GB2216279A

GB2216279A - Infra-red sensitive silver halide photographic emulsion

Info

Publication number: GB2216279A
Application number: GB8904524A
Authority: GB
Inventors: Susumu Baba; Katsuaki Iwaosa; Minoru Ohashi
Original assignee: Mitsubishi Paper Mills Ltd
Current assignee: Mitsubishi Paper Mills Ltd
Priority date: 1988-02-29
Filing date: 1989-02-28
Publication date: 1989-10-04
Also published as: GB8904524D0; JPH01221737A

Abstract

A silver halide photographic emulsion contains at least one sensitizing dye having a maximum spectral sensitivity in the wavelength region of at least 700 nm and at least one precursor for nitrogen-containing heterocyclic compound having mercapto group. This emulsion is especially improved in shelf stability. The precursor may be a thioether.

Description

SILVER HALIDE PHOTOGRAPHIC EMULSION BACKGROUND OF THE INVENTION The present invention relates to a spectrally sensitized silver halide photographic emulsion and in particular to a silver halide photographic emulsion improved in storage stability even if sensitized to infrared region.

Silver halide photographic light-sensitive materials are required to have high sensitivity at respectively different wavelengths depending on their use.

As one process for preparation of such lightsensitive materials, it has been well known that sensitivity at a specific wavelength region can be effectively enhanced by adding a certain sensitizing dye to silver halide emulsion.

On the other hand, with recent rapid progress in opto-electronics, laser beam, LED beam and the like have come to be used as a light source for output of digital image information in place of the conventional incandescent lamp and He-Ne laser, argon laser, red LED and semiconductor laser have already been put to practical use. Among them, semiconductor laser is advantageous in its small size, low price, easy modulation and long life and is promising in the future. Semiconductors of the systems such as Ga/As/P; Ga/Al/As; Ga/As; In/P; and In/As are used for semiconductor laser and wavelength of these laser beams is generally longer than 700 nm, mostly longer than 750 nm.

When silver halide emulsion is spectrally sensitized with sensitizing dyes in order to prepare a silver halide emulsion suitable for exposure with these semiconductor lasers, light-sensitive material having an emulsion spectrally sensitized to infrared region according to conventional method is highly desensitized when stored at room temperature and can no longer be used.

Therefore, the light-sensitive material must be refrigerated or frozen for storage. However, it is troublesome to keep the infrared sensitive-material refrigerated or frozen before use and besides it takes considerable cost.

Therefore, light-sensitive materials for infrared have been earnestly demanded which are less in reduction of sensitivity and increase of fog even if they are stored at room temperature.

The inventors have confirmed that even when light-sensitive materials for infrared have a tendency to increase in sensitivity when stored under forced conditions such as 500C, 80% RH which is known as preservation test method for silver halide photographic lightsensitive material, such material is desensitized when stored under natural conditions and thus there is a discord. It has not been considered that the mercapto compound such as l-phenyl-5-mercaptotetrazole is effective for improving storage stability of the light-sensitive material for infrared.

SUMMARY OF THE INVENTION The object of the present invention is to provide a silver halide photographic emulsion sensitive to infrared of wavelength longer than 700 nm which is excellent in storage stability under natural conditions.

The above object has been effectively attained by using in combination at least one sensitizing dye having a maximum spectral sensitivity in the wavelength region of at least 700 nm and at least one precursor for nitrogen-containing heterocyclic compound having a mercapto group.

DESCRIPTION OF THE INVENTION The precursor for nitrogen-containing heterocyclic compound having a mercapto group is a compound which is hydrolyzed with an alkali in a developer to liberate a nitrogen-containing heterocyclic compound having a mercapto group.

As the nitrogen-containing compound having a mercapto group there may be used those which are disclosed in U.S. Patent Nos. 2,981,624, 3,260,597 and 3,674,478 and Japanese Patent Kokai Nos. 57-76541, 57-135944, 57-135945, 57-136640, 61-196239, 61-196240 and 61-83532.

Preferred examples of the nitrogen-containing heterocyclic compounds having mercapto group used in the present invention are mercaptotetrazoles, mercaptobenzothiazoles, mercaptobenzoxazoles, mercaptobenzimidazoles, mercaptotriazoles, mercaptoxadiazoles and 1 mercaptothiadiazoles.

Examples of the precursors for nitrogen containing-heterocyclic compound having a mercapto group are enumerated below.

(A) N N II II N C-SCH2COOH ' (B) N N II N C-SCOC13H27 N (C) NN II N C-SCH2 OH ! (D) (D) N N 11 II N C- S I OCOCH3 OCOCH

(E) SUSCH*-R (F) SNk S---0 CQ CQ (G) PfO\ /0, (H) N N II II Ox N C - S 2v I (I) a ?$ffi! NSs N N - - HO II II II 11 < N C - S - CHrNss

(K) a z S - CH2 Pr/Ns cH, (L) - CHm!NH (M) NN II II -S- CH2NH (N) N N I1 Il N C - S - CH OH 2 I CH=N-C4H9 (0) S a N > 2 9 OH COOCZH (P) N N II II C oC - S - CH2 OH t COOCH3 The above are merely examples and are not limitative.

These compounds may be added at any time during preparation of silver halide photographic emulsion, but preferably are added as additive after completion of chemical ripening. Addition amount of these compounds is normally 5-500 mg, preferably 10-300 mg per 1 mol of silver halide.

When these compounds are added to silver halide emulsion spectrally sensitized with a sensitizing dye having a maximum spectral sensitivity in the wavelength region of 700 nm or longer, storage stability of lightsensitive materials containing this emulsion is markedly improved as compared with that of materials which contain ordinarily known stabilizers such as l-phenyl-5-mercaptotetrazole.

These compounds exhibit similar effect also when contained in layers other than silver halide photographic emulsion layer, for example, a protective layer, an intermediate layer and a subbing layer and allowed to diffuse into emulsion layer. In this case, however, amount to be added must be somewhat larger than the amount when added directly to emulsion layer.

The sensitizing dyes used in the present invention which have maximum spectral sensitivity in the wavelength region of 700 nm or longer can be those which are disclosed, for example, in U.S. Patent Nos. 2,095,854, 2,095,856, 2,955,939, 3,482,978, 3,552,974, 3,573,921, 1 3,582,344 and 3,623,881.

Preferred are dyes represented by the following formulas (I)-(IV).

Formula (I)

Formula (II)

Formula (III)

Formula (IV)

In the above formulas (I) - (IV), Z1 and Z2 which may be identical or different each represents group of atoms necessary to form 5-membered or 6-membered nitrogencontaining heterocyclic ring; R1 and R2 which may be identical or different each represents an alkyl group or an alkenyl group; R3 represents an alkyl group, an alkenyl group or an aryl group; R4-R10 which may be identical or different each represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group or an alkoxy group and R6 and R7 or R8 and Rg may link to each other to form a 5-membered or 6-membered ring;R11 and R12 which may be identical or different each represents an alkyl group or an aryl group and may link to each other to form a 5membered or 6-membered ring; Y represents a sulfur atom, an oxygen atom, > N-R13 (R13 is an alkyl group), X represents an acid anion; 1, m, n, p and q each represents 1 or 2 and Q represents a group of atoms necessary to form 5-membered or 6-inertibered ring.

As examples of Z1 and Z2 mention may be made of nitrogen-containing heterocyclic rings such as thiazole, benzothiazole, naphtho[l,2-d]thiazole, naphtho[2,l-d) thiazole, naphtho[2, 3-d]thiazole, -selenazole, benzoselenazole, naphtho[2,1-d]selenazole, naphtho [1,2-d]selenazole, oxazole, benzoxazole, naphtho[l,2-d]oxazole, naphtho[2,1-d]Oxazole, naphtho[2,3-d]oxazole, 2-quinoline, 4-quinolene, 3, 3-dialkylindolenine, imidazole, benzimidazole, naphtho[l,2-d]imidazole and pyridine.

These heterocyclic rings may have at least one substituent such as, for example, alkyl group (e.g., methyl, ethyl, butyl and trifluoromethyl), aryl group (e.g., phenyl and tolyl), hydroxy group, alkoxy group (e.g., methoxy, ethoxy and butoxy), carboxyl group, alkoxycarbonyl group (e.g., methoxycarbonyl and ethoxycarbonyl), halogen atom (e.g., fluorine, chlorine, bromine and iodine), aralkyl group (e.g., benzyl and phenethyl), cyano group and alkenyl group (e.g., allyl).

As alkyl groups for R1 and R2, mention may be made of, for example, lower alkyl groups such as methyl, ethyl, propyl and butyl, hydroxyalkyl groups such as ss-hydroxyethyl and y-hydroxypropyl, alkoxyalkyl groups such as ss-methoxyethyl and y-methoxypropyl, acyloxyalkyl groups such as ss-acetoxyethyl, y-acetoxypropyl and 8-benzoyloxyethyl, carboxyalkyl groups such as carboxymethyl and ss-carboxyethyl, alkoxycarbonylalkyl groups such as methoxycarbonylmethyl, ethoxycarbonylmethyl and 6-ethoxycarbonylethyl, sulfoalkyl groups such as ss- sulfoethyl, y-sulfopropyl and -sulfobutyl and aralkyl groups such as benzyl, phenethyl and sulfobenzyl.

Alkenyl groups for R1 and R2 include, for example, allyl group.

As R3, there are alkyl and alkenyl groups as exemplified for R1 and R2 and aryl groups such as, for example, phenyl, tolyl, methoxyphenyl, chlorophenyl and naphthyl.

R4-Rlo each represents a hydrogen atom, a halogen atom (e.g., chlorine, bromine, iodine and fluorine), an alkyl or aryl group as exemplified for R1 and R2 or an alkoxy group having an alkyl group as exemplified for R1 and R2 (namely, OR1) and 5-membered or 6-membered ring formed by R6 and R7 or R8 and R9 may have substituent such as lower alkyl group. R11 and R12 each represents an alkyl group or an aryl group as exemplified for R1 and R2 and R11 and R12 may link to each other to form a 5-membered or 6-membered ring.

R13 represents an alkyl group as exemplified for R1 and R2.

The acid anions of X include, for example, alkylsulfate ions such as methylsulfate and ethylsulfate, thiocyanate ion, toluenesulfonate ion, halogen ions such as chloride, bromide and iodide and perchlorate ion.

The acid anion is not present when the dye has a betaine analogous structure.

Especially preferred sensitizing dyes used in the present invention are those which are represented by the above formulas (I) and (IV).

Examples of the sensitizing dyes use in the present invention are enumerated below.

(4) g > CH-CH=CH-CH S S I D CHCHCHTh\N+ OC2H5 C2H5 I I CH2 (I 2)3 (CH2)3 SO3 (5) 0 0CH-CH=CH-CHS S CH-CH=CH- N+ C2H5 C H 0 C2H5 1 1 + X I SO3 (6) X CH-CH=CH-CHy S xS X OCE 3 C2H5 CH3 C2H5 C2H5 (7) CH3 CH3 \/ 3 SC > CH C2H5 3 1 CH C2H5

(8) H5C2-N n CH-CH - S OCH3 5 2 \=/ 1 S H-CH=CH < I O 1 0 + CH I 1 3 C2H5 C2H5 (9) H5 g H-CH=CH-CH=CH A B C2H5 I (10) CH3 CH3 101 H=CH-CH (1H (CH2)3 C2H5 I 2 SO3 (11) CH3CEI3 C (CH2)3S > ~ N I S CH~C=CH X I O I CH30 I W C2H5 C2H5

(12) CK3 CH3 25 CH5 C2H5 CH37 3SO3 (13) CH3 CH3 Xz CH3 CH-1Y OCH3 S QIONAC 0--')- O= ~ Nz C2H5 C2H5 j OCH3 2"5 CH S03 (14) CH3 CH3 /Q M, s\ OC,H, g ≈ O idol s í O - z CH-C=CH % J g (CH2)3 C2H5 l+ S03K I SO3

(15) CH3 CH3 > CH X S S d ss N s CH~CH=CH X e 1H3 - N/ NN+ &num;> C2H5 (1CH2)4 SO3 (16) CH3 t N) 4 CH-CH=CH-CH=CH N5'0 C2H5 I C H C2H5 (17) CH CH3 CH3 H3C > CHCH=CHCHW0N% H3 N1+ I C2H5 I C2H5 5 I (18) CH3 H=CH-CH= Ij0 I 25 1 I S03

(19) g > CH-C-CH=CH-CH S + CH3 C2H5 H3 SS,/ (20) 0 (CH2)730 CH3 \I\JS\ 05CH-CH=CH-CHSS CH3 CH3 NONCHC=CHN+QCH3 C2H5 C2H5 C2H5 CH3 4 0 ) SO3 (21) v CH-CH=CH-CH H N 1 z CH-C-CH C2H5 1 1+ C2H5 (CH2)3 SO 3 (22) CH3 CH3 \/ 3 N S CH~C=CH X H-C=CH/0 H C2H5 ON RN+/-CH3 5 n U C2H5 C1 H CH 3SO3

(23) H3C ss N S SCH=CH+=CH-CHA w 2 5 C2H5 I (24) CH3 < N > 4 C2H5 J- s CC2H5 C2H5 I l C2H5 C2H5 CH3 SO3 (25) CH3 CH3 ĭ$CH C X S 5O1C2H55 OCH3 s CH-C=CH- l O | I O= -NZ N+ ~ OCH3 C2H5 C1H C1H 25 25 2 5 C2H5 CK3S03

(26) )I. /1-CH-CH=CH-CH=i- S\ I 3 < s OCH3 I ONCHC=CHN+0 OCH3 (C1 H2)3 CH2-CH=CH2 C H I 2K SO 3K CH3 e SO3 (27) CH3 CH3 H3CO MCHH=CH-CH% NO 1+ I OCH3 C2H5 C2H5 2 5 (28) S CH3 H SC2NHCHCHCHCHN0 CH, 1+ CH3 C2H5 (29) CIH3 OCH3 H5 2 N g H-CH=C-CH=CH < v OCH3 (CH2) so3

(30) 9 H5C2-N N H-CH=CH-CH=CH + < m I + COOC2H5 CH3 3 (31) CH3 CH3 CH-M ICH I 0: z \ s tCH < < CH3 I CH3 C H CH 2 5 CH3 I (32) CH3 CH3 ;CH-C: CHJC H í C=CHA0+NTh C2H5 I -I C2H5 2 CH 7 SO3 (33) CH3 CH3 CHSCH=)) ON+i I I Br C2H5 C2H5 C2H5 C2H5 C2H5 3 < SO3

(34) CH3 -CH=t/ CH3 N+CHĭ)=cHCH 0 CH C2E5 25 25 CH e so, The sensitizing dyes used in the present invention may be synthesized by the methods known per se.

-6 Addition amount of the sensitizing dye is 1 x 10 6 5 x 10 3 mol, preferably 5 x 10 - lx 10 3 mol per 1 mol of silver halide.

The sensitizing dye may be directly dispersed in emulsion or may be dissolved in a water-miscible solvent such as methanol, ethanol, pyridine, methyl cellosolve, acetone or dimethylformamide (or a mixed solvent thereof) or diluted with water or dissolved in water and added to emulsion in the form of such solution.

Ultrasonic vibration can be applied to this dye solution or the solution may be added by the methods disclosed in U.S. Patent No. 3,469,987 and Japanese Patent Kokoku No.

46-24185. Further, there may be used such methods as disclosed in U.S. Patent Nos. 2,912,345, 3,342,605, 2,996,287 and 3,425,835.

The sensitizing dyes may be used alone or in combination of two or more and may contain other dyes.

The sensitizing dyes may be added at any time during preparation of silver halide emulsion and before coating of the emulsion.

Silver halide used in the present invention may be any of silver chloride, silver chlorobromide, silver iodobromide, silver chloroiodobromide, etc.

Silver halide may be of any form and can be prepared by any known process. For example, it may be precipitated by ammonia process, neutral process, acidic process or partial ammonia process comprising mixed neutral process and ammonia process. Furthermore, any of mixing processes such as normal mixing, reverse mixing and simultaneous mixing can be employed. Especially, a simultaneous mixing process called double jet process in which crystal habit is controlled under controlling of pAg can be employed. Besides, conversion process utilizing difference of solubility can also be employed.

The process of conversion type is disclosed, for example, in U.S. Patent No. 2,592,250. Furthermore, emulsion prepared by precipitation in the presence of a crystal habit modifier which is disclosed in J. Phot. Soc.

2139-50 (1973) may also be included.

Metals such as iridium and rhodium may be used during precipitation or physical ripening of silver halide.

These emulsions can be chemically sensitized by known methods. That is, sulfur sensitization can be carried out with sulfur compounds disclosed in U.S. Patent Nos. 1,574,944, 2,278,947, 2,410,689, 3.189,458 and 3,501,313 or sensitizing-type gelatins containing the sulfur compounds. Further, gold sensitization may also be effected with gold compounds disclosed in U.S. Patent Nos. 2,597,856, 2,597,915 and 2,399,083. Moreover, there may-also be effected reduction sensitization as disclosed in U.S. Patent Nos. 2,518,698, 2,521,925, 2,487,850 and 2,694,637. These sensitizations may also be carried out in combination.

The photographic emulsions used in the present invention can also be sensitized with quaternary ammonium salts, thioether compounds, polyethylene oxide derivatives and diketones. These methods are disclosed in U.S. Patent Nos. 2,708,162, 3,046,132, 3,046,133, 3,046,134 and 3,046,135 and British Patent No. 939,357.

As binder or protective colloid for photographic emulsion and non-light-sensitive layer used in the present invention, there may be used mainly gelatin derivatives such as phthalated gelatin or polyvinyl alcohol as well as lime-treated or acid-treated gelatin.

Furthermore, in combination therewith there may be used polyvinyl pyrrolidone or acryl based water-soluble copolymers or polysaccharides such as starch and its derivatives and cellulose derivatives. Furthermore, properties of gelatin film can be modified by adding a latex polymer and surface of film can be matted by adding silica, starch powder, colloidal silica or glass powder.

The photographic emulsion layer and the non light-sensitive layer may contain a coating aid, namely, surfactant to reduce surface tension and enhance effect of wetting. As effective coating aid, mention may be made of, for example, non-ionic surfactants such as saponin, alkylene oxide type, glycerin type, and glycidol type, cationic surfactants such as higher alkylamines, quaternary ammonium salts, heterocyclic compounds, e.g., pyridines, and sulfonium compounds, anionic surfactants containing acid group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester, and phosphate ester and amphoteric surfactants such as aminoacids, aminosulfonic acids, and esters of amino alcohol. The coating aids further include fluorinated surfactants disclosed in U.S. Patent No. 3,589,906 and West German Patent Publication (Laid-Open) Nos.

1,961,638 and 2,124,262.

The silver halide light-sensitive materials of the present invention can optionally contain known antifoggant, hardener, antistatic agent, developing agent, slip agent, fluorescent brightener, antihalation dye, anti-irradiation dye and dye for handling under safe light.

The support on which the emulsion of the present invention is coated is not critical. That is, the emulsion may be coated on any of film bases such as, for example, polyester film and cellulose triacetate film, paper bases such as, for example, baryta paper, resin treated paper and synthetic paper, photographic plate glass, metallic plate, etc.

The following nonlimiting examples will explain the present invention in more detail.

Example 1 An emulsion was prepared from the following formulation.

Solution I Gelatin 100 g Distilled water 2000 ml Potassium bromide 130 g Solution II Silver nitrate 170 g Distilled water 1000 ml 28% Ammonia water 150 ml Solution I was kept at 400C and solution II was added thereto under vigorous stirring. The mixture was ripened at 400C for 30 minutes and then pH was lowered to 6.0. Then, 100 g of gelatin was added and was dissolved, followed by cooling, coagulating, macerating and desalting by washing with water. The resulting emulsion was dissolved at 500C and adjusted to pH 6.5 and pAg 8.9, followed by adding 40 mg of sodium thiosulfate and 15 mg of ammonium gold thiocyanate per 1 mol of silver halide and then chemically ripening at 550C for 60 minutes.

This emulsion was divided into several parts and to each of them were added a sensitizing dye and a precursor for nitrogen-containing heterocyclic compound having mercapto group as shown in Table 1 and then a coating aid and a hardener were added thereto. Then, the emulsion was coated on a polyethylene-laminated paper of 100 p thick and dried to make a sample. Coating 2 amount of silver was 1.8 g/m These samples were divided into four groups and were respectively exposed and developed by the following methods, (1) just after coating, (2) after stored for 5 days at 500C, 80%RH, (3) after stored for 1 month at 350C, 80%RH and (4) after stored for 12 months under natural condition.

Exposure, development and measurement of properties of the samples were effected in the following manner: The sample was exposed using an actinometer having a light source of color temperature 5,400 K attached with a dark red filter which transmits a light of longer than 700 nm in wavelength. Subsequently, each sample was developed with D-72 developer at 200C for 90 seconds, stopped, fixed and washed with water to obtain a strip having a predetermined monochromatic image.

Density of the image was measured by MACBETH TD-504 densitometer supplied by Macbeth Corporation, U.S.A. to obtain a sensitivity to infrared ray. Standard 1 point of optical density for determination of the sensi tivity was the point of 0.75 in density in all cases.

The results are shown in Table 1.

Table 1

------------------------------------------------------------------------------------------ Relative Sensitizing dye Precursor Relative sensitivity Sample No. ------------------------------------------- sensitivity after storage Kind Amount Kind Amount just after of 5 days at mg/mol AgX mg/mol AgX coating 50 C 80% RH ------------------------------------------------------------------------------------------ 1 The present (10) 10 (A) 2 100 108 invention ------------------------------------------------------------------------------------------ 2 " (10) 10 (B) 2 102 110 ------------------------------------------------------------------------------------------ 3 " (10) 10 (I) 2 98 102 ------------------------------------------------------------------------------------------ 4 Comparative (10) 10 (K) 2 100 108 sample ------------------------------------------------------------------------------------------ 5 " (10) 10 - - 115 118 ------------------------------------------------------------------------------------------ (to be cont'd.)

Comparative compound Table 1 (Cont'd.)

Relative Relative sensitivity sensitivity after storage after storage of 1 month at of 12 months 35 C 80% RH under natural condition 98 99 100 100 95 96 60 67 85 92 As can be seen from the results of Table 1, sensitivity after storage of 5 days at 500C, 80%RH was higher for all samples than the sensitivity just after coating, but relative sensitivity after storage of 1 month at 350C, 80%RH and that after storage of 12 months under natural condition were lower for comparative samples 4 and 5 while higher for the samples 1-3 of the present invention than the sensitivity just after coating Example 2 Emulsion was prepared from the following formulation.

Solution V Phthalated gelatin 5 g 0.1N aqueous potassium bromide 20 ml solution Water to make up 200 ml.

1N sulfuric acid x ml Solution VI Silver nitrate 136 g Water to make up 400 ml.

Solution VII Potassium bromide 92.8 g Potassium iodide 3.3 g Phthalated gelatin 16 g Water to make up 400 ml.

Solution VIII 6N sulfuric acid x ml (for adjusting pH to 3.5) Solution V was kept at 600C and solution VI and solution VII were simultaneously added thereto under vigorous stirring over 30 minutes and pAg during the addition was controlled to 7.4. Then, solution VIII was added to adjust pH to 3.5 and the resulting precipitate was washed with water.

This original emulsion was a silver iodobromide emulsion containing 97.5 mol% of bromide which was a monodispersed emulsion of cubic form having an average grain size of 0.25 , at least 95% by weight of grains being within +20% of the average grain size.

This original emulsion was redissolved and gelatin was added thereto to adjust ph to 6.5. Then, 40 mg of sodium thiosulfate and 15 mg of ammonium goldthiocyanate per 1 mol of silver halide were added, followed by chemical ripening at 550C for 60 minutes.

This emulsion was divided into several parts and to each of them were added a sensitizing dye and a precursor for nitrogen-containing heterocyclic compound having mercapto group as shown in Table 2 and then, a coating aid and a hardener were added thereto. Then, each emulsion was coated on a polyethylene terephthalate film and dried. Coating amount of silver was 3.0 g/m2.

Each of the thus obtained samples was treated in the same manner as in Example 1. Sensitivity (relative value) obtained as a result of measurement of transmission density is shown in Table 2. Standard point of the transmission density for determination of the sensitivity was the point of 3.0 in density in all cases.

Table 2

------------------------------------------------------------------------------------------ Sensitizing dye Precursor Relative Relative Sample No ----------------------------------------- sensitivity sensitivity Kind Amount Amount just after after storage mg/mol Agx Kind mg/mol AgX costing of 1 month at 35 C, 80%RH ------------------------------------------------------------------------------------------ 1 The present (1) 10 (B) 300 100 96 invention ------------------------------------------------------------------------------------------ 2 " (1) 10 (G) 300 103 101 ------------------------------------------------------------------------------------------ 3 " (1) 10 (H) 300 102 98 ------------------------------------------------------------------------------------------ 4 " (9) 15 (I) 300 95 95 ------------------------------------------------------------------------------------------ 5 " (9) 15 (M) 300 96 97 ------------------------------------------------------------------------------------------ 6 " (9) 15 (O) 300 94 92 ------------------------------------------------------------------------------------------ 7 " (11) 20 (B) 300 105 102 ------------------------------------------------------------------------------------------ 8 " (11) 20 (G) 300 100 101 ------------------------------------------------------------------------------------------ Table 2 (Cont'd.)

9 The present (11) 20 (H) 30 108 105 invention 10 (31) 10 (I) 30 95 96 " 11 (31) 10 (M) 300 97 96 " 12 (31) 10 (O) 300 102 99 " 13 (32) 15 (B) 300 98 96 " 14 (32) 15 (G) 300 102 100 " 15 (32) 15 (H) 300 105 101 " 16 (33) 20 (I) 300 108 107 " 17 (33) 20 (M) 300 107 108 " 18 (33) 20 (O) 300 109 105 " Table (Cont'd.)

19 The present (34) 15 (H) 300 100 98 invention ------------------------------------------------------------------------- 20 " (34) 15 (O) 300 98 99 ------------------------------------------------------------------------- 21 Comparative (34) 15 (K) 300 101 63 sample ------------------------------------------------------------------------- 22 " (34) 15 - - 115 60 ------------------------------------------------------------------------- As can be seen from the results of Table 2, relative sensitivity of comparative samples 21 and 22 after stored for 1 month at 350C, 80%RH decreased markedly while the samples 1-20 of the present invention showed substantially no decrease.

Claims

WHAT IS CLAIMED IS:

1. A silver halide photographic emulsion which contains in combination at least one sensitizing dye having a maximum spectral sensitivity in the wavelength region of at least 700 nm and at least one precursor for nitrogen-containing heterocyclic compound having mercapto group.

2. A silver halide photographic emulsion according to claim 1 wherein amount of the precursor is 5-500 mg per 1 mol of silver halide.

3. A silver halide photographic emulsion according to claim 1 wherein amount of the sensitizing dye is 10 6 mol to 5 x 10 mol per 1 mol of silver halide.

4. A silver halide photographic emulsion according to claim 1 wherein the nitrogen-containing heterocyclic compound is a compound selected from the group consisting of mercaptotetrazoles, mercaptobenzothiazoles, mercaptobenzoxazoles, mercaptobenzimidazoles, mercaptotriazoles, mercaptoxadiazoles and mercaptothiadiazoles.

5. A silver halide photographic emulsion according to claim 1 wherein the sensitizing dye is selected from the group consisting of those which are represented by the following formulas (I)-(IV):

wherein Zl and Z2 which may be identical or different each represents group of atoms necessary to form 5-membered or 6-membered nitrogen-containing heterocyclic ring; R1 and R2 which may be identical or different each represents an alkyl group or an alkenyl group; R3 represents an alkyl group, an alkenyl group or an aryl group; R4-Rlo which may be identical or different each represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group or an alkoxy group and R6 and R7 or R8 and Rg may link to each other to form a 5-membered or 6-membered ring; R11 and R12 which may be identical or different each represents an alkyl group or an aryl group and may link to each other to form a 5-membered or 6-membered ring; Y represents a sulfur atom, an oxygen atom, > N-R13 (R13 is an alkyl group), X represents an acid anion; 1, m, n, p and q each represents 1 or 2 and Q represents a group of atoms necessary to form 5-membered or 6membered ring.

6. A silver halide photographic light-sensitive material which comprises a support and a silver halide photographic emulsion of claim 1 coated thereon.