This invention relates to a method of forming a , photographic colour image and in particular, to a

5 method of forming such an image by a redox amplification process.

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

10 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 to form a dye image. The redox amplifying solution contains a reducing agent, for

15 example a colour developing agent, and an oxidising agent which is more powerful than silver halide and 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

20 (usually contained in the photographic material) to form image dye. The amount of dye formed depends on the time of treatment or the availability of colour coupler rather than the amount of silver in the image as is the case in conventional colour development

25 processes. Examples of suitable oxidising agents include peroxy compounds including hydrogen peroxide, cobalt (III) complexes including cobalt hexammine complexes, and periodates. Mixtures of such compounds can also be used.

30 Since the amplifying solution contains both an oxidising agent and a reducing agent it is inherently k unstable. The best reproducibility for such a process is obtained by using a "one shot" system, where the oxidant is added to the developer and the solution

35 mixed and used immediately (or after a short built in delay) and then discarded. As a result chemical costs

are a maximum and the whole system is unattractive especially for a minilab environment where minimum effluent is required. An alternative to this approach is to use a two bath system wherein the exposed material is treated first in a colour developer bath wherein a dye and silver image is formed and second in an amplifier bath comprising the oxidising agent. By using separate baths it is hoped to keep the colour developing agent and oxidant apart to lengthen the life of the solutions. In practice, however, it is found that the carry-over of colour developer into the amplifier bath (essential for the amplification process to work) occurs due to it being leached out into the amplifier bath. This effect is often referred to as "seasoning".

It is the purpose of the present invention to reduce such seasoning effects in a two bath redox amplification process.

According to the present invention there is provided a process for producing a photographic colour image which comprises processing an imagewise exposed photographic silver halide colour material in a colour developer bath and a separate redox amplification bath wherein the processing time in the amplification bath is less than 60 seconds and preferably less than 30, more preferably less than 15 seconds, especially from 1 to 15 seconds.

Due to the short residence time in the amplifier bath minimal leaching out of colour developing agent occurs thus increasing the life of the amplifier bath considerably and, at best, more or less indefinitely. The short residence time also means that in a processing machine the amplifier tank can be relatively small in size. This also means that if the amplifier does need to be discarded its volume is low.

Furthermore, since the colour developer solution is now stable, a conventional machine tank may be used rather than a specially designed tank which is necessary for a combined developer/amplifier solution. The amplifier solution comprises an oxidant which may be hydrogen peroxide or a compound which provides hydrogen peroxide. It may also contain a buffer to keep the pH alkaline, preferably at from 10 to 11, for example potassium carbonate. If desired the amplifier solution could contain overflow from the developer solution at full strength or diluted. This would use what would otherwise be discarded as effluent.

The amplifier solution could for example merely comprise an aqueous hydrogen peroxide solution at from 0.01 to 0.20, preferably 0.02 to 0.10, molar which could optionally contain potassium carbonate at from 0.005 to 0.30, preferably 0.007 to 0.15, molar.

After dye image formation the material may be bleached and fixed or merely fixed.

The colour photographic material to be processed may be of any type but will preferably contain low amounts of silver halide. Preferred silver halide

2 coverages are in the range 5 - 50 mg/m , preferably in

2 the range 10 - 25 mg/ (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 comprises a resin-coated paper support and the emulsion layers comprise more than 80%, preferably more than 90% silver chloride and are more preferably

Preferably the amplification solution contains hydrogen peroxide and a colour developing agent. 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 following example is included for a better understanding of the invention.

EXAMPLE

The following processing solutions were used:

DEVELOPER (D)

l-Hydroxyethylidene-l,l-diphosphoric acid 1.2 g

Potassium Carbonate

Potassium Sulphate

Potassium Bromide

CD3 (colour developing agent)

Diethylhydroxylamine

Water to pH (3 27°C

FIXER (F)

Sodium Thiosulphate 10.0 g Sodium Sulphite 20.0 g

Acetic Acid (glacial) 20.0 ml Water to 1.0 Litre pH @ °C 4.8

AMPLIFIER

Amplifier (1) water + 5ml/l 100 vol hydrogen peroxide

Amplifier (2) l/8th strength developer (D) + 5 ml/1

100 vol hydrogen peroxide

Amplifier (3) water + 2.5 g/1 potassium carbonate +

5ml/l 100 vol hydrogen peroxide

Amplifier (4) (3) after 24 hours Amplifier (5) (4) + 5 ml/1 fresh 100 vol hydrogen peroxide

Amplifier (6) (3) after 144 hours Amplifier (7) (6) + 5ml/l 100 vol hydrogen peroxide

The processing cycle at 32 °C was as follows:

Wash 60 sec

A silver chloride colour paper containing a total of 13 mg/m^ silver was exposed to a colour wedge step tablet and processed. The densities (xlOO) obtained are listed below.

NEUTRAL D _max NEUTRAL D _min

It can be seen that the short amplification time has rendered the process relatively insensitive to the constitution of that bath. The recovery of activity by the simple addition of hydrogen peroxide to the amplifier is also demonstrated - the recovery is not total as the same, unreplenished developer was used throughout the experiment. The high neutral readings are due to the silver image still being present as no bleach was used in the processing.