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AssigneeOce-van der Grinten N.V.
InventorsAdrianus M. P. Hectors, Gerardus J. Crommentuyn
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Electrically conductive developer powder for developing electrostatic images by inductive attraction is provided, with avoidance of practical disadvantages of known "one-component" developer powders, by incorporating finely divided water-insoluble quaternary ammonium salt into thermoplastic resin particles forming the powder, with or without other finely divided additives such as coloring material and/or magnetically attractable material. The specific resistance of the resin particles is lowered to between 10.sup.7 and 10.sup.11 ohm. cm by from 8 to 35% by weight of the quaternary ammonium salt, and can be lowered further by additions of fine conductive material such as carbon black. The resin particles remain sufficiently fusible even when they also contain enough magnetically attractable material, e.g. about 50% by weight, to render them transportable by a magnetic powder-applicator. A further important feature of the invention consists in preparing thermoplastic resin particles of suitable size with the quaternary ammonium salt already finely dispersed in them simply by coagulating an aqueous resin emulsion that contains one of the ions required for forming said salt, in a coagulant liquid containing the other of said ions. When so desired, the other additives can also be finely dispersed in these resin particles via the coagulant liquid.
Process for preparing developer powder consisting essentially of particles of thermoplastic resin having dispersed therein, with or without other additive, a substantially water-insoluble quaternary ammonium salt rendering said particles substantially electrically conductive, which process comprises providing an aqueous emulsion of minute thermoplastic resin particles, which emulsion contains in solution an ion that will react with a second ion to form said quaternary ammonium salt, and mixing said emulsion with a coagulant liquid that will coagulate said minute resin particles and contains said second ion in solution, thereby in the resultant mixture forming said minute resin particles into resin coagula of substantially greater size and reacting said ions to form said salt in and substantially uniformly throughout the coagula, said ions being respectively a quaternary ammonium ion and an organic acid anion that forms with said quaternary ammonium ion a quaternary ammonium salt having a solubility of less than 3% by weight in water at 25.degree. C.
Process for preparing a developer powder consisting essentially of thermoplastic resin particles containing additive material finely dispersed therein and having a specific resistance of between approximately 10.sup.5 and 10.sup.11 ohm.cm, which process comprises forming an aqueous emulsion of minute thermoplastic resin particles by emulsion-polymerization of at least one monomer in an aqueous medium in the presence of an emulsifier that provides in said medium an ion that will react with a second ion to form a substantially water-insoluble quaternary ammonium salt;
Dependencies are inferred from the claim text.