Is there a chemist in the house? Epoxy resin question.

[moribundman]

Any idea what substance I could add to make a clear epoxy resin (more) UV-resistant. This is a fairly low-viscosity bisphenol-A resin and polyamine hardener.

[ April 20, 2005, 08:10 PM: Message edited by: moribundman ]

 

[labman]

Good luck. Ever wonder why nobody ever used epoxy top coats on cars? The UV kills the gloss of even pigmented epoxies. It has been 30 years since I looked at that problem. Maybe they have something now.

 

[moribundman]

Yes, I have noticed. I was simply hoping that the solution was too expensive for general use.

 

[hone eagle]

not a chemist but have worked on boats a few years and the west system is a good resourse.try the gougeon brothers in bay city mi,but as far as i remember they say that epoxy MUST always be covered.However they did many bright finished wood boats built of epoxy,so the epoxy was probibly covered in a clear spar varnish.so if you can find a clear hard coating that has uv inhibitors-they do exist for wood finishes but they are not very hard-you can try your project.

 

[chas3]

have you considered a marine product?

 

[moribundman]

I've looked all products, including the ones for marine use. They all yellow. There are polyurethane resins that don't yellow (they darken a little, but that's not a problem), but they don't adhere well to p/u resin.


Other possibility: what can I use to to coat polyurethane plastic? The finish needs to be clear, water and solvent resistent, fairly scratch-resistant and hard, but not brittle. Epoxy resin works, but it yellows over time.

 

[jthorner]

quote:

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what can I use to to coat polyurethane plastic

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Maybe a polyurethane varnish? It would be worth experimenting with some exterior grade polyurethane varnishes, normally used to put a clear finish on wood. There are both oil based and water based versions sold. I would try an oil base one like Miniwax Helmsman.

John

 

[moribundman]

I tried a few p/u varnishes, none worked well enough. All of them tended to bead and if they didn't bead the layer of varnish would be pretty thin and also too soft. p/u varnish has worked well on wood for me, though. The main problem is that polyurethane resin has a very low surface energy. Hence nothing wants to stick to it, even if the surface has some "tooth." So far epoxy resin seems to adhere best.

 

[JohnBrowning]

I was under the impression that Remington and Browning were both useing an epoxy coating on all of their wood stocks. They are chemical and weather resistant and do not yellow. They do not look or fell like a poly finish at all. THey are ultra thin!

I was also thinking that the current floor coating systems for garages are also epoxy based and you would think that UV resistance would have to be built in. I have not seen any of them in a clear finish though. Have you tried Dupont Tech. *** .?

 

[labman]

Urethanes are very hard to get coatings to stick. Perhaps the clear coat for bumpers and other automotive urethane components would work. It may just stick to the base coat, and not the urethane itself. You could try Sherwin Williams moisture curing urethane, I think Rexthane. It should stick to a scuff sanded urethane. Problem is, it only comes in a square gallon can for about $30. Do not confuse it with the Minwax crap. Ask what you use to thin it or clean up. It the guy says paint thinner, it is not what you want. I put it on my hard wood floor in 1998. Still looks good after 7 years of Lab toe nails, puppy accidents, etc.

 

[moribundman]

labman, I'll check out Rexthane. The price doesn't deter me. I'm using resins that can easily cost over $20 for a pint.