Dripping-onto-substrate capillary breakup extensional rheometry of low-viscosity printing inks

Abstract

In this manuscript, the capillary thinning dynamics of a series of solutions containing polymers commonly used in the coating industry as low-viscosity printing inks were studied. Four different polymer binders were studied in methyl-ethyl ketone. These included one acrylic polymer, one cellulose polymer and two vinyl polymers of different molecular weights. The dripping-onto-substrate capillary breakup extensional rheometry (CaBER-DoS) method was used to characterize the extensional rheology for solutions with viscosities as low as 3.5mPa.s. This technique is based on the measurement of the decay of a fluid filament under the influence of surface tension and has been shown to be capable of measuring relaxation times as low as 20 µs for weakly elastic liquids. The influence of the polymer concentration on the dynamics of filament breakup was investigated for each polymer solution and the results were compared to those obtained with different polymer binders. With an increase in polymer concentration, a critical polymer concentration was identified for the transition between the inertio-capillary, the visco-capillary and the elasto-capillary breakup regimes. With the onset of elasto-capillary breakup at moderate to high polymer concentrations, a delay in the filament breakup was observed due to an increase of the viscous and elastic stresses. This viscoelastic breakup delay would be detrimental to most ink jet printing applications. Within the elasto-capillary breakup regime, the transient extensional viscosity resulted in Trouton ratios ranging from just above the Newtonian limit of Tr = 3 to values close to Tr = 100.