This invention relates to improvements in chemical reaction systems, and particularly to such chemical reaction systems when applied to photographic processes. The invention also relates to apparatus for use therewith.

It is often the case in chemical reaction systems that a chemically reactive substrate is presented sequentially to a number of different reaction sites in sequence. One of the problems with such serial reactions is carry-over of reactive materials as a result of a wetting action of the reactive substrate by the chemical reactants concerned. Another problem is that even if reactants from a first bath are mutually compatible with reactants in a second or subsequent bath, very often the by-products of reaction in one bath have a deleterious effect on reactions to follow. This problem becomes worse as the relative speed of the reactive substrate

increases. This problem is particularly acute in the processing of photographic paper, but is of course equally applicable to serial treatment of textile webs for example where similar problems arise.

Accordingly the present invention provides in a first aspect a chemical reaction system comprising at least two baths through which a reactive substrate is passed sequentially, said baths containing respectively first and second reagents reactive with said substrate; the invention being characterised in that after passage through the first reagent, and before contact with the second reagent, the substrate is contacted with a further amount of the first reagent which is at least substantially free from reaction products formed in the first bath. As it will be appreciated it is often the case that deleterious by-products such as halide ions are formed during reaction between the reactive substrate and the first reagent. As a continuous reaction progresses there will be a build up of such deleterious by-products which result in a higher throughput of reactants or can eventually result in the whole contents of the bath having to be discarded. Not only does this provide environmental pollution

problems, but also results in comparatively high costs. It is most desirable therefore that the reactive contents of the baths should be utilized as long as possible. By causing the substrate to contact a further amount of the first reagent, unpolluted by by-products, the reactions uncompleted due to by-product interference can be completed. Further the amount of by-product can be substantially reduced by wash off and dipping effects; and by suitable arrangement of overflows the amount of first reagent removed by adherence to the substrate as it leaves the first bath can be compensated for by addition of the correct amount of further material.

Accordingly the reaction system of the present invention is improved when the passage of the substrate from the first bath results in a retention of reagent by the substrate as it leaves the bath thereby depleting the first bath by arranging that a further amount of first reagent is adapted to flow into the first bath after initial contact with the substrate; and in that the further amount of reagent is continuously topped up at a rate equivalent to the reagent retained by the substrate.

In a preferred form of the invention an auxiliary bath or baths are interposed between the first and second baths, said auxiliary bath or baths containing a further amount of the first reagent.

The above system may be conveniently applied to a photographic development system wherein the substrate is a photographic substrate such as a photographic colour paper, and the first reagent is a photographic developer solution. The second reagent may then be a photographic amplifier solution so that the further amount of the first solution will be in the form of a replenisher solution for the first bath.

In a preferred form of the invention the auxiliary baths may be formed of a first auxiliary bath adapted to overflow into the developer bath, and a second auxiliary bath adapted to overflow into the first auxiliary bath, whereby the substrate passes through at least two auxiliary baths countercurrent to the replenisher.

A preferred form of this aspect of the invention the kinetics of the reaction between the first reagent and the substrate are such that the reaction is substantially completed in the first bath.

In a further aspect of the invention there is provided a photographic development apparatus comprising a developer bath, an amplifier bath, and a bleach-fix or fixer bath adapted such that a photographic paper substrate path passes sequentially through said baths; the invention being characterised. in that at least one replenisher bath is provided which is operatively associated with the developer bath and is adapted to overflow thereinto, and in that the substrate path passes through the replenisher bath immediately after it leaves the developer bath.

The accompanying diagrammatic drawing to which reference is now made illustrates the application of the invention in a photographic process.

The apparatus generally comprises a first tank 1 containing developing solution 2 and a second tank 3 containing a bleach-fix of fixing solution 4.

A photographic substrate in this case a photographic paper coated with a low level of silver halide in gelatine, is fed into the tank 1 along a substrate path 5, initially over a roller 6 and around a lower roller 7 in the developing solution 2.

At the top of the tank 1 there is positioned a small tank 8 which contains one roller 9 over which the paper passes. From the tank 8 the paper passes over a roller 10 into a tank 11 comprising an intermediate stage for the process. The paper passes over the roller 12 in the bottom of the tank 11 and up over a roller 13. A developer-replenisher solution is fed into the tank at 14 and this has a rate of feed which is substantially equal to the loss of liquid from the developing tank 1 by virtue of carry-over of developer solution on the paper as it leaves the tank 1. Any excess liquid passes through an overflow pipe 15 into the tank 8.

The paper is fed from the roller 13 over a roller 16 into an amplification tank 17. The paper goes round a roller 18 at the bottom of the tank 17 and out over

an exit roller 19 into the bleach-fix solution 4 in tank 3.

In operation the paper to be processed is fed along substrate path 5, over roller 6 into the developing solution 2 and passes from this into the tank 8 and around the roller 9. In so doing the developer, which in this example is one similar in composition to that known as Kodak RA-4, reacts with the silver halide on the paper and consumes the developing agent known as Kodak CD3 and leaches out chloride ions to form a seasoned solution. This seasoned solution is taken into an auxiliary tank 8 by carry over on the paper as it passes from the developing tank. Tank 8 comprises developing agent of the same constitution as developing solution 2 but with very little by-product therein. From tank 8 the paper passes over roller 10 into the replenisher tank 11 which is constantly filled with replenisher 14. The input of replenisher is only slightly in excess of the loss rate through the carry-over of the replenisher on the paper and the excess replenisher overflows down tube 15 into auxiliary tank 8. In auxiliary tank 8 the paper is subjected to an intermediate treatment with

replenished developer. The liquid carried over into the replenishing tank 11 was thus less seasoned than that in tank 1.

The paper leaving tank 11 over rollers 13 and 16 is coated almost wholly with the replenisher and this paper is carried straight into the amplification tank 17, whereafter it passes over rollers 18 and 19 before entering the bleach-fix or fixing solution 4 in tank 3. The effect of the process is that no chloride ions were carried over into the amplifying tank 17 or were carried over in such minute quantities as to be of little effect.

As a result of the invention the rate of the addition of replenisher introduced into tank 14 was able to be controlled to a level such that it just kept the developing solution 2 topped up with a minimum or no overflow. This resulted in there being no, or very little, developer to be treated as an effluent discharge.

The following two examples show the effect of the invention:

EXAMPLE I

Three solutions consisting of a developer, a replenisher and an amplifier were prepared as described in table 1 below.

Samples of exposed paper were processed through three different cycles as follows:

Cycle 1. starts with a developer composition that would occur in a developer tank seasoned with replenisher at a replenishment rate of 3ml/sq.ft. This results in the highest KCl level that would be expected. The replenisher had a composition which was necessary to replenish the developer tank at 3ml/sq.ft. D ax and Dmin values through these three process cycles are shown in Table 3 for a coating (A) which contains a total of 13.4 mg/sq.ft of silver.

It can be seen that with the same total processing time as in cycle 1, cycle 2 gives higher Dmax values especially in the separations. This demonstrates the principle of the invention. Cycle 2 has lower Dmax values than cycle 3 and this indicates that cycle 2 would be etter if the developer time was shorter and replenisher time was longer.

In the above example the Anti-calcium agent was Kodak Anti-Cal N05 and the anti-oxidant was Kodak BD89.

EXAMPLE II

A second example is shown in Table 4 a coating (B) which contains 20.5 mg/sq.ft. of silver as measured by X-ray fluorescence.

The above examples were all processed in apparatus of the construction of the figure. It is possible, however, to vary this arrangement. For example, the system of multiple-application rollers could be used as the sole application method or, alternatively, the sole application system could be a U tube of a relatively small volume rather than the serial tanks are just described. In such a case the replenisher would be fed in at the exit side of the tube and there would be relatively little movement of the replenisher

through the tube, although what there was would be from the exit side to the inlet side. This would mean that the concentration of replenisher would gradually increase from 100% at the exit side to a lower figure at the paper entry side.

With a U-tube of a total volume of 300ml. a replenishment rate of the order of 15ml/sq.ft. is sufficient. This ensures that there is enough path length of uncontaminated replenisher solution to be carried into the amplifying tank 17.

It can thus be seen that the process of the invention avoids problems due to the build-up of halide ions in the developing solution which would inhibit amplification. The invention uses the minimum of materials and is thus likely to cause very little environmental pollution.