Easy dispersing alkali blue powder and process for manufacture

Abstract

An easy dispersing alkali blue type pigment product and a process for making the same is provided which retains the color strength per unit alkali blue present of a flushed color product, but which contains less oil phase than a flushed color and is a free-flowing powder. The pigment can be very easily dispersed in oleoresinous systems such as printing inks, paints, plastics and the like to develop an outstanding fineness of grind and substantially full color strength. The pigmentary product of this invention is free-flowing and contains at least about 50% by weight of alkali blue pigment solids, and preferably more, coprecipitated with at least one organic dispersant of the anionic class containing at least eight carbon atoms, said dispersant is soluble in aqueous alkaline solutions and precipitated therefrom upon acidification. The coprecipitated pigment and dispersant particles are fixed at spaced apart magnitudes by means of a quantity but not in excess of about 45% by weight of the pigment solids by means of a viscid water insoluble organic hydrophobic oil phase. The product is produced by forming an aqueous solution in alkaline medium of the defined dispersant and the alkali blue pigment, coprecipitating the two components by acidification. Before drying the coprecipitate, but either before or after adding an amount but not in excess of about 45% by weight of the pigmentary solids of a varnish-like hydrophobic oil phase thereto, the water-containing mass is subject to a heat treatment step at a temperature of from about 60.degree. C to about 120.degree. C, the time of heating varying somewhat with the nature of the selected dispersants, but less than 60 minutes if the selected temperature is about 100.degree. C. The heat treatment enhances the strength, color and degree of dispersion of the pigmentary product.