CA1039553A

CA1039553A - Photothermographic compositions, element and process

Info

Publication number: CA1039553A
Application number: CA215,566A
Authority: CA
Inventors: Cynthia G. Jones
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1974-01-02
Filing date: 1974-12-10
Publication date: 1978-10-03
Also published as: GB1480653A; CH607092A5; JPS50102326A; FR2256434A1; DE2460547C2; US3871887A; BE824051A; DE2460547A1; FR2256434B1; JPS5217415B2

Abstract

PHOTOTHERMOGRAPHIC COMPOSITION, ELEMENT AND PROCESS
Abstract of the Disclosure Improved sensitivity to certain wavelengths of light and improved contrast are provided by certain photo-thermographic compositions containing a sensitizing con-centration of a non-silver iodide salt. Such photothermo-graphic compositions, prepared by (A) preparing a dispersion of (a) an oxidation-reduction image-forming combination comprising (i) a silver salt oxidizing agent and (ii) an organic reducing agent, with (b) ex situ, synthetic polymer-peptized photosensitive silver halide, (c) a cyclic imide toner in (d) a non-gelatin polymeric binder, contain a sensitizing concentration of a non-silver iodide salt, such as lithium iodide. The described non-silver iodide salt can be mixed with described photothermographic compositions at different stages of preparation of the compositions.

Description

Background of the Invention Field o~ the Invention This invention relates to improved photothermographic compositions and processes of preparing them. In one o~ its aspects it relates to certain photothermographic elements having improved photosensitivity to certain wavelengths of light. In another of its aspects it relates to photothermographic com-positions comprising an oxidation-reduction image-forming combination with synthetic polymer peptized photosensitive silver halide having improved sensitivity to certain wavelengths of light and improved contrast. In another of its aspects it relates to preparation o~ the described photo-thermographic elements and compositions.

Description of the State of the Art Photothermographic materials and methods o~ their ;i~
preparation are l~no~n. Such photothermographic materials after ~ ;
imagewise exposure are overall heated to provide a developed - ;-image in the absence of separate processing solutions. Typical photothermographic materials are described, for example, in Belgian Patent 765,452 issued May 28, 1971; Belgian Patent `-765~602 issued May 28, 1971; Belgian Patent 765,601 issued May 28, 1971; Belgian Patent 766,590 issued June 15, 1971; -Belgian Patent 766,589 issued June 15, 1971; Belgian Patent 772,371 issued October 15, 1971; u.s. Patent 3,152,904 of Sorensen et al issued October 13, 1964; u. s . Patent 3, ~57,075 o~ Morgan et al issued July 22, 1969; u.s. Patent 3,392,020 ::
j, of Yutzy et al issued July 9, 1968 and British Specification - 1,161,777 published August 20, 1969.
, It has been desirable to provide increased photo-sensitivity to certain wavelengths of light in photothermographic materials. This is defined and employed herein as the sensitivity to ranges of electromagnetic radiation to which the photo-thermographic materials are exposed imagewise to provide a .......... ..

~l:)39553 latent image. It has also been desirable ln some cases to provide increased contrast of the images produced with the described photothermographic materlals.
One means, which has been proposed to increase photosensitivity, centers upon preparation of photosensitive silver halide in the photothermographic materials. This method provides so-called silver halide in situ. This is described, for example, in U.S. Patent 3,457,075 of Morgan et al issued July 22, 1969. Preparation of the photosensitive silver halide in situ is difficult to control. ~ccordingly, it is - desirable to provide the photosensitive silver halide separate from other components of the photothermographic composition -~
and then mix the silver halide with the described components.
This silver halide, prepared separate from other components of the photothermographic material, is referred to herein as ex situ silver halide. Photothermographic materials containing so-called ex situ silver halide are described, for example, ;i in Belgian Patent 774,436 issued November 12, 1971. The ;
` described photothermographic materials contain silver halide 20 which is prepared employing a polymeric peptizer. A typical polymeric peptizer employed for this purpose is poly(vinyl butyral~. The silver halide can then be mixed with other -components of the photothermographic composition such as an oxidation-reduction image-forming combination comprising (1~ a silyer salt oxidizing agent, such as silver behenate, and ( 2) ~
an organic reducing agent, such as a sulfonamidophenol reducing `;
agent.
- Other means have been employed for providing increased sensitivity in photothermographic materials such as addition 3Q of onium halides as described in U.S. Patent 3,679,422 of deMauriac and Hiller, issued ~uly 25, 1972. It was found, - . . , - .. :: .

~0395S3 however, tha~ mere addition o equivalent amounts of bromide ion or bromide compounds does not provide desired sensitivity.
This is illustrated in following comparative Example 6. Also, mere addition o~ silver iodide to a photothermographic composition comprising an oxidation-reduction image-forming combination containing (1) a silver salt oxidi~ing agent, such as silver behenate, with (2) an organic reducing agent, such as a sulfonamidophenol reducing agent, with poly(vinyl acetal) peptized silver halide in a polymeric binder does not provide -`
10 desired increased photosensitivity to the desired wavelength of light. ~
Iodide compounds have been added to certain silver ~ `
halide photosensitive materials as described in Photographic Science and Engineering, Vol. 14, No. 4, July-August, 1970, ~;~
pages 258-261 and 262-268. Neither U.S. Patent 3,679,422 nor the above article suggests the photothermographic materials or preparation as described herein.
There has been a continuing need to provide a photothermographic element, composition and process for 20 preparing the described photothermographic materials which .`
provides increased photQsensiti~ity to certain wavelengths of light ~ithout adversely affecting other desired sensitometric ` properties.
-~ Summary of the Invention It has been found according to the invention that increased photosensitivity to certain wavelengths of light -and, in some cases, increased contrast can be provided by a sensitizing concentration of a non-silver iodide salt, especially an alkali metal iodide such as lithium iodide i~ 30 of ammQnium iodide, in a photothermographic composition and -~ element comprising a dispersion of (a) an oxidation-reduction ~' image-forming combination comprising (i2 a silver salt oxidizing agent, and (ii) an organic reducing agent, with ., ~ . .
',:

.` ~i~
.

~039553 (b) ex situ, synthe-tic polymer peptized photosensitive silver halide, ~c) a cyclic imide toner, and (d) a polymeric binder wherein the non-silver iodide salt has the property of incréasing the desired photosensitivity o~ the photothermographic composition.
The described non-silver iodide salt can be mixed with the described photothermographic compositions at di~erent stages o~ preparation of the compositions depending on such factors as the wavelengths to be used ~or imagewise exposure and particular components o~ the photothermographic material.
- IO The surprising increase in photosensitivity -to certa m -~
wavelengths o~ light is illustrated by co~parative examples and the results set out in the ~ollowing tables.
Detailed Description of the Invention ,,~
A range of non-silver iodide compounds can be employed according to the invention. The non-silver iodide ; salt, however, must have the property o~ increasing the photo-sensitivity o~ the described photothermographic materials to the desired wavelengths o~ light for imagewise exposure.
Merely adding a silver iodide emulsion to the photothermographic materials does not provide the desired increase in photo-sensitivity. Accordingly, the term non-silver iodide compounds or salts as employed herein is intended to exclude silver iodide.
- One test which can be employed to determine a suitable non-silver - ~ ~-. iodide salt is set out in ~ollowing Example 1. According to this test, if increased relative speed is provided to the desired wavelengths o~ light for imagewise exposure by the non-silver iodide salt tested, the iodide is considered to be acceptable. The useful concentration o~ non-silver iodide ~;
salt in this test is about 0.01 mole to about 0.50 moles of the described non silver iodide salt per mole o~ the photo-sensitive silver halide in the photothermographic material.

. , ~ .
.. . .

~39553 Acceptable non-silver iodide salts according ~o the invention are, for instance, lithium iodide, ammonium iodide, sodium iodide, potassium iodide and mixtures of these iodides. Choice of an optimum non-silver iodide salt and the optimum step in preparation o~ the photothermographic material ~or addition o~ the non-silver iodide salt will depend upon the particular pho-tothermographic composition, desired image, processing conditions and the like. --Lithium iodide is especially useful when employing a sulfon-amidophenol reducing agent with a silver salt oxidizing agent, such as silver behenate, and an ex situ, poly(vinyl butyral) peptized photosensitive silver bromide in a polymeric binder such as poly(vinyl butyral).
A range of concentration of the described non-silver iodide salt can be employed The concentration must be - sufficient to provide the desired increase in photosensitivity in the described photothermographic composition. Typically, a . . . ~
concentration of non-silver iodide salt is about 0.01 mole to about 0.50 mole of the described non-silver iodide salt per i mole of photosensitive silver halide in the described photo~
- 20 thermographic material. A concentration of non-silver iodide salt which is about 0.01 mole to about 0.05 mole ' of the iodide~ typically lithium iodide~ per mole of the described silver halide is usually preferable. ~ ;
.
-, The method of preparing the described photothermo-graphic composition and element comprising a dispersion of ' oxidation-reduction image-forming combination with ex situ, i synthetic polymer peptized photosensitive silver halide, and a - cyclic imide toner in a polymeric binder can vary depending on the particular photothermographic material, desired image, -;
processing conditions and the like. A typical method of preparing the dispersion involves thoroughly mixing the described components. These can be mixed employing any suitable .-- . . .
~.. . .

~395S3 apparatus such as a ball-mill or similar mixing means. One method of preparing the described dispersion and means for preparing ~he dispersion are set out, ~or instance, in Belgian Patent 774,436 issued November 12, 1971.
The photothermographic elements and compositions - according to the invention comprise an oxidation-reduction image-forming combination which contains a silver salt oxidizing agent. The silver salt oxidizing agent can be a silver salt of an organic acid such as a fatty acid which is resistant to darkening upon illumination. An especially useful class of silver salts of organic acids is represented by the ; water insoluble silver salts of long-chain fatty acids which are stable to light. Compounds which are suitable silver salt oxidizing agents include, for instance, silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxy stearate, silver caprate, silver myristate and silver palmitate with silver stearate and silver behenate being especially useful. In some instances silver salts can be -~
employed as the silver salt oxidizing agent which are not ` 2Q silver salts of long-chain fatty acids. Such silver salt ~ -oxidizing agents which are useful include, for example, silver benzoate, silver benzotriazole, silver terephthalate, sllver phthalate and the like. In mQst instances, however, silver ... :
behenate is most useful.
A variety of organic reducing agents can be employed in the described oxidation-reduction image-forming combination.
Sulfonamidophenol reducing agents are especially use~ul in the described oxidation-reduction image-forming combination.
Sulfonamidophenol reducing agents in photothermographic 3Q materials are described in Research Disclosure, ~olume 105, January, 1973, Item 10513. The sulfonamidophenol ... .

;.
~ 7 ` A~
., '. . .. ,, . - ~ i --,-. ~ . , .
. ~,.. . - , , .. . . . .. . ` ~. . . . . .
.`.. .. .. .. .... . . ... . .
,` ,. .. . .. .. .. . . . . . . .

~3~553 reducillg agen-ts use~ul according to the invention can be prep~red employing known procedu:res .in the art and include such compounds as described in Canadian Patent 815,526 of Bard issued June 17, 1969. A useful class of` sul~onarnidophenol reducing - agents according to the invention, is represented by the : ~.
structure: . ~
OH : :

z3 . wherein R and R2 are each selected from the group consisting ;.
of hydrogen; chlorine; bromine; iodine; al.kyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl and butyl; aryl .
containing 6 to 12 carbon atoms such as phenyl and tolyl; aryl-: sulfonyl containing 6 to 12 carbon atoms, such as phenylsulfonyl;
amino; hydroxy; alkoxy containing 1 to 4 carbon atoms, such as methoxy and ethoxy; and atoms completing with Rl and R2 a - -naphthalene nucleus; ~.
Z and Z3 are each selected from the group consisting r ` of.hydrogen; bromine; chlorine; alkyl containing 1 to L~ carbon `
atoms, as described; aryl containing 6 to 10 carbon atoms, such : 20 as phenyl and tolyl; arylsulfonyl containing 6 to 12 carbon atoms, as described; amino; hydroxy; alkoxy containing l.to 4 carbon atoms, such as methoxy and ethoxy; and R~S02NH- wherein -~
R6 is alkyl containing 1 to 4 carbon atoms, such as methyl, `~
j ethyl, propyl and butyl; aryl containing 6 to 10 car~on atoms, such as phenyl and tolyl and hetero ring substituents, such as ~thienyl~ quinolinyl and thiazy]~ HO ~ -NHS02 ~ or , ~

:~ .

: . . . .

:~039553 HO~N~1S02~0 ~

; ~2 is hydrogen, alk~l containing 1 to L~ carbon atoms, such as methyl, ethyl, propyl or butyl, chlorine and bromine when Rl and R2 are other than atoms completing a naphthalene nucleus; at least one of zl, z2 and Z3 is R6S02NH-. -The described groups such as alkyl, alkoxy and aryl include such groups containing substituents which do no-t adversely a~ect the reducing properties and desired sen-sitometric properties of the described photothermographic elements and compositions. Examples of substituent groups which can be present are alkyl containing l to 3 carbon atoms such as methyl, ethyl, and propyl, chlorine, bromine and phenyl.
In some cases it is desirable to avoid an amino group as a substituent The amino group, in some cases, provides an ~ overly active reducing agent.
; One especially useful class of sulfonamidophenol reducing agents are compounds o~ the ~ormula:
OH
R ~ R4 NHSo2-R3 `
wherein R3 is phenyl, naphthyl, methylphenyl, thienyl, quinolinyl, thiazyl, or alkyl containing 1 to 4 carbon atoms, as described;
R4 is hydrogen, R3So2NH-, alkoxy containing 1 to 4 carbon atoms, hydroxy, alkyl containing 1 to 4 carbon atoms, bromine or chlorine; ~i R5 is hydrogen, bromine5 chlorine, alkyl containing 1 to 4 carbon atoms, such as methyl, ethyl, propyl or butyl~ or ; alkoxy containing 1 to 4 carbon atoms, such as methoxy, ethoxy '~

_ g _ .

1~39~i53 and propoxy R3, R~ and/or R5 can contain substituent groups ~hlch do not adversely affect the reducing properties of the described sulfonamidophenol reducing agents or the desired `
sensitometric properties of the photothermographic elements and materials of the invention. ~lese substituent groups are the same as described for generic structure I.
Another class of sulfonamidophenol reducing agents which are useful in photothermographic elements and compositions - of the invention are sulfonamidonaphthols of the formula: -OH

,~,H502~>

The sulfonamidophenol group in the described sulfonamidonaphthols can be in the ortho, meta or para position. The sulfonamido-naphthols are more active compounds within -the sulfonamidophenol reducing agent class. Also, within this class, sulfonamidophenols which contain three sulfonamidophenol groups are more active.
These sulfonamidophenols are employed for shorter developing times or with heavy metal salt oxidizing agents which are iess active than silver behenate. In some cases, image discrimination provided by photothermographic materials containing the sulfon~
amidonaphthols and trif~mctional sulfonamidophenols is less than that provided by other of the described sulfonamidophenols.
Combinations of sulfonamidophenol reducing agents, as described, can be employed in photothermographic materials and elements according to the invention. Especially useful sulfonamidophenol reducing agents include benæenesulfonamidophenol reducing agents~ such as 2,6-dichloro-4-benzenesulfonamidophenol and/or 4-benzenesulfonamidophenol.
Other organic reducing agents which can be employed -~
alone or in combination with the described sulfonamidophenol reducing agents include substituted phenols and naphthols, for :.............. .

1(~395S3 example, bis-~-naphthols, such as descrlbed in U.S. Patent 3,672,90~ o~ deMauriac, issued June 27, 1972. Suitable bis~
naphthols include, ~or instance, 2,2'-dihydroxy-1,1'-binaphthyl;
6~6'-dibromo-2,2'-dihydroxy-1~1'-binaphthyl; 6,6'-dinitro-2,2'-dihydroxy-l,l'-binaphthyl and/or bis-(2-hydroxy-1-naphthol) methane. Other reducing agents which can be employed in the described photothermographic materials according -to the invention include polyhydroxybenzenes such as hydroquinone, alkyl-substituted hydroquinones such as -tertiary butyl ; 10 hydroquinone, methyl hydroquinone, 2,5-dimethyl hydroquinone and 2,6-dimethyl hydroquinone, catechols and p~rogallols, aminophenol reducing agents, such as 2,l~-diaminophenols and - ;
methylaminophenols; ascorbic acid developing agents such as ascorbic acid and ascorbic acid derivatives such as ascorbic ~`
acid ketals; hydroxylamine developing agents; 3-pyrazolidone developing agents such as l-phenyl-3-pyrazolidone and the like.
Combinations o~ these reducing agents can be employed i~ desired, The selection of an optimum reducing agent or reducing agent combination will depend upon particular photothermographic `~
material, silver salt oxidizing agent, processing conditions, desired image and the like.
A so-called activator-toning agen-t, also known as an accelerator-toning agent or toner, can be employed in the photothermographic materials according to the invention to obtain a desired image. The activator-toning agent is a cyclic imide - and is typically useful in a range o~ concentration such as a `
concentration o~ about 0.10 mole to about 1.1 mole of activator- ~`
toning agent per mole of silver salt oxidizing agent in the `
photothermographic material. Typical suitable activator-toning agents are described in Belgian Patent 766,590 issued June 15, 1971. Typical activator-toning agents include~ `
~or example, phthalimide, N-hydroxyphthalimide, N-hydroxy-1,8-~ 39553 naph-thalimide, N-potassi~ phthalimide, N-mercury phthalimide~
succinimide and/or N-hydroxysuccinimide. Combinations of so-called activator-toning agents can be ernployed i~ desired. Other activator-toning agents which can be employed include phthalazinone, 2-acetyl-phthalazinone and the like.
A photothermographic element, as described according to the invention, can contain various non-gelatin compounds ~
alone or in combination as vehicles, binding agents and in various layers. Suitable materials can be hydrophobic or hydrophilic. They are transparent or translucent and include such synthetic polymeric substances as water soluble polyvinyl compounds like poly(vinyl pyrrolidone), acrylamide polymers and the like. Other synthetic polymeric compounds which can be employed include dispersed vinyl compounds such as in latex ` form and particularly those which increase dimensional stability of photographic materials. Effective polymers include water insoluble polymers of polyesters, polycarbonates, alkyl -acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates, methacrylates and those which have crosslinking sites which facilitate hardening or curing as well as those having recurring sulfobetaine units as described in Canadian Patent 774,054.
Especially useful high molecular weight materials and resins -include poly(vinyl butyral), cellulose acetate butyrate, polymethyl methacrylate, poly(vinyl pyrrolidone), ethylcellulose, polystyrene, polyvinyl chloride, chlorinated rubber, poly-isobutylene, butadiene-styrene copolymers, vinyl chloride vinyl acetate copolymers, copolymers o~ vinyl acetate, vinyl chloride and maleic acid and polyvinyl alcohol.
The described non-silver iodide salt can be mixed with the described photothermographic compositions at different stages of preparation of the composition. The optimum stage of addi-tion will depend on such ~actors as the wavelength ....... .. ..
. . ..

~3~553 to be used ~or imagewise exposure of the photothermographlc composition~ partlcular components o~ the pho-tothermographic materials, desired image, particular ac-tivator-toning agent and the like.
Accordingly, one embodiment o~ the invention comprises a method o~ preparing a silver hallde photothermographic com-position or element comprising respectively (A) preparing a dispersion o~ silver behenate in poly(vinyl butyral), (B) mixing with the resulting silver bèhenate dispersion ; about 0.01 to about 0.05 mole o~ lithium iodide per mole of silver halide in the photo-thermographic composition, (~) mixing with the resulting composition (i) an ex situ, poly(vinyl bu:tyral) peptized photosensitive silver halide, and (D) a poly(vinyl butyral) binder, and .-(E) mixing succinimide, a sulfonamidophenol reducing -:
agent and a spectral sensitizing dye with the .
resulting composition.
Another embodiment of the invention comprises a ~ -method o~ preparing a silver halide, photothermographic composition or element comprising respectively (A) preparing poly(vinyl butyral) peptized photo-sensitive silver halide, ;~
(B) mixing with said silver halide about 0.01 to . about 0.05 mole o~ lithium iodide per mole : o~ said silver halide, (~) mixing with the resulting composition a dispersion o~ silver behenate in poly(vinyl butyral), and -I

' :
., . :

:: . : , . .. . .

~L~395~3 (D) then mixing succinimide, a sul~onamidophenol reducing agent and a spectral sensitizing dye ;~
with the resulting composition.
In preparing a photothermographic material according to the invention, it is often desirable to mix the described non-silver iodide salt with the photothermographic material and then hold the resulting composition for a period of time until the desired sensitivity is achieved, such as about 10 seconds to about 48 hours at room temperature, that is about 20C. to about 30C. before any subsequent steps. It appears that this holding step provides some interaction which is desired for the described increase in photosensitivity. The exact mechanism of reaction which takes place is not fully understood.
After the holding period, the photothermographic composition can be coated on a suitable support to provide a photothermographic element.
Accordingly, a further embodiment of the invention , comprises preparing a photothermographic composition comprising (A~ preparing a dispersion of (a~ an oxidation-reduction image-forming combination comprising (i) a silver salt oxidizing agent, typically silver behenate, and (ii~ a sulfon-amidophenol reducing agent, with (b~ ex situ, synthetic polymer peptized photosensitive silver halide, in (cl a . poly(vinyl butyral~ binder, and, after preparing the dispersion, (B~ mixing with the dispersion about 0.01 mole to ;

~ about 0.5 mole of the described iodide salt, typically lithium i~ iodide, per mole of the silver halide, and then (C) holding the resulting composition for a period of time until the desired -~
30 sensitivity is achieved, such as about 10 seconds to about 48 ;
hours at about 2QC, to about 30C, before any subsequent step.

- 14 ~
.. ~ ~` .
~' . .
: . ~, .
.. .. .. .. . .

~39~53 Af-ter the holding step, a pho-tothermographic element can be prepared by coating the decicribed composition on a suitable support.
The photothermographic elements according to the invention can comprise a wide variety o~ supports. ~ypical supports include cellulose nitrate film, cellulose ester film, poly(vinyl acetal) ~ilm, polystyrene film, poly(ethylene terephthalate) film, polycarbonate film and related ~ilms or resinous materials, as well as glass, paper, metal and the like supports which can withstand the processing temperatures employed according to the invention. I~pically, a flexible support is employed.
- It is desirable, in some cases, to employ an image stabilizer and/or image stabilizer precursor in the described photothermographic materials of the invention. Typical image stabilizers or stabilizer precursors are described, ~or -~
example, in Belgian Patent 768,071 issued July 30, 1971.
Typical stabilizer precursors include, for example, azole thioethers and blocked azoline thione stabilizer precursors as described in this Belgian patent and described in U.S. Patent 3,700,457 o~ Youngquist, issued October 24, 1972.
The described photothermographic compositions and elements according to the in~ention can contain various addenda to aid the compositions and elements such as development modifiers that function as additional speed-increasing compounds, hardeners~ antistatic layers, plasticizers and lubricants, coating aids, brighteners, spectral sensitizing dyes, absorbing and filter dyes, also as described - in the Product Licensing Index, Volume 92, December, 1971, 30- publication 9232, pages 107-110.
Spectral sensitizing dyes can be used in the described photothermographic materials of the invention to con~er :: . - - . , -- -.,.. . ~ . . - .. ..

~39553 additional sensitivit~ to the elemen-ts and compositions of the invention. Useful sensitizing dyes are ~escribed, ~or example, in the Product Licensin~ I~dex, Volume 92, December, 1971, publication 9232, pages 107-110~ paragraph XV and Belgian Patent 772,371 issued October 15, L971. ~or example, when a photothermographic material is to be exposed imagewise to a so-called red laser, a spectral sensitizing dye which provides a sensitivity to the red region of the spectrum is employed in the described photothermographic material according to the invention.
The photothermographic compositions and other compositions according to the invention can be coated on a suitable support by various coating procedùres including dip coating, air knife coating, curtain coating or extrusion coating using hoppers such as described in U.S. Patent 2,681,294 o~ Beguin issued June 15, 1954. If desired, two or more layers can be coated simultaneously such as described in U.S.
Patent 2,761,791 of Russell, issued September 4, 1956 and British Patent 837,og5.

A range of concentration of various components of the photothermographic materials can be employed according to the invention. A useful concentration of reducing agent is typically about 0.25 mole to about 4 moles of reducing agent, such as ~ -sulfonamidophenol reducing agent, per mole of photosensitive silver halide in the photothermographic material. In relation to the silver salt oxidizing agent employed, a useful con-centration range of reducing agent is typically about 0.10 mole to about 20.0 moles-of reducing agent per mole of silver salt oxidizing agent, such as silver behenate and/or silver stearate. If a combination of reducing agents is employed, the total concentration of reducing agent is typically within the described concentration range.

.... .

~103~SS3 It is believed that upon imagewise exposure the latent image silver oî the described photosensi-tive silver halide ac-ts as a catalyst for the described oxldation image-forming combination. A typical concentration range of photosensitive silver halide is about 0.01 mole to about 20 moles of photosensltive silver halide per mole of silver salt oxidizing agent, for instance, per mole of silver behenate and/or silver stearate. Preferred photosensitive silver halides are silver chloride, silver bromide, silver bromoiodide, 10 silver chlorobromoiodide or mixtures thereof. The photosensitive silver halide can be coarse or fine-grain, very fine-~;rain - photosensitive silver halide being especially useful. The photosensitive silver halide can be chemically sensitized, can be protected against the production of fog and/or stabilized against the loss of sensitivity during keeping, as described in the Product Licensing Index reference mentioned previously.
The described ex situ, synthetic polymer peptized photosensitive silver halide can be prepared with a range of 20 synthetic polymer peptizers. Useful synthetic polymer peptizers include, for example, those described in U.S.
Patent 3,713,833 of Lindholm et al, issued January 30, 1973 and U.S. Patent 3,706,565 of Ericson, issued December 19, 1972, - and vinyl pyridine polymers,l e.g. polymers of 2-vinyl pyridine, 4-vinylpyridine and 2-methyl-5-vinylpyridine.
Poly(vinyl acetals), such as poly(vinyl butyral), are especially useful as peptizers in the described preparation of ex situ silver halide. The procedure can be carried out in a non-aqueous medium under controlled reaction conditions.
30 For instance, an organic solvent, such as acetone or methyl-isobutyl ketone, can be employed wi-th the peptizer, such as poly(vinyl butyral). An example of a suitable preparation :, -, - . .. , ...... , ; ., .. ., .. ::

~39S~3 of photosensitive sllver halide is as follows: Lithium bromide, silver trifluoroacetate and poly(vinyl butyral) are mixed in acetone under controlled conditions. The resulting, fine-grain silver bromide can then be mixed with an oxidation-reduction image-forming combina-t:ion, such as a sulfonamido-phenol with silver behenate, to provide a photothermographic material.
e silver halide employed in the practice of the invention can be unwashed or washed to remove soluble salts.
In the latter case, the soluble salts can be removed by - chill-setting and decantation or an emulsion containing the - silver halide can be coagulation washed.
Poly(vinyl acetal) peptized photosensitive silver halide is useful and is described, for example, in Belgian Patent 774,L~36 issued November 12, 1971. The photosensitive silver halide is prepared according to this method by mixing a source of silver ions with a source of halide ions in the presence o~ a poly(vinyl acetal) such as poly(vinyl butyral). ~ ~
mis polymer peptized photosensitive silver halide is ~-especially useful when the photothermographic material contains a polymeric binder which is the same as -the polymer employed to peptize the silver halide. For example, the - polymeric binder can be poly(vinyl butyral) which can also be employed to peptize the photosensitive silver ha-lide.
An especially useful embodiment of the invention is in a photothermographic composition comprising the combination of (a) an oxidation-reduction image-forming combination comprising (i) silver behenate and/or silver ' stearate with (ii) a sul~onamidophenol reducing agent, as ~ ~
described, with (b) poly(vinyl butyral) peptized silver halide in (c) a poly(vinyl butyral) binder, the improvement comprising ~03~SS3 (d) about 0.01 mole to abou-t 0.5 mole, such as about 0.01 mole to about 0.15 mole, o~ thium lodide per mole of the silver halide. With this composition an especially useful activator-toning agent is succinimide.
After imagewise exposure o~ the described photo-thermographic element according to the invention, typically to visible light, the resulting latent image can be developed merely by uni~ormly overall heating the element to moderately elevated temperatures. This merely involves overall heating the -described photothermographic element ~rom about 80C. to about -~ 250C. such as for about 0.5 second to about 60 seconds. By increasing or decreasing the length of time o~ heating, a higher or lower temperature within the described range can be employed depending upon the desired image, particular photothermographic material and the like. A developed image is typically produced within several seconds, such as about 0.5 second to about 60 seconds. A processing temperature o~ about 100C. to about 165C. is especially use~ul.
While visible light can be employed to produce the latent image, other sources o~ electromagnetic radiation can be employed. For example, the described photothermographic elements o~ the invention are use~ul ~or high intensity imagewise exposure. A laser can be employed to produce an image in the described photothermographic material.
Any suitable means can be used ~or providing the desired processing temperature range. The heating means - can be a simple hot plate, iron, roller or the like.
Processing is usually carried out under ambient conditions of pressure and humidity. Conditions outside normal atmospheric pressure and humidity can be employed if desired.

., - 19 - .

.

~0395~
If desired, one or more components of the photo-thermographic elemen-t desclibeA can be ln one or more layers o~ -the element. ~or e~ample, in certain cases it can be desirable to include certain percentages o~` the reducing agent, activator toner, image stabilizer and/or stabilizer precursor in a protective layer over the photothermographic element. This in some cases can reduce migration o~ certain addenda in the layers o~ the photo-thermographic element.
The ~ollowing examples are included ~or a ~urther understanding o~ the invention.

Example 1 This is a comparative example.
A silver behenate dispersion is prepared by ball-milling the ~ollowing components ~or 100 hours:
silver behenate 50.0 g poly(vinyl butyral) 15.0 g methylisobutyl ketone 500 ml A photothermographic composition is prepared by combining 100 ml o~ the above-described dispersion with the ~ollowing addenda in the order indicated:

Poly(vinyl butyral)-silver bromide 40.0 ml emulsion (6 l/mole Ag) Acetone solution containing 10~ by 10.0 ml weight succinimide ~Iold 10 minutes at room temperature.

Acetone solution containing 14~ by 36.0 ml weight poly(vinyl butyral) Acetone solution containing 6.3~ by 36.o ml weight 4-benzenesul~onamidophenol Acetone solution containing 5~ by 10.0 ml weight 2,4-dihydroxybenzophenone Acetone-toluene solution (1:1 by 6.o ml volume) containing 2~ by volume o~ a silicone surfactant (Silicone AF-70, a product of General Elec-tric Company~ U.S.A.) .~,-: ~ . -.. .,: :
,: . . .~.

103955~3 Ace-tone solution containing o.66 m~,/ml 12.0 ml o~ 2-(5,5-dicyano-4-phenyl-2,L~-penta- - ;
dienylldene)-l-ethyl-~-n~phthothiazoline sensitizing dye The composition is then held l~ hours at room temperature, i.e; about 20C.
The above composition is coated at 6.9 ml/ft2 on unsubbed poly(ethylene terephthalate) ~ilm suppor-t.~ The element is also overcoated with the following composition at 2.3 ml/ft2.

Poly~4,4'-(hexahydro-4,7-methanoindan-5- 5.0 g ylidene)diphenylene carbonate]
Dichloroethane 95 ml Acetone 4 ml Silicone sur~actant (Silicone L-522 0.5 ml o~ Union Carbide Co., U.S.~.) The dried element is exposed sensitometrically to light ~or 10 3 seconds with a Mark VII exposing device marketed by Edgerton, Germeshausen and Grier, Inc. and then overall heated ~or 5 seconds at 132C. The sensitometric results are given in Table I.

Example_2 Ihis example is like Example 1 except that ~ ml o~ an acetone solution containing 2.28~ by weight anhydrous lithium iodide is added to the described composition prior to coating. The element is sensitometrically exposed and processed by overall heating the exposed element for 5 seconds at 132C.
as described in Example 1. The sensitometric results appear in Table I.
.

Table I
:, *Relative Example SpeedContrast nmin Dmax 1 1001-73 0.17 2.02

2 ~592.12 0.17 1.80 *Measured at 0.30 above Dmi1l -1~39553 Density results are measured using a so-called Status A blue filter combination consisting of three Wratten~ L~7B
filters, one ~12740 -filter and one C9782 filter. This filter combination exhibits peak transmittance in the 440 nm region.

Example 3 Results similar to those achieved in Example 2 are observed when potassium iodide is employed in place of lithium iodide.

Example ~
. ~, Results similar to those achieved in Example 2 are observed when ammonium iodide is employed in place of lithium - iodide.

Example l~a Results similar -to those achieved in Example 2 are observed when sodium iodide is employed in place of lithium iodide.

Example 5 Results similar to those achieved in Example 2 are observed when the sensitizing dye anhydro-9-ethyl-3,3~-di(3-sulfopropyl)-~,5,4',5'-dibenzothiacarbocyanine hydroxide, sodium salt is employed in place o~ the sensitizing dye described in Example 2. The lithium iodide salt promotes J-aggregation of the dye at 680-690 nm.

Example 6 This is a comparative example.
No significant increase in photosensitivity is observed when the procedure described in Example 2 is repeated with the exception that sodium bromide is employed in place of lithium iodide. Sodium bromide accordingly does not have the property of increasing the photosensitivity , . . . . . -~3g~53 o~ the described photo-thermographic materials under these conditions, Example 7 -me prDcedure described in Example 2 is repeated with the exception that 0.05 mole o~ lithium iodide is employed per mole o~ the described photosensitive silver bromide in the photothermographic composition. Results similar to those o~
Example 2 are observed.

Example 8 -m e procedure described in Example 2 is repeated with the exception that 0.25 mole o~ lithium iodide is employed per mole of the descrlbed photosensitive silver bromide in the photothermographic composition. Results similar to those o~
Example 2 are observed.

Examples 9-12 me photothermographic compositions employed in the - photothermographic elements in Examples 9-12 are identical to those described in Example 2 except that the method o~
preparing the composition is changed. The accompanying Table II
shows the order of addition of the components and the speeds - observed.
mese exanples indicate that by starting with either the silver behenate dispersion or the poly(vinyl butyral) peptized emulsion and then adding either the lithium iodide or succinimide s'olutions be~ore all the other components, even greater photosensitivity can be obtained.

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Examples 13-20 -The pho~othermographic composi-tions employed in these elements are identical to those described in Example 2 except that the method of preparing the final composition is changed.
The order of addition for each component is indicated by a code in the far right hand column of the following Table III.
me code is explained at the bottom of Table III. The results of Examples 13-20 are given in following Table III.
In summary, -the element most sensitive to red light, i.e., light to which the elemen-ts have been spectrally sensitized, is Example 15. This element was prepared by combining the following components in the order indicated:
1. silver behenate-behenic acid dispersion 2. succinimide toner

3. lithium iodide

4. polyvinyl butyral-silver bromide emulsion

5. additional poly(vinyl butyral)

6. 4-benzenesulfonamidophenol developer

7. 2,4-dihydroxybenzophenone

8. silicone AF-70 Surfactant

9. spectral sensitizing dye The element most sensitive to clear exposure (non-filtered light) and blue exposures is Example 14 which is a repeat of Example 2. Example 13 shows the improvement over Example 14 obtained by adding lithium iodide to a photo-thermographic composition containing a silver bromide emulsion.
Examples 18-20 show that the variations in blue speed are consistent with elements that do not contain a spectral sensitizing dye.

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Examples 21-28 1~39553 The photothermographic compositi.ons employecl in these elements are the same as descr:ibed in Example 2. ..
The order of addition for each component is indicated by the code following Table IV. The resul.t,s are given in following Table IV. ~ .

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~039S5i3 The invention has been describecl 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.

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Claims

What is claimed is:

1. In a method of preparing a photothermographic composition comprising:
A) preparing a dispersion of:
a) an oxidation-reduction image-forming combination comprising:
i) a silver salt oxidizing agent and ii) an organic reducing agent with:
b) a synthetic polymer-peptized photosensitive silver halide, and c) a cyclic imide toner in d) a non-gelatin polymeric binder, the improvement comprising:
B) mixing with said dispersion a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition.

2. A method as in Claim 1 wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.

3. A method as in Claim 1 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide and ammonium iodide and combinations of these iodide compounds.

4. A method as in Claim 1 wherein said toner comprises succinimide.

5. A method as in Claim 1 of preparing a photothermo-graphic composition also comprising, after said mixing, holding the resulting composition for about 10 seconds to about 48 hours at about 20°C. to about 30°C. before any subsequent step.

6. A method of preparing a photothermographic composition comprising A) preparing a dispersion of:
a) an oxidation-reduction image-forming combination comprising i) silver behenate and ii) a sulfonamidophenol reducing agent with:
b) a cyclic imide toner comprising succinimide, c) a poly(vinyl butyral) peptized silver halide in d) a poly(vinyl butyral) binder, and, after preparing said dispersion:
B) mixing with said dispersion about 0.01 mole to about 0.50 mole of lithium iodide per mole of said silver halide.

7. A method of preparing a photothermographic composition comprising:
A) preparing a dispersion of:
a) an oxidation-reduction image-forming combination comprising:
i) silver behenate and ii) 4-benzenesulfonamidophenol and 2,4-dihydroxyben-zophenone, and b) a cyclic imide toner comprising succinimide, c) poly(vinyl butyral) peptized silver bromide in d) a poly(vinyl butyral) binder, and, after preparing said dispersion, B) mixing with said dispersion about 0.01 mole to about 0.05 mole of lithium iodide per mole of said silver bromide, and then C) holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20°C. to about 30°C. before any subsequent step.

8. A method of preparing a silver halide photo-thermographic composition comprising respectively (A) preparing a dispersion of silver behenate in poly(vinyl butyral), (B) mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition, (C) mixing with the resulting composition an ex situ, poly(vinyl butyral) peptized photosensitive silver halide, and (D) a poly(vinyl butyral) binder, and (E) mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition.

9. A method of preparing a silver halide photo-thermographic composition comprising respectively (A) preparing poly(vinyl butyral) peptized photo-sensitive silver halide, (B) mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide, (C) mixing with the resulting composition a dispersion of silver behenate in poly(vinyl butyral), and (D) then mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition.

10. In a method of preparing a photothermographic element comprising:

(A) preparing a dispersion of:
(a) an oxidation-reduction image-forming combination comprising:
i) a silver salt oxidizing agent and ii) an organic reducing agent with:
(b) synthetic polymer-peptized photosensitive silver halide, and (c) a cyclic imide toner in (d) a non-gelatin polymeric binder, the improvement comprising, after preparing said dispersion (B) mixing with said dispersion a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photothermographic composition, (C) holding the resulting composition for about 10 seconds to about 48 hours at about 20°C. to about 30°C. and then (D) coating the photothermographic composition on a support.

11. A method as in Claim 10 of preparing a photo-thermographic element wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photosensitive silver halide.

12. A method as in Claim 10 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide, ammonium iodide and combinations of these iodide compounds.

13. A method of preparing a photothermographic ele-ment comprising:
A) preparing a dispersion of:
a) an oxidation-reduction image-forming combination com-prising:
i) silver behenate and ii) 4-benzenesulfonamidophenol and 2,4-dihydroxyben-zophenone, and b) poly(vinyl butyral) peptized silver halide in c) a poly(vinyl butyral) binder, and, after preparing said dispersion:
B) mixing with said dispersion about 0.15 mole to about 0.30 mole of lithium iodide per mole of said silver bromide, then C) holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20° C. to about 30° C., and then D) coating the photothermographic composition on a support.

14. A method of preparing a photothermographic element comprising respectively (A) preparing a dispersion of silver behenate in poly(vinyl butyral), (B) mixing with the resulting silver behenate dispersion about 0.01 to about 0.05 mole of lithium iodide per mole of silver halide in the photothermographic composition, (C) mixing with the resulting composition a poly(vinyl butyral) peptized photosensitive silver halide, and (D) a poly(vinyl butyral) binder, (E) mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with the resulting composition, then (F) holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20°C.
to about 30°C., and then (G) coating the photothermographic composition on a support.

15. A method of preparing a photothermographic element comprising respectively (A) preparing poly(vinyl butyral) peptized photosensitive silver halide, (B) mixing with said silver halide about 0.01 to about 0.05 mole of lithium iodide per mole of said silver halide, (C) mixing with the resulting composition a dispersion of silver behenate in poly(vinyl butyral), (D) mixing succinimide, a sulfonamidophenol reducing agent and a spectral sensitizing dye with resulting composition, (E) holding the resulting photothermographic composition for about 60 minutes to about 4 hours at about 20°C.
to about 30°C. and then (F) coating the photothermographic composition on a support.

16. In a photothermographic composition comprising the combination of:
(a) an oxidation-reduction image-forming combination comprising:
i) a silver salt oxidizing agent with ii) an organic reducing agent, (b) a synthetic polymer-peptized photosensitive silver halide, and (c) a cyclic imide toner in a polymeric binder, the improvement comprising:

(d) a sensitizing concentration of a non-silver iodide salt, said iodide salt having the property of increasing the photosensitivity of said photo-thermographic composition.

17. A photothermographic composition as in Claim 16 wherein said sensitizing concentration is about 0.01 mole to about 0.50 mole of said iodide salt per mole of said photo-sensitive silver halide.

18. A photothermographic composition as in Claim 16 wherein said iodide salt is a compound selected from the group consisting of lithium iodide, potassium iodide, sodium iodide, ammonium iodide and combinations of these iodide compounds.

19. A photothermographic composition as in Claim 16 wherein said toner comprises succinimide.

20. In a photothermographic composition comprising the combination of:
(a) an oxidation-reduction image-forming combination comprising:
i) silver behenate with ii) a sulfonamidophenol reducing agent with (b) poly(vinyl butyral) peptized silver halide, (c) succinimide, and (d) a poly(vinyl butyral) binder for said composition, the improvement comprising:
(e) about 0.01 mole to about 0.05 mole of lithium iodide per mole of said silver halide.