GB1586412A - Process of producing a silver halide photographic emulsion - Google Patents

Description

(54) A PROCESS OF PRODUCING A SILVER HALIDE PHOTOGRAPHIC EMULSION (71) We, FUJI PHOTO FILM CO., LTD., a Japanese Company, of No.

210, Nakanuma, Minami Ashigara-Shi, Kanagawa, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a novel process of producing silver halide emulsions and to the emulsions so made.

It is well known that an increase in the size of silver halide grains can increase the photographic sensitivity. In a conventional method in which silver halide grains are prepared using ammonia as a silver halide solvent, large size silver halide grains can, however, be obtained only in a high pH region. Accordingly, it is difficult to attain a high degree of photographic sensitivity, since the fog level becomes high under high pH conditions. In addition, emulsions prepared using such a method are relatively sensitive to pressure. Therefore, the use of ammonia as a silver halide solvent is undesirable, and discovery of silver halide solvents which can be used to increase the size of silver halide grains even in a low pH region is desired.

Moreover, preparation of pressure-insensitive silver halide grains is also preferred.

Organic thioesthers have been proposed for increasing the size of silver halide grains in a low pH region as disclosed in Japanese Patent Publication No. 11386/72 (corresponding to U.S. Patent 3,574,628). However, organic thioethers tend to cause fog in photographic emulsions and, further, purification of the organic thioethers must be repeated numerous times in order to obtain organic thioethers with a desirable purity, so the synthesis of organic thioethers is industrially disadvantageous. Such being the case, the discovery of improved silver halide solvents has been desired.

Therefore, an object of the present invention is to provide a silver halide emulsion with high photographic sensitivity and reduced fog.

Another object of the present invention is to provide a novel silver halide emulsion comprising coarse silver halide grains.

A further object of the present invention is to provide a direct positive silver halide emulsion.

Still another object of the present invention is to provide a silver halide emulsion which is not sensitive to pressure.

Another object of the present invention is to provide a novel process for preparing such a silver halide emulsion as described above.

In accordance with this invention, it has been found that the above-described objects are attained by preparing the silver halide grains in the presence of 5 x 10-8 to 5 x 10-2 mol, per mol of silver halide, of a silver halide solvent represented by the general formula (I):

wherein X represents a sulfur or an oxygen atom; RO and R', which may be the same or different, each represents an optionally substituted alkyl group, aryl group, heterocyclic group or amino group, or RO and R' may together complete a 5- or 6membered heterocyclic ring; and R2 represents an optionally substituted alkyl or aryl group, or R2 and R' may together complete a 5- or a 6-membered heterocyclic ring containing one or more of a nitrogen atom, an oxygen atom and a sulfur atom.

The emulsion of this invention is preferably prepared in a process in which a water-soluble silver salt is reacted with a water-soluble halide in an aqueous solution of a hydrophilic colloid containing the silver halide solvent of the general formula (I).

The silver halide solvent represented by the general formula (I) may be added to the system for preparing the silver halide at any stage in the preparation where the size and the shape of the silver halide grains have not yet reached the size and shape desired.

The silver halide solvent of the general formula (I) may be added to, for example, a colloidal material in which silver halide is precipitated. Alternatively, the silver halide solvent of the formula (I) and either of the water-soluble silver halide or the water-soluble halide salt from which silver halide can be prepared, i.e., water-soluble silver salt (e.g., silver nitrate) or water-soluble halide (e.g., potassium bromide, sodium chloride and other alkali metal halides), may be added in a combination. Moreover, the silver halide solvent of the formula (I) may be added prior to or during the physical ripening of the silver halide. Furthermore, the silver halide solvent of the formula (I) may be added in one or more steps during the process of preparing the silver halide emulsion.

In a preferred embodiment of this invention, the silver halide solvent of the formula (I) is added prior to the physical ripening of silver halide produced.

The emulsions employed in the present invention can be prepared using various methods as described in, for example, P. Glalkides, Chimie et Phisique Photographique, Paul Montel, Paris, (1957), G. F. Duffin, Photographic Emulsion Chemistry, The Focal Press, London (1966), and V. L. Zelikman et al., Making and Coating Photographic Emulsions, The Focal Press, London, (1964).

Suitable methods for reacting a water-soluble silver salt with a water-soluble halide include, e.g., a single jet method, a double jet method or a combination thereof.

Also, a method in which silver halide grains are produced in the presence of excess silver ion (the so-called reverse mixing method) can be employed in this invention. On the other hand, the so-called controlled double jet method, in which the pAg of the liquid phase in which silver halide grains are to be precipitated is maintained constant, may be also employed herein.

The silver halide emulsions of the present invention are, in general, prepared .under conditions of a temperature ranging from about 30"C to about 90"C, in a pH range from about 2 to about 9, and preferably, from 2 to 8, and at a pAg of about 4 to about 10, preferably 5 to 10.

In a process of producing silver halide grains or allowing the produced silver halide grains to ripen physically, cadmium salts, zinc salts, thallium salts, iridium salts or complexes, rhodium salts or complexes, iron salts or complexes and/or the like may be present.

Examples of silver halides which may be present in the silver halide emulsions of this invention include silver bromide, silver iodide, silver chloride, silver chlorobromide, silver iodobromide, silver chlorobromoidodide and so on.

Preferred silver halide emulsions comprise silver halide grains in which the halide composition of the silver halide is at least about 50 mol% bromide and, more particularly, containing about 10 mol% iodide or less and the remainder bromide.

A suitable mean diameter of the silver halide grains ultimately produced by this invention ranges from about 0.2 micron to 4 microns, preferably from 0.25 micron to 2 microns. Particularly, silver halide grains having a mean diameter of about 0.5 to 2 microns provide good results. The grain size distribution may be narrow or broad. The mean diameter of the grains can be measured using conventional techniques as described in, for example, -The Photographic Journal, Vol. 79, pp. 330338, (1939).

The silver halide grains in the photographic emulsion produced in this invention may have a regular crystal form, such as that of a cube or an octahedron; an irregular crystal form, such as that of a sphere, a plate or so on; or a composite form thereof. A mixture of various crystal forms of silver halide grains may be also present.

The interior and the surface of the silver halide grains may differ or the silver halide grains may be uniform throughout. Further, either silver halide grains of the kind which form latent image predominantly at the surface of the grains or grains of the kind which mainly form latent image inside the grains can be used.

The silver halide emulsion is coated at a coverage of about 50 to about 600 mg of silver per square foot of the support.

Silver chloride is more soluble in aqueous solutions of the silver halide solvents represented by the formula (I) which are employed in the present invention than silver chloride is in water. As described in greater detail hereinafter, a 0.01 mol or less aqueous solution of the silver halide solvent represented by the formula (I) at 60"C is capable of dissolving a larger quantity of silver chloride than can be dissolved by water at 600C by a factor of 1.5 (by weight) or higher.

The silver halide solvents represented by the general formula (I) above which can be employed in the present invention have in each molecule either a sulfur atom or an oxygen atom, and at least one thiocarbonyl group attached to a nitrogen atom (i.e.,

where X is a sulfur atom or an oxygen atom), with the nitrogen atom not being substituted with hydrogen atoms.

Silver halide solvents employed in the present invention are represented by the aforesaid general formula (I), namely;

wherein X represents a sulfur atom or an oxygen atom; RO and R', which may be the same or different, each represents a straight or branched chain alkyl group (e.g., an alkyl group containing 1 to 4 carbon atoms which may be substituted with one or more of a carboxy group, a hydroxy group, an aryl group (e.g., a monocyclic aryl group and preferably a phenyl group) or a like group, with specific examples including a methyl group, an ethyl group, a propyl group, a butyl group, a carboxymethyl group, a carboxyethyl group, a carboxypropyl group, a sulfoethyl group, a sulfopropyl group, a sulfobutyl group, a hydroxyethyl group, a benzyl group, a phenethyl group and the like); an aryl group (e.g., an unsubstituted - monocyclic aryl group or a monocyclic aryl group substituted with one or more of, for example, a straight or branched chain alkyl group (preferably having 1 to 4 carbon atoms), a sulfo group, a straight or branched chain alkoxy group (preferably having 1 to 4 carbon atoms in the alkyl moiety thereof), a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, etc.) or the like, with preferred specific examples including a phenyl group, a 2 methylphenyl group, a 4-sulfophenyl group, a 4-ethoxyphenyl group, a 4 chlorophenyl group and the like); a heterocyclic group (e.g., a 5- or a 6-membered nitrogen-containing heterocyclic group, with specific examples including a 2 pyridyl group, a 3-pyridylwroup, a 4-pyridyl group and the like); and an amino group (preferably a substituted amino group, for example, an arylamino group in which the aryl moiety may be unsubstituted or substituted with one or more of a straight or branched chain alkyl group, a sulfo group, a carboxy group and the like, with preferred specific examples including a 4-sulfophenylamino group and like groups).

Further, RO and R' may be linked so as together complete a 5- or 6-membered heterocyclic ring containing one or more of a nitrogen atom, an oxygen atom and a sulfur atom as hetero atoms (e.g., piperidine, morpholine, piperazine or the like ring).

R2 in the formula (I) represents a straight or branched chain alkyl group (e.g., an alkyl group having I to 4 carbon atoms which may be unsubstituted or substituted with one or more of a carboxyl group, a sulfo group, a hydroxy group, an aryl group (e.g., a monocyclic aryl group and, preferably a phenyl group) or like groups, with specific examples including a methyl group, a ethyl group, a propyl group, a butyl group, a carboxymethyl group, a carboxyethyl group, a carboxypropyl group, a sulfoethyl group, a sulfopropyl group, a sulfobutyl group, a hydroxyethyl group, a benzyl group, a phenethyl group and so on); or an aryl group (e.g., an unsubstituted monocyclic aryl group or a monocyclic aryl group substituted with one or more of, for example, a straight or branched chain alkyl group (preferably having 1 to 4 carbon atoms), a sulfo group, a straight or branched chain alkoxy group (preferably having I to 4 carbon atoms in the alkyl moiety thereof), a halogen atom (e.g., a fluorine atom, a chlorine atom a bromine atom) or the like, preferably a phenyl group, a 2-methylphenyl group, a 4-sulfophenyl group, a 4-ethoxyphenyl group, a 4-chlorophenyl group or the like).

Also, R' and R2 may combine and form a 5- or a 6-membered heterocyclic ring containing one or more of a nitrogen atom, an oxygen atom and a sulfur atom as hetero atoms. Compounds with such a heterocyclic ring formed by R' and R2 are preferred silver halide solvents for use in the practice of the present invention.

Typical examples of such compounds are those having the following general formula (II):

wherein Q represents the atoms necessary to complete a heterocyclic ring containing one or more of a nitrogen atom, an oxygen atom and a sulfur atom as hetero atoms (which can be a 5- or a 6-membered ring and which can further include a heterocyclic ring condensed with an unsaturated ring containing 5 to 6 carbon atoms, for example, a benzene ring, a tetrahydrobenzene ring or the like), and X and RO each has the same meaning in the formula (I).

Compounds of the general formula (II) are illustrated in further detail below.

Q represents the atoms necessary to complete a teterocyclic ring (which preferably is a 5-membered ring), with specific examples including thiazolidine-2-thione rings (e.g., thiazolidine-2-thione, 5-methylthiazolidine-2-thione, 4-carboxythiazolidine-2thione and the like), 4-thiazoline-2-thione rings (e.g., 4-methyl-4-thiazoline-2thione, 4-carboxymethyl-4-thiazoline-2-thione, 4-carboxy-4-thiazoline-2-thione and the like), 1,3,4-thiadiazoline-2-thione rings (e.g., 5-ethylthio-1,3,4- thiadiazoline-2-thione and the like), benzothiazoline-2-thione rings (e.g., benzothiazoline-2-thione, 5-carboxybenzothiazoline-2-thione, 5sulfobenzothiazoline-2-thione, 5-methylbenzothiazoline-2-thione and the like), benzoxazoline-2-thione rings (e.g., benzoxazoline-2-thione, 5-sulfobenzoxazoline2-thione, 5-methylbenzoxazoline-2-thione and the like) and so on.

RO has the same meaning as RO in the general formula (I).

RO or the substituents which may be attached to the nucleus of the heterocyclic ring completed by Q may contain a sulfonate or a carboxylate moiety which is preferably water-soluble. Preferred cations forming such salt moieties are alkali metal ions and, more particularly, Na+ and K+.

The nitrogen-containing heterocyclic compounds represented by the general formula (II) include compounds represented by the general formulae (IIa), (IIb) and (tic), respectively. Particularly, compounds represented by the formula (IIa) are preferred since they are excellent silver halide solvents.

In the general formulae (IIa) to (tic), X represents a sulfur atom or an oxygen atom.

A and B in the formula (IIa), which may be the same or different, each represents a hydrogen atom, a carboxyl group, a straight or branched chain alkyl group which may be substituted, an aryl group which may be substituted, a straight or branched chain alkoxycarbonyl group or A and B may combine and represent the atoms necessary to complete an unsaturated ring containing 5 to 6 carbon atoms (e.g., a monocyclic ring such as a benzene ring, a tetrahydrobenzene ring, etc.) (which ring is preferably substituted with a substituent such as a sulfo group or a carboxy group).

However, where A and B combine and form an unsaturated ring having 5 to 6 carbon atoms, the compounds represented by the formula (lea) should contain at least one group selected from the group consisting of a hydroxy group, a sulfo group and a carboxy group.

Y in the formula (lIb) represents a hydrogen atom, a carboxy group, a straight or branched chain alkyl group, e.g., a methyl group, an ethyl group, etc., or an aryl group, e.g., a monocyclic aryl group such as a phenyl group, etc.

RO in the formulae (IIa) to (tic) has the same meaning as in the formula (I).

E and G in the formula (IIc), which may be the same or different, each represents a hydrogen atom, a straight or branched alkyl group or a carboxy group.

Compounds of the formulae (lea) to (lIc) are described in greater detail below.

A and B each represents a hydrogen atom; a sulfo group; a carboxy group; a straight or branched chain alkyl group (e.g., an alkyl group having 1 to 6, preferably 1 to 4 carbon atoms, which may be unsubstituted or substituted with one or more of a hydroxy group, a halogen atom, e.g., a fluorine atom, a chlorine atom, a bromine atom, etc., a carboxy group, a sulfo group, an aryl group (e.g., a monocyclic aryl group and preferably a phenyl group) or the like, with specific examples including a methyl group, an ethyl group, a butyl group, a hydroxyethyl group, a sulfopropyl group, a carboxymethyl group, a benzyl group or the like); an aryl group (e.g., an unsubstituted monocyclic aryl group or a monocyclic aryl group substituted with one or more of a straight or branched chain alkyl group, a hydroxy group, a halogen atom, e.g., a fluorine atom, a chlorine atom, a bromine atom, etc., a carboxy group, a sulfo group or the like, with specific examples including a phenyl group, a 4-methylphenyl group, a 4-hydroxyphenyl group, a 3- or a 4-chlorophenyl group, a 4-carboxyphenyl group, a 4-sulfophenyl group and so on); a straight or branched chain alkoxy-carbonyl group in which the alkyl moiety preferably has 1 to 5 carbon atoms (e.g., an ethoxycarbonyl group); or A and B when combined represents the atoms necessary to complete an unsaturated ring containing 5 to 6 carbon atoms, e.g., a benzene ring, a tetrahydrobenzene ring (in which the ring preferably is substituted with a substituent such as a sulfo group, a carboxy group or the like), with specific examples including a trimethylene group, a tetramethylene group or the like, or the atoms necessary to complete an unsubstituted or substituted benzene ring. Specific examples of substituents which can be present on the benzene ring formed by the combination of A and B are one or more of a straight or branched chain alkyl group (preferably having 1 to 4 carbon atoms, e.g., a methyl group, an ethyl group), an aryl group (e.g., a monocyclic aryl group such as a phenyl group), a straight or branched chain alkoxy group (with the alkyl moeity containing preferably 1 to 4 carbon atoms, e.g., a methoxy group, an ethoxy group), a halogen atom (e.g., a chlorine atom, a bromine atom), a straight or branched chain alkyl group substituted with a carboxyl group (in which the alkyl moiety contains preferably 1 to 3 carbon atoms, e.g., a carboxymethyl group), an arylamino group (in which the aryl moiety is preferably a phenyl group, e.g., anilino), a carboxy group, a sulfo group and so on.

Y in the formula (IIb) represents a hydrogen atom, a carboxy group, a straight or branched chain alkyl group (e.g., an alkyl group containing 1 to 6, preferably 1 to 4 carbon atoms, which may be unsubstituted or substituted with one or more of a hydroxy group, a sulfo group, a carboxy group or the like, with specific examples including a methyl group, an ethyl group, a carboxymethyl group, a carboxyethyl group, a hydroxyethyl group), or an aryl group (e.g., an unsubstituted monocyclic aryl group (preferably a phenyl group), or a monocyclic aryl group substituted with one or more of a sulfo group, a carboxy group or the like (e.g., p-sulfophenyl)).

E and G each represents a hydrogen atom, a straight or branched chain alkyl group (e.g., an alkyl group (preferably containing 1 to 4 carbon atoms) which may be unsubstituted or substituted with, for example, a carboxy group or the like, with specific examples including a methyl group, a carboxymethyl group, a carboxyheptyl group, or a carboxy group.

Specific examples of the silver halide solvents of the formula (I) which can be effectively used in the practice of the present invention are set forth below.

Compound (1) Compound (2)

Compound (3) Compound (4)

Compound (5) Compound (6)

Compound (7) Compound (8)

Compound (9) Compound (10)

Compound (1) Compound (12)

Compound (13) Compound (14)

Compound (15) Compound (16)

Compound (17) Compound (18) Compound (19)

The synthesis of these compounds employed as a silver halide solvent in the practice of the present invention is illustrated below. Unless otherwise indicated, all parts, percents, ratios and the like are by weight.

Synthesis Example 1.

Synthesis of Compound (2): 21.8 g (0.25 mol) or morpholine and 14 g (0.25 mol) of potassium hydroxide were dissolved in 200 ml of ethyl alcohol. The reaction mixture was cooled to a temperature below 5"C. To the cooled alcohol solution, 19 g (0.25 mol) of carbon disulfide was added with stirring. After continuing the stirring for 2 hpurs, 35.5 g (0.25 mol) of methyl iodide was added to the resulting solution and the solution was heated under reflux for 2 hours. Then, the reaction mixture was cooled and crystals precipitated. The resulting crystals were recovered by filtration, and recrystallized from ethanol. The yield was 22 g (50%), and the melting point was 86--87"C.

Synthesis Example 2.

Synthesis of Compound (4): 15.2 g (0.2 mol) of carbon disulfide in 100 ml of ethanol was added to a solution prepared by dissolving 25 g (0.2 mol) of taurine in 200 ml of water containing 22.4 g (0.4 mol) of potassium hydroxide while the reaction mixture was cooled to a temperature of below 5"C with stirring. The stirring was continued for 2 hours at room temperature (about 20 to 300C) to drive the reaction to completion. While the resulting solution was cooled (not higher than 5"C) and with stirring, 18.5 g (0.2 mol) of monochloroacetone was added dropwise thereto over a time of about 30 minutes. In order to force this reaction to-completion, the reaction mixture was allowed to stand for 3 hours at room temperature. Then, the reaction mixture was condensed and crystals deposited. The resulting crystals were separated by filtration, and dried. The dried crystals were suspended in ethanol. The pH of this suspension was adjusted to an acidic pH range (pH 34) using sulfuric acid and the suspension was heated under reflux for 30 minutes. Upon cooling, the product crystallized out. The resulting crystals were recovered by filtration, and recrystallized from a dilute aqueous solution of potassium hydroxide.

The yield was 10 g (20%), and the melting point was 300"C or above.

Synthesis Example 3.

Synthesis of Compound (7): 30 ml (0.5 mol) of carbon disulfide was added to a 250 ml of a methanol solution containing 44 g (0.5 mol) of p-aminopropionic acid and 28 g (0.5 mol) of potassium hydroxide while the reaction mixture was cooled to a temperature below 5"C with stirring. After continuing the stirring for 2 hours, a methanol solution containing 100 g (0.5 mol) of phenacyl bromide cooled to a temperature below 5"C was added dropwise thereto. After the dropwise addition, stirring was continued for 2.5 hours at room temperature. Next, to the reaction mixture, 220 ml of water was added and then methanol was removed therefrom by distillation at reduced pressure. The resulting solution was cooled and stirred in an ice bath, and acidified using hydrochloric acid (adjusted to pH 3 < ) with crystals separating. The crystals were recovered by filtration and washed with water. Thus, 116 g of 4-phenyl-3 (2-carboxy-ethyl)-4-hydroxythiazolidine-2-thione was obtained (m.p. 1320 C).

These crystals were dissolved in 500 ml of glacial acetic acid and heated under reflux for 30 minutes. After cooling, 1 liter of water was added thereto and the product separated out as crystals. The thus-obtained crystals were recovered by filtration.

The yield was 89 g (65%), and the melting point was 134--136"C.

Compounds (5), (6), (8), (9), (10), (11), (12), (13), (14) and (19) described above can be synthesized using methods as set forth above for the syntheses of Compounds (4) and (7).

Synthesis Example 4 Synthesis of Compound (17): 18.1 g (0.1 mol) of 2-methylthiobenzothiazole and 18 g (0.15 mol) of propane sultone were reacted with each other for 1 hour in the absence of a solvent in an oil bath at a temperature of 1300C. After the reaction, 50 ml of xylene was added to the reaction product and the system decanted. The residue was washed with 50 ml of acetone, and the resulting supernatant was decanted off. To the residue, 50 ml of water and 28.8 g (0.12 mol) of sodium sulfite were added sequentially. On stirring at room temperature, crystals separated out. The crystals were recovered by filtration, and recrystallized from isopropyl alcohol containing 20% by volume water.

The yield was 10 g (32%), and the melting point was 312"C (decomposition).

Compounds (15) and (16) can be synthesized according to the above-described process for the synthesis of Compound (17).

The syntheses of other silver halide solvents which can be employed in the present invention can be by reference to K. C. Kennard and J. A. Van Allen, J. Org.

Chem., Vol. 24, pp. 470473, (1959), R. W Lamon and W. J. Humphlett, J.

Heterocycl. Chem., Vol. 4, pp. 605609, (1967), M. Ohara, Japanese Patent Publication No. 26203/64, and M. Morita, Yakushi (Pharmaceutical Journal), Vol.82, pp. 3645, (1962).

The amount of the silver halide solvent represented by the general formula (I) in the present invention added to one or more of the silver halide emulsion-making components should be sufficient to effectively achieve the effect of the silver halide solvent to a desired extent. This amount will depend upon the kind of compound used, within the range from 5 x 10-8 mol to 5 x 10-2 mol of the compound represented by the formula (I) per mol of silver halide. Especially good results are obtained when the compound of the formula (I) is employed in the range of from about 1 x 10-5 to about 2.5 x 10-2 mol per mol of silver halide.

Removal of the soluble salts from the silver halide emulsion is, in general, carried out after the formation of the silver halide or after physical ripening. The removal can be effected using the noodle washing method which comprises gelling the gelatin, or using a coagulation process (thereby causing flocculation in the emulsion) taking advantage of a sedimenting agent such as a polyvalent anioncontaining inorganic salt (e.g., sodium sulfate), an anionic surface active agent or an anionic polymer (e.g., polystyrene sulfonic acid), or a gelatin derivative (e.g., an aliphatic acylated gelatin, an aromatic acylated gelatin, an aromatic carbamoylated gelatin or the like). Preferred sedimenting processes for this purpose are disclosed, for example, in U.S. Patents 2,614,928, 2,618,556, 2,565,418, 2,489,341 and so on.

The removal of soluble salts from the silver halide emulsion may be omitted, but it is preferred for the compound represented by the formula (I) of the present invention to be substantially removed from the silver halide emulsion prior to chemical sensitization.

The silver halide emulsion of this invention can be a so-called primitive (unsensitized) emulsion, that is to say, a chemically unsensitized emulsion.

Mowever, it is usual and preferred for the emulsion of this invention to also be chemically sensitized. Chemical sensitization can be carried out using processes described in P. Glafkides, supra, V. L. Zelikman et al., supra or H. Frieser, Die Gründlagen der Photographischen Prozesse mit Silberhalogeniden, Akademische Verlagesgesellschaft, (1968).

More specifically, sulfur sensitization using compounds containing sulfur capable of reacting with silver ion or active gelatin, reduction sensitization using reducing materials, sensitization with gold or other noble metal compounds and so on can be employed individually or as a combination thereof. Examples of suitable sulfur sensitizers which can be used include thiosulfates, thi compounds represented by the general formula (I) can be doped with metal ions from iridium salts, rhodium salts, lead salts and so on. Also, the silver halide emulsions of the present invention can be doped metal ion-free direct positive emulsions. The fogging can be attained by treating the silver halide grains chemically or physically using known methods.

The fogged nuclei can be produced by previously fogging chemically the silver halide emulsion used. More specifically, the fogged nuclei can be produced advantageously by addition of inorganic reducing compounds such as stannous chloride, boron hydride, etc., or organic reducing compounds such as hydrazine derivatives, formaldehyde, thiourea dioxide, polyamino compounds, amine boranes, methyldichlorosilane, etc. For instance, combinations of a reducing agent and a metal ion more noble than silver ion, and of a reducing agent and a halide ion may be employed. Such combinations are disclosed in, for example, U.S. Patents 2,497,875, 2,588,982, 3,023,102, 3,367,778 and 3,501,307, British Patents 707,704, 723,019, 821,251 and 1,097,999, French Patents 1,513,840, 739,755, 1,498,213, 1,520,822 and 1,520,824, Belgian Patents 708,563 and 720,660, Japanese Patent Publications 13488/68 and 40900/71, and so on.

The silver halide grains can be fogged either before or after the coating thereof on a support in the present invention.

Where the emulsions of the present invention are applied to direct positive light-sensitive materials, not only the above-described sensitizing dyes but also desensitizing agents or dyes, and the so-called electron acceptors can be present in the silver halide emulsions. Many useful electron acceptors are described in, for example, U.S. Patents 3,023,102, 3,314,796, 2,901,351, 3,367,779, 3,501,307 and 3,505,070, British Patents 723,019, 698,575, 667,206, 748,681, 698,576, 824,839, 796,873, 875,887, 905,237, 907,367, 940,152, 1,155,404 and 1,237,925, Japanese Patent Publications 13167/68, 14500/68 and 23513/71, and so on.

The photographic emulsions of the present invention may contain, for example, polyalkylene oxides and derivatives such as the ethers, esters and amines thereof, thioether compounds, thiomorpholines, quaternary ammonium salt compounds, urethane derivatives, urea derivatives, imidazole derivatives, 3pyrazolidones and so on in order to increase the sensitivity and the contrast thereof, or in order to accelerate the developing rate thereof. Examples of such compounds are described in, for instance, U.S. Patents 2,400,532, 2,423,549, 2,716,062, 3,617,280, 3,772,021, 3,808,003 and so on.

The silver halide emulsions of the present invention may contain antifoggants and stabilizers. The compounds described in "Antifoggants and Stabilizers", Product Licensing Index, Vol. 92, p. 107 can be employed herein.

Developing agents can be present in the silver halide emulsions of the present invention. Examples of suitable developing agents which can be employed are described in "Developing Agents", Product Licensing Index, Vol. 92, pp. 107 to 108.

The silver halide grains can be dispersed into a colloid capable of being hardened by various organic or inorganic hardeners. Examples of suitable hardeners are those described in "Hardeners", Product Licensing Index, Vol. 92, p.

108.

The silver halide emulsions can contain coating aids. Coating aids as described in "Coating Aids", emulsions can Product Licensing Index, Vol. 92, p. 108 can be employed.

The silver halide emulsions of the present invention can contain a color coupler. Suitable color couplers which can be employed are described in "Color Materials", Product Licensing Index, Vol. 92, p. 110.

'The photographic emulsion layers and/or other hydrophilic colloidal layers of the light-sensitive material prepared in accordance with the, present invention may contain dyes such as filter dyes, anti-irradiation dyes or dyes for other various purposes. Examples of such dyes are those described in "Absorbing and Filter Dyes", Product Licensing Index, Vol. 92, p. 109.

The silver halide photographic emulsions additionally may contain antistatic agents, plasticizers, matting agents, lubricants, ultraviolet light absorbing agents, brightening agents, aerial fog-preventing agents and so on.

Binders described in "Binders", Product Licensing Index, Vol. 92, p. 108 (Dec.

1971) can be employed in the silver halide emulsions used in the present invention.

The silver halide emulsions are coated on a support, optionally together with other photographic layers. Suitable coating techniques which can be used are described in "Coating Procedures", Product Licensing Index, Vol. 92, p. 109.

Suitable supports which can be employed are described in "Supports", Product Licensing Index, Vol. 92, p. 108.

The silver halide photographic emulsions of the present invention can be used in various ways, for example, as set forth in detail below.

The silver halide emulsions can be used as color positive emulsions, color paper emulsions, color negative emulsions, reversal color emulsions (with or without couplers), emulsions for photographic light-sensitive materials suitable for the graphic arts (e.g., lithographic films), emulsions used in light-sensitive materials for recording a cathode-ray tube display, emulsions used in light-sensitive materials for X-ray recording (particularly, for X-ray photography and fluorography utilizing a screen), emulsions employed for colloid transfer process (e.g., as described in U.S. Patent 2,716,059), emulsions for the silver salt diffusion transfer process (e.g., as described in U.S. Patents 2,352,014, 2,543,181, 3,020,155, 2,861,885 and so on), emulsions for the color diffusion-transfer process (as disclosed in U.S. Patents 3,087,817, 3,185,567, 2,983,606, 3,253,915, 3,227,550, 3,227,551, 3,227,552, 3,415,644, 3,415,645 and 3,415,646, ReseaPch Disclosure, Vol. 151, No. 15162, pp.

75-87 (Nov., 1976), and so on), emulsions employed for the dye transfer process (imbibition transfer process) (as disclosed in U.S. Patent 2,882,156 and so on), emulsions employed for the silver dye bleach process (described in Friedman, History of Color Photography, American Photographic Publishers Co., (1944), particularly Chapter 24, British Journal of Photography, Vol. 111, pp. 308-309 (Apr.

7, 1964), and so on), emulsions employed for direct positive light-sensitive materials (e.g., as disclosed in U.S. Patents 2,497,875, 2,588,982, 3,367,778, 3,501,306, 3,501,305, 3,672,900, 3,477,852, 2,717,833, 3,023,102, 3,050,395, 3,501,307 and so on), emulsions employed for heat-developable light-sensitive materials (e.g., as disclosed in U.S. Patents 3,152,904, 3,312,550 and 3,148,122, British Patent 1,110,046 and so on), emulsions employed for light-sensitive materials for physical development (e.g., as disclosed in British Patents 920,277, 1,131,238 and so on) and the like.

The emulsions of the present invention can, in particular, be utilized to advantage as emulsions employed for multi-layered coupler-in-emulsion type color films and, more particularly, reversal color and negative color films, emulsions for black-and-white negative films (including black-and-white highly sensitive negative films, micro-negative films and so on), emulsions for the color diffusion transfer process and emulsions for direct positive light-sensitive materials.

The exposure for obtaining a photographic image may be carried out in a conventional manner. Any various known light sources including natural light (sunlight), a tungsten lamp, a fluorescent lamp, a mercury lamp, a xenon arc lamp, a carbon arc lamp, a xenon flash lamp, cathode-ray tube flying spot and so on can be employed for the exposure; Suitable exposure times which can be used include not only exposure times commonly used in cameras ranging from about 1/1,000 to about 1 sec, but also exposure times shorter than 1/1,000 sec, for example, about l/104 to about 1/106 sec as used with xenon flash lamps and cathode-ray tubes.

.Exposure times longer than 1 sec can also be used. The spectral distribution of the light employed for the exposure can be controlled using color filters, if desired.

Laser beams can be also employed for the exposure. Moreover, the emulsions of the present invention may be also exposed to light emitted from phosphors excited by electron beams, X-rays, -rays, a-rays and the like.

Any known methods of photographic .processing can be employed for the photographic processings of the light-sensitive materials prepared using the emulsions of the present invention. For instance, the photographic processings described in "Processing", Product Licensing Index, Vol. 92, p. 110 can be employed.

The silver halide photographic emulsions prepared in the presence of the compounds represented by the general formula (I) have reduced fog and increased photographic sensitivity. These emulsions are insensitive to pressure. The compounds represented by the general formula (I) act as a silver halide solvent even in a low pH range and can be used to produce coarse silver halide grain containing emulsions. The photographic silver halide emulsions prepared in the presence of the compounds represented by the general formula (I) have a more highly increased internal sensitivity than that attained using silver halide photographic emulsions prepared in the presence of organic thioethers.

In accordance with one embodiment of the present invention, comparatively coarse silver halide grain-containing photographic emulsions can be prepared in the presence of the silver halide solvents represented by the general formula (I), with the mean diameter of the silver halide grains produced being preferably larger than about 0.25 micron, more particularly, larger than about 0.5 micron.

In another embodiment of the present invention, novel direct positive photographic emulsions which comprise previously fogged silver halide grains having a mean diameter larger than 0.25 micron can be produced.

In still another embodiment of the present invention, novel photographic emulsions which comprise silver halide grains doped with metal ions and having a mean diameter larger than 0.25 micron can be produced.

In a further embodiment of the present invention, photographic emulsions having a low degree of pressure sensitivity which comprise silver halide grains having a mean diameter larger than 0.25 micron can be obtained.

The present invention will now be illustrated in greater detail by reference to; the following examples.

Example 1.

An aqueous solution of potassium bromide and an aqueous solution of silver nitrate both were simultaneously added dropwise to an aqueous solution of gelatin over a period of about 90 minutes at a temperature of 75"C with vigorous stirring to produce a monodispersed silver bromide photographic emulsion containing silver bromide grains having a mean diameter of about 0.2 micron (Emulsion A). The pH of the reaction mixture was maintained at about 5 during the silver halide precipitation and the value of the pAg was held at about 8.7. The resulting emulsion was washed with water in a conventional manner.

A monodispersed silver bromide photographic emulsion (Emulsion B) which comprised silver bromide grains having a mean diameter of about 0.8 micron was prepared in the same manner as Emulsion A except that 0.6 g of 34-dimethyl-1,3- thiazoline-2-thione (Compound (11)) corresponding to the silver halide solvent represented by the general formula (I) was added to the aqueous gelatin solution prior to the precipitation of the silver bromide grains. Microscopic examination of these emulsions showed that the compound represented by the general formula (I) enlarged the grain size when such was present in precipitate incorporated in the emulsion. Each of these emulsions was sulfur with gold sensitized according to the method disclosed in U.S. Patent 2,399,083. Each of the emulsion samples was coated on a cellulose acetate film support at a coverage of 400 mg of silver and 656 mg of gelatin per square foot. Each of the coated samples was exposed through an optical wedge for 1/10 second using a tungsten light source of 400 lux and then developed for 10 minutes at 200C using a surface developing solution X.

Surface Developer X N-Methyl-p-aminophenol Sulfate 2.5 g Ascorbic Acid 10.0 g Potassium-Metaborate 35.0 g Potassium Bromide 1.0 g Water to make ll In each of the samples, the photographic sensitivity at an optical density of 0.1 higher than the fog density and the maximum density were determined in the same manner. The results obtained are shown in Table 1 below.

Table 1 Amount of Mean Grain Relative Emulsion Compound (11) Diameter Sensitivity Dmax (g/mol Ag) A - 0.23 100 2.11 (standard) B 0.65 0.80 794 2.00 It can be seen from the results in Table 1 that the emulsion coated in which the silver halide precipitate was produced in the presence of the compound represented by the general formula (I) exhibited markedly increased speed. Where an aqueous solution of a mixture of potassium bromide and potassium iodide was employed instead of potassium bromide alone, similar results were obtained.

A monodispersed silver bromide photographic emulsion (Emulsion C) comprising silver bromide grains having a mean diameter of about 0.8 micron was prepared in the same manner as Emulsion B except that ammonia was employed as a silver halide solvent instead of 3,4-dimethyl- 1 ,3-thiazoline-2-thione (Compound (11)), and the pH of the reaction mixture was maintained about 9.5 instead of a pH of about 5. This emulsion was sulfur and gold sensitized, coated and evaluated in a similar manner to that described above. The following results were obtained.

Table 2 Mean Grain Relative Emulsion Diameter Sensitivity Dmax Admin O B 0.80 200 2.00 0.20 C 0.80 100 1.92 0.30 It can be seen from the results in Table 2 that the emulsion in which the precipitate was produced in the presence of the compound represented by the general formula (I) has markedly increased sensitivity and greatly reduced L'min in comparison with the emulsion in which the precipitate was produced in the presence of ammonia.

Example 2.

An emulsion was prepared and evaluated in the same manner as Emulsion B except that Compound (4) (potassium 2-(4-methyl- 1 ,3.thiazoline-2-thione)-3-yl- ethylsulfonate) was employed as a silver halide solvent instead of using Compound (11) (3,4-dimethyl- 1 ,3-thiazoline.2-thione). Similar results to those obtained in Example 1 were obtained.

Example 3.

An aqueous solution of potassium bromide and an aqueous solution of silver nitrate were simultaneously added dropwise to an aqueous gelatin solution over a period of about 90 minutes at a temperature of 75"C with vigorous stirring to obtain a silver bromide emulsion comprising silver- bromide grains having a mean diameter of about 0.8 micron. 0.65 g of 3,4-dimethyl-1,3-thiazoline-2-thione was added to the gelatin aqueous solution before the silver halide precipitate separated out, the pH value was maintained at about 6 during the precipitation, and the pAg value was held at about 8.7. The resulting silver bromide grains were chemically sinsitized by adding 3.4 mg/mol of silver of sodium thiosulfate and 3.4 mg/mol of silver of potassium chloroaurate thereto. One portion of the chemically sensitized grains was further treated under the same conditions for the initial precipitation to achieve additional grain size growth. Thus, silver bromide grains having a final mean diameter of about 1.2 microns were obtained. Next, the surfaces of the silver halide grains in the resulting emulsion were chemically sensitized by adding thereto 0.26 mg/mol of silver of sodium thiosulfate and 0.35 mg/mol of silver of potassium chloroaurate and then by heating at 600 C. The thus-obtained emulsion (which comprised silver bromide grains with a core and a shell, and which had high internal sensitivity, but low surface sensitivity) was coated and exposed in the same manner as in Example 1. Then, the material was development-processed using the following Fogging Developer Y.

Fogging Developer Y N-Methyl-p-aminophenol Sulfate 5 g Hydroquinone lOg Sodium Sulfite lOg Sodium Metaborate 30 g Potassium Hydroxide Amount necessary to maintain the pH of the developer at 11.5 p-Tolylhydrazine Hydrochloride 0.1 g 5-Methylbenzotriazole 0.02 g Water to make 11 A good quality reversal image was obtained.

Example 4.

Thiourea dioxide (Additive 1) was added to each of Emulsion A and Emulsion B produced as described above in different amounts as set forth in Table 3 below and then the emulsions were heated for 60 minutes at 650 C. Next, potassium chloroaurate (Additive 2) was added to each of the resulting emulsions in different amounts as set forth in Table 3 below and then the emulsions were heated for 60 minutes at 650C. Thus, each of the emulsions was reduced and fogged with gold.

Further, pinakryptol yellow (Dye 1) which acts as an electron acceptor was added to each of the emulsions in different amounts as set forth in Table 3 below. Each of the emulsion samples was coated, exposed and developed with Surface Developer C as described in Example 1. In each of the samples, the photographic sensitivity at a density corresponding to half of the sum of the maximum and the minimum densities (DmaX+Dm,n/2), and the maximum density were evaluated in the same manner. The amounts of each of Additive 1, Additive 2 and Dye 1 set forth in Table 3 below were amounts providing optimum effects for each of the emulsions.

Table 3 Relative Emulsion Additive 1 Additive 2 Dye 1 Sensitivity Dmax (mg/mol Ag) (mg/mol Ag) (mg/mol Ag) A 0.20 2.0 100 100 1.82 B 0.16 0.65 30 1,420 1.53 It can be seen from the results in Table 3 that the emulsion comprising the precipitate produced in the presence of the compound represented by the general formula (I) exhibited markedly increased photographic sensitivity.

WHAT WE CLAIM IS: 1. A process of producing a silver halide photographic emulsion comprising precipitating silver halide grains in an aqueous solution of a hydrophilic colloid and in the presence of 5 x 10-0 to 5 x 10-2 mol, of silver halide, of a silver halide solvent represented by the general formula (I):

wherein X represents a sulfur atom or an oxygen atom; RO and R1, which may be the same or different, each represents an optionally substituted alkyl, aryl, heterocyclic or amino group, or RO and R' may together complete a 5- or 6membered heterocyclic ring; and R2 represents an optionally substituted alkyl or aryl group, or R2 and R' may together complete a 5- or 6-membered heterocyclic ring containing one or more of a nitrogen atom, an oxygen atom and a sulfur atom.

2. A process as claimed in Claim 1, wherein said silver halide solvent is represented by the general formula (ill):

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Potassium Hydroxide Amount necessary to maintain the pH of the developer at

   11.5 p-Tolylhydrazine Hydrochloride 0.1 g 5-Methylbenzotriazole 0.02 g Water to make 11 A good quality reversal image was obtained.

   Example 4.

   Thiourea dioxide (Additive 1) was added to each of Emulsion A and Emulsion B produced as described above in different amounts as set forth in Table 3 below and then the emulsions were heated for 60 minutes at 650 C. Next, potassium chloroaurate (Additive 2) was added to each of the resulting emulsions in different amounts as set forth in Table 3 below and then the emulsions were heated for 60 minutes at 650C. Thus, each of the emulsions was reduced and fogged with gold.

   Further, pinakryptol yellow (Dye 1) which acts as an electron acceptor was added to each of the emulsions in different amounts as set forth in Table 3 below. Each of the emulsion samples was coated, exposed and developed with Surface Developer C as described in Example 1. In each of the samples, the photographic sensitivity at a density corresponding to half of the sum of the maximum and the minimum densities (DmaX+Dm,n/2), and the maximum density were evaluated in the same manner. The amounts of each of Additive 1, Additive 2 and Dye 1 set forth in Table 3 below were amounts providing optimum effects for each of the emulsions.

   Table 3 Relative Emulsion Additive 1 Additive 2 Dye 1 Sensitivity Dmax (mg/mol Ag) (mg/mol Ag) (mg/mol Ag) A 0.20 2.0 100 100 1.82 B 0.16 0.65 30 1,420 1.53 It can be seen from the results in Table 3 that the emulsion comprising the precipitate produced in the presence of the compound represented by the general formula (I) exhibited markedly increased photographic sensitivity.

   WHAT WE CLAIM IS:

   1. A process of producing a silver halide photographic emulsion comprising precipitating silver halide grains in an aqueous solution of a hydrophilic colloid and in the presence of 5 x 10-0 to 5 x 10-2 mol, of silver halide, of a silver halide solvent represented by the general formula (I):

   wherein X represents a sulfur atom or an oxygen atom; RO and R1, which may be the same or different, each represents an optionally substituted alkyl, aryl, heterocyclic or amino group, or RO and R' may together complete a 5- or 6membered heterocyclic ring; and R2 represents an optionally substituted alkyl or aryl group, or R2 and R' may together complete a 5- or 6-membered heterocyclic ring containing one or more of a nitrogen atom, an oxygen atom and a sulfur atom.

   2. A process as claimed in Claim 1, wherein said silver halide solvent is represented by the general formula (ill):

   wherein Q represents the atoms necessary to complete a heterocyclic ring containing one or more ofa nitrogen atom, an oxygen atom and a sulfur atom; and X and RO each has the slime meaning as in Claim 1.

   3. A process as claimed in Claim 2, wherein said silver halide solvent is represented by the general formula (IIa):

   wherein A and B, which may be the same or different, each represents a hydrogen atom, a carboxyl group, an alkyl group, an aryl group or an alkoxycarbonyl group and A and B may together represent the atoms necessary to complete an unsaturated ring containing 5 to 6 carbon atoms containing at least a sulfo group or a carboxy group; X represents a sulfur atom or an oxygen atom; and RO has the same meaning as in the general formula (I).

   4. A process as claimed in Claim 3, wherein A and B each represents a hydrogen atom, a sulfo group, a carboxy group, an alkyl group containing 1 to 6 carbon atoms, an aryl group or an alkoxycarbonyl group in which the alkyl moiety contains 1 to 5 carbon atoms.

   5. A process as claimed in Claim 1, wherein said silver halide solvent is any of the compounds (1) to (19) shown hereinbefore.

   6. A process as claimed in Claim 5, wherein said silver halide solvent is 3,4 dimethyl- 1 ,3-thiazoline-2-thione or potassium 2-(4-methyl. 1 ,3-thiazoline-2-thione)- 3-yl-ethylsulfonate.

   8. A process as claimed in Claim 7, wherein the mixing of said solutions is conducted at a pH of 2 to 9 and at a pAg of 4 to 10.

   9. A process as claimed in Claim 8, wherein the mixing is conducted at a pH of 2 to 8 and at a pAg of 5 to 10.

   10. A process as claimed in Claim 7, 8 or 9, comprising mixing an aqueous silver nitrate solution with an aqueous solution of an alkali metal halide in an aqueous gelatin solution.

   11. A process as claimed in Claim 10, wherein the silver halide solvent is incorporated in the mixture in an amount of 10-5 to 0.05 mol per mol of silver prior to physical ripening of the emulsion.

   12. A process as claimed in any preceding Claim, wherein said silver halide grains are produced in the presence additionally of ammonia, potassium thiocyanate or an organic thioether.

   13. A process as claimed in Claim 1 of producing a silver halide photographic emulsion, substantially as hereinbefore described in any of the foregoing examples 1 to 4.

   14. A silver halide photographic emulsion produced by the process as claimed in any preceding claim.

   15. A photographic emulsion as claimed in Claim 14, wherein said silver halide grains are previously fogged silver halide grains.

   16. A photographic emulsion as claimed in Claim 14, wherein said silver halide grains have core/shell type structure and have high internal sensitivity with low surface sensitivity.

   17. A photographic emulsion as claimed in Claim 14, wherein said silver halide grains have a core/shell type structure and said silver halide solvent is present at least either at the time of core formation or at the time of shell formation.

   18. A silver halide photographic emulsion as claimed in Claim 14, substantially as hereinbefore described in any of the Examples.

   19. A photographic material which includes a layer of a photographic emulsion as claimed in any of Claims 14 to 18.

   20. A photographic material as claimed in Claim 19, which is a reversal colour film, a negative colour film or a black-and-white highly sensitive negative film.