Patent GB-813254-A (GB)
Title: Improvements in photographic reproduction processes and sensitive materials therefor
IPC: G03C5/315
Filed: 1956-04-05
Abstract: 813,254. Photographic reproduction processes. KODAK Ltd. April 5, 1956 [April 5, 1955], No. 10438/56. Drawing to Specification. Class 98(2) A process of photographic reproduction comprises exposing to a two-tone subject a layer of an unhardened or very slightly hardened (as defined in the Specification) gelatino silver halide emulsion of the internal latent image type, treating the exposed layer with a first alkaline solution in the presence of a tanning developing agent to develop a hardened gelatin and silver image therein, thereafter treating the layer with a second alkaline solution in the presence of a developing agent and a compound inhibiting tanning to develop an unhardened gelatin and silver image therein, one of the alkaline solutions containing a silver halide solvent and the other a hydrazine compound of the general formula RRN-NRR, in which at least two R's are H and when less than 4 R's are H, the remaining R's are aryl, aralkyl, acyl or carboxylic acid amide groups, then transferring in the presence of moisture a thin stratum of the unhardened gelatin and silver image to an absorbent sheet. In a modification, the hydrazine compound may be incorporated in the emulsion. In a negative-positive process, the first alkaline solution may contain the hydrazine compound and the second a silver halide solvent and a gelatin tanning inhibitor, while in a positive process the first alkaline solution contains a silver halide solvent and the second the hydrazine compound and gelatin tanning inhibitor. The tanning developing agent may be incorporated in the emulsion layer and may be hydroquinone, catechol, pyragallol, or preferably, 3 : 4-, 2 : 5- or 2 : 3 - dihydroxydiphenyl, 4 - phenoxycatechol, 4 - (2 - cyclopentenyl) - catechol, 1 : 2 - diethoxalyl - 4 - phenylcatechol, or 1 : 2 : 3 - triethoxalylpyrogallol. The hydrazine compound may be one of those described in Specifications 702,162 and 702,163. The silver halide solvent may be an alkali metal or ammonium thiosulphate or sulphite, an ammonium salt, ammonium hydroxide, an alkali metal thiocyanate, sodium bisulphite, or potassium metabisulphite, and the tanning inhibiting agent may be an alkali metal sulphite, borax, or an alkali metal formaldehyde bisulphite. The second alkaline solution may contain a gelatin softening agent such as urea, sodium nitrate, glycerol, formamide, or ethylene chlorohydrin. The emulsion may be exposed by contact (including reflex) or projection printing. Where the original contains both heavy black characters and fine light grey lines, the emulsion may be exposed through a halftone screen having about 120 or 133 lines per inch before or just after the image exposure step. Where a direct positive print is obtained by incorporating the silver halide solvent in the first alkaline solution and the hydrazine compound in the second and where the tanning developing agent is incorporated in the first alkaline solution and not in the emulsion, a tanning or non- tanning developing agent may be added to the second alkaline solution to ensure adequate density in the final print. In an example, a developer dispersion is prepared by dissolving 3 : 4 - dihydroxydiphenyl in dibutyl phthalate and pouring slowly into an aqueous solution of gelatin containing saponin, and the dispersion and an aqueous saponin solution is added to a melted internal latent image emulsion prepared as described in Specification 635,841. The emulsion is coated on paper. The material is exposed to a negative or positive line or halftone subject and is treated with an aqueous solution of sodium sulphite, p - (# - methylsulphonamideoethyl)- phenylhydrazine (if the hydrazine has not been incorporated in the emulsion layer), sodium carbonate and sodium hydroxide. The material is then treated with an aqueous solution of sodium sulphite, sodium carbonate, and sodium thiosulphate, which may also contain urea or other gelatin softening agent. The still moist emulsion layer is squeegeed on to paper to transfer a thin stratum of the unhardened gelatin and silver image thereto, and the material may be rewetted with the second alkaline solution to transfer further strata on to sheets of paper. Specifications 581,772, 581,773, 655,274, 725,667 and 813,253 also are referred to.