Silver halide photographic emulsion containing a gold salt and a polyalkylene oxide
United States Patent 3901711
The so-called high intensity reciprocity law failure of a silver halide photographic emulsion can be unexpectedly effectively prevented by adding to the silver halide photographic emulsion produced by the known method a gold salt and a polyalkylene oxide. The effect can be further improved by additionally adding thereto at least one compound selected from soluble salts of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead.
US Patent References:
4-hydroxy-6-alkyl-1, 3, 3a, 7-tetrazaindene stabilizers for emulsions sensitized with alkylene oxide polymers
Carroll et al. - August 1955 - 2716062
Tetrazaindene stabilizer for photographic emulsions sensitized with alkylene oxide polymers
Reynolds et al. - July 1956 - 2756147
4-hydroxy-6-alkyl-1, 3, 3alpha, 7-tetrazaindene stabilizers for photographic emulsions sensitized with polyalkylene esters, amides, and ethers
Carroll et al. - March 1957 - 2784091
Photographic emulsions sensitized with sulfonium salts and alkylene oxide polymers
Chechak et al. - August 1958 - 2848330
Photographic emulsions containing colloidal material and alkylene oxide polymers
Herz - November 1962 - 3062647
4-hydroxy-6-alkyl-1, 3, 3a, 7-tetrazaindene stabilizers for emulsions sensitized with alkylene oxide polymers
Carroll et al. - August 1955 - 2716062
Tetrazaindene stabilizer for photographic emulsions sensitized with alkylene oxide polymers
Reynolds et al. - July 1956 - 2756147
4-hydroxy-6-alkyl-1, 3, 3alpha, 7-tetrazaindene stabilizers for photographic emulsions sensitized with polyalkylene esters, amides, and ethers
Carroll et al. - March 1957 - 2784091
Photographic emulsions sensitized with sulfonium salts and alkylene oxide polymers
Chechak et al. - August 1958 - 2848330
Photographic emulsions containing colloidal material and alkylene oxide polymers
Herz - November 1962 - 3062647
Inventors:
Iwaosa, Katsuaki (Kyoto, JA)
Ebato, Seigo (Kyoto, JA)
Itoh, Noboru (Kyoto, JA)
Ebato, Seigo (Kyoto, JA)
Itoh, Noboru (Kyoto, JA)
Application Number:
05/389153
Publication Date:
08/26/1975
Filing Date:
08/17/1973
View Patent Images:
Export Citation:
Assignee:
Mitsubishi Paper Mills, Ltd.
Primary Class:
Other Classes:
430/536, 430/627
International Classes:
G03C1/043; G03C1/08; G03C1/09; G03C1/04; G03C1/06
Field of Search:
96/107,108,95
US Patent References:
| 3320068 | Silver halide emulsions with increased sensitivity | May 1967 | Muller-Bardorff et al. | |
| 3503749 | LIGHT-SENSITIVE SILVER HALIDE EMULSIONS CONTAINING SOLUBLE GOLD SALTS | March 1970 | Tavernier et al. | |
| 3707376 | December 1972 | Stappen et al. | ||
| 3720516 | March 1973 | Woodward et al. | ||
| 3737313 | June 1973 | Rosecrants et al. | ||
| 3761266 | September 1973 | Milton |
Primary Examiner:
Louie Jr., Won H.
Attorney, Agent or Firm:
Cushman, Darby & Cushman
Claims:
What is claimed is
1. A silver halide photographic emulsion suitable for preventing high intensity reciprocity law failure consisting essentially of said emulsion and either (1) a gold salt in terms of gold atoms of 0.1 to 200 mg per mole of the silver halide and a polyalkylene oxide or condensation product thereof with water, aliphatic alcohol, glycol, fatty acid, aliphatic amine, or dehydrated cyclic hexitol compounds, the amount of polyalkylene oxide or condensation product being 0.1 to 50 grams per mole of silva halide or (2) a mixture of (1) and at least one soluble salt selected from the group consisting of halide, nitrate and sulfate salts of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead in an amount of 10 mg to 50 grams per mole of the silver halide.
2. A silver halide photographic emulsion according to claim 1, wherein the gold salt is selected from chloroauric acid, potassium auric thiocyanate and ammonium aurothiocyanate.
3. A silver halide photograhic emulsion according to claim 1, wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide.
4. A silver halide emulsion according to claim 1 wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide and the gold salt is chloroauric acid, potassium auric thiocyanate or ammonium aurothiocyanate.
5. A silver halide emulsion according to claim 1 wherein it includes (2).
6. A silver halide photograhic emulsion according to claim 5, wherein the soluble salt is halide, nitrate or sulfate of cobalt, nickel or zinc.
7. A silver halide emulsion according to claim 5 wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide.
8. A method for producing a silver halide photographic emulsion suitable for preventing high intensity reciprocity law failure which consists essentially of adding to a silver halide photographic emulsion either (1) a gold salt or (2) a mixture of (1) and at least one soluble salt selected from the group consisting of halide, nitrate and sulfate salts of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead at a stage ranging from emulsification to after completion of ripening and adding a polyalkylene oxide or condensation product thereof with water, aliphatic alcohol, glycol, fatty acid, aliphatic amine, or dehydrated cyclic hexitol compounds at a stage ranging from second ripening to after completion of ripening.
9. A method according to claim 8 wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide.
10. A method according to claim 9 wherein there is added (2).
11. A method according to claim 8 wherein there is added (2).
1. A silver halide photographic emulsion suitable for preventing high intensity reciprocity law failure consisting essentially of said emulsion and either (1) a gold salt in terms of gold atoms of 0.1 to 200 mg per mole of the silver halide and a polyalkylene oxide or condensation product thereof with water, aliphatic alcohol, glycol, fatty acid, aliphatic amine, or dehydrated cyclic hexitol compounds, the amount of polyalkylene oxide or condensation product being 0.1 to 50 grams per mole of silva halide or (2) a mixture of (1) and at least one soluble salt selected from the group consisting of halide, nitrate and sulfate salts of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead in an amount of 10 mg to 50 grams per mole of the silver halide.
2. A silver halide photographic emulsion according to claim 1, wherein the gold salt is selected from chloroauric acid, potassium auric thiocyanate and ammonium aurothiocyanate.
3. A silver halide photograhic emulsion according to claim 1, wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide.
4. A silver halide emulsion according to claim 1 wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide and the gold salt is chloroauric acid, potassium auric thiocyanate or ammonium aurothiocyanate.
5. A silver halide emulsion according to claim 1 wherein it includes (2).
6. A silver halide photograhic emulsion according to claim 5, wherein the soluble salt is halide, nitrate or sulfate of cobalt, nickel or zinc.
7. A silver halide emulsion according to claim 5 wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide.
8. A method for producing a silver halide photographic emulsion suitable for preventing high intensity reciprocity law failure which consists essentially of adding to a silver halide photographic emulsion either (1) a gold salt or (2) a mixture of (1) and at least one soluble salt selected from the group consisting of halide, nitrate and sulfate salts of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead at a stage ranging from emulsification to after completion of ripening and adding a polyalkylene oxide or condensation product thereof with water, aliphatic alcohol, glycol, fatty acid, aliphatic amine, or dehydrated cyclic hexitol compounds at a stage ranging from second ripening to after completion of ripening.
9. A method according to claim 8 wherein the polyalkylene oxide or condensation product thereof is polyethylene oxide.
10. A method according to claim 9 wherein there is added (2).
11. A method according to claim 8 wherein there is added (2).
Description:
This invention relates to a process for preventing a silver halide photographic emulsion from the phenomenon called high intensity reciprocity law failure, and aims to prevent the photographic emulsion from failure caused when it is subjected to such high intensity exposure in an extremely short period of time as strobo exposure.
When a silver halide photographic emulsion is exposed to a high intensity light for a short period of time, e.g. for 10 -5 to 10 -6 seconds, the emulsion becomes soft in tone or is desensitized, in general, as compared with the case where it is subjected to ordinary medium exposure. This phenomenon is called high intensity reciprocity law failure. In order to prevent photograhic emulsions from such failure, various processes have heretofore been studied, and several of them have been patented. For example, Japanese Pat. publication No. 4,935/68 discloses a process for preventing a photograhic emulsion from high intensity reciprocity law failure by incorporation of iridium salt into the photographic emulsion, and Japanese Pat. publication No. 32,738/70 discloses a process in which the process of said Japanese Pat. publication No. 4,935/68 has been improved by use of gold salt in combination with iridium salt.
The present invention is a process which is of greater excellent in effect than the said prior art processes, and hence may be said to be an entirely novel invention. That is, the present invention is a process for preventing a silver halide photographic emulsion from said high intensity reciprocity law failure by incorporating into the photographic emulsion a gold salt in combination with a polyalkylene oxide or a derivative thereof and, preferably, with at least one member selected from the group consisting of soluble salts of metals such as cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead. According to the process of the present invention, the reciprocity law failure, the complete prevention of which has heretofore been difficult, can be prevented substantially ideally from the practical standpoint.
The incorporation of a gold salt into a silver halide photograhic emulsion which is a sensitization procedure known as gold sensitization, in general, is known to provide prominent effect of preventing the emulsion from reciprocity failure, particularly from high intensity reciprocity failure. The effect attained by incorporation of gold salt is far more excellent than that attained by incorporation of iridium salt. Further, polyalkylene oxides (synonymous with polyalkylene glycols) and derivatives thereof may be shown as well-known sensitizers. The present inventors have found that the said compounds also have the effect of preventing the reciprocity law failure, particularly the failure caused at the time of high intensity and short period exposure. For example, a photographic material containing in the silver halide photographic emulsion layer a polyethylene oxide, which has ordinarily been used as a sensitizer, is higher in sensitivity than a photograhic material containing no polyethylene oxide. This effect is marked when the photographic material is exposed to a higher intensity light for a shorter period of time, and the sensitization at the shoulder portion of characteristic curve of the photographic material is particularly marked, with the result that the high illuminance reciprocity law failure can be prevented. The above-mentioned effect is identical in tendency with that of a gold salt. The present inventors have confirmed that the prevention of high intensity reciprocity law failure can be accomplished to an extremely desirable extent by use of a gold salt in combination with a polyalkylene oxide. The inventors have further found that an ideal effect, which is substantially satisfactory from the practical standpoint, can be obtained when said gold salt and polyalkylene oxide are used in further combination with a soluble salt of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium, lead or the like metal other than gold.
While part of the effects of the above-mentioned gold salts have already been known, the effect attained by independent use of said gold salt is considerably lower than the effect attained by use of the gold salt in combination with a polyalkylene oxide, and no desirable results can be obtained unless the two are used in combination.
Typical examples of the gold salts referred to herein are as follows:
(1) Chloroauric acid HAuCl 4 (2) Potassium chloroaurate KAuCl 4 (3) Auric trichloride AuCl 3 (4) Potassium auric thiocyanate KAu(CNS) 4 (5) Potassium iodoaurate KAuI 4 (6) Tetracyanoauric acid HAu(CN) 4 (7) Ammonium aurothiocyanate NH 4 Au(CNS) 2 (8) Diethyl-monobromogold Au(C 2 H 5 ) 2 Br (9) Pyridino-trichlorogold (C 5 H 5 N)AuCl 3 .HCl
Further, there may be used gold compounds and complexes containing both sulfur atoms and gold atoms, such as 2-aurosulfobenzothiazole methachloride, gold sulfide, and alkali metal-ammonium aurous thiosulfate complexes. In addition thereto, all the metal compounds, which have ordinarily been used as gold sensitization substances, can effectively be used.
On the other hand, the polyalkylene oxides referred to herein are generally used polyethylene oxides having molecular weights in the range from 400 to 10,000. The scope of the present invention, however, is not limited thereto, and the same effects as above can be obtained even when other polyalkylene oxides and derivatives thereof are used. That is, condensation products (molecular weight 600 to 10,000) of alkylene oxides with at least one member selected from the group consisting of water, aliphatic alcohols, glycols, fatty acids, aliphatic amines, phenols, and dehydrated cyclic compounds of hexitol derivatives also display the same effects as above, and it is needless to say that all the said compounds are involved in the scope of the present invention.
The aforesaid soluble metal salts other than the gold salts are desirably used, in practice, in the form of halides, nitrates or sulfates, though this is, of course, not limitative.
The proportions of the individual materials used in the present invention vary depending on the kinds thereof, but are preferably such that the gold salt is used in a proportion of 0.1 to 200 mg., preferably 5 to 50 mg., in terms of gold atom, per mole of silver halide, the polyalkylene oxide in a proportion of 0.1 to 50 g. per mole of silver halide, and the soluble metal salt other than the gold salt in a proportion of 10 mg. to 50 g per mole of silver halide.
When the amount of the gold salt is less than said range, effect thereof is not conspicuous and when more than said range, adverse effects such as fogging, etc. are caused. When the amount of the polyalkylene oxide is less than said range, effect thereof is not conspicuous and when more than said range, adverse effects such as fogging, decrease in physical properties of gelatine, etc. are caused. When the amount of the soluble salt is less than said range, effect thereof is not conspicuous and when more than said range, adverse effects such as fogging, desensitization, decrease in physical properties of gelatine, etc. are caused. These materials may be incorporated into a photographic emulsion at such stages that the gold salt and the metal salt other than gold salt may be incorporated at any stage of emulsification, first ripening, second ripening or after completion of ripening, and the polyalkylene oxide may be incorporated at any stage of second ripening or after completion of ripening.
The present invention is illustrated in detail below with reference to examples.
EXAMPLE 1
A silver iodobromide emulsion containing 2% of silver iodide, which had been prepared according to a process known to those skilled in the art, was washed with water and then subjected to second ripening. In this case, one half of the emulsion was subjected to only sulfur sensitization (emulsion A), and the remainder was incorporated with 20 mg. per mole of silver halide of gold thiocyanate in terms of gold. The thus treated emulsions were individually adjusted to a pH of 6.0 and ripened at 50°C. for 90 minutes. Further, the latter emulsion was equally divided into 4 emulsions, and the first emulsion was left as it was (emulsion B), the second emulsion was incorporated with 1 g. per mole of silver halide of polyethylene oxide having a molecular weight of 6,000 (emulsion C), the third emulsion was incorporated with 3 g. per mole of silver halide of cobalt chloride (emulsion D), and the fourth emulsion was incorporated with 1 g. per mole of silver halide of polyethylene oxide in combination with 3 g. per mole of silver halide of cobalt chloride (emulsion E).
These emulsions were individually incorporated with a stabilizer, a hardener and an activator (saponin), coated on a base so that the amount of silver became 50 mg. per 100 cm 2 , and then dried to prepare samples A, B, C, D and E. Each of the samples was exposed for 10 seconds to a tungsten lamp and for 10 -5 seconds to a xenon flash lamp through a step type optical wedge having a density difference of 0.15, and then developed with a well-known Metol-hydroquinone developer of the following composition:
Water 700 ml. Metol 2 g. Hydroquinone 9 g. Anhydrous sodium sulfite 75 g. Sodium carbonate (monohydrate) 30 g. Potassium bromide 5 g. (Water to make 1,000 ml.)
As the result, photographic properties of the samples were as set forth in Table 1.
Table 1 ______________________________________ Exposure condi- Tungsten lamp, Xenon flash lamp, tions 10 seconds 10 -5 seconds Relative Relative Sample sensitivity Gamma sensitivity Gamma ______________________________________ A 100 3.5 40 2.0 B 200 3.3 150 2.5 C 250 3.7 230 3.3 D 190 3.3 160 2.8 E 230 3.7 228 3.7 ______________________________________
EXAMPLE 2
A silver iodochlorobromide emulsion containing 30 mole% of silver bromide and a slight amount of silver iodide was washed with water and then subjected to second ripening. In this case, one half of the emulsion was subjected to only sulfur sensitization (emulsion F), and the remainder was incorporated with 50 mg. per mole of silver halide of gold chloride in terms of gold. The thus treated emulsions were individually adjusted to a pH of 5.5 and ripened for 60 minutes. After the ripening, the latter emulsion was equally divided into 4 emulsions, and the first emulsion was left as it was (emulsion G), the second emulsion was incorporated with 0.5 g. per mole of silver halide of polyethylene glycol having a molecular weight of 2,000 (emulsion H), the third emulsion was incorporated with 1 g. per mole of silver halide of strontium chloride (emulsion I), and the fourth emulsion was incorporated with 0.5 g. per mole of silver halide of polyethylene glycol and 1 g. per mole of silver halide of strontium chloride (emulsion J). These emulsions were treated in the same manner as in Example 1 to prepare samples, which were then tested in photographic properties to obtain the results as set forth in Table 2.
Table 2 ______________________________________ Exposure condi- Tungsten lamp, Xenon flash lamp, tions 10 seconds 10 -5 seconds Relative Relative Sample sensitivity Gamma sensitivity Gamma ______________________________________ F 50 4.2 20 2.9 G 80 4.0 60 3.5 H 90 4.5 85 4.2 I 75 4.0 65 3.6 J 85 4.5 84 4.5 ______________________________________
As is clear from the above-mentioned Examples, practically sufficient effects can be obtained when a gold salt is used in combination with a polyalkylene oxide, and more satisfactory results can be obtained when the aforesaid soluble metal salt other than gold salt is used in further combination therewith.
The present process for preparing improved silver halide photographic emulsions does not disturb the effects of other sensitization processes, e.g. reduction sensitization and spectral sensitization (including supersensitization), and hence may be adopted in combination with said processes. Further, the same effects as mentioned above can be obtained even when the present process is applied to emulsions containing color couplers.
When a silver halide photographic emulsion is exposed to a high intensity light for a short period of time, e.g. for 10 -5 to 10 -6 seconds, the emulsion becomes soft in tone or is desensitized, in general, as compared with the case where it is subjected to ordinary medium exposure. This phenomenon is called high intensity reciprocity law failure. In order to prevent photograhic emulsions from such failure, various processes have heretofore been studied, and several of them have been patented. For example, Japanese Pat. publication No. 4,935/68 discloses a process for preventing a photograhic emulsion from high intensity reciprocity law failure by incorporation of iridium salt into the photographic emulsion, and Japanese Pat. publication No. 32,738/70 discloses a process in which the process of said Japanese Pat. publication No. 4,935/68 has been improved by use of gold salt in combination with iridium salt.
The present invention is a process which is of greater excellent in effect than the said prior art processes, and hence may be said to be an entirely novel invention. That is, the present invention is a process for preventing a silver halide photographic emulsion from said high intensity reciprocity law failure by incorporating into the photographic emulsion a gold salt in combination with a polyalkylene oxide or a derivative thereof and, preferably, with at least one member selected from the group consisting of soluble salts of metals such as cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium and lead. According to the process of the present invention, the reciprocity law failure, the complete prevention of which has heretofore been difficult, can be prevented substantially ideally from the practical standpoint.
The incorporation of a gold salt into a silver halide photograhic emulsion which is a sensitization procedure known as gold sensitization, in general, is known to provide prominent effect of preventing the emulsion from reciprocity failure, particularly from high intensity reciprocity failure. The effect attained by incorporation of gold salt is far more excellent than that attained by incorporation of iridium salt. Further, polyalkylene oxides (synonymous with polyalkylene glycols) and derivatives thereof may be shown as well-known sensitizers. The present inventors have found that the said compounds also have the effect of preventing the reciprocity law failure, particularly the failure caused at the time of high intensity and short period exposure. For example, a photographic material containing in the silver halide photographic emulsion layer a polyethylene oxide, which has ordinarily been used as a sensitizer, is higher in sensitivity than a photograhic material containing no polyethylene oxide. This effect is marked when the photographic material is exposed to a higher intensity light for a shorter period of time, and the sensitization at the shoulder portion of characteristic curve of the photographic material is particularly marked, with the result that the high illuminance reciprocity law failure can be prevented. The above-mentioned effect is identical in tendency with that of a gold salt. The present inventors have confirmed that the prevention of high intensity reciprocity law failure can be accomplished to an extremely desirable extent by use of a gold salt in combination with a polyalkylene oxide. The inventors have further found that an ideal effect, which is substantially satisfactory from the practical standpoint, can be obtained when said gold salt and polyalkylene oxide are used in further combination with a soluble salt of cadmium, zinc, cobalt, nickel, thallium, uranium, thorium, iridium, strontium, lead or the like metal other than gold.
While part of the effects of the above-mentioned gold salts have already been known, the effect attained by independent use of said gold salt is considerably lower than the effect attained by use of the gold salt in combination with a polyalkylene oxide, and no desirable results can be obtained unless the two are used in combination.
Typical examples of the gold salts referred to herein are as follows:
(1) Chloroauric acid HAuCl 4 (2) Potassium chloroaurate KAuCl 4 (3) Auric trichloride AuCl 3 (4) Potassium auric thiocyanate KAu(CNS) 4 (5) Potassium iodoaurate KAuI 4 (6) Tetracyanoauric acid HAu(CN) 4 (7) Ammonium aurothiocyanate NH 4 Au(CNS) 2 (8) Diethyl-monobromogold Au(C 2 H 5 ) 2 Br (9) Pyridino-trichlorogold (C 5 H 5 N)AuCl 3 .HCl
Further, there may be used gold compounds and complexes containing both sulfur atoms and gold atoms, such as 2-aurosulfobenzothiazole methachloride, gold sulfide, and alkali metal-ammonium aurous thiosulfate complexes. In addition thereto, all the metal compounds, which have ordinarily been used as gold sensitization substances, can effectively be used.
On the other hand, the polyalkylene oxides referred to herein are generally used polyethylene oxides having molecular weights in the range from 400 to 10,000. The scope of the present invention, however, is not limited thereto, and the same effects as above can be obtained even when other polyalkylene oxides and derivatives thereof are used. That is, condensation products (molecular weight 600 to 10,000) of alkylene oxides with at least one member selected from the group consisting of water, aliphatic alcohols, glycols, fatty acids, aliphatic amines, phenols, and dehydrated cyclic compounds of hexitol derivatives also display the same effects as above, and it is needless to say that all the said compounds are involved in the scope of the present invention.
The aforesaid soluble metal salts other than the gold salts are desirably used, in practice, in the form of halides, nitrates or sulfates, though this is, of course, not limitative.
The proportions of the individual materials used in the present invention vary depending on the kinds thereof, but are preferably such that the gold salt is used in a proportion of 0.1 to 200 mg., preferably 5 to 50 mg., in terms of gold atom, per mole of silver halide, the polyalkylene oxide in a proportion of 0.1 to 50 g. per mole of silver halide, and the soluble metal salt other than the gold salt in a proportion of 10 mg. to 50 g per mole of silver halide.
When the amount of the gold salt is less than said range, effect thereof is not conspicuous and when more than said range, adverse effects such as fogging, etc. are caused. When the amount of the polyalkylene oxide is less than said range, effect thereof is not conspicuous and when more than said range, adverse effects such as fogging, decrease in physical properties of gelatine, etc. are caused. When the amount of the soluble salt is less than said range, effect thereof is not conspicuous and when more than said range, adverse effects such as fogging, desensitization, decrease in physical properties of gelatine, etc. are caused. These materials may be incorporated into a photographic emulsion at such stages that the gold salt and the metal salt other than gold salt may be incorporated at any stage of emulsification, first ripening, second ripening or after completion of ripening, and the polyalkylene oxide may be incorporated at any stage of second ripening or after completion of ripening.
The present invention is illustrated in detail below with reference to examples.
EXAMPLE 1
A silver iodobromide emulsion containing 2% of silver iodide, which had been prepared according to a process known to those skilled in the art, was washed with water and then subjected to second ripening. In this case, one half of the emulsion was subjected to only sulfur sensitization (emulsion A), and the remainder was incorporated with 20 mg. per mole of silver halide of gold thiocyanate in terms of gold. The thus treated emulsions were individually adjusted to a pH of 6.0 and ripened at 50°C. for 90 minutes. Further, the latter emulsion was equally divided into 4 emulsions, and the first emulsion was left as it was (emulsion B), the second emulsion was incorporated with 1 g. per mole of silver halide of polyethylene oxide having a molecular weight of 6,000 (emulsion C), the third emulsion was incorporated with 3 g. per mole of silver halide of cobalt chloride (emulsion D), and the fourth emulsion was incorporated with 1 g. per mole of silver halide of polyethylene oxide in combination with 3 g. per mole of silver halide of cobalt chloride (emulsion E).
These emulsions were individually incorporated with a stabilizer, a hardener and an activator (saponin), coated on a base so that the amount of silver became 50 mg. per 100 cm 2 , and then dried to prepare samples A, B, C, D and E. Each of the samples was exposed for 10 seconds to a tungsten lamp and for 10 -5 seconds to a xenon flash lamp through a step type optical wedge having a density difference of 0.15, and then developed with a well-known Metol-hydroquinone developer of the following composition:
Water 700 ml. Metol 2 g. Hydroquinone 9 g. Anhydrous sodium sulfite 75 g. Sodium carbonate (monohydrate) 30 g. Potassium bromide 5 g. (Water to make 1,000 ml.)
As the result, photographic properties of the samples were as set forth in Table 1.
Table 1 ______________________________________ Exposure condi- Tungsten lamp, Xenon flash lamp, tions 10 seconds 10 -5 seconds Relative Relative Sample sensitivity Gamma sensitivity Gamma ______________________________________ A 100 3.5 40 2.0 B 200 3.3 150 2.5 C 250 3.7 230 3.3 D 190 3.3 160 2.8 E 230 3.7 228 3.7 ______________________________________
EXAMPLE 2
A silver iodochlorobromide emulsion containing 30 mole% of silver bromide and a slight amount of silver iodide was washed with water and then subjected to second ripening. In this case, one half of the emulsion was subjected to only sulfur sensitization (emulsion F), and the remainder was incorporated with 50 mg. per mole of silver halide of gold chloride in terms of gold. The thus treated emulsions were individually adjusted to a pH of 5.5 and ripened for 60 minutes. After the ripening, the latter emulsion was equally divided into 4 emulsions, and the first emulsion was left as it was (emulsion G), the second emulsion was incorporated with 0.5 g. per mole of silver halide of polyethylene glycol having a molecular weight of 2,000 (emulsion H), the third emulsion was incorporated with 1 g. per mole of silver halide of strontium chloride (emulsion I), and the fourth emulsion was incorporated with 0.5 g. per mole of silver halide of polyethylene glycol and 1 g. per mole of silver halide of strontium chloride (emulsion J). These emulsions were treated in the same manner as in Example 1 to prepare samples, which were then tested in photographic properties to obtain the results as set forth in Table 2.
Table 2 ______________________________________ Exposure condi- Tungsten lamp, Xenon flash lamp, tions 10 seconds 10 -5 seconds Relative Relative Sample sensitivity Gamma sensitivity Gamma ______________________________________ F 50 4.2 20 2.9 G 80 4.0 60 3.5 H 90 4.5 85 4.2 I 75 4.0 65 3.6 J 85 4.5 84 4.5 ______________________________________
As is clear from the above-mentioned Examples, practically sufficient effects can be obtained when a gold salt is used in combination with a polyalkylene oxide, and more satisfactory results can be obtained when the aforesaid soluble metal salt other than gold salt is used in further combination therewith.
The present process for preparing improved silver halide photographic emulsions does not disturb the effects of other sensitization processes, e.g. reduction sensitization and spectral sensitization (including supersensitization), and hence may be adopted in combination with said processes. Further, the same effects as mentioned above can be obtained even when the present process is applied to emulsions containing color couplers.