US2365206A - Processes of color development - Google Patents

Description

ly unexposed silver salts of the type Patented Dec. 19, 1944 Emery Mes'chter, Milltown, N. J.,

du Pont de Nemours & Company,

assignor to E. 1.

Wilmington,

Del., a corporation oi. Delaware No Drawing.

Application February 15, 1943,

Serial No. 475,976

14 Claims.

This invention relates to photography. More particularly it relates to processes of color photography wherein dyestuff images are produced by the color coupling development of silver salt images. Still more particularly it relates to dye generating'reducing compositions which are useful in color photography. Still more particularly it relates to .aqueous reducing baths containing an aromatic'polyamino developing agent having at least one unsubstituted amino group and a heterocyclic nitrogenous base free from negative j groups and hydroxyl groups attached to carbon, atoms. In one of its aspects it relates to aqueous reducing baths containing an aromatic polyamino developing agent having atleast one unsubstituted amino group and a heterocyclic nitrogenous base free from negative groups and hydroxyl groups attached to carbon, capable of energizing said developing agent so that it no longer acts preferentially on exposed silver salts. The invention also relates to processes of reducing photographic images utilizing the herein-described reducing baths, including photographic reversal processes.

This invention has for'an object the preparation of active color coupling reducing baths from photographic developing agents. A further object is to produce a color coupling reducing composition which will reducemetallic salts especialused in' photographic emulsions to metallic silver. A still further object is to provide an aqueous reducing bath which does not distinguish inits reducing action between unexposed and exposed silver salts in a photographic emulsion layer. A still further'object is to provide a reducing composition which may be used in a reversal process which requires no reexposure to light. Another object is to provide a reversal process which requires no reexposure to light. Another object is to provide a reducing bath which may be used for simultaneously reducing silver salts and forming colored dyes in situ therewith. Another object is to provide an aqueous-reducing composition which will increase the effective speed of pho- 'especially reverse images. Other objects include heterocyclic nitrogenous the oxidation product of the developing agent on photographic development to produce a dyestufi and (2) a heterocyclic nitrogenous base free from negative groups and hydroxyl groups attached 'to acyclic, carbon.

In a more limited sense the invention comprises the preparation and use for color coupling development of an aqueous bath containing an aromatic polyamino developing agent having at least one unsubstituted amino group and a strong base free from negative and hydroxyl groups attached to. carbon.

association exponent '20 tog raphic emulsions in forming colored images,

the production of developing or reducing compositions which when used in color coupling development processes of color-photography result in color photographs of improved quality, saturation of individual color components and brilliancy of individual and combined dye images A further object is to provide reducing baths which are of general utilityin the dyeing arts.

The above and other objects are accomplished by the hereindescribed invention which'comprises the development of silver salt images with a primary aromatic amino developing agent in the presence of (1) a compound which couples with is enhanced and the To be more specific the heterocyclic bases comprehended have such a basicity that they are capable of fogging a photographic silver halide layer. They have a basicity materially greater than pyridine possessing an association exponent greater than 9.00,.e. g. from 9.00 to 12.00. .The being the p Kab value which is derived from the formula:

Kb 11 Kab- -1og m where Kb and Kw are the dissociation constants for the base and water respectively.

It has been found that when such heterocyclic nitrogenous bases are used in photographic developingsolutions for the color coupling development of silver salt images that the color coupling efliciency of dye production. is materially increased. Coupling. reactions which proceed only slowly with an ordinary color developer and exposed silver bromide, for in-' stance, are greatly accelerated.

The amount of dye formed'is much greater in proportion to the amount of silver produced than when the heterocyclic nitrogenous bases are not used.

when the heterocyclic nitrogenous bases-are used in an amount of from 8 grams to 30 grams or 8 cos. to 30 cos. .in the. case of a liquid, per

liter of solution, the bases are capable of-energizing the aromatic primary amino color'developing agents so that they no longer act preferentially on exposedsilver salts. This property is of value in a reversal process wherein a dye image is formed in the second development step since it is not necessary to re-expose the element to light. The primary and secondary silver images can be removed after the second color forming development step. The heterocyclic nitrogenous bases are particularly useful with arylene diamino color developing agents having at leastfone unsubstituted amino group.

The present application is directed to an invention divided out of my copending applications, Serial Nos. 295,685, 295,686, and 295,687, new U. S.

Patents vNos. 2,310,980, 2,310,981, and 2,310,982,

respectively. and is a continuation in part. of such applications.

The heterocyclic nitrogen bases having an association exponent greater than 9.00 as previously stated are free from negative groups such as halogen atoms e. g. Cl and Br; nitro, $03M, wherein M is hydrogen or a metal, and hydroxyl groups attached to carbon. The heterocyclic nitrogenous bases may for example contain at least one heterocyclic nitrogen atom and 4 or 5 carbon atoms, and have the general formula:

wherein two 01' the Rs constitute a divalent hydrocarbon radical which form a heterocyclic nucleus with the nitrogen atom and the-other R is hydrogen or a lower alkyl or cycloalkyl radical, or three or the Rs may represent a single substituted Polymethylene radical which'with the nitrogen atom forms a heterocyclic nucleus of the general formula:

N-on

invention by the preparation of reducing compositions, particularlyaqueous baths containing an N-dialkyl phenylene diamine or the general formula R H O 3/ n I or a water soluble salt thereof, wherein R and R are the same or difl'erent-lower alkyl radicals, e. g. methyl and ethyl; and a heterocyclic nitrogenous base free from negative groups and hydroxyl groups attached to carbon and falling within one of the Formulae 1 and 2.

It has been found according to this invention that the arylene diamino compounds, particularly those of the type set forth in Formula 3 above and their water soluble salts become very active reducing agents when they are admixed with nitrogenbus bases of the above type especially those which are free from intracyclic double bonds. This discovery is of considerable importance in that it enables the relatively weak reducing agents, namely, thearylene diamino compounds.

t0 be used in a great many arts, wherein only powerful reducing agents have heretofore been used without the attendant disadvantages of the last mentioned agents.

In utilizingthe invention the reducing compositions may contain in addition to the aromatic polyamino photographic developing agent and nitrogenous base which energizes its reducing powers, 9. colori'ormer which will couple with the products formed during the reducing'action to form quinoneimine dyestufl! including a dyestuff of the indophenol, indoaniline and indamine class or oi the azomethine type. The color formers, however, may be present in the photographic elements treated as immobile or non-difiusing dye intermediates.

- The N-dialkyl p-phenylene diamines, which are rather weak' photographic developing agents, when used in conjunction with heterocyclic basic agents herein specified in amounts from 8 grams or ccs. to 30 grams or ccs. per liter of solution become highly energized and are no longer selective in their reducing action. They lose their ability to readily diflerentiate between exposed and unexposed silver halides in their reducing action and no longer act completely like selective photographic developing agents. they become overall reducing agents, acting'similarly to sodium hydrosulfite, sodium stannite, etc., in regard to silver salt reduction.

In addition to causing weak photographic developing agents, e. diamino-naphthalene, p-aminodiethyl aniline, pamlnodiethyltoluidine, etc., to become overall silver halide reducing agents, the addition of the heterocyclic nitrogenous bases free from negative groups and hydroxyl'groups vastly increases the dye-forming characteristics of these dye-generating baths which issurprising and unexpected. Thus, it has been found that with a given silver density produced by the conventional type of color-forming developer containing sodium or potassium carbonate as the alkali, a much greater density of 'dye image is produced with the same silver density by these dye-generating reducing baths. Furthermore, this occurs at the same pH condition of the bath as that containing alkaline carbonates. At least 30% and sometimes as much as of reduced silver halides is produced by these dyegenerating reducers compared with ordinary carbonate containing color-developers. In addition,

the rate of increase in dye-density with alkaline carbonate, or even caustic alkali, containing color-developers rapidly diminishes after 5-8 minutes developing time. With the dye-generating reducers oi the present invention, on the other hand, the increase in dye-density continues even after 15 minutes developing time. The specific types of nitrogen bases described above result in three major unexpected and surprising results when used with arylene-diamine developing agents in the presence of quinoneimine, azomethine and 2.20 dye-forming components: 1. Weak photographic developing agents become energetic overall reducers for silver halides and are no longer photographic developers. I

2. For the same amount or silver produced. these-dye-generating reducers yield greater amounts of dye.

3. The formation of dye with these dye-generating reducers continues long after the usual color-developers have ceased to produce greater dye density.

This invention will be further illustrated but is not intended to be limited by the following examples:

Example I A dye forming reducing bath of the following composition:

A-chloroethyl-acetoacetate g rams 2 p-Amino-N-diethy'laniline do 2 Piperidine cc 25 Sodium sulflte, anhy grams 2 Water to liter 1 was prepared by the above manner by dissolving the chloroethyl-acetoacetate in acetone and adding it and the other ingredients to water and;

bringing the solution upto 1 liter.

On the contrary.

g., 1:4-diaminobenzene, 1:4

greater dye density for the same amount A film which had been exposed and developed in a metolhydroquinone developer and the silver images removed by bleaching was treated in the above solution, whereby a reversed yellow dye and silver iinages were formed. The silver image was removed in the\ usual manner, leaving a yellow image.

Example II A,-chloroethyl-acetoacetate grams 2 p-Aminodiethylaniline i "do.-- 2 Piperidine cc 25 Sodium sulfite, anhy grams 2 Water to liter 1 An unexposed reversed silver salt image layer of a photographic element, when treated in the solution; forms a yellow image in situ with metallic silver. Upon removal of the silver a yellow image of excellent density and clarity was obtained.

When trichloronaphthol is substituted for the alpha chloroethyl-acetoacetate of Example II a blue-green image is formed in situ with the metallic silver. The trichloronaphthol can be dissolved in acetone and thus incorporated into the developer solution. Similarly, when the thioindoxyl-carboxylic acid is substituted a magenta ,image of good strength and clarity is formed.

In place of the aromatic color developing agents set forth in the above examples may be substituted 3, large number of 'other such specific compounds. Suitable additional color coupling developing agents include:

and their water soluble salts, e. g., chloride, sulfate, acetate, oxalate, etc. Similarly, fctheriheterocyclic nitrogen bases Y which enhance the color coupling reaction maybe substituted for the piperidine of the above examples.

Suitable additional compounds include the substituted piperidines wherein the nucleus or the nitrogen atom contains an innocuous substituent whichdoes not interfere with a color coupling reaction between the development products and the color former. Among the useful substitu ents are lower alkyl groups forming compounds such as N-methylpiperidine, N-ethylpiperidine,

'alpha-methylpiperidine, alpha-ethyl-piperidine,

liter with good results. The amount oi alkali metal or ammonium sulflte may vary from 15 to, 25 grams per liter of solution. The amount I of weak alkali, e. g., sodium carbonate may vary from 0 to 30 grams per liter. With regard to the nitrogenous base free from negative groups and hydroxyl, groups, it may vary from 8 to 30 grams or ccs. (if a liquid) perliter of solution.

Likewise, other color forming compounds may be substituted for the specific ones set forth in the above examples. As examples of representative suitable color formers which are soluble or readily dispersible in the reducing solutions are diacylacetamino-aryl-bis-thiazoles of U. S.

Patent 2,140,540, of which difuroylacetamino- 1,2,4,5- benzo-bis-thiazole' is preferred, the'acylacetarylides of U. S. Patent 2,108,602, acetyl, acetone, benzoyl acetone, B-naphthoyl acetone, acetoacetic esters, ethyl-alpha-chloroacetoacetate, ethyl-gamma-chloroacetoacetate, ethyimalbnate, ethyl-p-nitrophenyl-acetate, ethyl acetopropionate, ethyl acetone dicarboxylate; furoylacetic ester, the acylacetamino phenyl morpholines of i U. S. Patent 2,133,937, etc.

Suitable magenta color formers include nitriles, e. g., p-nitrobenzyl cyanide, o-nitro-ben'zylcyanide, 'p-toluyl-acetonitrile, w-cyanoacetyl-dibenzfuran, w-cyanoacetyl-acenaphthene, l-w-cyanoacetylcoumarone, 1,3 di (w-cyanoacetyl) benzene, acyl nitriles, e. g., cyanacetophenone. methoxy-alpha-naphthoylacetonitrile, cyanacetanilides, e. g., 1-cyanacet-aminobenzthiazole, etc.,

pyrazolones, e. g., 1-phenyl-3-furyl-5-pyraz0lone, I-p h e n y-l-3-carboxylic a c i d-5-pyrazolone, 1- phenyl-3-h y d r o x y-5-imino-pyrazolone, 1- (8'- quinolyl) '-3-methyl-5-pyrazolone, l-p h e n y 1-3- I methyl-5 thiopyrazolone, etc.

Suitable blue-green color formers include phenols, e. g., 'ortho and meta chlorophenol, o-bromophenol, o-iodophenol; naphthols, e. g., 2,3,4- trichlqrnaphthols, 2,6-d i b r o m o-1,5-dihydroxy naphthalene, etc. Other color, formers will be apparent to those skilled in the art. 7

The energetic dye-generating properties of the reducers described above makes them particular-'- ly useful as intensifiers for silver images of too low opacity to make them of satisfactory printing density. This embodiment of the invention is v illustrated in the following example:

Example III A low opacity silver image is bleached to a rediicible silver salt form by a chromic acid and sodium chloride. or bromid bleach bath or an alkaline-ferricyanidebleach. The washed fllm is treated with a dye-generating reducing bath of the above type which yields a neutral black or grey image. If the intensified image is to be used for \printing onto blue sensitive emulsions a: yellow-orange-to-red color former can seemployed.

Intensification processes employing color forming developers are described in Fischer U. S. Patent 1,079,756, but the process described above con.

2-hydroxy-3-ethyl-piperidine, 1-n-butyl-2-methylpiperidine, etc. Still other useful bases include morpholine andpiperazine. The saturated heterocyclic amines are preferred.

The proportions of the components of the reducing solutions may be varied considerably. For instance, the amount of arylene-diamino developing agent may vary from 2 to 12 grams per stitutes a distinct improvement over the known,

procedures. A major advantage resides in the substantial increa'se in image opacity obtained 4 hereby. In addition, the tonal graduations of the image as intensified by the present method do not depart as much from the original tonal scale as by the .prior art proceduresexemplified in the Fischerpatent.

his to b understood, however, that the dye forming reducing baths hereof are not limited to photographic uses although such uses are of major importance. On the contrary, they are of considerable utility in the textile and related industries. The production of dyed textile materials from natural, chemically modified, artificial and synthetic fibers is facilitated by employing reducing baths as described above; The treatment of cellulose derivatives, for instance, by the use of such baths, is of considerabl importance. The dyeing of such materials will be illustrated by the following example:

Example IV maintaining the temperature of the dye bath at 80 C. The material is then rinsed and dried. It is found that the depth of color is much greater the presence of color formers, especially those caand the color purity vastly improved by this method over the usual indophenol dyeing methods. The presence of the coupling energizer serves here also to aid in the dye penetration.

In place of the specific color formers and arylene diamino compounds may be substituted others as described above. Likewise, other mtrogenous bases and other textile material may" be'substituted. In a like manner, other oxidizing agents may be substituted for the sodium Der:

borate. Suitabl agents include hydrogen peroxide, persulfates, percarbonates, alkali metal peroxides, perorganic acids, e. g., peracetates, perpropionates, etc.

While the above examples are concerned with color developer solutions wherein the dye intermediate or color formers are in the treating solution, the invention is not limited to that aspect. On the contrary, the color formers may be used in water permeable layers or strata. To be more specific, color formers of the immobil or nondiflusing types, including those which are substantive to water permeable colloid binding agents, such as gelatin. The color formers can be incorporated in gelatino-silver halide emulsions, for example, or in separate color yielding layers or strata in operative association with such layers. Color formers which yield various colors, e. g., blue-green, yellow, magenta, and composite colors, such as black, may be used in accordance with the teachings of this invention. Single layer and multi-layer elements containing immobile color formers are comprehended.

One embodiment of the invention is therefore concerned with the use of aqueous baths of the above type containing a heterocyclic nitrogen base but free from color formers, for the treatment of multi-layer film composed of three superposed differentially sensitized silver halide emulsion layers containing immobile color former compounds which form colors complementary in color to the employedsensitivity range of the respective emulsion layers. This embodiment will be more fully described below. 7

The reversal process of this invention may be used with a widevariety of diflerent types of film structure. The. processes, however, all involve the development of a latent image or series of partial latent images corresponding to a scene inpable of forming indophenol or azomethine dyes.

The reversal processes hereof as previously stated, are of utility in th processing of multilayer film, including monoand multipacks composed of differentially color sensitive photographic emulsion layers. They are of especial utility in processing mono-packs comprising at least three difierentially color sensitive silver halide emulsion layers, each containing immobile color formers, which are borne by a transparent base member. One of the layers may b placed on one side of the base and two on the other. The layers may be separated by clear layers, e. g., colloid layers such as gelatin which may prevent migration of color formers, sensitizers, which may be dyed to act as temporary filter layers.

A preferred embodiment of the invention involves the reversal processing of multilayer film which is difierentially color sensitized and contains light barrier layers and especially treatment of such film wherein the respective color sensitive layers contain a color former which forms upon development a dye complementary in color to the sensitivity of the respective emulsion layer.

Photographic and film elements of the type lust described are claimed in U. S. P. 2,191,502 and Serial No. 287,154, filed July 28, 1939, now U. S. Patent 2,266,441. In such films at least one emulsion layer is protected from the action of light after the first development of a reversal process due to the fact that a layer of pre-fogged silver gelatino halide emulsion is interposed between at least two diiferentially color sensitized emulsion layers.

Example V A monopack comprising a cellulose acetate film base suitably subbed is coated with a gelatino silver bromide emulsion sensitized to red so as to exhibit very little sensitivity in the green spectral region by means of a green blind sensitizing dye, e. g., pinacyanol. To this blue-red sensitive emulsion layer is added 15 grams of a nonmigratory blue-green color former, e. g., a salicyclaldehyde-o-sulfobenzaldehyde acetal'of polyvinyl alcohol per 1000 grams-of emulsion. Over this blue-red sensitive layer is coated another silver halide emulsion layer which is sensitized to the blue-green region of the spectrum with a sensitizingdye, e. g., erythrosin, and contains a magenta (minus green) color former, e. g., l-(mstearoylaminophenyl) -3-methyl 5 pyrazolone. Over the last mentioned layer is coated a layer of gelatin solution containing a removable yellow filter dye, e. g., Tartrazine C. I. 640. Over the yellow filter layer is coated a bluesensitive silver halide emulsion containing a yellow color tormer, e. g., furoylacetbenzoylacet-benzidide.

The above described film element is exposed to a colored object scene whereby latent images representing diiferent color component aspects in the dinerent sensitive layers are formed as is dodecoylamino-phen'yl) --pyrazolone,

known in the art. See, for instance, Schinzel Austrian Patent No. 42,478. The film is then processed by the following steps:

1. Develop minutes in an ordinary metolhy droquinone positive developer. Wash 10 minutes. Reduce residual silver salts by treating for minutes in a dye generating reducer of the following formula:

Sodium sulflte, anhydrous grams 1.0 p-Aminodiethyl aniline dihydrochloride grams-.. 2.0 Piperidine. M Water to liter 1 I Wash 10 minutes.

. Bleach '1 minutes in a solution containing 3 /z by weight of potassium ferricyanide and made alkaline with ammonium hydroxide or sodium carbonate.

. Rinse.

7. Remove bleached silver in asolution of hypo (crystalline sodium thiosulfate) Wash 15 minutes and dry.

In place of the specific dye forming reducing.

baths of the preceding examples may be substituted a wide variety of reducing-baths having the above described characteristics. Thus any of the baths described in the aforedescribed application may be substituted with similar result.

Similarly, various other immobile color formers may be substituted for the specific color formers set forth in the above examples. Color formers which give excellent results include non-migratory yellow color formers, which may be used in the blue-sensitive layer, as follows: diacylacetamino-aryl-bis-thiazoles of U. S. Patent 2,140,540, of which difuroylacetamino-l,2,4,5-benzo-bisthiazole and di-acetoacetamino-l,2,4,5-benzobis-thiazole are especially useful as are 2-hydroxy-3-naphthoylamino-benzoyl-acetanilide, sodium stearoylamino-benzoyl-acetanilide-p-carboxylate, p-caproylamino, benzoylamino salicylic acid, furoylacet-p-amino phenyl amyl ether (U. S. P. 2,184,303), and di-picolinoyl-acet benzidine.

Suitable non-migratory magenta color formers which are especially useful are 1- (3'-sulfophenyl) -3- (4"-stearoyl-amino phenyl) -3- (4"- (3"-methyl pyrazolonyl-1")-diphenyl (described in US. P. 2,200,924), 4,4'-methylene-bis-(mstearoylaminophenyl) -methyl pyrazolone, and

*4,4'-o-sulfobenzylidene-bis- (phenyl methyl pyrazolone) (described in U. S. P. 2,294,909).

Suitable non-migratory blue-green color formers of especial utility include 4,4'-di-(1-hydroxy- Z-naphthoyl-amino) diphenyl, 1-hydroxy-2-car- Yellow T, then a pre-fogged emulsion layer, then I a green sensitive emulsion, another pre-fogged emulsion layer containing a soluble red dye. e. 3.,

carmosine M, then a red sensitive silver halide emulsion, and finally the base. The amount of silver salt in the pre-fogged layers and the fogging exposure given the layers is such that upon the first development'of the layers a light barrier layer will be formed therein so that substantially light does not substantially affect the other two layers because of their lack of sensitivity to the red light used as the printing light, and secondly, the black metallic silver barrier layer prevents substantially all of the printing light from passing through to the outer layers.

The film is now'developed in a color-forming developer of the following composition:

2:3:4-trichlor-alpha-naphthol "grains" 2 2-amino-5-diethylaminotoluene a.. do.... 5 Potassium carbonate ccs 10 Sodium sulflte, anhy "grams-.. 5. Water to liter 1 prepared by dissolving the trichlornaphthol in alcohol and adding the other ingredients to' water and bringing the solution up to one liter, whereby a blue-green (minus-yellow) dye image and silver image is formed. The film is then thoroughly washed.

The top or blue sensitive layer is then exposed to a blue or preferably a white printing light. This printing light does not affect the middle layer because of the metallic silver barrier layer between the top "and middle layers. The entire film is then treated with a yellow (minus-blue) color forming developer of the following composition:

Potassium carbonate grams 40 Sodium sulfite, anhy do.. 5 Diethyl-paraphenylenediamine hydro chloride I do Water in liter..-

, to which is added the following solution:

boxy-E-dodecoylamino naphthalene, l-N stearoyl-4-N-(1-oxy-2'-naphthoyl) phenylendiamine sodium sulfonate, resorcinol mono-n-dodecyl ether (described in U. S. P. 2,166,181), product of p-hydroxybenzoic acid and formaldehyde (described in McQueen, Serial No. 261,794, filed March 14,1939, now U. S. Patent 2,323,481),

product of polyvinyl alcohol and salicyaldehyde- (described in Dorough and McQueen, Serial No.

233,480, filed October 5, 1938, now U. S. Patent 2,3].0,94 3 granted-February 16, 1943)..

' Emmple'VI A multilayer film so disposed that light after passing through an optical aperture isflrst incident on .a -b lu'e sensitive silver halide emulsion containing a yellow'filter dye such as Luxci Fast 75 Water Benzoyl acetone-3 grams dissolved in 25 cc. of

ethyl alcohol.

After development, the blue sensitive layer will.

contain both metallic silver and yellow dye images. -It is then thoroughly washed.

The green sensitive middle layer on both sides of which are black, metallic silver barrier layers, remains. This layer is treated in a dye forming reducing bath of the type herein described 'containing an arylene diamino compound and a nitrogenous base and a magenta color former. A

suitable bathis compom of:

Thioindoxyl-carboxylic aei'd.-- grams 2 p-Amino-N-diethylaniline do. 3 Piperidine I 7 no 30 Sodium sulflte, anhy- "M4- 3 liter..' 1

Example VII A film element provided with a panchromatized silver halide emulsion layer coating of about 80 milligrams and containing about 15 grams of beta-naphthol as a black color former per kilogram of emulsion is processed after exposure as follows:

1. Develop 8 minutes in a metol-borax, fine-grain 8. Wash and dry.

If the fine-grain images are satisfactory in density as they are being washed in step No. 4, the silver images are allowed to remain and the film is simply dried after step 'No. 4. If, on the other hand, they appear too dense, the transmission of the images can be increased by removing the silver images, or a portion thereof by bleaching and fixing as described in steps 5, 6 and 7 above.

Example V11! To one kilogram of panchromatized silver gelatino bromide emulsion are added 20grams of a mixture composed of 9 parts by weight of m dodecoyl-aminophenyl-hydroxynaphthol-thiazole sulfonic acid .and 1 part by weight of l-(mstearoyl-aminophenyl) -3- methyl pyrazolone dissolved in sodium hydroxide alcohol solution. A 90 mg. coating of this neutral color forming emulsion is coated on subbed cellulose acetate film base, exposed and processed as described under Example I but substituting N-methyl piperidine in the reducing bath to reduce the reversed image. The simplified reversal process introduced by the present invention also makes possible an economical method for the production of enlarged black and white prints from colored transparencies. Recently several commercial film have become, available for the production of colored transparencies. It is ofttimes desirable to produce enlarged prints from such positive color transparencies but the required process of making an intermediate negative and projection-printing from this is costly if only a few prints are desired. The other method involving the reversal of printing paper by known methods does not yield satis factory results. The above disadvantages are overcome by this invention. The following example illustrates this embodiment hereof:

Example IX and containing 15 drops of concentrated ammonium hydroxide. After sensitizing for 4 minutes at 70 F., the paper is washed for five minutes in running water and then dried. The colored positive transparency is then enlarged directly on to the sensitized projection paper. The

then washed. The reversed image is reduced by treatment for 35 minutes in 2-amino-5-diethylamino-toluene grams 5 Piperazine cc 20 Sodium sulfite, anhydride grams.. 8 Water to..- r" 1 to which add 2-5-dimethylbenzoxazole grams 4 Ethyl alcohol dg 100 If the image is too dark, all or a portion of the silver image can be removed by the steps indicated under Example I. In place of 2-5-dimethylbenzoxazole, which produces a bluish-black image, 2-methylbenzoxazole and 2-5-dimethylbenzo-thiazole can be used to produce brownishblack images.

An important advantage of the present invention resides in the fact that the readily available weak arylene diamino types of developing agents may readily be converted into powerful reducing agents in a simple manner and with the aid of inexpensive and readily available additional agents.

A further advantage resides inthe fact that a weak developing agent of the arylene diamine type becomes readily converted into an excellent color developing agent producing a much greater dye density for the same amount of reduced silver by the addition of inexpensive and readily available photographic materials. Still other advantages will be apparent to those skilled inthe arts of this invention.

The present invention provides an improve ment over previous suggestions for reversal development, wherein residual silver halides are chemically exposed by means of sulfur bearing compounds such as thiourea, allyl'thiourea, etc., since .these proposals incur the need for additional tubes or tanks in processing machines, more wash water consumption and an extended total processing time. Furthermore, such conipounds are undesirable because of their objectionable odor.

A further advantage resides in the fact that a much greater density of dye image is produced with the same silver density as compared with the usual color developers containing alkaline carbonates as pH regulators.

An additional advantage resides in the fact that a very great increase in the coupling velocity of color formers is obtained b the use of the baths containing arylene diamino compounds and certain nitrogenous bases as energizers. Still other advantages will be apparent to those skilled in the art. r

The numerous advantages of this invention should be apparent to those skilled in the art.

. provement over the The reversal methods hereof wherein black dye images are produced represent a definite imart in that the silver image does not need to be removed. The reversal system involves only 8- steps and produces good black images. Prior reversal processesinvolving the use of sodium hydros'ulfite have various shortcomings and do not produce black images.

A further advantage is concerned with the fact that, due to its energetic dye producing action, the density of dye images is considerably greater, per density of silver produced than with ordinary color forming developers. This means the amount of silver halides in the emulsion can be,

materially reduced resulting in an economical manufacturing improvement over filmsfor ordinary reversal methods. This economy feature is borne out by the above examples. The coating weight of negative films for reversal processes is usually about 105 to'115 mgs., that is, thisamount of dried gelatino silver halide emulsion solution comprising a primary aromatic amino covers 100 square centimeters, By the present invention coating'weights of 80 rugs. are practical.

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 the invention is not to be limited to .the specific embodiments herein exceptas defined by' the appended claims.

I claim:

l. A color forming photographic developer comprising a primary aromatic amino developing agent, a compound which couples with the oxidation product of the developing agent onphotographic development to produce a dyestufi image and a heterocyclic nitrogenous base free from negative groups and hydroxyl groups attached to acyclic carbon.

2. A3 color forming photographic developer comprising'a primary aromatic amino developing agent, a compound which couples'with the oxidation product of the developing agent on photographic development to produce a dyestufi image and a heterocyclic nitrogenous base having an association exponent greater than 9.00. v

3. A color forming photographic developer comprising a primary aromatic amino developing agent, a. compound which couples with the oxidation product of the developing agent on photographic development to produce a dyestufi image and a heterocyclic nitrogenous base having an association exponent .greater than 9.00 in an amount of 8 grams to 30 grams. perliter of solution.

4. A color forming photographic developer comprising a color coupling primary aromatic amino developing agent, a compound which couples with the oxidation product of the developing agent on photographic development of a silver salt image to produce a dyestufi image and a saturated heterocyclic amine having an association exponent greater than 9.00.

5. A color forming photographic developer comprising a color coupling primary aromatic amino developing agent, a compound which couples with the oxidation product of the developing agent, on photographic development of a silver salt image to produce a dyestufi image and apiperidine base having an association exponentgreater than 9.00.

6. The process which comprises developinga groups and hydroxyl groups attached to acyclic carbon and a color former.

"L- The process which comprises. developing a photographic element containing a reducible silver salt image with a photographic developer solution comprising a primary aromatic amino color developing agent in the presence of a saturated heterocyclic amine and a color former.

8. A photographic reversal process which comprises developing a photographic element containing a, latent silver halide image in an ordinary developer to produce a negative image and developing the reversal silver'halide image without re-exposure with an aqueous reducing bath containing a primary aromatic amino color developing agent in the presence of a heterocyclic nitrogenous base free from negative groups and hydroxyl groupsattached to acyclic carbon-and a color former. v I

9. A photographic reversal process which comprises developing 'a photographic element containing a latent silver.- halide image in an ordinary developer to produce a negative image and developingthe reversal silver halide image without re-exposure with an aqueous reducing bath containing a primary aromatic amino color 7 bath containing a primary aromatic amino color developing agent in the presence of a piperidine base having an association exponent greater than 11. A photographic reversal process which comprises developing a photographic element containing a. latent silver halide image in anordinary developer to produce a negative image and developing the reversal silver halide image without re-expos'ure with an aqueous reducing bath containing a primary aromatic amino color developing agent in.the presence of piperidine and a color former.

12. A color forming photographic developer comprising a. primary aromatic amino developing agent, a compolmd which couples with the oxidation product of that developing agent on photographic development of asilver salt image to produce a dyestufi image and piperidine.

photographic element containing a reducible silver'salt image with a. photographic developer 13. A color forming photographic developer comprising a primary aromatic amino developmg agent, a compound which couples with the oxidation product of thatdevelonin a ent on photographic development of a silver salt imag to produce a dyestufl'. imag and Pil 14. A color forming-phic developer"- comprising a primary aromatic amino developing'agent, a compound which couples with the oxidation product of that developing agent on photographic development of a silver salt imag to produce a dyestufi image and morpholine.