Doping of silver halide emulsions with a potassium selenocyanate salt improved photoactive grains

Description

Technical Field

[0001] This invention relates to radiation sensitive material. It particularly relates to radiation sensitive silver halide grains and their preparation.

Background Art

[0002] In the preparation of high quality photographic materials it is generally necessary to increase the sensitivity of the radiation sensitive silver halides. Accordingly it is known that silver halide emulsions can be chemically sensitized by adding sensitizers of certain material such as sulfur or gold after formation of silver halide grains.

[0003] Photographic products may be chemically sensitized with chemical sensitizers such as with reducing agents such as sulfur, selenium, tellurium, gold, platinum, or palladium compounds.

[0004] In U.S. 4,439,520-Kofron et al and U.S. 4,433,048-Solberg et al it has been proposed that emulsions for use in photographic films be formed utilizing high aspect ratio silver halide grains. It has further been proposed that these high aspect ratio silver halide grains be chemically and spectrally sensitized in order to create particularly useful photographic products, note Kofron et al. It has been proposed in U.S. 3,772,031-Berry et al that doping of silver halide grains be carried out utilizing a variety of sulfur group compounds. The doping is carried out such that the compounds are substantially uniformly dispersed throughout the interior of the grains.

[0005] U.S. 2,222,264-Nietz et al describes the formation of silver halide emulsion utilizing thiocyanates.

[0006] The tabular silver halide grains such as disclosed in the above patents of Kofron et al and Solberg et al patents have been successful in producing grains that have superior speed-granularity relationship. Nevertheless it is desired that films of even higher performance be formed that can be enlarged to even greater extent without excessive granularity.

Disclosure of Invention

[0007] An object of the invention is to produce films having improved speed-granularity relationship.

[0008] Another object of the invention is to provide a process resulting in improved silver halide grains.

[0009] These and other objects of the invention are generally performed by the incorporation of a dopant during the precipitation of silver halide grains. The silver halide grains are preferably formed by an accelerated flow technique. The double jet precipitation technique is preferably used for the invention.

[0010] According to the present invention there is provided a method of forming silver halide grains comprising
   forming a precipitation dispersion for silver halide grains,
   precipitating silver halide grains by introducing silver and halide salts into the precipitation dispersion until 65 to 90 percent of the silver salt that will form the silver mass to be precipitated has been added to said precipitation dispersion, then
   adding to said precipitation dispersion potassium selenocyanate salt dopant in an amount between 1.4 X 10⁻⁶ and 7 X 10⁻⁵ mole per mole of silver, based on the total mass of silver to be precipitated,
   continuing precipitation until all the silver mass has been added and said silver halide grains reach a desired size, and
   ending the precipitation process,
with the further proviso that said silver halide grains comprise between 1 and 12 mole percent of silver iodide and between 88 and 99 mole percent silver bromide, and said silver halide grains at the completion of precipitation have an aspect ratio of at least 8 to 1.

[0011] Grains formed by this process will have their outer third comprising selenium with the silver halide.

Modes For Carrying Out the Invention

[0012] The invention provides several advantages over prior practices. The emulsions of the invention provide better raw stock keeping, and improved speed/fog ratio. By speed/fog ratio it is meant that a higher speed film is possible at the same amount of fog or less fog is possible at the same speed. Also the invention process is more efficient in that doping of the emulsions during precipitation produces a better speed/fog ratio than attempting to achieve the same effect by sensitization processes. This is because with doping it is easier to control fog and rate of sensitization.

[0013] Generally the formation of the silver halide emulsions of the invention may be carried out by processes such as generally disclosed in U.S. 4,439,520-Kofron et al referred to above and hereby incorporated by reference.

[0014] It has been discovered that improved silver halide emulsions may be formed by doping silver halide grain with a selenocyanate salt in an amount of between 0.2 and 1.0 mg per mole of silver during the later stage of precipitation. A silver halide grain is formed by emulsion precipitation process, sensitized, and coated into a multilayer color film to result in a film that has surprisingly improved raw stock keeping properties, improved speed/fog ratio and more reliable reproducibility than when the speed/fog ratio is attempted to be improved only by sensitization.

[0015] In forming the preferred tabular grain emulsions of this invention, a dispersing medium is initially contained in the reaction vessel. In a preferred form the dispersing medium is comprised of an aqueous peptizer suspension. Peptizer concentrations of from 0.2 to 10 percent by weight, based on the total weight of emulsion components in the reaction vessel, can be employed. It is common practice to maintain the concentration of the peptizer in the reaction vessel in the range of below 6 percent, based on the total weight, prior to and during silver halide formation and to adjust the emulsion vehicle concentration upwardly for optimum coating characteristics by subsequent supplemental vehicle additions. It is contemplated that the emulsion as initially formed will contain from 5 to 50 grams of peptizer per mole of silver halide, preferably 10 to 40 grams of peptizer per mole of silver halide. Additional vehicle can be added later to bring the concentration up to as high as 1000 grams per mole of silver halide. Preferably the concentration of vehicle in the finished emulsion is above 50 grams per mole of silver halide. When coated and dried in forming a photographic element the vehicle preferably forms 30 to 70 percent by weight of the emulsion layer.

[0016] Vehicles for the emulsions of the invention, including both binders and peptizers, can be selected from those conventionally employed in photographic silver halide emulsions. Preferred peptizers are hydrophilic colloids, that can be used alone or in combination with hydrophobic materials. Useful hydrophilic materials include both naturally occurring substances, such as proteins, protein derivatives, cellulose derivatives, such as cellulose esters, gelatin, such as alkali treated gelatin or acid treated gelatin, gelatin derivatives, such as acetylated gelatin and phthalated gelatin, polysaccharides, such as dextran, gum arabic, zein, casein, pectin, collagen derivatives, agar-agar, arrowroot and albumin and other vehicles and binders known in the photographic art. Gelatin is highly preferred.

[0017] The silver halide emulsions are preferably washed to remove soluble salts. Any of the processes and compositions known in the photographic art for this purpose are useful for washing the silver halide emulsions of the invention. The soluble salts can be removed by decantation, filtration, and/or chill setting and leaching, coagulation washing, by centrifugation, and by other methods and means known in the photographic art.

[0018] The photographic silver halide can be chemically sensitized by procedures and with compounds known in the photographic art. For example, the silver halide can be chemically sensitized with active gelatin, or with sulfur, selenium, tellurium, gold, platinum, indium, palladium, osmium, rhodium, rhenium, or phosphorous sensitizers or combinations of these sensitizers, such as at pAg levels within the range of 5 to 10 and at pH levels within the range of 5 to 8 at temperatures within the range of 30 to 80°C. The silver halide can be chemically sensitized in the presence of antifogants, also known as chemical finish modifiers, such as compounds known to suppress fog and increase speed during chemical sensitization, such a azaindenes, azapyridazines, azapyrimidines, benzothiazolium salts, and sensitizers having one or more heterocyclic nuclei. Optionally the silver halide can be reduction sensitized, such as with hydrogen, or through the use of other reducing agents, such a stannous chloride, thiourea dioxide, polyamines or amineboranes. The photographic silver halide emulsion can be spectrally sensitized by, for example, dyes of a variety of classes, including the polymethine dye class, including cyanines, merocyanines, complex cyanines and merocyanines, oxonols, hemioxonols, styryls, merostyryls and streptocyanines. Combinations of spectral sensitizers are also useful.

[0019] The photographic silver halide elements can be either single color (monochrome), or multicolor elements. In a multicolor element, a cyan dye-forming coupler is typically associated with a red-sensitive emulsion, a magenta dye-forming coupler is typically associated with a green-sensitive emulsion and a yellow dye-forming coupler is associated with a blue-sensitive emulsion. Multicolor elements typically contain dye-forming units sensitive to each of the three primary regions of the spectrum. Each unit can comprise a single emulsion layer or multiple emulsion layers. The layers of the element and the image-forming units can be arranged in various orders as known in the photographic art. Color photographic reversal materials are preferred for use of the emulsions of this invention.

[0020] The photographic element can contain added layers, such as filter layers, interlayers, overcoat layers, subbing layers and other layers known in the art.

[0021] In the following discussion of illustrative materials that are useful in elements of the invention reference will be made to Research Disclosure, December 1978, Item 17643, published by Kenneth Mason Publications Ltd., Dudley Annex, 21a North Street, Emsworth, Hampshire PO10 7DQ, England, the disclosures of which are incorporated by reference. The publication will be identified hereafter by the term "Research Disclosure".

[0022] Any coupler or combination of couplers known in the photographic art can be used with the silver halide emulsions as described. Examples of useful couplers are described in, for example, Research Disclosure Section VII, paragraphs D,E,F and G and in U.S. Patent 4,433,048 and the publications cited therein. The couplers can be incorporated as described in Research Disclosure Section VII and the publications cited therein.

[0023] The photographic emulsions and elements can contain addenda known to be useful in the photographic art. The photographic emulsions and elements can contain brighteners (Research Disclosure Section V), antifoggants and stabilizers (Research Disclosure Section VI), antistain agents and image dye stabilizers (Research Disclosure Section VII, paragraphs I and J), light absorbing and scattering materials (Research Disclosure Section VIII), hardeners (Research Disclosure Section XI), plasticizers and lubricants (Research Disclosure Section XII), antistatic agents (Research Disclosure Section XIII), matting agents (Research Disclosure Section XVI) and development modifiers (Research Disclosure Section XXI).

[0024] The photographic elements can be coated on a variety of supports, such as film and paper base, as described in Research Disclosure Section XVII and the references described therein.

[0025] The photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed to form a visible image using processes and compositions known in the art, such as described in Research Disclosure Section XIX and U.S. Patent 4,433,048 and the references described therein.

[0026] Processing of a color photographic element as described to form a visible dye image includes the step of contacting the element with a color photographic silver halide developing agent to reduce developable silver halide and oxidize the color developing agent. Oxidized color developing agent in turn reacts with at least one coupler to yield a dye.

[0027] Preferred color developing agents are p-phenylenediamines. Especially preferred are 4-amino-3-methyl-N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N-ethyl-N-β-(methanesulfonamido)-ethylaniline sulfate hydrate, 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulfate, 4-amino-3-β-(methanesulfonamido)ethyl-N,N-diethyl-aniline hydrochloride and 4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonic acid.

[0028] With negative working silver halide emulsions this processing step leads to a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniform fogging of the element to render unexposed silver halide developable. The silver halide emulsions of this invention are preferably employed in photographic elements designed to be processed to form a color negative image.

[0029] It is specifically contemplated that the doping of the invention will take place during the growth stage of the silver halide grains. During the precipitation process the silver halide grain size is increased by a double jet accelerated flow procedure with silver nitrate and potassium bromide and iodide. Dopant is added after 65 to 90% of the silver halide mass has been precipitated. After a desired size grain has been reached the grain growth is stopped by washing to remove the soluble salts, particularly nitrate and bromide. In accordance with the invention there is added during the last about 65 to 90% of the precipitation process an effective amount of selenocyanate salt.

[0030] The present invention provides color films utilizing the the grains which have better raw stock keeping and low fog. This addition of potassium selenocyanate at the latter stages of precipitation produces a grain that has dispersed in the outer third of its surface the doping material. The core remains the silver halide, preferably silver bromide and silver iodide, without the doping compound that is present in about the outer third of the grain.

[0031] The high aspect ratio tabular grain silver halide emulsions that have been doped with the Group VIB metallic salt, preferably potassium selenocyanate are then preferably chemically sensitized in conventional manner such as discussed in the above-referenced Kofron et al patent. A preferred sensitizing dye for use with the Group VI metal doped silver halide emulsions of the invention are anhydro- 5-chloro-9-ethyl-5'-phenyl-3'-(3-sulfobutyl)-3-(sulfo-propyl)oxa-carbocyanine hydroxide, sodium salt, and anhydro-11-ethyl-1,1'-bis(3-sulfopropyl)naphth[1,2-d]-oxazolocarbocyanine hydroxide, sodium salt.

[0032] Generally the emulsion is washed after precipitation is complete to a desired size grain. Washing by coagulation wash to remove the excess bromide ions to stop grain growth at the desired size is preferred. Further the emulsion is redispersed and chilled to 4.5°C to solidify. The emulsion may be remelted and liquefied prior to sensitization with conventional materials such as gold and sulfur. The addition of the inorganic selenium salt is preferably carried out between 65 and 90% of desired grain growth. If the selenium salt is added after 90% of grain growth is done it is at least partially removed during the washing operation and the grain will not have the desired properties. If it is added earlier in the grain formation, a higher level of dopant is required, it may produce higher fog, and it may produce poor raw stock keeping. The optimum time of addition is after 67 percent of the total silver halide mass to be precipitated has been added to the precipitation for best raw stock keeping and speed/fog ratio increase.

[0033] The grains of the invention are preferably formed with a silver halide comprising silver bromide and iodide. Generally the grains have an amount between 1 and 44 mole percent silver iodide with the remainder 56-99 mole percent silver bromide. A preferred amount has been found to be between 1 and 12 mole percent silver iodide with between 99 and 88 percent silver bromide. The grains suitably have a high aspect ratio of at least 8 to 1. The aspect ratio is preferred to be at least 20 to 1 for best performance as more surface area is present.

[0034] The following examples demonstrate the formation process of the silver halide grains of the invention. Further the examples demonstrate the superior performance in regard to raw stock keeping and speed/fog ratio of the emulsions of the invention as compared with other emulsions produced by the Kofron et al process referenced above.

Example

[0035] A 2.4 µm diameter and 0.12 µm thick silver bromoiodide (overall average iodide 3.0 mole percent) tabular grain emulsion prepared by a double-jet precipitation technique using accelerated flow as follows:

[0036] To a 16-liter aqueous gelatin solution (solution A, 0.087 molar sodium bromide, 0.6 percent by weight bone gelatin) at 35°C and pBr 1.18 are added with stirring over a minute and a half period (consuming 0.18 percent of the total silver) an aqueous silver nitrate solution (solution C-3, 0.376 molar). Twenty liters of aqueous phthalated gelatin solution (solution D, 4% by weight) are added to the reaction vessel. The temperature is then raised to 65°C. The pBr of the contents of the reaction vessel is 1.46 at 65°C. An aqueous solution of sodium bromide (solution B-1, 2.12 molar) and silver nitrate (solution C-1, 1.18 molar) are added by double jet addition using accelerated flow with pBr controlled at 1.46 at 65°C. An aqueous solution of sodium bromide (solution B-2, 4.78 molar) is then added with vigorous stirring. The pBr of the contents of the reaction vessel are 0.915 at 65°C. Two liters of aqueous phthalated gelatin solution (solution E, 2% by weight) are added, followed by the addition of silver iodide seed (solution G, 0.936 moles) with good stirring. The mixture in the vessel is then held for two minutes at 65°C with further stirring. At the end of the two-minute hold, 42.4 cc of an aqueous solution of potassium selenocyanate (solution H, 0.012 molar) is added with good stirring. The mixture in the vessel is held for another two minutes at 65°C with further stirring. At the end of the two-minute hold, an aqueous solution of silver nitrate (solution C-2, 1.88 molar) is added until a pBr of 2.45 is reached. Approximately 83.7% of the total silver is used. Thirty-six moles of silver are used to prepare this emulsion. The double jet, accelerated flow rate used is 10.5 times from start of the growth segment to finish, over 72 minutes and 40 seconds. The emulsion is cooled to 40°C, then coagulation washed twice.

[0037] A control emulsion is precipitated in the same manner as above, except the dopant potassium selenocyanate (solution H) is omitted.

[0038] Both of these emulsions are sensitized with 150 mg/Ag mole sodium thiocyanate, 4.5 mg/Ag mole sodium thiosulfate, 1.5 mg/Ag mole potassium tetrachloroaurate and 17 mg/Ag mole 3-methylbenzothiazolium iodide, and spectrally sensitized with 228 mg/Ag mole of dye E and 386 mg/Ag mole of dye F. The sensitized emulsion is combined with a cyan coupler 2-naphthalenecarboxamide, N-[4-[2,4-6(1,1-dimethylpropyl) phenoxy]butyl]-1 hydroxy in an amount of 55 mg/silver mole, then coated onto a polyester film, exposed for 1/100 second at 5500K, and processed in C-41 developer for two minutes and fifteen seconds. The photographic test results show that the selenium doped emulsion is 0.14 log E faster than the control emulsion without the dopant.

[0039] The invention has been described with preferred tabular silver halide emulsions. However the invention also would find advantages in doping of other types of silver halide grains for improved speed/fog and raw stock keeping. Further the invention also would find utilization in the formation of black and white films where improved speed/fog grain ratio is desirable as well as improved raw stock keeping. The invention is only intended to be limited by the scope of the claims attached hereto.

Claims

1. A method of forming silver halide grains comprising
   forming a precipitation dispersion for silver halide grains,
   precipitating silver halide grains by introducing silver and halide salts into the precipitation dispersion until 65 to 90 percent of the silver salt that will form the silver mass to be precipitated has been added to said precipitation dispersion, then
   adding to said precipitation dispersion potassium selenocyanate salt dopant in an amount between 1.4 X 10⁻⁶ and 7 X 10⁻⁵ mole per mole of silver, based on the total mass of silver to be precipitated,
   continuing precipitation until all the silver mass has been added and said silver
halide grains reach a desired size, and
   ending the precipitation process,
   with the further proviso that said silver halide grains comprise between 1 and 12 mole percent of silver iodide and between 88 and 99 mole percent silver bromide, and said silver halide grains at the completion of precipitation have an aspect ratio of at least 8 to 1.

2. The method of Claim 1 wherein said silver halide grains are precipitated utilizing an accelerated double jet technique.

3. The method of Claim 1 wherein said ending precipitation is performed by coagulation washing to remove bromide ion.

4. The method of Claim 1 wherein said salt is present in an amount 1.4 X 10⁻⁶ per mole of the silver based on the mass of silver precipitated in forming said grains.

5. The method of Claim 4 wherein 67 percent of said silver salt has been added when said potassium selenocyanate salt is added to said precipitation dispersion.

Ansprüche

1. Verfahren zur Herstellung von Silberhalogenidkörnern, bei dem man
eine Ausfällungsdispersion für Silberhalogenidkörner herstellt,
Silberhalogenidkörner durch Einführung von Silber- und Halogenidsalzen in die Ausfällungsdispersion ausfällt, bis 65 bis 90 % des Silbersalzes, das die auszufällende Silbermenge bildet, der Ausfällungsdispersion zugegeben worden sind,
der Ausfällungsdispersion ein Kaliumselenocyanatsalz-Dotiermittel in einer Menge von 1,4 x 10⁻⁶ bis 7 x 10⁻⁶ Molen pro Mol Silber, bezogen auf die Gesamtmenge des auszufällenden Silbers, zusetzt,
die Ausfällung fortsetzt, bis die gesamte Silbermenge zugegeben worden ist und die Silberhalogenidkörner eine bestimmte Größe erreicht haben und
den Ausfällungsprozeß beendet,
wobei ferner gilt, daß die Silberhalogenidkörner 1 bis 12 Mol-% Silberiodid und 88 bis 99 Mol-% Silberbromid enthalten und daß die Silberhalogenidkörner zum Zeitpunkt der Beendigung der Ausfällung ein Aspektverhältnis von mindestens 8 zu 1 aufweisen.

2. Verfahren nach Anspruch 1, bei dem die Silberhalogenidkörner mittels eines beschleunigten Doppeleinlaufverfahrens ausgefällt werden.

3. Verfahren nach Anspruch 1, bei dem die Ausfällung beendet wird durch eine Koagulationswäsche zum Zwecke der Entfernung von Bromidionen.

4. Verfahren nach Anspruch 1, bei dem das Salz in einer Menge von 1,4 x 10⁻⁶ pro Mol des Silbers,bezogen auf die Menge des ausgefällten Silbers,bei der Erzeugung der Körner vorliegt.

5. Verfahren nach Anspruch 4, bei dem 67 % des Silbersalzes zugegeben worden sind, wenn das Kaliumselenocyanatsalz zur Ausfällungsdispersion zugegeben wird.

Revendications

1. Procédé de préparation de grains d'halogénure d'argent consistant à
   former une dispersion par précipitation des grains d'halogénure d'argent,
   précipiter des grains d'halogénure d'argent en introduisant des sels d'argent et d'halogénure dans la dispersion de précipitation jusqu'à ce que 65 à 90 % du sel qui formera la masse d'argent à précipiter ait été ajouté à la dispersion de précipitation, puis
   ajouter dans la dispersion de précipitation un dopant sel de sélénocyanate de potassium en quantité comprise entre 1,4 x 10⁻⁶ et 7 x 10⁻⁵ mole par mole d'argent, par rapport à la masse totale d'argent à précipiter,
   continuer à précipiter jusqu'à ce que toute la masse d'argent ait été ajoutée et les grains d'halogénure d'argent atteignent la taille désirée, et
   terminer la précipitation avec la condition supplémentaire que les grains d'halogénure d'argent comprennent entre 1 et 12 % en mole d'iodure d'argent et entre 88 et 99% en mole de bromure d'argent, et que les grains d'halogénure d'argent à la fin de la précipitation aient un indice de forme d'au moins 8 à 1.

2. Procédé selon la revendication 1 dans lequel les grains d'halogénure d'argent sont précipités en utilisant une technique de double jet accéléré.

3. Procédé selon la revendication 1 dans lequel à la fin de la précipitation on effectue un lavage par coagulation pour éliminer l'ion bromure.

4. Procédé selon la revendication 1 dans lequel la quantité de sel est de 1,4.10⁻⁶ mole par mole d'argent par rapport à la masse d'argent précipité dans la formation des grains.

5. Procédé selon la revendication 4 dans lequel 67% du sel d'argent a été ajouté au moment de l'addition du sel de sélénocyanate de potassium à la dispersion de précipitation.