Investigation into the distribution of ink components throughout printed coated paper

Abstract

Abstract To maximise the performance of the offset litho printing process it is essential to have an understanding of the spatial arrangement of ink pigment and resin within a dry ink film. This arrangement has an effect on properties such as gloss, roughness and colour density. In the current study, the composition of a magenta process ink film printed onto kaolin coated paper substrates having different pore sizes and densities is investigated. Surface analytical techniques such as X-ray photoelectron spectroscopy (XPS) along with secondary ion mass spectroscopy (SIMS) are useful for investigating this chemical distribution in the ink film. Gentle ion etching was carried out in the z -direction through the ink film into the kaolin substrate to enable a continuous chemical analysis to be obtained. In all cases, both techniques clearly showed the presence of a hydrocarbon resin on the surface of the ink film. It was estimated that the resin thickness was approximately 35–50 nm. XPS gave some evidence that this resin thickness varied with coating porosity and ink film thickness. An initial model for this system is given and results compared with the optical and roughness measurements discussed in part 1 of this paper. SIMS showed that the ink pigment–kaolin interface was rough and it was concluded that this was due to the micro roughness of the kaolin coating. Comparison of the SIMS ink–paper interface with the micro roughness of the coating showed that none of the ink pigment penetrated into the paper coating layer. By comparison, ink films printed onto model non-porous substrates such as a polyester film showed a sharp ink–substrate interface.