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Summary:
Ink mileage curves have been studied for many years. Several models for curve fitting have been reported by different researchers. The regression coefficients derived from curve fitting were found to be very useful for comparing different inks, and were related to some properties of ink and paper. However, these models were based on the experimental data of prints made on IGT and/or Prufbau printability tester using offset inks. The quantity of transferred ink and hence the amount of ink on paper was determined by the weight difference of the printing disc before and after printing. Therefore, these models may not be applied to the ink mileage behavior of other ink types, nor on commercial printing presses. In this study, five coated papers for rotogravure were used as testing substrates, and printed on a Cerutti rotogravure web press. Commercial toluene based gravure coated inks were marked with a selected tracer, which can be detected after printing by means of Inductively Coupled Argon Plasma (ICAP/ICP) Atomic Emission Spectroscopy (AES). The amount of ink transferred was calculated from the ICP analyses of both wet ink and printed samples. The optical densities at different tone areas were measured with reference to the optical density of unprinted paper. The ink film thickness and optical density data were fitted using different models with OriginPro 7.5 software. The degree of fit was determined by the sum of the square of residuals and the distribution of residuals around zero point. Both Oittinen and Calabro-Savagnone models fitted the experimental data equally well. The regression coefficients derived from curve fitting were related to paper properties, such as surface roughness, gloss, porosity, and pore size. It was found that the Ds, m, and n parameters were correlated with porosity and pore size.