EP0055696A1 - Process for the production of photographic silverhalide emulsions - Google Patents

Abstract

Silver halide crystals are prepared by combining an organic solution containing a silver halide complex of the formula <IMAGE> in which E is hydrogen, an alkali metal or ammonium and Z is a divalent metal from main group 2 or subgroup 8 of the periodic table, X<1>, X<2> and X<3>, independently of one another, are halogen or pseudohalogen, and the indices p, q, n, n1, n2 and n3 satisfy the conditions 1 </= m </= 3, 2 </= n </= 5, in which n = n1 + n2 + n3, 0 </= p </= 4 and 0 </= q </= 2 with a medium in which the silver halide complex is unstable. After removing the soluble compounds, followed by physical and/or chemical digestion, the silver halide can be dispersed in a binder. The silver halide emulsions thus obtained are suitable for the production of photographic materials. <IMAGE>

Description

The present invention relates to a process for the preparation of photographic silver halide emulsions.

The silver halide emulsions used in photographic technology are generally prepared by precipitation of the silver halide from aqueous solutions, usually in the presence of a protective colloid. One starts with water-soluble salts of silver (e.g.

Silver nitrate) and from water-soluble halides (e.g. alkali metal halides). When these aqueous solutions are combined, the silver halide precipitates in water-insoluble, fine crystalline form.

However, the resulting suspension is traditionally called "emulsion" in photographic terminology.

A distinction is made between different precipitation techniques, whereby the size distribution and crystal costumes of the silver halides can be influenced to a large extent. Mainly, however, the single jet or double jet method is used.

In the single-jet method, an aqueous solution of one component is allowed to flow into an aqueous solution of the second component. The protective colloid is used in the solution presented, usually the aqueous halide solution. The size and crystal appearance of the resulting silver halide crystals can be influenced to a large extent by varying the temperature, concentration and the rate at which the solutions run in. In the two-jet method, the aqueous solutions of both components are simultaneously introduced into a solution which usually contains the protective colloid and, if appropriate, further components. This method allows the shape and size distribution of the crystals to be influenced even more, by not only increasing the concentration and speed of entry of the individual solutions supplied, but also the current ratio of halide to silver ions in the template play a decisive role. The two-jet method is therefore particularly suitable for the production of monodisperse emulsions. The ratio of the inlet speeds of the components is preferably controlled automatically on the basis of the silver ion concentration currently measured and / or the pH value in the template.

The production of photographic silver halide emulsions usually includes other operations in addition to the precipitation of the silver halides. Physical ripening or Ostwald ripening, which often follows immediately after the precipitation, causes the larger silver halide crystals to grow at the expense of the smaller ones. To favor it, the emulsion is kept at elevated temperature for some time, usually with the addition of silver halide solvents. The somewhat greater solubility of the small crystals then causes the above-mentioned redissolution. Another operation aims to remove the easily soluble salts formed during the precipitation reaction. It can be carried out in different ways, e.g. by flocculation, decanting and washing the silver halide sediment. In another method, the gelatin-containing emulsion is gelled by cooling, then cut into so-called "noodles" and washed for a long time with running water. Other methods used in the art are dialysis and ultrafiltration.

After the water-soluble salts have been removed, chemical ripening is carried out, the emulsion being treated with the addition of small amounts of so-called chemical sensitizers for some time at elevated temperature. Chemical sensitizers are, for example, sulfur compounds and also heavy metal compounds, such as gold, rhodium, platinum and cadmium compounds. The purpose of this treatment is to change the surface of the silver halide crystals, and the photosensitivity can be increased drastically. By The addition of antifoggants or stabilizers prevents the formation of spontaneously developable crystals, which can cause the so-called veil in the developed image.

The last operation, usually immediately before the emulsion is poured onto a carrier, is spectral sensitization, whereby the emulsion can be made selectively sensitive in certain wavelength ranges of the electromagnetic spectrum, which can range from blue to infrared, by adding certain dyes. However, it is also possible to carry out the spectral sensitization immediately after the silver halide has precipitated.

Another method for producing fine crystalline silver halide emulsions by precipitation from homogeneous solution is described in US Pat. No. 4,153,462. As is known, silver halides can be converted into water-soluble complexes by adding excess halide ions. Examples of such complexes are AgCl ₆ ^- , AgCl ₄ ^3- , AgBr ₃ ^2- , AgBr ₅ ^4- , AgJ ₂ , AgJ ₄ ^3- , AgC13Br and AgClBr ₃ ^3- . The properties of such complexes are described, for example, in TH James "The Theory of the Photographic Process" 4th ed. (Mac Millan Co., New York), pages 7 to 9. According to the above-mentioned US patent, aqueous solutions of such complexes are treated in this way that they disintegrate into 1: 1 compounds and then precipitate out in fine crystalline form. The complexes are destroyed by dilution in the process cited, it being possible for the diluent, in general water, to contain further additives to influence the precipitation process. Such additives are, for example, soluble halides, whereby these halides can differ from the complex-forming halide (s). Other additives include solvents such as dimethylformamide or dimethyl sulfoxide. The diluent used to precipitate the complexes can also contain wetting agents, which makes it easier to later disperse the crystals in a binder, eg gelatin. A particular advantage of this process is the high speed with which crystals of any size with a diameter of less than 0.1 to 10 µm can be produced. While this goal can only be achieved with the usual Ostwald ripening in a time that is generally almost an hour, the process described provides the desired crystals within a few seconds.

However, due to the use of water as a solvent for the silver halide complexes, the cited method has the disadvantage _{that large amounts of} solvent are always necessary, since the complexes are poorly soluble in water.

The object of the present invention is therefore to overcome this disadvantage by using suitable solvents for the silver halide complexes.

It has now been found that certain organic solvents, which have a much higher solvency for silver halide complexes, can be used advantageously for the preparation of photographic emulsions.

worin E Wasserstoff, ein Alkalimetall oder Ammonium und Z ein zweiwertiges Metall der 2. Hauptgruppe oder der 8. Nebengruppe des Periodensystems bedeutet, X¹, X2 und X unabhängig voneinander Halogen oder Pseudohalogen sind, und die Indizes p, q, m, n_l, n₂ und n₃ die Bedingungen

und

erfüllen, vorzugsweise in Gegenwart eines Schutzkolloides, mit einem Medium zusammenbringt, in dem der Silberhalogenidkomplex nicht stabil ist und zerfällt, gegebenenfalls die löslichen Verbindungen EX¹, EX², E_X ³,

und/oder

vom ausgefallenen Silberhalogenid abtrennt, gegebenenfalls ein Silberhalogenidbindemittel zugibt und die physikalische und/oder chemische Reifung durchführt.The invention thus relates to a process for the preparation of photographic silver halide emulsions, characterized in that a silver halide complex of the formula dissolved in an organic solvent

where E is hydrogen, an alkali metal or ammonium and Z is a divalent metal of the 2nd main group or the 8th subgroup of the periodic table, X ¹ , X2 and X are independently halogen or pseudohalogen, and the indices p, q, m, n _l , n ₂ and n ₃ the conditions

and

meet, preferably in the presence of a protective colloid, with a medium in which the silver halide complex is not stable and disintegrates, optionally the soluble compounds EX ¹ , EX ² , E _X ³ ,

and or

separated from the precipitated silver halide, optionally adding a silver halide binder and carrying out the physical and / or chemical ripening.

The invention further relates to the photographic silver halide emulsions obtained by the process according to the invention.

The invention further relates to the photographic materials containing the photographic silver halide emulsions produced according to the invention.

beschrieben werden. Darin bedeutet E eine einwertige Spezies wie z.B. Wasserstoff, Ammonium oder ein Alkalimetall. Als Alkalimetalle können z.B. Lithium, Natrium und Kalium in Frage kommen. Ammonium und Lithium sind besonders geeignet. Z ist ein zweiwertiges Metall. Es gehört vorzugsweise der zweiten Haupt- oder Nebengruppe oder der achten Nebengruppe des Periodensystems der Elemente (Mendelejeff) an. Geeignete Beispiele für Z sind Magnesium, Calcium, Strontium, Barium und--Zink sowie Eisen,Kobalt,Nickel, 1 2 3 Palladium, Iridium und Platin. X¹, X und X bedeuten Halogen oder Pseudohalogen und sind in der Regel unabhängig voneinander Chlor, Brom oder Jod sowie Cyano oder Thiocyano.The soluble silver halide complexes used according to the invention can be of the general formula

to be discribed. E means a monovalent species such as hydrogen, ammonium or an alkali metal. Examples of suitable alkali metals are lithium, sodium and potassium. Ammonium and lithium are particularly suitable. Z is a divalent metal. It preferably belongs to the second main or sub-group or the eighth sub-group of the Periodic Table of the Elements (Mendelejeff). Suitable examples of Z are magnesium, calcium, strontium, barium and zinc, as well as iron, cobalt, nickel, 1 2 3 palladium, iridium and platinum. X ¹ , X and X represent halogen or Pseudohalogen and are usually independently chlorine, bromine or iodine and cyano or thiocyano.

und

The following relationships apply to the indices m, n _l , n ₂₃ n _{3 '} p and q:

and

The good solubility of silver iodide in the presence of excess iodide in dimethylformamide is known from the literature (H. Chateau et MC Moncet, J. Chimie physique 60, 1060 (1963). From R. Alexander et al. J. Am. Ch. Soc 89, 3703 (1967), M. Le Demezet et al., Bull. Soc. Chim. France 1970, p. 365, MK Chantooni et al. J. Phys. Ch. 77, 1 (1973), M. Salomon , J. Phys. Ch. 79, 2000 (1975) and P. Bry, Bull. Soc. Chim. France (1979), 1-325, the high stability of the silver halide complexes in dipolar aprotic solvents is known. that solutions of these complexes in aprotic solvents can be used in such an advantageous manner for the production of photographic emulsions.

entsprechend der Gleichgewichtsreaktion

The solvents for the silver halide complexes which can be used for the process according to the invention are generally aprotic or amphiprotic and have a high dielectric constant. A suitable criterion for the selection of a solvent is, for example, its solubility constant. For complexes of the formula AgX ₂ , in which X is chlorine, bromine or iodine, this solubility constant is defined by the equation

according to the equilibrium reaction

The expressions in square brackets mean the concentration of the components in mol / liter.

wobei

There is also the relationship between the solubility constant K _{S2 '} the solubility product K _So and the stability constant β _{2 of} the complex AgX ₂

in which

sowie

gemäss der Gleichgewichtsreaktion

entsprechen. Siehe dazu L.G. Sillen und A.E. Martell "Stability Constants of Metal-Ion Complexes", special publication no. 17, The Chemical Society, London (1964).according to the equilibrium reaction

such as

according to the equilibrium reaction

correspond. See LG Sillen and AE Martell "Stability Constants of Metal-Ion Complexes", special publication no. 17, The Chemical Society, London (1964).

For water and X ¹ = X ² = X ³ = chlorine, log K _S2 = -4.5. Solvents which are particularly suitable for the process according to the invention should therefore have a greater solubility constant, ie log K _S2 > -4.5. Table 1 below shows the values of log K _So , log β ₂ and log K _S2 for some silver halides.

(Source: M. Salomon, J. Phys. Chem. 79, 2000 (1975)).

In the context of the present invention, it is of course also possible to use mixtures of various solvents, if appropriate also mixtures containing water, as solvents for the silver halide complexes.

Suitable aprotic or amphiprotic solvents for the process according to the invention are, for example, N-methylformamide (NMF), N, N-dimethylformamide (DMF), N-ethylformamide (NEF), N, N-diethylformamide (DEF), N, N'-tetramethylurea (TMU), N-methylacetamide (NMA), N, N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), dimethyl sulfoxide (D _MSO ), hexamethylphosphoric triamide (HMPT), tetramethylene sulfone (TMS) and tetrahydrofuran (THF).

Of these, solvents which are at least partially miscible with water are particularly suitable.

The particular advantage of the process according to the invention consists above all in the much higher solubility of the silver halide complexes in the organic solvents mentioned, compared with the solubilities of the aqueous complex solutions used in US Pat. No. 4,153,462. The aqueous complex solution described in this citation with 0.3 to 0.5 mol of silver and 8 to 10 mol of bromide per liter should represent the maximum solubility limit that can be achieved at elevated temperatures.

Die Herstellung der erfindungsgemässen Lösungen der Silberhalogenidkomplexe in den zitierten organischen Lösungsmitteln erfolgt dadurch, dass man ein zuvor auf konventionelle Weise, z.B. durch Fällung in wässriger Lösung in Gegenwart eines Schutzkolloides hergestelltes Silberhalogenid in einem organischen Lösungsmittel suspendiert. Zur Suspension wird dann Halogenwasserstoff, wie z.B. HCl, HBr oder HJ oder ein lösliches Halogenid, z.B. ein Chlorid, Bromid oder Jodid, eines Alkalimetalls wie z.B. Lithium, Natrium, Kalium, eines anderen Metalls wie z.B. Calcium, Barium oder Zink, oder einer quaternären Ammoniumverbindung. wie z.B.

worin R₁ bis R₄ unabhängig voneinander Wasserstoff,Tables 2 to 4 below show the solubility of various silver halide complexes which can be achieved at a temperature of 25 ° C. in mixtures of N-methylformamide with water from 0 mol% NMF (pure water) to 100 mol% NMF (pure solvent) for the systems AgCl / LiCl, AgBr / NH ₄ Br and AgJ / NH ₄ J. It is easy to see that as the solvent concentration increases, the solubility increases to such an extent that the required amount of solvent is finally the lowest when pure solvent is used.

The solutions of the silver halide complexes according to the invention in the organic solvents cited are prepared by suspending a silver halide previously prepared in a conventional manner, for example by precipitation in aqueous solution in the presence of a protective colloid, in an organic solvent. The suspension is then hydrogen halide, such as HCl, HBr or HJ or a soluble halide, such as a chloride, bromide or iodide, an alkali metal such as lithium, sodium, potassium, another metal such as calcium, barium or zinc, or a quaternary Ammonium compound. such as

wherein R ₁ to R _{4 are} independently hydrogen,

Methyl, ethyl, propyl or butyl, and X is chloride, bromide or iodide, added in the desired amount. When the emulsion is stirred and shaken, the solids go into solution and a solution is formed which contains the complex silver halide anion on the one hand and the metal or ammonium cation used for the complexation or the proton on the other hand. The complexes can contain up to three different halogen atoms at the same time.

The decomplexation leading to the precipitation of the silver halide can take place in various ways. The simplest method is to transfer the complex solution into a medium in which the silver halide complex is not stable.

Such a medium can be water, an organic solvent or a solvent mixture, the latter being able to be used with the addition of water. Examples are alcohols, glycols, esters, acetals, ethers and ketones such as, for example, methanol, ethanol, ethylene glycol, ethyl acetate, 1,1-diethoxyethane, ethylene glycol diethyl ether and ethyl methyl ketone. Methanol, ethanol, acetone and isopropanol are particularly suitable. By selecting suitable solvents or solvent mixtures, the decomposition of the complex can be carried out quickly or slowly. This gives smaller or larger silver halide crystals.

The silver halide can be precipitated so that the complex solution is poured into the solvent or solvent mixture in which the silver halide complex is not stable. However, it is also possible to present the complex solution and to add the solvent or solvent mixture. There is also the possibility of allowing the complex solution and the solvent or solvent mixture to flow together at the same time. Accordingly, the single-jet or double-jet processes used in conventional silver halide precipitation can be used in the process according to the invention. The feed of the complex solution and of the solvent or solvent mixture can, if appropriate, be controlled and limited as a function of the pH and pAg by regulating devices.

A medium in which the silver halide complex is not stable can also be a binder layer cast onto a carrier, provided that this contains sufficient solvents to decomplex the complex.

The silver complex can be incorporated into this binder layer in various ways, e.g. by dissolving the binder in the complex solution and applying the solution thus prepared as a layer on a support and drying. The complex can also be added subsequently, e.g. can be introduced into the binder layer by so-called bathing. To decomplex, the complex-containing binder layer is then immersed in water or a suitable solvent or solvent mixture, in which case the complex decomposes and the corresponding silver halide is deposited within the binder layer. The silver halide embedded in the binder matrix can be subjected to further conventional treatments such as desalination, ripening and sensitization.

The binder layer can consist of gelatin or other high-molecular compounds of natural or synthetic origin such as e.g. Cellulose derivatives, polysaccharides, chitin, polyvinyl alcohol, water-soluble homo- or copolymers of acrylic and methacrylic acid, acrylamide or vinyl pyrrolidone. However, gelatin can also be used in combination with one or more such colloids. However, the use of gelatin alone is preferred.

The binder layer can additionally e.g. Sensitizers, desensitizers, stabilizers and UV absorbers included.

While if a solvent or solvent mixture is used to precipitate the silver halide, it may have to be redispersed in a binder after separating soluble salts, this processing step is omitted in the last-described embodiment of the method according to the invention.

It is possible to influence the size, crystal dress, size distribution and other properties of the silver halide crystals, such as the composition or internal structure, by modifying compounds both of the solvent or binder in which the silver halide complex is not stable and of the complex solution before or during the Decomplexing are added. Such modifying compounds are, for example, nuclei, ie particles which are smaller than the resulting silver halide crystals and can thus act as centers of crystallization. Suitable crystallization centers are the silver halides produced by normal precipitation, such as AgCl, AgBr and AgJ, and also microcrystalline or colloidal particles of carbon, silicon dioxide or of metals, such as copper, silver, gold and platinum, their sulfides and oxides, such as C _U2 0 , Cu0, A ^g ₂ 0, PtO, Pt0 ₂ , Cu ₂ S, CuS, Ag ₂ S and PtS, as well as dioxides of tetravalent elements such as lead, zircon and titanium. AgCl, AgBr, AgJ, Ag ₂ O, Ag ₂ S and TiO ₂ are preferably used.

Other modifying compounds are e.g. soluble sulfides or halides which can be added to the solvent or binder in which the silver halide complex is not stable. Examples are ammonium sulfide or potassium iodide.

The effect of the halides depends on whether they contain the same halide as was used to form the complex or whether it is a different halide from the latter. If e.g. In the solvent or binder mentioned, the halide already used for the complexation is used as a modifying additive, the decomplexation is delayed, which leads to the formation of larger crystals. If a halide is used as an additive, the silver salt of which is less soluble than the silver halide contained in the complex, the poorly soluble silver halide is primarily precipitated. This precipitation is a faster process compared to the delayed precipitation process cited. In this case, smaller crystals are preferably formed. Under suitable conditions, so-called core-shell emulsions can also be produced in this way, which have a poorly soluble core as the core and a more easily soluble silver halide as the shell, e.g. a core of silver iodide and a shell of silver chloride or bromide.

Soluble silver salts such as e.g. Silver nitrate used.

Modifying compounds, which can be incorporated into the crystal lattice of the silver halides in small amounts in the sense of doping, are primarily heavy metals such as e.g. Gold, iridium, platinum, rhodium, cadmium, zinc or lead, which can be added in the form of soluble salts to the solvent or binder in which the silver halide complex is not stable, or to the complex solution.

Other modifying compounds are, for example, silver complexing agents such as ammonia, soluble alkali metal cyanides and rhodanides such as NaCN, KCN, NaSCN and KSCN; also high molecular compounds / protective colloids, which are soluble in organic, aprotic solvents, such as gelatin, cellulose derivatives or chitin, surface-active compounds such as sodium lauryl sulfate, alkylnaphthalenesulfonates, adducts of ethylene oxide and / or propylene oxide with higher alcohols or alkyl-substituted phenols.

The high molecular weight compounds / protective colloids play an important role in the formation of the silver halide crystals according to the invention. In principle, however, it is possible to produce the silver halides in the absence of protective colloids. The separation of the crystals and the washing out of soluble accompanying substances such as Halides of foreign metals are then relieved. In many cases, however, it will be preferred to precipitate the silver halide in the presence of protective colloids. In general, more stable emulsions are obtained which can be further processed into photographic products by conventional methods without difficulty.

Suitable protective colloid is primarily gelatin, which is ideally suited for the production of photographic layers due to its chemical, physical and colloidal chemical properties. Other protective colloids that can also be used alone or together with gelatin are water-soluble high-molecular compounds of natural or synthetic origin, such as e.g. Cellulose derivatives, polysaccharides, chitin, polyvinyl alcohol, water-soluble homo- or copolymers of acrylic and methacrylic acid, acrylamide or vinyl pyrrolidone. The protective colloids can be used both in the complex solution and in the decomplexing solution.

The further processing of the silver halide emulsions obtained according to the invention is carried out by the customary methods which can be used in photographic technology. For example, after decomplexing and excretion of the silver halide to influence the grain size distribution, Ostwald ripening can be carried out. In the solvent surrounding the silver halide crystals, after the decomplexing has ended, the halides used for the complex formation and, if appropriate, further additives are present as accompanying substances contain. The emulsion can be freed from such accompanying substances by the usual techniques such as flocculation, decanting, centrifuging, washing of gelled pasta, dialysis and ultrafiltration. The sediment which has been freed of accompanying substances is then redispersed in a binder in the customary manner. The binder is gelatin, optionally together with other natural or synthetic binders. Examples of such other binders are cited above. Further operations such as physical and / or chemical ripening and sensitization, spectral sensitization and stabilization do not differ in the emulsions according to the invention from the operations customary in photographic technology.

Additives such as spectral sensitizers, desensitizers, stabilizers and UV absorbers can also be dissolved in the complex solution and / or in the solvent in which the silver halide complex is not stable before the silver halide is precipitated.

To prepare the light-sensitive layers for photographic materials, the emulsions prepared and post-treated according to the invention can also be mixed with the usual additives, e.g. with color hardeners, wetting agents and preservatives.

• 1. Die Löslichkeit der Silberhalogenidkomplexe in den zitierten Lösungsmitteln ist wesentlich höher als in Wasser. Demgemäss können wesentlich konzentriertere Ausgangslösungen verwendet werden.
• 2. Die erfindungsgemässen Komplexlösungen in organischen Lösungsmitteln sind stabil und lichtunempfindlich und können daher am Tageslicht verwendet und aufbewahrt werden.
• 3. Für die Herstellung einer photographischen Emulsion mit gegebener Teilchengrössenverteilung muss viel weniger Zeit aufgewendet werden als nach den konventionellen Fällungsverfahren. Auf die Ostwald-Reifung kann in den meisten Fällen verzichtet werden.
• 4. Alle nach konventionellen Techniken herstellbaren Kristallformen können auch nachdem erfindungsgemässen Verfahren erzeugt werden. Insbesondere können auch Emulsionen mit hohem Anteil an oktaedrischen plättchenförmigen Zwillingskristallen hergestellt werden.
• 5. Die Verteilung der verschiedenen Halogenide in gemischten Silberhalogenidkristallen ist verschieden von derjenigen wie sie nach konventionellem Verfahren erhalten wird. So lassen sich einerseits Silberhalogenidkristalle mit geringem Jodidgehalt herstellen, bei denen die Jodatome gleichmässig auf das gesamte Kristallgitter verteilt sind. Anderseits können auch extreme Verteilungsinhomogenitäten wie z.B. in Core-Shell-Kristallen auf sehr einfache Art erzielt werden.
• 6. Dadurch, dass mindestens ein Teil des Verfahrens in organischen Lösungsmitteln durchgeführt wird, können organische, wasserunlösliche Zusatzstoffe wie Sensibilisatoren, Desensibilisatoren, Stabilisatoren und UV-Absorber auf besonders einfache Weise in die Emulsion eingearbeitet werden.

The technical advantages of the method according to the invention can be summarized as follows:

• 1. The solubility of the silver halide complexes in the solvents cited is much higher than in water. Accordingly, much more concentrated starting solutions can be used.
• 2. The complex solutions according to the invention in organic solvents are stable and insensitive to light and can therefore be used and stored in daylight.
• 3. Much less time is required to produce a photographic emulsion with a given particle size distribution than with conventional precipitation processes. Ostwald ripening can be dispensed with in most cases.
• 4. All crystal shapes that can be produced using conventional techniques can also be produced using the method according to the invention. In particular, emulsions with a high proportion of octahedral plate-like twin crystals can also be produced.
• 5. The distribution of the various halides in mixed silver halide crystals is different from that obtained by conventional methods. On the one hand, silver halide crystals with a low iodide content can be produced, in which the iodine atoms are evenly distributed over the entire crystal lattice. On the other hand, extreme distribution inhomogeneities such as in core-shell crystals can also be achieved in a very simple manner.
• 6. Because at least part of the process is carried out in organic solvents, organic, water-insoluble additives such as sensitizers, desensitizers, stabilizers and UV absorbers can be incorporated into the emulsion in a particularly simple manner.

• Fig. 1 zeigt eine Silberbromidemulsion (Kristalldurchmesser 0,10 bis 0,85 µm), die aus in NMF gelösten Komplexen des Systems AgBr/NH₄Br (Ueberschuss) und Gelatine hergestellt wird (Beispiel 2).
• Fig. 2 zeigt eine Silberbromidemulsion (Kristalldurchmesser 0,07 bis 0,50 pm),die aus in NMF gelösten Komplexen des Systems A^gBr/NH₄Br (Ueberschuss) und Gelatine in Gegenwart eines löslichen Silbersalzes hergestellt wird (Beispiel 5).
• Fig. 3 zeigt eine Silberchloridemulsion (Kristalldurchmesser 0,10 bis 0,50µm), hergestellt aus in NMF gelösten Komplexen des Systems AgCl/LiCl (Ueberschuss) und Gelatine (Beispiel 9).
• Fig. 4 zeigt eine Silberjodidemulsion (Kristalldurchmesser 0,05 bis 0,25 µm), hergestellt aus in NMF gelösten Komplexen des Systems AgJ/NH₄J (Ueberschuss) und Gelatine(Beispiel 10).
• Fig. 5 zeigt eine Silberbromidemulsion (Kristalldurchmesser 0,05 bis 0,55 µm), die aus in NMA gelösten Komplexen des Systems AgBr/NH₄Br (Ueberschuss) und Gelatine hergestellt wird (Beispiel 15).
• Fig. 6 zeigt eine Silberbromidjodidemulsion nach der Ostwald-Reifung (Kristalldurchmesser 0,2 bis 1,4 µm), hergestellt aus in NMF gelösten Komplexen des Systems AgBr/AgJ/NH₄Br/NH₃ und Gelatine (Beispiel 22).

Figures 1 to 6 show electron micrographs of silver halide emulsions produced according to the invention.

• 1 shows a silver bromide emulsion (crystal diameter 0.10 to 0.85 μm) which is produced from complexes of the AgBr / NH ₄ Br system (excess) and gelatin dissolved in NMF (example 2).
• 2 shows a silver bromide emulsion (crystal diameter 0.07 to 0.50 pm) which is prepared from complexes of the system A ^g Br / NH ₄ Br (excess) and gelatin dissolved in NMF in the presence of a soluble silver salt (Example 5).
• 3 shows a silver chloride emulsion (crystal diameter 0.10 to 0.50 μm), produced from complexes of the AgCl / LiCl system (excess) and gelatin (example 9) dissolved in NMF.
• 4 shows a silver iodide emulsion (crystal diameter 0.05 to 0.25 μm), produced from complexes of the AgJ / NH ₄ J system (excess) and gelatin (example 10) dissolved in NMF.
• 5 shows a silver bromide emulsion (crystal diameter 0.05 to 0.55 μm) which is prepared from complexes of the AgBr / NH ₄ Br system (excess) and gelatin dissolved in NMA (Example 15).
• 6 shows a silver bromide iodide emulsion after Ostwald ripening (crystal diameter 0.2 to 1.4 μm), produced from complexes of the AgBr / AgJ / NH ₄ Br / NH _{3 system} and gelatin dissolved in NMF (Example 22).

The following examples explain the process.

Example 1: Preparation of a silver halide complex solution

Weigh 46.95 g (0.25 mol) of dry silver bromide and 44.08 g of dry ammonium bromide (0.45 mol) in a 250 ml volumetric flask. The flask is then filled with NMF. Treat at room temperature by stirring or shaking or, preferably using ultrasound, until a clear solution is formed. After filling up to the 250 ml mark, a solution of various complexes of silver bromide with excess bromide is finally obtained, which contains 2.8 equivalents of Br and 1.8 equivalents of NH per liter of 1 equivalent of Ag.

Similar solutions can also be prepared by mixing concentrated aqueous solutions of silver nitrate and ammonium bromide with N-methylformamide. In this case, the solutions contain, in addition to the organic solvent, a quantity of water derived from the solutions used.

Example 2:

250 ml of the complex solution in NMF obtained according to Example 1 are added to 1000 ml of a 2% aqueous gelatin solution in a uniform jet within 60 seconds. The temperature of both solutions has previously been set to 40 ° C, and during the mixing process is stirred vigorously with a high-speed stirrer (5500 rpm). The mixture is then stirred at half the speed at the same temperature for a further 2 minutes. Then adjust the pH of the solution to 3.8. At a temperature of 30 ° C 2000 ml of water and 50 ml of a 5% solution of the compound of the formula

added. The silver halide, together with the gelatin present, is thereby flocculated and quickly settles out as sediment. It is decanted and then washed twice with 1000 ml of water.

An aqueous gelatin solution is then added so that the silver content of the emulsion is 5.1% and the gelatin content is 5.8%.

1 shows an electron micrograph of the emulsion. The evaluation shows a grain diameter of 0.10 to 0.85 µm

Grain diameter is an average value determined from different projections of a crystal.

Finally, the pH of the emulsion is adjusted to 6.0 and the pAg to 7.5. The emulsion prepared in this way is poured onto a polyester base with a layer thickness which corresponds to an application weight of 3.0 g of silver and 3.4 g of gelatin per m ² . A sample of the dried film is exposed to a wedge at 120,000 lux sec using an incandescent lamp and then developed for 4 minutes at 20 ° C. using the following solution:

The evaluation of the exposed and developed wedge gives the following sensitometric values:

Instead of the 2% aqueous gelatin solution, a water / methanol or water / ethanol mixture in a weight ratio of about 5: 1 can be used for the decomplexing.

Example 3:

Example 2 is repeated. However, the procedure for the decomposition of the silver halide complex is reversed by letting the aqueous gelatin solution run into the AgBr / NH ₄ Br complex solution. In this case, silver halide crystals in a size range of 0.45 to 1.50 μm are obtained

Example 4:

Example 2 is repeated, but the run-in time of the complex solution in the aqueous gelatin solution is extended from one minute to 28 minutes. This results in slightly larger AgBr crystals than in Example 2 in a size range between 0.15 and 1.15 µm

Example 5:

Example 2 is repeated, but the 2% gelatin solution additionally contains 0.4 mol of silver nitrate per liter. After the complex solution has flowed in, an extraordinarily fine-grained emulsion is obtained, the particles of which have a size between 0.07 and 0.50 μm. Fig. 2 shows the corresponding electron microscopic image.

After adjusting the pH to 6.0 and the pAg to 7.5, the emulsion treated in this way is poured onto a transparent polyester support with a layer thickness corresponding to a basis weight of 2.5 g of silver and 3.0 g of gelatin per m. A sample of the coated film is exposed and developed as indicated in Example 2. The following sensitometric data are obtained:

Example 6:

Example 5 is repeated, except that the silver nitrate-containing gelatin solution is added to the complex solution presented. An emulsion with crystals in the size range from 0.1 to 1.6 μm is obtained

Example 7:

Example 2 is repeated, except that 0.3 mol / liter of ammonium bromide solution are added to the aqueous 27% gelatin solution. Decomplexing is therefore slower, and a somewhat coarser-grained emulsion with particles in the size range between 0.10 and 0.95 μm is obtained accordingly.

As described in Example 2, the emulsion is poured onto a transparent polyester film and dried. A sample of the poured and dried film is exposed through a step wedge to 7500 lux sec and then developed according to example 2. The following sensitometric values are obtained:

Example 8:

In this example, the gelatin solution used to decompose the complex contains a soluble halide as a modifying substance, which is different from the halide used for complex formation.

For this purpose, the complex solution prepared according to Example 1, similar to that described in Example 2, is poured within 10 minutes into 1000 ml of a 2% gelatin solution which contains 0.05 mol of potassium iodide per liter. The mixing temperature is kept at 40 ° C. and the agitator is set to 5500 rpm. After stirring for a further minute, the pH is adjusted to 3.8, and the silver halide is flocculated and washed according to Example 2 and finally redispersed in fresh gelatin. The diameter of the silver halide crystals is between 0.06 and 0.60 pm.

Example 9:

22.2 g of dry silver chloride and 37.1 g of dry lithium chloride are dissolved in 250 ml of NMF according to Example 1. A complex solution is thus obtained which contains 0.62 mol of silver chloride and 3.5 mol of lithium chloride per liter of solution. This solution is poured in a uniform stream within 60 seconds in 1000 ml of a 1% aqueous gelatin solution. The experimental conditions and the further treatment of the resulting silver chloride emulsion are described in Example 2. The flocculated and washed silver halide is redispersed in gelatin solution as previously described.

3 shows an electron micrograph of the emulsion obtained. The crystals have a diameter between 0.1 and 0.50 µm

Example 10:

58.7 g of silver iodide and 18.1 g of ammonium iodide are dissolved in 250 ml of NMF according to Example 1. A complex solution is obtained which contains 1 mol of silver iodide and 0.5 mol of ammonium iodide per liter.

This solution is poured within 60 seconds into 1000 ml of a 2% aqueous gelatin solution, the same experimental conditions being observed as in Example 2.

Fig. 4 shows an electron micrograph of this emulsion. The crystals have a diameter between 0.05 and 0.25 µm

Example 11:

28.2 g of silver bromide and 13.7 g of ammonium bromide are dissolved in 100 ml of DMF. A complex solution is obtained which contains 1.5 mol of silver bromide and 1.4 mol of ammonium bromide per liter.

This solution is added according to Example 2 within 60 seconds in 400 ml of an aqueous 27% gelatin solution in a uniform stream.

The further processing of the emulsion is also carried out according to Example 2. After adjusting the pH to 6.0 and the pAg to 7.5, the emulsion is placed on a transparent polyester base with a layer thickness that is 2.2 g silver and Corresponds to 3.0 g of gelatin per m ² , cast. After drying, a sample of the cast material is exposed behind a step wedge with 120,000 lux sec and then developed as in Example 2. The following sensitometric data are obtained:

The silver halide crystals have a diameter of 0.08 to 0.82 µm

Example 12:

28.2 g of silver bromide and 18.6 g of ammonium bromide according to Example 1 are dissolved in 100 ml of DMS. A complex solution is obtained which contains 1.5 mol of silver bromide and 1.9 mol of ammonium bromide per liter. The solution is added according to Example 2 within 60 seconds in 400 ml of an aqueous 2% gelatin solution in a uniform stream. An emulsion is obtained, the crystals of which are cubic and octahedral in shape and have a diameter between 0.13 and 1.1 μm.

It is processed according to Example 2 and cast on a polyester support to form a layer which has 3.3 g of silver and 3.5 g of gelatin per m ² . After drying is a sample of the coated carrier exposed to 2000 lux sec using a step wedge and developed according to example 2. The following sensitometric data are obtained:

Example 13:

20.1 g silver chloride and 8.5 g lithium chloride are dissolved in 100 ml DMS. The complex solution contains 1.4 moles of silver chloride and 2 moles of lithium chloride per liter.

This solution is added to 400 ml of a 2% aqueous gelatin solution in a uniform jet within 60 seconds. The resulting emulsion is processed according to Example 2 and finally an emulsion with cubic crystals is obtained, the edge length of which measures between 0.15 and 0.75 μm.

After adjusting the pH to 6.0 and the pAg to 7.5, a layer is poured onto a polyester base that contains 2.7 g of silver and 3.0 g of gelatin per m.

A dried sample of the coated material is exposed behind a step wedge with 20,000 lux sec and then developed as in Example 2. The following sensitometric values are obtained:

Example 14:

24.4 g of silver bromide and 19.6 g of ammonium bromide are dissolved in 100 ml of DMA according to Example 1. A complex solution is obtained which contains 1.3 mol of silver bromide and 1.98 mol of ammonium bromide per liter.

According to Example 2, the solution is stirred into 400 ml of an aqueous 2% gelatin solution in a uniform jet within 60 seconds. After further processing according to Example 2, the pH is adjusted to 6.0 and the pAg is 7.5. The emulsion contains crystals with a diameter of 0.15 to 0.90 µm.

The solution is finally poured onto a polyester support so that the weight per unit area is 3.3 g of silver and 3.4 g of gelatin per m ² . A dried sample is exposed to 3750 lux sec through a step wedge and developed according to Example 2. The following sensitometric data are obtained:

Example 15:

9.4 g of silver bromide and 26.9 g of ammonium bromide are dissolved in 250 ml of NMA. A complex solution is obtained which contains 0.2 mol of silver bromide and 1.1 mol of ammonium bromide per liter. To prepare an emulsion, the solution is poured into 1000 ml of an aqueous solution containing 0.25% gelatin within 60 seconds.

5 shows an electron micrograph of the emulsion obtained after processing according to Example 2. The crystals have a diameter of 0.05 to 0.55 µm

Example 16:

9.4 g of silver bromide and 9.8 g of ammonium bromide are dissolved in 100 ml of HMPT. The complex solution contains 0.5 mol of silver bromide and 1.0 mol of ammonium bromide per liter. This solution is added to 400 ml of an aqueous 1% gelatin solution in a uniform jet within 60 seconds. After processing according to Example 2, an emulsion is obtained whose crystals have a diameter between 0.05 and 0.55 μm.

Example 17:

9.4 g of silver bromide and 9.8 g of ammonium bromide are dissolved in 100 ml of NHP. The complex solution contains 0.5 mol of silver bromide and 1.0 mol of ammonium bromide per liter. Decomplexing is done by pouring into

400 ml of a 2% aqueous gelatin solution within 3 minutes. After processing according to Example 2, an emulsion is obtained with crystals whose diameters are between 0.1 and 0.6 µm.

Example 18:

5.6 g of silver bromide and 3.6 g of ammonium bromide are dissolved in 100 ml of TMU. The complex solution contains 0.3 mol of silver bromide and 0.37 mol of ammonium bromide per liter. The solution is added to 400 ml of a 0.5% aqueous gelatin solution in a steady stream over the course of 2 1/2 minutes.

The resulting silver bromide emulsion is processed further in accordance with Example 2. The emulsion contains cubic silver bromide crystals with an edge length of 0.04 to 0.40 µm

Example 19:

A solution is prepared which contains 93.9 g (0.50 mol) of silver bromide and 143 g (1.77 mol) of hydrogen bromide per liter in a mixture of 80% NMF and 20% water. 100 ml of this solution are left in 400 ml of a 1% aqueous gelatin solution within 60 seconds flow in. After further processing according to Example 2, an emulsion with crystals with a diameter of 0.05 to 0.65 μm is obtained

Example 20:

5 different complex solutions in NMF of 250 ml each are prepared, each containing 1.0 mol of mixed silver bromide / iodide and 1.8 mol of ammonium bromide per liter, the molar ratio of silver bromide: silver iodide in the solution being between 99: 1 and 80: 20 is varied. However, the composition of the crystals can vary from that of the solution.

These solutions are mixed under the conditions described in Example 2 with 1000 ml of a 2% gelatin solution. After further processing according to Example 2, 5 different emulsions with particle sizes according to the following Table 5 are obtained.

Table 5: Particle sizes of silver bromide / iodide crystals as a function of bromide / iodide ratio. Composition of the crystals

The ratio of bromine: iodine in the crystals is determined using the X-ray fluorescence method.

Example 21:

44.8 g of silver bromide, 2.64 g of silver iodide and 44.1 g of ammonium bromide are dissolved in 250 ml of NMF. You get a complex solution, the pro Contains 0.955 moles of silver bromide, 0.045 moles of silver iodide and 1.8 moles of ammonium bromide. As described in Example 2, this solution is introduced into 1000 ml of a 2% aqueous gelatin solution, which contains 17 g (1.0 mol) of ammonia per liter, and then processed further.

An emulsion with octahedral crystals having a diameter of 0.15 to 0.80 µm is obtained. After adjusting the pH to 6.0 and the pAg to 7.5, a transparent polyester film is coated so that the weight per unit area is 2.8 g of silver and 3.3 g of gelatin per m ² .

A sample of the dried material is exposed behind a step wedge with 2000 lux sec and then developed according to example 2. The following sensitometric values are obtained:

Example 22:

250 ml of a complex solution in NMF are prepared, the per liter 179.35 g (0.955 mol) of silver bromide, 10.56 g (0.045 mol) of silver iodide, 176.33 g (1.8 mol) of ammonium bromide and 34 ml of NH ₃ 25 % (0.44 mol) contains ammonia.

This solution is mixed as described in Example 2 with 1000 ml of a 2% gelatin solution within 60 seconds and then processed further.

An emulsion of silver bromide iodide crystals with a diameter of 0.08 to 0.65 µm is obtained. After the Ostwald ripening (40 minutes at 40 ° C) the crystals grow to a diameter between 0.2 and 1.4 µm. 6 shows an electron micrograph of the emulsion after Ostwald ripening has ended.

After flocculation and redispersion according to Example 2, the pH is adjusted to 6.0 and the pAg to 7.5, and the emulsion is then poured onto a transparent polyester base. A sample of the coated and dried material is exposed under a step wedge with 20,000 lux sec that developed according to Example 2. The following sensitometric values are obtained:

Example 23:

56.34 g (0.3 mol) of silver bromide, 43.00 g of silver chloride (0.3 mol) and 127.2 g (3.0 mol) of lithium chloride are dissolved in 100 ml of NMF.

This solution is mixed with a 1% aqueous gelatin solution within 1/2 minutes and processed according to Example 2. An emulsion is obtained with cubic crystals which have an edge length of 0.15 to 0.45 pm.

The content of the crystals can be determined to be 48.3 mol% silver bromide and 51.7 mol% silver chloride using X-ray fluorescence spectroscopy.

Example 24:

250 ml of the NMF solution prepared according to Example 1, which contains 1.0 mol / liter of silver bromide and 1.8 mol / liter of ammonium bromide, and 225 ml of a 2-molar aqueous solution of silver nitrate added to 500 ml of a 4% aqueous gelatin solution at the same time using an apparatus equipped with two inlet nozzles. The temperature is kept at 50 ° C. during the entire running-in process. The inlet speed is 100 ml / h during the first 15 minutes; later it is increased to 400 ml / h. The ratio of the run-in speed of both solutions is regulated throughout the process so that a pAg value of 6.5 is maintained.

After the precipitation operation has ended, the product is flocculated as in Example 2, washed and redispersed in fresh gelatin solution. An emulsion with cubic crystals is obtained, the edge lengths of which are from 0.1 to 0.6 μm.

Example 25:

This example relates to the use of a synthetic polymer instead of gelatin in emulsion formation.

100 ml of a complex solution in NMF, which contains 0.95 mol of silver bromide and 1.8 mol of ammonium bromide per liter, is added within 3 minutes to 400 ml of an aqueous solution which contains 1% polyvinylpyrrolidone in a uniform stream. The temperature is 40 ° C.

After the decomplexation process is complete, the mixture is cooled to 20 ° C. and centrifuged. The crystals separated from the supernatant liquid are washed twice with water and then redispersed in a 5.8% gelatin solution. The crystals have a diameter of 0.07 to 0.55 µm.

Example 26:

250 ml of a complex silver bromide solution in NMF prepared according to Example 1 are added to 1000 ml of water within 60 seconds with vigorous stirring at 40 ° C. You let the arising Sediment crystals for 5 minutes at 25 ° C, pour off the supernatant solution and wash twice with water. The sediment is finally taken up in an aqueous solution containing 5.8% gelatin and dispersed for a few minutes with vigorous stirring. An emulsion is obtained whose crystals have a diameter of 0.6 to 2.1 μm.

Example 27:

According to Example 1, a highly concentrated complex solution of 1.8 mol of silver bromide and 2.7 mol of ammonium bromide in 1 1 NMF is prepared. 500 ml of this solution are stirred into 2000 ml of a 2% aqueous gelatin solution under the test conditions according to Example 2. After flocculation, washing and redispersion according to Example 2, an emulsion with crystals of 0.15 to 1.3 μm in diameter is obtained.

The pH is adjusted to 6.8 and the pAg to 7.4 and the emulsion is subjected to chemical ripening at 54 ° C. in the presence of 9.0 mg sodium thiosulfate and 12.0 mg ammonium aurothiocyanate. Samples are taken after 20, 50, 80, 110 and 140 minutes to track the maturation process.

After ripening, the pH of each sample is adjusted to 6.0 and the pAg to 7.5; The emulsion is then poured onto a transparent polyester base, so that the weight per unit area is 3.9 g of silver and 4.4 g of gelatin.

After drying, a sample of the coated material is exposed behind a step wedge with 1000 lux sec and then developed according to Example 1.

The course of the chemical ripening can be read from the sensitometric values according to Table 6 below.

The sensitometric values obtained are comparable to those of a conventionally produced emulsion of a similar grain size.

Example 28:

1000 ml of a complex solution in NMF containing 0.95 mol / liter silver bromide and 1.8 mol / liter ammonium bromide are added to 4000 ml of an aqueous 2% gelatin solution at 40 ° C. in a uniform jet within 3 minutes. One minute after the end of the feed, the temperature is raised to 55 ° C. 8 ml of a 1 molar solution of ammonia are added. The mixture is left to ripen physically at 55 ° C. for 10 minutes with further stirring. The pH is then lowered to 3.7 and the emulsion is flocculated, washed and redispersed according to Example 2. The diameter of the crystals after physical ripening is between 0.2 and 1.3 pm.

As a further operation, the emulsion is then subjected to chemical ripening as in Example 27 above after the pAg value has been adjusted to 7.8. The sensitometric values can be found in Table 7 below.

Example 29:

The starting solutions used in Example 2 are simultaneously fed to a static mixer at a flow rate of 375 ml / h or 1600 ml / h by means of one pump each. The temperature of the incoming solutions and the temperature in the mixer are kept at 40 ° C.

The emulsion emerging from the mixer is further treated according to Example 2. It then contains crystals with a diameter of 0.15 to 1.40 µm.

The static mixer used for the continuous mixing of the two components consists of a tube 10 cm long and 10 mm inside diameter, which has a number of spiral deflection elements arranged around a core in its interior. The residence time of the solutions in the mixing tube is about 8 seconds at the specified pumping speed.

Example 30:

A layer of 8 g / m ² hardened gelatin is poured onto a polyester support and dried.

In a mixture of 83% N-methylformamide and 17% water, a complex solution is prepared which contains 0.42 mol of silver bromide and 2.17 mol of ammonium bromide per liter.

The coated polyester backing is then immersed in the complex solution at room temperature for 4 minutes, then wiped off and finally immersed in water.

A microscopic examination of the gelatin layer shows that with this method, silver bromide crystals with a size between 0.05 and 1.2 μm were deposited evenly distributed in the gelatin layer.

Size distribution of the silver halide crystals

Vergleicht man die obigen Grössenverteilungen, so stellt man fest, dass durch den Zusatz von Ammoniumbromid zum Verdünnungsmittel das Teilchengrössenspektrum verbreitert, hingegen durch den Zusatz von Silberjodid und in etwas geringerem Mass auch durch den Zusatz von Silbernitrat verengt wird.

If one compares the size distributions above, it is found that the addition of ammonium bromide to the diluent widens the particle size spectrum, on the other hand it is narrowed by the addition of silver iodide and to a lesser extent also by the addition of silver nitrate.

Table 9 below shows the particle size distribution for two further emulsions from Examples 12 and 21. The former is pure silver bromide which is precipitated from a solution in dimethyl sulfoxide, the second is silver bromide iodide which is precipitated from a solution in N-methylformamide. This comparison also shows the narrower particle size spectrum of the iodide-containing emulsion.

Example 31:

According to Example 1, a solution of 47 g of silver bromide and 44.1 g of ammonium bromide in 250 ml of ^NM F is prepared. The complex solution contains 1.0 mol of silver bromide and 1.8 mol of ammonium bromide per liter. 1 l of a 0.01 molar silver sulfide suspension in a 2% aqueous gelatin solution is added to this solution over 5 minutes. The size of the silver sulfide crystals is about 0.3 µm. The temperature of the complex solution and the suspension has previously been set to 40 ° C. During the mixing process, the mixture is stirred vigorously with a high-speed agitator (5500 rpm). The mixture is then stirred at half the speed for a further 2 minutes, the temperature being kept at 40.degree. The emulsion obtained is then processed further in accordance with Example 2. The size of the silver bromide crystals is in a range from 0.6 to 1.2 µm

The emulsion is chemically ripened according to Example 27 for 60 minutes and then poured onto a polyester support and dried. The sensitometric data determined after exposure and development of this material (see Example 27) show that the emulsion is strongly desensitized on the one hand, but on the other hand has a major reciprocity error when exposed to light sources of low intensity. The emulsion is therefore suitable for the production of direct-positive and so-called bright-light materials.

Example 32:

250 ml of a complex solution prepared according to Example 31 are mixed with 6 mg Na RhCl ₆ · 12H20. This corresponds to a ratio of 4.1 mg rhodium per 1 mole of silver. According to Example 2, the solution is added to 1 1 of a 2% gelatin solution. After flocculation, washing and redispersion (see Example 2), an emulsion is obtained whose crystals have a size of 0.10 to 0.85 μm.

The pH of the emulsion is adjusted to 6.8 and the pAg to 8.0. The emulsion is then chemically ripened according to Example 27 for 60 minutes, poured onto a polyester support and dried. After exposure and development of the material according to Example 27, the sensitometric data compiled in Table 10 are obtained.

A second emulsion is prepared as described above, with the difference that no addition of rhodium salt is used. The sensitometric values obtained with this emulsion are shown in Table 10.

erhält man eine direkt positive Emulsion mit erhöhter Empfindlichkeit.The emulsion containing the rhodium salt is strongly desensitized. It can be masked in the presence of a reducing agent. After adding a sensitizer of the formula

you get a direct positive emulsion with increased sensitivity.

Claims (18)

1. A process for the preparation of photographic silver halide emulsions, characterized in that a silver halide complex of the formula dissolved in an organic solvent

wherein E is hydrogen, an alkali metal or ammonium and Z is a divalent metal of main group 2 or subgroup 8 of the periodic table, X ¹ , X ² and X ^{3 are} independently halogen or pseudohalogen, and the indices p, q, m, n ₁ , n ₂ and n ₃ the conditions

and

meet, optionally in the presence of a protective colloid, with a medium in which the silver halide complex is not stable 1 2 and disintegrates, optionally the soluble compounds EX ¹ , EX, _EX ³ ,

and or

separated from the precipitated silver halide, optionally adding a silver halide binder and carrying out the physical and / or chemical ripening. 2. The method according to claim 1, characterized in that the medium is a binder layer cast onto a carrier. 3. The method according to claim 1, characterized in that the medium is a solvent in which the silver halide complex is not stable. 4. The method according to claim 3, characterized in that the solvent in which the silver halide complex is not stable, water and / or a solvent from the group consisting of alcohols, glycols, esters, acetals, ethers and ketones, or an optionally water-containing mixture of such Is solvent. 5. The method according to claim 1, characterized in that the silver halide complex in an organic, aprotic or amphiprotic solvent which is at least partially miscible with water, in which the complex has a solubility constant (log K _s2 ) greater than -4.5, or in one optionally water-containing mixture of such solvents is dissolved. 6. The method according to any one of claims 4 and 5, characterized in that the complex solution and / or the solvent in which the silver halide complex is not stable contains compounds which modify the shape and / or the size distribution of the silver halides to be precipitated. 7. The method according to claim 6, characterized in that the modifying compounds are in the form of small, insoluble particles and are crystallization centers for silver halide crystals. 8. The method according to claim 7, characterized in that the modifying compound is a silver complexing agent, a soluble silver salt, a soluble halide, a surface-active compound acting as a protective colloid or a high molecular compound soluble in organic, aprotic or amphiprotic solvents. 9. The method according to any one of claims 4 and 5, characterized in that the complex solution or the solvent in which the silver halide complex is not stable contains a heavy metal which can be stored in the lattice of the resulting silver halide. 10. The method according to claims 3 to 9, characterized in that the complex solution in the solvent optionally containing the modifying compounds, in which the silver halide complex is not stable, is allowed to flow in at a limited speed with simultaneous mixing. 11. The method according to claims 3 to 9, characterized in that the solvent optionally containing the modifying compounds, in which the silver halide complex is not stable, is allowed to flow into the complex solution at a limited rate with simultaneous mixing. 12. The method according to claims 3 to 9, characterized in that the complex solution and the solvent optionally containing the modifying compounds, in which the silver halide complex is not stable, are allowed to flow continuously with simultaneous mixing. 13. The method according to claim 1, characterized in that the separation of the silver halide from dissolved salts is carried out by decanting, centrifuging, flocculating, pasta washing, dialyzing or ultrafiltration. 14. The method according to claim 1, characterized in that the binder used for the redispersion is gelatin, optionally together with other high molecular weight compounds of natural or synthetic origin. 15. The method according to claims 1 to 14, characterized in that the optionally freed of soluble salts and matured Silver halide layer spectrally sensitized. 16. The method according to claim 1, characterized in that spectral sensitizers, desensitizers, stabilizers and / or UV absorbers are dissolved before the precipitation of the silver halide in the complex solution and / or in the solvent in which the silver halide complex is not stable. 17. The photographic silver halide emulsion obtained according to any one of claims 1 to 16. 18. The photographic materials prepared with a silver halide emulsion according to claim 17.

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