While curing 3D-printed UV resin does seem like a straightforward procedure where not a whole lot can go wrong, there are some nuances to be aware of when carrying out the curing process to ensure that all parts of the resin harden correctly without any stickiness.
In this guide, we will discuss the factors that can cause your UV resin to stay sticky after curing it, explain what you can do to prevent the UV resin from staying sticky after curing and take a look at the things that you can do to get rid of the stickiness on the UV resin that you have already cured.
UV Resin Staying Sticky After Curing – Causes & Prevention
Since UV resin staying sticky after curing can be the product of a few different issues during any point of the entire process, which starts with printing and ends with post-processing, going through each possible cause will be necessary to resolve the problem in most cases.
Insufficient Curing Time
One of the most common reasons for UV resin to stay sticky after the curing process is the curing time being insufficient, as the amount of time required for the resin to cure will vary based on factors such as the size and the shape of your print, the color of the resin you’ve used (darker color resins take longer to cure), and the curing method you’re employing.
While finding the correct amount of curing time comes down to trial and error at the end of the day, which effectively means that you will have an easier time knowing how much curing time is required for any particular print after successfully curing prints of various sizes with the resin and the curing method of your choice, recommendations from the resin manufacturer should point you in the right direction in most cases, and ensure that you don’t end up under or over-curing too severely as a starting point.
Insufficient UV Light Exposure
Another widely encountered problem that can lead to your 3D printed UV resin staying sticky after curing is the UV light exposure being insufficient, with factors such as the size & the shape of the model and the curing method you’re using once again affecting the way you should conduct the curing process.
While this is unlikely to be an issue if you’re using a professional curing station, as it should be able to expose the entirety of your print to UV light without problems in most cases, utilizing methods such as sunlight or UV nail lamp curing can easily lead to some areas of the print curing less, and others curing more than necessary, especially when dealing with prints that are on the larger and more complex side.
Incompatible UV Light Wavelength
An issue you’re particularly likely to encounter if you have experienced the stickiness problem right after using a new resin or curing method is the wavelength of the UV light being incompatible with what’s required to cure the resin, as it’s possible to find UV resins that are compatible with a few different wavelengths (usually 365 nm, 385 nm, 405 nm, or all) on the market.
To find out whether this is what’s causing the problem in your case, the best thing you can do is to refer to the resin manufacturer’s specifications, where you can see the UV light wavelength the resin requires for successful curing and compare it to the wavelength of the UV light you’re using for the curing process, as this will directly tell you whether there is an incompatibility or not.
In a case where the wavelength of the UV light you’re using is a lot longer (larger value) than the wavelength required by the resin for curing, you will find that the effectiveness of the curing process drops, which will often result in very long curing times or incomplete curing that leads to the stickiness problem you’re experiencing.
For best results, we recommend purchasing a UV light source with a wavelength that falls into the wavelength range provided by the resin manufacturer, as this is practically the only way to ensure that incompatibility won’t be a problem anymore.
Improper Washing & Drying
While it’s a straightforward process for the most part, washing & drying the printed part correctly before moving forward with curing is still a critical step of the process to ensure that you don’t end up with stickiness, as you can otherwise end up with impurities and parts of uncured resin on the surface of your print that lead to problems during curing.
Our primary recommendation to ensure that you don’t have issues regarding the washing process is to double-wash the print in two separate containers while also making sure the IPA you’re using is clean enough and not too contaminated with resin from previous washes, which should practically guarantee that the print comes out clean without any uncured resin sticking to it.
Additionally, if you’re dealing with complex shapes that are naturally harder to wash due to it being more difficult for the isopropyl alcohol to come into contact with the more problematic areas, it’s usually a good idea to take extra steps such as giving the print extra time to wash, stirring the isopropyl alcohol to allow it to reach the problem areas, and rinsing the hard-to-reach areas afterward by spraying isopropyl alcohol directly on them.
Finally, remember to let your print fully dry before you move on to the curing process, which is yet another vital part of the process, as curing the resin as it’s still wet will cause moisture to be trapped inside, leading to a multitude of issues, including the stickiness problem you’re experiencing.
Resin Layers Too Thick
Another factor that can lead to your UV resin staying sticky after the curing process is printing with a high layer thickness value, and while this isn’t a reason in itself for the surface of your prints to stay sticky, it does increase the likelihood of under-curing the resin, as thicker layers naturally require more curing before they can solidify.
In this case, our primary recommendation would be to test with a reduced layer thickness value and see if the issue still takes place, especially if you have recently started printing with higher layer thicknesses, as this will allow you to easily see whether the problem actually stems from the increased thickness in particular or not.
Once you confirm the stickiness problem occurs due to working with thicker resin layers, you can increase the curing time your print undergoes, compensating for the increased thickness in layers and preventing any stickiness from troubling your prints.
Contaminated Resin
A factor that can easily lead to the stickiness problem you’re experiencing, especially considering that it’s one that’s likely to be overlooked, is the usage of contaminated resin for your prints, as dust, dirt, and even moisture in the resin can affect the curing process in a negative manner.
In most cases, contamination occurs as a result of the resin coming into contact with air, dust, dirt, and moisture as it’s still in its container due to improper storage conditions, where the resin container ends up staying open for a prolonged amount of time as it’s being used, with the chance of contamination increasing as more time passes with the resin container remaining unsealed.
That said, it’s also entirely possible for contamination to take place during usage due to factors such as the usage of equipment that’s pre-contaminated from earlier prints, whether it’s tools or containers, and even as the 3D printing process is taking place, usually due to the usage of a contaminated resin vat, which is something to keep in mind when printing with resin.
So, if you suspect that the resin you’re using is somehow getting contaminated due to any of the reasons we have mentioned above, whether in storage or during usage, our recommendation to rule this possibility out would be to thoroughly clean all the equipment you use (especially the resin vat), create a clean working environment, pick up a new bottle of resin, and ensure that the bottle remains unsealed for short amounts of time where contamination becomes highly unlikely.
Expired Resin
Last but not least, if none of the factors we have discussed so far seem to be what’s causing the problem in your case, it’s likely that the resin itself being expired is the culprit behind the stickiness issue you’re experiencing with your prints, especially if you have been using the same bottle of resin for a while now.
While UV resin lasts for a very long time when stored correctly, factors such as prolonged exposure to high temperatures & sunlight and the resin staying in an unsealed container, which then leads to it coming into contact with air & moisture, can lead to degradation taking place much sooner than the expiration date listed on the bottle, and prompt your prints to come out sticky even after curing.
So, in a case where you seem to be running out of options regarding solving the stickiness problem, we would highly recommend testing with a new and unopened bottle of resin to rule out the possibility of the issue stemming from the usage of expired resin, which should likely solve the issue at hand.
How to Get Rid of the Stickiness on Cured UV Resin?
While we can all agree that preventing the stickiness from occurring from the get-go is the best solution, there are also a few things you can do to get rid of the stickiness that’s troubling your already-cured UV resin if you would prefer to repair the print you have at hand instead of printing again.
Please note that these solutions may not work in every scenario due to the possibility of the stickiness issue stemming from many distinct causes, as we have discussed in the previous section.
Cure Again
In cases where the stickiness is caused by the curing being incomplete, whether due to insufficient UV light exposure or insufficient curing time, simply curing the resin again can help you get rid of the stickiness as long as you give it enough time and UV light exposure for the curing process to be successful.
When going through the curing process again, we highly recommend following the resin manufacturer’s guidelines on factors such as the optimal UV light wavelength to use and the amount of time required (based on the size of the print) for curing to complete while also ensuring that the entirety of the printed part gets exposed to the UV light (especially if it’s a complex shape), as this will considerably reduce the likelihood of coming across issues, whether it’s under-curing or over-curing.
Clean with Isopropyl Alcohol (IPA)
If the stickiness issue you’re experiencing on your print is caused by factors such as uncured resin residue sitting on the surface or dust and dirt that leads to the resin getting contaminated, thoroughly cleaning the surface with isopropyl alcohol is highly likely to solve the problem at hand.
While using a washing station will produce the best results here, placing your part in a container filled with isopropyl alcohol (the higher %, the better) and rinsing it until all the uncured resin and debris comes off, especially if you rinse multiple times, should do the trick and get rid of the stickiness that’s troubling your print.
Coat with Clear Resin, Varnish, or Acrylic Spray Paint
In a scenario where it seems to be impossible to get rid of the stickiness, a solution you can employ to save your print is to coat the printed model with a layer of clear resin, varnish, or acrylic spray paint, which will allow you to hide the sticky layer inside and create a surface that’s properly dry.
While the choice primarily comes down to your purposes, as each of these materials comes with distinct advantages and disadvantages, they will all allow you to cover the sticky outer layer up and make the stickiness a problem of the past.
Sand the Surface of the Print
Similar to the previous solution of coating the surface, you can also opt to sand the surface of your print down to get rid of the stickiness as an alternative solution since it’s likely that the problem is only affecting the surface of your print, with the resin layers inside correctly cured.
That said, as you will be removing material off your print by sanding the surface off, it might not be the best way to move forward in cases where your print has a lot of intricate details that you may end up losing as a result of the sanding process, which is something to keep in mind.
Conclusion
Even though it can be disappointing to go through the entirety of the printing, washing, and curing process only to find out that your UV resin is sticky, it’s not impossible by any means to save your 3D-printed part from this problem and get rid of the stickiness with some extra work.
That being said, considering that preventing this problem from happening again is the best solution at the end of the day, which practically comes down to nothing more than ensuring that you print and cure with the proper configuration, adjusting parameters, such as the curing time, to be optimal, is the best thing to do moving forward.
As a software developer by profession, David has been particularly interested in how 3D printing works even before he picked up his first 3D printer, and completely fell in love with the hobby once he got his hands on a Prusa i3 MK2 for the first time back in 2017. Due to him enjoying both the functional and the non-functional sides of 3D printing equally, you’ll rarely see David’s 3D printer in an idle state.