You can try reducing your exposure time somewhat, but it’s a delicate balance between reducing light bleed without reducing part hardness below the threshold necessary to hold the part together during a print.
You can print on the hard silicone bare. Don’t try it on the soft silicone. Hard silicone wears quickly in the areas where resin cures against the vat floor. The photoinitiator & polymerization reaction also reacts a little with the surface of the silicone and causes the silicone to become more opaque to light and UV. It can be a bit tricky to determine the extent of the wear because cloudy to visible light and cloudy to UV/near-UV aren’t the same thing. Autodesk and MadeSolid did some testing of silicone vat wear that they wrote up at:
The takeway is that the vat can appear cloudy to visible spectrum and still function fine, or may appear clear to visible spectrum yet become opaque to UV and near-UV as it wears.
This is why for other silicone vat based machines, manufacturers recommend printing in various different parts of the vat and to print at various different rotations to spread out the wear more evenly, rather than risk developing an unprintable spot.
Generally, speaking, I only print on bare silicone when I have huge solid flat parts like these:
In doing so, I’ve found a few tricks:
- Sweeping the resin every 100 layers or so to exposure the silicone layer to air dramatically reduces adhesion and improves vat life. That huge bottom part would start the print releasing with only 2-3mm of lift. Then as it progresses, the amount of lift necessary gradually increases, but if I pause the print and sweep the bottom, the release lift goes back down to 2-3mm. A print run with sweeping vs. w/o sweeping also results in dramatically less clouding at the end of a print run
- Be careful of long exposures. The longer your exposure, the more chemical damage will occur on the silicone surface. On teflon film, the main concern about long exposures is light bleed, lift height, and lift speed. On silicone, long exposures will dramatically reduce the life of your vat, and combined with long prints, can cause the vat floor to bond to your part during the print
- Be very careful of long prints or long e. The failure characteristics of the silicone surface is very different than for the teflon film surface. Generally speaking, when the lift forces max out at some point, but repeated cycles of high lift forces can lift the teflon off the silicone vat floor, creating bubbles or deforming the vat. Long prints with long cumulative exposures increase the chance of having some more catastrophic failure occur
The issue of cure time and overall print duration is not to be underestimated:
If you skip forward towards the middle and end of the video, you’ll see that the silicone bonded so strongly to the part, that it started to bend the part scary high before the silicone ripped out a chunk. I’m pretty lucky that this didn’t cause the to vat to break up and spill resin all over.