FR2714493A1 - Silver chlorobromide photographic emulsion, preparation and use in color reversal processes. - Google Patents

Abstract

The present invention relates to a photographic silver halide emulsion for use in color reversal photographic elements. This emulsion comprises grains containing a core of silver chlorobromide and a peripheral zone having a high content of silver chlorobromide. This emulsion has improved sensitivity characteristics.

Description

PHOTOGRAPHIC EMULSION WITH SILVER CHLOROBROMIDE,

  PREPARATION AND USE IN INVERSIBLE PROCESSES

COLORS

  The present invention relates to a silver halide emulsion for color photography containing chemically and spectrally sensitized silver halide grains having a core and shell structure (hereinafter referred to as core-shell). The present invention also relates to a process for obtaining such silver halide emulsions and

  their use in color reversal processes.

  Although photographic silver halide emulsions are generally known, there is a continuing need for photographic products having improved photographic properties, such as

  superior sensitivity and better granularity.

  One of the disadvantages of known emulsions is that the sensitizing dyes used to spectrally sensitize the emulsion, e.g., cyanine dyes, can cause some loss of the intrinsic sensitivity of the emulsion. This desensitization due to dyes is recognized by the art as a problem, and mentioned, for example, in The Theory of the Photographic Process, 4th Edition, Mc Millan Publishing Co., Inc., pp. 265 et seq. Given the considerable variety of sensitizing dyes available, one might think that if a particular dye produces unacceptable desensitization, a practical solution would be to choose another dye with the same

  sensitization characteristics without desensitization.

  However, optimally sensitizing a silver halide emulsion is generally the result of a complex compromise between antithetic factors and there are cases where specific dyes are used despite their desensitizing properties, because these dyes have the desired adsorption on the grains, or absorb the

  light in the desired region of the spectrum.

  It is also known that increasing the chloride content of the silver halide grains can improve the developability of these grains and enable rapid processing. Emulsions having a high chloride content, distributed in one or more phases or zones of the grain, are described in the art, for example, in U.S. Patents 4,590, 3,935,014 or in the Grande However, it is known that chloride emulsions have various disadvantages, such as insufficient stability or lower sensitivity, compared to

  bromide or bromoiodide emulsions.

  There is a specific need for chloride-containing emulsions which may have an optimal grain-sensitivity relationship without the previously mentioned disadvantages associated with the use of certain sensitizing dyes. The present invention eliminates the phenomenon of desensitization generally caused by certain sensitizing dyes, in order to use these dyes without obtaining the undesired effects that might have been expected. An object of the present invention relates to a spectrally sensitized and chemically sensitized halide emulsion comprising silver halide grains having a core and at least one shell, characterized in that said grains comprise from 1 to 50 mol% of chloride located in a zone of the periphery of the grain which is substantially free of iodide, a spectral sensitizing dye being adsorbed on said grains, said dye corresponding to the formula: Z1 C - (L1 L2) n_-CH = C Z2

N.N + N '

I I

R1 R2

  Z1 and Z2 independently represent the atoms necessary to complete a benzoxazole radical, a naphthoxazole radical, a benzothiazole radical, a naphthothiazole radical, a benzimidazole radical or a naphthimidazole radical, where the aromatic cycles may be substituted by groups such as alkyl groups. aryl, aralkyl, alkaryl, halo, cyano; L1 and L2 independently represent a methine group, such as -CH =, C (CH3) =, -C (C2H5) =; R1 and R2 independently represent a sulfoalkyl radical, such as P-sulfoethyl, o-sulfobutyl; and

n is 1 or 2.

  Examples of suitable dyes according to this formula are the following: ## STR5 ## (CH 2) 3 HN + (Et) 3 (CH 2) 2

S03- S0O3C CH

  ## STR5 ## wherein: ## STR1 ##

I I

03-03

  Another subject of the invention relates to a process for producing a chemically and spectrally sensitized silver halide photographic emulsion, said process consisting in forming a silver halide core emulsion to be formed on the periphery of this emulsion ( core), a zone substantially free of iodide containing from 1 to 50 mol% of chloride, and during or after the chemical sensitization step, to adsorb to the surface of the grains of the emulsion obtained, a sensitizing dye such as previously defined. According to the present invention, the terms "substantially free of iodide" mean that the shell of the grain can contain only a very small amount of iodide, generally

not more than about 0.5% M.

  Compared with a control emulsion using the same sensitizing dye and having similar characteristics, except that the chloride is replaced by bromide, the emulsion of the invention compensates for the loss of sensitivity resulting from desensitization due to

  to the dye and even get a gain of sensitivity.

  According to one embodiment, in the chlorohalogenide one-shell emulsion, the chloride is distributed around the periphery of the grain, and in this zone the chloride content may vary abruptly or gradually, forming high or low content zones. chloride, included in the previously mentioned ranges. As indicated, the chlorobromide shell of an emulsion according to the invention comprises from 1 to 50 mol%; preferably the shell contains from 1 to 30 mol% and more preferably from 2 to 20 mol% chloride relative to

  to the total amount of money in the grain.

  According to a preferred embodiment, the emulsion of the present invention comprises silver halide grains containing a core and several shells, the composition of the halides being different in the core and the shell or shells. . The peripheral zone containing the chloride preferably represents a thickness greater than 100 and less than 40% of the grain radius. Advantageously, the thickness of the peripheral zone containing the chloride represents from 10 to 35%

grain radius.

  The silver halide grains have the crystal structures generally used in silver halide photography; they are cubic, octahedral or cubo-octahedral grains. The core grains may consist of silver bromide, silver chloride, silver chlorobromide, silver chloroiodide, silver chlorobromoiodide, or mixtures thereof. When grains contain iodide in the heart, the amount of iodide limit is that which can be accepted by the cubic crystal lattice. In a cubic crystal lattice of silver bromide, up to about 40 mol% iodide may be incorporated depending on the precipitation temperature. When using iodide in the core, the grains preferably contain less than about 15 mol% iodide. In conventional photographic applications, the iodide concentrations are generally less than about mole%. The distribution of the iodide can be homogeneous (for example, resulting from the continuous iodide jet precipitation) or discrete, the structures resulting from a sudden addition of iodide during the precipitation. The emulsions may comprise coarse, medium or fine silver halide grains predominantly limited by [100] or [111] crystalline planes and may be of regular or irregular shape by

  example, of cubic or octahedral form.

  Emulsions comprising core grains can be prepared by various techniques, for example, single jet, double jet, accelerated flow precipitation techniques as described by Trivelli and Smith,

  The Photographic Journal, vol. LXXIX, May 1939, pp. 330-

  338, TH James, The Theory of the Photoqraphic Process, 4th Edition, Macmillan, 1977, Chapter 3, by Niertz et al in U.S. Patent 2,222,264, by Wilgus in German Patent Application No. 2 107,118, by Lewis in United Kingdom Patents 1,335,925, 1,430,465 and 1,469,480, by Irie et al in the US Pat.

  of America 3,650,757, by Morgan in the United States Patent

  United States of America 3,917,485, by Musliner in U.S. Patent 3,979,213, in Research Disclosure, Article 17643, Vol. 176, December. 1978, and Research Disclosure, Article 22434, Vol. 225, January 1983. Research Disclosure and its predecessor, Product Licensing Index, are publications of Industrial Opportunities Ltd .;

  Homewell, Havant; Hampshire, P09 1EF, United Kingdom.

  Modifying compounds may be present during grain precipitation. Such compounds may be initially in the reaction vessel or may be added together with one or

  several salts, according to the standard procedures.

  Modifying compounds, such as medium chalcogen (ie, sulfur, selenium and tellurium), gold and noble metals of group VIII (eg, iridium), may be present during of the precipitation of the halides, as described in

  Research Disclosure, Vol. 134, June 1975, Article 13452.

  An important feature of the invention is that the chloride is coprecipitated with another silver halide, so as to form a mixed phase of silver chlorohalide in the outer peripheral zone of the grain. According to a preferred embodiment, the process of the invention consists in precipitating a bromide or bromoiodide core emulsion (core), and then coprecipitating a chlorobromide emulsion on the core emulsion. Alternatively, the bromide or bromoiodide core emulsion may be first wrapped with a bromide emulsion, which will itself be coated by coprecipitating a chlorobromide emulsion. The parameters of these precipitation steps, such as pAg, flow rates, flow profiles, salt concentrations, number of moles precipitated as a function of time, temperature, depend largely on the type of emulsion considered and desired results and will be determined accordingly in each case by

the skilled person.

  The grain size of the emulsions is determined using a grain volume analyzer and the determination is based on the principle of direct electrolytic reduction. Such apparatus is described by A. Holland and A. Feinerman in J. Applied Photo. Eng. 8, 165 (1982). Such an apparatus makes it possible to obtain a volume distribution of the grain size from which a mean distribution volume (V) can be calculated, then an equivalent spherical diameter (ESD) and a standard deviation (SIGMA), Vi being the volume of a particular grain and N being

the number of grains counted.

  3 x V ESD = 2 x 3 --------- in micrometers 4 x x (Vi - v) 2 SIGMA = -i

NOT

  The coefficient of variation (VOC) is defined as 100 times the ratio of the standard deviation of volume and average volume of the SIGMA grain population

VOC = 100 x ----------

  These emulsions are preferably monodisperse, i.e. they have a narrow size distribution characterized for example by a coefficient of variation

  less than 20% and preferably less than 10%.

  The emulsions according to the invention are intended for invertible color (or inversion) color processes. The chromogenic products generally comprise a support coated with at least three silver halide emulsion layers, with which are associated one or more dye-forming couplers. Color inversion treatments are well known and generally include a first development in black and white, a veiling step, a chromogenic development and a step

bleach-fix.

  These emulsions may be chemically sensitized by any conventional technique or using any conventional sensitizer, such as those set forth in Research Disclosure No. 308, December 1989, paragraph III. These sensitizers include, for example, active gelatin, as described by T. H. James, The Theory of the Photographic Process, 4th Edition, Macmillan; 1977, pages 67-76, or sensitizers to sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhodium, rhenium, or phosphorus or combinations of these sensitizers, at pAg between 5 and 10, pH between 5 and 8 and temperatures between 30 and 80 C, as described in Research Disclosure, Vol. 120, April 1974, Article 12008, Research Disclosure, Vol. 134, June 1975, Article 13452, by Sheppard et al in U.S. Patent 1,623,499, by Matthies et al in U.S. Patent 1,673,522, by Waller et al in the US Pat. patent of the United States of America

  2,399,083, by Damschroder et al, in the US Pat.

  United States 2,642,361, by McVeigh in U.S. Patent 3,297,447, by Dunn in U.S. Patent 3,297,446, by McBride in United Kingdom Patent 1 315,755, by Berry et al in U.S. Patent 3,772,031, by Gilman et al in U.S. Patent 3,761,267, by Ohi et al in US Patent No. 3,857,711, by Klinger et al in U.S. Patent 3,565,633, by Oftedahl in U.S. Patents 4,901,714 and 3,904,415, and by Simons in US Pat. United Kingdom 1,396,696; the chemical sensitization may optionally be carried out in the presence of thiocyanates, preferably at concentrations of between 2 x 10-3 and 2 mol%, based on the total silver, as described by Damschroder in the US Pat. United States of America 2,642,361; sulfur-containing compounds of the type described in Lowe US Pat. No. 2,521,926

  et al., 3,021,215 to Williams et al. and 4,054,457 to Bigelow.

  It is specifically contemplated that chemical sensitization can be carried out in the presence of chemical sensitizing modifying compounds, i.e., compounds known to suppress haze and increase sensitivity when present during chemical sensitization, such as azaindenes, azapyridazines, azapyrimidines, benzothiazolium salts, and sensitizers comprising one or more heterocyclic rings. Examples of finishing modifiers are described in U.S. Patent Nos. 2,131,038 to Brooker et al., 3,411,914 to Dostes, 3,554,757 to Kuwabara et al., 3,565,631 to Oguchi et al., 3,901. 714 of Oftedahl, in Canadian Patent 778,723 to Walworth and in Duffin, Photographic Emulsion Chemistry, Focal Press (1966), New York, pp. 138-143. In addition, the emulsions can be sensitized by reduction - for example, with hydrogen, as described by Janusonis in U.S. Patent No. 3,891,446 and by Babcock et al, in the US Pat. US 3,984,249, by treatment using low pAg (e.g., less than 5) and / or high pH (e.g., greater than 8) or using reducing agents, such as stannous chloride , thiourea dioxide, polyamines, and amineboranes,

  as described by Allen et al in the US Pat.

  United States of America 2,983,609, Oftedahl et al in Research Disclosure, Vol. 136, August 1975, Article 13654, by Lowe et al, U.S. Patents 2,518,698 and

  2,739,060, by Roberts et al in US patents

  United States 2,743,182 and 2,743,183, by Chambers et al. In U.S. Patent 3,026,203 and by Bigelow et al in U.S. Patent 3,361,564. Superficial chemical sensitization, including under surface sensitization, described by Morgan in U.S. Patent 3,917,485 and Becker in U.S. Patent

  3 966 476 is specifically considered.

  Preferably, the outer peripheral zone containing the chloride or chlorobromide is sensitized to gold

and / or sulfur.

  In addition to being chemically sensitized, the silver halide emulsions of the present invention are also spectrally sensitized by means of spectral sensitizing dyes, as defined above, which exhibit absorption maxima in the blue and blue minus portions. , that is, green and red of the visible spectrum. In addition, in specialized applications, spectral sensitizing dyes can be used to improve the response.

  spectral beyond the visible spectrum.

  One or more spectral sensitizing dyes can be used. Dyestuffs having maximum sensitization at various wavelengths of the visible spectrum and having a high sensitivity are known.

  wide variety of shape of spectral sensitivity curve.

  The choice and relative proportions of dyes depend on the region of the spectrum where it is desired to obtain the sensitivity and shape of the desired spectral sensitivity curve. Dyes having overlapping spectral sensitivity curves often provide a combination in which a sensitivity in each wavelength of the overlap zone is approximately equal to or even greater (over-sensitization) than the sum of the sensitivities of the individual dyes. It is also possible to use combinations of dyes previously

  defined and other conventional sensitizing dyes.

  The invention is described in more detail in the following examples. The indicated silver potentials are measured using a saturated calomel electrode unless

otherwise stated.

  EXAMPLE 1 (Control) To a 20 liter precipitation vessel, 4.156 liters of distilled water, 57.8 g / l of phthalylated deionized gelatin, which is heated to 60 ° C., is added. An anti-foaming agent is added. and a thioether ripening agent before adjusting the pAg to 9.1 using NaBr solution and bringing the pH to 5.1. Nucleation of a stable population of AgBr microcrystals was performed by introducing 0.035 moles of AgNO3 and NaBr by double jet precipitation over a period of 70 seconds, using 0.5 M / l reagents. An excess of bromide is maintained in order to obtain a pAg

  equal to 9.1 at a temperature of 60 C.

  This nucleation is followed by a stopping period of seconds. This quenching period is followed by an initial growth period lasting 33.3 minutes, in which 2.0M / l of AgNO 3, 1.82M / l of NaBr and 0.18M / l of KI by accelerated double jet precipitation, so as to produce a mixed AgBrI phase while maintaining the temperature and pAg at the same values as before. 3.36 mol of silver halides are precipitated in this initial growth step. The precipitation is terminated by a final growth segment for 29 minutes in which 2.0 M / l of AgNO 3 and 2.0 M / l of NaBr are introduced by a double jet precipitation, while maintaining the temperature and the pAg. at the same values as before. 6.66 mol of silver halides are precipitated during this second growth stage. The emulsion is then washed using a conventional flocculation process. The final emulsion consists of octahedral grains having an equivalent spherical diameter of 0.639 micron and a total

iodide of 3 mol%.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position. The chemical sensitization is carried out for 20 minutes at 70 ° C. using: mg sodium thiocyanate per mole of Ag, 71 mg of sulfur in the form of Na 2 S 2 O 3 .5H 2 O per mole of Ag, 5.71 mg of gold under the form of potassium tetrachloroaurate per mole of Ag is then added 198.4 mg of sensitizing dye (Formula A) per mole of Ag for green sensitization. And where N (CH2) 3 HN + (Et) 3 2) 2 _o 3- S03 -CH

I

  CH 3 (A) The emulsion obtained is an octahedral emulsion with a 1S core and shell of sensitized bromide, having an equivalent spherical diameter (used as average grain size) of 0.639m, and a volume coefficient of variation of 10.8 %. The overall iodide content corresponds to 3 mol% and the content of the core in

iodide corresponds to 9 mol%.

  This bromide shell emulsion (El emulsion) is

used as a control.

  EXAMPLE 2 (Control) To a 20-liter precipitation vessel, 4.156 liters of distilled water is introduced, 57.8 g / l of phthalylated deionized gelatin which is heated to 700 ° C. An anti-foaming agent and a thioether ripening agent were added before the pAg was adjusted to 8.93 using NaBr solution and the pH was raised to 5.1. Nucleation of a stable population of AgBr microcrystals was performed by introducing 0.035 moles of AgNO3 and NaBr by double jet precipitation over a period of seconds, using 0.5 M / l reagents. An excess of bromide is maintained so as to obtain a pAg equal to 8.93

at a temperature of 70 C.

  This nucleation is followed by a stopping period of seconds. This quenching period is followed by an initial growth period of 34.3 minutes, during which 2.0M / l AgNO3, 1.82M / l NaBr and 0.18M / l are introduced. KI by accelerated double jet precipitation, so as to produce a mixed AgBrI phase while maintaining the temperature and pAg at the same values as before. A total of 3.36 moles of silver halides are precipitated in this initial growth step. Following this initial growth step, the pAg is modified to a value of 7.0 using a

  solution of 2.0 M / 1 AgNO3 introduced in 152 seconds.

  This change of pAg is followed by a stopping period of 120 seconds. The shutdown period is followed by a segment

of final growth.

  In the final growth segment, 2.0 M / l of AgNO 3 and 2.0 M / l of NaBr are introduced over a period of 20 minutes by accelerated double jet precipitation, while maintaining the temperature and the ag same values as before. A total of 6.69 moles of silver halides are precipitated during this second growth stage. The emulsion is then washed by a conventional flocculation process. The final emulsion consists of cubo-octahedral grains having an equivalent spherical diameter of 0.580 μm and an overall iodide content of 3

% in mole.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position 330. The chemical sensitization is carried out for minutes at 70 ° C. using: mg of sodium thiocyanate per mole of Ag, 97 mg of sulfur in the form of Na 2 S 2 O 3 .5H 2 O per mole of Agr 3,98 mg of gold under the form of potassium tetrachloroaurate per mole of Ag, then 217.0 mg of the sensitizing dye A

  mole of Ag for awareness in the green.

  The emulsion obtained is a cubo-octahedral emulsion with sensitized shell and shell having an equivalent spherical diameter (used as average grain size) of 0.580 gm, and a volume coefficient of variation of 11.9%. The overall iodide content corresponds to 3 mol% and the iodide content of the core corresponds to

9 mol%.

  This bromide shell emulsion (emulsion E2) is

used as a control.

  EXAMPLE 3 - (Invention) To a vessel of precipitation of N20 liters, 4.156 liters of distilled water, 57.8 g / l of phthalylated deionized gelatin which is heated to 700 ° C. are introduced. An anti-foaming agent and a thioether ripening agent were added before the pAg was adjusted to 8.93 using NaBr solution and the pH was raised to 5.1. The nucleation of a stable population of AgBr microcrystals was performed by introducing 0.035 moles of AgNO 3 and NaBr by a double jet precipitation over a period of 70 seconds, using 0.5 M / 1 of reagents. An excess of bromide is maintained in order to obtain a pAg

  equal to 8.93 at a temperature of 700C.

  This nucleation is followed by a stopping period of seconds. This quenching period is followed by an initial growth period of 34.3 minutes, in which 2.0M / l AgNO3, 1.82M / l NaBr and N0.18M / l are introduced. KI by means of an accelerated double jet process, so as to produce a mixed AgBrI phase while maintaining the temperature and the pAg at the same values as before. A total of 3.36 moles of silver halides are precipitated in this step of

initial growth.

  After this initial growth, the pAg is modified to 7.0 using a solution of 2.0 M / l

of AgNO3 introduced in 153 seconds.

  This change of pAg is followed by a stopping period of 120 seconds. The shutdown period is followed by a segment

of final growth.

  For the final growth segment, 2.0 M / l of AgNO 3, 1.82 M / l of NaBr and 0.18 M / l of NaCl are introduced in 20 minutes, producing accelerated double jet precipitation. while maintaining the temperature and pAg at the same values as before. A total of 6.69 moles of silver halides are precipitated during this second

stage of growth.

  The emulsion is then washed by a conventional flocculation process. The final emulsion consists of cubo-octahedral grains having an equivalent spherical diameter of 0.606 micrometers and an overall

iodide of 3 mol%.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position. The chemical sensitization is carried out for minutes at 70 ° C. using: mg of sodium thiocyanate per mole of Ag 4.60 mg of sulfur in the form of Na 2 S 2 O 3 .5H 2 O per mole of Ag 2.30 mg of gold under the form of potassium tetrachloroaurate per mole of Ag, then 313.9 mg of sensitizing dye A is added to

  mole of Ag for awareness in the green.

  The emulsion obtained (E3) is a cuboidal emulsion

  octahedral core and shell containing 9 mol% of chloride in the shell, wherein the silver chloride and the silver bromide are coprecipitated, and having an equivalent spherical diameter of 0.606 gm, and a coefficient

volume change of 11.6%. EXAMPLE 4 (Invention) is introduced into a precipitation vessel of

  liters, 4.156 liters of distilled water, 57.8 g / l of phthalylated deionized gelatin which is heated to 700 ° C. An anti-foaming agent and a thioether ripening agent were added prior to adjusting the pAg to 8.93 using NaBr solution and the pH was raised to 5.1. Nucleation of a stable population of AgBr microcrystals was performed by introducing 0.035 moles of AgNO3 and NaBr by double jet precipitation over a period of 70 seconds, using 0.5 M / l reagents. An excess of bromide is maintained in order to obtain a pAg

  equal to 8.93 at a temperature of 70 C.

  This nucleation is followed by a shutdown period of 180 seconds. This quenching period is followed by an initial growth period of 34.3 minutes, in which 2.0M / l of AgNO 3, 1.82M / l of NaBr and 0.18M / l of KI by accelerated double jet precipitation, so as to produce a mixed AgBrI phase while maintaining the temperature and pAg at the same values as before. A total of 3.36 moles of silver halides are precipitated in this initial growth step. This initial growth is followed by a Cdu pAg adjustment at a value of 7.0 using a solution of 2.0.

  M / l of AgNO3 introduced over a period of 153 seconds.

  This change in the pAg is followed by a stopping period of 120 seconds. The shutdown period is followed by a segment

of final growth.

  CCCn precipitates a final growth segment over a period of 20 minutes, during which 2.0 M / l of AgNO3, 1.70 M / l of NaBr and 0.3 M / l of NaCl are introduced by Accelerated double jet precipitation, while keeping the temperature and pAg at the same values as before. A total of 6.69 moles of silver halides are precipitated during this second growth stage. The emulsion is then washed by a conventional flocculation process. The final emulsion consists of cubo-octahedral grains having an equivalent spherical diameter of 0.630 micron and an overall

iodide of 3 mol%.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position. The chemical sensitization is carried out for minutes at 70 ° C. using: mg of sodium thiocyanate per mole of Ag 4.50 mg of sulfur in the form of Na 2 S 2 O 3 .5H 2 O per mole of Ag 3.0 mg of gold under the form of potassium tetrachloroaurate per mole of Ag, then 299.0 mg of sensitizing dye A (Formula A) per mole of Ag is added for green sensitization.

  The emulsion obtained (E4) is a cuboidal emulsion

  octahedral core and shell containing 15 mol% of chloride in the shell, in which the silver chloride and silver bromide were coprecipitated, and having an equivalent spherical diameter of 0.630 gm, and a

  volume coefficient of variation of 10.9%.

  EXAMPLE 5 (Invention) To a precipitation vessel of liters, 4.156 liters of distilled water, 57.8 g / l of phthalylated deionized gelatin, which is heated to 70 ° C., is added. An anti-foaming agent is added and a thioether ripening agent before adjusting the pAg to 8.93 using NaBr solution and bringing the pH to 5.1. Nucleation of a stable population of AgBr microcrystals was performed by introducing 0.035 moles of AgNO3 and NaBr by double jet precipitation over a period of 70 seconds, using 0.5 M / 1 reagents. An excess of bromide is maintained in order to obtain a pAg

  equal to 8.93 at a temperature of 70 C.

  This nucleation is followed by a shutdown period of 180 seconds. This quenching period is followed by an initial growth period lasting 34.3 minutes, in which 2.0M / l of AgNO 3, 1.82M / l of NaBr and 0.18M / l of KI by accelerated double jet precipitation, so as to produce a mixed AgBrI phase while maintaining the temperature and pAg at the same values as before. A total of 3.36 moles of silver halides are precipitated in this initial growth step. After this first initial growth, the 1S pAg is adjusted to a value of 7.0 using a solution of 2.0

  M / 1 AgNO3 introduced over a period of 153 seconds.

  This change in the pAg is followed by a stopping period of 120 seconds. The shutdown period is followed by a segment

of final growth.

  For the final growth segment, 2.0 M / l of AgNO 3, 1.50 M / l of NaBr and 0.50 M / l of NaCl were introduced in minutes by an accelerated double jet precipitation, while maintaining temperature and pAg at the same values as before. A total of 6.69 moles of silver halides are precipitated during this second growth stage. The emulsion is then washed by a conventional flocculation process. The final emulsion consists of cubo-octahedral grains having an equivalent spherical diameter of 0.620 micrometers and an overall

iodide of 3 mol%.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position. The chemical sensitization is carried out for 20 minutes at 70 ° C. using: mg of sodium thiocyanate per mole of Ag 3.50 mg of sulfur in the form of Na 2 S 2 O 3 .5H 2 O per mole of Ag 2.33 mg of gold in the form of potassium tetrachloroaurate per mole of Ag, then 306.9 mg of sensitizing dye A

  mole of Ag for awareness in the green.

  The emulsion obtained (E5) is a cuboidal emulsion

  octahedral core and shell containing 25 mol% of chloride in the shell, in which the silver chloride and the silver bromide were coprecipitated, and having an equivalent spherical diameter of 0.620 gm, and a

  coefficient of variation of 10.4%.

EXAMPLE 6

  Samples of emulsions E1, E2, E3, E4 and E5 are applied using a title of 8.07 mg / dm 2 of silver, 23.68 mg / dm 2 of gelatin, 16.15 mg / dm 2 of a magenta coupler (compound F) on a triacetate support. Each sample is then exposed for 1 / 100th of a second at a color temperature of 5500 K through a Wratten # 9 filter and a neutral density filter, and then the samples are subjected to the inversion treatment.

Kodak E-6 colors.

  The sensitometric results are shown in Table I below. The parameters used in Table I are defined as follows: - shoulder sensitivity: measured at a density D1 less than the maximum density for which a sensitivity variation of 0.60 Log E is observed when from D1 to D2 = 3 x D1, the sensitivity index (SI) being determined by SI = 100 x (1 - Log ED1), - sensitivity to D = 1: measured at a density of 1, the sensitivity index (SI) being determined by SI = 100 x (1 - Log E1), - contrast at mid-scale: maximum absolute value of the first derivative of the curve D = f (Log E), - contrast at the foot: measured between 2 points of density D1 = Dmin + 0.1 and D2 = Dmin + 0.3, the value being determined by the following equation: contrast at the foot = 0.2 / (Log E1 - Log E2) - granularity at D = 1 : measured at a density of 1 using a microdensitometer having a

48 pm.

  These results show that the emulsions E3, E4 and E5 have a higher sensitivity than the emulsion E2 (+ 0.10 Log E + 0.23 Log E, + 0.32 Log E, respectively), with virtually the same contrast and the

same granularity.

  These results also show that similar improvements can be obtained as compared with

  octahedral standard emulsion with heart and shell (El).

  EXAMPLE 7 (Control) To a liter precipitation vessel, 4.156 liters of distilled water, 57.8 g / l of phthalylated deionized gelatin, which is heated to 600 ° C., are introduced. An anti-foaming agent and a thioether ripening agent were added before the pAg was adjusted to 9.1 using NaBr solution and the pH was raised to 5.1. The nucleation of a stable population of AgBr microcrystals is carried out by introducing 0.035 moles of AgNO 3 and NaBr by a double jet pre-precipitation over a period of 70 seconds, using 0.5 M / l of reagents. An excess of bromide is maintained in order to obtain a pAg

  equal to 9.1 at a temperature of 60 C.

  This nucleation is followed by a stopping period of seconds. This quenching period is followed by an initial growth period of 33.3 minutes, in which 2.0M / l AgNO3, 1.82M / l NaBr and 0.18M / l are introduced. KI by accelerated double jet precipitation, so as to produce a mixed AgBrI phase while maintaining the temperature and pAg at the same values as before. A total of 3.35 moles of silver halides are precipitated in this initial growth step. A final growth segment is carried out over a period of 29 minutes, during which 2.0 M / l of AgNO 3 and 2.0 M / l of NaBr are introduced by a double jet precipitation while maintaining the temperature and the pAg. at the same values as before. 6.66 moles of silver halides are precipitated during this second growth stage. The emulsion is then washed by a conventional flocculation process. The final emulsion consists of octahedral grains having an equivalent spherical diameter of 1.135 micrometers and an overall

iodide of 3 mol%.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position. The chemical sensitization is carried out for 20 minutes at 70 ° C. using: mg of sodium thiocyanate per mole of Ag 3.08 mg of sulfur in the form of Na2S202.5H30 per mole of Ag 2.05 mg of gold under Potassium tetrachloroaurate form per mole of Ag Spectral sensitization in green is carried out during the chemical sensitization step using a mixture of 125.7 mg of sensitizing dye A per mole of Ag and 26.3 mg of dye

sensitizer B per mole of Ag.

And

N N

1 I

(CH2) 3 Na '(CH2) 3

50-503-

  3 so3 (B) The emulsion obtained is an octahedral emulsion with a base and shell of sensitized bromide having an equivalent spherical diameter (used as average grain size) of 1.135 μm, and a volume coefficient of variation of 7.1%. The overall iodide content corresponds to 3 mol% and the content of the core in

iodide corresponds to 9 mol%.

  This bromide shell emulsion (emulsion E6) is

used as a control.

  EXAMPLE 8 (Invention) To a precipitation vessel of liters, 4.156 liters of distilled water, 57.8 g / l of phthalylated deionized gelatin which is heated to 60 ° C. is added. An anti-foaming agent is added and a thioether processing agent before adjusting the pAg to 9.1 using NaBr solution and the pH was raised to 5.1. Nucleation of a stable population of AgBr microcrystals was performed by introducing 0.035 mole of AgNO3 and NaBr a double jet precipitation over a period of seconds, using 0.5 M / l of reagents. An excess of bromide is maintained so as to obtain a pAg equal to 9.1

at a temperature of 60 C.

  This nucleation is followed by a shutdown period of 120 seconds. This quenching period is followed by an initial growth period lasting 33.3 minutes, in which 2.0M / l of AgNO 3, 1.82M / l of NaBr and 0.18M / l of KI an accelerated double jet precipitation, so as to produce a mixed AgBrI phase while maintaining the temperature and the pAg at the same values as before. A total of 3.35 moles of silver halides are precipitated in this initial growth step. After this initial initial growth, the pAg is adjusted to 7.0, using a solution of 2.0 M / l AgNO3.

introduced in 156 seconds.

  This change of pAg is followed by a 60-second shutdown period. The shutdown period is followed by a segment

of final growth.

  For the final growth segment, 2.0 M / l of AgNO 3, 1.70 M / l of NaBr and 0.30 M / l of NaCl, a double jet precipitation, are introduced over a period of 39 minutes, while maintaining temperature and pAg at the same values as before. 6.66 mol of halides are precipitated

  of money during this second stage of growth.

  The emulsion is then washed by a conventional flocculation process. The final emulsion consists of octahedral grains having an equivalent spherical diameter of 1.107 μm and an overall iodide content of

3% in mole.

  This emulsion is sensitized chemically and spectrally at a certain point as being the optimal position. The chemical sensitization is carried out for minutes at 70 ° C. using: 200 mg of sodium thiocyanate per mole of Ag 2.0 mg of sulfur in the form of sodium thiosulfate pentahydrate per mole of Ag 1.33 mg of gold in the form of tetrachloroaurate

potassium per mole of Ag.

  A mixture of 166.0 mg of sensitizing dye A per mole of Ag and 48.0 mg of sensitizing dye B per mole of Ag is added during the chemical sensitization step to effect sensitization.

in the green.

  The emulsion obtained (E7) is a cubocahedral heart and shell emulsion containing 15 mol% of chloride in the shell in which the silver chloride and the silver bromide have been coprecipitated, and having a spherical diameter. equivalent of 1,107 gm and a coefficient

volume change of 6.2%.

EXAMPLE 9

  The emulsions of Examples 7-8 are layered, exposed to light and treated as described in Example 6. Results similar to those of Example 6 are observed, ie that the emulsion E7 has a higher sensitivity to the emulsion E6, without substantially affecting the contrast and

granularity.

EXAMPLE 10

  The procedure of Example 8 is repeated, except that dyes A and B are replaced by dye C. Dye C has the formula: ## EQU2 ## -C:

I I I \

CL--. N N

% / I 1 + 1

I I I

I I -1

  * - * - * - 0 3H * - e - SO-0 By exposure and treatment as in Example 6,

gets similar results.

EXAMPLE 11

  The procedure of Example 8 is repeated except that the dyes A and B are replaced by the dye D. The dye D has the formula:

/% / \ AND / \ /%

* * \ I / * I

  S | I I * = - * == -. He I PH-. *, 4 * .e PX --e to 4 / to -4

* N N TO

I 1 + 1

* I

I I

* I

II O

e, S J3H I i -1 I * - e * * - $ O

* I I

(1H *

  By exposure and treatment as in Example 6,

gets similar results.

EXAMPLE 12

  The procedure of Example 8 is repeated, except that the dyes A and B are replaced by the document E. The dye E has the formula:

* S S

\ / \ AND / \ /

  * * I / e I = e-e. I I CL-- / - * e-CL * tI

I 1 + 1

e I

I I

* e

I I

*!

S3

50IH TO

I -1

0 - O = S -O

  By exposure and treatment as in Example 8,

gets similar results.

TABLE I

  Sample sense. relative Contrast Contrast Granularity shoulder emulsion at D = 1 mid-scale at D = 1.0 * Example 1 E1 (control) 100 100 2.32 1.32 24.6 Example 2 E2 (control) 104 110 2.53 1.01 24.3 Example 3 E3 (invention) 114 120 3.26 1. 41 26.5 Example 4 E4 (invention) 127 136 3.01 1.25 26.8 Example 5 E5 (invention) 136 136 2.50 1.27 26.6

Claims (10)

  1 - silver halide photographic emulsion comprising silver halide grains having a core (core) of bromide or bromoiodide, characterized in that these grains comprise from 1 to 50 mol% of chloride, relative to the total amount of silver of the grain located in a zone, at the periphery of the grain, a spectral sensitizing dye being absorbed on said grains, said dye corresponding to the formula: Z1 C - (L1 = L2) n1-CH = C Z2% '- N + Ne I! R1 R2   Z1 and Z2 independently represent the atoms necessary to complete a benzoxazole, naphthoxazole, benzothiazole, naphthothiazole, benzimidazole or naphthoxidazole radical, where the aromatic rings may be substituted by groups such as alkyl, aryl, aralkyl, alkaryl, halogen, cyano groups ; L1 and L2 independently represent a methine group, such as -CH =, C (CH3) =, -C (C2H5) =; R1 and R2 independently represent a sulfoalkyl radical such as O-sulfoethyl, oe-sulphobutyl; and n is 1 or 2.   2 - The photographic emulsion of claim 1, which is monodisperse. 3 - Photographic emulsion according to claim 1 or 2, wherein the core of the grain contains up to 40 mol% of iodide relative to the total amount. of money present in the heart.   4 - photographic emulsion according to claims 1 to   3, in which the core and shell grains (core-   shell) contain from 1 to 30 mol% chloride based on the total amount of silver present in the grain. The photographic emulsion of claim 4, wherein the grains contain from 2 to 20 mol% chloride. 6 - photographic emulsion according to any one of   Claims 1 to 5, wherein the area   peripheral o is located the chloride has a thickness greater than 100 and represents less than 40 % of the grain radius.   7 - photographic emulsion according to claim 6, 1S characterized in that the peripheral zone o is placed the chloride has a thickness representing 10 to % of the grain radius.   8 - photographic emulsion according to any one of   Claims 1 to 7, wherein the heart grains   and shell have a bromoiodide core containing up to 15 mol% of iodide based on the total amount of silver of the heart and the peripheral zone of chlorobromide whose thickness is greater than 100   represents less than 40% of the grain radius.   9 - photographic emulsion according to claim 8, characterized in that the chloride content of the grain is between 2 and 20 mol% relative to the total amount of grain money.   - Photographic emulsion according to any one of   Claims 1 to 9, characterized in that the grains   include a heart (core), a first shell (shell) of silver bromide and a second outer shell comprising chloride.   11 - Photographic emulsion according to any one of   Claims 1 to 10, characterized in that it is   chemically sensitized optimally.   12 - photographic emulsion according to claim 11, characterized in that the shell containing chloride   receives optimal chemical sensitization.   13 - Invertible color photographic product characterized in that it contains an emulsion according to   any of claims 1 to 12.   14 - Process for preparing a color inhalable silver halide photographic emulsion, comprising the following steps: a) precipitation of a core emulsion; b) precipitation of a shell emulsion; c) chemical sensitization, characterized in that at least in a portion of IS step b), chloride or silver chlorobromide is precipitated, and further characterized in that during or after the step of chemical sensitization is added at least one dye represented by the following formula: Z1 C - (L1 = L2) n_1-CH = C Z2 IN R1 R2   Z1 and Z2 independently represent the atoms necessary to complete a benzoxazole, naphthoxazole, benzothiazole, naphthothiazole, benzimidazole or naphthoxidazole radical, where the aromatic rings may be substituted by groups such as alkyl, aryl, aralkyl, alkaryl, halogen, cyano groups ; L1 and L2 independently represent a methine group, such as -CH =, C (CH3) =, -C (C2H5) =; R1 and R2 independently represent a sulfoalkyl radical such as O-sulfoethyl, -sulfobutyl; and n is 1 or 2.