Evaluation of Thickness of Non-Immobilized Ink at Paper Surface in Offset Printing, 1999 Coating Conference Proceedings

P. Piette,V. Morin & C. Trehoult -- A series of printing trials was carried out to investigate how fast offset ink develops an immobilized ink layer on the paper surface. No laboratory technique is currently available to quantify this speed within the time scale of commercial printing, which is below 0.5 s, although it is of major interest in understanding back trap mottle. Printing was performed non-stop on different papers. A gap appeared suddenly in the optical density of printed sheets after changing paper, if the immobilizing speed of the ink was different on the new paper. The non-immobilized ink layer that splits at the nip exit of each blanket was evaluated by stopping ink transfer in printing unit 1. Wood-free papers were pilot coated with different coating color formulations: 100% clay and 80% calcium carbonate with 20% clay pigment composition, at different binder contents. It was shown that ink behaves differently depending on the pigment formulation. The technique can be used as a tool to evaluate the speed of ink immobilization in offset printing, in order to compare different paper qualities.