US3537858A

US3537858A - Reversal silver halide emulsions

Info

Publication number: US3537858A
Application number: US615360A
Authority: US
Inventors: Albert W Wise
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1966-03-11
Filing date: 1967-02-13
Publication date: 1970-11-03
Anticipated expiration: 1987-11-03
Also published as: DE1547780B2; GB1186719A; DE1547791B2; SE345528B; GB1186718A; US3531290A; BE695354A; BE695361A; CH470689A; DE1547791A1; US3501309A; BE695369A; DE1547788A1; DE1547780A1; US3510348A; DE1547791C3; GB1187411A; DE1547785A1; GB1186715A; JPS4831843B1

Description

United" States Patent 01 he e 3,537,858 Patented Nov. 3, 1970 3,537,858 REVERSAL SILVER HALIDE EMULSIONS Albert W. Wise, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey N Drawing. Filed Feb. 13, 1967, Ser. No. 615,360 Int. Cl. G03c 1/28, 1/08 U.S. Cl. 96-107 18 Claims ABSTRACT OF THE DISCLOSURE Halogen accepting compounds, particularly merocyanine dyes are employed to improve the photographic speed of direct-positive silver halide emulsions. A still further increase in photographic speed is obtained when the halogen accepting compounds are used in combination with sulfonated organic compounds as described. The photo graphic silver halide grains present in the direct-positive emulsions comprise a central core of silver halide containing centers which promote the deposition of photolytic silver and an outer shell or covering for such core of a fogged silver halide.

This invention relates to photographic emulsions, their preparationand use. In one of its aspects, this invention relates to a novel direct-positive or reversal emulsion. In a specific aspect, this invention relates to a fogged directpositive photographic silver halide emulsion containing a halogen accepting compound and to a photographic element comprising a layer of such emulsion.

It is known that photographic silver halide emulsions can be prepared from silver halide grains comprising a central core and one or more contiguous layers which can differ from one another in composition. Such grains can be prepared, e.g., as shown in Porter et al. US. Pat. 3,206,313 issued Sept. 14, 1965 and German Pat. 1,169,- 290 granted Apr. 30, 1964. Reversal or direct-positive emulsions can be prepared from fogged silver halide grains comprising a central core and one or more contiguous layers. Such reversal or direct-positive emulsions contain silver halide grains comprising a central core of silver halide containing centers which promote the deposition of photolytic silver and an outer shell or covering for such core of a fogged or spontaneously developable silver halide. The fogged shell of such grains develops to silver Without exposure. Reversal or direct-positive emulsions of this type represent a distinct advance in the art, but they do not exhibit the high photographic speed which is necessary or at least desirable for many applica tions, including, for example, use in the duplicating or electron recording fields.

It is accordingly an object of this invention to provide a novel class of photographic reversal or direct-positive emulsions.

It is another object of this invention to provide directpositive silver halide emulsions having high sensitivity or photographic speed.

It is another object of this invention to provide directpositive photographic silver halide emulsions that combine high sensitivity or photographic speed with a low background or Dmin density which emulsions can be processed with conventional surface developing compositions.

It is still another object of this invention to provide direct-positive silver halide emulsions that have higher sensitivity than conventional direct-positive silver halide emulsions utilizing the Herschel effect.

Still another object of this invention is to provide fogged direct-positive photographic silver halide emulsions containing silver halide grains comprising a central core and one or more contiguous layers and which have adsorbed to such grains a halogen accepting compound.

Still another object of this invention is to provide a means for effecting a substantial increase in the photographic speed or sensitivity of fogged direct-positive photographic silver halide emulsions.

These and other objects of this invention are accomplished with a uniformly fogged direct-positive photographic silver halide emulsion comprising (1) silver halide grains comprising a central core of silver halide containing centers which promote deposition of photolytic silver and an outer shell covering said core comprising a fogged silver halide that develops to silver without exposure and adsorbed to said fogged grains, (2) a halogen accepting compound having an anodic polarographic halfwave potential less than 0.85 and a cathodic polarographic halfwave potential which is more negative than 1.0.

It is a significant feature of this invention that the halogen accepting compounds adsorbed to the fogged silver halide grains have the polarographic halfwave potentials set forth hereinbefore. Thus, as shown by Example 2 which follows, fogged direct-positive silver halide emulsions containing halogen accepting compounds which do not have these polarographic halfwave potentials do not exhibit the excellent photographic speed or sensitivity characteristics of the emulsions of this invention.

Another significant feature of this invention is that certain high molecular weight organic compounds, particularly sulfonated compounds as described hereinafter, can be used in combination with halogen accepting compounds to effect an even greater increase in photographic speed or sensitivity. This feature of the invention is illustrated by Example 6 which follows.

The silver halide grains employed in the practice of this invention comprise a central core of a silver halide containing centers which promote the deposition of photolytic silver and an outer shell or covering for such core of a fogged or spontaneously developable silver halide. Silver halide grains containing such fogged shells develop to silver without exposure.

Before shell formation, the core forming photographic silver halide is chemically or physically treated by methods previously described in the prior art to produce centers to promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described herein. Chemical sensitization techniques of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, vol. XXVIII, January 1957, pages 57 to 65, are particularly useful. Such chemical sensitization includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitization, i.e., treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

When the core forming emulsion is chemically sensitized, it is preferably sensitized so that when examined according to normal photographic testing techniques by coating a test portion of the emulsion on a transparent support, exposing to a light intensity scale for a fixed time between 0.01 and 1 second and developed for 6 minutes at 68 F. in Developer A, as hereinafter defined, it has a sensitivity greater than the sensitivity of an identical test portion of the same emulsion (measured at a density of 0.1 above fog), which has been exposed in the same way, bleached 5 minutes in an aqueous 0.3 percent potassium ferricyanide solution at 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.

DEVELOPER A Grams N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0 Potassium metaborate 35.0 Potassium bromide 1.0 Water to 1.0 liter. pH of 9.6.

DEVELOPER B N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90.0 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5.0 Sodium thiosulfate 10.0

Water to 1.0 liter.

The core forming emulsions can be chemically sensitized by any method suitable for this purpose. For example, the core forming emulsions can be digested with naturally active gelatin, or sulfur compounds can be added, such as those described in Sheppard US. Pat. 1,574,944, issued Mar. 2, 1926; Sheppard et al. US. Pat. 1,623,499, issued Apr. 5, 1927; and Sheppard et al. US. Pat. 2,410,689, issued Nov. 5, 1946.

The core forming emulsions can also be chemically sensitized with gold salts as described in Waller et al. US. Pat. 2,399,083, issued Apr. 23, 1946, and Damschroder et al. US. Pat. 2,642,361, issued June 16, 1953. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

The core forming emulsions can also be chemically sensitized with reducing agents, such as stannous salts (Carroll US. Pat. 2,487,850, issued Nov. 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones US. Pat. 2,518,698, issued Aug. 15, 1950), polyamines, such as spermine (Lowe and Allen US. Pat. 2,521,925, issued Sept. 12, 1950), or bis (fl-aminoethyDsulfide and its watersoluble salts (Lowe and Jones US. Pat. 2,521,926, issued Sept. 12, 1950).

The core forming emulsions can also be treated during or after the formation of the silver halide with salts of polyvalent metals such as bismuth, the noble metals and/ or the metals of Group VIII of the Periodic Table, such as ruthenium, rhodium, palladium, iridium, osmium,

platinum and the like. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, sodium chloropalladite and the like.

The core forming emulsions can also be subjected to fogging by exposure to light either to low or high intensity light, to produce centers which promote the deposition of photolytic silver prior to forming the shell thereon.

The shell of the aforementioned silver halide grains can be prepared by precipitating over the core grain a light sensitive silver halide that can be fogged and which fog is removable by bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the silver halides to the core. The silver halide shell is surface fogged to make it developable to metallic silver with conventional surface image developing compositions. Substantially all of the silver halide grains in an emulsion are fogged prior to exposure and/ or processing, i.e., such emulsions are uniformly fogged. Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core forming emulsion, high intensity light and like fogging means Well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged, for example, reduction fogged with a reducing agent such as stannous chloride. Fogging by means of a reduction sensitizer, a noble metal salt such as a gold salt plus a reduction sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized.

In one embodiment of the invention, the core of the aforementioned grains is a coarse grained silver halide and a silver halide from a finer grained silver halide is deposited thereon by Ostwald ripening to form the shell. Also, coarse grained silver halides can be used to form a shell over a finer grained core when the shell-forming silver halide is more water-soluble than the core silver halide. In another embodiment of the invention the silver halide shell is formed immediately after formation of the core without interrupting the precipitation.

Generally, about 2 to 8 molar equivalents of shell silver halide per molar equivalent of core silver halides are used in the grains comprising the emulsion layers employed in this invention. These silver halides can be termed covered grains and emulsions containing them covered grain emulsions. The population of grains in such emulsions is substantially uniform in grain-size distribution, as contrasted with emulsion blends which contain at least two types of grains, which are separate and distinct in their physical, and frequently, photographic properties. The grain size of these covered grain emulsions Widely varies, typical emulsions having an average grain size of about 0.05 to 10 microns in diameter. Such grains are generally coated at silver coverages in the range of about 10 to about 400 mg. silver per square foot, preferably about 20 to about 100 mg. silver per square foot, and when exposed to an image and thereafter developed in a conventional surface image developer having low silver salt solvent action, form a reversal or direct-positive silver image. The unexposed grains develop without substantial reduction of the imagewise exposed grains.

The silver halide grains employed in the practice of this invention are fogged sufficiently to give a density of at least 0.5 when developed without exposure for five minutes in Developer A, described hereinbefore, when a directpositive emulsion layer containing such grains is coated at a coverage of about 50 to about 500 mg. of silver per square foot of support.

The halogen accepting compounds employed in practicing this invention are adsorbed to the fogged silver halide grains. The halogen acceptors which give particularly good results in the practice of this invention can be characterized in terms of their polarographic halfwave potentials, i.e., their oxidation reduction potentials determined by polarography. Cathodic measurements can be made with a 1 10 molar solution of the halogen acceptor in a solvent, for example, methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with the polarographic halfwave potential of the most positive cathodic wave being designated E Anodic measurements can be made With 1 10 molar aqueous solvent solution, for example methanolic solutions of the halogen acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste or pyrolytic graphite electrode, with the voltommetric half peak potential for the most negative anodic response being designated E In each measurement, the reference electrode can be an aqueous silver-silver chloride (saturated potassium chloride) electrode at 20 C. Electrochemical measurements of this type are known in the art and aredescribed in New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, N.Y., 1954; Polarography, by Kolthoif and Lingane, 2nd edition, Interscience Publishers, New York, N.Y., 1952; Analytical Chemistry, 36, 2426 (1964) by Elving; and Analytical Chemistry, 30, 1576 (1958) by Adams.

Compounds which can be employed as halogen acceptors in the practice of this invention include organic or inorganic compounds having an anodic polarographic halfwave potential E less than 0.85 and a cathodic polarographic potential E which is more negative than 1.0. A preferred class of halogen accepting compounds is characterized by an anodic halfwave potential which is less than 0.62 and a cathodic halfwave potential which is more negative than -1.3. A preferred class of halogen acceptors that can be used in the practice of this invention comprises the spectral sensitizing merocyanine dyes having the formula:

where A represents the atoms necessary to complete an acid heterocyclic nucleus, e.g., rhodanine, 2-thiohydantoin and the like, B represents the atoms necessary to complete a basic nitrogen containing heterocyclic nucleus, e.g., benzothiazole, naphthothiazole, benzoxazole and the like, each L represents a methine linkage, e.g.,

and n is an integer from 0 to 2, i.e., 0, 1 or 2.

Halogen accepting merocyanine dyes which can be employed in the practice of this invention can also be represented by the formula:

RI I-(LL)u 1b#LL)m =O C=O where R represents an alkyl group (including substituted alkyl) and preferably containing from 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, sulfoalkyl such as sulfopropyl or sulfobutyl, sulfatoalkyl such as sulfatopropyl or sulfatobutyl, or carboxyalkyl such as carboxyethyl or carboxybutyl, or an aryl group (including substituted aryl), e.g., phenyl, sulfophenyl, carboxyphenyl, tolyl and the like, each L represents a methine group, substituted or unsubstituted, n is a positive integer from 1 to 2, m is a positive integer from 1 to 3, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, e.g., a nucleus of the benzothiazole series, a nucleus of the benzoxazole series, a nucleus of the benzoselenazole series, a nucleus of the a-naphthothiazole series, a nucleus of the B-naphthothiazole series, a nucleus of the ot-naphthoxazole series, a nucleus of the fl-naphthoxazole series, a nucleus of the a-naphthoselenazole series, a nucleus of the B-naphthoselenazole series, a nucleus of the thiazoline series, a nucleus of the simple thiazole series (e.g., 4-methylthiazole, 4-phenylthiazole, 4-(2-thienyl)-thiazole, etc.), a nucleus of the simple selenazole series (e.g., 4-methylselenazole, 4-phenylselenazole, etc.) a nucleus of the simple oxazole series (e.g., 4-methyloxazole, 4-phenylthiazole, etc.), a nucleus of the quinoline series, a nucleus of the pyridine series, a nucleus of the 3,3-dialkylindolenine and the like, and Q represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing 5 atoms in the heterocyclic ring, e.g., a rhodanine nucleus, a 2-thio-2,4(3,5)-oxazoledione nucleus, 2. 2-thiohydantoin nucleus, a 5-pyrazolone nucleus, etc.

A more preferred class of halogen accepting compounds which can be employed in the practice of this invention can be represented by the formula:

r-r R-1 'Io=(oH-o11)r=o o=s where each R represents an alkyl group (including substituted alkyl) and preferably containing from 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, sulfoalkyl such as sulfopropyl or sulfobutyl, sulfatoalkyl such as sulfatopropyl or sulfatobutyl, or carboxyalkyl such as carboxyethyl or carboxybutyl, or an aryl group (including substituted aryl), e.g., phenyl, sulfophenyl, carboxyphenyl, tolyl and the like, n is a positive integer from 1 to 2, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, as defined in the previous formula, and X represents an oxygen atom, a sulfur atom, a selenium atom or a group of the formula --I IR where R represents an alkyl group (including substituted alkyl) and prefereably containing from 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, sulfoalkyl such as sulfopropyl or sulfobutyl, sulfatoalkyl such as sulfatopropyl or sulfatobutyl, or carboxyalkyl such as carboxyethyl or carboxybutyl, or an aryl group (including substituted aryl), e.g., phenyl, sulfophenyl, carboxyphenyl, tolyl and the like.

Suitable procedures for preparing dyes employed in the practice of this invention are described in Brooker et al U.S. Pats. 2,493,747 and 2,493,748, issued Jan, 10, 1950.

Specific examples of halogen accepting compounds which come within the dye formulae set forth hereinbefore are set out below. As shown by Example 2, such dyes must have the required polarographic halfwave potential to achieve the speed increase described herein. Dye

Number (I) 3-carboxymetl1y1 5 [(3etl1y1-2-benzo'blliazolinyldene) ethylidene] rhodanine 0C-NCH CO H 2 O G=CHCH=C CS (II) 3-ethyl-5-[ (3-ethy1-2-benzothiazolinylidene) e thylidene] rhodanine (III) 3- (2-dimethylamin oethyl) 5 [4- (3-ethyl-benzothiazollnylidene) -2-buteny1ldene] rhodanine O C-NCH2CH2N(CH C =0 HCH=OHCH=C C S (IV) 3-ethy1-5- (3-ethyl 2-benzoxazollnylidene)-ethylidene] rhotlanine (V) 3 carboxymebllyl 5 [(3-ethyl-2-benzoxazoliny1idene) ethylldeueJrhodanine (VI) 3-carboxymethyl-5-[ (3 metI1y1-2-thlazolidinyidene) -1- mebhylethylidene] rho danine XXIV [4- (3-etl1yl-2-benzothiazolinylideno) -2-bu tenylidene] -3-heptyl-Zthio-2,4-oxazolidinedione S O C-N-C5H11 C=CH-OH=CHOH=C C S O C2115 XXV 5-[(1,3-dial1ylimidazo[4,5-b]quinoxa1in-2(3H)- ylidene) ethyli dene] -3-ethylrhodanline (]JHCH=CH N N O C--N-C2Hs C=OH-CH=C\ S i (EH20 H=O H2 XXVI 4-[ (3-ebhyl-G-nlitre-2benzothiazolinylidene) ethylidene]-3-pheny1-2-isox azo1in-5-0ne S O :N O CO C=CH-CH=O N D ye Number XXVII Methyl-5-(3-methyl-2-thiazolidinylidene)-ethylidene]- 2rthio-2,4-oxazolidinedione XXIX 5-[(3-(2-earboxyethy1)-2-thiazolidiny1idene)-ethylidene]-3-ethylrhodanine XXX 5-[(3-methyl-2-thiazolidinylidene)-1-methylethy1idene]- 3-(2-morpho1inoethyl) rhodanine XXXI 5-[(3-(2-carboxyethyl)-2-thiazolidlnylidene)-1-methylethylidone]-3-carboxymethyl-rhodanine XXXII 5-[(3-(Z-carboxyathyl)-2-thiazolidinylidene)-1-methy1- ethyhdenel-Ii-(2-methoxyethyDrhodanine XXXIII 3-(3-dimethylaminopropy1)-5-[(3-methy1-2-thiazo1iudiny1- idene) ethylidenelrhodanine The halogen accepting compounds employed in the practice of this invention can be used in widely varying concentrations. However, the halogen accepting compounds are generally employed at concentrations in the range of about 100 mg. to about 1.0 g., preferably about 150 to about 600 milligrams per mole of silver halide.

As already indicated, the halogen accepting merocyanine dyes described herein can be employed in combination with certain types of high molecular weight organic compounds to achieve an even greater increase in the photographic speed of direct-positive emulsions. These compounds are sulfonated and comprise polynuclear aromatic compounds containing at least one sulfo group. The term polynuclear aromatic as used herein is intended to mean 2 or more benzene rings fused together (for example, as in naphthalene, pyrene, etc.), or at least 2 benzene rings or aromatic rings directly joined together (for example, as in diphenyl, terphenyl, quaterphenyl, etc.), or through an aliphatic linkage. Such sulfonated derivatives can conveniently be represented by the following general formula:

$03M wherein B represents a 2-benzotriazolyl group of a 1,3,5- triazin-6-ylamino group, B represents an aromatic group (i.e., benzene or substituted benzene) and M has the value given above.

Typical of sulfonated derivatives of Formula II above, wherein B represents a 1,3,5-triazin-6-ylamino group (i.e., a 1,3,5-triazin-2-ylamino group) are the compounds selected from those represented by the following general wherein M has the value given above and R, R R R each represents a hydrogen atom or a substituent group, such as hydroxyl, aryloxy (e.g., phenoxyl, o-toloxyl, psulfophenoxyl, etc.), alkoxyl (e.g., methoxyl, ethoxyl, etc.), a halogen atom (e.g., chlorine, bromine, etc.), a heterocyclic radial (e.g., morpholinyl, piperidyl, etc.), an alkylthio group (e.g., methylthio, ethylthio, etc.), an arylthio group (e.g., phenylthio, tolylthio, etc.), a heterocyclylthio group (e.g., benzothiazylthio, etc.), an amino group, an alkylamino group (e.g., methylamino, ethylamino, propylamino, dimethylamino, diethylamino, dodecylamino, cyclohexylamino, ,B-hydroxyethylamino, di-flhydroxyethyl amino, p-sulfoethylamino, etc.), an arylamino group (e.g., anilino, 0-, m, and p-sulfoanilino, 0-, m, and p-chloroanilino, 0-, m, and p-anisylamino, o-, m, and p-toluidino, 0-, m, and p-carboxyam'lino, hydroxyanilino, sulfonaphthylamino, o-, m, and p-aminoanilino, o-acetamidoanilino, etc.), and the like.

Compounds of Formula 1111 wherein R, R R and/or R each represents a heterocyclylamino group (e.g., 2- benzothiazolylamino, 2-pyridylamino, etc.), can also be used in practicing my invention.

Another group of sulfonated derivatives which are useful in practicing my invention are dibenzothiophene dioxides such as those represented by the following general formula:

' wherein R is an acylamido group (e.g., acetamido, sulfobenzamido, 4-methoxy 3-sulfobenzamido, Z-ethoxybenzamido, 2,4-diethoxybenzamido, p-tolylamido, 4-methyl-2- methoxybenzamido, l-naphthoylamino, 2-naphthoylamino, 2,4 dimethoxybenzamido, 2 phenylbenzamido, 2- thienylbenzamido) or a sulfo group, R represents an acylamido group (e.g., as defined by R, above) or a sulfoaryl group (e.g., sulfophenyl, p-sulfodiphenyl, etc.), and R represents a hydrogen atom or a sulfo group, said compound containing at least one sulfo group.

Still other useful sulfonated derivatives of Formula 1 above include compounds containing diphenyl, terphenyl, quaterphenyl, phenanthrene, pyrene, chrysene, etc., nuclei. Many of the sulfonated compounds described herein are shown in McFall et al. U.S. Pat. 2,933,290, issued Apr. 19, 1960 and Jones U.S. Pat. 2,961,318, issued Nov. 22, 1960.

Included among the sulfonated derivatives of Formula I are the following typical examples.

Compound: Name A Calcofluor White-MR. This is the trade name for a bis(s-triazine-Z-ylamino) stilbene-2,2-disulfonic acid, sodium salt.

B Leucophor B. This is the trade name for a bis(s-triazine-2-ylamino)stilbene 2,2 disulfonic acid, sodium salt.

C Sodium 6-(4-methoXy-3-sulfo-w-phenylacryloyl)-pyrene.

1 1 Compound: Name D 3,4-bis(4-methoxy 3 sulfobenzamido)-dibenzothiophene dioxide, sodium salt.

E 4',4"-bis(2,4-dimethoxy 5 sulfobenzamido)-p-terphenyl, disodium salt.

F Chyrsene-6-sulfonic acid, sodium salt.

G 4,4'-bis[2-phenoxy 4 (2 hydroxyethylamino)-1,3,5-triazine 6 ylamino1stilbene 2,2'-disulfonic acid, disodium salt.

These sulfonated derivatives are generally used in the same manner and in approximately the same concentrations disclosed in U.S. Pat. 2,937,089, i.e., in concentrations in the range of about 0.02 to about g. per mole of silver halide.

The silver halides employed in the practice of this invention include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide and the like. A preferred class of silver halides is the silver halides in which at least mole percent of the halide is chloride.

Various colloids can be used as vehicles or binding agents for the silver halide grains in the direct-positive materials of this invention. Satisfactory colloids which can 9 be used for this purpose include any of the hydrophilic colloids generally employed in the photographic field, including, for example, gelatin, colloidal albumin, polysaccharides, cellulose derivatives, synthetic resins such as polyvinyl compounds, including polyvinyl alcohol derivatives, acrylamide polymers, and the like. In addition to the hydrophilic colloids, the vehicle or binding agent can contain dispersed polymerized vinyl compounds, particularly those which increase the dimensional stability of photographic materials. Suitable compounds of this type include water-insoluble polymers of alkyl acrylates or methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, and the like.

The light sensitive compositions described herein can be coated on a wide variety of supports in practicing this invention. The photographic silver halide grains can be coated on one or both sides of the support which is preferably transparent and/or flexible. Typical continuous supporting sheets include, for example, cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and other polyester film as well as glass, paper, metal, wood and the like. Supports such as paper which are coated with OL-Olefin polymers, particularly polymers of a-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylenebutene copolymers, and the like, give good results.

The silver halide layers and any other hydrophilic colloid containing layers present in the elements of this invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides, such as oxy starch or oxy plant gums, and the like. The silver halide layers can also contain additional additives, parers can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, 3-pyrazoliclones, and the like.

It is sometimes advantageous to employ surface active agents or compatible mixtures of such agents in the preparation of the photographic materials described herein.

Suitable agents of this type include non-ionic, ionic and amphoteric types, as exemplified by polyoxyalkylene derivatives, amphoteric amino acid dispersing agents, including sulfobetaines, and the like. Such surface active agents are described in US. Pat. 2,600,831 issued June 17, 1952; US. Pat. 2,271,622, issued Feb. 3, 1942; US. Pat. 2,271,- 623, issued Feb. 3, 1942; US. Pat. 2,275,727, issued Mar. 10, 1942; US. Pat. 2,787,604, issued Apr. 2, 1957; U.S. Pat. 2,816,920, issued Dec. 17, 1957; US. Pat. 2,739,891, issued Mar. 27, 1956 and Belgian Pat. 652,862.

The halogen accepting dyes employed in the following working examples are identified by the number used in listing such dyes hereinbefore.

This invention can be further illustrated by the following examples of preferred embodiments thereof although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLE 1 A significant increase in photographic speed is obtained when halogen accepting compounds, as described herein, are incorporated into light sensitive photographic directpositive emulsions containing silver halide grains comprising a central core of silver halide containing centers which promote deposition of photolytic silver and an outer shell covering said core comprising a fogged silver halide that develops to silver without exposure. To illustrate, a silver bromide photographic emulsion having the desired reversal characteristics is prepared by simultaneously adding, over a period of about 20 minutes, a solution containing 340 g. of silver nitrate and 520 ml. of distilled water and a solution containing 2.40 g. of potassium bromide and 500 ml. of distilled water, to a well-stirred aqueous solution of 500 ml. of 0.004 molar potassium bromide at C., containing 20 g. of gelatin. A portion of the resulting silver halide core emulsion is cooled to a temperature of 40 C., and mg. of potassium chloroiridite (dissolved in 100 ml. of water) is added and the emulsion is heated to 70 C. This emulsion constitutes the silver bromide core containing discontinuities which trap electrons over which is formed a shell of silver bromide.

The shell of silver bromide is formed by adding to the core emulsion simultaneously, over a period of about 20 minutes, a solution containing 340 g. of silver nitrate and 520 ml. of distilled water and a solution containing 240 g. of potassium bromide and 500 ml. of distilled water, at a temperature of 70 C. 160 g. of gelatin previously soaked in 340 ml. of water is stirred and the emulsion cooled. An aqueous solution of potassium iodide is added equivalent to 2 mole percent of the silver present in the emulsion. 3.5 mg. of thiourea dioxide per mole are added to the emulsion at 40 C. The pH of the emulsion is adjusted to 9.5 and the emulsion is fogged by heating it to a temperature of 70 C. and holding for 5 minutes at this temperature. gois cooled immediately to 40 C. and the pH adjusted to The unsensitized portion of emulsion and a portion sensitized with 200 mg. of Dye VI per silver mole are coated in a conventional manner. A sample of each coatmg is exposed in an intensity scale sensitometer to tungsten light and developed for 30 seconds in Kodak D-72 Developer at 68 F., fixed, washed and dried. The results are as follows:

Relative speed mnx. Coaing: 1

ontro 100 0. 90 Dye VI 2, 1. 0O

EXAMPLE 2 13 l.0. To illustrate this feature of the invention, the halogen accepting compounds listed in the following table are added to separate portions of the control emulsion described in Example 1.

1 4 ified, and gelatin added to bring the total to 160 g. of gelatin per silver mole. Part of the emulsion is coated on a paper support at 1000 square foot per silver mole. Another part of the emulsion is spectrally sensitized by add- G. of Rel. Rel. dye/ Anodie Cathodic at speed mole potential, potential, 365 white Dye AgX u Eu 1 ght Dmnx. Gamma Dmiu.

None (control) 100 1. 2 1. 8 2. 65 09 VI 24 49 1. 47 795 316. 0 1. 36 4. 00 50 49 -1. 47 832 240. O 1. 1. 95 05 1. 00 49 -1. 47 1, 000 398. 0 1. 2. 66 05 24 53 1. 1, 050 479. 0 1. 54 5. 30 06 24 56 1. 45 813 331. 0 1. 38 4. 05 24 46 1. 36 603 126. 0 1. 46 5. 10 07 24 60 1. 37 725 263. 0 1. 51 4. 50 05 24 60 1. 31 1, 260 289. O 1. 40 3. 60 05 24 63 1. 48 447 83. 0 1. 34 1. 22 09 24 57 1. 27 200 22. 0 1. 64 1. 95 43 24 53 1. 525 166. 0 1. 58 4. 20 08 24 57 1. 68 692 282. 0 1. 60 5. 20 10 24 72(. 63) --1. 81 302 73. 0 1. 37 5. 10 05 24 1. 10 200 7. 8 1. 28 2. 58 11 .24 .31 1. 15 1.39 1.26 50 31 1. 15 132 13. 8 1. 02 1. 04 l0 24 37 1. 48 955 589. 0 98 1. 87 05 24 28 -1. 46 1, 200 912. 0 78 1. 25 06 24 22 1. 28 603 95. 0 90 73 .10 0 1.2 1.8 2.65 .09 24 85 1. 76 69 12. 3 1. 35 5. 40 06 1. 00 85 1. 76 91 13. 2 1. 34 2. 52 07 24 89 1. 72 33 3. 0 1. 55 4. 20 23 1. 00 .89 1.72 35 2. 0 1. 51 1.44 1. 00 24 86 -1. 70 80 32. 0 1. 28 6. 00 04 1. 00 86 1. 70 83 20. 0 1. 48 2. 38 07 1. 00 1.0 0. 61 28 1.76

1 E is determined on a polarograph using a methanol solution of the dye and a pyrolytie graphite electrode vs. a Ag/AgCl electrode in saturated K01 mercury electrode vs. a Ag/Ag Cl electrode in saturated KCL.

It can be seen from the above table, that a significant increase in photographic speed is obtained when the halogen accepting dyes have an anodic halfwave potential (E,,) less than 0.85 and a cathodic haltwave potential (E more negative than 1.0 are employed in the practice of this invention. It is also to be noted that a significant increase in blue speed (365 mg) is obtained with the direct-positive emulsions of this invention. Such an increase is completely unexpected, particularly in view of the fact that the halogen acceptors do not impart this blue speed increase to negative type silver halide emulsions.

EXAMPLE 3 A gelatin silver chloride photographic emulsion is prepared by simultaneously adding, over a period of about 20 minutes, 1000 ml. of a 4 molar silver nitrate aqueous solution and 1000 ml. of a 4 molar sodium chloride aqueous solution, to a well-stirred aqueous solution of 1000 ml. of 0.01 molar sodium chloride at 70 C. containing 40 grams of gelatin; 5000 ml. of water containing 280 grams of gelatin is added and the emulsion is cooled. One-eighth of the resulting gelatin silver chloride emulsion (containing 0.5 mole percent silver chloride) is melted at 40 C. 100 mg. of potassium chloroiridite (dissolved in water) is added, and the emulsion is heated to 70 C. This prepared emulsion constitutes the silver chloride core containing discontinuities which trap electrons over which is formed a shell of silver chloride.

The shell of silver chloride is formed by adding to the core emulsion 500 ml. of 4 molar silver nitrate aqueous solution and 500 ml. of 4 molar silver chloride aqueous solution simultaneously over a period of 20 minutes. 160 g. of gelatin, previously soaked in 340 ml. of water, is stirred in and the emulsion cooled. During both additions of the silver nitrate and sodium chloride (i.e., to form both the core and the shell), the two solutions are added ing to it 300 mg. of Dye XV per silver mole and coated as above. Portions of the coatings are exposed in a sensitometer to tungsten light and developed for 30 seconds in Kodak D-72 Developer (1:1) at 68 F., fixed, washed and dried. The results are as follows:

Relative Coating speed Din. Dinin- Control 100 1. 2 0. 1 300 mg. Dye XV/Ag mole 20,000 1. 2 0. 1

In the above procedure, the core forming emulsion is treated with potassium chloroiridite to form centers which promote deposition of photolytic silver. However, similar results are achieved when other Group VIII metal corn pounds or polyvalent metal compounds such as bismuth nitrate are used for this purpose.

EXAMPLE 4 Relative Coating speed Din. Dinin- Control 100 1. 30 0. 07 mg. Dye VI/Ag mole 87,000 1. 26 0. 02

EXAMPLE 5 A silver chloride emulsion is prepared as in Example 4. An unsensitized portion and a portion sensitized with 200 mg. of Dye XXVII per silver mole are coated as in Example 3; development is for 10 seconds as in Example 1. The results are as follows:

Relative Coating speed Dmax. Dmin.

Control 100 1. 03 0. 14 200 mg. Dye XXVII/Ag mole 9, 550 0. 99 0. 06

1 5 EXAMPLE 6 As pointed out previously, certain high molecular weight sulfonated compounds can be used in combination with the halogen accepting merocyanine dyes employed in the practice of this invention to obtain even greater 5 increases in speed.

To illustrate, the compounds listed in the following table are added to separate portions of the emulsion prepared as described in Example 4. Each portion is coated on a paper support, exposed and processed as described in Example 3. The following results are obtained.

Run II To one mole of the unfogged emulsion (as core or nuclei) obtained as in Run I (the salt solution and silver Mg./Ag Relative Coating mole speed max. Dm;1

Control 100 l. 32 0. 08 Dye VI 150 87, 000 1. 20 0. 08 Dye VI plus organic sulionlc acid 2 lggg 105 000 L 20 0 06 Dye XXIX plus organic sulionic acid 2 $28 159, 000 L 18 0. 07 Dye XXXI plus organic sulfonic acid 2 $28 251, 000 1' 28 03 Dye XXXII plus organic sulionic acid 2 2152g 398, 000 L 12 0. O3 Dye XXXIII plus organic sulfonic acid 2 hi gig 316 000 1. 15 03 1 No dye.

2 Sodium salt of bis(s-triazin-Z-ylamlno)stilbene-2,2-disulfonic acid.

EXAMPLE 7 ,lsolution in the same halide ratio and reci itation The photographic emulsions of this invention must be uniformly fogged in order to achieve the desired increase in speed. To illustarte, an internal image silver halide emulsion is prepared by the procedure described in Example 1 of Davey and Knott US. Pat. 2,592,250. The emulsion is divided into two portions. One portion is fogged by heating with 10 mg./silver mole of thiourea dioxide and heating for 5 minutes at 70 C. at a pH of 9.0. After fogging, the emulsion pH is adjusted to 5.5. The fogged and unfogged portions are coated with various amounts of Dye VI. Each portion is coated on a paper support at a laydown of 242 mg. of silver and 534 mg. of gelatin per square foot. Samples of each coating are exposed on an intensity scale sensitometer to blue light at a wavelength of 365 mu. Samples of each coating are processed in a hydroquinone-aminophenol developer such as Kodak D-72, fixed, washed and dried with the It can be seen from the above results that the dye gives a speed increase in the emulsion only when the emulsion has been fogged prior to image exposure.

EXAMPLE 8 Run I A silver chlorobromide (50/ 50 mole percent) emulsion is prepared by adding a salt solution (containing 234 g. of NaCl and 476 g. of KBr in 1400 cc. water) and a silver solution (containing 1360 g. of AgNO in 2030 cc. water) simultaneously to a gelatin solution (containing 80 g. of gelatin, 1.16 g. of NaCl and 2000 cc. of water) at 70 C. The emulsion is cooled to C. and a solution containing ,560 g. of gelatin and 600 cc. of water is added. The emulsion is surface fogged with 2 mg. of thiourea dioxide and 1.2 g. of KI per mole of silver halide for minutes at 65 C. and cooled to 40 C. The fogged emulsion is split into two portions and coated with and without Dye VI 011 a paper support at 125 mg. A'g/ square conditions as in Run I) are added to build up the grain size approximately two times larger than the original emulsion. This emulsion is surface fogged with 2 mg. of thiourea dioxide, 1.2 g. of KI per mole of silver halide for 30 minutes. Two portions are coated with and without Dye VI on a paper support at mg. of Ag per square foot and 185 mg. of gelatin per square foot.

Run III The procedure of Run II is repeated except the core emulsion is precipitated in the presence of 1.63 mole per cent KI.

The coatings prepared from the emulsions of Runs II and III are exposed for 1 second in a sensitometer to white light of 3000 K. and to blue light, developed for 10 seconds in Kodak D-72 Developer at 68 F., fixed, washed and dried with the results given in the following table.

Relative speed 1 White Blue light light Coating No. Dye exposure exposure Run I:

1 None 100 100 2 VI 1, 260 1, 590 Run II 1 None 100 100 1 Rclativespeeds determined at a density of 0A.

Silver halide emulsion made according to this invention can be used in photographic coatings intended for color photography; for example, emulsions containing colorforming couplers or emulsions to be developed by solutions containing couplers or other color generating materials. In addition, photographic emulsions made according to this invention can be used in diffusion transfer processes which utilize the non-developed silver halide in the exposed areas to form an image by dissolving the undeveloped silver halide and precipitating it on a receiving layer in close proximity to the original silver halide emulsion layer. Such processes are described in Rott U.S. Pat. 2,352,014, Land US. Pat. 2,543,181 and Yackel et al. US. Pat. 3,020,155. The silver halide emulsions described herein can also be used in color transfer processes which utilize the diffusion transfer of an imagewise distribution of developer, coupler or dye from a light-sensitive layer to a second layer while the two layers are in close proximity to one another. Color transfer processes of this type are described in Yutzy U.S. Pat. 2,856,142, Land et a1. U.S. Pat. 2,983,606, Whitmore et al. British Pats. 904,364 and 840,731 and Whitmore et al. U.S. Pat. 3,227,552. The silver halide emulsions of this invention can be processed in monobath processes such as described in Haist et al. U.S. Pat. 2,287,048 or in stabilization type processes.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. In a uniformly fogged direct-positive photographic silver halide emulsion which comprises silver halide grains comprising a central core of silver halide containing centers which promote deposition of photolytic silver and an outer shell covering said core comprising a fogged silver halide that develops the silver without light exposure, the improvement comprising adsorbed to said fogged grains a halogen-accepting merocyanine compound having an anodic polarographic halfwave potential less than 0.85 and a cathodic polarographic halfwave potential which is more negative than 1.0.

2. The photographic emulsion of claim 1 in which the halide in said silver halide grains comprises at least 50 mole percent chloride.

3. The photographic emulsion of claim 1 in which said fogged silver halide grains comprise a central core of silver halide having centers attributable to Group VIII metal ions, which centers promote deposition of photolytic silver.

4. The photographic emulsion of claim 1 in which said Group VIII metal ions are iridium ions.

5. The photographic emulsion of claim 1 in which said adsorbed merocyanine dye is present in a concentration of about 100 mg. to about 1 g. per mole of silver.

6. The photographic emulsion of claim 1 in which said merocyanine compound has the formula:

where A represents the atoms necessary to complete an acidic heterocyclic nucleus, B represents the atoms necessary to complete a basic nitrogen-containing heterocyclic nucleus, each L represents a methine linkage and n is an r integer of from 0 to 2.

7. The photographic emulsion of claim 1 in which said merocyanine compound has the formula:

where each R is an alkyl or aryl group, n is an integer of from 1 to 2, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring and X is an oxygen atom,

R'SO M where R represents a polynuclear group and M represents a cation.

13. The photographic emulsion of claim 1 comprising, in combination with said halogen-accepting merocyanine compound, a sulfonated compound having the formula:

I I CHZCH N \s I 803M $03M 12, R1

where M represents a cation, and each of R, R R and R represents a hydrogen atom, a hydroxyl group, an aryloxy group, an alkoxyl group, a halogen atom, a heterocyclic radical, an alkylthio group, an arylthio group, a heterocyclylthio group, an amino group, an alkylamino group or an acylamino group.

14. The photographic emulsion of claim 1 in which said halogen-accepting merocyanine compound is 3-carboxymethyl 5 [(3 methyl 2-thiazolidinylidene)-l-methyl ethylidene]rhodanine.

15. The photographic emulsion of claim 1 in which said halogen-accepting merocyanine compound is l-carboxymethyl 5 [(3-ethyl-2-benzoxazolinylidene)-ethy1idene] -3 -phenyl-2-thiohyd antoin.

16. A photographic element comprising a support and a layer of said uniformly fogged direct-positive photographic silver halide emulsion of claim 1.

17. In a uniformly fogged direct-positive photographic silver halide emulsion which comprises silver halide grains comprising a central core of silver halide containing centers which promote deposition of photolytic silver and an outer shell covering said core comprising a fogged silver halide that develops the silver without light exposure, the improvement comprising adsorbed to said fogged grains a halogen-accepting merocyanine compound which increases the blue-light sensitivity of said emulsion and has an anodic polarographic halfwave potential less than 0.85 and a cathodic polarographic halfwave potential which is more negative than 1.0.

18. A photographic element comprising a support and a layer of said uniformly fogged direct-positive photographic silver halide emulsion of claim 17.

References Cited UNITED STATES PATENTS 2,493,748 1/ 1950 Brooker et a1. 260-240 2,497,876 2/1950 Fallesen et a1. 96-64 3,364,026 1/ 1968 Rees 96-64 3,367,778 2/ 1968 Berriman 96-64 NORMAN G. TORCHIN, Primary Examiner ALFONSO T. SURO PICO, Assistant Examiner U.S. Cl. X.R. 96-102 mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION- Patent No. 3,537,858 Dated November 3, 1 970 Inventor(=s=)= Albert W. Wise It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I Column 2, line 2?, "characteristics" should read ---characteristic---. Column 6, line 8, "prefereably" should read preferably---; line L 3, that part of formula reading (3-ethylbenzothiazolinylidene)-" should read (3-ethyl-2-benzothiazolin lidene)- line 6, that part of formula reading 3 should re ad CH line 68, that part of formula reading "-thiazolidinyidene)-" should read thiazolidinylidene)- Column 7, line 8, that part of formula readng 1 I 0 H should read 0 H;

line 2L that part of formula reading "-L (1H)-" should read -L .(1H)- line 32, that part of formula reading "-C N5" should read -C H5 lines L .9-55, that part of formula reading should read 3 Column 8, lines 114,-! 7, that part of formula reading should read 3 line 31 that part of formula reading "-sulfophenyl-2-" should read -sulfo henyl)-2- line 67, that part of formula lreading 1 ,2-di should read 1 ,2-. Column 9, line Page 1 of 2 pages.

agga UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nmj 537 858 Dated November 3 1970 Inventortfi) Albert W. Wise It is certified that error'appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

E2, "of" should read ---or--. Column IO, line 16, "aryloxy" should read ---aryloxyl---; line 14.0, before the formula should be inserted ---III---; line 67, that part of formula reading "-triazine-" should read -triazinline 71 that part of formula reading "-triazine-" should read -triazin- Column 11 line 9, that part of formula reading "-triazine-" should read -triazin- Column 13, line 8, in the table heading, "365 u" should read -365 mi under table heading Dmin. next to last line, ".07" should read .O6--. Column 15, line 31 "illustarte" should read ---illustrate---. Column 16, line 7, after "blue" should be inserted ---light---; line 12, "Run I (the" should read ---Run I, the---. Column 1 7, line 8, "2,287,011.65" should read --2,875,0Lp8--.

SIGNED $.15!)

.- --qb.mo n

:SEAL Attest:

Edward M. Fl

VIII-LIAM E. Stratum, .m. Altesnng Officer fimissioner of Patents Page 2 of 2 pages.