Quote:
Originally Posted by Off in the Bushes
I don't understand, so if the light isn't strong enough then the glue doesn't full cure fast enough leaving it tacky? Isn't UV light just UV light.
|
OO OO OO. I know the answer to this one. I guess I even literally wrote a book about it (although nobody really reads graduate theses)
I was about to ask about your light source and then likely suggest something more powerful.
The sliminess and tackiness is because there are non-reacted resin molecules floating around
UV light is indeed UV light. When light interacts with a substance, there are 3 possible basic reactions: it can be transmitted, reflected/scattered, or absorbed.
There are also 2 critical metrics in quantifying light---total power and power density. A 100W incandescent light bulb is pretty bright to look at. A 100W laser will permanently ruin your eyes. This is because the a laser has a much higher power density, with the light energy basically focussing on a pin point.
The resin curing is a photochemical reaction. This means that the photon is
absorbed and the energy is used to convert the resin from liquid to solid.
When light is used as a tool, there are 2 basic categories: diagnostic uses or therapy/treatment. As a rule of thumb, diagnostic purposes use a much lower power intensity than therapy.
For the sake of diagnosis, like leak detection or the ones used in forensics, the purpose is to give a widely dispersed beam to cover a great deal of area. As well, diagnostic purposes are usually photophysical reactions leave the illuminated area unchanged, usually just using fluorescence of phosphorescence. These lights are only meant to react to a thin layer of external compounds, only penetrating 0.1-0.2mm
As a real world example, think of the x-rays. Diagnostic x-rays are much lower powered compared to the x-rays used to treat cancer---they are the same x-rays though. Not only are the treatment x-rays much more powerful, they are focussed, giving a much higher power density and penetrate deep into the body
While the UV resin look clear(ish), it is absorbing the UV photons. The penetration of photons into matter is an exponential decay. In order to penetrate more than 0.2mm, you need an exponentially more powerful light source. Sometimes, this means focussing several lower powered light sources or using a single powerful light source. For fly tying, a single powerful source is much more practical.
I use a 7W single LED source. It takes about 10 seconds with fresh batteries to fully cure about 1mm Loon Thin UV resin.