Photographic developer/amplifier compositions

Abstract: An aqueous redox amplifier composition comprising a colour developing agent, an antioxidant therefor and hydrogen peroxide or a compound which provides hydrogen peroxide contains nitrite ions to stabilise it against loss of active components.

Description: Field of the Invention This invention relates to photographic developer/amplifier solutions useful in redox amplification processes. 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; cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used. Problem to be Solved by the Invention A serious problem with developer/amplifier solutions containing hydrogen peroxide or a precursor thereof is their stability because they contain both an oxidising agent (the peroxide) and a reducing agent (the colour developing agent) which react together spontaneously thus leading to loss of activity in a matter of an hour or two. The addition of an antioxidant for the colour developer, eg a hydroxylamine compound is helpful but is, perhaps, not a complete solution. Previously proposals have been made to overcome this problem. One proposal is to discard the contents of the processing tank when the process is idle and to refill it on restart. Another is to remove oxidant from the solution when the process is idle and to top up to the correct concentration when it restarts. Both these solutions waste processing solution and can be complicated to implement. Summary of the Invention According the the present invention there is provided an aqueous redox amplifier composition comprising a colour developing agent, an antioxidant therefor and hydrogen peroxide or a compound which provides hydrogen peroxide characterised in that the composition contains nitrite ions in a concentration from 0.2 to 50 g/l (as potassium nitrite). Advantageous Effect of the Invention The developer/amplifier solution is stabilised against loss of dye yield on standing caused by loss of active components by spontaneous reaction or by aerial oxidation. Brief Description of the Drawings Fig 1 of the accompanying drawings represents results from Examples 1 and 2. Detailed Description of the Invention Many compounds have been proposed for colour developer antioxidants. Such compounds as hydrazines, hydroxylamines, hydroxyamic acids, oximes, nitroxy radicals, hydrazines, hydrazides, phenols, saccherides, monoamines, diamines, tertiary amines, polyamines, quaternary ammonium salts, alpha-hydroxy ketones, alcohols, diamides and disulphonamides. The preferred antioxidants are hydroxylamine compounds. Many antioxidants are described in European Patent No. 0 410 375. Preferred antioxidants are hydroxylamine itself or any aryl- or alkyl-substituted derivative thereof, eg a dialkyl or diaryl-hydroxylamine, eg diethylhydroxylamine or salts thereof. The concentration range of nitrite ions is from 0.2 to 50 g/l, particularly from 0.3 to 5 g/l and especially from 0.5 to 2.0 g/l (as potassium nitrite). The concentration range of the hydrogen peroxide is preferably from 0.1 to 10 ml/l, particularly from 0.3 to 7 ml/l and especially from 0.5 to 5 ml/l (as 30% w/w solution). The concentration range of the antioxidant may be from 0.1 to 6 g/l (as hydroxylamine sulphate), preferably from 0.3 to 4 g/l, particularly from 0.5 to 2 g/l. The pH may be buffered by a phosphate. The pH is preferably in the range 10.5 to 12, particularly from 11 to 11.7 and especially from 11 to 11.4. The nitrite ions are preferably added as an alkali metal nitrite, eg potassium or sodium nitrite. Typically the developer/amplifier contains colour developing agent at concentrations of 0.5 to 15 g/l, preferably from 2 to 5 g/l. The colour photographic material to be processed may be of any type but will preferably contain low amounts of silver halide. Preferred total silver halide coverages are in the range 6 to 300, preferably 10 to 200 mg/m 2 and particularly 10 to 100 mg/m 2 (as silver). The material may comprise the emulsions, sensitisers, couplers, supports, layers, additives, etc. described in Research Disclosure, December 1978, Item 17643, published by Kenneth Mason Publications Ltd, Dudley Annex, 12a North Street, Emsworth, Hants P010 7DQ, U.K. In a preferred embodiment the photographic material to be processed comprises a resin-coated paper support and the emulsion layers comprise more than 80%, preferably more than 90% silver chloride and are more preferably composed of substantially pure silver chloride. The photographic materials can be single colour materials or multicolour materials. Multicolour materials 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 materials, including the layers of the image-forming units, can be arranged in various orders as known in the art. A typical multicolour photographic material comprises a support bearing a yellow dye image-forming unit comprised of at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, and magenta and cyan dye image-forming units comprising at least one green- or red-sensitive silver halide emulsion layer having associated therewith at least one magenta or cyan dye-forming coupler respectively. The material can contain additional layers, such as filter layers. The processing may be carried out by hand or in a processing machine of which many types are known. Preferably 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. 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. The following Examples are included for a better understanding of the invention. EXAMPLE 1 - Comparative Example A developer/amplifier solution (D1) of the composition shown in Table 1 below was prepared and left to stand in glass cylinders in a water thermostat bath 32°C. At the start which was immediately after the hydrogen peroxide was added and at various time intervals thereafter sensitometric paper strips were processed in the developer/amplifier bath. Developer/amplifier D1 Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 HPO 4 .3H 2 O 40.0g/l KBr 1.0mg/l KCl 0.5g/l Catechol disulphonate (CDS) 0.3g/l Hydroxylamine sulphate(HAS) 1.0g/l KOH(50%) 10.0ml/l CD3 4.5g/l pH 11.4 H 2 O 2 (30%) 2.0ml/l Time 45 seconds Temperature 32°C Where Sequestrant 1 is 60% solution of 1-hydroxy ethylidene-1,1-diphosphonic acid, Sequestrant 2 is a 41% solution of the penta sodium salt of diethylene triamine penta acetic acid and the colour developing agent CD3 is N-[2-(4-amino-N-ethyl-m-toluidino)ethyl]-methanesulphonamide sesquisulphate hydrate. EXAMPLE 2 (Invention) Three developer/amplifiers were prepared similar to that in Table 1 except than potassium nitrite was included at 1, 5 and 10g/l (developer/amplifiers D2-D4). The standing stability observed was assessed by means of sensitometric strips. The process cycle was as follows: Developer 45 seconds Fixer 30 seconds Wash 2 minutes Dry The fixer consisted of glacial acetic acid(20ml/l), sodium sulphite(50g/l), sodium thiosulphate(20g/l) and sodium hydroxide(20g/l). A sensitive parameter in paper sensitometry is the maximum density of a neutral exposure of Dmax(N). In Table 2 the change in Dmax(N) with time is shown for the four developers above. These solutions are monitored with time while standing at operating temperature in glass measuring cylinders using standard paper control strips then the Dmax falls as shown in Table 2. Effect of nitrite on Neutral Dmax (x100) Time D1 D2 D3 D4 (Hrs) R1 G1 B1 R2 G2 B2 R3 G3 B3 R4 G4 B4 0 266 265 263 249 264 270 249 246 243 250 266 271 24 264 263 255 263 274 269 252 273 264 263 276 272 48 267 264 249 262 269 269 265 269 266 262 268 268 72 276 268 254 268 267 263 268 269 255 263 268 258 96 278 272 227 276 272 255 274 278 258 270 267 256 192 223 232 232 231 241 237 250 256 236 256 269 238 216 121 138 138 132 146 165 151 167 176 167 182 189 In the table R1, G1 and B1, etc refer to the red, green and blue densities for each of the developer/amplifiers described above. It can be seen that the Dmax densities are better maintained at longer standing times in the presence of potassium nitrite. The density difference between the control and test developer/amplifiers in the red, green and blue records at 216 hours standing time is plotted as a function of potassium nitrite level the curve in Fig 1 is obtained. It can be seen that there is a progressive improvement over the control developer with increase in potassium nitrite level. Example 3 (Invention) In this example the effect of nitrite ion on the stability of an RX developer-amplifier in a forced aeration test was examined. A control developer-amplifier without nitrite ion of the formula shown in Table 3 was used. Developer/Amplifier(D5) Sequestrant 1 0.6g/l Sequestrant 2 2.0ml/l K 2 HPO 3 .H 2 O 40g/l KBr 1mg/l KCl 0.5g/l Catechol disulphonate(CDS) 0.3g/l Hydroxylamine sulphate(HAS) 1.0g/l KOH(50%) 10.0ml/l CD3 4.5g/l Tween 80 0.4g/l Dodecylamine 0.1g/l pH 11.4 H 2 O 2 (30%) 2.0ml/l Time 45 seconds Temperature 32 C Where TWEEN 80 is a non-ionic polyoxyethylene surfactant and is a Trade Mark of Atlas Chemical Industries Inc. Another developer-amplifier(D6) was made by adding 20g/l of potassium nitrite to developer-amplifier D5. These two developer-amplifiers were then compared in an aeration test in which compressed air was bubbled through each solution for several hours. At intervals the bubbling was stopped and a sensitometric strip was processed in each developer-amplifier and the maximum density(Dmax) was monitored during the experiment. The change in Dmax with time is shown in Table 4. Effect of nitrite on aeration Time Bubbling (hours) Neutral Dmax(x100) D5 D6 R G B R G B 0 248 240 232 263 244 223 1 264 251 235 263 251 231 2 264 250 230 271 258 234 Overnight(no bubbling) 3 277 264 234 265 252 233 4 266 255 221 267 247 210 5 264 251 219 276 260 236 6 248 237 202 266 252 217 7 223 214 193 257 246 205 8 197 195 189 259 246 217 The loss of density(x100) over 8 hours aeration in D5 is 51 in red, 45 in green and 43 in blue. The corresponding loss in D6 is 4 in red, -2 in green and 6 in blue. This clearly shows that the presence of nitrite ion reduces density loss on aeration of the developer-amplifier.

Claims: An aqueous redox amplifier composition comprising a colour developing agent, an antioxidant therefor and hydrogen peroxide or a compound which provides hydrogen peroxide characterised in that the composition contains nitrite ions in a concentration from 0.2 to 50 g/l (as potassium nitrite). A composition as claimed in claim 1 in which the concentration range of the nitrite ions is from 5 to 20 g/l (as potassium nitrite). A composition as claimed claim 1 or claim 2 in which the concentration range of the hydrogen peroxide is from 0.5 to 7 ml/l (as 30% w/w solution). A composition as claimed in claim 3 in which the concentration range of the hydrogen peroxide is from 0.5 to 2 ml/l (as 30% w/w solution). A composition as claimed in any of claims 1-4 in which the antioxidant is hydroxylamine or an aryl or alkyl-substituted derivative thereof. A composition as claimed in claim 5 in which the hydroxylamine compound is present in a concentration of from 0.5 to 4 g/l (as hydroxylamine sulphate). A composition as claimed in claim 5 in which the hydroxylamine compound is present in a concentration of from 0.5 to 2 g/l (as hydroxylamine sulphate). A composition as claimed in any of claims 1-7 in which the ratio of hydrogen peroxide to hydroxylamine compound is from 1.5 to 2.5 (as ml/l 30% w/w hydrogen peroxide solution:g/l hydroxylamine compound as hydroxylamine sulphate). A composition as claimed in any of claims 1-8 in which the pH is from 11 to 11.7. A composition as claimed in any of claims 1-9 in which the pH is buffered by a phosphate.

Inventors: TWIST PETER J, WINSCOM CHRISTOPHER J, TWIST, PETER J., WINSCOM, CHRISTOPHER J., Twist, Peter J., c/o Kodak Ltd., Winscom, Christopher J., c/o Kodak Ltd.
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1995
Main classification: G03C7
IPC codes: G03C7