METHOD OF PHOTOGRAPHIC PROCESSING This invention relates to a method of processing a photographic silver halide material. In order to produce a visible image, an imagewise exposed photographic silver halide material is processed in one or more aqueous processing solutions. In one form of colour photography a negative colour image is formed in a film and a colour print is made by exposing a colour negative paper to the negative image. The paper is then processed in a colour developer to form a silver image and corresponding dye image in each of three colour layers thus together forming the desired full colour image. A typical second processing stage is a bleach-fix solution which bleaches the unwanted silver image and removes undeveloped silver halide. Photographic materials not containing silver halide layers are also known which are neverthless processed with solutions. The processing steps are usually accomplished by immersing the photographic material in the processing solutions, often in a processing machine, for a particular length of time at a particular temperature. Thus it is the combination of time and temperature which determines the extent of the processing. In the development stage in particular, the time and temperature have to be accurately controlled.

The present invention provides a method of controlling the amount of processing solution components entering the layer or layers of a photographic material hence controlling the processing itself by novel means.

According to the present invention there is provided a method of processing a photographic material comprising a support bearing at least one

swellable layer which method comprises contacting the material with a processing solution containing a component which limits the swell of the layer so that its ta e—up of processing solution components is controlled by the degree of said swell.

The photographic material may be a black—and—white or colour material and may contain a photosensitive silver halide layer comprising a hydrophilic colloid binder, eg gelatin, a gelatin derivative or polyvinyl alcohol. Non-hydrophilic binders may also be used especially in non—silver halide systems. The material may be one for use in physically developed systems including both photosensitive and non—photosensitive materials, for example, materials for the silver salt diffusion transfer process. In addition the material may be for the diazo, dye transfer or dye bleach process.

The solution containing the swell limiting compound is preferably aqueous but this is not essential. Non—aqueous solutions, for example comprising an alcohol, glycol, glycol ether or hydrocarbon solvents may also be employed.

In a particular preferred embodiment the photographic material is successively contacted with a number of processing solutions each one containing swell—limiting components in such amounts that the swell of the layer is increased with each solution so that further processing solution components are successively taken up by said layer. This enables the components needed by, say, a developer to be added to an emulsion layer separately or in groups.

The present invention provides a controlled way of processing photographic products using small amounts of liquid. Processing times can be shortened

as concentrations can be higher. More even processing can be achieved for surface applied solutions and processing normally undertaken above room temperature in a deep tank can be achieved at room temperature itself.

In addition, since the components can be added sequentially, the final combination and concentration of components may be impossible to obtain in the conventional way. For example the concentration of a component could be higher than could be achieved from a conventional, stable developer formulation or the particular combination might be one that would be unstable if combined in a single solution. The component that limits the swell of the emulsion layer may be a salt, particularly an alkali metal or ammonium salt. Such salts may be chlorides, sulphates or carbonates. Examples of particular salts are sodium chloride, potassium sulphate, potassium carbonate, ammonium sulphate, etc. Preferably the salt is chosen so as not to interfere with the processing function. Hence, for developers, potassium carbonate or sulphate would be suitable.

If the developing agent is added separately this could be from an acid solution while the remainder of the necessary components could be added subsequently with sufficient alkali to provide the desired pH for processing.

The processing solutions may contain a thickener and hence be viscous, such solutions being suitable for surface application.

The processing solution may contain any of the many components used in photography, for example as described in "Modern Photographic Processing" by Grant M. Haist, John Wiley and Sons, 1979.

The processing solution may be an amplification solution containing a colour developing agent and a redox amplification oxidant, e.g. a peroxide, periodate or cobalt (III) complex as described in US Patents 3 674 490 or 3 862 842. In such a case it is convenient to keep and apply the developing agent and the oxidant in separate solutions as a solution of them both is unstable.

The photographic material to be processed may be of many different kinds and contain a variety of additives as described in Research Disclosure Item 17643 December 1978 pages 22-31, Kenneth Mason Publications, Havant, Hampshire, UK. As is customary, silver halide emulsion layers comprise gelatin as binder which is hardened to a conventional extent. Such a hardened layer is however still able to swell in aqueous solutions. Other binders and polymers may also be present as described in the Research Disclosure article cited above. The following examples are given for a better understanding of the invention. All processing was carried out at 20°C. Example 1 — Conventional Colour Processing

In order to demonstrate the invention, the density of the yellow Dmax (blue sensitive) area was used to measure the extent of development in a two stage process. For conventional processing, samples of a colour negative paper comprising pure silver chloride emulsions were used. To process these, the paper was dipped into a test base solution (see table below for composition) for 20 seconds to allow the paper's gelatin layers to swell to their maximum extent (this was established using a swellmeter). The paper was then blotted using photographic blotting paper then plunged into a 20g/l solution of

4-N-ethyl—N-(β-Methanesulphonamidoeth l—o-toluidine sesquisulphate (CD3) for 3 seconds, before removing and blotting again. The sample was allowed to stand for 30 seconds (although the reaction appeared complete in 5 seconds) before washing in water for 3 minutes and then drying at room temperature. The sample was read at 10 random points, using a Macbeth densitometer, with a blue status A filter in the reflection head. From the 10 readings a mean and standard deviation (a measure of the evenness of the process) were calculated. Base Solutions

Soln 1 Soln 2 Soln 3 NaOH 20g/l 20g/l

K ₂ C0 ₃ anhydrous - lOOg/l lOOg/l

The potassium carbonate is present to control the swell of the paper gelatin in the base solution.

Swell measurements indicate that this restricts the swell of the the material to 12 microns, whereas in water it was 17.5 microns and in 20g/l sodium hydroxide, 21 microns. The results above demonstrate the action of the carbonate. Without the carbonate

(solution 1) the density is inferior to the experiment with carbonate and hydroxide (solution 2). The results also indicate that the presence of carbonate gives a more even result. Solution 3 was used to demonstrate that extra base contributed by the

carbonate was not responsible for all the density gain shown by solution 2.

Example 2 — Redox Amplification Processing

A negative colour paper which contained a low silver coating weight (as silver chloride) was used.

2 This has silver coating weights of lOmg/m , lOmg/m 2 and 40mg/m2 in the red, green and blue layers respectively. The dispersions were similar to those used in the paper of Example 1 and were coated at the same laydown. To process these, the paper was dipped into a test 'base solution' (same as for the previous example) for 20 seconds to allow the paper's gelatin layers to swell to its maximum extent. The paper was then blotted using photographic blotting paper then plunged into a 20g/l CD3 solution to which lOOg/l anhydrous sodium sulphate had been added, for 3 seconds, before removing and blotting again. The paper was then dipped into a third solution containing 50 mls/1 30% hydrogen peroxide for 3 seconds before blotting for the last time. The sample was allowed to stand for 30 seconds (again the reaction appeared complete in 5 seconds) before washing in water for 3 minutes and then drying at room temperature. The sample was read at 10 random points, using a Macbeth densitometer, with a blue status A filter in the reflection head. From the 10 readings a mean and standard deviation (a measure of the evenness of the process) were calculated.

Results:

Again the addition of the carbonate as a swell control agent in the first bath gave the coating space to expand in the second solution and therefore take up more developing agent than with conventional solutions, thus giving greater density. Further expansion was possible in the third solution because of the sodium sulphate added to the second bath, the CD3 solution.

In practice, if these three solutions had been mixed together they would have rapidly degraded. An experiment indicated that if the three solutions are mixed in equal proportions a black tar begins to form after 30 seconds. In the imbibed process no tarring was observed in the paper samples.