Tack Development: An Analysis of Ink/Paper Interaction in Offset Printing, 1994 Coating Conference Proceedings

P. A. C. Gane, E. N. Seyler

The development of tackiness of commercial offset inks on coated paper is dependent on the coating pore structure and wettability. Imbibition of the fluid phase of the ink controls the cohesive build within the ink layer. The complexity of blanket-ink-paper separation, however, is not dependent solely on ink cohesion. Improved computer control systems for data acquisition and processing on the ECC International tack tester enables detailed analysis of the separation force between blanket, ink and paper as a function of ink tack development with time. The initial rate of tack force development is related to the coating structure. A plateau frequently develops at maximum observed force, for prints on smooth microporous coatings, which is defined predominantly by the surface adhesion properties of the ink/coating interface. Initial results indicate that coating surfaced characteristics and ink type have a significant effect on the adhesive affinity of ink on a coated paper. The relationship between variations of the affinity of a coated surface for ink and print quality is illustrated by the observation that a particular offset ink used in secondary mottle testing (ECC International Ltd. Standard Test Method) shows mottle more easily than others and that same ink has also shown a relatively poor affinity for the coating surface. Furthermore, despite the conventionally slow ink setting rate of English clays in the presence of soluble binders/cobinders the affinity for ink is high when compare with U.S. clays and carbonates.