UV curing glue

[Phil1977]

Hi,

I hope this section is the right one for the question: I frequently use UV-curing glue like acrylic resin or the K-300 glass glue which AFAIK is based on cyanoacrylate.

The acrylic resin has a wonderful hardness and mostly produces a non-sticky surface that seems to be safe to touch directly after curing. The disadvantage of the acrylic resin is that it is not primarily intended to be a glue, and so it has no good adhesion to smooth surfaces like metal or even other plastics.

The K-300 type has much better adhesion on different surfaces, but all variations I tested so far release a sticky and/or oily film on the cured material that smells a little bit like Marzipan. It´s really nasty on the skin and even if you wash it from the parts and from your hands it feels not safe to be in contact with these substances.

Do you know a UV-activated glue with good adhesion and with surfaces that are dry and clean?

[thm_w]

I have similar issues with a "UV resin hard" where it has the oily film after curing.
K-300 is not cyanoacrylate based, its acrylic resin: https://kafuterthailand.com/en/k-300uv-2/

There is also K-302 and K-303.
Supposedly:
- K-300 best for large area of glass and crystal
- K-302 glass and glass, glass and metal, glass and wood
- K-303 PMMA, acrylic, glass, metal, plastic, ABS, PVC, PC
- K-3181 all around use

Maybe worth investigating:
https://www.permabond.com/products/uv-glue-uv-adhesive/
https://www.masterbond.com/products/uv-adhesives
https://www.henkel-adhesives.com/ca/en/products/industrial-adhesives/uv-adhesives-light-cure-adhesives.html
https://www.aliexpress.com/item/1005004677489423.html

[jpanhalt]

Disclaimer:  I have never used any of the adhesives mentioned by Phil.

That said, what you describe sounds similar to the difference between polyester and epoxy 2-part resins.  Polyester is initiated by a peroxide; epoxy by a much larger amount of reactive hardener.  Free-radical reactions are inhibited by air and water.  Most polyester resins contain a little wax, which floats to the surface and blocks water and oxygen.  Polyester without wax stays sticky, but resin below the surface gets hard.  Epoxy will cure thoroughly even under water.

This describes the curing in more depth: https://www.galindberg.se/en/Inspiration_and_knowledge/UV-curing-acrylic-vs-UV-curing-epoxy.  The second to last reference above addresses the same thing.  (Loctite anaerobic thread locker is an extreme example of inhibition of curing by oxygen.)

I suggest looking for a UV curing epoxy adhesive.

[thm_w]

Good tip, a few:
https://www.newport.com/f/uv-curing-epoxy 6g for $40
https://www.epotek.com/products/uv-and-uv-hybrid-epoxies/ - cant find any pricing

Looking at the loctite page they all said acrylic except this one:
Loctite 4310 https://www.henkel-adhesives.com/ca/en/product/light-curing-adhesives/loctite_4310.html - IS cyanoacrylate, says it will cure in dark areas, so UV is just an accelerator - 26g for $86

Lots more here to look through: https://www.ellsworth.com/products/adhesives/?category=Adhesives-UV-Curing

[Phil1977]

Thanks a lot for all the tips!

This oxygen inhibition is exactly what I have experienced. Results with the K-300 get much better by using a strong 365nm UV-light and by covering open glue surfaces with wrapping foil.

Epoxy based glues seem to be a good choice for even more demanding tasks. Especially the possibility to cure by UV and by heat sounds great, so you could fix things manually with the UV-light and then put it into an oven to get really strong. But the pricing and the low-temperature storage make these glues something I would only buy exactly when needed.