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Summary:
Surface tension and rheological properties are amongst the most critical factors driving spreading and leveling of inks and coatings. In water-based systems, surfactants are commonly used to control surface tension. Due to specific interactions with the polymers present in the inks, surfactants may have a significant impact on ink rheology. The effect of the interactions between polymers (SMA(r) 1000H; SMA(r) 1440H; Joncryl(r) 63 and Joncryl(r) 89) and acetylenic diol surfactants (Surfynol(r) 104H and Surfynol(r) 440) on rheological properties of water-based inks was studied using viscosity and flow measurements. Two samples of water-based pigmented inks having good and bad printability were used. Both inks contained three different levels of solids: press ready ink; virgin ink and waterless ink (no free water added during formulation). All inks had identical composition except for the nature of the surfactant used. Effect of interactions between polymer and surfactant on the rheology of polymer-surfactant mixture seems to be dependent on chemistry of both surfactant and polymer. For a given polymer ethoxylated surfactant affected viscosity more than the non-ethoxylated one and for a given surfactant interactions with hydrophobic polymers affected viscosity more than interactions with hydrophilic polymer. Viscosity of polymer solution-surfactant mixtures could be higher, unchanged or lower than the viscosity of the virgin polymer solution. For polymer dispersion viscosity of polymer-surfactant mixture was never lower than the viscosity of the original varnish. Surfactants may affect very strongly ink flow properties at low shear rates and thus may be one of dominating factors controlling printability.