UV Blocker


#1

Hello everyone.

I would like to inquire about UV blocker. In Ember resins you use Mayzo OB+ (2,2’-(2,5-thiophenediyl)bis(5-tert-butylbenzoxazole)) 0.160 %. If I understand correct it prevents UV light to be absorbed deep in the resin. That is why we can have certain height layers. Another important thing is that free radical polymerization occurs in Ember resins.

My question is if the same UV blocker is compatible with cationic polymerization systems?
I and a team are developing new resin, which is based on free radical promoted cationic polymerization. I was trying to do Working Curve Measurement with it. But the drawback is that the whole layer cast on PDMS window polymerizes at once after it gets UV light. And I can’t get varying height squares. All the sample is flat and the same thickness. What I’ve noticed more, the reactions continues after exposition is turned off till there is uncured resin.
Would UV blocker help to control layer height in cationic resins?

Any suggestions are welcome!
Best Regards,
Edvinas


#2

Hi
to answer your questions:

  • I don’t see why not but can’t be sure.
  • As long as you are using a photo-initiator or your resin is photo-curable in some way, then an UV absorber that absorbs at 405nm (Ember wavelength) should change the photo-curing behavior dramatically. In terms of working curve, the UV absorber will change the slope of the trend-line fitting your data (the penetration depth).
    Few suggestions:
  • is Mayzo OB+ soluble in your team’s resin? If it’s not then no reason to think about using it. I would try that first.
  • try a different approach to collect working curve data, e.g. cure a big droplet of resin on a glass slide for 2 seconds another at 4 sec ect etc and see if there’s any difference in thickness.
  • are you using a photo-initiator? Try using less. What is its absorbance spectrum? From what you wrote seems like the resin cures under visible light.
  • to prevent the resin from unwanted curing you can add inhibitors.

#3

Thank you for the quick response.

I haven’t tried yet if UV blocker is soluble in our resin. But I will check it definitely.
Yes, we are using Irgacure 819 photo-initiator, which is sensitive to 405 nm. It should not make the whole mixture sensitive to visible light. It stays liquid until affected to UV.
I believe, that inhibitor is the thing we need to stop unwanted curing.

Thank you for the advice. I’ll try to keep you updated what is new in our research.

Edvinas


#4

Look at this post for more information on Working Curves. Working Curve

I have developed my own ZIP file that includes several negative features and I track how each resins light bleed affects these features. I have alway believed that the resins with more UV blockers will allow for much better detail, but may not be able to print very thick layers (>100um). To that end, I would be interested in knowing if you find this to be true also.

Here is my ZIP files in case you are interested. To tune the working curve I print using successfully shorter exposure times until I get most of the print to be less than 200um in thickness.

PatternMode Working Cuver ver2 0,08sec.zip (257.8 KB)
PatternMode Working Cuver ver2 0,16sec.zip (257.8 KB)
PatternMode Working Cuver ver2 0,32sec.zip (257.8 KB)
PatternMode Working Cuver ver2 0,64sec.zip (257.8 KB)


#5

@scott_chabineau

Yes, I am familiar with the post. Also, I found yours .xlsx file with several resins’ working curve measurements. That was really helpful. I made Formlabs Form2 Flex working curve (WC) and Ameralab Voyager (new resin, still being developed, but I was able to print specific architecture „meta material” from it), too.

Thanks for your ZIP files. I keep in mind them, they can be useful developing our resin in future! At first, we need to make it more photosensitive (requires long exposure duration) and eliminate unwanted curing.

Edvinas


#6

Excellent!
In reading your original post again, have you tried to turn the exposure time way down (0.08 or lower) to get the varying height squares?


#7

No, I haven’t. Our resin is based on glycerol diglicidilether monomers and due to longer molecular chains, it needs to be prolonged exposure, for example, 1 minute to make it viscous. After longer exposures, it turns solid. The uncured resin can be dissolved in solvents like acetone, isopropanol and etc. Cured remains on the substrate. Employing Ember as dynamic projection lithography, I am able to cure selective micro-size features in the resin droplets.
We are working on how to make the resin more sensitive for 3D printing.


#8

Sounds very technical and highly specialized. Cheers!