Patent GB-1390871-A (GB)
Title: Electrographic developers
IPC: H01F1/26
Filed: 1973-03-15
Abstract: 1390871 Coated particles EASTMAN KODAK CO 15 March 1973 [21 March 1972 (3)] 12551/73 Heading B2E [Also in Division G2] A magnetically attractable particulate carrier vehicle for electrographic developer compositions comprises either (A) carrier particles having cores of magnetically attractable material coated with a composition comprising a metal ion-containing alpha-olefine-carboxylic acid copolymer in which the alphaolefine is of formula RCH-CH in which R is hydrogen or alkyl and the carboxylic acid is alpha, beta-ethylenically unsaturated carboxylic acid and in which 10-90% of the carboxylic groups are in metal ion-salt form; or (B) carrier particles having cores of magnetically attractable material coated with a composition comprising a terpolymer formed from (1) vinylidene chloride, (2) acrylonitrile, methacrylonitrile or an alkyl ester of acrylic or methacrylic acid having 1-18 carbon atoms in the alkyl group, and (3) an organic compound containing a vinyl group and a carboxylic acid or sulphonic acid group; or (C) a mixture of carrier particles of types A and B. An electrographic developer composition comprises a mixture of 1-10 weight percent of electroscopic toner particles and 90-99 weight percent of carrier particles, the carrier vehicle being either (A) or (B) or (C). The composition is especially suitable for magnetic-brush development and enables the production of acceptable solid area images within a wide range of exposure attitude. The coatings may also contain finely-divided electronically - conductive particles such as carbon black. The alpha-olefine in A preferably contains an alkyl group having 1-8 carbon atoms, e.g. ethylene, propylene, butene-1, pentene-1, hexene-1, heptene-1, 3-methylbutene-1 and 4-methylpentene-1 and is preferably present in the copolymer in amount at least 50 mole percent. Preferably the carboxylic acid in A has 3-8 carbon atoms, e.g. acrylic, methacrylic, ethacrylic, itaconic, maleic, fumaric acid and esters and anhydrides thereof. The preferred metal ions are alkali metal ions. Preferred copolymers in (A) have a free acid content of less than 2 milliequivalents of 1 normal sodium hydroxide per gram of the copolymer. The preferred copolymer of (B) is a vinylidene chloride-acrylonitrileacrylic acid terpolymer containing 5-30% acrylonitrile, 2-25% by weight of acrylic acid and 55-93% vinylidene chloride. Preferably the carrier vehicle comprises 20-95% by weight of core particles (A) and from 80- 5% by weight of core particles (B). The coatings may be applied by fluidised bed, dipping, spraying, brushing. The core materials may be iron, nickel, cobalt or an alloy or mixture thereof. The core may consist of solid particles of magnetic material or may be non- magnetic particles overcoated with ferromagnetic materials, rough-surfaced or smooth-surfaced magnetically responsive particles. The toner material comprises a resin binder and a colourant. The resin may be a natural resin, e.g. balsam, calophony, shellac, colophonymodified phenol resins, synthetic resins, e.g. polycarbonates, polyvinyl chloride, poylvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl ether, polyacrylic and polymethacrylic esters, polystyrene, polyesters of phenol-formaldehyde resins, ketone resins, polyamides, polyurethanes, chlorinated rubber, polyolefines. Examples of colourants are given.