Work & Turn
Work & Turn is a term used to describe the sheetfed litho practice of printing on both sides of a substrate. Typically, the first printing pass prints one side of the substrate. A second printing press pass follows as the job is turned and fed through the press again. The second pass can commence after the first pass inks are set and/or dry enough avoiding offsetting.UV or hybrid(UV) inks are immediately cured (dry) enough to turned and second pass printed without drying time delays. Conventional sheetfed offset (litho) inks and overprint varnishes are based on resin systems and oils that set and dry by time-dependent absorption and oxidation. Spray powders are used to dust these conventional litho inks and varnishes to prevent offsetting to the adjacent sheet back, when sheets are stacked in a pile at the end of a press.
Aqueous Coating Technology
Aqueous coatings were developed to overcome the issues inherent to conventional litho inks by protectively coating them with a thin fast drying film layer. Aqueous coatings demonstrated that spray powder use could be reduced radically, or even eliminated in some cases, which was quickly seen as a plus as press room cleanliness improved. The ability to in-line print and aqueous coat and proceed directly to finishing was quickly recognized as advantageous. This manifested itself in improved pressroom workflow from printing through the die-cutting and finishing process, resulting in desirable productivity gains.
Aqueous coating technology, now into its fifth decade of use by the graphics arts industry, continues to flourish due to achieved gains in productivity. Improved productivity equals improved profitability. Significant too are the attributes of aqueous coatings; a fast-drying, smooth, glossy, tough finish.
These improved aesthetic and physical properties lead to rapid adoption by the printing industry comprised of commercial, folding carton, and label printers. The benefits of aqueous coatings were especially meaningful to the litho segment of the market.
Considering jobs that require printing both sides of the substrate, ideally, the printer wants to work & turn, printing one side of a substrate, and then immediately taking a finished pile, and turning it to print the second side. The use of fast drying aqueous coating in-line over slow drying conventional inks provided this advantage. Initially, this proved to be challenging in that blocking of the finished load was a problem always lurking.