EP0247474B1 - Heat-developable colour-photographic recording material - Google Patents

Description

The invention relates to a color photographic recording material that can be developed by heat treatment and consists of a layer support with a binder layer which contains at least one coloring compound and a silver halide emulsion as layer additives, the crystals of which have zones of different halide composition and which is hereinafter referred to as zone emulsion. By using the zone emulsion, the sensitivity is improved, the veil is pressed and the processing latitude in the development of heat is expanded.

Heat-developable photographic recording materials with silver halide emulsions as a light-sensitive additive have already been described. An overview of the use of silver halide emulsions in thermographic processes in hydrophilic and hydrophobic media can be found, for example, in Research Disclosure 17029 (June 1978). In addition to the formation of the latent image, the silver halide can itself contribute to the image structure as metallic silver or can also serve as an oxidizing agent for subsequent color reactions. As possible coloring compounds u. a. conventional color couplers or leuco dye bases that generate a dye image on oxidation are suitable.

Particularly suitable as a color-imparting compound are those which can be embedded in the layer of a photographic recording material in non-diffusing form and which, as a result of the development, can release a diffusible dye (color releaser). The particular suitability of such color releasers is based on the fact that the colorants released in the image can be transferred to special image-receiving layers with the formation of a brilliant color image which is not overlaid by disruptive image silver or silver halide and accordingly does not require any post-treatment. Combining the heat development process with the color diffusion process thus results in an advantageous rapid process for producing colored images. A recording material suitable for this is described, for example, in DE-A-3215485.

According to this publication, a recording material having a layer which contains a combination of silver halide, silver benzotriazolate, a color releaser and guanidine trichloroacetate (base donor) is exposed imagewise and then subjected to heat treatment in contact with an image-receiving sheet, the image-released dye being transferred to the image-receiving sheet . For the production of multicolored images, several such combinations must be present, the silver halide in each of these combinations being sensitive to a different spectral range of the light and, in accordance with its spectral sensitivity, containing a color releaser which releases a dye of a different color, usually a color that is complementary is the color of the light for which the silver halide in question has a predominant sensitivity. Such assignments can be arranged one above the other in different layers.

Silver halide emulsions which are used in thermographic color diffusion processes are listed in EP-A-0123913. Silver halide emulsions with an iodide content between 4 to 40 mol% are described, which are mixed crystals. According to the X-ray diffraction diagram, the emulsions have no zones with pure silver iodide. The rapid development kinetics and good sensitivity of the emulsions are emphasized.

However, the image veil, which in many cases is still too high, is not without problems. This becomes particularly clear with thermal stress, for example with extended process times, which lead to a significant increase in the haze values. As a result, the processing latitude for such a material is greatly restricted, which naturally poses a problem for the uniformity of the image results. The sensitivity of such recording materials also needs to be improved.

The aim of the present invention is to provide a photothermographic recording material which has a low level of fog. Another object of the invention is to provide a heat-developable photographic material that has high fog stability, making the material less susceptible to process fluctuations. Another goal is to develop a recording material with an improved Dmin / Dmax ratio. Finally, another object of the invention is to produce a recording material with an improved sensitivity.

These objects and advantages of the invention are achieved by photothermographic recording materials with silver halide emulsions, the grains of which have at least three zones of different halide composition (as explained below), it being possible for the transition between two adjacent zones to take place continuously or discontinuously. In the simplest case, the grains have a core, an outer shell and a third zone arranged between them. However, two, three or more zones can also be arranged between the core and the outer shell. Each zone differs from the one or the immediately adjacent zones by the special halide composition. A zone is to be understood as a coherent area which extends over at least 0.5 mol% of the total silver halide of each grain and in which the silver halide composition is largely constant. The silver halide composition may have a gradient at the interfaces between two adjacent zones sen. The limit in this case is defined by the fact that the silver halide composition at this point corresponds to the mean value of the silver halide compositions in the homogeneous regions of the two adjacent zones.

The individual zones can contain inclusions of a different composition, in particular those with a higher iodide content. Each individual zone can contain as halide, chloride, bromide or iodide as well as mixtures thereof. If there is a gradient with respect to the iodide content, in a preferred embodiment the iodide content in the core or in the vicinity of the core is higher than in a zone located further out. In a further preferred embodiment, the core consists essentially of silver bromide, the outermost zone of a silver bromide iodide emulsion with relatively little iodide, e.g. B. in the range between 0 and 10 mol%, and at least one intermediate zone consisting of a silver bromide iodide emulsion with a relatively high silver iodide content, in particular of at least 5 mol%. In a very particularly preferred embodiment, at least one zone located between the core and the outermost shell contains a silver bromide iodide emulsion with 7 to 40 mol% iodide.

In a further preferred embodiment, the silver halide grains are constructed such that at least three zones of different halide composition follow one another from the grain surface to the grain center and the local iodide content assumes a maximum at at least one point which is not on the surface and not in the center, where the difference between the iodide content of the zone with the highest iodide content and the iodide content of the zone further away from the grain center with the lowest iodide content is at least 6 mol%, preferably at least 8 mol% and in a very particularly preferred embodiment at least 9 mol% and the molar fraction (mole fraction) of the zones in which the iodide content assumes a maximum is between 10 and 60%, preferably between 15 to 50% and very particularly preferably between 20 and 40%.

If chloride bromide emulsions are predominantly used, a preferred embodiment consists in that at least one zone is present in the interior of the grain, the chloride content of which is higher than the chloride content of the adjacent zones. The global chloride content of these emulsions is preferably between 0.5 and 95 mol%, the maximum local chloride content between 20 and 100 mol%.

The average diameter of the sphere, the volume of which is equal to the volume of the silver halide grains of the silver halide emulsions to be used according to the invention, is preferably between 0.15 μm and 2.3 μm, in particular between 0.2 μm and 1.3 μm.

The silver halide grains can be in any habit, e.g. B. as a cube, octahedron, tetradecahedron, etc

In a preferred embodiment, it is predominantly compact crystals, the z. B. are cubic or octahedral or have transitional forms. They can be characterized by the fact that they essentially have a thickness of more than 0.15 pm. The average ratio of diameter to thickness is preferably less than 8: 1, the diameter of the grain being defined as the diameter of a circle whose circle content is equal to the projected area of the grain.

The edges and corners of the silver halide grains can be rounded. The silver halide grains can have one or more twin planes, have depressions on at least one of their surfaces or can be provided with warts. The grain size distribution of the silver halide grains can be monodisperse, oligodisperse or polydisperse.

The silver halide emulsions can be prepared using 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 17643 (December 1978), sections I and II.

Photographically active compounds, such as compounds of copper, thallium, lead, bismuth, cadmium, ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, sulfur, selenium and tellurium, can be present during the precipitation.

The emulsions are preferably chemically sensitized on the grain surface to a high surface sensitivity. However, it is also possible to additionally chemically sensitize at least one of the inner zones before grain growth is complete. The known methods can be used for chemical sensitization, 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 90 ° C can fluctuate; 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 aminoboranes.

The surface ripening nuclei can also be present as troglodyte nuclei (sub-surface nuclei) according to DE-A-2306447 and US-A-3966476. Other methods are described in Research Disclosure 17643, Section III.

The emulsions can be used during and / or after the precipitation as well as before, during and / or are oxidized after chemical ripening, e.g. B. with iron (III) compounds, mercury (II) compounds, N- (m-nitrobenzyl) quinoline chloride.

The emulsions can be spectrally 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 described by FM Hamer in _" The Cyanine Dyes and related Compounds" (1964). In this regard, reference is made in particular to UIImann's Encyclopedia of Industrial Chemistry, 4th edition, volume 18, pages 431 ff., And to Research Disclosure 17643, section IV. Spectral sensitization can take place at any time during the preparation of the emulsion, i.e. during or after the silver halide precipitation and before, during or after chemical sensitization.

The color photographic recording materials usually contain at least one silver halide emulsion layer unit for recording light from each of the three spectral ranges red, green and blue.

The emulsions described are outstandingly suitable for use in photothermographic recording materials. With high developmental kinetics, they are characterized by low minimum densities, high maximum densities and high sensitivity.

The amount of light-sensitive silver halide in the layer structure can be between 0.01 and 3.0 g per m ² in the respective layer, the actual amount of silver halide used depending on the requirements of the reactants used and the desired effects.

The emulsions according to the invention can be mixed with one another or with other types of emulsions. Organic silver salts can also be added, which can act as accelerators in the development of heat. Examples of useful compounds are silver salts of aliphatic and aromatic carboxylic acids. Silver salts of compounds containing a mercapto or thione group can also be used. In addition, the silver salts of compounds containing imino groups can be used. In preferred examples, these include silver salts of benzotriazole and its derivatives, such as, for example, alkyl, hydroxy, sulfo or halogen-substituted benzotriazoles. The organic silver salt compound that is added can be added in molar excess or deficit or equimolar to the silver halide compound. It must be adapted to the respective requirements in the layer structure.

worin

• Qden erforderlichen Rest zur Vervollständigung einer heterocyclischen Gruppe mit mindestens einem 5- oder 6gliedrigen heterocyclischen Ring, und
• X eine Carbonsäure- oder Sulfonsäuregruppe oder einen eine Carbonsäure- oder Sulfonsäuregruppe enthaltenden Rest bedeuten, wobei die Carbonsäure- bzw. Sulfonsäuregruppe auch in anionischer Form vorliegen kann, z. B. als Alkali-, Erdalkali- oder Ammoniumsalz, wie auch Salz von organischen Basen wie Tri- oder Tetraalkylammoniumsalz.

Antifoggants and stabilizers can be used for the silver halide emulsion according to the invention. Veil-lowering compounds which correspond to the following formula I are advantageous:

wherein

• Q the residue necessary to complete a heterocyclic group with at least one 5- or 6-membered heterocyclic ring, and
• X represents a carboxylic acid or sulfonic acid group or a radical containing a carboxylic acid or sulfonic acid group, wherein the carboxylic acid or sulfonic acid group can also be present in anionic form, e.g. B. as an alkali, alkaline earth or ammonium salt, as well as salt of organic bases such as tri- or tetraalkylammonium salt.

worin

• Y -0-, -S-, -Se- oder -NR^3-;
• R¹, R², gleich oder verschieden, Wasserstoff, Alkyl, bevorzugt mit bis zu 6 C-Atomen wie Methyl, Ethyl, Alkenyl wie Allyl, Cycloalkyl wie Cyclohexyl, Aryl wie Phenyl, Aralkyl wie Benzyl, Halogen wie CI oder Br, oder R¹ und R² zusammen einen ankondensierten Benzolring;
• R³ Wasserstoff, Alkyl, bevorzugt mit bis zu 6 C-Atomen wie Methyl, Ethyl, Alkenyl wie Allyl, Cycloalkyl wie Cyclohexyl, Aralkyl wie Benzyl, Aryl wie Phenyl, wobei die genannten Reste weiter substituiert sein können, z. B. durch Hydroxy, Alkoxy oder Halogen, bedeuten.

Particularly advantageous haze-lowering compounds are those of the general formula II

wherein

• Y -0-, -S-, -Se- or -NR ^3-;
• R ¹ , R ² , the same or different, hydrogen, alkyl, preferably with up to 6 carbon atoms such as methyl, ethyl, alkenyl such as allyl, cycloalkyl such as cyclohexyl, aryl such as phenyl, aralkyl such as benzyl, halogen such as CI or Br, or R ¹ and R ² together form a condensed benzene ring;
• R ^{3 is} hydrogen, alkyl, preferably having up to 6 carbon atoms such as methyl, ethyl, alkenyl such as allyl, cycloalkyl such as cyclohexyl, aralkyl such as benzyl, aryl such as phenyl, where the radicals mentioned can be further substituted, for. B. by hydroxy, alkoxy or halogen.

The heterocyclic mercaptoazolecarboxylic acids or sulfonic acids mentioned are known compounds and their preparation is described in the relevant literature.

Another essential component of the photothermographic recording material according to the invention is a non-diffusing coloring compound. As a result of a redox reaction taking place during development, this can release a diffusible dye. In the following, it is referred to as a paint splitter.

The color releasing agents used according to the invention can be a variety of connection types, all of which are distinguished by a link which is redox-dependent in terms of their binding strength and which links a dye residue to a carrier residue containing a ballast residue.

In this context, a summary of the subject area in Angew. Chem. Int. Ed. Engl. 22 (1983), 191-209, in which the most important of the known systems are described.

• BALLAST - REDOX - FARBSTOFF,

worin bedeuten

• BALLAST einen Ballastrest,
• REDOX eine redoxaktive Gruppe, d. h. eine Gruppe, die unter den Bedingungen der alkalischen Entwicklung oxidierbar oder reduzierbar ist und je nachdem, ob sie im oxidierten oder im reduzierten Zustand vorliegt, in unterschiedlichem Ausmass einer Eliminierungsreaktion, einer nukleophilen Verdrängungsreaktion, einer Hydrolyse oder einer sonstigen Spaltungsreaktion unterliegt mit der Folge, dass der Rest FARBSTOFF abgespalten wird, und
• FARBSTOFF den Rest eines diffusionsfähigen Farbstoffes, z. B. eines Gelb-, Purpur- oder Blaugrünfarbstoffes, oder den Rest eines Farbstoffvorläufers.

Redox-active color releasers of the formula have proven to be particularly advantageous

• BALLAST - REDOX - DYE,

in what mean

• BALLAST a ballast remnant,
• REDOX is a redox-active group, i.e. a group that can be oxidized or reduced under the conditions of alkaline development and, depending on whether it is in the oxidized or in the reduced state, to different degrees of an elimination reaction, a nucleophilic displacement reaction, a hydrolysis or another cleavage reaction is subject to the result that the rest of DYE is split off, and
• DYE the rest of a diffusible dye, e.g. B. a yellow, purple or cyan dye, or the rest of a dye precursor.

Such residues are to be regarded as ballast residues which make it possible to store the color releasers according to the invention in a diffusion-resistant manner in the hydrophilic colloids usually used in photographic materials. Organic radicals which generally contain straight-chain or branched aliphatic groups with generally 8 to 20 C atoms and optionally also carboncyclic or heterocyclic, optionally aromatic groups are preferably suitable for this purpose. With the rest of the molecule, these residues are either directly or indirectly, e.g. B. connected via one of the following groups: -NHCO-, -NHS0 ₂ -, -NR-, where R is hydrogen or alkyl, -0- or -S-. In addition, the ballast residue can also contain water-solubilizing groups, such as. B. sulfone groups or carboxy groups, which may also be in anionic form. Since the diffusion properties depend on the molecular size of the total compound used, it is sufficient in certain cases, e.g. B. if the total molecule used is large enough to use shorter-chain residues as ballast residues.

Redox-active carrier residues of the BALLAST-REDOX structure and corresponding color releasers are known in a wide variety of embodiments. A detailed description can be omitted here with regard to the review article in Angew. Chem. Int. Ed. Engl. 22 (1983), 191-209.

For the sake of explanation only, some examples of redox-active carrier residues are listed below, from which a dye residue is split off in accordance with an image-related oxidation or reduction:

The groups enclosed in brackets are functional groups of the dye residue and are separated together with this from the remaining part of the carrier residue. The functional group can be a substituent which can have a direct influence on the absorption and, if appropriate, complex formation properties of the released dye. On the other hand, the functional group can also be separated from the chromophore of the dye by an intermediate member or a connecting member. Finally, the functional group together with the intermediate member may also be of importance for the diffusion and pickling behavior of the released dye. Suitable intermediate members are, for example, alkylene or aryl groups.

In principle, the residues of dyes of all classes of dyes are suitable as dye residues insofar as they are sufficiently diffusible to diffuse from the light-sensitive layer of the light-sensitive material into an image-receiving layer. For this purpose, the dye residues can be provided with one or more alkali-solubilizing groups. Suitable alkali-solubilizing groups include carboxyl groups, sulfo groups, Sulfonamide groups and aromatic hydroxyl groups. Such alkali-solubilizing groups can already be pre-formed in the dye releasers used according to the invention or can only result from the cleavage of the dye residue from the carrier residue containing ballast groups. Of dyes that are particularly suitable for the process according to the invention, mention should be made of: azo dyes, azomethine dyes, anthraquinone dyes, phthalocyanine dyes, indigo dyes, triphenylmethane dyes, including dyes that are complexed or complexable with metal ions.

The residues of dye precursors are to be understood as the residues of those compounds which, in the course of photographic processing, in particular under the conditions of heat development, either by oxidation, by coupling, by complex formation or by exposure of an auxochromic group in a chromophoric system, for example by saponification, can be converted into dyes. Dye precursors in this sense can be leuco dyes, couplers or dyes that are converted into other dyes during processing. Unless a distinction between dye residues and the residues of dye precursors is essential, the latter should also be understood below as dye residues.

• US-A-3227550, US-A-3443939, US-A-3443940, DE-A-1930215, DE-A-2242762, DE-A-24 02 900, DE-A-2406664, DE-A-2505248, DE-A-25 43 902, DE-A-2613005, DE-A-2645656, DE-A-2809716, DE-A-2823159, BE-A-861 241, EP-A-0004399, EP-A-0004400, DE-A-30 08 588, DE-A-3014669, GB-A-8012242.

Suitable color releasing agents are described, for example, in:

• US-A-3227550, US-A-3443939, US-A-3443940, DE-A-1930215, DE-A-2242762, DE-A-24 02 900, DE-A-2406664, DE-A-2505248, DE-A-25 43 902, DE-A-2613005, DE-A-2645656, DE-A-2809716, DE-A-2823159, BE-A-861 241, EP-A-0004399, EP-A-0004400 , DE-A-30 08 588, DE-A-3014669, GB-A-8012242.

In some embodiments of the heat development method according to the invention, the color releasers can be present as oxidisable or couplable color releasers, in others as reducible color releasers. Depending on whether the dye is released from the oxidized or from the reduced form of the color releasing agent, negative or positive illumination is obtained from the original when conventional negative-working silver halide emulsions are used. You can therefore create positive or negative images by selecting suitable color releasing systems.

DE-A-2645656 is described, for example, in oxidizable color releasers which are particularly suitable for the heat-developable recording materials according to the invention.

If the paint releaser can be oxidized, then it is itself a reducing agent which is oxidized directly or indirectly with the help of electron transfer agents (ETA) through the imagewise exposed silver halide. This creates a pictorial differentiation with regard to the ability to release the diffusible dye. If, on the other hand, the color releaser is reducible, then it is expediently used in combination with a reducing agent present in a limited amount, a so-called electron donor compound or an electron donor precursor compound, which in this case is contained in the same binder layer in addition to the color releaser and the photosensitive silver halide. The use of electron transfer agents can also prove to be advantageous in the case of the use of reducible color releasers in combination with electron donor compounds.

worin bedeuten

• R Alkyl oder Aryl;
• R² Alkyl, Aryl oder eine Gruppierung, die zusammen mit R³ einen ankondensierten Ring vervollständigt;
• R³ Wasserstoff, Alkyl, Aryl, Hydroxyl, Halogen wie Chlor oder Brom, Amino, Alkylamino, Dialkylamino einschliesslich cyclischer Aminogruppen (wie Piperidino, Morpholino), Acylamino, Alkylthio, Alkoxy, Aroxy, Sulfo, oder eine Gruppierung, die zusammen mit R² einen ankondensierten Ring vervollständigt;
• R⁴ Alkyl;
• R⁵ Alkyl oder vorzugsweise Wasserstoff,

und wobei mindestens einer der Reste R¹ bis R⁴ einen Ballastrest enthält.For example, a recording material according to the invention which contains reducible color releasers of the following formula is suitable for producing positive color images of positive originals (original) when using negative working silver halide emulsions:

in what mean

• R is alkyl or aryl;
• R ^{2 is} alkyl, aryl or a group which together with R ^{3 completes} a fused ring;
• R ^{3 is} hydrogen, alkyl, aryl, hydroxyl, halogen such as chlorine or bromine, amino, alkylamino, dialkylamino including cyclic amino groups (such as piperidino, morpholino), acylamino, alkylthio, alkoxy, aroxy, sulfo, or a group together with R ² completed a condensed ring;
• R ⁴ alkyl;
• R ^{5 is} alkyl or preferably hydrogen,

and wherein at least one of the radicals R ¹ to R ⁴ contains a ballast radical.

The electron donor compound used in combination with a reducible dye releasing agent serves equally as a reducing agent for the silver halide and the color releasing agent. Due to the fact that the silver halide and the color releaser compete with each other to a certain extent in the oxidation of the electron donor compound, but the former is superior to the latter, the silver halide present becomes determinant for the image areas within which the color releaser due to the electron donor compound in accordance with a previous imaging exposure its reduced form is transferred.

The electron donor compound, which is present in a limited amount, is developed under the conditions of development, e.g. B. when the imagewise exposed color photographic recording material is heated, oxidized in accordance with the extent of the exposure and is consequently no longer available for a reaction with the color releaser. This creates a kind of pictorial distribution of unused electron donor compound.

Derivatives of hydroquinone, benzisoxazolone, p-aminophenol or ascorbic acid (e.g. ascorbyl palmitate) which have not or only little diffusing have been described as electron donor compounds (DE-A-2809716).

Further examples of electron donor compounds are described in DE-A-2947425, DE-A-3006268, DE-A-31 30842, DE-A-31 44037, DE-A-3217877 and EP-A-0124915 and Research Disclosure 24305 (July 1984 ) known. It has been shown that the electron donor compounds mentioned also meet the requirements placed on them under the conditions of heat development and are therefore also suitable as electron donor compounds in the context of the present invention. Particularly suitable are those electron donor compounds that are formed in the layer from corresponding electron donor precursor compounds only under the conditions of heat development, i. H. Electron donor compounds that are only in a masked form in the recording material before development, in which they are practically ineffective. Under the conditions of heat development, the electron donor compounds, which are initially ineffective, are then converted into their effective form, for example by hydrolytically cleaving off certain protective groups. In the present case, the electron donor precursor compounds mentioned are also understood as electron donor compounds.

In a further embodiment it is also possible to use color releasers which can be coupled and which can release a diffusible dye as a result of a coupling reaction. There are two options. In the first case, the dye is only formed by chromogenic coupling, whereby a diffusion-inhibiting ballast group is split off from the coupling position. In the other case, there are non-diffusing couplers which contain an already formed dye residue as an escape group in the coupling point, which is split off by coupling and thus becomes diffusible. Such systems are described, for example, in US-A-3227550. The dye releasers can also be polymeric couplers of the dye-releasing type, as are described, for example, in DE-A-3422455.

The above-mentioned essential constituents of the recording material according to the invention, namely the special silver halide emulsion and the color releaser, optionally in combination with an electron donor compound, are dispersed next to one another in a binder. These can be hydrophobic as well as hydrophilic binders, but the latter are preferred. Gelatin is preferably used as the binder for the light-sensitive layer. However, this can be replaced in whole or in part by other natural or synthetic binders. On natural binders such. B. alginic acid and its derivatives such as salts, esters or amides, cellulose derivatives such as carboxymethyl cellulose, alkyl cellulose such as hydroxyethyl cellulose, starch and its derivatives and caragenates are suitable. Synthetic binders include polyvinyl alcohol, partially saponified polyvinyl acetate and polyvinyl pyrrolidone.

Examples of hydrophobic binders are polymers made from polymerizable, ethylenically unsaturated monomers such as alkyl acrylates, alkyl methacrylates, styrene, vinyl chloride, vinyl acetate, acrylonitrile and acrylamides. Polyester, polyurethane compounds and waxes can also be used. Such polymers can be used in latex form, for example.

For the production of monochrome color images, the light-sensitive binder layer contains one or more color releasers associated with the light-sensitive silver halide, from which dyes of a specific color are released. The overall resulting color can be obtained by mixing several dyes. In this way it is also possible to produce black and white images by precisely coordinating the mixing of several color separators of different colors. To produce multicolor color images, the color photographic recording material of the present invention contains a plurality, that is to say three, of assignments of color releasers and silver halide which has been sensitized differently, in each case preferably the absorption range of the dye released from the color releaser with the range of the spectral sensitivity of the assigned silver halide essentially coincides. The different assignments of color releaser and assigned silver halide can be accommodated in different binder layers of the color photographic recording material, with separating layers of a water-permeable binder, eg. B. gelatin, which contain, for example, a scavenger for developer oxidation products, which essentially have the function of separating the different assignments from one another and in this way counteracting color distortion. In such a case, the color photographic recording material of the present invention contains, for example, a light-sensitive binder layer in which the silver halide contained therein is predominantly red-sensitive due to spectral sensitization and in which a cyan color releaser is contained, a further light-sensitive binder layer in which the silver halide contained therein by spectral sensitization is predominantly green-sensitive and in which a purple dye releasing agent is contained, and a third light-sensitive binder layer in which the silver halogen contained therein is mainly blue-sensitive due to its intrinsic sensitivity or spectral sensitization and which contains a yellow dye releaser.

In a further embodiment of the present invention, each of the cited combinations of photosensitive silver halide and color releaser is used in the form of a so-called complex coacervate.

A complex coacervate is understood to mean a dispersion form in which a mixture of the essential constituents is enclosed in a common covering made of a hardened binder. Such dispersions are also called packet emulsions. They are obtained through complex coacervation.

Methods for producing a packet emulsion in which a color-forming substance is incorporated by complex coacervation are described, for example, in US-A-3276869 and US-A-3396026. The use of packet emulsions in heat-developable recording materials is described for example in DE-A-3232674.

The use of packet emulsions allows, according to the invention, the combination of several emulsion components, finally the relevant color releasers, in a single binder layer without the spectral assignment being lost and thereby a color falsification occurring. This is possible because the extent of the exposure of a particular silver halide particle is almost exclusively decisive for the extent of the dye release from the dye releaser which is in the same coacervate particle (package) as the silver halide. The use of packet emulsions thus enables the accommodation of one blue-sensitive, one green-sensitive and one red-sensitive silver halide emulsion and each of spectrally assigned color separators in the same binder layer without fear of serious color falsification.

In addition to the constituents already mentioned, the color photographic recording material according to the invention may contain further constituents and auxiliaries which are beneficial, for example, for carrying out the heat treatment and the color transfer taking place here. These further constituents or auxiliary substances can be contained in a light-sensitive layer or in a non-sensitive layer.

Such auxiliaries are, for example, auxiliary developers. These auxiliary developers generally have developing properties for exposed silver halide; in the present case, they primarily have a beneficial effect on the reactions taking place between the exposed silver halide and the reducing agent, the reducing agent being able to be identical to the latter when using oxidizable color releasers or, in turn, reacting with the color releasing agent when using reducible color releasing agents . Since this reaction mainly consists of electron transfer, the auxiliary developers are also referred to as electron transfer agents (ETA).

Examples of suitable auxiliary developers include hydroquinone, pyrocatechol, pyrogallol, hydroxylamine, ascorbic acid, 1-phenyl-3-pyrazolidone and their derivatives, e.g. B. 4-methyl-1-phenyl-3-pyrazolidone, 4,4-dimethyl-1-phenyl-3-pyrazolidone, 4-hydroxymethyl-4-methyl-1-phenyl-3-pyrazolidone, 4-hydroxymethyl-4- methyl-1-tolyl-3-pyrazolidone and 4,4-dihydroxy-methyl-1-phenyl-3-pyrazolidone. In certain cases it is advantageous to use them in masked form with a protective group that can be split off under alkaline conditions. Since the auxiliary developers have a catalytic function, it is not necessary for them to be present in stoichiometric amounts. In general, it is sufficient if they are present in the layer in amounts of up to 1/2 mol per mol of color releaser. The incorporation into the layer can take place, for example, from solutions in water-soluble solvents or in the form of aqueous dispersions which have been obtained using oil formers.

Color developers are required for coupling color systems. Reference is made here to the customary phenylenediamine developers and also to aminophenols. For reasons of stability, it is advantageous to use the developer additives in masked form, the protective group then being split off under the process conditions.

Other auxiliaries are compounds that activate development. Bases or base precursors, i.e. compounds with a pka value of 8 and more, are suitable. Examples of suitable inorganic bases are hydroxides, tertiary phosphates, borates, carbonates of alkali or alkaline earth metals, or ammonium hydroxide. Suitable organic bases are, for example, aliphatic amines, heterocyclic amines, amidines, cyclic amidines, guanidines or cyclic guanidines.

Base precursors are compounds that are capable of releasing a base component when heated. Salts of the above-mentioned bases with heat-decomposable organic acids such as trichloroacetic acid, acetoacetic acid, cyanoacetic acid, sulfonylacetic acid or acetylenecarboxylic acids are suitable. Also advantageous are base precursors with covalent binding of the base, which release the base in the heat, for example via a fractionation reaction. In this connection, reference is made to hydroxamic acid carbamates in EP-A-0120402 or to aldoxime carbamates in EP-A-0118078.

Other auxiliaries are, for example, compounds which are able to release water under the action of heat. In particular, inorganic salts containing water of crystallization come into question, e.g. B. Na ₂ SO ₄ .10H ₂ O, NH ₄ Fe (SO ₄ ) ₂ .12H20.

The water released during heating favors the development and diffusion processes required for image formation.

Other auxiliaries are, for example, the so-called thermal solvents, which are generally understood to mean non-hydrolyzable organic compounds which are solid under normal conditions but melt when heated up to the temperature of the heat treatment and thereby provide a liquid medium in which the development processes can take place more quickly. Such thermal solvents can act as diffusion accelerators, for example. Preferred examples of the thermal solvents include polyglycols as described, for example, in US-A-3,347,675, e.g. B. polyethylene glycol with an average molecular weight of 1500 to 20,000, derivatives of polyethylene oxide, such as its oleic acid ester, beeswax, monostearin. For example, compounds with a high dielectric constant are suitable which have a -S0 ₂ or -CO group.

In this context, reference is also made to the thermal solvents listed in the patent EP-A-0119 615; Urea, pyridines, pyridine-N-oxides, carboxamides, imides, sulfonamides, polyhydric alcohols, oximes, pyrazoles and imidazoles are mentioned.

Other suitable auxiliaries are development accelerators. Mention should be made here, for example, of sulfonamides, which are described in EP-A-0160313 and DE-A-33 39 810.

Furthermore, certain pH-lowering agents can be added, which above all help to stabilize the minimum densities. Suitable compounds are acid precursor compounds as described, for example, in DE-A-3442018 and DE-A-3515176.

The development of the imagewise exposed color photographic recording material according to the invention comprises the partial steps of silver halide development, generation of an imagewise distribution of diffusible dyes and diffusion transfer of this imagewise distribution into the image receiving layer. It is initiated by subjecting the exposed recording material to a heat treatment in which the light-sensitive binder layer is heated to an elevated temperature, e.g. B. is brought in the range of 80 to 250 ° C. As a result, suitable conditions for the development processes, including dye diffusion, are created in the recording material without the addition of a liquid medium, e.g. B. in the form of a developer bath. During development, dyes which are diffusible in terms of image are released from the dye releasers and transferred to an image-receiving layer which is either an integral part of the color-photographic recording material according to the invention or is in contact with it at least during the development period. Image-wise silver development, dye release and color transfer take place synchronously in a one-step development process.

In addition, the color image formation with the color photographic recording material according to the invention can also take place in a two-step development process, silver halide development and dye release taking place in a first step, followed by the color image transfer from the photosensitive part to a picture receiving part brought into contact with it in a second step, e.g. . B. by heating to a temperature between 50 and 150 ° C, preferably to 70 to 90 ° C, in which case diffusion aids (solvents) can be applied externally before the lamination of the light-sensitive part and the image receiving part.

The image-receiving layer can accordingly be arranged on the same layer support as the light-sensitive element (single sheet material) or on a separate layer support (two-sheet material). It essentially consists of a binder which contains mordants for the determination of the diffusible dyes released from the non-diffusing paint releasers. Long-chain quaternary ammonium or phosphonium compounds, e.g. B. as described in US-A-3271 147 and US-A-3271 148.

Furthermore, certain metal salts and their hydroxides, which form poorly soluble compounds with the acid dyes, can also be used. Also to be mentioned here are polymeric mordants, such as those described in DE-A-2315 304, DE-A-26 31 521 or DE-A-2941 818. Preferred stains are also polyvinylimidazole stains which are partially quaternized, for example with benzyl, hydroxyethyl, alkyl, epoxypropyl, propyl, methyl and ethyl halides, the degree of quaternization being between 1 and 50%. The dye mordants are dispersed in the mordant layer in one of the usual hydrophilic binders, e.g. B. in gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, completely or partially hydrolyzed cellulose esters. Of course, some binders can also act as mordants, e.g. B. Polymers of nitrogen-containing, optionally quaternary bases, such as of N-methyl-4-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, as described for example in US-A-2484430. Further usable binders are, for example, guanylhydrazone derivatives of alkyl vinyl ketone polymers, as described, for example, in US Pat. No. 2,882,156, or guanylhydrazone derivatives of acylstyrene polymers, as described, for example, in DE-A-20 09 498. In general, however, the binders mentioned last become other binders , e.g. B. add gelatin.

If the image-receiving layer remains in layer contact with the light-sensitive element even after development is complete, there is generally an alkali-permeable pigment-containing light-reflecting binder layer between them, which serves to separate the optical separation negative and positive and serves as an aesthetically pleasing background for the transferred positive color image.

If the image-receiving layer is arranged between the layer support and the light-sensitive element and is separated from the latter by a pre-formed light-reflecting layer, either the layer support must be transparent so that the color transfer image produced can be viewed through it, or the light-sensitive element together with the light-reflecting layer of the image-receiving layer are removed to expose the latter. However, the image-receiving layer can also be present as the top layer in an integral color photographic recording material, in which case the exposure is expediently carried out through the transparent layer support.

In the case of integral layer units comprising a photosensitive element and an image receiving element, stripping layers can also be included, which enable the two layer elements to be separated.

The supports for the light-sensitive element and, if applicable, for the image-receiving element must remain dimensionally stable at the process temperature. Usual film documents or paper documents come into question. Polyester materials are preferably used.

Conventional hardening agents, as well as rapid and instant hardeners, which are customary for photographic materials, can be used as hardening agents for both the photosensitive element and for the image receiving element.

example 1 Preparation of the emulsions Emulsion E1 (comparison emulsion)

A silver bromide iodide emulsion containing 88.3 mol% bromide and 11.7 mol% iodide was prepared by the double-jet process. The emulsion crystals were octahedron in shape and the mean diameter of the same-volume sphere was 0.475 µm.

In 7 kg of an aqueous solution, which contained 230 g of gelatin, 0.8 g of potassium bromide and 45 g of 1-methylimidazole, 2000 ml of 0.5 molar AgNO ₃ - were added at pH 6.35 and at 63 ° C. with stirring using the double enema method. Solution and 2000 ml of 0.5 molar KBr solution added.

Then 300 ml of 2-molar AgNO ₃ solution and the amount of 2-molar KBr _0.87 I _0.13 solution required to keep the pAg constant were added to pAg 8.0. The inlet speed was regulated so that the pAg was kept constant at 8.0. The pAg was then increased to 10.2 by adding 2 molar KBr _0.87 I _0.13 solution at a running-in rate of 10 ml / min.

In this pAg 10.2, 4200 ml of 2-molar AgN0 ₃ solution and the amount of 2-molar KBr _0.87 I _0.13 solution required to keep the pAg constant were then added using the double _{inlet method} .

The emulsion was then flocculated, washed and redispersed with 620 g of gelatin and so much water that the total weight of the emulsion was 6.67 kg. With 25% NaCl solution, the pAg was set to 9.0. The gelatin: AgNO ₃ ratio was 0.5 and the amount of AgNO ₃ per kg of emulsion was 254.8 g.

The emulsion was chemically ripened per mol Ag with 100 pmol Na ₂ S ₂ O ₃ .5H20, 30 pmol HAuCI ₄ and 1776 µmol KSCN and spectrally sensitized for the green and blue areas.

Emulsion E2 (according to the invention)

A silver chloride bromide iodide emulsion composed of 7 zones and containing 4.0 mol% of chloride, 88.7 mol% of bromide and 7.3 mol% of iodide was prepared by the double-inlet process. The crystals were cube-shaped, the mean diameter of the same-volume sphere was 0.30 pm.

To 7 kg of an aqueous solution containing 230 g of gelatin, 0.8 g of potassium bromide and 14.5 g of 1-methylimidazole, 2000 ml of 0.5 molar were added at pH 6.35 and at 63 ° C. with stirring using the double enema method AgNO ₃ solution and 2000 ml of 0.5 molar KBr solution were added.

Then 300 ml of 2-molar AgNO ₃ solution and the amount of 2-molar KBr solution required to keep the pAg constant were added to pAg 8.0 using pAg; the inflow speed of the KBr solution was regulated in such a way that the pAg value was kept constant at 8.9. The pAg was then reduced to 6.3 by adding a 2 molar AgNO ₃ solution at an inlet rate of 10 ml / min. With this pAg 6.3, 200 ml of 2-molar AgN0 ₃ solution and the amount of 2-molar KCl _0.5 Br _0.5 solution required to keep the pAg constant were then added using the double-run-in process, and then 500 ml of 2-molar KCl _0.5 Br _0.5 solution were added to the same pAg. molar AgNO ₃ solution and the amount of 2 molar KBr solution required to keep the pAg constant. Thereafter, the pAg was raised again to 8.0 by a single run-in of 2 molar KBr solution at a rate of 10 ml / min and then 1800 ml of 2-molar AgN0 ₃ solution and that were used for the pAg 8.0 Keeping the pAg constant 2-molar KBR _{O. 8} l ₀ . ₂ solution added. The pAg was reduced again to 6.3 by simply running in a 2 molar AgNO ₃ solution at a rate of 10 ml / min. Thereafter, after the double enema process, 6.3 200 ml of 2-molar AgN0 ₃ solution and the amount of 2-molar KCl _{or 5} Br _0.5 solution required to keep the pAg constant were added to pAg 6.3 and then 1500 ml of 2-molar solution were added after the double-enema process AgN0 ₃ solution and the amount of KBr _0.997 l _0.003 required to keep pAg 6.3 constant

The emulsion was then flocculated, washed and redi with 620 g of gelatin and as much water indicated that the total weight of the emulsion was 6.67 kg. The pAg was adjusted to 9.0 with 25% NaCl solution.

The gelatin: AgNO ₃ ratio was 0.5 and the amount of AgNO ₃ per kg of emulsion was 254.8 g.

The emulsion was chemically ripened per mole Ag at 53 ° C with 39 pmol of Na ₂ S ₂ O 3 5H ₂ 0,14,7 μmcl HAuCl ₄ and 870 .mu.mol KSCN.

Emulsion E3 (according to the invention)

An aqueous silver nitrate and a potassium bromide solution are metered into a 2.1% gelatin solution at a temperature of 63 ° C. within 15 minutes by means of a pAg-controlled double inlet. A silver bromide seed precipitation results with a narrow grain size distribution and an average particle size of 0.24 µm. By further simultaneous dosing of KBr and silver nitrate solutions, the crystals of the seed precipitation are increased to 1 0.2 times the grain volume. During this precipitation phase, the pAg value is kept constant at pAg 5.2. The metering rate is increased according to the information in Table 2 below.

By further pAg-controlled double entry of a KCI and a silver nitrate solution, an AgCI shell is struck on the crystals present. The emulsion precipitation is then continued by double entry of KBr and AgNO ₃ solutions, an AgBr shell being applied to the previously precipitated AgCI layer. The mean particle diameter of the zone emulsion produced in this way is 0.73 μm, with 14% of the crystals lying outside a range of 0.73 μm ± 10%, ie the emulsion produced is homodisperse. The chloride content is 4.8 mol%, based on the total halide.

The emulsion is freed from the soluble salts by washing in the customary manner and finally adjusted to a pAg of 7.8. The emulsion is then ripened by adding sodium thiosulfate pentahydrate in an amount of 40 μmol / mol silver halide and 42.5 mg of a triazaindolizine at 48 ° C. for 90 minutes. The emulsion was sensitized to the blue spectral range.

Example 2

A photosensitive member of a photothermographic recording material for the diffusion transfer process was prepared by coating the layers described below on a transparent substrate made of polyethylene terephthalate. The quantities given relate in each case to 1 m ² .

Layer 1

A layer with a green-sensitized silver halide emulsion E1 from 0.5 g AgN0 ₃ , with 5 mg 2-mercapto-5-sulfo-benzimidazole, 0.3 g color releasing agent A

Paint splitter A

(emulgiert in 0,15 g Diethyllauramid), 0,05 g Kaliumbromid, 1 g Polyesterurethan (folgender Zusammensetzung:

• 84,1% Polyester, aus Adipinsäure, 1,6-Hexandiol und Neopentylglykol,
• 13,1% Hexamethylendiisocyanat, und
• 2,7% N-Aminoethyltaurin) und
• 1,5 g Gelatine.

(emulsified in 0.15 g diethyl lauramide), 0.05 g potassium bromide, 1 g polyester urethane (with the following composition:

• 84.1% polyester, from adipic acid, 1,6-hexanediol and neopentyl glycol,
• 13.1% hexamethylene diisocyanate, and
• 2.7% N-aminoethyl taurine) and
• 1.5 g gelatin.

Layer 2

A layer with 1.5 g guanidine trichloroacetate, 0.035 g 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone, 8 mg sodium sulfite, 0.5 g compound B

Compound B

(emulgiert in Trikresylphosphat), 0,03 g der Verbindung C

(emulsified in tricresyl phosphate), 0.03 g of compound C

Compound C

und 1,5 g Gelatine.

and 1.5 g gelatin.

Layer 3

A protective layer with 0.5 g gelatin. The hardening agent is also applied with this protective layer.

The photosensitive member thus produced is referred to as Sample 1 and serves as a comparative sample. A further sample (sample 2) was produced in a corresponding manner, with the difference that in layer 1, instead of emulsion E1, emulsion E2 was used with the same silver application.

• 1. Eine Beizschicht mit 2 g Polyurethanbeize aus 4,4'-Diphenytmethandiisocyanat und N-Ethyldiethanolamin, quaterniert mit Epichlorhydrin gemäss DE-A-2631 521, Beispiel 1 ; 0,035 g der Verbindung C und 2 g Gelatine.
• 2. Eine Schutzschicht aus 0,8 g Gelatine. Mit dieser Schutzschicht wurde gleichzeitig Härtunsgmittel aufgetragen.

An image receiving part for the photothermographic recording material was produced in that the following layers were applied in succession to a support made of paper coated with polyethylene. The quantities given relate in each case to 1 m ² .

• 1. A pickling layer with 2 g of polyurethane pickling made from 4,4'-diphenytmethane diisocyanate and N-ethyldiethanolamine, quaternized with epichlorohydrin according to DE-A-2631 521, Example 1; 0.035 g of compound C and 2 g of gelatin.
• 2. A protective layer of 0.8 g gelatin. Hardening agent was applied simultaneously with this protective layer.

processing

One sheet of the photosensitive element (samples 1 and 2) was exposed through a step wedge. The development took place in two steps; in the first, the photosensitive element was heated at 120 ° C for 60 s. This was done with the help of a heating plate, the sample being placed on the layer on the heating plate and covered with another plate. In the second step, the sample was brought into contact with the image-receiving element on the layer side, the image-receiving element having previously been soaked with water. The set formed in this way was treated for 2 minutes at 70 ° C. using the same procedure as in the first step. During this time, the color transfer from the photosensitive element into the image receiving element took place. The two layer elements were then separated from one another. A purple negative image of the exposure original was obtained on the image receiving element.

In further development variants, the time in the first process step at 120 ° C was gradually reduced to 50 s, 40 s and finally 30 s.

The development results of samples 1 and 2 depending on the duration of the heating are summarized in table 3.

Table 3 shows that the fog level of the emulsion according to the invention is significantly lower than that of the comparison emulsion over a wide processing spectrum. This makes the emulsion less sensitive to process fluctuations. On the other hand, the emulsion according to the invention also shows a higher activity compared to the comparison emulsion with short process times. This is expressed in an increased sensitivity and in an increased maximum density.

Example 3

Example 2 was repeated, with the difference that the addition of 2-mercapto-5-sulfobenzimidazole was omitted in layer 1. Samples 3 and 4 were obtained, sample 3 containing the comparison emulsion E1 and sample 4 the emulsion E2 according to the invention. Processing was carried out as described in Example 2, the time in the first process step being set at 120 ° C at 30 s. The development results are summarized in Table 4. The improvement in the emulsion according to the invention in sample 4 compared to the comparison emulsion in sample 3 was particularly evident in a significantly lower level of fog.

Example 4

Example 2 was repeated, but with the difference that the layer 1 was additionally added with a dispersion of silver benzotriazolate from 0.25 g of AgNO ₃ for otherwise constant layer applications. Sample 5 contained the comparison emulsion E1, sample 6 the emulsion E2 according to the invention. With the same processing as in Example 2, the process time in the first step being 60 s, the following results were obtained, which are summarized in Table 5.

This example shows that even in the presence of development-promoting additives such as Silberbenzotriazolat the emulsion according to the invention has a high fog stability.

Example 5

Example 2 was repeated, with the difference that the color releasing agent D was added to the layer 1 instead of the coloring compound A. Sample 7 contained the comparison emulsion E1, sample 8 the emulsion E2 according to the invention.

Paint splitter D

Processing was carried out as described in Example 2, the development times in the first process step at 120 ° C. being 40 s, 30 s and 20 s. The development results are summarized in Table 6.

As can be seen from Table 6, the emulsion E2 according to the invention shows a significantly better fog behavior compared to the comparative emulsion E1 or, at comparable fog values, a significantly improved sensitivity.

Example 6

A photothermographic recording material was built up from the following layers:

Layer 1

A layer with a green-sensitized silver halide emulsion E1 from 1 g AgN0 ₃ , stabilized with 0.010 g 2-mercapto-5-sulfo-benzimidazole, with silver benzotriazolate from 0.5 g AgN0 ₃ , 0.29 g color releaser E. 0.05 g potassium bromide , 1 g polyester urethane from Example 2 and 1.5 g gelatin.

Paint splitter E

Layer 2

A layer with 1.5 g guanidine trichloroacetate, 0.24 g 4-methyl-4-hydroxymethyl-1-phenylpyrazolidone, 0.06 g sodium sulfite, 0.03 g compound C.

Layer 3

A protective layer like layer 3 from example 2.

This layer structure with the comparative emulsion E1 was designated sample 9; a corresponding layer structure with the emulsion E2 according to the invention was designated sample 10.

The processing was carried out as described in Example 2 at 60 s at 120 ° C. Since this is a positive-working color system, a lower emulsion haze is expressed in a higher color density. Sample 9 with the comparison emulsion E1 had a density of D = 1.52, sample 10 with the emulsion E2 according to the invention had a density of D = 1.62.

Example 7

A photothermographic recording material is produced with the following layers:

Layer 1

A blue-sensitized emulsion layer with the comparison emulsion E1 from 0.5 g AgN0 ₃ , with 0.005 g 2-mercapto-5-sulfo-benzimidazole, 0.26 g color releaser F, emulsified in 0.13 g diethyl lauramide, 0.02 g potassium bromide, 1 g polyester urethane from Example 2 and 1 g gelatin.

Paint splitter F

Layer 2

A layer with 1.5 g guanidine trichloroacetate, 0.035 g 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone, 0.008 g sodium sulfite, 0.3 g compound B, 0.03 g compound C and 1.8 g gelatin.

Layer 3

A protective layer with 0.5 g of gelatin with this layer was simultaneously applied to the hardening agent.

The photosensitive member thus produced was named Sample 11 and served as a comparative sample. A further sample 12 was produced in the same way, but with the difference that instead of the comparison emulsion E1, the emulsion E3 according to the invention was used in layer 1.

Processing was carried out as described in Example 2, the process time being varied from 40 s to 20 s in the first process step at 120 ° C. The development results are summarized in Table 7.

This example shows the high fog stability of the emulsion according to the invention under thermal stress, which leads to a strong increase in fog value in the comparison emulsion. At a comparable Dmin / Dmax level, the emulsion according to the invention is also distinguished by an improved sensitivity.

Claims (13)

1. A colour photographic recording material developable by heat treatment, containing at least one light sensitive silver halide emulsion layer, characterised in that the silver halide grains of the silver halide emulsion layer have at least three zones differing in their silver halide composition.

2. Recording material according to claim 1, characterised in that the silver halide emulsion used consists mainly of silver bromide and silver iodide.

3. Recording material according to claim 2. characterised in that the iodide content in the core or in the surroundings of the core of the silver halide grains is greater than that in a more outwardly lying zone.

4. Recording material according to claim 2, charaterised in that the iodide content of an intermediate zone situated between the core and the outermost sheath is higher than in the core and in the outermost sheath.

5. Recording material according to claim 4, characterised in that the iodide content in the intermediate zone is at least 5 mol% and in the outermost sheath 0-10 mol%.

6. Recording material according to claim 1, characterised in that the silver halide emulsion used consists mainly of silver chloride and silver bromide.

7. Recording material according to claim 6, characterised in that the total chloride content of the silver halide emulsion is from 0.5 to 95 mol% and the chloride content in at least one layer is from 20 to 100 mol%.

8. Recording material according to claims 1 to 7, characterised in that the light sensitive silver halide emulsion layer in addition contains a silver salt of an organic imino compound.

9. Recording material according to claim 8, characterised in that the organic imino compound is benzotriazole or a benzotriazole derivative.

10. Recording material according to one of the claims 1 to 9, characterised in that it contains a non-diffusible colour producing compound which is capable of releasing a diffusible dye as the result of development by heat treatment.

11. Recording material according to claim 10, characterised in that it contains, as colour producing compound, an oxidisable colour producing compound which is capable of releasing a diffusible dye as the result of an oxidation.

12. Recording material according to claim 10, characterised in that it contains, as colour producing compound, a reducible colour producing compound capable of releasing a diffusible dye as the result of a reduction, in combination with an electron donor compound.

13. Recording material according to one of the claims 1 to 12, characterised in that it contains three combinations, each comprising a light sensitive silver halide and a non-diffusible, colour producing compound which is capable of releasing a diffusible dye, the silver halide having a different spectral sensitivity in each of the three combinations and the colour producing compound associated with a given silver halide giving rise to a dye whose region of absorption substantially corresponds to the region of spectral sensitivity of the associated silver halide.