Radiation imagery chemistry: process – composition – or product th – Color imaging process – Using identified radiation sensitive composition in the...
Patent
1990-11-05
1992-12-15
Van Le, Hoa
Radiation imagery chemistry: process, composition, or product th
Color imaging process
Using identified radiation sensitive composition in the...
430414, 430455, G03C 538
Patent
active
051716585
DESCRIPTION:
BRIEF SUMMARY
This invention relates to photographic processing and, in particular, to a method of fixing.
Photographic silver halide materials are employed to form images by first imagewise exposing the material, e.g. in a camera, and then processing to form a visible image. The processing steps usually include (a) a development step in which the exposed areas of the material form a visible image and (b) a fixing step whereby the undeveloped silver halide is removed by treatment with a fixer solution which contains a silver halide solvent.
It is known that a number of compounds can be used as the silver halide solvent. These include sulphites and thiosulphates. Although it is known that sulphites have silver halide solvent activity, they have only been used in fixer solutions in combination with another silver halide solvent, e.g. thiosulphates and for the purpose of stabilising such solutions against sulphur precipitation. Sulphites have never been used alone as fixing agents in conventional photography due to the inordinately long time that would be needed to fix a typical photographic material. In practice it is the alkali metal or ammonium thiosulphates that have been exclusively used in commercially used processing solutions.
Thiosulphates however do have problems associated with their ease of safe disposal. In addition, under certain conditions some color couplers (as used in color materials) can continue to couple in a fixer (not a bleach fix) directly following a developer. Further, thiosulphate fixer solutions are unstable and can precipitate sulphur.
We have now found that alkali metal sulphite solutions can be employed to remove silver chloride from photographic materials in acceptable processing times.
According to the present invention there is provided a method of removing silver chloride from a photographic silver halide material during processing which comprises treatment with an aqueous solution containing an alkali metal sulphite as sole silver halide solvent. The solution will, of course, be essentially free of silver halide solvents other than alkali metal sulphites.
The present sulphite fixers, compared to existing thiosulphate fixers, are less environmentally harmful in that they have a lower biological and chemical oxygen demand; they do not precipitate sulphur; and they produce a relatively harmless sulphate on oxidation. Sulphites are inexpensive and readily avaliable and they do not allow continued coupling of a color coupler in the fixer.
The silver chloride removed in the present process may be the undeveloped portions of the silver halide layer(s) of photographic materials in which the silver halide is substantially pure silver chloride. Such materials preferably contain less than 10% other halides. Alternatively silver formed by development earlier in the process may be bleached to form silver chloride and then removed by the present method. In such a case which might arise in, for example reversal processing, the photographic material may have originally comprised halides other than chloride.
The alkali metal sulphite may be employed in a wide range of concentrations, for example at 5-200 g/litre (as anhydrous sodium sulphite); preferred solutions contain 10-150 g/liter.
Unlike conventional fixing solutions which are acid, the sulphite solutions, preferably have an alkaline pH, particularly a pH greater than 6. Additional pH-controlling compounds may be employed to achieve the higher or lower pH values within this range.
The present method is particularly suitable for silver chloride materials having total silver coating weights of from 1 mg-10 g/m.sup.2, the lower end of the scale being preferred, especially from 1 mg-1 g/m.sup.2. Clearly the less silver chloride contained in the material, the faster will be the fixing times.
The present method is suitable for both black-and-white and color materials. The silver halide emulsions may be negative-working (including those intended for reversal processing) or direct-positive. Their silver halide grains may be of any shape or dispersity. For
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G. Haist, Modern Photographic Processing, pp. 598-599.
Carlson Robert L.
Eastman Kodak Company
Goldman Michael L.
Le Hoa Van
Levitt Joshua G.
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