US3062643A - Photographic diffusion transfer process - Google Patents

Description

United States Patent Ofifice 3,062,643 PHOTOGRAPHEC DlFFUSlON TRANSFER PROCESS? Roy C. Bloom and Frederick A. Pomeroy, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed May 22, 1959, Ser. No. 814,971

3 Claims. ((31. 9629) This invention relates to photography and more particularly to a silver halide diffusion transfer process in the art of photography.

In the Yackel, Yutzy, Foster and Rasch US. patent application Serial No. 586,705, filed May 23, 1956, is described a diffusion transfer process employing an integral photosensitive element comprising a silver precipitating stratum such as colloidal silver on a support and adhered to this stratum an emulsion layer containing silver halide uniformly dispersed in alkali-soluble acidinsoluble carboxylated cellulose derivative such as an alkali-soluble acid-insoluble dibasic acid ester of a cellulose ethyl ether or an alkali-soluble acid-insoluble dibasic acid ester of a cellulose acetate. After exposure of the photosensitive element, the latent image therein is developed with a silver halide developing composition containing a silver halide solvent, thus forming a negative silver image in the emulsion layer together with an imagewise distribution of undeveloped silver halide which diffuses imagewise to the silver precipitating stratum, in the form of a silver complex with the silver halide solvent, to form a positive silver-containing image on the precipitating stratum. Thereafter, the emulsion layer is removed from the silver precipitating stratum leaving a readily visible positive silver-containing image thereon.

As is well known, the tone of the silver image obtained in the silver halide diifusion transfer processes is characteristically warm in tone rather than being cold or neutral toned as is desirable and in the above process the inventors recommend that certain sulfur-containing compounds be present during processing to obtain cold-toned images.

We have discovered that a pronounced improvement in image tone in the described process may be effected by use of common inorganic chemicals. The means we employ to produce the cold-toned images comprises the use in the silver halide developing composition of a mixture of a quaternary ammonium salt, a 3-pyrazolidone developing agent or a lower monoalkyl-p-aminophenol developing agent, e.g. monomethyl-p-aminophenol sulfate, a hydroquinone developing agent, a sulfite such as an alkali metal or amine sulfite, an alkaline material such as sodium carbonate, triosodium phosphate or sodium metaborate, a silver halide solvent, and potassium chloride. The image tone is decidedly neutral when these ingredients are present in the developer composition but when, for example, potassium chloride is not present in the composition, a brown-toned silver image is obtained whether or not the quaternary ammonium salt is present. Substitution of sodium chloride for potassium chloride in the formula results in the production of a warm-toned silver image. A specific effect obtained by use of trisodium phosphate as the source of alkali is to prevent the formation of bronze or metallic luster-toned images characterized by the use of other alkaline materials such as sodium carbonate.

The process of our invention is illustrated by the following examples:

Example 1 A percent gelatin solution (250 cc.) was diluted with 750 cc. of water and then 2.5 cc. of l-N-sodium sul' 3,062,643 Patented Nov. 6, 1962 fide were added to the solution. 250 cc. of water containing 26 cc. of 1 N zinc nitrate were added slowly to the sulfide solution through a jet, resulting in the formation of a colloidal dispersion of zinc sulfide. To this dispersion were added 10 liters of a 3% gelatin solution, 300 cc. of a 7.6% saponin solution and 134 cc. of a 10% formaldehyde solution. The mixture was dispersed at 40 C. and then coated on a photographic paper support at a coverage of 2 lb. of solution per sq. ft. of coated surface and dried, forming the silver precipitating layer.

Over the silver precipitating layer was coated a 1% aqueous solution of the sodium salt (or other alkali metal metal salt) of cellulose ether phthalate (an ethyl cellulose containing 45.8% ethoxyl phthalated to 22.7 phthalyl) at a coverage of 0.15 lb. per sq. ft.

A low gelatin cellulose ether phthalate emulsion as dis closed by Yackel et al. above was coated over the cellulose ether phthalate interlayer at a coverage of 600 sq. ft. per mole of silver halide and dried in the conventional manner. After exposure, the element was developed for about 1 minute in the following developer composition at 70 C.:

1-phenyl-3-pyrazolidone 0.8 Hydroquinone 5.5 Sodium sulfite (anhy.) 25.0 Sodium carbonate (anhy.) 32.0 Sodium thiosulfate-5H O 10.0 2-,8-phenethylisoquinolinium bromide 0.15 Potassium chloride 16.0 Potassium bromide 0.05

Water to 1.0 l.

The processed paper was washed for 20-30 seconds in cool water (30 C.) to remove the emulsion layer, leaving only the transferred positive image in the silver precipitating layer. The material was then rinsed in a 5 percent acetic acid stop bath for 5 seconds and dried. During the mentioned development step, a negative silver image was formed in the emulsion layer and the residual undeveloped silver halide was dissolved by the thiosulfate and transferred in the form of the complex silver thiosulfate salt to the zinc sulfide reception layer and was there converted to a silver-containing image which appeared as a neutral-tone image when the overlying emulsion was removed.

Example 2 The process of Example 1 was carried out in the same manner except using the following developer composition in which trisodium phosphate replaced sodium carbonate as the alkaline component:

1-phenyl-3-pyrazolidone 1.6 Hydroquinone 1 1.0 Sodium sulfite (anhy.) 50.0 Trisodium phosphate (hydrated) 100.0 Potassium bromide 0.5 Potassium chloride 16.0 2-{3phenethylisoquinolinium bromide 0.3 Sodium thiosu1fate-5H O 20.0

Water to 1.0 l.

The result was to obtain a print on the silver precipitating layer which was neutral in tone.

When the developer compositions of the above examples were used for processing a variety of silver halide emulsions similar to that of Example 1, differing in their mode of preparation, optical and chemical sensitizing and other factors, it was found that the formula of Example 2 containing trisodium phosphate in most cases yielded neutraltoned images while some emulsions showed a tendency aoeaeas to yield a somewhat warmer-toned image with the formula of Example 1.

The ingredients of the above formulas may be present in a fairly wide range of concentration and still favorable silver image tone will be obtained in the process. Useful results are obtainable by use of the following amounts per liter of solution, from about 0.05 to 0.3 gram of the quaternary ammonium salt, about 50 to 100 grams of trisodium phosphate, about 12 to 20 grams of potassium chloride and about 30 to 60 grams of sodium sulfite. Lower concentrations of sodium sulfite tend to reduce the image density and higher concentrations of sodium sulfite promote warm-toned image formation. As mentioned, if potassium chloride is replaced by sodium chloride, :1 warm-toned image results in the process.

The silver halide solvent of the developer composition is not especially critical and can be an alkali metal or ammonium thiosulfate, sodium thiocyanate, etc.

The 3-pyrazolidone silver halide developing agents useful in the solutions include 1-phenyl-3-pyrazolidone, lphenyl-4,4-dimethyl-3pyrazolidone and other 3-pyrazoliclones described in the James et al. U.S. Patent 2,751,300, granted June 19, 1956. The hydroquinone useful in the developing solution include hydroquinone itself, halogenated hydroquinones such as chloro and bromohydroquinones, dichloro and dibromohydroquinones and toluhydroquinone; etc.

Additional quaternary ammonium salts which may be used in the above formulas in place of the quaternary ammonium salt given are those disclosed in the Tregillus et al. U.S. Patent application Serial No. 724,828, filed March 31, 1958, including the following of which the cyclammonium quaternary ammonium salts are particularly useful.

Tetradecamethylene-bis (pyridinium perchlorate) a-Dimethyldithiocarbamatoethyl-N methyl pyridinium-ptoluene sulfonate Decamethylene-u,w bis (oxymethyl pyridinium perchlorate) 3,6,9,12,15,18,21,24-ctahexacosane 1,26 bis(-ethyl-2- methyl pyridinium methane sulfonate) 2-,8-phenethylisoquinolinium bromide 1-,8-phenethylquinolinium bromide 3,l4-dioxahexadecane-1,16-bis-(pyridinium methane sulfonate) l-methyl-2-nonanoyl pyridinium-p-toluene sulfonate Heptoxymethyl-ZA,6-trimethyl pyridinium chloride Tetradecamethylene bis(trimethyl ammonium perchlorate) 3-methyl-2-B-phenethyl isoquinolinium bromide l-fi-phenethyl-a-picolinium bromide 4,4,10,10-tetraoxo 4,10 dithiatridecane-bis-(pyridinium perchlorate) The useful quaternary ammonium compounds are characterized by having a chain of at least 7 atoms attached to the onium radical. Similar onium compounds containing short chains such as tetramethylammonium hydroxide, halides, perchlorates and other salts thereof, are not useful in the processes of our invention.

As mentioned above, the photosensitive elements useful in the processes of our invention include a silver halide emulsion layer, the colloid vehicle of which is an alkalisoluble acid-insoluble carboxylated cellulose derivative such as the alkali-soluble acid-insoluble dibasic acid halfesters of cellulose ethyl ethers e.g. the cellulose ether phthalates or the alkali-soluble acid-insoluble dibasic acid half-esters of cellulose acetate e.g. cellulose acetate phthalates. When these material are employed as vehicles for emulsion superposed on silver precipitating layers of a different solubility, the emulsion is quickly removed with aqueous alkaline solutions; that is, after the development step is complete and the soluble silver complex has migrated imagewise to the silver precipitating layer, the carbokylated cellulose derivative is present as the alkali metal, ammonium, or amine salt, which is highly soluble in water although not soluble in the alkaline developer because of its high salt content. Therefore, When the developed element is subsequently washed with Water, the emulsion disintegrates with surprising rapidity and the positive image which remains on the silver precipitating layer is quickly freed of any contaminating materials by a brief wash with water.

The acid-insoluble characteristic of the above carboxylated cellulose derivatives is likewise important due to the fact that the coating of these derivatives is greatly facilitated by this characteristic. That is, since the carboxylated cellulose derivatives are insoluble in acid, coatings thereof may be caused to quickly set during high speed coating operations by applying the coating to an acidic surface which in the present invention takes the form of a support having on its surface or in the silver precipitating layer an acidic material such as an organic acid, e.g., citric acid. The acid causes the carboxylated cellulose derivative coating to set, and subsequent drying operations can be carried out without undue distortion of the coating. Materials such as methyl cellulose being soluble in both aqueous alkali and aqueous acid do not possess the mentioned characteristic.

In a similar manner, the carboxylated cellulose derivative emulsions may be coated upon a surface containing metal salts such as calcium acetate, aluminum nitrate, cadmium acetate, magnesium chloride and nickel acetate with the result that the emulsion will readily set up and dry without distortion. The use of acids in the sensitive element is thus avoided. Yackel et al. above show that other organic colloids are not as useful as the carboxylated cellulose derivatives as the colloid vehicle for the emulsions and the same applies to the processes of our invention.

The silver precipitating layer or stratum referred to herein is a Water-permeable organic colloid layer containing a silver precipitating agent, that is, an agent capable of yielding with silver ion a dark-colored argental or silvercontaining substance, when dissolved silver salts from the emulsion layer come into contact with it. The silver precipitating agent may comprise either physical development nuclei or a chemical precipitant for silver ions.

Suitable silver precipitating agents for use in the silver precipitating layer for forming the argental image include sulfides, selenides, polysulfides, polyselenides, thiourea, mercaptans, stannous halides, heavy metals and heavy metal salts, and fogged silver halide. Heavy metal sultides such as lead, silver, zinc, antimony, cadmium and bismuth sulfides are useful, particularly the sulfides of lead and Zinc alone or in admixture, or complex salts of these with thioacetamide, dithio-oxamide, or dithio-biuret. The heavy metals include silver, gold, platinum, palladium and mercury preferably in the colloidal form. The noble metals are particularly efiicacious.

The silver precipitating agents may be applied directly to a support such as paper, or to suitably subbed cellulose derivative supports and synthetic polymer supports from solutions or dispersions of the silver precipitating agents in a colloid vehicle such as gelatin. The colloid vehicle of the silver precipitating layer is necessarily insoluble in the solution used for removing the carboxylated cellulose derivative emulsion layer in the final stage of the process. If gelatin is used, it should be hardened. Hydrophilic cellulose esters and synthetic polymers are useful as a vehicle in the silver precipitating layer insofar as they meet the requirement of having a solubility appreciably different from that of the colloid vehicle of the emulsion layer.

The silver halide component of the mentioned emulsions is not especially critical and can include various silver halides and mixtures of silver halides such as silver bromoiodide, silver chloride, silver chloro bromide or silver bromide optically sensitized in the usual manner. The emulsions may be developing-out emulsions designed for development to negative images in which case the image obtained in the silver precipitating layer is a positive with respect to the original subject. If desired, the emulsion can be of the direct positive type with the result that the silver image developed in the emulsion is a positive and the image in the silver precipitating layer a negative in respect to the original subject. The procedures of Leermakers U.S. Patent 2,184,013 and Kendall et al. U.S. Patent 2,541,472 are useful in conferring the direct positive characteristics to the emulsions.

As mentioned, the colloid vehicle of the silver halide emulsion applied to the silver precipitating layer is an alkali-soluble acid-insoluble carboxylated cellulose derivative such as a dibasic acid half-ester of a cellulose ethyl ether; however, a portion of the colloid vehicle may be some other water-soluble organic colloid such as unhardened gelatin in minor quantity and of a kind such that the removal of the emulsion layer is not adversely affected in the later stages of the process.

Representative carboxylated cellulose derivatives are the alkali-soluble acid-insoluble dibasic acid esters of the cellulose ethyl ethers including the phthalic, succinic, and maleic acid esters of ethyl celluloses and their ammonium, alkali metal and amine salts, the esters being made from cellulose ethyl ethers having an alkoxy content of at least 42 percent and the esters having a dicarboxylic acid radical content of at least 5 percent and preferably at least 20 percent.

The ethyl cellulose phthalates made from cellulose ethyl ethers having at least 42 percent ethoxyl and containing at least 5 and preferably about 20 percent phthalyl are particularly efficacious for use in the emulsion layer of the sensitive elements of our invention. Thus a satisfactory cellulose ether phthalate can be made by the esterification of a cellulose ethyl ether containing 42% ethoxyl until about 5 to phthalation has taken place. A preferred cellulose ether phthalate is thus made from a cellulose ethyl ether containing 45% ethoxyl, the final ester containing about 24% phthalyl. The viscosity of this ester was about 3 to 6 cps. in a 3% solution containing 70% ethyl alcohol, isopropyl alcohol and 10% butanol. The ethyl cellulose phthalates employed may vary also as to viscosity. We have found that in the case of low viscosity esters, such as those whose salts have a viscosity of less than 10 cps. in 4 percent solution in water, it may be desirable to incorporate some plasticizer, such as triacetin or polyethyleneglycol in the ethyl cellulose phthalate composition.

The preparation and properties of these ether phthalates and methods for preparing emulsions containing them, suitable for application over the silver precipitating layer of our sensitive elements is described more fully in the Talbot and McCleary U.S. Patent 2,725,293, granted November 29, 1955. In addition to the peptizing agents disclosed in the last-mentioned invention for preparing the cellulose ether phthalate emulsions, gelatin is equally useful as shown in the examples hereinafter. Malm et al. U.S. Patent 2,718,667 and Hiatt et al. U.S. patent application Serial No. 272,697, filed February 20, 1952, may also be referred to for a description and synthesis of useful cellulose ether phthalates.

The alkali-soluble acid-insoluble dibasic acid esters of cellulose acetate such as various cellulose acetate phthalates are likewise useful as the emulsion vehicle of the invention. A typical cellulose acetate phthalate contains 34% phthalyl and 19% acetyl. These esters can be made by methods known in the art or as shown in the above Hiatt et al. invention. Similarly, cellulose phthalate containing about 50% phthalyl can be used as the major part of the emulsion vehicle.

What we claim is:

1. A method of forming a photographic image which comprises exposing to a subject an element including a support, a silver precipitating stratum on the support, and adhered to said stratum a light-sensitive emulsion layer containing silver halide uniformly dispersed in a member of the class consisting of an alkali-soluble acid-insoluble dibasic acid ester of a cellulose ethyl ether and an alkalisoluble acid-insoluble dibasic acid ester of a cellulose acetate, developing the latent image in the emulsion layer with an alkaline silver halide developing solution containing a quaternary ammonium salt having a linear chain of at least 7 atoms attached to a quaternary nitrogen atom, a hydroquinone, sulfite, a silver halide solvent, potassium chloride and a member of the class consisting of a monoalkyl-paminophenol silver halide developing agent and a 3-pyrazolidone silver halide developing agent, to form a silver image and an imagewise distribution of a soluble silver complex in the emulsion layer, allowing a portion of said silver complex to diffuse imagewise to said silver precipitating stratum and the silver of said portion of silver complex to be precipitated in said stratum, and removing the emulsion layer from said stratum.

2. A method of forming a photographic image which comprises exposing to a subject an element including a support, a silver precipitating stratum on the support, and adhered to said stratum a light-sensitive emulsion layer containing silver halide uniformly dispersed in an alkalisoluble acid-insoluble cellulose ethyl ether phthalate, developing the latent image in the emulsion layer with an alkaline silver halide developing solution containing a quaternary ammonium salt having a linear chain of at least 7 atoms attached to a quaternary nitrogen atom, hydroquinone, sulfite, a silver halide solvent, potassium chloride and 1-phenyl-3-pyrazolidone, to form a silver image and an imagewise distribution of a soluble silver complex in the emulsion layer, allowing a portion of said silver complex to diffuse imagewise to said silver precipitating stratum and the silver of said portion of silver complex to be precipitated in said stratum, and removing the emulsion layer from said stratum.

3. A method of forming a photographic image which comprises exposing to a subject an element including a support, a silver precipitating stratum on the support, and adhered to said stratum a light-sensitive emulsion layer containing silver halide uniformly dispersed in an alkalisoluble acid-insoluble cellulose ethyl ether phthalate, developing the latent image in the emulsion layer with an alkaline silver halide developing solution containing trisodium phosphate, a quaternary ammonium salt having a linear chain of at least 7 atoms attached to a quaternary nitrogen atom, hydroquinone, a silver halide solvent, potassium chloride and 1-phenyl-3-pyrazolidone, to form a silver image and an imagewise distribution of a soluble silver complex in the emulsion layer, allowing a portion of said silver complex to diffuse imagewise to said silver precipitating stratum and the silver of said portion of silver complex to be precipitated in said stratum, and removing the emulsion layer from said stratum.

References Cited in the file of this patent UNITED STATES PATENTS 2,685,514 Haist Aug. 3, 1954 2,704,721 Land Mar. 22, 1955 2,725,293 Talbot et al. Nov. 29, 1955 2,855,299 Rogers Oct. 7, 1958

Claims (1)

1. A METHOD OF FORMING A PHOPTOGRAPHIC IMAGE WHICH COMPRISES EXPOSING TO A SUBJECT AN ELEMENT INCLUDING AA SUPPORT, A SILVER PRECIPITATING STRATUM ON THE SUPPORT, AND ADHERED TO SAID STRATUM A LIGHT-SENSITIVE EMULSION LAYER CONTAINING SILVER HALIDE UNIFORMLY DISPERSED IN A MEMBER OF THE CLASS CONSISITNG OF AN ALKALI-SOLUBLE ACID-INSOLUBLE DIBASIC ACID ESTER OF A CELLULOSE ETHYL ETHER AND AN ALKALISOLUBLE ACID-INSOLUBLE DIBASIC ACID ESTER OF A CELLULOSE ACETATE, DEVELOPING THE LATENT IMAGE IN THE EMULSION LAYER WITH AN ALKALINE SILVER HALIDE DEVELOPING SOLUTION CONTAINING A QUATERNARY AMMONIUM SALT HAVING A LINEAR CHAIN OF AT LEAST 7 ATOMS ATTACHED TO A QUATERNARY NITROGEN ATOM, A HYDRO-E QUINONE, SULFITE, A SILVER HALIDE SOLVENT, POTASSIUM CHLORIDE AND A MEMBER OF THE CLASS CONSISTING OF A MONOALKYL-P AMINOPHENOL SILVER HALIDE DEVELOPING AGENT TO FORM A SILVER OLIDONE SILVER HALIDE DEVELOPING AGENT, TO FORM A SILVER IMAGE AND AN IMAGEWISE DISTRIBUTION AGENT, TO FORM A SILVER COMPLEX IN THE EMULSION LAYER, ALLOWING A PORTION OF SAID SILVER COMPLEX TO DIFFUSE IMAGEWISE TO SAID SILVER PRECIPI-PLEX TO BE PRECIPITATED IN SAID STRATUM, AND REMOVING THE EMULSION LAYER FROM SAID STRATUM.