Antistatic properties for thermally developable materials Number:7,087,364 from the United States Patent and Trademark Office (PTO) owispatent The use of metal antimonates at high metal antimonate to binder ratios in buried backside conductive layers of thermographic and photothermographic materials allows the use of thin backside overcoat layers. The combination provides antistatic constructions having excellent antistatic properties that show less change in resistivity with changes in humidity. The thin backside overcoat layer serves to protect the buried antistatic layer.<H developable, properties, Antistatic, prop, 7087364.html, Patent, pto, 7087364

Title: Antistatic properties for thermally developable materials

Abstract: The use of metal antimonates at high metal antimonate to binder ratios in buried backside conductive layers of thermographic and photothermographic materials allows the use of thin backside overcoat layers. The combination provides antistatic constructions having excellent antistatic properties that show less change in resistivity with changes in humidity. The thin backside overcoat layer serves to protect the buried antistatic layer.

Patent Number: 7,087,364 Issued on 08/08/2006 to Ludemann, et al.

Inventors: Ludemann; Thomas J. (Maplewood, MN), LaBelle; Gary E. (Stillwater, MN), Philip; Darlene F. (Mahtomedi, MN), Koestner; Roland J. (Penfield, NY), Bhave; Aparna V. (Woodbury, MN)
Assignee: Eastman Kodak Company (Rochester, NY)

Appl. No.: 10/930,438

Filed: August 31, 2004

Current U.S. Class: 430/348 ; 430/353; 430/510; 430/517; 430/530; 430/531; 430/533; 430/534; 430/535; 430/536

Current International Class: G03C 1/498 (20060101); G03C 1/89 (20060101); G03C 5/16 (20060101)

Field of Search: 430/348,353,510,517,530,531,533,534,535,536

References Cited [Referenced By]

U.S. Patent Documents


4418141	November 1983	Kawaguchi et al.
5310640	May 1994	Markin et al.
5340676	August 1994	Anderson et al.
5368995	November 1994	Christian et al.
5547821	August 1996	Melpolder et al.
5731119	March 1998	Eichorst et al.
5827630	October 1998	Eichorst et al.
5866287	February 1999	Christian et al.
6342343	January 2002	Toya
6355405	March 2002	Ludemann et al.
6436622	August 2002	Geisler
6464413	October 2002	Oyamada
6468725	October 2002	Takamuki
6479227	November 2002	Kubo et al.
6689546	February 2004	LaBelle et al.
2001/0055490	December 2001	Oyamada

Foreign Patent Documents


7-295146	Nov., 1995	JP

Other References

JP Abstract 2003-029378. cited by other.

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

Claims

The invention claimed is:

1. A thermally developable material that comprises a support having on one side thereof, one or more thermally developable imaging layers comprising a binder and in reactive association, a non-photosensitive source of reducible silver ions, and a reducing agent composition for said non-photosensitive source reducible silver ions, and having disposed on the backside of said support, a non-imaging buried backside conductive layer comprising non-acicular metal antimonate particles in one or more binder polymers, and a non-imaging backside overcoat layer, wherein said non-imaging backside overcoat layer has a dry thickness of from about 0.8 to about 3 .mu.m and a dry coating weight of from about 0.7 to about 3.5 g/m.sup.2.

2. The thermally developable material of claim 1 wherein said non-imaging backside overcoat layer has a dry thickness of from about 1 to about 2.2 .mu.m and a dry coating weight of from about 0.9 to about 2.6 g/m.sup.2.

3. The thermally developable material of claim 1 wherein said non-imaging buried backside conductive layer is a carrier layer.

4. The material of claim 1 comprising on the backside of said support: a) a backside overcoat layer comprising a film-forming polymer, and b) said non-imaging backside conductive layer being interposed between said support and said overcoat layer and directly adhering said overcoat layer to said support, said non-imaging backside conductive layer comprising said non-acicular metal antimonate particles in a mixture of two or more polymers that include a first polymer serving to promote adhesion of said backside conductive layer directly to said support, and a second polymer that is different than and forms a single phase mixture with said first polymer, wherein said film-forming polymer of said overcoat layer and said second polymer of said backside conductive layer are the same or different polyvinyl acetal resins, polyester resins, cellulosic polymers, maleic anhydride-ester copolymers, or vinyl polymers.

5. The material of claim 4 wherein said film-forming polymer of said overcoat layer and said second polymer of said backside conductive layer are the same or different polyvinyl acetal resin or cellulosic ester polymer.

6. The material of claim 5 wherein said film-forming polymer of said overcoat layer and second polymer of said backside conductive layer are both polyvinyl butyral, or cellulose acetate butyrate.

7. The material of claim 4 wherein said first polymer is a polyvinyl acetal, cellulosic ester polymer, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyester resin, polystyrene, polyacrylonitrile, polycarbonate, acrylate or methacrylate polymer, maleic anhydride ester copolymer, or butadiene-styrene copolymer.

8. The material of claim 7 wherein said first polymer is a polyester resin.

9. The material of claim 4 wherein said backside conductive layer comprises a single-phase mixture of a polyester resin with either polyvinyl butyral or cellulose acetate butyrate.

10. The material of claim 1 wherein said backside conductive layer has a dry thickness of from about 0.05 to about 0.55 .mu.m, and the ratio of total binder polymers to said non-acicular metal antimonate particles is from about 0.75:1 to about 0.3:1, based on dry weights.

11. The material of claim 1 wherein said non-acicular metal antimonate particles comprise from 60 to about 76% by dry weight of said backside conductive layer.

12. The material of claim 11 wherein said non-acicular metal antimonate particles comprise from 70 to 76% by weight of said backside conductive layer.

13. The material of claim 1 wherein said non-acicular metal antimonate particles are present at a coverage of from about 0.06 to about 0.5 g/m.sup.2 and the dry thickness of said backside conductive layer is from about 0.09 to about 0.15 .mu.m.

14. The material of claim 1 wherein said non-acicular metal antimonate particles are present in an amount sufficient to provide a backside surface electrode resistivity measured at 21.1.degree. C. and 20% relative humidity of 1.times.10.sup.11 ohms/sq or less.

15. The material of claim 1 wherein said non-acicular metal antimonate particles having a composition represented by the following Structure I or II: M.sup.+2Sb.sup.+5.sub.2O.sub.6 (I) wherein M is zinc, nickel, magnesium, iron, copper, manganese, or cobalt, M.sub.a.sup.+3Sb.sup.+5O.sub.4 (II) wherein Ma is indium, aluminum, scandium, chromium, iron, or gallium.

16. The material of claim 1 wherein said non-acicular metal antimonate particles are composed of ZnSb.sub.2O.sub.6.

17. The material of claim 1 wherein said non-photosensitive source of reducible silver ions is a silver salt of an aliphatic carboxylate or a mixture of silver salts of aliphatic carboxylates, at least one of which is silver behenate.

18. A method of forming a visible image comprising thermal imaging of the material of claim 1 that is a thermographic material.

19. The method of claim 18 wherein said thermographic material comprises a transparent support and said image-forming method further comprises: C) positioning said imaged, heat-developed thermographic material with the visible image thereon between a source of imaging radiation and an imageable material that is sensitive to said imaging radiation, and D) thereafter exposing said imageable material to said imaging radiation through the visible image in said exposed and heat-developed thermographic material to provide an image in said imageable material.

20. A black-and-white thermographic material that comprises a transparent polymeric support having on one side thereof one or more thermally developable imaging layers comprising predominantly one or more hydrophobic binders, and in reactive association, a non-photosensitive source of reducible silver ions that includes silver behenate, a reducing agent composition for said non-photosensitive source reducible silver ions comprising an aromatic di- and tri-hydroxy compound having at least two hydroxy groups in ortho- or para-relationship on the same aromatic nucleus or mixture thereof, and a protective layer disposed over said one or more thermally developable imaging layers, and having disposed on the backside of said support: a) a backside overcoat layer comprising a film-forming polymer, and b) interposed between said support and said backside overcoat layer and directly adhering said backside overcoat layer to said support, a non-imaging backside conductive layer comprising non-acicular metal antimonate particles in a mixture of two or more polymers that include a first polymer serving to promote adhesion of said backside conductive layer directly to said support, and a second polymer that is different than and forms a single phase mixture with said first polymer, wherein said non-acicular metal antimonate particles comprise greater than 70 and up to 76% by dry weight of said backside conductive layer, are present at a coverage of from about 0.06 to about 0.2 g/m.sup.2, and the ratio of total binder polymers in said backside layer to said non-acicular metal antimonate particles is less than 0.75:1, based on dry weights, wherein said film-forming polymer of said overcoat layer and said second polymer of said backside conductive layer are the same or different polyvinyl acetal resins, polyester resins, cellulosic polymers, maleic anhydride-ester copolymers, or vinyl polymers, and wherein said overcoat layer has a dry thickness of from about 1 to about 2.2 .mu.m and a dry coating weight of from about 0.9 to about 2.6 g/m.sup.2.

Description

FIELD OF THE INVENTION

This invention relates to thermally developable materials having certain backside conductive layers. In particular, this invention relates to thermographic and photothermographic materials having conductive backside layers that show little change in resistivity with changes in humidity. This invention also relates to methods of imaging using these thermally developable materials.

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, the silver of the silver carboxylate 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 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.degree. C., resulting in the formation of an image.

Silver-containing photothermographic imaging materials (that is, photosensitive thermally developable imaging materials) that are imaged with actinic radiation and then developed using heat and without liquid processing have been known in the art for many years. Such materials 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 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. 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 photothermographic 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.

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 or a silver benzotriazole) 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. 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.

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).

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 Unconventional Imaging Processes, E. Brinckman et al. (Eds.), The Focal Press, London and New York, 1978, pp. 74 75, in 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, 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

Many of the chemicals used to make supports or supported layers in thermally developable materials have electrically insulating properties, and electrostatic charges frequently build up on the materials during manufacture, packaging, and use. The accumulated charges can cause various problems. For example, in photothermographic materials containing photosensitive silver halides, accumulated electrostatic charge can generate light to which the silver halides are sensitive. This may result in imaging defects that are a particular problem where the images are used for medical diagnosis.

Build-up of electrostatic charge can also cause sheets of thermally processable materials to stick together causing misfeeds and jamming within processing equipment. Additionally, accumulated electrostatic charge can attract dust or other particulate matter to the materials, thereby requiring more cleaning to insure rapid transport through the processing equipment and quality imaging.

Build-up of electrostatic charge also makes handling of developed sheets of imaged material more difficult. For example, radiologists desire a static free sheet for viewing on light boxes. This problem can be particularly severe when reviewing an imaged film that has been stored for a long period of time because many antistatic materials loose their effectiveness over time.

In general, electrostatic charge is related to surface resistivity (measured in ohm/sq) and charge level. While electrostatic charge control agents (or antistatic agents) can be included in any layer of an imaging material, the accumulation of electrostatic charge can be prevented by reducing the surface resistivity or by lowering the charge level. These results can usually be achieved by including charge control agents in surface layers such as protective overcoats. In thermally processable materials, charge control agents may be used in backing layers that are on the opposite side of the support as the imaging layers. Another approach taken to reduce surface resistivity is to include a "buried" conductive layer incorporating conductive particles.

A wide variety of charge control agents, both inorganic and organic, have been devised and used for electrostatic charge control and numerous publications describe such agents. Metal oxides are described in conductive layers in U.S. Pat. No. 5,340,676 (Anderson et al.), U.S. Pat. No. 6,464,413 (Oyamada), U.S. Pat. No. 5,368,995 (Christian et al.), and U.S. Pat. No. 5,457,013 (Christian et al.).

U.S. Pat. No. 5,731,119 (Eichorst et al.) describes the use of acicular metal oxides in aqueous-coated conductive layers for use in antistatic compositions. An aqueous-coated sample containing granular zinc antimonate served as comparison.

U.S. Pat. No. 6,355,405; (Ludemann et al.) describes thermally developable materials that include very thin adhesion-promoting layers on either side of the support. These adhesion-promoting layers include specific mixtures of polymers and other compounds to promote adhesion, and are also known as "carrier" layers.

U.S. Pat. No. 6,689,546 (LaBelle et al.) describes thermally developable materials that contain a backside conductive layer comprising non-acicular metal antimonate particles in the amount of from about 40 to about 55% (based on total dry weight).

Despite these advances, there is a continuing need in the industry to find more efficient and less costly ways to reduce electrostatic charge, particularly in "buried" layers on the backside of thermally developable imaging materials, without loss of adhesion of the conductive layer to underlying substrates. It is therefore desirable to develop constructions with improved conductive efficiency, so that the same performance can be achieved at lower coating weights.

Additionally, present thermographic and photothermographic materials typically have relatively thick backside overcoats. Coating weights of approximately 0.4 g/ft.sup.2 (4.3 g/m.sup.2) are not uncommon. The antistatic properties of these backside overcoats are strongly dependent in humidity. To compensate for loss of conductivity at low humidity these coatings contain a large amount of antistatic material. This also results in poor conductive efficiency. It is therefore also particularly desirable to provide materials of high conductive efficiency whose antistatic properties show little change with changes in humidity.

SUMMARY OF THE INVENTION

The present invention, provides a thermally developable material that comprises a support having on one side thereof, one or more thermally developable imaging layers comprising a binder and in reactive association, a non-photosensitive source of reducible silver ions, and a reducing agent composition for the non-photosensitive source reducible silver ions, and having disposed on the backside of the support, a non-imaging buried backside conductive layer comprising non-acicular metal antimonate particles in one or more binder polymers, and a non-imaging backside overcoat layer, wherein the non-imaging backside overcoat layer has a dry thickness of from about 0.8 to about 3 .mu.m and a dry coating weight of from about 0.7 to about 3.5 g/m.sup.2.

This invention also provides a photothermographic material that comprises a support having on one side thereof, one or more thermally developable imaging layers comprising a binder and in reactive association, a photosensitive silver halide, a non-photosensitive source of reducible silver ions, and a reducing agent composition for the non-photosensitive source reducible silver ions, and

having disposed on the backside of the support:

a) a backside overcoat layer comprising a film-forming polymer, and

b) interposed between the support and the overcoat layer and directly adhering the overcoat layer to the support, a non-imaging backside conductive layer comprising non-acicular metal antimonate particles in a mixture of two or more polymers that include a first polymer serving to promote adhesion of the backside conductive layer directly to the support, and a second polymer that is different than and forms a single phase mixture with the first polymer, wherein the non-acicular metal antimonate particles comprise greater than 40 and up to 85% by dry weight of the backside conductive layer, are present at a coverage of from about 0.06 to about 0.2 g/m.sup.2, wherein the film-forming polymer of the overcoat layer and the second polymer of the backside conductive layer are the same or different polyvinyl acetal resins, polyester resins, cellulosic polymers, maleic anhydride-ester copolymers, or vinyl polymers, and wherein the overcoat layer has a dry thickness of from about 0.8 to about 3 .mu.m and a dry coating weight of from about 0.7 to about 3.5 g/m.sup.2.

Preferred embodiments include a black-and-white photothermographic material that comprises a transparent polymeric support having on one side thereof one or more thermally developable imaging layers comprising predominantly one or more hydrophobic binders, and in reactive association, preformed photosensitive silver bromide or silver iodobromide present as tabular and/or cubic grains, a non-photosensitive source of reducible silver ions that includes silver behenate, a reducing agent composition for the non-photosensitive source reducible silver ions comprising a hindered phenol, and a protective layer disposed over the one or more thermally developable imaging layers, and

having disposed on the backside of the support:

a) a backside overcoat layer comprising a film-forming polymer that is cellulose acetate butyrate and an antihalation composition, and

b) interposed between the support and the backside overcoat layer and directly adhering the backside overcoat protective layer to the support, a non-imaging backside conductive layer comprising non-acicular metal antimonate particles in a mixture of two or more polymers that include a first polymer serving to promote adhesion of the conductive layer directly to the support, and a second polymer that is different than and forms a single phase mixture with the first polymer,

wherein the first polymer of the backside conductive layer is a polyester and the second polymer of the backside conductive layer is cellulose acetate butyrate, and

the non-acicular metal antimonate particles are composed of zinc antimonate and comprise from 70 to about 76% by dry weight of the backside conductive layer, are present at a coverage of from about 0.06 to about 0.2 g/m.sup.2, and the dry thickness of the backside conductive layer is from about 0.09 to about 0.15 .mu.m, and wherein the overcoat layer has a dry thickness of from about 1 to about 2.2 .mu.m and a dry coating weight of from about 0.09 to about 2.6 g/m.sup.2.

Preferred embodiments also include a black-and-white thermographic material that comprises a transparent polymeric support having on one side thereof one or more thermally developable imaging layers comprising predominantly one or more hydrophobic binders, and in reactive association, a non-photosensitive source of reducible silver ions that includes silver behenate, a reducing agent composition for the non-photosensitive source reducible silver ions comprising an aromatic di- and tri-hydroxy compound having at least two hydroxy groups in ortho- or para-relationship on the same aromatic nucleus or mixture thereof, and a protective layer disposed over the one or more thermally developable imaging layers, and

having disposed on the backside of the support:

a) a backside overcoat layer comprising a film-forming polymer, and

b) interposed between the support and the backside overcoat layer and directly adhering the backside overcoat layer to the support, a non-imaging backside conductive layer comprising non-acicular metal antimonate particles in a mixture of two or more polymers that include a first polymer serving to promote adhesion of the backside conductive layer directly to the support, and a second polymer that is different than and forms a single phase mixture with the first polymer, wherein the non-acicular metal antimonate particles comprise greater than 70 and up to 76% by dry weight of the backside conductive layer, are present at a coverage of from about 0.06 to about 0.2 g/m.sup.2, and the ratio of total binder polymers in the backside layer to the non-acicular metal antimonate particles is less than 0.75:1, based on dry weights, wherein the film-forming polymer of the overcoat layer and the second polymer of the backside conductive layer are the same or different polyvinyl acetal resins, polyester resins, cellulosic polymers, maleic anhydride-ester copolymers, or vinyl polymers, and wherein the overcoat layer has a dry thickness of from about 1 to about 2.2 .mu.m and a dry coating weight of from about 0.9 to about 2.6 g/m.sup.2.

This invention further provides a method of forming a visible image in thermographic materials that comprises: (A) thermal imaging of the thermographic material.

This invention also provides a method for forming a visible image in photothermographic materials that comprises: (A) imagewise exposing any of the photothermographic materials of the present invention to electromagnetic radiation to form a latent image, and (B) simultaneously or sequentially, heating the exposed photothermographic material to develop the latent image into a visible image.

These image-forming methods are particularly useful for providing a medical diagnosis of a human or animal subject.

The present invention provides a means for providing improved surface resistivity and electrostatic charge control on a backside conductive layer. The use of a conductive metal antimonate in a backside buried conductive layer with a thin protective overcoat layer above the buried conductive layer provides improved conductive efficiency. The use of a thin protective overcoat layer above the buried backside conductive layer also provides materials with little change in conductive properties with changes in humidity. An additional benefit of a thinner backside overcoat layer and a thin buried backside conductive layer is lower manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graphical representation of Surface Electrode Resistivity (SER) vs. Coating Weight for photothermographic materials prepared in Example 1 and having backside coatings containing non-acicular metal antimonate particles.

DETAILED DESCRIPTION OF THE INVENTION

The thermally developable materials described herein are 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 art that thermographic materials can be similarly constructed and used to provide black-and-white or color images using appropriate imaging chemistry and particularly non-photosensitive organic silver salts, reducing agents, toners, binders, and other components known to a skilled artisan. In both thermographic and photothermographic materials, the non-acicular metal antimonate particles described herein are preferably incorporated into a separate buried conductive ("antistatic") layer on at least the backside and optionally on both sides of the support.

The thermally developable 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 thermally developable materials are particularly useful for imaging of human or animal subjects in response to visible, X-radiation, or infrared radiation for use in a medical diagnosis. Such applications include, but are not limited to, thoracic imaging, mammography, dental imaging, orthopedic imaging, general medical radiography, therapeutic radiography, veterinary radiography, and autoradiography. When used with X-radiation, the photothermographic materials may be used in combination with one or more phosphor intensifying screens, with phosphors incorporated within the photothermographic emulsion, or with combinations thereof. Such materials are particularly useful for dental radiography when they are directly imaged by X-radiation. The materials are also useful for non-medical uses of X-radiation such as X-ray lithography and industrial radiography.

The photothermographic materials 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 preferred embodiments, the materials are sensitive to radiation greater than 700 nm (and generally up to 1150 nm). Increased sensitivity to a particular region of the spectrum is imparted through the use of various spectral sensitizing dyes.

In the photothermographic materials, the components needed for imaging can be in one or more photothermographic imaging layers on one side ("frontside") of the support. The layer(s) that contain the photosensitive photocatalyst (such as a photosensitive silver halide) or non-photosensitive source of reducible silver ions, or both, are referred to herein as photothermographic emulsion layer(s). The photocatalyst and the non-photosensitive source of reducible silver ions are in catalytic proximity 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 source of reducible silver ions 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 at least one buried conductive layer described herein, and optionally antihalation layer(s), protective layers, and transport enabling layers.

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.

For some embodiments, it may be useful that the thermally developable materials be "double-sided" or "duplitized" and have the same or different thermally developable coatings (or imaging layers) on both sides of the support. In such constructions each side can also include one or more protective topcoat layers, primer layers, interlayers, acutance layers, auxiliary layers, anti-crossover layers, and other layers readily apparent to one skilled in the art, as well as the required conductive layer(s).

When the thermally developable materials 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 thermally developable materials, "a" or "an" component refers to "at least one" of that component (for example, the specific conductive metal oxide described herein).

Unless otherwise indicated, when the terms "thermally developable materials," "photothermographic materials," and "thermographic materials" are used herein, the terms refer to materials of the present invention.

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 a support and at least one photothermographic emulsion layer or a photothermographic set of emulsion layers, wherein the photosensitive silver halide and the source of reducible silver ions are in one layer and the other necessary components or additives are distributed, as desired, in the same layer or in an adjacent coated layer. These materials also include multilayer constructions in which one or more imaging components are in different layers, but are in "reactive association." For example, one layer can include the non-photosensitive source of reducible silver ions and another layer can include the reducing composition, but the two reactive components are in reactive association with each other.

"Thermographic materials" are similarly defined except that no photosensitive silver halide catalyst is purposely added or created.

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 or by thermal heating using scanning laser radiation.

"Catalytic proximity" or "reactive association" means that the reactive components are in the same layer or in adjacent layers so that they readily come into contact with each other during imaging and thermal 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 source of reducible silver ions, or a reducing composition. Such layers can also contain additional components or desirable additives. These layers are usually on what is known as the "frontside" of the support, but they can also be on both sides 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.

Many of the chemical components used herein are provided as a solution. The term "active ingredient" means the amount or the percentage of the desired chemical component contained in a sample. All amounts listed herein are the amount of active ingredient added unless otherwise specified.

"Ultraviolet region of the spectrum" refers to that region of the spectrum less than or equal to 410 nm (preferably from about 100 nm to about 410 nm) although parts of these ranges may be visible to the naked human eye.

"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, and contrast have conventional definitions known in the imaging arts.

In photothermographic materials, the term D.sub.min (lower case) is considered herein as image density achieved when the photothermographic material is thermally developed without prior exposure to radiation. The term D.sub.max (lower case) is the maximum image density achieved in the imaged area of a particular sample after imaging and development. In thermographic materials, D.sub.min is considered herein as the image density in the areas with the minimum application of heat by the thermal printhead. In thermographic materials, the term D.sub.max is the maximum image density achieved when the thermographic material is thermally imaged with a given amount of thermal energy.

In both photothermographic and thermographic materials, the term D.sub.MIN (upper case) is the density of the unimaged material. In photothermographic materials, the term D.sub.MAX (upper case) is the maximum image density achievable when the photothermographic material is exposed and then thermally developed. In thermographic materials, the term D.sub.MAX is the maximum image density achievable when the thermographic material is thermally developed. D.sub.MAX is also known as "Saturation Density."

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 "silver organic 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 term "buried layer" means that there is at least one other layer disposed over the layer (such as a "buried" backside conductive layer).

The terms "coating weight," "coat weight," and "coverage" are synonymous, and are usually expressed in weight per unit area such as g/m.sup.2.

"Conductive efficiency" refers to the amount of conductive particles necessary to achieve a given conductivity. Samples with a high conductive efficiency require fewer conductive particles to achieve a given conductivity than those of a comparative sample. Alternatively, conductive efficiency can also refer to samples having a higher conductivity with the same number of particles (that is, the same coating weight).

As is well understood in this art, for the chemical compounds herein described, 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.

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 "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 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. It is 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, photothermographic materials include one or more photocatalysts in the photothermographic emulsion layer(s). Useful photocatalysts are typically photosensitive silver halides such as silver bromide, silver iodide, silver chloride, 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 mol % silver iodide.

In some embodiments of aqueous-based photothermographic materials, higher amounts of iodide may be present in homogeneous photosensitive silver halide grains, and particularly from about 20 mol % up to the saturation limit of iodide as described, for example, U.S. Published Application 2004-0053173 (Maskasky et al.).

The silver halide grains may have any crystalline habit or morphology 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 grains with different morphologies can be employed. Silver halide grains having cubic and tabular morphology (or both) are preferred.

The silver halide grains may have a uniform ratio of halide throughout. They may also 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 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.

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) as described in U.S. Pat. No. 6,413,710 (Shor et al.) that is 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. With this technique, one has the possibility of more precisely controlling the grain size, grain size distribution, dopant levels, and composition of the silver halide, so that one can impart more specific properties to both the silver halide grains and the resulting photothermographic material.

In some constructions, it is preferable to form the non-photosensitive source of reducible silver ions in the presence 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 in the presence of the preformed silver halide grains. Co-precipitation of the source of reducible silver ions in the presence of silver halide provides a more intimate mixture of the two materials [see U.S. Pat. No. 3,839,049 (Simons)] to provide a material often referred to as a "preformed soap."

In some constructions, it is preferred that preformed silver halide grains be added to and "physically mixed" with the non-photosensitive source of reducible silver ions.

Preformed silver halide emulsions can be prepared by aqueous or organic processes and can be unwashed or washed to remove soluble salts. Soluble salts can be removed by any desired procedure for example as 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 is also effective to use an in-situ process in which a halide- or a halogen-containing compound is added to an organic silver salt to partially convert the silver of the organic silver salt to silver halide. Inorganic halides (such as zinc bromide, zinc iodide, calcium bromide, lithium bromide, lithium iodide, or mixtures thereof) or an organic halogen-containing compound (such as N-bromo-succinimide or pyridinium hydrobromide perbromide) can be used. The details of such in-situ generation of silver halide are well known and described in U.S. Pat. No. 3,457,075 (Morgan et al.).

It is particularly effective to use a mixture of both preformed and in-situ generated silver halide. The preformed silver halide is preferably present in a preformed soap.

Additional methods of preparing silver halides and organic silver salts and blending them are described in Research Disclosure, June 1978, item 17029, U.S. Pat. No. 3,700,458 (Lindholm), U.S. Pat. No. 4,076,539 (Ikenoue et al.), JP Kokai 49-013224 (Fuji), JP Kokai 50-017216 (Fuji), and JP Kokai 51-042529 (Fuji).

The silver halide grains used in the imaging formulations can vary in average diameter of up to several micrometers (.mu.m) depending on the 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.

The average size of the photosensitive 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. Representative grain sizing methods are described 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.

The one or more light-sensitive silver halides 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 Sensitization

The photosensitive silver halides can be chemically sensitized using any useful compound that contains 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 371A1 (Lok et al.), all of which are incorporated herein by reference.

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

Certain substituted and unsubstituted thiourea compounds can be used as chemical sensitizers including those described in U.S. Pat. No. 6,368,779 (Lynch et al.) that is incorporated herein by reference.

Still other additional chemical sensitizers include certain tellurium-containing compounds that are described in U.S. Pat. No. 6,699,647 (Lynch et al.), and certain selenium-containing compounds that are described in U.S. Pat. No. 6,620,577 (Lynch et al.), that are both incorporated herein by reference.

Combinations of gold (3+)-containing compounds and either sulfur-, tellurium-, or selenium-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.

In addition, sulfur-containing compounds can be decomposed on silver halide grains in an oxidizing environment according to the teaching in U.S. Pat. No. 5,891,615 (Winslow et al.). Examples of sulfur-containing compounds that can be used in this fashion include sulfur-containing spectral sensitizing dyes.

Other useful sulfur-containing chemical sensitizing compounds that can be decomposed in an oxidized environment are the diphenylphosphine sulfide compounds represented by Structure (PS) described in copending and commonly assigned U.S. Ser. No. 10/731,251 (filed Dec. 9, 2003 by Simpson, Burleva, and Sakizadeh) which application is incorporated herein by reference.

The chemical sensitizers can be present 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.

Spectral Sensitization

The photosensitive silver halides may be spectrally sensitized with one or more spectral sensitizing dyes that are known to enhance silver halide sensitivity to ultraviolet, visible, and/or infrared radiation. Non-limiting examples of spectral 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. They may be added at any stage in chemical finishing of the photothermographic emulsion, but are generally added after chemical sensitization is achieved.

Suitable spectral sensitizing dyes such as those described in U.S. Pat. No. 3,719,495 (Lea), U.S. Pat. No. 4,396,712 (Kinoshita et al.), U.S. Pat. No. 4,439,520 (Kofron et al.), U.S. Pat. No. 4,690,883 (Kubodera et al.), U.S. Pat. No. 4,840,882 (Iwagaki et al.), U.S. Pat. No. 5,064,753 (Kohno et al.), U.S. Pat. No. 5,281,515 (Delprato et al.), U.S. Pat. No. 5,393,654 (Burrows et al.), U.S. Pat. No. 5,441,866 (Miller et al.