Method of continuously forming an aqueous colorant dispersion using a screw extruder

A continuous process for making a pigment dispersion, the continuous process comprising:

• continuously feeding a pigment into a feed section of a screw extruder at a controlled rate in the absence of a solvent;
• continuously feeding a surfactant in solid form into the feed section of the screw extruder at a controlled rate in the absence of a solvent;
• continuously feeding water downstream of the feed section at a rate of 40 g/min to 65 g/min to emulsify the pigment and the surfactant, forming a water-in-pigment dispersion;
• continuously feeding additional water downstream of the previously fed water at a rate of 65 g/min to 90 g/min to cause a phase inversion of the water-in-pigment dispersion, forming a pigment-in-water dispersion having a solid content that is less than a solid content of the water-in-pigment dispersion;
• continuously homogenizing the pigment-in-water dispersion in the screw extruder to create a homogenous aqueous pigment dispersion;
• and
• collecting the homogenous aqueous pigment dispersion from an exit section of the screw extruder.