WO1993002390A1

WO1993002390A1 - Gold compounds as antifoggants in high silver chloride emulsions

Info

Publication number: WO1993002390A1
Application number: PCT/US1992/006010
Authority: WO
Inventors: Jerzy Antoni Budz
Original assignee: Eastman Kodak Company
Priority date: 1991-07-22
Filing date: 1992-07-21
Publication date: 1993-02-04
Also published as: EP0548354A1; JPH06501789A

Abstract

The invention is accomplished by addition of a monovalent or trivalent gold compound in an amount of up to 3 x 10-5 mole per mole of silver as a dopant during emulsion formation. The invention is preferred for silver chloride emulsions.

Description

GOLD COMPOUNDS AS ANTTFOGGANTS TN HIGH SILVER CHLORIDE EMULSIONS

Technical Field This invention relates to silver halide photography and specifically to silver halide emulsions with high silver chloride content, and methods of forming silver halide with suitable photographic properties.

Background Art

All references to periods and groups within the periodic table of elements adopted by the American Chemical Society and published in the Chemical and Engineering News, February 4, 1985, page 26. In this form the prior numbering of the periods was retained, but the Roman numeral numbering of groups and designations of A and B groups (having opposite meanings in the U.S. and Europe) was replaced by simple left to right 1-18 numbering of the groups. The term "dopant" refers to a material other than a silver or halide ion contained within a silver halide grain.

Grain sizes, unless otherwise indicated, are edge length of a cube, where the crystals have a cubic morphology. It is well known that the sensitometric properties of silver halide photographic emulsions may be varied widely depending upon such factors as crystal structure, crystal size, crystal size distribution, chemical and spectral sensitization. This is described in, for example, "The Theory of the Photographic

Processes" by T. H. James, 4th Edition, Macmillan Co. Ltd., New York, 1977.

It is also known that the method of precipitation has an effect on the properties mentioned above. Physical ripening, commonly called Ostwald ripening, has the object of increasing the average grain size of the silver halide and, consequently, the sensitivity. Since physical ripening is dependent upon the solubility of the silver halide, the presence of an excess of soluble halide during emulsification increases the average grain size and, thus, increases the photographic sensitivity due to the formation of complex silver halide ions which render the silver halide more soluble than it is in water. Another method of increasing the solubility of the silver halide, which also permits the coalescence and recrystallization of particles to increase the average grain size, is the use of a silver/ammonia complex. Ammoniacal emulsions are prepared by adding ammonium hydroxide during precipitation and/or ripening. Although excess halide and ammonia are the most common ripening agents, others mentioned in literature include thiocyanates such as described in U.S. Patents 2,222,264 and 3,320,069 and thioethers as described in U.S. Patent 3,271,157. It is known that incorporating any of the above ripening agents during formation of the silver halide crystals or shortly thereafter provides an emulsion with increased grain size and usually increased photographic sensitivity.

Yet another way to enhance the photographic properties of an emulsion, which does not involve an increase in the size of the image recording grains, is the incorporation of modifying compounds which can be present during emulsion precipitation. Such compounds can be initially in the reaction vessel or can be added along with one or more of the reactants according to conventional procedures. Modifying compounds, such as compounds of copper, thallium, lead, bismuth, cadmium, zinc, middle chalcogens (i.e., sulfur, selenium, and tellurium) , gold, and group B to 10 noble metals having an atomic weight greater than 100, can be present during silver halide precipitation, as illustrated by Arnold et al U.S. Patent 1,195,432, Hochstetter U.S. 1,951,933,

Trivelli et al U.S. Patent 2,448,060, Overman U.S. Patent 2,628,167, Mueller et al U.S. Patent 2,950,972, Sidebotham U.S. Patent 3,488,709, Rosecrants et al U.S. Patent 3,737,313, Berry et al U.S. Patent 3,772,031, Atwell U.S. Patent 4,267,927, and Research Disclosure. Vol. 134, June 1975, Item 13452. Research Disclosure is published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire P010 7DD, England.

With further investigation, the art has recognized a distinct difference in the photographic effect of metal compounds in silver halide emulsions, depending upon whether the compound is introduced into the emulsion during precipitation of silver halide grains or subsequently in the emulsion preparation process. In the former instance, it has been generally accepted that the metal can enter the silver halide grain as a dopant and, therefore, be effective to modify photographic properties, though present in very small concentrations. When metal compounds are introduced into an emulsion after silver halide grain precipitation is complete, they can be adsorbed to the grain surfaces, but are sometimes largely precluded from grain contact by peptizer interactions. Orders of magnitude higher concentrations of metals are required to show treshold photographic effects when added following silver halide grain formation as compared to being incorporated in silver halide grains as dopants. The art of distinction between metal doping, resulting from metal compound addition during silver halide grain formation, and metal sensitizers, resulting from metal compound addition to an emulsion following silver halide grain formation, is illustrated by Research Disclosure, Vol. 176, December

1978, Item 17643, wherein Section IA, dealing with metals introduced during grain precipitation, and Section IIIA, dealing with metal sensitizers introduced during chemical sensitization, provide entirely different lists of prior art teachings relevant to each practice.

The metals most commonly incorporated into silver halide grains are the group 8 to 10 elements having an atomic weight greater than 100. The most common dopant of these is irrdiu , which is known to give a variety of useful photographic effects. B.H. Caroll, ^■Iridium Sensitization: A Literature Review", Photographic Science and Engineering, Vol. 24 , No. 6, Nov./Dec, 1980, pgs. 265-267, is cited for -f rther background on conventional photographic uses of iridium.

Rhodium introduced in the form of a rhodium hexachloride or hexabromide has also been extensively investigated. Grzeskowiak in published European Patent Application No. 0 242 190/A2 discloses reductions in high intensity reciprocity failure in silver halide emulsions formed in the presence of one or more complex compounds of rhodium (III) having 3, 4, 5, or 6 cyanide ligands attached to each rhodium ion.

Ruthenium and osmium has been investigated, but to a lesser extent. Although platinium and palladium opants have been investigated and are known to be effective, these elements have not been attractive, since they are known to form complexes with gelatin, hindering their incorporation in the presence of this common peptizer.

Other uses of metal dopants are known. Zinc, cadmium, mercury, and lead dopants have been used to obtain various photographic effects, as illustrated by McBride U.S. Patent 3,287,136; Iwaosa et al U.S. Patent 3,901,711; Shiba et al U.S. Patent 3,790,390; Ohkubo et al U.S. Patent 3,890,154; and Habu et al U.S. Patent 4,147,542 disclose silver halide grains doped with iron, cobalt, and nickel.

The silver halides of practical importance include silver iodide, bromide, chloride, and their mixed salts. It is well known that a silver chlorobromide emulsions do not consist of some crystals containing one halide and some containing the other, but rather that all the crystals are mixed crystals containing both halides. Inclusion of one halide into the lattice of the other results in some deformation in the lattice structure of mixed crystals. Because this deformation causes stresses within a silver halide grain, one can -change the total sensitivity and/or sensitivity distribution among grain sizes depending upon the way the bromide salt is introduced. In some applications, one halide can be epitaxially deposited on another as described by Maskasky U.S. Patent 4,435,501.

Recently, the time required for printing and processing photographic materials for prints has been considerably shortened. The strong demand has arisen for the photographic material which could be rapidly processed. Conventional chlorobromide emulsions do not permit reduction in developments time and are less desirable ecologically. A high silver chloride emulsions containing substantially no silver iodide are known as a preferable material for reducing the time of development, bleaching, and fixing steps. In high silver chloride emulsions, cubic grains having a (100) crystal plane are usually formed. Such emulsions, however, are prone to fog, especially when sensitized with the use of soluble gold. The problem is aggravated in color developer having high activity for rapid development, for example, Kodak RA-4 process. Reciprocity failure and storage fog generated when light sensitive high chloride photographic material is stored also poses problems.

Several methods have been proposed to solve these problems, as described by Nishikawa et al U.S. Patent 4,960,689. The use of a number of soluble and insoluble gold compounds added to the emulsion after final digestion, but before coating for emulsion stabilization, has been disclosed by Damschroder U.S. Patent 2,597,856 and Yutzy et al U.S. Patent 2,597,915. Addition of gold to silver halide emulsion improved lithographic printing characteristics of photographic material as described by Saikava et al U.S. Patent 4,621,041. German Offenlegugsschrift DE 38 28 312 suggests that the use of oxidized gelatin that has a gold number of not greater tha 10 μ mole per gram of gelatin and a cystein content not in excess of 6 ppm may be utilized in formation of silver chlorobromide emulsions that have lower fog. European Patent Application 0 315 833 alleges that the pure chloride emulsions prepared in a way as to minimize the iron content of the emulsion, exhibits sensitivity equal to check but at lower fog level. While the above emulsions have resulted in desirable photographic products, no disclosure, however, has been reported in which Gold(III) and Gold(I) compounds are applied specifically during precipitation stage of emulsion making in order to improve photographic properties, most notably reduce fog, in high chloride emulsions, when processed in rapid acting surface developers.

It is well known that high chloride emulsions are desirable in manufacturing ecologically cleaner and capable of rapid development photographic printing material. Such emulsions suffer elevated fog, high reciprocity failure, and poor storage properties as compared with the conventional photographic material. Therefore, it is desirable to find a way of minimizing fog level for chemically sensitized, high chloride emulsions, without comprising any of the above properties.

Disclosure of the Invention

An object of the invention is to overcome disadvantages of prior methods of emulsion formation and prior emulsions.

Another object is to reduce fog in photographic products.

Another additional object is to improve sensitivity to fog ratio in photographic products. A further object of this invention is to produce improved color paper. Another object of this invention is to produce rapidly developing color papers that are environmentally desirable.

These and other objects of the invention generally are accomplished by addition of a monovalent or trivalent gold compound in an amount of up to 3 X 10^~5 mole per mole of silver as a dopant during emulsion formation. In a preferred form of the invention, the silver halide is predominantly silver chloride and is utilized as a silver halide emulsion for color paper formation.

Modes For Carrying Out the Invention Silver Halide Grains Formation The silver halide emulsions can be comprised of silver bromide, silver chloride, silver chlorobromide, silver chloroiodide, silver bromoiodide, silver chlorobromoiodide, and mixtures thereof. The emulsion of this invention does not contain substantial amounts of silver iodide, which means that the molar content of silver iodide is 2% or less and more preferable 0.01 mole % or less.

At least 60% of the emulsion of this invention is silver chloride. More preferable, silver chloride content is 75% or more. Even more preferable, 90% or more and most preferable, 95% because of undesirable effects of bromide during RA-4 processing.

The emulsion grains of this invention may have a uniform composition or structured structure. Silver bromide or iodide in the quantities defined above may be introduced at any phase of emulsion production including that of epitaxial deposition of one or the other. The emulsion grain may be of any morphology with the cubic morphology characteristic for high chloride emulsions. The individual reactants can be added to the reaction vessel through surface or sub-surface delivery tubes by gravity feed or by delivery apparatus for maintaining of the rate of delivery and the pH and/or vAg of the reaction vessel constant, as illustrated by Culhane et al U.S. Patent 3,821,002, Oliver U.S. Patent 3,031,304, and Claes et al Photographishe Korrespondenz , 102 Band, No. 10, 1967, p. 162. In order to obtain rapid distribution of the reactants within the reaction vessel, specially constructed mixed devices can be employed, as illustrated by Audran U.S. Patent 2,996,287, McCrossen et al U.S. Patent 3,342,605, Frame et al U.S. Patent 3,415,650, Porter et al U.S. Patent 3,785,777, Saito et al German OLS 2,556,885, and Sato et al German OLS 2,555,364.

Although an average grain size of this invention is not limited, it is preferably 0.1 μm to 5 μm, and more preferably 0.2 μm to 3 μm for use in color paper with good image quality. A grain size distribution of this emulsion may be either polydisperse or monodisperse, with monodisperse being preferable.

In preparation of silver halide grains of this invention, a solvent for silver halide may be used. This may include thiocyanate ripened emulsions, as illustrated by Illingsworth U.S. Patent 3,320,069, thioether ripened emulsions, as illustrated by McBride U.S. Patent 3,271,157, Jones U.S. Patent 3,574,628, and Rosecrants et al U.S. Patent 3,737,313, or emulsions containing weak silver halide solvents, such as ammonium salts, as illustrated by Perignon U.S. Patent 3,784,381, and Research Disclosure, Vol. 134, June 1975, Item 13452. During formation or physical ripening of the silver halide grains, cadmium salt, zinc salt, lead salt, thallium salt, mercuric salt, iridium salt or its complex salt, osmium salt, rhodium salt or its complex salt, or iron salt or its complex salt may be used. Especially, iridium salt or rhodium salt is preferable because of improvements in reciprocity failure and other photographic properties. It is significant finding of this invention that Gold(I) and Gold(III) compounds, when added to the emulsion described above, significantly reduce its level of fog during subsequent sensitization without deleterious effect on the properties of the emulsions formed by the methods mentioned above. Further it is unexpected that gold used in larger amounts does not result in a particularly desirable sensitized product, whereas utilization of a very small amount of gold as in the invention does improve speed-fog performance at the level that does not induce significant sensitization. The amount of monovalent or trivalent gold utilized to produce the antifoggant properties of the silver halide of the invention may be any effective amount. It has been found that preferable concentration is up to about 3 X 10"⁵ moles of monovalent or trivalent gold compound per mole of silver. More preferred concentration is between about 3 X 10"^ and about 3 X 10-8. A most preferred concentration is between 3 X 10"^"6 and 3 X 10~⁷ moles of gold compound per mole of silver because optimum performance.

Typical of the gold compounds are potassium chloroaurate, KAUCI4; auric trichloride, AUCI3; gold sulfide, AU2S; myochrisine (gold sodium-thiomalate) ; KAu(CNS)4; solganol-B olesoum (aurothioglucose in sesame oil); pyridino-trichlorogold, (C5H5N)AuCl3.HCl; trichlorogold-dimethyl sulfide, AUCI3. (CH3)2S; diethyl- monobrom-gold, Au(C2H5)2Br; monochlorogold-dimethyl sulfide, AuCl. (CH3)2S; potassium aurothiocyanate, KAu(CNS)2; and bis(methylhydaintonato)gold(I) sodium salt (hereinafter referred to as Gold(I) compound).

The gold compounds can be added to the emulsion in the form of solutions in suitable solvents, e.g., water, methyl alcohol, ethyl alcohol, acetone, etc., or as dispersions in colloids, such as gelatin, polyvinyl alcohol, partially hydrolyzed cellulose acetate, casein, etc., or without any solvent or colloid. The gold co pound should, of course, be thoroughly dispersed throughout the emulsions, e.g., by stirring.

The gold compound may be added at any time during the emulsion formation that results in improved antifogging characteristics. It is preferred that the gold is added during substantially all of the precipitation, and most preferably as a component of silver feed solution (silver nitrate) , as this will give continuous antifogging protection during grain formation when it is believed the fogging takes place.

The soluble salts of the emulsion of this invention can be removed by coagulation washing, as illustrated by Hewitson et al U.S. Patent 2,618,556, Yutzy et al U.S. Patent 2.614,928, Yackel U.S. Patent 2,656,418, Hart et al U.S. Patent 3,241,969, Weller et al U.S. Patent 2,489,341, Klinger U.K. Patent 1,305,409, and Dersh et al U.K. Patent 1,167,159; by diafiltration with semipermeable membrane, as illustrated by Research Disclosure, Vol. 102, October 1972, Item 10208, Hagemaier et al Research Disclosure, Vol. 131, March 1975, Item 13122, Bonnet Research Disclosure, Vol. 135, July 1975, Item 13577, Berg et al German OLS 2,436,461 and Bolton U.S. Patent 1,459,918 or by employing an ion exchange resin, as illustrated by Maley U.S. Patent 3,782,953 and Noble U.S. Patent 2,827,428. The emulsions of this invention, with or without sensitizers, can be dried and stored prior to use as illustrated by Research Disclosure, Vol. 101, September 1977, Item 10152.

Chemical Sensitization

The silver halide emulsion of this invention can be chemically sensitized with sulfur, selenium, tellurium, gold, platinium, palladium, iridium, osmium, rhenium or phosphorous sensitizers or combinations of these sensitizers, such as pAg levels from 5 to 10, pH levels from 4 to 8, and temperatures of from 30 to 80°C, as illustrated by Research Disclosure, Vol. 120, April 1974, Item 12008, Research Disclosure, Vol. 134, June

1975, Item 13452, Shepperd et al U.S. Patent 1,623.499, Matthies et al U.S. Patent 1,673,522, Weller et al U.S. Patent 2,399,083, Damschroder et al U.S. Patent 2,642,361, McVeigh U.S. Patent 3,297,447, Dunn U.S.

Patent 3,297,446, McBride U.K. Patent 1,315,755, Berry et al U.S. Patent 3,772,031, Gilman et al U.S. Patent 3,761,267, Ohi et al U.S. Patent 3,857,711, Klinger et al U.S. Patent 3,565,633, Oftedahl U.S. Patents 3,901,714 and 3,904,415, and Simmons U.K. Patent 1,396,696; chemical sensitization being optionally conducted in the presence of thiocyanate derivatives, as described in Damschroder U.S. Patent 2,642,361; thioether compounds, as disclosed in Lowe et al U.S. Patent 2,521,962, Williams et al U.S. Patent 3,021,215, and Bigelow U.S. Patent 4,054,457 and azaindenes, azapyridazines, and azapyrimidines, as described in Dostess U.S. Patent 3,411,914, Kubawara et al U.S. Patent 3,554,757, Oguchi et al U.S. Patent 3,565,631, and Oftedahl U.S. Patent 3,901,714.

Spectral Sensitization

The silver halide emulsions of this invention can be spectrally sensitized with dyes from a variety of classes, including the polymethine dye class, which includes the cyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-, tetra-, and poly-nuclear cyanines and merocyanines) , oxonols, hemioxonols, styryls, merostyryls, and streptocyanines. The cyanine spectral sensitizing dyes include, joined by a methine linkage, two basic heterocyclic nuclei, such as those derived from quinolinium, pyridinium, isoquinolinium, 3H-indolium, benz(e)indolium, oxazolium, thiazolium, selenazolium, imidazolinium, benzoxazolinium, benzothiazolium, benzoselenazolium, benzimidazolium, naphtooxazolium, naphtothiazolium, naphtoselenazolium, thiazolinium dihydronaphtothiazolium, pyrylium, and imidazopyrazinium quaternary sats.

The merocyanine spectral sensitizing dyes include, joined by a methine linkage, a basic heterocyclic nucleus of the cyanine dye type and an acidic nucleus, such as can be derived from barbituric acid, 2-thiobarbituric acid, rhodanine, hydantoin, 2- thiohydantoin, 4-thiohydantoin, 2-pyrazolin-5-one, 2- isoxazoli-5-oneindan-l,3-dione, cyclohexan-1,3-dione, l,3-dioxan-4,6-dione, pyrazolin-3,5-dione, pentan-2,4- dione, alkylsulfonyl acetonitrile, melononitrile, isoquinolin-4-one; and chroman-2,4-dione.

One or more spectral sensitizing dyes may be used. Dyes with sensitizing maxima at wavelengths throughout the visible spectrum and with a great variety of spectral sensitivity curve shapes are known.

Combinations of spectral sensitizing dyes can be used which result in supersensitization; that is, spectral sensitization that is greater in some spectral region than that from any concentration of one of these dyes alone or that which would result from the additive effect of the dyes.

Any processing can be applied to the light- sensitive material of the present invention, including black-and-white and color processes. Processing for color paper, color reversal paper, a color positive film, a color negative film, and color reversal film is known.

The examples below are intended to be illustrative and not exhaustive of the practice of the invention.

EXftMPLE 1 TABLE I:

Silver halide emulsion, type (1) , was prepared as follows:

Solution 1 is heated up to 55°C, and Solution 2 and Solution 3 added to it simultaneously with agitation over 13 minutes at starting flow rate of 22 l/min. and final flow rate of 97 ml/min. Concentration of Solution 2 and Solution 3 is 4 mole/liter. Following a ramp flow, both solutions are fed into the reactor at 97 ml/min. over the time of 27 minutes. The ramp flow is linear. After that emulsion is cooled down to 43°C and desalted, and Solution 4 is added. The effective edge length of the resultant silver chloride cubic Emulsion #101, as shown in Table II, is 0.33 μm. For the preparation of

Emulsion #102, as shown in Table II, dilute solution of HgCl2 in the amount corresponding to 3 X 10^"7 mole Hg per mole Ag replaced some of the water in Solution 3. In the same manner during preparations of Emulsions #103 and #104 dilute solution of KAUCI4 in the amounts correspond- ing to 3 X 10^~7 mole Au per mole Ag and 3 X 10-6 mole Au per mole Ag, respectively, replaces some of the water in Solution 3. All the samples are chemically sensitized in the following manner: sodium thiosulfate, potassium chloroaurate, and potassium bromide are added to the emulsions and chemical ripening is performed for 60 minutes at 70°C. After cooling the emulsions down to 40°C, cyanine blue sensitizing dye anhydro-1-(3-sulfopro- pyl)-3'-methyl-4'-phenyl-naphtho(1,2-d)thiazolo-cyanine hydroxide, 1- (3-acetamidophenyl)-5-mercaptoterazole and sodium bromide are added, thereby preparing Emulsions #101 to #104, as presented in Table II. All these emulsions are coated at 280 mg of silver per square foot on cellulose acetate transparent film support and are subjected to sensitometric gradation exposure through heat absorbing filter using Macbeth sensitometer (color temperature = 5,500°K); exposure time was 1/100 second. The coatings are developed in Kodak black-and-white EAA-l process, and the results are summarized in the Table II below:

As is apparent from Table II, the gold compound added during precipitation exhibits a strong antifogging effect, comparable to that of less environmentally desirable mercuric chloride. The sensitivity to fog ratio, which can be used as a measure of emulsion photographic potential, is the highest for the Emulsion #104 treated with gold compound.

Solution 1 was heated up to 68.3°C, and Solution 2 and Solution 3 are added to it simultaneously, with agitation over 5 minutes at the flow rate of 49 ml/min. Concentration of Solution 1 and Solution 2 was 3.8 mole/liter. After one minute the thioether ripener 1,8-dithiaoctanediol, as described previously in the previous section, is added to the reactor. Then the flow rate is linearly ramped from 49 ml/min. up to 85 ml/min. over 6 minutes. The flow of the reactants is continued at 85 ml/min. for another 23 minutes. After that the emulsion is cooled down to 43°C and desalted, and Solution 4 is added. The effective edgelength of the resultant silver chloride cubic Emulsion #201, as shown in the Table IV, is 0.73 μm. For the preparation of the Emulsion #202, dilute solution of HgCl2 in the amount corresponding to 3 X 10^"7 mole Hg per mole Ag replaced some of the water in Solution 3. In the same manner during preparation of Emulsion #203 dilute solution of KACI4 in the amount corresponding to 3 X 10^"7 mole Au per mole Ag replaced some of the water in the Solution 3. All the samples are chemically sensitized in the following manner: potassium chloroaurate was added to the emulsions, and they are ripened for 65 minutes at 60°C, during which time the cyanine yellow sensitizing dye anhydro-5-chloro-3,3'-di-(3-sulfopropyl)aphto (1,2- d)thiazolothiacyanine hydroxide, 1-(3-acetamidophenyl)-5- mercaptotetrazole and potassium bromide are added to the emulsions. After cooling the emulsions down to 40°C and addition of sodium chloride Emulsions #201 to #203 were prepared, as presented in Table IV. The emulsified dispersion of yellow coupler is prepared by dissolving the following compound: -17-

( C H ₃

and gelatin in appropriate amount of water in order to obtain 11.95% and 9.12% of yellow coupler and gelatin, respectively. The solution of the emulsion stabilizer 2,5-dihydroxy-4-(1-methylheptadecyl)-benzenesulfonic acid in the form of its monosodium salt (120 g/L in 10% propanol/90% water) is also added at the amount corresponding to 13.7 cc per 1 kilogram of coupler. All these emulsions are coated at 26 mg of silver, 100 mg of coupler, and 77 mg of gelatin per square foot on resin coated paper support and were subjected to sensitometric gradation exposure through the set of Kodak filters and heat absorbing filter using a sensitometer IB (available from Eastman Kodak Company; color temperature of light source: 3,000° K) . Exposure times are 1/10 of a second. The coatings were developed in Kodak RA-4 chemistry (Research Disclosure, Vol. 308, 1989, p. 933), and the results are summarized below:

It is apparent from the above data that the gold compound, added during precipitation improved greatly emulsion properties. In case of no emulsion addenda unacceptably high fog is generated, offsetting higher speed gains, as is indicated by emulsion efficiency expressed by Sensitivity to Fog ratio. If mercuric chloride is added for emulsion protection, as in Emulsion #202, Sensitivity is lost. Only gold addition during the make, as in Emulsion #203, remedies the situation at the best Sensitivity to Fog ratio.

-19-

EXAMPLE 3 £&E E_tf:

Silver halide emulsion, type (3), was prepared as follows:

Solution 3 AgNθ3 1475 g

Water to make

Solution 4

H₂0 1347 ml

Gelatin 162 g

Solution 1 is heated up to 68.3°C, and Solution 2 and Solution 3 are added to it simultaneously over 5 minutes at the flow rate of 49 ml/min. Concentration of Solution 1 and Solution 2 is 3.0 mole/liter. Both solutions are fed into the reactor at the constant rate of 20 ml/min. over one minute. Then the flow rate is linearly ramped from 20 ml/min. up to 80 ml/min. over 39 minutes. The flow of the reactants is continued at 80 ml/min. for another 9 minutes. After that the emulsion is cooled down to 43°C and desalted, and Solution 4 is added. The effective edge length of the resultant silver chloride cubic Emulsion #301, as shown in Table VI, is 0.61 μm. For the preparation of Emulsion #302, dilute solution of Gold(I) compound, as described previously, in the amount corresponding to 3 X 10-6 mole per mole Ag replaced some of the water in Solution 3. In the same manner during preparation of Emulsion #303 dilute solution of KAUCI4 in the amount corresponding to 3 X

10"^ mole per mole Ag replaced some of the water in Solution 3. All the samples are chemically sensitized in the following way: gold sulfide is added to the emulsions, and they are ripened for 55 minutes at 60°C. After that the cyanine yellow sensitizing dye, same as the one in Example 2, followed by l-(3-acetamidophenyl)- 5-mercaptoterazole and potassium bromide are added. All the subsequent steps are identical as in Example 2. The results are summarized in Table VI.

TABLE VI

Remarks

301 None 183 0.38 0.48 Com arative

It is clear from the data presented above that both Gold(I) compound and KAUCI4, when added during precipitation, act as antifoggants and improve Sensitivity to Fog ratio. EXAMPLE 4 Silver halide emulsions of the type described in the Example 3, were chemically sensitized in the identical manner as described in Example 3 except that sodium thiosulfate and potassium chloroaurate were added to the emulsions instead of gold sulfide just prior to ripening. The resultant emulsions, Emulsion #401 to #403, undergo identical treatment as those described in the Example 3 and their photographic properties are presented in Table VII.

TABLE VII

This example shows a strong antifogging action of both gold compounds, i.e., Gold(I) compound and KAUCI4, when added during emulsion precipitation and sulfur plus gold sensitized emulsions. This type of emulsion cannot be sulfur plus gold sensitized to the comparable photographic sensitivity without the use of the above compounds. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifica¬ tions can be effected within the spirit and scope of the invention.

Claims

1. A method of forming a low fog silver halide emulsion comprising during silver halide grain formation doping of said emulsion with up to 3 X 10^~5 mole of monovalent or trivalent gold ions per mole of silver.

2. The method of Claim 1 wherein said gold is doped at between 3 X 10^"^ and 3 X 10~⁷ mole per mole of silver.

3. The method of Claim 1 wherein said silver halide comprises from 90 to 100 percent silver chloride and up to 10 percent silver bromide.

4. The method of Claim 1 wherein said gold is added to the precipitation feed solutions during silver halide grain formation.

5. The method of Claim 1 wherein said gold is added as is potassium chloroaurate, potassium arithio- cyanate, auric trichloride, or bis(methylhydaintoinato)- gold(I) sodium salt.

6. The method of Claim 1 wherein said gold is added during the entire time of silver nitrate addition to form said grains.

7. The method of Claim 1 wherein said gold is added as a compound able to provide Gold I or Gold III ions.

8. The method of Claim 1 wherein said gold comprises between 3 X 10~⁵ and 3 X 10"⁸ mole per mole of silver.

9. A silver halide emulsion wherein the silver halide grains comprise up to 3 X 10^~5 mole of monovalent or trivalent gold per mole of silver and said silver halide comprises between 90 and 100 percent silver chloride.

10. The emulsion of Claim 9 wherein said gold is present in an amount of between about 3 X 10"⁶ and 3 X 10^~7 mole^' per mole of silver.

11. T e emulsion of Claim 9 wherein said gold is substantially uniformly distributed in said grains.

12. The emulsion of Claim 9 wherein said grains are predominently cubic.

13. The emulsion of Claim 9 wherein said grains are chemically sensitized with the use of gold.

14. The emulsion of Claim 13 wherein said grains are sulfur sensitized.

15. The emulsion of Claim 9 wherein said gold is present in an amount of between about 3 X 10^"5 and 3 X 10^~8 mole per mole of silver.