GB2083640A - Photographic silver halide materials - Google Patents

Abstract

Granularity of silver halide dye- image-forming photographic materials is reduced by employing a coupler which yields a dye of such mobility that controlled image smearing occurs. This coupler is used in combination with another which yields a non-diffusable dye, both couplers being associated with the same or different silver halide emulsion layers. The mobile dye may be slightly mobile, e.g. by providing the coupler with two ballasting groups, one attached at the coupling position, the other attached elsewhere. Alternatively the dye may be diffusible out of its layer during development in which case the material also comprises a mordant layer for this dye. Exemplified are multi- colour photographic materials containing multiple slow/fast red-, green- and blue-sensitive colour forming units, the coupler yielding mobile dye being associated with at least one of the fast colour forming units. Also disclosed is the preparation of a coupler which yields a slightly mobile cyan dye.

Description

SPECIFICATION Photographic silver halide materials This invention relates to photographic photosensitive silver halide materials, in particular to such materials having reduced granularity.

Photographic silver halide materials containing incorporated colour couplers have been known for many years. The couplers and the image dyes produced therefrom contain ballasting groups of such molecular size and configuration that they are rendered nondiffusible in the element as coated, and during and subsequent to processing. Such photographic materials are processed by steps which include colour coupling development to produce both a silver image and a dye image and subsequent bleaching of the silver to leave the dye image alone.

As these materials are made with increasing photographic speed, larger silver halide grains are used. This results in an increase in the granularity of the dye image, other things being equal.

We have now discovered that if at least some of the image dye produced is allowed to diffuse to a limited extent, neighbouring clouds of image dye are smeared into each other leading to reduced image granularity.

According to the present invention there is provided a silver halide photographic material comprising at least one silver halide emulsion layer and nondiffusible dye-forming couplers associated with the emulsion layer or layers, characterised in that the nondiffusible dye-forming couplers comprise a first non-diffusible dye-forming coupler which, upon reaction with oxidized colour developing agent, yields a nondiffusible dye and a second nondiffusible dye-forming coupler which, upon reaction with oxidized colour developing agent, yields a dye of such mobility that controlled image smearing occurs.

Where the materials of this invention contain only one silver halide emulsion layer, that layer has associated therewith each of the first and second couplers. Where the materials of this invention contain more than one silver halide emulsion layer, the first coupler is associated with at least one of the emulsion layers and the second coupler may be associated with at least one other of the emulsion layers.

The first and second couplers may yield dyes which absorb in the same or different regions of the spectrum.

With the present materials neighbouring clouds of image dye are smeared into each other, and it is this effect which leads to reduced granularity. With multicolour photographic materials the reduction in granularity can be effected in any of the dye image-forming units. When the dye image forming units are comprised of more than one layer sensitive to each primary region of the visible spectrum, the reduction in granularity can be effected in each of the layers or in only one of the layers, preferably the faster emulsion layer. Similarly the reduction in granularity can be effected in layers sensitive to each of the primary regions of the visible spectrum or in only one or two such layers.

Since the reduction in granularity in a given layer may lead to a decrease in sharpness of the image formed in that layer, it is preferred that the layer or layers in which granularity is reduced in accordance with this invention be those which yield a dye to which the eye is less sensitive, such as a yellow dye forming layer.

Further, because the layer closest to the source of exposing radiation has the least amount of optical degradation (i.e., loss in sharpness) due to exposure, it is the layer in which the reduction in granularity in accordance with this invention preferably is effected. This layer again is usually a yellow dye forming layer.

The amount of silver usually employed in the layer in which image smearing occurs can be reduced, while still achieving acceptable granularity, thus allowing a thinner emulsion layer and hence increase sharpness in underlying layers.

As will be apparent to the photographic chemist, the properties of the components of the present photographic materials and the intended method of processing will be chosen so that the increase in image dye mobility leading to the desired reduction in granularity is balanced against the loss in sharpness which would occur if the image dye were allowed to diffuse over too great a distance.

Controlled image smearing in accordance with this invention can be achieved in a number of ways. In a first embodiment, the coupler which provides controlled image smearing is one which yields a dye which is slightly mobile so that the desired degree of image smearing has taken place by the time processing and drying is completed. In a second embodiment the coupler which provides controlled image smearing is one which yields a dye which is diffisuble, and a mordant for the dye is associated with the layer containing that coupler.In the embodiments where the element contains more than one silver halide emulsion layer, the coupler which provides controlled image smearing can be the only dye-forming coupler in the layer or other dye-forming couplers, such as couplers which yield nondiffusible dyes, can be present in the layer in amounts up to 99 percent by weight of the total dye forming couplers in the layer. The greater the proportion of coupler which provides controlled image smearing relative to other dye-forming couplers in the layer, the greater the amount of image smearing which occurs.

The couplers which form the dyes of controlled mobility employed in each of the embodiments have, in the coupling position, a ballast group which renders the coupler immobile. Upon coupling with oxidized colour developing agent the ballast group is detached, so that the dye formed is no longer immobilized and is thus able to diffuse in the layer to smear the image. Couplers employed in the first embodiment have, in a non-coupling position, a secondary ballast group which gives the dye the desired slight mobility. Couplers employed in the second embodiment have, in a non-coupling position, a solubilizing substituent which renders the dye diffusible so that it can diffuse to and be immobilized by the mordant.

A class of couplers which may be employed in the first embodiment are represented by the structure: COUP - SECONDARY BALLAST I MAIN BALLAST wherein; COUP is a dye-forming coupler moiety, the asterisk (*) denoting the coupling position thereof; MAIN BALLAST is a group, attached to the coupling position of COUP and detachable therefrom by means of reaction of COUP with oxidized colour developing agent, which is of such size and configuration as to render the coupler nondiffusible; and SECONDARY BALLAST is a group, attached to a noncoupling position of COUP, which is of such size and configuration that the dye formed by coupling of COUP with oxidized colour developing agent is slightly mobile.

The coupler moiety represented by COUP can be any coupler moiety known or used in the art to form a coloured reaction product with oxidized colour developing agent. Common yellow dye-forming couplers are acylacetanilides such as acetoacetanilides and benzoylacetanilides; common magenta dye-forming couplers are pyrazolones, pyrazolotriazoles, pyrazolobenzimidazoles and indazolones; and common cyan dyeforming couplers are phenols and naphthols. These couplers can form the coupler moiety COUP.

The main ballast group, as indicated, is a group of such molecular size and configuration as to render the coupler nondiffusible. The specific nature of the main ballast group is not critical, so long as it confers nondiffusibility on the coupler. Useful main ballast groups include alkyl groups and aryl groups having from 8 to 32 carbon atoms. These groups can be unsubstituted or substituted with groups which enhance the nondiffusibility of the coupler, modify the reactivity of the coupler or enhance the diffusibility of the ballast group after it is detached from the coupler. The main ballast group contains a linking group through which it is joined to the coupling position of the coupler moiety. Representative linking groups include oxy (-0-), thio (-S-), and azo (-N=N-).Preferred main ballast groups are alkoxy, aryloxy, alkylthio and arylthio groups containing from 8 to 32 carbon atoms.

The secondary ballast group is a group of moderate size and bulk so as to render the dye slightly mobile.

As will be appreciated the specific secondary ballast group will depend upon the particular coupler moiety employed, the nature of other substituents thereon, the particular colour developing agent which couples with the coupler to form dye and the nature of substituents thereon. The specific secondary ballast group employed is not critical so long as it confers upon the dye the desired degree of mobility. Useful secondary ballast groups can be selected from alkyl groups of 4 to 20 carbon atoms and aryl groups of 6 to 20 carbon atoms. These groups can be unsubstituted or substituted with groups which modify the spectral absorption characteristics of the dye or its diffusibility.For example, the secondary ballast group can contain base ionizable groups, such as hydroxy groups, carboxylic acid groups, sulphonic acid groups, and aminosulphonyl groups and ionizable salts thereof to render slightly mobile an otherwise immobile dye. The secondary ballast group can contain a linking group through which it is joined to the coupler moiety.

Representative linking groups include oxy, thio, carbonyl, carboxyl, amino, carbamoyl, aminocarbonyl, ureido, sulphamoyl and aminosulphonyl.

Preferred yellow couplers useful in this first embodiment can be represented by the formula:

wherein: R1 is an aryl group, (e.g., phenyl) or an alkyl group, especially a tertiary alkyl group, (e.g. a t-butyl group); R2 is the main ballast group as described above; R3 is the secondary ballast group as describd above; and R4 is hydrogen or one or more halogen, alkyl or alkoxy groups.

Preferred cyan couplers useful in this first embodiment have the formulae:

wherein: R2 is as defined above, one of R5 and R5 is the secondary ballast group as described above and the other is hydrogen or one or more halogen, alkyl, alkoxy or alkylamido groups.

In particularly preferred couplers of this type, R2 is:

R7 is a solubilizing group, (e.g. -COOH, -OH or -SO2NH2); m is 5 to 20 and R5 is -CONHR8 in which R8 is alkyl of 6 to 14 carbon atoms.

Preferred magenta couplers useful in this first embodiment can be represented by the formulae:

wherein: R2 is as defined above; one of R9 and R10 is the secondary ballast group, as described above, and the other is hydrogen or an alkyl, alkoxy, aryl or amino group; and R11 is hydrogen or one or more halogen, alkyl, alkoxy, or amino groups.

Unless otherwise indicated above, the alkyl, alkoxy and alkylamido substituents contain 1 to 8 carbon atoms; the aryl substituents contain 6 to 10 carbon atoms and the amino substituents include primary, secondary and tertiary amino groups. These substituents, as well as the primary and secondary ballast groups, can be further substituted with such groups as halogen, hydroxy, carboxy, amino, amido, carbamoyl, sulphamoyl, sulphonamido, alkyl, alkoxy and aryl. In all cases the substituents are selected so that the dye formed upon coupling has the desired slight mobility.

Couplers employed in the second embodiment can be represented by the structure: VII COUP-SOL I BALLAST wherein: COUP is a dye-forming coupler moiety, the asterisk (*) denoting the coupling position thereof; BALLAST is a group, attached to the coupling position of COUP and detachable therefrom by means of reaction of COUP with oxidized colour developing agent, which is of such size and configuration as to render the coupler nondiffusible; and SOL is a solubilizing substituent, attached to a noncoupling position of COUP, which renders the dye formed by coupling of COUP with oxidized colour developing agent diffusible in the alkaline environment present during photographic processing.

The coupler moiety represented by COUP is the same as defined above in connection with the couplers useful in the first embodiment. Similarly, the ballast group represented by BALLAST is the same as the MAIN BALLAST described above.

The solubilizing substituent represented by SOL is or contains an ionizable group which confers on the dye formed by coupling the desired diffusibility, such as ionizable hydroxy, carboxylic acid, sulphonic acid, and aminosulphonyl groups and ionizable salts thereof attached directly or indirectly to the coupler moiety.

Preferred yellow, cyan and magenta couplers for use in this second embodiment have the structures II through Vl shown above with the exception that the secondary ballast group represented by R3, R5 or R6, and R9 or R10 is replaced by a solubilizing substituent as defined above which can be represented as groups R13, R14, R15, R16, R19 and R20.Preferred solubilizing substituents are 1) a carboxylic acid group, a sulphonic acid group or an ionizable salt thereof attached directly to a noncoupling position of the coupler, 2) an alkyl group of 1 to 10 carbon atoms or an aryl group of 6 to 12 carbon atoms attached to a noncoupling position of the coupler and containing one or more carboxylic acid groups, sulphonic acid groups or ionizable salts thereof, and 3) groups as in (2) joined to the noncoupling position through an amido or carbamoyl group.

The alkyl and aryl groups which form a part of the solubilizing substituent can be further substituted with such groups as halogen, amino, amido, carbamoyl, sulphamoyl, sulphonamido, alkyl, alkoxy and aryl. In all cases, these further substituents are selected so that the dye formed upon coupling has the desired diffusibility.

It will be appreciated that the couplers employed in the first and second embodiments represent a continuum with regard to mobility or diffusibility, with couplers which yield slightly mobile dyes at one end and those which yield fully diffusible dyes at the other end. Thus, a given grouping of atoms may be a secondary ballast for some couplers and a solubilizing substituent for other couplers, depending upon the particular coupler moiety to which it is attached, the nature of other substituents on that coupler moiety, and the particular developing agent employed.

The couplers useful in this invention are often known compounds and can be prepared by known techniques for preparing dye-forming couplers. Certain couplers useful in the second embodiment are described in U.S. Patent 3,227,550 for use in colour diffusion transfer materials.

The nondiffusible couplers which form non-diffusible dyes that are employed in the present invention can be any known dye-forming coupler which yields a nondiffusible dye of the appropriate colour. Such couplers are present in at least one of the silver halide emulsion layers and, as indicated above, can be present in the same layer as the coupler which provides controlled image smearing.

The colour couplers used in the present materials can be incorporated therein in conventional amounts by known methods. A typical amount of total dye-forming coupler in each layer is from 0.02 to 2 grams per square metre. The hydrophobic couplers can be incorporated in droplets of coupler solvent, as is well known. Further details regarding couplers, methods for their incorporation and additives of varying type with which they can be employed are described in Research Disclosure, Item 17643, December 1978.

Research Disclosure is published by Industrial Opportunities Limited, Homewell, Havant Hampshire, PO9 1EF.

The mordant used in the second embodiment can be any mordant which will immobilize the dye formed as a result of the coupling reaction. Preferred mordants are basic polymeric mordants, e.g. polymers of amino guanidine derivatives of vinyl methyl ketone such as described in U.S. Patent 2,882,156, and basic polymeric mordants such as described in U.S. Patent Nos. 3,625,394 and 3,709,690 and 3,898,088. Other useful mordants are described in U.S. Patent No. 3,859,096 and pages 80-82 of the November 1976 edition of Research Disclosure.

It will be appreciated that the further the mordant is positioned away from the colour coupler, the greater will be the degree of image smearing. Hence the minimum smearing will occur when the mordant is incorporated in the coupler-containing layer. Increased image smearing can be obtained by spacing the mordant layer away from the coupler layer, for example with an inert interlayer, e.g. of gelatin. The amount of mordant employed will preferably be in the range 0.1 to 5 g/m2, more preferably 0.3 to 1.5 g/m2.

The present photographic materials can be single colour materials (including black and white elements) but are preferably multicolour materials comprising a blue sensitive or sensitized emulsion unit having associated therewith a yellow dye-forming colour coupler, a green sensitized emulsion unit having associated therewith a magenta dye-forming colour coupler and a red sensitized emulsion unit having associated therewith a cyan dye-forming colour coupler. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the visible spectrum. The layers of the material, including the layers of the emulsion units, can be arranged in various orders as is known in the art.

The coupler which forms the dye of increased mobility can be associated with one or more of the above emulsion layers. It might be advantageous, for example, to have this coupler associated with a blue sensitive layer as the human eye is not so sensitive to sharpness in yellow images.

When the present multilayer materials contain multiple blue, green and red emulsion layers; there can be relatively faster and relatively slower emulsion layers in each case. Such materials are well known and are described, for example, in British Specification 1,500,497. In such cases it is preferred to have the coupler which forms a dye of increased mobility associated with one or more of the faster layers.

In the following discussion of suitable components for use in the materials of this invention, reference will be made to Research Disclosure, December 1978, Item 17643, published by Industrial Opportunities Limited, Homewell, Havant, Hampshire, PO9 1 EF, United Kingdom. This publication will be identified hereinafter by the term "Research Disclosure".

The silver halide emulsions employed in the materials of this invention can be either negative-working or positive-working. Suitable emulsions and their preparation are described in Research Disclosure Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers of materials of this invention are described in Research Disclosure Section IX and the publications cited therein.

In addition to the couplers of this invention, the materials of the invention can include additional couplers as described in Research Disclosure Section VII, paragraphs D, E, F and G and the publications cited therein.

These couplers and the couplers of this invention can be incorporated in the elements and emulsions as described in Research Disclosure Section VII, paragraph C and the publications cited therein.

The photographic materials of this invention or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilizers (see Research Disclosure Section VI), antistain agents and image dye stabilizer (see Research Disclosure Section VII, paragraphs I and J), light absorbing and scattering materials (see Research Disclosure Section VIII), hardeners (see Research Disclosure Section XI), plasticizers and lubricants (see Research Disclosure Section XII), antistatic agents (see Research Disclosure Section Xl II), matting agents (see Research Disclosure Section XVI) and development modifiers (see Research Disclosure Section XXI).

The photographic materials can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein.

Photographic materials can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Discisoure Section XVIII and then processed to form a visible dye image as described in Research Disclosure Section XIX. Processing to form a visible dye image includes the step of contacting the element with a colour developing agent to reduce developable silver halide and oxidize the colour developing agent. Oxidized colour developing agent in turn reacts with the coupler to yield a dye.

Preferred colour developing agents are p-phenylene diamines. Especially preferred are 4-amino-N,Ndiethyl-aniline hydrochloride,4-amino-3-methyi-N-ethyl-N-~-(methanesulphonamido) ethylaniline sulphate hydrate,4-amino-3-methyl-N-ethyl-N-~-hydroxyethylaniline sulphate, 4-amino-3-p- (methanesu I phona mido)ethyl-N,N-diethyl-aniline hydrochloride and 4-amino-N-ethyl-N (2-methoxyethyl)m-toluidine di-p-toluene sulphonic acid.

With negative working silver halide this processing step leads to a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniformly fogging the material to render unexposed silver halide developable. Alternatively, a direct positive emulsion an be employed to obtain a positive image.

Development is followed by the conventional steps of bleaching, fixing, or bleach-fixing, to remove silver and silver halide, washing and drying.

The term "nondiffusible" used herein has the meaning commonly applied to the term in photography and denotes materials that for all practical purposes do not migrate nor wander through organic colloid layers such as gelatin in an alkaline medium in the photographic materials of the invention and preferably when processed in a medium having a pH of 10 or greater. The term "diffusible" has the converse meaning and denotes materials having the property of diffusing effectively through the colloid layers of the photographic elements in an alkaline medium. The term "mobility" refers to the ability to diffuse.

The term "associated with" means that the two materials concerned are intended to interact during processing; they are contained in the same or adjacent layers.

The following Examples are included for a better understanding of the invention. Experimental results are shown in Figures 1-8 of the accompanying drawings.

Preparative Example 1 Preparation ofa coupler which yields a slightly mobile cyan dye

1 (a) Ethyl-2-hrnmohexadecanoate rAJ 2-Bromohexadecanoic acid (10 g. 30 mmole) was heated under refluxwith ethanol (2.4 g 52 mmole) and benzene (10 ml). The apparatus was equipped with a Dean Stark trap for collecting the aqueous ethanol azeotrope. A trace of concentrated sulphuric acid was required to catalyze the esterification. After about 2 hours no more aqueous ethanol was being removed in the reaction.

After cooling, ethyl acetate (50 ml) was added and the solution extracted several times with 2% sodium hydrogen carbonate (NaHCO3) solution containing a little sodium chloride. After washing with brine the organic phase was dried with magnesium sulphate and evaporated to yield a very pale yellow oil. This solidifies in the refrigerator, the melting point being around 20 C. No distillation is required for purification.

Yield: 10 9. 93% C18H35BrO2 Requires: C 59.50; H 9.64; Br 22.04% Found: C 59.48; H 9.53; Br 21.97% 1 (b) Coupler (B) 1,4-Dihydroxy-2-naphthoic acid (5.3 g, 26 mmole) was dissolved in dry degassed dimethylsulphoxide (100 ml) and 50% sodium hydride oil dispersion (2.6 g 52 mmole) added with stirring under nitrogen at room temperature. The mixture was stirred and heated at 70-80 C under nitrogen until effervescence ceased. After cooling to room temperature the bromoester (A) (9.5 g 26 mmole) was added together with dry dimethylformamide (40 ml). After 1 hour the mixture was poured into dilute hydrochloric acid and the crude product filtered, washed with water and dried. Recrystallization was effected from ligroin.

Yield: 9.2 g 73% C29H42O5 Requires: C 71.60; H 8.64% Found: C71.15; H8.54% 1 (c) Acid chlo ride (C) The naphthol (B) (8.7 g 18 mmole) was converted to the acid chloride (C) by stirring with thionyl chloride (50 ml) and tetrahydrofuran (20 ml) at room temperature for 2 hours. The volatiles were removed in vacuo at 35-40 C yielding the acid chloride as a yellow/green solid. No purification is necessary.

Yield: quantitative 1 (d) Coupler(D) The acid chloride (C) was dissolved in dry ethyl acetate (100 ml) and the solution added portionwise to a stirred solution of octylamine (4.7 g 36 mmole) in dry ethyl acetate (50 ml) at room temperature. After stirring for 2 hours, the amine hydrochloride was removed by filtration and the filtrate evaporated to yield an oil which soon crystallized. Recrystallization was effected in acetic acid containing a few drops of water.

Yield: 8.5 g (79%) C37H59NO5.1/2H2O Requires: C 73.27; H 9.90; N 2.31 Found: C73.02; H 9.67; N 2.21% 1 (e) Product coupler Coupler (D) (6.0 g 10 mmole) was dissolved in dimethylformamide (80 ml) under nitrogen at room temperature. To this was added aqueous 10% sodium hydroxide (15 ml). After complete hydrolysis (30 minutes), the reaction mixture was poured into iced diluted hydrochloric acid (1 litre). The product was removed by filtration, washed with water and dried.

Recrystallization was effected from acetic acid.

Yield: 3.0 g (53%) C35H55NO5 Required: C 73.81; H 9.67; N 2.46 Found: C73.54; H9.81; N2.15% Example 1 A multilayer colour negative material (Coating A) containing blue-, green- and red-sensitive color forming units, each comprising a relatively fast and a relatively slow layer, was prepared having the structure set out below (pertinent coating weights in g/m2). The colour couplers in this and subsequent examples were incorporated in the silver halide emulsion by means of a coupler solvent.

Mordant layer GELATIN 1.81 MORDANT 3 1.00 Gelatin overcoat UV absorbing layer Relative fast, blue-sensitive emulsion layer SILVER HALIDE 1.56 GELATIN 1.81 COUPLER 2 0.17 Relative slow, blue-sensitive emulsion layer Yellow filter layer Green and red-sensitive emulsion layers Cellulose acetate film base A second control coating (Coating B) was made identical to Coating A except that Coupler 2 was replaced by an equimolar amount of Coupler 1 (0.24 g/m2) and the mordant layer was omitted. Coupler 2 yields a diffusible image dye whereas Coupler 1 and all the other couplers of both coatings yield a nondiffusible image dye.

The couplers and mordant were as follows: Coupler 1

Coupler 2

Mordant 3

Portions of the two coatings were given identical sensitometric stepped exposures and processed together through the negative colour process (C 41) described in the British Journal of Photography Annual 1977, pp.

204-5. The yellow densities of each sample were read and the RMS granularity determining by the method described in the Theory of the Photographic Process, 4th Edition, Edited by T. H. James, p. 619, using a scanning aperture of 48 microns. The density versus exposure curves obtained for Coatings A and B are shown in Figures 1 and 2. The red and green responses which are substantially the same in both cases are omitted for the sake of clarity. Coating A shows slightly more speed than Coating B in the lower scale of the blue record this being the normal region for assessing speed. The lower contrast of Coating A in the upper scale is due to the effect of the mordant layer on developability of the coating.

Also included in Figures 1 and 2 are granularity versus density measurements on the yellow images.

Figure 1 shows RMS Granularity (aD) While Figure 2 shows normalized granularity (oN). Normalized granularity is obtained from RMS granularity by dividing by density, having first subtracted the contribution to this density from any colored masking couplers in the film. It is a useful parameter for purposes of comparison in that the effect of different sensitometry between coatings, which can itself influence granularity, is removed. The Figures show that Coating A exhibits greatly reduced granularity compared to Coating B, especially in the lower to mid scale region where color negative materials commonly show their highest granularities.

Example 2 Multilayer coatings (Coatings C and D) were made identical to Coatings A and b except that: i) Coupler 1, which had been used in the slow blue sensitive, yellow forming, emulsion layer of Coatings A and B, was replaced by Compound 4 which is a ballasted hydroquinone; this forms a colourless compound hence, no dye is formed upon reaction with oxidized p-phenylenediamine developer. The yellow image from the Coatings C and D therefore originated exclusively from the fast, blue sensitive emulsion layer in each case.

ii) To compensate for insufficient maximum dye density contribution from the fast layer in the coating containing an equimolar amount of Coupler 2, the level of this coupler was increased by 30%. This figure was derived from the results, not shown here, of previous calibration coatings.

Compound 4 has the formula:

The coatings were exposed and processed as in Example 1. Figures 3 and 4 show the sensitometry resulting from imaging in the fast yellow layer only of Coatings C and D. The superior yellow sensitometry obtained from Coupler 2 is evident. Also shown in Figures 3 and 4 are the granularity results, which reveal that the reduction in aD and aN between Coatings C and D is at least as great as that between Coatings A and B.

Example 3 A control multilayer color negative material (Coating E) containing blue-, green- and red-sensitive colour forming units each comprising a relatively fast and a relatively slow emulsion layer was prepared having the following structure in which pertinent coating weights are in g/m2:: Coating E Gelatin supercoat UV-absorbing layer Fast blue-sensitive emulsion layer Slow blue-sensitive emulsion layer Yellow filter layer Interlayer Fast green-sensitive emulsion layer Silver halide 2.14 Gelatin 2.20 Coupler 5 0.35 Interlayer Fast red-sensitive emulsion layer Interlayer Slow green-sensitive emulsion layer Interlayer Slow red-sensitive emulsion layer Antihalation layer Cellulose acetate film base Coatings F, G and H were the same as Coating E except that they had a mordant layer coated over the gelatin supercoat containing Mordant 3 at 0.5 g/m2 and gelatin at 2 g/m2 and that Coupler 5 which forms a nondiffusible dye was progresively replaced with equivalent amounts (equal maximum dye density) of Coupler 6 which forms a diffusible dye as detailed below.

The couplers had the following formulae: Coupler 5

Coupler 6

The fast green-sensitive layers of Coatings F-H were as follows: Coating F Silver halide 2.14 Gelatin 2.20 Coupler 5 0.26 Coupler 6 0.13 Coating G Silver halide 2.14 Gelatin 2.20 Coupler 5 0.17 Coupler 6 0.25 Coating H Silver halide 2.14 Gelatin 2.20 Coupler 6 0.51 Samples of the above coatings were exposed and processed as described in Example 1 and plots of green density and granularity are shown in Figures 5 and 6 of the accompanying drawings.

The red and blue sensitometry and granularity data, which are unchanged throughout all these coatings, are omitted for the sake of clarity. Despite the higher fog and contrast introduced by Coupler 6 in Coatings F, G and H, the normalized granularity in which the effects of the differing sensitometry are removed, shows a progressive decrease as the proportion of Coupler 6 increases. Coating H therefore exhibits a greatly reduced granularity compared to Coating E.

Thin cross-sections cut from the processed films showed that the fast magenta image dye in Coating E remained in the layer in which Coupler 5 was coated. However, the image in Coating F appeared in both the fast magenta layer and in the mordant layer. An increased amount of dye appeared in the mordant layer for Coating G, and finally for Coating H all the dye was in the mordant layer and none in the fast magenta layer where Coupler 6 was coated. The image dye formed by Coupler 6 is therefore capable of complete migration to a remote mordant layer, and enables the observed reduction in granularity by dye smearing to be achieved.

Example 4 Colour negative materials were prepared having the coating structure described below. Pertinent coating weights are given in g/m2.

Gelatin 0.888 Sensitized silver halide 1.5 (as silver) Gelatin 3.0 Hardener 2% of total gelatin Coupler* Coupler solvent** Support *Coupler lay-down is calculated such that [ Ag:Coupler ] molar ratio is [ 16:1 ] .

**The Coupler solvent was tricresyl phosphate. Coupler to coupler solvent weight ratio was 1:1.

Coupler 7 Coupler X Coupler Y

The prepared coatings were exposed and processed as in Example 1. The cyan densities of each coating were read and the RMS granularity estimated as in Example 1. The sensitometric data obtained are listed in the table below.

TABLE Coupler Dmin Dmax Contrast Speed 7 0.20 1.46 1.24 342 X (Control) 0.19 1.47 1.13 339 Y (Control) 0.10 1.20 0.66 332 The characteristic curves obtained are shown in Figure 7 and a plot of normalized granularity vs. density is shown in Figure 8 of the accompanying drawings.

From the results it can be seen that compared with Coupler Y, Coupler 7 shows markedly reduced normalized granularities over the whole density range whereas Coupler X shows a granularity improvement only at low densities.

Claims (15)

1. A silver halide photographic material comprising at least one silver halide emulsion layer and nondiffusible dye-forming couplers associated with the emulsion layer or layers characterised in that the nondiffusible dye-forming couplers comprise a first nondiffusible dye-forming coupler which, upon reaction with oxidized colour developing agent, yields a nondiffusible dye and a second nondiffusible dye-forming coupler which, upon reaction with oxidized colour developing agent, yields a dye of such mobility that controlled image smearing occurs.

2. A photographic material as claimed in claim 1 wherein the material comprises at least two silver halide emulsion layers, the first coupler being associated with at least one of the emulsion layers and the second coupler being associated with at least one other of the emulsion layers.

3. A photographic material as claimed in claim 2 wherein each of the silver halide emulsion layers contains a coupler which yields a non-diffusible dye.

4. A photographic material as claimed in claim 1 wherein said first and second couplers yield dyes which absorb in the same region of the visible spectrum.

5. A photographic material as claimed in claim 1 wherein said first and second couplers yield dyes which absorb in different regions of the visible spectrum.

6. A photographic material as claimed in any of claims 1 to 5 wherein the second coupler yields a dye of limited mobility and has the structure: COUP - SECONDARY BALLAST I MAIN BALLAST wherein: COUP is a dye-forming coupler moiety, the asterisk (*) denoting the coupling position thereof; MAIN BALLAST is a group, attached to the coupling position of COUP and detachable therefrom by means of reaction of COUP with oxidized colour developing agent, which is of such size and configuration as to render the coupler nondiffusible; and SECONDARY BALLAST is a group, attached to a noncoupling position of COUP, which is of such size and configuration that the dye formed by coupling of COUP with oxidized colour developing agent is slightly mobile.

7. A photographic material as claimed in claim 6 wherein COUP is an acylacetanilide, pyrazolone, pyrazolotriazole, phenol or naphthol coupler moiety; MAIN BALLAST is an alkyl or aryl group of 8 to 32 carbon atoms, which may be substituted, joined to the coupling position of COUP through a linking group; and SECONDARY BALLAST is an alkyl group of 2 to 20 carbon atoms or an aryl group of 6 to 20 carbon atoms, either of which may be substituted.

8. A photographic material as claimed in any of claims 1 to 7 wherein the second coupler has one of the structures:

wherein: R1 is an aryl group or an alkyl group either of which may be substituted; R2 is the main ballast group; R3 is the secondary ballast group; R4 is hydrogen or one or more halogen, alkyl or alkoxy groups either of which may be substituted; one of R5 and R6 is the secondary ballast group and the other is hydrogen or one or more halogen, alkyl, alkoxy or alkylamido groups any of which alkyl moieties may be substituted; one of R9 and R10 is the secondary ballast group and the other is hydrogen or an alkyl, alkoxy, aryl or amino group; and R11 is hydrogen or one or more halogen, alkyl, alkoxy or amino groups any of which groups may be substituted.

9. A photographic material as claimed in any of claims 1 to 8 wherein the second coupler has the structure:

wherein: R2 is the main ballast group, R7 is a solubilising group, R8 is an alkyl group of 6-14 carbon atoms, and m is 5-20.

10. A photographic material of any of claims 1 to 5 wherein the second coupler yields a diffusible dye and has the structure: COUP - SOL * I BALLAST wherein: COUP is a dye-forming coupler moiety, the asterisk (*) denoting the coupling position thereof; BALLAST is a group, attached to the coupling position of COUP and detachable therefrom by means of reaction of COUP with oxidized colour developing agent, which is of such size and configuration as to render the coupler nondiffusible; and SOL is a solubilizing substituent, attached to a non-coupling position of COUP, which renders the dye formed by coupling of COUP with oxidized colour developing agent diffusible in the alkaline environment present during photographic processing and, associated with the layer containing the second coupler, a mordant which immobilizes the diffusible dye.

11. A photographic material as claimed in claim 10 wherein the mordant and the second coupler are in the same layer.

12. A photographic material as claimed in claim 10 wherein the mordant and the second coupler are in contiguous layers.

13. A photographic material as claimed in claim 10 wherein the mordant and the second coupler are separated by an intervening layer.

14. A photographic material as claimed in claim 10 wherein the mordant is a basic polymeric mordant.

15. A photographic material according to claim 1 substantially as described herein and with reference to the Examples.