GB2093603A - Light-sensitive cuprous halide emulsions and method for their preparation - Google Patents

Abstract

Disclosed in a light-sensitive cuprous emulsion which comprises crystals of a cuprous halide containing from 1 to 100 molar % of a silver halide relative to the cuprous halide. Also disclosed is a method for the preparation thereof which comprises forming said crystals of the cuprous halide with use of (a) halogen ions, (b) silver ions or colloidal silver halide grains and (c) cuprous ions formed by reducing cupric ions, in an aqueous solution containing a hydrophilic polymer as a protective colloid.

Description

SPECIFICATION Light-sensitive cuprous halide emulsions and method for their preparation The present invention relates to a novel photographic emulsion, and more particularly to a novel photographic emulsion using a cuprous halide and a method for its preparation.

Heretofore, as a photographic system requiring high sensitivity, there have been widely used common silver halide photographic systems. The silver halide photographic systems have a number of desirable characteristics such as the high sensitivity, high quality, and continuous tone as well as capabilities such as speedy treatment or dry treatment. However, in general, they require a considerable amount of silver since they use silver compounds as the light-sensitive substance and as the image forming substance (or as the intermediate medium for the formation of a colour image in the case of a silver halide colour photographic system). On the other hand, in most cases i.e. except for some, the above photographic systems do not include means for recovery or reuse of the silver.This makes the silver halide photographic systems generally expensive ones and represents a drawback of the photographic systems using silver, since the shortage of silver resources is now worried and the price of silver has rapidly been increased in recent years.

Accordingly, it is desired to develop a photographic system wherein the use of silver is minimal or a photographic system wherein no silver is used.

There have been reported a number of non-silver salt photographic systems, but they are generally inferior in the sensitivity as compared with the photographic system wherein silver is used. Further, most of the non-silver salt light-sensitive materials are not capable of forming an image having a continuous tone.

Among these non-silver salt light-sensitive materials, there have been disclosed light sensitive materials using cuprous halides or photographic systems using cuprous complexes as non-silver salt light-sensitive materials which have a relatively high sensitivity and which are capable of forming a continuous tone, in Research Disclosure Nos. 15166,15251, and 15252 and U.S. Patents 3,859,092; 3,860,500; 3,860,501 and 3,880,724.

According to these publications, cuprous halides or complexes of monovalent copper ions are sensitive to ultraviolet rays, and when such compounds are coated on a sheet, exposed to a ultraviolet ray, and they developed with a physical developer or a chemical developer, a colour image having a continuous tone is obtainable.

As a method for preparing a coating solution in which light-sensitive cuprous halide crystals are dispersed in a binder, Research Disclosure No. 15166 discloses the following method: Firstly, as a method for preparing cuprous halide crystals, there is a method disclosed in "Inorganic Synthesis" Vol. 2, page 1 (1946) by R.N. Keller, and H.D. Wycoff, wherein cuprous halide crystals are prepared by reducing a cupric halide in an aqueous cupric halide solution with use of sodium sulfite in accordance with the following reaction: 2CuX2 + Na2SO3 + H20 , 2CuX + Na2SO4 + 2HX (1) According to this method, the cuprous halide crystals are prepared in the absence of a substance having a nature of protective colloid, and accordingly, the crystals thereby formed are coarse.Therefore, the coarse crystals are pulverized by a ball mill, and the cuprous halide crystal powders thereby obtained are dispersed in a solution which has been prepared by dissolving a polymer compound such as cellulose acetate butyrate or polyvinylbutyrate in an organic solvent such as acetone. The dispersion thereby obtained is then coated on a support to prepare a light-sensitive film.

However, this method thus involving the pulverization of the coarse crystals into fine particles, has the following drawbacks: (1) it takes a long time for the pulverization treatment to obtain fine particles, (2) the grain size distribution of the crystals of the cuprous halide obtained by the pulverization is so wide that the tone of the image formed by development will be extremely soft and presents a low contrast, and (3) the image formed by developement has poor graininess, and the colour density is low.

On the other hand, a report by Antoni Gulecki and Jan Wojtezak is presented in "Prace Komisji Mat.

Przyrod" Vol.7 (No 4), pages 3 to 12 (1956), which discloses that "it is possible to prepare Cul crystals by reducing Cu2+ in an aqueous gelatin solution containing copper sulfate and at the same time to disperse the crystals in the gelatin solution." However, this method has drawbacks such that (1) cuprous halide crystals are likely to readily grow and tend to form coarse crystals, and (2) since the cuprous halide crystals are coarse and the grain size distribution is wide, the image obtained by developing the light-sensitive material has low contrast, the graininess of the image is inferior and the colour density of the image is low.

Other than the above mentioned drawbacks, the light-sensitive materials obtained by both of the above methods, have a common drawback that "the sensitivity is extremely poor in a dried state to such an extent that they have virtually no sensitivity." However, it is possible to obtain a colour image by exposing such light-sensitive materials in their wet state e.g. by a polar solvent such as water, an alcohol or glycol or by a developer, and then developing them.

Richard S. Vinal at al. have discussed various methods for imparting sensitivity to such light-sensitive materials in their dried state. Namely, a first method comprises forming coarse crystals of a cuprous halide by the method employed by R.N. Keller and H.D. Wycoff, then pulverizing the crystals by a ball mill, mixing them with readily reducible silver acetate, silver nitrate, silver halide, palladium halide or cobalt halide, and coating the mixture together with a binder, on a support (see Research Disclosure 15962).Another method comprises pulverising the coarse crystals of a cuprous halide prepared by the above method, by a ball mill, then dispersing them in an acetone solution of cellulose acetate butyrate, and coating the dispersion on a thin metal film (the metal includes Cu, Bi, Ag, Fe, Cr, Zn, Sn and Co) which has been previously vapour-deposited on a support (see Research Disclosure No. 15252). A further method comprises dispersing a mixture of the cuprous halide crystals prepared by the above method with a borane hydride, in a binder solution, and coating the dispersion on a support (see Resereach Disclosure No. 15961). However, in each of these methods, the crystals of cuprous halide are coarse and the grain size distribution is wide, as mentioned above.Beside, in a dried state, the sensitivity is extremely low, and the developed image is inferior in the contrast and in the colour density.

Accordingly, a first object of the present invention is to provide a cuprous halide emulsion having sensitivity in its dry state.

A second object of the present invention is to provide a light-sensitive cuprous halide emulsion composed of fine crystals.

Athird object of the present invention is to provide a cuprous halide emulsion which is capable of forming an image having a superior graininess when a film prepared by coating the cuprous halide emulsion is developed.

Afourth object of the present invention is to provide a cuprous halide emulsion which is capable of forming an image having high contrast when a film prepared by coating the cuprous halide emulsion is developed.

Afifth object of the present invention is to provide a method for preparing such a cuprous halide emulsion.

As a result of extensive researches, it has been found that the above objects can be achieved by a light-sensitive cuprous halide emulsion which comprises crystals of a cuprous halide containing from 1 to 100 molar % of a silver halide relative to the cuprous halide, and a method for preparing a light-sensitive cuprous emulsion which comprises forming fine crystals of a cuprous halide containing from 1 to 100 molar % of a silver halide relative to the cuprous halide with use of (a) halogen ions, (b) silver ions of silver halide grains and (c) cuprous ions formed by reducing cupric ions, in the presence of a protective colloid.

The light-sensitive cuprous halide emulsion of the present invention (hereinafter referred to as "the photographic emulsion of the present invention") is an emulsion wherein fine crystals of a cuprous halide containing from 1 to 100 molar % of a silver halide relative to the cuprous halide (hereinafter referred to as "the crystals of the present invention") are dispersed in a protective colloid. The halogen constituent of said crystals is at least one halogen selected from the group consisting of chlorine, bromine and iodine.

The reducing agent to be used in the present invention may be used in an amount within a range of from 30 to 300 molar % relative to the concentration of Cu2+ ions to be reduced. However, it is preferred to use the reducing agent within a range of from 70 to 250 molar %. Namely, if the amount is less than 30 molar %, a part of the total Cu2 ions will remains without being reduced, and the supernatant after the reaction containing the remaining Cu2+ ions exhibits a blue colour. On the other hand, if the amount is greater than 300 molar %, the Cu2+ ions will be reduced firstly to Cu+ ions and then to metal copper. Namely, the optimal range of the amount of the reducing agent required to reduce the total Cu2+ ions to Cu+ ions is from 70 to 250 molar %.

The reduction reaction can be conducted at a pH within a range of from 0 to 7. However, when a sulfite or a nitrite is used as a reducing agent, the reduction reaction readily proceeds at a pH of not more than 4, and if the pH is higher than this, the reduction reaction hardly proceeds. Further, if the pH exceeds 6, it is likely that cuprous hydroxide is formed besides the cuprous halide. Thus, it is preferred to carry out the reduction reaction within a pH range of from 0 to 4.

With respect to the crystals of the invention, if the silver halide content is less than 1 molar % relative to the cuprous halide, a light-sensitive material having such a photographic emulsion layer gives an extremely weak sensitivity in its dry state. On the other hand, if the photographic emulsion contains more than 100 molar % of a silver halide relative to the cuprous halide, the Ag+ ions used in the preparation of the emulsion tend to be readily reduced by the reducing agent. Namely, the reduced metal silver will be incorporated in the crystals of the cuprous halide, and the light-sensitive material prepared by coating such a photographic emulsion tends to form fogging.

As a preferred embodiment for carrying out the method for preparing the photographic emulsion of the present invention, there may be mentioned a method wherein the divalent copper ions are reduced by a reducing agent in the presence of (a) a protective colloid, (b) halogen ions and (c) silver ions and/or colloidal silver halide grains.

In this embodiment, as the protective colloid which provides an environment in which the fine crystals of a cuprous halide are formed by the reduction of the divalent copper ions or such crystals are grown, a hydrophilic polymer compound is preferred, and its concentration is preferably within a range of from 0.1 to 5% by weight and the pH of said environment is preferably within a range of from 0 to 6. The amount of the halogen ions is generally at least stoichiometrically equivalent amount, preferably at an amount ranging from 100 to 400 molar %, and more preferably, within a range of from 120 to 350 molar % relative to the total amount of cuprous ions to be formed, and silver ions when existed.Further, the amounts of the divalent copper ions and the silver ions and/or silver halide grains are determined depending upon the ratio of the silver halide to the cuprous halide to be contained in the crystals of the present invention. The grain size of the silver halide grains is preferably not more than 11,u.

In the method for preparing the photographic emulsion of the present invention including the above-mentioned embodiment, the reducing power of the reducing agent can effectively be controlled by adjusting the concentration of the halogen ions.

Now, preferred embodiments for carrying out the method for the preparation of the photographic emulsion of the present invention will be described in further detail.

(I) In an aqueous acidic solution of a hydrophilic polymer compound having silver halide colloidal grains dispersed therein, Cu2+ ions are reduced in the presence of halogen ions with the silver halide colloidal grains as seed nuclei. The dispersion comprising the silver halide colloidal grains dispersed in the aqueous solution of the hydrophilic polymer compound, can be prepared in accordance with a known method.

This embodimentwil be described more specifically as follows: For instance, while stirring 1000 me of an aqueous solution (A) prepared by dissolving 1.0 mole/# of a cupric halide in an aqueous solution containing from 0.50 to 2.0% by weight of gelatin, at a temperature of the solution being from 25 to 50"C, 100 mt of an aqueous solution (B) prepared by dissolving from 1.0 to 20 molar % of silver nitrate relative to the cupric halide, is instantaneously added, whereby a colloidal dispersion of the silver halide is obtainable.

Three seconds after the initiation of the mixing of the solutions (A) and (B), an aqueous solution (C) having from 100 to 250 molar % (relative to the cupric bromide) of L-ascorbic acid dissolved therein is instantaneously added to and mixed with said colloidal dispersion, whereupon the Cu2+ ions are reduced to Cu+ ions and crystals of the cupric halide start to grow with the preliminarily formed silver halide colloidal grains as the seed nuclei. The solution is stirred for 2 to 10 minutes, whereupon the photographic emulsion of the present invention having an average grain size of from 0.1 to 2 p is obtainable.

(11) While forming colloidal grains of a silver halide in an aqueous hydrophilic polymer solution, Cu2+ ions are reduced in the presence of halogen ions and said colloidal grains as the seed nuclei.

This embodiment will be described more specifically as follows: For instance, while vigorously stirring 1000 me of an aqueous solution prepared by dissolving 1 mole/# of a cupric halide in an aqueous solution containing from 0.50 to 2.0% by weight of gelatin and acidified with sulfuric acid (pH: 0 to 4), at a temperature of the solution being from 25 to 650C, an aqueous solution (B) having sodium sulfite (1.0 to 2.5 mole/f) and silver nitrate (0.01 to 0.5 mole/f) dissolved therein, is instantaneously added and mixed, whereby colloidal crystals of the silver halide form and at the same time the Cu2+ ions are reduced to Cu+ ions, and crystals of the cuprous halide start to grow with the silver halide colloidal grains as the seed nuclei.

The solution is stirred for 2 to 10 minutes, whereupon the photographic emulsion of the present invention having an average grain size of from 0.1 to 2 y is obtainable.

(III) Cuprous halide crystals are formed in an aqueous hydrophilic polymer solution, and then from 1 to 100 molar % of a silver halide relative to the cuprous halide is precipitated thereon with said crystals as the seed nuclei. The crystals of the cuprous halide may be prepared by reducing a water-soluble inorganic cupric salt in an aqueous solution by a reducing agent (preferably L-ascorbic acid) in the presence of a hydrophilic polymer compound.

This embodiment will be described more specifically as follows: For instance, while vigorously stirring 1000 mt of an aqueous solution (A) prepared by dissolving 1 mole/# of a cupric halide in an aqueous solution containing from 0.50 to 2.0% by weight of gelatin, at a temperature of the solution being from 25 to 65 C, an aqueous solution (B) of L-ascorbic acid (1.0 to 2.0 molest) is instantaneously added and mixed, whereupon crystals of the cuprous halide are formed. After mixing the solutions (A) and (B), physical ageing is carried out from 2 to 5 minutes, and then an aqueous solution containing from 0.1 to 1 mole/# of silver nitrate is slowly added, whereupon the silver halide precipitates on the cuprous halide grains as the nuclei.

After completion of the addition of the aqueous silver nitrate solution, the stirring is continued for 2 to 10 minutes for the physical ageing, whereupon the photographic emulsion of the present invention having an average grain size of from 0.6 to 3 ii is obtainable.

(IV) The photographic emulsion of the present invention can be obtained by simultaneously mixing an aqueous acidic solution containing halogen ions and a reducing agent and an aqueous solution containing Cu2+ ions and Ag+ ions in an aqueous solution of a hydrophilic polymer compound.

This embodiment will be described more specifically as follows: For instance, while stirring an aqueous solution containing from 0.50 to 2.0% by weight of gelatin, 1000 mb of an aqueous solution (B) having 1 mole/# of cupric nitrate and from 0.01 to 1.0 mole'# of silver nitrate dissolved therein and 900 me of an aqueous solution (C) containing from 1.0 to 3.0 moles'# of a halide and from 1.0 to 2.5 moles/# of L-ascorbic acid, are poured into said solution (A) by means of a double jet method, and the simultaneous mixing and physical ageing are carried out, whereupon the photographic emulsion of the present invention having an average grain size of from 0.1 to 3 p is obtainable.

As the source for supplying the Cu2+ ions used for the preparation of the photographic emulsion of the present invention, there may be mentioned water soluble inorganic cupric salts, such as cupric nitrate, copper sulfate, cupric chloride, bromide. It may by optionally selected for use from these copper salts.

As the source of supplying the halogen ions, it may be optionally selected for use from alkali metal halides such as potassium chloride, sodium chloride, potassium iodide, sodium iodide, potassium bromide and sodium bromide. In a case where cupric halide is used as the source for providing Cu2+ ions, it is unnecessary to add an alkali metal halide as the source for supplying the halogen ions. However, in a case where mixed crystals containing two or more halides, such as cuprous chlorobromide or cuprous iodobromide, are to be prepared, suitable alkali metal halides are added depending upon the desired mixed crystals.

As the source for supplying the silver ions, silver nitrate is preferably used.

Further, the silver halide colloidal grains are fine grains having a diameter of not more than 0.1 u and composed substantially of a silver halide such as silver chloride, silver bromide, silver iodide, silver chlorobromide, silver iodobromide or silver chloroiodobromide.

As the reducing agent used for reducing Cu2+ ions in the preparation of the photographic emulsion of the present invention, there may be advantageously used, e.g., sulfurous acid, an alkali metal salt of sulfurous acid, nitrous acid, an alkali metal salt of nitrous acid, L-ascorbic acid, an ascorbic acid derivative (such as araboascorbic acid, -erythro-ascorbic acid ora-glycoascorbic acid), an alkali metal salt of an ascorbic acid derivative, hydrazine, phenyl hydrazine, triphenyl phosphite, aminoborane, a dialkylaminoborane (such as dimethylaminoborane).

In the present invention, as the protective colloid, there may be used any suitable hydrophilic polymer compound commonly used in silver halide emulsions, which includes a natural polymer compound such as gelatin, gum arabic, albumin, or agar, and a synthetic polymer compound such as a gelatin derivative, polyvinyl alcohol, polyvinylpyrrolidone, cellulose ether, or partially hydrolyzed cellulose acetate.

The combination of the components used for the preparation of the photographic emulsion of the present invention, such as a cupric salt, a silver salt, a halide, a reducing agent to provide the reducing environment, a pH controlling agent such as an acid and a hydrophilic polymer compound as the protective colloid, and the order of mixing the solutions, may be selected in an optional manner so long as the conditions for the method of the present invention are satisfied. However, in the preparation of the photographic emulsion of the present invention, it is desirable that silver ions, the silver halide, the cuprous ions and the cuprous halide are not subjected excessively to the reducing environment.

The photographic emulsion of the present invention is coated on a support to provide a light-sensitive material. As the support, there may be used a porous support such as paper which is suitable for absorption of the photographic emulsion, or a support on which the emulsion can be coated to form an emulsion layer.

As a support of latter type, there may be mentioned glass or a sheet of metal such as aluminum, copper, zinc or tin. Otherwise, the photographic emulsion may be coated on a film support of conventional type such as cellulose acetate, cellulose nitrate, cellulose acetate butyrate, polyethylene terephthalate, polystyrene, baryta paper or resin-modified paper.

The light-sensitive material using the photographic emulsion of the present invention as the light-sensitive element coated or absorbed and dried on the above support, has a light-sensitivity in its dry state, as opposed to a pure cuprous halide emulsion, and it can be developed by application of the development treatment method disclosed in Research Disclosure Nos. 15166(1976) and 15251 (1976) after the exposure in an image forming fashion with a light source having a wave length within a range of from 260 to 450 my. For instance, by conducting the development of the photographic emulsion in an aqueoustriethylenetetramine solution for from 30 to 180 seconds, a stable image having superior graininess, high contrast and a neutral colourtone can be obtained.

On the other hand, a cuprous bromide emulsion prepared by reducing cupric bromide in an aqueous gelatin solution by ascorbic acid to obtain a dispersion of cuprous bromide crystals which are then subjected to demineralization and washing and thereafter redispersed in an aqueous gelatin solution, and a silver bromide emulsion prepared by a conventional method for the preparation of a silver halide emulsion, i.e. by adding an aqueous potassium bromide solution and an aqueous silver nitrate solution to an aqueous gelatin solution by means of a double jet method thereby carrying out simultaneous mixing and physical ageing to form a dispersion of silver bromide crystals which are then subjected to demineralization and washing and thereafter redispersed in an aqueous gelatin solution, were mixed so that the silver bromide constitutes from 1.0 to 100 molar % relative to the cuprous bromide.The mixed emulsion was coated on a support and dried, and thereafter subjected to exposure and development treatment in an aqueous triethylenetetramine solution in the same manner as the above method. The sensitivity thereby obtained was lower than that obtained by the photographic emulsion of the present invention, and the developed image had poor graininess and the contrast of the image was low.

From the comparison of the photographic emulsion of the present invention or the method for its preparation with the conventional methods such as a method in which the divalent copper ions are reduced by sodium sulfite in an aqueous cupric halide solution containing no protective colloid and the coarse crystals of the cuprous halide thereby formed are pulverized by a ball mill and then dispersed in a solution prepared by dissolving a polymer compound in an organic solvent; a method in which a cupric halide is reduced by sodium sulfite in an aqueous gelatin solution, whereby a cuprous halide emulsion is prepared; or a method in which preliminarily prepared cuprous emulsion and silver halide emulsion are mixed together, it has been found that, according to the present invention; (1) it is possible to prepare a photographic emulsion composed of fine cuprous halide crystals containing a silver halide and having a grain size of from 0.1 to 3.0 ; (2) the photographic emulsion of the present invention is a cuprous halide photographic emulsion having superior photographic properties such that the light-sensitive material obtained by coating the photographic emulsion of the present invention has sensitivity in a dry state, and the image obtained by development has superior graininess, high contrast and a neutral colour tone; and (3) after the development, it is possible to stabilize the image without reducing the image density, by fixing treatment with an aqueous solution of a solubilizerfor a cuprous halide, such as a thiosulfate or a thiocyanate.

Now, the present invention will be described in further detail with reference to Examples. It should be understood, however, that the present invention is not restricted to these Examples.

Example 1 An emulsion comprising cuprous bromide crystals containing silver bromide was prepared with use of two kinds of the solutions shown in Table 1 in such a manner that the two solutions were mixed so that, while colloidal grains of silver bromide were formed, crystals of cuprous bromide were prepared with the colloidal grains as the nuclei.

TABLE 1 Solution 1: Ossein gelatin 40 g Distilled water 1.0 t Cupric bromide 200 g Conc. sulfuric acid 50 mt (1 part)/purewater (1 part) Solution 2: Na2SO3 190 g AgNO3 15g Distilled water 1.0# While stirring the Solution 1 adjusted at a pH of 1.0, the Solution 2 was instantaneously added and mixed.

The stirring was continued for 10 minutes while maintaining the reaction temperatures at 350C. Thereafter, washing and demineralization treatments were carried out in the following manner: As precipitation reagents, an aqueous solution containing 5% of Demol-N manufactured by Kao Atlas Co.

and an aqueous solution containing 30% of magnesium sulfate were added in a ratio of 1 : 7 until the precipitates formed. After settling the precipitates of the fine cuprous bromide crystals containing silver bromide, the supernatant was decanted, and 3000 mt of distilled water was added to redisperse the precipitates. A 30% magnesium sulfate aqueous solution as added until the precipitates again formed. After settling the crystal grains, the supernatant was decanted, an aqueous ossein gelatin solution (containing 45g of gelatin) was added, and the stirring was continued at 40 C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1000 me.

This emulsion will hereinafter be referred to as EM-1. From the electron microscopic photography, this EM-1 was found to have an average grain size of 0.2 t 0.05 #. Further, this EM-1 was examined by an elemental analysis for the composition of the emulsion, and it was found that it contained 91.0 molar % of Cu+1 and 9.0 molar % of Ag+.

Example 2 An emulsion comprising cuprous bromide crystals containing silver bromide was prepared with use of two kinds of the solutions shown in Table 2 in such a manner that the two solutions were mixed so that, while colloidal grains of silver bromide were formed, crystals of cuprous bromide were prepared with the colloidal grains as the nuclei.

TABLE 2 Solution 3: Ossein gelatin 30 g Cupric bromide 200 g Conc. sulfuric acid 70 me (1 part)/purewater (1 part) Distilled water 2.0 e Solution 4 Na2SO3 190 g Ag NO3 74.8 g Distilled water 2.0 C While stirring the Solution 3 adjusted at a pH of 1.0, the Solution 4 was instantaneously added and mixed.

The stirring was continued for 15 minutes while maintaining the reaction temperature at 45 C. Thereafter, washing and demineralization treatments were conducted in a manner similar to Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 50 g of gelatin) was added, and the stirring was continued at 40 C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1250 mC.

This emulsion will hereinafter be referred to as EM-2. From its electron microscopic photography, this EM-2 was found to have an average grain size of 1.0 + 0.1 p Further, this EM-2 was examined by an elemental analysis for the composition of the emulsion, and found to contain 69 molar % of Cu+ and 31 molar% ofAg+.

Example 3 An emulsion comprising fine crystals of copper chlorobromide containing silver chlorobromide with use of three types of the solutions shown in Table 3 in such a manner that firstly fine crystals of silver chlorobromide were formed and then cuprous bromide was precipitated thereon with the crystals as the nuclei.

TABLE 3 Solution 5: Ossein gelatin 30 g Cupric bromide 157.2 g Cupric chloride 23.7 g Distilled water 1.5 e Solution 6: AgNO3 7.5 g Distilled water 50 mC Solution 7: L-Ascorbic acid 1159 Distilled water 1.0 C While stirring the Solution 5 at a temperature of 40"C, the Solution 6 was instantaneously added and mixed, and 5 seconds after the initiation of the mixing of the two solutions, the Solution 7 was instantaneously added and mixed. The stirring was continued for 10 minutes while maintaining the reaction temperature at 400C, for physical ageing. Thereafter, washing and demineralization treatments were conducted in the manner similar to Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 30 g of gelatin) was added and the stirring was continued at 40 C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1000 mC.

This emulsion will hereinafter be referred to as EM-3. From the electron microscopic photography, this EM-3 was found to have an average grain size of 0.3 + 0.05 u Further, this EM-3 was examined by an elemental analysis for the composition of the emulsion, and found to contain 96.3 molar % of Cut, 3.7 molar % of Age, 15.2 molar % of Ce- and 84.8 molar % or Br-.

Example 4 An emulsion comprising fine crystals of cuprous iodobromide containing silver iodobromide was prepared with use of three kinds of the solutions shown in Table 4 in such a manner that firstly fine crystals of silver iodobromide were prepared and cuprous iodobromide was precipitated thereon with the crystals as the nuclei.

TABLE 4 Solution 8: Ossein gelatin 40 g Cupric bromide 157.2 g Potassium iodide 29.2 g Distilled water 1.0 C Solution 9: AgNO3 29.9 g Distilled water 100 mC Solution 10: L-ascorbic acid 173g Distilled water 1.0 e While stirring the Solution 8 at a temperature of 45 C, the Solution 9 was instantaneously added and mixed, and 30 seconds after the initiation of the mixing of the two solutions, the Solution 10 was instantaneously added and mixed. The stirring was continued for 20 minutes while maintaining the reaction temperature at 45 C for physical ageing. Thereafter, washing and demineralization treatments were conducted in a manner similarto Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 50 g of gelatin) was added, and the stirring was continued at 400C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1000 me.

This emulsion will hereinafter be referred to as EM-4. From the electron microscopic photography, this EM-4 was found to have an average grain size of 0.5 + 0.05 y. Further, this EM-4 was examined by an elemental analysis for the composition of the emulsion, and found to contain 80.3 molar % of Cu+, 19.7 molar % of Ag+, 82.4 molar % of Br- and 17.6 molar % of 1-.

Example 5 An emulsion comprising fine crystals of copper chlorobromide was prepared with use of three kinds of the solutions shown in Table 5 in such a manner that firstly fine crystals of copper chlorobromide were prepared and silver chlorobromide was precipitated thereon with the crystals as the nuclei.

TABLE 5 Solution 11: Ossein gelatin 50 g Copper nitrate 169.0 g (Cu(NO3)2 3H20) KBr 31.3 g KCC 116.29 Distilled water 1.5 C Solution 12: L-Ascorbicacid 1159 Distilled water 700 mC Solution 13: AgNO3 11.9g Distilled water 100 mt While vigorously stirring the Solution 11 at a temperature of 45"C, the Solution 12 was instantaneously added and mixed, and after 3 minutes of physical ageing, the Solution 13 was instantaneously added and the physical ageing was carried out for further 5 minutes. Thereafter, washing and demineralization treatments were conducted in a manner simiiarto Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 45 g of gelatin) was added and the stirring was continued at 400C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1300 mC.

This emulsion will hereinafter be referred to as EM-5. From the electron microscopic photography, this EM-5 was found to have an average grain size of 0.7 i 0.05 # Further, this EM-5 was examined by an elemental analysis for the composition of the emulsion and was found to contain 91.2 molar % of Cut, 8.7 molar % of 83.2 molar % of Ct - and 16.7 molar % or Br-.

Example 6 An emulsion comprising fine crystals of copper iodobromide containing silver iodobromide was prepared with use of three kinds of the solutions shown in Table 6 in such a manner that firstly fine crystals of copper iodobromide were prepared and silver iodobromide was precipitated thereon with the crystals as the nuclei.

TABLE 6 Solution 14: Ossein gelatin 40 g KBr 151.3 9 KI 37.2g L-Ascorbic acid 159 g Distilled water 1.0 t Solution 15: CU(No3)23H2o 212.sag Distilled water 1.0 C Solution 16: AgNO3 10.5g Distilled water 100 me While stirring the Solution 14 at a temperature of 50"C, the Solution 15 was instantaneously added and mixed, and after 5 minutes of physical ageing, the Solution 16 was instantaneously added and the physical ageing was carried out for further5 minutes. Thereafter, washing and demineralization treatments were conducted in a manner similar to Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 50 g of gelatin) was added and the stirring was continued at 40 C) for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1100 mC.

This emulsion will hereinafter be referred to as EM-6. From the electron microscopic photography, this EM-6 was found to have an average grain size of 0.4+ 0.02 u Further, this EM-6 was examined by an elemental analysis for the composition of the emulsion, and found to contain 93 molar % of Cut, 7 molar % of 84 molar % of Br- and 16 molar % of I-.

Example 7 A photographic emulsion comprising fine crystals of copper bromide having silver bromide was prepared with use of three kinds of the solutions shown in Table 7.

TABLE 7 Solution 17: Ossein gelatin 16 g Distilled water 800 mC Solution 18: KBr 128.5g L-Ascorbic acid 78.7 g Distilled water 800 mt Solution 19: Cu(NO3)23H2O 144.6g AgNO3 10.2 g Distilled water 990 mC While stirring the Solution 17 at a temperature of 45 C, the Solutions 18 and 19 were simultaneously added by a double jet method. The Solution 18 was added at a rate of 40 me/min in 20 minutes. Whereas, the Solution 19 was added at a rate of 45 me/min in 22 minutes. The temperature was maintained at 450C during the physical ageing. Upon completion of the addition of the Solutions 18 and 19, washing and demineralization treatments were conducted in a manner similar to Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 45 g of gelatin) was added, and the stirring was continued at 400C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1300 me.

This emulsion will hereinafter be referred to as EM-7. From the electron microscopic photography, this EM-7 was found to have an average grain size of 0.8+ 0.07 y Further, this EM-7 was examined by an elemental analysis for the composition of the emulsion and found to contain 90.5 molar % of Cue, and 9.0 molar % of Age.

Example 8 A photographic emulsion comprising fine crystals of cuprous bromide containing silver bromide was prepared with use of three kinds of the solutions shown in Table 8.

TABLE 8 Solution 20: Ossein gelatin 20 g Distilled water 800mC Solution 21: KBr 285.6 g L-Ascorbic acid 88.6 g Distilled water 800 me Solution 22: CU(No3)23H2o 144.6g AgNO3 102 g Distilled water 900 mt While stirring the Solution 20 at a temperature of 45 C, the Solutions 21 and 22 were simultaneously added by a double jet method. The Solution 21 was added at a rate of 40 mC/min in 20 minutes. Whereas, the Solution 22 was added at a rate of 45 mC/min in 22 minutes. The temperature was maintained at 450C during the physical ageing. Upon completion of the addition of the Solutions 21 and 22, washing and demineralization treatments were carried out in a manner similar to Example 1.After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 50 g of gelatin) was added and the stirring was continued at 40 C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1200 mC.

This emulsion will hereinafter be referred to as EM-8. From the electron microscopic photography, this EM-8 was found to have an average grain size of 0.7 f 0.03 y Further, this EM-8 was examined by an elemental analysis for the composition of the emulsion and found to contain 49 molar % of Cue, and 51 molar % of Ag+.

Example 9 A photographic emulsion comprising fine crystals of cuprous iodobromide containing silver iodobromide was prepared with use of three kinds of the solutions shown in Table 9.

TABLE 9 Solution 23: Ossein gelatin 30 g Distilled water 500 me Solution 24: KBr 63,8 g KI 8.8 g L-Ascorbic acid 47.6 g Distilled water 550 mt Solution 25: Cu(NO3)23H2O 63.8 g AgNO3 4.5 g Distilled water 330 mC While stirring the Solution 23 at a temperature of 40 C, the Solutions 24 and 25 were simultaneously added by a double jet method. The solution 24 was added at a rate of 110 mf/min in 5 minutes. Whereas, the Solution 25 was added at a rate of 60 mC/min in 5 minutes and 30 seconds. The temperature was maintained at400C for the physical ageing. Upon completion of the addition of the Solutions 24 and 25, washing and demineralization treatments were conducted in a manner similar to Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 20 g of gelatin) was added, and the stirring was continued at a temperature of 400C for 30 minutes for redispersion.

Then, distilled water was added to have the total volume adjusted to 500 mC.

This emulsion will hereinafter be referred to as EM-9. From the electron microscopic photography, this EM-9 was found to have an average grain size of 0.8 i 0.03 u Further, this EM-9 was examined by an elemental analysis for the composition of the emulsion and found to contain 92 molar % of Cue, 8.0 molar % of Age, 91 molar % of Br- and 9.0 molar % of I-.

Example 10 A photographic emulsion comprising mixed crystals of CuBrl~AgBrl was prepared with use of three kinds of the solutions shown in Table 10.

TABLE 10 Solution 26: Ossein gelatin 30 g Distilled water 500 me Solution 27: KBr 63.8 g Kl 13.8g L-Ascorbic acid 47.69 Distilled water 550 me Solution 28: Cu(NO3)23H2O 63.8g Ag N O3 22.4g Distilled water 330 mC While stirring the Solution 26 at a temperature of 40 C, the Solutions 27 and 28 were simultaneously added by a double jet method. The Solution 27 was added at a rate of 110 m~/min in 5 minutes. Whereas, the Solution 28 was added at a rate of 60 m~/min in 5 minutes and 30 seconds. The temperature was maintained at400C during the physical ageing.Upon completion of the addition of the Solutions 27 and 28, washing and demineralization treatments were conducted in a manner similar to Example 12.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 20 g of gelatin) was added and the stirring was continued at 40 C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 500 me.

This emulsion will hereinafter be referred to as EM-10. From the electron microscopic photography, this EM-10 was found to have an average grain size of 0.9 l 0.10 . Further, this EM-10 was examined by an elemental analysis for the composition of the emulsion and found to contain 69 molar % of Cue, 31 molar % of Age, 86 molar % of Br-, and 14 molar % of I-.

Comparative Example 7 Cuprous bromide crystals were formed with use of two kinds of the solutions shown in Table 11.

TABLE 11 Solution 29: Ossein gelatin 50 g Cuprous bromide 100 g Conc. sulfuric acid 50 mC (1 part)/distilled water (1 part) Distilled water 2.0 C Solution 30: Anhydrous sodium 95 g sulfite Distilled water 1.0 C While stirring the Solution 29 at a temperature of 35 C, the Solution 30 was instantaneously added.

Physical ageing was carried out for 10 minutes while maintaining the reaction temperature at 35"C.

Thereafter, washing and demineralization treatments were conducted in the same manner as in Example 1.

After the washing and demineralization treatments, an aqueous ossein gelating solution (containing 50 g of gelatin) was added, and the stirring was continued at 400C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 1000 me.

This emulsion will hereinafter be referred to as EM-11.

Comparative Example 2 A silver halide emulsion was prepared with use of three kinds of the Solutions shown in Table 12.

TABLE 12 Solution 31: Ossein gelatin 30 g KBr 1.6g Distilled water 1.5 C pH 6.0 Solution 32: KBr 142.8 g Distilled water 1.0 t Solution 33: AgNO3 170g Distilled water 800 mC While stirring the Solution 31 at a temperature of 35 C, the Solutions 32 and 33 were simultaneously added by a double jet method. The Solution 32 was added at a rate of 50 me/min in 20 minutes. Whereas, the Solution 33 was added at a rate of 38 my'mien and the rate of addition of the Solution 33 was controlled so that the silver potential of the solution mixture was kept constant. It took 23 minutes for the addition of the Solution 33. The temperature was maintained at 350C during the physical ageing.Upon completion of the addition of the Solution 33, washing and demineralization treatments were conducted in a manner similar to Example 1.

After the washing and demineralization treatments, an aqueous ossein gelatin solution (containing 30 g of gelatin) was added, and the stirring was continued at 400C for 30 minutes for redispersion. Then, distilled water was added to have the total volume adjusted to 500 mC.

This emulsion will hereinafter be referred to as EM-12.

The EM-11 prepared in Comparative Example 1 and the EM-12 prepared in this Example were mixed in a ratio of CuBr : AgBr being 90 : 10 (molar ratio).

This emulsion will be referred to as EM-13.

Example 11 Each of thirteen different kinds of chemically non-sensitized emulsions EM-1 to EM-13 was prepared to have a ratio of gelatin/crystal grains being 8/1 and to have a gelatin content of 4%, and then coated on a film support to have a coated silver and copper amount of 2500 mg/m2. (Samples 1 to 13) Each of these Samples was exposed through an optical wedge at 1 x 103 ##erg/cm2 with use of a light source of a ultraviolet ray having a wave length within a range of from 260 to 420 um, and then subjected to development treatment for 5 minutes at 200C in a developer having the following composition. Thereafter, fixing and washing treatments were carried out.

Composition of the developer: Triethylenetetramine 0.25 mole Distilled water To make up 1.0 C (The developer was adjusted at a pH of 8.5 with dilute H2SO4.) Fixing solution: Hypo 240 9 Na2SO3 109 Sodium hydrogensulfite 25 9 Water To make up 1.0 e The results of the development and the sensitometry are shown in Table 13.

TABLE 13 Photographic properties of light-sensitive cuprous halide materials Sam- Relative Graininess of pies EM-No. sensitivities Dmjn Dmax the photographic No. images 1 EM-1 100 0.6 3.2 2 EM-2 150 0.7 2.8 3 EM-3 85 0.5 2.9 4 EM-4 400 0.7 3.5 5 EM-5 200 0.8 3.3 good 6 EM-6 240 0.5 3.4 7 EM-7 300 0.6 3.1 8 EM-8 1200 0.5 3.3 9 EM-9 2000 0.7 3.2 10 EM-10 7000 0.6 3.5 11 EM-11 (com- no para- sensitivity no development tive) 12 EM-13 (com- 10 0.9 1.3 extremely para- poor tive) Note: The relative sensitivity was measured at the point of Dmin + 0.10 and it was evaluated based on the sensitivity of the EM-1 which was set to be 100.

As is apparent from the results shown in Table 13, the Sample 11 coated with the cuprous bromide emulsion containing no silver halide, had no sensitivity in its dry state.

Further, in the case of the light-sensitive material (Sample 12) coated with an emulsion prepared by mixing the preliminarily prepared cuprous halide emulsion and silver halide emulsion, the relative sensitivity was low, the image obtained by developement had a low contrast with the Dmin being high and the Dmax being low, and the graininess of the image was inferior.

Whereas, it is seen that the Samples 1 to 10 coated with emulsions prepared by the present invention, all had high sensitivity in their dry state, and the photographic images thereby obtained by developement following the exposure, had superior contrast with the Dmin being low and the DmaX being high, and the graininess of the photographic images was very good.

Claims (7)

1. A light-sensitive cuprous halide emulsion which comprises crystals of a cuprous halide containing from 1 to 100 molar % of a silver halide relative to the cuprous halide.

2. The light-sensitive cuprous halide emulsion according to Claim 1, wherein said cuprous halide is selected from the group consisting of cuprous chloride, cuprous bromide, cuprous iodochloride cuprous bromochloride, cuprous iodobromide and cuprous iodobromochloride.

3. The light-sensitive cuprous halide emulsion according to Claim 1 or 2, wherein said silver halide is selected from the group consisting of silver chloride, silver bromide, silver iodochloride, silver iodobromide, silver bromochloride and silver iodobromochloride.

4. A method for preparing a light-sensitive cuprous halide emulsion which comprises forming fine crystals of a cuprous halide containing from 1 to 100 molar % of a silver halide relative to the cuprous halide with use of (a) halogen ions, (b) silver ions or colloidal silver halide grains and (c) cuprous ions formed by reducing cupric ions, in an aqueous solution containing a hydrophilic polymer as a protective colloid.

5. A light-sensitive cuprous halide emulsion according to Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 10.

6. A method according to Claim 4 and substantially as hereinbefore described with reference to any of Examples 1 to 10.

7. A light-sensitive photographic material which comprises a film support coated with a light-sensitive cuprous halide emulsion according to any of Claims 1 to 3 and 5.