US2357809A

US2357809A - Electrophotographic apparatus

Info

Publication number: US2357809A
Application number: US365888A
Authority: US
Inventors: Chester F Carlson
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-11-16
Filing date: 1940-11-16
Publication date: 1944-09-12
Anticipated expiration: 1961-09-12
Also published as: GB679533A

Description

Sept' 12, 1944. c. F. CARLSON 2,357,809

ELEGTRO-PHOTOGRAPHIC APPARATUS vFiled NOV. 16, 1940 k5 Sheets-Sheet l INVENTOR @ME-FM Sept 12, 1944. c. F. cARLlsoN 2,357,809

` ELECTRO PHOTO GRAPHI C APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 2 INVENTOR sim* Sept. 12, 1944.

c. F. CARLSON 2,357,809

ELECTRO-PHOTOGRAPHIC APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 5 'FY'N 9&2

\l&\ m j Q 21@ u QQ 5s N Y x Q N N w kg INVENTOR .Sept 12, 1944. F CARLSON 2,357,809

ELECTRO-PHOTOGRAPHIC APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 4 INVENTOR wim-W Sept. l2, 1944. c. F. CARLSON 2,357,809

ELECTRO-PHOTOGRAPHIC APPARATUS Filed Nov. 16, 1940 5 Sheets-Sheet 5 SHEET INVENTOR @mi CPO/M Patented Sept. 12, 1944 UNITED STATES PATENT OFFICE 2,357,809 ELECTROPHOTOGRAPHIC APPARATUS Chester F. Carlson, Jackson Heights, N. Y.

Application November 16, 1940, Serial No. 365,888

20 Claims.

This invention relates to photographic devices and particularly to devices for use in electrophotography.

An object of the invention is to improve devices for use in electrophotography, particularly electrophoto reproducing and copying equipment.

Another object is to produce an electrophoto copying machine which is substantially automatic in operation.

Further objects are to improve various parts of electrophoto reproducing apparatus.

Other objects of the invention will be apparent from the following description and accompanying drawings taken in connection with the appended claims.

The invention comprises the features of construction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the drawings.

In the drawings:

Figure 1 is a top view of a copying machine embodying features of the present invention, part of the top casing being cut away;

Figure 2 is a vertical section on the line 2-2 of Figure 1;

Figure 3 is a vertical section on the line 3-3 of Figure 2;

Figure 4 is a diagram of the electric circuit for the machine of Figures 1 to 3;

Figure 5 is a vertical section of a modified copying machine according to the invention;

Figure 6 illustrates a circuit therefor;

Figure '7 shows a modified charging device;

Figure 8 illustrates a belt discharge attachment; I

Figure 9 represents a modified transfer mechanism; and

Figures 10 and 11 show special forms of electrophoto plates.

In my co-pending application Serial Number 265,925, led April 4, 1939, now Patent No. 2,297,691 of October 6, 1942, is described a methodl of photography which may be termed electrophotography and which in its preferred embodiment comprises charging the surface of a layer of photo-conductive insulating material supported on a conductive backing with an electric charge, then exposing the layerto a light image to discharge the charge in the illuminated areas and leave an electrostatic latent image on the layer corresponding to the light image. The latent image is subsequently developed by applying finely divided electrostatically attractable material, such as powder, to the surface where it is retained in the charged areas by the charge thereby producing a visible deposited image. The deposited image may then be transferred to a paper sheet.

The present invention relates to the machines and devices for carrying out such a process and contemplates a substantially automatic machine for performing the necessary functions in sequence. The -invention also relates to improved parts and devices for use in the process.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the construction of parts without departing from the spirit of the invention. In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring to the drawings, Figures 1 to 3 illustrate an automatic copying machine for making single copies of original records such as tracings of drawings, films, typewritten letters and generally anything drawn, written or printed on transparent or translucent sheets.

The machine comprises a sheet metal frame including a bottom plate 20 and a pair of spaced parallel side Walls 2| and 22 from which the operating parts are supported.

The photosensitive plate comprising a sheet of metal foil or metallized paper 23 having a layer 24 of photo-conductive insulating material (for example, sulfur or anthracene) adhering to its outside surface is clamped over the outer surface of a metal drum 25 secured to an axial drive shaft 2B which is pivoted in bearings 2'! mounted in the two side walls 2| and 22. Foil 23 extends about one-third of the distance around the drum and is clamped at its ends under metal strips 28 in longitudinal slots in the drum surface.

Drive shaft 26 carries a large gear wheel 29 which is driven by a worm 30 on the shaft of controlled speed electric motor 3l mounted on the outside of side wall 2|. Means are provided for starting and stopping the motor so as to rotate drum 25 through one revolution at a time from the starting position shown, as will be described later. The drum rotates in a clockwise direction as seen in Figure 2.

A roller 32 covered with a brushl or plush cover 33 is mounted on a drive shaft 34 pivoted in bearings 35. the roller being mounted in such a posi.. tion that the plush surface is in contact with the surface of drum 25 in a path extending longitudinal of the drum and is at the leading edge of foil 23 when the drum is in starting position. The surface of drum 25 is of aluminum or chromium or other metal which does not readily produce any loose oxide, sulphide or other dirt, since it is of considerable importance that the operating surfaces be kept clean and particularly free of any loose conductive material.

Plush-covered roller 32 is rapidly driven by a motor 36 mounted on the outside of side wall 2l and coupled to the end of shaft 34. Motor 3S operates whenever motor 3l is operating. Roller 32 is preferably rotated in a clockwise directionas shown in Figure 2. A metal rod 31 is supported from the side walls so as to loosely touch the surface of plush 33 to drain oi any electric charge from the plush.

Immediately to the right of roller 32 as seen in Figure 2 is a paper` feed slot formed by a pair of spaced sheet metal plates 38 and 39 which extend across between side walls 2l and 22 and are nearly vertical. The lower end of plate 33 terminates just short of the surface of drum 25 and plate 38 is somewhat shorter. The plates are curved away from each other at the top of the machine to form a slot into which a sheet may readily be inserted.

A rod 40 is pivoted along the lower edge of plate 39 and has several spring fingers 4l extending out from it to normally press against the lower edge of plate 38, held by bias spring 42 secured to side wall 2l. A cam 43 mounted on shaft 26 co-operates with a cam-following arm 44 on the end of rod 4D to move spring fingers 4| away from plate 38 and release the sheet original to be copied from the slot at the proper stage of rotation of drum 25.

A frame carrying a pair of spaced parallel flanged rollers 46 and 41 upon which is mounted an endless transparent belt 48 is spring-pressed against drum 25 immediately below the feed slot. The frame comprises a pair of end plates 45 clamped in spaced parallel relation by rods 49 upon which rollers 46 and 41 are pivoted. The frame is spring-pressed toward drum 25 by coil springs 50 mounted in side walls 2l and 22 and bearing against bolts secured to the frame plates 45. Beltl 48 is as wide as drum 25 and of such length as to be drawn firmly against the drum surface when rollers 46 and 41 are in contact with the drum. Hence as the drum rotates the transparent belt 48 rolls against the drum surface. The belt may be of cellulose acetate sheet reinforced at the edges with Scotch tape or cemented cloth strips, or it may be a flexible vinyl resin or other transparent flexible sheet material.

Rollers 46 and 41 are spaced apart to leave an opening equal to about one-fourth the circumference of drum 25 or less and a source of illumination is mounted so as to illuminate this opening. This comprises one or more incandescent lamps, such as lamp 52 and a light confining and directing box 54. If desired, a light diffusing screen may be interposed, or belt 48 made translucent to diffuse the light.

A trough 55 containing an electrostaticallyattractable powder 56 and a rotatable brush agitator 51 is mounted underneath drum 25 with the open top of the trough substantially closed by the surface of drum 25 with just sufflcient spacing between the drum and trough edges to provide operating clearance. Brush 51 comprises a central shaft 58 having bristles extending radially from it in all directions. Shaft 58 is pivoted in bearings in the ends of trough and rotated at relatively slow speed by electric gear motor 59 whenever the machine is operated. A metal rod 60 extends longitudinally of trough 55 near the top surface of brush 51 to flip the ends of the bristles as they pass thus throwing dust particles 56 into the air of the trough chamber.

Powder 56 may be manually introduced into trough 55 in small charges through aperture 6l as it becomes depleted. Any of a variety of powders can be used. The powder must be such as to adhere to an electrostatic charge on layer 24 and should be in a finely divided state. Suitable powders are dyed thermoadhesive resins such as rosin, gum copal, gum sandarac, Vinsol, ethyl cellulose, Egyptian asphalt and the like.

A very satisfactory thermoadhesive powder can be produced by dissolving equal parts of ethyl cellulose and Vinsol resin in acetone together with a small amount of spirit soluble aniline dye such as nigrosine or aniline blue and spray-drying the solution to produce an extremely ne powder having substantially spherical particles. Dyed lycopodium powder is suitable where thermoadhesive properties are not required of the powder, as is also starch, cellulose flour, powdered metal and carbon powder.

Whether fusible, thermoadhesive or non-fusible powders or others are used the particle size is preferably near the limit of definition of the eye under ordinary reading conditions. Excessive powder size contributes to graininess in appearance of the image. On the other hand extremely fine powder may be undesirable in many instances due to its tendency to ball up or cling together in clusters and also to the possibility of extremely ne powder particles clinging to the photoconductive layer and interfering with the proper functioning of the layer. It is desirable, therefore, to use a powder in which substantially all the particles are within the size range from 0.1 to 1 mil. If spherical powders are used this refers to their diameter, otherwise to the largest dimension. For most purposes it is preferred to use an equidimensional powder particle, the sphere being the preferred form. A still more limited preferred range of sizes may be given as from 0.3 to 0.8 mil.

A roller mechanism is provided at the left of the drum (as seen in Figure 2) for transferring the powder image from the photo-conductive surface to a sheet of paper or like material. This comprises a pressure roll 62 of yielding material such as rubber or felt and a wetting roller '63 pressing against the under surface of roll '62 and running in a trough of water or other liquid 64. Pressure roll 62 is pivoted on a shaft 65 supported in end arms 66 which are spring pressed by springs 61 toward main drum 25. A pair of cams 68 are mounted on shaft 26 at the ends of the drum 25 and a pair of cam-following disc rollers 69 are pivoted on shaft 65 at the ends of pressure roll 62 and roll upon the cams 68. These cams are so shaped as to hold roll 62 a small fraction of an inch away from the surface of drum 25 during the greater part of the rotation of drum 25 but to allow springs 61 to press roll 62 against the photoconductive surface 24 of plate 23 when it comes opposite the roll.

A paper feed plate 10 is tiltably mounted on pivots 'Il and extends under roll 52 to a position adjacent wetting roll 63. A small guide roller 12 asczsoo 3 is mounted on plate 18 to roll against pressure roll l2.

An electric oven comprising a pair of spaced parallel plate-like heating elements 13 and 14 is mounted above feed plate 1I and generally parallel thereto and extends to a position adjacent the upper edge of pressure roll 62. Suitable paper guides 15 are mounted around roll 62 to guide a sheet oi' paper around the roll from feed-plate 1I to the slot between elements 13 and 14 comprising the oven. The oven serves to melt the resin powder image onto the paper as will later appear.

A rotary cleaning brush 16 is mounted'above the transfer apparatus just described to brush oir any retained dust from the surface of the drum or layer 24, the brush being surrounded by a collecting chamber 11to retain the removed dust. Brush 16 is driven by a belt or chain drive 18 from the shaft 34.

Figure 4 is a diagram of the preferred electric circuit for the machine above described. Electric current from an A. C. source is used to operate motors 3|, 36 and 59 and to energize lamp 52 and heating elements 19 and 80 for heating plates 13 and 14.

A pair of cams 8| and 82 are mounted on the end of shaft 26 of the main drum and control a pair of snap-acting power switches. for example, "Microswitches 83 and 84 respectively having normally-closed contacts which are opened when their control levers are engaged by the cams. Microswitch 83 is connected in series with lamp 52 and the A. C. power line. The cam 8| is arranged to turn olf lamp 52 when the machine is in rest position and to light the lamp during the part of the cycle when electrophoto layer 24 passes in front of the lamp.

A manually-controlled main switch 85 is connected in one branch of the A. C. line between the A. C. source and the motors and heating elements with their associated controls. Heating element 88 is a quick heater for the hot plates 13 and 14 and is connected across the line through I a snap-acting Microswitch 86 controlled by thermostat 81 mounted within the oven. When the oven heats up, the thermostat operates to disconnect element from the line. Heat maintaining element 19 is a slowheater designed to maintain the desired oven temperature once it has been heated up. Element 19 is connected directly across the line.

Cam-controlled Microswitch 84 is connected between the power lineand motors 3|, 36 and 59. A

second energizing circuit for the motors is provided, however, through the back (normallyopen) contacts of thermostat switch 86 and a push-button'switch 88 in series. Cam 82 is arranged to open switch 84 at the rest position of the machine but allows switch 84 to be closed through the rest of the cycle. A snap switch 89 is arranged to by-pass the back contacts of thermostat switch 86 when desired.

Motors 3|, 36 and 59 have rheostats 93. 94 and respectively connected in series with them for adjusting their speeds.

Operation To initiate operation of the machine the operator turns on the current by closing snap switch 85. 'This immediately starts heating elements 19 and 88 to heat plates 13, 14 of the oven to the desired temperature. As soon as this temperature is reached thermostat 81 operates switch 85 to open the circuit of fast heat-up element 80 and close the back contacts of the switch. I'his places the machine under control of push-button switch 8l.

The operator in the mean time places an original sheet 88 to be copied, such as a typewritten letter, a drawing or tracing, a film or any other translucent design in the slot between plates 38, 39 with its lower edge resting on ngers 4| and the written, drawn or printed side facing toward drum 25. 'I'he operator also places a blank sheet of paper 3| on feed plate 18 with its leading edge held between rolls 62 and 12.

The operator now presses push button 88 moentarily, thereby completing energizing circuits for motors 3|, 3-6 and 59, all of which start to rotate. Motor 3| rotates drum 25 slowly in a clockwise direction (as seen in Figure 2) thereby advancing the photoconductive layer 24 under plush roller 32. Roller 32 is rapidly rotated by motor 36 and the frictional rubbing of the plush 33 thereby creates an electrostatic charge of substantial voltage uniformly over the surface of A round brush may be used in place of the plush roller, if desired.

As soon as drum 25 has rotated a few degrees cam 82 is moved out of engagement with switch 84 allowing it to close and thereby establishing a shunt circuit around push-button 88 so that 88 may be released without stopping the machine. At about the same time cam 8| allows switch 83 to close an energizing circuit for lamp 52.

Layer 24 continues to rotate and when its leading edge comes adjacent the lower edge of the sheet 90 the cam 43 engages arm 44 to release f spring lingers 4| and thereby allow sheet 90 to slip down and enter between drum 25 and transparent belt 48 where it passes around roller 46. As the rotation thus continues the charged photoconductive layer 24 is moved past the area illuminated by lamp 52 with original sheet 90 carried along tightly held against its surface by the belt 48, the image side of sheet 90 being in direct contact with layer 24. The layer 24 is thus exposed to illumination from lamp 52 as modied by the image on sheet 90 as they pass together around that part of the drum between rollers 46 and 41. The illuminated areas of layer 24 are thereby rendered suillciently conductive while illuminated to allow the electrostatic charge thereon to drain ofi' to the metal backing 23 through the layer. However, where layer 24 is protected from illumination by the dark lines or letters on sheet 90 the electrostatic charge remains. An electrostatic latent image corresponding to a mirror reverse of the original image is thus produced on layer 24.

As sheet 98 passes out from under belt 48 it separates from the drum and is deposited in the space 92. The layer 24 passes over the top of trough 55 which, at this time, is filled With an atmosphere of floating powder particles due to the agitation created by brush 51 driven by geareddown motor 59. A substantial number of the dust particles are attracted by the charge image and deposit themselves on layer 24 in a visible image. It is probable that the attracted powder particles carry an electric charge of opposite sign to that of the electrostatic latent'image. Since the image produced as herein described is normally negative in charge the deposited powder particles are prob ably positively charged. There are probably also negatively charged particles in the chamber which do not deposit on the image.

The layer 24 carrying its electrostatically attracted powder image is carried around to the transfer position where the dust image is transferred to blank sheet 9|. As the leading edge of layer 24 approaches roller 62 the cams 60 mounted at the ends of drum 25, which have so far held roller 62 out of contact with the drum, allow roller 62 to come into pressure contact with the drum and be driven thereby. As roller 62 starts to rotate it moves the leading edge of blank sheet 9| around against wetting roller 63 and up into contact with drum 25. The surface of sheet 9| is thereby wetted and as it rolls between roll 62 and layer 24 the wet surface is pressed against and picks up the powder image from layer 24.

Sheet 9|, due to the expansion of its wet surface and due to guides l5 curls away from layer 24 as soon as it emerges from between roller 62 and the drum. The sheet, carrying the adhering dust image, passes between hot plates 73 and 14. Since these are, at this time, heated to the melting point, or at last the thermoadhesive point, of powder 56 the paper is rapidly dried out and the powder image melted onto the sheet. The operator can then remove the copy from the machine by grasping the free edge of sheet i where it projects from the upper edge of the slot between plates 13 and 14.

As layer 24 continues its rotation any slight moisture lm adhering to it after the transfer rapidly evaporates and any remaining dust is cleaned from its surface by rotating cleaning brush 16. When one revolution of drum 25 has been completed cam 82 opens switch 64 to stop the rotation of all the parts. Cam 8| has opened the circuit for lamp 52 as soon as it completed its function.

If a thermoadhesive powder, such as a resin, is used a sheet of ordinary paper 9| can be used for receiving the copy, such as a sheet of bond paper, Manilla paper, newsprint paper, calendered paper, or almost any other type. The image can also be transferred to a sheet already carrying writing or printing, such as a letterhead or other insignia, rulings or the like. If a non-thermoadhesive powder is used it is necessary to use a sheet 9| having a thermoadhesive coating already applied thereto such as ethyl cellulose, hard wax or a resin. In either case the finished copy will be a full size positive copy of the original.

Figure illustrates, in section, the essential parts of a modified photographic copying machine embodying a. camera having a lens for focussing the image to be copied onto the photoconductive layer. Such a machine is capable not only of copying the translucent matter previously mentioned but also visual intelligence on opaque sheets or on sheets having printing on both faces so as to interfere with copying by the contact method.

Figure 6 is a diagram of a circuit for the machine of Figure 5. Referring to Figures 5 and 6, the layer of photoconductive insulating material |00 is deposited on an endless conductive belt |0| of flexible material such as steel or other metal, or paper or other organic material having a metal or other conductive surface applied thereto by metal spraying, cathode sputtering, electroplating or chemical reduction methods prior to deposition of the photoconductive layer. Layer |00 may cover the entire outside surface of the belt or may cover only a limited area as shown. Belt |0| runs on two spaced drums |02 and |03 and has sprocket holes along its edges which mesh with sprockets |04 on drum |02.

Drum |02 and brushes |05 and |06 are driven by suitable motors '|00 and H0 respectively in a clockwise manner similar to that described for Figures 1 to 4.

A pair of dusting chambers or troughs and i I2 are mounted underneath drum |03 with their open tops close to the surface of belt |0| and are provided with powder agitating rotary brushes H3 and H4 of the type previously described. Brush ||3 is connected to the shaft of a geared down electric motor i5 and brush I |4 to a similar motor ||6. Manually controlled switches lll and ||8 are adapted to connect either or both motors to the energizing circuit to thereby render either or both dusting chambers operative. Similar dusting powders ||9 may be in each chamber or two powders may be used of differing color or other characteristics. Switches ||l and H8 thereby enable selection for deposition of powders of different colors or other characteristics at the will of the operator.

The gear ratio between gears |20 and |2| is the same as the ratio between the circumference of drum |02 and the length of belt 80| (such as 1:2) so that cam |22 is carried through one complete revolution during one completercycle of rotation of belt |0|.

Shaft |39, to which one (or both) gears |2| is secured carries a pair of switch actuating cams |40 and |4| for controlling switches for the drive motors.

A camera is provided to the right of the mechanism (as shown) comprising a plate |30 supporting the sheet |3| carrying the printing, writing, drawing, or pictorial matter to be copied. Lamps |32 and |33 for illuminating the face of the sheet are suitably disposed in front of it near opposite edges and reflectors |35 aid in confining and directing the light.

If desired plate |30 may be translucent and another lamp |34 may be disposed at an appropriate distance behind plate |30 and used supplementary to lamps |32 and|33 where translucent sheet material is to be copied. This results in illumination from the front and back at the same time thus enabling more rapid exposures.

Lamps |32 and |33 (and |34 when used) are under the joint control of cams |40 and |4| and a timing cam |42 driven by an electric clock motor |43. The circuit, insofar as it differs from that of Figure 4 will be apparent from reference to Figure 6 and from the following description of the operation of the mechanism of Figures 5 and 6.

Cam plate |42 is removable and can be replaced by other cams to give different exposure periods.

Figure 7 shows a modified form of charging brush for the photoconductive layer. This comprises a belt |60 running on a drive roller |6| and an idler roll |62 and having an outer plush surface |63 rubbing against the surface of photoconductive layer |64. Surface |63 may be plush, fur, wool, woven or knit cotton, wool, silk or rayon fabric, felt, hair, velvet or other suitable charging material. A metal rod |65 may be mounted so as to just touch the surface |63 to drain olf accumulated charges.

Figure 8 shows an improvement applicable to the machine of Figures 1 to 4 and comprises a felt wick |10 dipping in a container |1I of Water and lightly pressing against transparent belt 48 which serves to hold the sheet original against the drum. Wick |10 extends for the full belt width and performs the function of discharging any static charge which may be present on the belt and which might, in some cases, interfere with the proper discharge of the photoconductive layer. The amount of moisture picked up by the belt from wick |10 is so slight that the belt dries almost instantly.

Figure 9 illustrates a modied powder image transfer mechanism and comprises a pressure roll preferably felt covered, a heater plate |8|, and oven |82. Plate |8| may comprise chromium-plated copper having embedded insulated heating wires |83. The blank paper sheet |84 is fed between plate |8| and roller |80 and is advanced by roller |80 in co-operatlon with idler roll |85 mounted in an aperture in plate |8I. As sheet |84 is advanced to a position to engage the surface of photoconductive layer |86 carrying the electrostatically deposited resin dust image its surface is heated by plate |8| to a temperature Within the thermosoftening range of the dust image. When paper sheet |84 is rolled against layer |86, therefore, it is hot enough to melt onto itself the resin dust particles thereby transferring the image to the paper. Due to the rapidity with which the operation is performed, however, layer |86 and its supporting metal base remain relatively cold and hence the powder does not stick to the layer |86 when it is tnus heated. The heat-softened or semi-melted resin does not adhere to the cold surface although it sticks readily to the hot paper. It may be that the adhesion will be sufficient so that iurtner nxing is not required. In such event oven |82 can be eliminated from the device or need not vbe used. It is also possible, in this as well as the other transfer mechanisms to leave off the top half of the oven so that the melting of the resin onto the sheet may be more readily observed. Or a glass cover may be substituted for the top half of the oven.

It may be that for some copying work it will be desired to use a standard form which will appear on all copies in addition to certain matter which will be different on different copies. Such a form may comprise a letterhead, for example, or a trade-mark or possibly special rulings to block off different columns or parts of the photographically copied matter. For this purpose a specially prepared photoconductive plate |90 may be used comprising a metal foil base |9| having a layer |92 of photoconductive insulating material such as anthracene deposited thereon as shown in Figure 10. The standard form to be reproduced is applied to the surface of layer |92 as an adhering layer of insulating material |93 such as resin, shellac or other charge-holding material conforming to the design or form in mirror-reverse. Layer |93 may be applied by printing, stamping, stencilling, drawing or by the photographic process herein described. In the photographic process, the plate |9| carrying layer |92 is charged in the usual way, exposed to the image of the form to be applied and dusted with resin powder. However, instead of transferring the powder image, it is left on the layer and the layer is heated to melt the resin into the surface of layer |92, thereby producing the completed plate.

In whatever way the plate is made it functions in the following y manner when used. The charging brush applies an electrostatic charge not only to layer |92 but also to layer |93 constituting the form. Upon exposure to alight image an electrostatic latent image is produced on the exposed areas of layer |92 as before but in addition the electric charge remains on the letters and other designs comprising layer |93 since these areas are not photoconductive. Thus when the layer is dusted the form will attract the dust as well as the photographic electrostatic latent image present on the other areas. The sheet to which the dust image is transferred will therefore receive the form as well as the photographic part of the image.

The processes and apparatus of the present invention are also adaptable to the production of master plates from which a large number of copies may be rapidly reproduced.

According to one method of preparing a lithographic master plate a conventional lithographie sheet of prepared aluminum, zinc or of paperlike composition, such as the Duplimat sheets produced for use on Multilith machines, is used in place of paper sheet 9| to receive the transfer of the resin powder image from the photoconductive layer. The resin is melted onto the litho sheet to complete the master suitable foroffset press operation. According to another method of producing either a lithographie or hectograph master an electrophoto plate may be used having a metal foil backing and a photoconductive coating of anthracene or other heat volatile photoconductive material. Ari electrostatic 1atent image is produced as previously described and the layer is dusted with a resin powder. However, instead of transferring the powder image the plate is removed from the machine and heated to evaporate the anthracene. The resin may melt before or after the anthracene is dispersed, depending upon its melting point, but in any event it is desired to nally heat the plate suiciently to melt the resin onto it. The result is a master plate such as shown in Figure 11 comprising a metal foil base 20|) having a resin image 29| melted thereon.

If the master plate is to be used for lithographic reproduction base 209 should be an aluminum or zinc plate prepared for lithography and the resin should be of a type adapted to attract lithographie ink. This is true of most resins, such as rosin. Vinsol, copal and sandarac. If desired, powdered lithographie crayon can be used, or a mixture of equal parts crayon and one of the resins mentioned melted together. If the plate is to be used in the oilset process the image should not be a mirror reverse, but a direct image.

If the plate is to be used for spirit duplication the resin should be at least slightly soluble in alcohol or the other spirits to be used and should contain a high concentration of spirit soluble dye. Copies are made by rolling or pressing paper sheets moistened with the spirits against the plate to dissolve off a little of the dye each time and thus produce a copy.

A further multi-copy method is also possible with this plate. The resin being an insulator it can be electrically charged to pick up dust particles and hence if the plate is placed in the machine of Figures 1 to 3 and the machine operated copies can be produced. If this plate is used the exposure step is, of course, eliminated and lamp 52 as well as the transparent belt and its supports can be removed from the machine,

or temporarily withdrawn from operation as they are unnecessary.

It is also contemplated that plates of the type shown in Figure l1 can be made by other methods for use in the machine of Figures 1 to 3 in the manner described above.

Since the operation of the photographic process described herein depends upon an electrostatic charge upon the photoconductive layer it might be assumed that high atmospheric humidity would deleteriously affect the operation of the process. However, I have not found this to be the case, perhaps due to the non-hygroscopic nature of the photoconductive materials used. For extreme humidity conditions it may be desirable, however, to include in the copying machines, at strategically located positions, electric heating elements for slightly heating the machine parts to disperse any surface moisture. For example, heaters may be located within the shell of the drum (or drums) against which the metal sheet carrying the photoconductive layer is held.

It is also contemplated that in some cases the dusting can be improved by charging the electroscopic powder from an 4outside source. For example, the dusting chamber 55 and its associated parts may be insulated from the rest of the machine and connected to the positive terminal of a high voltage source such as a transformerrectifier circuit, or an electrostatic generator. This will place a positive charge upon a larger proportion of the dust particles so that they will more readily deposit upon the negative charge image. y

The charge applied to the photoconductive layer by brush or plush 33 may also be enhanced by connecting the negative terminal of a high voltage source to rod 3l, which rod in this case should be insulated from the rest of the machine.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material, means for charging said layer, means for projecting a iight image onto said layer,

means for bringing a iinely-divided material ad jacent said layerl and means for transferring said material from said layer to an image-receptive surface, said means being adapted to cooperate with said layer in the sequence named.

2. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material, means for charging said layer, means for projecting a light image onto said layer, means for bringing a finely-divided material adjacent said layer, and means for transferring said material from said layer to an image-receptive surface, and means for bringing said electrophoto plate into co-operative relation with said means in sequence.

3. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material, a charging device for placing an electrostatic charge on said layer, an illuminating device for projecting a light image onto said layer, a dusting device for dusting said layer with a powder, a transfer device for transferring powder from said layer to a receiving sheet, and means to move said plate into co-operative relation with said charging device, said illuminating device, said dusting device and said transfer device in sequence.

4. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material, means for applying an electrostatic charge image to said layer, means for subsequently dusting said layer with powder, and means for then transferring dust adhering to said layer to a flexible sheet.

5. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material, means for applying an electrostatic charge image to said layer, means for subsequently dusting said layer with powder, and means for then transferring dust adhering to said layer to a flexible sheet, and means for subsequently fixing said powder permanently to said sheet.

6. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material and means for moving said plate through a series of positions in sequence in a path parallel to its own surface, a frictional charging member for electrostatically charging said layer by friction in the first of said positions, light image projecting means for projecting a light image onto said layer in the second of said positions, a dusting device for dusting said layer in the third of said positions, and transfer means for pressing a, dust receiving sheet against said layer in the fourth of said positions.

7. An electrophotographic copying machine comprising, in combination, a drum, an electrophoto plate comprising a layer of photoconductive insulating material secured to the outer surface thereof, means for rotating said drum, a frictional charging brush in contact with the surface of said drum and means for rotating said brush to charge said layer, means for guiding an image-carrying sheet against the surface of said layer and means for illuminating said layer through said sheet, a dusting chamber having an opening adjacent said drum and means for producing a dust atmosphere in said chamber for dusting said layer, and transfer means including a roller for rolling a transfer sheet against said layer to transfer transfer sheet.

I 8. An electrophotographic camera comprising a belt having a layer of photoconductive insulating material thereon, guiding and driving means for moving said belt along in a direction substantially parallel to its own surface, a frictional charging brush in contact with the surface of said belt and means for rotating said brush to charge said layer, a lens, said guiding and driving means guiding said belt in front of said lens and being adapted to temporarily halt the forward motion of said belt for exposure to an image projected by said lens, a dusting chamber having an opening adjacent the surface of said belt for dusting said layer and transfer means including a roller for rolling a transfer sheet against said layer to transfer dust from said layer to said transfer sheet.

9. In combination, an electrophoto plate comprising a layer of photoconductive insulating material, and means for electrostatically charging said layer preparatory to photographic exposure thereof comprising a rotary brush, means for rotating said brush, and means for simultaneously moving said plate and brush relative to each other to bring all parts of said layer into frictional engagement with said brush.

10. In combination, means for moving a layer carrying an electrostatic charge image in a path parallel to its surface, and means for dusting the surface of said layer with electroscopic powders comprising a plurality of dust chambers having openings therein adjacent the path of travel of said surface, means individual to each of said chambers for agitating dust in said chambers, and means for selectively operating said agitating means.

11. An electrophotographic copying machine comprising in combination, an electrophoto plate comprising a layer of photoconductive insulating material and means for moving said plate through a series of positions in sequence in a path parallel dust from said layer to said to its own surface, a frictional charging member for electrostatically charging said layer by friction in the first of said positions, light image projecting means for projecting a light image onto said layer in the second of said positions, a dusting device for dusting said layer in the third of said positions, transfer means for pressing a dust receiving sheet against said layer in the fourth of said positions, and plate cleaning means to clean off residual dust on said plate in the fth of said positions.

12. An electrophotographic copying machine comprising, in combination, an electrophoto plate having a bare layer of photoconductive insulating material on its surface, a frictional charging brush, means for bringing said brush into frictional contact with said layer to charge said layer, and a conductor in contact with said brush to drain oi accumulated charges thereon.

13. An electrophotographic copying machine comprising, in combination. an electrophoto plate having a bare layer of photoconductive insulating material on its surface, means for charging said layer and means for subsequently rolling a master sheet to be copied against said layer and illuminating said layer through said master sheet, said rolling means including alight transmitting pressure applying layer.

14. An electrophotographic copying machine comprising, in combination, an electrophoto plate having a bare layer of photoconductive insulating ing said layer in sequence and means fox` transferrng the dust therefrom to a transfer sheet, and a heating element adjacent to said electrophoto plate to disperse moisture from the surface of said layer.

16. A device for transferring a configuration of thermoadhesive dust particles from a surface to a sheetcomprising, in combination, a body having a surface carrying a design of looselyadhering dust particles, a roller for rolling said sheet against said surface and a heater for preheating said sheet prior to its contact with said surface, said heater having a heated surface for pressing against the dust-engaging face of said sheet.

17. A device for transferring a configuration of dust particles from a surface to a sheet comprising, in combination, a body having a surface carrying a design of loosely adhering dust particles, a roller for rolling a sheet against said surface and means for wetting the dust receiving side of said sheet prior to its contact with said surface.

18. A device for transferring a configuration of thermo-adhesive dust particles from a surface to a sheet comprising, in combination, a body having a surface carrying a design of loosely adhering dust particles, a roller for rolling a sheet against said surface and means for pre-heating said sheet prior to its contact with said surface.

19. An electrophoto plate comprising a conductive layer, a layer of photoconductive insulating material adhering to the surface thereof and a design permanently adhering to the surface of said photoconductive layer, said design being formed of insulating material.

20. An electrophoto plate comprising a conductive backing sheet, a coating of photoconductive insulating material on said sheet and e. design of insulating material on said photoconductive coating, whereby an electrostatic latent image may be produced on said plate comprising portions formed by the electrostatic charge on said insulating material design and other portions formed by modication of the electrostatic charge condition of said photoconductive coating resulting from exposure to an optical image.

CHESTER F. CARLSON.