Transparent pigment dispersion process

Claim 1

A process for preparing a transparent pigment dispersion which comprises A. in a first stage, dispersing a pigment selected from at least one member of the group consisting of iron oxide, phthalocyanine green, phthalocyanine blue, anthrapyrimidine yellow, flavanthrone yellow, imidazole orange, quinacridone red, carbozole blue, dioxazine blue, indanthrene blue, azo browns, isoindolinones and high molecular weight azo pigments in an acrylic resin solution, wherein the acrylic resin is a film-forming acrylic copolymer made by polymerizing acrylic monomers with a free radical producing catalyst, in a pigment to resin ratio of about 2.5:1 to about 3.5:1 and at a solids content of about 55 to about 65 weight percent using as solvents aromatic hydrocarbons and oxygenated solvents having boiling points above 240° F., under high speed, high shear, high impact conditions so that the temperature rises from room temperature to 200° to 240° F. over a period of at least 3 hours, the shear stress increases from about 300 to 600 gm./cm.sec. 2 to about 5,000 to 6,000 gm./cm.sec. 2 , the flow of the dispersion changes from turbulent to laminar flow as measured by a Reynolds Number change of about 25,000 to about 30,000 down to about 1,500 to about 2,500; and B. in a second stage at a pigment to resin ratio of about 0.5 to about 1 at a solids content of about 50 to about 65 weight percent, completing the dispersion of pigment to a fineness of 8 as measured on a Hegman scale under conditions of maximized shear and minimized impact for a period of about 12 to about 25 hours at a temperature of about 90° to about 140° F.