US2624674A

US2624674A - Photographic emulsion sensitized with gold compounds and sulfur sensitizers

Info

Publication number: US2624674A
Application number: US680514A
Authority: US
Inventors: Raife G Tarkington; Wesley G Lowe
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1946-06-29
Filing date: 1946-06-29
Publication date: 1953-01-06
Anticipated expiration: 1970-01-06
Also published as: FR959922A; GB631243A; BE474236A

Description

Patented Jan. 6, 1953 PHOTOGRAPHIC EMULSION SENSITIZED WITH GOLD COMPOUNDS AND SULFUR SENSITIZERS Raife G. Tarkington and Wesley G. Lowe, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application June 29, 1946, Serial No. 680,514

14 Claims.

This invention relates to sensitized photographic emulsions and to a process for preparing the same.

Photographic silver halide emulsions prepared in non-gelatin vehicles (or carrier) are, in general, sensitized with sulfur compounds (1, e. sulfur sensitizers) with more difflculty than the corresponding silver halide emulsions prepared in gelatin.

We have now found, however, that non-gelatin silver halide emulsions can be sensitized by adding to the emulsions one or more soluble gold compounds (i. e. one or more gold compounds which provide gold ions in aqueous media) and one or more sulfur sensitizers. The speed increases caused by the combination of gold compound and sulfur sensitizer in the non-gelatin emulsions are at least equal to, and in some cases very much greater than, the speed increases which can be obtained employing a combination of gold compound and sulfur sensitizer in a gelatino-silver-halide emulsion.

It is, accordingly, an object of our invention to provide new photographic emulsions. A further object is to provide a process for preparing such emulsions. Other objects will become apparent hereinafter.

In accordance with our invention, we incorporate in a non-gelatin photographic silver halide emulsion, at any stage of its preparation, at least one soluble gold compound and at least one sulfur sensitizer. Our invention is directed primarily to non-gelatin developing-out silver halide emulsions in which the silver halide is predominately silver bromide, i. e. silver halide emulsions in which the silver halide is Wholly silver bromide and silver bromide emulsions containing smaller amounts of silver chloride or silver iodide or both.

Among the non-gelatin silver halide emulsions advantageously employed in practicing our invention are silver halide emulsions prepared using as the vehicle or carrier polyvinyl alcohol (polyvinyl alcohol is herein intended to include all water-soluble hydrolyzed polyvinyl esters containing an ester group content equivalent to from to by weight of polyvinyl ester); silver halide emulsions prepared using as the vehicle or carrier hydrolyzed polyvinyl acetate containing an acetate group content equivalent to from 59 to 71% by weight of polyvinyl acetate; silver halide emulsions prepared using as the vehicle or carrier polyvinyl acetals containing a large proportion of polyvinyl alcohol hydroxyl groups, e. g. polyvinyl acetaldehyde acetals containing polyvinyl acetaldehyde acetal groups equivalent to at least 50% by weight of polyvinyl acetaldehyde acetal and polyvinyl alcohol hydroxyl groups equivalent to at least 15% by weight of polyvinyl alcohol, polyvinyl propionaldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to from 45 to by weight of polyvinyl alcohol, and polyvinyl butyraldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to from 60 to by weight of polyvinyl alcohol, etc. Any polyvinyl compound, especially those containing only carbon, hydrogen and oxygen atoms, or those containing carbon, hydrogen, oxygen and amino nitrogen atoms or ammonium nitrogen atoms, which is soluble in a mixture of ethyl alcohol and water (containing from 0 to 50% by volume of ethyl alcohol) to the extent of 10 g. per g. of solvent can be employed as the vehicle or carrier in preparing our non-gelatin silver halide emulsions. Moreover, any other resinous or colloidal material soluble in an ethyl alcohol-water mixture or in water, as stated above, can be employed in preparing our nongelatin silver halide emulsions, e. g. soluble polyamide resins, such as described in United States Patent 2,384,072, dated September 4, 1945, and hydrolyzed copolymers of vinyl esters and ethylene or propylene, such as described in United States Patent 2,397,866, dated April 2, 1946. Still further examples of colloidal materials which can be employed as vehicles or carriers in preparing our non-gelatin emulsions are hydrolyzed cellulose carboxylic esters, such as hydrolyzed cellulose acetate or hydrolyzed cellulose acetate propionate, containing from 19 to 33% by weight of acyl groups, for example. Any cellulose compound, especially those containing only carbon, hydrogen and oxygen atoms, or those containing only carbon, hydrogen, oxygen and amino nitrogen atoms or ammonium nitrogen atoms, which is soluble in a mixture of ethyl alcohol and water (containing from 0 to 50% by volume of ethyl alcohol) to the extent of 10 g, per 100 g. of solvent can be employed as the vehicle or carrier in preparing our non-gelatin silver halide emulsions.

In connection with the non-gelatin colloidal materials, such as polyvinyl alcohol, the silver halide emulsions can be prepared using gelling agents, such as phenols, e. g. orcinol, gallic acid, 2,4-dihydroxybenzoic acid, 4-chlororesorcinol, anaphthol, phloroglucinol, 2,7 -dihydroxynaphthalene, etc. Moreover, the non-gelatin silver halide emulsions can be prepared using silver halide dispersing agents, 6. g. starch acetate, gum arabic, a copolymer of maleic anhydride and vinyl acetate, low viscosity methyl cellulose, water-soluble amino carbohydrate dispersing agents (e. g. diethanolamine cellulose acetate or any other of these agents described in United States Patent 2,360,238, dated October 10, 1944) amino resin dispersing agents (e. g. dimethylaminobenzaldehyde acetals of polyvinyl alcohol, or watersoluble polyvinyl acetals in which at least a part of the acetal groups are 4-formylphenyltrialkylammonium salt acetal groups, such as the polyvinyl acetal of 4-formylphenyl trimethylammonium methylsulfate and other such compounds described in United States Patent 2,358,836, dated September 26, 1944), etc.

Polyvinyl compound silver halide emulsions and their preparation are described in United States Patents 2,286,215, dated June 16, 1942;

2,276,322, dated March 17, 1942; 2,276,323, dated March 17, 1942; 2,311,058, dated February 16, 1943; 2,311,059, dated February 16, 1943; 2,367,- 511, dated January 16, 1945; 2,376,371, dated May 22, 1945, and 2,110,491, dated March 8, 1938.

In non-gelatin silver halide emulsions where the colloidal material used as vehicle or carrier for the silver halide is a relatively poor protective colloid as is the case with the hydrolyzed cellulose carboxylic esters, the speeds obtained with the combination of gold salt and sulfur sensitizer are sometimes as great as ten times the speeds that can be obtained with sulfur sensitizers alone. Where the colloidal material is a relatively good protective colloid the speeds are more of the order of 3 to 4 times the speeds obtained with the sulfur sensitizers alone.

Typical soluble gold compounds which we employ in practicing our invention are gold halides, such as auric chloride, or complex goldhalides,

such as potassium auric chloride (KAU.C14),

auric sulfate, sodium auric chloride, potassium or sodium auric bromide, potassium or sodium auric iodide, complex goldsalts, such as alkali metal aurous thiosulfates, alkali metal aurous sulfites, a complex salt formed by the interaction of thiourea and auric chloride, complex salts, such as gold thiosinamine complexes, etc. One or more gold compounds can be used.

The gold compound is advantageously employed in a concentration equal to from about 0.0005 to about 0.025% by moles of the silver halide present. Optimum results are obtained ordinarily at concentrations between about 0.001 and 0.02% by moles of the silver halide present.

The gold compounds can be added to the emulsions at any stage of their preparation. The gold compounds are advantageously incorporated in the emulsions in the form of their solutions in a suitable solvent such as water, methyl or ethyl alcohol.

Typical sulfur sensitizers which we employ in practicing our invention are sulfur compounds containing C=S groups and -SS groups, e. g. thiourea, allyl isothiocyanate, thiosinamine, etc. Metal or ammonium thiocyanates, e. g. sodium, potassium, ammonium, cadmium, calcium, etc. thiocyanates can also be employed. One or more sulfur sensitizers can be employed, and one or more thiocyanates selected from the group consisting of metal and ammonium thiocyanates can be employed in conjunction with a sulfur sensitizer other than a thiocyanate containing a cation selected from the group consisting of metal and ammonium cations. The sulfur sensitizers are advantageously incorporated in the emulsions 4 in the form of their solutions in a suitable solvent, such as water, methyl or ethyl alcohol.

The sulfur sensitizers can be incorporated in the emulsions at any stage of the preparation of the emulsion, i. e. during precipitation of the silver halides, during washing of the emulsions or during digestion or heat treating of the emulsions. When incorporating thiocyanates in the emulsions prior to washing, the amount can vary widely. Advantageously, however, an amount of thiocyanate equal to from about 2 to about 15 per cent by moles of the silver halide in the emulsion is employed. If the thiocyanate or other sulfur sensitizer is not added until later in the preparation, e. g. after washing, it is advantageous to employ an amount equal to from about 0.1 to about 2.5 per cent by moles of the silver halide present in the emulsion in the case of metal and ammonium thiocyanates, and an amout equal to from about 0.006 to about 0.06 er cent by moles of the silver halide in the case of other sulfur sensitizers.

It is advantageous to digest, i. e. heat treat. the emulsion with both the gold compound and the sulfur sensitizer present. Depending upon whether or not the emulsions are prepared employing organic solvents which vaporize readily, the digestion can be carried out at from to 150 F. for example. The lower the temperature of digestion, the longer it will require to arrive at optimum speed. Ordinarily at F., digestion for from 1 to 2 hours produces optimum speed. During digestion, the pH of the emulsion is advantageously adjusted to th acid side of neutrality, e. g. between 5 and 6.5 for aqueous systems. Maintenance of the emulsion on the acid side of neutrality is also advantageous during coating.

The following examples will serve to illustrate further the manner of practicing our invention.

Example 1.Polyvinyl alcohol emulsion 200 g. of silver nitrate .l {Watcr to 400 cc. volume ,JTempu-awm Blli5723 g. (ill potassium bronldc uni g. 0 p0 assium iodi e 'lcm .i-raiurc 80 l".

Water to 400 cc. volume U] T To the resulting mixture were added 2500 cc. of a 10% (by weight) solution of polyvinyl alcohol in water. Then 200 cc. of glacial acetic acid were added. The resulting emulsion was heated to F. and then 300 cc. of a 7% (by weight) solution of a-naphthol (gelling agent) in ethanol were added. The resulting emulsion was set by chilling. It was then shreaded, washed with water and melted. The pH of the melted emulsion was adjusted to 5.5.

One-half of the melted emulsion was coated on a cellulose acetate film base in the usual manner. Upon exposure and development for 6 minutes at 70 F. in Eastman Kodak Companys D-16 developer, the coated emulsion showed a speed (IO/i) of 0.20, and a gamma of 1.5.

To the other half of the melted emulsion were added 800 mg. of sodium thiocyanate and 28 g. of KAuCle. The emulsion was then heated for one hour at 120 F. and then coated on cellulose ace- 5. tate film base in the usual manner. On exposing and developing as above, this coated emulsion showed a speed (IO/i) of 0.84 and a gamma of 1.28.

Example 2.-Hydrolyzed cellulose acetate propionate emulsion A hydrolyzed cellulose acetate propionate silver bromiodide emulsion was prepared as follows:

40 g. of partially hydrolyzed cellulose acetate propionate (containing an acyl group content equivalent to about 23 by weight of acetyl) were dissolved in 2200 cc. of ethanol and 960 cc. of water, and the temperature of the solution was adjusted to 80 F. The following two solutions A and B were then allowed to run into the aforesaid solution simultaneously with stirring over a 20- minute interval:

200 g. of silver nitrate Water to 400 cc. volume AiThen add sufficient concentrated ammoni-}Temperature 80 F.

um hydroxide to precipitate and completely redissolve the silver.

152.3 g. of potassium bromide B{4.75 g. of potassium iodide .}Temperature 80 F.

Water to 400 cc. volume To the resulting mixture were added 380 cc. of a 50% (by weight) solution of citric acid in water and 3200 cc. of a (by weight) solution of partially hydrolyzed cellulose acetate propionate (acyl group content equivalent to about 23% by weight of acetyl) in a mixture of ethyl alcohol and water (equal volumes). 7 The emulsion was precipitated by pouring the resulting solution into water with stirring. The precipitated emulsion was washed with water until free from ethyl alcohol. The washed emulsion was pressed to a weight of 2500 g. and the following solvents were added:

2500 cc. ethanol 400 cc. ethylene glycol diacetate Upon heating, the emulsion dissolved in these solvents.

To one-half of this emulsion dispersion were added 40 mg. of 3-ethyl-5-(2-ethyl-l-benzothiazolylidene-2-thio-2A (3,5) -oxazoledione and the resulting emulsion was coated on cellulose acetate film base in the usual manner. On exposure and 6 minutes development in Eastman Kodak Companys D-l6 developer at 70 F., the coated emulsion showed a speed (10/2') of 1.40 and a gamma of 2.5.

To the other half of the emulsion dispersion were added 0.65 g. of sodium thiocyanate and 24 mg. of KAuCh and the emulsion was heated for one hour at 120 F. 40 mg. of 3-ethyl-5-(2-ethyll benzothi-azolylidene 2 thio 2,4(3,5) oxazoledione were then added and the emulsion was coated on cellulose acetate film base. On exposure and development as above, the coated emulsion showed a speed of 11.2 and a gamma of 2.5.

Example 3 F. 8 g. of urea and 2 cc. of con- 40 g. silver nitrate Water to cc. volume A Then add sulficient concentrated ammo- Temperature 80 F.

nium hydroxide to precipitate and completely redissolve the Silver.

pionate (23% apparent acetyl) dissolved in 300 cc. of water and 300 cc. of acetone. The emulsion was precipitated by pouring the resulting solution into water with stirring. The precipitated emulsion was washed with water until free from organic solvents. It was then pressed to a weight of 360 g. and the following solvents added:

Water 440 Acetone 280 Monoethyl ether of ethylene glycol 200 Monoacetin 24 The resulting emulsion was then split into four equal parts of which three were treated as follows:

Amount of KAuCh added Mg. No. l 0 heated 1 hour, at F. No. 2 0. 1 Do. No. 3 0. 6 Do.

Then, 4 mg. of 3-ethyl-5-(2-ethyl-l-benzo-thiazolylidene-2 thio 2,4(3,5) oxazoledione were added to each portion and then each portion was coated on cellulose acetate film. The coated emulsions on exposure and development for 6 minutes in Eastman Kodak Companys D-16 developer at 70 F., showed the following results:

Speed (10/i) Gamma Fog Example 4 An emulsion was prepared as in Example 2. Instead of dividing the emulsion into halves and adding sodium thiocyanate and gold compound as in Example 2, portions of the emulsion were treated as follows:

idene-2 thio 2,4(3,5) oxazoledione were then added to each portion of emulsion and then each portion of emulsion was coated on cellulose ace- }Temperature 80 F tate film. Upon exposure and developing as in Example 1, the following results were obtained:

Speed (lo/i) Gamma Fog Example 5 An emulsion was prepared as in Example 2. Instead of dividing the emulsion into halves and adding sodium thiocyanate and gold compound as in Example 2, portions of the emulsion were treated as follows:

7 mg. of 3-ethyl-5(2-ethyl-l-benzothiazolylidene- 2-thio-2,4(3,5)-oxazoledione were then added to each portion of emulsion and then each portion of emulsion was coated on cellulose acetate film. Upon exposure and development as in Example 1, the following results were obtained:

Speed (IO/i) i Gamma Fog B-ethyl xanthate propionic acid employed as a sulfur sensitizer above has the following formula:

As pointed out above, non-gelatin silver halide emulsions do not respond to sensitization with sulfur sensitizers readily, and heretofore, it has been desirable to use silver halide dispersing agents such as water-soluble amino carbohydrate dispersing agents or water-soluble amino resin dispersing agents in order to arrive at sulfur sensitized non-gelatin silver halide emulsions having speeds paralleling those of gelatino-silverhalide emulsions. By means of our invention, however, non-gelatin silver halide emulsions of greatly enhanced sensitivity can be obtained without the use of the aforesaid dispersing agents, although our invention contemplates non-gelatin silver halide emulsions, sensitized as described herein, containing the aforesaid dispersing agents.

The thiocyanates which we have found are most advantageously employed in practicing our invention are the alkali metal thiocyanates, e. g. sodium or potassium thiocyanate, the alkaline earth metal thiocyanates, e. g. calcium thiocyanate, and the ammonium .thiocyanates, e. g. NHrSCN. Of course, thiocyanates containing cations which cations are known to have, in themselves, a deleterious effect on silver halide emulsions should be avoided. Otherwise the beneficial effects attained by our invention would be partiallynullified by thedeleterious action ofthe cation. Thus, iron thiocyanate which contains the iron cation should be avoided.

sensitizing dyes of all types can be employed to spectrally (optically) sensitize our new emulsions, e. g. erythrosin, Congo red, any of the sensitizing cyanine dyes (monomethine, trimethine, pentamethine, heptamethine, etc.,), any of the sensitizing merocyanine dyes (see United States Patent 2,078,233, dated April 27, 1937, for example), any of the sensitzing hemicyanine dyes (see United States Patent 2,166,736, dated'July 18, 1939, for example), any of the sensitizing hemioxonol dyes (see United States Patent 2,216,441, dated October 1, 1940, and United States Patent 2,165,339, dated July 11, 1939, for example), etc.

Photographic elements comprising our new emulsions can be made up in the usual manner by coating the flowable emulsions onto a support of a suitable material, such as glass, photographic paper, cellulose derivative or resinfilm, etc. to desired thickness, and then setting the coated emulsion.

Our new emulsions can contain hardening agents, setting agents, stabilizing agents, supersensitizing combinations of sensitizing dyes or a supersensitizing combination of one or more sensitizing dyes and another substance.

What We claim as our invention and desire to be secured by Letters Patent of the United States is:

1. A photographic silver halide emulsion in which the carrier for the silver halide is a colloidal material selected from the group consisting of polyvinyl alcohol, hydrolyzed polyvinyl acetate containing an acetate group content equivalent to from 59 to 71 percent by weight of polyvinyl acetate, polyvinyl acetaldehyde acetals containing polyvinyl acetaldehyde acetal groups equivalent to at least 50 percent by weight of polyvinyl acetaldehyde acetal and polyvinyl alcohol hydroxyl groups equivalent to at least 15 percent by weight of polyvinyl alcohol, polyvinyl propionaldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to from 45 to 60 percent by weight of polyvinyl alcohol, polyvinyl butyraldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent tofrom 60 to percent by weight of polyvinyl alcohol and hydrolyzed cellulose carboxylic esters in which the acyl groups contain from 2 to 3 carbon atoms, said cellulose esters containing from 19 to 33 percent by weight of said acyl groups, sensitized with a soluble gold compound and a sulfur sensitizer, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 per cent by mols of the silver halide present in the emulsion, and the concentration of the sulfur sensitizer being equal to about 0.006 to about 2.5 percent by mols of the silver halide present in the emulsion.

2. A photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is polyvinyl alcohol, sensitized with a soluble gold compound and a thlocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 per cent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

3. A photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a hydrolyzed cellulose carboxylic ester in which the acyl groups contain from 2 to 3 carbon atoms, said cellulose ester containing from 19 to 33 percent by weight of said acyl groups, sensitized with a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to

about 2.5 percent by mols of the silver halide present in the emulsion.

4. A photographic silver halide emulsion in Which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a hydrolyzed cellulose acetate propionate containing from 19 to 33 percent by weight of acyl groups, sensitized with a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

5. A photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a hydrolyzed polyvinyl acetate containing an acetate group content equivalent to from 59 to 71 percent by weight of polyvinyl acetate, sensitized with a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the sulfur sensitizer being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

6. A photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a polyvinyl acetaldehyde acetal containing polyvinyl acetaldehyde acetal groups equivalent to at least 50 percent by weight of polyvinyl acetaldehyde acetal and polyvinyl alcohol hydroxyl groups equivalent to at least percent by weight of polyvinyl alcohol, sensitized with a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from 0.0005 to about 0.025 per cent by mols of the silver halide present in the emulsion, and the concentration of the sulfur sensitizer being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

7. A photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a polyvinyl propionaldehyde acetal containing polyvinyl alcohol hydroxyl groups equivalent to from 45 to 60 percent by weight of polyvinyl alcohol, sensitized with a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the sulfur sensitizer being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

8. In a process for preparing a sensitized photographic silver halide emulsion in which the carrier for the silver halide is a colloidal material selected from the group consisting of polyvinyl alcohol, hydrolyzed polyvinyl acetate containing an acetate group content equivalent to from 59 to 71 percent by weight of polyvinyl acetate, polyvinyl acetaldehyde acetals containing polyvinyl acetaldehyde acetal groups equivalent to at least 50 percent by weight of polyvinyl acetaldehyde acetal and polyvinyl alcohol hydroxyl groups equivalent to at least 15. percent by weight of polyvinyl alcohol, polyvinyl propionaldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to 45 to 60 percent by weight of polyvinyl alcohol and polyvinyl butyraldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to from 60 to percent by weight of polyvinyl alcohol and hydrolyzed cellulose carboxylic esters in which the acyl groups contain from 2 to 3 carbon atoms, said cellulose ester containing from 19 to 33 percent by Weight of said acyl groups, the step which comprises digesting the emulsion in the presence of a soluble gold compound and a sulfur sensitizer, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the sulfur sensitizer being equal to from about 0.006 to about 2.5 percent by mols of the silver halide present in the emulsion.

9. In a process for preparing a sensitized photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is polyvinyl alcohol, the step which comprises digesting the emulsion on the acid side of neutrality in the presence of a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

10. In a process for preparing a sensitized photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a hydrolyzed cellulose carboxylic ester in which the acyl groups contain from 2 to 3 carbon atoms, said cellulose ester containing from 19 to 33 percent by weight of said acyl groups, the step which comprises digesting the emulsion on the acid side of neutrality in the presence of a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

11. In a process for preparing a sensitized photographic silver halide emulsion in which the silver halideis predominantly silver bromide and in which the carrier for the silver halide is a hydrolyzed cellulose acetate propionate containing from 19 to 33 percent by weight of acyl groups, the step which comprises digesting the emulsion on the acid side of neutrality in the presence of a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

12. In a process for preparing a sensitized photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a hydrolyzed polyvinyl acetate containing an acetate group content equivalent to from 59 to 71 percent by weight of polyvinyl acetate, the step which comprises digesting the emulsion on the acid side of neutrality in the presence of a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 per cent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

13. In a process for preparing a sensitized photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a polyvinyl acetaldehyde acetal containing polyvinyl acetaldehyde acetal groups equivalent to at least 50 percent by weight of polyvinyl acetaldehyde acetal and polyvinyl alcohol hydroxyl groups equivalent to at least percent by weight of polyvinyl alcohol, the step which comprises digesting the emulsion on the acid side of neutrality in the presence of a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in 12 the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

14. In a process for preparing a sensitized photographic silver halide emulsion in which the silver halide is predominantly silver bromide and in which the carrier for the silver halide is a polyvinyl propionaldehyde acetal containing polyvinyl alcohol hydroxyl groups equivalent to from to percent by weight of polyvinyl alcohol, the step which comprises digesting the emulsion on the acid side of neutrality in the presence of a soluble gold compound and a thiocyanate selected from the group consisting of alkali metal and ammonium thiocyanates, the concentration of the gold compound in the emulsion being equal to from about 0.0005 to about 0.025 percent by mols of the silver halide present in the emulsion, and the concentration of the thiocyanate being equal to from about 0.1 to about 2.5 percent by mols of the silver halide present in the emulsion.

RAIFE G. TARKINGTON. WESLEY G. LOWE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 836,461 Poulsen Nov. 20, 1906 1,574,944. Sheppard Mar. 2, 1925 1,995,444 Berry Mar. 26, 1935 2,001,951 Berry May 21, 1935 2,110,491 Salo Mar. 8, 1938 2,399,083 Waller Apr. 23, 1946 FOREIGN PATENTS Number Country Date 6,609 Great Britain of 1901 496,049 Great Britain Nov. 21, 1938 692,828 Germany June 27, 1940 OTHER, REFERENCES Photographische Industrie, October 19, 1925. page 1145.

Claims

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION IN WHICH THE CARRIER FOR THE SILVER HALIDE IS A COLLOIDAL MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYVINYL ALCOHOL, HYDROLYZED POLYVINYL ACEATE CONTAINING AN ACETATE GROUP CONTENT EQUIVALENT TO FROM 59 TO 71 PERCENT BY WEIGHT OF POLYVINYL ACETATE, POLYVINYL ACETALDEHYDE ACETAL CONTAINING POLYVINYL ACETALDEHYDE ACETAL GROUPS EQUIVALENT TO AT LEAST 50 PERCENT BY WEIGHT OF POLYVINYL ACETALDEHYDE ACETAL AND POLYVINYL ALCOHOL HYDROXYL GROUPS EQUIVALENT TO AT LEAST 15 PERCENT BY WEIGHT OF POLYVINYL ALCOHOL, POLYVINYL PROPIONALDEHYDE ACETALS CONTAINING POLYVINYL ALCOHOL HYDROXYL GROUPS EQUVALENT TO FROM 45 TO 60 PERCENT BY WEIGHT OF POLYVINYL ALCOHOL, POLYVINYL BUTYRALDEHYDE ACETALS CONTAINING POLYVINYL ALCOHOL HYDROXYL GROUPS EQUIVALENT TO FROM 60 TO 80 PERCENT BY WEIGHT OF POLYVINYL ALCOHOL AND HYDROLYZED CELLULOSE CARBOXYLIC ESTERS IN WHICH THE ACYL GROUPS CONTAIN FROM 2 TO 3 CARBON ATOMS SAID CELLULOSE ESTERS CONTAINING FROM 19 TO 33 PERCENT BY WEIGHT OF SAID ACYL GROUPS, SENSITIZED WITH A SOLUBLE GOLD COMPOUND AND A SULFUR SENSITIZER, THE CONCENTRATION OF THE GOLD COMPOUND IN THE EMULSION BEING EQUAL TO FROM ABOUT 0.0005 TO ABOUT 0.025 PER CENT BY MOLS OF THE SILVER HALIDE PRESENT IN THE EMULSION, AND THE CONCENTRATION OF THE SULFUR SENSITIZER BEING EQUAL TO ABOUT 0.006 TO ABOUT 2.5 PERCENT BY MOLS OF THE SILVER HALIDE PERSENT IN THE EMULSION.