| abstract |
An ink composition comprising (a) water, (b) pigment particles dispersed with a dispersant or self dispersing without the need for a dispersant, (c) at least one humectant, and (d) at least one polyurethane additive which is distinct from the dispersant, having an average molecular weight of at least 10,000 and a sufficient number of acid groups to provide an acid number greater than 60, the polyurethane being present at a level of at least 10 percent by weight relative to the pigment particles and comprising a polyether segment having a molecular weight greater than 250 and less than 2900, wherein the acid groups on the polyurethane are at least partially neutralized only with a monovalent inorganic base. |