Patent GB-1106618-A (GB)
Title: Electrically conducting coatings
IPC: G11B5/72
Filed: 1965-04-20
Abstract: A support is coated with an electrically conducting layer by forming a solution in a volatile solvent of a semiconducting metal salt in the form of a complex with a volatile nitrile, trialkyl phosphite, or a dialkyl sulphide complexing agent, dissolving a polymeric filmforming binder in the solution with the addition of a further solvent or solvents if necessary, coating the solution on the support and drying the coated layer.  The final coating is said to constitute particles of the metal salt dispersed in the binder.  Metal salts mentioned are: cuprous iodide; silver iodide; cuprous, silver, bismuth, gold, indium, iridium, lead, nickel, palladium, rhenium, tin, tellurium and tungsten halides; cuprous, cupric and silver thiocyanates; and iodomercurates.  The complexing agent may be acetonitrile, trimethyl phosphate, diethyl sulphide.  The complexing agent may also be a solvent for the binder.  A list of suitable ketone solvents and of organic solvents to be used in ad-mixture with the ketone solvent to facilitate solubilizing of the binder material is given.  Binders mentioned are: gelatin, poly(vinyl alcohol), poly(vinyl acetate), carboxylated poly(vinylacetate) poly (vinyl acetate-erotonic acid), poly(vinyl formal), poly(vinyl acetal), poly(vinyl chloride), poly (vinyl phthalate), poly(vinyl methyl ethermaleic anhydride), poly(vinyl chloride-vinyl acetate) poly(methyl methacrylate), poly(vinyl acetalphthalate), poly(styrene-butadiene-acrylonitrile), poly(styrene-maleic acid), poly(vinylidene chloride-acrylonitrile), poly(vinylidene chloride-acrylonitrile-acrylic acid) poly(methylmethacrylate-methacrylic acid), p poly(butylmethacrylate-methacrylic acid), cellulose acetate, cellulose acetate-butyrate, cellulose acetatephthalate, cellulose ethylether-phthalate, methylcellulose, ethylcellulose, poly(methylacrylatevinylidene chloride-itaconic acid), poly(2-vinyl pyridine), cellulose acetate-diethyl amino-acetate, methyl cellulose-diethylamino acetate, poly(vinyl methyl ketone), poly (vinyl acetophenone), poly(vinyl benzophenone), poly(vinyl methyl acrylate-methacrylic acid), poly(vinyl acetate-maleic anhydride), poly (acrylonitrileacrylic acid), poly(styrene-butadiene), poly (ethylene-maleic acid), poly(4-vinyl pyridine), carboxylic esters of resin lactones, polystyrene, cellulose nitrate, polyurethanes, polyamides, phenolic resins, urea resins, melamine resins, ethyl cellulose-diethylamino acetate, basic polymers, polybasic acid polymers, polyesters, epoxy resins and alkyds.  The solution may be applied by for example whirl coating, either with or without heat, dip coating, spray coating, bead application on continuous coating machines, wick application to a continuously moving web, or hopper coating. The coated solution may be dried at ambient or elevated temperature and the dried coating further heated to improve conductivity.  The coating may contain an alkali soluble binder so that the coating is removable say by alkaline photographic developer solutions, and/or a water soluble or alkali soluble stripping layer between the support and the conductive coating may be provided e.g. using an aqueous solution of poly(vinyl methyl ether-maleic acid). The conducting layers are suitable for use as transparent, antistatic, electrically conductive surfaces or subcoatings on a variety of supports especially conductive surface coatings on an insulating support, e.g. a photographic film, a fabric or a printed surface.  They can be used for: a subcoating to serve as an electrode on an insulating support, providing a conductive base for electrophoretic application of subsequent coatings, e.g. in metal plating of insulating synthetic resins; as thin conductive electrodes in making electrical condensors, resistors and other electrical and electronic manufactures; as antistatic coatings for photograph records or magnetic record tapes; as antistatic coating for synthetic fibres and filaments, fabric webs and carpets; as conductive film coated under a photo-conductive layer in an electrophotographic element; as the conductive overcoat on an electron sensitive photographic plate on an electron recording plate; as the conductive undercoat in recording papers; as conducting layers in recording mediums.  As antistatic coatings for photographic films, the conductive coating may be used either as a surface coating or as a sub-surface coating and may be coated on the side of the support with the sensitive material or on the back side opposite the sensitive material.  A protective layer for the coating may be provided. The Examples relate to the coating of polyester films.  In Example VII, a subbed polyester film is coated with a solution containing cuprous iodide complexed with trimethyl phosphite and a methyl acrylate-vinylidene chloride-itaconic acide terpolymer and the coated polyester film was further coated with a protective polyvinyl acetate layer followed by a cellulose nitrate subbing layer a gelatin subbing layer and a gelatin-silver halide photographic emulsion of the Lippman type.  The film, especially with polyethylene terephthalate support, is said to be suitable for direct electron recording, e.g. as a recording film in an electron microscope.  The coated polyester film with or without the protective overcoat may also be coated with a photoconductive insulating layer such as a dispersion of photoconductive zinc oxide or organic compound in an insulating binder to make a photoconductive recording element.  Alternatively a photographic film is produced by coating the subbing and photographic emulsion layers on the side of the film support opposite the conductive coating which serves as an antistatic backing with or without the application of the protective coating.  Example VIII relates to a direct electron recording film comprising a polyethylene terephthalate film support subbed with a terpolymer of vinyl methacrylate, vinylidene chloride and itaconic acid, followed by a sensitive gelatin-silver bromoiodide emulsion layer containing saponin, muchloric acid as hardener and preservative, an overcoat of hardened gelatin, and finally the conductive coating.  Example IX relates to a transparent electrostatic recording film comprising a polyethylene terephthalate film support coated with a solution containing poly(vinyl formal), poly(vinyl alcohol) and poly(vinyl acetate), a polyisocyanate cross-linking agent, acrylonitrile and cuprous iodide, overcoated with a solution containing poly (vinyl butyral) having vinyl alcohol and vinyl acetate residues therein. Reference has been directed by the Comptroller to Specification 998,642.