Questions about curing clear resin with a UV light


#1

Hi, everyone… I was looking for a little help with a project OUTSIDE the realm of the printer itself but in relation to resin.

So to preface what I am doing is taking a drop of clear resin, placing it on a small plastic disc and letting it self level/dome to form a miniature lens for miniature glasses I am making. Once self-leved the “lenses” look amazing, so I then place them under a UV light I bought on Amazon linked here --> https://www.amazon.com/gp/product/B07ZF9J3CF/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The clear resin cures VERY quickly, EXCEPT for the very outside layer. No matter how long I leave the resin discs under the lamp the very outside NEVER cures. Is this because of the whole oxygen preventing curing thing? Once cured I can wipe off the outside uncured portion and I am left with a lovely disc of cured resin underneath, but by have to wipe it off it eliminate the absolutely PRISTINE , smooth outer appearance of the lens. Don’t get me wrong it still looks good, but it is every so slightly less perfect.

I understand I can place the prints in water and do a second cure to provide an oxygen free environment, but with the resin layer being still tacky I have had issues with the water causing a slight rippling in the surface so when it is cured it actually looks worse than if I were to just wipe off the uncured resin.

I just wanted to make sure there wasn’t something I am doing overtly WRONG, or is it just the nature of UV cured resin.


#2

Instead of putting the light above your project to cure, have you tried putting the uv light from Underneath, if applicable. And see if different results happen? my thought is, hit the project from a different angle, to see if a change occurs. or compensate for what happening, and readjust the mold itself. … quaratine thoughts…

afterall when the form prints the laser is from the bottom causing curing, so maybe using this same sort of logic w/ this project, put the UV light under it, since I think you stated you were using a clear petri type dish to make mini glasses?


#3

I’m pretty confident you’re correct that it’s the oxygen inhibiting the cure on the surface. My initial thought is rather than using a liquid to shield the resin from the oxygen in the air whether you could use carbon dioxide? If you were to place your substrate with the uncured resin drop into a vessel such as a mug, beaker or such like then pour enough CO2 gas into the vessel to cover the drop and then expose it to the UV. The CO2 is denser than air so will sink and displace the air in the container. You can get your CO2 by opening a fizzy drink bottle over the container and there should be enough gas expelled to cover your ‘blob’. Alternatively you can always make some CO2 by adding some Sodium Bicarbonate to an acid such as vinegar.

Hope this is of some help. Let us know if you give it a go and whether it was successful.


#4

So I tried curing under water and that didn’t work at all.

I ended up soaking the lenses in a little alcohol to wash the uncured layer off and then let them air dry. They are SUPER smooth but lost the super shiny luster I was hoping for.

Here you can see the cured lenses before washing the outer layer off. No matter how long they sat in water or in the air but under the UV light, the outermost layer would never cure. The resin is dark because I added resin dye. And no, that’s not the cause, because I get the same curing issues with undyed resin.


Here are the lenses after washing the outer layer off. Super smooth but lost the perfect shine.


#5

thats crazy

can you measuring the wet resin using a caliper, then compensating, I was in the market for figurienes / small objects.

chalk it up to; residue drip.


#6

What I did for clear lens parts was basically cure them sanded them with a very fine wet sandpaper and used Mothers mag and aluminum polish.


#8

The glasses are darling! What about using a doming resin, or just a thin layer of craft resin on top? Rio Grand jewelry used to sell doming resin but maybe Resin Obsession has it, they have everything else, and there is an article up there on getting shiny resin, but again it’s epoxy resin so not sure how close to Form Labs. y


#9

Since these aren’t optical parts that need precise dimensions, I would just do what you did with the IPA wash and then do a very light coating of clear coat spray to get your luster and shine back. I’ve done this on parts that have loose tolerances in clear and the parts come out amazingly glossy/clear.


#10

Thanks! The only issue im having with epoxy resins is the cured parts are turning out a bit rubbery. It may be because im mixing very small amounts for my prototyping and thus if I’m off a tiny bit it my measuring it throws off the ratio significantly. I probably need to mix larger amounts so there’s more tolerance in the mixing ratio.


#11

I like this idea. Sometimes im not happy with even the finish once a clear coat dries on other parts ive done before, but considering the lens underneath is super smooth I’d imagine the clear coating would dry super smoothly as well. I think I’ll give this a shot.


#12

Leonhart88 is correct. Below is a part that was just gone similarly… Though this was sanded with 400-800-1500 before spraying. (the wrapper it’s sitting on its only for effect/text :ok_hand:)


#13

Very nice. I shouldn’t even have to sand since I’m simply curing perfect little domes of resin, thus they’re already super smooth.


#14

Check this out; maybe it can help. I know you stated about sanding but, why not give it a try…

https://support.formlabs.com/s/article/Polishing-Clear-Resin-for-a-Transparent-Finish?language=en_US


#15

Wow! Beautiful! Curious: any reason you sanded to 1500? My understanding has always been you don’t want to go beyond a certain grit (can’t remember 220, 320, 400?) to maintain mechanical adhesion between the substrate and the spray…or?


#16

Which brand spray did you use for this impressive result!?