GB1031903A - Photographic silver halide materials and processes - Google Patents

Abstract

1,031,903. Photographic silver halide materials and processes. E. I. DU PONT DE NEMOURS & CO. Dec. 7, 1962 [Nov. 8, 1962(3)], No.46345/62. Heading G2C. Photographic elements which give positive images on exposure followed by treatment with a silver halide solvent comprise a silver halide emulsion containing a compound which is (i) an alkyl mercaptan in which the alkyl group may be substituted, (ii) a dimercaptan of the formula HS-R<SP>11</SP>-SH where R<SP>11</SP> is hydrocarbon which may be substituted by alkyl, alkoxy, carboxyl, amido or cyano groups or by halogen atoms, (iii) a compound of the formula P-R<SP>111</SP>CONHC 6 H 4 SH where R<SP>111</SP> is a hydrocarbon or an alkoxy or nitro-substituted aryl group, (iv) a substituted thiourea or thioamide or (v) a heterocyclic mercaptan containing a nitrogen atom in the heterocyclic ring, or a salt of any one of the above, the particular compound and the amount used being determined by tests as set out in the Specification. In general the amounts are said to be between 0.125 and 314g.per mole of silver halide. Compounds of class (i) which comply with the tests are alkyl mercaptans having alkyl groups of 3 to 12 carbon atoms, mercapto-undecanoic acid, benzyl mercaptans wherein the benzine ring may be sutstituted by methyl, ethyl or methoxy groups, methyl or ethyl mercapto-acetate, isooctyl thioglycollate iso-octyl-3-mercapto-propionate, mercapto bis (ethyl mercapto-acetate)sulphide and di-t-nonylpolysulphide. Compounds of class (ii) are 2, 3-dimercaptocapto-propanol, toluene 3, 4-dithiol, cyclohexane-1, 1-dithiol, (CN) 2 = C = C(SNa) 2 ,NH 2 .CO.C(CN) = C(SNa) 2 , CN-C(SNa) = C(SNa)-CN, and CN-C(S<SP>-</SP>)-CN. 2(CH 3 ) 4 N+. Compounds of class (iii) are those wherein R<SP>111</SP> is methyl, iso-porpylmethyl, hexyl, octyl, dodecyl, cyclohexyl, naphthyl, or phenyl substituted by a nitro, methoxy or amyloxy group. The thiourea of class ‹iv) may be one in which the nitrogen atoms(s) is or are substituted by one or more of ethyl, butyl, octyl, allyl, benzyl, phenyl, naphthyl or amino, and the thioamide may be thio-acetanetede, thiobenzanilide or thiocarbanilide or its 2, 2<SP>1</SP>-dilthyl derivative. Heterocyclic mercaptans of class (v) are specified wherein the heterocyclic group is thiazole, benzthiazole, naphthothiazole, tetrazole, iminazole, benzimidazole, benzoxazole quinoline, 1; 3; 4-thiadiazole and quinoxaline. In the examples, a film base coated with a silver chlorabiomide emulsion is bathed in an aqueous alcoholic solution of the compound, dried and exposed. Treatment with aqueous sodium thiosulphate followed by bathing in a fogging developer comprising 1 -phenyl-4 -methyl- 3-pyrazolidone, hydroquinone and potassium iodide gives a positive image. In other examples, 0. 4g. of the compound is added per mole of silver halide, and after exposure and treatment with thiosulphate, the emulsion is flashed with white light and the image reduced chemically to silver.