EP1298486A1

EP1298486A1 - Internal latent image-type direct positive silver halide emulsion and color diffusion transfer light-sensitive material using the same

Info

Publication number: EP1298486A1
Application number: EP02021808A
Authority: EP
Inventors: Munehisa Fujita
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 2001-09-28
Filing date: 2002-09-26
Publication date: 2003-04-02
Also published as: JP2003107619A

Abstract

An internal latent image-type direct positive silver halide emulsion comprising a core/shell structure silver halide which is composed of a chemically sensitized core and a chemically sensitized shell and which is not prefogged, and a compound of formula (I): Formula (I)
(X)_k-(L)_m-(A-B)_n wherein X represents a light-absorbing group or a silver halide-adsorbing group having at least one atom selected from the group consisting of N, S, P, Se and Te; L represents a divalent linking group having at least one atom selected from the group consisting of C, N, S and O; A represents an electron-donating group; B represents a leaving group or a hydrogen atom, which leaves or undergoes deprotonation after being oxidized, to form a radical A^•; k and m each independently are an integer of 0 to 3; and n is 1 or 2. A color diffusion transfer light-sensitive material containing the emulsion.

Description

FIELD OF THE INVENTION

The present invention relates to an internal latent image-type direct positive silver halide emulsion, and a color diffusion transfer light-sensitive material using the same.

BACKGROUND OF THE INVENTION

A photographic method using a silver halide, which is superior in sensitivity and gradation properties to other photographic methods, such as an electronic photographic method and a diazo photographic method, has been used in a wide range of applications. Among these photographic methods using a silver halide is one in which a direct positive image is formed. According to this method, for example, as disclosed in U.S. Patent No. 3,761,276 and JP-B-60-55821 ("JP-B" means examined Japanese patent publication), a positive image is obtained when an internal latent image-type direct positive silver halide emulsion is subjected to development using a surface developing solution (i.e., a developing solution that allows the latent image-forming portions inside the silver halide grains to remain substantially undeveloped) by uniform exposure to light or by use of a nucleating agent. Such a direct positive silver halide emulsion is superior, in that a positive image can be obtained by a single processing, compared with use of a negative emulsion. Generally, an internal latent image-type direct positive silver halide emulsion is prepared according to the following steps. That is, a soluble silver salt and a soluble halide are mixed together in an aqueous gelatin solution, to form silver halide grains (core grains), and the core grains are chemically sensitized. After that, silver halide deposition is carried out, to form shells. Then, a desalting treatment is carried out, and, if necessary, a chemical sensitization is carried out. For example, JP-B-52-34213 (U.S. Patent No. 3,761,276) describes an internal latent image-type emulsion that is useful as a direct positive emulsion. This emulsion is characterized in that a dopant is incorporated in the interior of silver halide grains, and the grain surface is chemically sensitized. That is also taught in U.S. Patent No. 3,317,322, issued to Porter et al. However, even in the internal latent image-type direct positive silver halide emulsions that are prepared in the ways described above, the decrease of sensitivity as illumination intensity is reduced (low intensity reciprocity law failure) is still greater relative to negative emulsions. Therefore, these conventional internal latent image-type direct positive silver halide emulsions still leave room for improvement.
In industrial fields, internal latent image-type direct positive silver halide emulsions are often used in color diffusion transfer light-sensitive materials. Among the color diffusion transfer light-sensitive materials, instant photographic light-sensitive materials are used in various applications and are important as recording materials. In the application range of instant photographic light-sensitive materials, important uses include taking photographs for certificates and test photographing for reversal films. In these uses, since photographs are taken inside a room using tungsten light, in many cases, long exposure time at a low illumination intensity is inevitable. Therefore, under these circumstances, a need from users exists for a color diffusion transfer light-sensitive material with improved low intensity reciprocity law failure.
It is generally known that doping with an iridium compound having mainly a halogen as a ligand is effective for improving low intensity reciprocity law failure of a silver halide emulsion. For example, JP-B-43-4935 discloses that the gradation fluctuation in a wide range of exposure times is reduced by adding an iridium compound, at the time of preparing silver halide grains. Also, U.S. Patent No. 4,997,751 describes that reciprocity law failure is improved by adding iridium (compound) from the silver halide grain surface. However, the doping an internal latent image-type direct positive silver halide emulsion with an iridium compound is not put to practical use because of the following problems. First, the maximum density is reduced, and although reciprocity law failure is improved, S/N becomes inferior. Second, although sensitivity at a low illumination intensity is increased by doping with an iridium compound, the sensitivity at a high illumination intensity is lowered as the doping amount of the iridium compound increases.
JP-A-2-269337 ("JP-A" means unexamined published Japanese patent application) discloses that an internal latent image-type direct positive silver halide emulsion, which produces soft contrast by exposure to a high illumination intensity and produces high contrast by exposure to a low illumination intensity, is obtained by adding a heavy metal cation, such as Ir, Pb, Rh, or the like. This patent publication also refers to the possibility of changing the reciprocity characteristics of an emulsion by doping a polyvalent metal ion into the grain. However, although this patent publication describes to contrast (gradation), it does not refer to S/N and does not provide a technique that can be put to practical use, because the maximum density is reduced by the doping of the polyvalent metal ion into the grain.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an internal latent image-type direct positive silver halide emulsion that has a high S/N ratio and avoids the problem of a reduction in sensitivity when exposed to a high illumination intensity, and whose low intensity reciprocity law failure is improved. Another object of the present invention is to provide a color diffusion transfer light-sensitive material using the emulsion.
Other and further objects, features and advantages of the invention will appear more fully from the following description.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors found that the above-noted problems can be solved by the following means.
(1) An internal latent image-type direct positive silver halide emulsion comprising a core/shell structure silver halide which is composed of a chemically sensitized core and a chemically sensitized shell and which is not pre-fogged, and a compound represented by the following formula (I): Formula (I) (X)k-(L)m-(A-B)n wherein X represents a light-absorbing group or a silver halide-adsorbing group having at least one atom selected from the group consisting of N, S, P, Se, and Te; L represents a divalent linking group having at least one atom selected from the group consisting of C, N, S, and O; A represents an electron-donating group; B represents a leaving group or a hydrogen atom, which leaves or undergoes deprotonation after being oxidized, to form a radical A*; k and m each independently represent an integer of 0 to 3; and n represents 1 or 2.
(2) The internal latent image-type direct positive silver halide emulsion according to the above item (1), wherein the silver halide emulsion contains tabular silver halide grains having aspect ratio (equivalent-circle diameter/thickness of each individual silver halide grain) of 5 or more but not more than 100, in an amount such that the projected area of the tabular silver halide grains occupies 50% or more of the projected area of the total silver halide grains, and the average grain diameter of the tabular silver halide grains is 0.3 µm or more.
(3) The internal latent image-type direct positive silver halide emulsion according to the above item (1) or (2), wherein the silver halide at the time of completion of grain formation before a desalting step is silver bromide.
(4) A color diffusion transfer light-sensitive material, having at least one unit of light-sensitive silver halide emulsion layers, on a support, wherein at least one of the emulsion layers contains the internal latent image-type direct positive silver halide emulsion described in any one of the above items (1) to (3).
The present invention is explained below in detail.
First, the compound represented by the formula (I) is explained. Formula (I) (X)k-(L)m-(A-B)n wherein X represents a light-absorbing group or a silver halide-adsorbing group having at least one atom selected from the group consisting of N, S, P, Se, and Te; L represents a divalent linking group having at least one atom selected from the group consisting of C, N, S, and O; A represents an electron-donating group; B represents a leaving group or a hydrogen atom, which leaves or undergoes deprotonation after being oxidized, to form a radical A*; k and m each independently represent an integer of 0 to 3; and n represents 1 or 2.
The compound that is used in the present invention is explained below in detail. In the formula (I), the silver halide-adsorbing group represented by X has at least one selected from the group consisting of N, S, P, Se, and Te and is preferably of a silver ion ligand structure. In the case where k is 2 or more, the plural X's may be the same or different. Examples of the silver ion ligand structure include the following. Formula (X-1) -G1-Z1-R1
In the formula (X-1), G₁ is a divalent linking group which represents a divalent heterocyclic group or a divalent group formed by combining a divalent heterocyclic group with any one of substituted or unsubstituted alkylene, alkenylene, alkynylene, arylene, and SO₂ groups. Z₁ represents a S, Se, or Te atom. R₁ represents a hydrogen atom or an ion, i.e., sodium ion, potassium ion, lithium ion, or ammonium ion, which is necessary as a counter ion in the case where Z₁ becomes dissociated.
Formulas (X-2a) and (X-2b) each represent a ring structure. Form of the ring is a 5- to 7-membered heterocyclic saturated ring, heterocyclic unsaturated ring, or unsaturated carbocycle. Z_a represents an O, N, S, Se, or Te atom. n₁ represents an integer of 0 to 3. R₂ represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, or an aryl group. In the case where n₁ is 2 or greater, the plural Z_a's may be the same or different. Formula (X-3) -R3-(Z)2n2-R4
In the formula (X-3), Z₂ represents a S, Se, or Te atom; n₂ represents an integer of 1 to 3. R₃ is a divalent linking group which represents an alkylene group, an alkenylene group, an alkynylene group, an arylene group, a divalent heterocyclic group, or a divalent group formed by combining a divalent heterocyclic group with any one of alkylene, alkenylene, alkynylene, arylene, and SO₂ groups. R₄ represents an alkyl group, an aryl group, or a heterocyclic group. In the case where n₂ is 2 or greater, the plural Z₂'s may be the same or different.
In the formula (X-4), R₅ and R₆ each independently represent an alkyl group, an alkenyl group, an aryl group, or a heterocyclic group.
In the formula (X-5a) and (X-5b), Z₃ represents a S, Se, or Te atom. E₁ represents a hydrogen atom, NH₂, NHR₁₀, N(R₁₀)₂, NHN(R₁₀)₂, OR₁₀, or SR₁₀. E₂ is a divalent linking group which represents NH, NR₁₀, NHNR₁₀, O or S. R₇, R₈, and R₉ each independently represent a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or a heterocyclic group. R₈ and R₉ may bond together to form a ring. R₁₀ represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or a heterocyclic group.
In the formulas (X-6a) and (X-6b), R₁₁ is a divalent linking group which represents an alkylene group, an alkenylene group, an alkynylene group, an arylene group, or a divalent heterocyclic group. G₂ and J each independently represent COOR₁₂, SO₂R₁₂, COR₁₂, SOR₁₂, CN, CHO, or NO₂. R₁₂ represents an alkyl group, an alkenyl group, or an aryl group.
The formula (X-1) is explained in detail below. Examples of the linking group represented by G₁ include a substituted or unsubstituted, straight-chain or branched alkylene group having 1 to 20 carbon atoms (e.g., a methylene group, an ethylene group, a trimethylene group, a propylene group, a tetramethylene group, a hexamethylene group, a 3-oxapentylene group, a 2-hydroxytrimethylene group), a substituted or unsubstituted cycloalkylene group having 3 to 18 carbon atoms (e.g., a cyclopropylene group, a cyclopentylene group, a cyclohexylene group), a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms (e.g., an ethene group, a 2-butenylene group), an alkynylene group having 2 to 10 carbon atoms (e.g., an ethyne group), and a substituted or unsubstituted arylene group having 6 to 20 carbon atoms (e.g., an unsubstituted p-phenylene group, an unsubstituted 2,5-naphthylene group).
In the formula (X-1), examples of the SO₂ group represented by G₁ include a -SO₂- group, as well as a -SO₂- group which is combined with a substituted or unsubstituted, straight-chain or branched alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted, cyclic alkylene group having 3 to 6 carbon atoms, or an alkenylene group having 2 to 10 carbon atoms.
Further, examples of the divalent linking group represented by G₁ include a divalent heterocyclic group; a divalent group in which a divalent heterocyclic group is combined with any one of an alkylene group, an alkenylene group, an alkynylene group, an arylene group, and an SO₂ group; and the above divalent groups whose heterocyclic portion is formed by benzo- or naphtho-condensation (e.g., 2,3-tetrazole-diyl, 1,3-triazole-diyl, 1,2-imidazole-diyl, 3,5-oxadiazole-diyl, 2,4-thiazole-diyl, 1,5-benzoimidazole-diyl, 2,5-benzothiazole-diyl, 2,5-benzoxazole-diyl, 2,5-pyrimidine-diyl, 3-phenyl-2,5-tetrazole-diyl, 2,5-pyridine-diyl, 2,4-furan-diyl, 1,3-piperidine-diyl, 2,4-morpholine-diyl).
In the formula (X-1), G₁ may have a substituent(s) in so far as possible. The substituent is indicated below and is herein referred to as a substituent Y.
Examples of the substituent include halogen atoms (e.g., a fluorine atom, a chlorine atom, a bromine atom), an alkyl group (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, a t-butyl group), an alkenyl group (e.g., an allyl group, a 2-butenyl group), an alkynyl group (e.g., a propargyl group), an aralkyl group (e.g., a benzyl group), an aryl group (e.g., a phenyl group, a naphthyl group, a 4-methylphenyl group), a heterocyclic group (e.g., a pyridyl group, a furyl group, an imidazolyl group, a piperidinyl group, a morpholyl group), an alkoxy group (e.g., a methoxy group, an ethoxy group, a butoxy group, 2-ethylhexyloxy group, an ethoxyethoxy group, a methoxyethoxy group), an aryloxy group (e.g., a phenoxy group, a 2-naphthyloxy group), an amino group (e.g., an unsubstituted amino group, a dimethylamino group, a diethylamino group, a dipropylamino group, a dibutylamino group, an ethylamino group, an aniline group), an acylamino group (e.g., an acetylamino group, a benzoylamino group), a ureido group (e.g., an unsubstituted ureido group, an N-methylureido group), a urethane group (e.g., a methoxycarbonylamino group, a phenoxycarbonylamino group), a sulfonylamino group (e.g., a methylsulfonylamino group, a phenylsulfonylamino group), a sulfamoyl group (e.g., an unsubstituted sulfamoyl group, an N,N-dimethylsulfamoyl group, an N-phenylsulfamoyl group), a carbamoyl group (e.g., an unsubstituted carbamoyl group, an N,N-diethylcarbamoyl group, an N-phenylcarbamoyl group), a sulfonyl group (e.g., a mesyl group, a tosyl group), a sulfinyl group (e.g., a methylsulfinyl group, a phenylsulfinyl group), an alkyloxycarbonyl group (e.g., a methoxycarbonyl group, an ethoxycarbonyl group), an aryloxycarbonyl group (e.g., phenoxycarbonyl group), an acyl group (e.g., an acetyl group, a benzoyl group, a formyl group, a pivaloyl group), an acyloxy group (e.g., an acetoxy group, a benzoyloxy group), a phosphoric acid amido group (e.g., an N,N-diethyl-phosphoric acid amido group), a cyano group, a sulfo group, a thiosulfonic acid group, a sulfinic acid group, a carboxy group, a hydroxy group, a phosphono group, a nitro group, an ammonio group, a phosphonio group, a hydrazino group, and a thiazolino group. In the case where two or more substituents are present, the substituents may be the same or different. The substituent may further have a substituent.
Preferred examples of the formula (X-1) are given below.
In a preferred example of the formula (X-1), preferable examples of G₁ include a substituted or unsubstituted arylene group having 6 to 10 carbon atoms, a heterocyclic group forming a 5- to 7-membered ring which is combined with a substituted or unsubstituted alkylene group or arylene group or which is benzo- or naphtho-condensed; preferable examples of Z₁ include S and Se; and preferable examples of R₁ include a hydrogen atom, a sodium ion, and a potassium ion.
More preferably G₁ is a heterocyclic group forming a 5- to 6-membered ring which is combined with a substituted or unsubstituted arylene group having 6 to 8 carbon atoms or which is benzo-condensed; and most preferably G₁ is a heterocyclic group forming a 5- to 6-membered ring which is combined with an arylene group or which is benzo-condensed. Z₁ is more preferably S; and R₁ is more preferably a hydrogen atom or a sodium ion.
The formulas (X-2a) and (X-2b) is explained in detail below.
In these formulas, examples of an alkyl group, an alkenyl group, and an alkynyl group represented by R₂ include a straight-chain or branched, and substituted or unsubstituted alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a t-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a t-octyl group, a 2-ethylhexyl group, a 2-hydroxyethyl group, a 1-hydroxyethyl group, a diethylaminoethyl group, an n-butoxypropyl group, a methoxymethyl group), a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms (e.g., a cyclopropyl group, a cyclopentyl group, a cyclohexyl group), an alkenyl group having 2 to 10 carbon atoms (e.g., an allyl group, a 2-butenyl group, a 3-pentenyl group), an alkynyl group having 2 to 10 carbon atoms (e.g., a propargyl group, a 3-pentynyl group), an aralkyl group having 6 to 12 carbon atoms (e.g., a benzyl group). Examples of an aryl group include a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., an unsubstituted phenyl group, a 4-methylphenyl group).
The above-described R₂ may further have a substituent Y or the like.
Preferred examples of the formulas (X-2a) and (X-2b) are given below.
In the formulas, preferably R₂ is a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; Z_a is O, N, or S; and n₁ is an integer of 1 to 3.
More preferably R₂ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; Z_a is N or S; and n₁ is 2 or 3.
Next, the formula (X-3) will be explained in more detail below.
In the formula (X-3), examples of a linking group represented by R₃ include a straight-chain or branched, and substituted or unsubstituted alkylene group having 1 to 20 carbon atoms (e.g., a methylene group, an ethylene group, a trimethylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, a 3-oxapentylene group, a 2-hydroxytrimethylene group), a substituted or unsubstituted cycloalkylene group having 3 to 18 carbon atoms (e.g., a cyclepropylene group, a cyclepentynylene group, a cyclehexylene group), a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms (e.g., an ethene group, a 2-butenylene group), an alkynylene group having 2 to 10 carbon atoms (e.g., an ethyne group), a substituted or unsubstituted arylene group having 6 to 20 carbon atoms (e.g., an unsubstituted p-phenylene, an unsubstituted 2,5-naphthylene group); and examples of a heterocyclic group include a substituted or unsubstituted heterocyclic group, and a heterocyclic group combined with an alkylene group, an alkenylene group, an arylene group, or another heterocyclic group (e.g., 2,5-pyridine-diyl, 3-phenyl-2,5-pyridine-diyl, 1,3-piperidine-diyl, 2,4-morpholine-diyl).
In the formula (X-3), examples of an alkyl group represented by R₄ include a straight-chain or branched, and substituted or unsubstituted alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a t-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a t-octyl group, a 2-ethylhexyl group, a 2-hydroxyethyl group, 1-hydroxyethyl group, a diethylaminoethyl group, a dibutylaminoethyl group, an n-butoxymethyl group, a methoxyethyl group), a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms (e.g., a cyclopropyl group, a cyclopentyl group, a cyclohexyl group); and examples of an aryl group represented by R₄ include a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., an unsubstituted phenyl group, a 2-methylphenyl group).
Examples of the heterocyclic group represented by R₄ include an unsubstituted heterocyclic group, and a heterocyclic group substituted by an alkyl group, an alkenyl group, an aryl group, or another heterocyclic group (e.g., a pyridyl group, a 3-phenylpyridyl group, a piperidyl group, a morpholyl group).
The above-described R₄ may further have a substituent Y or the like.
Preferred examples of the formula (X-3) are given below.
In the formula, preferably, R₃ is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, or a substituted or unsubstituted arylene group having 6 to 10 carbon atoms; R₄ is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; Z₂ is S or Se; and n₂ is an integer of 1 to 2.
More preferably, R₃ is an alkylene group having 1 to 4 carbon atoms; R₄ is an alkyl group having 1 to 4 carbon atoms; Z₂ is S; and n₂ is 1.
Next, the formula (X-4) is explained in detail below.
In the formula (X-4), examples of an alkyl group and an alkenyl group represented by R₅ and R₆ include a straight-chain or branched, and substituted or unsubstituted alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a t-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a t-octyl group, a 2-ethylhexyl group, a hydroxymethyl group, a 2-hydroxyethyl group, a 1-hydroxyethyl group, a diethylaminoethyl group, a dibutylaminoethyl group, an n-butoxymethyl group, an n-butoxypropyl group, a methoxymethyl group), a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms (e.g., a cyclopropyl group, a cyclopentyl group, a cyclohexyl group), and an alkenyl group having 2 to 10 carbon atoms (e.g., an allyl group, a 2-butenyl group, a 3-pentenyl group). Examples of the aryl group include a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., an unsubstituted phenyl group, a 4-methylphenyl group). Examples of the heterocyclic group include an unsubstituted heterocyclic group, and a heterocyclic group substituted by an alkylene group, an alkenylene group, an arylene group, or another heterocyclic group (e.g., a pyridyl group, a 3-phenylpyridyl group, a furyl group, a piperidyl group, a morpholyl group).
The above-described R₅ and R₆ may further have a substituent Y or the like.
Preferred examples of the formula (X-4) are given below.
In the formula, preferably R₅ and R₆ each independently are a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms.
More preferably R₅ and R₆ each independently are an aryl group having 6 to 8 carbon atoms.
Next, the formulae (X-5a) and (X-5b) are explained in detail. In the formulae (X-5a) and (X5-b), examples of the group represented by E₁ include NH₂, NHCH₃, NHC₂H₅, NHPh, N(CH₃)₂, N(Ph)₂, NHNHC₃H₇, NHNHPh, OC₄H₉, OPh, and SCH₃; and examples of the group represented by E₂ include NH, NCH₃, NC₂H₅, NPh, NHNC₃H₇, and NHNPh (wherein Ph means a phenyl group (the same applies hereinafter)).
In the formulas (X-5a) and (X-5b), examples of an alkyl group and an alkenyl group represented by R₇, R₈ and R₉ include a straight-chain or branched, and substituted or unsubstituted alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a t-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a t-octyl group, a 2-ethylhexyl group, a hydroxymethyl group, a 2-hydroxyethyl group, a 1-hydroxyethyl group, a diethylaminoethyl group, a dibutylaminoethyl group, an n-butoxymethyl group, an n-butoxypropyl group, a methoxymethyl group), a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms (e.g., a cyclopropyl group, a cyclopentyl group, a cyclohexyl group), and an alkenyl group having 2 to 10 carbon atoms (e.g., an allyl group, a 2-butenyl group, a 3-pentenyl group). Examples of an aryl group include a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., an unsubstituted phenyl group, a 4-methylphenyl group); and examples of a heterocyclic group include an unsubstituted heterocyclic group, and a heterocyclic group substituted by an alkylene group, an alkenylene group, an arylene group, or another heterocyclic group (e.g., a pyridyl group, a 3-phenylpyridyl group, a furyl group, a piperidyl group, a morpholyl group).
R₇, R₈, and R₉ may further have a substituent Y or the like.
Preferred examples of the formulae (X-5a) and (X-5b) are given below.
In the formulae (X-5a) and (X-5b), preferably E₁ is an alkyl-substituted or unsubstituted amino group or alkoxy group; E₂ is an alkyl-substituted or unsubstituted amino linking group; R₇, R₈, and R₉ each are a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; and Z₃ is S or Se.
More preferably E₁ is an alkyl-substituted or unsubstituted amino group; E₂ is an alkyl-substituted or unsubstituted amino linking group; R₇, R₈, and R₉ each are a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms; and Z₃ is S.
Next, the formulae (X-6a) and (X-6b) are explained in detail below.
In the formula (X-6b), examples of the groups represented by G₂ and J include COOCH₃, COOC₃H₇, COOC₆H₁₃, COOPh, SO₂CH₃, SO₂C₄H₉, COC₂H₅, COPh, SOCH₃, SOPh, CN, CHO, and NO₂.
In the formula (X-6a), examples of the linking group represented by R₁₁ include a straight-chain or branched, and substituted or unsubstituted alkylene group having 1 to 20 carbon atoms (e.g., a methylene group, an ethylene group, a trimethylene group, a propylene group, a tetramethylene group, a hexamethylene group, a 3-oxapentylene group, a 2-hydroxytrimethlene group), a substituted or unsubstituted cycloalkylene group having 3 to 18 carbon atoms (e.g., a cyclopropylene group, a cyclopentylene group, a cyclohexylene group), a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms (e.g., an ethene group, a 2-butenylene group), an alkynylene group having 2 to 10 carbon atoms (e.g., an ethyne group), and a substituted or unsubstituted arylene group having 6 to 20 carbon atoms (e.g., an unsubstituted p-phenylene, an unsubstituted 2,5-naphthylene).
Further, examples of the divalent linking group represented by R₁₁ include a divalent heterocyclic group, or a divalent group formed by combining a divalent heterocyclic group with any one of an alkylene group, an alkenylene group, an alkynylene group, an arylene group, and a SO₂ groups (e.g., a 2,5-pyridine-diyl group, a 3-phenyl-2,5-pyridine-diyl group, a 2,4-furan-diyl group, a 1,3-piperidine-diyl group, a 2,4-morpholine-diyl group).
In the formulas, R₁₁ may further have a substituent Y or the like.
Preferred examples of the formulae (X-6a) and (X-6b) are given below.
In the formulae (X-6a) and (X-6b), preferably G₂ and J each are a carbonyl or an ester of carboxylic acid having 2 to 6 carbon atoms; and R₁₁ is a substituted or unsubstituted alkylene group having 1 to 6 carbon atoms, or a substituted or unsubstituted arylene group having 6 to 10 carbon atoms.
More preferably G₂ and J each are an ester of carboxylic acid having 2 to 4 carbon atoms; and R₁₁ is a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms or a substituted or unsubstituted arylene group having 6 to 8 carbon atoms.
The order of preference of formulae of the silver halide-adsorbing group represented by X is (X-1)>(X-2a)>(X-2b)>(X-3)>(X-5a)>(X-5b)>(X-4)>(X-6a)>(X-6b).
Next, the light-absorbing group represented by X in the formula (I) is explained in detail below.
Examples of the light-absorbing group represented by X in the formula (I) include the following:
In the formula (X-7), Z₄ represents a group of atoms necessary to form a 5- or 6-membered nitrogen-containing heterocycle; L₂, L₃, L₄, and L₅ each represent a methine group; p₁ represent 0 or 1; n₃ represents an integer of 0 to 3; M₁ represents a counter ion for electric charge balance; m₂ represents a number of 0 to 10 necessary for the neutralization of the charge of the molecule; and an unsaturated carbocycle such as a benzene ring may be condensed with the nitrogen-containing heterocycle formed by using Z₄.
In the formula (X-7), examples of the 5- or 6-membered nitrogen-containing heterocycle represented by Z₄ and other members include a thiazolidine nucleus, a thiazole nucleus, a benzothiazole nucleus, an oxazoline nucleus, an oxazole nucleus, a benzooxazole nucleus, a selenazoline nucleus, a selenazole nucleus, a benzoselenazole nucleus, a 3,3-dialkylindolenine nucleus (e.g., 3,3-dimethylindolenine), an imidazoline nucleus, an imidazole nucleus, a benzoimidazole nucleus, a 2-pyridine nucleus, a 4-pyridine nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a 1-isoquinoline nucleus, a 3-isoquinoline nucleus, an imidazo[4,5-b]quinoxaline nucleus, an oxadiazole nucleus, a thiadiazole nucleus, a tetrazole nucleus, and a pyrimidine nucleus.
The 5- or 6-membered nitrogen-containing heterocycle represented by Z₄ and other members may have the aforementioned substituent Y.
In the formula (X-7), L₂, L₃, L₄, and L₅ each represent an independent methine group. The methine groups represented by L₂, L₃, L₄, and L₅ each may have a substituent. Examples of the substituent include a substituted or unsubstituted alkyl group having 1 to 15 carbon atoms (e.g., a methyl group, an ethyl group, a 2-carboxyethyl group), a substituted or unsubstituted aryl group having 6 to 20 carbon atoms (e.g., a phenyl group, an o-carboxyphenyl group), a substituted or unsubstituted heterocyclic group having 3 to 20 carbon atoms (e.g., an N-diethylbarbituric acid), a halogen atom (e.g., a chlorine atom, a bromine atom, a fluorine atom, an iodine atom), an alkoxy group having 1 to 15 carbon atoms (e.g., a methoxy group, an ethoxy group), an alkylthio group having 1 to 15 carbon atoms (e.g., a methylthio group, an ethylthio group), an arylthio group having 6 to 20 carbon atoms (e.g., a phenylthio group), and an amino group having 0 (zero) to 15 carbon atoms (e.g., an N,N-diphenylamino group, an N-methyl-N-phenylamino group, an N-methylpiperazine group).
The methine group may join with another methine group to form a ring. Alternatively, it may form a ring with other moiety.
In the formula (X-7), M₁ is included in the formula, to show the presence of a cation or anion, when M₁ is necessary for the neutralization of the ionic charge of the light-absorbing group. Typical examples of the cation include hydrogen ion (H⁺); inorganic cations, such as alkali metal ions (e.g., sodium ion, potassium ion, lithium ion); and organic cations, such as ammonium ions (e.g., ammonium ion, tetraalkylammonium ion, pyridinium ion, ethylpyridinium ion). The anion may also be any of an inorganic anion and an organic anion. Examples of the anion include halide ions (e.g., fluoride ion, chloride ion, iodide ion), substituted arylsulfonate ions (e.g., p-toluenesulfonate ion, p-chlorobenzenesulfonate ion), aryldisulfonate ions (e.g., 1,3-benzenedisulfonate ion, 1,5-naphthalenedisulfonate ion, 2,6-naphthalenedisulfonate ion), alkylsulfate ions (e.g., methylsulfate ion), sulfate ion, thiocyanate ion, perchlorate ion, tetrafluoroborate ion, picrate ion, acetate ion, and trifluoromethanesulfonate ion. Further, a light-absorbing group having an ionic polymer or an opposite electric charge may be used.
In the present invention, for example, although a sulfo group is denoted by SO₃ ^- and a carboxyl group is denoted by CO₂ ^-, these groups may be denoted by SO₃H and by CO₂H, respectively, when the counter ion is a hydrogen ion.
In the formula (X-7), m₂ represents a number necessary for balancing the electric charges, and it is 0 when an intramolecular salt is formed.
Preferred examples of the formula (X-7) are given below.
In a preferred example of the formula (X-7), Z₄ is a benzooxazole nucleus, a benzothiazole nucleus, a benzoimidazole nucleus, or a quinoline nucleus; L₂, L₃, L₄, and L₅ each are an unsubstituted methine group; p₁ is 0; and n₃ is 1 or 2.
More preferably, Z₄ is a benzooxazole nucleus or a benzothiazole nucleus; and n₃ is 1. Particularly preferably, Z₄ is a benzothiazole nucleus.
In the formula (I), k is preferably 0 or 1, and more preferably 1.
Specific examples of the X group for use in the present invention are shown below, but the compounds for use in the present invention are not limited to these examples.
Next, the linking group represented by L in the formula (I) is explained in detail below.
Examples of the linking group represented by L in the formula (I) include a substituted or unsubstituted, straight-chain or branched alkylene group having 1 to 20 carbon atoms (e.g., a methylene group, an ethylene group, a trimethylene group, a propylene group, a tetramethylene group, a hexamethylene group, a 3-oxapentylene group, a 2-hydroxytrimethylene group); a substituted or unsubstituted cycloalkylene group having 3 to 18 carbon atoms (e.g., a cyclocpropylene group, a cyclopentylene group, a cyclohexylene group); a substituted or unsubstituted alkenylene group having 2 to 20 carbon atoms (e.g., an ethene group, a 2-butenylene group); an alkynylene group having 2 to 10 carbon atoms (e.g., an ethyne group); a substituted or unsubstituted arylene group having 6 to 20 carbon atoms (e.g., an unsubstituted p-phenylene group, an unsubstituted 2,5-naphthylene group); a heterocyclic linking group (e.g., a 2,6-pyridine-diyl group); a carbonyl group; a thiocarbonyl group, an imido group; a sulfonyl group; a sulfonate group; an ester group; a thioester group; an amido group; an ether group; a thioether group; an amino group; a ureido group; a thioureido group; and a thiosulfonyl group. Further, these linking groups may join together to form a new linking group. In the case where m is 2 or greater, the plural L's may be the same or different.
L may further have the aforementioned substituent Y or the like.
Preferred examples of the linking group L include an unsubstituted alkylene group having 1 to 10 carbon atoms and an alkylene group having 1 to 10 carbon atoms, which is combined with an amino group, an amido group, a thioether group, a ureido group, or a sulfonyl group. More preferred examples of the linking group L include an unsubstituted alkylene group having 1 to 6 carbon atoms and an alkylene group, which is combined with an amino group, an amido group, or a thioether group and which has 1 to 10 carbon atoms.
In the formula (I), m is preferably 0 or 1 and more preferably 1.
Next, the electron-donating group A is explained in detail.
When the moiety A-B undergoes oxidation and fragmentation to generate an electron, a radical A^• is formed. Further, the radical A^• undergoes oxidation to generate an electron. As a result, a high level of sensitization is attained. This reaction process is described below.
Since A is an electron-donating group, it is preferable that a substituent on the aromatic group is chosen such that A is brought into a state in which electrons are in excess in any structure. For example, it is preferable to control the oxidation potential, by the introduction of an electron-donating group when the aromatic ring is not oversupplied with electrons, or conversely by the introduction of an electron-withdrawing group in the case in which electrons are in excess remarkably as in anthracene.
Preferred examples of the group A are represented by any one of the following formulae.
In the formulae (A-1) and (A-2), R₁₂ and R₁₃ each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkylene group, or an arylene group, each of which groups may be substituted or unsubstituted; R₁₄ represents an alkyl group, COOH, a halogen, N(R₁₅)₂, OR₁₅, SR₁₅, CHO, COR₁₅, COOR₁₅, CONHR₁₅, CON(R₁₅)₂, SO₃R₁₅, SO₂NHR₁₅, SO₂NR₁₅, SO₂R₁₅, SOR₁₅, or CSR₁₅; Ar₁ represents an arylene group or a heterocyclic group; R₁₂ and R₁₃, and R₁₂ and Ar₁ may join together, respectively, to form a ring; Q₂ represents O, S, Se, or Te; m₃ and m₄ each represent 0 or 1; n₄ represents an integer of 1 to 3; L₂ represents N-R (where R represents a substituted or unsubstituted alkyl group), N-Ar, O, S, or Se; the ring form resulting from R₁₂ and R₁₃, or R₁₂ and Ar₁, joined together, is a 5- to 7-membered heterocycle or unsaturated ring; and R₁₅ represents a hydrogen atom, an alkyl group, or an aryl group. The ring form of the formula (A-3) is a substituted or unsubstituted 5- to 7-membered unsaturated ring or heterocycle.
Next, the formulas (A-1), (A-2), and (A-3) will be explained in detail.
In the formulas, examples of the alkyl groups represented by R₁₂ and R₁₃ include a straight-chain or branched, and substituted or unsubstituted alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a t-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a t-octyl group, a 2-ethylhexyl group, a 2-hydroxyethyl group, a 1-hydroxyethyl group, a diethylaminoethyl group, a dibutylaminoethyl group, an n-butoxymethyl group, a methoxymethyl group), a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms (e.g., a cyclopropyl group, a cyclopentyl group, a cyclohexyl group). Example of the aryl group include a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., an unsubstituted phenyl group, a 2-methylphenyl group).
Examples of the alkylene group include a straight-chain or branched, and substituted or unsubstituted alkylene group having 1 to 10 carbon atoms (e.g., a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a methoxymethylene group). Examples of the arylene group include a substituted or unsubstituted arylene group having 6 to 12 carbon atoms (e.g., an unsubstituted phenylene group, a 2-methylphenylene group, a naphthylene group).
Examples of the group represented by R₁₄ in the formulas (A-1) and (A-2) include an alkyl group (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a 2-ethylhexyl group, a 2-hydroxyethyl group, an n-butoxymethyl), a COOH group, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom), OH, N(CH₃)₂, NPh₂, OCH₃, OPh, SCH₃, SPh, CHO, COCH₃, COPh, COOC₄H₉, COOCH₃, CONHC₂H₅, CON(CH₃)₂, SO₃CH₃, SO₃C₃H₇, SO₂NHCH₃, SO₂N(CH₃)₂, SO₂C₂H₅, SOCH₃, CSPh, and CSCH₃.
Examples of Ar₁ in formulas (A-1) and (A-2) include a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., a phenyl group, a 2-methylphenyl group, a naphthyl group), and a substituted or unsubstituted heterocyclic group (e.g., a pyridyl group, a 3-phenylpyridyl group, a piperidyl group, a morpholyl group).
Examples of L₂ in formula (A-1) include NH, NCH₃, NC₄H₉, NC₃H₇(i), NPh, NPh-CH₃, O, S, Se, and Te.
Examples of the ring form of the formula (A-3) include an unsaturated 5- to 7-membered carbocycle and heterocycle (e.g., furyl, piperidyl, morpholyl).
R₁₂, R₁₃, R₁₄, Ar₁, and L₂ in the formulae (A-1) and (A-2), and the ring of the formula (A-3) each may further have the aforementioned substituent Y or the like.
Preferred examples of the formulae (A-1), (A-2), and (A-3) are given below.
In the formulae (A-1) and (A-2), preferably, R₁₂ and R₁₃ each are a substituted or unsubstituted alkyl or alkylene group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; R₁₄ is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, an amino group which is mono- or di-substituted by an alkyl group having 1 to 4 carbon atoms, a carboxylic acid group, a halogen atom, or an ester of a carboxylic acid having 1 to 4 carbon atoms; Ar₁ is a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; Q₂ is O, S, or Se; m₃ and m₄ each are 0 or 1; n₄ is 1 to 3; and L₂ is an alkyl-substituted amino group having 0 to 3 carbon atoms.
In the formula (A-3), a preferred ring form is a 5-to 7-membered heterocycle.
In the formulae (A-1) and (A-2), more preferably R₁₂ and R₁₃ each are a substituted or unsubstituted alkyl or alkylene group having 1 to 4 carbon atoms; R₁₄ is an unsubstituted alkyl group having 1 to 4 carbon atoms, or a monoamino-substituted or diamino-substituted alkyl group having 1 to 4 carbon atoms; Ar₁ is a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; Q₂ is O or S; m₃ and m₄ each are 0; n₄ is 1; and L₂ is an alkyl-substituted amino group having 0 to 3 carbon atoms.
In the formula (A-3), a further preferred ring form is a 5- to 6-membered heterocycle.
The site at which the group A is linked to the group L (or the group X, if m=0) is Ar₁ and R₁₂ or R₁₃.
Specific examples of the A group for use in the present invention are shown below, but the compounds for use in the present invention are not limited to these examples.
Next, the group B is explained in detail below.
In the case where B is a hydrogen atom, B undergoes oxidation and thereafter deprotonation by an intramolecular base so that a radical A^• is formed.
Preferred examples of the group B include a hydrogen atom and groups represented by the following formulae.
In the formulae (B-1), (B-2) and (B-3), W represents Si, Sn, or Ge; R₁₆ each independently represent an alkyl group; and Ar₂ each independently represent an aryl group.
The formulas (B-2) and (B-3) can be combined with the adsorbing group X, respectively.
Next, the formulas (B-1), (B-2), and (B-3) will be explained in detail. In the formulas, examples of the alkyl group represented by R₁₆ include a straight-chain or branched, and substituted or unsubstituted alkyl group having 1 to 6 carbon atoms (e.g., a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, a t-butyl group, a 2-pentyl group, an n-hexyl group, an n-octyl group, a t-octyl group, a 2-ethylhexyl group, a 2-hydroxyethyl group, a 1-hydroxyethyl group, n-butoxyethyl group, a methoxymethyl group) and a substituted or unsubstituted aryl group having 6 to 12 carbon atoms (e.g., a phenyl group, a 2-methylphenyl group).
R₁₆ and Ar₂ in the formulae (B-2) and (B-3) each may further have the aforementioned substituent Y or the like.
Preferred examples of the formulae (B-1), (B-2), and (B-3) are given below.
In the formulae (B-2) and (B-3), preferably, R₁₆ is a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms; Ar₂ is a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; and W is Si or Sn.
In the formulae (B-2) and (B-3), more preferably, R₁₆ is a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms; Ar₂ is a substituted or unsubstituted aryl group having 6 to 8 carbon atoms; and W is Si.
Among the formulae (B-1), (B-2), and (B-3), the most preferable is COO^- as (B-1) and Si-(R₁₆)₃ as (B-2).
In the formula (I), n is preferably 1.
In the case where n is 2 in the formula (I), the two (A-B) moieties may be the same or different.
Specific examples of the A-B group for use in the present invention are shown below, but the present invention is not limited to these examples.
Examples of the counter ion necessary for the electric charge balance of the compound A-B include a sodium ion, a potassium ion, a triethylammonium ion, a diisopropylammonium ion, a tetrabutylammonium ion, and a tetramethylguanidinium ion.
The oxidation potential of A-B is preferably in the range of 0 to 1.5V, more preferably in the range of 0 to 1.0V, and further preferably in the range of 0.3 to 1.0V.
The oxidation potential of the radical A^• (E₂) resulting from the bond cleavage reaction is preferably in the range of -0.6 to -2.5V, more preferably in the range of -0.9 to -2V, and further preferably in the range of -0.9 to -1.6V.
The method of measuring the oxidation potential is as follows.
The measurement of E₁ can be carried out by cyclic voltammetry. The electron donor A is dissolved in a 80%/20% (vol. %) solution of acetonitrile/water containing 0.1 M of lithium perchlorate. A glass-like carbon disk is used as a working electrode, a platinum wire is used as a counter electrode, and a saturated calomel electrode (SCE) is used as a reference electrode. The measurement is carried out at a potential scanning speed of 0.1 V/sec at 25°C. An oxidation potential vs. SCE is taken at a peak potential of the cyclic voltammetry wave. The E₁ values of these A-B compounds are described in European Patent No. 93,731 A1.
The measurement of oxidation potential of a radical is carried out by transient electrochemical and pulse radiolytic methods. These are reported in J. Am. Chem. Soc. 1988, 110,. 132, ibid. 1974, 96,. 1287, and ibid. 1974, 96,. 1295.
Specific examples of the compound represented by the formula (I) are shown below, but the compounds for use in the present invention are not limited to these examples.
The compounds represented by the formula (I) can be easily synthesized according to the methods described in U.S. Patent Nos. 5,747,235 and 5,747,235, European Patent Nos. 786,692A1, 893,731A1, and 893,732A1, WO99/05570, and the like, or according to a method similar to these methods.
The compound represented by the formula (I) can be added to a light-sensitive emulsion layer, and to a non-light-sensitive layer such as a non-light-sensitive emulsion layer and an interlayer, and it is added preferably to a light-sensitive emulsion layer and most preferably directly to the emulsion to be used at the time of preparation of the emulsion. The amount of the compound represented by the formula (I) to be added is preferably 1 x 10^-9 to 1 x 10^-2 mol, and more preferably 1 x 10^-7 to 1 x 10^-3 mol, per mol of silver halide in the emulsion layer.
The compound represented by the formula (I) for use in the present invention may be added as a solution of the compound dissolved in water or as a solution of the compound dissolved in a mixed solvent composed of water and a proper water-miscible organic solvent (e.g., alcohols, ethers, glycols, ketones, esters, amides).
Next, the internal-latent-image-type direct positive silver halide emulsion used in the present invention is explained in detail below.

The internal-latent-image-type direct positive silver halide emulsion (hereinafter abbreviated as "internal-latent-image-type silver halide emulsion" as the case may be) is such a silver halide emulsion as to form a latent image primarily in the inside of the silver halide grains when exposed image-wise. Specifically, this emulsion is defined as those that ensure that the maximum density obtained when the silver halide emulsion is applied in a given amount onto a transparent support, exposed to light for a fixed time as long as 0.01 to 1 second, and subjected to development at 20°C for 5 minutes in the following developer A ("internal type" developer), is at least five times the maximum density obtained when a second sample that is exposed like the above is developed at 20°C for 5 minutes in the following developer B ("surface type" developer). Here the maximum density is measured using the usual method of measuring photographic density.

Developer A
N-methyl-p-aminophenol sulfite	2 g
Sodium sulfite (anhydride)	90 g
Hydroquinone	8 g
Sodium carbonate (monohydrate)	52.5 g
Potassium bromide	5 g
Potassium iodide	0.5 g
Water is added to be	1 liter
Developer B
N-methyl-p-aminophenol sulfite	2.5 g
L-ascorbic acid	10 g
Potassium methaborate	35 g
Potassium bromide	1 g
Water is added to be	1 liter

Examples of the internal-latent-image-type silver halide emulsion include conversion-type silver halide emulsions, as described in U.S. Patents No. 2,456,953 and No. 2,592,250; laminate structure-type silver halide emulsions in which the halogen compositions of a first phase and a second phase differ from each other, as described in U.S. Patent No. 3,935,014, and core/shell-type silver halide emulsions prepared by applying a shell to each core grain that is doped with a metal ion or chemically sensitized. Among these silver halide emulsions, the core/shell-type silver halide emulsions are used as the internal-latent-image-type silver halide emulsion of the present invention. Examples of the core/shell-type silver halide emulsions include those described, for example, in U.S. Patents No. 3,206,313, No. 3,317,322, No. 3,761,266, No. 3,761,276, No. 3,850,637, No. 3,923,513, No. 4,035,185, No. 4,184,878, No. 4,395,478 and No. 4,504,570, JP-A-57-136641, JP-A-61-3137, JP-A-63-151618 and JP-A-1-131547. In order to obtain a direct positive image, the entire surface of the light-sensitive layer is subjected to uniform second exposure before or at the time of a developing process ("light-fog method", e.g., GB Patent No. 1,151,363) after the internal-latent-image-type silver halide emulsion is exposed image-wise, or alternatively a developing process is performed in the presence of a nucleating agent ("chemical-fog method", e.g., Research Disclosure, Vol. 151, No. 15162, pp.76-78). In the present invention, a method in which a positive image is directly obtained by the "chemical fog method" is preferred. In the present invention, an emulsion, which is not pre-fogged, is used as the internal latent image-type direct positive silver halide emulsion. The nucleating agent that can be used in the present invention will be explained later. As mentioned above, in order to obtain a direct positive image by using the internal-latent-image-type silver halide emulsion, the entire surface is exposed to uniform second exposure before or at the timing of a developing process after image-wise exposure is finished, or alternatively a developing process is performed in the presence of a nucleating agent. Examples of the nucleating agent for use in the present invention include hydrazines described in U.S. Patents No. 2,563,785 and No. 2,588,982; hydrazides and hydrazones described in U.S. Patent No. 3,227,552; heterocyclic quaternary salt compounds described in GB Patent No. 1,283,835, JP-A-52-69613, JP-A-55-138742, JP-A-60-11837, JP-A-62-210451, JP-A-62-291637 and U.S. Patents No. 3,615,615, No. 3,719,494, No. 3,734,738, No. 4,094,683, No. 4,115,122, No. 4,306,016 and No. 4,471,044; sensitizing dyes having, in a dye molecule, a substituent with nucleation action, as described in U.S. Patent No. 3,718,470; thio-urea-bonded-type acylhydrazine-series compounds described in U.S. Patents No. 4,030,925, No. 4,031,127, No. 4,245,037, No. 4,255,511, No. 4,266,013 and No. 4,276,364 and GB Patent No. 2,012,443; and acylhydrazine-series compounds bound, as an adsorbing group, a thioamido ring or a heterocyclic group, such as triazole or tetrazole, as described in U.S. Patents No. 4,080,270 and No. 4,278,748 and GB Patent No. 2,011,391B. The amount of the nucleating agent to be used is desirably such an amount as to impart satisfactory maximum density when the internal-latent-image-type emulsion is developed using a surface developer. In practically, the amount differs depending upon the characteristics of the silver halide emulsion to be used, the chemical structure of the nucleating agent and development conditions, and hence an appropriate content varies in a wide range. Generally, the amount ranging from about 0.1 mg to 5 g per 1 mol of silver contained in the internal-latent-image-type silver halide emulsion is practically useful, and a preferable amount is about 0.5 mg to about 2 g per mol of the silver. When the nucleating agent is contained in a hydrophilic colloid layer adjacent to the emulsion layer, it may be contained in an amount like the above, to the amount of silver contained in the internal-latent-image-type emulsion in the same area.
In the present invention, silver halide grains in various forms can be used. Examples of the crystal forms include regular crystals, such as cubes, octahedrons, tetradecahedrons, and rhombic dodecahedrons; irregular crystals, such as spherical crystals and tabular crystals; crystals having high-order faces ((hkl)faces); and a mixture of grains of these crystal forms. As to grains having high-order faces, reference can be made to Journal of Imaging Science, Vol. 30 (1986), pages 247-254. In the silver halide grains used in the present invention, in accordance with the purpose, any of regular crystals having no twin plane, and those described in "Shashin Kogyo no Kiso, Ginen Shashin-hen", edited by Nihon Shashin-gakkai (Corona Co.), page 163, such as single twins having one twin plane, parallel multiple twins having two or more parallel twin planes, and nonparallel multiple twins having two or more nonparallel twin planes, can be chosen and used. An example in which grains different in shape are mixed is disclosed in U.S. Patent No. 4,865,964, and if necessary this method can be chosen. In the case of regular crystals, cubic grains having (100) planes; octahedral grains having (111) planes; and dodecahedral grains having (110) planes, as disclosed in JP-B-55-42737 and JP-A-60-222842, can be used. Further, (h11) plane grains represented by (211), (hh1) plane grains represented by (331), (hk0) plane grains represented by (210) planes, and (hk1) plane grains represented by (321) planes, as reported in "Journal of Imaging Science", Vol. 30, page 247 (1986), can be chosen and used in accordance with the purpose, although the preparation is required to be adjusted. Grains having two or more planes in each individual grain, such as tetradecahedral grains having (110) and (111) planes in one grain, grains having (100) and (110) planes in one grain, or grains having (111) and (110) planes in one grain, can be chosen and used in accordance with the purpose.
As the silver halide composition of these grains, any silver halide among silver bromide, silver iodobromide, silver iodochlorobromide, silver chlorobromide, silver chloroiodide, and silver chloride may be used, and silver bromide and silver iodobromide are preferable. Silver salts other than those listed above, for example, silver thiocyanate, silver cyanate, silver sulfide, silver selenide, silver carbonate, silver phosphate, and silver salts of organic acids may be incorporated as another grains or as part of the silver halide grains.
In the silver halide grain, the interior and the surface each may have a different phase or may have the same uniform phase. The silver halide composition inside the grain may be uniform or the inner part and the outer part each may have a different silver halide composition. A lamellar structure is also possible (as described in JP-A Nos. 57-154232, 58-108533, 58-248469, 59-48755, and 59-52237, U.S. Patent Nos. 3,505,068, 4,433,048, and 4,444,877, European Patent No. 100,984, and U.K. Patent No. 1,027,146). The grain may have a dislocation line.
It is important that in the case of that two or more silver halides are present as mixed crystals, or as silver halide grains having structures, the halogen composition distribution among grains is controlled. The method of measuring the halogen composition distribution among grains is described in JP-A-60-254032. A desirable property is that the halogen distribution among grains is uniform. In particular, a highly uniform emulsion having a deviation coefficient of 20 % or below is preferable. Another preferable mode is an emulsion in which the grain size and the halogen composition are correlated.
It is important to control the halogen composition near the surface of grains. An increase in the silver iodide content or the silver chloride content at the part near the surface changes the adsorption of a dye or the developing speed. Therefore, the halogen composition can be chosen in accordance with the purpose. To change the halogen composition at the part near the surface, either the structure enclosing the whole of a grain or the structure wherein only part of a grain is attached (to another silver halide different in halogen composition), can be chosen. For example, in the case of a tetradecahedral grain having (100) and (111) planes, only one plane is changed in halogen composition, or in another case, any one of the main face and the side face of a tabular grain is changed in halogen composition.
The grain size of the emulsion used in the present invention is evaluated, for example, by the diameter of a circle equivalent to the projected area of each individual grain (herein abbreviated to "circle-equivalent diameter" or "equivalent-circle diameter") using an electron microscope; by the diameter of a sphere equivalent to the grain volume (herein abbreviated to "sphere-equivalent diameter"), calculated from the projected area and the grain thickness; or by the diameter of a sphere equivalent to the grain volume, using the Coulter Counter method. A selection to use can be made from ultrafine grains having a sphere-equivalent diameter of 0.05 µm or below, and coarse grains having a sphere-equivalent diameter over 10 µm. Preferably, the grain size is 0.1 µm or more but 3 µm or below. The grain size distribution of the silver halide grain is arbitrarily but may be monodispersion. Here, the monodispersion is defined as a dispersion system in which 95% of the grains to the total weight or total number of silver halide grains contained therein have sizes falling in a range of generally ±60% and preferably ±40% of the number average grain size. Here, the number average grain size is a number average diameter of the projected area diameter of the silver halide grains. Monodispersed emulsions are described in U.S. Patent Nos. 3,574,628 and 3,655,349, and U.K. Patent No. 1,413,748, and the like. These monodispersed emulsions may be used as a mixture.
Two or more of these silver halides differing in crystal habit, halogen composition, grain size, grain size distribution, or the like may be used together, and they may also be used respectively in different emulsion layers and/or in the same emulsion layer.
In the present invention, tabular silver halide grains can be used. As to the tabular silver halide grains, methods of making the grains and techniques of using the grains are already disclosed by Cleve, in Photography Theory and Practice (1930), page 131; Gutoff, Photographic Science and Engineering, Vol. 14, pages 248-257 (1970); U.S. Patent Nos. 4,434,226, 4,414,310, 4,433,048, 4,439,520, 4,414,306, and 4,459,353, U.K. Patent No. 2,112,157, JP-A-59-99433, JP-A-62-209445, and the like. In particular, tabular internal latent image-type direct positive silver halide emulsions are described in detail in U.S. Patent Nos. 4,395,478, 4,504,570, and 4,996,137, JP-B-64-8327, JP-A-1-131547, and the like. These tabular internal latent image-type direct positive emulsions are excellent in that these emulsions provide a direct positive image characterized by good sharpness, rapid progress of development, and little dependence on development temperature.
As the shape of an individual tabular grain contained in the silver halide emulsion used for the present invention, a triangle, hexagon, circle or the like may be selected. An equilateral hexagonal form with six sides having almost the same length, as described in U.S. Patent No. 4,996,137, is a preferable mode.
In the present invention, the tabular grain is a silver halide grain having an aspect ratio (the circle equivalent diameter/grain thickness of an individual silver halide grain) of generally 2 to 100, and it is preferable that 50% or more (in terms of projected area of grains) of all the silver halide grains in the emulsion used in the present invention is occupied by the tabular grains. The emulsion contains silver halide grains having an aspect ratio of preferably 5 to 100, more preferably 5 to 8, in a content of preferably 50% (in terms of area) or more, more preferably 70% or more, and particularly preferably 85% or more, of the total silver halide grains contained therein. Here, in the tabular grain, the circle equivalent diameter indicates the circle equivalent diameters of two facing principal planes which are parallel or close to parallel (the diameter of a circle having the same projected area as the principal planes), and the grain thickness indicates the distance between these principal planes. An aspect ratio exceeding 100 is undesirable because it gives rise to the problem that the emulsion is deformed or broken in the stage before the emulsion is completed as a coating product.
The circle equivalent diameter of the tabular grain is generally 0.3 µm or more, preferably 0.3 to 10 µm, more preferably 0.3 to 5.0 µm, further preferably 0.5 to 5.0 µm, and furthermore preferably 0.5 to 3.0 µm.
The thickness of the tabular grain is generally less than 1.5 µm and preferably 0.05 to 1.0 µm.
An emulsion, in which the coefficient of variation of the grain thickness is 30% or less, and which has highly uniform thickness is preferable. Moreover, grains in which the grain thickness and the plane-to-plane distance between the twin planes are defined, as described in JP-A-63-163451, are preferable.
The grain diameter and grain thickness of the tabular grain can be measured and determined by means of an electron micrograph of grains, like in the method described in U.S. Patent No. 4,434,226.
The distribution of grain size of the tabular grain is arbitrarily but preferably monodispersion. Here, the monodispersion is defined as a dispersion system in which 95% of the total weight or total number of silver halide grains contained therein has sizes falling in a range of generally ±60% and preferably ±40% of the number average grain size. Here, the number average grain size is a number average diameter of the projected area diameter of the silver halide grains.
The structure and production method of the monodispersed tabular grains are described, for example, in JP-A-63-151618. These monodispersion emulsions may be used by mixing them.
The silver halide emulsion used in the present invention may be subjected to a treatment for making grains round, as disclosed, for example, in European Patent Nos. 96,727(B1) and 64,412(B1), or it may be improved in the surface, as disclosed in West Germany Patent No. 2 306 447(C2) and JP-A-60-221320. Generally, the grain surface has a flat structure, but it is also preferable in some cases to make the grain surface uneven intentionally. Examples are a technique in which part of crystals, for example, vertexes and the centers of planes, are formed with holes, as described in JP-A-58-106532 and JP-A-60-221320; and ruffled grains, as described in U.S. Patent No. 4 643 966.
The silver halide grains used for the present invention can be prepared, for example, by the methods described in Research Disclosure (hereinafter abbreviated to as RD) No. 17643 (December 1978), pp. 22 - 23, "I. Emulsion preparation and types", and ibid. No. 18716 (November 1979), p. 648, and ibid. No. 307105 (November, 1989), pp. 863 - 865; the methods described by P. Glafkides, in Chemie et Phisique Photographique, Paul Montel (1967), by G.F. Duffin, in Photographic Emulsion Chemistry, Focal Press (1966), and by V.L. Zelikman et al., in Making and Coating Photographic Emulsion, Focal Press (1964). That is, the preparation can be performed by any method selected from an acidic method, a neutral method, an ammoniacal method, and the like. Further, as to the method in which a soluble silver salt and a soluble halogen salt are caused to react with each other, any method selected from a single jet method, a double jet method, and a combination thereof may be employed. It is also possible to employ a method (so-called back mixing method) in which grains are formed in a condition where an excess of silver ions is present. Further, it is also possible to employ a method wherein the pAg of the liquid phase in which the silver halide is formed is maintained at a constant value, i.e., a controlled double jet method, as a kind of the double jet method. This method provides a silver halide emulsion in which grain crystal forms are regular and the grain sizes are nearly uniform. The tabular grains can be prepared easily using each of the methods described, for example, by Gutoff, in Photographic Science and Engineering, Vol. 14, pp.248-257 (1970); in U.S. Patents No. 4,434,226, No. 4,414,310, No. 4,433,048 and No. 4,439,520 and GB Patent No. 2,112,157.
The silver halide emulsion composed of the above-described regular grains is obtained by controlling pAg and pH during grain formation. Details thereof are described in, for example, Photographic Science and Engineering, Vol.6, pages 159-165 (1962); Journal of Photographic Science, Vol.12, pages 242-251 (1964); U.S. Patent No. 3,655,394, and G.B. Patent No. 1,413,748. Monodispersed emulsions are described, for example, in JP-A-48-8600, JP-A-51-39027, JP-A-51-83097, JP-A-53-137133, JP-A-54-48521, JP-A-54-99419, JP-A-58-37635, JP-A-58-49938, JP-B-47-11386, U.S. Patent No. 3,655,394, and G.B. Patent No. 1,413,748.
A method in which previously precipitated and formed silver halide grains are added to a reaction vessel for the preparation of an emulsion, and the methods described, for example, in U.S. Patent No. 4,334,012, No. 4,301,241, and No. 4,150,994, are preferable in some cases. These can be used as seed crystals, or they are effective when they are supplied as a silver halide for growth. In the latter case, it is preferable to add an emulsion having a small grain size. The method adopted to add the emulsion may be selected from a method in which entire amount of the emulsion is added at once, a method in which entire amount of the emulsion is divided and added in several times, and a method in which the emulsion is continuously added. Further, in some cases, it is also effective to add grains having different halogen compositions in order to modify the surface.
The method in which a large part or only a small part of the halogen composition of silver halide grains is converted by the halogen conversion method is disclosed, for example, in U.S. Patent Nos. 3,477,852 and 4,142,900, European Patent Nos. 273,429 and 273,430, and West German Publication Patent No. 3,819,241, and it is an effective method for forming grains. To convert to a more hardly soluble silver salt, it is possible to add a solution of a soluble halogen or to add silver halide grains. Selection can be made from respective methods in which the conversion is made at one stroke, in several steps, and continuously.
In the present invention, the halogen composition upon completion of grain formation before a desalting step is preferably silver bromide.
In addition to the method in which the grain growth is made by adding a soluble silver salt and halogen salt at constant concentrations and at constant flow rates, grain formation methods wherein the concentration is changed or the flow rate is changed, as described in British Patent No. 1,469,480 and U.S. Patent No. 3,650,757 and No. 4,242,445, are preferable methods. By increasing the concentration or increasing the flow rate, the amount of the silver halide to be supplied can be changed as a linear function, a quadratic function, or a more complex function, of the addition time. It is preferable depending on the situation to reduce the amount of the silver halide to be supplied as required. Moreover, in the case of adding a plurality of soluble silver salts having different solution compositions, or adding a plurality of soluble halides having different solution compositions, an addition system in which one party is increased whereas another party is decreased is effective. A mixing vessel that is used when a solution of a soluble silver salt and a solution of a soluble halogen salt are reacted can be selected for use from methods described in U.S. Patent No. 2,996,287, No. 3,342,605, No. 3,415,650, and No. 3,785,777, and West German Publication Patent No. 2,556,885 and No. 2,555,364.
When an emulsion containing tabular grains is produced, a method is preferable in which the adding rate, amount to be added, and addition concentration of a silver salt solution (e.g., an aqueous AgNO₃ solution) and halide solution (e.g., an aqueous KBr solution) are increased to accelerate the growth of grains. For example, descriptions in G.B. Patent No. 1,335,925, U.S. Patents No. 3,672,900, No. 3,650,757 and No. 4,242,445, and JP-A-55-142329 and JP-A-55-158124 may serve as references for these methods.
The presence of a salt of a metal ion at the time of the preparation of the emulsion of the present invention, for example, at the time of grain formation, desalting step, chemical sensitization, or before coating, is preferable depending on the purposes. The doping of the metal ion, as described above, makes it possible to increase the amount of excessive exposure amount without necessitating additional re-conversion, and to lower the minimum density. The metal ion is added preferably at the time of grain formation in the case where the metal ion is to be doped into the grain. The metal ion is added at a stage after grain formation but before the completion of chemical sensitization in the case where the metal ion is used for the modification of grain surface or as a chemical sensitizer. As to the doping of grains, selection can be made from a case in which the whole grains are doped, one in which only the core parts of the grains are doped, one in which only the shell parts of the grains are doped, one in which only the epitaxial parts of the grains are doped, and one in which only the substrate grains are doped. For example, Mg, Ca, Sr, Ba, Al, Sc, Y, La, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ru, Rh, Pd, Re, Os, Ir, Pt, Au, Cd, Hg, Tl, In, Sn, Pb, and Bi can be used. These metals can be added if they are in the form of a salt that is soluble at the time when grains are formed, such as an ammonium salt, an acetate, a nitrate, a sulfate, a phosphate, a hydroxide, a six-coordinate complex salt, and a four-coordinate complex salt. Examples include CdBr₂, CdCl₂, Cd(NO₃)₂, Pd(NO₃)₂, Pb(CH₃COO)₂, K₃[Fe(CN)₆], (NH₄)₄[Fe(CN)₆], K₃IrCl₆, NH₄RhCl₆, and K₄Ru(CN)₆. As a ligand of the coordination compound, any one can be selected from halo, aquo, cyano, cyanate, thiocyanate, nitrosyl, thionitrosyl, oxo, and carbonyl. With respect to these metal compounds, only one can be used, but two or more can also be used in combination.
It is preferable that the metal compound is added after being dissolved in water or a suitable solvent such as methanol, acetone, or the like. It is possible to employ a method in which an aqueous solution of hydrogen halide (e.g., HCl, HBr) or an alkali halide (e.g., KCl, NaCl, KBr, NaBr) is added for the stabilization of the solution. Further, if necessary, an acid, an alkali, or the like may be added. The metal compound may be added to the reaction vessel before the grain formation or may be added in a midway of the grain formation. Alternatively, the metal compound may be added to the aqueous solution of a water-soluble silver salt (e.g., AgNO₃) or to the aqueous solution of an alkali halide (e.g., NaCl, KBr, KI) so that the metal compound is added continuously during the silver halide grain formation. It is also possible to prepare a solution of the metal compound independent of the water-soluble silver salt and alkali halide and to add the solution of the metal compound continuously at a proper stage during the grain formation. Furthermore, it is also preferable to combine various methods of adding the metal compound. In the present invention, it is preferable that the above-mentioned metal complex salt is present during the formation of the silver halide grain.
In some cases, a method wherein a chalcogenide compound is added during the preparation of the emulsion, as described in U.S. Patent No. 3,772,031, is also useful. In addition to S, Se, and Te, a cyanate, a thiocyanate, a selenocyanate, a carbonate, a phosphate, or an acetate may be present. These are described, for example, in U.S. Patent No. 2,448,060, No. 2,628,167, No. 3,737,313, No. 3,772,031, and in Research Disclosure, Vol. 134, Item 13452 (June 1975).
As stated above, the internal latent image-type silver halide grains to be used in the present invention have a core/shell structure. A method for the production of the shell may refer to, for example, the examples of JP-A-63-151618 and U.S. Patents No. 3,206,316, No. 3,317,322, No. 3,761,276, No. 4,269,927 and No. 3,367,778. The mol ratio (mol ratio by weight) of core/shell in this case is preferably 1/30 to 5/1, more preferably 1/20 to 2/1, and further preferably 1/20 to 1/1.
The silver halide emulsion of the present invention is chemically sensitized, after core grains subjected to chemical sensitization are coated with a shell. The chemical sensitization may be carried out by a known method, for example, a method comprising using an activated gelatin, as described by T.H. James, in The Theory of the Photographic Process, 4th ed., pp.67-76, Macmillan, 1977; and at a pAg of 5 to 10, a pH of 4 to 8 and a temperature of 30 to 80°C, by using sulfur, selenium, tellurium, gold, platinum, palladium, iridium, rhodium, osmium or rhenium, or a combination of two or more of these sensitizers, as described in Research Disclosure, Vol. 120, April 1974, 12008, Research Disclosure, Vol. 34, June 1975, 13452, U.S. Patents No. 2,642,361, No. 3,297,446, No. 3,772,031, No. 3,857,711, No. 3,901,714, No. 4,266,018 and No. 3,904,415 and G.B. Patent No. 1,315,755.
The chemical sensitization can be carried out in the presence of a chemical sensitization auxiliary. As a chemical sensitization auxiliary, a compound can be used that is known to suppress fogging and to increase the sensitivity in the process of chemical sensitization, such as azaindene, azapyridazine, and azapyrimidine. Examples of the chemical sensitization auxiliary are described in U.S. Patent No. 2,131,038, No. 3,411,914, and No. 3,554,757, JP-A-58-126526 and JP-A-62-253159, and by G. F. Duffin in "Photographic Emulsion Chemistry" mentioned above, pages 138 to 143, Forcal Press (1966).
As for silver halide emulsions, the inside of grains can be reduction-sensitized in a precipitate-producing step, as described in JP-B-58-1410 and Moiser et al., Journal of Photographic Science, Vol. 25, pp.19-27 (1977). As the chemical sensitization, the following reduction sensitization may be utilized. For example, hydrogen is used to conduct reduction sensitization, as described in U.S. Patents No. 3,891,446 and No. 3,984,249. Also, reduction sensitization can be carried out by using a reducing agent or by a treatment performed at a low pAg (e.g., less than 5) or at a high pH (e.g., greater than 8), as described in U.S. Patents No. 2,518,698, No. 2,743,182 and No. 2,743,183. As typical examples of the reduction sensitizer, stannous salts, ascorbic acid and its derivatives, amines and polyamines, hydrazine derivatives, formamidinesulfinic acid, silane compounds, borane compounds, and the like are known. For the reduction sensitization for use in the present invention, an appropriate sensitizer selected from these known reduction sensitizers may be used, and also a combination of two or more of these compounds may be used. As the reduction sensitizer, stannous chloride, thiourea dioxide, dimethylamineborane, and ascorbic acid and its derivatives are preferable compounds. The chemical sensitizing methods described in U.S. Patents No. 3,917,485 and No. 3,966,476 may be also applied in the present invention.
The sensitizing methods using an oxidizing agent, as described in JP-A-61-3134 and JP-A-61-3136 may also be applied. The oxidizing agent for silver refers to a compound that acts on metal silver to convert it to silver ions. Particularly useful is a compound that converts quite fine silver grains, which are concomitantly produced during the formation of silver halide grains and during the chemical sensitization, to silver ions. The thus produced silver ions may form a silver salt that is hardly soluble in water, such as a silver halide, silver sulfide, and silver selenide, or they may form a silver salt that is easily soluble in water, such as silver nitrate. The oxidizing agent for silver may be inorganic or organic. Examples of the inorganic oxidizing agent include ozone, hydrogen peroxide and its adducts (e.g. NaBO₂·H₂O₂·3H₂O, 2NaCO₃·3H₂O₂, Na₄P₂O₇·2H₂O₂, 2Na₂SO₄·H₂O₂·2H₂O); oxygen acid salts, such as peroxyacid salts (e.g. K₂S₂O₈, K₂C₂O₆, K₂P₂O₈), peroxycomplex compounds (e.g. K₂[Ti(O₂)C₂O₄] · 3H₂O, 4K₂SO₄·Ti(O₂)OH·SO₄·2H₂O), permanganates (e.g. KMnO₄), and chromates (e.g. K₂Cr₂O₇); halogen elements, such as iodine and bromine; perhalates (e.g. potassium periodate), salts of a metal having high atomic valence (e.g. potassium hexacyanoferrate (II)); and thiosulfonates. Examples of the organic oxidizing agent include quinones, such as p-quinone; organic peroxides, such as peracetic acid and perbenzoic acid; and compounds that can release active halogen (e.g. N-bromosuccinimide, chloramine T, chloramine B). Preferable oxidizing agent for use in the present invention is such inorganic oxidizing agents as ozone, hydrogen peroxide and its adducts, halogen elements, and thiosulfonates, and such organic oxidizing agents as quinones. Use of a combination of the above reduction sensitization with the oxidizing agent for silver is a preferable mode. Use can be made of one selected from a method wherein after an oxidizing agent is used, reduction sensitization is carried out; a method wherein after reduction sensitization is carried out, an oxidizing agent is used; and a method wherein an oxidizing agent and a reduction sensitizer are present simultaneously. These methods can be selected and used also in the step of forming grains or in the step of chemical sensitization.
As a dispersion medium (protective colloid) used in the preparation of the emulsion for use in the present invention, gelatin is used advantageously, but another hydrophilic colloid can also be used.
Use can be made of, for example, a gelatin derivative, a graft polymer of gelatin with another polymer, a protein such as albumin and casein; a cellulose derivative, such as hydroxyethyl cellulose, carboxymethyl cellulose, and cellulose sulfates; sodium alginate, a saccharide derivative, such as a starch derivative; and many synthetic hydrophilic polymers, including homopolymers and copolymers, such as a polyvinyl alcohol, a polyvinyl alcohol partial acetal, a poly-N-vinylpyrrolidone, a polyacrylic acid, a polymethacrylic acid, a polyacrylamide, a polyvinylimidazole, and a polyvinylpyrazole.
As the gelatin, in addition to lime-processed gelatin, acid-processed gelatin, and enzyme-processed gelatin described in Bull. Soc. Sci. Photo. Japan, No. 16, page 30 (1966), can be used. Further a hydrolyzate or enzymolyzate of gelatin can also be used.
Many impurity ions are contained in a gelatin. It is preferable to use a gelatin reduced in the amount of inorganic impurity ions by ion exchange treatment.
Preferably, the silver halide emulsion for use in the present invention is washed with water for desalting and is dispersed in a freshly prepared protective colloid. The temperature at which the washing with water is carried out can be selected in accordance with the purpose, and preferably the temperature is selected in the range of 5 to 50 °C. The pH at which the washing is carried out can be selected in accordance with the purpose, and preferably the pH is selected in the range of 2 to 10, and more preferably in the range of 3 to 8. The pAg at which the washing is carried out can be selected in accordance with the purpose, and preferably the pAg is selected in the range of 5 to 10. As a method of washing with water, one can be selected for use from the noodle washing method, the dialysis method using a semipermeable membrane, the centrifugation method, the coagulation settling method, and the ion exchange method. In the case of the coagulation settling method, selection can be made from, for example, the method wherein sulfuric acid salt is used, the method wherein an organic solvent is used, the method wherein a water-soluble polymer is used, and the method wherein a gelatin derivative is used.
In the present invention, spectral sensitization may be carried out using a sensitizing dye. Examples of the sensitizing dye to be used include cyanine dyes, merocyanine dyes, composite cyanine dyes, composite merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. Specific examples include sensitizing dyes described, for example, in U.S. Patent No. 4,617,257, JP-A-59-180550, JP-A-60-140335, JP-A-61-160739, RD17029 (1978), pp.12-13, and RD17643 (1978), p23.
These sensitizing dyes can be used singly or in combination, and a combination of these sensitizing dyes is often used, particularly for the purpose of supersensitization. Typical examples thereof are described in U.S. Patent No. 2,688,545, No. 2,977,229, No. 3,397,060, No. 3,522,052, No. 3,527,641, No. 3,617,293, No. 3,628,964, No. 3,666,480, No. 3,672,898, No. 3,679,428, No. 3,703,377, No. 3,769,301, No. 3,814,609, No. 3,837,862, and No. 4,026,707, British Patent No. 1,344,218 and No. 1,507,803, JP-B-43-4936 and JP-B-53-12375, and JP-A-52-110618 and JP-A-52-109925.
Together with the sensitizing dye, a dye having no spectral sensitizing action itself, or a substance that does not substantially absorb visible light and that exhibits supersensitization, may be included in the emulsion. (Examples thereof are described in U.S. Patent No. 3,615,613, No. 3,615,641, No. 3,617,295, No. 3,635,721, No. 2,933,390, No. 3,743,510, and JP-A-63-23145.) The timing when the sensitizing dye is added to the emulsion may be at any stage known to be useful in the preparation of emulsions. The addition is carried out most usually at a time after the completion of chemical sensitization and before coating, but it can be carried out at the same time as the addition of a chemical sensitizer, to carry out spectral sensitization and chemical sensitization simultaneously, as described in U.S, Patent No. 3,628,969 and No. 4,225,666; it can be carried out prior to chemical sensitization, as described in JP-A-58-113928; or it can be carried out before the completion of the formation of the precipitate of silver halide grains to start spectral sensitization. Further, as taught in U.S. Patent No. 4,225,666, these foregoing compounds may be added in portions, i.e., part of these compounds is added prior to chemical sensitization, and the rest is added after the chemical sensitization, and also the addition may be carried out at any time during the formation of silver halide grains, as disclosed, for example, in U.S. Patent No. 4,183,756.
The amount of the sensitizing dye to be added can be 10^-8 to 10^-2 mol per mol of the silver halide, but when the silver halide grain size is 0.2 to 1.2 µm, which is more preferable, the amount of the sensitizing dye to be added is more effectively about 5 x 10^-5 to 2 x 10^-3 mol per mol of the silver halide.
The coating amount of the light-sensitive silver halide used in the present invention is generally in the range of 1 mg/m² to 10 g/m² in terms of silver.

In the present invention, various antifoggants and photographic stabilizers may be used for the purpose of preventing a reduction in sensitivity and the occurrences of a fog. Examples of antifoggants and photographic stabilizers include azoles and azaindenes described in RD17643 (1978), pp.24-25 and U.S. Patent No. 4,629,678; carboxylic acids and phosphoric acids containing nitrogen, as described in JP-A-59-168442; mercapto compounds and their metal salts described in JP-A-59-111636; and acetylene compounds described in JP-A-62-87957. These additives are described in more detail in Research Disclosure, Item 17643 (December 1978); Research Disclosure, Item 18176 (November 1979); and Research Disclosure, Item 307105 (November 1989), and the particular parts are given below in a table.

Kind of Additive	RD 17643 (December, 1978)	RD 18716 (November, 1979)	RD 307105 (November, 1989)
1. Chemical sensitizers	p.23	p.648 (right column)	p.866
2. Sensitivity-enhancing agents	-	p.648 (right column)	-
3. Spectral sensitizers and Supersensitizers	pp.23-24	pp.648 (right column)-649 (right column)	pp.866-868
4. Brightening agents	p.24	pp.647	p.868
5. Antifogging agents and Stabilizers	pp.24-25	p.649 (right column)	pp.868-870
6. Light absorbers, Filter dyes, and UV Absorbers	pp.25-26	pp.649 (right column)-650 (left column)	p.873
7. Anti-stain agent	p.25 (right column)	p.650 (left column-right column)	p.872
8. Dye image stabilizers	p.25	p.650 (left column)	p.872
9. Hardeners	p.26	p.651 (left column)	pp.874-875
10. Binders	p.26	p.651 (left column)	pp.873-874
11. Plasticizers and Lubricants	p.27	p.650 (right column)	p.876
12. Coating aids and Surfactants	pp.26-27	p.650 (right column)	pp.875-876
13. Antistatic agents	p.27	p.650 (right column)	pp.876-877
14. Matting agents	-	-	pp.878-879

Next, the color diffusion-transfer light-sensitive material of the present invention will be explained.
A color diffusion-transfer film unit typically has a structure in which an image receiving-element and a light-sensitive element are laminated on one transparent support, and it is unnecessary to peel off the light-sensitive element from the image-receiving element after a transferred image is completed. To state in more detail, the image-receiving element comprises at least one mordant layer, and the light-sensitive element comprises, in a preferred embodiment, a combination of a blue-sensitive emulsion layer, a green-sensitive emulsion layer, and a red-sensitive emulsion layer, a combination of a green-sensitive emulsion layer, a red-sensitive emulsion layer, and an infrared-sensitive emulsion layer, or a combination of a blue-sensitive emulsion layer, a red-sensitive emulsion layer, and an infrared-sensitive emulsion layer, wherein a yellow dye image-forming compound, a magenta dye image-forming compound and a cyan dye image-forming compound are combined with the aforementioned emulsion layers respectively (here, the "infrared-sensitive emulsion layer" means an emulsion layer having a maximum spectral sensitivity to a light at generally 700 nm or more and particularly 740 nm or more). In addition to the above, a white reflecting layer containing a solid pigment such as titanium oxide can be provided between the mordant layer and the light-sensitive layer or the layer containing a dye image-forming compound, so as to view a transferred image through the transparent support.
A light-shielding layer may be further disposed between the white reflecting layer and the light-sensitive layer, to make it possible to finish development processing under a light. Also, a peelable layer may be formed at a proper position so that all or a part of the light-sensitive element can be peeled off from the image-receiving element, if desired. Such an embodiment is described in, for example, JP-A-56-67840 and Canadian Patent No. 674,082.
Another embodiment, which is peelable laminate layer type, include a color diffusion-transfer photographic film unit as disclosed in JP-A-63-226649. This film unit comprises: a light-sensitive element having at least one silver halide emulsion layer combined with at least (a) a layer having a neutralizing function, (b) a dye image-receiving layer, (c) a peelable layer, and (d) a dye image-forming compound, in this order, on a white support; an alkali processing composition containing a light-shielding agent; and a transparent cover sheet, wherein a layer having a light-shielding function is disposed on the side opposite to the side of the emulsion layer where the processing composition is developed.
Also, in a further peel-less form, the aforementioned light-sensitive element is coated on one transparent support, a white reflecting layer is coated on the light-sensitive element, and an image-receiving layer is further laminated on the reflecting layer. An embodiment in which an image-receiving element, a white reflecting layer, a peelable layer, and a light-sensitive element are laminated on the same support, and the light-sensitive element is peeled intentionally from the image-receiving element, is described in U.S. Patent No. 3,730,718.
On the other hand, typical forms in which a light-sensitive element and an image receiving element are separately coated on two supports respectively, are roughly classified into two categories. One is a peel-apart type and another is a peel-less type. To state these types in detail, in a preferred embodiment of a peel-apart type film unit, at least one image-receiving layer is coated on one support, and a light-sensitive element is coated on another support provided with a light-shielding layer. This film unit has a devised structure in which the coating surface of a light-sensitive layer (the surface of the light-sensitive element of the side with which the light-sensitive layer is coated) does not face the coating surface of a mordant layer (the surface of the image receiving element of the side with which the mordant layer is coated) before exposure is finished, and after exposure is finished (for example, during development processing), the coating surface of the light-sensitive layer turns over in an image-forming apparatus so that it is brought into contact with the coating surface of the image-receiving layer. After a transferred image is completed in the mordant layer, the light-sensitive element is rapidly peeled off from the image-receiving element.
Further, in a preferred embodiment of a peel-less type film unit, at least one mordant layer is coated on a transparent support, and a light-sensitive element is coated on a support that is transparent or is provided with a light-shielding layer, wherein the coating surface of the light-sensitive layer and the coating surface of the mordant layer are overlapped on facing each other.
A container (processing element), which contains an alkaline processing solution and can be ruptured by pressure, may be further combined with the aforementioned embodiments. Especially, in the peel-less type film unit in which an image-receiving element and a light-sensitive element are laminated on one support, such processing element is preferably disposed between the light-sensitive element and a cover sheet, which is to be overlapped on the light-sensitive element. Also, in the form in which a light-sensitive element and an image-receiving element are separately coated on two supports respectively, the processing element is preferably disposed between the light-sensitive element and the image-receiving element, by the time of processing at the latest. The processing element preferably contains one or both of a light-shielding agent (e.g. carbon black, a dye, which varies in color corresponding to pH) and a white pigment (e.g., titanium oxide), corresponding to the form of the film unit. Further, in a color diffusion transfer-system film unit, a neutralizing timing mechanism that comprises a combination of a neutralizing layer and a neutralizing timing layer, is preferably incorporated into a cover sheet, an image-receiving element, or a light-sensitive element.
Each structural element, which may be used for the light-sensitive material of the present invention, will be hereinafter explained in more detail.

I. Light-sensitive sheet

A) Support

As the support of the light-sensitive sheet for use in the present invention, any one of smooth transparent supports, which are usually used for photographic light-sensitive materials, may be used. For example, cellulose acetate, polystyrene, polyethylene terephthalate, polycarbonate, and the like is used. The support is preferably provided with an undercoat layer. The support preferably contains a minute amount of a dye or pigment such as titanium oxide in general, to prevent light-piping.
The thickness of the support is generally 50 to 350 µm, preferably 70 to 210 µm, and more preferably 80 to 150 µm.
A curl-balancing layer, or an oxygen-shielding layer as described in JP-A-56-78833 may be applied to the backside of the support according to the need.

B) Image-receiving layer

The dye image-receiving layer for use in the present invention is a layer containing a mordant in a hydrophilic colloid. This dye image-receiving layer may be a single layer or may have a multilayer structure, in which mordants having different mordant powers are coated such that they are overlapped on each other. There are descriptions concerning this in JP-A-61-252551. As the mordants, polymer mordants are preferable.
The polymer mordants are, for example, polymers containing a secondary or tertiary amino group, polymers having a nitrogen-containing heterocyclic moiety, and polymers containing a quaternary cation, and those having a molecular weight of generally 5,000 or more, and particularly preferably 10,000 or more.
The amount of the mordant to be applied is generally 0.5 to 10 g/m², preferably 1.0 to 5.0 g/m², and particularly preferably 2 to 4 g/m².
As the hydrophilic colloid for use in the image-receiving layer, a gelatin, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, or the like is used, and a gelatin is preferably used.
An anti-fading agent as described in JP-A-62-30620, JP-A-62-30621, and JP-A-62-215272, may be incorporated into the image-receiving layer.

C) White reflecting layer

A white reflecting layer that forms a white background of a color image, generally contains a white pigment and a hydrophilic binder.
As the white pigment for the white reflecting layer, barium sulfate, zinc oxide, barium stearate, silver flakes, silicates, alumina, zirconium oxide, sodium zirconium sulfate, kaolin, mica, titanium dioxide, or the like can be used. Further, non-filming polymer particles made of styrene or the like can also be used. Also, these pigments may be used singly, or by mixing them as far as an intended reflectance is obtained.
A particularly useful white pigment is titanium dioxide.
The whiteness of the white reflecting layer varies depending on the type of pigment, the mixing ratio of the pigment and the binder, and the amount of the pigment to be applied. It is, however, preferable that the layer has light reflectance of 70% or more. Generally, the whiteness increases with an increase in the amount of the pigment to be applied. However, when an image-forming dye diffuses through this layer, the pigment resists the diffusion of the dye. It is therefore preferable to make the amount to be applied appropriate.
A white reflecting layer, which is coated with titanium dioxide in an amount of generally 5 to 40 g/m², and preferably 10 to 25 g/m², and has a light reflectance of 78 to 85% for light having a wavelength of 540 nm, is preferable.
Titanium dioxide may be selected from a variety of commercially available brands for use.
Among these titanium dioxides, particularly, rutile type titanium dioxide is preferably used.
Most of commercially available products are surface-treated using alumina, silica, zinc oxide or the like. Titanium dioxide, which is surface-treated to an extent of 5% or more in amount, is preferable to obtain a high reflectance. Examples of commercially available titanium dioxide includes those described in Research Disclosure No. 15162, besides Ti-pure R931 (trade name) manufactured by Du Pont K.K.
As the binder for the white reflecting layer, an alkali-penetrative polymer matrix, for example, a gelatin, polyvinyl alcohol, and cellulose derivative such as hydroxyethyl cellulose, and carboxymethyl cellulose, may be used.
A particularly desirable binder for the white reflecting layer is a gelatin. The ratio of the white pigment to the gelatin is generally 1/1 to 20/1 (mass ratio), and preferably 5/1 to 10/1 (mass ratio).
An anti-fading agent as described in JP-B-62-30620 and JP-B-62-30621 is preferably incorporated into the white reflecting layer.

D) Light-shielding layer

A light-shielding layer containing a light-shielding agent and a hydrophilic binder may be provided between the white reflecting layer and the light-sensitive layer.
As the light-shielding agent, any material having a light-shielding function can be used, and carbon black is preferably used. Decomposable dyes described, for example, in U.S. Patent No. 4,615,966 may also be used.
As the binder to coat the light-shielding agent, any binder may be used as far as it can disperse carbon black, and gelatin is preferable.
As raw materials of carbon black, those produced by an arbitrary method, such as a channel method, thermal method, and furnace method, as described, for example, by Donnel Voet, "Carbon Black", Marcel Dekker, Inc. (1976), can be used. Although no particular limitation is imposed on the size of a carbon black particle, those having a particle size of 90 to 1800 Å are preferable. The amount of a black pigment to be added as the light-shielding agent may be controlled corresponding to the sensitivity of the light-sensitive material to be shielded, but the amount is preferably about 5 to about 10 in terms of optical density.

E) Light-sensitive layer

In the present invention, a light-sensitive layer comprising a silver halide emulsion layer combined with a dye-image-forming compound is provided as an upperlayer of the aforementioned light-shielding layer. Structural elements of the light-sensitive layer will be hereinafter explained.

(1) Dye-image-forming compound

Specific examples of the dye-image-forming compound are described in the following literatures.

Examples of yellow dyes:

Those described in U.S. Patents No. 3,597,200, No. 3,309,199, No. 4,013,633, No. 4,245,028, No. 4,156,609, No. 4,139,383, No. 4,195,992, No. 4,148,641, No. 4,148,643, and No. 4,336,322; JP-A-51-114930, JP-A-56-71072; Research Disclosures No. 17630 (1978) and No. 16475 (1977).

Examples of magenta dyes:

Those described in U.S. Patents No. 3,453,107, No. 3,544,545, No. 3,932,380, No. 3,931,144, No. 3,932,308, No. 3,954,476, No. 4,233,237, No. 4,255,509, No. 4,250,246, No. 4,142,891, No. 4,207,104, and No. 4,287,292; JP-A-52-106727, JP-A-53-23628, JP-A-55-36804, JP-A-56-73057, JP-A-56-71060, JP-A-55-134, JP-A-7-120901, JP-A-8-286343, JP-A-8-286344, and JP-A-8-292537.

Examples of cyan dyes:

Those described in U.S. Patents No. 3,482,972, No. 3,929,760, No. 4,013,635, No. 4,268,625, No. 4,171,220, No. 4,242,435, No. 4,142,891, No. 4,195,994, No. 4,147,544, No. 4,148,642; U.K. Patent No. 1,551,138; JP-A-54-99431, JP-A-52-8827, JP-A-53-47823, JP-A-53-143323, JP-A-54-99431, JP-A-56-71061; European Patents (EP) No. 53,037 and No. 53,040; Research Disclosures No. 17,630 (1978) and No. 16,475 (1977).
Dye image-forming compounds, which each form a dye upon coupling, may be used. For example, these compounds are described in JP-A-8-286340, JP-A-9-152705, and Japanese Patent Applications No. 8-357190, No. 8-357191, No. 9-117529, and the like.
Positive type dye image-forming compounds may also be used. In this case, a negative emulsion may be used as the silver halide emulsion. Examples are described in JP-A-4-156542, JP-A-4-155332, JP-A-4-172344, JP-A-4-172450, JP-A-4-318844, JP-A-356046, JP-A-5-45824, JP-A-5-45825, JP-A-5-53279, JP-A-5-107710, JP-A-5-241302, JP-A-5-107708, JP-A-5-232659, and U.S. Patent No. 5,192,649.
These compounds can be dispersed by a method described in JP-A-62-215272, pp. 144-146. Also, dispersions of these compounds may contain a compound described in JP-A-62-215272, pp. 137-144. As specific examples of these dye-forming compounds, the following compounds may be given. "Dye" in the following compounds respectively represent a dye group, a dye group that is temporarily short-waved, or a dye precursor group.

(2) Silver halide emulsion

The silver halide emulsion used in the present invention is an internal-latent-image-type direct positive emulsion, which forms mainly a latent image inside of a silver halide grain.

(3) Structure of the light-sensitive layer

To reproduce a natural color by a subtractive color process, a light-sensitive layer that comprises at least two combinations of the emulsion, which is spectrally sensitized by the above spectral sensitizing dye, and the aforementioned dye-image-forming compound, which donates a dye having selective spectral absorption in the same wavelength range as the emulsion, is used. The emulsion and the dye-image-forming compound may be coated such that they are overlayer as separate layers, or may be coated as one layer by mixing them. When the dye image-forming substance has absorption in the spectral sensitive range of the emulsion combined therewith, in the condition that the dye-image-forming substance is applied, the separate layer system is preferable. Also, the emulsion layer may consist of a plurality of emulsion layers having different sensitivities, and further an optional layer may be formed between the emulsion layer and the dye-image-forming compound layer. For example, a layer containing a nucleating development accelerator, as described in JP-A-60-173541, or a bulkhead layer as described in JP-B-60-15267, is formed to raise the density of a color image, and also a reflecting layer may be formed to improve the sensitivity of the light-sensitive element.
The reflecting layer is a layer generally containing a white pigment and a hydrophilic binder. The white pigment is preferably titanium oxide and the hydrophilic binder is preferably a gelatin. The amount of titanium oxide to be applied is generally 0.1 g/m² to 8 g/m², and preferably 0.2 g/m² to 4 g/m². Examples of the reflecting layer are described in JP-A-60-91354.
In a preferable multilayer structure, a combination unit of a blue-sensitive emulsion, a combination unit of a green-sensitive emulsion, and a combination unit of a red-sensitive emulsion are arranged in order, from the exposure side.
Arbitrary optional layers may be provided as required between each emulsion layer units, respectively. Particularly, intermediate layers are preferably formed to prevent an undesirable influence of the effect due to the development of a certain emulsion layer, on other emulsion layer unit.
As necessary, an irradiation-preventing layer, a layer containing a UV absorbing agent, a protective layer, and the like are also formed, if necessary, in the present invention.

F) Peeling layer

In the present invention, a peeling layer may be provide, which is peeled off in any position of the light-sensitive sheet in the unit after processing, according to the need. Therefore, this peeling layer needs to be easily peeled off after the processing.
As the raw materials of the peeling layer, those described in, for example, JP-A-47-8237, JP-A-59-220727, JP-A-59-229555, JP-A-49-4653, U.S. Patents No. 3,220,835 and No. 4,359,518, JP-A-49-4334, JP-A-56-65133, JP-A-45-24075, and U.S. Patents No. 3,227,550, No. 2,759,825, No. 4,401,746 and No. 4,366,227, and the like may be used. As one specific example of the raw material, water-soluble (or alkali-soluble) cellulose derivatives may be given. Examples of the cellulose derivative include hydroxyethyl cellulose, cellulose acetate phthalate, plasticized methyl cellulose, ethyl cellulose, cellulose nitrate, and carboxymethyl cellulose. Other examples include a variety of natural polymers, for example, alginic acid, pectin, gum arabic, and the like. Also, various modified gelatins, for example, an acetylated gelatin, a phthalated gelatin, and the like may be used. Further, as other examples, water-soluble synthetic polymers can be mentioned. Examples are polyvinyl alcohols, polyacrylates, polymethyl methacrylates, polybutyl methacrylates, or copolymers of these compounds.
The peeling layer may be a single layer, or one made of a plurality of layers as described in JP-A-59-220727, JP-A-60-60642, or the like.
It is preferable that the color diffusion-transfer light-sensitive material in the present invention is provided with neutralizing function between the support and the light-sensitive layer, or between the support and the image-receiving layer, or on the cover sheet.

G) Support

As the support of the cover sheet for use in the present invention, any smooth and transparent support, which is usually used for photographic light-sensitive materials, may be used. As the support, a cellulose acetate, polystyrene, polyethylene terephthalate, polycarbonate, and the like may be used. The support is preferably provided with an undercoat layer.
The support preferably contains a minute amount of a dye to prevent light-piping.

H) Layer having neutralizing function

The layer having neutralizing function for use in the present invention is a layer generally containing an acidic substance in an amount enough to neutralize an alkali delivered from processing compositions, and it may be one having a multilayer structure comprising a neutralizing rate-controlling layer (timing layer), an adhesion-reinforcing layer, and the like, according to the need. A preferable acidic substance is a substance that contains an acidic group having a pKa of 9 or less (or a precursor group providing such an acidic group by hydrolysis). More preferable examples of the acidic substance include higher fatty acids, such as oleic acid, as described in U.S. Patent No. 2,983,606; and polymers of acrylic acid, methacrylic acid, or maleic acid, and its partial esters or acid anhydrides, as disclosed in U.S. Patent No. 3,362,819; copolymers of an acrylic acid and an acrylate, as disclosed in French Patent No. 2,290,699; and latex-type acidic polymers, as disclosed in U.S. Patent No. 4,139,383 or Research Disclosure No. 16102 (1977).
Besides the above compounds, acidic substances as disclosed in U.S. Patent No. 4,088,493, JP-A-52-153739, JP-A-53-1023, JP-A-53-4540, JP-A-53-4541, JP-A-53-4542, and the like may be given as examples.
Specific examples of the acidic polymer include a copolymer of a vinyl monomer, such as, ethylene, vinyl acetate and vinyl methyl ether, with malic acid anhydride, and its n-butylester, copolymer of butylacrylate and acrylic acid, cellulose, acetate/hydrogen phthalate, and the like.
The aforementioned polymer acid may be used by mixing with a hydrophilic polymer. Examples of such a polymer include polyacrylamide, polymethylpyrrolidone, polyvinyl alcohol (including partially saponified products), carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polymethyl vinyl ether, and the like. Among these compounds, polyvinyl alcohol is preferable.
Also, a polymer, such as cellulose acetate, other than the hydrophilic polymers, may be mixed with the above polymer acid.
The amount of the polymer acid to be applied is controlled corresponding to the amount of an alkali developed in the light-sensitive element. The equivalent ratio of the polymer acid to the alkali per unit area is preferably 0.9 to 2.0. When the amount of the polymer acid is too small, the hue of a transferred dye is changed, and stains occur on a white background portion; whereas when the amount is too large, this brings about disadvantages such as a change in the hue and reduced light resistance. A more preferable equivalent ratio is 1.0 to 1.3. The quality of photographs is also lowered if the amount of the hydrophilic polymer to be mixed is too large or too small. The mass ratio of the hydrophilic polymer to the polymer acid is generally 0.1 to 10, and preferably 0.3 to 3.0.
Additives may be incorporated in the layer having a neutralizing function that can be used in the present invention, for various purposes. For example, a hardener well-known to a person skilled in the art may be added for the purpose of film-hardening of this layer, and a polyvalent hydroxyl compound, such as polyethylene glycol, polypropylene glycol, or glycerol, may be added for the purpose of improving brittleness of the film. In addition, an antioxidant, a fluorescent whitening agent, a development inhibitor or its precursor, and the like may be added, if necessary.
As a material for the timing layer that can be used in combination with the neutralizing layer, useful examples are a polymer that reduces alkali-permeability, such as gelatin, polyvinyl alcohol, partially acetalized polyvinyl alcohol, cellulose acetate, or partially hydrolyzed polyvinyl acetate; a latex polymer, which is produced by the copolymerization with a small amount of a hydrophilic comonomer such as an acrylic acid monomer, and which raises an active energy for the permeation of an alkali; and a polymer having a lactone ring.
Among these polymers, cellulose acetates used for forming the timing layer, as disclosed in JP-A-54-136328, and U.S. Patents No. 4,267,262, No. 4,009,030, No. 4,029,849, and the like; latex polymers, which are produced by the copolymerization of a small amount of a hydrophilic comonomer such as an acrylic acid, as disclosed in JP-A-54-128335, JP-A-56-69629, JP-A-57-6843 and U.S. Patents No. 4,056,394, No. 4,061,496, No. 4,199,362, No. 4,250,243, No. 4,256,827, No. 4,268,604, and the like; polymers having a lactone ring, as disclosed in U.S. patent No. 4,229,516; and other polymers as disclosed in JP-A-56-25735, JP-A-56-97346, JP-A-57-6842, European Patent (EP) No. 31,957A1, EP No. 37,724A1 and EP No. 48,412A1, and the like, are particularly useful.
In addition to the above, those described in the following literatures may also be used:
U.S. Patent No. 3,421,893, U.S. Patent No. 3,455,686, U.S. Patent No. 3,575,701, U.S. Patent No. 3,778,265, U.S. Patent No. 3,785,815, U.S. Patent No. 3,847,615, U.S. Patent No. 4,088,493, U.S. Patent No. 4,123,275, U.S. Patent No. 4,148,653, U.S. Patent No. 4,201,587, U.S. Patent No. 4,288,523, U.S. Patent No. 4,297,431, West Germany Patent Application (OLS) No. 1,622,936, ibid. 2,162,277, and Research Disclosure 15162, No. 151 (1976).
The timing layer using these materials may be a single layer, or a combination of two or more layers.
To the timing layer made from any of these materials may be incorporated, a development inhibitor and/or its precursor, as disclosed in, for example, U.S. Patent No. 4,009,029, West Germany Patent Application (OLS) No. 2,913,164, ibid. No. 3,014,672, JP-A-54-155837, JP-A-55-138745 and the like; a hydroquinone precursor as disclosed in U.S. Patent No. 4,201,578, and other useful photographic additives or their precursors.
Moreover, as the layer having a neutralizing function, to provide an auxiliary neutralizing layer as described in JP-A-63-168648 and JP-A-63-168649 has an effect in view of reducing a change of transferred density due to the lapse of time after processing.

I) Others

Other than the layer having a neutralizing function, a backing layer, protective layer, filter dye layer, and the like, may be provided as layers having auxiliary functions.
The backing layer is provided to control curling, and to impart lubricity. The filter dye may be added to the backing layer.
The protective layer is used primarily to prevent adhesion to the backface of the cover sheet, specifically to prevent the adhesion of the cover sheet to the protective layer of the light-sensitive material when the light-sensitive material and the cover sheet are overlaid (superimposed) on each other.
The cover sheet is allowed to contain a dye to control the sensitivity of the light-sensitive layer. The filter dye may be added directly to the inside of a support of the cover sheet, or to the layer having a neutralizing function, and further, to the aforementioned backing layer, protective layer, or capture mordant layer. Alternatively, a single layer containing the filter dye may be formed.

II. Alkaline processing composition

The processing composition that can be used in the present invention is a composition, which is developed (applied) uniformly on the light-sensitive element after the light-sensitive element is exposed, and is positioned on the backface of the support or on the side opposite to the processing solution of the light-sensitive layer, thereby forming a pair with the light-shielding layer to shield the light-sensitive layer completely from external light, and at the same time, the processing composition serves to develop the light-sensitive layer with the components contained in the composition. For this purpose, the composition may contain, for example, an alkali, a viscosity-enhancing agent, a light-shielding agent, and a developing agent, further a development accelerator, a development inhibitor, each of which controls development, an antioxidant for preventing deterioration of a developing agent. A light-shielding agent is always contained in the composition for light-shielding.
The alkali is those sufficient to make the pH of the solution in a range from 12 to 14. Examples of the alkali include hydroxides of an alkali metal (e.g., sodium hydroxide, potassium hydroxide, lithium hydroxide), phosphates of an alkali metal (e.g., potassium phosphate), guanidines, and hydroxides of a quaternary amine (e.g., tetramethylammonium hydroxide). Among these compounds, potassium hydroxide and sodium hydroxide are preferable.
The viscosity-enhancing agent is required to develop the processing solution uniformly, and to maintain the adhesion between the light-sensitive layer and the cover sheet. For example, as the viscosity-enhancing agent, an alkali metal salt of polyvinyl alcohol, hydroxyethyl cellulose or carboxymethyl cellulose, is used, and preferably hydroxyethyl cellulose or sodium carboxymethyl cellulose is used.
As the light-shielding agent, any one of a dye and a pigment or a combination thereof may be used insofar as it does not diffuse into the dye image-receiving layer to occur stains. As typical examples of the light-shielding agent, carbon black can be mentioned.
As a preferable developing agent, use can be made of any one of those which cross-oxidize a dye image-forming substance and cause substantially no stains even if it is oxidized. These developing agents may be used either singly or in combinations of two or more, and they can be used in the form of a precursor. The developing agent may be contained in a proper layer of the light-sensitive sheet, or in an alkaline processing solution. As specific examples of such a compound, aminophenols and pyrazolidinones can be given. Among these compounds, pyrazolidinones are particularly preferable because of decreased occurrence of stains.
Given as examples of these pyrazolidinones are 1-phenyl-3-pyrazolidinone, 1-p-tolyl-4,4-dihydroxymethyl-3-pyrazolidinone, 1-(3'-methyl-phenyl)-4-methyl-4-hydroxymethyl-3-pyrazolidinone, 1-phenyl-4-methyl-4-hydroxymethyl-3-pyrazolidinone, 1-p-tolyl-4-methyl-4-hydroxymethyl-3-pyrazolidinone, and the like.
Any one of the light-sensitive sheet, the cover sheet, and the alkali processing composition may contain a development accelerator described on pp. 72-91, a hardener described on pp. 146-155, a surfactant described on pp. 201-210, a fluorine-containing compound described on pp. 210-222, a viscosity-enhancing agent on pp. 225-227, an antistatic agent described on pp. 227-230, a polymer latex described on pp. 230-239, a matte agent described on page 240, and the like, each of which is described in JP-A-62-215272. Also, it may contain a tertiary amine latex as described in JP-A-6-273907, JP-A-7-134386, JP-A-7-175193, and JP-A-7-287372.
Also, the alkali solution composition is preferably developed on the light-sensitive element, in a development thickness (the amount of the processing solution per m², after the processing solution is transferred) of 20 to 200 µm.
Further, the processing temperature in the case of processing the light-sensitive material is preferably 0 to 50 °C, and more preferably 0 to 40 °C.
The details of the heat-developable color light-sensitive material (dye-fixing element) using the dye image-forming compound in the present invention, and the exposure and heating methods and the apparatuses, which can be applied to the present invention, are described in, for example, the publication of JP-A-7-219180, Paragraphs [0128] to [0159].
The silver halide emulsion of the present invention may be used for conventional light-sensitive materials. Applicable examples of the light-sensitive material include light-sensitive materials for color or black-and-white printing paper, light-sensitive materials for color slide, and light-sensitive materials for microfilm.
The internal latent image-type direct positive silver halide emulsion of the present invention exhibits excellent effects that it has a high S/N ratio, it does not cause the reduction in sensitivity when exposed to a high illumination intensity, and its low intensity reciprocity law failure is slight.
Consequently, the color diffusion transfer photographic light-sensitive material of the present invention, which uses this internal latent image-type direct positive silver halide emulsion, does not cause the decrease of the maximum density of the image obtained, it does not cause the decrease of the sensitivity at a high illumination intensity, and its low intensity reciprocity law failure is slight. Therefore, the color diffusion-transfer light-sensitive material of the present invention exhibits excellent effect that it forms a satisfactory high-quality image even in photographing under indoor lighting conditions.
The present invention will be explained in more detail by way of the following examples, but the invention is not intended to be limited thereto.

EXAMPLE

Example 1

First, a method of the preparation of a silver halide emulsion will be explained.
The following types of silver halide emulsions 101 to 109 were prepared according to the preparation method of emulsion grains shown below.

Emulsion-101:

To 6 L of an aqueous gelatin solution containing potassium bromide at a concentration of 0.006 mol/L and 0.09% by mass of low-molecular-weight gelatin having an average molecular weight of 20,000 or less, were added 325 mL of an aqueous solution of silver nitrate at a concentration of 0.16 mol/L and 363 ml of an aqueous solution containing potassium bromide at a concentration of 0.14 mol/L and 0.9% by mass of low-molecular-weight gelatin having an average molecular weight of 20,000 or less, at the same time, with vigorous stirring, over a period of 1 minute by a double-jet method (1st addition). During the addition, the aqueous gelatin solution was kept at 35 °C. After 3.8 g of potassium bromide was added, the temperature of the solution was raised to 75 °C at a gradient of 1.5 °C/minute.
After the temperature reached 75 °C, 1.8 L of an aqueous gelatin solution containing 9.5% by mass of deionized gelatin having a Ca content of 100 ppm or less (1st addition) and an aqueous solution containing 10.4 g of the compound E-1 were added. Subsequently, 21 mL of a 50% ammonium nitrate aqueous solution and 121 mL of an aqueous solution of sodium hydroxide at a concentration of 1 mol/L were added to the mixture, and the resulting solution was ripened for 10 minutes. After the ripening was finished, 10 mL of 100% acetic acid, 7.5 g of potassium bromide, and 40 mg of sodium benzenethiosulfate were added.
Subsequently, an aqueous solution of silver nitrate at a concentration of 0.6 mol/L and an aqueous solution of potassium bromide at a concentration of 0.6 mol/L were added, while maintaining pBr at 2.05, at an accelerated flow rate (the final flow rate was 1.7 times the initial flow rate) over a period of 16 minutes by a double-jet method (2nd addition, the amount of the aqueous solution of silver nitrate used was 500 mL).
Next, 1.8 L of an aqueous gelatin solution containing 9.5% by mass of deionized gelatin having a Ca content of 100 ppm or less was added (2nd addition). Subsequent to the addition, 15 mg of lead acetate was added (this lead acetate was added as an aqueous solution). After that, an aqueous solution of silver nitrate at a concentration of 2 mol/L and an aqueous solution of potassium bromide at a concentration of 2 mol/L were added, while maintaining pBr at 2.70 and accelerating the flow rate of the addition (such that the final flow rate was 2.6 times the initial flow rate), over a period of 110 minutes, by a double-jet method (3rd addition, the volume of the aqueous solution of silver nitrate used was 3.83 L).
After 39 g of potassium bromide was added, the resulting emulsion was washed with water according to a usual flocculation method, and a deionized gelatin, 2-phenoxyethanol, and methyl p-hydroxybenzoate were added to the emulsion. After the addition, pH was adjusted to 6.5 and pAg was adjusted to 9.3 in order that 1.7 mol of silver and 42 g of gelatin were contained per kg of the emulsion. The thus prepared emulsion is hereinafter referred to as a core emulsion.
The diameter of a circle, whose area is equal to the projected area of an individual grain when seen in the main plane direction thereof, is referred to as an circle equivalent diameter. As a result of the observation by means of an electron microscope, the average of grain thicknesses hi (= Σhi x ni / Σni) was 0.22 µm and the average of circle equivalent diameters Di of grains (= ΣDi x ni / Σni) was 1.6 µm. The average aspect ratio defined by the average of circle equivalent diameters Di/the average of grain thicknesses hi was 7.7.
To 4720 g of the core emulsion-101, which was dissolved at 40°C, were added 2510 mL of water, 77 mL of a 5% acetic acid aqueous solution, and 5.7 g of potassium bromide. The temperature of the resulting solution was raised to 75 °C. After that, 495 mg of sodium benzenethiosulfate, 6.8 mg of potassium tetrachloroaurate, and 6.6 mg of the compound E-2 were added. Next, after the solution was kept at 75 °C for 90 minutes under heat, 40 L of water, 1870 g of deionized gelatin, and 460 g of potassium bromide were added.
Subsequently, an aqueous solution of silver nitrate at a concentration of 0.55 mol/L and an aqueous solution of potassium bromide at a concentration of 0.55 mol/L that contained the compound E-3 at a concentration of 35 mg/L, were added, while maintaining pBr at 2.75 and accelerating the flow rate of the addition (the final flow rate was 2 times the initial flow rate), over a period of 80 minutes, by a double-jet method (the volume of the aqueous solution of silver nitrate used was 22.2 L).
Subsequently, an aqueous solution of silver nitrate at a concentration of 1.7 mol/L and an aqueous solution of potassium bromide at a concentration of 1.7 mol/L were added, while maintaining pBr at 2.75 and accelerating the flow rate of the addition (the final flow rate was 1.9 times the initial flow rate), over a period of 95 minutes, by a double-jet method (the volume of the aqueous solution of silver nitrate used was 30 L).
Next, after 870 g of potassium bromide was added, the resulting emulsion was washed with water according to a usual flocculation method. After that, deionized gelatin, 2-phenoxyethanol, and methyl p-hydroxybenzoate were added. After the addition, pH was adjusted to 6.5 and pAg was adjusted to 9.3 in order that 0.7 mol of silver and 62 g of gelatin were contained per kg of the emulsion.
As a result of the observation by means of an electron microscope, the average of grain thicknesses hi (= Σhi x ni / Σni) was 0.39 µm and the average of circle equivalent diameters Di of grains (= ΣDi x ni / Σni) was 2.85 µm. The average aspect ratio defined by the average of circle equivalent diameters Di/the average of grain thicknesses hi was 7.4.
Next, the chemical sensitization of grain surface was carried out by adding 280 mL of an aqueous solution, which was prepared by dissolving 150 mg of sodium thiosulfate and 40 mg of sodium tetraborate in 1000 mL of water, further adding 430 mg of poly(N-vinylpyrrolidone) and heating the resulting emulsion at 70°C for 100 minutes. Subsequent to the chemical sensitization, potassium bromide in an amount of 5.8 x 10^-3 mol per mol of silver was added. Further, the sensitizing dye (1), the sensitizing dye (2), the sensitizing dye (3), the sensitizing dye (4), and the sensitizing dye (5) were added in amounts of 1.3 x 10^-4 mol, 4.0 x 10^-6 mol, 2.6 x 10^-5 mol, 2.4 x 10^-5 mol, and 4.3 x 10^-5 mol, respectively, per mol of silver. After the addition, the emulsion was ripened for 20 minutes, and it was then cooled. The emulsion obtained in this way was the final emulsion. The sensitizing dye (5) was added as an aqueous solution. The sensitizing dye (1), the sensitizing dye (2), the sensitizing dye (3), and the sensitizing dye (4) were added as an aqueous dispersion, which was prepared by the steps of mixing these sensitizing dye powders together, adding the mixture to a 5% aqueous gelatin solution, and dispersing the mixture by means of a dissolver. The compounds used in the preparation of the emulsion are shown below.

(E-3)
K₄[Fe(CN)₆] • 3H₂O
Next, Emulsions-102 to -109 were prepared in the same manner as in the preparation of Emulsion-101, except that the compounds represented by the formula (I) for use in the present invention were added in the amounts (per mol of silver nitrate) as shown in Table 1, and according to the addition methods as specified in Table 1.

Next, light-sensitive elements-101 to -109 having the constructions shown in the following Tables 2 to 5 were prepared. These elements were subjected to exposure, development, and density measurement, thereby the photographic performances of these elements were evaluated. As to the constructions of the light-sensitive elements, the light-sensitive elements, in which the emulsions-101 to 109 were used in the 8th layers, respectively, were designated as light-sensitive elements-101 to 109. The emulsions, which were used in the other emulsion layers, are all shown in Table 6. These emulsions can be prepared by referring to the examples of JP-A-6-51423. At the final stage of the preparation of these emulsions, sensitizing dyes were added to the emulsions. The amounts and addition method of these sensitizing dyes are shown in Table 7.

Constitution of Light-Sensitive Elements 101 to 109
Number of layer	Name of layer	Additive	Coated amount (g/m²)
22nd layer	Protective layer	Matting agent(1)	0.15
	Gelatin	0.25
	Surfactant(1)	5.3×10^-3
	Surfactant(2)	4.1×10^-3
	Surfactant(3)	3.9×10^-3
	Additive(1)	8.0×10^-3
	Additive(5)	0.009
21st layer	Ultraviolet absorbing layer	Ultraviolet absorber(1)	0.09
	Ultraviolet absorber(2)	0.05
	Ultraviolet absorber(3)	0.01
	Additive(2)	0.17
	Surfactant(3)	0.013
	Surfactant(4)	0.019
	Additive(1)	8.0×10^-3
	Additive(5)	0.023
	Hardener(1)	0.050
	Hardener(2)	0.017
	Gelatin	0.52
20th layer	Blue-light-sensitive layer (high sensitivity)	Internal-latent-image-type direct positive emulsion : A	0.38 (in terms of silver)
	Nucleating agent(1)	2.9×10^-6
	Additive(3)	4.0×10^-3
	Additive(4)	0.013
	Additive(5)	3.8×10^-3
	Additive(1)	9.0×10^-3
	Surfactant(5)	9.0×10^-3
	Gelatin	0.42
19th layer	Blue-light-sensitive layer (low sensitivity)	Internal-latent-image-type direct positive emulsion :B	0.07 (in terms of silver)
	Internal-latent-image-type direct positive emulsion :C	0.10 (in terms of silver)
	Nucleating agent(1)	2.5×10^-6
	Additive(3)	0.022
	Additive(5)	9.0×10^-3
	Additive(1)	0.013
	Surfactant(5)	9.0×10^-3
	Gelatin	0.35
18th layer	White reflection layer	Titanium dioxide	0.30
	Additive(1)	9.0×10^-3
	Surfactant(1)	7.2×10^-5
	Additive(5)	0.011
	Additive(8)	2.8×10^-3
	Gelatin	0.37

Number of layer	Name of layer	Additive	Coated amount (g/m²)
17th layer	Yellow color material layer	Yellow dye-releasing compound (1)	0.62
	High-boiling organic solvent (1)	0.27
	Additive (6)	0.18
	Additive (7)	0.09
	Surfactant (4)	0.062
	Surfactant (5)	0.030
	Additive (9)	0.031
	Additive (1)	6.0×10^-3
	Gelatin	0.87
16th layer	Intermediate layer	Additive (10)	0.013
	Surfactant (1)	4.0×10^-4
	Additive (1)	7.0×10^-3
	Gelatin	0.42
15th layer	Color mixing prevention layer	Additive (11)	0.47
	High-boiling organic solvent (2)	0.23
	Poly(methyl methacrylate)	0.81
	Surfactant (5)	0.019
	Additive (1)	2.0×10^-3
	Additive (12)	0.61
	Gelatin	0.81
14th layer	Green-light-sensitive layer (high sensitivity)	Internal-latent-image-type direct positive emulsion : D	0.69 (in terms of silver)
	Nucleating agent (1)	2.5×10^-6
	Additive (3)	0.12
	Additive (5)	0.014
	Additive (1)	3.0×10^-3
	High-boiling organic solvent (2)	0.07
	Surfactant (5)	0.06
	Gelatin	0.97
13th layer	Green-light-sensitive layer (low sensitivity)	Internal-latent-image-type direct positive emulsion : E	0.11 (in terms of silver)
	Internal-latent-image-type direct positive emulsion : F	0.08 (in terms of silver)
	Nucleating agent (1)	2.7×10^-6
	Additive (3)	0.011
	Additive (4)	0.033
	Additive (5)	1.5×10^-3
	Additive (1)	0.010
	Surfactant(5)	0.024
	Gelatin	0.26
12th layer	Intermediate layer	Additive (1)	0.014
	Surfactant (1)	0.038
	Surfactant (3)	4.0×10^-3
	Additive (5)	0.014
	Gelatin	0.33

Number of layer	Name of layer	Additive	Coated amount (g/m²)
11th layer	Magenta color material layer	Magenta dye-releasing compound (1)	0.56
	High-boiling organic solvent (1)	0.18
	Additive (13)	9.3×10^-4
	Additive (5)	0.02
	Surfactant (4)	0.04
	Additive (14)	0.02
	Additive (1)	7.0×10^-3
	Gelatin	0.45
10th layer	Intermediate layer	Additive (10)	0.014
	Surfactant (1)	3.0×10^-4
	Additive (1)	9.0×10^-3
	Gelatin	0.36
9th layer	Color-mixing prevention layer	Additive(11)	0.38
	High-boiling organic solvent (2)	0.19
	Poly(methyl methacrylate)	0.66
	Surfactant(5)	0.016
	Additive(1)	2.0×10^-3
	Additive(12)	0.49
	Gelatin	0.65
8th layer	Red-light-sensitive layer (high sensitivity)	Internal-latent-image-type direct positive emulsion (which was prepared in this Example)	0.33 (in terms of silver)
	Nucleating agent (1)	6.1×10^-6
	Additive (3)	0.04
	Additive (5)	0.01
	Additive (1)	1.0×10^-3
	Additive (2)	0.08
	High-boiling organic solvent (2)	0.04
	Surfactant (5)	0.02
	Gelatin	0.33
7th layer	Red-light-sensitive layer (low sensitivity)	Internal-latent-image-type direct positive emulsion : G	0.10 (in terms of silver)
	Internal-latent-image-type direct positive emulsion : H	0.11 (in terms of silver)
	Nucleating agent (1)	2.5×10^-5
	Additive (3)	0.047
	Additive (5)	0.016
	Additive (1)	8.0×10^-3
	Surfactant (5)	0.02
	Gelatin	0.57
6th layer	White reflection layer	Titanium dioxide	1.87
	Additive (1)	7.0×10^-3
	Surfactant (1)	4.0×10^-4
	Additive (5)	0.02
	Additive (8)	0.015
	Gelatin	0.73

Number of layer	Name of layer	Additive	Coated amount (g/m²)
5th layer	Cyan color material layer	Cyan dye-releasing compound (1)	0.25
	Cyan dye-releasing compound (2)	0.14
	High-boiling organic solvent (1)	0.05
	Additive (3)	0.06
	Additive (5)	0.01
	Surfactant (4)	0.05
	Additive (9)	0.05
	Additive (1)	4.0×10^-3
	Hardener (3)	0.014
	Gelatin	0.40
4th layer	Light-shielding layer	Carbon black	1.50
	Surfactant (1)	0.08
	Additive (1)	0.06
	Additive (5)	0.06
	Additive (14)	0.15
	Gelatin	1.43
3rd layer	Intermediate layer	Surfactant (1)	6.0×10^-4
	Additive (1)	9.0×10^-3
	Additive (5)	0.013
	Gelatin	0.29
2nd layer	White reflection layer	Titanium dioxide	19.8
	Additive (15)	0.378
	Additive (16)	0.094
	Surfactant (6)	0.019
	Additive (8)	0.16
	Hardener (1)	0.02
	Hardener (2)	0.007
	Gelatin	2.45
1st layer	Image-receiving layer	Polymer mordant (1)	2.22
	Additive (17)	0.26
	Surfactant (7)	0.04
	Additive (5)	0.11
	Hardener (1)	0.03
	Hardener (2)	0.01
	Gelatin	3.25
Support (90 µm of polyethylene terephthalate containing titanium dioxide for preventing light piping, and provided with an undercoat)
Backing layer	Curl controlling layer	Ultraviolet absorber (4)	0.40
	Ultraviolet absorber (5)	0.10
	Diacetylcellulose (Acetylation degree 51%)	4.20
	Additive (18)	0.25
	Barium stearate	0.11
	Hardener (4)	0.50

Emulsions used in Samples 101 to 109
Number of layer	Name of emulsion	Sphere equivalent diameter(µm)	External shapes of grain	Aspect ratio
20th layer	A	1.3	tabular (hexagonal)	7
19th layer	B	1.1	tabular (hexagonal)	5
19th layer	C	0.9	tabular (hexagonal)	4
14th layer	D	1.1	tabular (hexagonal)	7
13th layer	E	1.0	tabular (hexagonal)	5
13th layer	F	0.9	tabular (hexagonal)	4
7th layer	G	0.8	octahedron	-
7th layer	H	0.7	octahedron	-

The compounds used for the preparation of the light-sensitive elements are shown below.

Additive (8)

Carboxymethyl cellulose
(CMC CELLOGEN 6A, trade name, manufactured
by Dai-ichi Kogyo Seiyaku Co., Ltd.)

Additive (9)

Polyvinyl alcohol (PVA-220E, trade name)
Polymerization degree about 2,000
Saponification degree 88%

Matt agent (1)

Latex of sphere polymethyl methacrylate
(average particle diameter: 3 µm)
Hydroquinone A: 2,5-di-t-octylhydroquinone

Hardener (1)

CH₂=CHSO₂CH₂CONH(CH₂)₂NHCOCH₂SO₂CH=CH₂

Hardener (2)

CH₂=CHSO₂CH₂CONH(CH₂)₃NHCOCH₂SO₂CH=CH₂
A cover sheet was produced as follows. Formation of a cover sheet

Application was performed onto a transparent support having a thickness of 75 µm so as to have a layer constitution shown in Table 8. Thus, a cover sheet was formed.

Layer constitution of cover sheet
Number of layer	Name of layer	Additive	Coated amount (g/m²)
Third layer	Temperature compensating layer	Temperature compensating polymer (1)	0.30
	Temperature compensating polymer (2)	0.80
	Surfactant (8)	0.005
Second layer	Alkali barrier layer	Cellulose acetate (Acetylation degree 51%)	4.30
	Additive (20)	0.20
	Additive (21)	0.20
	Hardener (2)	0.40
First layer	Neutralization layer	Acid polymer (1)	10.40
	Cellulose acetate	0.70
	(Acetylation degree 45%) Hardener (5)	0.10
Support (75 µm of polyethylene terephthalate undercoated by gelatin and containing additive (22) for preventing light piping)
Backing layer	Curl controlling layer	Cellulose acetate	9.10
Backing layer	(Acetylation degree 55%) Silica (average particle diameter: 3 to 4 µm)	0.04

The followings show chemical structures and the like of compounds used in the cover sheet.

An alkaline processing composition was prepared with the formulation shown below.

Silver nitrate	0.10 g
Carbon black (Dai-nichi Seika Co.)	160 g
Additive (23)	8.60 g
Na salt of carboxymethyl cellulose	58.0 g
Benzylalcohol	2.50 g
Additive (24)	2.10 g
Potassium sulfite (anhydride)	1.90 g
5-methylbenzotriazole	2.50 g
1-p-tolyl-4-hydroxymethyl-4-methyl -3-pyrazolidone	7.00 g
1-phenyl-4-hydroxymethyl-4-methyl -3-pyrazolidone	10.0 g
Potassium hydroxide	56.0 g
Aluminum nitrate	0.60 g
Zinc nitrate	0.60 g
Additive (25)	6.60 g
Additive (14)	1.80 g
1,2-benzisothiazoline-3-one	0.003g

Next, each of the above-described light-sensitive elements 101 to 109 was exposed to light through a gray continuous wedge from the emulsion layer side, and each was then overlapped with the above described cover sheet. Then the above alkali processing composition was developed between the both materials so that the thickness became 51µm, by means of a pressure roller. The exposure to light was carried out under two conditions of 1/100-second exposure and 10-second exposure, with adjusting the illumination intensity for the exposures such that a constant light exposure amount was provided. The evaluation was made with respect to two items, i.e., the sensitivity when exposed to a high illumination intensity (1/100-second exposure) and the sensitivity when exposed to a low illumination intensity (10-second exposure). The processing was carried out at 25°C, and, 2 hours later, the transferred dye density was measured by a color densitometer (automatic densitometer X-Rite 310TR (trade name), manufactured by X-Rite Corp.). The cyan maximum density and midpoint sensitivity were measured.

The midpoint sensitivity was defined as follows. A characteristic curve was drawn by plotting the logarithms of exposure amounts along the abscissa and the developed color densities along the ordinate. The midpoint sensitivity was defined as the sensitivity that gave the middle density between the maximum density and the minimum density. The sensitivity was given as a relative value (antilogarithm) by taking the sensitivity of Sample 101 as 100. These results are shown in Table 9.

Results of evaluations
	Maximum density	Relative sensitivity (1/100 sec)	Relative sensitivity (10 sec)
	C_y	C_y	C_y
101 (Comparative example)	2.70	100	100
102 (The present invention)	2.69	136	172
103 (The present invention)	2.72	138	170
104 (The present invention)	2.68	108	115
105 (The present invention)	2.71	115	126
106 (The present invention)	2.70	140	175
107 (The present invention)	2.71	141	177
108 (The present invention)	2.69	141	173
109 (The present invention)	2.70	133	168

As is apparent from the results shown in Table 9, the light-sensitive elements-102 to 109, prepared using Emulsions-102 to 109 according to the present invention, exhibited the remarkable increase of 10-second exposure sensitivity without causing deterioration of the maximum density or 1/100-second exposure sensitivity. It was found that, in the light-sensitive elements 102, 103, and 105 to 109, the 1/100-second exposure sensitivity was raised.
The emulsions according to the present invention were also applied for the green-sensitive emulsion layer(s) and the blue-sensitive emulsion layer(s) of the above light-sensitive elements, and it was found that the thus-obtained elements exhibited the similar effects as those exhibited by "the present invention" samples in which the present invention was applied to the red-sensitive emulsion layers.

Example 2

The method of preparing the silver halide emulsion is explained below.
According to the following preparation method of emulsion grains, the following 48 kinds of silver halide emulsion grains, which were not pre-fogged, were prepared (Emulsions-BH201 to -BH208, Emulsions-BL201 to -BL208, Emulsions-GH201 to -GH208, Emulsions-GL201 to -GL208, Emulsions-RH201 to -RH208, and Emulsions-RL201 to -RL208). Preparation of Emulsion-H201 (octahedral internal latent image-type direct positive emulsion, Comparative Examples):
To 1100 ml of an aqueous gelatin solution containing 0.05 M of potassium bromide, 1.3 g of 3,6-dithia-1,8-octanediol, 0.13 mg of lead acetate, and 70 g of deionized gelatin containing 100 ppm or less of Ca, were added, with keeping the temperature at 75 °C, a 0.3 M aqueous silver nitrate solution and a 0.3 M aqueous potassium bromide solution in a controlled double jet method. During this addition, 86 ml of the aqueous silver nitrate solution was added over 3 minutes, while controlling the addition rate of the aqueous potassium bromide solution so that pBr was maintained at 1.50. After the ripening was carried out for a predetermined period of time, a 0.6M silver nitrate aqueous solution and a 0.6M potassium bromide aqueous solution were added, wherein 630 mL of the silver nitrate aqueous solution was added, with adjusting the addition rate of the potassium bromide aqueous solution such that pBr was maintained at 1.40, over a period of 45 minutes, by a controlled double-jet method.
When the addition was completed, octahedral silver bromide crystals (hereinafter referred to as core grains), being uniform in grain size, with an average grain diameter (sphere equivalent diameter) of about 0.64 µm, were produced.
Next, chemical sensitization of the core was performed in the following conditions.
1. Tank: a tank having a hemispherical bottom, whose metal surface was Teflon-coated with a fluororesin material FEP developed by Du Pont K.K. in a thickness of 120 µm.
2. Stirring fan: a seamless integrated propeller type, whose metal surface was Teflon-coated.

(Teflon is a trade name of Du Pant for polytetrafluoroethylene.)

Next, a potassium bromide aqueous solution was added to a preparation solution of the core grain emulsion prepared above, to adjust the pBr to 1.15. After that, the chemical sensitization was carried out by adding 9 mg of sodium thiosulfate and 16 mL of an aqueous solution, which was prepared by dissolving 90 mg of potassium tetrachloroaurate, and 1.2 g of potassium bromide in 1000 mL of water, and subsequently heating the resulting solution at 75°C for 110 minutes. To the thus chemically-sensitized emulsion solution, was added a 0.11 M potassium bromide. Thereafter, in the same manner as in the preparation of the core grains, to the resultant solution, were added, with keeping the temperature at 75 °C, a 0.1 M aqueous silver nitrate solution and a 1.0 M aqueous potassium bromide solution in a controlled double jet method. During this addition, 440 ml of the aqueous silver nitrate solution was added over 40 minutes, while controlling the addition rate of the aqueous potassium bromide solution to maintain the pBr at 0.95.
This emulsion was washed with water in a usual flocculation method, and then thereto were added the above-mentioned gelatin, 2-phenoxyethanol and methyl p-hydroxybenzoate, to obtain octahedron silver bromide crystal (hereinafter referred to as internal-latent-image-type core/shell grains) being uniform in grain size and having an average grain diameter (sphere equivalent diameter) of about 0.8 µm.

Preparation of Emulsions-BH201, -GH201, and -RH201 (octahedral internal latent image-type direct positive emulsions, Comparative Examples):

Next, the chemical sensitization of shells was carried out by adding 7 mL of an aqueous solution, which was prepared by dissolving 150 mg of sodium thiosulfate and 40 mg of sodium tetraborate in 1000 mL of water, to the internal latent image-type core/shell emulsions, further adding 8 mg of poly(N-vinylpyrrolidone) and thereafter ripening under heat at 75°C for 100 minutes. At the end of the chemical sensitization of shells, sensitizing dyes were added as shown in Table 10, to obtain octahedral internal latent image-type direct positive emulsions BH201, GH201, and RH201.

Preparation of Emulsion-L201 (octahedral internal latent image-type direct positive emulsion, Comparative Example):

To 1150 ml of an aqueous gelatin solution containing 0.07 M of potassium bromide, 26 mg of 1,8-dihydroxy-3,6-dithiaoctane, 0.47 mg of lead acetate, and 67 g of deionized gelatin containing 100 ppm or less of Ca, were added, with keeping the temperature at 75 °C, a 0.6 M aqueous silver nitrate solution and a 0.6 M aqueous potassium bromide solution in a controlled double jet method; during this addition, 340 ml of the aqueous silver nitrate solution was added over 16 minutes, while controlling the addition rate of the aqueous potassium bromide solution to maintain the pBr at 1.40.
When the addition was completed, octahedral silver bromide crystals (hereinafter referred to as core grains), being uniform in grain size and having an average grain diameter (sphere equivalent diameter) of about 0.32 µm, were produced.
Next, chemical sensitization of the core was performed in the following conditions.
1. Tank: a tank having a hemispherical bottom, whose metal surface was Teflon-coated with a fluororesin material FEP developed by Du Pont K.K. in a thickness of 120 µm.
2. Stirring fan: a seamless integrated propeller type, whose metal surface was Teflon-coated.
To a preparation solution of the emulsion of the above-described core grains, were added 4.0 mg of sodium thiosulfate, and 15 ml of an aqueous solution, which was prepared by dissolving 90 mg of potassium tetrachloroaurate and 1.2 g of potassium bromide in 1000 ml of water, and then the solution was heated at 75 °C for 80 minutes to conduct chemical sensitization. After the completion of the chemical sensitization, in the same manner as in the preparation of the core grains, to the resultant solution were added, with the temperature being kept at 75 °C, in a controlled double jet method of adding, 1.0M aqueous silver nitrate solution and 1.0 M aqueous potassium bromide solution; during this, 790 ml of the aqueous silver nitrate solution was added, over 64 minutes, while controlling the addition rate of the aqueous potassium bromide solution to maintain the pBr at 1.30.
This emulsion was washed with water in a usual flocculation method, and then thereto were added the above-mentioned gelatin, 2-phenoxyethanol and methyl p-hydroxybenzoate, to obtain octahedron silver bromide crystal (hereinafter referred to as internal-latent-image-type core/shell grains), being uniform in size and having an average grain diameter (sphere equivalent diameter) of about 0.55 µm.

Preparation of Emulsions-BL201, -GL201, and -RL201 (octahedral internal latent image-type direct positive emulsions, Comparative Examples):

Next, 4.4 mL of an aqueous solution, which was prepared by dissolving 200 mg of sodium thiosulfate and 40 mg of sodium tetraborate in 1000 mL of water, was added to the internal latent image-type core/shell emulsion, and further 54 mg of poly(N-vinylpyrrolidone) was added. The resulting solution was ripened under heat at 75 °C for 90 minutes. After the completion of the ripening under heat, 0.007 M of potassium bromide was added to the mixtures to finish the chemical sensitization of shells. After the completion of chemical sensitization of shells, sensitizing dyes were added as shown in Table 10, to obtain octahedral internal latent image-type direct positive emulsions-BL201, -GL201, and -RL201.
Next, Emulsions-BH202 to -BH208, Emulsions-GH202 to -GH208, and Emulsions-RH202 to -RH208, and also Emulsions-BL202 to -BL208, Emulsions-GL202 to -GL208, and Emulsions-RL202 to -RL208 were prepared in the same manner as in the preparation of Emulsions-BH201, -GH201, and -RH201, and also of -BL201, -GL201, and -RL201, respectively, except that the compounds represented by the formula (I) according to the present invention were added in the amounts (per mol of silver nitrate) and according to the addition methods as specified in Table 11.
Next, light-sensitive elements-201 to -208 were prepared in the same manner as in the preparation of the light-sensitive element-101, except that the emulsions of the 7th layer, the 8th layer, the 13th layer, the 14th layer, the 19th layer, and the 20th layer were changed, respectively, to the emulsions shown in the following Table 12. These light-sensitive elements were subjected to exposure to light, development, and density measurement, thereby the photographic performances of these elements were evaluated.
Each of the above light-sensitive elements 201 to 208 was exposed to light through a gray continuous wedge from the emulsion layer side, each was then overlapped with the aforementioned cover sheet. Between the two materials, the aforementioned alkali processing composition was developed so that the thickness became 51µm, by means of a pressure roller. The exposure to light was carried out under two conditions of 1/100-second exposure and 10-second exposure, with adjusting the illumination intensity for the exposure such that a constant light exposure amount was provided. The evaluation was made with respect to two items, i.e., the sensitivity when exposed to a high illumination intensity (1/100-second exposure) and the sensitivity when exposed to a low illumination intensity (10-second exposure). The processing was carried out at 25°C, and, 2 hours later, the transferred dye density was measured by a color densitometer (automatic densitometer X-Rite 310TR (trade name), manufacture by X-Rite Corp.). The yellow, magenta and cyan maximum density and midpoint sensitivity were measured.

The midpoint sensitivity was defined as follows. A characteristic curve was drawn by plotting the logarithms of exposure amounts along the abscissa and the developed color densities along the ordinate. The midpoint sensitivity was defined as the sensitivity that gave the middle density between the maximum density and the minimum density. The sensitivity was given as a relative value (antilogarithm) by taking the sensitivity of Sample 201 as 100. These results are shown in Table 13.

Results of evaluations
	Maximum density	Relative sensitivity (1/100 sec)	Relative sensitivity (10 sec)
	C_y	M	Y	C_y	M	Y	C_y	M	Y
201 (Comparative example)	2.65	2.40	2.00	100	100	100	100	100	100
202 (The present invention)	2.63	2.42	1.98	138	135	142	174	170	173
203 (The present invention)	2.65	2.39	1.99	139	137	142	175	176	175
204 (The present invention)	2.66	2.38	2.02	107	110	110	115	117	120
205 (The present invention)	2.64	2.40	2.00	115	112	115	129	126	126
206 (The present invention)	2.65	2.37	2.01	141	138	145	174	178	178
207 (The present invention)	2.63	2.41	1.99	143	138	145	177	177	178
208 (The present invention)	2.67	2.39	2.00	140	136	143	175	174	173

As can be seen from Table 13, the light-sensitive elements 202 to 208, prepared with using Emulsions-BH202 to -BH208, Emulsions-BL202 to -BL208, Emulsions-GH202 to -GH208, Emulsions-GL202 to -GL208, Emulsions-RH202 to -RH208, and Emulsions-RL202 to -RL208 of the present invention, exhibited the remarkable increase of 10-second exposure sensitivity without causing the decrease of the maximum density or 1/100-second exposure sensitivity. It was found that, in the light-sensitive elements 202, 203, and 206 to 208, each of which contained the compound according to the present invention in large amount, not only the low intensity reciprocity law failure was improved but also the 1/100-second exposure sensitivity was raised.
The emulsions described above were applied in the peel-apart type color diffusion transfer light-sensitive material described in the Japanese Patent Application No. 2001-144024 and their effects were evaluated. As a result, it was found that the similar effects as in the examples in this Example 2 were exhibited.
Having described our invention as related to the present embodiments, it is our intention that the invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

Claims

An internal latent image-type direct positive silver halide emulsion comprising a core/shell structure silver halide which is composed of a chemically sensitized core and a chemically sensitized shell and which is not pre-fogged, and a compound represented by formula (I): Formula (I) (X)k-(L)m-(A-B)n wherein X represents a light-absorbing group or a silver halide-adsorbing group having at least one atom selected from the group consisting of N, S, P, Se, and Te; L represents a divalent linking group having at least one atom selected from the group consisting of C, N, S, and O; A represents an electron-donating group; B represents a leaving group or a hydrogen atom, which leaves or undergoes deprotonation after being oxidized, to form a radical A*; k and m each independently represent an integer of 0 to 3; and n represents 1 or 2.
The internal latent image-type direct positive silver halide emulsion according to Claim 1, wherein the silver halide emulsion contains tabular silver halide grains having aspect ratio (equivalent-circle diameter/thickness of each individual silver halide grain) of 5 or more but not more than 100, in an amount such that the projected area of the tabular silver halide grains occupies 50% or more of the projected area of the total silver halide grains, and the average grain diameter of the tabular silver halide grains is 0.3 µm or more.
The internal latent image-type direct positive silver halide emulsion according to Claim 1 or 2, wherein the silver halide at the time of completion of grain formation before a desalting step is silver bromide.
The internal latent image-type direct positive silver halide emulsion according to Claim 1, wherein the silver halide-adsorbing group represented by X in the formula (I) has a silver ion ligand structure.
The internal latent image-type direct positive silver halide emulsion according to Claim 1, wherein the light-absorbing group represented by X in the formula (I) is represented by formula (X-7):

wherein, in the formula (X-7), Z₄ represents a group of atoms necessary to form a 5- or 6-membered nitrogen-containing heterocycle; L₂, L₃, L₄, and L₅ each represent a methine group; p₁ represent 0 or 1; n₃ represents an integer of 0 to 3; M₁ represents a counter ion for electric charge balance; m₂ represents a number of 0 to 10 necessary for neutralization of electrical charge of the molecule; and an unsaturated carbocycle may be condensed with the nitrogen-containing heterocycle formed by using Z₄.
The internal latent image-type direct positive silver halide emulsion according to Claim 1, wherein the oxidation potential of the A-B moiety in the formula (I) is in the range of 0 to 1.5V.
The internal latent image-type direct positive silver halide emulsion according to Claim 1, wherein the oxidation potential of the radical A* resulting from the bond cleavage reaction of the A-B moiety in the formula (I) is in the range of -0.6 to -2.5V.
The internal latent image-type direct positive silver halide emulsion according to Claim 1, wherein the amount of compound represented by formula (I) to be added is 1 x 10^-9 to 1 x 10^-2 mol, per mol of silver halide.
A color diffusion transfer light-sensitive material, having at least one unit of light-sensitive silver halide emulsion layers on a support, wherein at least one of the emulsion layers contains the internal latent image-type direct positive silver halide emulsion as claimed in any one of Claims 1 to 7.
The color diffusion transfer light-sensitive material according to Claim 9, wherein the amount of compound represented by formula (I) to be added is 1 x 10^-9 to 1 x 10^-2 mol, per mol of silver halide in the at least one emulsion layer.