A clear well hardened UV resin casting or coating is every crafter’s ultimate goal and joy. Unfortunately, sometimes, the results are below expectations.
Now, you could live with a bubble here and there, but certainly not stickiness. Tacky UV resin after complete curing is utterly frustrating and renders your craft useless if not corrected.
But what causes UV resin to be sticky after curing? Inadequate treatment by UV light, often as a result of oxygen inhibition, is what causes UV resin to be sticky after curing. While oxygen inhibition is the primary cause of a gooey topcoat, there are other factors too that can play a role in a similar outcome.
Keep reading to learn more about what causes UV resin to be sticky after curing. We’ll also tell you how to fix and prevent the same in the future.
What Is UV Resin?
UV resin is a fluid compound, usually polymers, that hardens when brought under UV light. The energy from UltraViolet light initiates a photochemical reaction that cures the resin.
Fully cured UV resin is solidified and resistant to liquids and chemicals. It has several industrial applications in dentistry, packaging, and adhesive industries.
DIY enthusiasts also use it to make crafts. As a crafter, you might prefer this resin over others like epoxy because it has a remarkably short wait time. UV resin cures in just a few minutes.
Moreover, there’s no lengthy mixing involved as with epoxy. UV resin is a one-part resin and comes ready to use.
Also, it will not harden until induced by UV light. This means that you don’t have to rush through the process. UV resin comes with a couple of downsides too. First, it is significantly expensive, with a limited shelf life of just 6 months.
Also, it can only work in very thin layers. Consequently, it is ideal for casting small items like jewelry, bookmarks, and keychains.
Lastly, you must invest in a UV lamp, as only UV light can trigger the curing process.
3 Reasons Why UV Resin Would Be Sticky After Curing
When crafting with UV resin, the most common issue encountered is stickiness on the surface long after the expected curing time. The following factors could spur such an outcome.
Oxygen inhibition is the primary cause of a tacky surface on cured UV resin. This sticky layer is referred to as an oxygen inhibition layer (OIL).
It occurs when the UV resin reacts with oxygen once it comes into contact with air. In other words, it undergoes free radical polymerization, which interferes with the amount of UV light penetration and reach.
Consequently, the UV light fails to activate the curing of the UV resin at the top, and the unreached resin remains sticky. Oxygen inhibition typically affects the superficial layer in direct contact with air. The sides and bottom usually harden well.
Weak UV Light Intensity
The curing of UV resin is triggered by UV light. But not just any UV lamp will get the job done satisfactorily.
When the UV light produced is of very low intensity, it doesn’t have enough heat to cure all the resin within the expected timeframe.
The wavelength produced by your lamp may also be less than what the UV resin needs to cure.
Quality Issues With UV Resin
Sometimes, despite doing everything right, your UV resin is still gummy. In this case, the manufacturer might actually be to blame.
A low-quality UV resin brand will exhibit problems hardening all the way. Other times, the resin brand may be of good quality but might have gone bad and is, therefore, no longer potent.
Ways To Prevent Sticky UV Resin
Prevention is always better than cure. So having gone over why UV resin ends up sticky post curing, you are in a better position to understand what needs to be done to stop it.
Purchase High-Quality Resin
It is best to buy a high-quality brand of UV resin, even if it means spending a little extra. You’ll save yourself a lot of headaches.
In addition, you must also check its expiration date to ensure it is still usable and potent. If you do not finish all the resin in one go, ensure you don’t take too long to utilize the leftover.
Use A Powerful UV Lamp
For best results, opt for a powerful UV lamp or torch that emits high-intensity UV light. Go for at least 35 watts or above. Halogen UV nail lamps are seemingly the best kind of lamps for the job.
Also, check that it produces longer wavelengths (minimum 320 nm). Longer wavelengths promote deeper curing. But if you decide to use a torch instead, ensure the batteries are working well and enabling the torch to shine to its fullest potential.
Give Water Curing A Chance
Combating oxygen inhibition is nearly impossible if curing resin normally because air is everywhere. However, curing your pieces in a water bath might just work, and many resin experts swear by this method.
So what’s the science behind it? Well, water has about 1% oxygen concentration compared to 21% in air. Therefore, there’s less oxygen to inhibit resin curing in water than in air, thus promoting better surface hardness.
In addition, the UV light penetrates well through water and only absorbs a small amount. Therefore, the remaining light will still get to the UV resin and cure it.
You can create a water bath curing station for your UV resin crafts using a clear glass or container filled with water and submerge your items. Cure them while submerged in water under a UV lamp within the time stipulated.
Avoid Opaque Molds And Pigments
If anything blocks the penetration of UV light such that some parts of the UV resin go unreached, they might not cure. Stickiness is often a result of uncured resin.
This could happen if you cast the UV resin in an opaque mold. The same applies to using excess additives such as dark pigments and light blockers.
If you must use these, add just a little and keep the ratio of resin to pigment high. Also, give your UV resin extra curing time under the lamp.
In addition to leaving it in longer, you can also flip it and turn it around, so all sides get access to the UV light.
Check That The Surrounding Conditions Are Ideal
Environmental elements such as humidity and temperature, to some extent, affect the rate at which resin cures.
Very low temperature and high humidity levels slow down the curing process. If these are the current conditions you are in, it could be why you end up with an undercooked layer every time.
Therefore, ensure your UV resin is curing in a room with optimum temperatures (75-80°F) and humidity levels (About 50-60%). You can employ devices such as a heat fan or dehumidifier to reach the ideal levels if necessary.
For some more information on avoiding rookie mistakes and the basics of resin crafting, take a look at this video from 97 Projects on YouTube.
How To Remove Sticky Residue From UV Resin
Even after following all the rules for curing UV resin to the latter, do not be surprised to encounter sticky results still. Do not worry. It happens more often than you think, even to the most experienced UV resin crafter.
At this point, the next best thing to do is to try and get rid of the tacky film. Here are a few ways to fix sticky UV resin after curing.
Using Rubbing Alcohol
Rubbing alcohol dissolves resins. Therefore you can use it to mop up the sticky layer.
With the help of cotton swabs, dab a bit of rubbing alcohol (70% is ok) on them and wipe the sticky surface gently. This action will get rid of the sticky residue. You can also use acetone in place of rubbing alcohol.
Sand It Down
Another way to get rid of post curing tackiness is to sand away the residue. You can begin with low grit sandpaper and switch to a higher grit.
Sanding always works and takes away the stickiness leaving the resin smooth.
However, you should be prepared to give up the lovely glossy finish always anticipated with resin. That’s because sanding leaves the surface with a matte appearance.
Apply A Clear Top Coat Over It
Acrylic sealers can safely be applied over resin. You can choose a clear glossy spray sealer and spray it over the sticky residue.
Ensure you spray the sealer very lightly and evenly. You want to cover the tacky layer using a very thin coat of sealant.
Leave The Item Alone
This might be a surprise, but sometimes all it takes to get rid of the sticky residue on cured UV resin is to leave the item alone.
If you are lucky enough to have some sunny days, place it under direct sun rays for a few hours a day and let it be for at least three days.
Sunlight produces UV rays which slowly cook UV resin and hardens it if given a chance.
We hope this article has been an eye-opener to you and will be a game changer for your next project.
To recap, the three things that cause sticky UV resin after curing are oxygen inhibition or other UV light blockers, bad UV resin, and weak UV light.
Check and fix the three anytime you want to craft with UV resin, and you’ll be de-molding your well-hardened crafts with a smile every time.