Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...
Reexamination Certificate
2000-03-23
2001-05-01
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Two or more radiation-sensitive layers containing other than...
C430S507000, C430S631000, C430S639000, C430S641000, C430S598000, C430S599000, C430S600000, C430S607000, C430S611000, C430S613000, C430S570000, C430S572000, C430S583000, C430S955000, C430S543000
Reexamination Certificate
active
06225036
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to color photography. More specifically, the invention relates to color photographic elements that contain layer units that contain radiation-sensitive silver halide emulsions and produce dye images.
DEFINITIONS
A tabular grain emulsion is one in which at least 50 percent of total grain projected area is accounted for by tabular grains.
As employed herein the term “tabular grain” is employed to indicate grains that have two parallel major faces substantially larger than any remaining face and that exhibit an aspect ratio of at least 2.
Aspect ratio is the ratio of tabular grain equivalent circular diameter (ECD) divided by thickness (t). The average aspect ratio of a tabular grain emulsion is the ratio of average grain ECD divided by average grain thickness.
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.
In referring to grains and emulsions containing two or more halides, the halides are named in order of descending concentrations.
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 which 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. For tabular emulsions, the photographic speed would be proportional to the projected area (or diameter, d squared)-see for example James “The Theory of the Photographic Process” 4
th
ed. p 105 (where the photographic speed is measured as some threshold density value). 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 . Again for tabular emulsions, granularity is generally proportional to the square root of the grain area ie proportional to the grain diameter, d (James “The Theory of the Photographic Process” 4
th
ed. p 625).
Thus, larger silver halide emulsion grains have higher sensitivity to light (proportional to d
2
) but also lead to higher granularity in the reproduced image (proportional to d). 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.
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. As a result, 3D AgBrI emulsions with light absorption enhanced by high iodide content are generally employed in the fast yellow emulsion layer of the highest speed color photographic films. Unfortunately, these large fast yellow 3D emulsions scatter light in a very diffuse (sideways) manner and thereby compromise the acutance of underlying light sensitive layers. Tabular grains as fast yellow emulsions offer advantages for acutance of underlying layers due to the specular manner (forward direction) in which they scatter light but up until now have been deficient for adequate speed/granularity. Here our usage of the term acutance is that generally offered in standard reference works such as James “The Theory of the Photographic Process” 4
th
ed. Pp 602-607.
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 have smaller apertures (higher f-numbers) than comparable fixed focus lenses. 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.
A dramatic increase in photographic speeds in silver halide photography began with the introduction of tabular grain emulsions into silver halide photographic products in 1982. A tabular grain is one which has two parallel major faces that are clearly larger than any other crystal face and which has an aspect ratio of at least 2. Tabular grain emulsions are those in which tabular grains account for greater than 50 percent of total grain projected area. Kofron et al U.S. Pat. No. 4,439,520 illustrates the first chemically and spectrally sensitized high aspect ratio (average aspect ratio >8) tabular grain emulsions. In their most commonly used form tabular grain emulsions contain tabular grains that have major faces lying in {111 } crystal lattice planes and contain greater than 50 mole percent bromide, based on silver. A summary of tabular grain emulsions is contained in
Research Disclosure,
Item 38957, I. Emulsion grains and their preparation, B. Grain morphology, particularly sub-paragraphs (1) and (3).
The use of cationic starch as a peptizer for the precipitation of high bromide {111} tabular grain emulsions is taught by Maskasky U.S. Pat. Nos. 5,604,085, 5,620,840, 5,667,955, 5,691,131, and 5,733,718. Oxidized cationic starches are advantageous in exhibiting lower levels of viscosity than gelatino-peptizers. This facilitates mixing. Under comparable levels of chemical sensitization higher photographic speeds can be realized using cationic starch peptizers. Alternatively, speeds equal to those obtained using gelatino-peptizers can be achieved at lower precipitation and/or sensitization temperatures, thereby avoiding unwanted grain ripening.
To increase the speed of silver halide emulsions independent of spectral sensitization, the grain surfaces are treated with chemical sensitizers. A summary of chemical sensitizers is provided by
Research Disclosure,
Item 38957, cited above, IV. Chemical sensitization.
It has been recently recognized that a further enhancement in photographic speed can be realized by associating with the silver halide grain surfaces a fragmentable electron donating (FED) sensitizer. While no proof of the mechanism of FED sensitization has yet been generated, one plausible explanation is as follows: When, as noted above, photon capture within a grain results in electron promotion from a valence shell to a conduction energy band, a common loss factor is recombination. That is, the promoted electron simply returns to a hole in the valence shell, created by promotion to the conduction band of the same or another electron. When recombination occurs, the energy of the captured photon is dissipated without contributing to latent image formation. It is believed that t
Friday James A.
Maskasky Joe E.
Reed Kenneth J.
Scaccia Victor P.
Eastman Kodak Company
Letscher Geraldine
Rice Edith A.
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