GB998642A - Electrically conducting coatings - Google Patents

Abstract

An electrically conducting layer comprising a colloidal dispersion of a semi-conducting metal salt in a polymeric binder, wherein the salt particles are less than one-tenth of a micron in diameter, is formed on a support by preparing a coating solution comprising a solution or a colloidal dispersion of particles less than one-hundredth of a micron in diameter of the semi-conducting metal salt and the polymeric binder, coating the support with the solution and drying. Dispersions of semi-conductors in polymeric binders may be prepared by grinding the solids in a colloid mill to obtain particles of appropriate size, or by precipitating the semi-conductor in the form of a sol or colloid having particles of appropriate size. Preferably, the coating is prepared by dissolving the semi-conducting metal salt in a solvent or solvent mixture as a complex compound with a solubilizing agent and subsequently dissolving the polymeric binder in the solution or adding the polymeric binder to the solution dissolved in a solvent. The polymeric binder may be dissolved in a solvent or solvent mixture or may be a latex dispersion in water. The coated layer may be treated, e.g. by heating or washing with water, acidic, basic, or salt solutions or organic solvents, to remove or decompose the solubilizing agent. The conducting layer may be transparent and may be heated to reduce the resistivity of the layer. The surface resistivity may be less than 1010 ohms per square. The coated layer may be overcoated with a thin layer of a water-impermeable polymer. Semi-conducting metal salts specified are the halides of silver, copper, nickel, palladium, indium, tin, tellurium, tungsten, rhenium, iridium, gold, lead, and bismuth. The solubilizing or complexing agent may be an alkali metal halide or a mixture thereof, such as the fluoride, chloride, bromide or iodide of lithium, sodium, potassium, rubidium, caesium, or ammonium; the fluoride, chloride, bromide or iodide of beryllium, magnesium, calcium, strontium, barium, boron, aluminium, scandium, yttrium, or lanthanum; fluorine, chlorine, bromine or iodine; hydrogen fluoride, chloride, bromide, or iodide; interhalogen compounds such as iodine monochloride; halogen-substituted organic compounds such as iodomethane, iodoform, di- and tetra-iodomethane, tetra bromo- and tetra chloro - methane; quaternary ammonium iodides such as N,N-dimethyl-N,N-didodecyl ammonium iodide, N - methyl - N,N,N - tridodecyl ammonium iodide, N,N,N-trimethyl-N-dodecyl ammonium iodide, ethylene bis(dimethyl, 5,5,7,7, tetra methyl-2-octenyl ammonium iodide) and ethylene bis(dimethyl dodecyl ammonium iodide); quaternized polymers; ammonia, amines, cyanides, thiocyanates, organic acids, urea, thiourea or thiosulphates, or mixtures thereof. The complexing agent may be added as a separate entity or may be a substituent group on a polymer molecule which may comprise the binder. The polymeric binder may be polyvinyl-acetate, -acetal, -chloride, -phthalate, -acetophenone, -benzophenone, -acetal phthalate, -methyl ketone; carboxylated polyvinyl acetate; polyvinylidene chloride, poly(vinyl methyl ether-maleic anhydride), polymethyl methacrylate, poly(styrene-butadiene-acrylonitrile), poly(styrene-maleic acid), poly-(vinylidene chloride-acrylonitrile), poly(methyl or butyl methacrylate-methacrylic acid), poly-(methyl acrylate-vinylidene chloride-itaconic acid), poly-2- and -4-vinyl pyridine, poly(vinyl methyl acrylate-methacrylic acid), poly(vinyl acetate-maleic anhydride), poly(acrylonitrile-acrylic acid), poly(styrene-butadiene), poly-(ethylene-maleic acid), polystyrene, polyurethane, polyamide, phenolic, urea, melamine, epoxy, alkyd and polyester resins, polybasic acid polymers, carboxylic esters of resinic lactones; cellulose acetate, acetate - butyrate, acetate-phthalate, ethyl ether phthalate, acetate-diethylamino-acetate, nitrate, methyl and ethyl cellulose, methyl and ethyl cellulose diethylamino-acetate. Water-impermeable polymers are poly(vinylidene chloride-vinyl chloride or acrylonitrile), polystyrene, polymethyl-methacrylate and polyvinyl chloride. Organic solvents are ethylene diamine, ethanolamine, pyridine, acetonitrile, dimethyl formamide, methyl sulphoxide, N-methyl-2-pyrrolidone, acetone, methyl ethyl ketone, 2- and 3-pentanone, 2- and 3-hexanone, 2- and 4-heptanone, methyl and ethyl isopropyl ketone, diisopropyl ketone, methyl isobutyl ketone, methyl t-butyl ketone, diacetyl, acetyl-acetone, diacetone alcohol, mesityl oxide, chloroacetone, cyclo-pentanone and hexanone, acetophenone, and benzophenone, methyl, ethyl, n-propyl, n-butyl, iso-propyl or iso-amyl acetate, tetrahydrofuran, dimethyl formamide, ethyl lactate, methyl "Cellosolve" (Registered Trade Mark) and methyl "Cellosolve" acetate. Non-solvents may be included in the solvent system, such as water, alcohols, ethers, esters, the "Cellosolve" solvents, paraffinic, cyclic and aromatic hydrocarbons, and heterocyclic compounds. The support may be of paper, cellulose, cellulose esters or mixed esters, acrylics, alkyds, polyesters and vinyl polymers, e.g. cellulose acetate, polystyrene, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, nylon, "Orlon", "Dacron", and "Saran" (Registered Trade Marks). The support may be pretreated, e.g. by alkali hydrolysis, oxidizing acids, flame treatment, electrical treatments, precoating or by silane monolayer application. The coating may be applied to filaments or textiles, or to a photographic film support carrying a photographic silver halide emulsion layer on the other side.