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The Mysteries and Myths of UV Curing

(December 2006) posted on Wed Dec 27, 2006

Discover how UV inks differ from other formulations and what it takes to print and cure them successfully.

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By Bea Purcell

The last issue in using UV technology is safety. While UV inks aren't characterized by dangerous solvents, the monomers they contain can cause allergic reactions in users who are sensitive to this chemistry. Monomers used in UV inks are tested for toxicity (skin irritation) and assigned a rating from one to ten, where one is least toxic and ten most toxic. But even with low-toxicity monomers, it is always a good idea to wear protective clothing, including eye and hand protection, when handling UV inks.

Besides UV energy, UV lamps also emit very bright visible light that could be harmful to the eyes if workers are exposed to it frequently or for long periods. This is why it is important to block light from escaping through the curing-chamber conveyor openings by installing shields.

One other safety issue to keep in mind concerns ozone, which is a very unstable molecule of oxygen. Ozone is generated when an electric discharge passes through air (e.g., lightning) or when oxygen is exposed to high-intensity UV energy. Ozone generated by curing units can lead to respiratory problems for those who work near the curing units, so it's important to make sure that curing units are well vented to evacuate ozone from the work area.

UV myths

Now that we've explored the mysteries of UV technology, let's clear away the myths that surround it. These myths are widely held beliefs that, upon closer examination, are not grounded in scientific facts or principles and can't be supported by logic or practicality.

When printing multiple colors, undercure the first color to prevent it from becoming overcured when successive colors are cured. Undercured UV ink exhibits adhesion problems. When the ink layer at the bottom is not thoroughly cured, it will remain undercured regardless of how many passes it makes through the curing unit. The problem is that printing another layer of ink on top of the undercured ink will inhibit any more UV energy from penetrating to the ink interface. With undercured ink the possibility of the top layer rewetting the bottom layer is also a concern. Each and every layer of ink must be thoroughly cured.

