at chemistry much less in translating it from theory to practice. But crucially, I won't ever blame a contributor should something happen down the line to my mics that is related to info presented here, and I hope no one else would think that as a reasonable response as well. When people become reticent to offer input out of concern for how the info may be used*, we all lose out. I'm grateful for the people contributing here, and the knowledge gained from their contributions. The last thing I want to do is discourage this.

*This is very much separate from the issue of people combing threads of this community with the primary intent to rip off other members' R&D for their own commercial gain. I've nothing but contempt for such actions.

 

[k brown]

For the bottom cushion how about good ol' wool felt?

For bonding layers of Kazen, my first thought would be silicone adhesive; once all the acetic acid has evaporated, it doesn't off-gas and is quite permanent; never becomes brittle.

 

[ccaudle]

once all the acetic acid has evaporated

I heard mention of an electronics compatible silicone adhesive formulation which does not offgas so much acetic acid (to prevent corrosion of nearby traces and wiring when e.g. gluing down a large capacitor).
Is anyone familiar with that who might have a link to an example product?

 

[GeorgeToledo]

If glue hasn’t fully outgassed, you would almost definitely smell it after having the case closed for a bit and then reopening it. That’s my ultra scientific method for detecting if glue would still be curing.

 

[klem]

I heard mention of an electronics compatible silicone adhesive formulation which does not offgas so much acetic acid (to prevent corrosion of nearby traces and wiring when e.g. gluing down a large capacitor).
Is anyone familiar with that who might have a link to an example product?

The chip-quik line? (I've yet to look up SDS sheets, not seeing them linked on the amazon pages.)

 

[Brian Roth]

IIRC, GE makes (made?) silicon products that don't stink up the room for days <g> which are intended for electronic applications.

Bri

 

[ccaudle]

The chip-quik line? (I've yet to look up SDS sheets, not seeing them linked on the amazon pages.)

I did not realize that chip-quik made some, but yes, I think that exactly what I was referring to, the description says it is for corrosion sensitive applications.