EP0154920B1 - Emulsion with a high silver chloride content, photographic registration material and process for obtaining a photograhic registration - Google Patents

Description

The invention relates to an emulsion rich in silver chloride, a photographic recording material and a method for producing photographic recordings.

Numerous types of silver halide emulsions are known which contain chloride, bromide, iodide or mixtures thereof as the halide. Silver bromide and silver bromide iodide emulsions are generally used for more sensitive recording materials. A disadvantage of the last-mentioned emulsions is that they have an intrinsic sensitivity in the blue spectral range. Therefore, in color recording materials, green and red sensitive layers are generally placed behind a filter that absorbs blue light. Furthermore, such emulsions cannot be developed as quickly as silver chloride emulsions.

Proposals for the use of silver chloride emulsions are known from various publications. Since silver chloride has almost no inherent sensitivity in the visible spectrum, when using chloride-rich silver halide emulsions in a color photographic recording material Cjuf filter layers for absorbing the blue light (yellow filter) can be dispensed with. A disadvantage of silver chloride emulsions is their low sensitivity. According to EP-A-0 017 148, an improvement in sensitivity is to be achieved by metal doping. Chloride-rich silver halide emulsions also have poor storage stability and therefore tend to obscure. According to EP-A-0 072 695, the use of silver halide solvents is said to reduce the fog during chemical ripening.

Chloride-containing silver halide emulsions are also known, the grains of which have a layered structure. Such grains have a core and at least one layer which surrounds the core and whose properties differ from the core. From DE-AS-1 169 290 and GB-1 027 146 it is known to coat a silver chloride shell on a silver bromide core. DE-OS-2 308 239 and US-3,935,014 relate to emulsions for producing directly positive images with silver halide grains which have a localized phase with a high silver chloride content.

From EP-A-0 080 905 silver halide emulsions with silver chloride-rich grains are known, which have a layer consisting essentially of silver bromide on their surface.

However, the known chloride-rich silver halide emulsions are still in need of improvement, particularly with regard to their sensitivity and tendency to fog.

It was therefore an object of the present invention to provide chloride-rich silver halide emulsions which have improved sensitometric properties. In particular, it was a task to increase the sensitivity and reduce the tendency to fog, but without impairing the development kinetics.

A photographic silver halide emulsion was found which essentially contains chloride as the halide and whose grains have a layered grain structure composed of at least two areas of different halide composition - e.g. B. a core and at least one shell - have.

• 1. mindestens 60 Mol.-% des Halogenids Chlorid ist und
• 2. mindestens ein Bereich B wenigstens 10 Mol.-% Silberbromid, vorzugsweise wenigstens 25 Mol.-% Silberbromid, aber weniger als 50 Mol.-% Silberbromid enthält.

The silver halide grains are characterized in that

• 1. at least 60 mol% of the halide is chloride and
• 2. at least one region B contains at least 10 mol% of silver bromide, preferably at least 25 mol% of silver bromide, but less than 50 mol% of silver bromide.

The area B can be present both as a core and as a shell around a core. In addition to AgBr, the region B contains AgCI and optionally Agl, preferably up to a maximum of 10%. The grains preferably contain a core enveloped by at least one region B. In this case, region B can be present as a shell within the silver halide grain or on the surface of the crystal.

In a special embodiment of the present invention, the crystal nucleus is successively provided with two shells containing silver bromide, the bromide content of the two shells being significantly different.

A bromide-containing shell with a local concentration of 30 to 45 mol.-0 / o bromide is preferably located on the crystal surface of the chloride-rich silver halide crystal.

In a further embodiment, the bromide concentration is 3 to 8 mol%, based on the total halide.

In principle, the silver halide grains can have chloride, bromide, iodide or mixtures thereof in the core and in the areas other than halide. The transition from one area to an adjacent area of a different composition can be sharp or continuous.

In a preferred embodiment, the chloride content of the total halide content is at least 85, in particular at least 90, mol%.

The silver halide emulsions according to the invention can be prepared by means of the customary procedures (eg single entry, double entry, with constant or accelerated material flow). It is particularly preferred to use the double-inlet process under control of the pAg value. Reference is made to Research Disclosure No. 17643 of December 1978, Sections I and 11, published by Industrial Opportunities Ldt., Homewell Havant, Hampshire, P09 1 EF in the UK. The precipitation can be carried out in the presence of conventional dopants, e.g. B. in the presence of Ir compounds.

The silver halide grains can be designed, for example, as cubes, octahedra or tetradecahedra. The grain size is preferably between 0.1 and 2.5 J.1m, in particular between 0.2 and 1.0 µm.

In one embodiment of the invention, the emulsion has a narrow grain size distribution. In particular, at least 95% by weight of the grains have a diameter which does not deviate from the average grain diameter by more than 40%. However, the emulsions can also have a broad grain size distribution. Here, at least 10%, preferably 20%, of the silver halide grains have a diameter which deviates from the average grain diameter by at least 40%.

The present invention further relates to a photographic recording material which contains at least one silver halide emulsion layer according to the invention on a support. The invention further relates to a method for producing photographic recordings by developing an exposed recording material according to the invention.

The emulsions according to the invention are preferably chemically sensitized to a high surface sensitivity on the grain surface. They can be chemically sensitized using known methods, e.g. B. with active gelatin or with compounds of sulfur, selenium, tellurium, gold, palladium, platinum, iridium, the pAg values between 4 and 10, the pH values between 3.5 and 9 and the temperatures between 30 ° C. and can fluctuate 90 ° C; chemical sensitization can be carried out in the presence of heterocyclic nitrogen compounds such as imidazoles, azaindenes, azapyridazines and azapyrimidines and thiocyanate derivatives, thioethers and other silver halide solvents. Alternatively or additionally, the emulsions according to the invention can be subjected to a reduction sensitization, e.g. B. by hydrogen, by low pAg (z. B. less than 5) and / or high pH (z. B. above 8), by reducing agents such as tin (II) chloride, thiourea dioxide and aminoborane. The surface ripening nuclei can also be present as troglodyte nuclei (sub-surface nuclei) according to DE-OS-2 306 447 and US Pat. No. 3,966,476. If necessary, the grains can also be matured inside. Other methods are described in the above. Research Disclosure No. 17643 in Section 111.

The emulsions can be optically sensitized in a manner known per se, e.g. B. with the usual polymethine dyes such as neutrocyanines, basic or acid carbocyanines, rhodacyanines, hemicyanines, styryl dyes, oxonols and the like. Such sensitizers are from F.M. Hamer in "The Cyanine Dyes and related Compounds", (1964). In this regard, reference is made to EP-A-0 082 649 and in particular to Ullmann's Encyclopedia of Industrial Chemistry, 4th edition, volume 18, pages 431 ff and to Research Disclosure No. 17643, section IV indicated above. The spectral sensitization can be too at any time during the preparation of the emulsion, d. H. during or after silver halide precipitation and before, during or after chemical sensitization.

The commonly used antifoggants and stabilizers can be used.

Particularly suitable stabilizers are azaindenes, preferably tetra- or penta-azaindenes, in particular those which are substituted by hydroxyl or amino groups. Such connections are e.g. B. in the article by Birr, Z.Wiss.Phot. 47, 1952), pp. 2-58. Other suitable stabilizers and antifoggants are given in Research Disclosure No. 17643 above in Section IV.

The recording material according to the invention is preferably a color photographic recording material. In a preferred embodiment, the color image is generated using color couplers. It is possible to let the color coupler diffuse into the recording material only during development.

In a preferred embodiment, however, the photographic material itself contains the usual color couplers, which can react with the oxidation product of developers, generally p-phenylenediamines, to form dyes. 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 a-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 type usually being used. The blue-sensitive layer can contain, for example, a non-diffusing color coupler for generating the yellow partial color image, usually a color coupler with an open-chain ketomethylene grouping. In the color couplers it can be, for. B. are 6-, 4- and 2-equivalent couplers, including the so-called white couplers, which do not give any dye when reacted with color developer oxidation products. Suitable couplers are known, for example, from the publications "Color Coupler" by W. Pelz in "Messages from the Research Laboratories of Agfa, Leverkusen / Munich", Volume 111, page 111 (1961), K. Venkataraman in "The Chemistry of Synthetic Dyes", Vol. 4, 341 to 387, Academic Press (1971) and TH James, "The Theory of the Photographic Process", 4th Ed., Pp. 353-362, and from Research Disclosure No. 17643, Section VII.

The recording material can also contain DIR compounds. DIR compounds are understood to mean those compounds which, when reacted with color developer oxidation products, release diffusing organic compounds which inhibit the development of silver halide. The inhibitors can be eliminated directly or via non-inhibiting intermediates. Reference is made to GB-953 454, US-3 632 345, US-4 248 962 and GB-2 072 363.

The color couplers and DIR compounds can be incorporated into the materials according to the invention by customary, known methods. If the compounds are soluble in water or alkali, they can be added in the form of aqueous solutions, optionally with the addition of water-miscible organic solvents such as ethanol, acetone or dimethylformamide. Insofar as the color couplers and DIR connectors are insoluble in water or alkali, they can be prepared in a manner known per se dispersed form can be incorporated into the recording materials. For example, a solution of these compounds in a low-boiling organic solvent can be mixed directly with the silver halide emulsion or initially with an aqueous gelatin solution and the organic solvent can then be removed. The dispersion of the respective compound thus obtained can then be mixed with the silver halide emulsion. If necessary, so-called oil formers are also used, usually higher-boiling organic compounds, which include the color couplers and DIR compounds to be dispersed in the form of oily droplets. 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 recording materials according to the invention preferably contain at least one silver halide emulsion layer unit for recording blue, green and red light.

The red-sensitive silver halide emulsion layer unit can be arranged closer to the layer support than the green-sensitive silver halide emulsion layer unit and this in turn can be arranged closer than the blue-sensitive one. In the case of copying materials in particular, however, the position of the blue and red sensitive layers can also be interchanged. The recording material may optionally contain a yellow filter layer; However, this can be dispensed with in particular if at least the red- and green-sensitive layers contain an emulsion according to the invention.

In a preferred embodiment, at least one of the units for recording green, red and blue light consists of at least two sub-layers. It is possible to combine sub-layers of different spectral sensitization according to their sensitivity.

The usual substrates can be used for the materials according to the invention, e.g. B. carriers made of cellulose esters, for. B. cellulose acetate and polyester. Also suitable are paper supports, which can optionally be coated, for. B. with polyolefins, especially with polyethylene or polypropylene. In this regard, reference is made to Research Disclosure No. 17643, Section XVII.

The usual hydrophilic film-forming agents are suitable as protective colloid or binder for the layers of the recording material, e.g. B. proteins, especially gelatin, alginic acid or their derivatives such as esters, amides or salts, cellulose derivatives such as carboxymethyl cellulose and cellulose sulfates, starch or their derivatives or hydrophilic synthetic binders such as polyvinyl alcohol, partially saponified polyvinyl acetate, polyvinyl pyrrolidone and others. In a mixture with the hydrophilic binders, the layers can also contain other synthetic binders in dissolved or dispersed form, such as homopolymers or copolymers of acrylic or methacrylic acid or their derivatives, such as esters, amides or nitriles, and also vinyl polymers, such as vinyl esters or vinyl ethers. Reference is also made to the binders specified in Research Disclosure 17643 above in Section IX.

The layers of the photographic material can be hardened in the usual manner, for example with hardeners of the epoxy type, the heterocyclic ethylene imine and the acryloyl type. Furthermore, it is also possible to harden the layers in accordance with the process of German laid-open specification 2 218 009 in order to obtain color photographic materials which are suitable for high-temperature processing. It is also possible to harden the photographic layers or the color photographic multilayer materials with hardeners of the diazine, triazine or 1,2-dihydroquinoline series or with hardeners of the vinyl sulfone type. Further suitable hardening agents are known from German laid-open documents 2 439 551, 2 225 230, 2 317 672 and from Research Disclosure 17643, section XI given above.

The photographic materials according to the invention may also contain other substances, in particular plasticizers, wetting agents, screen dyes, light scattering agents, light reflecting agents, lubricants, antistatic agents, matting agents, etc. Reference is made to Research Disclosure 17643 and "Product Licensing Index" from December 1971, pages 107 -110.

Suitable color developer substances for the material according to the invention are in particular those of the p-phenylenediamine type, e.g. B. 4-amino-N, N-diethyl-aniline hydrochloride; 4-amino-3-methyl-N-ethyl-N-β- (methanesulfonamido) ethylaniline sulfate hydrate; 4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulfate; 4-amino-N-ethyl-N- (2-methoxyethyl) -m-toluidine-di-p-toluenesulfonic acid and N-ethyl-N-ß-hydroxyethyl-p-phenylenediamine. Further useful color developers are described, for example, in J.Amer.Chem.Soc. 73, 3100 (1951) and in G. Haist, Modern Photographic Processing, 1979, John Wiley and Sons, New York, pages 545 ff. The color developers may contain the usual other ingredients, e.g. B. lime and antioxidants and anti-fogging agents such. B. bromide or stabilizers known per se.

After color development, the material is usually bleached and fixed. Bleaching and fixing can be carried out separately or together. The usual compounds can be used as bleaching agents, e.g. B. Fe ³ + salts and Fe ^{3 + -} complex salts such as ferricyanides, dichromates, water-soluble cobalt complexes, etc. Particularly preferred are iron III complexes of aminopolycarboxylic acids, especially z. B. ethylenediaminetetraacetic acid, nitrilotriacetic acid, iminodiacetic acid, N-hydroxyethylethylenediaminetriacetic acid, alkyliminodicarboxylic acids and corresponding phosphonic acids. Persulphates are also suitable as bleaching agents.

Emulsion A according to the invention

A silver chloride emulsion is produced within 25 minutes by pAg-controlled double entry of a 0.3 N NaCl and a 0.3 N AgNO ₃ solution to a 2.5% gelatin solution brought to a temperature of 55 ° C. The average particle size is 0.15 µm and the emulsion has a monodisperse distribution. The crystals of this starting emulsion are enlarged to 36 times the volume by further addition of 2 n NaCl and 2 n AgNO ₃ solutions. The pAg value is kept constant at 6.8.

An AgBr / AgCI shell is struck on the AgCI grains thus produced by simultaneous introduction of KBr / NaC1 and AgNOg solutions, the KBr / NaCI solution containing 40 mol% bromide.

The crystals of the emulsion produced in this way have a monodisperse particle size distribution and an average particle diameter of 0.53 μm; the volume fraction of the Br / CI shell is 10% based on the total volume of the silver halide crystals. The AgBr content is 4 mol%, based on the total halide.

Comparative Emulsion B

For comparison purposes, a silver halide emulsion such as emulsion A is prepared by pAg-controlled double enema. The KBr / NaCI solution is replaced by a pure KBr solution of identical concentration. An AgBr shell is applied to the silver chloride crystals by controlled double entry in such a way that the bromide concentration is 5 mol%, based on the total halide. The average particle diameter of the emulsion produced in this way is 0.55 μm and the crystals have a monodisperse particle size distribution.

Emulsions A and B are freed from the soluble salts by flocculation and washing in the usual way and then adjusted to a pAg of 7.6. All emulsions are then chemically sensitized by adding sodium thiosulfate at 55 ° C for 120 minutes. For the sensitometric test, the ripened emulsions are mixed with a sensi dye that absorbs in the green spectral range and a usual magenta coupler emulsate and applied to a layer support, the silver application being kept constant for all layers.

After exposure behind a step wedge and processing in the color development process known from British Journal of Photography, [1974] p. 597, the sensitometric data given in Table 1 are obtained.

Table 1 shows the significantly higher sensitivity and a steeper gradation with an otherwise identical sensitometry.

For a further test after ripening, both emulsions are mixed with a sensi dye that absorbs in the blue spectral range and a conventional yellow coupler emulsate and applied to a layer carrier with a silver coating corresponding to 3.2 g AgN0 ₃ per m ² .

After exposure behind a step wedge and processing (as indicated above), the sensitometric data given in Table 2 below are obtained.

It can be seen from Table 2 that the emulsion according to the invention is superior to the comparative emulsion in all sensitometric data.

Claims (12)

1. A photographic silver halide emulsion which substantially contains chloride as halide and the grains of which have a layered grain structure, characterised in that

1. at least 60 mol.-% of the silver halide of the emulsion is silver chloride, and

2. at least one region B contains at least 10 mol.-% AgBr, but less than 50 mol.-% AgBr.

2. A photographic silver halide emulsion according to claim 1, characterised in that the grains have a core encased by at least one region B.

3. A photographic silver halide emulsion according to claim 1, characterised in that at least 85 mol.-% of the total quantity of halide is in the form of silver chloride.

4. A photographic silver halide emulsion according to claim 2, characterised in that region B contains at least 25 mol.-% silver bromide.

5. A photographic silver halide emulsion according to claim 1, characterised in that the average grain size is from 0.1 to 2.5 µm.

6. A photographic silver halide emulsion according to claim 1, characterised in that it has a narrow grain size distribution.

7. A photographic silver halide emulsion according to claim 1, characterised in that the emulsion has a wide grain size distribution.

8. A photographic silver halide emulsion according to claim 1, characterised in that the grains on the surface are chemically and/or spectrally sensitized.

9. A photographic recording material having a substrate and at least one silver halide emulsion layer applied thereto, characterised in that the material contains at least one emulsion according to claim 1.

10. A process for the production of photographic recordings by developing an exposed recording material, characterised in that a recording material according to claim 9 is used.