Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...
Reexamination Certificate
2001-11-21
2003-04-15
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Two or more radiation-sensitive layers containing other than...
C430S566000, C430S543000, C430S559000, C430S618000, C430S620000, C430S964000
Reexamination Certificate
active
06548236
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to color photothermographic capture films that are intended to be developed by the application of heat, preferably in the absence of conventional processing solutions. In particular, this invention relates to novel non-photosensitive core/shell particles comprising organic silver salts and their use in imaging compositions, and methods for preparing such particles.
BACKGROUND OF THE INVENTION
Photographic imaging elements that can be processed, after imagewise exposure, simply by heating the element are referred to as photothermographic elements. Subsequent processing steps may employ liquid processing. Preferably, photothermographic films do not require any processing solutions and instead contain within them all the chemistry required for the formation of a photographic image in the film. These film chemistries are designed so that at room temperature they are inactive, but at elevated temperatures (greater than 120° C.) the film chemistries become functionally active.
In such materials, a photosensitive catalyst is generally a photographic-type photosensitive silver halide that is considered to be in catalytic proximity to a non-photosensitive source of reducible silver ions. Catalytic proximity requires intimate physical association of these two components either prior to or during the thermal image development process so that when silver atoms, (Ag
o
)
n
, also known as silver specks, clusters, nuclei, or latent image, are generated by irradiation or light exposure of the photosensitive silver halide, those silver atoms are able to catalyze the reduction of the reducible silver ions within a catalytic sphere of influence around the silver atoms (Klosterboer, Neblette's Eighth Edition:
Imaging Processes and Materials,
Sturge, Walworth & Shepp (eds.), Van Nostrand-Reinhold, New York, Chapter 9, pages 279-291, 1989). It has long been understood that silver atoms act as a catalyst for the reduction of silver ions, and that the photosensitive silver halide can be placed in catalytic proximity with the non-photosensitive source of reducible silver ions in a number of different ways (see, for example,
Research Disclosure,
June 1978, item 17029). The non-photosensitive source of reducible silver ions is typically a material that contains reducible silver ions. Typically, the preferred non-photosensitive source of reducible silver ions is a silver salt of an organic compound.
Non-photosensitive core/shell silver salts as sources of reducible silver ions for monochromic systems is described in commonly assigned and copending U.S. Ser. No. 09/761,954 (filed Jan. 17, 2001 by Whitcomb and Pham), incorporated here by reference. These silver salts include a core comprised of one or more silver salts and a shell having one or more different silver salts.
Core/shell silver halide emulsions are known, as disclosed by H. Hirsch,
J. Photog. Sci.,
vol. 10, pp. 129-134, 1962, H. Hirsch,
J. Photog. Sci.,
vol. 10, pp. 134-146, 1962; E. Klein and E. Moisar, German Patent DT 1,169,290, 1964; L. Ketellapper, H. Horignon, and L. Libeer,
J. Photog. Sci.,
vol. 26, p. 189, 1978; T. Sugimoto and S. Yamada, U.S. Pat. No. 4,665,012, 1987; S. Matsuzaka et. al, European Patent EP 202,784, 1986; and S. Bando, Y. Shibahara, and S. Ishimaru,
J. Imaging Sci.,
vol. 29, p. 193, 1985. However, silver-halide core/shell particles are for the purpose of photoefficiency and improved intrinsic blue light absorption.
PROBLEM TO BE SOLVED BY THE INVENTION
As indicated above, in photothermographic materials, all of the “chemistry” for imaging is incorporated within the material itself. For example, they include a developer (that is, a reducing agent for the reducible silver ions) while conventional photographic materials usually do not. Even in so-called “instant photography”, the developer chemistry is physically separated from the photosensitive silver halide until development is desired.
Moreover, color photothermographic films, as compared to black & white photothermographic films, require at least three color records, so that there are even a greater number of potentially reactive components that can prematurely react during storage. Furthermore, color photothermographic film involves radically new chemical systems, in which new and complex combinations of components may be subject to unpredictable and undesirable interactions, incompatibilities, and side reactions. The imaging chemistry must be designed to provide fast, high-quality latent image formation during image capture, but must not interact prematurely to any significant degree. Similarly, the film must be capable of fast development and high-quality image formation during thermal processing, but the same components must not prematurely interact before the processing step.
A problem in designing photothermographic films is to obtain good Raw Stock Keeping (hereafter “RSK”) with equivalent fresh performance. This problem is particularly acute since, as mentioned above, the components of a photothermographic film are in intimate proximity, in potentially reactive association, prior to development. It has been found that certain properties may degrade over time. The incorporation of the developer into photothermographic materials can lead to increased formation of various types of “fog” or other undesirable sensitometric side effects which can undesirably contribute to a higher Dmin in the film. Higher Dmins lower the image quality and makes it more difficult to scan the image. Therefore, much effort has gone into the preparation and manufacture of photothermographic materials to minimize these problems during the preparation of the photothermographic emulsion as well as during coating, use, storage, and post-processing handling.
In particular, it is necessary that photothermographic elements be capable of maintaining its imaging properties, including low Dmin, during storage periods. This is referred to as raw stock keeping. Ideally, film should be storage stable, under normal conditions, preferably for at least 12 months, more preferably at least 24 months or more. If a film unduly degrades during storage, poor or unacceptable image formation can occur.
There remains a need for a photothermographic film that does not exhibit any significant degradation in imaging properties during extended period of storage, subsequent to manufacture and prior to use. In particular, there is a continuing need for improving the reactivity of the compounds used to provide reducible silver ions, while at the same time providing improved raw stock keeping and low Dmin upon image formation.
SUMMARY OF THE INVENTION
One aspect of the present invention is directed to a photothermographic element comprising core/shell particles each of which comprise a mixture of at least two non-photosensitive organic silver salts, which particles comprise at least one shell comprising a first organic silver salt covering a core or central portion comprising a second organic silver salt. The organic silver salt in the shell has a higher pKsp, relative to the organic silver salt in the core or central portion. The invention is alternately defined to cover particles, also referred to as core/shell particles, in which a distinct core/shell boundary may not be indicated in the particle due to continuous concentration changes of the materials used to make the particle, but in which the concentrations of the different organic silver salts in the particle are such as to be tantamount to a core/shell type of particle.
This invention also provides a composition comprising the core/shell particles of non-photosensitive organic silver salt. These core/shell particles can be mixed with non-photosensitive non-core/shell particles of organic silver salt, for use in a color or monochrome photothermographic element. Other components of a composition according to the present invention may comprise (in addition to non-photosensitive core/shell particles of organic silver salt) a photocatalyst, a binder, and a blocked developer and/or other reducing agent
Black Donald L.
Hanna JoAnn D.
Irving Mark E.
Levy David H.
Stoker Stephen C.
Chea Thorl
Eastman Kodak Company
Konkol Chris P.
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