Micromedia milling process

Abstract

A process for forming a dispersion of milled solid particles of a compound comprising forming a milling mixture of a liquid medium, milling media having an average particle size of less than or equal to about 300 microns, and a solid compound in a mixing vessel, and agitating the milling mixture with a mixer to contact the milling media and solid compound and to reduce the solid compound to a desired average particle size to form a dispersion of milled solid particles in the liquid medium, wherein the volume ratio of the milling media to the combined volume of the liquid media and solid compound in the milling mixture is less than 1, a rotor-stator mixer comprising rotor and stator elements separated by a rotor-stator gap of greater than the average particle size of the milling media and not greater than about 2.5 mm is employed to agitate the milling mixture in a milling chamber of the rotor-stator mixer, and the solid compound is milled to a volume-weighted average equivalent sphere diameter particle size of less than or equal to about 200 nm. In a preferred embodiment, the milling media is a polymeric resin having a mean particle size of less than 100 micrometers. The method enables significantly reduced levels of milling media and facilitates separation of the dispersion from the milling media in the milling mixture.