This invention relates to the use of lH-pyrazolo[l,5-b]-l,2,4—triazole couplers in photographic materials. lH-Pyrazolo[1,5,-b]-l,2, -triazole couplers have been described in, for example, US Patent 4,621,046. In European Patent Specification 0,177,765 such a coupler having the formula:

is incorporated in a silver chlorobromide (507. bromide) emulsion. The coupler is said to provide dye images of good fastness and freedom from yellow stain.

Currently photographic colour paper processable in the RA4 process is comprised of silver halide emulsions having at least 80% silver chloride and preferably substantially pure silver chloride. Most lH—pyrazolo[l,5—b]—l,2,4—triazole couplers when incorporated into silver chloride emulsions provide photographic materials having poor raw stock keeping properties. That is, the material when stored after manufacture but before exposure and processing, shows ^' significantly increased D . compared to freshly coated materials.

The present invention is directed to the use of certain 1H—pyrazolo[l,5—b]—1,2,4—triazole couplers in photographic silver chloride materials to improve their raw stock keeping properties.

Accordingly the present invention is directed to the use of lH-pyrazolo[l,5-b]-l,2,4- triazole couplers containing a tertiary carbon group on the coupler nucleus in photographic silver halide materials of which the halide comprises more than 80% chloride, in order to improve raw stock stability.

The present invention also provides a photographic material comprising a support bearing at least one photosensitive silver halide emulsion of which the halide is at least 80% molar chloride having in or adjacent the emulsion layer a lH-pyrazolo[l,5-b]-l,2,4—triazole coupler containing a tertiary carbon group on the coupler nucleus.

Preferably the silver halide emulsion comprises at least 90% silver chloride especially substantially pure silver chloride.

The preferred couplers have the formula

R ² R ¹ I " R ³ \ / \ /

II I II N N N

wherein R 1 and R3 are each an alkyl or substituted alkyl group, and

R is a hydrogen or a coupling off group, at least one of R 1 and R3 comprising a group of the formula:

R ,4

- C -

wherein R4, R5 and R6 are individually a halogen atom or an alkyl, cycloakyl, amino, aryl, cyano, nitro, heterocyclic or — —R group wherein L is a linking group and R is an alkyl, aryl, heterocyclic group and

4 5 6 wherein any two of R , R and R can form a heterocyclic or alicyclic ring, any of the groups R 4, R5 and R6 being optionally substituted, all of the above groups and substituents being such that they do not adversely affect the desired properties of the coupler. In the above general formula when R 1 or R3 are a tertiary alkyl group they preferably contain 4-8 carbon atoms and may be t-butyl, t-pentyl or t—octyl. R 1 and R3 may otherwise contain 1—25 carbon atoms and may comprise a ballast group to render the coupler non—diffusible in photographic layers. Examples of R 4, R5 and R6 are chlorine, bromine and fluorine; alkyl groups containing 1 to 20 carbon atoms, for example, methyl, ethyl, propyl, butyl, pentyl, ethylhexyl and eicosyl; cyclohexyl and cyclopentyl; dioctylamino, dimethylamino and dodecylamino; aryl containing 6 to 20 carbon atoms, or example, phenyl, naphthyl and mesityl; cyano; nitro; a heterocyclic group comprised of atoms selected from carbon, oxygen, nitrogen and sulphur atoms necessary to complete a 5— or 6-membered ring, for example, pyrrolyl, oxazolyl and pyridyl. Examples of L are:

-0 in which R8 and R9 are individually

hydrogen, alkyl, such as alkyl containing 1 to 30 carbon atoms, for example, methyl, ethyl, propyl,

butyl or eicosyl, or aryl, such as aryl containing 6 to 20 carbon atoms, for example, phenyl or naphthyl; or a heterocyclic group comprised of atoms selected from carbon, nitrogen, oxygen, and sulphur atoms necessary to complete a 5- or 6— ember heterocyclic ring, for example, pyrrolyl, oxazolyl and pyridyl.

Examples of R are an alkyl containing 1 to 30 carbon atoms, for example, methyl, ethyl, propyl, butyl, pentyl and eicosyl; aryl, such as aryl containing 6 to 20 carbon atoms, for example, phenyl and napthyl; or a heterocyclic group, such as a 5- or 6—membered heterocyclic group comprised of atoms selected from carbon, nitrogen, oxygen and sulphur atoms, for example an oxazole, pyridine, pyrrole or thiophene ring. When any two of R 4, R5 and R6 form a heterocyclic ring this may be an oxazole, pyridine, pyrrole and thiophene; or when they form an alicyclic ring system, this may be cyclohexyl, norbornyl or adamantyl.

2 The coupling-off group R may be a halogen atom or an aryloxy or arylthio group.

The couplers used in the present invention may be prepared by methods known in the art. Typically, the couplers are associated with a silver halide emulsion layer coated on a support to form a photographic element. As used herein, the term "associated with" signifies that the coupler is incorporated in the silver halide emulsion layer or in a layer adjacent thereto where, during processing, it is capable of reacting with silver halide development products.

The photographic elements can be single colour elements or multicolour elements. In a multicolour element, the magenta dye-forming couplers of this invention would usually be associated with a

green—sensitive emulsion, although they could be associated with an emulsion sensitised to a different region of the spectrum, or with a panchromatically sensitised, orthochromatically sensitised or unsensitised emulsion. Multicolour elements contain dye image— orming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art.

A typical multicolour photographic element comprises a support bearing yellow, magenta and cyan dye image-forming units comprising at least one blue-, green- or red-sensitive silver halide emulsion layer having associated therewith at least one yellow, magenta or cyan dye-forming coupler respectively, at least one of the magenta dye-forming couplers being a coupler of this invention. The element can contain additional layers, such as filter and barrier layers.

In the following discussion of suitable materials for use in the emulsions and elements of this invention, reference will be made to Research Disclosure, December 1978, Item 17643, published by Industrial Opportunities Ltd., The Old Harbourmaster's, 8 North Street, Emsworth, Hants P010 7DD, U.K. This publication will be identified hereafter as "Research Disclosure".

The silver halide emulsion employed in the elements of this invention can be either negative-working or positive— orking. 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 elements of this invention are described in Research Disclosure Section IX and the publications cited therein.

In addition to the couplers of this invention, the elements 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. The couplers of this invention and any additional couplers can be incorporated in the elements and emulsions as described in Research Disclosures of Section VII, paragraph C and the publications cited therein.

The photographic elements of this invention or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilisers (see Research Disclosure Section VI), antistain agents and image dye stabiliser (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), plasticisers and lubricants (see Research Disclosure Section XII), antistatic agents (see Research Disclosure Section XIII), matting agents (see Research Disclosure Section XVI) and development modifiers (see Research Disclosure Section XXI).

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

Photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure 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 oxidise the colour developing agent. Oxidised 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-3—meth l— ,N—diethylaniline hydrochloride, 4-amino-3-meth l-N-ethyl-N-β-(methanesulphonamido)- ethylaniline sulphate hydrate, 4—amino—3—methyl—N— ethyl-N-β-hydroxyethylaniline sulphate, 4-amino- 3-β-(methanesulphonamido)eth l-N,N-diethylaniline hydrochloride and 4-amino-N-ethyl-N-(2-methoxy- eth l)-m-toluidine di-p-toluene sulphonate. With negative-working silver halide emulsions 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 uniform fogging of the element to render unexposed silver halide developable. Alternatively, a direct positive emulsion can 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 following examples are included for a better understanding of the invention. EXAMPLE 1 Couplers were dispersed and coated as follows. The test coupler (3.0 mmol), dissolved in half its weight of di-n-butyl phthalate and ethyl acetate (2.0g), was dispersed in aqueous gelatin (36g, 12.5%) using ultrasonic agitation. The gelatin solution contained a small amount (0.5%) of di-isopropyl-naphthalene sulphonic acid (sodium salt)

as a surfactant. The resultant coupler dispersion was diluted to 200g with water and mixed with a green-sensitised silver chloride photographic emulsion (lOOg, 1.49% Ag, 4.5% gel). The mixture was spread on a resin-coated paper support to give a layer of the following composition:

Ag 0.267g.m~ ²

__2 Coupler O.54mmol.m

Gelatin l.βlg.πf ² A protective gel supercoat containing hardener was applied to the coating.

Sample strips of the coatings were exposed through a step tablet (density range 0-3, 0.15 increments) and developed in standard "KODAK" RA-4 process solutions.

Sample strips from each coating were exposed and processed with RA4 chemistry within a few days of coating. Similar strips were put aside in a light-tight box and stored under ambient conditions for 29 weeks before exposure and processing.

The sensitometric parameters of the two sets of coatings were measured. It was observed that the stored coatings showed significantly higher Dmin values than the freshly processed coatings. However, the increase in Dmin was much smaller for the 6—t—Bu substituted examples lb and Id than for their analogous 6—Me couplers,la and Ic. (See Table below)

Cl H

R -ft Λ.Λ ■lrl ^(CH 2 ⁾ 3- / — NH-Ball (I)

N- -Ji¬ -N

Fresh Stored

Coupler Ball Dmin Dmin

la Me ) ⁽ⁿ -?12 ^H 25 / ^fc - ^Bu 0.12 0.21

) lb t-Bu) COCHO y - OH 0.11 0.15

EXAMPLE 2

Couplers Ila and lib were examined as described in Example 1, except that the storage time was reduced to 17 weeks. The sensitometric data shown below confirmed the advantage of the 6-t—Bu substituent.

(II) ₇ (t

Coupler R Fresh D.min Stored D.min Ila Me 0.11 0.20 lib t-Bu 0.10 0.12

Couplers Ilia and Illb were dispersed with the stabilising compound IV in the following proportions:

Coupler 2

Stabiliser 1

Solvent 3

(dibutyl phthalate)

Me Me

The dispersions were coated with a green sensitive silver chloride emulsion so as to give the following coverages: Coupler: O.57mmole.m

Silver: 2.4mmole.m _2

One pair of sample strips from each coating was incubated for 7 days at 50°C, 50%RH in the dark for comparison with an identical pair stored at ambient temperature. Both pairs were step wedge exposed and processed (RX4). The sensitometric data shown below show that the strips stored at elevated temperature showed a much greater Dmin than those stored at room temperature, but the difference was dramatically lower for the 6—t-Bu example (Illb) than for Ilia.

I I I

Coupler R ΔDmin (inc - fresh)

Ilia Me +1.39

Illb t-Bu +0.28