A type of ink vehicle—the fluid carrier of the ink pigment—that dries upon contact with various types of radiation, designed to obviate the need for spray powders in sheetfed printing and to eliminate air pollution generated by the solvents in traditional heatset inks. Photo-reactive vehicles contain resins, along with monomers and special chemicals called "initiators" that, upon exposure to high amounts of ultraviolet radiation, release free radicals that polymerize and harden the vehicle, leaving behind the hard, solid resin. These inks do not require heat (but they do require UV radiation) and due to their complex chemistry tend to be much more expensive than traditional inks. However, they emit no harmful or volatile substances. There are currently two varieties of photo-reactive vehicles. See Ultraviolet (UV) Curing Ink and Electron Beam (EB) Curing Ink. (See also Vehicle.)
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