Imbibition behavior of offset inks Part 1: gravimetric determination of oil imbibition rate into pigmented coating structures.

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.

In this two-part paper, the authors experimentally examine the competitive rate of removal of ink vehicle from a setting commercial offset ink. The competition is established by the absorptive forces of a porous coating network acting against the progressive concentrating boundary ink film. The experiments are made gravimetrically using a compressed tablet of calcium carbonate coating pigment brought into contact with a supersource of oil (Part 1) and ink (Part 2).

The porosities of the model substrates were determined by mercury intrusion porosimetry. The authors consider effects such as polymer and ink resin size exclusion at the interface between the ink and the surface of the porous medium. Results are compared with a number of different models. A good correlation is seen with the earlier prediction of fluid loss based on the increase in ink tack observed on commercial offset paper with an ink surface interaction tester:

These supersource data confirm the finding from the thin film application that the weight fraction of oil lost from an ink is linear with time during the time when tack is increasing. In effect, the rate at which oil mass is lost from an ink decays according to an approximate inverse square law with time. The implications for print quality are discussed in relation to the dominance of a preferred network absorption pathway characterizing the initial tack rise regime. Control of this pathway dynamic in relation to the total pore volume is shown to be a major factor in controlling the press runnability performance of coated paper in relation to the development of tack. S1

Schoelkopf is a senior scientist, Gane is vice-president of research and development of paper and pigment systems, Ridgway is a senior scientist, and Spielmann is the group leader of paper research at Omya AG, CH 4665 Oftringen, Switzerland. Matthews is a reader in Applied Physical Chemistry with the Environmental and Fluids Modelling Group, Department of Environmental Sciences, University of Plymouth, PL4 8AA Devon, U.K. Email Schoelkopf at [e-mail].