GB2061993A

GB2061993A - Photographic dyestuffs

Info

Publication number: GB2061993A
Application number: GB7937012A
Authority: GB
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1979-10-25
Filing date: 1979-10-25
Publication date: 1981-05-20
Also published as: GB2061993B

Abstract

Novel ballasted derivatives of H- acid have the formula: <IMAGE> where either X or Y represents at least one electronegative substituent and the other of X and Y represents a ballasting group which comprises at least 16 carbon atoms or both X and Y represent a ballasting group which comprises at least 16 carbon atoms and A<+> is a cation. The use of these dyestuffs as the bleachable dyes in the catalyst diffusion process of British Patent Application No. 2007378A is also described.

Description

SPECIFICATION Novel chemical compounds This invention relates to novel dyestuffs, to silver halide photographic material containing these dyestuffs and to methods of processing this 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. We have discovered 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.

In British patent application No. 2007378 there is described a process for the production of a photographic image which comprises silver halide development and in which there are provided the steps of: (a) imagewise exposing a photographic 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 substantive bleachable dye image dye and a photobase, 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 a bleach/developer compound (as hereinafter defined), thereby to develop the latent silver image in the silver 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(s) to the substantive bleachable dye image dye and there to modify reductively the image substance.

In British patent application no. 2007378 bleach/developer compound is defined as a compound which is able to develop a latent silver image and also able to bleach a bleachable dye layer which corresponds to the areas of the undeveloped silver and so to obtain a photographic image.

In B.P.A. no 2007378 various bleachable dyes are described but the preferred ones are stated to be certain azo dyestuffs of the type used in silver dye bleach processes.

We have now discovered a novel class of azo dyes which are of use in the process described in B.P.A. No.

2007378.

Therefore according to the present invention there are provided dyestuffs of the general formula I:

where either X or Y represents at least one electronegative substituent and the other of X and Y represents a ballasting group which comprises at least 16 carbon atoms or both X and Y represent a ballasting group which comprises at least 16 carbon atoms and A+ is a cation.

Preferably when either X or Y represents a ballasting group containing at least 16 carbon atoms there is present in this ballasting group an electronegative substituent or there is also present attached to the phenyl group to which X or Y is attached at least one electronegative substituent.

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

Examples of suitable cations are sodium and potassium ions.

The preferred compounds of formula I are those wherein X represents at least one electronegative substituent and Y represents a ballasting group containing at least 16 carbon atoms.

Most preferably X represents two chlorine atoms substituted in the 2 and 5 positions in the phenyl group.

Examples of two preferred groups Y are 4-N-methyl-(2,4-ditertamylphenoxy acetyl) amino and 3-chloro-4 N-methyl-(2,4-ditertamylphenoxy acetyl) amino.

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

with one equivalent of a diazonium compound under acidic conditions to yield the monoazo dye of formula 111:-

The monoazo dye is optionally isolated and reacted furtherwith a diazonium compound oftheformula

under mildly alkaline conditions (sodium or lithium acetate buffer) to yield the dyestuff of formula I, B being an anion. Preferably B is borofluoride.

According to another aspect 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, a layer containing a bis-azo dye of the general formula i and a photobase, 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 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 compound of formula I and there to bleach the compound to form a dye image.

In the process as just set forth 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 bleach-developer compounds tend to be unstable and thus alternative ways of treating the exposed photographic assembly to ensure that sufficient active bleach-developer compound enters the silver halide emulsion layer(s) and especially that sufficient bleach-developer compound diffuses to the layer containing the compound of formula I are preferred.

Thus in one such method 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 photographic 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 bleach-developer compound. Thus in this method in step (b) a solution or dispersion of an inactive 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 bleach-developer compound is present initially in a layer in the photographic 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 bleach-developer compound may be treated in the assembly by providing in the assembly as well a substance in layer form which renders active the inactive bleach-developer 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 bleach-developer compound to the active form in the assembly.

Similarly electrolysis may be used to convert a solution or dispersion of the inactive 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 processes herein before 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, a layer containing a compound of formula I and a photobase there being optionally one or more interlayers between each of said components.

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 bleach-developer compound in the latent image areas of the silver halide emulsion layer(s) the bleach-developer compound develops the latent silver image and becomes oxidised and thus inactive both as a silver halide developing agent and as a bleaching agent for the compound of formula I. However in the non-latent image areas of the silver halide emulsion layer(s) the bleach-developer 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 bleach-developer compound reaches the layer which contains the compound of formula I, it bleaches the compound to form a photographic image which is of the same type as the silver image formed in the silver halide 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 positive image then the dye image formed in the bleachable dye layer is a positive.

It is to be understood that the image part of the photographic assembly as just defined, that is to say the portion of the assembly which includes both the layer which comprises the compound of formula I and the photobase, may be joined initially to the photosensitive portion of the assembly that is to say the portion of the assembly which includes the silver halide emulsion layer(s) or the photosensitive portion of the assembly and the image portion of the assembly may be separate components which are brought together during processing. If the photographic assembly comprises a separate image portion, not connected initially to the photosensitive portion, after the image has been formed in this portion the two components may be separated. However it is sometimes preferred that after processing the two sheets are retained together.

Preferably when the photographic assembly is in two sections the supercoat layer or some other layer is such as to be able to act as a base for the silver halide emulsion layer(s) and the other layers of this section of the assembly.

It is to be understood that the photographic assembly can and usually does include a number of layers other than the supercoat layer, the silver halide emulsion layer(s), the image substance layer and the optional interlayer or layers between the image dye layer and the photobase. For example there may be opaque layers, there may be light reflecting layers, there may be timing layers which release alkali or acid or other substances as required and/or there may be mordant layers. Examples of assemblies of use in the present invention are shown in Figures 1 to 23 of B.P.A. 2007378. However these assemblies are merely representative of the very great number of assemblies which can be be used in the process of the present invention.

By bleach developer compound is meant a compound which is able both to develop a latent silver halide image and to bleach a compound of formula I. Various classes of bleach-developer compounds are known and 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 silver areas. Silver dye bleach catalysts work in an acid solution.

The most widely used dye bleach catalysts are diazine compounds, for example pyrazines, quinoxalines and phenazines.

Examples of suitable diazines are pyrazine itself and its derivatives and quinoxaline compounds, especially those which are substituted in the 2-, 3-, 5-, or 7-position by methyl groups, methoxy groups or acylated or non-acylated hydroxymethyl groups or by acylated or non-acylated amino groups.

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 B.P. 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.

We have discovered that metallic ions and complexes of metallic ions with suitable ligands which are capable of acting as developing agents for latent silver images in aqueous acid solution are able also to act in an acid solution as bleaching agents for compounds of formula I. 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 Cur++, 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 diaminetetraacetic 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 an aqueous acid solution. However the method of the present invention is not limited to the use of bleach-developer compounds which act only as an aqueous acid solution.

The photographic assembly of the type defined may as previously described consist of two components, one the image portion and the other the photosensitive portion. After exposure of the silver halide emulsion layer(s) processing liquid is introduced between them or coated on one of the portions and the two portions are brought together in close contact.

When an assembly of this type is used to perform the invention the processing fluid may contain a bleach-developer compound or an inactive form of the bleach-developer compound which is not able to act either as silver halide developing agent or as dye bleaching agent. In the second case there may be present in the photosensitive portion of the assembly preferably between the supercoat layer and the silver halide emulsion layer(s) a metallic layer as hereinafter described. When the processing fluid is introduced between the image portion and the photosensitive portion the bleach-developer compound 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 image portion there bleaching the dye to form a dye image. Thereafter the image portion containing the dye image may be removed from contact with the photosensitive portion of the assembly. If a preformed bleach-developer compound is used in a two-component assembly preferably the supercoat layer comprises one component and the photosensitive portion and image portion are both coated on the photobase and comprise the second component. After exposure of the assembly processing fluid containing the preformed bleach-developer is introduced between the supercoat layer and the emulsion layer. The supercoat layer can be separated from the second component after processing.

However sometimes it is preferable that after processing the two portions of the assembly are not separated but are caused to adhere together. This avoids the production of a disposable photosensitive portion of the assembly.

The formation of the photographic assembly in two halves is of particular use when in-camera processing is to be carried out. In this case in the photographic assembly the photosensitive portion and the image portion may be in contact but not joined. After exposure of the silver halide emulsion layer(s) the processing liquid can be introduced between the two portions, possibly by introducing a pod between the two portions, rupturing the pod and causing the liquid to spread between the two portions which are held in close contact.

However when the photographic assembly is initially in one piece there may be a stripping layer or a stripping position. This layer or position is between the silver halide emulsion layer(s) and the image dye layer. When there is such a stripping layer or stripping position sometimes a final step in the process of the present invention is required to activate the stripping effect and to separate the portion of the photographic assembly which comprises the developed silver image from the portion which contains the final dye image on the photobase.

If there is a stripping layer this may be dissolved in a final wash or solution bath. An example of a suitable stripping layer is a phthalated gelatin layer which is swellable in water. However usually the stripping effect takes place during the processing, because, for example, phthalated gelatin is swellable in an acid processing solution.

Alternatively there may be a stripping position, that is to say the interface between two layers is such that adhesion failure between the two layers can be caused. This adhesion failure may be caused, for example, by change of pH or temperature. The stripping position should be between the silver halide emulsion layer(s) and the image dye later so that the final step in the process may be to activate the adhesion failure so separating the photosensitive portion from the image portion. However it is usual for adhesion failure to occur towards the end of processing so that often no actual step to activate stripping is required.

When the photographic assembly is initially in two portions or there is either a stripping layer or stripping position in the photographic assembly as hereinbefore defined all the silver used as the photosensitive agent can be recovered as the portion of the material containing the silver may be separated from the final image portion.

However there is considerable saving in silver even when the image portion is not separated from the portion containing the silver. In this case the final viewable image is the dye image which is viewed through the transparent photobase, there being also a silver image in the photographic material which is likely to be separated from the dye image by a white opaque layer. In such material the amount of silver halide present in the silver halide emulsion layer can be less than that which would be required if a viewable image were to be formed in the silver halide emulsion layer(s).

The solution of bleach-developer compound of use in the preferred process of the present invention may be prepared and applied to the photographic 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 photographic 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 electro-chemical 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 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 agentforthe 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, a) a preformed acid solution of the metallic ions may be used, b) the acid solution of the metallic ions may be formed externally to the photographic assembly but as a step in the processing sequence, c) 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 a) 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 b) is used a strip 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, for example zinc, tin, iron, gallium or indium may be used 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 c) 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 metals are aluminium, zinc, tin, gallium or indium. Also in method c) 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 inthe book "Stability Constants of Metal-Ion Complexes, Special Publication No.17, London: The Chemical Society, Burlington House, W.L., 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 CaF3 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 following Examples 1 to 5 relate to the preparation of dyes which are used in the Use Example 6.

EXAMPLE 1 Preparation of the intermediate dye A which is a red-brown monoazo dye of the formula:

Naphthalene-4-amin o-3-(Z 6-dichiorophen ylazoj-5-h ydroxy-2, 7-disuiph onic acid sodium salt 2,5-Dichloroaniline (16.5 g) was dissolved in a mixture of 2-methoxyethanol and 42% hydrofluoroboric acid (80 ml), cooled to 50C and diazotised by the addition of a solution of sodium nitrite (8.0 g) in water (10 ml). It was diluted with methanol (150 ml) and cooled to 5 C.

A solution of H acid (36 g of mono sodium salt) was prepared in water (2000 ml) and added rapidly to the diazonium mixture and stirred for 1 hr. Methanol (1500 ml) was added, followed by sodium bicarbonate (20.6 g). A solution of sodium acetate (17 g) in hot methanol (500 ml) was added with stirring and the mixture heated to 750C, then cooled to 1 OOC. The dyestuff was filtered off, washed with isopropyl alcohol and dried.

Yield 53 g, red-brown solid.

Naphthalene-4-amin o-3- (2, 5-dichlorophen Wazo)-6-l'2, 4-ditent-am ylphenoxyacetyl)-4, N- methylaminophenylazoj -5-hydroxy-2, 7-disuiphonic acid mono sodium salt. Dye 1 The monoazo dye A (4.8 g) and lithium hydroxide H2O (0.4g) were dissolved in methanol (150 ml) then filtered and treated with a solution of acetic acid (0.6 g) in methanol (50 ml). The mixture was cooled to 7 C and a slurry of 2,4-ditertamylphenoxyacetyl-4,N-methylaminophenyl diazonium borofluoride (4.9 g) in methanol (50 ml) added in portions, then allowed to stir for 1 hr. Sodium acetate (0.9 g) dissolved in methanol was added and the solution of the dye allowed to stand at 200C for 17 hr.The mixture was heated to boiling, filtered, then boiled down to 25 ml, cooled to 25 C and water (60 ml) added followed by 30% w/v sodium chloride (80 ml) and a further quantity of water (440 ml). The dye was collected and washed with a mixture of methanol (250 ml), water (500 ml) and 30% NaCI (80 ml), then dried. It was recrystallised from a mixture of acetone/ethanol/isopropanol. Yield 8.5 g.

Thin layer chromatography SiO2/glass in methanol-chloroform showed only a single blue spot and no mono azo dye.

The dyestuff (0.1 g) was dissolved in a water-methanol mixture and made up to a volume of 20 ml such that the gelatin content was 2% and a wetting agent (0.25 ml of a 1% saponin solution) added. The mixture was coated on film base and dried, to yield an intense blue coating.

EXAMPLE 2 Naphthalene-4-amino-3-(2, 5-dichlo rophen ylazo)-6- f3-chlo ro -N- (Z 4-dftentam ylphen ox yacet yl)-4, N- methylaminophenylazoj-5-hydroxy-2, 7-disuiphonic acid mono sodium salt Dye 2 The dichlorophenyl mono azo dye A (2.75 g) and lithium hydroxide (0.2 g) were dissolved in methanol (75 ml) and treated with a solution of acetic acid (0.3 g) in methanol (20 ml) then cooled to 80C. A slurry of 3-chloro-(2,4-ditertamylphenoxyacetyl)-4,N-methylaminophenyldiazonium borofluoride (2.5 g) in methanol (20 ml) was added in portions, followed by addition of a solution of sodium acetate (0.45 g) in methanol.The mixture was allowed to stand 17 hr, heated to boiling and lithium hydroxide (0.3 g) added: when dissolved the solution was filtered and boiled down to 100 ml, then cooled to 25 C. Water (25 ml) was added followed by 30% w/v sodium chlooride (25 ml) and water (175 ml). The dye was collected and washed with a mixture of methanol (100 ml), water (200 ml) and 30% NaCI (25 ml), then dried. Yield 4.7 g.

Thin layer chromatography SiO2/glass in methanol-chloroform showed the presence of a single blue spot and no mono azo dye.

The dye (100 mgm) was dissolved in an oil solution (1 ml) [prepared from ethyl acetate (4 ml) and tricresyl phosphate (1 ml) ] then dispersed in a 6% gelatin solution (6.5 ml) with the aid of a wetting agent (0.25 ml of a 1% saponin solution), and diluted to 20 ml total volume. The dispersion was coated onto film base then dried to yield an intense blue coating.

EXAMPLE 3 Preparation of the intermediate dye B - a red-brown mono azo dye of the formula :-

Naphthalene-4-amin o-3-f2-chloro-5- (2,4-ditentan ylphenoxyacetyl)aminojphen ylazo-5-hydroxy-2, 7 disulphonic acid sodium salt H-acid (1 g) was suspended in methoxy ethanol (15 ml), cooled to 10 C and 2-chloro-5-(2,4 ditertamylphenoxyacetyl)aminophenyl diazonium borofluoride (0.4 g) added and the mixture stirred for 17 hr. The mixture was filtered from the excess H-acid and washed with methoxyethanol to yield an intense magenta solution (30 ml).

Naphthalene-4-amino-3, 6-bis-12-chloro-5-(2, 4-ditentam ylphenoxyacetyl)amino ] phen ylazo-5-h ydroxy-2, 7disulphonic acid sodium salt Dye 3 The mono azo dye B solution (30 ml) was treated with 2-chloro-5-(2,4-ditertamylphenoxyacetyl)aminophenyl diazonium borofluoride (0.4 9) followed by sodium acetate (0.3 g) dissolved in 2-methoxyethanol. The blue solution was stirred for 12 hr, then heated to 900C and filtered, cooled to 25 C and water (135 ml) added followed by 30% w/v sodium chloride (22 ml) added dropwise. The dye was collected and washed with a mixture of 2-methoxy ethanol (120 ml), water (150 ml) and 30% NaCI (30 ml) and dried.

The blue dye was coated in an oil dispersion as described in Example 2, yielding an intense blue layer.

EXAMPLE 4 Preparation of the intermediate red-brown monoazo dye C of the following formula :-

Naphthalene-4-amino-3-(5-chloro-2-carboxyphenylazo)-5-hydroxy-2, 7-disulphonic acid sodium salt 2-Amino-4-chlorobenzoic acid (17 g) was dissolved in a mixture of acetic acid (200 ml) and 42% hydrofluoroboric acid (80 ml), cooled to 8 C and diazotised by the addition of sodium nitrite (10 g) in water (10 ml). Water (200 ml) was slowly added and the solution filtered. It was added to a solution of H-acid (36 g) in water (2000 ml) at 15 C. The mixture was allowed to stand for 17 hr, then ethanol (2500 ml) added and the crystalline dye filtered off. It was washed with ethanol and dried. Yield 35 g, red-brown solid.

Naphthalene-4-amino-3-(5-chloro-2-h ydroxycarbon ylphen ylazo)-6-l(2, 4-ditertam ylphenoxyacetyl)-4, N- methylaminophenylazoj-5-hydroxy-2, 7-disulphonic acid sodium salt Dye 4 The blue dye was prepared essentially as described in Example 1. Thin layer chromatography SiO2/glass in chloroform-methanol showed a singel blue spot and no mono-azo dye.

In a similar manner were prepared dyes 5 to 13 as hereinafter set forth.

EXAMPLE 5 Preparation of the intermediate dyeD, a red-brown monoazo dye of the following formula:

Naphthalene-4-amino-3-f3-chloro-N-(2, 4-ditertam ylphenoxyacetyl)-4, N-meth ylaminophen ylazoj-5-h ydroxy- 2, 7-disulphonic acid sodium salt 3-Chloro-N-(2,4-ditertamyl phenoxyacetyl)-4,N-methylaminophenyl diazonium borofluoride (tetrafluoroborate) (1.6 g) was added to a suspension of H-acid (4 g) in 2-methoxyethanol (60 ml) and the mixture allowed to stir for 20 hr. The thixotropic mixture was filtered and the residue washed with solvent to yield a total volume (180 ml). Water (133 ml) was added followed by a 30% w/v sodium chloride solution (180 ml) and the precipitated dye collected, washed with a mixture of methanol (10 ml), water (20 ml) and 30% w/v sodium chloride (2.5 ml) and dried.Yield 2.2 g.

Naphthalen e-4-amino-3- 3- ch lo ro -N- (2, 4-dite,tam ylphenoxyacetyl)-4, N-meth ylamin ophen ylazo ] -6-(2, 5- dichlorophenylazoJ-5-hydroxy-2, 7-disulphonic acid sodium salt Dye 14 The monoazo dye D (0.2 g) was dissolved in methanol (4 ml) and 2,5-dichlorophenyl diazonium borofluoride (0.07 g) added, followed by dropwise addition of a solution of sodium acetate (0.05 g) in methanol (1 ml). The blue solution was stirred for 17 hrthen a solution of lithium hydroxide (0.025 g) in water (10 ml) added. 30% w/v Sodium chloride (2.5 ml) was added dropwise and the dye slowly crystallised. It was collected, washed with a mixture of methanol (10 ml), water (20 ml) and 30% sodium chloride (2.5 ml), then dried. Yield 0.2 g.

Thin layer chromatography (SiO2/glass) in methanol-chloroform showed a single blue spot and no magenta monoazo dye.

The dye is soluble in both hot water and ethyl acetate. The dye was coated as described in Example 2, with virtually the same result.

In a similar manner were prepared dyes 15 and 16.

Dye 3 NH2 OH #I CH,- #o)#;a#;'##NHCOCH2#O Dye 4 Ct Q NH2OH COOM y,,,,#N N#ICHa SQOH SO2ONa ( I cH2-opL, Dye5 CH3 CH 2#N I > 1: NX OH ##J 5 4#J N: N# COCH 2 - ot Dye 6 CH3 0- CH2CO-N NH, OH Ct-- N,,, ICH3 SO2OH So2ONa CIl#COCH2 O# 5020H 5020Na - COCH 2 - og3X, Dye 7 CI ::N CI 5020H 5020Na N #coc#2

Dye 8 CI CI N#N/CH3 SO2OH SO2ONa N@t 1N / 5020H 5020Na \ a CocH2-osAs Dye 9 CH, CON CON > NH2 OH #Hz OH COCH2- so20No N COCH2-O Dye 10 cl Q~ NH2 OH YN =N > SO ONo Nx SO2OH SO2ONo N COC17H35n Dye 11 cl OH N OH #e #s-# FH3 SCION SO2ONo

Dye 12 CI ##" CI ""I ) S020NaN SO2OHSO2ONa N COICH2)3 Ct5 H 31 Dye 13 Cl #-~~ NH2 OH N:N# CI o /CH3 N' 9 Dye 14 CH3 #OCH2 -CO-N NH2 OH CI X Ct N N ,,,1#N:N,1 SO,OH SO,ONI CI Dye 15 CH3 #OcH2-CO-N# NH2 OH CI N N :Nx I:: s020 SO2ONa

Dye 16 CH2 ,t OCH 2 - CO - N N--N ;1;N## N# SOaOH S02ONa SCHI

Dyes 1,2,4,7,8,9, 10, 11, 12, 14 and 15 are water soluble. These dyes may be added to an aqueous colloid (preferably gelatin) coating solution and coated as a layer in photographic material. The ballasting group renders them substantive to the coated layer.

Dyes 3, 5, 9, 13 and 16 are not sufficiently water soluble to be coated in this manner. They are dissolved in an oil former, e.g. dibutyl phthalate ortricresyl phosphate and then dispersed in the aqueous colloid coating solution. Such oil dispersions of the dyes are substantive to the colloid layer in which they are coated.

Additionally dyes 2 and 14 may be coated either from aqueous solution or as an oil dispersion in the aqueous colloid.

In Figure 1 there is shown a photographic assembly of use in the present invention which comprises two separate components. The first component consists of a supercoat 8 which has coated thereon a layer 7 which consists of powdered zinc in a gelatin binder. The other component comprises a transparent photobase 1 having coated thereon in order a bleachable dye image layer 2, a white reflecting layer 3, a silver halide layer 4 and a supercoat layer 5. Between the supercoat layer 5 and the zinc layer 7 is shown a pod 6 which contains an unreduced bleach-developer compound.

The assembly of Figure 1 is also of use in a self-processing camera of the type known per se. In operation the assembly with the zinc layer 7 in close contact with the supercoat layer 5 is imagewise exposed in a camera. Preferably the pod 6 is present in the assembly with its outlet between two edges of the supercoat and silver halide layers but is so positioned that close optical contact between these two layers is not impaired.

After exposure the assembly is led through a pair of driven rollers which rupture the pod 6 and cause the processing fluid contained therein to spread evenly between the supercoat layer 5 and the zinc layer 7. The unreduced bleach-developer compound is reduced by the zinc layer and then diffuses into the silver halide layer and develops the latent image therein in the latent image areas. In the non-latent image areas it diffuses in a counter-imagewise manner through the white reflecting layer 3 and into the dye(s) + gelatin layer 2 where it bleaches the bleachable layer to form a dye image. The image can then be viewed by reflection through the photobase 1.

An example of a suitable white reflecting layer for use in the material of Figure 1 is as follows: Titanium dioxide (mean particle size 1.5# 15g Gelatin (4% aqueous solution) 50 ml Sodium dodecyl sulphate (28% aqueous solution) 0.3 ml Aryl alkyl polyethylene oxide condensate 3.0 ml (6% solution in 50/50 ethanol/water) dispersed using a homogeniser or ultrasonic mixer coated to give a layer containing 27 g/m2 TiO2.

There may be present in the photographic material of the present invention yet other layers for example a neutralising layer, a timing layer, a mordant layer which may be used to trap amines released during the bleaching of azo dyes when such dyes are used as the image dye, or a layer to control the swelling of the gelatin layers. Preferably any of the above layers, if present, are located between the supercoat layer and the silver halide emulsion layer or between the dye layer and the photobase so as not to prolong or interfere with the diffusion path of the bleach development compound to the bleachable dye layer.

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 photobase used may be of any of the usual bases used for photographic materials, for example if the base is transparent it may be composed of cellulose triacetate, cellulose acetatebutyrate, oriented and subbed polystyrene, polycarbonate or polyester, such as polyethylene terephthalate. If the base 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 base having a baryta coating thereon or polyethylene coated paper base. Alternatively it may be voided polyester base.

As herein before 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 atoms 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, HC104,HNO3, H2SO4, H3PO4 and H2CO3; also HSO38, SO2, sulphamic acid. Suitable buffers are: Al(H20)63f3and HBF4.

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

The following Example will serve to illustrate the invention.

EXAMPLE 6 Use Example An assembly as shown in Figure 1 was prepared by coating sequentially onto 0.004 in. thick transparent cellulose triacetate photobase the following layers: Part 1 1. A gelatin layer containing 0.9 g/m-2 of dye 1 in gelatin 5 g/m2 2. Awhite reflecting layer 3. A photosensitive silver halide gelatin emulsion layer containing 5.1 g/m-2 silver in the form of silver bromoiodide (98.5 mol % AgBr and 1.5 mol % Agl) 4. A supercoat layer containing gelatin 1.0 g/m-2.

Part2 1. A zinc powder layer containing 1.6 g/m#2 of zinc dust in gelatin 3.2 g/m-2.

This assembly was not tested in a camera but in dark-room conditions. The test procedure was as follows: After exposure of the light sensitive part of the assembly to light behind a grey wedge the material was processed in the dark by contacting the emulsion side with the zinc powder layer of part 2 onto which had been applied a processing composition of the following formulation:- Pyrazine .5g Sulphuric acid (5N) 10 ml Hydroxyethyl cellulose 2 9 (Natrosol type 250HH) Water to 100 ml The two assembly parts were separated after 40 seconds. A dye image wedge was obtained in layer 1. The density of this image was acceptably dark as a final image.

Claims

1. A dyestuff of the general formula I:

2. A dyestuff according to claim 1 wherein when either X or Y represents a ballasting group containing at least 16 carbon atoms there is present in this ballasting group an electronegative substituent or there is also present attached to the phenyl group to which X or Y is attached at least one electronegative substituent.

3. A dyestuff according to claim 1 wherein X is at least one electronegative substituent and Y represents a ballasting group containing at least 16 carbon atoms.

4. A dyestuff according to any one of claims 1 to 3 wherein the electronegative substituents are halogen atoms, cyano, acylamino or carboxylic acid groups.

5. A dyestuff according to claim 3 wherein X represents two chlorine atoms substituted in the 2 and 5 positions in the phenyl group.

6. A dyestuff according to claim 3 wherein Y is 4-N-methyl-(2,4-ditertamylphenoxy acetyl) amino or 3-chloro-4-N-methyl-(2,4-ditertamylphenoxy acetyl) amino.

7. 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, a layer containing a bis-azo dye of the general formula I as defined in claim 1 or as modified in any one of claims 2 6, and a photobase, 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 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 compound of formula I and there to bleach the compound to form a dye image.

8. A process according to claim 7 wherein the bleach-developer compound is in the form of a preformed solution or dispersion which is applied to the exposed photographic assembly in step (b).

9. A process according to claim 7 wherein 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 orwhilstthe solution or dispersion is applied to the exposed photographic assembly in step (b).

10. A process according to claim 7 wherein a solution or dispersion of an inactive form of the bleach-developer compound is applied to the photographic assembly in step (b), the photographic assembly comprising either in the supercoat layer or below the supercoat layer and above the bottom-most silver halide emulsion layer a compound in layer form which renders active the inactive bleach-developer compound.

11. A process according to claim 7 wherein the bleach-developer compound is present initially in a layer in the photographic 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 covert the compound to the active form.

12. A process according to claim 11 wherein the solution of the inactive form of the bleach-developer compound is rendered active by bringing it into contact with a substance which renders the compound active and which is also present in layer form in the photographic assembly.

13. A process according to claim 7 wherein the bleach developer compound is in an inactive form and a solution or dispersion of this compound is subjected to electrolysis to convert the inactive compound to the active form just before or whilst the solution or dispersion is applied to the photographic assembly.

14. A process according to claim 11 wherein the photographic assembly is subjected to electrolysis at the same time or just after the solvent is applied to the assembly thereby converting the inactive form of the compound to the active form in the assembly.

15. A process according to claim 7 wherein the photographic assembly is prepared as two sections, one section comprising the supercoat and the silver halide emulsion layer(s) and the other section comprising the layer which contains the compound offormula I and the support base.

16. A process according to claim 7 wherein the photographic assembly is prepared as a single assembly which comprises the supercoat, the silver halide emulsion layer(s) and the layer which contains the compound of formula I all coated on the support base.

17. A process according to claim 16 wherein in the photographic assembly used there is either a stripping layer or a stripping position between the silver halide emulsion layer(s) and the layer which comprises the compound of formula I.

18. A process according to claim 17 wherein the stripping layer comprises phthalated gelatin.

19. A process according to any one of claims 7 to 18 wherein the silver halide emulsion is a negative working silver halide emulsion.

20. A process according to any one of claims 7 to 18 wherein the silver halide emulsion is a direct positive silver halide emulsion.

21. A process according to any one of claims 7 to 20 wherein the bleach-developer compound is an azine compound in its reduced form and the aqueous processing bath is an aqueous acid bath.

22. A process according to claim 21 wherein the azine is pyrazine.

23. A process according to claim 21 wherein the azine is a quinoxaline compound which is substituted in the 2-, 3-, 5-, 6- or 7-position by a methyl group, methoxy group or an acylated or a non-acylated hydroxymethyl group or by an acylated or non-acylated amino group.

24. A process according to any one of claims 7 to 20 wherein the bleach-developer compound is a metallic ion which is able to act as a silver halide developer in an acid solution.

25. A process according to claim 24 wherein the metallic ion is chromous, vanadous or titanous.

26. A process according to any one of claims 21 to 25 wherein a non-reduced azine or metallic ion in a higher valency state than the active form in an acid solution or dispersion is contacted with a reducing agent just before or as it is applied to the photographic assembly.

27. A process according to claim 26 wherein the reducing agent is a metal which in the electrochemical series is above silver and up to and including aluminium.

28. A process according to claim 27 wherein the metal is in the form of a metal strip.

29. A process according to claim 28 wherein the metal strip is composed of iron, zinc, tin or aluminium.

30. A process according to claim 27 wherein the metal is in the form of a paste coated on a base.

31. A process according to claim 30 wherein the paste comprises aluminium, zinc, tin, indium or gallium or alloys which include such metals.

32. A process according to any one of claims 21 to 25 wherein a non-reduced azine or metallic ion in a higher valency state than the active form is applied as an acid solution or dispersion to the photographic assembly which comprises in a layer thereof a dispersion of a metal which in the electrochemical series is above silver and up to and including lanthanum.

33. A process according to claim 32 wherein the metal used is aluminium, zinc, tin, indium, lanthanum or gallium or alloys which include such metals.

34. A process according to any one of claims 7 to 33 wherein in the photographic assembly there is at least one light opaque layer adjacent to a silver halide emulsion layer.

35. A process according to claim 34 wherein there is one silver halide emulsion layer and there is a light-opaque layer in each side thereof.

36. A process according to any one of claims 7 to 35 wherein in the photographic assembly there is a white reflecting layer adjacent to the layer containing compound of formula I on the side remote from the photobase.

37. A process according to any one of claims 7 to 35 wherein the photographic assembly comprises in order a supercoat layer, a light opaque layer, a silver halide emulsion layer, a light opaque layer, a layer containing a compound of formula I and a support base.

38. A process according to claim 37 wherein there is present between the second mentioned light opaque layer and the layer containing the compound of formula I a stripping position.

39. A process according to claim 38 wherein the stripping position is a stripping layer.

40. A process according to claim 37 wherein there is present between the second mentioned light opaque layer and the layer containing the compound of formula I a white reflecting layer.

41. A process according to claim 40 wherein there is present between the second mentioned light opaque layer and the white reflecting layer a stripping position.

42. A process for the production of a photographic image substantially as hereinbefore defined with reference to the foregoing Examples.

43. Photographic material which comprises in order a supercoat layer, optionally at least one interlayer, a silver halide emulsion layer, at least one interlayer, a layer containing a compound of formula I as defined in claim 1 and a support base wherein there is present either in the supercoat layer or in another layer above the layer containing the compound of formula I a layer which comprises a substance which is able to activate a non-active bleach-developer compound.

44. Photographic material according to claim 43 wherein there is present between the silver halide emulsion layer and the layer containing a compound of formula I a light opaque layer.

45. Photographic material according to claim 43 wherein there is present between the silver halide emulsion layer and the layer containing a compound of formula I a white reflecting layer.

46. Photographic material according to claim 43 wherein there is present in order a supercoat layer, optionally at least one interlayer, a silver halide emulsion layer, a light opaque layer, a white reflecting layer, a compound of formula I layer and a photobase.

47. Photographic material according to any one of claims 44 to 46 wherein there is present between the supercoat layer and the silver halide emulsion layer a light-opaque layer.

48. Photographic material according to claim 43 wherein the activator substance is a metal which in the electro-chemical series is above silver and up to and including lanthanum.

49. Photographic material according to any one of claims 43 to 48 wherein there is present in the material between the silver halide emulsion layer and the layer containing a compound of formula I a stripping position or stripping layer.

50. Photographic material which comprises a supercoat layer, a silver halide emulsion layer, a layer which comprises a substance which is able to activate a non-active bleach-developer compound, a silver halide emulsion layer, optionally at least one interlayer, a layer which comprises a compoundofformula I and a support base.

51. Photographic material according to claim 50 wherein there is present between the second mentioned silver halide emulsion layer and the support base a white reflecting layer.

52. Photographic material according to claim 51 wherein there is present between the second mentioned silver halide emulsion layer and the white-reflecting layer a stripping position or stripping layer.

53. Photographic material according to any one of claims 43 to 52 which comprises either in the supercoat layer or in an interlayer above the topmost silver halide emulsion layer a layer which comprises a bleach-developer in an inactive form.

54. Photographic material according to any one of claims 43 to 53 wherein the photographic material also comprises a mordant layer which is capable of mordanting amine compounds released during the processing of the photographic material.

55. Photographic material according to any one of claims 43 to 54 which also comprises a neutralising layer.