US2380033A - Photographic elements containing polyvinyl acetal color formers - Google Patents

Description

PHOTOGRAPHIC s PATENT OFFICE POLYVINYL ACETAL COLOR FOBMERS George Lowrance Dorough, Niagara Falls, N. Y.,

and David Malcolm McQueen, Newark, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware i No Drawing. Original application March 24, 1942, Serial No. 436,056. Divided and this application --May 17, 1944, Serial No. 536,026. In Canada April 15, 1941 6 Claims.

(Cl. 95-in- This invention relates to photography and more particularly to photographic color processes and compositions and elements useful therein. Still more particularly it relates to photographic color processes, compositions and elements wherein polyvinyl acetals are used as dye intermediates or color formers. Still more particularly it relates to water-permeable colloid layers comprising as an essential dye component a polyvinyl acetal capable of reacting with a diazo compound to form a dye. The invention further relates to developer and treating solutions containing such -acetals and to their preparation and use, particularly in photographic development processes.

This invention has for an object the provision of new and useful photographic compositions containing dye intermediates or color i'ormers which are immobile in water permeable colloid layers, such as gelatin layers.

A further object is to provide photographic compositions and elements which contain novel polymeric dye intermediates; A still further object is to provide a new photographic color process,especial1y a photographic color development process involving the use of polyvinyl acetals. Another object is the. preparation of photographic emulsions which contain new and improved water-soluble dye intermediates or color formers which yield dyes by coupling with the oxidation products of photographic developing agents or by treatment with aromatic or heterocyclic dlazo compounds. Other objects are to provide alternative photographic compositions and processes and to contribute a general advance in the art. Still other objects will be apparent from the following description of the invention.

The above objects are accomplished by the preparation and use of photographic compositions and elements containing polyvinyl acetals which are capable of reacting with a diazo compound to form a dye.

In a more limited sense, they are accomplished ylene group. The ortho or para positions may be reactive by being unsubstituted or by having a. replaceable group such as a halogen atom, e. 3., chlorine or a sulfonic acid group. One or more of such groups may be present.

In one important aspect of the invention, it involves the preparation and use oi. photographic compositions, e. g., colloid layers, light-sensitive emulsion layers and coating compositions therefor, and developer solutions containing polyvinyl acetals which are soluble in dilute alkaline solu tions and are capable of coupling with diam. compounds to form a dye.

The acetals of this invention, because of their structure and the'nature of the, aldehyde nuclei, couple with diazo compounds to form a dye. As examples of such latter compounds, mention is made of the diazonium salts, syndiazotates, diazoanhydrides and diazo inner salts oi the general formula A--N=NX, wherein A is an aromatic or an unsaturated heterocyclic residue or compounds resulting from intramolecular elimination of HX therefrom. X may suitably be OH, or salts thereof, such as ONa, OK and ONH4, or salt forming anions, such as Cl, Br-, N03", and SO3H Elimination oi. HX. is exemplified by diazotized oaminopheno1 of the formula and by diazotized sulianillc acidof the :iormula (G The acetals furthermore react with the oxidation products of an aromatic amino developing agent under conditions of the usual photographic development processes to form a dye. 111eacetals which contain as solubilizing groups carboxylic or sulfonic acid groups constitute the preferred embodiment of the invention. These groups need not be present in the nuclei containing color iorming groups which are joined through acetal linkages to the polyvinyl alcohol nuclei, but may be in radicals free from color forming groups Joined to the latter nuclei through acetal linkages.

The dye-forming polyvinylacetals of this in vention are conveniently prepared by the following general manner. I acting polyvinyl alcohol under conditions suitable for the formation ofan acetal, with an aldehyde capable of reacting with a diazocompound to One method comprises reproduce a dye. The most important of such aldehydcs are ,those containing an aromatic nucleus on which is substituted a phenolic hydroxyl,

amino, including unsubstituted and substituted amino groups, e. g., alkylamino, arylamino, or mixed alkylarylamino group, at least one of the positions oriented by such groups (OlthO and para) being reactive. Thus the positions may be unsubstituted or have a replaceable group, 0. g., chlorine, sulfonic acid, etc. Other suitable aldehydes are those having active methylene groups, such as, for example, those containing pyrazolone and acetoacetamino groups.

The polyvinyl acetals just described are also capable of reacting with the oxidation products of photographic aromatic primary amino developing agents to form azomethine or quinone-iminedyes including indophenol. indoaniline, and indamine dyes.

An alternative method comprises reacting an aldehyde which does not have the above-described structurewith a polyvinyl alcohol and then chemically modifying the acetal so that it has the desired structure. The methods are illustrated below.

These polymeric dye intermediates may be incorporated in a colloid binding agent including a light-sensitive emulsion and coated on a support by any of thegeneral or known methods to form an element having a light-sensitive or photographic layer. After exposure, the intermediates are converted into dyes, 'for example, by development of the images produced with a color-forming developer, such as p-aminodicthylaniline, or by some other suitable procedure such as a treatment with aromatic diazo comble of forming water-permeable films or layers such as gelatin, agar agar, or polyvinyl alcohol by forming aqueous or alcoholic dispersions or emulsions of the same and coating them upon a support which maybe a transparent or nontransparent support or film base. Suitable supports include cellulose derivatives, e. g., cellulose acetate, cellulose nitrate, cellulose -aceto-propionate, etc., synthetic resins, e. g., polyvinyl acetals such as polyvinylisobutyraldehyde acetal: polymeric compounds such as nylon and paper, etc. The layers may be deposited on a subbing layer which is used to anchor silver halide emulsion layers on a film base or on another colloid layer which may be a gelatin silver halide layer. One or more of such layers containingone or. more of the novel polyvinyl acetals hereof may be present in the resulting element. v

The polyvinyl acetals hereof may be incorporated into colloid compositions containing lightsensitive materials, e. g., silver halides and photographic layers formed on suitable supports as described-in the preceding paragraph. A plurality of such layers may form a multilayer photographic element. the respective layers should, however, be'capable of forming different colored azo and/or azomethine or quinoneimine dyes.

The invention will be further illustrated but is not intended to be limited by the following examples in which the parts stated are parts by weight.

Example 1 Thirty-two parts of polyvinyl alcohol, 45 parts The polyvinyl acetals of 2,sso,osa

of salicylaldehyde, 525 parts 0! glacial acetic acid, and 5 parts of 85% phosphoric acid were stirred and heated at -70 C. for nine hours. The reaction product obtainedin translucent solution was precipitated by addition of ethanol and water and was washed successively with water and methanol and was dried. The yield 0! dry product amounted to 39 parts. This resin, when placed in a photographic emulsion, e. g., a

,gela'tino-silver-iodo-bromide emulsion, exposed and developed with p-aminodiethylaniline, gave a blue-green image. This color is presumably due to coupling with an oxidation product of the developer at the free, position para to the phenolic hydroxyl, giving an indophenol. dye of the probable structure (assuming polyvinyl alcohol to be a 1,3-glycol) CzHs Example 2 The same ingredients as in Example 1 were used. However, after stirring and heating for four hours at 60-70" C., 4.5 parts of isobutyraldehyde was added. On heating one hour further, the translucent, hazy solution at first obtained became clear. The resin was worked up in the manner described under Example 1 and was found to have the same properties in regard to dye formation, but was of lower softening point and enhanced solubility.

Example 3 Twenty-two parts of polyvinyl alcohol, 23 parts of redistilled salicylaldehyde, 250 parts of glacial acetic acid, and 2 parts of 85% hosphoric acid were heated and stirred at C. for four and one-half hours, at which time a milky solution had formed. Nine and four-tenths parts or phthalaldehydic acid was then added and heating was continued -for three hours further. The

' resin was precipitated by addition of ethanol and water and was washed successively with water and methanol and was dried. The yield of dry product amounted to 26 parts. This resin is soluble in aqueous alkali and may thus be suitably introduced into photographic emulsions. When a silver halide emulsion, e. g.,- a silveriodobromide emulsion containing thisproduct is coated on a suitable support, is exposed and developed with p-methylaminophen'ol, a black and white negative is obtained. Subsequent development, after re-exposure, with paminodiethylaniline gives a blue-green positive after removal of silver and silver salts. The dye thus obtained, in common with those from the resins of Examples 1 and 2, transmits little or no red light and is thus eminently suitable for use in subtractive processes of color photography.

' In spite of its solubility in dilute alkali, the dye is not at all removed by the alkaline processing baths and may even b leached for long periods in 5% sodium carbonate solution without removal.

Example 4 Twenty-two parts of polyvinyl alcohol, 250 parts of glacial acetic acid, 23 parts of salicylaldehyde, 9.4 parts of phthalaldehydic acid, and 4 parts of phosphoric acid were heated and stirred on a water bath maintained at 65 C. for five and one-quarter hours. A clear, light .yellow solution was obtained from which the resin was precipitated by the addition of methanol. Aiter Washing several times with methanol and cold water, the product was dried in a vacuum oven.-

Twenty-tour parts or white, finely divided resin were obtained. The product was dissolved in dilute alkali and coated in a photographic silver halide emulsion sensitive only to blue light. After exposure and development'with p-methylamino-phenol and fixation, a yellow dye was produced throughout the, whole film by treatment with diazotized p-nitraniline. The film may then be differentially bleached by any selective bleaching process, e. g., according to the process of 'Christensen (c. 1. Br. Patent 133,034 or United States Patent 1,517,049). After removal of the silver image there will remain a yellow positive image.

' Erample 5 Forty-four parts of polyvinyl alcohol, 46 parts of m-hydroxybenzaldehyde, 500 parts of glacial,

acetic acid, 18.4. parts of phthalaldehydic acid.

' and 8 parts of 85% phosphoric acid were stirred At this and heated at 65 C. for eleven hours. time 1.6 additional parts of 85% phosphoric acid was added and heating continued for ten hours further. Most of the resin at this stage was in the form of a gelatinous mass. This was dissolved in dioxane and reprecipitated in fibrous'form with water. After washing the product with water and aqueousmethanol and drying, 58 parts of resin were obtained. Treatment with oxidized .p-aminodiethylaniline gave a blue-green dye.

Example 6 a Eight parts of polyvinyl alcohol, 84 parts of glacial acetic acid, 8 parts of o-nitrobenzaldehyde,

6 parts of phthalaldehydic acid, and 3.2 parts of 85%- phosphoric acid were heated and stirred at 65 C, for five hours. The resin was precipitated by addition of methanol and cold water and was.

CHIC 0 01110 O -HN -cmononlon- COOH After reprecipitating with acetone, washing, and drying, the product was introduced into a photoa,sso,oss

graphic silver halideemulsion which was subsequently coated on a celluloseacetate film. ex-

posed and developed with p-aminodimet-hyianiline, a yellow dye being formed.

Example 7' v Twenty-two parts of polyvinyl alcohol was suspended in 250 parts of glacial acetic acid. To

this were added 15.5 parts of 2-hydroxy-3- methylbenzaldehyde, 19 parts of phthalaldehydic acid, and 4.3 parts of 85% phosphoric acid and" the mixture was heated on a water bath at 65 C. with vigorous stirring for 11 hours. At the end of this time a thick translucent solution had formed. The resin was precipitated from the solution with methanol and was washed in methanol and in water. Upon incorporation of the acetal in an emulsion after the manner v set forth in Example 6, and after subsequent exposure and development with p-aminodliethylaniline, a blue-green color was formed.

Example 8 I In place of the 2-hydroxy-3-methylbenzaideof the preceding example, 12 parts of 3-chlor-2- hydroxybenzaldehyde was used. After 5 hours heating at 65 C. the resin was precipitated from the reaction mixtureand washed with methanol and water. Upon incorporation of the acetal in an emulsion and after treatment of the emulsion as set forth in Example 6, a blue-green color was formed.

1 Example 9 The procedure of Example 7 was carried -out,

using the following quantities of reactants:

- Parts Polyvinyl alcohol 22 5-chlor-2-hydroxyhenzaldehyde 20 Phthalaldehydic acid 19 Glacial acetic acid 250 phosphoric acid Five and a halt hours heating at 65 C. on a water bath was required to complete the reaction. The reaction product was precipitated with methanol, washed with methanol, then with water. This yielded a white solid soluble in dilute alkaline solutions. The acetal was incorporated in a silver halideemulsion which was treated after the manner set Iorth in Example 6, whereupon a bluegreen color was formed.

Example 10 Twenty-five parts of 3-ailyl-2-hydroxybenzaldehyde, 19 parts of phthalaldehydic acid, 22 parts of polyvinyl alcohol, 250 parts of glacial acetic acid and 8.5 parts of 85% phosphoric acid were stirred and heated on a water bath at a temper.- ature of 6540 C. for 7.5 hours. At the end of this time a clear, homogeneous solution was obtained; The resin was precipitated by addition of methanol, was redissolved in dioxan, and was finally precipitated in fibrous form by pouring into water. The product was thoroughly washed in water and dried. The polyvinyl acetal was soluble in aqueous alkali and, when incorporated in a photographic silver halide emulsion, a bluegreen image was formed after exposure and development with p-aminodiethylaniline.

Example 11 Sixparts of 1-hydroxy 2-naphthaldehyde, 4 parts of phthalaldehydic acid, 6.5 parts of polyvinyl alcohol, 63 parts of glacial acetic acid and 3.4 parts of 85% phosphoric acid were heated and stirred on a water bath at a temperature of 65-70 C. for 10-hours. The resin was then precipitated by stirring in methanol and was washed thoroughly with methanol and finally with water. The polyvinyl acetal was found to be soluble in dilute alkali and, when incorporated in a photoa graphic silver halide emulsion which was exposed and developed with p-amino-diethylaniline, a blue-green picture was obtained.

Example 12 A mixture of 33 parts of 3,5-dichlorosalicylaldehyde, 22 parts of polyvinyl alcohol, 263 parts of glacial acetic acid and parts of 85% phosphoric acid was stirred and heated on a water bath at 85 C. for one hour. At the end of this time the mixture was a clear homogeneous solution.

Twenty-five parts benzaldehyde-o-sodium sulfonate of 58.6% purity was then added and the mixture was heated one hour further under the same conditions. The resin was precipitated by adding acetone, was washed with acetone, and was dried. Forty-three parts of a white solid, readily soluble in dilute sodium carbonate solution, was obtained. This may be incorporated into a photographic silver halide emulsion and processed after the manner of Example 1.

Example 13 A mixture of 36 parts of 3,5-dichlorosalicylaldehyde, 10 parts of phthalaldehydic acid, 22 parts of polyvinyl alcohol, 236 parts of glacial acetic acid, and 6.8 parts of 85% phosphoric acid was stirred and heated at 70 C. for eight hours. At the end of this time an additional 3.4 parts of 85% phosphoric acid was added and heating was continued for two hours further. At the end of this period this product was a very viscous solution. The

resin was preciptated by adding methanol and was washed with methanol and finally with water. After drying in air, a white solid was obtained which was readily soluble in dilute sodium carbonate solutions. This may be incorporated into a photographic silver halide emulsion and processed after the manner of Example 1.

. Example 14 Example 15 Eighty-eight parts of polyvinyl alcohol, 945

' parts of glacial acetic acid, 122 parts of salicylaldehyde and 16.9 parts of 85% phosphoric acid were mixed in a reaction vessel surrounded by a water bath. With continuous stirring the mixture was heated to a bath temperature of 8590 C. and held there for 3.5 hours. Sixty parts benzaldehyde-o-sodium sulfonate of 50.1% purity was then added and heating and stirring were continued for one hour further at the same temperature. After precipitating the reaction product with acetone, washing thoroughly with acetone and drying, 140 parts of a light-colored resin was obtained. This polymer is completely soluble in five per cent sodium carbonate soiution.. This may be incorporated into a photographic silver halide emulsion and processed after the manner of Example 1.

Example 16 cipitated by adding acetone and after washing and drying, a light-colored powder was obtained. This polymer was soluble in water, dilute alkaline solutions and in water-alcohol mixtures. This may be incorporated into a photographic silver halide emulsion and processed after the manner of Example 1.

The term "polyvinyl alcohol has been used herein to designate a substantially completely hydrolyzed polyvinyl ester. The acetal formation may also be carried out with a partially hydrolyzed polyvinyl ester. The acetals may also be conveniently prepared in one step from a polyvinyl ester by a simultaneous hydrolysis and acetalization. They may also be prepared from a mixture of aldehydes by simultaneous or stepwise reaction. An important modification of the process of acetal formation consists in using a process of acetal interchange. in the following example.

Example 17 Nine parts of polyvinyl alcohol, 15 parts of salicylaldehyde. 6 parts of the diethyl acetal of glyoxylic acid, 105 parts of glacial acetic acid and 6.8 parts of phosphoric acid were stirred and heated together on a water bath at'65-70" C. for six hours.

ter. After drying in air overnight the product was found to be soluble in dilute aqueous alkali and to yield a blue-green color upon development with oxidized p-aminodiethylaniline.'

Example 18 phosphoric acid were added. After continued stirring-at 85 C. for 1 hour, parts of benzaldehyde ortho-sodium sulfonate were added and the reaction mixture was stirred at 80 C. for an additional hour. The reaction product was then precipitatedby means of acetone, the resin was washed with acetone and dried. Two hundred parts of a light orange-colored product were obtained which dissolved completely in 5% sodium carbonate. The product is a polyvinyl acctal with the benzaldehyde ortho-sodium suifonate and the reaction product of the amino pyrazolone with. "the beta-chloro-propionaldehyde acetal and has the following probable color-forming unit structure:

This is illustrated The reaction product in the obtainedviscous solution was, precipitated by stirring in aqueous methanol and was then washed with wa-' A 20 part sample of this resin can be dissolvedin50 parts of 4% sodium carbonate and when this is incorporated in a silver halide emulsion sensitive to green light and processed as in Example 1, a magenta. dye image is obtained.

Other polymeric color formers which have been found as a result of this invention to be of value in color photographic processes are the polyvinyl acetals of 1,4-hydroxynaphthaldehyde, 3-dimethylaminobenzaldehyde, 4 hydroxy 3. methoxybenzaldehyde, l- (3-formylphenyl) -3-methyl'-5- pyrazolone, l-(bformylphenyl)-3-methyl-5-pyrazolone and 1 '(2 formylphenvll Y pyrazolone, 0-, m-, and p-acetoacetaminobenzaldehyde, 3-brom-2-hydroxybenzaldehyde, 2 hydroxy-3-nitrobenzaldehyde, fi-hydroxy-Z-methylben'zaldehyde, and 2-hydroxy-5-methylbenzaldehyde. The acetals may be suitably prepared from aldehydes in which the aldehyde group is not directly substituted on the aromatic nucleus,

' for example, as in the polyvinyl acetal of phydroxyphenylacetaldehyde.

Acetals containing active methylene groups for colorcoupling have been described above and in the working examples. An active methylene group is a methylene group having one hydrogen replaceable in am coupling reactions or replaceable by alkali metal in alkaline solution. This group derives its reactivity by reason of the fact that it is attached by a single valence directly to one of the following groups:

the remaining valence of the active methylene groups being also attached to one of these same 'ucts soluble in dilute sodium carbonate solutions.

The introduction of phenolic hydroxyl and mercaptan groups in suflloient number also promotes alkali solubility but the resins are not in general soluble in solutions made alkaline with carbonates. Since these products may conveniently be introduced into photographic emulsions from dilute carbonate solutions, they are uniquely suitable for incorporation into the slightly alkaline photographic emulsions where they manifest full compatibility and thus lead to bright, intense colors free from haze. Since acetal formation need not proceed to substantial completion to produce I a satisfactory color forming product, the acidic salt forming groups may conveniently be introduced by reaction of the unreacted portion of the polyvinyl alcohol molecule. Procedures of this type are illustrate in the examples.

any other suitable reaction such as half-asteriflcation with anhydrides or dibasic acids, e. g., phthalic or maleic anhydrldes, or etheriflcation with halogenated acids, e. g., chloracetic acid. In general, the introduction of the color forming nuclei and the acidic salt forming groups into the polyvinyl alcohol molecul may proceed simultaneously or successively in any desired order. The acidic salt forming group may form an integral part of the color forming nucleus as in the case of 3-carboxy-2-hydroxy-benzaldehyde, in which case the reaction of one compound with polyvinyl alcohol introduces both the color form ing nucleus and the acidic salt forming group. In certain cases the acidic salt forming group may be introduced by sulfonation oi the polymer.

It is often found that acetalization of polyvinyl alcohol with the complex aromatic aldehydes contemplated in the present invention occurs to only a limited extent. In general. only a small percentage of acetal formation is necessary to obtain a compound with color-forming properties, but the physical properties of the polymer, e. g., solubility, may not be all that is desired. In-this case, additional reaction with the partially ac'etallzed product may be carried out to give the polymer the desired properties. This additional reaction is preferably further 'acetal formation with a different aldehyde or cyclic ketone or a mixture of aldehydes and/or cyclic ketones, as illustrated in the examples, but may be any other suitable reaction, such as half-esteriflcation with dibasic acids or etherification with halogenated acids. Furthermore, the acetal formation may be carried out upon polyvinyl alcohol or upon a partially hydrolyzed polyvinyl ester, and the hydrolysis products of interpolymers of vinyl esters and other unsaturated compounds.

polyvinyl acetate, by simultaneous hydrolysis and acetalization. They may also be prepared from a mixture of aldehydes by simultaneous or stepwise reaction. .Acetal interchange may also be resorted to.

Among the suitable acetal forming compounds which may be used as modifying constituents for the acetals are formaldehydes, acetaldehydes, propionaldehyde, nand iso-butyraldehyde, etc. Suitable cyclic ketones include cyclohexanone, 3-methylcyclohexanone, 3,5-dimethylcyclohexanone, 2-methylcyclohexanone, l-ethylcyclohexanone, 2-bromocyclohexanone and oxotetrahydronaphthalenes. The aliphatic aldehydes are preferred.

The polyvinyl acetals of this invention. have a degree of acetaliaation from the color-forming aldehyde used of about 10 to about 50% and preferably about 20 to about 30%. The degree of acetalizatlon resulting from the non-color-forming aldehyde, that is, from the modifying or solubilizing aldehyde, is about 10 to about 50%, preferably 20 to 30%. The total degree of acetalization is 40 to 75% and usually 50 to By "degree of acetalization is meant the percentage of original hydroxyl (or ester) groups which have been converted to acetal groups.

The products are most conveniently solubilized I by reaction of the polyvinyl alcohol or partial acetal thereof with aldehydes containing carboxyl 0r sulfonic acid groups. Suitable compounds for this purpose are phthalaldehydic acid,

benzaldehyde-o-sulfonic acid, glyoxylic acid and propionaldehyde beta-sulfonic acid. In place of social formation with aldehydo-acids, th acidic salt-forming groups may also be introduced by Practically any condensation catalyst of acid reaction may be employed. Suitable catalysts in- The acetals may also be prepared from polyvinylesters, e. g., y

While acetic acid is the preferred solvent for the preparation of the acetals of this invention,

other organic solvents may be resorted to. As 7 further examples of suitable solvents, mention is made of methyl, ethyl, propyl, isopropyl, and n-butyl alcohols and dloxane.

The color yielding elements may contain lightsensitive layers composed of simple or mixed silver halides which may contain the usual sensitizers, desensitizers, stabilizers, fog inhibitors, emulsion hardeners, etc. Suitable types include silver chloride, silver bromide, silver c'hloro-bromide-iodide, etc., which may contain cyanine,

carbocyanine, polymethine cyanine, cyazine, carbocyazine, pseudocyanine, kryptocyanine, merocyanine, rhodanine, etc., salts and bases. The

' mide, silver. chloride-bromide-iodide, silver brosilver halide layers may be anchored to the suppounds such as paraphenylene-diamine and its substitution products constitute a practical class of such agents. These developers may be substituted in the amino groups as well as in the ring, preferably the former, to constitute compounds such as the monoand di-alkyl arylenediamines, including the monoand di-alkyl naphthylenediamines, alkylphenylenediamines and alkyl toluylenediamines. The compounds, of

course, must have one free primary or unsubstituted amino group which enables the oxidation product of the developer to couple with the colorforming compounds. As examplesof developers of the class described, there may be mentioned p-aminodiethylaniline, 1,4 naphthylenediamine,

4-diethylamino-l-naphthylamine and their acid salts. The salts of the bases which may be organic or inorganic are, in general, more soluble and more stable than the free bases. The hydrochlorldes and sulfates have great utility.

All of the acetals couple with diazo compounds so that they are, therefore, suitable for transgelatin, gum arable or albumen. Appropriate methods of developing dye images after exposure then include the process of removal of the unexposed colloid with hot water and dye development of the exposed portions with p -nitrosoaniline or its derivatives and the process of development with dye coupling developers.

All of the compounds contemplated in the in-, vention possess the major advantage oi. being nonmigratory in emulsion layers. The significance of this fact is that incorrect color values cannot then arise from migration of one of the color formers" into a layer adjacent to the one in which it is placed. Furthermore, no bleeding can take place into processing baths. This observation is striking when it is recalled that the preferred products are soluble in dilute alkali and certain of the processing solutions are alkaline in nature.

The polyvinyl acetals hereof have the further advantage that they do not have a deleterious eflect on the photographic characteristics of silver halide emulsion layers of photographic elements.

This application is a division of our copending application Serial Number 436,056- filed March 24, 1942, which in turn is a continuation-in-part of application Serial Number 233,480 filed October 5, 1938, now United States Patent No. 2,310,943.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments herein except as 5 defined by the appended claims.

What is claimed is:-

1. A silver halide emulsion containing as a color former fast to difiusion an amide of a color former and the acetal obtained by the condensa- 40 tion of polyvinyl alcohol with an aromatic aminoformation to azo dyes, followed by differential bleaching in the presence of silver images, as known in the art. These compounds are also especially useful in the azo process of application, Serial Number 335,416 filed May 15, 1940, now United States Patent No. 2,297,732.

The above-described acetals may also be incorporated in colloid layers sensitized by treatment with bichromate. Any colloid capable of this sensitization may be used, as, for example,

aldehyde.

2. The composition as defined in claim 1 wherein the aldehyde is an aminobenzaldehyde.

3. The .process which comprises developing a photographic element containing a reducible silver salt image in the presence of an amide of a color former and the acetal obtained by the condensation of polyvinyl alcohol with an aromatic aminoaldehyde.

4. A silver halide emulsion containing as a color former fast to diilusion, an acetoacetaminobenzaldehyde polyvinylacetal.

5. A silver halide emulsion containing as a color former fast to diffusion, a meta-acetoacetaminobenzaldehyde polyvinylacetal.

6.-A silver halide-emulsion containing as a color former fast to diffusion, an ortho-acetoacetaminobenzaldehyde phthaladehydic acid polyvinyl acetal.

GEORGE L'OWRANCE DOROUGH. DAVID MALCOLM MCQUEEN.