Photothermographic materials and process

A covering power imaging heat developable and heat stabilizable photographic material comprising in reactive assocation (a) photographic silver salt, (b) a photographic silver salt developing agent, (c) an activating concentration of a certain development activator precursor and (d) a polymeric binder, enables an image to develop and be stabilized even though the photothermographic material contains no separate post-processing image stabilizer, and also enables silver image development efficiency of at least 90% when the material is heated to a temperature within the range of about 120.degree. to 200.degree. C. An image can be developed in this heat developable and heat stabilizable photographic material by merely heating the material after imagewise exposure to moderately elevated temperatures. Other addenda employed in heat developable materials can be employed in the described heat developable photographic materials.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to heat developable and heat stabilizable materials 
and processes for developing an image employing the described materials. 
In one of its aspects it relates to a heat developable and heat 
stabilizable photographic element comprising the described combination of 
components. In another aspect it relates to a heat developable and heat 
stabilizable photographic composition comprising the described imaging 
combination. A further aspect of the invention relates to a process of 
developing and stabilizing an image in a heat developable photographic 
material containing the described imaging combination. 
2. Description of the State of the Art 
It is known to obtain an image in an imaging material, especially a 
photographic imaging material, by what is known as dry processing with 
heat. These materials are sometimes described as heat developable 
photographic materials or photothermographic materials. Such heat 
developable photographic materials are imagewise exposed to provide a 
latent image. They are then heated to provide a developed image in the 
absence of separate processing solutions or baths. Typical heat 
developable imaging materials or photothermographic materials are 
described, for example, in U.S. Pat. No. 3,152,904 of Sorenson et al, 
issued Oct. 13, 1964; U.S. Pat. No. 3,457,075 of Morgan et al, issued July 
22, 1969; U.S. Pat. No. 3,152,903 of Shepard et al, issued Oct. 13, 1964; 
U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; and British 
Specification No. 1,161,777 published Aug. 20, 1969. 
Most heat developable photographic materials or photothermographic 
materials comprising photosensitive silver compounds have required a 
separate post-processing image stabilizer or stabilizer precursor to 
enable a stable image after processing. Typically, the post-processing 
stabilizer or stabilizer precursor has been incorporated in the 
photothermographic material and is a sulfur-containing compound. Upon 
heating the image stabilizer or stabilizer precursor forms a stable silver 
mercaptide or silver complex with the silver compounds in the non-image 
areas of the photographic material. This provides post-processing image 
stabilization. Sulfur-containing stabilizers or stabilizer precursors of 
this class are described, for example, in U.S. Pat. No. 3,301,678 of 
Humphlett et al, issued Jan. 31, 1967; U.S. Pat. No. 3,506,444 of Haist et 
al, issued Apr. 14, 1970; and U.S. Pat. No. 3,669,670 of Haist et al, 
issued June 13, 1972. Typical sulfur-containing image stabilizer 
precursors are isothiouronium compounds which provide stabilization of a 
developed image upon heating of the material containing the described 
stabilizer precursors. It has been advantageous to provide a material 
which enables a stabilized image in the absence of these image stabilizers 
or stabilizer precursors or other compounds designed as post-processing 
stabilizers. However, none of the above patents suggest a solution to this 
problem. 
It has also been typical to incorporate what is known as an activator or 
activator precursor in a heat developable and heat stabilizable 
photographic material. Such activators or activator precursors upon 
heating provide activation of the imaging process. Usually these compounds 
enable activation of the developing agent or developing agent precursor to 
provide development of the latent image in the heat developable material. 
These activators or activator stabilizers are typically alkali-release or 
base-release compounds which provide the desired increase in pH in the 
photographic material upon heating of the activator or activator 
precursor. Examples of activators or activator precursors in heat 
developable photographic materials or photothermographic materials are 
described, for instance, in U.S. Pat. No. 3,531,285 of Haist et al, issued 
Sept. 29, 1970. An example of an activator precursor which has been used 
in a heat developable material is guanidinium trichloroacetate which 
provides an increase in pH in the described heat developable photographic 
material. It has been desirable in these heat developable photographic 
materials to provide an increased development efficiency of the latent 
image. Typically the development efficiency of the latent image is far 
less than 90% and typically within the range of about 30 to 50% 
development efficiency. Accordingly, a significant concentration of the 
photographic silver salt remains unused in the development process. The 
mass of silver developed in these heat developable materials has been 
dependent upon the degree of imagewise exposure provided. It has been 
desirable to provide a material which is less dependent upon exposure and 
more dependent upon the development process to provide the desired 
development efficiency. The described activator precursors have not 
provided the desired increased development efficiency or enabled 
post-processing image stabilization in the absence of a separate image 
stabilizer or stabilizer precursor. 
Further, it has been desirable to provide heat developable photographic 
materials which enable the stabilization of a processed image and provide 
development efficiency greater than 90% and still enable the use of 
conventional silver salt developing agents, especially silver halide 
developing agents, known to be useful in heat developable photographic 
materials. Many heat developable photographic materials used commercially 
employ unconventional reducing agents which require costly processes of 
preparation. It has been desirable to eliminate this problem with a heat 
developable photographic material which provides the described advantages 
and also enables use of conventional developing agents or developing agent 
precursors which can be incorporated in photographic materials without 
adversely affecting the desired properties of the photographic material. 
Commercially available photothermographic materials have used such a 
reducing agent as 2,2'-methylene bis(4-methyl-6-tertiary butylphenol) 
which is not a conventional, easily prepared silver halide developing 
agent. This reducing agent also does not provide the desired development 
efficiency nor does it enable stabilization of an image in the absence of 
a separate post-processing image stabilizer. 
It has been desirable to provide a heat developable photographic material 
which enables the use of a reduced concentration of silver in the imaging 
process and material. The heat developable materials described have not 
enabled the desired degree of reduction of silver in a heat developable 
material. 
One of the advantages of a photographic material which is heat developable 
and employs no separate post-processing image stabilizer or stabilizer 
precursor is that improved processing temperature latitude can be provided 
due to the fact that no stabilization reaction is required to compete with 
the image development reaction. Also, light stability of a processed 
material in the absence of a separate stabilizer can be superior to that 
of heat developable materials comprising a sulfur-containing stabilizer 
because no silver mercaptide is formed which can photolytically form 
silver sulfide over an extended time. Also, in the absence of the silver 
mercaptide, better light absorption characteristics can be observed to 
provide improvement in image contrast when observed with near ultraviolet 
radiation. This is advantageous in the graphic arts area involving 
reproduction of materials which are sensitive to ultraviolet radiation. 
Another property which has been desirable in heat developable materials as 
described has been the property of non-volatility of the activators or 
activator precursors which are useful in heat developable materials. 
Unfortunately, heat developable photographic materials or 
photothermographic materials containing such an activator or activator 
precursor as guanidinium trichloroacetate do not provide this advantage. 
Photographic materials which provide for development of a latent image by 
conventional processing solutions or baths are well known. It is also 
known to provide development of an image in such materials by what is 
known as covering power imaging. A fundamental difference exists between 
conventional silver development processes and what are known as covering 
power imaging processes. In most conventional photographic silver 
materials, changes in optical density with exposure arise primarily from 
differences in the amount of silver reduced at the latent image sites. In 
silver covering power imaging the amount of silver reduced does not vary 
greatly with exposure. In such covering power imaging, density variations 
at image areas are due, for the most part, to differences in silver 
covering power at various exposure levels. Silver covering power imaging 
as used herein is intended to mean imaging in a photographic material in 
which variations in optical density of the developed image derive 
primarily from variations in silver covering power as a function of 
exposure. Covering power as used herein is intended to mean the measure of 
the silver opacity in the developed image and is derived arithmetically by 
dividing (a) the optical density by (b) the grams of developed silver per 
square decimeter in the layer of the material containing the developed 
image. Covering power and covering power imaging are known in conventional 
photographic materials which provide development with processing solutions 
or baths. This is described, for example, in the article by K. Murofushi, 
J. Soc. Sci. Phot., Japan, Volume 30 (4), 193-198 (1967), Canadian Pat. 
No. 808,585 and "The Theory of the Photographic Process," 3rd Ed., by 
Mees, 1966, pages 74-75 and 419-420. None of the photographic materials 
described have used covering power imaging in heat developable and heat 
stabilizable materials. 
It has been desirable to provide a heat developable and heat stabilizable 
photographic material which provides development efficiency of an image of 
at least 90% and enables a developed and stabilized image to be provided 
in the absence of a separate post-processing image stabilizer or 
stabilizer precursor. 
SUMMARY OF THE INVENTION 
It has been found according to the invention that the described advantages 
can be provided in a covering power imaging, heat developable and heat 
stabilizable photographic material comprising in reactive association (a) 
photographic silver salt, especially photographic silver halide, (b) a 
photographic silver salt developing agent, especially a photographic 
silver halide developing agent, (c) an activating concentration of a 
development activator precursor represented by the formula: 
EQU A.sup..sym. .multidot. B.sup..crclbar. 
wherein A.sup..sym. is a protonated primary, secondary or tertiary amine 
having a pKa within the range of about 8 to 12; and B.sup..crclbar. is a 
carboxylate ion, as described herein, wherein the activator precursor 
releases a non-volatile amine moiety at a temperature within the range of 
120.degree. to 200.degree. C, (d) a polymeric binder, and wherein the heat 
developable and heat stabilizable photographic element (1) contains no 
separate post-processing image stabilizer and (2) provides silver image 
development efficiency of at least 90% when heated to a temperature within 
the range of 120.degree. to 200.degree. C. Development and stabilization 
of an image in the described heat developable and heat stabilizable 
materials can be provided by merely heating the material at moderately 
elevated temperatures until the desired image is developed, such as for 
several seconds, at a temperature within the range of about 120.degree. to 
about 180.degree. C. No processing solutions or baths are required to 
provide a developed image having the described properties. Also, none of 
the described development activator precursors have been used in the past 
in processing baths or solutions for covering power imaging as described. 
DETAILED DESCRIPTION OF THE INVENTION 
An important embodiment of the invention is a covering power imaging, heat 
developable and heat stabilizable photographic element comprising a 
support having thereon in reactive association the described components 
(a), (b), (c), and (d). An especially useful embodiment is one containing 
the described components in which the photographic silver salt is 
photographic silver halide and the photographic silver salt developing 
agent is a 3-pyrazolidone silver halide developing agent, including 
combinations of such a developing agent with other suitable developing 
agents. 
The term "covering power imaging" as employed herein is intended to refer 
to a photographic silver salt material in which the imaging mechanism is 
one in which the required mass of silver developed is essentially 
independent of exposure. It is also intended to include those materials in 
which covering power variations responsible for imaging arise from silver 
particle size differences in the exposed and unexposed areas primarily. 
The particles developed in the unexposed areas of the photographic 
material with covering power imaging are formed by what is believed to be 
solution physical development on fog centers, and typically have particle 
diameters ten times as large and contain about 1,000 times as much silver 
as the silver particles in the exposed and maximum density areas of the 
developed photographic material. In the resulting image areas, a roughly 
ten-fold difference in transmission density between maximum density and 
minimum density can be expected. In view of the fact that development is 
essentially complete throughout the element, that is a development 
efficiency of at least 90% occurs, no need is present for fixation or 
stabilization of undeveloped silver ions. The excellent photolytic 
stability of the photographic materials upon development is a direct 
consequence of the fact that no photosensitive or other silver salts or 
complexes remain in any part of the element to print-up after processing. 
Total development to a degree of at least 90% in the exposed and unexposed 
areas of the element also provides insurance against undesired fog 
formation from over processing and results in desired processing 
temperature latitude. 
The term "protonated primary, secondary or tertiary amine" is intended to 
mean a moiety that provides the desired activation of the silver salt 
developing agent as described and enables the desired covering power 
imaging. The term "protonated" is intended to mean an amine moiety to 
which one or more hydrogen ions (H.sup.+) is attached forming a positively 
charged ion. 
An especially useful covering power imaging, heat developable and heat 
stabilizable element according to the invention comprises a support having 
thereon in reactive association described components (a), (b), (c), and 
(d) and wherein the development activator precursor is one in which 
A.sup..sym. is represented by the formula: 
##STR1## 
wherein R.sup.1 and R.sup.2 are independently selected from the group 
consisting of hydrogen and alkyl containing 1 to 10 carbon atoms such as 
methyl, propyl, pentyl and the like. Alkyl as employed herein is intended 
to include alkyl containing substituent groups which do not adversely 
affect the desired properties of the heat developable and heat 
stabilizable photographic materials of the invention. A suitable 
substituent group which does not adversely affect the desired properties 
is hydroxyl. 
Another especially useful photothermographic element as described is one in 
which the carboxylate ion moiety B.sup..crclbar. in the activator 
precursor is an alpha-sulfonylacetic acid. An especially useful 
alpha-sulfonylacetic acid is one represented by the formula: 
##STR2## 
wherein w is 1 or 2; R.sup.3 is alkyl containing 1 to 10 carbon atoms, 
such as methyl, ethyl, propyl, and butyl; aryl containing 5 to 10 carbon 
atoms, such as phenyl and pyridyl; or carboxymethyl when w is 1 and 
alkylene containing 1 to 6 carbon atoms, such as ethylene or arylene 
containing 6 to 8 carbon atoms, such as phenylene and phenylethylene when 
w is 2; R.sup.4 and R.sup.5 can be the same or different and individually 
represent hydrogen, alkyl containing 1 to 6 carbon atoms, such as methyl, 
ethyl, propyl and hexyl, or aryl containing 5 to 10 carbon atoms, such as 
phenyl and pyridyl. Aryl, alkylene, arylene and alkyl as employed herein 
are intended to include the described groups which are unsubstituted or 
contain substituent groups which do not adversely affect the desired 
properties of the described heat developable and heat stabilizable 
photographic materials of the invention. Examples of suitable groups which 
can be used as substituents include hydroxyl, carboxamido, carbamoyl and 
alkylsulfonyl. 
Examples of useful protonated primary amines as described are: 
##STR3## 
Examples of useful protonated secondary amines as described are: 
##STR4## 
Examples of useful protonated tertiary amines as described are: 
##STR5## 
An especially useful activator precursor, as described, is 
1-(.beta.-aminoethyl)-2-imidazolidone trichloroacetate. 
The concentration of the described activator precursor in the heat 
developable and heat stabilizable materials of the invention is important. 
The concentration must be an activating concentration, that is, it must be 
sufficient to provide the desired activation and to provide the solution 
physical development on the latent image and fog centers to provide the 
desired degree of development efficiency. The optimum concentration useful 
for the described invention will depend upon such factors as the 
particular heat developable and heat stabilizable photographic material, 
desired image, processing conditions, particular activator precursor, 
other components in the material and the like. A typically useful 
concentration of activator precursor is within the range of 0.4 to 3.0 
moles of the described development activator precursor per mole of silver 
in the heat developable and heat stabilizable photographic material. When 
the described 1-(.beta.-aminoethyl)-2-imidazolidone compound is employed 
as the activator precursor, the activating concentration is typically 
within the range of about 1.0 to 2.0 moles of the activator precursor per 
mole of silver in the element. 
Combinations of the described activator precursors are also useful. The 
optimum combination of activator precursors can be determined based on 
such factors as the particular heat developable and heat stabilizable 
photographic material, desired image, processing conditions, other 
components in the photographic material, and the like. An example of a 
combination of activator precursors is the combination of 
1-(.beta.-aminoethyl)-2-imidazolidone trichloroacetate with 
4-aminopyridine trichloroacetate. 
Preparation of the described activator precursors can be carried out using 
procedures known in the art. For example, the described 
1-(.beta.-aminoethyl)-2-imidazolidone trichloroacetate can be prepared by 
dissolving the acid and base components of the compound in a solvent, such 
as methanol and ethanol, mixing the components, and then adding a 
sufficient quantity of a less polar solvent, such as ether, to provide 
full precipitation of the carboxylate salt. Another example is the 
preparation of the trichloroacetate salt of 4-aminopyridine. In this 
preparation a solution of 10 grams of trichloroacetic acid in 40 
milliliters of ethanol is mixed with 5 grams of 4-aminopyridine in 60 
milliliters of ethanol. The desired salt precipitates on addition of 100 
milliliters of diethylether to the resulting composition. The desired salt 
can be purified, such as by filtration and washing with an additional 50 
milliliters of ether. 
The described heat developable and heat stabilizable materials according to 
the invention are typically aqueous formulations, such as aqueous gelatino 
photographic emulsions. However, the materials can be non-aqueous and 
contain hydrophobic materials, such as ethyl cellulose and poly(vinyl 
butyral). 
The covering powering imaging, heat developable and heat stabilizable 
photographic materials of the invention contain a photographic silver 
salt. The term "photographic silver salt" as employed herein is intended 
to include silver materials which can be either salts, complexes or other 
forms which are sensitive to radiation to provide a developable latent 
image. Especially useful silver salts are photographic silver halides due 
to their high degree of photosensitivity. The term "photographic" is 
intended to include photosensitive materials. A typical concentration of 
photographic silver salt in the described materials is within the range of 
about 0.02 to about 0.3 millimoles of the photographic silver salt per 
dm.sup.2 of support in the photographic material. For example, a typically 
preferred concentration range of photographic silver halide is within the 
range of about 0.05 to about 0.15 moles of photographic silver halide per 
dm.sup.2 of support in the described photographic materials of the 
invention. Other photographic materials can be used in combination with 
the described photographic silver salt if desired. It is necessary, 
however, that the other photographic materials not adversely affect the 
desired described properties of the covering power imaging materials of 
the invention. For example, useful photosensitive silver salts which can 
be used as the described photographic silver salt include silver dye 
complexes such as described in U.S. Pat. No. 3,647,439 of Bass, issued 
Mar. 7, 1972. Especially useful photographic silver halides are silver 
chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide or 
mixtures thereof. For purposes of the invention, silver iodide is also 
considered to be a useful photographic silver halide. Fine-grain 
photographic silver halides are especially useful although coarse or 
fine-grain photographic silver halide can be employed if desired. The 
photographic silver halide can be prepared by any of the procedures known 
in the photographic art, especially those procedures which involve the 
preparation of photographic silver halide gelatino emulsions. Useful 
procedures and forms of photographic silver halide for purposes of the 
invention are described, for example, in the Product Licensing Index, 
Volume 92, December 1971, publication 9232 on page 107. The photographic 
silver halide, as described, can be washed or unwashed, can be chemically 
sensitized using chemical sensitizing procedures known in the art, can be 
protected against production of fog and stabilized against the loss of 
sensitivity during keeping as described in the above Product Licensing 
Index publication. 
The described heat developable and heat stabilizable photographic materials 
can comprise a variety of photographic silver salt developing agents, 
especially organic silver salt developing agents that are typically 
photographic silver halide developing agents. Combinations of photographic 
silver salt developing agents, typically combinations of silver halide 
developing agents, can be useful in the described materials of the 
invention. Developing agents which are especially useful are silver halide 
developing agents including polyhydroxybenzenes, such as hydroquinone, 
alkyl-substituted hydroquinone, including tertiary butylhydroquinone, 
methylhydroquinone, 2,5-dimethylhydroquinone, and 
2,6-dimethylhydroquinone; catechol and pyrogallol developing agents; 
chloro-substituted hydroquinones such as chlorohydroquinone or 
dichlorohydroquinone; alkoxy-substituted hydroquinone, such as 
methoxyhydroquinone or ethoxyhydroquinone; aminophenol reducing agents, 
such as 2,4-diaminophenols and methylaminophenols; ascorbic acid 
developing agents, such as ascorbic acid, ascorbic acid ketals and other 
derivatives of ascorbic acid; hydroxylamine reducing agents, such as 
N,N-bis[2-(4'-pyridyl)-ethyl]-hydroxylamine; 3-pyrazolidone developing 
agents such as 1-phenyl-3-pyrazolidone and 
4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone; reductone developing 
agents, such as 2-hydroxy-5-methyl-3-piperidino-2-cyclopentanone; gallic 
acid ester developing agents, such as methylgallate; phenylenediamine 
developing agents such as paraphenylenediamine and the like. Especially 
useful developing agents are 3-pyrazolidone silver halide developing 
agents as described. 
A useful concentration of developing agent in a heat developable and heat 
stabilizable photographic material, as described, is typically within the 
range of about 0.25 mole to about 2.0 moles of developing agent per mole 
of silver salt in the described material. An especially useful 
concentration of developing agent is within the range of about 0.5 to 
about 1.0 moles of developing agents per mole of silver salt in the 
described material. When a combination of developing agents is used, the 
total concentration of the combination is within the described 
concentration ranges. The optimum concentration of developing agent can be 
determined based upon such factors as the particular components in the 
heat developable material, desired image, processing conditions and the 
like. 
The heat developable photographic materials as described can contain a 
variety of colloids and polymers, alone or in combination, as vehicles, 
binding agents and in various layers. Useful materials as described are 
preferably hydrophilic materials although some hydrophobic materials can 
be useful. The colloids and polymers are transparent or translucent and 
include both naturally-occurring substances, such as proteins, for 
example, gelatin, gelatin derivatives, cellulose derivatives, 
polysaccharides, such as dextran and the like; and synthetic polymeric 
substances such as water soluble polyvinyl compounds like poly(vinyl 
pyrrolidone), acrylamide polymers and the like. Other synthetic polymeric 
compounds which can be useful include dispersed vinyl compounds such as in 
latex form and particularly those that increase dimensional stability of 
photographic materials. Effective polymers which are useful as binders 
include high molecular weight materials, especially polymers and resins 
which are compatible with the described components of the heat developable 
photographic material of the invention. Especially useful polymeric 
binders include gelatin, poly(vinyl pyrrolidone), and poly(vinyl alcohol). 
Other useful polymeric binders include copolymers of acrylamide with 
1-vinylimidazole and copolymers of acrylamide with 
2-acetoacetoxyethylmethacrylate. Combinations of the described colloids 
and polymers can also be useful as the polymeric binder. 
The heat developable and heat stabilizable photographic materials according 
to the invention can contain an image toner, especially a thionamide image 
toner, in order to provide a more neutral or black tone image upon 
processing. The optimum toning agent will depend upon such factors as the 
particular heat developable photographic material, the desired image, 
particular processing conditions and the like. In some cases certain image 
toning agents provide better results with certain activator precursors and 
photographic silver salts. A simple screening test can be used to select 
an optimum image toning agent. One such test is described in following 
Example 2. In this test the most useful toning agent is typically that 
toning agent which provides a ratio of (a) visible maximum density to (b) 
blue light maximum density exceeding a value of about 0.8. Useful toning 
agents include, for instance, 3-amino-4-phenyl-1,2,4-triazolidene-5-thione 
and 3-mercapto triazole. Combinations of toning agents can be useful if 
desired. 
A range of concentration of tonging agent is useful in a heat developable 
photographic material as described. A typically useful concentration of 
toning agent is within the range of about 0.005 to 0.10 moles of toning 
agent per mole of photographic silver salt in the heat developable 
photographic material of the invention. The optimum concentration of 
toning agent will depend upon such factors as the particular heat 
developable photographic material, processing conditions, desired image 
and the like. 
It can be useful in certain instances to provide a development restrainer 
or development modifier in the described photographic material to provide 
the desired degree of development. Development modifiers or development 
restrainers as used herein are intended to mean compounds which restrict 
the number of development sites in unexposed areas thereby producing low 
apparent fog in processed fresh or incubated materials according to the 
invention. Examples of useful development restrainers or modifiers include 
1-methyl-3-[2-(methylcarbamoylthio)ethyl]urea and sodium bromide. 
Combinations of development restrainers or development modifiers can also 
be used if desired. 
A range of concentration of development modifier or development restrainer 
can be useful in the described heat developable photographic materials. A 
typically useful concentration of development modifier or development 
restrainer is within the range of about 0.01 to about 0.2 moles of 
development modifier or development restrainer per mole of silver in the 
described heat developable photographic material. The optimum 
concentration of development modifier and development restrainer will 
depend upon such factors as described hereinabove. 
It can be useful to include a melt-forming compound in the heat developable 
photographic materials according to the invention to provide an improved 
developed image. The term "melt-forming compound" as employed herein is 
intended to mean a compound which upon heating to the desired processing 
temperature provides an improved reaction medium, typically a molten 
medium, within which the described image-forming combination can provide 
better image development. The exact nature of the reaction mixture at 
processing temperatures described is not fully understood; however, it is 
believed that at the reaction temperatures a melt occurs which permits the 
reaction components to better interact. Useful melt-forming compounds are 
typically separate components from the image-forming materials, although 
the image-forming combination can enter into the melt formation. Typically 
useful melt-forming compounds are sorbitol, raffinose and 
N,N'-di(methylcarbamoyl)-2-(2-aminoethyl)amino ethanol that are compatible 
with other components of the heat developable photographic material and do 
not adversely affect the desired properties of the photographic material, 
especially the desired sensitometric properties. Combinations of 
melt-forming compounds can be useful if desired. 
A range of concentration of melt-forming compound can be useful in the heat 
developable photographic materials described. A typically useful 
concentration range of melt-forming compound is about 0.2 to about 2.0 
moles of melt-forming compound per mole of silver in the photographic 
material. The optimum concentration of the melt-forming compound will 
depend upon the particular heat developable material, desired image, 
processing conditions an the like. 
Spectral sensitizing dyes can be useful in the described materials of the 
invention to confer additional sensitivity to the materials. Useful 
sensitizing dyes are described, for example, in the Product Licensing 
Index, Volume 92, December 1971, Publication 9232, pages 107-110, 
paragraph XV. An advantage of the heat developable photographic materials 
according to the invention is that a wide range of spectral sensitizing 
dyes is useful due to the fact that the photographic materials enable use 
of silver halide gelatino emulsions. Combinations of sensitizing dyes can 
be useful in the materials of the invention. 
The optimum concentration of the components of a heat developable 
photographic material according to the invention will depend upon a 
variety of factors as described. An especially useful heat developable 
photographic material according to the invention comprises for each mole 
of photographic silver salt, especially photographic silver halide, 0.5 to 
1.0 moles of the described developing agent and 0.6 to 2.0 moles of the 
described development activator precursor. 
"pKa" as employed herein is intended to mean the negative log (base 10) of 
the equilibrium constant between the protonated amine (BH.sup.+) and the 
basic form (B), that is 
##STR6## 
It is possible in some cases to use a development activator precursor, as 
described, providing a pKa in the materials of the invention above 12 if a 
buffer component is added to the material to provide a desired balance of 
reactants. The pKa of the described materials can be determined by methods 
known in the photographic art. A typical method of determining pKa which 
is useful for materials, as described, is published in "The Determination 
of Ionization Constants", by A. Albert and E. P. Serjeant. 
The range of melt pAg of the heat developable photographic materials can be 
wide. The pAg can be measured using conventional calomel and silver-silver 
chloride electrodes, connected to a commercially available digital pH 
meter. The typical melt pAg in a heat developable photographic material 
according to the invention is within the range of about 6 to about 12 with 
a preferred range of pAg being 8 to 10. The optimum pAg will depend upon 
the described factors, such as the particular heat developable 
photographic material, desired image, processing conditions and the like. 
The heat developable photographic materials according to the invention 
typically have a melt pH range which is about 2 to about 7. A typically 
useful melt pH for a heat developable photographic material according to 
the invention is within the range of about 4 to about 5. 
During development or processing of the exposed photographic material the 
pH range increases to a degree that provides desired development. 
It is in some cases useful to have an overcoat or protective layer on the 
heat developable photographic element according to the invention to 
provide resistance to abrasion marks and other undesired marks. The 
overcoat or protective layer can be one or more of the described polymers 
which are also useful as binders. However, other polymeric materials which 
are compatible with the heat developable layer can be useful, especially 
those which can tolerate the processing temperatures employed according to 
the invention. Such other binders or polymeric materials include, for 
instance, ethyl cellulose and poly(methylmethacrylate). Combinations of 
polymeric materials can be useful for overcoat purposes if desired. 
The heat developable materials according to the invention can contain other 
addenda such as compounds which function as speed-increasing compounds, 
hardeners, plasticizers and lubricants, coating aids, brighteners, 
absorbing and filter dyes, antistatic materials or layers, and the like. 
These are described, for example, in the Product Licensing Index, Volume 
92, December 1971, Publication 9232, pages 107-110. 
The heat developable elements according to the invention can comprise a 
variety of supports which can tolerate the processing temperatures 
employed according to the invention. Typical supports include cellulose 
ester film, poly(vinyl acetal) film, poly(ethylene terephthalate) film, 
polycarbonate film and polyester film supports as described in U.S. Pat. 
No. 3,634,089 of Hamb, issued July 11, 1972 and U.S. Pat. No. 3,725,070 of 
Hamb et al, issued Apr. 3, 1973. Related film and resinous support 
materials as well as glass, paper, metal and the like supports which can 
withstand the processing temperatures described are also useful. Typically 
a flexible support is most useful. 
The compositions according to the invention can be coated on a suitable 
support by various coating procedures known in the photographic art 
including dip coating, air-knife coating, curtain coating or extrusion 
coating using hoppers, such as described in U.S. Pat. No. 2,681,294 of 
Beguin, issued June 15, 1954. If desired, two or more layers can be coated 
simultaneously such as described in U.S. Pat. No. 2,761,791 of Russell, 
issued Sept. 4, 1956 and British Pat. No. 837,095 published June 9, 1960. 
The described components of the heat developable materials according to the 
invention can be in any suitable location in the heat developable element 
which provides the desired image. For example, if desired, one or more 
components of the heat developable element according to the invention can 
be in one or more layers of the element. In some cases it can be desirable 
to include certain percentages of the described developing agents and/or 
other addenda in a protective layer over the heat developable element. In 
some cases this can reduce migration of certain addenda between layers of 
the described element. 
It is necessary that the photographic silver salt, especially photographic 
silver halide, as described, and other components of the photographic 
materials of the invention be in reactive association with each other in 
order to provide the desired image. The term "in reactive association" as 
employed herein is intended to mean that the photographic silver salt, 
especially the photographic silver halide, and the activator precursor and 
developing agent, as described, are in a location with respect to each 
other which enables the desired processing and provides a more useful 
developed image. It is possible, for example, to have a portion of the 
photographic silver salt in one layer and other components of the 
described photographic material in other layers. However, it is necessary 
that the components be in a location as described which enables the 
described covering power imaging. 
If desired, other heat developable photographic materials can be used in 
combination with the heat developable photographic materials according to 
the invention. The other heat developable photographic materials must be 
compatible with and not adversely affect the image formation in a heat 
developable material according to the invention. For example, a heat 
developable photographic element can comprise respectively a support 
having thereon a heat developable photographic layer comprising (a) a 
complex of silver with a nitrogen acid compound, such as a silver complex 
described in copending U.S. application Ser. No. 684,699 of deMauriac, 
filed May 10, 1976, (b) a developing agent with (c) photographic silver 
halide in a separate layer with a covering power imaging heat developable 
and heat stabilizable material. It is necessary, however, that the other 
photographic materials not adversely affect the desired covering power 
imaging advantages of the invention. 
An especially useful embodiment of the invention is a covering power 
imaging heat developable and heat stabilizable photographic element 
comprising a support having thereon in reactive association (a) a 
photographic silver halide gelatino emulsion, (b) a photographic silver 
halide developing agent, such as a 3-pyrazolidone silver halide developing 
agent, (c) and activating concentration of a development activator 
precursor consisting essentially of 1-(.beta.-aminoethyl)-2-imidazolidone 
trichloroacetate, (d) a polymeric binder, such as a gelatino binder, and 
wherein the photographic element (1) contains no separate post-processing 
image stabilizer or stabilizer precursor, and (2) provides silver image 
development efficiency of at least 90% when heated to a temperature within 
the range of 120.degree. to 200.degree. C. This photographic element can 
contain, for example, 1-methyl-3-[2-(methylcarbamoylthio)ethyl]urea as 
development restrainer and 3-imino-4-phenyl-1,2,4-triazolidine-5-thione as 
an image toning agent. 
Various imagewise exposure means are useful with the heat developable 
materials according to the invention. The materials according to the 
invention are typically sensitive to the ultraviolet and blue regions of 
the spectrum when they contain no sensitizing dye and exposure means which 
provide this radiation are preferred. Typically, however, if a spectral 
sensitizing dye is employed in the heat developable materials, exposure 
means using other ranges of the spectrum are useful. Typically, a 
photosensitive element according to the invention is exposed imagewise 
with a visible light source such as a tungsten lamp, although other 
sources of radiation are useful such as lasers, electron beams and the 
like. 
A visible image can be developed in an exposed heat developable material, 
as described, within a short time merely by heating the heat developable 
material to moderately elevated temperatures. For example, an image can be 
developed in the described heat developable material by heating the 
element to a temperature within the range of about 120.degree. to about 
200.degree. C. Heating is carried out until a desired image is developed, 
typically within about 1 to about 90 seconds, such as within about 1 to 
about 30 seconds. The heat developable material according to the invention 
is preferably heated to a temperature within the range of about 
140.degree. to about 170.degree. C, typically for about 1 to about 30 
seconds. 
An advantage of the invention is that the process also stabilizes the image 
in a covering power imaging, heat developable and heat stabilizable 
photographic element as described. 
The heat developable materials according to the invention are useful for 
forming a negative or positive image. The formation of a negative or 
positive image will depend primarily upon the selection of the 
photographic silver salt, especially the photographic silver halide. One 
class of useful photosensitive silver halide materials is the class of 
direct positive photographic silver halide materials designed to produce 
positive images. Internal image silver halide emulsions can be used for 
this purpose such as those described in U.S. Pat. No. 2,592,250 of Davey 
et al, issued Apr. 8, 1952; U.S. Pat. No. 3,206,313 of Porter et al, 
issued Sept. 14, 1965; U.S. Pat. No. 3,367,778 of Berriman et al, issued 
Feb. 6, 1968; and U.S. Pat. No. 3,447,927 of Bacon et al, issued June 3, 
1969. If desired, mixtures of surface and internal image silver halide 
emulsions can be used as described in U.S. Pat. No. 2,996,382 of Luckey et 
al, issued Apr. 14, 1961. 
Processing according to the invention is usually carried out under ambient 
conditions of pressure and humidity. Pressures and humidity outside normal 
atmospheric conditions can be used if desired. However, normal atmospheric 
conditions are preferred. 
A variety of means can be employed to provide the necessary heating of the 
described heat developable materials to provide a developed image. The 
heating means can be a simple hot plate, iron, roller or the like.

The following examples are included for a further understanding of the 
invention. 
EXAMPLE 1 
Use of 1-(.beta.-Aminoethyl)-2-Imidazolidone Trichloroacetate in a Covering 
Power Imaging, Heat Developable and Stabilizable Photographic Element 
A covering power imaging heat stabilizable photographic element was 
prepared by mixing and coating at a 4 mil wet coating thickness on a 
poly(ethylene terephthalate) film support the following: 
______________________________________ 
photographic gelatin 20 mg/dm.sup.2 
surfactant (Surfactant 10G, 
0.8 mg/dm.sup.2 
a nonylphenoxypolyglycidol 
available from Olin Corporation, 
U.S.A.) 
1-(.beta.-aminoethyl)-2-imidazolidone 
50 mg/dm.sup.2 
trichloroacetate 
4-hydroxymethyl-4-methyl-1-phenyl- 
10 mg/dm.sup.2 
3-pyrazolidone 
sodium bromide 0.15 mg/dm.sup.2 
silver bromoiodide gelatino emulsion 
10 mg Ag/dm.sup.2 
(unsensitized, 0.1 micron particle 
size, 2.5 mole % iodide) 
______________________________________ 
The composition was mixed prior to coating with a solvent consisting of 
water containing about 5% by volume methanol. The resulting layer was 
permitted to dry at 43.degree. C. A sample of the resulting element was 
imagewise exposed to white light in a commercial sensitometer to provide a 
developable latent image. The image was developed by uniformly heating the 
element for 10 seconds at 140.degree. C. A light stable developed image 
was obtained. The developed image produced less than 0.01 increase in 
density units when exposed to 50,000 foot candle hours of white light 
illumination. The resulting developed image had a diffuse maximum 
transmission density of 1.6 and a minimum density of 0.2. 
The maximum density of the image was 3.6 to blue light with a minimum 
density of 0.2. 
The energy of exposure required to produce a developed density in the 
element of 0.1 above fog was about 200 ergs/cm.sup.2. Efficiency 
measurements indicated that total development had occurred in both minimum 
density areas and maximum density areas. Developed silver particles had a 
particle size of 0.4 microns in the minimum density areas and a particle 
size of 0.05 microns in the maximum density areas respectively. Developed 
images provided satisfactory contrast when observed with ultraviolet 
radiation. 
The activator precursor, that is the imidazolidone trichloroacetate 
compound, in the above formulation melts and decarboxylates at 112.degree. 
C and liberates 1-(.beta.-aminoethyl)-2-imidazolidone which has a 
satisfactorily low volatility at the desired processing temperature. 
The procedure was repeated with the exception that 0.45 milligrams per 
square decimeter of 1-methyl-3-[2-(methylcarbamoylthio)ethyl]urea was 
added to the described formulation. The resulting element had improved 
preprocess stability. The photosensitive composition containing this urea 
compound was exposed to 38.degree. C at 50% relative humidity conditions 
for one week. After this incubation period, the element was imagewise 
exposed and processed, as described above, to provide a loss in maximum 
density in the image of 0.1 and an increase in minimum density of 0.1. 
EXAMPLE 2 
Use of a Toning Agent 
The procedure described in Example 1 was repeated with the exception that 
0.15 milligrams per square decimeter of the toning agent, 
3-imino-4-phenyl-1,2,4-triazolidine-5-thione, was added to the described 
formulation. Upon imagewise exposure and processing of the resulting 
element for 10 seconds at 140.degree. C, a developed image was produced 
having a brown-black (neutral) image tone with a maximum density of 1.7 
and a minimum density of 0.2. 
The added toning agent also reduced the energy required to produce a 
density of 0.1 above fog to about 40 ergs/cm.sup.2. 
EXAMPLE 3 
Use of a Silver Halide Photographic Emulsion Having Increased Grain Size 
The procedure described in Example 1 was repeated with the exception that 
an unsensitized silver bromoiodide gelatino emulsion having a grain size 
of 0.15 microns was used in place of the described silver halide emulsion. 
The silver bromoiodide emulsion containing the 0.15 micron grain size was 
used at 12 mg Ag/dm.sup.2. 
A developed image was produced using this procedure. The developed image 
had a black tone with a maximum density of 1.8 and a minimum density of 
0.2. The energy required to provide a density of 0.1 above fog was reduced 
to about 30 ergs/cm.sup.2. 
EXAMPLE 4 
Heat Developable Element Containing Two Layers 
A heat developable and heat stabilizable element was prepared like that 
described in Example 1 with 1-(.beta.-aminoethyl)-2-imidazolidone 
trichloroacetate excluded. This element was then overcoated with 40 
mg/dm.sup.2 of 1-(.beta.-aminoethyl)-2-imidazolidone trichloroacetate with 
15 mg/dm.sup.2 of ethyl cellulose. This composition was coated from a 
methanol solvent. After coating, the layer was permitted to dry to provide 
the desired element. The heat developable and heat stabilizable element 
was imagewise exposed as described in Example 1 to provide a developable 
latent image. The image was developed by heating the element for 10 
seconds at 160.degree. C. The developed image was stable to light and had 
a maximum density of 1.6 and a minimum density of 0.3. 
EXAMPLE 5 
Use of Covering Power Imaging Formulation at Lower Levels 
A heat developable and heat stabilizable photographic element was prepared 
by mixing and coating at a 4 mil wet coating thickness on a poly(ethylene 
terephthalate) film support the following components: 
______________________________________ 
photographic gelatin 25 mg/dm.sup.2 
surfactant (Surfactant 10G) 
0.8 mg/dm.sup.2 
1-(.beta.-aminoethyl)-2-imidazolidone 
26 mg/dm.sup.2 
trichloroacetate 
4-hydroxymethyl-4-methyl-1-phenyl- 
5 mg/dm.sup.2 
3-pyrazolidone 
1-methyl-3-[2-(methylcarbamoylthio) 
0.4 mg/dm.sup.2 
ethyl]urea (development restrainer) 
silver bromoiodide gelatino emulsion 
5.5 mg Ag/dm.sup.2 
(unsensitized, 0.1 micron particle 
size, 2.5 mole % iodide) 
______________________________________ 
The resulting element was imagewise exposed to light to provide a 
developable latent image in the element. The image was developed by 
heating the element for 10 seconds at 160.degree. C. The resulting 
developed image was stable to light and had a maximum density of 1.2 and a 
minimum density of 0.2 to white light. The developed image had a maximum 
density of 2.8 and a minimum density of 0.3 to blue light. 
The photographic material of this example was capable of providing an image 
having a resolution of 400 lines per millimeter. It accordingly was useful 
for microimaging purposes. 
EXAMPLE 6 
Use of another 3-Pyrazolidone Developing Agent 
The following composition was mixed and then coated on a poly(ethylene 
terephthalate) film support as described in Example 1: 
______________________________________ 
photographic gelatin 25 mg/dm.sup.2 
surfactant (Surfactant 10G) 
1 mg/dm.sup.2 
1-(.beta.-aminoethyl)-2-imidazolidone 
50 mg/dm.sup.2 
trichloroacetate 
4-methyl-1-phenyl-3-pyrazolidone 
10 mg/dm.sup.2 
sodium bromide 0.2 mg/dm.sup.2 
silver bromoiodide gelatino emulsion 
10 mg Ag/dm.sup.2 
(unsensitized, 0.1 micron particle 
size, 2.5 mole % iodide) 
______________________________________ 
The resulting element was imagewise exposed as described in Example 1 to 
provide a developable latent image. The image was developed by heating the 
element for 10 seconds at 160.degree. C to provide a developed image 
having a maximum density of 1.4 and a minimum density of 0.3. 
EXAMPLE 7 
Overcoated Element 
The following aqueous composition was mixed and then coated at a 4 mil wet 
coating thickness on a poly(ethylene terephthalate) film support: 
______________________________________ 
photographic gelatin 25 mg/dm.sup.2 
surfactant (Surfactant 10G) 
1 mg/dm.sup.2 
1-(.beta.-aminoethyl)-2-imidazolidone 
50 mg/dm.sup.2 
trichloroacetate 
4-hydroxymethyl-4-methyl-1-phenyl 
10 mg/dm.sup.2 
3-pyrazolidone 
sodium bromide 0.2 mg/dm.sup.2 
1-methyl-3-[2-(methylcarbamoylthio) 
5 mg/dm.sup.2 
ethyl]urea (development restrainer) 
silver bromoiodide gelatino emulsion 
10 mg Ag/dm.sup.2 
(unsensitized, 0.1 micron particle 
size, 2.5 mole % iodide) 
______________________________________ 
The resulting heat developable photographic element was permitted to dry 
and then was overcoated with 5 mg/dm.sup.2 of a copolymer of 
cyclohexane-1,4-dicarboxylic acid and 1,4-di(hydroxymethyl)cyclohexane. 
The resulting element was permitted to dry and then was imagewise exposed 
as described in Example 1 to provide a developable latent image. The image 
was developed by heating the element for 10 seconds at 160.degree. C. This 
provided a developed image which was stable to light having a maximum 
density of 1.7 and a minimum density of 0.2 to white light. The developed 
image had a maximum density of 2.9 and a minimum density of 0.2 to blue 
light. The resulting processed element was dry to the touch and after 
processing provided good post-processing clarity. 
EXAMPLE 8 
Use of Another Binder 
An aqueous melt was prepared and coated at a wet coating thickness of 4 
mils on a poly(ethylene terephthalate) film support. The aqueous melt had 
the following composition: 
______________________________________ 
polymeric binder consisting of the 
20 mg/dm.sup.2 
copolymer of methyl methacrylate/3- 
methacryloyloxypropane-1-sulfonic 
acid, sodium salt/2-acetoacetoxy- 
ethyl methacrylate with weight 
ratio of monomers being 30:60:10% 
surfactant (Surfactant 10G) 
1 mg/dm.sup.2 
1-(.beta.-aminoethyl)-2-imidazolidone 
50 mg/dm.sup.2 
trichloroacetate 
4-hydroxymethyl-4-methyl-1-phenyl- 
10 mg/dm.sup.2 
3-pyrazolidone 
sodium bromide 0.2 mg/dm.sup.2 
silver bromoiodide gelatino emulsion 
10 mg Ag/dm.sup.2 
(unsensitized, 0.1 micron particle 
size, 2.5 mole % iodide, low 
gelatin level) 
______________________________________ 
The resulting heat developable photographic element was permitted to dry 
and then imagewise exposed to light to provide a developable latent image 
as described in Example 1. The resulting image was developed by heating 
the element for 10 seconds at 160.degree. C. The developed image had a 
maximum density of 1.2 and a minimum density of 0.1. 
EXAMPLE 9 
Non-Aqueous Formulation for Covering Power Imaging 
The following components were mixed and coated at a 4 mil wet coating 
thickness on a poly(ethylene terephthalate) film support using a solvent 
consisting of 4 parts by volume ethanol and one part by volume toluene: 
______________________________________ 
poly(vinyl butyral) (polymeric binder) 
18 mg/dm.sup.2 
4-hydroxymethyl-4-methyl-1-phenyl- 
10 mg/dm.sup.2 
3-pyrazolidone 
silver bromoiodide poly(vinyl 
10 mg Ag/dm.sup.2 
butyral) peptized emulsion 
(unsensitized, 0.08 micron 
particle size, 2.5 mole % 
iodide) 
______________________________________ 
The resulting layer was permitted to dry and was then overcoated with the 
following composition: 
______________________________________ 
ethyl cellulose 20 mg/dm.sup.2 
1-(.beta.-aminoethyl)-2-imidazolidone 
60 mg/dm.sup.2 
trichloroacetate 
5-methylbenzotriazole (antifoggant) 
2 mg/dm.sup.2 
______________________________________ 
The composition which was overcoated was coated from a methanol solvent. 
The resulting overcoat layer was permitted to dry to provide the desired 
covering power imaging, heat developable and heat stabilizable 
photographic element. The element was imagewise exposed to light as 
described in Example 1 to provide a developable latent image in the 
element. The image was developed by heating the element for 10 seconds at 
140.degree. C. The resulting developed image was stable to light and had a 
maximum density of 1.2 and a minimum density of 0.1. The developed image 
had a maximum density of 1.6 and a minimum density of 0.2 to blue light. 
The processed element upon storage provided good clarity. 
EXAMPLE 10 
Use of Activator Precursor Containing A bis(sulfonylacetic acid) moiety 
The procedure described in Example 1 was repeated with the exception that 
the 1-(.beta.-aminoethyl)-2-imidazolidone salt of methylene 
bis(sulfonylacetic acid) was used as an activator precursor in place of 
the described activator precursor. The bis(sulfonylacetic acid) compound 
was used at 40 mg/dm.sup.2 in the described element. 
The resulting photographic element was imagewise exposed to light as 
described in Example 1 to provide a developable latent image. The image 
was developed by heating the element for 10 seconds at 150.degree. C. The 
developed image was stable to light and had a maximum density of 1.6 and a 
minimum density of 0.2. 
EXAMPLE 11 
Use of Tyramine Trichloroacetate as Activator Precursor 
The procedure described in Example 1 was repeated with the exception that 
tyramine trichloroacetate was used in place of the described activator 
precursor at 45 mg/dm.sup.2. 
The resulting photographic element was imagewise exposed to light to 
provide a developable latent as described in Example 1. The image was 
developed by heating the element for 10 seconds at 160.degree. C. The 
resulting developed image had a maximum density of 1.6 and a minimum 
density of 0.2. The developed image had a maximum density of 3.6 and a 
minimum density of 0.3 to blue light. 
The resulting developed image was exposed to 10,000 foot candle hours of 
white light exposure. The print-up density observed after this light 
exposure was 0.05. This illustrated that the image was very stable to 
light exposure following processing. 
The procedure was repeated with the exception that the element prior to 
imagewise exposure was incubated for one week at 38.degree. C and 50% 
relative humidity. The resulting element provided no significant loss in 
maximum image density upon imagewise exposure and processing. Minimum 
density increased by approximately 0.1. This illustrated that the heat 
developable and heat stabilizable element according to the invention was 
very stable prior to imagewise exposure and processing. 
EXAMPLE 12 
Use of 4-Aminopyridine Trichloroacetate as Activator Precursor 
The procedure described in Example 1 was repeated with the exception that 
4-aminopyridine trichloroacetate was used as an activator precursor in 
place of the described activator precursor. The 4-aminopyridine 
trichloroacetate was used at a concentration of 50 mg/dm.sup.2 of support. 
The resulting photographic element was imagewise exposed to light to 
provide a developable latent image as described in Example 1. The image 
was developed by heating the element for 10 seconds at 160.degree. C. The 
resulting developed image had a purple tone with a maximum density of 2.1 
and a minimum density of 0.2. 
The resulting developed image was exposed to 50,000 foot candle hours of 
light exposure. The print-up density after this exposure period was about 
0.1. This illustrated that the resulting developed image was very stable 
to light exposure. 
EXAMPLE 13 
Use of Equivalent Activator Precursor Composition 
The following components were mixed and coated at a 4 mil wet coating 
thickness from an aqueous solution on poly(ethylene terephthalate) film 
support: 
______________________________________ 
photographic gelatin 25 mg/dm.sup.2 
surfactant (Surfactant 10G) 
1 mg/dm.sup.2 
sodium trichloroacetate 
40 mg/dm.sup.2 
malonamide 20 mg/dm.sup.2 
4-hydroxymethyl-4-methyl-1- 
10 mg/dm.sup.2 
phenyl-3-pyrazolidone 
sodium bromide 0.2 mg/dm.sup.2 
silver bromoiodide gelatino 
10 mg Ag/dm.sup.2 
emulsion (unsensitized, 0.1 micron 
particle size, 2.5 mole % iodide) 
______________________________________ 
The resulting coating was permitted to dry at 43.degree. C and was then 
overcoated with 5 mg/dm.sup.2 of poly(ethylmethacrylate) from 
dichloromethane solvent. The overcoat was permitted to dry. 
The resulting photographic element was imagewise exposed to light to 
provide a developable latent image as described in Example 1. The image 
was developed by heating the element for 20 seconds by immersing the 
element in a fluorocarbon bath at 140.degree. C. A developed image was 
produced having a maximum density of 1.7 and a minimum density of 0.3. 
EXAMPLE 14 
(Comparative Example) 
The following composition was coated similarly to Example 1: 
______________________________________ 
photographic gelatin 30 mg/dm.sup.2 
surfactant (Surfactant 10G) 
1 mg/dm.sup.2 
guanidinium trichloroacetate 
66 mg/dm.sup.2 
4-hydroxymethyl-4-methyl-1-phenyl- 
15 mg/dm.sup.2 
3-pyrazolidone 
silver bromoiodide gelatino emulsion 
12 mg/dm.sup.2 
(sulfur and gold chemically 
sensitized, 0.15 micron particle 
size, 2.5 mole % iodide) 
______________________________________ 
Following sensitometric exposure of the resulting element and processing 
for 10 seconds at 150.degree. C, a D.sub.max of 2.2 and a D.sub.min of 1.7 
was obtained. No covering power imaging was observed. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.