Patent GB-564267-A (GB)
Title: Improvements in sensitive photographic materials
IPC: G03C1/053
Filed: 1943-03-01
Abstract: Sensitive photographic material comprises a support coated, without the use of a gelatine-containing subbing layer, with a light-sensitive silver emulsion in which at least 90 per cent by weight of the binder is a hydrolysed polyvinyl acetate containing above 71 per cent and up to 95 per cent by weight of acetate calculated as vinyl acetate, the remainder of the compound being substantially polyvinyl alcohol.  Small quantities of other binders may be present.  The subbing layer may be omitted altogether.  The support may be glass; cellulose ester (e.g. nitrate); metal, e.g. aluminium (including anodised aluminium) steel, stainless steel, silver, and zinc; wood; paper; stone; or cloth (including waterproofed linen).  The method of determining the acetate content is defined, and the polyvinyl acetate may be obtained by hydrolysing polyvinyl acetate of higher acetate content, e.g. "Gelva" (Registered Trade Mark) resins.  The hydrolysing may be effected by dissolving in ethyl alcohol and adding dilute caustic soda solution.  The polyvinyl acetate may be dissolved or dispersed in an aqueous organic solvent (e.g. aqueous ethyl alcohol) and the silver salt (one or more silver halides) precipitated therein.  Aqueous alcoholic solutions of silver nitrate and a halide may be added simultaneously and with stirring to an aqueous alcoholic solution of polyvinyl acetate.  An aqueous silver nitrate solution may be used.  Ammonia may be added.  A further quantity of polyvinyl acetate is added, and the emulsion washed by pouring into water.  The precipitate is dissolved in a solvent, e.g. ethyl alcohol, which may contain n-butyl alcohol or the monoethyl ether of ethylene glycol.  The emulsion may be digested at 40-60 DEG  C. with a sulphur sensitizer (e.g. allyl isothiocyanate, isopropylthiocarbamate, a thiourea, or a thiourethane).  The silver salt may be precipitated in a solution of a rather more hydrolysed polyvinyl acetate and an acetate of higher acetate content added subsequently.  The support may first be coated with cellulose nitrate lacquer which may contain a pigment, e.g. white.  The emulsion can be coated by rollers or spreaders or by spraying or brushing, and may be coated on to large, irregular, or curved metal surfaces.  The emulsion may be dye-sensitized, e.g. with 5-(1-phenyl-3-methyl-2-thiohydantion)-2-(3-ethylbenzoxazole) - dimethinemerocyanine.  The development time should be short, and neutral or acid developers may be advantageous.  The developed emulsion may be iodized or fixed.  Fixation may be accelerated by adding ethyl alcohol or by using ammonium thiosulphate or thiocyanate.  The iodizing solution may comprise an aqueous solution of potassium iodide and sodium metabisulphite.  In example 1, solutions are prepared (A) of polyvinyl acetate 85-90 per cent acetate content in ethyl alcoholic solution, industrial spirit, and water; (B) of silver nitrate ammonium hydroxide, and water; and (C) ammonium bromide, potassium iodide, industrial spirit, and water. Industrial spirit is added to solution B just before use, and solutions B and C are run separately into solution A, the addition of solution C commencing slightly before that of B.  More of the 10 per cent polyvinyl acetate solution is added, and the emulsion stirred and poured into water.  The precipitate is dispersed in spirit, a spirit solution of isopropylthiocarbamate added, and the emulsion digested at 55 DEG  C. For spraying, the emulsion may be diluted with n-butyl alcohol, ethyl acetate, and ethyl lactate.  For brushing, the mono-ethyl ether of ethylene glycol may be added.  In example 2, the ammonium hydroxide is omitted from B and added to A.  In example 3, the emulsion is prepared as in example 1 but using polyvinyl acetate of 80 per cent acetate content, and after dilution is sprayed on to anodized aluminium.  A suitable developer comprises elon, sodium sulphite, hydroquinone, sodium carbonate, and potassium bromide.  The developed emulsion may be iodized.  In example 4, polyvinyl acetate of 80 per cent acetate content is added, the ammonium hydroxide is added to solution A, and the finished emulsion is coated on to iron previously coated with cellulose nitrate from a composition comprising cellulose nitrate, trio-o-cresyl phosphate, titanium dioxide, acetone, and n-butyl acetate.  The fixation may be effected with a mixture of ammonium thiosulphate and thiocyanate.  In example 5, polyvinyl acetate of 85 or 75 per cent acetate content is used and no ammonium hydroxide is added and no digestion is effected.  Cloth impregnated with a spirit dispersion of the emulsion may be developed in a developer comprising hydroquinone, potassium metabisulphite, potassium bromide, and potassium hydroxide.  In example 6, four solutions are prepared: (A) comprising a 10 per cent ethyl alcoholic solution of polyvinyl acetate of 81 per cent acetate content, ethyl alcohol, and water; (B) silver nitrate, and water; (C) potassium bromide, potassium iodide, and water; and (D) 10 per cent ethyl alcoholic polyvinyl acetate solution, and water. Solutions B and C are added simultaneously to A.  D is added, the product is heated for 20 minutes at 40 DEG  C., poured into water, and the precipitate pressed and dispersed in a solution comprising acetone, ethylene glycol mono-ethyl ether, and water.  After adding 2-31-diethyl-41-methyl-oxathiacarbocyanine iodide as sensitizer, the emulsion is coated on paper having no baryta coating.  Fixing may be effected in hypo solution containing ethyl alcohol or in potassium cyanide solution. Specifications 542,703 and 542,704, [both in Group XX], are referred to.