EP0381160A2

EP0381160A2 - Direct positive photographic material

Info

Publication number: EP0381160A2
Application number: EP90101839A
Authority: EP
Inventors: Hatsumi Tanemura
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1989-01-30
Filing date: 1990-01-30
Publication date: 1990-08-08
Also published as: JPH02199449A; EP0381160A3

Abstract

A direct positive photographic material and process for forming a direct positive photographic image with the same, comprising, a support and at least one photosensitive layer positioned on the support and comprising a non-prefogged internal latent image silver halide emulsion. The emulsion, in turn, comprises silver bromide and has a core-shell structure of at least two layers. Further, the core has been chemically sensitized under conditions so that the bromide ion concentration of the core is greater than 2.0 x 10-² mole/I. The disclosed material is capable of rapidly and stably forming direct positive images having a high maximum image density and a low minimum image density. Additionally, the gradational changes in highlighted portions are reduced, even when developing times are altered during processing in color development solutions of a relatively low pH.

Description

FIELD OF THE INVENTION

This invention relates to direct positive photographic materials, and in particular it relates to direct positive photographic materials having a photosensitive layer which contains a non-prefogged internal latent image type of silver halide emulsion with a core/shell structure.

BACKGROUND OF THE INVENTION

Photographic methods for obtaining a direct positive image without the need of a reversal processing stage or a negative film are well known.
Excluding some special methods, the methods which are generally used to produce a positive image using conventional direct positive silver halide photographic materials can be divided into 2 types from the point of view of their practical effectiveness.
The first type is one in which a prefogged silver halide emulsion is used. The direct positive image is obtained after development by destroying the fogged nuclei in the exposed portions (the latent image) making use of solarization or the Herschel effect or the like.
The other type is one in which an unfogged internal latent image silver halide emulsion is used. The direct positive image is obtained after image exposure by effecting surface development after carrying out a fogging process or while carrying out a fogging process.
Furthermore, the internal latent image silver halide photographic emulsion mentioned above has photosensitive nuclei mainly on the inside of the silver halide grain. The latent image forms mainly within the grain upon exposure.
The latter method generally involves higher photographic speeds and is better suited to applications requiring a high speed than the former method. This invention relates to this latter method.
Various techniques are already known for forming direct positive images using internal latent image silver halide emulsions. The main techniques are those described, for example, in the specifications of U.S. Patents 2,592,250, 2,466,957, 2,497,875, 2,588,982, 3,317,322, 3,761,266, 3,761,276, 3,796,577 and G.B. Patents 1,151,363, 1,150,553 (and 1,011,062).
Furthermore, details of direct positive image formation mechanisms are described, for example, in The Theory of the Photographic Process by T.H. James, Fourth Edition, Chapter 7, pp. 182 - 193 and in U.S. Patent 3,761,276.
In brief, it is believed that the initial image exposure causes fogging nuclei to occur selectively only on the surfaces of silver halide grains in unexposed portions due to a surface desensitizing action which occurs in what is known as the internal latent image arising within the silver halide. The photographic image (direct positive image) is then formed in the unexposed portions by carrying out a common so-called surface development process.
The method generally known as the "light fogging method" in which a second exposure is made over the whole surface of the photosensitive layer (for example see G.B. Patent 1,151,363) and the method known as the "chemical fogging method" which employs nucleating agents are both known as a means of selectively producing fogged nuclei as discussed above. The latter method is described, for example, on pages 76 - 78 of The Research Disclosure Journal, Vol. 151, No. 15162 (November 1976).
The formation of a direct positive color image can be achieved by effecting a surface color development process either after having carried out a fogging process or while carrying out a fogging process on an internal latent image silver halide photosensitive material and then carrying out bleaching and fixing (or bleach-fixing) processing. Washing and/or stabilization processing is usually carried out after bleaching and fixing processing.
With conventional chemical fogging methods in which the fogging processing is effected using nucleating agents, the action of the nucleating agents is obtained only at a high pH of 12 or above. The developer is therefore unstable and readily degraded by atmospheric oxidation under such high pH conditions. As a result, there is the disadvantage that the developing activity is markedly reduced. Furthermore, there is the disadvantage that the processing time is extended due to the slowness of the developing rate and that even longer processing times will be required particularly if low pH developing solutions are employed.
Meanwhile, the "light fogging method", in which a second exposure is made of the entire surface of the photosensitive layer, is comparatively practical since high pH conditions are not required. However, it has various technical shortcomings when used for various purposes in wide-ranging photographic fields. To elaborate, because the light fogging method is based on the formation of fogged nuclei by photodecom- position of silver halide, the appropriate exposure illumination and exposure amounts will differ with the type and the characteristics of the silver halide used. Therefore, there are the disadvantages that it is difficult to obtain a fixed performance and also that the developing equipment is complicated and expensive.
With conventional fogging methods it was therefore difficult to obtain both a stable and a good direct positive image. Compounds which exhibit a nucleating action at pH 12 and below have been proposed in JP-A-52-69613 (the term "JP-A" as used herein means an "unexamined Japanese Patent Application") (which corresponds to U.S. Patent 4,115,122), U.S. Patents 3,615,615 and 3,850,638 as a means of resolving the problem. But these nucleating agents have disadvantages in that they either act upon the silver halide during the storage of the photosensitive material prior to processing or that the nucleating agent itself degrades and thus reduces the maximum image density after final processing.
An increase in the developing rate for intermediate densities using hydroquinone derivatives has been described in U.S. Patent 3,227,552. However the speed of development is insufficient even when these derivatives are used and, in particular, insufficient developing rates alone are obtained with developing solutions of a pH of 12 or below.
An increase in the maximum image density by adding mercapto compounds having carboxylic acid groups or sulfonic acid groups is described in JP-A-60-170843. However, the effect is slight when these compounds are added. In addition, the pH of the developing solution is 12.0 and the stability of the developing solution is insufficient.
JP-A-55-134848 describes the prevention of re- reversal negative images and a reduction in minimum image density by processing in a processing solution (pH 12.0) containing a tetraazaindene-based compound in the presence of nucleating agents. However, with this method there is no increase in the maximum image density, and the developing rate is not increased.
Further, JP-B-45-12709 (the term "JP-B" as used herein means an "examined Japanese Patent Publication") (which corresponds to U.S. Patent 3,733,198) describes the addition of triazoline-thione and tetrazoline-thione-based compounds, as antifoggants, to photosensitive materials which form direct positive images by the light fogging method. However, it has not proved possible to attain high maximum image densities or rapid development rates with these methods either.
Thus, in processing of short duration there has hitherto been no technique for stably achieving direct positive color images having high maximum color image densities and low minimum image densities in color developing solutions of a low pH (pH 12 or less).
In order to resolve this problem, there is a disclosure of a gold sensitization technique for the surface of internal latent image silver halide grains (JP-A-63-47766). However, it has become clear that with this technique there is the disadvantage that when the developing time is altered the maximum image density and the gradation of the highlighted portions are likely to vary.
Confronted by this problem, the inventors have discovered that an improved result is obtained in silver halide grains by incorporating manganese, copper, zinc, cadmium, lead, bismuth or metals of Group VIII of the Periodic Table (JP-A-1-52146), but this result is not sufficient.
An object of this invention is therefore to provide non-prefogged internal latent image silver halide photosensitive material which is capable of rapidly and stably forming direct positive images having high maximum image densities and low minimum image densities. Further, gradational changes in highlighted portions are reduced even when developing times are altered during processing in color development solutions of a relatively low pH.

SUMMARY OF THE INVENTION

The abovementioned object of this invention is achieved by means of a direct positive photographic material comprising a support, having thereon at least one photosensitive layer containing a non-prefogged internal latent image silver halide emulsion, the emulsion comprising silver bromide and having a core/shell structure comprising at least 2 layers. The core is chemically sensitized under conditions such that the bromide ion concentration of the core is greater than 2.0 x 10-² mole/t.

DETAILED DESCRIPTION OF THE INVENTION

The non-prefogged internal latent image silver halide emulsion used in this invention is one in which the surfaces of the silver halide grains have not been prefogged and which contains silver halide forming the latent image mainly on the insides of the grains. More specifically, the silver halide emulsion is one in which, when a fixed amount (0.5 - 3 g/m²) is coated onto a transparent support and is exposed for a fixed period of from 0.01 to 10 seconds. The emulsion is then developed in the following developing solution A (internal developing solution) at 18°C for 5 minutes. The maximum density, as measured by a common photographic density measuring method, is preferably at least 5 times, and more preferably at least 10 times the maximum density obtained when a silver halide emulsion (which has been coated in the same amount and exposed in the same way as described above) is developed in the following developing solution B (surface developing solution) at 20° C for 6 minutes.
The internal latent image silver halide grains in the photosensitive materials of this invention comprise silver bromide and are of the core_/shell type comprising at least 2 layers. After formation of the core grain, it is chemically sensitized under conditions such that the bromide ion concentration of the core is greater than 2.0 x 10-² mole/t. The bromide ion concentration is preferably 3.1 x 10-² mole/t or more and more preferably 3.8 x 10-² mole/t or more, with preferably maximum of 4.5 mole/t. The ripening temperature is preferably in the range of 55 C to 100°C and more preferably in the range of 65 C to 100°C. Most preferably it is in the range of 70° C to 100° C. As regards ripening times, the optimum time will vary with the temperature and the amount of sensitizer but, generally speaking, it will be from around 10 minutes to 5 hours. The pH is preferably 2-9.
The chemical sensitizers which are added to chemically sensitize the core in this invention are now explained. It is possible to employ the customarily used sensitizers in this invention, and more specifically it is possible to use the compounds described from line 18 on the bottom left column to line 16 on the bottom right column of page 12 of the report of JP-A-62-215272 or those disclosed on pages 675 - 734 of Die Grundlagen der photographischen Prozesse mit Silberhalogeniden (The Fundamentals of Silver Halide Photographic Processes) edited by H. Friezer (Akademische Verlagsgesellschaft 1968).
Thus, it is possible to use sulfur sensitizers, reduction sensitizers and precious metal sensitizers (particularly gold sensitizers) as the sensitizer. It is particularly desirable to use gold sensitizers in this invention.
Gold sensitization in this invention can be effected using a common method to add compounds containing gold ions such as the acids AuCl₄ ^-, AuBr₄ ^-, Au(SCN)-, Au(CN)₂- and Au(S₂O₃)₂3- and the potassium and sodium salts thereof to the emulsion preferably at 5 x 10-^{6 -} 5 x 10-³ mole, and more preferably at 1 x 10-^{5 -} 5 x 10^-4 mole, per mole of silver in the core grain (for example, see The Theory of the Photographic Process edited by T.H. James, Macmillan Publishing Co. Inc. 1977, pp. 154 - 155, and Research Disclosure Journal 7643, p. 23).
If appropriate, sulfur sensitizers, reduction sensitizers and the like can be used together with gold sensitizers to ripen the core of this invention.
As sulfur sensitizers, there are active gelatin and compounds containing sulfur which are able to react with silver such as thiosulfates, thioureas, mercapto compounds and rhodanines. As reduction sensitizers there are reducing substances such as stannous salts, amines, hydrazine derivatives, formamidine sulfinic acid and silane compounds.
The average grain size of the silver halide grains (expressed as an average based on the projected surface area taking the grain diameter as the grain size in cases involving spherical and nearly spherical grains and taking the edge length as the grain size in cases involving cubic grains) is preferably in the range of 2.0 /.Lm to 0.1 u.m and particularly preferably in the range 1.2 µm to 0.2 um. The grain size distribution may be narrow or broad although, in view of the improvements in the graininess and sharpness, in this invention it is preferable to use a so-called "monodisperse" silver halide emulsion with a narrow grain size distribution such that 90% or more, and in particular 95% or more, of all the grains either by grain number or weight come within ± 40% of the average grain size (and more preferably within ± 30% and most preferably within ± 20%). Furthermore, in order to satisfy the gradation expected of the photosensitive material, it is possible to carry out multi-layer coating in separate layers or to mix into one layer a plurality of grains of the same size but different photographic speeds or 2 or more monodisperse silver halide emulsions with different particle sizes in emulsion layers having essentially the same color sensitivity. Moreover, it is also possible to use combinations of 2 or more types of polydisperse silver halide emulsion, or a combination of monodisperse emulsion and polydisperse emulsion either by mixing or in several layers.
The form of the silver halide grains used in this invention may have cubic, octahedral, dodecahedral, tetradecahedral or other such regular crystal form, it may have spherical or other such irregular crystal form, or it may have a complex form of the other two crystal forms. Furthermore, tabular grains are also acceptable. In particular it is possible to use emulsions in which tabular grains with a length/thickness ratio value of 5 or more (or more particularly 8 or more) occupy 50% or more of the total projected surface area of the grains. Emulsions consisting of a mixture of these types of crystal forms are also acceptable.
The silver halide emulsions used in this invention can also be chemically sensitized by sulfur or selenium sensitization, reduction sensitization, precious metal sensitization or the like on the surfaces, either singly or in combination.
The silver halide emulsions used in this invention may contain, for example, manganese, copper, cadmium, zinc, lead, bismuth or metals in Group VIII of the Periodic Table which are described, for example, in U.S. Patents 4,395,478, 3,761,276 and JP-A-59-216136.
The photographic emulsions of this invention are spectrally sensitized by photographic sensitizing dyes using a customary method. Dyes which are classified as cyanine dyes, merocyanine dyes or complex merocyanine dyes are particularly useful dyes. These dyes can be used either singly or in combination. Furthermore, supersensitizers may be used conjointly with the dyes mentioned above. More detailed and more specific examples and methods of use are described, for example, in RD17643 (December 1978) IV.
The photographic emulsions used in this invention can contain benzenethiosulfonates, benzenesul- finates, thiocarbonyl compounds and the like to prevent fogging during the production, storage and photographic processing of the photosensitive material or to stabilize photographic performance.
More detailed specific examples of the antifoggants and stabilizers and the methods for using them are described, for example, in U.S. Patents 3,954,474, 3,982,947, JP-B-52-28660, RD 17643 (December 1978) IV A - IV M and Stabilization of Photographic Silver Halide Emulsions by E.J. Burr (Focal Press, 1974).
The photosensitive materials of this invention preferably contain compounds which can be represented by the following general formula [N-I] or [N-II] as nucleating agents.
In the formula. Z represents a group of non-metallic atoms necessary to form a 5- or 6-membered heterocyclic ring and Z may be substituted by substituent groups. R' is an aliphatic group, and R² is a hydrogen atom, aliphatic group or aromatic group. R' and R² may be substituted by substituent groups. Furthermore, R² may also bind with the hetroacyclic ring completed by Z to form a ring. However, at least one of the groups represented by R', R² and Z either contains an alkynyl group, acyl group, hydrazine group or hydrazone group, or a 6-membered ring is formed by R' and R² to create a dihydropyridinium skeleton. Moreover, at least one of the substituent groups for R', R² and Z may possess a group promoting adsorption onto silver halides. Y is a counterion for the purpose of charge balance, and n is 0 or 1.
Examples of the hetero ring completed by Z are quinolinium, benzothiazolium, benzimidazolium, pyridinium, thiazolinium, thiazolium, naphthothiazolium, selenazolium, benzoselenazolium, imidazolium, tetrazolium, indolenium, pyrrolinium, acridinium, phenanthri-dinium, isoquinolinium, oxazolium, naphthoox- azolium and benzooxazolium nuclei. Substituent groups for Z include, for example, alkyl, alkenyl, aralkyl, aryl, alkynyl, hydroxyl, alkoxy and aryloxy the amino, alkylthio, arylthio, acyloxy, acylamino, sulfonyl, sulfonyloxy, sulfonylamino, carboxyl, acyl, carbamoyl, sulfamoyl, sulfo, cyano, ureieo, urethane, carbonic acid ester, hydrazine, hydrazone and imino groups and halogen atoms. By way of example, at least one of the substituent groups mentioned above is selected as a substituent group for Z. In cases where there are two or more substituents, they may be identical or different. Furthermore, the substituent groups mentioned above may be further substituted by these substituent groups.
Moreover, the substituent group for Z may be a heterocyclic quaternary ammonium group connected to Z via a suitable linking group L. In this case it adopts what is known as a dimer structure.
Hetero rings completed by Z include quinolinium, benzothiazolium, benzimidazolium, pyridinium, acridinium, phenanthridinium and isoquinolinium nuclei. Quinolinium and benzothiazolium are more preferred and quinolinium is most preferred.
The aliphatic groups for R' and R² are unsubstituted alkyl groups with 1 - 18 carbon atoms and substituted alkyl groups with 1 - 18 carbon atoms in the alkyl moiety. By way of substituent groups, it is possible to mention those cited as substituent groups for Z. Moreover, R² can form a ring by linking with the heterocyclic ring completed by Z.
The aromatic group represented by R² is one with 6 - 20 carbon atoms, for instance a phenyl group or a naphthyl group. Substituent groups thereto include those mentioned as substituent groups for Z. R² is preferably an aliphatic group and most preferably a methyl group or a substituted methyl group. Or it may bind with the hetero ring completed by Z to form a ring.
At least one of the groups represented by R', R² or Z either has an alkyl, acyl, hydrazine or hydrazone group or a 6-membered ring is formed by R¹ and R² to create a dihydropyridinium skeleton. The alkyl, acyl, hydrozine, hydrozone and dihydropyrinidium may be substituted by the groups mentioned previously as substituent groups on the group represented by Z.
Embodiments in which at least one of the substituent groups on the groups or rings represented by R¹, R² and Z is an alkyhyl group or an acyl group, and embodiments in which R' and R² link to form a dihydropyridinium skeleton is preferred, the case where there is at least one alkynyl group is further preferred, the propargyl group being particularly preferred.
Among the groups promoting adsorption onto silver halides having the substituent groups of R', R² and Z, those represented by X¹ L' _m are preferred. Here, X' a group promoting adsorption onto silver halides, L' is a divalent linking group and m is 0 or 1.
Preferred examples of groups promoting adsorption onto silver halides, which are represented by X' include a thioamido group, a mercapto group and 5- and 6-membered nitrogen-containing heterocyclic groups.
They may be substituted by those substituent groups cited as substituents for Z. Non-cyclic thioamido groups (for example thiourethane and thioureido groups) are the preferred thioamido groups.
Heterocyclic mercapto groups (for example 5-mercaptotetrazole, 3-mercapto-1,2,4-triazole, 2-mercapto-1,3,4-thiadiazole and 2-mercapto-1,3,4-oxadiazole) are preferred as the mercapto groups for X'.
Preferable 5- or 6-membered nitrogen-containing heterocyclic rings represented by X' are those which produce iminosilver, for example benzotriazole and aminothiatriazole.
Divalent linking groups represented by L include atoms or atomic groups comprising at least one of the following C, N, S or 0 atoms. More specifically, there are alkylene groups, alkenylene groups, alkynylene groups, arylene groups, -0-, -S-, -NH-, -N =, -CO- and -SO₂- either singly or in combination (and these groups may have substituent groups). The following are preferred combinations of these groups.
The counterion Y which is for charge balance may be, for example, a bromide ion, a chloride ion, a iodide ion, a p-toluenesulfonic acid ion, an ethyl sulfonic acid ion, a perchlorate ion, a trifluoromethanesulfonate ion, a thiocyanate ion, a tetrafluoborate ion and a hexafluorophosphate ion.
These compounds and methods for their synthesis are described, for example, in the patents cited in Research Disclosure Journal, No. 22, 534 (January 1983, pages 50 - 54) and ibid. No. 23, 213 (August 1983, pages 267 - 270), and in JP-B-49-38,164,JP-B-52-19,452,JP-B-52-47,326,JP-A-52-69,613, JP-A-52-3,426, JP-A-55-138,742, JP-A-60-11,837 and in U.S. Patents 4,306,016 and 4,471,044.
Specific examples of compounds represented by general formula [N-I] are given below, but the invention is not limited to these.

in which, R²¹ represents an aliphatic group, aromatic group or heterocyclic group; R²² represents a hydrogen atom, or alkyl, aralkyl, aryl, alkoxy, aryloxy or amino group; G represents a carbonyl, sulfonyl, sulfoxy, phosphoryl or iminomethylene group
R²³ and R²⁴ either both represent hydrogen atoms or one of them represents a hydrogen atom and the other an alkylsulfonyl, arylsulfonyl or acyl group. Additionally, it is possible to form a hydrazone structure
in a form containing G, R23, _R24 and hydrazine nitrogen. Furthermore, where possible, the groups mentioned above may be substituted by substituent groups.
The R²¹ group may be substituted by substituent groups, such as the following substituent groups. Examples include alkyl, aralkyl, alkoxy, alkyl- or aryl- substituted amino, acylamino, sulfonylamino, ureido, urethane. aryloxy, sulfamoyl, carbamoyl, aryl, alkylthio, arylthio, sulfonyl, sulfinyl, hydroxyl, a halogen atom, cyano, sulfo and carboxyl groups or phosphoric acid amide groups. These groups may be further substituted.
Of these, the ureido group and the sulfonylamino group are particularly preferred.
Where possible, these groups may link to form rings.
Aromatic groups, aromatic heterocyclic or aryl-substituted methyl groups are preferred, and aryl groups (for example phenyl, napthyl) are more preferred as R²¹.
Hydrogen atoms, alkyl groups (for example methyl), aralkyl groups (for example, 2-hydroxybenzyl), or aryl groups (for example 2-hydroxymethylphenyl) are preferred and hydrogen atoms are particularly preferred for the groups represented by R2:2.
In addition to the application of the substituent groups listed in connection with R²¹, acyl, acyloxy, alkyl or aryloxycarbonyl, alkenyl, alkynyl, nitro groups and the like can be applied as substituent groups for R²².
These substituent groups may be further substituted by these substituent groups. Furthermore, where possible, these groups may link together to form rings.
It is preferable that R²¹ or R²², particularly R²¹, contains a coupler or another diffusion-resistant group otherwise known as a ballast group, particularly one that it is linked with a ureido or sulfonylamino group.
It may have the group X² L² m₂ which promotes adsorption to the surfaces of the silver halide grains. Here, X² has the same meaning as X¹ in general formula [N-I] and is preferably a thioamido (excluding thiosemicarbazide and substituted forms thereof), mercapto or 5- or 6-membered nitrogen-containing heterocyclic group. L² represents a divalent linking group and has the same meaning as L' discussed in connection with [N-I]. m² is 0 or 1.
More preferably, X² is an acyclic thioamido group (for example thioureido or thiourethane), a cyclic thioamido group (which is to say a mercapto-substituted nitrogen-containing hetero ring such as 2-mercaptothiadiazole, 3-mercapto-1,2,4-triazole, 5-mercaptotetrazole, 2-mercapto-1,3,4-oxadiazole or 2-mer- captobenzooxazole) or a nitrogen-containing heterocyclic group (for example benzotriazole, benzimidazole or indazole).
The most preferable X² will vary in accordance with the material used. For example, in color materials, a mercapto-substituted nitrogen-containing hetero ring or a nitrogen-containing hetero ring which forms iminosilver will be preferred when use is made of a colorant (a so-called coupler) which forms the dye through a coupling reaction with the oxidized form of a p-phenylenediamine-based developer. Also in color materials, an acyclic thioamido group or mercapto-substituted nitrogen-containing hetero ring will be preferred as X² when use is made of a colorant (a so-called DRR compound) which forms a diffusible dye through cross oxidation with the oxidized form of the developer. Again, with black-and-white materials a mercapto-substituted nitrogen-containing hetero ring or a nitrogen-containing hetero ring which forms iminosilver will be preferred as X².
Hydrogen atoms are most preferred as R²³ and R²⁴. A carbonyl group is most preferred as G in general formula [N-II].
Those compounds represented by general formula [N-II] which have a group adsorbing onto silver halides and those having a ureido or sulfonylamino group are more preferable.
Examples of hydrazine-based nucleating agents which have a group adsorbing onto silver halides and this method of manufacture are described, for example, in U.S. Patents 4,030,925, 4,080,702, 4,031,127, 3,718,470, 4,269,929, 4,276,364, 4,278,748, 4,385,108, 4,459,347, 4,478,922, 4,560,632, G.B. Patent 2,011,391 B, JP-A-54-74,729, JP-A-55-163,533, JP-A-55-74,536 and JP-A-60-179,734.
Hydrazine-based nucleating agents are also described, for example, in JP-A-57-86,829, U.S. Patents 4,560,638, 4,478,928, 2,563,785 and 2,588,982.
Specific examples of compounds represented by general formula [N-II] are given below. However, in the invention it is possible to use compounds other than those shown below.
It is desirable to add these nucleating agents to an internal latent image type of silver halide emulsion layer, but it is also acceptable to add them to other layers such as the intermediate layers, the undercoating layers and the backing layers provided that they diffuse during coating or during processing and that the nucleating agent is adsorbed onto the silver halide.
The amount of nucleating agent used is preferably 10^{-8 -} 10-² mole, and more preferably 1-^{7 -} 10-³ mole, per mole of silver halide.
Furthermore, two or more nucleating agents may be used conjointly.
The following nucleation accelerators can be used to accelerate the action of the abovementioned nucleating agents in this invention.
Tetraazaindenes, triazaindenes and penta-azaindenes having at least one mercapto group, optionally substituted with an ammonium group or an alkali metal atom, or the compounds described in JP-A-63-106656 (pages 6 - 16) may be used as nucleation accelerators.
Specific examples of nucleation accelerators are given below but the present invention is not limited to these.

(A-1) 3-Mercapto-1,2,4-triazolo[4,5-a]pyridine
(A-2) 3-Mercapto-1,2,4-triazolo[4,5-a]pyrimidine
(A-3) 5-Mercapto-1,2,4-triazolo[1,5-a]pyrimidine
(A-4) 7-(2-Dimethylaminoethyl)-5-mercapto-1,2,4-triazolo[1,5-a]pyrimidine
(A-5) 3-Mercapto-7-methyl-1,2,4-triazolo[4,5-a]pyrimidine
(A-6) 3,6-Dimercapito-1,2,4-triazolo[4,5-B]pyridazine
(A-7) 2-Mercapto-5-methylthio-1,3,4-thiadiazole
(A-8) 3-Mercapto-4-methyl-1,2,4-triazole
(A-9) 2-(3-Dimethylaminopropylthio)-5-mercapto-1,3,4-triadiazole, hydrochloric acid salt
(A-10)2-Morpholinoethylthio)-5-mercapto-1,3,4-thia diazole, hydrochloric acid salt

The nucleation accelerator can be included in the photosensitive material and, within the photosensitive material, it is preferably included in an internal latent image type of silver halide emulsion layer or other such hydrophilic colloid layer (for example intermediate layer or protective layer). Within the silver halide emulsion layer or a layer adjacent thereto is particularly preferred.
Various color couplers can be used in this invention to form a direct positive color image. Color couplers are compounds which produce or release essentially non-diffusible dyes via a coupling reaction with the oxidized form of a primary aromatic amine color developer, and it is preferable that they themselves are essentially non-diffusible compounds. Typical examples of useful color couplers are naphtholic or phenolic compounds, pyrazolone- or pyrazoloazole- based compounds and open-chain or heterocyclic ketomethylene compounds. Specific examples of cyan, magenta and yellow couplers used in this invention are described in the patents cited in, and are the compounds described in, Research Disclosure Journal, No. 17643 (December 1978), p. 25, Section VII-D, ibid. No. 18717 (November 1979) and JP-A-62-215272.
In order to compensate for unwanted absorption which the dye formed has in the short wavelength region, it is also possible to use colored couplers, couplers in which the color-forming dye has a suitable degree of diffusibility, colorless couplers, DIR couplers which release development inhibitors following the coupling reaction, and polymerized couplers.
It is advantageous to use gelatin as a binder or protective coloid which can be used in the emulsion layers and intermediate layers of the photosensitive materials of this invention, but it is also possible to use other hydrophilic colloids.
Anti color-fogging agents and anti color-mixing agents can be used in the photosensitive materials of this invention.
Representative examples of these are described in JP-A-62-215272, pages 185 - 193.
Color-formation intensifiers can be used to improve the color-forming properties of the couplers of this invention. Representative examples of these compounds include those described in JP-A-62-215272, pages 121 - 125.
Dyes for preventing irradiation and halation, ultraviolet absorbers, plasticizers, fluorescent brighteners, matting agents, aerial antifoggants, auxiliary coating agents, film hardeners, antistatic agents, slip enhancers and the like can be added to the photosensitive materials of the invention. Representative examples of these additives are described in Research Disclosure Journal, No. 17643 VIII - Xill (December 1978), pp. 25 - 27 and ibid. 18716 (November 1979), pp. 647 -651.
This invention can be applied to multi-layers multi-color photographic materials consisting of emulsions having at least 2 different spectral sensitivities on a support. Multi-layer natural color photographic materials normally have at least one red-sensitive emulsion. layer, green-sensitive emulsion layer and blue-sensitive emulsion layer respectively. The order of these layers can be chosen arbitrarily as required. The order of the preferred layer sequence is, from the support, red-sensitive, green-sensitive, blue-sensitive or green-sensitive. red-sensitive, blue-sensitive. Furthermore, each of the emulsion layers mentioned above may consist of two or more emulsion layers with differing speeds, or a non-photosensitive layer may be present between two or more emulsion layers which have the same color sensitivity. Normally, a cyan-forming coupler is included in the red-sensitive emulsion layer, a magenta-forming coupler in the green-sensitive emulsion layer and a yellow-forming coupler in the blue-sensitive emulsion layer, but on occasion different combinations can be used.
The photosensitive materials according to this invention are preferably provided with a protective layer, intermediate layers, filter layers antihalation layers, backing layers, white reflective layers and other such auxiliary layers in addition to the silver halide emulsion layers, as may be appropriate.
With the photographic materials of this invention, the photographic emulsion layers and other layers are coated onto supports as described in Research Disclosure Journal, No. 17643, section V VII (December 1978) p. 28 and as described in European Patent 0,102,253 and JP-A-61-97655. Furthermore, it is possible to use the coating methods described in Research Disclosure Journal, No. 17643, section X V, pp. 28 - 29.
This invention can be applied to various color photosensitive materials.
For example, it is possible to use the present invention color reversal films for slide or televisual use, color reversal papers and instant color films as typical examples. Furthermore, it can also be applied to full color photocopiers and color hard copies for preserving CRT images. This invention can also be applied to black-and-white photosensitive materials which make use of 3-color coupler mixing as described, for example, in Research Disclosure Journal, No. 17123 (July 1978).
Moreover, this invention can also be used in black-and-white photographic materials.
The black-and-white (B/W) photographic materials in which this invention can be used include the B/W direct positive photographic materials described in JP-A-59-208540 and JP-A-60-260039 (for example X-ray materials, duplicating materials, micro materials, photographic materials and printing materials).
The photographic materials of the invention contains a color image forming coupler and is preferably developed with color developers. The color developers are preferably surface developing solutions which contain an aromatic primary amine type color developing agent. Furthermore, the photographic materials of the invention is preferably treated in the presence of at least one of the compounds represented by formulae [N-1] and [N-ll]. Aminophenol-based compounds are useful as these color developers, but p-phenylenediamine-based compounds are preferred, and representative examples of these include 3-methyl-4-amino-N,N-dyethylaniline, 3-methyl-4-amino-N-ethyl-N-β-hydroxyethylaniline, 3-methyl-4-amino-N-ethyl-N-j-methanesulfonamidoethylaniliene and 3-methyl-4-amino-N-ethyl-M-β-methoxyethylaniline and the sulfuric acid salts, hydrochloric acid salts_' or p-toluenesulfonic acid salts thereof. Two or more of these compounds may be used conjointly in accordance with the intended purpose.
The pH of these color developers is 9 - 11.5 and preferably 9.5 - 11.5.
After color development, the photographic emulsion layers are normally bleached. The bleaching may be carried out simultaneously with the fixing (bleach-fixing) or it may be carried out separately. Moreover, a processing method involving bleaching followed by bleach-fixing may be carried out to provide for increased rapidity in the processing. Furthermore, processing in a bleach-fixing bath in which two tanks are linked, fixing prior to the bleach-fixing or fixing after bleach-fixing may be carried out arbitrarily as is appropriate.
The silver halide color photographic materials of this invention generally underg6 washing and/or stabilization stages after a desilvering process. The amount of washing water in the washing stage can be set over a wide range in accordance with various conditions such as the characteristics of the photosensitive material (for example the couplers and other such colorants used), its application and the washing water temperature, the number of washing tanks (number of stages), the direction of flow and the replenishment method (for example direct current). Of these, the relationship between the number of washing tanks and the amount of water in a multistage countercurrent system can be determined by the method described in the Journal of the Society of Motion Picture and Television Engineers, Vol. 64, p. 248 - 253 (May 1955).
Color developing agents may be incorporated into the silver halide color photosensitive materials of this invention in order to simplify and speed-up processing. It is preferable to use precursors of the color developing agent for the incorporation:

Various known developing agents can be used for developing black-and-white photosensitive materials of this invention. Thus, it is possible to use, either singly or in combination: polyhydroxybenzenes such as hydroquinone, 2-chlorohydroquinone, 2-methylhydroquinone, catechol and pyrogallol; aminophenols such as p-aminophenol, N-methyl-p-aminophenol and 2,4-diaminophenol; 3-pyrazolidones such as 1-phenyl-3-pyrazolidone, 1-phenyl-4,4'-dimethyl-3-pyrazolidone, 1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidone, 5,5-dimethyl-1-phenyl-3-pyrazolidone and the like; and ascorbic acid and its analogues. In addition, the developing solutions described in JP-A-58-55928 can be used.

Detailed and specific examples of the developing agents, preservatives, buffers and developing methods for black-and-white photosensitive materials and the methods for using these are described, for example, in Research Disclosure Journal, No. 17643 (December 1978), sections XIX - XXI.
The invention is discussed in detail below using examples but it is not limited by these.

EXAMPLE 1

Preparation of Emulsion A-1 (this invention):

An octahedral monodisperse silver bromide emulsion with an average grain diameter of approximately 0.40 µm was obtained by simultaneously adding aqueous solutions of potassium bromide and silver nitrate to an aqueous gelatin solution, to which 0.3 g of 3,4-dimethyl-1,3-thiazoline-2-thione had been added for every 1 mole of Ag, while stirring vigorously at 75 C for approximately 20 minutes.
The core grain emulsion which was obtained in this way was desalted by a common method and then an aqueous potassium bromide solution was added and the bromide ion concentration adjusted to 4.0 x 10^-2 mole/t. After this, chemical sensitization was carried out by adding to the grains 6 mg of sodium thiosulfate and 7 mg of chloroauric acid (tetrahydrate) for every 1 mole of silver and heating at 75^. C for 80 minutes. The silver bromide grains so obtained were treated as the core and were again grown under the same percipitation conditions as in the first stage to finally obtain an octahedral monodisperse core/shell silver bromide emulsion with an average grain size of 0.7 u.m. The grain size variation coefficient was approximately 10%.
This emulsion was desalted by a common method and then chemical sensitization was carried out by adding 1.5 mg of sodium thiosulfate and 1.5 mg of chloroauric acid (tetrahydrate) for every 1 mole of silver and heating at 60 C for 60 minutes to obtain the internal latent image silver halide Emulsion A-1.

Preparation of Emulsion A-2 (this invention):

This was prepared in the same way as Emulsion A-1 except that the bromide ion concentration during the chemical sensitization of the core in Emulsion A-2 was adjusted to 3.3 x 10-² mole/t.

Preparation of emulsion A-3 (this invention):

This was prepared in the same way as Emulsion A-1 except that the bromide ion concentration during the chemical sensitization of the core in Emulsion A-3 was adjusted to 2.1 x 10-² Mole/ℓ.

Preparation of Emulsion A-4 (comparative example):

This was prepared in the same way as Emulsion A-1 except that the bromide ion concentration during the chemical sensitization of the core in Emulsion A-4 was adjusted to 1.5 x 10-² molelt.
Multi-layer color photosensitive material samples 1 -4, with the layer compositions shown below, were prepared using the emulsions described above on paper supports which had been laminated on both sides with polyethylene.

Layer Structures

The compositions of the various layers are given below. The figures represent coated amounts per m² in grams. For silver halide emulsions and colloidal silver they represent the coated amount calculated as silver in grams, while for spectrally sensitizing dyes they represent the amount added per mole of silver halide in moles.

SUPPORT

Polyethylene-laminated paper (containing a blue dye (ultramarine) and a white pigment (Ti0₂) in the polyethylene on the side of layer E1)

Layer E6:

The same as layer E4

Layer B2:

The same as layer E9
In addition to the above constituents, the gelatin hardener ExGK-1 and surfactants were added to each layer.
Compounds used in the preparation of the samples

(ExCC-1) Cyan Coupler

(ExCC-2) Cyan Coupler

(ExMC-1) Magenta Coupler

(ExYC-1) Yellow Coupler

(ExSS-1) Spectrally Sensitizing Dye

(ExSS-2) Spectrally Sensitizing Dye

(ExSS-3) Spectrally Sensitizing Dye

(ExSS-4) Spectrally Sensitizing Dye

(ExS-1) Solvent

(ExS-2) Solvent

(ExS-3) Solvent

a 1:1 mixture (volume ratio) of
and
(ExS-4) Solvent
(ExUV-1) Ultraviolet Absorber a 5 : 8 : 9 mixture (weight ratio) of (1) : (2) : (3)

(ExUV-2) Ultraviolet Absorber a 2 : 9 : 8 mixture (weight ratio) of (1) : (2) : (3) mentioned above

(ExSA-1) Color Image Stabilizer

(ExKB-1) Anti Color-Mixing Agent

(ExGC-1) Development Regulator

(ExA-1) Stabilizer 4-Hydroxy-5,6-trimethylene-1,3,3a,7-tetraazaindene (ExZS-1) Nucleation Accelerator 2-(3-Dimethylaminopropylthio)-5-mercapto-1,3,4-thiadiazole hydrochloride (ExZK-1) Nucleating Agent 6-Ethoxythiocarbonylamino-2-methyl-1-propargylquinolinium trifluoromethanesulfonate (ExGK-1) Gelatin Hardener Sodium 1-oxy-3,5-dichloro-S-triazine
The color photosensitive materials prepared in this way were subjected to wedge exposures (1/10 sec., 100 CMS) after which the following processing stages were carried out and color image densities were measured after a color development time of 135 sec. and 155 sec.
A so-called countercurrent replenishment system was adopted for the replenishment system for the washing water whereby the supply was made to the washing bath (2), and the overflow solution from the washing bath (2) was lead into the washing bath (1). At this time the amount of bleach-fixing solution carried over by the photosensitive material from the bleach-fixing bath into the washing bath (1) was 35 ml/m² and the amount of washing water replenishment was 9.1 times the amount of bleach-fixing solution carried over.
The compositions of the various processing solutions were as follows:

Washing water

Both parent solution and replenishment solution

Mains water was treated to attain calcium and magnesium ion concentrations of 3 mg/t or less by passing it through a mixed bed column charged with an H-type strongly acidic cation exchange resin (Amberlite IR-120B made by the Rhome & Haas Co.) and an OH-type anion exchange resin (Amberlite IR-400 from the same company). Subsequently, 20 mg/mt of sodium isocyanurate dichloride and 1.5 g/ℓ of sodium sulfate were added. The pH of this liquid was within the range 6.5 - 7.5.
Similar results were also obtained for magenta and cyan.
As can be seen from Table 1, the emulsions of this invention all had a smaller toe-sensitivity variation due to development time than did the comparative example.

EXAMPLE 2

Samples 11-1 to 11-3 which were prepared in exactly the same way as Sample 1-1 in Example 1, except that the nucleating agents shown in Table 2 were used.
Table 2 shows the results obtained from exposing and processing these samples in the same way as in Example 1. Furthermore, the results after adjusting the pH of the color developing solution to 12.0 using potassium hydroxide are also given in Table 2.
Even at a pH of 10.5 or 12.0, Dmax's which were high to the same degree were obtained when using compounds represented by formulae (N-I) and (N-II) as nucleating agents (N-I-16 and N-II-10), but the ageing stability of the color developing solution was poor at pH 12.0 and it was unable to withstand actual use.
A high Dmax was obtained at pH 12.0 when using compounds represented by (Z-1) as the nucleating agent, but the ageing stability of the color developing solution was poor while only a low Dmax was obtained at pH 10.5 which is not desirable.
With the direct positive photographic materials of this invention it is possible to form, both rapidly and stably, direct positive images with high maximum image densities and low minimum image densities for which there is little gradation variation in highlighted portions even when the developing time is altered during processing with a low pH color developer.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. A direct positive photographic material comprising, a support and at least one photosensitive layer positioned on said support and comprising a non-prefogged internal latent image silver halide emulsion which comprises silver bromide and has a core-shell structure of at least two layers, wherein the core has been chemically sensitized under conditions so that the bromide ion concentration is greater than 2.0 x 10^-2 mole/ℓ.

2. The direct positive photographic material of claim 1, wherein the bromide ion concentration is 3.1 x 10-² mole/ℓ or more.

3. The direct positive photographic material of claim 1, wherein the bromide ion concentration is 3.8 x 10-² mole/ or more.

4. The direct positive photographic material of claim 1, wherein the sensitizing conditions include a temperature in the range of 55 to 100° C.

5. The direct positive photographic material of claim 1, wherein the more is chemically sensitized by sulfur or selenium sensitization, reduction sensitization, and precious metal sensitization, either singly or in combination.

6. The direct positive photographic material of claim 1, wherein the photosensitive material contains nucleating agent represented by formula [N-I] or [N-II]

wherein Z represents a group of non-metallic atoms, which may be substituted, to form a 5- or 6-membered heterocyclic ring; R' is an aliphatic group, which may be substituted; and R² is a hydrogen atom, aliphatic group or aromatic group, those of which may be substituted and may also bind with the hetroacyclic ring completed by Z to form a ring; with proviso that at least one of the R', R² and Z either contains an alkenyl group, acyl group, hydrazine group or hydrazone group, or a 6-membered ring formed by R¹ and R² to create a dihydrophridinium skeleton, and at least one of the substituent groups for R', R² and Z may possess a group promoting adsorption onto silver halides; Y is a counterion fo the purpose of charge balance; and n is 0 or 1;

wherein R²¹ represents an aliphatic group, aromatic group or heterocyclic group, those of which may be substituted; R²² represents a hydrogen atom, or alkyl, aralkyl, aryl, alkoxy, aryloxy or amino group, those of which may be substituted; G represents a carbonyl, sulfonyl, sulfoxy, phosphoryl or iminomethylene group (HN=C), those of which may be substituted; R²³ and R²⁴ either both represent hydrogen atoms or one of them represents a hydrogen atom and the other substituted or unsubstituted alkyl-sulfonyl, arylsulfonyl or acy group; and a hydrazone structure

may be formed in which G, R²³, R²⁴ and hydrazine nitrogen are contained.

7. The direct positive photographic material of claim 1, wherein the silver halide emulsion contains grains whose average grain size is in the range of 2.0 to 0.1 microns.

8. The direct positive photographic material of claim 1, wherein the silver halide emulsion contains grains whose average grain size is in the range of 1.2 to 0.2 microns.

9. A process for forming a direct positive color image which comprises imagewise exposing a photographic material comprising a support, and a non-prefogged internal latent image silver halide emulsion and color image forming coupler on said support, followed by developing in a surface color developer, bleaching and fixing thereof, wherein said internal image silver halide emulsion comprises silver bromide, and has a core/shell structure of at least two layers, in which the core has been chemically sensitized under conditions so that the bromide ion concentration is greater than 2.0 x 10^-2 mole/t, and said developer has a pH of not higher than 11.5.

10. The process for forming a direct positive color image of claim 9, wherein the bromide ion concentration is 3.1 x 10^-2 mole/ℓ or more.

11. The process for forming a direct positive color image of claim 9, wherein the bromide in concentration is 3.8 x 10-² mole/ℓ or more.

12. The process for forming a direct positive color image of claim 9, wherein the sensitizing conditions include a temperature in the range of 55 to 100° C.

13. The process for forming a direct positive color image of claim 9, wherein the core is chemically sensitized by sulfur or selenium sensitization, reduction sensitization, and precious metal sensitization, either singly or in combination.

14. The process for forming a direct positive color image of claim 9, wherein the photosensitive material contains nucleating agent represented by formula [N-I] or [N-II]

wherein Z represents a group of non-metallic atoms, which may be substituted, to form a 5- or 6-membered heterocyclic ring; R¹ is an aliphatic group, which may be substituted; and R² is a hydrogen atom, aliphatic group or aromatic group, those of which may be substituted and may also bind with the hetroacyclic ring completed by Z to form a ring, with proviso that at least one of the R¹, R² and Z either contains an alkenyl group, acyl group, hydrazine group or hydrazone group, or a 6-membered ring formed by R¹ and R² to create a dihydrophridinium skeleton, and at least one of the substituent groups for R¹, R² and Z may possess a group promoting adsorption onto silver halides; Y is a counterion fo the purpose of charge balance; and n is 0 or 1;

wherein R²¹ represents an aliphatic group, aromatic group or heterocyclic group, those of which be substituted; R²² represents a hydrogen atom, or alkyl, aralkyl, aryl, alkoxy, aryloxy or amino group those of which may be substituted; G represents a carbonyl, sulfonyl, sulfoxy, phosphoryl or iminomethylene group

those of which may be substituted; R²³ and R²⁴ either both represent hydrogen atoms or one of them represents a hydrogen atom and the other substituted or unsubstituted alkyl-sulfonyl, arylsulfonyl or acyl group; and a hydrazone structure

may be formed in which G, R²³, R²⁴ and hydrazine nitrogen are contained.

15. The process for forming a direct positive color image of claim 9, wherein the silver halide emulsion contains grains whose average grain size is in the range of 2.0 to 0.1 microns.

16. The process for forming a direct positive color image of claim 9, wherein the silver halide emulsion contains grains whose average grain size is in the range of 1.2 to 0.2 microns.