US3510348A - Direct positive recording film - Google Patents

Description

United States Patent 3,510,348 DIRECT POSITIVE RECORDING FILM Dugald A. Brooks, Evan T. Jones, and Richard W. Spayd, Rochester, N .Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed June 20, 1966, Ser. No. 558,585 Int. Cl. B4411 N18 US. Cl. 117-201 31 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electron-sensitive recording elements and processes of exposing to electrons an electrically conductive element comprising a support and a layer comprising electron-sensitive, direct-positive, fogged silver halide grains.

This invention relates to electron sensitive recording elements, their preparation and use. In one of its aspects this invention relates to electrically conducting electron sensitive elements comprising a support in which silver halide layers for-m direct-positive images upon development following exposure to e ectrons. In another of its aspects, this invention relates to electron sensitive films and plates which can be exposed to electrons in a vacuum to obtain direct-positive silver images.

Electron sensitive films and plates are useful in many applications for recording an image by direct exposure to an electron beam, for example in a cathode ray tube, in electron microscopes, data recording apparatus and the like. Such films and plates comprise a layer of electron sensitive material that forms an image in the layer by direct imagewise exposure in an electron beam The image produced can be directly visible as in a layer of monomeric material that polymerizes upon electron beam exposure or it can be a latent image that requires development to produce a visible image as with silver halide materials.

In some recording apparatus that employ direct electron beam recording film, an image recorded on the film or plate is read back or viewed by projecting a beam of ultraviolet or other radiation through the developed film onto a fluorescent screen to produce a fluorescent image on the screen. However, for many uses it is desirable to view the image directly on the film by irradiating a fluorescent layer which is coated on the film or plate after exposure and prior to read-out. See, for example, B. Miller, Electron Beam Read-Out Shows Potentia Aviation Week and Space Technology, Apr. 13, 1964, pages 107-110, and a paper presented at the National Aerospace Electronics Conference, 17th. Dayton, Ohio, 1965, by E. V. Boblett and K. F. Wallace, entitled Electron Beam Readout of Silver Halide Transparencies. The fluorescent layers employed in electron beam recording films or plates can be incorporated into such materials during their manufacture in order to facilitate handling prior to read-out.

In the past, the electron sensitive materials employed in electron recording films and plates have been negative silver halide layers, i.e., those which upon simple or single stage development give negative silver images. In many cases, however, it is desirable or even necessary to obtain positive silver images. Unfortunately, the negative silver halide layers used for this purpose require complex multi. stage reversal processing in order to obtain a positive image. Furthermore, silver halides having fine grains are especially useful in electron sensitive films and plates due to their high resolution and low graininess characteristics. However, when employing conventional multistage reversal processing techniques with fine grain silver halide 3,510,348 Patented May 5, 1970 ice layers it is extremely diflicult to obtain the sensitometric characteristics required in electron recording.

Accordingly, it is an object of this invention to provide electron sensitive elements which contain a layer of silver halide grains. It is another object of this invention to provide an electrically conductive element comprising a support and a layer of electron sensitive direct-positive fogged silver halide grains. Still another object of this invention is to provide an electron sensitive element which can be processed by simple one-stage development to obtain a positive silver image. Still another object of this invention is to provide an electron sensitive element that can be exposed to electrons in a vacuum to obtain a positive silver image upon simple one-stage development. It is another object of this invention to provide a simple, rapid and economical means for obtaining a positive silver image with an electron sensitive photographic element. Other objects and advantages of this invention will become apparent from an examination of the specification and claims which follow.

The above and other objects of this invention are obtained with direct eectron recording films and plates having radiation sensitive layers which comprise fogged silver halide grains which form a direct-positive silver image upon simple or single stage development following exposure to electrons. Since these fogged silver halide grains form positive silver images after exposure to electrons without complex multistage reversal processing they are referred to in the following specification and claims as electron sensitive direct-positive fogged silver halide grains.

To obtain fogged silver ha ide grains which will form direct-positive silver images upon exposure to electrons it is sometimes desirable or even necessary to include an electron acceptor, more specifically a photoelectron acceptor or a desensitizing dye in the layer with the fogged silver halide grains. Such electron accepting compounds are absorbed to the silver halide grains and often improve the electron sensitivity of such grains. In the past, electron acceptors have been used in light sensitive direct-positive silver halide layers to improve the reversal characteristics of the layer upon exposure to light. How ever, a surprising feature of this invention is that many light sensitive direct-positive silver halide layers containing electron acceptors are not electron sensitive and cannot be used in the practice of this invention, as shown in Example 3. Furthermore, certain of the fogged silver halide grains disclosed herein, as illustrated in the following Example 1, exhibit very useful reversal characteristics in the absence of an electron accepting compound.

The silver halide grains employed in the practice of this invention are light sensitive, i.e., they are photographic silver halides, as well as being sensitive to electrons and can be prepared using methods known in the photographic art. A preferred class of silver halide grains comprises 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 development 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 minutes in an aqueous 0.3 percent 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.

DEVELOPER A Grams N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0 Potassium meta'borate 35.0 Potassium bromide 1.0 Water to make 1 liter. pH of 9.6.

DEVELOPER B Grams 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 make 1 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 U.S. Pat. 1,574,944, issued Mar. 2, 1926; Sheppard et a1. U.S. Pat. 1,623,499, issued Apr. 5, 1927; and Sheppard et al. U.S. 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. U.S. Pat. 2,399,083, issued Apr. 23, 1946, and Damschroder et a1. U.S. 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 U.S. Pat. 2,487,850, issued Nov. 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones U.S. Pat. 2,518,698, issued Aug. 15, 1950), polyamines, such as spermine (Lowe and Allen U.S. Pat 2,521,925, issued Sept. 12, 1950), or bis(p-aminoethyl)sulfide and its Water-soluble salts (Lowe and Jones U.S. 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 sufiicient 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. 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 above grains in the electron sensitive layer 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 watersoluble 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, as shown in Example -1. Generally, about 2 to 8 molar equivalents of shell silver halide per molar equivalent of core silver halide are used in the grains comprising the electron sensitive 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 are 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/fif preferably about 20 to about mg. silver/ft. 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.

Another class of electron sensitive direct-positive fogged silver halide grains that can be employed in the practice of this invention are the non covered grain fogged silver halides. Such grains can be fogged by chemically sensitizing into fog with the sensitizing agents described for chemically treating the core-forming emulsions described hereinbefore. Thus, suitable fogging methods include 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. The silver halide grains can be fogged with high intensity light, reduction fogged with a reducing agent such as thiourea dioxide or stannous chloride or fogged with gold or other noble metal compounds. Combinations of reduction fogging agents with gold compounds or compounds of another metal more electropositive than silver, for example, rhodium, platinum or iridium, can be used in fogging the silver halide grains.

The silver halide grains employed in the practice of this invention are fogged sufliciently to give a density of at least 0.5 when developed without exposure for five minutes in Kodak DK-SO developer when a direct-positive emulsion layer containing such grains is coated at a coverage of about 50 to about 500 mg. of silver per square foot of support.

As previously stated, the direct-positive fogged silver halide grains employed in the conducting elements of this invention can comprise reduction and gold fogged silver halide grains, which are fogged with a combination of a reduction fogging agent and a gold fogging agent. When a low concentration of gold and reducing agent is employed in such a combination the fogged silver halide grains are characterized by a rapid loss of fog upon chemical bleaching, as described hereinafter.

In practicing this invention, the silver halide grains can be fogged prior to coating or they can be coated prior to fogging. The reaction conditions during fogging of the silver halide grains are subject to wide variation although the pH is generally in the range of about 5 to about 7, the pAg is generally in the range of about 7 to about 9 and the temperature is generally in the range of about 40 to about 100 C., most often about 50 to about 70 C. During fogging the silver halide grains can be suspended in a suitable vehicle such as gelatin which is generally employed at a concentration in the range of about 40 to about 200 grams per mole of silver halide.

As previously indicated, a preferred class of silver halide grains are those which are characterized by a rapid loss of fog upon chemical bleaching. These grains will lose at least about 25% and generally at least about 40% of their fog when bleached for ten minutes at 68 F., in a potassium cyanide bleach composition as described hereinvent solution, for example methanolic solutions of the electron acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste of pyrolytic graphite electrode, with the voltometric 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 are described in New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, N.Y., 1954; Polarography, by Kolthoff and Lingane, 2nd Edition, Interscience Publishers, New N. Y., 1952; Analytical Chemistry, 36, 2426 (1964) by Elving; and Analytical Chemistry, 30, 1576 (1958) by Adams. Compounds which can be employed as electron acceptors in the practice of this invention include organic compounds having an anodic polarographic halfway potential (E,,) and a cathodic polarographic halfway potential (E which when added together give a positive sum of greater than 0.5, preferably greater than 0.97. Some specific electron acceptors which give outstanding results in the practice of this invention are cyanine dyes having at least one methine group wherein the hydrogen atom thereof is replaced with a halogen atom having an atomic Weight in the range of about 35 to about 127, i.e., chlorine, bromine or iodine atoms. Suitable halogen containing cyanine dyes can be repreafter. This fog loss can be illustrated by coating the regusented by the formula:

lar silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 When processed for six minutes at about 68 F., in Kodak DK-SO developer and comparing the densit of such a coating with an identical coating which is processed for six minutes at 68 F., in Kodak DK-50 developer after being bleached for about 10 minutes at 68 F., in the potassium cyanide bleach composition. The maximum density of the unbleached coating will be at least 30% greater, generally at least 60% greater than the maximum density of the bleached coating. Kodak DK-50 developer is described in the Handbook of Chemistry and Physics, 30th Edition, 1947, Chemical Rubber Publishing Co., Cleveland, Ohio, page 2558, and has the following composition:

Water, about 125 F. (52 C.)500 cc. N-methyl-p-aminophenol sulfate2.5 grams Sodium sulfite, desiccated30.0 grams Hydroquinone-2.5 grams Sodium metaborate10.0 grams Potassium bromide-05 gram Water to make 1.0 liter 7 In practicing this invention, it is sometimes desirable or even necessary to employ an electron accepting compound with the fogged silver halide grains in order to obtain optimum reversal characteristics. Suitable electron accepting compounds include the photoelectron accepting compounds or desensitizing dyes often used in photographic reversal systems. These electron accepting compounds are absorbed to the fogged silver halide grains. The electron 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 1 10- molar solution of the electron acceptor in a solvent, for example methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with a polarographic halfwave potential for the most positive cathodic wave being designated E Anodic measurements can be made with l 10 molar aqueous sol- /p-l\ jut-1 wherein Z and Z each represent the non-metallic atoms necessary to complete a heterocyclic nucleus of the type used in cyanine dyes, such as a nucleus of the benzothiazole series (e.g., benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole, 7-chlorobenzothiazole, 4- methylbenzothiazole, S-methylbenzothiazole, S-bromobenzothiazole, 4-phenylbenzothiazole, S-phenylbenzothiazole, 6-phenylbenzothiazole, 4-methoxybenzothiazole, 5- methoxybenzothiazole, 5-iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, 5-hydroxybenzothiazole, etc.); the naphthothiazole series (e.g., tat-naphthothiazole, fi-naphthothiazole, S-methoxy-B-naphthothiazole, S-ethyI-fi-naphthothiazole, 8-methoxy-a-napthothiazole, 7-methoxy-tat-naphthothiazole, etc.); those of the benzoxazole series (e.g., benzoxazole, S-chlorobenzoxazole, S-methylbenzoxazole, S-phenylbenzoxazole, S-methoxybenzoxazole, 5-ethoxybenzoxazole, S-hydroxybenzoxazole, etc.); those of the naphthoxazole series (e.g., a-napthoxazole, fl-naphthoxazole, etc.); those of the benzoselenazole series (e.g., benzoselenazole, 5-chlorobenzoselenazole, S-methylbenzoselenazole, S-hydroxybenzoselenazole, etc.); those of the naphtthoselenazole series (e.g., a-naphthoselenazole, ,B-naphthoselenazole, etc.); those of the quinoline series including the 2-quinolines (e.g., quinoline, 3-methylquinoline, S-methylquinoline, 7-methylquinoline, S-methylquinoline, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquinoline, 6-hydroxyquinoline, 8-hydroxyquinoline, etc.); the 4-quinolines (e.g., quinoline, 6-methoxyquinoline, 7-methoxyquinoline, 8-methoxyquinoline, etc.); those of the isoquinoline series (e.g., the l-isoquinoline, the 3-isoquinolines, etc.); X and X each represents an atom selected from the group consisting of hydrogen, chlorine, bromine and iodine, at least one of X and X being chlorine, bromine or iodine; R and R each represents alkyl, e.g., lower alkyl such as methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, etc., a sulfoalkyl group in which the alkyl group has from 1 to 4 carbon atoms, such as sulfomethyl, sulfoethyl, sulfopropyl, sulfobutyl, etc. and a carboxyalkyl group in which the alkyl group has from 1 to 4 carbon atoms such as carboxymethyl, carboxyethyl, carboxypropyl, carboxybutyl, etc.; A represents an acid anion such as chloride, bromide, iodide, p-toluenesulfonate, thiocyanate, methyl sulfate, ethyl sulfate, perchlorate, and the like; and d, m, n and p each represents a positive integer of from Ito 2.

The halogen containing cyanine dyes described herein can be prepared by halogenating a cyanine dye with chlorine, bromine or iodine. Any suitable halogenating agent may be used, such as aqueous alcoholic (e.g., methanol or ethanol) solutions of the halogen, N-chlorosuccinimide, N-bromosuccinimide, N-iodosuccinirnide, or

a commercially available halogen-pyrrolidone complex,

such as the bromo-pyrrolidone complex sold by General Aniline and Film Corp. Using such halogenating agents causes replacement by halogen or a hydrogen atom in the methine chain. In carbocyanines, or dicarbocyanines, analysis indicates that halogen substitution occurs on the terminal carbon atoms of the methine chain. Typical preparations for the halogen containing electron acceptors are as follows:

EXAMPLE A To 40 ml. of solution of ethyl alcohol containing 1() grams of the sensitizing dye, 1,1-diethyl-2,2- cyanine chloride is added 29 ml. of an aqueous solution containing 2X10' grams of a bromine-pyrrolidone complex sold by the General Aniline and Film Corp. The mixture of these two solutions results in the conversion of the previously red colored solution of the dye (absorption max-540 m to a blue colored solution (absorption max590 m The blue form of the dye is light sensitive and should be prepared and used only in total darkness to prevent spontaneous decomposition.

A series of halogenated dyes are prepared by the drop- Wise addition of a solution of 8 mg. N-bromosuccinimide (NBS) per ml. methanol to a methanolic solution of cyanine dye (8 mg. dye in cc. methanol), until no further color change occurs. At least one hydrogen atom in the methine chain of the dye is replaced with a bromine atom. The dyes used are listed below, together with the number of equivalents NBS employed.

(A) l,1',3,3-tetramethyl-2,2-cyanine iodide, 2 NBS (B) 3,3'-diethylthiacyanine iodide, 2 NBS (C) 3,3-diethylthiacarbocyanine iodide, excess NBS (D) 3,3-diethylthiadicarbocyanine iodide, excess NBS (E) 3,3-diethylthiatricarbocyanine iodide, excess NBS (F) 3,3-diethyl-9-methylthiacarbocyanine bromide, ex-

cess NBS (G) 9-ethyl-3,3'-dimethyl-4,5,4',5-dibenzothiacarbocyanine chloride, excess NBS (H) 1,1'-diethyl-2,2'-cyanine chloride, 2 NBS (K) 3,3'-dimethylthiacyanine bromide, 1 NBS (M) 3-bromo-l,1'-diethyl-2,2-cyanine iodide, 3 NBS (N) l,l'-dimethyl-2,2-cyanine iodide, 3 NBS (O) l-ethyl-l'-methyl-2,2'-cyanine iodide, 3 NBS (P) l,3-dimethylthia-2'-cyanine iodide, 2 NBS (Q) 1'-ethyl-2-methylthia-2'-cyanine iodide, 2 NBS (R) 1'-methyl-3-ethylthia-2'-cyanine iodide, 2 NBS (S) l',3-diethylthia-2'-cyanine iodide, 2 NBS (T) 3-ethyl-3-methylthiacyanine iodide, 2 NBS (U) 1,1'-diethyl-l,2,2'-cyanine iodide, l NBS Another group of compounds which can be absorbed onto the fogged silver halide grains to improve reversal characteristics are halogen accepting compounds. Compounds of this type, organic or inorganic, can be characterized by having an anodic polarographic potential less than 0.85 and a cathodic polarographic potential 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.

8 Particularl preferred halogen acceptors are merocyanine dyes having the following structure:

B=atoms required to complete a basic nitrogen-containing heterocyclic nucleus, e.g., benzothiazole, naphthothiazole, benzoxazole, etc.

-A=atoms required to complete an acidic heterocyclic nucleus, e.g., rhodanine, 2-thiohydantoin, etc. Particularly good results are obtained with merocarbocyanine dyes (n=l) and with thiazole-rhodanine dyes.

Dyes of this class can be prepared by the methods described in Brooker et al. US. Pat. 2,493,747 and US. Pat. 2,493,748, issued Jan. 10, 1950.

Examples of suitable halogen accepting merocyanine dyes which can be used in the practice of this invention include:

Dye I--l -carboxymethyl-5-[ (3-ethyl-2-benzoxazolinylidene) ethylidene] -3-phenyl-2-thiohydantoin Dye II3-carboxymethyl-5-[ (3-methyl-2-thiazolidinylidenel-methylethylidene] rhodanine Dye II-I3-ethyl-5- 3-methyl-Z-thiazolidinylidene ethylidene] -2-thio-2,4-oxazolidinedione Dye IV 5 3-{2-carboxyethyl}-2-thiazolidinylidene ethylidene] -3-ethylrhodanine Dye V--5- (3-methyl-2-thiazolidinylidene) -1-methylethylidene] -3- 2-rnorpholinoethyl) -rhodanine Dye VI5- (3-{2-carboxyethyl}-2-thiazolidinylidene) l-methylethylidene] -3-carboxyrnethylrhodanine Dye VII5- (3-{2-carboxyethyl}-2-thiazolidinylidene) l-methylethylidene] -3- 2-methoxyethyl rhodanine Dye VIII-3- 3-dimethylaminopropyl -5-[ (3-methyl- 2-thiazolidinylidene ethylidene] rhodanine Dye IX5-[ (3-methyl-2-thiazolidinylidene) -1-methylethylidene] -3- (2-sulfoethyl) rhodanine The compounds which accept electrons or halogen in the practice of this invention can be employed in widely varying concentrations. However, the electron accepting compounds are generally employed at concentrations in the range of about 200* to about 800, preferably about 300 to about 600 milligrams per mole of silver halide. The halogen accepting compounds are generally employed at somewhat lower concentrations.

The silver halides employed in the preparation of the electron sensitive compositions described herein include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, and the like. Silver halide grains having an average grain size less than about one micron, preferably less than about 0.5 micron, give particularly good results. The silver halide grains can be any suitable shape such as cubic or octahedral and preferably have a rather uniform diameter frequency distribution. For example, at least by weight, of the photographic silver halide grains can have a diameter which is within about 40%, preferably within about 30% of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXIX, 1949, pages 330-338. A preferred class of photographic silver halides comprises at least 50 mole percent bromide, e.g., silver bromoiodide containing less than about ten mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

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 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 silver halides can be coated without the use of a hydrophilic colloid, e.g., from an aqueous solution or using vacuum deposition.

The electron sensitive compositions described herein can be coated on a wide variety of supports in preparing the electrically conducting elements of this invention. The photographic silver halide grains can be coated on one or both sides of the support which is preferably substantially free of volatile solvent to prevent out gassing in a vacuum and in preferably also transparent and/or flexible. Typical continuous supporting sheets include, e.g., 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 a.-olefin polymers, particularly polymers of OL-OlCfiIlS containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylenebutene copolymers, and the like, give good results.

The electron-sensitive recording elements of this invention advantageously carry a layer of electrically conductive material, preferably one having a surface resistivity of less than 10' ohms per square. This material can be coated on the opposite side of the support from the electron sensitive layer but it is generally coated on the same side of the support that carries the sensitive layer. This conductive layer serves to prevent accumulation of a static charge and consequent image distortion where an electron beam strikes the sensitive element. This conductive layer can be the outermost layer on the emulsion side of the support. However, in some embodiments, it can be effectively located beneath other coated layers on the support, i.e., beneath a fluorescent layer, a sensitive layer, or both. If the conductive layer is beneath permanent layers, then of course it must be able to withstand Whatever processing chemicals are to be used. If the layer is outermost it must be substantially electron transparent and it must be permeable by whatever processing solutions are used. Preferably it is one that will not be removed by processing chemicals and is optically transparent. This permanent conductive outer layer prevents static accumulations on the surface during igmaewise exposure in an electron beam and again if the finished film is irradiated in an electron beam to view a fluorescent image. The outer conductive layer may also be one that is removed during processing, preferably by the same chemicals used for photographic development, and in this case it need not be visually transparent though it must be substantially electron transparent. A preferred conductive layer for use in the practice of this invention comprises a layer of film-forming vehicle or resin binder in which are dispersed colloidal particles of a semi-conducting metal compound such as cuprous iodide or silver iodide, either as a colloidal dispersion or as a complexed solute. If desired, a conducting material can be impregnated in the support to render the element an electrically conducting element and eliminate the use of a separate electrically conductive continuous layer.

The electrically conductive elements of this invention can contain barrier layers which are coated between a conducting layer or support and the layer of electron sensitive material. Such barrier layers can substantially improve the stability of the electron sensitive layer. In a preferred embodiment of this invention a continuous barrier layer is coated outward from the supporting sheet and over a conductive layer and under a layer of electron sensitive fogged silver halide grains. Such a barrier layer is moisture impermeable and preferably comprises a film of water-impermeable resin. A preferred class of resins for this purpose comprises homoand copolymers of vinylidene chloride including copolymers containing substantial amounts of vinylidene chloride with acrylic monomers such as acrylonitrile, methyl acrylate, and the like. However, other suitable resins which can be used in the preparation of barrier layers are electrically insulating resins generally having good water impermeability properties when coated as thin films. Examples of such resins include polyvinyl butyryl, polymethyl methacrylate, polyvinyl chloride, cellulose nitrate, polystyrene, polyesters such as polyethylene terephthalate, polycarbonates and the like.

The direct electron recording films and plates described herein can also contain fluorescent layers or coatings to facilitate read-out. Such coatings or layers are located outward from the support and over the layer of fogged silver halide grains. Examples of suitable organic fluorescent compounds which can be used in the fluorescent layers are those described as organic fluors and organic scintillators in Organic Scintillation Detectors by E. Schram and R. Lombaert, Elsevier Publishing Company, 1963, as exemplified by such organic water-insoluble fluorescent compounds as Tinopal SFG, p-terphenyl, pquaterphenyl, anthracene, 20% Fluolite casein, tetraphenyl butadiene, Blancopho-r AW, triazinyl-stilbenes such as those described in McFall et al. US. Patent 2,933,390, bis(8 hydroxyquinolino)-magnesium, tris (4,4,4 trifluoro 1) 2 (triethyl-l,3-butanediono)- europium, 1,4-bis-2-(5-phenyloxazolyl)-benzene, Leucophor B (triazinyl amino stilbene) and coumarins such as those described in British Pat. No. 786,234. These compounds are mentioned only as examples of the many organic, water-insoluble fluorescent compounds and mixtures thereof which can be used in practicing this invention. Layers of such fluorescent compounds can be prepared using any procedure suitable for this purpose. For example, the fluorescent compounds can be coated as a dispersion in a hydrophilic film-forming binder such as gelatin, polyvinyl alcohol and other binders that can be coated from aqueous solution to form Water permeable films. The fluorescent organic compounds generally have a particle size up to about 5 microns. A preferred class of binders which can be employed for the fluorescent compound are vinyl polymers, e.g., alkyl acrylate styrene copolymers in which the alkyl groups preferably contain 1-8 carbon atoms, as exemplified by ethyl, methyl, butyl and the like, alkyl acrylateprotein and styrene-alkyl acrylate-protein emulsion polymerized latexes of the type described in US. Pat. 2,852,382 as well as emulsion polymerized resin binders of the type described in Fowler US. Pat. 2,772,166, issued Nov. 27, 1956, Dann et al. US. Pat. 2,831,767, issued Apr. 22, 1958 and Gates et al. US. Pat. 2,853,457, issued Sept. 23, 1958. Mixtures of such binders can also be employed in forming the fluorescent layers described herein.

The electron sensitive silver halide layers and other 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, oxypoly-saccardies, such as oxy starch or oxy plant gums, and the like. The silver halide layers can also contain .additonal additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, plasticizers, and the like. These layers can also contain absorbing dyes which confine diffuse visible radia tion emitted by any fluorescent layer which is present during the exposure of the element of this invention to electrons. Although such dyes generally reduce the sensitivity of photographic elements to light, they have substantially no effect upon the electron sensitivity of the elements described herein. Examples of suitable absorbing dyes include blue radiation absorbing dyes such as tartrazine and dyes of the type described in Van Campen US. Pat. 2,956,879, issued Oct. 18, 1960. The fogged silver halide layers described herein can also contain spectral sensitizing dyes which are advantageously employed where the silver halide layer is exposed to ultraviolet, infrared or visible radiation and read-out in an electron beam. Suitable spectral sensitizers include the cyanines, merocyanines, complex (trinuclear) cyanines, complex (trinuclear) merocyanines, styryls and hemicyanines. The silver halide layers can also be developed using incorporated developers such as polyhydroxybenzenes, aminophenols, B-pyrazolidones, and the like.

It is sometimes advantageous to employ surface active agents or compatible mixtures of such agents in the preparation of the electrically conductive 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 U.S. Pat. 2,600,831, issued June 17, 1952; U.S. Pat. 2,271,622, issued Feb. 3, 1942; U.S. Pat. 2,271,623, issued Feb. 3, 1942; U.S. Pat. 2,275,727, issued Mar. 10 1942; U.S. Pat. 2,787,604, issued Apr. 2, 1957; U.S. Pat. 2,816,920, issued Dec. 17, 1957; U.S. Pat. 2,739,891, issued Mar. 27, 1956 and Belgian Pat. 652,862.

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 The electron sensitive, direct-positive fogged silver halide grains employed in the electron sensitive layers of the electrically conductive elements of this invention can be the covered grain type. To illustrate, a gelatin silver bromoiodide emulsion containing iridium centers in the core is prepared by simultaneously adding at 70 C., over a period of about 35 minutes in a controlled pAg of 8.9, (a) 1200 milliliters of a 3.81 molar aqueous solution of potassium bromide and a 0.1 molar, aqueous solution of potassium iodide and (b) 1275 milliliters of a 3.69 molar aqueous solution of silver nitrate, to 4000 milliliters of a 5% gelatin aqueous solution. Fifty milligrams of potassium chloroiridate (III), i.e., K IrCl is added five minutes after the run is started. At the end of the run the emulsion is cooled to 40 C., gelatin is added to a total of 159 grams per mole of silver and the emulsion is chilled for about 15 hours, noodled and washed to remove soluble salts. The emulsion is then melted at 40 C. adjusted to a final Weight of 12.4 kilograms a pH of 6.5 and a pAg of 8.2. Thiourea dioxide, in aqueous solution, is added to the melted emulsion at a concentration of 0.002 gram per mole of silver. The melt is then digested for one hour at 55 C. While holding at 55 C., 40 milligrams per mole of silver of patassium chloroaurate is added to the melt from aqueous solution. The melt is then digested for 20 minutes at 65 C. and then cooled to 40 C. The emulsion is coated on a conventional cellulose acetate film sup port bearing a cuprous iodide conducting layer at a coverage of 100 milligrams of silver per square foot in 384 milligrams of gelatin per square foot.

Samples of the coated film are exposed to electron bombardment (50 kv.) in a conventional electron microscope (RCA Electron Microscope, Model U2D) at a pressure of approximately 10- millimeters mercury for 0, 2, 4 and 8 seconds. The exposed samples are processed for six minutes in an elonhydroquinone developer such as Kodak Developer D-19, fixed, washed and dried. The maximum density at each of the exposure levels is as follows:

TABLE 1 Exposure (seconds): Density From the above table can be seen than an increase in electron exposure significantly reduces density, i.e., there is obtained good reversal characteristics. Similar results are obtained when the potassium chloriridate in the above procedure is replaced by other water soluble salts of metals of Group VIII of the Periodic Table, for example, ammonium chloro palladate, potassium chloro platinate, sodium chloro palladate and like salts which provide metal ions which promote deposition of photolytic silver in the core of the fogged silver halide grains.

EXAMPLE 2 As previously indicated herein, electron acceptors can be absorbed to the fogged silver halide grains in the sensitive layer. To illustrate, a fine-grain, gelatino-silver bromoiodide emulsion is melted at 40 C. Thiourea dioxide, in aqueous solution, is added to the melted emulsion at a concentration of 0.002 g./mole silver. The melt is then digested for one hour at 55 C. While holding at 55 C., 40 mg./mole silver of potassium chloroaurate is added to the melt from aqueous solution, and the melt is then digested for 20 minutes at 65 C. The melt is cooled to 40 C. rapidly, and split into portions. From 2 00 to 800 mg./mole silver of the electron acceptor, 1,1'-diethy1-2,2'- cyanine iodide reacted with an equal weight of N-bromosuccinimide (identified as Dye U in Example B hereof), is added to various portions of the melt from methanol solution. Finally, the following addenda are added to each melt: 10 cc./mole Ag 10% aqueous formaldehyde, 25 cc./mole Ag saponin and 820 g./mole Ag 10% aqueous gelatin. These melts are coated on an electrically conductive film support at coverages of 256 mg. Ag/ft. and 338 mg. gelatin/K A sample of each coating is exposed 2, 4 and 8 seconds to electrons (50 kv.) in a conventional electron microscope at a pressure of approximately 10- mm. Hg. The exposed samples are processed 8 minutes in Kodak Developer D-19, fixed, washed and dried. The maximum and minimum densities for each sample are as follows:

TABLE 2 Dye (mg. /mole Coating Ag) Dmax} min 1 This value is the density of the unexposed areas of each example. 2 This value is the density resulting from an 8 second exposure.

Upon exposure and development after bleaching for 10 minutes at 68 F. in the bleach composition described hereinbefore, each of the above coatings exhibits a loss of over 45% in maximum density.

EXAMPLE 3 TABLE 3 14 4 mil polyethylene terephthalate containing a cuprous iodide conducting layer at coverages of 80 mg./ft. of silver and 45 mg./ft. of gelatin. For comparison purposes a coating (Coating 2) is prepared from an identical portion of the aforementioned emulsion which also contains 400 mg. of dibrominated 1,1'-diethyl-2,2'-cyanine iodide (identified hereinbefore as Dye U). The coatings are given identical time scale exposures to electrons (15 kv.), developed for 6 minutes in Kodak Developer D-19,

1O fixed, washed and dried. The results are as follows: Dye Light Exposure Electron exposure TABLE 4 a D 1. ma. D in Coatmg (mg [mole Ag) Dm D x m Coating Relative speed Durex. D 1 200 3.0 0.67 3.0 3.0 2 400 a. 0. 39 a. 0 a. 0 1 100 2. 0. 1s a 800 3.0 0.26 3.0 3.0 2 490 2.08 0.11 change From the above table it can be seen that the addition E M L 4 of an electron acceptor such as Dye U significantly in It is advantageous to include an absorbing dye in an electron sensitive layer of an electrically conductive element used in the practice of this invention. To illustrate, a silver bromoiodide photographic emulsion containing approximately 5 mole percent iodide and having an average grain size of about 0.08 micron is prepared by simultaneously adding, over a period of 4.5 minutes at 55 C. (a) 1200 ml. of a 3.81 M KBr+0.1 M KI aqueous solution and (b) 1275 ml. of a 3.69 M AgNO aqueous solution to 4000 ml. of a 5% gelatin aqueous solution containing 2.0 g. of K IrCl At the end of the additions, the emulsion is cooled, chill-set, noodled and washed to remove soluble salts. The emulsion is reduction and gold fogged by first adding 1.8 mg. of thiourea dioxide and heating for 60 minutes at 65 C. and then adding 3.0 mg. of potassium chloroaurate per mole of silver halide and heating for 40 minutes at 65 C. Four hundred mg. of anelectron acceptor (dibrominate 1,1- diethyl-2,2'-cyanine chloride identified as Dye U herein) per mole of silver halide are added. A hardener and coating aid are added to the emulsion in the conventional manner, and the emulsion is coated on a 4 mil polyethylene terephthalate support coated with a conducting layer containing cuprous iodide. The emulsion is coated at coverages of approximately 85 mg. of silver and 45 mg. of gelatin/fe Over the emulsion layer is coated a fluorescent or scintillator layer at a coverage of 200 mg. of solids/ft. The binder for the scintillator layer comprises 30% gelatin and 70% of a polymeric latex (70% butyl acrylate and 30% styrene copolymer). The polymeric latex contains a mixture of two scintillators (3 diphenyloxazole and 0.3% 1,4-bis[2-(5 phenyl oxazolyl)]- benzene.

A similar coating is prepared except that the emulsion layer contains an absorbing dye (tartrazine) at a concentration of 23 mg./it. Tartrazine is a yellow dye which absorbs blue light in the same region that the scintillator layer fluoresces.

A sample of each coating is exposed to electrons (15 kv.) in a vacuum at 5 10- torr. The exposed coatings are processed for 6 minutes in a conventional elon-hydroquinone developer, fixed, washed and dried.

Upon inspection, it can be seen that the developed images in the coating containing the absorbing dye is considerably more sharp in comparison to the coating in which no absorbing dye is present in the emulsion layer.

EXAMPLE 5 The halogenated dyes described herein are particularly effective electron acceptors in the practice of this invention. To illustrate, a gelatin silver bromoiodide (95:5 mole percent) is prepared using the procedure of Example 1 except that the concentration of K IrCl is increased to 0.425 g. per mole of Ag. The emulsion is coated (Coating 1) using the precedure of Example 1 on creases the electron sensitivity of the fogged silver halide grains. I

Similar results are obtained when Dye U is replaced by such electron acceptors as Dyes A, B, E, G, N, as identified hereinbefore.

EXAMPLE 6 Halogen accepting compounds can a so be absorbed onto the fogged silver halide grains employed in the electron sensitive layers described herein. To illustrate, a gelatin silver chloride emulsion is prepared by simultaneously adding at 70 C., 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 containing 40 grams of gelatin. Five thousand 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 0.05 mole percent silver chloride) is melted at 40 C., mg. of potassium chloroiridite (dissolved in water) is added and the emulsion heated to 70 C. This prepared emulsion constitutes the silver chloride core 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. One hundred sixty (160) grams 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 at approximately constant rates. Sufiicient silver chloride is formed in the shell to give a ratio of 4 moles of shell silver chloride to 1 mol of core silver chloride. The emulsion is washed in a conventional manner to remove soluble salts. The resulting covered grain emulsion is melted, the gelatin content increased to 160 grams per mole of silver chloride and water added to 4000 grams per mole of silver chloride.

.025 milligrams of thiourea dioxide and 0.25 mg. of

potassium chloroaurate per mole are added to the emulsion at 40 C. The emulsion is fogged by heating it to 65 C. and holding it for 20 minutes at this temperature. It is cooled immediately to 40 C. One hundred fifty mg./mole of Ag of 3-carboxymethyl-5-[(3-methyl- 2(3H)-thiazolinylidene) methylethylidene[rhodanine is incorporated into the emulsion. The emulsion is coated with a conventional hardening agent and coating aid upon an electrically conducting polyethylene terephthalate support at covereages of 360 mg. of Ag and 270 mg. of gelatin/ft? The coating is exposed to electron bombardment (15 kv.,), developed for 2 minutes in Kodak Developer D-19, fixed, washed and dried. The coating shows good reversal clfiaragteristics and exhibits a D of 2.48 and a D o 0.1

Similar results are obtained when the halogen acceptor employed in the above procedure is replaced with other halogen acceptors such as Dyes I, III, VI and IX, as identified hereinbefore or when silver chlorobromide grains, particularly those having a 50:50 molar ratio of halide are used in place of the silver chloride grains.

Thus by the practice of this invention there is provided electrically conductive direct-positive silver halide elements suitable for use in direct electron recording. Such elements can be used in data recording, television recording, electron microscopes and the like. They can be exposed to electrons using any voltages generally suitable for this purpose although in most applications they are exposed at voltages in the range of about to about 50 kv., and most often in the range of about to about 40 kv.

We claim:

1. An electrically conductive element comprising a support and a layer comprising electron-sensitive, directpositive, fogged silver halide grains (A) wherein said fogged silver halide grains contain internal centers which promote the deposition of photolytic silver and have a covering comprising a fogged 'silver halide that develops to silver without exposure or (B) wherein said fogged silver halide grains (1) are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-SO developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide-50 mg. Acetic acid .(glacial)-3.47 cc. Sodium acetate-41.49 g. Potassium bromide-119 mg. Water to1 liter and (2) have absorbed thereon about 200 to about 800 mg. per mole of silver of an electron-accepting cyanine dye having at least one methine group wherein the hydrogen atom is replaced with a halogen atom having an atomic weight in the range of about 35 to about 127.

2. The electrically conductive element of claim 1 in which said fogged silver halide grains comprise 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.

3. The electrically conductive element of claim 1 in which (1) said fogged silver halide grains are such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-50 developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-SO developer after being bleached for about 10 minutes at about '68" F. in a bleach composition of:

Potassium cyanide-50 mg.

Acetic acid (glacial)3.47 cc.

Sodium acetate11.49 g.

Potassium bromidel19 mg.

Water to1 liter and (2) adsorbed on saidfo-gged silver halide grains is about 200 to about 800 mg. per mole of silver of an electron accepting cyanine dye having at least one methine group wherein the hydrogen atom thereof is replaced with a halogen atom having an atomic weight in the range of about 35 to about 127.

4. The electrically conductive element of claim 3 in which said electron accepting cyanine dye has the following general formula:

9 OX \CH GH/N \GH ext/ c (L L)u 1 35 R2 A wherein Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus containin from 5 to 6 atoms and including a hetero atom selected from the group consisting of oxygen, sulfur, nitrogen and selenium; L represents a methine group; X and X each represents an atom selected from the group consisting of hydrogen, chlorine, bromine and iodine atoms, at least one of X and X being selected from the group consisting of chlorine, bromine and iodine; R and R each represents an alkyl substituent; A represents an anion; and d, m, n and 11 each represents a positive integer of from 1 to 2.

5. The electrically conductive element of claim 2 in which said silver halide grains are fogged with a combination of a reduction fogging agent with a gold fogging agent.

6. The electrically conductive element of claim 3 in which said silver halide grains are fogged with a combination of a reduction fogging agent with a gold fogging agent.

7. The electrically conductive element of claim 2 in which said fogged silver halide grains comprise a central core of silver halide containing centers attributable to Group VIII metal ions which centers promote deposition of photolytic silver and an outer shell covering said core comprising a fogged silver halide that develops to silver without exposure.

8. The electrically conductive element of claim 7 in which there is adsorbed on said fogged silver halide grains about 200 to about 800 mg. per mole of silver, of an electron accepting cyanine dye having at least one methine group wherein the hydrogen atom thereof is replaced with a halogen atom having an atomic weight in the range of about 35 to about 127.

9. The electrically conductive element of claim 7 in wnich said Group VIII metal ions are iridium ions.

10. The electrically conductive element of claim 5 in which said reduction fogging agent is thiourea dioxide, said gold fogging agent is potassium chloroaurate and said fogged silver halide grains have an average grain size less than about 1 micron.

11. The electrically conductive element of claim 6 in which said reduction fogging agent is thiourea dioxide, said gold fogging agent is potassium chloroaurate and said fogged silver halide grains have an average grain size less than about 1 micron.

12. The electrically conductive element of claim 2 in which said fogged silver halide grains have an average grain size less than about 1 micron and comprise at least 50 mole percent 'bromide.

13. The electrically conductive element of claim 3 in which said fogged silver halide grains have an average grain size less than about 1 micron and comprise at least 50 mole percent bromide.

14. The electrically conductive element of claim 8 in which there is adsorbed on said fogged silver halide grains about 200 to about 800 mg. per mole of silver of 1,1-diethyl-2,2-cyanine chloride wherein each of the hydrogen atoms of the methine chain thereof is replaced with a bromine atom.

15. The electrically conductive element of claim 13 in which there is adsorbed on said fogged silver halide grains about 200 to about 800 mg. per mole of silver of 1,1'-di- 17 ethyl-2,2'-cyanine chlorine wherein each of the hydrogen atoms of the methine chain thereof is replaced with a Ibromine atom.

16. The electrically conductive element of claim 1 in which said support comprises a continuous supporting sheet, an electrically conductive continuous layer on said supporting sheet and a water-impermeable continuous barrier layer outward from said supporting sheet over said conductive layer and under said layer comprising fogged silver halide grains.

17. The electrically conductive element of claim 16 in which said electrically conductive layer comprises dispersed cuprous iodide in a film-forming vehicle and said water-impermeable barrier layer comprises a film of water-impermeable resin.

18. The electrically conductive element of claim 16 in which said continuous supporting sheet is a linear polyester sheet.

19. The electrically conductive element of claim 1 which comprises a fluorescent layer outward from said supporting sheet over said layer of fogged silver halide grains, said fluorescent layer comprising an organic water-insoluble fluorescent compound dispersed in a film of hydrophilic film-forming binder.

20. The electrically conductive element of claim 19 in which said hydrophilic film-forming binder is a copolymer of an alkyl acrylate with styrene.

21. The electrically conductive element of claim 19 in which said layer of fogged silver halide garins comprises an absorbing dye.

22. The process which comprises exposing to electrons, an electrically conductive element comprising a support and a layer comprising electron sensitive direct-positive fogged silver halide grains.

23. The process according to claim 22 wherein said electrically conductive element is exposed to electrons in a vacuum.

24. The process according to claim 22 wherein said electrically conductive element is exposed at a pressure of about 10 millimeters of mercury.

25. A method of forming an image record which can be developed to a discernible positive image comprising exposing to electrons an electrically conductive element comprising a support and a layer comprising electronsensitive-direct-positive, fogged silver halide grains.

26. A process according to claim 25 wherein said fogged silver halide grains will record an image record when exposed to electrons in a vacuum.

27. A process according to claim 25 wherein said fogged silver halide grains will record an image record when exposed to electrons at an atmospheric pressure of about 10- millimeters of mercury.

28. A process according to claim 25 wherein said fogged silver halide grains comprise 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.

29. A process according to claim 25 wherein said fogged silver halide grains are such that:

(l) a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-SO developer after being bleached for about 10 minutes at about 68 F. in a bleach composition:

Potassium cyanidemg. Acetic acid (glacial)3.47 cc. Sodium acetate11.49 g. Potassium bromidel19 mg. Water to-1 liter and (2) adsorbed on said fogged silver halide grains is about 200 to about 800 mg. per mole of silver of an electron-accepting cyanine dye having at least one methine group wherein the hydrogen atom thereof is replaced with a halogen atom having an atomic weight in the range of about 35 to about 127.

30. A process according to claim 25 wherein said electrically conductive element comprises at least one layer containing .an electrically conductive material having a surface resistivity of less than 10 ohms per square.

31. A method according to claim 25 wherein said silver halide grains have an average size of less than about 1 micron.

References Cited UNITED STATES PATENTS 3,184,313 5/1965 Rees et al 250 X 3,237,008 2/1966 Dostes et al. 25065 3,303,341 2/1967 Fram et al. 25065 3,353,185 11/1967 Nitka 25049.5 X 2,996,382 8/ 1961 Luckey et al. 9668 3,206,313 9/1965 Porter et al. 96l08 3,367,778 2/ 1968 Berriman 9664 FOREIGN PATENTS 1,027,146 4/ 1966 Great Britain.

WILLIAM L. JARVIS, Primary Examiner US. Cl. X.R.

727 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,51 O, 3MB Dated ay 5, 1 97 Invencor(s) Dugald A. Brooks, Evan T. Jones and Richard W. Spayd It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I'" Column 1 line 35, after "beam" should be inserted "I Column 2, line 22, "eectron" should read --electron--. Column 5, line 73, "a" should read --the--. Column 6, after line 30,

the formula reading line 56, "naphtthoselenazole" should read --naphthoselenazole-. Column 7, line 16, after "halogen", "or" should read --of--; line 25, the dye formula commencing with "1 ,1-" should read 1 ,1 line 26, "29 ml." should read --20 ml.--; line 614., that portion of dye (U) set forth as "-1 ,2,2' should read -2,2 Column 9, line 58, "igmaewise" should read -imagewise--; line 37, that portion of formula reading "-1 )-2 (triethyl-" should read -1-)-2- (thienyl)- Column 1 0, line 70, "oxypolysaccardies" should read --oxy"polysaccharides--. Column 11 line 65, "patassium" should read --potassium--. Column 13, line 36, "dibrominate" should read --dibrominated--. Column 114., line 53, "mol" should read --mole--; line 65, that portion of formula reading "-methylethylidenef" should read -methylethyliden line 69, "covereages" should read --coverages--. Column 15, line #8, "absorbed" should read --adsorbed-- Page 1 of 2 pages i -W UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 ,3 L Dated y 5, 97

Inventor(s) Dugald A.Brooks,Evan T.Jones and Richard W.Spayd It is certified that error appears in the above-identified patent and tn'lt said Letters Patent are hereby corrected as shown below:

Eolumn '16, after columnar line 9, that portion of the formula '1 reading Column 17, line 29, "gar-ins" should read -grains--. Column 18, line 16, after "composition" should be inserted --of--.

SIGNED ANI. QEALED BEAL) AM Edward H. Fletcher, Ir. A g Officer III-LIA! I. W, 38. M11 Comissioner of Patents L .1

Page 2 of 2 pages