Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
2000-06-19
2003-12-09
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S523000, C430S536000, C430S538000, C430S583000, C430S599000, C430S600000, C430S603000
Reexamination Certificate
active
06660464
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a photographic element having improved photographic response.
BACKGROUND OF THE INVENTION
It is a long-standing objective of 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 size of the emulsion grains. Larger grains capture more light. Upon development of black and white photographic elements, the captured light is ultimately converted into silver deposits which constitute the reproduced image. For color photographic elements, development leads to a reproduced image provided by dye deposits. However, the granularity expressed by the silver or 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.
Chemical sensitizing agents have been used to enhance the intrinsic sensitivity of silver halide. Conventional chemical sensitizing agents include various sulfur, gold, and group VIII metal compounds. A summary of chemical sensitizers is provided by
Research Disclosure
, Vol. 389, September 1996, Item 38957, IV. Chemical sensitization.
Spectral sensitizing agents, such as cyanine and other polymethine dyes, have been used alone, or in combination, to impart spectral sensitivity to emulsions in specific wavelength regions. These sensitizing dyes function by absorbing long wavelength light that is essentially unabsorbed by the silver halide emulsion and using the energy of that light to cause latent image formation in the silver halide. A summary of spectral sensitizing dyes is provided by
Research Disclosure
, Item 38957, cited above, V. Spectral sensitization and desensitization, A. Sensitizing Dyes.
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. Fragmentable electron donors are compounds that have been designed to undergo a bond fragmentation reaction after capturing the photohole created by absorption of light in a silver halide emulsion. This fragmentation reaction removes the photohole from the emulsion, thus reducing the probability of recombination with the photoelectron and giving improved light sensitivity. For some compounds, termed fragmentable two electron donors, the radical resulting from the bond fragmentation reaction is designed to be sufficiently energetic so as to inject an electron into the silver halide emulsion. Consequently, absorption of one photon by a silver halide emulsion containing a fragmentable two electron donor results in creation of two electrons in the silver halide emulsion, the first resulting from the initial absorption of the photon and the second resulting from the sequence of reactions caused by capture of the photohole at the fragmentable two electron donor. The production of this second electron leads to increased photographic speed. Fragmentable electron donors have been described in U.S. Pat. Nos. 5,747,235, 5,747,236, 5,994,051, 6,010,841, and 6,054,260 and published European Patent Application 893,732. These references disclose speed gains associated with the use of fragmentable electron donors in a wide variety of silver halide emulsions. However, it is also frequently found that addition of a fragmentable electron donor to an emulsion increases the storage fog, particularly for storage temperatures above room temperature. making it necessary to limit the amount of fragmentable electron donor used in order to avoid excessive storage fog. In such cases, the extent of practical speed gain obtainable from the fragmentable electron donor may be reduced.
Consequently, it is of interest to find means to reduce the storage fog associated with the presence of fragmentable electron donors in a photographic element.
SUMMARY OF THE INVENTION
We have discovered that coating the photographic layer(s) containing the fragmentable electron donor on a support with low oxygen permeability, such as a polyester support, substantially decreases the high temperature storage fog as compared to the same layer formulation coated on a support with high oxygen permeability, such as cellulose acetate support.
This invention provides a silver halide photographic element comprising a support with low oxygen permeability and at least one silver halide emulsion layer containing 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 present in the emulsion layer, 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 potential≦−0.7V (that is, equal to or more negative than about −0.7V).
DETAILED DESCRIPTION OF THE INVENTION
In accordance with this invention the silver halide emulsion contains a fragmentable electron donating (FED) compound which enhances the sensitivity of the emulsion. The fragmentable electron donating compound is 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 present in the emulsion layer, 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 potential ≦−0.7V (that is, equal to or more negative than about −0.7V).
Compounds wherein X—Y′ meets criteria (1) and (2) but not (3) are capable of donating one electron and are referred to herein as fragmentable one-electron donating compounds. Compounds which meet all three criteria are capable of donating two electrons and are referred to herein as fragmentable two-electron donating compounds.
In this patent application, oxidation potentials are reported as “V” which represents “volts versus a saturated calomel reference electrode”.
In embodiments of the invention in which Y′ is Y, the following represents the reactions that are believed to take place when X—Y undergoes oxidation and fragmentation to produce a radical X
•
, which in a preferred embodiment undergoes further oxidation.
where E
1
is the oxidation potential of X—Y and E
2
is the oxidation potential of the radical X
•
.
E
1
is preferably no higher than about 1.4 V and preferably less than about 1.0 V. The oxidation potential is preferably greater than 0, more preferably greater than about 0.3 V. E
1
is preferably in the range of about 0 to about 1.4 V, and more preferably from about 0.3 V to about 1.0 V.
In certain embodiments of the invention the oxidation potential, E
2
, of the radical X
•
is equal to or more negative than −0.7V, preferably more negative than about −0.9 V. E
2
is preferably in the range of from about −0.7 to about −2 V, more preferably from about −0.8 to about −2 V and most preferably from about −0.9 to ab
Muenter Annabel A.
Szatynski Steven P.
Baxter Janet
Eastman Kodak Company
Rice Edith A.
Sarah Meeks Roberts
Walke Amanda C.
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