GB2070795A

GB2070795A - Photographic process

Info

Publication number: GB2070795A
Application number: GB8006848A
Authority: GB
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1980-02-28
Filing date: 1980-02-28
Publication date: 1981-09-09

Abstract

A bleach-development process is described using aqueous acid processing conditions and reduced diazines or metallic ions in their lower valency state as bleach-developer compounds, to obtain a dye-reinforced silver image. The bleachable dyes described include azo dyes, azamethine dyes and derivatives of H-acid.

Description

SPECIFICATION Photographic process This invention relates to novel methods of processing imagewise exposed photographic material to produce photographic images.

Ever since the advent of photography silver halide salts have been used as the photosensitive agent and for the most part developed silver has been used as the image although in colour photography final dye images have replaced the silver image. However in a large number of photographic materials the final image is still a silver image, e.g. in X-ray materials, microfilms and in graphic arts films as well as in normal black and white high speed camera films. Recently, however, the price of silver has increased to such an extent that ways have been sought in which silver halide can still be used as the photosensitive agent but in which a final dye image is formed even in the photographic materials listed above. By such means there can be either an almost total recovery of the silver used or at least a great reduction in the amount of silver used.

In one method of colour photography the photosensitive agent is a silver salt and a dye developer is used which develops the silver halide and at the same time releases a dye which diffuses out of the photosensitive layers into a receptor layer which can be peeled apart from the photosensitive layer. Thus a final dye image is obtained whilst leaving all the silver in the residual material and thus recoverable. There is described in our published British patent application no. 2007378A a novel photographic diffusion process which does not involve the diffusion of dyes in the photographic material but wherein a final dye image is obtained.

Thus in no. 2007378A there is isdescribed a process for the production of photographic images which comprises the steps of (a) imagewise exposing a photgraphic assembly which comprises at least during the silver halide developing step, in order optionally a supercoat layer, at least one silver halide emulsion layer, a layer containing a modifiable image substance and a support, there being optionally one or more interlayers between each of said components, (b) treating the exposed photographic assembly with an aqueous processing bath so as to provide in the silver halide emulsion layer or layers a solution or dispersion of an image substance modifying/silver halide developing compound, thereby to develop the latent silver image in the silver halide emulsion(s), and (c) in the non-latent image areas allowing the image substance modifying/silver halide developing compound to diffuse in a counter-imagewise manner from the silver halide emulsion layer(s) to the layer containing the modifiable image substance and there to modify reductively the image substance.

Various modifiable image substances are described in no. 2007378A including bleachable dyes.

In the process as described in no. 2007378A the final dye or other substance image is the required image and this is separated from the developed silver image by (a) making the assembly in two parts, one part containing the silver halide emulsion layer and the other part containing the modifiable image substance layer and separating the two parts after the image has been formed in the modifiable image substance layer, or (b) by providing in the photographic assembly a stripping position or stripping layer between the silver halide emulsion layer and the modifiable image substance layer and after the image has been formed in the modifiable image substance layer causing the stripping effect to take place and so separating the two portions of the assembly, or (c) providing a white reflecting layer between the silver halide emulsion layer and the modifiable image substance layer so that in the final processed material the silver image is separated from the image in the modifiable image substance layer by the white reflecting layer and thus is not visible when this image is inspected through a transparent support base.

It has now been discovered that if the silver image and the image derived from the modifiable image substance are located in adjacent layers and are of the same sign, that is to say both positive or negative, a very valuable reinforcement of the silver image is obtained by the image density contributed by the image substance. This enables a high density final image to be obtained even though a relatively low silver coating weight is used in the silver halide emulsion layer or layers.

Therefore according to the present invention in a process for the production of a photographic image which comprises silver halide development there are provided the steps of (a) imagewise exposing a photographic assembly which comprises optionally a supercoat layer, at least one silver halide emulsion layer and adjacent thereto a layer containing a modifiable image substance and a support, there being optionally one or more interlayers in the assembly, (b) treating the exposed photographic assembly with an aqueous acid processing bath so as to provide in the silver halide emulsion layer or layers a solution or dispersion of an image substance modifying/silver halide developing compound (as hereinafter defined), thereby to develop the latent silver image in the silver halide emulsion or emulsions, (c) in the non-latent image areas allowing the image substance modifying/silver halide developing compound to diffuse in a counter-imagewise mannerfrom the silver halide emulsion layer(s) to the layer containing the modifiable image substance and thereto modify reductively the image substance in such a manner that in the fully processed material a coloured image in the modifiable image substance layer reinforces the silver image in the silver halide emulsion layer or layers, and (d) fixing out the unexposed silver halide in the silver halide layer or layers.

By adjacent thereto is meant that the silver halide emulsion layer and the layer containing the modifiable image substance are either contiguous or are sufficiently close for the final dye image to enhance the final silver image.

Preferably there is only one silver halide emulsion layer and this is on the side of the modifiable image substance layer remote from the base.

However there may be two silver halide emulsion layers adjacent on one side or the other of the modifiable image substance layer or the modifiable image substance layer may be sandwiched between two silver halide emulsion layers.

By "image substance modifying/silver halide developing compound" (hereinafter referred to as a dymodev compound) is meant a compound which is able to develop a latent silver image and also able to modify an image substance in such a way as to leave an image in the areas which correspond to the developed silver but leave no image substance in the areas which correspond to the areas of undeveloped silver in the modifiable image substance layer and so obtain a photgraphic image.

The choice of dymodev compound used in the process of the present invention depends on the image substance present in the image substance layer. For examle if the image substance is a dye which can be bleached imagewise when present in a layer then the dymodev compound is one which is able to bleach the image dye when the compound diffuses into the image substance layer. Other forms of image substance modification include rendering a dye which is originally layer substantive either solvent soluble or layer non-substantive and able to be washed out of the layer in a further treatment step.

Thus dymodev compounds work in such a way that the image substance remains in the areas of the image layer into which the dymodev compound has not diffused.

However the preferred image substances of use in the process of the present invention are bleachable dyes and the dymodev compound is a compound which is able to act both as a silver halide developing agent and as an image substance bleaching compound. Such compounds are hereinafter referred to as bleach-developer compounds.

Therefore according to a preferred method of the present invention there is provided a process for the production of a photographic image which comprises the steps of (a) imagewise exposing a photographic assembly which comprises at least during a silver halide developing step, in order optionally a supercoat layer, at least one silver halide emulsion layer, adjacent thereto a layer containing a substantive bleachable image dye and a support, there being optionally one or more interlayers between each of said components, (b) treating the exposed photographic assembly with an aqueous acid processing bath so as to provide in the silver halide emulsion layer or layers a solution or dispersion of a bleach-developer compound thereby to develop the latent silver image in the silver halide emulsion(s), and (c) in the non-latent image areas allowing the bleach-developer compound to diffuse in a counter imagewise manner from the silver halide emulsion layer or layers to the layer containing the bleachable image dye and there to bleach the image dye to form a photographic image so that in the fully processed material a coloured dye image in the substantive bleachable image dye layer reinforces the silver image in the silver halide emulsion layer(s), (d) fixing out the unexposed silver halide from the silver halide layer or layers.

In either the process first set forth or in the preferred process as just set forth the dymodev compound or the bleach-developer compound may be in the form of a preformed solution or dispersion which is applied to the exposed photographic assembly in step (b).

However dymodev compounds and in particular bleach-developer compounds tend to be unstable and thus alternative ways of treating the exposed photographic assembly to ensure that sufficient active dymodev compound enters the silver halide emulsion layer(s) and especially that sufficient dymodev compound diffuses to the image substance layer are preferred.

Thus in one such method the dymodev (or the bleach-developer) compound is an inactive form and a solution or dispersion of this compound is contacted with a substance which renders the compound active just before or whilst the solution or dispersion is applied to the exposed photographic assembly.

In an alternative to this method the photgraphic assembly comprises either in the supercoat layer or below the supercoat layer but above the bottom-most silver halide layer a compound in layer form which is able to render active a solution or dispersion of an inactive dymodev compound. Thus in this method in step (b) a solution or dispersion of an inactive dymodev compound (or bleach-developer compound) is applied to the exposed photographic assembly and when the inactive compound comes into contact with the activating compound it is rendered active and thus able to develop the latent silver image.

In a further alternative method the dymodev compound (or bleach-developer compound) is present initially in a layer in the photgraphic assembly in an inactive form and in step (b) a solvent for the compound is applied to the exposed photographic assembly and the thus formed solution of the inactive compound is treated in the assembly to convert the compound to the active form. The dymodev compound may be treated in the assembly by providing in the assembly as well a substance in layer form which renders active the inactive dymodev compound. In another method at the same time or just after the solvent is applied in step (b) the photographic assembly is subjected to electrolysis. This converts the dymodev compound to the active form in the assembly.

Similarly electrolysis may be used to convert a solution or dispersion of the inactive dymodev (or bleach-developer) compound to the active form, the electrolysis being applied just before or whilst the solution or dispersion is applied to the photographic assembly.

The term photographic assembly of the type defined as used hereinafter means a photographic assembly as defined in (a) of the two processes hereinbefore set forth, that is to say a photographic assembly which comprises at least during the development of the silver halide emulsion an optional supercoat layer, at least one silver halide emulsion layer, adjacent thereto a layer containing a modifiable image substance and a support, there being optionally one or more interlayers between each of said components. According to a modification there is present in this material either in the supercoat layer or in another layer above the layer containing the modifiable image substance (preferably above the silver halide emulsion layer) a layer which is able to activate the non-active dymodev compound.

Thus in the process of the present invention when the exposed photographic assembly of the type defined is treated with an aqueous processing bath so as to provide in the silver halide emulsion layer or layers a solution or dispersion of the dymodev compound in the latent image areas of the silver halide emulsion layer(s) the dymodev compound develops the latent silver image and becomes oxidised and thus inactive both as a silver halide developing agent and as a modifying agent for a modifiable image substance.

However in the non-latent image areas of the silver halide emulsion layer(s) the dymodev compound in solution or dispersion is able to diffuse through the silver halide emulsion, the compound being unaffected by the non-latent image silver halide. When the dymodev compound reaches the modifiable substance layer it modifies the substance which leads to or forms a photographic image which is of the same type as the silver image formed in the silver halide emulsion layer(s). Thus if the image formed in the silver halide emulsion layer(s) is a negative image then a negative dye image is formed in the bleachable dye layer. If the image formed in the silver halide emulsion layer(s) is a direct positive image then the dye image formed in the bleachable dye layer is a direct positive image.

It is to be understood that the photographic assembly can include a number of layers other than the supercoat layer, the silver halide emulsion layer(s) the image substance layer and the optional inter layer or layers between the image dye layer and the support. For example there may be timing layers which release alkali or acid or other substances as required and/or there may be mordant layers. The mordant layer(s) may be used for example to mordant released amines when bleachable azo dyes are used as the bleachable image dye.

The term "image substance" includes preformed image dyes of the type often used in photographic material such as for example azo dyes, anthraquinone dyes and triphenylmethane dyes. It includes also other coloured compounds such as inorganic dyes, in particular pigments, which can provide an image and which can be modified. For example, it includes metallic oxides such as manganese dioxide which can be imagewise bleached.

It is to be understood that the term "bleachable image dye" covers a single dye or a mixture of dyes of the same or different colour.

By use of the present invention it is possible to form either a negative dye image when using a conventional silver halide emulsion or a direct positive dye image when using a direct positive silver halide emulsion, preferably of the suface fogged type. When using a conventional silver halide emulsion in the process of the present invention after exposure the latent silver images will be in the areas of the silver halide emulsion which have been light exposed. However when using direct positive silver halide material in the process of the present invention the latent silver images will be in the areas of the silver halide emulsion which have not been light-exposed.

Bleachable image dyes are used in a silver dye bleach process, for example the well-known CIBACHROME (Registered Trade Mark) silver dye bleach process.

In the conventional silver dye bleach process layer-substantive dyes are reductively destroyed in the presence of photographically developed silver. Such dyes are usually azo dyes and their destruction can be represented thus: R - N + N - R1 + 4H±, RNH2 + R'NH2 The customary known azo dyes, for example those known from British Patent Specifications 923265, 999996, 1042300 and 1077628 and U.S. Patent Specifications 3178290,3178291,3183225 and 3211556, can be used for carrying out the process of the invention.

Suitable bleachable dyes are, moreover, described for example in the Colour Index (third edition) published by the Society of Dyers and Colourists, publishers Lund Humphreys, Bradford and London. In addition to azo dyes it is possible, for example, to use formazan, azoxy, xanthene, azine, triphenylmethane, anthraquinone, nitroso, indigo and phthalocyanine dyes, as well as other known dyes, for carrying out the process according to the invention. It is also possible to use precursors of these dyes, for example hydrazo and diazonium compounds, which give azo dyes, and tetrazolium salts which produce formazan dyes. Out of the group of azo dyes which are suitable the ease with which the azo linkages can be broken depends on the nature of the substituents on the nitrogen atoms.

Examples of suitable bleachable image dyes of the azo type are:

Dye A as used in Example 3.

Another suitable class of bleachable dyes are azamethine dyes of the general formula I

where both D and E represent the atoms necessary to complete an optionally substituted heterocyclic or aromatic ring.

A particularly preferred class of compounds of formula I are those of formula Il:-

where R1 represents an amino or substituted amino group or a hydroxy group, R represents substituent groups which may be the same or different, m is 0 to 3 and D1 is a substituted aromatic ring.

The preferred compounds of formula 11 for use in the process of the present invention are the hydroxypyridone dyes described in our German published patent application no. 2808825.

Therefore in a preferred form of the process according to the present invention there is provided a process for the production of a photographic image by the process as just described wherein the compound of formula I is a hydroxypyridone compound of the general formula Ill:-

wherein R7 represents a hydrogen atom or an optionally substituted alkyl, aralkyl, cycloalkyl, aryl or heterocyclic radical or an optionally substituted amino group, Y represents a hydrogen atom or a hydroxy, -CN, -COOR1, -CONR1R2 or -COR1 group or an optionally substituted alkyl, aralkyl, cycloalkyl, aryl or heterocyclic radical and Z is H or represents a -CN, -COOR3, -CONR3R4, -SO3H, -SO3-, or -COR3 group, where R', R2, R3 and R4 each independently represent a hydrogen atom or an optionally substituted alkyl, aralkyl, cycloalkyl, aryl or heterocyclic radical, R2, R3, R4 each independently represent a hydrogen atom, a halogen atom, an optionally substituted alkyl or cycloalkyl group, an alkoxy group, and R5 and R5 each indepenently represent a hydrogen atom or an optionally substituted alkyl, aralkyl, cycloalkyl, aryl or heterocyclic radical or R5 and R5 together with the nitrogen atom to which they are attached form a 5- or 6membered nitrogen containing heterocyclic ring, or R3 and R5 together with the nitrogen atom N and R5 and R5 together with the nitrogen atom N form two nitrogen containing heterocyclic rings.

The preferred compounds of formula III for use in the process of the present invention are those wherein Z is -CN, -COOR3, -CONR3R4 and -COR3, the most preferred being those wherein Z is -CN.

Preferably both Y and R7 are alkyl or substituted alkyl groups and most preferably both Y and R1 are alkyl groups having from 1 to 4 carbon atoms.

Another preferred class of compounds of formula Ill for use in the process of the present invention are those wherein R7 is hydrogen. Such compounds may exist in the tautomeric form which may be written as formula IV:

where the symbols have the meanings assigned to them above.

Preferably in the compounds of formulae Ill and IV R2, R3 and R4 are each hydrogen atoms. Preferably Y is an alkyl group having from 1 to 4 carbon atoms. Preferably R5 and R8 are the same and each are alkyl or alkoxy groups wherein the alkyl moiety contains from 1 to 4 carbon atoms.

Particularly suitable compounds for use in the process of the present invention are the compounds of formula V:

and the compound of formula VI:-

Another useful class of hydroxypyridone compounds are those of the general formula VII:

where Z, Y, R, m and R7 have the meanings assigned to them above.

An example of a compound of formula VIII is the compound of formula VIII:

Another useful class of compounds of formula I in the process-of the present invention are pyrazolone compounds of the general formula IX:

where R, R1 and m have the meanings assigned to them above and T and R8 are each a hydrogen atom or a substituent group.

Preferably in the pyrazolone compounds of formula IX m is O and R1 is a dialkyl substituted amino group.

Also preferably R8 is an aryl group and most preferably a substituted phenyl group. Examples of such substituents include halogen, alkyl and alkoxy groups. T may be for example an alkyl, alkoxy, amino, or aryl group any one of which may be optionally further substituted, also an acyl group such as an ester or acid.

Other compounds of formula I of use in the process of the present invention are derivatives of barbituric acid orthiobarbituric acid of the general formula X:

where R, R1, and m have the meanings assigned to them above and Rg and Rlo are each hydrogen atoms or alkyl or aryl groups each of which may be optionally substituted, and Q is O or S.

Also derivatives of ninhydrin of the general formula Xl:

where R, R1 and m have the meanings assigned to them above.

Also derivatives of oxindole of the general formula XII:-

wherein R, R1 and m have the meanings assigned to them above and R13 is a hydrogen atom or an alkyl or aryl group.

And derivatives of dimedone or Meldrum's acid of the general formula XIII:

where R, R1 and m have the meanings assigned to them above and X is -CH2 or -O-.

Another useful class of compounds of formula I are compounds of formula XIV:

where both D2 and D3 represent the atoms necessary to complete a heterocyclic ring which is the coupler moiety of a coupled colour coupler. D2 and D3 may be the same or different.

Particularly useful groups D2 and D3 are hydroxypyridone groups of the formula XV:

where Y, Z and R7 have the meanings assigned to them in connection with formula Ill, pyrazolone groups of the formula XVI:

where T and R8 have the meanings assigned to them in connection with formula IX, and barbituric acid groups of the formula XVII:

where Rg and Rlo have the meanings assigned to them in connection with formula X.

A particularly useful dye of this class is murexidewhich has the formula XVIII:

Another useful class of dyes of formula XIV are bishydroxypyridone dyes of general formula XIX:

where each of R14, R15, R16 and R17 are selected from methyl or ethyl.

The hydroxypyridone compounds of formula Ill may be prepared as described in OLS 2808825.

The other compounds of formula I may be prepared by methods well known in the literature, for example by condensing the parent group of the formula XX:

with a nitroso compound of the general formula XXI:

where in the above two formulae D and E have the meanings assigned to them above.

Advantageously the reaction is carried out in a solvent, preferably acetone, ethanol or acetic acid, with or without heating.

The compounds of formula I and in particular the hydroxypyridone compounds of formula Ill and the pyrazolone compounds of formula IX are preferably present in the layer of the photographic material as a solid dispersion.

A method of making such a solid dispersion using gelatin as the binder is as follows: A slurry of the dye (5-20 g) in Olin 10G (1.0 g of 10% solution) and Triton 770X (1.0 g of 10% solution) in water (78 g) was milled in a colloidal mill (e.g. a Dyno Mill, at 3000 rpm charged with 0.7 to 1.0 mm grinding media) to a particle size distribution of less than 1 lim in diameter (mean 0.4 to 0.51lem).

A solution of 4% gelatin (decationised blend, pH 6-7) containing 0.15% wetting agent was added gradually to the stirred dispersion. Hardener may be added at this stage if so desired. The concentration of the dispersion was adjusted so as to give a density of 3 at hoax. (Corresponding to coating weights of 20-30 mg dm-2 of gelatin and 8-10 mg dm-2 of the dye).

Other useful bleachable dyes are bis-azo dyes of the general formula XXII :-

where X is at least one electronegative substituent, Y is also at least one electronegative substituent group or is an alkoxy or aryloxy group and A+ is either the cation of a heavy metal or is a cationic polymeric mordant.

Examples of preferred electronegative substituents are halogen atoms and particularly chlorine atoms, cyano, acylamino and carboxylic acid groups.

Most preferably Y is at least one electronegative substituent.

Examples of suitable heavy metal cations which serve to render the bis-azo dye of formula XVII substantive to the layer in which it is coated are barium and calcium cations.

Examples of suitable cationic polymeric mordants are: Polyvinylamine

Polyvinylguanidine

Polydialkylaminoethyl methacrylate .* .

where R and R' are each alkyl groups. Preferably both R and R' are methyl groups.

The polymeric mordant serves to render the bis-azo of formula XVII substantive to the layer in which it is coated. Similar ballasted dyes to those of formula XVII may also be used.

The bis-azo dyes of formula XVII may be prepared by reacting H-acid which has the formula XXIII:

with one equivalent of a diazonium compound X under acidic conditions to yield the monoazo dye of formula XXIV:

The monoazo dye is isolated and reacted further with a diazonium compound of the formula

under mildly alkaline conditions (sodium or lithium acetate buffer) to yield the dye of formula XXV:

where B is an anion.

Dyes of formula XXII where A+ is a cation of a heavy metal may be prepared from dyes of formula XXV by addition of an aqueous solution of the salt of the heavy metal to an aqueous solution of the dye of formula XXV.

Dyes of formula XXII where A+ is a cationic polymeric mordant are most usually prepared in a gelatin solution. Thus an aqueous solution of the dye of formula XXV may be added to an aqueous gelatin solution which comprises the cationic mordant. This gelatin solution may then be used as a coating solution to prepare the layer of the photographic assembly which comprises the dye of formula XXII.

The dyes of formula XXII when A+ is a heavy metal cation are preferably present in the layer of photographic material as a solid dispersion.

By bleach developer compound is meant a compound which is able both to develop a latent silver halide image and to bleach a bleachable image dye. Various classes of bleach developer compounds are known.

Perhaps the best known class is the reduced form of silver dye bleach catalysts. Silver dye bleach catalysts are used in the silver dye bleach process in which they accelerate greatly the silver dye bleach process to bleach the dye in accord with the developed silver areas. Silver dye bleach catalysts work in an acid solution.

The most widely used dye bleach catalysts are diazine compounds, especially 1,4-diazines, for example pyrazines, quinoxalines and phenazines in their reduced form.

Examples of suitable diazines are pyrazine and its derivatives and quinoxaline compounds, especially those which are substituted in the 2-, 3-, 5-, and/or 7- position by lower alkyl, hydroxyalkyl or alkoxy (C1-C4), especially methyl, hydroxymethyl or methoxy, further by acylated hydroxymethyl groups (CH2 SO3H), amino or acylated (acetylated) amino groups, carboxyl, sulphonic acid (SO3H), benzoyl, acetyl, phenyl, benzyl or pyridyl.

The 1, 4-diazine compounds are preferably used in the form of aqueous solutions. The solution can also contain a mixture of two or more diazines.

The diazines can be present in the photographic assembly in suspension or as a solution in a high-boiling solvent. Furthermore, the diazines can be incorporated in capsules in the photographic assembly which can be broken by a change in pressure, temperature or pH, in the light-sensitive layer or in an adjacent layer.

Usable dye bleach catalysts are also described in German Auslegeschriften 2010707,2144298 and 2144297, in French Patent Specification 1489460 and in U.S. Patent Specification 2270118.

It is known from British patent specification 1183176 that the reduced form of such diazine compounds can act as silver halide developing agents.

Another particularly useful class of bleach-developer compounds are salts of metallic ions and complexes of metallic ions with suitable ligands which are capable of acting as silver halide developing agents.

Metallic ions which are capable of acting as developing agents for latent silver images are well known (see for example Photographic Processing Chemistry by L.F.A. Mason, Focal Press, 2nd Edition, 1975, pages 177-180). Such metallic ions are the lower valency state ions of variable valency metals. In general they act at low pHs to preserve their active lower valency state.

Metallic ions and complexes of metalic ions with suitable ligands which are capable of acting as developing agents for latent silver images in an aqueous acid solution are able also to act in an acid solution as bleaching agents for bleachable dyes. However they are not silver dye bleach catalysts because after bleaching the bleachable dye they become oxidised to their higher valency state but can not be reduced to their lower valency state by metallic silver as are silver dye bleach catalysts.

Preferred metallic ions for use as silver halide developing agents in the process of the present invention are chromous that is to say Cr++, vanadous that is to say V++ and titanous that is to say Ti+++.

There may be present also in the bleach-developer solution which comprises such metal ions a ligand, e.g.

ethylene diamine tetraacetic acid, which beneficially modifies the redox potential of the metal ions.

The preferred bleach-developer compounds of use in the present invention, that is to say the reduced dye bleach catalysts and the lower valency ions of metallic salts or complexes as hereinbefore defined, both act in highly acid aqueous solutions.

When.an assembly of the type hereinbefore described is used to perform the invention the processing fluid may contain a preformed dymodev compound or an inactive form of the dymodev compound which is not able to act either as silver halide developing agent nor as dye bleaching agent. In the second case when the dymodev compound used is a bleach-developer compound there may be present in the photosensitive portion of the assembly preferably between the supercoat layer and the silver halid emulsion layer(s) a metallic layer as hereinafter described. When the processing fluid is applied to the supercoat layer of the assembly it diffuses into this metallic layer and there is reduced to its active state.It then diffuses into the silver halide emulsion layer(s) and there the latent image areas of the silver halide are developed by the compound but in the non-latent image areas the compound diffuses into the adjacent image portion there bleaching the dye to form a dye image. If a preformed bleach-developer compound is used in a two-component assembly preferably the dummy web is one component and the photosensitive portion and image portion are both coated on the support base and comprise the second component. After exposure of the assembly processing fluid containing the preformed bleach-developer is introduced between the dummy web and the emulsion layer. The dummy web can be separated from the second component after processing.

The solution of bleach-developer compound of use in the preferred process of the present invention may be prepared and applied to the photgraphic assembly in a number of different ways.

For example if the bleach-developer compound used is a reduced diazine compound, this compound may be applied to the photgraphic assembly as a preformed reduced compound. The methods of forming a reduced derivative of 1,4-diazine compound are described in British Patent Specification No. 1183176.

Alternatively, and this is preferred, the reduced diazine compound is produced during the processing step, from a diazine compound or from a N-oxide derived therefrom by use of a reducing agent in layer form in an acid medium, the said reducing agent being a metal which in the electrochemical series of the elements is above silver and up to and including aluminium. This method of processing is described in B.P. Specification No.1330755.

For the present invention the reducing agents can be metals, which are in the electrochemical series above silver and up to and including lanthanum, preferably up to and including aluminium, such metals are e.g.

copper, iron, lead, tin, nickel, cobalt, indium, gallium, cadmium, manganese, aluminium lanthanum and the lanthanides. Further alloys containing these metals or said metals in amalgamated form can be used.

For example there may be used a vacuum deposited coated metal strip for example a tin or copper film base strip, and there is coated on to this coated strip or on the exposed photographic material a solution or paste which comprises a 1,4-diazine compound in an acid solution. The diazine compound is reduced by the metal and diffuses into the photographic material where the reduced diazine compound in the presence of the acid solution acts as a developing agent for the exposed silver halide.

Alternatively there may be present in the photographic material a layer which contains a fine or colloidal dispersion of a metal which in the electrochemical series is above silver and up to and including aluminium.

In fact a colloidal dispersion of aluminium is particularly useful.

In a further alternative method the reduced diazine compounds may be formed in the assembly during the development step by electrolysis.

Similarly if the bleach-developer compound comprises simple or complexed metallic ions in a reduced state these ions may be prepared and applied to the photographic assembly in a number of different ways.

For example (a1) a preformed acid solution of the metallic ions may be used, (b1) the acid solution of the metallic ions may be formed externally to the photographic assembly but as a step in the processing sequence, (c1) the acid solution of the simple or complexed reduced metallic ions may be formed in situ in the photographic assembly during the processing sequence.

Thus in the method (a1) above the reduced metal ion may be preformed by known methods, such as electrolytic reduction of a suitable oxidised form or formation of the required metal ion complex by admixture of suitable starting materials in the required oxidation state.

When method (b1) is used a strip (foil) of a second metal or a strip having a fine colloid dispersion of a second metal coated thereon is used: the second metal having a reduction potential sufficiently negative to achieve reduction of the oxidised form of the metallic ion to the reduced form of the metallic ion. The metal strips are, e.g. composed of aluminium, iron, zinc or tin; further of indium or alloys which include such metals. When employed in a fine colloid dispersion the metals are for example zine, tin, iron, nickel, aluminium or indium may be used; further gallium, lanthanum, or alloys containing these metals.

There is coated on to this coated strip which is then applied to the exposed photographic assembly a solution or paste which comprises an oxidised form of the metallic ion in acid solution. The oxidised form of the metallic ion is reduced by the second metal and diffuses into the photographic assembly where the reduced form of the metallic ion in the presence of the acid solution acts as a developing agent for the latent silver halide. In case (c1) there may be present in the photographic assembly a layer which contains a fine or colloid dispersion of a second metal which can reduce oxidised forms of the metallic ions to produce the active form of the ions. Such metal are aluminium, copper, zinc, tin, iron, nickel, gallium or indium, further lanthanum or alloys which include such metals.Also in method (c1) the reduced metallic ions may be formed electrolytically in the assembly during the silver halide developing step.

Preferred metals amongst these are those which do not react rapidly with atmospheric oxygen and water at room temperature.

If desired, complex-forming agents for the metals can also be employed during processing.

For example, the fluoride ion forms complexes with aluminium-lll ions and the copper-l ion is bonded as a complex by, for example, nitriles, olefines, chloride ions, bromide ions and thioethers. A large number of ligands and also the stability constants of the complexes formed therefrom with various metal ions are listed in the book"Stability Constants of Metal-Ion Complexes", Special Publication No. 17, London: The Chemical Society, Burlington House, W. 1, 1964.During processing, a complex-bonded metal ion forms from the complex-forming agent (for example fluoride ions from NH4F or CaF2 for Al), incorporated in the processing solution or in the material, and the metal, which is present in the form of a layer in the photographic material or is brought into contact with the photographic material during processing, with interposition of the processing bath, and by this means an increase in the reactivity of the metal is achieved.

The use of sparingly soluble compounds as donors of complex-forming agents, for example CaF2 as a fluoride ion donor, has the advantage that an adequate amount of ligand for forming the complex is available without, at the same time, a momentarily undesirable high excess of ligand being present in the solution.

The metals can be distributed in the form of small particles in a layer containing a silver salt or in an adjacent auxiliary layer which may be present. Auxiliary layers can be bonded to the silver salt emulsion layer in an inseparable or readily separable manner. The particles can be dispersed direct in a layer colloid or can additionally be surrounded by a coating of a polymeric substance, Furthermore, the metal particles can be contained in capsules which can be broken open by a change in pressure, temperature or pH. In addition the metals can be supplied for use from small particles of a polymeric substance provided with a metallic, coating.

The accompanying Figures show three assemblies of use in the present invention.

In Figure 1 a support base 1 is coated with a bleachable dye layer 2, on which is coated a silver halide emulsion layer 3. On the silver halide layer is coated a supercoat layer 4.

The assembly of Figure 1 may be processed by the method (a1) as just set forth. That is to say, the exposed assembly may be processed using a preformed bleach-developer compound or the bleach-developer compound is produced during the processing step by electrolysis.

In Figure 2 a support base 1 has coated thereon a bleachable dye layer 2, on which is coated a silver halide emulsion layer 3. On the silver halide emulsion layer is coated a supercoat layer 4. Above this assembly there is shown a layer which comprises a zinc paste layer 5 coated on a thin film base 6.

The assembly of Figure 2 may be processed by the method (b1) as just set forth. That is to say the exposed assembly may be processed by applying an acid solution of an inactive bleach-developer compound (that is to say an oxidised metallic ion or diazine compound) to either the supercoat layer 4 or the zinc paste layer 5 and then pressing these two layers into close contact.

In Figure 3 a support base 1 has coated thereon a bleachable dye layer 2, on which is coated a silver halide emulsion layer 3. On the silver halide emulsion layer is coated a supercoat layer 4 which comprises finely divided zinc particles.

The assembly of Figure 3 may be processed by the method (cl) as just set forth. That is to say the exposed assembly may be processed by applying to the supercoat layer 4 an acid solution of an unreduced diazine or an oxidised metallic ion.

The preferred binder for all layers is gelatin. However so called gelatin extenders may be present for example those derived from synthetic colloid latexes, especially acrylic latexes. Other natural or synthetic binders may be used either alone or in admixture with the gelatin, for example albumin, casein, polyvinyl alcohol and polyvinyl pyrrolidine.

The halide content and ratio of the silver halide present in the silver halide emulsion layer depends on how the material is to be used but all the usual pure bromide, chlorobromide, iodobromide and chlorobromoiodide silver halides are of use in the photographic material in use in the process of the present invention.

There may also be present in the silver halide emulsion layer any of the usual addenda present in silver halide emulsion layers, such as sulphur and gold sensitisers, emulsion stabilizers, wetting agents and antifoggants.

The support used may be of any of the usual supports used for photographic materials, for example if the support is transparent it may be composed of cellulose triacetate, cellulose acetatebutyrate, oriented and subbed polystyrene, polycarbonate or polyester, such as polyethylene terephthalate. If the support is opaque it may be of any of the above listed film base materials which has been pigmented for example with barium sulphate or titanium dioxide to render its coated surface reflecting, or it may be a paper support having a baryta coating thereon or polyethylene coated paper base. Alternatively it may be voided polyester support.

As hereinbefore stated processing is preferably carried out in an aqueous medium and this is preferably rendered acid with a suitable acid or a buffer mixture, advantageously to a pH value between 0 and 4. The processing and developing speed and the gradation can be varied within wide limits, as a function of the pH value. Preferred suitable acids are: aliphatic, aromatic or heterocyclic mono-, di- and tri-carboxylic acids, which can also contain substituents such as chlorine, bromine and iodine atomes or hydroxyl, nitro, amino or acylamino groups, and also aliphatic or aromatic sulphonic acids or phosphoric acid and mineral acids such as HF, HCI, HBr, He104, HNO3, H2SO4, H3PO4 and H2CO3; also HSO3e, SO2, sulphamic acid.Suitable buffers are: [ Al(H2O)5 ] #, HBF4, Na2S207 or Na2S2O5.

Preferably an antifoggant is present in the aqueous acid processing medium for example iodide or bromide ions or 1 -phenyl-5-mercapto-tetrazole.

The following Examples will serve to illustrate the invention Example 1 A photographic assembly as shown in Figure 2 was prepared by coating sequentially onto 0.1 mm thick uncoloured transparent celluslose triacetate base the following layers:1. a gelatin layer containing 12 mg/dm2 of the dye of formula V in 20 mg/dm2 of gelatin, 2. a photosensitive gelatino silver halide emulsion layer containing 30 mg/dm2 of silver as silver bromide in 40 mg/dm2 of gelatin, 3. a gelatin supercoat containing 10 mg/dm2 of gelatin.

The activator strip comprised zinc paste coated onto a cellulose triacetate support. The zinc paste was prepared by adding 10 g of zinc powder to 100 ml of a 4% by weight gelatin solution in the presence of a wetting agent and mixing.

The photosensitive portion of the assembly was imagewise exposed to a step-wedge and then processed in darkroom conditions by applying to the zinc paste strip a processing solution of the following composition: pyrazine 5g sulphuric acid 100 ml of 5 N thickening agent 20 g water to 1000 ml pH less than 1.

The zinc paste coated with the processing solution thereon was then applied to the supercoat layer of the exposed photosensitive portion of the assembly and held firmly in overall contact for 20 seconds.

The photosensitive portion was then washed and a 20% aqueous solution of ammonium thiosulphate was applied to the supercoat layer to fix out the unexposed silver halide. The photosensitive portion was then washed and the image density was determined. After measuring the density of the combined silver and dye image the silver image in a cut-off portion of the processed portion of the assembly was bleached by use of a 5% cupric bromide solution and the density of the dye image alone was determined. Then the dye image in another cut-off portion of the assembly was bleached by use of the acidic pyrazine solution used above and the density of the silver image alone was determined.

Results Dye Silver Dye + silver density density density D min 0.00 0.08 0.08 Dmax 2.35 0.80 3.15 Example 2 A photographic assembly as shown in Figure 3 was prepared by coating sequentially onto 0.1 mm thick uncoloured cellulose triacetate base the following layers:1. a gelatin layer containing 15 mg/dm2 of the azo dye diphenyl black FG as set forth in the Colour Index No.

35435 in 25 mg/dm2 of gelatin, 2. A photosensitive gelatino silver chlorobromide emulsion (15% chloride, 85% bromide) at a silver coating weight of 15 mg/dm2 in 20 mg/dm2 of gelatin, 3. an activating layer consisting of a zinc (9%)/tin (91%) alloy 15 mg/dm2 in gelatin at a coating weight of 25 mgldm2, 4. a gelatin supercoat layer containing 10 mg/dm2 of gelatin.

The photographic assembly was imagewise exposed to a step-wedge and then processed in darkroom conditions by immersing the assembly for 3 minutes in a processing bath of the following composition: 2-methyl-3-acetyl quinoxaline 3 9 70% HCI04 solution 36 ml ethylene glycol monomethyl ether 40 ml 1 -phenyl-5-mercaptotetrazole 0.19 water to 1 litre pH less than 1 The assembly was then washed, fixed in the ammonium thiosulphate solution and washed again as in Example 1 and the densities of the total image, dye image alone and silver image alone were determined as in Example 1. The density of unexposed material was determined to find out the density due to the Zn/Sn layer.

Results Dye Silver Density due Total density density to Zn/Sn layer density D min 0.00 0.03 0.03 0.06 Dmax 1.80 1.10 0.03 2.93 Example 3 A photographic assembly as shown in Figure 2 was prepared by coating sequentially onto a 0.1 mm thick uncoloured transparent cellulose triacetate base the following layers:1. a gelatin layer containing 15 mg/dm2 of the cyan azo dye A as hereinbefore set forth in 20 mg/dm2 gelatin 2. a photosensitive gelatino silver iodobromide emulsion (3% iodide, 97% bromide) at a silver coating weight of 20 mg/dm2 in 30 mg/dm2 gelatin.

The activator strip comprised indium paste coated onto a cellulose triacetate support. The indium paste was prepared by adding 10 g of indium powder to 100 ml of a 4% aqueous gelatin solution in the presence of a wetting agent and mixing.

The photosensitive portion of the assembly was imagewise exposed to a step wedge and then processed in darkroom conditions by applying to the indium paste strip a solution of the following composition: quinoxaline 1 g 5NH2SO4 20 ml KBr 0.5g thickening agent 3.0 g water to 100 ml pH less than 1 The indium paste strip with the processing solution thereon was then applied to the supercoat layer of the exposed photosensitive portion of the assembly and held firmly in overall contact for 2 minutes. This portion of the assembly was then washed, fixed and washed again as in Example 1 and the total image density and the densities due to the silver image alone and to the dye image alone were determined as in Example 1.

Results Dye Silver Dye + silver density density density D min 0.00 0.02 0.02 D max 2.65 0.25 2.90 Example 4 A photographic assembly as shown in Figure 1 was prepared by coating sequentially onto a 0.1 mm thick uncoloured transparent cellulose triacetate base the following layers:1. A gelatin layer containing 10 mg/dm2 ofthedye of theformula:-

in 15 mg/dm2 gelatin 2. a photosensitive gelatino silver iodobromide layer (3% iodide, 97% bromide) at a silver coating weight of 35 mg/dm2 in 40 mg/dm2 gelatin 3. a gelatin supercoat containing 10 mg/dm2 gelatin.

The assembly was imagewise exposed to a step-wedge and then processed in darkroom conditions by coating on the assembly a freshly-made processing bath of the following composition: titanium trichloride (15% solution in water) 100 ml diethylenetriamine penta-acetic acid 125 ml (25% solution) KBr 4g thickening agent 25g water to 1 litre pH 1.2 After 4 minutes the coating bath was washed off the assembly which was then washed, fixed and washed again as in Example 1. The total image density, the density of the silver image alone and the dye image alone was then determined as in Example 1.

Results Dye Silver Dye + silver density density density D min 0.03 0.05 0.08 D max 1.65 0.40 2.05

Claims

1. In a process for the production of a photographic image which comprises silver halide development the steps of: (a) imagewise exposing a photographic assembly which comprises optionally a supercoat layer, at least one silver halide emulsion layer and adjacent thereto a layer containing a modifiable image substance and a support, there being optionally one or more interlayers in the assembly, (b) treating the exposed photographic assembly with an aqueous acid processing bath so as to provide in the silver halide emulsion layer or layers a solution or dispersion of an image substance modifying/silver halide developing compound (as hereinbefore defined), thereby to develop the latent silver image in the silver halide emulsion or emulsions, (c) in the non-latent image areas allowing the image substance modifying/silver halide developing compound to diffuse in a counter-imagewise manner from the silver halide emulsion layer(s) to the layer containing the modifiable image substance and there to modify reductively the image substance in such a manner that in the fully processed material a coloured image in the modifiable image substance layer reinforces the silver image in the silver halide emulsion layer or layers, and (d) fixing out the unexposed silver halide in the silver halide layer or layers.

2. A process according to claim 1 which comprises the steps of: (a) imagewise exposing a photographic assembly which comprises at least during a silver halide developing step, in order optionally a supercoat layer, at least one silver halide emulsion layer, adjacent thereto a layer containing a substantive bleachable image dye and a support, there being optionally one or more interlayers between each of said components, (b) treating the exposed photographic assembly with an aqueous acid processing bath so as to provide in the silver halide emulsion layer or layers a solution or dispersion of a bleach developer compound thereby to develop the latent silver image in the silver halide emulsion(s), (c) in the non-latent image areas allowing the bleach-developer compound to diffuse in a counter imagewise manner from the silver halide emulsion layer or layers to the layer containing the bleachable image dye and there to bleach the image dye to form a photographic image so that in the fully processed material a coloured dye image in the substantive bleachable image dye layer reinforces the silver image in the silver halide emulsion layer(s), and (d) fixing out the unexposed silver halide from the silver halide layer or layers.

3. A process according to either claim or claim 2 wherein the photographic assembly comprises either in the supercoat layer or below the supercoat layer but above the bottom-most silver halide emulsion layer a compound in layer form which is able to render active a solution or dispersion of an inactive dymodev compound or an inactive bleach-developer compound.

4. A process according to claim 3 wherein the compound in layer form which is able to render active a solution or dispersion or a dymodev compound or a bleach-developer compound is a metal which in the electrochemical series is above silver and up to and including lanthanum.

5. A process according to any one of claims 1 to 4 wherein the dymodev compound or bleach-developer compound is a 1,4-diazine compound in its reduced form which is able to act as a silver dye bleach catalyst.

6. A process according to claim 5 wherein the 1,4-diazine is a pyrazine, a quinoxaline or a phenazine in its reduced form.

7. A process according to any one of claims 1 to 4 wherein the dymodev compound or bleach-developer compound is a lower valency state ion of a variable valency metal which is able to act in aqueous acid conditions as a silver halide developing agent.

8. A process according to claim 7 wherein the metallic ion is chromous, vanadous or titanous.

9. A process according to claim 2 wherein the bleachable dye is an azo dye.

10. A process according to claim 2 wherein the bleachable dye is an azamethine dye of formula I as hereinbefore set forth.

11. A process according to claim 2 wherein the bleachable dye is a hydroxypyridone azamethine dye of formula III as hereinbefore set forth.

12. A process for the production of a photographic image according to claim 1 substantially as hereinbefore described with reference to the foregoing Examples and accompanying Figures.