Further Investigation into the Effect of Dampening Solution Hardness on Offset Lithography

The literature often mentions the hardness of water in dampening solutions as a possible source of problems (in terms of water pick-up, ink transfer, and deposits). A paper we presented at TAGA '97 showed that the damping water hardness had a clear effect on both the viscosity of emulsions and the contrast of printed sheets. Such results encouraged us to further investigate some rheological properties of emulsions obtained at different levels of hardness, as well as emulsification measurements, and related physico-chemical properties. The experiments, carried out in a laboratory and on a sheetfed press, involved model inks (cyan, magenta and black) and fountain solutions of different hardness. Intermediate levels of hardness (70 to 200 ppm as CaCO3) enhanced the elastic character of the cyan emulsion and improved the tone value increase on press. An increasing hardness affected the efficiency of a non ionic surfactant (ethylene oxide-propylene oxide copolymer). The dampening solutions of higher hardnesses tended to emulsify more in the inks, not only during laboratory experiments, but also during printing tests.