The present invention relates to photographic processes and is more particularly concerned with the processing of colour photographic paper using redox amplification chemistry.
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.
A particular application of this technology is in the processing of silver chloride colour paper, especially such paper with low silver levels.
Redox amplification processes can be carried out in one a number of ways, for example, in a single developer/amplifier (DEV/AMP), in a developer followed by a peroxide (or other amplification agent) amplifier (DEV, AMP) containing no developing agent, in an amplifier followed by a developer or developer/amplifier (AMP, DEV or AMP, DEV/AMP) or in a developer followed by a developer/amplifier (DEV, DEV/AMP).
When the development and amplification process is to be carried out the ways described above there are chemical stability advantages to holding at least some of the developing agent and oxidant in separate baths. However there is a difficulty in achieving a sufficiently high Dmax.
It is an object of the present invention to provide a method of processing photographic paper using redox development and amplification processes which produce improved results.
In accordance with one aspect of the present invention, there is provided a method of forming a photographic colour image by a redox amplification method from an imagewise exposed photographic silver halide material containing at least one dye image-forming colour coupler which comprises treating the material with one of the processing sequences:
The method of the present invention provides an improved Dmax when processing in a developer followed by either a peroxide amplifier containing no developing agent or a developer/amplifier.
Colour contamination is reduced compared with the known single application process.
The high concentration of colour developing agent needed for the single application process can be reduced in the first developer making it easier to replenish, less likely to crystallise-out and more resistant to discolouration from oxidised developing agent.
The present method while involving more processing steps than the prior art can still be completed in the same total process time.
For a better understanding of the present invention reference will be made to the accompanying drawings which illustrate the results of the working Examples below in which:-
In one embodiment the material is treated in a developer as the first processing step.
In another embodiment the second processing step comprises treatment in an amplifier or developer/amplifier.
Optionally a wash step may be introduced between any of the processing steps defined above.
In one embodiment of the present invention the material is treated in a developer and then an amplification bath and this sequence is repeated one or more times. Alternatively the sequence developer followed by developer/amplifier may be repeated or any combination of these steps may be employed as long as at least one step is repeated.
It is preferred to remove excess peroxide from the silver halide material after an AMP or DEV/AMP bath before returning it to a colour developing agent-containing bath. This may be achieved by washing or by using a solution that will destroy peroxide, for example a sulphite solution. A similar result can be achieved when returning to developer straight from the amplifier if sulphite is present in the developer. This will react with the hydrogen peroxide of the amplifier to remove it and hence prevent any degradation of the developer.
While a single repetition of the processing sequence may be employed, more than one repetition can be used enabling colour developing agent levels to be further reduced.
A particular application of this technology is in the processing of silver chloride colour paper, for example paper comprising at least 85 mole percent silver chloride, especially such paper with low silver levels, for example levels below 300 mg/m2, preferably below 200 mg/m2 and especially below 150 mg/m2.
The photographic materials can be single colour elements or multicolour elements. 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 and subbing layers.
Suitable materials for use in the emulsions and elements used in this invention are described in Research Disclosure, December 1989, Item 308119, published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND, which will be identified hereafter by the term "Research Disclosure."
Preferred colour developing agents are p-phenylenediamines. Especially preferred are:
With negative working silver halide a negative image can be formed. Optionally positive (or reversal) image can be formed.
The following Examples are included for a better understanding of the invention.
A developer and amplifier of the composition shown in Table 1 were made up and used to generate sensitometric strips. The photographic colour paper used was currently available silver chloride-based colour paper hahving a total silver coverage of 670 mg/m2 as the control and a similar paper having a total silver coverage of 145 mg/m2 as the paper for the redox amplification process of the invention.
*solution 1 is a 60% solution of 1-hydroxy ethylidene-1,1-diphosphonic acid,
***CD3 is N-[2-4-amino-N-ethyl-m-toluidino)ethyl]-methanesulphonamide sesquisulphate hydrate.
After the strips were placed in developer for 20s followed by amplifier for 10s, they were then placed in the RA4 bleach-fix bath for 45s and then washed for 2min. Sensitometric curves were obtained and plotted from the strips processed in this way. These curves are shown as dotted lines in Figure 1. The results obtained for the control strips processed in the RA4 process were also plotted and these are shown as solid lines in Figure 1.
From Figure 1, it can be seen that the Dmax for the red and blue in particular are low compared with the RA4/control strips.
An experiment similar to that described in Example 1 was then carried out but with the CD3 level increased to 12.0g/l. The results obtained are shown in Figure 2. As before, the redox amplification process is shown as dotted lines and the RA4/control strips as solid lines.
Figure 2 illustrates an improvement in the Dmax values but the Dmax value obtainable for the red record is still below aim even though the CD3 level in the developer is higher than acceptable.
The developer and amplifier formula were adjusted as shown in Table 2 for this example.
solutions 1 and 2 and CD3 were as defined in Example 1
As before, the developer and amplifier were followed by the bleach-fix of Example 1 for 45s and a wash for 2min. The results obtained are shown in Figure 3 as dotted lines with the results for RA4 shown as solid lines. As can be seen from Figure 3, there are some deficiencies in the redox amplification process curve when compared with the RA4/control strips curve in terms of low contrast, soft toes, high Dmin and lack of Dmax.
Using the developer and amplifier formula given in Table 2, a double application of developer and amplifier was applied to the strips in the following sequence at 35°C:-
The results obtained are shown in Figure 4. Here contrast and Dmax levels are matching those obtained for RA4/control strips and in the case of the green record now too high. The Dmin level is also too high but now that adequate Dmax is available it is likely that coating or formulation optimisation would eliminate this.
It is to be noted that sensitometry can be achieved with full Dmax using the multiple application of the developer and amplifier in the same total process time as for a single application of the developer and amplifier.
The high concentration of colour developing agent needed for the single application process can be reduced in the developer making it easier to replenish, less likely to crystallize out and more resistant to discolouration from oxidised developing agent.