US2955938A

US2955938A - Xerography

Info

Publication number: US2955938A
Application number: US525496A
Authority: US
Inventors: Frank A Steinhilper
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1955-08-01
Filing date: 1955-08-01
Publication date: 1960-10-11
Anticipated expiration: 1977-10-11

Description

Oct. 11, 1960 F. A. STEINHILPER Filed Aug. 1, 1955 21- NEGATIVE HIGH VOLTAGE SOURCE 17 2 25 12 9 16 i zs C POSITIVE HIGH VOLTAGE 22 SOURCE ZZ\ POSITIVE HIGH VOLTAGE SOURCE NEGAT|VE HIGH VOLTAGE 50 U RC E 2 Sheets-Sheet 1 mzzzzmd INVENTOR. FRANK A. STEINHILPER Arrmr Oct. 11, 1960 F. A. STEINHILPER 2,955,938

XEROGRAPHY Filed Aug. 1, 1955 2 Sheets-Sheet 2 NEGATIVE f2] POSITIVE NEGATIVE -21 POSITIVE HIGH VOLTAGE 2 HIGH VOLTAGE HIGH VOLTAGE 22 HIGH VOLTAGE SOURCE SOURCE SOURCE SOURCE L 1/ 10 3a +Hux++++ WWW J l .L 5'7 .i. 37

N EGATIVE HIGH VOLTAGE SOU RC E \5;

66, POSITIVE HIGH VOLTAGE SOURCE A NEGKAST'LVE POSITIVE HIGHVOLTAGE T GE 0 wz becz SOURCE -75 FIXING STATION POWDER C LOUD \9/ GENERATOR y- 9 INVENTOR.

FRANK A. STEINHILPER ATTORNEY United States 2,955,935 XEROGR'APHY Frank A. Steinhilper, Rochester, N.Y., assignor to Haloid Xerox'Inc a corporation of New York Filed Aug. 1', i955, Ser. N6. 35,496- 6 Claims. (11, 96-'-1) This invention relates to xerogr'aphy. M in terography, it is usual to form an electrostatic charge pattern on the surface of a Xerographic plate composed of a photoconductive insulating layer on a conductive backing member. The pattern is formed by first sensitizing the plate by placing an electrostatic charge on the surface of the photoconductive insulating layer.- While in a serisitized condition, the plateis exposed to anactivating radiationpattern such as a light image or the like. The activating energy such as light causes dissipation of charge whereas areas not affected by exposure, i.e.- areas for egran ple not struck by light remain in their charged condition Thus, after exposure to a pattern of activating riadialtioman electrostatic image of electrostatic charges I e itists on the surface of the xerographic plate; This pattern inay be developed or otherwise utilized; If develeped, usual grerographic development techniques such as eascade or powder cloud development may be used to make the electrostatic image pattern visible. A developed imageon the plate surface may be viewed, photographed or the like or may be transferred to a transfer base where it may be permanently afiix'ed.

Charging to about 100 to 800 volts or sensitization of the photoconductive insulating layer ofthe xerographic plate, is generally accomplished through the deposition ions created by a corona discharge electrode moving at a uniform rate above the plate surface.- The ions deposit due to the electrostatic fields of force; which exist between the corona electrode and the backing member of theplate which is held at a grounded potential;

It has nowbeen found that the art of xerography may be extended through the use of a photoconductive insulating layer which is not on a conductive support base, Speeiiically, iterography carried out in this invention using plates comprising photoconductive insulating layers on insulating support bases and also self supporting films of photoconductive insulating material. It is therefore an object of this inventionto devise a xa-agtaphic plate comprising a photoconductive insulating layer on an insulating support base;

It is a further object of this invention to devise n'ovel methods of applying auniform electrostatic field through a photoconductive insulating layer.

is a still further object of this invention to'devise novel methods of sensitizing a self-supporting film "of photoconductive insulating material;

It is yet another object of this invention to devise novel methods of sensitizing a photoconductive insulating layer backed by an insulating layer. a

It is another object of this invention to devise novel methods of image formation in the art of nerography. I

It is a further object of this invention to devise methods of xro'g'raphy image formation on a Xerograpliic plate comprising a photocon'ductive insulating layer hot Bagged by a conductive backing layer.

elt is a still further objectof this invention -to devise hovel methods of xei'dgra'plii'c image formation on the Patent C) "ice Patented- Oct; 11-, 1960 2. surface of a photo'conductive' insulating layer on an insulating support base. I

It is a further object of this invention to" devise new means and apparatus in the art of xerography.

It is still further an object of this invention to devise an automatic xerographic machine using a plate" nre'mb'er comprising a photo'conductive insulating layer on an insula'ting support base.

In the drawing:

Fig. 1 is a transverse sectional view of an embodiment of a xerographic plate comprising a photoconductive insulating layer supported ori an insulating support base;

Fig. 2' is a transverse sectional view of an embodiment of a xerographic plate comprising a self-supporting film of photoconductive insulating material;

Fig. 3 is a diagrammatic representation of anernbodiment of a first charging step of the xerographic plate illustrated in Fig. -1;

Fig. 4 is a diagrammatic representation of an embodiment of the second charging step following charging as illustrated in Fig. 3 to create a sensitive plate;

Fig. 5 illustrates exposure of a sensitive plate;

Fig. 6 is a flow step illustrating development of an electrostati'e image b'earin'g plate;

Fig: 7 is a diagrammatic illustration of another embodiment of the first charging step of either the plate illustrated in Fig; 1 or the plate illustrated in Fig. 2; Fig. 8 is a diagrammatic illustration of another embodiment of the second charging step following charging as illustrated in Fig. 7 resulting in a sensitive plate ac;- cording to this invention;

Fig. 9 is an embodiment of an automatic machine according to this invention;

For a better understanding of this invention, together with other further objects thereof, reference is now had to the following description taken in connection with the accompanying drawings, and the scope of the invention will be pointed out in the appended claiins.

Referring now to the drawings, in Figure 1 there is innstrated one embodiment of a plate to' which this invention is directed; The plate is composed of a photocoiiducftive insulating layer 12, overlying a support member 11 of iiisulating material: The photocoriductive insulating layer 12 may be any of a number of materials, as for example, amorphous or vitreous selenium, anthracene, sulphur, tellurium, various mixtures of these materials or photooiiductive insulating materials in insulating binders as for examplezine oxide in a resin binder. Other photoconduetive insulating materials include, but are in no way limited to, zinc=magnesiuni oxide, zinc sulfide, zinc cadrnium sulfide, cadmium sulfide, cadmium strontium suifide, zinc silicate, calcium tungstate, slenides an'd iiiiied selepides of cadmium and zinc, anthracene, titanium di-'- oxide, and the like. These materials are, in some iiistances, coated directly on the surface and in other instances they are coated in a resin binder on the surface of the material. Desirably, they are activated with small amounts, that is 001% to '0;001% of metallic impurities, as is well known to those skilled in the art. I

I The base member 11 is composed of insulating mate'- rial whether rigid or flitible and desirably comprises a layer of equal thickness throughout having smooth surfaces. Materials which may be used are mica, plastics, glass, rubber, insulating cloth materials and other insal ating materials generally known to the art. Photocom ductive insulating layer 12 may be placed on insii "ting support member 11, using conventional coating techniques such as dipping, spray coating, evaporation, casting or the lilge.

In Fig; 2 there is illustrated a plate comprising a selfsupporting film of photoconductive insulating material 10. The photoconductive material may comprise any of the various material described in connection with Fig. 1. These materials are in some instances prepared immediately as a self-supporting film, whereas in other instances they are coated on a surface and then stripped from the surface. One which is presently preferred has been made using the stripping technique by forming a layer of zinc oxide in a resin binder on a polyethylene coated surface and then stripping it therefrom. Desirably, the self-supporting film is uniform in thickness throughout and has smooth surfaces.

In Fig. 3 there is illustrated an embodiment of the first step of plate sensitization according to this invention. The plate composed of photoconductive insulating layer 12 overlying insulating backing member 11, is passed between

corona electrodes

13 and 15 in a direction as illustrated by the arrow. Positioned in close proximity to corona electrode 13 are lamps 23. The lamps 23 are illuminated during charging. Although in this embodiment lamps are illustrated, any form of uniform radiation may be used as for example a beta source or the like and such modifications are intended to be included herein. Corona electrode 13 comprises corona discharge Wire or wires 16 surrounded by shield 17 held at a ground potential. The corona discharge wire or wires 16 are biased to a negative high voltage which is supplied from negative high voltage source 21. Corona discharge electrode 15 comprises shield 20 held at ground potential and corona discharge wire or wires 18. Corona discharge electrode 15 is biased to a positive high voltage which is supplied from positive high voltage source 22 to corona discharge wire or wires 18. The positive high voltage on corona wire or wires 18 of corona electrode 15 supplies positive ions to the exposed surface of support member 11 whereas the negative potential applied to the discharge wire or wires 16 of corona electrode 13 creates negative ions for deposition on the photoconductive insulating layer 12. Since the photoconductive insulating layer is illuminated by lamps 23, this layer is conductive and thus the negative ions which reach the surface of photoconductive insulating layer 12 are drawn through the layer to the interlayer area between photoconductive insulating layer 12 and insulating support member 11. The negative charges 26 deposit at the interlayer area, it is believed, due to electrostatic fields created by the combined effect of the positive ions sprayed by corona electrode 15, some of which deposit as positive charges 25 on the surfaces of insulating support member 11, and the positively biased corona electrode 15.

In Fig. 4 there is illustrated an embodiment of the next step in sensitizing a photoconductive layer when such a layer is supported on an insulating base. In this figure as in Fig. 3, the plate composed of photoconductive insulating layer 12 overlying insulating support base 11 is again passed between

corona electrodes

13 and 15. As in the previous figure corona electrode 13 comprises a grounded shield 17 and a corona discharge wire or corona discharge wires 16 and corona discharge electrode 15 comprises a grounded shield 20 and a corona discharge wire or corona discharge wires 18. Corona discharge wire or wires 16 of corona electrode 13 are now connected to the positive voltage source 22 and thus spray positive ions whereas corona discharge wire or wires 18 of corona electrode 15 are now connected to the negative high voltage source 21 and thus corona discharge electrode 15 sprays negative ions. The plate is being moved in this figure from left to right as is illustrated by the arrow and thus the left portion of the plate has not as yet passed between

corona discharge electrodes

13 and 15. Those portions of the plate not yet exposed to the charging mechanism carry negative charges 26 at the interlayer area and positive charges 25 on the exposed side of the insulating support member 11. Negative charges 26 and positive charges 25 were deposited during the charging operation discussed in connection with Fig. 3. Those portions of the plate exposed to the charging mechanism of this figure carry positive charges 27 from the positive sprayed corona discharge electrode 13 on the upper surface of the photoconductive insulating layer 12 whereas the charges on the exposed or lower surface of the insulating support base 11 are neutralized by the negative spraying corona discharge electrode 15 which deposits negative charges in an amount equal to the positive charges which were deposited during the operation illustrated in Fig. 3, and the negative and positive charges 28 on the exposed or lower surface of the insulating support member 11 combine and neutralize each other. Thus, there is created, following the two charging operations shown in Figs. 3 and 4, a layer of charge 26 at the interlayer area and a layer of charge 27 on the exposed surface of the photoconductive insulating layer 12. An electrostatic field exists between charges 26 and charges 27. This field would normally draw the charges to one another. However, charges remain bound in place due to the insulating characteristics of photoconductive insulating layer 12 while the layer is kept in darkness.

In Fig. 5 there is illustrated exposure of a sensitized xerographic plate composed of a photoconductive insulating layer 12 overlying an insulating support base 11. However, it is to be realized that the plate used during exposure in this figure is for illustrative purposes only and that the self-supporting film of photoconductive insulating material may be used as well. Just prior to exposure a layer of charge 26 exists at the interface between the photoconductive insulating layer 12 and support base 11 and a layer of charge 27 exists throughout the top turface of photoconductive insulating layer 12. During exposure, areas of photoconductive insulating layer 12 struck by light, become conductive and in those areas the bound charges of charged layer 27 and of charged layer 26 becomes unbound and migrate toward one another to become neutralized or dissipated resulting in discharged areas 33. There is illustrated in this figure the projection of the light pattern of copy 36* which is illuminated by lamps 31. The light pattern is projected through lens 32 to the surface of photoconductive insulating layer 12. It is to be realized that although projection exposure is illustrated in this figure there is no intent to be limited thereto, instead it is intended that the various means of exposure known to those in the art as for example contact exposure or the like may be used and are intended to be included herein. It is also to be realized that although exposure only to a light pattern is shown, there is intended to be included herein exposure to all forms of activating radiation as for example X-rays or the like.

The time of exposure will depend on various factors such as the intensity of the lamps, whether contact exposure or projection exposure is being used, the potential of charge on the xerographic plate, the speed of the photoconductive insulating layer 12, and the like. Depending on the various combinations of elements used, exposure may vary from a fraction of a second to many minutes and there is no intent in this application to be limited to any particular time of exposure.

It is also to be realized that when the backing member or the support layer is transparent, exposure may be made through the backing member instead of directly to photoconductive insulating layer 12. It is also to be realized that depending on the particular material and characteristics of photoconductive insulating layer 12, if the backing member is transparent reflex exposure is also possible and is intended to be included herein.

Reference is now had to Fig. 6 wherein is illustrated one technique of development of charged patterns. The xerographic plate being developed is composed of a photoconductive insulating layer 12 overlying an insulating backing support 11. However, it is to be realized that the particular plate is included for illustrative purposes only and development may be carried out in a similar fashion with self-supporting films of photoconductive instrains material; The technique of sevens Y trated ....fi re is en a ly owain. 495, as cad s' s'l em: vT s. o m a v op iit nd ya us developing materials are described in Wise U.S. ifat n't asis s sz Walkup and Wise s. Patent 2';6'38;41 6,' Walkup Us. Patent 2,618,551 and various 9 er 'atents'. I Cascade type of developer comprises finerp'articlesadhering, due to electrostatic attraction, to er-awe... a In this' figure there is illustrated a developing tray 35 w h a plateagainst the bottom thereof. The developer illustrated-as cascading across the surface of the which carries the electrostatic charge pattern and ge development takes place through depositing of the fin Y particles on the charged area of photoconductive insul ing layer 12. Generally it is desirable whenusing e development to cascade the particles back and across the surface a few times to assure dense dea Since areas as yet undeveloped which carry are sensitive' to light, it is desirable to carry out pnient in the dark. This may he accomplished in tray sirnilar-to tray 35 by placing a shield or dark v acrossthe open area of the tray following positioning of the plate in darkness against the base thereof. Other means that keep the plate in darkness are intended to be included herein. v V r k p h Although cascade development of the image is ilrustrated there is no intent to be limited thereto insteadit is intended that the various means of development known if those in the art maybe used. For example, a techniknown as powderclouddeveloprnent is describ ed in pa 2,221,776 and could be used to develop charge p t rnsforrned according to this invention. It is also to realized that development techniques otherthan those illustrated which are known to those in the are also intended. to be included herein as for example magnetic development or the like. p

n Figs. 7 and 8 there is, illustrated anotherembodiinent of sensitization of a plate according to this inventicn. In these figures a plate comprising a self-supporting filrn' of photoconductive insulating material 10 is positioncd on a conductive grounded electrode 37., A corona electrode comprising a grounded conductive shield 42 and a corona wire or wires 43 is positioned over the plate surface and theplate is moved in the direction of .the arrow. the first charging pass as is illustrated in Fig. 7 alanip 40 .is illuminated thus making the photoconducinsulating layer 10 conductive. In Fig, 7 switch 41 cdrinects corona discharge wireor wires 43 of corona discharge electrode 44 to positive high voltage source 22 a thus there is deposited positive charges 38 at the lower surface of photoconductive insulating layer 10. Ihe negative high voltage source-21 may be connected thropgh switch 4l to the corona discharge wire or wires but is not -soconnected in Fig. 7. Following positive electrostatic charging of the plate switch 41 is thrown to position illustrated in Fig. 8 negative highvoltage is sprayed from corona discharge electrode 44 supplied with negative high voltage to corona discharge wire or ires43 of the discharge electrode from source 21 through 41. Thus, in the second pass of the electrode over the surface, there is sprayed negative corona to the surface of the photoconductive insulating layer 16 positioned on conductive grounded electrode 37. The plate in Fig. 8 is moved, in the direction indicated by the arrow and the shield 42 is again grounded. Following passage of corona discharge electrode 44 as indicated in Figs. 7 and 8 there is deposited a layer of negative charge 45 on the uppersurface ofphotoconductive insulating layer 10 and a layer of positive charge 38 atthe lower surface of photoconductive insulating layer l0. There is thus created a sensitive xerographic plate which is ready forexposure and then development as discussed in connection with lfl' andfi- .7.

Optionally, and in accordance with this invention devloprnent of the image maybe or ni tted andin 4 electrostatic charge pattern may be usedfor irn g fo altion as" for example by scanning; transfer; or the like" as is well known the art. c i H H I j v Although the plate used in Figs. 7 and 8 co self-supporting film of photoco'n'ductiye n 1 I rial, it is to be realized that the particular platehasl been used for illustrative purposes only. plate illustrated in Fig. 1 comprising a photoconductive' insulating la r on an insulating layer may also usedi whenchargl is carried out as is illustratedin fig. 7 using a platej co j prising a photoconductive insulating layer on an insu'l support base the positive charges sprayed to: the p e will deposit at the interface of the photoconductivellnsulating layer and the insulating 'support base. charge is sprayed as illustrated in Fig; 8, negative charges will deposit on the surface of the photoconductiveinsulat: ing layer resultingin a charge sensitive xerographic plate similar to the charged plate created renewing charging in When using the plate illustratedin Figs, 7 andfi charg ing in Fig. 7 results charge deposition at the ldwer surface of the self-supporting film 10. The charges rernain in position on the plate and not travel to electrode 37 y due to a minute air gap which will separate ute o from electrode 37 when these elements are in normal surface contact. This air gap provides a suflici tinsulating. dielectric layer-to prevent charge; transfer dissipation. By preventing charge movement to' the el trode, the air gap .or other gas gap aids creating the surface charge desired at the lower sjurface which br ngs about the surface chargedesired on the upper surface creating the fields of force necessary to cause charge deposition as is illustratedinFigg 8. Reference is now had to Fig.2 w'li thereis' sho'wn an embodiment of an automatic rriaclnrie according to this invention. A drum 50 driven at its sassy rnctc 52 57 negative high voltage is supplied to baron -as" ge wires 62 of corona discharge electrode by neg high voltage source 63, and positive highv'ol ge. supplied to corona discharge wires 65o]? corona electrode 60 hy positive hig voltage source '66. the previous embodiments, the shields 67 and 68 held at ground potential At the second charging station, gen} erally designated 70, positiveliigh voltage is supplied ,tig corna discharge wires 71 of corona discharge electrode 72 from positive high voltage source "73, and negative high voltage is supplied to corona discharge of corona discharge electrode 76 from negative high voltage, sdiirefe 77. Shield 78' of corona discharge el'cltjrc d 7min shield 80 of corona discharge electrode 72 are held at ground potential. Following chargiiig at stations 57' a d spool through the of pro'e'aibhana then yv ind up spool 86; The wind-" ip; spool is by Gr 87 h g shbs 8 Mo s l ti is f0 ,7 a synchronizing pace with he speed at o atlng drum 511. Various other news tclmique's or existing as; is a 7 moving drum may be used and are intended to be included Within the scope of this invention.

Following exposure, the drum is next rotated to development station 90. In this embodiment a powder cloud generator 91 generates an aerosol of xerographic developer particles and passes the aerosol through conduit 92 to the surface of the photoconductive insulating layer 55 to be developed. Also there is diagrammatically shown in this figure a development electrode 93 and development takes place as is well known in the art on the surface of the photoconductive image bearing layer beneath development electrode 93. Next in the path of movement of the rotating drum 50 is a transfer station 95. Various techniques of transferring a developed electrostatic image may be used, as for example, electrostatic transfer or the like, transfer to single sheets or the like, and the like. In this embodiment there is illus trated what has generally become known as adhesive transfer. A supply spool 96 provides a web of material 97 carrying an adhesive coating on one surface thereof. The adhesive coating is pressed against the surface of the photoconductive insulating layer 55 by a pressure roller 98 and the web 97 is then fed through a fixing station 100 wherein the image on the surface of web 97 is made permanent as, for example, through heat fusing, vapor fusing, by applying a protective coating, or the like. The web 97 may be cut up following fixing into individual copies or prints or, as illustrated, may be Wound up on take-up spool 101. A motor 104 is illustrated in this figure as driving take-up spool 101 through belt 105. The movement of web 97 is synchronized with the movement of drum 50 and optionally may be driven by motor 52 which may also be used to drive copy 82. Drum 50 is next fed to a cleaning station generally designated 102 whereat a rotating brush 103 wipes clean the surface of the photoconductive insulating layer. The material removed from the surface may be drawn away from the surface with vacuum cleaning means or the like. Fol lowing cleaning, drum 50 is ready for re-cycling through the various stations or stages described.

Although the charging grid described throughout has been of the same type, it is to be realized that there is no intention to limit this invention thereto. For example, the corona discharge device may be of the type described in Walkup application Serial No. 154,295, filed April 6, 1950, for Charging Device. This comprises a grid of fine wires which is held at several thousand volts potential with respect to a grounded shield similar to the one shown and a control grid of coarser wires than the discharge wires located between the corona discharge wires and the surface to be charged. The grid of coarser wires is held at an intermediate potential of several hundred volts above ground potential and serves to control or limit the potential placed upon the surface being charged. Also, there may be used stationary corona charging grids as is known to the art, or radioactive charging means, or the like.

The high voltage power supply may comprise known circuits such as a transformer-rectifier circuit and a voltage dividing resistance for supplying the required potentials, or the like.

The potential supplied to the corona discharge wires should be in the order of several thousand volts as, for example, 6,000 to 8,000 volts. Although there is no intent to limit this invention to any particular theory of operation, it is presently believed that, when a layer of charge exists at the interface between the photoconductive insulating layer and the insulating support base when using plates comprising photoconductive layers overlying an insulating support base or when a layer of charge exists at the lower surface of the photoconductor when using self-supporting films, and an opposite charge exists on the outer surface of the photoconductive insulating layer, complete discharge of charges in areas exposed to light takes place. Development of such a charge pat- '8 tern results in copy having high contrast and very little background.

Following charging, as illustrated in Figs. 3 and 4, the potential on the uncoated surface of the insulating base ll is substantially neutralized and thus the plate may be positioned on substantially any surface as, for example, a ground metallic conductor, a table top, or the like. Similarly, in connection with the embodiment illustrated in Figs. 7 and 8 if a photoconductor supported on an insulator is being used substantially no potential is found on the uncoated surface of the support base; thus, no problems are encountered during exposure or subsequent development whether the surface of the support base is or is not in contact with a grounded or conduo tive electrode. If a slight potential exists on the rear or uncoated surface of the support base, the potential would tend to increase as the support base is separated from the grounded conductor 37. A point in separation would likely be reached, in such an instance, at which the po.- tential would become sufficient to bring about a form of air breakdown and transfer of charge to the surface of the support base. However, breakdown if it takes place would be substantially uniform and charges transferred would not distort image formation or a formed image on the photoconductive insulating layer.

When dealing with the self-supporting film of photoconductive insulating material of Fig. 2, it is to be realized that charging as illustrated in Fig. 3 results in discharge of the charge through the illuminated and thus conductive photoconductive layer. Also, it is to be realized, that a charged and sensitive plate comprising a selfsupporting film of photoconductive material according to this invention carries a surface charge on the bottom and top surfaces. Since it is desirable to maintain the charge through to exposure and since it is desirable to form the charge pattern during exposure and maintain the formed pattern for development without distortion by stray charge deposition, it is preferred that the steps of exposure and development are carried out when using a self-supporting film of photoconductive insulating material without contacting the plate to an electrode. This may be accomplished keeping the plate in air during the various steps of image formation, by positioning the plate on an insulating support surface, or the like.

The use of the term ground throughout this application is intended to have the usual conventional meaning of a relative reference point. There is no desire for ground to limit this invention in any way to a specific value such as zero potential although in some instances ground may indicate zero potential. Instead, ground is intended to indicate a reference point from which other potential values vary upward when positive or downward when negative.

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

What is claimed is:

1. The method of sensitizing a xerographic plate comprising a self supporting film of photoconductive insulating material prior to exposure and image formation in xerography, said method comprising applying a first polarity corona generated electrostatic charge to a first surface of the photoconductive insulating film while said photoconductive insulating layer is uniformly illuminated by radiation which causes said film to become electrically conductive and while an electric field is applied through said film in a direction to move electrostatic charge directed to said first surface to the opposite and second surface of said photoconductive insulating film, said charge moved to said second surface being maintained at said second surface through the absence of any electrode in electrical contact therewith, and then in the absence of illumination of said photoconductive insulating film applying a second and opposite polarity corona generated electrostatic charge to said first surface of said photoconductive insulating film forming a sensitive xerographic plate with said first polarity charge at said second surface and said second polarity charge at said first surface of said photoconductive insulating film.

2. The method of sensitizing a xerographic plate comprising a layer of photoconductive insulating material overlying an insulating support member prior to exposure and image formation in xerography, said method comprising applying a first polarity corona generated electrostatic charge to the outer and first surface of the photoconductive insulating layer of said Xerographic plate while said photoconductive insulating layer is uniformly illuminated by radiation which causes said layer to become electrically conductive and while an electric field is applied through said plate in a direction to move electrostatic charge directed to said first surface to the opposite and second surface of said photoconductive insulating layer in contact with the insulating member, said charge moved to said second surface being maintained at said second surface through the absence of any electrode in electrical contact therewith, and then in the absence of illumination of said photoconductive insulating layer applying a second and opposite polarity corona generated electrostatic charge to said first and outer surface of said photoconductive insulating layer forming a sensitive xerographic plate with said first polarity charge at said second surface and said second polarity charge at said first surface of said photoconductive insulating layer.

3. The method of image formation in xerography in which a developable electrostatic charge pattern is formed on the surface of a xerographic plate comprising a self supporting film of photoconductive insulating material, said method comprising applying a first polarity corona generated electrostatic charge to a first surface of a photoconductive insulating film while said photoconductive insulating film is uniformly illuminated by radiation which causes said film to become electrically conductive and while an electrostatic field is applied through said film in a direction to move electrostatic charge directed to said first surface to the opposite and second surface of said photoconductive insulating film, said charge moved to said second surface being maintained at said second surface through the absence of any electrode in electrical contact therewith, then in the absence of illumination of said photoconductive insulating film applying a second and opposite polarity corona generated electrostatic charge to said first surface of said photoconductive insulating film forming a sensitive xerographic plate with said first polarity charge at said second surface and said second polarity charge at said first surface of said photoconductive insulating film, and exposing said sensitive xerographic plate to an image pattern of information to be recorded.

4. The method of claim 3 in which said developable electrostatic charge pattern formed on said Xerographic plate is developed with electroscopic marking material forming a visible pattern of the recorded information.

5. The method of image formation in xerography in which a developable electrostatic charge pattern is formed on the surface of a xerographic plate comprising a layer of photoconductive insulating material overlying an insulating support member, said method comprising applying a first polarity corona generated electrostatic charge to the outer and first surface of the photoconductive insulating layer of said xerographic plate while said photoconductive insulating layer is uniformly illuminated by radiation which causes said film to become electrically conductive and while an electric field is applied through said plate in a direction to move electrostatic charge directed to said first surface to the opposite and second surface of said photoconductive insulating layer in contact with the insulating member, said charge moved to said second surface being maintained at said second surface through the absence of any electrode in electrical contact therewith, then in the absence of illumination of said photoconductive insulating layer applying a second and opposite polarity corona generated electrostatic charge to said first and outer surface of said photoconductive insulating layer forming a sensitive xerographic plate with said first polarity charge at said second surface and said second polarity charge at said first surface of said photoconductive insulating layer, and exposing said sensitive xerographic plate to an image pattern of information to be recorded.

6. The method of claim 5 in which said developable electrostatic charge pattern formed on said xerographic plate is developed with electroscopic marking material forming a visible pattern of the recorded information.

References Cited in the file of this patent UNITED STATES PATENTS 2,277,013 Carlson Mar. 11, 1942 2,297,691 Carlson Oct. 6, 1942 2,543,051 Oughton et al. Feb. 27, 1951 2,573,881 Walkup et al. Nov. 6, 1951 2,588,699 Carlson Mar. 11, 1952 2,624,652 Carlson Jan. 6, 1953 2,663,636 Middleton Dec. 22, 1953 2,693,416 Butterfield Nov. 2, 1954 2,703,280 Butterfield et al. Mar. 1, 1955 2,730,023 Greig Jan. 10, 1956 2,777,745 McNaney Jan. 15, 1957 2,825,814 Walkup Mar. 4, 1958 2,833,648 Walkup May 6, 1.958 2,833,930 Walkup May 6, 1958 OTHER REFERENCES Young et al.: RCA Review, vol. XV, No. 4, pages 469-484 (1954).

Claims

1. THE METHOD OF SENSITIZING A XEROGRAPHIC PLATE COMPRISING A SELF SUPPORTING FILM OF POTOCONDUCTIVE INSULATING MATERIAL PRIOR TO EXPOSURE AND IMAGE FORMATION IN XEROGRAPHY, SAID METHOD COMPRISING APPLYING A FIRST POLARITY CORONA GENERATED ELASTROSTATIC CHARGE TO A FIRST SURFACE OF THE PHOTOCONDUCTIVE INSULATING FILM WHILE SAID PHOTOCONDUCTIVE INSULATING LAYER IS UNIFORMLY ILLUMINATED BY RADIATION WHICH CAUSES SAID FILM TO BECOME ELECTRICALLY CONDUCTIVE AND WHILE AN ELECTRIC FIELD IS APPLIED THROUGH SAID FILM IN A DIRECTION TO MOVE ELECTROSTATIC CHARGE DIRECTED TO SAID FIRST SURFACE TO THE OPPOSITE AND SECOND SURFACE OF SAID PHOTOCONDUCTIVE INSULATING FILM SAID