Commercial Six-Color Press Runnability and the Rate of Ink-Tack Build as Related to the Latex Polymer Solubility Parameter, 1994 Coating Conference Proceedings
R. L. Van Gilder, R. D. Purfeerst
Commercial offset printing presses in the United States are running faster, using six or more color stations and using faster-setting inks. These changes can result in a greater occurrence of coating pick, commonly referred to as carry-over piling and tail-edge picking, during web and sheet-offset printing. For web-offset printing in particular, coating pick has prevented the use of linear (low gel) carboxylated styrene (s) butadiene (B) latex polymers in the coating for superior blister resistance.
Coating pick problems, particularly on commercial presses with six or more color stations, usually result when the rate of ink-tack build is too fast. The rate of ink-tack build, in this work, was related to the degree of latex polymer solubility in the ink solvents and its influence on the ink latex film interaction.
The solubility of the latex polymer was shown to be dependent both on the physical state of the polymer (linear vs. cross-linked) as well as the chemical structure (surface energy/polarity level). By increasing the solubility parameter of the polymer further away from that of the ink solvents, the interaction of the ink with the polymer film could be decreased. This required modifying the latex polymer to a higher surface energy/polarity level. As a result, the rate of ink-tack build was reduced significantly and the coatings ran on the commercial six-color presses without coating pick.