Chemical sensitization of photothermographic silver halide emulsions

Chemical sensitization of silver halide photothermographic emulsions used in photothermographic elements, can be effected by the decomposition of sulfur containing compounds on or around the surface of the silver halide grains, usually under oxidizing conditions at elevated temperatures. Alignment of the sulfur containing compounds on the surface of the grains, can be accomplished with spectral sensitizing dyes and appears to be particularly effective in providing strong chemical sensitization effects.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
This invention relates to the chemical sensitization of silver halide 
photothermographic emulsions. 
2. Background of the Art 
Silver halide-containing photothermographic imaging 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 also known as "dry silver" compositions or emulsions and 
generally comprise a support having coated thereon: (a) a photosensitive 
compound that generates silver atoms when irradiated; (b) a relatively or 
completely non-photosensitive, reducible silver source; (c) a reducing 
agent (i.e., a developer) for silver ion, for example the silver ion in 
the non-photosensitive, reducible silver source; and (d) a binder. 
Photographic silver halide has its own natural response to radiation, both 
in wavelength (i.e., spectral sensitivity) and efficiency (i.e., speed). 
Each of the various pure halides (silver bromide, silver chloride and 
silver iodide) have their own distinctive wavelengths of sensitivity 
within the UV, near UV and blue regions of the electromagnetic spectrum. 
The primary halides used in the formation of photographic silver halides 
are the chlorides and bromides, with the iodides present as minor 
proportions, almost always less than 25 molar percent of the total crystal 
composition. Mixtures of the various silver halides within single grains 
(e.g., silver chlorobromide, silver chloroiodide, silver 
bromochloroiodide, silver iodobromide, etc.) would have sensitivities to 
various different regions of the electromagnetic spectrum, but still 
within the UV to blue region of the spectrum. The silver halide grains, 
when constructed and composed of only silver and halogen atoms would also 
have defined levels of sensitivity based upon their halide content, 
crystalline morphology (the shape and structure of the crystals or 
grains), and other artifacts which may or may not have been readily 
controlled by the silver halide chemist over the years. Such features as 
crystal defects, crystal stresses, dopants, halide composition, and other 
structural features have been noted as influential on the sensitometric 
response of grains and have been purposefully introduced over the years to 
affect the sensitometry of the emulsions. 
The efforts to influence the speed of silver halide grains in general may 
be broken down into the following categories: 
1) Crystal composition, 
2) Crystal shape or morphology, 
3) Crystal structure, 
4) Chemical sensitization (and particularly sulfur sensitization), 
5) Reduction sensitization, 
6) Dopants, 
7) Spectral sensitization, and 
8) Supersensitization. 
The first three mechanisms have been briefly described above. 
Chemical sensitization is a process during the crystal making process in 
which sensitizing specks of materials such as silver salts (e.g., Ag.sub.2 
S) or even silver metal are introduced onto (usually) or into the 
individual grains. The introduction of silver sulfide specs, for example, 
is usually done by direct reaction of active sulfur contributing compounds 
with the silver halide during various stages in the silver halide growth 
process. The presence of the specks increases the speed or sensitivity of 
the grains to light and/or development. The first observation of sulfur 
sensitization came from early findings that different gelatin binders 
would often produce different degrees of sensitivity in silver halide 
emulsions, so the source of the speed increasing component was 
investigated and found to be sulfur contributing compounds. Thiosulfate 
compounds are still typically used as a labile sulfur compound. Other 
materials such as allylthiourea are also used. Certain studies (e.g., by 
Sheppard, Trevelli and Wightman J. Franklin Inst., 1923, 196, 653,673) 
using micrography, found that the treatment of silver halide grains with 
allylthiourea solution followed by carbonate solution resulted in the 
formation of black specks rather than a distribution of silver halide over 
the grain surface (Mees and James, The Theory of the Photographic Process, 
4th edition, 1977, p. 152.). It has also been suggested that the thiourea 
rearranges itself on the surface of the grains to active configurations in 
the generation of silver sulfide specks (Mees and James, supra, p. 153). 
It has also been suggested that the thiosulfate acts to sensitize the 
silver halide by AgSO.sub.3.sup.- adsorbed to the crystal surface. 
Reduction sensitization is somewhat similar to chemical sensitization, but 
distinguishable therefrom, and is a process by which other chemical 
species, besides silver sulfide, are deposited or reacted into or onto the 
silver halide grains during a segment of the silver halide grain growth 
and finishing steps. The term reduction sensitization, although 
generically considered within the term of chemical sensitization, refers 
specifically to describe emulsions sensitized by the action of reducing 
agents on the silver halide grains. Materials which have been used as 
reduction sensitizers include stannous chloride, hydrazine, ethanolamine, 
and thioureaoxide. 
Dopants most importantly include gold sensitization where the silver halide 
grains are treated with gold containing ions such as tetrachloroaurate 
(III) or dithiocyanurate(I). Thiocyanate has been suggested as being 
capable of increasing gold sensitization (Mees and James, supra, p.155). 
The gold is most preferably added at the later stages of silver halide 
grain formation, such as during ripening, after grain growth. Other metals 
such as platinum and palladium are also known in the art to have some 
effects similar, but not as specifically beneficial as gold. Still other 
metal dopants such as iridium, rhodium, ruthenium and the like are known 
more for contrast or high intensity reciprocity effects than for speed 
sensitization effects. 
Spectral sensitization is the addition of compounds to silver halide grains 
which absorb radiation at wavelengths other than those to which silver 
halide is naturally sensitive (i.e., only within the UV to blue) or which 
absorb radiation more efficiently than silver halide (even within those 
natural regions of spectral sensitivity). It is generally recognized that 
spectral sensitizers extend the responses of photosensitive silver halide 
to longer wavelengths and can accomplish spectral sensitization in the UV, 
visible or infrared regions of the electromagnetic spectrum. These 
compounds, after absorption of the radiation, transfer energy to the 
silver halide grains to cause the necessary local photoinduced reduction 
of silver salt to silver metal. The compounds are usually dyes, and the 
best method of spectrally sensitizing silver halide grains causes or 
allows the dyes to align themselves on the surface of the silver halide 
grain, particularly in a stacked, almost crystalline pattern on the 
surface of the individual grains. 
Supersensitization is a process whereby the speed of a spectrally 
sensitized photographic silver halide is increased by the addition of 
another compound, which may or may not be a dye. This is not merely an 
additive effect of two compounds, as it is understood in the art. For 
example, where two separate dyes are used, one as the spectral sensitizer 
and the other as a supersensitizer, the surface of the grain still may not 
have more than a defined amount of dye present, yet the combination of the 
two dyes will provide a speed which is superior to that of either dye 
alone, even when optimized. 
These various speed enhancing processes may of course be combined in the 
formulation of a specific photographic emulsion, as the situation 
requires. 
In photothermographic emulsions, the photosensitive compound is generally 
photographic silver halide which must be in catalytic proximity to the 
non-photosensitive, reducible silver source. Catalytic proximity requires 
an intimate physical association of these two materials so that when 
silver atoms (also known as silver specks, clusters, or nuclei) are 
generated by irradiation or light exposure of the photographic silver 
halide, those nuclei are able to catalyze the reduction of the reducible 
silver source within a catalytic sphere of influence around the silver 
specs. It has long been understood that silver atoms (Ag.degree.) are a 
catalyst for the reduction of silver ions, and that the photosensitive 
silver halide can be placed into catalytic proximity with the 
non-photosensitive, reducible silver source in a number of different 
fashions. The silver halide may be made "in situ," for example by adding a 
halogen-containing source to the reducible silver source to achieve 
partial metathesis (see, for example, U.S. Pat. No. 3,457,075); or by 
coprecipitation of silver halide and the reducible silver source (see, for 
example, U.S. Pat. No. 3,839,049). The silver halide may also be 
pre-formed (i.e., made "ex situ") and added to the organic silver salt. 
The addition of silver halide grains to photothermographic materials is 
described in Research Disclosure, June 1978, Item No. 17029. The reducible 
silver source may also be generated in the presence of these ex situ, 
pre-formed silver halide grains. It is reported in the art that when 
silver halide is made ex situ, one has the possibility of controlling the 
composition and size of the grains much more precisely, so that one can 
impart more specific properties to the photothermographic element and can 
do so much more consistently than with the in situ technique. 
The non-photosensitive, reducible silver source is a compound that contains 
silver ions. Typically, the preferred non-photosensitive reducible silver 
source is a silver salt of a long chain aliphatic carboxylic acid having 
from 10 to 30 carbon atoms. The silver salt of behenic acid or mixtures of 
acids of similar molecular weight are generally used. Salts of other 
organic acids or other organic compounds, such as silver imidazolates, 
have been proposed. U.S. Pat. No. 4,260,677 discloses the use of complexes 
of inorganic or organic silver salts as non-photosensitive, reducible 
silver sources. 
In both photographic and photothermographic emulsions, exposure of the 
photographic silver halide to light produces small clusters of silver 
atoms (Ag.degree.). 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 photosensitive emulsion must be further 
processed to produce a visible image. This is accomplished by the 
reduction of silver ions which are in catalytic proximity to silver halide 
grains bearing the clusters of silver atoms, (i.e., the latent image). 
This produces a black and white image. In photographic elements, the 
silver halide is reduced to form the black-and-white negative image in a 
conventional black-and-white negative imaging process. In 
photothermographic elements, the light-insensitive silver source is 
reduced to form the visible black-and-white negative image while much of 
the silver halide remains as silver halide and is not reduced. 
The reducing agent for silver ion of the light-insensitive silver salt, 
often referred to as a "developer," may be any compound, preferably any 
organic compound, that can reduce silver ion to metallic silver, and is 
preferably of relatively low activity until it is heated to a temperature 
above 100.degree. C. At elevated temperatures, in the presence of the 
latent image, the non-photosensitive reducible silver source (e.g., silver 
behenate) is reduced by the reducing agent for silver ion. This produces a 
negative black-and-white image of elemental silver. 
While conventional photographic developers such as methyl gallate, 
hydroquinone, substituted-hydroquinones, catechol, pyrogallol, ascorbic 
acid, and ascorbic acid derivatives are useful, they tend to result in 
very reactive photothermographic formulations and fog during preparation 
and coating of photothermographic 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 elemental silver (Ag.degree.), one cannot 
readily decrease the amount of silver in the emulsion without reducing the 
maximum image density. However, reduction of the amount of silver is often 
desirable to reduce the cost of raw materials used in the emulsion and/or 
to enhance 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. Pat. 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-releasing 
compounds in the emulsion. Upon imaging, the dye-forming or dye-releasing 
compound is oxidized, and a dye and a reduced silver image are 
simultaneously 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 elements and processes are described in, for example, 
U.S. Pat. No. 5,185,231. 
Many cyanine and related dyes are well known for their ability to impart 
spectral sensitivity to a gelatino silver halide element. The wavelength 
of peak sensitivity is a function of the dye's wavelength of peak light 
absorbance. While many such dyes provide some spectral sensitization in 
photothermographic formulations, the dye sensitization is often very 
inefficient and it is not possible to translate the performance of a dye 
in gelatino silver halide elements to photothermographic elements. The 
emulsion making procedures and chemical environment of photothermographic 
elements are very harsh compared to those of gelatino silver halide 
elements. The presence of large surface areas of fatty acids and fatty 
acid salts restricts the surface deposition of sensitizing dyes onto 
silver halide surfaces and may remove sensitizing dye from the surface of 
the silver halide grains. The large variations in pressure, temperature, 
pH and solvency encountered in the preparation of photothermographic 
formulation aggravate the problem. Thus sensitizing dyes which perform 
well in gelatino silver halide elements are often inefficient in 
photothermographic formulations. In general, it has been found that 
merocyanine dyes are superior to cyanine dyes in photothermographic 
formulations as disclosed, for example, in British Patent No 1,325,312 and 
U.S. Pat. No. 3,719,495. Recently, certain cyanine dyes have been 
disclosed as spectral sensitizers for use in photothermographic elements. 
For example, U.S. Pat. Nos. 5,441,866 and 5,541,054 describe 
photothermographic elements spectrally sensitized with benzothiazole 
heptamethine dyes substituted with various groups, including alkoxy and 
thioalkyl. 
Although spectral sensitizing dyes for photothermographic elements are now 
known which absorb throughout the visible and near-infrared regions (i.e., 
400-850 nm) photothermographic emulsions which provide higher photospeeds 
and which have improved shelf-life stability, sensitivity, contrast and 
low Dmin are still needed for photothermography. 
U.S. Pat. No. 4,207,108 (Hiller) describes improved speed in 
photothermographic materials by addition of a photographic speed 
increasing concentration of a certain non-dye, thione speed increasing 
addendum (including compounds with cyclic thiocarbonyl &gt;C.dbd.S! groups 
within the cyclic structure). No decomposition of the cyclic thione 
compounds is reported. 
U.S. Pat. No. 5,541,055 (Ooi et al.) describes photothermographic elements 
which comprise both a cyanine dye and a colorless cyclic carbonyl 
compound. Rhodanine, hydantoin, barbituric acid, or derivatives thereof 
(all shown to be monocyclic in columns 4-6) are particularly preferred as 
the colorless cyclic carbonyl compound. 
The recent commercial availability of relatively high powered semiconductor 
light sources, and particularly laser diodes which emit in the red and 
near-infrared region of the electromagnetic spectrum, as sources for 
output of electronically stored image data onto photosensitive film or 
paper is becoming increasingly widespread. This has led to a need for high 
quality imaging articles which are sensitive at these wavelengths and has 
created a need for more highly sensitive photothermographic elements to 
match such exposure sources both in wavelength and intensity. Such 
articles find particular utility in laser scanners. 
Differences Between Photothermography and Photography 
The imaging arts have long recognized that the field of photothermography 
is clearly distinct from that of photography. Photothermographic elements 
differ significantly from conventional silver halide photographic elements 
which require wet-processing. 
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 essential for development and temperatures of over 
100.degree. C. are routinely required. In contrast, conventional 
wet-processed photographic imaging 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 temperature 
(e.g., 30-50.degree. C.). 
In photothermographic elements only a small amount of silver halide is used 
to capture light and a different 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 physical development of the non-photosensitive, reducible 
silver source. In contrast, conventional wet-processed black-and-white 
photographic elements use only one form of silver (e.g., silver halide); 
which, upon chemical development, is itself converted to the silver image; 
or which upon physical development requires addition of an external silver 
source. Additionally, photothermographic elements require an amount of 
silver 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-insensitive silver salt, such as 
silver behenate, which participates with the developer in developing the 
latent image. In contrast, chemically developed photographic systems do 
not employ a light-insensitive silver salt directly in the image-forming 
process. As a result, the image in photothermographic elements is produced 
primarily by reduction of the light-insensitive silver source (silver 
behenate) while the image in photographic black-and-white elements is 
produced primarily by the silver halide. 
In photothermographic elements, all of the "chemistry" of the system is 
incorporated within the element itself. For example, photothermographic 
elements incorporate a developer (i.e., a reducing agent for the 
non-photosensitive reducible 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 chemistry is physically separated from 
the photosensitive silver halide until development is desired. Much effort 
has gone into the preparation and manufacture of photothermographic 
elements to minimize formation of fog upon coating, storage, and 
post-processing aging. 
Similarly, in photothermographic elements, the unexposed silver halide 
inherently remains after development and the element must be stabilized 
against further development. In contrast, the silver halide is removed 
from photographic elements after development to prevent further imaging 
(i.e., the fixing step). 
In photothermographic elements the binder is capable of wide variation and 
a number of binders are useful in preparing these elements. In contrast, 
photographic elements are limited almost exclusively to hydrophilic 
colloidal binders such as gelatin. 
Because photothermographic elements require thermal processing, they pose 
different considerations and present distinctly different problems in 
manufacture and use. In addition, the effects of additives (e.g., 
stabilizers, antifoggants, speed enhancers, sensitizers, supersensitizers, 
etc.) which are intended to have a direct effect upon the imaging process 
can vary depending upon whether they have been incorporated in a 
photothermographic element or incorporated in a photographic element. 
Because of these and other differences, additives which have one effect in 
conventional silver halide photography may behave quite differently in 
photothermographic elements where the underlying chemistry is so much more 
complex. For example, it is not uncommon for an antifoggant for a silver 
halide system to produce various types of fog when incorporated into 
photothermographic elements. 
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; in 
Unconventional Imaging Processes; E. Brinckman et al, Ed; The Focal Press: 
London and New York: 1978, pp. 74-75; and in C. Zou, M. R. V. Shayun, B. 
Levy, and N. Serpone J. Imaging Sci. Technol. 1996, 40, 94-103. 
SUMMARY OF THE INVENTION 
The present invention provides a method for chemically sensitizing silver 
halide grains in a photothermographic emulsion. The method comprises the 
steps of: 
(a) providing a photothermographic emulsion comprising silver halide grains 
and a non-photosensitive silver source; 
(b) providing a sulfur-containing compound positioned on or around the 
silver halide grains; 
(c) sensitizing the silver halide grains by decomposing the 
sulfur-containing compound on or around the silver halide grains. 
The present invention also provides chemically sensitized silver halide 
photothermographic emulsions prepared by the method described above. 
The present invention provides a method of making a photothermographic 
element comprising: 
(a) preparing a chemically sensitized photothermographic emulsion as 
described above; 
(b) adding a reducing agent and a binder to the photothermographic 
emulsion; 
(c) coating the photothermographic emulsion on a substrate. 
The present invention also provides a photothermographic element 
(black-and-white or color) prepared by the method described above. 
The present invention additionally provides a method for chemically 
sensitizing silver halide grains comprising the steps of: 
(a) providing silver halide grains; 
(b) providing a sulfur-containing compound on or around the surface of 
silver halide grains; 
(c) decomposing the sulfur-containing compound thereby chemically 
sensitizing said grains. 
The chemically sensitized photothermographic elements of this invention can 
be used, for example, in conventional black-and-white, monochrome, or full 
color photothermography; in electronically generated black-and-white or 
color hardcopy recording; in the graphic arts area (e.g., 
phototypesetting); in digital proofing; and in digital radiographic 
imaging. The chemically sensitized photothermographic elements of this 
invention provide high photospeed; with stable, strongly absorbing, high 
density, black-and-white or color images of high resolution and good 
sharpness; and provide a dry and rapid process. 
When the photothermographic elements of this invention are imagewise 
exposed and then heat developed, preferably at a temperature of from about 
80.degree. C. to about 250.degree. C. (176.degree. F. to 482.degree. F.) 
for a duration of from about 1 second to about 2 minutes, in a 
substantially water-free condition, a (black-and-white or 
color-containing) silver image is obtained. 
Heating in a substantially water-free condition as used herein, means 
heating at a temperature of 80.degree. to 250.degree. C. with little more 
than ambient water vapor present. The term "substantially water-free 
condition" means that the reaction system is approximately in equilibrium 
with water in the air, and water for inducing or promoting the reaction is 
not particularly or positively supplied from the exterior to the element. 
Such a condition is described in T. H. James, The Theory of the 
Photographic Process, Fourth Edition, Macmillan 1977, page 374. 
As used herein: 
"Photothermographic element" means a construction comprising at least one 
photothermographic emulsion layer or a two trip photothermographic set of 
layers (the "two-trip coating where the silver halide and the reducible 
silver source are in one layer and the other essential components or 
desirable additives are distributed as desired in an adjacent coating 
layer) and any supports, topcoat layers, image-receiving layers, blocking 
layers, antihalation layers, subbing or priming layers, etc. 
"emulsion layer" means a layer of a photothermographic element that 
contains the non-photosensitive, reducible 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 (sometimes marginally inclusive up to 405 or 410 nm, although these 
ranges are often visible to the naked human eye), 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; 
"infrared region of the spectrum" means from about 750 nm to about 1400 nm; 
preferably from about 750 nm to about 1000 nm. 
"visible region of the spectrum" means from about 400 nm to about 750 nm; 
and 
"red region of the spectrum" means from about 600 nm to about 750 nm. 
Preferably the red region of the spectrum is from about 630 nm to about 
700 nm. 
As is well understood in this area, substitution is not only tolerated, but 
is often advisable and substitution is anticipated on the sulfur 
containing chemical sensitizing compounds used in the present invention. 
In the compounds disclosed herein, when a general structure is referred to 
as "a compound having the central nucleus" of a given formula, any 
substitution which does not alter the bond structure of the formula or the 
shown atoms within that structure is included within the formula, unless 
such substitution is specifically excluded by language (such as "free of 
carboxy-substituted alkyl"). For example, where there is a rigidized 
polymethine chain shown between two defined benzothiazole groups, 
substituent groups may be placed on the chain, on the rings in the chain, 
or on the benzothiazole groups, but the conjugation of the chain may not 
be altered and the atoms shown in the chain or in the benzothiazole groups 
may not be replaced. 
When a general structure is referred to as "a general formula" it 
specifically allows for such broader substitution of the structure. When a 
general structure is referred to as having "the formula" it is more 
limited and allows only such conventional substitution as would be 
recognized as equivalents or by one skilled in the art (e.g., shifts 
wavelengths of absorbance, changes solubility, stabilizes the molecule, 
etc.). 
As a means of simplifying the discussion and recitation of certain 
substituent groups, the terms 1) "group" and 2) "compound" or "moiety" are 
used to differentiate between those chemical species that may be 
substituted and those which may not be so substituted. Thus, when the term 
"group," such as "aryl group," is used to describe a substituent, that 
substituent includes the use of additional substituents beyond the literal 
definition of the basic group. Where the term "moiety" is used to describe 
a substituent, only the unsubstituted group is intended to be included. 
For example, the phrase, "alkyl group" is intended to include not only 
pure hydrocarbon alkyl chains, such as methyl, ethyl, propyl, t-butyl, 
cyclohexyl, iso-octyl, octadecyl and the like, but also alkyl chains 
bearing substituents known in the art, such as hydroxyl, alkoxy, phenyl, 
halogen atoms (F, Cl, Br, and I), cyano, nitro, amino, carboxy, etc. For 
example, alkyl group includes ether groups (e.g., CH.sub.3 --CH.sub.2 
--CH.sub.2 --O--CH.sub.2 --), haloalkyls, nitroalkyls, carboxyalkyls, 
hydroxyalkyls, sulfoalkyls, etc. On the other hand, the phrase "alkyl 
moiety" is limited to the inclusion of only pure hydrocarbon alkyl chains, 
such as methyl, ethyl, propyl, t-butyl, cyclohexyl, iso-octyl, octadecyl, 
and the like. Substituents that react with active ingredients, such as 
very strongly electrophilic or oxidizing substituents, would of course be 
excluded by the ordinarily skilled artisan as not being inert or harmless. 
Other aspects, advantages, and benefits of the present invention are 
apparent from the detailed description, examples, and claims. 
DETAILED DESCRIPTION OF THE INVENTION 
Chemical sensitization of photothermographic silver halide emulsions has 
been attempted for many years. Convention chemical sensitization 
treatments for wet processed silver halide emulsions have been tried 
unsuccessfully for photothermographic emulsions containing silver halide 
grains. The reasons for these failures are not completely understood, but 
to date, significant spectral sensitization has not been achieved, 
particularly in commercial quality materials. It is therefore surprising 
that in the practice of the present invention a novel chemical 
sensitization method is described which produces a significant and even 
high level of chemical sensitization in silver halide grains, which are 
observed in both wet processed photographic emulsions and dry processed 
photothermographic emulsions. 
Applicants believe that the process of the present invention may be most 
broadly described as providing a sulfur-containing compound on or about 
the surface of silver halide grains in a silver halide photothermographic 
or photographic emulsion and then decomposing the sulfur-containing 
compound. 
Decomposition of the sulfur-containing chemical sensitizing compound and/or 
the sources for the chemical sensitizing compounds is preferably carried 
out in an oxidizing environment by an oxidizing agent, preferably by a 
strong oxidizing agent. The oxidizing agent, and the preferably strong 
oxidizing agent must be strong enough to decompose the sulfur-containing 
compounds on the silver halide grains, and form the species that acts as 
the chemical sensitizer, either at ambient temperature or at temperatures 
up to about 40.degree. C., preferably up to about 30.degree. C. 
The efficiency of the chemical sensitization processes is influenced by the 
function of the decomposing (oxidizing) agent, the sulfur-containing 
sensitizing compound, the length of time of the reaction, and the 
temperature used. For example, when pyridinium perbromide hydrobromide 
(hereinafter PHP) is used as the oxidizing agent to decompose the 
sulfur-containing compound, it is preferred to use a temperature of from 
about 20.degree. C. to about 40.degree. C., preferably from about 
20.degree. C. to about 30.degree. C. for 30 minutes. More reactive 
oxidizing agents could be used at lower temperatures or for shorter 
periods of time (or a balance of the two), while less reactive oxidizing 
agents could be used at higher temperatures or for longer periods of time 
(or a balance of the two). 
Preferred oxidizing compounds include hydrobromic acid salts of 
nitrogen-containing heterocyclic ring compounds which are further 
associated with a pair of bromine atoms. These compounds are also known as 
quaternary nitrogen-containing rings which are associated with hydrobromic 
acid (HBr)-perbromide (Br.sub.2) as HBrBr.sub.2 !. Compounds of this type 
are described in U.S. Pat. No. 5,028,523 (Skoug) incorporated herein by 
reference. The heterocyclic ring group may be unsubstituted or further 
substituted with such groups as alkyl, alkoxy, and aryl groups, halogen 
atoms, hydroxy groups, cyano groups, nitro groups, and the like. Exemplary 
and preferred heterocyclic ring groups include pyridine, pyrolidone, 
pyrrolidinone, pyrolidine, phthalazinone, phthalazine, etc. A particularly 
preferred compound is pyridinium perbromide hydrobromide (PHP). 
The preferred materials for use as the sulfur-containing source or chemical 
sensitization compounds are compounds with sulfur atoms directly attached 
to cyclic rings within the structure, particularly dye structures, more 
preferably with at least some sulfur atoms attached or incorporated as 
thiocarbonyl groups (i.e., &gt;C.dbd.S) or as --S-- groups within the actual 
ring structure of the compounds. Compounds with both types of sulfur atom 
positioning i.e., both &gt;C.dbd.S and --S--; or --S--(C.dbd.S)--! are also 
desirable in the practice of the present invention. 
Many of the sulfur-containing chemical sensitization precursors or 
compounds are either dyes or have dye-like structures. These types of 
sulfur-containing compounds are preferred. They are preferred because 
their structure apparently allows them to be distributed on the surface of 
the silver halide grains in an orderly and regular manner. Additionally, 
the mechanisms for promoting the alignment of these types of compounds on 
the surface of silver halide grains is well understood in the art. 
Furthermore, the residual products of these types of compounds are well 
understood for their effects or non-effects on photographic and/or 
photothermographic silver halide grains and emulsions. Thus, less 
background structural design is needed in proposing or selecting a wide 
range of choices for these materials from the known available supply of 
chemical compounds. There are also many classes and types of these 
compounds known to the photographic and photothermographic chemist which 
contain sulfur groups. Nevertheless, it is clear that certain compounds 
within these classes which are not dyes and are not known as dyes, may be 
used in the practice of the present invention to form chemically 
sensitized grains prior to the formation of latent images on the silver 
halide grains. 
Particularly preferred sulfur containing chemical sensitizing compounds 
contain the thiohydantoin nucleus, rhodanine nucleus, and the 
2-thio-4-oxo-oxazolidine nucleus. These nuclei are shown below. 
##STR1## 
Representative sulfur containing chemical sensitizing compounds useful in 
the present invention and their methods of preparation and sources are 
known in the art. The presently preferred structures are shown below. 
These representations are exemplary and are not intended to be limiting. 
##STR2## 
Although a specific theory can not be absolutely proposed as the basis for 
chemical sensitization as described in the present invention, one possible 
explanation is that the sulfur-containing compound may align itself along 
the surface of the silver halide grains as commonly occurs with efficient 
spectral sensitizing dyes. This ordered arrangement of dyes on the surface 
of the grains acts as a template for chemical sensitization. Upon 
decomposition of the sulfur containing sensitization precursors or 
compounds, the residue or reaction product of the sulfur-containing 
chemical compound reacts locally with the silver halide grains to provide 
a more ordered and efficient distribution of sensitization sites on the 
silver halide grains. These sites may be in a form such as silver sulfide 
or silver specks. The more efficient distribution of these sensitizing 
sites on the silver grains provides a higher speed to the emulsion. 
For example, when decomposition is carried out by the preferred oxidizing 
agents (e.g., the PHP), they may react with the sulfur-containing 
compounds aligned on the surface of the silver halide grain to produce or 
generate a compound such as, for example, HSBr which will then in turn 
directly react with the surface of the silver halide grain to form the 
more ordered distribution of sensitization sites thereon. For the 
formation of compounds such as HSBr from bromine and sulfur compounds such 
as H.sub.2 S or NaHS see M. Schmidt, J. Lowe Angew. Chem. 1960, 72, 79 and 
V. A. Rimas, A. A. Sauka Uch. Zap. Rizhsk. Politekh. Inst. 1965, 16, 
229-203 (C.A. 1967, 67, 70148m). 
The Photosensitive Silver Halide 
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 chlorobromoiodide, silver chloroiodide, 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. 
The silver halide may be in any form which is photosensitive including, 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 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. Pat. No. 5,382,504. A core-shell silver 
halide grain having an iridium doped core is particularly preferred. 
Iridium doped core-shell grains of this type are described in U.S. Pat. 
No. 5,434,043. 
The silver halide may be prepared ex situ, (i.e., be pre-formed) and mixed 
with the organic silver salt in a binder prior to use to prepare a coating 
solution. The silver halide may be pre-formed for addition to the 
photothermographic system by any means, (e.g., in accordance with U.S. 
Pat. No. 3,839,049). Materials of this type are often referred to as 
"preformed emulsions." Methods of preparing these silver halide and 
organic silver salts and manners of blending them are described in 
Research Disclosure, June 1978, item 17029; U.S. Pat. Nos. 3,700,458 and 
4,076,539; and Japanese Patent Application Nos. 13224/74, 42529/76, and 
1721675. 
It is desirable in the practice of this invention with photothermographic 
elements to use pre-formed silver halide grains of less than 0.25 .mu.m, 
and preferably less than 0.12 .mu.m in a photothermographic element. Most 
preferably the number average particle size of the grains in a 
photothermographic element is between 0.01 and 0.09 .mu.m. It is also 
preferred to use iridium doped silver halide grains and iridium doped 
core-shell silver halide grains as disclosed in U.S. patent application 
Ser. No. 08/072,153 (abandoned in favor of continuation application Ser. 
No. 08/297,598, pending filed Aug. 29, 1994; continuation-in-part 
application Ser. No. 08/314,211, pending filed Sep. 28, 1994; and 
divisional application Ser. No. 08/822,200, pending filed Mar. 20, 1997) 
and U.S. Pat. No. 5,434,043 described above. 
Pre-formed silver halide emulsions when used in the element of this 
invention can be unwashed or washed to remove soluble salts. In the latter 
case, the soluble salts can be removed by chill-setting and leaching or 
the emulsion can be coagulation washed, e.g., by the procedures described 
in U.S. Pat. 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-containing compound is added to an organic silver salt to 
partially convert 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, or in other parameters from 0.5 to 15% by weight of the 
emulsion (light sensitive layer), preferably from 1 to 10% by weight of 
said emulsion layer. 
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 supersensitizer can be used which increases the 
sensitivity. For example, preferred infrared supersensitizers are 
described in U.S. patent application Ser. No. 08/091,000 (filed Jul. 13, 
1993) and include heteroaromatic mercapto compounds or heteroaromatic 
disulfide compounds of the formula: 
EQU Ar--S--M 
EQU Ar--S--S--Ar 
wherein M represents a hydrogen atom or an alkali metal atom. 
In the above noted supersensitizers, Ar represents a heteroaromatic ring or 
fused heteroaromatic ring containing one or more of nitrogen, sulfur, 
oxygen, selenium or tellurium atoms. Preferably, the heteroaromatic ring 
comprises benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, 
benzoxazole, naphthoxazole, benzoselenazole, benzotellurazole, imidazole, 
oxazole, pyrazole, triazole, thiazole, thiadiazole, 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 substituents 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. 
Most preferred supersensitizers are 2-mercaptobenzimidazole, 
2-mercapto-5-methylbenzimidazole (MMBI), 2-mercaptobenzothiazole, and 
2-mercapto-benzoxazole (MBO). 
The supersensitizers are used in general amount of at least 0.001 moles of 
sensitizer per mole of silver in the emulsion layer. Usually the range is 
between 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. The non-photosensitive reducible silver source that can be used in 
the present invention 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 
80.degree. C. or higher in the presence of an exposed photocatalyst (such 
as silver halide) and a reducing agent. 
Silver salts of organic acids, particularly silver salts of long chain 
fatty carboxylic acids, are preferred. 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 palmitate, 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 benzoate, such as silver 
3,5-dihydroxybenzoate, silver o-methylbenzoate, silver m-methylbenzoate, 
silver p-methylbenzoate, silver 2,4-dichlorobenzoate, silver 
acetamidobenzoate, silver p-phenylbenzoate, etc.; silver gallate; silver 
tannate; silver phthalate; silver terephthalate; silver salicylate; silver 
phenylacetate; silver pyromellitate; a silver salt of 
3-carboxymethyl-4-methyl-4-thiazoline-2-thione or the like as described in 
U.S. Pat. No. 3,785,830; and a silver salt of an aliphatic carboxylic acid 
containing a thioether group as described in U.S. Pat. No. 3,330,663. 
Soluble silver carboxylates having increased solubility in coating 
solvents and affording coatings with less light scattering can also be 
used. Such silver carboxylates are described in U.S. Pat. No. 5,491,059. 
Silver salts of compounds containing mercapto or thione groups and 
derivatives thereof can also be used. Preferred examples of these 
compounds 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-aminothiadiazole; 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. Pat. No. 4,123,274, for example, 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. 
Pat. No. 3,201,678. 
Furthermore, a silver salt of a compound containing an imino group can be 
used. Preferred examples of these compounds include: silver salts of 
benzotriazole and substituted derivatives thereof, for example, silver 
methylbenzotriazole and silver 5-chlorobenzotriazole, etc.; silver salts 
of 1,2,4-triazoles or 1-H-tetrazoles as described in U.S. Pat. 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. Pat. Nos. 4,761,361 and 4,775,613. 
It is also found convenient to use silver half soaps. A preferred example 
of a silver half soap is an equimolar blend of silver behenate and behenic 
acid, which analyzes for about 14.5% by weight solids of silver in the 
blend and which is prepared by precipitation from an aqueous solution of 
the sodium salt of commercial behenic acid. 
Transparent sheet elements made on transparent film backing require a 
transparent coating. For this purpose a silver behenate full soap, 
containing not more than about 15% of free behenic acid and analyzing 
about 22% silver, can be used. 
The method used for making silver soap emulsions 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. Pat. No. 3,985,565. 
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 adjacent 
layers, or in layers separated from each other by an intermediate layer 
having a thickness of less than 1 micrometer (1 .mu.m). It is preferred 
that the silver halide and the non-photosensitive reducible silver source 
be present in the same layer. 
The source of reducible silver generally constitutes 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-Photosensitive Reducible Silver Source 
When used in black-and-white photothermographic elements, 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 reducing agents are preferred. 
A wide range of reducing agents has been disclosed in dry silver systems 
including amidoximes, such as phenylamidoxime, 2-thienylamidoxime and 
p-phenoxy-phenylamidoxime; azines, such as 
4-hydroxy-3,5-dimethoxybenzaldehydeazine; a combination of aliphatic 
carboxylic acid aryl hydrazides and ascorbic acid, such as 
2,2'-bis(hydroxymethyl)propionyl-.beta.-phenylhydrazide in combination 
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 with 
p-benzenesulfonamidophenol or 2,6-dichloro-4-benzenesulfonamidophenol; 
.alpha.-cyanophenylacetic acid derivatives, such as ethyl 
.alpha.-cyano-2-methylphenylacetate, ethyl .alpha.-cyano-phenylacetate; 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 
anhydrodihydropiperidone-hexose reductone; sulfonamidophenol reducing 
agents, such as 2,6-dichloro-4-benzenesulfonamidophenol and 
p-benzenesulfonamidophenol; 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 1-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 
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 different phenyl rings. Hindered phenol developers include, for 
example, binaphthols (i.e., dihydroxybinaphthyls), biphenols (i.e., 
dihydroxybiphenyls), bis(hydroxynaphthyl)methanes, 
bis(hydroxyphenyl)methanes, hindered phenols, and naphthols. 
Non-limiting representative bis-o-naphthols, such as by 
2,2'-dihydroxyl-1-binaphthyl, 6,6'-dibromo-2,2'-dihydroxy-1,1'-binaphthyl, 
and bis(2-hydroxy-1-naphthyl)methane. For additional compounds see U.S. 
Pat. No. 5,262,295 at column 6, lines 12-13, incorporated herein by 
reference. 
Non-limiting representative biphenols include 
2,2'-dihydroxy-3,3'-di-t-butyl-5,5-dimethylbiphenyl; 
2,2'-dihydroxy-3,3',5,5'-tetra-t-butylbiphenyl; 
2,2'-dihydroxy-3,3'-di-t-butyl-5,5'-dichlorobiphenyl; 
2-(2-hydroxy-3-t-butyl-5-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 compounds see 
U.S. Pat. No. 5,262,295 at column 4, lines 17-47, incorporated herein by 
reference. 
Non-limiting representative bis(hydroxynaphthyl)methanes include 
2,2'-methylene-bis(2-methyl-1-naphthol)methane. For additional compounds 
see U.S. Pat. No. 5,262,295 at column 6, lines 14-16, incorporated herein 
by reference. 
Non-limiting representative bis(hydroxyphenyl)methanes include 
bis(2-hydroxy-3-t-butyl-5-methylphenyl)methane (CAO-5); 
1,1-bis(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexane (Permanex.TM. 
or Nonox.TM.); 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. Pat. 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 1-naphthol; 
4-methyl-1-naphthol; 4-methoxy-1-naphthol; 4-chloro-1-naphthol; and 
2-methyl-1-naphthol. For additional compounds see U.S. Pat. No. 5,262,295 
at column 6, lines 17-20, incorporated herein by reference. 
The reducing agent should be present as 1 to 15% by weight of the imaging 
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 20%, tend to be more desirable. 
Photothermographic elements of the invention may contain contrast 
enhancers, co-developers or mixtures thereof. For example, the trityl 
hydrazide or formyl phenylhydrazine compounds described in U.S. Pat. No. 
5,496,695 may be used; the amine compounds described in U.S. Pat. No. 
5,545,505 may be used; hydroxamic acid compounds described in U.S. Pat. 
No. 5,545,507 may be used; the acrylonitrile compounds described in U.S. 
Pat. No. 5,545,515 may be used; the N-acyl-hydrazide compounds as 
described in U.S. Pat. No. 5,558,983 may be used; the 2-substituted 
malondialdehyde compounds described in U.S. Pat. No. 5,705,324; the 
4-substituted isoxazole compounds described in U.S. Pat. No. 5,654,130; 
the 3-heteroaromatic-substituted acrylonitrile compounds described in U.S. 
Pat. No. 5,635,339; and the hydrogen atom donor compounds described in 
U.S. Pat. No. 5,673,449 may be used; 
Further, the reducing agent may optionally comprise a compound capable of 
being oxidized to form or release a dye. Preferably the dye-forming 
material is a leuco dye. 
Photothermographic elements of the invention may also contain other 
additives such as shelf-life stabilizers, toners, development 
accelerators, acutance dyes, post-processing stabilizers or stabilizer 
precursors, and other image-modifying agents. 
The Binder 
The photosensitive silver halide, the non-photosensitive reducible source 
of silver, the reducing agent, and any other addenda used in the present 
invention are generally added to at least one binder. The binder(s) that 
can be used in the present invention can be employed individually or in 
combination with one another. It is preferred 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 translucent hydrophilic 
colloid. Examples of hydrophilic binders include: a natural substance, for 
example, a protein such as gelatin, a gelatin derivative, a cellulose 
derivative, etc.; a polysaccharide 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 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 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 preferred. 
Although the binder can be hydrophilic or hydrophobic, preferably it is 
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. 
Where the proportions and activities of the reducing agent for the 
non-photosensitive reducible source of silver require a particular 
developing time and temperature, the binder should be able to withstand 
those conditions. Generally, it is preferred that the binder not decompose 
or lose its structural integrity at 250.degree. F. (121.degree. C.) for 60 
seconds, and more preferred that it not decompose or lose its structural 
integrity at 350.degree. F. (177.degree. C.) 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. 
Photothermographic Formulations 
The formulation for the photothermographic emulsion layer can be prepared 
by dissolving and dispersing the binder, the photosensitive silver halide, 
the non-photosensitive reducible source of silver, the reducing agent 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 essential to the element. Toners can be 
present in an amount of about 0.01-10% by weight of the emulsion layer, 
preferably about 0.1-10% by weight. Toners are well known compounds in the 
photothermographic art, as shown in U.S. Pat. Nos. 3,080,254; 3,847,612; 
and 4,123,282. 
Examples of toners include: phthalimide and N-hydroxyphthalimide; cyclic 
imides, such as succinimide, pyrazoline-5-ones, quinazolinone, 
1-phenylurazole, 3-phenyl-2-pyrazoline-5-one, and 2,4-thiazolidinedione; 
naphthalimides, such as N-hydroxy-1,8-naphthalimide; cobalt complexes, 
such as cobaltic hexamine trifluoroacetate; mercaptans such as 
3-mercapto-1,2,4-triazole, 2,4-dimercaptopyrimidine, 
3-mercapto-4,5-diphenyl-1,2,4-triazole and 
2,5-dimercapto-1,3,4-thiadiazole; N-(aminomethyl)aryldicarboximides, such 
as (N,N-dimethylaminomethyl)phthalimide, and 
N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide; a combination of 
blocked pyrazoles, isothiuronium derivatives, and certain photobleach 
agents, such as a combination of 
N,N'-hexamethylene-bis(1-carbamoyl-3,5-dimethylpyrazole), 
1,8-(3,6-diazaoctane)bis(isothiuronium)trifluoroacetate, 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, phthalazinone derivatives, or metal 
salts or these derivatives, such as 4-(1-naphthyl)phthalazinone, 
6-chlorophthalazinone, 5,7-dimethoxyphthalazinone, and 
2,3-dihydro-1,4-phthalazinedione; a combination of phthalazine plus one or 
more phthalic acid derivatives, such as phthalic acid, 4-methylphthalic 
acid, 4-nitrophthalic acid, and tetrachlorophthalic anhydride, 
quinazolinediones, benzoxazine or naphthoxazine derivatives; rhodium 
complexes functioning not only as tone modifiers but also as sources of 
halide ion for silver halide formation in situ, such as ammonium 
hexachlororhodate (III), rhodium bromide, rhodium nitrate, and potassium 
hexachlororhodate (III); inorganic peroxides and persulfates, such as 
ammonium peroxydisulfate 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-hydroxy4-aminopyrimidine, and azauracil; and 
tetraazapentalene derivatives, such as 
3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5,6a-tetraazapentalene and 
1,4-di-(o-chlorophenyl)-3,6-dimercapto-1H,4H-2,3a,5,6a-tetraazapentalene. 
The photothermographic elements used in this invention can be further 
protected against the production of fog and can be further stabilized 
against loss of sensitivity during storage. While not necessary for the 
practice of the invention, it may be advantageous to add mercury (II) 
salts to the emulsion layer(s) as an antifoggant. Preferred mercury (H) 
salts for this purpose are mercuric acetate and mercuric bromide. 
Other suitable antifoggants and stabilizers, which can be used alone or in 
combination include the thiazolium salts described in U.S. Pat. Nos. 
2,131,038 and U.S. Pat. No. 2,694,716; the azaindenes described in U.S. 
Pat. No. 2,886,437; the triazaindolizines described in U.S. Pat. No. 
2,444,605; the mercury salts described in U.S. Pat. No. 2,728,663; the 
urazoles described in U.S. Pat. No. 3,287,135; the sulfocatechols 
described in U.S. Pat. No. 3,235,652; the oximes described in British 
Patent No. 623,448; the polyvalent metal salts described in U.S. Pat. No. 
2,839,405; the thiuronium salts described in U.S. Pat. No. 3,220,839; 
palladium, platinum and gold salts described in U.S. Pat. Nos. 2,566,263 
and 2,597,915; and the 2-(tribromomethylsulfonyl)quinoline compounds 
described in U.S. Pat. No. 5,460,938. Stabilizer precursor compounds 
capable of releasing stabilizers upon application of heat during 
development can also be use in combination with the stabilizers of this 
invention. Such precursor compounds are described in, for example, U.S. 
Pat. Nos. 5,158,866, 5,175,081, 5,298,390, and 5,300,420. 
Photothermographic elements of the invention can contain plasticizers and 
lubricants such as polyalcohols and diols of the type described in U.S. 
Pat. No. 2,960,404; fatty acids or esters, such as those described in U.S. 
Pat. Nos. 2,588,765 and 3,121,060; and silicone resins, such as those 
described in British Patent No. 955,061. 
Photothermographic elements containing emulsion layers described herein may 
contain matting agents such as starch, titanium dioxide, zinc oxide, 
silica, and polymeric beads including beads of the type described in U.S. 
Pat. Nos. 2,992,101 and 2,701,245. 
Emulsions in accordance with this invention may be used in 
photothermographic elements which contain antistatic 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. Pat. Nos. 2,861,056, and 3,206,312 or insoluble inorganic salts such 
as those described in U.S. Pat. No. 3,428,451. 
The photothermographic elements of this invention may also contain 
electroconductive under-layers to reduce static electricity effects and 
improve transport through processing equipment. Such layers are described 
in U.S. Pat. No. 5,310,640. 
Photothermographic Constructions 
The photothermographic elements of this invention may be constructed of one 
or more layers on a support. Single layer elements should contain the 
silver halide, the non-photosensitive, reducible silver source, the 
reducing agent 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 (often referred to as two-trip constructions 
because of the coating of two distinct layers on the support) should 
contain silver halide and non-photosensitive, reducible silver source in 
one emulsion layer (usually the layer adjacent to the support) and some of 
the other ingredients in the second layer or both layers. Two layer 
constructions comprising a single emulsion layer coating containing all 
the ingredients and a protective topcoat are also envisioned. 
Multicolor photothermographic dry silver elements can contain sets of these 
bilayers for each color or they can contain all ingredients within a 
single layer, as described in U.S. Pat. No. 4,708,928. 
Barrier layers, preferably comprising a polymeric material, can also be 
present in the photothermographic element of the present invention. 
Polymers for the barrier layer can be selected from natural and synthetic 
polymers such as gelatin, polyvinyl alcohols, polyacrylic acids, 
sulfonated polystyrene, and the like. The polymers can optionally be 
blended with barrier aids such as silica. 
Photothermographic emulsions used in this invention can be coated by 
various coating procedures including wire wound rod coating, dip coating, 
air knife coating, curtain coating, slide coating, or extrusion coating 
using hoppers of the type described in U.S. Pat. No. 2,681,294. If 
desired, two or more layers can be coated simultaneously by the procedures 
described in U.S. Pat. Nos. 2,761,791; 5,340,613; and British Patent No. 
837,095. A typical coating gap for the emulsion layer can be about 10-150 
micrometers (.mu.m), and the layer can be dried in forced air at a 
temperature of about 20-100.degree. C. It is preferred that the thickness 
of the 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 Densitometer Model TD 504 using the color filter 
complementary to the dye color. 
Photothermographic elements according to the present invention can contain 
acutance dyes and antihalation dyes. The dyes may be incorporated into the 
photothermographic emulsion layer as acutance dyes according to known 
techniques. The dyes may also be incorporated into antihalation layers 
according to known techniques as an antihalation backing layer, an 
antihalation underlayer or as an overcoat. It is preferred that the 
photothermographic elements of this invention contain an antihalation 
coating on the support opposite to the side on which the emulsion and 
topcoat layers are coated. Antihalation and acutance dyes useful in the 
present invention are described in U.S. Pat. Nos. 5,135,842; 5,226,452; 
5,314,795, and 5,380,635. 
Development conditions will vary, depending on the construction used, but 
will typically involve heating the photothermographic element in a 
substantially water-free condition after, or simultaneously with, 
imagewise exposure at a suitably elevated temperature. Thus, the latent 
image obtained after exposure can be developed by heating the element at a 
moderately elevated temperature of, from about 80.degree. C. to about 
250.degree. C. (176.degree. F. to 482.degree. F.), preferably from about 
100.degree. C. to about 200.degree. C. (212.degree. F. to 392.degree. F.), 
for a sufficient period of time, generally about 1 second to about 2 
minutes. When used in a black-and-white element, a black-and-white silver 
image is obtained. When used in a monochrome or full-color element, a dye 
image is obtained simultaneously with the formation of a black-and-white 
silver image. 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. Pat. 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 
wide range of materials depending on the imaging requirement. Supports may 
be transparent or at least translucent. Typical supports include polyester 
film, subbed polyester film (e.g., polyethylene terephthalate or 
polyethylene naphthalate), cellulose acetate film, cellulose ester film, 
polyvinyl(e.g., film, polyolefinic film (e.g., polyethylene 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 priming agent. Preferred polymeric materials for the support 
include polymers having good heat stability, such as polyesters. 
Particularly preferred polyesters are polyethylene terephthalate and 
polyethylene naphthalate. 
A support with a backside resistive heating layer can also be used 
photothermographic imaging systems such as shown in U.S. Pat. No. 
4,374,921. 
Use as a Photomask 
The possibility of low absorbance of the photothermographic element in the 
range of 350-450 nm in non-imaged areas facilitates the use of the 
photothermographic elements of the present invention in a process where 
there is a subsequent exposure of an ultraviolet or short wavelength 
visible radiation sensitive imageable medium. For example, imaging 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 or short 
wavelength visible radiation where there is no visible image. The 
developed element 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 
medium such as, for example, a photopolymer, diazo compound, or 
photoresist. This process is particularly useful where the imageable 
medium comprises a printing plate and the photothermographic element 
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 are readily available from 
standard commercial sources, such as Aldrich Chemical Co. (Milwaukee, 
Wis.). All percentages are by weight unless otherwise indicated. The 
following additional terms and materials were used. 
Acryloid.TM. A-21 is a poly(methyl methacrylate) polymer available from 
Rohm and Haas, Philadelphia, Pa. 
Butvar.TM. B-79 is a poly(vinyl butyral) resins available from Monsanto 
Company, St. Louis, Mo. 
BZT is benzotriazole. 
CAB 171-15S and CAB 381-20 are cellulose acetate butyrate polymers 
available from Eastman Chemical Co., Kingsport, Tenn. 
CBBA is 2-(4-chlorobenzoyl)benzoic acid. 
MBO is 2-mercaptobenzoxazole. It is a supersensitizer. 
MEK is methyl ethyl ketone (2-butanone). 
MMBI is 5-methyl-2-mercaptobenzimidazole. It is a supersensitizer. 
4-MPA is 4-methylphthalic acid. 
NonoX.TM. 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 
Permanax.TM. WSO. 
Vitel.TM. PE-2200 is a polyester resin available from Shell, Houston Tex. 
PET is polyethylene terephthalate. 
PHZ is phthalazine. 
PHP is pyridinium hydrobromide perbromide. 
#810 Scotch.TM. Brand Tape is available from 3M Company, St. Paul, Minn. 
TCPAN is tetrachlorophthalic anhydride. 
TCPA is tetrachlorophthalic acid. 
THDI is Desmodur.TM. N-3300, a biuretized hexamethylenediisocyanate 
available from Bayer Chemical Corporation. 
Vinol 523 is a polyvinyl alcohol available from Air Products, Allentown, 
Pa. 
Antifoggant 1 (AF-1) is 2-(tribromomethylsulfonyl)quinoline. It is 
described in U.S. Pat. No. 5,460,938 and has the structure shown below. 
##STR3## 
Fluorinated Terpolymer A (FT-A) has the following random polymer structure, 
where m=7, n=2 and p=1. The preparation of fluorinated terpolymer A is 
described in U.S. Pat. No. 5,380,644. 
##STR4## 
Spectral Sensitizing Dye-1 (SSD-1) is described in U.S. Pat. No. 5,541,054 
and has the structure shown below. 
##STR5## 
Spectral Sensitizing Dye-2 (SSD-2) has the structure shown below. 
##STR6## 
Spectral Sensitizing Dye-3 (SSD-3) has the structure shown below. 
##STR7## 
Spectral Sensitizing Dye-4 (SSD-4) has the structure shown below. 
##STR8## 
Spectral Sensitizing Dye-5 (SSD-5) has the structure shown below. 
##STR9## 
Spectral Sensitizing Dye-6 (SSD-6) has the structure shown below. 
##STR10## 
Spectral Sensitizing Dye-7 (SSD-7) has the structure shown below. 
##STR11## 
Spectral Sensitizing Dye-8 (SSD-8) has the structure shown below. 
##STR12## 
Compounds CN-02 and CN-08 are described in U.S. Pat. No. 5,545,515 and have 
the structures shown below. 
##STR13## 
Compounds PR-01 and PR-08 are described in U.S. Pat. No. 5,686,228 and have 
the structures shown below. 
##STR14## 
Antihalation Dye-1 (AH Dye-1) is described in Example 1f of U.S. Pat. No. 
5,380,635 and has the structure shown below. 
##STR15## 
Antihalation Dye-2 (AH Dye-2) is described in PCT Publication No. WO 
95/23357 and has the structure shown below. 
##STR16## 
Vinyl Sulfone-1 (VS-1) is described in European Laid Open Patent 
Application No. 0 600 589 A2 and has structure shown below. 
##STR17## 
The photothermographic emulsion and topcoat were coated using a dual knife 
coater. This apparatus consists of two hinged knife-coating blades in 
series. After raising the hinged knives the support was 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 thickness of the support plus the desired coating gap 
for the emulsion layer (layer #1). Knife #2 was raised to a height equal 
to the desired thickness of the support plus the desired coating gap for 
the emulsion layer (layer #1) plus the desired coating gap for the topcoat 
layer (layer #2). 
Aliquots of photothermographic emulsion #1 and topcoat #2 were 
simultaneously poured onto the support in front of the corresponding 
knives. The support was immediately drawn past the knives and into an oven 
to produce a double layered coating. The coated photothermographic or 
thermographic element was then dried by taping the support to a belt which 
was rotated inside a BlueM.TM. oven. 
Photothermographic emulsion and topcoat formulations were coated onto a 
polyethylene terephthalate (PET) support provided with an antihalation 
coating on the back side of the support. All formulations and samples were 
prepared and coated using safelights appropriate to the wavelengths of 
spectral sensitivity of the photothermographic emulsions. 
Sensitometric Measurements: The images obtained were evaluated on custom 
built computer scanned densitometers using a filter appropriate to the 
sensitivity of the photothermographic element (when required) and are 
believed to be comparable to measurements from commercially available 
densitometers. 
Examples 1-4 
Sensitometry measurements made in Examples 1-4 use the definitions shown 
below. Sensitometric results include Dmin, Dmax, Speed-2, Speed-3, Average 
Contrast-1, and Average Contrast-3. 
Dmin is the density of the non-exposed areas after development. It is the 
average of eight lowest density values on the exposed side of the fiducial 
mark. 
Dmax is the highest density value on the exposed side of the fiducial mark. 
Speed-2 is the Log (1/E)+4 corresponding to the density value at 1.00 above 
Dmin. E is the exposure in ergs/cm.sup.2. 
Speed-3 is the Log (1/E)+4 corresponding to the density value at 2.90 above 
Dmin. E is the exposure in ergs/cm.sup.2. Speed-3 is important in 
evaluating the exposure response of a photothermographic element to high 
intensity light sources. 
AC-1 (Average Contrast 1) is the absolute value of the slope of the line 
joining the density points at 0.60 and 2.00 above Dmin. 
AC-3 (Average Contrast 3) is the absolute value of the slope of the line 
joining the density points at 2.40 and 2.90 above Dmin. 
Example 1 
Photothermographic Emulsion A 
A pre-formed iridium-doped core-shell silver behenate full soap was 
prepared as described in U.S. Pat. No. 5,434,043 incorporated herein by 
reference. 
The pre-formed soap contained 2.0 wt % of a 0.05 .mu.m diameter 
iridium-doped core-shell silver iodobromide emulsion (25% core containing 
8% iodide, 92% bromide; and 75% all bromide shell containing 
1.times.10.sup.-5 mol of iridium). A dispersion of this silver behenate 
full soap was homogenized to 21.9% solids in 2-butanone containing 1.3% 
Butvar.TM. B-79 polyvinyl butyral resin. 
To 208 g of this full silver soap dispersion, maintained at 22.degree. C. 
and rapidly stirred at 1000 rpm, was added a solution of 0.02 g of 
chemical sensitizing compound CS-1 dissolved in 4 g of methanol. 
After stirring for 30 minutes 0.20 g of pyridinium hydrobromide perbromide 
dissolved in 1 mL of methanol was added. After 60 minutes, a solution of 
0.10 g of CaBr.sub.2.xH.sub.2 O or CaBr.sub.2.2H.sub.2 O dissolved in 1.0 
mL of methanol was added. Mixing for 30 minutes was followed by addition 
of a solution of 0.128 g of MMBI and 1.42 g of CBBA in 5 g of methanol. 
The solution was then cooled to 12.8.degree. C. (55.degree. F.) and 40 g of 
Butvar.TM. B-79 was added. Stirring for 30 minutes was followed by 
addition of a solution of 1.10 g of Antifoggant-1 (AF-1) dissolved in 15 
mL of 2-butanone. After 15 minutes, 10.45 g of Nonox.TM. was added. After 
15 minutes 0.28 g of THDI was added. Finally, after 15 minutes, 0.85 g of 
PHZ and 0.36 g of TCPA were added. 
The mixture was then warmed to 22.degree. C. and 0.45 g 4-MPA in 4 g of 
methanol was added and stirred for 15 minutes. 
A topcoat solution was then prepared in the following manner; 4.5 g 
Acryloid.TM. A-21 and 115 g of CAB 171-15S were mixed until dissolved in 
1,236 g 2-butanone and 147 g of methanol. To 100 g of this stock solution 
was added 0.515 g of Fluorinated Terpolymer A (FT-A). 
A second photothermographic emulsion and topcoat were prepared but without 
incorporating any CS-1 into the photothermographic emulsion layer. This 
sample (1-2) served as a control. 
The photothermographic emulsion and topcoat formulations were coated onto a 
7 mil (176 .mu.m) blue tinted polyethylene terephthalate support provided 
with an antihalation back-coating containing AH Dye-1 in CAB 381-20 resin. 
The coating gap for the photothermographic emulsion layer was 3.8 mil 
(96.5 .mu.m) over the support and 5.5 mil (140 .mu.m) over the support for 
the topcoat layer. The samples were each dried at 185.degree. C. for 4 
minutes. 
The coated and dried photothermographic elements were cut into 1.5 inch by 
8 inch strips (3.8 cm.times.20.3 cm) and exposed using an EG&G 
sensitometer for 0.001 seconds using a Xenon flash and a 0 to 3 continuous 
wedge. No wavelength filters were used. The samples were then developed on 
a round drum thermal processor for 15 seconds at 250.degree. F. 
(121.degree. C.). 
The results, shown below demonstrate that Speed-2 of the sample containing 
chemical sensitizing compound CS-1 was 0.22 logE faster than the Control. 
______________________________________ 
Ex. Dmin Dmax Speed-2 
AC-1 
______________________________________ 
1-1 Invention 0.214 4.12 2.63 7.1 
1-2 Control 0.229 4.08 2.41 7.5 
______________________________________ 
Samples of the two coatings were also exposed using a wedge spectrograph 
and developed at 250.degree. F. (121.degree. C.) for 15 seconds. The 
response clearly demonstrated that there was no residual blue sensitivity 
as one would expect from undecomposed CS-1 dye. It is therefore apparent 
that the chemical sensitization has occurred from the CS-1 dye fragments 
resulting from reaction with the PHP. 
Example 2 
This example demonstrates the use of an infrared spectral sensitizer in 
chemically sensitized photothermographic emulsions. 
Photothermographic Emulsion B 
A pre-formed iridium-doped core-shell silver behenate full soap was 
prepared as described in U.S. Pat. No. 5,434,043 incorporated herein by 
reference. 
The pre-formed soap contained 2.0 wt % of a 0.07 .mu.m diameter 
iridium-doped core-shell silver iodobromide emulsion (25% core containing 
8% iodide, 92% bromide; and 75% all bromide shell containing 
1.times.10.sup.-5 mol of iridium). A dispersion of this silver behenate 
full soap was homogenized to 21.9% solids in 2-butanone containing 1.3% 
Butvar.TM. B-79 polyvinyl butyral resin. 
To 208 g of this full silver soap dispersion, maintained at 22.degree. C. 
and rapidly stirred at 1000 rpm, was added a solution of 0.02 g of 
chemical sensitizing compound CS-1 dissolved in 3 g of methanol. 
After stirring for 30 minutes 0.20 g of pyridinium hydrobromide perbromide 
dissolved in 1 mL of methanol was added. After 60 minutes, a solution of 
0.10 g of CaBr.sub.2.xH.sub.2 O or CaBr.sub.2.2H.sub.2 O dissolved in 1.0 
mL of methanol was added. Mixing for 30 minutes was followed by addition 
of a solution of 0.003 g of spectral sensitizing dye SSD-1, 0.128 g of 
MMBI and 1.42 g of CBBA in 5 g of methanol. 
The solution was then cooled to 12.8.degree. C. (55.degree. F.) and 40 g of 
Butvar.TM. B-79 was added. Stirring for 60 minutes was followed by 
addition of a solution of 1.10 g of antifoggant-1 dissolved in 15 mL of 
2-butanone. After 15 minutes, 10.45 g of Nonox.TM. was added. After 15 
minutes 0.28 g of THDI was added. Finally, after 15 minutes, 0.85 g of PHZ 
and 0.36 g of TCPA were added. After 15 minutes, a solution of 0.45 g 
4-MPA dissolved in 4 g of methanol was added. 
The mixture was then warmed to 22.degree. C. 
A second photothermographic emulsion and topcoat were prepared but without 
incorporating any CS-1 into the photothermographic emulsion layer. This 
sample (2-2) served as a control. 
A topcoat solution was then prepared as in Example 1. 
The solutions were dual knife coated and dried as described above. 
The samples were exposed using a laser sensitometer incorporating a 810 nm 
laser diode. After exposure, the film strips were processed by heating at 
250.degree. F. (121.degree. C.) for 15 seconds to give an image. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of the photothermographic emulsion increased Speed-2 by 0.53 
log E. 
______________________________________ 
Example Dmin Dmax 
______________________________________ 
2-1 Invention 0.255 4.02 
2-2 Control 0.241 3.97 
Ex. Speed-2 Contrast-1 
Contrast-3 
2-1 1.936 3.83 5.04 
2-2 1.408 3.49 4.17 
______________________________________ 
Example 3 
This example demonstrates the utility of the chemical sensitizing compounds 
of this invention with a high-contrast co-developer to form a 
high-contrast photothermographic element. 
Two photothermographic emulsions were prepared using photothermographic 
emulsion B described in Example 2. Again, a second photothermographic 
emulsion was prepared but without incorporating any CS-1 into the 
photothermographic emulsion layer. This sample served as a control (3-2). 
CN-02 (0.50 g per 100 g of topcoat solution) was added to the topcoat 
formulation of each solution. The solutions were dual knife coated, dried, 
imaged, and developed as described in Example 2 above. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of the photothermographic emulsion increased Speed-2 by 0.45 
log E. 
______________________________________ 
Example Dmin Dmax 
______________________________________ 
3-1 Invention 0.285 4.57 
3-2 Control 0.253 4.88 
Ex. Speed-2 Contrast-1 
Contrast-3 
3-1 2.408 20 26 
3-2 1.95 28 36 
______________________________________ 
Example 4 
This example demonstrates the utility of the present invention with a green 
spectral sensitizing dye, spectral sensitizing dye SSD-2. 
Two photothermographic emulsions were prepared using photothermographic 
emulsion B described in Example 2 above. In these emulsions, 0.20 g of 
green spectral sensitizing dye SSD-2 replaced the infrared sensitizing dye 
SSD-1 used in Example 2. Again, the second photothermographic emulsion did 
not incorporate CS-1 into the photothermographic emulsion layer. This 
sample served as a control (4-2). 
A topcoat solution was then prepared as described in Example 1. 
The solutions were dual knife coated, and dried as described in Example 1 
above. Samples were prepared as described above and exposed using an EG&G 
sensitometer with a Xenon flash exposure for 0.001 seconds through a green 
filter and a 0-4 wedge, and developed as described in Example 1 above. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of the photothermographic emulsion increased Speed-2 by 0.4 
log E. 
______________________________________ 
Ex. Dmin Dmax Speed-2 
Contrast-1 
______________________________________ 
4-1 Invention 0.076 4.2 2.79 7.2 
4-2 Control 0.09 3.5 2.37 5.5 
______________________________________ 
Examples 5-24 
Samples prepared in Examples 1-4 have very different silver emulsion 
coating weights than those of Examples 5-24. They also have different 
amounts of ingredients and were coated onto different supports having 
different antihalation back-coats. In addition, samples of Examples 1-4 
were imaged on different laser sensitometers, having different spot size, 
scan line overlap, and laser contact time than samples of Examples 5-24. 
Also, samples of Examples 1-4 were evaluated on different densitometers 
using different computerized programs than samples of Examples 5-24. Thus, 
the results of Examples 1-4 and 5-24 are not directly comparable. 
Photothermographic Emulsion C 
A pre-formed iridium-doped core-shell silver behenate full soap was 
prepared as described in U.S. Pat. No. 5,434,043 incorporated herein by 
reference. 
The preformed soap contained 2.0 wt % of a 0.05 .mu.m diameter 
iridium-doped core-shell silver iodobromide emulsion (25% core containing 
8% iodide, 92% bromide; and 75% all bromide shell containing 
1.times..sup.-5 mol of iridium). A dispersion of this silver behenate full 
soap was homogenized to 21.9% solids in 2-butanone containing 1.3% 
Butvar.TM. B-79 polyvinyl butyral resin. 
To 186.5 g of this silver full soap dispersion, maintained at 21.1.degree. 
C. and stirred at 500 rpm, was added a solution of 0.0135 g of chemical 
sensitizing compound CS-1 dissolved in 2.788 g of methanol. 
After mixing for 30 minutes, 1.00 mL of a solution of 0.42 g of pyridinium 
hydrobromide perbromide dissolved in 2.35 g of methanol was added. After 
60 minutes of mixing, 1.00 mL of a solution of 0.632 g of 
CaBr.sub.2.2H.sub.2 O dissolved in 2.35 mL of methanol was added. Mixing 
for 30 minutes was followed by addition of a solution of spectral 
sensitizing dye (dyes SSD-01-SSD-08) prepared by mixing the following 
ingredients. 
______________________________________ 
Material Amount 
______________________________________ 
CBBA 2.44 g 
Spectral Sensitizing Dye 
amount indicated 
MMBI 0.0907 g 
2-MBO 0.0118 g 
MeOH 8.18 g 
______________________________________ 
After 1 hour of mixing, the temperature was lowered from 21.1.degree. C. to 
11.6.degree. C. After 30 minutes at 11.6.degree. C., 34.1 g of Butvar.TM. 
B-79 was added. With stirring at 1500 rpm for 30 minutes, the following 
components were added every 15 minutes. 
______________________________________ 
Material Amount 
______________________________________ 
Antifoggant-1 1.20 g 
Permanax .TM. 10.02 g 
THDI 0.822 g dissolved in 
MEK 0.822 g 
PHZ 1.00 g dissolved in 
MeOH 1.18 g 
TCPA 0.451 g dissolved in 
MEK 0.226 g 
MeOH 0.226 g 
4-MPA 0.500 g 
MeOH 3.03 g 
______________________________________ 
This photothermographic emulsion was used "as is" to prepare a continuous 
tone photothermographic element. Continuous tone coatings were prepared by 
dual knife coating the photothermographic and topcoat formulations at 4.0 
mil (101.6 .mu.m) and 5.8 mil (147.3 .mu.m), respectively over the 
support. 
High-contrast coatings were prepared by adding a solution of 0.0072 g of 
compound CN-08 dissolved in 1.5 g of methanol to a 15 g aliquot of the dye 
sensitized silver premix as described above. 
A topcoat solution was prepared in the following manner; 1.29 g of 
Acryloid.TM. A-21 and 33.57 g of CAB 171-15S were mixed until dissolved in 
404.7 g 2-butanone and 53.4 g of methanol. To 197.2 g of this premix was 
then added 0.196 g of vinylsulfone VS-1. The topcoat was diluted by the 
addition of 42.5 g of 2-butanone. 
The photothermographic emulsion layer and topcoat were dual knife coated 
onto a 4 mil polyester support. The coating gap for the photothermographic 
emulsion layer was 2.4 mil and 3.5 mil, (over the photothermographic 
emulsion layer) respectively on a 4 mil PET support containing a removable 
red antihalation back-coat and dried for 5 minutes at 185.degree. F. 
The samples were exposed at either 633 nm or 670 nm using a laser diode 
sensitometer. The coatings were processed on a heated roll processor for 
15 seconds at 250.degree. F. unless otherwise indicated. 
Removable Red Antihalation Back-Coat 
A removable red antihalation back-coat was prepared in the following 
manner: To 405 g of water at 180.degree. F. was added 45 g of Vinol.TM. 
523. After the Vinol.TM. 523 had dissolved, the temperature was lowered to 
140.degree. F., 450 g of methanol was added, and mixing continued for 60 
minutes. A solution of 18.2 g of polyvinylpyrrolidone dissolved in 72.7 g 
of methanol was then added and mixed for 2 hours. The temperature was 
lowered to 70.degree. F., and 9.0 g of Victoria Pure Blue was added and 
mixed for 1 hour. 
The resultant antihalation solution was knife coated on the backside of the 
photothermographic element using a knife coater. The coating gap for the 
back-coat was 3 mil. After exposure and processing the antihalation 
back-coat was removed using a piece of #810 Scotch.TM. Brand Tape and the 
sensitometric response was measured. 
##STR18## 
For samples exposed using a 633 nm or a 670 nm laser the following 
definitions are used: 
Dmin is the density of the non-exposed areas after development. It is the 
average of eight lowest density values on the exposed side of the fiducial 
mark. 
Dmax is the highest density value on the exposed side of the fiducial mark. 
Speed-1 is Log(1/E)+4 corresponding to the density value at 1.00 above Dmin 
where E is the exposure in ergs/cm.sup.2. 
Speed-2 is Log(1/E)+4 corresponding to the density value at 1.00 above Dmin 
where E is the exposure in ergs/cm.sup.2. 
Speed-3 is Log(1/E)+4 corresponding to the density value at 3.00 where E is 
the exposure in ergs/cm.sup.2. 
Speed-5 is Log(1/E)+4 corresponding to the density value at 3.00 above Dmin 
where E is the exposure in ergs/cm.sup.2. 
Contrast A is the absolute value of the slope of the line joining the 
density points at 0.07 and 0.17 above Dmin. 
Contrast C is the absolute value of the slope of the line joining the 
density points at 0.50 and 2.50 above Dmin. 
Contrast D is the absolute value of the slope of the line joining the 
density points at 1.00 and 3.00 above Dmin. 
Example 5 
Samples of photothermographic emulsion C were prepared incorporating 
chemical sensitizing compound CS-1 at three levels 0.0090 g (-), 0.0135 g 
(0), and 0.018 g (+). A sample was also prepared without any CS-1. This 
sample served as a control. The photothermographic emulsions were 
sensitized with 2.times.10.sup.-5 mol of red spectral sensitizing dye 
SSD-3. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 633 nm laser, developed, and evaluated as 
described above. 
Samples 5-1 to 5-4 were continuous tone photothermographic elements. 
Samples 5-6 to 5-8 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. Samples 5-1 and 5-5 contained 
no CS-1 and served as controls. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of a photothermographic silver halide emulsion results in an 
increase in speed of the resulting photothermographic element. This occurs 
in both continuous tone and high-contrast emulsions. 
In the high-contrast elements, an increase in Speed-2 of 0.1 logE at the 
lower (-) concentration, of 0.2 logE at the normal (0) concentration, and 
of 0.4 logE at the higher (+) concentration was observed. 
In the continuous tone elements, an increase in Speed-2 of 0.06 logE at the 
lower (-) concentration, of 0.2 logE at the normal (0) concentration, and 
of 0.56 logE at the (+) higher concentration was observed. Loss of 
contrast and increase in Dmin were observed in the high-contrast 
photothermographic elements incorporating CS-1 at the higher (+) 
concentration. 
______________________________________ 
Ex. Level of CS-1 Dmin Dmax 
______________________________________ 
5-1 none 0.096 4.574 
5-2 (-) 0.083 4.259 
5-3 (0) 0.093 4.395 
5-4 (+) 0.156 4.507 
5-5 none 0.049 3.952 
5-6 (-) 0.052 4.471 
5-7 (0) 0.051 4.124 
5-8 (+) 0.062 3.326 
Ex. Speed-2 Speed-5 Contrast-A 
Contrast-D 
5-1 1.898 1.53 0.68 5.53 
5-2 1.95 1.545 0.514 4.495 
5-3 2.087 1.659 0.474 4.675 
5-4 2.46 1.923 0.531 3.746 
5-5 2.011 1.91 1.821 19.812 
5-6 2.106 2.051 2.07 22.197 
5-7 2.19 2.067 1.168 17.527 
5-8 2.41 2.18 0.607 9.39 
______________________________________ 
Example 6 
The effect of replacing CaBr.sub.2.2H.sub.2 O with an equimolar amount of 
InBr.sub.3 on the speed of the resulting photothermographic element was 
studied. 
Samples of photothermographic emulsion C were prepared with and without 
chemical sensitizing compound CS-1. Additionally, CaBr.sub.2 was replaced 
with InBr.sub.3 at 0.28 or 1.57 molar equivalent to the CaBr.sub.2. The 
photothermographic emulsion was sensitized with 2.times.10.sup.-5 mol of 
red spectral sensitizing dye SSD-3. 
Samples 6-1 to 6-6 were continuous tone photothermographic elements. 
Samples 6-7 to 6-12 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 633 nm laser, developed, and evaluated as 
described above. 
The results are shown below. In a continuous tone photothermographic 
element, chemical sensitization resulted in an increase in Speed-2 of 0.25 
logE using 1.00 mol equivalent of CaBr.sub.2, an increase in speed of 0.1 
logE using 0.78 mol equivalent of InBr.sub.3 and an increase in speed of 
0.32 logE using 1.57 mol equivalent of InBr.sub.3. In a high-contrast 
photothermographic element, chemical sensitization resulted in an increase 
in Speed-2 of 0.2 logE using 1.00 mol equivalent of CaBr.sub.2, an 
increase in Speed-2 of 0.1 logE using 0.78 mol equivalent of InBr.sub.3, 
and an increase in Speed-2 of 0.2 logE using 1.57 mol equivalent of 
InBr.sub.3. 
______________________________________ 
Ex. CS Added Metal Bromide 
Dmin Dmax 
______________________________________ 
6-1 none CaBr2 .multidot. 2H.sub.2 O 
0.101 4.077 
6-2 CS-1 CaBr2 .multidot. 2H.sub.2 O 
0.127 3.905 
6-3 none 0.78 equiv. InBr.sub.3 
0.092 3.898 
6-4 CS-1 0.78 equiv. InBr.sub.3 
0.1 3.713 
6-5 none 1.57 equiv. InBr.sub.3 
0.103 3.636 
6-6 CS-1 1.57 equiv. InBr.sub.3 
0.111 4.139 
6-7 none CaBr2 .multidot. 2H.sub.2 O 
0.054 3.819 
6-8 CS-1 CaBr2 .multidot. 2H.sub.2 O 
0.061 3.881 
6-9 none 0.78 equiv. InBr.sub.3 
0.05 3.448 
6-10 CS-1 0.78 equiv. InBr.sub.3 
0.062 3.714 
6-11 none 1.57 equiv. InBr.sub.3 
0.058 3.099 
6-12 CS-1 1.57 equiv. InBr.sub.3 
0.058 2.731 
Ex. Speed-2 Speed-5 Contrast-A 
Contrast-D 
6-1 1.865 1.413 0.687 4.438 
6-2 2.113 1.548 0.469 3.571 
6-3 1.927 1.514 0.706 4.875 
6-4 2.011 1.551 0.507 4.391 
6-5 1.663 1.17 0.717 4.196 
6-6 1.983 1.528 0.764 4.482 
6-7 1.975 1.863 1.651 18.07 
6-8 2.165 2.054 0.721 18.118 
6-9 1.962 1.817 1.017 13.748 
6-10 2.07 1.953 0.69 17.241 
6-11 1.783 -- 0.829 -- 
6-12 1.956 -- 1.014 -- 
______________________________________ 
Example 7 
The effect of replacement of CaBr.sub.2.2H.sub.2 O with 1.18 molar 
equivalent of ZnBr.sub.2 on the speed of the resulting photothermographic 
element was studied. The effect of development time on these samples was 
also studied. 
Samples of photothermographic emulsion C were prepared incorporating either 
CaBr.sub.2.2H.sub.2 O or 1.18 molar equivalent of ZnBr.sub.2. The 
photothermographic emulsion was sensitized with 2.times.10.sup.-5 mol of 
red spectral sensitizing dye SSD-3. A sample was also prepared without any 
CS-1. This sample served as a control. 
All samples contained 0.0072 g of compound CN-08 and were high-contrast 
photothermographic elements. Samples were developed on a heated roll 
processor for 15 seconds at 250.degree. F. and for 20 seconds at 
250.degree. F. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
The results are shown below. An increase in Speed-1 of 0.17 logE was found 
with the addition of CS-1 using CaBr.sub.2.2H.sub.2 O and 0.30 logE using 
ZnBr.sub.2. When processed for 20 seconds at 250.degree. F. these effects 
are more pronounced. An increase in Speed-1 of 0.23 logE was found with 
the addition of CS-1 using CaBr.sub.2 and 0.45 logE using ZnBr.sub.2. 
______________________________________ 
CS Development 
Metal 
Ex. Added Conditions Bromide Dmin Dmax 
______________________________________ 
7-1 none 15 sec/250.degree. F. 
CaBr.sub.2 .multidot. 2H.sub.2 O 
0.062 4.733 
7-2 CS-1 15 sec/250.degree. F. 
CaBr.sub.2 .multidot. 2H.sub.2 O 
0.065 4.352 
7-3 none 20 sec/250.degree. F. 
CaBr.sub.2 .multidot. 2H.sub.2 O 
0.077 4.97 
7-4 CS-1 20 sec/250.degree. F. 
CaBr.sub.2 .multidot. 2H.sub.2 O 
0.089 4.753 
7-5 none 15 sec/250.degree. F. 
ZnBr.sub.2 
0.052 4.478 
7-6 CS-1 15 sec/250.degree. F. 
ZnBr.sub.2 
0.058 4.444 
7-7 none 20 sec/250.degree. F. 
ZnBr.sub.2 
0.06 4.836 
7-8 CS-1 20 sec/250.degree. F. 
ZnBr.sub.2 
0.093 4.939 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-C 
7-1 1.666 1.556 1.373 17.4 
7-2 1.839 1.738 1.046 18.517 
7-3 1.876 1.8 2.85 21.117 
7-4 2.108 2.009 1.782 20.383 
7-5 1.729 1.648 2.278 23.121 
7-6 2.031 1.929 1.429 18.665 
7-7 1.946 1.872 4.097 21.446 
7-8 2.405 2.264 1.256 13.008 
______________________________________ 
Example 8 
Samples of photothermographic emulsion C were prepared incorporating 
chemical sensitizing compound CS-1. A sample was also prepared without any 
CS-1. This sample served as a control. The photothermographic emulsions 
were sensitized with 2.times.10.sup.-5 mol of spectral sensitizing dyes 
SSD-3, SSD-4, or SSD-5. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
Samples 8-1 to 8-6 were continuous tone photothermographic elements. 
Samples 8-7 to 8-18 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of a photothermographic silver halide emulsion results in an 
increase in speed of the resulting photothermographic element. This occurs 
in both continuous tone and high-contrast emulsions. In the continuous 
tone elements, an increase in Speed-1 of 0.14 logE was observed with CS-1 
and SSD-3, an increase in Speed-1 of 0.29 logE was observed with CS-1 and 
SSD-4, and an increase in Speed-1 of 0.23 logE was observed with CDS-1 and 
SSD-5. In the high-contrast elements, an increase in Speed-1 of 0.17 logE 
was observed with CS-1 and SSD-3, an increase in Speed-1 of 0.28 logE was 
observed with CS-1 and SSD-4, and an increase in Speed-1 of 0.23 logE was 
observed with CS-1 and SSD-5. 
As shown in Examples 8-13 through 8-18, when samples of these high contrast 
photothermographic elements were developed for 20 seconds at 250.degree. 
F. (i.e., a longer development time), additional increases in Speed-1 were 
found. For example, an increase in Speed-1 of 0.23 logE was observed with 
CS-1 and SSD-3, an increase in Speed-1 of 0.38 logE was observed with CS-1 
and SSD-4, and an increase in Speed-1 of 0.33 logE was observed with CS-1 
and SSD-5. 
______________________________________ 
Ex. CS Added SSD Used Dmin Dmax 
______________________________________ 
8-1 none SSD-3 0.098 3.968 
8-2 CS-1 SSD-3 0.115 3.774 
8-3 none SSD-4 0.088 3.545 
8-4 CS-1 SSD-4 0.104 3.545 
8-5 none SSD-5 0.076 4.129 
8-6 CS-1 SSD-5 0.083 4.112 
8-7 none SSD-3 0.062 4.733 
8-8 CS-1 SSD-3 0.065 4.352 
8-9 none SSD-4 0.056 4.622 
8-10 CS-1 SSD-4 0.059 4.339 
8-11 none SSD-5 0.045 4.537 
8-12 CS-1 SSD-5 0.052 4.488 
8-13 none SSD-3 0.077 4.97 
8-14 CS-1 SSD-3 0.89 4.753 
8-15 none SSD-4 0.06 4.854 
8-16 CS-1 SSD-4 0.074 4.848 
8-16 none SSD-5 0.05 4.788 
8-18 CS-1 SSD-5 0.057 4.81 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-C 
8-1 1.597 1.238 0.647 5.17 
8-2 1.738 1.332 0.542 4.774 
8-3 1.649 1.146 0.804 4.14 
8-4 1.938 1.493 0.58 4.335 
8-5 1.393 1.114 0.823 5.994 
8-6 1.626 1.31 0.696 5.496 
8-7 1.666 1.556 1.373 17.4 
8-8 1.839 1.738 1.046 18.517 
8-9 1.713 1.614 1.619 19.365 
8-10 1.994 1.879 1.272 16.561 
8-11 1.584 1.514 1.338 24.673 
8-12 1.809 1.736 0.834 23.756 
8-13 1.876 1.8 2.85 21.117 
8-14 2.108 2.009 1.782 20.383 
8-15 1.893 1.818 2.842 21.271 
8-16 2.271 2.175 2.117 16.835 
8-17 1.742 1.672 3.471 28.317 
8-18 2.066 2.001 2.909 26.651 
______________________________________ 
Example 9 
Samples of photothermographic emulsion C were prepared incorporating 
chemical sensitizing compound CS-1. A sample was also prepared without any 
CS-1. This sample served as a control. The photothermographic emulsions 
were sensitized with 2.times.10.sup.-5 mol of spectral sensitizing dye 
SSD-6. 
Continuous tone formulations were prepared incorporating an additional 
antifoggant in the topcoat solution. PR-01 This compound was added at an 
amount of 0.045 g per 15 g of topcoat solution for samples 9-1 and 9-2. 
High-contrast coatings were prepared by adding a solution of 0.0108 g of 
compound CN-08 dissolved in 1.5 g of methanol to a 15 g aliquot of the dye 
sensitized silver premix for samples 9-3 and 9-4. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 633 nm laser, developed, and evaluated as 
described above. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of a photothermographic silver halide emulsion results in an 
increase in Speed-2 of the resulting photothermographic element. This 
occurs in both continuous tone and high-contrast emulsions. In the 
continuous tone elements, an increase in Speed-2 of 0.13 logE was 
observed. In a high-contrast element, an increase in Speed-2 of 0.22 logE 
was observed. 
______________________________________ 
Ex. CS Added Dmin Dmax 
______________________________________ 
9-1 none 0.099 4.332 
9-2 CS-1 0.104 4.142 
9-3 none 0.055 4.65 
9-4 CS-1 0.065 4.72 
Ex. Speed-2 Speed-5 Contrast-A 
Contrast-D 
9-1 1.932 1.588 0.573 5.812 
9-2 2.064 1.65 0.511 4.835 
9-3 2.143 2.043 2.315 20.045 
9-4 2.364 2.235 1.547 15.573 
______________________________________ 
Example 10 
Samples of photothermographic emulsion C were prepared incorporating 
chemical sensitizing compound CS-1. A sample was also prepared without any 
CS-1. This sample served as a control. The photothermographic emulsions 
were sensitized with 2.times.10.sup.-5 mol of spectral sensitizing dye 
SSD-7. MBO was not added to the formulation. Samples were prepared with 
and without the addition of MMBI. 
Samples 10-1 to 10-8 were continuous tone photothermographic elements. 
Samples 10-9 to 10-16 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
The results are shown below. In a continuous tone photothermographic 
element containing no MMBI, the addition of CS-1 increased Speed-1 by 0.16 
logE. With MMBI in the topcoat, the addition of CS-1 increased the Speed-1 
by 0.21 logE; however an increase in Dmin was also observed. To improve 
the Dmin, the antifoggant PR-01 was added at two levels, 0.0225 g (-) and 
0.0338 g (+) per 15 g of the topcoat formulation. At (-)PR-01 the addition 
of CS-1 increased the speed 0.1 logE. The Dmin decreased with the addition 
of PR-01 into the topcoat. The addition of CS-1 with these coatings was 
0.17 logE at (-)PR-01 and 0.15 logE at (+)PR-01. 
In a high-contrast photothermographic element containing no MMBI, the 
addition of CS-1 increased the Speed-1 by 0.1 logE. With MMBI in the 
photothermographic element, the addition of CS-1 increased Speed-1 by 0.32 
logE. The addition of PR-01 at 0.0117 g (-) or 0.0176 g (+) to the 
high-contrast formulation also improved the Dmin of the CS-1 coatings. 
With these coatings a Speed-1 increase 0.27 logE at (-)PR-01 and 0.20 logE 
at (+)PR-01 was observed. 
______________________________________ 
CS-1 MMBI PR-01 
Ex. Added Added Added Dmin Dmax 
______________________________________ 
10-1 no no no 0.091 
4.383 
10-2 yes no no 0.138 
4.434 
10-3 yes no yes(-) 0.105 
4.3 
10-4 yes no yes(+) 0.099 
4.258 
10-5 no yes no 0.185 
4.216 
10-6 yes yes no 0.254 
4.306 
10-7 yes yes yes(-) 0.204 
4.178 
10-8 yes yes yes(+) 0.175 
4.288 
10-9 no no no 0.049 
4.947 
10-10 yes no no 0.059 
4.81 
10-11 yes no yes(-) 0.056 
4.808 
10-12 yes no yes(+) 0.057 
4.723 
10-13 no yes no 0.071 
4.641 
10-14 yes yes no 0.104 
4.646 
10-15 yes yes yes(-) 0.096 
4.658 
10-16 yes yes yes(+) 0.085 
4.613 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-C 
10-1 1.787 1.443 0.587 4.95 
10-2 1.948 1.588 0.52 4.561 
10-3 1.882 1.545 0.507 4.42 
10-4 1.838 1.476 0.494 4.632 
10-5 1.648 1.265 0.505 4.258 
10-6 1.862 1.511 0.451 4.061 
10-7 1.824 1.496 0.471 4.335 
10-8 1.798 1.434 0.504 4.667 
10-9 2.015 1.94 4.02 22.126 
10-10 2.125 2.043 1.804 23.197 
10-11 2.003 1.918 2.669 20.432 
10-12 1.898 1.822 1.685 21.519 
10-13 1.819 1.722 1.426 18.252 
10-14 2.148 2.047 1.531 16.17 
10-15 2.085 1.974 1.263 16.821 
10-16 2.022 1.914 1.005 17.551 
______________________________________ 
Example 11 
This example demonstrates the improvement in chemical sensitization by 
carrying out the chemical sensitization at an elevated temperature. 
Samples of photothermographic emulsion C were prepared by carrying out the 
initial steps in the preparation of the photothermographic emulsion at 
23.9.degree. C. and incorporating CS-1. A sample was also prepared without 
any CS-1. This sample served as a control 
Additionally, MMBI and MBO were not added; 
Additionally, CaBr.sub.2.2H.sub.2 O was replaced by 1.18 molar equivalent 
of ZnBr.sub.2. 
The photothermographic emulsions were sensitized with 2.times.10.sup.-5 mol 
of spectral sensitizing dye SSD-8. 
Samples 11-1 and 11-2 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
The sensitometric results, shown below, demonstrate that chemical 
sensitization of a high-contrast photothermographic silver halide emulsion 
at elevated temperature results in an increase in Speed-1 of 0.25 logE in 
the resulting photothermographic element even when no supersensitizers are 
added. 
______________________________________ 
Ex. CS Added Dmin Dmax 
______________________________________ 
11-1 none 0.041 5.036 
11-2 CS-1 0.043 5.05 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-D 
11-1 2.372 2.289 2.682 24.384 
11-2 2.618 2.534 2.669 23.811 
______________________________________ 
Example 12 
The effects of temperature at which the chemical sensitizing compounds are 
added on Speed-2 of the resulting photothermographic element was studied 
as described in Example 11. 
Samples of photothermographic emulsion C were prepared incorporating 
chemical sensitizing compound CS-1 in the photothermographic emulsion at 
temperatures of 21.1.degree. C. or 22.8.degree. C. 
Formulations employing SSD-4 had 2.times.10.sup.-5 mol of spectral 
sensitizing dye and no MBO and no MMBI. 
Formulations employing SSD-5 had 3.times.10.sup.-5 mol of spectral 
sensitizing dye and incorporated MBO and MMBI. 
Samples 12-1 to 12-6 were continuous tone photothermographic elements. 
Samples 12-7 to 12-12 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. Samples 12-1, 12-4, 12-7, and 
12-10 contained no chemical sensitizing compound and served as controls. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
The sensitometric results, shown below, demonstrate that the temperature of 
the emulsion at the time of addition of the chemical sensitizing compound 
is critical to the chemical sensitization process and to the increase in 
Speed-2. This occurs in both continuous tone and high-contrast emulsions. 
For example, in continuous tone samples, when chemical sensitization was 
carried out at 21.1.degree. C. using CS-1 as the chemical sensitizing 
compound and SSD-5 as the spectral sensitizer, an increase in Speed-2 of 
0.1 logE was observed; when the same chemical sensitization was carried 
out at 22.8.degree. C. an increase in Speed-2 of 0.15 logE was observed. 
When chemical sensitization was carried out at 21.1.degree. C. using CS-1 
as the chemical sensitizing compound and SSD-4 as the spectral sensitizer, 
an increase in Speed-2 of 0.21 logE was observed; when the same chemical 
sensitization was carried out at 22.8.degree. C., an increase in Speed-2 
of 0.31 log E was observed. 
In high contrast samples, when chemical sensitization was carried out at 
21.1.degree. C. using CS-1 as the chemical sensitizing compound and SSD-5 
as the spectral sensitizing dye, an increase in Speed-2 of 0.13 logE was 
observed; when the same chemical sensitization was carried out at 
22.8.degree. C. the Speed-2 increase was 0.16 logE. When chemical 
sensitization was carried out at 21.1.degree. C. using CS-1 as the 
chemical sensitizing compound and SSD4 as the spectral sensitizing dye, an 
increase in Speed-2 of 0.1 logE was observed; when the same chemical 
sensitization was carried out at 22.8.degree. C., an increase in speed-2 
of 0.14 log E was observed. 
______________________________________ 
Ex. CS Added SSD-Added Temp. Dmin Dmax 
______________________________________ 
12-1 none SSD-4 21.1.degree. C. 
0.081 3.315 
12-2 CS-1 SSD-4 21.1.degree. C. 
0.086 3.511 
12-3 CS-1 SSD-4 22.8.degree. C. 
0.093 3.425 
12-4 none SSD-5 21.1.degree. C. 
0.079 4.116 
12-5 CS-1 SSD-5 21.1.degree. C. 
0.079 4.111 
12-6 CS-1 SSD-5 22.8.degree. C. 
0.085 4.171 
12-7 none SSD-4 21.1.degree. C. 
0.049 4.857 
12-8 CS-1 SSD-4 21.1.degree. C. 
0.053 4.766 
12-9 CS-1 SSD-4 22.8.degree. C. 
0.051 4.746 
12-10 none SSD-5 21.1.degree. C. 
0.051 4.713 
12-22 CS-1 SSD-5 21.1.degree. C. 
0.05 4.631 
12-12 CS-1 SSD-5 22.8.degree. C. 
0.053 4.514 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-C 
12-1 1.419 0.84 0.711 3.763 
12-2 1.63 1.086 0.814 3.918 
12-3 1.726 1.116 0.763 3.884 
12-4 1.485 1.167 0.945 5.765 
12-5 1.573 1.228 0.708 5.161 
12-6 1.639 1.331 0.738 5.455 
12-7 1.74 1.671 3.305 25.601 
12-8 1.843 1.773 2.12 23.851 
12-9 1.877 1.797 2.326 20.714 
12-10 1.698 1.646 3.996 30.64 
12-11 1.825 1.771 2.375 29.452 
12-12 1.86 1.798 2.216 25.732 
______________________________________ 
Example 13 
The effects of both temperature at which the chemical sensitizing compounds 
are added and replacement of CaBr.sub.2 with an equimolar amount of 
ZnBr.sub.2 on the speed of the resulting photothermographic element was 
studied. 
Samples of photothermographic emulsion C were prepared by carrying out the 
initial steps in the preparation of the photothermographic emulsion at 
21.1.degree. C. or at 23.9.degree. C. and incorporating CS-1. A sample was 
also prepared without any CS-1. This sample served as a control. 
Additionally, CaBr.sub.2.2H.sub.2 O was replaced by 1.18 molar equivalent 
of ZrBr.sub.2. The photothermographic emulsions were sensitized with 
2.times.10.sup.-5 mol of spectral sensitizing dye SSD-3. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 633 nm laser, developed, and evaluated as 
described above. 
Samples 13-1 to 13-3 were continuous tone photothermographic elements. 
Samples 13-4 to 13-6 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. Samples 13-1 and 134 contained 
no CS-1 and served as controls. 
The sensitometric results, shown below, demonstrate the critical importance 
of temperature at which chemical sensitization of a photothermographic 
silver halide emulsion is carried out. 
For example, in continuous tone elements, when chemical sensitization was 
carried out at 21.2.degree. C. using CS-1 as the chemical sensitizing 
compound and SSD-3 as the spectral sensitizing dye, an increase in Speed-2 
of only 0.02 log E was observed; when the same chemical sensitization was 
carried out at 23.9.degree. C. an increase in Speed-2 of 0.24 logE was 
observed. In high-contrast photothermographic samples, when chemical 
sensitization was carried out at 21.2.degree. C. using CS-1 as the 
chemical sensitizing compound and SSD-3 as the spectral sensitizing dye, 
an increase in Speed-2 of only 0.02 log E was observed; when the same 
chemical sensitization was carried out at 23.9.degree. C. an increase in 
Speed-2 of 0.34 logE was observed. 
______________________________________ 
Ex. CS Added SSD-Added Temp. Dmin Dmax 
______________________________________ 
13-1 none SSD-3 21.1.degree. C. 
0.085 4.278 
13-2 CS-1 SSD-3 21.1.degree. C. 
0.086 4.162 
13-3 CS-1 SSD-3 23.9.degree. C. 
0.111 4.066 
13-4 none SSD-3 21.1.degree. C. 
0.045 4.783 
13-5 CS-1 SSD-3 21.1.degree. C. 
0.053 4.797 
13-6 CS-1 SSD-3 23.9.degree. C. 
0.058 4.79 
Ex. Speed-2 Speed-5 Contrast-A 
Contrast-D 
13-1 1.912 1.588 0.746 6.18 
13-2 1.936 1.555 0.518 5.248 
13-3 2.163 1.726 0.587 4.57 
13-4 2.126 2.052 3.143 27.037 
13-5 2.142 2.069 2.677 27.56 
13-6 2.473 2.379 2.333 21.112 
______________________________________ 
Example 14 
Photothermographic emulsion C was prepared incorporating 
2.98.times.10.sup.-5 mol of various chemical sensitizing compounds. 
Samples were also prepared without any chemical sensitizing compounds. 
These samples served as controls. Additionally, CaBr.sub.2.2H.sub.2 O was 
replaced by 1.18 molar equivalent of ZnBr.sub.2. The photothermographic 
emulsions were sensitized with 2.times.10.sup.-5 mol of spectral 
sensitizing dye SSD-3. 
Samples 14-1 to 14-13 were continuous tone photothermographic elements. 
Samples 14-14 to 14-26 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 633 nm laser, developed, and evaluated as 
described above. 
The results are shown below. For a continuous tone photothermographic 
element incorporating CS-7, processing for 15 seconds at 250.degree. F. 
had little effect on Speed-2, CS-3 increased Speed-2 by only 0.06 logE, 
CS-4 and CS-5 increased Speed-2 by less than 0.1 logE, and CS-6 increased 
Speed-2 by 0.18 logE. The speed increase for CS-1 was 0.26 logE. 
In high-contrast photothermographic elements, CS-7 had little effect on 
Speed-2, CS-3 increased Speed-2 only 0.05 logE, CS-4 and CS-5 increased 
Speed-2 by 0.1 logE, CS-6 increased Speed-2 by 0.25 logE, and CS-1 
increased Speed-2 by 0.30 logE. 
When the photothermographic elements were developed for 20 seconds at 
250.degree. F., Speed-2 increases were higher than those observed for 
identical samples developed for 15 seconds. For example, when 
high-contrast photothermographic elements were developed for 20 seconds at 
250.degree. F., an additional Speed-2 increase of 0.25 logE was found for 
CS-1, CS-5, and CS-6, a Speed-2 increase of 0.24 logE was found for. CS-3, 
a Speed-2 increase of 0.15 logE for CS-4, and a 0.15 logE Speed-2 increase 
for CS-7. 
______________________________________ 
CS Development 
Ex. Added Conditions Dmin Dmax 
______________________________________ 
14-1 none 15 sec/250.degree. F. 
0.08 4.466 
14-2 CS-1 15 sec/250.degree. F. 
0.091 
4.372 
14-3 CS-5 15 sec/250.degree. F. 
0.07 4.268 
14-4 CS-7 15 sec/250.degree. F. 
0.075 
4.258 
14-5 CS-3 15 sec/250.degree. F. 
0.086 
4.342 
14-6 CS-4 15 sec/250.degree. F. 
0.086 
4.427 
14-7 CS-6 15 sec/250.degree. F. 
0.094 
4.33 
14-8 CS-1 20 sec/250.degree. F. 
0.127 
4.172 
14-9 CS-5 20 sec/250.degree. F. 
0.101 
4.238 
14-10 CS-7 20 sec/250.degree. F. 
0.092 
4.278 
14-11 CS-3 20 sec/250.degree. F. 
0.093 
4.233 
14-12 CS-4 20 sec/250.degree. F. 
0.12 4.309 
14-13 CS-6 20 sec/250.degree. F. 
0.139 
4.214 
14-14 none 15 sec/250.degree. F. 
0.042 
4.323 
14-15 CS-1 15 sec/250.degree. F. 
0.047 
4.211 
14-16 CS-5 15 sec/250.degree. F. 
0.046 
4.277 
14-17 CS-7 15 sec/250.degree. F. 
0.045 
4.177 
14-18 CS-3 15 sec/250.degree. F. 
0.043 
4.291 
14-19 CS-4 15 sec/250.degree. F. 
0.046 
4.314 
14-20 CS-6 15 sec/250.degree. F. 
0.049 
4.216 
14-21 CS-1 20 sec/250.degree. F. 
0.059 
4.558 
14-22 CS-5 20 sec/250.degree. F. 
0.054 
4.719 
14-23 CS-7 20 sec/250.degree. F. 
0.051 
4.605 
14-24 CS-3 20 sec/250.degree. F. 
0.051 
4.612 
14-25 CS-4 20 sec/250.degree. F. 
0.056 
4.535 
14-26 CS-6 20 sec/250.degree. F. 
0.064 
4.533 
Ex. Speed-2 Speed-5 Contrast-A 
Contrast-C 
14-1 1.843 1.53 0.763 6.444 
14-2 2.096 1.639 0.595 4.442 
14-3 1.928 1.538 0.554 5.17 
14-4 1.819 1.457 0.685 5.617 
14-5 1.9 1.564 0.642 5.994 
14-6 1.924 1.561 0.587 5.514 
14-7 2.019 1.593 0.577 4.726 
14-8 2.211 1.63 0.469 3.44 
14-9 2.01 1.47 0.546 3.8 
14-10 1.928 1.453 0.772 4.257 
14-11 1.962 1.378 0.529 3.485 
14-12 2. 1.491 0.623 3.929 
14-13 2.147 1.602 0.502 3.688 
14-14 1.972 1.885 2.345 23.075 
14-15 2.265 2.158 1.413 18.781 
14-16 2.07 1.979 1.742 22.177 
14-17 1.99 1.905 2.339 23.585 
14-18 2.019 1.929 1.755 22.351 
14-19 2.076 1.99 2.168 23.427 
14-20 2.22 2.122 1.748 20.652 
14-21 2.522 2.396 2.512 16.488 
14-22 2.313 2.226 2.594 23.13 
14-23 2.151 2.082 3.124 29.029 
14-34 2.26 2.18 3.282 25.178 
14-25 2.246 2.156 2.545 22.577 
14-26 2.488 2.39 2.284 20.336 
______________________________________ 
Example 15 
Photothermographic emulsion C was prepared at 23.9.degree. C. incorporating 
2.98.times.10.sup.-5 mol of CS-2 or CS-6. A sample containing no chemical 
sensitizing compound was also prepared. It served as a control. 
Additionally, MMBI and MBO were not added. 
Additionally, CaBr.sub.2.2H.sub.2 O was replaced by 1.18 molar equivalent 
of ZnBr.sub.2. 
All Samples contained 0.0072 g of compound CN-08 and were high-contrast 
photothermographic elements. 
The photothermographic emulsion was sensitized by addition of 
2.times.10.sup.-5 mol of spectral sensitizing dye SSD-8. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
The sensitometric results, shown below, demonstrate an increase in Speed-1 
of 0.26 logE with the addition of CS-2 and an increase in speed of 0.30 
logE with the addition of CS-6 in high-contrast formulations. 
______________________________________ 
Ex. CS Added Dmin Dmax 
______________________________________ 
15-1 none 0.036 4.615 
15-2 CS-2 0.04 4.733 
15-3 CS-6 0.049 4.811 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-D 
15-1 2.155 2.048 1.532 18.681 
15-2 2.423 2.301 1.811 16.384 
15-3 2.461 2.339 1.886 16.485 
______________________________________ 
Example 16 
Photothermographic emulsion C was prepared at 23.9.degree. C. incorporating 
2.98.times.10.sup.-5 mol of chemical sensitizing compounds CS-1, or CS-8. 
A sample containing no chemical sensitizing compound was also prepared. 
This sample served as a control. A sample containing a dye that is not a 
chemical sensitizing compound, non-CS-A, was also evaluated. 
##STR19## 
Additionally, MMBI and MBO were not added. 
Additionally, CaBr.sub.2.2H.sub.2 O was replaced by 1.18 molar equivalent 
of ZnBr.sub.2. 
The photothermographic emulsion was sensitized by addition of 
2.times.10.sup.-5 mol of spectral sensitizing dye SSD-8. 
Samples 16-1 to 16-4 were continuous tone photothermographic elements. 
Samples 16-5 to 16-8 contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. Samples 16-1 and 16-5 contained 
no CS-1 and served as controls. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 670 nm laser, developed, and evaluated as 
described above. 
The results are shown below. In a continuous tone photothermographic 
element, chemical sensitization resulted in an increase in Speed-2 of 0.32 
logE using CS-1 (with some increase in Dmin), an increase in Speed-2 of 
0.12 logE with CS-8 (and no increase in Dmin), and a decrease in Speed-2 
of 0.34 logE using non-CS-A. In a high-contrast photothermographic 
element, chemical sensitization resulted in an increase in Speed-2 of 0.25 
logE using CS-1, an increase in speed of 0.04 logE with CS-8, and a 
decrease in speed of 0.25 logE using non-CS-A. 
______________________________________ 
Ex. CS Added Dmin Dmax 
______________________________________ 
16-1 none 0.086 3.888 
16-2 CS-1 0.132 3.958 
16-3 CS-8 0.085 3.924 
16-4 non-CS-A 0.094 3.515 
16-5 none 0.041 5.036 
16-6 CS-1 0.043 5.05 
16-7 CS-8 0.042 4.963 
16-8 non-CS-A 0.04 4.99 
Ex. Speed-1 Speed-3 Contrast-A 
Contrast-D 
16-1 1.968 1.452 0.481 3.882 
16-2 2.28 1.612 0.526 2.996 
16-3 2.09 1.467 0.544 3.213 
16-4 1.635 0.998 0.395 3.144 
16-5 2.372 2.289 2.628 24.384 
16-6 2.618 2.534 2.669 23.811 
16-7 2.411 2.332 2.744 25.525 
16-8 2.112 2.009 1.76 19.457 
______________________________________ 
Example 17 
The effect chemical sensitization and silver halide grain size used in the 
photothermographic emulsion was studied. A large grain photothermographic 
emulsion containing 0.12 .mu.m size grains was compared with the small 
grain emulsion used in photothermographic emulsion C. Both formulations 
were prepared incorporating 2.times.10.sup.-5 mol of spectral sensitizing 
dye SSD-3 in the photothermographic emulsion. 
Samples 17-1 and 17-2 incorporated a small grain photothermographic 
emulsion. Samples 17-3 and 17-4 incorporated a large grain 
photothermographic emulsion. 
All of these samples contained 0.0072 g of compound CN-08 and were 
high-contrast photothermographic elements. 
The photothermographic emulsion layer and topcoat layer were dual knife 
coated, dried, exposed using a 633 nm laser, developed, and evaluated as 
described above. 
The sensitometric results are shown below. The samples prepared using CS-1 
in small silver halide grain emulsions showed a Speed-2 increase of 0.04 
logE upon chemical sensitization. The photothermographic emulsion prepared 
using CS-1 in large silver halide grains showed a Speed-2 increase of 0.08 
logE above that using the small silver halide grain emulsion. 
Additionally, the photothermographic emulsion using the large size silver 
halide grains showed a further speed increase of 0.80 logE upon chemical 
sensitization. It should be noted that photothermographic elements 
prepared from the large grain photothermographic emulsion had slightly 
higher Dmin (+0.01) and lower contrast (15.9) than those prepared from the 
small grain emulsion. 
______________________________________ 
Ex. CS Added Dmin Dmax 
______________________________________ 
17-1 none 0.056 4.908 
17-2 CS-1 0.056 4.743 
17-3 none 0.064 4.823 
17-4 CS-1 0.096 4.515 
Ex. Speed-2 Speed-5 Contrast-A 
Contrast-D 
17-1 2.166 2.092 2.812 26.975 
17-2 2.204 2.112 2.268 21.839 
17-3 2.247 2.12 2.214 15.886 
17-4 3.043 2.864 1.271 11.203 
______________________________________ 
Examples 18-24 
Examples 18-24 demonstrate the criticality of the order of addition of the 
chemical sensitizing compound, the oxidizing agent, and the spectral 
sensitizing dye. 
Photothermographic emulsion C was prepared incorporating 2.times.10.sup.-5 
mol of spectral sensitizing dye SSD-3 in the photothermographic emulsion. 
As described above, the initial steps of the preparation of the 
photothermographic emulsion were carried out at 23.9.degree. C.; the final 
steps were carried out at 11.6.degree. C. 
MBO was not added to the formulation. 
Additionally, CaBr.sub.2.2H.sub.2 O was replaced by 1.18 molar equivalent 
of ZnBr.sub.2. 
Examples 18-24 contained 0.0072 g of compound CN-08 and were high-contrast 
photothermographic elements. 
The order of addition of the relevant materials is shown below. 
Example 18 
Control 
PHP 
ZnBr.sub.2 
SSD-3/MMBI spectral sensitizing dye solution 
Antifoggant-1 
This sample had no chemical sensitizing compound 
Example 19 
Invention 
Chemical sensitizing compound CS-1 
PHP 
ZnBr.sub.2 
SSD-3/MMBI spectral sensitizing dye solution 
Antifoggant-1 
Example 20 
PHP 
ZnBr.sub.2 
Chemical sensitizing compound CS-1 
SSD-3 MMBI spectral sensitizing dye solution 
Antifoggant-1 
In this sample, the chemical sensitizing compound was added after the PHP 
and before the spectral sensitizing dye solution. 
Example 21 
PEP 
ZnBr.sub.2 
SSD-3 MMBI spectral sensitizing dye solution 
Chemical sensitizing compound CS-1 
Antifoggant-1 
In this sample, the chemical sensitizing compound was added after the PHP 
and after the spectral sensitizing dye solution. 
Example 22 
SSD-3/MMBI spectral sensitizing dye solution 
PHP 
ZnBr.sub.2 
Chemical sensitizing compound CS-1 
Antifoggant-1 
In this sample, the spectral sensitizing dye solution was added before the 
PHP and the chemical sensitizing compound was added after the PHP. 
Example 23 
PHP 
ZnBr.sub.2 
Chemical sensitizing compound CS-1 
Antifoggant-1 
In this sample the chemical sensitizing compound was added after the PHP 
and no spectral sensitizing dye solution was added. 
Example 24 
Chemical sensitizing compound CS-1 
ZnBr.sub.2 
SSD-3/MMBI spectral sensitizing dye solution 
Antifoggant-1 
In this sample no PHP was added. 
For all samples, the photothermographic emulsion layer and topcoat layer 
were dual knife coated, dried, exposed using a 633 nm laser, developed, 
and evaluated as described above. 
The results, shown below, demonstrate that the chemical sensitizing 
compound must be added before the oxidizing agent to produce 
photothermographic materials with high speed and low fog. 
In Example 19, where the CS-1 was added before the PEP, a Speed-2 increase 
of 0.53 log E was found when compared with Example 18, the control sample 
containing no CS-1. There is a small increase of 0.04 in Dmin and some 
loss in contrast. As in the examples above, this small increase in Dmin 
and loss in contrast can be reduced by decreasing the amount of chemical 
sensitizing compound added or reducing the initial temperature during this 
addition. 
In Example 20, where the CS-1 was added after the PHP, there was virtually 
no effect on the sensitometric response such as the speed increase 
observed in Example 19. The sensitometry of Example 20 was very similar to 
Example 18. 
In Example 21, where the CS-1 was added after the spectral sensitizing dye, 
there was virtually no effect on the sensitometric response such as the 
speed increase observed in Example 19. The sensitometry of Example 21 was 
very similar to Example 18. 
In Example 22 where the chemical sensitizing compound was added before the 
PHP, the samples fogged. 
In Example 23, where the chemical sensitizing compound was added after the 
PHP, but without a spectral sensitizing dye no image was obtained. 
In Example 24, where the chemical sensitizing compound was added but PHP 
was not added, the samples fogged. 
______________________________________ 
Ex. Dmin Dmax 
______________________________________ 
18 0.05 4.576 
19 0.092 4.107 
20 0.042 4.383 
21 0.046 4.408 
22 Fogged -- 
23 No Image -- 
24 Fogged -- 
Ex. Speed-2 Speed-5 Contrast-1 
Contrast-3 
18 2.066 1.971 1.28 21.114 
19 2.595 2.426 0.973 12.086 
20 2.043 1.939 1.985 19.406 
21 2.049 1.95 1.611 20.448 
22 -- -- -- -- 
23 -- -- -- -- 
24 -- -- -- -- 
______________________________________ 
Examples 25-30 
Examples 25-30 demonstrate the criticality of the place in the preparation 
of the photothermographic emulsion where the chemical sensitizing compound 
must be added. Examples 25-30 also demonstrate the use of 
2-thio-3-phenethyl-4-oxo-oxazolidine described in U.S. Pat. No. 4,207,108 
(Hiller) in a photothermographic element. This compound was prepared by 
the general procedure of Tsukamoto, S. et. al. J. Med Chem. 1993, 36, 
2292-2299. It has the structure shown below. 
##STR20## 
Photothermographic Emulsion D 
A pre-formed iridium-doped core-shell silver behenate full soap was 
prepared as described in U.S. Pat. No. 5,434,043 incorporated herein by 
reference. 
The pre-formed soap contained 2.0 wt % of a 0.05 .mu.m diameter 
iridium-doped core-shell silver iodobromide emulsion (25% core containing 
8% iodide, 92% bromide; and 75% all bromide shell containing 
1.times..sup.-5 mol of iridium). A dispersion of this silver behenate full 
soap was homogenized to 26.5% solids in 2-butanone containing 1.3% 
Butvar.TM. B-79. 
To 172 g of this silver full soap dispersion, maintained at 76.degree. F. 
(24.4.degree. C.) and stirred at 400 rpm, was added 23 g of 2-butanone. 
For Examples 27 and 28, stirring for 10 minutes was followed by addition 
of a suspension or solution of the chemical sensitizing compound in 3.00 g 
of methanol. After mixing for 30 minutes, a solution of 0.23 g of 
pyridinium hydrobromide perbromide dissolved in 1.5 g of methanol was 
added. After 30 minutes of mixing, a solution of 0.17 g of 
CaBr.sub.2.2H.sub.2 O dissolved in 1.5 mL of methanol was added. For 
Example 29, stirring for 5 minutes was followed by addition of a 
suspension or solution of the chemical sensitizing compound in 3.00 g of 
methanol. Mixing for 30 minutes was followed by addition of a solution of 
spectral sensitizing dye SSD-1 prepared by mixing the following 
ingredients. 
______________________________________ 
Material Amount 
______________________________________ 
MMBI 0.098 g 
CBBA 1.59 g 
SSD-1 0.0448 
MeOH 72.1 g 
2-Butanone 22.4 g 
______________________________________ 
After 60 minutes of mixing, the temperature was lowered from 24.4.degree. 
C. to 10.0.degree. C. and 0.96 g of a 25% solution of Vitel.TM. PE-2200 in 
2-butanone was added. Mixing for 30 minutes was followed by addition of 
45.8 g of Butvar.TM. B-79. After stirring at 850 rpm for 30 minutes, the 
following components were then added every 15 minutes. 
______________________________________ 
Material Amount 
______________________________________ 
Antifoggant-1 1.23 g dissolved in 
MEK 15 g 
Permanax .TM. 10.6 g 
THDI 0.63 g dissolved in 
MEK 1.5 g 
TCPA 0.35 g dissolved in 
MEK 1.0 g 
PHZ 1.05 g dissolved in 
MeOH 6.00 g 
4-MPA 0.47 g dissolved in 
MEK 3.5 g and 
MeOH 0.5 g 
______________________________________ 
In Examples 30, stirring for 15 minutes was followed by addition of a 
suspension or solution of chemical sensitizing in 3.00 g of methanol as 
described below. 
This photothermographic emulsion was used "as is" to prepare a continuous 
tone photothermographic element. 
A topcoat solution was prepared in the following manner; 13.95 g of CAB 
171-15S was dissolved in 551 g of 2-butanone. To this was added 1.86 g of 
Acryloid.TM. A-21. To this premix was then added 0.86 g of vinylsulfone 
VS-1 (71% solids in ethanol), 0.51 g of antihalation dye AH-2 and the 
indicated amount of PR-01 or PR-08 if used. 
The photothermographic emulsion layer and topcoat were dual knife coated 
onto a 7 mil (176 .mu.m) blue tinted polyethylene terephthalate support 
provided with an antihalation back-coating containing AH Dye-2 in CAB 
381-20 resin. The coating gap for the photothermographic emulsion layer 
was 3.8 mil (96.5 .mu.m) over the support and the coating gap for the 
topcoat layer was 5.2 mil (132 .mu.m) over the support. The samples were 
each dried at 185.degree. C. for 4 minutes. 
Example 25 contained no chemical sensitizing compound. It served as a 
control. 
Example 26 contained 0.020 g of CS-1 (1.times.level). 
Example 27 contained 0.013 g of 2-thio-3-phenethyl-4-oxo-oxazolidine 
(1.times.level). 
Example 28 contained 0.026 g of 2-thio-3-phenethyl-4-oxo-oxazolidine 
(2.times.level). 
Example 29 contained 0.013 g of 2-thio-3-phenethyl-4-oxo-oxazolidine 
(1.times.level) added after the CaBr.sub.2. 
Example 30 contained 0.013 g of 2-thio-3-phenethyl-4-oxo-oxazolidine 
(1.times.level) added at the end of the preparation of the 
photothermographic emulsion. 
Samples 25-2, 26-2, 27-2, 28-2, 29-2, and 30-2 contained 0.31 g of PR-01. 
Samples 25-3, 26-3, 27-3, 28-3, 29-3, and 30-3 contained 0.12 g of PR-08. 
Samples were stored in the dark for 5 days under ambient conditions. They 
were then cut into 1.5 inch by 8 inch strips (3.8 cm.times.20.3 cm) and 
exposed using a laser sensitometer incorporating a 810 nm laser diode as 
described in Example 2 above. After exposure, the film strips were 
developed on a round drum thermal processor for 15 seconds at 255.degree. 
F. (123.9.degree. F.). Sensitometry was determined as described in 
Examples 14 above. 
The results, shown below, demonstrate that the chemical sensitizing 
compound must be added before the oxidizing agent to achieve chemical 
sensitization and to produce photothermographic materials with high speed 
and low fog. In general, the samples where the chemical sensitizing 
compound was added before the oxidizing agent have higher Dmax, Speed-2, 
Speed-3, and Contrast-3 than the samples in which the chemical sensitizing 
compound was added either after the addition of the CaBr.sub.2 or at the 
end of the preparation of the photothermographic emulsion. The samples in 
which the chemical sensitizing compound was added after the CaBr.sub.2 had 
high levels of fog (i.e., high Dmin). The samples in which the chemical 
sensitizing compound was added at the end of the preparation of the 
photothermographic emulsion have similar sensitometry to the control 
sample which contained no chemical sensitizing compound. It should also be 
noted that 2-thio-3-phenethyl-4-oxooxazolidine provides less chemical 
sensitization of photothermographic emulsions than CS-1, even when used at 
twice the amount. 
______________________________________ 
Ex. PR Compound Added Dmin Dmax 
______________________________________ 
25-1 none 0.228 3.85 
25-2 PR-01 0.204 3.74 
25-3 PR-08 0.204 3.67 
26-1 none 0.219 4.37 
26-2 PR-01 0.190 4.33 
26-3 PR-08 0.190 4.17 
27-1 none 0.191 3.63 
27-2 PR-01 0.183 3.72 
27-3 PR-08 0.181 3.52 
28-1 none 0.195 3.69 
28-2 PR-01 0.188 3.85 
28-3 PR-08 0.186 3.74 
29-1 none 1.04 4.38 
29-2 PR-01 0.630 4.24 
29-3 PR-08 0.581 4.04 
30-1 none 0.209 3.55 
30-2 PR-01 0.188 3.57 
30-3 PR-08 0.188 3.61 
Ex. Speed-2 Speed-3 Contrast-1 
Contrast-3 
25-1 1.59 1.11 4.08 2.99 
25-2 1.50 1.07 4.13 3.98 
25-3 1.48 0.99 3.63 3.72 
26-1 1.98 1.55 4.11 3.69 
26-2 1.92 1.54 4.46 4.71 
26-3 1.87 1.46 3.94 5.04 
27-1 1.58 1.07 4.00 2.70 
27-2 1.50 1.08 4.12 4.27 
27-3 1.48 0.98 3.58 3.58 
28-1 1.68 1.19 4.03 2.75 
28-2 1.64 1.22 4.39 3.63 
28-3 1.59 1.12 3.77 3.85 
29-1 2.23 1.26 3.27 1.12 
29-2 2.12 1.59 3.49 2.87 
29-3 2.02 1.38 2.90 2.72 
30-1 1.52 1.03 3.88 3.07 
30-2 1.44 0.98 4.28 3.26 
30-3 1.44 0.96 3.77 3.64 
______________________________________ 
Examples 31-34 
Examples 31-34 further demonstrate the criticality of the place in the 
preparation of the photothermographic emulsion where the chemical 
sensitizing compound must be added. They also demonstrate the use of 
N-ethyl-rhodanine described in U.S. Pat. No. 4,207,108 (Hiller) in a 
photothermographic element. 
Photothermographic Emulsion E 
The following procedure was carried out under red light. A pre-formed 
iridium-doped core-shell silver behenate full soap was prepared as 
described in U.S. Pat. No. 5,434,043 incorporated herein by reference. 
The pre-formed soap contained 2.0 wt % of a 0.05 .mu.m diameter 
iridium-doped core-shell silver iodobromide emulsion (25% core containing 
8% iodide, 92% bromide; and 75% all bromide shell containing 
1.times.10.sup.-5 mol of iridium). A dispersion of this silver behenate 
full soap was homogenized to 22.3% solids in 2-butanone containing 1.1% 
Butvar.TM.. 
To 257.87 g of this silver full soap dispersion, maintained at 67.degree. 
F. (19.4.degree. C.) and stirred at 400 rpm, was added 11.19 g of 
2-butanone. In Examples 31 and 32, stirring for 30 minutes was followed by 
addition of a suspension or solution of chemical sensitizing compound as 
described below. 
After mixing for 30 minutes, a solution of 0.286 g of pyridinium 
hydrobromide perbromide dissolved in 1.62 g of methanol was added. After 
60 minutes of mixing, a solution of 0.218 g of CaBr.sub.2 .cent.2H.sub.2 O 
dissolved in 1.24 g of methanol was added. The red safelights were changed 
to infrared safelights; mixing for 30 minutes was followed by addition of 
a solution of spectral sensitizing dye prepared by mixing the following 
ingredients. 
______________________________________ 
Material Amount 
______________________________________ 
SSD-1 0.0040 g 
MMBI 0.181 g 
CBBA 2.01 g 
MeOH 10.44 g 
2-Butanone 2.61 g 
______________________________________ 
After 60 minutes of mixing, the temperature was lowered to 50.degree. F. 
(10.degree. C.). After 30 minutes, 65.55 g of Butvar.TM. B-79 was added. 
While stirring at 1000 rpm for 30 minutes, the following components were 
added every 15 minutes. 
______________________________________ 
Material Amount 
______________________________________ 
Antifoggant-1 1.55 g dissolved in 
MEK 17.88 g 
Permanax .TM. 13.45 g 
THDI 0.79 g dissolved in 
MEK 0.79 g 
TCPA 0.444 g dissolved in 
MEK 1.26 g 
PHZ 1.333 g dissolved in 
MeOH 4.73 g 
4-MPA 0.666 g dissolved in 
MEK 3.87 g 
______________________________________ 
In Examples 34 and 35, stirring for 15 minutes was followed by addition of 
a suspension or solution of chemical sensitizing compound as described 
below. 
Each of these photothermographic emulsions was used "as is" to prepare a 
continuous tone photothermographic element. 
A topcoat solution was prepared in the following manner; 45.52 g of CAB 
171-15S was dissolved in 255.13 g of 2-butanone. To this was added a 
solution of 1.15 g of CaCO.sub.3 in 1.55 g of CAB 171-15S and 8.77 g of 
2-butanone. 281.94 g of MEK was added, followed by 1.81 g of Acryloid.TM. 
A-21. To this premix was then added 0.79 g of VS-1, a vinylsulfone (79% 
solids in ethanol), 0.31 g of BZT, and 0.072 g of antihalation dye AH-2. 
Each of the photothermographic emulsions and a 20 g aliquot of topcoat 
formulations were dual knife coated onto a 7 mil (176 .mu.m) blue tinted 
polyethylene terephthalate support. The coating gap for the 
photothermographic emulsion layer was 3.7 mil (94.0 .mu.m) over the 
support. The coating gap for the topcoat layer was 4.9 mil (124.5 .mu.m) 
over the support. The samples were each dried at 175.degree. C. for 4 
minutes. All samples were continuous tone photothermographic elements. 
Example 31 contained no chemical sensitizing compound; it serves as a 
control. 
Example 32 contained 0.0195 g of CS-1 in 11.19 g of MEK/MeOH (50:50 wt %); 
it was added before the PHP oxidizing agent. 
Example 33 contained 0.0069 g of N-ethyl-rhodanine in 11.19 g of MEK/MeOH 
(50:50 wt %); it was added before the PHP. 
Example 34 contained 0.0195 g of CS-1 in 8.0 g of MEK; it was added at the 
end of the preparation of the photothermographic emulsion. 
Example 35 contained 0.0069 g of N-ethyl-rhodanine in 8.0 g of MEK; it was 
added at the end of the preparation of the photothermographic emulsion. 
Samples were stored in the dark for 5 days under ambient conditions. They 
were then cut into 1.5 inch by 8 inch strips (3.8 cm.times.20.3 cm) and 
exposed using a laser sensitometer incorporating a 810 nm laser diode as 
described in Example 2 above. After exposure, the film strips were 
developed on a heated round drum thermal processor for 15 seconds at 
255.degree. F. (123.9.degree. F.). Sensitometry was determined as 
described in Examples 1-4 above. 
The results, shown below, further demonstrate that the chemical sensitizing 
compound must be added before the oxidizing agent to achieve chemical 
sensitization and to produce photothermographic materials with high speed 
and low fog. The samples where the chemical sensitizing compound was added 
before the oxidizing agent have higher Dmax, Speed-2, Speed-3, and 
Contrast-3 than the samples in which the chemical sensitizing compound was 
added at the end of the preparation of the photothermographic emulsion. 
The samples in which the chemical sensitizing compound was added at the 
end of the preparation of the photothermographic emulsion have similar 
sensitometry to the control sample which contained no chemical sensitizing 
compound. 
______________________________________ 
Ex. Dmin Dmax 
______________________________________ 
31 0.229 3.69 
32 0.238 3.99 
33 0.304 3.96 
34 0.234 3.56 
35 0.262 3.44 
Ex. Speed-2 Speed-3 Contrast-1 
Contrast-3 
31 1.53 1.06 4.25 3.18 
32 1.79 1.33 4.20 3.43 
33 1.78 1.29 4.06 5.45 
34 1.51 1.00 4.35 2.57 
35 1.50 0.90 4.09 1.96 
______________________________________ 
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.