Patent GB-631243-A (GB)
Title: Improvements in sensitive photographic emulsions
IPC: G03C1/09
Filed: 1946-09-03
Abstract: 631,243. Photographic silver halide emulsions. KODAK, Ltd. (Eastman Kodak Co., Tarkington, R. G., and Lowe, W. G.). Sept. 3, 1946, No. 26450. [Class 98 (ii)] A non-gelatin silver halide emulsion has sensitivity increased by treatment with a soluble gold compound (e.g. auric chloride or sulphate ; potassium or sodium aurichloride, auribromide, or auri-iodide ; alkali metal aurous thiosulphates or sulphites ; or complex salts, e.g. that formed by the reaction of auric chloride and thiourea or gold thiosinamine complexes) and a sulphur sensitizer (e.g. thiourea, allyl iso-thiocyanate, thiosinamine, or metal or ammonium thiocyanates). More than one gold compound and more than one sulphur sensitizer, including mixture of thiocyanate and non-thiocyanate sulphur sensitizers, may be used. The emulsion may contain silver halide dispersing agents, e.g. watersoluble amino carbohydrate or resin dispersing agents, and may contain gelling agents. The gold and sulphur compounds may be incorporated in the emulsion at any stage in its preparation, and the emulsion is advantageously digested with both present and with the pH adjusted to the acid side of neutrality, such pH being preferably maintained during coating. The emulsion may be sensitized with erythrosin, Congo Red, or any of the usual cyanine (methine and polymethine), hemicyanine, merocyanine, or hemioxonol dyes, and may be coated on to the usual supports. Supersensitizing combinations may be used, and hardening, setting, and stabilizing agents may be incorporated. In example 1 an aqueous silver nitrate solution and a solution containing potassium bromide and potassium iodide are run simultaneously into an aqueous ammoniacal polyvinyl alcohol solution, and an aqueous solution of polyvinyl alcohol, glacial acetic acid, and (after heating) an ethanol solution of a-naphthol (gelling agent) are successively added. The emulsion is set, shredded, washed, and melted, and the pH adjusted to 5.5. One-half of the emulsion is coated on to cellulose acetate film, and the other half is similarly coated after the addition of NaCNS and KAuCl 4  and heating. A comparison is made between the speeds and gammas of the two exposed and developed films. In example 2, the procedure is similar, using as binder partially hydrolyzed cellulose acetate propionate and dye-sensitizing with 3 - ethyl - 5 - (2'- ethyl - 1 - benzthiazolylidene)- 2 - thio - 2 : 4 - (3 : 5) - oxazoledione. In example 3, the binder is also partially hydrolyzed cellulose acetate propionate, but ammonium hydroxide and urea are added to the solution before addition of the silver nitrate and halide solutions, and aqueous NaCNS is added immediately following the addition of the latter. After the usual treatment, including the addition of further binder, quantities of KAuC1 4  are added, and also the sensitizing dye of example 2. In example 4, the procedure is similar to example 2, but varying quantities of NaCNS and KAuC1 4  are added. Example 5 is similar to example 4, using as sulphur sensitizer #-ethylxanthate propionic acid. Specifications 515,145, 517,769, 542,703 and 543,854 are referred to.