I was looking for ways to mix UV blockers into epoxy resin (to mix an UV blocker into the solarez zerovoc – the cheapest UV resin I found so far), and I found this: http://www.dymax.com/pdf/pds/3069.pdf
Nothing new here… an adhesive from Dymax that cures fast on UV and blue light… but what catch my eye was the second page… the 2 graphs showing the depth of cure relation with time of exposition and light intensity… And then I realize:
If this product has a depth/exposion time relation, it means that it already partially blocks the light from penetrating deep into the material, which means that we MAY be able to control the cure by just adjusting the exposure time per layer… If we do the math right, we may be able to cure JUST the amount we want from the bottom, by doing really quick expositions, specially if the material is NOT SO FAST to cure… actually, the slower it is, the more difficult it would be to cure a ticker layer… which is EXACTLY what we want! 🙂
We could also experiment with adding SOLVENT to the mix instead of a blocker, just to make it HARDER to form the reaction that cures the material, increasing the chances of curing just a tiny layer… just some more to think about it and experiment once we get a prototype working!
Last, but not least, in case someone runs into figuring what viscosity “cP” is, this is a nice useful table to figure how viscous a material is:
| Some typical viscosities (cP at 20°C) | |||
| air | 0.02 | motor oil SAE 20 | 125 |
| acetone | 0.3 | motor oil SAE 50 | 540 |
| methanol | 0.6 | castor oil | 986 |
| water | 1.0 | glycerin | 1490 |
| ethanol | 1.2 | pancake syrup | 2500 |
| mercury | 1.5 | maple syrup | 3200 |
| linseed oil (raw) | 28 | treacle | 20,000 |
| corn oil | 72 | peanut butter | 250,000 |
| olive oil | 84 | window putty | 100,000,000 |
1:24 am, May 26, 2011Jon Watson /
Any thoughts on opaque UV resins? Is this even possible? I think some service bureaus have an option for black & white opaque resins which they use in their STL or Objet machines. Would adding an opaque dye act as a UV blocker? Would being opaque block too much light? I’m just thinking out loud here. It would be really nice to have the option to build parts in other “opaque” colors eventually. That way, you wouldn’t have to paint everything if you’re making “usable” parts that you don’t want to be translucent clear or amber in color. Just throwing that out there to ponder. 🙂
9:43 pm, May 26, 2011hradec /
This question would be perfect to be asked in our forum, so not only us but others could work on answers!! Do you mind throw it in there and we continue?
thanks Jon…
-H
10:47 pm, May 29, 2011Traumflug /
If this product has a depth/exposion time relation, it means that it already partially blocks the light from penetrating deep into the material, which means that we MAY be able to control the cure by just adjusting the exposure time per layer… If we do the math right, we may be able to cure JUST the amount we want from the bottom, by doing really quick expositions, specially if the material is NOT SO FAST to cure… actually, the slower it is, the more difficult it would be to cure a ticker layer… which is EXACTLY what we want!
Here I can talk a bit about my experience as an operator of a 3D Systems stereolithography system. Early SLA resins were all clear, and they produced quite even layer thicknesses. So, coloring the resin isn’t essential at all.
When you expose UV-curable resin to light, it starts hardening at the top (where “top” = “closer to the light source”) and the more light you bring in, the thicker this layer gets. However, the exposure has to be above some threshold to work at all. Not enough light and no hardening takes place.
To find out the relation between exposure and layer thickness, simply expose just one layer, then take this single layer out, postprocess (wash) it as normal, and you can measure the thickness. The minimum layer thickness is very low, like 0.01 mm. Much lower than you can reasonably handle.
Minimum layer thickness also isn’t essential to build accuracy or layer thickness. It’s no problem to advance in 0.1 mm steps, but to expose for 0.2 or 0.3 mm. This way, parts of the resin get exposed twice or three times, wich doesn’t hurt at all.
After all, the SLA slicing algorithm makes the bottom layer (here the top layer) intentionally extra thick, to achieve better build accuracy. More accuracy, because the first layer is more mechanically stable (think of overhangs). The drawback is, this introduces some complications in the slicing algorithm to compensate for this extra thickness. In other words, you have more fun creating a good slicing software.
9:24 pm, May 30, 2011hradec /
@Traumflug
AWESOME INFO!!! thanks for sharing this, Traumflug!!!
I’ll keep that in mind about the thickness variation in the slicing algorithm… Makes a lot of sense for sure…
Actually, this reinforces the idea that me and TJ were discussion some time ago about not having much thickness precision on the first layer. So we could start a print by leaving the print plate a little higher to avoid it touching the vat base by accident. So the first layer would be 0.1 or 0.2mm, and would be treated as a support base layer that we snap it off after print.
if you don’t mind, I think this info deserves a blog entry of its own, so I’ll copy/paste it on the chemical section, if its ok with you!!