Clean Up Your Resin-Printing Rinse With Dialysis

There’s a lot to like about resin 3D printing. The detail, the smooth surface finish, the mechanical simplicity of the printer itself compared to an FDM printer. But there are downsides, too, not least of which is the toxic waste that resin printing generates. What’s one to do with all that resin-tainted alcohol left over from curing prints?

How about sending it through this homebrew filtering apparatus to make it ready for reuse? [Involute] likens this process to dialysis, and while we see the similarities, what’s going on here is a lot simpler than the process used to filter wastes from the blood in patients with failing kidneys — there are no semipermeable membranes used here. Not that the idea suffers from its simplicity, mind you; it just removes unpolymerized resin from the isopropyl alcohol rinse using the same photopolymerization process used during printing.

[Involute] did some initial experiments to see what would happen to used IPA when exposed to UV light. The video below shows the results — the unreacted resin quickly clumps, making it easy to filter out of the IPA. Turning that into an actual process was a bit trickier, requiring a pump to send the resin through a long loop of UV LED-wrapped clear vinyl tubing, where the cross-linking occurs. From there the plastic-IPA mixture passes through two filters, 5 microns followed by 0.5 microns, after which it’s ready for reuse. [Involute] also added a timer to control the pump, making this a walk-away process — although since IPA is pretty flammable, we’d probably stay close by.

At more than seven times the price of gasoline, 99% IPA isn’t something you want to be throwing away. And flushing resin-tainted alcohol down the drain is a big no-no. So something like this can not only save resin-printing fans big bucks, but make the whole process a little greener, too. Kudos to [Involute] for that.

64 thoughts on “Clean Up Your Resin-Printing Rinse With Dialysis

    1. What I meant to add was that I think this is a great idea (addresses the major shortcoming with resin printing) and I’m amazed that no one has thought of it before or commercialized it.

          1. IPA as a vapour would be quite dangerous. I’m not sure, but it might come under the same laws as an alcohol still (for example a rectifiers licence in the UK).

          2. There are commercial distillation devices for doing just this. A guy i know who does a lot of resin printing has one. Seems a lot less expensive and simpler than this hack.

          3. Creator here. I (and others) have actually tried distillation. I was unable to get it to work consistently (the IPA would just boil off without condensing). Even those who claim success are only able to recover, at most, half the IPA they put in. While I used a water distiller, it had an adjustable temperature, so I set it to the boiling point of IPA. Still wasn’t reliable.

    2. Given the state of rinsers for the part, it makes sense why this isn’t a commercial product yet, that’s the best place to incorporate a filter. But relative to the resin, the printer and the countless cards or other scraping apparatuses, the alcohol feels like a small cost of the system. Maybe if you have one of those giant 500mm resin printers that cost $10k and you need liters of IPA for rinsing this becomes necessary, but then again the alcohol seems like a cheap cost. This feels more like the missing piece to a totally autonomous system that handles resin selection and setup, printing, cleaning, and final curing that just happens to recycle the rinsing agent. Still, props to bringing the solution to a problem you didn’t realize you had and let’s hope the creator can continue advancing the resin printing market that feels like it’s been stagnant for some time.

      1. Creator here. Cost was one of two reasons I made this. The other was convenience. Even if the IPA were free you still have to dispose of it somehow. For me, that means transferring it to disposable containers (which need to be acquired) and taking it to a hazmat collection site. Not impossible, but a minor pain point this machines eliminates.

        1. this guy is being responsible. how many folks just dump it inappropriately? how many fully disclose to hazmat what the alcohol is full of? reusing your solvents is just good practice.

        2. The better solution here is to pour it into a disposable open container (I use aluminum cooking trays) and let it evaporate and cure in the sun. No need to take it to a hazmat…

      2. Great idea. If you do it in a modified basket container, I can’t remember what it’s called oddly I want to say pickle something, you could just lift all that out of there at once. Really great idea. Simple, effective, cheap.

    3. There are no purpose built IPA recyclers on the market yet. I don’t think there is any profit on the consumer side for this and industrials aren’t really feeling the pain of IPA supply. Then again, homebrew solutions are so much cooler. I currently have 2 methods but my favorite and by far fastest method of cleaning IPA is with a centrifuge. I also do the glas jar, settle, set in cure chamber or outside method. And someone in my 3d printing group just introduced me to a distilling process that I’m eager to try.

  1. It is a sound idea. With resin printers becoming more common now I wonder if a Chinese company will steal it and make a commercial unit? If I make one I think a small centrifuge of stainless steel gauze would be better than filters. As the resin solidifies it will go to the outside of the drum and the remaining fluid can be slowly drained from the middle to be recycled.

        1. I don’t believe that link only addresses the third point properly, and the second point only through a heavy stretch of the imagination.

          Nothing will be as cheap as a couple of bag filters, a pump, and accessories, even in maintenance. I guarantee the linked machine requires a bunch of love regularly.

  2. I’m curious which contaminants from the resin don’t get removed by this process… Resin is a complex concoction of a whole bunch of chemicals, some toxic, and this article implies (through omission) that all of that gets magically swept up and trapped by the cured resin clumps. I seriously doubt that is true, so implying that the resulting IPA is “clean” or “pure” seems problematic if it’s still significantly more toxic?

    1. Creator here. By “clean” I meant useful for washing prints. There could still be “stuff” in the IPA, but I just care about recovering something I can continue to use for washing. So far, it does that.

  3. An off the cuff, ill-informed idea (but hey, this is Hackaday)…

    Is 99% IPA really necessary? Ignoring local laws, could a 90+% homebrew ethanol work? If so, the distilling process itself, after precipitating most of the resin with UV light, could be an inexpensive way to both produce and reuse the solvent. There are plenty of cheap “water” distillers available and worst case, you have a failed experience and the “solution” to your woes.

    1. I (and others) have actually tried distillation. I was unable to get it to work consistently (the IPA would just boil off without condensing). Even those who claim success are only able to recover, at most, half the IPA they put in.

      1. That’s a fair point, for IPA. If you were willing to make your own solvent with sugar and yeast, losing half wouldn’t be a big deal.

        If you’re making your own, it might even just be easier/more energy efficient to avoid reusing the solvent at all, and set it outside in the sun in a pan to evaporate off the liquid and leave behind a small amount of contaminates that could be safely disposed of. That would also keep the resin out of the distillation process and allow you to repurpose the solvent as needed.

      2. Has anyone tried a vacuum distillery?
        If I understand how they work correctly, it wouldn’t have the 50% loss like a standard distillery.
        And it would require lower temperature which would be good from a fire hazard as well as avoiding chemical reactions in the resins (I tried to build a standard distillery but the waste turned brown and smelled like death, so, I worry about heating resin waste to much)

    1. You’re correct, it’s flocculation and filtration. Dialysis requires, by definition, a semi-permeable membrane through which particles of different sizes diffuse; and osmotic pressure is the dominant motive force in dialysis, as opposed to fluid or atmospheric pressure for filtration.

  4. put the resin/alcohol solution in an empty pop
    bottle outside and wait while my two favorite
    open energy sources do there stuff
    gravity and uv light are free and well,non optional,
    so use them for something other than getting burnt and short

    1. does the bottle pass UV? I have a friend that simply puts the used IPA into a flat pan and allows the IPA to evaporate and then just tossing the hardened resin. I have to say the problem is very interesting over all. I could see using a distillation system to replace the filter. maybe us some chilled IPA and bubble the vapor through it to cool it and recover the IPA.
      Nothing wrong with the filter solution and good work on solving a problem. I just wonder what other possible solutions could be tried.

  5. Seems like simply sticking a tub of alcohol with resin in a UV cure box and letting it sit would harden up all the resin without needing fancy equipment. Hit it with UV for a while then pour through a screen to get the large chunks, then a coffee filter, followed by a filter that’s finer than the coffee filter.

  6. I would not consider IPA to be particularly expensive, and other than flammability there is nothing particularly hazardous about it. Still no excuse to waste it, so if it can recovered cheaply and easily enough, go for it!
    FYI: Cheapest place to get it by far is the beauty supply store. $13 USD per gallon for 99%.

  7. At work we clean our IPA with an OES solvent distiller which basically nothing but a distiller with an explosion proof enclosure which lets you set temperature and vacuum profiles for various solvents.

  8. So, this process doesn’t actually make the IPA clean better.

    Source: using a commercial grade measuring device we tested the cleaning efficacy of 99% IPA before and after an process similar to this. Spoiler, the IPA is no better at cleaning resin after

        1. All I can say is that it’s been working for me. I.e., the stuff coming out of the machine (after multiple passes) does a better job of cleaning my prints than it did before. If that changes, I’ll update the project.

          1. ??? I don’t need to measure it. The part goes into the wash dripping resin and comes out resin-free. Nothing even comes off on my fingers. With dirty IPA, the resin stays on the part.

  9. I guess a somewhat simpler way would be to have two rinsing containers, leave one on a shelf for a while until the resin residue settles, then decant the alcohol off the top, then switch containers.
    From my experience the resin settles down completely after a long undisturbed period.
    (That is for low volume printing obviously)

  10. We’re assuming that Involute who I replied to was using the same thing you were talking about? Well okay, but just because one of those devices doesn’t work well doesn’t mean that something other than simple distillation needs to be used. (E.G. fractionating or vacuum, etc). Simple distillation is fine if there’s a big difference in boiling points.

    Maybe I’m the crazy one, but I’m slightly horrified at the thought that someone who put alcohol into a countertop device to be distilled was merely disappointed rather than being alarmed to see half of it was missing. That wasn’t anywhere in my expectations, because I took it as a given that people know that venting most of your product into the air isn’t just an unavoidable part of distillation. You need to make basic adjustments such as not adding more heat than the condenser can remove…

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