EP0462581A1

EP0462581A1 - Silver halide photographic emulsion

Info

Publication number: EP0462581A1
Application number: EP91110004A
Authority: EP
Inventors: Yoshiro Ito; Syoji Matsuzaka
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 1990-06-21
Filing date: 1991-06-19
Publication date: 1991-12-27

Abstract

A silver halide photograpgic emulsion is disclosed, which has a high develpability. The emulsion comprises polyhedral silver halide grains and each of crystal surfaces of each silver halide grain has an outward protrusion at the center of the surface.

Description

FIELD OF THE INVENTION

The present invention relates to a silver halide emulsion for photographic use, more specifically to a silver halide emulsion which offers high sensitivity and good developability.

BACKGROUND OF THE INVENTION

In recent years, there have been increasing demands for improvements in silver halide emulsions for photographic use. Specifically, there have been demands for increasingly higher levels of photographic properties such as high sensitivity, excellent graininess, high sharpness, low fogging density and sufficient optical density. Also demanded is good developability.
Particularly, to provide an emulsion which offers high sensitivity, various methods have been proposed. For example, a silver iodobromide emulsion having a silver iodide content of not more than 10 mol% is well known. Examples of conventional methods used to prepare such emulsions include the ammoniacal method, the neutral method, the acidic method and other methods for controlling pH and pAg conditions, and the single jet method, the double jet method and other methods for mixing the components.
On the basis of these known techniques, various technical approaches to higher sensitivity, improved graininess, high sharpness and low fogging have been attempted and brought into practical application. Particularly, with respect to silver bromide and silver iodobromide emulsions, research has been made to develop new emulsions wherein even the silver iodide content distribution in each silver halide grain, as well as the crystal phase and grain size distribution, is controlled.
The most orthodox approach to the desired photographic properties such as high sensitivity, excellent graininess, high sharpness, low fogging density and sufficient covering powder as described above is to increase the silver halide quantum efficiency. Attempts have been made for this purpose, which are based on findings in solid physics and other fields. A study of theoretical calculation of this quantum efficiency has shown that it is effective on the improvement of quantum efficiency to prepare a monodispersed emulsion with narrow grain size distribution. In addition, it is speculated that a monodispersed emulsion is advantageous also for efficient achievement of high sensitivity while maintaining a low fogging property in the chemical sensitization process for silver halide emulsion.
For the industrial production of monodispersed emulsions, it is necessary to control the rates of silver ion and halide ion supply to the reaction system as determined theoretically and ensure satisfactory stirring conditions while strictly controlling the pAg and pH values, as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 48521/1979. The silver halide emulsion produced under such conditions comprises so-called normal crystal grains in the form of either a cube, octahedron or tetradecahedron, which have various ratios of the {100} surface and {111}surface on the surface thereof. Such normal crystal grains are known to contribute to sensitivity improvement.
Among silver halide grains which offer high sensitivity are silver iodobromide grains having the {110} surface with excellent photographic properties, disclosed in Japanese Patent O.P.I. Publication Nos. 35440/1986 and 222842/1985. Japanese Patent Examined Publication No. 42737/1980 discloses a photographic emulsion containing rhombic dodecahedral silver chlorobromide grains having the {110} surface which is not liable to fogging.
On the other hand, Japanese Patent O.P.I. Publication No. 83531/1986 discloses silver bromide and silver iodobromide grains having the crystal structure wherein a ridge is present on the center of the {110} surface, showing the possibility of further improvement in the sensitivity. This crystal surface is considered to be of high Miller indices, and its properties are described in Japanese Patent O.P.I. Publication No. 83531/1986.
This crystal plane is represented by (nnl) and exemplified by the {331} surface.
Other planes are described in Japanese Patent O.P.I. Publication Nos. 124551/1987, 124550/1987 and 123447/1987.
On the other hand, a conventional silver iodobromide emulsion comprising polydispersed twin crystal grains are known as a silver halide emulsion suitable to high speed photographic films.
Also known are silver iodobromide emulsions containing flat twin crystals, disclosed in Japanese Patent O.P.I. Publication No. 113927/1983 and other publications.
In the field of chemical sensitization, it is a well-known fact that chemical sensitization on normal crystals depends highly upon crystal phase, for example, more sulfur sensitization nuclei are produced on the {111} surface than on the {100} surface in the ordinary method of chemical sensitization, and latent image formation is sparse and less efficient, which results in poor sensitization efficiency. It has therefore been recognized as disadvantageous or difficult to bring into practical application silver halide grains having the {111} surface as described above.
For example, Japanese Patent O.P.I. Publication No. 63914/1975 and German Patent Application OLS No. 2419798 state that the sensitivity is increased by adding a hydroxytetrazaindene compound after sulfur sensitization of a monodispersed emulsion comprising cubic silver halide grains having a silver bromide content exceeding 80%. The same Japanese publication also states that the sensitivity decreases or the degree of increase is very low in the case of a non-cubic crystal configuration, such as octahedral grains which are substantially enclosed by {111} surfaces.
As stated above, crystallographic research to improve the photographic properties of silver halide light-sensitive materials is in remarkable progress. However, most investigations deal with crystals having an outward projection except for minute hollows in twin crystals and hollows in eroded crystals; there is only little work on a crystal having a significantly large ruggedness on the crystal plane.
Among the publicized means are the silver halide emulsions comprising octahedral or tetradecahedral crystal grains having a hollow on the center of the {111} surface, described in Japanese Patent O.P.I. Publication No. 106532/1983. Also, Japanese Patent O.P.I. Publication No. 75337/1986 discloses a silver halide emulsion containing silver halide grains having a hollow passage from the surface to the inside. As for tabular grains other than normal crystals, a silver halide emulsion of tabular silver halide grains comprising parallel {111} surfaces facing each other and having a hollow or empty space on the center thereof is disclosed in Japanese Patent O.P.I. Publication No. 311244/1988.
These emulsions all aim at improvements in the sensitivity, preservability and developability by concentrating the latent images or development starting points on the hollow or empty space on the silver halide grains.
However, all of the method for making these grains involve the process of dissolving and eliminating a part of the formed silver halide grains using a silver halide solvent, which results in increase in minute ruggedness on the silver halide grains other than the hollow or empty space; therefore, the obtained effect is unsatisfactory from the viewpoint of concentration of latent images or development starting points.
Japanese Patent O.P.I. Publication Nos. 244030/1988, 264739/1988, 89949/1987, 269948/1987, 38930/1988 and 179140/1989 each disclose a silver halide emulsion comprising silver halide grains having a silver halide projection on their surface. However, in all these cases, the projection occupies only a very small part of the surface area of the corresponding face. In addition, the silver halide is a silver chlorobromide containing no silver iodide, or the silver halide projection is substantially silver chloride, or the silver halide projection is present in an extremely large number. For these reasons, none of these silver halide emulsions offer a satisfactory sensitivity improving effect.
As stated above, the prior art does not offer satisfactory improvements in the sensitivity or developability by centralization of latent images or development starting points; there have been demands for crystallographic research by another approach.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a silver halide emulsion for photographic use which offers high sensitivity and improved developability.
The silver halide emulsion of the present invention comprises silver halide polyhedral crystal grains and each of crystal surfaces of each grain has an outward protrusion at the center of the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 and 2 are electron micrographs showing the grain structure of the silver halide grains of emulsions EM-1 and EM-3 of the present invention obtained in Examples 1 and 2, respectively. Figure 3 is a schematic oblique view of a grain of EM-3.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, "a protrusion at the center of a crystal surface" means that there is a wide (occupies not less than 50% of the area of the surface) protrusion in any shape near the center of the surface (any position, as long as it almost serves as the center), i.e., a non-marginal position. The protrusion is often quadrangular, but its shape varies depending upon conditions of grain preparation. The diameter of the protrusion expressed as the diameter of the circle converted from the area of the projection of the protrusion varies according to the diameter of the parent octahedral or tetradecahedral grain, but preference is given to 0.005 to 20 µm, more preferably 0.005 to 2.0 µm. The height of the protrusion is preferably over 0.005 µm, more preferably over 0.02 µm, in the direction perpendicular to the corresponding plane of the grain.
For example, with respect to the grain structure photographed in Figure 1, which shows the grain structure of EM-1, a mode of the emulsion of the present invention described in detail later, every {111} surface of the octahedron is triangular strictly speaking, triangular with every vertex cut out, and has thereon a triangular protrusion which is almost concentric to the triangle, which is smaller than the triangle and which has almost the same shape as the triangle.
With respect to the grain structure photographed in Figure 2, which shows the grain structure of EM-3, another mode of the emulsion of the present invention, a slightly round prismatic protrusion is present on every {100} surface of the cube, with the root of these protrusions surrounded by a groove-like hollow. Figure 3 schematically shows a magnified view of a grain of EM-3, in which symbol 1 denotes the silver halide grain, symbol 2 denotes the protrusion and symbol 3 denotes the hollow.
In general, with respect to the silver halide crystal grains contained in a silver halide emulsion, a crystal surface having particular Miller indices according to the silver ion and silver halide ion density thereon, lattice energy, surface energy and/or grain growth conditions occurs predominantly to provide a particular crystal phase for the crystal. Furthermore, when there is a grain size difference among the crystal grains, the crystal grains have different crystal habits according to surface size despite that they have the same Miller indices.
On the other hand, since "the eventual crystal plane is the plane that has the minimum rate of growth in the normal direction" (A. Johnsen, 1910), it is possible to provide a crystal configuration in the desired crystal phase even for a silver halide crystal belonging to the cubic system by choosing appropriate growth conditions.
For example, for providing a hexahedral (cubic) crystal configuration as a crystal phase for silver halide grains in the cubic system, the object is accomplished by delaying the growth of grains, i.e., the deposition of silver ions and halide ions, on the cubic surfaces in comparison with that on the crystal surfaces having another combination of Miller indices.
For changing the crystal phase of a silver halide octahedral crystal grain surrounded by {111} surfaces as the host grain to the hexahedral (cubic) configuration, silver halide is additionally precipitated under such growth conditions that the growth of the cubic {100} surfaces are suppressed, whereby a tetrahedron which is a cubic octahedron or an octahedron with its six vertexes cut out occurs intermediately, followed by gradual reduction in the {111} surfaces, which in turn results in the formation of crystal grains exclusively with cubic planes, followed by thickening of cubic crystal grains with the addition of silver halide.
It is also possible to convert cubic crystal grains as the host grain to octahedral crystal grains.
Similarly, octatriacontahedral crystal grains can be derived from cubic crystal grains as the host grain. Accordingly, when precipitation of silver halide is continued under such growth conditions that the growth in the normal direction with respect to the octatriacontahedral crystal surface is slower than that on surfaces with other Miller indices, a octatriacontahedral crystal surface first appears, and eventually the host grain is totally covered by octatriacontahedral crystal surfaces.
Also for crystal grains having a hexatetracontahedral, rhomboidal tetracosacontahedral or octahexacontahedral crystal configuration, the desired crystal grain can be obtained by choosing such growth conditions that the growth of the surface which provides the corresponding crystal surface is suppressed.
A preferred mode of the embodiment of the present invention is a silver halide emulsion containing octahedral or tetradecahedral crystal grains of silver halide having a protrusion on the center of at least one, preferably all, of the {111} surfaces, or cubic or tetradecahedral crystal grains of silver halide having a protrusion on the center of at least one, preferably all, of the {100} surfaces.
The growth of the silver halide grains having various crystal phases described above is affected by a large number of factors such as silver halide composition, ion density on the crystal surfaces, temperature, lattice or surface energy, adsorbents and silver halide solvent. Another factor is a growth modifier which retards the deposition of silver halide on the crystal surfaces.
A large number of compounds are already known to work as growth modifiers. Among the compounds which work well as growth modifiers for photographic silver halide are surface-adsorptive photographic dyes such as cyanine dyes and stabilizers and antifogging agents such as azaindene and imidazole, disclosed in the above-mentioned Japanese patent publications, Japanese Patent Application No. 159280/1987 and other publications.
The silver halide grains having a protrusion on the center of at least one crystal plane, contained in the silver halide emulsion of the present invention, (hereinafter also referred to as the silver halide grains of the present invention) may be prepared by any of the acidic method, neutral method and ammoniacal method. These grains may be grown continuously or grown with stepwise formation of seed grains. The method of preparing the seed grain and the method of its growth may be identical or not.
The silver halide composition of the silver halide emulsion of the present invention is not subject to limitation, but it is preferable that the silver halide be substantially silver bromide or silver iodobromide. The emulsion of the present invention preferably contains iodine. In this case, iodine ions may be added in an ion solution such as a potassium iodide solution during grain growth, and may be added as grains with a solubility product smaller than that of the growing silver halide grains. This iodine is preferably supplied as silver halide grains with a solubility product equivalent to, or lower than that of the growing grains.
Accordingly, a preferred mode of the growth of the silver halide grains of the present invention (for the purpose of convenience, referred to as AgX grains 1 in the description of the grain growth process) is that the silver halide grains are grown in the presence of fine grains of silver halide with a solubility product equivalent to, or lower than that of the silver halide grains of the present invention (hereinafter referred to as AgX grains 2 like AgX grains 1) during at least a given period of the grain growth process.
"Equivalent or lower solubility product" means that the solubility product of AgX grains 2 is equivalent to, or lower than, that of AgX grains 1. In the present specification, the solubility product is used in the common sense in chemistry.
In this mode of embodiment, AgX grains 1 are grown in the presence of AgX grains 2, which have a solubility product equivalent to, or lower than, that of AgX grains 1, during at least a given period of the process of growth of AgX grains 1. Here, AgX grains 2 can be used to allow AgX grains 1 to grow before completion of the supply of grain growth elements for AgX grains 1, such as a halogen ion solution and a silver ion solution.
The average grain size of AgX grains 2 is usually smaller than that of AgX grains 1, but the former is greater than the latter in some cases. Also, AgX grains 2 are usually substantially non-sensitive to light. The average grain size of AgX grains 2 is preferably 0.001 to 0.7 µm, more preferably 0.01 to 0.3 µm, and ideally 0.01 to 0.1 µm.
It is preferable to add AgX grains 2 to the suspension system in which AgX grains 1 are prepared (hereinafter referred to as the mother liquid) at latest until completion of the growth of AgX grains 1.
When using silver halide seed grains, AgX grains 2 may be added to the mother liquid before the seed grains are added, or added to the mother liquid containing seed grains before adding grain growth elements, or added during addition of grain growth elements, or added in separate stages of the addition period.
When grains are grown in the absence of seed grains after silver halide nucleus formation, it is preferable to add AgX grains 2 after nucleus formation, whether the addition of AgX grains 2 is before or during addition of grain growth elements or in separate stages.
Addition of AgX grains 2 and grain growth elements may be simultaneous, continuous or intermittent.
AgX grains 2 and grain growth elements are preferably added to the mother liquid by a multi-jet method such as the double jet method at a rate suitable to grain growth while controlling the pH, pAg, temperature and other factors.
AgX grains 2 and silver halide seed grains may be prepared in the mother liquid, or added to the mother liquid after it is prepared outside the mother liquid.
The solution of water-soluble silver salt used to prepare AgX grains 2 is preferably an ammoniacal solution of silver salt.
As for the halogen composition of AgX grains 2, silver iodide or a silver iodobromide having an iodine content higher than that of the growing silver iodobromide grains is preferred when AgX grains 1 are of silver iodobromide, and silver bromide or a silver chlorobromide having a bromine content higher than that of the growing silver chlorobromide grains is preferred when AgX grains 1 are of silver chlorobromide. When AgX grains 1 are of silver iodobromide, AgX grains 2 are preferably of silver iodide.
When AgX grains 1 are of silver iodobromide or silver chloroiodobromide, it is preferable that the iodine for grain growth be supplied as AgX grains 2, but some of it may be supplied in an aqueous solution of silver halide, as long as it does not interfere with the effect of the present invention.
A known silver halide solvent, such as ammonia, thioether or thiourea, may be present during the growth of silver halide grains.
During formation and/or growth of silver halide grains, cadmium, zinc, lead, thallium, iridium, rhodium and iron may be contained inside and/or on the grains by adding ions of these metal elements using at least one kind selected from the group comprising cadmium salt, zinc salt, lead salt, thallium salt, iridium salt, rhodium salt, iron salt and complex salt thereof. Also, the silver halide grains may be provided with a reduction sensitization nucleus therein and/or thereon by keeping them under appropriate reductive conditions.
The silver halide emulsion of the present invention may have the undesirable soluble salts removed therefrom after completion of their growth or may remain containing them. Removal of these salts can be achieved in accordance with the method described in Research Disclosure (hereinafter referred to as RD) No. 17643, Paragraph II.
The average grain size of the silver halide grains of the present invention is preferably 0.05 to 30 µm, more preferably 0.1 to 3.0 µm.
The silver halide emulsion of the present invention may take any form, including a polydispersed emulsion with a broad grain size distribution and a monodispersed emulsion with a narrow grain size distribution.
The silver halide emulsion of the present invention may comprise a single emulsion or a mixture of two or more emulsions.
Here, the grain size ri which gives a maximum value for the product of ni and ri³ (ni x ri³) wherein ni is the number of grains having a grain size of ri with an average of r is defined (significant up to three digits, rounded off at the last digit).
Accordingly, the grain diameter ri is defined as the diameter of the silver halide grain when it is spherical or the diameter converted from a circle with the same area from the projected image of the silver halide grain when it is not spherical.
Grain size can be obtained by measuring the diameter of the grain or the area of the projected circle on an electron micrograph taken at x 10000 to 50000 (the number of subject grains should be not less than 1000 randomly).
A highly monodispersed emulsion preferred for the present invention has a distribution width of not more than 20%, more preferably not more than 15%, defined by the following equation.
Here, the average grain size and standard deviation are calculated from ri defined above.
A monodispersed emulsion can be prepared by adding a solution of water-soluble silver salt and a solution of water-soluble halide by the double jet method while controlling the pAg and pH. This method is applicable to the present invention.
The addition rate can be determined with reference to Japanese Patent O.P.I. Publication Nos. 48521/1979 and 49938/1983.
To obtain a still more highly monodispersed emulsion, the method of grain growth in the presence of tetrazaindene disclosed in Japanese Patent O.P.I. Publication No. 122935/1985 is applicable.
The silver halide emulsion of the present invention preferably maintains uniformity with respect to grain shape.
Uniformity with respect to grain shape means that at least crystal habit and grain size are uniform among the subject grains when their shape is observed by scanning electron micrography at a magnification of exceeding x 10000. For observing the fine surface structure, it is preferable to use a low accelerated voltage below 2 kV.
Uniformity with respect to grain shape is described below with reference to normal crystal grains. All the subject grains must meet the following requirements:

(1) Have the same ratio of the {111}, {100}, {331} and other surfaces.
(2) When the silver halide grains are of the core/shell type, the grains must be free of a portion where shell formation did not occur.
(3) Have the same surface properties such as surface ruggedness.
(4) Contains no twin crystals.
(5) Free of too fine grains, too coarse grains and aggregated grains comprising two or more grains adhering to each other (these grains can be found by microscopic observation).

Specifically, it is preferable that not less than 70%, more preferably not less than 80%, and still more preferably not less than 90% of the grains in the emulsion keep uniformity with respect to the shape described above.
Also, the silver halide emulsion of the present invention preferably keeps uniformity with respect to the silver iodide content among the silver halide grains.
The silver iodide content of each silver halide grain in the emulsion of the present invention and the average silver iodide content of the silver halide grains can be calculated by the EPMA method of electron probe microanalyzer method.
In this method, a sample is prepared by thoroughly dispersing emulsion grains apart from each other and making elemental analysis of very small portions of the sample using X-ray excited by electron beam irradiation.
This method permits determination of the halogen composition of each grain by determining the intensities of the silver and iodine characteristic X-rays from each grain.
If we determine the silver iodide content of each of at least 50 grains by the EPMA method, then we can calculate the average silver iodide content by averaging the obtained values.
The apparatus used for this measurement does not need special specifications. In the examples of the present invention described below, the X-ray microanalyzer model JXA-8621, produced by JEOL Ltd. was used to determine the silver iodide content of the emulsion. Measurements were made while cooling the sample to avoid damage by the electron beam.
The relative standard deviation for the silver iodide content of each grain is obtained by multiplying by a factor of 100 the quotient of the standard deviation for the silver iodide content by the average silver iodide content obtained in the measurement on at least 50 emulsion grains.
The emulsion of the present invention preferably has a relative standard deviation of not more than 20% with respect to the silver iodide content of each silver iodobromide grain. The emulsion of the present invention preferably has more uniformity of iodine content among the grains. Specifically, the relative standard deviation for the iodine content distribution among the grains determined by the EPMA method is preferably not more than 20%, more preferably not more than 15%, and still more preferably not more than 10%.
The silver halide grains of the present invention can be formed under various sets of conditions as described above, but a preferred mode of embodiment, e.g., octahedral or tetradecahedral crystal grains of silver halide having a protrusion on the center of the {111} surface, or cubic or tetradecahedral crystal grains of silver halide having a protrusion on the center of the {100} surface, can be prepared by the method described below.
A suspension of fine silver halide seed grains is prepared by an ordinary method. A solution of water-soluble silver halt and a solution of water-soluble bromide are added in the presence of a nitrogen-containing compound and fine grains of silver iodide or silver iodobromide, and a low iodine silver halide phase with a silver iodide content of not more than 10 mol% is grown on the seed grains. By adjusting the solution to the desired pAg, cubic, octahedral or tetradecahedral grains can be prepared optionally. Accordingly, a pAg of 7.6 to 9 yields octahedral grains, and a pAg below 7.6 yields cubic grains. Tetradecahedral grains can be formed by setting the pAg at a critical level around 7.6. The grain formation temperature is preferably above 50°C.
To the emulsion containing octahedral or tetradecahedral silver halide grains thus obtained, a solution of water-soluble silver salt and a solution of water-soluble halide are added to form a high iodine phase having a silver iodide content higher by not less than 10 mol%, preferably not less than 15 mol%, than that the surface silver iodide content of each grain outside the low iodine phase in each grain, followed by growth thereon of an outer low iodine phase having an iodine content lower by 1 to 10 mol% than the surface iodine content of the high iodine phase, whereby an emulsion containing octahedral or tetradecahedral silver halide grains of the present invention, which has a protrusion on the {111} surface, is obtained. The volume ratio of the low iodine phase to the high iodine phase is preferably not less than 30%, and the pAg during grain growth is preferably below 9.
To the emulsion containing cubic or tetradecahedral silver halide grains thus obtained, a solution of water-soluble silver salt and a solution of water-soluble halide are added to form a high iodine phase having a silver iodide content higher by not less than 10 mol%, preferably not less than 15 mol%, than the surface silver iodide content of each grain outside the low iodine phase of each grain, followed by growth thereon of an outer low iodine phase having an iodine content lower by 15 to 35 mol% than the surface iodine content of the high iodine phase, whereby a silver halide emulsion of the present invention, which comprises grains having a protrusion on the center of the {100} surface, is obtained. In this case, the volume ratio of the high iodine phase to the low iodine phase is preferably not less than 50%, and the volume ratio of the outer low iodine phase to the high iodine phase is preferably not more than 30%. The pAg during grain growth is preferably below 9.
The silver halide emulsion of the present invention may be chemically sensitized by the conventional method.
The silver halide emulsion of the present invention may be optically sensitized in the desired wavelength band using a sensitizing dye known in the photographic industry. The sensitizing dye may be used singly or in combination of two or more kinds.
The silver halide emulsion may contain an antifogging agent, stabilizer and other additives. It is advantageous to use gelatin as the binder for the emulsion.
In the preparation of a light-sensitive material using the silver halide emulsion of the present invention, the emulsion layer and other hydrophilic colloidal layers of the light-sensitive material may be hardened, and may contain a plasticizer and a dispersion (latex) of a water-insoluble or sparingly water-soluble synthetic polymer.
The silver halide emulsion of the present invention can serve well for the formation of a color photographic light-sensitive material, and when it is used in the emulsion layer, it is used in the presence of a coloring coupler.
Moreover, it is possible to use a colored coupler having a color correction effect, a competing coupler and a compound which releases a photographically useful fragment such as a development accelerator, bleaching accelerator, developer, silver halide solvent, toning agent, hardener, fogging agent, antifogging agent, chemical sensitizer, spectral sensitizer and desensitizer by coupling with the oxidation product of a developing agent.
In the preparation of a light-sensitive material using the silver halide emulsion of the present invention, auxiliary layers such as a filter layer, anti-halation layer and anti-irradiation layer may be formed in the light-sensitive material. These layers and/or the emulsion layers may contain a dye which oozes out or is bleached from the light-sensitive material during development.
The light sensitive-material may contain a formalin scavenger, a fluorescent whitening agent, a matting agent, a lubricant, an image stabilizer, a surfactant, an antifogging agent, a development accelerator, a development retarder and a bleaching accelerator.
Any material can be used as the support for the light-sensitive material, such as polyethylene-laminated paper, a polyethylene terephthalate film, baryta paper and cellulose triacetate.
A dye image can be obtained using the light-sensitive material of the present invention by exposure followed by an ordinary color photographic process.

EXAMPLES

Example 1

Preparation of silver iodide fine grain emulsion AI-1

An aqueous solution containing 5% by weight ossein gelatin was added to a vessel. While stirring at 40°C, a 3.5 N aqueous solution of 1 mol of silver nitrate and a 3.5 N aqueous solution of 1 mol of potassium iodide were added at constant rate over a period of 30 minutes.
The pAg was kept at 13.5 by the ordinary method of pAg control during the addition.
The resulting silver iodide was a mixture of β-AgI and γ-AgI having an average grain size of 0.06 µm.
This emulsion is hereinafter referred to as emulsion AI-1.

Preparation of emulsion EM-1

The four solutions described below were used to yield an emulsion EM-1 of the present invention.
To Solution a-1 of the composition shown above while being vigorously stirred at 60°C, a seed emulsion having an average grain size of 0.27 µm and an average AgI content of 2 mol% in an amount equivalent to 0.407 mol was added, and acetic acid and an aqueous solution of KBr were added to obtain the desired pH and pAg levels.
Then, while maintaining a pH of 7.0 and a pAg of 7.8, Solutions a-2, a-3 and a-4 were added by the triple jet method at the flow rates shown in Tables 1, 2 and 3, respectively.
After completion of the addition, the mixture was desalted and washed by conventional methods and dispersed in an aqueous solution containing gelatin.
Electron microscopic observation revealed that this emulsion is a highly monodispersed emulsion with a coefficient of variance of grain size distribution of 11.2%, comprising octahedral grains having a protrusion on the {111} surface which account for 92% of all silver halide grains, with an average grain size of 0.46 µm.
Table 4 shows the grain structure of silver halide grains contained in this emulsion.
Figure 1 is an electron micrograph of a silver halide grain contained in this emulsion of the present invention.
A comparative emulsion EM-2 was prepared in accordance with the methods described in Japanese Patent O.P.I. Publication Nos. 246740/1986, 275741/1986 and 286845/1986, which comprises octahedral grains having the same halogen composition, grain size distribution and average grain size as those of the aforementioned emulsion EM-1 and having no protrusion on the {111} surface in-the final configuration.
The emulsions EM-1 and EM-2 thus prepared were subjected to optimum gold-sulfur sensitization and then spectrally sensitized in the green band by adding 350 mg of the following sensitizing dye I and 240 mg of the sensitizing dye II per mol AgX. Then, TAI and 1-phenyl-5-mercaptotetrazole were added to stabilize the emulsions. Here, AgX represents silver halide.
Separately, the following magenta coupler M-1 at 5 x 10⁻³ mol per mol AgX, the following magenta coupler M-2 at 6.2 x 10⁻³ mol per mol AgX and the following colored magenta coupler CM-1 at 4.0 x 10⁻³ mol per mol AgX were dissolved in di-t-nonyl phthalate, and this solution was emulsified and dispersed in an aqueous solution containing gelatin. The resulting dispersion was added to each emulsion, followed by the addition of ordinary photographic additives such as an extender and a hardener to yield a coating solution. This coating solution was coated and dried on a subbed film base by a conventional method to yield sample Nos. 101 and 102.
In accordance with the conventional method, sample Nos. 101 and 102 were each subjected to exposure through an optical wedge via a yellow filter, after which they were processed with the following processing solutions in the following processing procedures I and II and subjected to sensitivity determination.

Processing procedure I (35°C)

Development 15 seconds

Fixation 25 seconds

Washing 25 seconds

Drying 15 seconds

Processing procedure II (35°C)

Development 25 seconds

Fixation 25 seconds

Washing 25 seconds

Drying 15 seconds
The processing solutions used in the processing procedures had the following compositions.

Developer

Potassium sulfite	55.0 g
Hydroquinone	25.0 g
1-phenyl-3-pyrazolidone	1.2 g
Boric acid	10.0 g
Sodium hydroxide	21.0 g
Triethylene glycol	17.5 g
5-methylbenzotriazole	0.07 g
5-nitroindazole	0.14 g
1-phenyl-5-mercaptotetrazole	0.015 g
Glutaraldehyde bisulfite	15.0 g
Glacial acetic acid	16.0 g
Potassium bromide	4.0 g
Triethylenetetraminehexacetate	2.5 g

Water was added to make a total quantity of 1ℓ, and the solution was adjusted to a pH of 10.20.

Fixer

Disodium ethylenediaminetetraacetate	5.0 g
Tartaric acid	3.0 g
Ammonium thiosulfate	130.9 g
Anhydrous sodium sulfite	7.3 g
Boric acid	7.0 g
Acetic acid (90 wt%)	5.5 g
Sodium acetate trihydrate	25.8 g
Aluminum sulfate octadecahydrate	14.6 g
Sulfuric acid (50 wt%)	6.77 g

Water was added to make a total quantity of 1ℓ, and the solution was adjusted to a pH of 4.20.
The results are given in Table 6. Sensitivity is shown in the reciprocal of the exposure amount which gives a minimum density (fogging) of + 0.1, expressed in percent ratio to the sensitivity of sample No. 102 processed in the processing procedure I.
As is evident from Table 5, the sample prepared using the emulsion of the present invention showed sufficiently high sensitivity even when the developing time was short, demonstrating that the emulsion of the invention offers excellent developability and high sensitivity.

Example 2

Preparation of emulsion EM-3

The four solutions described below were used to yield an emulsion EM-3 of the invention. The silver iodide fine grain emulsion for solution a-4 is the same as used in Example 1.
To the aqueous solution a-1 of the composition shown above while being vigorously stirred at 60°C, a seed emulsion having an average grain size of 0.27 µm and an average AgI content of 2 mol% in an amount equivalent to 0.208 mol was added, and acetic acid and an aqueous solution of KBr were added to obtain the desired pH and pAg levels.
Then, while maintaining a pH of 7.0 and a pAg of 7.5, Solutions a-2, a-3 and a-4 were added by the triple jet method at the flow rates shown in Tables 6, 7 and 8, respectively.
After completion of the addition, the mixture was desalted and washed by ordinary methods and dispersed in an aqueous solution containing gelatin.
Electron microscopic observation revealed that this emulsion is a highly monodispersed emulsion having a coefficient of variance of grain size distribution of 11.2%, comprising nearly cubic grains having a protrusion on the {100} surface with an average grain size of 0.68 µm, which account for 92% of all silver halide grains.
Table 9 shows the grain structure of silver halide grains contained in this emulsion.
Figure 2 is an electron micrograph of a silver halide grain contained in this emulsion EM-3 of the present invention.
A comparative emulsion EM-4 was prepared in accordance with the method described in Japanese Patent O.P.I. Publication 246740/1986, 275741/1986 and 286845/1986, which comprises cubic grains having the same halogen composition, grain size distribution and average grain size as those of the aforementioned emulsion EM-3 and having no protrusion on the {100} surface in the final configuration.
The emulsions EM-3 and EM-4 thus prepared were subjected to optimum gold-sulfur sensitization and then spectrally sensitized in the green band by adding 166 mg of sensitizing dye I and 110 mg of sensitizing dye II per mol AgX. Then, TAI and 1-phenyl-5-mercaptotetrazole were added to stabilize the emulsions. Here, AgX represents silver halide.
Separately, magenta coupler M-1 at 5 x 10⁻³ mol per mol AgX, magenta coupler M-2 at 6.2 x 10⁻³ mol and the following colored magenta coupler CM-1 at 4.0 x 10⁻³ mol were dissolved in di-t-nonyl phthalate, and this solution was emulsified and dispersed in an aqueous solution containing gelatin. The resulting dispersion was added to each emulsion, followed by the addition of ordinary photographic additives such as an extender and a hardener to yield a coating solution. This coating solution was coated and dried on a subbed film base by a conventional method to yield sample Nos. 103 and 104.
Each sample was subjected to exposure and processing in the same manner as in Example 1. The results are shown in Table 10. Sensitivity is shown in the reciprocal of the exposure amount which gives a minimum density (fogging) of + 0.1, expressed in percent ratio to the sensitivity of sample No. 103 processed in the processing procedure I.
As is evident from Table 10, the sample prepared using the emulsion of the present invention showed sufficiently high sensitivity even when the developing time was short, demonstrating that the emulsion of the invention offers excellent developability and high sensitivity.

Claims

A silver halide photographic emulsion comprising polyhedral silver halide grains wherein each of crystal surfaces of each silver halide grain has an outward protrusion at the center of said furface.
An emulsion of claim 1, wherein said silver halide grain is an octahedral configuration and each of {111} surfaces thereof has an outward protrusion at the center of said surface.
An emulsion of claim 2, wherein said outward protrusion occupies not less than 50% of the area of said {111} surface.
An emulsion of claim 1, wherein said silver halide grain is a cubic configuration grain and each of {100} surfaces thereof has an outward protrusion on the center of said surface.
An emulsion of claim 4, wherein said outward protrusion occupies not less than 50% of the area of said {100} surface.
An emulsion of claims 1 and 2 to 5, wherein said silver halide grains have a monodispersed state.
An emulsion of claims 1 and 2 to 6, wherein said silver halide grains comprise silver bromide or silver bromoiodide.
An emulsion of claim 7, wherein said silver halide grains are each comprising silver bromoiodide and the relative standard deviation of iodide content of each grain is not more than 20%.
An emulsion of claims 1 or 2 to 8, wherein said silver halide grains are chemically and optically sensitized.