Re: Resistance of epoxies to ozone


> Dear all,
>
> We've got a wide range of 2-component epoxy coatings and I was recently
> asked which one is best suitable against ozone. The application is on inox
> substrate, which mustn't be of high quality as it already corrodes under > ozone beam.
> Does someone has an idea of which chemical family to use ?
> Phenol-novolaques, bisphenol A resins or epoxy-vinylester (Derakane
> products) ? And what about the hardener ? We use to formulate our own
> adducts or hardeners and we've got a wide range of raw materials to help us
> get through this.
> Any tip ?
Most epoxies are based on diglycidylated aromatic nuclei. Ozone
cleaves benzene rings as well as all other unsaturated systems. You
are eaten if you are limited to common organics.
One hope is to load the epoxy with inorganic filler to blunt ozone's
attack by physical blockage. Finely dispersed oxides are a good idea
(silica or alumina; fumed silica will tremendously thicken the mix at
low loadings). Metallic aluminum dust or paint flake would be even
more interesting, as would waste silicon dust from semiconductor
sawing. Ozone attack on the filler would give alumina or silica of
greater volume than the elements, swelling the attacked surface into a
protective cap as the organic degraded. That might be clever.
Have you tried something cheap and easy, like dipping a layer of
paraffin wax to block the ozone? Straight paraffin shrinks too much
when it solidfies, but it is easy to compound to render it flexible.
Just be careful that all components are fully saturated aliphatics.
Reply to
Uncle Al
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Thank you Al,
In fact, it was a question a customer asked me on an epoxy that has long been released. I don't intend to reformulate it, I only wanted to have an idea of its behaviour in such conditions. At first, I thought that the aromatic ring could be resistant enough, ... but it seems not. If, one day, we want to create more resistant epoxies, I would probably try your second solutions, which seems to me a better and easier way. Anyway, thank you very much for your time.
Regards.
Nicolas DELFAU Peintures SOB FRANCE snipped-for-privacy@wanadoo.fr
Reply to
Nicolas DELFAU

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