US2768079A

US2768079A - Method of preparing washed photographic emulsions

Info

Publication number: US2768079A
Application number: US406061A
Authority: US
Inventors: Frederick J Russell
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1954-01-25
Filing date: 1954-01-25
Publication date: 1956-10-23
Anticipated expiration: 1973-10-23
Also published as: GB764446A; FR1121979A; BE535054A

Description

United States Patent METHOD OF PREPARING WASHED PHOTO- GRAPHIC EMULSIONS Frederick J. Russell, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application January 25, 1954,

Serial'No. 406,061

7 Claims. (Cl. 95-7) No Drawing.

: following compounds The preparation of the dispersed silver halide in gelatin 9 by mixing a water solution of the silver salt (such as silver nitrate) with a water solution of a water-soluble halide (such as sodium chloride). The gelatin may be dissolved in either or both of the solutions or in a separate solution. After the silver halide is formed the dispersion thereof may be digested or treated in some other manner to impart the desired characteristics. To refine the silver halide dispersion it is first chilled and allowed to set or gel. The gel thus formed is noodled or otherwise comminuted and the water soluble salts present therein are dialyzed out with water having a low temperature. After the salts have been removed and the water is drawn off, the washed emulsion may then be melted by warming and gelatin or some other chemicals may be added to condition the silver halide grains thus obtained.

I have found a process for preparing silver halide emulsions in which the chilling and setting steps are eliminated and the time required for subsequent steps is considerably lessened. 7

One object of my invention is to provide a method for preparing washed silver halide emulsions in which the silver halide may be coagulated without the necessity of altering the pH thereof. Another object of my invention is to provide a method for washing fine grained emulsions in which the tendency to form grain clumps is diminished. Another object of my invention is to provide a method for preparing washed silver halide emulsions in which change of the pH of the mass is not necessary to obtain coagulation of the emulsion. A further object of my invention is to provide a method of purifying a gelatin emulsion in which the salts of certain metals have been found to be quite useful.

The prior art has suggested the washing of emulsions by coagulating the same, and for this purpose there had been used as agents, salts of an alkali metal or a metal of group II. Methods of coagulating have also been described in which gelatin derivatives have been employed as the carrier for the silver halide. In both of those cases, however, the pH of the silver halide dispersion was lowered to 4 or less to obtain coagulation. In the case of emulsions characterized by fine grain the settling of the coagulated material often occurs slowly and such emulsions exhibit a tendency to form grain clumps which are difficult to redisperse after the washing has occurred.

I have now found that it is possible to coagulate emulsions in which the silver halide is dispersed in certain gelatin derivatives, by the addition to those silver halide dis persions of relatively small amounts of water soluble salts of-certain metals. The coagulation thus obtained occurs 2,768,079 i atenied Oct. 23, 1956 over'a considerable range in pH and the step of lowering the pH which has been necessary in many previous processes can be omitted. I have found that this method of coagulation washing of dispersed silver halide is particularly advantageous in the case of fine grained emulsions as rapid settling is obtained and the tendency to clump is reduced to a minimum.

The gelatin derivatives which I have found to be useful as peptizers for dispersing silver halide for preparing washed emulsions in accordance with my invention are the aromatic sulfonyl chloride derivatives of gelatin, the

derivatives of gelatin, the carcarboxylic acid chloride boxylic anhydride derivatives of gelatin, the aromatic isocyanate derivatives of gelatin and the l,4-diketone derivatives of gelatin. The preparation of these gelatin derivatives is known in the prior art as disclosed, for example, in U. S. Patent No. 2,614,929 of Yutzy and Russell, October 21, 1952. As an example of gelatin derivatives which are useful for preparing washed emulsions in accordance with my invention, the reaction products of any of the with. gelatin may be employed for that purpose.

Sulfonyl chlorides Carboxylic acid chlorides Phthalyl .chloride p-Nitrobenzoyl chloride Benzoyl chloride Ethyl chlorocarbonate Furoyl chloride Acid anhydrides Phthalic anhydride Benzoic anhydride Succinic anhydride Maleic anhydride Is-atoic anhydride n-Heptyl succinic anhydride Hexahydrop'hthalic anhydride Isocyanates Phenyl isocyanate p-Bromophenyl isocyanate p-Chlorophenyl isocyanate p-Tolyl isocyanate p-Nitrophenyl isocyanate Alpha-naphthyl isocyanate fl-Naphthyl isocyanate The preparing of a washed emulsion in accordance with my invention is carried out by forming silver halide in an aqueous solution of the gelatin derivative followed by adding to the so obtained dispersion of silver halide a small amount of an aqueous solution of a metal salt of the type specified herein as being suitable. The metal salt is employed in a proportion within the range of l/ 2 gram to 20 grams per mol of silver halide, the amount needed depending upon the conditions residing in the emulsion.

It. appears that a greater concentration of the salt is desirablewithan increase in pH anda lowertemperature. The salts which I have foundto be useful for coagulating dispersions of silver halide in gelatin derivatives are the watersoluble salts of cadmium; zinc, aluminum, iron,

nickel; chromium; and lanthanum. The acoag'u'lationv has been found to occur at any pH below 10, henceno adjust ment'of the pH is ordinarily necessary. The amount. of v the metal salt which gives maximum coagulation will vary depending upon; the particular salt. employed, the temperature of the dispersion and the pH of the emulsion at the time of coagulation. For instance, in thecase of a dispersion-of silver halide in a gelatin derivative having a temperature of 30 C. and a pH of the-amount of cadmiumchloride which will give optimum result's'has been: foundto. be approximately 15.5 grams per mol of silver .halide. If the pH tends toward the acid side the amountvof salt neededto obtain optimum coagulation becomes less as is also the case where the temperature is higher. tin derivative having a pH of 4.8 and a temperature of 60 C. I have found that the optimum amount of lanthanum nitrate when employed as the coagulating salt is. 1.3-2gms. In the use of cadmium chloride in a dispersionhaving a pH of 4.8 at a temperature of optimum results are obtained when 3.45 grams of the cadmium chloride per mole of silver halide is used. If the temperature is increased to C. the amount of'cadmium chloride necessary for optimum results in 2.3 grams while.

if the temperature is increased to 50 C., .57 grams of cadmium chloride per mol of silver halide give optimum results. If the temperature of the dispersion is at 30 C. but the pH is at 6, 13.7 grams of cadmium chloride per mol of silver halide is desirable, While if the pH is at 8-10,

15.5 grams of cadmium chloride is desirable per mol of silver halide. -If, however, the temperature of the dispersion is at 50 C., the amount of cadmium chloride to obtain optimum results is 8.5 grams per mol of silver halide. Likevariations occur in the case of the other salts specified to obtain optimum coagulation conditions- As was pointed out above the use of lanthanum nitrate in a silver halide dispersion having a pH of 4.8 and a temperature of 60, 1.32 gms. thereof is the optimum for coagulation. If, however, the temperature is dropped to 30 C. then 1.76 gins. of lanthanum nitrate is the most desirable amount per mol of silver halide to obtain coagulation.

After the dispersion of silver halide in the gelatin derivative has been coagulated the liquid portion thereof is removed from the settled portion such as by decantation. The silver halide may then be redispersed by adding water to the particle mass, preferably with the use of a slightly elevated temperature and if desired, a washing withwater having a temperature of 10 C. may be employed prior to redispersion. If desired, the dispersion may be recoagulated by again adding salt and decanting off the mother liquor. Upon redispersion it is desirable to 'addthereto a solution of a carrier for the silver halide such as gelatin or far-hydrolyzed cellulose acetate to form a photographic emulsion of the desired silver halide concentration.

The following examples illustrate my invention:

Example 1 potassium chloride and 2.6 grams of potassium iodide in 3000 cc. of distilled water at 60 C. This wasaccomplished by-adding thesilver nitrate solution to the second.

solution over a period of approximately 10 minutes and maintainingthe mixture at a temperature of;60 C. After the silver nitrate was added theernulsion was. cooled to 40 C. and 24 grams of cadmium chloride in. solution:in:

250 cc. of distilled water was added-thereto,;th'e-pH of the system being.6 .3 and a coagulum of gelatin derivative and silver halide formed. This coagulum was allowedato set -1 In the case of a silver halide dispersion in a gelatle and the mother liquor was decanted therefrom. 6 liters was dispersed for 5 minutes at 40 C. and there was added to this dispersion a solution of 10 grams of cadmium chloride in 1 00 cc. of distilled water at a pH of 6.3. The emulsion was again coagulated and upon settling the supernatant liquor was decanted. There was then added 540 grams of photographic gelatin and additional distilled water to result in a total weight of the mass of 14 lbs. The emulsion was held while agitating for 20 minutes at 40 C. at a pH of 6.0. The so obtained emulsion was coated onto a cellulose acteate film base and upon exposing in an Eastman Ib sensitometer for A of a minute and developed for 4 minutes inDeveloper D-19 at 68 F. the following characteristics were found:

lO/i Speed21.5; Gamma 2.60; Fog 0.05 Example 2 A dispersion of silver halide was preparedby mixinga solution of 400 grams of silver nitrate in 3600 cc. .of distilled water at 30 C. with a solution of 59 grams of benzene sulfonyl chloride gelatin derivative, 142 grams of potassium chloride and 57 grams of potassium bromide dissolved in 3400 cc. of distilled water at 30 C. The silver nitrate solution was added to the alkali halide gelatin solution over a period of approximately 2 minutes .with good stirring. The dispersion thus formed was heated to 40 C. and the mass was found to have a pH of 5.95.

There was then added thereto an aqueous solution of 14.2. grams of 'cadium chloride. The silver halide and gelatin derivative coagulated and settled. After several minutes the mother liquor was decanted Off. The coagulum. was rinsed in cold tap water and 8 liters of distilled water was added to thecoagulum and the mass was stirred at 40 C. until dispersion occurred. An aqueous solutionof 800 grams of photographic gelatin was added and sufficient distilled water was then added to bring the total weight of the mass to 20 lbs. The emulsion was stirred at 40 C'. to obtain-completedispersion and the pH was adjusted to 6.5 by the addition of the required amount of the aqueous sodium hydroxide. The mass was digested- Example 3 A dispersion of silver halide in gelatin derivative was prepared by mixing a solution of 400 grams of 'silver nitrate in 4100 cc. of distilled water at 72 C. with a solution 'of 59 grams of n-heptyl succinic anhydride gela- 1 tin derivative, 330 grams of potassium bromide and 6 grams of potassium iodide in 3400 cc. of distilled water at 70 C. The silver nitrate solution was added to the second solution over a period of approximately 5 /2 minutes with good stirring, the temperature having beenmaintained at 70 C. The dispersion was then stirred for 20 minutes at 70 C. and cooled at 40 C. 27 grams of cadmiumchloridein aqueous solution were added ata pH of 6.0 which coagulated the emulsion and the coagulum was allowed to settle for a few minutes. The residual liquid was decanted off and the coagulum was rinsed in cold tap water. The particle mass thus obtained was mixed with 16 lbs. of distilled water and the mass was stirred for 5 minutes at 40 C. 590 grams of photographic gelatin was added and the mass was stirred for 20 1ninutes-at40 C. until complete dispersion had been effected. Distilled water was then .added to bring the veloped for 4 minutes in D-19 developer at 68 F., it was found to have the following characteristics:

30/E Speed 40; Gamma 1.97; Fog 0.04 Example 4 A dispersion of silver halide was prepared in substantially the same manner as described in Example 3 but 59 grams of a hexahydrophthalic anhydride derivative of gelatin was employed instead of the n-heptyl succinic anhydride gelatin derivative. The coagulation was induced by the use of lanthanum nitrate rather than cadmium chloride. The emulsion finally obtained was coated onto a cellulose acetate film support and Was exposed and developed as in the preceding example. The emulsion was found to have the following characteristics:

30/E Speed 102; Gamma 2.80; Fog 0.06

The salts which may be employed for coagulating silver halide dispersions in accordance with my invention may be any of the water soluble salts of the metal referred to. This would include the nitrates or chlorides of all of the metals listed although in many cases other salts would be useful providing the negative ion of the salt does not have any adverse eifect photographically or otherwise on the silver halide dispersion.

I claim:

1. In a process of preparing a washed silver halide dispersion the steps which comprise preparing a dispersion of silver halide in an aqueous solution of a gelatin derivative selected from the group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin, the carboxylic acid anhydride derivatives of gelatin and the aromatic isocyanate derivatives of gelatin, coagulating that dispersion while at a pH of 4.5- by adding thereto 1/2-20 grams, per mole of silver halide, of a water soluble salt selected from the water soluble salts of cadmium, zinc, aluminum, iron, nickel, chromium and lanthanum whereby silver halide-gelatin granules form and separating those granules from the liquid portion of the mass.

2. In a method of preparing a washed silver halide dispersion the steps which comprise forming a dispersion of silver halide in an aqueous solution of a benzene sulfonyl chloride gelatin derivative, coagulaing that dispersion while at a pH of 4.5l0 by adding thereto an aqueous solution of 1/2-20 grams per mole of silver halide of a salt selected from the water soluble salts of cadmium, zinc, aluminum, iron, nickel, chromium and lanthanum whereby silver halide-gelatin granules are formed and separating the thus formed granules from the liquid portion of the mass.

3. In a method of preparing washed silver halide dispersions the step which comprises forming a dispersion of silver halide in an aqueous solution of hexa hydro phthalic anhydride-gelatin derivative, coagulating that dispersion while at a pH of 4.5-10 with 1/2-20 grams of lanthanum nitrate per mole of silver halide whereby silver halide-gelatin granules are formed and separating those granules from the liquid portion of the mass.

4. In a method of preparing washed silver halide dispersions the steps which comprise forming a dispersion of silver halide in an aqueous solution of a N-heptyl succinyl anhydride derivative of gelatin, coagulating that dispersion while at a pH of 4.5-10 by adding thereto an aqueous solution of 1/2-20 grams of cadmium chloride per mole of silver halide whereby silver halide-gelatin granules are formed and separating those granules from the liquid portion of the mass.

5. In a method of preparing washed silver halide dispersions the steps which comprise forming a dispersion of silver halide in an aqueous solution of a benzene sulfonyl chloride derivative of gelatin, coagulating the silver halide dispersion while at a pH greater than 4.5 and not more than 10 by adding thereto an aqueous solution of 1/2-20 grams of cadmium chloride per mole of silver halide whereby silver halide-gelatin granules are formed and separating those granules from the liquid portion of the mass.

6. In a method of preparing a washed silver halide dispersion the steps which comprise forming a dispersion of a silver halide in an aqueous solution of a gelatin derivative selected from the group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin, the carboxylic acid anhydride derivatives of gelatin and the aromatic isocyanate derivatives of gelatin, coagulating the silver halide dispersion while at a pH of 4.5-10 by adding thereto an aqueous solution of 1/2-20 grams of cadimum chloride per mole of silver halide whereby silver halide-gelatin granules are formed and separating those granules from the liquid portion of the mass.

7. In a process of preparing a washed silver halide dispersion the steps which comprise preparing a dispersion of silver halide in a gelatin derivative selected from the group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin, the carboxylic acid anhydride derivatives of gelatin and the aromatic isocyanate derivatives of gelatin, having a pH of 4.5-10 coagulating that dispersion without adjustment of the pH thereof by adding thereto 1/ 2-20 grams per mole of silver halide of a water soluble cadmium salt whereby silver halide-gelatin granules form and separating those granules from the liquid portion of the mass.

References Cited in the file of this patent UNITED STATES PATENTS 2,614,928 Yutzy et al. Oct. 21, 1952 2,614,929 Yutzy et al. Oct. 21, 1952 2,618,556 Hewitson et al Nov. 18, 1952

Claims

1. IN A PROCESS OF PREPARING A WASHED WILVER HALIDE DISPERSION THE STEPS WHICH COMPRISE PREPARING A DISPERSION OF SILVER HALIDE IN AN AQUEOUS SOLUTION OF A GELATIN DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF THE AROMATIC SULFONYL CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID ANHYDRIDE DERIVATIVES OF GELATIN AND THE AROMATIC ISOCYANATE DERIVATIVES OF GELATIN, COAGULATING THAT DISPERSION WHILE AT A PH OF 4.5-10 BY ADDING THERETO 1/2-20 GRAMS, PER MOLE OF SILVER HALIDE, OF A WATER SOLUBLE SALT SELECTED FROM THE WATER SOLUBLE SALTS OF CADMIUM, ZINC, ALUMINUN, IRON, NICKEL, CHROMIUM AND LANTHANUM WHEREBY SILVER HALIDE-GELATIN GRANULES FORM AND SEPARATING THOSE GRANULES FROM THE LIQUID PORTION OF THE MASS.