BE894963A - DIRECT POSITIVE PHOTOGRAPHIC PRODUCTS - Google Patents

Description

       

  Positive-direct photographic products.

  
The present invention relates to a positive-direct photographic product comprising a support, at least one emulsion layer containing a dispersion medium and photosensitive silver halide grains capable of forming an internal latent image, and a nucleating agent.

  
The most commonly used photographic products contain one or more layers of photosensitive silver halide emulsion. Their wide use is due to their ability to provide excellent quality images and their high sensitivity which allows them to be used in portable cameras under very different lighting conditions.

  
However, silver halide photographic products are significantly limited with regard to observing the photographic image. First, photographic exposure of an emulsion layer to silver halides does not produce an immediately visible photographic image; it produces in the emulsion an invisible latent image which it is necessary to develop to produce a visible image. Historically, this means that the photographic product must be removed from the camera and treated in one or more aqueous solutions, to obtain a visible image. Secondly, in most cases, the first image obtained is negative, and a second exposure of another photographic product must be carried out, behind the negative image, and

  
when processing this product, to obtain a visible positive image of the subject initially photographed.

  
The first limitation can be overcome by using diffusion transfer imaging techniques, and the second limitation can be overcome by using positive-direct imaging methods, in particular the positive-direct imaging methods by inversion.

  
A - Direct positive image formation by inversion

  
Photographic products which make it possible to obtain images whose optical density is directly related to the lumination received at the exhibition are called negative effect photographic products. A positive photographic image can be formed by first producing a negative photographic image and by forming therefrom a second photographic image which is a negative with respect to the first negative image, i.e. a positive image. In the photographic technique, a "direct positive image" is called the positive image obtained without passing through a negative image.

   In color photography, we usually form positive dye images which are not direct positive images, by implementing an inversion treatment process in which we first form a negative silver image, then we form in the same product. photographic an image complementary to the silver image which is a positive dye image. The expression "positive-direct by inversion" applies to photographic products and photographic processing methods, direct positive, which make it possible to obtain a positive dye image without passing through a negative silver image.

   Direct positive photography in general and positive reverse direct photography in particular are advantageous techniques in that they provide more direct means for obtaining positive photographic images.

  
A common means for forming direct positive images is to use photographic products which contain grains of silver halides forming an internal latent image. After image exposure, the silver halide grains are developed by a surface developer, i.e. a developer which hardly reveals the image sites

  
  <EMI ID = 1.1>

  
silver genure. Simultaneously, either by uniform exposure to light or by the use of a nucleating agent, the silver halide grains are subjected to development conditions which would cause haze of an image forming photographic product. latent on the surface. The silver halide grains forming an internal latent image which are subjected to the exposure during the exposure following an image develop, under these conditions, at a slow speed when compared to the rate of development of the silver halide grains forming an internal latent image which have not been exposed according to an image. This results in the formation of direct positive silver images.

   In color photography, the oxidized developer that is formed during film development is used to form a direct positive dye image by inversion. Much work has been done on the problems of multi-color photographic imaging directly by inversion in conjunction with photographic imaging by transfer transfer.

  
It has been found advantageous to use nucleating agents, preferably on exposure to uniform light, in the process as described above. The expression "nucleating agent" is the expression customary in the photographic art and applies to a veiling agent capable of ensuring the selective development of the silver halide grains forming an internal latent image which have not been exposed according to an image, preferably to the silver halide grains having an internal latent image formed by the exposure following an image.

  
Although nucleating agents have been known for a long time in the photographic art, more recent research has been made on nucleating agents which are effective at relatively low concentration levels and which can be incorporated directly into silver halide emulsions.

  
Positive-direct inversion emulsions, useful in the presence of nucleating agents adsorbed on the grains, include emulsions capable of forming latent image centers, mainly inside the silver halide grains, in contrast

  
on their surface, these emulsions being hereinafter called emulsions forming an internal latent image. These emulsions may take the form of converted silver halide emulsions.

  
The inverting positive-direct emulsions have well-known drawbacks when compared to conventional silver halide emulsions with a negative effect. Although it is possible to increase photographic sensitivities by appropriately balancing surface sensitivities and

  
internal sensitivities, direct positive emulsions by inversion cannot reach the photographic sensitivities of emulsions with silver halides, forming a latent image on the surface, the fastest. Second, direct positive emulsions by inversion have limited exposure latitude. When the lumination used during the exposure is too great a second inversion occurs, that is to say, in the ranges which receive the most important lumination, a negative image is produced. This second drawback significantly limits the use, in cameras, of positive-direct photographic products by inversion, since a shot on the spot does not always make it possible to ensure the control of the conditions of exposure .

   For example, a scene which one wishes to photograph and which presents a very high contrast can lead to the phenomenon of second inversion in certain image ranges.

  
A schematic representation of the phenomenon of second inversion is provided by FIG. 1, which represents the curve providing the density as a function of the exposure. Characteristic curve 1, which is simplified to exaggerate the characteristic features of the curve, represents the characteristic curve of a positive-direct emulsion by inversion. When such an emulsion is applied in a layer on a support, then exposed and treated, a density is obtained. The characteristic curve is obtained by joining the points corresponding to different density levels obtained according to the exposures. For exposures below point A, underexposure occurs, and a maximum density is obtained which does not vary with exposure.

   For exposure levels between A and B, positive-direct image formation is obtained by inversion, since the density varies inversely with exposure. If the exposure level is between points B and C, there is an overexposure and in this interval B, C,

  
the density no longer varies according to the exposure. If a subject to be photographed exhibits intensities of reflected light which vary locally over a large interval, a photographic product which contains a positive-direct emulsion by inversion could be exposed simultaneously, in different ranges, to exposure levels lower than point A and higher than point B. The photographic image obtained could still be pleasant to see, but this image would not represent the details in the shaded areas and in the areas of great light of the subject. If you try to increase the exposure of such a subject, to reach the details in the dark areas, you may increase the exposure in the areas of bright light at levels above point C.

   In this case, the phenomenon of double inversion would occur, that is to say that the areas subjected to overexposure beyond the level C would appear in the form of a very annoying negative image, because the density of this image would then increase directly depending on the exposure. However, the useful exposure latitude can be increased by increasing the exposure difference between points A and B, but this means is not always desirable since it decreases the contrast below optimal levels for most topics. Consequently, to reduce the phenomenon of double inversion, it is more profitable to increase the exposure interval which separates the points B and C so that the overexposed areas are less likely to provide negative images.

   In actual practice, the characteristic curves have less sharp angles than those in Figure 1.

  
B - Image transfer photography

  
Image transfer photography has reduced the time between exposure and obtaining a visible image. The photosensitive silver halide emulsion layer (s) can be contacted with a treatment solution immediately after exposure. While the development of the silver halides takes place, a silver image (black and white) or a dye image can be formed by transfer in a receiving layer where this image is visible. In this way, one can have access to a visible photographic image in a few minutes, and even a few seconds.

  
However, although measured in seconds, the image access time remains an important limitation of silver halide photography by image transfer. The opportunities to photograph a subject can be fleeting, and the photographer needs to visually verify as quickly as possible whether the photographic image is acceptable.

  
While image transfer processes have reduced the image access time of silver halide photographic products, this advantage has not been achieved without further sacrifice. An important long-term problem in image transfer photography has long been money consumption. Color photographic products, whether conventionally processed, or dye image transfer products, require relatively high silver titers to provide maximum photographic speed. Usually it takes about 1000 mg of silver per m2 in each of the elements recording blue, green and red. In a conventionally processed color product, the final image does not contain silver, which is, in principle, fully recoverable. On the contrary, in

  
photography by image transfer, silver is rarely recovered, and in composite products with a unitary structure, all the money remains in the product containing the visible image.

  
Another drawback inherent in image transfer photography is the reduction in image clarity due to scattering. When the image-forming substances diffuse from the silver halide emulsion layers or from adjacent layers, this diffusion occurs both towards the receiving layer and laterally, which causes the image to spread and loss of sharpness. Sharpness can be improved by shortening the diffusion path to the receiving layer. This can be done by adjusting the number and thickness of the layers to be crossed.

  
Unfortunately, the minimum thickness of the silver halide emulsion layers is limited by the size of the silver halide grains and by the ratio of the gelatin mass to that of the silver halides.

  
In addition, in composite products operating by image transfer, which contain three superimposed dye-forming elements, the dyes diffusing towards the receiving layer must pass through the intermediate dye-forming elements and the separating interlayers.

  
Another problem with image transfer photography is the variability of image density as a function of temperature. Since the opportunities to take photographs arise in a wide variety of temperature conditions, and the main advantage of image transfer photography being rapid access to the image, it follows that the ability

  
to give acceptable images under various temperature conditions is also an important factor for products operating by image transfer. In this respect, image transfer photography is very different from conventional photography, because in the latter, processing is rarely carried out without regulation of

  
temperature.

  
There are a number of limitations in the production of images transferred with dyes. For example, high silver securities, such as

  
as noted above, and also greater amounts of dye-forming substances than required by stoichiometry are required to obtain maximum acceptable densities of the transferred images.

  
Since the transfer efficiency of the dye is less than the stoichiometric amount, more dye-forming substances must be incorporated into the photographic products, and the thickness of the layers must be increased to introduce increased amounts of these substances. In addition, the speed of release of the dyes to be transferred can have an effect on the time of access to the visible image. Where the development reaction product serves to prevent transfer of the dye, as in the case of many conventional positive-effect dye image formers, the rate of development of silver halides also limits the maximum rate to which

  
the dye becomes available for transfer, because too rapid release of the dye compared to

  
the rate of development of silver halides can result in loss of discrimination.

  
Improving one or more of these factors can therefore significantly improve the transfer

  
of the dye image.

  
C - Tabular silver halide grains

  
Different grain patterns, regular and irregular, have been observed in photographic silver halide emulsions. Regular grains are often cubic or octahedral in shape. The grain edges can be rounded due to ripening effects and, in the presence of strong ripening agents such as ammonia, the grains can even be spherical or have the form of thick, almost spherical tablets, as described , for example, in the United States patent

  
3,894,871 and by Zelikman and Levi in "Making and Coating Photography Emulsions", Focal Press, 1964, pp. 221-223. We have frequently observed in variable proportions rod-shaped or tabular-shaped grains associated with grains of other shape, especially when the pAg (i.e. the negative logarithm of the silver ion concentration) of the emulsions were modified during precipitation, as is the case, for example, in single-jet precipitation processes.

  
Tabular grains, that is to say grains whose surface is extended in two directions in comparison to their thickness, have given rise to numerous studies, but the grains thus studied were often grains of large size without photographic utility.

  
What, in the present description, is understood to be a tabular grain is a grain delimited by two parallel or practically parallel crystalline faces which each have a significantly larger surface than any other face of the crystal constituting the grain. The shape index, i.e. the ratio of the diameter to the thickness of a tabular grain, is therefore clearly greater than 1: 1. Tabular-grain silver bromide emulsions of high shape index have been described by De Cugnac and Chateau in "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening", Science and Photographic Industries Vol. 33, N [deg.] 2
(1962), pp. 121-125.

  
From 1937 until around the 1950s, the Eastman Kodak Company sold a film for radiography called "Duplitized" and whose reference was "No Screen X-ray Code 5133". This product included on each side of a film support a sulfur-sensitized silver bromide emulsion. Since the emulsions were intended for direct exposure to X-rays, they were not spectrally sensitized. The grains were tabular and had an average shape index of 5 to 7: 1 and these tabular grains represented more than 50% of the projected surface, while the non-tabular grains represented more than 25% of the projected surface.

  
However, none of the tabular grain emulsions of silver bromoiodide described in the prior art has, in fact, a high average shape index. The question of tabular grains of silver bromoiodide is discussed by Duffin, Photographie Emulsion Chemistry, Focal Press, 1966, pp. 66-72 and by Trivelli and Smith, in "The Effect of Silver Iodide Upon The Structure of Bromo-Iodide Precipitation Series", in The Photographic Journal, Vol. LXXX, July 1940, pp. 285-
288. According to Trivelli and Smith, there is a marked decrease in the grain size and the shape index as iodide is introduced.

  
Gutoff, in "Nucleation and Growth Rates During the Precipitation of Silver Halide Photography Emulsions", Photography Sciences and Engineering, Vol. 14, N [deg.] 4, July-August 1970, pp. 248-257, describes the preparation of bromide and silver bromoiodide emulsions by

  
a single jet process using a continuous precipitation apparatus.

  
Methods for preparing emulsions consisting mainly of silver halides in the form of tabular grains have recently been described in publications. The patent of the United States

  
4,063,951 describes the formation of tabular silver halide crystals bounded by cubic faces (100) and whose shape index (calculated with respect to the edge length) is between 1.5 and 7: 1. The tabular grains have a square and rectangular shape characteristic of the crystal faces
(100). US Patent 4,067,739 describes the preparation of silver halide emulsions consisting mainly of twin crystals of the octahedral type; these crystals are formed by first preparing crystalline seed seeds which are then grown by Ostwald ripening

  
in the presence of a silver halide solvent and the grain growth is completed without renucleation or maturation of Ostwald by controlling the pBr (negative logarithm of the bromide ion concentration). U.S. Patents 4,150,994 and 4,184,877 relate to the formation of tabular twin silver halide grains of octahedral shape from seed crystals with an iodide content of at least 90 % by mole. In several of these references, the increase in covering power is mentioned and it is indicated that the emulsions obtained are useful for black and white and color films. According to U.S. Patent 4,063,951,

  
the upper limit of the shape index of these tabular grains is 7: 1; but, according to the very low shape indices obtained in the examples (2: 1), this upper limit of 7: 1 appears to be overestimated. It is clear, as the reproduction of the examples and the examination of the published photomicrographs show, that the grain shape indices obtained according to the above references are also less than 7: 1.

  
U.S. Patent 4,184,878, as well as British Patent 1,570,581 and published German patent applications 2,905,655 and 2,921,077, describe methods of direct positive image formation using emulsions with tabular grains practically similar to those described in US Pat. No. 4,184,877, but which include an internal sensitizer, these emulsions being, moreover, treated with a developer which contains a nucleating agent.

  
The present invention relates to a direct positive photographic product which comprises a support to which is applied at least one emulsion layer which comprises a dispersion medium, grains of silver halides capable of forming an internal latent image and an agent. nucleation material which is characterized in that at least 50% of the total projected area of the silver halide grains is provided by tabular grains which have a thickness

  
  <EMI ID = 2.1>

  
greater than 8: 1, this shape index being defined by the ratio of the diameter of the grain to the thickness of the grain, the diameter of the grain being defined by the diameter of a circle having an area equal to the projected area of this grain.

  
The present invention therefore uses the advantages of tabular grain emulsions to form positive-direct images, and more particularly positive-direct images by inversion. The photographic products according to the invention which comprise the emulsions as defined above have improved stability, and make it possible to obtain images under conditions which are less dependent on temperature when compared to positive-direct emulsions by inversion with non-tabular grains- In addition, the photographic products according to the invention, in certain particularly advantageous embodiments, allow a greater latitude of exposure without the disadvantage of the phenomenon of second inversion.

  
The photographic products according to the invention which comprise tabular grain emulsions, of high shape index, chemically and spectrally sensitized, have significant advantages as regards the relation speed / granularity, the sharpness of the images, and the differences in sensitivity to blue and blue minus. Tabular grain emulsions with a high shape index improve the clarity of the images obtained in the underlying emulsion layers when they are arranged so as to receive exposure light which is devoid of diffuse light . These emulsions are particularly effective from this point of view when applied in layers so that they receive the exposure light first.

  
When these emulsions are sensitized spectrally outside the blue region of the spectrum, the silver bromide and silver bromoiodide emulsions, with tabular grains, of high shape index, exhibit a great separation in their sensitivity to blue spectrum by comparison to the region of the spectrum to which they are spectrally sensitized. Silver bromide and silver bromoiodide emulsions, with tabular grains, of high shape index, sensitized to blue minus, are much less sensitive to blue than to blue minus

  
protective filter to provide acceptable minus blue exposure records when exposed to neutral light, for example daylight corresponding to a color temperature of

  
  <EMI ID = 3.1>

  
Tabular, high shape index, have improved speed / granularity relationships compared to prior art tabular grain emulsions and compared to prior art silver bromoiodide emulsion having the best known speed / granularity relationships. Very considerable increases in the sensitivity to blue of silver bromide and silver bromoiodide emulsions, with tabular grains of high shape index, can be obtained, compared to their natural sensitivity to blue when incorporating spectral blue sensitizers.

  
Composite photographic films forming transfer diffusion images which contain one or more layers of emulsion, with tabular grains, of high shape index, can form visible images with a shorter access time after the start of the treatment. . In addition, composite imaging films by transfer diffusion can form images having improved clarity. These composite films are particularly advantageous when applied to the formation of dye images,

  
to several colors, because they make it possible to reduce the titles in silver, ensure a more efficient use of the dye image formers, allow more advantageous layer arrangements and make it possible to reduce or eliminate the substances used as yellow filters.

  
  <EMI ID = 4.1>

  
the simplified characteristic curve of a positive-direct image-forming emulsion by inversion, and FIG. 2 represents a schematic diagram corresponding to a device for determining the angular diffusion of the exposure light.

  
D - Tabular emulsions forming latent images

  
internal

  
The emulsions of the photographic products according to the invention are emulsions forming latent iternal images, with grained grains, of high shape index. These emulsions include a dispersion medium, grains of silver halides capable of forming an internal latent image and a nucleating agent.

  
According to the present invention, the term "high shape index" has the following meaning: it applies to silver halide grains whose average shape index is greater than 8: 1 and they represent at least 50 % of the total projected area of the silver halide grains.

  
The tabular silver halide grains forming an internal latent image, as defined in the present description, or an average shape index greater than 8: 1 and advantageously greater than 10: 1.

  
Under optimal preparation conditions, grains can be prepared whose shape index can reach 50: 1 and even 100: 1 or more. For a determined diameter, the smaller the thickness of the grains, the higher their shape index. The grains which have a desired shape index according to the present invention are those whose average thickness is less than

  
  <EMI ID = 5.1>

  
most particularly less than 0.2 µm. Tabular grains are usually of medium thickness

  
  <EMI ID = 6.1>

  
although thinner tabular grains can be used, for example tabular grains whose thickness

  
  <EMI ID = 7.1>

  
the silver halide grains which have the characteristics of diameter and thickness indicated above represent at least 70% and preferably at least 90% of the total projected surface of the silver halide grains.

  
The grain characteristics of the silver halide emulsions indicated above, in particular the average shape indices and the percentage of the total projected surface area of the tabular silver halide grains can be easily demonstrated by well-defined methods. known in the art. As indicated, the expression "shape index" designates the ratio of the diameter of the grain to the thickness of these grains. The term "diameter" itself is defined as the diameter of a circle having an area equal to the projected area of the grain as it appears on a photomicrograph or on an electron micrograph of the sample. emulsion.

   From the shadows cast by an electron micrograph of an emulsion, it is possible to determine the thickness and diameter of each grain and to identify the tabular grains.

  
These grains have large, substantially flat opposite main faces. The opposite main crystal faces of each tabular grain are much larger than any other crystalline face of the grain. By measuring the length of the shadow cast by each tabular grain, we can determine its thickness.

  
By comparing the thickness to the diameter, the shape index is determined. In practice it is usually much simpler to obtain an average thickness and an average diameter of the tabular grains and to calculate the average shape index in the form of the ratio of these means. Either we use the average of the individual shape indices to determine the average shape index, or we use the means of thicknesses and diameter to determine this average shape index, we obtain, within the measurement tolerances possible grains, average shape indices which do not differ significantly. We can do

  
the sum of the areas projected by the tabular silver halide grains and the areas projected

  
of the other non-tabular silver halide grains on a micrograph and from these two different results it is possible to calculate the percentage of the total projected area of the silver halide grains corresponding to the tabular grains. The expression "projected surface" has the same meaning as the expression "projection surface" or "projective surface" usually used in this field as mentioned, for example, by James and Higgins, Fundamentals of Photography Theory. Morgan and Morgan, p. 15.

  
The emulsions with tabular grains and high shape index forming internal latent images of the photographic products according to the invention can be prepared simply by modifying the methods of preparation of the emulsions with tabular grains and high shape index so as to promote the formation of center internal latent image for exposure. These results can be obtained using techniques similar to those described in the examples of U.S. Patents 3,206,313, 3,761,276, 3,923,513, and 4,035,185 cited above, which illustrate the preparation of direct emulsion by usual inversion. The silver halide grains forming internal latent images prepared by these methods have a mean diameter

  
  <EMI ID = 8.1>

  
grains with a high form index are degraded if high levels of halide conversion are used, preferably the silver halide conversion processes will not be used. Preferred methods for modifying tabular grain and high shape index emulsions during their preparation to promote internal latent image formation are described in the description below.

  
Perhaps the simplest way to promote the formation of internal latent images is to incorporate a metallic dopant inside the tabular grains at the time of their formation. The doping agent may be present in the container where the grains are formed before the introduction of the silver salt. According to another embodiment, the metal dopant can be introduced during the stage of growth of the silver halide grains, at any time during the precipitation, either by interrupting the additions of silver salts. and halides either without interrupting these introductions.

  
Iridium is a metal dopant which is particularly advantageous. It is preferably incorporated into the silver halide grains at a concentration

  
  <EMI ID = 9.1>

  
mole of money. Iridium can easily be introduced into the container where precipitation takes place, in the form of a water-soluble salt, such as an alkali metal salt of a halogeniridium coordination complex, such as sodium or potassium hexachloroiridate or hexabromoiridate. Examples of incorporation of iridium-based dopants in the silver halide grains are described in US Patent 3,367,778.

  
Lead is also a metal dopant which is particularly appreciated for promoting formation

  
of internal latent image centers. Lead is a dopant usually used to prepare direct darkening or photodevelopable emulsions and can be used in a similar concentration range.

  
  <EMI ID = 10.1>

  
lead base is present at a concentration at least equal to moles per mole of silver. Lead concentrations of up to 5 x 10, advantageously

  
2 x 10-2 moles per mole of silver is useful. Lead-based dopants can be introduced by operating as for iridium-based dopants, in the form of a water-soluble salt, such as lead acetate, lead nitrate and lead cyanide. Lead-based dopants are particularly described in US Patents 3,287,136 and 3,531,291.

  
Another method of promoting the formation of internal latent image centers consists in stopping the precipitation of the silver halide grains after the formation of the nuclei used to prepare the grains by subsequent deposition, then in chemically sensitizing the surface of these nuclei. . Then we continue to precipitate the silver halides to form an outer envelope surrounding the nuclei. The particularly advantageous chemical sensitizers for this purpose are the sensitizers based on medium chalcogen, that is to say the sensitizers based on selenium sulfur and / or tellurium. Advantageously, the sensitizers based on medium chalcogen are used at concentrations of between 0.05 mg and 15 mg per mole of silver. Preferred concentrations are between 0.1 mg and
10 mg per mole of silver.

   Other advantages can be obtained by using gold-based sensitizers in combination with these sensitizers. Advantageously, these sensitizers based on gold are used at concentrations whose value is between 0.5 and 5 times the value of the concentrations of the sensitizers.

  
based on medium chalcogen. Preferred concentrations of sensitizers based on gold are usually between 0.01 and 40 mg per mole of silver, more particularly between 0.1 mg and 20 mg per mole of silver. The value of the contrast factor can be controlled by controlling the ratio of the medium chalcogen-based sensitizer to the gold-based sensitizer, as mentioned more particularly in United States patent 4,035,185. United States of America 3,761,276 and 3,923,513 provide specific examples of internal awareness

  
means of sensitizers based on medium chalcogen.

  
Although it is usually advantageous to include foreign substances, i.e. substances other than silver and halogens, to form the internal sensitization sites in the tabular grains, this is not essential . The formation of awareness sites by the introduction of foreign substances is defined below "formation of internal chemical awareness sites" to distinguish this process from the process of forming internal physical awareness sites. It is possible to form internal physical awareness sites by forming irregularities in the crystal lattice to capture electrons formed photolytically.

   These internal irregularities can be created by discontinuities during the precipitation of silver halide grains, or by sudden changes in the halide content of tabular grains. For example, it has been noted that if we first precipitate nuclei of tabular silver bromide and then if we envelop these nuclei with an external envelope of silver bromoiodide whose iodide content is greater than 5 % by mole, it is not necessary to chemically sensitize the interior of the silver halide grains to form direct images by inversion.

  
The silver halides surround the internal sensitization site in the tabular grains, The minimum quantity of silver halides in the outer shell is that which is just sufficient to prevent access to the developer used in the treatment of internal latent image. This minimum amount will vary depending on the dissolving power of the silver halide grains which the developer has during development. When using developers having very low silver halide dissolving power, the latent image centers can be arranged only a few planes of the crystal lattice below the surface of the tabular silver halide grains.

   If the internal latent image centers form at the center of the grain or near the center of the grain, as when a metallic dopant is used in the container where the precipitation of silver halides takes place, at the beginning of this precipitation, then most or all of the silver halides forming will be between the latent image sites and the surface of the grain. On the other hand, if tabular silver halide grains are precipitated so as to obtain practically their final size and shape index, before internal sensitization, it is sufficient to add only a small quantity of halide additional money to protect the awareness sites from the action of the surface developer or by sub-surface action.

  
The arrangement of internal awareness sites in silver halide grains is particularly illustrated in US Patent 3,917,485 and in "Research Disclosure" Vol. 181, May 1979, Article 18155. Since the formation of germs is critical if one wishes to obtain tabular grains with a high shape index, it is usually preferred to delay internal sensitization until the stage of growth of tabular grain formation is at least started. When the internal sensitization is delayed until the tabular grains have practically reached their desired shape and shape index, the additional silver halides can then be precipitated on

  
tabular grains by any conventional method of precipitating silver halides, including

  
by operating according to the Ostwald maturation process of a mixed envelope emulsion, as described in US Patents 3,206,313 and 3,317,322.

  
The dose of overexposure which can be tolerated without encountering the phenomenon of second inversion can be increased by incorporating into the tabular silver halide grains metal dopants suitable for this purpose. It is possible, for example, to use dopants based on divalent and trivalent metal cations. The preferred divalent and trivalent metallic dopants are the dopants based on manganese, copper, cadmium, zinc, lead, bismuth and the lanthanides. The lanthanides are elements 56 to 71 of the periodic table of the elements. Erbium is a particularly advantageous lanthanide. These dopants are advantageously used at lower concentrations

  
  <EMI ID = 11.1>

  
moles per mole of silver must be present in the container where the precipitation of the silver halides takes place. The doping agent modifying the phenomenon

  
second inversion is effective if we introduce it

  
at any stage in the precipitation of silver halides. If the tabular silver halide grains consist of a nucleus and an external envelope, the doping agent modifying the phenomenon of second inversion can be incorporated either in the nucleus or in the external envelope or in both . It is advantageous to introduce the doping agent during the last stages of precipitation, for example during the precipitation of the external envelope for the reasons which have been mentioned previously. These metal dopants can be introduced into the container in which the precipitation of silver halides takes place, in the form of a water-soluble metal salt, such as halides of bivalent and trivalent metals. Doping agents for silver halides based on zinc, lead and cadmium,

  
at similar concentrations, but for other purposes, are described in U.S. Patents 3,287,166, 2,950,972, 3,920,711 and

  
4,269,927. Other methods can be used independently or in combination with the metallic dopants as described above to improve the characteristics of second inversion.

  
Tabular grain emulsions with high shape index, forming internal latent images, which are particularly useful for preparing the photographic products according to the invention are the silver bromide and silver bromoiodide emulsions. Taking into account the modifications necessary to form the internal sensitization sites and to incorporate the metallic dopants as described above, the silver bromoiodide emulsions with tabular grains having a high form index can be prepared by a precipitation process which is described below.

  
A dispersion medium is introduced into a conventional reactor for the precipitation of silver halides, equipped with an appropriate stirring device. In general, the dispersion medium thus introduced initially into the reactor represents at least approximately 10% and preferably from 20 to 80% of the total mass of the dispersion medium which will be present in the silver bromoiodide emulsion at the end of precipitation. The dispersion medium can be removed from the reactor by ultrafiltration during the precipitation of the silver bromoiodide grains, according to the indications of Belgian patent 886,645 and French patent

  
2,471,620; however, the volume of dispersion medium initially present in the reactor may be equal to or even slightly greater than the volume of the silver bromoiodide emulsion which will be in the reactor

  
at the end of the grain precipitation. Preferably, the dispersion medium introduced at the start consists of water or a dispersion of peptizer in

  
  <EMI ID = 12.1> water possibly containing other substances, for example one or more agents for the maturation of silver halides and / or metal dopants, described in more detail below. When a peptizing agent is present at the start, its concentration represents at least
10% and preferably at least 20% of the total of the peptizing agent present at the end of the precipitation of silver bromoiodide. An additional quantity of the dispersion medium is added to the reactor with the silver salt and the halides and optionally by means of a separate jet. Usually, the proportion of dispersing medium is adjusted, in particular in order to increase the proportion of peptizing agent, once the addition of the salts is complete.

  
  <EMI ID = 13.1>

  
by mass of bromide used to form grains of silver bromoiodide, is initially present in the reactor to adjust the concentration of bromide ions at the beginning of the precipitation of silver bromoiodide. In addition, at the start of precipitation, the dispersion medium contained in the reactor must in principle not contain iodide ions; in fact, the presence of iodide ions before the introduction of silver salt and bromide promotes the formation of thick grains which are not tabular.

   When in the present description, it is indicated that the reactor does not in principle contain iodide ions, this means, with regard to the ingredients present in the reactor, that if iodide ions are present in the reactor, their concentration relative to the ions bromide is insufficient to cause precipitation of a distinct phase of silver iodide. This is why, in practice, it is preferred to maintain the iodide concentration in the reactor below 0.5 mol% relative to the total amount of halides present in the reactor before the introduction of the silver salt. If the pBr of the dispersion medium is initially too high, the tabular grains of silver bromoiodide produced will be comparatively thick and therefore have a low shape index.

   Care is therefore taken to maintain the initial pBr of the reactor at a value equal to or less than 1.6 and preferably less than 1.5.

  
On the other hand, if the pBr is too low, this promotes the formation of silver bromoiodide grains which are not tabular; this is why, the pBr can be maintained equal to or greater than 0.6 and preferably greater than 1.1. It will be recalled that pBr is the negative logarithm of the concentration of bromide ions and that the pH, pCl, pI and pAg are respectively defined in the same way for the concentrations of hydrogen, chloride, iodide and silver ions.

  
During precipitation, the silver salt, bromide and iodide are added to the reactor according to well known techniques. In general, a solution of a soluble silver salt, for example a silver nitrate solution, is introduced into the reactor, together with bromide and iodide solutions. Bromide and iodide are also introduced in the form of an aqueous solution of one or more ammonium or alkali metal salts, for example sodium or potassium, or

  
  <EMI ID = 14.1>

  
magnesium or calcium. Silver salt, at least

  
at the start, is introduced into the reactor by a separate jet from that of the iodide. The iodide and bromide can be added to the reactor separately or as a mixture.

  
When a silver salt is introduced into the reactor, the nucleation phase of the grain formation process is started. A population of germs capable of constituting precipitation sites for silver bromide and silver iodide is formed as the addition of the silver salt, bromide and iodide continues . The precipitation of bromide and silver iodide on existing germs constitutes the growth phase of grain formation. The shape index of the tabular grains formed according to the present invention is less influenced by the concentration of iodide and bromide during the growth phase than during the nucleation phase. That’s why during

  
during the growth phase, it is possible to increase the latitude for fixing the pBr so as to have, during the introduction of the salts, a pBr of between approximately 0.6 and 2.2 and preferably between 0.8 and 1.6 . This latter interval is particularly preferred when the rate of germ formation continues appreciably during the introduction of the salts, as is the case in the preparation of emulsions with high polydispersity. If the pBr rises above 2.2 during the growth of the tabular grains, this leads to the formation of thicker grains, but there is in many cases a tolerance which makes it possible still to obtain shape indices greater than 8 : 1.

  
A variant for the introduction of silver salts, bromide and iodide consists in introducing these salts at the start or in the growth phase, in the form of fine grains of silver halides in suspension in a dispersion. The diameter of the grains is such that their maturation from Ostwald to form larger seeds is possible as soon as they are introduced into the reactor, if such seeds are present. The maximum useful grain diameter depends on the specific conditions prevailing in the reactor, for example the temperature and the presence of a solubilizing or maturing agent.

   It is thus possible to introduce grains of silver bromide, silver iodide and / or silver bromoiodide; since bromide and / or iodide preferentially precipitates over chloride, it is also possible to use grains of silver chlorobromide and silver chlorobromoiodide; these silver halide grains are preferably very small, that is to say that their average diameter is less than

  
  <EMI ID = 15.1>

  
Depending on the conditions relating to pBr set out above, the concentration and the flow rate of the jets of silver salts, bromide and iodide can be produced in suitable conventional forms. The silver salts and the halides are preferably introduced at a concentration of between 0.1 and 5 moles per liter, although wider intervals can be envisaged ranging from 0.01 mole per liter to saturation. The preferred precipitation techniques are those which make it possible to obtain the

  
shortest precipitation times by increasing the flow rates of silver salts and halides introduced during precipitation. This increase can be obtained by increasing either the flow rate or the concentration of the salt jets. It is preferred to increase the flow rate of the jets, but by keeping it below a threshold above which the formation of new germs would be favored, that is to say from which there would be a re-nucleation according to the indications given in the patents from the United States of America 3,672,900, 3,650,757,

  
4,242,445, as well as the publication of the German patent application 2,107,118, to the European patent application
80102242 and by Wey in Photography Science and Engineering, Vol. 21 N [deg.] 1, January / February 1977 p. 14 et seq. By avoiding the formation of additional germs in the growth stage, relatively monodispersed populations of tabular silver halide grains can be obtained. Emulsions with coefficients of variation of less than about 30% can be prepared. Recall that the coefficient of variation is the standard deviation of the grain diameter multiplied by one hundred and divided by the average grain diameter. If deliberately promoting renucleation during the growth phase, it is of course possible to form polydispersed emulsions whose coefficient of variation is significantly higher.

  
The iodide concentration in the silver bromoiodide emulsions according to the present invention can be controlled by acting on the introduction of the iodide. Any conventional concentration of iodide can be used. Even very low concentrations, for example as low as 0.05 mole percent, can be, as is known, advantageous. Preferably, the emulsions according to the invention contain approximately at least 0.1 mol% of iodide. Silver iodide can be incorporated into tabular grain emulsions of silver bromoiodide until the solubility limit of silver iodide in silver bromide is reached at the grain formation temperature. So for

  
  <EMI ID = 16.1>

  
in silver iodide can reach 40% by mole in the tabular grains of silver bromoiodide. In practice, the precipitation temperature can be lowered almost to room temperature, that is to say up to 30 [deg.] C, but in general, it is preferred to carry out the precipitation at temperatures between 40 and
80 [deg.] C. For most photographic applications, the maximum iodide concentration is limited to about 20% and preferably does not exceed about 15%.

  
The respective amounts of iodide and bromide introduced into the reactor during precipitation can be maintained in a fixed ratio, so as to obtain tabular grains of silver bromoiodide whose iodide concentration has a uniform profile, but it is possible to do vary this profile to obtain various photographic effects. Particular advantages can be obtained as regards the photographic sensitivity and / or the grain by increasing the proportion of iodide in an annular or eccentric region of the silver bromoiodide grains with a high shape index; this means that in these regions of the tabular grain, the iodide concentration is higher than it is in the center of the grain. The iodide concentration in the center of the grain can be between 0 and 5 mol% and that in the

  
  <EMI ID = 17.1>

  
minus 1 mol%, at the previous one, the iodide concentration can go up to the solubility limit of silver iodide in silver bromide; preferably the iodide concentration can reach up to
20% by mole, and optimally up to approximately
15% by mole.

  
A variant is to stop the addition of iodide or the addition of bromide and iodide before stopping the addition of silver salt, so that the excess bromide reacts with the silver salt . As a result, a shell of silver bromide is formed on the tabular grains of silver bromoiodide. It is therefore clear that the tabular grains of silver bromoiodide according to the invention can have practically uniform or variable iodide concentration profiles and that this variation can be controlled, if desired, to promote a higher iodide concentration. either inside or near or on the surface of the tabular grains of silver bromoiodide.

  
It has been unexpectedly noted that an increased latitude of exposure can be achieved before the onset of the second inversion by using higher iodide concentrations in the outer annular regions of the grains rather than in the central regions seeds. For example, if the grain is in the form of a nucleus surrounded by one or more external envelopes, it has been noted that one can increase the dose of exposure necessary to form the second inversion if one incorporates in one or more outer envelopes an amount of iodide which is at least 2 mol% higher than the iodide concentration present in the kernel of the grains. It is advantageous that at least one of these external envelopes has an iodide content which

  
is at least 6 mol% higher, particularly at least 10 mol% higher than the iodide content of the seed kernel. In a particularly advantageous embodiment, the core of the grains can be practically free of iodide. The relative iodide proportions of the cores and of the external envelopes of the grains are advantageously similar to those which have been described for the central and annular regions in the preceding paragraph. We can form 2,3 or even several external envelopes, the iodide content of each of them increasing relative to the content

  
silver halide iodide located in a more internal region.

  
Preparation of silver tabular grain bromoiodide emulsions with high form index

  
has been described with reference to a process providing emulsions which are neutral or non-ammoniacal; but the present invention is not limited to this particular process. Another process constitutes an improvement on that described in United States patent 4,150,994, as well as in the publications of German applications 2,985,655 and 2,921,077. In a preferred form, the concentration of silver iodide in the reactor below 0.05 mole per liter and the maximum diameter of the silver iodide grains initially present in the reactor below

  
  <EMI ID = 18.1>

  
Tabular grain silver bromide emulsions of high form index without iodide can be prepared by the method described in detail above and modified so as not to use iodide.

  
High bromide tabular grain silver bromide emulsions can also be prepared according to a method based on the indications given by De Cugnac and Chateau in the publication cited above.

  
High bromide silver bromide emulsions consisting of square and rectangular grains can be prepared by a method of using seed grains of

  
  <EMI ID = 19.1>

  
By keeping the pAg of the emulsion of seed seeds between 5.0 and 8.0, the emulsion is matured practically in the absence of a complexing agent of the silver ion other than the halides, so as to form tabular grains of silver bromide with an average shape index of at least 8: 1. The examples below provide other methods of preparing high-index-index tabular-grain silver bromide emulsions without iodide.

  
The variety of emulsions which can be used according to the invention can be illustrated by the fact that tabular grains of silver chloride can be prepared, the interior of which contains practically neither silver iodide nor silver bromide. To this end, a double-jet precipitation method is used according to which chloride and a silver salt are introduced at the same time into a reactor containing a dispersion medium in the presence of ammonia.

  
During the introduction of the chloride, the pAg in the dispersion medium is maintained between 6.5 and 10 and the pH between 8 and 10. At high temperature, the presence of ammonia tends to cause the formation of thick grains. This is why the precipitation temperature does not exceed 60 [deg.] C to obtain silver chloride emulsions with tabular grains of high shape index.

  
It is also possible to prepare tabular grains containing at least 50 mol% of chloride and, of which two opposite crystalline faces are in crystalline planes (111), at least one peripheral edge, according to a preferred embodiment, being parallel to a crystallographic vector (211) in the plane of one of the main faces. Such tabular grain emulsions can be prepared by reacting aqueous solutions of silver salt and halides containing chloride in the presence of an amount of an aminoazaindene, in an amount suitable for modifying the crystalline form. , and a peptizing agent containing a thioether bridge.

  
It is also possible to prepare tabular grain emulsions in which the grains contain chloride and bromide at least in one annular region of the grain and preferably throughout the grain. The regions of the tabular grains containing silver, chloride and bromide are formed by maintaining the molar ratio of chloride to bromide between 1.6: 1 and
260: 1 and maintaining the total concentration of halide ions in the reactor between 0.10 and 0.90 N during the introduction of the silver salt, chloride and bromide and possibly iodide, into the reactor. The molar ratio of silver chloride to silver bromide in tabular grains is between 1:99 and 2: 3.

  
The silver salts and the halides can be added to the reactor by means of surface or sub-surface supply tubes, by gravity feed or by means of devices which allow the rate of addition to be regulated. as well as the pH, pBr, and / or pAg of the contents of the reactor, as indicated in the patents of the United States of America

  
3 821 002 and 3 031 304 and by Claes in Photographische Korrespondenz, volume 102, n [deg.] 10, 1957, page 162. To obtain a rapid distribution of the reactants in the reactor, specially adapted mixing devices such as than those described in United States patents 2,996,287, 3,342,605,

  
3,415,650, 3,785,777, 4,147,551 and 4,171,224, British patent application 2,022,431A, German patent applications 2,555,364 and 2,556,885 and in Research Disclosure, volume 166, February 1978, publication 16662.

  
To precipitate tabular grain emulsions, a dispersing medium is initially present in the reactor. Advantageously, the dispersing medium is formed of an aqueous suspension of peptizer. The concentration of peptizer can be between 0.2 and about 10% by mass relative to the total mass of the constituents of the emulsion in the reactor. It is common to keep the peptizing concentration in the reactor below about 6% of the total mass, before and during the formation of the silver halide, and to later adjust the concentration to higher values. in vehicle of the emulsion (the term vehicle including the binder and the peptizer), by additional additions of vehicle, to obtain the optimal coating characteristics.

   The emulsion initially formed may contain about 5 to 50 g of peptizer per mole of silver halide, preferably about 10 to 30 g per mole of silver halide.

  
An additional amount of vehicle can be added later to bring the concentration up to

  
1000 g / mole of silver halide. Advantageously, in the finished emulsion, there are more than 50 g of vehicle per mole of silver halide. Once coated and dried in a photographic product, the vehicle forms approximately 30 to 70% by mass of the emulsion layer.

  
Vehicles can be chosen from the substances usually used in silver halide emulsions for this purpose. The preferred peptizers are hydrophilic colloids which can be used alone or in combination with hydrophobic substances. Suitable hydrophilic vehicles include substances such as proteins, protein derivatives, cellulose derivatives, for example cellulose esters, gelatin, for example gelatin treated with an alkaline agent (of

  
skin or bone gelatin) or gelatin treated with an acid agent (pigskin gelatin), gelatin derivatives, for example acetylated gelatin, and phthalylated gelatin. These and other vehicles are described in Research Disclosure, vol. 176, December 1978, publication 17643, section IX.

  
The vehicle, in particular hydrophilic colloids, as well as useful hydrophobic substances combined with them, can be used not only in the emulsion layers of the photographic products of the invention, but also in other layers, such as overlays , interlayers and layers placed below the emulsion layers.

  
The preparation of the silver halide emulsions according to the invention can comprise a step

  
of grain maturation and the preferred way consists in carrying out the maturation of the grains in the reactor during at least the formation of the silver bromoiodide grains. Solvents of known silver halides are used to promote maturation, such as for example an excess of bromide ion in the reactor. It is known, for example, that the bromide solution introduced into the reactor can itself promote maturation.

  
It is also possible to use other maturing agents, which can be entirely incorporated into the dispersing medium, in the reactor before the addition of the silver salt and the halides, or which can be introduced into the reactor at the same time as a or more of the silver salts, halides or peptizer. According to another embodiment, the curing agent can be introduced independently during the addition of the halide and the silver salt. Although ammonia is a known curing agent, it does not constitute a preferred curing method for the emulsions according to the invention, the speed / granularity relationship of which is the highest.

  
Advantageous ripening agents are those which contain sulfur. Thiocyanates can be used as the alkali metal salts, usually sodium and potassium, and ammonium thiocyanate. Conventional amounts of thiocyanate can be used, but preferred concentrations are generally between about 0.1 and 20 g of thiocyanate per mole of silver halide. The use of thiocyanates as maturing agents is described in US Patents 2,222,264, 2,448,534 and 3,320,069. Thioethers, such as those described in US Patents, can also be used conventionally. United States of America

  
3,271,157, 3,574,628 and 3,737,313.

  
Tabular grain emulsions of high shape index are preferably washed to remove soluble salts, by known techniques such as decantation, filtration and / or by jelly and filtration, as described in Research Disclosure , Flight. 176, December 1978; publication 17643, section II. It is particularly advantageous according to the present invention to complete the maturation of the tabular grains by washing after the end of precipitation, to avoid increasing their thickness, reducing their shape index and / or excessive increase in their diameter. Emulsions with or without a sensitizer can be dried and stored before use.

  
The methods for preparing tabular grains described above make it possible to obtain emulsions in which the tabular grains of index

  
high form represent at least 50% of the total projected area of the total population of silver halide grains; but additional benefits can be obtained by increasing the proportion of tabular grains. It is advantageous that at least 70% (and optimally at least 90%) of the total projected area is represented by tabular silver halide grains. Although the presence of small amounts of non-tabular grains is fully compatible with most photographic applications, the proportion of tabular grains can be increased to obtain the full benefits of flat grains.

  
Larger tabular silver halide grains can be mechanically separated from smaller, non-tabular grains in a mixed grain population using conventional separation means, such as a centrifuge

  
or a hydrocyclone. Separation by hydrocyclone is illustrated in US Patent 3,326,641.

  
The high-index-index tabular grain emulsions forming an internal latent image of the photographic products according to the invention are advantageously chemically sensitized on the surface, intentionally, to increase their photographic sensitivity. Surface chemical sensitizers are described, for example, in U.S. Patents 3,761,276, 3,923,513 and 4,035,185.

   Any surface chemical sensitizing agent which is known to be useful in silver halide surface forming emulsions may be used, but the height of the level of chemical surface sensitization is limited to the level which would increase the inversion sensitivity of the emulsion forming an internal latent image, but which would not compete with the internal awareness sites until displacing the centers of latent images, formed by exposure to light, from the inside the tabular grains towards the surface of the latter.

  
It is therefore advantageous to maintain a balance between internal sensitization and surface sensitization so as to obtain maximum speed, but internal sensitization will remain predominant. The tolerable levels of chemical surface sensitization can easily be determined by operating as follows:

  
A sample of a silver halide emulsion with tabular grains and high shape index, forming an internal latent image, with a silver content of 4 g / m is applied to a transparent film. The photographic product is then exposed to

  
the light provided by a 500 W tungsten filament lamp, through an object placed at 60 cm, for a period of between 0.01 s and 1 s. The photographic product is then developed in The developer Y, described below, which is a developer of the internal type, the concentration of iodide which will allow the interior of the grain to be noted, at 20 [deg.] C, for 5 min, then filter, wash and dry. The previous test is reproduced with a second identical sample which is exposed in the same way. It is then treated identically, but the developer X described below, which is a surface type developer, is used in place of the developer Y.

   The emulsion used in the context of the present invention will be declared an emulsion forming an internal latent image if, after development in the developer of the internal type, developer Y, it has a maximum density which is at least 5 times greater than the maximum density obtained with the same sample developed in the developer X of the superficial type. This difference between the densities obtained positively shows that the latent image centers of the silver halide grains are formed predominantly inside the grains, and are, for the most part, inaccessible to the developer of the type. superficial.

  
Developer X includes the following substituents:

  

  <EMI ID = 20.1>


  
below:

  

  <EMI ID = 21.1>
 

  

  <EMI ID = 22.1>


  
Silver halide emulsions, with tabular grains, high shape index, internal latent image, can be chemically sensitized at the surface with active gelatin, as indicated by TH James, The Theory of the Photographic Process 4th Ed., Macmillan, 1977, pp. 67-76; chemical sensitization can also be carried out with sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhodium, rhenium, or phosphorus sensitizers or with combinations of these different sensitizers and with a pAg of, for example, between 5 and 10 and a pH of

  
  <EMI ID = 23.1>

  
Disclosure, Vol. 120, April 1974, $ 12008, Research Disclosure, Vol. 134, June 1975, $ 13,452, to patents in the United States of America 1,623,499, 1,673,522, 2,399,083,

  
2,642,361, 3,297,447, 3,297,446; to the English patent

  
1,315,755; to United States of America patents

  
3,772,031, 3,761,267, 3,857,711, 3,565,633, 3,901,714

  
and 3,904,415 and English patent 1,396,696; chemical sensitization is optionally carried out in the presence of thiocyanates, as described in patent of the United States of America 2,642,361, in the presence of compounds containing sulfur such as those described in the patents of United States of America 2 521 926,

  
3,021,215 and 4,054,457. Emulsions can be chemically sensitized in the presence of chemical sensitization modifiers, that is, compounds known for their ability to suppress haze and increase speed under these conditions; such compounds are for example azaindenes, azapyri-dazines, azapyrimides, benzothiazolium salts and sensitizers having one or more heterocyclic rings. Examples of modifiers are given in US patents

  
2,131,038, 3,411,914, 3,554,757, 3,565,631, 3,901,714 as well as Canadian patent 778,723 and by Duffin in Photographic Emulsion Chemistry, Focal Press (1966), New York, pp. 138-143. In addition to the various chemical sensitizations defined above, or as an alternative to these sensitizations, the emulsions can be sensitized by reduction, for example with hydrogen, as described in the patents

  
  <EMI ID = 24.1>

  
again by subjecting them to conditions bringing together

  
a low pAg, for example less than 5 and / or at a high pH, for example greater than 8 or by means of various reducing agents such as stannous chloride, thiourea dioxide, polyamines and borane amines, as is described in U.S. Patents 2,983,609, 2,518,698, 2,739,060,

  
2,743,182, 2,743,183, 3,026,203, 3,361,564, as well as in Research Disclosure, Vol. 136, August 1975, $ 13654. One can carry out a chemical sensitization on the surface or a chemical sensitization in an area located immediately below the surface, as described in the patents of the United States of America 3 917 485 and

  
3,966,476.

  
Besides chemical sensitization, tabular grain emulsions with a high shape index

  
of the present invention can also be spectrally sensitized. It is particularly useful to use spectral sensitizing dyes which exhibit maximum absorption in blue and minus blue, that is to say in the red and in the green of the visible spectrum. In addition, for certain particular uses, spectral sensitizing dyes can be used which improve the spectral response in the region of the spectra situated beyond the visible part.

  
One can, for example, use absorbent spectral sensitizers in the infrared region.

  
Silver halide, tabular grain, high index form emulsions can be spectrally sensitized with dyes belonging to various classes, including cyanines and merocyanines, cyanines and complex merocyanines (tri-, tetra-, or polynuclear), oxonols, hemioxonols, styryl, merostyryl dyes and streptocyanines.

  
Spectral sensitizing dyes of the cyanine type comprise two heterocyclic rings of basic character linked by a methine bond; these heterocyclic rings are derived, for example, from quaternary salts of quinoleinium, pyridinium, isoquinoline. 3H-indolium, benz [e] indolium, oxazolium, oxazolinium, thiazolinium, thiazolium, selenazolium, sélénazolinium, imidazolium, imidazolinium, benzoxazolium, benzothiazolium, benzoselenazolium, benzimidazolium, naphthoxazolium, naphthothiazolium, naphthoselenazolium, dihydronaphtothiazolium, pyrylium and imidazopyrazinium.

  
The spectral sensitizing dyes of the merocyanine type comprise, linked by a methine bond, a nucleus of basic character of the type found in the formula of cyanines and an acid nucleus derived, for example, from barbituric acid, the 2-thiobarbituric acid, rhodanin, hydantoin, 2-thiohydantoin, 4-thiohydantoin, 2-pyrazoline-5-one, 2-isoxazoline-5-one, indan-1,3dione, cyclohexane -1,3-dione, 1,3-dioxane-4,6dione, pyrazolin-3,5-dione, pentane-2,4-dione, alkylsulfonyl acetonitrile, malononitrile, isoquinoline-4- one and chroman-2,4-dione.

  
One or more spectral sensitizing dyes can be used. Dyes are known with maximum sensitivities for wavelengths distributed over the entire extent of the visible spectra and providing spectral sensitivity curves of very different shape. The choice and the relative proportions of the dyes depends on the region of the spectrum to which the grains are to be sensitized and on the shape of the spectral sensitivity curve which it is desired to obtain. Dyes with partially overlapping spectral sensitivity curves often provide, when used in combination, a curve such that the sensitivity at each wavelength in the overlap region is approximately the sum of the sensitivities of each dyes.

   Thus, it is possible to use combinations of dyes having different maxima, in order to obtain a spectral sensitivity curve having a maximum situated between the sensitization maxima of each of the dyes.

  
Certain combinations of spectral sensitizing dyes produce an oversensitizing effect, i.e. provide in a region of the spectrum, a higher spectral sensitization

  
to that resulting from the use of one of the dyes alone at any concentration, or resulting from the addition of several dyes. Supersensitization can be achieved with selected combinations of spectral sensitizing dyes and other additives, such as stabilizers, anti-stars, developmental accelerators or inhibitors, coating aids, optical brighteners and antistatics. Mechanisms for explaining supersensitization and compounds for achieving it, are described by Gilman in "Review of the Mechanisms of Supersensitization", Photographic Science and Engineering, Vol. 18, 1974, pp. 418-430.

  
Spectral sensitizing dyes can also exert other actions on emulsions. These dyes can also play the role of anti-veil, stabilizers, accelerators or inhibitors of development, halogen acceptors or electron acceptors, as described in the United States patents. America 2,131,038 and

  
3,930,860.

  
For the spectral sensitization of grains of non-tabular silver halides or of weak shape index, the conventional amounts of dyes can be used. To take full advantage of the advantages offered by the present invention, it is preferable to absorb an optimal quantity of sensitizing dyes on the surface of the tabular grains of high shape index. By optimum quantity is meant the quantity sufficient to reach at least 60% of the maximum photographic speed which it is possible to achieve with these grains under the conditions provided for the exposure. The amount of dye to be used depends on the nature of the dye or the combination of dyes chosen, or on the size and shape index of the grains.

   It is known in the photographic technique that optimal spectral sensitization can be obtained with organic dyes when these dyes are used in an amount which makes it possible to produce a monolayer over approximately 25% to 100% or more of the total surface. available silver halide grain with surface sensitivity, as described for example by West in "The Adsorption of Sensitizing Dyes in Photographic Emulsions", Journal of Phys. Chem., Vol. 56, p. 1065, 1952; by Spence et al. in "Desensitization of Sensitizing Dyes", Journal of Physical and Colloid Chemistry, vol. 56 n [deg.] 6, June 1948, pp. 1090-1103; and by Gilman et al. in U.S. Patent 3,979,213.

   The optimum amounts and concentrations of dyes can be determined by the methods indicated by Mees, in Theory of the Photography Process, pp. 1067-1069, already cited.

  
In order to record the exposure to blue light in the emulsion layers, it is generally sufficient to use the natural sensitivity in the blue of bromide or silver bromoiodide; but appreciable advantages can be obtained by using spectral sensitizers, even with sensitizers whose main absorption is located in the region of the spectrum where these emulsions have their natural sensitivity. For example, the present invention particularly relates to obtaining specific advantages linked to the use of spectral sensitizing dyes for blue.

   Even when the emulsions of the present invention consist of tabular grains with a high bromide and silver bromoiodide shape index, significant increases in speed can be achieved by using spectral blue dyes. When it is planned to expose the emulsions of the present invention in the region of their natural sensitivity, gains in sensitivity can be obtained by increasing the thickness of the tabular grains to a value of

  
  <EMI ID = 25.1>

  
To sensitize in blue, silver bromide and bromoiodide emulsions with tabular grains of high shape index, dyes can be chosen from all known classes of spectral sensitizing dyes. Spectral blue sensitizers, which are preferred, belong to the class of polymethine dyes such as cyanines, merocyanines, hemicyanins, hemioxonols, merostyrylics. In general, it is possible to choose spectral sensitizers for blue, useful in these classes of dyes according to the absorption characteristics, that is to say according to the shade. Correlations have, however, been established with structural features which can serve as a guide for advantageous selection of blue sensitizers.

   In principle, the shorter the methine chain, the shorter the wavelength of the maximum sensitization. The nuclei also have an influence on absorption. The addition of cycles attached to the nucleus tends to favor absorption towards the longer wavelengths. The substituents can also modify the absorption characteristics.

  
Sensitizing dyes useful for sensitizing emulsions to silver halides are those described in "Research Disclosure", Vol.
176, December 1978, article 17643, section III.

  
Spectral sensitization can be carried out at any stage of the preparation of the emulsion

  
which has been found useful for this purpose. Habitually,

  
we carry out spectral awareness after the end

  
of chemical awareness. However, spectral sensitization can be carried out, either at the same time as chemical sensitization, or entirely before chemical sensitization, and even one

  
may start before the precipitation of the silver halide grains, according to the indications given to the patents of the United States of America 3 628 960 and 4 225 666. The patent of the United States of America

  
4,225,666 specifically provides for introducing the spectral sensitizing dye into the emulsion in stages, so that part of this dye is present before chemical sensitization, while another part is introduced after sensitization chemical. Unlike what is shown in U.S. Patent 4,225,666, it is particularly advantageous to add the spectral sensitizer after 80% of the silver halide has been precipitated. Sensitization can be improved by adjusting the pAg, including through cyclic variations, during chemical sensitization and / or spectral sensitization. A specific example of pAg adjustment is given in Research Disclosure, volume 181, May 1979, publication 18155.

  
It has been noticed quite unexpectedly that the silver halide emulsions with tabular grains of high shape index, when they are chemically and spectrally sensitized, have a better speed / granularity relationship better than that obtained heretofore with conventional halide emulsions having the highest known speed / granularity ratio or with silver halide emulsions with tabular grains of the prior art. These improvements in the speed / granularity relationship are particularly remarkable for the silver bromide and bromoiodide emulsions according to the invention which are spectrally sensitized in green and / or red by dyes sensitizing to blue minus.

  
Although it is not necessary to obtain all of their advantages, the emulsions defined according to the invention are preferably chemically and spectrally sensitized in an optimal manner, con-firmly with current manufacturing practices. This means that their speed represents at least 60% of the maximum of the logarithm of the speed that can be expected from grains in the spectral region of sensitization and under expected conditions of use and treatment. The logarithm of speed is defined as 100 (1-log E), where E is measured in lux. second at a density of 0.1 below the maximum density. Once the silver halide grains of a product have been characterized, it is possible to estimate, from other analyzes made on

  
the product and the evaluation of its performance, if an emulsion layer of this product has been sensitized chemically and spectrally in an optimal manner, by comparison with other comparable commercial products.

  
Nucleating agents

  
The tabular grain emulsions, with a high shape index, forming an internal latent image, of the photographic products according to the invention comprise a nucleating agent to promote the formation of a direct positive image by treatment. This nucleating agent can be incorporated into the emulsion during the treatment, but it is advantageously introduced into the photographic product during its manufacture, usually before coating. This way of operating makes it possible to reduce the quantities of nucleating agent required. The amount of nucleating agent required can also be reduced by decreasing the mobility of the nucleating agent in the photographic product. Large organic substituents are usually used capable of acting, to a certain extent, as ballast, in nucleating agents.

   It has been found that nucleating agents which include one or more groups promoting absorption of the nucleating agent to the surface of silver halide grains are effective at extremely low concentrations.

  
A general class of nucleating agents advantageous for the practice of the present invention is represented by aromatic hydrazides.

  
Particularly advantageous aromatic hydrazides are those in which the aromatic nucleus is substituted by one or more groups so as to restrict the mobility of the nucleating agent, and advantageously to promote the adsorption of the hydrazide on the surface of the grains of silver halides. The hydrazides specifically preferred are those which correspond to the formula Hereinafter:

  

  <EMI ID = 26.1>


  
or :

  
D represents an acyl group,

  
0 represents a phenylene group or a phenylene group substituted, for example by a halogeno, alkyl, or alkoxy group, and

  
M represents a group capable of reducing mobility, for example a group promoting adsorption.

  
A particularly advantageous class of phenylhydrazides consists of the acylhydrazinophenylthioureas represented by formula II below:

  

  <EMI ID = 27.1>


  
or :

  
R represents a hydrogen atom or an alkyl, cycloalkyl, haloalkyl, alkoxyalkyl, or phenylalkyl substituent, or a phenyl ring whose electron acceptor characteristic, derived from the Hammett sigma value is more positive than - 0.30 ,

  
R represents a phenylene group or a phenylene group substituted by alkyl, halogeno or alkoxy radicals,

  
R <2> represents a hydrogen atony, a benzyl, alkoxybenzyl, halobenzyl or alkylbenzyl group,

  
R <3> represents an alkyl, haloalkyl, alkoxyalkyl or phenylalkyl substituent of 1 to 18 carbon atoms, a cycloalkyl substituent, a phenyl nucleus whose electron acceptor characteristic derived from the Hammett sigma value is less positive than + 0 , 50, or the naphthyl substituent,

  
R4 represents a hydrogen atom, or a

  
  <EMI ID = 28.1>

  
5 or 6-membered heterocyclic ring, the constituent atoms of the ring are chosen from nitrogen, carbon, oxygen, sulfur and selenium atoms,

  
with the condition that at least one of the

  
  <EMI ID = 29.1>

  
that the alkyl radicals, unless otherwise indicated, comprise, in each case, 1 to 6 carbon atoms and the cycloalkyl groups 2 to 10 carbon atoms.

  
As the substituents corresponding to the radical R of formula II show, the preferred acylhydrazinophenylthioureas contain an acyl group which is the residue of a carboxylic acid which can be chosen from acyclic carboxylic acids,

  
including formic, acetic, propionic, butyric acids and higher homologues of these acids containing up to 7 carbon atoms and derivatives thereof substituted by halo, alkoxy, phenyl, etc. In advantageous embodiments, the acyl group is derived from an unsubstituted acyclic aliphatic carboxylic acid of 1 to 5 carbon atoms. Particularly advantageous acyl groups are the formyl and acetyl groups.

  
When comparing two nucleating agents of this type which differ only in that one of them comprises a formyl group and the other an acetyl group, the compound which contains the formyl group is a more effective nucleating agent . The alkyl groups of the substituents of the carboxylic acids advantageously have 1 to 6 carbon atoms, more particularly 1

  
to 4 carbon atoms.

  
In addition to the residues of the acyclic aliphatic carboxylic acids as described above, R can represent a cycloaliphatic group from 3 to

  
10 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, cyclooctyl, cyclodecyl, and bridged cyclic groups such as bornyl, isobornyl groups. The cyclohexyl group is the particularly preferred cycloalkyl substituent. It is also possible to use cycloalkyl substituents substituted by alkoxy, cyano, halo groups, etc.

  
As the substituents R described above in formula II show, the preferred acylhydrazinophenylthioureas contain a phenylene group or a substituted phenylene group. Particularly advantageous phenylene groups are the meta and paraphenylene groups. Examples

  
preferred substituents of phenylene groups

  
are represented by the alkoxy substituents from 1 to

  
6 carbon atoms, alkyl groups from 1 to 6 carbon atoms, the fluoro, chloro, bromo and iodo substituents. It is particularly advantageous to use unsubstituted paraphenylene groups. The particularly advantageous alkyl groups are those which contain 1 to 4 carbon atoms. Although the preferred linking groups are phenylene groups and substituted phenylene groups, other bivalent aryl groups playing an equivalent role can also be used, for example naphthylene groups.

  
According to various embodiments, the radical R <2> represents an unsubstituted benzyl group or the substituted equivalents thereof, for example benzyl groups substituted by alkyl, halo or alkoxy radicals. In the advantageous embodiments, the substituents of the benzyl groups contain not more than 6 carbon atoms and more particularly not more than 4 carbon atoms. The substituents of the benzyl groups are advantageously substituents in para. Particularly useful substituted benzyl groups are represented by benzyl groups substituted in position 4 by a halo group, or, in this same position, by a methoxy group or a methyl group. In another preferred embodiment, R <2> represents a hydrogen atom.

  
When we refer again to the formula

  
  <EMI ID = 30.1>

  
various forms. A particularly useful form may be an alkyl group, a substituted alkyl group, such as a haloalkyl, alkoxyalkyl, phenylalkyl group or an equivalent group the total number of carbon atoms of which may reach 18, but advantageously 12. More particularly the groupings

  
  <EMI ID = 31.1>

  
methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl or higher homologs up to 18 carbon atoms or derivatives thereof substituted by fluoro, chloro, bromo or iodo groups, derivatives of the latter substituted by methoxy, ethoxy, propoxy, butoxy or higher alkoxy homologs, in which the total number of carbon atoms is necessarily from 2 to 18, and derivatives of the latter substituted by a phenyl group in which the total number of carbon atoms is necessarily at least equal to 7, as, for example, in the benzyl group, and can reach up to 18. In a mode

  
  <EMI ID = 32.1>

  
the form of an alkyl or phenylalkyl substituent in which the alkyl groups have 1 to 6 carbon atoms, in each case.

  
in addition to the acyclic and aromatic aliphatic groups, as described above, R <3> and / or

  
R4 can also take the form of a cycloaliphatic substituent, such as cycloalkyl groups

  
from 3 to 10 carbon atoms, for example cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, cyclooctyl, cyclodecyl, and bridged cyclic groups, such as bornyl, and isobornyl groups. The cyclohexyl group and

  
the preferred cycloalkyl group. It is also possible to use cycloalkyl groups substituted by alkoxy, cyano, halo, etc. radicals.

  
  <EMI ID = 33.1>

  
an aromatic substituent, such as phenyl, naphthyl, for example 1-naphthyl or 2-naphthyl, or an equivalent aromatic group, for example,

  
  <EMI ID = 34.1>

  
which is either an electron donor nucleus or an electron acceptor nucleus, but phenyl groups whose electron acceptor properties are too pronounced can lead to nucleating agents whose properties are inferior.

  
The characteristic of electron acceptor or electron donor of a determined phenyl nucleus can be defined by reference to the Hammett sigma values. We can assign to this determined phenyl nucleus an electron acceptor characteristic, derived from Hammett sigma values which is the algebraic sum of the Hammett sigma values of its substituents, i.e. the Hammett sigma values of phenyl group substituents. Indeed, the literature provides the Hammett sigma values of each substituent and it suffices to make the algebraic sum of these values to obtain the Hammett sigma values of the substituents of the phenyl group. Hammett sigma values for electron acceptor substituents are positive, while Hammett sigma values for electron donor substituents are negative.

  
Examples of Hammett sigma values

  
of substituents arranged in meta- or para- and the methods for their determination are described, for example, in J. Hine, Physical Organic Chemistry,

  
2nd edition, page 87, (1962), H. VanBekkum, P. E. Verkade and B.M. Wepster Rec. Trav. Chim., Volume 78, page 815, (1959), P.R. Wells Chem. Revs., Volume 63, page 171, (1963), H.H. Jaffe Chem. Revs., Volume 53, page 191, (1953), M.J.S. Dewar and P.J. Grisdale

  
J. Amer. Chem. Soc., Volume 84, page 3548, (1962) and Barlin and Perrin Quart. Revs., Volume 20, page 75 et seq, (1966). For the present invention, we assign

  
to the ortho substituents on the phenyl group the same values as those of the para substituents.

  
It is advantageous that the radicals R2 and / or R <3> or a phenyl nucleus whose electron acceptor characteristic, derived from Hammett sigma values, is less positive than + 0.50. It is particularly useful that the radicals R2 and / or R <3> are phenyl rings comprising substituents chosen from the group consisting of the cyano, fluoro, chloro, bromo, iodo radicals, alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 carbon atoms. The substituents of the phenyl rings are advantageously located in the para or 4 position of the phenyl rings.

  
In addition to the substituents which the radicals R3 and R4 may each represent separately, the radicals R and R4, considered together, can form, with the nitrogen atom in position 3 of the thiourea, a 5 or 6-membered heterocycle. the constituent atoms of the ring can be chosen from nitrogen, carbon, oxygen, sulfur and selenium atoms. The heterocycle necessarily contains at least one nitrogen atom. Examples of heterocycles include the heterocyclic morpholine, piperidine, pyrrolidinyl, pyrrolinyl, thiomorpholine, thiazolidinyl, 4-thiazolinyl, selenazolidinyl, 4-selenazolinyl, imidazolidinyl, imidazolinyl, oxazolidinyl and 4-oxazolinyl groups. Particularly advantageous cycles are saturated or have a configuration which prevents any electron removal from the nitrogen atom

  
in position 3.

  
The nucleating agents of the class of acylhydrazinophenylthioureas and their method of preparation are described in more detail in United States patents 4,030,925 and 4,276,364. A variant of the nucleating agents of the class of acylhydrazinophenylthioureas are described in the patent of United States of America 4,139,387 and British patent application 2,012,443A.

  
Another particularly advantageous class of nucleating agents of the phenylhydrazide type consists of nucleating agents of the class of N- (acylhydrazinophenyl) -thioamides, such as the compounds which correspond to formula III below:

  

  <EMI ID = 35.1>


  
or .

  
  <EMI ID = 36.1>

II,

  
  <EMI ID = 37.1>

  
complete a 5-membered heterocyclic ring,

  
R2 represents a substituent chosen from the hydrogen atom, the phenyl, alkyl, alkyphenyl and phenylalkyl group, each alkyl group comprising 1 to 6 carbon atoms.

  
These compounds include those which have a 5-membered heterocyclic thioamide ring, such as the 4-thiazoline-2-thione, thiazolidine-2thione, 4-oxazoline-2-thione, oxazolidine-2-thione, 2pyrazoline-5-thione rings, pyrazolidine-5-thione, indoline-2thione and 4-imidazoline-2-thione. A particularly preferred subclass of heterocyclic thioamide rings comprises the compounds of formula III pre-

  
  <EMI ID = 38.1>

  
formula IV below:

  

  <EMI ID = 39.1>


  
or :

  
X represents the oxygen or sulfur atom.

  
Particularly preferred examples of

  
  <EMI ID = 40.1> <EMI ID = 41.1>

  
to think that certain 6-membered nuclei, such as thiobarbituric acid may be equivalent to 5-membered nuclei included in formula III.

  
Another particularly preferred subclass of heterocyclic thioamide ring comprises the compounds which correspond to the formula III in la-

  
  <EMI ID = 42.1>

  
after

  

  <EMI ID = 43.1>


  
or

  
L represents a methine group;

  
T represents a group which corresponds to one of the following formula

  

  <EMI ID = 44.1>


  
R <3> represents an alkyl substituent, R4 represents a hydrogen atom, a

  
alkyl group,

  

  <EMI ID = 45.1>


  
, or an alkoxy substituent,

  
Z represents the non-metallic atoms necessary to complete a basic heterocyclic nucleus of the type of heterocyclic nuclei constituting cyanine dyes,

  
n and d each represent the integer 1 or 2,

  
  <EMI ID = 46.1>

  
hydrogen, the phenyl radical, an alkyl, alkylphenyl, or phenylalkyl group, and

  
the alkyl groups of the various groups mentioned above comprise from 1 to 6 carbon atoms.

  
The heterocyclic thioamide nucleus in <EMI ID = 47.1>

  
similar to a nucleus substituted by a methine radical

  
  <EMI ID = 48.1>

  
vant various particularly advantageous embodiments, the heterocyclic thioamide nucleus is advantageously a heterocyclic nucleus substituted by a methine group, this nucleus being chosen from the 2thiohydantoin, rhodanine, isorhodanine and 2-thio-2,4oxazolidinedione nuclei. The heterocyclic thioamide nucleus which

  
  <EMI ID = 49.1>

  
substituted, either directly or via a methine bond, by a basic heterocyclic ring of the type used in cyanine dyes or else by a benzylidene ring which may be substituted.

  
Z advantageously represents the non-metallic atoms necessary to complete a basic heterocyclic ring with 5 or 6 members of the type used in cyanine dyes which include atoms constituting the ring chosen from carbon, nitrogen, oxygen and sulfur atoms and selenium.

  
The nucleating agents of the class of N- (acylhydrazinophenyl) thioamides and their method of preparation are more particularly described in the patent of United States of America 4,080,207.

  
Another advantageous class of nucleating agents of the phenylhydrazide type consists of nucleating agents of the class of phenylhydrazides substituted with a triazole group. According to a particularly advantageous embodiment, these nucleating agents correspond to formula VI below:

  

  <EMI ID = 50.1>


  
or :

  
  <EMI ID = 51.1>

II,

  
A represents an alkylene or oxyalkylene radical,

  
AT <2> corresponds to one of the formulas

  

  <EMI ID = 52.1>


  
AT <3> represents a triazolyl or benzotriazolyl heterocyclic, the alkyl and alkylene groups of each of the groups comprising 1 to 6 carbon atoms.

  
Other nucleating agents of the phenylhydrazide type substituted by a triazole group are those which correspond to formula VII below:

  

  <EMI ID = 53.1>


  
R represents a hydrogen atom and the methyl group,

  
R represents a group

  

  <EMI ID = 54.1>


  
  <EMI ID = 55.1>

  
E represents an alkyl group of 1 to 4 carbon atoms.

  
Nucleating agents of the phenylhydrazide type substituted by a triazole group and their method of preparation are described in US Patent 4,278,748. Nucleating agents of similar structure but which have groups ensuring a somewhat adsorption interval wider are described in the British patent application

  
2,011,391 A.

  
The aromatic hydrazides represented by formulas II, III and VI all contain substituents promoting adsorption. In many applications, it is advantageous to use, in combination with these aromatic hydrazides, other additional hydrazides or hydrazones which do not contain a substituent whose specific purpose is to promote adsorption on the surface of the halide grains d 'silver. These hydrazides or hydrazones, however, often contain substituents to decrease their mobility when introduced into photographic products. These hydrazides or hydrazones can be used as the sole nucleating agents, if desired.

  
These hydrazides and hydrazones include the compounds which correspond to formulas VIII and IX below:

  

  <EMI ID = 56.1>


  

  <EMI ID = 57.1>


  
or :

  
T represents an aryl radical, including a substituted aryl radical,

  
  <EMI ID = 58.1>

  
T2 represents an alkylydene radical, including a substituted alkylydene radical.

  
Examples of aryl radicals represented

  
  <EMI ID = 59.1>

  
where T <3> represents an aryl radical such as phenyl, 1-naphthyl or 2-naphthyl and M can be a substituent chosen from the hydrogen atom, hydroxy, amino, alkyl or alkylamino groups; arylamino, heterocyclic amino, that is to say an amino radical containing a heterocyclic group, alkoxy, aryloxy, acyloxy, arylcarbonamido, alkylcarbonamido, heterocyclic carbonamido, that is to say a carbonamido group containing a heterocyclic group, arylsulfonamido, alkylsulfonamido, and heterocyclic sulfonamido, i.e.

  
a sulfonamido group containing a heterocyclic group.

  
Examples of acyl radicals representing

  
the substituent T corresponds to the following formulas:

  

  <EMI ID = 60.1>


  
or :

  
Y can represent a substituent chosen from alkyl, aryl and heterocyclic radicals,

  
G can represent a hydrogen atom or the same substituent as the group Y as well as the radicals corresponding to the following formula:

  

  <EMI ID = 61.1>


  
and, in the latter case, it thus forms oxalyl radicals or A represents an alkyl, aryl or heterocyclic radical.

  
Alkylidene radicals useful for representing the substituent T <2> correspond to the formula = CH-D, where D represents a hydrogen atom or an alkyl, aryl or heterocyclic radical.

  
Aryl substituents useful in hydrazides and hydrazones, as described above, include phenyl, naphthyl and biphenyl. Examples of heterocyclic substituents for hydrazides and hydrazones, as described above, include azoles, azines; furans, thiophenes, quinolines and pyrazoles. Examples of alkyl or alkylidene substituents for the hydrazides and hydrazones described above may include 22 carbon atoms there, for example the methyl, ethyl, isopropyl, n-propyl, isobutyl, nbutyl, tert-butyl, amyl, n groups. -octyle, n-décyle, ndodécyle, n-octadécyle, n-eicosyle et n-docosyle.

  
The hydrazides and hydrazones represented by formulas VIII and IX and their method of preparation are described in US Patent 3,227,552.

  
Another general class of nucleating agents which comes in second order preferably for the implementation of the present invention consists of the quaternary cycloammonium salts substituted on nitrogen. Particularly useful nucleating agents of this general class are those which correspond to formula X below:

  

  <EMI ID = 62.1>


  
or :

  
  <EMI ID = 63.1>

  
complete a nucleus which comprises a heterocycle consisting of 5 or 6 atoms, including the quaternary nitrogen atom, the other constituent atoms of this heterocycle being chosen from carbon, nitrogen, oxygen, sulfur atoms and selenium,

  
j represents the positive integer 1 or 2, a represents a positive integer from 2 to 6,

  
  <EMI ID = 64.1>

  
formyl, (b) a radical corresponding to the following formula:

  

  <EMI ID = 65.1>


  
or :

  
  <EMI ID = 66.1>

  
ment, represents an alkoxy radical or an alkyl-

  
  <EMI ID = 67.1>

  
the atoms necessary to complete a cyclic radical chosen from cyclic oxyacetals and cyclic thioacetals of 5 to 6 atoms in the heterocyclic acetal ring, and (c) a 1-hydrazonoalkyl radical, and,

  
  <EMI ID = 68.1>

  
an alkyl radical, an aralkyl radical or an alkylthio radical is an aryl radical, such as phenyl and naphthyl, including substituted aryl radicals.

  
Nucleating agents from the class of nitrogen-substituted quaternary cycloammonium salts, corresponding to formula X, and their method of preparation are described in US Patents 3,615,615 and 3,759,901. variant, the group E1 can be a bivalent alkylene group of 2 to 4 carbon atoms linking two substituted heterocyclic rings, as represented in formula X. These nucleating agents and their method of preparation are described in the United States patent. 'America 3,734,738.

  
According to another variant, the substituent of the quaternized nitrogen atom of the heterocyclic ring can itself form a ring condensed with the heterocycle. These nucleating agents are represented by the quaternary dihydroaromatic salts which comprise a 1,2-dihydroaromatic heterocyclic ring including a quaternary nitrogen atom. Particularly advantageous 1,2 dihydroaromatic rings include rings such as the 1,2-dihydropyridinium ring.

  
Particularly useful nucleating agents from the class of dihydroaromatic quaternary salts include those corresponding to formula XI below:

  

  <EMI ID = 69.1>


  
  <EMI ID = 70.1>

  
Z represents the non-metallic atoms necessary to complete a nucleus which comprises a heterocycle consisting of 5 to 6 atoms, including the quaternary nitrogen atom, the other constituent atoms of this heterocycle being chosen from carbon and nitrogen atoms , oxygen, sulfur and

  
selenium.

  
n represents the positive number 1 or 2, and when n is equal to 1, R represents a substituent chosen from the group consisting of the hydrogen atom, the alkyl, alkoxy, aryl, aryloxy and carbamido radicals, and when n is equal to 2, R represents an alkylene radical of 1 to 4 carbon atoms, each of

  
  <EMI ID = 71.1>

  
among the hydrogen atom, the alkyl radicals and the aryl radicals, and

  
'1 X- represents an anion.

  
Nucleating agents from the class of dihydroaromatic quaternary salts and their method of preparation are described in US Patent 3,719,494.

  
A particularly advantageous class of nucleating agents from the class of nitrogen substituted quaternary cyloammonium salts is represented by the compounds which comprise one or more alkynyl substituents. These nucleating agents include the compounds which correspond to the generic formula represented by the formula XII below:

  

  <EMI ID = 72.1>


  
or :

  
Z represents the atoms necessary to complete a 5- or 6-membered heterocyclic ring, R 1 represents an aliphatic group, R <2> represents a hydrogen atom or an aliphatic group,

  
  <EMI ID = 73.1>

  
different, each represents a hydrogen atom, a halogen atom, an aliphatic, alkoxy, hydroxy, or aromatic group, at least one of the groups

  
  <EMI ID = 74.1>

  
R, R, R and R representing a propargyl, butynyl group or a substituent which contains such butyny le or propargyl groups,

  
  <EMI ID = 75.1>

  
n is equal to 1 or 2, n being 1 when the compound forms an internal salt.

  
These nucleating agents of the class of quaternary cycloammonium salts substituted by an alkynyl group and their method of preparation are described in US Patent 4,115,122.

  
There are many factors that can influence the choice of a specific nucleating agent.

  
The nucleating agents of the aforementioned US Patent 4,080,207 are particularly advantageous in most applications because they are effective at very low concentrations. Minimum concentrations as low as 0.1 mg of nucleating agent per mole of silver, concentrations preferably at least equal to 0.5 mg per mole of silver and optimal concentrations at least equal to 1 mg per mole of silver silver, are described in United States patent 4,080,207. The nucleating agents of United States patent 4,080,207 are particularly advantageous because they reduce loss of speed and because , in some cases, they allow gains in speed when the processing temperatures are increased.

   When the nucleating agents of United States patent 4,080,207 are used in combination with those of United States patent 3,227,552,

  
variations in speed can be minimized depending on the temperature of the treatment.

  
Aromatic hydrazide nucleating agents are usually preferred in photographic products intended to be treated at relatively high pH value levels, for example pH values above 13. Nucleating agents of the cycloammonium salt class quaternaries substituted by an alkynyl group are particularly useful for treating photographic products which contain them at a pH less than or equal to 13. US Pat. No. 4,115,122 describes that these nucleating agents are useful when treating the products which contain them in a pH range of between 10 and 13, advantageously from 11 to 12.5.

  
In addition to nucleating agents, as described above, there are other nucleating agents which are useful in photographic products treated in a pH range of 10 to

  
13. A nucleating agent from the class of nitrogen substituted quaternary cycloammonium salts which comprises one or more alkynyl substituents is a representative example of a class of nucleating agent useful in a photographic product which can be treated at a pH less than 13. These nucleating agents are represented by the formula XIII below:

  

  <EMI ID = 76.1>


  
or :

  
Z represents the atoms necessary to complete an aromatic carbocyclic ring of 6 to 10 carbon atoms;

  
  <EMI ID = 77.1>

  
of bivalent oxygen, a bivalent sulfur atom or the

  
  <EMI ID = 78.1>

  
  <EMI ID = 79.1>

  
complete a heterocycle of the type used in cyanines,

  
A represents a group promoting adsorption,

  
m and n are each equal to 1 or 2, and

  
  <EMI ID = 80.1>

  
titrant selected from the group consisting of hydrogen, alkyl, aryl, alkaryl and aralkyl radicals, and, in addition, R and R3 each represent a substituent selected from the group consisting of acyl, alkenyl, and alkynyl radicals , the aliphatic groups of these substituents containing up to 5 carbon atoms and the aromatic groups of these substituents containing 6 to 10 carbon atoms.

  
When these nucleating agents are used in the photographic products according to the invention, it is advantageous to treat these photographic products at a pH which is in the range of 10.2

  
to 12.0. Nucleating agents of this type represented by formula XIII and their method of preparation are described, for example, in United States patent 4,306,016.

  
Another class of nucleating agents useful in the photographic products according to the invention which can be treated at a pH of from 10 to 13, advantageously from 10.2 to 12 is represented by the products of double condensation between salicylated aldehyde and at least one heterocyclic ammonium salt, of the dihydrospiropyran type. According to a particularly advantageous embodiment, these nucleating agents correspond to the. formula XIV below:

  

  <EMI ID = 81.1>


  
or :

  
X and Y each represent a sulfur atom, a selenium atom or the group -C (R <1> R <2>) -,

  
  <EMI ID = 82.1>

  
lower kyl of 1 to 5 carbon atoms, or, taken together, they represent an alkylene radical of 4 to 5 carbon atoms,

  
  <EMI ID = 83.1>

  
hydrogen atom, a hydroxyl radical or a lower alkyl radical or a lower alkoxy radical of 1 to 5 carbon atoms,

  
Z <1> and Z2 each represent the non-metallic atoms necessary to complete a nitrogen heterocyclic ring of the type used in cyanine dyes and,

  
  <EMI ID = 84.1>

  
attached to the heterocyclic nitrogen atom of the type used in cyanine dyes. According to various modes before

  
  <EMI ID = 85.1>

  
each feel the atoms necessary to complete a 5 or 6-membered heterocycle, advantageously condensed with at least one benzene nucleus, and the heterocyclic structure of which comprises carbon atoms, a single nitrogen atom and possibly a sulfur or selenium atom .

  
Nucleating agents of this type, corresponding to formula XIV and their method of preparation are described, for example, in United States patent 4,306,017.

  
Another class of nucleating agents, useful in the photographic products according to the invention which can be treated at a pH of 10 to 13, advantageously from 10.2 to 12, is represented by the nucleating agents of the class diphenylmethane. These nucleating agents are represented by the formula

  
  <EMI ID = 86.1>

  

  <EMI ID = 87.1>


  
or :

  
  <EMI ID = 88.1>

  
res to complete a phenyl ring,

  
  <EMI ID = 89.1>

  
alkyl radical of 1 to 6 carbon atoms, and

  
  <EMI ID = 90.1>

  
hydrogen, halogen an alkyl, hydroxyl, alkoxyl, aryl, alkaryl or aralkyl radical, or else R <3> and

  
  <EMI ID = 91.1>

  
in bivalent chalcogenic bond, or else the group of formula

  

  <EMI ID = 92.1>


  
where each alkyl group contains from 1 to 6 atoms

  
carbon, and each aryl group contains 6 to

  
10 carbon atoms.

  
The nucleating agents of this type, corresponding to formula XV above and their method of preparation are described, for example, in US Patent 4,315,986.

  
Analog image formation

  
Once the high grain flat index emulsions have been produced by the processes

  
precipitation, washed and sensitized as described above, preparation can be completed by incorporating nucleating agents

  
as described above and conventional photographic additives, and can be used in photographic applications requiring the production of a silver image, for example conventional photography

  
in black and white.

  
The photographic products according to the invention intended to form silver images can

  
be sufficiently tanned to avoid having to incorporate additional tanning agents during processing. This makes it possible to increase the covering power, by comparison with similar photographic products tanned and treated, but containing emulsions with non-tabular grains or emulsions with tabular grains with a high index of shape index. Specifically, it is possible to tan the flat grain emulsion layers of high shape index and the other hydrophilic colloid layers of a black and white photographic product to a degree sufficient to reduce the swelling of the layers to less than 200%. . We determine

  
the percentage of swelling (a) by incubating the photographic product at 38 [deg.] C for three days at a relative humidity of 50%, (b) by measuring the thickness

  
of layer (c) by immersing the photographic product in distilled water at 21 [deg.] C for 3 minutes and (d)

  
by measuring the change in layer thickness. It is specifically advantageous to tan the photographic products intended to form silver images

  
to a degree which does not require the addition of tanning agents in the treatment solutions, but the emulsions used according to the present invention can be tanned in a conventional manner. It is also specifically planned to incorporate tanning agents in the processing solutions, as described for example in Research Disclosure, vol. 184, August 1979, publication 18431, paragraph K, concerning in particular the treatment of radiographic products.

  
Usually useful tanning agents (or pre-tanning agents) are described in Research Disclosure, vol. 176, December 1978, article 17643, section X.

  
We can prevent the instability that decreases

  
the maximum density in the direct positive emulsion layers by incorporating stabilizing agents,

  
anti-stars, agents inhibiting the action of mechanical stresses, agents stabilizing the latent image and similar additives in the emulsion and the adjacent layers before coating, as described in Research Disclosure, volume 176, December
1978, article 17643, Section VI. Most anti-stars effective in emulsions can also be used in developers, and can be classified into a few general categories, as described by C.E.K. Mees, The Theory of the Photography Process, 2nd edition, MacMillan, 1954, pages 677 to 680.

  
In certain applications, improved results are obtained when the direct positive emulsions of the photographic products according to the invention are treated in the presence of certain haze inhibitors, such as those described in the patent of the United States of America 2,497,917. Examples of such useful haze inhibitors include benzotriazoles, such as benzotriazole, 5-methylbenzotriazole, and 5-ethylbenzotriazole, benzimidazoles, such as 5-nitrobenzimidazole, benzothiazoles, such as 5-nitrobenzothiazole and 5. -methylbenzothiazole, heterocyclic thiones such as 1-methyl-2-tetrazoline-5-thione, triazines such as 2,4-dimethylamino-6-chloro-5-triazine, benzoxazoles such

  
than ethylbenzoxazole and pyrroles, such as 2,5dimethylpyrrole.

  
In certain embodiments, good results are obtained when the photographic products according to the invention are treated in the presence of haze inhibitors, such as those mentioned above, at high concentrations. When using, for example, benzotriazoles, we get

  
good results when these photographic products are treated with a treatment solution which may contain up to 5 g of benzotriazole per liter of solution, advantageously from 1 to 3 g of benzotriazole per liter. When these haze inhibitors are introduced into the photographic product, they can be used

  
at concentrations up to 1000 mg per mole of silver and advantageously 100 mg to 500 mg per mole of silver.

  
In addition to sensitizers, tanning agents, anti-stars and stabilizers, various other conventional photographic additives can be added. The choice of additives depends on the exact nature of the photographic application and is within the technician's reach. Various useful additives are described in Research Disclosure, volume 176, December 1978, publication 17643. Optical brightening agents can be introduced, as described in publication 17643 in paragraph V. They can be used in the emulsion layers or in the separate layers of photographic products according to the invention of absorbent and diffusing substances, described in paragraph VIII.

  
Coating aids described in section XI, and plasticizers and lubricants described in section XII can be added. Antistatic layers described in paragraph XIII can be added. Methods of introducing the additives are described in paragraph XIV. Matting agents described in paragraph XVI can be incorporated. It is possible, if desired, to incorporate developers and development modifiers described in paragraphs XX and XXI. When the photographic products according to the invention are to be used for radiographic applications, the emulsion and the other layers of the radiographic product can take all the forms specifically described in Research Disclosure, publication 18431 cited above.

   The emulsion layers described here as well as the other conventional silver halide emulsion layers, interlayers, overlays and substrates possibly present in the photographic product according to the invention can be coated and dried as described in Research Disclosure, volume 176, December 1978, publication 17643, paragraph XV.

  
The tabular grain emulsions with a high shape index, forming an internal latent image, as defined above, can be mixed either with each other or with usual silver halide photosensitive emulsions, for the purpose of '' obtain specific photographic characteristics. It is possible to mix together two or more emulsions with tabular grains, of high shape index, forming an internal latent image, as defined above, which differ in their average grain diameter. Such silver halide grains can be mixed forming an internal latent image having a similar grain size distribution, with the aim of minimizing the migration of photographic additives between different grain populations.

   When separate emulsions with a similar grain size distribution are used in combination, the performance of these emulsion combinations can be particularized, using emulsions with different levels of surface sensitization, using emulsions with differences in this

  
which relates to the adsorbed nucleating agents, or else emulsions which exhibit differences with regard to the proportions of internal sensitizers used, as described in US Pat. No. 4,035,185. When emulsions with a nucleus are mixed silver halide surrounded by an outer shell, in the mass ratio of

  
1: 5 to 5: 1, the first emulsion having a coefficient of variation of less than 20% and the second emulsion having an average grain diameter whose ratio to that of the first emulsion is less than 65%, this may result in a unexpected and surprising increase in the covering power of the silver image. It is also possible to obtain an increase in speed, even when the coating titles are reduced. The ratio of the first emulsion to the second emulsion is advantageously from 1: 3 to 3: 1, calculated on the basis of the mass in silver, and the ratio of the average diameter of the grains of the second emulsion to that of the grains of the first emulsion is advantageously less than 50%, and preferably less than 40%.

   The second emulsion used can be any usual emulsion forming an internal latent image, but this second emulsion is advantageously practically devoid of chemical sensitization at the surface.

  
In the simplest form, the photographic products according to the invention are formed of a single emulsion layer containing a silver halide emulsion with flat grains of high shape index and a photographic support. Of course, they can comprise more than one layer of silver halide emulsion as well as an overlay, a substratum and interlayers. Instead of mixing the emulsions as described above, one can generally obtain the same result by applying the emulsions to be mixed in the form of separate layers.

   Applying separate layers to achieve the desired exposure latitude is well known in the art and has been described by Zelikman and Levi, Making and Coating Photography Emulsions Focal Press,
1964, pages 234 to 238 and to the patent of the United States of America 3,662,228 and to the British patent 923,045. It is moreover well known that one can obtain an increased photographic speed when one applies in distinct layers of emulsions fast and slow emulsions, which is opposite to mixing. Usually, the fast emulsion layer is applied closer to the source of exposure than the slow emulsion layer. This means can be extended to at least three superimposed layers of emulsion. Such layer arrangements are specifically provided for in the production of the products according to the invention.

  
The layers of the photographic products can be applied on various supports. Typical photographic supports include polymer films, wood fiber, e.g. paper, plates

  
and metallic sheets, glass and ceramic supports, provided with one or more substrates

  
to improve the adhesive, antistatic, dimensional, abrasive, antihalo, hardness and friction characteristics, and / or other properties of the support. These supports are well known in the art. See for example Research Disclosure, Volume 176, December 1978, publication 17643, Section XVII.

  
The photographic products according to the invention can be exhibited photographically in any usual manner. See in particular Research Disclosure, publication 17643, cited above, paragraph XVIII. The present invention is particularly advantageous when the photographic exposure is carried out with electromagnetic radiation in the region of the spectrum for which the included spectral sensitizers exhibit absorption maxima. When photographic products are to register blue, green, red or infrared exposures, spectral sensitizers absorbing in the blue, green, red or infrared portions of the spectrum are present.

   For the formation of black and white images, it is advantageous that the photographic products are sensitized orthochromatically or panchromatically, in order to extend the sensitivity throughout the visible spectrum. The radiation energy used for the exposure can be non-coherent or coherent, produced by lasers. Within the limits of useful response determined by conventional sensitometric techniques, it is possible to use photographic exposures under conditions of temperature and / or of ambient pressure, high or reduced, exposures of low or high intensity, continuous or intermittent exposures, exposure times on the order of a minute to relatively short times on the order of a millisecond or microsecond, as described by TH

   James, The Theory of the Photography Process, 4th edition, MacMilland,
1977, Chapters 4, 6, 17, 18 and 23.

  
After exposure, the photosensitive silver halide contained in photographic products can be treated in a conventional manner to form a visible image by bringing the silver halide into contact with an aqueous alkaline medium in the presence of a contained developer. in this environment or in the product.

  
The developers used to process the photographic products according to the invention are surface developers. The expression "surface developer" applies here to developers which reveal the surface latent image centers of the silver halide grains, but which practically do not reveal the internal image centers in an emulsion forming a latent image internally, under the processing conditions usually used to develop surface-sensitive silver halide emulsions.

   Surface developers usually include any silver halide developing agent, but they are usually substantially free of solvents for silver halides, such as water-soluble thiocyanates, water-soluble thioethers , water-soluble thiosulfates, ammonia, etc., which would cause dislocations in the silver halide grains or dissolve them to practically reveal the internal image. The surface developer used sometimes comprises small quantities of excess halides or else this excess of halides is incorporated into the emulsion in the form of compounds releasing halide ions, but it is usually avoided to use

  
large amounts of iodide or iodide ion-releasing compounds to prevent significant dislocation of the silver halide grains.

  
Silver halide developing agents which can be used in these surface developers include hydroquinones, pyrocatechols, aminophenols, 3-pyrazolidinones, ascorbic acid and its derivatives, reductones, phenylenediamines or mixtures of these developers. These developing agents can be incorporated into the photographic products in which they are brought into contact with the silver halides after the image exposure, but in certain preferred modes

  
of implementation, they are used in the developer.

  
Once the image of silver has formed in the photographic product, it is common practice

  
to fix the undeveloped silver halide. The emulsions with flat grains, with a high shape index, of the invention are particularly advantageous in that they allow fixing to be carried out more quickly, which makes it possible to obtain shorter treatment times.

Dye image formation

  
The photographic products and techniques described above for producing silver images can be readily adapted to the production of color images, through the use of colorants.

  
Probably the simplest way to obtain a projectable color image is to incorporate a conventional dye into the support of a photographic product, and to form a silver image as described above. In the areas where the silver image is formed, the product can practically no longer transmit light, and in the remaining areas, the light is transmitted with a color corresponding to the color of the support. One can easily form a colored image this way. The same results can also be obtained by using a layer or a separate product containing a color filter together with a product containing a transparent support.

  
Dye images can be formed in silver halide photographic products by selective destruction or formation of dyes. Photographic products, as described above, can be used to form silver images for the purpose of forming dye images by treating these products with developers containing dye image formers, such as couplers for example. those described in Research Disclosure, volume 176, December 1978, publication 17643, section XIX, paragraph D. The developer contains a chromogenic developer, for example a primary aromatic amine, which is capable in its oxidized form of reacting with the coupler form a dye.

  
Dye-forming couplers can also be incorporated into photographic products in a conventional manner. They can be incorporated in various quantities to obtain different photographic results. For example, we can limit the concentration of coupler in relation to the silver grade

  
at values lower than those normally used in emulsion layers of intermediate or faster sensitivity.

  
Dye-forming couplers are generally chosen which are colorless, non-diffusible and capable of forming images of primary dyes, by a subtractive process, that is to say yellow, magenta and blue-green dyes. Dye-forming couplers, having varying reaction rates in separate layers or in a single layer, can be used to achieve the desired results in specific photographic applications.

  
Dye-forming couplers can liberate, at the time of coupling, photographically useful groups, such as inhibitors or

  
development accelerators, bleaching accelerators, developers, silver halide solvents, tone modifiers, tanning agents, veiling agents, anti-veil, competing couplers, chemical or spectral sensitizers and desensitizers. Couplers releasing a development inhibitor (DIR) are well known in the art. Dye-forming couplers and non-dye-forming compounds are also known which, by coupling, release various photographically useful groups. It is also possible to use DIR compounds which do not form a dye by reaction with oxidized chromogenic developers. It is also possible to use DIR compounds which cut through oxidation.

   Relatively light-insensitive silver halide emulsions such as Lipmann emulsions as interlayers and overlays have been used to prevent or control migration

  
development inhibitor groups.

  
Couplers, dye formers,

  
such as those used to form full face masks for negative color images, and / or competing couplers.

  
Photographic products may, in addition, contain conventional stabilizers for the dye image. All that has just been indicated is

  
described in Research Disclosure, volume 176, December 1978, publication 17643, Section VII.

  
The dye images can be formed or amplified by methods which consist in associating with

  
a dye image reducing agent a

  
oxidizing agent in the form of an inert complex of a

  
transition metal ion and / or peroxide.

  
Color images can be produced in the photographic products according to the invention by selective destruction of dyes or precursors

  
dyes, for example by methods of bleaching silver colors.

  
In the formation of color images in photographic silver halide products,

  
money usually developed by bleaching is eliminated. The bleaching can be improved by incorporating a bleaching accelerator or a bleaching accelerator precursor into the treatment solution or into a layer of the product.

  
In some cases the amount of silver formed by development is small compared to the amount of dye produced, particularly in processes comprising image enhancement of dye, such as

  
as described above, and you can remove money laundering without significant results, for the observation of the image. In other applications, the silver image is kept and a dye image is produced to increase or supplement the density provided by the silver image. When it is desired to enhance the silver image with a dye, it is usually preferred to form a neutral dye or a combination of dyes which together produce a neutral image.

  
Color photography

The present invention can be used to form multi-color photographic images.

  
The color image-forming photographic product according to the invention can be in the form of a direct positive color image-forming photographic product by inversion, usual but in which at least one layer of emulsion has been placed. silver halides forming an internal latent image which has been improved simply by the fact that it comprises, in whole or in part, a tabular grain emulsion of high shape index forming an internal latent image, as described above. above.

  
The present invention also provides significant advantages when color photographic products make it possible to form multi-color images by combinations of primary dyes by a subtractive process. Such photographic products consist of a support on which are applied, for example, three layers of superimposed silver halide emulsion to record the exposures to blue, green and red light respectively, in the form of images of yellow, magenta and blue-green dye. Although the photographic product according to the invention forming images

  
in color can contain at least one emulsion layer with tabular grains of high shape index forming an internal latent image, particular advantages are obtained when the emulsions contained in the photographic product according to the invention forming color images are silver bromide or silver bromoiodide emulsions with tabular grains of high shape index forming an internal latent image.

   The present description therefore relates to certain particularly advantageous embodiments of photographic products according to the invention which comprise silver bromide or silver bromoiodide emulsions, but the photographic products according to the invention forming color images can comprise high latency tabular grain emulsions forming an internal latent image which contain any silver halide, if desired. Unless otherwise indicated, the photographic products according to the invention forming color images can include the various characteristics of the photographic products described above.

  
according to a particularly advantageous embodiment, the photographic product according to the invention forming color images which comprises at least three layers of emulsions which respectively record the exposure to blue, green and red light, comprises in at least the one of the emulsion layers intended to record the green or red exposure light a silver bromide emulsion

  
or silver bromoiodide with tabular grains of high shape index, forming an internal latent image, sensitized to the blue minus, as described above, the average thickness of the tabular grains is less than 0.3 μm . This layer of tabular grain emulsion is arranged in the photographic product in such a way that, during the exposure of the latter to neutral light whose color temperature is <EMI ID = 93.1>

  
receives blue light in addition to the light at which this emulsion is intended to record. The relationship between blue light and the light of blue minus

  
that the layer receives, can be expressed as

  
  <EMI ID = 94.1>

  

  <EMI ID = 95.1>


  
log AND representing the logarithm of the exposure to green light or red light depending on what the tabular grain emulsion is intended to record, and,

  
log EB representing the log of the exhibition

  
to the blue light that these tabular grains also receive. (In each case E is expressed in lux / s. Unless otherwise indicated).

  
In practice, according to the present invention, log E possibly being less than 0.7 and preferably less than 0.3, an acceptable reproduction of a polychrome subject is also obtained. This is a surprising fact if we consider the high proportion of grains in the emulsion of the photographic products according to the invention which has an average diameter greater than 0.7 / μm. With an emulsion with grains of comparable silver halides, but not tabular or consisting of grains whose shape index is lower, (but of the same composition and of the same average diameter) the

  
color rendering is disturbed in a more important way and unacceptable in general. It is known in the art that aberrations in color rendering from sensitized emulsions in green and in red can be reduced by using grains of smaller average diameter. However, these results are obtained at the cost of a limitation

  
maximum photographic speeds that can be obtained in this way.

  
With the emulsions of the present invention, it is not only possible to obtain an advantageous separation of the speeds in the blue and in the blue minus, but in addition, this advantage can be retained without any limitation as regards the maximum speeds that can be get in the blue minus. According to a specific and preferred embodiment, a product according to the invention comprises a series of three layers of emulsions recording blue, green and red of which, at least those recording blue minus are bromide or bromoiodide emulsions silver according to the indications given above. It is also expected that the emulsion layer registering the blue of this series of three emulsions may advantageously be an emulsion with tabular grains of high index index according to the present invention.

   According to a preferred embodiment, the tabular grains present in each of the emulsion layers of this series of three elements have an average diameter

  
at least equal to 1.0 / µm and preferably at least equal

  
  <EMI ID = 96.1>

  
In the present invention, the products for color protography have an ISO sensitivity index at least equal to 180.

  
The products for color photography according to the present invention do not need to contain a yellow filter layer placed between the exposure source and the emulsion layers with tabular grains and with high form index sensitive to green and / or to red to protect these layers from exposure to blue light. However, such a yellow filter layer can be present and in this case its density can be reduced to a value lower than that of any other yellow filter layer that has been used until now to protect the emulsion layers sensitive to green and red of photographic products intended to be exposed to daylight.

   According to a preferred embodiment, there is no emulsion layer recording the blue between the emulsion layers recording the green and / or the red and the radiation source used for the exposure.

  
This is why the photographic product contains practically no blue-absorbing substances between the emulsion layers sensitive to green and / or red and the incident radiation.

  
If only one of the layers of green bromide or silver bromoiodide emulsion

  
or red is made up of tabular grains with a high shape index, the product for color photography contains at least three distinct emulsions to record blue, green and red respectively. The other emulsions, that is to say the emulsions other than those consisting of tabular qrains with high shape index which register green or red can be the usual emulsions forming internal latent images, but with non-tabular grains as described for example to USA patents 3,761,276,

  
3,923,513 and 4,035,185. In a preferred embodiment of the present invention, all of the emulsion layers contain grains of silver bromide or bromoiodide. In particular at least one emulsion layer recording green and at least one emulsion layer recording red consist of tabular grains with a high shape index, in accordance with the present invention. If the product comprises more than one emulsion layer to register the green and / or the red, the preferred embodiment consists in that at least the fastest emulsion layer contains grains of tabular emulsion d 'high form index, as indicated above.

  
Of course, all the emulsion layers recording the blue, green and red of a photographic product can advantageously consist of tabular grains such as those described above, although this is not necessary for setting of the present invention.

  
The present invention applies perfectly to products for color photography, as described above, in which the speed and the contrast of the emulsion layers recording

  
blue, green and red can be very variable. Since the silver bromide or bromoiodide emulsion layers with tabular grains of high shape index, spectrally sensitized in green or red have a relatively low sensitivity in blue, it is possible to arrange these layers emulsion recording green and / or red anywhere in a product to

  
color photography, without taking into account the remaining emulsion layers and without taking the conventional precautions to prevent exposure of these emulsion layers to blue light.

  
The present invention is particularly applicable to products for color photography intended for the reproduction of colors by exposure to daylight. Photographic products of this type are characterized in that they provide recordings of blue, green and red exposures whose contrasts are practically harmonized and whose velocities exhibit limited variations when exposed to a source of

  
  <EMI ID = 97.1>

  
(day light). The expression "practically harmonized contrast" means that the contrast of the blue, green and red records differ by less than 20% and preferably by less than 10% with respect to the value of the contrast of the recording in blue. Limited variations in the speed of recording in blue, green and red can be expressed as a 4 log E variation which is less than 0.3 log E. The variation in speed is the largest of the differences between the speed of green and red recording and speed of blue recording.

  
The products for color photography according to the present invention allow the reproduction of colors when exposed to daylight and they provide particular advantages compared to conventional products having these characteristics. In the photographic products according to the invention, the speed in blue of the tabular silver bromide or bromide iodide emulsion layers, spectrally sensitized in green and red, is limited and this limited speed can be used to separate the speed in the blue of the emulsion layer recording the blue speed in the blue in emulsion layers recording the blue minus.

   Depending on the application considered, the use of tabular grains in the emulsion layers recording green and red may in itself provide sufficient separation of the responses in blue from the emulsion layers recording blue and blue minus. In certain particular applications, the use of tabular grains in the emulsion layers recording green and red can, in itself, make it possible to obtain a great separation, in the response to blue, between the emulsion layer recording the blue and the emulsion layers recording the blue minus.

  
For some applications, it may be desirable to further increase the separation between the speed in blue of the layers recording the blue and the speed in the blue of the emulsion layers recording the blue minus; for this, use is made of conventional separation techniques which thus add to the separation possibilities obtained using the tabular grains with a high shape index according to the present invention. For example, in a color photographic product, the fastest emulsion layer recording green can be placed in the position closest to the radiation source and the emulsion layer recording blue is the most fast in the position farthest from the source of exposure; in

  
in this case, the separation of the velocities in the blue of the emulsion layers recording the blue and the green, although they have a difference of a power of
10 (1.0 log E) when applied in separate layers and exposed separately, can be effectively decreased by the arrangement of the layers, since the emulsion layer registering green receives all blue light during exposure, but the emulsion layer recording green and the other layers above it can absorb or reflect part of the blue light before it reaches the emulsion layer recording blue.

   In such a case, increasing the proportion of iodide in the blue-recording emulsion layer can help to increase the separation of the velocities in the blue from the blue-recording layers and the blue minus which is already obtained using the tabular grains. When you have an emulsion layer recording blue in a position closer to the radiation source serving

  
at the exposure that the emulsion layer recording

  
the blue minus, you can use a yellow filter layer of limited density between the emulsion layers recording the blue and the blue minus in order to increase the separation between the blue and the blue minus. However, it is never necessary to use any of these conventional techniques for separating velocities as they are used in the prior art to obtain a deviation of 1 log E or something similar for the separation of speed in blue. However, this remains possible if one wishes an exceptional separation of the velocities in the blue and in the blue minus, for a determined application.

  
Thus, the present invention makes it possible to achieve the objectives which in color photography condition the exact reproduction of colors under balanced lighting conditions, while allowing a wider choice in the production of the photographic product, compared to the prior possibilities. .

  
Products for color photography are often described so as to highlight the different color-forming elements that compose them. Most often, these products contain three of these superimposed elements, each containing at least one layer of silver halide emulsion capable of recording an exposure corresponding to a distinct third of the spectrum and at the same time producing the dye image. complementary primary subtractive. In this way, the elements recording blue, green and red respectively provide yellow, magenta and cyan dye images. The dye-forming substances need not be in the dye-forming elements; they can be supplied entirely from the processing solutions.

   When the dye-forming substances are incorporated into the photographic products, they can be placed in an emulsion layer or in a layer intended to collect an oxidized developer.

  
or an oxidized electron transfer agent from an adjacent emulsion layer of the same dye-forming element.

  
In order to prevent the migration of oxidized developers or oxidized electron transfer agents between dye-forming elements, and thus avoid the resulting color alteration, it is common practice to use reactive substances with these oxidation products. Such substances can be incorporated into the emulsion layers themselves, according to the indications of the patent of United States of America 2 937 086, and / or into interlayers between each dye-forming element, according to the indications of the patent of United States of America 2,336,327.

  
Each color forming element may contain only one layer of emulsion, but most often it contains 2, 3 or more, having different photographic speeds. When the order of the layers does not allow to arrange this set

  
layers of emulsion of different speed in a single element, it is common to make a photographic product with several (usually 2 or 3) elements recording blue, green and / or red.

  
According to the present invention, at least one emulsion layer registering green or red and containing tabular grains of bromide or silver bromoiodide in accordance with the invention, is arranged in the photographic product so as to receive a proportion more strong blue light during exposure of the photographic product. The increased proportion of blue light reaching the tabular grain emulsion layer with a high shape index may be the result of a lower absorption of blue light by a superimposed yellow filter layer, or may result advantageously from the elimination superimposed yellow filter layers.

   The higher proportion of blue light reaching the tabular emulsion layer with a high shape index can also result from a new arrangement of the dye-forming element which contains this emulsion layer so that this element is closer to the source of exposure. For example, elements recording red and green and containing tabular grain emulsions of high shape index recording green and red, may be placed closer to the source of exposure than the element recording blue.

  
The products for color photography according to the present invention can have any shape compatible with the conditions defined above. Any of the six structures presented in "Spectral Studies of the Photographic Process" (table 27-a, p. 211), Focal Press, New York, can be used. In order to provide a simple example, it is possible during the preparation of a conventional silver halide product for color photography, to add to it one or more layers of tabular grain emulsion of high shape index, sensitized to the blue minus and arranged to receive the exposure before the other emulsion layers. However, in most cases, it is preferable to replace one or more layers of conventional emulsions recording the minus

  
blue by corresponding layers made up of tabular grains with a high shape index, possibly by modifying the order of the layers.

  
To illustrate the invention, a number of preferred structures have been shown below.

  

  <EMI ID = 98.1>
 

  

  <EMI ID = 99.1>
 

  

  <EMI ID = 100.1>
 

  

  <EMI ID = 101.1>


  
B, V and R respectively designate dye-forming elements recording blue, green and red, of any conventional type.

  
T, in prefix, means that where the emulsion layers contain tabular grains of index

  
high form of silver bromide or silver branoiide.

  
F, in prefix, means that the element has a higher speed than that of at least one other element which, in the structure registers light in the same part of the spectrum.

  
L, in prefix, means that the element

  
is slower, that is to say has a lower speed than that of at least one other element of the structure recording light in the same part of the spectrum, and

  
I, denotes an interlayer containing a substance to react with the oxidation products, but practically without a yellow filter.

  
Each fast or slow element may have a different photographic speed than that of another element of the structure which records light in the same third of the spectrum, owing to its arrangement in the structure, its inherent speed properties or the association of these two factors.

  
In the structures there VII, the place of the support has not been represented. In general, the support is the most distant from the source of exposure, that is to say, on the diagrams, it would be under the layers. If the support is colorless and transmits non-scattered light, that is to say if it is transparent, it can be placed between the exposure source and the layers. More generally, the support may be disposed between the exposure source and any color forming layer recording radiation for which the support is transparent.

  
In structure I, we see that there is no yellow filter. However, in accordance with practice, in products which contain a yellow filter, the blue-forming color forming element is arranged closest to the source of exposure. In its simplest form, each element of this product consists of a single layer of silver halide emulsion. Alternatively, each color forming element may contain two, three or more different layers of silver halide emulsion.

  
In the case of sets of three elements, we compare the layers which in each element have the strongest speed, we preferably harmonize the contrasts, and in this case, the photographic speeds of the layers recording the green and the red differ from the speed of the layer registering blue by a difference of less than 0.3 log E. When, in each element, there are two or three layers of emulsion of different speed or more, there are also preferably two or three sets of three or more emulsion layers in structure I, the contrast of which is thus fixed and the velocities of which have this relationship. The absence of a yellow filter below the element recording the blue increases the photographic speed of this element.

  
The absence of a yellow filter in the interlayers is not absolutely necessary in the case of structure I. It is possible to have, between the elements recording the blue and the green, a yellow filter, at the rate of a quantity less than normal. conventional, without departing from the scope of the present invention. In addition the interlayer separating the elements recording the green and the red can in the same way also contain a yellow filter at a rate of a quantity which can go up to that used in a conventional way. When using such amounts of yellow filter, it is not necessary to limit the composition of the red recording element to the tabular grains of silver bromoiodide, as noted above, but it is possible to use any conventional grain shape consistent with the required considerations of contrast and speed.

  
We will not return to the common aspects of structures II to IX. The explanations which follow relate only to the aspects specific to each of the structures. In structure II, blue, green and

  
red are each recorded by two separate elements instead of incorporating the slow and fast emulsion layers recording blue, red or green respectively in the same elements. It is only necessary that the emulsion layer or layers of the fastest elements consist of tabular grains of silver bromoiodide according to the invention. The slower elements registering green and red, because of their slower speed, and the presence of the layer registering the faster blue which is above, benefit from appropriate protection against exposure to blue light, without the need to use a yellow filter.

   The use of silver bromoiodide emulsions with tabular grains of high shape index in the low-speed emulsion layer (s) recording green and red is not excluded. If you place the fastest element recording red on the slowest element recording green, you can increase the speed

  
according to the indications of the patent of the United States of America 4 184 876 as well as to the publications of German application

  
2,704,797, 2,622,923, 2,622,924 and 2,704,826.

  
Structure III present with structure

  
  <EMI ID = 102.1>

  
The element recording blue is furthest from the source of exposure. As a result, the element recording green is closest to the exposure source and the element recording red is closer to the exposure source than in the conventional case.

  
  <EMI ID = 103.1>

  
maintain very sharp color images with excellent color quality. The element recording green which contributes the most to the visual impression of the color image, being closest to the source of exposure,

  
can provide a very sharp image, since there is no interposed layer to diffuse the light. The element recording red, which comes second for the contribution to the visual impression of a color image, receives a light which has passed through

  
  <EMI ID = 104.1>

  
blue. Of course, the element recording the blue undergoes, by comparison with the structure I, a loss of sharpness, but this disadvantage is not significant

  
compared to the advantages resulting from the arrangement of the elements recording the green and the red, since the contribution of the element recording the blue to the visual impression of the color image is by far the least important.

  
Structure IV derives from structure III; it includes distinct, fast and slow elements for registering green and red, made up of tabular grain emulsions with a high shape index.

  
The structure V differs from the structure IV by the presence of an additional element recording the blue, arranged on the elements of low speed recording the green, the red and the blue. The fastest blue recorder includes a silver index bromoiodide emulsion with tabular grains of high shape index. In this case, the fastest blue recording element helps absorb blue light and

  
consequently to attenuate the transmission of the blue light on the elements registering the green and the red of weaker speed. A structural modification consists in not using an emulsion with tabular grains of high index in the elements registering the green and the red, of slower speed.

  
Structure VI differs from Structure IV in the presence of a tabular grain element recording blue, between the elements recording green and red and the source of exposure. As indicated above, the tabular grain element registering the blue may consist of one or more tabular grain layers registering the blue and when there are thus several layers of emulsion registering the blue , their speed may be different. To counterbalance the effects of the less favorable position occupied by the element registering the red, structure VI provides a second rapid element registering the red which is placed between the tabular grain element registering the blue and the source of exposure.

   Because of its favorable arrangement, this second rapid element registering the red is faster than the first rapid element registering the red, this insofar as these two elements consist of identical emulsions. Of course, this first and second rapid elements recording the red can be made up of identical or different emulsions, the relative speeds of which can be adjusted by known techniques. Instead of using two rapid elements recording red, the second rapid element recording red can be replaced by a second rapid element recording green.

  
Structure VII is identical to structure VI, except that it provides for both a second rapid element recording red and a second rapid element recording green arranged between the exposure source and the tabular grain element recording blue .

  
Structures VIII and IX are of the classic type where an interlayer with a yellow filter is placed under the layer recording the blue. However, in these structures, a silver halide emulsion with tabular grains of high shape index is used in the emulsion layer closest to the source of exposure. These tabular grain emulsions can be sensitized to record red light

  
or to record the green light, or can be sensitized in pairs to record the red and green lights respectively.

  
Many other interesting structures are also possible. The structures I to IX shown are only examples. In each of these structures, the position of the elements registering green and red can be exchanged: the position of the fastest elements registering red and green can be exchanged in the different structures and / or it can be the same for the slowest elements registering green and red.

  
In general, for color photography, the emulsions are arranged so as to form a set of superimposed layers containing substances forming dyes incorporated, for example couplers, but this is not essential.

  
Three chromogenic components each containing a silver halide emulsion recording light corresponding to a third of the spectrum and a coupler forming the complementary primary subtractive dye, can be arranged together in a single layer of a product for color photography. Examples of such products are given in U.S. Patents 2,698,794 and 2,843,489.

  
It is thanks to the relatively large separation between the sensitivities in the blue and the blue minus of the elements recording the green and the red and consisting of emulsions of silver bromoiodide with tabular grains, that the quantity of filter can be reduced. yellow or even eliminate these yellow filters and / or arrange the layers according to new structures. To measure the relative response of elements recording green and red to blue light in a product for color photography, one technique is to expose a sample of such a product through a density scale with neutral light, that is to say with

  
  <EMI ID = 105.1>

  
to process the sample. A second sample is then exposed in the same way, but by inserting a Wratten 98 filter which transmits light only between
400 and 490 nm; the product is then treated in the same way as above. Using the densities by transmission in blue, green and red, determined according to the American standard PH2.1-1952 mentioned above, we can draw three characteristic curves

  
  <EMI ID = 106.1>

  
the speed in blue of the element (s) recording blue and the speed in blue respectively of the element (s) recording green and red, can be determined from the following relationships:

  

  <EMI ID = 107.1>


  
in which

  
  <EMI ID = 108.1>

  
recording exposed blue through a Wratten 98 filter;

  
VW98 is the speed in the blue of the element recording the green, exposed through the Wratten 98 filter;

  
  <EMI ID = 109.1>

  
registering red, exposed through the Wratten filter
98;

  
BN is the rapidity in blue of the element registering blue, exposed to neutral light;

  
VN is the speed in the green of the element registering the green exposed to neutral light and;

  
RN is the rapidity in red of the element recording red, exposed to neutral light.

  
In the present description, it is accepted that the densities in blue, green and red are due only to the elements recording respectively blue, green and red, which amounts to neglecting the parasitic spectral absorptions of the dyes yellow, magenta and Blue green. In fact, the importance of these parasitic absorptions is rarely sufficient to have a practical effect on the results obtained in the applications mentioned.

  
The elements recording the blue of the products for color photography according to the invention exhibit, in the absence of any yellow filter, a speed in the blue which is at least equal to six times, preferably at least equal to eight times, and according to the optimal embodiment at least equal to ten times, the speed in the blue of the elements recording the green and / or the red consisting of emulsions with tabular grains of high shape index conforming to the above indications.

  
The separation between the sensitivities in blue and in the blue minus of a product for color photography according to the invention can be measured in another way. This other measure consists in comparing the speed in the green of an element recording the green, or the speed in the red of a recording element

  
red, with the rapidity in blue of these same elements. The exposure and treatment techniques described above are still used, with this diff-

  
  <EMI ID = 110.1>

  
exposure to blue minus is used by inserting a Wratten 9 filter which transmits light only beyond 490 nm. We thus determine the differences

  
  <EMI ID = 111.1>

  

  <EMI ID = 112.1>


  
  <EMI ID = 113.1>

  
above.

  
  <EMI ID = 114.1>

  
registering the exposed green through the Wratten 9 filter and,

  
RW9 is the speed in the red of the element recording the red exposed through the Wratten filter
9.

  
As previously, the parasitic spectral absorption produced by the dyes, which is rarely significant, is neglected.

  
Elements registering red and green and containing tabular silver bromoiodide emulsions as indicated above have velocities in blue and in the spectrum region where they are spectrally sensitized which are at least in a ratio 10 (1.0 log E) when the tabular grains have an average thickness of less than 0.3 µm.

  
If we compare relations A and B and relations C and D for the same product, the results are not identical, even if the elements recording

  
green and red are identical, except for the wavelengths of their spectral sensitization. Indeed, in most cases, the element recording the red receives a light which has already passed through the element recording the green. However, if we prepare a second product identical to the first, but in which we have changed the position of the elements recording the green and the red, we see that the element recording the red of the second product presents practically identical values for relations B and D compared to the values of relations A and C for the elements recording the green of the first product.

   In other words, the choice of spectral sensitization in green as opposed to spectral sensitization in red has no determining effect on the quantitative values obtained with the above relationships. This is why it is customary not to distinguish the rapidities in the green and in the red when they are compared to the rapidity in the blue, but to designate them in a generic way under the name of rapidity in the blue minus.

Reduced wide-angle scattering

  
Tabular grain emulsions of index

  
of high form according to the invention are advantageous,

  
because, compared to non-tabular emulsions or with a lower shape index, they make it possible to reduce the scattering of light at large angles.

  
The characteristic advantages which can be obtained with regard to sharpness, by using the tabular grains with a high shape index according to the invention, result from the reduction in scattering at large angles. We can give a quantitative demonstration of this. According to what is shown in FIG. 2, a sample of emulsion 1, in accordance with the present description, is applied to a transparent support 3 at the rate of 1.08 g of silver per square meter. Preferably, the emulsion and its support are immersed in a liquid
(not shown in the figure) having an appropriate refractive index to reduce the effects of reflections

  
Fresnel on the surfaces of the support and the emulsion.

  
The emulsion layer is exposed in a direction perpendicular to the plane of the support by means of a collimated light source. From the source, the light follows a path materialized by the dotted line 7, forming an optical axis, which meets the emulsion at

  
point A. The light passing through the support and the emulsion can be detected at a constant distance from the emulsion on a hemispherical detection surface 9. In one

  
point B which is at the intersection of the extension of the optical path and the detection surface,

  
a maximum light intensity is detected.

  
An arbitrary point C is chosen on the detection surface. The dotted line connecting A and C forms an angle 0 with a layer of the emulsion. By moving point C on the detection surface, you can vary the angle 0 from 0 to 90 [deg.]. By measuring the intensity

  
  <EMI ID = 115.1>

  
sible, because of the symmetry of the light scattering around the optical axis 7, to determine the cumulative light distribution as a function of 0. For this distribution, one can consult DePalma and Gasper, "Determining the Optical Propoerties of Photographic Emulsions by the Monte Carlo Method ", Photographic Science and Engineering, Vol. 16, N [deg.] 3, May-June 1971, pp. 181-191.

  
After determining the cumulative light distribution as a function of 0 for values of 0

  
at 90 [deg.] in the case of emulsion 1 according to the invention, the same process is repeated in the case of a conventional emulsion consisting of grains whose average volume is the same and applied with the same silver grade on another part of the support 3. We compare the cumulative light distributions as a function of 0, in the case of

  
  <EMI ID = 116.1>

  
  <EMI ID = 117.1>

  
comparison shows that the quantity of scattered light is lower with the emulsions according to the invention. In figure 2, the angle 9 is complementary to the angle
0. Diffusion is therefore evaluated by reference to the angle

  
  <EMI ID = 118.1>

  
high form according to the invention, have less diffusion at large angles. Since the wide-angle scattering contributes significantly to reducing the sharpness of the image, the emulsions according to the invention make it possible in each case to increase this sharpness.

  
In the present description, the term "angle

  
  <EMI ID = 119.1>

  
half of the light that reaches the detection surface is contained in a surface subtended by a cone formed by the rotation of the line AC around the polar axis of angle 6 while the other half of the light which reaches the detection surface is in the remaining part of the surface.

  
The following theoretical considerations regarding the reduction of wide angle scattering cannot limit the present invention.

  
It is assumed that the main faces of a tabular crystal, of high shape index, as well as the orientation of the grains in the layer are responsible for the improvements in sharpness. It has been observed that the tabular grains present in the silver halide emulsion layers are approximately aligned parallel to the flat surface of the support on which the layer is applied. Thus, the light, whose direction is perpendicular to the photographic product, has an incidence also perpendicular to one of the main faces of the crystals. The small thickness of the tabular grains, as well as their orientation in the layer, allows the emulsions according to the invention to be applied in thinner layers than conventional emulsions, which also contributes to improving the sharpness.

   However, the emulsion layers of a product according to the invention see their sharpness improved, even when their thickness is comparable to that of conventional emulsion layers.

  
According to a specific embodiment of the invention which is also preferred, the emulsion layers consist of tabular grains with shape index

  
  <EMI ID = 120.1>

  
  <EMI ID = 121.1>

  
grains, you can get both better speed and better sharpness. Although the maximum useful average grain diameters may vary according to the granularity tolerable in a given application, the diameters. maximum means of the high shape index grains of the emulsions according to the invention are in all cases lower

  
  <EMI ID = 122.1>

  
  <EMI ID = 123.1>

  
Although it &#65533; possible to reduce the wide-angle scattering with monolayers of tabular grain emulsion of high shape index according to the invention, this does not necessarily mean that the wide-angle scattering is reduced in the layers of a product for color photography. In certain layer assemblies for color photography, it is possible to obtain an improvement in the sharpness of the image formed in the layers of emulsion with tabular grains, of high shape index of. the present invention, but in other assemblies of layers for color photography, the emulsions with tabular grains of high shape index * according to the invention can in fact cause an alteration in the sharpness of the underlying layers. .

  
In structure I, it can be seen that the emulsion layer recording the blue is closest to the radiation source used for the exposure, while the underlying emulsion layer recording the green consists of 'a tabular grain emulsion according to the invention. This emulsion layer registering green is itself above the emulsion layer registering red. If the emulsion layer recording the blue contains grains with an average diameter between 0.2 and 0.6 m m, as is generally the case for many non-tabular emulsions, we will observe maximum diffusion of light passing through this layer before reaching the emulsion layers recording green and red.

   Unfortunately, if the light has already been scattered before reaching the high shape index tabular grain emulsion layer forming the green registering layer, the tabular grains can scatter the light passing through them more than a conventional emulsion. to reach the red registering layer. Consequently, the choice of emulsions and the arrangement of the layers entail in this particular case a significant deterioration in the sharpness of the emulsion layer registering the red, degradation which is greater than that which would be observed if this product did not include emulsion according to the invention.

  
In order to obtain the best advantages of the present invention with regard to sharpness, in an emulsion layer which is located under a tabular grain layer of high shape index according to the invention, it is desirable that this tabular grain layer is arranged in such a way that it receives practically non-scattered light, preferably light which is transmitted in a substantially specular manner. In other words, in the photographic products according to the present invention, improvements in sharpness are obtained in the emulsion layers arranged under the tabular grain emulsion layers only if these tabular grain emulsion layers are not themselves arranged under a layer whose turbidity causes a diffusion of light.

   For example, if an emulsion layer recording green, consisting of tabular grains with a high shape index, according to the invention, is placed on an emulsion layer recording red and under a layer of Lippmann emulsion and / or a layer of emulsion recording blue with tabular grains of high shape index according to the invention, the clarity of the layer registering red will be improved by the presence of the layer or layers of emulsion with tabular grains which are at -above. If the angle of capture of the layer

  
or layers on the emulsion layer recording green which includes tabular grains

  
  <EMI ID = 124.1>

  
can improve the sharpness of the red recording layer. It is of course unimportant that the layer registering the red is itself a layer with tabular grains of high shape index according to the invention, at least as regards the effects of the layers above on the sharpness of the layer recording the red.

  
In a product for color photography containing several color forming elements arranged one above the other, it is preferable that at least the emulsion layer intended to be closest to the radiation source used for the exposure, either consisting of an emulsion with tabular grains of high shape index, in order to take advantage of the advantages procured by this invention as regards image clarity. According to a particularly preferred embodiment of the present invention, each emulsion layer which is arranged so as to be the closest to a radiation source with respect to another emulsion layer, consists of an emulsion with tabular grains with a high form index. Layers II layouts

  
to VII described above constitute examples of products for color photography which, according to the present invention, make it possible to obtain a significant improvement in the sharpness of the underlying emulsion layers.

  
Products for color photography have been used to illustrate the advantages that high shape index tabular grain emulsions provide with regard to sharpness; but we can also improve the sharpness of multi-layer products for black and white photography, that is to say products forming silver images.

  
In a common way, we separate the emulsions forming black and white images into fast layers and slow layers. If tabular grain emulsions according to the present invention are used in the layers closest to the source of exposure, the clarity of the underlying emulsion layers is improved.

  
Dye image transfer

  
It is possible to prepare a composite dye image-forming film by transfer diffusion, according to the invention, by applying to a support, a single dye image-forming element which comprises a layer of emulsion photosensitive to silver halides. tabular, as described above, and at least one dye image-forming compound located either in the emulsion layer itself, or in a layer adjacent to the latter. Furthermore, the diffusion-transfer dye image-forming composite film comprises a dye image-receiving layer capable of etching after

  
its migration, the dye image formed. To obtain the transferred dye image, the tabular grain emulsion layer is exposed according to an image, then

  
it is treated with a basic treatment composition, by juxtaposing the emulsion layers with the dye-receiving layer. In a particularly advantageous embodiment, where a monochromatic transferred dye image is formed, a combination of dye image-forming compounds is used, making it possible to obtain a neutral transferred dye image. One can, however, form an image of monochromatic transferred dye having the desired hue.

  
The multi-color diffusion-forming image forming films according to the invention comprise three dye image-forming elements, namely (1) a blue-green dye image-forming element which comprises an emulsion silver halide sensitive to red with which a blue-green dye imaging compound is associated, (2) a magenta dye imaging member which comprises a green sensitive silver halide emulsion with which is associated with a magenta dye imaging compound, and (3) a yellow dye imaging element which comprises a blue sensitive silver halide emulsion with which is associated a yellow dye imaging compound .

   Each dye imaging element contains one, two, three or more layers of distinct silver halide photosensitive emulsion, and the dye imaging compound contained therein may be disposed in one or more layers of emulsion, where in one or more separate layers forming part of the dye imaging element. Any one or more emulsion layers may contain silver halide, tabular grain, high shape index emulsions, as described above.

   According to an advantageous embodiment of the invention, at least the fastest emulsion layers of the image-forming elements of blue-green and magenta dyes of the photographic products according to the invention are silver halide emulsions with tabular grains, with a high shape index, as described above.

   The photographic product according to the invention can also comprise, at least in the quickest emulsion layer of the image-forming element of yellow dye, a silver halide emulsion with tabular grains with shape index high, as described above, but it is also possible to use, in the yellow dye imaging element, conventional silver halide emulsions, while maintaining in the imaging elements of blue-green and magenta dyes of silver halide emulsions with tabular grains with high form index.

  
Depending on the dye imaging compound used, it can be incorporated into the silver halide emulsion layer or in a separate layer associated with the emulsion layer. The dye image-forming compound can be a conventional compound, such as dye-forming couplers, developer dyes, dye-releasing compounds by oxidation-reduction, and the dye-image-forming compound used will depend on the structure of the dye. image forming element or desired image quality. The imaging compounds useful in composite films for transfer-transfer contain a dye group and a controller group.

   The controller group, in the presence of the basic treatment composition, and depending on the development of the silver halides, ensures a modification of the mobility of the dye group. These dye image-forming compounds can be initially diffusible or mobile and can be made non-diffusible or immobile depending on the development of the silver halides, as described in US Pat. No. 2,983,606. According to other embodiments, these dye image-forming compounds can be initially non-diffusible or immobile and can be made mobile or diffusible, in the presence of a basic treatment composition,

  
depending on the development of silver halides. This latter class of compounds includes compounds which release dyes by redox. In these compounds, the controller group is a carrier group

  
from which the dye is released as a direct function of the development of silver halides or as an inverse function of the development of silver halides. The compounds which release dyes as a direct function of the development of the silver halides are called dye-releasing compounds according to

  
a negative process, while compounds which release dyes in inverse function to the development of silver halides are called dye-releasing compounds in a positive process.

  
Since the image-forming emulsions, with internal latent image, as defined above, develop in unexposed areas, in the presence of a nucleating agent and a surface developer, it is possible to obtain images transferred dyes, positive, using compounds releasing dyes in a negative process and the latter compounds are therefore particularly useful.

  
Compounds releasing dyes following a negative process are para-sulfonamidphenols

  
and para-sulfonamidonaphthols, as described in U.S. patents. 4,054,312, 4,055,428 and 4,076,529. In these compounds, the dye group is attached

  
to a sulfonamido group which is itself located in

  
ortho or para relative to the hydroxyphenolic group and which is released by hydrolysis, after oxidation of the sulfonamido compound during development.

  
Another useful class of dye-releasing compounds in a negative process are ballasted dye-forming couplers or non-dye-forming couplers which include a mobile dye attached to a site separating at coupling. By coupling with an oxidized chromogenic developing agent, such as paraphenylenediamine, the mobile dye is moved and can be transferred to an image receiving element. The use of such dye image-forming compounds in a negative process is described, for example, in U.S. patents. 3,227,550 and 3,227,552 and British patent 1,445,797.

  
Since the silver halide emulsions used in the diffusion diffusion composite imaging films according to the invention are positive emulsions, the use of dye-releasing compounds in a positive process would provide negative transferred dye images . Compounds releasing dyes in a positive process, useful, are the compounds of the class of nitrobenzene and quinones, as described in the patent of the U.S.A. 4,139,379, hydroquinones as described in the U.S. Patent. 3,980,479 and the benzisoxazolone compounds as described in the U.S. Patent. 4,199,354.

  
Further details regarding the dye-releasing compounds as described above, their modes of action and the methods by which they can be prepared are described in these patents.

  
The dye image-receiving layer of the composite films according to the invention can contain any substance insofar as it can etch or fix the dye which diffuses towards it. The choice of the best substance will naturally depend on the specific dye or the dyes to be etched. The dye receiving layer may further contain ultraviolet absorbing compounds to protect the dye image from weakening due to ultraviolet light, optical brighteners, and other agents to protect or enhance the color. dye image.

   The image-receiving layer may also contain a polyvalent metal, advantageously immobilized by association with a polymer, to form a complex with the transferred dye image, or else this polyvalent metal may be placed in a layer adjacent to the image-receiving layer, as described, for example in US patents 4,239,849 and 4,241,163. Useful dye image receptor layers and substances useful in their preparation are described in "Research Disclosure", Vol. 151, s. 15162 (November 1976) and to the U.S. Patent 4,258,151.

  
The basic treatment composition used in the composite dye image forming films by transfer diffusion according to the invention can be an aqueous solution of a basic compound, such as a hydroxide or a carbonate of an alkali metal, for example sodium hydroxide or potassium carbonate, or an amine, for example diethylamine. This basic composition advantageously has a pH value greater than 11. The substances useful for preparing these compositions are described in "Research Disclosure", Art. 15162 cited above.

  
A developing agent is advantageously present in the basic treatment composition, but it can also be present in a solution distinct from the basic treatment solution or in the treatment sheet, or it can be present in any layer of the film composite which can be crossed by the treatment composition. When the developing agent is not present in the basic treatment composition, the latter serves to activate the developing agent and allows the latter to come into contact and to develop the silver halides.

  
A wide variety of silver halide developing agents can be used to treat the composite films of the invention. Choosing the best developer will depend on the type of composite film it is used with and the particular dye imaging compound used. Suitable developing agents can be chosen from compounds such as hydroquinones, aminophenols, for example, N-methylaminophenol, 1phenyl-3-pyrazolidinone, 1-phenyl-4,4-dimethyl-3pyrazolidinone, l-phenyl -4-methyl-4-hydroxymethyl-3-

  
  <EMI ID = 125.1>

  
diamine, etc. It is advantageous to use the non-chromogenic developers of the above list in composite dye image forming films by transfer diffusion according to the invention, because their tendency to form parasitic colorations in the dye image receiving layers are reduced.

  
One of the advantages of the composite dye image forming films by transfer diffusion according to the invention lies in the fact that the transferred dye image quickly becomes visible and observable. This rapid access of the visible transferred image is directly linked to the presence of one or more silver halide emulsions with tabular grains, with high shape index, as defined above. Without being bound by any particular theory, it is reasonable to think that the geometric configuration of the tabular silver halide grains allows rapid access to the transferred images. The geometry of the tabular grains provides a very large surface area for the silver halide grains relative to their volume, and it is believed that, in turn, this result influences the speed of their development.

   In image transfer diffusion formation processes, it is the development of silver halide grains which is modulated according to an image as a function of their exposure which in turn modulates a transferred image. In certain processes, for example in those which use dye-releasing compounds following a negative process, as described above, the development of the silver halides is directly linked to the image-forming substances transferred. It follows that the substances which form the image are made visible all the more quickly as the silver halides develop more quickly.

  
The fact of using tabular grains to reduce the time which separates the beginning of the treatment from the moment when the transferred image becomes visible, that is to say to decrease the access time, does not in any way prevent the use of conventional means in the composite films according to the invention, conventional means which are known to reduce the duration of access. When we put

  
implementing the present invention in combination with usual means for reducing the duration of access, additive results are usually obtained. In addition, the composite diffusion imaging dye films according to the invention have unique additional characteristics which contribute to reducing the duration of access. These additional features are discussed below.

  
  <EMI ID = 126.1>

  
diffusion-forming image formers according to the invention resides in the fact that the characteristics of the transferred image vary little as a function of the temperature. These variations in small amplitude of the characteristics of the transferred image result directly from the use one or more layers of tabular silver halide emulsion, as described above. Without being bound by any particular theory, it is possible to think that the grains of tabular silver halides exhibit rates of development which vary little as a function of temperature.

   In transfer diffusion imaging methods in which the development of silver halides is directly related to the image forming substances transferred, this reduced dependence of the development of tabular silver halide grains on of temperature has the direct result of obtaining visible images whose variations in characteristics are also reduced.

   In methods that employ competition mechanisms to form visible images, the small variation in the development of silver halides as a function of temperature can reduce the variation in the transferred image to the extent that this variation is due to the variation in the development of the silver halides and to the extent that this variation is added to the temperature variations in the competition mechanisms used in the formation of the images.

  
It has been remarked, surprisingly, that the composite films forming dye image by transfer transfer according to the invention have, at a lower silver content, photographic sensitivities significantly higher than comparable conventional composite films. It is well known that, when the silver titer is reduced below a certain threshold, a reduction in the photographic sensitivity is obtained as determined on the transferred dye image. Although the photographic sensitivity decreases when the silver titers of the silver halide emulsions decrease, this reduction in sensitivity is much more gradual when using emulsions with tabular grains, with high form index, these emulsions making it possible to use weaker silver titles.

  
Acceptable photographic sensitivities are usually obtained in conventional composite films forming multi-color images by transfer diffusion, using yellow, magenta and blue-green image-forming elements, the silver halide layers of which contain silver titles. about 1000 mg / m <2> or

  
higher titles. The implementation of the present invention makes it possible to use, in the photographic products according to the invention, significantly lower silver titers. When the silver halide grains of the photosensitive emulsions of the yellow, magenta and blue green image forming elements respectively of the composite color image films by transfer diffusion according to the invention are tabular, as described above, can use these emulsions in a silver titer of between approximately 150 mg / m <2> and 750 mg / m <2>, advantageously between approximately 200 mg / m2 and 700 mg / m2 and very particularly between 300 mg / m and 650 mg / m <2>. If we use lower or higher silver film titles, we obtain

  
lower or higher photographic sensitivities, but the aforementioned silver titer ranges provide an effective balance in photographic performance versus silver titer for most imaging applications. When the composite diffusion imaging image forming film according to the invention contains a single dye image forming element which contains tabular silver halide grains, the silver titles, as described above, are applicable to this unique dye image-forming element. When the next composite film

  
  <EMI ID = 127.1>

  
the invention comprises three dye imaging elements which contain tabular silver halide emulsions, silver savings which are at least additive can be obtained.

  
The composite films according to the invention image forming by transfer diffusion can have any arrangement of the layers used in conventional composite films which comprise a

  
or several layers of silver halide emulsion. In addition, the special properties of tabular silver halide emulsions make it possible to lay out layers which are particularly advantageous and hitherto unknown. The specific arrangements of the layers described below are given simply by way of example, but other arrangements are also possible.

  
To avoid unnecessary repetitions, the description of the layers entering into each structure of the composite films according to the invention will relate to

  
the distinctive characters of these films compared to those of previous films. Expressed in another way, the characteristics and advantages of the arrangement of the layers are described in detail only with the first composite film in which this arrangement of the layers appears. If a characteristic or advantage does not appear in the arrangement of the layers of a subsequent composite film, this difference is specifically noted.

  
  <EMI ID = 128.1>

  
broadcast transfer

  
This composite film according to the invention forming a dye image by diffusion-transfer, after lamination and separation, has the following structure:

  

  <EMI ID = 129.1>


  
  <EMI ID = 130.1>

  
usual composite image forming by diffusion transfer after lamination and separation. After image-based exposure, a latent developable image is obtained in the tabular silver halide emulsion layer, operating in a positive process, at sites within the exposed grains. The dye image receiving layer is then laminated on the exposed photosensitive member, and a basic processing composition, not shown, is released between the dye image receiving layer and the emulsion layer. On contact with the basic processing composition, the tabular silver halide grains which contain internal latent image sites develop much more slowly than the silver halide grains which do not contain these image sites internal latent.

   When a dye image forming compound operating on a negative process is used, a dye image is released in the ranges corresponding to the silver image and this dye image migrates to the dye image receiving layer where it is retained by the bite. This produces a positive dye image transferred to the dye image receiving layer. The treatment is stopped by laminating the reflecting support which carries the dye image-receiving layer of the residual composite film.

  
Although the layering of the

  
composite film I is usual and that these layers contain the usual compounds, with the exception of the tabular silver halide emulsion, this composite film makes it possible to obtain significantly superior results. The access time to obtain a visible image in the receiving layer is significantly reduced. It is believed that this result can be attributed to the particular advantages provided by the tabular silver halide grains, which form the internal lantern image. Internal latent image forming tabular silver halide grains, as defined above, develop at a faster rate than comparable non-tabular internal silver forming internal halide grains .

  
Although the development is entirely responsible for the faster access time obtained in the composite film I according to the invention, it is also possible to use another characteristic of the tabular grain emulsions to obtain a further reduction in this access time. Although it is possible to apply emulsions with tabular grains, with a high deformation index, in thicknesses similar to those of the usual emulsions, it is however advantageous.

  
to reduce the thickness of the silver halide emulsion layers with tabular grains, with a high shape index, compared with the thicknesses of the usual emulsion layers. With the usual silver halide emulsions used in transfer-forming image-forming emulsion layers, the thickness of these layers is significantly greater than the average diameter of the silver halide grains, calculated from the surfaces projected grains. In addition, the thickness of the layer is important enough to

  
  <EMI ID = 131.1>

  
but also the larger grains. Thus, if the largest non-tabular silver halide grains in a silver halide emulsion layer of a diffusion-forming composite film

  
  <EMI ID = 132.1>

  
more important. On the other hand, it is possible to use tabular silver halide grains, as defined above, having diameters, measured according to the means of the projected surfaces, of

  
  <EMI ID = 133.1>

  
of these tabular grains either less than 0.5 µm) or even less than 0.3 µm. Thus, for example, with an emulsion containing tabular grains whose thickness-

  
  <EMI ID = 134.1>

  
layers of emulsion with tabular grains, with a high shape index, as described above, advantageously have a thickness which is equal to less than four times the average thickness of the tabular grains and more particularly the thickness of these layers d emulsion at a value less than twice the average thickness of the tabular grains. Significantly reducing the thickness of tabular-grain silver halide emulsion layers with a high shape index can help reduce access times by reducing the length of the diffusion paths. In addition, by reducing the length of the diffusion paths, it is thus possible to improve the sharpness of the images.

  
Composite film II image by diffusion transfer

  
This composite film according to the invention, with a unitary structure, image forming of monochromatic dye by transfer transfer has the following structure:

  

  <EMI ID = 135.1>
 

  
contains the opacifier is not originally placed in the above mentioned location. As a result, exposure following an image reached

  
the tabular silver halide emulsion layer. A latent image is thus obtained corresponding to the exposed areas of the emulsion layer. To start treatment, apply the composition

  
basic processing in the location described above. Although it is not essential, it is customary to remove the composite film, image forming by diffusion transfer, from the camera where it was exposed, immediately after the application of the composition of basic treatment and opacifying agent. The opacifying agent with the opaque layer prevents further exposure of the emulsion layer. By development, a mobile dye or a mobile dye precursor is released from the emulsion layer. This mobile dye or precursor dye penetrates through the opaque layer and the reflective layer and is etched in the dye image receiving layer in the form of an image which can be observed through the upper transparent support. Treatment is stopped by

  
the retarding layer and by the neutralization layer.

Composite film III bleaching diffusion forming image

  
This composite film according to the invention, with a unitary structure, image forming with multiple colors by transfer diffusion, has the following structure:

  

  <EMI ID = 136.1>
 

  

  <EMI ID = 137.1>


  
Composite film III is similar to composite film II, except that it comprises three separate dye-forming elements, each of which comprises a tabular silver halide emulsion layer, with index high form, and a layer containing a dye imaging compound, instead of the single layer of composite film II which includes a silver halide emulsion

  
with high form index tabular grains and a dye image-forming compound. We can have

  
the dye image-forming compound, either in the emulsion layer itself, or in an adjacent layer, in composite films II and III, both arrangements being also possible.

  
To avoid color contamination in adjacent dye image forming elements, an interlayer containing an oxidizing developer immobilizer is disposed between two dye image forming elements. It is therefore envisaged to use immobilizing agents for the oxidized developer in interlayers and / or in dye image-forming elements. In certain embodiments, it is also possible to reduce the minimum density on the edge of the image by incorporating a negative silver halide emulsion in the interlayers.

  
According to a variant of the embodiment of the composite film III, the interlayers are removed in the previous structure. Since the silver halide emulsion layers with tabular grains having a high shape index can be very thin, compared to the usual silver halide emulsion layers usually used in composite imaging films by diffusion transfer, it is possible to arrange each layer of silver halide emulsion with tabular grains having a high shape index between two layers of compound forming a magenta dye. The two layers which contain the magenta dye-forming compound advantageously do not contain an immobilizing agent

  
the oxidized developer, but, if desired, these layers may contain such an immobilizing agent, depending on the sensitivity of each dye image-forming element to color contamination and according to the specific choice of image-forming compounds dye. By placing a layer containing a dye image-forming compound adjacent to each side of the silver halide emulsion layer with tabular grains having a high shape index,

  
a close association is provided between the dye image-forming compounds and the silver halides. This arrangement of the layers is particularly advantageous when the dye image-forming compounds of each dye image-forming element are originally incorporated, or at least have a maximum absorption which has been shifted so that the dye imaging compound does not absorb in the region of the spectrum to which silver halides are sensitive.

  
When the yellow dye-forming compound is originally yellow, it acts, in association with the silver halide emulsion layer with tabular grains, high shape index, sensitive to blue, so as to intercepting blue light which could otherwise reach the silver halide emulsion layers with tabular grains, with high form index, sensitive to green and red respectively. When the silver halide emulsion layers sensitive to green and sensitive to red contain grains of silver bromide or silver bromoiodide in a conventional composite film forming an image with several colors by transfer diffusion, it is necessary to intercept blue light which could contaminate the dye images formed in the emulsion layers sensitive to green and sensitive to red.

   However, when the green-sensitive and red-sensitive emulsions are tabular grain emulsions, with a high shape index, forming internal latent images, as described above, it is not necessary to filter the blue light from so that it is attenuated before reaching these green-sensitive emulsion layers

  
and sensitive to red. Thus, when the yellow dye image-forming compound is originally colorless or at least does not absorb in the blue region of the spectrum, it is however possible to obtain correct color reproduction in the formative layers d image of dye, respectively magenta and blue-green, without interposing a layer of yellow filter dye. Furthermore, as described in more detail below, the dye imaging elements may be located in any desired order.

Diffusion-transfer bleaching composite film IV

  
This composite film according to the invention, with a unitary structure, image forming with several colors by transfer diffusion has the following structure:

  

  <EMI ID = 138.1>
 

  

  <EMI ID = 139.1>


  
During the exposure following an image of the composite film IV, the basic treatment composition which contains the reflecting substance and the indicator dye is not in the position indicated above, but is released in this position, after the following exposure an image, so as to allow processing. The indicator dye has a high density at the high pH value where the treatment takes place. It thus protects the silver halide emulsion layers from further exposure if the composite film is removed from the camera during processing. When the neutralizing layer decreases the pH value in the composite film to stop processing, the indicator dye changes to a practically colorless form.

   The basic treatment composition further contains an opaque reflective substance which provides a white background for observing the transferred dye image after treatment and for preventing further exposure.

  
The dye-forming composite film IV by diffusion transfer is an example of a composite film, unitary structure, multi-color image-forming by transfer diffusion, in which the exposure according to an image and the observation takes place. do through the same support. Composite film IV differs from composite films of the prior art not only by the use of silver halide emulsions with tabular grains, with high shape index, but also by the arrangement of the various image forming elements of dye. The silver halide emulsion layer with tabular grains, with a high form index, sensitive to green, is the closest to the source of exposure, while the silver halide emulsion layer with tabular grains, high form index, sensitive

  
blue, is the farthest from the source of exposure. This arrangement of the layers is possible without contamination of the colors because of the relatively large separation of the responses to blue and to blue minus that allow silver halide emulsions with tabular grains, with high shape index, spectrally sensitized to blue minus. By arranging the magenta dye imaging element

  
the closer to the source of exposure and the closer to the dye image receiving layer, the sharpness of the magenta dye image is improved and its access time is reduced. The magenta dye image is, of course, the most important dye image for viewing the multi-color image. The blue-green dye image is 1 '' the second most important dye image for visual observation and its arrangement is also closer to the exposure source and the dye image receiving layer than in a dye image forming element by transfer diffusion, usual.

   Thus, the transfer diffusion dye image forming composite film IV provides significant advantages in terms of reduced access time and increased image clarity, in addition to the improvements attributable to tabular silver halide grains at high form index, discussed above, in conjunction with the other layering arrangements. Although the diffusion diffusion imaging composite film IV can contain any silver halide having tabular grains, with a high shape index, it is particularly advantageous to use silver bromide or bromoiodide grains. high form index tabular silver.

  
Although the photographic products according to the invention have been described with reference to certain particularly advantageous modes of arrangement of the layers, it will be noted that it is not always necessary for the silver halide emulsions with tabular grains, with index of high form, are present in the form of flat and continuous layers. These layers can be subdivided into discrete fraction moved laterally. In composite films forming multi-color images by transfer diffusion, the layers which compose it are not necessarily superimposed on each other, but may be present in the form of interleaved layer segments.

   It is possible to use silver halide emulsions with tabular grains, with a high shape index, as described above, in arrangements of microcellular composite films forming image by transfer diffusion, as described in. PCT patent application published WO80 / 01614, published August 7, 1980. The present invention is also applicable to microcellular composite films forming by diffusion transfer imaging which contain microcells, which are improvements to the composite films described at the request of PCT patent cited above and which are described in British patent 2,091,433.

  
Although all the advantages attributed to tabular grain silver halide emulsions with high shape index can be obtained in microcellular composite imaging films by transfer diffusion, the significant separations of sensitivity to blue and to blue minus which can be obtained with silver halide emulsions

  
with tabular grains, with a high shape index, more particularly in silver bromide and silver bromoiodide emulsifiers, are particularly advantageous in microcellular composite films forming image by diffusion transfer intended for obtaining images in several colors. Since the groups of microcells intended to respond

  
the blue, green and red light respectively are arranged so as to receive the same incident light, yellow filters are usually interposed when conventional silver bromide and silver bromoiodide emulsions are used to improve the separation of the sensitivity to blue and blue minus. This result may require an additional coating step or an additional cell filling step and may reduce photographic sensitivity.

   Tabular-grain, high-index silver halide emulsions, as described above, are useful for preparing multi-color, image-forming microcellular composite films by transfer diffusion without using yellow filters. which significantly simplifies the preparation of these films and improves their performance.

EXAMPLES:

  
The following examples illustrate the invention.

  
In each emulsion preparation, the container is vigorously agitated where the precipitation of the silver halides takes place during the addition of the silver salt. Unless otherwise indicated, the percentages given are percentages by mass.

  
Unless otherwise indicated, the molar concentrations are expressed by the letter M. All the solutions used are aqueous solutions.

  
Preparation of the emulsion

  
The emulsions useful in the photographic products according to the invention are prepared by operating as follows:

  
Emulsion A -

  
Tabular silver bromoiodide grain emulsion whose nuclei consist of silver iodide

  
A silver iodide emulsion intended to constitute the nuclei of the grains of the final emulsion is prepared, using a double-jet precipitation technique, at a pI equal to 2.85 and at 35 [deg.] C . To a container which contains 60 g of deionized bone gelatin dissolved in 2.5 l of water is added a 5.0 M silver nitrate solution and a 5.0 M sodium iodide solution. , in 3 min 30 s. An emulsion is thus obtained which contains 0.125 mol of silver iodide, the average grain diameter of which is 0.027 / μm and the crystals of which are of bipyramidal hexagonal structure.

  
An amount of emulsion is taken which contains 2.4 × 10 -3 mole of silver iodide in which 1.75 mole of silver bromide is precipitated by the double jet technique. To this end, a 4.0 M silver nitrate solution and a solution are added.

  
  <EMI ID = 140.1>

  
using the accelerated flow technique, the flows at the end of the precipitation being equal to 6 times the flows used at the start of the precipitation. The pBr value is maintained at 1.3 for the first 5 minutes, then the pBr value is adjusted to 2.2 for the next 3 minutes, then this value is maintained at 2.2 during the rest of the precipitation .

  
Tabular bromoiodide crystals

  
  <EMI ID = 141.1>

  
12.5: 1 average and silver bromoiodide crystals that meet these characteristics represent more than 90% of the total projected area of silver halide grains.

  
Emulsion A is chemically sensitized with 1.9 mg of sodium thiosulfate pentahydrate per mole of silver and 2.9 mg of potassium tetrachloroaurate.

  
  <EMI ID = 142.1>

  
Emulsion B -

  
Tabular silver bromoiodide grain emulsion with a core surrounded by an outer shell

  
0.22 mole of silver halide contained in chemically sensitized emulsion A and prepared as described in the preceding paragraph is introduced into a container, with a pBr of 1.7 and at 80 [deg.] C. Then precipitated on the silver halide grains of emulsion A, 5.78 mole of silver bromide, by the double jet technique, adding a 4.0 M silver nitrate solution and a 4.0 M sodium bromide solution, in 46 min 30 s., keeping the pBr equal to 1.7, and operating by the accelerated flow technique, the flow rate at the end of the addition being equal to 4 times

  
the flow at the start of the addition. The silver bromoiodide tabular crystals thus obtained have an average diameter of 3.0 µm, an average thickness of

  
  <EMI ID = 143.1>

  
90% of the total projected surface of the silver halide grains meet these characteristics.

  
Emulsion B is chemically sensitized by adding 1.0 mg of sodium thiosulfate pentahydrate per mole of silver, for 40 min, at 74 [deg.] C, and it is spectrally sensitized to red by adding 250 mg of an -

  
  <EMI ID = 144.1>

  
thiacarboncyanine hydroxide per mole of silver.

  
Emulsion C -

  
Silver bromoiodide emulsion with internal latent image, tabular grains doped with cadmium

  
Emulsion C is prepared by operating as for emulsion B, except that, after 8 minutes of precipitation, cadmium bromide representing 0.05 mol per mol of silver contained in the silver halides is added of the external envelope, during the stage of formation of the latter.

  
Emulsion D -

  
Control emulsion

  
As control emulsion D, an emulsion as described in Example 7 of the U.S. Patent is used. 3,923,513, which is an octahedral silver bromide emulsion, with an internal latent image, monodispersed, with an average grain size of

  
  <EMI ID = 145.1>

  
it is chemically sensitized with 0.4 mg of sodium thiosulfate pentahydrate per mole of silver and with 0.6 mg of potassium tetrachloroaurate per mole of silver.

  
An outer shell of silver bromide is then precipitated on the nuclei thus formed and the final emulsion is chemically sensitized with 0.35 mg of sodium thiosulfate pentahydrate per mole of silver. The emulsion is then sensitized spectrally with 100 mg of 5-5'-dichloro-9-ethyl-3,3'-bis- anhydrohydroxide
(3-sulfobutyl) thiacarbocyanine per mole of Ag.

  
Emulsion E -

Internal bromoiodide silver emulsion with tabular grains

  
An emulsion is prepared constituting the nuclei of the final emulsion to be prepared, similar to emulsion A as described above. This emulsion is then chemically sensitized with 2.5 mg of sodium thiosulfate pentahydrate per mole of Ag and 3.75 mg of potassium tetrachloroaurate per mole of Ag, to

  
  <EMI ID = 146.1>

  
of silver contained in this chemically sensitized emulsion, an additional quantity of silver bromide representing 0.133 mol is precipitated, by adding, by the double jet technique, a 5.0 M silver nitrate solution and a bromide solution sodium

  
5.0 M, for 16 min 36 s., At a pBr of 2.4 and at 80 [deg.] C. The tabular silver bromoiodide crystals obtained contain less than 0.10 mole% of iodide, have

  
  <EMI ID = 147.1>

  
average sor of 0.14, um and an average shape index of
10.7: 1 and represent more than 85% of the total projected surface of the silver halide grains formed. Emulsion F -

  
Image silver bromoiodide emulsion

  
  <EMI ID = 148.1>

  
An emulsion is prepared constituting the nuclei of the silver halide grains to be formed and chemically sensitized, operating as described for Emulsion E above. After the chemilue sensitization, an outer envelope of silver romoiodide is precipitated from 0.067 mole of silver halides contained in this emulsion, in the following manner. ) n adds, at constant flow rate, a 5.0 M silver nitrate solution and a 5.0 M halide solution,

  
at a pBr of 2.4, at 80 [deg.] C, for 11 min 6 s. The silver halides formed comprise 90% by mole of bromide and 10% by mole of iodide. A total amount of 0.045 mole of additional silver bromoiodide is thus added. A second external envelope similar to the first is then precipitated, with the difference that the halides comprise 80 mol%

  
bromide and 20 mol% iodide. A third envelope is likewise precipitated on the second external envelope, similar to the latter, with the difference that the halides comprise 70% by mole of bromide and 30% by mole of iodide. The obtained tabular silver bromoiodide crystals which contain
13.3% by mole of iodide have an average diameter of

  
  <EMI ID = 149.1>

  
and an average shape index of 10.7: 1 and represent more than 85% of the total projected surface of the silver halide grains obtained.

  
EXAMPLE 1A:

  
This example shows that emulsion B which

  
is an emulsion with internal latent image, with tabular grains, sensitized to red, has better developability, over a wide temperature interval, when compared to an emulsion with octahedral grains, with internal latent image, and sensitized to red from the prior art, the control emulsion D, in a photographic product forming an image with several colors by diffusion transfer using a compound releasing a dye by redox, compound RDR, for example a compound RDR sulfonamidonaphthol.

  
A photographic product with a unitary structure is prepared comprising an integrated image-receiving element and having the arrangement of the layers described below, the titles being in (g / m <2>) or in [mg / mole Ag]. The exact structure of the immobilizers for the oxidized developers, the nucleating agents and the RDR compounds are mentioned in the appendix which follows the examples.

  
Layer 16

  
Overlay which contains the immobilizing agent of oxidized developer VIII (0.11), gela-

  
  <EMI ID = 150.1>

  
as tanning at a concentration of 1% relative to the mass of gelatin.

  
Layer 15:

  
Silver halide emulsion layer sensitive to blue similar to control emulsion D with octahedral grains, but sensitized to blue. It comprises silver halides (1.34 Ag) the nucleating agent V [13.0], the nucleating agent IV [0.41] the immobilizing agent of the oxidized developer VII

  
[4000] and gelatin (1.34). Layer 14:
Interlayer which contains titanium dioxide (0.27) and gelatin (0.65). Layer 13:
Layer which contains the compound RDR I, releasing a yellow dye, (0.65) and gelatin (0.86). Layer 12:
Interlayer: negative silver bromide emulsion (0.11 Ag), the oxidizing developer VIII (1.1) and gelatin (1.3) immobilizer. Layer 11:
Silver halide emulsion layer sensitive to green. This emulsion is similar to the control emulsion D with octahedral grains but it is sensitized to green. It includes silver halides (1.34 Ag), nucleating agent V [17.0], nucleating agent VI [0.87] and oxidizing developer immobilizer VII [4000 ] and gelatin (1.34). Layer 10:
Interlayer which contains titanium dioxide (0.32) and gelatin (0.65).

   Layer 9:
Layer containing the RDR II compound releasing a magenta dye (0.43) and gelatin (0.86). Layer 8:
Interlayer which contains a negative emulsion with silver bromoiodide (0.05 Ag), the immobilizing agent of the oxidized developer VIII (1,1) and of gelatin (1,2). Layer 7:
Silver halide emulsion layer sensitive to red: emulsion B (1.34 Ag), nucleating agent V [2.0] immobilizing agent for oxidized developer VII [4000], and gelatin (1.34) . Layer 6:
Gelatin interlayer (0.43). Layer 5:
Interlayer which contains titanium dioxide (0.81) and gelatin (0.65). Layer 4:
Layer which contains the RDR III compound releasing a blue-green dye (0.43) and gelatin
(0.65).

   Layer 3:
Opaque layer which contains carbon (1.9) the compound RDR IV (0.02) the immobilizing agent of the oxidized developer VII (0.03) and gelatin (1.2). Layer 2:
Reflective layer that contains titanium dioxide (22.0) and gelatin (3.4). Layer 1:
Receiving layer which includes the mordant IX (4.8) and gelatin (2.3). The above layers are applied to a transparent polyester support in the order indicated. A control photographic product is prepared, with a unitary structure, with an integrated image-receiving element, having the arrangement of the preceding layers, with the exception that layer 7 comprises the emulsion D with the silver title of 1.4 / m .

   To treat the two preceding photographic products, a treatment composition contained in a frangible capsule is used which comprises the following constituents:
  <EMI ID = 151.1>
 * The Tamol SN product is manufactured by the Rohm et Haas Company:
The treatment sheets used to treat the two photographic products comprise, applied to a transparent polyester support, in the order indicated, the following layers:
Layer 2:
Retardant layer which comprises a mixture in the 1: 1 ratio of two polymers applied to a <EMI ID = 152.1> ment the terpolymer of acrylonitrile, vinylidene chloride and acrylic acid in the mass ratio
14:79:

  7, isolated in the form of latex, dried and dispersed in an organic solvent, and the second polymer is a lactone carboxyester formed by cyclization of a copolymer of vinyl acetate and maleic anhydride in the presence of 1-butanol so as to form a partial butyl ester, with a mass ratio of acid to butyl ester of 15:85, prepared as described in the US patent 4,229,516. This layer further contains t-butylhydroquinone monoacetate as a competing developer (0.22) and 5 (2-cyanoethyl) -phenyltetrazole as a blocked inhibitor (0.11). Layer 1:
Acid layer which comprises the copolymer of butyl acrylate and acrylic acid in the mass ratio 30:70, representing 140 milli-equivalents of acid / m <2>.

   Composite photographic films forming image by diffusion transfer, including the treatment composition and the treatment sheet, are used in the following manner:
Each composite photographic product is exhibited with a unitary structure, and with an integrated image-receiving element, multi-color image-forming element, for 0.01 s, in a sensitometer, through a shade scale and with ex light. - <EMI ID = 153.1>
(daylight balanced towards neutral), then they are treated, at a controlled temperature, (either at 16 [deg.] C, or at 22 [deg.] C), using a viscous treatment composition contained in a frangible capsule.

   The treatment composition is spread out between the composite photographic products and the transparent treatment sheet, then the assembly is passed between a pair of juxtaposed rollers so as to obtain a layer of treatment composition of approximately 65 μm. After a contact time of more than 1 hour, the density in red light of the shade scale is read. The minimum density Dmin and the maximum density Dmax are measured from the sensitometric curve. The results obtained are collated in Table IA.

TABLE IA

  

  <EMI ID = 154.1>


  
The results of Table IA show that the photographic product according to the invention, which contains a tabular grain emulsion, makes it possible to obtain higher maximum densities of red dye when

  
  <EMI ID = 155.1>

  
maximum tee read in red light for these two temperatures is lower in the case of the photographic product according to the invention which contains the tabular grain emulsion than for the control photographic product which contains an emulsion with octahedral grains, which demonstrates that the red-sensitized layer

  
of the product according to the invention has a latitude

  
improved treatment temperature compared to the control product. The sensitivity of the emulsions and photographic products according to the invention and of the control photographic product are practically equivalent:

  
EXAMPLE 1B:

  
Photographic products similar to those of Example 1A are prepared, but these photographic products form single-color images and do not contain layers 15 to 8, the overlay 16 being applied to the emulsion layer. silver halides sensitive to red 7. The treatment composition contained in the frangible capsule and the treatment sheet are similar to those described in Example 1A, but the

  
treatment sheet contains the inhibiting agent and the competing developer, each at 0.043 g / m <2>.

  
The results obtained are collated in Table IB.

TABLE IB

  

  <EMI ID = 156.1>


  
The results of Table IB show that the photographic product according to the invention which comprises a single dye image-forming element has the same advantages as a photographic product as described in Example 1A, that is to say that it has an improved processing temperature latitude and a maximum density Dmax-improved for the temperature

  
low development.

  
EXAMPLE 2:

  
This example shows that a photographic product according to the invention, for example a photographic product which comprises a layer of emulsion B with tabular grains, with internal latent image, sensitized to red, such as that which is used in Example 1A , has improved storage properties at room temperature when compared to a control emulsion such as emulsion D with octahedral grains.

  
The photographic product according to the invention used is the same as the photographic product forming a single-color image described in Example 1B. On the other hand, two controls similar to the control photographic product of Example 1B are used, but the layer 7 of these two control photographic products contains an octahedral emulsion whose grains have a diameter respectively equal to 1.4 μm and 1.8, um. The capsule, the treatment composition and

  
the treatment sheet are similar to those described in Example 1B.

  
Treatment conditions are similar

  
  <EMI ID = 157.1>

  
tion of the treatment temperature which is only the temperature of 22 [deg.] C. To determine the stability of photographic products in storage, exposure and processing of a series of photographic products in the newly prepared state is carried out, and another series of photographic products stored at room temperature are exposed and processed.

  
7 weeks.

  
The results obtained are collated in Table II.

TABLE II

  

  <EMI ID = 158.1>


  
The results of Table II show that the two control photographic products which comprise emulsions with octahedral grains exhibit a much more considerable decrease in maximum density when stored at room temperature for

  
7 weeks as the photographic product according to the invention which comprises emulsion B. The variations in the minimum density and the sensitivity between the control photographic products and the photographic products according to the invention are not very significant. EXAMPLE 3:

  
This example shows that the photographic products according to the invention which contain emulsions with internal latent image, with tabular grains, sensitized to red, exhibit both an improvement in the inversion sensitivity and a better separation between the first and the second. inversion, when doped with a cadmium compound.

  
The control photographic product contains an emulsion without a doping agent containing cadmium, such as emulsion B, which is the same as that used in Example 1B. The photographic product according to the invention contains emulsion C which is doped with a compound containing cadmium, as defined above. The structure of the control product and of the product according to the invention comprises layers 16 and 7 to 1, as defined in Example 1B. The frangible capsule, the treatment composition and the treatment sheet are similar to those of Example 1B. The exposure and treatment conditions are analogous to those of Example 1A, with the exception of the treatment temperature which is only room temperature. Sensitivities

  
at the inversion threshold are measured at a density of 0.3 below the maximum density, and the separation between the first and the second inversion is measured at the density of 0.7. A difference of 30 relative sensitivity units corresponds to 0.30 log E.

  
The results obtained are collated in Table III.

TABLE III

  

  <EMI ID = 159.1>


  
The results of Table III show that the cadmium doped emulsion has a sensitivity which is greater than 0.20 log E and a separation of sensitivity between the first and second inversion which is greater than 0.37 log E relative to the values corresponding obtained with an emulsion devoid of doping agent containing cadmium. It is highly desirable that the sensitivity of the first inversion become faster and the sensitivity of the second inversion become slower.

  
The experimental results have furthermore shown that the surface negative image can be reduced significantly if the fraction of the external envelope of the tabular grains of the emulsion is doped either with lead II or with erbium III .

  
EXAMPLE 4:

  
This example shows that the products according to the invention which contain emulsions with an internal latent image and with tabular grains exhibit an increase in the separation of the sensitivity between the first inversion and the second inversion corresponding to the negative surface image, when the fraction of the outer shell of the tabular grains of the emulsion contains iodide ions. whose molar concentration increases towards the surface of the crystal.

  
We emulsify spectrally

  
E and F, as defined above, using

  
  <EMI ID = 160.1>

  
1'-diethyl-3-3'-di (3-sulfobutyl) benzimidazolcarbocyanine per mole of Ag and 125 mg of anhydrohydroxide

  
  <EMI ID = 161.1>

  
bocyanin per mole of Ag. These emulsions are then applied to a polyester film with a silver titer of 2.15 g / m and a gelatin titer of 4.52 g / m. The photographic products are then exposed to the light provided by a xenon flash lamp for

  
0.01 s, on a continuous density scale, in an Edgerton Germeshausen and Grier sensitometer, then treated for 4 minutes in a developer which contains hydroquinone and N-methyl-p-aminophenol sulfate , as well as <EMI ID = 162.1>

  
methylbenzotriazole. On the other hand, control tests are carried out with spectrally non-sensitized emulsions.

  
The results obtained are collated in Table IV.

  

  <EMI ID = 163.1>


  

  <EMI ID = 164.1>
 

  
The results of Table IV show that the emulsion F which contains tabular grains whose iodide concentration of the fraction of the external envelope increases towards the outside of the silver halide grain, presents a separation between the first and the second inversions significantly larger than that of emulsion E, the outer envelope of which is made of pure silver bromide. The spectrally sensitized emulsion F has a sensitivity separation between the first and second upper inversion of 3.26 log E units for a density of 0.70, while the spectrally sensitized control emulsion E has a corresponding separation of 1 , 22 log E.

   It has also been noted that the emulsion F spectrally sensitized undergoes a lesser desensitization of blue sensitivity than the control emulsion E spectrally sensitized.

  
EXAMPLE 5:

  
A silver bromide emulsion with an internal latent image, with tabular grains, with a high shape index, of which the average grain diameter is 5.5 / μm, the average grain thickness of 0.12, μm, is prepared. and the average shape index of 46: 1, the tabular grains representing 85% of the total projected surface of the grains, operating as follows:

  
We precipitate by the double technique

  
  <EMI ID = 165.1>

  
of silver intended to constitute the cores of the silver bromide grains to be formed, cores with an average diameter

  
  <EMI ID = 166.1>

  
then chemically sibilizes this emulsion constituting the nucleus of the grains by means of 0.9 mg of sodium thiosulfate to 5 molecules of water per mole of Ag and 0.6 mg of potassium chloroaurate per mole of Ag, for <EMI ID = 167.1>

  
kernels of the grains to be formed, an additional quantity of silver bromide is then precipitated to a pBr

  
  <EMI ID = 168.1>

  
the silver bromide emulsion, with tabular grains, with a nucleus surrounded by an external envelope.

  
This emulsion is then applied to a polyester film with a silver grade of 2.15 g / m <2> and

  
  <EMI ID = 169.1>

  
second photographic product, the emulsion layer of which contains 50 mg of 1- (2-propynyl) -2 methylquinoline bromide per mole of Ag. These two photographic products are exposed for 0.1 s to the light provided by a tungsten filament lamp of

  
  <EMI ID = 170.1>

  
then they are treated in a developer with hydroquinone and with N-methyl-p-aminophenol sulfate which contains 0.25 g / l of 5-methylbenzotriazole, at 20 [deg.] C, for

  
3 mins.

  
The sensitometric results obtained show that the control product does not provide an image by inversion. On the other hand, the photographic product which contains the emulsion, with tabular grains, with nucleus and external envelope and which contains bromide of

  
  <EMI ID = 171.1>

  
an inversion image with a maximum density of 0.69 and a minimum density of 0.18.

  
Appendix

  
  <EMI ID = 172.1>

  
redox dyes have structures as described in "Research Disclosure" Vol. 182,

  
  <EMI ID = 173.1>

  
  <EMI ID = 174.1>

  

  <EMI ID = 175.1>


  
(in dispersion in Di-n-butyl phthalate)

  
II. RDR magenta compound

  

  <EMI ID = 176.1>


  
(in dispersion in diethyllauramide) III. Blue-green RDR compound

  

  <EMI ID = 177.1>


  
(in dispersion in N-n-butylacetanilide)

  
IV. Blue-green RDR compound

  

  <EMI ID = 178.1>


  
(in dispersion in N-n-butylacetanilide)

  
The nucleating agents V and VI correspond to the following formulas:

  

  <EMI ID = 179.1>


  

  <EMI ID = 180.1>


  
The immobilizing agents VII and VIII of the oxidized developer correspond to the following formulas:

  

  <EMI ID = 181.1>


  

  <EMI ID = 182.1>


  
The mordant used is the following compound:

IX.

  
Terpolymer of styrene, 1-vinylimidazole and 3-benzyl-1-vinylimidazolium chloride in the approximate mass ratio 50:40:10.

CLAIMS

  
the projected area of this grain.

  
1.- Direct positive photographic product comprising a support on which is applied at least

  
an emulsion layer which comprises a dispersion medium, grains of silver halides capable of

  
to form an internal latent image and a nucleating agent, characterized in that at least 50% of the total projected surface of the silver halide grains

  
consist of tabular grains which have an average thickness of less than 0.5 µm and an index of

  
average shape greater than 8: 1, the shape index being

  
defined by the ratio of the diameter of the grain to the thickness of the grain, the diameter of the grain being defined by

  
the diameter of a circle whose area is equal to

  
2.- Photographic product conforming to the


    

Claims (1)

Claim 1, characterized in that the silver halide grains consist of silver bromide. 3. Photographic product according to claim 1, characterized in that the silver halide grains are silver bromoiodide grains. 4.- Photographic product conforming to any one of claims 1 to 3, characterized in that the tabular silver halide grains have an average shape index at least equal to 10: 1. 5. Photographic product according to any one of claims 1 to 4, characterized in that the tabular silver halide grains represent at least 70% of the total projected area silver halide grains. 6. Photographic product according to any one of claims 1 to 4, characterized in that the tabular silver halide grains represent at least 90% of the total projected area of the silver halide grains. 7. Photographic product according to any one of Claims 1 to 6, characterized in that the said emulsion, when applied to an <EMI ID = 183.1> exposed to the light provided by a 500 W tungsten filament lamp, placed at a distance of 60 cm, for a period of between 0.01 s and 1 s, then developed in the developer Y defined below, at 20 [deg.] C, for 5 min, then fixed, washed and dried, provides maximum density at least equal to 5 times the maximum density provided by an identical emulsion which has been exposed in the same way and developed in developer X defined below, at 20 [deg.] C, for 6 min, then fixed, washed and dried, developer X comprising the following constituents:  <EMI ID = 184.1> and the developer Y comprising the following constituents:  <EMI ID = 185.1> 8.- photographic product according to any one of claims 1 to 7, characterized in that the tabular silver halide grains contain internal physical sensitization sites. 9. Photographic product according to any one of claims 1 to 7, characterized in that the tabular silver halide grains contain internal chemical sensitization sites. 10. Photographic product according to claim 9, characterized in that the internal sensitization sites are formed by at least one doping agent chosen from the group of doping agents containing iridium and lead. 11. Photographic product according to claim 9, characterized in that the internal chemical sensitization sites are formed by a medium chalcogen incorporated in the tabular grains. 12. Photographic product according to any one of claims 1 to 11, characterized in that the tabular silver halide grains comprise, in addition, gold incorporated inside the grains. 13.- Photographic product according to any one of claims 1 to 12, characterized in that the tabular silver halide grains contain at least one compound of a metal chosen from the group consisting of lead, cadmium , zinc and erbium, at a concentration sufficient to reduce the formation of the second inversion. 14.- Photographic product according to any one of claims 1 and 3 to 13, characterized in that the tabular silver halide grains are silver bromoiodide grains and in that at least one spectral sensitizer blue is present in said emulsion, this sensitizer being chosen from the group consisting of cyanines, merocyanines, hemicyanins, hemioxonols, and merostyrylic dyes. 15.- Photographic product according to any one of claims 1 to 14, characterized in that the nucleating agent of the emulsion is chosen from the group consisting of nucleating agents of the class of aromatic hydrazides, agents of nucleation from the class of N-substituted quaternary cycloammonium salts and mixtures thereof. 16. Photographic products according to any one of claims 1 to 15, characterized in that the nucleating agent is a hydrazyde which corresponds to the following formula:  <EMI ID = 186.1> or : D representing an acyl group, 0 represents a phenylene group, or phenylene substituted by a halo, alkyl or alkoxy group, and ,, M is a group capable of reducing mobility. 17. Photographic product according to any one of claims 1 to 15, characterized in that the nucleating agent is a phenylhydrazyde corresponding to the following formula:  <EMI ID = 187.1> or : R represents a hydrogen atom, an alkyl, cylcoalkyl, haloalkyl, alkoxyalkyl or phenylalkyl radical or a nucleus, phenyl having an electron acceptor characteristic derived from the Hammett sigma value more positive than the value -0.30,  <EMI ID = 188.1> phenylene radical substituted by an alkyl, halogen or alkoxy group, <EMI ID = 189.1> benzyl, alkoxybenzyl, halogenbenzyl, or alkylbenzyl group, R represents an alkyl, haloalkyl, alkoxyalkyl or phenylalkyl group of 1 to 18 carbon atoms, a cycloalkyl group, a phenyl nucleus whose electron acceptor characteristic derived from the Hammett sigma value is less positive than +0, 50, or the naphthyl group, R4 represents a hydrogen atom, or one  <EMI ID = 190.1>  <EMI ID = 191.1> 5 or 6-membered heterocyclic ring, the atoms of the heterocyclic ring of which are chosen from the group consisting of nitrogen, carbon, oxygen, sulfur, and selenium, alkyl groups, unless otherwise indicated, comprising from 1 to 6 carbon atoms, and cycloalkyl groups from 3 to 10 carbon atoms and at least one of the radicals R2 and R3 necessarily representing the hydrogen atom . 18. Photographic product according to any one of claims 1 to 15, characterized in that the nucleating agent is a hydrazyde or a hydrazone corresponding to one of the following formulas:  <EMI ID = 192.1> or : T represents a phenyl or naphthyl substituent,  <EMI ID = 193.1>  <EMI ID = 194.1> from 1 to 22 carbon atoms. 19. A photographic product according to claim 1, capable of forming a direct positive dye image by inversion, which comprises gelatin or a peptizing agent derived from gelatin, silver bromide or silver bromoiodide grains. surface chemically sensitized, capable of forming an internal latent image, a dye image-forming compound, and a nucleating agent, characterized in that at least 70% of the total projected surface of these grains is supplied by tabu-  <EMI ID = 195.1> the average thickness less than 0.3 / µm and the average shape index of at least 10: 1, and, when this emulsion is applied to a transparent film, with a silver content of 4 g / m <2 >, then exposed to the light of a 500 W tungsten filament lamp, placed at 60 cm, for a period of between 0.01 s and 1 s, then developed in the developer Y defined below, at 20 [deg.] C, for 5 min, then fixed, washed and dried, provides maximum density silver film at least equal to 5 times the maximum density of an identical emulsion which has been exposed in the same way and developed in developer X defined below, at 20 [deg.] C, for 6 min, then fixed, washed and dried, the developers X and Y being as defined in claim 7. 20.- Photographic product according to claim 19, characterized in that the tabular grains contain iridium as doping agent  <EMI ID = 196.1> 10 -4 mole per mole of silver. 21. Photographic product according to claim 19, characterized in that the tabular grains contain lead as internal doping agent at a concentration of between 10 'and 5 x 10 &#65533; <2> mole per mole of silver. 22. Photographic product according to any one of Claims 19 to 21, characterized in that the tabular grains are sensitized inside the grains by sulfur, possibly associated with gold. 23. Photographic product according to one of claims 19 to 22, characterized in that the tabular grains consist of a core and at least one external envelope which contains cadmium, lead, or mixtures of these last, at a con-  <EMI ID = 197.1> 24. Photographic product according to any one of claims 19 to 23, characterized in that the tabular grains consist of silver bromoiodide. 25.- Photographic product according to claim 24, characterized in that a more external region of the tabular grains contains iodide ions at a concentration greater than at least 2 mol% to that of a more central region of these tabular grains. 26.- Photographic product according to claim 24, characterized in that the tabular grains contain a core and at least one outer shell, and in that the iodide concentration of this outer shell is at least 6% higher in mole to the iodide concentration of the said nucleus. 27.- Photographic product forming a direct positive image with several colors by inversion, according to any one of claims 1 to 26, which comprises a support on which are applied. emulsion layers for recording blue, green and red spectrum light respectively, emulsions which include a dispersing medium, silver halide grains forming an internal latent image and a nucleating agent, the emulsion layers sensitive to green and red respectively containing spectral sensitizing dyes to green and red, photographic product characterized in that, in at least one of the sensitive emulsion layers in green and red, at least 50% of the total projected surface of the silver halide grains are provided by tabular silver halide grains, forming an internal latent image, having a thickness  <EMI ID = 198.1> minus 0.6, µm and an average shape index greater than 8: 1. 28.- Photographic product according to claim 27, characterized in that one of these emulsion layers which contains tabular silver halide grains is arranged so as to receive the exposure light before the other layers. emulsion of said photographic product. 29.- Photographic product according to claim 27, characterized in that one of the emulsion layers which contains grains of tabular silver halides is arranged so as to receive the light transmitted in the manner of a mirror. and in that this emulsion layer is superimposed on at least one other emulsion layer of said photographic product. 30.- Photographic product according to any one of claims 27 to 29, characterized in that the tabular silver halide grains of said emulsion layer have an average diameter at  <EMI ID = 199.1> 31.- Photographic product according to any one of claims 27 to 30, characterized in that the blue-sensitive emulsion layer comprises grains of tabular silver halides, forming an internal latent image, the thickness of which mean is less than 0.5 µm and the mean diameter of which is <EMI ID = 200.1> 50% of the total projected surface of the said silver halide grains present in the said emulsion layer. 32.- photographic product according to any one of claims 27 to 31, characterized in that at least one of said emulsion layers sensitive to green and red contains tabular grains which consist of silver bromide or silver bromoiodide. 33.- Photographic product forming a direct positive image with several colors by inversion, according to claim 1, which comprises a film. to which color image forming elements are applied to register blue, green and red light respectively and which contain dye forming couplers respectively yellow, magenta and blue-green, characterized in that these image forming elements of dyes are such that, when this photographic product is exposed to a light whose color temperature is equal to 5500 [deg.] K, through a spectral non-selective shade scale, then it is processed to obtain an image in color, this photographic product presents, compared to the contrast and the sensitivity in blue light, variations in contrast in green light and in red light, less than 20%, and variations with a sensitivity in green light and in red light less than 0.3 log E, each of the elements forming the color image comprising at least one emulsion layer which contains a dispersion medium, grains of silver halides and a nucleating agent, the silver halide grains of at least one of the emulsion layers for recording blue, green and red light respectively being arranged to receive the exposure light before the grains of another emulsion layer having an average diameter of at least 2.0 µm, and at  <EMI ID = 201.1> silver bromide or tabular silver bromoiodide, forming an internal latent image, contained in at least one of the emulsion layers sensitive to green and red have an average thickness less than  <EMI ID = 202.1> with an average shape of at least 10: 1, the tabular grains forming an internal latent image in these emulsion layers sensitive to green and red being both chemically sensitized inside the grains and on the surface of the grains. 34.- photographic product according to claim 33, characterized in that it does not include a yellow filter substance or that it comprises an amount of yellow filter substance less than the usual amount which is interposed between the incident exposure radiation on the photographic product and at least one of the emulsion layers which contains tabular grains. 35.- photographic product according to claim 33, characterized in that at least one of the layers which contains tabular grains is arranged so as to receive the exposure light before the blue-sensitive emulsion layer. 36.- Photographic product according to claim 33, characterized in that at least one of the layers which contains tabular grains is arranged so as to receive the exposure light before all the other layers of halide emulsion d money from the photographic product. 37.- Photographic product according to any one of claims 33 to 36, characterized in that the tabular grains are present either in the layer sensitive to green, either in the layer sensitive to red, or in these two layers of emulsion. 38.- Photographic product according to claim 1, in the form of a composite film forming image by diffusion transfer, which comprises a support on which is applied at least one emulsion layer which contains a dispersion medium, photosensitive silver halide grains forming an internal latent image and a nucleating agent, a dye image-forming compound being present either in the emulsion layer or in a layer adjacent thereto, and a receptor layer dye image for obtaining a visible transferred dye image after image exposure and treatment of the emulsion layer, this photographic product being characterized in that tabular silver halide grains forming an internal latent image in at least one of the emulsion layers have a  <EMI ID = 203.1> at least 0.6 / µm and an average shape index greater than 8: 1, these tabular grains representing at least 50% of the total projected surface of said photosensitive silver halide grains present in said layer d 'emulsion. 39.- Photographic product according to claim 38, characterized in that said dye image receiving layer is arranged in position adjacent to a second support. 40.- photographic product according to claim 39, characterized in that said second support is a reflective support. 41.- Photographic product according to claim 39, characterized in that said second support is a transparent support. 42.- Photographic product according to claim 38, characterized in that said dye image-receiving layer is disposed between said support and said emulsion layers. 43.- Photographic product according to any one of claims 38 to 42, characterized in that the said tabular silver halide grains represent at least 70% of the total projected surface of the photosensitive grains present in said layer d 'emulsion. 44.- Photographic product according to any one of claims 38 to 43, characterized in that the said silver halide grains are grains of silver bromide or silver bromoiodide. 45.- Photographic product according to any one of claims 38 to 44, characterized in that the said tabular silver halide grains have an average shape index at least equal to 10: 1. 46.- Photographic product according to claim 1, in the form of a composite film forming dye image by transfer diffusion, which comprises a transparent support to which is applied at least one emulsion layer which contains a medium dispersion, photosensitive silver halide grains, forming an internal latent image, and a nucleating agent, a dye image-forming compound being disposed in said emulsion layer or in a layer adjacent to it this, a transparent treatment sheet, a dye image-receiving layer applied to this treatment layer, a basic treatment solution, and means for releasing this basic treatment solution in contact with the emulsion layers, this photographic product being characterized in that at least 70% of the total projected area of the photosensitive silver halide grains is provided by tabular silver halide grains forming an internal latent image whose average thickness is  <EMI ID = 204.1> 0.66um and the average shape index of at least 10: 1. 47.- Photographic product according to claim 46, characterized in that it comprises, in addition, means for stopping the development of the silver halides located in an adjacent position said support or said treatment sheet. 48.- Photographic product according to one of claims 46 or 47, characterized in that it further comprises a reflective layer located in position adjacent to said receiving layer, and disposed between the image receiving layer of dye and the said emulsion layer. 49.- Photographic product according to any one of claims 46 to 48, characterized in that the tabular silver halide grains have an average thickness of less than 0.3 µm. 50.- Photographic product according to claim 1, in the form of a composite image-forming film with several colors by transfer diffusion, which comprises a support on which dye-forming elements are applied, each one comprising at least one dye image-forming compound and at least one silver halide emulsion which contains a dispersing medium, photosensitive silver halide grains forming an internal latent image, and a nucleating agent , these dye image-forming elements comprising a dye-forming element which contains a red-sensitive emulsion and a blue-green dye-forming compound, a dye image-forming element which contains a green-sensitive emulsion and a magenta dye imaging compound,  and a dye imaging element which contains a blue-sensitive emulsion and a yellow dye image-forming compound, and a dye image-receiving layer which provides a multi-color, transferred, visible image after image exposure and processing, the photographic product being characterized in that at least 70% of the total projected area grains of photosensitive silver halides in at least one of said emulsion layers are provided by tabular silver halide grains, forming an internal latent image, the average thickness of which is less than 0, 5 / um, the average diameter is at least  <EMI ID = 205.1> 10: 1. 51.- Photographic product according to claim 50, characterized in that the tabular silver halide grains represent at least 90% of the total surface of the grains of said emulsion layer. 52.- Photographic product according to any one of claims 50 and 51, characterized in that said emulsion which contains the tabular grains is a silver bromide or silver bromoiodide emulsion sensitive to green or sensitive to red and which is arranged so as to receive the exposure light before the other layers silver halide emulsion of said photographic product. 53.- Photographic product according to any one of claims 50 to 52, characterized in that the dye image-forming compounds are compounds which release dyes by redox following a negative process. 54.- Photographic product according to any one of claims 50 to 53, characterized in that the tabular grains contain at least one compound of a metal chosen from the group consisting of lead, cadmium, zinc and erbium, at a concentration sufficient to reduce the formation of the second inversion. 55.- Photographic product according to any one of claims 50 to 54, characterized in that the nucleating agent is a hydrazyde corresponding to the following formula:  <EMI ID = 206.1> or : D represents an acyl group, 0 represents a phenylene group or a phenylene group substituted by a halo, alkyl or alkoxy group, and, M is a group capable of ensuring mobility.