JPH1184571A - Silver halide photographic sensitive material for direct positive printing and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silver halide photographic sensitive material for direct positive printing in a light room having high max. density (Dmax) and especially sufficiently low min. density (Dmin). SOLUTION: (1) The material consists of core/shell type silver halide particles having >=90 mol.% silver chloride content and has chemical sensitizing nuclei on the surfaces of the cores. (2) The material consists of core/shell type silver halide particles having ∞90 mol.% silver chloride content and contains a group VIII metal of the Periodic Table in the core parts. In both cases (1) and (2), the ratio of the average diameter of the crystalline particles of the core parts to that of the entire crystalline particles including the shell parts satisfy the equation I2 /I1 <=0.6 (where I1 is the average diameter of the crystalline particles including the shell parts and I2 is the average diameter of the crystalline particles of the core parts.).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fogged direct positive silver halide photographic material, and more particularly to a direct positive silver halide photographic material which can be handled in a bright room. And a method of manufacturing the same.

[0002]

2. Description of the Related Art A silver halide photographic light-sensitive material for direct positive use is often used mainly in the "return" process in the photolithography process in the printing industry. In this "return" process, the original document image is reproduced from a positive image to a positive image or from a negative image to a negative image, but the important point in this process is to faithfully reproduce the fine lines and halftone images of the original image. Required.

The photographic characteristics of the direct positive silver halide emulsion used to satisfy these requirements are such that the tone is high (particularly the foot is hard), the maximum density (Dmax) is high, and the minimum density (Dmin) is high. There is a need for low fouling, good storability, and low dissolution physical development fog.

Emulsions generally used for direct positive silver halide photographic light-sensitive materials are roughly classified into two types. One is an emulsion of the type comprising silver halide grains having an electron trapping compound which is said to be electron trapped inside the silver halide grains, and the surface of which is previously fogged.
Inverts itself directly. The other emulsion is an emulsion in which the surface of the grain is fogged without forming an electron trapping compound inside the silver halide grains, and is inverted only by adding an organic desensitizer. The present invention belongs to the former type.

The former emulsion is disclosed in JP-A-2-2649.
No. 38, No. 2-271347, No. 4-6552, and U.S. Pat. Nos. 3,367,778 and 3,632,340. In these patents, a core emulsion is prepared in advance, and the core emulsion is subjected to a chemical sensitization treatment such as sulfur sensitization, gold sensitization, or reduction sensitization, or a metal belonging to Group 8 of the periodic table (rhodium, palladium, iridium). Osmium, platinum, ruthenium, etc.) to cover the shell and then fog the surface of the shell to directly produce a reversal emulsion for positive. When a metal belonging to Group VIII of the periodic table is used as an electron trapping compound, a method of adding a silver halide precipitate when an emulsion is formed is also a known technique.

However, the reversal emulsions produced by these methods do not always produce a good reversal image, and the reversal image is soft or the minimum density (Dmin) is high. In particular, at present, it is difficult to sufficiently obtain the quality required as a direct positive silver halide photographic material used in the "return" step in the photoengraving step in the printing industry.

[0007] On the other hand, in order to realize easy handling in a bright room, it is required that the fluorescent lamp (safelight) for preventing fading, in which ultraviolet light is cut, has high safelight safety. Therefore, it is necessary to use an emulsion mainly composed of silver chloride. However, these emulsions have a problem of high Dmin and a problem of easily causing dissolution physical development fog. On the other hand, when fog is suppressed by an additive or the like, there is a problem that the sensitivity and the maximum density are reduced.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a silver halide photographic material for direct positive use having a high maximum density (Dmax), particularly a sufficiently low minimum density (Dmin), and a method for producing the same. It is. It is another object of the present invention to provide a direct positive silver halide photographic light-sensitive material having improved storage stability without occurrence of fusing physical development fog. Still another object of the present invention is to provide a silver halide photographic material for direct positive use which can be handled in a bright room.

[0009]

The above objects of the present invention are as follows.
(1) A direct positive silver halide photographic material comprising core / shell type silver halide grains having a silver chloride content of 90 mol% or more and having a chemical sensitizing nucleus on the surface of the core,
A silver halide photographic material for direct positive, characterized in that the ratio of the average diameter of the crystal grains in the core portion to the average diameter of the crystal grains including the shell portion satisfies the condition of the following formula (1): l ₂ / l ₁ ≦ 0.6 (1) l ₁ : Average diameter of crystal grains including shell part l ₂ : Average diameter of crystal grains in core part (2) Core / shell having silver chloride content of 90 mol% or more Silver halide photographic material for direct positive use comprising a silver halide grain of the type, wherein the core portion contains a metal belonging to Group VIII of the Periodic Table, including the average diameter of the crystal grains in the core portion and the shell portion. A silver halide photographic material for direct positive use, wherein the ratio of the average diameter of crystal grains satisfies the condition of the above formula (1); Rhodium, and the rhodium is added in an amount of 1 × per mole of silver halide in the core. 0 ^-6 positive silver halide photographic light-sensitive material directly to molar or more, (4) the (2) or (3), the shell surface chemical sensitization nucleus (fog nuclei)
A silver halide photographic material for direct positive use, wherein the ratio of the reduction sensitizer to the gold sensitizer used for forming the compound is from 1:10 to 10: 1 in terms of mole number. 20. The method for producing a direct-positive silver halide photographic light-sensitive material according to any one of the above items, wherein the pAg of the coating solution for the direct-positive silver halide emulsion is 7 or more. And a method for producing a silver halide photographic light-sensitive material.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The silver halide used in the present invention is silver chloride, silver chlorobromide, silver chlorobromoiodide and has a silver chloride content of 90 mol% or more. In order to realize easy handling in a bright room, it is required that a safe light is high for a fluorescent lamp (safelight) for preventing fading, which cuts ultraviolet light. Therefore, it is necessary to use an emulsion mainly composed of silver chloride.

The halogen composition of the silver halide used in the present invention is such that silver chloride is 90 mol% or more. When the amount of silver chloride is less than this, in Dmin and safelight property,
The effectiveness of l ₂ / l ₁ ≦ 0.6 is not established, and therefore, in the present invention, 90 mol% or more of silver chloride is essential.

Although the present invention has a core-shell type crystal structure, the present invention is not particularly limited to the core-shell structure with respect to the halogen composition. That is, it is sufficient that the silver chloride content satisfies 90 mol% or more over the entire crystal.
At least mol% of silver bromide or silver iodobromide may be partially localized in the silver halide crystal.

Although these silver halides are produced by various methods, those having high monodispersity by a double jet method are preferable because they require high photographic properties. Particles having a particle size of 0.05 μm to 0.5 μm, preferably 0.1 μm to 0.3 μm are used. The grains are basically cubic because of the high silver chloride content, but octahedral, spherical and rectangular parallelepipeds can also be made by using special physical inhibitors.

The present invention is of a type having a chemical sensitizing nucleus for trapping electrons described above inside a crystal, and does not have a chemical sensitizing nucleus only on the surface. In the present invention, a chemical sensitizing nucleus for forming a core and trapping electrons is first formed on the core surface, and then a shell is placed on the core, and further a chemical sensitizing nucleus is formed on the shell surface. In other words, a chemical sensitizing nucleus for trapping electrons is formed inside the crystal, and a chemical sensitizing nucleus for trapping holes is formed on the crystal surface.

At this time, it has been revealed in the study of the present inventors that the position of the chemical sensitization nucleus inside the crystal (core) is very important. We have found that the positional relationship between the chemical sensitization nuclei on the inside and the surface is not the absolute distance, but the relative positional relationship in the crystal size is important.

On the other hand, regarding the type having a compound that traps electrons (a metal belonging to Group 8 of the periodic table) in the core portion, the relationship between the average diameter of the core crystal grains and the average diameter of the crystal grains including the shell is important. I found it.

In the present invention, the measurement of l ₂ shown in the formula (1) can be obtained as an average particle size by taking an electron micrograph when a core is made. The measurement of l ₁ is performed as follows. A shell is placed over the core particles, and when the shell coating is completed, an electron micrograph is taken and the average particle size can be determined.

In the present invention, the chemical sensitization nucleus formed on the surface of the core is a nucleus of a generally known sulfur sensitization nucleus, gold sensitization nucleus, reduction sensitization nucleus or a combination thereof.

In the case of chemical sensitization, for example, in the case of a gold compound and a thiosulfate, 3 × 10 ⁻⁷ to 4 × 10 ⁻⁵ mol of the gold compound per mol of silver halide in the core emulsion. ,
The addition amount of the thiosulfate is preferably in the range of 3 × 10 ⁻⁵ to 4 × 10 ⁻⁴ mol.

The aging temperature may be from 40 to 70 ° C., the pH may be from 4 to 10, and the time may be from 30 to 120 minutes. These conditions may be appropriately selected according to desired photographic characteristics. Further, the silver halide grains may have a multilayer structure of two or more layers, such as a so-called core / shell, or a single layer structure of silver halide.

In the present invention, when the core contains a Group 8 metal, it is mixed in when a silver halide crystal is produced.
Group 8 metals include rhodium, palladium, iridium, osnium, platinum, ruthenium and the like, of which rhodium is preferably used. The content of rhodium is preferably 1 × 10 ⁻⁶ mol or more, more preferably 1 × 10 ⁻⁶ to 1 × 10 ⁻⁴ per mol of silver halide in the core.
, Whereby a sufficiently low Dmin can be obtained. Rhodium may be contained in the silver halide in any kind of form _{but, Rh 2 0 3, RhF 3} , RhCl 3, RhCN 3, Rh 2
(SO ₄ ) ₃ .nH ₂ O, NaRh (SO ₄ ) ₂ .12H ₂ O, [Rh (NH ₃ ) ₆ ] Cl ₃ , K
₃ [RhCl ₆ ] or the like is dissolved in water and mixed when silver halide crystals are formed.

When the core crystal grains contain a Group VIII metal, the core surface may be subjected to chemical sensitization, but in the case of the present invention, the chemical sensitization is made very weak or rather not. Is better. The chemical sensitization on the core surface is 1/1 of the chemical sensitizer that performs chemical sensitization on the shell surface when compared with the number of moles of the chemical sensitizer.
10 or less. When the core surface is chemically sensitized, sulfur sensitization, gold sensitization, reduction sensitization or a combination thereof is used.

The provision of fog nuclei on the surface of a silver halide grain shell carried out in the present invention is described in US Pat. No. 3,367,7.
No. 78, 3,632, 340, 3,501, 30
No. 5, JP-A-50-66133, or a reducing agent alone or with a reducing agent and a known method such as a gold compound or light.

In particular, a combination of a reducing agent and a gold compound is preferred. The fogging conditions may be variously changed depending on the desired photographic characteristics. Generally, the pH is in the range of 4 to 10, and the temperature is in the range of 40 to 80 ° C.

As the reducing agent, aldehydes such as formalin, hydrazine, triethylenetetramine, thiourea dioxide, stannous chloride, amine borane and the like are used.
The amount of reducing agent used is 1 per mole of silver halide.
X10 ^{-5 to} 2 × 10 ^-2 mol is preferred.

The gold compound is a monovalent or trivalent water-soluble gold salt such as chloroauric acid, gold thiocyanate, sodium chloroaurate, potassium aurate, potassium chloroaurate, potassium bromoaurate, or potassium iodoaurate. , Potassium gold cyanide, potassium gold thiocyanate, sodium gold thiomaleate,
Gold thioglycose or the like is used. The amount used is preferably 3 × 10 ^{−6 to} 5 × 10 ⁻³ mol per mol of silver halide.

In the present invention, when the group 8 metal is contained in the core crystal grains, particularly when rhodium is contained, the reduction of the chemical sensitizing nuclei (fogging nuclei) formed on the surface of the silver halide shell is reduced. The molar ratio of the sensitizer and the gold sensitizer is preferably 1:10 to 10: 1. Thereby, the hardening of the foot portion on the photographic characteristic curve and the occurrence of fusing physical development fog are suppressed.

The fusing physical development fog will be described below. When a photosensitive material is processed by an automatic developing machine, the photosensitive material is transported from a developing solution to a fixing solution. At this time, since the emulsion film contains a developing solution, silver ions generated from silver halide crystals dissolved at the moment the photosensitive material enters the fixing solution react with the developing agent, so-called dissolution physical development fogging. Cause This fog is brownish rather than black, and is not uniform, so that it can be distinguished from normal fog (chemically sensitized fog). In this physical development, a physical development nucleus that takes electrons from the developing agent and serves to pass electrons to dissolved silver ions is necessary, but the present inventor does not only perform silver sensitization when performing chemical sensitization, It is thought that this chemical sensitization nucleus is generated in some gelatin molecules and acts as a physical development nucleus.

Therefore, the silver halide photosensitive material for direct positive has been subjected to excessive chemical ripening as compared with the negative type, so that
Basically weak against this physical development fog. If a large amount of a physical inhibitor such as mercaptotetrazole or triazole can be added, this dissolution physical development fog can be eliminated, but the positive type has the troublesome property that it does not reverse when a large amount of the physical inhibitor is added. .

Further, in recent years, since high-temperature rapid processing is performed and a large amount of processing is performed in a short period of time, an environment in which physical dissolution development is more likely to occur has been provided. Therefore, there is a strong demand in the market for a direct-positive photosensitive material that can withstand high-temperature rapid processing.

Gelatin is most preferred as the protective colloid and binder for silver halide grains and the binder for the adjacent hydrophilic colloid layer used in the practice of the present invention. , Polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyvinylimidazole, polyethyleneglycol, maleic anhydride, polystyrenesulfonic acid, polyvinylpyridine, methylcellulose, hydroxymethylcellulose, carboxymethylcellulose, and other cellulose derivatives and their monomers. Some or all of gelatin can be replaced by a polymer or the like.

Gelatin used is alkali-treated, acid-treated gelatin (isoionic point 5-9), enzyme-treated gelatin, low calcium content gelatin (content 100 ppm or less), high jelly strength gelatin (PAGI method jelly strength 270 or more) ), Gelatin derivatives (eg, phthalated gelatin) and the like.

A polymer latex can also be used as part of the binder to improve dimensional stability. Examples of the polymer latex include polyvinyl acetate, polyacrylic acid such as polymethyl acrylate, ethyl, and butyl, polymethacrylic acid such as polymethyl methacrylate, ethyl, and butyl, polystyrene, polybutadiene, and the like. There is a copolymer of monomers and the like. The physical properties such as the particle size and glass transition point of the polymer latex are not particularly limited, but the particle size is desirably 1 μm or less.

In the practice of the present invention, a dye having an absorption wavelength between 300 nm and 700 nm can be used. These dyes can be added to an emulsion layer, a protective layer, an intermediate layer, an undercoat layer, and a backing layer. Particularly in the case of direct positive silver halide light-sensitive materials for bright rooms, it is necessary to reduce or cut the sensitivity of the silver halide in the visible light range in order to improve the safelight property in bright rooms. Is preferably a dye having a wavelength of 300 to 550 nm, which is eluted during the development processing of the light-sensitive material or decolorized by an alkali or a reducing agent in the processing solution. Examples of these dyes include oxonol dyes, azo dyes, benzylidene dyes, merocyanine dyes, styryl dyes, and quinoline dyes. JP-A-59-154439
No. 58-176635, No. 58-215643, No. 52-20822, No.
No. 49-5616 discloses a dye having an absorption maximum at 300 to 700 nm. The amount of each used layer (for example, protective layer,
A backing layer, etc.) in 1 m ² per 0.02～0.3G, preferably 0.05
It can be used in the range of 0.20.2 g.

Known additives can be added to the direct-positive silver halide photographic light-sensitive material of the present invention. Stabilizers include mercapto compounds, benzotriazole compounds, oxazole compounds and the like, and hardeners are not particularly limited, but aldehyde compounds, 2-hydroxy-4,6-dichloro-1,3,5-triazine, N-methylol Compounds, vinyl sulfone compounds, saponin as coating aids,
Alkylene oxide-based, glycidol-based nonionic surfactants, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate groups, and phosphate groups, amphoteric surfactants such as amino acids and aminosulfonic acids Agents and polyalkylene oxide compounds are used.

The support used in the practice of the present invention can be, for example, glass, a film base such as cellulose acetate, polyethylene terephthalate, baryta paper, resin coated paper, aluminum foil, concrete and the like.

The direct-positive silver halide photographic light-sensitive material of the present invention may further contain a whitening agent, an ultraviolet absorber,
A matting agent, an antistatic agent and the like can be contained.

In the present invention, a silver halide emulsion is coated on the support described above, and it has been found that the pAg of the silver halide emulsion at the time of coating is important. In particular, in the emulsion having the core / shell particle diameter ratio of the present invention and containing rhodium in the core, the fluctuation of the sensitivity during storage and the increase of the minimum density are suppressed by setting the pAg of the emulsion coating solution to 7 or more. Is done. P of the emulsion coating solution targeted by the present invention
Ag is usually about 5 to 6 and the pAg is adjusted to 7 or more by adding sodium chloride or the like. Preferably, the pAg is 7 to
Set to the range of 10.

The direct-positive silver halide photographic light-sensitive material of the present invention can be processed under various conditions.
Processing such as high-speed rapid automatization processing for up to 60 seconds and dish development processing is not particularly limited.

As the developing solution, any of a developing solution used for a general silver halide photographic light-sensitive material and a lith developing solution can be used.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the embodiments of the present invention are not limited thereto.

[0042]

【Example】

Example 1 A core emulsion was prepared by adding a silver nitrate aqueous solution having the same concentration as a 2N sodium chloride solution to a gelatin aqueous solution kept at 50 ° C for X minutes by a control double jet method. Subsequently, 50 mg of sodium thiosulfate and 4 mg of chloroauric acid were added as an aqueous solution to 1 kg of silver halide (in terms of silver nitrate), followed by chemical ripening at 50 ° C. for 70 minutes. Further, an aqueous solution of halogen and silver nitrate (120
-X) A core / shell emulsion was prepared by mixing for minutes and chemically sensitizing the core. That is, the position of the internal chemical sensitization nucleus was variously changed.

The emulsion was washed with desalted water by flocculation, and an aqueous solution of inert gelatin was added to the emulsion, which was then redissolved at 40 ° C. The average grain size of these silver halide grains is
It was 0.20 μm.

To the emulsion after re-dissolution, 10 mg of thiourea dioxide and 18 mg of chloroauric acid were added as an aqueous solution to 1 kg of silver nitrate.
Heating was carried out at pH 6, 60 ° C. for 70 minutes to fog the surface of the silver halide grains.

This emulsion was treated with benzotriazole and, as a hardener, 2-hydroxy-4,6-dichloro-1,
An appropriate amount of 3,5-triazine and sodium lauryl sulfonate as a surfactant were added, and the mixture was applied to a 100 μm thick polyethylene terephthalate film base so that the amount of silver nitrate was 5 g / m ² . At the same time, a gelatin solution containing a yellow dye having the following structural formula (100 mg / m ² ) as a protective layer was applied so as to be 1 g / m ² of gelatin.

[0046]

Embedded image

The used polyethylene terephthalate film base had previously been coated with a gelatin backing layer containing 100 mg of the above yellow dye per m ² .

The coated sample was heated at 50 ° C. for one day and then subjected to sensitometry. Exposure was performed 20 times with a light room printer (Dainippon Screen P-627 printer) through a light wedge for sensitometry. The film was developed with a developer having the following composition at 35 ° C. for 30 seconds, and then fixed, washed with water and dried.

Developer Formulation Hydroquinone 35.0 g Phenidone 0.2 g Sodium hydroxide 12 g Potassium tertiary phosphate 83 g Sodium sulfite 65 g Ethylenediaminetetraacetic acid disodium 1.5 g 3-Diethyl-amino-1,2-propanediol 15 g 5- 1.7 g of methylbenzotriazole Make up to 1 liter with water. (PH11.6)

The developed sample was measured for transmission density with a Macbeth transmission densitometer (RD 917) to calculate photographic characteristics.
Table 1 shows the results.

[0051]

[Table 1]

As can be seen from Table 1, when l ₂ / l ₁ was 0.6 or less, Dmin was low and good results were obtained. No sensitivity was determined for the samples of NO.1 to NO.4 because Dmin was high.

For comparison, Sample No. 1, 1 and 3, 1 mg / m ² of 1,1′-dimethyl-2,2′-diphenyl-3,3′-indolocarbocyanine bromide as an organic desensitizer, or the following as a fog inhibitor: 2
A sample was prepared by adding 3 × 10 ⁻³ mol / mol AgNO ₃ to the above compound and tested in the same manner. These samples were all D
min was reduced, but development progress was slow, and sensitivity and D
max was reduced.

[0054]

Embedded image

Example 2 Next, the grain size of a crystal of 100 mol% of silver chloride was changed variously. The experimental method was basically the same as in Example 1, except that the mixing temperature was changed between 53 ° C and 45 ° C. At this time, the core particle size was also changed at the same time. However, the chemical ripening of the core and the shell was performed at the same temperature as in Example 1.

When mixed at 53 ° C., the average particle size is 0.25 μm, 45 ° C.
And the average particle size became 0.15μ. Table 2 shows the results.

[0057]

[Table 2]

Although the average particle size was changed as shown in Table 2, the ratio of l ₂ / l ₁ (Dm is required to be less than 0.60 if the average particle size is not less than 0.60).
It is interesting that Dmin is determined only by the fact that in does not decrease, and the effectiveness of the present invention was shown.

Example 3 A core emulsion was prepared by adding a silver nitrate aqueous solution having the same concentration as a 2N sodium chloride solution to a gelatin aqueous solution kept at 50 ° C. for X minutes by a control double jet method. In preparing the core emulsion, 10 ^-5 mol of rhodium chloride was contained per mol of silver halide. Further, in order to attach a shell to the core, the emulsion was prepared by mixing with the same halogen and silver nitrate aqueous solution as in the mixing of the core emulsion for (120-X) minutes.
That is, by changing X, the size of the core was variously changed.

After this emulsion was washed with desalted water by flocculation, an aqueous solution of inert gelatin was added and redissolved at 40 ° C. The average grain size of these silver halide grains is
It was 0.20 μm.

After re-dissolving the two emulsions, 1 kg of silver nitrate was added.
Then, 10 mg of thiourea dioxide and 18 mg of chloroauric acid were added as an aqueous solution, and the mixture was heated for 70 minutes under the conditions of pH 7.5 and 60 ° C. to fog the shell surface of the silver halide grains.

This emulsion was added with benzotriazole and, as a hardener, 2-hydroxy-4,6-dichloro-1,
An appropriate amount of 3,5 triazine and sodium lauryl sulfonate as a surfactant were added, and a backing layer used in Example 1 was added to a 100 μm thick polyethylene terephthalate film base so that the amount of silver nitrate was 5 g / m ^2. And applied to a polyethylene terephthalate film. At the same time, the protective layer shown in Example 1 was coated on the emulsion layer.

The coated sample was heated at 50 ° C. for one day and then tested in the same manner as in Example 1. Table 3 shows the results.
Shown in

[0064]

[Table 3]

From Table 3, it can be seen that also when rhodium is contained in the core, Dmin is greatly reduced by setting l ₂ / l ₁ to 0.6 or less.

The samples Nos. 6 to 10 and 31 to 33 were exposed to a safe light (fluorescent lamp for preventing fading: 100 lux) on the emulsion surface for 20 minutes in order to check the handling safety in a bright room. Irradiation was no problem.

Example 4 A core-shell emulsion containing Rh in the core was prepared in the same manner as in Example 3. The ratio of l ₂ / l ₁ was set to 0.5, and the ratio of thiourea dioxide to chloroauric acid at the time of chemical sensitization of the shell was varied. Sample NO. In the case of Nos. 34 to 37, the amount of thiourea dioxide was fixed at 10 mg per kg of silver nitrate, and the amount of chloroauric acid was changed. Sample NO. In the case of 38 to 40, the amount of chloroauric acid was fixed at 20 mg per kg of silver nitrate, and the amount of thiourea dioxide was changed. The obtained samples were evaluated for photographic characteristics and dissolution physical development fog. Table 4 shows the results.

For the dissolution physical development fog, the above developer and a fixer CF-901 (1: 2 dilution) manufactured by Mitsubishi Paper Mills were placed in an automatic developing machine LD-280 manufactured by Dainippon Screen Co., Ltd.
The exposed sample of m was continuously passed through three sheets, and the fogging state was observed. The fogging state is 1 to 5 as shown below.
Scored.

5: No dissolution physical development fog occurs. 4: Slight occurrence but no practical problem. 3: Slightly generated but at a practically problematic level. 2: It can be seen immediately that fogging has occurred. 1: It occurs on the entire surface.

[0070]

[Table 4]

As can be seen from Table 4, as long as the molar ratio of thiourea dioxide to chloroauric acid is from 1:10 to 10: 1, Dmin is low, the footprint is good, and the dissolution physical development fog is small.

Example 5 An emulsion was prepared in the same manner as in Example 3 (l ₂ / l ₁ was 0.5), and sodium chloride was added to the coating solution to obtain a pAg of the coating solution.
Was changed. The obtained sample was allowed to stand at 50 ° C. and 80% for 7 days, and the sensitivity and the storage stability of Dmin were evaluated. Table 5 shows the results. Based on the raw sample, the variation in sensitivity was rated as ○ when the variation was within 5%, Δ when 6 to 10%, and × when 11% or more. For Dmin, the difference was described based on the raw sample.

[0073]

[Table 5]

As shown in Table 5, the storage stability is improved by increasing the pAg of the emulsion coating solution to 7 or more.

[0075]

According to the present invention, a direct positive silver halide photographic material having a high maximum density (Dmax) and particularly a sufficiently low minimum density (Dmin) can be obtained. Further, it is possible to obtain a direct positive silver halide photographic light-sensitive material having improved storage stability without occurrence of dissolution physical development fog. Further, a direct positive silver halide photographic material which can be handled in a bright room can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03C 1/36 G03C 1/36

Claims (5)

[Claims] 1. A direct positive silver halide photographic material comprising core / shell type silver halide grains having a silver chloride content of 90 mol% or more and having a chemical sensitization nucleus on the surface of said core, A silver halide photographic material for direct positive use, wherein the ratio of the average diameter of the crystal grains in the core portion to the average diameter of the crystal grains including the shell portion satisfies the condition of the following formula (1). l ₂ / l ₁ ≦ 0.6 (1) l ₁ : average diameter of crystal particles including shell portion l ₂ : average diameter of crystal particles in core portion 2. A direct positive silver halide photographic light-sensitive material comprising core / shell type silver halide grains having a silver chloride content of 90 mol% or more, wherein the core portion contains a metal belonging to Group 8 of the periodic table. Wherein the ratio of the average diameter of the crystal grains in the core portion to the average diameter of the crystal grains including the shell portion satisfies the condition of the above formula (1). 3. The metal of Group 8 of the periodic table is rhodium, and the rhodium is added in an amount of 1 × per mole of silver halide in the core.
The silver halide photographic material for direct positive use according to claim 2, which contains 10 ^-6 mol or more. 4. The silver halide photographic material for direct positive use according to claim 2, wherein a reduction sensitizer and a gold sensitizer are used for forming a chemical sensitization nucleus (fog nucleus) on a shell surface. A silver halide photographic material for direct positive use, wherein the ratio of the sensitizer is 1:10 to 10: 1 in terms of mole number. 5. The method for producing a direct positive silver halide photographic light-sensitive material according to claim 1, wherein the pAg of the coating solution for the direct positive silver halide emulsion is 7 or more. A method for producing a direct positive silver halide photographic material.