CA2173185A1 - Hydantoin compounds as antifoggants, print stabilizers, and speed enhancers for photothermographic elements - Google Patents

Abstract

Hydantoin compounds compounds have been found to function as antifoggants and post-processing print stabilizers in photothermographic elements.

Description

Patent DocketNo. 51623CAN4A
HYDANTOIN COMPOUNDS AS ANTIFOGGANTS, PRINT
STAB~ 71F,RS, AND SPEED ENHANCERS FOR
PHOTO'l'~;~MOGRAPHIC ELEMENTS

BACKGROUND OF THE INVENTION
Field of Invention:
This invention relates to novel, heat-developable photothermographic f~1~nn~nts and in particular, it relates to hydantoin compounds as antifoggants, post-processing print stabilizers, and speed enhancers for photothermographic elements.
Background of the Art Silver halide-co~ inE, photothermographic im~ging materials (i.e., heat-developable photographic elements) processed with heat, and without liquid development, have been known in the art for many years. These materials are alsoknown as "dry silver" compositions or emulsions and generally comprise a supporthaving coated thereon: (a) a photosensitive compound that generates silver atomswhen irr~ ted; (b) a non-photosensitive, reducible silver source; (c) a reduçinEagent (i.e., a developer) for silver ion, for example the silver ion in the non-photo-sensitive, reducible silver source; and (d) a binder.
The photosensitive compound is generally photographic silver halide which must be in catalytic plo~ y to the non-photosensitive, reducible silver source.
Catalytic plo~illlily requires an intim~te physical association ofthese two materials so that when silver atoms (also known as silver specks, clusters, or nuclei) aregenerated by irradiation or light exposure of the photographic silver halide, those nuclei are able to catalyze the reduction of the reducible silver source. It has long been understood that silver atoms (Ag) are a catalyst for the reduction of silver ions, and that the photosensitive silver halide can be placed into catalytic ploxh,lily with the non-photosensitive, reducible silver source in a number of di~erenl fashions. The silver halide may be made "in sifu, " for example by adding a halogen-co..~ E source to the reducible silver source to achieve partial metathesis (see, . ~ ~1731~5 for example, U.S. Patent No. 3,457,075); or by coprecipitation of silver halide and the reducible silver source (see, for example, U.S. Patent No. 3,839,049). The silver halide may also be made "ex si~u " and added to the organic silver salt. The addition of silver halide grains to photothermographic materials is described in ResearchS Disclosure, June 1978, Item No. 17029. It is also reported in the art that when silver halide is made ex si~u, one has the possibility of controlling the composition and size of the grains much more precisely, so that one can impart more specificproperties to the photothermographic element and can do so much more consictçntly than with the in situ technique.
The non-photosensitive, reducible silver source is a material that contains silver ions. Typically, the p--erelled 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 molecularweight are generally used. Salts of other organic acids or other organic compounds, such as silver imidazolates, have been proposed. U.S. Patent No. 4,260,677 discloses the use of complexes of inorganic or organic silver salts as non-photo-sensitive, reducible silver sources.
In both photographic and photothermographic emulsions, exposure of the photographic silver halide to light produces small clusters of silver atoms (Ag).
The imagewise distribution of these clusters is known in the art as a latent image.
This latent image is generally not visible by ordinary means. Thus, the photo-sensitive emulsion must be further processed to produce a visible image. This isaccomplished by the reduction of silver ions which are in catalytic proximity tosilver halide grains bearing the clusters of silver atoms, (i.e., the latent image). This produces a black and white image. In photographic elen~çnt~, the silver halide is reduced to form the black-and-white image. In photothermographic elements, the light-in.~en~itive silver source is reduced to form the visible black-and-white image while much of the silver halide remains as silver halide and is not reduced.
In photothermographic element~ the reducing agent for the organic silver salt, often referred to as a "developer," may be anycompound, preferably any organiccompound, that can reduce silver ion to metallic silver. At elevated ~ 21731~5 temperatures, in the presence of the latent image, the non-photosensitive reducible silver source (e.g., silver behenate) is reduced by the reducin~ agent for silver ion.
This produces a negative black-and-white image of element~l silver.
While conventional photographic developers such as methyl gallate, hydro-5 quinone, substituted-hydroquinones, catechol, pyrogallol, ascorbic acid, and ascorbic acid derivatives are useful, they tend to result in very reactive photo-thermographic formulations and fog during preparation and coating of photo-thermographic elements. As a result, hindered phenol developers (i.e., reducing agents) have traditionally been preferred.
As the visible image in black-and-white photothermographic elements is usually produced entirely by element~l silver (Ag), one cannot readily decrease the amount of silver in the emulsion without reducing the m~imllm image density.
However, reduction of the amount of silver is o~en desirable to reduce the cost of raw materials used in the emulsion and/or to enh~nce performance. For example, toning agents may be incorporated to improve the color of the silver image of the photothermographic elements as described in U.S. Patent Nos. 3,846,136;
3,994,732; and 4,021,249.
Another method of increasing the maximum image density in photographic and photothermographic emulsions without increasing the amount of silver in the emulsion layer is by incorporating dye-forming or dye-rele~.cing compounds in the emulsion. Upon im~ging the dye-forming or dye-rele~sing compound is oxidized, and a dye and a reduced silver image are simult~neously formed in the exposed region. In this way, a dye-enhanced black-and-white silver image can be produced.
Dye enhanced black-and-white silver image forming compounds and processes are described in U. S. Patent No. 5,185,231.
The im~ing arts have long recognized that the field of photothermography is clearly distinct from that of photography. Photothermographic elements differsignificantly from conventional silver halide photographic element.e which require wet-prccescing In photothermographic imaging elements, a visible image is created by heat as a result of the reaction of a developer incorporated within the element. Heat is _ --4--essenti~l for development and temperatures of over 100C are routinely required. In con~.asl, conventional wet-processed photographic im~ging elements require processing in aqueous processing baths to provide a visible image (e.g., developing and fixing baths) and development is usually performed at a more moderate 5 temperature (e.g., 30-50C).
In photothermographic elçrnçnt~ only a small amount of silver halide is used to capture light and a di~rerenl form of silver (e.g., silver behenate) is used to generate the image with heat. Thus, the silver halide serves as a catalyst for the development of the non-photosensitive, reducible silver source. In contrast, 10 conventional wet-processed black-and-white photographic elements use only oneform of silver (e.g., silver halide) which, upon development, is itself converted to the silver image. Additionally, photothermographic elements require an amount ofsilver halide per unit area that is as little as one-hundredth of that used in conventional wet-processed silver halide.
Photothermographic systems employ a light-insçn.~itive silver salt, such as silver bçhen~te, which participates with the developer in developing the latent image. In contrast, photographic systems do not employ a light-in~çn~itive silver salt directly in the image-forming process. As a result, the image in photothermo-graphic elemçnts is produced primarily by reduction of the light-insensitive silver 20 source (silver b~-en~te) while the image in photographic black-and-white elements is produced primarily by the silver halide.
In photothermographic elements, all of the "chçmi~try" of the system is incorporated within the element itsel For example, photothermographic elements inco,~o,~te a developer (i.e., a reduc.ing agent for the non-photosensitive reducible 25 source of silver) within the element while conventional photographic elements do not. The incorporation of the developer into photothermographic elements can lead to increased formation of "fog" upon coating of photothermographic emulsions.
Even in so-called instant photography, the developer cllçmistry is physically separated from the photosensitive silver halide until development is desired. Much 30 effort has gone into the preparation and m~n~lf~cture of photothermographic elen-ents to minimi7e formation offog upon coating, storage, and post-processingaging.
Similarly, in photothermographic element~, the unexposed silver halide inherently re.,.ah~s after development and the element must be stabilized against further development. In contrast, the silver halide is removed from photographicelemPn~s after development to prevent further im~p,in~ (i.e., the fixing step).
In photothermographic elements the binder is capable of wide variation and a number of binders are useful in prepa, ing these elements. In contrast, photographic elernent~ are limited almost exclusively to hydrophilic colloidal binders such as gelatin.
Because photothermographic elements require thermal processing, they pose di~erel,l considerations and present distinctly different problems in m~nllf~ct-lre and use. In addition, the effects of additives (e.g., stabilizers,antifoggants, speed enhancers, sen.~iti7erS~ supersensitizers, etc.) which are intç-lded to have a direct effect upon the im~ging process can vary depending upon whetherthey have been incorporated in a photothermographic element or incorporated in aphotographic ebment Distinctions between photothermographic and photographic elements are described in Imaging Processes and Materials (Neblette's Eighth Edition); J.
Sturge et al. Ed; Van Nostrand Reinhold: New York, 1989; Chapter 9 and in Unconventional Imaging Processes; E. Brinckman et al, Ed; The Focal Press:
London and New York: 1978; pp. 74-75.
Because of these and other differences, additives which have one effect in conventional silver halide photography may behave quite di~eren~ly in phototherrnographic elements where the underlying chemistry is so much more complex. For example, it is not uncommon for an antifoggant for a silver halide systems to produce various types of fog when incorporated into photothermo-graphic elements.
Various techniques are typically employed to try and gain higher sensitivity in a photothermographic material. In efforts to make more sensitive photothermo-graphic elements, one of the most difficult parameters to m~int~in at a very low 21 73~5 level is the various types of fog or Dmin. Fog is spurious image density which appears in non-imaged areas of the element after development and is often reported in sensitometric results as Dmin. Photothermographic emulsions, in a manner similar to photographic emulsions and other light-sensitive systems, tend to suffer from5 fog.
Traditionally, photothermographic elem~nts have suffered from fog upon coating. The fog level of freshly prepared photothermographic elements will be referred to herein as initial fog or initial Dmin.
In addition, the fog level of photothermographic elements often rises as the 10 material is stored, or "ages." This type of fog will be referred to herein as shelf-aging fog. Adding to the difficulty of fog control on shelf-aging is the fact that the developer is incorporated in the photothermographic element. This is not the case in most silver halide photographic systems. A great amount of work has been done toimprove the shelf-life characteristics of photothermographic elements.
A third type of fog in photothermographic systems results from the instability of the image and/or background after proces~qin~ The photoactive silver halide still present in the developed image may continue to catalyze formation of metallic silver during room light handling or post-processing exposure such as in graphic arts contact frames. This is known as "post-procesqing fog" or "silver print-20 out." Without having acceptable resistance to fog, a commercially useful material is difficult to prepare. Thus, there exists a need for "print stabilizers" to stabilize the unreacted silver halide. Various techniques have been employed to improve sensitivity and m~int~in resistance to fog.
In color photothermographic elements, often unreacted dye forming or dye 25 rele~qi~ compounds may slowly oxidize and form areas of color in the unexposed areas. In these elements, stabilizers are often added to reduce "leuco dye backgrounding."
The addition of separate post-processing image stabilizers or stabilizer precursors provides the desired post-processing stability. Most often these are 30 sulfur-con~ g compounds such as mercaptans, thiones, and thioethers as described in Research Disclosure, June 1978, item 17029. U.S. Patent No.

4,245,033 describes sulfur compounds of the mercapto-type that are development restrainers of a photothermographic system. See also U.S. Patent Nos. 4,837,141 and 4,451,561. Mesoionic 1,2,4-triazolium-3-thiolates as fixing agents and silver halide stabilizers are described in U.S. Patent No. 4,378,424. Substituted 5-mercapto-1,2,4-triazoles, such as 3-amino-5-benzothio-1,2,4-triazole, used as post-proces~ing stabilizers are described in U.S. Patent Nos. 4,128,557; 4,137,079;
4,138,265; and Research Disclosure 16977 and 16979.
Some of the problems with these stabilizers include thermal fogging during processing or losses in photographic sensitivity, m~ximl-rn density, or contrast at effective stabilizer concentrations.
Stabilizer precursors have blocking or modifying groups that are cleaved during processing with heat, light, and/or alkali. This provides an active stabilizer that can combine with the photoactive silver halide in the unexposed areas of the photographic material to form a light- and heat-stable complex. For example, in the presence of a stabilizer precursor in which the blocking group on a sulfur atom is cleaved upon proces~ing the res--lting silver mercaptide will be more stable than silver halide to light, and heat.
Blocking groups that are thermally-sensitive have also been used. These blocking groups are removed by heating the im~ging material during processing.
For example, U.S. Patent No. 5,158,866 describes the use of omega-substituted 2-propionamidoacetal or 3-propionamidopropionyl stabilizer precursors as post-processing stabilizers in photothermographic elements. U. S. Patent No. 5,175,081 describes the use of certain azlactones as st~bili7ers. U.S. Patent No. 5,298,390 describes the use of certain alkyl sulfones as blocked compounds capable of rele~ing stabilizers with heat. U.S. Patent No. 5,300,420 describes the use of certain nitriles as blocked compounds capable of rele~ing stabilizers with heat.Various disadvantages attend these di~rere,ll blocking techniques. Highly basic solutions that are necessary to cause unblocking of the alkali-sensitive blocked derivatives are corrosive and irritating to the skin. With photographic stabilizers that are blocked with a heat-removable group, it is often found that the liberated reagent or by-product can react with other components of the photothermographic ~173185 element and cause adverse effects. Also, premature release of the stabilizing moiety within the desired time during processing may occur, resulting in fogging of theemulsion or loss of sensitivity.
There is a continued need for improved stabilizer compounds that inhibit fog 5 and do not have any detrimental effects on the photothermographic element.

SUMMARY OF THE INVENTION
The present invention provides heat-developable, photothermographic çlem~nts which are capable of providing high photospeed; stable, high density 10 images of high resolution and good sharpness; and good shelf stability.
The present invention provides photothermographic elements coated on a support wherein the photothermographic element comprises:
(a) a photosensitive silver halide;
(b) a non-photosensitive, reducible source of silver;
(c) a reduçing agent for the non-photosensitive, reducible source of sllver;
(d) a binder; and (e) a hydantoin compound.
When the photothermographic elem~nt used in this invention is heat 20 developed, preferably at a temperature offrom about 80C to about 250C (176F
to 482F) for a duration of from about 1 second to about 2 minutçs, in a subst~nti~lly water-free condition after, or simult~neously with, imagewise exposure, a black-and-white silver image is obtained.
The reducing agent for the non-photosensitive silver source may be any 25 conventional photographic developer such as methyl gallate, hydroquinone, substituted-hydroquinones, catechol, pyrogallol, ascorbic acid, and ascorbic acid derivatives. However, it is prere-led that the reduc.ing agent be a hindered phenol developer. Further, the reducing agent may optionally comprise a compound capable of being oxidized to form or release a dye. Preferably the dye-forming 30 material is a leuco dye.
In photothermographic elements of the present invention, the layer(s) that contain the photographic silver salt are referred to herein as emulsion layer(s).

` ~17318~
g According to the present invention, one or more hydantoin compounds is added either to the emulsion layer(s) or to a layer or layers adjacent to the emulsionlayer(s). Layers that are adjacent to the emulsion layer(s) may be, for example,protective topcoat layers, primer layers, interlayers, opacifying layers, antih~lation S layers, barrier layers, auxiliary layers, etc. It is preferred that the reducing agent system be present in the photothermographic emulsion layer or topcoat layer.
The present invention also provides a process for the formation of a visible image by first exposing to electroma~nP,tic radiation and thereafter heating theinventive photothermographic element described earlier herein.
The present invention also provides a process comprising the steps of:
(a) exposing the inventive photothermographic element described earlier herein to electrom~gne~ic radiation, to which the silver halide grains of the element are sensitive, to generate a latent image;
(b) heating the exposed elemPnt to develop the latent image into a visible image;
(c) positioning the element with a visible image thereon between a source of ultraviolet or short wavelength visible radiation energy and an ultraviolet or short wavelength radiation photosensitive imageable me~ m; and (d) thereafter exposing the imageable medium to ultraviolet or short wavelength visible radiation through the visible image on the element, thereby absorbing ultraviolet or short wavelength visible radiation in the areas of the element where there is a visible image and tran~mitting ultraviolet or short wavelength visible radiation through areas of the element where there is no visible image.
The photothermographic element may be exposed in step (a) with visible, hlrlaled~ or laser radiation.
The photothermographic elements of this invention may be used to prepare black-and-white, monochrome, or color images. The photothermographic material 30 of this invention can be used, for example, in conventional black-and-white or color photothermography, in electronically generated black-and-white or color hardcopy .
recol.iing, in the graphic arts area (e.g., phototypesetting), in digital proofing, and in digital radiographic im~ging The material of this invention provides high photo-speeds, provides strongly absorbing black-and-white or color images, and provides a dry and rapid process.
~e~ting in a subst~nti~lly water-free condition as used herein, means heating at a temperature of 80 to 250C. The term "subst~nti~lly water-free condition"
means that the reaction system is approxim~tely 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 element. Such a condition is described in T. H. James, The Theory of ~he Photographic Process, Fourth Edition, Macmill~n 1977, page 374.
As used herein:
"photothermographic element" means a construction comprising at least one photothermographic emulsion layer and any supports, topcoat layers, image receiving layers, blocking layers, antih~lation layers, subbing or priming layers, etc;
"emulsion layer" means a layer of a photothermographic element that contains the non-photosensitive silver source and the photosensitive silver halide;
"ultraviolet region of the spectrum" means that region of the spectrum less than or equal to about 400 nm, preferably from about 100 nm to about 400 nm.
More preferably, the ultraviolet region of the spectrum is the region between about 190 nm and about 400 nm;
"short wavelength visible region of the spectrum" means that region of the spectrum from about 400 nm to about 450 nm; and "infrared region of the spectrum" means from about 750 nm to about 1400 nm; "visible region ofthe spectrum" means from about 400 nm to about 750 nm; and "red region of the spectrum" means from about 640 nm to about 750 nm. Preferably, the red region of the spectrum is from about 650 nm to about700 nm.
As is well understood in this area, substitution is not only tolerated, but is often advisable and substitution is anticipated on the hydantoin compounds used in the present invention. As a means of simplifying the discussion and recitation of ~173185 certain substituent groups, the terms "group" and "moiety" are used to dirrel el.tiate between those chemical species that may be substituted and those which may not be so substituted. Thus, when the term "group," or "aryl group," is used to describe a substituent, that substituent includes the use of additional substituents beyond the 5 literal definition of the basic group. Where the term "moiety" is used to describe a substitu~nt, only the unsubstituted group is intended to be included For example, the phrase, "alkyl group" is intended to include not only pure hydrocarbon alkylchains, such as methyl, ethyl, propyl, t-butyl, cyclohexyl, iso-octyl, octadecyl and the like, but also alkyl chains bearing substituçnt~ known in the art, such as 10 hydroxyl, alkoxy, phenyl, halogen atoms (F, Cl, Br, and I), cyano, nitro, amino, carboxy, etc. For example, alkyl group includes ether groups (e.g., CH3-CH2-CH2-O-CH2-), haloalkyls, nitroalkyls, carboxyalkyls, hydroxyalkyls, sulfoalkyls, etc. On the other hand, the phrase "alkyl moiety" is limited to theinclusion of only pure hydrocarbon alkyl chains, such as methyl, ethyl, propyl, 15 t-butyl, cyclohexyl, iso-octyl, octadecyl, and the like. Substituçnts that react with active ingredients, such as very strongly electrophilic or oxi~i7in~ substituent.~, would of course be excluded by the ordinarily skilled artisan as not being inert or harmless.
Other aspects, advantages, and benefits of the present invention are apparent 20 from the detailed description, examples, and claims.

DETAILED DESCRIPTION OF THE INVENTION
Hydantoin compounds useful in this invention may be prepared by a variety of means. For a recent review of hydantoin chemistry see C. A. Lopez and G. G.
25 Trigo The Chemistry of Hydantoins; Advances in Heterocyclic Chemistry Vol 38;~c~dçln:c Press; Orlando, FL, 1985; pp 177-228. As shown below, by appropriate substitution, a wide variety of hydantoins may be prepared.
For example, hydantoins may be prepared by the reaction of an amino acid with a cyanate. The cyanate may be a salt such as potassium cyanate, or an alkyl or 30 aryl cyanate.

OOH 1~
R~ H + R-NCO (~ ~o NH2 E N~H

Hydantoins may also be prepared by the Bucherer-Bergs synthesis involving the reaction of potassium cyanide, and ammonium carbonate with a carbonyl derivative.

~C=NR + KCN NH4CO

In the present invention, the hydantoin compound has the formula:

~
R~N~

wherein:
Rl and R2 independently l epresent hydrogen, alkyl groups of up to 20 carbon atoms, alkenyl groups of up to 20 carbon atoms, aryl groups of up to 14 carbon atoms, aralkyl groups of up to 14 carbon atoms, carboxyalkyl groups of up to 10 carbon atoms, alkoxycarbonyl groups of up to 12 carbon atoms, a cycloalkyl group of up to 7 carbon atoms, a carboxyl group; or Rl and R2 taken together represent the necessary atoms to complete a 5-, 6-, or 7-membered carbocyclic or heterocyclic ring; and R3 and R4 independently represent hydrogen, alkyl groups of up to 20 carbon atoms, alkenyl groups of up to 20 carbon atoms, aryl groups of up to 14 carbon atoms, aralkyl groups of up to 20 carbon atoms,, a cycloalkyl group of up to 7 carbon atoms, a -13- 217318~

carboxyl group; a hydroxyl group, or a 5-, 6-, or 7-membered carbocyclic or heterocyclic ring group.
Represenlali~e hydantoin compounds useful in the present invention, include: hydantoin, l-methylhydantoin, 5-hydantoin-acetic acid, 5,5-dimethyl-hydantoin, 5-methyl-5-phenylhydantoin, 5-(4-methylphenyl)-5-phenylhydantoin, and5,5-diphenylhydantoin. These compounds are merely exemplary and are not intended to be limiting.
The hydantoin compounds of the present invention typically comprise from about 0.1 wt% to 50 wt%, and prefe~ably from about 1.0% to about 30%, ofthe dried layer of the photothermographic element in which they are placed. They maybe incorporated directly into the silver-cont~ining layer, into an adjacent layer, or an image-receiving layer. The hydantoin compounds of the present invention are especially useful in elements and compositions for the preparation of black-and-white, monochrome, and full color images.
The amounts of the above-described hydantoin stabilizer compounds that are added to the photothermographic element of the present invention may be varied depending upon the particular compound used, upon the type of emulsion layer (e.g., black-and-white vs. color), and whether the stabilizer is located in the emulsion layer, topcoat layer, or image receiving layer.
Photothermographic elements of the invention may contain other stabilizers or stabilizer precursors in colllbinalion with the hydantoin compounds of the invention, as well as other additives in combination with the compounds of the invention such as shelf-life stabilizers, toners, development accelerators, and other image-modifying agents.
The Photc-e~sitive Silver ~Ialide As noted above, the present invention includes a photosensitive silver halide.
The photosensitive silver halide can be any photosensitive silver halide, such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromo-iodide, silver chlorobromide, etc. The photosensitive silver halide can be added to the emulsion layer in any fashion so long as it is placed in catalytic proximity to the organic silver compound which serves as a source of reducible silver.

14 ~1731~5 The silver halide may be in any form which is photosensitive incl~l~ine, but not limited to cubic, octahedral, rhombic dodecahedral, orthorhombic, tetrahedral, other polyhedral habits, etc., and may have epitaxial growth of crystals thereon.
The silver halide grains may have a uniform ratio of halide throughout; they 5 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 halide ratio, and a discrete shell of another halide ratio. Core-shell silver halide grains useful in photothermographic elements and methods of preparing these materials are described in U.S. Patent No. 5,382,504. A core-shell 10 silver halide grain having an iridium doped core is particularly pr~r~lled. Iridium doped core-shell grains of this type are described in U.S. Patent Application Serial number 08/239,984 (filed May 9, 1994).
The silver halide may be prepared ex si~u, (i.e., be pre-formed) and mixed with the organic silver salt in a binder prior to use to prepare a coating solution. The 15 silver halide may be pre-formed by any means, e.g., in accordance with U.S. Patent No. 3,839,049. For example, it is effective to blend the silver halide and organic silver salt using a homogenizer for a long period of time. Materials of this type are often referred to as "pre-formed emulsions." Methods of preparing these silver halide and organic silver salts and manners of bl- ndine them are described in 20 ResearchDisclosure, June 1978, item 17029; U.S. Patent Nos. 3,700,458 and 4,076,539; and Jaranese Patent Application Nos. 13224/74, 42529/76, and 17216/75.
It is desirable in the practice of this invention to use pre-formed silver halide grains of less than 0.10 ~lm in an infrared senciti7e(l~ photothermographic element. It 25 is also prere"ed to use iridium doped silver halide grains and iridium doped core-shell silver halide grains as disclosed in U.S. Patent Application Serial Nos.
08/072,153, and 08/239,984 described above.
Pre-formed silver halide emulsions when used in the material of this invention can be unwashed or washed to remove soluble salts. In the latter case, the 30 soluble salts can be removed by chill-setting and leaching or the emulsion can be -15- 217~
-coagulation washed, e.g., by the procedures described in U.S. Patent Nos.
2,618,556; 2,614,928; 2,565,418; 3,241,969; and 2,489,341.
It is also effective to use an in situ process, i.e., a process in which a halogen-co~ ining compound is added to an organic silver salt to partially convert 5 the silver of the organic silver salt to silver halide.
The light sensitive silver halide used in the present invention can be employed in a range of about 0.005 mole to about 0.5 mole; preferably, from about 0.01 mole to about 0.15 mole per mole; and more preferably, from 0.03 mole to 0.12 mole per mole of non-photosensitive reducible silver salt.
10 Sensitizers The silver halide used in the present invention may be chemically and spectrally senciti7ed in a manner similar to that used to sensitize conventional wet-processed silver halide photographic materials or state-of-the-art heat-developable photothermographic elements.
For example, it may be chemically sensitized with a chemical sensitizing agent, such as a compound cont~inin~ sulfur, selçnium, tellurium, etc., or a compound cont~ining gold, pl~tinum, p~ m, ruthenium, rhodium, iridium, etc., a reduçin~ agent such as a tin halide, etc., or a combination thereof. The details of these procedures are described in T.H. James, The Theory of the Photographic 20 Process, Fourth Edition, Chapter 5, pp. 149 to 169. Suitable chemical sensitization procedures are also desclosed in Shepard, U.S. Patent No. 1,623,499; Waller, U.S.
Patent No. 2,399,083; McVeigh, U.S. Patent No. 3,297,447; and Dunn, U.S. Patent No. 3,297,446.
Addition of sensitizing dyes to the photosensitive silver halides serves to 25 provide them with high sensitivity to visible and infrared light by spectral se~ i,; (ion. Thus, the photosensitive silver halides may be spectrally sçneiti7ed with various known dyes that spectrally sçnciti7e silver halide. Non-limiting examples of senciti7.ing dyes that can be employed include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar 30 cyanine dyes, hemicyanine dyes, styryl dyes, and hemioxanol dyes. Ofthese dyes, cyanine dyes, merocyanine dyes, and complex merocyanine dyes are particularly -16- ~1731~5 -useful. Suitable sensitizing dyes are described, for example in U.S. Patent Nos,3,719,495 and 5,393,654.
An approp, iate amount of sen.~iti7ing dye added is generally about 10-' to 10~1 mole; and preferably, about 10-8 to 10-3 moles per mole of silver halide.
S Supersensitizers To get the speed of the photothermographic elements up to maximum levels and further enhance sensitivity, it is often desirable to use supersensitizers. Any supersen~iti7er can be used which increases the sensitivity. For example, preferred infrared supersensilize-~ are described in U.S. Patent Application Serial No.
10 08/091,000 (filed July 13, 1993) and include heteroaromatic mercapto compounds or heteroaromatic disulfide compounds of the formula:
Ar-S-M
Ar-S-S-Ar wherein: M represents a hydrogen atom or an alkali metal atom.
In the above noted supersen~iti7ers, Ar represe"ls a heteroaromatic ring or fused heteroaromatic ring cont~ining one or more of nitrogen, sulfur, oxygen, selenil-m or tellurium atoms. Preferably, the heteroaromatic ring is benzimidazole, naphthimid~701e, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselen~7ole, benzotellurazole, imidazole, oxazole, pyrazole, triazole, thi~di~7.ole, tetrazole, triazine, pyrimidine, pyridazine, pyrazine, pyridine, purine, quinoline or quinazolinone. However, other heteroaromatic rings are envisioned under the breadth of this invention.
The heteroaromatic ring may also carry substituents with examples of preferred substituf!nts being selected from the group consisting of halogen (e.g., Br and Cl), hydroxy, amino, carboxy, alkyl (e.g., of 1 or more carbon atoms, preferably 1 to 4 carbon atoms) and alkoxy (e.g., of 1 or more carbon atoms, preferably of 1 to 4 carbon atoms.
P~fe"ed supersensitizers are 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, 2-mercaptobenzothiazole, and 2-mercaptobenzoxazole.
The supersen~ e, s are used in general amount of at least 0.001 moles of sen~ er per mole of silver in the emulsion layer. Usually the range is between 21731~5 0.001 and 1.0 moles of the compound per mole of silver and preferably between 0.01 and 0.3 moles of compound per mole of silver.
The Non-Photosensitive Reducible Silver Source The present invention includes a non-photosensitive reducible silver source.
5 The non-photosensitive reducible silver source that can be used in the presentinvention can be any compound that contains a source of reducible silver ions.
Preferably, it is a silver salt which is comparatively stable to light and forms a silver image when heated to 80C or higher in the presence of an exposed photocatalyst (such as silver halide) and a reduçing agent.
Silver salts of organic acids, particularly silver salts of long chain fatty carboxylic acids, are ple~lled. The chains typically contain 10 to 30, preferably 15 to 28, carbon atoms. Suitable organic silver salts include silver salts of organic compounds having a carboxyl group. Examples thereof include a silver salt of an aliphatic carboxylic acid and a silver salt of an aromatic carboxylic acid. Preferred examples of the silver salts of aliphatic carboxylic acids include silver behenate, silver stearate, silver oleate, silver laureate, silver caprate, silver myristate, silver palmit~t~, silver maleate, silver fumarate, silver tartarate, silver furoate, silver linoleate, silver butyrate, silver camphorate, and mixtures thereof, etc. Silver salts that can be substituted with a halogen atom or a hydroxyl group also can be effectively used. Preferred examples of the silver salts of aromatic carboxylic acid and other carboxyl group-containing compounds include: silver benzoate, a silver-substituted ben70~te, such as silver 3,5-dihydroxyben70~tç, silver o-methyl-ben7.0~te, silver m-methylben70ate, silverp-methylbçn70flte, silver 2,4-dichloro-ben7.oate, silver acet~midoben70ate, silverp-phenylbçn70ate, etc.; silver gallate;
silver t~nn~te; silver phth~l~te; silver terephth~late; silver salicylate; silver phenylacet~te; silver pyromellilate; a silver salt of 3-carboxymethyl-4-methyl-4-thiazoline-2-thione or the like as described in U.S. Patent No. 3,785,830; and a silver salt of an aliphatic carboxylic acid containing a thioether group as described in U. S. Patent No. 3 ,330,663 .
Silver salts of compounds cont~ining mercapto or thione groups and derivatives thereof can also be used. r~e~ll ed examples of these compounds -18- h1731$~

include: a silver salt of 3-mercapto-4-phenyl-1,2,4-triazole; a silver salt of 2-mercaptobenzimidazole; a silver salt of 2-mercapto-5-aminoth~ ole; a silver salt of 2-(2-ethylglycolamido)benzothiazole; a silver salt of thioglycolic acid, such as a silver salt of a S-alkylthioglycolic acid (wherein the alkyl group has from 12 to 22 carbon atoms); a silver salt of a dithiocarboxylic acid such as a silver salt of dithioacetic acid; a silver salt of thioamide; a silver salt of 5-carboxylic-1-methyl-2-phenyl-4-thiopyridine; a silver salt of mercaptotriazine; a silver salt of 2-mercaptobenzoxazole; a silver salt as described in U. S. Patent No. 4,123,274, for e~ample, a silver salt of a 1,2,4-mercaptothiazole derivative, such as a silver salt of 3-amino-5-benzylthio-1,2,4-thiazole; and a silver salt of a thione compound, such as a silver salt of 3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione as disclosed in U.S. Patent No. 3,201,678.
Furtherrnore, a silver salt of a compound cont~inin~ an imino group can be used. Preferred examples of these compounds include: silver salts of benzotriazole and substituted derivatives thereof, for example, silver methylbenzotriazole andsilver 5-chlorobenzotriazole, etc.; silver salts of 1,2,4-triazoles or l-H-tetrazoles as described in U.S. Patent No. 4,220,709; and silver salts of imidazoles and imidazole derivatives.
Silver salts of acetylenes can also be used. Silver acetylides are described in U.S. Patent Nos. 4,761,361 and 4,775,613.
It is also found convenient to use silver half soaps. A prerelled example of a silver half soap is an equimolar blend of silver behenate and behenic acid, which analyzes for about 14.5 % silver and which is prepared by precipitation from an aqueous solution of the sodium salt of commercial behenic acid.
2S T,ansparenl sheet materials made on transparent film backing require atransparent coating. For this purpose a silver behenate full soap, cont~ining not more than about 15 /O of free behenic acid and analyzing about 22 % silver, can be used.
The method used for making silver soap dispersions is well known in the art and is disclosed in Research Disclosure, April 1983, item 22812, Research Disclosure, October 1983, item 23419, and U.S. Patent No. 3,985,565.

~ 2173~

-The silver halide and the non-photosensitive reducible silver source that form a starting point of development should be in catalytic proximity, i.e., reactive association. "Catalytic proximity" or "reactive association" means that they should be in the same layer, in adjacçnt layers, or in layers separated from each other by an inte~ e~ te layer having a thickness of less than 1 micrometer (l llm). It is plere"ed that the silver halide and the non-photosensitive reducible silver source be present in the same layer.
Photothermographic emulsions co~ e pre-formed silver halide in accordance with this invention can be sen~iti7ed with chemical sensitizers, or with spectral sen.eiti7ers as described above.
The reducible silver source generally conctitutes about 5 to about 70 % by weight of the emulsion layer. It is preferably present at a level of about 10 to about 50 % by weight of the emulsion layer.
The Reducing Agent for the Non-Phot~s~Fsi~ive Reducible Silver Source When used in black-and-white photothermographic elern~nts, the reducing agent for the organic silver salt may be any compound, preferably organic compound, that can reduce silver ion to metallic silver. Conventional photographic developers such as phenidone, hydroquinones, and catechol are useful, but hindered bisphenol reduçing agents are pre~elled.
A wide range of reducing agents has been disclosed in dry silver systems incl~lding amidoximes, such as phenylamidoxime, 2-thienylamidoxime and p-phenoxy-phenylamidoxime; azines, such as 4-hydroxy-3,5-dimethoxybenz-aldehydeazine; a combination of aliphatic carboxylic acid aryl hydrazides and ascorbic acid, such as 2,2'-bis(hydroxymethyl)propionyl-~-phenylhydrazide in col~billalion with ascorbic acid; a combination of polyhydroxybenzene and hydroxylamine; a reductone and/or a hydrazine, such as a combination of hydroquinone and bis(ethoxyethyl)hydroxylamine, piperidinohexose reductone, or formyl-4-methylphenylhydrazine; hydroxamic acids, such as phenylhydroxamic acid,p-hydroxyphenylhydroxamic acid, and o-alaninehydroxamic acid; a combination of azines and sulfonamidophenols, such as phenothiazine withp-benzenesulfonamido-phenol or 2,6-dichloro-4-benzenesulfonamidophenol; a-cyanophenylacetic acid 21 73~8~

derivatives, such as ethyl a-cyano-2-methylphenyl~cet~te, ethyl a-cyano-phenyl-acetate; a combination of bis-o-naphthol and a 1,3-dihydroxybenzene derivative, such as 2,4-dihydroxybenzophenone or 2,4-dihydroxyacetophenone; 5-pyrazolones such as 3-methyl-1-phenyl-5-pyrazolone; reductones, such as dimethylaminohexose reductone, anhydrodihydroaminohexose reductone, and anhydrodihydro-piperidone-hexose reductone; sulfonamidophemol reducing agents, such as 2,6-dichloro-4-benzenesulfonamidophenol andp-bçn7enesulfonamidophenol;
indane-1,3-diones, such as 2-phenylindane-1,3-dione; chromans, such as 2,2-dimethyl-7-t-butyl-6-hydroxychroman; 1,4-dihydropyridines, such as 2,6-dimethoxy-3,5-dicarbethoxy-1,4-dihydropyridine; ascorbic acid derivatives, such as l-ascorbylpalmitate, ascorbylstearate; unsaturated aldehydes and ketones;
certain 1,3-indanediones, and 3-pyrazolidones (phenidones).
Hindered bisphenol developers are compounds that contain only one hydroxy group on a given phenyl ring and have at least one additional substituent lS located ortho to the hydroxy group. They differ from traditional photographic developers which contain two hydroxy groups on the same phenyl ring (such as is found in hydroquinones). Hindered phenol developers may contain more than one hydroxy group as long as they are located on dirrerenl phenyl rings. Hindered phenol developers includç, for example, binaphthols (i.e., dihydroxybinaphthyls), biphenols (i.e., dihydroxybiphenyls), bis(hydroxynaphthyl)meth~nes, bis(hydroxy-phenyl)meth~nes, hindered phenols, and naphthols.
Non-limiting representative bis-o-naphthols, such as by 2,2'-dihydroxyl-l-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl, and bis(2-hydroxy-l-naphthyl)meth~ne. For additional compounds see U.S. Patent No. 5,262,295 at column 6, lines 12-13, incorporated herein by reference.
Non-limiting r epresenlati~e biphenols include 2,2'-dihydroxy-3,3'-di-t-butyl-S,S-dimethylbiphenyl; 2,2'-dihydroxy-3,3',5,5'-tetra-t-butylbiphenyl;
2,2'-dihydroxy-3,3'-di-t-butyl-S,S'-dichlorobiphenyl; 2-(2-hydroxy-3-t-butyl-S-methylphenyl)-4-methyl-6-n-hexylphenol; 4,4'-dihydroxy-3,3',5,5'-tetra-t-butyl-biphenyl; and 4,4'-dihydroxy-3,3',5,5'-tetramethylbiphenyl. For additional -21- 2~731~S

compounds see U.S. Patent No. 5,262,295 at column 4, lines 17-47, incorporated herein by reference.
Non-limiting representative bis(hydroxynaphthyl)meth~nes include 2,2'-methylene-bis(2-methyl-1-naphthol)methane. For additional compounds see U.S. Patent No. 5,262,295 at column 6, lines 14-16, incorporated herein by reference.
Non-limiting representative bis(hydroxyphenyl)meth~nes include bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane(CAOTM-5); 1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane (PermanaxTM or NonoxTM);
1,1'-bis(3,5-tetra-t-butyl-4-hydroxy)methane; 2,2-bis(4-hydroxy-3-methylphenyl)-propane; 4,4-ethylidene-bis(2-t-butyl-6-methylphenol); and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane. For additional compounds see U.S. Patent No.
5,262,295 at column 5 line 63 to column 6, line 8 incorporated herein by reference.
Non-limiting representative hindered phenols include 2,6-di-t-butylphenol;
2,6-di-t-butyl-4-methylphenol; 2,4-di-t-butylphenol; 2,6-dichlorophenol;
2,6-dimethylphenol; and 2-t-butyl-6-methylphenol.
Non-limiting representative hindered naphthols include l-naphthol;

4-methyl-1-naphthol; 4-methoxy-1-naphthol; 4-chloro-1-naphthol; and 2-methyl-l-naphthol. For additional compounds see U.S. Patent No. 5,262,295 at column 6, lines 17-20, incorporated herein by re~.e.-ce.
The reduçin~ agent should be present as 1 to 10% by weight ofthe im~ein~
layer. In multilayer elements, if the reducing agent is added to a layer other than an emulsion layer, slightly higher proportions, of from about 2 to 15%, tend to be more desirable.
The Optional Dye-Forming or Dye-Releasing Material As noted above, the reducing agent for the reducible source of silver may be a compound that can be oxidized directly or indirectly to form or release a dye.Leuco dyes are one class of dye-forming material that form a dye upon oxidation. Any leuco dye capable of being oxidized by silver ion to form a visible image can be used in the present invention. Leuco dyes that are both pH sensitive and oxi~i7~ble can also be used, but are not preferred. Leuco dyes that are sensitive -22- 217318~

only to changes in pH are not included within scope of dyes useful in this invention because they are not oxidizable to a colored form.
As used herein, a "leuco dye" or "blocked leuco dye" is the reduced form of a dye that is generally colorless or very lightly colored and is capable of forming a 5 colored image upon oxidation of the leuco or blocked leuco dye to the dye form.
Thus, the blocked leuco dyes (i.e., blocked dye-rele~irg compounds), absorb lessstrongly in the visible region of the electromagnetic spectrum than do the dyes. The res -lt~nt dye produces an image either directly on the sheet on which the dye is formed or, when used with a dye- or image-receiving layer, on the image-receiving 10 layer upon diffusion through emulsion layers and interlayers.
Representative classes of leuco dyes that can used in the photothermo-graphic elements ofthe present invention include, but are not limited to:
chromogenic leuco dyes, such as indoaniline, indophenol, or azomethine leuco dyes;
imidazole leuco dyes, such as 2-(3,5-di-t-butyl-4-hydroxyphenyl)-4,5-diphenyl-imidazole, as described in U.S. Patent No. 3,985,565; dyes having an azine, diazine, oxazine, or thiazine nucleus such as those described in U.S. Patent Nos. 4,563,415;
4,622,395; 4,710,570; and 4,782,010; and benzylidene leuco compounds as described in U.S. Patent No. 4,923,792.
Another preferred class of leuco dyes useful in this invention are those derived from azomethine leuco dyes or indoaniline leuco dyes. These are often rere-,ed to herein as "chromogenic leuco dyes" because many ofthese dyes are useful in conventional, wet-processed photography. Chromogenic dyes are preparedby oxidative coupling of ap-phenylene~ mine compound or ap-arninophenol compound with a photographic-type coupler. Reduction of the corresponding dye as described, for example, in U.S. Patent No. 4,374,921 forms the chromogenic leuco dye. Leuco chromogenic dyes are also described in U. S. Patent No.
4,594,307. Cyan leuco chromogenic dyes having short chain carbamoyl protecting groups are described in European Laid Open Patent Application No. 533,008. For areview of chromogenic leuco dyes, see K. Venkataraman, The Chemistr y of Synthetic Dyes, ~cadennic Press: New York, 1952; Vol. 4, Chapter VI.

-23- 2173i8~

Another class of leuco dyes useful in this invention are "alda_ine" and "ket~7ine" leuco dyes. Dyes of this type are described in U.S. Patent Nos.
4,587,211 and 4,795,697. Ben_ylidene leuco dyes are also useful in this invention.
Dyes of this type are described in U. S. Patent No. 4,923,792.
Yet another class of dye-rele~cing compounds that form a diffusible dye upon oxidation are known as pre-formed-dye-release (PDR) or redox-dye-release (RDR) compounds. In these compounds, the reducing agent for the organic silver source releases a mobile pre-formed dye upon oxidation. Examples of these compounds are disclosed in Swain, U.S. Patent No. 4,981,775.
Further, other image-forming compounds where the mobility ofthe compound having a dye part changes as a result of an oxidation-reduction reaction with silver halide, or an organic silver salt at high temperature can be used, as described in Japanese Patent Application No. 165,054/84.
Still further the reducing agent may be a compound that releases a conventional photographic dye coupler or developer on oxidation as is known in the art.
The dyes formed or released in the various color-forming layers should, of course, be different. A difference of at least 60 nm in reflective maximum absorbance is prefe.,ed. More preferably, the absorbance maximum of dyes formed or released will differ by at least 80- 100 nm. When three dyes are to be formed, two should preferably differ by at least these minimllm.~, and the third should preferably differ from at least one of the other dyes by at least 150 nm, and more preferably, by at least 200 nm. Any red~lçing agent capable of being oxidi7ed by silver ion to form or release a visible dye is useful in the present invention as previously noted.The total amount of optional leuco dye used as a reducing agent used in the present invention should preferably be in the range of 0.5-25 wt%, and more preferably, in the range of 1-10 wt%, based upon the total weight of each individual layer in which the red~lcin~ agent is employed.

-24- ~ 5 The Binder The photosensitive silver halide, the non-photosensitive reducible source of silver, the reducing agent system, and any other addenda used in the present invention are generally added to at least one binder. The binder(s) that can be used 5 in the present invention can be employed individually or in combination with one another. It is prefe"ed that the binder be selected from polymeric materials, such as, for example, natural and synthetic resins that are sufficiently polar to hold the other ingredients in solution or suspension.
A typical hydrophilic binder is a transparent or tr~nslucent hydrophilic 10 colloid. Examples of hydrophilic binders include: a natural substance, for example, a protein such as gelatin, a gelatin derivative, a cellulose derivative, etc.; a poly-saccharide such as starch, gum arabic, pullulan, dextrin, etc.; and a synthetic polymer, for example, a water-soluble polyvinyl compound such as polyvinyl alcohol, polyvinyl pyrrolidone, acrylamide polymer, etc. Another example of a 15 hydrophilic binder is a dispersed vinyl compound in latex form which is used for the purpose of increasing dimensional stability of a photographic element.
Examples of typical hydrophobic binders are polyvinyl acetals, polyvinyl chloride, polyvinyl acetate, cellulose acetate, polyolefins, polyesters, polystyrene, polyacrylonitrile, polycarbonates, methacrylate copolymers, maleic anhydride ester 20 copolymers, butadiene-styrene copolymers, and the like. Copolymers, e.g., terpolymers, are also included in the definition of polymers. The polyvinyl acetals, such as polyvinyl butyral and polyvinyl formal, and vinyl copolymers such as polyvinyl acetate and polyvinyl chloride are particularly pl~r~lled.
Although the binder can be hydrophilic or hydrophobic, preferably it is 25 hydrophobic in the silver containing layer(s). Optionally, these polymers may be used in combination of two or more thereof.
The binders are preferably used at a level of about 30-90 % by weight of the emulsion layer, and more preferably at a level of about 45-85 % by weight. Wherethe proportions and activities of the reduçing agent system for the non-photo-30 sensitive reducible source of silver require a particular developing time andtemperature, the binder should be able to withst~nrl those conditions. Generally, it 21731~

is prefe.,ed that the binder not decompose or lose its structural integrity at 250F
(121C) for 60 seconds, and more prere--ed that it not decompose or lose its structural integrity at 350~F (177C) for 60 seconds.
The polymer binder is used in an amount sufficient to carry the components dispersed therein, that is, within the effective range of the action as the binder. The effective range can be appropriately determined by one skilled in the art.
~hotothermographic Formulations The formulation for the photothermographic emulsion layer can be prepared by dissolving and dispersing the binder, the photosensitive silver halide, the non-photose.n.citive reducible source of silver, the reducing agent system for the non-photosensitive reducible silver source, and optional additives, in an inert organic solvent, such as, for example, toluene, 2-butanone, or tetrahydrofuran.
The use of "toners" or derivatives thereof which improve the image, is highly desirable, but is not essentiql to the elennent. Toners can be present in an amount of about 0.01-10 % by weight ofthe emulsion layer, preferably about 0.1 -10 % by weight. Toners are well known materials in the photothermographic art, as shown in U.S. Patent Nos. 3,080,254; 3,847,612; and 4,123,282.
Examples of toners include: phthqlimide and N-hydroxyphthqlimide; cyclic imides, such as succinimide, pyrazoline-5-ones, quinazolinone, l-phenylurazole, 3-phenyl-2-pyrazoline-5-one, and 2,4-thiazolidinedione; naphthqlimidec, such as N-hydroxy-1,8-naphthqlimide; cobalt complexes, such as cobaltic hexamine trifluoroacetate; mercaptans such as 3-mercapto-1,2,4-triazole, 2,4-dimercapto-pyrimidine, 3-mercapto-4,5-diphenyl-1,2,4-triazole and 2,5-dimercapto-1,3,4-thia-diazole; N-(aminomethyl)aryldicarboximides, such as (N,N-dimethylaminomethyl)-phthqlimide, and N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide; a combination of blocked pyrazoles, isothiuronium derivatives, and certain photo-bleach agents, such as a combination of N,N'-hexamethylene-bis(l-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,6-diazaoctane)bis(isothiuronium)trifluoroacetqte, and 2-(tribromomethylsulfonyl benzothiazole); merocyanine dyes such as 3-ethyl-5-[(3-ethyl-2-benzothiazolinylidene)-1-methyl-ethylidene]-2-thio-2,4-o-azolidinedione; phthalazinone, phthLqlq.7inone derivatives, or metal salts or these derivatives, such as 4-(l-naphthyl)phth~1~7.inone, 6-chlorophth~1~7inone, 5,7-dimethoxypht~ 7.inone, and 2,3-dihydro-1,4-phth~1~7inedione; a combination of phthql~7ine plus one or more phthalic acid derivatives, such as phthalic acid, 4-l..elhrlphthalic acid, 4-nitrophthalic acid, and tetrachlorophthalic anhydride, 5 quinazolinediones, benzoxazine or naphthoxazine derivatives; rhodium complexesfunctioning not only as tone modifiers but also as sources of halide ion for silver halide formation in sit~, such as ammonium hexachlororhodate (III), rhodium bromide, rhodium nitrate, and potassium hexachlororhodate (III); inorganic peroxides and persulf~tç~, such as ammonium peroxy~ .llf~te and hydrogen peroxide; benzoxazine-2,4-diones, such as 1,3-benzoxazine-2,4-dione, 8-methyl-1,3-benzoxazine-2,4-dione, and 6-nitro-1,3-benzoxazine-2,4-dione; pyrimidines and asym-triazines, such as 2,4-dihydroxypyrimidine, 2-hydroxy-4-aminopyrimidine, and azauracil; and tetraazapentalene derivatives, such as 3,6-dimercapto-1,4-diphenyl-lH,4H-2,3a,5,6a-tetraazapentalene and 1,4-di-(o-chlorophenyl)-3,6-dimercapto-lH,4H-2,3a,5,6a-tetraazapentalene.
The photothermographic elements used in this invention can be further protected against the additional production of fog and can be stabilized against loss of sensitivity during storage. While not necess~. y for the practice of the invention, it may be advantageous to add mercury (II) salts to the emulsion layer(s) as an 20 antifoggant. P~ere, . ed mercury (II) salts for this purpose are mercuric acetate and mercuric bromide.
Other suitable antifoggants and stabilizers, which can be used alone or in co...bination, with the hydantoin stabilizers of this invention include the thiazolium salts described in U.S. Patent Nos. 2,131,038 and U.S. Patent No. 2,694,716; the~7.~indçnes described in U.S. Patent Nos. 2,886,437; the triazaindolizines described in U.S. Patent No. 2,444,605; the mercury salts described in U.S. Patent No.
2,728,663; the urazoles described in U.S. Patent No. 3,287,135; the sulfocatechols described in U.S. Patent No. 3,235,652; the oximes described in British Patent No.
623,448; the polyvalent metal salts described in U.S. Patent No. 2,839,405; the thiuronium salts described in U.S. Patent No. 3,220,839; and p~ lm, platinum and gold salts described in U.S. Patent Nos. 2,566,263 and 2,597,915.

27 ~17318~
.
Photothermographic elements of the invention can contain plasticizers and lubricants such as polyalcohols and diols ofthe type described in U.S. Patent No.
2,960,404; fatty acids or esters, such as those described in U.S. Patent Nos.
2,588,765 and 3,121,060; and silicone resins, such as those described in BritishPatentNo. 955,061.
Photothermographic elements cont~inin~ emulsion layers described herein may contain matting agents such as starch, tit~nium dioxide, zinc oxide, silica, and polymeric beads including beads ofthe type described in U.S. Patent Nos.
2,992,101 and 2,701,245.
Emulsions in accordance with this invention may be used in photothermo-graphic ~l~nnent~ which contain ~nti~t~tic or conducting layers, such as layers that comprise soluble salts, e.g., chlorides, nitrates, etc., evaporated metal layers, ionic polymers such as those described in U.S. Patent Nos. 2,861,056, and 3,206,312 orinsoluble inorganic salts such as those described in U.S. Patent No. 3,428,451.
The photothermographic elements of this invention may also contain electroconductive under-layers to reduce static electricity effects and improve transport throuch processing equipment. Such layers are described in U.S. PatentNo. 5,310,640.
Photothermographic Constructions The photothermographic elements of this invention may be constructed of one or more layers on a support. Single layer constructions should contain the silver halide, the non-photosensitive, reducible silver source, the reducing agent system for the non-photosensitive reducible silver source, the binder as well as optional materials such as toners, acutance dyes, coating aids, and other adjuvants.
Two-layer constructions should contain silver halide and non-photosensitive, reducible silver source in one emulsion layer (usually the layer adjacent to thesupport) and some of the other ingredients in the second layer or both layers. Two layer constructions comprising a single emulsion layer coating cont~ining all the ingredients and a protective topcoat are also envisioned.

-28- 2i 731~
.
Multicolor photothermographic dry silver constructions can contain sets of these bilayers for each color or they can contain all ingredients within a single layer, as described in U.S. Patent No. 4,708,928.
Barrier layers, preferably comprising a polymeric material, can also be present in the photothermographic element of the present invention. Polymers forthe barrier layer can be selected from natural and synthetic polymers such as gelatin, polyvinyl alcohols, polyacrylic acids, sulfonated polystyrene, and the like. Thepolymers can optionally be blended with barrier aids such as silica.
Photothermographic emulsions used in this invention can be coated by various coating procedures inclutling wire wound rod coating, dip coating, air knife coating, curtain coating, or extrusion coating using hoppers of the type described in U.S. Patent No. 2,681,294. If desired, two or more layers can be coated simultaneously by the procedures described in U.S. Patent Nos. 2,761,791;
5,340,613; and British Patent No. 837,095. Typical wet thickness ofthe emulsion layer can be about 10-150 micrometers (llm), and the layer can be dried in forced air at a temperature of about 20-100C. It is prerelled that the thickness ofthe layer be selected to provide maximum image densities greater than 0.2, and, more preferably, in the range 0.5 to 4.5, as measured by a MacBeth Color DensitometerModel TD 504 using the color filter complement~ry to the dye color.
Photothermographic elements according to the present invention can contain acut~nce dyes and antihalation dyes. The dyes may be incorporated into the photo-thermographic emulsion layer as acutance dyes according to known techniques. Thedyes may also be incorporated into antihal~tion layers according to known techniques as an ~ntih~lation backing layer, an antih~l~tion underlayer or as anovercoat. It is plefelled that the photothermographic elemçnts ofthis invention contain an ~ntihql~tion coating on the support opposite to the side on which theemulsion and topcoat layers are coated. ~ntih~l~tion and acut~nce dyes useful in the present invention are described in U.S. Patent Nos. 5,135,842; S,226,452;
5,314,795.
Development conditions will vary, depending on the construction used, but will typically involve heating the photothermographic elçn ent in a subst~nti~lly -29- ~17~1 8~

water-free condition after, or Simlllt~neously with, imagewise exposure at a suitably elevated tempelalure. Thus, the latent image obtained after exposure can be developed by heating the element at a moderately elevated temperature of, from about 80C to about 250C (176F to 482F), preferably from about 100C to about 200C, (212F to 392F), for a sufficient period oftime, generally about 1second to about 2 minlltes When used in a black-and-white element, a black-and-white silver image. When used in a monochrome or full-color element, a dye imageis obtained ~im-llt~qneously with the formation of a black-and-white silver image is obtained. Heating may be carried out by the typical heating means such as an oven, a hot plate, an iron, a hot roller, a heat generator using carbon or titanium white, or the like.
If desired, the imaged element may be subjected to a first heating step at a temperature and for a time sufficient to intensify and improve the stability of the latent image but insufficient to produce a visible image and later subjected to a second heating step at a temperature and for a time sufficient to produce the visible image. Such a method and its advantages are described in U.S. Patent No.
5,279,928.
The Support Photothermographic emulsions used in the invention can be coated on a wide variety of supports. The support, or substrate, can be selected from a widerange of materials depending on the imqging require",enl. Supports may be llans~arelll or at least trqn~lucent Typical supports include polyester film, subbed polyester film (e.g.,polyethylene terephthql-q-te or polyethylene naphth~l~te), cellulose acetate film, cellulose ester film, polyvinyl acetal film, polyolefinic film (e.g., polethylene or polypropylene or blends thereof), polycarbonate film and related or resinous materials, as well as glass, paper, and the like. Typically, a flexible support is employed, especially a polymeric film support, which can be partially acetylated or coated, particularly with a polymeric subbing or primingagent. P- ~fe- led polymeric materials for the support include polymers having good heat stability, such as polyesters. Particularly prefelled polyesters are polyethylene terephthqlqte and polyethylene naphth~ql~qte.

21731~

A support with a backside resistive heating layer can also be used photo-thermographic im~ing systems such as shown in U.S. Patent No. 4,374,921.
The Image-Receiving Layer When the re~ct~nts and reaction products of photothermographic systems S that contain compounds capable of being oxidized to form or release a dye remain in contact after imqging, several problems can result. For example, thermal development often forms turbid and hazy color images because of dye co~ tion by the reduced met~llic silver image on the exposed area of the emulsion. In addition, the resulting prints tend to develop color in unimaged 10 background areas. This is often referred to as "leuco dye backgrounding." This "background stain" is caused by slow post-processing reaction between the dye-forming or dye-rele~ing compound and reducing agent. It is therefore desirable to transfer the dye formed upon imaging to a receptor, or image-receiving layer.
Thus, the photothermographic elçrnf~nt may further comprise an image-15 receiving layer. Images derived from the photothermographic eletnçnt,s employingcompounds capable of being oxidized to form or release a dye, such as, as forexample, leuco dyes, are typically transferred to an image-receiving layer.
If used, dyes generated during thermal development of light-exposed regions of the emulsion layers migrate under development conditions into the an image-20 receiving or dye-receiving layer wherein they are retained. The dye-receiving layer may be composed of a polymeric material having affinity for the dyes employed.
Necessarily, it will vary depending on the ionic or neutral characteristics of the dyes.
The image-receiving layer can be any flexible or rigid, transparent layer made of thermoplastic polymer. The image-receiving layer preferably has a 25 thiçl~ness of at least O l llm more .preferably from about 1-10 llm, and a glass transition temperature (Tg) of from about 20C to about 200C. In the present invention, any thermoplastic polymer or combination of polymers can be used, provided the polymer is capable of absorbing and fixing the dye. Because the polymer acts as a dye mordant, no additional fixing agents are required.
30 Thermoplastic polymers that can be used to prepare the image-receiving layer include polyesters, such as polyethylene terephth~l~tes; polyolefins, such as poly-2173 1 8~

ethylene; cellulosics, such as cellulose acetate, cellulose butyrate, cellulose propionate; polystyrene; polyvinyl chloride; polyvinylidine chloride; polyvinyl acet~te; copolymer of vinyl chloride-vinyl acetate; copolymer of vinylidene chloride-acrylonitrile; copolymer of styrene-acrylonitrile; and the like.
The optical density of the dye image and even the actual color of the dye image in the image-receiving layer is very much dependent on the characteristics of the polymer of the image-receiving layer, which acts as a dye mordant, and, as such, is capable of absolbing and fixing the dyes. A dye image having a reflection optical density in the range offrom 0.3 to 3.5 (preferably, from 1.5 to 3.5) or a tran~mi~sion optical density in the range offrom 0.2 to 2.5 (preferably, from 1.0 to 2.5) is desirable.
The image-receiving layer can be formed by dissolving at least one thermo-plastic polymer in an organic solvent (e.g., 2-butanone, acetone, tetrahydrofuran) and applying the resulting solution to a support base or substrate by various coating methods known in the art, such as curtain coating, extrusion coating, dip coating, air-knife coating, hopper coating, and any other coating method used for coatingsolutions. After the solution is coated, the image-receiving layer is dried (e.g., in an oven) to drive off the solvent. The image-receiving layer may be strippably adhered to the photothermographic element. Strippable image-receiving layers are described in U.S. Patent No. 4,594,307.
Selection of the binder and solvent to be used in preparing the emulsion layer significantly affects the strippability of the image-receiving layer from the photosensitive element. Preferably, the binder for the image-receiving layer is impermeable to the solvent used for coating the emulsion layer and is incompatible with the binder used for the emulsion layer. The selection of the pre~e. I ed binders and solvents results in weak adhesion between the emulsion layer and the image-receiving layer and promotes good strippability of the emulsion layer.
The photothermographic element can also include coating additives to improve the strippability of the emulsion layer. For example, fluoroaliphatic poly-esters dissolved in ethyl acetate can be added in an amount of from about 0.02-0.5 wt% ofthe emulsion layer, preferably from about 0.1-0.3 wt%. A

` ` ~1731~5 replese.llali~re example of such a fluoroaliphatic polyester is "Fluorad FC 431", (a fluorinated surfactant available from 3M Company, St. Paul, MN). Alternatively, a coating additive can be added to the image-receiving layer in the same weight range to enh~nce strippability. No solvents need to be used in the stripping process. The 5 strippable layer preferably has a del~min~ting resi~t~nce of 1 to 50 g/cm and a tensile strength at break greater than, preferably at least two times greater than, its del~ g resistance.
Preferably, the image-receiving layer is adjac~nt to the emulsion layer in order to facilit~te transfer of the dye that forms after the imagewise exposed 10 emulsion layer is subjected to thermal development, for example, in a heated shoe-and-roller-type heat processor.
Photothermographic multi-layer constructions cont~ining blue-sensitive emulsions cont~ining a yellow dye-forming or dye-rele~ing compound can be overcoated with green-sensitive emulsions cont~ining a magenta dye-forming or l S dye-releasing compound. These layers can in turn be overcoated with a red-sensitive emulsion layer containin~ a cyan dye-forming or dye-rele~ing compound. Tm~ping and heating to form or release the yellow, magenta, and cyan dyes in an imagewise fashion. The dyes so formed or released may migrate to an image-receiving layer.The image-receiving layer can be a permanent part of the construction or it can be 20 removable, "i.e., strippably adhered," and subsequently peeled from the construction. Color-forming layers can be m~int~ined distinct from each other bythe use of functional or non-functional barrier layers between the various photo-sensitive layers as described in U.S. Patent No. 4,460,681. False color address, such as that shown in U.S. Patent No. 4,619,892, can also be used rather than blue-25 yellow, green-magenta, or red-cyan relationships between sensitivity and dye formation or release. False color address is particularly useful when im~ging ispel~ll,led using longer wavelength light sources, especially red or near infrared light sources, to enable digital address by lasers and laser diodes.
If desired, the dyes formed or released in the emulsion layer can be 30 transferred onto a separately coated image-receiving sheet by placing the exposed emulsion layer in intim~te face-to-face contact with the image-receiving sheet and ~ 1731~

heating the resulting composite construction. Good results can be achieved in this second embodiment when the layers are in uniform contact for a period of time ofabout 0.5-300 seconds at a temperature of about 80-220C.
In another embodiment, a multi-colored image can be prepared by super-5 imposing in register a single image-receiving sheet s~lcces.~ively with two or more imagewise exposed photothermographic elemçnts, each of which forms or releases a dye of a di~erenl color, and heating to transfer the thus formed or released dyes as desclil,ed above. This method is particularly suitable for the production of color proofs especially when the dyes formed or released have hues that match the 10 internationally agreed standards for color reproduction (Standard Web Offset Printing colors or SWOP colors). Dyes with this property are disclosed in U.S.
Patent No. 5,023,229. In this embodiment, the photothermographic elements are preferably all sensitized to the same wavelength range regardless of the color of the dye formed or released. For example, the PlemPnt.~ can be sen~iti7ed to ultraviolet 15 radiation with a view toward contact exposure on conventional printing frames, or they can be sel-~;l;7ed to longer wavelçn~h~, especially red or near infra-red, to enable digital address by lasers and laser diodes. As noted above, false color address is again particularly useful when imaging is performed using longer wavelength light sources, especially red or near infrared light sources, to enable digital address by 20 lasers and laser diodes.
Use as a Photomask As noted above, the possibility of low absorbance of the photothermo-graphic element in the range of 350-450 nm in non-imaged areas f~cilit~tes the use of the photothermographic elements of the present invention in a process where 25 there is a subsequent exposure of an ultraviolet or short wavelength visible radiation sensitive im~gç~ble medium. For example, im~ging the photothermographic element with coherent radiation and subsequent development affords a visible image. The developed photothermographic element absorbs ultraviolet or short wavelength visible radiation in the areas where there is a visible image and transmits ultraviolet 30 or short wavelength visible radiation where there is no visible image. The developed el~PmP~nt may then be used as a mask and placed between an ultraviolet or short -wavelength visible radiation energy source and an ultraviolet or short wavelength visible radiation photosensitive imageable metlium such as, for example, a photopolymer, diæo material, or photoresist. This process is particularly usefulwhere the imageable medium comprises a printing plate and the photothermo-graphic elem~nt serves as an imagesetting film.
Objects and advantages of this invention will now be illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention EXAMPLES
All materials used in the following examples, incl~l-ling the hydantoin compounds, were readily available from standard commercial sources, such as Aldrich Chemical Co. (Milwaukee, WI). All percentages are by weight unless other~vise indic~ted. The following additional terms and materials were used.
AcryloidTM A-21 is a polymethyl methacrylate polymer available from Rohm and Haas, Philadelphia, PA.
ButvarTM B-76 is a polyvinyl butyral resin available from Monsanto Company, St. Louis, MO.
CA 398-6 is a cellulose acetate polymer available from F~ctm~n Chemical Co., Kingsport, TN.
CAB 171-lSS cellulose acetate butyrate polymer available from F~.~tm~n Chemical Co., Kingsport, I~N.
CAOTM 5 is bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane, an antioxidant available from Rohm and Haas, Philadelphia, PA. It is a hindered phenol reducingagent (i.e., a developer) for the non-photosensitive reducible source of silver. CBBA is 2-(4-chlorobenzoyl)benzoic acid.
MEK is methyl ethyl ketone (2-butanone).
MMBI is 5-methyl-2-mercaptobenzimidazole.
4-MPA is 4-methylphthalic acid.
NBS is N-bromosuccinimide.

2 i 73185 -NonoxTM is 1,1-bis(2-hydroxy-3, 5-dimethylphenyl)-3, 5, 5-trimethylhexane [CAS RN=7292-14-0] and is available from St. Jean PhotoChemicals, Inc., Quebec.
It is a hindered phenol reducing agent (i.e., a developer) for the non-photosensitive reducible source of silver. It is also known as PermanaxTM WSO.
S PHZ is phth~l~7ine.
PHP is pyridinium hydrobromide perbromide.
TCPAN is tetrachlorophthalic anhydride.
THDI is DesmodurTM N-100, a biuretized hexamethylenediisocyanate available from Miles Chemical Corporation.
Sen~iti7ing Dye-l is described in U.S. Patent No. 5,393,654 and has the structure shown below.

(CH2)sCO2 (CH2)sco2H
Sensiti7ing Dye-2 is described in U.S. Patent No. 3,719,495 and has the structure shown below.

CH3CH2OW~ \ ~S

CIJb~-~

Example 1 A silver halide-silver behenate dry soap was prepared by the procedures described in U. S. Patent No. 3,839,049. The silver halide totaled 9% of the total silver while silver behenate comprised 91% ofthe total silver. The silver halide was a 0.055 llm silver bromoiodide emulsion with 2% iodide.
The following steps were carried under green safe lights. A photothermo-graphic emulsion was prepared by homogeni7.ing 300 g ofthe silver halide-silver behenate dry soap described above, 1675 g of 2-butanone, and 50 g of ButvarTM
B-76 polyvinyl butyral. The homogenized photothermographic emulsion (531 g) ~1 ~31~5 and 19.0 g of 2-butanone was cooled to 67F (19.4C) with stirring. A solution of 0.55 g of pyridinium hydrobromide perbromide (PHP) in 4.24 g of methanol was added and stirred for 1 hour. A solution of 0.43 g of calcium bromide in 3.20 g of meth~nQl was added and followed by 30 minutes of stirring.
After stirring for 30 minutes7 the following steps were then carried out under infrared safe lights. To the stirred emulsion was added a solution of 0.35 g of methylmercaptobenzimidazole (MMBI), 3.92 g of 2-(4-chlorobenzoyl)benzoic acid (CBBA), and 0.072 g of Se~ .ii-g Dye-l in 26.0 g of meth~nol. The emulsion was stirred for 1 hour at 67F (19.4C) at which time the temperature was changed to52F (11C). Additional ButvarTM B-76 (128.0 g) was added. Stirring was m~int~ined for 30 minutes at which time 26.3 g of NonoxTM was added. After 15 minlltes of stirring, a solution of 1.55 g of THDI in 7.8 g of 2-butanone was added.
After 15 minutes of stirring, a solution of 0.87 g oftetrachlorophthalic acid in2.48 g of 2-butanone was added. This was followed by additon of 2.61 g of phth~l~7ine (PHZ).
A master batch of topcoat solution was prepared by mixing 401 g of 2-butanone, 54.85 g of meth~nol, 36.6 g of CAB 171-lSS cellulose acetate butyrate, 1.37 g of 4-methylphthalic acid, and 1.40 g AcryloidTM A-21 acrylate resin.
Three levels of each hydantoin compound was added 20 g of the master batch of topcoat solution prepared above. The solutions were then placed in an ultrasonicbath for 20 rninl~tes.
The photothermographic emulsion and topcoat formulations were coated onto a 7 mil (176 ~m) polyethylene terephth~l~te support using a dual-knife coater.
This apparatus consists of two knife coating blades in series. The support was cut to a length suitable to the volume of solution used, and after raising the hinged knives, placed in position on the coater bed. The knives were then lowered and locked into place. The height of the knives was adjusted with wedges controlled by screw knobs and measured with electronic gauges. Knife #1 was raised to a clearance corresponding to the thic~ne.ss of the support plus the desired wet thic~ness of the emulsion layer (layer #1). Knife #2 was raised to a height equal to the desired ~17318~

thic~ness ofthe support plus the desired wet thickness the emulsion layer (layer #l) plus the desired wet thickness of the topcoat layer (layer #2).
The photothermographic emulsion layer was coated onto a wet thickness of 4.3 mil (109 ~m) above the support to give a dry coating weight of 1.69 g/ft2. The 5 topcoat was coated over the photothermographic emulsion layer at a wet thickness of 5.S mil (140 llm) above the support to give a dry coating weight of 0.24 gm/ft2.
The co~tingc were dried for four minutes at 180F (82C).
The photothermographic element was imaged by exposing with a laser sensitometer at 813 nm using an infra-red light source. After exposure, the strips 10 (1.0 inch x 7 inches; 2.5 cm x 17.8 cm) were processed at 255F (121C) by heating for 15 seconds on a hot roll processor.
Sensitometry measurements were made on a custom-built computer-scanned densitometer and are believed to be comparable to measurements obtainable from commercially available densitometers.
The photothermographic elements were stored in the dark at room temperature for 1 day and for 7 days before im~gin~ These samples are referred to herein as 1 day and 7 day naturally aged samples.
Sensitometric evaluation results for the I day naturally aged samples, shown below, demonstrate that incorporation of hydantoin compounds into photothermo-20 graphic elements provides improved Dmin stability toward shelf-aging fog.
1 Day Shelf-Aging Stability Results ComPound/Amount Dmin Dmax SPeed Hydantoin 0.0000 g 0.63 4.14 1.70 0.0040 g 0.53 4.50 1.83 0.0160 g . 0.50 4.16 1.89 0.0800 g 0.44 4.43 2.10 l-Methylhydantoin 0.0000 g 0.63 4.14 1.70 0 0045 g 0.50 4.57 1.80 0.0182 g 0.47 4.43 1.87 0.0900 g 0.40 4.59 1.97 ~1 7318.~

-5-Hydantoin-acetic acid 0.0000 g 0.63 4.14 1.70 0.0063 g 0.40 4.11 1.74 0.0250 g 0.36 4.10 1.76 50.1260 g 0.31 3.77 1.78 5,5-Dimethylhydantoin 0.0000 g 0.63 4.14 1.70 0.0051 g 0.37 4.64 1.78 100.0200 g 0.31 4.56 1.79 0.1024 g 0.29 4.48 1.84 5-Methyl-5-phenylhydantoin 0.0000 g 0.63 4.14 1.70 150.0076 g 0.37 4.88 1.83 0.0300 g 0.31 4.60 1.88 0.1520 g 0.26 4.25 1.92 5-(4-Methylphenyl)-5-phenylhydantoin 200.0000 g 0.63 4.14 1.70 0.0106 g 0.32 4.57 1.78 0.0420 g 0.29 4.35 1.78 0.2120 g 0.24 4.15 1.84 255,5-Diphenylhydantoin 0.0000 g 0.63 4.14 1.70 0.0041 g 0.29 4.67 1.78 0.0165 g 0.26 4.35 1.78 0.1214 g 0.24 4.15 1.80 30 Speed is log lIE + 4 needed to achieve a density of 0.6 above Dmin. E is the exposure in ergs/cm2. In these samples, the higher the speed number, the "faster"
the film.
Sensitometric results for the 7 day naturally aged samples, shown below, again demonstrate that addition of hydantoin compounds provides improved 35 stabilization against shelf-aging fog. In addition, the hydantoin compounds provided a speed enhancernent of from 0.04 to 0.40 Log E over the 1 day naturally aged samples.

21731~

-7-Day Shelf-Aging Stability Results Compound/Amount Dmin Dmax Seed *
~Iydantoin 0.0000 g 1.12 3.81 1.53 S0.0040 g 0.63 4.90 1.88 0.0160 g 0.55 4.71 1.80 0.0800 g 0.49 4.01 2.00 1-Methylhydantoin 100.0000 g 1.12 3.81 1.53 0.0045 g 0.60 4.78 1.74 0.0182 g 0.54 4.29 1.75 0.0900 g 0.49 4.14 1.79 155-~Iydantoin-acetic acid 0 0000 g 1.12 3.81 1.53 0.0063 g 0.45 4.56 1.77 0.0250 g 0.40 4.29 1.78 0.1260 g 0.36 4.14 1.80 5,S-Dimethylhydantoin 0.0000 g 1.12 3.81 1.53 0.0051 g 0.42 4.68 1.80 0.0200 g 0.37 4.54 1.82 250.1024 g 0.33 4.42 1.87 5-Methyl-5-phenylhydantoin 0.0000 g 1.12 3.81 1.53 0.0076 g 0.42 4.68 1.79 300.0300 g 0.37 4.51 1.82 0.1520 g 0.32 3.86 1.89 5-(4-Methylphenyl)-5-phenylhydantoin 0.0000 g 1.12 3.81 1.53 350.0106 g 0.40 4.48 1.79 0.0420 g 0.37 4.60 1.79 0.2120 g 0.28 3.99 1.82 5,5-Diphenylhydantoin 400.0000 g 1.12 3.81 1.53 0.0041 g 0.32 4.57 1.73 0.0165 g 0.28 4.30 1.73 0.1214 g 0.25 4.10 1.75 Speed is log 1/E + 4 needed to achieve a density of 0.6 above Dmin. E is the 45 exposure in ergs/cm2. In these samples, the higher the speed number, the "faster"
the film.

~17318~

-The samples that had been naturally aged for 1 day were used to test post-processing print stability. The optical density of the samples were measured on a MacBeth TR 924 Densitometer using the additive blue filter. Samples were then placed in a heat and light chamber controlled to 45C and 20% RH for 10 hours atS 1200 foot-candles illl-minAtion After 72 hours the samples were removed and their optical density rçrne~eured on the MacBeth TR 924 Densitometer.
The sensitometric results, shown below, demonstrate that the hydantoin compounds of this invention provide improved post-processing print stability. In all caes, the print stability improved as the amount of hydantoin compound was 10 increased. For example, the addition of 5-(4-methylphenyl)-5-phenylhydantoin resulted in print stability improvements of from 13% (upon addition of 0.0106 g) to 50% (upon addition of 0.2120 g). ~Dmin is Dmin (Final) - Dmin (Initial).
Post-Processing Print Stability ComPound/Amount ~ Dmin Hydantoin 0.0000 g 0.30 0 g 0.26 0.0160 g 0.24 0.0800 g 0.21 201-Methylhydantoin 0.0000 g 0.30 0 0045 g 0.20 0.0182 g 0.18 0.0900 g 0.17 255-Hydantoin-acetic acid 0.0000 g 0.30 0.0063 g 0.22 0.0250 g 0.20 0.1260 g 0.19 305,5-Dimethylhydantoin 0.0000 g 0.30 0.0051 g 0.21 0.0200 g 0.19 0.1024 g 0.18 -5-methyl-5-phenylhydantoin 0.0000 g 0.30 0.0076 g 0.22 0.030 0.21 0.1520g 0.18 5-(4-Methylphenyl)-5-phenylhydantoin 0.0000 g 0.30 0.0106 g 0.26 0.0420 g 0.19 0.2120 g 0.15 5,5-Diphenylhydantoin 0.0000 g 0.30 0.0041 g 0.26 0.0165 g 0.20 0.1214 g 0.17 Example 2 A 13.6 wt % emulsion of silver bçh~n~te/behenic acid half soap was made in acetone by homogenization. To 201.5 g of this emulsion was added 1.12 g of ButvarTM B-76 polyvinyl butyral and the mixture was stirred for 30 minutes Three1.00 mL aliquots of a solution of 10.0 g zinc bromide in 100.0 mL meth~nol were added sequentially with stirring for 10 minutes after each addition. Toluene (66.66 g) was added and the mixture was stirred for an additional 15 minutes A
solution (2.40 mL) cont~ining 4.00 g of pyridine in 100 mL 2-butanone was added with continued stirring for 15 minutes The emulsion was allowed to stand for 4 hours at room temperature.
To this emulsion was added 31.75 g of ButvarTM B-76 polyvinyl butyral and the emulsion stirred for 30 minutes. This was followed by the addition of 2.73 mL
of a solution of 1.33 g N-bromosuccinimide (NBS) in 100 mL meth~nol. CAOTM 5 (4.20 g) was added with stirring for 5 mimltes AcryloidTM A-21 (27.22 g) was added with stirring for 5 minutes The following steps were carried under green safe lights. A 6.00 mL aliquot of a solution of 0.03 g of Sçn~iti7ing Dye-2 in 25.00 mL of meth~nol and 75 mL of toluene was added to the above emulsion and the mixture was stirred for 5 minutes The viscosity of the resultant solution should be between 180 and 220 centipoise. If greater than 220 centipoise, acetone should be added to bring the viscosity into the ~ :~ 7~185 applopliate range. If the viscosity is greater than 220 centipoise, acetone should be added to bring the viscosity into the desired range. The photothermographic emulsion was coated at 4.4 mil (112 ~lm) wet th;c~ness onto paper and dried at 180F (82.2C) for one minute.to give a dry coating weight of 1.25 gm/ft2.
S A master batch of topcoat solution was prepared by mixing 164.728 g of acetone, 82.350 g of 2-butanone, 33.300 g of methanol, 13.500 g of CA 398-6 cellulose acetate, 1.542 g of phth~l~7.ine (PHZ), 1.068 g of 4-methylphthalic acid (4-~A), 0.636 g oftetrachlorophthalic acid, and 0.800 g oftetrachlorophthalic anhydride.
T hree levels of 5,S-diphenylhydantoin was ev~hl~ted by addition to a 7.00 g aliquot of the master batch of topcoat solution before coating. The samples werethen placed in an ultrasonic bath for 20 min~ltes. All solutions were dec~nted to remove any materials that were not soluble.
The topcoat formulation was coated at 2.8 mil (71 ~m), wet thickness, on top ofthe silver emulsion and dried for 3 min~tes at 70C to provide a dry coating weight of 0.24 gm/ft2.
The coated paper was imaged by exposing a sample with a photometric sensitometer equipped with an F~etm~n Kodak #101 t~lngeten light source. After exposure, the strips (1 inch x 7 inches; 2.5 cm x 17.8 cm) were processed at 250F
(121C) by heating for 6 seconds in a hot roll processor.
Sensitometry measurements were made on a custom-built computer-sc~nned densitometer and are believed to be comparable to measurements obtainable from commercially available densitometers.
Sensitometric results for the 1 day naturally aged samples, shown below, demonstrate that addition of hydantoin compounds provide improved Dmin stabilitytowards shelf-aging fog. The Dmin improvement was from 79% (0.0041g) to 84%
(0.1214 g). The use of S,S-diphenylhydantoin shows that speed was enh~nced from a range of 0.03 to 0.14 Log E.

~173185 -l-Day Shelf-Aging Stability Results ComPound/Amount Dmin Dmax SPeed 5,5-Diphenylhydantoin 0.0000 g 0.70 1.78 0.79 0.0041 g 0.15 1.71 0.76 0.0165 g 0.15 1.69 0.70 0.1214 g 0.11 1.68 0.65 Speed is log E needed to achieve a density of 0.6 above Dmin. E is the exposure in ergstcm2. In these samples, the higher the speed number, the "slower" the film.
Sensitometric results for the 7 day naturally aged samples, shown below, again demonstrate that addition of 5,5-diphenylhydantoin provides improved stabilization against shelf-aging fog.
7-Day Shelf-Aging Stability Results ComPound/Amount Dmin Dmax Speed^
1 5 5,5-Diphenylhydantoin 0.0000 g 0.85 Highly Fogged 0.0041 g 0.14 1.65 0.78 0.0165 g 0.13 1.62 0.73 0.1214 g 0.10 1.60 0.69 20 Speed is log E needed to achieve a density of 0.6 above Dmin. E is the exposure in ergs/cm2. In these samples, the higher the speed number, the "slower" the film.
Reasonable modifications and variations are possible from the foregoing disclosure without departing from either the spirit or scope of the present invention as defined by the claims.

Claims (20)

1. A photothermographic element comprising a support bearing at least one photosensitive image-forming photothermographic emulsion layer comprising:
(a) a photosensitive silver halide;
(b) a non-photosensitive, reducible source of silver;
(c) a reducing agent for the non-photosensitive, reducible source of silver;
(d) a binder; and (e) a hydantoin compound.

2. The photothermographic element according to Claim 1 wherein the hydantoin compound has the formula:

wherein:
R1 and R2 independently represent hydrogen, alkyl groups of up to 20 carbon atoms, alkenyl groups of up to 20 carbon atoms, aryl groups of up to 14 carbon atoms, aralklyl groups of up to 14 carbon atoms, carboxy-alkyl groups of up to 10 carbon atoms, alkoxycarbonyl groups of up to 12 carbon atoms, a cylcoalkyl group of up to 7 carbon atoms, a carboxyl group; or R1 and R2 taken together represent the necessary atoms to complete a 5-, 6-, or 7-membered carbocyclic or heterocyclic ring; and R3 and R4 independently represent hydrogen, alkyl groups of up to 20 carbon atoms, alkenyl groups of up to 20 carbon atoms, aryl groups of up to 14 carbon atoms, arylalkyl groups of up to 20 carbon atoms, a cycloalkyl group of up to 7 carbon atoms, a carboxyl group; a hydroxyl group, or a 5-, 6-, or 7-membered carbocyclic or heterocyclic ring group.

3. The photothermographic element according to Claim 1 wherein the hydantoin compound is selected from the group consisting of: hydantoin, 1-methyl-hydantoin, 5-hydantoin-acetic acid, 5,5-dimethylhydantoin, 5-methyl-5-phenyl-hydantoin, 5-(4-methylphenyl)-5-phenylhydantoin, and 5,5-diphenylhydantoin.

4. The photothermographic element according to Claim 1 wherein the hydantoin compound comprises from about 0.1 wt% to 50 wt% of the dried layer of the photothermographic element in which it is placed.

5. The photothermographic element according to Claim 1 wherein the hydantoin compound comprises from about 1.0% to about 30% of the dried layer of the photothermographic element in which it is placed.

6. The photothermographic element according to Claim 1 wherein the silver halide is silver bromide, silver chloride, silver iodide, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide, or mixtures thereof.

7. The photothermographic element according to Claim 1 wherein said non-photosensitive, reducible source of silver is a silver salt of a C1 to C30 carboxylic acid.

8. The photothermographic element according to Claim 3 wherein said non-photosensitive silver source is silver behenate.

9. The photothermographic element according to Claim 1 wherein said reducing agent is a compound capable of being oxidized to form or release a dye.

10. The photothermographic element according to Claim 9 wherein said compound capable of being oxidized to form or release a dye is a leuco dye.

11. The photothermographic element according to Claim 1 wherein said binder is hydrophilic.

12. The photothermographic element according to Claim 1 wherein said binder is hydrophobic.

13. The photothermographic element according to Claim 1 wherein said reducing agent is a hindered phemol.

14. The photothermographic element of Claim 13 wherein said hindered phenol is selected from the group consisting of binaphthols, biphenols, bis(hydroxy-naphthyl)methanes, bis(hydroxyphenyl)methanes, hindered phenols, and naphthols.

15. The photothermographic element of Claim 14 wherein said hindered phenol is a bis(hydroxyphenyl)methane.

16. A process for the formation of a visible image comprising exposing the photothermographic element of Claim 1 to light to form a latent image and subsequently heating said exposed element.

17. A process comprising the steps of:
(a) exposing the photothermographic element of Claim 1 to electro-magnetic radiation, to which the silver halide grains of the element are sensitive, to generate a latent image;
(b) heating the exposed element to develop the latent image into a visible image;
(c) positioning said element with a visible image thereon between a source of ultraviolet or short wavelength visible radiation and an ultraviolet or short wavelength visible radiation photosensitive imageable medium; and (d) then exposing said ultraviolet or short wavelength visible radiation sensitive imageable medium to ultraviolet or short wavelength visible radiation through said visible image on said element, thereby absorbing ultraviolet or short wavelength visible radiation in the areas of said element where there is a visible image and transmitting ultraviolet or short wavelength visible radiation where there is no visible image on said element.

18. The process of claim 17 wherein said imageable medium is a resist developable, ultraviolet or short wavelength visible radiation sensitive imageable medium.

19. The process of claim 17 wherein said exposing of said element in step (a) is done with a red or infrared emitting laser or red or infrared emitting laser diode.

20. The process of claim 17 wherein said ultraviolet or short wavelength visible radiation sensitive imageable medium is a printing plate, a contact proof, or a duplicating film.