Short Time Spreading of Offset Printing Liquids

Liquid–solid interactions are important for numerous natural and industrial processes in agriculture, coating, filtration, painting and printing. Understanding the effects of sequential absorption of oil components and water, in various arrangements, on porous coatings during the very short time it takes for a paper to pass through a printing machine is a prerequisite for a successful printing operation. Phenomena in the printing nip occur under far from equilibrium conditions, and therefore the interactions of liquids with the coating should also be studied in nonequilibrium conditions. When a droplet of liquid is placed on a surface its spreading is controlled by the balance of driving and resisting forces. The driving force for initial impact spreading is kinetic energy of the droplet, whereas flow resistance is provided by viscosity and surface tension of the liquid. As the kinetic energy of the impact dissipates, the wetting forces become important. Spreading of a liquid on a specific solid surface is also influenced by chemical heterogeneity and surface topography. On porous surfaces, the spreading mechanics is further complicated by capillary absorption into the porous structure. Numerous studies have investigated both droplet spreading on non-porous surfaces and liquid absorption into porous structures [1–8]. Simultaneous spreading and absorption has not received as much attention. Computational modeling of liquid spreading and sorption on a porous surface utilizing lubrication approximation has been done for example by Davis et al. [9] and Alleborn and Raszillier on thick [10] and layered [11] substrates. Volume-of-fluid method has been used to study the droplet impact spreading and absorption on horizontal and inclined solid surfaces [12], over saturated pores [13] and on topographically irregular surfaces [14].