Chemistry of inorganic compounds – Phosphorus or compound thereof – Oxygen containing
Reexamination Certificate
2002-12-19
2004-02-10
Le, Hoa Van (Department: 1752)
Chemistry of inorganic compounds
Phosphorus or compound thereof
Oxygen containing
Reexamination Certificate
active
06689335
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to silver ion sequester and release agent compositions, to a process for the preparation thereof, and to photographic elements containing sequestered silver ions which may be released upon exposure to photographic processing solutions.
BACKGROUND OF THE INVENTION
The photographic system, in its most basic form, is comprised of silver halide (capable of detecting light and storing it as latent image) and developer molecules (capable of converting the latent image to a visible image). These two chemistries, however, are incompatible, as unexposed silver halide is thermodynamically unstable with respect to reduction in the presence of developer molecules. The consequence of this is that modern photography typically requires multiple steps: exposure and processing.
The effect of Ag ion upon the photographic system has long been a topic of study (see, e.g., “The Theory of the Photographic Process”, T. H. James, ed.; 4
th
ed., Chapter 13, 1977). Control of the Ag ion concentration is known to be important in the manufacture of silver halide emulsions, and in the production and processing of silver halide imaging elements. Most notably, the introduction of Ag ion into a silver halide imaging element may induce a phenomenon known as “solution physical development”, in which silver ion in solution is adsorbed onto developing silver halide grains. The silver ion is then reduced by the developer, forming silver metal, and thereby can advantageously add to the overall density of the image. This process, however, is most often indiscriminate and leads to the build-up of fog in the system with no net gain in imaging efficiency. As a result of this, solution physical development process is generally avoided in most photographic systems, with the exception of some reversal processes. It would be desirable to provide photographic materials in which silver ions are effectively sequestered prior to photographic processing, so as to minimize build up of fog density, and which are released upon introduction of common photographic processing solutions and made available for enhancement of the photographic image.
Incorporation of active chemistry directly into film formulations, to either simplify or improve processing after exposure, has long been a goal in the photographic industry. Some photographically useful compounds are difficult to incorporate in a stable fashion into a light-sensitive material, however, or cause serious deterioration in the photographic capability if incorporated. These compounds, if incorporated directly into the photographic elements, typically need to be stabilized or rendered harmless by chemical modification prior to photographic processing. Methods of incorporating development and other active chemistries into photographic element formulations have been described in a number of patents and publications. Schleigh and Faul, in Research Disclosure 129 (1975) describe methods of appending color developers with “blocking” chemistry to prevent premature reaction. U.S. Pat. No. 6,261,757 to Irving et al. describes photographic articles in which developers and other photographic chemistries are ionically bound to the surface of ion-exchange resins.
U.S. Pat. No. 4,942,119 discloses materials comprising radiation sensitive silver compositions entrapped or encapsulated in the cages of a microporous sodalite lattice, prepared from synthetic sodium sodalites by a silver ion exchange process. There is no disclosure, however, of the use of such materials as a source of silver ions during processing of a photographic element comprising a silver halide emulsion.
EP 0 909 981 discloses silver halide photographic materials comprising zeolites loaded with a photographically useful group. Use of zeolites loaded with aqueous soluble silver salts and halide salts for the in situ preparation of ultramicrocrystalline silver halides for ripening onto coarser silver halide grains in a reaction vessel is also disclosed, but there is no disclosure of the use of such materials to incorporate sequestered silver ions which are to be released during processing of a photographic element.
Clearfield and Cheng (
J. Inorg. Nucl. Chem.,
42, 1341 (1980)) have reported compositions and methods of preparing the following materials: Zr(AgPO
4
)
2
.H
2
O, ZrAg
0.22
H
1.78
(PO
4
)
2
and ZrAg
0.75
H
1.25
(PO
4
)
2
. There is no disclosure, however, of the use of such materials as a source of silver ions during processing of a photographic element comprising a silver halide emulsion.
Copending, commonly assigned, Bringley et al. U.S. Ser. No. 10/033,517, filed Dec. 28, 2001, describes a photographic material wherein sequestered silver ions are incorporated into at least one hydrophilic colloid layer in the form of a silver ion containing material which sequesters silver ions prior to photographic processing (so as to minimize the generation of photographic fog) and releases silver ions upon exposure to photographic processing solutions (so as to result in an observed increase in photographic speed or developability). In one embodiment, the silver ion containing material may comprise a silver ion-exchanged intercalation composition comprising a layered host material having silver ions inserted as guest ions between the layers of the host material. In a particular described embodiment, the silver ion containing composition host material may comprise a layered metal hydrogen phosphate composition, and the resulting silver ion containing material comprises a silver ion exchangeable material of the formula:
M(H
1−x
Ag
x
PO
4
)
2
:yH
2
O;
where M is Zr, Ti, Sn, Ge or Hf or any combination thereof; x is a number from 0 to 1; and y is a rational number between 0 and 10.
The ability of host materials to sequester silver ion in photographic elements as described in U.S. Ser. No. 10/033,517 is directly related to levels of observed fog increase, especially upon prolonged keeping of the element. Also, to minimize the addition of non-sequestered silver ion along with the silver ion exchangeable material, such materials need to be prepared of in a form which is practically free of non-sequestered residual silver ions. The referenced copending application describes the preparation of such materials by combining the host material and silver ions such that the silver ions can be ion exchanged into the host material, and subsequently washing and/or filtering of the combination to remove non-sequestered residual silver ions. It would be desirable to provide silver ion containing materials which demonstrate improved silver ion sequesterability. It would also be desirable to provide silver ion containing materials which may be prepared for similar uses in a more efficient process which would not require residual silver ion removal steps.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the invention, a silver ion sequester and release agent is described which comprises a silver ion exchangeable material of the formula:
M(H
1−x−y
Ag
x
M′
y
PO
4
)
2
.nH
2
O;
where M is Zr, Ti, Sn, Ge or Hf or any combination thereof, M′ is an alkali or alkaline earth metal; x is a number from 0.10 to 0.80; y is a number from 0.15 to 0.85; (x+y) is a number from 0.25 to 0.95; and n is a rational number between 0 and 10. The invention is also directed at processes for preparing such silver ion sequester and release agent material comprising combining in an aqueous medium a crystalline or amorphous metal hydrogen phosphate ion exchange host material of the formula M(HPO
4
)
2
.nH
2
O with less than 2 molar equivalents of silver ions relative to the amount of ion exchange host material such that silver ions are exchanged for protons in the host material, and adding a base compound to the aqueous medium to achieve a pH of at least 4.4 and sequester at least 95% of the combined silver ions into the host material. The invention is further directed towards compositions comprising particles of such silver ion sequester and release agent material in an aqueo
Bringley Joseph F.
Liebert Nancy B.
Lok Roger
Anderson Andrew J.
Le Hoa Van
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