SHEETFED DRYING/CURING SYSTEMS -- Running Hot and Cold
UV coatings lose some gloss when applied over wet inks, agrees Elinor Midlik, president of Prime UV Systems in Carol Stream, IL. When used as recommended, though, she contends that the process offers the highest measurable gloss and resistance to chemicals and abrasion. This enhances consumer appeal for applications such as catalogs, publications and packaging, according to Midlik.
"Another benefit of UV materials is that they dry instantly when exposed to the UV dryer, so finishing can be done in-line or immediately after printing," Midlik continues. "Also, in comparison to IR dryers, UV curing is a cool process so it is recommended for use with plastic substrates of all types."
Building on the benefits already mentioned, Holger Kuehn notes that UV technology is suited to applications requiring heavy ink coverage, high-gloss spot coatings or higher brilliance on uncoated stocks. Kuehn handles sales and support for IST UV-Systems at technotrans america, which assumed responsibility (in the U.S.) for sales and service of the UV equipment for sheetfed applications.
The capability does come at a price. Printing with UV inks requires that a press be dedicated to the process. It also has an impact on the operating environment.
Kuehn counters that hybrid inks are now making it much easier for sheetfed printers to enter the UV market. As the name implies, "hybrid" systems try to bridge the gap between conventional and UV printing. The technology eliminates the need for special rollers and blankets, which means a press doesn't have to be dedicated to UV printing. In addition, the inks can be applied in a wet trapping process, which reduces the number of inter-station/inter-deck UV curing units required—in comparison to a full UV setup.
Traditional UV inks have a problem wet trapping, so inter-deck UV curing is required after each unit to prevent contamination of the cylinders downstream, explains Dave Douglas, vice president of business development at Printing Research (PRI) in Dallas. "Since hybrid inks can be wet trapped, one UV curing station after the final printing unit is able to cure up to four colors in-line before the sheet enters the coater," he adds.