White powder?

[garethashenden]

I’ve been printing things with green resin, then I clean them off with isopropyl alcohol and put them in a UV box to cure. As they cure a white powder appears on some of the details, as if it got stuck in a corner. It comes off, but does anyone know what this is and how to avoid it? Thanks!

[Mark W]

Its from resin dissolved in your IPA, which is left behind as the IPA evaporates under UV. 

Let the parts dry completely prior to UV cure.   

[narrowminded]

Its from resin dissolved in your IPA, which is left behind as the IPA evaporates under UV. 

Let the parts dry completely prior to UV cure.

I'm also suspicious that the 95%+ IPA strength, repeatedly recommended in all instructions I've seen, is probably more important than would meet the eye.  The lower strengths are diluted with water and (except for water based resin) it is mentioned in various resin reference sheets that it is not water soluble nor well cleaned with soap and water, but only recommend IPA and the pretty pure stuff.  Because of those instructions and their specificity about the strength I purchased some and that's all I've used, satisfactorily.  I suspect the water is at least much slower to dry and maybe that's the reason for the recommended IPA strength and why the instructions were so specific about the strength, and maybe there's something more to it beyond my understanding. 

[Chris333]

I blow all my parts off with an air gun right after alcohol and before curing.

[garethashenden]

That’s what I was suspecting the issue to be. I’ve been using 70% because that’s what’s on hand. Some 99% is on its way from amazon and will be here tomorrow. I’ve alao been a bit impatient with cleaning in general, I should slow down and be more careful.

[Chris333]

I use 91% from Walmart ($2.50) and I scrub the parts with chip brushes from Harbor Freight.
https://www.harborfreight.com/36-piece-1-in-industrial-grade-chip-brushes-61491.html

[narrowminded]

I have a soft toothbrush and a bunch of brushes just like those Chris linked to.  I've had and used those for years.  I've only used 99% alcohol and have rinsed at least twice, have tried cleaning them in the ultrasonic cleaner, brushed them, didn't brush them, and I can't say that I've seen any real difference among any of those procedures.  Two soaks in a jar while sloshing them around a few times has been the minimum I have done and seems to be adequate. 

Where I have been using the brush is making sure to clear the debris from the coupler pocket generated by the drill while cleaning out the coupler pin hole.  It is fairly narrow and deep so begs to trap debris.  And I'm doing that before to final cure so the material is still a little soft and I fear that any debris in there, all only partially cured, could become fused to those pocket surfaces during curing which would cause trouble.  I haven't had any of that trouble but also addressed this as described right from the start so I don't really know that it would be trouble.  The kind of thing where most of the time it's OK but then... that was most of the time.   

The soak time total has probably not been less than five minutes and when busy, maybe let it go as much as a half hour.  I also think that when it soaks longer than seems to be required, it may get a little more flexible than usual but also settled back to normal if left to sit.  And that's anecdotal, not something I can say with certainty.  Letting it sit for a few hours or even a few days after washing and before to trim the supports and then cure, doesn't seem to hurt.  If anything the parts might be slightly more stable while handling for those operations.  Again, nothing hard fact about that but it seems true but also isn't dramatically different, like a must do. 

Hope that helps a little.

[Mark W]

I use the same $2.50 91% as Chris. 

My Clean and Cure process:

1. Sideways drip (5+ minutes)
Remove build plate and put back on the Z axis arm sideways to let resin run down and drip back into the vat.

2. 1st of 3 IPA baths (1 minute or less)
This bath is the double used IPA, intended to get the remaining globs of resin off the model. If necessary, a soft bristle toothbrush is used to clear resin from cavities.

3. 2nd bath  (1-5 minutes)
This bath is used IPA from the first bath. Intended to dissolve uncured surface resin. 

4. Ultrasonic Bath (3 minutes) 
This IPA is first use.  Intended to free/dissolve all remaining resin.

5.  Blow Dry (30 seconds)
Set my airbrush at 20-30psi and blow dry.

6. Air Dry (seconds - days)
No rush to get the part cured.  If the part is accidentally left in IPA for more than 10 minutes, I will air dry minimum 1 hour. 
I find IPA can 'soak' into the printer cured resin and cause platforms and parts to warp.  Sometimes as the part air dries it will re-settle and return to the intended shape, sometimes it wont.

7. UV Cure (3 minutes)
Part is put on a solar turn-table under the UV hood.  Once it's done, it's done!



Once IPA from the Ultrasonic cleaner begins to get cloudy, it is removed and either added to or replaces bath #2.  When bath #2 is replaced, the old bath #2 is added to/replaces bath #3. 

[narrowminded]

This is what I've been using.  I also have a salvaged pump sprayer that fits a bottle, siphon tube length cut to fit.  It's handy especially when cleaning the build plate.  99% is a bit more expensive but also doesn't consume much once the wash cycles are established.
https://www.amazon.com/gp/product/B0793KYR9W/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

@Mark W have you seen any definite benefit to the ultrasonic cleaner?  I did that for several parts cycles and can't say that I detected any benefit so did the last few without that step.  It's not like it's that hard to set up if there is a benefit. 

[Mark W]

I do find it helps quite a bit actually.  I judge a part's cleanliness by the amount of glossy resin residue.  Without an Ultrasonic cycle, dunking and swishing a part around in a tub of IPA can only release so much surface resin, no matter how long I swished. Once blow-dried, I could always clearly see a lot of remaining residue.  With the Ultrasonic cleaner, I don't need to dunk/swish the part nearly as much, and after the 3 minute cycle there's no remaining residue.

But to re-iterate, I'm using 91% in the Ultrasonic cleaner too.  Was that you're method as well, or just water?  That might make a difference. 
 

[narrowminded]

But to re-iterate, I'm using 91% in the Ultrasonic cleaner too.  Was that you're method as well, or just water?  That might make a difference.

Thanks for the reply.

 I was using the 99% in a separate glass container with a lid, set in the water to isolate the alcohol from the machine.  That's pretty typical of how I've used the ultrasonic cleaner in general.  I wonder if the strength of the 99% might be why I feel I've seen success with just a wash?   And maybe I'm not getting them as clean as I think.   I'll be looking much closer at the next batch to see what there is to see but the ones I've done this far looked good, felt extremely "dry", dimensionally good especially in the pockets where the fit really matters, and as much as I looked, nice and shiny.   They also painted well.

I probably won't be printing anything for a few days now but will be looking at the next batches very closely.

[garethashenden]

I have a follow up cleaning question. When the alcohol is past it’s best, how do you dispose of it?

[wvgca]

I have a follow up cleaning question. When the alcohol is past it’s best, how do you dispose of it?

i've just washed it down the sink drain, with a follow up of warm water to rinse the container out, and to wash the alcohol down the drain

[narrowminded]

I have a follow up cleaning question. When the alcohol is past it’s best, how do you dispose of it?

I have sat it outside and let it evaporate.  The residue also hardens in the light and I scrape that out and put it in the trash.

[Mark W]

i've just washed it down the sink drain, with a follow up of warm water to rinse the container out, and to wash the alcohol down the drain

This really is not a good idea.  The IPA will contain a lot of dissolved uncured resin which is toxic in many ways to many things, including humans and aquatic life. 
Filtering the IPA first won't really do anything either.  You can set it outside in sunlight and cure some of that resin, which you can then scoop out and throw in the bin.  However the IPA will still never be safe enough to just dump. 

I empty all my used IPA into a 5 Gal. bucket with lid in the garage, then drop it off at chemical disposal location.  Auto-centers and many hardware stores accept chemical waste, often for free, or for a nominal fee at most.