EP0595031A1 - Process for the production of silver halide emulsions - Google Patents

Abstract

The preparation of a silver halide emulsion containing up to 20 mol % of AgI by precipitation of a silver halide emulsion A containing up to 100 mol % of AgI and addition of a silver halide emulsion B containing up to 40 mol % of AgI and having a maximum mean particle size of 0.25 mu m, where emulsion B always has higher solubility in aqueous gelatin solution than emulsion A either due to its particle size or due to its iodide content, in the presence of at least two compounds from the series consisting of imidazole, histidine ( alpha -amino- beta -imidazolyl-(5)-propionic acid) and other monocyclic, 5- or 6-membered, heterocyclic compounds which contain at least one ring nitrogen atom, but no SH groups, and form, in weakly acidic to neutral aqueous solution, low-solubility silver salts which redissolve on addition of ammonia at a pH of > 9, where one of the at least two compounds is imidazole or histidine and at least one other compound is not imidazole or histidine, gives emulsions having an improved sensitivity/particle size ratio.

Description

The invention relates to a method for producing silver halide emulsions, in which emulsions of different solubility are mixed and redissolved.

Silver halide emulsions are generally prepared by precipitating silver halide in a binder, preferably gelatin as the binder. The silver halide can be precipitated by adding an aqueous solution of a silver salt to a gelatin-containing halide solution. The size of the silver halide grains obtained is inter alia controlled by the temperature of the solution, the run-in time and the excess of halide.

The grain size and the grain size distribution of the silver halide grains of the emulsions obtained are still determined primarily by the so-called Ostwald ripening. Under the Ostwald ripening is the dissolution Easily soluble silver halide grains are understood to be the action of silver halide solvents and subsequent separation of the dissolved silver halide on less soluble silver halide grains.

It is also known to run the aqueous solutions of a silver salt and a halide into a receiver at the same time (double-jet method).

For the production of silver halide emulsions, processes are also known for mixing emulsions of different grain sizes and for effecting a redissolution in the presence of silver halide solvents. A prerequisite for such processes is that the silver halide crystals used in the redissolution have different solubilities. Different solubilities can be caused by different grain size and / or different halide composition. Such methods are described in US Pat. Nos. 2,146,983, 3,206,313, 3,317,322, German Auslegeschrift 1,207,791, D. Markocki and W. Romer in "Korpuskular Photographie", IV (1963), page 149 ff., from "Zhurnal Nauchnoi Prikladnoi Fotografi Kinematografi 5, No. 2 (1960), pages 81-83 and EP-PS 42 060 known.

The more readily soluble silver halide emulsion used in these processes is preferably a fine grain silver halide emulsion with an average grain diameter smaller than that of the less soluble silver halide emulsion.

The advantages of the specified redeployment procedures include: in controlled Ostwald ripening and above all in avoiding local silver ion oversaturation.

Examples of known silver halide solvents are: halides, preferably alkali and ammonium halides, in particular bromides or chlorides; Ammonia; Thiocyanates, especially alkali or ammonium thiocyanate; Sulfites, especially alkali or ammonium sulfites; Thiosulfate; organic amines; Thioether and imidazole derivatives. Suitable thioethers are described, for example, in US Pat. Nos. 3,271,157, 3,507,657, 3,531,289 and 3,574,628. Particularly suitable thioethers are also described in German Offenlegungsschriften 2,614,862 and 2,824,249. Suitable imidazole derivatives are described in US Pat German Offenlegungsschrift 27 58 711.

Both high-sensitivity and fine-grain silver halide emulsions can be produced by the processes mentioned, but it has not hitherto been possible to achieve both properties to a sufficient extent together.

The object of the invention is therefore to find a process for the production of highly sensitive, fine-grained silver halide emulsions which have low fog.

This task is solved by an improved redeployment process.

The invention therefore relates to a process for the preparation of a silver halide emulsion with up to 20 mol% AgI by precipitation of a silver halide emulsion A with up to 100 mol% AgI and addition of a silver halide emulsion B with up to 40 mol% AgI and an average grain size of at most 0.25 µm, emulsion B in aqueous gelatin solution always being more soluble than emulsion A either because of its grain size or because of its iodide content, in the presence of at least two compounds from the series imidazole, histidine (α-amino-β-imidazolyl - (5) -pro-pionic acid) and other monocyclic, free of SH groups, 5- or 6-membered, heterocyclic compounds with at least one ring nitrogen atom, which form poorly soluble silver salts in weakly acidic to neutral aqueous solution, which with the addition of ammonia go back into solution at pH> 9, one of the at least two compounds imidazole or histidine and little At least one other compound is not imidazole or histidine.

Monocyclic compounds are understood to mean those which have no fused rings in the entire molecule. Grain size is always understood to mean the diameter of the same-volume ball.

The iodide content of emulsion A is preferably 10 to 90 mol%.

Suitable are e.g. Imidazoles, oxazoles, thiazoles, triazoles, thiadiazoles, oxadiazoles, pyridines, tetrazoles and pyrimidines which are substituted by alkyl, preferably having up to 4 carbon atoms such as methyl, ethyl, isopropyl; Alkenyl such as allyl; Aryl such as phenyl, halogen such as chlorine or bromine, carboxylic acid groups or derivatives such as carbalkoxy or carbonamido: sulfonic acid groups, sulfonamide, sulfones, thioethers such as methylthio or carboxyalkylthio; substituted or unsubstituted amino groups can be substituted.

The solution is preferably carried out at an E _Ag value of -20 to -120 mV, in particular -40 to -100 mV, at a pH of 4 to 10, in particular 6 to 8 and a temperature of 40 to 90 ° C. especially 50 to 75 ° C. Under these conditions, the redissolution is usually complete after 20 minutes (E _Ag is the potential between a silver electrode and a saturated calomel electrode).

The gelatin / silver halide weight ratio, expressed as the amount of silver nitrate used, is preferably 0.05 to 1.0, in particular 0.1 to 0.5, when the solution is redissolved.

Emulsions A and B, expressed as the amount of silver nitrate used, are preferably mixed with one another in a weight ratio of 1: 1 to 1:20, preferably 1: 2 to 1:10. Emulsions A and B are essentially silver bromoiodide emulsions. They can also contain small amounts of silver chloride. The grain size of emulsion A ranges in particular from 0.1 to 1.5 μm, the grain size of emulsion B in particular from 0.01 to 0.2 μm.

If the iodide content of emulsion A is between 40 and 90 mol%, the emulsion consists predominantly of grains with about 40 mol% AgI and pure AgI grains.

The iodide content of emulsion A can be adjusted by appropriate selection of the mixture of soluble halides intended for the precipitation. An emulsion with a lower iodide content can also be precipitated first and then converted to the desired higher iodide content with the addition of KI.

Suitable SH group-free N-heterocycles are given below:

1,2,4-triazoles:

Thiadiazole:

Tetrazoles:

Pyrimidines:

Thiazoles

Oxadiazoles:

Imidazole:

Pyridines:

• a)
  
  Diese Verbindungen bilden Silbersalze, die sich unter Zusatz von Ammoniak bei pH > 9 nicht mehr lösen.
• b)
  
  
  Diese Verbindungen besitzen SH-Gruppen oder sind nicht monocyclisch.

Unsuitable connections are, for example

• a)
  
  These compounds form silver salts that no longer dissolve when ammonia is added at pH> 9.
• b)
  
  
  These compounds have SH groups or are not monocyclic.

In a preferred embodiment, emulsion A is first prepared as a precipitate, which can optionally be concentrated and desalted. The further supply of substance, which is carried out according to the invention by adding emulsion B, can be set up in such a way that more than 50 mol%, preferably more than 80 mol%, of the silver halide used is added in the form of emulsion B. Emulsion B can also be concentrated and desalted.

In principle, emulsion B and the silver halide solvents to be used according to the invention can be added simultaneously or at different times, all at once or in several parts or continuously. The concentrations of the silver halide emulsions B and A used can be varied within wide limits. The amount of the silver halide solvent to be used according to the invention can generally be easily determined in a series of tests and, in the case of imidazole and histidine, is preferably between 10⁻⁵ and 2.0 mol per mol of silver halide used, in particular between 10⁻³ and 0.3 mol per Mol used silver halide and in the case of compounds other than imidazole and histidine preferably 10⁻⁶ and 0.5 mol per mol of silver halide used.

According to the invention, emulsions can in principle be prepared for a wide variety of photographic materials, e.g. Negative working emulsions with high surface sensitivity, negative working emulsions with high internal sensitivity, directly positive working emulsions that can be superficially veiled or superficially unveiled, emulsions with layered grain structure, print-out emulsions, reverse emulsions, emulsions for black and white and for color materials as well as with defined grain distribution and halide topography , in particular with a defined halide, in particular iodide gradient.

To remove the water-soluble salts, the silver halide emulsions prepared according to the invention and the starting emulsions A and B can either be solidified, pasta-coated and soaked in a known manner or can also be coagulated with a coagulating agent and then washed, as is known, for example, from German Offenlegungsschrift 2,614,862. Desalination is particularly advantageously carried out by ultrafiltration.

The emulsion produced according to the invention and optionally also the starting emulsions, in particular emulsion A, can be chemically sensitized, for example by adding sulfur-containing compounds during chemical ripening, for example allyl isothiocyanate, allyl thiourea, sodium thiosulfate. Reducing agents, For example, the tin compounds described in the Belgian patent specifications 493 464 or 568 687, and also polyamines such as diethylenetriamine or aminomethylsulfinic acid derivatives, for example in accordance with the Belgian patent specification 547 323, can be used. Selenium compounds are also suitable.

Precious metals or noble metal compounds such as gold, platinum, palladium, iridium, ruthenium or rhodium are also suitable as chemical sensitizers. This method of chemical sensitization is described in the article by R. Koslowsky, Z. Wis. Phot. 46, 65-72 (1951).

Both emulsion A and emulsion B can be added with foreign ions for doping during the precipitation. This addition is also possible before, during and after the redeployment. Suitable compounds are for example Ir- and. Rh compounds.

Both emulsion A and emulsion B can be subjected to reduction ripening during the precipitation. Such reduction sensitization is also possible before, during and after the redissolution.

This measure and suitable connections are described, for example, in EP 348 934, 368 304, 369 424, 371 338, 369 491, 378 841, 404 142, 435 270, 435 355 and US 4 917 997.

Furthermore, it can be advantageous to carry out an oxidation step either in subsequent precipitation steps or before chemical sensitization. Suitable compounds for this are, for example, thiosulfonic acid derivatives, H₂O₂ and mercury (II) compounds.

It is also possible to sensitize the emulsions with polyalkylene oxide derivatives, for example with polyethylene oxide with a molecular weight between 1,000 and 20,000, furthermore with condensation products of alkylene oxides and aliphatic alcohols, glycols, cyclic dehydration products of hexitols, with alkyl-substituted phenols, aliphatic carboxylic acids, aliphatic amines, aliphatic diamines and amides. The condensation products have a molecular weight of at least 700, preferably more than 1,000. To achieve special effects, these sensitizers can of course be used in combination, as in the Belgian patent 536 278 and in the British patent
727,982.

The emulsions can also be optically sensitized, for example with the usual polymethine dyes such as neutrocyanines, basic or acidic carbocyanines, rhodacyanines, hemicyanines, styryl dyes, oxonols and the like. Such sensitizers are described in FM Hamer: "The Cyanine Dyes and Related Compounds" 1964, Interscience Publishers, John Wiley and Sons.

The emulsions can contain the usual stabilizers, e.g. homeopolar or salt-like compounds of mercury with aromatic or heterocyclic rings such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts and other mercury compounds. Also suitable as stabilizers are azaindenes, preferably tetra- or penta-azaindenes, in particular those which are substituted by hydroxyl or amino groups. Such connections are in Birr: Z. Wiss. Phot. 47 (1952), 2-58. Other suitable stabilizers include heterocyclic mercapto compounds, e.g. Phenylmercapto compounds, quaternary benzothiazole derivatives and benzotriazole.

According to the invention, it is advantageous to use gelatin as a binder or protective colloid for the photographic emulsion according to the invention, but other colloids can also be used. For example, various high molecular weight synthetic hydrophilic materials such as graft polymers of gelatin and other high molecular weight materials; Proteins such as albumin, casein and the like; Cellulose derivatives such as hydroxyethyl cellulose, carboxymethyl cellulose, cellulose sulfate and the like; Saccharide derivatives such as sodium alginate, starch derivatives and the like; Homopolymers or copolymers, such as polyvinyl alcohol, partially acetalized polyvinyl alcohol, poly-N-vinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinylimidazole and polyvinylpyrazole can be used.

Suitable gelatin graft polymers that can be used in the present invention are those obtained by grafting homopolymers or copolymers of vinyl monomers such as acrylic acid, methacrylic acid, derivatives thereof, e.g. the esters, amides, acrylonitrile, styrene on gelatin. Graft polymers of gelatin with polymers of acrylic acid, methacrylic acid, acrylamide, methacrylamide and hydroxyalkyl methacrylates are particularly preferred.

The emulsions can be hardened in a customary manner, for example with formaldehyde or halogen-substituted aldehydes which contain a carboxyl group, such as mucobromic acid, diketones, methanesulfonic acid esters and dialdehydes.

Furthermore, the photographic layers can be hardened with hardeners of the epoxy type, the heterocyclic ethylene imine or the acryloyl type. Examples of such hardeners are e.g. in German laid-open specification 2 263 602 or in British patent 1 266 655. Furthermore, it is also possible to harden the layers in accordance with the process of German Offenlegungsschrift 2 218 009 in order to obtain color photographic materials which are suitable for high-temperature processing.

It is also possible to coat the photographic layers or the color photographic multilayer materials with hardeners of the diazine, triazine or 1,2-dihydroquinoline series to harden, as described in British Patents 1 193 290, 1 251 091, 1 306 544, 1 266 655, French Patent 71 02 716 or German Laid-Open Specification 2 332 317. Examples of such hardeners are diazine derivatives containing alkyl or arylsulfonyl groups, derivatives of hydrogenated diazines or triazines, such as, for example, 1,3,5, -hexahydrotriazine, fluorine-substituted diazine derivatives, for example fluoropyrimidine, esters of 2-substituted, 1,2-dihydroquinoline or 1,2-dihydroisoquinoline-N-carboxylic acid, vinyl sulfonic acid hardeners, carbodiimide or carbamoyl hardeners can also be used, as described, for example, in German Offenlegungsschriften 2,263,602, 2,225,230 and 1,808,685, French Patent 1,491,807 and German Patent 872 153 and DD-A-7218. Other useful resins are described, for example, in British Patent 1,268,550.

The present invention can be applied to both black and white and color photographic images. Colored photographic images can e.g. according to the known principle of chromogenic development in the presence of color couplers, which react with the oxidation product of color-giving p-phenylenediamine developers to form dyes.

The color couplers can, for example, be added to the color developer according to the principle of the so-called development process. In a preferred embodiment the photographic material itself contains the usual color couplers, which are usually incorporated into the silver halide layers. For example, the red-sensitive layer can contain a non-diffusing color coupler for producing the blue-green partial color image, usually a coupler of the phenol or α-naphthol type. The green-sensitive layer can contain, for example, at least one non-diffusing color coupler for producing the purple partial color image, color couplers of the 5-pyrazolone, indazolone or pyrazoloazole type usually being used. For example, the blue-sensitive layer can contain a non-diffusing color coupler for producing the yellow partial color image, usually a color coupler with an open-chain ketomethylene grouping. Color couplers of this type are known in large numbers and are described in a large number of patents. Examples include the publication "Color coupler" by W. Pelz in "Messages from the research laboratories of Agfa, Leverkusen / Munich", Volume III (1961) and K. Venkataraman in "The Chemistry of Synthetic Cyes", Vol. 4, 341 -387, Academic Press, 1971.

2-equivalent couplers can be used as further non-diffusing color couplers; these contain a removable substituent in the coupling point, so that they only require two equivalents of silver halide to form the color, in contrast to the usual 4-equivalent couplers. The 2-equivalent couplers that can be used include, for example, the known DIR couplers, in which the cleavable residue is released as a diffusing development inhibitor after reaction with color developer oxidation products. Furthermore, the so-called white couplers can be used to improve the properties of the photographic material, which provide a colorless coupling product.

The non-diffusing color couplers and coloring compounds are added to the light-sensitive silver halide emulsions or other casting solutions by customary known methods. If the compounds are soluble in water or alkali, they can be added to the emulsions in the form of aqueous solutions, optionally with the addition of water-miscible organic solvents such as ethanol, acetone or dimethylformamide. If the non-diffusing color couplers and coloring compounds are water- or alkali-insoluble compounds, they can be emulsified in a known manner, for example by dissolving these compounds in a low-boiling organic solvent directly with the silver halide emulsion or initially with an aqueous gelatin solution is mixed, whereupon the organic solvent is removed in a conventional manner. A gelatin emulsate of the respective compound thus obtained is then mixed with the silver halide emulsion. If necessary, so-called coupler solvents or oil formers are additionally used to emulsify such hydrophobic compounds; these are generally higher-boiling organic compounds which include the compounds in the form of oily droplets which split off and emulsify in the silver halide emulsions and do not diffuse color couplers and development inhibitors. In this connection, reference is made, for example, to US Pat. Nos. 2,322,027, 2,533,514, 3,689,271, 3,764,336 and 3,765,897.

The emulsions prepared according to the invention can be applied to the customary layer supports, for example supports made from cellulose esters such as cellulose acetate or cellulose acetobutyrate, furthermore polyesters, in particular polyethylene terephthalate or polycarbonates, in particular based on bisphenylol propane. Also suitable are paper supports, which can optionally contain water-impermeable polyolefin layers, for example made of polyethylene or polypropylene, and supports made of glass or metal.

The emulsion B used in the examples below is a silver bromide emulsion which has an average grain size of 0.05 μm and contains 1.25 mol of silver halide per kg and 18 g of gelatin per kg.

example 1

The AgBrI emulsion A1 is produced using a double jet process and contains 1 mol of silver halide and 32 g of gelatin per kg. The average grain size is 0.4 µm, the iodide content is 25 mol%.

3000 g of emulsion B are mixed with 1500 g of emulsion A1 and digested in the presence of the substances listed in Table 1 at 65 ° C, pH 7.5 and an E _Ag value of -60 mV until the redissolution is complete ( after about 20 minutes). It is then coagulated, washed and finally redispersed with the addition of water and gelatin. Then an optimal ripening with gold and sulfur compounds is carried out. The average grain size is 0.7 µm, the iodide content 7 mol%.

Example 2

The AgBrI emulsion A2 is produced using a double jet process and contains 1 mol of silver halide and 32 g of gelatin per kg. The average grain size is 0.7 µm, the iodide content is 40 mol%.

In each case 9000 g of emulsion B are mixed with 1500 g of emulsion A2 and digested in the presence of the substances listed in Table 2 at 60 ° C., pH 7.5 and an E _Ag value of -60 mV until the redissolution is complete ( after about 20 minutes). The further processing corresponds to Example 1. The average grain size is 1.1 µm, the iodide content 4.7 mol%.

Example 3

The AgBrI emulsion A3 is produced using a double jet process and contains 1 mol of silver halide and 32 g of gelatin per kg. The average grain size is 0.5 µm, the iodide content is 70 mol%, with an iodide content of 30 mol% first being precipitated and then converted to the stated iodide content by adding KI.

5800 g of emulsion B are mixed with 1500 g of emulsion A3 and digested in the presence of the substances listed in Table 3 at 70 ° C., pH 7.5 and E _Ag -60 mV until the redissolution is complete after about 20 minutes, The further processing corresponds to example 1.

The average grain size is 1.1 µm, the iodide content is 12 mol%.

Example 4

Both the emulsions produced after 1.1 and after 1.3 are subjected to an optimal ripening of gold sulfur as well as an optimal ripening, in which, in addition to gold and sulfur compounds, selenium compounds are also present. Suitable selenium compounds for this are described for example in EP 428 041, 458 278, 476 345. emulsion maturation E S 1.1 S / Au 100 21 1.1a S / Se / Au 104 28 1.3 S / Au 165 18th 1.3a S / Se / Au 208 26

In example 1.3 according to the invention there is a significantly greater increase in sensitivity due to the addition of selenium than in example 1.1 not according to the invention.

Claims (10)

Process for the preparation of a silver halide emulsion with up to 20 mol% AgI by precipitation of a silver halide emulsion A with up to 100 mol% AgI and addition of a silver halide emulsion B with up to 40 mol% AgI and an average grain size of at most 0.25 µm, wherein emulsion B in aqueous gelatin solution always has greater solubility than emulsion A, either because of its grain size or because of its iodide content, in the presence of at least two compounds from the series imidazole, histidine (α-amino-β-imidazolyl- (5) -propionic acid ) and other monocyclic, 5- or 6-membered, heterocyclic compounds free of SH groups with at least one ring nitrogen atom, which form sparingly soluble silver salts in weakly acidic to neutral aqueous solution, which dissolve again with the addition of ammonia at pH> 9 , wherein one of the at least two compounds imidazole or histidine and at least one other compound not Imi is dazol or histidine. A method according to claim 1, characterized in that the iodide content of emulsion A is 10 to 90 mol%. A method according to claim 1, characterized in that the redissolution takes place at E _Ag -20 to -120 mV, pH 4 to 10 and 40 to 90 ° C. Process according to Claim 1, characterized in that the redissolution takes place at E _Ag -40 to -100 mV, pH 6 to 8 and 50 to 75 ° C. A method according to claim 1, characterized in that the gelatin / silver halide weight ratio, expressed as the amount of silver nitrate used, is 0.05 to 1 during the redissolution. A method according to claim 1, characterized in that the gelatin / silver halide weight ratio, expressed as the amount of silver nitrate used, is 0.1 to 0.5 during the redissolving. Process according to Claim 1, characterized in that the emulsions A and B, expressed as the amounts of silver nitrate used, are used in a weight ratio of 1: 1 to 1:20 for the redissolution. A method according to claim 1, characterized in that the emulsions A and B, expressed as the amounts of silver nitrate used, are used in a weight ratio of 1: 2 to 1:10 for the solution. Process according to Claim 1, characterized in that the monocyclic heterocyclic compounds which are different from imidazole and histidine and which are free of SH groups Compounds with at least one ring nitrogen atom, which form sparingly soluble silver salts in weakly acidic to neutral aqueous solution, which again dissolve in ammoniacal solution with the addition of ammonia at pH> 9, belong to the following classes: imidazoles, oxazoles, thiazoles, triazoles, thiadiazoles, oxadiazoles , Pyridines, tetrazoles and pyrimidines. Process according to Claim 1, characterized in that imidazole and / or histidine in an amount of 10⁻⁵ to 2.0 mol / mol of silver halide and the compounds other than imidazole and histidine in an amount of 10⁻⁶ to 0.5 mol / Mol of silver halide can be used.