Patent GB-618061-A (GB)
Title: Improvements in sensitive photographic materials
IPC: G03C1/09
Filed: 1946-05-06
Abstract: 618,061. Photographic emulsions. KODAK, Ltd., DAVEY, E. P., and BERRIMAN, R. W. (Eastman Kodak Co., Trivelli, A. P. H., and Smith, W. F., in part). May 6, 1946, Nos. 13667/46 and 14913/47 (divided out of 602,158). [Class 98 (ii)] A sensitive silver halide developing-out emulsion free from iron salts is stabilized by the incorporation of a complex halide of platinum. The halide may have the formula R2PtX4 or R2PtX6, wherein R is H, NH4, or an alkali metal such as Na or K and X is a halogen atom (e.g. Cl or Br). The compounds sometimes increase the speed, and in this case may be used in very small quantities. Details of speed, gamma and fog values for specified additions and conditions with a given developer are given. The stabilized emulsions may be developed with developers containing hydroquinone, p-aminophenol or its derivatives, pyrogallol, p-phenylenediamine or its derivatives, or phenylhydroxylamine. The compounds used may be ammonium, sodium and potassium chloroplatinate, chloroplatinite and bromoplatinate, and may be added before or during precipitation of the silver halides, before or during the first or second digestions of the emulsion, or just before coating and before or after the addition of sensitizing dyes. The compounds may be added in solution in water or methyl or ethyl alcohol. One or more sulphur sensitizers (e.g. thiourea, allylisothiocyanate, thiosinamine or sodium, potassium, ammonium, cadmium or calcium thiocyanates), including one or more thiocyanates with a sulphur sensitizer other than a thiocyanate, may be added, advantageously in solution in water or methyl or ethyl alcohol, and during precipitation of the silver halides or the first or second digestions. Both the metal compound and the sulphur sensitizer are preferably present during the second digestion, and the pH of the emulsion is preferably adjusted to between 5 and 7. In example (1) a comparison is drawn between the speed, gamma and fog figures for a gelatino-silver bromiodide emulsion to which has been added (a) sodium thiocyanate before the first digestion (ripening); (b) as (a) to which also has been added ammonium chloroplatinite at the beginning of the precipitation of the silver halides; (c) as (a) with the addition after the precipitation of the silver halides of ammonium chloroplatinite and ascorbic acid; and (d) as (a) with the addition after the first digestion of ammonium chloroplatinite and ascorbic acid. In example (2), a similar comparison is made, with six portions of emulsion, each containing sodium thiocyanate and sodium thiosulphate and each alternate portion containing a thiocarbocyanine sensitizing dye, the first two portions containing no addition of complex halide, the second two containing ammonium chloroplatinate, and the third ammonium chloroplatinite. The emulsions may be sensitized with any of the usual dyes, e.g. erythrosin, Congo Red, monometine-, trimethine-, pentamethine- or heptamethine-cyanines, merocyanines, hemicyanines or hemioxonols, and super-sensitizing mixtures may be used. Hardening agents, setting agents or stabilizing agents may also be added. Specifications 20022/13, [Class 98 (ii)], 450,958, 479,970, 515,145 and 517,769 are referred to.