Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-04-11
2001-10-09
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S619000
Reexamination Certificate
active
06300050
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to photothermographic elements, a method of preparing said elements and a method of preparing a light sensitive silver halide emulsion.
BACKGROUND OF THE INVENTION
Thermally processable imaging elements, including films and papers, for producing images by thermal processing are well known. These elements include photothermographic elements in which an image is formed by imagewise exposure to light followed by development by uniformly heating the element. Such elements typically include photosensitive silver halide, prepared in situ and/or ex situ, as a photosensitive component, in combination with an oxidation-reduction image forming combination, such as silver behenate with a phenolic reducing agent. Such elements are described in, for example, Research Disclosure, June, 1978, Item No. 17029, U.S. Pat. Nos. 3,457,075; and 3,933,508.
Photothermographic elements are typically processed by a method which comprises imagewise exposure of the element to actinic radiation to form a latent image therein followed by heating of the imagewise-exposed element to convert the latent image to a visible image. The simplicity of this method is highly advantageous. Photothermographic elements have been described heretofore in numerous patents.
PROBLEM TO BE SOLVED BY THE INVENTION
The problem to be solved by this invention is to provide photothermographic elements having improved the photosensitivity, in particular, photothermographic elements comprising a silver halide emulsion in which the silver halide comprises at least 10% silver iodide, and a method of making such photothermographic elements.
SUMMARY OF THE INVENTION
We have now discovered that preparing a silver halide emulsion with the use of a solid ionic conductor increases the speed (i.e. photosensitivity) of the silver halide emulsion.
One aspect of this invention comprises a photothermographic element comprising a support bearing an imaging layer comprising:
a silver salt;
a reducing agent;
a binder; and
a photosensitive material comprising silver iodide produced by dispersing a solid ionic conductor of the formula MAg
4
I
5
in an organic solvent, whereby the ionic conductor decomposes to produce silver iodide, and wherein M is a monovalent cation and said solid ionic conductor has an ionic conductivity of >0.001 ohm
−1
cm
−1
at 25° C.
Another aspect of this invention comprises a method of preparing a photothermographic element comprising:
dispersing a binder in an organic solvent;
adding to the resulting dispersion a solid ionic conductor of the formula MAg
4
I
5
having ionic conductivity of >0.001 ohm
−1
cm
−1
,
then adding a silver salt and a reducing agent, to the dispersion; and
coating the resulting dispersion onto a support.
Yet another aspect of this invention comprises a method of preparing a light sensitive silver iodide emulsion which comprises dispersing, in an organic solvent, a solid ionic conductor of the formula MAg
4
I
5
, whereby the solid ionic conductor decomposes to produce silver iodide, and wherein M is a monovalent cation and the solid ionic conductor has an ionic conductivity of >0.001 ohm
−1
cm
−1
.
The solid ionic conductor preferably has an ionic conductivity between 0.001 ohm
−1
cm
−1
and 0.5 ohm
−1
cm
−1
.
ADVANTAGEOUS EFFECT OF THE INVENTION
This invention provides photothermographic elements having increased speed (i.e., photosensitivity). In preferred embodiments, this invention provides a process for generating photothennographic elements, having increased photosensitivity, that may be regarded as an alternative to solution precipitation. In contrast to the conventional approach to generating photothermographic elements, which involves mixing a solution containing silver ions with a solution containing halide ions. In the process described in this invention, a powder of a solid ionic conductor, such as RbAg415, which is generated by melt crystallization and ball milling, is dispersed in a suitable organic solvent such as acetone, to undergo decomposition and generate the photothermographic elements. A significant advantage of this process is the elimination of the precipitation step which utilizes a significant quantity of organic solvents; i.e. minimizes the quantity of waste solvent generated during the process. Hence this process may be regarded as an environmentally friendlier process. In addition, the photothermographic elements generated by this process appear to have enhanced photosensitivity compared to the analogous elements generated by solution preparation.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides silver halide emulsion in an organic solvent having improved speed. This is achieved by the use of solid ionic conductors comprising silver and halide ions. In preferred embodiments of the invention, the solid ionic conductor comprises silver and iodide ions. The solid ionic conductor preferably comprises a compound of the formula MAg
4
X
5
where M is monovalent cation and X is a halide ion. Illustrative cations for use in the solid ionic conductor include, for example, Na
+
, K
+
, Rb
+
, Cs
+
or NH
4
+
. The organic solvent is preferably a polar, solvent, such as acetone and methyl isobutyl ketone.
In a preferred embodiment of the invention the silver halide emulsion is prepared in situ by decomposing the compound MAg
4
X
5
in the organic solvent. The compound MAg
4
X
5
is prepared from AgX and MX by melt crystallization followed by ball milling to produce a fine powder. This powder is then dispersed in the organic solvent.
It is believed that the following represents the decomposition reaction:
2MAg
4
X
5
→M
2
AgX
3
+7AgX.
In preferred embodiments of the invention X is iodide.
While not wishing to be bound by any theory, it is believed that the AgI may be chemically sensitized by trace amounts of MAg
4
I
5
, by M
2
AgI
3
(one of the decomposition products) or by some other material generated during the decomposition process. In any event, we have discovered that MAg
4
I
5
decomposed in the presence of acetone has enhanced photosensitivity.
The photothermographic elements utilized in this invention can be black-and-white imaging elements or dye forming elements, including elements adapted for dye image transfer to an image receiver layer. Illustrative of the many patents describing photothermographic elements are U.S. Pat. Nos. 3,457,075, 3,764,329, 3,802,888, 3,839,049, 3,871,887, 3,933,508, 4,260,667, 4,267,267, 4,281,060, 4,283,477, 4,287,295, 4,291,120, 4,347,310, 4,459,350, 4,741,992, 4,857,439 and 4,942,115.
The photothermographic elements as described in the prior art comprise a variety of supports. Examples of useful supports include poly(vinyl acetal) film, polystyrene film, poly(ethyleneterephthalate) film, polycarbonate films and related films and resinous materials, as well as glass, paper, metal, and other supports that can withstand the thermal processing temperatures.
The layers of the photothermographic element are coated on the support by coating procedures known in the photographic art, including dip coating, air knife coating, curtain coating or extrusion coating using coating hoppers. If desired, two or more layers are coated simultaneously.
Commonly utilized photothermographic elements comprise a support bearing, in reactive association, in a binder, such as poly(vinyl butyral), (a) photosensitive silver halide, prepared ex situ and/or in situ, and (b) an oxidation-reduction image-forming combination comprising (i) an organic silver salt oxidizing agent, preferably a silver salt of a long chain fatty acid, such as silver behenate, with (ii) a reducing agent for the organic silver salt oxidizing agent, preferably a phenolic reducing agent. The photothermographic silver halide element can comprise other addenda known in the art to help in providing a useful image, such as optional toning agents and image stabilizers. A preferred photothermographic element comprises a support bearing, in re
Blanton Thomas N.
Chatterjee Dilip K.
Dankosh Heidi E.
Gisser Kathleen R.
Jagannathan Seshadri
Chea Thorl
Eastman Kodak Company
Konkol Chris P.
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