EP0262930B1

EP0262930B1 - Process for forming a colour positive image

Info

Publication number: EP0262930B1
Application number: EP19870308628
Authority: EP
Inventors: Atushi Kamitakahara; Keiji Ogi
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 1986-09-29
Filing date: 1987-09-29
Publication date: 1993-08-11
Anticipated expiration: 2007-09-29
Also published as: JPS63184739A; CA1317502C; EP0262930A3; DE3786974D1; DE3786974T2; EP0262930A2

Description

The present invention relates to a process for forming a color positive image from an internal latent image type light-sensitive silver halide photographic material.
In recent years, it has become possible to obtain a photograph from an original, such as a manuscript or typescript for printing or a reversal film, on an internal latent image type light-sensitive silver halide photographic material by utilizing a copying apparatus, followed by fogging in a color developing solution and thereafter developing to obtain a positive image directly on a sheet of color photographic paper or on a color film. For this reason, such a copying apparatus is installed in, for example, photograph shops and copy shops.
However, in order to obtain a stable, good quality image it is required that the processing performances of the processing solutions be always kept constant. Accordingly, since the processing solutions are consumed and deteriorated when a large quantity of light-sensitive materials are processed in, for example, color development, it is necessary to use replenishing solutions for replenishing the processing solutions to make up any shortage, or to recover the deteriorated activity of processing solutions to maintain the initial activity to carry out stable processing. Particularly, when the deteriorated processing solutions are replenished, it follows as a matter of course that the processing solutions overflow and are collected as waste liquor. The waste liquor may sometimes contain harmful components or components undesirable in terms of environmental pollution, and therefore it is necessary to make them harmless before the waste liquor is thrown away. It requires much cost and labor to make the harmful components harmless. In particular, an organic solvent having a log P (as defined later) of 0.4 or more, such as benzyl alcohol acting as a color development accelerator, has such high values for BOD and COD that it is desirably used in as small an amount as possible or not at all.
However, if color developing is carried out using the organic solvent such as benzyl alcohol in an amount which is as small as possible or without using it, there can be a problem that the oxidized product of a color developing agent produced by the color development reaction may preferentially react with sulfite ions used as an antioxidant for the color developing agent in the developing solution, rather than undergo a coupling reaction with a coupler in a light-sensitive material, thereby causing a lowering of the image density. To solve this problem it is effective to lower the concentration of the sulfite ions to enhance the coupling reaction. If, however, the processing is carried out with a color developing solution having a lowered sulfite ion concentration, there can be a problem that the image may suffer great variation depending on the variation of the processing conditions. For example, in the light-sensitive material containing internal latent image type silver halide grains comprising a silver bromide shell as described in US-A-3,206,313, there can be a problem of variation of a positive image depending on the conditions at the time of fogging.
This variation, when using fogging by light, may occur because the illuminance of light may decrease due to deterioration of a light source, or the exposure at a light-sensitive face may decrease due to filter action caused by coloring due to oxidation of the color developing solution. When fogged by a fogging agent, the concentration of the fogging agent may be lowered, for example because of air oxidation. In particular, the maximum density of the image obtained is sometimes extremely lowered because of the above variation.
A technique for restraining the lowering of the image density is to apply chemical ripening to a certain degree on the surface of silver halide grains (see US-A-3,761,276). This, however, is not necessarily satisfactory.
DE-A-2,416,814 describes a process for developing positive silver halide materials. Example 2 describes a developing solution containing no benzyl alcohol and 2 g/litre sodium sulfite. The material processed contains silver halide grains of the core/shell type in which the outer surface is pure silver bromide.
The present invention seeks to provide a process for forming a color positive image from an internal latent image type light-sensitive silver halide photographic material which is stable and which can be processed by a processing solution having a reduced environmental load of waste liquor.
The present invention provides a process for forming a color positive image which comprises subjecting an internal latent image type light-sensitive silver halide photographic material comprising photographic constituent layers in which silver halide grains contained in at least one layer thereof comprise a core and at least one shell layer covering said core, said shell containing at least 50 mol% silver chloride as its surface composition, to surface development processing, after fogging has been carried out and/or while fogging is carried out, with a color developing solution comprising 1 g/liter or less of a solvent having a log P of 0.4 or more and having a sulfite ion concentration of 2 x 10⁻² mole or less per liter of the color developing solution, wherein log P of the solvent may be calculated from the partition coefficient P of n-octanol/water from the formula:
The silver halide grains contained in at least one photographic layer comprises a core and at least one shell layer covering the core, the shell containing at least 50 mol% silver chloride as its surface composition. Accordingly, there can be used silver halides having any halogen composition as the surface composition so long as the surface composition of the shell contains at least 50 mol% silver chloride. For example, they include silver chloride, silver chlorobromide, silver chloroiodobromide and silver chloroiodide.
The shell layer of the silver halide grains may entirely cover the surface of the silver halide grain, or may selectively cover part of the surface. The shell surface layer containing silver chloride preferably occupies 10 % or more of the grain surface.
The shell in the silver halide grains may comprise a single layer having a compositionally single silver halide, or may be a composite shell comprising two or more layers. Preferably the amount of silver chloride in the silver halide grains is 50 mole % or more.
When a composite layer shell is used it comprises at least an outermost layer and a layer contiguous thereto, but it may have a structure such that layers having different silver halide compositions from each other are laminated.
The shell layer of the composite layer may also have a structure such that the silver halide composition continuously changes in the diametrical direction of the silver halide grain.
When the above composite layer shell is used, the whole of the grain or the inside thereof may have any silver halide composition so long as 50 mole % or more of silver chloride is contained in the outermost layer, or at least the surface thereof, of the composite layer shell, or the surface portion of the shell corresponding to the layer contiguous to the outermost layer. There may be included, for example, silver iodobromide, silver bromide, silver chlorobromide, silver chloroiodide or silver chloroiodobromide.
The shell preferably covers 50 % or more of the surface area of the core, and particularly preferably covers the core entirely.
The core preferably chiefly comprises silver bromide, or may further contain silver chloride and/or silver iodobromide. The silver halide grains which form the core may be of any shape, for example, cubes, regular octahedrons, dodecahedrons, tetradecahedrons, or a mixture thereof; or spheres, flat plates, free-shaped grains, or a mixture thereof. The average grain size and grain size distribution of the silver halide grains constituting the cores can vary within a wide range depending on the photographic performance desired, but a grain size distribution of a narrower width is more preferred. In other words, the silver halide grains constituting the cores are preferably substantially monodispersed.
The "core comprises monodispersed silver halide grains" means that in the silver halide grains constituting the cores, the weight of silver halide grains included in a grain size range of ± 20 % with an average grain size r as the central value is 60 % or more, preferably 70 % or more, particularly preferably 80 % or more, of the total silver halide weight.
The average grain size r refers to the grain size r_i at which the product of the frequency n_i of the grain having the grain size r_i, and r_i³, i.e., $n_{i} {x r}_{i} ³$
, is a maximum (effective numeral: three figures; smallest figure number is rounded).
The grain size herein mentioned is the diameter in the case of a spherical silver halide grain, and, in the case of a grain other than a spherical grain, is the diameter assumed by calculating its projected image into a round image having the same area.
The grain size can be determined, for example, by projecting the grain with 10,000 to 50,000 magnification under an electron microscope, and actually measuring on a print obtained the grain diameter or area at the time of projection (assuming that the number of grains measured is a random selection of 1,000 or more).
As methods for producing the above monodispersed core emulsion, there can be used, for example, the double jet method as disclosed in JP-B-36890/1973, JP-A-48520/1979 and JP-A-65521/1979. In addition, there can be also used the pre-mixing method as disclosed in JP-A-158220/1979.
In the working of this invention, the core of the silver halide grains may be subjected to chemical sensitization or doped with a metallic ion, or neither or both of these may be applied.
As chemical sensitization, there can be employed sulfur sensitization, gold sensitization, reduction sensitization, noble metal sensitization or a combination of any of these sensitizing methods. Thiosulfate, thioureas, thiazoles, rhodanines and other compounds can be used as a sulfur sensitizer. Such methods are described, for example, in US-A-1,574,944, US-A-1,623,499, US-A-2,410,689 and US-A-3,656,955.
The cores of the silver halide grains can be also sensitized by a water soluble gold compound as described, for example, in US-A-2,399,083, US-A-2,597,856 and US-A-2,642,361, or can be also sensitized with a reduction sensitizer. Such methods are described in, for example, US-A-2,487,850, US-A-2,518,698 and US-A-2,983,610.
Additionally noble metal sensitization can be carried out with noble metal compounds such as those of platinum, iridium or palladium. Such methods are described in, for example, US-A-2,488,060 and GB-A-618,061.
The cores of the silver halide grains can also be doped with a metallic ion. The metallic ion may, for example, be added in the form of a water soluble salt at any time during the formation of the core grains. Examples of the metallic ions include lead, antimony, bismuth, gold, osmium and rhodium. These metallic ions may be used in a concentration of 1 x 10⁻³ to 1 x 10⁻⁴ mol per mol of silver.
However, the cores need not be subjected to the above chemical sensitization or doping with metallic ions. In such a case, a sensitivity center is produced by, for example, the formation of a crystal distortion at the interface between the core and shell when the core particle is covered with the shell. Reference to this is made in US-A-3,935,014 and US-A-3,957,488.
For forming the shell on the core, the double jet method or the pre-mixing method can be used. Alternatively, the shell can be formed by mixing finely particulate silver halide into a core emulsion, followed by Ostwald ripening.
As mentioned above, the silver halide grains are of the core/shell type, and the surface composition is controlled to contain 50 mole % or more of silver chloride, so that the fogging can be effectively carried out to increase the maximum density of the resulting image and obtain a good and stable image.
The amount of silver chloride in the silver halide grains is not particularly limited. Silver halide grains containing a large amount of silver chloride depending upon the demand of speed of processing time may be used. In a preferred embodiment, the amount of silver chloride is at least 50 mole %, more preferably 80 mole % or more, based on the total amount of silver halide. In another preferred embodiment, a light-sensitive material containing a silver halide having a great amount of silver chloride is used with a heterocyclic compound having a mercapto group, to provide an excellent positive image.
As the heterocyclic compound having a mercapto group, the following compound of formula (I) is preferred:

wherein M is a hydrogen atom, an alkali metal atom, an ammonium group or a mercapto protecting group; and Z is a group of non-metallic atoms which, together with the carbon and nitrogen atoms to which it is attached, forms a heterocyclic group which optionally has one or more substituents or is fused.
Examples of mercapto protecting groups represented by M are groups forming a mercapto group by cleavage in the presence of an alkali, and more specifically include an acyl group, an alkoxycarbonyl group or an alkylsulfonyl group.
The heterocyclic group represented by

may have, for example, carbon, nitrogen, oxygen, sulphur or selenium atoms in its constituting rings, and in preferably a 5- to 6-membered ring.
Examples of the heterocyclic ring are imidazole, benzoimidazole, naphthoimidazole, thiazole, thiazoline, benzothiazole, naphthothiazole, oxazole, benzoxazole, naphthoxazole, selenazole, benzoselenazole, naphthoselenazole, triazole, benzotriazole, tetrazole, oxadiazole, thiadiazole, pyridine, pyrimidine, triazine, purine and azaindene.
As the substituent which may be bonded to the heterocyclic group, there may be mentioned, for example, a halogen atom, or hydroxy, amino, nitro, mercapto, carboxy and its salts, sulfo and its salts, alkyl, alkoxy, aryl, aryloxy, alkylthio, arylthio, acylamino, sulfonamide, carbamoyl and sulfamoyl groups.
Preferred compounds of formula (I) are of formulae (II), (III) and (IV):
In formulae (II) to (IV), M is as defined for M in formula (I).
In formula (II), Ar is a phenyl group, a naphthyl group or a cycloalkyl group; and R¹ is a hydrogen atom or a substituent.
In formula (III), Z¹ is an oxygen atom, a sulfur atom, a selenium atom or a -NH- group; and R² is a hydrogen atom or a substituent.
In formula (IV), Z² is an oxygen atom, a sulfur atom, a selenium atom or a

group wherein R⁴ is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, -COR⁵, -SO₂R⁵, -NHCOR⁶ or -NHSO₂R⁶, wherein R⁵ is an alkyl group, an aryl group or an amino group and R⁶ is an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group; and R³ is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, a heterocyclic group or an amino group.
Examples of compounds of formula (I) are:
The above compounds can be easily synthesized by known methods. For example, they can be obtained in accordance with the method disclosed in US-A-2,403,927 and US-A-3,376,310, JP-A-59463/1980 or Journal of the Chemical Society, p. 4237 (1977). Some of the compounds are commercial products.
The above compounds can be added to the light-sensitive material elements by dissolving them in water or a water-miscible organic solvent such as methanol or acetone, or by dissolving them in a weak alkali or a weak acid. The amount varies depending on the kind of compound used or the layer to which it is added. When it is added to a silver halide emulsion layer, the amount is from 10⁻⁶ to 10⁻³ mole, preferably from 10⁻⁵ to 10⁻³ mole, per mole of silver halide.
The compound may be added, in addition to the silver halide emulsion layer of the light-sensitive material, to any layers of the constituent layers of a conventional light-sensitive material such as a protective layer, an intermediate layer, a filter layer, a halation preventive layer or a subbing layer, but the silver halide emulsion layer is particularly preferred.
The internal latent image type silver halide emulsion used in this invention will now be further described.
Overlapping emulsions having different sensitivities as emulsion layers can be used, or they can be mixed in order to widen the exposure latitude. In this instance, the proportion of the coated silver amount in the emulsion layers can be arbitrarily determined depending on the photographic performance required.
In the present invention, internal latent image type silver halide grains that have not preliminarily been fogged can be used as the internal latent image type silver halide grains. In this instance, what is meant by the grain surface having not preliminarily been fogged is that the density is not more than 0.6, preferably not more than 0.4, when a test piece produced by coating the emulsion to be used on a transparent film support so as to have 35 mgAg/cm² is, without exposure to light, developed for 10 minutes at 20°C with a surface developing solution A:

Metol 2.5 g

ℓ-Ascorbic acid 10 g

NaBO₂·4H₂O 35 g

KBr 1 g

Made up to 1 liter with water.
As the silver halide emulsion used in the silver halide emulsion layer for the formation of the color positive image in the light-sensitive material, there is preferably used an emulsion that can give a sufficient density when a test piece of the light-sensitive material containing internal latent image type silver halide grains that have not preliminarily been fogged and which has been prepared in the above manner, is exposed to light followed by developing with an internal developing solution B:

Metol 2 g

Sodium sulfite (anhydrous) 90 g

Hydroquinone 8 g

Sodium carbonate (monohydrate) 52.5 g

KBr 5 g

KI 0.5 g

Made up to 1 liter with water.
More specifically, it is an emulsion that can show, when a part of the above test piece is exposed to light through a luminous intensity scale over a certain period not longer than 1 second followed by development for 10 minutes at 20°C with internal development solution B, a density of at least 5 times, preferably at least 10 times, greater than that obtained when another part of the test piece exposed to light under the same conditions is developed for 10 minutes at 20°C with surface developing solution A.
The silver halide emulsion usable in working this invention can be chemically sensitized by a sensitizing dye usually used. It is useful also for the silver halide emulsion to use in combination a sensitizing dye used in the supersensitization of, for example, internal latent image type silver halide emulsions or negative silver halide emulsions. Reference to the sensitizing dye is made in Research Disclosures No. 15162 and No. 17643.
The direct positive image can be readily obtained by carrying out image exposure (or photographing) followed by surface developing. Specifically, the principal steps for producing the positive image comprise subjecting to image exposure a light-sensitive photographic material having an internal latent image type silver halide emulsion layer that has not preliminarily been fogged, and thereafter carrying out surface developing during or after producing a fog nucleus by chemical action or optical action. The fogging can be carried out by applying whole surface exposure or by using a compound capable of producing a fog nucleus, i.e. a fogging agent.
The whole surface exposure is carried out by dipping a light-sensitive material subjected to image exposure in or wetting by, a developing solution or other aqueous solution followed by wholly and uniformly exposing it to light. Any light having a wavelength which is within the wavelength region in which the above light-sensitive photographic material is sensitive to light may be used. Alternatively, a highly luminous light such as a flash light can be irradiated, or a weak light may be irradiated for a long time. The time for the whole surface exposure can vary within a wide range so as to finally obtain an optimum positive image, depending on the light-sensitive photographic material, developing conditions and the light source used. As for the amount of exposure, most preferred is an exposure amount of a certain given range in combination with the light-sensitive material. Usually an excessive exposure amount causes an increase in the minimum density or desensitization to lower the image quality. However, employment of the light-sensitive material used in the present invention makes it possible to lessen the degree of image deterioration and obtain a stable image.
A fogging agent that can be used in the fogging of the light-sensitive photographic material is now further described. There can be used compounds of a wide range of types. The fogging agent may be present at the time the developing is carried out, and thus, for example, it may be contained in a constituent layer, other than a support, of the light-sensitive photographic material (preferably in a silver halide emulsion layer), or in the developing solution or a processing solution precedent to the developing. It can be also used in an amount which can vary within a wide range depending on the purpose, and, when used by adding it in the silver halide emulsion layer, in an amount of 1 to 1,500 mg, preferably 10 to 1,000 mg, per mol of silver halide. Also, when used by adding it to a processing solution such as the developing solution, it is preferably added in an amount of 0.01 to 5 g/liter, particularly preferably 0.05 to 1 g/liter.
The fogging agent used may be, for example, the hydrazines described in US-A-2,563,785 and US-A-2,588,982 or the hydrozide or hydrazine compounds described in US-A-3,227,522; the heterocyclic quaternary nitrogen chloride compounds described in US-A-3,615,615, US-A-3,718,479, US-A-3,719,494, US-A-3,734,738 and US-A-3,759,901; and also a compound having a group adsorptive to the surface of silver halide, such as the acylhydrazinophenylthioureas described in US-A-4,030,925. These fogging agents can also be used in combination. For example, Research Disclosure No. 15162 discloses a combined use of a non-adsorptive fogging agent with an adsorptive fogging agent. This technique of combined use may also be effective in this invention. The fogging agent used in this invention may be any of the adsorptive type or non-adsorptive type, which may also be used in combination.
The developing agent that can be used in the surface developing solution may, for example, be selected from usual silver halide developing agents, for example, polyhydroxybenzenes such as hydroquinone, aminophenols, 3-pyrazolidones, ascorbic acid and derivatives thereof, reductones and phenylenediamines, or a mixture of these. Specifically, it may, for example, be hydroquinone, aminophenol, N-methylaminophenol, 1-phenyl-3-pyrazolidone, 1-phenyl-4,4-dimethyl-3-pyrazolidone, 1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone, ascorbic acid, N,N-diethyl-p-phenylenediamine, diethylamino-o-toluidine, 4-amino-3-methyl-N-ethyl-N-(β-methanesulfonamidoethyl)aniline or 4-amino-3-methyl-N-ethyl-N-(β-hydroxyethyl)aniline. The developing agent may also be previously contained in an emulsion so that it can act on silver halide when the light-sensitive photographic material is dipped in an aqueous solution having a high pH.
The developing solution used in this invention may further contain a particular antifoggant and a developing restrainer. It is also possible to incorporate these additives for the developing solution in a constituent layer of the light-sensitive photographic material in an arbitrary fashion.
When the light-sensitive photographic material is used for full color photography, at least one of each of a red-sensitive silver halide emulsion layer, a green-sensitive silver halide emulsion layer and a blue-sensitive silver halide emulsion layer are coated on a support as photographic constituent layers. At least one layer of the light-sensitive silver halide emulsion layers contains the core/shell type grains comprising a core and a shell covering said core, containing 50 mole% or more of silver chloride as the surface composition of the shell. Of course, all of the light-sensitive silver halide emulsion layers preferably contain the internal latent image type silver halide grains as used in the present invention. Each of the light-sensitive silver halide emulsion layers may be a single light-sensitive layer or may be separated into two or more layers each having different sensitivities. In such an instance, at least one of the same light-sensitive layers having different sensitivities may contain the internal latent image type silver halide grains as used in the present invention, but all of the emulsion layers preferably contain these internal latent image type silver halide grains.
The color developing solution is now further described. The color developing solution contains 1 g/liter or less of a solvent having a log P of 0.4 or more and has a low sulfite ion concentration.
The log P refers to a value determined from the partition coefficient P with n-octanol/water. P can be determined from the formula:
The logarithm of P thus determined is log P, which value has been hitherto widely used in the fields of agricultural chemicals and pharmaceuticals as a measure of oil solubility. The value log P can be known also from log P_oct in the table disclosed in Chemical Review, Vol. 71, No. 6, pp. 555-613, 1971. It can also be theoretically determined by the method disclosed in Ecological Chemistry, Vol. 6, pp. 3-11, but an experimental value is more preferably used, and a value observed by using n-octanol is particularly more preferably used.
The solvent having a log P of 0.4 or more, that is not desired to be added to the developing solution, includes aliphatic alcohols, aliphatic glycol ethers and alicyclic alcohols or aromatic alcohols, particularly those having from 5 to 20 carbon atoms.

Specific examples are:

Benzyl alcohol	log P 1.0
o-Hydroxybenzyl alcohol	log P 0.73
Cyclohexanol	log P 1.23
2-Benzyloxyethanol	log P 0.41
Anisyl alcohol	log P 0.70
1-Pentanol	log P 0.4 or more
Phenylethyl alcohol	log P 1.36
p-Tolylcarbinol	log P 1.36
Phenol	log P 0.4 or more
p-Hydroxybenzyl alcohol	log P 0.4 or more
Benzylamine	log P 0.4 or more
Diethylene glycol monobutyl ether	log P 0.41.

The above solvents are, as mentioned above, compounds that may accelerate the coupling reaction of an oxidized product of a color developing agent with a coupler in the light-sensitive material, and the content thereof is controlled to be 1 g/liter or less. By controlling it to such a low concentration, the BOD or COD values can be reduced to low values even when the above color developing solution is deteriorated and thrown away, and there can be provided an effective countermeasure for environmental pollution. Moreover, by controlling the concentration of the sulfite ions serving as a preservative to a lower concentration, it is intended to restrain the reaction with the above solvent to enhance the coupling reaction in the color development processing. What is meant by "having a low sulfite ion concentration" in this invention is that the sulfite ions are present in such a concentration that they can serve as a preservative and at the same time can suppress the reaction with the above solvent having a log P of 0.4 or more, so as not to inhibit the coupling reaction in the color developing solution. Thus, the concentration is 2.0 x 10⁻² mole or less, preferably about 1.0 x 10⁻² mole, per liter of the color developing solution.
Since the coupling reaction can be effectively carried out by controlling the sulfite ion concentration to a low concentration as mentioned above, it is possible to increase the maximum density of the color image color-developed by the above color developing solution, and to obtain a good image.
In addition, conjointly with the employment of the core/shell grains containing 50 mole % or more of silver chloride in the surface composition of the internal latent image type silver halide grain, it is possible to obtain a light-sensitive material that is stable in processing and which can have good image quality.
The present invention is now further described in the following Examples.

Example 1

An aqueous solution of silver nitrate and an aqueous solution of potassium bromide in equimolar amounts were Simultaneously added over a period of about 40 minutes at 50°C according to the controlled double jet method, to obtain a tetradecahedral silver bromide emulsion having an average grain size of 0.4 µm. However, 5 minutes after the addition of the aqueous solution of silver nitrate and the aqueous solution of potassium bromide was started, potassium hexachloroiridate was added in an amount of 0.02 mg per mol of silver. To the emulsion thus obtained, sodium thiosulfate was added in an amount of 2.0 mg per mol of silver, followed by chemical sensitization for 60 minutes at 60°C to obtain emulsion A.
Using this emulsion A for the formation of core grains, core/shell emulsions B to E shown below were obtained.

Emulsion B:

Using emulsion A for the formation of core grains, an aqueous solution of silver nitrate and an aqueous solution of potassium bromide were further simultaneously added to obtain a tetradecahedral core/shell emulsion having an average grain size of 0.6 µm.

Emulsion C:

Using emulsion A for the formation of core grains, an aqueous solution of silver nitrate and an aqueous solution of potassium bromide were further simultaneously added to be grown up to grains of 0.5 µm, and successively an aqueous solution of silver nitrate and an aqueous solution of sodium chloride were further simultaneously added to obtain a cubic core/shell emulsion having an average grain size of 0.6 µm.

Emulsion D:

Core/shell emulsion D was obtained in substantially the same manner as for the above emulsion C. This emulsion D, however, was prepared by adding an aqueous solution containing potassium bromide and sodium chloride (KBr : NaCl = 1 : 3 in molar ratio) in place of the aqueous solution of sodium chloride.

Emulsion E:

Core/shell emulsion E was obtained in substantially the same manner as for the above emulsion C. This emulsion E, however, was prepared by adding an aqueous solution containing potassium bromide and sodium chloride (KBr : NaCl = 1 : 1 in molar ratio) in place of the aqueous solution of sodium chloride.

Emulsion F:

Core/shell emulsion F was obtained in substantially the same manner as for the above emulsion C. This emulsion F, however, was prepared by adding an aqueous solution containing potassium bromide and sodium chloride (KBr : NaCl = 3 : 1 in molar ratio) in place of sodium chloride.
To each of emulsions B to F obtained above, there was added a dispersion obtained by dissolving a sensitizing dye sodium 5,5'-diphenyl-9-ethyl-3,3'-disulfoproplyoxycarbocyanate and a magenta coupler 1-(2,4,6-trichlorophenyl)-3-(2-chloro-5-octadecylsuccinimidoanilino)-5-pyrazolone in a solvent, followed by emulsification dispersion in an aqueous gelatin solution, to which a hardening agent was further added. The resulting emulsion was coated on a resin-coated paper support to provide a coated silver amount of 4 mg/100 cm², followed by drying to obtain samples No. 1 to No. 5.

Each of these samples was subjected to wedge exposure through a yellow filter, followed by developing for 3 minutes at 38°C with a developing solution formulated as follows.

4-Amino-3-methyl-N-ethyl-N-(β-methanesulfonamidoethyl)aniline sulfate	5 g
Sodium sulfite (anhydrous)	1 x 10⁻² M/l
Sodium carbonate (monohydrate)	15 g
Potassium bromide	0.6 g
Made up to 1 liter with water (Adjusted to pH 10.2 with potassium hydroxide.)

For 20 seconds after 20 seconds from the starting of the developing, however, the whole surface was uniformly exposed to white light in an exposure amount shown in Table 1 below, followed by bleach-fixing and washing according to a conventional manner, and drying. Thereafter, samples No. 1 to No. 5 were developed under the same conditions as those described above except that the concentration of sodium sulfite in the color developing solution was controlled to 0.03 M/liter.
As is clear from the results shown in Table 1, silver chloride is contained in the surface composition of the outermost layer of the core/shell grains used in the present invention, so that the maximum density is remarkably improved and there is obtained a good positive image stable also to changes in the fogging exposure amount.
The maximum density of the resulting image is abruptly lowered when the sulfite ion concentration in the color developing solution is altered from 1 x 10⁻², which is a low concentration as used in the present invention, to 3 x 10⁻² which is not a low concentration.
An image having a high maximum density can be obtained when the sulfite ion concentration is controlled to the low concentration.

Example 2

An aqueous solution of silver nitrate and an aqueous solution of potassium bromide in equimolar amounts were Simultaneously added at 50°C and mixed to obtain a tetradecahedral silver bromide emulsion G having an average grain size of 0.4 µm.
Using this emulsion G for the formation of core grains, there were obtained core/shell emulsions H to L as shown below.

Emulsion H:

Using emulsion G for the formation of core grains, an aqueous solution of silver nitrate and an aqueous solution of potassium bromide were further simultaneously added to obtain a tetradecahedral core/shell emulsion having an average grain size of 0.6 µm.

Emulsion I:

Using emulsion G for the formation of core grains, an aqueous solution of silver nitrate and an aqueous solution of sodium chloride were simultaneously added to obtain a cubic core/shell emulsion having an average grain size of 0.6 µm.

Emulsion J:

Core/shell emulsion J was obtained in substantially the same manner as for the above emulsion I. This emulsion J, however, was prepared by adding an aqueous solution containing potassium bromide and sodium chloride (KBr : NaCl = 1 : 4 in molar ratio) in place of the aqueous solution of sodium chloride.

Emulsion K:

Core/shell emulsion K was obtained in substantially the same manner as for the above emulsion I. This emulsion K, however, was prepared by adding an aqueous solution containing potassium bromide and sodium chloride (KBr : NaCl = 1 : 1 in molar ratio) in place of the aqueous solution of sodium chloride.

Emulsion L:

Core/shell emulsion L was obtained in substantially the same manner as for the above emulsion I. This emulsion L, however, was prepared by adding an aqueous solution containing potassium bromide and sodium chloride (KBr : NaCl = 4 : 1 in molar ratio) in place of sodium chloride.
To each of the above emulsions H to L, a sensitizing dye of the following formula was added:
Also prepared was an emulsified solution obtained by dispersing 2,4-dichloro-3-methyl-6-[α-(2,4-di-tert-amylphenoxy)butylamido)phenol as a cyan coupler in dibutyl phthalate and ethyl acetate and dispersed in an aqueous gelatin solution.
Next, this emulsified dispersion was added and mixed in each emulsion to which the above sensitizing dye was added, to which a hardening agent was added. The resulting emulsion was coated on a resin-coated paper support to provide a coated silver amount of 5.0 mg/100 cm², followed by drying to obtain samples No. 6 to No. 10.

Each of these samples was subjected to wedge exposure through a yellow filter, followed by developing for 3 minutes at 38°C with the following developing solution:

4-Amino-3-methyl-N-ethyl-N-(β-methanesulfonamidoethyl)aniline sulfate	5.0 g
Sodium sulfite (anhydrous)	6 x 10⁻³ M/l
Potassium carbonate	20 g
Potassium bromide	0.5 g
Benzyl alcohol	0.6 g
β-Acetyl-phenylhydrozine (fogging agent) in the amount as shown in Table 2 Made up to 1 liter with water (Adjusted to pH 12.0 with potassium hydroxide.)

Subsequently, bleach-fixing and washing was carried out in a conventional manner, followed by drying. On each sample thus obtained, the maximum density and minimum density of a cyan positive image were measured to obtain the results as shown in Table 2 below.
As is clear from the results shown in Table 2, silver chloride is contained in the surface composition of the outermost layer of the core/shell grains used in the present invention, so that the maximum density is remarkably improved and a good positive image having a high maximum density is stably obtained even with varied concentration of fogging agent.

Example 3

An aqueous solution of silver nitrate and an aqueous solution of potassium bromide in equimolar amounts were simultaneously added at 50°C and mixed to obtain a cubic silver bromide emulsion M having an average grain size of 0.2 µm.
Using this emulsion M for the formation of core grains, an aqueous solution of silver nitrate and an aqueous solution of potassium bromide were further simultaneously added to obtain a cubic core/shell emulsion N having an average grain size of 0.7 µm (silver chloride content: 98 mole %).
To the above emulsion N, an emulsified solution prepared by dissolving α-[4-(1-benzyl-2-phenyl-3,5-dioxo-1,2,4-triazolidinyl)]-α-pyvalyl-2-chloro-5-[δ-(2,4-di-tert-amylphenoxy)butyramido]acetanilide as a yellow coupler in a solvent and dispersing in an aqueous gelatin solution was added. Then, a hardening agent was added to the emulsion to which the above sensitizing dye was added. The resulting emulsion was coated on a resin-coated paper support to provide a coated silver amount of 6 mg/100 cm², followed by drying to obtain sample No. 11.
Samples No. 12 and No. 13 were prepared in the same manner as in sample No. 11 except for adding a heterocyclic mercapto compound (3) described hereinbefore.

Each of these samples was subjected to wedge exposure, followed by developing for 1 minute at 38°C with the following developing solution:

4-Amino-3-methyl-N-ethyl-N-(β-methanesulfonamidoethyl)aniline sulfate	5 g
Triethanolamine	8 ml
N,N-Diethylhydroxylamine	4 ml
Sodium sulfite (anhydrous)	0.15 g
Sodium chloride	2 g
Sodium carbonate	15 g
Made up to 1 liter with water (Adjusted to pH 10.2 with sodium hydroxide.)

For 5 seconds after 10 seconds from the starting of the developing, however, the whole surface was uniformly exposed to white light and with the exposure amount as shown in Table 3 below, followed by bleach-fixing and washing in a conventional manner, and drying.
As is clear from the results shown in Table 3, by processing the light-sensitive material containing the emulsion N of the core/shell grains as used in the present invention with the above color developing solution containing no benzyl alcohol and having a low sulfite ion concentration, a good positive image is stably obtained even with varied concentration of fogging agent (sample No. 11). Also, by using the heterocyclic mercapto compound, the positive image can further be improved since the minimum density is restrained (sample No. 12). However, as disclosed in JP-B-12709/1970 (which corresponds to US-A-3,733,198), when the heterocyclic compound is used in a large amount (sample No. 13), the maximum density is lowered while the effect of the present invention can be obtained.
As described above, it is possible to provide an internal latent image type light-sensitive silver halide photographic material which has a high maximum density of the positive image formed by the color developing, and is stable to the variation in the fogging conditions, when processed in a particular manner.
The image is of good quality as mentioned above even when processed with processing solutions having a small environmental load such as BOD and COD.

Claims

A process for forming a color positive image which comprises subjecting an internal latent image type light-sensitive silver halide photographic material comprising photographic constituent layers in which silver halide grains contained in at least one layer thereof comprise a core and at least one shell layer covering said core, said shell containing at least 50 mol% silver chloride as its surface composition, to surface development processing, after fogging has been carried out and/or while fogging is carried out, with a color developing solution comprising 1 g/liter or less of a solvent having a log P of 0.4 or more and having a sulfite ion concentration of 2 x 10⁻² mole or less per liter of the color developing solution, wherein log P of the solvent may be calculated from the partition coefficient P of n-octanol/water from the formula:
A process according to claim 1 wherein the solvent having a log P of 0.4 or more is at least one of an aliphatic alcohol, aliphatic glycol ether, alicyclic alcohol or aromatic alcohol.
A process according to claim 1 or 2 wherein the solvent has from 5 to 20 carbon atoms.
A process according to any one of the preceding claims wherein the solvent is at least one of benzyl alcohol, o-hydroxybenzyl alcohol, cyclohexanol, 2-benzyloxyethanol, anisyl alcohol, 1-pentanol, phenylethyl alcohol, p-tolylcarbinol, phenol, p-hydroxybenzyl alcohol, benzylamine and diethylene glycol monobutyl ether.
A process according to any one of the preceding claims wherein the sulfite ion concentration is 1 x 10⁻² mole or less per liter of the color developing solution.
A process according to any one of the preceding claims wherein the light-sensitive material comprises a heterocyclic mercapto compound.
A process according to claim 6 wherein the heterocyclic mercapto compound is of formula:
wherein M is a hydrogen atom, an alkali metal atom, an ammonium group or a mercapto protecting group; and Z is a group of non-metallic atoms which, together with the carbon and nitrogen atoms to which it is attached, forms a heterocyclic group which optionally has one or more substituents or is fused.
A process according to claim 7 wherein the heterocyclic mercapto compound is of formula (II), (III), or (IV):
wherein M is a hydrogen atom, an alkali metal atom, an ammonium group or a mercapto protecting group; Ar is a phenyl group, a naphthyl group or a cycloalkyl group; R¹ is a hydrogen atom or a substituent; R² is a hydrogen atom or a substituent; R³ is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, a heterocyclic group or an amino group; Z¹ is an oxygen atom, a sulfur atom, a selenium atom or a -NH- group; and Z² is an oxygen atom, a sulfur atom, a selenium atom or a
group wherein R⁴ is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an aralkyl group, -COR⁵, -SO₂R⁵, -NHCOR⁶ or -NHSO₂R⁶, wherein R⁵ is an alkyl group, an aryl group or an amino group and R⁶ is an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group.
A process according to any one of claims 6 to 8 wherein the heterocyclic mercapto compound is present in an amount of from 10⁻⁵ to less than 10⁻³ mole per mole of Ag.
A process according to any one of the preceding claims wherein the content of silver chloride in the silver halide grains is 50 mole % or more.
A process according to any one of the preceding claims wherein the concentration of bromide ions in the developing solution is 5 x 10⁻³ mole or less per liter of developing solution.