The present invention relates to color photographic products, and more particularly to reversal color papers and films, exhibiting an improved sensitivity. Background __f _____ invention

The color photographic products generally comprise three layers or three types of silver halide emulsion layers, sensitized to a separate third of the visible spectrum, i.e., to the blue, green, and red regions, respectively. As the silver halides are intrinsically blue sensitive, the blue sensitized layer(s) are generally placed on the exposure side. Thus, most of the blue light is absorbed. The remaining blue light is absorbed by a filter layer absorbing the blue light, generally placed between the blue sensitized layer(s) and the green and red sensitized layers, in order to avoid that the green and red sensitized layers which are intrinsically blue sensitive be disturbed by the blue light. This blue light portion absorbed by the filter has not been used in the blue sensitized layer, which corresponds to a decrease of the sensitivity of the blue sensitized layer.

In order to overcome this drawback, the prior art has suggested to use, in the blue sensitized layer or in an underlying layer," fine light—scattering particles, such as of titanium dioxide, zinc oxide, barium sulfate particles or a silver halide emulsion comprising very fine grains which are not photosensitive. Such method is disclosed in "Research Disclosure" No 134 (1975), p. 47, item 13452. However, this method exhibits the drawback of increasing granularity and reducing sharpness.

US Patent 4,539,289 discloses a layer order arrangement allowing to avoid these drawbacks, by placing the layer of scattering particles at specific locations in the structure of the photographic product. On the other hand, emulsions containing tabular silver halide grains are known. Thus, for example, US Patent 4,439,520 (Kofron) discloses tabular grains having a thickness lower than 0.5 μm, a diameter higher than 0.6 μm and an average aspect ratio higher than 8:1, accounting for more than 50% of the total projected surface area of the silver halide grains. These tabular grains are used in color photographic products as photosensitive grains forming a developable latent image. They are advantageous because they exhibit a native sensitivity to the blue light lower than the one of the non-tabular grains, thus reducing the interference of the blue light with green and red sensitized layers, and allowing to modify the layer order on the support, if desired.

In the present application, the wording "light-scattering" grains denotes grains which scatter the light in all directions, and the wording "light reflective grains" denotes grains which reflect the light in the exposure direction.

The optical characteristics of the tabular grains can be foreseen according to their thickness. This is disclosed in "Research Disclosure" May 1985, item 25330. The percentage variation of the light reflected by the tabular silver halide grains versus the wavelength and the thickness of the grains is illustrated in Figure 1 of this item. However, Fig. 1 shows calculated theoretical curves on the other hand, it is mentioned in this publication that a tabular grain layer underlying the blue sensitized layer and reflecting the blue light significantly reduces the sharpness of the image formed in the blue sensitized

layer .

It must also be noted that tabular halide grain layers substantially insensitive to light, i.e., which do not take part in the image formation in the structure of a color photographic product, are not mentioned in the prior art.

Due to the complexity of the physical and chemical interactions in a photographic product, it was not possible to foresee that a reflective grain underlayer could allow to obtain an improved sensitivity of the yellow layer, without the disadvantages bonded to the light scattering grain layers of the prior art.

It could also have been thought that the advantages obtained with the blue layer would be cancelled by the unfavorable effects on the other layers, such as a decrease of the sensitivity in the minus blue or unfavorable interimage effects. Summary __f_ ___£ Invention The object of the present invention relates to a color photographic product exhibiting an improved sensitivity to the blue light without defavorably affecting the other properties of the photographic product. The product according to the invention comprises a support, and coated thereon a red sensitized layer or layer unit associated with a cyan color—forming coupler, a green sensitized layer or a layer unit associated with a magenta color—forming coupler, and a blue sensitized layer or layer unit associated with a yellow color forming coupler, characterized in that it comprises, under one of the blue sensitized layers or under each blue sensitized layer, an intermediate layer comprising gelatin and tabular silver halide grains having an intrinsic sensitivity lower than the sensitivity of the image forming photosensitive silver halide grains, by at

least the value of the modulation range of the curve

D/Log E of said photosensitive grains, having a thickness ranging from 0.03 to 0.2 μm and an aspect ratio higher than 2:1, and preferably higher than 5:1,

2 at a coverage ranging from 2 to 10 mg/dm and

2 preferably from 3 to 5 mg/dm The term "layer unit" in the present application denotes layers sensitized to the same portion of the visible spectrum and placed at adjacent or not locations in the product. Description __£ Preferred Embodiments

In addition to the features noted above, the invention has the following significant features:

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

In the intermediate tabular grain layer according to the invention, tabular grains having an average thickness ranging from 0.03 to 0.2 μm can be used. The reflectivities of these grains can be calculated, as above mentioned. The most blue selective grains with respect to the minus blue have an average thickness of about 0.15 μm. These grains are assumed to be the most advantageous to reflect only the blue light towards the blue layer, and to let pass through the minus blue light towards the red and green sensitized underlying layers: a color photographic product having a conventional structure, the blue sensitized layer is the outermost with respect to the support and is positioned on the exposure side. However, it has been found that grains having a thickness of 0.05 μm exhibiting also a high reflection in the blue but which are not selective, are also useful and do not significantly reduce the minus blue sensitivity of the red and green sensitized underlying emulsions.

It has also been found that the grains having a thickness of 0.05 μm, are more advantageous than

the grains having a thickness of 0.15 μm, since they exhibit a better reflection for the same silver coverage in the layer. The reflection of the tabular grains having a thickness of 0.15 μm could be improved by increasing the silver coverage of the emulsion, Thus, tabular grains having thicknesses ranging from 0.03 to 0.2 μm can be used, the choice of the thickness depending on the desired results and on the photographic product where the tabular grains of the invention are used. However, grains having thicknesses ranging from 0.03 to 0.07 μm are preferred because they allow to use emulsions having lower silver coverages, which is always advantageous, without however deteriorating the sensitometric properties of the red and green sensitized underlying layers, contrary to what could have been foreseen.

The aspect ratio of the tabular grains used in the intermediate layer according to the invention depends on their diameter once the thickness is defined. The unwanted scattering phenomenon increases as the diameter decreases. It is therefore advantageous to use tabular grains having an aspect ratio of at least 2:1, and preferably higher than 5:1. Said tabular grains can have any form, for example, they can be hexagonal, triangular, square,, rectangular.

The intrinsic sensitivity of said tabular grains is lower than the sensitivity of the image-forming photosensitive silver halide grains, by at least the value of the modulation range of the curve D/Log E of said photosensitive grains. The modulation range of the curve D/Log E (density versus the logarithm of the exposure) of a photographic emulsion, is the difference of the exposure values between the toe and the shoulder, or between the maximum density and the minimum density. The tabular grains used in the intermediate layer of the invention

should not be photosensitive within the modulation range of the image-forming photosensitive grains. For example, in a color reversal photographic paper, the intrinsic sensitivity of the tabular grains used in the present invention should be lower by 2 Log E than the sensitivity of the image—forming grains. The intrinsic sensitivity represents the sensitivity of silver halide grains before any treatment such as addition of sensitizing dyes, and in particular before fog formation, if fogged grains are used.

Any halide can be used to form the tabular grains. Tabular grains exhibit equivalent reflections for the same thickness whatever their composition. However tabular grains of silver chloride exhibit a reflection intensity lower than silver bromide. As regards the bromoiodide grains, the presence of iodide released during the development, tends to inhibit the development of the grains in the adjacent layer, and thus reduce the sensitivity, and that, significantly if the iodide content in the tabular grains is high. In practice, silver bromide tabular grains are preferred.

Tabular grains having a thickness ranging from 0.03 μm to 0.2 μm can be prepared by the method disclosed in US Patent 4,439,520 (or its French counterpart 2,516,256). Thus, for example, Example 3, Table II of this patent discloses a method for preparing tabular grains having a thickness of 0.15 μm and an aspect ratio of "19:1. In Table XI, grains of 0.19 μm, 0.07 and 0.06 μm and aspect ratios of

40:1, 40:1, 27:1, respectively, are shown. In Table

XVIII, emulsion 1 contains grains having a thickness of 0.10 μ and an aspect ratio of 16:1.

The silver coverages of the intermediate tabular grain layer according to the invention can

2 vary from 2 to 10 mg/dm . It has been found that beyond such limits, the increases in sensitivity are

two small to be useful.

Said intermediate layer is placed, as previously indicated, under one of the blue sensitized emulsion layer or under each blue sensitized layer in a color photographic product. Preferably, said layer is adjacent to a blue sensitive layer. However a gelatin layer comprising photographically useful addenda can be interposed between the blue sensitive layer and the intermediate layer. Said intermediate layer of tabular grains can itself contain addenda such as those disclosed in "Research Disclosure". Vol 176, December 1978, Item 17643, Sections V, VI and IX to XII, and also photographically useful materials. Color photographic products where the intermediate tabular grain layer according to the invention can be used, encompass all the products having a conventional structure formed of three units or layer units, a blue sensitized layer or layer unit, a green sensitized layer or layer unit, a red sensitized layer or layer unit, one of the blue sensitized layers being placed on the exposure side. Such products are disclosed, for example, in "Research Disclosure", vol 176, December 1978, Item 17643, Section VII, paragraphs C to C, I and J.

The photosensitive emulsions of the color photographic product of the invention can contain any kind of silver halide, such as chlorides, bromides, bromoiodides, chlorobromides, etc. as well as any grain shape, such as coarse grains, fine grains, octahedral grain, core/shell grains, tabular grains, etc.

The above mentioned reference discloses all what relates to the emulsion preparation (sections I and II), the chemical and spectral sensitizations (sections III and IV) the additives, such as optical brightening agents (section V), the antifogging and

stabilizing agents (section VI), the vehicles (section X), the hardeners .(section VIII), the coating additives (section XI), the plasticizers and the lubricants (section XII). The intermediate tabular grain layer according to the invention can be coated with the other layers of the photographic product by any known coating method, such as those disclosed in the above mentioned reference of Research Disclosure, section XV, on supports such as those disclosed in the same reference, section XVII. The support of the photographic product can be a transparent film or it can be reflective, such as a paper.

In a preferred embodiment of the invention, the photographic product is a reversal product, i.e., it is processed in a first black and white developer, in order to develop the silver halide in the exposed areas, fogged by exposure or chemically fogged, then developed in a color developer in order to obtain, after bleaching of the silver, a positive color image of the original. In this case, the tabular grains of the intermediate layer are previously fogged, in order to be developed in the first black and white development and to not interfere with the subsequent color development. The tabular grains can be fogged by exposure or chemically fogged with any fogging agent known in the art. For example, stannous chloride can be used.

The following exaϊaples illustrate the invention.

EXAMPLES 1 to 4

In order to show the effect of the intermediate tabular grain layer on the sensitivity of a blue sensitized emulsion layer, single layer products were prepared, comprising a support made of polyethylene coated paper having thereon in the order

₂

- an underlayer containing 1.7 mg/dm of Carey-Lea

2 silver and 12 mg/dm of gelatin,

- a layer containing a silver bromide emulsion, having the grain dimensions indicated in the following Table I, fogged with a stannous chloride aqueous solution at a coverage of 1 g of

SnCl-/mol Ag, incorporated during the melting,

2 at a coverage of 4 mg of silver/dm and 12

2 mg/dm of gelatin, - a layer containing a silver bromoiodide emulsion,

2 at a coverage of 4.7 mg of silver/dm , spectrally blue sensitized, a yellow color forming

2 coupler and 12 mg/dm of gelatin,

2

- plain an overcoat containing 8 mg/dm of gelatin. TABLE I

Examples Average diameter Thickness

1 0.5 μm 0.05 μm

2 1.73 μm 0.10 μm

3 1.60 μm 0.15 μm 4 1.69 μm 0.20 μm

Another similar product was prepared, but not containing the intermediate layer, in order to serve as control.

Both products were exposed through a step tablet, under the following conditions : 0.5 s, neutral density + 1.36, 2850 ^β K, AC 13 heat-absorbing filter.

They were developed by means of a reversal standard processing for Ektachrome R3 paper, and

TM then were read with a XRite densitometer.

The difference between the control product sensitivity and those of the products according to the invention was determined. This difference is indicated in the following Table II

A color photographic product having the following structure was prepared:

Ag Gelatin

Covera e Covera e

Layer containing a blue 4.7 12 sensitized silver bromo— iodide emulsion and a yellow color forming coupler

Intermediate layer of 3.00 12 silver bromide tabular grains

Layer containing 1.7 12

Carey—Lea silver

Layer containing a green 3.95 17.6 sensitized silver bromo— iodide emulsion and a magenta color forming coupler

Filter layer containing 1.5 8 reduced silver (Gray-Gel)

Layer containing a red 3.00 13.00 sensitized silver bromo— iodide emulsion and a cyan color forming coupler

Underlayer 25

Support paper

The silver bromide tabular grains of the intermediate layer were those of Example 1 (0.05 μm thick) and were fogged as in Examples 1 to 4.

Another similar product was prepared, but not containing the intermediate tabular grain layer, in order to serve as control.

Both products were exposed and processed as indicated for the products of examples 1 to 4. The sensitivities of both products are indicated in the following Table III.

TABLE III Sensitivities in the blue in the green in the red region region region Control 89 91 76

Example 5 109 98 79

A significant increase of the sensitivity in the blue region can be observed, without defavorably affecting in a significant manner the green and red regions. EXAMPLE 6

This example shows that the intermediate layer with reflective tabular grains according to the invention does not defavorably affect the interimage effects in a reversal color photographic paper.

The product of Example 5 was taken again and each layer was exposed separately through filters, one of the layers being exposed through a step tablet, and the two others uniformly exposed at two different exposure values. The product was then processed as in Examples 1 to 4.

Two tests were carried out on a product according to the invention and on a control product which did not contain the intermediate layer with tabular grains.

TEST I: modulated exposure of the magenta layer and uniform exposure of the cyan and yellow layers.

TEST II: modulated exposure of the cyan and magenta layers and uniform exposure of the yellow layer. The interimage effect is expressed as the ΔD density difference between the 2 extreme steps of the step tablet, for each product, in the uniformly exposed yellow layer.

Results are gathered in the following Table IV. TABLE IV

ΔD in the yellow layer high exposure low exposure Test I

Control - 0.31 - 0.28 Example 6 - 0.23 - 0.24

Test II

Control - 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 reference product. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.