GB2303933A - Forming a colour image - Google Patents

Abstract

A method for processing a colour photographic silver halide material which contains a photographic silver halide emulsion layer containing, or adjacent to a layer containing, a yellow dye-forming coupler includes a colour image-forming redox amplification step wherein the material is treated with a colour developer solution and a peroxide amplifier solution in separate steps wherein the yellow dye-forming coupler is a compound having the general formula: wherein ```R 1 is a ballast group, and ```R 2 is an arylalkoxy group, ```dispersed in droplets containing the coupler and a high boiling coupler solvent which is a trialkyl phosphate or dialkyl phthalate.

Description

METHOD OF FORMING A PHOTOGRAPHIC COLOUR IMAGE Field of the Invention This invention relates to forming a colour image in a photographic material by the redox amplification process.

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 developeramplifier) 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.

Due to the low amount of silver in photographic materials intended for redox amplification processing the number of dye clouds formed is smaller than with conventional silver halide materials having higher silver coverages. The result of this is that yellows in particular are not reproduced as well in the low silver materials.

One solution to this problem has been described in our EP-A-0 551 468 where an extra gelatin layer below the yellow layer is employed. The use of an extra layer is however not attractive as an extra layer needs to be coated.

Problem to be Solved by the Invention The present invention provides a solution to the problem of poor reproducticn of yellows in materials processed by the redox amplification process which does not involve coating an extra layer in the photographic material.

Summary of the Invention According to the present invention there is provided a method of processing a colour photographic silver halide material which contains a photographic silver halide emulsion layer containing, or adjacent to a layer containing, a yellow dye-forming coupler which method includes a colour image-forming redox amplification step wherein the material is treated with a colour developer solution and a peroxide amplifier solution in separate steps wherein the yellow dye-forming coupler is a compound having the general formula:

wherein R1 is a ballast group, and R2 is an arylalkoy group, dispersed in droplets containing the coupler and a high boiling coupler solvent which is a trialkyl phosphate or dialkyl phthalate.

Advantageous Effect of the Invention The yellow dye formed appears more "lemon" in this method than the corresponding combined developer/amplifier (DEVAMP) redox amplification due to a narrowing of the bandwidth of the dye. This leads to improved colour reproduction in the finished print.

The yellow dye formed also appears brighter than the corresponding DEVAMP process even though the strips contain the same amount of image silver.

Although not wishing to be bound by any theory, the dye bandwidth narrowing is thought to be brought about by the increased swell that the emulsion layer experiences when the paper is transferred from the developer to the amplifying solution. The increased sell, caused by the low ionic strength of the amplifier bath and the decomposition of peroxide to water and oxygen on the silver surface results in the effective dilution of the coupler droplets. Hence dye is formed over a larger distance as oxidised developer has te travel further to form dye. On drying, these larger dye clouds are flattened into large diffuse discs of dye and the dye is spread more evenly over the paper area. This results in less bandwidth broadening than is seen with conventional dye cloud shape.

Detailed Description of the Invention The group R1 of formula (I) may be any group of sufficient size and configuration which renders the coupler non-diffusible in the photographic material.

Examples of such groups are:

where m is 6 to 20 and R4 is an alkyl group of 6 to 20 carbon atoms.

The group R2 may be phenylmethoxy, phenylethoxy, or phenylpropoxy group.

The yellow coupler is preferably of the formula:

Coupler 1 The coupler solvents are preferably dibutyl phthalate, dihexyl phthalate, tri(2-ethylhexyl) phosphate, tri n-octyl phosphate, trihexyl phosphate or triheptyl phosphate.

The pH of the colour developer may be in the range 9.5 to 12. Preferably the pH is in the range 10 to 12, particularly fro 10 to 11.7.

The developing solution may contain an alkali material that buffers the developer solution. Examples of such materials are alkali metal carbonates and phosphates, for example sodium or potassium carbonates or phosphates. Additional alkali may also be present, eg an alkali metal hydroxide. The carbonates may be present in the colour developer in amounts of 10 to 60 g/l, preferably 15 to 45 gIl and particularly 20 to 30 g/l as potassium carbonate while the phosphates may be present in the colour developer in amounts of 20 to 80 g/l, preferably 25 to 65 g/l and particularly 30 to 50 g/l as potassium phosphate.

The colour developer solution may also contain compounds which increase its stability, for example hydroxylamine, diethylhydrc ylamine or a long chain compound which can adsorb to silver, eg dodecylamine.

The amplification solution may also contain such a long chain compound.

The colour developer may contain from 5 to 12 g/l of colour developing agent, preferably from 7 to 10 g/l. The preferred colour developing agents are pphenylenediamines, for example: 4-amino N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N-ethyl-N-(bhydroxyethyl)aniline sulfate, 4-amino-3-b- (methanesulfonamido) ethyl-N,N- diethylaniline hydrochloride and 4-amino-N-ethyl-N- (2-methoxyethyl) -m-toluidine di-p-toluene sulphonic acid.

Especially preferred is 4-N-ethyl-N-(ss- methanesulphonamidoethyl)--toluidine sesquisulphate which is known as CD3.

The peroxide amplification bath preferably contains 1 to 50 ml/l of 30% wlw hydrogen peroxide and has a pH in the range 5 to 12, preferably 7 to 10.

Optionally an alkali meta' 'carbonate or phosphate buffer is present. Carbonate buffers in the range pH 7-11 while phosphate buffers in the range 10-12, preferably 11 to 11.7.

The developer and amplification steps may be followed by a bleach and/or fix step. If the silver coating weight is low enough either or both of these steps may be dispensed with.

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 total silver levels below 130 mg/m2, eg from 2C to 123 mg,m2, preferably below 100 mg/m2 and particularly in the range 20 to 100 mg/m2.

Within these total ranges the blue sensitive emulsion layer unit may comprise 20 to 60 mg/m2, preferably 25 to 50 mg/m2 with the remaining silver divided between the red and green-sensitive layer units, preferably more or less equally between the red and greensensitive layer units.

The photographic elements processed in the present invention 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 a 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 greensensitive 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 assocated therewith at least one yellow dye-forming coupler The element can contain additional layers, suc as filter layers, interlayers, overcoat layers, subbing layers, and the like.

In the following discussic of suitable materials for use in the elements processed in the present invention, reference will be made to 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." The contents of the Research Disclosure, including the patents and publications referenced therein, are incorporated herein by reference, and the Sections hereafter referred to are Sections of the Research Disclosure.

The silver halide emulsions can be either negative-working or positive-working. Suitable emulsions and their preparation as well as methods of chemical and spectral sensitisation are described in Sections I through IV. Colour materials and development modifiers are described in Sections V and XXI. Vehicles are described in Section IX, and various additives such as br;ghteners, antifoggants, stabilisers, light absorbing and scattering materials, hardeners, coating aids, plasticisers, lubricants and matting agents are described , for example, in Sections V, VI, VIII, X, XI, IX, and XVI.

Manufacturing methods are described in Sections XIV and XV, other layers and supports in Sections XIII and XVI I, processing methods and agents in Sections XIX and XX, and exposure alternatives in Section XVIII.

With negative working silver halide a negative image can be formed. Optionally positive (or reversal) image can be formed.

The present processing solutions may be applied to the photographic material by immersion, dipping, spraying, coating, wiping or application from a roller. Preferably the method o processing may be 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 dm3/m2, preferably less than 3 dm3/m2.

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 ano 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 channe; have a configuration in accordance with the following relationship: 0.6 > F/A S 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 (LVTT) systems are described in more detail in the following patent specifications: US 5,294,956, EP 0,559,027, US 5,179,404, L 0,559, 025, US 5,27D,762, EP 8,559,026, 92/10790, wO 92/1'819, WO 93/04404, WO 92/17370, WO 91/19226, WO 91/12567 WO 92/07302, WO 93/00612, WO 92/07301, and tO 92/09932.

The following Examples are included for a better understanding of the invention.

EXAMPLE 1 A series of photographic paper coatings containing Yellow Coupler 1 and a silver chloride emulsion coated at 0.0269 g/m2 were exposed to a normal 0-3 Log E, 0.15 increment step wedge. The coatings contained different ratios of the coupler to coupler solvent S1 (tris(2-ethylhexyl)phosphate), one coating contained the solvent S2 (dibutyl phthalate).

Strips of the coatings were processed in the DEVAMP formulation for 45 seconds, fixed for 45 seconds in C-41 fixer diluted 100 mls/l and washed.

The same procedure was conducted with the split development formulation, strips were soaked in the developer for 20 seconds, ecess developer was squeegee'd from the surface and the strip transferred into the amplifier bath for 10 seconds. These strips were the fixed and washed as before.

Devamp formula Split development formula 1-hydroxyethylidene-1,1'- 0.6g/l 0.6g/l diphosphonic acid Pentetic acid 0.81g/l 0.81g/l K2HPO4.3H2O 409/l 409/l KBr 1 mg/l lmg/l kOl 1g/l 1 gel HAS 0.6g/l Diethylhydroxylamine ------ 3.0ml/l CD3 4.1g/l lOg/I 50% KOH to pH @; 25 C 11.40 11.40 H202 (30%w/w) 1.85mls/l ----- Time 45 seconds 20 seconds Temperature 35 C 35 C Amplifier solution H202 (30%w/w) 6 mls/l The results are expressed in terms of the colour contamination of the blue record by unwanted absorption's in the red and the green of the spectrum.

The red and green densities should be as low as possible. The method by which the colour contamination numbers are calculated is thus: The red, green and blue status A densities of the yellow single layer strips ere read with a densitometer. The red Dmin was subtracted from the red densities and this process was repeated for the green and blue densities using the respective green and blue Dmin densities.

The blue density (with the Dmin subtracted) was then plotted against the red and green densities (minus Dmin). The colour contamination data below is shown as the red and green density contamination at a blue density of 1.0 in both the split development system and the devamp. Ideally the colour contamination should be as low as possible.

Coupler Coupler solvent Ratio Split Dev Devamp Red Green Red Green 1 Si 1:0.25 0.02 0.18 0.04 0.15 1 S1 1:0.5 0.03 0.16 0.04 0.18 S1 1:0.75 0.02 0.13 0.04 0.17 1 52 1:0.25 0.03 0.16 0.04 0.22 1 (rut) S1 1:0.25 0.04 0.14 0.04 0.18 It can be seen that the colour contamination of the blue layer is reduced by the use of split development. This gives a more "lemon" appearance to the blue layer.

EXAMPLE 2 A multilayer coating containing a total of 58 mg/m2 of silver chloride with 25 mg/m2 of silver chloride in the blue record, with the yellow image Coupler 1 and solvent S1 at a ratio of 1:1.04 was exposed to 0-3 Log E step wedge with blue light.

One strip of this coating was developed in the Devamp formula in Example 1 for 45 seconds, fixed and washed as before. Another strip was developed for 30 seconds in the following formula.

Carbonate Split development 1 -hydroxyethylidene 1 1' 0.6g/l diphosphonic acid Pentetic acid 0.81g/l K2C03 24.1 8g/i KBr lmg/l KCI vigil Diethylhydroxylamine 3.0ml/l CD3 lOg/I 50% KOH to pH @ 25"C 10.0 Time 30 seconds Temperature 35"C The strip was then squeegee'd and immersed in the same amplifier solution as in Example 1 for 10 seconds. The strip was then fixed and washed.

The colour contamination was determined for the yellow layer as previously described in Example 1.

The following table shows the red and green contamination of the blue record at a blue density of 1.0, for the carbonate split developer and the devamp.

Coupler:solvent Carbonate Devamp Ratio split dev Red Green Red Green 1:1.04 0.04 0.15 0.06 0.24 It can be seen that the colour contamination in the carbonate pH 10.0 split development system also shows less colour contamination than the devamp system.

Claims (10)

CLAIMS:

1. A method of processing a colour photographic silver halide material which contains a photographic silver halide emulsion layer containing, or adjacent to a layer containing, a yellow dye-forming coupler which method includes a colour iage-forming redox amplification step wherein the material is treated with a colour developer solution and a peroxide amplifier solution in separate steps wherein the yellow dye-forming coupler is a compound having the general formula:

wherein R1 is a ballast group, and R2 is an arylalkoxy group, dispersed in droplets containing the coupler and a high boiling coupler solvent which is a trialkyl phosphate or dialkyl phthalate.

2. A method as claimed in claim 1 in which the coupler has the formula:

3. A method as claimed in claim 1 or 2 in which the colour developer solution has a pH in the range 9.5-12.

4. A method as claimed in any of claims 1-3 in which the colour developer solution has a phosphate buffer and has a pH in the range 10-12.

5. A method as claimed in any of claims 1-3 in which the colour developer solution has a carbonate buffer and has a pH in the range 9-11.

6. A method as claimed in any of claims 1-5 in which the photographic material is a silver halide colour paper having red- green- and blue-sensitive layer units whose halide comprises at least 85 mole percent silver chloride.

7. A method as claimed in claim 6 in which the total silver halide coating weight is in the range 20130 mg/m2.

8. A method as claimed in claim 6 or 7 in which the total silver level is from 2e to 120 mg/m2, the silver level in the blue sensitive emulsion layer unit is from 25 to 50 mg/m2 and the remaining coated silver weight is divided between the red and green-sensitive layer units.

9. A method as claimed n any of claims 1-8 in the processing is carries @ut cy 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 tank volumes per minute.

10. A method as claimed n claim 9 in which the ratio of tank volume to maximum area of photographic material accomodatable there@n (ie maximum path length x width of material) is less than 11 dm3?m2.