US3910795A

US3910795A - Fogged, direct positive silver halide emulsion sensitized with a nitrophenyl mercapto heterocyclic compound

Info

Publication number: US3910795A
Application number: US426146A
Authority: US
Inventors: Keisuke Shiba; Masanao Hinata; Reiichi Ohi; Tadao Shishido
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1972-12-19
Filing date: 1973-12-19
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07
Also published as: GB1424850A; DE2363308A1; JPS4984639A

Abstract

A silver halide photographic emulsion for direct positives, containing at least one compound represented by the general formula (I),

in which Z represents a group of non-metallic atoms necessary for forming a heterocyclic ring and n represents an integer of from 1 to 3.

Description

United States Patent mi Shiba et al.

[Ill 3,910,795

[ FOGGED, DIRECT POSITIVE SILVER HALIDE EMULSION SENSITIZED WITH A NITROPHENYL MERCAPTO HETEROCYCLIC COMPOUND [75] Inventors: Keisuke Shiba; Masanao Hinata;

Reiichi ()hi; Tadao Shishido, all of Kanagawa. Japan [731 Assignees Fuji Photo Film Co., Ltd.,

Kanagawa, Japan 221 Filed: Dec. 19, 1973 211 Appl.Noi:426,l46

Stewart et a1 96/101 Soma et al 96/101 8/1960 Ill/I971 Primary ExaminerWon H. Louie. Jr. Attorney, Agent, or FirmSughrue Rothwcll, Mion. Zinn & Macpeak [57] ABSTRACT A silver halide photographic emulsion for direct positives containing at least one compound represented by the general formula (I).

in which Z represents a group of non-metallic atoms necessary for forming a hetcrocyclic ring and n represents an integer of from 1 to 3.

26 Claims, N0 Drawings FOGGED, DIRECT POSITIVE SILVER HALIDE EMULSION SENSITIZED WITH A NITROPI-IENYL MERCAPTO HETEROCYCLIC COMPOUND BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a silver halide photographic emulsion and, more particularly, it is concerned with a silver halide photographic emulsion for direct positives containing a nitrophenylmercapto group-containing heterocyclic compound.

2. Description of the Prior Art When a silver halide light-sensitive material is exposed to light with in the light-sensitive wavelength range of this light-sensitive material and developed, the blackened density increases and leads to a maximum value with an increase of the quantity of exposure, but decreases again and forms finally a positive image with a further increase in the quanity of exposure. Such a phenomenon is generally called solarization." A similar reversal phenomenon is also found with a silver halide which as been fogged optically or chemically in the process of producing the silver halide emulsion to that by light. The expression direct positive emulsion" or emulsion for direct positive as used throughout this specification is to be understood as an emulsion which is processed to form a positive image by ordinary exposure and development.

The instant invention relates to a direct positive emulsion sensitive to the blue color region by the incorporation of an organic densensitizer. For example, in US. Pat. No. 3,50l ,307 an emulsion of the type that is reversed by the use of an organic densensitizer such as pinakryptol yellow or 5-m-nitrobenzilidene rhodanine is disclosed. It is known that an emulsion fogged using a relatively small amount of a gold compound or salt and a reducing agent and containing at least 50 mol of silver bromide can be advantageously used to obtain a particularly high reversal sensitivity and that an organic densensitizer is effective for the sensitization of such an emulsion. However, known organic densensitizers which have hitherto been used for the sensitization in the blue color region have various disadvantages.

In general, an organic densensitizer having a relatively high reversal sensitivity reduces the maximum density of an original emulsion, while, on the other hand, a sensitizer which does not reduce the maximum density gives only a low reversal sensitivity. In this specification, an organic densitizer-free emulsion will hereinafter be referred to as an original emulsion. For example, pinakryptol yellow reduces the maximum density of an original emulsion and colors a photographic material used yellow. 3-Ethyl-5-m-nitrobenzilidene rhodanine does not reduce the maximum density as much, but the clarity is bad, that is, the value of minimum density is large. S-m-Nitrobenzilidene rhodanine Compound 1 does not reduce the maximum density as much and the value of minimum density is small, that is, the clarity is good, but a lower reversal sensitivity is obtained. Therefore, it is very important to find an organic densitizer for sensitizing in the blue color region, which is capable of giving a high reversal sensitivity without reducing the maximum desnity and with a high clarity.

It is a principal object of the invention to provide a silver halide photographic emulsion for direct positives, which contains an organic desensitizer for sensitization in the blue color region, capable of giving a high sensitivity, being substantially free from any residual coloring and without reducing the maximum density of an original emulsion.

SUMMARY OF THE INVENTION The objects can be accomplished by the incorporation of at least one compound represented by the following general formula (I) in an original emulsion,

General Formula (I) in which Z represents a group of nometallic atoms necessary for forming a heteroeyclic ring and n represents an integer of from 1 to 3.

DETAILED DESCRIPTION OF THE INVENTION Suitable examples of heterocyclic rings in the above described general formula are 1,2,4-triazole ring. a 1,3,4-thiadiazole ring, a l,3,3a,7-tetrazaindene ring, a benzothiazole ring, a benzoimidazole ring and a pyrimidine ring.

The heterocyclic ring formed by Z can be either a substituted ring or an unsubstituted ring. The particular substituent(s) on the ring is not important so long as the substituent(s) used does not deteriorate substantially the photographic properties in terms of sensitivity, residual coloring and maximum density.

Suitable examples of substituents include an alkyl group preferably having up to 20 carbon atoms (e.g., CH n-C H n-C H n-C I-I etc.), an aryl group {e.g., an unsubstituted aryl and a substituted aryl substituted with a substituent such as a halogen atom (e.g., a chlorine atom), an alkyl group (e.g., a methyl group) and an alkoxy group (e.g., a methoxy group)}, a nitro group, a hydroxy group, a halogen atom (e.g., a chlorine, bromine, or iodine atom), an alkoxy group (e.g., a methoxy or ethoxy group), and an amide group {i.e., an NI-ICORo group (R0 is an alkyl group having up to 8 carbon atoms)}.

Suitable examples of compounds which can be used in the invention are given in the following without intending to limit the invention.

M.P. 248C Continued Compound 12 Compound 2 2 M.P. 172C K1 Compound 21 or, we

Compound 22 Compound 22 A general method of synthesis of the compound repwere added to a 10% aqueous solution of sodium hyresented by the general formula is as follows: droxide followed by heating for 4 hours on a warm water bath. After the heating, the reaction solution was cooled and the solution made acidic with hydrochloric acid. The so obtained crystals were recrystallized from 20.2 g of 4-phenylthiosemicarbazide was dissolved in methanol to obtain 21.2 g of needle-like crystals meltml of pyridine and stirred with along with cooling ing at 103C. 14.3 gof this crystal was dissolved in a sowith ice, added to ice water and the resulting crystals iution of 2.6 g of sodium methylate dissolved in ml Synthesis Example I (Compound 5) Elementary Analysis for C, .,H,,N,O,S

C 58.74 (58.85] H 5.93 5.76) N 14.93 (14.93)

The numbers in values.

the parentheses are the calculated Synthesis Examples 2 (Compound 18 2.7 g of sodium methylate was added to 200 ml of absolute methanol and stirred under cooling with ice. To this solution was added gradually 8.3 g of 4-mercapto- 6-methyl-l,3,3a,7-tetrazaindene. Then 12.4 g of picryl chloride was dissolved in 150 ml of methanol and dropwise added gradually thcreto at C. After the dropwise addition, the solution was stirred for 2 hours under ice cooling and then allowed to stand at room temperature for one night. Yellow crystals were removed by filtration and recrystallized from a mixed solvent of ethanol and dimethylformamide thus to obtain 5 g of yellow crystals having a melting point of 165C.

Analysis for C,,H,N,(),,S

C 38.14 (38.11) H 1.80 l 1.86) N 26.211 (25.99)

The calculated values are shown in parentheses.

Syntheses Example 3 (Compound 19) C 46.143 (46.85) H 2.19 2.19) N 12.58 (12.61)

The calculated values are shown in parentheses.

As the emulsion of the type that is reversed using a compound represented by the general formula (1), a previously fogged silver halide emulsion is favorably used which does not have free electron trapping nuclei in the interior of silver halide. An emulsion of this type is a silver halide emulsion consisting of normal crystals, preferably pure silver bromide, which has no twin surface and hardly has any crystal defects. This emulsion can further be improved with respect to the maximum density (Drnax), sensitization and clearness by the addition of bromide ions or iodide ions in an amount of from 1 to 20 mol preferably 3 to 10 mol of bromide or from 0.2 to 3 mol preferably from 0.5 to 2 mol of iodide per mole of silver. This emulsion does not provide directly a positive image by itself but a high reversal sensitization is provided by the incorporation of the nitrophenylmercapto group-containing heterocyclic compound of this invention. Examples of using an original emulsion having no electron trapping nuclei are described in British Pat. Nos. 1,186,717; 1,186,714 and 1,186,716; U.S. Pat. Nos. 3,501,306; 3,501,307; 3,501,310 and 3,531,288; French Pat. Nos. 1,520,821; 1,520,817; 1,522,354 and 1,520,824; and Belgian Pat. Nos. 795,354; 395,355; 395,359, 395,262 and Moreover, the nitrophenylmercapto group-containing heterocyclic compound used in this invention can also be used for the sensitization of a previously fogged silver halide photographic emulsion having free electron trapping nuclei in the interior of silver halide. In order to provide free electron trapping nuclei, it is desirable to use a chemical sensitizer or a salt of Group V111 metal as disclosed in, for example, U.S. Pat. Nos. 3,445,235; 3,537,858; 3,023,102 and 2,717,833; and British Pat. No. 707,704 during the formation of the silver halide precipitate. in addition, this emulsion can be improved by the addition of bromide ions or iodide ions with respect to the maximum density (Dmax), sensitization and clarity. Examples of the use of an original emulsion having electron trapping nuclei are described in Japanese Pat. No. Publications 4125/1968 and 29405/1968; U.S. Pat. Nos. 2,401,051, 2,717,833, 2,976,149, and 3,023,102; British Pat. Nos. 707,704, 1,097,999 and 690,997; French Pat. Nos. 1,520,822, 1,520,324, 1,520,817 and 1,523,626; Belgian Pat. Nos. 713,272, 721,567 and 681,768; and British Application No. 16,507,166.

The silver halide photographic emulsion used in the invention is previously fogged optically or chemically as disclosed in U.S. Pat. Nos. 2,497,875 and 3,537,858. The chemical fogging nuclei can be provided by the addition of organic reducing compounds, for example, hydrazine derivatives, formaldehyde, thiourea dioxide, a polyamine compound, an aminoborane and methyldichlorosilane.

The joint use of the reducing agent with metal more noble than silver or with a halide ion has been proposed as described in, for example, U.S. Pat. Nos. 2,497,875, 2,588,982, 3,023,102 and 3,367,778; British Pat. Nos. 707,704, 723,019, 821,251 and 1,097,999; French Pat. Nos. 1,513,840, 1,518,095, 1,498,213, 1,518,094, 1,520,822 and 1,520,824; Belgian Pat. Nos. 708,563 and 720,660; and Japanese Patent Publication 1 3488/1968. in the emulsion of the invention, gelatin is mainly used as a protective colloid and, in particular, an inert gelatin is preferably used. In place of the gelatin, photographically inert acylated gelatin derivatives such as phthalated gelatin, and water-soluble synthetic polymers such as polyvinyl acrylate, polyvinyl alcohol, polyvinylpyrrolidone and polyvinyl aginate can be used.

The silver halide emulsion according to the invention can also contain mercapto compounds, thione compounds and tetrazaindene compounds as a stabilizer for the fog nuclei as disclosed in US. Pat. Nos. 2,444,605; 2,444,606; 2,444,607 and 2,444,608; stilbene compounds and triazine compounds as a modifier of the clarity; chrome alum, 2,4-dichloro-s-triazine compounds, aziridine compounds, epoxy compounds and mucohalogenic acid compounds, halogenoformyl and maleic acid compounds as a brightening agent as disclosed in US. Pat. Nos. 3,406,070 and German Pat. Nos. 972,067 and 1,150,274, an ultraviolet ray absorbing agent and a hardener as disclosed in US. Pat. Nos. 3,288,775; 3,017,280 and 2,983,611; and British Pat. No. 1,167,207; sodium polyoxyalkylene sulfonates, saponins and anionic surface active agents having a betaine structure as a coating aid as disclosed in US. Pat. Nos 2,600,831, 3,068,101 and 3,415,649; vinyl compounds such as polyalkyl acrylates nd copolymers of an alkyl acrylate and acrylic acid, and polyalkylene oxide compounds as a preservative and plasticizer', and color couplers as disclosed in US. Pat. Nos. 2,376,679, 2,698,794, 3,046,129 and 3,227,554.

For these photographic emulsions, a spectrally sensitizing dye is used jointly with the nitrophenylmercapto group-containing heterocyclic compound. Suitable spectral sensitizers are dyes such as cyanines, merocyanines, composite trinuclear cyanines, composite trinuclear merocyanines, styryl dyes and hernicyanines.

In particular, a high sensitivity emulsion is obtained by the joint use of a dimethine dye such as is described in US. Pat. Applications Ser. Nos. 318,047, filed on Dec. 26, 1972; 351,386, filed Apr. 16, 1973; and 379,887, filed on July 16, 1973.

These emulsions can contain color couplers or can be developed with solutions containing couplers. Such color couplers can be incorporated in silver halide photographic emulsions for direct positives using suitable techniques as disclosed in US. Pat. Nos. 2,322,027, 2,801,171, 1,055,155, 1,102,028 and 2,186,849.

The grain size of silver halide in the photographic emulsion used in the invention is not limited, but the average grain size is preferably 0.05 to 1.0 microns. The form of the silver halide used can be either regular or irregular, but, in particular, the regular form is preferable. The effect of the invention is favourably provided by a monodispersed emulsion, although other emulsions than the monodispersed emulsion can, of course, be used.

The quantity of the nitrophenylmercapto group-containing heterocyclic compound used in the invention will vary depending upon the quantity of silver halide in the emulsion, the surface area and the end-use desired, and, preferably, 1 X 10 to 5 X mol per 1 mol of the silver salt is generally employed. The nitrophenylmercapto group-containing heterocyclic compound is ordinarily added in the form of a solution in a suitable solvent such as water and organic solvents miscible with water, e.g., alcohols such as methanol and ethanol, ethers such as ethylene glycol monomethyl ether, ketones such as methyl ethyl ketone and acetone, N-con' taining compounds such as pyridine or mixtures of these solvents.

The addition of the nitrophenylmercapto group-containing heterocyclic compound to an emulsion is preferably carried out immediately before coating, but can be carried out during the chemical ageing or during the precipitating of the silver halide. The silver halide photographic emulsion for direct positives according to the instant invention is suitable for not only high contrast light-sensitive materials for direct positives, such as light-sensitive materials for lith-film copying originals, but also relatively low contrast light-sensitive materials for direct positives, such as light-sensitive materials for microphotographs or X-ray photographs. Moreover, it can be adapted to color light-sensitive materials, in particular, blue-sensitive layers, and, in addition to the use of light radiation, irradiation with electron rays, X'-rays and 'y-rays can also be used.

A first feature of the invention is to obtain a high reversal sensitivity within the blue range (e.g., about 400 to 500 nm) where a nitrophenylmercapto group-containing compounds used for sensitization. In particular, a phenylmercapto group-containing compound substituted with two nitro groups such as Compound 2 and Compound 6 described previously gives a high sensitiv ity. Where the heterocyclic ring of the general formula (1) is a 1,2,4-triazole ring, l,3,3a,7-tetrazaindene or 7- tetrazaindene ring, in particular, a high sensitivity can be attained.

A second feature of the invention is that the nitrophenylmercapto group-containing heterocyclic compound used in the invention does not reduce the maximum density (Dmax) of an original emulsion.

A third feature of the invention is that a direct positive emulsion sensitized with the nitrophenylmercapto group-containing compound of the invention retains a predetermined maximum density and, simultaneously, retains a good clearness.

A fourth feature of the invention is that the nitrophenylmercapto group-containing heterocyclic compound used in the invention leaves substantially no residual color on a light-sensitive material after processing.

The nitrophenylmercapto group-containing heterocyclic compound of the invention can be used not only for the sensitization of previously fogged emulsions for direct positives, but also for various photographic objects in which a known desensitizer for silver halide photography is used. For example, (1) using an aqueous solution of the desensitizer as a pretreatment bath, a high sensitivity photographic material photographed is treated in this bath and developed while observing the progress of the development under a relatively bright illumination; (2) development is carried out in a mixed solution of the desensitizer and a developer used, whereby the sensitivity of a photographic lightsensitive material is reduced and the development can be accomplished under a relatively bright illumination; and (3) as described in Japanese Pat. Disclosure No. 3285/1972, the desensitizer can be used for an emulsion consisting of an internally latent image type silver halide doped with a multi-valent metal ion. Examples of suitable metal ions include Pb, Sb, As, Au, Bi, Rh, Pt, Os, 1r and lr as disclosed in Japanese Patent Application Laid Open to Inspection No. 32813/72.

The following examples are given to illustrate the invention in greater detail without limiting the invention. Unless otherwise indicated, all parts, percents, ratios, etc, are by weight.

EXAMPLE 1 The method of preparing the emulsion used in this example was follows.

To a first solution prepared by adding 8 g of an inert gelatin to 5 ml of a l N solution of potassium bromide and 500 ml of water and warming to dissolve at 60C were added a second solution prepared by adding l g of silver nitrate to 500 ml of water and warming to dissolve at 60C and a third solution prepared by add ing 70 g of potassium bromide to l50 m] of water and warming to dissolve at 60C with stirring for a period of 50 minutes. and then the mixture was subjected to physical ageing for minutes. Then ml ofa 0.2 N solution of potassium iodide was added and the pAg was adjusted to 6.0 using a solution of silver nitrate. Hydrazine (0.005 mm per mol of silver halide) and a chloroaurate (0.005 mm per mol of silver halide) were added to the mixture and the pH of the mixture was adjusted to 10 using a solution of sodium hydroxide, followed by ageing of the mixture. The mixture was then neutralized with citric acid. washed with water. melted and then mixed with a fourth solution prepared by dissolving 75 g of an inert gelatin in 300 ml of water to obtain a silver halide emulsion (original emulsion). The resulting emulsion had silver halide average grain size of about 0.2 micron in diameter and contained silver halide grains of normal tetragonal system having a l00) plane.

The compound of the invention was added to the above described original emulsion with 2.0 ml of an aqueous solution containing 1% by weight of saponin per kg of emulsion, and coated onto a film of cellulose triacetate to provide a thickness of 5 microns on dry basis. The coated specimen was exposed to a tungsten light at a color temperature of 2,854K through an optical wedge, developed at C for 2 minutes with the following developer, fixed to give a strip and the strip was then subjected to a measurement of the density using a P-type Densitometer manufactured by the Fuji Photo Film Co, Ltd. thus obtaining a characteristic curve. The results of sensitometry are shown in Table Composition of Developer Metol Anhydrous Sodium Sulfite Hydroquinone Sodium Carbonate Monohydrate Potassium Bromide Water to Table l Test Compound (molar concen- Dmax Dmin lration) ml/l00 g emulsion Sensitivity 240 Bit) H0 200 I74 l4l 132 I62 2l4 Table l-continued Test Compound (molar concen- Sensitivity Dmax Dmin No. tration) mI/l00 g emulsion ll 15(8 X l0) I6 224 2.0 0.04 l2 If: (8 X l0) 32 200 2.0 0.04 l] A (8 X 10' I6 I00 1.3 0.05 l4 A (8 X l0) Z4 87 1.3 0.04 l5 B (8 X l0*) I6 89 2.2 0.23 lo B (8 X I0) 24 7B 2.] 0.20 l7 C (R X 10") lo 46 2.2 0.05 18 C (8 X 10*)24 40 ll 0.04

Compound A: Pinakryptol Yellow Com ound 8' 3-Ethyl-S-m-nitrobenzilidene Rhodanine Compound C: 5-m-Nilrobenzilidcne Rhodanine The Compounds A, B and C were used for comparison.

As is evident from the results in Table l the dyes represented by the general formula of the invention provide a direct positive silver halide emulsion having excellent photographic properties.

EXAMPLE 2 The method of preparing the emulsion used in this example was as follows.

To a first solution prepared by adding 10 g of an inert gelatin to 5 ml of a l N solution of sodium chloride and 500 ml of water and warming to dissolve at 60C were added with agitation for a period of 20 minutes a second solution prepared by adding 100 g of silver nitrate to 500 ml of water and warming to dissolve at 60C and a third solution prepared by adding 35 g of sodium chloride to 300 ml of water and warming to dissolve at 60C.

After the addition, the mixture was aged for 5 minutes, mixed with agitation with a fourth solution prepared by adding M g of potassium bromide to 200 ml of water and warming to dissolve at 60C, for a period of 20 minutes, then aged for l0 minutes, cooled and washed with water. After melting, the pH was adjusted to l0. Hydrazine and a chloroaurate, both in the proportion used in Example 1, were then added followed by ageing for 10 minutes and the pH was adjusted to 6.5 using citric acid. A fifth solution was prepared by dissolving g of an inert gelatin in 300 ml of water and added to obtain a silver halide emulsion. The thus resulting silver halide emulsion (original emulsion) contained silver halide of an average grain size of about 0.15 micron in diameter.

To the above described original emulsion were added a 2-phenylindole nucleus-containing dimethine dye as shown in Table 2, a nitrophenylmercapto group-containing heterocyclic compound, ml/kg-emulsion of a 10% aqueous solution of potassium bromide and 20 ml of an aqueous solution containing l% by weight of saponin per kg of emulsion and 50 cc of an aqueous solution containing 2% by weight of mucochloric acid per kg of emulsion, and then the resulting emulsion was coated onto a film of cellulose triacetate to provide a thickness of 2 microns on dry basis. The coated specimen was exposed to a tungsten light at a color temperature of 2,854K through an optical wedge, developed at 20C for 3 minutes with a developer consisting mainly of a polyhydroxybenzene as described in Example 1, fixed to give a strip and the strip was then subjected to a measurement of the density using a P-type Densitometer manufactured by the Fuji Photo Film Co., Ltd. thus obtaining a characteristic curve. The results of the sensitometrv are shown in Table 2.

Table 2 Test Dye (molar con- Compound (molar Sensi- Din-ax Dmin No. centration) concentration tivity Iltll W emulsion ml/ I00 g emulsion l I (8 X I0") 8 I00 3.0 0.l$ 2 2 (ll X ill") 32 409 2.74 0.04 3 3 (l X I0) 64 324 3.0 0.04 4 ll (8 X l0") l6 I00 3.5 (H4 5 4 (l X I0") 64 245 3J6 0.04 6 6 (ll X I0") 64 264 3.38 0.04 7 lllltl x I0") I I00 3.5 0.12 I 7 (8 X I0") 64 l2) 3.46 0.05 9 8 (ll X I0") 32 ll! 3.30 0.04 l0 IV (8 X l0") l6 I00 3.4 0. ll 2 (8 X") 2) 32 398 3.4 0.04 l2 8 (8 X "1") 372 3.4 0.04 V (8 x 10")32 I00 3.5 0.15 l3 l4 2 (8 x l0") l6 Jill 3.4 0.04 I5 8 (8 X I0") 32 372 3.5 0.04

Cll=Clil l n so 9 As is evident from the results contained in Table 2. a silver halide photographic emulsion for direct positives. which has a higher sensitivity and greatly improved clearness, is provided by the combination of the compound represented by the general formula of the invention with a sensitizer.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

l. A silver halide photographic emulsion for direct positives, containing fogged silver halide grains and an amount of at least one compound sufficient for sensitization in the blue color region represented by the general formula (I) in which Z represents a group of non-metallic atoms necessary for forming a heteroeyclic ring selected from the group consisting of a 1,2,4-triazole ring, a 1,3,4- thiadiazole ring, a l,3.3a.7-tetrazaindene ring, a beamthiazole ring, a benziomidazole ring and a pyrimidine ring. and n represents an integer of from 1 to 3.

2. The silver halide photograhic emulsion of claim 1, wherein said heterocyclic ring is a 1,2,4-triazole ring.

3. The silver halide photographic emulsion of claim 1, wherein said heterocyclic ring is a l,3,3a.7-tetrazaindene ring.

4. The silver halide photographic emulsion of claim I, wherein said heterocyclic ring is a l.3,4-thiadiazole rlng.

5. The silver halide photographic emulsion of claim I, wherein said heterocyclic ring is a pyrimidine ring.

6. The silver halide photographic emulsion of claim I, wherein said heterocyclic ring is a benzothiazolc ring.

7. The silver halide photographic emulsion of claim 1, wherein said heterocyclic ring is a benzoimidazole ring.

8. The silver halide photographic emulsion of claim 1, wherein said silver halide grains are chemically fogged.

9. The silver halide photographic emulsion of claim 8, wherein said silver halide grains are fogged with a reducing agent and a gold compound.

I0. The silver halide photographic emulsion of claim I, wherein said emulsion contains a photographic color coupler.

11. The silver halide photographic emulsion of claim 1, wherein said emulsion contains a spectral sensitizer.

12. The silver halide photographic emulsion of claim I, wherein said compound is n 5 N E 02H r m2 c n n 02H N s-Z no x l 2 n-C H N 2 W N A 11 n-C ll 0 R Q Y- 11 23 N T N 2 kn) 13 2? Z B' T 5 N02 f wug n Continued 11- N02 s H OH l0 O N s -C-(CH co 13. A silver halide photographic material for direct Q N positives, comprising a support having coated thereon a the silver halide photographic emulsion of claim 1.

14. The silver halide photographic material of claim N s l3, wherein said heterocyclic ring is a l,2,4-triazole /& H ring. N

IS. The silver halide photographic material of claim 9 19 13, wherein said heterocyclic ring is a l,3,3a,7-tetrazaindene ring.

16. The silver halide photographic material of claim 13, wherein said hetcrocyclic ring is a 1,3.4-thiadiazole ring. O

17. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a pyrimidine ring. N 3

18. The silver halide photographic material of claim 2 13, wherein said heterocyclic ring is a benzothiazole ring. 45 11 g3 19. The silver halide photographic material of claim [3, wherein said heterocyclic ring is a benzoimidazole ring.

20. The silver halide photographic material of claim 13, wherein said silver halide grains are chemically fogged.

2]. The silver halide photographic material of claim 0 20, wherein said silver halide grains are fogged with a reducing agent and a gold compound. N S

22. The silver halide photographic material of claim 2 13, wherein said emulsion contains a photographic color coupler. N

23. The silver halide photographic material of claim 13, wherein said emulsion contains a spectral sensitizer.

24. The silver halide photographic material of claim 13, wherein said compound is a (i? N S 2 Q" T N02 R I 27 28 Cnlinued 0 c n CH 2: s 5 1, 2

0 S 0 H 2 l5 2" s D 'F QI 25. The silver halide photographic emulusion of claim I, wherein said compound is present in an 2 amount of 1X10 to 5X10 mol per 1 mol of silver 3 halide. N 26. The silver halide photo raphic material of claim 8 S no 13, wherein said compound is present in an amount of 2 1X10 to 5X10 mol per l mol of silver halide.

3o i I i

Claims

1. A SILVER HALIDE PHOTOGRAPIC EMULSION FOR DIRECT POSITIVES, CONTAINING FOGGED SILVER HALIDE GRAINS AND AN AMOUNT OF AT LEAST ONE COMPOUND SUFFICIENT FOR SENSITIZATION IN THE BLUE COLOR REGION REPRESENTED BY THE GENERAL FORMULA (1)

3. The silver halide photographic emulsion of claim 1, wherein said heterocyclic ring is a 1,3,3a,7-tetrazaindene ring.

4. The silver halide photographic emulsion of claim 1, wherein said heterocyclic ring is a 1,3,4-thiadiazole ring.

5. The silver halide photographic emulsion of claim 1, wherein said heterocyclic ring is a pyrimidine ring.

6. The silver halide photographic emulsion of claim 1, wherein said heterocyclic ring is a benzothiazole ring.

10. The silver halide photographic emulsion of claim 1, wherein said emulsion contains a photographic color coupler.

12. The silver halide photographic emulsion of claim 1, wherein said compound is

13. A silver halide photographic material for direct positives, comprising a support having coated thereon the silver halide photographic emulsion of claim 1.

14. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a 1,2,4-triazole ring.

15. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a 1,3,3a,7-tetrazaindene ring.

16. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a 1,3,4-thiadiazole ring.

17. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a pyrimidine ring.

18. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a benzothiazole ring.

19. The silver halide photographic material of claim 13, wherein said heterocyclic ring is a benzoimidazole ring.

21. The silver halide photographic material of claim 20, wherein said silver halide grains are fogged with a reducing agent and a gold compound.

22. The silver halide photographic material of claim 13, wherein said emulsion contains a photographic color coupler.

24. The silver halide photographic material of claim 13, wherein said compound is

25. The silver halide photographic emulusion of claim 1, wherein said compound is present in an amount of 1 X 10 5 to 5 X 10 2 mol per 1 mol of silver halide.

26. The silver halide photographic material of claim 13, wherein said compound is present in an amount of 1 X 10 5 to 5 X 10 2 mol per 1 mol of silver halide.