US2757089A - Phytic acid sensitizer for silver halide emulsions - Google Patents

Description

PHY TIC ACID SENSITIZER FOR SILVER HALlDE EMULSIONS Gustave William Moessen, New Brunswick, N. J assignor to E. I. du Pont de Nemours and Company, Wilmiug= ton, Del., a corporation of Delaware No Drawing. Application January 5, 1954, Serial No. 402,405

'10 Claims. (Cl. 95-7) This invention is concerned with photographic silver halide emulsions and emulsion layers and their preparation. More particularly, it relates to photographic silver halide emulsions which contain phytic acid or an alkali metal or ammonium salt thereof and a polyoxyalkylene glycol or an ether or ester thereof. Still more particularly it relates to water-permeable colloid silver halide emulsions and emulsion layers containing said mixtures of compounds.

An object of this invention is to provide photographic silver halide emulsions of improved properties. Another object is to provide photographic silver halide emulsions which exhibit increased photolytic and development responses. Yet another object is to provide such emulsions which have good speeds and stability. A related object is to provide such emulsions which have low fog values upon extended aging. A further object is to provide such emulsions which can be made in a simple manner.

Still other objects will be apparent from the following description of the invention.

It has been found that the above objects may be attained and photographic silver halide emulsions and emulsion layers possessing good sensitometric stability, speed, gamma, and low fog values can be made by incorporating in an aqueous dispersion or emulsion of light sensitive silver halides in a water-permeable colloid a small amount of (a) phytic acid or. an alkali metal or ammonium salt thereof, and (b) a water-soluble polyoxyalkylene glycol, preferably a polyoxyethylene glycol, or an ether or ester thereof having a molecular weight of at least 400 containing at least one linear radical of the formula (-CH2)mO)n wherein m is 2 or 3 and n is a positive number from 7 to 200 inclusive. Mixtures of two or more of the compounds of group (a) can be used with one or a mixture of two or more of compounds of group (b).

The phytic acid or phytate salt may be used in an amount from 0.0004 to 0.006 mol and preferably from 0.001 to 0.003 mol per mol of silver in the silver halide emulsion. The polyoxyalkylene compound may be used in an amount of 0.03 to 1.5 grams per mol of silver in the silver halide emulsion depending on the molecular weight and type of polyoxyalkylene compound used. In the preferred aspect of the invention from 0.04 to 010 gram per mole of silver of a polyethylene glycol having an average molecular weight of 3600 is incorporated in the silver halide emulsion or dispersion.

The phytic compound can be added to the colloidsilver halide emulsion or dispersion at any stage in its preparation prior to the completion of the digestion period. Thus the phytic acid compound may be added to the acqueous media during the silver halide precipitation step, during the ripening period, or prior to or during the initial stages of the digestion step but are preferably added just prior to, or during the early stages of, the digestion period. The polyoxyalkylene compound preferably is added after the digestion period. The aqueous emulsions or dispersions are. then. prepared for coating 2,757,089 Patented July 31, 1956 in any usual manner and coated onto a suitable plate, film or paper sheet to form a light-sensitive layer.

Phytic acid (meso-inositol hexaphosphate) and its alkali metal salts, e. g., lithium, sodium and potassium salts and also the ammonium salts are known compounds and are commercially available. Phytic acid can be made from inositol, phosphoric acid and phosphorous pentoxide but is usually obtained from natural sources, i. e., plant and animal. It has been represented by the formula:

HCOP OzHg The salts can be made by neutralization of the free acid thiosulfate, and sodium hyposulfite, sensitizing metals and metal compounds, e. g., gold, palladium, mercury, iron, and thallium and their chlorides including mixtures of two, three or more of these.

The polyoxyalkylene glycols and their ethers and esters which are useful in the present invention may be represented by the general formula:

wherein R is a member taken from the group consisting of hydrogen and aliphatic acyl radicals of 1 to 18 or more carbon atoms, R is a member taken from the class consisting of hydrogen and aliphatic acyl radicals of 1 to 18 or more carbon atoms and which may be the same or different from R and n is 7 to 200 or more. Their preparation is described in The Chemistry of Synthetic Resins, pages 990-994, published by Reinhold Publishing Corp. (1935).

The carboxylic acid esters can be made by acylating or esterifying the glycols with one or two mols of a carboxylic acid or a carboxylic acid chloride or anhydride so that one or both of the hydroxyl groups of the polyglycols are converted into ester groups. Among the useful specific agents useful for such reactions are: acetic acid, caproic acid, pelargonic acid, myristic acid, lauric acid, oleic acid, ricinoleic stearic acid, propionyl chloride, valeryl chloride, heptoyl chloride, palmityl chloride, butyric anhydride, etc. Such esters can be made according to the process of Example 2 of Schoeller et al. U. S. 1,970,578.

Useful polyoxyalkylene ethers include those of the formula:

wherein R" is an alkyl radical of l to 18 carbon atoms including methyl, ethyl, propyl, dodecyl, etc.

Other suitable ethers and esters include the polyoxyalkylene ethers of hexitol ring dehydration products. They are essential non-ionic in character and can be made by reacting hexitan or hexide with an alkylene oxide, e. g., ethylene oxide or propylene oxide to introduce two to 20 or more oxyalkylene groups in one or more chains and, if desired, with a monofunctional etherification agent or esterification agent to introduce a lipophilic group, e. g., an aliphatic hydrocarbon chain of 8 to 18 or more carbon atoms or the hexitans or hexides may be firstesterified or etherified with such agents and the resulting long chain ethersor esters later reacted with an alkylene oxide. Suitable long chain etherification or esterification reactants include normal alkyl halides of 8 to 20 carbon atoms, e. g., nroctylchloride, n-dodecyl bromide, n-tetradecylchloride, n-octadecyl bromide, and n-hexadecylbromide, or a fatty acid halide of 8 to 20 carbon atoms, e. g., octadecoylchloride, dodecoylchloride, tetradecoyl bromide, n-oleyl chloride, etc.

' A class of especially useful products have a structure which is exemplified by the following hexitans and hexide derivative formulae:

wherein in the formulae one of the Rs is an alkyl radical of 8 to 20 carbon atoms or an acyl radical of the formula R-CO- wherein R is of the same order and the other Rs are hydrogen and n is 2 to 20 or more. When only one (CH2CH2O)n radical is present then it should be 6 or more.

The polyoxyalkylene compounds described above have been used in photographic emulsions and while commercially useful show marked improvements when admixed with phytic acid and/or its alkali metal or ammonium salts inaccordance with this invention. The latter compounds have a synergistic eifect and the combinations confergreater sensitizing action than the compounds used alone. The combinations of the two classes of compounds (a) and (b) of this invention increase the sensitivity of silver halide emulsions throughout the whole range of the spectrum. The emulsions have lower fog levels upon aging than the polyoxyalkylene glycols and their ethers'and estersand mixtures with lowerglycols, e. g., ethylene and propylene glycol.

The invention will be further illustrated, but is not intended to be limited by the following examples wherein the emulsion preparation and subsequent operations are carried out in the substantial absence of actinic light.

Example I A washed undigested highly sensitive gelatin siliver halide emulsion containing approximately 1.5% silver iodide and 98.5% silver bromide was divided into 3 parts. To the first part was added 0.00202 mol of phytic acid per mol of silver, to the second part was added an equivalent number of mols of sodium hexametaphosphate (0.00202 mol of hexametaphosphate per mol of silver) and the third portion was reserved as a control. The pl-Is of the three portions were adjusted to 6.3 with 3-normal NaOH and the same digestion treatment was given to each portion. After digestion, each of the three portions was subdivided into two equal parts and to the first of each subdivision is added 0.050 gram of polyethylene glycol having an average molecular weight of 3600. The same remaining post digestion additions were then made to all six portions and'they were coated onto a suitable film base and dried. The coated filmswere then exposed, developed and fixed with the following sensitometric results:

as that in Example I, there was added 0.00202 mol of phytic acid per mol of silver and a second portion was used as the control. The pH of each portion was adjusted to 6.3 with 3-normal NaOH and the same digestion treatment was given to each portion. After digestion, each portion was subdivided into two equal portions and to one of the sub-portions was added 0.050 gram per gram mol of silver of a polyethylene glycol having an average molecular Weight of 3600. The same normal postdigestion additions were made to all four portions. The emulsions were coated onto a suitable film base dried and the coated films were exposed, fixed, washed and dried and tested and the following sensitometric data were obtained:

as that in Example I there was added 0.00126 mol of phytic acid per mol of silver and a like portion was reserved as a control. The pH'of each portion was adjusted to 6.3 with 3-normal NaOH and the same digestion treatmentjwas given to both portions. After digestion each portion was subdivided into two equal parts. To the first portion of each subdivision there was added 0.050 gram permol of silver of a polyethylene glycol having an average molecular weight of 3600. Other postdigestion additions were the same to all four portions. The emulsions were coated onto a suitable film base and dried. The coated films were exposed, fixed, washed and dried and tested. The following sensitometric data were obtained:

To one portion of a washed gelatino silver iodobromide emulsion having the sameconstitution as that in Example I there was added 0.00101 mole of phytic acid per mol of silver. A like portion was retained as control. The pH of each part was adjusted to the same value as in Example I and, both parts were given the same digestion treatment. After digestion, to each portion there was added a polyethylene oxide-ricinoleic acid ester having a molecular weight of approximately 1000 in an amount of 0.50 gram of .the ester per mol of silver. Other postdigestion additions were the same for both portions. The emulsions were-coated onto asuitable film base and dried. The coated films were exposed, fixed, washed and dried and tested. The following sensitometric data were obtained:

The invention is not limited to the preparation of colloid silver iodobromide emulsions as illustrated in the foregoing examples, but can be used in emulsions containing other simple or mixed silver halides, e. g., silver chloride, silver bromide, silver chlorobromide, silver chloroiodobromide, etc., emulsions.

Similarly, the invention is not limited to the use of gelatin as the peptizing or dispersing or binding agent for the silver halide grains. Thus various other water-permeable or hydrophilic colloids, including those having reversible characteristics, can be substituted for all, or a portion of the gelatin. Suitable additional colloids include agar agar, polyglycuronic acid, zein, colloidon, water-soluble cellulose derivatives, e. g., hydrolyzed cellulose acetate, cellulose lactate, cellulose glycollate, cellulose acid phthalate and its alkali metal salts; polyvinyl alcohol, partially hydrolyzed polyvinyl esters and polyvinyl acetals including those containing color former nuclei, polyamides (water-permeable), poly( 1,3-dioxolanes) polymethacrylic acids and copolymers thereof with other vinyl compounds, e. g., styrene, isobutylene, acrylonitrile, etc., and other synthetic or natural resins and superpolymers having hydrophilic or water-perrneable characteristics and which are capable of forming smooth, hard films.

The emulsions can, of course, be coated onto various types of film bases including cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose propionate, and cellulose nitrate and films made from superpolymers, e. g., nylon, polyethylene terephthalate, polystyrene, polyvinyl chloride and copolymers thereof, e. g., poly(vinyl chloride co vinyl acetate), etc., paper and any of the usual sheet supports used for making photographic films and papers.

The photographic films bearing above emulsions which contain phytic acid or an alkali or ammonium salt of phytic acid and the polyoxyalkylene compound can be used for various purposes including camera or portrait film, motion picture film, lithographic film, and X-ray film. The emulsions are especially useful in medical X-ray films and provide stable, high-speed medical X-ray films which have high block speeds and gammas and low fog values, even when stored for relatively long periods of time.

This invention has the advantage that it provides a simple and effective means for providing silver halide emulsions of high speeds and low development fog values. Another advantage is that it provides silver halide emulsions which have good stability upon aging. A further advantage is that the emulsion adjuvants are economical and their incorporation in emulsions does not require any tedious or involved procedure.

I claim:

1. A photographic emulsion comprising light-sensitive silver halide grains dispersed in a water-permeable colloid containing a small amount of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts and a small amount of a compound taken from the group consisting of water-soluble polyoxyalkylene glycol and its ethers and esters having a molecular weight of at least 400 containing at least one linear radical of the formula (CH2)m-O)n wherein m is a positive integer from 2 to 3 and n is a positive number from 7 to 200.

" 2. A photographic emulsion comprising light-sensitive "silver halide grains dispersed in a water-permeable colloid containing 0.0004 to 0.006 mol of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts and 0.03 to 1.5 grams of a compound taken from the group consisting of water-soluble polyoxyalkylene glycol and its ethers and esters having a molecular weight of at least 400 containing at least one linear radical of the formula (CH2)m-O)n wherein m is a positive integer from 2 to 3 and n is a positive number from 7 to 200, per mol of silver in said silver halide grains.

3. A photographic emulsion comprising light-sensitive silver halide grains dispersed in a water-permeable colloid containing 0.001 to 0.003 gram mol of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts and 0.03 to 1.5 grams of a compound taken from the group consisting of water-soluble polyoxyalkylene glycol and its ethers and esters having a molecular weight of at least 400 containing at least one linear radical of the formula (CH2)7n--O)n wherein m is a positive integer from 2 to 3 and n is a positive number from 7 to 200, per mol of silver in said silver halide grains.

4. An emulsion as set forth in claim 3 wherein said colloid is gelatin.

5. A photographic emulsion comprising light-sensitive silver halide grains dispersed in a water-permeable colloid containing from 0.0004 to 0.006 mol of phytic acid and 0.03 to 1.5 grams of a polyoxyethylene glycol having a molecular weight of at least 400 per mol of silver in said emulsion.

6. An emulsion as set forth in claim 5 wherein said colloid is gelatin.

7. A photographic emulsion comprising light-sensitive silver halide grains dispersed in a water-permeable colloid containing from 0.0004 to 0.006 mol of sodium phytate and 0.03 to 1.5 grams of a polyoxyethylene glycol having a molecular weight of at least 400 per mol of silver in said emulsion.

8. A photographic element comprising a sheet support bearing a layer of emulsion as set forth in claim 1.

9. The process of making a photographic silver halide emulsion involving precipitation, washing and digestion operations, the step which comprises admixing with said emulsion, at some stage prior to the completion of the final digestion operation a small amount of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts and after the digestion period a small amount of a compound taken from the group consisting of water-soluble polyoxyalkylene glycol and its ethers and esters having a molecular weight of at least 400 containing at least one linear radical of the formula (CH2)mO)n wherein m is a positive integer from 2 to 3 and n is a positive number from 7 to 200.

10. The process of making a photographic silver halide emulsion involving precipitation, washing and digestion operations, the step which comprises admixing with said emulsion, at some stage prior to the completion of the final digestion operation 0.0004 to 0.006 mol of a compound taken from the group consisting of phytic acid and its alkali metal and ammonium salts and after the digestion period 0.03 to 1.5 grams of a compound taken from the group consisting of water-soluble polyoxyalkylene glycol and its ethers and esters having a molecular weight of at least 400 containing at least one linear radical of the formula (CH2)m-O)n wherein m is a positive integer from 2 to 3 and n is a positive number from 7 to 200, per mol of silver in said silver halide grains.

References Cited in the file of this patent UNITED STATES PATENTS 1,574,943 Sheppard Mar. 2, 1926 1,591,499 Sheppard July 6, 1926 2,400,532 Blake May 21, 1946 2,423,549 Blake July 8, 1947 2,441,389 Blake May 11, 1948 OTHER REFERENCES Thorpe: Dictionary of Applied Chem, publ. Longmans Green & Company, New York, 1924, vol. V, page 281.

Claims (1)

1. A PHOTOGRAPHIC EMULSION COMPRISING LIGHT-SENSITIVE SILVER HALIDE GRAINS DISPERSED IN A WATER-PERMEABLE COLLOID CONTAINING A SMALL AMOUNT OF A COMPOUND TAKEN FROM THE GROUP CONSISTING OF PHYTIC ACID AND ITS ALKALI METAL AND AMMONIUM SALTS AND A SMALL AMOUNT OF COMPOUND TAKEN FROM THE GROUP CONSISTING OF WATER-SOLUBLE POLYOXYALKYLENE GLYCOL AND ITS ETHERS AND ESTERS HAVING A MOLECULAR WEIGHT OF AT LEAST 400 CONTAINING AT LEAST ONE LINEAR RADICAL OF THE FORMULA (-CH2)M-O)N WHEREIN M IS A POSITIVE INTEGER FROM 2 TO 3 N IS A POSITIVE NUMBER FROM TIVE INTEGER FROM 2 TO 3 AND N IS A POSITIVE NUMBER FROM 7 TO 200.