[BangHaus]

Hi,

I am working on a product that uses a backing made from clear semi-rigid plastic.  I can use either PET or PVC.  The product will have some electronics on the plastic backing, and I need a clear, flexible sealant to cover the electronics to waterproof the whole thing.

I've tried a rubberized coating - Rustoleum LeakSeal Clear - but it is perhaps too flexible.  If you begin peeling it, you can easily peel it all off.
I've also tried an oil based polyurethane intended for outdoor use.  Either that needs more time to cure, or it will not be durable enough.  I can scrape it off with a fingernail.

Ideally, I'd like to find something that is flexible enough to bend with the backing, can be applied with a paint sprayer, is durable, can handle temperatures down to -40F, and is not too expensive.

I'm also going to try acrylic enamel.  Don't know if that will be flexible enough.

Thanks to anyone who can help.

[billnotgatez]

Can we assume something like
Loctite Clear Silicone Waterproof Sealant
will not work?

[Enthalpy]

Up to now I believe PVC is always opaque. Or is it very thin? Or is it polyvinyl acetate rather?

A hot glue gun would be my very first choice
https://en.wikipedia.org/wiki/Hot-melt_adhesive
Very strong joint on PET and PVC, waterproof and reliable, rather clear if not too thick. As applied with a gun, a nice result depends on the operator. Maybe a machine can apply it better.

I don't like silicone glues on polymers. They adhere naturally on ceramics, not on polymers nor metals, where only a primer gives some success chances. Too unreliable in my experience.

Dissolving PVC makes excellent glues , and I believe PET too. Alas, the solvents can be nasty, like vinyl monomer for PVC. Finding an acceptable solvent would lead to success. Check the "material compatibility list" for PVC and PET, where you see a strongly incompatible solvent which isn't too harmful, it's a candidate. If your material is polyvinyl acetate instead, this gets easier.

So-called polyvinyl acetate glues are candidates on PVC
https://en.wikipedia.org/wiki/Polyvinyl_acetate

In gluing, the main condition of success is the preparation of the surfaces, mechanically and chemically.

Consider welding. Far better than glueing where possible. Hot glue guns exist specifically for PVC, with a feed of PVC wire. Other apparatus exists, with hot air, light, RF power, vibrations, and so on.