Heat developable photographic material
[ HEAT DEVELOPABLE PHOTOGRAPHIC MATERIAL [75] Inventor:  
 [73] Assignee: Fuji Photo Film Co., Ltd.,  
 Kanagawa, Japan 22 Filed: Feb. 5, 1974 21 Appl. No.: 439,771  
 Takao Masuda, Saitama, Japan [30] Foreign Application Priority Data Feb. 6, 1973 Japan 48-14916 [52] US. Cl 96/67; 96/48 HD; 96/114; 96/114.1; 96/114.6; 96/127 [51] Int. Cl. G03c l/28; G03c 1/72 [58] Field of Search... 96/48 l-lD, 127, 114.1, 114.6, 96/114, 67  
 [56] References Cited UNITED STATES PATENTS 2,535,993 12/1950 Thompson 96/127 X 3,679,422 7/1972 de Mauriac et a1... 96/48 HD X 3,734,733 5/1973 Poot et al 96/48 l-lD Primary Examiner-Norman G. Torchin Assistant ExaminerAlfonso T. Suro Pico Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn and Macpeak Apr. 15, 1975 [5 7] ABSTRACT A heat developable photographic material having at least one photosensitive layer on a support, the layer containing the following components:  
 a. an organic silver salt,  
 b. a catalytic amount of a photosensitive silver halide or a compound which reacts with the organic silver salt (a) to produce a photosensitive silver halide,  
 c. a reducing agent,  
 d. a binder, and  
 e. a compound of the following formula:  
 wherein R and R each represents a hydrogen atom,  
 an alkyl group or a phenyl group, and X and Y each represents amonovalent or divalent atomic group necessary for forming a five-membered or six-membered heterocyclic group containing a nitrogen atom(s), the heterocyclic group optionally containing substituent(s) and&#39;lortfused ring(s).  
 l&#39;lfiClaims, No Drawings HEAT DEVELOPABLE PHOTOGRAPI-IIC MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to heat developable photographic materials, and in particular, it relates to those having at least one photosensitive layer of especially high sensitivity.  
  More specifically, this invention relates to heat developable photographic materials having at least one photosensitive layer on a support, the layer containing (a) an organic silver salt, (b) a catalytic amount of a photosensitive silver halide or a compound which reacts with the organic silver salt (a) to produce a photosensitive silver halide, (c) a reducing agent, (d) a binder, and (e) as a sensitizer, a compound represented by the general formula described herein.  
 2. Description of the Prior Art A photographic process using silver halide is one which has heretofore been most widely practiced due to the excellent photographic properties thereof such as high sensitivity and good gradation over all other processes such as an electro-photographic process or a diam-photographic process. However, silver halide photographic materials used in the photographic process are developed with a developer after image-wise exposure thereof, and then they are subjected to several after-treatments such as stopping, fixation, washing with water or stabilization so that the developed images are not discolored or deteriorated under normal illumination or so that the non-developed part (hereinafter referred to as background) is not blackened. Accordingly, these treatments require superfluous time and labor, and in addition, there is danger to the human body due to the chemicals used in the treatment and troublesome problems in that the interior of processing rooms and the hands and clothes of operators are stained. Therefore, in the photographic process using silver halide, it is extremely desired to improve the treatment thereof so that the treatment can be carried out in a dry state without a solution treatment and that the treated image can be rendered stable. For this, various efforts have heretofore been made.  
  A first process is the so-called one-bath development and fixation method as described in, for example, US. Pat. No. 2,875,048, British Pat. No. 954,453 and German Pat. No. 1,163,142, where the twooperations of development and fixation in the conventional silver halide photographic process are carried out in one bath. A second process is to try to change the wet-type treatment which has been employed in the present silver halide photographic process, to a dry-type treatment, for example, described in German Pat. No. 1,174,159, British Pat. Nos. 943,476 and 951,644, etc. A third process is to try to use, as photosensitive elements, a combination of a main component of a long chain aliphatic carboxylic acid silver salt such as silver behenate, or another silver salt such as silver saccharin or silver benzotriazole, and a catalytic amount of silver halide, for example, as described in Japanese Patent Publication No. 22185/70, and US. Pat. Nos. 3,152,904; 3,457,075; 3,635,719; 3,645,739 and 3,756,829; etc. i  
  This invention belongs to the third method of the above described three types of methods.  
  However, sufficient photosensitivity has not as yet been attained in conventional heat developable photographic materials, for example those containing compositions comprising a fatty acid silver salt, a reducing agent and a catalytic amount of silver halide.  
 Regarding conventional techniques for sensitization of conventional heat developable photographic materials, the above described US. Pat. No. 3,457,075, which belongs to the third method, discloses that known merocyanine dyes are effective as a so-called optical sensitizer to silver halide emulsions.  
  However, those optical sensitizers which are effective for silver halide emulsions, in general, are not always effective for every heat developable photographic material, and it is difficult to predict what kind of sensitizer of what structure is effective for heat developable photographic materials.  
 SUMMARY OF THE INVENTION The present inventors have found after various studies on sensitizers that the compounds represented by the general formula described hereinafter have espe cially excellent sensitizing effects for heat developable photographic materials of this invention.  
  Therefore, an object of this invention is to provide heat developable photographic materials having at least one sensitized photosensitive layer.  
  More specifically, the present invention provides sensitized heat developable photographic materials having at least one photosensitive layer on a support, this layer containing the following components:  
 a. an organic silver salt,  
 b. a catalytic amount of a photosensitive silver halide or a compound which reacts with the organic silver salt (a) to produce a photosensitive silver halide,  
 c. a reducing agent,  
 d. a binder, and  
 e. a compound of the following formula:  
 wherein R and R each represents a hydrogen atom, an alkyl group or a phenyl group, and X and Y each represents a monovalent or divalent atomic group necessary for forming a fivemembered or six-membered heterocyclic group containing nitrogen atom(s), with the heterocyclic group optionally containing substituent(s) and/or fused ring(s).  
  The photographic materials of this invention produce images of high sensitivity and high density.  
 DETAILED DESCRIPTION OF THE INVENTION Suitable alkyl groups for R and R are alkyl groups having 1 to 18 carbon atoms such as, for example, methyl, ethyl propyl, isopropyl, butyl, iso-butyl, secbutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-  
 ethylhexyl, decyl, dodecyl etc., and preferably the alkyl Examples of suitable atomic groups represented by X and Y are, for example, those derived from thiazoline,  
 thiazole, benzoxazole, benzthiazole, benzselenazole, tetrazole, naphthothiazole, dimethylindolenine, quinoline, pyridine, etc. Suitable substituents for the X and Y nuclei are alkyl groups having 1 to 18 carbon atoms, preferably having 1 to 12 carbon atoms. Examples are as described above for R and R Representative examples of the heterocyclic group X s T CH a N/ N N I 1 5 N l l c= u N 7 T/ and N\N/&#39;C\\ l l R15 R17 lil 21 groups having 1 to 12 carbon atoms described above.  
 In the above formulae, R R R, R&#34;, R, R. ,.R R,  
 R, R&#34;, and R each represents a hydrogen atom or an alkyl or aryl group; R, R, R and R each represents a hydrogen atom or an alkyl, alkoxy or aryl group; and X represents an anion such as C11, Br, I, C2H5SO4 f l0 N0 or C10 Se.\ RLQ C: a N  
  Representative examples of the heterocyclic group Y are as follows 5 6 In the above formulae, R R R R R R R and R each represents a hydrogen atom or an alkyl or aryl group; R and R each represents a hydrogen atom or an alkyl, alkoxy or aryl group; and X represents an anion such as Cl, Br, I, C H SO 5 Suitable alkyl groups for R to R are alkyl groups having from 1 to 18, preferably 1 to 12, carbon atoms as described for R and R above. Suitable aryl groups for R to R are phenyl or phenyl groups substituted with at least one alkyl group having 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms as described above. Suitable examples of alkoxy groups for R, R R R&#39;, R and R are alkoxy groups having 1 to l8, preferably 1 to 12, carbon atoms. Specific examples thereof are the alkoxy groups corresponding to the i above described specific examples of alkyl groups, e.g.,  
 l0 methoxy, ethoxy, etc.  
  Examples of preferred compounds which are suitable for the present invention are as follows:  
  Com ound No. 2  
  =CH-CH=C S S I Ch paz v t Y Q N CH C h N Z 5 z s (L Compound No. 2  
  w -S C=CH-Ch=C s N i c 0 II C C: H- H 0 \N/ C Compound No. 5  
  C=CH-CH=C-S CH\N 0 CH 0 l H 0/ \N/c i I 5 H l i 2 5 C 11 I CHCH=Z S \N =CH-C 4 3 o I w FR w O VN C Com ound N0.  
 Com ound N0.  
 Com ound No.  
 Com ound No. l  
 Com ound No. l  
 N IN--C H N N C=CH-CH=C -S 1: 3 M w F Comncund No. l  
 Compound No. 16  
 C=CH-C=C s N/ J l o N 2 5 g j Compound No. 17  
 /S CH3 N C=CH-C=(l: S L H c -CH-\+ 2 5 N Compound No. 18  
  cn-cn=c--s ia N i ri=cti-c I l \N c n \N The amount of the component (e), which is a compound effective as a sensitizer in the present invention, which can be added is suitably about to l0 &#39;mole per 1 mole of organic silver salt. This amount can be varied, depending upon the kind of compound used, the kind of organic silver salt, the kind of the catalytic amount of silver halide, the kind of reducing agent, the treating temperature, etc. If the amount of the component (e) exceeds the above described range, the degree of coloration of the light sensitive layer increases very often, which is disadvantageous in some uses. However, when the material is applied to such uses where coloration is not a problem or when compounds of less coloration are used as the component (e), the amount of the component (e) which can be used can exceed this range.  
  As the organic silver salt (component a) which can be used in the present invention, for example, silver salts of organic compounds containing imino, mercapto or carboxyl group are suitable.  
  Representative examples of these organic silver salts are silver benzotriazole, silver saccharin, silver phthalazinone, the silver salt of 3-mercapto-4-phenyl- 1,2,4-triazole, the silver salt of 4-hydroxy-6-methyll,3,3a,7-tetrazaindene, the silver salt of 2-(S-ethylthioglycolamido)-benzothiazole, silver caprate, silver laurate, silver myristate, silver palmitate, silver stearate, silver behenate, silver adipate, silver sebacate, etc.  
 Suitable organic silver salts are described in US. Pat. Nos. 3,761,279; 3,589,903; 3,457,075; 3,152,904; 3,635,719; 3,645,739 and 3,756,829.  
  The component (b) of the present invention is (1) a compound which reacts with the silver salt of the component (a) to form a silver halide, or (2) a silver halide.  
  Representative examples of the former compounds (1) are inorganic compounds of the formula MXn; where M represents a hydrogen atom, an ammonium group or a metal atom (such as a strontium, cadmium,  
 zinc, tin, chromium, sodium, barium, iron, cesium, lanthanum, copper, calcium, nickel, magnesium, potassium, aluminum, antimony, gold, cobalt, mercury,.lead,  
 &#39;- beryllium, lithium, manganese, gallium, indium, rho- I dium, ruthenium, palladium, iridium, platinum, thal- &#39;lium, bismuth, etc., atom), X represents a halogen bromoethanol, dichlorobenzophenone, iodoform, bromoform, carbon tetrabromidegjcarbon tetrachloride,  
 etc., are also included in the scope of the compound (1). The silver halide&#39;of the latter compound (2) includes silver chloride, silver bromide, silver chloroiodide, silver iodobromide, silver iodobromochloride, silver bromochloride and silver iodide.  
  The photosensitive silver halide can be in any form of crude particles and fine particles, and in particular, an emulsion of extremely fine particles is especially useful. A suitable particle size ranges from about 0.001 to l 1., preferably 0.01 to 0.1 p.-  
  The emulsion containing the photosensitive silver halide can be optionally prepared using any of the convcrntional methods which are known in the photographic art. For example, suitable emulsions are emulsions by the single-jet process, emulsions by the doublejet process, for example, Lippmann emulsions, ammonia process emulsions, thiocyanate or thioether digested emulsions, for example, emulsions as described in U.S. Pat. Nos. 2,222,264 and 3,320,069 and 3,271,157.  
  The silver halide which can be used in this invention can be sensitized using conventional chemical sensitizers which are generally used for silver halide emulsions, for example, reducing agents, sulfur or selenium compounds, gold, platinum or palladium compounds or a mixture thereof. Suitable methods for sensitization are described, for example, in US. Pat. Nos. 2,623,499; 2,399,083; 3,297,447 and 3,297,446.  
  The compound of the above described component (b) can be used alone or in the form of a mixture of two or more compounds. The amount of the component (b) which can be added is suitably in the range of about 0.001 to 0.5 mole, preferably 0.005 to 0.1 mole, per 1 mole of organic silver salt. If the amount of the component (b) is less than this range, the sensitivity of the material is reduced, but on the contrary, if the amount thereof exceeds this range, the existence of too large an amount of the component (b) causes a disadvantageous phenomenon in that when the material is left under normal illumination after heat development thereof, the non-image part gradually becomes blackened, resulting in a damage to the contrast between the non-image part and the image part.  
  The reducing agent of the component (c) of the present invention must be one suitable for the reduction of organic silver salts to form silver images, when heated in the presence of the exposed silver halide as a catalyst.  
  A suitable reducing agent is determined based on the combination with the organic silver salt used, and for example, substituted phenols, substituted or unsubstituted bisphenols, substituted or unsubstituted naphthols, dior poly-hydroxy benzenes, dior poly-hydroxy naphthalenes, hydroquinone monoethers, ascorbic acid or derivatives thereof, 3-pyrazolidones, pyrazol-S- ones, reducing succharides, kojic acid, hinokitiol, etc., are suitable.  
  Representative examples of these compounds are exemplified in the following:  
  Hydroquinone, chlorohydroquinone, bromohydroquinone, methylhydroquinone, phenylhydroquinone, hydroquinone-monosulfonate, toctylhydroquinone, t-butylhydroquinone, 2,5-dimethylhydroquinone, 2,6-dimethylhydroquinone, methoxyhydroquinone, ethoxyhydroquinone, pmethoxyphenol, p-ethoxyphenol, hy-  
 droquinonemonobenzylether, catechol, pyrogallol, resorcin, p-aminophenol, o-aminophenol, N-methyl-paminophenol, 2-methoxy-4-aminophenol, 2,4- diaminophenol, 2-B-hydroxy ethyl-4-aminophenol, p-tbutylphenol, p-t-amylphenol, p-cresol, 2,6-di-t-butyl-pcresol, p-acetophenol, p-phenylphenol, ophenylphenol, 1,4-dimethoxyphenol, 3,4-xylenol, 2,4- xylenol, 2,6-dimethoxyphenol, l-amino-2-naphthol-6- sodium sulfonate, l-naphthylamine-7-sulf0nic acid, 1- hydroxy-4-methoxy-naphthalene, l-hydroxy-4-ethoxynaphthalene, l,4-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, l-hydroxy-4-aminonaphthalene, l,S-dihydroxynaphthalene, l-hydroxy-2-phenyl-4- methoxynaphthalene, l-hydroxy-2-methyl-4- methoxynaphthalene, a-naphthol, B-naphthol, 1,1- dihydroxy-2,2 -binaphthyl, 4,4&#39;-dimethoxy-l,1&#39;-dihydroxy-2,2&#39;-binaphthyl, 6,6-dibromo-2,2&#39;-dihydroxy- 1,1&#39;-binaphthyl, 6,6-dinitro-2,2-dihydroxyl ,1 binaphthyl, bis(Z-hydroxy-1-naphthyl)-methane, bisphenol A, l,l-bis(2-hydroxy-3,S-dimethylphenyl)- 3,5,5-trimethylhexane, 2,4,4-trimethylpenthyl-bis(2- hydroxy-3,S-dimethylphenyl)methane, bis(2-hydroxy- 3-t-butyl-5-methylphenyl )-methane, bis( 2-hydroxy- 3,S-di-t-butylphenyl)methane, 2,2-bis-(3,5-dimethyl-4- hydroxyphenyl )propane, 2,2-bis( 3-methyl-4-hydroxyphenyl )propane, 4,4 -methylenebis( 3-methyl-5-tbutylphenol), 4,4-methylenebis(2,6-di-t-butylphenol), 2,2&#39;-methylenebis(2-t-butyl-4-ethylphenol), 2,6- dimethylenebis(2-hydroxy-3-t-butyl-5-methylbenzyl)- 4-methylphenol, 3,3 ,5 ,5 -tetra-t-butyl-4 ,4 dihydroxydiphenyl, l-ascorbic acid, l-ascorbic acid monoester, l-ascorbic acid diester, p-oxyphenylglycine, N,N-diethyl-p-phenylenediamine, furoin, benzoin, dihydroxyacetone, glycerinaldehyde, rhodizonic acid-tetrahydroxyquinone, methyl gallate, propyl gallate, hy-  
 droxytetronic acid, N,N-di( 2-ethoxyethyl hydroxylamine glucose, lactose 1-phenyl-3 pyrazolidone, 4-methyl-4-hydroxymethyl-1-phenyl-3- pyrazolidone, bis( 3-methyl-4-hydroxy-5 -tbutylphenyl )sulfide, 3 ,5-di-t-butyl-4-hydroxybenzyldimethylamine, a,a&#39;-(3,5-di-t-butyl-4-hydroxyphenyl)- dimethylether, etc. These reducing agents can be used in the form of a mixture of two or more of them.  
  As described above a suitable reducing agent is selected in combination with the organic silver salt. For example, higher fatty acid silver salts such as silver behenate are relatively difficulty reduced, and therefore relatively strong reducing agents, for example, bisphenols such as 4,4-methylenebis(3-methyl-5-tbutylphenol) are suitable therefor. On the other hand, relatively weak reducing agents, for example substituted phenols such as p-phenylphenol, are suitable for silver salts which are relatively easily reduced, such as silver laurate. in addition, strong reducing agents such as ascorbic acid type reducing agents are suitable for silver salts which are extremely difficultly reduced, such as silver benzotriazole.  
  The amount of reducing agent which can be used in this invention as described above will vary depending upon the organic silver salt used and the kind of the reducing agent used, and therefore, the amount cannot be set forth unequivocally, but in general, a range of about 0.1 to 5 moles, preferably 0.5 to 2 moles, per 1 mole of organic silver salt is suitable.  
  As is evident from the above explanation, in the formation of the heat developable photographic materials of the present invention, an appropriate reducing agent can be selected and used in combination with a specific organic silver salt, and therefore it is unnecessary to specifically define the organic silver salt and reducing agent which are used.  
  In the present invention, the components (a), (b), (c) and (e) are preferably dispersed in a binder and applied on a support. in this application to a support, all of the components (a)(b)(c) (e) together can be dispersed in a binder and applied to a support as one layer, or alternatively, these components (a)(b)(c)(e) can be divided into groups and dispersed separately in a binder and then the respective dispersions are applied to a support as individual layers. As the binder component ((1) which can be used, any and every conventional binder which has heretofore been used in this field is suitable. In general, hydrophobic binders are preferred,  
 but hydrophilic binders can also be used. These binders are preferably transparent or semi-transparent, and examples are, for example, natural substances, such as gelatin, gelatin derivatives or a mixture thereof with latex type vinyl polymers, cellulose derivatives, and  
 polymer, polyvinyl alcohol, polyvinyl acetate, benzyl cellulose, cellulose acetate, cellulose propionate, cellulose acetatephthalate, etc. If desired, two or more of these binders can optionally be used in admixture. The amount of binder is suitably in a ratio (by weight) of about 4:1 to 1:4, preferably 3:1 to 1:3, on the basis of the organic silver salt. If the component (a) or (c) is a high molecular weight substance which can function as a binder, the use of binder can be omitted.  
 With respect to the support which can be used in the present invention, various kinds of substances over broad range can be used. Representative supports are, for example, a cellulose nitrate film, a cellulose ester i )3: S l =cs-cs=cs-cs= s N k N I l o n s 3 I J/:N/\  
 polyvinyl 20 cs-c o c a film, a poly(vinylacetal) film, a polystyrene film, a poly( ethylene-terephthalate) film, a polycarbonate film, and glass, paper, metal, etc. A suitable coating amount ranges from 0.2 to 3 g, preferably 0.3 to L5 g, (as silver) per square meter of the support.  
  An antistatic layer or a conductive layer can be provided in the heat developable photographic materials of this invention. In addition, an anti-halation substance and an anti-halation dye can also be incorporated therein. Suitable example of conductive layers are disclosed in U.S. Pat. No. 3,748,137 and examples of anti halation layers in U.S. Pat. Nos. 3,769,019; 3,745,009; and 3,615,432.  
  In addition, the heat developable photographic materials of this invention can optionally contain a matting agent, such as starch, titanium dioxide, zinc oxide and silica. Further, fluorescent brightening agents such as stilbene, triazine, oxazole and coumarin type fluorescent brightening agents can also be contained therein.  
  The heat developable photosensitive layer of this invention can be applied to a support using various coating methods, for example, using a dip method, a airknife method, a curtain coating method as well as an extrusion coating method with a hopper as described in U.S. Pat. No. 2,681,294. If desired, two or more layers can simultaneously be applied.  
  Some kinds of optical sensitizing dyes which have heretofore been used for silver halide emulsions can advantageously be used in the heat developable photographic materials of the present invention for imparting additional sensitivity thereto. Suitable examples are the cyanine dyes and merocyanine dyes as optical sensitizing dyes which can be used in the present invention. These are well known in the art and examples suitable for use are disclosed in U.S. Pat. Nos. 3,457,075, 3,719,495, 3,761,279, etc.  
 Examples of merocyanine dyes are as follows:  
  o N c H 2 s 5 23 C l-I CH-C Examples of cyanine dyes are as follows:  
  s s N CH-CE=CH-CH=CH- 4 2 5 12 5 151% U -CH-CH=CH- N N 01 J; c1  
  2H5 11 I r N s cH-cH=c L CN I (i H I- These sensitizing dyes are preferably added to the 40 lose, cellulose acetate-butyrate, cellulose acetate, polyphotographic materials in the form of a solution or dispersion dissolved or dispersed in an organic solvent. In this invention, the use of the optical sensitizing dye together with the sensitizer component (e) of this invention causes an increase in the sensitivity of the resulting heat developable photographic material. The content of the optical sensitizing dye in the photographic material of this invention generally is about to 10 mole per 1 mole of the organic silver salt component (a). If the sensitizer of the present invention is effective also as an optical sensitizer, the optical esnsitizing dye need not necessarily be used.  
  In addition, an over-coating polymer layer can optionally be provided on the photosentitive layer of the heat developable photographic material of this invention, for the purpose of increasing the transparency of the photosensitive layer, increasing the density of the image formed and improving the storage stability to that it originally possesses (that is, the ability to maintain the original photographic properties, or those immediately possessed after the preparation of the photographic material, even after storage thereof). The thickness of the over-coating polymer layer film is suitably l to pt.  
  Suitable polymers for the top-coating layer are, for example, as follows: Polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral, polystyrene, polymethylmethacrylate, polyurethane rubber, xylene resin, benzyl cellulose, ethyl celluvinylidene chloride, chlorinated polypropylene, polyvinyl pyrrolidone, cellulose propionate, polyvinyl formal, cellulose acetate-phthalate, polycarbonate, cellulose acetate-propionate, etc.  
  The above described heat developable photographic materials can be developed merely by heating the same, after&#39;exposure to a light source such as a xenon lamp, a tungsten lamp, a mercury lamp, etc. The temperature in the heating is suitably in the range of about to 160C, more preferably to C. Higher temperatures or lower temperatures can be selected within the above described range, by prolonging or reducing the heating time. The time for development is in general about 1 to 60 seconds.  
  Various means can be employed for the heat development of the photographic materials of this invention, for example, the photographic material can be brought into contact with a simple hot plate or the like, or can be brought into contact with a heated drum, or as the case may be, can also be passed through a heated space. In addition, high frequency induction heating or laser beam heating can also be utilized.  
  Now, the present invention will be explained in greater detail by reference to the following Examples. Unless otherwise indicated, all parts, percents, ratios and the like are by weight.  
  EXAMPLE 1 3.4 g of behenic acid were dissolved in 100 ml of toluene at 60C and the resulting solution was adjusted to 60C. While stirring with a stirrer, 100 ml of a diluted nitric acid aqueous solution (pH=2.0 at 25C) were added and mixed therewith. The resulting mixture solution was kept at 60C, and while continuously stirring with a stirrer, 100 ml of an aqueous solution containing a silver-ammonium complex were added thereto. (The complex solution was prepared as follows: Aqueous ammonia was added to about 80 ml of an aqueous solution containing 1.7 g of silver nitrate to form a silverammonium complex, and water was added thereto to make the total 100 ml of aqueous solution). Thus, a dispersion containing fine crystals of silver behenate was obtained. This dispersion was left at room temperature (about -30C) for 20 minutes, whereby an aqueous layer and a toluene layer separated from each other.  
  The aqueous layer was first removed, and 400 ml of water were added anew to the remaining toluene layer, which was then washed therewith according to a decantation method. This operation was repeated three times, and then 400 ml of toluene were added to separate the silver behenate by centrifuging. 4 g of silver behenate were obtained in the form of spindle-shaped crystals (long side: about 1 t: short side; about 0.05 p).  
  2.5 g of the obtained silver behenate were added to 20 ml of an isopropyl alcohol solution containing 2 g of polyvinyl butyral and subjected to ball-milling for 1 hour to form a polymer dispersion. To 20 ml of the thus formed silver salt-polymer dispersion were added the following components to prepare a heat developable photographic composition, which was then applied to a polyethylene terephthalate film support in an amount of 1.5 g (silver content)/m (support) to produce heat developable photographic material (A).  
 N-Bromosuccinimide 1 ml (2.5 wt% methyl cellosolve solution) Ammonium Bromide l ml (2.5 wt% methanol solution) Compound No. l 5 ml (0.025 wt% methyl cellosolve solution) 2.2-Methylenebis(6-t-butyl-4-methyl- 3 ml phenol) wt% methyl cellosolve solution) Phthalazinone 1 ml (2.5 wt% methyl cellosolve solution) Anhydrous Tetrachlorophthalic Acid 1 ml (0.6 wt% methanol solution) oe -C On the photosensitive layer of each of these photographic materials A) t&#39;o (&#34;C)was further over-coated a 15 wt percent tetrahydrofuran solution of a vinyl chloride-vinyl acetate copolymer (consisting of wt percent ofvinyl chloride and 5&#39;wt percent of vinyl ace tate), to form an over-coating film of a thickness of 10 .1. (after drying).  
  These three kinds of photographic materials were exposed to a tungsten light source in an exposure amount of 240,000 luc. sec through an optical wedge, and thereafter heated for 10 seconds for development. In each of the thus developed materials, the photographic transmission density thereof was measured. The reciprocal of the amount of exposure required for imparting a higher photographic transmission density than fog (transmission density occurring upon heating of the non-exposed part) by 0.1 was selected as an estimation of the sensitivity. The relative sensitivity of the material (B) was set equal to and the other data are shown in the following Table.  
 Material (A) Material (B) Material (C) Relative 40,000 100 600 Sensitivity From the above results, it can be seen that the sensitizer of the present invention has an extremely high sensitizing effect, on comparison of the material (A) with the other material (B) or (C).  
 EXAMPLE 2 Material (B) Material (A) Material (C) (containing (containing (containing the compound neither merocyanine (l) and compound (I) dye only) merocyanine nor merocydye) anine dye) Relative 60,000 lOO 600 Sensitivity EXAMPLE 2&#39; The same amount of the cyanine dye of the following formula was used together with Compound (1), in place of the latter Compound (1) only, and the others were same as&#34; in Example 1.  
  The results obtained are shown in the following Table. It can be seen therefrom that the sensitizer of the present invention displays an even more excellent sensitizing effect due to the joint use with the cyanine dye.  
 Material (A) Material (B) Material (C) Relative 50,000 100 600 Sensitivity EXAMPLE 3 Material (A) Material (8) Material (C) Relative 30,000 100 600 Sensitivity EXAMPLE 4 The same amount of the above described Compound (9) was used in place of Compound (1), and the others were the same as used in Example 1.  
 The results obtained are shown in the following Table.  
 Material (A) Material (B) Material (C) Relative 35,000 100 600 Sensitivity The effect of the present sensitizer was similar to that obtained in Example 1.  
 EXAMPLE 5 A solution of 11 g of lauric acid dissolved in 100 ml of isoamyl acetate was kept at 5C, and, while stirring, 100 ml of a diluted nitric acid aqueous solution (pl-l=2.0 at 25C) were added thereto and admixed, and then while further continuously stirring, 50 ml of a silver nitrate-ammonium complex aqueous solution (cooled to C) containing 8.5 g of silver nitrate were added thereto over the course of 1 minute thereby to react the lauric acid and the silver ion.  
  Spindle-shaped crystals of silver laurate were obtained (long side: about 0.8 pt; short side: about 0.04 a). After the thus prepared silver salt was washed with water and then with methanol, 3.0 of polyvinyl butyral and 20 ml of isopropyl alcohol (per 2.7 g of silver laurate) were added thereto to disperse the silver salt in a ball-mill, whereby a silver salt-polymer dispersion was prepared.  
  To 20 ml of this silver salt-polymer dispersion were added the following components to prepare a heat developable photographic composition, which was then applied to a polyethylene terephthalate film support in an amount of 1.7 g (silver content)/m (support) to produce a heat developable photographic material (A).  
 l,3-Dibromo-5.S-dimethylhydantoin 1 ml (2.5 wt% methyl cellosolve solution) Ammonium Bromide 1 ml (2.5 wt% methanol solution) -Continued Compound (7) ml (0.025 wt% methyl cellosolve solution) p-Phenylphenol 3 ml (70 wt% methyl cellosolve solution) 5 Phthalazinone 1 ml (2.5 wt% methyl cellosolve solution) Anhydrous Tetrachlorophthalic Acid 1 ml (0.6 wt% methanol solution) Separately from this, two other kinds of heat developable photographic materials (B) and (C) were prepared in a similar manner for comparison: the former (B) not containing the sensitizer of the present invention, the above Compound (7), and the latter (C) containing, as sensitizing dye, the same amount of the merocyanine dye (of Example 1) in place of Compound (7).  
  On &#39;the photosensitive layer of each of the thus produced photographic materials (A) to (C) was further over-coated a wt percent tetrahydrofuran solution of a vinyl chloride-vinyl acetate copolymer (consisting of 95 wt percent of vinyl chloride and 5 wt percent of vinyl acetate), to form an over-coating film of a thickness of 10 p. (after drying).  
  These three kinds of photographic materials (A) to (C) were exposed to a tungsten light source in an exposure amount of 200,000 lux.sec through an optical wedge, and thereafter heated for 7 seconds at 120C for development. In each case, the photographic transmission density was measured and the relative sensitivity was calculated in a manner similar to Example 1. The results obtained are shown in the following Table.  
 Material (A) Material (B) Material (C) Relative 100 500 Sensitivity From the above results, it can be seen that the sensitizer of this invention displays an extremely excellent sensitizing effect.  
 EXAMPLE 6 Using the same process of Example 5, the same amount of the above described Compound (2) was used in place of Compound (7). The results obtained are shown in the following Table.  
 Material (A) Material (B) Material (C) Relative I00 500 Sensitivity It can be seen that Compound (2) has an excellent sensitizing effect similar to Compound (7) of Example EXAMPLE 7 Material (A) Material (B) Material (C) Relative 500 50,000 Sensitivity 23 Compound also was effective as a sensitizer, similar to Compound (7) of Example 5.  
 EXAMPLE 8 6 g of benzotriazole were dissolved in 100 ml of isoamyl acetate at 50C and then cooled and adjusted to l5C. While stirring with a stirrer, a solution of 8.5 of silver nitrate dissolved in 100 ml of a diluted nitric acid aqueous solution (pH=2.0 at 25C), which was adjusted to 3C, was added thereto. Thus a dispersion containing fine crystals of silver benzotriazole was prepared. The resulting dispersion was left at room temperature for 20 minutes, whereupon an aqueous phase and an isoamyl acetate phase separated from each other. The aqueous phase was first removed, and 400 ml of water was added anew to the remaining phase to wash the same by a decantation method. This operation was repeated three times, and then 400 ml of methanol were added to separate the silver benzotriazole by centrifuging. Thus, 8 g of silver benzotriazole were obtained. The particles of the silver benzotriazole were of a nearly spherical form, having a particle size of about 1 ,1 (diameter). 2.5 g of the thus formed silver benzotriazole were added to 40 ml of as isopropyl alcohol solution containing 4 g of polyvinyl butyral and subjected to ball-milling for 4 hours, to disperse the same, whereby a silver salt-polymer dispersion was prepared. To 40 ml of the resulting silver salt-polymer dispersion were added the following components to form a heat developable photographic composition, which was then applied to a polyethylene terephthalate film support in an amount of 1.2 g (coated silver content)/m (support) to produce a heat developable photographic material (A).  
 Ammonium Iodide 1 ml (8.5 wt% methanol solution) Solution Containing 2 g of Ascorbic 10 ml Acid Monopalmitate and 2 g of Ascorbic Acid Dipalmitate in 10 ml of Methyl Cellosolve Compound (4) 1 ml (0.2 wt% methyl cellosolve solution) N-Ethyl-N&#39;-dodecylurea 2 ml (2.5 wt% methyl cellosolve solution) Separately from this, two other kinds of heat developable photographic materials (B) and (C) were prepared in a similar manner for comparison: the former (B) not containing the sensitizer of the present invention, the above Compound (4), and the latter (C) containing, as a sensitizing dye, the same amount of the merocyanine dye (of Example 1) in place of Compound (4).  
  On the photosensitive layer of each of the thus produced photographic materials (A) to (C) was further over-coated a wt% tetrahydrofuran solution of a vinyl chloride-vinyl acetate copolymer (consisting of wt% of vinyl chloride and 5 wt% of vinyl acetate), to form an over-coating film of a thickness of 8 (after drying).  
 Small pieces of these three kinds of photographic ma- Material (A) Material (B) Material (C) Relative 600 I00 200 Sensitivity From the above results, it can be seen that the sensitizer of this invention displays an excellent sensitizing effect.  
 EXAMPLE 9 Using the same process of Example 8, the same amount of the above described Compound (3) was used in place of Compound (4). The results obtained are shown in the following Table.  
 Material (A) Material (B) Material (C) Relative 700 I00 200 Sensitivity It can be seen that Compound (3) has an excellent sensitizing effect similar to Compound (4) of Example 8.  
 EXAMPLE 10 Using the same process of Example 8, the same amount of the above described Compound (6) was used in place of Compound (4). The results obtained are shown in the following Table.  
 Material (A) Material (8) Material (C) Relative 200 Sensitivity Compound (6) also is effective as a sensitizer, similar to Compound (4) of Example 8.  
  While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.  
 What is claimed is:  
  1. A heat developable photographic material comprising a support having at least one photosensitive layer containing the following components:  
 a. an organic silver salt,  
 b. a catalytic amount of a photosensitive silver halide or a compound which reacts with said organic silver salt (a) to produce a photosensitive silver halide terials (A) to (C) were exposed to a tungsten light 65 a reducing agent,  
 source in an exposure amount of 1,200,000 lux.sec through an optical wedge, and thereafter heated for 30 d. a binder, and e. a compound of the following formula:  
 i l C CH Y I O N I wherein R and R each represents a hydrogen atom, an gen atom or an alkyl group, an alkoxy group or an aryl alkyl group or a phenyl group, and X and Y each repregroup; and X represents an anion. sents a monovalent or divalent atomic group necessary I 4. The photographic material as claimed in claim 1, for forming a five-membered or six-membered heterowherein Y forms a heterocyclic group of the following cyclic group containing a nitrogen atom(s), said heterformulae: ocyclic group optionally containing substituent(s) and- /or fused ring(s). R  
  2. The photographic material as claimed in claim 1 wherein X and Y each form a thiazoline, thiazole, benzl oxazole, benzthiazole, benzselenazole, tetrazole, naphthothiazole, dimethylindolenine, quinoline or pyridine N nucleus. 19 X 3. The photographic material as claimed in claim 1,  
 wherein X represents a heterocyclic group of the follag lowing formulae: R  
  N CH L 5 X- or \N/ where R, R R R R R R and R each rep- L resents a hydrogen atom an alkyl group, or an aryl R 7 group; R&#34; and R each represents a hydrogen atom or an alkyl group, an alkoxy group or an aryl group; and where R&#34;, R R&#34;, R&#34;, R&#34;, R R R, R, R&#34; and R X represents an anion. each represents a hydrogen atom, an alkyl group or an 5. The photographic material as claimed in claim 1, aryl group: R, R, R and R each represents a hydrowherein the component (e) is Compound No.6  
 Compound No.7  
  4H Q N I 2 5 Comgound No.8  
 Compound No.9  
 Com ound No.10  
 Compound No l6 Compound No 12 Compound No.18  
 6. The photographic material as claimed in claim 1,  
 wherein said component (e) is present in an amount ranging from about to 10 mole per 1 mole of said organic silver salt.  
  7. The photographic material as claimed in claim 1, including an optical sensitizing dye in an amount of about 10&#39; to 10 mole per 1 mole of said organic silver salt.  
  8. The photographic material as claimed in claim 1, including an overcoating layer superposed on said photosensitive layer.  
  9. The photographic material as claimed in claim 1, wherein said organic silver salt (a) is a silver salt of an organic compound containing an imino group, mercapto group or carboxyl group.  
  10. The photographic material as claimed in claim 1, wherein said component (b) which is capable of forming a lightsensitive silver halide by reaction with said organic silver salt (a) is selected from the group consisting of (i) inorganic halides of the general formula MX wherein M is a hydrogen atom, an ammonium group or a metal atom, X is a halogen atom, and n is 1 when M is a hydrogen atom or an ammonium group or represents the valency of said metal atom when M is a metal, and (-ii) organic halogen compounds.  
  1 l. The photographic material as claimed in claim 1, wherein said reducing agent (c) is selected from the group consistingiof substituted phenols, substituted or unsubstituted bisphenols, substituted or unsubstituted naphthols, dior poly-hydroxybenzenes, dior polyhydroxynaphthalenes, hydroquinone monoethers, ascorbic acid, ascorbic acid derivatives, 3- pyrazolidones, pyrazoline-S-ones, reducing saccharides, kojic acid, and hinokitiol.  
  12. The photographic material as claimed in claim 10, wherein said metal is strontium, cadmium, zinc, tin, chromium, sodium, barium, iron, cesium, lanthanum, copper, calcium, nickel, magnesium, potassium, aluminum, antimony, gold, cobalt, mercury, lead, beryllium, lithium, manganese, gallium, indium, rhodium, ruthenium, palladium, platinum, thallium or bismuth and wherein said X is chlorine, bromine or iodine.  
  13. The photographic material as claimed in claim 10, wherein said compound capable of forming a lightsensitive silver halide by the reaction thereof with said organic silver salt (a) is triphenylmethyl chloride, triphenylmethyl bromide, 2-bromo-2-methylpropane, 2- bromobutyric acid, 2-bromoethanol, dichlorobenzophenone, iodoform, bromoform, carbon tetrabromide or carbon tetrachloride. I  
  14. The photographic material as claimed in claim 1, wherein said light-sensitive silver halide is silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide, silver iodide or silve&#39;r chloroiodide.  
 15. The photographic material as claimed in claim 1,  
 wherein said binder is a hydrophobic binder or a hydrophilic binder.  
  16. The photographic material as claimed in claim 15, wherein said binder is gelatin, gelatin phthalide,  
 &#39;polyacrylamide, polyvinyl butyral, cellulose acetate- 16, wherein said binder is polyvinylbutyral.