If there is something that can be used to “condition” the PDMS, I want to hear about it. (PVA, for instance? Although I fear PVA would contaminate the resin.)
Yea sure Thomas,
It’s called “Price Driscoll’s Ultra 4 Urathane Parafilm”.
The stuff is sold as a silicone conditioner for silicone molds. I was on the lookout for contamination, but it didn’t seem to happen to me. But I would definitely recommend applying it when the tank is new instead of how I had to do it.
Here’s the story I was referring too:
The tray was only about 2 weeks old. It had been cleaned out once, just prior to the black resin prints above. I cleaned it out according to http://forum.formlabs.com/t/emptying-cleaning-the-resin-tray-safely/734/9 (which I don’t remember having the updated language 2 days earlier…doesn’t matter in any case).
@JoshK as far as let it breath…I basically followed the instructions to rinse out the tray and then let it dry out (not more than an hour), then added the new resin. In other words it didn’t sit out for very long.
One other point regarding the peel force required for these pieces…it may not be clear from the photos if the flat surfaces were parallel to the build surface or not. They were NOT. Everything was slanted to minimized the peel force required.
I’m very interested to hear FL’s response regarding conditioning the PDMS.
So your PDMS did get lots of oxygen and that sure didn’t make your next print go any better.
I think the IPA ruined it in my opinion. I think the IPA dried out your silicone, leaving it starving for lubrication. When your next print started the resin soaked into the silicone and cured there. Bingo, massive adhesion and destruction.
I suppose so? But why is this not a problem when the trays ship new? Are they coating it with something like your spray (first hit’s for free?) for initial use? If so, they should be discouraging people from emptying the tanks at all. I have only read about the dangers of IPA on the acrylic, not the PDMS.
When silicone is brand new it is always plump and juicy, there seem to be few pores. As it gets stuff peeled off of it repeatedly it gets drier and rougher, which makes it get drier and rougher even faster as the other material keeps some of the lubrication on itself and may even tear off very tiny bits of the surface. (and eventually large bits, which many people have reported) IPA is hell on silicone lubricants.
After 5 good prints, 15 failed…and then, WITHOUT cleaning the mirrors, I used a new resin tank to create 9 successful parts that are LARGE, TALL and THIN, (3 packed in each print). Just by deduction, parts fail because mostly do to the resin tanks deteriorate for one or all of these reasons;
- lower silicone quality after multiple prints
- resin contaminating silicone over time
- resin properties changing - either pigment uniformity or resin strength to silicone peeling force changes
- quality of resin, we should all report date resin was ordered to triangulate bad batch. I have found tiny INSECTS in some of my resins
- inconsistencies in motor peeling forces and layer height adjustments
I am glad we have an active community. We should all help trouble shoot since the alternative printers are very expensive. I am sure these issues will be fixed in Form2 (anyone know when that is).
I have resin tanks that I have been using since the first form1 I got.
Leaving resin in the tank for months, doesn’t damage it. All I had to do is clean out the resin best I can, and use IPA to clean the rest then let the tank dry on a paper towel. No problems at all. IPA doesn’t damage the silicone because it evaporates. If you leave ipa in your tank it may crack the plastic, so I don’t leave it in there, just wash the silicone with a small amount of it.
Worked for me so far.
You must have clear resin in that tank. I remember the days before we were tempted by black resin and tanks lasted forever too 
Using IPA in the tank can also increase the risk of the PDMS pulling out of the tank completely. The IPA can wick into the seams at the edges of the tank cause the silicone layer to delaminate similar to how it can remove hot glue (which is an awesome useful trick)
Just a helpful warning for anyone attempting to follow that advice.
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I’ve never had that happen to me, so I don’t know. But I guess it’s possible if you leave the IPA in the tank. I squirt a little amount of it in the tank and loosen the left over resin and then empty the tank. Repeat until the tank is clean. Never had a problem.
Try at your own risk though. 
To be fair, I’ve only done this to the tanks that I use for experimenting with. The good practice is to have a separate tank for each production resin type.
Ben -
is it possible that your PDMS layer was failing (pulling away from the Resin Tank) the whole time? If the layer isn’t staying stationary relative to the Resin Tank, it would probably do a poor job peeling away from your model.
The basic problem with the silicone peeling off the acrylic vat bottom is due to the inherent lack of adhesion between acrylic and silicone. Acrylic also degrades when exposed to alcohols, yet alcohol (IPA) is the only way to clean the resin out of the vats. The only advantage that acrylic has is that it’s really easy to cut with lasers. But that’s an advantage only for Formlabs, not for users of these machines.
What I’d really like to try is a glass vat;, preferably borosilicate glass (Pyrex). It would be a little bit harder to make, but it would last a lot longer, it could be cleaned (even fingerprints on the bottom of the vat are nearly impossible to remove without repolishing the acrylic) and silicone rubber bonds much better to glass than to acrylic.
Andrew Werby
www.computersculpture.com
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@Thomas_Alberti that’s sort of what I was thinking at this point…but I still can’t rationalize the sandwich problem. Maybe the peel created a bubble of sorts under then PDMS which was causing sandwich failures?
Update from the FL engineering team:
Hi Ben,
I did hear from engineering. In their words,
"I’ve noticed lately that taller parts struggle to maintain a smooth surface finish the higher and higher you go, sometimes leading to explosions.
There are several factors at play here.
- Stiffness: if the part is wobbly on supports that allow the part to bend during peel, it will get worse higher up. The part won’t return to the exact same spot as before, and there will be minor layer shifting, in this case just a bad surface finish. The same effect arises from a part itself that is not structurally strong and can bend during the print
- Flakes: cured bits of resin accumulate during prints. During a long print, more will accumulate and build up on the surface. Usually, these can be cleaned off after the print finishes. This can be exacerbated by a more densely packed build platform."
They also mentioned that IPA should be kept out of the tank. We should be removing any instructions from our site that suggest using IPA in the tank.
This isn’t exactly new info and still doesn’t explain the sandwich problem which was the whole impetus for this thread in the first place…
I will say that FL support has been super responsive in replacing the tray and sending me some mirror cleaning materials (the official line is: do NOT touch the mirror without contacting support first). Going to try a few more prints today hopefully. Will update when prints are complete.