Ultraviolet Curing Ink

A type of radiation-curing ink that dries, or "sets," with the application of ultraviolet light. UV curing ink vehicles are composed of fluid oligomers (small polymers), monomers (light-weight molecules that bind together to form polymers), and initiators that, when exposed to ultraviolet radiation, release free radicals (extremely reactive atoms or molecules that can destabilize other atoms or molecules and start rapid chain reactions) that cause the polymerization of the vehicle, which hardens to a dry ink film containing the pigment. UV curing inks are designed to replace heatset inks whose solvents emit potentially toxic gaseous emissions. However, UV curing inks are as much as three times the cost of regular heatset inks, and are used only in specialty printing, such as liquor cartons, cosmetic packaging, metal decoration, screen printing, and flexography.

The most common configuration of UV curing equipment is a mercury vapor lamp. Within a quartz glass tube containing charged mercury, energy is added, and the mercury is vaporized and ionized. As a result of the vaporization and ionization, the high-energy free-for-all of mercury atoms, ions, and free electrons results in excited states of many of the mercury atoms and ions. As they settle back down to their ground state, radiation is emitted. By controlling the pressure that exists in the lamp, the wavelength of the radiation that is emitted can be somewhat accurately controlled, the goal being of course to ensure that much of the radiation that is emitted falls in the ultraviolet portion of the spectrum, and at wavelengths that will be effective for ink curing. UV radiation with wavelengths of 365:366 nanometers provides the proper amount of penetration into the wet ink film to effect drying. (See Photo-Reactive Vehicle.) A newer variation of radiation curing inks, Electron Beam (EB) Curing Inks, have some advantages over UV curing inks, but although the formulation of the inks is less expensive, the EB curing equipment is more expensive. (See ["Electron Beam [EB] Curing inks"].)

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