DE69421878T2 - Silver halide emulsion - Google Patents

Description

SCOPE OF INVENTION

The present invention relates to a silver halide emulsion useful in photography. More particularly, the invention relates to a silver halide emulsion containing tabular silver halide grains having {100} major faces.

BACKGROUND OF THE INVENTION

Japanese Patent Provisional Publication No. 51(1976)-88017, Japanese Patent No. 64(1989)-8323 and European Patent Publication No. 0534395A1 disclose silver halide emulsions containing tabular silver halide grains having {100} major faces. European Patent Publication No. 0534395A1 further discloses high chloride tabular grains shown in the photographs of Figs. 1 to 5. Referring to the figures, twinned crystal grains are remarkably observed in the photographs. Furthermore, the grains shown in the photographs have a relatively broad grain size distribution. Fig. 1, which shows a statistically reliable number of the grains, will now be described in detail.

With respect to the grains shown in Fig. 1, the ratio of twinned crystal grains to tabular grains having an aspect ratio of not less than 2 is about 11% in terms of projected areas of the grains. Further, the grain size distribution of the tabular grains having a thickness of not more than 35 µm is relatively broad. The grain size distribution of relatively large tabular grains is particularly broad, which affects the photographic property of the grains. Specifically, the relatively large grains have a distribution coefficient of more than 0.12, with the relatively large grain comprising 70% of the tabular silver halide grains in terms of the projected areas of the grains. Further, the amount of tabular silver halide grains having a square projected shape is relatively small. Specifically, about 40% of the Tabular silver halide grains have a square projected shape in that the ratio of a long side to a short side is not more than 1.4.

According to a study by the inventor of the present application, the above-mentioned properties shown in Fig. 1 of European Patent Publication No. 0534395A1 lower the sensitivity and image quality of a silver halide photographic material.

Further, Japanese Patent Provisional Publication 63(1988)-271335 discloses a silver halide emulsion containing the above-described tabular grains and acicular grains.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a silver halide emulsion containing silver chloride which is improved in sensitivity and image quality.

The present invention provides a silver halide emulsion containing silver halide grains dispersed in a dispersing medium,

wherein at least 60% of the silver halide grains, based on projected areas of the grains, are tabular grains having an aspect ratio of not less than 2, the tabular silver halide grains have a chloride content in the range of 20 to 99.99 mol%, {100} major faces and a thickness of not more than 0.35 µm, and

wherein twinned crystal grains contained in the emulsion comprise not more than 10% of the tabular silver halide grains based on projected areas of the grains, and the tabular silver halide grains are formed from grain cores having at least one separation surface with varying halide composition.

The inventor of the present application has prepared a new silver halide emulsion having the specific properties defined above. The new silver halide grains are superior to conventional tabular silver halide grains having {100} major faces in terms of sensitivity and image quality (particularly graininess).

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a photomicrograph (about 6500X) showing the silver halide grains obtained in Example 1 according to the present invention.

Fig. 2 is a photomicrograph (about 5000X) showing the silver halide grains obtained in Example 2 according to the present invention.

characters

3a (about 18000 times) and

3b (about 13,000 times) are photomicrographs showing the silver halide grains obtained in Example 3 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the present description, silver halide grains contained in emulsions are evaluated according to the available characteristics (1) to (9):

(1) a ratio of tabular grains having an aspect ratio (diameter per thickness) of not less than 2 to the total silver halide grains (%, based on projected areas of the grains);

(2) a chloride content of the tabular grains having an aspect ratio of not less than 2 (mol%);

(3) crystallographic planes of the major faces of the tabular grains having an aspect ratio of not less than 2;

(4) a tabular grain thickness having an aspect ratio of not less than 2 (µm);

(5) a ratio of twinned crystal grains to tabular grains having an aspect ratio of not less than 2 (% based on projected areas of the grains);

(6) Halide composition of the grain cores from which tabular grains having an aspect ratio of not less than 2 are formed;

(7) a distribution coefficient of relatively large tabular silver halide grains, wherein the relatively large grains comprise 70% of the tabular silver halide grains having an aspect ratio of not less than 2, based on projected areas of the grains;

(8) a ratio of specific square tabular grains to tabular silver halide grains having an aspect ratio of not less than 2, the square tabular grains having a square projected area such that a ratio of a long side to a short side is not more than 1.4 (% based on projected areas of the grains); and

(9) a ratio of specific rectangular tabular grains to tabular silver halide grains having an aspect ratio of not less than 2, the rectangular tabular silver halide grains having a rectangular projected area such that one angle is rounded compared with the other three angles (% based on projected areas of the grains).

The photographic emulsion according to the present invention is characterized in that:

(1) is at least 60%;

(2) is in the range of 20 to 99.99 mol%;

(3) are {100} principal faces;

(4) is not more than 0.35 µm;

(5) is not more than 10%; and

(6) are cores that have at least one interface with varying halide composition.

The conditions defined in the present invention are described in more detail below.

Condition (1) is calculated according to the following formula:

(1) = 100 · (total projected area of tabular grains having an aspect ratio of not less than 2 per total projected area of whole silver halide grains).

According to the present invention, the condition (1) is at least 60%, preferably at least 70%, and more preferably at least 80%.

The aspect ratio means diameter per thickness. The diameter (d) is calculated using the following formula;

d = 2x · S/π (S: total projected grain area)

Thickness means a distance between two main planes of a tabular grain.

The condition (2), namely, that the chloride content of the tabular grains is in the range of 20 to 99.99 mol%, preferably in the range of 50 to 99.9 mol%, more preferably in the range of 75 to 99.9 mol%, and particularly preferably in the range of 90 to 99.9 mol%.

As for condition (3), the tabular grains have {100} major faces. The major face means the largest crystal plane of a silver halide grain.

The condition (4), namely that the thickness of the tabular grains is not more than 0.35 µm, preferably in the range of 0.05 to 0.3 µm, and further preferably in the range of 0.05 to 0.25 µm.

In addition, the tabular silver halide grains preferably have an average aspect ratio in the range of 2 to 25, and more preferably in the range of 4 to 20.

Condition (5) is calculated using the following formula:

(5) = 100 · (total projected area of twinned crystal grains per total projected area of tabular grains having an aspect ratio of not less than 2).

According to the present invention, the condition (5) is in the range of 0 to 10%, preferably in the range of 0 to 8%, more preferably in the range of 0 to 5%, and particularly preferably in the range of 0 to 2%.

Condition (6) is described below with reference to the preparation of silver halide grains.

The photographic emulsion according to the present invention preferably has at least one of the following characteristics (7) to (9):

(7) is in the range of 0 to 0.11;

(8) is at least 47%; or

(9) is at least 10%.

Condition (7) is evaluated in the following way:

(7a) tabular silver halide grains having an aspect ratio of not less than 2 are selected from the silver halide grains;

(7b) projected areas of the tabular silver halide grains are measured;

(7c) the tabular grains are recorded in order of projected area size;

(7d) Grains having a large projected area are selected in sequence from the tabular grains until the total projected area of the selected large grains comprises 70% of the total projected area of the total tabular grains;

(7e) the diameters (d) of the selected large tabular grains are calculated using the following formula;

d = 2 · S/π (S: total projected grain area)

(7f) the mean diameters ( ) of the selected large tabular grains are calculated using the following formula; and

(di: individual diameter, calculated as above, n: number of calculated grains)

(7g) The standard deviation (σ) of the selected large tabular silver halide grains is calculated by the following formula: and

(7h) The partition coefficient (σ/ ) is obtained from the mean diameter ( ) and the standard deviation (σ).

The condition (7) is preferably in the range of 0 to 0.11, more preferably in the range of 0 to 0.09, and particularly preferably in the range of 0 to 0.06.

Condition (8) is calculated using the following formula:

(8) = 100 · (total projected area of the special square tabular grains per total projected area of tabular silver halide grains having an aspect ratio of not less than 2).

Condition (8) is preferably at least 47%, more preferably at least 50%, even more preferably at least 55%, even more preferably at least 75% and particularly preferably at least 85%.

With respect to the particular square tabular grains, the ratio of a long side to a short side is in the range of 1 to 1.4, preferably in the range of 1 to 1.3, and most preferably in the range of 1 to 1.2.

With respect to the square shape, a corner of the square may be rounded to a certain extent. The ratio of the volume incomplete by the rounded corner to the rectangular prism volume is preferably not more than 0.2, and more preferably not more than 0.1. The rectangular prism volume means a volume of a rectangular prism theoretically formed by extending edges of the grain.

In a high chloride emulsion according to the present invention, a corner tends to be primarily rounded as defined in condition (9).

Condition (9) is calculated using the following formula:

(9) = 100 · (total projected area of the special rectangular tabular grains per total projected area of tabular silver halide grains having an aspect ratio of not less than 2).

Condition (9) is preferably at least 10%, more preferably at least 15% and particularly preferably at least 35%.

The special rectangular tabular grains have such a rectangular projected shape that one angle is rounded compared to the other three angles. In other words, one corner of the rectangle is primarily rounded. The incomplete volume caused by the rounded corner is preferably twice or more, more preferably 4 times or more, and particularly preferably 8 times or more as the incomplete volume caused by another corner.

In addition, the tabular silver halide grains preferably have an average diameter in the range of 0.2 to 10 µm, and more preferably in the range of 0.3 to 5 µm. The iodide content of the tabular silver halide grains is preferably not more than 13 mol%, more preferably not more than 6 mol%, and most preferably in the range of 0 to 3 mol%.

The tabular silver halide grains in the emulsion according to the present invention are formed from grain cores having at least one interface with a changing halide composition according to the condition (6).

The tabular grains grow primarily along the direction of the edges. The primary growth is promoted by a crystal defect in the grain cores. A crystal defect in the grain cores for the formation of a tabular grain is called a spiral dislocation crystal defect. The crystal defect is formed by at least one (preferably 1 to 3, and more preferably 1 or 2) interfaces with changing halide composition in the cores. The crystal defect is preferably formed by disposing a layer of a silver halide with a low solubility (AgX₂) on a layer of another silver halide (AgX₁) with a high solubility. Accordingly, the interface with changing halide composition composition is effectively formed by a halide conversion reaction. The solubility of silver halide decreases in the order of AgCl, AgBr and Agl. Accordingly, silver halide with a higher chloride content and a lower iodide content has a higher solubility. For example, a halide composition in the grain cores has a structure of AgX₁ AgX₂ or AgX₁ AgX₄ AgX₃.

The structure can be formed by simultaneously mixing a silver (Ag) solution with a halide (X⁻) solution and discontinuously changing a halide composition of the halide solution at the interface. Further, a halide solution and a silver solution can be added to a solution of a dispersing medium to form AgX₁, and then another halide solution and a silver halide solution can be added to the medium to form a structure of AgX₁ AgX₂. The above-mentioned methods can be used in combination.

In the structure of AgX₁ AgX₂ or AgX₁ AgX₄ AgX₃, the difference in chloride content or bromide content between AgX₁ and AgX₂, AgX₁ and AgX₄, or AgX₄ and AgX₃ is preferably in the range of 25 to 100 mol%, more preferably in the range of 50 to 100 mol%, and particularly preferably in the range of 75 to 100 mol%. Alternatively, the difference in iodide content is preferably in the range of 5 to 100 mol%, more preferably in the range of 10 to 100 mol%, and particularly preferably in the range of 30 to 100 mol%. There may be differences in the chloride or bromide content and the iodide content. In such a case, the difference in chloride or bromide content is defined above, and the difference in iodide content is preferably in the range of 0 to 5 mol%. The grain cores preferably have a diameter of not more than 0.15 µm, and are more preferably in the range of 0.01 to 0.1 µm.

In the structure of AgX₁ AgX₂ or AgX₁ AgX₄ AgX₃, the molar ratio of AgX₁ : AgX₂ or AgX₁ : AgX₄ : AgX₃ can be experimentally determined to obtain the optimum embodiment of the present invention. In the structure of AgX₁ AgX₂, the layer of AgX₂ preferably has such a thickness that on average one lattice of AgX₂ covers the surface of AgX₁. The thickness of the AgX₂ layer is further preferably in the range of an average of three lattices to 10⁴ mol of the AgX₁ layer. In the structure of AgX₁ AgX₄ AgX₃, the amount of the AgX₄ layer is preferably in the range of 0.01 to 10 mol, and more preferably in the range of 0.1 to 3 mol, based on 1 mol of the AgX₁ layer. The crystal defect in grain cores is more frequently formed by increasing the difference of the pitch in a halide content.

The structure of AgX₁ AgX₄ AgX₃ can also be formed by forming AgX₁ nuclei, adding a 4-salt solution to the nuclei to form a structure of AgX₁ AgX₄ according to a halide conversion reaction, and then an Ag⁺ salt solution and an X₃ salt solution to form the nuclei. The X₄⁻ salt preferably satisfies the condition that the solubility of AgX₄ is lower than that of AgX₁. The amount of X₄⁻ contained in the solution is preferably in the range of 0.01 to 10 mol, and more preferably in the range of 0.03 to 3 mol, based on 1 mol of AgX₁. The amount of AgX₄ based on the amount of AgX₁ can be reduced by increasing the difference in the halide composition distance.

In the most preferred embodiment of the present invention, the differences in chloride content and bromide content are in the range of 25 to 100 mol%, more preferably in the range of 50 to 100 mol% and most preferably in the range of 75 to 100 mol%.

The structure of AgX₁ AgX₄ AgX₃ is particularly preferred.

When the nuclei are formed, the atmosphere of the dispersing medium solution is adjusted to form {100} faces. When the nuclei are formed in the presence of an excess amount of chloride, the usual conditions (pCl: 0.8 to 3.0, pH 2 to 8) are under the atmosphere for forming {100} faces. The frequency of formation of the crystal defect is increased by increasing the pH (in the range of 1 to 7) and pCl (= -log [Cl -mol per liter]). When numerous crystal defects are introduced into a silver halide grain, thick grains are increased in the finally obtained silver halide emulsion. Accordingly, the number of crystal defects is appropriately adjusted. The conditions for forming the crystal defects are adjusted to obtain the silver halide emulsion according to the present invention. The separation surface surface having varying halide composition is uniformly formed in each of the grains to achieve the embodiment of the present invention.

A dispersing medium for forming nuclei is preferably used in the form of a 0.1 to 10 wt% solution, and more preferably a 0.3 to 5 wt% solution. The solution of the dispersing medium is preferably adjusted to pH 1 to 10, and more preferably to pH 2 to 8. The temperature of the solution is preferably adjusted to 10 to 80°C, and more preferably to 30 to 60°C. When the temperature is 30°C or lower, the frequency of formation of the crystal defect is lowered. A certain temperature is required for formation of the crystal defect. The excess bromide content is preferably not more than 10-2 mol per liter, and more preferably not more than 10-2.5 mol per liter. The excess chloride content is preferably in the range of 0.8 to 3.0 pCl and more preferably in the range of 1.2 to 2.8 pCl.

The dispersing medium may be added to a silver salt solution and/or a halide salt solution to form uniform grain cores. The concentration of the dispersing medium in the silver salt or the halide salt solution is preferably not less than 0.1 wt%, more preferably in the range of 0.1 to 2 wt%, and particularly preferably in the range of 0.2 to 1 wt%.

The dispersing medium is preferably gelatin, which more preferably has a molecular weight in the range of 3,000 to 60,000 and most preferably in the range of 8,000 to 40,000.

The silver salt solution and the halide solution are preferably added through a porous addition system. The system preferably has 3 to 10¹⁵ pores, and more preferably 30 to 10¹⁵ pores. The porous system is described in Japanese Patent Provisional Publications No. 3(1991)-21339 and No. 4(1992)-193336 and Japanese Patent Application No. 4(1992)-40283. The frequency of formation of the crystal defect is increased by lowering the methionine content in the gelatin. Gelatin is preferably selected in terms of the methionine content in the range of 1 to 60 µmol per 1 g of gelatin.

A ratio of twin crystal grains can be lowered by decreasing the excess halide salt solution or the excess silver salt solution in the formation of the grain cores. The ratio is increased by decreasing the concentration of the dispersing medium or by worsening the stirring conditions. The conditions can be experimentally determined to obtain silver halide grains of the present invention.

A spiral dislocation crystal defect is formed by forming the interface of a changing halide composition and a halide conversion at the interface in the formation of the grain nuclei. After the crystal defect is formed, the silver halide grains are ripened as the temperature is increased at least 10°C and further preferably 20 to 70°C. The ripening atmosphere is preferably set to form {100} faces. The ripening conditions are selected from the above-mentioned conditions for the formation of the grain nuclei. In the ripening, tabular grains primarily grow and non-tabular grains are decreased. In this way, the ratio of tabular grains is increased. The ripening rate can be increased by increasing the pH in the range of 1 to 6 and by increasing the Cl- content in the range of 1 to 3 pCl.

After the ratio of tabular grains is increased, solutes are added to the grains to further grow the tabular grains. The solutes may be added by an ion addition method (adding Ag+ solution and X- solution), a fine grain addition method (adding fine silver halide grains formed beforehand), or a combination thereof. The tabular grains grow primarily along the direction of the edges under the conditions that the concentration of supersaturation is lowered as long as the tabular grains are not subjected to Ostwald ripening. Accordingly, the concentration should be precisely adjusted to a low supersaturation concentration. In order to precisely adjust the concentration, the fine grain addition method is preferably used. The method is also advantageous for making the tabular grains grow uniformly.

In the fine grain addition method, the fine silver grains have an average particle size of not more than 0.15 µm, preferably not more than 0.1 µm and are ter preferably in the range of 0.06 to 0.006 µm. The fine grains are subjected to Ostwald ripening to grow tabular grains. The fine grains are continuously or discontinuously added to the emulsion. For example, the fine grains can be continuously formed by mixing an AgNO₃ solution and an X⁻ salt solution in a vessel located near a reaction vessel and immediately and continuously adding them to the reaction vessel. Further, the fine grains can be continuously formed in another vessel by a batch method and continuously or discontinuously adding them to a reaction vessel. The fine grains are used in the form of an emulsion or a dry powder. The dry powder of the fine grains can be dispersed in water before addition.

The conditions in the fine grain addition method are preferably set so that the fine grains are dissolved within 20 minutes, more preferably within 10 seconds to 10 minutes. As the time for dissolving the fine grains is increased, the grains are ripened and the grain size is increased. Accordingly, the time for dissolving the fine grains is preferably shortened. For example, the grains are gradually added to the reaction vessel. It is preferred that the fine grains contain substantially no multi-twin crystal grains. The term multi-twin crystal means a grain having two or more twin planes. It is also preferred that the fine grains contain substantially no single-twin crystal grains. It is further preferred that the fine grains have substantially no spiral dislocation. The term "substantially containing (or having) no" means that the proportion of the specific grains is not more than 5% (preferably not more than 1% and more preferably not more than 0.1%).

The halide composition of the fine grains is preferably AgCl, AgBr, AgBrI (wherein the I- content is preferably not more than 10 mol%, and more preferably not more than 5 mol%) or a mixture thereof (solid solution). The halide compositions of the fine grains are described in Japanese Patent Application No. 4(1992)-214109.

For the formation of grain nuclei, grain ripening and grain growth, various dispersing media are available for a conventional silver halide emulsion. Gelatin is preferably used as the dispersing medium. The methionine content of the gelatin is preferably in the range of 0 to 50 µmol, and more preferably in the range of 0 to 30 µmol. When gelatin having a low methionine content is used in grain ripening or grain growth, thin tabular grains having a uniform grain size distribution are formed. Such tabular grains are preferred. Furthermore, a synthetic polymer is available as the dispersing medium. The synthetic polymers are described in Japanese Patent Publication No. 52(1977)-16365, Journal of Japan Photographic Society, Vol. 29 (1), 17, 22, (1966), Vol. 30 (1), 10, 19 (1967), Vol. 30 (2), 17 (1967) and Vol. 33 (3), 24 (1967). A crystal habit adjuster is also available. The adjuster is described in European Patent Publication No. 0534395A1. The concentration of the dispersing medium is preferably in the range of 10⁻¹ to 10⁻⁶ mol per liter. The concentration of the adjuster is preferably in the range of 10⁻¹ to 10⁻⁶ mol per liter. and more preferably in the range of 10⁻² to 10⁵ mol per liter. The medium and agent may be added at all stages from nucleation to grain growth. A dispersing medium may be used in addition to the medium previously present in an emulsion. A dispersing medium may also be added to the emulsion after the previously present medium has been removed from the emulsion.

In the grain ripening and growth, the concentration of the dispersing medium, pH, the concentration of the X- salt solution, the addition methods of the Ag+ solution and the X- solution (porous addition system and dispersing medium) can be adjusted with reference to the conditions for forming the nuclei described above. The temperature for the grain ripening and growth is preferably not lower than 25°C, and more preferably in the range of 30 to 80°C. The atmosphere of the grain growth is also preferably adjusted to form {100} faces.

The atmosphere for forming {100} faces during nuclei formation, grain maturation or grain growth is adjusted so that 60 to 100% (preferably 80 to 100% and more preferably 90 to 100%) of the grain surface is {100} faces The ratio of the {100} faces can be measured, for example, using a method described in T. Tani, Journal of Imaging Science, Volume 29, 165 (1985).

The silver halide emulsion of the present invention can be prepared by another method. For example, the grains can be formed by (a) forming the nuclei, (b) selectively growing tabular grain under a low supersaturated concentration to increase the size difference between the tabular grains and non-tabular grains, and (c) dissolving the non-tabular grains by Ostwald ripening. The grains can also be formed by (a) forming the nuclei and (b) growing tabular grain under conditions of a supersaturated concentration and Ostwald ripening at a temperature increased by 10°C or more. As described above, the tabular grains grow while non-tabular grains are dissolved.

The tabular grains mainly contain silver chloride. Various halide compositions can be introduced into the grain structures. For example, the grains have a multiple structure described in Japanese Patent Application No. 5(1993)-96250. The grain structures include embodiments having a higher Br⁻ and/or I⁻ content on the surface of the grains, along the edges of the grains and on the major faces of the grains. The high Br⁻ content is preferably not less than 1 mol% higher than the Br⁻ content in the other part, more preferably 3 to 100 mol% higher, and particularly preferably 5 to 70 mol% higher. The high I⁻ content is preferably not less than 1 mol% higher than the I⁻ content in the other part, more preferably 2 to 30 mol% higher, and particularly preferably 3 to 10 mol% higher.

The tabular grains have {100} major faces. Ag+ and X- are arranged alternately on the major faces. When a spectral sensitizing dye is adsorbed on the faces, the dye can be directly reacted with Ag+. In the silver halide grains, Ag+ forms a conductive band and X- forms an electron-loaded band. Accordingly, the lowest free level of the dye can be directly reacted with the conductive band of Ag+. Therefore, the efficiency of electron injection is high when the dye is excited with light. In this way, the efficiency of spectral sensitization is improved.

On the other hand, a sensitizing dye adsorbed on tabular grains with {111} major faces reacts with the conductive band of Ag+ through an X- layer. The surface of the X- layer has an excess negative charge because the chemical bond at the surface is broken. The electron is injected across the barrier of the negative charge. Therefore, the efficiency of electron injection is low. In this way, the efficiency of spectral sensitization is low when tabular grains with {111} major faces are used.

For the reasons mentioned above, the silver halide grains having {100} major faces are superior to the conventional grains having {111} major faces. Further, the conventional tabular grains having {111} major faces have a tendency to inherent desensitization. When the conventional grains are excited with light within the inherent region, the positive hole formed tends to be captured by the highest occupied orbit of the dye through the X- layer. The captured positive hole is again combined with the excited electron to reduce the inherent desensitization. The positive hole is easily trapped with the X- layer of the {111} major faces. Such inherent desensitization hardly occurs in the silver halide grains having {100} major faces.

Epitaxial grains can be formed from the obtained silver halide grains. Further, grains having dislocation lines within the grains can be formed by using the obtained grains as grain cores. Further, the obtained grains can be used as a substrate for other grains formed by forming silver halide layer on the substrate. The halide composition of the layer is different from that of the substrate. The other various silver halide grains can be formed from the grains used in the present invention.

A grain of chemical sensitization is usually introduced into the silver halide grains. The location and number (per cm²) of the chemical sensitization grains are preferably adjusted. The adjustment is described in Japanese Patent Provisional Publications No. 64(1989)-74540, No. 1(1989)-201651, No. 2(1990)- 838, No. 2(1990)-146033 and No. 3(1991)-121445 and in Japanese Patent Applications No. 3(1991)-73266, No. 3(1991)-140712 and No. 3(1991)-115872.

A flat internal latent image emulsion can be prepared using the tabular grains as a core. A core/shell emulsion can also be prepared. These emulsions are described in Japanese Patent Provisional Publications No. 59(1984)-133542 and No. 63(1988)-151618 and in U.S. Patents No. 3,206,313, No. 3,317,322, No. 3,761,276, No. 4,269,927 and No. 3,267,778.

The silver halide emulsion of the present invention can be mixed with one or more other emulsions. The mixing ratio of the emulsion of the invention to other emulsions can be suitably adjusted within the range of 1.0 to 0.01.

There is no specific restriction on additives used from grain formation to emulsion coating. Examples of the additives include silver halide solvents, dopants for silver halide grains (such as group VIII metal compounds or other metals, chalcogen compounds and SCH compounds), dispersants, antifoggants, spectral sensitizing dyes (such as blue, green, red, infrared, panchromatic or orthochromatic sensitizers), supersensitizers, chemical sensitizers (such as sulfur sensitizers, selenium sensitizers, tellurium sensitizers, gold or other noble metals such as group VIII metal sensitizers, phosphorus compounds, rhodane compounds or reduction sensitizers), fogging agents, emulsion precipitants, surfactants, hardeners, dyes, color image forming agents, additives for color photography, soluble silver salt, latent image stabilizer, developing agent (such as hydroquinone compounds), agents to prevent desensitization by printing and matting agents. Two or more additives (such as chemical sensitizers) may be used in combinations.

The silver halide grains and emulsion of the present invention are available in various conventional photographic materials. Examples of the photographic materials include black-and-white photographic materials (such as X-ray sensitive materials, photosensitive materials for printing, pho tographic papers, negative films, microfilms, direct positive photosensitive materials, ultrafine grain dry photosensitive materials for LSI photomasks, shadow masks or liquid crystal masks) and color photographic materials such as negative films, color photographic papers, reversal films, direct positive color photosensitive materials, silver dye bleaching type photographic materials). The silver halide emulsion is also available in diffusion transfer photosensitive materials (such as color diffusion transfer element, silver salt diffusion transfer element), heat developable (black/white or color) photosensitive materials, high density digital recording photosensitive materials and holographic photosensitive materials.

In the photographic material, the coating amount of silver is preferably not less than 0.01 g/m². There is no particular limitation on the structure of the photographic material (such as the layer structure, the molar ratio of silver to color forming agents, the amounts of silver in the layers), the conditions for exposure and development, the equipment for preparing the photographic materials and the dispersing methods of additives. There are numerous conventional structures, additives, methods, equipment and conditions.

The conventional structures, additives, methods, equipment and conditions are described in Research Disclosure, Volume 176, No. 17643 (December 1978), and Volume 307, No. 307105 (November 1989); Duffin, Photographic Emulsion Chemistry, Focal Press, New York (1966); EJ Birr, Stabilization of Photographic Silver Halide Emulsions, Focal Press, London (1974); TH James, The Theory of Photographic Process, 4th edition, Macmillan, New York (1977); P. Glafkides, Chimie et Physique Photographiques, 5th edition, Edition de l'usine Nouvelle, Paris (1987), and 2nd edition, Paul Montel, Paris (1957); VL Zelikman et al., Making and Coating Photographic Emulsion, Focal Press (1964); KR Hollister, Journal of Imaging Science, Volume 31, pages 148 to 156 (1987); JE Maskasky, Journal of Imaging Science, Volume 30, pages 247 to 254 (1986), Volume 32, pages 160 to 177 (1988), Volume 33, pages 10 to 13 (1989); Frieser et al.,. The fundamentals of photographic processes with silver halides, Akademische Verlagsgesellschaft, Frankfurt (1968); Journal of Japan Chemical Society, pages 18 to 27, December (1984); and Journal of Japan Photographic Society, Volume 49, pages 7 to 12 (1986), Volume 52, pages 144 to 166 (1989), Volume 52, pages 41 to 48 (1989).

The photographic materials are also disclosed in Japanese Patent Provisional Publications No. 58(1983)-113926, No. 58(1983)-113927, No. 58(1983)-113926, No. 59(1984)-90841, No. 58(1983)-111936, No. 62(1987)-99751, No. 60(1985)-143331, No. 60(1985)143332, No. 61(1986)-14630, No. 62(1987)-6251, No. 63(1988)-220238, No. 63(1988)-151618, No. 63(1988)-281149, No. 59(1984)-133542, No. 59(1984)45438, No. 62(1987)-269958, No. 63(1988)-305343, No. 59(1984)-1 42539, No. 62-(1987)-253159, No. 62(1987)-266538, No. 63(1988)-107813, No. 64(1989)-26839, No. 62(1987)-157024, No. 62(1987)-192036, No. 1 (1989)-297649, No. 2(1990)-127635, No. 1 (1989)- 158429, No. 2(1990)42, No. 2(1990)-24643, No. 1(1989)-146033, No. 2(1990)-838, No. 1990)-28638, No. 3(1991)-109539, No. 3(1991)-175440, No. 3(1991)-121443, No. 2(1990)-73245, No. 3(1991)-119347, in U.S. Patent Nos. 4,636,461, No. 4,942,120, No. 4,269,927, No. 4,900,652, No. 4,975,354, European Patent Publication No. 0355568A2 and Japanese Patent Applications No. 2(1990)-326222, No. 2(1990)415037, No. 2(1990)-266615, No. 2(1990)43791, No. 3(1991)-160395, No. 2(1990)-142635, No. 3(1991)-146503 and No. 4(1992)-77261.

The silver halide emulsion of the present invention is advantageously used in photographic materials described in Japanese Patent Provisional Publications No. 62(1987)-269958, No. 62(1987)-266538, No. 63(1988)-220238, No. 63(1988)- 305343, No. 59(1984)-142539, No. 62(1987)-253159, No. 1(1989)-131541, No. 1(1989)- 297649, No. 2(1990)-42, No. 1(1989)-158429, No. 3(1991)-226730, No. 4(1992)-151649, Japanese Patent Application No. 4(1992)-179961 and European Patent Publication No. 0508398A1.

EXAMPLE 1

1200 ml of gelatin solution (containing 18 g of deionized alkali-treated bone gelatin with a methionine content of about 40 umol/g, pH: 4.3) were introduced into a reaction vessel. At the same time, 12 ml of Ag-1 solution (containing 20 g of silver nitrate, 0.8 g of the above-mentioned gelatin, 0.2 ml of 1 N nitric acid in 100 ml) and 12 ml of X-1 solution (containing 16.9 g of sodium chloride, 0.8 g of the above-mentioned gelatin, 0.3 ml of 1 N sodium hydroxide solution in 100 ml) at a feed rate of 24 ml per minute while keeping the temperature at 43 °C. After the mixture was stirred for 2 minutes, to the mixture were simultaneously added 19 ml of Ag-2 solution (containing 2 g of silver nitrate, 0.8 g of the above-mentioned gelatin, 0.2 ml of 1 N nitric acid in 100 ml) and 19 ml of X-2 solution (containing 1.4 g of potassium bromide, 0.8 g of the above-mentioned gelatin, 0.2 ml of 1 N sodium hydroxide solution in 100 ml) at a feed rate of 31 ml per minute. After the mixture was stirred for 2 minutes, 36 ml of Ag-1 solution and 36 ml of X-1 solution were added to the mixture simultaneously at a feed rate of 48 ml per minute.

In this way, grain nuclei were formed. The structure of the nuclei is AgCl AgBr AgCl. The difference in chloride content or bromide content between AgX₁ and AgX₄ or AgX₄ and AgX₃ was 100%.

Further, 20 ml of NaCl-1 solution (containing 10 g of sodium chloride in 100 ml) was added to the grain kernels. The mixture was adjusted to pH 4.8 and heated to 75°C. After the emulsion was ripened for 20 minutes, the emulsion was cooled to 60°C and adjusted to pH 5.0. Then, Ag-3 solution (containing 10 g of silver nitrate in 100 ml) and X-3 solution (containing 3.6 g of sodium chloride in 100 ml) were added to the emulsion by a controlled double jet method while maintaining the silver potential at 130 mV. The feed rate at the start of the addition was 7 ml per minute. The rate was gradually increased by 0.1 ml per minute. Finally, 400 ml of Ag-3 solution was added to the emulsion.

After a precipitant was added to the emulsion, the emulsion was cooled to 30°C. The emulsion was precipitated and washed with water. After a gelatin solution was added to the emulsion, the obtained emulsion was adjusted to pH 6.2 and pCl 3.0 at 38°C. A part of the emulsion was sampled, and a copy of the grains of the emulsion was made. The copy was observed through a transparent electron microscope (TEM). The micrograph (about 6500 times) of the silver halide grains is shown in Fig. 1. The properties of the grains are described below.

(1) The ratio of tabular grains having an aspect ratio (diameter per thickness) of not less than 2 to the whole silver halide grains (% based on projected areas of the grains) is 91%.

(2) The chloride content of the tabular grains having an aspect ratio of not less than 2 (mol%) is 99.25%.

(3) The tabular grains having an aspect ratio of not less than 2 have {100} major faces.

(4) The thickness of the tabular grains having an aspect ratio of not less than 2 (µm) is 0.29 µm.

(5) The ratio of twinned crystal grains to tabular grains having an aspect ratio of not less than 2 (% based on projected areas of the grains) is 0%.

(6) The grain cores from which tabular grains with an aspect ratio of not less than 2 are formed have two interfaces with varying halide composition.

(7) The distribution coefficient of relatively large tabular silver halide grains, the relatively large grains comprising 70% of the tabular silver halide grains having an aspect ratio of not less than 2, based on projected areas of the grains, is 0.059.

(8) The ratio of specific square tabular grains to tabular silver halide grains having an aspect ratio of not less than 2, the square tabular grains having a square projected area such that a ratio of a long side to a short side is not more than 1.4 (% based on projected areas of the grains), is 94%.

Furthermore, the average aspect ratio of tabular grains having an aspect ratio of not less than 2 is 3.4. The average diameter of tabular grains having an aspect ratio of not less than 2 is 1.0 µm.

EXAMPLE 2

Into a reaction vessel was placed 1200 ml of gelatin solution (containing 20 g of deionized alkali-treated gelatin, pH: 4.3). Into the vessel were added 12 ml of Ag-1 solution and 12 ml of X-1 solution at a feed rate of 50 ml per minute while keeping the temperature at 41°C. After the mixture was stirred for 2 minutes, 22 ml of Ag-2 solution and 22 ml of X-2 solution were added to the mixture at a feed rate of 62 ml per minute. After the mixture was stirred for 2 minutes, 38 ml of Ag-1 solution and 38 ml of X-1 solution were added to the mixture at a feed rate of 50 ml per minute.

In this way, grain nuclei were formed. The structure of the nuclei is AgCl AgBr AgCl. The difference in chloride content or bromide content between AgX₁ and AgX₄ or AgX₄ and AgX₃ was 100%.

Further, to the grain cores, 23 ml of NaCl-1 solution was added. The mixture was adjusted to pH 5.0 and heated to 75°C. After the emulsion was ripened for 20 minutes, the emulsion was cooled to 65°C. A silver chloride fine grain emulsion (average grain size: 0.08 µm) was added at an AgCl feed rate of 4 x 10-3 mol per minute over 10 minutes. Further, the fine grain emulsion was added to the emulsion over 70 minutes at an accelerating feed rate of 10-4 mol per minute. After the addition, the emulsion was ripened for 8 minutes.

After a precipitating agent was added to the emulsion, the emulsion was cooled to 30ºC. The emulsion was precipitated and washed with water. After a gelatin solution was added to the emulsion, the resulting emulsion was adjusted to pH 6.2 and pCl 3.0 at 38ºC. A portion of the emulsion was sampled and a copy of the grains of the emulsion was prepared. The copy was observed through a transparent electron microscope (TEM). The photomicrograph (about 5000X) of the silver halide grains is shown in Fig. 2. The properties of the grains are described below.

(1) The ratio of tabular grains having an aspect ratio (diameter per thickness) of not less than 2 to the total silver halide grains (%, based on projected areas of the grains) is 92%.

(2) The chloride content of the tabular grains having an aspect ratio of not less than 2 (mol%) is 99.59%.

(3) The tabular grains having an aspect ratio of not less than 2 have {100} major faces.

(4) The thickness of the tabular grains having an aspect ratio of not less than 2 (µm) is 0.22 µm.

(5) The ratio of twinned crystal grains to tabular grains having an aspect ratio of not less than 2 (% based on projected areas of the grains) is 0%.

(6) The grain cores from which tabular grains having an aspect ratio of not less than 2 are formed have two interfaces with varying halide composition.

(7) The distribution coefficient of relatively large tabular silver halide grains, the relatively large grains comprising 70% of the tabular silver halide grains having an aspect ratio of not less than 2, based on projected areas of the grains, is 0.077.

(8) The ratio of special square tabular grains to tabular silver halide grains having an aspect ratio of not less than 2, the square tabular grains having a square projected area such that a ratio of a long side to a short side is not more than 1.4 (% based on projected areas of the grains) is 82%.

Furthermore, the average aspect ratio of tabular grains having an aspect ratio of not less than 2 is 4.5. The average diameter of tabular grains having an aspect ratio of not less than 2 is 1.0 µm.

EXAMPLE 3

After grain formation in Example 2, the emulsion was heated to 72°C. The emulsion was further ripened for 10 minutes. A precipitating agent was added to the emulsion, and the emulsion was cooled to 30°C. The emulsion was precipitated and washed with water. After a gelatin solution was added to the emulsion, the resulting emulsion was adjusted to pH 6.2 and pCl 3.0 at 38°C. A part of the emulsion was sampled, and a copy of the grains of the emulsion was prepared. The copy was observed through a transparent electron microscope (TEM). It was found that about 38% (in terms of projected area) of the tabular grains having an aspect ratio of not less than 2 had the specific structures shown in Figs. 3a and 3b.

COMPARISON EXAMPLE 1

Silver halide grains were formed in the same manner as in Example 11B of European Patent Publication No. 0534395A1. A precipitating agent was added to the emulsion, and the emulsion was cooled to 30°C. The emulsion was precipitated and washed with water. After a gelatin solution was added to the emulsion, the resulting emulsion was adjusted to pH 6.2 and pCl 3.0 at 38°C. A part of the emulsion was sampled, and a copy of the grains of the emulsion was made. The copy was observed through a transparent electron microscope (TEM). It was found that the shapes of the grains are similar to those shown in Fig. 5 of European Patent Publication No. 0534395A1. The properties of the grains are described below.

(1) The ratio of tabular grains having an aspect ratio (diameter per thickness) of not less than 2 to the total silver halide grains (% based on projected areas of the grains) is 65%.

(2) The chloride content of the tabular grains having an aspect ratio of not less than 2 (mol%) is 100%.

(3) The tabular grains having an aspect ratio of not less than 2 have {100} major faces.

(4) The thickness of tabular grains having an aspect ratio of not less than 2 (µm) is 0.13 µm.

(5) The ratio of twinned crystal grains to tabular grains having an aspect ratio of not less than 2 (% based on projected areas of the grains) is 19%.

(6) The grain cores from which tabular grains having an aspect ratio of not less than 2 are formed do not have interfaces with varying halide composition.

(7) The distribution coefficient of relatively large tabular silver halide grains, the relatively large grains comprising 70% of the tabular silver halide grains having an aspect ratio of not less than 2, based on projected areas of the grains, is 0.17.

(8) The ratio of specific square tabular grains to tabular silver halide grains having an aspect ratio of not less than 2, the square tabular grains having a square projected area such that a ratio of a long side to a short side is not more than 1.4 (% based on projected areas of the grains), is 53%.

Furthermore, the average aspect ratio of tabular grains having an aspect ratio of not less than 2 is 10.0. The average diameter of tabular grains having an aspect ratio of not less than 2 is 1.3 µm.

EVALUATION OF EMULSIONS

The emulsions of Examples 1 to 3 and Comparative Example 1 were sensitized in the following manner.

After the emulsions were heated to 40°C, the following spectral sensitizing dye was adsorbed onto the silver halide grains. The amount of the dye was 65% of the saturation amount. After the emulsions were further heated to 55°C, a sodium chloride solution was added to the emulsion to adjust pCl to 2.0. Then, hypo- (2 x 10-5 mol per 1 mol of silver) and chloroauric acid (10-5 mol per 1 mol of silver) were added to the emulsions. After the emulsions were ripened, the following antifogging agent (10-3 mol per 1 mol of silver) was added to the emulsions. The emulsions were then cooled to 40°C. (Sensitizing dye) (Antifogging agent)

A viscous agent and a coating aid were added to the emulsions. Each of the emulsions and a protective layer were coated on a triacetyl cellulose film support. The film was dried to obtain samples.

The coated samples were exposed through a minus blue filter (transmitted light of 520 nm or more) for 10-2 minutes. The samples were developed and immersed in a development stop bath and then in a fixing solution. The samples were then washed with water and dried. The photographic quality was evaluated as speed per grain. The quality is improved by increasing the speed value or by decreasing the grain value.

It was found that the evaluation of

Example 1 115

Example 2 118

Example 3 121

Comparison example 1 100

Thus, the superior quality of the present invention was confirmed.

EXAMPLE 4

In a reaction vessel, 1200 ml of gelatin solution (containing 25 g of deionized alkali-treated bone gelatin with a methionine content of about 30 µmol/g, pH: 4.3) was placed. Into the vessel were simultaneously added Ag-41 solution (containing 20 g of silver nitrate in 1.00 ml) and X-41 solution (containing 16.9 g of sodium chloride and 0.8 g of the above-mentioned gelatin in 100 ml) at a feed rate of 50 ml per minute for 20 seconds while maintaining the temperature at 40ºC. After the mixture was stirred for 30 seconds, 53 mL of X-42 solution (containing 0.73 g of potassium bromide and 0.36 g of sodium chloride in 100 mL) was added to the mixture at a feed rate of 60 mL per minute. After the mixture was stirred for 2 minutes, Ag-41 solution and X-41 solution were simultaneously added to the mixture at a feed rate of 50 mL per minute for 40 seconds.

In this way, grain nuclei were formed. The structure of the nuclei is AgCl AgBr0.5Cl0.5 AgCl. The difference in chloride content or bromide content between AgX₁ and AgX₄ was 50%.

Further, 13 ml of NaCl-1 solution was added to the grain kernels. The mixture was adjusted to pH 5.0 and heated to 75ºC. After the emulsion was ripened for 20 minutes, Ag-3 solution and X-3 solution were added to the emulsion by a controlled double jet method while the silver potential was maintained at 140 mV. The feed rate at the start of the addition was 7 ml per minute. The rate was gradually increased by 0.1 ml per minute. Finally, 400 ml of Ag-3 solution was added to the emulsion.

A portion of the emulsion was sampled and a replica of the grains of the emulsion was prepared. The replica was observed through a transparent electron microscope (TEM). The properties of the grains are described below.

(1) The ratio of tabular grains having an aspect ratio (diameter per thickness) of not less than 2 to the total silver halide grains (%, based on projected areas of the grains) is 93%.

(2) The chloride content of the tabular grains having an aspect ratio of not less than 2 (mol%) is 99.39%.

(3) The tabular grains having an aspect ratio of not less than 2 have {100} major faces.

(4) The thickness of tabular grains having an aspect ratio of not less than 2 (µm) is 0.2 µm.

(5) The ratio of twinned crystal grains to tabular grains having an aspect ratio of not less than 2 (% based on projected areas of the grains) is 0%.

(6) The grain cores from which tabular grains with an aspect ratio of not less than 2 are formed have two interfaces with varying halide composition.

(7) The distribution coefficient of relatively large tabular silver halide grains, the relatively large grains comprising 70% of the tabular silver halide grains having an aspect ratio of not less than 2, based on projected areas of the grains, is 0.06.

(8) The ratio of specific square tabular grains to tabular silver halide grains having an aspect ratio of not less than 2, the tabular silver halide grains having such a square projected area that a ratio of a long side to a short side is not more than 1.4 (% based on projected areas of the grains), is 95%.

Furthermore, the average aspect ratio of tabular grains having an aspect ratio of not less than 2 is 5.5. The average diameter of tabular grains having an aspect ratio of not less than 2 is 1.2 µm.

After the addition was completed, the emulsion was ripened for 5 minutes. A precipitant was added to the emulsion. A coating sample was prepared from the emulsion in the same manner as in Examples 1 to 3 and Comparative Example 1. The samples were then evaluated in the same manner as in the sensitivity measurement of Examples 1 to 3 and Comparative Example 1. As a result, the evaluation of Example 4 (sensitivity per grain) was 125.

Claims (9)

1. A silver halide emulsion comprising silver halide grains dispersed in a dispersing medium, wherein at least 60% of the silver halide grains, based on projected areas of the grains, are tabular grains having an aspect ratio of not less than 2, the tabular silver halide grains have a chloride content in the range of 20 to 99.99 mol%, {100} major faces and a thickness of not more than 0.35 µm, and wherein twinned crystal grains contained in the emulsion comprise not more than 10% of the tabular silver halide grains based on projected areas of the grains, and the tabular silver halide grains are formed from grain cores having at least one interface with varying halide composition. 2. The silver halide emulsion as claimed in claim 1, wherein the tabular silver halide grains have a grain size distribution such that relatively large grains have a distribution coefficient of not more than 0.11, the relatively large grains comprising 70% of the tabular silver halide grains, based on projected areas of the grains. 3. The silver halide emulsion as claimed in claim 1, wherein at least 47% of the tabular silver halide grains, based on projected areas of the grains, have a square projected shape such that a ratio of a long side to a short side is not more than 1.4. 4. The silver halide emulsion as claimed in claim 1, wherein at least 10% of the tabular silver halide grains, based on projected areas of the grains, have a rectangular projected shape such that one angle is rounded in comparison with the other three angles. 5. The silver halide emulsion as claimed in claim 1, wherein at least 70% of the silver halide grains, based on projected areas of the grains, are tabular grains. 6. The silver halide emulsion as claimed in claim 1, wherein the tabular silver halide grains have a chloride content in the range of 50 to 99.9 mol%. 7. The silver halide emulsion as claimed in claim 1, wherein the tabular silver halide grains have a thickness in the range of 0.05 to 0.30 µm. 8. The silver halide emulsion as claimed in claim 1, wherein the tabular silver halide grains have an aspect ratio in the range of 2 to 25. 9. The silver halide emulsion as claimed in claim 1, wherein twinned crystal grains contained in the emulsion comprise not more than 8% of the tabular silver halide grains based on projected areas of the grains.