Adhesive needed to adhese polycarb to Al

We are working on an electronics display unit that will require a lens to cover the display. The only way we can see at this point is to machine a bevel into the case and set a lens down into it. We would apply glue before setting in place.

This will be an out door devise and subject to all sorts of pressure washing, thermal deltas, vibration, etc. We are envisioning something similar to windshield adhesive but it needs to be clear. There is also concern of adhesion to the polycarbonate. Well, actually there is a sun shield film that is adhesed to the lens material so the glue would stick to this film.

We only need a small amount and would apply with a paint brush. Anything other than clear would be a problem. We are not bound to polycarb but it does meet our impact requirement and is durable. Acrylic might also work if it is proved to be better in the sun.


So - requirement

Adhese polycarb or similar plastics to Aluminum

Very high bond strength - (never come off kind of strong)

clear in color

Will allow a small amount of thermal expansion due to expansive properties of the 2 materials.


Does this sound doable?

It's done often in aerospace. Polycarbonate is a low surface energy material and needs processing to bond as you require. A vendor you might contact is NuSil Technologies, they are experts with this sort of problem.

I suggest making the opening square, not bevel, and making a very precise lens to inlay the opening.

Place the workpiece good side down, on a smooth flat surface, and peen the aluminum to grip the lens. Use a centerpunch as your peening tool, don't get carried away with force. I suggest a punch mark every 1/16 inch or so, around the lens.

Trust me, it works. And it looks really nice, if you can keep the lens flush.

Now that you have mechanical grip, you can come back and apply a thin line of solvent cement to run into the joint.

SW, when I said bevel, I should have said inset or relief. That is exactly what we planned to do but Mechanical bonding is out on this one. Asthetics kind of dictate what we can do here. We will inset the lens to be flush with the main housing surface.

Dave, when you say "processed", do you mean "mixed"? ie, an epoxy type product? We are really trying to stick with an easy to work with product if at all possible. They wont see 2000psi of water but 100psi possibly but not at close range. Ie, if you are dumb enough to get that close with a power washer, we can't be liable for that. That being said, we are trying to protect against it. The glue will also be subject to UV incase that is an issue.

viper said:

SW, when I said bevel, I should have said inset or relief. That is exactly what we planned to do but Mechanical bonding is out on this one. Asthetics kind of dictate what we can do here. We will inset the lens to be flush with the main housing surface.

Dave, when you say "processed", do you mean "mixed"? ie, an epoxy type product? We are really trying to stick with an easy to work with product if at all possible. They wont see 2000psi of water but 100psi possibly but not at close range. Ie, if you are dumb enough to get that close with a power washer, we can't be liable for that. That being said, we are trying to protect against it. The glue will also be subject to UV incase that is an issue.

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No, by "processed" he means treating the lens for bonding, either flame or corona treatment come to mind, not that I know very much about either, only that it is often required to get ink markings to stick to PC.

How about installing the lenses from the back side of the part? Machine the holes with a slight step to keep the lenses slightly recessed, then groove the holes for a retaining ring? Strong (can be as strong as the lens material) permanent, and if it also needs to be waterproof, set the lenses with silicone sealant.

Dennis

You did not provide the size of the lens but a thick piece of acrylic would probably work fairly well for impact resistance. Acrylic can be somewhat brittle but is much more scratch resistant than polycarb (although the latter has high impact qualities). In addition, PC typically needs a UV inhibitor or it will yellow.

I can't tell you the exact grade that will fit this application but both Loc-tite and Henkel Adhesives have broad lines of one and two part glues - I'm sure they have something to fit the bill. The modern two part epoxies are applied with a small dual cylinder "caulk-gun" that has a mixing nozzle so are very easy to use.

I once worked for a company that bonded bulletproof 15/16" glass laminate to aluminum for bank teller windows and we used a two part Henkel adhesive worked great in the application (it was a milky color when applied and dried clear). That sandwich was made up of acrylic, polycarb and glass to provide clarity and protection.

We are very open to other lens material options. PC is just an easy reach. A thick enough arcylic will do great. Lens is only 1x2".

TO answer Modelman's question, the lens cannot me installed from the back. We originally had it designed that way but was creating too many other headaches. Face mounting is the direction we need to go.

Majority of time Aluminum requires more adhesion prep than acrylic. Aluminum is either Pasa-gel 105 cleaned and then treated with BR-127 adhesion promoter, or "Sol-Gel" treated for adhesion promotion. Glass, or acrylics is either chemically etched or scuff sanded then clean with MIBK then dry wiped with rumple cloth before being bonded. Adhesive used in aerospace is usually an two part epoxy. Most times a Hysol E/A 956 type that is then vacuum bagged to remove any exotherm.

We are currently working with 3M and Loc-Tite to ID target adhesives for this application.

Another question I had was common gasses used for dry air fill. We do not have a stringent requirement on this but it would be a good measure to help prevent against condensate. We discussed simply using a gas that has enough mass to simply flow down into the instrument cavity and simply lay there while we add the lens. We would not be able to run a gas purge system in this like what is done in windows.

Loctite speedbonder works well with plastics and aluminum. McMaster-Carr

And many marine binoculars are filled with nitrogen. Don't know if the Loctite Speedbonder is the appropriate adhesive to make a tight seal. The binoculars probably use O-rings.

if the inset or relief is wide enough why not just use one of 3M's killer transfer tapes? shouldn't be a problem to find a vendor that can make the lens with the glue area nicely printed and the tape precut and applied. you just peel and stick, no dicking around. 1/4" around the perimeter should be plenty.