FR2656434A1 - PRODUCTS FOR COLOR PHOTOGRAPHY CONTAINING A LAYER OF REFLECTIVE TABULAR GRAIN. - Google Patents

Abstract

The present invention relates to a multilayer product for colour photography. The product is comprised of, under one of the layers or under each blue-sensitive layer, an intermediary layer including non photosensitive tabular silver halogenide grains having a thickness comprised between 0.03 and 0.2 mu m. Application to a product for colour photography with improved sensitivity.

Description

PRODUCTS FOR COLOR PHOTOGRAPHY CONTAINING A
LAYER OF REFLECTIVE TABULAR GRAIN
The present invention relates to products for color photography, and more particularly to reversible color films and papers, having improved sensitivity.

 Products for color photography usually comprise three layers or three types of silver halide emulsion layers sensitive respectively to a distinct third of the visible spectrum, that is to say to blue, green and red. Because silver halides are inherently blue sensitive, the blue sensitive layer (s) are generally placed on the exposure side. Most of the blue light is thus absorbed. The rest of the blue light is absorbed by a filter layer absorbing the blue light which is generally placed between the layer or layers sensitive to blue and the layers sensitive to green and red, in order to avoid that the layers sensitive to green and red intrinsically sensitive to blue are not bothered by blue light.

This part of the blue light absorbed by the filter was not used in the blue sensitive layer, which corresponds to a reduction in the sensitivity of the blue sensitive layer.

 To overcome this drawback, it has already been proposed in the prior art to use in the blue-sensitive layer or in an underlying layer of fine light-diffusing particles such as particles of titanium dioxide, zinc oxide , barium sulfate or a very fine grained, non-photosensitive silver halide emulsion. Such a process has been described in "Research Disclosure" No 134 (1975) 'p. 47, item 13452. However, this process has the disadvantage of increasing the granularity and reducing the sharpness.

 U.S. Patent 4,539,289 describes a layer structure which avoids these disadvantages by placing the layer of diffusing particles at specific locations in the structure of the photographic product.

 On the other hand, there are known emulsions containing tabular silver halide grains. Thus, for example, United States patent 4,439,520 (Kofron) describes tabular grains having a thickness of less than 0.5 µm, a diameter of more than 0.6 lira and an average shape index greater than 8/1, representing more than 50% of the total projected surface of the silver halide grains. These tabular grains are used in products for color photography, as photosensitive grains forming developable latent image. They have the advantage of having a lower sensitivity to blue light than non-tabular grains, which reduces the interference of blue light in the layers sensitive to green and red, and makes it possible to modify the order of the layers on the support if desired.

 In the present application the grains diffusing the light designate grains diffusing the light in all the directions, and grains reflecting the light indicate grains reflecting the light in the direction of the exposure.

 It is known to calculate by calculation the optical characteristics of the tabular grains, as a function of their thickness. This is described in "Research Dislosure" May 1985, item 25330. The variation of the percentage of light reflected by tabular silver halide grains as a function of the wavelength and thickness of the grains is illustrated in Figure 1 of this publication.

However, these are calculated theoretical curves; it is also mentioned in this publication that a layer of tabular grains underlying the blue sensitive layer and reflecting blue light significantly reduces the sharpness of the image formed in the blue sensitive layer.

 It should also be noted that layers of tabular halide grains practically insensitive to light, that is to say not participating in the image in the structure of a product for color photography, are not mentioned. in the prior art.

 Given the complexity of the physical and chemical interactions in a photographic product, it was not possible to foresee that an underlayer of reflective grains could make it possible to obtain an improved sensitivity of the yellow layer, without the disadvantages of the layers of diffusing grains of the prior art.

 One could also think that the advantages obtained on the blue layer would be destroyed by unfavorable effects on the other layers, such as a reduction in sensitivity in the blue minus, or unfavorable interimage effects.

 The subject of the present invention is a product for color photography whose sensitivity to blue light is improved, without any adverse effect on the other properties of the photographic product.

 The product according to the invention comprises, on a support, a layer or a set of layers sensitive to red light, associated with a coupler forming cyan dye, a layer or a set of layers sensitive to green light, associated with a coupler forming a magenta dye and a layer or a set of layers sensitive to blue light associated with a coupler forming yellow dye, and it is characterized in that it comprises, under one of the layers or under each layer sensitive to blue, an intermediate layer comprising gelatin and tabular silver halide grains whose intrinsic sensitivity is lower than the sensitivity of the photosensitive silver halide grains forming the image, by at least the value of the interval for modulating the D / Log E curve of said photosensitive grains, having an average thickness of between 0.03 and 0.2 lira and a shape index of at least 2: 1, and preferably greater than 5: 1, at a rate of 2 to 10 mg / dm2, and preferably from 2 3 to 5 mg / dm2.

 The expression “set of layers” in the present application designates layers sensitive to the same part of the visible spectrum and which are placed in the product in a contiguous or non-contiguous manner.

 According to a preferred embodiment, tabular silver halide grains having an average thickness of between 0.03 and 0.07 µm are used.

 Can be used in the intermediate layer of tabular grains according to the invention tabular grains of average thickness between 0.03 and 0.2 lira. The reflective powers of these grains can be calculated, as indicated above. The most selective grains for blue compared to the blue minus have an average thickness of about 0.15 lira It is assumed that these grains are the most advantageous for reflecting only blue light towards the blue layer, while they are crossed by the blue minus lights which reach the underlying layers sensitive to green and red in a product for color photography having a conventional structure, the blue sensitive layer is the outermost with respect to the support and located on the side of the exhibition. However, it has been observed that grains of 0.05 lira thickness, which also have good reflection in blue, but which are not selective, are also useful, and do not significantly reduce the sensitivity to blue minus of underlying emulsions sensitized to green and red.

 It has also been observed that the grains of 0.05 lira thickness also have the advantage, compared to the grains of 0.15 lira thickness, of having better reflection for the same silver content on the layer. . We could increase the reflection of the flat grains by 0.15 lira thick by increasing the silver content of the emulsion. Thus, it is possible to use flat grains having thicknesses of between 0.03 and 0.2 μm, the choice of thickness depending on the desired results and on the photographic product in which the layer of tabular grains of the invention is used. The grains having thicknesses between 0.03 and 0.07 lira are however preferred since they allow the use of emulsions with lower silver titers, which is always advantageous, without degrading the sensitometric properties of the layers. underlying sensitive to green and red, contrary to what might have been expected.

 The shape index of the tabular grains used in the intermediate layer according to the invention depends on their diameter, the thickness being defined. The smaller the diameter of the grains, the more the diffusion phenomenon which we want to overcome will appear. It is therefore advantageous to use tabular grains whose shape index is at least 2: 1, and preferably greater than 5: 1. These tabular grains can have any shape. For example they can be hexagonal, triangular, square, rectangular.

 The intrinsic sensitivity of these tabular grains is less than the sensitivity of the photosensitive silver halide grains forming the image, by at least the value of the modulation interval of the D / Log E curve of said photosensitive grains. The modulation interval of the curve D / Log E (density as a function of the logarithm of the exposure) of a photographic emulsion, is the difference of the exposure values between the foot and the shoulder of the curve, or between maximum density and minimum density. The tabular grains used as an undercoat in the invention must not be photosensitive within the modulation range of the photosensitive grains forming the image. For example, in a color reversible photographic paper, the intrinsic sensitivity of the tabular grains used in the present invention must be 2 log E less than the sensitivity of the grains forming the image. The intrinsic sensitivity represents the sensitivity of the silver halide grains before any treatment such as the addition of sensitizing dyes, and in particular before formation of the haze, in the case where hazy grains are used.

 Any halide can be used for tabular grains. The tabular grains have equivalent reflections for the same thickness whatever their composition. However, the tabular grains of silver chloride have a lower intensity of reflection than those of silver bromide. With regard to the bromoiodide grains, the presence of iodide which is released during development, tends to inhibit the development of the grains of the neighboring layers, and therefore to decrease the sensitivity, all the more so as the content of iodide in the tabular grains is higher.

In practice, tabular grains of silver bromide are preferred.

 Tabular grains of thickness between 0.03 lira and 0.2 lira can be prepared by the preparation methods described in US Patent 4,439,520 (or its French correspondent 2,516,256). Thus, for example, Example 3 of Table VI of this patent gives a process for the preparation of tabular grains 0.15 lira thick and with a shape index of 19: 1. In Table XI, grains of 0.19 µm, 0.07 and 0.06 lira are found, having shape indices of 40: 1, 40: 1 and 27: 1, respectively. In Table XVIII, emulsion 1 contains grains 0.10 lira thick, and with a shape index of 16: 1.

 The silver titles of the intermediate layer of tabular grains according to the invention can vary from 2 to 2 10 mg / dm2. It has been shown in fact that outside these limits the increases in sensitivity obtained, although present, are too small to be useful.

 This layer is located, as indicated above, under one of the layers or under each layer of emulsion sensitive to the blue of a color photographic product. Preferably, it is adjacent to a blue-sensitive layer. However, it can optionally be separated from it, for example by a layer of gelatin containing photographically useful adjuvants.

 The intermediate layer of tabular grains may itself contain adjuvants such as those described in Research Disclosure, Vol 176, December 1978, Article 17643, Sections V and VI and IX to XII, and possibly photographically useful substances.

 Color photographic products in which the intermediate layer of tabular grains according to the invention can be used are all products having the conventional structure in three layers or three sets of layers sensitive respectively to blue, green and red light, one of the layers sensitive to blue on the exposure side.

Such products are described, for example, in the journal "Research Disclosure", Vol. 176, December 1978, item 17643, Section VII, paragraphs C to G, I and J.

 The photosensitive emulsions of the color photographic product of the invention can contain all kinds of silver halide, such as chlorides, bromides, bromoiodides, chlorobromides, etc., as well as all forms of grains, such as coarse grains, fine grains, octahedral grains, heart and shell grains, tabular grains, etc.

The reference cited above contains all that relates to the preparation of emulsions (sections I and II), chemical and spectral sensitizations (sections III and IV), adjuvants such as optical brightening agents (section V) , anti-stars and stabilizers (section VI), vehicles (section IX), tanning agents (section X), coating aids (section
XI), plasticizers and lubricants (section XII).

 The intermediate layer of tabular grains according to the invention can be applied with the other layers of the photographic product by any known coating process, such as those described in the Research Disclosure reference cited above, section XV, on supports such as those described in the same reference section XVII. The support for the photographic product can be a transparent film or it can be reflective, such as paper.

 In a preferred embodiment of the invention, the photographic product is an invertible product, that is to say it is treated in a first black and white developer to develop the silver halide in the exposed areas , veiled by exposure or chemically, then developed in a chromogenic developer to obtain, after money laundering, a positive color image of the original. In this case, the tabular grains of the intermediate layer are previously veiled, so as to be developed in the first black and white development and not to interfere in the subsequent chromogenic development. The tabular grains can be veiled by exposure or chemically, with any veiling agent known in the art. One can use for example, stannous chloride.

The following examples illustrate 1 invention
EXAMPLES 1 to 4
To show the effect of the intermediate layer of tabular grains on the sensitivity of an emulsion layer sensitive to blue, monolayer products are prepared comprising, on a paper support coated with polyethylene, in order
- an undercoat containing 1.7 mg / dm2 of silver
Carey-Lea and 12 mg / dm2 of gelatin,
- a layer containing a silver bromide emulsion
with tabular grains having dimensions indicated in
table I below, veiled with a solution
aqueous stannous chloride at a rate of 1 g of
SnCl2 / mole Ag, introduced at recast, at the rate of 2 2
4 mg silver / dm2, and 12 mg / dm2 gelatin,
- a layer containing a bromoiodide 2 emulsion
silver, at a rate of 4.7 mg silver / dm2,
spectrally sensitized to blue, a coupler
yellow dye trainer, and 12 mg / dm2 of
gelatin 2
- an overlay containing 8 mg / dm2 of gelatin.

TABLE I
Examples Average diameter thickness
1 0.5 will read 0.05 will read
2 1.73 lira 0.10 lira
3 1.60 lira 0.15 lira
4 1.69 lira 0.20 lira
Another identical product, but not containing the intermediate layer, is prepared to serve as a control.

 The two products are exposed under a density scale under the following conditions: 0.5 s, neutral density + 1.36, 2850 K, AC13 heat filter, in status A.

 They are developed with a standard reversible treatment for Ektachrome R3 paper, then they are read with an XRite densitometer.

 The difference between the sensitivity of the control product and that of the products according to the invention is determined.

This difference is shown in Table II below.

TABLE II
Examples Relative sensitivity
Witness 100
1,123
2,115
3,116
4,109
EXAMPLE 5
We are preparing a product for color photography with the following structure
Title in Ag Title in gelatin
(mg / dm2) (mg / dm2)
Overlay 8.00
Layer containing a 10.6
anti-W compound
Layer containing a 4.7 12 blue bromoiodide emulsion sensitized to blue and a coupler forming yellow dye
Intermediate layer of 3.00 12 tabular grains of silver bromide
Layer containing 1.7 12 Carey-Lea Silver
Layer containing 3.95 17.6 green bromoiodide emulsion sensitized to green and a magenta dye-forming coupler
Filter layer containing 1.5 8 reduced silver (Gray-Gel)
Layer containing a 3.00 13.00 silver bromoiodide emulsion sensitized to red and a coupler forming cyan dye
Underlay 25
SUPPORT PAPER
The tabular grains of silver bromide in the intermediate layer are those of Example 1 (0.05 lira thick) and they are veiled as in Examples 1 to 4.

 Another identical product, but not containing the intermediate layer of tabular grains, is prepared to serve as a control.

 The two products are exposed and treated as indicated for the products of Examples 1 to 4.

The sensitivities of the two products are given in Table III below
TABLE III
Sensitivities
in blue in green in red
Witness 89 91 76
Example 5,109 98,79
We can observe a significant gain in sensitivity in blue, with no significant adverse effect in green or red.

EXAMPLE 6
This example shows that the intermediate layer of reflecting flat grains according to the invention has no unfavorable influence on the interimage effects in a photographic paper in invertible color.

 The product of Example 5 is taken up and each layer is exposed separately through filters, one of the layers being exposed on a sensitometric scale, and the other two uniformly at two exposure values. The product is then treated as in Examples 1 to 4.

 Two tests are carried out on a product according to the invention and on a control product not containing the intermediate layer of flat grains.

Test I: modulated exposure of the magenta layer and
uniform of the yellow and cyan layers,
Test II: modulated exposure of the magenta and cyan layers
and uniform yellow layer.

 The interimage effect is expressed as the difference in density AD between the two extreme degrees of the sensitometric scale, for each product, in the yellow layer exposed uniformly.

 The results are collated in Table IV below.

AD in the yellow layer
High exposure Low exposure
Trial I
Witness -0.31 -0.28
Example 6 -0.23 -0.24
Test It
Witness -0.27 -0.51
Example 6 -0.26 -0.36
This table shows that the interimage effects in the product according to the invention are equivalent or better than in the control product.

Claims (8)

1 - Photographic product for color photography  comprising, on a support, a layer or an assembly  silver halide emulsion layers  sensitive to red light, associated with a coupler  cyan dye trainer, layer or set  silver halide emulsion layers  sensitive to green light, associated with a coupler  magenta dye trainer and a layer or a  set of halide emulsion layers  silver sensitive to blue light associated with a  yellow dye-forming coupler, characterized by  what it includes, under one of the layers or under each  blue-sensitive layer, an intermediate layer  comprising gelatin and halide grains  tabular silver whose intrinsic sensitivity  is less than grain sensitivity  photosensitive silver halides forming the image,  at least the value of the modulation interval of  the curve D / Log E of said photosensitive grains, having  an average thickness between 0.03 and 0.2 will read  and a form index of at least 2: 1, 2 to 2  10 mg / dm2. 2 - Photographic product according to claim 1,  characterized in that the grain shape index  tabular silver halide in the layer  intermediate is greater than 5: 1. 3 - Photographic product according to any one of  claims 1 or 2, characterized in that  the thickness of the silver halide grains  tabular in the middle layer is included  between 0.03 and 0.07 will read. 4 - Photographic product according to any one of  claims 1 to 3, wherein the grains  tabular silver halide in the layer  intermediate are silver bromide grains.  5 - Photographic product according to any one of  Claims 1 to 4, the support of which is a support  of transparent film. 6 - Photographic product according to any one of  claims 1 to 4, the support of which is  reflective. 7 - Photographic product according to any one of  Claims 1 to 6, in which the grain size  tabular silver halide in the layer  intermediate is between 3 and 5 mg / dm2. 8 - Photographic product according to one of claims  1 to 7, characterized in that it is treated according to a  reversible mode and that the halide grains  silver tabular middle layer are  previously veiled in the photographic product.