Patent GB-585758-A (GB)
Title: Improvements in or relating to the production of photographic emulsions
IPC: G03C1/015
Filed: 1944-10-30
Abstract: 585,758. Photographic emulsions. HART, J. A. H., PANKHURST, K.'G. A., and SMITH, R. C. M. Oct. 30, 1944, Nos. 21091 and 24778. [Class 98 (ii)] . A photographic emulsion contains a complex of gelatin formed with an anion soap or a sulphonic acid containing a highly hydrophobic anion, the complex containing dispersed silver halide, dispersed in a predominantly organic solvent medium. The emulsion may have incorporated therein a proportion of another colloid which is soluble in the solvent medium already present in the emulsion or which is soluble in a solvent medium which is miscible with the solvent medium already present: The anion soap solution or a solution of the free acid corresponding thereto may be added to a gelatino silver halide emulsion and the gelatin complex allowed to sediment out. The emulsion may have a pH value (e.g. 2.5 to 3.0, or even as low as 2.0) below the isoelectric point of the gelatin, or a higher pH value and contain an electrolyte. A method is described of determining the optimum ratio of the soap to the gelatin which results in a gelatin complex of the highest solubility in organic solvents. The anion of the anion soap should be as hydrophobic as possible, and the electrolyte concentration in the solution should be as low as possible. The emulsion may be used at a pH below the isoelectric point of the gelatin and either the free acid of the anion soap added or the anion soap itself together with sufficient mineral acid to neutralize the cation of the anion soap. Anion soaps specified are soluble salts of (a) long-chain alkyl carboxylic acids, e.g. of fatty acids containing 8 or more carbon, atoms such as oleic, ricinoleic, linoleic, stearic and palmitic acids ; (b) of long-chain alkyl sulphonic acids ; (c) of sulphated higher fatty alcohols, e.g. in which the alkyl group contains at least 8 carbon atoms such as lauryl and oleyl hydrogen sulphates; (d) of sulphated secondary alcohols containing at least 8 carbon atoms in the chain ; (e) of alkylated aromatic sulphuric acids, e.g. alkyl benzene, alkyl naphthalene, and alkylated hydroxydiphenyl sulphonic acids ; and (f) of long-chain alkyl esters of sulphated succinic acid. Alkali metal (sodium or potassium), ammonium, or amine (triethanolamine or cyclohexylamine) salts may be used. The anion may contain an amino residue as in sodium oleoylaminoethanesulphonate. Numerous commercial anion soaps are specified. Sulphonic acids specified are 2 - naphthol - 1 - sulphonic acid, 1 - naphthol - 4 - sulphonic acid, anthraquinone-2-sulphonic acid, Kiton Fast Yellow 3G and Naphthalene Orange GS. The aqueous gelatino silver halide emulsion may have already been washed and digested. The organic solvent may contain hydroxy groups, e.g. methyl or ethyl alcohol, ethylene glycol.monomethyl ether, ethyl lactate, or diacetone alcohol, or may be acetone, methyl ethyl ketone, dioxane, methylene chloride, chloroform, or mesityl oxide, with or without water or methyl alcohol. Esters such as methyl .or butyl acetate, ethers such as diethyl ether, or hydrocarbons such as benzene or toluene may be added. The complex may be swollen in the organic solvent medium and dispersion facilitated by gentle warming. The additional colloid may be a cellulose ester such as cellulose nitrate or acetate or a far-hydrolysed cellulose acetate, a polyvinyl acetate or acetal, a methyl methacrylate polymer or a partially hydrolysed derivative thereof, an alkyd resin, or a interpolymer of maleic acid or anhydride with styrene or methyl methacrylate. In example 1, to a diluted aqueous gelatino silver iodobromide emulsion is added an aqueous solution of " Agral N " (Registered Trade Mark), which is essentially a sodium alkylnaphthalene sulphonate, followed by dilute hydrochloric acid. The precipitated complex is washed, dissolved in warm methyl alcohol, reprecipitated by adding water, and redissolved in warm methyl alcohol. In example 2, ethylene glycol monomethyl ether, a methyl alcohol solution of cellulose nitrate and acetone are successively added to the solution prepared according to example 1, to give an emulsion suitable for spraying on to cellulose nitrate lacquered metal. In example 3, to portions of a diluted digested and stabilized gelatino silver halide emulsion whose pH is adjusted to 3.0 by addition of acid, are added the following anion soaps: sodium dodecyl sulphate, " Gardinol 30 (Registered Trade Mark), " Agral N " (Registered Trade Mark), "Perminal N" (Registered Trade Mark), " Aresklene 375," " Teepol X," " Santomerse D," "Aresket 240 " and " Igepon T " (Registered Trade Marks). The precipitated complexes are washed, dissolved in methyl alcohol, reprecipitated with water, redissolved in methyl alcohol and coated on to glass or other supports. In example 4, Aresket 240 is added to portions of a gelatino silver halide emulsion at different dilutions. In example 5, complexes are formed with the soaps Teepol X and Santomerse D and an emulsion whose pH has been adjusted to 7.3 and to which ammonium nitrate has been added. In example 6, Aresket 240 is added to an emulsion made with an acid-processed gelatin of high isoelectric point whose pH has been adjusted to 6.0, and the pH is maintained at 6.0 by addition of hydrochloric acid. The complexes may also be dissolved in ethyl alcohol or ethylene glycol monomethyl ether. - Sensitizing dyes, sulphur sensitizers such as allyl isothiocyanate, gold salts as in Specification 570,393, stabilizers, anti-fogging agents and other agents for modifying the speed, contrast, graininess, fog level and developed image colour may be added. The emulsions may be prepared in a dry form for later redispersion in the spray-coating of lacquered metal sheets for use in the production of photographic templates by film drying, spray drying, or air drying of the emulsion in the form of a shredded set jelly, or by air-drying of the precipitate obtained by addition to water. In example 7, to a melted gelatino silver halide emulsion are successively added " Celite 204 " (purified diatomaceous earth) dispersed in aqueous gelatin solution, " Teepol X " (Registered Trade Mark) and hydrochloric acid. The precipitate is washed, dissolved in warm methyl alcohol, reprecipitated by adding water, redissolved in warm methyl alcohol, and cellulose nitrate and acetone added. The emulsion is reprecipitated by pouring into water, is shredded, soaked in water, and spread out to dry. In example 8, an emulsion prepared as in example 7 is set to a jelly, shredded into water, washed, drained and dried. The emulsion is reconstituted by allowing to swell in methyl alcohol and melting at 125‹ F. The cellulose nitrate may be omitted and the emulsion reconstituted in water or aqueous alcohol, e.g. by soaking in water containing sufficient sodium bicarbonate to neutralize the acid, and melting at 120‹ F. An emulsion for spraying may be made using the dried emulsion shreds, sodium bicarbonate, water and ethyl alcohol. In the production of silk screen stencils, the emulsion is sprayed on to stretched' silk, dried, exposed, developed in a tanning developer and washed in hot water. The development may be effected in alkaline pyrocatechol, the silk plunged into hot water and the wash-out relief image fixed in an acid fixing bath. The wash-out relief image may be prepared on a separate support and transferred to the silk. For colour photography, the emulsions may contain dyes or dyeintermediates, e.g. colour formers. Colour formers may be included in the original emulsion and precipitated with the complex, or may be added to the final emulsion. By suitable selection of an additional colloid (e.g. cellulose nitrate or a hydrophobic colloid containing acid groups), emulsions of varying degrees of developer-permeability may be made for use in multi-layer material in which the layers are developed separately by adjusting the constitution of the developers, e.g. by adding organic solvents. Colour developers containing different colour formers may be used, The emulsions, which may contain other colloids, e.g. cellulose nitrate or a methyl.methacrylatemethacrylic acid copolymer, may be used in the production of negatives to be printed from while wet. A supercoat of a plain gelatinanion soap complex, as described in Specification 585,759 may be provided. Specification 580,504 also is referred to.