The first thing that you need to consider is the absorption spectra of the photosensitive element of the emulsion. In the case of CPS Ultra Coat 535 and CPS Ultra Coat Triton this is acrylate and diazo.
Acrylate sensitiser – Combined with Diazo in dual cure emulsions
Diazo – Alone in single cure emulsions
SBQ – Photopolymer emulsions
Click on the picture to the right of this text for information on absorption spectra.
It is then necessary to match the adsorption of the photosensitive element with the lamp.
These are the common lamps that are used in UV driers. Their spectral output is in the region of 365nm and this is to match the absorbance of screen printing UV inks and varnishes.
Iron Iodide is a broad emitter and enhances the spectral output of the lamp in the 380nm region. This can be used with good effect on photopolymer (CPS Ultra Coat HB, CPS Ultra Coat 900, CPS Ultra Coat CTS-L etc) and daylight film exposure systems.
Gallium Iodide has the effect of introducing spectral lines at 403nm and 417nm of the electromagnetic spectrum. This is particularly useful with Diazo (CPS Ultra Coat 200, CPS Ultra Coat 535, CPS Ultra Coat Triton etc) type exposure processes.
Halogen lamps are used by start-up companies and hobbyist for exposing screen printing emulsions. In comparison to the above lamps, these are very inefficient for exposing emulsions as there spectral output is between 600nm and 900nm, outside the absorbance spectra of dual cure, diazo and photopolymer emulsions. This results in long exposure times and high energy usage during exposure, it could also compromise the durability of the finished stencil.
For a lamp to be suitable to cure a particular emulsion it must emit light in the region that the photosensitive component of the emulsion absorbs. So a Gallium Iodide doped lamp would not be suitable to cure a photopolymer emulsion since the photopolymer does not absorb above 400nm but the lamp mainly emits at 405 and 417nm. A Gallium Iodide lamp would be perfect for a dual cure system like CPS Ultra Coat Triton because the sensitizers absorb at 405 and 417nm and the longer wavelengths penetrate better giving better through cure than a pure mercury lamp.
Lamp information from http://www.heraeusamba.com
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Name: William Shorter
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