UV Resin Sticky After Curing: Causes, Prevention & Fixes

Resin printing can unlock the next level of 3D printing. This material is a much better choice than FDM filament for parts that need detail and accuracy more than strength and durability. 

However, UV resin can be tricky to cure and remain tacky no matter what you do.

Over- or under-curing are the two main reasons for sticky UV resin. Washing with water instead of IPA or exposure to high levels of oxygen are other possible culprits. Isopropyl alcohol, solvent, or a specific resin cleaner could help you get rid of the stickiness, enhancing the part’s durability and aesthetics.

Common Culprits of Sticky UV Resin

There is nothing more frustrating than feeling the UV resin still tacky after what seems a proper printing a curing technique.

The most common culprits are an excess of oxygen in the room or printer enclosure, inadequate curing time, and incorrect washing.

Oxygen Inhibition 

One of the most common 3D printing advice is that of keeping the printer enclosure or room well-ventilated. 

Ventilation helps reduce the concentration of toxic fumes and particulates generated during the printing process. It also lowers the fire hazard. 

To do that, the vents or fans circulate the air in the room. This is mostly a good thing, but not when you’re printing with UV resin – as an excess of oxygen leads to a phenomenon known as oxygen inhibition.

Perhaps the most important thing to learn when switching to SLA or LCD 3D printing from FDM is that most 3D printing resin hardens through a chemical reaction called polymerization. 

Polymerization happens in the presence of UV light – hence, the reason why you need a SLA or LCD printer for the purpose. At the same time, the reaction is sensitive to oxygen. 

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It is obvious that you can’t get rid of all the oxygen in the air, especially if you’re not printing in a controlled environment (i.e., a laboratory).

However, keeping its levels to a minimum by reducing ventilation can help prevent under-curing and the stickiness of your final object.

Wrong Printing Parameters 

When switching from FDM filaments like PLA or ABS to resin printing, you may believe that standard parameters work on any machine you’re using. 

However, while this is true for FDM, the rule doesn’t apply to resins. 

Because 3D printing resin is much more demanding than solid filament, you have to tweak the printer parameters from machine to machine. 

For example, Liqcreate Deep Blue resin requires 32 seconds of UV light exposure for a layer thickness of 100µm when printed on an Anycubic Photon.

See also  How To Cure UV Resin Without UV Light: Is It Possible?

For the same layer thickness, the resin requires 35 seconds of UV light exposure on an Elegoo Mars, but only 9.5 seconds on an Elegoo Mars 2 or Mars 2 Pro. 

Since UV resin is light-sensitive, other colors require different curing times, even if they are the same brand. 

For instance, the Premium White option from Liqcreate has a curing time of 16 seconds on Anycubic Photon, 14 seconds on Elegoo Mars, and only 2 seconds on a Mars 2 or Mars 2 Pro, for a layer thickness of 100µm.

In some cases, the differences seem minimal. Nonetheless, setting the wrong parameters can lead to under- or over-curing, which leads to tacky UV resin.

Inadequate Curing Time 

We mentioned printer parameters and the importance of getting them right. 

That’s because incorrect parameters can lead to inadequate curing time. There are two possible scenarios: 

  • Over-curing: Over-curing happens when the resin is exposed to UV light for a longer time than necessary. This leads to a softer outer surface that is nearly impossible to wash properly. As a result, the resin remains sticky after drying and its surface becomes opaque.
  • Under-curing: As you can imagine, it means UV exposure for a shorter time than necessary. The layers don’t form properly, remaining malleable and sticky.

Incorrect Washing 

Washing the 3D printing resin at the end of the printing process (when all layers have been cured) is crucial. 

This step ensures that all residual resins that have not reacted during the curing process are washed off. Otherwise, they can react with the oxygen in the atmosphere and affect your print’s durability and aesthetics. 

A common mistake among beginners is trying to wash off these unreacted resins with water. 

However, water cannot dissolve these superficial layers. No matter how many times or for how long you wash the object, it will still feel tacky.

Instead of water, you should use isopropyl alcohol, ethanol over 85% concentration, or a resin cleaner (preferably from the same brand as your resin). 

Note: Some resins are water-washable (Elegoo manufactures such a product). However, they are usually an exception rather than the norm.

Incorrect Post-Curing Processing

Incorrect washing is not the only post-curing process that can keep your resin sticky after drying

In fact, after being washed and dried, most resins must be UV post-cured. This means they need further exposure to a UV lamp or natural sun. 

The post-curing time depends on the UV light source and object size. 

For instance, a 100mm object needs around 2 to 8 minutes of post-curing time in a curing station. Under a UV nail polish lamp, the same object requires between 30 and 45 minutes of post-curing.

When exposed to sunlight, post-curing can take as much as 40 hours. 

Note: All UV resins require UV curing during printing as well as post-curing exposure. For post-curing, it is essential that your part is fully dry before exposing it to UV light.

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Exposure to Heat or Moisture

Humidity and temperature are less of a problem with UV resins, because the material is cured by light, not heat or air. 

However, keeping the room temperature and moisture level within the ranges recommended by the resin manufacturer can help.

At certain temperature intervals, the resin is appropriately thin without becoming too oozy, which improves printing and speeds up curing.

Incorrect Mixing Ratios

UV resin almost always come as a one-step, ready-to-print product. However, there are resins (typically the epoxy kind) that require you to mix two components). 

If you’re using that type of resin instead of UV resin, pay attention to respect the mix ratio. Otherwise, the resin will not harden completely after printing, remaining tacky.

3 Ways To Remove Stickiness From Cured UV Resin

The only way to remove stickiness from UV resin is by washing it properly before post-curing. Sadly, you won’t be able to get the sticky surface off of a post-cured object by simply washing it.

There are still things that you can try, though. 

1. Sand The Surface 

When 3D printing with UV resin, the machine prints one layer at a time and exposes the material to UV light. 

This step cures the resin, but some parts may not cure completely.

Once the object is printed, the washing process removes all uncured fragments and prepares the rest of the resin for post-curing.

If the washing process doesn’t remove all the uncured fragments, the post-curing UV exposure will harden them just enough so that they stick to the rest of the resin permanently, but not enough to remove stickiness. 

Re-washing a post-cured object won’t help much, but you can get rid of the sticky surface by sanding it down. 

Use fine-grit sandpaper and a rotating tool to effectively sand all exposed surfaces. Wipe with isopropyl alcohol to remove sanding dust. 

2. Clean With Rubbing Alcohol 

If sanding and wiping alone didn’t do the trick, you can now wash the object in a bath of rubbing alcohol. If the rubbing alcohol of your choice is ethanol-based, make sure it has a concentration of at least 85%. 

Dip the object in the alcohol bath and let it sit for a couple of minutes. Let it dry completely. If the surface still feels tacky, repeat the process a few times.

3. Protect With Nail Polish 

Sanding and cleaning with rubbing alcohol can get rid of most of the tackiness, but the surface will ultimately remain a bit sticky.

To fix this, you can protect the object with a thin layer of clear nail polish. 

The best kind to use is UV nail polish – you’ll need a nail lamp for the purpose. Follow the instructions on the nail polish bottle to apply and cure the product properly. 

Not only will nail polish enhance your object’s durability and remove stickiness, but it can also enhance the print’s visual appeal. 

See also  How To 3D Print Resin For Molds (For Beginners & Experts)

Tips To Prevent Tacky UV Resin

Tacky surfaces can be annoying, and can even hinder the function of medical or dental parts. These tricks can help you prevent the problem. 

Check Your Printer’s Settings 

The most important thing to remember before hitting the start button on your printer is that every UV resin may require a different curing time. 

Curing times can change based on layer thickness, but also from a type of color to another in resins that come from the same brand. 

Luckily, most brands provide clear instructions regarding printing parameters. Thus, read the label on the resin bottle and make sure all printing parameters are right.

Use The Right Cleaning Agent 

Another thing to read on the label is the type of cleaning solution recommended for washing. 

While there are some exceptions, most UV resins formulated for 3D printing don’t mix well with water. If in doubt, use isopropyl alcohol or ethanol (85% at least). 

Using water to wash a non-water-washable resin can result in a tacky surface that’s near impossible to get rid of.

Only Post-Cure Clean and Dry Objects

Proper cleaning requires you to dip the object in the washing agent (alcohol or water if you’re using a water-washable resin) and leave it for a few minutes. Remove it from the solution, pat with a paper towel, and rinse again.

After the rinsing process, it is crucial to let it dry properly.

You could use an air compressor to blow all droplets off the part or expose the print to some heat (a hair dryer held at a distance or a heated fan could work wonders). Blot with paper towels when done to make sure all moisture is removed. 

All these steps are crucial to ensure that you’re only post-curing clean and dry objects. 

Any kind of cleaning agent that remains on the surface can interfere with UV light refraction and prevent the proper post-curing of the resin. This would lead to a tacky surface that’s hard to fix.

Final Thoughts

UV resin can remain sticky after curing due to an improper curing or post-curing process or due to incorrect cleaning. If this happens, you may be able to fix the surface by sanding, rinsing, and covering it in clear nail polish.

Setting the right printing parameters, using a proper rinsing agent, and making sure that the resin is dry before post-curing can help you prevent the problem.

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