Method of photographic processing and fixer compositions therefor

Abstract: A method of reducing the environmental impact of ammonium thiosulphate photographic fixers without increasing fixing time comprises replacing up to 60% molar of the total ammonium thiosulphate by an alkali metal thiosulphate.

Description: This invention relates to a method of photographic processing and to fixer compositions for use therein. The photographic process known as fixing is the processing step in which undeveloped silver halide in a developed silver halide emulsion layer is removed so that further darkening due to reduction of silver halide does not occur. Thiosulphate salts have been widely used for this purpose for many years, initially the sodium salt (usually known as "hypo") and later the ammonium salt. Recently ammonium thiosulphate has been preferred because of the superior speed with which the fixing is accomplished. This use is described in Mees and James "Theory of the Photographic Process", 4th edition, page 443. From the environmental point of view, ammonium ions are undesirable as they are toxic to aquatic life and encourage eutrophication. The problem to which the present invention is directed is how to reduce the amount of ammonium ion in photographic fixers without slowing the fixing process down. US Patent 4 029 510 describes photograpic processing solutions (both developer and fixer) which each contain at least two developing agents and at least two fixing agents respectively. A dry powder fixer composition is described which contains anhydrous sodium sulphite, anhydrous sodium thiosulphate, ammonium chloride and ammonium thiosulphate. This particular combination of the last three compounds appears to be necessary in order to prevent the powder turning into an intractible solid as ammonium thiosulphate does on its own. Also, this formulation is particularly high in ammonium ions due to the additional ammonium chloride present. No explanation of the reason for using more than one developing or fixing agent is given. According the the present invention there is provided a method of reducing the environmental impact of ammonium thiosulphate photographic fixers without increasing fixing time comprises replacing ammonium thiosulphate by an alkali metal thiosulphate so that, at the working strength, the fixer contains ammonium thiosulphate in an amount equivalent to from 25 to 60 g/l anhydrous ammonium thiosulphate and an alkali metal thiosulphate in an amount equivalent to from 100 to 250 g/l of sodium thiosulphate pentahydrate with the proviso that the fixer is free from ammonium chloride. It has been found, surprisingly, that such a considerable replacement of ammonium thiosulphate does not affect the fixing time to any substantial degree. The present invention further provides a photographic fixer composition comprising, in the working strength solution, ammonium thiosulphate in an amount equivalent to from 25 to 60 g/l anhydrous ammonium thiosulphate and an alkali metal thiosulphate in an amount equivalent to from 100 to 250 g/l sodium thiosulphate pentahydrate with the proviso that the fixer composition is free from ammonium chloride. The alkali metal thiosulphate may, for example, be potassium or, preferably, sodium thiosulphate. The fixer composition also preferably contains sulphite ions as is conventional. The present fixer composition preferably comprises, in the working solution, ammonium thiosulphate in an amount equivalent to from 30 to 50 g/l of anhydrous ammonium thiosulphate. The composition preferably also contains, in the working solution, an alkali metal thiosulphate in an amount equivalent to from 150 to 230 g/l sodium thiosulphate pentahydrate. The present fixer compositions may also contain sulphite ions, as is conventional. Preferably the fixer contains sodium sulphite at a concentration such that the working strength solution contains from 2 to 20 g/l sodium sulphite. The present fixer compositions may be used to fix any type of photographic silver halide materials, eg films or papers. Such materials are described in Research Disclosure Item 308119, December 1989 published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom. The fixing composition may further contain compounds customarily added to fixer solutions, for example fix accelerators. The fixing process may take place at any desired temperature, for example between 15 and 35 °C. The following Examples are included for a better understanding of the invention. EXAMPLE 1 A multilayer 400 ASA speed colour film having silver laydowns of 1.1 g/m 2 in the cyan dye image forming unit, 1.6 g/m 2 in the magenta dye image forming unit and 1.6 g/m 2 in the yellow dye image forming unit having an overall silver iodide percentage of the total halide present of 4.2% was cut into strips. Each strip was then fixed in a model seasoned fixer of the following formula: The thiosulphate was added as different mixtures of ammonium and sodium thiosulphates. The silver bromide and iodide ratio was also varied with the total silver halide content being kept constant. This was to simulate a fixer seasoned by films containing differing halide ratios. The maximum amount of iodide in the bromide/iodide mixture was at a molar ratio of 8%. The test film strips were put in a transparent cell containing the test fixer. The infra-red density of the film was monitored continuously. During the fixing step agitation was carried out by a nitrogen gas burst of 0.5 second every 4 seconds. The fixing time was taken as the first time there was no further decrease in infra-red density. The results are tabulated below. Ammonium ion (%) Fixer Iodide (%) Fixing Time ± 5 (secs) 0 2 115 20 2 85 40 2 65 60 2 65 80 2 65 100 2 65 0 4 140 20 4 80 30 4 50 40 4 35 50 4 35 60 4 40 80 4 35 100 4 35 0 8 255 20 8 200 40 8 145 60 8 150 80 8 145 100 8 140 The results show that 40% ammonium fixers are just as fast as 100% ammonium fixers at these levels of iodide. The reduced ammonia fixer would then have 60% less ammonia in the overflow and therefore reduced ammonia in the effluent from the process.

Claims: A method of reducing the environmental impact of anhydrous ammonium thiosulphate photographic fixers without increasing fixing time comprises replacing ammonium thiosulphate by an alkali metal thiosulphate so that, at the working strength, the fixer contains ammonium thiosulphate in an amount equivalent to from 25 to 60 g/l anhydrous ammonium thiosulphate and an alkali metal thiosulphate in an amount equivalent to from 100 to 250 g/l of sodium thiosulphate pentahydrate with the proviso that the fixer is free from ammonium chloride. A method as claimed in claim 1 in which the fixer contains, at the working strength, ammonium thiosulphate in an amount equivalent to from 30 to 50 g/l anhydrous ammonium thiosulphate and an alkali metal thiosulphate in an amount equivalent to from 150 to 230 g/l of sodium thiosulphate pentahydrate. A method as claimed in claim 1 or 2 in which the alkali metal thiosulphate is sodium thiosulphate. A photographic fixer composition comprising, in the working strength solution, ammonium thiosulphate in an amount equivalent to from 25 to 60 g/l anhydrous ammonium thiosulphate and an alkali metal thiosulphate in an amount equivalent to from 100 to 250 g/l of sodium thiosulphate pentahydrate with the proviso that the fixer composition is free from ammonium chloride. A photographic fixer composition as claimed in claim 4 comprising, in the working strength solution, ammonium thiosulphate in an amount equivalent to from 30 to 50 g/l anhydrous ammonium thiosulphate and an alkali metal thiosulphate in an amount equivalent to from 150 to 230 g/l of sodium thiosulphate pentahydrate. A composition as claimed in claim 4 or 5 which also contains sulphite ions. A composition as claimed in claim 6 which contains sodium sulphite at a concentration such that the working strength solution contains from 2 to 20 g/l sodium sulphite.

Inventors: FYSON JOHN RICHARD, FYSON, JOHN RICHARD, FYSON, JOHN RICHARD, C/O KODAK LIMITED
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1992
Main classification: G03C5
IPC codes: G03C5