A Novel Pigment Dispersant and Surfactant For Radiation Curable Waterborne Ink Jet Inks

Abstract

The development of waterborne radiation curable ink formulations for ink jet applications is challenged by the need for hydrolytic stability. Most conventional waterborne inks are formulated in the basic pH range (pH ≥ 8). In this case, stable waterborne pigment dispersions are formulated with conventional anionic and nonionic pigment dispersants. However, if these same dispersions are used in combination with water-soluble acrylate monomers and oligomers, the basic pH often causes hydrolysis of the acrylic esters. The result is a decrease in pH, changes in viscosity, and poor overall stability. Conversely, if the basic pigment dispersions are added to the acid stable radiation curable monomer and oligomers, the dispersions become unstable, resulting in pigment flocculation and changes in viscosity. To address this dilemma, a novel radiation curable pigment dispersant and a co-functioning surfactant are introduced that yield acid stable pigment dispersions that remain stable when added to the water-soluble acrylate monomers and oligomers. The utilization of these additives is demonstrated in red, yellow, blue and black waterborne radiation curable ink jet formulations.