Silver halide photographic elements containing aryl hydrazines

Abstract

 The present invention relates to a silver halide photographic element comprising a support bearing at least one silver halide emulsion layer including negative acting surface latent image-type silver halide grains in reactive association (prior to image-wise exposure) with a hydrazine compound represented by the following formula (I) :

wherein Ar is an aryl group, G is CO, SO, SO₂, PO₂, PO₃ or C=NR₂; R, R₁, R₂, which can be the same or different, are hydrogen, alkyl of 1 to 6 carbon atoms, an alkyl sulfinyl of 1 to 6 carbon atoms or a trifluoroacetyl group;
n is an integer from 1 to 3;
Z₁ and Z₂, being the same or different, are electron-withdrawing groups.
This silver halide photographic element can be developed with a conventional aqueous alkaline Rapid Access type developer solution, at a pH value lower than 11.0, containing a developing agent and an auxiliary developing agent, to give high contrasts.

Description

FIELD OF THE INVENTION

[0001] This invention relates to photographic elements, in particular to black-and-white photographic elements containing aryl hydrazines useful in obtaining ultra high contrasts for graphic arts films.

BACKGROUND OF THE INVENTION

[0002] In forming high contrast images necessary for Graphic Arts processes by development of silver halide photographic elements, special developers known in the art as "lith" developers are used. The high contrast is achieved by means of the infectious development as described in Journal of the Franklin Institute, vol. 239, 221-230 (1945). These developers exhibit an induction period prior to the development of exposed silver halides, after which the infectious development occurs, which gives rise to the high contrast.

[0003] The typical "lith" developer contains only a single developing agent of the dihydroxybenzene type, such as hydroquinone. To enhance the infectious development, "lith" developers contain a low content of alkali sulfite. This low sulfite content renders the developer more prone to aerial oxidation, especially when it is used in combination with processing machines and, more particularly, with Rapid Access type processing machines, where developer degradation is accelerated.

[0004] The delay in the start of development caused by the long induction period of hydroquinone developers lengthens the processing time and delays access to the finished material. While the induction period has been eliminated and processing time reduced by using the so called "Rapid Access" developers, which contain both hydroquinone and a superadditive developing agent such as phenidone or metol, these Rapid Access developers are not useful for lithographic purposes because they cannot produce the necessary high contrast. This is because Rapid Access developers have a high sulfite content which prevents infectious development and causes a lower contrast than "lith" developers.

[0005] Several alternatives to using a hydroquinone developing agent with a low sulfite content of the "lith" processing system to achieve high contrast development are known in the art. They are the so-called "high contrast" processing systems which use a hydrazine compound, either in the photographic element or in the developing solution, to promote high contrast. The use of hydrazine compounds allows the use of auxiliary developing agents in combination with the dihydroxybenzene developing agent to increase the developing capacity. It also allows the use of relatively high sulfite concentration to protect the developing agents against oxidation, and thereby increasing the developer stability. The high pH level, about 10.5 to 12.8, necessary to obtain the high contrast from the use of hydrazine compounds makes the life of the developing solution relatively short.

[0006] Processes which make use of hydrazine are disclosed, for example, in US 2,419,975; 4,168,977 and 4,224,401. Modifications and improvements to the hydrazine process are disclosed in GB 598,108 and in US 2,410,690; 2,419,974; 4,166,742; 4,221,857; 4,237,214; 4,241,164; 4,243,739; 4,272,606; 4,272,614; 4,311,871; 4,323,643; 4,332,878; 4,337,634; 4,686,167; 4,746,593; 4,798,780; 4,914,003; 4,925,832; 4,975,354; 4,988,604; 4,994,365; 5,041,355; 5,126,227; 5,232,818; 5,252,426; 5,279,919; 5,284,732; 5,316,889 and in Research Disclosure No. 235, Nov. 1983, item 23510 "Development nucleation by hydrazine and hydrazine derivatives".

[0007] US 4,937,160; 5,013,844; 5,130,480 and 5,190,847 describe photographic silver halide materials containing aryl hydrazines with a quaternary nitrogen heterocyclic cationic group to obtain ultrahigh contrasts at relatively low pH value.

[0008] It would be desirable to obtain a photographic element providing very high contrasts upon development with conventional Rapid Access type developer solution at a pH value lower than 11.0.

SUMMARY OF THE INVENTION

[0009] The present invention relates to a silver halide photographic element comprising a support bearing at least one silver halide emulsion layer including negative acting surface latent image-type silver halide grains in reactive association (prior to image-wise exposure) with a hydrazine compound represented by the following formula (I) :

wherein Ar is an aryl group, G is CO, SO, SO₂, PO₂, PO₃ or C=NR₂; R, R₁, R₂, which can be the same or different, are hydrogen, an alkyl group, an alkyl sulfinyl group or a trifluoroacetyl group;
n is an integer from 1 to 3;
Z₁ and Z₂, being the same or different, are electron-withdrawing groups.

[0010] This silver halide photographic element can be developed with a conventional aqueous alkaline Rapid Access type developer solution, at a pH value lower than 11.0, containing a developing agent and an auxiliary developing agent, to give high contrasts.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The group Ar in the formula (I) is represented by a substituted or unsubstituted aryl group, e.g. a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group. Such aryl groups may be substituted with one or more substituents, such as straight or branched-chain alkyl groups preferably having from 1 to 20 carbon atoms (e.g. methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, n-octyl, n-hexyl, tert.-octyl, n-decyl, n-dodecyl, etc.), aralkyl groups having from 6 to 20 carbon atoms (e.g. benzyl, phenethyl, etc.), alkoxy groups having from 1 to 20 carbon atoms (e.g. methoxy, ethoxy, 2-methyl-propyloxy, etc.), amino groups which are monoor disubstituted with alkyl groups, acylaminoaliphatic groups (e.g. acetylamino, benzoylamino, etc.), etc., as disclosed in US 4,168,977 and 4,937,160 and in CA 1,146,001. Such aryl groups may also be substituted with a ureido group of formula:

wherein R₃ and R₄ (which may be same or different) each represents hydrogen, an aliphatic group (such as a straight or branched-chain alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an alkenyl group and an alkynyl group), an aryl group (such as a phenyl group and a naphthyl group) or a heterocyclic group; R5 represents hydrogen or an aliphatic group (such as those listed above) as described in US 4,323,643.

[0012] Although many aryl groups may be considered for the group Ar, substituted phenyl groups are preferred because of easier availability.

[0013] G is represented by the groups CO, SO, SO₂, PO₂, PO₃ or C=NR₂; preferably G is represented by a carbonyl group.

[0014] R, R₁, R₂, which can be the same or different, are hydrogen, an alkyl group of 1 to 6 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl), an alkyl sulfinyl group of 1 to 6 carbon atoms (e.g., methylsulfinyl, ethylsulfinyl, propylsulfinyl, isopropylsulfinyl, n-butyl-sulfinyl, isobutylsulfinyl), or a trifluoroacetyl group.

[0015] Z₁ and Z₂, being the same or different, are electron-withdrawing groups, such as, for example, COOH, COOCH₃, COOC₂H₅, CF₃, SO₂CH₃, CN, NO₂ groups, and the like, as defined in "Advanced Organic Chemistry", J.March, third edition, pages 242-250. Preferred electron-withdrawing groups are COOC₂H₅, CF₃, SO₂CH₃, CN groups.

[0016] When the term "group" or "nucleus" is used in the present invention, the described chemical material includes the basic group or nucleus and that group or nucleus with conventional substituents. When the term "moiety" is used to describe a chemical compound or substituent, only an unsubstituted chemical material is intended to be included. For example, "alkyl group" includes not only such alkyl moieties as methyl, ethyl, octyl, stearyl, etc. but also such moieties bearing substituent groups such as halogen, cyano, hydroxyl, nitro, amine, carboxylate, etc. On the other hand, "alkyl moiety" or "alkyl" includes only methyl, ethyl, octyl, stearyl, cyclohexyl, etc.

[0017] Preferably, the silver halide photographic element of the present invention contains a hydrazine compound represented by formula (II):

wherein R₆ is an alkyl group of 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl) or an alkoxy group of 1 to 10 carbon atoms (e.g., methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy) and Z₁and Z₂, being the same or different, are defined as in previous formula (I).

[0018] More preferably, the silver halide photographic element of the present invention contains a hydrazine compound represented by formula (III):

wherein R₇ is an alkyl group of 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl); Z₁and Z₂, being the same or different, are defined as in previous formula (I).

[0019] Specific examples of hydrazine compounds useful in the present invention are those listed in the following, but the invention is not limited to them.

[0020] The aryl hydrazine according to this invention can be synthesized by various processes in a simple way from equimolar quantities of the aryl hydrazine with the corresponding carboxylic acid and dicyclo-hexylcarbodiimide (cfr. "Methoden der Organische Chemie" (Houben-Weyl), 4th edition, Vol. X/2, page 355) or from equimolar quantities of the aryl hydrazine with the corresponding acyl halide. Other possibilities of synthesis are known to the expert.

Synthesis of compound (H-1)

[0021] 4.5 g (0.02 moles) of 1-carboxymethyl-4-methylmercapto-pyridinium chloride and 1.6 g (0.02 moles) of malononitrile were suspended in 10 ml of absolute ethanol with 6.6 mol of triethylamine. The mixture was refluxed for 4 hours and then the solvent was evaporated. The residue was dissolved in 5 ml of water and acidified to pH=1 with HCl 6M. The yellow solid separated was filtered and dried under reduced pressure at 50°C. 3.07 g (0.015 moles) of the obtained carboxylic acid were then suspended in dry acetonitrile with 0.015 moles of triethylamine. After complete dissolution, 0.015 moles of p-methoxy-phenylhydrazine hydrochloride were added and the suspension was stirred for twenty minutes. 0.015 moles of dicyclohexylcarbodiimide were added and the mixture was stirred at room temperature for 3 hours. The solid was filtered off and the solvent evaporated. The residue was crystallized from methanol and the hydrazide was obtained as a pale yellow solid.

[0022] The hydrazine compounds are incorporated into the photographic element, for example in a silver halide emulsion layer or in a hydrophilic colloidal layer, preferably a hydrophilic colloidal layer adjacent to the emulsion layer in which the effect of the hydrazine compound is desired. It can, of course, be present in the photographic element distributed between the emulsion and the hydrophilic colloidal layers, such as subbing layers, interlayers and protective layers.

[0023] The hydrazine compound is incorporated into the photographic element using various methods well-known in the photographic art. With a ballasting group present, the most common method of incorporation is that of dissolving the hydrazine derivatives in a high boiling crystalloidal solvent and dispersing the mixture in the emulsion, as described, for example, in US 2,322,027.

[0024] The amount of said hydrazine compounds is from about 5x10^-5 to 10^-2 moles per mole of silver, preferably from about 5x10^-4 to 5x10^-3 moles per mole of silver.

[0025] The silver halide photographic element of the present invention preferably contains contrast promoting agents useful for high contrast images.

[0026] Contrast promoting agents useful for high contrast images include hydroxymethylidine group containing compounds, such as diarylmethanol compounds, as described in US 4,693,956. Examples of such contrast promoting agents are methyl alcohol, 1,3-butanediol, 1,4-cyclohexanediol, phenylmethylcarbinol and the like.

[0027] Preferred contrast promoting agents to be incorporated in the photographic element include diarylcarbinol compounds as described in US 4,777,118, such as, for example, benzhydrol, 4,4'-dimetoxydiphenyl-methanol, 4,4'-dimethyldiphenylmethanol, 2,2'-di-bromodiphenylmethanol, and the like, and poly(oxyethylene) substituted benzylic alcohols contrast promoting agents having the following general formula (I):

wherein Ar' is a substituted aryl group (e.g., phenyl, naphthyl) containing at least 3 repeating ethyleneoxy units, preferably at least 6, more preferably at least 10 repeating ethyleneoxy units, and

[0028] R₈ and R₉, the same or different, each represents hydrogen, an alkyl group preferably containing 1 to 8 carbon atoms (e.g., methyl, ethyl, propyl, allyl, butyl, amyl, hexyl, octyl), and more preferably containing 1 to 4 carbon atoms; or an aryl group, preferably containing 6 to 10 carbon atoms (e.g., phenyl, naphthyl).

[0029] Other contrast promoting agents useful for high contrast images are, for example, the alkanolamine compounds comprising a hydroxyalkyl group of 2 to 10 carbon atoms and a mercapto compound, as described in US 4,668,605 or certain trialkyl amines, monoalkyl-dialkanolamines or dialkylmonoalkanol amines, as described in US 4,740,452. Useful contrast promoting agents also include certain amino compounds which function as incorporated booster described in US 4,975,354. These amino compounds contain within their structure a group comprised of at least three repeating ethylenoxy units.

[0030] The amount of said contrast promoting agents is from about 10^-4 to 10^-1 moles per mole of silver, preferably from about 10^-3 to 5x10^-2 moles per mole of silver.

[0031] Examples of contrast promoting agents useful for the purpose of the present invention are listed hereinbelow, but the invention is not limited to them:

CP.1)

methyl alcohol

CP.2)

1,3-butanediol

CP.3)

1,4-cyclohexanediol

CP.4)

phenylmethylcarbinol

CP.5)

benzhydrol

CP.6)

4,4'-dimetoxydiphenylmethanol

CP.7)

4,4'-dimethyldiphenylmethanol

CP.8)

2,2'-di-bromodiphenylmethanol

CP.9)

n-butyldiethanolamine

CP.10)

n-propyldiethanolamine

CP.11)

2-di-isopropylaminoethanol

CP.12)

N,N-di-n-butylethanolamine

CP.13)

3-di-propylamino-1,2-propanediol

CP.14)

CP.15)

CP.16)

CP.17)

CP.18)

CP.19)

CP.20)

CP.21)

[0032] The silver halide emulsions for use in the present invention may he silver chloride, silver chloro-bromide, silver iodo-bromide, silver iodo-chloride, silver iodo-chloro-bromide or any mixture thereof. Generally, the iodide content of the silver halide emulsions is less than 10% silver iodide moles, said content being based on the total silver halide. The chloride content is generally of at least about 50% of the total silver halide. The silver halide emulsions are usually monodispersed or narrow grain size distribution emulsions, as described for example in US 4,166,742; 4,224,401; 4,237,214; 4,241,164; 4,272,614 and 4,311,871.

[0033] The silver halide emulsions may comprise a mixtures of emulsions having different grain combinations, for example a combination of an emulsion having a mean grain size below 0.4 µm with an emulsion having a mean grain size above 0.7 µm, as described in Japanese Patent Application S.N. 57-58137 or a combination of two emulsions, both having a grain size below 0.4 µm, such as for example a first silver halide emulsion having a mean grain size from 0.1 to 0.4 µm and a second silver halide emulsion with particles having a mean grain volume lower than one half the particles of the first emulsion.

[0034] The silver halide grains of the emulsions of the present invention are capable of forming a surface latent image, as opposed to those emulsions forming an internal latent image. Surface latent image-forming silver halide grains are most employed in negative type silver halide emulsions, while internal latent latent image-forming silver halide grains, though capable of forming a negative image when developed in an internal developer, are usually employed with surface developers to form direct-positive images. The distinction between surface latent image and internal latent image-forming silver halide grains is well-known in the art. Generally, some additional ingredients or steps are required in the preparation of silver halide grains capable of preferentially forming an internal latent image instead of a surface latent image.

[0035] In the silver halide emulsions of the present invention, the precipitation or the growth of the silver halide grains may be carried out in the presence of metal salts or complex salts thereof, such as rhodium and indium salts or complex salts thereof. According to the present invention, it has been found, anyhow, that the presence of rhodium or iridium is not necessary for obtaining the high contrasts. Silver halide grains free of rhodium or iridium, as well as those formed or ripened in the presence of rhodium or iridium may be used to the purposes of the present invention.

[0036] The silver halide emulsions of the present invention may not be chemically sensitized, but are preferably chemically sensitized. As chemical sensitization methods for silver halide emulsions, the known sulfur sensitization employing sulfur compounds, the reduction sensitization employing mild reducing agents and the noble metal sensitization can be used, either alone or in combination.

[0037] The silver halide emulsions can be spectrally sensitized with dyes from a variety of classes, including the polymethine dye class, such as cyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-, tetra- and poly-nuclear cyanines and merocyanines), oxonols, hemioxonols, styryls, merostyryls and streptocyanines. The silver halide emulsions can be spectrally sensitized at different wavelengths to be exposed to all the laser exposures, i.e. at 488, 633 and 670 nm.

[0038] The binder or protective colloid for the silver halide layer and the layers of the photographic element is preferably gelatin, but other hydrophilic colloids or synthetic water insoluble polymers in the form of latexes can be used to partially or completely replace gelatin.

[0039] In addition, the photographic elements of the present invention may also contain any photographic additives known in the art, such as for example stabilizers, antifoggants, hardeners, plasticizers, development accelerators, gelatin extenders, matting agents.

[0040] The dihydroxybenzene developing agents employed in the aqueous alkaline developing solution for use in the practice of this invention are well--known and widely used in photographic processings. The preferred developing agent of this class is hydroquinone. Other useful dihydroxybenzene developing agents include chlorohydroquinone, bromohydroquinone, isopropylhydroquinone, tolylhydroquinone, methylhydroquinone, 2,3-di-chlorohydroquinone, 2,5-dimethylhydro-quinone, 2,3-dibromohydroquinone, 1,4-dihydroxy-2-acetophenone-2,5-dimethylhydroquinone, 2,5-diethyl-hydroquinone, 2,5-di-p-phenethylhydroquinone, 2,5-di-benzoylhydroquinone, 2,5-diacetaminohydroquinone.

[0041] The preferred auxiliary developing agents are those described in US 5,236,816; particularly useful are the auxiliary developing agents such as aminophenol and substituted aminophenol (e.g., N-methyl-p-aminophenol, also known as Metol and 2,4-diaminophenol) and the 3-pyrazolidone developing agents (e.g. 1-phenyl-3-pyrazolidone, 1-phenyl-4,4-dimethyl-3-pyrazolidone, 1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone and 1-phenyl-4,4-dihydroxymethyl-3-pyrazolidone. Other useful 3-pyrazolidone developing agents include: 1-phenyl-5-methyl-3-pyrazolidone, 1-p-aminophenyl-4-methyl-4-propyl-3-pyrazolidone, 1-p-chlorophenyl-4-methyl-4-ethyl-3-pyrazolidone, 1-p-acetamido-phenyl-4,4-di-ethyl--3-pyrazolidone, 1-p-hydroxyethylphenyl-4,4-dimethyl-3-pyrazolidone, 1-p-hydroxyphenyl-4,4-dimethyl-3-pyrazolidone, 1-p-methoxyphenyl-4,4-diethyl-3-pyrazolidone, 1-p-tolyl-4,4-dimethyl-3-pyrazolidone).

[0042] The aqueous alkaline photographic developing solution for use in the practice of this invention contains a sulfite preservative at a level sufficient to protect the developing agents against the aerial oxidation and thereby assure good stability characteristics. Useful sulfite preservatives include sulfites, bisulfites, metabisulfites and carbonyl bisulfite adducts. Typical examples of sulfite preservatives include sodium sulfite, potassium sulfite, lithium sulfite, ammonium sulfite, sodium bisulfite, potassium metabisulfite, sodium formaldehyde bisulfite salt. Also ascorbic acid is a known preservative agent against aerial oxidation of the developer for use in the bath.

[0043] The aqueous alkaline developing solutions for use in the practice of this invention can vary widely with respect to the concentration of the various ingredients included therein. Typically, the dihydroxybenzene developing agent is used in an amount of from 0.040 to 0.70 moles per liter, more preferably in an amount of from 0.08 to about 0.40 moles per liter; the 3-pyrazolidone developing agent is used in an amount of from 0.001 to 0.05 moles per liter, more preferably in an amount of from 0.005 to 0.01 moles per liter; the sulfite preservative is used in an amount of from 0.03 to 1.0 moles per liter, more preferably in an amount of from 0.10 to 0.70 moles per liter.

[0044] In carrying out the method of this invention, it is preferred to use an organic antifogging agent to minimize fog formation in the processed element. The organic antifogging agent can be incorporated in the photographic element or can be added to the developing solution or can be both incorporated in the photographic element and added to the developing solution. According to the present invention, it has been found that more preferred organic antifogging agents for specific use in the developing solutions are benzotriazole and/or a benzimidazole antifogging agents, which proved to have beneficial effects on increasing contrast. Useful compounds are both substituted and unsubstituted benzotriazole and benzimidazole compounds, with the proviso that electron withdrawing substituents at least as strong as nitro groups are excluded. As a matter of fact, nitro substituted benzotriazole and benzimidazole compounds, although good to prevent fog, do not provide beneficial effects with reference to contrast increase. Benzimidazoles and benzotriazoles, as a class, are believed to be useful in the practice of this invention. Anyhow, as indicated, difficulties in obtaining significantly improved performance with benzotriazoles and benzimidazoles having strong electron withdrawing groups have been encountered. Benzotriazoles and benzimidazoles are therefore preferred not to have any substituents on the aromatic rings which are electron attracting groups as strong as or stronger than a nitro group. Other substituents known in the art such as lower alkyl groups (having 1 to 5 carbon atoms) and halogen substituents (chlorine) proved to be substituents good to the purposes of the invention. Said benzotriazole and benzimidazole antifogging and contrast promoting agents are normally used in amounts effective to prevent fog, although quantity can be optimized to get the best results from the contrast point of view. Useful quantities, when they are included in the emulsion, may vary from 1 to 100 milligrams per 100 grains of emulsion and, when included in the developing bath, as preferred, may vary from 0.01 to 5 grams per liter.

[0045] In addition to the essential components specified hereinabove, the developing solutions can optionally contain any of a wide variety of addenda, as known, useful in photographic developing solutions. For example, they can contain solvents, buffers, sequestering agents, development accelerators, agents to reduce swelling of the emulsion layers, and the like.

[0046] The invention is further illustrated by the following examples.

EXAMPLE

[0047] A cubic AgBr_0.30Cl_0.70 emulsion of narrow grain size distribution and mean grain size of 0.30 µm was prepared by the conventional double jet procedure. The emulsion was then coagulated and washed in the conventional manner and reconstituted to give a final gelatin to silver ratio of 100 g gelatin/silver mole. The emulsion was then doped with ruthenium and iridium and was sulfur and gold chemically sensitized. A coating composition was prepared by mixing this emulsion with a wetting agent, a formaldehyde hardener and was optically sensitized at 633 nm.

Sample 1 (Invention)

[0048] Hydrazide compound H-1 (0.8 millimoles per mole of silver) and contrast promoting agent CP-13 (5.0 millimoles per mole of silver) were added to the emulsion. A coating was then prepared by the application of the described mixture onto a subbed polyester base at silver coverage of 3.2 g/m².

Sample 2 (Invention)

[0049] As Sample 1, but the hydrazide H-2 of the present invention replaced the hydrazine compound H-1, in the same amount.

Sample 3 (Comparison)

[0050] As Sample 1, but the comparison hydrazide A replaced the hydrazine compound H-1, in the same amount.

Sample 4 (Comparison)

[0051] As Sample 1, but the comparison hydrazide B replaced the hydrazine compound H-1, in the same amount.

[0052] The Samples were evaluated after exposure with a 633 nm red diode laser for a dwell time of 10^-6 seconds and development in a 3M RDC V Rapid Access chemistry for 30 seconds at 35°C, at a pH value of 10.5.

[0053] Table 1 shows the sensitometric values in terms of speed, Toe Contrast A (the absolute value of the slope of the line joining the density points of 0.07 and 0.17 above Dmin), Contrast B (the absolute value of the slope of the line joining the density points of 0.17 and 0.37 above Dmin), Shoulder Contrast C (the absolute value of the slope of the line joining the density points of 0.50 and 2.50 above Dmin) and Average Contrast Θ₁ (the absolute value of the slope of the line joining the density points of 0.10 and 2.50 above Dmin).

Table 1

Sample	Speed	Contr. A	Contr. B	Contr. C	Θ1
1 (inv.)	3.3	3.0	6.3	24.0	16.0
2 (inv.)	3.3	3.1	6.4	22.5	15.3
3 (comp.)	3.4	3.4	4.1	22.5	13.5
4 (comp.)	3.4	3.4	4.0	17.5	11.3

[0054] Table 1 shows that Samples 1 and 2, containing the aryl hydrazide of the present invention, present higher Contrast B and C values, compared with regards to Samples 3 and 4, respectively containing comparison hydrazides A and B.

Comparison hydrazide A (compound II-25 of US 4,937,160)

[0055] 

Comparison hydrazide B (compound according to US 4,925,832)

[0056] 

Claims

1. Silver halide photographic element comprising a support bearing at least one light-sensitive silver halide emulsion layer including negative acting surface latent image-type silver halide grains in reactive association with a hydrazine compound represented by formula:

wherein Ar is an aryl group, G is CO, SO, SO₂, PO₂, PO₃ or C=NR₂; R, R₁, R₂, which can be the same or different, are hydrogen, alkyl of 1 to 6 carbon atoms, an alkyl sulfinyl of 1 to 6 carbon atoms or a trifluoroacetyl group;
n is an integer from 1 to 3;
Z₁ and Z₂, being the same or different, are electron-withdrawing groups.

2. Silver halide photographic element of claim 1 wherein the hydrazine compound is represented by formula:

wherein R₆ is an alkyl group or an alkoxy group;
Z₁ and Z₂, being the same or different, are electron-withdrawing groups.

3. Silver halide photographic element of claim 1 wherein the hydrazine compound is represented by formula:

wherein R₇ is an alkyl group and Z₁ and Z₂, being the same or different, are electron-withdrawing groups.

4. Silver halide photographic element of claim 1 wherein the hydrazine compound is represented by formula:

wherein R₇ is an alkyl group.

5. Silver halide photographic element of claim 1 wherein the amount of said hydrazine compounds is from about 5x10^-5 to 10^-2 moles per mole of silver.

6. Silver halide photographic element of claim 1 wherein the amount of said hydrazine compounds is from about 5x10^-4 to 5x10^-3 moles per mole of silver.

7. Silver halide photographic element of claim 1 containing a contrast promoting agent having formula :

wherein Ar' is a substituted aryl group containing at least three repeating ethyleneoxy units; R₈ and R₉, the same or different, being hydrogen, an alkyl group or an aryl group.

8. Silver halide photographic element of claim 1 containing a contrast promoting agent in an amount from about 10^-4 to about 10^-1 moles per mole of silver.

9. Process for obtaining high contrast images by treating a silver halide photographic element as described in any of previous claims with an aqueous alkaline developer solution containing a developing agent and an auxiliary developing agent, at a pH value lower than 11.0.