Rheological Characterization of Printing Inks: Correlations between Laboratory Measurements and Pressroom Performance

The main purpose of rheological measurements applied to printing inks is the prediction of their press perfomance. During the last two decades, inkmakers and printers have found the characterization of the viscoelasticity of printing inks increasingly useful in addition to the more straight forward flow properties. As a consequence, new quality criteria are being elaborated on the basis of this more thorough approach. However, difficulties of interpretation remain, including a certain lack of correlations between laboratory and press performance. Moreover, standardization of the test procedures is still needed. The aim of this communication is to give, on the one hand, a review of the existing techniques related to the different rheological measurements on printing inks, namely viscosity data over a wide range of shear rates, dynamic aspects, viscoelastic properties, characterization and control of offset ink emulsions and tack. On the other hand, the scientific relevance and the practical implications of the laboratory results will be discussed. Examples stemming from the study of tack of offset inks are presented.