Imbibition behavior of offset inks - I: gravimetric determination of oil imbibition rate into pigmented coating structures

In this first part of a two-part paper, the authors 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 film of the ink. The experiments were carried out gravimetrically with a compressed tablet of calcium carbonate coating pigment brought into contact with a supersource of oil (Part 1) and ink (Part 2). Results correlate well 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 period when tack is increasing. The rate at which oil mass is lost from an ink decays according to an approximate inverse square law with time. The initial tack rise is characterized by the dominance of a preferred network absorption pathway. 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.