Patent GB-580504-A (GB)
Title: Improvements in or relating to the production of photographic silver halide emulsions
IPC: G03C1/015
Filed: 1944-07-04
Abstract: 580,504. Photographic emulsions. WALLER, C., and WOOSLEY, D. P. July 4, 1944, No. 12688. [Class 98 (ii)] An organic complex containing silver halide in suspension is produced by forming a suspension of silver halide in an aqueous solution of gelatin or other protein colloid and adding thereto at low pH value or in the presence of an electrolyte, sufficient of an anion soap to cause precipitation of the protein phase containing the silver halide, and separating the so-formed protein/anion soap complex containing silver halide. The complex may be washed and re-dispersed in an aqueous medium. The complex may be re-precipitated by addition of an organic non-solvent, washed, and redispersed in an aqueous medium. The emulsion may be ripened before addition of the anion soap and digested after re-dispersion in an aqueous medium. The precipitated complex may be dried,to form a particle emulsion. The pH of the emulsion should not be greater than the isoelectric point of the protein employed. The anion soap may be a soluble salt of a long-chain alkyl carboxylic acid, e.g. a fatty acid containing 8 or more carbon atoms such as oleic, ricinoleic; linoleic, stearic, and palmitic acids, a soluble salt of a long-chain alkyl sulphonic acid, a soluble salt of a sulphated higher fatty alcohol, e.g. of lauryl or oleyl hydrogen sulphate, a soluble salt of a sulphated secondary alcohol containing at least 8 carbon atoms. in the chain, a soluble salt of an alkylated aromatic sulphonic acid, e.g. of an alkyl benzene sulphonic acid, alkyl naphthalene sulphonic acid, or alkylated hydroxydiphenyl sulphonic acid, or a soluble salt of a long-chain alkyl ester of sulphated succinic acid. The soluble salt may be an alkali metal (N or K), ammonium, or amine (triethanolamine or cyclohexylamine) salt. The soap may contain an amino-substituted anion, e.g. sodium oleoylaminoethane sulphonate. The compounds known under the Registered Trade Marks " Agral " N, " Dispersol " RT, " Gardinol," " Igepon T, "Lissapol" A or C, " Lissatan " A, " Nekal " A or BX, " Perminal" W, or sulphonated " Lorol " TA, NH, or CY or '' Ocenol," and the compounds Aerosol OT, Aresklene 375, Lohrinol, Santomerse D, Teepol, or Tergitol 4 or 7 may be used.. Electrolytes specified are ammonium nitrate, sodium chloride, magnesium sulphate, and potassium citrate. A table is given for the amounts of the anion soaps sodium dodecylsulphate, sodium tetradecyl sulphate, sodium hexadecyl sulphate, and triethanolamine laurylsulphate to cause precipitation of the protein phase with and without silver halide. The separated protein phase may be re-dispersed, with or without previous washing, in a suitable liquid, e.g. predominantly aqueous ethyl alcohol or an aqueous ethyl alcoholic gelatin solution, reprecipitated by adding excess organic non- solvent, e.g. ethyl alcohol, and then washed. In example 1, complexes are formed by adding aqueous solutions of (a) triethanolamine laurylsulphate, (b) " Nekal A " (Registered Trade Mark), and (c) Aresklene 375 to an aqueous gelatino silver iodobromide emulsion containing ammonium nitrate. The pH of the emulsion may be adjusted to 9.5 by adding ammonia. The precipitated complexes may be redispersed in warm water, in warm aqueous alcohol, or in warm gelatin solution. In example 2, complexes are formed by adding the same aqueous solutions to an aqueous gelatino silver iodobromide emulsion whose pH has been adjusted to 2.2 by addition of dilute sulphuric acid, and may be redispersed in weak alkali solution (e.g. aqueous borax) or in warm gelatin solution. In example 3, " Teepol " (Registered Trade Mark), which is an aqueous solution of a mixture of secondary sodium alkyl (mainly dodecyl and tetradecyl) sulphates, is added to an aqueous gelatino silver halide emulsion containing ammonium nitrate, ammonium bromide, and ammonia, and the precipitated complex is dispersed in an aqueous ethyl alcoholic gelatin solution, is reprecipitated by addition of ethyl alcohol, is soaked in water, and redispersed in gelatin. The anion soap may be added in in successive portions, the suspension being allowed to settle between the additions. The precipitated complex may be dried. Albumen or casein silver halide emulsions may be similarly treated.