Time for another look?
By Jerry Davis
Nitrogen curing is able to create an extremely hard coating surface, which is typically cured to the point where surface energies on the ink-film surface are virtually zero. In single-color applications for which nitrogen curing is specified, this is a desired effect. But for multicolor prints, it means that overprinted ink layers don't form enough electron attachments between one another, which translates to poor intercoat adhesion. If the job requires trapping or other overlapping ink layers, this is definitely not a desirable effect.
In the past, many shops became enthralled with the unique properties of nitrogen curing and adopted the technology, only to find little success when they tried to expand their capabilities with multicolor printing. One example is a company that was producing vinyl notebook covers. Attempts to print two- and three-color jobs, as well as process colors with nitrogen curing resulted in serious intercoat adhesion failure on its products.
At that time, UV curing technology was not fully understood and was, in fact, considered by many to be a form of "drying." Printers did not understand that drying involved the removal of a solvent from a coating or ink, and curing referred to a molecular realignment that changed fluid ink to polymerized film. The molecular changes that took place in nitrogen curing simply did not allow for good adhesion between overprinted colors.
The shop in the previous example struggled with nitrogen UV curing before it finally came to understand that the problem was not in its production procedures, but in the capabilities of the equipment and materials it was using. Conversion to conventional UV-curing equipment led to successful multicolor work, and the resulting lack of intercoat adhesion problems improved production rates.
The heyday of nitrogen systems came early in the UV-curing revolution, and as printers became familiar with the limitations of nitrogen-curing technology in multicolor printing, conventional curing systems began to dominate the market. Many shops retired their nitrogen-curing units to the scrap heap or sold them to eager buyers overseas. However, some nitrogen systems are still in use today, and owners of older nitrogen equipment are thinking they could place the units back in active service.
Did you enjoy this article? Click here to subscribe to the magazine.