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Nitrogen UV Curing

(September 1999) posted on Wed Jan 05, 2000

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By Jerry Davis

Over the years, the growth of UV curing in a non-nitrogen environment has been explosive. In the early years, any graphics shop needing to speed up the "drying" operation was a sure candidate for UV technology. Since other attributes of UV inks and coatings, such as surface hardness, scratch resistance, and textured surface were typically secondary, most printers were satisfied with the solutions offered by the developers of conventional UV inks and curing systems.

However, as the market for textured nameplates and faceplates continues to expand, increasingly stringent requirements for hardness and scratch resistance sometimes go beyond the capabilities of conventional UV curing. Products such as instrumentation displays and graphic overlays for air craft, marine, and industrial controls all face harsh environments, and as a result, nitrogen curing is once again becoming a necessity in many applications.

What is nitrogen curing?

Nitrogen curing involves curing specially formulated UV ink in an environment where the oxygen is replaced with nitrogen. Nitrogen comprises 80% of the air we breathe, so nitrogen is always present in any UV-curing process.

The remaining 20% is basically oxygen, and oxygen is a known UV inhibitor, meaning that it restricts the full UV energy of the curing system from reaching and polymerizing (curing) the ink film. In short, nitrogen curing is a process that takes place in an environment where the concentration of nitrogen is increased to exclude oxygen, consequently influencing the hardness and appearance of the cured surface.

In a nitrogen-curing system, oxygen is replaced with a pure nitrogen environment. The presence of nitrogen has no chemical impact on the curing process; it just displaces the oxygen. Take the UV-curing process into outer space, where there is no need to evacuate oxygen, and the results would be similar to what occurs with nitrogen curing.

What are the advantages of replacing the oxygen with nitrogen? Polymerization can be carried further when oxygen molecules don't interfere with the transmission of UV energy to the ink film. When UV ink polymerizes under a nitrogen blanket, the result is a very hard, very tough coating, one that lends itself to a variety of specialty surface textures.


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