CA1037101A - Electrographic recording process and apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method and apparatus for producing visible images in certain charge sensitive, dry processable recording ele-ments. Image recording is accomplished by flowing, in a re-cording element containing a reducible metal compound, an image-wise pattern of electrical current of sufficient magnitude to produce therein a storable latent image. The metal compound in the latent image areas is subsequently reduced by a dry development technique to produce a visible image.

Description

103710~
Background of the Invention This invention relates to image recording and, more particularly, to a novel image recording process and apparatus wherein latent images are ~ormed in certain metal-salt-containing recording elements by flowing a small im~ge-wise pattern of electrical current therein and then dry processed to produce a visual image.
In recent years, a large research effort has ~ been directed toward the development of new, as well as the improvement of old, image recording processes. The better known and commercially more successful of these i recording processes can be broadly classified as being ; photographic, thermographic or electrographic or, as being a combination of two or more of these techniques, for example photothermographic. The terms photographic, thermographic and electrographic as used herein refer to recording processes in which the phenomena of light, heat ~^ and electricity, respectively, are used for the purpose of recording and reproducing patterns in viewable form. Each of the known image recording processes has its own advantages in particular applications but suffers from disadvantages which limit its usefulness in other applications. For ' example, conventional photography has the disadvantage of ! requiring chemical development procedures, thermography requires an imagewise heating procedure, and xerography, one form of electrography, requires a mechanical dust pattern transfer procedure.
It is known that images can be ~ormed in certain recording materials by passing an electrical current therethrough and considerable effort has been expended in investigating this electrogaphic image recording technique.

2 , ` ~ :

For instance, K S. ~ion et al in a report entitled "Investigation in the Field of Image Intensification, Final ` ~eport," in Air Force Cambridge Research Laboratories AFCRL
64-133, January 31, 1964, Contract No. AF 19(605)-5704 disclose an electrographic process in which the recording element com-prises a conventional light-sensitive photographic emulsion which is positioned adjacent to a photooonductive layer. Upon applying a uniform electric ~ield across the photoconductive and photographic layers and simultaneously imagewise exposing the photoconductive layer to a light pattern, an imagewise current is produced in the photographic layer. This imagewise c-urrent flow, in turn, produces a chemically developable latent image in the photographic layer, which is more intense for a given light exposure than an image produced by imagewise exposing , the photographic layer directly. The amplification is partic-, ularly pronounced when the incident light is of a color to 'l which the photoconductor is responsive, but to which the photographic emulsion is not responsive. I
While the Lion et al. recording technique presumably offers advantages in the form of increased sensitivity, it ' suffers the disadvantages associated with the use of a light sensitive, chemically developable recording layer. Moreover, the production of a latent image in a conventional light ~
sensitive photographic emulsion requires a substantial current , . _ . . . __ . .
ilow in the emulsion; hen¢e, a relatively lengthy exposure time with low current flow or a high ourrent flow with a short exposure time is required.
Another approach to the production of visible images is disclosed in U.S. Patent No. 3,138,457 issued in the name of B. L. Clark. This approach involves the use of a light-insensitive, electrosensitive recording layer composed of particles of a reducible metal compound capable of electrical reduction in situ. The recording layer is disposed on an electrically conductive backing, and recording is effected by contacting the layer with an electrically charged stylus, thereby causing a current to flow through the layer. This current is sufficient to reduce the particulate metal com-pound, in the dry state, to provide a visible image.
A drawback of the recording process disclosed by Clark is that it incorporates no gain or amplification. For each reduction event leading to an increase in density of the final image, an additional quantity of electronic charge flowing through the recording element must ~e provided. Thus, relatively high current densities must be provided in order to produce a visible image in a reasonable period of time.
Still another recording technique is di.sclosed in U.S. Patent Nos. 2,798,959 and 2,79~,960 issued July 9, 1957 in the name of A. J. Moncrieff-Yeates. In accordance with the teachings of this reference, a photoconductive material and a heat sensitive material are interposed between and in electrical contact with a pair of electrodes. An optical image is pro-jected on the photoconductive material while a voltage isapplied across the electrodes. The flow of electric current heats the photoconductive material, the heating effect in each increment of area being a function of the amount of current ~..
flowing, the resistivity of the photoconductive mdterial and the intensity of the illumination. The heat image thus pro-duced in the photoconductive material changes the heat sensitive material to ~orm a permanent image therein.
; One disadvantage of the Moncrieff-Yeates recording process is that high current flows are required in the photo-conductive material in order to produce sufficient quantities of thermal energy for image formation. Furthermore, this 1037~01 recording process, in common with the Clark process requires an incremental increase in current flow for each incremental increase in density of the final image.
An image recording process which incorporates gain is disclosed by Tokumoto et al. in U.S. Patent No. 3,425,916.
According to this process, chemically-developable nuclei are formed in a reagent layer by imagewise exposing the layer to a relatively minute current flow. Unlike direct print-out image recording processes, such as mentioned above, the current flow itself need not be sufficient to produce a visible reaction in the reagent layer in situ. Rather, it need only be sufficient to produce nuclei which, during a subsequent chemical development step, can be amplified to produce a visible image.
While the Tokumoto et al. process requires relatively low current flow to produce a developable latent image, the overall process requires that the recording material be moistened during the latent image or nuclei forming step.
I Moreover, the recording element on which the nuclei forming .,1 process is carried out requires chemical liquid development in order to intensify and thereby render visible the current produced nuclei. Furthermore, once developed, the visible ; image must be stabilized by washing and fixing, as in ordinary photographic processes. For these and other reasons, this process has not, to date, enjoyed substantial commercial use.
Summary of the Invention It is, therefore, an object of the invention to eliminate the aforementioned drawbacks of the prior art by providing an electrographic recording process and apparatus therefor which forms latent images in certain charge-sensitive, dry-processable recording layers by passing a relatively minute amount of electrical charge through the layers in an imagewise ~. ' 1037~0~
pattern and then amplifies these latent images by a dry development technique to render them visible.
The term "dry development", as used herein, denotes a procedure wherein a recording material is uniformly heated overall, without addition of chemical compounds or elements, to produce a visible image, such procedure appearing to the user to be dry from start to finish.
A "charge sensitive material" as used herein, denotes a material which, when subjected to an electrical current, undergoes a chemical and/or electrical change which forms a latent image. The term n latent image" as used herein, denotes an invisible or partially visible image which is capable of amplification in a subsequent dry development process.
The process of the present invention has many advantages over prior art image recording systems. Both the image formation and development steps are dry. For the user, the inventive process is, therefore, cleaner, simpler and more convenient than image recording systems which moisten or wet the recording material during the image formation and/or development procedures.
Thus, in accordance with the present invention, a dry electrographic recording process is provided for producing a visible image in a charge-sensitive recording element which has an ohmic resistivity of at least about 1 x 101 ohm-cm and contains at least one reducible metal salt. The process comprises the steps of applying an electrical potential to selected portions of the recording element of a magnitude and for a sufficient period of time to produce in the portions a charge density of from approximately 1 microcoulomb/cm to approximately 1 millicoulomb/cm , the charge density forming a developable pattern of latent image sites. The entire recording element is heated substantially uniformly with the metal salt in the ~ - 6 -B

presence of a reducing agent until a sufficient quantity of metal salt is reduced at the image sites to form a visible image.
Since the charge exposure is necessary only for ~atent image formation the magnitude of such charge exposure has been found to be several orders of magnitude less than that required by prior art dry direct image recording processes. This eliminates the need for bulky and relatively expensive sources of electrical potential. Furthermore, latent image formation can be effected with electrical fields of either polarity. This feature greatly enhances the user's flexibility in choosing the appropriate source of potential for a particular recording situation.
In developing the latent images, thermal energy is applied uniformly to the entire recording material rather B - 6a --; ` 1037101 than imagewise as in some prior art electrothermographic processes. The development process is, therefore, reduced to a procedure of high speed simplicity.
Another advantage is that the charge sensitive materials useful in the practice of the present invention can be made light insensitive if desired. A light insensitive recording material is advantageous in certain applications because there is no additional printout when the recording material is room light exposed.
The inventive process is versatile as well as simple. For example, a variety of devices can be used to regulate the current flow in the recording material in-cluding an electrostatically charged stencil, stylus or screen, a grid controlled charging device or a suitable photoconductive layer adjacent the image forming layer of the charge sensitive material.
Another advantage is the ability of the inventi~e process to record information emanating from a variety of ; exposure sources including tungsten lamps, xenon lamps, helium-neon laser beams, infra-red radiation and X-ray radiation by appropriate selection of a photoconductor which serves as an opto-electrical transducing device. Any source of radiation to which the photoconductor is responsive may be used as the exposure source, provided that the dynamic resis-tance of the photoconductor closely matches the dymanic resis-tance of the recording material in the operating voltage range of the invention.
The invention and its objects and advantages will become more apparent by referring to the accompanying drawings and to the ensuing detailed description of the preferred embodiment which follows.

~037101 BRIEF DESCRIPTION OF lHE DRAWINGS
Figs. la and lb illustrate schematically an image recording process according to one illustrative embodiment ; of the invention; and ~ 'igs. 2a and 2b illustrate schematically an electro-photographic process embodied by the invention.
Fig. 3 is a schematic diagram of an electrographic recording apparatus for carrying out the process of the in-vention.
D~TAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
-Initially, it should be noted that although the present invention can be practiced in the manner subsequently described, the mechanism by which the latent image is formed in the recording material is not presently understood. Various hy-potheses have been formulated regarding the formation of ~, these latent images. According to one hypothesi~
the injection of an electron, due to the electric iield, into a reducible metal ion source results in the formation of a developable image site. It is further believed that the development of the latent image is accomplished by a reaction in the recording material whereby metal from the metal ion source is deposited or otherwise provided on the latent image site.
A variety of image-recording materials are useful according to the described invention. The optimum image-recording material will depend upon such factors as the desired image, processing condition ranges, current sensitivity of the material and the like.
A typical charge sensitive, dry developable recording material useful in the process of the invention comprises an electrically conductive support (or, alternatively, a support i coated with a conducting layer), the support or conducting ~ .
. , . , , ~

103~101 layer having thereon at least one layer comprising an image-forming combination including (i) a reducible metal salt with ~ii) a reducing agent for the reducib~e metal salt in (iii) a ~inder for the layer.
A variety of reducible metal salts are usefùl in the described charge sensitive materials. Typical metal salts are silver salts of organic acids, such as fatty acids, which are resistant to darkening upon illumination. An especially useful class of silver salts is the visible light insensitive silver salts of long-chain fatty acids which include, for example, silver behenate, silver stearate, silver oleate, silver laurate, silver hydroxystearate, silver caprate, silver myristate and silver palmitate. Silver salts can be employed which are not i silver salts of long-chain fatty acids if desired. Also, combinations of silver salts of long-chain fatty acids with other silver salts can be employed. Useful silver salts which are not silver salts of long-chain fatty acids include, for example, silver benzoate, silver benzotriazole, silver terephthalate, silver phthalate, and the like. Silver salts of a heterocyclic thione compound are examples of other silver salts which are useful. These include, for example, silver salts of 3-carboxymethy1-4-methyl-4-thiazoline-2-thione, 3-(2-carboxyethyl)-4-hydroxymethyl-4-thiazoline-2-thione, 3-(2-carboxyethyl)-benzothiazoline-2-thione, 3-(2-carboxyethyl)-4-methyl-4-thiazoline-2-thione, and combinations of these silver salts.
Examples of useful metal salts which are not silver salts include nickel perchlorate, lead behenate, copper stearate and the like. Useful reducible metal salts are also described in U.S. Patent 3,437,075 of Morgan et al. issued July 22, 1969; U.S. Patent 3,152,904 of Sorensen ~ et al. issued October 13, 1964; U.S. Patent 3,152,903 of I Sorensen et al. issued October 13, 1964; British Specification 1,161,777 published August 20, 1969; U.S. Patent 3,672,904 _9_ of deMauriac issued June 27, 1972; and pending U.S. Patent No.

3,785,830 of Sullivan et al, issued January 15, 1974.
Visible light sensitive, reducible metal salts, which are also charge sensitive, can be used in lieu of, or in com-bination with, the previously described visible light insen-sitive metal.salts. The charge sensitive materials can, for example, contain photosensitive salts, such as photosensitive sllver salts including for example, photographic.silver halide.. Useful photographic silver halides include, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobromoiodidie or mixtures thereof. For purposes Or the invention,'silver iodide is also useful and included within the scope of the term photographic silver halide. The photosensitive silver halide can be prepared in situ in the charge sensitive materia~ by pracedures as described, for example, in U.S. Patent 3,457,075 and/or the photosensitive silver halide can be prepared separate from other components of the charge sensitive.material and'then mixed with the described other components at the desired time. The photo-sensitive silver halide can be a coarse or fine grain, very .fine grain photosènsitive silver halide being specially use-ful. The photographic silver halide can be prepared by any of the well-known procedures employed in the photographic art, such as described in the above patent.
The photosensitive silver halide can be chemically .
'sensitized, and can contain addenda commonly employed in phr~to-graphic silver halide.materlals, such as sensitizing dyes, sta-bilizers,'antifoggants, hardeners, coating aids and the like.

A variety of reducing agents for the reducible metal salts areluseful in the described.charge sensitive ~,~,~
. .. ~,. .

1~)37101 materials. Useful reducing agents include, for exam-ple, sulfonamidophenol reducing agents, as described in U.S. Patent No. 3,801,321 o~ Evans et al, issued April 2, 1974; polyhydroxyben~enes such as hydroquinone, alkyl substituted hydroquinones, such as tertiary butyl hydroquinone, methylhydroquinone, 2,5-dimethylhydroquinone and 2,6-dimethylhydroquinone; catechols and pyrogallols;
- aminophenol reducing agents, such as 2,4-diaminophenols and methylaminophenols; ascorbic acid reducing agents such as ascorbic acid and ascorbic acid derivatives; hydroxylamine reducing agents; 3-pyrazolidone reducing agents such as 1-phenyl-3-pyrazolidone and 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone; and bis-beta-naphthols, such as described in ~.S. Patent 3,672,904 of deMauriac, issued June 27, 1972, and the like. Combinations of such reducing agents can be employed if desired.
A range of concentration of reducing agent can be employed in the described current sensitive materials. A useful concentration of reducing agent utilized with a reducible metal salt, such as silver behenate or silver stearate, is typically about 0 1 mole to about 10 moles of reducing agent per mole of reducible metal salt. When reducing agents are employed in combination, the total concentration of reducing agent is typically within the described concentration range.
The most useful concentration of reducible metal salt in a par-ticular charge sensitive material will depend upon several factors, such as the current sensitivity of the materials in the recording element, the desired image, processing conditions and the like.
3o The described charge sensitive materials can include a variety of binders, especially polymeric binders, also known as vehicles. Useful polymeric binders can be hydrophobic or hydrophilic. They include both naturally occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and ; synthetic polymeric substances such as water-soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers and the like. Other synthetic polymeric compounds which are useful include dispersed vinyl compounds such as in latex form and particularly those which increase dimensional stability of the current sensitive materials. Effective polymers include water insoluble polymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkylacrylates, methacrylates and those which have crosslinking sites which facilitate hardening or curing as well as those having recurring sulfobetaine units as described in Canadian Patent 774,054. Especially useful polymers include poly-carbonate, poly(vinyl butyral), cellulose acetate butyrate, poly(methylmet~acrylate), poly(vinylpyrrolidone), ethyl cellulose, polystyrene, polyvinyl chloride, chlorinated rubber, polyisobuty-lene, butadiene-styrene copolymers, vinyl cllloride-vinyl acetate copolymers, copolymers of vinyl acetate, vinyl chloride and ; maleic acid and poly(vinyl alcohol). Choice of an optimum polymer as a binder for the described charge sensitive materials will depend upon the particular charge sensitive material, the particular reducible metal salt, the particular reducing agent, processing conditions, and the like. It is essential that the binder not adversely affect the desired properties of the charge sensitive material. Useful polymeric binding agents are described in the previously mentioned patents describing useful reducible metal salts, The charge sensitive layer of a recording material employed in the practice of the invention can be on a wide .. _ . _ .. . . _ _ _ variety of supports. Typical supports include cellulose nitrate film, cellulose ester film, poly(vinyl acetal) film, polystyrene film, poly~ethylene terephthalate) film, polycarbo-nate film and related films or resinous materials, as well as ; glass, paper, metal and the like. However, if the support is an insulator, the recording element must also include an electrically conductive layer positioned between the support and the charge sensitive layer. Typically a flexible support is employed, especially a paper support. The paper support can be coated with baryta and/or a solvent holdout layer.
The charge sensitive layers used in the practice of the invention can contain addenda commonly employed in thermo-graphic and photothermographic elements. Addenda in the charge sensitive layers useful in the practice of the invention include toners, also known as activator toners, such as described in U.S. Patent 3,457,075 of Morgan et al., issued July 22, 1969; U.S. Patent 3,672,904 of deMauriac, issued June 27, 1972 and U.S. Patent No. 3,801,321 o~ Evans et al, issued April 2, 1974; plasticizers and/or lubricants, sur-factants, matting agents, brightening agents, lightabsorbing materials, filter dyes, and the like also as de-scribed in these patents.
The various components of the charge sensitive materials employed in the practice of the invention can be prepared for coating by mixing such components with aqueous solutions or suitable organic solvent solutions depending on the particular charge sensitive material. The components can be added using various procedures known in the photographic art.
The charge sensitive layer of a recording material em-ployed in the practice of the i~vention can be coated by usingvarious coating procedures known in the photographic art , '`\

including dip coating, air knife coating, curtain coating or extrusion coating using hoppers of the type describ~d in U.S.
Patent 2~681,294 of Beguin, issued June 15, 1954. If desired, two or more layers can be coated simultaneously by procedures known in the art.
An especially useful charge sensitive, dry developable recording material comprises an electrically con-ductive support having thereon a layer comprising ~a) an image-forming combination including (i) a silver salt of a long chain fatty acid, such as silver behenate or silver stearate, with (ii) a reducing agent as described, in (b) a polymeric binder, also as described. The visible light in-sensitivity of this recording material allows it to be handled in room light; and with the appropriate choice of image to current converter, the recording material has the ability to record images from a wide spectrum of different forms of radiation. Further, the proper choice of image to current converter allows the recording process to function selectlvely in environments containing more than one form of radiation, e.g. light exposures in the presence of X-rays.
Overall heating of the recording material can be accomplished in a variety of known ways, for example, by placing the recording material on a heated platen, by passing the recording material between heated rollers, or by applying radiant energy, e.g. ~rom heating lamps, microwave devices, ultrasonic devices, etc., to the recording material. A
useful temperature for producing t~ desired developed image is typically within the range of about 80 C to about 250 C
such as about 100C to about 160C. The optimum range will depend on several factors such as the dbsired image, the ingredients of the particular recording material~ etc. The time of overall heating typically ranges from about 0.1 second to about 120 seconds depending upon the particular recording material and more importantly, the type of heating device employed. ~eating is accomplished under atmospheric pressure conditions, however, pressure above or below this i level may be used if desired. Wilen the recording material is J heated above the critical temperature, the metal compound and reducing agent react in the image areas reducing the metal ~ compound to the corresponding free metal. The ~ree metal ¦ thereby produced provides a visible reproduction of the applied ¦ electrical currént which varies in intensity according to the charge density produced in the recording material.
Referring now to the drawings, and particularly to Figs. Ia and lb, one embodiment of the novel electrographic process of`the invention is depicted schematically. In this embodiment, a recording layer 10 is placed upon a grounded ~ electrically conducting backing or support plate 15. A current `~ is selectively applied to the recording layer 16 by the point of a metal stylus l6, which is raised to a voltage relative to the backing 15 by a voltage source 17, and brought into l ~ moving contact with the exposed surface of the recording layer ¦ 10. Upon contacting the recording layer with the stylus 16, a current flows in the areas of the recording layer contacted by the stylus and forms a developable pattern of nuclei sites i (i.e. a latent image) thereon. The charge density produced by the stylus in the contacted areas of the recording layer need not be sufficient to produce a visible change in the recording layer 10; however, the charge density is sufficient I to produce a latent image in the recording layer in those areas I contacted by the stylus. Although a particular technique to produce an imagewise current flow through the recording layer j 10 has been described, techniques generally known to the art -30- may be used and are intended to be encompassed herein. These ' ~037101 known techniques include, for example, contacting the re-cording layer 10 with an electrostatically charged stencil and scanning the layer 10 with a beam of electrons.
To develop the latent image formed in the recording element by any one of the procedures described above, the recording element is moved into contact with a heated metal platen 20 which serves to substantially uniformly heat the entire recording layer 10. Platen 20 may be brought into contact with either of the planar surfaces of the recording element to effect development of the latent image. Upon heating the recording element to a temperature at which the latent image becomes visible, the recording element is immediately moved out of contact with the heated platen 20.
Using a typical charge sensitive recording layer (Type 7743 photothermographic paper manufactured by Minnesota Mining and Manufacturing Co.), and an electrode of known area, the following reflection densities in the developed image areas were achieved as a function of charge density for four dif-ferent applied voltages.
20Charge Density (Microcouloumb/cm2) Reflection Density .72 .50 .51 .64 .39 1.08 .93 1.0 1.0 1.0 1.80 1.4 1.4 1.4 1.5 Voltage 3.0 3.5 4.0 4.5 (Kilovolts) The table shows that the reflection density is de-pendent among other factors on the charge density and is substantially independent of the voltage applied.
3o Another embodiment of the inventive process is illu-strated in Figs. 2a and 2b. In this embodiment, the developable 103710~
nuclei sites, i.e , latent image, is formed by sandwiching a recording layer 10 and an image to current converter 30, pre~erably a photoconductive layer, between a pair of elect-rically conductive backings 15 and 35, respectively. A ~ield ; is established across the photoconductive and recording layers by connecting the conductive backings 15 and 35 to a D.C.
voltage s~ rce 40. Advantageously, a photoconductive layer 30 is selected so that, at the operative voltages o~ the invention, the relative impendances of the recording layer 10 and photo-conductive layer are within a preferred range. Since the electrical characteristics of both the photoconductive layer and the recording layer can be non-linear, a photoconductive layer 30 is selected whose differential resistance in the operating voltage range of the invention matches the differen-tial resistance of the recording layer 10 within a factor of approximately 105 ohms. ~he electric field across the layers is controlled by a switch 42. Latent image formation is effected by imagewise exposing the photoconductive layer 30 through the transparent conductor 35, to actinic radiation. Such ex-posure serves to selectively increase the conductivity of the I photoconductive layer in those regions exposed to actinic i radiation. When switch 42 is closed, thereby establishing an electrical field across the layers, an imagewise current flow is produced through the recording layer 10, such current flow occurring in those regions of the recording layer in juxta-position with the exposed portions of the photoconductive layer. After a charge density of less than 1 millicouloumb/cm2, ,.

preferably approximately l microcouloumb/cm2, has ~een produced in the current exposed portions of the recording layer, switch 42 is opened, thereby disrupting the current flow. The recording element is then moved out of contact with the photoconductive layer and uni-formly heated to render the latent image in layer 10 visible.
Such heating is effected by merely positioning the recording element in heat-transfer relationship with the heated metal platen 20. Upon heating the entire recording element to a temperature ` lO at which the latent image becomes visible, the recording elemellt is removed from the platen.
It is to be noted that in the above-described embodi-ment of the invention, the application of voltage across the photoconductive and recording layers can be accomplished by a variety of techniques known in the art. Thus, for example, a grid controlled corona charger could be substituted for the ; voltage source 40 and conducting backing 15 of the recording element 10. Alternatively, the charging and exposure steps can be accomplished with a grid-controlled corona charger as described in U.S. Patent No. 3,370,212 issued to L. E. Frank.
Referring now to Fig. l, an illustrative embodiment j of a recording apparatus for producing a visible image in an electrosensitive recording element is depicted schematically.
The recording apparatus comprises generally a supply hopper 50, a transport assembly 52, an exposure station 54, a process-ing station 56 and control circuitry 58. To operate the apparatus, a plurality of recording elements are loaded in a stacked condition onto a feeder shelf 60 of the supply hopper 50. A feed roller 62 extends through an opening in the feeder shelf 60 and is maintained in frictional contact with the lowermost recording element in the stack. ~hen the apparatus is turned on by depressing a start button (not " 103710~
shown), the control circuitry 58 energizes a motor 64 and activates clutches 66 and 68 which couples the drive from the motor 64 to the feed roller 62 and the transport assembly 52, respectively.
A recording element is fed by the feed roller 62 from the bottom of the recording element stack through a pair of separator rollers 70 and 72 and onto an electrically conductive, heat resistant conveyor belt 74. As the record-ing element moves along the conveyor belt 74, means are pro-10 vided to sense the arrival of the leading edge of the recording element at the exposure station 54. The sensing means com-prises a microswitch 76 arranged and disposed so that the leading edge of the recording element closes a contact 77 of the microswitch 76 as the recording element passes therepast.
' The closing of the contact 77 causes a signal to be sent to the control circuitry 58 which deactivates the clutches 66 and 68 stopping the recording element at the exposure station 54.
j The control circuitry then closes a switch 78 coupling ¦ a source of potential 79 to a metal stylus 80, raising the 1 20 voltage of the stylus relative to the conveyor belt 74. The :, .
control circuitry then activates the stylus driver logic 82 which moves the stylus 80 into contact with the recording element in accordance with an image pattern that is to be ~, recorded. Upon contacting the recording element, a current flows in the areas of the recording element contacted by I the stylus and forms a developable pattern of nuclei sites (i.e. a latent image) thereon. The charge density produced i by the stylus 80 in the contacted areas of the recording element need not be sufficient to produce a visible change in 30 the recording element; however, the charge density is suffi-cient t-o produce a latent image in the recording element in those areas contacted by the stylus 80.

... .

10371Ql ~ `develop the latent image formed in the recording element, the control circuitry 58 activates the clutch 68 to again couple the drive from the motor 64 to the conveyor belt 74. As the recording element moves along the conveyor belt 74, means are provided to sense the arrival of the lead-ing edge of the recording element in the processing station 56. The sensing means comprises a second microswitch 84 arranged and disposed so that the leading edge of the record-ing element closes a contact 85 of the microswitch 84 as the recording element passes therepast. The closing of the contact 85 causes a signal to be sent to the control circuitry 58 ! which deactivates the clutch 68 stopping the recording ele-ment at the processing station 56. The control circuitry ¦ then activates a heating means 86, such as an infrared lamp surrounded by a re~lector 87 which serves to substantially uniformly heat the entire recording element. Upon heating the recording element to a temperature at which the latent image becomes visible, the control circuitry 58 activates the clutch 68 coupling the drive from the motor 64 to the conveyor 20 belt 74 which feeds the recording element into a receiving hopper 88.
If desired, the recording apparatus can be readily modified to provide continuous operation. To accomplish this result, the control circuitry 58 is rnodified so as to contin-uously couple the transport assembly 52 to the drive motor 64 and the exposure station 56 is modified to include a plur-ality of stylii which are selectively energized as the record-ing element moves therepast.

-` 103710~
Although a particular technique to produce an image-wise current flow has been described for use in the recording apparatus, other techniques generally known to the art may be used and are intended to be encompassed herein. These known techniques include, for example, using a photoconductive layer as an image to current converter in the manner shown in Fig.
2a, contacting the recording element with an electrostatically charged stencil and scanning the recording element with a beam of electrons. Llkewise, heating of the recording element can be accomplished by other techniques generally known to the art, for example, by passing the recording elemént over a heated platen or through heated rollers.
The ~ollowing examples will serve to further illus-trate the present invention.
; EXAMPLE 1 A sheet .of Type 777 photothermographic'paper, manu-I factured by Minnesota Mining and Manufacturing Company, was placed on a metal plate with the emulsion slde of the paper fac-lng away from the plate. The plate potential was raised to ` 20 3,000 volts positive with respect to a metal stylus. The 'grounded metal stylus was brought into cont'act with the emul-'~ ` slon side of the paper and was moved across the emulsion at the , . .
rate of about 5 inches per second. The Type 777 paper wasthen removed from the metal plate and brought into contact ;~; - w1th a heated metal platen. Upon uniformly heating the Type 777 paper for three seconds at 140C an image appeared in those areas contacted by the grounded electrode. ;' ,~ , . .
- An aggregate photoconductive composition comprising poly-4,4'-isopropylidenediphenylene carbonate ~whlch is sold by the General Electric Company under the trademark Lexan 145), the photoconductor 4,4'-dlethyl-amlno-2,2'-dimethyltriphenylmethane (40% by weight of the total solids) and 2% by weight of dye com-prising a 60:40 weight ratio mixture of 4-(4~dimethylaminophenyl)-.. ; .
_ 21 -. . , , . --. _ -~` 10;~7~01 2~6-di-phenylthiapyrylium fluoroborate and 4-(4-dimethyl-aminophenyl)-2-(4 ethoxyphenyl)-6-phenylthlapyrylium fluoro-borate and dichloromethane solvent was prepared by the tech-nique described in U.S. Patent No. 3,679,408 issued July 25, 1972. The resultant-composition was coated on a conductive support compri.sed of po~y(ethylene terephthalate) film base having a transparent conductive layer on the surface thereof.
The photoconductive layer was then overcoated with cellu-lose.nitrate at a coverage of 0.194 g/ft2. The photo-conductive element was placed in a sandwich with a sheet ofType 790 photothermographlc paper manufactured by the Minnesota Mining and Manufacturing Company so that the active surfaces of the element and the paper were in interfacial contact. An image was optically pro~ected on the photoconductive layer through the transparent conductive backing thereof. ~An Eastman Kodak Company Wratten filter No. 70 was placed between the photoconductlve layer and the pro~ector to eliminate any direct exposure of the Type 790 paper to visible radiation to whlch it is sensitive. The unfiltered intensity of the 20 tungsten source pro~ector was 20 foot-candles. A voltage of 2500 volts was applied across the sandwich formed by the aggregate photoconductor and the Type 790 paper sumul-taneously with the imagewise exposure of the photoconductive layer. The conductive backing of the photoconductor was made positive with respect to a metal filled, rubber conducting layer sold under the tradename "Eccoshield SV" by Emerson and Cummings which was placed in electrical contact with the pa~er side of the Type 790 paper. The simultaneous voltage appli-cation and imagewise exposure of the photoconductor was main-tained for 3 seconds followed by separation of the Type 790 - paper from the photoconductor in the dark after the voltage ~ .

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r , , _ . . .,, ~___ 103710~
was reduced to zero. The Type 790 paper was processed by uni-formly heating the emulsion side for 10 seconds at 130C. The current exposed portions of the paper darkened producing a negative-to-positive image of good quality. The steady state current dens~ty to obtain DmaX was measured to about 0.1 to 1. 0 miCroampere/cm2-i EXAMPLE 3 A print was made under identical conditions to that of Example 2 except that the polarity of the applied voltage I 10 was reversed. Again, a good quality negative-to-positive image was obtained.

A sheet of the light sensitive, Type 777 photothermo-graphic paper manufactured by the Minnesota Mining and Manufacturing Company was placed in face to face contact with a transparent aggregate photoconductive element prepared as described in Example 2. The Type 777 paper was then electrically exposed by the procedure described in Example 2 and heat processed to produce a visible image. Next, the Type 777 paper containing the heat processed image was again brought into contact with the photoconductive element and electrically exposed by optically projecting an image onto the photoconductive element which was rotated with respect to the first exposure. Again, the paper was heat processed to produce a superimposed visible image corresponding to the rotated projected image.
A second sheet of the light sensitive, Type 777 photographic paper was light exposed to an optical image and heat processed to produce a visible image. The Type 777 paper containing the heat processéd image was then brought into contact with the photoconductive element and electrically exposed by the procedure described in Example 2 but with the image pro~ected onto the photoconductive element rotated with respect to the first exposure. Again the paper was heat processed to produce a superimposed, rotated image.
A third sheet of the Type 777 photothermographic paper was placed in face to face contact with the photocon-ductive element and electrically exposed by the procedure described in Example 2 and heat processed to produce a visible image. The Type 777 paper containing the heat processed image was viewed under red safe light conditions and then light exposed to an optical image which was rotated with res-pect to the first exposure. Again the paper was heat pro-cessed to produce a superimposed, rotated image.
This example illustrates the capability of the present inventio~.to record information on a charge sensitive recording material and subsequently update such information.
If the charge sensitive recording element is also light sensitive, a combination of electrical and light exposures can be used to form the original and updated images on the recording element.

A photoconductive composition was prepared by the transformation of yellow othorombic lead oxide (Evans Lead Corporation) designated as Evans Fumed Lithagel to tetragonal lead oxide. The transformation was performed in accordance with the teaohings of U.S. Patent No. 3,577,272 issued May 4, 1971. Forty grams of the tetragonal lead oxide powder was placed in a 250 milliliter mill ~ar, 26.7 grams of Pliolite S-5, 30% in toluene, (Pliolite is a trademark of Goodyear Tire and Rubber Co. for . ~ , ' ' .

- 24 _ ~, . . .

... _ .. _ . ... .. .. .

~ 037101 a 85:15 styrene-butadiene copolymer) and 29.3 grams toluene were added to produce a 50% solids mixture. The mixture was ball milled for 24 hours and then filtered through silk bolting cloth (550 mesh) and coated on a polyester film support which was vacuum deposited with aluminum. The 90 micron thick coating was then placed in a dark drying box for 72 hours. The active surface of the photoconductive element was placed in face to face contact with the active surface of a sheet of Type 790 photothermographic paper manufactured by the Minnesota Mining and Manufacturing Co. A voltage of 3500 volts was supplied across the sandwich formed by the photoconductor and the Type 790 paper simultaneously with an X-ray exposure of the photoconductive layer. The conductive backing of the photoconductor was made positive with respect to an Emerson Cummings "Eccoshield SV" metal filled, rubber conducting layer which was placed in electrical contact with the paper side of the Type 790 paper. The X-ray source was an unfiltered Faxitron 504 unit operating at 110 KV and 3 ma. The simul-taneous voltage application and imagewise exposure of the photoconductor was maintained for 5 seconds followed by a separation of the Type 790 paper from the photoconductor in the dark. The Type 790 paper was processed by uniformly heating the emulsion side for 4 seconds at 140C. A radiographic print of good quality resulted. The steady state current density to obtain DmaX was measured to be approximately 0.1 micro-ampere/cm2. Control experiments consisting of either (1) 45-second exposure of the lead oxide photoconductive layer with no field applied; or (2) 2-minute exposure directly on the Type 790 paper followed in both instances by the heating step pro-duced no visible images.

EXAMPL~ 6 A print was made under identical conditions to that of Example 5 except that the charge sensitive paper used did not contain any light sensitive silver halide. The charge sensitive layer was prepared by ball-milling the following , components for 72 hours:
Silver behenate 168.0 grams Behenic acid68.0 grams Poly(vinyl butyral) 120.0 grams Phthalimide34.0 grams Acetone-toluene 2.0 liters This silver behenate-behenic acid dispersion was then combined with the following addenda in the order indicated, mixed thoroughly and coated on a suitable paper support at 6.0 g/ft2 Silver behenate-behenic acid dispersion 142.0 ml ! (preparation described above) Acetone-methanol solution (33:1 by volume) containing 0.1% by weight 3-carboxymethyl-! 5-[(3-methyl-2-thiazolidinylidene)-1-methylethylidene]rhodanine and 0.03% by volume triethylamine 7.2 ml Acetone solution containing 10% by weight 2,2'-dihydroxyl-1,1'-binaphthyl 33.0 ml Acetone solution containing 10% by weight 2,4'-dihydroxybenzophenone 5.0 ml Acetone-toluene ~1:1 volume) 46.0 ml Methanol solution containing 1% by weight mercuric acetate 12.0 ml The resolution of the resultant prints after exposure and f 30 thermal processing was 10 lines/mm with brownish appea~ing DmaX areas. All of the processing steps were carried out under red safe light conditions as an added precaution.

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1037~0~
Another piece of the same recording element was pre-exposed to room lights through 0.3 neutral density step wedge.
The exposure was for 1 hour at an intensity of about 100 ft.
candles. A second recording element, identical in every respect to the recording element described above except that it did contain silver halide, was pre-exposed with light as outlined above. Both samples were subsequently electrically exposed as in Example 5 in the same regions as the light exposure and heat processed. The recording element containing no silver halide was heat processed under room light conditions; the recording element containing silver halide was heat processed under red safe light conditions. The recording layer contain-ing the silver halide showed extreme fogging due to the light exposure resulting in a low radiographic image discrimination.
The recording layer which did not contain silver halide pro-duced a good quality radiographic image with excellent image discrimination.

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~03710~
Yet another piece of the recording element con-~ taining no light sensitive silver halide was overcoated with ; a photoconductor containing a solvent hold-out layer. The integral photoconductor-recording element package was electri-cally exposed by applying a positive 2 kilovolt potential between the conducting layer of the photoconductor and a flexible conducting layer, sold under the trademark Velostat by Custom Materials, placed in contact with the recording element while simultaneously exposing the photoconductor to an imagewise pattern of light. The exposure was made through a negative silver original using a Xenon light saurce which provided 40 foot candles of illumination. As an added pre-caution, a Wratten No. 70 filter was placed between the light source and the integral package. The package was then pro-cessed for 10 seconds at 100C to produce a negative to positive image in the recording layer. Finally, the negative to positive image was thermally transferred to a clear thermoplastic support.
Two other integral photoconductor-recording ele-ment packages were electrically exposed as described above except that a negative 2 kilovolt potential was applied be-tween the photoconductive and recording layers. The latent images in the recording elements were thermally transferred to clear thermoplastic supports and then heat processed to produce negative to positive images.

A Print-a-Pix tube ~a trademark of the Litton Corp-oration used to designate a cathode ray tube having a plurality of wires embedded in the tube face) was used to electrically _ . , .. . ... ..... .. . . . _ - 1037~0~
expose two recording elements. The recording elements were a sheet of Type 777 paper manufactured by Minnesota Mining and Manufacturing Company and a sheet of material prepared as described in Example 6. The electron beam of the Print-a-Pix tube was focused and deflected so that it scanned across only a single line of the fine wires ~1000/inch). The time required to scan the 1-1/4 inch single line of wires was about 50 microseconds with a blank retrace time of about 10 microseconds. The electron beam spot size was approximately equal to the wire diameter and had a current of 5 microamperes.
The accelerating potential was 20 kilovolts. Each of the recording elements was brought into virtual contact with the face of the tube and exposed for 1 second. The two elements were heat processed after electrical exposure for 10 seconds.
The Type 777 paper was heated to 120C and the other to 100C.
A line image corresponding to the fine wires was visible on each of the recording elements.

A grid controlled corona (GCC) device as disclosed in U.S. Patent No. 3,370,212 to L. E. Frank was used to expose Type 777 photo~hermographic paper. The GCC device consisted of a

4 by 5 inch array of corona wires surrounded by a NESA ~a trademark of PPG Industries used to designate an electrically I conductive glass) shield on one side and a bare metal stainless i steel wire ~400 holes/inch) woven screen grid on the other side.
~' Below the screen was a second grid identical to the first grid but coated with a thin organic photoconductive composition.
;~ The photoconductive coating covered all surfaces of the screen but did not seal off the openings of the grid. A first sheet of the Type 777 paper was positioned just below the second . ' ~ ` ` 103710~
grid and held flat against a metal vacuum platen which also served as the bottom electrode. With the photoconductive grid in the dark, the exterior surface of the photoconductor was charged by a negative corona to -200 volts with respect to its metal core. The photoconductor was allowed to charge for 3-1/2 seconds. The photoconductor was then exposed for 3/4 of a second to a light image. The projection source was a xenon lamp which provided 4 footcandles of illumination on the photo-conductive grid. A Wratten No. 29 (red) filter was placed between the lamp and the Type 777 paper to eliminate any direct exposure of the paper to visible radiation to which it is sen-sitive: During the exposure step all elements of the device were grounded and the photoconductor surface voltage decayed according to the amount of light absorbed. To form a latent image on the Type 777 paper, the imagewise charge pattern on the photoconductive grid was biased with respect to the metal grid such that the negative ions from the corona were attracted through the photoconductive grid in the light struck areas and repelled in the dark areas. During the image forming step 20 the platen was raised to +2 kilovolts to overcome the high series resistanse of the paper base and the heat developable layers. After 70 seconds, the elements were again grounded, the Type 777 paper removed and processed for 6 seconds at 130C
on a heated platen. A useful negative-to-positive image re-sulted.
A second sheet of Type 777 paper was positioned on the vacuum platen and, with the photoconductive grid in dark-ness,its exterior surface was charged by a positive corona to ~200 volts with respect to its metal core. The exposure, image forming and development steps were then carried out as described above, except that the bias on the photoconductive grid was of ,' ' ~ `' ' 10~7101 ' opposite polarity such that the negative ions from the corona .
were repelled in the light struck areas and attracted through the dark areas. The resulting image produced was a positive-to-positive copy of the orlginal light image.
, EXAMPLE 9 A sheet of Type 777 photothermographic paper manu-factured by the Minnesota Mining and Manufacturing Company was over-coated with a solvent holdout layer (polyvinyl alcohol-PVA2 and a layer of Kalvar film [Kalvar is a trademark for vesicular ; l0' film havlng a poly(vinylidene chlorlde)acrylonitrile copolymer binder and,a diazonium salt sensitizer]. This multilayer ele-ment was placed with the Type 777 paper in contact with a trans-" parent aggregate photoconductor, electrically exposed by the procedure described in Example 2 and heat processed at 130C
for 10 seconds to,,produce a negative-to-positive image in the ~ ' Type 777 paper. Thls developed image was then used as an ,', opti,cal mask while the lntegral Kalvar ~ilm was exposed to a J source of ultraviolet light. Again the multilayer element was heat processed but at a higher temperature, i.e. 150C, 20 for 10 seconds to develop a positive-to-positive image in the Kalvar film. Finally, the positive-to-positive image was ,~ .
thermally transferred to a clear thermoplastic support.
, EXAMPLE 10 A persistent photoconductive composition was prepared by adding 40 grams of a 3-(p-diphenylamino2 phenyl propionic acid to 840 gra~s Or sol~ent (1,2 dichloromethane) and stirring for, ~;l 10 minutes. One hundred twenty grams of Vitel P E 101 (a trade-;~ mark of Goodyear Tlre and Rubber Company for a polyester having ~, the chemical formula C29H3008) was then added to the solution 30 , w1th a power stirring for one hour. Next, 4.8 grams of a Garbocyanine green sensitizing dye was added to the solution . ' - 31,-~ . ' .
~ ~' ' . ' .

and stirred for 1/2 hour. Finally, just prior to filtration, 4.0 grams of Modaflow, 10% in 1,2 dichloromethane ~Modaflow is a trademark of Monsanto Company for a copoly(ethylene ethylacrylate) coating aid) was added to the solution and the dope was stirred for another 1/4 hour. The dope was then filtered and coated on a conductive support comprised of poly(ethylene terephthalate) film base having a 0.4 neutral density nickel evaporated on the surface thereof. The photo-conductor was exposed with a number 2 photoflood for 15 seconds at a 10 inch distance while being contacted with a transparency containing clear letters on a high density background. After light exposure, the active surface o~ the photoconductor was brought into face to face contact with the active surface of a sheet of Type 777 photo~hermographic paper while workin~ under red safe light conditions. A negative 3 kilovolt potential with respect to the Type 777 paper was applied to the photoconductor's electrode for 3 seconds. The Type 777 paper was then heat processed at 130C for 10 seconds to reveal a negative to positive reproduotion of the original image. The resolution of the print after thermal processing was approximately lO
lines/millimeter. Two additional prints were made in the .
same manner without re-exposing to a light image. The image quality of these prints was approximately the same as the image quality of the first print. To show that the polarity of the applied voltage was insignificant, a fourth print was made by applying a positive three kilovolt potential to the photoconductor. The fourth print was practi-cally indistinguishable from the other three prints.

~- 30 A conventional electrographic, zinc oxide photo-conductive layer was charged, exposed to an imagewise pattern of actinic radiation and developed with a single component developer comprising iron beads about 1/2 mil in diameter.

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1037101 s The developed photoconductive layer was brought into face to face contact with a sheet of Type 777 photothermographic paper manufactured by Minnesota r.lining and ManufacturiNg Co. The ; photoconductor and Type 777 paper were placed between two electrodes and 2,000 volts was applied across the package.
After separation of the Type 777 paper in the dark and heat processing thereof at 130F for 10 seconds, a recognizable image appeared corresponding to the area containing the electrically conducting iron particles. . ----- -I

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_ _ _ . _ . _ _ . . ..... _ . _ .. .
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1037~Ql An electroeraphic recording element was prepared in the following manner:
A charge sensitive recording layer was prepared by dissolving 1.5 grams of Formvar 12/85 (a polyvinylformal resin from Monsanto Company) in a solvent mixture consisting of 17.2 ml of toluene and 17.2 ml of acetone by stirring the polymer in the solvent with a magnetic stirrer for two hours at room temperature. The resultant solution of Formvar 12/85 in solvent, 4.2 grams of silver behenate, 0.34 grams of 1,2-H-phthalazinone and 30 agate balls were placed in a 125 ml glass bottle. The mixture was ball milled at approximately 100 rpm for 16 hours. In a separate bottle, 1 gram of Formvar 12/85, 3.0 grams of 2,2'-methylene bis (6-tert-butyl-4 methylphenol) and 0.05 grams of mercuric chloride were dissolved in a solvent mixture consisting of 11.4 ml of toluene and 11.4 ml of acetone by stirring the solids in the solvent for 1 hour at room temperature. After ball milling, the ball milled dispersion and the solution were mixed under red safelight conditions. A hand coating of o.oo6 inches wet thickness of the charge sensitive recording layer was made under red safelight conditions on baryta paper.
The composite coating was dried in the dark for 16 hours at room temperature in a circulating air box.
Three strips of the electrographic recording were electrically exposed by the procedure described in Example 2 with two exceptions: (1) a step wedge of 0.3 neutral density was used to modulate the light impinging on the photoconductor;
and (2) the exposure time was for 10 seconds at a light in-tensity of 25 foot candles. A small section of each of therecording element strips, cut at right angles to the step ; wedge, was immediately heat processed. The remaining portions of the recording element strips were not immediately heat processed but were stored under ambient room conditions of temperature and humidity in a dark envelope. At later times, specifically 6 and 14 days after exposure additional small sections of each recording element strip were heat processed.
The strips were processed at 90C for 15 seconds.
The reflection densities of each of the sections was measured after heat processing and the composite average of such densities are shown in the table below.

Exposure Step No. (0.3 ND) Reflection DensitY
,, ~
7 .2 .2 .2 6 .3 .3 .3 .4 .4 .4 4 .7 .6 .6 3 1.1 .9 1.0 2 1.5 1.2 1.4 ~, 1 1.7 1.6 1.6 Days 1 8 1 7 1 8 i The data in the table illustrates the capability of the present invention to store the latent image formed during the imagewise charge exposure of the recording layer for extremely long periods of time with little or no image degradation.

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103710~
From the foregoing, the beneficial effects of the present invention are readily apparent, a novel electrographic process has been disclosed which avoids the chemical procedures inherent to photography, the mechanical dust pattern transfer procedure of xerography and the moistening procedure of electro-lytic electrography. By applying minute imagewise currents directly to the charge sensitive recording materials followed by uniform heating, the recording process is reduced to a pro-cedure of high speed, precision and simplicity. Still another advantage is that the latent image formed during the imagewise charge exposure of the charge sensitive recording material has a long storage life. Consequently, the exposure and develop-ment steps of the inventive process can be separated by an extended period of time. Still another advantage is that add-on images can be obtained since the nonexposed, processed areas can be re-exposed and processed again. Still another advantage is that radiographic images produced in accordance with the teachings of the present invention have increased resolution over radiographic images produced with fluorescent phosphors. For embodiments in which the charge sensitive materials contain no photographically active species, another advantage is that when the recording material is exposed to room light, there is little or no background printout.
The invention has been described in detail with reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, image colors other than black can be realized by incorporating different reducing agents.
~, 103qlQl A mixture of the current sensitive forming components with the photoconductors could be incorporated into a single layer. To form a latent image, a voltage would be applied to the single layer recording element which is insufficient to generate a current flow through the layer in the absence of light, simultaneously with an imagewise light exposure. After exposure, a visible image would be formed by heat processing.
~ The reducing agents needed for development of the developable sites in the charge sensitive layer couid be coated in a separate layer and then joined together tcmporarily after the exposure step. One advantage of having separate layers would be a reduction of material cost since one layer conlaining the reducing agent could be used to develop many layers containing the reducible metal salts.
Two sided copies can be produced using a multilayer element comprising a first charge sensitive layer, a conducting support and a second charge sensitive layer. 'l~he cnarge s~nsi-tive layers can be electrically exposed sequentially or simult-aneously using a photoconductive element or elements as an opto-electrical transducer and applying an electrical potentialacross the photoconductive element(s) and charge sensitive j layer(s). After each charge sensitive layer has been electrically exposed, the mul~ilayer element is heat processed ~o produce separate images on each side of the element.
A multicolored print can be produced using a two element recording device. The first element comprises: (a) an electrically conducting support; (b) a pan-sensitive photoconductive layer; (c) the second element comprises a charge sensitive layer; and (d) an optically transparent electrode; and (e) a multicolored additive filter mosaic divided into a multitude of color filter elements which are constructed to effect selective transmission of predetermined ~, .' 10~1~1 portions of the visible electromagnetic spectrum substantially corresponding to its red, green and blue regions. To produce a color print, the recording element is imagewise exposed to a color original through the mosaic while an electrical poten-tial is applied across the photoconductive and charge sensi-tive layers. The resulting latent image is then developed by uniformly heating the recording element to produce a color negative image.

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Claims (19)

WE CLAIM:

1. A dry electrographic recording process for producing a visible image in a charge-sensitive recording element having an ohmic resistivity of at least about 1 x 1010 ohm-cm and containing at least one reducible metal salt, said process comprising the steps of:
a) applying an electric potential to selected portions of said recording element of a magnitude and for a suffic-ient period of time to produce in said portions a charge density of from approximately 1 microcoulomb/cm2 to approximately 1 millicoulomb/cm2, said charge density forming a developable pattern of latent image sites; and b) heating the entire recording element substantially uniformly with the metal salt in the presence of a reducing agent until a sufficient quantity of metal salt is reduced at said image sites to form a visible image.

2. The process of claim 1 wherein said potential applying step comprises disposing one surface of said recording element in electrical connection with a conductive member and contacting portions of the opposite surface of said recording element with an electrode in an imagewise pattern while maintaining an electric field strength of about 1 x 105 volts/cm between said electrode and said conductive member.

3. The process of claim 1 wherein said recording element is heated to a temperature in a range of about 80°C
to about 250°C.

4. The process of claim 1 wherein said recording element is heated to a temperature in a range of about 100°C
to about 160°C.

5. The process of claim 4 wherein the time of heating said recording element ranges from about 0.1 second to about 120 seconds.

6. The process of claim 4 wherein said heating step is performed while said recording element is in face to face contact with an element containing a reducing agent for said metal salt.

7. The process of claim 4 wherein said recording element contains at least one reducible metal salt of an organic fatty acid and a reducing agent therefor.

8. The process according to claim 7 wherein said metal salt is selected from the group consisting of salts of silver, lead, nickel and copper.

9. The process according to claim 7 wherein said metal salt is a silver salt of an organic acid.

10. The process according to claim 9 wherein said silver salt is selected from the group consisting of silver behenate, silver stearate, silver oleate, silver hydroxy-stearate, silver laurate, silver palmitate, silver caprate and silver myristate.

11. The process of claim 1 wherein said potential applying step comprises the steps of:
a) imagewise altering the conductivity of a photocon-ductive layer in accordance with a pattern which is to be recorded;

b) positioning the imagewise altered photoconductive layer adjacent said recording element; and c) applying an electric potential across said photoconduc-tive layer and said recording element of a magnitude and for a sufficient period of time to produce in the areas of said recording element corresponding to the imagewise altered portions of said photoconductive layer a charge density of from approximately 1 micro-coulomb/cm2 to approximately 1 millicoulomb/cm2, such charge density forming in said areas a developable pattern of latent image sites.

12. The process of claim 11 further including the steps of:
a) positioning the imagewise altered photoconductive layer adjacent a second recording element having an ohmic resistivity of at least about 1 x 1010 ohm-cm and con-taining at least one reducible metal salt;
b) applying an electrical potential across said photocon-ductive layer and second recording element of a magni-tude and for a sufficient period of time to produce in the areas of said second recording layer corresponding to the imagewise altered portions of said photoconductive layer a charge density of from approximately 1 micro-coulomb/cm2 to approximately 1 millicoulomb/cm2, said charge density forming in said areas a developable pattern of latent image sites; and c) uniformly heating the entire recording element in the presence of a reducing agent until a sufficient quan-tity of said metal salt is reduced at said image sites to form a visible image.

\

13. The process of claim 1 wherein said potential applying step comprises the steps of:
a) positioning said recording element in face to face contact with a photoconductive element; and b) exposing said photoconductive element to an imagewise pattern of actinic radiation while simultaneously applying an electrical potential having a field strength of at least about 1 x 105 volts/cm across said photocon-ductive and recording element for a sufficient period of time to produce a developable pattern of latent image sites in the areas of said recording element corresponding to the exposed areas of said photocon-ductive elements.

14. The process of claim 13 wherein the impedance of said recording element differs from the impedance of said photoconductive element by no more than approximately 105 ohm-cms when said latent image forming electrical potential is applied across said photoconductive and recording elements.

15. The process of claim 13 wherein said latent image forming electric potential produces a charge density of from approximately 1 microcoulomb/cm2 to 1 millicou-lomb/cm2 in the areas of said recording element correspond-ing to the exposed areas of said photoconductive element.

16. The process of claim 13 wherein said record-ing element is heated to a temperature of about 100°C to about 160°C for a time period of about 0.1 second to about 120 seconds.

17. The process according to claim 13 wherein said photoconductive element is x-ray sensitive and the con-ductivity of such element is imagewise altered by exposing said photoconductive element to x-ray radiation in accord-ance with the pattern to be recorded.

18. The process of claim 17 wherein said photo-conductive element comprises a dispersion of lead oxide in an insulating binder coated on an electrically conducted, x-ray transparent support.

19. The process of claim 1 wherein said potential applying step comprises the steps of:
a) forming a conductivity pattern on a dielectric mater-ial; and b) sequentially positioning said dielectric material con-taining said conductivity pattern in face to face contact with a plurality of said charge-sensitive recording elements and establishing a potential dif-ference across said dielectric and recording elements of a magnitude and for a sufficient period of time to produce a charge density of from approximately 1 micro-coulomb/cm2 to approximately 1 millicoulomb/cm2 in the area of each recording element corresponding to said conductivity pattern, said charge density being suffi-cient to form a latent image in said recording material.