Black resin turns grey?

This is a bit of a stab in the dark as I don’t have any pictures to show what I mean. But yesterday I had a request if I could immediately print 5 objects and have them done and delivered 6 hours later. Challenge accepted!! :smile:

I set up the prints and printed them in black at 0.1mm which took about 3 hours. Afterwards a quick clean in the IPA bath, then straight under the UV lamp in a bowl of water) to harden the print and supports. I took off the supports an sanded the parts.

The strange thing was… the parts turned grey (nearly the color of the grey resin). I’ve only used black resin in the current tank so there wasn’t any contamination. And after sanding the parts were black again. so only the outer layer was grey. Luckily color didn’t matter in this case as the parts will get a color coating anyway, but I’m still wondering what happened.

Is this perhaps the quick-curing in water under the UV-lamp which creates this grey layer?

Unfortunately, Because of the time constraints I didn’t have any chance to take pictures.

Perhaps one of you have encountered similar issues.

@Alex_Vermeer, I would speculate that the IPA left on the surface of the parts may have affected the curing process. have you tried to reproduce the effect?

Why did you have them in a bowl of water? I try to cure parts out in the sun but if I can’t I use some grow lights. The sun works the best but the lights work too.

I’ve only used the under water cure method once, and my parts immediately hazed up (nearly to that grey resin color you describe) when transferring from IPA to H20. That made me panic a bit, so I gently rubbed the surface of the parts while under water, and ran more water over the parts. After sitting in my UV sterilizer for a few minutes they came out every so slightly lighter than black parts processed with the non-water method, but certainly not grey.

Here is a comparison of my results with air vs water cure. Not a true apples to apples comparison as the layer height is different, but they were printed using the exact same .form file

Yes, I seem to have had similar effects except mine was a lot more greyish than yours. I just printed another object in black and cured it in air and that didn’t turn black at all, So it does seem that the water has an effect on the coloring of the print.

@ScottBarbour, I cure them in a bowl of water because it cures easier than when curing in air. this is because there are less oxygen diffusing into the uncured resin which allows it to cure faster. As I had to have the prints delivered in a matter of hours, this was the only way to achieve this. Apparently, this happens so quicly that it overcures the outer layer, making it grey?

It doesn’t over cure. The problem is that if you water cure immediately after the print is complete the outer layer is so soft it actually starts to dissipate in the water, this may also be exacerbated by IPA remaining on the print. Either way after it starts to dissipate it cures so you get that cloudiness.

One way to avoid this is to scrub the part really well with a brush in the IPA bath then give it another rinse and good scrubbing in a second clean IPA bath to remove the soft resin from the outer layer and ensure no dissolved resin from the IPA bath remains on it. The problem with this method is you have to actually scrub off some of the desired part of the print so you will lose some detail.

Another way to prevent the hazing is to partially cure the part before doing the water cure, this is the method I usually use. The idea here is you wash your part in IPA as you normally would then throw it in your curing chamber of choice, Then sometime later after the outside layer has had some time for the IPA to fully dry off of it and harden up some use a water cure to rapidly finish the process. I don’t really have specific suggested times for the first part of the cure process, and it seems to vary, I just leave it in there till I get impatient. This method obviously is not as fast as just a water cure but is still significantly faster than just a chamber cure alone.

Another method I have played with and had some success with is a two stage rapid cure. Start your cure in a alcohol bath, then switch to a water bath. The idea here is the alcohol does not cloud the print and also blocks oxygen so you can rapid cure the outside, however the longer the part sits in the alcohol the more damage the alcohol does to the print eventually leading to warping and brittleness, so you want to leave the part in the alcohol part of the rapid cure for a minimal amount of time, then switch to the water bath. I have only played around with this method a little and never really experimented enough to get the timing down. If someone out there takes the time to play with this and gets the timing down it may yield really good results. I did get good results out of it a couple times so I think it has potential, however I have taken to trying to minimize exposure to alcohol as much as possible so I have abandoned this method for the previous one.

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.