US3442653A - Sensitized silver halide systems with activated nonlabile selenium compounds - Google Patents

Description

United States Patent 3,442 653 SENSITIZED SILVER HALIDE SYSTEMS WITH ACTIVATED NONLABILE SELENI- UM COMPOUNDS Joseph S. Dunn, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 468,972, July 1, 1965. This application Mar. 29, 1968, Ser. No. 717,396

Int. Cl. G03c 1/50, N

US. Cl. 96-108 Claims ABSTRACT OF THE DISCLOSURE Sensitizing photographic systems such as a silver halide emulsion with a noble metal and labile selenium formed in situ by activating a non-labile selenium compound. Specific activation methods include the use of reducing agents.

This application is a continuation-in-part of my copending application Ser. No. 606,587 filed Jan. 3, 1967, now abandoned, which is a continuation-in-part of my application Ser. No. 468,972 filed July 1, 1965, now US. Patent No. 3,297,446 which in turn was a continuationin-part of Ser. No. 343,465 filed Feb. 10, 1964, now abandoned.

This invention relates to photography. In one aspect, this invention relates to processes of sensitizing photographic systems.

In my earlier-filed application Ser. No. 468,972, now US. Patent 3,297,446, I found that a sensitizer combination of a noble metal and labile selenium produced a synergistic effect in photographic systems. There are many readily available selenium compounds which are not labile, however, and it would be desirable to employ these compounds in a sensitizing process. The invention provides a way for employing these compounds in such a sensitizing process.

It is an object of this invention to provide a process for sensitizing photographic systems with a noble metal and labile selenium wherein a non-labile selenium compound is employed in the process.

Another object of this invention is to provide a process for sensitizing photographic silver halide emulsions with a noble metal and labile selenium wherein a non-labile selenium compound is employed in the process.

Still another object of this invention is to provide a process for sensitizing photographic systems and more particularly silver halide emulsions with gold and labile selenium wherein a non-labile selenium compound is employed in the process.

Yet still another object of the invention is to provide a sensitizing process for photographic systems which can be easily controlled.

Other objects will become apparent hereinafter.

These and other objects of the invention are accomplished by sensitizing photographic systems and more particularly silver halide emulsions with a noble metal and labile selenium which is formed in situ by activating a non-labile selenium compound. It was previously thought Patented May 6, 1969 whenever desired by activating the non-labile selenium compound at that time. The degree of sensitization can also be controlled by varying the intensity of activation. A predetermined sensitivity of a photographic system can thus be obtained with the sensitizing process of this invention.

Any method for activating non-labile selenium compounds can be used in this invention so long as it renders the selenium compounds labile. A preferred way of activating non-labile selenium compounds to make them labile is by employing reducing agents. Other methods for activating non-labile selenium compounds to make them labile are disclosed and claimed in copending application Ser. Nos. 606,586 and 606,588 both entitled sensitizing Photographic Systems of my co-worker Mc- Veigh filed concurrently herewith.

The term labile has a meaning well understood by those skilled in the art of photography and is defined in my earlier-filed application Ser. No. 468,972, filed July 1, 1965 now US. Patent 3,297,446, as being a material which yields a silver selenide that is insoluble in water at room temperature (20 C.) upon addition to an aqueous silver nitrate solution. Likewise, the term non-labile as used herein in describing selenium compounds has a meaning well understood by those skilled in the art of photography, i.e., a material which does not yield a .silver selenide that is insoluble in water at room temperature (20 C.) upon addition to an aqueous silver nitrate solution. For example, potassium selenocyanate and selenous acid are nonlabile selenium compounds since silver selenide does notprecipitate when these compounds are added to an aqueous silver nitrate solution.

Non-labile selenium compounds which can be used in this invention include, for example, potassium selenocyanate, selenous acid, inorganic isoselenocyanate complexes, etc.

The concentration of the non-labile selenium compound which is activated to form labile selenium in situ can be varied considerably depending upon the particular nonlabile selenium compound employed, the nature of the photographic system, the amount and chemical nature of the noble metal sensitizer, etc. In silver halide systems, for example, I have found that useful results can be obtained using amounts as small as 0.05 mg. of non-labile selenium compound per mole of silver halide although considerably larger amounts can also be employed, such as 5.0 mg. or more per mole of silver halide.

The noble metal sensitizers useful in my invention include the well-known gold sensitizers and other noble metals such as palladium, platinum and any of those disclosed in Smith et al., US. Patent No. 2,448,060, issued Aug. 31, 1948. Typical suitable gold sensitizers are described in Waller et al., US. Patent No. 2,399,083, issued Apr. 23, 1946, and Damschroder et al., US. Patent 2,642,- 361, issued June 16, 1953.

Illustrative addenda suitable for furnishing the noble metal moiety in the sensitizer combinations of the invention include:

gold chloride,

potassium aurate,

potassium auriaurite,

potassium auricyanide,

potassium aurithiocyanate,

gold sulfide,

gold selenide,

gold iodide,

potassium chloroaurate, ethylenediamine-bis-gold chloride, I ammonium chloroplatinite, i.e. (NH PtCl ammonium chloropalladate, i.e. (NHQ PdCl and 3 organic gold sensitizers having the formulas:

C-SAu II. s

G-SAu III:

N-C H o=orr-on=o (I 2 5 SAI1 N S 31115 IV: (H)

\ N-onn C=C 'SAu /CCH; 03H; A1101 VI. /S\ g2 g2 C-CH=CHN 011, c-C N\ H2 2 C AuClt VII.

OH N N N CzHt AuCh CgHs AuCll The concentration of noble metal sensitizer useful in my invention can be any amount suitable for the intended purpose. I have found, for example, that amounts varying from about 0.1 to about 5.0 mg. of gold sensitizer per mole of silver halide are quite satisfactory.

In Example 8 of my earlier-filed application Ser. No. 468,972, U.S. Patent 3,297,446, I disclosed that compounds containing a selenium atom which is not labile do not provide the very high increase in speed described therein for combinations including nabile selenium'compounds. I have found, however, that non-labile selenium compounds can be activated in accordance with the instant invention to convert the selenium to a labile state. After activation, these compounds, in combination with noble metals, perform in the same manner as the labile selenium compounds in my previous case and act as a synergistic sensitizer combination to give the very high photograhic speed disclosed in said previous case.

As was previously indicated, a preferred method of the invention for activating non-labile selenium compounds is by employing a reducing agent. Any reducing. agent can be employed which is effective for the intended purpose. Among reducing agents which can be used are benzothiazolium salts such as benzothiazole methiodide, benzothiazole methbromide, 2 -hydroxy-methyl-benzothiazole ethyliodide, 2 hydroxymethyl-benzothiazole methiodide, etc.; mercaptans such as Z-mercaptobenzoic acid, thiolactic acid, Z-mercapto benzothiazole, etc.; disulfides such as diphenyl disulfidie; triphenylphosphine; stannous chloride; benzothiazoline compounds such as 3-methyl-benzothiazoline, 2-methyl-3-methyl-benzothiazoline, 2,2-dimethyl- 3-methyl-benzothiazoline, etc.; alkali metal sulfites such as potassium sulfite, sodium sulfite, etc.

The reducing agent can be added directly to the sensitizer mixture and reacted with the non-labile selenium compound to form labile selenium in situ or it can be added to the photographic system, e.g., a silver halide emulsion, after the sensitizers are added to form labile selenium in situ. If desired, the reducing agent can also be previously incorporated into the photographic system, such as in the gelatin of a silver halide emulsion. The concentration of the reducing agent can, of course, be considerably varied depending upon the particular non-labile selenium compound employed, the concentration of the non-labile selenium compound, the nature of the photographic system, etc. Preferably, the concentration of the reducing agent is in stoichiometric excess of the non-labile selenium compound being reduced. Suitable concentrations include, e.g., 1 to about 50 mg. per silver mole.

It has been found that particularly useful results are obtained when the sensitizer mixture used in the .sensitizing process of the invention contains a watersoluble thiocyanate compound. Typical thiocyanates include sodium thiocyanate, potassium thiocyanate, ammonium thiocyanate, etc. The amount of thiocyanate compound used can be varied depending upon the particular system being sensitized, relative amounts of scnsitizers employed, etc.

The sensitizing addenda, before or after activation according to my invention, can be added in a variety of ways to photographic systems and at various stages in the preparation of such. In general, with respect to silver halide emulsions, such addenda can be added with useful effects at the completion of the Ostwald ripening and prior to one or more of the final digestion operations. The sensitizing addenda are preferably added to silver halide emulsions after the silver halide grains are substantially in their final size and shape. The addenda can be added in the form of their aqueous solutions, where they are soluble in water, or in an innocuous organic solvent where the sensitizer does not have suflicientsolubility in water to be used in the form of an aqueous solution. Particularly useful organic solvents include ethanol, methanol, pyridine, acetone, dioxane, etc. Organic solvents which have a rather high degree of polarity are preferred. Where it is desired to add the sensitizing addenda in some other form than a solution, this procedure is also possible, especially where the sensitizer is available in the form of a colloidal suspension. In some cases, it is possible to add the sensitizers suspended in an organic solvent which forms very small suspended particles in the photographic emulsion similar to the type of colloidal particle produced in preparing coupler dispersions. Dispersing media useful for this purpose include tricresyl phosphate, dibutyl phthalate, triphenyl phosphate, etc.

Vacuum deposited photographic systems substantially free of conventional vehicles, binders or dispersing agents can also be sensitized in accordance with the invention by incorporating the sensitizers, before or after activation, in a coating or layer contiguous to the vacuum deposited light-sensitive material. Suitable vacuum deposited silver halide systems that can be sensitized in accordance with the invention are disclosed in Rasch et a1. application U.S. Ser. No. 415,596 filed Dec. 3, 1964; Rees application U.S. Ser. No. 421,725 filed Dec. 28, 1964 now US. Patent 3,384,490; and Belgian Patent 639,020.

The silver halide emulsion of a photographic element which can be sensitized according to this invention can contain conventional addenda such as gelatin plasticizers, coating aids, antifoggants such as the azaindines and hardeners such as aldehyde hardeners, e.g., formaldehyde, mucochloric acid, glutaral'dehyde bis(sodium bisu-lfite), ma leic dialdehyde, aziridines, dioxane derivatives and oxypolysaccharides. The addenda may be added to the emulsion before or after sensitizing dyes, if any, are used. Sensitizing dyes useful in sensitizing such emulsions are described, for example, in US. Patents 2,526,632 and 2,503,776. Spectral sensitizers which can be used are the cyanines, merocyanines, complex (trinuclear) cyanines, complex (trinuclear) merocyanines, styryls and hemicyanines. Developing agents can also be incorporated into the silver halide emulsion if desired or can be contained in a separate underlayer. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide or silver bromoiodide.

The silver halide emulsion layer of a photographic element which can be sensitized according to the instant invention can contain any of the hydrophilic waterpermeable binding materials suitable for this purpose. Suitable materials include gelatin, colloidal albumin, polyvinyl compounds, cellulose derivatives, acrylamide polymers, etc. Mixtures of these binding agents can also be used. The binding agents for the emulsion layer of the photographic element can also contain dispersed polymerized vinyl compounds. Such compounds are disclosed, for example, in US. Patents 3,142,568; 3,193,386; 3,062,674; and 3,220,844, and include the water-insoluble polymers of alkyl acrylates and methacrylates acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The silver halide emulsion of a photographic element which can be sensitized according to the instant invention may be coated on a wide variety of supports. Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal 'film, polystyrene film, poly(ethylene terephthalate) film and related films or resinous materials as well as glass, paper, metal and the like. Supports such as paper which are coated wtih a-olefin polymers, particularly polymers of wolefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene butene copolymers and the like can also be employed.

I have found that the speed of photographic emulsions sensitized according to the invention can be further increased by including in the emulsions a variety of hydrophilic colloids, such as carboxymethyl protein of the type described in US. Patent 3,011,890, issued Dec. 5, Canadian Patent 635,206.

Photographic emulsions sensitized according to the invention can contain speed increasing compounds such as quaternary ammonium compounds, polyethylene glycols or thioethers. Frequently, useful effects can be obtained by adding the aforementioned speed increasing compounds to the photographic developer solutions instead of, or in addition to, the photographic emulsions.

The sensitizing process of the invention can be used for various kinds of photographic systems. In addition to being useful in X-ray and other nonoptically sensitized systems, they can also be used in orthochromatic, panchromatic, and infrared sensitive systems. The sensitizing addenda can be added to photographic systems before or after any sensitizing dyes which are used.

The sensitizing process of the invention can be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials, emulsions of the mixed-packet type, such as described in Godowsky US. Patent 2,698,794 issued J an. 4, 1955; in silver dye-bleach systems; and emulsions of the mixed-grain type, such as described in Carroll and Hanson US. Patent 2,592,243, issued Apr. 8, 1952.

The sensitizing process of the invention can be utilized to sensitize any photographic system that can be sensitized with noble metals. The invention thus has utility, not only for silver halide photographic systems, but also for other light-sensitive systems such as other light-sensitive silver salts, thallous halides, cuprous halides, lead halides and related light-sensitive heavy metal salts.

Photographic elements which have been sensitized according to the process of the instant invention may be stabilized with labile sulfur compounds in accordance with application Ser. No. 486,235 of McVeigh filed Sept. 9, 1965, now US. Patent 3,297,447. These labile sulfur compounds provide a particularly efficacious means of controlling fog without deleteriously affecting the speed of the stabilized photographic system. Particularly useful labile sulfur compounds include the water-soluble thiosulfates such as alkali metal thiosulfates including sodium and potassium thiosulfates, as well as ammonium thiosulfate; thioureas such as thiourea, allylisothiourea, diacetyl thiourea; thiosemicarbazide; thiocarbamates such as isopropylthiocarbamate; etc.

The amount of labile sulfur compound used to stabilize photographic systems sensitized by the process of this invention can vary considerably depending upon the particular sensitized photographic system employed, finishing conditions, including temperature and time of digestion and ripening, etc. In silver halide photographic systems, particularly useful results have been obtained at concentrations of about 0.1 to 10 mg. per mole of silver halide. Larger or smaller quantities can be employed without adversely affecting the sensitometric properties of the photographic system. The labile sulfur compounds are efficaciously added to be present during the chemical sensitization of the photographic system.

The following examples will illustrate the invention but are not to be construed to limit it in any way.

EMMPLE 1 Activation by reducing agents A medium grain silver bromoiodide emulsion containing 3.4 mole percent iodide is prepared. A first portion of the emulsion is chemically sensitized by the addition of 2 mg. of potassium chloroaurate per silver mole, mg. of potassium thiocyanate per silver mole and 1.6 mfi. of potassium selenocyanate per silver mole. The emulsion is then heated for 40 minutes at 65 C.

A second portion of the emulsion is sensitized in the same manner as the first portion but with'the addition of 10.1 mg. of benzothiazole methiodide per silver mole and heating for 9 minutes at 65 C.

A third portion of the emulsion is sensitized in the same manner as the first portion except for the addition of 8.2 mg. of benzothiazole methbromide per silver mole and heating for 9 minutes at 65 C.

A fourth portion of the emulsion is sensitized in the same manner as the first portion except for the addition 8 per silver mole.The emulsion is then heated for 30 minutes at 60 C.

A second portion of the emulsion is sensitized in the same manner as the first portion except for the addition of 2.8 mg. of triphenylphosphine per silver mole and of 11.7 mg. of 2-hydroxymethy1benzothiazole ethyliodide 5 heating for 6 minutes at 60 C. per silver mole and heating for 12 minutes at 65 C. A third portion of the emulsion is sensitized in the These emulsions are then coated on a cellulose acesame manner as the first portion except for the addition tate support at a coverage of 540 mg. of silver per square of 10.1 mg. of benzothiazole methiodide per silver mole foot. The coatings are then exposed on an intensity scale and heating for 20 minutes at 60 C. sensitometer, processed for 5 minutes in Kodak Developer These emulsions are then coated and processed in the DK-SO, fixed, washed and dried. same manner as in Example 1 with the following results:

The following results are obtained:

Relative R01 ative 15 Portion Reducing agent speed Fog Portion Reducing agent speed g First None 10 Q 02 Second... Triphenylphosphine 100 0.06 ggi fothiazole methiodide Benzothlazole methlodldo 100 Third Benzothiazole methbromi 240 0.21 Fourth 2-hydroxymethyl-benzothiazole 204 0.27

methiodide. Th1s example shows that reducing agents convert a non-labile selenium compound into a labile form WhlCh This example shows that reducing agents activate pois a efl tiv sensitizer, tassium selenocyanate to make it labile with an increase EXAMPLE 4 in speed of up to 140%. E 1 H M 1 t th quiva ence o a 1 e se enium sens1 12ers W1 EXAMPLE 2 activated non-labile selenium compounds Actlvatlon by other reducmg agents A first portion of the emulsion of Example 1 is chemi- A first portion of the emulsion of Example 1 is chemcally sensitized with 2 mg. of potassium chloroaurate per ically sensitized with 2 mg. of potassium chloroaurate silver mole, 100 mg. of potassium thiocyanate per silver per silver mole, 100 mg. of potassium thiocyanate per mole and 0.8 mg. of N,N-dimethylselenourea per silver silver mole and 1.6 mg. of potassium selenocyanate per mole. The sensitized emulsion is then heated for 15 minsilver mole. The sensitized emulsion is then heated for utes at 65 C. 40 minutes at 65 C. A second portion of this emulsion is chemically sensi- A second portion of the emulsion is chemically sensitized with 4 mg. of potassium chloroaurate per silver tized with 4 mg. of potassium chloroaurate per silver mole, 100 mg. of potassium thiocyanate per silver mole, mole, 100 mg. of potassium thiocyanate per silver mole, 1.6 mg. of potassium selenocyanate per silver mole and 1.6 mg. of potassium selenocyanate per silver mole and 20.2 mg. of benzothiazole methiodide per silver mole. 20.2 mg. of benzothiazole methiodide per silver mole. This portion of the emulsion is also heated for 15 minutes This portion is then heated for 15 minutes at 65 C. at 65 C.

A third portion of the emulsion is sensitized in the 40 These emulsions are then coated and processed in the same manner as the second portion except that the benzosame manner as in Example 1 with the following results:

Relative Portion sensitizers Reducing agent speed Fog First Potassium chloroaurate-N,N- None 1,000 0.21

dimethylselenourea. Second--- Potassium ehloroaurate-Po- Benzothiazole methi- 970 0.17

tassium selenocyanate. odide.

Relative Portlon Reducing agent speed Fog First None 100 0.03 Second. Benzothiazole methiodide.. 302 0. 17 Third 2-mercaptobenzoic acid 289 0.20

EXAMPLE 3 Activation by reducing agents in the absence of a noble metal A first portion of the emulsion of Example 1 is chemically sensitized with 100 mg. of potassium thiocyanate per silver mole and 1.6 mg. of potassium selenocyanate This example shows that non-labile compounds which are activated by reducing agents are equivalent in their sensitizing action to labile selenium compounds.

EXAMPLE 5 Equivalence of labile selenium sensitizers with activated non-labile selenium compounds A first portion of the emulsion of Example 1 is chemically sensitized with mg. of potassium thiocyanate per silver mole and 0.8 mg. of N,N-dimethylselenourea per silver mole. This emulsion is then heated for 9 minutes at 60 C.

A second portion of this emulsion is sensitized with 100 mg. of potassium thiocyanate per silver mole, 1.6 mg. of potassium selenocyanate per silver mole and 1.4 mg. of triphenylphosphine per silver mole. This emulsion is then heated for 6 minutes at 60 C.

These emulsions are then coated and processed in the same manner as in Example 1 with the following results:

Portion Sensitizer Relative 9 EXAMPLE 6 Synergistic effect of reducing agent with non-labile selenium compound A first portion of the emulsion of Example 1 is sensitized with 100 mg. of potassium thiocyanate per silver mole and 2.8 mg. of triphenylphosphine per silver mole. This emulsion is then heated for 30 minutes at 60 C.

A second portion of the emulsion is sensitized with 100 mg. of potassium thiocyanate per silver mole and 1.6 mg. of potassium selenocyanate per silver mole and then heated for 30 minutes at 60 C.

A third portion of the emulsion is sensitized in the same manner as the first portion but the addition of 1.6 mg. of potassium selenocyanate per silver mole and heating for 6 minutes at 60 C.

dimethyl selenourea is disclosed as being labile in my earlier filed application Ser. No. 468,972, filed July 1, 1965, now US. Patent 3,297,446).

EXAMPLE 8 Comparison of activated non-labile selenium compounds With conventional sensitizers Relative Portion Sensitizer Reducing agent speed Gamma Fog First Sodium thiosulfate-potassium chloro- None 750 0. 93 0, 14

aura e.

Second. Selenous acid potassium chloroaurate. Sodium sulfite. 1,000 1. 03 0.14

These emulsions are then coated and processed in the same manner as in Example 1 with the following results:

This example illustrates the synergistic eifect which is obtained when a reducing agent is combined with a nonlabile selenium compound. An increase in speed of 1000% is obtained.

This example shows that gold and non-labile selenium compounds which have been made labile with reducing agents are better sensitizers than conventional sulfur and gold sensitizers.

EXAMPLE 9 Synergistic effect of reducing agent with non-labile selenium compound Portion of an emulsion similar to that of Example 1 are sensitized with various sensitizers as set forth below. These emulsions are then coated and processed in the same manner as in Example 1 with the following results:

Reducing Relative Portion sensltizer agent speed Gamma Fog First None 30 1 0.80 0.03 Second Selenous acid (3.27) (non- 30 24 0.37 0. 03

labile selenium compound).

Third Sodium sulfite (6.3) (re- 30 1 0. 12 0.03

ducing agent). Fourth Pzgagfium chloroaurate 25 24 0.28 0.08 Fifth Selehoirs acid (3.27 so 25 0.22 0.09

Flogassium chloroaurate Sixth Sodium suifite (6.3) a0 12 0.22 0.13 fiOSdSSil-lfll chloroaurate 30 12 0. 22 0. 13 Seventh. Selenous acid (3.27) 10 250 1. 42 0.18

Sodium sultite (6.3). Eighth Selenous acid (3.27) 80- 25 1,000 1.68 0.20

EXAMPLE 7 Effect of reducing agents on labile selenium compounds dium sulfite (6.3) Potassium chloroaurate (1.0)

A first portion of the emulsion of Example 1 is chemi- This example shows that activating a non-labile selenium compound with a reducing agent will increase the relative speed of an emulsion by over l000%.' This example also shows that the addition of a gold compound plus a reducing agent to a non-labile selenium compound will increase the relative speed of an emulsion by over 4000%.

EXAMPLE 10 A first portion of an emulsion similar to that of Example 1 is chemically sensitized with 4 mg. of potassium chloroaurate per silver mole, 100 mg. of sodium thiocyanate per silver mole, 1.6 mg. of potassium selenocynate per silver mole and 20.2 mg of benzothiazole methiodide This example shows that reducing agents have no effect per silver mole and is then heated for 15 minutes at on selenium compounds which are already labile (N,N- 65 C.

A second portion of the emulsion is chemically sensitized in the same manner as the first portion but with the addition of 4 mg. of sodium thiosulfate per silver mole and heating for minutes at 60 C.

Relative Portion Sensitizer speed Fog First None 1, 000 0.17 Second"... Sodi mthiosuliate 970 0.03

This example shows that sulfur compounds, such as sodium thiosulfate, act as stabilizers in reducing the fog of emulsions sensitized with gold and activated non-labile selenium compounds.

EXAMPLE 11 except that 50 grams per silver mole of a naturally active gelatin was utilized.

These portions of the emulsion are then coated and processed in the same manner as in Example 1 with the following results:

Relative Portion Gelatin speed Fog First Inert 100 0.16 Second Active 118 0. 22

This example illustrates the unpredictability connected with using potassium selenocyanate in combination with noble metals as a sensitizer with various gelatins. U.S. Patent 3,243,298, column 68, lines 35-38, and British Patent 861,984, page 2, lines 42-44 disclose the use of potassium selenocyanate as a sensitizer. There is no disclosure of the use of this compound in combination with noble metals, however, or that activation of this compound will give synergistic sensitizing results in combination with noble metals. The limited disclosure in these reference should thus be qualified as being dependent upon the type of gelatin employed. By employing the process of my invention, 1 can obtain reproducible results which are not dependent upon the particular type of gelatin employed.

7 EXAMPLE 12 Test for labile and non-labile selenium compounds To 10 m1. of distilled water in a test tube is added 6 mg. of potassium selenocyanate. To this solution approximately 15 ml. of 0.1 N silver nitrate is added. No silver selenide is formed which indicates that potassium senelocyanate is a non-labile selenium compound.

To 10 ml. of distilled water in a test tube is added 6 mg. of potassium selenocyanate. To this solution is added 50 mg. of sodium sulfite. No reaction occurs. To this solution approximately 5 ml. of 0.1 N silver nitrate is added. A black'precipitate (silver selenide) immediately forms. This indicates that the potassium selenocyanate becomes labile in the presence of sodium sulfite, a reducing agent.

In one embodiment of the present invention we employ a complex formed by gold salt with phosphine. This complex is not itself a sensitizer but it is added as a source of both gold salt as a sensitizer and phosphine as an activator for the non-labile selenium added separately. Triphenylphosphinegold (I) chloride is a well defined complex which has been isolated and purified. See Journ. Chem. Soc., 5751 (1965). When added to the emulsion the complex dissociates liberating the gold salt and triphenylphosphine components.

EXAMPLE 13 Lack of sensitizing ability of the complex by itself; lack of sensitizing ability of non-labile selenium by itself.

A medium grained silver bromoiodide emulsion containing 3.4 percent iodide was chemically sensitized with (per mole of silver halide) 4.75 mg. triphenylphosphinegold (I) chloride and mg. sodium thiocyanate.

A second portion of the emulsion was sensitized with 100 mg. sodium thiocyanate and 1.4 mg. potassium selenocyanate.

A third portion was sensitized with 4 mg. potassium chloroaurate (equimolar amount of gold, compared to sample 1) and 100 mg. sodium thiocyanate.

Each of the three samples was heated for 40 minutes at 65 C.

These emulsion samples were then coated on a cellulose acetate support at a coverage of 540 mg. silver per square foot. The coatings were exposed on an intensity scale sensitometer, processed for 5 minutes in Kodak Developer DK-SO, fixed, washed, and dried.

EXAMPLE 14 Activation of a non-labile selenium compound with the complex; simultaneous activation of the gold compound to produce a gold-sensitization The emulsion of example 13 was chemically sensitized with (per mole of silver) 4.75 mg. triphenylphosphinegold (I) chloride, 100 mg. sodium thiocyanate, and 1.4 mg. potassium selenocynate. Th sample was heated for 40 minutes at 65 C.

A second portion of the emulsion was sensitized with 4 mg. potassium chloroaurate (equimolar to the amount of gold in portion 1), 100 mg. sodium thiocyanate, and 1.4 mg. potassium selenocyanate. The sample was heated for 40 minutes at 65 C.

A third portion of the emulsion was sensitized with 100 mg. sodium thiocyanate, 1.4 mg. potassium selenocyanate and 2.55 mg. triphenylphosphine (equimolar to the amount of phosphine in the complex of sample 1). This portion was heated 1 minute at 65.

These emulsion samples were coated, exposed, and processed as in Example 13.

Relative Portion (description) speed Fog First (phosphine-gold complex-l-KSeON) 151 0. 12 Seoon (gold sensit1zer+KSeCN) 100 0. 07 Third (phosphine-i-KSeCN) r 74 0. 13

EXAMPLE 15 Inability of the complex to chemically sensitize with labile selenium The emulsion of Example 13 was chemically sensitized with (per mole of silver) 4 mg. of potassium chloroaurate, 100-mg. sodium thiocyanate, and 1.45 mg. N,N-dimethylselenourea. The portion was heated for 5 minutes at 65 C.

A second portion was sensitized with 4.75 mg. triphenyl- 13 phosphine-gold (I) chloride, (equimolar in gold to the gold-sensitizer used in sample 1), 100 mg. sodium thiocyanate, and 1.45 mg. N,N-dimethylselenourea. This sample was heated for 20 minutes at 65 C.

The samples were coated, exposed, and processed as in Example 1.

A coarse grained silver bromoiodide emulsion containing 6 mole percent iodide was chemically sensitized with (per mole of silver 2 mg. potassium chloraurate, 50 mg. sodium thiocyanate, 4 mg. sodium thiosulfate pentahydrate, and 0.5 mg. N,N-dimethylselenourea. The sample was heated for 5 minutes at 65 C.

A second portion was sensitized with 7.8 mg. triphenylphosphine-goldfl) chloride, 100 mg. sodium thiocyanate and 2.06 mg. Complex D. The sample was heated for 25 minutes at 65 C.

A third portion of the emulsion was chemically sensitized with 7.8 mg. triphenylphosphine-gold(I) chloride, 100 mg. sodium thiocyanate and 1.8 mg. potassium selenocyanate. The sample was heated 20 minutes at 65 C.

The emulsion samples were then coated on a cellulose acetate support at a coverage of 540 mg. silver per square foot. The coatings were exposed on an intensity scale sensitometer, processed for 4 minutes in Kodak Developer D-19, fixed, washed, and dried.

Relative Portion (description) speed Fog First (Optimum gold-Hablle selenium finish for this emulsion) 100 0.08 Second (gold-phosphine complex+isoselenocyanate complex) 1 105 0. Third (gold-phosphine complex+KSeGN) 95 0.08

Although the invention has been described in detail with reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

I claim:

1. A process comprising sensitizing a photographic silver halide emulsion with a sensitizing amount of a noble metal and labile selenium, said labile selenium being formed in situ by activating a non-labile selenium compound.

2. The process of claim :1 wherein said non-labile selenium compound is activated by a reducing agent.

3. The process of claim 1 wherein said noble metal is gold.

4. The [process of claim 2 wherein said noble metal is gold.

5. The process of claim 1 wherein said non-labile selenium compound is either potassium selenocyanate or selenous acid.

6. The process of claim 3 wherein said non-labile selenium compound is either potassium selenocyanate or selenous acid.

7. The process of claim'4 wherein said non-labile selenium compound is potassium selenocyanate or selenous acid.

8. The process of claim 2 wherein said reducing agent is a benzothiazolium salt, 2-mercaptobenzoic acid, triphenylphosphine, stannous chloride or an alkali metal sulfite.

9. The process of claim 4 wherein said reducing agent is a benzothiazolium salt, Z-mercaptobenzoic acid, triphenylphosphine, stannous chloride or an alkali metal sulfite.

10. The process of claim 7 wherein said reducing agent is a benzothiazolium salt, 2-mercaptobenzoic acid, triphenylphosphine, stannous chloride or an alkali metal sulfite.

11. The process of claim 1 wherein said sensitizing is carried out in the presence of a water-soluble thiocyanate compound.

12. The process of claim 4 wherein said sensitizing is carried out in the presence of a water-soluble thiocyanate compound.

13. The process of claim 1 wherein said silver halide emulsion is stabilized with a labile sulfur compound.

14. The process of claim 4 wherein said silver halide emulsion is stabilized with a labile sulfur compound.

15. The process of claim 11 wherein said silver halide emulsion is stabilized with a labile sulfur compound.

References Cited UNITED STATES PATENTS 3,297,446 1/1967 Dunn 96107 3,297,447 1/ 1967 McVeigh 96107 X NORMAN G. TORCHIN, Primary Examiner. RICHARD E. FICHTER, Assistant Examiner.