A Concept of Ink Transfer in Printing.

Measurements of the ink transfer curves for a group of oil-based inks and coated papers at a series of speeds and pressures were described in the previous paper. Satisfactory analysis of these curves for percent ink transfer as a function of amount of ink on the plate should lead to much fuller understanding of the printing process. Examination of these data and the prints produced has led to the following concept of the mechanism of ink transfer during printing. The contact of the ink with the paper is incomplete at very low ink film thicknesses but improves rapidly with increasing ink film thickness. The paper surface has a definite capacity for taking up or immobilizing a given ink during impression. A constant fraction of the remaining, or free ink, is transferred to the paper. An equation has been derived from this concept which fits the experimental curves very well over the full range of ink film thickness. The equation's three constants may be evaluated from the data for each ink-paper combination and express the printing smoothness of the paper, the ink immobilization capacity for the ink and paper as well as the fraction of the free ink transferred. The dependence of these properties on pressure, speed, and ink and paper properties has also been studied. This equation has also been applied with equal success to the printing of boxboard.