GB2052776A - A process for alleviating partial inactivation of colour couplers - Google Patents

Abstract

A process is disclosed for alleviating the partial inactivation of colour couplers e.g. pyrazolone couplers caused, for example, by reaction with vapours of formaldehyde or a vinyl monomer. Partial inactivation is evidenced by decreased spectral absorptivity of the dye produced by the reaction of the colour coupler with a colour dye-forming compound, such as oxidized photographic colour developing agents. The process comprises contacting a partially inactivated coupler or the reaction product of such a coupler and dye-forming compound, with a solution comprising an oxidizing agent (e.g. a peroxide such as hydrogen peroxide) and an oxidation accelerator e.g. potassium ferrocyanide, sodium anthraquinone disulphonate or disodium iron EDTA, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

Description

SPECIFICATION A process for alleviating partial inactivation of colour couplers This invention relates to the formation of a colour dye by the reaction of a colour coupler with another dye-forming compound and especially relates to the imagewise formation of colour dyes in a photographic material. More particularly, the invention relates to a process for alleviating the partial inactivation of a colour coupler. A partially inactivated colour coupler is one which, when reacted with another dye-forming compound e.g. an oxidized developing agent, requires further oxidation to produce the dye. Such inactivation may occur when the colour coupler has also reacted with a compound which inhibits dye formation e.g. formaldehyde.

It is well known to use silver halide photographic materials containing colour couplers to form colour photographic images by means of imagewise coupling reactions of the colour couplers with oxidized primary aromatic amino colour developing agents. The developing agents are oxidized by reaction with imagewise exposed silver halide.

Silyer halide photographic materials may contain one or more colour couplers which can be affected between manufacture and'prncessing by formaldehyde vapour or a vapour with like effect e.q.

a vapour of a vinyl monomer. This sometimes occurs, for example, through contact of a photographic material with polluted air. This problem is well known in the photographic art, especially in relation to many pyrazolone colour couplers which are used to form magenta dyes in photographic materials. The reaction with formaldehyde inactivates the reaction of the coupler with oxidized developer and leads to a deficit in the production of the intended amount of dye.

If a colour coupler susceptible to this problem comes into contact with a large amount of formaldehyde, it can become totally inactivated; i.e., it will not couple at all with an oxidized primary aromatic amino colour developing agent, and no dye will be formed during processing. However, it is more commonly the case that a photographic material will adventitiously come into contact with only smaller amounts of formaldehyde. When this occurs, colour couplers susceptible to the problem may be only partially inactivated. A!though the mechanism of partial inactivation is not well understood, it is known that a partially inactivated colour coupler will still react with oxidized developing agent to form a dye, but the dye will exhibit a less-than-normal degree of spectral absorptivity.It is theorized that in such cases the reaction with formaldehyde has only partially inhibited the coupling reaction or has otherwise reacted with the colour coupler to tie up colour-forming sites and prevent full colour formation when the coupler combines with oxidized developing agent to form a dye. Whatever the true explanation for this phenomenon, its effect is well known.

It is also known that the effect of partial inactivation can be substantially overcome if, after the photographic material is developed with a primary aromatic amino colour developing agent, subjected to a development stop bath and then washed during processing, the material is treated with an aqueous bleaching solution comprising a very potent bleaching agent, such as potassium ferricyanide, which has a very strong oxidizing effect. Such a bleaching agent will overcome the partial inactivation of a colour coupler by formaldehyde and cause the spectral absorptivity of the dye formed by reaction of the colour coupler with oxidized developing agent to be increased.

However, in order to achieve compactness of processing apparatus and speed of photographic processing operations, it is desirable to omit baths such as stop baths and washing baths from between the colour development and bleaching baths. In addition, while the bleaching bath (the main purpose of which is to oxidize silver image for easy removal) has in the past been followed by a separate fixing bath (to remove oxidized silver image and unexposed silver halide from the material), it is desirable and known to further increase compactness and speed by incorporating the bleaching agent and fixing agent into a single bleach-fix bath.These practices require that a mild oxidizing agent be used as the bleaching agent, because a strong oxidizing agent such as potassium ferricyanide would cause indiscriminate formation of dye in the material if stop and wash baths were omitted after development, and, if incorporated in the same solution with a fixing agent, a strong oxidizing agent would oxidize the fixing agent making it useless for its fixing function. To avoid these problems, it is desirable to use a mild oxidizing agent as the bleaching agent (e.g., a complexed form of ferric ion such as iron ammonium ethylenediaminetetraacetic acid).Unfortunately, such mild bleaches are incapable of overcoming the partial inactivation of colour couplers by formaldehyde, and it has heretofore been thought that, in order to overcome such partial inactivation, further steps of re-bleaching with a potent oxidizing agent and then washing out the bleach would have to be used. However, this would once again slow the processing operation and require new, less compact processing apparatus, because of the additional baths which would have to be used; and, in addition, it would once again raise the environmental problems of disposing of noxious substances such as ferricyanides.

Therefore, it is apparent that a need exists for a method of alleviating the partial inactivation of colour couplers, which does not require increasing photographic processing time by adding new processing baths and which does not require that new, less compact processing apparatus be used in order to practice the method. The present invention provides a method which satisfies this need.

More particularly, the invention provides a solution to the problem of how to produce dye from a partially inactivated colour coupler in a photographic material which is processed in equipment which cannot be altered to incorporate extra stages of treatment. Using the process of the invention, it is possible to recover most of the dye in a manner that requires no modification of the physico-mechanical arrangements of the processing equipment.

The invention provides a process for alleviating the partial inactivation of a colour coupler which process comprises contacting the colour coupler with a solution comprising an oxidizing agent and an oxidation accelerator, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

Generally, the colour coupler is contacted with the solution used in this process after the coupler has already reacted with another dye-forming compound (such as an oxidized primary aromatic amino colour developing agent) to form a dye having less-than-normal spectral absorptivity.

Accordingly, the invention also provides a process for producing dye from the reaction product of a partially inactivated colour coupler and an oxidized colour developing agent which process comprises treating the product with a solution comprising an oxidizing agent and an oxidation accelerator, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

Having regard to photographic materials, the invention provides a process for producing a dye image in an imagewise exposed photographic material containing a silver halide and a colour coupler suceptible to partial inactivation. The method comprises the steps of: a. contacting the material with a colour developing agent, e.g., a primary aromatic amino colour developing agent to produce within the material a silver image and an associated dye image formed by reaction of the colour coupler with oxidized colour developing agent, b. contacting the material with a bleaching agent and a fixing agent either simultaneously or successively in order to remove unexposed silver halide and the silver image from the material while retaining the dye image, and c. contacting the material with a solution, preferably an aqueous solution, comprising an oxidizing agent and an oxidation accelerator in order to alleviate any partial inactivation of the colour coupler which may have occurred, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

Step c. above is preferably carried out by combining an aqueous solution of the oxidizing agent and the oxidation accelerator with a washing bath conventionatly used after the fixing step or with a stabilizing bath conventionally used after the washing bath. In this way, the step in the process for alleviating partial inactivation of colour coupler can be carried out simultaneously with other steps (e.g., washing or stabilization), and, therefore, will not require a longer processing time or the use of new or modified processing apparatus. Alternatively, the aqueous solution of step c. may be applied to the photographic material by a roller or other means, rather than in a processing bath. Also, no washing step is required after this treatment, in contrast to conventional ferricyanide re-bleaching techniques which do require a washing step.

It has been found that the process of the present invention will increase the spectral absorptivity of dyes formed by reaction of partially inactivated couplers with other dye-forming compounds to nearly the levels that can be achieved by using the previously known technique of separate ferricyanide rebleaching followed by washing.

The oxidizing agent used is preferably one which can be applied to the colour coupler without requiring the use of a further washing step to remove the oxidizing agent from the dye-containing material (e.g., photographic material). Thus, the oxidizing agent is preferably one which can remain in a photographic material without producing undesirable side effects or one which can be removed from the material without washing. A preferred oxidizing agent for use in the process of the invention is one which is volatile, so that it can be removed from a photographic material merely by drying at normal atmospheric conditions or in a heated drying cabinet (conventionally at temperatures of from 240C to 700 C). Peroxides such as hydrogen peroxide (including deuterium peroxide), are good examples of suitable volatile oxidizing agents.An aqueous solution of hydrogen peroxide is a particularly preferred oxidizing agent.

The concentration of oxidizing agent in an aqueous solution should be at a level effective to alleviate the partial inactivation of colour coupler without producing undesirable side effects. If the concentration is too low, coupler inactivation may not be alleviated or may be alleviated to a lesser degree, while if the concentration is too high, dye decomposition may result. In a particularly preferred embodiment of the process of the invention, hydrogen peroxide is used as the oxidizing agent in the aqueous solution at a concentration of from 0.3 percent to 0.6 percent by weight of the total aqueous solution (from 1 to 2 'volume').

Apart from hydrogen peroxide which may be used by itself in alleviating partial inactivation of couplers, the invention requires the use of an oxidation accelerator to act as a catalyst for the oxidizing agent. In fact, the performance of hydrogen peroxide at low concentration can be greatly improved by the addition of a trace of an oxidation accelerator. Suitable oxidation accelerators are potential mediators capable of acting as electron-transfer agents between the oxidizing agent and an oxidizable substance by undergoing reversible oxidation-reduction without an appreciable degree of decomposition or degradation. Such compounds are known in the art of electrochemistry, where they are used to accelerate the eq-uiiibration of oxidation-reduction reactions.

Preferably, the oxidation accelerator does not leave a residue that would strongly colour a photographic material, nor does it adversely affect the stability of the dye formed by reaction of colour coupler with the other dye-forming compound. Therefore, the concentration of oxidation accelerator in the aqueous solution is preferably very low, i.e., the oxidation accelerator preferably comprises less than 10 parts per million or less than 0.001 percent by weight of the aqueous solution. More preferably, less than 5 pom'of the oxidation accelerator is used. Examples of oxidation accelerators suitable for use in the process of this invention include potassium ferricyanide, sodium anthraquinonedisulphonate, and disodium iron ethylenediaminetetraacetic acid. Potassium ferricyanide is preferred.

In a particularly preferred embodiment of the present invention, the aqueous solution comprises from 0.3 percent to 0.6 percent by weight of hydrogen peroxide as the oxidizing agent and from 0.0001 percent to 0.0003 percent by weight of potassium ferricyanide as the oxidation accelerator.

It is advantageous for the material treated with the dilute oxidizing agent to be subsequently heated. Such heating may be provided in existing processing equipment by the passage of the material through a heated drying cabinet.

When the process of the invention is embodied in a process for producing a dye image in an imagewise exposed silver halide photographic material, the solution used to alleviate the partial inactivation of couplers is advantageously combined with one of the various processing baths which follow the developing, bleaching, and fixing baths in a conventional photographic colour processing method. For example, in one embodiment, an aqueous solution of an oxidizing agent and accelerator is incorporated into an aqueous washing bath which conventionally follows the fixing bath. In another embodiment it is incorporated into a stabilizing and/or wetting agent bath which follows the washing bath just mentioned.Alternatively, the aqueous solution is applied to the photographic material in a separate bath by itself or is applied by a roller or other means; but incorporation into an already existing bath is more desirable, because it avoids any lengthening of overall processing time and also avoids the need for any modifications to existing processing apparatus. A conventional stabilizing bath with which the aqueous solution of the oxidizing agent and accelerator may be combined comprises a stabilizing agent, such as formaldehyde, in water and sometimes also comprises a buffer system to maintain the pH at a desired level. A conventional wetting bath (which is often combined with the stabilizing bath, but may be separate) contains a wetting agent, such as a non-ionic derivative of polyethylene glycol, in water.The composition and use of such stabilizing and wetting baths are well known in the photographic processing art.

The composition and use of conventional, developing, bleaching, and fixing baths preceding the above-described washing and stabilizing baths are also well known in the art of processing imagewise exposed silver halide photographic materials which contain incorporated colour couplers.

Conventionally, the exposed photographic material is first contacted with a primary aromatic amino colour developing agent (e.g., N-ethyl-N'-hydroxyethyl-p-toluidine) to produce within the material a silver image and an associated dye image formed by the reaction of incorporated colour couplers with the oxidized colour developing agent. It is now conventional to omit subsequent stop and wash baths and, instead, move the developed photographic material next into a bleaching bath comprising a mild bleaching agent, such as iron ammonium ethylenediaminetetraacetic acid, which is incapable of overcoming the possible partial inactivation of colour couplers by, for example, formaldehyde or vinyl monomers. The bleaching bath is followed by a wash and a fixing bath (or is combined with a fixing bath) containing a fixing agent (e.g., ammonium thiosulphate).The purpose of the bleaching and fixing baths is to remove the silver image and any unexposed silver halide from the photographic material while retaining the associated dye image within the material. After washing and treatment with a stabilizer and/or a wetting agent, the material is then dried at atmospheric conditions or, more conventionally, in a drying cabinet heated to from 240C to 700 C.

A typical process which the invention may be used is the Kodak C4 1 process which involves the direct transfer of an emulsion layer wet with colour developer into a bleaching bath which has insufficient oxidizing power to produce dye from any partially inactivated coupler.

The process of the present invention is useful in the processing of any silver halide photographic material containing colour couplers (including negative and positive photographic films and papers). The method is, of course, most advantageously applied to photographic materials containing colour couplers which are susceptible to partial inactivation by formaldehyde or vinyl monomers, i.e., materials containing couplers such as pyrazolones. The process of the invention alleviates such partial inactivation of couplers, so that the dyes formed by reaction of the couplers with oxidized developing agents have spectral absorptivities approaching the levels achieved by using the previously known technique of separate ferricyanide re-bleaching followed by washing.

The following example is provided to further illustrate a preferred embodiment of the process of the invention.

EXAMPLE Samples of a conventional multilayer colour negative photographic film, comprising a blue-lightsensitive gelatin silver halide emulsion layer containing a yellow-dye-forming coupler, a green-lightsensitive gelatin silver halide emulsion layer containing a magenta-dye-forming coupler and a red-lightsensitive gelatin silver halide emulsion layer containing a cyan-dye-forming coupler, were subjected for 66 hours in a closed vessel to the vapour from 10 g. paraformaldehyde. The samples receiving such treatment were compared with untreated samples by exposing all samples to light to create maximum exposure and then processing all samples through conventional baths of developer, bleach, fixer and rinse (the developer comprised a primary aromatic amino colour developing agent, and the bleach comprised iron ammonium EDTA, a mild oxidizing agent).The measured density to green light of the resultant untreated film samples was 2.31, while the density of the formaldehyde-treated film samples was only 1.70. When some samples of the treated film were re-bleached in a ferricyanide solution containing 20 gm/litre potassium ferricyanide for 1 minute and then washed with water for 3 minutes, their density increased to 2.00.

Table 1 shows the results of the tests above and of oxidizing some of the formaldehyde-treated materials with a formalin stabilizing bath to which hydrogen peroxide was added to a concentration of 0.6 percent by weight and to which various small concentrations of oxidation accelerators (namely potassium ferricyanide, sodium anthraquinone-disulphonate, or disodium iron EDTA) were added. The data in Table 1 indicates that treatment with hydrogen peroxide plus small amounts of oxidation accelerator results in dye densities approaching those achievable by re-bleaching with ferricyanide. In this respect, the aqueous solution containing 0.6 weight percent hydrogen peroxide and 0.0002 weight percent potassium ferricyanide performed best among those solutions tested.

The accompanying Figure also shows the results of the tests above. The results are expressed as the percentage of magenta dye recovered relative to that for the full ferricyanide bleach taken as 100 percent. It can be seen that the effectiveness of the hydrogen peroxide is greatly increased by the addition of a small concentration of the redox mediator.

TABLE I

Sample Sample % By Weight % By Weight of % By Weight of % By Weight Optical Sample Re-Bleached Treated With Of Hydrogen Potassium Ferry- Sodium Anthra- of Disodium Density of Treated With With 20 g/l Formalin Peroxide in cyanide in quinonedisulfonate Iron EDTA ln Sample to Formaldehyde? Ferricyanide? Stabilizer Stabilizer Bath Stabilizer Bath in Stabilizer Bath Stabiliser Bath Green Light No No No - - - 0 2.31 Yes No No - - - 0 1.70 Yes Yes No - - - 0 2.00 Yes No Yes 0.6 0 0 0 1.79 Yes No Yes 0.6 0.0001 0 0 1.90 Yes No Yes 0.6 0.0002 0 0 1.96 Yes No Yes 0.6 0.0003 0 0 1.85 Yes No Yes 0.6 0 0.0001 0 1.91 Yes No Yes 0.6 0 0.0002 0 1.82 Yes No Yes 0.6 0 0 0.0001 1.90 Yes No Yes 0.6 0 0 0.0002 1.87

Claims (15)

1. A process for alleviating the partial inactivation of a colour coupler which process comprises contacting the colour coupler with a solution comprising an oxidizing agent and an oxidation accelerator, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

2. A process for producing dye from the reaction product of a partially inactivated colour coupler and an oxidized colour developing agent which process comprises treating the product with a solution comprising an oxidizing agent and an oxidation accelerator, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

3. A process for producing a dye image in an imagewise exposed photographic material comprising a silver halide and a colour coupler susceptible to partial inactivation, which process comprises: (a) contacting the material with a colour developing agent to produce within the material a silver image and an associated dye image formed by reaction of the colour coupler with oxidized colour developing agent, (b) contacting the material with a bleaching agent and a fixing agent either simultaneously or successively in order to remove unexposed silver halide and the silver image from the material, while retaining the dye image, and (c) contacting the material with a solution comprising an oxidizing agent and an oxidation accelerator, provided that when the oxidizing agent is hydrogen peroxide the presence of an oxidation accelerator is optional.

4. A process as claimed in any one of Claims 1, 2, or 3 wherein the oxidizing agent comprises a peroxide.

5. A process as claimed in Claim 4 wherein the peroxide is hydrogen peroxide.

6. A process as claimed in Claim 5 wherein the solution is an aqueous solution comprising from 0.3 percent to 0.6 percent by weight of the hydrogen peroxide.

7. A process as claimed in any one of the preceding Claims wherein the solution comprises more than 0 percent and less than 0.001 percent by weight of the oxidation accelerator.

8. A process as claimed in any one of the preceding claims wherein the oxidation accelerator is potassium ferricyanide, sodium anthraquinonedisulphonate, or disodium iron ethylenediaminetetraacetic acid.

9. A process as claimed in any one of Claims 1, 2 or 3 wherein the solution comprises from 0.0001 percent to 0.0003 percent by weight of the oxidation accelerator, and the oxidation accelerator comprises potassium ferricyanide.

10. A process as claimed in any one of the preceding claims wherein the solution comprises formaldehyde.

1 A process as claimed in any one of Claims 1 to 9 wherein the solution comprises a wetting agent.

12. A process as claimed in any one of Claims 1 to 9 wherein the solution comprises a pH buffer.

13. A process as claimed in Claim 3 further comprising drying the photographic material after carrying out the steps described in Claim 3.

14. A process as claimed in Claim 13 wherein the drying is carried out at a temperature of from 240Cto700C.

15. A process as claimed in any one of the preceding claims wherein the colour coupler comprises a pyrazolone.