Cause of PDMS Clouding?

I’m reading a few different theories about what clouds the PDMS in the resin tray. One is that the laser somehow interacts with the PDMS itself, and another is that since the PDMS is permeable, the resin permeates the PDMS and the clouding is actually minute particles of laser-cured resin embedded in the PDMS. I haven’t had my printer long enough to tell, but it seems like the tank for my gray resin clouded much sooner than that for my clear resin. This would seem to support the second cause, wherein resins with more pigment would mean more clouding. What do you more experienced users think, if you even take the time to dwell on such things as I tend to do far too often?

I believe (please correct me if I am wrong) that clear has the lowest curing requirement of the FL resins due to not having any pigment and less non-curing additives to block/absorb UV. Therefore, to the best of my knowledge, both of your stated theories align with grey clouding faster than clear.

Most likely it’s due to the chemical reaction of the curing resin against the surface of the PDMS. If it was the PDMS absorbing resin/pigment then that would also happen over time which isn’t the case.

A note though, PDMS also lasts longer if it is exposed to oxygen which helps the resin not to stick to the PDMS. That’s one of the benefits of the wiper, and also why it’s good to use the scraper to stir the resin before printing.

I’m thinking it could be the localized temperature difference at the PDMS/resin interface. The laser heats mico air bubbles in the PDMS at the surface, expands and ruptures them, and this allows tiny amounts of resin to get into these ‘bowls’. These bigger that half a sphere containers of resin get hardened, and are locked into the surface. Their connection to the layer above is tenuous, and it breaks during peel, remaining embedded into the PDMS surface.

I notice that when I heat the resin to ~43C, clouding is essentially non-existent. I think this is because the PDMS is more fluid, and this makes it more resilient to stress during the rapid localized temp changes. It could also be that the hardended bowl shape of resin gets pulled out of it’s PDMS mold during peel instead of breaking off.

I’m totally pulling this out of my ass. I have no actual hard data to back this up, it’s just something that seems plausible to me. YMMV. :slight_smile:

Hah! Logic seems solid though. How much magnification do you suppose you would need to spot these “bowl” defects on a part?

Interesting - I didn’t think the laser beam itself is that hot, because I have a pointer of the same color, but then again I think its interaction with the resin is… I’ve read how someone burned his finger from using a laser pointer to harden resin on it. Hot enough to re-liquefy solid silicone though? What little I know about the chemistry of all the substances concerned is working against my accepting this theory. Of course, it works against my accepting of the concept of clouding in the first place, and you can see how that worked out.

The clouding is actually the surface pitting. As the layers are cured they stick a little to the surface, the more over exposure the more it will tear the surface causing it to cloud. Under exposure the layers won’t form so there is a fine balance with the laser intensity, speed and mix of the material to get an optimum life on the PDMS.

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