After going through all the trouble of printing a part in resin, discovering it feels sticky or tacky to the touch is pretty unwelcome. Giving the model some extra ultraviolet (UV) curing seems like it should fix the problem, but it probably does not. So, what can be done?
The best thing to do with a sticky print is to immediately re-wash it in clean isopropyl alcohol (IPA) before the UV present in ambient light cures stray resin. If the part remains sticky after it is dry, more aggressive steps can be taken.
We’ll get into those more extreme procedures shortly, but first let’s understand a bit more about how resin works, then look at how that applies to preventing and removing tacky surfaces on finished prints.
How Resin Cures, and the Need to Wash
The resin used in stereolithography (SLA) is a syrupy liquid that is UV-cured, meaning it hardens when exposed to the right wavelength of light. But this process is not a perfectly binary one where all exposed resin becomes completely solid, while unexposed resin remains equally and totally liquid. It happens in degrees, and taking advantage of this is indeed part of how SLA printers operate.
In the SLA process, objects are created one slice at a time, and each slice is a thin layer of resin selectively exposed to UV so that it becomes hard. But this curing process is not always driven to absolute completion. Some of the resin in a layer remains in what is called a green state, which can be thought of as solid but not fully cured. This gives the next layer something to bond to. ..
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