US3028799A - Apparatus for electrophotographic printing - Google Patents

Description

April 1962 D. F. KELLER ETAL 3,028,799

APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Filed March 8, 1957 2 Sheets-Sheet 1 Fag. Z

A ril 10, 1962 D F. KELLER ETAL 3,028,799

APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Filed March 8, 1957 2 Sheets-Sheet 2 United States atent ce 3,028,799 Patented Apr. I 10, 1 962 3,028,799 APPARATUS FOR ELECTROPHOTOGRAPHIC PRINTING Daniel Franklin Keller, 525 Sheridan Road, Kenilworth, Ill., and Harry E. Gunning, Hazel Crest, Ill., assiguors, by mesne assignments, to Daniel Franklin Keller, Kenilworth, Ill.

Filed Mar. 8, 1957, Ser. No. 644,754 16 Claims. (Cl. 951.7)

This application is a continuation-in-part of our copending application Serial No. 590,621, filed June 11, 1956, now US. PatentNo. 3,000,735 issued September 19, 1961.

This invention relates generally to electrophotography and electrophotograhic printing and, more particularly, to improved methods and apparatus for producing latent charge images on surface means suitable for use in printing and reproduction procedures, for example, by electrophotographic means.

By exposing photoemissive or photoconductive layers or surfaces to radiation having a desired image or pattern, there is produced a corresponding emission of electrons in the areas receiving the radiation whereupon an electrostatic latent image is produced. The electric charge pattern which forms the electrostatic latent image may be rendered visible by various developing procedures, for example, by depositing a suitable material such as finely divided particles which come under the influence of the charge pattern.

In following the procedures outlined heretofore, it has been necessary to utilize bulky equipment oftentimes necessitating the use of high voltage generating equipment. Artisans in the field have been confronted with serious problems with respect to the uniformity of a charging field, the lack of flexibility with respect to the size of the images reproduced and the safety factors which are present in connection with the high voltage equipment employed.

Further, methods heretofore used have not been adaptable to, utilization in an apparatus of a size and weight and having simplicity to be used as a camera or to be used in a printing system. In accordance with the prinmanent image by electrophotographic means. The present invention also contemplates the provision of methods and apparatus which may be utilized in a relatively uncomplicated printing arrangement wherein copies or prints are rapidly and directly made from the permanent image with the utilization of electrophotographic processes.

In accordance with the principles of the present invention, it is contemplated to provide as a charging means in an electrophotographic process a layer formed from an electrically stressed substance and providing an eifective working surface which exhibits a permanent electrostatic field as high as 30,000 volts per centimeter. A layered member so provided is sometimes referred to in the electrostatic arts as an electret.

A feature of the present invention is to provide a camera wherein the light radiation passing through the lens falls upon a photoconductive strip backed by an electret and wherein the strip is subsequently drawn through a dusting chamber and thereafter through a fixing chamber so that the dust which is gathered upon the surface in the form of the image will be permanently fixed to the strip of material.

It is another feature of the invention to provide a method and apparatus for the printing of copies from permanent images by 'an electrophotograpln'c process wherein a surface means bearing a permanent image is placed against one surface of a transparent electret and light radiation projected through the surface means and electret wherein a latent image is formed on a photoconductive coating on the opposite surface of the electret. The image is rendered visible by applying a dusting powder and this image is transferred by a surface having an afiinity for the powder and carried to an electret having a polarity opposed to the polarity of the first electret surface whereby the image will be attracted to a paper placedbetween the transfer surface and the second elec tret.

Another feature of the invention lies in the provision of a method and apparatus for utilization in a camera wherein a photoconductive layer is utilized as a surface bearing a latent charge image and succeedingly passd over ends of an electret or" opposite polarity and thereafter positioned against a grounding plate and exposed to radiation from an image and the image is subsequently fixed on the photoconductive surface by passing it through a dusting chamber. The surface bearing means is subsequently passed through a spray chamber wherein the a printing method and mechanism wherein a surface hearing an image is placed against a surface of an electret and a photosensitive insulating material on thin plastic is placed over the surface and exposed to a light and subsequently passed to a dust chamber.

The plastic material with the photoconductive insulating surface is subsequently exposed to another light and carried against a copy material held against an electret surface having an outer surface of opposite polarity from the surface beneath the surface bearing the image whereby dust which has been placed on the surface of the plastic material in accordance with the density of the image is transferred to the copy material producing a printed copy of the image.

It is, therefore, an object of the present invention to provide an electrophotographic method and apparatus wherein a strip of supporting material coated with a photoconductive insulator may be fed through a camera to produce a latent charge image by an electrophotographic process conducted entirely within the camera.

Another object of the invention is to provide a mechanism wherein a permanent image is produced Within a camera by drawing a clear plastic film coated with a photoconductive insulating material over an electret and exposing the film to radiation and subsequently drawing the film through a dust chamber and a spray chamber to develop and fix the film.

Another object of the invention is to provide a camera wherein a film coated with a photosensitive layer is sequentially drawn over surfaces of opposite polarity on the electret and thereafter placed against a ground plate and exposed to the radiation of an image and substantially drawn through a dust chamber and spray chamber to develop and fix the image on the film.

Another object of the invention is to provide an improved photoelectric printing method and apparatus which is simple in construction and operation and wherein copies or prints 'may be directly and continuously made by a photoelectric process obviating the necessity of providing expensive and complex equipment such as has heretofore been necessary.

Another object of the invention is to provide an electrophotographic printing process which finds utility in a printing mechanism wherein a powder deposited in the form of an image is carried by a transfer blanket to a printing paper.

Another object is to provide another form of mecha- 3 nism wherein the powder may be transferred directly to, a printing paper and fixed thereon.

Other objects and advantages will become more apparent in the teachings of the principles and features of the invention with the disclosure of the preferred embodiments thereof in the specification, claims and drawings, in which:

FIGURE 1 is a somewhat schematic vertical sectional view of one form of a camera employing the principles of the invention;

FIGURE 2 is another vertical sectional view taken through the camera and showing schematically another form of the camera;

FIGURE 3 is a vertical sectional view shown in schematic form of a printing mechanism for making copies or prints of images; and

FIGURE 4 is avertical sectional view shown in schematic form of another arrangement of a printing mechamsm.

In the embodiments of FIGURES 1 and 2, the invention is shown using an electret in a box or similar hand camera for purposes of making permanent images.

As used herein, the term electret denotes a permanent- 1y electrified substance exhibiting electrical charges of opposite sign at its extremities and of the type disclosed in our acknowledged co-pending application.

Electrets are made from solid substances which are capable of being melted without chemical decomposition and which possess a finite dipole movement in liquid state, for example, carnauba wax-beeswax mixtures, mixtures of carnauba wax with various synthetic, thermoplastic or polar resin such as polyvinyl chloride polymers, etc., soda-lime glass, Pyrex glasses, quartz, and sulfur.

A permanent charge is imposed upon the substance of the electret by allowing the liquid electret-forming substance to solidify in a strong electric field. For example, the substance may be melted while interposed between two electrically-independent tinfoil electrodes attached to opposite poles of a high voltage D.C. source furnishing a DC. field of not less than 10,000 volts per centimeter. The liquid substance is allowed to remain in the fluid state within the field for at least one hour and is, thereafter progressively cooled at a slow rate within the field until completely solidified.

It has been found that electrets so formed are permanently volume-polarized and possess permanent electrostatic fields of opposite polarities at the extremities or surfaces thereof to which the electrodes were attached.

In the electrophotographic processes of the prior art, charges in the range of 4500 to 6000 volts per centimeter have been utilized, The permanent electrostatic fields possessed by electrets may range from a few hundred volts per centimeter and may exceed as high as 30,000 volts per centimeter at the working surfaces of the electret and, accordingly, it is contemplated according to the principles of the present invention that the electret will be provided with surfaces exhibiting a permanent electrostatic field in the order of magnitude of a few hundred volts to an upper limit determined by the breakdown potential of the air in contiguity to the charged surface.

Although the principles of the present invention find specific utility in the embodiments illustrated and described, it will be understood that the features and advantages of the invention may be utilized in other environments and the specific forms shown are for purposes 7 of illustration and for purposes of disclosing the preferred forms.

As illustrated in FIGURE 1, a camera is illustrated as having a housing shown diagrammatically at 10 with a bellows 12 or similar lightproof enclosure defining a camera chamber 14. At the front of the camera chamber is a lens and shutter assembly 16 with lenses 18 and a shutter system 20. The lens and shutter arrangement are the type known to the art whereby the shutter system 20 maybe opened for a predetermined period of time to permit the passage of light radiation through the lens in accordance with the reflective properties of the image to be photographed.

At the focal point of the lens is a reflector plate 22 which is set at a 45 angle with the camera shown in the horizontal position, so that the image is reflected upwardly against a supporting surface adapted to have a latent charge image formed thereon, sometimes referred to herein as a film 24.

The film may conveniently comprise a backing or carrying layer with a layer of photo-conductive material thereon such as sulfur, anthracene or mercuric sulfide. Means for supplying the film are shown in the form of a supply roll 26 from which the film is threaded to be positioned against the ground plate 28 in the picture taking location. The end of the film next passes through a dusting chamber 38 and then passes into a spraying chamber 40.

The spraying chamber is provided with a hinged door 42 which may be swung open about its supporting hinge 4+4 to remove the developed and fixed end of the film at 46.

In advancing the film into the camera, the film is first drawn over a scanning bar or roller 48 positioned to be in engagement with the film. The scanning bar 48 is of a polarity determined by electret 50.

The electret member 50 comprises a body 52 with a first lower surace 54 and a second upper surface 56. The surfaces 54 and 56 are spaced from each other and parallel and exhibit a permanent electrical charge with the surfaces 54 and 56 being of opposed polarity in accordance with the definition of theterm electret.

As illustrated in FIGURE 1; the electret 50 is provided on the surface 54 with an electrically conductive layer 58. The surface 56 is provided with an electrically conductive layer 60.

Attached to the first electrically conductive layer 58 is an electrical lead 61 which is electrically connected to the scanning bar 48 so as to place a charge on the surface of the coated paper in accordance with the electrostatic charge on the surface 54 of the electret.

As the film 24 is drawn forwardly to an image-forming location 62, it passes over the electrically conductive sur-- is positioned in juxtaposed relationship to the ground plate 28.

The light-conducting film has been in location to receive light radiations of the image. As the shutter system 2.0 is opened, the film 24 is exposed to radiation and surface electrons are discharged to the ground plate 28 in the shape and density of the image.

The film 24 is next rolled forward to pass through the dusting chamber 38. The dusting chamber exposes the photoconductive surface to fine pigment particles and these particles are picked up in the shape and density of the image.

Guide pins 41 or the like may be provided to guide the film as it passes with its surfaces 43 exposed to the dusting chamber 38. The dusting chamber 38 may be provided with seals at its edges to avoid the escape of dust down into the camera chamber 14 or up into the spray chamber 40. The dust may be created by agitation means or may be applied by a brush similar to an iron filing brush of the type known to the art.

After being developed, the dust coated film is drawn up into the spray chamber 40 where the image is fixed. The fixing is accomplished by applying a spray such as by nozzle 64 which sprays over the surface ofthe end of the image and causes a permanent adherence of the dust to the film in the density and shape of the image. A plastic solution spray such as Krylon or any solid 3 plastic dissolved in a volatile solvent, which solvent is compatible with the film material, may be applied to fix the image.

In the form show in FIGURE 2, the camera is pro: vided with a housing 66 having a lightproof bellows 6-8 forming a camera chamber 70. At the front of the chamber is located a lens and shutter assembly 72 carrying lenses 74 with a shutter system 76. The assembly 72 is arranged so that the shutter may be opened for a predetermined length of time to permit light radiation corresponding to the image to pass rearwardly within the camera chamber 70. At the back of the camera in an image-forming location 78 is the film 80. The film may be a backing paper with a photoconductive insulating material thereon and is preferably formed of a roll of clear plastic with a photoconductive insulating surface.

The film is supplied from a supply roll 82 housed in an upper portion 84 of the housing 66 and feeds downwardly to the image-forming location 78 and subsequently through a dust chamber 86 and a spray or fixing chamber 88.

In moving to the image-forming location 78, the film 80 passes .a lateral ground brush 91. The ground brush may be moved across the face of the film along the guide 93 or it may be more feasible to position the ground to contact the film as it comes off the roll 82 as a ground on the face of the electret may bring charges to the surface.

In the picture-taking location, the film is backed by an electret'90 which is shown in the form of a flat plate 92 having opposed parallel surfaces 94 and 96, which exhibit permanent electrostatic charges of opposing polarity.

In the picture-taking location, the shutter system is opened whereupon the film 80 is exposed to radiation. A latent electrostatic image is produced on the film in the configuration and density of the image.

After the image has been formed on the film, it is rolled downwardly to pass into the dusting chamber 86. In this chamber, the film is exposed to a finely separated pigment or dust which attaches itself to the surface in the configuration and density of the image and changes the latent electrostatic image to a visible image. The film portion 98, which is in the dust chamber 86, is guided by spaced horizontally extending guiding bars 160'.

The leading end 102 of the film is rolled forwardly into the spray or fixing chamber 8-3. At this location a spray nozzle 104 is supplied from a manifold or container 106 and sprays a material such as a clear plastic coating to fix the powdered material to the surface of the film end 102. The end 102 of the film upon which the visible image has been fixed, may be removed by swinging back a door 106 which is hinged to the back of the housing. by a hinge 108.

FIGURE 3 illustrates another form of the method of the invention for printing copies from a permanent image by an electrophotographic process. A housing is illustrated at 112 wherein a hollow, cylindrically shaped or tubular electret 114 is located to rotate about a horizontal axis. The tubular electret is made of a transparent material such as a clear plastic, glass or the like and the outer surface 118 is coated with a photoconductive insulative material. The outer surface 118 of the electret, beneath the coating 116, and the inner surface 120 are of opposite polarity and are permanently electrostatically against the inner surface of the electret by means of clips or similar holding devices that will retain it against the surface, but which are not shown. As illustrated, the film is held to the inner surface 120 by a sheet of clear semirigid plastic 124 which may be supported between rigid 1 stops, not shown.

The inside of the tube contains a light source 126 i that location. A light source can also be placed very near to the inner surface of the electret at a point where the image transfer to the photoconductive surface 116 is to take place.

A light shield 128 is provided to restrict the light to the required longitudinal area. As illustrated, the shield 128 has a break or slit 130 along one side in order that the light rays may pass therethrough to pass through the transparent holder 124; the negative 122,-and the electret 114.

A grounding brush 132 is provided supported on a holder 134 to be in brushing contact with the outer photo conductive layer 116. The brush grounds the outer layer and removes stray charges which would create a false image.

As the electret tube 114 rotates in a clockwise direction, as illustrated in FIG. 3, the outer photoconductive coating or surface 116 passes through a dusting-box 136. The dusting box exposes the photoconductive surface 116, which has had the latent image photoelectrically placed thereon in passing the light exposure of the slit 130, to a fine pigment dust. The dust is attracted to the coating 118 in the form and density in accordance with the latent image on the film.

As the coated surface 118 carrying the image, made visible by the attracted powder, leaves the dusting box 136 it is engaged by transfer cylinder 138 carrying a blanket transfer surface 140. The transfer cylinder is geared to the electret cylinder, in a drive not shown, so that where their surfaces meet at a nip 142 they will have an equal peripheral speed. It should also be understood that the transfer cylinder 13-8 and the electret cylinder 114 can be conveniently made of the same diameter thereby insuring equal peripheral speeds.

' The blanket or transfer surface on the cylinder, is of a nature that will have a greater affinity for the powder or dust on the electret cylinder than the surface 118 of the electret cylinder. The dust will thus be transferred to the surface 140 of transfer cylinder remaining in the form of the image. The dust or powder, which has been transferred to the blanket surface 140 by contact and stantially meet. The paper is rolled from a supply roll 148 onto a take-up roll 150.

The electret roll or cylinder 146 has anouter surface 152 exhibiting a permanent electrostatic charge of a polarity opposite that of the outer surface 118 of the electret tube 114. Thus the powder forming the visible image, which is coated on the surface 140 of the transfer roll, is attracted to the electret roll 146 and coats on the image-receiving paper 144.

The blanket surface 140 of the transfer cylinder 138 may be coated with a material such as rubber which has a greater afiinity for the powder image than the insulating surface 116 of the electret tube 114. In one form it is advisable to ground the surface 116 of the electret to expedite transfer of the image to the blanket 140. This may be accomplished by embedding small particles of copper or similar substance into the blanket surface .140 of the transfer, cylinder 138.

After the image has been transferred to the paper 144, it is carried upwardly on the surface of the paper to a fixing element 154 which may be in the form of a spray or vapor or a heating element. As illustrated, the fixing element 154 provides a heating element 156 which fixes the image to the paper 144.

In the form shown in FIGURE 4, a hollow electret tube 160 is carried partially exposed in a housing 162 to-rotate about a horizontal axis. The electret has an outer surface 163 exhibiting a permanent electrostatic charge.

In this form of the invention, the film 164 is clamped to the outer surface 163 of the electret cylinder tube 160. The film may be held to the surface by various means but may be pulled tightly thereto by a thin outer sheet of plastic material 166. This plastic material may be a material such as Mylar polyester film which is available commercially.

The thin plastic sheet is clamped to the cylinder at one end drawn tightly by appropriate clamps (not shown in detail) at the other end, with the clamped ends being shown generally at 168.

The outer thin material 166 is dipped in a thin solution of photoconductive insulating material and is coated thereby.

The light source is shown at 170 and in this form is on the outside of the electret tube 160. The light source may be placed within a housing 172 having a nan row slit 174 across the front to expose the photoconduct-ive layer 166 of the film 1 64 to the light across an axially extending area.

A ground brush 176 is provided carried on a holder 177 to neutralize the outer plastic material and remove stray electrostatic fields therefrom.

When the photoconductive material 166 has been carried past the light source, it next passes through a dust chamber 178. In the dust chamber 178, the surface of the photoconductive material 166 is exposed to a fine dust or pigment which is attracted to the surface in the shape and density of the image to be printed.

After the dust chamber, the continued rotation of the electret tube 160 exposes the photoconductive material 166 to alight source 180. This light source brings a charge to the entire surface.

In the form embodied in FIGURE 4, the transfer roll is omitted and the photoconductive layer 166 is next pressed against a copy material such as a paper 182 fed from a supply roll 184 and rolled onto a take-up roll 186. The paper passes between the photoconductive layer 166 and a paper electretroll 188. The paper electret roll has an outer surface 190 which is opposite in polarity to the outer surface 163 of the electret tube 160. This causes an attraction and a transfer of the visible image formed by the powder on the 'photoconductive material 166 to the paper 182.

The image, carried on the paper 182, next passes over the image fixing element 192. The fixing element may be in the form of a heating element 194, as illustrated, or may spray vapor on the surface to fix the powder thereto.

The method is well adapted to use in printing or copying permanent images and employs simple, easily maintained and simply constructed apparatus. Copies can be continuously and rapidly printed with the advantages referred to.

Thus, it will be seen that we have provided methods and apparatus for electrophotographically taking permanent images and printing copies embodying principles and features of the invention hereinbefore set forth. The features of invention are well adapted to use with a camera and avoid the necessity of providing the cumbersome and complicated devices necessary with methods and apparatus heretofore used.

We have, in the drawings and specifications, presented a detailed disclosure of the preferred embodiments of our invention, but it is to be understood that we do not intend to limit the invention to the specific forms disclosed, but

intend to cover all modifications, changes, and alternative constructions and methods falling within the scope of the principles taught by our invention.

We claim as our invention: 7

1. In combination, a camera means for making an image by an electrophotographic process which comprises a lens, a closed camera chamber exposed to light only through the lens, a shutter system for controlling the opening of the lens and exposing the camera chamber to an exterior image for a controlled period of time, an electret within the camera chamber having a surface face ing the lens and including opposed coextensive parallel surfaces each exhibiting permanently charged electrostatic fields of opposite polarity, means at one side of said electret supplying an area of image-forming material with a photoconductive layer thereon md adapted to be placed over the electrostatically charged surface facing the lens, a movable grounding element adapted to be moved over the surface of the image-forming material whereby stray charges on the surface thereof are discharged, and means for subjecting the image-forming area to contact with electrostatically attracted material to form a visible image on the surface of said image-forming material.

2. An electrophotographic camera combination comprising means forming a closed lightproof camera chamher, a' lens positioned to expose the interior of the chamadapted to open the lens for a predetermined period of time wherein light radiation enters the camera chamber,

a plate of permanently electrically pre-stressed substance having parallel surfaces exhibiting permanently charged electrostatic fields of opposite polarity with one of said surfaces facing the light radiation which enters the camera chamber through the lens, means for movably supplying an image-forming strip of material having a photoconductive layer adjacent a second layer whereby radiation maybe projected through the lens onto said photoconductive layer while it is in proximate relationship to the surface of the electrically stressed plate, a stationary ground bar located so that the moving image-forming strip will pass in close proximity thereto to remove stray electrostatic fields from the photoconductive surface thereof, and means located adjacent the electrically pre-stressed plate providing an atmosphere of electrostatically attracted material whereby the surface of said imageforming strip is coated with the material in a shape and density varying with the radiation received in accordance with the light emitting properties of the image, and means for fixing the layer of electrostatically attracted material on the image-forming strip to render the image permanent.

3. In a mechanism for producing an image by an electrophotographic process comprising a closed lightproof camera chamber, an electret plate within said chamber having opposed parallel spaced surfaces being charged with a permanent strong electrostatic field withropposite surface having opposite polarity, a lens for said camera chamber located so that radiation passing through the lens will engage an area adjacent one surface of the elec: tret, a shutter system for the lens adapted to permit pas-' sensitive pigment particles whereby the particles are coated on the image-forming material with a shape and density varying with the latent image on the surface thereof in accordance with the radiation received, and means for fixing the pigment particles on the surface of the image-forming material.

4. A camera for making an image by an electrophotographic process Which comprises a lightproof camera chamber, a lens and shutter combination at the front of the chamber adaptedto open the lens for radiation to the back of the chamber in accordance with an image to be reproduced, an electret plate at the back of the chaml a 9 reproduced, a developing chamber having means for providing an atmosphere of electrostatic responsive pigment in minute particles which will coat the image-forming strip with a shape and density in accordance with the radiation received through the lens, and a second fixing chamber with means to spray a coating of material over the image-forming strip whereby the visible image is' fixed on the surface of the image-forming strip.

5. In a photoelectric camera combination, a charging means having an electret plate having opposing parallel coextensive surfaces each charged with a permanent electrostatic field with opposite surfaces having opposing polarity, a camera housing supporting said plate and forming a lightproof camera chamber, a lens at one end of the chamber located to expose an image forming strip to radiation emitted from an imageexternally of the camera, a shutter system for the lens adapted to open the lens for a predetermined length of time, means with- 4 10 conductive insulation layer on the outer surface of the electret element, means for moving and supporting a film on the inner surface of the electret element, a light source Within the tubular electret whereby light radiation will pass through the film and transparent electret to impress a latent image on the photoconductive insulation layer, means for applying a powdered pigment material to the insulation layer on the surface which is attached to the layer in accordance with the latent image thereon, a transthe particles are transferred to the surface thereof, and

in the housing supplying a strip of image-forming material ofa clear plastic with a photoconductive insulating surface thereon, said image-forming material being drawn across the surface of the electret plate, a developing chamber filled with dust particles of pigment susceptible to electrostatic attraction whereby the pigment particles are coated on the image-forming strip with a shape and density dependent upon the radiation received by the image-forming strip, and a fixing chamber adjacent the developing chamber provided with a-coating spray whereby the pigment particles are adhered to the surface of the image-forming strip to permanize the image.

6. In an electrophotographic apparatus comprising a camera housing defining a lightproof camera chamber, a lens member at the front of the chamber for admitting radiation in accordance with the character of an image, a shutter assembly for the lens, a light-reflecting surface at the back of the camera chamber positioned substantially at an angle of 45 with the axis of the lens whereby the'light rays will be reflected vertically upwardly to an image-receiving position'when the camera is positioned horizontally, means for movably' supplying a strip of image-forming material in theimage-receiving position across the top of the camera chamber, said material having a layer of photoconductive material thereon, an electret having a surface located for engagement with the imageforming strip as it is drawn into image-receiving position, whereby radiation will produce a latent charge image on said photoconductive layer, and means for developing and. fixing said latent image into a permanent image by subjectingthe strip to an electrostatically attracted dust and by adhering the dust to the strip after it is accumulated thereon in the shape and density of the latent image,

7. In an electrophotographic apparatus, an electret member having opposed surfaces permanently charged with electrostatic fields of opposite polarity and having coatings of electrically conductive material over each of said surfaces, means for passing an image-forming material in effective electrical engagement with the first layer of electrically conductive material and subsequently in engagement with the second layer of electrically conductive material, means for placing a grounded plate in coextensive juxtaposed relationship with the image-forming material after it has been passed over the conductive layers, a camera lens system exposing the photoconductive layer on the image-forming material to a radiation in accordance with an image to be reproduced, and deveioping and fixing means for permanizing the latent image on the photoconductive layer by dusting the layer with an electrostatically attracted powder and adhering the powder in its attracted positions in densities and shapes varying with the radiation received by the material.

'8. A mechanism for reproducing images electrophotographically comprising a tubular shaped transparent electret element having inner and outer surfaces permanently charged electrostatically with opposed polarity, a photomeans for fixing the particles transferred to said material. 9. A mechanism for reproducing images in accordance with claim 8 wherein electrical conductive material is embedded in the surface of the transfer cylinder to ground the surface of the electret tube in contact with the transfer cylinder to expedite transfer of the image to the cylinder.

10. A mechanism for reproducing images electrophotographically comprising a transparent electret element having first and second surfaces permanently picture charged electrostatically with opposed polarity, a photoconductive layer on the second surface of the electret element, a light source located adjacent the first surface whereby light rays may be projected through a film place againstrthe first surface and through the transparent electret to the photoconductive insulation layer, means for applying a powdered material attracted by the charge on the insulated surface whereby a visible image will be produced thereon dependent on the intensity of the radiated latent image thereon, a transfer blanket means having a greater afiinity for the powdered material than the insulated surface and adapted to remove the powdered material in the charge pattern in which it has formed on the insulated surface, a second electret element having a permanently charged electrostatic surface with .a polarity opposed to that of said'second surface of the transparent electret, whereby the second electret may be. pressed against the transfer means with an image-receiving meansv therebetween and the powdered material will attract itself to the image-receiving means in the pattern of the image, and means for fixing the material to said image-receiving means.

11. A mechanism for rotary printing of images by an electrophotographic process which comprises a hollow cylindrically-shaped electret having inner and outer surfaces with a permanent electrostatic charge of opposed polarity, means on the inner surface of the electret cylinder for supporting a film, a light source positioned within the electret cylinder, a light shield having a narrow lightpassing strip extending axially across the cylinder and limiting the light passage through the film and the electret to the narrow strip, a coating of photoconductive insulation material on the outer surface of the electret, means for applying a material to the outer surface of the cylinder which will afiix itself thereto in the pattern of the image impressed on it by the light radiation passing through the electret and film, a transfer roll rotatable about an axis parallel to the electret cylinder and having an outer blanket surface with an afiinity for the material attached to the surface of the electret cylinder to thereby remove said material in the pattern of the image, a second rotatable electret having an outer permanently charged electrostatic surface with a polarity opposite that of the outer surface of the electret cylinder, means for passing a strip of image-receiving material between the transfer roll and the second electret whereby the image will aifix itself to the material, and means for receiving the material from the second electret and operative to fix the attracted material to the surface for a permanent print.

a bearing means on the. inner surface on the electret element, a light source within the tubular electret whereby light radiation will pass through the image and transparent electret to impress a latent image on the photo-j conductive insulation layer, means for applying a powdered pigment material to the insulation layer on the surface which is attached to the layer in accordance with the latent image thereon, a transfer cylinder positioned to be rotated about an axis parallel with the tube and having an outer surface with an affinity for the powdered pigment, a grounding brush positioned in contact with the insulation layer after contact with the transfer cylindena copy material adapted to be rolled in engagment with the transfer cylinder whereby the particles are transferred to the surface thereof, and means for fixing the particles transferred to said copy material.

13. A mechanism for reproducing images electropho'tographically comprising a rotating cylinder forming an electret with the inner and outer surfaces of opposing polarity, means for attaching a thin plastic material with a photoconductive insulating surface thereon to the outer peripheral surface of the cylinder wherein an image-bearing film may be held between the plastic material and cylinder, a light source exteriorly of the cylinder adapted to apply light radiation to the photoconductive surf-ace of the thin plastic material, a dust chamber for applying a .pigment dust to the outer surface of the plastic material whereby the latent image is rendered visible, and a second electret cylinder having an outer surface permanently electrostaticall-y charged and being of a polarity opposing the polarity of the outer surface of the first electret cylinder, means for passing a copy paper between said cylinders, said paper receiving'the image in its visible form from the layer of thin plastic material as attracted by the surface of the second electret.

14. In combination in a camera for making an image by electrophotography comprising a closed light-proof camera chamber, a lens located at one end of the chamber, a shutter device to be opened to expose the interior of the closed chamber through the lens to an image to be photographed, an electret in said camera having a flat surface facing said lens and possessing a permanently precharged electric fieldof a given polarity, film advancing and guide means movably positioning strip form imageforming material having a layer of photoconductive material in adjacent coextensive relationship across said flat surface of said electret, whereby radiation may be projected into said photoconductive layer when said lens is opened, and a developing chamber into which said strip material is moved away from said electret and having an atmosphere of charge-responsive material coating the image-forming material non-uniformly with a shape and density varying with the radiation received from the image. I Y

15. An electrophotographic reproduction apparatus which includes, an electret,.means passing. a layer'of image-forming material having a photoconductive layer through the permanent electrostatic field adjacent the surface of the electret, means forming a grounded surface in close proximity to the image-forming material, camera lens means for exposing the photoconductive layer of image-forming material to a radiation in an image to be reproduced to form a latent electrostatic image in the image-forming material, and means for developing the image to render it visible.

16. An electrophotographic reproduction apparatus including an electret, means passing an image-forming material having a photoconductive layer attached thereto through the "permanent electrostatic field adjacent the surface of an electret, means passing the image-forming material in electrical contact with a layer of electrically conductive material on a first surface of said electret, and subsequently with a second layer of electrically conductive material on another surface of said electret, means placing a coextensive ground adjacent the image-forming material, a camera lens system for exposing the imageforming material to a radiation in accordance with an image to be reproduced to formulate an electrostatic image on the photoconductive layer, and means for developing and fixing the image on the image-forming material. V V g V References Cited in the file of this patent UNITED STATES PATENTS 2,221,776 I Carlson Nov. 16, 1940 2,297,691 ,Carlson Oct. 6, 1942 2,543,051 Oughton et a1 Feb. 27, 1951 2,551,582 Carlson May 8, 1951 2,693,416 Butterfield Nov. 2, 1954 2,695,363 Marvin Nov. 23, 1954 2,732,775 Young et al. Jan. 31, 1956 2,781,704 Mayo et al. Feb. 19, 1957 2,831,409 Bixby et al. Apr. 22, 1958 2,843,084 I-Iayford July 15, 1958 "OTHER REFERENCES page 470.

Electrical Engineering, October 1953, pages 869-872. I

Radio Electronics, January 1950, pages 8-82.

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