Hi,
Irgacure 500 is a combination of Benzophenone and Irgacure 184, which absorbs at around 250 nm and 360 nm. For the photo polymerization reaction, which one I should use for irradiation?
Short wavelength? or Long Wavelength?
Broad band sources such as mercury lamps are usually used for two component systems like this. You need radiation at or below 360 nm.
Short wavelength, i.e. a medium pressure mercury lamp. The mixture has peak absorbance at 249nm so is readily activated by the lamp's emission band at 254nm. The mixture does absorb at longer wavelengths in the region of lamp emission band at 313nm, but it is much weaker. The 84 component is there for for surface cure while benzophenone effects depth cure - the latter needs an amine synergist present to be effective. You could use longer wavelengths, e.g. 365nm from LED, but only if you add a suitable sensitiser, e.g. 0.1-1.0% of a thioxanthone-derived sensitiser.
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