Color Variation in Sheetfed Offset Printing as a Function of Ink-Coated Paper Interactivity.

A series of coated papers exhibiting a wide range of interactivity with ink was prepared and printed in a variety of sheet-to-sheet sequences on a six-unit commercial sheetfed press. The measure of ink-coated paper interactivity was quantified as the rate of increase in splitting force between a controlled thickness ink film and a printing blanket over precise intervals of time. Sheet-to-sheet sequences were selected to mimic various types of multi-roll sheeting. Resultant shifts in ink density and percent trap were repetitive and predictable in direction and magnitude from differences in ink-paper interactivity. The range of ink density variation was up to 0.4 units. Percent trap varied by up to twenty-eight percent. A fundamental conclusion of the work was reached by examining the sixth printing unit, where no backtraps occur. For multicolor printing, the major effect of ink-coated paper interactivity lies primarily in film splitting phenomena subsequent to the initial film split in the printing nip. The film splits follow the fundamental form of the Walker-Fetsko equation, if one considers that both the ink available for splitting on the paper and/or on the blanket are primarily controlled by the ink-coated paper interactivity and sequence of paper interactivities presented to the press. A fundamental conclusion of the work was reached by examining the sixth printing unit, where no backtraps occur. For multicolor printing, the major effect of ink-coated paper interactivity lies primarily in film splitting phenomena subsequent to the initial film split in the printing nip. The film splits follow the fundamental form of the Walker-Fetsko equation, if one considers that both the ink available for splitting on the paper and/or on the blanket are primarily controlled by the ink-coated paper interactivity and sequence of paper interactivities presented to the press. The work confirms earlier work with respect to transitions and equilibrium in printed ink density (Robie, 1992) and is expanded in scope to potential print quality impacts resulting from multi-roll sheeting.