The Impact of Pore Network Structure on the Absorption of Inkjet Inks, 2005 TAPPI Coating Conference

In digital inkjet printing, the ink vehicle, the continuous liquid phase, is removed by absorption into the porous network structure, which forms, for example, a coated paper surface, whilst selectively adsorbing dyestuffs or promoting a filtration of ink pigment at the coating surface. The mechanism of liquid absorption into coating pigment structures has been previously investigated [1], where it was shown that despite the presence of big pores, associated with highly porous paper surfaces, liquid is absorbed observably slower than when fine pores are also present despite an often lower porosity and permeability associated with the finer pores. This cannot be explained using the Washburn equation [2] alone but requires the inclusion of a pore differentiating mechanism [1], [3]. In this study, the absorption dynamics of three typical inkjet inks into four speciality porous coatings (a high surface area silica, a lower surface area silica, a PCC and a specially surface modified GCC) are investigated. The absorption dynamic of water at short time-scale is contrasted with the absorption behaviour of real water-based pigmented black inkjet inks. Dissolved polymers, such as surfactants, and the formation of a pigment-rich filtercake, whose forming rate and volume are dependent on the speed of initial absorption, are shown to result in retardation of the absorption dynamic.