Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied after imaging
Reexamination Certificate
2000-09-21
2002-04-09
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied after imaging
C430S510000, C430S517000, C430S527000, C430S600000, C430S603000, C430S611000, C430S613000, C430S944000
Reexamination Certificate
active
06368779
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to thermally-developable imaging materials such as photothermographic materials that exhibit high speed imaging characteristics. In particular, this invention relates to the use of certain chalcogen compounds as chemical sensitizers in photothermographic materials to provide increased photothermographic speed. This invention also relates to methods of imaging using these photothermographic materials, and to a method of making imaging formulations used in them.
BACKGROUND OF THE INVENTION
Photothermographic imaging materials that are developed with heat and without liquid development have been known in the art for many years. Such materials are used in a recording process wherein images are generated by the use of thermal energy. In direct photothermography, a visible image is formed by imagewise exposure of the photothermographic material to specific electromagnetic radiation (for example, visible, ultraviolet or infrared radiation). These materials, also known as “dry silver” materials, generally comprise a support having coated thereon: (a) photosensitive catalyst (such as silver halide) that upon such exposure provides a latent image in exposed grains that are capable of acting as catalysts for the formation of a silver image, (b) a relatively or completely non-photosensitive source of reducible silver ions, (c) a reducing composition (usually including a developer) for the reducible silver ions, and (d) a hydrophilic or hydrophobic binder. The latent image is then developed by application of thermal energy.
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 an intimate physical association of these two components either prior to or during the thermal image development process so that when silver atoms [Ag(0)]
n
, (also known as silver specks, clusters or nuclei) 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 into 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 No. 17029). Other photosensitive materials, such as titanium dioxide, cadmium sulfide, and zinc oxide have been reported to be useful in place of silver halide as photocatalysts in photothermographic materials [see, for example, J. W. Shepard,
J. Appl. Photog. Eng.
1982, 8(5), 210-212; S. 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 on the surface of the silver halide grains [see, for example, U.S. Pat. No. 3,457,075 (Morgan et al.)].
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 photothermographic material. The preformed silver halide grains may be introduced prior to and be present during the formation of the silver soap. Co-precipitation of the silver halide and reducible silver source 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 reducible silver salt.
The non-photosensitive source of reducible silver ions is a material that contains 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.” Silver salts of other organic acids or other organic compounds, such as silver imidazoles, silver benzotriazoles, silver benzotetrazoles, silver tetrazoles, silver benzothiazoles and silver acetylides, have been proposed. U.S. Pat. No. 4,260,677 (Winslow et al.) discloses the use of complexes of various non-photosensitive inorganic or organic silver salts.
In photothermographic emulsions, exposure of the photographic silver halide to light produces small clusters of 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 emulsion 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 clusters of silver atoms (that is, the latent image). This produces a black-and-white image. The non-photosensitive silver source is 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 silver ions of the light-insensitive reducible silver salt, often referred to as a “developer,” may be any compound that, in the presence of the latent image, can reduce silver ions 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 silver ions are reduced by the reducing agent. In photothermographic materials, upon heating, this reaction occurs preferentially in the regions surrounding the latent image. This reaction produces a negative image of metallic silver having a color that ranges from yellow to deep black depending upon the presence of toning agents and other components in the imaging layer.
Differences Between Photothermography and Photography
The imaging arts have long recognized that the field of photothermography is clearly distinct from that of photography. Photothermographic materials differ significantly from conventional silver halide photographic materials that require processing with aqueous solutions to provide visible images.
As noted above, in photothermographic imaging materials, a visible image is created by heat as a result of the reaction of a developer incorporated within the material. Heating at 50° C. or more is essential for this dry development. In contrast, conventional photographic imaging materials require processing in aqueous processing baths at more moderate temperatures (from 30° C. to 50° C.) to provide a visible image.
In photothermographic materials, only a small amount of silver halide is used to capture light and a non-photosensitive source of reducible silver ions (for example a silver carboxylate) is used to generate the visible image using thermal development. Thus, the photosensitive silver halide serves as a catalyst for the physical development of the non-photosensitive source of reducible silver ions. In contrast, conventional wet-processed, black-and-white photographic materials use only one form of silver that, upon chemical development, is itself converted into the s
Lynch Doreen C.
Shor Steven M.
Simpson Sharon M.
Willett Brian C.
Zou Chaofeng
Chea Thorl
Tucker J. Lanny
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