Method of treating direct positive silver halide sensitive material
FIELD OF THE INVENTION 
     The present invention relates to silver halide photographic sensitive materials which form direct positive photographic images and, particularly, to a method of improving the quality of direct positive images. 
     BACKGROUND OF THE INVENTION 
     In the field of silver halide photographic processes, a photographic process capable of obtaining positive images without forming negative images or carrying out intermediate treatment for negative images is called a direct positive photographic process. Photographic sensitive materials and emulsions used for such photographic processes are called direct positive sensitive materials and direct positive photographic emulsions, respectively. 
     Although there are many kinds of direct positive photographic processes, a process which comprises exposing previously fogged silver halide particles to light in the presence of a desensitizer and thereafter developing and a process which comprises exposing a silver halide emulsion having sensitive nuclei in principally the inner part of silver halide particles to light and thereafter developing in the presence of a fogging agent are most useful. The present invention relates to the latter. The silver halide emulsion having sensitive nuclei in principally the inner part of silver halide particles, which forms latent images in principally the inner part of particles is called an inner latent image type silver halide emulsion which is distinguished from a silver halide emulsion forming latent images on the surface of particles. 
     A process for obtaining direct positive images which comprises carrying out surface development of the inner latent image type silver halide photographic emulsion in the presence of a fogging agent and photographic emulsions and photographic sensitive materials used for such a process are described in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318, 3,227,552, and 3,761,276, British Pat. Nos. 1,011,062 and 1,151,363, and Japanese Patent Publication No. 29405/68, etc. 
     In the above-described process for obtaining direct positive images, the fogging agent may be added to a developing solution. However, if the fogging agent is added to a photographic emulsion layer or another layer in the sensitive material so as to be adsorbed on the surface of silver halide particles, better reversal property can be obtained. 
     Examples of useful fogging agents used in the above-described processes for obtaining direct positive images include hydrazine and derivatives thereof described in U.S. Pat. Nos. 2,563,785, 2,588,982 and 3,227,552. Particularly, in U.S. Pat. No. 3,227,552, it has been described that hydrazides which are hydrazine derivatives and hydrazine compounds can be used by adding them not only to a developing solution but also to a sensitive layer. 
     Further, heterocyclic quaternary salt compounds described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738 and 3,759,901 and Japanese Patent Application (OPI) Nos. 3426/77 and 69613/77 (the term &#34;OPI&#34; as used herein refers to a &#34;published unexamined Japanese patent application&#34;) are known to be useful as fogging agents. 
     Moreover, the use of acylhydrazinophenylthiourea compounds is described in U.S. Pat. Nos. 4,030,925 (corresponding to German Patent Application (OLS) No. 2,635,316) and 4,031,127 (corresponding to German Patent Application (OLS) No. 2,635,317). 
     However, these known fogging agents are not desirable because of their bad influence upon preservability of the direct positive sensitive materials, they have an insufficient ability with respect to fogging the inner latent image type silver halide having a small particle size, the reversal property varies greatly due to variations in the bromine ion concentration of the developing solution, and the reversal property varies greatly due to variations in the amount of the fogging agent added. 
     On the other hand, direct positive images obtained by using a core/shell type emulsion together with a fogging agent represented by the general formula (I) as described later are not desirable because their images are inferior in sharpness and edge effect to form the so-called loose images, the reason of which is not clear. Further, the process is not desirable because its application is restricted, though it is the process by which high speed B/W direct positive images are now generally obtained. 
     SUMMARY OF THE INVENTION 
     Accordingly, the first object of the present invention is to provide a process by which the sharpness and edge effect of direct positive images are improved. A second object is to provide a process by which the reversal property does not vary due to variations in the bromine ion concentration of the developing solution or the pH thereof. A third object is to provide a process by which variations in the reversal property due to variations in the amount of a fogging agent is improved. 
     The above-described objects of the present invention have been attained by treating a direct positive silver halide sensitive material containing a compound represented by the general formula (I) in at least a sensitive silver halide photographic emulsion layer or another hydrophilic colloid layer applied to a base in the presence of a compound represented by the general formula (II) to obtain direct positive images: ##STR3## wherein R 1  and R 2 , which may be identical or different, represent each a hydrogen atom, an aliphatic residue, an aromatic residue or a heterocyclic residue, R 3  represents a hydrogen atom or an aliphatic residue, R 4  represents a hydrogen atom, an aliphatic residue or an aromatic residue, and X represents a divalent aromatic residue; ##STR4## wherein R&#39; 1 , R&#39; 2 , R&#39; 3  and R&#39; 4 , which may be identical or different, represent each an alkyl group which may be substituted, an alkenyl group or an aryl group which may be substituted, and R&#39; 1  and R&#39; 2 , R&#39; 2  and R&#39; 3  or R&#39; 3  and R&#39; 4  may form a 5- or 6-member heterocyclic ring including imidazolidinethione, piperidine and morpholine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows density patterns in the width direction of linear images having a width of 300μ which are measured by a microdensitometer. The ordinate indicates the optical density of linear images and the abscissa indicates the width direction of the linear images. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described in greater detail with respect to compounds represented by the general formula (I). The aliphatic residues of R 1 , R 2  and R 3  include straight chain or branched chain alkyl groups, cycloalkyl groups and those having substituents, alkenyl groups and alkynyl groups. Examples of the straight chain or branched chain alkyl groups of R 1  and R 2  include alkyl groups having 1 to 18 carbon atoms and, preferably, 1 to 8 carbon atoms, examples of which include a methyl group, an ethyl group, an isobutyl group and a t-octyl group, etc. Straight chain or branched chain alkyl groups of R 4  include those having 1 to 10 carbon atoms, examples of which include a methyl group, an ethyl group and a propyl group, etc. 
     Cycloalkyl groups of R 1 , R 2  and R 4  include those having 3 to 10 carbon atoms, examples of which include a cyclopropyl group, a cyclohexyl group and an adamantyl group, etc. Examples of substituents for the alkyl groups and the cycloalkyl groups include alkoxy groups (for example, a methoxy group, an ethoxy group, a propoxy group and a butoxy group, etc.), alkoxycarbonyl groups, carbamoyl groups, a hydroxy group, alkylthio groups, amido groups, acyloxy groups, a cyano group, sulfonyl groups, halogen atoms (for example, chlorine, bromine, fluorine and iodine, etc.) and aryl groups (for example, a phenyl group, halogen substituted phenyl groups and alkyl substituted phenyl groups), etc., examples of which include a 3-methoxypropyl group, an ethoxycarbonylmethyl group, a 4-chlorocyclohexyl group, a benzyl group, a p-methylbenzyl group and a p-chlorobenzyl group, etc. The alkenyl group may be an allyl group. The alkynyl group may be a propargyl group. 
     Aromatic residues of R 1 , R 2  and R 4  include a phenyl group, a naphthyl group and those having substituents (for example, an alkyl group, an alkoxy group, an acylhydrazino group, a dialkylamino group, an alkoxycarbonyl group, a cyano group, a carboxyl group, a nitro group, a alkylthio group, a hydroxyl group, a sulfonyl group, a carbamoyl group, a halogen atom, an acylamino group, a sulfonamido group and a thiourea group, etc.). Examples of the residues having substituents include a p-methoxyphenyl group, an o-methoxyphenyl group, a tolyl group, a p-formylhydrazino group, a p-chlorophenyl group, an m-fluorophenyl group, an m-benzamido group, an m-acetamido group, an m-benzenesulfonamido group and an m-phenylthiourea group, etc. 
     The heterocyclic residues of R 1  and R 2  include 5-member or 6-member monocyclic or fused rings having at least one of oxygen, nitrogen, sulfur and selenium atoms, which may have substituents. Examples of the residues include a pyrroline ring, a pyridine ring, a quinoline ring, an indole ring, an oxazole ring, a benzoxazole ring, a naphthoxazole ring, an imidazole ring, a benzimidazole ring, a thiazoline ring, a thiazole ring, a benzothiazole ring, a naphthothiazole ring, a selenazole ring, a benzoselenazole ring and a naphthoselenazole ring, etc. 
     These heterocyclic rings may be substituted by alkyl groups having 1 to 4 carbon atoms such as a methyl group or an ethyl group, etc., alkoxy groups having 1 to 4 carbon atoms such as a methoxy group or an ethoxy group, etc., aryl groups having 6 to 18 carbon atoms such as a phenyl group, etc., halogen atoms such as chlorine or bromine, etc., alkoxycarbonyl groups, a cyano group and an amido group, etc. 
     It is preferred that at least one of R 1  and R 2  represents a hydrogen atom. Further, it is preferred that R 4  represents a hydrogen atom or a methyl group and, particularly, a hydrogen atom. 
     The aliphatic residue represented by R 3  includes straight chain or branched chain alkyl groups, cycloalkyl groups and those having substituents, alkenyl groups and alkynyl groups. Examples of straight chain or branched chain alkyl groups include alkyl groups having 1 to 18 carbon atoms and, preferably, 1 to 6 carbon atoms, specific examples of which include a methyl group, an ethyl group and an isopropyl group, etc. Useful cycloalkyl groups include those having 3 to 10 carbon atoms, examples of which include a cyclopentyl group and a cyclohexyl group, etc. Examples of substituents include alkoxy groups (for example, a methoxy group and an ethoxy group, etc.), alkoxycarbonyl groups, aryl groups (for example, a phenyl group, a halogen substituted phenyl group, an alkoxyphenyl group and an alkylphenyl group, etc.), amido groups and acyloxy groups, etc. Examples of the groups having substituents include a 3-methoxypropyl group, a benzyl group, a p-chlorobenzyl group, a p-methoxybenzyl group and a p-methylbenzyl group, etc. Alkenyl groups include those having 3 to 12 carbon atoms, preferable examples of which include an alkyl group and a 2-butenyl group. 
     R 3  is preferably a hydrogen atom. 
     X represents a divalent aromatic residue, examples of which include a phenylene group, naphthylene groups (1,2-, 1,4-, 2,3-, 1,5- and 1,8-, etc.) and those having substituents. 
     Examples of substituents of the divalent aromatic residues include alkyl groups having 1 to 20 carbon atoms (which may be branched), aralkyl groups having 1 to 3 carbon atoms in the alkyl part, alkoxy groups (preferably having 1 to 20 carbon atoms), substituted alkoxy groups (preferably having 1 to 20 carbon atoms), mono- or di-substituted amino groups substituted by alkyl groups or substituted alkyl groups (1 to 20 carbon atoms), aliphatic acylamino groups (preferably having 2 to 21 carbon atoms), aromatic acylamino groups, alkylthio groups, hydroxyl groups and halogen atoms (for example, chlorine, etc.), etc. 
     A more preferred example of X is a phenylene group. Among compounds represented by the general formula (I), particularly preferred compounds are those represented by: ##STR5## wherein R 1  and X each represent the same meaning as in general formula (I). 
     Examples of the fogging agent useful in the present invention are described in the following. 
     I-1: 1-Formyl-2-[4-(3-phenylureido)phenyl]hydrazine 
     I-2: 2-{4-[3-(4-Chlorophenyl)ureido]phenyl}-1-formylhydrazine 
     I-3: 2-{4-[3-(2-Chlorophenyl)ureido]phenyl}-1-formylhydrazine 
     I-4: 1-Formyl-2-{4-[3-(4-methoxyphenyl)ureido]phenyl}hydrazine 
     I-5: 1-Formyl-2-{2-methoxy-4-[3-(4-methylphenyl)ureido]phenyl}hydrazine 
     I-6: 1-Formyl-2-{4-[3-(2-methoxyphenyl)ureido]phenyl}hydrazine 
     I-7: 2-{4-[3-(3-Acetamidophenyl)ureido]phenyl}-1-formylhydrazine 
     I-8: 1-Formyl-2-[3-(3-phenylureido)phenyl]hydrazine 
     I-9: 1-Formyl-2-[4-(3-methylureido)phenyl]hydrazine 
     I-10: 2-[4-(3-Ethylureido)phenyl]-1-formylhydrazine 
     I-11: 1-Formyl-2-[4-(3-propylureido)phenyl]hydrazine 
     I-12: 2-[4-(3-n-Butylureido)phenyl]-1-formylhydrazine 
     I-13: 2-[4-(3-t-Butylureido)phenyl]-1-formylhydrazine 
     I-14: 1-Formyl-2-[4-(3-pentylureido)phenyl]hydrazine 
     I-15: 2-[4-(3-Dodecylureido)phenyl]-1-formylhydrazine 
     I-16: 1-Formyl-2-[4-(3-octadecylureido)phenyl]hydrazine 
     I-17: 2-[4-(3-Cyclohexylureido)phenyl]-1-formylhydrazine 
     I-18: 2-[4-(3-Benzylureido)phenyl]-1-formylhydrazine 
     I-19: 2-[4-(3-Allylureido)phenyl]-1-formylhydrazine 
     I-20: 2-[4-(3-Ethoxycarbonylmethylureido)phenyl]-1-formylhydrazine 
     I-21: 1-Formyl-2-{4-[3-(2-pyridyl)ureido]phenyl}hydrazine 
     I-22: 1-Formyl-2-{4-[3-(2-thienyl)ureido]phenyl}hydrazine 
     I-23: 2-[4-{3-[3-(2,4-Di-t-amylphenoxyacetamido)phenyl]ureido}phenyl]-1-formylhydrazine 
     I-24: 2-{4-[3-(2-Benzothiazolyl)ureido]phenyl}-1-formylhydrazine 
     I-25: 1-Formyl-2-{4-[3-(4-methylthiazol-2-yl)ureido]phenyl}hydrazine 
     I-26: 2-{4-[3-(3-Benzamidophenyl)ureido]phenyl}-1-formylhydrazine 
     I-27: 2-{4-[3-(3-Benzenesulfonamidophenyl)ureido]phenyl}-1-formylhydrazine 
     I-28: 1-Formyl-2-{4-[3-(3-nitrophenyl)ureido]phenyl}hydrazine 
     I-29: 1-Formyl-2-[4-{3-[3-(3-phenylthioureido)phenyl]ureido}phenyl]hydrazine 
     I-30: 1-Acetyl-2-[4-(3-phenylureido)phenyl]hydrazine 
     I-31: 1-Benzoyl-2-[4-(3-phenylureido)phenyl]hydrazine 
     I-32: 1-(4-Chlorobenzoyl)-2-[2-methyl-4-(3-phenylureido)phenyl]hydrazine 
     I-33: 1-Cyclohexylcarbonyl-2-[4-(3-phenylureido)phenyl]hydrazine 
     I-34: 1-Formyl-2-{4-[3-(4-methylphenyl)ureido]phenyl}hydrazine 
     Among these examples, particularly preferred compounds are I-1, I-2, I-6, I-23, I-27 and I-34. 
     In the direct positive sensitive materials of the present invention, the compound represented by the general formula (I) is preferred to be incorporated in an inner latent image type silver halide emulsion, but it may be incorporated in a hydrophilic colloid layer adjacent to the inner latent image type silver halide emulsion layer. As such a layer, any layer may be utilized if it does not prevent diffusion of the fogging agent into the inner latent image type silver halide, such as a sensitive layer, an intermediate layer, a filter layer, a protective layer or an antihalation layer, etc. 
     It is preferred that the fogging agent of the invention is present in the layer in an amount such that a maximum density (for example, 1.70 or more) is obtained when the inner latent image type emulsion is developed in a surface developing solution. In practice, a suitable amount can vary over a wide range, because it depends upon properties of the silver halide emulsion used, chemical structure of the fogging agent and development condition. However, the inventors have found that a useful amount is in the range of from about 0.1 mg to 5,000 mg per mol of silver in the inner latent image type silver halide emulsion and, preferably, about 0.5 mg to about 2,000 mg per mol of silver. When the fogging agent is incorporated into a hydrophilic colloid layer adjacent to the emulsion layer, it may be used in the same amount as described above based on silver content contained in the same area of the inner latent image type emulsion. 
     The compounds represented by the general formula (I) can be easily synthesized according to the process described in U.S. Pat. No. 4,374,923. 
     Compounds represented by the general formula (II) used in the present invention include tetrasubstituted thiourea, namely, thiourea derivatives having no hydrogen atom on 1 and 3 positions, which do not substantially form silver sulfide in the presence of silver ions, because they do not form a thiol structure as a tautomer. Accordingly, these compounds do not substantially function as sulfur sensitizers. 
     Preferred tetra-substituted thiourea used in the present invention is represented by the following general formula (II). ##STR6## 
     In the formula, R&#39; 1 , R&#39; 2 , R&#39; 3  and R&#39; 4  each represent an alkyl group which may be substituted, an alkenyl group (an allyl group, etc.) or an aryl group which may be substituted, which may be identical or different one another. The total of carbon atom numbers in R&#39; 1  to R&#39; 4  is preferably 30 or less. Further, R&#39; 1  and R&#39; 2 , R&#39; 2  and R&#39; 3  or R&#39; 3  and R&#39; 4  may form a 5- or 6-member heterocyclic ring such as imidazolidinethione, piperidine or morpholine, etc., by linking together. The above-described alkyl group may be any straight or branched chain group. 
     Examples of substituents for the alkyl group include a hydroxyl group (--OH), a carboxyl group, a sulfonic acid group, an amino group, an alkoxy group having 1 to 5 carbon atoms (O-alkyl), a phenyl group and a 5- or 6-member heterocyclic residue (furan, etc.). Examples of substituents for the aryl group include a hydroxy group, a carboxyl group and a sulfonic acid group. 
     Particularly preferred compounds are those wherein 3 or more of R&#39; 1  to R&#39; 4  represent alkyl groups having each 1 to 5 carbon atoms, the aryl group is a phenyl group, and the total of carbon atom number in R&#39; 1  to R&#39; 4  is 20 or less. 
     Examples of compounds which can be used in the present invention are as follows. 
     
         ______________________________________                                    
II-1                                                                      
      ##STR7##                  Melting point 79° C.               
  II-2                                                                    
      ##STR8##                  (Boiling point) 266° C.            
  II-3                                                                    
      ##STR9##                  89° C.                             
  II-4                                                                    
      ##STR10##                 (Boiling point) 99° C./ 0.8 mm Hg  
  II-5                                                                    
      ##STR11##                 58° C.                             
  II-6                                                                    
      ##STR12##                 79° C.                             
  II-7                                                                    
      ##STR13##                 120° C.                            
  II-8                                                                    
      ##STR14##                 127- 128° C.                       
  II-9                                                                    
      ##STR15##                 103- 105° C.                       
  II-10                                                                   
      ##STR16##                 61-62° C.                          
  II-11                                                                   
      ##STR17##                 (Boiling point) 177- 178° C./ 3 mm 
                                Hg                                        
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     Among these examples, II-1, II-2 and II-4 are particularly preferred. 
     Processes for producing the above exemplified compounds have been described in, for example, J. Braun and K. Weizbach, Berichte der Deutschen Chemischen Gesellschaft, 63, 2846 (1930), V. Mozolis and S. Jokubaityte, Lietuvos T S R Mokslu Akademijos Darbai, Ser. B 1969. (3), 125-31, H. Wedinger and H. Eilingsfeld, German Patent No. 1,119,843, R. A. Donia et al., Journal of Organic Chemistry, 14, 946-951 (1949), F. B. Zienty, Journal of American Chemical Society, 68, 1388-1389 (1946), and L. G. S. Brooker et al., Journal of American Chemical Society, 73, 5329-5332 (1951). 
     In order to carry out treatment in the presence of a compound represented by the general formula (II) of the present invention, the compound represented by the general formula (II) may be added to one or more of the layers which make up the above-described photographic sensitive material or it may be added to a developing solution. 
     When adding a compound of general formula (II) to a layer composing the photographic sensitive material, it is preferably added in an amount in the range of 10 -3  mol to 20 mols and, preferably, 5×10 -3  mol to 2 mols per mol of silver halide. The compound is preferably added to a photographic emulsion layer or an adjacent layer thereof. 
     When added to the developing solution, the amount of the compound represented by the general formula (II) of the present invention is peferably added in the range of 5 mg to 15 g, more preferably, 10 mg to 10 g per liter of the developing solution. 
     An inner latent image type emulsion suitable for the present invention contains core/shell type silver halide particles having a chemically sensitized surface which are composed of a silver halide inner nucleus subjected to metal ion doping and/or chemical sensitization and an outer shell which covers at least the sensitization site of said inner nucleus, and a binder. 
     In the present invention, examples of useful silver halides include silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide and silver chlorobromoiodide, etc. Preferable silver halide emulsions contain at least 50% by mol of silver bromide, and the most preferred emulsions are silver bromoiodide emulsions and, particularly, those containing less than about 10% by mol of silver iodide. 
     In the present invention, silver halide particles having various particle sizes can be used, but silver halide particles having an average particle size of about 0.1 to 4 microns, preferably, about 0.2 to 3 microns and, more preferably, about 0.2 to 1.5 microns make it possible to obtain good results. 
     The silver halide particles may have a regular crystal form such as a cube or octahedron, etc., or an irregular crystal form such as a sphere or plate, etc., or both of these types of crystals may be present. Further, they may be composed of a mixture of particles having various crystal forms. 
     The core/shell type silver halide particles which make up the emulsion of the present invention can be obtained by a process comprising carrying out metal ion doping or chemical sensitization or both of them to prepare silver halide inner nuclei, thereafter coating their surfaces with a silver halide outer shell, and carrying out chemical sensitization of the outer shell. It is not necessary to cover the whole face of the particles of inner nuclei with the outer shell. It is sufficient if at least a sensitization site of the inner nuclei (the part where photolysis silver is formed by exposure) is covered. In order to dope the inner nuclei with metal ions, it is possible to adopt a method of carrying out the step of silver halide formation for inner nuclei or the step of physical ageing in the presence of a metal ion source such as cadmium salts, zinc salts, lead salts, thallium salts, iridium salts or complex salts thereof, rhodium salts or complex salts thereof, or iron salts or complex salts thereof, etc. The metal ions are generally used in an amount of 10 -6  mol or more per mol of silver halide. In place of carrying out doping with metal ions, the silver halide inner nuclei may be subjected to chemical sensitization using one or more of noble metal sensitizers, sulfur sensitizers and reduction sensitizers. When subjected to gold sensitization and sulfur sensitization, the sensitivity increases. Such treatment of the silver halide inner nuclei and the process for covering the surface of silver halide particles which make up the inner nuclei with silver halide as an outer shell are known. For example, processes described in U.S. Pat. Nos. 3,206,316, 3,317,322, 3,367,778 (exclusive of a step for fogging the surface of particles) and 3,761,276, etc., can be advantageously adopted. 
     The ratio of silver halide of the inner nuclei to silver halide of the outer shell is arbitrarily determined. Generally, 2 to 8 mols of the latter per mol of the former are used. 
     The silver halide of the inner nuclei preferably has the same composition as that of the outer shell, but they may each have a different composition. 
     The surface of core/shell type silver halide particles prepared as described above is then subjected to chemical sensitization. 
     The chemical sensitization of the surface of core/shell type silver halide particles is carried out by known methods described in Glafkides, Chimie et Physique Photographique (published by Paul Montel Co., 1967), V. L. Zelikman et al., Making and Coating Photographic Emulsion (published by The Focal Press, 1964) and Die Grundlagen der Photographischen Prozesse mit Silberhalogeniden, edited by H. Frieser (Akademische Verlagsgesellschaft, 1968), etc. 
     The condition for carrying out chemical sensitization may be arbitrarily determined, but good results are generally obtained by carrying out sensitization at a pH of 9 or less, a pAg of 10 or less and a temperature of 40° C. or more. However, if necessary, the condition may be determined outside the above-described range. Of course, the chemical sensitization of the surface of core/shell type silver halide particles is carried out to such an extent that the property as inner latent image type of the core/shell type silver halide particles is not damaged. 
     Here, &#34;property as inner latent image type&#34; means the fact that the maximum density measured by a conventional photographic densitometry, of a silver halide emulsion applied to a transparent base which is exposed to light for a fixed time of 0.01 to 10 seconds and developed with the following developing solution A (inner type developer) at 20° C. for 3 minutes is at least 5 times higher than the maximum density obtained by developing the same exposed silver halide emulsion as described above with the following developing solution B (surface type developer) at 20° C. for 4 minutes. 
     
         ______________________________________                                    
Developing Solution A:                                                    
Hydroquinone              15     g                                        
Monomethyl-p-aminophenol sesquisulfate                                    
                          15     g                                        
Sodium sulfite            50     g                                        
Potassium bromide         10     g                                        
Sodium hydroxide          25     g                                        
Sodium thiosulfate        20     g                                        
Water to make             1      l                                        
Developing Solution B:                                                    
p-Oxyphenylglycine        10     g                                        
Sodium carbonate          100    g                                        
Water to make             1      l                                        
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     Useful inner latent image type emulsions suitable for the present invention include emulsions described in the above-mentioned U.S. Pat. No. 2,592,250 as well as emulsions described in Japanese Patent Publication No. 34213/77, British Pat. No. 1,027,146 and U.S. Pat. Nos. 3,206,313, 3,511,662, 3,447,927, 3,737,313, 3,761,276 and 3,271,157. However, the present invention is not limited to them. 
     In the direct positive photographic sensitive materials of the present invention, various kinds of hydrophilic colloids can be used as binders. 
     Examples of useful colloids include hydrophilic colloids conventionally used in the photographic field such as gelatin, colloidal albumin, polysaccharides, cellulose derivatives, or synthetic resins such as polyvinyl compounds including polyvinyl alcohol derivatives and polyacrylamide, etc. Hydrophobic colloids, for example, dispersed polyvinyl compounds and, particularly, those which increase dimensional stability of the photographic materials can be incorporated together with the hydrophilic colloid. Preferred examples of this kind of compound include water-insoluble polymers produced by polymerizing vinyl monomers such as alkyl acrylate, alkyl methacrylate, acrylic acid, sulfoalkyl acrylate or sulfoalkyl methacrylate. 
     In order to prevent deterioration of sensitivity or occurrence of fogs when producing sensitive materials, during preservation or during processing, various compounds can be added to the above-described photographic emulsions. Examples of such compounds include a number of known compounds, examples of which include heterocyclic compounds including 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene, 3-methylbenzothiazole and 1-phenyl-5-mercaptotetrazole, mercury containing compounds, mercapto compounds and metal salts. 
     Examples of useful compounds are described in K. Mees, The Theory of the Photographic Process (3rd Edition, 1966) where original literatures are cited, and U.S. Pat. Nos. 1,758,576, 2,110,178, 2,131,038, 2,173,628, 2,697,040, 2,304,962, 2,324,123, 2,394,198, 2,444,605 to 2,444,608, 2,566,245, 2,694,716, 2,697,099, 2,708,162, 2,728,663 to 2,728,665, 2,476,536, 2,824,001, 2,843,491, 2,886,437, 3,052,544, 3,137,577, 3,220,839, 3,226,231, 3,236,652, 3,251,691, 3,252,799, 3,287,135, 3,326,681, 3,420,668 and 3,622,339 and British Pat. Nos. 893,428, 403,789, 1,173,609 and 1,200,188, etc. 
     In the sensitive materials of the present invention, various kinds of photographic bases can be used. The silver halide emulsions can be applied to one or both sides of the base. 
     In the sensitive materials of the present invention, photographic silver halide emulsion layers and other hydrophilic colloid layers can be hardened by suitable hardening agents. Examples of these hardening agents include vinyl sulfonyl compounds described in Japanese Patent Application Nos. 151636/76, 151641/76 and 154494/76, active halogen containing hardening agents, dioxane derivatives and oxypolysaccharides such as oxystarch, etc. 
     Other additives, particularly, additives useful for photographic emulsions such as lubricants, sensitizers, light absorbing dyes or plasticizers, etc., can be added to the photographic silver halide emulsion layers. 
     Further, in the present invention, compounds which release iodine ion (for example, potassium iodide, etc.) may be added to the silver halide emulsions, and desired images can be obtained using a developing solution containing iodine ions. 
     In the sensitive materials of the present invention, the hydrophilic colloid layers may contain water-soluble dyes as filter dyes or for the purpose of preventing irradiation or halation or for other various purposes. Examples of such dyes include oxonol dyes, hemioxonol dyes, styryl dyes, merocyanine dyes, cyanine dyes and azo dyes. Among them, oxonol dyes, hemioxonol dyes and merocyanine dyes are useful. 
     In the sensitive materials of the present invention, hydrophilic colloid layers may be mordanted by cationic polymers when they contain dyes or ultraviolet ray absorbing agents, etc. For example, it is possible to use polymers described in British Pat. No. 685,475, U.S. Pat. Nos. 2,675,316, 2,839,401, 2,882,156, 3,048,487, 3,184,309 and 3,445,231, German Patent Application (OLS) No. 1,914,362 and Japanese Patent Application (OPI) Nos. 47624/75 and 71332/75. 
     The sensitive materials of the present invention may contain surface active agents for various purposes. Any of nonionic, ionic and ampholytic surface active agents can be used according to the purpose. For example, there are polyoxyalkylene derivatives and amphoteric amino acids (including sulfobetaines), etc. Such surface active agents have been described in U.S. Pat. Nos. 2,600,831, 2,271,622, 2,271,623, 2,275,727, 2,787,604, 2,816,920 and 2,739,891 and Belgian Patent 652,862. 
     In the sensitive materials of the present invention, the photographic emulsions may be spectrally sensitized to blue light having comparatively long wavelengths, green light, red light or infrared light with sensitizing dyes. Useful sensitizing dyes include cyanine dyes, merocyanine dyes, complex cyanine dyes, complex merocyanine dyes, holopolar cyanine dyes, styryl dyes, hemicyanine dyes, oxonol dyes and hemioxonol dyes. 
     Useful sensitizing dyes used in the present invention have been described in, for example, U.S. Pat. Nos. 3,522,052, 3,619,197, 3,713,828, 3,615,643, 3,615,632, 3,617,293, 3,628,964, 3,703,377, 3,666,480, 3,667,960, 3,679,428, 3,672,897, 3,769,026, 3,556,800, 3,615,613, 3,615,638, 3,615,635, 3,705,809, 3,632,349, 3,677,765, 3,770,449, 3,770,440, 3,769,025, 3,745,014, 3,713,828, 3,567,458, 3,625,698, 2,526,632 and 2,503,776, Japanese Patent Application (OPI) No. 76525/73 and Belgian Patent 691,807, etc. 
     In the present invention, the sensitive dyes are used in an amount similar to that used for conventional negative silver halide emulsions. It is particularly advantageous to use them in such an amount that they do not substantially deteriorate intrinsic sensitivity of the silver halide emulsions. It is preferred to use the sensitizing dyes in an amount of about 1.0×10 -5  to about 5×10 -4  mol per mol of silver halide and, particularly, about 4×10 -5  to 2×10 -4  mol per mol of silver halide. 
     The sensitive materials of the present invention may contain dye image forming couplers. Alternatively, they may be developed with a developing solution containing dye image forming couplers. In order to add the couplers to the silver halide emulsions of the present invention, known suitable methods can be used. For example, methods described in U.S. Pat. Nos. 1,055,155, 1,102,028, 2,186,849, 2,322,027 and 2,801,171 can be used. In the present invention, developing agents such as polyhydroxybenzenes, aminophenols or 3-pyrazolidones, etc., may be added to the emulsions or sensitive materials. In the present invention, the photographic emulsions may be non-hardened ones and they may contain tanning developing agents such as hydroquinone or catechol, etc. 
     Matting agents and/or smoothing agents may be added to the emulsion layers or the protective layer in the direct positive sensitive materials of the present invention. Examples of useful matting agents include organic compounds such as water dispersive vinyl polymers such as polymethyl methacrylate, etc., having a suitable particle size (particularly 0.3 to 5μ) and inorganic compounds such as silver halide, strontinu barium sulfate, etc. The smoothing agents are effective for preventing troubles caused by adhesion, likewise the matting agents, and particularly effective for improving friction properties which are related to camera adaptability when photographing or during the projection of movie films. Examples of such agents include waxes such as liquid paraffin or higher aliphatic acid esters, etc., polyfluorohydrocarbons and derivatives thereof, and silicones such as polyalkylpolysiloxane, polyarylpolysiloxane or alkylene oxide addition derivatives of them. 
     In the sensitive materials of the present invention, it is possible to provide various auxiliary layers such as a protective layer, an intermediate layer, a filter layer or an antihalation layer, etc. 
     In order to develop the sensitive materials of the present invention, known various developing agents can be used. Examples of such agents include polyhydroxybenzenes such as hydroquinone, 2-chlorohydroquinone, 2-methylhydroquinone, catechol or pyrogallol, etc., aminophenols such as p-aminophenol, N-methyl-p-aminophenol or 2,4-diaminophenol, etc., 3-pyrazolidones such as 1-phenyl-3-pyrazolidones, 4,4-dimethyl-1-phenyl-3-pyrazolidone or 5,5-dimethyl-1-phenyl-3-pyrazolidone, etc., and ascorbic acids, etc., which may be used alone or as a combination of them. 
     The developing solution may contain sodium sulfite, potassium sulfite, ascorbic acid or reductones (for example, piperidinohexose-reductone), etc., as preservatives. 
     The sensitive materials of the present invention can be developed with a surface developing solution to obtain direct positive images. When the surface developing solution is used, the development step is induced substantially by latent images or fogging nuclei present on the surface of silver halide particles. Although it is preferred that the developing solution does not contain silver halide solubilizing agents, a small amount of them (for example, sulfites) may be added, if inner latent images do not substantially contribute to development before conclusion of the development by surface development center of silver halide particles. 
     The developing solution may contain sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, trisodium phosphate, sodium metaborate, etc., as alkali agents and buffer agents. These agents are added in such an amount that the pH of the developing solution is 10 to 13 and, preferably, 11 to 12.5. 
     In order to further decrease the minimum density of direct positive images, the developing solution preferably contains compounds conventionally used as anti-fogging agents, such as benzimidazoles, for example, 5-nitrobenzimidazole, or benzotriazoles, for example, benzotriazole and 5-methylbenzotriazole, etc. 
     The sensitive materials of the present invention can be treated with a viscous developing solution. This viscous developing solution is a liquid composition containing components necessary to develop silver halide emulsions and to form diffusion transfer dye images, wherein a chief solvent is water and hydrophilic solvents such as methanol or methyl cellosolve may be contained. The processing composition has a sufficient pH to cause development of the emulsion layers and contains alkalis in an amount sufficient to neutralize acids formed during various steps of development and dye image formation (for example, hydrohalogenic acids such as hydrobromic acid, etc., and carboxylic acids such as acetic acid, etc.). Useful alkalis include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, tetramethyl ammonium hydroxide, alkali metal salts, alkaline earth metal salts and amines such as sodium carbonate, trisodium phosphate or diethylamine, etc. Caustic alkali is preferably present in an amount sufficient to make the pH 10 or more, more preferably 12 or more at room temperature. More preferably; the processing composition contains hydrophilic polymers such as polyvinyl alcohol having a high molecular weight, hydroxyethyl cellulose or sodium carboxymethyl cellulose. These polymers are preferably used for the processing composition in order to provide a viscosity of 1 poise or more and, preferably, several hundred poises (e.g., about 500 to 600) to 1,000 poises. 
     The processing composition also preferably contains light absorbing substances such as TiO 2 , carbon black or pH indicator dyes or desensitizers described in U.S. Pat. No. 3,579,333 in order to prevent fogging of silver halide emulsions by outside light during or after treatment in case of, particularly, a monosheet film unit. Further, development restrainer such as benzotriazole can be added to the processing composition. 
     It is preferred that the above-described processing composition is used by putting it in a destructible container as described in U.S. Pat. Nos. 2,543,181, 2,643,886, 2,653,732, 2,723,051, 3,056,491, 3,056,492 and 3,152,515, etc. 
     In the following, examples of the present invention are illustrated, but the present invention is not limited to them. 
     EXAMPLE 1 
     Solutions of silver nitrate and potassium bromide having each the same molar concentration were simultaneously blended at a temperature of 55° C. for 20 minutes according to a controlled double jet method to obtain a silver bromide emulsion. After conclusion of precipitation, cubic crystals having an average side length of 0.1μ were formed. To the silver bromide emulsion, 40 mg of sodium thiosulfate per mol of silver and 40 mg of chloroauric acid (4 hydrate) per mol of silver were added and chemical sensitization was carried out by heating to 75° C. for 60 minutes. Using the resulting silver bromide particles as cores, crystals were grown by adding solutions of silver nitrate and potassium bromide by a simultaneous blending method to obtain octahedral core/shell particles having an average side length of 0.25μ. In order to carry out surface sensitization, 3.4 mg of sodium thiosulfate per mol of silver and 3.4 mg of chloroauric acid (4 hydrate) per mol of silver were added and the mixture was heated to 60° C. for 60 minutes to prepare an inner latent image type direct positive emulsion (Emulsion I). 
     To the Emulsion I, the fogging agent I-1 represented by the general formula (I) of the present invention was added in an amount of 100 mg per mol of silver, and, further, Compounds II-1, II-2 and II-4 of the present invention (general formula (II)) were added as described in Table 1. These emulsions were applied to polyethylene terephthalate bases so as to result in a silver content of 3,000 mg/m 2 , and a gelatin protective layer was applied to the resulting emulsion layer to produce Samples 1 to 4. On these samples, a line having a width of 300μ was superposed together with a stepwedge, and the samples were exposed to light for 1 second by a 1 kw tungsten lamp at a color temperature of 2,854° K. and then developed at 35° C. for 1 minute with the Developing Solution (A) described in Table 2. Then, stopping, fixation and water wash were carried out according to conventional methods. The developed films had a positive step image and a linear image having a width of about 300μ which was formed on the step image. In order to examine sharpness of the image, a density pattern in the width direction of the linear image having a width of about 300μ on the part where the density of step image was 0.5 was measured by a microdensitometer. Results of measurement are shown in FIG. 1. The results show that the edge effect is remarkable and the sharpness of the linear image is improved in Films No. 2, No. 3 and No. 4 as compared with Film No. 1. Their linear image is also visually sharp. 
     
                       TABLE 1                                                     
______________________________________                                    
                      Amount of Compound                                  
                      Represented by                                      
                      General Formula (II)                                
Sample     Compound   (mg/mol Ag)                                         
______________________________________                                    
Film No. 1 Only I-1   --                                                  
Film No. 2 (I-1) + (II-1)                                                 
                      40                                                  
Film No. 3 (I-1) + (II-2)                                                 
                      80                                                  
Film No. 4 (I-1) + (II-4)                                                 
                      100                                                 
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                       TABLE 2                                                     
______________________________________                                    
Developing Solution (A):                                                  
Sodium sulfite             50      g                                      
Potassium carbonate        40      g                                      
Sodium bromide             5       g                                      
Pyrazon                    2       g                                      
Hydroquinone               22      g                                      
5-Methylbenzotriazole      20      ml                                     
Water to make              1       l                                      
pH was adjusted to 11.6 with potassium hydroxide                          
Stopping Solution:                                                        
5 wt % aqueous solution of acetic acid                                    
Fixing Solution:                                                          
Ammonium thiosulfate       200     g                                      
Sodium sulfite             30      g                                      
Water to make              1       l                                      
pH was adjusted to 7.0                                                    
______________________________________                                    
 
    
     EXAMPLE 2 
     To Emulsion I prepared in Example 1, the fogging agent I-1 was added in an amount of 800 mg per mol of silver. The emulsion was applied to a polyethylene terephthalate base so as to result in a silver content of 3,000 mg/m 2 , and a gelatin protective layer was applied to the resulting layer. A line having a width of 300μ was put on the resulting sample, and the sample was exposed to light for 1 second by a 1 kw tungsten lamp at a color temperature of 2,854° K. and then developed at 35° C. for 1 minute with Developing Solutions (A), (B), (C) and (D) described in Tables 2 and 3. 
     Then, stopping, fixation and water wash were carried out according to conventional methods (similar to Example 1). On the samples, a linear image having a width of about 300μ was obtained. In order to examine sharpness of the linear image, a density pattern was measured by a microdensitometer. In the viewpoint of image sharpness and the sense of sight, films treated with Developing Solutions (B), (C) and (D) had far better sharpness than the film treated with Developing Solution (A). 
     
                       TABLE 3                                                     
______________________________________                                    
                Developing Solution                                       
                (B)    (C)     (D)                                        
______________________________________                                    
Sodium sulfite    50 g     &#34;       &#34;                                      
Potassium carbonate                                                       
                  40 g     &#34;       &#34;                                      
Sodium bromide     5 g     &#34;       &#34;                                      
Pyrazon            2 g     &#34;       &#34;                                      
Hydroquinone      22 g     &#34;       &#34;                                      
5-Methylbenzotriazole                                                     
                  20 mg    &#34;       &#34;                                      
Compound II-1      5 mg    --      --                                     
Compound II-2     --       10 mg   --                                     
Compound II-4     --       --      15 mg                                  
Water to make      1 l     &#34;       &#34;                                      
pH was adjusted to 11.6                                                   
with potassium hydroxide.                                                 
______________________________________                                    
 
    
     EXAMPLE 3 
     To Emulsion I prepared in Example 1, the following Comparative Fogging Agents A, B and C were added in amounts of 27 mg, 10 mg and 130 mg per mol of silver, respectively. These emulsions were applied to polyethylene terephthalate bases to produce Films No. 5, No. 6 and No. 7. 
     Comparative Fogging Agent ##STR18## 
     B ##STR19## (Fogging agent described in U.S. Pat. No. 4,030,925) 
     C ##STR20## (Fogging agent described in U.S. Pat. No. 3,759,901) 
     These films were treated together with Films No. 1, No. 2, No. 3 and No. 4 in Example 1 with Developing Solution (A) and the following Developing Solutions (E) and (F) having each a different pH and a different amount of NaBr at 35° C. for 1 minute, and thereafter stopping, fixation and water wash were carried out according to conventional methods. 
     D max  and D min  of the developed films were measured. Results are shown in Table 4. 
     
         ______________________________________                                    
                 Developing Solution                                      
                 (E)   (F)                                                
______________________________________                                    
Sodium sulfite     50    g     50     g                                   
Potassium carbonate                                                       
                   40    g     40     g                                   
Sodium bromide     5     g     8      g                                   
Pyrazon            2     g     2      g                                   
Hydroquinone       22    g     22     g                                   
5-Methylbenzotriazole                                                     
                   20    mg    20     mg                                  
Water to make      1     l     1      l                                   
pH was adjusted with                                                      
                   11.4    11.6                                           
potassium hydroxide                                                       
______________________________________                                    
 
    
     
         ______________________________________                                    
       Developing Solution                                                
       (A)       (E)         (F)                                          
       D.sub.max                                                          
             D.sub.min                                                    
                     D.sub.max                                            
                             D.sub.min                                    
                                   D.sub.max                              
                                         D.sub.min                        
______________________________________                                    
The present                                                               
invention                                                                 
Film No. 1                                                                
         2.50    0.08    2.30  0.08  2.20  0.07                           
Film No. 2                                                                
         2.65    0.08    2.65  0.08  2.60  0.07                           
Film No. 3                                                                
         2.55    0.08    2.55  0.08  2.50  0.07                           
Film No. 4                                                                
         2.60    0.08    2.60  0.08  2.55  0.07                           
Comparative                                                               
example                                                                   
Film No. 5                                                                
         2.50    0.08    1.50  0.08  1.00  0.07                           
Film No. 6                                                                
         1.50    0.13    0.80  0.09  0.50  0.08                           
Film No. 7                                                                
         2.00    0.05    1.00  0.04  0.70  0.04                           
______________________________________                                    
 
    
     Table 4 shows that the D max  and D min  are stable to variations of pH and NaBr when using the fogging agents of the present invention (Film No. 1) as compared with the case of using comparative fogging agents (Films No. 5, No. 6 and No. 7). 
     Further, it is understood that D max  and D min  are stabler in Films No. 2, No. 3 and No. 4 containing the compound of the present invention than in film No. 1. 
     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.