Absorption and adsorption of dye-based inkjet inks by coating layer components and the implications for print quality

Inkjet printed surfaces should have good ink fastness properties so that the printed paper can be finished and remain durable during post-treatment and use. To achieve this, the ink colorant requires adequate fixing to the paper surface. In the case of coated inkjet papers, the coating layer surface is engineered to generate good printability using parameters of pore network structure, surface area and surface chemistry of coating pigment(s), and polymer additive properties. The aim of this work was to clarify how the ionic charge, and particularly its distribution in the coating layer, combines with binder to impact on the dye fixation properties of dye-based inkjet inks. The studied pigments were a specially chosen ionically surface-inert organo silica and a modified calcium carbonate (MCC) and binders were non-ionic polyvinyl alcohol (PVOH) and anionic styrene acrylate (SA) latex. Additionally, surface treatment, by applying a cationic polymer (polyDADMAC), was used to study the effect of surface charge on the ink penetration and the resulting print quality. The absorption/adsorption of ink colorant was studied with UV-VIS spectroscopy to evaluate the absorbance resulting from ink dye mixed with model coating structure suspensions, which were prepared by grinding. sieving and suspending in aqueous dispersion. The results showed that addition of PVOH into a coating formulation based on anionically dispersed coating pigment increased the colorant absorption/adsorption. The PVOH supports interpolymer diffusion of the polar ink vehicle, which opens the polymer matrix so that the colorant can transfer into the binder network and remain there. Additionally, providing an opposite charge between the coating and inkjet ink is well known to act to bind the colorant most effectively. When applied to paper, the use of a cationic additive application specifically to the coating layer surface slowed down the ink penetration into the paper structure, by reducing coating permeability, and bound the anionic colorant at the top layer by charge interaction, so that reduced bleeding and improved water fastness could be achieved. (C) 2011 Elsevier B.V. All rights reserved.