The Effects of Paper Coating on Gravure Ink Mileage


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Renmei Xu, Yu Ju Wu, Alexandra Pekarovicova, Paul D. Fleming, and Michelle X. Wang


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An ink mileage curve is a plot of the printed optical density of an ink on a substrate as a function of ink film thickness. It is helpful to predict how much ink is needed to achieve target density and has been studied for many years. It was found that it was affected by both paper properties and ink properties. However, most of the previous research was done for offset lithographic printing and little was done for gravure printing, due to the difficulty of measuring gravure ink mileage. In our previous studies, ink mileage was measured using two methods based on the same analytical principle: the tracer method by adding a tracer into the ink, and the direct method utilizing metal ions that already exist in the ink. In this study, both of the two methods were used. The substrates used were pilot coated papers using different coating formulations. The coated papers were printed on a pilot rotogravure web press. The concentrations of copper ions in both cyan liquid ink and ink film were analyzed by atomic absorption spectroscopy (AAS) and used to calculate the amount of ink transferred to the paper. The ink was also doped with a metal ion tracer, and the amount of ink transferred was obtained in the same way. It was found that the transferred amounts of cyan pigments were higher than those of the tracer, thus the direct method is slightly more reliable. The analysis of the obtained ink film coat weight and reflection density data showed that both the Oittinen and Calabro-Savagnone model fitted the experimental data well, with the latter a little better. The relationships between regression coefficients and tested paper properties were studied. Saturation density Ds correlated with all of the tested paper properties, but not strongly. Higher roughness, air permeability, pore size, or porosity resulted in higher saturation density. Density smoothness m was found to correlate very well with roughness and air permeability. Higher roughness and air permeability resulted in lower m, thus lower density. No significant correlations were found between the ink film coat weight exponent n and tested paper properties.

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