DE2921077A1 - METHOD FOR MANUFACTURING TWIN-TYPE SILVER HALOGENIDE CRYSTALS CONTAINING PHOTOGRAPHIC SILVER HALOGENIDE EMULSIONS - Google Patents

Description

DR. BERG DifL.-ING. STAFF DIPL.-ING. SCHWABE DR. DR. SANDMaIR

PATENTANWÄLTE PO Box 860245 8000 Munich 86 2921077

Attorney's file: 30 135 May 23, 1979

CIBA-GEIGY AG
Klybeckstrasse
CH- 4002 Basel

Process for the production of silver halide crystals from Twin-type silver halide photographic emulsions

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• (0 (9) 981272 Tdtmmme: Bank account: Hrpo-Bank MOndm 4410122 »»

73 BERCSTAPFPATENT Manchen (BLZ 70020011) Swill Cad ": HYPO OE MM

988274 TELEX: Bay «Verenjbmk Munich 453100 (BLZ 70020270)

913310 052456OBEROd Poetxhedc MOachco «5343-JOMBLZ 700100KO

CIBA-GEIGY AG 8-11721 / ILF 1174 / +

Basel, Switzerland)

Process for the preparation of silver halide photographic emulsions containing twin-type silver halide crystals

The present invention relates to improved silver halide photographic emulsions and a process for making such emulsions and provides an improvement or modification of the invention according to DE-OS '2725993.

Silver halide emulsions are composed in a colloid medium, which often consists of gelatin, dispersed silver halide crystals together. The properties of photographic emulsions vary widely significantly different from the various, used to manufacture the photographic emulsion carried out steps and in each case of the ratio and the order one or more such stages.

Thus, one common method of making such an emulsion is initial precipitation (Nucleation) of microscopic silver halide crystals, usually a silver salt solution with a solution of a water-soluble halide salt

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mixed, growth of these crystals by further addition of reagent solutions, washing the emulsion to remove more water-soluble, as a by-product of the double conversion reaction in the previous precipitation stages salts formed as well as sensitization to the intrinsic sensitivity of the finished emulsion through treatment with chemical sensitizers such as sulfur and gold salts, and in many cases by adding spectral sensitizers Dyes, increase.

The stages of such an emulsion preparation process can be tailored precisely to the various to achieve desirable goals so that one can obtain emulsions with the required photographic Properties can get. The precipitation stages in the process can be adapted so that the average size of the silver halide crystals (which generally determines the sensitivity of photographic Emulsion), the size distribution of such crystals (which influences the photographic contrast), the shape and habit of the crystals (including the outer lattice surfaces and the degree twinning) and the halide composition of the crystals. It is of particular advantage the uniformity of the halide distribution within the crystal population and the halide composition profile control within each crystal. Possess the shape and internal structure of the crystals also an important influence on the photographic behavior of the emulsion. In particular, they are twinned Silver halide crystals in many applications because of their high photographic sensitivity and Opacity (ratio of the developed blackness to the weight of developed silver) is favorable.

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ORIGINAL INSPECTED

This invention particularly relates to silver halide crystals which have a specific shape and have a special habitus. In order to achieve this selection in shape and habitus, however, one has to some restriction on the composition of shark ogenides as well proved necessary. Specifically, this invention provides an improved method for Production of twin-type emulsions from silver iodobromide, Silver iodochloride or silver iodochlorobromide through the targeted incorporation of silver iodide into the silver halide crystals during their growth.

Improved photographic properties are often observed when precipitating the silver halide a mixture of water-soluble halides is used. As from Gutoff in the U, S. U.S. Patent No. 3,773,516 There are two generally accepted methods of controlling the precipitation of silver halide, namely Single nozzle and the double nozzle emulsification method. In the single nozzle process, aqueous silver nitrate solution becomes one added a small amount of gelatin and a mixture of soluble halides containing solution. The crystal size distribution can be after partial or complete introduction of the silver nitrate by a Control Ostwald's maturation level, whereby one can control the Holds emulsion in the presence of a silver halide solvent at elevated temperatures. During this stage the least soluble large crystals grow by diffusion and incorporation of the more soluble ones small crystals of dissolved silver halide.

The maturation stage leads to an increase in the average crystal size of the emulsion (and often an increase in the photographic speed of the finished emulsion) and a broadening the crystal size distribution. Because of the big one

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Excess of halide ions, which during the precipitation and ripening stages are present, indicate those after Single nozzle processes often produced photographic emulsions predominantly in the crystal habit of twinned ones Octahedron crystals. This applies in particular to iodine bromide precipitations. "An Introduction to Crystallography [Introduction to Crystallography] "by F.C. Phillips, 3rd Edition, Longmans (1966), pp. 162-165 and "The Crystalline State" by P. Gay, Oliver and Boyd (1972), pp. 328-338, give a description of crystal twins. The disadvantage of such a single nozzle method is there in that the twinned crystals produced in the process inevitably have a relatively broad size distribution exhibit. On the other hand, in the double nozzle process, aqueous solutions of silver nitrate and soluble ones Halide salts are simultaneously added to a gelatin solution with stirring. The flow velocities the reagent solutions can be regulated so that the amount of excess halide is kept constant and predominantly non-twinned crystals are formed.

Silver halide crystals of flat or tabular shape show extremely good development results Opacity, and this results in very good silver utilization compared to other silver halide crystals Shape, for example cubic crystals. Many twinned octahedral crystals belong to this Type, especially if the crystals contain more than one twin plane and the twin planes are parallel are. It is a particular object of the present invention, the proportion of twin crystals with parallel Increase twin levels in an emulsion.

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As there are improvements in the commercial manufacture of photographic emulsions, there is another Task is to increase the contrast of the finished material, something for the graphic industry and radiography products represents a desirable property. This can be partially achieved by narrowing the size distribution as described, for example, in British Patent Specification No. 1,469,480, as well as partly by the fact that there is a greater similarity between the iodide content and the iodide distribution in different types Ensures silver halide crystals in the emulsion. It is well known that the point where soluble influences Iodide salt is added in various emulsification processes, the sensitivity and size distribution

the emulsion (Research Disclosure No. 13,452 (1975)) The application of photographic emulsions that

Twin crystals contained in materials with increased sensitivity and increased contrast was therefore made by the lack of traditional emulsification procedures, especially the uncontrolled one Incorporation of iodide into the crystals. An Improved Process for Making Photographic Prints Emulsions of silver iodobromide, silver iodochloride or silver iodochlorobromide were described in DE-OS '2,725,993 described, wherein iodide ions are obtained by dissolving a uniform dispersion of silver iodide crystals feeds the growing crystals. The conditions under which this Process promotes the desired tabular twinned habit and largely uniform photographic Emulsion crystals of this type can be produced.

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- / I O

For example, DE-OS ¹ · 2 725 993

a method for preparing a twin-type silver halide emulsion is described, wherein one is stepwise (a) Silver halide crystals containing at least 90 mol% iodide forms in a colloid dispersing medium, (b) an aqueous silver salt solution and an aqueous alkali or Ammonium bromide or chloride solution or mixtures thereof into the one containing these silver halide crystals Dispersing medium mixed in, so that twinned silver halide crystals form, the iodide and the or containing the added halide (s), (c) the dispersing medium mixed with a silver halide solvent and thus growth due to Ostwald's ripening of the twinned crystals, if necessary

(d) by adding further aqueous silver salt solution and further alkali or ammonium halide to the colloidal Dispersion allows the twinned crystals to increase in size and eventually afterwards if necessary

(e) the water-soluble salts formed are removed and the emulsion is chemically sensitized.

It has now been found that the method just described can be modified by using the at least 90 mol% iodide-containing silver halide crystals in Stage (a) chemically sensitized.

The present invention is accordingly a A method for preparing a twin-type silver halide emulsion which is characterized in that: stepwise (a) silver halide crystals containing at least 90 mol% iodide forms in a colloidal dispersion medium, these crystals predominantly having the hexagonal lattice structure have, and then this at least 90 mol% Iodide-containing silver halide crystals chemically sensitized, (b) an aqueous silver salt solution and a aqueous alkali or ammonium bromide or chloride solution or mixtures thereof into the these silver halide crystals

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containing dispersing medium mixed in, so that twinned Form silver halide crystals containing iodide and the added halide (s), (c) the Dispersing medium with a silver halide solvent offset and thus growth through Ostwald's ripening of the twinned crystals, if necessary (d) by adding further aqueous silver salt solution and further alkali or ammonium halide for colloidal dispersion, the twinned crystals increase in size and finally, optionally thereafter (e), the water-soluble salts formed are removed and the surface is removed the silver halide crystals of the emulsion are chemically sensitized.

In the method according to the invention, they serve first high iodide silver halide crystals formed in step (a) as seeds for the in step (b) formed twinned crystals. Silver halide crystals with a high iodide content, i.e. about 90 to 100 mol% Iodide, predominantly have the hexagonal lattice structure. Methods for the production of silver iodide with predominantly hexagonal lattice structures are well known and for example by B.L. Byerley and H. Hirsch, J.Phot.Sei., Vol 18, pp. 53 (1970). ■ Have such crystals the shape of hexagonal pyramids or bipyramids. The base surfaces of these pyramids represent the lattice planes (000l \ dar. Silver iodide crystals with a hexagonal lattice structure are shown in Figure la.

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Silver halide crystals that contain minor amounts of iodide (i.e. up to about 45 mole percent iodide) however, the face-centered lattice structure and an octahedral crystal form (the outer forms [ill] lattice planes). It is known that these crystal forms are modified by twinning can, so that twin crystals face-centered cubic lattice structure the shape of triangular or hexagonal May have plates, the shape depending on the number and geometry of the twin planes formed.

In the inventive method in step (b) aqueous solutions of a silver salt and a Alkali or ammonium bromide or chloride (or mixtures thereof) compared to the predominantly hexagonal silver iodide crystals Lattice structure-containing dispersion medium added so that silver bromide (or chloride or chloride bromide) is precipitated. However, there is no overall growth The S can take place via iodide crystals of this structure, nuclei of the added SiI superhalide form as very small crystals of the face-centered cubic lattice type, because the iodide content in these Crystals is very small. During this stage, however, the silver iodide crystals initially formed dissolve on, and silver iodide will be in the growing crystals with it Face-centered cubic lattice built in. Electron micrographs have shown that in stage (b) while no overall circumferential growth of the silver iodide crystals takes place, the crystals of the halide added in step (b) are face-centered cubic lattice type and oriented on the base surfaces of the silver iodide crystals formed in step (a) grow up. Oriented growth between {OOOl} AgJ surfaces and {III ^ - AgBr or AgCl surfaces is possible, since both are hexagonal close-packed, homoionic lattice planes. In electron microscopy

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it was observed that the crystals grow in an oriented manner as long as they are bound to the silver iodide base crystal have a high degree of twinning (recognizable by the fact that several of them intersect the surface Twin planes characteristic parallel stripes). It is believed that this twinning is caused by the continuous supply of iodide ions to the growing (face-centered cubic, fzk) phase is favored, either by mass diffusion through the dispersing medium through or by anionic diffusion through the crystal interface. Generally imagines twinned (fzk) crystal on the single base of a hexagonal pyramidal silver iodide crystal, while twinned crystals each on the beddea base surfaces of the hexagonal bipyramidal silver iodide crystal. FIG. 1 illustrates the recrystallization schematically and with the aid of electron microscope images of silver iodide crystals with hexagonal Lattice, around silver iodobromide crystals with cubic lattice to build. It is shown as a hexagonal bipyramidal Silver iodide crystal a recrystallization according to the oriented growth mechanism. In general, the twinned silver iodobromide crystals are formed each on the base of the (truncated) hexagonal bipyramidal silver iodide crystal (a). As step (b) progresses and the precipitation of silver halide continues, the iodide content falls of the total halide suspended in the dispersion medium below 30-40 mol% of silver iodide. - The resolution of the originally formed silver iodide crystals becomes predominant, and one observes the "dumbbell" -shaped, in figure 1 (b) crystals shown. In the course of this stage the twinned crystals increase in size

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to and the silver iodide crystals off. Finally will the superiodide link between the two twinned Crystals are broken, and the two twinned crystals are released (ic). The rest of the silver iodide can remain on the twinned crystals with face-centered cubic lattice, or it can will eventually be dissolved away. The lower part of FIG. 1 shows electron microscope images (enlargement 30,000 x), the progress of the formation of dumbbell-shaped crystals and the eventual release the hexagonal or triangular platelet shapes characteristic of twinned silver halide crystals illustrate. After the Ostwald's have been carried out Maturation stage (c) are the smaller ones, also produced and in the last electron microscopic Inclusion of visible, um / twin crystals preferably dissolve.

In the recrystallization of silver iodide under Formation of silver iodochloride or silver iodochlorobromide crystals a similar process takes place.

In the process of the present invention, chemically sensitized silver halide crystals are obtained in step (a) high iodide content. It was found that such crystals correspondingly form during step (b) the formation of twinned crystals dissolve and the chemical sensitization products with the incorporation of the iodide are transferred to the twinned crystals, giving the finished crystals an enhanced photographic appearance Gives sensitivity.

There are four main known methods of chemically sensitizing silver halide emulsions. These consist of gold and other precious metal sensitization, heavy metal sensitization with for example Bismuth and lead salts, sulfur and others

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Middle chalcogen sensitization as well as reductive sensitization. Any of these methods are applicable to the method of the present invention. Likewise a combination of these methods can be carried out at the same time, for example gold and sulfur sensitization. This sensitization method is illustrated using the preparation of emulsion A in the following example.

A particularly suitable method ^for sensitizing silver halide crystals is the use of noble metals from Group VIII. Metal compounds suitable for such sensitization are, for example, polyvalent cations, including divalent ions (e.g. lead), trivalent ions (e.g. antimony, bismuth, arsenic, gold, iridium and rhodium) as well as tetravalent ions (e.g. osmium, iridium and platinum).

The noble metal compounds typically used include ammonium and potassium chloropalladate, Ammonium, sodium and potassium chloroplatinate, ammonium, potassium and sodium bromoplatinate, ammonium chlororhodate, Ammonium chlororuthenate, ammonium chloroiridate, ammonium, potassium and sodium chloroplatinite as well as ammonium, potassium and sodium chloropalladite, etc. Gold sensitizers include, for example, potassium auricyanide, Potassium aurorhodanide, gold sulfide, gold selenide, gold iodide, potassium chloroaurate, ethylenediamine-bis-gold chloride as well as various organic gold compounds of the types disclosed in U.S. U.S. Patent No. 3,753,721.

Among the compounds used for reductive sensitization are hydrazine, thiourea and Called tin-II-salts.

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Both sulfur compounds such as thiosulfate and selenium compounds such as selenosulfate are also used used for chemical sensitization.

In the process according to the invention, it goes without saying that the twinned crystals formed at the end of step (b) can be comparatively very small, so that they can often only be used as seed crystals. These crystals can be grown to a usable size during step (d). However, as indicated above, it is possible to extend step (b) so that useful crystals are obtained at the end of it. Nevertheless, in the process according to the invention, steps (b) and (c) can pass over to step (d) without in any way interrupting the addition of the aqueous solutions. However, the twinned crystals formed at the end of step (b) are generally seed crystals, so that the silver iodide detached from the silver iodide crystals formed in step (a) will be present in the seed crystal and therefore in the core of the crystal after the growth step (d), if iodide is not added in stage (b). After the products of chemical sensitization have been transferred from the chemically sensitized silver iodide formed in stage (a), the chemically sensitized twinned crystals formed in stage (b) are therefore in their size in stage (c \ the Ostwald's ripening stage, as well as in stage (d ), which is preferably carried out in the process according to the invention, and these twinned crystals thus form the core of the finished crystals formed after step (d) ) is chemically sensitized, the rhodium will therefore become trapped in the growing twin crystals during step (b).

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After steps (c) and (d) the rhodium is then present as part of the core of the finished silver halide crystals. The method according to the invention thus represents a novel method for chemical sensitization of the core of core / shell silver halide emulsions.

Chemical sensitization using this method has several advantages; For example, only the twinned crystals are sensitized in step (b) and not the rest of untwinned crystals formed in step (b), what would occur if _f chemical sensitization in step (b) would take place. It is also possible to chemically sensitize the silver iodide under chemical conditions which would be inconvenient for other silver halides when the chemical sensitization is carried out during step (b).

The chemical sensitization of silver iodide in step (a) can take place at any point in time in step (a), e.g. during the formation of the silver iodide crystals or as the end portion in step (a) after the production of the silver iodide crystals in this step has been completed.

The chemical sensitization is carried out by using the various chemical sensitizers mentioned above added to the emulsion reagents.

You can use these compounds either continuously add during part or all of the crystallization process in step (a), for example by introducing them to the raw material solutions; or you can also use the crystallization process

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- <fS

stop, treat the partially grown crystals with the appropriate reagent and resume growth.

A few mole percent of other halides, for example Silver bromide or silver chloride can add to the silver iodide crystals be added by precipitating them with the silver iodide. This can increase the effectiveness the chemical sensitization or the developability of the silver iodide emulsions can be improved, such as by James and Vanselow, Photographic Science and Engineering 5.1 (I96I) in attempts to determine the progress of the ripening process to track, described.

A large number of the agents normally used in chemical sensitization can be used; For example, stabilizers can be added to effectively terminate the sensitization (chemical ripening), or the sensitization can take place in the presence of retarders such as nucleic acids or cysteine. The chemical conditions are to be selected in such a way that the optimum properties are achieved. For example, it is preferable to use sulfur and gold salts at a fixed pAg, e.g. 8-9, and pH, e.g. 5-7, and elevated temperature (50-6O ⁰ C) as well as in the case of heavy metal sensitization, using for example bismuth or To sensitize lead salts _f at a relatively low pH, for example 3.

The _f chemically sensitized silver emulsions prepared in step (a) can be removed by flocculation and washing, by any known method of water soluble salts or excess Sensibilierungsmitteln prior to step (b).

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Preferably, pure silver iodide crystals are formed in step (a), but up to 1DMol% other halides (chloride or bromide) can be present in the silver iodide crystals as long as they still predominantly retain their hexagonal lattice shape. It is therefore understood that the term SxLterjodidkristall also includes crystals with up to 10 mol% of other halides. It goes without saying that a small proportion of the crystals formed in step (a) (ie up to 30%, in terms of weight or number, of the crystals) are predominantly silver chloride or bromide and can belong to the face-centered cubic lattice type without clearly affecting the method according to the invention to have an impact. Preferably, no additional iodide is added to the HalogenuLo ¹ solution in stage (b), but the possibility of adding small amounts is not excluded (ie up to 10 mol% of the halide added in this stage can be iodide).

The mean linear magnitude should preferably be cter Silver iodide crystals formed in step (a) in the range 0.05 -5.0 microns, more preferably in the range 0.1-1 microns. Preferably the silver iodide content in the dispersing medium should be at the beginning of stage (b) in the range 0.05-2.0 mol / liter, particularly preferably in the range Ο, ΙΟ-Ι, ΟΜοΐ / liter.

It's a special feature of the present!

Invention that in order to produce a crystal population of the highest uniformity in step (b), which can be used for the preparation of monodisperse emulsions, the rates of addition used in step (b) Silver halide solutions can be predetermined by experiment. The optimal flow velocities in this regard depend on the type of halide and increase with the number of silver iodide crystals in the aqueous dispersion medium, the crystal size of the silver iodide crystals, the pAg in the range indicated above and the temperature.

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For example, in the production of silver iodine chloride or silver iodochlorobromide emulsions, higher addition rates required than with their iodine bromide equivalents.

In the recrystallization process (b) it is preferred to use such volumes of silver nitrate and ammonium or alkali halide solutions that the silver iodide makes up 0.01-20 mol% of the total silver halide in the finished emulsion. As a guideline for an appropriate flow rate, the rate should be adjusted until the dissolution of the silver iodide is nearly complete by the time the amount of silver nitrate added is one to three times equivalent to the silver iodide. The optimal speed therefore be determined from electron micrographs derived _f taken at various times during recrystallization, as the Silberjodidkristal-Ie with its characteristic crystal habit of the silver halide of the usual face-centered cubic lattice can be distinguished.

From the above discussion of the mechanism of the method according to the invention it is evident that electron micrographs of emulsion samples taken during test preparations, in which the rate of addition is varied in the course of step (b), as a further indication of the optimal flow rates can be used. A constant one is preferably used in stage (b) Flow rate, and electron micrographs of the finished, ripened emulsion at the end of the Stage (c) can be used to find the optimal move? - speed during stage (b), which is a population of twinned crystals of the largest single

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would create uniformity and shape. The optimal flow rate during stage (b) which best corresponds to the conditions chosen for the ripening stage (c) can thus be determined by means of preliminary tests. Preferably, one should also select the feed rates so that no ^one Ostwald ripening see under the existing population of twinned crystals takes place. The preliminary experimental tests necessary to ensure that the applicable range of flow velocities is optimal are similar to those described in British Patent No. 1,469,480. Too low an addition rate in stage (b) would lead to incomplete recrystallization of the silver iodide crystals formed in stage (a) and, through Ostwald's ripening, to excessive broadening of the size distribution of the twinned crystals formed. Too high a rate of addition in stage (b) would lead to a considerable formation of new nuclei of non-twinned crystals, which are easily detectable due to their characteristic regular cubic or octahedral shape. In this case, the dissolution of the non-twinned crystals during the Ostwald ^T 's ripening stage (c) may be incomplete, which leads to a broad distribution of the iodide content and a bimodal size distribution of the finished emulsion. Both of these effects would result in a loss of photographic contrast in the final emulsion. The selection of an appropriate intermediate rate of addition during step (b) results in a population of twin crystals of more uniform size and shape.

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It has been shown that the products produced by the process of DE-OS 2,725,993 Silver halide emulsions have a high intrinsic sensitivity to non-twinned silver halide emulsions and this is shown in the example. According to the method according to the invention, however, it is possible to increase the internal sensitivity of the finished silver halide emulsions considerably, and this is shown in the example explained.

The sensitivity of internally sensitized emulsions can usually be increased by adding one or more increased reagents used for negative emulsion. In particular, you can use these emulsions spectrally sensitize with dyes of the kind usually used in surface-sensitive negative emulsions. It is advantageous to use such a high amount of dye that it is surface-sensitized in one Emulsion of the same size would cause desensitization because the inside Image is not subject to dye-induced desensitization.

Imagewise exposed internally sensitive emulsions can be made from any of the prior art known method can be developed into an internal image. These are mainly a standard type developer with the addition of certain amounts of either free iodide or a silicon overhalide solvent such as alkali thiosulfate. If necessary, the surface can be used before developing bleach with an oxidizing agent to remove a surface image (Sutherns, J. Ehot. Sci. 9, 217 (1961)).

If the silver halide layer is thin (approx 15 lattice levels), so the crystal can be in a surface developer to be developed; this technique provides an emulsion that has a conventional surface appearance results, but also that of large dye

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additives to surface-sensitive emulsions avoids desensitization resulting from additives.

When using a surface developer, which contains certain fogging agents (or nucleating agents), one can use the internally sensitive ones described above Emulsions produce a direct-positive image.

Commonly used nucleating agents or fogging agents contain a hydrazine, hydrazone or a nitrogenous one heterocyclic ring or combinations thereof. Suitable hydrazine compounds are in British Patents 702 162, 712 355, 1,269,640 and 1,385,039 and hydrazone compounds are given in British Patent 1,371,366 (the latter can also be act as sensitizing dyes). Examples of heterocyclic N-containing systems can be found in the British Nos. 1,363,772, 1,362,859, and 1,283, and U.S. Pat. Patent 3,850,638. Except Organic fogging agents sometimes become inorganic compounds, typically stannous complex chelates or boron compounds used, for example, in French Patent 1,579,422 and U.S. Pat. Patents 3 617 282 and 3 246 987- A veil can also be obtained by means of one containing a veil agent Pre-bath achieved or a fogging agent can be in the emulsion layer or an adjacent separate layer to be built in. As in the U.S. Patent specification 3 796 577 described a veil can also by a uniform exposure before or during processing in a surface developer.

The inventive method can be used for the production direct-positive emulsions are used where an otherwise known technique is used, as for example in British Patent 723 019 and in the article by Vanassche et al., J. Phot.

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Sci. 2_2, 121 (1974-). According to the invention The method prepared silver halide emulsion is made using the combination of a reducing agent (Thiourea dioxide, hydrazine, tin salts and several others are known to do so) and one Combination of a more electropositive metal than silver (gold and / or palladium are preferred) with a Veil. An electron capturing compound, which is preferably also a spectral sensitizer for the direct positive process is added. After pouring, imagewise exposure and treatment with a surface developer, the emulsion will give a direct positive image. If necessary the usual additives can be applied to the direct-positive emulsion, for example soluble halides to increase sensitivity, sensitizing or desensitizing dyes for Expansion of the spectral range as well as compounds that increase sensitivity in the blue. You can too Protect the surface veil against air oxidation by covering it with a thin layer of silver halide so covered that it is still accessible for conventional surface developers.

In order to change the properties of the finished silver halide crystals, it is possible to use the during To change stage (b) added halides or, in the transition from stage (b) to stage (d), the halides used To completely switch halides or halide ratios. This allows layers with a certain halide ratio obtained in the finished crystals by ensuring that a certain halide or halide mixture in successive sections in stage (b) or in stage (d) is used.

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Are the emulsions prepared by the process according to the invention for negative working photographic Material are used, so it is expedient after the recrystallization stage (b) and the maturation stage (c) to add the halides in step (d) so that up to 10 mol% of iodide in one of the "core" from in step (b) formed twinned crystals surrounding "shell"

like xtfird as well as that up to 10 mol% chloride in the outermost shell of the crystals is felled. Thus, silver iodochlorobromide emulsions with "inside lying "iodide (in addition to that derived from the original silver iodide crystals) and" surface "chloride layers containing crystals are produced according to the invention.

Shall the emulsions for direct-positive materials produced by the process according to the invention or for other purposes where internally sensitive crystals are desired, it is advisable to that the halide precipitated during the first section or the entire recrystallization stage (b) is predominantly Is chloride and the halide precipitated during the entire growth stage (d) or its last section is predominantly bromide. Thus, according to the invention, silver iodochlorobromide emulsions with “inside lying crystals containing "chloride" and "surface" bromide layers.

Such "core / shell" emulsions are well known and also described in British Patent 1,027,146.

The inventive method is particularly for Production of monodisperse emulsions suitable.

In order to prepare monodisperse emulsions using the process of the present invention, belongs

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preferably the silver iodide emulsion prepared in step (a) itself is of the monodisperse type. Such emulsions can be prepared by mixing aqueous silver salt and alkali or ammonium iodide solutions at a fixed temperature and fixed pAg into a solution of a protective colloid with stirring. The final crystal size of the silver iodide emulsion is preferably in the range 0.05-5.0 microns. Preferably the halide solution contains ammonium or potassium iodide alone, but up to about 10 mole percent ammonium chloride or bromide can optionally be used. Practical to apply high rates of addition to, the production temperature is preferably at least 60 ⁰ C, and the pAg of the solution is adjusted to a controlled value in the range 3-5 or in the region 11 - held. 13 Particularly preferred keeping the pAg at a value of about 11.8 to 0.3 · Very practical can pAg comply means of a suitable electrode system and automatic adjustment of the flow rate of one of the solutions.

As just indicated, the preferred size range of the silver iodide crystals produced in step (a) is between 0.05 and 5.0 microns. The silver iodide crystals produced in step (a) can also be monodisperse be. It was found that the average size of the silver iodide crystals formed in step (a) affects the size of the twinned crystals formed in step (b). The bigger the in Stage (a) formed silver iodide crystals, the larger are generally the twinned crystals formed in step (b).

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One method of increasing the size of the silver iodide crystals formed in step (a) is to that step (a) is carried out in the presence of a silver iodide solvent performs. The solubility of silver iodide can also be conveniently changed by changing the temperature, the amount of excess iodide and the amount of silver iodide solvent regulate in the dispersing medium.

It is also evident that the crystal size distribution of the final twinned emulsion also depends on the crystal size distribution of the silver iodide formed in step (a). So should for high contrast Applications such as X-ray films use the silver iodide crystals in stage (a) it should preferably be monodisperse, but for low-contrast applications such as camera films it may be preferable to have a relatively polydisperse to prepare twinned silver halide emulsion according to the present process in such a way that one in the silver iodide crystals formed in step (a) relatively wide size distribution generated. Such a broad size distribution can also be achieved by that one monodisperse silver iodide emulsions of different Large mixed before the start of step (b). A mastery of the size and size distribution of the twinned silver halide crystals produced in steps (b) and (c) or (d) can thus be selected the size and size distribution of the silver iodide crystals formed in step (a).

The water-soluble salts formed in the process of the present invention can be determined by any well known method Remove method. Such methods are often the silver halide and to coagulate the colloid dispersant, to remove this coagulate from the now aqueous medium, it to wash and redisperse it in water.

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As just stated, emulsions prepared according to the invention can have a tendency to form latent images in the interior of the crystals, such emulsions being particularly suitable for use with solvent developers with the formation of a negative image as shown in FIG direct-positive image, as shown in Figure 3, are suitable. However, by appropriate chemical surface sensitization in optional step (e) of the present process, using any of the agents described above, one can give the emulsions a much greater tendency to form latent surface images upon exposure, which is then evident with a standard type negative working developer would kick. Depending on the type or extent of the chemical sensitization processes used in step (a) and step (e), a precisely targeted balance between the formation of latent images inside and on the outside of the crystal is possible. For example, the chemical sensitization carried out in step (a) could be achieved by adding rhodium or iridium salts in appropriate amounts _} and the chemical sensitization, step (e), on the surface of the crystals could be achieved by longer ripening with sulfur and gold salts. Such a method would be particularly suitable for those emulsions prepared according to the invention which predominantly contain silver chloride, which gives emulsions ₉ which in a negative working standard developer a negative image

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produce, which, however, compared to a similar emulsion, in which the sensitization in stage (a) was omitted j, has an increased contrast » Numerous other combinations of such Intern ™ and surface sensitization methods are readily apparent to those skilled in the art "

It is also easy to see that the photographic contrast could be regulated by that you have two or more emulsions prepared by the present process, but to different extents or are chemically sensitized by different methods in either step (a) or (e).

The emulsions prepared by the process according to the invention can be prepared by adding optical Sensitizers, for example carbocyanine and merocyanine dyes ^ visually sensitize to the emulsions.

Optionally, the emulsions contain any the additives generally used in photographic emulsions, for example wetting agents such as Polyalkylene oxides, stabilizers such as tetraazaindenes, Metal chelating agents as well as commonly used for silver halide, growth or crystal habit modifying agents such as adenine.

The dispersing medium is preferably gelatin or a mixture of gelatin and a water-soluble one Latex, for example a vinyl acrylate containing latex polymer. If such a latex is present in the finished emulsion, it is particularly preferred to add it.

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ben after the crystal growth has ceased completely is. Other water-soluble colloids, for example casein, polyvinylpyrrolidone or polyvinyl alcohol, are however, it can be used on its own or together with gelatin.

The silver halide emulsions prepared by the process of the present invention are desirable Extremely high opacity and high development speed, as shown in the example below.

The silver halide emulsions prepared by the process of the present invention are therefore in many Types of photographic materials useful as in X-ray film, in both black and white and color films for cameras, in paper products and in direct positive materials.

The invention thus comprises silver halide emulsions produced by the process according to the invention and cast silver halide photographic material containing at least one such emulsion.

example

The following emulsions are made: Emulsion A

This example explains the production of a monodisperse twinned octahedral emulsion according to the invention, in which internally sensitive twinned crystals are generated by recrystallization of silver iodide crystals, which are chemically sensitized by heat treatment with sulfur and gold salts, and which are used to generate a direct-positive image by suitable processing is used. Production of monodisperse silver iodide emulsion (stage a)

The mixture is stirred 1 liter of 5% aqueous solution of inert gelatin at 65 ⁰ C and 200 rpm with 2 ml of n-octanol as an anti-foaming agent. Every hour, 3000 ml of aqueous 4,7111 silver nitrate and potassium iodide solutions are sprayed into the gelatin solution with stirring until

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for adding 150 ml of silver nitrate solution. During the precipitation the pAg reaches a value of 11.8 held.

At this stage, the growth of the silver iodide crystals is interrupted and chemical sensitization carried out by the emulsion at 57 ⁰ C for 100 minutes at pH 6.3 and in the presence of 14 ρAg mg of sodium thiosulfate and 8.8 mg 2.4 sodium tetrachloroaurate dihydrate ripens per mole of silver halide.

The precipitation is then continued with the addition of further volumes of 4.7m silver nitrate and potassium iodide solutions at 2100 ml per hour up to an addition of 525 ml silver nitrate solution. The pAg is again kept at a value of 11.8. The crystals of this silver iodide emulsion have an average size of 0.18 microns.
Recrystallization and maturation (levels b and c)

230 g of the silver iodide emulsion prepared in step (a) are added to 1 liter of 5% strength aqueous solution an inert gelatin with stirring at 200 rpm at 65 ° C. with 2 ml of n-octanol and 30 ml of 5N sulfuric acid. Aqueous 4.7m solutions of silver nitrate and ammonium bromide are stirred into the silver iodide emulsion with a Sprayed at a speed of 3000 ml per hour up to an addition of 500 ml of silver nitrate. The pAg becomes continuous held at 7.7 pounds 0.3,

Ostwald's ripening is carried out in the presence of 100 ml of 11.8m ammonia solution, which is added with the halide solution so that the ammonia concentration increases as recrystallization occurs. At the end of the addition of the silver nitrate and ammonium halide solutions, the dissolution of the non-twinned crystals by Ostwald ¹ see ripening is essentially complete, and predominantly twinned crystals of silver iodobromide remain.

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Further growth (stage d)

The pH of the emulsion prepared in stage (c) is adjusted to 5.0 with 5N sulfuric acid to neutralize the ammonia present. At a flow rate of 3000 ml per hour under Aufrechterhai further processing the temperature at 65 ⁰ C and the pAg at 9.5 _4> 7m solutions of silver nitrate and ammonium bromide with stirring at 200 rpm to an addition of 750 ml of silver nitrate solution was added. The finished emulsion has an average crystal size of 0.76 microns with a scattering coefficient of 16%. The emulsion is flocculated using conventional methods _f washed and redispersed with a total of 210 g limed Knochenleimgelatine. In this case no further chemical sensitization takes place, ie the optional step (e) is omitted. The emulsion is adjusted to pH 6.3 and pAg 8.8 and with a pouring

2
weight of 50 mg Ag / dm cast on a photo carrier.

Emulsion B

This example explains the production of a monodisperse twinned silver iodochlorobromide emulsion according to the invention which contains twinned crystals with a "core" of silver iodid chloride and an outer "shell" of silver bromide and which are produced by recrystallization of silver iodide crystals which are chemically sensitized by adding a rhodium salt during the precipitation will. Production of monodisperse silver iodide emulsion (stage a)

A monodisperse silver iodide emulsion is made exactly according to the method given in step (a) of Example 1 produced, but omitting the ripening with the sulfur and the gold salts.

Instead, after the silver iodide crystals have finished growing, they are given a medium size of 0.18 micron 35 ml of a 35. 10 g in 1On lithium chloride An aqueous solution containing dissolved sodium hexachlororhodite to form a silver iodide emulsion to form rhodium

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built into the surface layers of the silver iodide crystals, most likely in the form of an adsorbed rhodium complex ion species. The emulsion is stirred for 15 minutes at 65 ° C to allow adsorption and chemical sensitization to occur. Recrystallization and maturation (levels b and c)

One gives 230 g of the silver iodide emulsion prepared in step (a) to 1 liter of 5% aqueous solution of inert gelatin with stirring at 200 rpm at 65 ⁰ C with 2 ml of n-octanol and 30 ml of 5N sulfuric acid. Aqueous 4.7m solutions of silver nitrate and ammonium chloride are sprayed into the silver iodide emulsion with stirring at a rate of 3500 ml per hour up to an addition of 75 ml of silver nitrate solution. The pAg is kept at 7 _y 3 - 0.2 throughout. Until a further 425 ml of silver nitrate solution has been added, aqueous 4.7m solutions of silver nitrate and ammonium bromide are sprayed into the emulsion at a rate of 3000 ml per hour while stirring. During this precipitation period the pAg is maintained at 7.7 "£ 0.2.

Ostwald's ripening is carried out in the presence of 100 ml of 1.8m ammonia solution, which is added with the halide solutions during this stage, so that the ammonia concentration increases as the chemically sensitized silver iodide crystals recrystallize. At the end of the addition of the silver nitrate and ammonium halide solutions, the dissolution of the non-twinned 'crystals by Ostwald's ripening is essentially complete, and predominantly twinned crystals of silver iodochlorobromide remain. The size and habit of the crystals are similar to those in Emulsion A.
Further growth (stage d)

This emulsion is just as described for step (d) of the preparation of the emulsion A for further growth subjected and for casting on photo carrier with a

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Cast weight of 50 mg Ag / dm prepared as described above.
Emulsion C

For comparison, an emulsion is produced by a method according to Belgian patent specification 855 519, where the high internal sensitivity of the emulsion as produced is used to create a direct-positive image for comparison with that from emulsion A.

A monodisperse twinned octahedral emulsion is prepared exactly as described for emulsion A, but omitting the chemical sensitization of the silver iodide emulsion with sulfur and gold salts as described in step (a) of Example A. Emulsion D

An untwinning monodisperse cubic silver bromide emulsion of 0.39 microns is used as a reference standard average edge length. The cubic monodisperse emulsion is after that in the British PAg-controlled as described in U.S. Patent 1,335,925 Technique produced, but with the implementation of a chemical sensitization inside and on the surface to obtain a satisfactory reversal characteristic. The making of this Emulsion comprises the following stages:

(i) growth of crystals to 0.12 micron average edge length,
(ii) Maturation at pH 6.3 and pAg 7.8 for 40 minutes

7O ⁰ C and 14 mg of sodium thiosulfate and 0.6 mg of sodium tetrachloride oaurat dihydrate per mole of silver halide, (iii) Further growth of the cubic crystals of 0.39 micron average edge length.

(iv) Other ripening at pH 6.3 and pAg 8.8 for 40 minutes at 57 ⁰ C and 12.5 mg of sodium thiosulfate and 1.8 mg of sodium tetrachloroaurate dihydrate per mole of silver halide.

The reference emulsion is then poured with a

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weight of 30 mg Ag / dm cast on photo carrier. If the ripening in stage (ii) is omitted, a constant density (D max) without reversal is obtained. If the surface sensitization in stage (iv) is omitted, a very low maximum density (D max) is observed. Photographic results

The cast strips are then placed under a tungsten source with an intensity of 1000 lux for 0.2 seconds imagewise exposed on an intensity scale sensitometer.

To assess the internal sensitivity of the emulsions of the cast samples are 4 minutes at 20 ⁰ C in an internal developer (solvent developer) of the following composition:

DEVELOPER I

Methyl p-aminophenol sulfate hydroquinone

Sodium sulfite (anhydrous) sodium carbonate

Sodium thiosulfate potassium bromide

Water to 1 liter

processed, then fixed, watered and dried in the usual way. The photographic obtained Results are shown in FIG.

Before pouring, all emulsions were obtained by adding 0.2 mg of the cyanine dye anhydro- [3- (3-sulfopropyl) -2-benzothiazole] - (3-ethyl-2-benzothiazole) -β-methyltrimethine cyanine hydroxide has been spectrally sensitized per mole of silver halide.

In order to obtain a direct positive image, the cast samples are 8 minutes at 2O ⁰ C in a fog developer with the following composition:

DEVELOPER II

1-phenyl-3-pyrazolidone 0.25 g

Hydroquinone 10 g

Sodium sulfite (anhydrous) 25 g

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0.7 G 2.7 G 25th G 12.5 G 10 G 0.7 G

Sodium carbonate 12.5 g

Sodium hydroxide 10 g

Potassium bromide O ₍ 7 g

5-methylbehzotriazole 50 mg

N-Formyl-N'-p-tolylhydrazine 50 mg of water per 1 liter

processed, then fixed, watered and dried in the usual way. The photographic results obtained are shown in FIG. Discussion of the photographic results

The photographic results shown in Figures 2 and 3 demonstrate the improved photographic performance of the emulsions prepared in accordance with the invention.

The results obtained for the internal development of the cast strips are shown in the usual form as development density / log exposure curves in FIG. These demonstrate the increased internal sensitivity resulting from the chemical sensitization carried out in step (a) of the new process according to the invention, for the case of emulsions A and B compared to that emulsion C which was produced by a process according to DE-OS '2,725,993

became. Similar results are obtained if the cast strips are bleached with a ferricyanide Removal of any surface image pretreated as described by Sutherns, J. Phot. May be. S), 217 (1961). It is also evident that the two procedures The twinned emulsions produced have considerably greater internal sensitivity than the reference emulsion D, an untwinning cubic silver bromide emulsion »

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FIG. 3 shows the development of fog caused by cast strips obtained photographic results. These demonstrate that the higher internal sensitivity of emulsions A and B to a corresponding improvement in the direct reversal characteristics compared to the Emulsions C and D leads. The on the cast strips after processing in the fog developer II (a direct positive image is obtained) measured photographic sensitivities have values which internal sensitivities measured after processing in solvent developer I are similar. the end Figure 3 can be seen that for the inventive twinned emulsions have excellent reversal characteristics without the chemical surface sensitization treatment, which is necessary for the non-twinned reference emulsion D, can be obtained.

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Claims (21)

Claims; ^/ l) A process for the preparation of silver halide emulsions of the twin type, characterized in that stepwise (a) silver halide crystals containing at least 90 mol% iodide are formed in a colloidal dispersion medium, these crystals predominantly having the hexagonal lattice structure, and then these at least 90 mol-96 Iodide-containing silver halide crystals are chemically sensitized, (b) an aqueous silver salt solution and an aqueous alkali or ammonium bromide or chloride solution or mixtures thereof are mixed into the dispersing medium containing these silver halide crystals, so that twinned silver halide crystals form, the iodide and the added ( n) contain halide (s), (c) adding a silver halide solvent to the dispersing medium and thus causing the twinned crystals to grow through Ostwald's ripening, optionally (d) by adding further aqueous silver salt solution and further alkali or ammonia ium halide for colloidal dispersion allows the twinned crystals to increase in size and finally, if necessary, (e) removes the water-soluble salts formed and chemically sensitizes the surface of the silver halide crystals of the emulsion. 2. The method according to claim 1, characterized in that the chemical sensitization in step (a) consists in a gold or other precious metal sensitization. 3. The method according to claim 2, characterized in that that the other precious metal is platinum, iridium or rhodium. 4. The method according to claim 1, characterized in that the chemical sensitization in step (a) takes place by means of a heavy metal compound. 5. The method according to claim 4, characterized in that the heavy metal compound is a lead or wis- 909848/09 0 0 - VT- mutsalz is. 6. "The method according to claim I _1, characterized in that the chemical sensitization in step (a) consists of a sulfur or selenium sensitization. 7. The method according to claim 1, characterized in that that the chemical sensitization in step (a) consists of a reductive sensitization. 8. The method according to claim 7, characterized in that that the reducing agent used is a tin (II) salt, thiourea, a hydrazine or formaldehyde. 9. The method according to claim 1, characterized in that in step (a) two types of chemical Carries out awareness. 10. The method according to claim 9, characterized in that the two types of chemical sensitization consist of gold and sulfur sensitization, 11. The method of claim 2 or 6, characterized in that the sensitization at 8-9 fixed pAg and fixed pH 5-7 at elevated temperature between 50 and 60 ⁰ C. 12. The method according to claim 5, characterized in that the sensitization at a pH of about 3 he follows. 13. The method according to any one of claims 1 to 12, characterized in that step (d) is carried out and the silver halide crystals formed in step (b) the core and the halide added in step (d) represent the shell of the finished silver halide crystals. 14. The method according to any one of claims 1 to 12, characterized in that in step (b) the at least The halide precipitated in the initial stage of the stage is predominantly chloride and in stage (d) it is at least in the final stage the halide precipitated at the stage is predominantly bromide. 15. The method according to any one of claims = 1 to 14, characterized marked that the surface of the. Silver halo 9 0 9 8 4 8/0900 genide crystals chemically sensitized in stage (e) will. 16. The method according to claim 15, characterized in that the chemical sensitization in a sulfur and gold sensitization exists. 17. The method according to any one of claims 1 to 14, characterized in that the surface of the silver halide crystals is veiled in step (e). 18. The method according to claim 17, characterized in that the concealment using a reducing agent along with a compound of a more electropositive Metal than silver. 19. The method according to claim 18, characterized in that an electron trapping compound on the Surface of the silver halide crystals is adsorbed. 20. According to the method according to one of the claims to 19 prepared silver halide emulsion. 21. Ehotographic material, characterized in that that it has at least one layer containing a silver halide emulsion according to claim 20. 909848/0900