Performance of high speed emulsions for color film

Details Performance of high speed emulsions for color film Performance of high speed emulsions for color film

1999-12-20

2001-06-12

Letscher, Geraldine (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Identified radiation sensitive composition with color...

C430S955000, C430S555000, C430S557000, C430S558000, C430S567000, C430S570000, C430S598000, C430S599000, C430S600000, C430S603000, C430S607000, C430S611000, C430S613000

Reexamination Certificate

active

06245497

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a color photographic element having improved photographic response. In particular, it relates to a high speed emulsion with improved performance for use in a color film.
DEFINITIONS
A 3D emulsion is one in which at least 50 percent of total grain projected area is accounted for by 3D grains. As used herein, the term “3D grain” refers to non-tabular morphologies, for example cubes, octahedra, rods and spherical grains, and to tabular grains having an aspect ratio of less than 2.
A core/shell emulsion as used herein is a bromoiodide emulsion with at least one inner or “core” region containing a higher iodide concentration than an outer or “shell” region.
A fragmentable electron donor (FED) is a chemical compound that enhances the sensitivity of the emulsion through fragmentation of the molecule and release of an electron.
As used herein, the term “one equivalent couplers” refers to imaging couplers where a preformed dye in a shifted state is linked to the coupling position of the coupler. The dye image comprises the coupler derived azomethine dye and the released dye that have essentially the same hue.
BACKGROUND OF THE INVENTION
It is a long-standing objective of color photographic origination materials to maximize the overall response to light while maintaining the lowest possible granularity. Increased photographic sensitivity to light (commonly referred to as photographic speed) allows for improved images captured under low light conditions or improved details in the shadowed regions of the image. In general, the overall light sensitivity provided by the light sensitive silver halide emulsions in such systems is determined by the grain size of the emulsions. Larger emulsions capture more light. In color photographic elements, upon development, the captured light is ultimately converted into dye deposits which constitute the reproduced image. However, the granularity expressed by these dye deposits is directly proportional to the grain size of the silver halide emulsion. Thus, larger silver halide emulsion grains have higher sensitivity to light but also lead to higher granularity in the reproduced image. It has been a long-standing problem to provide materials which maximize the response to light of a silver halide emulsion for any given grain size.
3D, core/shell bromide emulsions containing high iodide regions have long been a staple of the blue-sensitive layer in color film. Their intrinsic light absorption in the blue region together with their low response to pressure, continue to make them an attractive choice, especially as the fast component. Recent techniques have been developed to improve the photographic performance of such emulsions by introducing twin planes (Matemaghan in U.S. Pat. No. 4,184,877), producing grains with a particular iodide architecture (Takada et al in U.S. Pat. No. 4,668,614, Ishikawa et al in U.S. Pat. No. 4,963,467), narrowing the range of iodide in individual grains (Shibahara et al in U.S. Pat. No. 4,728,602), and growing grains free of renucleation while obtaining a narrow distribution of grains with a high iodide content (Chang et al, U.S. Pat. No. 5,570,327). Although these techniques have, indeed, increased performance of core/shell emulsions there continues to be a need for further improvements to yield color film with the highest possible image quality for the consumer.
It is of particular interest to find solutions to this problem for large emulsions with the potential for providing high speed (preferably ISO 400 or greater) color photographic materials. Such high-speed materials have a number of potential applications. They are particularly valuable for use in cameras with zoom lenses and in single use cameras (also called “film with lens” units). Zoom lenses generally are limited to smaller apertures than non-zoom lenses, which reduces light intensity. Thus, zoom lenses, while giving increased flexibility in composition of a pictorial scene, deliver less light to the camera film plane. Use of high-speed films allows the flexibility of zoom lenses while still preserving picture-taking opportunities at low light levels. In single use cameras, lens focus is fixed. Here, high-speed films allow use of a fixed aperture having a higher f-number, thus increasing the available depth of field, an important feature in a fixed focus camera. For single use cameras with flash, higher film speed allows pictures to be taken with a less energetic flash, enabling more economical manufacture of the single use unit. The introduction of the Advanced Photo System has further increased demand on film image quality by reducing camera size and, concomitantly, the size of the image-capturing element.
3D, core/shell emulsions, while capable of the highest speeds of any emulsion type in the blue record, have the particular disadvantage of producing a relatively low contrast where contrast is defined as the slope or gradient of the linear portion of the density vs. log exposure or D-Log E curve. The low contrast originates chiefly from two sources: the relatively wide dispersity in grain size characteristic of large, grains and the high iodide content of the grains. Both of these features, i.e., large grain size and high iodide content are required to obtain the greatest possible blue speed and, therefore, are inherent in this type of emulsion. A need, thus, exists for an additional and independent technique for improving performance.
PROBLEM TO BE SOLVED BY THE INVENTION
The problem of maximizing response of the emulsion grain to light is particularly important for the blue sensitive emulsions of high-speed materials, since standard scene illuminants are at least somewhat deficient in blue light. Furthermore, the blue record is the last color-recording layer coated in conventional color film putting it near the top where it is most effected by inadvertent pressure applied to the film. As a result, 3D, core/shell, AgBrI emulsions with light absorption enhanced by high iodide content and having low pressure sensitivity are generally employed in the fast yellow emulsion layer of the highest speed color photographic films. Unfortunately, these large fast yellow emulsions often do not deliver enough contrast in their response to light.
SUMMARY OF THE INVENTION
We have discovered that adding a fragmentable electron donor to an emulsion comprising 3D, core/shell grains and utilizing a one equivalent coupler in the layer containing these grains enables these emulsions to simultaneously achieve improved speed and contrast.
One aspect of this invention comprises a multicolor photographic element comprising a support bearing a cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, wherein at least one of said layers comprises
a) an emulsion with 3D, core/shell grains of at least 0.40 &mgr;m average diameter having a high iodide content in the core of the grain with a shell containing a lesser amount of iodide,
b) a one-equivalent image-dye forming coupler, and
c) a fragmentable electron donating compound of the formula: X—Y′ or a compound which contains a moiety of the formula —X—Y′;
wherein
X is an electron donor moiety, Y′ is a leaving proton H or a leaving group Y, with the proviso that if Y′ is a proton, a base, &bgr;
−
, is covalently linked directly or indirectly to X, and wherein:
1) X—Y′ has an oxidation potential between 0 and about 1.4 V; and
2) the oxidized form of X—Y′ undergoes a bond cleavage reaction to give the radical X
•
and the leaving fragment Y′; and, optionally,
3) the radical X
•
has an oxidation pot

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