DYES FOR PHOTOGRAPHIC EMULSIONS

FIELD OF THE INVENTION This invention relates to a process for preparing concentrated dye-water compositions for the spectral sensitization of photographic emulsions.

BACKGROUND OF THE INVENTION Dyes for spectrally sensitizing silver halide emulsions are known to be substantially insoluble in water for all practical purposes. Accordingly, such dyes, as well as other photographic additives which are capable of being adsorbed on the grain surfaces of silver salts, have been added to photographic silver halide emulsions in the form of solutions in suitable water miscible solvents such as methyl alcohol, dimethylformamide or the like.

However, spectrally sensitizing dyes are difficult to dissolve in the usual solvents.

Consequently, large quantities of solvent are often needed for satisfactory dissolution of such additives. This presents a significant problem since the presence of residual solvent generally causes diffusion and migration of spectrally sensitizing dyes in the emulsion. Further, even minute residues of solvent promote recrystallization processes in the photographic layer which, in turn, adversely affect not only the dyes and other additives introduced using solvent but other additives in the emulsion as well. Moreover, if residues of polar organic solvents miscible with water remain in a silver halide emulsion, particularly a silver-rich emulsion having a high silver packing density, the residual solvent considerably reduces the stability of the casting emulsion which in turn causes a reduced stability during processing including phase separation between hydrophilic

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and hydrophobic phases, agglomeration, and coalescence as well as flocculation before casting.

Additives which need not be held on the surface of silver halide crystals by adsorption after their introduction into a photographic emulsion have long been incorporated into silver haliάe emulsions in the form of dispersions. For that purpose, the additive is usually dissolved in a suitable solvent, which is generally immiscible with water, in the presence of an oil former and wetting agent, and then emulsified into an aqueous gelatin solution. The low boiling solvent generally used for this purpose is subsequently removed from the emulsion and the resulting dispersion is added to the photographic silver halide emulsion. Unfortunately, the complete removal of the solvent from the resulting dispersion is difficult to achieve, even when low boiling solvents are employed, and particularly when polar solvents are employed. Polar solvents, in particular polar protic solvents, can be removed from gelatin dispersions only by heating, a process which adversely effects the stability of the sensitizing dye molecule. Alternatively, the use of a vacuum to remove the solvent often causes considerable foaming. One method for obviating the harmful effects of using water miscible or immiscible organic solvents to incorporate substantially insoluble additives into silver halide emulsions and dispersions as described in British Patent 1,570,362 is to sand mill such additives in water to a particle size of less than 1 micron in the presence of a surfactant which gives rise to a surface tension of not less than 38 dynes/cm in water when used in a quantity of lg/1.

A similar process is disclosed in U.S. Patent 4,006,025 which teaches milling or homogenizing at an elevated temperature in the presence of a surfactant in which the sensitizing dye is at least partially

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soluble. The process is complicated and the use of surfactant increases finish time.

The process described in U.S. Patent 4,474,872 also requires milling but teaches that the use of a surfactant can be eliminated, but only if the dye is mechanically ground to a fine grain size (1 micron or less) . Very elevated temperatures

(60°-80° C) are employed for preparing the dispersion, and processing conditions such as pH are strictly controlled. Such a process merely eliminates one problem while introducing a multiplicity of others.

SUMMARY OF THE INVENTION

A process for preparing concentrated sensitizing dye-water compositions for the sensitization of photographic emulsions which is devoid of the foregoing disadvantages is provided which comprises adding a sensitizing dye having a solubility in water as low as about 0.005 weight percent to water or a water- polymer medium with agitation at a temperature ranging from about 20° to about 50° C and continuing agitation for from about 30 minutes to about 5 hours.

The process of the invention is simple, versatile and forgiving. It does not require the use of solvents, surfactants, milling of the dye to very fine starting grain sizes, use of highly elevated temperatures, pH control, or the like.

The concentration of dye employed in the process generally exceeds that amount of dye which is soluble in the dispersion medium at the preparation, usage, or storage temperatures. Preferably, amounts ranging from about 0.5 to about 5 weight percent of dye based on the total weight of the mixture are employed. Cyanine dyes which have a solubility of at least about 0.005% by weight in water are preferably used in the process of the invention. Preferred dyes have the formula

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i= (CH-CH) _p =N-A ⁺ -SO

wherein Z^ and Z2 each independently represents the atoms necessary to complete a substituted or unsubstituted heterocyclic nucleus, each L independently represents a substituted or unsubstituted methine group, n is a positive integer of from 1 to 4, p and q each independently represents 0 or 1 , X represents a cation needed to balance the charge of the molecule, and A and A' each, independently represents a divalent alkyl or substituted alkyl linking group.

Even more preferred are dyes having the formula

x

wherein n is 0 or 1; X^ and X2 each independently represents oxygen or sulfur; Q]_, Q2, Q3 and Q4 each independently represents halogen, alkyl, alkoxy or may contain the atoms necessary to form a beta or linear naphtho-fused ring; R]_ and R2 each independently

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represent a sulfoalkyl or substituted sulfoalkyl group; and X ⁺ is a cation such as sodium, hydrogen, triethyl- am onium or ethyl pyridinium.

DETAILED DESCRIPTION OF THE INVENTION

Although the process of the invention provides concentrated sensitizing dye-water compositions that are homogeneous, solvent-free and dispersant-free, such compositions are nevertheless resistant to settling. If some settling does occur, slight agitation or mixing renders the composition homogeneous once again.

Generally, a solid sensitizing dye powder that is somewhat soluble in water is mixed into an "aqueous medium", which term includes a polymer-containing aqueous medium (water-polymer medium) , preferably containing gelatin, at a concentration of dye greater than that which will dissolve in the medium at the temperature, pressure, or other conditions of processing, storage, or use of the composition. Amounts ranging from about 0.5 to about 5 weight percent based on the total weight of the components of the composition are preferred. Because the process can be carried out in the absence of either solvent or surfactant, it is simpler, faster, more forgiving, and more flexible than prior processes. Preferably, the medium to which the dye is added is heated to a preparation temperature ranging from about 20° to about 50° C and maintained at that temperature throughout dye addition and mixing. When gelatin is employed, it is preferred that a temperature greater than about 40° C is used although lower temperatures can be used with other polymers. The process is also flexible in that one temperature can be

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t -Λ during addition while a different temperature is used during mixing.

Mixing or agitation is continued after the addition of the dye is complete and until little evidence of the particles of the original dye powder can be observed. This generally requires from about 30 minutes to about 5 hours.

The composition can be mixed or agitated by any suitable means using any suitable device including magnetically driven stirring bars of various shapes and motor driven shaft stirrers of the propellor or Cowles type. A formula provided by J. Y. Oldshue in "Fluid Mixing Technology", McGraw-Hill, New York, 1983, p. 83, can be used to calculate the preferred amount of agitation to be used in which wherein p/kg = (Diameter) ⁵ x (RPM)3 / Batch size in which Diameter = diameter of Cowles or other blade in inches and Batch size = kg. Best results in terms of minimizing the number of undispersed dye particles can be obtained when p/kg > 50 x 10 ⁹ .

The process of the invention can be employed using spectrally sensitizing dyes, particularly spectrally sensitizing cyanine dyes, having a solubility as low as about 0.005% by weight of the dye in water despite the absence of solvents, dispersants, surfactants or wetting agents. Preferred dyes have the formula

/

4= (CH-CH) _p =N-A ⁺ -SO _;

X

/ \

(L=L) .1 (CH=CH) -N-A ⁺ -SO-

wherein Z]_ and Z2 each independently represents the atoms necessary to complete a substituted or unsubstituted heterocyclic nucleus, each L independently represents a substituted or unsubstituted methine group, n is a positive integer of from 1 to 4, p and q each independently represents 0 or 1, X represents any suitable cation which will balance the charge of the molecule, and A and A' each independently represents a divalent alkyl or substituted alkyl linking group.

Even more preferred are dyes having the formula

Z.

/ \

d= (CH-CH) =N-A ⁺ -SO-

X

/ \

(L=L) _n _ _α -L=C- (CH=CH) _q -N-A'-S0 ₃ ^'

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wherein n is 0 or 1; X]_ and X2 each independently represents oxygen or sulfur; Q]_, Q2, Q3 and Q4 each independently represents halogen, alkyl, alkoxy or may contain the atoms necessary to form a beta or linear naphtho-fused ring; R^_ and R2 each independently represent a sulfoalkyl or substituted sulfoalkyl group; and X ⁺ is a cation such as sodium, hydrogen, triethyl- ammonium or ethyl pyridinium.

Most preferred to be used in the practice of this invention include structures I through XII.

HN ⁺ (C 2H ^xi 5 _ς )' 3

HΝ ⁺ (C ₂ H ₅ )

II

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C

III

HN ⁺ (C ₂ H ₅ ) ₃

IV

(CH,) ₃ SO _: ( CH, ) ₂ CH(S0 ₃ ^" )CH,

HN ⁺ (C,H 5 _ς ) ' 3

V

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VI

(CH ^L 2,) ' 3,S' O ^' (CH ₂ ) ₂ cH(S0 ₃ - )CH,

H ⁺

VII

Na ⁺

VIII

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,

IX

X

HN" (C ₂ H ₅ ) ₃

XI

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XII

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The solvent-free, dispersant-free, dye-water compositions prepared by the process of the invention and containing from about 0.5 to about 5 weight percent of the dyes defined herein are resistant to settling. Similar compositions prepared by prior methods or containing other dyes require either a solvent or surfactant to provide similar results or else complicated and difficult preparatory methods.

Concentrated sensitizing dye-water compositions of the invention for the spectral sensitization of photographic emulsions can be prepared by any suitable method. However, in accordance with the invention, the concentrated dye-water compositions are preferably prepared by first mixing gelatin with water and then heating to prepare an initial gelatin solution. The gel solution is heated and stirred or mixed or otherwise agitated while a sensitizing dye of the invention is introduced, preferably in the form of a powder slowly and uniformly over the surface of the mixture being stirred. When the addition of the sensitizing dye is completed, stirring is continued for a period of time, generally ranging from about 30 minutes to about 5 hours or longer as desired, to produce the concentrated dye-water composition of the invention. More specifically, a dispersion of a salt of a sensitizing dye of the invention is prepared in a 24.75 cm high stainless steel can having a diameter of about 20 cm into which was introduced about 300 g of dry, deionized, bone gelatin and about 4675 g of distilled water. The mixture was placed in a refrigerator overnight in order to allow the gelatin to swell. The resulting gel-water mixture was then melted and maintained at a temperature of about 50° C until the gelatin dissolves. While maintaining the temperature at 50° C, a

10 cm Cowles-type stirrer driven by an electric motor was introduced with the blade of the stirrer positioned in

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the center of the can parallel to and about 7.6 cm from the bottom of the can. Stirring speed is maintained at about 500 rpm. while adding about 25 g of a powder of structure IX slowly and uniformly over the surface of the stirred mixture near the vortex and over a time period of about two minutes. The powder is prepared by grinding the dye using a mortar and pestle until the dye passes through a sieve having 1 mm openings.

The blade of the stirrer is then lowered to about 5 cm from the bottom of the can and the rpms are increased to about 660. Stirring is continued for about one hour. The final dye dispersion contains about 0.5% by weight of dye and about 6% by weight of gelatin based on the weight of the entire dispersion. The dye compositions of the invention can also contain a polymeric binder or protective colloid which can be used in the photographic emulsion layers of intermediate layers of a photographic light-sensitive material. Gelatin is advantageously used although other hydrophilic colloids can be used alone or together with gelatin. Either lime processed or acid processed, deionized gelatin can be used.

Any suitable silver halide such as silver bromide, silver iodobromide, silver chlorobro ide, silver chloride and the like can be used in the photographic emulsion layer of the photographic light-sensitive material sensitized in accordance with the invention. Particular kinds of silver halide particles and photographic emulsions as described in U.S. Patent 4,741,995, which is hereby incorporated by reference for all that it discloses, can be employed.

The photographic emulsion can be prepared b any suitable method including an acid process, a neutral process, an ammonia process or the like using a controlled jet process to obtain regular, nearly uniform grain size silver halide crystals which can be ripened in the presence of cadmium salts, zinc salts, lead salts,

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thallium salts, iridium salts or its complex salts, rhodium salts or its complex salts, iron salts or its complex salts, and the like.

Silver halide emulsions are usually chemically sensitized, for example by sulfur sensitization using active gelatin or compounds such as thiosulfates, thioureas, mercapto compounds and rhodanines containing sulfur capable of reacting with silver; a reduction sensitization process using reducing substances such as stannous salts, amines, hydrazine derivatives, formamidinesulfinie acid, silane compounds and the like; a noble metal sensitization process using noble metal compounds such as complex salts of the Group VIII metals of the Periodic Table including platinum, iridium, palladium and the like as well as gold complex salts; alone or in combination with each other.

The photographic emulsion can include various compounds for preventing fog formation or stabilizing photographic characteristics during production, storage, or processing. For example, antifoggants or stabilizers include azoles such as benzothiazolium salts, nitroimidazoles, nitrobenzimidazoles, chlorobenzimid- azoles, bromobenzimidazoles, mercapto-thiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, aminotriazoles, benzotriazoles, nitrobenzotriazoles, mercaptotetrazoles particularly 1- phenyl-5-mercaptotetrazole; mercaptopyrimidines, mercapto-triazines, thioketo compounds such as oxazolinethione, azaindenes such as triazanidenes, tetraazaindenes particularly 4-hydroxy substituted

1,3,3a,7 tetraazaindenes, pentaazaindenes, benzenethio- sulfonic acids, benzenesulfinic acids, benzenesulfonic amides and the like.

Various surface active agents can be incorporated into the photographic emulsion or other hydrophilic colloid layers of the photographic light- sensitive materials sensitized in accordance with the

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invention as coating aids, to prevent charging, improve slip properties, accelerate emulsification and dispersion, prevent adhesion, improve photographic characteristics such a accelerating development, high contrast, sensitization, and the like.

The photographic emulsion layer can also contain compounds such as polyalkylene oxide or its ether, ester, amine or the like derivatives, thioether compounds, thiomorpholines, quaternary ammonium salt compounds, urethane derivatives, urea derivatives, imidazole derivatives, and 3-pyrazolidones to increase sensitivity or contrast or accelerate development.

Water insoluble or only sparingly soluble synthetic polymer dispersions can be incorporated into the photographic emulsion layer or other hydrophilic colloid layer to improve dimensional stability and the like. Some synthetic polymers which can be used include homo or copolymers of alkyl acrylate or methacrylate, alkoxyalkyl acrylate or methacrylate, glycidyl acrylate or methacrylate, acrylamide or methacrylamide, vinyl esters such as vinyl acetate, acrylonitrile, olefins, styrene and the like and copolymers thereof with acrylic acid, methacrylic acid, alpha, beta-unsaturated dicarboxylic acid, hydroxyalkyl acrylate or methacrylate, sulfoalkyl acrylate or methacrylate, styrenesulfonic acid and the like.

In addition to the concentrated dye-water composition of the invention for spectrally sensitizing photographic emulsions prior to coating on a support, other sensitizing dyes can be used which do not in themselves give rise to spectral sensitization but provide a supersensitizing effect such as, for example, aminostyryl compounds substituted with a nitrogen- containing heterocyclic group including those described in U.S. Patents 2,933,390 and 3,635,721 which are hereby incorporated herein by reference, aromatic organic acid- formaldehyde condensates such as those described in U.S.

Patent 3,743,510 which is hereby incorporated herein by reference, cadmium salts, azaindene compounds and the like.

The concentrated dye-water sensitizing compositions of the invention can be used in multilayer multicolor photographic materials containing layers sensitive to at least two different spectral wavelength ranges on a support. A multilayer natural color photographic material generally possesses at least one red-sensitive silver halide emulsion layer, at least one green-sensitive silver halide emulsion layer, and at least one blue-sensitive silver halide emulsion layer on a support. The order of the layers can be varied as desired. Ordinarily, a cyan forming coupler is present in the red-sensitive emulsion layer, a magenta forming coupler is present in the green-sensitive emulsion layer, and a yellow forming coupler is present in the blue- sensitive emulsion layer, respectively. Different combinations can be employed as desired. Any suitable dye-forming couplers, that is, compounds capable of forming color upon oxidative coupling with aromatic primary amine developing agents such as phenylene-diamine derivatives, aminophenol derivatives and the like during color development processing, can be incorporated into the same or different photographic silver halide emulsion layer as desired. Examples of some such couplers include magenta couplers such as 5- pyrazolone coupler, cyanoacetylcoumarone couplers and open chain acylaceto- nitrile couplers, and the like; yellow couplers such as acylacetamide couplers including benzoylacetanilides, pivalpoylacetanilides and the like; cyan couplers such as naphthol couplers and phenol couplers and the like. Preferably, nondiffusible couplers containing a hydrophobic group or ballast group within the molecule or polymeric coupler is used. They may be either 4- equivalent or 2-equivalent with respect to silver ions.

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Colored couplers capable of exerting color correction effects or couplers capable of releasing development inhibitors during the course of development or DIR couplers, can also be used. Two or more couplers can be employed.

The photographic material can contain inorganic or organic hardeners in the emulsion layer or other hydrophilic colloid layer thereof. For example, chromium salts such as chromium alum, chromium acetate and the like; aldehydes such as formaldehyde, glyoxal, glutaraldehyde and the like; N-methylol compounds such as dimethylolurea, methyloldimethyl-hydantoin and the like; dioxane derivatives such as 2,3-dihydroxydioxane and the like; active vinyl compounds such as 1,3,5- triacryloylhexahydro-s-triazine and the like; mucohalogenic acids such as mucochloric acid, mucophenoxy-chloric acid and the like can be used, either alone or in combination.

When dyes, ultraviolet light absorbing agents, and the like are incorporated in the hydrophilic colloid layers of a photographic light-sensitive material, they may be mordanted with cationic polymers and the like. The photographic light-sensitive material can also contain hydroquinone derivatives, aminophenol derivatives, gallic acid derivatives, ascorbic acid derivatives and the like as color fog preventing agents.

Dyes which can be incorporated into the hydrophilic colloid layers of a photographic lighr sensitive material of the invention include benzotriazole compounds substituted with aryl groups, and 4- thiazolidone, benzophenone, cinnamic acid ester, butadiene, benzoxazole and the like compounds.

Ultraviolet light absorbing couplers such as alpha naphthol type cyan dye forming couplers and ultraviolet light absorbing polymers can also be used. Such ultraviolet light absorbing agents can also be mordanted in a specific layer, if desired.

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Photographic light sensitive elements prepared using the spectrally sensitized emulsions of the invention may contain water soluble dyes in the hydrophilic colloid layers as a filter dye or for other purposes such as irradiation prevention and the like. Some such suitable dyes include oxonol, hemioxonol, styryl, merocyanine, cyanine, azo and the like dyes. Oxonol, hemioxonal, and merocyanine dyes are particularly useful. Any suitable color fading prevention agents can also be used as well as color image stabilizers, either alone or in combination with each other. Some suitable color fading prevention agents include hydroquinone derivatives, gallic acid derivatives, p-oxyphenol derivatives, bisphenols, and the like.

Silver halide photographic emulsions sensitized in accordance with the invention can also contain various other additives used for photography including any suitable hardeners, surfactants, fluorescent whiteners, physical property modifiers such as humectants, water dispersants and the like; condensates of phenols and formalin and the like.

Silver halide emulsions sensitized in accordance with the invention can be coated on any suitable support and dried to prepare a light sensitive silver halide photographic element. Some suitable supports include paper, glass, cellulose acetate, cellulose nitrate, polyester, polyamide, polystyrene and the like or laminated products of two or more substrates such as laminated products of paper and a polyolefin such as polyethylene, polypropylene and the like. The support may be subjected to various surface modification treatments for improving adhesion to the silver halide emulsion such assubbing, electrom impact treatment and the like.

Coating and drying of the silver halide photographic emulsion on the support may be carried out

conventionally by dip coating, roller coating, multislide hopper coating, curtain flow coating and the like followed by drying.

By combining various photographic layers from layers sensitized to other wavelengths such as green sensitive and red sensitive silver halide emulsion layers, intermediate layers, protective layers, filter layers, antihalation layers, backing layers and others, a light sensitive color photographic element can be formed. In such a case, each light sensitive emulsion layer can comprise two emulsion layers with different sensitivities.

Although the invention has been described in considerable detail in the foregoing it is to be understood that such detail is solely for the purpose of illustration and that variations can be made by those skilled in the art without departing from the spirit and scope of the invention except as set forth in the claims.

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