Influence of Coating Pore Structure and Ink Set Property on Dryback in Sheet-Fed Offset Printing, 2001 Coating Conference Proceedings

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Takayuki Kishida, Kouichirou Azuma, Terunobu Fukui, Sumio Kanou--The term ink dryback denotes the decrease in the optical density after the ink has dried immediately following printing. With large dryback, it comes to be impossible to match the optical density of the printed matter to the target density.

In consideration of this, we investigated factors influencing dryback, by using commercially available matte coated paper and model-coated paper with different pigment particle sizes and latex properties. As a result, we found that dryback can be characterized as a reduction in the print density via fluid ink penetrating the coating layer with time, and we confirmed that ink penetrates the coating layer of paper by SEM observations of coated paper cross-sections. In addition, we found that dryback is influenced by the coating pore structure and ink set property, where the dryback becomes larger as the coating pore size becomes larger and as the ink set becomes slower.

With large pigment particle sizes (e.g., matte coated paper), dryback becomes larger since the ink set becomes slower the same time the coating pore size becomes larger. However, it is possible to quicken the ink set by strengthening the interaction of the latex used in the coating layer with ink solvent, and accordingly, reduce dryback.