Silver compounds and compositions, thermally developable materials containing same, and methods of preparation Number:6,803,177 from the United States Patent and Trademark Office (PTO) owispatent Novel silver compounds can include a primary core of a photosensitive silver halide and a shell covering the primary core. This shell includes one or more non-photosensitive silver salts, each silver salt including an organic silver coordinating ligand. Other novel silver compounds are homogeneous silver salts of organic silver coordinating ligands throughout (non-core-shell). Still other silver compounds can include a primary core of a non-photosensitive metal salt and a shell covering the primary core. This shell includes one or more non-photosensitive silver salts, each silver salt including an organic silver coordinating ligand. These types of silver compounds can be used as sources of reducible silver ions in thermally developable imaging materials including thermographic and photothermographic materials.<H compositions, preparation, Silver, compound, 6803177.html, Patent, pto, 6803177

Title: Silver compounds and compositions, thermally developable materials containing same, and methods of preparation

Abstract: Novel silver compounds can include a primary core of a photosensitive silver halide and a shell covering the primary core. This shell includes one or more non-photosensitive silver salts, each silver salt including an organic silver coordinating ligand. Other novel silver compounds are homogeneous silver salts of organic silver coordinating ligands throughout (non-core-shell). Still other silver compounds can include a primary core of a non-photosensitive metal salt and a shell covering the primary core. This shell includes one or more non-photosensitive silver salts, each silver salt including an organic silver coordinating ligand. These types of silver compounds can be used as sources of reducible silver ions in thermally developable imaging materials including thermographic and photothermographic materials.

Patent Number: 6,803,177 Issued on 10/12/2004 to Bokhonov, et al.

Inventors: Bokhonov; Boris B. (Novosibirsk, RU); Burleva; Lilia P. (Maplewood, MN); Whitcomb; David R. (Woodbury, MN); Howlader; Nepal C. (Woodbury, MN); Leichter; Louis M. (Mendota Heights, MN)
Assignee: Eastman Kodak Company (Rochester, NY)

Appl. No.: 10/208,603

Filed: July 30, 2002

Current U.S. Class: 430/350 ; 430/223; 430/230; 430/567; 430/619; 430/620

Current International Class: G03C 1/498 (20060101)

Field of Search: 430/619,567,620,350,223,230

References Cited [Referenced By]

U.S. Patent Documents


3457075	July 1969	Morgan et al.
3839049	October 1974	Simons
5382504	January 1995	Shor et al.
5677121	October 1997	Tsuzuki
5705324	January 1998	Murray
6211116	April 2001	Defieuw et al.
6391537	May 2002	Lelental et al.

Foreign Patent Documents


0 962 814	Dec., 1999	EP
0 962 815	Dec., 1999	EP
0 964 300	Dec., 1999	EP
1 168 069	Jan., 2002	EP

Other References

BB. Bokhonov et al., Silver Halide/Silver Carboxylate Photothermographic Imaging Systems: Characteristic Properties of Structure and Development, pp. 38-41 50.sup.th IS&T Conference, Boston, MA 1997. .
V.M. Belous et al., Chemical Sensitization of Internal Light Sensitive Photographic Emulsions with Heterophase MicrocrystalsI, Zhur. Nauch. I Priklad. Fotogr. I Kinematogr., 36, 1991, 416. .
(Translation) V.M. Belous et al., Chemical Sensitization of Internal Light Sensitive Photographic Emulsions with Heterophase MicrocrystalsI, Zhur. Nauch. I Priklad. Fotogr. I Kinematogr., 36, 1991, 416..

Primary Examiner: Chea; Thor
Attorney, Agent or Firm: Tucker; J. Lanny Leichter; Louis M.

Claims

We claim:

1. A photothermographic material comprising a support having thereon one or more layers comprising: a) a source of non-photosensitive silver ions comprising a core-shell silver compound comprising a primary core comprising one or more photosensitive silver halides, and a shell covering said primary core, wherein said shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, b) a reducing composition for said non-photosensitive silver ions, c) a binder, and d) a photocatalyst.

2. The photothermographic material of claim 1 wherein said photocatalyst includes one or more silver halides, and said binder is a hydrophilic binder.

3. The photothermographic material of claim 2 wherein said photocatalyst comprises core-shell silver halide grains.

4. The photothermographic material of claim 1 wherein said photocatalyst includes one or more silver halides, and said binder is a hydrophobic binder.

5. The photothermographic material of claim 1 wherein said organic silver coordinating ligand is a benzotriazole or a substituted derivative thereof, a long chain aliphatic carboxylate, or a mixture or two or more of these.

6. The photothermographic material of claim 5 wherein said organic silver coordinating ligand is a benzotriazole or a substituted derivative thereof, behenate, stearate, or a mixture or two or more of these.

7. The photothermographic material of claim 1 that provides a color image and wherein said reducing composition comprises a dye-forming or -releasing compound.

8. A method comprising: A) imagewise exposing the photothermographic material of claim 1 to electromagnetic radiation to form a latent image, and B) simultaneously or sequentially, heating the exposed material to develop the latent image into a visible image.

9. The photothermographic material of claim 1 wherein the molar ratio of said one or more non-photosensitive silver salts in said shell to said one or more silver halides in said primary core of said core-shell silver compound is from about 100:1 to about 1:100.

10. The photothermographic material of claim 1 wherein said primary core of said core-shell silver compound contains predominantly silver bromide.

11. The photothermographic material of claim 1 wherein said primary core of said core-shell silver compound contains silver chlorobromide, silver iodobromide, or silver bromide.

12. The photothermographic material of claim 1 wherein said shell of said core-shell silver compound comprises a mixture of silver salts comprising different organic silver coordinating ligands.

13. The photothermographic material of claim 12 wherein said shell of said core-shell silver compound comprises a silver carboxylate as one of said silver salts.

14. The photothermographic material of claim 13 wherein said shell of said core-shell silver compound comprises a silver long chain aliphatic carboxylate as one of said silver salts.

15. The photothermographic material of claim 1 wherein said core-shell silver compound has an average particle size of from about 50 nm to about 10 .mu.m.

16. The photothermographic material of claim 1 where said primary core of said core-shell silver compound is composed of an inner region comprising a first silver halide and an outer region comprising a different silver halide.

17. The photothermographic material of claim 16 wherein said inner region of said core-shell silver compound is composed predominantly of a mixture of silver bromide and silver iodide, and said outer region is composed of predominantly silver bromide.

18. The photothermographic material of claim 1 wherein said organic silver coordinating ligand contains imino groups.

19. The photothermographic material of claim 18 wherein said organic silver coordinating ligand is a benzotriazole or substituted derivative thereof, a 1,2,4-triazole, a 1-H-tetrazole, or an imidazole derivative.

Description

FIELD OF THE INVENTION

This invention relates to novel silver compounds that can be used as a source of reducible silver ions in thermally developable imaging materials. The invention also includes imaging compositions and methods of making the silver compounds. In particular, the invention relates to thermographic and photothermographic materials containing these silver compounds.

BACKGROUND OF THE INVENTION

Silver-containing thermographic and photothermographic imaging materials (that is, thermally developable imaging materials) that are imaged and/or developed using heat and without liquid processing have been known in the art for many years.

Silver-containing thermographic imaging materials are non-photosensitive materials that are used in a recording process wherein images are generated by the use of thermal energy. These materials generally comprise a support having disposed 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 suitable 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, and ascorbic acid derivatives, 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 or thermal facsimile. In such, 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.degree. C. resulting in the formation of an image.

Silver-containing photothermographic imaging materials are photosensitive materials that are used in a recording process wherein an image is formed by imagewise exposure of the photothermographic material to specific electromagnetic radiation (for example, X-radiation, or ultraviolet, visible, or infrared radiation) and developed by the use of thermal energy. These materials, also known as "dry silver" materials, generally comprise a support having coated thereon: (a) a photocatalyst (that is, a photosensitive compound such as silver halide) that upon such exposure provides a latent image in exposed grains that are capable of acting as a catalyst for the subsequent formation of a silver image in a development step, (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 intimate physical association of these two components either prior to or during the thermal image development process so that when silver atoms (Ag.sup.0).sub.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. H. Klosterboer, Imaging Processes and Materials, (Neblette's Eighth Edition), J. Sturge, V. Walworth, and A. Shepp, Eds., Van Nostrand-Reinhold, New York, 1989, Chapter 9, pp. 279-291]. 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 Yu. E. Usanov et al., J. Imag. Sci. Tech. 1996, 40, 104]. 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 Yu. E. Usanov et al., International Conference on Imaging Science, Sep. 7-11, 1998, pp.67-70).

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 may also be used. 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.sup.0).sub.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 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(s).

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 processing solutions.

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.degree. 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.degree. C. to 50.degree. 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 imaged photosensitive silver halide serves as a catalyst for the physical development process involving the non-photosensitive source of reducible silver ions and the incorporated reducing agent. In contrast, conventional wet-processed, black-and-white photographic materials use only one form of silver (that is, silver halide) that, upon chemical development, is itself at least partially converted into the silver image, or that upon physical development requires addition of an external silver source (or other reducible metal ions that form black images upon reduction to the corresponding metal). Thus, photothermographic materials require an amount of silver halide per unit area that is only a fraction of that used in conventional wet-processed photographic materials.

In photothermographic materials, all of the "chemistry" for imaging is incorporated within the material itself. For example, such materials include a developer (that is, a reducing agent for the reducible silver ions) while conventional photographic materials usually do not. Even in so-called "instant photography," the developer chemistry is physically separated from the photosensitive silver halide until development is desired. The incorporation of the developer into photothermographic materials can lead to increased formation of various types of "fog" or other undesirable sensitometric side effects. Therefore, much effort has gone into the preparation and manufacture of photothermographic materials to minimize these problems during the preparation of the photothermographic emulsion as well as during coating, use, storage, and post-processing handling.

Moreover, in photothermographic materials, the unexposed silver halide generally remains intact after development and the material must be stabilized against further imaging and development. In contrast, silver halide is removed from conventional photographic materials after solution development to prevent further imaging (that is in the aqueous fixing step).

In photothermographic materials, the binder is capable of wide variation and a number of binders (both hydrophilic and hydrophobic) are useful. In contrast, conventional photographic materials are limited almost exclusively to hydrophilic colloidal binders such as gelatin.

Because photothermographic materials require dry thermal processing, they present distinctly different problems and require different materials in manufacture and use, compared to conventional, wet-processed silver halide photographic materials. Additives that have one effect in conventional silver halide photographic materials may behave quite differently when incorporated in photothermographic materials where the underlying chemistry is significantly more complex. The incorporation of such additives as, for example, stabilizers, antifoggants, speed enhancers, supersensitizers, and spectral and chemical sensitizers in conventional photographic materials is not predictive of whether such additives will prove beneficial or detrimental in photothermographic materials. For example, it is not uncommon for a photographic antifoggant useful in conventional photographic materials to cause various types of fog when incorporated into photothermographic materials, or for supersensitizers that are effective in photographic materials to be inactive in photothermographic materials.

These and other distinctions between photothermographic and photographic materials are described in Imaging Processes and Materials (Neblette's Eighth Edition), noted above, Unconventional Imaging Processes, E. Brinckman et al. (Eds.), The Focal Press, London and New York, 1978, pp. 74-75, in Zou et al., J. Imaging Sci. Technol. 1996, 40, pp. 94-103, and in M. R. V. Sahyun, J. Imaging Sci. Technol. 1998, 42, 23.

Problem to be Solved

While a number of useful thermographic and photothermographic materials are available in the market and described in the art for medical and graphic arts use, there is a continuing need for improving the reactivity of the imaging composition in such materials to provide reducible silver ions. In particular, there is a need for imaging materials that utilize non-photosensitive silver compounds that can be imaged and/or developed at lower temperatures while providing high D.sub.max, good image tone, quality, and stability.

SUMMARY OF THE INVENTION

The present invention provides a core-shell silver compound comprising a primary core comprising one or more photosensitive silver halides, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises a organic silver coordinating ligand.

This invention also provides a composition comprising: a) a core-shell silver compound comprising a primary core comprising one or more photosensitive silver halides, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, and b) a non-photosensitive non-core-shell silver salt.

In another embodiment, this invention provides a composition comprising: a) a first core-shell silver compound comprising a first primary core comprising one or more photosensitive silver halides, and a first shell at least partially covering the first primary core, wherein the first shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, and b) a second core-shell silver compound comprising a second primary core comprising one or more photosensitive silver halides, and a second shell at least partially covering the second primary core, wherein the second shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, the first and second core-shell silver compounds differing in composition in either their primary cores and/or shells.

In one embodiment, the composition further comprises a binder. In another embodiment, the composition comprises a reducing agent composition for reducible silver ions. In yet another embodiment, the composition further comprises a photocatalyst. A preferred photocatalyst is a photosensitive silver halide.

Further, a thermally developable emulsion comprises: a) a source of non-photosensitive silver ions comprising a core-shell silver compound comprising a primary core comprising one or more photosensitive silver halides, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, b) a reducing composition for the non-photosensitive silver ions, and c) a binder.

In one embodiment, the thermally developable emulsion further comprises a photocatalyst. A preferred photocatalyst is a photosensitive silver halide.

In addition, a thermally developable imaging material comprises a support having thereon one or more imaging layers comprising: a) a source of non-photosensitive silver ions comprising a core-shell silver compound comprising a primary core comprising one or more photosensitive silver halides, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, b) a reducing composition for the non-photosensitive silver ions, and c) a binder.

In a preferred embodiment, this invention provides a photothermographic material comprising a support having thereon one or more layers comprising: a) a source of non-photosensitive silver ions comprising a core-shell silver compound comprising a primary core comprising one or more photosensitive silver halides, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, b) a reducing composition for the non-photosensitive silver ions, c) a binder, and d) a photocatalyst.

This invention also provides a method of making the core-shell silver compounds described above, the method comprising mixing a core-shell photosensitive silver halide with one or more ammonium or alkali metal salts of organic silver coordinating ligands for sufficient time to form the core-shell silver compound. comprising a primary core comprising one or more photosensitive silver halides, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts comprised of one or more organic silver coordinating ligands.

The present invention also provides a core-shell silver compound comprising a primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand.

This invention also provides a composition comprising: a) a core-shell silver compound comprising a primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, and b) a non-photosensitive non-core-shell silver salt.

In another embodiment, this invention provides a composition comprising: a) a first core-shell silver compound comprising a first primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a first shell at least partially covering the first primary core, wherein the first shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, and b) a second core-shell silver compound comprising a second primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a second shell at least partially covering the second primary core, wherein the second shell comprises one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, the first and second core-shell silver compounds differing in composition in either their primary cores and/or shells.

In one embodiment, the composition further comprises a photocatalyst. A preferred photocatalyst is a photosensitive silver halide.

Further, this invention also provides a thermally developable emulsion comprising: a) a source of non-photosensitive silver ions comprising a core-shell silver compound comprising a primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which non-photosensitive silver salts comprises an organic silver coordinating ligand, b) a reducing composition for the non-photosensitive silver ions, and c) a binder.

In addition, a thermally developable imaging material comprises a support having thereon one or more imaging layers comprising: a) a source of non-photosensitive silver ions comprising a core-shell silver compound comprising a primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, each of which non-photosensitive silver salts comprises an organic silver coordinating ligand, b) a reducing composition for the non-photosensitive silver ions, and c) a binder.

This invention also provides a method of making core-shell silver compounds, the method comprising: mixing a core-shell non-photosensitive metal salt comprising a primary core comprising one or more non-photosensitive inorganic metal salts or non-silver-containing organic salts, and a shell at least partially covering the primary core, wherein the shell comprises one or more non-photosensitive silver salts, with one or more ammonium or alkali metal salts of organic silver coordinating ligands for sufficient time to form a core-shell silver compound comprising a primary core comprising one or more non-photosensitive metal salts, and a shell at least partially covering said primary core, which shell comprises one or more non-photosensitive silver salts comprised of said one or more organic silver coordinating ligands.

Also provided by this invention is a surfactant-free composition comprising a non-photosensitive organic silver salt comprising an organic coordinating ligand, the organic silver salt having an average particle size of less than or equal to 0.5 .mu.m.

A thermally developable composition comprises: a) the surfactant-free composition noted above containing a non-photosensitive organic silver salt having an average particle size of less than or equal to 0.5 .mu.m, and b) a reducing agent for the non-photosensitive silver salt.

In addition, a thermally developable imaging material comprises a support having thereon one or more imaging layers comprising: a) the surfactant-free composition noted above containing a non-photosensitive organic silver salt having an average particle size of less than or equal to 0.5 .mu.m, b) a reducing composition for the non-photosensitive silver ions, and c) a binder.

Further, a photothermographic material comprises a support having thereon one or more layers comprising: a) the surfactant-free composition noted above containing a non-photosensitive organic silver salt having an average particle size of less than or equal to 0.5 .mu.m, b) a reducing composition for the non-photosensitive silver ions, c) a binder, and d) a photocatalyst.

This invention also provides a method of making the non-photosensitive organic silver salts described above, the method comprising mixing a non-photosensitive silver halide with one or more ammonium or alkali metal salts of an organic silver coordinating ligand for a sufficient time to form the organic silver salt. This method can be used to prepare the non-photosensitive organic silver salts having an average particle size of less than or equal to 0.5 .mu.m, described above.

The present invention further provides organic silver compounds comprising one or more non-photosensitive silver salts, each of which silver salts comprises an organic silver coordinating ligand, the organic silver compound formed by reaction of a silver halide with one or more ammonium or alkali metal salts of an organic silver coordinating ligand for a sufficient time to form the organic silver compound.

In another embodiment, the present invention provides a method comprising imagewise exposing the thermally developable material of this invention to thermal energy to form a visible image.

In another embodiment, the present invention provides a method comprising: A) imagewise exposing the photothermographic material of this invention to electromagnetic radiation to which the photocatalyst (for example, a photosensitive silver halide) of the material is sensitive, to form a latent image, and B) simultaneously or sequentially, heating the exposed material to develop the latent image into a visible image.

Thermographic and photothermographic materials incorporating both the novel core-shell silver compounds and the novel non-core-shell compounds of this invention as the non-photosensitive source of reducible silver ions can provide images with desired image stability, D.sub.max, and tone. They can be imaged and/or developed at lower temperatures.

The novel core-shell silver compounds of this invention are prepared using a novel and simple method whereby core-shell photosensitive silver halide grains are mixed with a salt comprising an organic silver coordinating ligand (such as a carboxylate or a benzotriazolate). The organic silver coordinating ligand reacts with the silver in the "shell" portion of the silver halide grains to provide a "shell" of non-photosensitive silver salt around the unreacted core of silver halide. The novel core-shell silver compounds so formed have different reactivity and crystal morphology from core-shell silver compounds prepared by previously used methods.

Similarly, the novel non-core-shell silver compounds of this invention are also prepared using a novel and simple method whereby non-photosensitive silver halide grains are mixed with a salt comprising an organic silver coordinating ligand (such as a carboxylate or a triazolate). The organic silver coordinating ligand replaces the halide in the silver halide grains to provide a non-photosensitive silver salt. The novel non-core-shell silver compounds so formed have different reactivity and crystal morphology from core-shell silver compounds prepared by previously used methods.

Additionally, the novel core-shell silver compounds of this invention are prepared using a novel and simple method whereby non-photosensitive metal salt grains are mixed with a salt comprising an organic silver coordinating ligand (such as a carboxylate or a triazolate). The organic silver coordinating ligand replaces the anion of the metal salt to provide a non-photosensitive silver salt. The novel -core-shell silver compounds so formed have different reactivity and crystal morphology from core-shell silver compounds prepared by previously used methods.

The invention provides a means for providing predetermined organic silver salts with varying reactivity and unique imaging properties, particularly at the core-shell interface. Thus, thermally imageable materials can be prepared having specific predetermined properties.

DETAILED DESCRIPTION OF THE INVENTION

The thermally developable materials of this invention include both thermographic and photothermographic materials. While the following discussion will often be directed primarily to the preferred photothermographic embodiments, it would be readily understood by one skilled in the imaging arts that thermographic materials can be similarly constructed (using one or more imaging layers) and used to provide black-and-white or color images using the non-photosensitive core-shell silver compounds of this invention, reducing compositions, binders, and other components known to be useful in such embodiments.

The thermographic and photothermographic materials of this invention can be used in black-and-white or color thermography and photothermography and in electronically generated black-and-white or color hardcopy recording. They can be used in microfilm applications, in radiographic imaging (for example digital medical imaging), X-ray radiography, and in industrial radiography. Furthermore, the absorbance of these photothermographic materials between 350 and 450 nm is desirably low (less than 0.5), to permit their use in the graphic arts area (for example, imagesetting and phototypesetting), in the manufacture of printing plates, in contact printing, in duplicating ("duping"), and in proofing. The thermographic and photothermographic materials of this invention are particularly useful for medical, dental, and veterinary radiography to provide black-and-white images.

The photothermographic materials of this invention can be made sensitive to radiation of any suitable wavelength. Thus, in some embodiments, the materials are sensitive at ultraviolet, visible, infrared, or near infrared wavelengths of the electromagnetic spectrum. In other embodiments they are sensitive to X-radiation.

The materials of this invention are also useful for non-medical uses of visible or X-radiation (such as X-ray lithography and industrial radiography). In such imaging applications, it is sometimes useful that the photothermographic materials be "double-sided."

In the photothermographic materials of this invention, the components needed for imaging can be in one or more layers. The layer(s) that contain the photosensitive photocatalyst (such as a photosensitive silver halide in photothermographic materials) or the non-photosensitive core-shell silver compounds, or both, are referred to herein as photothermographic emulsion layer(s). The photocatalyst and the non-photosensitive core-shell silver compounds are in catalytic proximity (that is, in reactive association with each other) and preferably are in the same emulsion layer.

Similarly, in the thermographic materials of this invention, the components needed for imaging can be in one or more layers. The layer(s) that contain the non-photosensitive core-shell silver compounds are referred to herein as thermographic emulsion layer(s).

Where the materials contain imaging layers on one side of the support only, various non-imaging layers are usually disposed on the "backside" (non-emulsion or non-imaging side) of the materials, including antihalation layer(s), protective layers, antistatic layers, conducting layers, and transport enabling layers.

In such instances, various non-imaging layers can also be disposed on the "frontside" or imaging or emulsion side of the support, including protective topcoat layers, primer layers, interlayers, opacifying layers, antistatic layers, antihalation layers, acutance layers, auxiliary layers, and other layers readily apparent to one skilled in the art.

In some applications it may be useful that the photothermographic materials be "double-sided" and have thermally developable coatings on both sides of the support. In such constructions each side can also include one or more protective topcoat layers, primer layers, interlayers, antistatic layers, acutance layers, auxiliary layers, anti-crossover layers, and other layers readily apparent to one skilled in the art.

When the thermographic and photothermographic materials of this invention are heat-developed as described below in a substantially water-free condition after, or simultaneously with, imagewise exposure, a silver image (preferably a black-and-white silver image) is obtained.

Definitions

As used herein:

In the descriptions of the photothermographic materials of the present invention, "a" or "an" component refers to "at least one" of that component. Thus, the core-shell silver compounds of this invention can be used individually or in mixtures.

Heating in a substantially water-free condition as used herein, means heating at a temperature of from about 50.degree. C. to about 250.degree. C. with little more than ambient water vapor present. The term "substantially water-free condition" means that the reaction system is approximately in equilibrium with water in the air and water for inducing or promoting the reaction is not particularly or positively supplied from the exterior to the material. Such a condition is described in T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastman Kodak Company, Rochester, N.Y., 1977, p. 374.

"Photothermographic material(s)" means a construction comprising at least one photothermographic emulsion layer or a photothermographic set of layers wherein the photocatalyst (such as silver halide), and the source of reducible silver ions are in one layer and the other essential components or desirable additives are distributed, as desired, in an adjacent coating layer, as well as any supports, topcoat layers, image-receiving layers, blocking layers, antihalation layers, subbing, or priming layers. These materials also include multilayer constructions in which one or more imaging components are in different layers, but are in "reactive association" so that they readily come into contact with each other during imaging and/or development. For example, one layer can include the non-photosensitive core-shell silver compounds and another layer can include the reducing composition, but the two reactive components are in reactive association with each other.

"Thermographic material(s)" are similarly defined except that no photocatalyst is present.

When used in photothermography, the term, "imagewise exposing" or "imagewise exposure" means that the material is imaged using any exposure means that provides a latent image using electromagnetic radiation. This includes, for example, by analog exposure where an image is formed by projection onto the photosensitive material as well as by digital exposure where the image is formed one pixel at a time such as by modulation of scanning laser radiation.

When used in thermography, the term, "imagewise exposing" or "imagewise exposure" means that the material is imaged using any means that provides an image using heat. This includes, for example, by analog exposure where an image is formed by differential contact heating through a mask using a thermal blanket or infrared heat source, as well as by digital exposure where the image is formed one pixel at a time such as by modulation of thermal print-heads.

"Catalytic proximity" or "reactive association" means that the materials are in the same layer or in adjacent layers so that they readily come into contact with each other during thermal imaging and development.

"Emulsion layer," "imaging layer," "thermographic emulsion layer," or "photothermographic emulsion layer" means a layer of a thermographic or photothermographic material that contains the photosensitive silver halide (when used) and/or non-photosensitive core-shell silver compounds. It can also mean a layer of the thermographic or photothermographic material that contains, in addition to the photosensitive silver halide (when used) and/or non-photosensitive core-shell silver compounds, additional essential components and/or desirable additives. These layers are usually on what is known as the "frontside" of the support.

"Photocatalyst" means a photosensitive compound such as silver halide that, upon exposure to radiation, provides a compound that is capable of acting as a catalyst for the subsequent development of the image-forming material.

"Ultraviolet region of the spectrum" refers to that region of the spectrum less than or equal to 410 nm, and preferably from about 100 nm to about 410 nm, although parts of these ranges may be visible to the naked human eye. More preferably, the ultraviolet region of the spectrum is the region of from about 190 to about 405 nm.

"Visible region of the spectrum" refers to that region of the spectrum of from about 400 nm to about 700 nm.

"Short wavelength visible region of the spectrum" refers to that region of the spectrum of from about 400 nm to about 450 nm.

"Red region of the spectrum" refers to that region of the spectrum of from about 600 nm to about 700 nm.

"Infrared region of the spectrum" refers to that region of the spectrum of from about 700 nm to about 1400 nm.

"Non-photosensitive" means not intentionally light sensitive.

The sensitometric terms "photospeed," "speed," or "photographic speed" (also known as sensitivity), absorbance, contrast, D.sub.min, and D.sub.max have conventional definitions known in the imaging arts. In photothermographic materials, D.sub.min is considered herein as image density achieved when the photothermographic material is thermally developed without prior exposure to radiation. In thermographic materials, D.sub.min is considered herein as image density in the non-thermally imaged areas of the thermographic material. It is the average of eight lowest density values on the exposed side of the fiducial mark.

The sensitometric term "absorbance" is another term for optical density (OD).

"Transparent" means capable of transmitting visible light or imaging radiation without appreciable scattering or absorption.

As used herein, the phrase "organic silver coordinating ligand" refers to an organic molecule capable of forming a bond with a silver atom. Although the compounds so formed are technically silver coordination compounds they are also often referred to as silver salts.

The terms "double-sided" and "double-faced coating" are used to define photothermographic materials having one or more of the same or different thermally developable emulsion layers disposed on both sides (front and back) of the support.

In the compounds described herein, no particular double bond geometry (for example, cis or trans) is intended by the structures drawn. Similarly, the alternating single and double bonds and localized charges are drawn as a formalism. In reality, both electron and charge delocalization exists throughout the conjugated chain.

As is well understood in this art, for the chemical compounds described herein, substitution is not only tolerated, but is often advisable and various substituents are anticipated on the compounds used in the present invention unless otherwise stated. Thus, when a compound is referred to as "having the structure" of a given formula, any substitution that does not alter the bond structure of the formula or the shown atoms within that structure is included within the formula, unless such substitution is specifically excluded by language (such as "free of carboxy-substituted alkyl"). For example, where a benzene ring structure is shown (including fused ring structures), substituent groups may be placed on the benzene ring structure, but the atoms making up the benzene ring structure may not be replaced.

As a means of simplifying the discussion and recitation of certain substituent groups, the term "group" refers to chemical species that may be substituted as well as those that are not so substituted. Thus, the term "group," such as "alkyl group" is intended to include not only pure hydrocarbon alkyl chains, such as methyl, ethyl, n-propyl, t-butyl, cyclohexyl, iso-octyl, and octadecyl, but also alkyl chains bearing substituents known in the art, such as hydroxyl, alkoxy, phenyl, halogen atoms (F, Cl, Br, and I), cyano, nitro, amino, and carboxy. For example, alkyl group includes ether and thioether groups (for example CH.sub.3 --CH.sub.2 --CH.sub.2 --O--CH.sub.2 -- and CH.sub.3 --CH.sub.2 --CH.sub.2 --S--CH.sub.2 --), haloalkyl, nitroalkyl, alkylcarboxy, carboxyalkyl, carboxamido, hydroxyalkyl, sulfoalkyl, and other groups readily apparent to one skilled in the art. Substituents that adversely react with other active ingredients, such as very strongly electrophilic or oxidizing substituents, would, of course, be excluded by the ordinarily skilled artisan as not being inert or harmless.

Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 147 West 24th Street, New York, N.Y. 10011).

Other aspects, advantages, and benefits of the present invention are apparent from the detailed description, examples, and claims provided in this application.

The Photocatalyst

As noted above, the photothermographic materials of the present invention include one or more photocatalysts in the photothermographic emulsion layer(s). Useful photocatalysts are typically silver halides such as silver bromide, silver iodide, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, and others readily apparent to one skilled in the art. Mixtures of silver halides can also be used in any suitable proportion. Silver bromide and silver bromoiodide are more preferred, with the latter silver halide generally having up to 10 mole % silver iodide. Silver bromide is most preferred. Typical techniques for preparing and precipitating silver halide grains are described in Research Disclosure, 1978, item 17643.

The shape of the photosensitive silver halide grains used in the present invention is in no way limited. The silver halide grains may have any crystalline habit including, but not limited to, cubic, octahedral, tetrahedral, orthorhombic, rhombic, dodecahedral, other polyhedral, tabular, laminar, twinned, or platelet morphologies and may have epitaxial growth of crystals thereon. If desired, a mixture of these crystals can be employed. Silver halide grains having cubic and tabular morphology are preferred.

The silver halide grains may have a uniform ratio of halide throughout. They may have a graded halide content, with a continuously varying ratio of, for example, silver bromide and silver iodide or they may be of the core-shell type, having a discrete core of one or more silver halides, and a discrete shell of one or more different silver halides. Core-shell silver halide grains useful in photothermographic materials and methods of preparing these materials are described for example in U.S. Pat. No. 5,382,504 (Shor et al.), incorporated herein by reference. Iridium and/or copper doped core-shell and non-core-shell grains are described in U.S. Pat. No. 5,434,043 (Zou et al.) and U.S. Pat. No. 5,939,249 (Zou), both incorporated herein by reference.

The photosensitive silver halide can be added to (or formed within) the emulsion layer(s) in any fashion as long as it is placed in catalytic proximity to the non-photosensitive source of reducible silver ions.

It is preferred that the silver halides be preformed and prepared by an ex-situ process. The silver halide grains prepared ex-situ may then be added to and physically mixed with the non-photosensitive source of reducible silver ions.

It is more preferable to form the source of reducible silver ions as a shell on the surface of ex-situ-prepared silver halide. In this process, the source of reducible silver ions, such as a long chain fatty acid silver carboxylate (commonly referred to as a silver "soap"), is formed by exchange of some of the halide ion of the preformed silver halide grains by an organic silver coordinating ligand. Formation of the reducible source of silver ions as a shell on the surface of the silver halide provides a more intimate mixture of the two materials. Materials of this type are often referred to herein as "preformed soaps."

The silver halide grains used in the imaging formulations can vary in average diameter of up to several micrometers (.mu.m) depending on their desired use. Preferred silver halide grains are those having an average particle size of from about 0.01 to about 1.5 .mu.m, more preferred are those having an average particle size of from about 0.03 to about 1.0 .mu.m, and most preferred are those having an average particle size of from about 0.05 to about 0.8 .mu.m. Those of ordinary skill in the art understand that there is a finite lower practical limit for silver halide grains that is partially dependent upon the wavelengths to which the grains are spectrally sensitized. Such a lower limit, for example, is typically from about 0.01 to about 0.005 .mu.m.

The average size of the photosensitive doped silver halide grains is expressed by the average diameter if the grains are spherical, and by the average of the diameters of equivalent circles for the projected images if the grains are cubic or in other non-spherical shapes.

Grain size may be determined by any of the methods commonly employed in the art for particle size measurement. Representative methods are described by in "Particle Size Analysis," ASTM Symposium on Light Microscopy, R. P. Loveland, 1955, pp. 94-122, and in C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Third Edition, Macmillan, New York, 1966, Chapter 2. Particle size measurements may be expressed in terms of the projected areas of grains or approximations of their diameters. These will provide reasonably accurate results if the grains of interest are substantially uniform in shape.

Preformed silver halide emulsions used in the material of this invention can be prepared by aqueous or organic processes and can be unwashed or washed to remove soluble salts. In the latter case, the soluble salts can be removed by ultrafiltration, by chill setting and leaching, or by washing the coagulum [for example, by the procedures described in U.S. Pat. No. 2,618,556 (Hewitson et al.), U.S. Pat. No. 2,614,928 (Yutzy et al.), U.S. Pat. No. 2,565,418 (Yackel), U.S. Pat. No. 3,241,969 (Hart et al.), and U.S. Pat. No. 2,489,341 (Waller et al.)].

It may also be effective to use an in-situ process in which a halide-containing compound is added to the organic silver salts of this invention to partially convert the silver of the organic silver salt to silver halide. The halogen-containing compound can be inorganic (such as zinc bromide or lithium bromide) or organic (such as N-bromosuccinimide).

Mixtures of both preformed and in-situ generated silver halide may also be used if desired.

In some instances, it may be helpful to prepare the photosensitive silver halide grains in the presence of a hydroxytetrazaindene (such as 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene or an N-heterocyclic compound comprising at least one mercapto group (such as 1-phenyl-5-mercaptotetrazole) to provide increased photospeed. Details of this procedure are provided in U.S. Pat. No. 6,413,710 (Shor et al.), that is incorporated herein by reference.

The one or more light-sensitive silver halides used in the photothermographic materials of the present invention are preferably present in an amount of from about 0.005 to about 0.5 mole, more preferably from about 0.01 to about 0.25 mole, and most preferably from about 0.03 to about 0.15 mole, per mole of non-photosensitive source of reducible silver ions.

Chemical Sensitizers

The photosensitive silver halides used in the photothermographic emulsions and materials of the invention may be may be employed without modification. However, one or more conventional chemical sensitizers may be used in the preparation of the photosensitive silver halides to increase photospeed. Such compounds may contain sulfur, tellurium, or selenium, or may comprise a compound containing gold, platinum, palladium, ruthenium, rhodium, iridium, or combinations thereof, a reducing agent such as a tin halide or a combination of any of these. The details of these materials are provided for example, in T. H. James, The Theory of the Photographic Process, Fourth Edition, Eastman Kodak Company, Rochester, N.Y. 1977, Chapter 5, pp. 149-169. Suitable conventional chemical sensitization procedures are also described in U.S. Pat. No. 1,623,499 (Sheppard et al.), U.S. Pat. No. 2,399,083 (Waller et al.), U.S. Pat. No. 3,297,447 (McVeigh), U.S. Pat. No. 3,297,446 (Dunn), U.S. Pat. No. 5,049,485 (Deaton), U.S. Pat. No. 5,252,455 (Deaton), U.S. Pat. No. 5,391,727 (Deaton), U.S. Pat. No. 5,912,111 (Lok et al.), U.S. Pat. No. 5,759,761 (Lushington et al.), and EP 0 915 371 A (Lok et al.).

In addition, mercaptotetrazoles and tetraazindenes as described in U.S. Pat. No. 5,691,127 (Daubendiek et al.), incorporated herein by reference, can be used as suitable addenda for tabular silver halide grains.

When used, sulfur sensitization is usually performed by adding a sulfur sensitizer and stirring the emulsion at an appropriate temperature predetermined time. Examples of sulfur sensitizers include compounds such as thiosulfates, thioureas, thiazoles, rhodanines, thiosulfates and thioureas. In one preferred embodiment, chemical sensitization is achieved by oxidative decomposition of a sulfur-containing spectral sensitizing dye in the presence of a photothermographic emulsion. Such sensitization is described in U.S. Pat. No. 5,891,615 (Winslow et al.), incorporated herein by reference.

In another embodiment, certain substituted and unsubstituted thiourea compounds can be used as chemical sensitizers. Particularly useful tetra-substituted thioureas are described in U.S. Pat. No. 6,368,779 (Lynch et al.), that is incorporated herein by reference.

Other useful chemical sensitizers include certain tellurium-containing compounds that are described in U.S. Pat. No. 6,699,647 (Lynch et al.), that is incorporated herein by reference.

Combinations of gold (3+)-containing compounds and either sulfur- or tellurium-containing compounds are also useful as chemical sensitizers as described in U.S. Pat. No. 6,423,481 (Simpson et al.), that is also incorporated herein by reference.

Still other useful chemical sensitizers include certain selenium-containing compounds that are described in U.S. Pat. No. 6,620,577 (Lynch et al.), that is also incorporated herein by reference.

The chemical sensitizers can be used in making the silver halide emulsions in conventional amounts that generally depend upon the average size of the silver halide grains. Generally, the total amount is at least 10.sup.-10 mole per mole of total silver, and preferably from about 10.sup.-8 to about 10.sup.-2 mole per mole of total silver for silver halide grains having an average size of from about 0.01 to about 2 .mu.m. The upper limit can vary depending upon the compound(s) used, the level of silver halide and the average grain size, and would be readily determinable by one of ordinary skill in the art.

Spectral Sensitizers

The photosensitive silver halides may be spectrally sensitized with various spectral sensitizing dyes that are known to enhance silver halide sensitivity to ultraviolet, visible, and/or infrared radiation. Non-limiting examples of sensitizing dyes that can be employed include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxanol dyes. Cyanine dyes are particularly useful. The cyanine dyes preferably include benzothiazole, benzoxazole, and benzoselenazole dyes that include one or more thioalkyl, thioaryl, or thioether groups. Suitable visible sensitizing dyes such as those described in U.S. Pat. No. 3,719,495 (Lea), U.S. Pat. No. 4,439,520 (Kofron et al.), and U.S. Pat. No. 5,281,515 (Delprato et al.) are effective in the practice of the invention. Suitable infrared sensitizing dyes such as those described in U.S. Pat. No. 5,393,654 (Burrows et al.), U.S. Pat. No. 5,441,866 (Miller et al.) and U.S. Pat. No. 5,541,054 (Miller et al.) are also effective in the practice of this invention. A summary of generally useful spectral sensitizing dyes is contained in Research Disclosure, item 308119, Section IV, December 1989. Additional classes of dyes useful for spectral sensitization, including sensitization at other wavelengths are described in Research Disclosure, 1994, item 36544, section V. All of the references and patents above are incorporated herein by reference.

An appropriate amount of spectral sensitizing dye added is generally about 10.sup.-10 to 10.sup.-1 mole, and preferably, about 10.sup.-7 to 10.sup.-2 mole per mole of silver halide.

Non-Photosensitive Source of Reducible Silver Ions

In some embodiments, the non-photosensitive source of reducible silver ions used in thermographic and photothermographic materials of this invention includes at least one of the core-shell silver compounds of this invention. These compounds have a shell that provides reducible silver (1+) ions in th