US3573920A - Fine grain silver halide emulsions containing novel dye combinations - Google Patents

Abstract

FINE GRAIN PHOTOGRAPHIC SILVER HALIDE EMULSIONS ARE SPECTRALLY SENSITIZED WITH THE COMBINATION OF (1) A CARBOCYANINE DYE HAVING A MAXIMUM SENSITIVITY PEAK AT A WAVELENGTH SHORTER THAN 6563 A., AND (2) A CARBOCYANINE DYE HAVING A MAXINUM SENSITIVITY PEAK AT A WAVELNGTH LONGER THAN 6563 A.; EACH OF THE DYES COMPRISING HETEROCYCLIC NUCLEI SELECTED FROM A 3-SULFOALKYLBENZOTHIAZOLE NUCLEUS, A 3-SULFOALKYLBENZOELENAZOLE NUCLEUS AND A 1SULFOALKYLNAPHTHO(1,2-D) THIAZOLE NUCLEUS, THE TWO HETEROCYCLIC NUCLEI OF EACH OF SAID DYES BEING JOINED BY A TRIMETHINE CHAIN WHICH CONTAINS AN ALKYL GROUP ON THE MESO CARBON ATOM THEREOF.

Description

"United States Patent 3,573,920 FINE GRAIN SILVER HALIDE EMULSIONS CON- TAINING NOVEL DYE COMBINATIONS Gary L. Hiller, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y.

No Drawing. Continuation-impart of abandoned application Ser. No. 686,831, Nov. 30, 1967. This application Sept. 5, 1968, Ser. No. 757,789

Int. Cl. G03c 1/22, 1/28 US. Cl. 96-104 41 Claims ABSTRACT OF THE DISCLOSURE Fine grain photographic silver halide emulsions are spectrally sensitized with the combination of (1) a carbocyanine dye having a maximum sensitivity peak at a wavelength shorter than 6563 A., and (2) a carbocyanine dye having a maximum sensitivity peak at a wavelength longer than 6563 A.; each of the dyes comprising heterocyclic nuclei selected from a 3-sulfoalkylbenzothiazole nucleus, a 3-sulfoalkylbenzoselenazole nucleus and a 1- sulfoalkylnaphtho[1,2-d]thiazole nucleus, the two heterocyclic nuclei of each of said dyes being joined by a trimethine chain which contains an alkyl group on the meso carbon atom thereof.

This application is a continuation-in-part of my copending US. application Ser. No. 686,831, filed Nov. 30, 1967 now abandoned.

This invention relates to novel combinations of cyanine dyes for extending the sensitivity of photographic silver halide emulsions to certain wavelength radiations in the red region of the spectrum, and more particularly to novel silver halide emulsions containing these novel dye combinations, and to photographic elements prepared therewith.

It is Well known in the art of making photographic silver halide emulsions that certain cyanine dyes in combination extend the sensitivity of photographic silver halide emulsions in greater degree than do the individual dyes in such emulsions. This effect has often been referred to in the prior art as a kind of supersensitization. Such proposed combinations in conventional emulsions having an average silver halide grain size greater than about 0.5 micron have been found useful in a number of photo graphic applications. However, none have proved entirely satisfactory for use in recording certain narrow bands in the red region of the spectrum. For example, in the field of recording solar or astronomical observations, none of the proposed combinations have shown the required sensitivity and desired freedom from graininess of image for satisfactory recording of the H-u line which lies at 6563 A. This is also true in the field of information recording, where it is desirable to obtain maximum speed at this line with a minimum of graininess in the image. There is evident need, therefore, for new and improved photographic materials having good speed and maximum sensitivity in a relatively narrow band centered at about 6563 A.

It is, accordingly, an object of this invention to provide novel cyanine dye combinations for extending the sensitivity of photographic silver halide emulsions to the red region of the spectrum with maximum sensitivity occurring at about 65 63 A. Another object of this invention is to provide novel silver halide emulsions capable of accurate recording of fine detail at about 6563 A. Another object of this invention is to provide photographic elements comprising a support material having at least one layer thereon containing a novel emulsion of the invention. Other objects will be apparent from this disclosure and the appended claims.

I have now made the surprising discovery that highly advantageous dye combinations comprising (1) certain carbocyanine dyes having a maximum sensitivity peak at a Wavelength shorter than 6563 A. and preferably from about 6350 A. to 6550 A. (i.e., 635 to 655 nm.) and (2) certain closely related carbocyanine dyes having a maximum sensitivity peak at a wavelength longer than 6563 A. and preferably from about 6600 A. to 6850 A. (i.e., 660 to 685 nm.) are particularly useful for extending the spectral sensitivity range of fine grain photographic silver halide emulsions. These emulsions are useful for recording a variety of wavelength exposures. They are especially useful for recording fine detail of astronomical observations through narrow band exposures which may have a band width of /2 transmission (i.e., as measured at the 50 transmission point) of 0.5 A. to 3.0 A. These dye combinations, I have further discovered, have the added advantage that they increase the inherent blue speed of fine grain emulsions, and reduce granularity by a factor of 4 or 5 times over that of larger, coarser grained emulsions heretofore employed in this recording field. The increased inherent blue speed obtained with the dye combination is particularly unexpected because the dyes, When used individually or even in combinations have a substantial desensitizing effect on the inherent blue speed of conventional emulsions, i.e., emulsions having an average silver halide grain size greater than about 0.5 micron. Furthermore, the novel dye combinations of the invention give homogeneous and smooth flowing fine grain emulsions having excellent keeping stability, and cause little, if any, fogging in fresh or incubated emulsions. Accordingly, this invention provides photographic materials well suited for recording the radiations in the above specified region of 6563 A. in fine detail.

From the foregoing description, it will be apparent that the principal advantages of this invention, as compared with prior art proposals, may be summarized as follows:

(1) Increased inherent blue speed of fine grain emulslons;

2) Increased speed at 65 63 A. for recording fine detail; and

(3) Improvement in granularity over other products that use the H-a line exposure.

As used herein and in the appended claims, the term fine grain refers to silver halide emulsions wherein the silver halide grains have an average grain size of less than about 0.5 micron, and preferably about from 0.04 to 0.40 micron.

The novel dye combinations of the invention comprise (1) a carbocyanine dye having maximum sensitivity peak at a wavelength shorter than 6563 A., and preferably from about 635 to 655 nm., and (2) a carbocyanine dye having maximum sensitivity peak at a wavelength longer than 6563 A., and preferably from about 660 to 685 nm., said dyes 1) and (2) in each instance comprising first and second heterocyclic nuclei selected from the group consisting of a 3-sulfoalkylbenzothiazole nucleus, a 3- sulfoalkylbenzoselenazole nucleus, and a l-sulfoalkylnaphtho[1,2-d]thiazole nucleus, the two heterocyclic nuclei of each dye being joined together by a trimethine linkage having an alkyl group substituted at the mesocarbon atom thereof.

The proportions of the dyes employed in the dye combinations of the invention can vary over practically any limits and still give good results; however, the most efiicacious combinations are those containing the respective dyes in the proportions of about from 10 to 90% by weight of dye (1) and conversely about from 90 to 10% by weight of dye (2). The total amount of these dyes is advantageously about from 0.10 to 1.0 gram per mole of silver.

The preferred carbocyanine dye compounds (1) of the invention have maximum sensitivity at a wavelength of about 635 to 655 nm., and include those dyes represented by the following formula:

wherein R represents an alkyl group (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, etc.; R and R each represents a sulfoalkyl group, e.g., B-sulfoethyl, 'y-sulfopropyl, 'y-sulfobutyl, w-sulfobutyl, etc.; and Z and Z each represents the non-metallic atoms necessary to complete a benzothiazole nucleus, e.g., benzothiazole, 5-chlorobenzothiazole, S-bromobenzothiazole, S-methoxyhenzothiazole, 5 butoxybenzothiazole, 5 methylbenzothiazole, 5butylbenzothiazole, and the like nuclei.

The preferred carbocyanine dye compounds (2) of the invention have maximum sensitivity at a wavelength of from about 660 to 685 nm., and include those dyes represented by the following formula:

wherein R R and R each represents a value given for R, R and R respectively; and, Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from (a) wherein each of Z and Z is a benzoselenazole nucleus, e.g., benzoselenazole, S-methoxybenzoselenazole, S-methylbenzoselenazole, etc., (b) wherein each of Z and Z is a naphtho- [1,2-d] thiazole nucleus, and (c) wherein Z is a naphtho- [1,2-d] thiazole nucleus and Z is a benzothiazole nucleus.

It will be understood that certain mono salts of the dyes defined by Formulas I and II above are included in these definitions, since such salts improve the solubility of the dyes without materially altering the sensitivity maximum peaks thereof. For example, useful mono salts of the dyes are alkali metals such as the monosodium, the monopotassium etc. salts, the mono salts of the dyes with trialkylamines such as the monotriethylamine, etc. salts, and the like.

The following dyes designated Dye 0-1 and Dye C-II are representative of the prior art (outside this invention) and are included herein only for comparison purposes.

C-II 3,3,9-triethy1'5,5-diehloro-thiacarbocyanine bromide.

D ye

III Anhydro-5,5-dichlin'o-9-ethyl-3,3-di(4-sulfobutyl) thiacarbocyanine hydrox e.

1 0 Compound 1 CH2) 4 S 0 H cyanine hydroxide.

30 V Anhydr0-9-ethyl-5,5-dimethyl-3,3-di(3-sulfopropyl) thiacarbocyanine hydroxide, triethylamine salt.

Included among the carbocyanine dyes defined by Formula II above are the following typical dye compounds.

Dye No. Compound VI Anhydro-Q-ethyl-fi-methoxy-3,3-di(3-sulfopropyl) selenacarbocyanine hydroxide, sodium salt VIII Anhydro-9-ethyl-3,3-di(3-su1fopropyl)-4,5-benzothiacarbocyanine hydroxide, sodium salt The above Dyes III to VII and related dyes have, in general, been previously described in the prior art and are prepared, for example, by the general methods set forth in R. H. Sprague US. Pat. No. 2,503,776, issued Apr. 11, 1950; and A. E. Rosenoff U.S. Pat. No. 3,177,- 210, issued Apr. 6, 1965.

PREPARATION OF DYE VIII A mixture of 2.7 g. (1 mol.) anhydro-2-methyl-3-(3- sulfopropyl)benzothiazolium hydroxide and 4.1 g. (1 mol.) of anhydro-Z-(Z-ethoxy 1 butenyl)-1-(3-sulfopropyl)naphtho[1,2-d]thiazolium hydroxide in 25 ml. of cresol is refluxed for 2 minutes. The mixture is chilled, stirred with an excess of ether, the ether decanted from the sticky residue, more ether added with stirring, and the ether again decanted. The residue is treated with 5.1 g. of sodium iodide in 300 ml. of acetone, with stirring. The dye precipitates as the monosodium salt and is collected on a filter funnel, washed with acetone and dried. The yield of dye is 4.3 g. (66%), MP. 244245 C.

The above intermediate anhydro-2-(2-ethoXy-l-butenyl) 1 (3 sulfopropyl)naphtho[1,2-d]thiazolium hydroxide is prepared by refluxing for a period of 5 minutes a mixture of 64.2 g. (1 mol.) of anhydro-2- methyl-1(3-sulfopropyl)naphthol[1,2 d]thiazolium hydroxide and 70.4 g. (1 mol. +100% excess) of triethyl orthopropionate in 70 ml. of distilled cresol. On cooling the mixture the product crystallizes from solution. The light green solid is then collected, washed with acetone and dried. The crude yield of this compound 2o 23 4 2) is 64 g. (79%).

According to the invention, one or more of the carbocyanine dyes represented by Formula I above are incorporated with one or more of the carbocyanine dyes rep resented by Formula II above. The invention is particularly directed to fine grain gelatino-silver-halide developing-out emulsions, including fine cubic grain silver halide emulsions. However, the dye combinations can also be employed in silver halide emulsions in which the carrier or vehicle is a hydrophilic colloid other than gelatin, such as for example, albumin, agar-agar, gum arabic, alginic acid, etc., or a hydrophilic resin such as polyvinyl alcohol, polyvinyl pyrrolidone, a cellulose ether, a partially hydrolyzed cellulose acetate, acrylamide polymers, etc., which has no deleterious effect upon the light-sensitive silver halide. The dyes of Formula I and Formula II can be employed in the combinations of the invention in various concentrations depending upon the particular emulsion, concentration of the silver halide, particular results desired, etc. The optimum concentration of an individual sensitizing dye can be determined in a manner Well known to those skilled in the art by measuring the sensitivity of a series of test portions of the same emulsion, each portion containing a different concentration of the sensitizing dye. As previously mentioned, the preferred combinations range about from to 90% to the carbocyanine dye of Formula I and conversely about from 90 to 10% of the carbocyanine dye of Formula II. The optimum concentration of the dye combinations can, of course, be readily determined in the same manner, by measuring the sensitivity of a series of test portions of the same emulsion, each portion containing different concentrations of the individual dyes in the combination. In determining the optimum concentration for the subject dye combinations, it is advantageous to employ, at first concentrations of the individual dyes less than their optimum concentrations. The concentrations of the individual dyes can be increased until the optimum concentration of the dye combination is determined.

The methods of incorporating sensitizing dyes in silver halide emulsions are well known to those skilled in the art and these known techniques are employed in dispersing the dyes of the invention in the emulsions. These dyes can be directly dispersed in the emulsions, or they can first be dissolved in some convenient solvent, such as pyridine, methyl alcohol, acetone, etc. (or mixtures of such solvents), or diluted with water in some instances, and added to the emulsions in the form of these solutions. If desired, the dyes can be separately dissolved in a given solvent and added separately to the emulsion, or they can be dissolved in the same or different solvent and these solutions mixed together before addition is made to the silver halide emulsions. The dyes of the invention can be dispersed in the finished emulsions and should be uniformly distributed throughout the emulsions before the emulsions are coated on a suitable support, such as paper, glass, cellulose ester film, polyvinyl resin film (e.g., polystyrene film, polyvinyl chloride film, etc.), polyester film, etc. The following procedure has been found quite satisfactory: Stock solutions of the dyes of Formulas I and II above are prepared by separately dissolving these dyes in appropriate solvents as described above. Then, to the flowable silver halide emulsion, the desired amount of stock solution of one of the dyes is slowly added while stirring the emulsion. Stirring is continued until the dye is thoroughly incorporated in the emulsion. Then, the desired amount of stock solution of the other dye is slowly added to the emulsion while stirring. Stirring is continued until the second dye is thoroughly incorporated in the emulsion. The emulsions can then be coated on a suitable support and the coating allowed to dry. In some instances, it may be desirable to heat the sensitized emulsion for a few minutes before coating onto the suitable support. The details of such coating techniques are well known to those skilled in the art. The foregoing procedure and proportions are to be regarded only as illustrative. Clearly, the invention is directed to any fine grain silver halide emulsion containing a combination of the aforesaid dyes whereby a supersensitizing effect is obtained, e.g., gelatino silver chloride, -chlorobromide, -chloroiodide, chlorobromoiodide, bromoiodide, etc., emulsions.

The fine grain emulsions employed in accordance with this invention can be prepared in any suitable manner, such as by the process described in the article entitled Properties of Photographic Emulsion Grains by Klein and Moisar, The Journal of Photographic Science, vol. 12, 1964, pages 242-245; or, by the method described by Illingsworth in French Patent 1,497,202 and corresponding U.S. patent application Ser. No. 500,366, filed Oct. 21, 1965, and now abandoned by maintaining, during emulsion precipitation, a pH of no more than 4.0 and the pAg within the range of 8.6 to 9.2. Also useful are the very fine grain silver halide emulsion prepared in the presence of an acid substituted aryl mercaptan, e.g., thiosalicylic acid, as described by Sutherns in U.S. patent application Ser. No. 622,034, filed Mar. 10, 1967, and now U.S. Pat. No. 3,519,427.

The invention is further illustrated by the following examples. Comparison Example 1 employs prior art coarse grain silver halide.

Example 1 This example illustrates the desensitizing effect of the individual dyes defined by Formulas I and II and certain combinations thereof on conventional type emulsions when incorporated therein. The dyes are added to a silver bromoiodide emulsion containing 0.77 mole percent iodide of the type described by Trivelli and Smith, Phot. Journal, 79, 330 (1939), and having an aver-age grain size of 0.75 micron. The individual dyes and dye combinations, dissolved in suitable solvents, are added to separate portions of the emulsion at the concentrations indicated in Table 1 hereinafter. In each case, after being digested at about 50 C. for 10 minutes, the emulsion is coated at a coverage of 432 mg. silver per square foot on a cellulose acetate film support. A sample of each coating is exposed on an Eastman IB Sensitometer through Kodak Wratten Filters 35 +38A to determine blue sensitivity and to a wedge spectrograph, processed for three minutes in Kodak Developer D-l9 which has the following composition:

G. N-methyl-p-aminophenol sulfate 2.0 Hydroquinone 8.0 Sodium sulfite (desiccated) 90.0 Sodium carbonate (monohydrate) 52.5 Potassium bromide 5.0

Water to make 1.0 liter.

and then fixed in a conventional sodium thiosulfate fixing bath, washed and dried. Densitometric measurements are then made of the developed images of each coating. The relative speed values are calculated based on an arbitrary relative speed of 100 for the control containing no dye. The results are listed in the following table together with the sensitizing ranges and maximum sensitivities.

sitize conventional silver halide emulsions having an average silver halide. grain size above 0.5 micron.

Example 2 This example illustrates that the combination of dyes of the invention defined by Formulas I and II above greatly increase the relative speed of fine grain emulsions, in the desired maximum sensitivity region of 6563 A., as compared with (a) the speed of the individual dyes in the same fine grain emulsion, and (b) as compared with the speed of the prior art combination of Dye C-I and Dye C-II in both the fine grain and in the large coarse grain emulsion, which latter is arbitrarily set at 100 for comparison purposes. The procedure for the above testing is as follows.

A fine grain silver bromoiodide gelatin emulsion is prepared in essentially the same manner as described in Example 1 of Illingsworth US. patent application Ser. No. 500,366 filed Oct. 21, 1965, and is sulfur and gold sensitized. The average grain size of the silver halide crystals in this fine grain emulsion is of the order of about 0.35 micron. Also prepared is a coarse grain 0.75 micron emulsion duplicating that of above Example 1. The dyes comprising comparison Dyes C-I and 0-H and Dyes III to VIII of the invention are incorporated individually, and in certain combinations thereof in separate portions of the above emulsions, specific concentrations, as indicated in Table 2 hereinafter. A control of the fine grain emulsion containing no dye is also included in this table. After digestion at C. for 10 minutes, each of the samples is then coated at a coverage of 450 mg. silver per square foot on a cellulose acetate film support. The cured coatings are then exposed and processed by the procedure described in above Example 1. The sensitization ranges and the relative blue speed and the relative speed at 6563 A. are measured. The results are recorded in the following Table 2.

TABLE 2 601107 dye, Sensitization Relative speed g. m e range Dye N0. silver (nm.), to Blue At 6,563 A.

0.75,. emulsion c-1 and 0-11...{ 700 106 100 0.85;. emulsion Control 0. 00 71 730 58 69 0.20 700 78 o. 30 700 76 73 0.15 750 91 0.15 750 107 0.15 800 118 132 0.20 756 112 13s III+VI 8: 750 118 174 III-l-VII 95%? 790 91 182 0.125 IV+VI 075 740 92 V+VI 8: 760 123 166 1v+vn 8: 780 118 166 V+VIII 8: 750 126 Referring to above Table 1, it will be seen that the relative blue speed for each of the dyes and dye combinations listed is substantially less than that shown for the control containing no dye. This result clearly shows that the dyes employed in this invention actually desen- Referring to above Table 2, it will be noted that the dye combinations of the invention provide fine grain emulsions and photographic elements therewith that are characterized by markedly increased relative speeds ranging from 145 to 182 at the desired 6563 A. line, as

compared to the prior art combination of Dyes C-I and C-II showing in the 0.75 and the 0.35 1 emulsions relative speeds of only 100 and 60, respectively, for this spectral line.

Example 3 This example illustrates the significant improvement in granularity of the novel fine grain emulsions of the invention containing the novel dye combinations. RMS granularities (see I. H. Altman The Measurement of RMS Granularity, Applied Optics, vol. 3, No. 1, January 1964, pp. 35-38) are run and plotted at a density of 0.6 log E above fog. For this test, the same fine grain emulsion is used for the dye combinations of the invention, while the same 0.75 micron grain size emulsion is used for the prior art dye combination (C-I and C-II), as described in above Example 2. Also, the same coating and processing procedures are carried out in each case, as set forth in Example 2. The results are listed in the following Table 3 wherein the higher the number shown for granularity, the grainier is the sample tested.

TABLE 3 Dye cnc., g./1 nole silver Dye No.

o-I and CII rv+vn IV+VL Control By reference to above Table 3, it will be seen that the lowest granularity, i.e., 0.35, is recorded by the fine grain control sample, and that the samples containing the dye combinations of the invention (IV+VII, and IV+VI) show only a moderate increase in granularity over the control to 0.6. In contrast thereto, the prior art sample containing the dye combination C-I and C-II shows a relatively large value for granularity of 3.0. These results clearly indicate that the novel emulsions and elements of the invention are 4 or 5 times less grainy as compared to the conventional prior art large grain emulsion sample containing the dye combination of C-1 and C-II.

Fine grain photographic silver halide emulsions such as those listed above, containing the dye combinations of the invention can also contain such addenda as chemical sensitizers, e.g., sulfur sensitizers (e.g., allyl thiocarbamate, thiourea, allylisothiocyanate, cystine, etc.), various gold compounds (e.g., potassium chloroaurate, auric tri chloride, etc. (see Baldsiefen, U.S. Pat. No. 2,540,085, issued Feb. 6, 1951; Damschroder, U.S. Pat. No. 2,597,- 856, issued May 27, 1952 and Yutzy et a1. U.S. Pat. No. 2,597,915, issued May 27, 1952), various palladium compounds such as palladium chloride (Baldsiefen, U.S. Pat. No. 2,540,086, issued Feb. 6, 1951), potassium chloropalladate (Stautfer et al., U.S. Pat. No. 2,598,079, issued May 27, 1952), etc., or mixtures of such sensitizers; antifoggants such as ammonium chloroplatinate (Trivelli et al. U.S. Pat. No. 2,566,245, issued Aug. 28, 1951), ammonium chloroplatinite (Trivelli et al., U.S. Pat. No. 2,566,263, issued Aug. 28, 1951), benzotriazole, nitrobenzimidazole, 5 nitroimidazole, benzidine, mercaptans, etc. (see Mees-The Theory of the Photographic Process, MacMillan Pub., 1942, page 460), or mixtures thereof. The fine grain photographic silver halide emulsions containing the dye combination of the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxy starch or oxy plant gums, and the like. The emulsion layers can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain in some cases additional spectral sensitizing dyes. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. Among the useful color formers are the monomeric and polymeric color formers, e.g., pyrazolone color formers, as well as phenolic, heterocyclic and open chain couplers having a reactive methylene group. The color forming couplers can be incorporated into the photographic silver halide emulsions using any suitable technique, e.g., techniques of the type shown in Jelley et al. U.S. Pat. 2,322,027, issued June 15, 1943, Fierke et al. U.S. Pat. 2,801,171, issued July 30, 1957, Fisher U.S. Pats. 1,055,155 and 1,102,028, issued March 4, 1913 and June 30, 1914, respectively, and Wilmanns U.S. Pat. 2,186,849 issued Jan. 9, 1940. They can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazolidones, and the like.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be efiected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

I claim:

1. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to by weight of a carbocyanine dye having a maximum sensitivity peak at a wavelength shorter than 6563 A., and (2) 90 to 10% by weight of a carbocyanine dye having a maximum sensitivity peak at a wavelength longer than 6563 A., said dyes (1) and (2) each comprising first and second heterocyclic nuclei selected from the group consisting of a 3-sulfoalkylbenzothiazole nucleus, a 3-sulfoalkylbenzoselenazole nucleus and a l-sulfoalkylnaphtho [1,2-d]thiazole nucleus, said first and second nuclei of each dye being joined together by a trimethine linkage which is substituted on the meso carbon thereof by an alkyl group, the total weight of the dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion.

2. A fine grain emulsion in accordance with claim 1 wherein said silver halide has an average grain size of about from .04 to 034 micron.

3. A fine grain emulsion in accordance with claim 1 containing a color former.

4. A fine grain emulsion in accordance with claim 1 wherein the total weight of said dyes is about from 0.10 to 1.0 gram per mole silver.

5. A fine grain emulsion in accordance with claim 1 wherein said emulsion is a silver bromoiodide emulsion.

6. A fine grain emulsion in accordance with claim 1 wherein said dye (1) has a maximum sensitivity peak at from about 635 to 655 nm., and said dye (2) has a maximum sensitivity peak at from about 660 to 685 nm.

7. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of from about 0.04 to less than 0.5 micron, containing a dye combination of (1) 10 to 90% by weight of a carbocyanine dye having a maximum sensitivity peak at from about 635 to 655 nm. and represented by the formula:

and (2) 90 to by weight of a carbocyanine dye having a maximum sensitivity peak at from about 660' to 685 nm. and represented by the formula:

wherein R and R each represents an alkyl group containing from 1 to 4 carbon atoms; R R R and R each represents a sulfoalkyl group containing 1 to 4 carbon atoms; Z and Z each represents the non-metallic atoms necessary to complete a benzothiazole nucleus; and Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of: (a) wherein each of Z and Z is a benzoselenazole nucleus; (b) wherein Z and Z each represents a naphtho[l,2-d]thiazole nucleus; and, (c) wherein Z is a naphtho[1,2-d]thiazole nucleus and Z is a benzothiazole nucleus, the total weight of dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion.

8. A fine grain emulsion in accordance with claim 7 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

9. A fine grain emulsion in accordance with claim 7 containing a color former.

10. A fine grain emulsion in accordance with claim 7 wherein the total weight of said dyes is from 0.10 to 1.0 gram per mole of silver.

11. A fine grain emulsion in accordance with claim 7 wherein said emulsion is a silver bromoiodide emulsion.

12. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to 90% by weight of the dye anhydro-S,5-dichloro-9-ethyl-3,3- di(4-sulfobutyl)-thiacarbocyanine hydroxide and (2) 90 to 10% by weight of the dye anhydro-9-ethyl-5-methoxy- 3,3 di(3 sulfopropyl) selenacarbocyanine hydroxide, sodium salt, the total weight of dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion.

13. A fine grain emulsion in accordance with claim 12 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

14. A fine grain emulsion in accordance with claim 12 wherein said silver halide emulsion is a silver bromoiodide emulsion.

15. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to 90% by weight of the dye anhydro-5,5'-dichloro-9-ethyl-3,3'- di(4-sulfobutyl)-thiacarbocyanine hydroxide and (2) 90 to 10% by weight of the dye anhydro-9-ethyl-3,3'-di(3- sulfopropyl -4,5 ;4',5 '-dibenzothiacarbocyanine hydroxide salt, the total weight of dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion.

16. A fine grain emulsion in accordance with claim 15 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

17. A fine grain emulsion in accordance with claim 15 wherein said silver halide emulsion is a silver bromoiodide emulsion.

18. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to 90% by weight of the dye anhydro-S,5-dichloro-9-ethyl-3,3- di(3-sulfobutyl)-thiacarbocyanine hydroxide and (2) 90 to 10% by weight of the dye anhydro-9-ethyl-5-metlioxy- 3,3-di(3-sulfopropyl)-selenacarbocyanine hydroxide salt, the total Weight of dye combination present in the emul- 12 sion being an amount effective to spectrally sensitize said emulsion.

19. A fine grain emulsion in accordance with claim 18 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

20. A fine grain emulsion in accordance with claim 18 wherein said silver halide emulsion is a silver bromoiodide emulsion.

21. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size Within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to by weight of the dye anhydro-9-ethyl-5,5-dimethyl-3,3-di (3-sulfopropyl)-thiacarbocyanine hydroxide salt and (2) 90 to 10% by weight of the dye anhydro-9-ethyl-5-methoxy-3,3 -di 3-sulfopropyl -selenacarbocyanine hydroxide salt, the total weight of dye combination present in the emulsion being an amount effective to spectrally semitize said emulsion.

22. A fine grain emulsion in accordance with claim 21 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

23. A fine grain emulsion in accordance with claim 21 wherein said silver halide emulsion is a silver bromoiodide emulsion.

24. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to 90% by Weight of the dye anhydro-S,5-dichloro-9-ethyl-3,3'-di(3- sulfobutyl)thiacarbocyanine hydroxide and (2) 90 to 10% by weight of the dye anhydro-9-ethyl-3,3'-di(3-sulfopropyl) 4,5;4',5 dibenzothiacarbocyanine hydroxide salt, the total weight of dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion.

25. A fine grain emulsion in accordance with claim 24 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

26. A fine grain emulsion in accordance with claim 24 wherein said silver halide emulsion is a silver bromoiodide emulsion.

27. A fine grain photographic siliver halide emulsion wherein said silver halide grains have an average grain size within the range of 0.04 to less than 0.5 micron, containing a dye combination comprising (1) 10 to 90% by Weight of the dye anhydro-9-ethyl-5,5'-dimethyl-3,3'-di (3-sulfopropyl)-thiacarbocyanine hydroxide salt and (2) 90 to 10% by weight of the dye anhydro-9-ethyl-3,3'-di (3-sulfopropyl)-4,5 benzothiacarbocyanine hydroxide salt, the total weight of dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion. v

28. A fine grain emulsion in accordance with claim 27 wherein said silver halide has an average grain size of about from .04 to 0.4 micron.

29. A fine grain emulsion in accordance with claim 27 wherein said silver halide emulsion is a silver bromoiodide emulsion.

30. A photographic element comprising a support coated with at least one layer of a fine grain photographic silver halide emulsion of claim 1.

31. A photographic element comprising a support coated with at least one layer of a fine grain photographic silver halide emulsion of claim 7.

32. A photographic element comprising a support coated with at least one layer of a fine grain silver halide emulsion of claim 12.

33. A photographic element comprising a support coated with at least one layer of a fine grain photographic silver halide emulsion of claim 15.

34. A photographic element comprising a support coated with at least one layer of a fine grain photographic silver halide emulsion of claim 18.

35. A photographic element comprising a support coatedwith at least one layer of a fine grain photographic silver halide emulsion of claim 21.

36. A photographic element comprising a support coated with at least one layer of a fine grain silver halide emulsion of claim 24.

37. A photographic element comprising a support coated with at least one layer of a fine grain silver halide emulsion of claim 27.

38. A fine grain photographic silver halide emulsion wherein said silver halide grains have an average grain size within the range of from about 0.04 to less than 0.5 micron, containing a dye combination of (l) 10 to 90% by weight of a carbocyanine dye having a maximum sensitivity peak at from about 635 to 655 nm. and represented by the formula:

and (2) 90 to 10% by Weight of a carbocyanine dye having a maximum sensitivity peak at from about 660 to 685 nm. and represented by the formula:

/'Z2\ I l l 1 l e R5'NC=CH|C=O=NR9 wherein R and R each represents an alkyl group; R R R and R each represents a sulfoalkyl group; Z and Z each represents the non-metallic atoms necessary to complete a benzothiazole nucleus; and, Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of: (a) wherein each of Z and Z is a benzoselenazole nucleus; (b) wherein Z and Z each represents a naphtho [l,2-d]thiazole nucleus; and, (c) wherein Z is a naphtho[1,2-d]thiazo1e nucleus and Z is a benzothiazole nucleus, the total weight of dye combination present in the emulsion being an amount effective to spectrally sensitize said emulsion.

39. A fine grain emulsion in accordance with claim 38 containing a color former.

40. A fine grain emulsion in accordance with claim 38 wherein the total Weight of said dyes is from 0.10 to 1.0 gram per mole.

41. A fine grain emulsion in accordance with claim 38 wherein said emulsion is a silver bromoiodide emulsion.

References Cited UNITED STATES PATENTS 2,533,426 12/1950 Carroll et a1 96-l04 NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 96106