DE68924693T2 - SILVER HALIDE PHOTOGRAPHIC MATERIAL AND METHOD FOR PRODUCING THE SAME. - Google Patents

Description

TECHNICAL AREA

The invention relates to a silver halide photographic material useful in the field of photography, and a method for producing a completely homogeneous phase of the halide composition inside the silver halide grains. More particularly, the invention relates to a photographic light-sensitive material using a silver halide emulsion containing silver halide grains, wherein the microscopic halide distribution inside each mixed silver halide crystal is completely homogeneous and wherein preferably the inside of the silver halide crystals does not contain reduced silver generated during the formation of the silver halide grains.

STATE OF THE ART

Recently, the requirement for improving the performance of silver halide photographic materials has become more and more serious, and in particular, the increase in sensitivity while suppressing the reduction in graininess and sharpness as low as possible and the increase in development speed have been desired.

In order to meet these requirements, the development of a so-called core/shell type emulsion having different halide composition between the interior and the surface layer of the silver halide grains was carried out. In a silver iodobromide emulsion, it is disclosed that the interior (core) of the grains consists of silver iodobromide with a high silver iodide content and the surface (shell) is composed of silver iodobromide having a lower silver iodide content or pure silver bromide. These techniques are disclosed, for example, in JP-A-57-15432, JP-A-60-14331, JP-A-60-138538, JP-A-60-147727, JP-A-61-245151 and JP-A-61-14364 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Also, a core/shell emulsion in which the surface of the grains is composed of silver chloride or silver chlorobromide is disclosed in JP-A-58-9137, JP-A-58-9537, JP-A-59-48755, JP-A-61-215540 and JP-A-62-69621. Furthermore, the core/shell emulsion in which the silver iodide content of the surface of the grains is higher than that in the interior thereof is disclosed in JP-A-56-78831 and JP-A-62-19843.

In these core/shell emulsions, the increase in light absorption, the increase in the efficiency for the formation of the latent image by forming the layered structure of core and shell and the improvement in the development speed are achieved, on the other hand, in these grains, it has been confirmed that there exists a microscopic heterogeneous distribution of halide in the grains, which disturbs the movement of the electrons generated by exposure to reduce the efficiency for the formation of the latent image, and an improvement therefor has been demanded.

In general, silver halide grains are produced by reacting an aqueous silver salt solution and an aqueous halide solution in an aqueous colloid solution in a reaction vessel. For this purpose, a single jet method in which an aqueous solution of a protective colloid such as gelatin and an aqueous halide solution are introduced into a vessel and an aqueous silver salt solution is added thereto with stirring for a certain period of time, and a double jet method in which an aqueous gelatin solution is introduced into a reaction vessel and an aqueous halide solution and an aqueous silver salt solution are stirred for a certain period of time. The comparison of the two processes shows that the two-jet process produces silver halide grains with a narrow grain size distribution and furthermore the halide composition can be freely changed with the growth of the grains.

It is also known that the growth rate of silver halide grains is greatly influenced by the silver ion (or halogen ion) concentration of the reaction solution, the concentration of a silver halide solvent and distance between grains, and by grain sizes. In particular, the heterogeneity of the concentration of silver ions or halogen ions formed by an aqueous silver salt solution and an aqueous halide solution added to a reaction vessel causes a difference in the growth rate of silver halide grains by the concentration of each solution, resulting in heterogeneity of the obtained silver halide emulsion. Therefore, in order to homogenize the concentrations of silver ions or halogen ions in the reaction vessel, it is necessary to quickly and uniformly mix an aqueous silver salt solution and an aqueous halide solution, which are to be added to an aqueous colloid solution to cause the reaction. In the conventional method of adding an aqueous halide solution and an aqueous silver salt solution to the surface of an aqueous colloid solution in a reaction vessel, the concentrations of halogen ions and silver ions become higher near the locations of the added reaction solutions, making it difficult to produce homogeneous silver halide grains.

As methods for improving the localization of the concentrations, the techniques disclosed in US-A-3 415 650, GB-B-1 323 464 and US-A-3 692 283 are known.

In these processes, a hollow rotary mixer (the interior of which is filled with an aqueous colloid solution, and preferably the mixer is divided into an upper space and a lower space by a disk) of intermediate size with slits on the cylindrical wall is placed in a reaction vessel filled with an aqueous colloid solution so that its axis of rotation is vertical, and an aqueous halide solution and an aqueous silver salt solution are introduced from the upper and lower openings thereof into the mixer rotating at high speed through feed pipes to rapidly mix them and cause the reaction (if the mixer is divided into an upper and lower space by the partition disk, the aqueous halide solution and the aqueous silver salt solution added into the upper and lower spaces are diluted with the aqueous colloid solution filled into each space and rapidly stirred with each other near the outlet slits of the mixer to cause the reaction), and the silver halide grains formed are mixed into the aqueous colloid solution in the reaction vessel to cause grain growth.

On the other hand, a technique for preventing the heterogeneous growth of silver halide grains by improving the localization of concentrations is disclosed in JP-B-55-10545 (the term "JP-B" as used herein means "an examined Japanese patent publication"). This method stands for a technique in which an aqueous silver halide solution and an aqueous silver salt solution are separately introduced into a mixer filled with an aqueous colloid solution via addition tubes from the lower open portions, the mixer being arranged in a reaction vessel filled with an aqueous colloid solution, and the reaction solutions are abruptly stirred and mixed by means of lower stirring blades (turbine blades) with which the mixer is equipped to grow silver halide grains, and the silver halide grains thus grown are immediately introduced into the aqueous colloid solution. in the reaction vessel from the upper open area of the mixer through upper stirring blades arranged at the upper area of the aforementioned lower stirring blades.

JP-A-57-92523 also discloses a manufacturing process for silver halide grains for improving the heterogeneity of the concentrations. This method is a manufacturing method of silver halide grains, wherein an aqueous halide solution and an aqueous silver salt solution are separately introduced into a mixer filled with an aqueous colloid solution from the lower open portions thereof, the mixer being arranged in a reaction vessel filled with an aqueous colloid solution, to mix both reaction solutions with the aforementioned aqueous colloid solution, and to abruptly stir and mix both reaction solutions by means of the lower stirring blades with which the mixer is equipped, and to immediately discharge the silver halide grains thus grown into the aqueous colloid solution in the reaction vessel from the upper open portion of the mixer, wherein both reaction solutions diluted with the aqueous colloid solution are passed through the gap formed between the inner wall of the mixer and the upper ends of the stirring blades without passing through any gap between the To be passed through stirring blades, whereby both reaction solutions are abruptly sheared and mixed at the spacing area with the formation of silver halide grains.

However, although the above-mentioned methods can certainly cope with the local heterogeneity of the concentrations of silver ions and halogen ions in a reaction vessel, in these methods the heterogeneity of the concentrations still exists in the mixer, and in particular, there is a considerably large concentration distribution near the nozzles for discharging the aqueous silver salt solution and the aqueous halide solution at the lower portions of the stirring blades and the stirring portion. Furthermore, the silver halide grains discharged into the mixer enter the mixer together with the protective colloid through such regions with the heterogeneous concentration distribution, and the silver halide grains grow abruptly at these locations. In other words, in the aforementioned methods, a concentration distribution exists in the mixer, and the growth of the silver halide grains occurs abruptly in the mixer, and the goal of uniform growth of silver halide grains in a stage without concentration distribution is not achieved.

In order to cope with the heterogeneous distribution of the concentrations of silver ions and halogen ions by mixing them more completely, attempts were made to separate the reaction vessel and the mixer and to fill an aqueous silver salt solution and an aqueous halide solution into the mixer to mix them abruptly and grow silver halide grains. For example, JP-A-53-37414 and JP-B-48-21045 disclose a method and an apparatus for producing silver halide grains by circulating an aqueous protective colloid solution containing silver halide grains in a reaction vessel from the bottom of the reaction vessel by means of a pump, equipping a mixer to a circulation system, discharging an aqueous silver salt solution and an aqueous halide solution into the mixer, and abruptly mixing both aqueous solutions in the mixer to grow silver halide grains.

Also, US-A-3 897 935 discloses a method of circulating an aqueous protective colloid solution (containing silver halide grains) in a reaction vessel from the bottom of the reaction vessel and pouring an aqueous halide solution and an aqueous silver salt solution into the circulation system by means of a pump. Likewise, JP-A-53-47397 discloses a method and an apparatus for producing silver halide grains by circulating an aqueous protective colloid solution (containing silver halide emulsions) in a reaction vessel from the bottom of the reaction vessel by means of a pump, wherein first an aqueous alkali metal halide solution is poured into the circulation system is poured to disperse until the mixture becomes uniform, and then an aqueous silver salt solution is poured into the system and subsequently mixed to form silver halide grains.

These methods can certainly independently change the flow rate of the aqueous solution in the reaction vessel when circulating to the circulation system and the mixing efficiency in the mixer, and are capable of carrying out the growth of silver halide grains under a homogeneous condition for the concentration distribution, but the silver halide grains sent from the reaction vessel together with the aqueous protective colloid solution grow at the inlets for pouring the aqueous silver salt solution and the aqueous halide solution. Accordingly, as described above, it is impossible in principle to homogenize the concentration distribution at the mixing portion or in the vicinity of the inlets for pouring, and therefore, in other words, the object of uniformly growing silver halide grains in a state where there is no concentration distribution will not be achieved.

DE-A-1 472 745 discloses a process for preparing silver halide dispersions, wherein the dispersion is prepared in two stages, and the precipitation reaction is carried out in a relatively small reaction chamber and the physical ripening is subsequently carried out in a ripening vessel.

The aim of the invention is to provide a silver halide photographic material which gives little fog, has a high sensitivity, has improved graininess, sharpness and opacity and has excellent storage stability and printing resistance by completely homogenizing the microscopic halide distribution in the interior (core) of silver halide grains and/or homogenizing reduced silver in the grains in a so-called core/shell emulsion with different halide composition. the surface (shell) of the grains and the interior (core) of the grains, and also to provide a method for producing a completely homogeneous phase of the halide composition inside the silver halide grains.

DISCLOSURE OF THE INVENTION

The above object of the invention has been achieved by the invention by providing a silver halide photographic material having at least one silver halide emulsion layer on a support, characterized in that the interior of the light-sensitive silver halide grains contained in the silver halide emulsion layer is composed of at least one phase containing at least silver chlorobromide or silver iodobromide whose halide composition is completely homogeneous, the completely homogeneous phase of the halide composition having a half-width for X-ray diffraction of not more than the half-width shown by step A in Fig. 1 when the silver halide emulsion grains are silver chlorobromide grains, or the half-width shown by curve A in Fig. 2 when the silver halide emulsion grains are silver iodobromide grains, and the surface of the silver chlorobromide and silver iodobromide grains having a different halide composition from the interior of the silver chloride and silver iodobromide grains, adjacent to the surface, and

by a process for producing a completely homogeneous phase comprising mixing an aqueous solution of a water-soluble silver salt and an aqueous solution of a water-soluble halide in a mixer arranged outside a reaction vessel to cause nucleation and/or crystal growth of photosensitive silver halide grains to form silver halide with fine grain sizes, feeding the silver halide into the reaction vessel immediately after its formation for carrying out the nucleation and/or crystal growth of photosensitive silver halide grains, and further forming silver halide having a different composition from the grains outside the silver halide grains, wherein a protective colloid solution contained in the reaction vessel is not circulated into the mixer, the temperature of the mixer is not higher than 40°C and the temperature of the reaction vessel is not lower than 50°C, and wherein the fine silver halide formed in the mixer comprises two or more types of halide.

The feature of the silver halide grains in this invention is that the grains have a so-called core/shell structure and the core region has a completely homogeneous halide distribution.

The shell region must be different in halogen composition from the core region adjacent to the shell region, and it is necessary that the halide composition of the shell region be completely homogeneous. Also, the halide composition may be a single composition or a so-called mixed crystal.

An example of the silver halide emulsion grains having "completely homogeneous halide distribution" in this invention is explained for tabular silver iodobromide grains having a silver iodobromide phase.

The term "completely homogeneous silver iodide distribution" means a more microscopic distribution which is completely different from a conventional silver iodide distribution.

Up to now, an analytical electron microscope has been widely used as a means of measuring the silver iodide distribution in silver iodobromide grains. For example, the topography result for the silver iodide content in tabular silver iodobromide grains is in MA King, MH Lorretto, TJ Maternaghan and FJ Berry, The Investigation of Iodide Distribution by Analytical Electron Microscopy, Progress of Basic Principles of Imaging System, International Congress of Photographic Science Cologne, 1986. The size of the sample for electron beam irradiation used in the investigation is 50 Å, but the electron beam is actually broadened by the elastic scattering of electrons, and the diameter of the electron beam spot irradiated on the surface of the sample becomes about 30 nm (300 Å). Accordingly, a silver iodide distribution finer than the diameter cannot be measured by this method. In JP-A-58-113927, a silver iodide distribution was measured in the same manner, but the size of the electron beam spot used was 0.2 µm.

Therefore, it is impossible to measure a more microscopic (positional change on the order of 10 nm (100 Å) or less) silver iodide distribution by these measuring methods. The microscopic silver iodide distribution can be observed by a direct method using a transmission electron microscope at low temperature, as described, for example, in J.H. Hamilton, Photographic Science and Engineering, Vol. 11, p. 57, 1967, and Takekimi Shiozawa, Journal of the Society of Photographic Science and Technology of Japan, Vol. 35, No. 4, p. 213, 1972. That is, silver halide grains taken out under safe light so that the emulsion grains are not printed out are set on a grid for electron microscopic observation, and the observation of the sample is carried out in the state of cooling by liquid nitrogen or liquid helium for preventing the occurrence of damage (printing out) of the sample by electron beams.

In this case, the accelerating electric voltage for the electron microscope is higher and clearer transmitted images are obtained, however, 200 kV is preferably used for grains with a thickness of up to 0.25 μm, and 100 kV is preferably used for grains with thicker thickness. Since the accelerating voltage is higher, the damage to the grains becomes more serious for the irradiating electron beams, and it is more preferable to cool the sample with liquid helium than with liquid nitrogen.

The photographic magnification can be appropriately changed according to the size of the grains, but is 20,000 to 40,000 times magnification.

When the transmission type electron micrograph of tabular silver iodobromide grains is taken as described above, a very fine annual ring-like striped pattern is observed in the silver iodobromide phase region. An example of this is shown in Fig. 5. The tabular grains shown in the figure are grains formed of tabular silver bromide grain as the core and silver iodobromide containing 10 mol% of silver iodide as the shell on the outside of the core, and the structure can be clearly confirmed by the transmission type electron micrograph. That is, since the core region is silver bromide, only homogeneous flat images are obtained, but on the other hand, a very fine annual ring-like striped pattern is clearly confirmed in the silver iodobromide phase. The striped pattern has a very fine pitch on the order of 10 nm (100 Å) or less, which shows a very microscopic heterogeneity. It can be clarified by various methods that the very fine striped pattern shows the heterogeneity of silver iodide distribution, but the aforementioned fact can be clearly concluded that if the tabular grains are heated under the condition where iodide ions can migrate in the silver halide crystal (for example, at 250°C, 3 hours) welded, the striped pattern has completely disappeared.

The annual ring-shaped striped pattern showing the heterogeneity of silver iodide distribution of the tabular silver iodobromide emulsion grains and described above is clearly observed in the transmission type electron micrograph attached to the above-mentioned JP-A-58-113927 and is also clearly shown in the transmission type electron micrograph for the study carried out by King et al. and mentioned above. From these facts, it is clear that conventional silver iodobromide grains prepared with a defined silver iodide content to obtain a homogeneous silver iodide distribution have a very microscopically heterogeneous distribution of silver iodide contrary to the intention for their preparation, and neither the technique for homogenizing the distribution nor the preparation process for such silver halide grains has been disclosed. The invention discloses the core/shell emulsion having the core region wherein the microscopic distribution of silver iodide is completely homogeneous and the manufacturing process thereof.

As described above, the silver halide grains having "the completely homogeneous halide distribution" can be clearly distinguished from conventional silver halide grains by observing the transmitted images of the grains using a cooling type transmission electron microscope. That is, inside the silver halide grains of the invention, there exist at most two microscopic lines caused by the microscopic heterogeneity of silver iodide of, for example, the aforementioned silver iodobromide at a distance of 0.2 µm in the transverse direction of the lines, preferably one such line is present, and particularly, no such line is present.

The lines forming the annual ring-shaped striped pattern, which show the microscopic heterogeneity of silver iodide, originate from the form of crossing the growth direction of the grains, which results in a concentric distribution of these lines from the center of the grain. For example, in the case of the tabular grains shown in Fig. 5, the lines constituting the annual ring-shaped striped pattern showing the heterogeneity of silver iodide cross at right angles the growth direction of the tabular grains, the lines become parallel to the grain edge, the direction crossing the line at right angles points to the center of the grain, and the lines are distributed concentrically around the grain center.

Therefore, if the silver iodide content is abruptly changed during the growth of grains, the boundary line can be observed as a similar line as above by the aforementioned observation method, but a change in the silver iodide content forms only a single line and can be clearly distinguished from those formed by multiple lines caused by the microscopic heterogeneity of silver iodide. Furthermore, the line resulting from the change in the silver iodide content can be clearly confirmed by measuring the silver iodide content on both sides of the line by the analytical electron microscope described above.

Such a line due to change in the content of silver iodide is completely different from the lines resulting from the microscopic heterogeneity of silver iodide and shows a "macroscopic silver iodide distribution".

Even if the silver iodide content is changed substantially continuously during the growth of the grains, the above-mentioned line showing the macroscopic change in the silver iodide content is not observed because there is no abrupt change in the silver iodide content, and therefore, if at least three lines with a spacing of 0.1 µm are present, it indicates that the microscopic heterogeneity in the silver iodide content is present.

Therefore, "silver halide core grains having a completely homogeneous halide distribution" of this invention are mixed crystals containing silver chlorobromide and silver iodobromide, and are silver halide core grains having at most two lines, preferably one line, particularly no line, showing the microscopic halide distribution with a pitch of 0.2 µm in the direction perpendicularly crossing the line of the transmitted images of the grains obtained using a cooling type transmission electron microscope. Further, it is preferred that the grains having such a homogeneous interior account for at least 60%, preferably at least 80%, and particularly at least 90% of the entire grains.

Conventional silver halide grains, referred to as silver halide grains containing, for example, homogeneous silver iodide, are simply prepared by adding silver nitrate and a mixture of halides having a defined composition (a defined silver iodide content) to a reaction vessel by means of a double-jet process as the grains grow, and therefore in such grains the macroscopic silver iodide distribution may certainly be constant, but the microscopic silver iodide distribution is not homogeneous. In this invention, such grains are referred to as grains having "a constant halogen composition" and are clearly distinguished from grains according to the invention which exhibit "complete homogeneity".

The above explanation applies to silver iodobromide core grains, for example, but the problems regarding microscopic halide composition are the same for all mixed silver halide crystals, such as silver chlorobromide, silver chloroiodide, silver chloroiodide, etc.

The homogeneity of the microscopic halide distribution for mixed silver halide crystals can be further measured using X-ray diffraction.

It is well known to one skilled in the art to measure the halogen composition using an X-ray diffractometer. The operation is briefly explained below.

By measuring a Bragg angle in X-ray diffraction, a lattice constant a can be determined using the following Bragg formula:

2dhklsinθhkl = λ λ : wavelength of the X-ray

θhkl : Bragg angle of the (hkl) plane

dhkl = a/ [h²+k² +l²] dhkl : distance of the (hkl)plane

a : lattice constant

Now, according to the first chapter of T.H. James, The Theory of the Photographic Process, 4th edition, Macmillan Co., Ltd., New York, the reaction for the lattice constants a for halogen compositions is shown for silver iodobromide, silver chlorobromide and silver iodochloride. As shown in this book, if the lattice constant (halogen composition) is different, the positions of the diffraction peaks are different. Accordingly, in silver halide grains with excellent homogeneity of the halogen composition distribution, the dispersion of the lattice constant is small and the half-width of the diffraction profile becomes narrow. For the measurement of the diffraction profile, the Kα line with higher intensity and good monochromaticity is preferably used before the Kβ line. In addition, since the Kα line consists of double lines, it is possible to determine the half-width from a simple profile obtained using a Rachinger method.

As a sample, powdered particles obtained by removing gelatin from a silver halide emulsion are used, or a coated silver halide emulsion film immersed in 50% glycerin solution for 20 minutes to remove the gelatin pressure applied to the surface of the grains in the dry film according to the method of G.C. Farnell, R.J. Jenkins and L.R. Solman, Journal of Photographic Science, Volume 24, page 1 (1976), can be used.

To accurately determine the angle for a diffraction profile, a method is used in which a Si powder or NaCl powder, whose diffraction angle is known, is mixed with the sample. Furthermore, it is known that to measure the diffraction angle and the line width of the diffraction profile with good accuracy, a diffraction profile with a large diffraction angle from a higher index plane is used. Accordingly, in this patent, the diffraction profile of a (420) plane was measured in the range of the diffraction angle (2 times Bragg angle) of 71º to 77º by the Kα line of a copper core.

In addition, for X-ray diffraction measurement, the coated emulsion film gives better measurement accuracy than the powder, and therefore the measurement was carried out on the coated emulsion film in the examples described below.

Now, the half-width of the diffraction profile of the system which does not cause strain by an external stress, such as the sample shape described in this patent, is not only determined by the distribution of the halogen composition, but further includes a half-width from an optical system for a diffractometer and a half-width by the sizes of the crystallites of the sample. Accordingly, in order to obtain the half-width which comes from the distribution of the halogen composition, it is necessary to The proportion of half-widths must be deducted from the previously mentioned contributions.

The half-width through an optical system of a diffractometer can be obtained as the half-width of the diffraction profile of a single crystal of at least 25 µm grain size without strain (without dispersion of lattice constant). The use of an α-quartz of 25 to 44 µm (500 mesh on, 350 mesh under) welded at 800ºC as such a sample is described in X- Sen Kaisetsu no Tebiki (Manual of X-Ray Diffraction), revised edition, Chapter 2, Paragraph 8, by Rigaku Denki K.K. Si particles, Si single crystal wafers, etc. can also be used. Since the half-width through an optical system has a diffraction angle reliability, it is necessary to obtain half-widths on various diffraction profiles. By applying, if necessary, an extrapolation or an interpolation, the half-width for an optical system is obtained with respect to the diffraction angles of the measured system.

On the other hand, the half-width due to the sizes of the crystals is shown by the following formula.

β; = Kλ/Dcosθ X 180/π

β: Half-width (º) through the sizes of the crystallites

K: constant (generally 0.9)

D: Size (Å) of the crystallite

λ: wavelength (Å) of the X-ray beam

θ: Bragg angle

By subtracting the half-width of an optical system thus obtained and the half-width due to the sizes of the crystallites from the half-width of the measured diffraction profile, the half-width for the distribution of the halogen composition is determined The half-width for an optical system of mixed crystal grains and the half-width for the sizes of the crystallites which were measured are equivalent to the half-width of the diffraction profile of the silver halide grains having a homogeneous distribution of the halogen composition (defined lattice constant) and having the same crystallite size as the size of the grains to be measured. In general, if no stretching by external stress occurs, the grains have no lattice defect and the size of the grain (length of the side), diameter corresponding to the space of the same volume, etc., agrees with the crystallite size. Regarding the above, it is reported by FW Willets, British Journal of Applied Physics, Vol. 16, page 323 (1965), that the size of the crystallite of AgBr obtained by the diffraction line width corresponds to the size of the grain, although the measurement was carried out not by a diffraction method but by a photographic method. In this report, the Scherrer constant is chosen to be 1.44, using a photographic technique that does not use the half-width but uses the standard deviation of the profile.

In our measurement system using a diffractometer, it was found that the size of the crystallite obtained subtracting the half-width from which the half-width for an optical system using Si single crystals is obtained is in good agreement with the size of the grain in AgBr grains prepared by an equilibrium double-beam method.

In other words, the half-width of mixed crystal emulsion grains for an optical system and the half-width for the sizes of crystallites can be obtained as the half-width of the diffraction profile of AgBr grains, AgCl grains and AgJ grains having the same grain size as the size of the mixed crystal emulsion grains.

The half-width for the halogen composition distribution only for mixed crystal emulsion grains is obtained by subtracting the half-width for the diffraction profile for AgBr grains, AgCl grains or AgJ grains with the same grain size as that of the grains to be measured from the half-width of the measured diffraction file.

The half-width of the X-ray diffraction profile for silver halide emulsion grains having a homogeneous microscopic halogen composition by the aforementioned method is shown in Fig. 1 for silver chlorobromide and in Fig. 2 for silver iodobromide. In Fig. 1 and Fig. 2, the homogeneity of the grains of each halogen composition is shown by the value obtained by subtracting the half-width for pure silver chloride or pure silver bromide having the same grain size as the aforementioned grains from the half-width of the X-ray diffraction for each grain. The grains of the present invention have a half-width of not more than the half-width shown by curve A, preferably not more than the half-width shown by curve B. The halide compositions for the core region and the shell region can be measured by an X-ray diffraction method.

Examples of applying an X-ray diffraction technique to silver halide grains are given in H. Hilsh, Journal of Photographic Science, Volume 10, page 129, infra (1962). When the lattice constant is determined by the halogen composition, the diffraction peak appears at the diffraction angle that satisfies the Bragg condition (2d sinθ = nλ).

The measuring method for X-ray diffraction is described in detail in Kiso Bunseki Kagaku Koza "Fundamental Analytical Chemistry Course) 24, "X-Ray Analysis", published by Kyoritsu Shuppan and X-Sen Kaisetsu no Tebiki (Manual of X-Ray Diffraction), by Rigaku Denki KK. In the standard measurement method, Cu is used as the nucleus, and the diffraction curve of the (220) plane of silver halide is obtained by using the Kß line of Cu as an X-ray source (tube voltage 40 kV, tube current 60 mA). In order to increase the resolving power of the measuring device, it is necessary to properly select the slit widths (divergence slit, light receiving slit, etc.), the time constant of the device, the scanning speed of a goniometer and the recording speed, and to confirm the measurement accuracy using a standard sample such as silicon.

When the curve for the diffraction intensity versus the diffraction angle of the (220) plane of silver halide is obtained using the Kβ line of Cu, there are cases where the diffraction peaks corresponding to the core region and the shell region are detected as clearly separated states, and cases where the peaks overlap each other and are not clearly separated as two peaks.

A method for resolving the diffraction curve formed by two diffraction components is well known and described, for example, in Jikken Butsurigaku Koza 11 Koshi Kekkan (Experimental Physics Course 11 Lattice Defect) published by Kyoritsu Shuppan.

It is also useful to analyze the diffraction curve using a curve analyzer manufactured by Du Pont, assuming a Gaussian or Lerenzian function for the curve.

In the silver halide grains to be used in the invention, the aforementioned peaks corresponding to the core region and the shell region may or may not be clearly distinguished.

In the case of an emulsion in which two types of grains coexist, which do not have a clear layer structure and which each have different halogen compositions, two peaks appear in X-ray diffraction.

Such an emulsion cannot exhibit the excellent photographic performance obtained in the invention.

Whether a silver halide emulsion is the emulsion of the present invention or the aforementioned emulsion in which two kinds of silver halide grains without a clear layer structure are present can be determined using an EPMA (Castaing Microprobe) method (Electron-Probe Micron Analyzer method) in addition to the X-ray diffraction method.

In the method, a sample in which emulsion grains are well dispersed so that they do not come into contact with each other is irradiated by an electron beam. The elemental analysis of a fine region can be carried out by X-ray analysis by electron beam excitation.

From the characteristic X-ray intensities for silver and halogen emitted from each grain obtained by the above method, the halogen composition for each grain can be determined.

By confirming the halogen composition of at least 50 grains by the EPMA method, it can be determined whether the emulsion is an emulsion of the invention or not.

It is preferred that in the emulsion according to the invention the distribution of the halogen composition in the grains, especially the halogen composition distribution in the core regions of the grains, is more homogeneous. If the distribution of the halogen composition in the grains (for example the distribution of the silver iodide content in silver iodobromide or the distribution of the silver bromide content in silver chlorobromide) is measured by the EPMA method, the relative standard deviation of the halogen content is preferably less than 50%, in particular less than 35% and particularly preferably less than 20%.

If there is a greater overlap of the diffraction peaks corresponding to the core region or the shell region, or if the halide composition of the shell region cannot be determined because the ratio of the shell region to the grain is very small and the diffraction peak corresponding to the shell region is weak, the halide composition in the surface of the grain is measured.

The halide composition in the surface of the grain is measured by a surface analysis technique XPS (X-ray photoelectron spectroscopy) (i.e. the depth to be measured is about 50 Å).

The basis of the XPS method used for the analysis of the halogen content near the surface of silver halide grains is described in Junichi Aihara et al., Denshi no Bunko (Spectrum of Electron), Kyoritsu Library 16, published by Kyoritsu Shuppan, 1978.

In the XPS standard measurement method, Mg-Kα is used as an X-ray for excitation, and the intensities of photoelectrons of halogen and silver (Ag) (usually Cl-2p, Br-3d, I- 3d5/2 and Ag-3s5/2) emitted from silver halide grains in appropriate sample shape.

For example, the iodine content can be determined from the calibration curve from the intensity ratio of the photoelectrons of iodine (J) and silver (Ag) (ie intensity (J)/intensity (Ag)) prepared using different types of standard samples with known iodine content. For a silver halide emulsion, the XPS measurement must be carried out after gelatin adsorbed on the surfaces of the silver halide grains has been degraded with a proteolytic enzyme, etc. and subsequently removed.

The embodiments of the silver halide grains according to the invention are as follows.

(1) When the halide compositions of the core region (in the case of cores having two or more layers, the core region adjacent to the shell region) and the shell region are composed of the same halide, it is desirable that the difference between both halide compositions be at least 5 mol%, preferably at least 10 mol%, and particularly preferably at least 20 mol%. That is, in the case of, for example, silver chlorobromide containing silver chloride, the difference in silver chloride content between the core region and the shell region is as described above. The types of halide differ between the core region and the shell region, and it is desirable that the content of different halide be at least 3 mol%, preferably at least 6 mol%, particularly at least 10 mol%. That is, in the case of, for example, the shell is composed of AgBr and the core of AgBrCl, the silver chloride content in the core is as described above.

(2) The molar ratio of the core region to the shell region may be optional, but the molar ratio for the shell is preferably not higher than 50 mol%, more preferably not higher than 30 mol%, and most preferably not higher than 10 mol%.

(3) The microscopic halide composition of the core region is completely homogeneous, but the microscopic Halide composition of the shell region can be completely homogeneous or heterogeneous.

(4) The core region may be a single-layer structure or a multi-layer structure consisting of two or more layers.

The following explains the manufacturing process for silver halide core grains in which the microscopic halide composition inside the mixed silver halide crystals according to the invention is completely homogeneous, and preferably the inside of the silver halide crystals does not contain reduced silver generated during the formation of the grains.

A silver halide prepared in advance to a fine size is added to a reaction vessel to form nuclei for the grains and/or to form crystals, whereby the nucleation and/or crystal growth of the silver halide core grains is carried out in the reaction vessel.

In the invention, by adding the previously prepared silver halide grains of fine size to the reaction vessel, the nuclei of the grains can be formed, and further the crystal growth can be carried out in the reaction vessel.

Furthermore, by adding the previously prepared silver halide grains of fine size to the reaction vessel in which the nuclei of the grains have been previously formed by a conventionally known method, the growth of the crystals can also be carried out.

Specific methods for adding the fine silver halide are as follows.

(1) A method for adding fine silver halide grains from a mixer arranged outside the reaction vessel. By immediately adding the fine grains formed by mixing an aqueous solution of a water-soluble silver salt and an aqueous solution of water-soluble halides in a mixer arranged outside the reaction vessel for causing nucleation and/or crystal growth to the reaction vessel, nucleation and/or crystal growth of the silver halide core grains is carried out (hereinafter referred to as Process A).

The system for such a grain formation process is shown with reference to Fig. 3.

In Fig. 3, a reaction vessel 1 contains an aqueous solution 2 of a protective colloid. The aqueous protective colloid solution is stirred by a rotary blade 3 attached to the rotation axis. An aqueous silver salt solution, an aqueous halide solution and an aqueous protective colloid solution are fed into a mixer 7 outside the reaction vessel via addition systems 4, 5 and 6 (in this case, the aqueous protective colloid solution can be added as a mixture with the aqueous halide solution and/or the aqueous silver salt solution). These solutions are quickly and vigorously mixed in the mixer, and the formed grains are immediately fed into the reaction vessel 1 via a system 8. Details of the mixer 7 are shown in Fig. 4. A reaction chamber 10 is formed in the mixer 7, and the reaction chamber is equipped with a stirring blade fixed to the rotation axis 11. An aqueous silver salt solution, an aqueous halide solution and an aqueous protective colloid solution are added to the reaction chamber 10 through the three inlets (4, 5 and one inlet is omitted in the figure). By rotating the rotation axis at a high speed (at least 1000 rpm, preferably at least 2000 rpm and particularly at least 3000 rpm), the mixture is mixed quickly and vigorously, and a solution containing very fine grains thus formed is immediately taken out from the outlet.

The very fine grains formed in the mixer are then charged into the reaction vessel, easily dissolved due to the fineness of the grain size to form silver ions and halogen ions again and cause the formation of homogeneous nuclei and/or the growth of the grains. The halide composition of the very fine grains is selected to be the same as the halide composition of the silver halide grains produced. These fine grains charged into the reaction vessel are dispersed in the reaction vessel by stirring in the reaction vessel to release halogen ions and silver ions of the halide composition formed from each fine grain. The grains formed in the mixer are very fine, the number of grains is very high, and since the silver ions and halogen ions (in the case of mixed crystal growth, the desired halogen ion composition is formed) are released from a very large number of grains and are released throughout the protective colloid in the reaction vessel, the growth of completely homogeneous grains can be achieved. It is important that the silver ions and halogen ions are never added to the reaction vessel as an aqueous solution thereof, except for pAg control, and that the protective colloid solution in the reaction vessel is not circulated in the mixer. The method can give an amazing effect on the homogeneous growth of silver halide grains, different from conventional methods.

The fine grains formed in the mixer have a very high solubility because their grain size is very small, and are dissolved when added to the reaction vessel to reform silver ions and halogen ions, and nuclei are formed or they are deposited on the grains already existing in the reaction vessel. However, since the fine grains have a high solubility, in this case the fine grains cause what is known as Ostwald ripening before being added to the reaction vessel, thereby increasing the grain sizes. If the size of the fine grains is increased, their solubility is lowered with increase in size, and their dissolution in the reaction vessel is delayed, and the grain growth rate is greatly reduced, and in some cases the fine grains cause grain growth in the form of their nuclei without being dissolved.

These problems are solved by the following three techniques in the invention.

1) After the fine grains are formed in the mixer, the fine grains are immediately added to the reaction vessel.

In the invention, the occurrence of Ostwald hoops is prevented by arranging the mixer very close to the reaction vessel and shortening the residence time of the solutions added to the mixer and thus by immediately adding the formed fine grains to the reaction vessel. The residence time (t) of the solutions added to the reaction vessel is practically shown as follows.

t = v/a+b+c v: volume (ml) of the reaction in the mixer.

a: Addition amount (ml/min) of the silver nitrate solution.

b: Addition rate (ml/min) of the halide solution.

c: Addition amount (ml/min) of the protective colloid solution.

In the production process according to the invention, t is not longer than 10 minutes, preferably not longer than 5 minutes, particularly preferably not longer than 1 minute, and particularly preferably not longer than 20 seconds. Therefore, the fine grains formed in the mixer are immediately added to the reaction vessel without causing an increase in grain size.

2) Solutions are stirred vigorously and effectively in the mixer.

In T.H. James, The Theory of the Photographic Process, page 93, it is described that "another form in addition to Ostwalt ripening is coalescence." In coalescence ripening, widely separated crystals are brought into contact with each other and adhere to each other to form larger crystals, and therefore the grain sizes suddenly change. Both Ostwalt ripening and coalescence ripening occur not only after the completion of precipitation but also during precipitation. The coalescence ripening described in the aforementioned book occurs easily when the grain sizes are very small, and especially it occurs easily when there is insufficient agitation. In extreme cases, it sometimes happens that large, massive grains are formed. In the invention, the stirring blade in the reaction chamber can be rotated at a high rotation number since a sealed type mixer is used as shown in Fig. 4, but this is impossible in a conventional open type reaction vessel (for example, in an open type reaction vessel, if a stirring blade is rotated at a high speed, the liquid is thrown away by centrifugal force and therefore such an operation is practically inapplicable and an additional problem of foaming occurs). That is, in the invention, it is possible to apply mixing by strong and effective stirring to prevent the occurrence of the aforementioned coalescence ripening, thereby forming very fine grains having very fine grain sizes.

In the invention, the rotation speed of the stirring blade is at least 1000 rpm, preferably at least 2000 rpm, and especially at least 3000 rpm.

3) Pour an aqueous protective colloid solution into the mixer.

The occurrence of the aforementioned coalescence ripening can be markedly prevented by a protective colloid for the silver halide grains. In the invention, an aqueous protective colloid solution is added to the mixer as follows.

(a) An aqueous protective colloid solution is added individually to the mixer.

The concentration of the protective colloid is at least 0.2% by weight, preferably at least 0.5% by weight, and the flow rate thereof is at least 20%, preferably at least 50%, particularly at least 100%, of the sum of the flow rate of an aqueous silver nitrate solution and the flow rate of an aqueous halide solution.

(b) The protective colloid is incorporated into an aqueous halide solution.

The concentration of the protective colloid is at least 0.2 wt.%, preferably at least 0.5 wt.%.

(c) The protective colloid is incorporated into an aqueous silver nitrate solution.

The concentration of the protective colloid is at least 0.2% by weight, preferably at least 0.5% by weight. If gelatin is used, since gelatin silver is generated by silver ions and gelatin, and gelatin silver forms silver colloid to cause photodecomposition and thermal decomposition, it is better to mix an aqueous silver nitrate solution and an aqueous gelatin solution immediately before use.

The above methods (a) to (c) can be used individually or in combination. Furthermore, the three methods can be used simultaneously.

(2) Method of adding a previously prepared fine silver halide grain emulsion.

In the invention, a method of adding a fine silver halide grain emulsion containing fine grain size silver halide grains prepared in advance to a reaction vessel to cause the formation of nuclei and/or the growth of grains (hereinafter referred to as method B) is employed.

In this case, it is better than the aforementioned case that the grain size of the previously prepared emulsion is very small. In the method, an aqueous silver salt solution is not added to the reaction vessel to cause nucleation and/or grain growth, except for pAg control, as in the aforementioned method.

In the method A described above, the temperature of the mixer is not higher than 40°C and preferably not higher than 35°C, and the temperature of the reaction vessel is not less than 50°C, preferably not less than 60°C and especially not less than 70°C.

In method B, the temperature for forming the grain for the fine grain emulsion prepared beforehand is not higher than 40°C, preferably not higher than 35°C, and the temperature of the reaction vessel to which the fine grain emulsion is added is not lower than 50°C, preferably not lower than 60°C, and especially not lower than 70°C.

The grain size of the fine grain silver halide grains for use in the invention can be determined by a transmission type electron microscope on a screen, and the magnification is preferably 20,000 to 40,000. The grain size of the fine silver halide grains to be used in the invention is not larger than 0.1 µm, preferably not larger than 0.06 µm, particularly not larger than 0.03 µm.

The halide composition of the grain core emulsion obtained in the invention may be silver iodobromide, silver chlorobromide, silver chloroiodobromide or silver chloroiodide, and according to the invention, mixed silver halide grains having a homogeneous microscopic halide distribution, i.e. a "complete homogeneity" are obtained.

Furthermore, the method of the present invention is also very effective for producing core grains composed of pure silver bromide or pure silver chloride. According to a conventional production method, the existence of the local distributions of silver ions and halogen ions in a reaction vessel is inevitable, and the silver halide grains in the reaction vessel are brought into a state different from other homogeneous regions upon passing through the local heterogeneous regions, whereby the growth of the grains becomes heterogeneous, as well as in a high concentration region of, for example, silver ions, and reduced silver or veiled silver is formed. Accordingly, in the case of silver bromide or silver chloride, a heterogeneous halide distribution is not surely present, but other heterogeneity described above occurs. This problem can be completely solved by the method of the present invention. Therefore, the core grains obtained in the method of the present invention include a silver halide having a single composition. Therefore, it is preferred that such reduced silver is not distributed in the core grains.

In the method of the present invention, by using a silver halide solvent for the reaction system in the reaction vessel, a higher dissolution rate for the fine grains and a higher growth rate for the grains in the reaction vessel can be obtained.

Known silver halide solvents include water-soluble bromides, water-soluble chlorides, thiocyanates, ammonia, thioethers, thioureas, etc.

For example, thiocyanates are known (US-A-2,222,264, 2,448,534, 3,320,069), ammonia, thioether compounds (for example US-A-3,271,157, 3,574,628, 3,704,130, 4,297,439 and 4,276,347), thione compounds (for example JP-A-53-144319, JP-A-53-82408 and JP-A-55-77737), amine compounds (for example JP-A-54-100717), thiourea derivatives (for example JP-A-55-2983), imidazoles (for example JP-A-54-100717) and substituted Mercaptotetrazoles (e.g. JP-A-57-202531).

There is no particular limitation on the grain size of the completely homogeneous silver halide emulsion grains thus obtained, but the grain size is preferably at least 0.3 µm, particularly at least 0.8 µm, and even more preferably at least 1.4 µm.

The shape of the silver halide grains in the invention may be a regular crystal form (normal crystal grains) such as hexahedral, octahedral, dodecahedral, tetradecahedral, tetracosahedral and octatetracosahedral, may be an irregular crystal form such as a spherical shape or potato-like shape, or may be various shapes having one or more twin crystal planes, particularly hexagonal tabular grains or triangular tabular twin grains having two or parallel thin planes.

The method for forming the shell in the invention is explained below. After the formation of the core described above, the shell is produced, and Method A or Method B can be used to produce the shell. Details of these methods are described above.

For the formation of the shell in the invention, conventional methods for forming silver halide grains can be used. That is, an aqueous silver salt solution and an aqueous halide solution are added to the reaction vessel containing an aqueous solution containing the core silver halide grains and a protective colloid with efficient stirring.

Practical procedures for preparing the shell are described in P. Glafkides, Chimie et Phisique Photographique (published by Paul Montel, 1967), G.F. Duffin, Photographic Emulsion Chemistry (published by The Focal Press, 1966) and V.L. Zelikman et al., Making and Coating Photographic Emulsion (published by The Focal Press, 1964).

That is, an acid process, a neutralization process and an ammonia process may be used, and a system for reacting a soluble silver salt with soluble halides, a single-jet process, a double-jet process or a combination thereof may also be used. A method for forming the shell in the presence of excess silver ions (so-called reverse mixing method) may also be used. As one of the double-jet processes, a so-called controlled double-jet process in which the pAg in the liquid phase is kept constant when the silver halide grains are formed may be used.

In the step of forming or physically ripening the core/shell emulsion grains of the invention, a cadmium salt, a zinc salt, a lead salt, a thallium salt, an iridium salt or a complex salt thereof, a rhodium salt or a complex salt thereof, or an iron salt or a complex iron salt thereof.

It is also preferable to grow the grains rapidly in the range not exceeding the critical supersaturation by using a method in which the addition rates of an aqueous silver nitrate solution and an aqueous alkali halide solution are changed according to the rate of grain growth, as described in GB-B-1 535 016 and JP-B-48-36890 and JP-B-52-16364, or by a method in which the concentration of aqueous solution(s) is changed, as described in US-A-4 242 445 and JP-A-55-158124. These methods are preferably used because the re-formation of the nuclei does not occur and the core silver halide grains are homogeneously covered.

In the core/shell type silver halide grains according to the invention, the shape of the core portion is the same as the shape of the entire grain containing the shell therearound in one case, and is different from the entire grain in another case. Practically, the core portion has a cubic shape, and the shape of the entire grain with the shell is a cube or octahedron. In contrast, in another case, the shape of the core portion is an octahedron, and the shape of the entire grain with the shell is a cube or octahedron. In another case, the core portion is a clear regular grain, and the entire grain with the shell is slightly deformed or is amorphous. Furthermore, the core/shell grains of the present invention may have not only a simple double structure, but also a triple or multiple structure as described in JP-A-60-222844, or a structure formed by adhering a thin silver halide layer having a different composition to the surface of the core/shell structured grain.

To form the internal structure of the grains, grains having not only the aforementioned compound structure may be formed. Examples thereof are disclosed in JP-A-59-133540, JP-A-58-108526, EP 199290A2, JP-B-58-24772 and JP-A-59-16254. The compound crystals may be formed at the edge portions, corner portions or flat portions of the host crystals having a different composition from the host crystal. The host crystals on which the compound crystals are formed may be homogeneous in terms of halogen composition or may have a core/shell type structure.

In the case of the compound structure, the combination of silver halides with each other can of course be used, however, a combination of a silver salt compound which does not have a rock salt structure such as silver rhodanide and silver carbonate and silver halide can be used for the compound structure. Also, a non-silver salt compound such as PbO can be used if possible.

In the case of silver iodobromide grains having the above-mentioned structure, for example, in core/shell type grains, the silver iodide content may be higher in the core region and lower in the shell region, or vice versa, and the silver iodide content may be lower in the core region and higher in the shell region. Similarly, in grains having a compound structure, the silver iodide content may be higher in the host crystal and relatively low in the compound crystal, or the relationship may be reversed.

Also, the boundary region between the regions of the grain with the above-mentioned structure, each of which has a different halogen composition, may form a clear boundary, an indefinite boundary by forming mixed crystals due to the difference in the halogen composition form, or may have a continuously changing structure, positively formed.

The silver halide emulsion for use in the invention may be subjected to a grain rounding treatment as disclosed in EP 0096727 81 and EP 0064412 81 or the surface modification treatment as disclosed in DE 2306447 C2 and JP-A-60-221320.

The silver halide emulsion for use in the invention is preferably of the surface latent image type, but an internal latent image type emulsion may be used by selecting an appropriate developer or developing condition as described in JP-A-59-133542. Also, an internal latent image type surface emulsion having a thin shell coated thereon may be used depending on the purpose.

In the invention, it is very important to apply chemical sensitization such as redox sensitization, sulfur sensitization and gold sensitization. The area which is chemically sensitized differs depending on the composition, structure and shape of the emulsion grains or the purpose of using the emulsion. There is a case of forming the chemically sensitized core in the inside of the grain, a case of forming the chemically sensitized core in the position near the surface of the grain, or a case of forming the chemically sensitized core on the surface thereof. The invention is effective for any of the cases described above, but the case where the chemically sensitized core is formed in the vicinity of the surface is particularly preferable. In other words, the surface latent image type emulsion is more effective than the internal latent image type emulsion in the invention.

The silver halide emulsion according to the invention is usually spectrally sensitized.

As the spectral sensitizing dye for use in the invention, methine dyes are usually used, and the dyes include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes. To these dyes, there can be applied nuclei which are usually used for cyanine dyes as basic heterocyclic nuclei, i.e., pyrroline nuclei, oxazoline nuclei, thiazole nuclei, pyrrole nuclei, oxazole nuclei, thiazole nuclei, selenazole nuclei, imidazole nuclei, tetrazole nuclei and pyridine nuclei; nuclei which are formed by fusing an aliphatic hydrocarbon ring with the foregoing nuclei; and nuclei formed by fusing an aromatic hydrocarbon ring with the above-mentioned nuclei, such as indolenine nuclei, benzindaizolenine nuclei, indole nuclei, benzoxazole nuclei, naphthoxazole nuclei, benzothiazole nuclei, naphthothiazole nuclei, benzoselenazole nuclei, benzimidazole nuclei and quinoline nuclei, can be used for the above-described dyes. These nuclei may be substituted at the carbon atoms.

For merocyanine dyes or complex merocyanine dyes, 5- or 6-membered heterocyclic nuclei such as pyrazolin-5-one nuclei, thiohydantoin nuclei, 2-thiooxazolidine-2,4-dione nuclei, thiazolidine-2,4-dione nuclei, rhodanine nuclei and thiobarbituric acid nuclei can be used as the nucleus with ketomethylene structure.

The amount of sensitizing dye to be added during the preparation of the silver halide emulsion depends on the type of additive and the amount of silver halide, but may be a usual amount for a sensitizing dye which is added in a conventional process.

That is, the amount of the sensitizing dye is preferably 0.001 to 100 mmol, particularly 0.01 to 10 mmol.

The sensitizing dye is added after chemical ripening or before chemical ripening. It is particularly preferred in the invention to add the sensitizing dye to the silver halide grains during chemical ripening or before chemical ripening (for example, during grain formation or during physical ripening).

Together with the sensitizing dye, a dye which does not exhibit a spectral sensitizing effect itself or a material which does not absorb substantially visible light but exhibits a supersensitizing effect may be present in the silver halide emulsion according to the invention. The emulsion may contain, for example, aminostyryl compounds (for example, those described in US-A-2,933,390 and 3,635,721), aromatic organic acid-formaldehyde condensates (for example, those described in US-A-3,743,510), cadmium salts, azaindene compounds, etc. Furthermore, the combinations described in US-A-3,615,613, 3,615,641, 3,617,295 and 3,635,721 are particularly useful.

The silver halide emulsion according to the invention is usually chemically sensitized. For chemical sensitization, the processes described in H. Frieser, The Fundamentals of Photographic Processes with Silver Halides, pages 675-734 (1968), can be used.

That is, a sulfur sensitization process using active gelatin or a sulfur-containing compound capable of reacting with silver (e.g., thiosulfates, thioureas, mercapto compounds, and rhodanines); a reduction sensitization method using a reducing agent (e.g., tin salts, amines, hydrazine derivatives, formamidine sulfinic acid, and silane compounds); and a noble metal sensitization method using a noble metal compound (e.g., gold complex salts and complex salts of metals of Group VIII of the periodic table such as Pt, Ir, Pd, etc.) may be used individually or in combination.

The photographic emulsions for use in the invention may contain various compounds for inhibiting fogging during the manufacture, storage and photographic processing of the photographic materials or for stabilizing the photographic performance. That is, many compounds are known as antifoggants or stabilizers, such as azoles, for example, benzothiazole salts, nitroindazoles, triazoles, benzotriazoles and benzimidazoles (particularly nitro or halogen substituted products); heterocyclic mercapto compounds, for example, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, mercaptotetrazoles (particularly 1-phenyl-5-mercaptotetrazole), and mercaptopyrimidines; the aforementioned heterocyclic mercapto groups having a water-soluble group such as a carboxy group and sulfone group; Thioketo compounds, for example oxazolinethione; azaindenes, for example tetraazaindenes (especially 4-hydroxy-substituted (1,3, 3a,7)tetraazaindenes); benzenethiosulfonic acids; and benzenesulfinic acids.

The antifoggant or stabilizer is usually added to the silver halide emulsion after chemical sensitization, but the addition time may preferably be selected from times during chemical ripening and before initiating chemical ripening. That is, the addition may be carried out during addition of a silver salt solution, at a step of adding the silver salt solution for initiating of chemical ripening, or during chemical ripening (ie during chemical ripening, preferably within 50% of the time from initiation and especially within 20% of the time), in the step of forming the silver halide emulsion grains.

The silver halide emulsion of the present invention can be used for light-sensitive photographic materials having one or two layers or any optional layer structure.

A silver halide multilayer color photographic material using the emulsions of the invention has a multilayer structure having laminated thereon emulsion layers containing a binder and silver halide grains for separately recording blue light, green light and red light, and each emulsion layer is composed of at least two layers, i.e., a high-sensitivity layer and a low-sensitivity layer. Specifically, practical layer structures are as follows:

(1) BH/BL/GH/GL/RH/RL/S,

(2) BH/BM/BL/GH/GM/GL/RH/RM/RL/S,

(3) BH/BL/GH/RH/GL/RL/S, described in US-A-4 184 876, and

(4) BH/GH/RH/BL/GL/RL/S described in RD-22534, JP-A-59-177551 and JP-A-59-177552.

Wherein B denotes a blue-sensitive layer, G a green-sensitive layer, R a red-sensitive layer, H a layer with highest sensitivity, M a layer with medium sensitivity, L a layer with low sensitivity and 5 a support. In the above layer structures, protective layer(s), filter layer, intermediate layer(s), antihalation layer, underlayer(s), etc. are omitted. In the above layer structures, (1), (2) and (4) are preferred.

The layer structures

(5) BH/BL/CL/GH/GL/RH/RL/S and

(6) BH/BL/GH/GL/CL/RH/RL/S,

described in JP-A-61-34541 are preferred.

CL means a layer that causes an interlayer effect and the others have the same meaning as above.

The arrangement of the high sensitivity layer and the low sensitivity layer in the same color-sensitive layer can be reversed.

The silver halide emulsion of the present invention can be applied to color photographic materials as described above, but can also be applied to other light-sensitive materials having one or two layers, such as photosensitive materials for X-rays, black-and-white light-sensitive materials for use in cameras, photosensitive materials for the photomechanical process and photographic papers.

There is no particular limitation on various additives for the silver halide emulsions of the present invention, such as binders, chemical sensitizers, spectral sensitizers, stabilizers, gelatin hardeners, surfactants, antistatic agents, polymer latexes, matting agents, color couplers, ultraviolet absorbers, fading inhibitors and dyes, as well as the supports of the photographic materials using these emulsions, coating methods, exposure methods, development processing methods, etc., and reference can be made to the descriptions of, for example, Research Disclosure, Volume 176, Item 17616 (RD-17643), ibid., Volume 187, Item 18716 (RD-18716) and ibid., Volume 225, Item 22534 (RD-22534).

The descriptions of these research publications are shown in the following table. Additives Chemical sensitizer Sensitivity enhancer, Spectral sensitizer, Super color sensitizer Brightening agent Antifogging agent, Stabilizer Light absorber, Filter dye, Ultraviolet absorber Stain inhibitor Color image stabilizer Hardening agent Binder Plasticizer, Lubricant Coating aid, Surfactant Antistatic agent Color coupler Page right column left column

As gelatin hardeners, active halogen compounds (2,4-dichloro-6-hydroxy-1,3,5-triazine and its sodium salts) and active vinyl compounds (1,3-bisvinylsulfonyl-2-propanol, 1,2-bis(vinylsulfonylacetamido)ethane and vinyl polymer having a vinylsulfonyl group in the side chain) can be preferably used because they rapidly harden a hydrophilic colloid such as gelatin to give stable photographic characteristics. N-carbamoylpyridinium salts [(1-morpholinocarbonyl-3-pyridinio)methanesulfonate] and haloamidinium salts [1-(1-chloro-1-pyridinomethylene)pyrrolidinium-2-naphthalenesulfonate] are excellent in hardening speed.

The color photographic materials using the silver halide photographic emulsions of the present invention can be processed by the ordinary methods described in Research Disclosure, No. 17643, pages 28-29, and ibid., No. 18716, page 651, left column to right column.

After developing and bleach-fixing or fixing the color photographic materials using the silver halide photographic emulsions of the present invention, washing or stabilization is usually applied.

Washing is generally carried out by a countercurrent washing process using two or more baths to save water. As a stabilization process, a multi-stage countercurrent stabilization process as described in JP-A-57-8543 is used as a typical example instead of one washing step.

BRIEF EXPLANATION OF THE DRAWINGS

Fig. 1 and Fig. 2 show X-ray diffraction curves showing the homogeneity of silver halide grains, wherein the ordinate axis represents the half-width of an X-ray diffraction profile and the abscissa axis shows the halogen composition of the silver halide grains.

Fig. 3 shows schematically the process of the invention.

1: Reaction vessel

2: Aqueous protective colloid solution

3: Wings

4: Addition system for the aqueous halide solution

5: Addition system for the aqueous silver salt solution

6: Addition system for the protective colloid

7: Mixer

Fig. 4 shows details of the mixer in the invention.

4, 5, 6 and 7 have the same meaning as in Fig. 4.

8: Filling system for the reaction vessel

9: Stirring blade

10: Reaction chamber

Fig. 5 shows a transmission type electron microscope image showing the crystal structure of conventional tabular silver halide grains without completely homogeneous iodine distribution of the silver iodobromide phase.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention is then further explained with reference to the examples.

example 1 Fine Silver Iodobromide Grain Emulsion 1-A:

To 2.6 liters of a 2.0 wt% gelatin solution containing 0.126 M potassium bromide, 1,200 ml of a 1.2 M silver nitrate solution and 1,200 ml of an aqueous halide solution containing 0.9 M potassium bromide and 0.3 M potassium iodide were added by a double jet method with stirring over a period of 15 minutes. During the addition, the gelatin solution was kept at 35°C. Thereafter, the emulsion thus obtained was washed by an ordinary precipitation method, and after adding 30 g of gelatin and dissolving it, the pH and pAg of the emulsion were adjusted to 6.5 and 8.6, respectively. The average grain size of the obtained fine silver iodobromide grains (silver iodide content 25 wt%) was 0.05 µm.

Octahedral silver iodobromide core emulsion 1-B (invention):

To 1.2 liters of a 1.5% aqueous gelatin solution containing 0.05 M potassium bromide was added 60 ml of 0.5% 3,6-dithiaoctane-1,8-diol with stirring at 75°C in a reaction vessel, and an emulsion obtained by adding 270 ml of water to 100 g of the fine silver iodobromide grain emulsion 1-A (containing silver equivalent to 10 g as silver nitrate) to conduct nucleation. The average grain size of the octahedral silver iodobromide core grains was 0.4 µm.

Subsequently, 1,000 g of the fine grain emulsion 1-A (containing silver, corresponding to 100 g of silver nitrate) was continuously added to the reaction vessel over a period of 100 minutes. Thereafter, the emulsion was cooled to 35°C, washed with water by an ordinary precipitation method, and 70 g of gelatin was added, and the pH and pAg were adjusted to 6.2 and 8.8, respectively.

The obtained core emulsion grains were an octahedral silver iodobromide emulsion with an average diameter corresponding to the projected area of 1.2 µm (with an iodide content of 25 mol%).

Octahedral silver iodobromide core emulsion 1-C (invention):

To 1.2 liters of a 1.5 wt% aqueous gelatin solution containing 0.05 M potassium bromide was added 20 ml of 0.5% 3,6-dithiaoctane-1,8-diol with stirring at 75°C in a reaction vessel. To a mixer arranged near the reaction vessel were added 100 ml of a 0.59 M aqueous silver nitrate solution, 100 ml of an aqueous solution containing 0.44 M potassium bromide and 0.148 M potassium iodide, and 300 ml of a 2 wt% aqueous gelatin solution over a period of 5 minutes by a triple jet method. The temperature of the mixer was 20°C and the rotation number of the stirring blade of the mixer was 6000 rpm. The mean grain size of the fine grains, confirmed by a direct method using a transmission-type electron microscope at 20,000× magnification, was 0.01 µm.

The fine grains formed in the mixer were continuously fed into the reaction vessel maintained at 75°C. The average grain size of the octahedral silver iodobromide core grains (silver iodide content 25 mol%) was 0.4 µm.

Then, 600 ml of an aqueous solution of 1 M silver nitrate, 600 ml of an aqueous solution containing 0.75 M potassium bromide and 0.25 M potassium iodide, and 800 ml of an aqueous solution of 2 wt% gelatin were added to the mixer by a three-jet method at 75°C. The grain size of the fine grains thus formed in the mixer was 0.02 µm, and the fine grains were continuously added to the reaction vessel. In this case, the mixer was kept at 20°C. The emulsion formed in the reaction vessel was washed with water. and their pH and pAg were controlled as in the case of emulsion 1-B. The core emulsion grains were an octahedral silver iodobromide emulsion (silver iodide content 25 mol%) with a mean diameter, corresponding to the circle of projected area, of 0.2 µm

Octahedral silver iodobromide core emulsion 1-D (comparison emulsion):

To 1.2 liters of an aqueous 3.0 wt% gelatin solution containing 0.06 M potassium bromide was added 50 ml of 3,6-dithiaoctane-1,8-diol with stirring at 75°C in a reaction vessel, and then 50 cc of an aqueous 0.3 M silver nitrate solution and 50 cc of an aqueous solution containing 0.063 M potassium iodide and 0.19 M potassium bromide were added to the reaction vessel at 75°C by a double jet method over a period of 3 minutes. Thus, silver iodobromide grains having an average diameter corresponding to a circle for projected area of 0.4 µm and a silver iodide content of 25 mol% were obtained to form nuclei.

Then, 600 ml of a 1 M silver nitrate aqueous solution and 600 ml of an aqueous solution containing 0.75 M potassium bromide and 0.25 M potassium iodide were added sequentially to the reaction vessel by a double jet method. The emulsion thus formed was washed with water and its pH and pAg were adjusted in the same way as in Emulsion 1-B. The obtained core emulsion grains were an octahedral silver iodobromide emulsion (silver iodide content 25 mol%) with an average diameter corresponding to the circle of projected area of 1.2 µm.

To determine the microscopic iodide distribution of emulsions 1-B, 1-C and 1-D, X-ray diffraction of the (420) plane was measured using the Kα line described above. In this case, the X-ray diffraction of a pure silver bromide emulsion with the same grain size as above was also measured. The results are shown in Table 1. Table 1 Emulsion Half-width Half-width of pure AgBr

The value of (A-B) in Table 1 shows a heterogeneous distribution of iodide, and it can be seen that the half-width of the emulsion grains 1-B and 1-C is less than 1/2 of the half-width of the comparative emulsion 1-D.

Example 2

On the core emulsion obtained in Example 1, a shell of pure AgBr was formed by a double jet method at a pag of 9.0. The content of the formed shell is shown in Table 2 below. Table 2 Emulsion Core emulsion (invention) (comparison)

Each of the emulsions 2-A to 2-F thus obtained was optimally chemically sensitized using sodium thiosulfate, potassium chloroaurate and potassium thiocyanate, and after adding the following The emulsion was coated onto a triacetylcellulose film support with an undercoat layer.

(1) Emulsion layer:

Emulsion --- Emulsion according to Table 3

Matchmaker

Tricresyl phosphate

Sensitizing dye: 5-chloro-5'-phenyl-4- ethyl-3,3'-(3-sulfopropyl)oxacarbocyanine sodium

Stabilizer: 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene

Coating aid: sodium dodecylbenzenesulfonate

(2) Protective layer

2,4-Dichloro-6-hydroxy-s-triazine sodium salt

Gelatin

Each of these samples was exposed sensitometrically and subjected to the following color development process.

The density of the processed sample was then measured using a green filter. The results for the The obtained photographic performance are shown in Table 3.

The following development process was carried out at 38ºC.

1. Colour development 2 minutes 45 seconds

2. Bleaching 6 minutes 30 seconds

3. Wash 3 minutes 15 seconds

4. Fix 6 minutes 30 seconds

5. Wash 3 minutes 15 seconds

6. Stabilize 3 minutes 15 seconds

The composition of the process solution used for each step was as follows.

Color developer

Sodium nitrilotriacetate 1.0 g

Sodium sulphite 4.0 g

Sodium carbonate 30.0 g

Potassium bromide 1.4 g

Hydroxylamine sulfate 2.4 g

4-(N-ethyl-N-β-hydroxyethylamino)- 2-methylaniline sulfate 4.5 g

Water to 1 liter

Bleaching solution

Ammonium bromide 160.0 g

Aqueous ammonia (28%) 25.0 ml

Ethylenediaminetetraacetic acid sodium salt 130 mg

Glacial acetic acid 14 ml

Water to 1 liter

Fixing solution

Sodium tetrapolyphosphate 2.0 g

Sodium sulphite 4.0 g

Ammonium thiosulfate (70%) 175.0 g

Sodium hydrogen sulfite 4.6 g

Water to 1 liter

Stabilization solution

Formalin 8.0 ml

Water to 1 liter Table 3 Emulsion C/S (molar ratio) Relative sensitivity Fog content Invention Comparison

As the results in Table 3 show, it is evident that the emulsions according to the invention have a higher sensitivity than the comparison emulsions.

Example 3 Fine Silver Chlorobromide Grain Emulsion 3-A:

To 1.3 liters of a 2.3 wt.% gelatin solution containing 0.01 M potassium bromide and 0.05 M potassium chloride were added 600 ml of an aqueous 1.2 M silver nitrate solution and 600 ml of an aqueous Solution containing 0.72 M potassium bromide and 110 M sodium chloride was added by a double jet method with stirring over a period of 25 minutes. During the addition, the temperature of the gelatin solution in the reaction vessel was maintained at 35°C. Then, the resulting emulsion was washed with water by an ordinary precipitation method, and after dissolving 30 g of gelatin in the emulsion, the pH was adjusted to 6.5. The average grain size of the fine silver chlorobromide grains (silver chloride content 40%) thus obtained was 0.09 µm.

Cubic silver chlorobromide grain emulsion 3-B (comparison emulsion)

To 1.2 liters of a 3.0 wt% gelatin solution containing 0.065 M potassium bromide and 0.3 M sodium chloride were added 4.5 ml of a 1% N,N'-dimethylimidazoline-2-thione solution in a reaction vessel maintained at 75°C and 50 cm3 of an aqueous 0.3 M silver nitrate solution and 50 cm3 of an aqueous solution containing 0.18 M potassium bromide and 0.8 M sodium chloride by a double jet method with stirring over a period of 3 minutes.

By the above method, silver chlorobromide grains having an average grain size of 0.2 µm and a silver chloride content of 40 mol% were obtained to thereby carry out nucleation. Subsequently, 800 cc of an aqueous solution containing 150 g of silver nitrate and 800 cc of an aqueous solution containing 63 g of potassium bromide and 43 g of sodium chloride were similarly added by a double jet method at 75°C over a period of 100 minutes. Then, the emulsion was cooled to 35°C, washed by an ordinary flocculation method, and after adding 70 g of gelatin, the pH and pAg were adjusted to 6.2 and 7.8, respectively. The grains thus obtained were cubic silver chlorobromide grains with an average grain size of 1.1 µm and a silver chloride content of 40 mol%.

Cubic silver chlorobromide grain emulsion 3-C (invention):

In a reaction vessel, to 1.0 liter of an aqueous 0.5 wt% gelatin solution containing 0.065 M potassium bromide and 0.3 M sodium chloride was added 4.5 ml of a 1% solution of N,N'-dimethylimidazoline-2-thione with stirring, and the fine grain emulsion 3-A described above was added to the reaction vessel at 75°C by means of a pump. The addition rate was such that the fine grain emulsion corresponding to 5 g calculated as the amount of silver nitrate was added over a period of 10 minutes.

Subsequently, the fine grain emulsion 3-A was added to the reaction vessel at 75°C by means of a pump. The addition rate was such that the fine grain emulsion of 150 g, calculated as the amount of silver nitrate, was added over a period of 100 minutes.

In this case, 20 g of sodium chloride was previously dissolved in the fine grain emulsion. Thereafter, the obtained emulsion was washed with water as in the case of Emulsion 1-B, and the pH and pAg were adjusted to 6.5 and 7.8 at 40°C. The obtained grains were cubic silver chlorobromide grains having an average grain size of 1.1 µm and a silver chloride content of 40 mol%.

Octahedral silver chlorobromide grain emulsion 3-D (invention)

After carrying out the nucleation as in the case of Emulsion 1-C, 800 cm³ of an aqueous solution containing 150 g of silver nitrate, 800 cm³ of an aqueous solution containing 63 g of potassium bromide and 43 g of sodium chloride, and 800 cm³ of a 10 wt% aqueous solution of low molecular weight gelatin (average molecular weight 20,000) were fed to a mixer having a strong and efficient mixing device arranged in the vicinity of the reaction vessel by a three-jet method over a period of 100 minutes. Very fine grains (average grain size 0.02 µm) formed by stirring the reaction mixture in the mixer were immediately continuously fed into the reaction vessel from the mixer. During the feeding, the temperature of the mixer was maintained at 25ºC and the temperature of the reaction vessel at 75ºC.

Thereafter, the emulsion was washed with water as in the case of Emulsion 1-B, and the pH and pAg were adjusted to 6.5 and 7.8 at 40°C. The grains thus obtained were cubic silver chlorobromide grains with an average grain size of 1.1 µm and a silver chloride content of 40 mol%.

Each of emulsions 3-B, 3-C and 3-D was coated on a film base support at a silver coverage of 3 g/m², and to determine the microscopic distribution of the halide, the X-ray diffraction of the (420) plane was measured using the Kα line described above. In this case, the X-ray diffractions were obtained for pure silver chloride and pure silver bromide each having the same mean grain size as above. The results are shown in Table 4. Table 4 Emulsion half-width

The value of (AB) in Table 4 shows the microscopic heterogeneity and the half-widths of the emulsion grains 3-C and 3-D according to the invention are very small compared to the Comparison emulsion 3-B and are very close to silver bromide (silver chloride).

Example 4

The core emulsion obtained in Example 3 was kept at 60°C in the reaction vessel, and an aqueous solution of 1 M silver nitrate and an aqueous solution of 1 M potassium bromide were added thereto with stirring by a double jet method to form a silver bromide shell. The extent of shell formation is shown in Table 5. Table 5 Emulsion Core emulsion C/S (molar ratio) Comparison Invention

Each of Emulsions 4-A to 4-F was optimally chemically sensitized with sodium thiosulfate, potassium chloroaurate and potassium thiocyanate and coated on a support as in Example 2 to prepare coated samples. The results obtained by performing sensitometry as in Example 2 are shown in Table 6. Emulsion C/S (molar ratio) Relative sensitivity Fog content Comparison Invention

From the results in Table 6 it can be seen that the emulsions according to the invention show a higher sensitivity than the comparative emulsions.

The thus obtained silver halide photographic material containing the silver halide emulsion of the present invention has a completely homogeneous halide distribution of the silver halide core grains contained in the emulsion and can have excellent characteristics such as sensitivity, gradation, graininess, sharpness, resolving power, covering power, storage stability, latent image stability and printing resistance.

Claims (2)

1. A silver halide photographic material having at least one silver halide emulsion layer on a support, characterized in that the interior of the light-sensitive silver halide grains contained in the silver halide emulsion layer is composed of at least one phase which contains at least silver chlorobromide or silver iodobromide whose halide composition is completely homogeneous, the completely homogeneous phase of the halide composition having a half-width for X-ray diffraction of not more than the half-width shown by step A in Fig. 1 when the silver halide emulsion grains are silver chlorobromide grains, or the half-width shown by curve A in Fig. 2 when the silver halide emulsion grains are silver iodobromide grains, and the surface of the silver chlorobromide and silver iodobromide grains having a different halide composition from the interior of the Silver chloride and silver iodobromide grains, adjacent to the surface. 2. A process for producing a completely homogeneous phase of the halide composition inside the silver halide grains according to claim 1, comprising mixing an aqueous solution of a water-soluble silver salt and an aqueous solution of a water-soluble halide in a mixer arranged outside a reaction vessel for causing nucleation and/or crystal growth of photosensitive silver halide grains to form silver halide having fine grain sizes, supplying the silver halide into the reaction vessel immediately after its formation to carry out nucleation and/or crystal growth of photosensitive silver halide grains, and further forming silver halide having a different composition from the grains outside the silver halide grains, wherein a protective colloid solution contained in the reaction vessel is not circulated into the mixer, the temperature of the mixer is not higher than 40°C and the temperature of the reaction vessel is not lower than 50°C, and wherein the fine silver halide formed in the mixer comprises two or more kinds of halide.