Patent GB-987766-A (GB)
Title: Process for developing electrostatic latent images
IPC: G03G9/18
Filed: 1962-04-18
Abstract: 987,766. Electrophotography. AGFA A. G. April 18, 1962 [April 19,1961; Dec. 5, 1961; Feb. 3, 1962], No.15078/63. Heading G2H. A latent electrostatic image formed by exposure of a charged photoconductive layer on a support is developed with an aqueous developer which wets the charged areas but is repelled by the uncharged areas. The aqueous developer may be a solution of dispersion of colour material or a solution of a colourless reaction component which reacts with another component in the photoconductive layer to produce a coloured compound, and the moist developed image may be transferred by printing it on to a further support. The developer may be applied to the latent image by a roller having a screen like surface e.g. a roller of roughened soapstone, a roller having a patterned surface, or a rubber roller covered with a polyamide fabric, a fabric spread over and moistened with the aqueous developer, a sand cushion saturated with developer, a saturated cushion of nylon fabric filled with polystyrene beads, or by rolling the latent image layer attached to a roller over doctored layer of paste formed by sand and a dyestuff solution. In examples the electrophotographic material comprises a layer of a ZnO dispersion in a polysiloxane resin on a paper support developed with an aqueous solution of Crystal Violet (Ex. 1) or potassium permanganate (Ex. 2), an aqueous dispersion of a pigment with or without a water-soluble binder (Exs. 8 to 11), a solution of diethylaniline and potassium ferricyanide (Ex. 20) an acid solution of Bromophenol Blue or Bromocresol Green with subsequent treatment of the developed image with gaseous ammonia (Ex. 13), a solution of cobalt chloride subsequently turned black with sulphuretted hydrogen (Ex. 17), or an aqueous sodium hydroxide solution of α -naphthol, the colourless developed image then being contacted with a support coated with a diazo compound (Ex. 21). Alternatively the ZnO-in-silicone resin layer may also contain phenolphthalein (Ex. 12) developed with sodium hydroxide), Rose Bengal which also acts as a sensitized (Ex. 14) (developed with formic acid to give a negative image) lead acetate (Ex. 16) (developed with an alkaline solution of thioacetamide or with sodium sulphide), Crystal Violet (Ex. 15) (developed with a solution of hydrazine hydrate), sodium pyrollidinothiocarbamate (Ex. 18) (developed with ferrous ammonium sulphate solution), a diazo compound and Crystal Violet (Ex. 19) (developed with alkaline α-naphthol), or a diazo compound, α-naphthol and Crystal Violet (Ex. 22) (developed with sodium hydroxide solution). A latent image on an electrophotographic material comprising baryta paper coated with ZnO in an isocyanate modified alkyd resin may be developed with a solution of Rose Bengal (Ex. 3), a latent image on aluminium-coated paper bearing a layer of ZnO in an alkyd resin may be developed with an aqueous solution of a black dye (Ex. 4) or a solution containing tannin, gallic acid ferrous sulphate, hydrochloric acid, phenol and gum arabic (Ex. 5); while an image on aluminium-coated cellulose acetate bearing a layer of ZnO in polystyrene may be developed with ferrous ammonium citrate solution (Ex. 6) or a tannin-gallic acid-iron salt solution containing also a blue-black dye (Ex. 7).