Visualisation of the distribution of offset ink components printed onto coated paper

Abstract

Abstract The design of minerals for coated papers to maximise ink hold out and printed colour density has been an area of much study over the years. It is desirable in terms of cost and press runnability to achieve the required colour density with the minimum amount of ink applied. In this work, a series of heatset offset ink components was printed separately onto a coated paper and then combined into a varnish and then a whole ink. The ink components were visualised by focused ion beam (FIB) to determine which of the ink components entered the coating layer. The ink varnish was also applied to modified thin layer chromatography (TLC) plates, which had been coated with the same coating formulation as the paper samples. The separation of the ink components on modified TLC plates was assessed using FTIR spectroscopy. The results show that ink components, which enter the coating layer after offset printing, can be visualised in the FIB instrument. An exception to this was the mineral oil, which did not remain in the coating layer after drying and placing under vacuum due to its volatile nature. It was noticed that the contrast of the FIB image increased significantly when the samples with wax dissolved in the oil were imaged, which also allowed for a very clear imaging of the porous structure of coating layer. This type of image would be excellent for fundamental studies of detailed pore structure within a coating layer. This work agrees with other published findings which show that the pigments and hard resins remain on the surface of the coating, whereas the mineral and vegetable oils are mobile and penetrate into the coating layer. Ester solvent and dissolved wax also penetrate into the coating layer.