Photographic material with increased exposure latitude

There is described a photographic element in which increased exposure latitude is obtained by having a dye-forming coupler in a non-light-sensitive interlayer between two light-sensitive silver halide emulsion layers. One of the silver halide emulsion layers is sensitive to a first region of the spectrum and contains a dye-forming coupler that forms a dye complementary in color to the region of the spectrum to which that layer is sensitive. The second emulsion layer is sensitive to a second region of the spectrum and contains a second coupler that forms a dye complementary to the second region of the visible spectrum. The exposure latitude in the layer sensitive to the first region of the spectrum is increased when the coupler in the interlayer forms a dye complementary in color to the second region of the spectrum, but as a function of development in the first region of the spectrum.

This invention relates to color photographic materials with extended 
exposure latitude. In a particular aspect, it relates to such a material 
which yields a positive image that is directly viewable. 
BACKGROUND OF THE INVENTION 
Color positive photographic prints intended for direct viewing are 
typically made by imagewise exposing a support coated with layers 
sensitive to each of the blue, green and red regions of the visible 
spectrum and which yield yellow, magenta and cyan dye images, 
respectively. Exposure is commonly to a color negative film which contains 
a negative image of the original scene. If the exposure latitude of the 
color print material is less than the full range of densities recorded in 
the film, reproduction of detail in the print will be poor. 
Exposure latitude is a measure of the ability of a recording material to 
represent differences in intensity of exposure by differences in density. 
Thus, materials with a wide exposure latitude would respond to a wide 
range of exposure intensities by showing differences in image density, 
while materials with a narrow exposure latitude would, for the same range 
of exposure intensities, show fewer differences in density. Heretofore, 
exposure latitude typically has been modified by manipulation of the 
silver halide emulsion. For example, increasing the range of grain sizes 
in an emulsion is known to extend the exposure latitude, while narrowing 
the range of grain sizes is known to decrease exposure latitude. U.S. Pat. 
No. 3,663,228, issued May 16, 1972, to C. W. Wyckoff, discloses other 
techniques for extending the exposure latitude of color photographic 
materials. 
In my copending U.S. Pat. Application Ser. No. 87,276, filed Aug. 20, 1987, 
now U.S. Pat. No. 4,902,609 issued Feb. 20, 1990 I describe a novel 
technique for extending exposure latitude of photographic materials. In 
accordance with that invention, there is provided a color photographic 
element comprising a support and first and second silver halide emulsion 
layers. The first emulsion layer is sensitized to a first region of the 
spectrum and the second emulsion layer is sensitized to a second region of 
the spectrum and, to a limited degree, to the first region of the 
spectrum. Dye density formed in the second emulsion layer as a result of 
its exposure to the first region of the spectrum, adds to the dye density 
formed in the first emulsion layer and thereby extends the exposure 
latitude. This is perceived as an increase in the degree of detail 
viewable in the image. 
While this is a useful technique, it requires adjusting the degree of 
spectral sensitivity of the emulsion in the second emulsion layer for two 
different regions of the spectrum. It would be desirable to provide a 
means for accomplishing a similar extension of exposure latitude without 
having to manage the spectral sensitivity of an emulsion to two different 
regions of the spectrum. 
I have found that exposure latitude can be extended by providing a color 
photographic material comprising; 
a support 
first and second silver halide emulsion layers each sensitive to a 
different region of the electromagnetic spectrum and each layer containing 
a coupler that forms a dye complementary in color to the principal 
spectral sensitivity of the emulsion, and 
a non-light sensitive interlayer between the two emulsion layers, 
wherein: 
the interlayer contains a coupler that forms, as a function of development 
of the first emulsion layer, a dye complementary in color to the principal 
sensitivity of the second emulsion layer.

In a specific embodiment of this invention, a cyan dye forming coupler is 
in an interlayer between a green sensitive silver halide emulsion layer 
and a red sensitive silver halide emulsion layer, the relative proportions 
of materials being such that oxidized developing agent generated in the 
areas of the green sensitive layer receiving maximum exposure migrates to 
the interlayer to couple to form cyan dye. This results in extension of 
exposure latitude of the green sensitive layer by the addition of cyan dye 
density in the maximum density region of the magenta dye image. In a high 
density red image, comprised of yellow and magenta dye, this would be seen 
in the viewable image as an increase in detail of the red image. 
Similarly, detail of the high-density green image is increased, and 
exposure latitude of the red sensitive emulsion extended, when the 
interlayer contains a magenta dye-forming coupler and forms magenta dye 
density as a function of red light exposure. 
Dye-forming couplers have been placed in non-light-sensitive layers 
adjacent image-forming layers. In some instances, these have been 
development inhibitor-releasing couplers which were not present for the 
image-forming character of the coupler itself, but rather as a carrier for 
a development inhibitor to be released. U.S. Pat. No. 4,359,521 is 
illustrative of such patents. In other instances, the coupler forms a dye 
complementary to the sensitivity of the emulsion layer from which the 
oxidized developing agent migrates. German DAS 1,002,626 and U.S. Pat. No. 
4,186,011 are illustrative of such patents. In column 4, lines 37-42, of 
the '011 patent it is stated that coupling between oxidized developing 
agent migrating from an emulsion layer of one color with a coupler forming 
dye of a different color is undesirable and should be suppressed. The 
present invention, on the other hand, makes use of such coupling to 
achieve an extension of exposure latitude. 
As indicated above, the relative proportions and locations of the emulsions 
and couplers in the two light-sensitive layers and the interlayer should 
be such that oxidized developing agent is generated in the maximum density 
areas of the first emulsion layer in such an amount that there is excess 
oxidized developing agent available to migrate to the interlayer where it 
will couple. Such a condition can be assured by having less coupler in the 
first emulsion layer than is theoretically capable of reacting with all of 
the oxidized developing agent generated at maximum exposure. This 
condition has been referred to in the art as "coupler starvation." 
However, some oxidized developing agent would be available for migration 
even under non-coupler starved conditions. Therefore, it is not necessary 
that the emulsion be coupler starved in order for the benefits of the 
invention to be observed. 
The amount of oxidized developing agent which migrates to the interlayer 
can be determined by measuring and plotting the density of dye generated 
in the interlayer as a function of exposure of the first emulsion layer. 
The slope of the resulting curve is referred to as contrast, or 
gamma(.gamma.). Useful effects can be obtained when the contrast of the 
interlayer, measured in the region where the first emulsion layer is 
within 10% of maximum density, is in the range of 0.03 to 7.0, preferably 
in the range of 0.07 to 3.5. Especially preferred is an interlayer 
contrast of 0.2 to 0.4. 
The contrast of the interlayer can also be related to the secondary 
contrast of the first emulsion layer measured in the same region of the 
spectrum as is the interlayer. This is referred to herein as the 
corresponding contrast. Useful effects can be obtained when the contrast 
of the interlayer is in the range of 10% to 200% of the corresponding 
contrast of the first emulsion layer. Preferably the corresponding 
contrast is 40% to 200%. The corresponding contrast of each layer is 
measured as a function of exposure of the first emulsion layer. The 
corresponding contrast of the first emulsion layer is that of the straight 
line portion of the curve. The contrast of the interlayer is measured over 
the exposure region where the principal density of the first emulsion 
layer is within 10% of maximum density. 
This can be illustrated by reference to FIG. 1 of the invention, which 
shows the response obtained with a material like that illustrated in 
Example 1, compared with the control. In this example, the first emulsion 
layer is sensitive to the green region of the spectrum and contains a 
magenta dye-forming coupler, and, in the material of the invention, the 
interlayer contains a cyan dye-forming coupler. The curve labeled Gg 
represents the green density, i.e. the principal density, generate in the 
element as a function of exposure of the green sensitive layer. The curve 
labelled Rg represents the red density generated in the element as a 
function of exposure of the green sensitive layer. It is composed of two 
parts. The first, labelled 1, is derived from absorption of red light by 
the magenta dye formed in the green layer. This is the secondary density 
of the dye formed in the green sensitive layer. The second, dashed curve, 
labelled 2, represent the cyan dye formed in the interlayer as a function 
of development of the green sensitive layer. The additional red density, 
represented by the dashed curve labelled 2, adds to the green density in 
the maximum density region of the image thus extending exposure latitude 
and enhancing image detail. 
An additional or alternative means for controlling migration of oxidized 
color developing agent is by the use of a barrier layer. There can be 
located between the interlayer and the second emulsion layer a barrier 
layer containing a scavenger for oxidized developing agent. Suitable 
scavengers include ballasted reducing agents such as 
2-(-2-octadecyl)-5-sulfohydroquinone, diiso octylhydroquinone, 
2-5,-didodecylhydroquinone, 4-benzenesulfonamido-1-hydroxy-2-(N,N 
didodecyl) naphthamide. The presence of such a material in this location 
will restrict the opportunity for the coupler in the interlayer to respond 
to the second emulsion layer rather than to the first emulsion layer. 
The present invention is of primary use in materials intended for direct 
viewing, such as reflection prints. The contribution to maximum density 
from two different regions of the spectrum results in some desaturation of 
the color in the maximum density portions of the image. This is not a 
significant factor in reflection print materials. The invention also can 
be employed with color negative, and other intermediate materials, where 
desaturation of the color in maximum density regions is acceptable. 
Color photographic elements intended for direct viewing by reflection 
generally comprise an opaque support on which is coated, in order, a 
blue-sensitive, yellow dye forming layer, a green-sensitive magenta 
dye-forming layer, and a red-sensitive cyan dye-forming layer. In a 
preferred embodiment of the present invention, the non-light interlayer 
containing the dye-forming coupler is coated between the red-sensitive and 
green-sensitive emulsion layers. 
Any conventional silver halide emulsion can be employed. For color print 
applications, silver chloride, silver bromide and silver chlorobromide 
emulsions are commonly employed. The silver halide emulsions employed in 
positive print materials are in most applications negative working. 
Illustrative silver halide emulsion types in preparations are disclosed in 
Research Disclosure, Volume 176, January, 1978, Item 17643, paragraph I. 
Particularly preferred silver halide emulsions are high aspect ratio 
tabular grain emulsions such as those described in Research Disclosure, 
January, 1983, Item 22534. Research Disclosure is published by Kenneth 
Mason Publications, Ltd., The Old Harbourmaster's, 8 North Street, 
Emsworth, Hampshire P010 7DD, ENGLAND. 
Dye-forming couplers are chosen to form subtractive primary (i.e. yellow, 
magenta and cyan) image dyes and are non-diffusible colorless compounds 
such as 2- and 4-equivalent couplers of the open-chain ketomethylene, 
pyrazolone, pyrazolotriazole, phenol and naphthol types that are 
hydrophobically ballast for incorporation in high-boiling organic 
solvents. Suitable types and classes of couplers, as well as methods for 
their incorporation in color photographic materials, are described in 
Research Diclosure, Item 17643, December, 1978, Section VII, Paragraphs C, 
D, E, F and G, Incorporated herein by reference. 
Specifically preferred couplers for use in the reflection print materials 
of this invention include the following: 
##STR1## 
The photographic element can be comprised of any conventional photographic 
support. Typical photographic supports include wood fiber, e.g. paper, 
metallic sheets and foils, glass and ceramic supporting elements provide 
with one or more subbing layers to enhance the adhesive, antistatic, 
dimensional, abrasive hardness, frictional antihalation or other 
properties of the support services. Typically, useful supports are further 
disclosed in Research Disclosure, Item 17643, paragraph XVII. 
In addition to the features described above, the photographic elements can 
contain other conventional features known in the art, which can be 
illustrated by reference to Research Disclosure, Item 17643, cited above. 
For example, the silver halide emulsions can be chemically sensitized, as 
described in Paragraph III; contain brighteners, as described in Paragraph 
V; contain antifoggants and stabilizers, as described in Paragraph VI; 
absorbing and scattering materials, as described in Paragraph III, the 
emulsion and other layers can contain vehicles, as described in Paragraph 
IX; the hydrophilic colloid and other hydrophilic colloid layers can 
contain hardeners, as described in Paragraph X; the layers can contain 
coating aids, as described in Paragraph XI; the layers can contain 
plasticizers and lubricants, as described in Paragraph XII; and the 
layers, particularly the layers farthest from the support, can contain 
matting agents, as described in Paragraph XVI. This exemplary listing of 
addenda and features is not intended to restrict or imply the absence of 
other conventional photographic features compatible with the practice of 
the invention. 
Following imagewise exposure, multilayer color photographic elements of 
this invention can be processed by any conventional technique of producing 
a dye image by color development, whereafter the concurrently generated 
silver is removed by bleaching. Residual, undeveloped silver halide can be 
removed in a separate fixing step or concurrently with bleaching. A 
separate pH lowering solution, referred to as a stop bath, may be employed 
to terminate development prior to bleaching. A stabilizer bath is commonly 
employed for final washing and hardening of the bleached and fixed 
photographic element prior to drying. Conventional techniques for 
processing are illustrated by Research Disclosure, Item 17643, cited 
above, Paragraph XIX. 
The following example further illustrates the invention. 
EXAMPLE 1 
A control color photographic material was prepared by coating the following 
layers in sequence on a polyethylene laminated paper support. The coating 
was hardened with bis(vinylsulfonyl) methyl ether at 1.8% of the total 
gelatin weight. Except as noted, all coverages in parenthesis are in 
g/m.sup.2. 
______________________________________ 
Layer 7 Gelatin (1.35) 
Layer 6 Gelatin (0.69) - UV absorber 
Layer 5 Chemically sensitized and red spectrally 
sensitized monodisperse silver chloride 
emulsion, average grain diameter 0.48 .mu.m, 
silver coverage (0.23), gelatin coverage 
(1.08), and the cyan dye-forming coupler C* 
(0.43) 
Layer 4 Gelatin (0.69) - UV absorber 
Layer 3 Chemically sensitized and green spectrally 
sensitized monodisperse silver chloride 
emulsion, average grain diameter 0.38 .mu.m, 
silver coverage (0.33), gelatin coverage 
(1.23), and the magenta dye-forming coupler 
M* (0.47) 
Layer 2 Gelatin (1.50) 
Layer 1 Chemically sensitized and blue spectrally 
sensitized monodisperse silver chloride 
emulsion, average grain diameter 0.8 .mu.m, 
silver coverage (0.42), gelatin coverage 
(1.50), and the yellow dye-forming coupler 
Y* (1.08) 
Support Polyethylene coated paper 
______________________________________ 
C=Cyan dye-forming coupler 
2-[.alpha.-(2,4-ditert-amylphenoxy)butyramido]-4,6-dichloro-5-ethyl phenol 
M=Magenta dye-forming coupler 
1-(2,4,6-trichlorophenyl)-3-[2-chloro-5-(.alpha.-[4-hydroxy-3-tert-butylph 
enoxy]tetradecanoamido)anilino]-5-pyrazolone 
Y=Yellow dye-forming coupler 
.alpha.[4-(4-benzyloxyphenylsulfonyl)phenoxy]-.alpha.-pivalyl-2-chloro-5-[ 
.gamma.(2,4-t-amylphenoxy)-butyramido]-acetanilide 
A color photographic material according to this invention was prepared. It 
differed from the one described above in that layer 4 contained 100 
mg/m.sup.2 of cyan dye-forming coupler C and an additional 0.69 g/m.sup.2 
of gelatin. 
Each of these photographic materials was imagewise exposed through a green 
separation test object (Wratten 99 filter) and then processed at 
35.degree. C. in a three step process consisting of a 45-second 
development step, a 45-second bleach fix step, and a 90-second stabilizing 
step, followed by a one minute drying step at a temperature of 60.degree. 
C. 
The color developing, bleach-fixing and stabilizing compositions used in 
the process were as follows: 
______________________________________ 
Color Developing Composition 
______________________________________ 
Lithium salt of sulfonated polystyrene 
0.25 mL 
(30% by wt) 
Triethanolamine 11.0 mL 
N,N-diethylhydroxylamine (85% by wt) 
6.0 mL 
Potassium sulfite (45% by wt) 
0.5 mL 
Color developing agent* 5.0 g 
Stain reducing agent** 2.3 g 
Lithium sulfate 2.7 g 
Potassium chloride 2.3 g 
Potassium bromide 0.025 g 
Kodak Anti-Calcium No. 5*** 
0.8 mL 
Potassium carbonate 25.0 g 
Water to total of 1 liter 
(pH 10.04) 
______________________________________ 
*4-(N-ethyl-N-2-methanesulfonamidoethyl)-2-methylphenylenediaminesesquisu 
fate monohydrate. 
**A stilbene compound available under the trademark KODAK EKTAPRINT 2 
StainReducing Agent from Eastman Kodak Company. 
***An organic phosphonic acid 
______________________________________ 
Bleach-Fixing Composition 
Ammonium thiosulfate 58. g 
Sodium sulfite 8.7 g 
Ethylenediaminetetraacetic acid ferric 
40. g 
ammonium salt 
Acetic acid 9.0 mL 
Water to total 1 liter, pH adjusted to 6.2 
Stabilizing Composition 
Sodium citrate 1 g 
Dearside 45 ppm 
(a biocide produced by Rohm and Haas) 
Water to total 1 liter, pH adjusted to 7.2 
______________________________________ 
The control material developed 11 visible steps while the invention 
material developed 15 visible steps. A similar increase in exposure 
latitude is obtained when the level of magenta dye forming coupler M in 
layer 3 is reduced to 0.38 g/m.sup.2 and the level of cyan dye forming 
coupler C in layer 4 is 0.32 mg/m.sup.2. 
This data leads to the conclusion that the invention materials have 
extended exposure latitude compared with the control material and can 
record more detail in high density regions of the image. 
EXAMPLE 2 
The control and invention color photographic print materials described in 
Example 1 were imagewise exposed to a color negative image and processed 
as in Example 1. Visual inspection of the resulting prints showed 
significantly greater detail in the red-image areas on the print materials 
of the invention compared to the control. 
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.