# Best UV flashlight for curing adhesives



## PhotonWrangler (Dec 31, 2021)

I recently purchased some UV curing optical adhesive for an application where I need to attach an IR transmitter to the bezel of a TV. It used to be attached by silicone caulk but that eventually softened up from the heat of the TV and succumbed to gravity, so I'm trying this route.

Anyway I thought the light from my Tattu 365nm flashlight would be enough to cure it, but after a minute or so of exposure the adhesive remains tacky and un-cured. I think I need to improve on a few parameters here -

1) Focus. The output beam of the Tattu is splotchy. I kept the hotspot focused on the adhesive but there was so much random spill that I'm not getting all of the optical power focused where I need it.

2) Output power. Is there a stronger focused light that's better for UV curing?

3) Wavelength. Is 365nm a good wavelength for UV curing, or should I be looking at something else?

Any advice is greatly appreciated! BTW this isn't Norland adhesive. It's a no-name LOCA adhesive.


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## PhotonWrangler (Jan 1, 2022)

Well after some research I've learned that shorter wavelengths are better for curing the surface of an adhesive but longer wavelengths are better for penetrating a thick layer of the stuff. This makes sense to me and explains why my tests with a 365nm flashlight produced a dry, more or less cured skin with a gooey not-so-cured layer underneath. Looks like I need to use soemthing between 400 nm violet and dental blue.


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## PhotonWrangler (Jan 8, 2022)

PhotonWrangler said:


> Well after some research I've learned that shorter wavelengths are better for curing the surface of an adhesive but longer wavelengths are better for penetrating a thick layer of the stuff. This makes sense to me and explains why my tests with a 365nm flashlight produced a dry, more or less cured skin with a gooey not-so-cured layer underneath. Looks like I need to use something between 400 nm violet and dental blue.


After some more research online it seems that the sweet spot for my application is around 405nm, what most call near-uv and some call UVV (UV-Violet). The latter is a new acronym for me.

Anyway it dawned on me that I bought a 405nm violet laser pointer a few years ago for the novelty value and to see if it could fluoresce some minerals. I found that this cured my adhesive much faster and more thoroughly than the other LEDs that I tried. Now I'm tempted to open up the pointer and see if I can throw off the focal point a little bit to get a wider beam.


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## datiLED (Jan 8, 2022)

This is interesting. I have used 365nm UV LEDs to cure Norland optical adhesive, and they cured fully in a matter of seconds. Even a thick drop (about 2mm tall) can be cured in 30 seconds, or so. What brand of adhesive did you use? Does it have good shear strength?


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## PhotonWrangler (Jan 8, 2022)

This was an off-brand that I found online, not Norland or Bondic. For all I know it could be repackaged 3D resin printing fluid. I was looking for something that could bond with plastic and cure optically clear as that was my use case.

I should probably look into Norland. I rejected Bondic for this case as it cures with a yellow tint.


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## alpg88 (Feb 7, 2022)

i use convoy 365nm with LG led to cure a resin. works great. it works great with glue, and 3 printing resin.


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