A device used in the manufacture of ink to disperse the solid pigment particles in the fluid ink vehicle, utilizing steel or ceramic balls to chop up the pigment particles and disperse them thoroughly. The ball mill consists of a closed horizontal metal cylinder, containing the balls at the bottom. The ink slurry is put into the machine to partially fill the cylinder. The cylinder is rotated, and the tumbling of the balls generates frictional forces which break up and disperse the pigment particles. The nature of the sealed cylinder makes ball milling well-suited for the processing of inks containing highly-volatile solvents which would be likely to evaporate and escape from the mixture in an open system. Inks used in flexography and gravure printing, which have thin, volatile, solvent-based vehicles, are commonly produced in ball mills. The longer the slurry remains in the mill, the more finely the particles are broken up. Often, geometrical shapes other than spheres can be utilized. (See also Three-Roll Mill, Sand/Shot Mill, and Colloid Mill.)
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