By: Mark Fitzgerald New keyless inker holds promise for single-fluid lithography sp.
NEWSPAPER PRESSMAKERS ARE on the verge of realizing single-fluid lithography, which needs no dampener, is not sensitive to operating temperatures or speeds ? and prints with today's low-cost litho plates. That was the contention of Goss Newspaper Products vice president and general manager P. Michael Kienzle in a presentation at this year's Nexpo in Las Vegas. Recently introduced "positive feed" keyless offset technology has eliminated a big barrier to single-fluid lithography, Kienzle said. Previous attempts to move to single-fluid lithography, he said, foundered because most early-generation keyless offset systems used anilox metering. These systems impose their greatest shear rate (which determines when water separates from ink in an emulsion) at the metering point between the doctor blade and the anilox roller. "An ink and water mixture stable enough to survive this encounter will be too stable to separate properly at the plate," Kienzle said. " Conversely, less-stable emulsions will separate at the doctor blade, introducing free water at this critical metering point." Kienzle said this problem can be overcome with a technology that feeds the ink-water emulsion into the keyless system in such a way that the emulsion encounters its greatest shear rate in the plate-to-form roller nip. "In this system, the fluid is a controlled emulsion instead of the circumstantially generated emulsion inherent in keyless offset systems with dampeners," he said. Rockwell's just-introduced Goss Newsliner employs positive feed keyless offset. Another key to single-fluid lithography, Kienzle said, will be finding a way to generate an emulsion with a controlled water content and controlled dispersion of the water throughout the ink. This emulsion would contain a minimum amount of water, which would be dispersed so that it is readily released at the plate, but nowhere else. This is under development, Kienzle said. "Full-scale experiments conducted on a Goss Colorliner modified to incorporate a positive-feed keyless inker have demonstrated that single-fluid lithography can be accomplished at double-width press speeds with no need for temperature controls, and no need for special plate technologies," Kienzle said. "Remembering that dampening has always been a weak link in the ever-strengthening chain forged by offset lithography," Kienzle said, "single-fluid lithography carries the promise of ultimate elimination of this weak link without the need to sacrifice one of offset's greatest advantages: the low-cost litho plate."