US3925085A

US3925085A - Direct positive silver halide emulsion

Info

Publication number: US3925085A
Application number: US426145A
Authority: US
Inventors: Akira Sato; Akira Ogawa; Keisuke Shiba; Masanao Hinato
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1972-12-19
Filing date: 1973-12-19
Publication date: 1975-12-09
Anticipated expiration: 1992-12-09
Also published as: JPS5547373B2; DE2363216A1; JPS4984640A; GB1431606A

Abstract

A direct positive silver halide emulsion containing at least one dimethinecyanine dye wherein the 3-position of a pyrrolo(2,3 b)pyridine nucleus is bonded through a dimethine chain to the 1-, 2-, 3- or 4-position of a cyanine hetero ring nucleus, provided that where the bonding is in the 4-position the cyanine nucleus is a quinoline nucleus or a pyridine nucleus and where the bonding is in the 1- or 3-position the cyanine nucleus is an isoquinoline nucleus.

Description

Unite States Patent 1 91 1111 3,

Sato et al. Dec. 9, 1975 [54] DIRECT POSITIVE SHJVER HALIDE 3,767,651 10/1973 Chapman .1 96/101 EMULSION 3,832,184 8/1974 Sato et a1. 96/101 Inventors: Akira Sato; Akira Ogawa; Keisuke Shiba; Masanao Hinato, all of Kanagawa, Japan Fuji Photo Film Co., Ltd., Minami-Ashigara, Japan Filed: Dec. 19, 1973 Appl. No.: 426,145

Assignee:

Foreign Application Priority Data Dec. 19, 1972 Japan 47-127574 US. Cl. 96/101; 96/107; 96/108; 96/130; 96/131; 260/240 E Int. Cl. G03C 1/28; G03C l/16 Field of Search 96/107, 108, 130, 131, 96/101; 260/240 E References Cited UNITED STATES PATENTS 8/1971 Mee et a1 96/107 Primary ExaminerW0n H. Louie, Jr. Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT 14 Claims, No Drawings DIRECT POSITIVE SILVER HALIDE EMULSION BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates to a silver halide emulsion and, more particularly, it relates to a direct positive silver halide emulsion sensitized with a novel dimethinecyanine dye.

2. DESCRIPTION OF THE PRIOR ART When a silver halide light-sensitive material is exposed to light of wave-lengths to which the light sensitive material is sensitive and is development-processed, the resulting photographic density increases as the exposure amount increases and, ultimately, the photographic density reaches a maximum value. However, when the exposure amount is further increased, the photographic density again is reduced. This phenomenon is generally called solarization. Also, with a silver halide lightsensitive material which has been fogged in an optical or chemical manner in the production of the silver halide emulsion, the same reversal phenomenon (the phenomenon in which the photographic density is reduced with the increase in the exposure amount) as in the case with light is observed. Positive images can be obtained by utilizing the above-described phenomenon.

The term direct positive silver halide emulsion as used herein in the invention means a silver halide emulsion prepared so that a positive image can be formed by the usual exposure through a positive original using light followed by development processing.

As sensitizers for conventional negative emulsions, many dyes such as monomethinecyanines, trimethinecyanines, merocyanines, rhodacyanines, and the like are known. However, when these dyes are applied to the sensitization of a direct positive silver halide emulsion, in many cases, a number of defects results, for example, the characteristic curve becomes non contrasty (or becomes flat) and a re-reversal phenomenon (i.e., a reincrease in the photographic density after the reduction thereof with an increase in the exposure amount) occurs.

In addition, those dyes which have so far been known as sensitizers for direct positive light-sensitive silver halide emulsions have the defect that some of the dye remains (hereinafter remaining of the dye or dye remaining) in the lightsensitive material after processing. Such remaining of dye is inconvenient particularly with photographic papers. Because, when such dyes are used as the sensitizer, a high whiteness cannot be obtained with a black-and-white photographic paper and, with a color photographic paper, true color reproduction becomes impossible. Furthermore, such remaining of the dye is even more inconvenient with a constrasty light-sensitive material, for a copying lithographic type film, an X-ray film, a film for copying microphotographs, and the like.

Dyes which are used for sensitizing direct positive emulsions must not possess any of the abovedescribed defects and must not reduce the maximum density of the image.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a direct positive silver halide emulsion which provides a high sensitivity, which maintains definite maximum image density and which does not cause a substantial remaining of dye.

As a result of extensive investigations to attain the above-described objects, the inventors have achieved the present invention. That is, the present invention provides a direct positive silver halide emulsion containing at least one dimethinecyanine dye wherein the 3position of a pyrrolo[2,3-b]pyridine nucleus is connected to the l-, 2-, 3- or 4-position of a cyanine hetero ring nucleus (provided that when the 4-position is the bonding position, the cyanine nucleus is a quinoline or a pyridine and when the 1- or 3-position is the bonding position the cyanine nucleus is an isoquinoline) through a dimethine chain, and containing, if desired, an organic desensitizer.

DETAILED DESCRIPTION OF THE INVENTION Specific examples of the substituent at 2-position of the pyrrolo[2,3b]pyridine nucleus of the dimethinecyanine dye which is used in the present invention include a lower alkyl group (e.g., having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a butyl group, etc.), an aryl group (e.g., a phenyl group, etc.). A haloaryl group (e.g., a p-chlorophenyl group, etc.), and a lower alkyl substituted aryl group (e.g., tolyl, etc.).

Specific examples of the cyanine hetero ring nucleus of the dimethinecyanine dye which is used in the invention are, e.g., an oxazoline nucleus, an oxazole nucleus, 21 benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, a naphthothiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a Z-pyridine nucleus, a 2-quinoline nucleus, a 4- quinoline nucleus a benzoimadazole nucleus, an indolenine nucleus, a 3,3-dialkylindolenine nucleus, an imidazo[4,5b]quinoxaline nucleus, a pyrrolindine nucleus, etc. These hetero rings and/or benzene nucleusfused hetero rings can obtained substituents. Suitable such substituents are, for example, an alkyl group (e.g., a lower alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group), an aryl group e.g., a lower alkylsubstituted aryl group (e.g., a tolyl group, etc.), a halogensubstituted aryl group (e.g., a pchlorophenyl group, etc.) a hydroxyl group, an alkoxy group (e. g., a lower alkoxy group such as a methoxy group and an ethoxy group), a carboxy group, an alkoxycarbonyl group (e.g., a lower alkoxycarbonyl group such as a methoxycarbonyl group and an ethoxycarbonyl group), a nitro group, a halogen atom (e.g., a chlorine atom, a bromine atom, a fluorine atom, an iodine atom), and the like.

Specific examples of these cyanine rings are as follows: thiazoles including thiazole, 4-methylthiazole, 4- phenylthiazole, 4-(p-hydroxyphenyl)-thiazole, 5- methylthiazole, 5-phenylthiazole, 4,5-dimethylthiazole, 4,5diphenylthiazole, and the like; benzothiazoles including benzothiazole, S-hydroxybenzothiazole, 5-

fluorobmzothiazole, 4-chlorobenzothiazole, 5 chlorobenzothiazole, 6-chlorobenzothiazole, 7- chloroben zothiazole, 7-methylben zothiazole, 5 methylbenzothiazole, 6-methylbenzothiazole, 5 ,6-

dimethylbenzothiazole, 5-bromobenzothiazole,- 6- bromobenzothiazole, S-phenylbenzothiazole, o-phenylbenzothiazole, 7phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, 7-methoxybenzothiazole, 5iodobenzo thiazole, 6-iodobenzothiazole, 5-ethoxybenzothiazole, 6-ethoxybenzothiazole, 5-ethoxycarbonylbenzothiazole, tetrahydrobenzothiazole, thylarnido)benzothiazole, thiazole, -hydroxybenzothiazole, 6-hydroxybenzothiazole, S-nitrobenzothiazole, o-nitrobenzothiazole, 5-chloro-6-nitrobenzothiazole, and the like; naphthothiazoles including a-naphthothiazole, B-naphthothiazole, [3,B-naphthothiazole, 5-methoxy-B-naphtho thiazole, 5-ethoxy-B-naphthothiazole, 7-ethoxy-oznaphthothiazole, 5-hydroxy-Bnaphthothiazole, 5- ethyl-B-naphthothiazole, and the like; oxazoles including oxazole, 4-methyloxazole, 5-methyloxazole, 4- phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-dimethyloxazo1e, S-phenyloxazole, and the like; benzoxazoles including benzoxazole, 5-chlorobenzoxazole, S-methylbenzoxazole, 5-phenylbenzoxazole, 6- methylbenzoxazole, 6-nitrobenzoxazole, 5,6-dimethyl- 5-(N,N-dime- 5 ,o-dimethoxybenzobenzoxazole, 5-methoxycarbonylbenzoxazole, 5- methoxybenzoxazole, 5-ethoxybenzoxazole, 5- chlorobenzoxazole, S-methoxybenzoxazole, 5 -trilike; l-isoquinolines including isoquinoline, 3- methylisoquinoline, 4-methylisoquinoline, 7- methylisoquinoline, 8-ethy1isoquinoline, 6-

chloroisoquinoline, 6-methoxyisoquinoline, 8methox yisoquinoline, and the like; 3-isoquinolines including isoquinoline, S-methylisoquinoline, l-methylisoquinoline, 6-chloroisoquinoline, 6-methoxyisoquinoline, 8- methoxyisoquinoline, and the like; indolenines including indolenine, 3,3-dimethylindolenine, 5-hydroxy-3,3- dimethylindolenine, 3,3-dimethy1-6-chloroindolenine, 3,3,S-trimethylindolenine, 3,3-dimethyl-S-nitroindolenine, and the like; 2-pyridines including pyridine, 4- butylpyridine, 4-decylpyridine, 4-octadecylpyridine, 4,6-dibutylpyridine, 4-benzylpyridine, 4-phenylpyridine, 4,6-diphenylpyridine, 4,6-dinaphthylpyridine, 4- chloropyridine, 4-bromopyridine, 4,6-dich1oropyri- 6-nitroimidazo4,5-bquinoxaline, 1,3- diphenylimidazo[4,5b]quinoxaline, 6-chlorol ,3- diphenylimidazo4,5-b-quinoxaline, 1,3-diallylimidazo[4,5b]quinoxaline, 1,3-dicyclohexylimidazo[4,5b-quinoxaline, and the like; and benzimidazoles including l-ethylbenzimidazole, l-ethyl-S- nitrobenzoimidazole, l-ethyl-5,6-dichlorobenzimidazole, and the like.

The above-illustrated dimethinecyanine dyes which is used in the present invention can be synthesized by reacting under heating a pyrrolo[2,3b]pyridine compound aldehyde derivative at 3-positi0n with an alkylsubstituted quaternary ammonium salt of a desired cyanine hetero ring nucleus-containing compound using a molar ratio of about 1:1 in a chemically inert solvent such as acetic acid anhydride, alcohols (e.g., ethanol, isopropanol, butanol, etc.), nitrobenzene, dimethylformamide, acetonitril, pyridine and morpholine. The solution preferably has a concentration of from about 0.2 to about 1 mol/l. Where acetic acid anhydride is employed as the solvent, it is preferred that the reaction be performed at about 150C for about 10 minutes and where ethanol is used as the solvent, it is preferred that the reaction be performed at about C for about 10 minutes. Basic catalysts such as basic nitrogen-containing organic compounds (e.g., pyperidine, morpholine, triethylamine, etc.) with pyperidine being preferred. However, it is not necessary to use such a catalyst where acetic acid anhydride is used, since the solvent also functions as a catalyst.

Preferable dimethinecyanine dyes which can be used in the present invention can be represented by the following general formula (I);

wherein R represents a hydrogen atom or a lower alkyl group having 1 to 3 carbon atoms, R represents a hydrogen atom, a lower alkyl group having 1 to 4 carbon atoms or an aryl group, R represents an alkyl group having 1 to 6 carbon atoms, a substituted alkyl group, an allyl group or an aryl group, L, represents a methine group, L represents a substituted or unsubstituted methine group (the substituent of L and R can be connected to each other to form a methylene chain), m and n each represents 1 or 2, X- represents an anion, and Z represents the non-metallic atoms necessary to complete a cyanine hetero ring nucleus.

R and Z in the general formula (I) above have al ready been described in detail before.

Specific examples of suitable alkyl groups for R and 3) R include, e.g., a methyl group, an ethyl group, a propyl group, a butyl group, etc., and this alkyl group can E further be substituted with a substituent. Preferred alkyl groups for'R and R are a methyl group or an ethyl group. Specific examples of alkyl groups having 1 to 6 carbon atoms for R are, for example, a methyl group, an ethyl group, a propyl group, a hexyl group, a 10 hydroxyalkyl group (e.g., a B-hydroxyethyl group, 1 CHZOH etc.), an alkoxyalkyl group (e.g., a B-methoxyethyl max 3 93mm group, etc.), a carboxyalkyl group (e.g., a B-carboxypropyl group, etc.), a sulfoalkyl group (e.g., a y-sulfo* propyl group, etc.), an aralkyl group (e.g., a phenethyl group, a benzyl group, etc.), and the like. Particularly (l4) preferable examples of the aryl group for R are, e.g., a phenyl group, a tolyl group, a p-chlorophenyl group and the like. R preferably is a methyl group, an ethyl group or a sulfoalkyl group (e.g., a sulfopropyl group). Specific examples of L include a methine group substituted with, e.g., a lower alkoxyalkyl group (e.g., a methoxyethyl group, a ethoxyethyl group, etc.). This-substituent can be connected to R to form a methylene CH OH chain. In this case, 5- or 6-membered ring formation is particularly preferable.

Specific examples of X are, for example, a chloride ion, a bromide ion, an iodide ion, a p-toluenesulfonate ion, an ethylsulfonate ion, a perchlorate ion, etc. n represents I when the compound represented by the general formula (I) has a betainelike structure and represents 2 in other cases.

Severalspecific examples of the compound represented by the aforesaid general formula (I) are illustrated below together with the data for the absorption maximum wave-length (A in a methanol solution.

G) N I l z s z s CH CH OH A 461mm CHQOH k 168mm 63 '1 cu -cu -cu-cu,

A CHaOH Lfllnm max C11=CH (1s) I I N N N I l CzHs A CHaOH 14 mm max (19) CH=CH- I I \N 1;!

I cansso H cmon A max Elnm t e on,

N N I CH; H

cn on A max 447mm Examples of the synthesis of the compounds which are used in this invention are described below. Unless otherwise indicated all parts, percents, ratios and the like given hereinafter are by weight.

SYNTHESIS EXAMPLE 1 Synthesis of Dye (1):

ml of acetic anhydride was added to a mixture of 0.8 g of 1-methyl-2-ethyl-3-formylpyrrolo2,3bpyridine and 1.3g of Z-methyl-l-ethylbenzothiazolium iodide and refluxed for about 10 minutes to react. Then, the reaction mixture was cooled with ice-water and the crystal precipitated was collected by filtration. The thus obtained crystal was recrystallized from a methanol-chloroform mixed solvent to obtain 0.6g of dye (l) (m.p.:256C).

SYNTHESIS EXAMPLE 2 Synthesis of Dye (8):

20ml of acetic anhydride was added to a mixture of 4g of l-methyl-2-ethyl3-formylpyrrolo[2,3b]pyridine and 9g of 2-methyl-1.3diethylimidazo-4,5-b-quinoxalinium p-toluenesulfonatc and refluxed for about 10 minutes to react. After cooling, the dye was precipitated with the diethylether and crystallized by adding thereto a sodium iodide aqueous Solution and collected by filtration. The thus obtained crystals were recrystallized from a methanol-chloroform mixed solvent to ob-. tain 1.6g of dye (8) (mp: 263C).

Other dimethinecyanine dyes can be synthesized according to the above-described synthesis methods.

It is much more preferable to further incorporate an organic desensitizier in the direct positive emulsion of the present invention.

The organic desensitizer which can be used in the invention is a substance which is capable of capturing free electrons generated in the silver halide grains upon irradiation with radiation and which is adsorbed on the silver halide grains. Further, the organic desensitizer is defined as a Substance having a minimum vacant electron energy level which is lower than the electron energy level of the conduction band of the silver halide grains. Preferable desensitizers are compounds having a maximum occupied electron energy level which is lower than the valence electron band of the silver halide grains. The electron energy level of the desensitizer can be measured through complicated procedures are required.

For example. specific examples of determination on extremely symmetric cyanine dyes are given in Tani and Kikuchi; Photographic Science and Engineering, vol. 1 1 (3), p. 129 (1967), and the specific examples of determination on typical merocyanine dyes are given in Shiba and Kubodera; Pre-prinl (N0. B-l2), International Congress of Photographic Science, 1970 (Moscow). It is known that the electron energy level of these compounds is linearly related to both the anode polarographic half-wave potential (E01) and the cathode polarographic half-wave potential (B Many of such organic densensitizers are described in, e.g.. U.S. Pat. Nos. 3,023,102; 3,314,796; 2,901,351; 3,367,779; British Pat. Nos. 723,019; 698,575; 698,576; 834,839; 667,206; 748,681; 796,873; 875,887; 905,237; 907,367; 940,152; French Pat. Nos. 1,520,824; 1,518,094; 1,518,095; 1,520,819; 1,520,823; 1,520,821; 1,523,626; Belgian Pat. Nos. 722,457; 722,594; Japanese Pat. Publication Nos. 13167/68; 14500/68; and the like.

As the organic desensitizers which can be used in the invention, any of those as described above can be employed. However, particularly preferable results can be provided by compounds which have a cathode polarographic half-wave potential (E more positive'than -l .0 volt and are represented by the following general formula (III);

x (III) wherein Z, X and m are the same as defined in the general formula (I), R represents an alkyl group or an allyl group (eg, having from 1 to 8 carbon atoms, pref erably l to 4 carbon atoms), and a represents 1 or 2.

Specific examples of R include a methyl group, an ethylgroup, a butyl group, a hydroxyalkyl group (e.g., a hydroxyethyl group, etc. a carboxyalkyl group (e.g., a carboxymethyl group, a 3-carboxypropyl group, etc.), a sulfoalkyl group (e.g., a 2-sulfoethyl group, a 4-sulfobutyl group, etc), and the like.

Specific organic desensitizers which can be used in the invention are, e.g., phenosafranine, pinakryptol yellow, -m-nitrobenzylidenerhodanine, 3-ethyl-5-mnitrobenzylidenerhodanine, 3-ethyl-5-(2,4-dinitrobenzylidene)rhodanine, 5-o-nitrobenzylidene3-phenylr hodanine, 1,3-diethyl-6-nitrothia-2-cyanine iodide, 4-nitro-6-chlorobenzotriazole, 3,3-diethyl-6,6'-dinitro-9-phenylthiacarbocyanine iodide, 2-(p-dimethylaminophenyliminomethyl) benzothiazole ethoeth' ylsulfate, Crystal Violet, 3,3 -diethyl-6,6-dinitrothiacarbocyanine ethylsulfate, 1 ,3-diethyl-6-nitrothia2 cyanine iodide, 1,3-diamin-5-methylphenazinium chloride, 4-nitro-6chlorobenzotriazole, 3,3-di-p-nitrobenzylthiacarbocyanine bromide, 3,3- di-p-nitrophenylthiacarbocyanine iodide, 3,3-dionitrophenylthiacarbocyanine perchlorate, 3,3'-dimethyl-9-trifluoromethylthiacarbocyanine iodide, 9-(2,4- dinitrophenylmercapto 3 ,3 -diethylthiacarbocyanine iodide, bis(4,6-diphenylpyrryl-2-trimethinecyanine perchlorate, anhydrous Z-p-dimethylaminophenyliminomethyl-6-nitro-3-(4-sulfobutyl)-benzothiazolium hydroxide, l-( 2benzothiazolyl)-2-(p-dimethylaminostyryl)-4,6-diphenylpyridinium iodide, 1,3- diethyl-5l ,3-neopentylene-6-( 1 ,3,3-trimethyl-2- indolynilidene)-2,4-hexadienylidene-2-thiobarbituric acid, 2,3,5-triphenyl-ZH-tetrazolium chloride, 2-(4- iodophenyl)-3-(4-nitrophenyl)-5-phenyl-tetrazolium chloride, l-methyl-8-nitroquinolinium methylsulfate, 3,6-bis-4-(3-ethyl-2-benzothiazo1ynilidene)-2-butenylidene-l ,2.4,5-cyclohexanetetrone, and the like.

As the silver halide emulsions which can be used in the invention, there are, e.g., a silver chloride emulsion, a silver bromide emulsion, a silver chlorobromide emulsion, a silver chloroiodide emulsion, silver iodobromide emulsion, silver chloroiodide emulsion, and the like, as disclosed in U.S. Pat. Nos. 2,401,051; 2,717,833; 2,976,149; 3,023,102; 3,501,306; 3,501,307; 3,501,310 and 3,531,288.

The size of the silver halide grains in these emulsions can be within the range usually employed. However, when the mean grain size is 0.05;; to 1.0a, preferably 0.2 to 1 a, particularly advantageous results can be obtained. Also, the silver halide grains which can be used in the invention can be either regular grains or irregular grains, though the former provides better effects in the present invention.

Either monodispersed emulsion or mon-monodispersed emulsion can be used in the present invention, although the former is more preferable.

In general, original emulsions which can be used for the direct positive silver halide light-sensitive material are classified into the following two groups.

One group of light-sensitive materials are those which have, in the inside of the silver halide crystal, nuclei capable of trapping free electrons, the surface of the silver halide having previously been chemically fogged. This type of emulsion is characterized by the ability per se to provide a positive image directly. They can be made highly sensitive due to spectral sensitization through the addition of a sensitizing dye and, in ad dition, the sensitivity in the intrinsic absorption region can be increased. With this type of emulsion, the silver composition must be formulated so that the chemical sensitizer and the salt of Group VIII metal which is used for imparting free electrontrapping nuclei can be absorbed inside the silver halide grains. By the addition of the organic desensitizer, clearing property can be improved and, in particular, re-reversal can be pre vented. Also, by the addition of bromide ions and iodide ions, the maximum density and sensitivity can be increased and the clearing property can be improved.

Another type of light-sensitive materials for the original emulsions are those which are not provided with free electrontrapping nuclei inside the silver halide grains, the surface of the grains having been chemically fogged. This type of emulsion contains as little lattice defects as is possible and, preferably comprises pure silver bromide regular crystals having no twin plane. This type of emulsion itself provides no direct positive image. However, when an organic desensitizer is adsorbed on the silver halide grains of this emulsion, a direct positive image can be obtained with high sensitiv ity.

In the present invention, either type of emulsions can be used. In other words, either type of original emulsion can effectively be sensitized by the compound represented by the general formula (I). These emulsions are well known and examples thereof are disclosed in U.S. Pat. Nos. 2,401,051; 2,717,833; 3,976,149; 3,023,102; 3,501,306; 3,501,306; 3,501,307; 3,501,310 and 3,531,288.

The silver halide emulsions which can be used in the invention are fogged optically or chemically as disclosed in U.S. Pat. Nos. 2,497,875; 2,588,982; 3,023,102; and 3,367,778. Chemical fogging nuclei are provided by adding a reducing organic compound such as hydrazine derivative, formaldehyde thiourea dioxide, a polyamine compound, an amineborane, methyldichlorosilane or the like. In addition, a method of imparting fogging nuclei by the combined use of the reducing agent and an ion of metal more noble than silver (e.g., a gold ion, a platinum ion, an iridium ion, etc.) or, further, a halogen ion can be ap'plied.

In the emulsion which can be used in the present invention, gelatin is mainly used as the protective colloid. Inert gelatin is particularly advantageous. In addition, in place of gelatin, photographically inert gelatin derivatives (e.g., phthaloylated gelatin, etc.), watersoluble synthetic polymers (e.g., polyvinyl acrylate, polyvinylalcohol, polyvinylpyrrolidone, polyvinylalginic acid, carboxymethyl cellulose, hydroxymethyl cellulose, etc.), or the like can also be used. i

In the direct positive silver halide emulsion of the present invention a fogging nuclei-stabilizing agent (e.g., a mercapto compound, a thione compound, tetrazaindene compound. etc. as disclosed in U.S. Pat. Nos. 2,444,605; 2.444,606; 2.444,607 and 2,444,608), a clearing property-improving agent (e.g., a stylbene compound, a triazine compound, etc. as disclosed in U.S. Pat. No. 3,023,102), a brightening agent (as dis closed in U.S. Pat. No. 3,406,070), an ultraviolet absorbant (as disclosed in U.S. Pat, No. 3,434,837), a hardening agent chromium alum, a 2,4dichloro' S-triazine compound, an aziridine compound, an epoxy compound, a mucohalogenic acid (a halogen formyl maleic acid compound as disclosed in US. Pat. Nos. 3,288,775; 3,017,280 and 2,983,611)), a coating aid (e.g., sodium polyalkylenesulfonate, saponin, an anionic surface active agent having a betaine structure, etc. as disclosed in US. Pat. Nos. 3,068,101; 3,415,649 and 2,600,831), an antiseptic as disclosed in British Pat. No. 987,010, a plasticizer (e.g., a polyalkyl acrylate, a copolymer of alkyl acrylate and acrylic acid, or a like vinyl polymer, a polyalkylene oxide, etc.), a color coupler as disclosed in US. Pat. Nos. 2,376,679; 2,698,794; 3,046,129 and 3,227,554, or like additives can be incorporated.

The amount of the dimethine dye which can be used in the invention cannot be set forth specifically since the amount varies depending upon the amount of silver halide in the emulsion and the surface area of the silver halide grains. However, an amount of about 1 X 10 to 2 X 10 mol per 1 mol of silver salt provides particularly preferable results. These dyes are used by dissolving in water or a water-miscible solvent such as methanol, ethanol, ethylene glycol monomethyl ether, methyl ethyl ketone, acetone, pyridine, and' the like. Ultrasonic vibration can be used for the dissolution of these dyes. Also, methods employed upon sensitizing negative-type emulsions described in, e.g., US. Pat. Nos. 3,482,981; 3,585,195; 3,469,987; 3,649,286; 3,485,634; 3,342,605 and 2,912,343, etc. can be used.

The addition of the dyes to an emulsion is conveniently conducted immediately before coating. However, the dyes can be added during chemical ripening or upon formation of the silver halide.

The amount of the organic desensitizer which can be used in the invention cannot be set forth specifically since it also varies depending upon the kind of the desensitizer used. However, the desensitizer is added preferably in an amount of about 2 X l to 10 mol per 1 mol of the silver halide.

The emulsion in accordance with the present invention can be applied to various supports to prepare photographic elements. Preferably the thickness ranges from about to p The emulsion can be applied to the one side or both sides of the support, which can be either transparent or opaque. Representative examples of supports include a cellulose nitrate film, a cellulose acetate film, a polyvinyl acetal film, a polystyrene film, a polyethylene terephthalate film, and other polyester films, glass, metal, wood, etc. In addition, a support prepared by laminating paper with a plastic can also be used,

The emulsion of the present invention can be suitably processed, after exposure, using the conventionally known processing baths for development, fixation, stabilization, or using a combined processing bath.

A first feature of the present invention is the sensitization of a direct positive silver halide emulsion with a novel dimethine dye having a pyrrolo-2,3-b-pyridine nucleus, which substantially does not cause any remaining of dye.

US. Pat. No. 2,323,187 describes that a large amount of sensitizing dye having sensitizing action on conventional negative emulsions, particularly a carbocyanine dye, is effective for the sensitization of direct positive emulsions. However, this method is not preferred since the dye strongly colors the emulsion and results in the dye remaining. On the otherhand, British Pat. Nos. 970.621 and 1,186,714 describe that dimethine dyes having a 2phenylindole nucleus or a 2 pyridylindole nucleus shows excellent reversal property. However, even such dyes are not satisfactory due to the dye remaining. In addition, when such dyes are added to the direct positive emulsion to the extent that maximum sensitivity is provided, the tendency of the dye to remain becomes particularly great.

The dimethine dyes having a pyrrolo[2,3b]pyridine nucleus of the present invention are characterized in that the remaining of the dye is markedly reduced.

A second feature of the present invention is that the maximum density of the direct positive emulsion is not substantially lowered.

In many cases, dimethine dyes having a 2-phenylindole nucleus, as well as carbocyanine dyes and merocyanine dyes useful for thesensitization of conventional negative emulsions, reduce the maximum density of the direct positive emulsion. The reduction in maximum density occurs during storage with the passage of time as well as immediately after coating the direct positive emulsion. This deterioration of the direct positive photographic light-sensitive material with the passage of time tends to be greater than the deterioration in conventional negative light-sensitive materials. Therefore, removal of this defect has been of great concern. The novel dimethine dye which is used in the present invention shows excellent characteristics in this respect, also.

A third feature of the present invention is that the dimethine dyes which are used in the present invention result in less remaining of the dye and the characteristic curve is not so flat (non-contrasty). In general, a carbocyanine dye or a merocyanine dye useful for the sensitization of a negative emulsion has a strong tendency to have a flatened characteristic curve. This phenomenon of the characteristic curve becoming flat is not preferable for a contrasty direct positive light-sensitive material such as a film for a copying lithographic typefilm.

Also, the direct positive silver halide emulsion sensitized with the dimethine dye of the invention has the feature that'the clearing property (minimum density) is good and rereversal phenomenon substantially is not caused. I

The novel dimethine dye which is used in the present invention has the excellent characteristicsas described above. The reversal sensitivity can be enhanced even more by the combined ,use of the dye and an organic desensitizer. This combined use enables the production of a direct positive silver halide emulsion having a good clearing property.

The direct positive silver halide emulsion of the present invention can be used for contrasty direct positive .silver halide light-sensitive materials such as a light-sensitive material for copying lithographic type films, a light-sensitive material for duplicating original drawings and, in addition, for comparatively non-contrasty direct positive silver halide light-sensitive materials such as a light-sensitive material for copying microphotographis, and a light-sensitive material for copying X-ray photographs. In addition, it can be used for color light-sensitive materials.

The direct positive silver halide emulsion in accordance with the present invention can be exposed using the irradiation of electron beams, X-rays, gamma-rays, etc. as well as the irradiation with light.

The present invention will now be illustrated in greater detail by reference to the following non-limiting examples of preferred embodiments of the invention. Additionally, the dye used for comparison in the examples was the following compound. (A)

EXAMPLE 1 First, in order to prepare an original emulsion, Solutions 1 4 having the following formulations were prepared.

Solution 1 lnert Gelatin 8 g An aqueous Solution of Potassium cc Bromide (1 N) Water (60C) 500 cc Solution 2 Silver Nitrate 100 g Water (60C) 500 cc Solution 3 Potassium Bromide 70 g Water (60C) 150 cc Solution 4 lnert Gelatin 75 g Water 300 cc Solution 2 and Solution 3 were added to Solution 1 over a 50 minute period while maintaining the temperature at 60C and then subjected to physical ripening for 5 minutes. Then, 15cc of a 0.2 N potassium iodide solution was added thereto and the pAg was adjusted to 6.0 using a silver nitrate solution. The pH of the solution was adjusted to using a sodium hydroxide aqueous solution. Then, hydrazine (0.005 millimole per mole of silver halide) and gold chloride (0.005 millimole per mole of silver halide) were added thereto and the ripening was conducted for 10 minutes. After neutralizing with citric acid, the emulsion was washed with water. Then, Solution 4 was added thereto after melting to thereby obtain an original emulsion. The thus obtained emulsion contained regular tetragonal silver halide grains of a mean grain size of about 0.2 which have the crystal face of (100). I

To the resulting original emulsion portions were added the dye as set forth and in the amount described in Table l and, further, saponin was added (20ml of a 1% solution per kg of emulsion) to the emulsion. Each of the resulting emulsion portions was applied to a cellulose triacetate film in a dry thickness of about 5 microns to obtain samples. Each sample was wedgewise exposed using a 2854K tungsten light as a light source. Then each of them was development-processed at 20C for 2 minutes using the following developer and fixed in an acidic hardening and fixing solution. The density was measured using a Model P densitometer made by the Fuji Photo Film Co., Ltd. to obtain characteristic curves. The results of sensitivity, maximum optical density (Dmax) and minimum optical density (Dmin) obtained are shown in Table 1. Additionally, the sensitivity is represented in terms of the reciprocal of the exposure amount necessary for providing a density of Dmax Dmin 16 taking the sensitivity of the dye (A) for comparison as 100.

Composition of the Developer:

Metol 3.1 g Anhydrous Sodium Sulfite 45 g Hydroquinone 12 g Sodium Carbonate Monohydrate 79 g g l Potassium Bromide I 2 Water to make 1 Upon use, this composition was diluted 1:1 by volume with water.

From the results contained in Table 1, it can be seen that, as compared with the dye for comparison, the dye used in the present invention has such excellent properties that it provides a high Dmax, a good clearing property and a high sensitivity.

EXAMPLE 2 First, an original emulsion was prepared in the following manner. Solution 2 (prepared by adding 500cc of water to 100g of silver nitrate and heating to 60C to dissolve) and Solution 3 (prepared vby adding 300g of water to 35g of sodium chloride and heating to 60C to dissolve) were added to Solution 1 (prepared by adding Sec of a 1 N sodium chloride solution and 500cc of water to 10g of inert gelatin and heating to 60C to dissolve) over a 20 minute period under stirring while maintaining the temperature at 60C. After the completion of the addition, ripening was conducted for 5 minutes. Then, Solution 4 (prepared by adding 200cc of water to 14g of potassium bromide and heating to 60C to dissolve) was added thereto over a 5 minute period under stirring. Then, ripening was conducted for 10 minutes and, after reducing the temperature, the emulsion was washed with water. Then, it was again heated to dissolve, and the pH was adjusted to 10 followed by adding hydrazine (0.005 millimole per mole of silver halide) and a gold chloride salt (0.005 millimole per mole of silver halide) to ripen for 10 minutes. Thereafter, the pH was adjusted to 6.5 using citric acid. Further, Solution 6 (prepared by adding 30000 of water to g of inert gelatin to dissolve) was added thereto to obtain an original emulsion. The thus obtained original emulsion contained silver halide grains of a mean grain size of about 0.15 micron.

To the resulting original emulsion portions were added 32cc of a methanol solution of pinakryptol yellow of a molar concentration of 5 X 10 and the dye in the amount as set forth in Table 2. Further, mucochloric acid (20ml of a 2% solution per kg of emulsion) and saponin (20ml of a 1% solution per kg of emulsion) were added thereto in suitable amounts. Each of the resulting emulsion portions was applied to a cellulose triacetate film in a dry thickness of about 2 microns to obtain samples.

Each sample was exposed through an optical wedge using as a 2854K tungsten light as a light source followed by development-processing at 20C for 3 minutes with a developer having the following formulation and fixing in an acidic hardening and fixing solution.

Composition of the Developer:

Water (about 30C) 50 cc Anhydrous Sodium Sulfite 30 g Paraformaldehyde 7.5 g Sodium Bisulfite 2.2 g Boric Acid 7.5 g Hydroquinone 22.5 g Potassium Bromide 1.6 g

Water to make The density was measured using a Model P densitometer made by the Fuji Photo Film Co., Ltd. to obtain 1 TABLE 2 Dye (Molar Concen- Density of Samp tration) cc/lg SenSi Remaining No. Emulsion tivity Dmax Dmin Dye 9 1(8 X 10 2) 24 H7 30- 0.04 0.0l l0 3 (8 X l0 8 l5l 3.l 0.05 0.06 ll 4 (8 X 10 32 257 2.9 0.04 0.01 12 7 (8 X 10 8 132 3.0 0.06 0.05 l3 l4 (8 X 10 I6 112 3.2 0.04 0.04 l4 l6 (8 X 10) 24 115 2.8 0.04 0.0] 15 17(8 X 10 24 151 3.0 0.04 0.01 16 (8 X 10*) 32 228 2.8 0.04 0.01 l7 A (8 X l0" l6 lOO 2.5 0.08 0.08

From the results contained in Table 2, it can be seen that, as compared with the dye for comparison, the dye used in the invention shows excellent sensitivity, maximum optical density and clearing property and, in addition, causes less remaining of the dye, when used in combination with the organic desensitizer.

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 18 changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A direct positive prefogged silver halide emulsion containing at least one dimethinecyanine dye wherein the 3-position of a pyrrolo [2.3b] pyridine nucleus is bonded through a dimethine chain to the 1-, 2-, 3 or 4-position of a cyanine hetero ring nucleus, provided that where the bonding is in the 4-position said cyanine nucleus is a quinoline nucleus or a pyridine nucleus and where the bonding is in the lor 3-position said cyanine nucleus is an isoquinoline nucleus, said dimethincyanine dye being present in an amount sufficient to sensitize said emulsion.

2. The direct positive silver halide emulsion as claimed in claim 1, wherein said emulsion contains an organic desensitizer.

3. The direct positive silver halide emulsion as claimed in claim 1, wherein said cyanine hetero ring nucleus is an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, a naphthiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a 2-pyridine nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a benzoimidazole nucleus, an indolenine nucleus, a 3,3-dialkyindolenine nucleus, an imida- Zo[4,5b]quinoxaline nucleus, or a pyrrolidine nucleus.

4. The direct positive silver halide emulsion as claimed in claim 1, wherein said dimethinecyanine dye is represented by the following general formula (I);

wherein R represents a hydrogen atom or a lower alkyl group, R represents a hydrogen atom, a lower alkyl group or an aryl group, R represents an alkyl group having 1 to 6 carbon atoms, L represents a methine group, L represents a methine group, wherein said L and R can be connected to each other to form a methylene chain, In and n each represents 1 or 2, X represents an anion, and Z represents the non-metallic atoms necessary to complete a cyanine hetero ring nucleus.

5. The direct positive silver halide emulsion as claimed in claim 4, wherein said alkyl group for R, is a methyl group, an ethyl group, or a propyl group; wherein said alkyl group for R is a methyl group, an ethyl group, or a butyl group wherein said aryl group for R is a phenyl group, a tolyl group or a p-chlorophenyl group; wherein said alkyl group for R is an alkyl group, a hydroxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, a sulfoalkyl group, or an aralkyl group; wherein said aryl group for R is a phenyl group, a tolyl group or a p-chlorophenyl group; wherein said methine group for said L is a methine group or a lower alkoxyalkyl-substituted methine group, said substituent being a methoxyethyl group or an ethoxyethyl group and wherein the non-metallic atoms represented by Z form an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, :1 benzothiazole nucleus, 21

naphthothiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenezole nucleus, a 2-pyridine nucleus, a Z-quinoline nucleus, a 4-quinoline nucleus, a benzoimidazole nucleus, an indolenine nucleus, a 3,3-dialkylindolenine nucleus, an imidazo[4,5b]quinoxaline nucleus, or a pyrrolidine nucleus. 6. The direct positive silver halide emulsion as claimed in claim 3, wherein said cyanine hetero ring nucleus is a benzothiazole nucleus, a benzoselenazole nucleus, at benzoxazole nucleus, 3,3-dialkylindolenine nucleus, or an imidazo[4,5b] quinoxaline nucleus.

halide emulsion contains-a photographic color coupler.

1 l. The direct positive silver halide photographic emulsion as claimed in claim 2, containing at least one dye selected from the dyes represented by the following general formula (I);

2 (cH-cii) -N-R3 (I) N I (x wherein R represents a hydrogen atom or a lower alkyl group, R represents a hydrogen atom, a lower alkyl group or an aryl group, R represents an alkyl group having 1 to 6 carbon atoms, L, represents a methine group, L represents a methine group, wherein said L and R can, be connected to each other to form a methylene chain, In and n each represents 1 or 2, X represents an anion, Z represents the non-metallic atoms necessary to complete a cyanine hetero ring nucleus, and an organic desensitizer represented by the following general formula (Ill); 7

7. The direct positive silver halide emulsion as claimed in claim 1, wherein said silver halide of said emulsion comprises chemically fogged silver halide grains.

8. The direct positive silver halide emulsion as claimed in claim 7, wherein said silver halide of said emulsion comprises silver halide grains fogged with a reducing agent and a gold compound.

9. The direct positive silver halide emulsion as claimed in claim 7, wherein at least 95% by weight of said fogged silver halide grains have a diameter within about of the mean grain size of said silver halide grains.

10. The direct positive silver halide emulsion as claimed in claim I. wherein said direct potitive silver (III) wherein R represents an alkyl group or an allyl group, X, Z, and m are the same as defined above, and a represents l or 2.

12. A direct positive silver halide light-sensitive material comprising a support having thereon the direct positive silver halide emulsion as claimed in claim 1.

13. The direct positive silver halide photographic emulsion as claimed in claim 1 wherein the sensitizing amount is within the range of from l X 10 to 2 X 10 mol of dye per mol of silver halide.

14. The direct positive silver halide lightsensitive material as claimed in claim 12 wherein the sensitizing amount is within the range of from l X 10' to 2 X l0 mol of dye per mol of silver halide.

l l l

Claims

1. A DIRECT POSITIVE PREFOGGED SILVER HALIDE EMULSION CONTAINING AT LEAST ONE DIMETHINECYANINE DYE WHEREIN THE 3-POSITION OF A PYRROLO (2,3B) PYRIDINE NUCLEUS IS BONDED THROUGH A DIMETHINE CHAIN TO THE 1-, 2-, 3- OR 4-POSITION OF A CYANINE HETERO RING NUCLEUS, PROVIDED THAT WHERE THE BONDING IS IN THE 4-POSITION SAID CYANINE NUCLEUS IS A QUINOLINE NUCLEUS OR A PYRIDINE NUCLEUS AND WHERE THE BONDING IS IN THE 1- OR 3-POSITION SAID CYANINE NUCLEUS IS AN ISOQUINOLINE NUCLEUS, SAID DIMETHINCYANINE DYE BEING PRESENT IN AN AMOUNT SUFFICIENT TO SENSITIZE SAID EMULSION.

3. The direct positive silver halide emulsion as claimed in claim 1, wherein said cyanine hetero ring nucleus is an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, a naphthiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a 2-pyridine nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a benzoimidazole nucleus, an indolenine nucleus, a 3,3-dialkyindolenine nucleus, an imidazo(4,5b)quinoxaline nucleus, or a pyrrolidine nucleus.

5. The direct positive silver halide emulsion as claimed in claim 4, wherein said alkyl group for R1 is a methyl group, an ethyl group, or a propyl group; wherein said alkyl group for R2 is a methyl group, an ethyl group, or a butyl group wherein said aryl group for R2 is a phenyl group, a tolyl group or a p-chlorophenyl group; wherein said alkyl group for R3 is an alkyl group, a hydroxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, a sulfoalkyl group, or an aralkyl group; wherein said aryl group for R3 is a phenyl group, a tolyl group or a p-chlorophenyl group; wherein said methine group for said L2 is a methine group or a lower alkoxyalkyl-substituted methine group, said substituent being a methoxyethyl group or an ethoxyethyl group and wherein the non-metallic atoms represented by Z form an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, a naphthoThiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenezole nucleus, a 2-pyridine nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a benzoimidazole nucleus, an indolenine nucleus, a 3,3-dialkylindolenine nucleus, an imidazo(4,5b)quinoxaline nucleus, or a pyrrolidine nucleus.

6. The direct positive silver halide emulsion as claimed in claim 3, wherein said cyanine hetero ring nucleus is a benzothiazole nucleus, a benzoselenazole nucleus, a benzoxazole nucleus, 3,3-dialkylindolenine nucleus, or an imidazo(4,5b) quinoxaline nucleus.

9. The direct positive silver halide emulsion as claimed in claim 7, wherein at least 95% by weight of said fogged silver halide grains have a diameter within about 40% of the mean grain size of said silver halide grains.

10. The direct positive silver halide emulsion as claimed in claim 1, wherein said direct potitive silver halide emulsion contains a photographic color coupler.

11. The direct positive silver halide photographic emulsion as claimed in claim 2, containing at least one dye selected from the dyes represented by the following general formula (I);

13. The direct positive silver halide photographic emulsion as claimed in claim 1 wherein the sensitizing amount is within the range of from 1 X 10 6 to 2 X 10 2 mol of dye per mol of silver halide.

14. The direct positive silver halide lightsensitive material as claimed in claim 12 wherein the sensitizing amount is within the range of from 1 X 10 6 to 2 X 10 2 mol of dye per mol of silver halide.