US3695881A

US3695881A - Positive image production with unfogged internal image silver halide emulsion containing mercaptan retarder and a surface latent image silver halide emulsion

Info

Publication number: US3695881A
Application number: US92907A
Authority: US
Inventors: George W Luckey
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1970-11-25
Filing date: 1970-11-25
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03
Also published as: IT941236B; AU461131B2; AU3611271A; GB1372204A; BE775774A; CA988354A; FR2115933A5

Abstract

EXPOSED GRAINS OF A SILVER IODOHALIDE COATING SUCH AS A SURFACE IMAGE EMULSION CONTAINING SILVER IODO BROMIDE ARE DEVELOPED, RELEASING IODIDE IONS. THE IODIDE IONS RELEASED IMAGEWISE IN CONTACT WITH A DIFFERENT, UNEXPOSED SILVER HALDE LAYER, SCH AS AN INTERNAL IMAGE EMULSION, ACCELERATE SOLUTION OF THESE UNEXPOSED SILVER HALIDE GRAINS WHICH HAVE BEEN TREATED WITH A HETEROCYCLIC NITROGEN COMPOUND WHICH RETARDS SOLUTION OF THE SILVER HALIDE GRAINS IN A SILVER HALIDE SOLVENT SUCH AS SODIUM THIOSULFATE. THIS, FIXING OF THE UNEXPOSED LAYER PRODUCES A POSITIVE IMAGE OF SILVER HALIDE. POSITIVE OR NEGATIVE IMAGES CAN BE PRODUCED FROM THIS SILVER HALIDE IMAGE BY METHODS KNOWN IN THE ART SUCH AS SOLVENT TRANSFER, DYE BLEACH, DYE TRANSFER, REDUCTION AND INCORPORATED COUPLER SYSTEMS. X-RAY IMAGES CAN ALSO BE ENHANCED USING THE SYSTEM DESCRIBED IN THIS INVENTION.

Description

United States Patent 3,695,881 POSITIVE IMAGE PRODUCTION WITH UN- FOGGED INTERNAL IMAGE SILVER HALIDE EMULSION CONTAINING MERCAPTAN RE- TARDER AND A SURFACE LATENT IMAGE SILVER HALIDE EMULSION George W. Luckey, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Nov. 25, 1970, Ser. No. 92,907 Int. Cl. G03c 1/76, 3/00, 5/54 US. Cl. 96-49 12 Claims ABSTRACT OF THE DISCLOSURE 'Exposed grains of a silver iodohalide coating such as a surface image emulsion containing silver iodo bromide are developed, releasing iodide ions. The iodide ions released imagewise in contact with a different, unexposed silver halide layer, such as an internal image emulsion, accelerate solution of these unexposed silver halide grains which have been treated with a heterocyclic nitrogen compound which retards solution of the silver halide grains in a silver halide solvent such as sodium thiosulfate. Thus, fixing of the unexposed layer produces a positive image of silver halide. Positive or negative images can be produced from this silver halide image by methods known in the art such as solvent transfer, dye bleach, dye transfer, reduction and incorporated coupler systems. X-ray images can also be enhanced using the system described in this invention.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to photography and particularly to processes and elements for forming images in exposed photographic silver halide layers. More particularly, this invention concerns the production of photographic images by a direct positive process, and to the production of photographic images with a light-sensitive element having negative and positive layers.

In one aspect, this invention relates to a new simplified negative-positive process. In another aspect it relates to the preparation of direct positives by a novel process utilizing a photographic element having negative and positive layers in a single photographic element that can be activated or developed with an aqueous alkaline composition. In still another aspect it relates to a new direct positive process suitable for reproducing line and halftone originals.

Description of the prior art It is known that the silver halide crystals of the type employed in photographic emulsions have both surface and internal sensitivity to light, and that these types of sensitivity may be varied considerably among different emulsions. Silver halide crystals having a high ratio of surface to internal sensitivity comprise the silver halide grains used in the majority of photographic emulsions.

lSilver halide grains having a high ratio of internal to surface sensitivity are also well known but are less generally employed in practice. Emulsions containing such grains are described, for example, in Mees, The Theory of the Photographic 'Frocess, p. 221 Revised Edition,

3,695,881 Patented Oct. 3, 1972 ice 1954; in Journal of the Optical Society of America, 31 (1941), p. 385, and in Davey and Knott, US. 'Pat. 2,592,- 250, issued Apr. 8, 1952.

It has been disclosed in Capstaif, US. Pat. 1,303,635, that a two layer photographic film may be processed to yield an image in the upper layer which is subsequently used to modulate printing light to form an image of opposite sign in the lower emulsion. Luckey et al., US. Pat. 2,996,382 issued Aug. 15, 1961, discloses that iodide ion liberated during the development of a surface latent image in a silver bromiodide emulsion migrates to some prefogged internal image silver halide emulsion grains, either in the same or in an adjacent emulsion layer, to catalyze the development of said grains and thus intensify the original silver image. Although these references disclosed secondary image formation, each of the processes requires a number of steps such as the second exposure to light in the former reference and the necessity of using internal prefogged silver halide in the latter.

It is an object of this invention to provide new simplified negative-positive processes and elements.

It is another object of this invention to prepare direct positives by a novel process utilizing a photographic element or elements having negative and positive layers whereby there is a built-in safety factor against over exposure of the positive layer.

It is another object of this invention to prepare a direct positive by a new process with a single photographic element that can be activated or developed with any conventional developing composition.

It is also an object of this invention to prepare by a new method direct positives from a photographic element containing iodide ion which is liberated during the development of a surface latent image.

Other objects will be evident from the following:

SUMMARY OF THE INVENTION We have now discovered that the development of exposed grains of a silver halide coating in which the halide comprises 0.5 to mole percent iodide in appropriate solutions releases iodide ion which accelerates solution in certain fixing baths of other grains of silver halides which have been treated or coated With an agent such as phenyl mercapto tetrazole that retards solution in an aqueous fixing bath. The property of the silver iodide or silver iodohalide emulsion to release iodide ion is used to obtain positive and negative images simultaneously, by exposing the coating of silver iodide or iodohalide emulsion, developing the exposed coating in contact with a layer of treated silver halide grains, separating the two layers, and finally fixing both coatings in appropriate solutions. Areas of the second silver halide layer that have been in contact with developing areas of the silver iodide or iodohalide layer fix out more rapidly so a positive image composed of silver halide is obtained. This image may be used Without further treatment or the silver halide may be developed or treated with intensifying solutions.

It has also been discovered that an unhardened silver iodide or iodohalide layer can be coated on top of the treated silver halide layer. In this case, the exposed and developed silver iodide or iodohalide layer is removed such as by washing before fixing the treated silver halide layer.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT One embodiment of this invention relates to a process for obtaining positive and negative images simultaneously. This process involves the exposing of a silver halide emulsion, in which said halide comprises iodide and which is a surface latent image emulsion, developing the exposed coating in contact with the layer of retarding agent treated silver halide grains in an emulsion which is preferably an internal image emulsion, separating the two layers, and fixing both coatings in appropriate solutions.

Another embodiment of this invention relates to processes used to obtain positive and negative images simultaneously wherein the silver iodide or iodohalide layer is coated on top of the retarding agent treated silver halide layer.

In another embodiment this invention relates to a photographic element having a support and layers which consist of a first discrete silver halide emulsion layer which has been previously treated with an agent to retard solution and a second contiguous discrete silver iodide or iodohalide emulsion layer. The layers may be coated in either order.

In still another embodiment, photographic elements of this invention can be used in photographic dye-bleach systerns.

The light sensitive silver iodide or iodohalide can be silver iodide or any of the iodohalides used in photographic emulsions, such as for example, iodobromide, iodobromochloride, and iodochloride. The halide comprises about 0.5 to 100 percent iodide, preferably about 5 to 30 percent iodide. The silver iodide or iodohalide emulsion can be one which forms a latent image predominantly on the surface of the silver halide grains known as a surface latent image emulsion.

The surface latent image emulsions used in the practice of this invention have a relatively high degree of surface sensitivity and relatively low internal sensitivity while the internal image emulsions used have a high degree of internal sensitivity but relatively low surface sensitivity. The surface latent image emulsions contain silver halide grains that have substantial surface sensitivity and form latent images when exposed to light on the surface thereof. Any of the photographic silver halides can be used in the preparation of the surface latent image emulsions and include, for example, silver bromoiodide, silver chloroiodide, silver chlorobromoiodide, and the like, the preferred halide being bromoiodide. For a description of suitable emulsions that form latent images on the surface of the silver halide grains, reference is made to Trivelli and Smith in The Photographic Journal, volume LXXX, July 1940, (pp. 285-288). Typically, such emulsions are those which, when measured according to normal photographic testing techniques by coating a test portion of the emulsion on a transparent support, exposing the test portion to a light intensity scale for a fixed time between 0.01

.and 1 second and development for 6 minutes at 68 in Developer A as hereinafter defined, have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of the same emulsions which has been exposed in the same Way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F., and developed for 5 minutes at 65 F. in Developer B as hereinafter defined. Developer A is the usual type of surface image developer and Developer B is an internal developer having high silver halide solvent activity.

The degree of internal sensitivity of the surface latent image emulsions is subject to wide variation. The surface latent image emulsions can have relatively little internal se n sitivity or they can have a fair amount of internal sensitivity, but preferably not greater than the surface sensitivity. The surface latent image emulsions can have high or low contrast since useful effects can be obtained with both types of emulsions. The surface latent image emulsions can also be characterized as having a D greater than about 0.50 when coated at a coverage of about 540 mg. silver per square foot, exposed to a step wedge and processed for 12 minutes in Developer C as hereinafter defined. Particularly good results are obtained with surface image silver iodohalide surface latest image emulsions such as silver bromoiodide emulsions. Such emulsions can contain varying concentrations of iodide although especially useful results are obtained with such iodohalide surface latent image emulsions containing from about 0.5 to about 99 mole percent iodide as decribed in U.S. Pat. 2,996,382 issued to Luckey et al. Aug. 15, 1961.

The internal latent image photographic silver halide emulsions employed in the practice of this invention contain internal latent image silver halide grains. Any of the photographic silver halides can be used in the preparation of these grains and include for example silver bromide, silver chloroiodide, silver chlorobromoiodide, silver chlorobromide, silver chloride and the like. For a description of suitable emulsions that form latent images internal to the silver halide grains reference is made to Davey et al. U.S. Pat. 2,592,250 issued Apr. 8, 1952, Luckey and Hoppe U.S. Pat. 2,996,382 issued Aug. 15, 1961 and Luckey and Hoppe U.S. Pat. 3,178,282 issued Apr. 13, 1965. Typically, such emulsions are those which, when measured according to normal photographic techniques in their unfogged state by coating a test portion of the emulsion on a transparent support, exposing to a light intensity scale having a fixed time between 0.1 and 1 second, bleaching 5 minutes in 0.3% potassium ferricyanide solution at 65 F. and developing for about 5 minutes at 65 F. in Developer B described hereinafter, have a sensitivity measured at a density of 0.1 above fog appreciably greater (for example, at least 1.4 log E greater) than the sensitivity of an identical test portion which has been exposed in the same way and developed for 6 minutes at 68 F. in Developer A described hereinafter. The surface D of the unfogged internal image emulsions is generally less than about 0.30 when the emulsions are exposed to Dmax and processed for 8 minutes in Developer C identified hereinafter.

The ratio of the surface latent image emulsion to the internal image emulsion can be varied, depending upon the types of emulsions used, the contrast of the emulsions and other known variables.

The following developing solutions are referred to hereinabove.

Grams N-methyl-p-aminophenol sulfate 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5 Water to make 1 liter.

N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to make 1 liter.

N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite, desiccated 3O Hydroquinone 2.5 Sodium metaborate 10 Potassium bromide 0.5

Water to make 1 liter.

The dispersing agent for the silver'halide can be gelatin or other hydrophilic materials such as colloidal albumin, cellulose derivatives, synthetic resins, such as polyvinyl compounds, acrylamide polymers and the like.

The emulsion layers of the invention can be coated on a wide variety of supports. Typical supports include those generally employed for photographic elements, as exemplified by cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film, and related films or resinous materials as well as glass, paper, metal, wood and the like. Supports, such as paper that are coated with a-olefin polymers, particularly polymers of a-olefins containing 2-10 carbon atoms, as for example, polyethylene, polypropylene, ethylene butene copolymers, and the like, can also be employed.

The photographic emulsions and elements can also contain additional additives, particularly those known to be beneficial in photographic emulsions, as exemplified by optical sensitizers, chemical sensitizers, speed increasing materials, hardeners, plasticizers, and the like, such as those described in Barnes et al. US. Pat. 3,392,019 issued July 9, 1968, Blout et al. US. Pat. 2,949,359 issued Aug. 16, 1960, Ilford British Pat. 999,146 issued July 21, 1965 and Dunn US. Pat. 3,297,446 issued Ian. 10, 1967.

The emulsions can be used in photographic elements intended for color photography and thus can contain color-forming couplers or used as emulsions to be developed by solutions containing couplers or other colorgenerating materials or emulsions of the mixed-packet type.

Solution retarding agents are those which, when added to or coated on silver halide grains reduce the solubility of the grains in an aqueous solution of solubilizing agent, such as sodium thiosulfate, commonly referred to as hypo. Typical solution retarding agents for treating silver halide grains include compounds containing a mercapto group. Particularly useful compounds are, for example, heterocyclic nitrogen compounds containing at least one mercapto function, which is bonded to a carbon atom which is in the alpha position with respect to a nitrogen atom in a heterocyclic ring. The heterocyclic nucleus of such compounds contains one or more heterocyclic rings Where in the heterocyclic atoms (i.e., atoms other than carbon, including nitrogen, oxygen, sulfur, selenium and tellurium) are members of at least one heterocyclic ring. In the monoheterocyclic nitrogen compounds, the heterocyclic atoms are members of a single heterocyclic ring which can be fused or condensed to one or more rings which do not contain heterocyclic atoms. In contrast, diheterocyclic nitrogen compounds contain fused or condensed heterocyclic rings in which the heterocyclic atoms are members of two heterocyclic rings. Suitable heterocyclic nitrogen compounds from which the heterocyclic nuclei can be derived include the azoles, oxazoles, selenazoles, triazoles (e.g., 1,2,4-triazoles, especially those containing an amino substituent in addition to the mercapto function), diazoles (e.g. imidazoles, benzimidazoles, imidazolines), pyrimidines, 1,2,4-triaziues, s-triazines, monoazoles (e.g., benzoxazoles, benzothiazoles), azaindenes (e.g. tetrazaindenes) and the like.

Marcapto heterocyclic nitrogen compounds which can be employed in the practice of this invention can be represented by the formula:

1 'I=o-sX where Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6, preferably 5, atoms in a heterocyclic ring and SX is a mercapto function. The mercapto function or group can be in the free (Sl-I) form or in the salt (-SX) form. X is a cation, for example, hydrogen, an alkali metal such as sodium or potassium, ammonium or an organic amine residue of such amines as triethyl amine, triethanol amine morpholine, and the like. In addition, many of the mercapto heterocyclic nitrogen compounds can be in the tautomeric form, for example, in the thione form, in which case the labile hydrogen atom in the mercapto function becomes bonded to the nitrogen atom and the group becomes a thiocarbonyl O=S) group.

Any of the heterocyclic compounds which contain at least one nitrogen atom and a mercapto function, as described herein, will act as solution retarding agents in the practice of this invention. However, particularly good results are obtained with the mercapto azoles, especially the S-mercapto tetrazoles 5 mercapto tetrazoles which can be employed in the practice of this invention include those having the formula:

I I\ I l-R I SX where R is an aliphatic or aromatic radical containing up to 30 carbon atoms and SX is as defined hereinbefore. R can be hydrocarbon or non-hydrocarbon and includes alkyl or aryl radicals which can contain atoms or groups NHCOR' wherein R is a hydrocarbyl radical containing up to 22 carbon atoms and SX is as defined. hereinbefore. Suitable R groups include, for example, alkyl, aryl, alkaryl, aralkyl or alkaralkyl radicals, the preferred R groups being alkyl radicals containing l-8 carbon atoms. As shown in the formula, the -NHCOR' group on the phenyl ring can be in the ortho, meta or para position. Such compounds can be prepared by the reaction of the 1- (aminophenyl) 5-mercaptotetrazole hydrochloride with an acid chloride having the formula RCOCl where R has the above indicated meaning. The l-(aminophenyl)- S-mercaptotetrazole is prepared by reaction of an aminoacetanilide (ortho-, meta-, or para-It, with thiophosgene to result in the formation of the corresponding acetamidophenyl isothiocyanate which is the reacted with an azide to form the mercaptotetrazole ring. This product is hydrolyzed with concentrated hydrochloric acid to form the 1-(aminophenyl)-5-mercaptotetrazole hydrochloride. The formation of the mercaptotetrazole ring has been described by Stolle and Strittmatter in the Journal fuer Praktische Chemie, vol. 133, pp. 60 to 64 and by Stolle and Fr. Henke-Stark in the same journal, vol. 124, pp. 261-300. An alternate method for the production of the l-phenyl-5-mercaptotetrazole is to react an acetamidophenyl substituted thiosemicarbazide with nitrous acid as described by Freund and Hempel in Berichte der Deutschen Chemischen Gesselsdarft, vol. 28 at p. 77.

Acid chlorides which can be employed in the reaction with the mercaptotetrazole hydrochloride include the chlorides of the following acids: acetic, aceto-acetic, difluoroacetic, propionic, valeric, iso-valeric, caproic, caprylic, undecanoic, stearic, benzoic, o-acetoxybenzoic, anthranilic, 3-amino-6-nitro-benzoic, p-tolyl acetic, 2,4- dinitrophenyl-acetic, methyl-sulfonic, o-toluene sulfonic, benzene sulfonic, p-bromobenzene sulfonic and o-formylbenzene sulfonic acid.

Some specific heterocyclic nitrogen compounds which can be employed in the practice of this invention are, for example,

Z-mercaptol-phenyl-tetrazole,

2-mercapto-5 -phenyl-1 ,3,4-octadiazole,

1- 3-capramido -phenyl-S-mercaptotetrazole,

1- 3-pelargonamido -phenyl--mercaptotetrazole, 2,6-dimethyl-1,3 ,3a,7-tetrazaindene-4-thiol, Z-mercapto benzoxazole, 1-phenyl-S-mercaptotetrazole, 5-ethyl-6-methyl-1,2,3 a,7-tetrazaindene-4-thio, 2-mercapto imidazole, 4-methy1-1,2,3a,7-tetrazaindene-6-thio, 4-thiono-4a-azanaphthalene, Z-mercapto-B-naphthoxazole-2-thionothiazolidone, 4-mercapto-l-thia-3 ,5 ,7-triazaindene, 4-hydroxy-6-methyl-1,2,3 a,7-tetrazaindene-3-thiol, 3-mercapto-1,2,4-triazole,

Z-mercapto-S- (p-hydroxy-phenyl 1,3 ,4-oxadiazole and Z-mercapto benzothiazole.

A number of such suitable mercapto heterocyclic nitrogen compounds are disclosed in Tregillus et al. U.S. Pat. 3,017,270, issued Jan. 16, 1962. The solution retarding agents employed in the practice of this invention which retard solution in a silver halide solvent such as sodium thiosulfate, are adsorbed to the silver halide grains. This can be accomplished by adding the agent to the emulsion prior to coating the emulsion. The agent can be added to the emulsion in aqueous solution or in any convenient solvent not injurious to the emulsion, such as lower aliphatic alcohols, acetone, and the like. In general, solution retarding agents are used in the silver halide emulsion in concentrations of about 50 mg. to about 5 grams, preferably about 250 mg. to about 2 /2 grams per mole of silver halide.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 One gram of 1-(3-capramido)-phenyl-5-mercaptotetrazole is added to an amount of unfogged silver chlorobromide internal image emulsion equivalent to 1 mole of silver and the mixture is coated on film support in the usual way at a coverage of 175 mg. Ag/ft A coating of coarse grain silver iodobromide emulsion With 206 mg. Ag/ft. is exposed for 12 seconds to the light from a tungsten lamp filtered by a Kodak Wratten No. 47B Filter and a neutral density of 0.9. The light passes through a negative of a printed image which has clear letter areas. (When this exposure is decreased to /25 of the value used in this run, it produces a density 0.3 above gross fog on a high speed panchromatically sensitized silver bromoiodide emulsion coating after development for 8 minutes in Kodak Developer DK-SO at 68 F., fixing, and washing.)

After exposure, the silver iodobromide emulsion is dipped for 10 seconds in a developer that is prepared in the following manner:

Dissolve 1 gram of l-phenyl-S-pyrazolidone and 0.2 gram of the sodium salt of 2-anthraquinone sulfonic acid, 20 grams of hydroquinone, 50 grams of anhydrous sodium sulfite, 20 grams of sodium metaborate (S-H O), and grams of potassium bromide in sufiicient water to make 1 liter of solution.

The temperature of the developer is 73 F. The silver iodohalide emulsion is then removed from the developer,

shaken, and rolled down lightly on a dry piece of film support containing the unfogged silver chlorobromide emulsion described above containing the tetrazole, that is placed on a stainless steel block and kept at a temperature of 75 F. by circulation of water from a constant temperature bath. After 2 minutes, the two films are removed from the block, placed in a stop bath and separated. The lights are turned on and the film support containing the unfogged silver chlorobromide interal image emulsion is placed in a solution of sodium thiosulfate which is at a temperature of 70 F. A good positive image is produced in 8 seconds. The areas of the film support containing the unfogged silver chlorobromide internal image emulsion that have been in contact with developing areas of the negative fix much more rapidly than areas that have been in contact with undeveloping areas of the negative. The film support containing the unfogged silver chlorobromide internal image emulsion is then removed from the fixing bath and washed with running water. The silver iodobromide emulsion is fixed and Washed in the usual Way. Another fixing bath is used for this, so that the bath used for the film support containing the unfogged silver chlorobromide internal image emulsion is not contaminated with iodide ion from the silver iodobromide. The negative image is also of good quality. Similar results are obtained when other heterocyclic nitrogen compounds containing a mercapto group are employed in the above procedure. For example, other compounds which give good results using the above procedure are 1- (3 pelargonamido)-phenyl S-mercaptotetrazole, 2,6-dimethyl 1,3,3a, 7 tetrazaindene-4-thio, Z-mercapto benzoxazole, 1 phenyl 5 mercaptotetrazole, Z-mercaptoimidazole, 3 mercapto 1,2,4-triazole and Z-mercaptobenzothiazole.

EXAMPLE 2 The example described in Example No. 1 is repeated, but this time, the unexposed coating of unfogged silver chlorobromide internal image emulsion on film support is also bathed in the developer before placing it on the steel block. The rest of the procedure is the same, except that the time on the block is seconds, the temperature of the fixing bath is 71 F., and the film support containing the unfogged silver chlorobromide internal emulsion is treated in the fixing bath for 10 seconds. In this case, one end of the negative is given a graded light exposure, and this gradation is reproduced in the positive. Thus, continuous tone can be achieved with the process.

EXAMPLE 3 Example No. 1 is repeated, but the time on the coating block is only 50 seconds. The time required to obtain a positive image in the fixing bath with the film support containing the unfogged silver chlorobromide internal image emulsion is 20 seconds instead of 8 seconds. The other conditions are similar to those described in Example No. 1.

EXAMPLE 4 Example No. 1 is repeated, but this time the silver iodobromide emulsion is not immersed in the developer and the film support containing the unfogged silver chlorobromide internal image emulsion is immersed for 30 seconds in the developer before placing it on the block. After development for seconds at 75 F., the layers are separated in the stop bath, and the film support containing the unfogged silver chlorobromide internal image emulsion is placed in the fixing bath. A good positive image forms in 10 seconds, and a good negative image is obtained by fixing and washing the silver iodobromide emulsion in the usual manner.

EXAMPLE 5 Example No. 4 is repeated, and the positive image is treated with the developer after exposure to a mercury vapor lamp. The density and contrast of the positive image is improved by this treatment.

EXAMPLE 6 One gram of 1-(3-capramido)-phenyl-5-mercaptotetrazole is added to an amount of unfogged silver chlorobromide internal image emulsion equivalent to 1 mole of silver and the mixture is coated on a film support in the usual way and then hardened by incorporation of hardening agents as disclosed in Burness et al., Belgian Pat. 723,807, published Jan. 15, 1969. A coating of unhardened silver iodobromide emulsion is then applied using conventional coating technique over the internal image emulsion.

These layers are then exposed for 15 seconds to the light from a tungsten lamp.

After exposure, the layers are dipped for 10 seconds in a developing solution as described in Example 1.

The silver iodohalide emulsion is then washed olf and a good quality positive image is obtained in the hardened layer after fixing.

The sensitometric characteristics of the positive images can be controlled by varying the times and conditions of fixing. The fixing process may be performed in room light thereby permitting an inspection step during processing. The sensitometric speed of the positive images is essentially equal to that of the negative image. The fixing time can be quite short, e.g. times of 5-10 seconds are possible.

The developers that are useful, according to this invention are those which have been generally used to develop photographic systems. It is, however, preferable to adjust the solvent characteristics of the developer so that very little iodide ion is released by unexposed areas of the silver iodohalide coating. Preferably, the developer should be a low solvent or surface developer and should not contain excessive amounts of sulfite, bromide, or other agents which increase the solution of silver halide grains.

The photographic elements of this invention may contain incorporated developing agents such as hydroquinones, catechols, aminophenols, 3-pyrazolidones, ascorbic acid and its derivatives, reductones and phenylenediamines. Combinations of developing agents can be employed in the practice of the invention. The developing agents can be in a silver halide emulsion and/or in another suitable location in the photographic element. The developing agents may be added from suitable solvents or in the form of dispersions as described in Yackel US. Pat. 2,592,368 and Dunn et a1. French Pat. 1,505,778.

The photographic and other hardenable layers used in the practice of this invention can be hardened by various organic or inorganic hardeners, alone or in combination, such as the aldehydes, and blocked aldehydes, ketones, carboxylic and carbonic acid derivatives, sulfonate esters, sulfonyl halides and vinyl sulfonyl ethers, active halogen compounds, epoxy compounds, aziridines, active olefins, isocyanates, carbodiimides, mixed function hardeners and polymeric hardeners such as oxidized polysaccharides like dialdehyde starch and oxyguargum and the like.

This invention is also readily adaptable to dye-bleach processes as described in Chapter 24 of History of Color Photography, J. S. Friedman, American Photographic Publishing Co., Barton (1944), wherein a silver halide layer contains an image dye with a color complementary to its sensitivity. The image dye is destroyed in the area of silver development, leaving dye image in those areas where no development occurs. In this instance the dye is contained in the layer having therein a solution retarding agent; when the image silver is removed by being fixed out very quickly, the dye remains. The non-image areas are then reduced to silver and the element is given the usual bleach and fix bath to remove the silver and leave the dye only in the originally exposed areas.

This invention is also readily adaptable for using a dye-bleach element in X-ray photographic systems. The

X-rays and screen emission expose an image pattern on the film herein described. In the areas of exposure the silver becomes fixable and a positive silver halide image is formed in the unexposed areas. This silver halide is developed and then the silver and dye in unexposed areas are removed with the bleach and fix bath, leaving a negative dye image which has high contrast.

This system can be used to make color images particularly for color proofing by incorporating the necessary ingredients into both the photographic elements and/or in the processing baths. One of the advantages of this system for color proofing is that after initial treatment, the dye destruction or formation can take place in room light so the operator can readily evaluate the degree of processing to get the image quality desired.

The silver halide image can also be converted to a silver image with high covering power by a solvent transfer process, or the silver image formed from the silver halide image can be intensified by methods described in Chapter 31 of Chimie Photographique, P. Glafkides, Publications Paul Montel, Paris, France (1957).

The invention has been described in detail with particu lar reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A photographic element comprising a support, a discrete unfogged internal image silver halide emulsion layer containing a mercapto heterocyclic nitrogen compound retarding agent which retards solution of silver halide in an aqueous silver halide solvent and contiguous to said discrete silver halide layer, a discrete layer of a surface latent image silver halide emulsion in which said halide comprises about 0.5 to about mole percent iodide.

2. An element of claim 1 in which said retarding agent is a S-mercaptotetrazole.

3. An element according to claim 1 wherein said retarding agent is 1 (3 capramido) phenyl 5 mercapto-tetrazole.

4. An element according to claim 1 wherein said retarding agent is 1-phenyl-5-mercaptotetrazole.

5. An element of claim 1 in which said surface latent image silver halide layer containing silver iodide comprises an unhardened emulsion coated over said first discrete internal image silver halide emulsion layer.

6. An element of claim 1 in which from 50 mg. to about 5 g. of said retarding agent per mole of silver halide is contained in said discrete unfogged layer.

7. A process for forming an image which comprises:

(a) developing with a silver halide surface developer an imagewise exposed surface latent image emulsion layer in which said halide comprises about 0.5 to 100 mole percent iodide contiguous to a separate unfogged internal image silver halide emulsion layer comprising a mercapto heterocyclic nitrogen compound retarding agent which retards solution of silver halide in an aqueous silver halide solvent to release iodide ion in the developed areas of said exposed surface latent image silver halide emulsion,

(b) separating said layers, and

(c) fixing said internal image silver halide layer with a silver halide solvent. 8. A process for forming an image which comprises: (a) developing with a silver halide surface developer an imagewise exposed surface latent image silver halide emulsion layer in which said halide comprises about 0.5 to 100 mole percent iodie on a support,

(b) bringing the developing exposed surface latent image silver halide emulsion into contact with a discrete unfogged internal image silver halide emulsion layer on a support, said emulsion comprising a mercapto heterocyclic nitrogen compound retarding agent which retards solution of silver halide in aqueous sodium thiosulfate,

(c) separating the two layers, and

1 1 (d) fixing said internal image silver halide emulsion layer with a silver halide solvent and fixing said imagewise exposed surface latent image silver halide layer. 9. A process of claim 7 in which said agent is a S-mercaptotetrazole.

10. A process according to claim 7 wherein said agent is 1-(3-capramido)pheny1-S-mercaptotetrazole.

11. A process according to claim 7 wherein said agent is 1-phenyl-S-mercaptotetrazole.

12. A process of claim 7 in which said exposed silver halide layer containing silver iodide comprises an unhardened emulsion.

12 References Cited UNITED STATES PATENTS NORMAN G. TORCHIN, Primary Examiner 10 W. H. LOUIE, JR., Assistant Examiner US. Cl. X.R.