Method of processing photographic silver halide materials

Abstract: A method of processing an imagewise exposed photosensitive photographic silver halide colour material comprising at least 85% silver chloride and having a total silver coating weight of 10 to 500 mg/m 2 comprises treating the material with the following processing baths in the sequence recited: (a) a developer-amplifier containing a colour developing agent and hydrogen peroxide or a compound that yields hydrogen peroxide, (b) a fixer comprising an alkali metal sulphite or a material that yields sulphite as fixing agent, (c) a bleach comprising hydrogen peroxide or a compound that yields hydrogen peroxide and an alkali metal halide wherein the pH is in the range 8-11.

Description: Field of the Invention This invention relates to the processing of colour materials intended for redox amplification processing. Background of the Invention Redox amplification processes have been described, for example in British Specification Nos. 1,268,126, 1,399,481, 1,403,418 and 1,560,572. In such processes colour materials are developed to produce a silver image (which may contain only small amounts of silver) and then treated with a redox amplifying solution (or a combined developer-amplifier) to form a dye image. The developer-amplifier solution contains a colour developing agent and an oxidising agent which will oxidise the colour developing agent in the presence of the silver image which acts as a catalyst. Oxidised colour developer reacts with a colour coupler to form the image dye. The amount of dye formed depends on the time of treatment or the availability of colour coupler and is less dependent on the amount of silver in the image as is the case in conventional colour development processes. Examples of suitable oxidising agents include peroxy compounds including hydrogen peroxide and compounds which provide hydrogen peroxide, eg addition compounds of hydrogen peroxide or persulphates; cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used. In conventional processing (non-RX) of colour materials, a bleach-fix bath which both bleaches silver image and removes all silver from the material is employed. Such solutions typically contain ferric EDTA complexes which are considered environmentally undesirable. In the field of low silver coverage photographic materials intended for redox amplification (RX) processes it has been proposed to use a fixer comprising an alkali metal sulphite as fixing agent and a bleach comprising a peroxide and an alkali metal halide. These proposals are described in our European Application Nos. 0 540 619, 0 506 909, and 0 470 083. Both sulphites and hydrogen peroxide are environmentally acceptable. Because of the small amounts of silver present in the photographic material it has also been proposed to leave out the processing stages that bleach and fix because the degradation of the image is minimal. However, if it is desired to gain the highest quality image, all image silver has to be removed so that it does not degrade the dye images (especially the yellow image) and unreduced silver halide has similarly to be removed so that it does not darken or print out with time. It has been found that when using a bleach-fix bath after an RX step, a stop bath must be interposed otherwise staining occurs. A stop bath may be dispensed with if the RX step is followed by a fixer bath. If the redox amplification is immediately followed by a bleach bath, redox amplification can continue in the bleach bath leading to poorly controlled sensitometric results. Problem to be Solved by the Invention The present invention seeks to provide a high quality process after the formation of the amplified dye image so that image degradation caused by image silver or unreduced silver halide is eliminated without using environmentally unfriendly processing solutions and without increasing processing time. Summary of the Invention We have now found that if an RX step is followed by a sulphite fixer and then a peroxide bleach, the remaining unfixed rehalogenated silver is not sensitive to light and can be left in the material without causing any unwanted darkening. According to the present invention there is provided a method of processing an imagewise exposed photosensitive photographic silver halide colour material comprising at least 85% silver chloride and having a total silver coating weight of 10 to 500 mg/m 2 , preferably of 50 to 200 mg/m 2 , which comprises treating the material with the following processing baths in the sequence recited: (a) a developer-amplifier containing a colour developing agent and hydrogen peroxide or a compound that yields hydrogen peroxide, (b) a fixer comprising an alkali metal sulphite, or a material that yields sulphite, as the sole fixing agent, (c) a bleach comprising hydrogen peroxide or a compound that yields hydrogen peroxide and an alkali metal halide wherein the pH is in the range 7-11. Advantageous Effect of the Invention In spite of the material having no fix step after the bleach, the silver salt remaining in the material is not sensitive to light and no print out occurs. Detailed Description of the Invention The sulphite fixer may comprise an alkali metal sulphite which provides sulphite in an amount equivalent to 20 to 150 g/l sodium sulphite. Corresponding levels of materials that provide sulphite during processing, e.g. an alkali metal metabisulphite, can also be used. The fixer may have a pH above 6.4, preferably in the range 6.5 to 9, especially 7.0. A buffering material may be used, for example an alkali metal acetate in order to maintain the desired pH. The bleach bath may contain 10 to 200 g/l, preferably 30 to 100 g/l of 30% w/w hydrogen peroxide solution. The bleach bath may also contain an alkali metal halide which provides halide in an amount equivalent to from 0.5 to 50, preferably 1 to 30 g/l sodium chloride. The bleach may also contain metal-chelating agents to which metals might otherwise catalyse the decomposition of the hydrogen peroxide. Such compounds may be of the 1-hydroxyethylidene-1,1'-diphosphonic acid and/or diethyltriamine-pentaacetic acid type. The bleach preferably has a pH in the range 8 to 11 and is preferably about 10. It may contain a buffer, for example an alkali metal carbonate. The total processing time is preferably from 30 to 600 seconds, especially from 45 to 250 seconds at 35°C. The photographic elements can be single colour elements or multicolour elements having a paper or a transparent film base. Multicolour elements contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer. A typical multicolour photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like. Suitable materials for use in this invention, can have any of the components described in Research Disclosure Item 36544, September 1994, published by Kenneth Mason Publications, Emsworth, Hants P010 7DQ, United Kingdom. The present processing solutions are preferably used in a method of processing carried out by passing the material to be processed through a tank containing the processing solution which is recirculated through the tank at a rate of from 0.1 to 10 tank volumes per minute. The preferred recirculation rate is from 0.5 to 8, especially from 1 to 5 and particular from 2 to 4 tank volumes per minute. The recirculation, with or without replenishment, is carried out continuously or intermittently. In one method of working both could be carried out continuously while processing was in progress but not at all or intermittently when the machine was idle. Replenishment may be carried out by introducing the required amount of replenisher into the recirculation stream either inside or outside the processing tank. It is advantageous to use a tank of relatively small volume. Hence in a preferred embodiment of the present invention the ratio of tank volume to maximum area of material accomodatable therein (ie maximum path length x width of material) is less than 11 dm 3 /m 2 , preferably less than 3 dm 3 /m 2 . The shape and dimensions of the processing tank are preferably such that it holds the minimum amount of processing solution while still obtaining the required results. The tank is preferably one with fixed sides, the material being advanced therethrough by drive rollers. Preferably the photographic material passes through a thickness of solution less than 11 mm, preferably less than 5 mm and especially about 2 mm. The shape of the tank is not critical but it could be in the shape of a shallow tray or, preferably U-shaped. It is preferred that the dimensions of the tank be chosen so that the width of the tank is the same or only just wider than the width of the material to be processed. The total volume of the processing solution within the processing channel and recirculation system is relatively smaller as compared to prior art processors. In particular, the total amount of processing solution in the entire processing system for a particular module is such that the total volume in the processing channel is at least 40 percent of the total volume of processing solution in the system. Preferably, the volume of the processing channel is at least about 50 percent of the total volume of the processing solution in the system. In order to provide efficient flow of the processing solution through the opening or nozzles into the processing channel, it is desirable that the nozzles/opening that deliver the processing solution to the processing channel have a configuration in accordance with the following relationship: 0.6 ≥ F/A ≤ 23 wherein: F is the flow rate of the solution through the nozzle in litres/minute; and A is the cross-sectional area of the nozzle provided in square centimetres. Providing a nozzle in accordance with the foregoing relationship assures appropriate discharge of the processing solution against the photosensitive material. Such Low Volume Thin Tank systems are described in more detail in the following patent specifications: US 5,294,956, US 5,179,404, US 5,270,762, EP 559,025, EP 559,026, EP 559,027, WO 92/10790, WO 92/17819, WO 93/04404, WO 92/17370, WO 91/19226, WO 91/12567, WO 92/07302, WO 93/00612, WO 92/07301, and WO 92/09932 The following Example is included for a better understanding of the invention. EXAMPLE The photographic material used in this invention was a colour paper with a total silver laydown of 65 mg/m 2 . The material was exposed in a sensitometer at 1/10s through a 0.15 log wedge with correction filters added to try to get a neutral grey scale. The wedge also included red, green and blue separations. To demonstrate the effects of improved colour the blue separation (yellow dye) was measured on the processed strips in all three colours, retained silver showing up as increased density in all three layers. The following solutions were made up to be used in the processes that follow: Developer amplifier 1-hydroxyethylidene-1,1'-diphosphonic acid 0.6g diethyltriamine-pentaacetic acid 2.0g Dipotassium hydrogen phosphate.3H 2 O 40.0g Hydroxylamine sulphate 0.5g 4-N-ethyl-N-(β-methanesulphonamidoethyl)- o -toluidine sesquisulphate 4.5g Water to pH adjusted to 11.7 with sodium hydroxide 1 litre 20mls 3% w/w hydrogen peroxide was added just before use Thiosulphate Fixer Sodium sulphite (anhydrous) 20.0g Sodium thiosulphate.5H 2 O 20.0g Sodium acetate 40.0g Water to pH adjusted to 5.5 with acetic acid 1 litre Sulphite Fixer Sodium sulphite (anhydrous) 50.0g Sodium acetate 40.0g Water to pH adjusted to 7.0 with sulphuric acid 1 litre Rehalogenating peroxide bleach 1 1-hydroxyethylidene-1,1'-diphosphonic acid 0.6g diethyltriamine-pentaacetic acid 2.0g Sodium chloride 1.0g Sodium hydrogen carbonate 20.0g Hydrogen peroxide (30%) 50.0g Water to pH adjusted to values in Table 1 with sodium hydroxide or sulphuric acid 1 litre Rehalogenating peroxide bleach 2 1-hydroxyethylidene-1,1'-diphosphonic acid 1.0g Sodium chloride 20.0g Sodium hydrogen carbonate 3.0g Sodium carbonate 4.0g Hydrogen peroxide (30%) 50.0g Water to pH adjusted to 10.0 with sodium hydroxide or sulphuric acid 1 litre Rehalogenating dichromate bleach Potassium dichromate 10.0g Sodium chloride 10.0g Sulphuric acid (concentrated) 10ml Water to 1 litre Bleach-fix Ammonium iron (III) EDTA solution (1.56M) 50ml Ammonium thiosulphate 50g Sodium sulphite 20g Acetic acid (glacial) 15ml Water to pH adjusted to 6.0 1 litre Stop bath Acetic acid (glacial) 30ml Water to 1 litre The following is a list of process used to test the invention. All were carried out at 35°C. It is indicated for each process whether it is a comparison or an example of the invention. Process 1 Developer amplifier 45s Stop 45s Bleach-fix 45s Wash 60s Dry Process 2 Developer amplifier 45s Bleach-fix 45s Wash 60s Dry Process 3 Developer amplifier 45s Thiosulphate fixer 45s Wash 60s Dry Process 4 Developer amplifier 45s Peroxide bleach 1( pH 10.0) 45s Thiosulphate fixer 45s Wash 60s Dry Process 5 Developer amplifier 45s Thiosulphate fixer 45s Peroxide bleach 1( pH 10.0) 45s Wash 60s Dry Process 6 Developer amplifier 45s Sulphite fixer 45s Peroxide bleach 1(pHs 7 to 11) 45s Wash 60s Dry Process 7 Developer amplifier 45s Sulphite fixer 45s Peroxide bleach 2 45s Wash 60s Dry Process 8 Developer amplifier 45s Sulphite fixer 45s Dichromate bleach 45s Wash 60s Dry Process 9 Developer amplifier 45s Stop 45s Peroxide bleach 2 45s Wash 60s Dry The results of the experiment are shown in Table 1: Process Red Density Green Density Blue Density 1 comp. 0.20 0.65 2.33 2 comp. 0.35 0.72 2.40 3 comp. 0.26 0.71 2.38 4 comp. 0.26 0.72 2.57 5 comp. 0.27 0.70 2.37 6 (bleach pH = 7.0) comp. 0.25 0.69 2.36 6 (bleach pH = 8.0) inv. 0.20 0.65 2.33 6 (bleach pH = 9.0) inv. 0.20 0.65 2.34 6 (bleach pH = 10.0) inv. 0.20 0.64 2.33 7 comp. 0.19 0.65 2.32 8 comp. 0.20 0.66 2.34 9 comp. 0.21 0.67 2.33 Process 1 is the control process and an aim for the best yellow hue with least red and green unwanted absorptions. This process involved a stop and an environmentally unfriendly bleach-fix but should not contain any silver in the image. Process 2 results show the effect of having no stop between the developer amplifier and bleach-fix steps. A large amunt of cyan stain was generated which showed over the whole strip. Process 3 results show the yellow image densities when all the silver developed was present as this had only been fixed. When compared to Process 1 we see an increase in density in all layers due to the unwanted silver adsorption. Process 4 results show much increased yellow density with similar red and green densities to Process 3 but the yellow colour appeared 'cleaner' implying there was less silver in the image. However more colour density was formed as the RX development continued into the bleach which was acting as an amplifier. Process 5 results are similar to those of process 3 and silver appears to have been retained. The bleach does not appear to be working after the thiosulphate fixer, Process 6 with the bleach pH at 7.0 results look like those of Process 3 and silver is retained. This suggests that the bleach does not work at this pH for at higher pHs the results are similar to those of process 1 and the yellow is 'cleaner' with less unwanted neutral colour. The sulphite fixer does not inhibit the bleaching at pHs > 8.0 Process 7 appears to work as well as Process 6 with the bleach at pH>8.0 as does process 8 with a dichromate bleach. This latter may not be environmentally acceptable but this bleach does remove the silver. Process 9 has all the silver retained with no fixer. The yellow density is similar to that of process 1 and the silver appears to have been bleached. In order to test the strips to see if the image would print-up in sunlight, after initial sensitometric reading, each of the strips from the experiment was taped to a south facing window at midday in bright sunshine for one hour. The strips were read again and the differences recorded in Table 2 below. Process ΔRed Density ΔGreen Density ΔBlue Density 1 comp. 0.00 0.00 0.01 2 comp. 0.00 -0.01 0.00 3 comp. 0.00 -0.01 0.00 4 comp. -0.01 0.00 0.00 5 comp. 0.00 0.00 -0.01 6 (bleach pH = 7.0) comp. 0.00 0.01 0.00 6 (bleach pH = 8.0) inv. 0.00 0.00 0.00 6 (bleach pH = 9.0) inv. 0.01 0.00 0.00 6 (bleach pH = 10.0) inv. -0.01 0.01 0.00 7 inv. 0.00 0.00 0.01 8 inv. 0.01 0.00 0.00 9 inv. 0.04 0.05 0.04 The only process that was seriously affected by sunlight was process 9. This had had no fixing step and all the silver halide was retained. The silver printed out over all the strip. It might be expected for reasons on consistency that strips from processes 6 (pH>8.0), 7 and 8 would have printed out in image areas as silver halide should have been retained in such areas, but it appeared to be insensitive to sunlight thus demonstrating the invention. In order to check that the silver halide was retained in Process 6 (pH>8), Process 7 and Process 8 but was insensitive to sunlight a drop of 0.5% sodium sulphide solution was applied to the yellow image areas. It immediately caused an increase in density with the formation of silver sulphide, indicating the presence of retained, but light insensitive silver halide.

Claims: A method of processing an imagewise exposed photosensitive photographic silver halide colour material comprising at least 85% silver chloride and having a total silver coating weight of 10 to 500 mg/m 2 which comprises treating the material with the following processing baths in the sequence recited: (a) a developer-amplifier containing a colour developing agent and hydrogen peroxide or a compound that yields hydrogen peroxide, (b) a fixer comprising an alkali metal sulphite or a material that yields sulphite as the sole fixing agent, (c) a bleach comprising hydrogen peroxide or a compound that yields hydrogen peroxide and an alkali metal halide wherein the pH is in the range 7-11. A method as claimed in claim 1 in which the developer/amplifier has a pH in the range 9 to 13. A method as claimed in claim 1 or 2 in which the fixer comprises an alkali metal sulphite which provides sulphite in an amount equivalent to 20 to 150 g/l sodium sulphite. A method as claimed in any of claims 1-3 in which the bleach contains from 10 to 200 g/l of hydrogen peroxide (30% w/w). A method as claimed in any of claims 1-4 in which the bleach contains an alkali metal halide which provides halide in an amount equivalent to from 0.5 to 50 g/l sodium chloride. A method as claimed in any of claims 1-6 in the total silver coating weight is in the range from 50 to 200 mg/m 2 . A method as claimed in any of claims 1-7 in which the total processing time is from 30 to 600 secs at 35°C. A method as claimed in any of claims 1-8 in which the processing is carried out by passing the material to be processed through a tank containing the processing solution which is recirculated through the tank at a rate of from 0.1 to 10 tank volumes per minute. A method as claimed in any of claims 1-9 in which the processing is carried out in a machine wherein the ratio of tank volume to maximum area of material accomodatable therein (ie maximum path length x width of material) is less than 11 dm 3 /m 2 , preferably less than 3 dm 3 /m 2 .

Inventors: EVANS GARETH BRYN, FYSON JOHN RICHARD, EVANS, GARETH BRYN, FYSON, JOHN RICHARD
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1996
Main classification: G03C7
IPC codes: G03C1, G03C7