CA1121644A - Silver halide precipitation and methine dye spectral sensitization process and products therefor - Google Patents

Abstract

SILVER HALIDE PRECIPITATION AND METHINE DYE SPECTRAL
SENSITIZATION PROCESS AND PRODUCTS THEREOF

Abstract of the Disclosure A method Or precipitating silver halide is disclosed in which a methine spectral sensitizing dye is introduced into the reaction vessel in which precipitation of silver halide is performed after nucleation of the silver halide grains has occurred and before completion of silver halide precipitation. The silver halide grains spectrally sensitized in this manner exhibit relatively high minus blue speeds.

Description

Thls dlsclosure ls directed to a process Or preparlng spectrally sensltlzed sllver hallde gralns and to-products formed by the spectrally sensltlzed sllver hallde gralns.
In spectrally sensltizing silver halide emulsions it is conventional practice to adsorb the spectral sensitlzing dyes to the surfaces of the silver halide gralns after they have been completely formed. However, there are some variant teachings in the art.
Hill U.S. Patent 2,735,766, issued February 21, 1956, discloses that photographlc spectral sensitlzing dye wandering can be eliminated or reduced by introduclng a merocyanine spectral sensitizing dye during silver halide precipitation. H111 teaches to blend the spectral sensitizing dye with either the silver salt or the halide salt prior to bringlng these salts together to form silver halide. Hill speciflcally states that the teachings do not extend to other optical sensitizing dyes, such as those of the carbocyanine class.
Philippaerts U.S. Patent 3,628,960, issued December 21, 1971, in discussing methlne dye spectral sensitization Or a blended emulsion states that the dyes can be incorporated in a separate addition or can be added as a mixture with one or more ingredlents used in the formatlon of the dlfferent sllver halide grains, during physlcal or chemical ripening or during another step preceding the coating of the emulsion.

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. .

'-"` 112i64g In one aspect, thls lnventlon ls dlrected to a method of preparing a spectrally sensltlzed radlatlon-sensitlve sllver hallde emulslon comprlsing lntroduclng lnto a reactlon vessel an aqueous solutlon of a sllver salt, an aqueous solutlon of a hallde salt, a peptlzer and a methlne spectral sensltlzlng dye. The dye ls added to the reactlon vessel durlng the course of lntroducing at least one of the aqueous salt solutlons. In thls method the lmprovement comprises delaylng addltlon of the spectral sensltizing dye until sllver halide grain nuclei are present wlthln the reactlon vessel.
In another aspect, the invention relates to the products of the process descrlbed above.
Thls lnventlon offers one or more of the following advantages: (1) improved photographic speeds, partlcularly minus blue speeds; (2) better shelf life sta-billty; (3) substantial eliminatlon of dye desorptlon and staining; (4) altered dye absorptlon characterlstlcs, and/or (5) control or modificatlon of the sllver hallde grain crystal hablt.
Thls method ls generally appllcable to any con-ventlonal method of forming radiatlon-sensltive sllver hallde gralns in whlch an aqueous solution of a silver 112~6~4 salt and an aqueous solution of a hallde salt are brought into association to form radiatlon-sensltlve sllver halide grains as a reactlon product. Thls method ls particularly appllcable to the spectral sensitlzatlon of radiatlon-sensitlve sllver chlorlde, sllver lodlde, silver bromlde, silver bromoiodide, sllver chlorobromlde, sllver chlorolodlde and sllver chlorobromolodlde crystals.
It is generally preferred that the sllver halolodlde crystals contaln less than about 10 mole percent lodide, based on total hallde, although in specialized appllcations high iodide sllver halolodldes can be advantageous.
The method of thls inventlon for preparing and concurrently spectrally sensitizing silver halide emulsions can be practiced by modifying, in the manner descrlbed below, conventional procedures for slngle Jet and double ~et preparation of silver halide emulsions. In single Jet precipltatlons an aqueous solution of a silver salt, such as sllver nltrate, is run into a reaction vessel containing an aqueous solution of a halide salt, such as an alkali e.g. sodium or potassium halide, and a peptizer. In double Jet preclpltatlons the aqueous silver salt and the aqueous halide salt are concurrently and separately introduced into the reaction vessel. Typlcally at least a portion of the peptizer is initially present in the reaction vessel and additional peptizer is commonly introduced into the reaction vessel during the run. An illustrative conventional single Jet silver halide precipitation technique is that disclosed by Trivelli and -:112~644 and Smlth, "The Photographlc Journal", No. LXXIX, May 1939, pp. 330-338. Nletz and Russell U.S. Patent 2,222,264, lssued November 19, 1940, ls lllustratlve of a double ~et silver hallde emulslon preclpltatlon process. Single and double ~et sllver hallde emulslon preclpitation methods are also discussed in Chapters I and II of Mees and James, The Theory of the Photographlc Process, Third Editlon, the MacMillan Company, 1966.
Upon inltial introduction lnto the reactlon vessel the dlssolved sllver salt reacts wlth dlssolved hallde salt to form silver hallde crystals. This initial phase of silver halide emulsion preparation in whlch new silver hallde crystals are being formed is referred to as nucleation. During subsequent addition of silver salt, additional silver halide formed as a reaction product can be precipitated onto these nuclei causing the mean size of the silver halide grains to increase, ultimately resulting in silver halide grains of the desired mean particle size.
Although nucleation and continued silver halide grain growth most commonly occur in a single reaction vessel, it is recognized that nucleation can be undertaken in one reaction vessel, employing single or double ~et precipitation tech-niques, and the resulting fine grained silver halide emul-sion fed into a second reaction vessel along with or in advance of additional amounts of halide and silver salts to facilitate continued grain growth. Multiple stage or cascade silver halide precipitation techniques of this type are 112i6~4 illustrated by Terwilliger et al, "Precipitation of Silver Halide Emulsions in a Continuous Reaction", Item 14987, Research Disclosure, September 1976, and Terwilliger et al U.S. Patent 4,o46,576, issued September 6, 1977.
While introducing the aqueous silver salt into the reaction vessel containing the silver halide nuclei a conventional methine spectral sensitizing dye is introduced into the reaction vessel. Where the spectral sensitizing dye is itself soluble, it can be introduced as an aqueous solution without any additional or auxiliary solvent being present. In most instances it is convenient to dissolve the spectral sensitizing dye in an organic water-miscible solvent, such as acetone or an alcohol of from 1 to 3 carbon atoms. Surfactants and/or peptizers can also be present in the spectral sensitizing dye solutions. The spectral sensitizing dye solution can be introduced into the reaction vessel in a separate jet or can be introduced by mixing with the aqueous silver salt and/or the aqueous halide salt being run into the reaction vessel. The spectral sensitizing dye can be introduced into the reaction vessel continuously or can be introduced into the reaction vessel in discrete increments. For example, the introduction of the silver salt and/or the halide salt can be periodically interrupted while the spectral sensitizing dye is introduced. Except as specifically discussed below, techniques similar to those employed by Hill U.S. Patent 2,735,766, cited above, can be employed -il2~ 4 as well as conventional techniques ~or introducing spectral sens-Ltizing dyes into preformed silver halide emulsions, such as those disclosed in Paragraph XVII., Product Licensing Index, Vol. 92, December 1971, publication 9232.
By delaying introduction of the spectral sensitiz-ing dye until silver halide nuclei are present in the reaction vessel interference with nucleation is avoided.
Preferably introduction of the spectral sensitizing dye is delayed until the mean diameter of the silver halide nuclei is at least about 0.01 (most preferably 0.05) of the mean diameter of the silver halide grains in the finished emulsion. In the most common instance, that is, where the reaction vessel is initially free of silver halide nuclei at the beginning of the silver salt run, adequate nucleation in the absence of dye is achieved by delaying dye introduction until at least about 1 per-cent of the silver salt has been run into the reaction vessel, preferably about 2 percent, optimally at least about 5 percent. (Although spectral sensitizing dye addition is referenced to silver salt addition, it can alternatively be referred to halide salt addition and the same numerical lirnits applied.) Where silver halide nuclei are separately formed and introduced into the reaction vessel, spectral sensitizing dye introduction into the reaction vessel can be commenced concurrently with or even slightly in advance of silver and/or halide salt introduction.

~3 11216~4 The lntroductlon of the spectral sensltlzln~ dye ls preferably regulated so that a substantlal portion of the sllver hallde graln, at least about 10 percent of the sur-Pace area, remalns substantially free of adsorbed dye before precipltation of sllver hallde onto the graln surfaces has been completed. Where the dye ls added ln lncrements durlng lnterruptlons ln the lntroductlon of one or both of the aqueous salts separately contalning sllver and hallde ions, lt is preferred that dye concentrations be limlted to less than about ~0 percent, preferably less than about 10 per-cent, of that requlred to provlde a monolayer coverage of the sllver halide grains. Based on the surface area of the flnal sllver hallde gralns, lt is preferred that the total dye lntroductlon durlng sllver halide precipitatlon--that ls, before completlon of the sllver salt run--be maintalned wlthln about 20 to 80 percent, optlmally between about 30 to 40 percent, of the dye concentration necessary to provlde monolayer coverage. Silver hallde graln coverages can be approxlmately calculated knowlng the graln-slze dlstributlon (i.e., the proportion of gralns falllng lnto differing graln slze classes) of the emulslon and assuming a monomolecular coverage of the adsorbed dye. In actuality, lt has been observed that dye adsorptlon varies as a function of the crystallographlc plane of the sllver halide graln surface, thereby selectively leavlng those planes less favored for adsorption substantially free of dye when the proportlon of the spectral sensltizlng dye ls llmlted.

llZ1644 Introduction Or the spectral sensltlzing dye lnto the reactlon vessel after silver hallde nuclel are present can contlnue throughout sllver hallde preclpltation and can extend beyond sllver hallde precipitatlon. The spectral sensitlzing dye is introduced into the reaction vessel in a spectral sensitizlng amount before at least about 85 percent of the silver salt has been run into the reactlon vessel, preferably before 80 percent of the silver salt has been introduced and most preferably before 75 percent of the silver salt has been introduced. Where no silver halide nuclel are present ln the reaction vessel at the commence-ment of the silver salt run, introduction of the spectral sensitizing dye is advantageous when from 1 to 85 percent, preferably 2 to 80, and most preferably 5 to 75 percent of the silver salt has been introduced.
For best results, after an approprlate delay to permit nucleation (quantltatlvely referenced to the sllver halide nuclei diameters or the 1, 2 and 5 percent silver salt introduction levels, identified above), the spectral sensitizing dye is incrementally or continuously added to the reaction vessel over the course of silver salt lntroductlon thereto and is preferably completed before silver salt introduction to the reaction vessel is completed (quantltatively referenced to the 85, 80 and 75 percent sllver salt lntroductlon levels identified above). The rate of contlnuous dye introduction can be maintained constant or can be accelerated to reflect the increasing .

surface area of the silver halide grains being formed.
Where the dye is added in discrete increments, the in-crements of dye addltion are preferably selected to approximate continuous dye introduction over the selected interval of silver salk introduction. Where introduction of the spectral sensitizing dye is delayed until after larger proportions of the silver salt have been intro-duced into the reaction vessel, larger than about 75 percent of the silver salt, the spectral sensitization achieved begins to approach more closely that observed when the spectral sensitizing dye is run into the reaction vessel after silver precipitation is completed according to conventional techniques.
Where spectral sensitizing dye is run into the reaction vessel during silver salt addition as required above and is additionally run into the reaction vessel during the latter stages of silver salt addition--that is, after at least about 75 percent of the silver salt has been introduced--and/or added to the silver halide emulsion by conventional techniques after silver halide precipita-tion is complete, a further unexpected improvement in spectral sensitization can be obtained. Thus, further spectral sensitization by conventional techniques and/or toward the end of the silver salt run in combination with spectral sensitization according to the preferred embodiments of this method as described above is specifi-cally contemplated and recognized to be advantageous.
Any conventional spectral sensitizing dye which will alone improve the spectral response of the emulsion can be employed in combination llZ164~

wlth the methine spectral sensltizlng dyes lntroduced lnto the reaction vessel accordlng to the method descrlbed above.
It ls speciflcally contemplated to use the same methine dyes to spectrally sensitize the emulsions during silver halide precipitation as described above and during the latter stages of silver halide precipitation or after completion of silver halide precipitation.
One or more conventional methine spectral sensitiz-ing dyes can be introduced into the reaction vessel during silver halide precipitation as described. Such dyes are described, for example, in Brooker et al U.S. Patent 2,526,632 issued October 24, 1950; Sprague U.S. Patent 2,503,776 issued April 11, 1950; Brooker et al U.S. Patent 2,493,748 issued January 10, 1950; and Taber et al U.S. Patent 3,384,486 issued May 21, 1968. Spectral sensitizers which can be used include the cyanines, merocyanines, complex (tri- or tetra-nuclear) cyanines, holopolar cyanines, styryls, hemicyanines (e.g. enamine hemicyanines), oxonols and hemioxonols.
Dyes of the cyanine classes suitable for sensi-20 tizing silver halide can contain such basic nuclei as thethiazolines, oxazolines, pyrrolines, pyridines, oxazoles, thiazoles, selenazoles and imidazoles. Such nuclei can contain alkyl, alkylene, hydroxyalkyl, sulfoalkyl, carboxyalkyl, aminoalkyl and enamine groups and can be fused to carbocyclic or heterocyclic ring systems either unsubstituted or substituted with halogen, phenyl, alkyl, haloalkyl, cyano, or alkoxy groups. The dyes can be symmetrical or unsymmetrical and can contain alkyl, phenyl, llZ164~

enamine or heterocycllc substltuents on the methine or polymethine chaln.
` The merocyanlne dyes can contain the basic nuclel mentioned above as well as acid nuclei such as thiohydantoins, rhodanines, oxazolldenedlones, thlazolidenediones, barbituric acids, thiazolineones, and malononitrlle. These acid nuclel can be appropriately substltuted with alkyl, alkylene, phenyl, carboxyalkyl, sulfoalkyl, hydroxyalkyl, alkoxyalkyl, alkylamino groups, or heterocyclic nuclei. Combinations of these dyes can be used, if desired. In addition, super-sensltizlng addenda which do not absorb visible light can be lncluded, for lnstance, ascorbic acid derivatives, azaindenes, cadmium salts, and organic sulfonic acids as described ln McFall et al U.S. Patent 2,933,390 issued April 19, 1960; and Jones et al U.S. Patent 2,937,089 issued May 17~ 1960.
The methine dyes employed in the practice of this invention are in one preferred form imidazole, oxazole and thiazole methine spectral sensitizing dyes. That is, they are conventional methine spectral sensitizing dyes con-taining at least one lmidazole, oxazole or thiazole nucleus.
In a specifically preferred form~ the spectral sensitizing dyes are cyanine dyes in which at least two nuclei of the dye are chosen from imidazole, oxazole and thiazole nuclei. Specifically preferred are cyanlne dyes in which both of the nuclei are lmldazole, oxazole or thlazole nuclei, such as those represented by the formula:

`` llZiL6~4 -- Z _ __ z ' ~
Rl-N~L=L~d-~C=L~L=L~m--C~L-L~n-~N-Rz wherein d and n each represents a posltive lnteger Or from 1 to 2, m represents a positive integer of from 1 to 3, L represents a methlne group (e.g., -CH= and ( 3) ), Rl and R2 each represents an alkyl group, prefer-ably a lower alkyl contalning from one to four carbon atoms, (e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, decyl or dodecyl)~ a substituted alkyl group, preferably a substituted lower alkyl group containing one to four carbon atoms, such as a hydroxyalkyl group (e.g., ~-hydroxyethyl, y-hydroxypropyl or ~-hydroxybutyl), an alkoxyalkyl group (e.g., ~-methoxyethyl or ~-butoxybutyl), a carboxyalkyl group (e.g., ~-carboxyethyl or ~-carboxybutyl), a sulfoalkyl group (e.g., ~-sulfatoethyl or ~-sulfatobutyl), an acyloxyalkyl group (e.g., ~-acetoxyethyl or ~-propionyloxybutyl), an alkoxy-carbonylalkyl group (e.g., ~-methoxycarbonylethyl or ~-ethoxycarbonylbutyl), an allyl group, an aralkyl group (e.g., benzyl or phenethyl) or an aryl group (e.g., phenyl, tolyl, chlorophenyl, sulfophenyl or carboxyphenyl), and Z and Zl each represents an imidazole nucleus (e.g., lmidazole, alkyl imldazoles, l-aryl lmldazoles, benzlmldazole, l-alkyl benzlmldazoles, l-aryl benzlmlda-zoles, 5-chloro-1-alkyl benzimldazoles, 5-chloro-1-aryl llZ1644 benzimidazoles, 5,6-dichloro-1-alkyl benzlmidazoles, 5,6-dichloro-1-aryl benzimidazoles, 5-methoxy-1-alkyl benzimida-zoles, 5-methoxy-1-aryl benzimidazoles, 5-cyano-1-alkyl benzimidazoles, 5-cyano-1-aryl benzimidazoles, naphth[l,2-d]lmidazole, l-alkylnaphth[1,2-d]imidazoles or l-arylnaphth-[1,2-d]imidazoles), an oxazole nucleus (e.g., oxazole, 4-alkyl oxazoles, 4,5-dialkyl oxazoles, 4-aryl oxazoles, 4,5-diaryl oxazoles, 4-nitrooxazole, benzoxazole, 5-chlorobenzOX-azole, 5- or 6-nitrobenzoxazole, 5-arylbenzooxazole, 5- or 6-alkoxy benzoxazole, 5- or 6-hydroxy benzooxazole, naphtho-[1,2-d]oxazole or nitro-substltuted naphth[1,2-d]oxazoles) or a thiazole nucleus (e.g., thiazole, 4-alkyl thiazoles, 2-thienyl thiazoles, 4-aryl thiazoles, 4,5-diaryl thiazoles, benzothiazole, 5- or 6-chloro or bromobenzothiazoles, 4-alkyl benzothiazoles, 5- or 6-alkoxy benzothiazoles or 4-aryl benzothiazoles).
It will be noted that in some instances, the acid anion, represented by X in the above formula, is included in the substituent represented by R2, such as in dyes containing the betaine type structure. In the nuclei substituents referred to above the alkyl moieties preferably contain from 1 to 4 carbon atoms and the aryl substituents contain from 6 to 10 carbon atoms, e.g., phenyl and naphthyl.
Imidazole, oxazole and thiazole cyanine spectral sensitizing dyes are well known in the art and are disclosed, for example, by A. H. Herz, Photographic Science and Engineering, Vol. 18, No. 2, March-April 1974, pages 207 through 215; VanLare, U.S. Patent 3,482,981, issued December 9, 1962; and in numerous other patents and publications.

l~Zi6~4 Illustratlve o~ preferred merocyanlne spectral sensltizlng dyes are those dlsclosed by Hlll U.S. Patent

2,735,766.
By employlng a slngle Jet or double ~et preclplta-tion technlque as descrlbed above modlfled by the lntroduc-tlon of a methlne spectral sensltlzlng dye lnto the reactlon vessel after sllver hallde nucleatlon has commenced and before completion of the sllver salt run, a silver hallde emulslon can be prepared having unlque propertles. Such an emulslon when coated onto a conventlonal photographlc fllm or paper support to form a photographlc element exhlblts a unlque spectral response whlch dlstlngulshes lt from other-wlse ldentlcally formed photographlc elements ln which the spectral sensitizing dye ls added to the emulsion after completlon of the sllver hallde precipitation. Additional preferred and unexpected characteristics can be imparted to the photographic sllver halide emulslons and elements by employlng ln comblnatlon materials and procedures more specifically discussed below.
Although additional silver hallde graln formatlon (additional nucleation~ can occur after lntroductlon of spectral sensltizing dye into the reaction vessel, it is preferred that nucleation of silver halide grains (forma-tion of new grains) be substantially complete before spectral sensitizing dye is run into the reaction vessel.
One technique which has been found particularly suitable for insuring that additional silver halide precipitates onto existing silver halide grain nuclei is either stepwise or gradually to lncrease the rates of halide and silver salt additions. Such techniques are 6~4 well known ln the art and are dlsclosed, for example, by Kurz U.S~ Patent 3~672~900~ issued June 27~ 1972~ Kurz teaches increasing the rates of silver and halide salt introductions accordlng to the formula:

at 2 + bt + c whereln t equals tlme of preclpitation and a, b and c are constants dependent on factors such as, for example, temper-ature, concentration, metal ion concentratlon and the llke, and wherein the constants can be derived theoretlcally or preferably are derived empirically for the particular condi-tions of operation. The constants are preferably determined for a value wherein new nuclei will not form after initial precipitation whereby all grains will generally grow at the same rate to produce a substantially monodispersed emulsion.
~ he reaction vessels as well as the apparatus and techniques for associating the aqueous silver and halide salt solutions and handling the silver halide emulsion which is formed as a reaction product can be of any convenient conventional type. Such apparatus and techniques are illustrated by Hill, Philippaerts, and Product Licensing Index publication 9232~ paragraph XVII, each cited above.
Such techniques and apparatus are further illustrated by Culhane et al U.S. Patent 3~821~002; Brltlsh Patent 1~302~405; Irie et al U.S. Patent 3~650~757; Audran U.S.
Patent 2~996~382; British Patent 846~190; Frame et al U.S. Patent 3~415~650; Porter et al U.S. Patent 3~785~i77;
Porter et al U.S. Patent 3~782~954; West German OLS 2~555~364;

West German OLS 2~555~885; Posse et al U.S. Patent 3~790~386;
and Forster et al U.S. Patent 3~897~935 `` llZ~64~

Photographic compositions and elements lncluding si~ver halide grains spectrally sensitized as described above can include a number of compatible, conventional features not specifically described. Such conventional aspects of the composition and element types and processes for their preparation and use are disclosed in Product Licensing Index, Vol. 92, December 1971, publication 9232, pages 107-110. The silver halide emulsions can be either unwashed or washed as disclosed by paragraph II.
Emulsion washing. The emulsions can be chemically sensitiz-ed as disclosed by paragraph III. Chemical sensitizing.
The emulsions can contain development modifiers, anti-foggants and stabilizers, developing agents and hardeners, as disclosed in paragraphs IV through VII. Any of the conventional vehicles for the emulsions disclosed in paragraph VIII can be employed. The emulsions and other element layers can be coated on photographic supports as disclosed in paragraph X. Supports. Any conventional spectral sensitizing dye can be incorporated into the emulsion in addition to the spectral sensitizing dyes added during silver halide precipitation. Typical conventional dyes are disclosed in paragraph XV. Spectral sensitization. These additional spectral sensitizing dyes as well as other addenda can be introduced into the emulsion compositions by the techniques disclosed, for example, in paragraph XVII. Methods of addition. The remaining paragraphs of the Product Licensing Index publi-cation disclose still other photographic features and methods of photographic `' \ ' , 11~1644 procesælng whlch can be employed ln comblnatlon with the features of thls lnventlon speclflcally dlsclosed. Both Product Llcensln~ Index and Research Dlsclosure are pub-llshed by Industrlal Opportunltles Llmlted, Homewell, Havant Hampshire, P09 lEF, Unlted Klngdom.
The lnvention ls further illustrated by the followlng examples:
Example 1 - Illustratlng Spectral Sensltlzatlon of a Silver Chloride with a Benzothiazole Merocyanine The following solutions were employed:

Solutlon A
Phthalated gelatin 240 g 1,8-Dihydroxy-3,6-dithiaoctane2.1 g 21.9% by welght sodium chloride in water 246 ml Distilled water 8400 ml Solution B
Sodlum chloride 520 g Distilled water to total volume of 3460 ml Solutlon C
Silver nltrate 1020 g Dlstllled water to total volume of 3460 ml `` ~lZ1644 Solutlon D
Dye I* o.78 g 1:1, volume ratio, acetone to water 500 ml Distilled water 127 ml Solution A was placed in a reaction vessel equipped with a mechanical agitator and ad~usted to a pH of 5.6 and pAg of 6.7 at 60C. Whlle agltatlng Solutlon A, Solutions B and C were separately lntroduced lnto the reaction vessel ln separate ~ets at a uniform rate over a period of 40 minutes while maintaining the pAg of the composition wlthin the reaction vessel at 6.7. Two minutes after starting the lntroductlon of Solutlons B and C, Solutlon D was introduced into the reaction vessel in a separate Jet at a uniform rate, and the addition of Solution D was halted two minutes prlor to the end of the addltlon of Solutions B and C.
The emulslon produced was coagulated by lowering the pH and the supernatant liquid was decanted. After decantlng the supernatant liquid, the coagulum was redispersed in water. This procedure was repeated twice. The final coagulum was dispersed in water at 40C/pH 5.6/pAg 7.6.

*Dye I
5-(3-Ethyl-2-benzothiazolldinylldene)-3-~-sulfoethylrhodanine C H

,, --l!?--.~

`` ~lZ~644 Electron micrographs showed that the sllver halide grains were predomlnantly octahedral.
The emulslon was chemically sensltlzed wlth gold sulflde, comblned with a cyan dye-forming coupler, l-hydroxy-2-~-(2,4-di-tert-amylphenoxy)-n-butyl]naphthamide, and coated on a cellulose acetate fllm support at 1.62 g Ag/m2, 7.0 g gelatin/m2 and 1.78 g coupler/m2.
The drled coating was exposed for 1/25 second to tungsten light which was filtered to provide a 470 nm exposure and processed for 60 seconds/31C in the color developer set forth in Table I.

Table I
Color Developer 4-amino-3-methyl-N-ethyl-N-~-(methanesulfonamldo)ethylanlllne sulfate hydrate 4.3 g Potasslum bromide 0.15 g Potassium chloride 1.0 g Benzyl alcohol 11.0 g Hydroxylamlne sulfate3.4 g Potassium carbonate31.0 g Potassium bicarbonate0.5 g Potassium sulflte 2.0 g Hydroxyethylcellulose (Natrosol 250L trademark) 0. o6 Water to 1 liter (P~:10.08) 112~ 4 The silver chloride emulsion exhibited a mean ~rain diameter of 0.65 micron. The silver chloride grains were mono-dispersed and of octahedral grain morphology. The contrast of the emulsion was 2.0a, the minimum density 0.10 and the maximum density 2.00. For purposes of comparison with the remaining examples, a relative speed value of 100 was assigned to the emulsion. Speed was measured at 0.30 above minimum density on the characteristic curve.
Example 2 - Illustrating Varied Dye Additions The procedure of Example 1 was repeated, except that addition of Solutions B and C were halted 30 minutes after the beginning of the precipitation step, and Solution D was then added to the reaction vessel over a period of 5 minutes. After Solution D's addition was complete, Solutions B and C were added to the reaction vessel to complete precipitation of silver halide.
The silver halide emulsion produced was polydispersed with mean grain diameters falling within the range of from 0.45 to 0.95 micron. The contrast of the emulsion was 2.16, the minimum density 0.10 and the maximum density 2.00. The relative speed, compared to Example 1, was 46.

I) In a separate run, when the lntroductlon of Solutlon D was delayed untll after Solutlons B and C had been run for 35 minutes, the resultlng emulslon exhlblted comparable minlmum and maximum densltles, but a somewhat lower speed and contrast.

(Comparatlve) Example 3 - Comparing a Conventlonal Post-Precipitation Spectrally Sensitized Emulslon To provlde a dlrect comparison with conventional precipitation techniques, the procedure of Example 1 was repeated, except that Dye I was not present during the precipitation step. Dye I was added ~ust prior to coating the emulsion on the support at a coverage of 130 mg/mole Ag.
The emulsion was monodispersed having a mean grain diameter of 0.70 micron. The silver chloride grains were cublc. The contrast was 2.20, the mlnimum denslty 0.10 and the maximum denslty 2.00. The relative speed, compared to Example 1, was 25.
This example, compared with Examples 1 and 2, demonstrates that the method herein dlsclosed ls capable of producing silver halide emulsions of very signlflcantly enhanced speeds and that dlfferent grain structure can be obtalned as a result of lntroduclng the spectral sensltizlng dye after nucleatlon and durlng sllver hallde preclpitation.
When Examples 1 and 3 were repeated, but with an exposure of 365 nm being chosen to ascertain the lntrlnslc speeds of the emulslons outside of the region of spectral sensitlzatlon, lt was determined that the element produced by Example 1 was 100 percent faster than that produced by Example 3.

.. , .. ... .. .. . . _ . . . . _ . .. ... . .. . .
." ' .

1~21644 When the elements produced by Examples 1 and 3 were separately immersed in an agitated 1:1 (weight ratio) methanol-water solution, it was observed that spectral sensitizing dye entered the solution from the element of Example 3. No spectral sensitizing dye was removed from the element of Example 1. This showed the dye in the Example 1 element to be so tightly held as to be non-wandering. It is not understood exactly how the spectral sensitizing dye added during silver halide precipitation is associated with the silver halide grains, but it appears that the relationship of the dye to the grains produced by this method is demonstratably different than that produced by introducing the spectral sensitizing dye after silver halide precipitation.
(Comparatlve) Example 4 - Illustrating Prenucleation Dye Additions The concept of introducing the spectral sensitizing dye lnto the reaction vessel along with one of the silver or halide salts before silver halide nucleation is known in the art, as illustrated by the teachings of Hill and Philippaerts, cited above. When Example 1 was repeated with Dye I

.

llZ1644 incorporated ln the aqueous hallde salt golutlon, Solutlon B, a markedly inferlor, polydlspersed sllver hallde emulslon was obtalned. The relatlve speed of the emulslon, compared wlth Example l, was only 1. When the procedure was performed agaln, but wlth the spectral sensltlzlng dye combined wlth the aqueous sllver salt solutlon, Solutlon C, the llquld ln the reactlon chamber separated lnto two separate phases, and the experiment was dlscontinued.

Example 5 - Illustratlng the Use o~ Cyanlne Spectral Sensitlzing Dyes Example l was repeated substituting in each instance one of the dyes listed below for Dye I:

Dye II - Anhydro-5-chloro-9-ethyl-5'-phenyl-3'-(3-sulfo-butyl)-3-(3-sulfopropyl)oxocarbocyanlne hydroxlde, sodium salt p /-=CH-CH-CH=CH--~

(CH2) 3 ( lc 2) 3 Na 503e CHSO3 Dye III - Anhydro-5,5',6,6'-tetrachloro-1,1',3-triethyl-

3'-(3-sulfobutyl)benzimidazolocarbocyanine hydroxide c I I p ; ,C=CH-CH=CH-C~ ~ p t Cl CH CH
~ 2 ; -24-Dye IV - Anhydro-9-ethyl-5',6'-dlmethoxy-5-phenyl-3'-(3-sulrobutyl)-3-(3-sul~opropyl)oxathiocarbocyanlne hydroxlde, sodium salt a \;~ =cH--C-CH-~ I 0 = pheny I

(CH2) ~S03e~a0 (CHZ) 2CHSOe Dye V - Anhydro-3,3'-bis(3-sulfopropyl)-4,5,4',5'-dibenzo-- thiocyanine hydroxide, sodium salt ~-=CH~

(CHZ) 3SOS
(( :H2) 3SO3 eNa0 Dye VI - Anhydro-5,5'-dimethoxy-3,3'-bis(3-sulfopropyl) thiocyanine hydroxide, sodium salt I lt \.=CH--~ n (CH2') 3SO3Na~

The results obtalned were qualltatlvely slmllar to those of Example 1, although ln some lnstances an alteratlon ln graln morphology was observed. Whereas Dye I
produced monodlspersed octahedral sllver hallde grains, Dye II produced very pronounced cubic grain structures.
This suggests that Dye I adsorbs preferentially on 111 crystal surfaces, thereby promotlng octahedral graln growth, whereas Dye II adsorbs best on 100 crystal surfaces, thereby enhanclng the probabllity of cubic crystal formation occurring.

Example 6 - Illustrating the Effect of Comblning Spectral Sensitization Durlng the Silver Salt Run with Post-Precipitatlon Spectral Sensltization Substitutlng Dye II for Dye I, Example 3 was repeated uslng two different dye concentrations set out below in Table II, and Example 1 was repeated using 250 mg of Dye II per mole of silver, as set out in Table II. In a fourth run Example 1 was repeated using 200 mg of Dye II ~;
per mole of silver and Dye II was also added to the emulsion ~ust prior to coating to bring the total Dye II concentration to 450 mg per mole of silver. The relative speeds are set out in Table II.

llZ~644 ~ I
h ~ ~
C~ ~ t) o o u, o P~ a~
~d O ~ o ~n ~ ~ ~ C J~
O ~ O ~ O J~ O O
E a) N o N o N c) ~ N
o h O Q) O ~ O ~ O F~ a~

O ~
~ ~ ~ o a~

H C~
q:~
a~

j~; N N =1- :~

OH
E~ H

a~
~ ~1 ~
,1 ~ E ~ ~D
E ~ x a~
X ~
E .Y E ~d .

llZ16~4 The relatlve speeds show a dlstinct advantage for post-nucleatlon spectral sensltizatlon as compared to post-preclpltation spectral sensltization. Additionally, where post-nucleation and post-preclpltatlon spectral sensltlzatlon are comblned, the improvement ln relatlve speeds ls unexpectedly enhanced.

Example 7 - Illustrating Spectral Sensltization of Silver Bromolodlde The following solutions were employed:

llZ:~6~4 Solution A
Phthalated gelatin 116 g KBr 609 g XI 4.4 g Distilled water 4943 ml So lut l on B
KI 46.6 g Distilled H 0 to total volume2 2070 ml Solution C
AgN03 822 g HgC12 .13 mg Distilled H 0 t~>
total volume 9300 ml Solution D
Dye VI 1.1 g Distilled H 0 to total volume 63 9 ml .
.
.

112~644 Step 1: Solution A was placed ln a reactlon vessel and ad~usted to a temperature of 80C.
Step 2: Solutlon B and C were run lnto Solution A
(with agitation) such that the B solution was completely added ln 20 minutes and the C solution was completely added in 40 minutes. Two minutes after starting the flow of Solutions B and C, Solution D was added to A. The addition of D was completed in 35 minutes.
Step 3: One minute after the completion of the addition of Solution C, temperature of the solution was lowered to 50C, 60 grams of sodlum thiocyanate were added to the solution, and the resulting mixture was stirred for 25 minutes.
Step 4: The emulsion was coagulated by lowering the pH and the supernatant liquid was decanted. The coagulum was then redispersed in water. To the redispersed solution, 5.6 grams of KBr were added and the solution was stirred for 3 minutes at 30C. The coagulation procedure was then repeated two more times. The final coagulum was dispersed in water at 40C/pH 6.5/pAg 8.o.
Photomicrographs of this emulsion showed that the emulsion grains ranged in size from less than 0.2 ~m in diameter to greater than 3.0 ~m ln diameter.

For purposes of comparison a control emulsion was prepared as described above, except that the dye was added to the emulsion ~ust prior to coating. Photomicrographs indicated that this emulsion was in the size range of 0.3 to 3.5 microns in mean grain diameter with most of the grains being in the range of 0.5 to 0.7 micron. This latter size llZi644 class contributed markedly to llght scatter and was not nearly a~ prevalent in the emulslon formed above by dye addltion after nucleation.
Both of the above emulslons were gold and sulfur sensltlzed and coated ln a color photographic format on a cellulose acetate fllm support at 1.62 g Ag/m2 and 7.0 g gelatln/m2. These elements were exposed to a tungsten light source for 1/25 second, color processed in a color developer containing ~-phenylenediamine as a developing agent at 80~C
and a pH of 10, and compared sensitometrically. It was found that the post-precipitatlon spectrally sensitized control element had a higher contrast than the post-nuclea-tion spectrally sensitized element prepared according to this process, but that both elements had identical threshold sensitivities. Turbidlty of the control emulsion was higher than for the emulsion according to this process. This result lndicated an lmproved speed/ sharpness characteristic for the element prepared according to this method.

Example 8 - Illustrating Spectral Sensitization of Silver Chlorobromide ' ' . ' ~ `'' ' llZ~44 Solutlon A
Phthalated gelatln 240 g 21.9% solution of NaCl/H20 260 ml

4.4% solutlon of KBr/H2O 147 ml Dlstllled water 8400 ml Solutlon B
NaCl 489 g NaBr 51-7 g Distllled water to total volume 3380 ml Temperature 50C

Solution C
AgN03 1020 g Distilled water to total volume 3380 ml Temperature 50C

Solutlon D
Dye I 0.78 g 1:1 methanol H2O 500 ml Distllled water 127 ml Temperature 50C

~ . . .

1~216~4 Step 1: Solution A was ad~usted to 80C/pH 5.55/vAg 89 mv.
Step 2: Solutions B and C were added simultaneouslY
to Solution A with agitation over a period of 90 minutes.
Ten minutes after Solutlons B and C were started, Solutlon C
was added to Solution A over a period of 34 minutes.
Step 3: The emulsion was cooled to 33C and coagulated by lowering the pH to 3.90. The supernatant was decanted and the coagulum was redispersed in water at pH 6.o/40C.
This procedure was repeated and the emulsion was redispersed at pH 5.6/pAg 7.6 after adding a solution of distilled water t600 ml) and bone gelatin (120 g).
Electron micrographs shows a polydispersed, 0.75 ~m -1.25 ~m, cubo-octahedral emulsion. The emulsion was chemically sensitized, combined with a coupler, coated exposed and processed as described for Example 1. This emulsion had a relative speed of 25 in comparisor. to Example 1.

Example 9 - Illustrating Incremental Dye Additlon During Silver Iodide Precipitation The following solutions were prepared:

Solution A
Gelatin 17.5 g Water 1.5 1 Temperature 35C
pH 6.o llZ~;'14 Solutlon B
200 ml of a 2.5 molar aqueous solution of Sodium lodlde Solution C
200 ml of a 2. 5 molar solutlon of silver nitrate Solution D*
170 ml contalning 606 mg Dye-VII anhydro-

5,5~ ,6,6l ,-tetrachloro-1,1'-diethyl-3,3'-di(3-thiosulfatopropyl)benzimidazolocarbocyanine hydroxide, tetramethylguanidinium salt.

Solution A was placed in a reaction vessel and ad~usted to a pAg of 6.45 with Solution B. Solutions B and C were then added simultaneously at an accelerated flow rate (1 ml/minute initial flow rate, 9 ml/min final flow rate) to the reaction vessel containlng Solution A over a period of 50 minutes. At the time intervals lndicated below the introduction of Solutions B and C were interrupted and the indicated amounts of Solution D were added:

Time (min) 5 11 18 22.2 ml Solution D 3.9 7.25 11.1 15.6 Time tmin) 28.2 34.2 39.2 44.3 ml Solution D 21.15 27. 3 32.6 37.5 After each dye addition, the emulsion was ad~usted to pH 7.5, held for 2 minutes, read~usted to pH 6.o and then precipita-tion was resumed by introducing Solutions B and C once again.

~Dye VII was dissolved in phenoxyethanol (trademark Dowanol), acidified and then diluted to 170 ml total volume with methanol.

llZ1~4q~
At the completion Or the run the pAg of the emulslon was ad~usted wlth an additlonal quantlty of Solutlon C. At the completion of the run the emulsion contalned 1.1 grams of Dye VII per mole of sllver. The excess soluble salts were removed from the emulsion wlth an lon exchange resln by the procedure described ln Maley U.S. Patent 3,782,953. The emulslon was ad~usted to 4.5 kg/mole sllver, pH of 3.0 and a pAg of 2Ø
Generally slmilar emulslon making procedures were employed to prepare emulsions each containing one of the following dyes:

Dye VIII anhydro-9-methyl-3,3'-di(3-sulfobutyl)benzo-thiazolocarbocyanine triethylamine, sodium salt Dye IX 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenz-imidazolocarbocyanine _-toluene sulfonate Dye X 3,3'-diethyl-5,5'-diphenylbenzoxazolocarbocyanine iodide.
The emulsions were coated on transparent photo-graphic film supports at coverages of 8.07 mg sllver per square declmeter and 97.9 mg gelatln per square decimeter.
Coating melts contained saponln and 2-methyl-2,4-pentanediol as a spreading agent and humectant, respectively. The emulsion was ad~usted to a pH of 4 and a pAg of 6 at 35C
prior to coating. Samples of the photographic elements were exposed using wedge spectrographs and developed for 10 mlnutes at room temperature ln Kodak D-l9 developer con-talnlng 1 gram of poly(ethylene oxlde) and flxed uslng Kodak F5 fix solutlon. Correspondlng controls were prepared, exposed and processed whlch ln each instance varled only in that the dye was added to the emulslon after sllver halide precipitation was completed ln accordance with conventional practlce.

. ... ... . .
.

16~

The photographlc elements prepared accordlng to the method of this invention using Dye VII showed a stronger absorptlon band at 545 nm at a coatlng pAg of 6.5 and a red-shlft J-band was observed when the element was coated at a pAg of 10.5. Dye VIII showed a bathochromic adsorptlon shift as compared to the control and J-bandlng whlch was absent from the control. With Dye IX a large enhancement in maxlmum densities were obtained throughout the visible spectrum as well as an enhancement in J-bandlng. With Dye X
an enhancement of blue sensitivity was obtained. Although variations ln response attrlbutable to runnlng the dye lnto the reaction vessel during silver halide precipitation appeard to be a functlon of the particular dye chosen, in each lnstance lt was apparent that the emulsion prepared accordlng to the process of this invention differed in its properties from the control emulsion.
The invention has been described with reference to particular preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims (25)

In the Claims:

1. In a method of preparing a spectrally sensitized radiation-sensitive silver halide emulsion comprising introducing into a reaction vessel an aqueous solution of a silver salt, an aqueous solution of a chloride, bromide, or iodide salt, a peptizer and a methine spectral sensitizing dye, the improvement comprising adding the spectral sensitizing dye to the reaction vessel after at least the partial addition of both the aqueous solution of a silver salt and the aqueous solution of a chloride, bromide, or iodide salt and before completion of the silver halide precipitation, the addition of the spectral sensitizing dye being delayed until silver halide grain nuclei are present in the reaction vessel.

2. In a method according to claim 1 the further improvement in which the chloride, bromide, or iodide salt is a chloride salt.

3. In a method according to claim 1 the further improvement in which the chloride, bromide, or iodide salt is a bromide salt.

4. In a method according to claim 1 the further improvement in which the chloride, bromide, or iodide salt is an iodide salt.

5. In a method according to claim 1 the further improvement in which the methine dye is a merocyanine dye.

6. In a method according to claim 1 the further improvement in which the methine dye is a cyanine dye.

7. In a method according to claim 6 the further improvement in which the cyanine dye contains a benzothia-zole, benzimidazole or benzoxazole nucleus.

8. In a method according to claim 1 the further improvement in which introduction or the spectral sensitiz-ing dye into the reaction vessel is delayed until the silver halide grain nuclei have a mean diameter which is at least 0.01 of the mean diameter of the silver halide grains of the radiation-sensitive silver halide emulsion to be pre-pared.

9. In a method according to claim 1 the further improvement in which introduction of the spectral sensitiz-ing dye into the reaction vessel is delayed until the silver halide grain nuclei have a mean diameter which is at least 0.05 of the mean diameter of the silver halide grains Or the radiation-sensitive silver halide emulsion to be pre-pared.

10. In a method according to claim 1 the further improvement in which a spectral sensitizing amount of the dye is added to the reaction vessel before 85 percent by weight of the silver salt solution has been introduced.

11. In a method according to claim 1 the further improvement in which a spectral sensitizing amount of the dye is added to the reaction vessel before 75 percent by weight of the silver salt solution has been introduced.

12. In a method according to claim 1 the further improvement in which additional spectral sensitizing dye is added to the emulsion following silver halide precipitation.

13. In a method of preparing a spectrally sensi-tized radiation-sensitive silver halide emulsion comprising introducing into a reaction vessel an aqueous solution of a silver salt, an aqueous solution of a chloride, bromide, or iodide salt, a peptizer and a methine spectral sensi-tizing dye, the improvement comprising adding the spectral sensitizing dye to the reaction vessel after at least the partial addition of both the aqueous solution of a silver salt and the aqueous solution of a chloride, bromide, or iodide salt and before completion of the silver halide precipitation, the addition of the spectral sensitizing dye being delayed until silver halide grain nuclei are present in the reaction vessel having a mean diameter which is at least 0.01 of the mean diameter of the silver halide grains of the radiation-sensitive silver halide emulsion to be prepared, a spectral sensitizing amount of the dye being added to the reaction vessel before 85 percent by weight of the silver salt solution has been introduced.

14. In a method of preparing a spectrally sensi-tized radiation-sensitive gelatino-silver chloride emulsion comprising introducing into a reaction vessel an aqueous solution of a silver salt, an aqueous solution of a chloride salt, a gelatin peptizer and a cyanine or merocyanine spectral sensitizing dye, the improvement comprising adding the spectral sensitizing dye to the reaction vessel after at least the partial addition of both the aqueous solution of a silver salt and the aqueous solution of the chloride salt and before completion of the silver halide precipitation, the addition of the spectral sensitizing dye into the reaction vessel being delayed until at least 1 percent by weight of the silver salt solution has been introduced.

15. In a method according to claim 14 the further improvement in which introduction of the spectral sensitizing dye into the reaction vessel is delayed until at least 2 percent by weight of the silver salt solution has been introduced and introduction of the spectral sensitizing dye is completed before 80 percent by weight of the silver salt solution has been introduced.

16. In a method according to claim 14 the further improvement in which introduction of the spectral sensitizing dye into the reaction vessel is delayed until at least 5 percent by weight of the silver salt solution has been introduced and introduction of the spectral sensitizing dye is completed before 75 percent by weight of the silver salt solution has been introduced.

17. In a method according to claim 14 in which at least a portion of the silver salt solution and the chloride salt solution are concurrently added to the reaction vessel.

18. In a method of preparing a spectrally sensitized radiation-sensitive gelatino-silver bromoiodide emulsion comprising introducing into a reaction vessel an aqueous solution of a silver salt, an iodide salt and a bromide salt contained in one or more aqueous solutions, a gelatin peptizer and a cyanine spectral sensitizing dye, the improvement comprising adding the spectral sensitizing dye to the reaction vessel after at least the partial addition of both the aqueous solution of a silver salt and the aqueous solution(s) of the iodide and bromide salts and before completion of the silver bromoiodide precipitation, delaying introduction of the spectral sensitizing dye into the reaction vessel until at least 2 percent by weight of the silver salt solution has been introduced and completing introduction of the spectral sensitizing dye before 80 percent by weight of the silver salt solution has been introduced.

19. In a method according to claim 18 the further improvement in which spectral sensitizing dye is added in increments during interruptions in silver salt introduction.

20. In a method according to claim 18 the further improvement in which the silver salt solutions and the bromide and iodide salt solutions are introduced into the reaction vessel at an accelerating rate.

21. In a method of preparing a spectrally sensitized radiation-sensitive gelatino-silver iodide emulsion comprising introducing into a reaction vessel an aqueous solution of a silver salt, an aqueous solution of an iodide salt, a gelatin peptizer and a cyanine spectral sensitizing dye, the improvement comprising adding the spectral sensitizing dye to the reaction vessel after at least the partial addition of both the aqueous solution of a silver salt and the aqueous solution of an iodide salt and before completion of the silver halide precipitation, delaying introduction of the spectral sensitizing dye into the reaction vessel until at least 2 percent by weight of the silver salt solution has been introduced and completing introduction of the spectral sensitizing dye before 80 percent by weight of the silver salt solution has been introduced.

22. The product of the process of claim 1.

23. The product of the process of claim 14.

24. The product of the process of claim 18.

25. The product of the process of claim 21.