EP0741318A1 - Photographic silver bromoiodide emulsion and process for its production - Google Patents

Abstract

In a photographic AgBrI emulsion contg. a dispersion medium and AgBrI grains, the AgI content of the grains: (a) averages 0.5-9.0 mole%; (b) is at an almost constant max. of 3-25 mole% in a zone extending over at least 10% of the distance between the centre and surface; (c) follows a gradient between this zone and a point near the surface; and (d) is max. 2 mole % at the surface. Also claimed are: (i) a method of producing the emulsion as above; and (ii) a photographic material with Ag halide (AgX) emulsion layer(s), including at least one emulsion as above, and opt. ancillary layer(s) on at least one side of a base.

Description

The invention relates to a photographic silver bromide iodide emulsion for the production of photographic recording materials with improved photographic properties, in particular those which provide images with improved image sharpness and can thereby be processed quickly, and to a method for producing such a photographic silver halide emulsion.

The radiation sensitive silver halide emulsions used in photography are known to contain a dispersion medium, typically an aqueous gelatin solution, with grains of radiation sensitive silver halide dispersed therein. Certain properties of the silver halide grains, such as, for example, the grain size, grain shape, halide composition and halide distribution, have an influence on numerous chemical, physical and photographic properties of the photographic recording materials produced therewith.

For example, silver bromide iodide emulsions with the largest possible grain volumes are used when high sensitivity of the silver halide photographic recording materials to be produced therefrom is required. However, the grain size can only be varied within certain limits, since the grain size in turn influences the properties of the photographic silver halide recording materials produced with it, such as, for example, the grain size or the time required for chemical film processing.

It is known that the sensitivity of silver halide grains increases with the iodide content in certain areas. It is also known that the sensitivity of a silver bromide iodide grain can be increased by certain changes in the iodide content within the silver halide grain.

So far, high sensitivity with a constant grain size and grain shape can be achieved with the aid of grains with a high iodide content (based on the total amount of halide in the silver halide grain). However, this increases the development and fixing times of the photographic recording material produced therewith and the gradient of the recording material undesirably decreases.

Silver bromide iodide grains with a layered grain structure, that is to say with at least two zones with a different ratio of bromide to iodide content, are known. This structure is often referred to in the literature as the "core / shell structure".

In the European patent EP-B 01 52 822 and in the German patent application DE-A 42 24 027, for example, a silver halide emulsion with a silver bromide iodide grain with at least 3 areas of different halide composition was described. The silver halide grain consists of a core of silver bromide, a first inner zone with an iodide-rich composition and a further outer zone with a lower iodide concentration compared to the inner zone. EP-B 02 02 784 describes a silver halide grain with 4 zones.

A core / shell structure is defined by a discontinuous change in the iodide content in the silver bromide iodide grain. In the X-ray powder diffraction diagram, this leads to the formation of additional diffraction lines and / or additional turning points in the case of existing diffraction lines. Silver bromide iodide grains with a core / shell structure are described, for example, in EP-A 03 37 377.

Silver bromide iodide grains without a so-called "core / shell structure" with an area of maximum iodide content inside the silver halide grain, a total iodide content of 10 mol% and a continuously decreasing iodide content from the aforementioned area to the grain surface and their Production are described in EP-A 05 81 200 and EP-A 03 30 508.

The average iodide content of silver bromide iodide grains and the course of the iodide concentration can be determined, for example, using X-ray powder diffraction analysis or by the methods described in EP-A 330 508 and EP-A 0 581 200.

Such silver bromide iodide grains are produced, for example, by the double inlet process, in which case, in addition to an aqueous solution of silver ions, aqueous solutions of halides are used side by side or in succession, optionally with a different ratio of bromide to iodide content. Alternatively, when producing silver halide emulsions in the grain growth phase, halide and silver ions in the form of finely crystalline silver halide, as described, for example, in EP-A 05 81 200, can also be added.

The object of the invention is to provide a photographic silver bromide iodide emulsion containing a dispersion medium and silver bromide iodide grains, which is characterized by improved photographic properties and is particularly suitable for the production of photographic recording material which provides images with improved sharpness and allows rapid processing, and such to provide photographic recording material and a method for producing such a photographic silver bromoiodide emulsion. A maximum iodide content of 9 mol% of the silver halide grains should be observed for a suitability of the emulsion for rapid processing.

The object is achieved by a photographic silver halide emulsion according to claim 1 and by a method for producing such a photographic silver halide emulsion according to claim 12 and a photographic recording material according to claim 14.

Dispersion medium for the preparation of photographic silver halide emulsions is preferably an aqueous gelatin solution. The gelatins used therein can have been produced by acidic or alkaline digestion of bovine bones or pig skins. Alkaline digested bovine bone gelatins are preferably used. Optionally, the gelatin can be exchanged for ions. The dispersion medium can contain other substances such as those for adjusting the pH and / or pAg, wetting agents, soluble halide salts, substances which form complexes with silver ions such as ammonia, substances which influence the growth properties of the silver halide grains (growth modifiers), photographic Stabilizers such as 7-hydroxy-5-methyl-1,3,4-triazaindolizine, sensitizers, polymers and / or color sensitizers contain.

The average proportion of iodide is defined as the average proportion of iodide based on the total silver halide grain. The average iodide content can be determined, for example, by evaluating X-ray diffraction diagrams from the corresponding silver halide emulsion. Furthermore, it can be calculated via the molar amounts and the molar ratio of the halides used in the production of the silver halide grains.

The average iodide content of the photographic silver bromide iodide emulsion according to the invention is in the range from 0.3 to 9.0 mol%. The range from 0.5 to 6.0 mol% is preferred, the range from 0.5 to 4.5 mol% being particularly preferred.

The silver halide crystals in the silver halide emulsion can have a regular crystal shape such as, for example, cubes, octahedra or cubo-octahedra, or a less regular shape such as twinned octahedra, plates, single twins with (111) and / or (100) boundary surfaces or spheres. Furthermore, silver halide emulsions can also Contain mixtures of at least two of these crystal forms. Silver halide emulsions which contain essentially twinned octahedra are particularly preferred.

Those silver halide crystals in which the average ratio of the smallest to the largest dimension (aspect ratio) is between 1.0: 1.1 and 1.0: 2.0 are considered to be approximately spherical. Examples of such silver halide crystals are cubes, octahedra, cubo-octahedra and single twins with (111) and / or (100) boundary surfaces.

Spherical silver halide crystals have a ratio of smallest to largest dimension between 1.0: 1.1 and 1.0: 1.0. Plate-shaped silver halide crystals have an aspect ratio of at least 1.0: 2.0.

The mean grain diameter of a spherical or approximately spherical silver halide emulsion is understood to mean the diameter of a sphere which is equal to the mean grain volume. This makes it possible to compare different grain shapes that approximate spherical silver halide crystals, such as cubes, single twins with (111) and / or (100) boundary surfaces or twinned octahedra, both with each other and with spherical silver halide crystals.

Of plate-shaped silver halide emulsions, preference is given to those whose silver halide crystals have an average grain diameter between 0.8 μm and 2.0 μm and on average have a ratio of grain diameter to grain thickness between 2: 1 and 30: 1. The average grain diameter of plate-shaped silver halide emulsions is defined as the average diameter of the circles of the same area of the plate-shaped silver halide grains.

The mean grain diameter of a silver halide emulsion can be determined, for example, with the aid of electron micrographs of the corresponding emulsion, if appropriate freed from binders. The grain diameter of a plate-shaped silver halide grain is defined as the diameter of the area of the same area of the projection surface of the plate-shaped silver halide grain. The aspect ratio is the ratio of the average grain diameter to the average thickness of the plate-shaped silver halide grains.

The average grain volume can be determined, for example, by the method described in German patent DE-C 20 25 147.

The average grain diameter of the silver bromide iodide emulsion according to the invention is in the range from 0.3 to 5.0 μm. The range between 0.3 and 2.0 µm is preferred.

The average grain volume of the silver bromide iodide emulsion according to the invention is in the range from 0.014 to 0.65 μm ³ . The preferred range is 0.15 and 0.5 µm ³ .

A gradient-shaped course of the iodide portion in the silver halide grain is defined in the sense of the invention as a monotonous change in the iodide portion in the silver halide composition with the distance from the center of the silver halide grain. A silver bromide iodide emulsion is preferably used, the silver bromide iodide grains of which have such a gradient course of the iodide portion over a distance of on average at least 5% of the mean grain radius.

Such a monotonous change in the iodide content in the silver halide composition of silver halide grains of a photographic silver halide emulsion can be achieved, for example, by a monotonically changed molar ratio of iodide to total halide addition during the growth phase of the silver halide grains.

The range of maximum iodide is defined as the percentage of the distance on a straight line between the grain center and the grain surface, which is defined by the two places between which the highest Iodide content and where the iodide content only makes up 90% of the maximum iodide content, based on the total length of the route.

The location closer to the grain surface with a minimum value of the iodide content contains at most 2 mol% iodide. It preferably contains less than 1 mol% iodide and can also be essentially iodide-free.

According to the invention, silver halide grains are preferably used, the iodide content of which decreases from the area of the maximum iodide content to the grain surface by at least 50% of the value of the maximum iodide content.

There are several methods available for determining the halide distribution in the structured grain structure:

The element distribution on thin sections of silver halide grains is determined with very high spatial resolution using STEM / EDX (Scanning Transmission Electron Microscope / Energy Dispersive X-Ray Analyzer) [M. Inoue, Int. Symp. Charac. Silver Halides, Japan, (1989) 2].

The investigation with BSEI (Back Scattered Electron Imaging) [X. is particularly suitable for element distribution in plate-shaped silver halide grains. Gao et al., J. Imag. Sci. 33 (1989) 87].

Element depth profiles and surface distributions on silver halide grains can be determined with SIMS (Secondary Ion Mass Spectroscopy) and high-resolution SIMS [T. Maternaghan et al., J. Imag. Sci. 34 (1990) 58].

The one in A. Russow, W. Schmal, H. Fuess and T. Müssig is particularly well suited; J. Imag. Sci. 38 (1994) 532 under the title "Characterization of AgBr _1-x I _x Emulsions by Rietveld Refinement of X-ray Powder Diffraction Data".

The width of the zone of maximum iodide content can also be determined by the ratio of the simultaneously processed amounts of bromide and Iodide can be calculated during grain production and its course over time, assuming immediate incorporation into the grain surface of the existing silver halide grains.

Growth nuclei are the silver halide grains at the end of the so-called nucleation phase. The end of the nucleation phase is characterized by an end to the formation of new silver halide grains.

Photographic silver bromide iodide emulsions are produced, for example, by generating growth nuclei in a dispersion medium and a subsequent phase of growth by controlled addition of solutions and / or suspensions containing halide and silver ions.

The growth nuclei can have different forms and iodide proportions. However, growth nuclei are preferably used which contain at least one twin level and have a maximum of 10 mol% iodide content. Growth nuclei with regular crystal form are further preferred. Particularly preferred are those with a twin level and with an iodide content of 2 to 8%, which can lead to twinned octahedra in the further course of grain production. Alternatively, those with a twin level and with an iodide content of at most 0.5% are particularly preferred, which can lead to plate-shaped silver halide grains in the further course of the grain production.

Silver halide grains with at least one twin plane are described, for example, in DE-A 39 31 629 (quadruple twin crystals) and EP-A 0 600 753.

Such silver halide emulsions can be prepared, for example, by the double inlet precipitation process using an additional adjustable pump for an aqueous solution of a soluble iodide salt or an aqueous solution of a soluble iodide salt and a soluble bromide salt. Such a manufacturing process is for example in the American patent US 4,722,886. Examples of such soluble salts are potassium bromide, sodium bromide, potassium iodide, magnesium iodide, magnesium bromide, lithium iodide and sodium iodide.

• a) zunächst eine Fällung von Silberhalogenidkeimen mit 0 bis 10 Mol-% Iodidanteil bei einer Temperatur von 30° bis 85°C und einer Bromidkonzentration von pBr = 0,6 bis 3,0 durch Doppeleinlauf gebildet,
• b) in einem Teil der anschließenden Wachstumsphase Silberionen sowie Bromid und Iodid in einem konstanten Verhältnis zugegeben, sodaß die Iodidkonzentration in dem Reaktionsgefäß innerhalb einer bestimmten Zeitspanne konstant bleibt,
• c) wenigstens eine weitere Silberhalogenidschicht aufgefällt, wobei die zuzugebende Menge von Iodid relativ zu der zuzugebenden Menge an Bromid kontinuierlich sinkt, so daß die Iodidkonzentration in dem Reaktionsgefäß kontinuierlich abnimmt und der Iodidanteil im Silberhalogenidkorn einen kontinuierlichen gradientenförmigen Verlauf nimmt.

In such a production process for the silver bromide iodide emulsion according to the invention, in an optionally temperature-controlled reaction vessel which contains at least part of the dispersion medium, the amount of aqueous silver salt, bromide and iodide solutions added is checked over time

• a) first, a precipitation of silver halide nuclei with 0 to 10 mol% iodide content at a temperature of 30 ° to 85 ° C and a bromide concentration of pBr = 0.6 to 3.0 is formed by double entry,
• b) in a part of the subsequent growth phase, silver ions and bromide and iodide are added in a constant ratio so that the iodide concentration in the reaction vessel remains constant within a certain period of time,
• c) at least one further silver halide layer is noticeable, the amount of iodide to be added continuously decreasing relative to the amount of bromide to be added, so that the iodide concentration in the reaction vessel decreases continuously and the iodide content in the silver halide grain takes a continuous gradient.

In a preferred embodiment, at least one flow-controlled pump is used in this method to control the iodide content, with which at least one of the aqueous solutions of bromide and / or iodide salts is metered into the reaction vessel.

The emulsion according to the invention can also be used in combination and / or as a mixture with at least one other silver halide emulsions.

Of those in light-sensitive silver halide photographic materials according to the invention Silver halide grains used should advantageously consist of at least 75% by weight, preferably all, based on the total amount of grains in the same silver halide emulsion layer, of the silver halide grains according to the invention.

In addition to one or more spectrally sensitized emulsion layers, the silver halide photographic material can contain one or more different auxiliary layers on both sides of the support material, such as, for example, adhesion-promoting layers, sliding layers, protective layers, intermediate layers, anti-roll or NC layers (NC = non-curling), antistatic layers and colorants containing layers such as antihalation layers.

The protective layer is the layer that is furthest away from the base and does not contain any silver halide. In addition to hydrophilic binders such as gelatin, which can be produced by both acidic and alkaline digestion, and such surface-active substances, such protective layers optionally also contain other substances which influence the chemical, physical and mechanical properties of the photographic recording material. These substances include, for example, lubricants, surface-active substances containing perfluoroalkyl groups, latices (polymeric organic particles), stabilizers, finely divided SiO ₂ dispersions, matting agents (spacers), curing agents, antistatic substances and preservatives.

Metal ions such as cadmium, zinc, thallium, mercury, iridium, rhodium and iron or their complexes may be present during the production and / or physical ripening of the silver halide emulsion.

After crystal formation has been completed or at an earlier point in time, the soluble salts are removed from the emulsion, for example by pasta and washing, by flakes and washing, by ultrafiltration or by means of ion exchange.

The silver halide emulsion is generally subjected to chemical sensitization under defined conditions - pH, pAg, temperature, gelatin, silver halide and sensitizer concentration - until the optimum sensitivity and fog are reached. In chemical sensitization, chemical sensitizers such as active gelatin, sulfur, selenium or tellurium compounds, salts or complexes of gold, platinum, rhodium, palladium, iridium, osmium, rhenium, ruthenium can be used alone or in combination. Procedures are described, for example, by H. Frieser "The basics of photographic processes with silver halides" page 675-734, Akademische Verlagsgesellschaft (1968) or in TH James, The theory of the photographic process, 4th ed., Macmillan Publishing Co., Inc. , New York, pp. 149-160 and in the publications cited therein.

A compound suitable for reduction sensitization can be added to the silver halide emulsion in the course of the preparation. The term "reduction sensitization" here means that a reducing agent is added to the emulsion and thereby the photosensitivity of the silver halide emulsion is increased. The addition can take place at any time in the production process, for example during the precipitation of the silver halide and before, during or after chemical ripening. Suitable reducing agents are, for example, tin (II) chloride, hydrazine and certain hydrazine derivatives, glutardialdehyde, glutardialdehyde bisulfite, formamidinesulfinic acid, thiourea dioxide, silanes, reductones such as ascorbic acid, ascorbic acid derivatives and comparable reducing sugars, polyamines such as, for example, dimethylene triamine and boramine Dimethylaminoborane.

The reduction sensitization can also be brought about by treating the emulsion with gaseous hydrogen or by digesting the emulsion with excess silver ions.

The layers of the photographic recording material can contain substances for stabilizing the emulsion against fog or for stabilizing other photographic properties such as, for example, sensitivity. These substances include, for example, bromides, benzothiazolium, nitroindazole, nitrobenzimidazoles, mercaptothiazoles, Mercaptobenzothiazoles, Mercaptobenzimidazoles, mercaptothiadiazoles, chlorobenzimidazoles, bromobenzimidazoles, aminotriazoles, benzotriazoles, nitrobenzotriazoles, mercaptopyrimidines, mercaptotriazines, thioketo such as oxazolinthione, Azaindolizine as triazaindolizines and Tetraazaindolizine as the most preferred 5-hydroxy-7-methyl-1,3,4, -triazaindolizine, and mercaptotetrazoles such as 1-phenyl-5-mercaptotetrazole. These substances can be contained alone or in combination with other substances of this group in the layers of the photographic recording material.

To produce the photographic silver halide recording materials according to the invention, the layers containing hydrophilic binders can contain organic or inorganic hardening agents. The hardening of a layer can also be effected by covering the layer to be hardened with a layer which contains a diffusible hardening agent, as described, for example, in DE-A 38 36 945. The curing agent can be added in the course of the preparation of emulsion solutions and / or casting solutions for auxiliary layers. Another possible form of addition of hardening agents is to inject a solution of the hardening agent into at least one emulsion or casting solution during the transport of the solution from the storage kettle to the casting device. In addition to water, other suitable solvents are water-miscible organic solvents such as ethanol, acetone, dimethyl sulfoxide or 1,4-dioxane.

To stabilize the hardening agent solution, substances or mixtures of substances can be present which adjust and / or buffer the pH value of the hardening agent solution. An example of this is the borate buffer described in DE-C 28 20 108.

Examples of such hardening agents which can be used in photographic recording media are chromium salts such as chromium alum, aldehydes such as formaldehyde, glyoxal and glutardialdehyde, N-methylol compounds such as N, N'-dimethylolurea, compounds containing reactive vinyl groups such as 1,3-bis- (vinylsulfonyl) -2-propanol , Bis (vinylsulfonyl) methyl ether, N, N ', N' '- trisacryloylhexahydrotriazine, polymeric curing agents as described for example in DE-C 32 23 621, 1,3-bis-carbamoylimidazolium compounds as described in DE-B 41 19 982 or carbamoylpyrimidinium compounds as described for example in DE-C 23 17 677. Two or more curing agents can also be used side by side. In a preferred embodiment, formaldehyde is used at least in part as the curing agent.

Spectral sensitizers in the silver halide emulsion can include, for example, cyanine dyes, merocyanine dyes, oxonol dyes, hemioxonol dyes, hemicyanine dyes, styryl dyes. A spectral sensitizer alone or a combination of at least two spectral sensitizers can be used.

Such spectral sensitizers or combinations of spectral sensitizers are usually used in silver halide emulsions in an amount of 20 mg to 3.0 g per mole of silver halide.

The photographic recording material can each have one or more silver halide emulsion layers on one or both sides of the support material. In a preferred form, the photographic contains Recording material only on one side of the carrier material at least one silver halide emulsion layer.

Silver coating is understood to mean the weight of silver in the form of its ions in the layers containing the silver halide crystals, based on the unit area of the silver halide photographic material. The values for the silver application are given in grams / square meter and relate to the sum of all layers of the recording material containing silver halide.

In the case of spectrally sensitized silver halide recording materials, the silver application is usually in the range between 0.5 g / m ² and 8 g / m ² .

As a protective colloid for the silver halide crystals in the emulsion layer and as a hydrophilic binder, alkaline digested bovine bone gelatin is preferably used. This can be exchanged for ions.

In addition, other hydrophilic binders can also be used in the various layers of the silver halide recording material. Examples of hydrophilic binders are synthetic polymers such as polymers or copolymers of vinyl alcohol, N-vinylpyrrolidone, acrylamide, acrylic acid, methacrylic acid, vinylimidazole, vinylpyrazole and natural polymers such as casein, gelatin (acid or alkaline digested, made from bovine bones or pigskins), cellulose and cellulose derivatives , Alginates, albumin, starch and modified polymers such as hydroxyethyl cellulose, hydrolyzed gelatin, chemically modified gelatin as described for example in EP-A 03 75 522, chemically modified and hydrolyzed gelatin as described for example in DE-B 21 66 605 and US 3,837,861.

In the silver halide photographic material, the hydrophilic binder in the silver halide emulsion layers as well as other auxiliary layers such as protective layers, Adhesive layers, intermediate layers or non-light-sensitive layers may be included.

In addition to the hydrophilic binders, further binders and matting agents can be contained in the layers of the photographic recording material. Examples of such binders are latices (polymeric organic particles) which are introduced into the corresponding casting solution in the form of aqueous dispersions which are usually stabilized by wetting agents.

The silver halide emulsion and the mixtures for the production of auxiliary layers can contain surface-active substances for various purposes, for example as coating aids, to prevent electrostatic charging, to improve the sliding properties, to emulsify the dispersion, to prevent adhesion and to improve photographic properties Characteristics (e.g. acceleration of development, high contrast, sensitization).

In addition to natural surface-active compounds such as saponin, synthetic surface-active compounds (surfactants) are mainly used: nonionic surfactants which contain oligo- or polyoxyalkylene groups, glycerol compounds and glycidol compounds, cationic surfactants, for example higher alkylamines, quaternary ammonium salts, pyridine compounds, and other heterocyclic compounds, sulphonium compounds or Phosphonium compounds, anionic surfactants containing an acid group, for example carboxylic acid, phosphoric acid, sulfuric acid ester or phosphoric acid ester group, ampholytic surfactants such as amino acid and aminosulfonic acid compounds, and sulfur and phosphoric acid esters of an amino alcohol.

The layers of the photographic recording material can contain filter dyes such as oxonol dyes, hemioxonol dyes, styryl dyes, merocyanine dyes, anthraquinone dyes, cyanine dyes, azomethine dyes, Contain triarylmethane dyes, phthalocyanines and azo dyes.

The carrier material of the photographic recording material can consist, for example, of an optionally resin-coated paper, of optionally coated aluminum or of a transparent and optionally colored plastic film. Such a plastic film can be produced, for example, from plastics such as polyethylene terephthalate, cellulose acetate, cellulose acetate butyrate, polystyrene or polycarbonate and may have further layers such as adhesive layers or antistatic layers.

Carrier materials made of aluminum are used, for example, in the production of offset printing plates.

The surface of the carrier material is preferably treated by a corona discharge before a first coating in order to improve the adhesion properties.

Various casting methods can be used to make the photographic material. Examples of this are curtain casting, cascade casting, dip casting, wash-on casting, slot casting. If necessary, several layers can be applied simultaneously.

A general overview of photographic silver halide emulsions, their preparation, additions, processing and use is in the monograph of TH JAMES "The Theory of the photographic process" 4th edition, Macmillan Publishing Co., Inc. New York, 1977, in Research Disclosure, Vol. 365, number 36544 (September 1994) and Research Disclosure, Vol. 308, number 308119 (December 1989) and the quotations contained therein. [Research Disclosure is published by Kenneth Mason Publications Ltd., Dudley Annex, 21a North Street, Elmsworth, Hampshire P010 7DQ, England.]

The emulsions according to the invention can be used extremely versatile in photographic recording materials and recording units for image transfer processes. Examples of these are color negative films, color reversal films, color positive films, black / white and color photographic papers, CRT films, photographic recording materials for the production of offset printing plates, reprofilms and X-ray films. For example, they can be used for the production of radiographic recording materials, in the production of which a radiation-transmissive support is coated on both sides with at least one radiation-sensitive layer.

The sensitometric evaluation of the photographic recording materials produced with the silver bromide iodide emulsion according to the invention can be carried out, for example, with the aid of the 4th edition of TH JAMES "The Theory of the photographic process", Macmillan publishing Co., Inc. New York, 1977, chapters 17 and 18 and if necessary with the help of the literature cited there.

The sensitivity and the gradation of a photographic recording material for radiography produced using the silver bromide iodide emulsion according to the invention can, for example, according to the German standard DIN 6867 (April 1985) or as in "Image quality in X-ray diagnostics", edited by H.-S. Stender and F.-E. Stieve, Deutscher Ärzte-Verlag Cologne, 1990 described.

The silver bromide iodide emulsion according to the invention additionally has an improved ratio of sensitivity to silver color of the photographic recording materials produced therewith and, when used in green and / or blue-sensitized layers, an improved ratio of red sensitivity to sensitivity of the photographic layer or in other words an improved Darkroom security of the photographic recording materials produced therewith.

Furthermore, the photographic recording materials produced with the silver bromide iodide emulsion according to the invention advantageously have a particularly strongly advanced foot gradient in the sensitometric curve. As a result, the use of the silver bromide iodide emulsion according to the invention is particularly well suited for the production of such photographic recording materials which are suitable for the production of black and white and color images on paper supports.

When the silver bromide iodide muslion according to the invention is used in medical X-ray films, the X-ray image produced therewith has a higher diagnostic information content.

Examples:

The silver bromide iodide emulsions VT1 to VT8 as comparison emulsions and ET1 to ET6 as emulsions according to the invention having a tabular grain shape are produced by the double-inlet precipitation method described in US Pat. No. 4,722,886, and the emulsions EO1 and EO2 according to the invention with a shape of the grains of twinned octahedra. The growth nucleus in the tabular crystal nuclei consisted of pure silver bromide. The growth nuclei of the twinned octahedra each contained silver bromide iodide with 2% iodide content. The iodide content in the silver halide grains was checked in each case by regulating the metering of an aqueous solution of potassium iodide and potassium bromide with the aid of an additional sequence-controlled pump. The emulsions were then subjected to post-ripening consisting of gold / sulfur ripening and reduction sensitization. The aspect ratio of the tabular silver halide grains was on average between 1: 4 and 1: 6 for each emulsion. The average grain diameter was about 1.2 µm and the average Grain thickness was about 0.24 µm in each case. The mean grain volumes V (50) of the twinned octahedra or of the silver halide emulsions containing plate-shaped grains are described in Table 1.

Table 1 also shows the grain structures, the maximum iodide content Imax, the respective average iodide content Iges, the sensitivity of the silver halide emulsion in tenths of decadic logarithmic units and the percentage of the width of the zone of maximum iodide content in the grain radius DP based on the grain radius and the average grain volume V (50).

Furthermore, the sensitivity and the gradient, measured in each case at density 1 via fog, of photographic recording materials which have an adhesion-promoting layer on a substrate of blue-colored polyethylene terephthalate and in each case the silver halide emulsion to be investigated in a silver halide emulsion layer with a basis weight of silver of 2.2 g / m ² included, shown in Table 1.

The sensitivity and the gradation of the silver halide photographic materials thus prepared were as described in "Image Quality in X-ray Diagnostics" published by H.-S. Stender and F.-E. Stieve, Deutscher Ärzte-Verlag Cologne, 1990 described.

The grain structures, the maximum iodide content Imax and the average iodide content were determined with the aid of X-ray powder diffraction analyzes according to the methods described in A. Russow, W. Schmal, H. Fuess and T. Müssig; J. Imag. Sci. 38 (1994) 532. The width of the zone of maximum iodide content results from the ratio of the simultaneously processed amounts of bromide and iodide during the grain production and its course over time.

The mean grain volume V (50) of the silver halide emulsions was determined using the method described in German Patent DE-C 20 25 147. Table 1 emulsion structure DP [%] Imax [%] Iges [%] sensitivity gradient V (50) [µm ³ ] VT1 Core / Shell 75 10th 2.6 68.2 0.8 0.22 VT2 Core / Shell 80 10th 3.7 68.5 1.0 0.22 VT3 Core / Shell 52 20th 2.3 67.7 1.6 0.23 VT4 Core / Shell 75 20th 5.1 64.5 1.0 0.22 VT5 Core / Shell 80 20th 7.4 66.0 1.0 0.23 VT6 Core / Shell 52 10th 1.1 67.7 1.6 0.21 VT7 Core / Shell 52 20th 2.2 67.0 0.8 0.20 VT8 unstructured. 100 10th 10th 67.5 1.2 0.20 ET1 gradient 22 10th 0.8 69.5 1.4 0.22 ET2 gradient 22 20th 1.7 68.0 1.0 0.24 ET3 gradient 56 5 1.9 69.5 1.7 0.25 ET4 gradient 56 10th 3.8 69.9 1.6 0.28 ET5 gradient 56 20th 7.6 68.8 1.2 0.22 ET6 gradient 80 10th 7.5 68.9 1.0 0.18 EO1 gradient 56 10th 3.7 70.5 1.6 0.22 EO2 gradient 22 10th 0.9 70.0 1.4 0.24

From the values shown in Table 1 it can be seen that the silver bromide iodide emulsions ET1 and ET2 and EO1 and EO2, which have a continuous decrease in the iodide concentration, compared to the comparative emulsions VT1 to VT8 an improved sensitivity with a comparable gradient and have comparable grain volume. The two emulsions EO1 and EO2 containing octahedral silver halide grains have a higher sensitivity compared to the two plate-shaped emulsions ET1 and ET2 containing silver halide grains. The comparison of the two emulsions ET4 and EO1 also shows that, for emulsions of the same sensitivity and gradation, an emulsion containing essentially octahedra requires silver halide grains with a lower average grain volume V (50) than an emulsion containing plate-shaped silver halide grains.

Claims (14)

Photographic silver bromide iodide emulsion containing a dispersion medium and essentially silver bromide iodide grains which meet the following requirements a) to d): a) The silver halide grains have an average molar iodide content of 0.5 to 9.0 mol%; b) the silver halide grains have a range of maximum molar iodide content, located between the center of the grain and the grain surface, with a molar iodide content of 3 to 25 mol%, based on the total amount of halide. This area takes up at least 10% of this distance on an imaginary line from the center of the grain to the surface of the grain and has an essentially constant iodide content; c) the silver halide grains have a gradient-shaped course of the iodide portion in the silver halide grain between the range of maximum molar iodide portion and a location closer to the grain surface; d) the silver halide grains have a molar iodide content of at most 2 mol% on the grain surface. Photographic silver halide emulsion according to claim 1, characterized in that the mean grain diameter is between 0.3 and 2.0 µm. Photographic silver halide emulsion according to claim 1 or 2, characterized in that the average grain volume is between 0.15 and 0.5 µm ³ . Photographic silver halide emulsion according to Claims 1 to 3, characterized in that the area within the silver halide grains in which the maximum value of the iodide concentration is present is at least 0.1 µm from the center of the grain. Photographic silver halide emulsion according to Claims 1 to 4, characterized in that a regular growth nucleus containing at least one twin level and containing a maximum iodide content of 10 mol% is used for the production thereof. Photographic silver halide emulsion according to Claims 1 to 5, characterized in that a plate-shaped growth nucleus with an iodide content of at most 0.5 mol% or a growth nucleus in the form of an octahedron with an iodide content of 2 to 8 mol% is used for the production thereof. Photographic silver halide emulsion according to Claims 1 to 6, characterized in that a growth nucleus in the form of a twinned octahedron with an iodide content of 2 to 8 mol% is used for the production thereof. Photographic silver halide emulsion according to Claims 1 to 7, characterized in that the grain shape of the silver bromide iodide grains consists essentially of twinned octahedra. Photographic silver halide emulsion according to Claims 1 to 8, characterized in that the range of the maximum value of the iodide concentration is 10 to 85% of the grain radius. Photographic silver halide emulsion according to Claims 1 to 9, characterized in that the iodide content in the range of the maximum iodide concentration is between 3 mol% and 25 mol%. Photographic silver halide emulsion according to Claims 1 to 10, characterized in that the iodide content in the range of the maximum iodide concentration is between 5 mol% and 16 mol%. A process for the preparation of a photographic silver bromide iodide emulsion according to any one of claims 1 to 11 by a time and quantity controlled Introduction of silver, bromide and iodide salt solutions into a reaction vessel which contains at least part of the dispersion medium, characterized in that a) first a precipitation of silver halide nuclei with 0 to 10 mol% iodide content is formed at a temperature of 30 to 85 ° C and a bromide concentration of pBr = 0.6 to 3.0 by double entry, b) silver ions, bromide and iodide are added in a constant ratio in the subsequent growth phase, c) at least one further layer of silver halide is noticeable, the amount of iodide to be added continuously decreasing relative to the amount of bromide to be added, so that the iodide concentration in the reaction vessel remains essentially constant within a certain period of time and decreases continuously from a certain point in time during the grain growth. A process for the preparation of a photographic silver bromide iodide emulsion according to claim 12, characterized in that at least one sequence-controlled pump is used to control the iodide content, which pumps in at least one of the aqueous solutions of water-soluble bromide and / or iodide salts. Photographic recording material consisting of a support material and at least one silver halide emulsion layer and optionally auxiliary layers on at least one side of the support material, characterized in that at least one of the silver halide emulsion layers contains a photographic silver halide emulsion according to one of Claims 1 to 11.