The Effect of Water Hardness of Dampening Solutions on Printing Quality in Offset Lithography.

Even though water hardness is often mentioned in the literature as possibly disturbing the offset lithographic process, most of its effects have only been described qualitatively. The purpose of this study was to determine if water hardness actually affects print quality. A project led in 1995 by IFRA and EFPG had produced interesting results, especially when measuring contrast on samples printed on a newspaper press. Because of these results, showing a maximum contrast at intermediate levels of hardness, it was decided to look more closely into rheological properties of emulsions. Tests were carried out with 3 model inks and 5 model dampening solutions of increasing hardness. Printing tests displayed higher contrasts at 2 intermediate levels of hardness (70 and 140 PPM as CaCO3). Viscosity measurements, out of flow curves plotted at various temperatures, showed a clear drop in viscosity at these same levels of hardness. These two phenomena are not necessarily connected, but do occur in the same range of hardness. Therefore, we can say that water hardness affects the lithographic process, as well as the resulting printed product.