METHOD OF COATING CARRIER BEADS

1,239,621. Coated carrier beads. RANK XEROX Ltd. 18 June, 1968 [23 June, 1967], No. 28903/68. Heading B2E. [Also in Division G2] A method of coating the carrier beads employed in electrostatography comprises the steps of:- (a) contacting a plurality of carrier beads in a container with a mixture of a resin and a liquid; (b) agitating the beads and the mixture by simultaneously vibrating the beads and moving them as a stream in a generallycyclical path; (c) evaporating the liquid while the beads and the mixture are being agitated; and (d) recovering free flowing carrier beads coated with a resin coating. The evaporation may be aided by blowing a hot gas onto the beads and mixture or by heating the container. In a preferred embodiment the container holding the carrier beads and the resin/liquid mixture is vibrated by a device which imparts to it a regular oscillatory motion thereby causing the vibration of the individual particles relative to one another and also causing them to move with the resin/liquid mixture in a generally cyclical path. Further the carrier beads may be heated prior to contacting them with the mixture. By the term "resin" is meant a polymer, or a prepolymer or mixtures of monomers, the prepolymer or mixtures of monomers forming a polymer on evaporation of a liquid vehicle. Typical carrier bead materials are sodium chloride, ammonium chloride, aluminium potassium chloride, Rochelle salt, sodium nitrate, granular zircon, granular silicon, glass, silicon dioxide, flintshot, iron, steel, ferrite, nickel, carborundum and mixtures thereof. The resin may be a natural resin, an addition polymer or a condensation polymer of which many are listed but of which styrene-n-butyl methacrylate is particularly preferred. Any suitable solvent may be used of which toluene is preferred.