| abstract |
A process of forming milled solid particles of a compound comprising milling solid particles of the compound in a liquid organic medium continuous phase in the presence of polymeric milling media to reduce the average size of the compound particles, wherein the liquid continuous phase comprises a solvent for the milling media polymer in the uncrosslinked form and the milling media is crosslinked sufficiently to prevent 50 vol. % swelling of the polymeric milling media in the liquid continuous phase within four hours at 25 DEG C. In various preferred embodiments of the invention, polymeric milling media having a mean particle size of less than about 100 mu m in the unswelled state (i.e., prior to addition to the liquid organic continuous phase) is used; the compound particles are milled to an average particle size of less than 100 nm; the compound comprises electrophotographic toner pigment; the liquid continuous phase comprises an ethylenically unsaturated polymerizable monomer; and the milling media polymer comprises polymerized styrene and divinylbenzene monomers. In an additional preferred embodiment of the invention wherein the compound comprises electrophotographic toner pigment and the liquid organic medium continuous phase comprises an ethylenically unsaturated polymerizable monomer, electrophotographic toner particles are formed by polymerizing the ethylenically unsaturated polymerizable monomer after the toner pigment compound is milled. It is a particularly advantageous feature of this invention that there is provided a method of preparing extremely fine solid particles of a compound free of unacceptable contamination and/or discoloration using polymeric milling media in a liquid continuous phase which is an effective solvent for the milling media polymer in uncrosslinked form. It is a further advantage of the invention to allow for preparing electrophotographic toner particles directly from a milled toner pigment particle dispersion without first needing to separate the milled particles from the liquid milling medium continuous phase. The ability to form extremely fine, e.g., less than 100 nm, size pigment particles in accordance with the invention is especially advantageous where toner particles are subsequently formed by suspension polymerization of ethylenically unsaturated monomers after milling of the pigment particles. |