GB1303267A - - Google Patents

Abstract

1303267 Magnetic compositions EASTMAN KODAK CO 12 Feb 1970 [17 Feb 1969] 6844/70 Heading H1H [Also in Division G2] A magnetically responsive carrier particle for use in electrographic printing comprises a core of magnetic material bearing a thin continuous coating of an electrically conducting metal having a resistance to aerial oxidation greater than that of iron, the coating having been applied by a controlled self-perpetuating reduction of dissolved metal ion. Suitable core materials are ferrites and other magnetic oxides iron and ferromagnetic alloys of iron, nickel and/or cobalt. Specified coatings are Cd, Cr, Co, Cu, Au, Ni, Ag, Zn, Ru, Rh, Pa, Os, Ir, Pt or alloys thereof. The core may be coated by electroless (or catalytic chemical) plating or by electroplating. An underlying palladium or other catalytic layer may be required on the core. This may be applied by chemical displacement or vacuum deposition. The average core diameter may be 40-1200 Á, and the coating is suitably 1/20 to 100 Á thick. The proportion of toner (many specified) may be 1-10% by wt. of the composition. In examples, iron powder is electroplated with nickel, zinc or copper, and a nickel coating is electrolessly deposited over a palladium layer on (a) ironpowder, (b) a manganese-zinc ferrite, (c) chromous oxide granulated with urea formaldehyde prepolymer, (d) carbonyl iron dispersed in polyvinyl acetate. The carrier particles thus formed are mixed with black toner comprising nigrosine colourant in polystyrene binder to form developer compositions (Division G2).