What is thermoplastic coating?

Any ideas on what I could use for a hardwearing, uv resistant, clear coating for plastic?

• Hi, Im currently working on a project that uses fused plastic bags ironed to plywood boxes. Weve got the bags to fuse to the box with an iron but need a clear protective coating to encapsulate it all so we can still see the layered plastic bags underneath. Its going to be kept outdoors and so will need to be weather and uv resistant. Weve tried plastikote clear gloss spray which peeled off. Weve also tried a clear satin wood varnish which didnt bond to the plastic well. Can anyone recommend a coating that would work? weve been thinking of PVA glue but not sure where to find a uv resistant tub of the stuff many thanks!

• Answer:

  PVA glue wouldn't be highly water-resistant though it would be flexible which is good. So it would be more susceptible to later cloudiness and even scratching. You could try one of the better brands of polyurethane like Varathane, which is UV resistant and also is better at sinking down into surfaces than most other brands of polyurethane. It comes in indoor and outdoor versions, and also in gloss, satin, or matte finishes. The outdoor version will be a bit more resistant to water (soaking, etc), but since it's petroleum-solvent based it could perhaps eat into other plastics and is a hassle to use and clean up. The indoor version is pretty water-resistant though. Polyurethanes aren't flexible though, so you'd want to apply a number of coats perhaps. None of those may really "bond with" the plastics, but you'd be creating a mechanical hold when then finishes seeped all in and around them and hopefully also on the rest of the box. How much stress would these receive? You could also use a (2-part) epoxy resin (sometimes called bartop resin, Envirotex Lite Pour On is one common brand) which will give a thicker coat in one go. Resins could react with the plastic too though?, so you could use a coat of thinned PVA (or a "decoupage medium" like ModPodge, etc) first. Also don't know if any epoxy resins are UV resistant, but you could always add a coat of Varathane on top if not. .