1992-10-02
1994-10-04
Rutledge, D.
354324, G03D 308, G03D 302
Patent
active
053530845
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
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 stage are mutually compatible with reactants in a second or subsequent stage, very often the by-products of reaction in one stage 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.
In our WO-A-8702150 there is described a multi-stage countercurrent contacting process wherein a solid is introduced sequentially to a plurality of stages and is reacted with a liquid reactant flowing in the opposed sense.
In this disclosure the depleted liquid reactant is removed from the last contacting stage for disposal or upgrading.
SUMMARY OF THE INVENTION
Accordingly the present invention provides in a first aspect a chemical reaction process comprising at least two stages through which a reactive substrate is passed sequentially, said stages containing respectively first and second reagents reactive with said substrate, wherein 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, whereby the passage of the substrate from the first stage results in a retention of reagent by the substrate as it leaves the stage thereby depleting the first stage, and wherein a first and a second auxiliary stage are interposed between the first and second stages; said first auxiliary stage being adapted to overflow into said first stage, and the second auxiliary stage being adapted to overflow into the first auxiliary stage, and in that the substrate passes countercurrent from the first stage and sequentially through the first and said auxiliary stages, characterised in that the amount of first reagent supplied from the second auxiliary stage at least substantially equates to the depletion rate of the first reagent in the first stage. Each stage is conveniently effected in a 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 a 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.
The above process 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 a
REFERENCES:
patent: 2139224 (1938-12-01), Douden
patent: 3879203 (1975-04-01), Schranz et al.
Henson David M.
Twist Peter J.
Eastman Kodak Company
Pincelli Frank
Rutledge D.
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