Offset ink tack and theology correlation Part 1: ink rheology as a function of concentration.

Application: Controlling the dynamics of a preferred network absorption pathway in relation to the total pore volume is a major factor in controlling the press runnability of coated paper in relation to the development of tack.

This study is divided into two parts, with the aim to compare visco-elastic structure relaxation of a pres-heared offset ink with observed ink tack development on a representative absorbent multi-coated paper. The methods used include oscillatory and shear rheometry in Part 1, and comparison with the SeGan Ink Surface Interaction Tester (ISIT) in Part 2. By diluting the ink with mineral oil, a plot of viscosity against solids content could be established. The viscosity of the progressively diluted ink was then extrapolated back toward increasing concentration. In this way a relation is developed between the viscous character of the ink at a given concentration and that of the ink as it will be on the substrate, i.e. effectively the ink-on-paper viscosity and solids content in respect to the tack force measurement. This novel approach allows the solids and viscous parameters of the ink to be analyzed as the initial ink setting actually occurs on real papers, as discussed in Part 2. S!

Gane is vice president, research and development, and Schoelkopf is senior scientist at OMYA AG, Oftrigen, Switzerland, and Matthews is reader in applied physical chemistry in the Department of Environmental Sciences, University of Plymouth, Devon, UK. Email Schoelkopf at [e-mail].