Water-based pigment dispersion, use thereof and process for the production thereof

An inkjet recording liquid containing the water-based pigment dispersion comprising 100 parts by weight of a fused polycyclic pigment, 3 to 30 parts by weight of a sulfonic acid group-containing pigment derivative and water, wherein the sulfonic acid group-containing pigment derivative has only one sulfonic acid group in a molecule of a pigment of which the type is the same as the type of the pigment to be dispersed, the sulfonic acid group forms at least one salt selected from the group consisting of ammonia salt, an organic amine salt and a salt in which at least 15% of the sulfonic acid group is liberated and the rest is a salt with monovalent metal, the content of metal ion having a valence of at least 2 in a solid matter of the above water-based pigment dispersion is 500 ppm or less, and the above pigment is dispersed in water according to electrostatic repulsion due to the sulfonic acid group-containing pigment derivative adsorbed on the particle surface of the pigment.

A process for the production of a water-based pigment dispersion, comprising a step of introducing at least one sulfonic acid group into a molecule by sulfonating a pigment, a step of obtaining a sulfonic acid group-containing pigment derivative having only one sulfonic acid group by removing a pigment derivative having at least two sulfonic acid groups from a reaction product, and a step of dispersing the sulfonic acid group-containing pigment derivative obtained in the above step and a fused polycyclic pigment having the same type pigment molecule structure as the structure of the above sulfonic acid group-containing pigment derivative in water.