Yet another OT- hygroscopic coatings

[darryl]

I've seen some of those videos showing how a coating repels water so strongly that virtually no liquid will remain on it. I have one of the kits but haven't used it yet. I'm wondering how well it would work as a release agent for casting resins- anybody have any experience with that? Seems to me it would be a sort of semi-permanent anti-stick surface. Either the unhardened but catalyzed resin would react with it to form the toughest glue known to man, or it would work as slick as snot as a mold release.

Lately I've been experimenting with snow slider material as a mold material. I heat-form it and cast resin into it, and it then releases reasonably well with no damage to either surface. But heat forming it is an imperfect science, at least in my home shop, and I want something that works slicker than that. I can spin-cast the shapes I need using finishing epoxy resin, which leaves the desired 'optically smooth' surface, but still requires a mold release agent to be applied. Regular mold release works ok but takes some finesse to get a really smooth and streak-free surface out of it. I want to skip this step if I can.

I know I'll end up doing the experiment with the hygroscopic coating (NeverWet I think is the name for the stuff I have). Just wondering if anybody has tried this-

[mattthegamer463]

I don't know much about it but I think it's basically a microscopic rough coating, which due to the surface tension of various liquids (mainly water) it prevents the water from getting traction on the surface. Essentially, air is trapped in the small valleys on the surface of the coating. The coating is also a moisture barrier to prevent absorption.

Putting resin in there may or may not allow the effect to work the same. It may not produce a fine finish like you want. I think you will need to try it on some level to know for sure.

[Optics Curmudgeon]

Hydrophobic,not hydroscopic

[darryl]

Hydrophobic, yes. For some reason I had hygroscopic on my brain. That's the exact opposite I think-

I just read the instructions on the box- it says dries to a light haze, which isn't what I want. But I'm about to try it on some glass, so we'll see.

The other idea which could have some usefulness is that epoxy and polyester resins apparently don't play well together. Epoxy will stick to cured polyester, but polyester may not stick well to epoxy. Yesterdays experiment had the epoxy mold coated with release agent, and the resulting part was ejected using pressure through a small hole in the very bottom of the mold. I actually threaded the hole and used a bolt to force the part out of the mold. I filled the hole with water and screwed the bolt in, but the water just ejected out around the bolt instead of forcing into the mold. Then I tried dropping several tiny shards of wax into the hole and compressing that with the bolt. That worked well enough, so now I think I'll melt a plug of wax into the hole before applying the release agent and casting the resin. At release time it should pop the part without damaging the surface.

Epoxy resin works so much better than polyester resin for self-levelling and curing in that perfectly smooth mirror-like surface when exposed to air, so one of my next experiments will be to see if a layer of epoxy over the cured polyester part will make invisible the slight rippling on the top of the polyester part. Heading to the kitchen to mix that up now.

[darryl]

Well, the coating works, but it's sure not very durable. I tried polishing up a section of it and it just destroyed it. Then the base coat peeled up off the glass like nothing. I did everything by the instructions.

It's definitely way too hazy to give me a good result, so I'm back to using regular mold release.

It will be a couple days before I can report on the epoxy over polyester experiment.

[Joe Rogers]

I can’t think of anything applied to glass as a coating that woul be durable without etching the glass.
Joe

[Glug]

You mentioned streaks in your mold release. Have you tried spraying it?
What MR have you tried?

[darryl]

I'm using something called Fiberlease, which is PVA. I have tried spraying it in the past, but not with the best of results. Maybe time to explore that again. My best result lately has been to brush it on, then pour a little extra in the mold, then roll that around and invert the mold so it drips out.

Back to the hydrophobic coating, just for laughs- I poured a couple molds last night and the excess resin I poured onto the coating to see what it would do. The resin beaded up but didn't want to roll off like water does. It ended up spreading out like it usually would, though it took much longer to do that. When I peeled it this morning, part of the coating stayed behind and part of it stayed with the layer of resin. The resin had feathered out probably even more so than it would have done on any regular surface. I thought that was interesting- almost like the resin was defying the hydrophobic surface.

In another experiment, pouring a layer of epoxy over a cured clear polyester pour- this turned out really well. The surface leveled out as you'd expect and left a beautifully smooth surface that I could not get from the casting resin itself. Since these parts are going to be lenses in front of leds I wanted the best result I could get. The epoxy filled in the surface imperfections in the poly resin and there are no optical aberrations that I can see. Better than expected here. The epoxy is not perfectly clear whereas the casting resin is- but in a thin layer you can't really tell. The resulting lens looks like a well-made glass lens, just as clear and without distortions. Totally happy with this result.

My last experiment involved using 5 min epoxy to secure one of these lenses into an aluminum ring. This would be a cast resin lens without the surface epoxy pour at this point. I turned a recess into the ring (finally some machining content) to accept the lens and glued it in. Visually I could see a full bead of epoxy all around the lens where it sits in the ring, so I figured I had it sealed. This would be important because the last step of doing the clear epoxy pour on the inside would need to be contained. Turns out there must have been some gap somewhere as the epoxy came through in one spot and ran onto the front of the lens a bit. Not a big deal, it's a small flaw and this is experimental anyway. But now I have my procedure worked out and I can make these to look good and work well.

[Machine]

Hydrophobic,not hydroscopic

Hygroscopic not hydroscopic.

[Optics Curmudgeon]

Yes, my correction stands corrected