Copolymers and photographic emulsions containing the same

2,829,053

Patented Apr. 1, 1958

United States Patent Office

2,829,053

COPOLYMERS AND PHOTOGRAPHIC EMULSIONS CONTAINING THE SAME

Clay Weaver, Wilmington, Del., assignor ίο E. I. du Pont de Nemours and Company, Wilmington, Dei., a corporation of Delaware

No Drawing. Application November 8,1954 Serial No. 467,641

Claims. (Cl. 96—114)

This invention relates to photographic emulsions and more particularly to silver halide emulsions containing amine and quaternary ammonium derivatives of vinyl alcohol/allyl glycidyl ether copolymers.

Gelatin has generally been employed as the protective colloid for photosensitive silver halide since it has the ability to form a thin coating containing dispersed silver halide. Gelatin has good water permeability coupled with insolubility at relatively low temperatures. However, photographic emulsions based on gelatin are somewnat brittle, unstable, susceptible to decomposition by bacteria and fungi, difficult to maintain and process under conditions cf high humidity and temperature.

Considerable effort has been made to replace gelatin with a synthetic polymeric colloid binder and moderate success has been obtained with polyvinyl alcohols, and particularly the polyvinyl acetals that are soluble in hot water but insoluble in cold water. Amino acetals of polyvinyl alcohol have been employed as silver halide dispersing agents, as shown in U. S. 2,276,322. When such amino acetals are employed in synthetic colloid gelatin-free systems, the resulting photographic product generally does not have the light sensitivity exhibited by gelatin systems.

An object of this invention is to provide new synthetic colloid-silver halide emulsions. Another object is to provide such emulsions which have good sensitivity and speed characteristics. A further object is to provide such emulsions to which substantial amounts of water-permeable colloids can be added. A related object is to provide such emulsions which can be made ready for coating by the addition of substantial amounts of polyvinyl alcohol or water-soluble or hydrophilic acetals. Still other objects will be apparent from the folowing description of the invention.

It has been found that particularly useful photosensitive emulsions are obtained by the dispersion of a photosensitive silver halide in a protective colloid system that is substantially gelatin free and contains at least 1% and preferably 10-50% or more of an ammonia, monoamine, or quaternary ammonium derivative of a hydrolyzed polyvinyl ester/allyl glycidyl ether copolymer in which the copolymer ratio of allyl glycidyl ether to vinyl ester groups is within the range of from Vis to !4.

The hydrolyzed copolymers just described, by reason of the large initial proportion of vinyl ester units, may be called amine- or quaternary ammonium-modified polyvinyl alcohols. They are 98 to 100% hydrolyzed and consist essentially of recurring intralinear units of the formulae:

-CHj-CH2.

⁴ (I) ' and —CHiCH— I CHj

- i H ⁸ I· J.

CHa— CH- CH 4 4 (II) j₀ wherein A is a member taken from the group consisting of —OH and esterified —OH, the esterification being in an amount from 0% to 2% based on the weight of the copolymer, and one of the radicals X and Y is hydroxyl (—OH) and the other is an amino or trialkylamino 15 cation radical ((alkyl) A

-N ) cation /

These hydrolyzed copolymers are new compounds and are obtained from vinyl ester/allyl glycidyl ethers by reaction with ammonia or a monoamine followed by hydrolysis of the ester groups to hydroxyl groups. The hydrolyzed copolymers will contain 94% to 51% by 25 weight of —CH₂—CHOH— groups, 6% to 49% by weight of groups of Formula II and 0% to 2% of vinyl ester groups.

The photosensitive compositions can be prepared by precipitating light-sensitive silver halide in an aqueous 30 solution of the hydrolyzed copolymers described above or by admixing an aqueous dispersion of silver halide with an aqueous solution of such copolymers. The resulting solution can be admixed with or bulked up with additional copolymer or with a different water-permeable 35 colloid and made ready for coating on a suitable sheet support, e. g., film or paper, by admixing therewith a sensitizing dye or dyes, color-former, sulfur sensitizer and other emulsion adjuvants. Thus, the solutions can be admixed with polyvinyl acetal color-formers to form 40 color-forming emulsion layers.

The following, examples, in which the parts are by volume unless specified by weight (in which case the amount corresponds to the weight of the same volume of water), illustrate the preparation and properties of the photographic emulsions of this invention. The silver halide emulsions and coatings, of course, are made in the substantial absence of actinic light.

Example I 50

A solution containing 50 parts of a 2.5% solution of the quaternary ammonium-modified polyvinyl alcohol prepared by hydrolysis from vinyl acetate/allyl glycidyl ether of 91.4/8.6 composition (described in Webers U. S. ,_r Patent 2,676,166) and dimethylaminoacetamide, 23 parts of 3 N ammonium bromide, 1.2 parts of 0.5 N potassium iodide and 50 parts of water is treated with a solution of the soluble complex formed by adding 20% ammonium hydroxide to 10 parts 3 N silver nitrate until the θθ precipitate which is originally formed is completely redissolved and 50 parts of water. The emulsion is ripened at 40° C. for one hour or more, coagulated with acetone and the coagulum washed by decantation. Fifty parts (by weight) of a 5% solution of completely hydrolyzed 05 polyvinyl alcohol, having a viscosity between 12 and 50 poises, is added and the emulsion is stirerd at 70° C. for 30 minutes. The viscosity is reduced by dilution with 20% ethanol, if desired, a surface-active wetting agent is added and the emulsion is coated on paper or a trans70 parent film base. When the film is exposed and proc.

2,829,083 essed by standard photographic methods, a black and white image of good gradation is obtained and the photographic speed of the emulsion is found to be four times as fast as a control emulsion made in completely hydrolyzed polyvinyl alcohol without the amine-modified polyvinyl alcohol.

Example II

Photographic silver halides are prepared as described in assignee’s Weaver application Ser. No. 362,151, filed June 16, 1953, now U. S. Patent No. 2,752,246, by stirring a solution consisting of 46 parts of 3 N ammonium bromide, 2.5 parts 0.5 N potassium iodide, 50 parts of distilled water and 25 parts of a 10% solution of the condensation product of 20 moles of ethylene oxide with 1 mole of oleyl alcohol and adding a solution consisting of the soluble complex formed by adding 20% ammonium hydroxide to 20 parts of 3 N silver nitrate until the precipitate which is originally formed is completely redissolved and sufficient distilled water to make a total volume of 250 parts. The silver halides are ripened by stirring slowly at 30° C. for 30 minutes. The precipitate of silver halides is allowed to settle and separated by decantation and washed with water, again allowing to settle and decanting. To Vz of the silver halide precipitate is added a solution consisting of 5 parts (by weight) of the quaternary ammonium-modified polyvinyl alcohol derived from a vinyl acetate/allyl glycidyl ether copolymer (91.4/8.6) and a mixture of dimethylaminoacetamide and triethylamine (1/3) followed by hydrolysis, dissolved in 10 parts of ethanol and 25 parts of water. The dispersion is stirred for one hour at 30° C., treated with 70 parts of a 5% aqueous solution of completely hydrolyzed polyvinyl alcohol, having a viscosity between 12 and 50 poises, and stirred an additional hour at 60° C. Coating aids are added, the viscosity of the emulsion is adjusted by adding 20% ethanol, and a coating is made on a transparent film support. When photographic exposure and processing is carried out according to standard photographic procedure, the speed of this film is about ten times that of a control emulsion in which the second half of the silver halides was dispersed in polyvinyl alcohol alone and no quaternary ammonium-modified polyvinyl alcohol was employed.

Example III

A mixture of 200 parts of isopropyl alcohol and 100 parts of a 55.5% solution of a vinyl acetate/allyl glycidyl ether copolymer (4.6% allyl glycidyl ether) in methyl ethyl ketone is stirred at room temperature and treated with a solution of 8 parts (by weight) of triethylamine in 50 parts of isopropyl alcohol and 5 parts of distilled water. The reaction mixture is heated under reflux for 5 hours to bring about amination (quaternization) of the glycidyl ether groups. Hydrolysis of the vinyl acetate groups is accomplished by adding a solution of 10 parts (by weight) of sodium methylate in 50 parts of isopropyl alcohol and stirring at room temperature for 15-30 minutes. Alternatively, the hydrolysis can be carried out. by adding the polymer solution to a methanol solution of sodium methylate. The product is separated by filtration and purified by dissolving in a small amount of water and precipitating with methanol and acetone. The product is finally washed with methanol ’and acetone and when dried, about 40 parts (by weight) of slightly yellow-colored polymer is obtained. From the nitrogen content of the polymer, 76% of the allyl glycidyl ether groups in this polymer are substituted with quaternary ammonium groups.

Silver halides are prepared as described in Example II and the precipitate retained after decantation is treated with 10 parts of a 5% aqueous solution of the hydrolyzed quaternary copolymer, and a suitable sulfur sensitizer and stirred, at 40“ C. for. 15 minutes. The dispersion is treated, with 150 parts of a 5% solution of a yellow color-forming polyvinyl acetal (i. e., one of those de4 scribed in the examples of U. S. Patent 2,465,067) and stirred at 50° C. for 15 minutes. The viscosity of the emulsion is adjusted with 20% ethanol, 4 parts of a 1% solution of C-cetyl betaine (coating assistant) and an 5 antifogging agent are added and the emulsion is coated on a transparent support. Exposure in a camera and standard photographic processing produces negatives of good gradation from which acceptable photographic prints can be made.

⁷⁸ Example IV

A solution consisting of 100 parts (by weight) of a 65% solution of vinyl acetate/allyl glycidyl ether copolymer (95/5) in methyl ethyl ketone, 200 parts· of ]5 methyl ethyl ketone and 5 parts of water is stirred at 25-30° C. while 10 parts (by weight) of trimethylamine is introduced from a cylinder. The reaction mixture is stirred for one hour then heated to 60-70° C. for 3 hours. During the heating cycle a slow stream of tri20 methylamine is introduced into the reaction mixture. After standing overnight at room temperature, heat is again applied to expel excess amine, 300 parts of methanol is added and the polymer is hydrolyzed by pouring it into a solution of 20 parts (by weight) of sodium 25 methylate in 200 parts of methanol as described in Example III. Analysis for nitrogen indicates that approximately 93% of the glycidyl groups are substituted with trimethylamine groups.

When preformed silver halide grains are treated with 30 a solution of the trimethylamine-modified polyvinyl alcohol as described in Example III, improvement is obtained in speed, gamma and fog values as compared with’control emulsions containing no amino polymer.

Example V

A solution of 100 parts (by weight) of vinyl acetate/allyl glycidyl ether (95/5) copolymer solution (65% in methyl ethyl ketone), 200 parts of methyl ethyl-ketone and 5 parts of water is stirred at room temperature, 40 and 20 parts (by weight) of gaseous dimethylamine introduced. The mixture is refluxed under a constant stream of dimethylamine for one hour, allowed to stand for 12 hours at room temperature and is again saturated, with dimethylamine and heated under reflux for 3 hours. Excess dimethylamine is removed by evaporation and-the ⁰ polymer is hydrolyzed as described in Example IV.

When the dimethylamine-modified polyvinyl alcohol is employed in. a photographic emulsion-as described in: Example. Ill, the speed, gamma and fog values are? considerably improved over those of a. control, emulsion ⁰⁸ containing no amine polymer.

Example VI

The amine of Example III is replaced by an equivalent amount of methylamine and the reaction mixture is stirred ³³ and refluxed while a slow stream of methylamine is introduced during a period of 6 hours. The reaction mixture is allowed to stand overnight and refluxed an additional hour. The aminated copolymer is hydrolyzed and isolated as described in Example ΠΙ. Analysis for nitro⁸⁰ gen indicates that about 78% of the glycidyl groups are converted to methylamino groups. When the amino polymer is employed in the preparation of a photographic emulsion utilizing preformed silver halides as described in Example III, emulsion coatings are obtained which 6° can be exposed and processed to images of good density and gradation which are superior to a control emulsion containing no amino polymer.

Example VII

A mixture of 100 parts (by weight) of vinyl acetate/ allyl glycidyl ether (95/5) polymer solution (66% solids in methyl ethyl ketone), 105 parts of isopropyl alcohol and 100 parts of concentrated ammonium hydroxide is stirred at room temperature for one hour and allowed 7ό to stand overnight. After heating at 70-75° C. for one

2.829.063 liour, the reaction mixture is concentrated under partial vacuum to remove ammonia and solvent. Isopropyl alcohol (100 parts) is added and the solution again concentrated under vacuum. Methanol (200 parts) is added and the copolymer is hydrolyzed and isolated as described in Example III. Analysis for nitrogen indicates that about 81% of the glycidyl ether groups are substituted by amino groups. When the polymer is tested in a {photographic emulsion as described in Example III, coatings are obtained which have markedly improved speed, gamma, fog and density characteristics as compared to a control emulsion containing no amino polymer. , The copolymer of allyl glycidyl ether and a vinyl ester, preferably vinyl acetate, employed in the preparation of the hydrolyzed amine-modified or trialkylamino-cation modified polyvinyl esters consists of from 3 to 30% of the allyl glycidyl ether and from 70 to 97% of vinyl acetate (this corresponds to a molar ratio of between 1/45 to 1/3). The preferred copolymers contain 5 to 20% of allyl glycidyl ether and 80 to 95% of vinyl acetate, or on a molar basis of between 1/30 to 1/5. The copolymers are prepared by polymerizing together in suitable proportions allyl glycidyl ether and vinyl acetate in a homogeneous medium in the presence of a free radical-generating catalyst, e. g., benzoyl peroxide. The monomers are generally converted to copolymers in high yields, e. g. 7599%. The resulting copolymers have molecular weights of the order of 1000 to 10,000. These copolymers and their preparation are described in assignee’s Rothrock and Wilkinson application Ser. No. 415,682, filed March 11, 1954, which is a continuation-in-part of assignee’s application Ser. No, 218,884, filed April 2, 1951, now abandoned, and in Webers U. S. Patent 2,676,166.

The allyl glycidyl ether copolymer obtained as described above contains epoxy or oxirane groups. Ammonia and monoamines react with the epoxy group to give polyamines which contain an alcoholic hydroxyl group on the carbon adjacent to the carbon bearing the amino group. The following equations illustrate (1) the reaction of a hydrogen-bearing amine with the epoxy group and (2) the reaction of a tertiary amine with the epoxy group in the presence of an acid:

—A---A— + RNHa ---> — A- A—

V OH NHR (1) . — A—-- A— + r₃n + hx —» —A—A—

Ah jAr₃+x~ (2)

In the above equations R represents an organic radical, i. e., a hydrocarbon radical or a substituted-hydrocarbon radical wherein the substituent is unreactive with epoxy groups and HX is an acid which is preferably inorganic.

The monoamines which can be employed in the reaction can be represented by the formula NR^R, wherein Ri, R₂ or R₃ are hydrogen or organic radicals as described above and preferably alkyl of 1 to 5 carbon atoms or -acetamido. When the R’s are hydrogen, the compound is ammonia and when two are hydrogen, the compound is a .primary amine, e. g., ethylamine, propylamine, butylamine, pentylamine, and benzylamine. When only one of the R groups is hydrogen, the compound is a secondary amine and useful amines of this class include dipropylamine, dibutylamine, and diamylamine. Tertiary amines that can be employed include tri-n-octylamine, 2-ethylpyridine, and dimethylaminodimethylacetamide.

The amines employed have only one basic nitrogen group per molecule. The basicity equivalent corresponds to an ionization constant of at least 1 χ 10~⁹. The nitrogen-containing compounds included preferably contain no more than 24 carbons and generally less than 8 carbons. Preferably they are saturated (i. e., free from ethylenic unsaturation). In the reaction, at least 0.5 equivalent of ammonia or amine is present per epoxy group. Generally the amine is present in considerable excess, with 2 to 5 or more equivalents of amine per epoxy group usually being employed. Inert solvents or diluents can be present but are not necessary.

When a tertiary amine is reacted with an epoxy-containing polymer in the absence of an acid or under basic 5 conditions, the quaternary formed is obtained as the hydroxide. In the presence of acid, a quaternary salt is formed. When ammonia, a primary or secondary amine is the reactant, the resulting product is a primary, secondary or tertiarj' amine, respectively. In the presence 10 of acids having a dissociation constant of at least 1X IO^-5, the latter copolymers are in the form of acid salts of the amines. However, when used in photographic emulsions, the acid salts generally are not present, unless the pH of the emulsion is less than 6, which is not usually the 15 case.

For the purpose of the present invention, i.e., the production of superior silver halide emulsions, at least 50% and preferably at least 75% of the epoxy groups are reacted with ammonia or an amine. The resulting 20 polymer has a nitrogen: content of generally between 0.3 and 5 % by weight. The preparation of the quaternaries is described in Webers U. S. Patent 2,676,166, while the ammonia and hydrogen-bearing amine derivatives are described in Cupery U. S. application Ser. No. 295,127. 25 Any of the specific copolymers described in the patent and application can be used to make the hydrolyzed products used in accordance with this invention.

When the polyvinyl esters containing amine or quaternary ammonium groups as aforedescribed, are subject 30 to hydrolysis (including alcoholysis), particularly by alcoholic alkali or an alkali metal alcoholate in alcohol, substantially all (98-100%) of the ester groups in the polymer are replaced by hydroxyl groups, i. e., the vinyl ester units become vinyl alcohol units, i. e., ³⁵ — CH₂—CH(OOCalkyl)— becomes — CH₂—CHOH—.

The hydrolyzed copolymers form thin layers which are strong, smooth, coherent, but freely water-permeable. They are soluble in hot water and water containing 10% or more, by weight, of ethanol. The hydrolyzed copolymers are also useful as water-permeable colloid binding agents in filter and anti-halation layers in photographic films and as textile sizing agents.

The photographic emulsions of this invention contain silver halides in dispersed form in the hydrolyzed vinyl ester/allyl glycidyl ether-amine or quaternary derivative. They are prepared by dispersing precipitated light-sensitive silver halides in an aqueous medium which 50 contains 1-5% or more on a weight basis of the amine or quaternary ammonium polymeric material. The emulsions which contain the silver halide and polymer, of course, are prepared and coated on a film support in the substantial absence of actinic light.

The emulsions of this invention may be coated onto various types of rigid or flexible supports, e. g., glass, paper, metal, films, super-polymers, resins, cellulose derivatives, etc. Suitable materials include paper, aluminum, polymethacrylic acid methyl and ethyl esters, vinyl 60 chloride polymers, polyvinylacetals, nylon, polyesters, e. g., ethylene glycol-terephthalic acid polymers, cellulose acetate, cellulose nitrate, cellulose propionate, etc.

The hydrolyzed copolymers of this invention are not only useful as the sole protective colloid in photographic 65 silver halide dispersions or emulsions but can be advantageously used in the preparation of silver halide dispersions or emulsions to be bulked with another colloid prior to coating in the form of a photographic layer. For example, the initial silver halide dispersion can be admixed 70 with a different bulking colloid, e. g„ gelatin, a watersoluble or water-permeablle polyvinyl alcohol, polyvinyl acetal, cellulose derivative, polyamide or other synthetic resin or superpolymer. Suitable polyvinyl acetals which can be admixed with the hydrolyzed Copolymers of this 75 invention, include hydrophilic o-sulfobenzaldehyde and

2,829,053 benzaldehyde polyvinyl acetals which contain a large number Of recurring intralinear.

—CH₂—CHOH— groups and hydrophilic polyvinyl acetal color formers containing such latter groups and color former nuclei. Suitable polyvinyl acetals of the just mentioned types are described in the Journal of the American Chemical Society, vol. 73, pp. 4930-4 (1951) and in U. S. Patents 2,310,943, 2,320,422, 2,397,864, and in British Patents 535,341 and 598,47/. The methacrylamide/acrylic acid and related copolymers described in U. S. Patents 2,311,548, 2,592,107 and 2,611,763 are examples of other specific copolymers which can be admixed with the hydrolyzed copolymers of this invention.

Another advantage of the invention is that it enables one to prepare silver halide dispersions or emulsions with sensitive well-formed grains and in the absence of gelatin. The silver halide emulsions are uniform in properties and have a high degree of photosensitivity for gelatin-free systems. Still further advantages of the invention will be apparent from the above description.