Water Curing: It's the Best Way to Cure Your Resin 3D Prints

by Christopher Lannon May 11, 2020

Hey, what’s up Resin Heads?

Today, I’m going to talk to you about how to water cure your resin 3D prints. I think that, after I show you this method, you’ll be convinced that there is no better way to cure your resin 3D prints. OK… so, let’s MAKE 3D!

If you’re tired of dealing with sticky, under-cured areas on your prints, you need to try water curing. This is a very straight-forward, simple method of curing. After you clean your print and remove the supports, simply drop the print into a clear container-- a glass jar or zip-lock bag, and set the container in the sun or curing chamber for about half the time that you would normally cure your print.

How UV Curing Works

I found this paper, from Charles E. Hoyle at the University of Mississippi, that explains how photopolymerization works. It also talks about the role of oxygen in inhibiting the process. Here’s another article on FacFox.com that explains it, along with a nice illustration showing the process. It also talks about how to stop these resins from turning yellow. By the way, you can slow yellowing or avoid it altogether by immediately spraying your print with a UV clear coat.I’ll provide the links to these resources in the description.

UV resin is known as a liquid photopolymer. It contains properties that change when exposed to ultraviolet (or UV) light-- the light that is within the visible spectrum of light. In our case, it’s typically in the wavelength of 405nm. When UV light hits a photopolymer, it initiates a process called “Photopolymerization.” This process manifests a structural change in the resin resulting in cross-linking, or hardening of the resin.

Why Water Curing is Better

Here’s why water curing is better than the traditional method:

When you cure your print the traditional way, oxygen from the air permeates the uncured resin on the surface of the print. This oxygen inhibits polymerization by attaching to the ends of growing polymerization chains and terminating them. This means that the resin doesn’t fully cure. This can leave your prints sticky, or tacky, and soft, which makes it easier to ruin the texture of your print, by leaving fingerprints on it for example.

Curing your print in water allows the water to act as an oxygen inhibitor, allowing more through curing of the resin. Water contains less oxygen than air does. Air contains about 21% oxygen, whereas water contains less 1% oxygen. Now, water does absorb UV light, but not the wavelengths that cure the resin. The water also uniformly refracts the light around the container, and the light reaches small crevasses in the print that traditional curing sometimes can’t reach. This uniform curing also means that your print ends up with a harder surface and a cleaner finish. Depending on the temperature of the water, it can also keep your print from getting too hot, preventing that discoloration that makes the print look burned. In addition, typical curing time can be cut in half by using the water curing method. Curing in water is the primary method that resin 3D manufacturers like Peopoly recommend.

Here are the steps to water curing:

Pour tap water into a clear glass or plastic container or zip lock bag. Make sure it can hold enough water to completely cover your print.
After cleaning your print and removing your supports, place your model into the water container. You want to handle your model with gloves-- not only to avoid contact with any uncured resin, but also to avoid getting figure prints on your model. Any tacky, uncured resin will easily take up fingerprints, ruining the texture of your model.
Expose the container to sunlight or UV light in a curing chamber.
Cure your print for at least half the time that you would normally cure your print without water-- just long enough to eliminate any tackiness on the print.
Let your model air-dry completely.
Run the left-over water through a paint filter before discarding the water and filter.

References:

https://radtech.org/proceedings/2004/papers/104.pdf

https://facfox.com/docs/can-we-stop-the-photosensitive-resin-photopolymer-from-yellowing