Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/485—Direct positive emulsions
  • G03C1/48538—Direct positive emulsions non-prefogged, i.e. fogged after imagewise exposure
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/005—Silver halide emulsions; Preparation thereof; Physical treatment thereof; Incorporation of additives therein
  • G03C1/485—Direct positive emulsions
  • G03C1/48538—Direct positive emulsions non-prefogged, i.e. fogged after imagewise exposure
  • G03C1/48569—Direct positive emulsions non-prefogged, i.e. fogged after imagewise exposure characterised by the emulsion type/grain forms, e.g. tabular grain emulsions
  • G03C1/48576—Direct positive emulsions non-prefogged, i.e. fogged after imagewise exposure characterised by the emulsion type/grain forms, e.g. tabular grain emulsions core-shell grain emulsions
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/76—Photosensitive materials characterised by the base or auxiliary layers
  • G03C1/7614—Cover layers; Backing layers; Base or auxiliary layers characterised by means for lubricating, for rendering anti-abrasive or for preventing adhesion
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C2200/00—Details
  • G03C2200/40—Mercapto compound

Definitions

• the present invention relates to direct positive black-and-white photographic materials. More particularly it relates to direct positive materials containing stabilizers of a particular type.
• Photographic black-and white materials producing a density upon development which is directly related to the radiation received on exposure are termed negative working. From such a negative image a positive image resembling the original recorded scene can be produced by copying it on another negative working material.
• Direct positive images are understood in photography to be formed without intervention of a negative image by development of photographic emulsion layers containing specially designed so-called direct positive emulsions.
• the application of two main types of emulsions can be distinguished, the first one being externally fogged emulsions, usually containing an electron acceptor, the second one being unfogged internal latent image-forming emulsions, which are positive-working by fogging development, preferably in the presence of a so-called nucleating agent.
• stabilizers or anti-foggants are well known ingredients which can be incorporated in photographic materials and/or in photographic developing solutions. Their principal function consists in minimizing the obtained fog level on developing exposed photographic materials and/or to reduce the rise of development fog after prolonged storage of the photographic material compared to the fog level of a freshly coated material.
• Numerous chemical classes of stabilizers are disclosed in photographic scientific and patent literature. Suitable examples are e.g.
• heterocyclic nitrogen-containing compounds such as benzothiazolium salts, imidazoles, nitroimidazoles, benzimidazoles, nitrobenzimidazoles, chlorobenzimidazoles, bromobenzimidazoles, indazoles, nitroindazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, aminotriazoles, benzotriazoles (preferably 5-methyl-benzotriazole), nitrobenzotriazoles, mercaptotetrazoles, in particular 1-phenyl-5-mercapto-tetrazole, mercaptopyrimidines, mercaptotriazines, benzothiazoline-2-thione, oxazoline-thione, triazaindenes, tetrazaindenes and pentazaindenes, especially those described by Birr in Z.
• benzothiazolium salts imidazo
• direct positive silver halide emulsions exhibit various disadvantages as compared to negative working emulsions.
• the high level of sensitivity which can be routinely attained with negative emulsions cannot easily be reached with direct positive emulsions. It is not easy to reconciliate the various demands of high maximum density, good contrast, low minimum density and sufficient speed.
• More particularly direct positive emulsions of the internal sensitivity type can suffer from a second disadvantage known as rereversal on overexposure.
• Several patent publications disclose particularly useful classes of antifoggants or stabilizers in connection with direct positive materials in order to counteract their specific disadvantages.
• So JP-A 62229134 describes benzotriazoles in backing layers of materials containing core-shell type direct positive emulsions in order to improve processing stability.
• the addition of several kinds of mercapto-substituted N-containing heterocyclic compounds to direct positive emulsions of the internal sensitivity type are disclosed in JP-A's 63029752, 01197742, 63040148 and 63040148.
• JP-A 57096331 the addition after physical maturation to direct positive emulsions of specific mercaptotriazoles in order to improve raw stock stability is described.
• Stauffer US-P 2,497,917 recognized that certain antifoggants when used in internal latent image-forming direct positive elements not only reduce the minimum density but also increase maximum density.
• Members of this special class of antifoggants are known to be effective whether incorporated in the photographic element itself or in a developing solution. Further applications of maximum density enhancing antifoggants are illustrated in Evans US-P 3,761,276 cited above.
• Hoyen US-P 4,572,892 discloses a black-and-white direct positive photographic element comprising one or more emulsion layers containing internal latent image-forming silver halide grains and further a maximum density enhancing 1,2,3-triazole antifoggant (preferably a benzotriazole derivative) which has to be incorporated in an undercoat layer between the emulsion layer(s) ; in the preferred embodiment a nucleating agent is present, e.g. an arylhydrazide derivative.
• a nucleating agent is present, e.g. an arylhydrazide derivative.
• a photographic direct positive material comprising a support and one or more radiation sensitive emulsion layers containing internal latent image-forming silver halide grains characterized in that a hydrophilic non-light-sensitive interlayer adjacent to said emulsion layer(s) and coated between said emulsion layer(s) and the support comprises a nucleation inhibitor releaser which is characterised by a half-life of from 1 to 180 seconds, more preferably of from 5 to 40 seconds, and still more preferably from 10 to 30 seconds, said half-life being defined as the time necessary to convert (1-1/e) th of the inhibitor releaser to its inhibitor in the developing step of the exposed material at a developer temperature of 36°C.
• Said inhibitor releaser preferably corresponds to the general formula (I), wherein BALLAST means an inert hydrophobic aliphatic group limiting the diffusion of the molecule; LINK means a divalent linking group which contains at least one functional group which cleaves or hydrolyses during processing in an alkaline developing or activating bath; and Q represents the necessary atoms to complete a heterocyclic or aliphatic aromatic ring and which forms a photographically useful group or PUG, together with the terminal -SM group, wherein S represents sulphur and M represents an alkali metal or a NH 4 -group.
• BALLAST means an inert hydrophobic aliphatic group limiting the diffusion of the molecule
• LINK means a divalent linking group which contains at least one functional group which cleaves or hydrolyses during processing in an alkaline developing or activating bath
• Q represents the necessary atoms to complete a heterocyclic or aliphatic aromatic ring and which forms a photographically useful group or PUG, together with
• PUG represents a substituted or unsubstituted phenylmercaptotetrazole compound.
• a preferred one is 1-(p-carboxyphenyl)-5-mercaptotetrazole.
• the described direct positive material is meant to be processed in a surface developer (a) in the presence of a nucleating agent or (b) with light flashing of the photographic element.
• procedure (a) constitutes the preferred embodiment.
• an acylhydrazide nucleating agent is used which is preferably incorporated in an emulsion layer too.
• the compounds represented by formula (I) comprising a preferred phenylmercaptotetrazole inhibiting group are forming a free stabilizing substituted or unsubstituted phenylmercaptotetrazole molecule under the alkaline pH conditions commonly occuring during the development step.
• nucleator inhibiting releaser may be incorporated in at least one of the emulsion layers.
• the said nucleator inhibiting releaser is incorporated in a layer adjacent to the emulsion layer and is situated between said emulsion layer and the support, in order to avoid losses of the active product in the developer and in order to make the product work effectively in the emulsion layer.
• the nucleation will be inhibited some time after its start in order to avoid further nucleation at the surface of more and more new crystals.
• an increasing developablity of more and more emulsion crystals leads to a decrease in sensitivity of the direct-positive material in which said emulsion crystals are coated.
• nucleator inhibiting releasing compound used in the photographic material according to this invention that the inhibiting moiety only becomes active after some initial development time.
• half-life of the nucleator inhibiting releaser is important and is defined as "the time necessary to convert (1-1/e) th of the inhibitor releaser to its inhibitor in the developing step at a temperature of the developer of 36°C".
• half-life can easily be determined by following the spectral changes of the inhibitor releaser in the developer or the developer conditions, like pH and the like, at 36°C. It is clear that a short half-life versus the development time will result in a low maximum density as the development is blocked then rather quickly, whereas a long half-life will result in a normal maximum density and a high minimum density: preferred half-life times are from 5 to 40 seconds and still more preferably from 10 to 30 seconds.
• the said compound is preferably incorporated in an adjacent layer, from which it takes some time to diffuse to the emulsion layer, where its active PUG is able to block the nucleating action of the nucleating agent(s).
• the concentration of the compound according to the general formula (I) in the layer adjacent to the emulsion layer(s) is preferably comprised between 5x10 -7 and 5x10 -2 mole per mole of silver halide and more preferably between 5x10 -5 and 5x10 -3 .
• Preferred latent image-forming silver halide emulsions are so-called core-shell emulsions consisting of a core and at least one shell having the same or different halide compositions. Both shell(s) and core can mutually independently be composed of silver bromide, silver chloride, silver chlorobromide, silver chloroiodide, silver bromoiodide and silver chlorobromoiodide.
• the emulsions can show a coarse, medium or fine average grain size and be bounded by (100), (111), (110) crystal planes or combinations thereof.
• high aspect ratio tabular core-shell emulsion grains can be contemplated as disclosed in US-P 4,504,570.
• the core-shell emulsions contain internal sensitization sites which can be of various nature and which form an internal latent image upon exposure.
• a first type of core-shell emulsions contains internal physical sensitization sites formed by crystallographic irregularities in the phase bounderies between a core and a shell of distinctly different halide composition, e.g. a silver bromide core and a silver bromoiodide shell with a relatively high iodide percentage.
• Another simple method for applying internal sensitization sites consists of incorporating a polyvalent metal ion dopant in the core grains during their formation.
• This metal dopant can be placed in the reaction vessel prior to precipitation or it can be added to one or more of the solutions taking part in the precipitation.
• Preferred polyvalent metal dopants are metals from the group VIII of the Periodic System, e.g., Iridium, as disclosed in US 3,367,778, Rhodium or Ruthenium, as disclosed, e.g., in EP-S 0 336 425 and 0 336 426, in EP-A 0 617 323 and in US-P 4,643,965. They are preferably used in the form of a soluble salt or coordination complex.
• the usual concentration range is comprised between 10 -8 and 10 -4 mole per mole of silver halide.
• the most common method of creating internal sensitization sites consists of interrupting the precipitation after completion of the core and applying chemical sensitization or even fogging to this core, after which process the precipitation of the shell is resumed.
• the usual chemical ripening agents containing middle-chalcogen elements like sulphur, selenium and tellurium can be used as has been disclosed, e.g., in US-P 3,761,276.
• they are combined with compounds containing noble metal atoms, e.g., gold. Contrast can be controlled by optimizing the ratio of middlechalcogen amount to gold sensitizer amount as has been described in US-P 4,035,185.
• the core-shell emulsions used in the photographic direct-positive material according to this invention are emulsions wherein at least the core of said core-shell grains is chemically ripened.
• the choice of the halide composition of the shell portion will depend on the requirements of the specific photographic application. In order to achieve fast developability emulsion shells with a high chloride content are best suited. On the contrary when high sensitivity is required bromide or iodobromide grain shells are preferred.
• the shell portion of the grain must contain a sufficient percentage of the total silver halide in order to restrict access of a surface developer to the internal sensitization centers.
• the surface of the finished core-shell emulsion grains can be chemically sensitized or not. For obtaining good reversal speed and maximum density a moderate degree of surface sensitization using conventional techniques can be applied. This degree of chemical sensitization is usually limited to that which will realize an optimal balance between internal and surface sensitivity, the internal sensitization usually remaining predominant.
• two or more internal latent image-forming emulsions can be blended before coating and thus be applied in the same emulsion layer.
• several different emulsions can be used each in a different emulsion layer arranged in a pack.
• one emulsion layer is coated containing one direct positive emulsion or a blend of several direct positive emulsions.
• the internal latent image-forming emulsions can, if desired, be spectrally sensitized according to the exposure source to be used depending on the specific photographic application.
• Dyes that can be used for the purpose of spectral sensitization include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, hemicyanine dyes, styryl dyes and hemioxonol dyes.
• Particularly valuable dyes are those belonging to the cyanine dyes, merocyanine dyes and complex merocyanine dyes as described by F.M. Hamer in "The Cyanine Dyes and Related Compounds", 1964, John Wiley & Sons.
• the process of spectral sensitization can take place at any stage of the emulsion preparation but most commonly spectral sensitization is undertaken subsequent to the completion of surface chemical sensitization, if any.
• a preferred orthochromatic spectral sensitizing dye (SD-1) is
• the photographic materials of the present invention can be image-wise exposed and then subjected to uniform flash lighting during processing.
• the direct positive image is formed with the aid of a so-called nucleating agent (or development nucleator) which triggers development.
• This nucleating agent can be present in the developing solution but most preferably it is present in the photographic material itself. Since in the preferred embodiment of this invention there is an undercoat non-light sensitive layer the nucleating agent can be incorporated therein, but preferably it is incorporated in the emulsion layer(s).
• the development nucleators are present in a concentration of preferably 10 -5 mole to 10 -1 mol per mole of silver halide.
• Suitable development nucleators are, e.g., propargylammonium salts, e.g., N-propargyl quinaldinium tosylate, 2-acetoxy-1,2-di(2-pyridyl)-ethanone,dihydroquinazolinium bromide,etc.
• propargylammonium salts e.g., N-propargyl quinaldinium tosylate, 2-acetoxy-1,2-di(2-pyridyl)-ethanone,dihydroquinazolinium bromide,etc.
• Acylhydrazides are preferred nucleating agents for use in photographic materials according to this invention.
• Preferred examples of such compounds are N-1 to N-4, the formulae of which are given hereinafter.
• nucleating agents comprises N-substituted cycloammonium quaternary salt.
• Preferred examples of such compounds are given in the formulae N-5 to N-8:
• the development nucleator(s) Prior to the coating of the composition that will form the photographic layer comprising at least one development nucleator, the development nucleator(s) can be dissolved in an organic solvent, e.g. alcohol, N-methyl-pyrrolidone, and added to said composition.
• an organic solvent e.g. alcohol, N-methyl-pyrrolidone
• the development nucleator(s) can be added in dispersed form to the hydrophilic colloid composition that will form said emulsion layer.
• the dispersion can be prepared by dissolving these nucleators first in at least one water-immiscible, oil-type solvent or oil-former, adding the resulting solution to an aqueous phase containing a hydrophilic colloid, preferably gelatin, and a dispersing agent, passing the mixture through a homogenizing apparatus so that a dispersion of the oily solution in an aqueous medium is formed, mixing the dispersion with a hydrophilic colloid composition, e.g, a gelatin silver halide emulsion, and coating the resulting composition in the usual manner to produce a system in which particles of development nucleator(s), surrounded by an oily membrane, are distributed throughout the gel matrix.
• a hydrophilic colloid composition e.g, a gelatin silver halide emulsion
• the dissolution of the development nucleator(s) in the oil-former may be facilitated by the use of an auxiliary low-boiling water-immiscible solvent, e.g., ethylacetate, which is removed afterwards by evaporation.
• an auxiliary low-boiling water-immiscible solvent e.g., ethylacetate
• the binder of the photographic element can be hardened with appropriate hardening agents such as those of the epoxide type, those of the ethylenimine type, those of the vinylsulfone type, e.g., 1,3-vinylsulphonyl-2-propanol, chromium salts, e.g., chromium acetate and chromium alum, aldehydes, e.g., formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds, e.g., dimethylolurea and methyloldimethylhydantoin, dioxan derivatives, e.g., 2,3-dihydroxy-dioxan, active vinyl compounds, e.g., 1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds, e.g., 2,4-dich
• the photographic element of the present invention may further comprise various kinds of surface-active agents in the photographic emulsion layer or in at least one other hydrophilic colloid layer.
• Suitable surface-active agents include non-ionic agents such as saponins, alkylene oxides, e.g., polyethylene glycol, polyethylene glycol/polypropylene glycol condensation products, polyethylene glycol alkyl ethers or polyethylene glycol alkylaryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkylamines or alkylamides, silicone-polyethylene oxide adducts, glycidol derivatives, fatty acid esters of polyhydric alcohols and alkyl esters of saccharides; anionic agents comprising an acid group such as a carboxy, sulpho, phospho, sulphuric or phosphoric ester group; ampholytic agents such as aminoacids, aminoalkyl sulphonic acids, aminoalkyl
• Such surface-active agents can be used for various purposes, e.g., as coating aids, as compounds preventing electric charges, as compounds improving slidability, as compounds facilitating dispersive emulsification, as compounds preventing or reducing adhesion.
• Preferred surface-active agents are compounds containing perfluorinated alkyl groups.
• the photographic element of the present invention may further comprise various other additives such as, e.g., compounds improving the dimensional stability of the photographic element, antistatic agents, spacing agents, light absorbing dyes, e.g., antihalation dyes, filter dyes or acutance dyes, lubricants, opacifying compounds, e.g., titanium dioxide, and plasticizers.
• additives such as, e.g., compounds improving the dimensional stability of the photographic element, antistatic agents, spacing agents, light absorbing dyes, e.g., antihalation dyes, filter dyes or acutance dyes, lubricants, opacifying compounds, e.g., titanium dioxide, and plasticizers.
• Antistatic agents can be used in one or more of the layers on the emulsion side or in a backing layer.
• Suitable additives for improving the dimensional stability of the photographic element are, e.g., dispersions of a water-insoluble or hardly soluble synthetic polymer, e.g., polymers of alkyl(meth)acrylates, alkoxy(meth)acrylates, glycidyl (meth)acrylates, (meth)acrylamides, vinyl esters, acrylonitriles, olefins, and styrenes, or copolymers of the above with acrylic acids, methacrylic acids, ⁇ - ⁇ -unsaturated dicarboxylic acids, hydroxyalkyl (meth)acrylates, sulphoalkyl (meth)acrylates, and styrene sulphonic acids.
• a water-insoluble or soluble synthetic polymer e.g., polymers of alkyl(meth)acrylates, alkoxy(meth)acrylates, glycidyl (meth)acrylates, (meth)acrylamides,
• Spacing agents can be present of which, in general, the average particle size is comprised between 0.2 and 10 ⁇ m. Suitable spacing agents can be made e.g. of polymethyl methacrylate, of copolymers of acrylic acid and methyl methacrylate, and of hydroxypropylmethyl cellulose hexahydrophthalate. Other suitable spacing agents have been described in US 4,614,708. Spacing agents can also serve as matting agents. Other common matting agents consist of silica particles of which different size classes can be used.
• one or more non-light-sensitive hydrophilic colloid undercoat and/or backing layers can be present.
• the support of the photographic material may be opaque or transparent, e.g., a paper support or resin support.
• a paper support preference is given to one coated at one or both sides with an Alpha-olefin polymer, e.g. a polyethylene layer which optionally contains an anti-halation dye or pigment.
• an organic resin support e.g. cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film, polycarbonate film, polyvinylchloride film or poly-Alpha-olefin films such as polyethylene or polypropylene film.
• the thickness of such organic resin film is preferably comprised between 0.07 and 0.35 mm.
• These organic resin supports are preferably coated with a subbing layer which can contain water insoluble particles such as silica or titanium dioxide.
• the photographic direct positive materials of the present invention can be exposed in any convenient way according to their particular application, e.g. by daylight or by artificial light like tungsten light, xenon, metal-halogen lamps, quartz-halogen lamps, by laser sources or invisible radiation like ultraviolet, X-rays and infrared.
• the processing of the photographic materials of the present invention proceeds in a surface developer composed according to specifications dependent on the particular use of the material.
• the developing solution preferably contains one or more developing agents, sulphite ions, bromide ions and polyalkyleneoxides.
• Preferred developing agents are e.g hydroquinone and derivatives, 3-pyrazolidinone derivatives like 1-phenyl-5-pyrazolidinone ("Phenidone") and analogues, aminophenols, hydroxylamin, hydrazine derivatives, and ascorbic acid and analogues.
• Phenidone 1-phenyl-5-pyrazolidinone
• Other adjuvants well known to those skilled in the art may be added to the developer liquid of the present invention.
• a survey of conventional developer addenda is given by Grant Haist in "Modern Photographic Processing” - John Wiley ans Sons - New York (1979) p. 220-224.
• addenda examples include complexing agents for calcium and magnesium ions, present in hard water, e.g., ethylene diamine tetraacetic acid and analogues compounds. Further can be present anti-foaming agents, surface-active agents, biocides, thickening agents like polystyrene sulphonate and antioxidants like benzoate and cyclodextrine.
• the developing liquid can contain so-called anti-sludge agents in order to reduce dirt streaks on developed photographic material.
• the alkaline pH value of the developing solution is preferably established by means of conventional buffering agents like phosphate buffers, carbonate buffers and borax buffers.
• the pH can be additionally adjusted to the desired value by means of an alkali hydroxide, e.g., sodium or potassium hydroxide.
• the solution can contain hardening agents including latent hardeners.
• an automatically operating apparatus is used provided with a system for automatic replenishment of the processing solutions.
• the development step can be followed by a washing step, a fixing solution and another washing or stabilization step. Finally the photographic material is dried.
• the photographic direct positive materials of the present invention can be used in various types of photographic elements such as e.g. in photographic elements for graphic arts, for general amateur and professional photography, for cinematographic recording and duplicating, for radiographic recording and duplicating purposes, and in diffusion transfer reversal photographic elements.
• a preferred application however is micrographic recording, e.g., in a microfilm for computer output.
• direct-positive materials comprising nucleation inhibitor releasers
• the said releasers can also be useful in negative working materials, preferably in combination with hydrazides.
• a cubic silver bromide core-shell emulsion showing a final average grain size of 0.26 ⁇ m was prepared by simultaneous addition of equimolar solutions of silver nitrate and potassium bromide to a stirred aqueous gelatin solution.
• the precipitation of the core was carried out at 70 °C and at a pAg value of +106 mV versus a Ag/AgCl reference electrode.
• the core grains were chemically sensitized by means of 19.4x10 -3 mmole of sodium thiosulphate, 12.3x10 -3 mmole of aurochloric acid and 27.5x10 -3 mmole of p-toluenethiosulphonic acid sodium salt, all expressed per mole of silver halide. Then the grains were further grown under the same precipitation conditions until the final average grain size was reached.
• the gelatin / silver ratio was brought to 0.5 by the addition of extra gelatin and the core-shell emulsion was surface sensitized by means of 1.62x10 -3 mmole of p-toluenethiosulphonic acid sodium salt, 17.2x10 -3 mmole of sodium thiosulphate, 3x10 -3 of aurochloric acid and 33.5x10 -3 mmole of ammoniumthiocyanate, all expressed per mole of silver halide.
• the finished emulsion was divided in different samples in order to prepare different coating solutions for the emulsion layer having the following composition:
• the protective antistress layer was composed of:
• Table 1 illustrates the more extented development latitude for processing at different developer temperatures and a lower rereversal when the nucleator inhibiting releaser according to this invention is present in a layer, adjacent to the emulsion layer, as in this case, in the protective antistress layer.

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