Ink jet ink comprising encapsulated pigment dispersions with minimal free polymer

摘要

The present disclosure provides an inkjet ink comprising an aqueous vehicle and an encapsulated pigment dispersion. A process for encapsulating pigment dispersions is provided where a pigment is dispersed with a polymeric dispersant in an aqueous solvent system. The free polymer dispersant in the pigment dispersion is limited to less than 0.12 grams per gram of pigment. This dispersed pigment is then encapsulated by adding acrylate monomers and optionally acrylic and vinyl monomers and polymerizing. In the encapsulated pigment dispersion the weight ratio of final free polymer to polymer found to the final encapsulated pigment is less than 0.9. The free polymer dispersant is measured by a centrifugation method and the final free polymer is measured by a density gradient centrifugation method. Such encapsulated pigment dispersions may be used in inkjet inks and are stable to heat, aging test conditions, and solvent challenges. Prints from these inks have better durability.

主权项

1. An inkjet ink comprising an aqueous ink jet vehicle and an aqueous pigment dispersion, wherein said aqueous pigment dispersion is an encapsulated pigment dispersion which is prepared by the steps of:
a) dispersing a pigment using a polymeric dispersant in an aqueous vehicle wherein the polymeric dispersant not bound to the pigment is less than 0.12 grams per gram of pigment in the pigment dispersion, and the polymer dispersant bound to the pigment is less than 0.33 grams per gram of pigment, where the polymeric dispersant not bound to the pigment is measured by a centrifugation method and is not removed from said pigment dispersion before said pigment dispersion is formulated into said ink; b) adding at least one encapsulation monomer to the aqueous vehicle of step (a) to form a first dispersed pigment/encapsulation monomer/aqueous mixture and wherein the encapsulation monomer comprises acrylate monomers; c) dispersing the encapsulation monomer/aqueous mixture using high shear mixing to form a second dispersed pigment/encapsulation monomer/aqueous mixture; and d) polymerizing the encapsulation monomer by adding a polymerization initiator to the second dispersed pigment/encapsulation monomer/ aqueous mixture, wherein for the final encapsulated pigment dispersion the weight ratio of final free polymer to bound polymer is less than 0.9 and the final free polymer is measured by a density gradient centrifugation method; and wherein said polymeric dispersant is crosslinked after the pigment is dispersed and before the encapsulation monomer is added.