Time for another look?
By Jerry Davis
Nitrogen concentration An even concentration of nitrogen yields the most consistent results. Older nitrogen-curing units introduced nitrogen to the curing area with a nitrogen knife. But this arrangement was vulnerable to variations in nitrogen concentration created by air movements outside of the total system. For example, a fan or fast-moving forklift outside the curing chamber was often sufficient to disturb the nitrogen within and affect the textured appearance of the ink film. Newer designs use alternate methods to introduce nitrogen in the curing area and are much more successful at maintaining a proper concentration.
Ink chemistry Inks are specially formulated for nitrogen curing. These inks contain a different photoinitiator balance than you would find in conventional UV inks because the nitrogen doesn't inhibit the UV energy and allows the ink to cure more quickly and completely. In other words, the inks are tuned specifically for the nitrogen environment.
Little published documentation exists about the correlation between texture characteristics and processing conditions. Most curing parameters come from empirical data that individual users gather at their job site. Not surprisingly, those printers who have developed successful nitrogen-curing procedures have been very reluctant to share their hard-won data.
The ability to create a textured surface with nitrogen curing has made it attractive for those who print nameplates and overlays used in industrial manufacturing. Producers of appliances, autos, aircraft, water craft, and medical instruments value the hardness and durability of nitrogen-cured coatings, as well as the unique textures they provide. On a graphic panel, these textured areas help users distinguish between information zones and data entry or control points, such as membrane-switch buttons on a dashboard, gas pump, or industrial machine.
The last 15-20 years has seen explosive growth in the use of UV curing. It has moved from a specialty process for applications such as hardcoating and texturing to a favored method for printing everything from demanding electronic components to colorful display graphics. But as UV curing found its way into more graphics-oriented shops, printers soon discovered that the strengths of nitrogen curing were not always beneficial, particularly in multicolor applications.
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