Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified radiation sensitive composition with color...
Reexamination Certificate
1999-12-20
2002-07-09
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified radiation sensitive composition with color...
C430S551000, C430S557000, C430S558000, C430S599000, C430S600000, C430S583000
Reexamination Certificate
active
06416941
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.
BACKGROUND OF THE INVENTION
The characteristic that is primarily responsible for the dominance of silver halide photography is the image amplification capability of silver halide grains. During imagewise exposure of a silver halide photographic element, incident photons are absorbed by the silver halide grains. When a photon is absorbed, an electron in the silver halide crystal lattice structure of a grain is promoted from a valence band energy level to a higher, conduction band energy level at which it is capable of migrating within the crystal lattice of the grain. When a few conduction band electrons are captured by crystal lattice silver ions in close proximity, a cluster of Ag° atoms is created, commonly referred to as a latent image site. The latent image site of a grain is capable of catalyzing the overall reduction of silver ions in the grain to Ag°, a huge amplification of the few original Ag
+
reductions to Ag° created by imagewise exposure. An imagewise exposed silver halide emulsion is brought into contact with a developer to produce a viewable image. A developer is an aqueous solution containing a developing agent, a reducing agent capable of selectively reducing latent image bearing silver halide grains to Ag°. Contacting a photographic element with aqueous solutions, including a developer, to produce a viewable image is referred to as photographic processing.
Although many factors come into play in obtaining desirable photographic images, one of the most fundamental is the speed of the photographic element employed. While silver halide photography with its internal amplification mechanism exhibits much higher photographic speeds than other imaging systems, the search for higher photographic speeds in silver halide photography has continued since its inception to the present time, a time period of well over a century. The speed of a photographic element is measured by exposing sample portions of the element at differing levels and then correlating image density following photographic processing. By plotting image density (D) as an ordinate against the log of exposure (E) in lux-seconds, a characteristic curve is generated. The characteristic curve typically contains a portion that exhibits no change in density (minimum density or D
min
) as a function of exposure transitioning with increased exposures to a portion in which density increases as a function of increased exposure, often resulting in a linear characteristic curve segment (i.e., &Dgr;D/&Dgr;logE remains constant) transitioning with still higher exposures to a portion in which further exposure does not increase density (maximum density or D
max
) Photographic element speeds are usually reported as differences in log E required to produce the same density in compared elements.
Silver halide emulsions possess a native sensitivity to light having wavelengths ranging from the ultraviolet into the blue region of the visible spectrum. Spectral sensitizing dyes are adsorbed to the silver halide grain surfaces to extend sensitivity to longer wavelength portions of the spectrum. A summary of spectral sensitizing dyes is provided by
Research Disclosure
, Item 38957, cited above, V. Spectral sensitization and desensitization, A. Sensitizing Dyes. The function of a spectral sensitizer is to capture for latent image formation a photon of a wavelength the silver halide grain cannot itself capture.
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 the FED sensitizer reduces recombination by donating an electron to fill the hole created by photon capture. Thus, fewer conduction band electrons return to hole sites in valence bands and more electrons are available to participate in latent image formation.
When the FED sensitizer donates an electron to a silver halide grain, it fragments, creating a cation and a free radical. The free radical is a single atom or compound that contains an unpaired valence shell electron and is for that reason highly unstable. If the oxidation potential of the free radical is equal to or more negative than −0.7 volt, the free radical immediately upon formation injects a second electron into the grain to eliminate its unpaired valence shell electron. When the free radical also donates an electron to the grain, it is apparent that absorption of a single photon in the grain has promoted an electron to the conduction band, stimulated the FED sensitizer to donate an electron to file the hole left behind by the promoted electron, thereby reducing hole-electron recombination, and injected a second electron. Thus, the FED sensitizer contributes one or two electrons to the silver grain that contribute directly or indirectly to latent image formation.
FED sensitizers and their utilization for increasing photographic speed are disclosed in Farid et al U.S. Pat. Nos. 5,747,235 and 5,7547,236, and in the following commonly assigned filings: Lenhard et al U.S. Ser. No. 08/739,911, filed Oct. 30, 1996, and Gould et al U.S. Ser. No. 09/118,536, Farid et al U.S. Ser. No. 09/118,552, and Adin et al U.S. Ser. No. 09/118,714, each filed Jun. 25, 1998. The entire disclosures of these applications are incorporated herein by reference.
When silver halide is reduced to silver during development, the neutral density of the developed silver can be relied upon to create a black-and-white photographic image. Another imaging approach is to employ a primary amine color developing agent during development. The oxidized color developing agent is then reacted (coupled) with a dye image providing coupler to form an image dye. So-called “chromogenic” black-and-white images can be formed in which a combination of image dye forming couplers are employed to produce a black dye image which can be used in place of or in combination with developed silver to produce a black-and-white image. Where an image hue other than black (typically a subtractive primary hue) is sought, the neutral density of silver is removed by bleaching and fixing, and the dye formed by the reaction product of the image dye forming coupler and the color developing agent is relied upon exclusively for image dye formation. Dye imaging is extensively used, since a photographic element containing red, blue and green recording layer units capable of producing three spectrally distinguishable dye image records permits a photographic image to be obtained for viewing that acceptably replicates the natural hues of the subject photographed.
In the last two decades enhancements in dye images attributable to the incorporation of dye image modifying couplers have become common. These couplers, which often do not form an image dye on coupling, can be relied upon for immediate or timed release of photographically useful fragments, such as development accelerators, development inhibitors, bleach accelerators, bleach inhibitors, de
Lunt Sharon R.
Muenter Annabel A.
Reed Kenneth J.
Southby David T.
Baxter Janet
Eastman Kodak Company
Rice Edith A.
Walke Amanda C.
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