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Publication numberUS2693416 A
Publication typeGrant
Publication dateNov 2, 1954
Filing dateMay 19, 1950
Priority dateMay 19, 1950
Publication numberUS 2693416 A, US 2693416A, US-A-2693416, US2693416 A, US2693416A
InventorsButterfield Louis Boydston
Original AssigneeWestern Electric Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of electrostatic electrophotography
US 2693416 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

1954 L. B. BUTTERFIELD 2,693,416

METHOD OF ELECTROSTATIC ELECTROPHOTOGRAPHY Filed May 19, 1950 I ATTORNEY United States Patent Ofi" 2,693,416 Patented Nov. 2, 1954 iVmTl-IOD OF ELECTROSTATIC ELECTRO- PHOTOGRAPHY Louis Boydston Butterfield, Plainfield, N. J., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application May 19, 1950, Serial No. 163,007 6 Claims. (Cl. 95-1.9)

This invention relates to electrostatic electrophotography and more particularly to a method for reproducing images from an image bearing sheet of material.

Previous methods for reproducing images by use of electrostatic electrophotographic processes may be summarized broadly as processes wherein an invisible electrostatic image is formed on a surface of photoconductive material and then a visible powder is sprinkled on the photoconductive surface to develop a visible image from the latent electrostatic image. The next step is to transfer the visible powder image from the photoconductive surface to a sheet of paper and then to fix permanently the image to the paper by heat.

It is an object of this invention to provide a simplified method of electrostatic printing wherein the steps necessary to carry out the process are reduced.

It is an additional object of this invention to improve methods for economically reproducing designs, configurations or outlines of solid objects.

A further object of this invention is to provide a method for producing an electrostatically charged image on a sheet of insulating material in accordance with a light image projected onto the sheet of material.

Another object of the invention contemplates a method wherein an electrostatically charged image acts through a transparent or translucent sheet of material to attract powder to form a visible image.

A still further object of this invention is to provide a method for projecting a light image through a transparent or translucent sheet of material to form an electrostatic image on a photoconductive surface.

In accordance with one embodiment of the present method, a film having an image to be reproduced is placed in front of a light source. The image on the film is projected by a beam of light through an electrostatically charged transparent or translucent sheet of material onto a photoconductive layer whereupon the portions of the photoconductive layer subjected to the light are rendered conductive. Charges of opposite polarity to those on the transparent or translucent material now migrate, by attraction, through the lighted portions of the photoconductive layer to the under side of the transparent or translucent sheet of material to form electric couples which have negligible external fields. Thus the charges on the portions of the transparent or translucent sheet of material not subjected to light remain with an effective external field. The transparent or translucent sheet of material is then sprinkled with an electrostatically attractable visible powder to form a visible image of the electrostatic image. The sheet of material is then removed from contact with the photoconductive surface and finally the powder is fixed by any suitable process to the sheet of material to form a permanent visible image.

Other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a perspective view illustrating apparatus suitable for use in charging a photoconductive plate in accordance with the invention;

Figs. 2, 3 and 4 are views showing apparatus employing various methods of projecting an image through a sheet of material onto the photoconductive element;

Fig. 5 is a sectional view illustrating an arrangement of apparatus for applying powder onto an electrostatic image bearing sheet of material;

' Fig. 6 is a perspective view showing the removal of a electrostatically charged image sheet of material bearing a reproduced powdered image from the photoconductive plate;

Fig. 7 is a perspective view illustrating apparatus for permanently fixing a powdered image to the sheet of material;

Fig. 8 is a perspective view disclosing an alternative arrangement of elements suitable for use in electrostatically charging the photoconductive plate.

Referring to the drawing wherein like reference numerals designate the same elements throughout the several views, there is shown in Fig. 1 a metallic plate 10 having coated thereon a thin photoconductive layer 11. The metallic plate 10 may be made of copper, aluminum or any other suitable conductive or semi-conductive material which does not chemically react perniciously with the photoconductive layer 11.

Any one of a variety of photoconductive materials may be used for the layer 11 such as amorphous selenium, sulphur, germanium, lead sulphide, copper oxide, silver chloride, silver iodide and various combinations of selenium and sulphur. The term photoconductive material as used in this application includes those materials having such a change in their electrical characteristics in the transition from darkness to light that an electrostatic image can be produced and maintained by said materials during an electrostatic printing cycle.

A sheet of transparent or translucent electrically insulating material 12 is placed on top of the photoconductive layer 11. This sheet of material is made of any suitable electrically insulating material such as paper, cloth, or cellulose acetate, polystyrene or other plastics. It is upon this sheet of material that an image is to be reproduced.

A battery 13 or other suitable source of D. C. energy is connected by a wire 14 to the under side of the metallic plate 10. A corona discharge wire 15 is positioned above the sheet of material 12 and in close proximity thereto. This corona discharge wire is connected by a conductor 16 to the battery 13. It is preferable that the source of D. energy be suitable to maintain a potential of 5,000 to 10,000 volts between the corona discharge wire 15 and the metallic plate 10. Therefore, as the metallic plate 10, together with the selenium layer 11 and the sheet material 12 are reciprocated beneath the wire 15 a discharge takes place in the region between the corona discharge wire 15 and the sheet of insulating material 12. This particular procedure is carried out in a darkened space and as a result, the charges produced by the corona wire 15 are retained on the surface of the overlying sheet of insulating material 12.

Referring now to Fig. 2, a fihn to be reproduced is placed on top of the sheet of transparent or translucent material 12. The assembled film 17, transparent or translucent sheet of material 12, photoconductive layer 11 and metallic plate 10 are positioned with respect to a light source 18 arranged to uniformly illuminate the film 17. The light readily passes through those portions of the film 17 not having the image and through the sheet of transparent or translucent material 12 onto the photoconductive layer 11. Upon the light striking the photoconductive layer 11, the layer 11 is illuminated in the outline of the image to be reproduced. The portions of the photoconductive layer 11 subjected to the light are rendered more conductive thereby allowmg electrostatic charges of opposite polarity with those on the surface of the sheet of insulating material 12 to migrate through the photoconductive layer 11 to the under side of the sheet of insulating material 12 to form electric couples with the charges on the outer surface. These electric couples will be formed over the entire area subjected to light and have a negligible external field. An remains on those portions of the surface of the sheet of insulating material 12 which are not subjected to suflicient light to render conductive the underlying layer of photoconductive material 11. There is thus obtained on the transparent or translucent sheet of insulating material 12 an electrostatic latent image corresponding to the image contained on the film 17.

It is to be understood that original image bearing materials other than films may be used to produce the light image. Among the various types of originals that may be satisfactorily used to produce a light image are type- 17 hearing an image 3 written pages of transparent or translucent paper, drawings on tracing paper or cloth, designs contained on trans parent or translucent sheets of plastic material, solid objects, the outline of which is desired to be reproduced, etc.

Fig. 3 illustrates another method of exposing thephotoconductive layer 11 to a light source 20. The image bearing film 21 or other material containing a configuration to be reproduced is placed beneath the light source 2'0 and the image is projected through a lens 22 onto the transparent or translucent sheet of material 12. The light passes through the transparent or translucent. sheet of material 12 to render the photoconductive layer 11 conductive in. the outline of the image to be reproduced. The portions. of the photoconductive layer 11,. rendered conductive by the light, permit the migration of charges of opposite. polarity to the under side of the sheet of insulating material 12 to neutralize the eifect of the charges on the outer surface of the sheet of insulating material in the outline of the light image. Therefore, an electrostatically charged image with an efiective external field remains on the surface of the sheet of insulating material 12. This charged image is a reproduction of the image on the film 21..

Fig. 4 illustrates an alternative method of projecting the image onto the photoconductive layer 11. A source of light 3%) projects light onto an image bearing surface 31 to reflect the image through a lens 32 and through a sheet of transparent or translucent electrostatically charged insulating material 12 onto the photoconductive layer 11. The image bearing surface 31 in this instance need not be made of transparent or translucent material since opaque material serves. to reflect adequately the light to. produce the desired light image. The areas on the photoconductive layer 11 not sufficiently illuminated by light, corresponding to the image on the sheet, 31, remain non-conductive. The remaining portions of the photoconductive layer 11 subjected to. light are rendered conductive to permit. the migration of charges to the under side of the sheet of insulating material 12. Inasmuch as these migrating charges are of opposite polarity with the charges on the outer surface of the sheet of insulating material 12, electric couples in the outline of the light image are formed which render non-effective the external field of the charges subjected to light leaving an effective electrostatically charged image in the outline of the image on the surface 31..

Upon exposure of the photoconductive layer 11 in any of the manners shown in Figs. 2, 3 and 4, an electrostatic latent image, is. produced on the transparent or translucent sheet of insulating material 12. This latent image may be made. visible by sprinkling finely divided powder 35 over the surface of the transparent or translucent material 12 as illustrated in Fig. 5. This powder 35' may be of any type depending upon the type of. finished print desired. Pulverized resins. of many vari-- eties may be used; however, resins which can be. melted or made adhesive. by heating are preferred. The powder 35 passing over the transparent or translucent material 12 is attracted to and adheres. to the sheet of material. in the outline of the electrostaticallycharged image contained on the surface 12.

The sheet of transparent or translucent material 12. 7

now hearing the powdered image, as shown in Fig, 6,, is removed from the photoconductive layer 11 and heated by any of a number of arrangements, such as the radiant heater 49, illustrated in Fig. 7. The heat acts to fix permanently or set the powdered image 37. to the sheet of transparent or translucent material 12 by melting or. rendering the powder adhesive so. that: it is retained on.

the sheet 12. Other means may be. used to secure the.

powder on the sheet, 12. such as by spraying; the pow-- dered image with a. glue, lacquer or fluid adhesive com-- pound.

In Fig. 8. there is illustrated an alternative method of charging the photoconductive. layer 11.. In this. instance, the sheet of, transparent. or translucent material is. not placed in contact. with the. photoconductive layer 11' during the charging operation bythe corona discharge wire 15., The photoconductive layer 11 is charged by reci'pro-- eating the layer 11 and the metallic plate 10 beneath the corona dischargewire 15. This procedure is carried out in a darkened space inorder that the photoconductive layer remains non-conductiveto retainthecharge on-sthe surfaceof the photoconduct-ive layer. e

The next step in this alternative method is to place a sheet of transparent or translucent insulating material onthe surface of the photoconductive layer 11. The film 17 is next placed on the sheet of transparent or translucent insulating material and then the assembled film 117, sheet of insulating material 12, together with the selenium coated metal plate 1% are subjected to a source of light as illustrated in Fig. 2. Upon the light striking the photoconductive layer 11, the lighted surface portions of the layer 11 are discharged through the now conductive portions of the photoconductive layer 11, through the conductive plate 16 and thence to ground 19. There remains on the outer surface of the photoconductive layer 11 an electrostatically charged latent image having a configuration identical with the image on the film 17.

The electrostatic latent image may also be produced on the photoconductive layer 11 by the methods dis- .closed relative to Figs. 3 and 4. The effective electrostatic field of the charged latent image acts through the sheet of transparent or translucent insulating materialto attract the electrostatically attractable powder toform a powdered image of the latent charged image. The visible image is then fixed on this sheet of insulating material by the method disclosed with regard to Fig. 7.

it is to be understood that the above-described methods and arrangements are simply illustrative of the application of the principles of the invention, and that many other modifications may be made without departing fromthe invention.

What is claimed is:

l. A method of electrostatic electrophotographic reproduction of images which comprises electrostatically charging the outer surface of a sheet of insulating material while its under surface is in contact with a photoconducti-ve layer, producing an electrostatic image on said outer surface of said sheet by exposure to a light image, applying electrostatically attractable powder to the charged outer surface of said sheet, removing said sheet from said photocond'uctive layer, and then permanently affixing the powder to said sheet of insulating material.

2. A method of reproducing indicia on a sheet of light transmitting insulating material, which comprises producing an eifective electrostatic field over the entire outer surface of a sheet of light transmitting insulating material, while the inner surface. of said sheet is in contact with a layer of photoconductive material, projecting a light image of the indicia to: be reproduced through said sheet onto said photoconductive layer to neutralize the portions of the electrostatic field subjected to. light, applying" electrostatically attractahle powder to said outer surface of' said sheet to develop a visible powdered image in the area of the remaining effective electrostatic field, separating said sheet. from said layer, and thereafter fix i'rfig' the powdered image tosaid outer surface of said s eet.

3. The method of making a reproduction of an image which comprises: placing a sheet of light transmitting insulating material in contact with a photoconductive layer on an electrically conductive plate, advancing the material, photoconductive layer and electrically conductive plate through an electrostatic field to place anelectrostatic charge on the outer surface of the light transmitting material, subjecting the image to be reproduced to a source of light to form a light image, projecting the light image through the light transmitting material onto the surface of the photoconductive layer to render the lighted portions of the photoconductive layer conductive to produce a charged image on the outer surface of the light transmitting material corresponding to the projected light image, dusting the outer surface of the light transmitting material with afinely divided electrostatically attracta-ble powder to form apowdered image of the. electrostatic image, removing saidv sheet. from said photo'- conductive layer, and then permanently fixing the powder to the sheet of light transmitting material.

4 The method of reproducing a design from a sheet of material: having a design thereon which comprises positioning a sheet of light transmitting insulatingmaterial in contact with a layer of photoconductive material, elect-rostatically' charging the surface of the light transmitting' material, reflecting light off the surface of the design bearing sheet of material to form a light image of the design, projecting the light image through the light transmitting insulating material onto the photeconductive layertorender the portions of the photoconductive layer subjected to light conductive to permit charges to migrate to the under side of the sheet of light transmitting insulating material to neutralize the charge on the outer surface of the light transmitting insulating material in the outline of the design, developing the portions of the photoconductive layer which remain charged by placing electrostatically attractable powder on the said charged portions of the sheet of light transmitting insulating material, separating the sheet of light transmitting insulating material from the photoconductive layer, and permanently fixing the powder to the sheet of light transmitting insulating material.

5. The method of electrostatic electrophotography wherein a sheet of material whose conductivity varies with illumination is placed with one side in contact with a sheet of inert conductive material, a sheet of trans lucent insulating material is placed in contact with the other side of the variable-conductance material, the outer surface of said translucent insulating material is electrostatically charged in the dark by exposing said insulating material to an electrical field produced by a potential of from approximately 5,000 volts to approximately 10,000 volts, an image whose configuration is desired to be reproduced is placed between a potential source of illumination and the three superimposed sheets, the source of illumination is energized to project light rays around the image so that the configuration thereof will appear on the charged outer surface of the translucent insulating material, said light rays passing through the translucent material to the variable-conductance material, thereby increasing the conductivity of the variable-conductance material and causing the charge on the outer surface of the insulating material corresponding to the illuminated areas of the variable-conductance material to be rendered ineffective whereby an electrostatic latent image is formed on the outer surface of the translucent insulating material, applying electrostatically attractable powder to the outer surface of the sheet of translucent insulating material to form a visible powder image thereon, separating the sheets of translucent insulating material and the variable-conductance material from each other, and then permanently fixing the powdered image to the sheet of translucent insulating material.

6. The method of electrostatic electrophotographic reproduction of images which comprises the steps of coating a metallic member with a photoconductive material, placing light transmitting insulating material on said coating of photoconductive material, subjecting the coated metallic member with said light transmitting insulating material thereon to an electrostatic field to place an electrostatic charge on the outer surface of said light transmitting insulating material, causing a light image of the image to be reproduced to be projected on the outer surface of ductive material, dusting the References Cited in the file of this patent UNITED STATES PATENTS

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2756676 *May 4, 1953Jul 31, 1956Haloid CoMethod for the production of electrophotographic prints
US2758524 *Dec 30, 1953Aug 14, 1956Rca CorpElectrostatic photographic printing
US2758525 *Dec 30, 1953Aug 14, 1956Rca CorpElectrostatic photographic printing
US2793135 *Dec 1, 1955May 21, 1957Sperry Rand CorpMethod and apparatus for preparing a latent magnetic image
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Classifications
U.S. Classification430/124.5, 361/229, 430/97, 430/125.31, 101/DIG.370, 430/121.1
International ClassificationG03G15/22
Cooperative ClassificationG03G15/226, Y10S101/37, G03G15/22
European ClassificationG03G15/22, G03G15/22D