Asymmetric silver salt dimers and imaging compositions,...

Details Asymmetric silver salt dimers and imaging compositions,... Asymmetric silver salt dimers and imaging compositions,...

2001-03-20

2002-10-29

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Thermographic process

Heat applied after imaging

C430S617000, C430S619000, C430S620000, C503S210000

Reexamination Certificate

active

06472131

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to novel non-photosensitive silver dimer compounds and their use in imaging compositions, materials and methods. In particular, it relates to novel silver dimer compounds comprising two different silver salts. These asymmetric dimer compounds are useful in thermally-developable imaging materials such as thermographic and photothermographic imaging materials.
BACKGROUND OF THE INVENTION
Silver-containing thermographic and photothermographic imaging materials (that is, heat-developable photographic materials) that are developed with heat and without liquid development have been known in the art for many years.
Thermography or thermal imaging is a recording process wherein images are generated by the use of thermal energy. In direct thermography, a visible image is formed by imagewise heating a recording material containing matter that changes color or optical density upon heating. Thermographic materials generally comprise a support having coated thereon: (a) a relatively or completely non-photosensitive source of reducible silver ions, (b) a reducing composition (usually including a developer) for the reducible silver ions, and (c) a hydrophilic or hydrophobic binder.
In a typical thermographic construction, the image-forming layers are based on silver salts of long chain fatty acids. Typically, the preferred non-photosensitive reducible silver source is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of acids of similar molecular weight are generally used. At elevated temperatures, silver behenate is reduced by a reducing agent for silver ion such as methyl gallate, hydroquinone, substituted-hydroquinones, hindered phenols, catechols, pyrogallol, ascorbic acid, ascorbic acid derivatives, and the like, whereby an image of elemental silver is formed. Some thermographic constructions are imaged by contacting them with the thermal head of a thermographic recording apparatus, such as a thermal printer, thermal facsimile, and the like. In such constructions, an anti-stick layer is coated on top of the imaging layer to prevent sticking of the thermographic construction to the thermal head of the apparatus utilized. The resulting thermographic construction is then heated to an elevated temperature, typically in the range of from about 60 to about 225° C., resulting in the formation of an image.
Thermal recording materials become photothermographic upon incorporating a photosensitive catalyst (such as a silver halide) that upon exposure to irradiation energy (ultraviolet, visible or IR radiation) is capable of providing a latent image. This latent image can be developed by application of thermal energy. Photothermographic materials are also known as “dry silver” materials.
In such materials, the photosensitive catalyst is generally a photographic type photosensitive silver halide that is considered to be in catalytic proximity to the 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)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 [D. Klosterboer,
Imaging Processes and Materials
(
Neblette's Eighth Edition
), Sturge, Walworth & Shepp (Eds.), Van Nostrand-Reinhold, New York, Chapter 9, pp. 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). Other photosensitive materials, such as titanium dioxide, cadmium sulfide, and zinc oxide, have also been reported to be useful in place of silver halide as the photocatalyst in photothermographic materials [see for example, Shepard,
J. Appl. Photog. Eng.
1982, 8(5), 210-212, Shigeo et al.,
Nippon Kagaku Kaishi,
1994, 11, 992-997, and FR 2,254,047 (Robillard)].
The photosensitive silver halide may be made “in situ,” for example, by mixing an organic or inorganic halide-containing source with a source of reducible silver ions to achieve partial metathesis and thus causing the in-situ formation of silver halide (AgX) grains throughout the silver source [see, for example, U.S. Pat. No. 3,457,075 (Morgan et al.)]. In addition, photosensitive silver halides and sources of reducible silver ions can be coprecipitated [see Usanov et al.,
J. Imag. Sci. Tech.
40, 104 (1996)]. Alternatively, a portion of the reducible silver ions can be completely converted to silver halide, and that portion can be added back to the source of reducible silver ions (see Usanov et al., International Conference on Imaging Science, Sep. 7-11, 1998) The silver halide may also be “preformed” and prepared by an “ex situ” process whereby the silver halide (AgX) grains are prepared and grown separately. With this technique, one has the possibility of controlling the grain size, grain size distribution, dopant levels, and composition much more precisely, so that one can impart more specific properties to both the silver halide grains and the photothermographic material. The preformed silver halide grains may be introduced prior to, and be present during, the formation of the source of reducible silver ions. Co-precipitation of the silver halide and the source of reducible silver ions provides a more intimate mixture of the two materials [see for example, U.S. Pat. No. 3,839,049 (Simons)]. Alternatively, the preformed silver halide grains may be added to and physically mixed with the source of reducible silver ions.
The non-photosensitive source of reducible silver ions is a material that contains reducible silver ions. Typically, the preferred non-photosensitive source of reducible silver ions is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms, or mixtures of such salts. Such acids are also known as “fatty acids” or “fatty carboxylic acids” . Silver salts of other organic acids or other organic compounds, such as silver imidazoles, silver tetrazoles, silver benzotriazoles, silver benzotetrazoles, silver benzothiazoles and silver acetylides have also been proposed. U.S. Pat. No. 4,260,677 (Winslow et al.) discloses the use of complexes of various inorganic or organic silver salts.
In photothermographic materials, exposure of the photographic silver halide to light produces small clusters containing silver atoms (Ag
0
)
n
. The imagewise distribution of these clusters, known in the art as a latent image, is generally not visible by ordinary means. Thus, the photosensitive material must be further developed to produce a visible image. This is accomplished by the reduction of silver ions that are in catalytic proximity to silver halide grains bearing the silver containing-clusters of the latent image. This produces a black-and-white image. The non-photosensitive silver source is catalytically reduced to form the visible black-and-white negative image while much of the silver halide, generally, remains as silver halide and is not reduced.
In photothermographic materials, the reducing agent for the reducible silver ions, often referred to as a “developer, ” may be any compound that, in the presence of the latent image, can reduce silver ion to metallic silver and is preferably of relatively low activity until it is heated to a temperature sufficient to cause the reaction. A wide variety of classes of compounds have been disclosed in the literature that function as developers for photothermographic materials. At elevated temperatures, the reducible

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