CA1061399A - Electrophotographic process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The electrophotographic process of this invention is achieved by subjecting a photosensitive screen to a matched perfor-mance of voltage applications and image irradiation to form a primary electrostatic latent image for modulating the flow of corona ions to create a secondary electrostatic latent image on a recording mem-ber disposed in close proximity to the screen bearing the primary electrostatic latent image. The screen is made of a conductive member as its basic element, a photoconductive member covering a substantial part of the conductive member, and a surface insulating member also covering a substantial part of the conductive member and of the photoconductive member, in which the conductive member is partly exposed at one surface side of the screen, or it is entire-ly covered by the surface insulating member with another conductive member to be exposed being provided on said insulating member, and the coating thicknesses of the photoconductive and surface insula-ting members are thicker at the portion opposite to the surface part d the conductive member to be exposed.

Description

~063L399 BACKGROUND 0~` THE INVENTI 0 a. Field of the Invention This invention relates to an electrophotographic process and, more particularly, it relates to an electrophotographic process for forming an image by use of a photosensitive plate having a plurality of openings.

b. Discussion of Prior Art ~-- ' :.
In conventionaL electrophotography, there have bee-n pro-posed a direct process such as, for example~ electrofax, and an indirect process such as xerography. In the direct electrophoto-graphic process, use is made of a specially treated image recording member coated with a photoconductive material such as æinc oxide.
This direct method, however, has a drawback in that as the ima~e ~ormed on the recording member lacks in brightness, contrasts in the tones of the reproduced image are poor. Moreover, owing to a parti- '~
cular treatment rendered on the recording member, it is heavier than conventional paper, and hence a particular feeding means which is -` `
different from that for ordinary paper ~hould be employed.
According to the indirect process, an image of high con-trast and ~ood quality can be obtained by using ordinary paper asthe imaye recording member. However, in this indirect process, when a toner image is transferred to the recording member, the latter in-evitably contacts the surface of the photosensitive member and, furthermore, a cleaning means vigorously touches the suxface of the . .
photosensitive member for removal of the residual toner thereon with the conse~usnce that the photosensitive member is impaired at every time the transfer and cleaning operations are carried out. ~s a resu~t of this, life o~ the expensive photosensitive member b~comes shortened, which unavoidably results in a high c09-t in the image -1~ ~ .

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.~--~ 06~L3~9 reproduction.
In order therefore to remove such drawbacks i~herent in the conventional electrophotographic processes, there have been proposed various methods such as, for example, those taught in the United States Patents No, 3,220,324, granted November 30, 1965, to Xerox Corporation, No. 3,645,614, granted February 29, 1972, to Electroprint, Inc.~ No. 3,647,291, granted March 7, 1972 to Electroprint, Inc., No. 3,680,954, granted ~ugust 1, 1972 to Eastman Kodak Company, and No. 3,713,734, granted January 30, 1973 to Electroprint, Inc. In these patents, there is used a photosensitive member of the screen type or the grid type having a number of openings in the form of a fine net.
The electrostatic latent image is formed on the recording member by modulating the flow path of ions through the screen or grid, after which the latent image formed on the recording material is visualized. In this case, the screen or grid which corresponds to the photosensitive member need not be developed nor cleaned, and hence the life of the screen or grid can be prolonged.
U.S. patent No. 3,220,324 teaches the use of a conductive screen coated with a photoconductive material, through which an image exposure is effected onto a recording member simul-taneously with a corona discharge. The flow o corona ions produced as a consequence of the corona discharge is modulated by the screen, whereby an electrostatic latent image is formed on the recording member. In this process, wherein the screen charging and the image exposure are simultaneously effected, it is difficult to charge the photoconductive material coated on the conductive screen at a sufficiently high potential.
Accordingly, the efficiency in the image exposure becomes lowered, which makes it difficult to obtain an image repro-duction of high quality. Further, at the dark image por-

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tions where the corona ions pass, iE the potential to the conductive screen is raised too high, the applied corona ions are repulsed with the consequence that they are directed to the bright image portions in the vicinity of the dark image portions of the exposed conductive screen, and hence a satisfactory image reproduction can not be expected.
U.S. patent ~oO 3,680,954 teaches the use of a conductive grid coated with a photoconductive material, and a conductive control - ,.
grid, in which an electrostatic latent image is formed on the con-ductive grid, and different electric fields are formed on both the conductive grid and the control grid so as to modulate the flow of the corona ions for forming an image on the recording me~ber. In this patented process, however, it is quite difficult to hold the control grid and the conductive grid to form an electrostatic late~t image over a large area with finely spaced intervals therebetween.
Moreover, the control grid absorbs the corona ions to be imparked to the recording member with the result that the image recording ~ `
officiency becomes lowered. In the case of iorming a positive image, the flow of the corona ions having a polarity opposite to that of `
the latent image is applied, and almost the entire part of the ion flow directs to the latent image to negate the latent image, so that the desired positive image is difficult to be reproduced.
In U.S~ patent ~o. 3,645,614, the screen comprises an inSulating material overlaid with a conductive material, and the in-sulating material comprises a photoconduc~ive material. An electric field to prevent the ion flow fxom passing ~hrough the screen is foxmed at the openings or perforations for permitting the ion flow to pass therethrough owing to the electrostatic latent image formed on the screen, This process has a drawback in that an image to be

- 3 -., )6~39~ ~
formed on the recording member is the image reversal of the latent image on the screen.
U.S. patent No. 3,713,734 teaches the use of a four-layer screen consisting of a photoconductive substance, a first conductive substance, an insulating substance, and a second ;
conductive substance, in which an electrostatic latent image is formed on the photoconductive substance in conformity to the original picture image by the processes of electric charging and image exposure. Also, in the case of forming an image on the recording member by modulating the flow of the corona ions through the electrostatic latent image, the second conductive substance of the screen is imparted by a voltage having a polarity opposite to that of the electrostatic latent image on the screen, since the image is in a single polarity. By this appiication of the electric field, there are formed two regions, i,e., a region to permit the ion flow to pass through the screen in accordance with the latent image on the screen, and another region to inhibit the passage of the ion flow, whereby a desired electrostatic latent image is formed on the recording member. According to this patented process, it is possible to reproduce a favorable positive image, although the process has two major disadvant~ges in that two layers of the conductive substance must be provi~ed on the thinly formed screen, which entails complexity in the manufacture of such screen, and that instability remains between the facing layers of the conductive substance owing to electric discharge. Fur-thermore, the electric charge on the photoconductive substance layer is liable to attenuate, and the configuration of the layer tends to fluctuate largely in the course of it~ manufacturing, on account of which it becomes difficult to obtain a persistent electrostatic latent image on the photoconductive substance layer over a long period of time, and to modulate the ion flow for .. . .. . . ..

6~39~
many repeated times by the electrostatic latent image on the . . . ,: . .
one and same screen.
U.S. patent No. 3,647,291 teaches to form an electro-static latent images having mutually different polarities on a two-layer screen consisting of a conductive substance and a photoconductive substance in correspondence to a bri~ht image portion and a dark image portion so as to modulate passage of the corona ion flow by the latent image formed on the screen.
However, according to this patented method, as described in its specification, it is very difficult to form a latent image of both polarities on the photoconductive insulating substance in ~ ~
laminar form. Rather, in the case of forming the electrostatic latent image on this laminar insulating substance, it is necessary to transfer the latent image once formed on a separate photosensitive body. That is, according to the patented method as outlined above, there takes place àn electric charge loss in the course of the image forming process, and the construction of the electrophotographic device inevitably becomes complicated.
More particuarly, in the case where the electrostatic latent image is to be transferred onto the screen from the photosen-sitive body, the latent image tends to flow toward the conductive substance which has been exposed at the side of the screen openings, on account o which the desired electrostatic latent image can hardly be obtained on the screen with satis-factory contrast in the tones of image.

SUMM~RY OF THE INVENTION
In view of the foregoing discussion o~f various prior patents known to the applicant, it is a primary object of the present invention to provide an improved electrophotographic reproduction process free from all disadvantages and defects inherent in the known processes.

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It is a secondary objec~ of the present inven~ion to provide an improved electrophotographic process which enables a reproduced image to be formed on various kinds of recording members.
It is a tertiary object of the present invention to provide an improved electrophotographic process which has successfully solved the afore-described defects in the conven-tional electrophotographic processes, and which enables both positive and negative images on the recording member in exact conformity to the original image.
It is a quaternary ob~ect of the~present invention to provide an improved electrophotographic process, by which is obtained a complete reproduced image of sufficient contrast in the tones of the image and free from fog.
It is a quinary object of the present invention to provide an improved electrophotographic process which enables the ion flow to be modulated over many repeated times from the one and same electrostatic image formed on the screen.
The foregoing ma~or objects and other objects, as well as the construction and function of the present invention will become more readily understandable from the following detailed description thereof with its resulting effects, when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING ~ ..
Figure 1 is an enlarged cross-sectional view o~ a photo-sensitive screen for use in the electrophotographic reproduction process according to the present invention;
Figures 2 to 4 are respectively schematic diagrams to explain the forming processes of a primary electrostatic latent image on the photosensitive screen shown in Figure l;
Figures 5 and 6 are respectively schematic diagrams to ~L O 6 ~IL 39g , explain the forming processes of a secondary electrostatic latent image by the same screen as shown in Figure l;
Figures 7 to 13 inclusive are respectively schematic side elevational views in longitudinal cross-section showing one embodi~
ment of the electrophotographic reproduction device, in which the photosensitive screen of Figure 1 is incorporated;
Figures 14 to 17 inclusive are respectively enlarged cross-sectional views of the modified photosensitive screens to be used m for the present invention;
Figures 18 to 20 inclusive are respectively schematic diagrams to explain the format.ion o~ the primary electrostatic latent ~ .
image on the modified screen shown in Figure 14 above;
Figure 21 is a schematic diagram to expLain the forming process of the secondary electrostatic latent image by the photo- ;~ -sensitive screen as shown in Figure 14;
Figures 22 to 24 inclusive are respectively schematic diagrams to explain the forming processes of the primary electro-static latent image on the modified screen shown in Figure 16;
Figure 25 is a schematic diagram to explain the forming '~
process oE the secondary electrostatic latent image by the same .
screen as shown in Figure 16; .
Flgures 26 to 28 are respectively schematic diagrams to explain the forming processes of the primary electrostatic latent image by the modified screen shown in Figure 17;
. Figure 29 is a sc~ematic diagram to explain the'forminy process of the secondary electrostatic latent image by the same screen as shown in Figure 17; .
Figure 30 is a graphical representation showing curves of the surface potential of -the screen in Figure 17 at the time of _ 7 - :

,.,. ... , .. .. -~ ~613~9 forming the primary electrostatic latent image;
Figures 31 to 34 inclusive are respectively schematic diagrams to explain the forming processes of the primary electro-static latent image on the screen;
Figure 35 is a schematic diagram to explain the forming processes of the secondary electrostatic latent image by the screen;
Figures 36 to 38, and Figures 40 to 42 inclusive are respectively schematic diagrams to explain the foxming processes of the primary electrostatic latent image on the screen;
Figures 39 to 43 are respectively schematic diagrams to explain the forming processes of the secondary electxostatic Iatent image by the same screen;
Figure 44 which precedes Flgure 43, is a graphical representation of the surface potential on the screen.at every process step shown in Figures 36 to 39;
Figures 45 and 46 are respectively schematic diagrams to explain the forming processes of the primary electrostatic latent image on the screen;
Figure 47 is a schematic diagram to expla.in the forming process of the secondary electrostatic latent image by the screen;
Figure 48 is a graphical representation showing the surface potential curve of the image forming steps shown in ~Figures 46 and 47; ~-Figures 49 to 53 inclusive are respectively schematic diagrams to explain the forming processes of the primary ~:
electrostatic latent image on the screen;
Figure 54 is a schematic diagram to explain the forming 30 - process of the secondary electrostatic latent image by the same screen; ~.
Figures 55 to 59 inclusive are respectively schematic dia-39~
grams to explain the fo.rming processes of the primary elec-trostatic latent image on the screen;
Figure 60 is a schematic diagram to explain the forming process of the secondary electrostatic latent image by the same screen; ~
Figures 61 to 64 inclusive are respectively schematic ;~:
diagrams to explain the forming processes of the primary electro-static latent image on the screen; -~
Figure 65 is a schematic diagram to explain the forming process of the secondary electrostatic latent image by the same screen;
Figure 66 is a graphical representation showiny the surface potential curve o the screen in the latent image forminy steps shown in Figures 49 to 53;
Figure 67 is a graphical representation showing the surface ~:
potential cuxve of the screen in the image forming steps shown in Figures 55 to 59;
Figure 68 is a graphicaL representation showing the surface potential curve of the screen in the image forming steps shown in Figure~ 61 to 64 -Figure 69 is a table showing the polarity of voltage for use at ~he time o~ applying ~he primary, secondary, and ~ertiary voltages in the electrophotographic processes according to the present invention;
Figures 70 to 73 inclusive are respectively schematic dia-grams to explain the forming processes of the primary elec~rostatic latent imaye on the screen;
Figure 74 is a schematic diagram to explain the forming process of the secondary electrostatic latent .image by the same _ g _ ~.

screen, and Figure ~5 is a graphical representation showing the surface potential curve of the screen in the image forming steps shown in Pigures 70 to 73.

DETAILED DESCRIPTIO~ OF THE INVENTION
At the outset, the electrophotographic reproduction process according-to the present invention will be outlined in the ~ollowing.
The photosensitive screen to be used for the electrophoto-graphic reproduction process is provided therein with a multitude of ;10 small openings. Its basic construction is composed of a conductive member as the base, on which a photoconductive member and a surface insulating member are laminated. One surface part of this screen is r~ndered electrically conductive, partially or in its entirety. A
primary electrostatic latent image is formed on the screen by carry-ing out the voltage application step such as electric charging, removal of such charge, etc., and the irradiation step such as irradiation of an original image, overall irradiation of the latent image surface to be per~ormed, as the case may be, etc., in combina- ;
tion. Subsequently, a secondary electrostatic latent image is formed on the same screen by applying modulated corona ions onto an elec-trically chargeable member such as recording member, and so on. The modulated corona ions are obtained by first impressing a flow of corona ions from a generating source of such ions onto the above-mentioned screen, and then modulating the ion flow passing through the screen by the primary electrostatic latent image formed thereon.
For the purpose of the present invention, -the texm "primary electrostatic latent image" means an electrostatic latent image formed on the photosensitive screen in conEormity to the original image through the process steps as describe~ above, and the term ~6~3~9 : ~
"secondary electrostatic latent image" means one formed on the electrically chargeable member by the flow of corona ions which has been modulated with the a~ove-mentioned primary electro-static latent image on the screen in the course of its passage therethrough.
The above-outl~ned invention will be described in more detail hereinbelow with reference to preferred embodiments as illustrated in the accompanying drawing.
The first embodiment of the present invention is the electrophotographic process comprising the application of a primary voltage to electrically charge the entire surace of a screen in a uniform manner so as to form a primary electrostatic latent image thereon; irradiation of an original image to take place subsequently; and application of a secondary voltage to vary the surface potential of the screen already subjected to the primary voltage impression.
The photosensitive screen to be used for this electro-photographic process basically is composed, as already has been mentioned, of a conductive member as the base, on which a 20 - photoconductive member and a surface insulating member are provided. One embodiment of such photosensitive screen is shown in Figure 1 in an enlarged cross-section. As seen from Figure 1, the screen 1 has a multituds of openings, in each of which a conductive member 2 is placed in a manner to be partially exposed outside and, surrounding the conductive member 1, a photoconductive member 3 and a surface insulating member 4 are provided in sequence.
For the conductive member 2 to constitute the screen 1, a flat plate of a substance of high electric conductivity such as nickel, stainless steel, copper, aluminum, tin, etc. is etched to form many small openings (the cross-sections of which mostly are of rectangular shape), or a net is produced by electro-:. .

~, ~061399 plating or it is made o~ wires of the above-mentioned metallic substance (the cross-sections of the openings mostly are of roundish shape). The conductive member 2, for the purpose of reproduction in general offices, may have from 100 to 300 meshes in the screen 1 from the standpoint of ~he required resolution.
Also, when the conductive member is to be ;produced from the flat plate as mentioned above, the optimum thickness of the plate may be determined from the mesh size and the shape of the small openings. On the other hand, when the conductive member 2 is manufactured from metal wires, the optimum diamater of the wires may be determined in correspondence to the mesh size of the screen to be obtained.
The photoconductive member 3 is formed on the concluctive member 2 by vacuum evaporation of an alloy or of an inter-metallic compound containing S, Se, PbO, and S, S~, Te, As, Sb, Pb, etc.. Also, according to the sputtering method, a high melting point photoconductive substance such aszno, Cd~ Tio2~ etc.
can be adhered onto the conductive member 2. By the spraying method, it is possible to use organic semiconductors such as polyvinyl carbazole (PVCz), anthracene, phthalocyanine, etc., and those semiconductors with increased sensitivity for coloring ; -sub~tances and Lewis acid, and a mixture of these semiconductors and an insulative binder. For this spray method, a mixture o~ ~ ~
'' ' '".:
ZnO, CdS, TiO2, PbO, and other inorganic photoconductive particles and an insulative binder can also be used suitably.
For the insulative binder to be used for preparing the mixture of the inorganic photoconductive substances and organic semiconductors, any organic insulative substance and inorganic insulative substance for use as the surface insulating member to be described h~reinafter may prope~ly be ~sed.

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~ ~6~399 The thickness of the photoconductive member 3 to be -deposited on the conductive member 2 by any of the above~
mentioned expedients may appropriately range from 10 to 80 microns at the maximum, although it depends on the class and the characteristics of the photoconductive substance to be used.
The surface insulating member 4 essentially should be highly resistive, electric charge sustainable, and transparent ~ -to permit irradiated light to pass therethrough. The member is not always required to have high resistance against wear and tear. Materials to satisfy the above-mentioned requirements are polyethylene, polypropylene, polystyrene ! polyvinyl chloride, polyvinyl acetate, acrylic resin, polycarbonate, silicon resin, fluorine resin, epoxy resin, and other organic insulative substances; copolymers or mixtures of these monomeric substances in solvent type, thermal polymerization type and photopoly-merization type. These materials can be formed on the photo~
conductive member 3 by the spray method or by vacuum evaporation.
Vacuum-evaporated layers of organic polymer substances obtained by vapor-phase polymerization such as parylene (a generic name for thermoplastic film polymers based on para-xylylene), and inorganic insulative substances are also effective for the purpose. The thickness of the surface insulating member to be formed on the photoconductive member 3 by the above-mentioned method appropriately may be determined in relation to the thickness of the photoconductive member 3.
Since the photosensitive screen according to the present invention should essentially have one surface part thereof rendered electrically conductive, the screen is required to be conducted in such a manner that the conductive member 2 be exposed to one surface part of the screen 1. On account of ;
this, when the photoconductive member 3 and the surface insu-- 13 ~

6~39~ ~
lating member 4 are formed on the conductive member 2, as in the above-described screen construction, each of thesesubstances should be adhered from one side of the conductive member 2, i.e., a side opposite to the side to be exposed. It also may be possible to spray or vapor-evaporate these substances from a slant direction so as to secure good adh~sion of these photo~
conductive and surface insulating substances onto the side surface of the openings. Should it happen that these photo-conductive and surface insulating substances unavoidably come round to the one surface part of the conductive member to be exposed, these substances may be removed by various expedients such as by an abrasive agent, whereby the necessar~ part of the conductive member 2 again becomes exposed.
In the present invention, the primary electrostatic latent image is formed on the surface insulating member 4 which covers substantially the entire sur~ace of the photosensitive screen 1, the effect of which will be as follows. By forming the primary electrostatlc latent image on the insulating member 4, attenua-tion of the latent image becomes remarkably ~ow in comparison with that of a latent image formed on a photoconductive member which is in an insulated state. The reason for this may be that the pure insulating member has a higher electric resistance than the p~otoconductive member which is in the insulated state by the insulating member, on account of which the screen 1 is capable of storing a high electric charge, hence the primary electrostatic latent image can be formed at high electrostatic contrast. Further, since the primary electrostatic latent image formed on the insulating member 4 has very low attenuation, it becomes possible to modulate the ion-flow over many repeated times by the same primary electrostatic latent image, whereby so-called retention copying, which obtains a multitude of .

.. .. . . ~ . ~. . . .

~ 6139~
reproduced images from one and the same primary electrostatic latent image, becomes feasible.
The process steps for ~orming the primary and the secon- :
dary electrostatic laten-t image by the electrophotographic process according to the present invention usi~g the above mentioned photosensitive screen 1 will now be described with .
reference to Figures 2 to 5 which show, respectively, the primary voltage application onto the screen, the image irradia- .
tion and the secondary voltage application, the irradiation of the overall surface of the screen, and the secondary electro-static latent image formation to be carried out by modulation of the ion-flow through the primary electrostatic latent image ..
formed on the screen by the preceding process steps. The -explanations hereinbelow of the electrophotography wi:Ll be made on the assumption that the photoconductive substances such as :.
selenium and its alloys with the hole as the principal carrier therefore are used. In addition, the conventional type of electric voltage applying means such as the corona discharger and the roller discharger, are applicable for the purpose o:E
the voltage impression. Of these known expedients, the corona discharger is particularly preferable; hence the èxplanations which follow will be made with reference to the co~ona discharger.
. In the primary volt,age application step as shown in Figure 1, the screen 4 is uniformly charged with a negative polarity by the corona discharger as the voltage application.
means which takes electric power from a power source 6 through .
a corona wire 5 of the discharger. By this electric charge, a :
negative charge is accumulated on the surface of the insulating membex 4, while a charge having a polarity opposite to that of the insulating member 4, i.e., a positive charge, is accumulated at the photoconductive member 3 in the vicinity of the insulating .

~ ' :

~ 6~39g member 4. Where the interface between the conductive member 2 and the photoconductive member 3, and the photoconductive member 3 per se are of such nature as to permit injection of the majority carrier, but does not permit injection of the minority carrier, and that has the rectifiability as the screen, ~ ~ .
the layer of electric charge can be formed in the photoconduc-tive member 3 at a place adjacent to the insulating member 4.
With the screen not having such rectifiability, or not forming -the electric charge layer as mentioned above, the primary ;:
voltage can be impressed thereon by the charging method of the insulating member as taught in U.S. patent No. 2,955,938, :;
granted October 11, 1960, to Haloid Xerox Inc. .~
In the primary voltage application step as described :
above, it is preferable that the electric vol-tage be applied to :
the screen from the surface thereof where the insulating member

4 e~ists ~this surface hereinafter will be called "surface A"). :
In contradistinction, satisfactory charging is difficult to be realized on the insulating member 4 even when the corona dis-charge is impressed on the surface when the conductive member 2 is present (this surface hereinafter will be called "sur~ac~ :
B"), because the corona ions flow into the conductive member Z.
~igure 3 indicates a result of the simultaneous image irradiation and secondary voltage impression onto the screen 1 ~ :
which has undergone the above-mentioned first voltage impression.
The reference numeral 7 designates a corona wlre for the corona discharger, the numeral 8 designates a power source for the - corona wire 7, the numeral 9 is a power source for bias vo~taye, ;
the numberal 10 is an original image, of which the referènce . ~-letter D indicates a dark image portion and the letter L . : .
indicates a bright image portion, and the axrows 11 designate-llght from a light source (not shown). : .:. .-- 16 - :

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.:

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, . . .. -,. .
.. . , : : . . . . .

, ~06~399 In the embodiment shown in Figure 3, el.ectric discharge is carried out by the corona discharge through the corona wire 7, on which an alternating current voltage superposed by a direct current voltage of positive polarity in such a manner that the surface potential of the insulating member 4 may have ~ .
substantially positive polarity. When the A. C. corona dis-charge is used, the surface potential of the insulating member 4 must be substantiall~ .zero due to alternate discharge of positive and negative polarities. However, in the actual :
phenomenon to take place, the negative corona discharge gener-ated thereby is.stronger than the positive corona discharge with the consequent difficulty to render the surface potential of the insulating member 4 to be in the positive polarity as mentioned above. For this reason, various measures are taken to make it easier to render the surface potential positive such as, for example, superposing a positive bias vol~age on the A.C.
voltage, or reducing the negative current in the A.C. power .
source. It goes without saying that, for the purpose of the -secondary voltage application, a D.C. corona discharge of a 20 polarity opposite to that of the.primary voltage application can be used besides use of the A.C. voltage so as to render the sur~ace potential of the insulating member 4 to a polarity opposite to that of the primary voltage application.
As described previously, when the surface potential of the insulating member 4 is rendered posi*ive, the substance constituting the photoconductive me~ber 3 becomes conducti~e at the bright image portion L due to the image i-rrad~iation, in consequence of which the surface potential of the insulating member 4 becomes positive. On the other hand, however, the surface potential of the insulating member 4 at the dark image portion D remains negative on account of the positive charge ': . ' ' , 1~61399 layer present in the photoconductive member 3 to the side ofthe insulating member 4.
The relationship between the image irradiation step and the secondary voltage application step as in the above- ;~
exemplified transmission system is such that, when the substance constituting the photoconductive member 3 has a persistent photoconductivity, the two steps are not carried out simul-tanevusly, contrar~ to the foregoing explanation, but may be done sequentially. Furthermore, the direction for the image irradiation may preferably be from the surface A of the screen 1, although it can also be done from the surface B. In the latter case, however, the resolution and the sensitivity of the repro-duced image may be inferior to those of the former case. For the purpose of the image irradiation, a light source generally is used. Besides the light source, radioactive rays which indicate response to the substance of the photoconductive member 3 may be used.
Considering now the changing speed of the polarity of the potential on the insulating member 4 of the screen in the above-described steps, it is observed that the portion of the insu-lating member 4 facing the corona wire 7 exhibits the quickest change in polarity, and the side surface portion and its vicinity sandwiching the above-mentioned portion facing the corona wire 7 changes its polarity a bit later than the sand-wiched portion. Accordingly, in the image irradiating portion, the electric potential at the surface B of the screen 1 corres-_ ~ -ponds to that of the conductive member 2, and the potential assumes a state of gradual increase as it shifts from the surface B to the surface A.
Figure 4 indicates a result of conducting uniform exposure over the entire surface of the screen 1 which has been subjected to the image irradiation step and the secondary voltage appli-cation step.

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~ In the drawlng, the arrows 12 indicate light from a light source. ::
By this overall irradiation step, the electric potential oE the dark : -image portion D on the screen 1 changes in proportion to the elec~
tric charge quantity on the suxface of the insulating member 4. As a result of this potential change, the following relationship is established between the contrast V o~ the resultant electrostatic latent image and the eLectric charge potential Va obtained by the primary voltage application step:

C Ci ~ cp Va , .......................... ( 1 ) -, 10 .
where Ci is the electrostatic capacitance of the insulating member 4, and Gp is the electrostatic cap~tance o:E the photoconductive member 3. ~ r When a photosensitive body o~ a three-layer structure con- . .
sisting of a conductive base plate, a photoconductive layer, and a sur~ace insulating layer is used, it is desirable that the electro-static capacitance ratio between Ci (insulating layer) and C (photo-conductive layer) be 1 to 1 or so. However, in the case of the ~ . electrophotographic process using the photosensitive screen, parti-cularly in the retention copying as is the case with the presentinvention, an e~ective result can be obtained if the electxostatic capacitance ratio between Ci and Cp is set at 2 to 1 or so. Also, the coatLng thickness of the photoconductive member 3 surrounding the conductive member 2 becomes consecutively thinner ~rom the sur- .
face A toward the surface B. On account of this, as the charge layer in the photoconductive membsr 3 is extinguished by the overall irra-diation at the dark image portion, the electric potential in the screen gradually changes to a higher negative potential ~rom the surface B toward the sur~ace A of the screen 1. Incidental:Ly, the -- 19 -- ~

. ~

r ~ L399 above-described overall irradiation step is not always necessary.
However, by conducting this process step, it becomes possible to quickly form the primary electrostatic latent image on the screen 1 :
where the electrostatic contrast should be kept high.
Figure 5 indicates the secondary electrostatic latent imaye forming process, wherein a positive electrostatic latent image in con-formity to the original image is formed on the recording member by the primary electrostatic latent image on the screen 1. In the drawing, the reference numeral 13 designates a conductive support .~:~
member which also serves as an opposite electrode of the corona wire ~ :
14 of the corona discharger, and the reference numeral 15 designates a recor~i~g member such as electrostatic recording paper which is disposed in such a manner that its chargeable surface is faced toward the screen 1, while its conductive surface is made to contact the conductive support member 13. The chargeable surface o~ the record-ing member 15 is disposed facing toward the surface A of the screen 1 at an appropriate space interval therebetween of from 1 r~m to 10 mm or so.
.. . . .
When the secondary electrostatic latent image is to be formed on the recording member 15, the flow of corona ions is direc-ted to the recording member 15 from the corona wire 8. At this time, the bright image portion of the screen 1 is constantly changing its potential dif:Eersnce from the surface A to the surEace B, thereby creating an electric field as indicated by solid lines ~ in Figure 5, whereby the pass~ge of the corona ions through the openings o~ the screen 1 is inhibited to result in flowing of the corona ions into the partly exposed conductive member 2, If it is assumed that the surface B of the screen 1 is entirely covered with the insulating ::
me!~ber 3, the screen is charged in the polarity oE ~he corona ions ' ' : . . ' ~06~399 from the corona wire 14, and the passage of the corona ions throughthe openings of ths screen is accelerated by the charged potential.
In other words, as the corona ions pass. through even the bright image portion, ~og is caused in the secondary electrostatic latent image formed on the recording member 15. In contrast to this, the electric potential is continuously changing smoothly at the dark image portion of the screen 1 from the surface B to the surface A, whereby an electric field as shown by solid li.nes ~ is created, and the corona ions, in spite of their being of an opp~site polarity to that of the electrostatic latent image on the insula~ing member .
4, reach the recording member 15 in an effQctive manner in a state of causing the latent image to be extinguished to a lesser degree.
Inversely, when the original image is to bs formed on the recording member by way of a positive electrostatic latent image, an electric voltage having the same polarity as that of the electric charge on the insulating member 4 to the dark image portion of the screen 1.
The re~erence numeral 16 in Figure 5 designates a power source for the corona wire 14, and the numeral 17 designates another power source to the conductive supporting member 13. In such construction, the electric voltage may be impressed on the screen 1 in such a manner that an electric potential difference may occur in the direc- ` ..
tion of from the corona wire 14 to the conductive supporting member .-13 by way of the screen 1.
On the-other hand, the voltage impression to the corona wire can be done not only by the D.C. voltage as mentioned above, but also by the A.C~ voltage. In this case, wherein the primary electrostatic latent image on the screen 1 is in the above-mentioned.
state, if a voltage of negative polarity is impressed onto the side of the conductive supporting member 13, a positive electrostatic .
.
.. , . . . ' . '~

- ` ~1[~61399 ` : ::
latent image can be obtained and, if a voltage of the positive polarity is impressed, a negative electrostatic latent image can be obtained. The dotted lines 18 in the drawing designate the flow of the corona ions frorn the corona wire 14.
For the recording member 15, not only those having a two-layer structure consisting of the chargeable layer and the conduc-tive layer such as the electrostatic recording paper, but also any insulating member such as polyethylene terephthalate are usable. In using such an insulating mer~er as mentioned above, however, the insulating member must be sufficiently closely adhered onto the conductive supporting member 13, otherwise, irxegularities in the secondary electrostatic latent image formed on the recording member will occur. A~ a means of removing a defect such as is mentioned above, application of the voltage to the recording member 15 by the corona discharge instead of using the conductive supportin~ mer~er -13 is effective.
The reason for such favoxable results when the screen 1 of the afore-described constxuction is used, particulaxly for xetention copying, i8 considexed to be the fact that the primary elsctrostatic Z~ latent image having a smooth pokential change is formed on th& in-sulating member 4 at the opening part of the screen 1. Furthermore, `~
such effect is presumed to be derived fxom the function such that the 8uxplus flow of the corona ions from the corona wixe is absorbed by the conductive member exposed to the side of the surface B of the screen l.
~ oreover, i~ carrying out the retention copying, there sometimes occurs a situation in which the quantity of flowing corona ions passing through the screen 1 is rather small at the tirne of forming the secondary electrostatic latent image on the xecording `
- 22 ~

member 15 and, more particularly, at the time of modulating the ion flow at the initial stage. If the latent image formed on the rècording member under such electric conditions is developed, a reproduction image of varying density results. The cause for this undesirable phenomenon is thought to be the fact that a part of the corona ions flows toward the part in the vicinity of the surface B from the opening part of the screen 1. Upon undergoing the above-described phenomenon, the corona ions which flow toward the above-described part quench to attain a con-dition of equilibrium. When the above-described phenomenon tends to occur, the phenomenon can be preven~ed by the following methods. The first method is to increase the corona discharge current for the secondary electrostatic latent image formation by 10 to 100% or so to the ordinary level with respect to the first sheet or several sheets of the retention copy in accord-ance with the increase in the voltage to be impressed on the corona wire 14, or the change in the position of the corona wire 14. The second method is to apply to the s~reen 1 from its surface B a separate corona discharge having the same polarity as that of the corona discharge for the secondary electrostatic image formation, the corona discharge of which is dierent from that for the secondary electrostatic latent image formation. The electric current for this corona discharge may be sufficient to be from a few fractions of~ to several times the amount of ordinary current. In the second method, however, the presencè of the conductive supporting member 13 which functions as the opposite electrode to the corona wire 1~ is desirable for the following reason. If there is no opposite electrode on which electric voltage is impressed, it may happen that even the principal part of the primary electrostatic latent image becomes quenched.
On the other hand, when the corona discharge by the D.C.
.

...... . ., , , .. .. .. .. : .

~ 6~L39g3 voltage application is used for forming the secondary electrostatic latent image as mentioned a~ove, the secondary electrostatic .image formed on the recording member, etc. becomes the electrostatic latent image of a single polarity, either positive or negative. On account of this, there may take place a fogging phenomenon, with the devel-oped image depending on the electric potential of the electrostatic ..
latent image, and hence a good reproduction image cannot be obtained.
However, the contrast in the secondary electrostatic latent image in ..
its development possibly is heightened by the following method, in : . .
.; .- .
which the polarity of the voltage to be impressed on the discharge electrode for the flow of the corona ions that is applied onto the recoraing mem~er, etc. through the screen 1 for the secondary elec- .
trostatic latent image formation, and the polarity of the voltage to be impressed on the opposite electrode such as the above-mentioned conductive supporting member, etc. which faces the corona discharge electrode are. o mutually different polarities, i.e., positive (~
and negative (-), or vice versa. Examples of the above-mentioned alternate polarities are one in which an alternating current ~A.C.) -~ .
voltage is mutually shifted by 180 degrees in phase, or one or more pairs of direct current corona discharge having positive and nega- .. .
tive polarities are used. One example of such method will be descri- .
bed with particular reference to Figure 6, in which.like partsi are ..; :.
designated by the same reference numerals as are used in E~igure 5. ..
In the arawings, reference numeral 19 designates a variable capacitor, .
~;1 '' " ' numeral 20 designates a rectifiar, numeral 21 designates a trans-former, and numeral 22 refers to an A.C. power source. ~he construc-tion of the screen and the electrostatic latent image forming process for ion modulation axe not limited to those mentioned above, but it is only sufficient if the primary electrostatic laten-t image on the ~ ~4 ~

. . :;. . . ~:
:. - . . :
. . ~ , . . ~

~L06~!L399 screen 1 is almost symmetrical from the standpoint of electric charging in the bright and dark image portions of the original image. The recording member, too, is not limited to rec~rding paper, but any chargeable member may satisfy the requirements.
Moreover, as in the basic devi.ce shown in Figure 6, an output constantly lagged in phase by 180 degrees can be obtained by using an A.C. power source 22 and a transformer 21 having inter-mediate terminals, one being connected to the corona wire 14 of the corona discharger by way of the variable resisto.r 19 and the rectifier 20, and the other being connected to the conductive supporting member 13. In this circuit construction, the variable resistor l9'and the rectifier 20 function to adjust the intensity of the polarity (positive and negative) o:E the A.C. voltage as well as to control the conditions of the secondary electrostatic latent image on the recording member 15. The interval between the screen 1 and the recording member 15 is appropriately from 1 to 10 mm, and the electric voltage to be applied to the screen 1 preferably is 0.5 to 5 KV or so at peak value. Of course it is possible tha~ electrical components other than the above-mentioned variable resistor 19 and rectifier 20 may be used toobtain an output constantly lagged in phase by 180 as mentioned above using the alternate current power source 22.
It is also possible to impress the A.C. corona discharge on the recording member 15 by the corona discharger from a side opposite to the screen 1 without using the conductive support member 13. In any case, when the corona ions to be modulated are of alternating current, it is desirable that an electical voltage of a mutually opposite polarity be impressed betwesn - the corona wire 14 and the conductive suppor-ting member 13 over substantially the entire period of the ion flow modulating step. For this reason, the use of the transformer 21 is nothing . ~ but an example of the ion flow modulating method. This transformer ~
can be replaced by various methods such as, for example, control- -ling by means of a relay ~wo direct c~rrent power sources having mutually opposite polarities. By using such method, the conduc~
tive support mem~er 13 is maintained in a negative polaxity, so long as the corona wire 1~ is maintained in a positive polarity, whereby the positive ions pass through only the portion where the screen 1 is maintained in the negative polarity, and adhere onto the xecording member 15. on the other hand, while the coxona 10 ~ wir~ 14 is in a nega~ive polarity, the conductive support member 13 is kept in a positive polarity, whereby th2 negative ions pas~ through only the portion where the screen l is maintained in the positive polarity and adhere onto the recording member 15.
As a result o such processing, there is ~ormed a secondary electrosta~ic latent image on the recording member, wherein the dark image portion is in the negative polarity and the bright image portion is i~ the positive polarity. When this se~ondary electrostatic latent image is developed by the use o~ colouring particles such as toner having a positive polarity, a reproduc-tion of the original image free from the fogging can easily beobtained. Also, harmony in the reproduced image can be adjusted~
appropriately by the variable resistor 19~ Needless to say, production o~ a negative image is al~o possible when a toner of negative polarity is used.

~' " .

, .

_ 26 -~06~399 ~
DESCRIPTION OF THE PREFE~RED EMBODIMENTS
In order to enable persons ~illed in the art to reduce to practice the present invention, the following pre~erred em-bodiments of the electrophotographic method are presented. It should be noted however that changes and modi~ica~ions may be made to the extent that they do not depar~ from the spirik and scope o~ the inYention as recited in the appended claims.
First Emb~diment In the production of a pho~osensiti~e screen fox use in the electrophotographic method according to the inven-tion~ selenium (Se) i~ deposited by vacuum-evaporation onto a conductive member o 200 mesh made of stainl~ss ste 1 wire 40 microns in diametex in such a manner that the openings o the conductive member are not closed by the evaporated metal. ~t this time, deposition o~ the vacuum-ev~porated selenium i~ con-ducted so as to bring the thicknes~ o ~he depo~ited layer on the conductive member at its thickest portion to approximately 50 microns.
Subsequently, parylene as the insulative substance is adhered onto the selenium photoconductive member thus obtained to a thickness o~ about 10 microns~ Since parylene i~ coated on the entire sur~ace of the photoconductive member, the sur~ace oppo~ite to that where selenium as a screen ~or the conductive member i~ deposi~ed at its maxim~m thickness is ground by an abrasive a~ent ~o as to expose a part of ~he con-ductive member to the external atmosphera. For the sur~ace in-sulating member, a thinner solution of polystyrene ca,n be spra~-coated on the photoconductive member in place Q~ the above-mentioned parylene~

~' !
6~399 The screen produced in the above process steps is then ~ .
charged to -500 V in the primary voltage application step.
Following this electric charging, irradiation of an image to be reproduced is conducted wi~h an exposure light of 30 lux per second and, at almost ~ame time~ corona discharge is im-parted to an electric current in the negat:ive direction by means of an A.C. current through a resistance component of 10 MQ . After this, when the overall surface of the screen is irradiated, a primary electrosta~ic image is formed on the ;
surace insulating member of ~he screen, the surface potential at the bright image portion being ~150 V, while that at the i:
dark image portion being -200 V. An electrostatic recording paper is then placed acing the thus formed primary electro-static latent image at a space interval therebetween o~ 3 mm, and a positive corona discharge is carried out onto the recor-ding paper through the primary electrostatic latent image formed on the surace insulating member of the screen, while maintaining the potential o the recording paper at -2 KV with -respect to the conductive member, whereby the flow of corona ions is modulated by the primary electrostatlc latent image, and the secondary electrostatic laten~ image is ~ormed on the recording paper.
The recording papar bearing the secondary electro~tatic latent image formed by the:afore-described processe~ i~
then subjected to development by the use of negatively charged ~olour developing particles in a liquid developer. The re3~1t i5 a ~eproduced image having high re301ution and capable o~
reproducing even interme~iate cGlour tones in the original at high fidelity.

.

When retention copying is done ~or 50 consecutive times using one and the same primary electrostatic latent image formed on the ~creen, it is found that the image density of the fiftieth reproduced image is slightly lower, although no in- :
convenience whatsoever is suffered from a practical ~iewpoint.
In forming the secondary electrostatic latent imaye, i~ it is assumed that the screen is stationary, the corona discharger for the ion 1OW modulation can be moved at velocities of 3~ cm/~ec, and higher, so that the design of a high speed and compact type reproduction machine becomes possible.
Second Embodiment ..
In the production of a photosensitive screen for u~e in the electrophotographic process according to the present inven-tlon, a solution oE CdS powder used as a photosensitive body in oxd~nary electxophotography and 2~% by weight of solvent type epoxy resin as a binder is spray-coated from on0 direction onto a metal net of 200 mesh made of stainle~s steel wire 30 microns in diameter as the conductive member in such a manner that the openings of the conductive member will not be closed, thereby forming the photoconductive member. A~ter drying and polymerizing the coated epoxy resin, the same resin as the above-mentioned binder is spray-coated in the same manner as in coating the photoconductive member in a manner not to close the opening~ of the conductive member, thereby forming the surace insulating member.
In forming the primary e~ectrostatic latent image, the electric voltage to be applied to the corona discharge in the primary voltage application step is made an opposite pQlarity to the case of the first embodiment, and the corona discharge '; ' ' 29 - ~

: ~ :

6~ 9 i5 conducted.
The image irradiation step is carried out by irradiating the image with an exposure light of 8 lux/second. As a result, there i~ foxmed on the screen a primary electrostatic l~tent image having a surface poten~ial o -100 V at the bright image portion and ~200 V at the dark image portion.
In forming the secondary electrostat:ic latent image, a negative corona discharge is carried outO ana the secondary electro~tatic latent image formed on the electrostatic re~or- ;
: . , .: .
ding member is developed by positively charged colouring particles in the dry development method. The reproduced image obtained thereby ha~ a high image resolution as in the ore-going ~irst embodiment, and is capable o reproducing with high fidelity the intermediate colour tones of the original image.
Also, in the same man~er as in the first embodiment, the retention copying is carried out by use o~ a photosen~itive screen bearing the electrostatic latent image formed by the a~ore-described process steps. The result is such that a good ~uality image which is not much different from the initial copy can be reproduced even after copying more than thirty sheets.
Figures 7 to 13 inclusive indicate one example of the electropho~ographic reproduction machine, in which the afore-described photosensitive screen 1 is applicable.
I~ the present invention, the corona discharge fox Porming the primary. electrostatic latent image is carried out fr~m the surface A, and the other corona discharge for the image irradiation and the secondary electrostatic latent image ':

: . , . . ~, . , . . , :

~l(J 6139~

formation is carried out Erom the ~urface B. Accordingly, when the screen 1 is flat and stationary, the recording memb~r should be caused to pass through a charging device for the latent image formation or a discharging device between the photosensitive screen and a conveying device for positioning the recording member adjacent to the screen 1~ ~;
- The electrophotographic reproduction device 23 shown in Figure 7 comprise~ a fixed table 24 on which may be placed an original ~mage 25 to be reproduced, a lamp 26 to illuminate the original image 25, a movable optical sys~em 27 consisting o a reflection mean~ and a lens, a corona discharger 28 to carry out the primary voltage application to~the flat, stationary type photosen~i~ive screen 1, another corona discharger 29, a lamp 30 for overall surface irradiation, and a container 31 to hold the corona dischargers 28 and 29 and the lamp 30, which container i8 shiftable in parallel with the screen 1. The device further comprises a cassette 32 for accommodating electro-static recording paper 33 in cut sheets, a feeding roller 34 to send out the recording paper 33 sheet by sheet, a conveyor bel~ 3S provided with a 5axon conveying mechani~m and to carry the recording paper beneath the screen l, a corona discharger 36 to form a secondary electrostatic latent image, a magnetic brush developing means 37, a heating roller-type f~xing means 38, and a tray 39 to receive and hold the rec~rding paper 33, on which the original image has been reproduced.
The electrophotographic device of the above-described con~truction is operated in the following fashion. Reerring to Figure 7, the original image 25 on the fixed table 24 i~
illuminated by the lamp 26, and i~s image is irradiated 4n the ~' ' ' ;- :
- 31 - ~

i, .. . . . . .

6~L39~ :
- `screen 1 through the opti~al system 27. At the time o illum-inating the above-mentioned original image, the lamp 26 , the :::
optical system 27, and the container 31 move in parallel with .
and in the vicinity of the fixed photosensikive screen at the same speed and in the same direction, whereby ~he primary electroYtatic image is formed on the screen 1. The conveyor belt 35 beneath the screen 1 is coLoured i.n a low brightness such as black so a~ to prevent light which has passëd through the openings of the screen 1 from sca~tering to other parts of the device. The record;ng paper 33 i5 forwarded sheet by shee* by the paper feeding roller 34 onto the conveyor belt 35, and i9 positioned by the conveyor belt 35 facing the screen 1 at the stage of the primary electro~tatic latent image having been formed on the screen 1. Then, the ~low of corona ions ~rom the corona discharger 36 for the secondary electrostatic image formation is modulated by the primary electrostatic latent image on the screen 1 to thereby form the secondary electro-static latent image on ~he recording paper 33. Thereafter, the secondary electrostatic latent image iB developed by the developing means 37, and the developed image is fixed by the .
fixing means 38. The recording paper 33 with the image repro- ~`
duced thereon`is received and held in the tray 39 out~ide the reproduction device. The corona discharger 36 i5 capa~le of : . ~
increasing its moving speed higher than 30 cm/sec.; hence it -.
can be operated at a very high speed at the time o the reten-tion copying.
For the purpose of the retention copying, the la~p 26, the optical system 27, and the container 31 are in a stationary state, only the corona discharger 36 moving above the screen 1.

_ 32 ~

'` ' ~ '- ` ' , ' . ' ' . ', , ; ~ . .

ll ;
~ 6~;399 The operation~ of the discharger 36 and of the recording paper 33 at this time are as follows. The recording paper stops at its designated position below the ~creen 1, when the corona discharger 36 comes along above the screen 1, whereby the secondary electrostatic latent image is formed on the recording paper. Immediately upon formation of the secondary electro-static latent image on the recording paper 33, it is ~hited toward the developing means 37 and the fixing means 38, and the next succeeding recording paper i~ fed to the position beneath the screen 1. In this ca~e, before the paper comes to the designated position and stops, the corona discharger 36 returns t~ it~ starting position. In other words, at the time o~ the retention copying, only the corona dischxrger 36 ~oves among various.means for the electrostatic latent image orma-tion, and hence the device is able to operate at hi~h speed and with a small load imposed thereon.
The electrophoto~raphic reproduction device 40 sh~w~ in Figure 9 is the 3ame in hasic construction as the device 23 shown in Figure 7. In this reproduction device, however, the screen 1 is so designed that it is shifted in close proximity `..
to the conveyor belt 35 ~o a~ to narrow the space interval .
between the screen 1 and the recording paper 33 as shown in Figure lOo whereby the flow of the corona ions from the :
corona discharger 36 ~or the necondary electrostatic latent ..
image ~oxmation i8 modulated by the primary.. electrostatic ~:
latent image on the screen 1 to form the secondary electrostatic ~ :
latent image on the recording paper 33. At the ~rmation of the secondar~ electrosta~ic latent image, the screen 1 is ' ,:
maintained in a state o its havin~ ~hifted in close proximity ~ .

; `; ~06~399 ,~
-- to the recording paper 33 as shown in Figure 10, in the course of which the recording paper 33 is fed and brought to the designated posi~ion. As soon as the paper stops at the de~tin-ation, the above-mentioned corona discharger 36 bagins to shift.
As stated previously, displacement of the photosensitive screen 1 in close proximity to the recording paper 33 makes it possible to reduce the electric voltage to be impres~ed on the corona discharger 36 to form the secondary e}sctrostatic latent image lower than that in the device shown in Figure 7 For example, when the distance between the screen 1 and the recoxding paper 33 is 20 mm, a voltage o~ 6 to 20 kV or s~ is necessary. However, when the distance therebetween is 3 mm, voltage application o~ 2 to 3 kV or so would be su~Eicient to or~ the secondary electrostatic latent image.
The electrophotographic reproduction device 41 shown in Figure 11 is diferent from the device shown in Figure 9 -~
i~ that, upon formation of the primary electrostatic latent i~age, the conv~yor belt ~2 moves upward to the fixed screen 1 and stops immediately helow it a~ shown in Figure 12~ By thus narrowing the space interval between the screen 1 and the re-cording paper 33, the same e~ect as explained in con~ection with ~he device of Figure 9 can be attained. In Figure 1~
the developing vessel 43 is ~f a wet ~ype, and the fixing means 44 is a chamber type heat-drying fixing device. Also, the reference numeral 45 designates a ~eparating pawl to separate the recording paper 33 from ~he conveyor belt 42. ThQ separ-ating pawl 45 and the guide members provided thereaxound move simultaneou~ly with the conveyor belt 42. It will be convenient .
- 3~ -- .

. ~ . .

~06~L39~
that the positional relationship of the separatiny pawl 45 be made changeable at a stage before and after the simultane ous shifting so that the pawl 45 may not touch the developing vessel 43 or other meJ~bers. In the state as shown in Figure 11, the tip end of the separating pawl 45 does not contact the conveyor ~elt ~2, and the other end of ~he~ yuide member is dis- .
posed at a position di3tant from the developing vessel 43.
When the primary electro3tatic latent image formation is c~mplete and the conveyor belt 42 moves up ~o ~he position i~mediately below the screen 1, the separating pawl 45 also moves and the tip end of this pawl is so actuated that it is in a state of readily separating the recording paper 33 on the conveyo.r belt 42 therefrom, while the other end o~ the separating pawl 45 exhibits its function to guide the recording paper 33 tv the ~.
developing vessel 43.
IncidentaIly, in Figures 7 to 12 inclu~ive, componen~
members in the devices having ~he ~ame functions are designated by like reference numerals. `
The reproduction device 46 ~hown i~ Figure 13 ~orms the photosensitive screen 1 in a cylindrical ~hape. In this figure, an ~riginal image 47 placed on the fixed plate is il-lu~inated by a lamp 48 and exposed on the.cylindrical screen 1 by mea~ of an optical sy~tem comprising mirrors 49, 50 and 51 and an optical lens 52. The screen 1 rotates in a clock ;:
wise direction as ~hown by an arrow, and has its conductive member inwardly exposed. The primary electrost~tic latent image is formed on this cylindrical screen in ~uch a way ~hat, upo~ it~ passag0 through a corona discharger 53 for the primary voltage application and ~ubsequently through a coro~a discharger , .
. . . . .

`
~ 61399 54, the screen is irradiated by a lamp 55 on the entire surface :
thereof. An electrostatic recording paper 56 which is the recording member is conveyed through the route indicated by a dot-and-dash line. A secondary electrostatic latent image is formed on the recording paper held on a conductive suppor-ting member 58 by modulating the flow of corona ion~ from a corona discharger 57 by the primary electrostatic latent image formed on the screen. ~fter the secondary electro~ta~ic latent image formation, the recording paper 56 is forwarded to a dry type developing vessel 59 and subsequently to a fixing vessel 60 where the latent image is developed and fixed, and the ~.
original image is ther~y reproduced on the recording paper.
When multiple repxoductions are desired to be obtained from . the ~i~gle original image, the forming proce~s of the secondary electrostatic latent i~age alone is carried out, while ~ynchro~
nizing the rotation o the screen 1 and the paper eed. It is ~:
also possible to re-use the screen 1 after the primary electrG-static latent image which has become unnecessary is remQved by a corona discharger 61 ~or removing the electric charge, and a lamp 6~.
In the following, the construction o~ a ~creen capable of forming primary and secondary electrosta'tic late~t ~mages by the electrost~tic latent image forming process will be ex-plained with re~erence to Figures 14 to 17 inclusive which indicate enlarged cros~-sections o~ photosensitive scre~ns constructed according to the prese~t invention~ The screen 63 in Figure 14 is o such a construction that A photoconductive member 65 is coated on a conductive member 64 to be the active part of the screen 63 at a poxtion substantially to one ~ide ~:

.

there~f, a surface insulating member 66 is further coated on the partially exposed conductive member 64 and the photo-conductive member 65 so as to wrap both parts, and a ~eparate co~ductive member 67 which is different from the above-mentioned conductive mem~er is provided on one part of the surface in-sulating member 66. The conductive member 67 is deposited on the insulating member 66 hy the vacuum-ev2lporation o metals such as alwminum, c~pper, gold, indium and nickel, or by spray-coating o a mixture of a resin as a binder and a conductive ` : :
resin containing therein quaternary ammonium salt~ carbon I .
powder, or a fine powder of metals such as ~ilver and copper. .;
The screen 68 shown in Figure 15 i~ substantially the same as the screen 63 in ~igure 14 with the exception that a photocon-~ .
ductive member 70 i5 provided around a conduc~ive member 69 so ~ ::
as to surround it completely. In the screen 73 of Figure 16, a photoconductive member 75 is provided around a conductive me~ber 74 ~o be the base or the screen 73 in such a manner that i a part of the conductive member 74 may be exposed, and also a sur~ace insulating member 76 i~ provided on the photoconduc- ~.
tive member 75 in such a manner that a part of the latter member ~ay beeKposed to the opening of the æcreen 73~ Further, . the ~creen 77 shown in ~igure ~7 is so constructed that an insulating member 79, a photoconductive member 80, and a ':
surface insulatin~ ~ember 81 are provided one after the other .
in such a manner that a conductive membex 78 to be the base ~or the screen 77 may be exposed as i~ the case with each o the afore-described screens of di~ferent ~truc~ures~ The material~ and the method to be used for fabricating the aore- -described screens may be the same as those usecl in fabricatin~
'' ' ' .,. .'''.
, j . ~06~399 the screen 1 of Figure 1~
The latent image forming processes u~ing each of the abvve-explained screens will be describ~d hereinbelow. How-ever, as the processes are not much different rom ~he case of the screen 1 shown in Figure 1, only an outline of each tep will be given. Also, throughout the explanation, the photoconductive member is the one that is exemplified in Figure 1. ~n explanation o~ the screen 68 in Figure lS is di~pensed with in view o the explanation of the screen 63 in Figure 14.
Figures 18 to 22 indicate the state o the electric charge in the screen 63 o~ ~igure 14 due to the elec~rophoto-graphic method accordin~ to the present invention, o~ which Figure 18 shows the primary voltage application process to the ~creen 63 and hence it indicates a s~ate o~ the surface insulating member 66, for example, being uniformly charged in negative polarity by a corona discharger. Owing to thi~
electric charging, ~he surface o~ the surface insulating member 4 i5 negatively charged, whereby a positively charged layer which is the opposite polarity to that o the insulating member 4 i~ formed in the photoconductive membe~ 65 at a positio~ contiguous ~o the vicinity of the insulating member 4 of the conductive member 64. Figure 19 shows a result of ~imultaneous image irradiation and the ~econdary ~oltage application processes having bee~ carried out on the screen 63 which has undergone the above-mention~d voltage applica~ion process. The referen~ numeral 82 designates an original image to be reproduced; wherein the part D ia a dark image portion and the part L is a bright image portion. In Figure 20 _ 38 -~ 6~399 the sur~ace ins~lating me~ber 66 is shown to be discharged by the corona discharger with an A.C. voltage as a power source, on which a voltage of positive polarity has been super- ~.
posed, in such a manner that the surface potential o~ the in- ~ :
sulating member 66 may be made in substantially a positive polarity. When the sur~ace potential o~ the insulating member ;.
66 is thus made in the opposite polari~y to that a~ the time of the primary voltage application process, the sur~aee `~
potential of the insulating member 66 takes a positive ` ~
polarity in the light image portion L, although the dark `.~ -image portion D of the insulating member 66 remains in a nega~
tive polarity. Figure 20 shows the result o~ conductin~ a uniform.exposure on the centre ~urface o the screen 63 which ...
has under~one the above-mentioned process s~eps~ By this overall exposure, the dark ~mage portion D of the screen 63 . :
~hanges its potential in proportion to the charged quantity .;
on the surface of the insulating member 6~. As a consequence, there is ~ormed on the ~creen 63 the primary electrostatic :.
la~ent image in conformity to the original image to be repro-duced~ . .
Figure 21 shows a state of the secondary elect~o3tatic `~ .
latent image being formed on the recording member by way o~
the primary electrostatic latent i~age.on the screen 63. The xeference numeral 84 in thi~ figure designates a corona wire, the numeral 85 designate~ a recording member held on a con- ..
ductlve suppor~ member 86 which al~o function~ as the opposi~e electrode to the corona wire 84. The corona wire 84 is im-pressed by a voltage of positive polarity, and the conduc~ive ' ', ..
. .
. - 39 -. . . :, , . : -, . .: .
. . ~ s :~6~399 support member 86 is maintained at zero potential. The '' dotted lines in this figure show ~he ion flow from the co~ona `'~
wire 84. The principle of modulating the ion flow is as de-scribed in the foregoing with regard to the formation of the secondary electrostatic latent image shown in Figure 5. Also ~ ~, as mentioned previously, the image irradiation and the secon-dary voltage application may be carried out in se~uence de- , pending on characteristics of the phot~conductive ~ubstance constituti'ng'the screen. This holds goocl ~or other proces3e~ `' of the present invention as will be described hereinafter, Throughout ~he processes as de~cribed above~ the conductive members 64 and 67 are electrically continuous, and th~y are ' able to adjust the pa~sion ion flow at the time of modulating the! corona ion 1OW by impressing a bias voltage.
Figures 70 to 74 ~nclusive indicate respectively t,he , ,' charged states in the screen which, unlike that explained with reference to Figure 1, does not cause the carrier injection at the tim0 of the primary voltage application. Fi~ure 75 is a graphical xepresentation showing variation~ in the ~urface '`
,20 potential of the screen in each process step in Figures 70 to 7~. A screen 204 in Figure 70 has a conductive ~embex 208 provided at only one surface side of a conductiva ~ember 205 to be the basic element or the screen 204, a photoconduc- -~
~ive member 206, an insula~ing member 207 nd the sc~een 204 '~
per se. This figure show~ the primary voltage application pr~cess,to the above-mentioned screen'204 by way o~ a corona wire 209 and a power ~ource 210. In the illustrated example, the screen 204 is in a ~tate o~ being charged in a positive polarity at the dark image portion D. In the above-described ' -- ~0 --, , 6:~L39 .. . .,~ .
process step, a positive electrostatic charge i9 adhered o~to '- ~
the insulating member 207. However, as the photoconductive ~:
member 206 exhibits a highly insulative property, no negative ~:
,.,:: . .
charge layer corresponding to the positive electrostatic ., charge can be formed.
Figure 72 indicates the image ir~adia~ion process, wherein an original image 211 is irradiated by a light 212 for ~ :
the exposure. By this ima~e irradiation process, the photo~
.. .. .
conductive member 206 at the bright image portion of the screen 204 lower~ its resistance ~alue with the consequent formatio~
of a negative charge layer corresponding to the above-mentioned .
positiYe static charge in t~e neighborhood of t~e insulating member 207 conti~uous to the photo¢onductive mem~er 206. Fiyure 72 shows a resuLt o~ applying onto the dark image portion o~
the screen 204 a secondary voltage having a polarity opposite to that o~ the primary voltage by means o~ a corona wire 213 and a powsr source 214. For the purpose o~ the latent image formatîon, the secondary voltage may either be o~ ~he sama polarity a~ that of the primary voltage, or it may be an alter-nate current. By this secondary voltage appli~ation process, the electrical potential a~ the dark image portion on the screen ~`
204 becomes zero while, at the bright ima~e portion, the posi- .
tive charg~ on the sur~ace of the screen i eli~inated to some , ..
extent. .
Figu~e 73 shows a result of the overall surace exposure o~ the screen 204 whereby the primary electrostatic latent image having a high electrostatic contrast i~ ~ormed on the screen 204. The refer~nce numeral 215 designates an exposure light~ .

,~ .
. - ~1 - , .

)6~399 Figure 74 shows the secondary eleckrostatic latent image forming process by way of the screen 204. In this figure the re~erence numeral 216 designates a corona wire, the numeral 217 designates a conductive support membex, the numeral 218 . :~
designates recording member, the numeral :219 designates a power source for the corona wire, and the numeral 220 designates a power source for forming a bias field bet~een the screen 204 and the recording member 218. When the flow of the corona ions a~
indica~ed by dotted line~ 1~ the drawing and having the same polarity as that of the sur~ace charge at the bright image portion of the screen 204 is directed to the recording member ~ .
218, the ion flow is modulated by the pr.imary electro~tatic .~;latent image on the screen 204, and the secondary electrostatic latent image is formed on the recording member 218. In order , ~;
~or the ion flow to be satisfactorily modulatedr formation o~
a bias field by an electrode 221 between the conductive members 205 and 208 may be effective. In this secondary electrostatic latent image forming process, the ima~e irradia$ion and the ~econdary voltage application cannot be performed simultaneously. .
~urning back now to the previous figures o~ the drawings Figure 22 to 25 indicate xespectively a state of the electric charge on the ~creen 63 of Figure 16 for use in`the electro-photographic process according to the present invention.
Figure 22 shows the primary voltage a~plication process to the ~creen 73, wherein the sur~ace in~ulati~g member 76 is indi~
c~ted to b9 charged in ne~ative polarity by the coro~a dis-charger~ ~y the above-mentioned charging, an el~ctrLc charge layer of positi~e polarity which is opposite to the char~e polarity on the in3ulating member 76 is formed on the photo-s ~ 106~39~
conductive member 75 at a position contiguous to the insulating :~
member 76. Figure 23 indi~ates a result of perorming the simultaneous image irradiation and the secondary voltage appli-cation onto the screen 73, wherein the re~erence numeral 87 designates the original image to ~e reproduced, the reference letter D designates a dark image por~ion, the letter L a bright image portionJ and the numeral 88 the light for exposure.
Figure ~3 indicates a result of discharging the screen 73 by the aorona discharger using an A.C. power source, on which a `~
voltage of positive polarity has been superposed, in such a manner that the sur~ace potential of the screen 73 may take substantially the po~itive polarity. As a consequence o~ this corona di~charge, the surace potential of the insulati~g member 76 can be made in the opposite polariky ~o the previou~
pxocess step, although the surface.potential of the insulating member 76 at the dark image portion D remains in the negative polarity. Also, the photoconductive member 75 expo~ed to the openings of the screen 73 on some occasion has a~ electric charge adhered on its surface due to ~he secondary voltage application in ca~e insu~ficient light reache~ the photoconduc-tive member 75. Figuxe 24 indicates a result of carrying out sufficient expasure to the overall surface of the screen 73 which ha~ undergone the aore-me~tioned process steps. By this light exposureO the dark image portion D of the ~creen 73 changes i~s electric potential in proportion to the chaxge ~ -~ua~tity on the surface of the insulating mem~er 76, as a result v which the primary electro~tatic latent image is formed on the screen 73 in conormity to the original image to be re- . .
.
produced. Figure 25 indicates formation of the secondary - 43 ~

` ,'~ 6~ 399 electrostatic latent image on a recording member, wherein the xecording member 90 is held on a conductive support member 91.
The flow of corona ions is generated from a corona wire 89 ..
as indicated by the dotted lines in the drawing and is directed to the recording member 90 passing through the primary electro-static latent image on the screen 73 where it is modulated.
Incidentally, the conductive support member 91 also serves a~ :
the opposite electrode. The corona wire is impressed by a vol-:
tage of positive polarity. The principle of modulating the ion flow shown b~ dotted lines is in respect of the secondary .`~ -electrostatic latent image forming process o Figure 5.
Figures 26 to 29 inclusive respectively indicate a ~kate o electric charge on the screen 77 in E~igure 17 by the eleckrophotographi~ process accord.ing to the present inventi.on.
A~ illustrated in Figure 26, the primary voltage application charges the surface insulating member 81 in negative polarity.
By the above-mentioned electric charging, the carrier exisking in the interior of the photoconductive member 80 moves, or the carrier formed by the overall exposure o the screen to ~`
be carried out simultaneously with the electxic charging moves toward the surface insulating member 81 and the above-mentioned carrier of positive charge is captured at the interace bs-~ween the photoconductive member 80 and the insulating member 81. As a consequence, the ~harge layer is formed in the in-t~rior of the screen 77. Figure 27 indicate~ a result of con-ducting khe simultaneous. image irradiation.and the secondary volta~e application on the screen 77 which has undergone the above-mentioned primary voltage application process, wherein the oxiginal image 93 having the dark image - 4~ -'. ' ' ' ' ' ' ' ' ~
: . :

6~3g9 portion D and the bright imaqe portion L is irradiated by exposure light 92 represented by arrows~ As has been mentioned previously, Figure 26 also indica~es a result of discharging the screen 77 by the use of a corona discharge with an A.C.
voltage, on which a volta~e of positive polarity has been super-posed, as the power source in such a way tha~ the surface po-tential of the insulatin~ member 81 may become substantially o:e positive polarity. As descrihed above, a~ the time of the secondary voltage application, the surface potential of the in- :
sulating member 81 take~ an opposite polarity to that o:E the prLmary voltage application although, at ~he dark ima~e por~ion D of the insulating member 81, there still remains the negative charge on the sura~e thereof. Figure 28 shows a result o ~: , . . . .
conducting a uni~orm, ovexall exposure to the screen 77. By . ..
this overall expo~ure of the screen, the electrical potential at the dark image portion D of the screen 77 varies in propor-tion to the charge quantity on the surface of the insulating member 81, in consequence of which the primary electrostatic latent image i~ formed on the screen 77 in conformity to the original image to be reproduced. Figure 29 indicates the ~ecvndary electrostatic latent image being formed on the sur- :
face o~ the recording mem~e~ 95 wh.ich is held on the conductive support ~ember 96 which also serves as the opposite electrode to the corona wire 94. The corona wlre 94 is impressed by a voltage of positi~e polarity. The principle o the ion flow modulation as indicated b~ the dotted lines is as already :
described in the secondar~ electrostatic latent image foxming process of Figure 5.
Figure 30 shows the potential cur~es on the sur~ace of ,., ~ ' , - ~5 -613~9 the insulating member at each process step of formin~ the electrostatic la~ent image as described in the foregoing. As .
will be seen.from this graphical representation, when.the surface of the insulating member of ~he screen is negatively charged for example, by the corona discharger, the surface potential of the insulating member lowers with lapse of the charging time to ind.icate the charac~eristic as represented by the curve Vp. ~ext, when the image irradiation and the re-charging with A.C. corona discharge biassed in positive polarity .~.
to some extent are carried out, the negakive charge in the bright image portion of the image is entirely discharged t~ be charged in ~ubstantially the positive polarity as represented . .
by the characteristic curve VL. Also, in the dark image portion, th~ nega~ive charge formed on the surface o~ the insulating ~`
member by the above-mentioned charging is not discharged com-pletely as in the bright image portion, even if the above-mentioned secondary voltage application is carried out, hence the sur~ace potential in the dark image portion is as shown by the char~cteris~ic curve VD. Thus, when khe overaLl surface exposure of the screen is conducted after the image irradia- ;
tion and the secondary voltage impression to orm the electro-static latent image on the surace o~ the insulating member, no remaxkable change takes place in the above-menkioned bri~ht i~age portion o~ the photocondu.ctive member, so that the ~ur~ace potential becomes as ~hown by the curve VL~. In contradistinction, in the above-mentioned dark image partion, the xe~istance value of the photoconductive member lower~
abruptly.~o become conductive~ as a result o~ which the e~ectric cha~ye within the photo~onauctive member remains t~ be ~lightly ' - 46 - j r~ ~ 1061399 captured by the negative charge field on the sur~ace of the r insulating member, and the surface potential thereo abruptly reduces as represented by the characteristic curve VDL.
Through the foregoing process steps, the primary electrostatic latent image is ormed on the screen. ~ -In Figures 21, 25 and 29, the reerence numerals 97 t~ ~02 designate a power source for the corona wire, a screen, and a conductive support member. Also, in the formation of the primary electrostatic latent image on the screens 63, 68, 73 and 77, the voltage u~ed for the secondary voltage applica-tion process may be one having the opposite polarity to that u~ed for the primary voltage application, besides the A.C.
voltage, on which a D,Cv voltage is superposed as men~ioned above. Further, ~s to ~he direction o~ the image irradiation, it can be done from the side where the conductive member is exposed, be3ides the afore-~entioned direction. In this case, however, if the screen to be used is of such construction as shown in Figures 14 and 15 (the screen 63 and 68) that another conductive member is further provided on ~he surface insulating member, it is necessary that the conductive member also be made o~ a transparent material. It goes without saying that the retention copying is feasible even in the case o using ~uch screen.
The screen as mentioned with reference to Figure 31 dif~ers from the ~creens that have been described hereinbefore in that it shows the insulative property at its on~ surface side due to the sur~ce insulating member 106 and, at its other surface side, it has both a conductive portion and an insulative portion~ The screen 103 as shown in the figure ~' ' ~ 6~399 is basically constructed by a conductive member 104 to be the base for the screen, a photoconductive member 105 provided around the conductive member 104, and a surface insulating member 106 The forming material of the ~creen 103 can be the same as that used in the screen of Figure 1. The fabrication of the screen can be done, for example, by forming the insu-lating member 106 in such a manner as to surround the conduc-tive member 104 and the pho~oconductive member lOS, and then -by grinding only one side of the scxeen 103 by an appropriate grinding means. More particularly, when the conductive member 104 has up~ and downs in its cross-section as in the case o a metal net, i~ one side of the screen 103 is ground uni~ormly the higher portion thereof is ground, resulting in the construc-tion as illustrated. The latent image forming process with the above-mentioned screen 103 is almost the same as men~ioned in the ~oregoing, the outline of which will be given hereinbelow.
Figures 31 to 35 respectively indicate the state o~
the electric charge in the screen 103 o~ Figure 31 by proce~ses ~ubsta~tially the same a~ the aore-de cribed electrophoto-graphic processes. Figure 31 indicates the primary voltageapplication to the screen 103, in which the sur~ace insulating member 106 is shown to have been charged uniformly in negative polarity, for example, by the coro~a discharger. By the above-mentioned electric charging, the surface of the insulating member 106 is charged in negative polarity, whereby a charge layer having a positive polaxity which i~ opposite ko that o~
the electric charge on the insulatin~ member 106 is formed in the photoconductive member 105 at the po~ition in the vicini~y of the insulating member 106. Figure 32 shows a result o~

conducting the simul~aneous image irradiation and the secon-dary voltage application onto the screen 103 which has under- -gone the primary voltage application, wherein the re~erence numexal 107 designates an original image having a dark image portion D and a bright image portion L, and the numeral 108 (arrows) designate~ light for exposure. In Figure 32, the electric discharge is conducted by the corona discharger using an A.C. voltage power source, on which a voltage of positive pGlarity is superposed, or a po~er source of a voltage having ~
the opposite polarity to that used in the primary vol~ge ap- -plication. ~he discharge is carried out in such a manner that the sur~ace potential of the insulating member 106 may become substantially positive in polarity. In this case~ as the ph~toconduc~ive member 105 in the dark image portion D has a high resistance, the surface charge o the insu1ating mem~er 106 remains ~egative due to the a~ove-mentioned charge layer.
Figure 33 shows a result o~ conducting ~he u~iform exposure on the entire surface of the screen 103 which has undergone the afore-mentioned process steps. By this exposure, the potential at the dark image poxtion D of the screen 103 ~arie~
in accordance with the electric charge c~antity on the surface of the in~ulati~g member 106. As a result of this~ the pri-mary electrostat-c latent image is formed on the scree~ 103 in conormity to the original image.
Figure 34 shows the process for xemoving unnecessary electri~ charge on the insulating member 106 existing on the exposed surface side of the conductive member o~ the above-mentioned screen. This process can be clispensed with. The re~erence numer~l 108 in this ~igure designates ~ corona wire _ ~9 _ ..

6~3~9 and the numeral 109 represents a power source for the corona wire 108. The polarity of the voltage to be applied onto khe corona wire 108 may be selected from A.C. voltage and D.C~ voltage which are capable of eliminating the above-mentioned unnecessary electric charge. Incidentally, this unnecessary charge is considered to be formed at the t:ime of the primary and secondar~ voltage applications. This unnecessary charge removal needs not be done every time in the case of retention copying.
Figure 35 indicates a state of forming the secondary electrostatic latent image to the recording member, wherein the latent image is formed on th2 recording member 102 held on tha. conductive support m~mber 103 b~ way o~ the corona wire.
The conductive support member 103 also serves as the oppo~ing electrode to the corona wire 101. This corona wire is impres-sed by a voltage of positive polarity, and the electric potential on the conductive support member 103 is maintained at zero. ~he principle of modulating the ion ~low as indica-ted by dotted lines is the same as is already explained with regard to the secondary electrostatic latent image forming process of Figuxe 5~ In the drawing, the re~er~nce numerals 104 and lOS designa*e the power source to the corona wire 101 and to the screen 103, respectively~
The electrophotographic pxoces~ accordi~g to thi~
second embodiment comprises the primary voltage application process to uniformly charge the screen according to the present invention or the purpose of the primary electrostatic latent image ~ormation~ the image irradiation process, and the sécond vol~ag~ application proces~ to be conducted kherea~ter -- 50 _ ~()613~9 - " to vary the surface potential of the screen in acc~rdance with the dark and bright patterns due to the above-mentioned image irradiation. The screen to be used in this electrophoto-graphic process is the same as that mentioned in the first embodiment. Here, the electrophotographic process will be explained with ra~erence to Figures 36 to 39 using the scree~
14 of the construction shown in Figure 14. The screen 106 to -be used in this embodiment consis~s of a conductive member 107 to be the base f~r the screen, a photoconducti~e member 108, a surface insulating member 109, and a conductive member 110 provided only at one surface side of the ~creen 106. The substance to be used fox the photoconductive member 108 i~
ei~her those that do not cau~e the carrier injection by the primary voltage application, or those that do not ~orm the electric charge layer in the photoconductive member 108 at a position in the vicinity of the insulating material depending o~ the kind of charge~
Figure 36 indicates the simultaneous image irradiation and the primary voltage application processes, wherein the surface insulating member 109 is charge~, ~or example, in positive polarity by the corona wire 111 through a power source 114, and an original image 112 havin~ a dark image p~rtion D and a bright image portion L is irradiated by an exposure light 113 in the arrow direction. By this electric charging, the positi~e charge is accumulated on the surface of the insulating member 109 and, parti~ularly, a negative charge layer is ~ormed in the photoconductive member 108 at the bright image portion in the vicinity of the insulating member while, at the dark image portion, the electric charge varies in , ` ~6~399 s ~ . .
proportion to the capacity of the photoconductive member 108, as it is insulative.
Figure 37 indicates the secondary vol~age application by a corona wire 115 and a power source 116 therefor. In this voltage application process, there is applied a voltage of a direction to eliminate the electric charge on the insu-lative member 109. The voltage t~ be applied is either an A.C. voltage, or a voltage having the opposite polarity to that in the primaxy voltage application. As a result o~ this, both bright and dark i~age portions of the screen 106 take the same surface potential.
Figure 38 indicates a result of conducting a uniform expo~ure with a light 118 in the arrow direction over the en-tixe surface o~ the screen 106. By thi~ tot~l exposure, the `~
electric charge within the screen 106 moves again, and the electrostatic contrast increases, whereby the primary electro-static latent image is ~ormed on the screen.
Figure 39 shows the secondary electrostatic latent image forming process. The principle of modulating the ion flow shown in dotted lines is the same as that already mentioned f with respect o~ Figures 5 and 21: hence detailed explanations are dispensed with. In Fi~ure 39, the reference numeral 119 designates a corona wire, the numeral 120 designates a power source for the corona wire 119, the numeral 121 designates a recording member held on a conductive support member 122, the ~umeral 123 represents a power source for forming the bias field.
between the screen 106 and the conductive support member 122, ;
and 124 designates a power source for forming the bias field between the conductive members 107 and 110. As mentioned .

- ~2 -s; I ~06139~
above, when the bright and the dark image portions are not in m~tually opposite polarities as in the screen 106 and the primary electrostatic latent image can be formed in the same polarity, it is efective to intensify the accelerating and inhibiting fields by forming the bias field between the con-ductive member~ 107 and 110 in the screen 106 of the a~ove~
described construction~
Figures 40 to 43 inclusive indicate the applica~ion o a secondary voltage having the same polarity as that of the~ -. -primary voltage application to the screen 106. On account o~ this application of a voltage having the same polarity, the pri~ary electrostatic latent image as forme~ becomes high in ..
contrast~ However, by adjusting the bias voltage to be ap-plied be~ween the conduc~ive members 107 and 110, a second~ry `
el~ctrostatic latent image having less ~og can be obtained. ...
In Figure 40, the primary voltage application is carried ou~ onto the screen 106 by means of a coron~ wire 128, a power source 127, and an exposure light 126 in the arxow direction to illuminate an origina} image 125 having a dark image portion D and a bright image portion L. By this primary voltag~ application, i~ the screen 106 is charged, for example, in positi~e polarity, it ~ again impressed by a voltage of the same positive po~arity in the subsequent secondary voltage application as shown in Figure 41.
In Figure 41, the reference numeral 12~ designates a power sourc~ for a corona wire 130. Figure 42 indicates a result of conducting a uniform exposure o~er the enti~e surface o the above-mentioned screen 106 by an expo~ure light 131 in the arrow direction, whereby the primary electrostatic .
. :' ,,: : . , :. , . ;: . .. .
,, , ~ , . .: , , 6~399 latent image is formed on the screen 106. Figure 43 indi-cates the secondary electrostatic latent image forming process, wherein the reerance numeral 132 designates a corona wire, the numeral 133 designates a power source ~or the wire, the numeral 134 de~ignates a recording member, the numeral 135 designates a conductive support member, the numeral 136 desig-nates a power source for ~orming the bias field between the conductive member 107 and the conductive support member 135, and the numeral 137 represents ~ power source for form:ing the bias field between the conductive members 107 and llOv F~gure 44 shows sur~ace potential curYes which vary - on th~ screen surface in each process stap as -~hown in FigUres 36 to 38 inclusive.
Third ~mbodim~nt ~ he photoconductive member is ~orme~ on one ~ur~ace o~ a conductive member as the base for a screen which is made of stainles~ steel wire o~ 30 micron~ in diameter in the form ..
of a metal wire net of 200 mesh size, by vacuum-evaporation of selenium ~Se) containing therein 5% of tellurium ~Te) to a thickness at the thickest portion thereof of approximately 50 microns. Subsequently, from b~th surfaces o~ the screenO
a ~olution o~ a copolymer of viny} chloride and vinyl acetate .:
in methyl iso~utyl ketone is spray-coated to a thic~ness o ~:;
approximately 15 mlcrons to orm an insulating member on the photoconduc~ive me~ber. ~hereafter, aluminum is deposited by evaporation to a thickness of 2,000 angs~roms onto the sur~ace side of the ~creen opposite to that where selenium is coated by evaporation, whereby the screen f~r use in the electrophoto- .
graphic pxocess according to the presenk invention is ~a~ricated.
' ' ,: ' .~: ." . ' . .
- 54 ~ :

:. . , . . ... . . . ~ . .: . . . . . .
. , :: . . : . . . .; . .. ,, . , ~ . . . . . .

' ~61399 -The image exposure is conducted from the surface side of the screen coa~ed with ~elenium with the amount of the exposure light at the bright image portion being about 6 lu~sec.
acco~panied by a simultaneous corona discharge at ~7 kV. After this when an A.C. corona discharge of 6.5 kV is applied to the screen as a secondary voltage application process followed by a total ~urface exposure, a primary electrostatic latent image is ~ormed having a surface potential of approximately O V at the dark image portion and approximately ~250 V at the bright 10 image portion. Thsn an electrostatic recording paper is dis- -posed facing the primary electrostatic latent image surface o~ the screen at a space interval of 3mm between them. The stainless steel wire as the conductive member of the screen is earthed, the aluminum la~er deposited on the screen is im-pressed by a voltage of ~180 V, while the recording paper is impxessed by a voltage of -3kV, and the corona discharge of ~7 kV is applied ~rom the side o the screen opposite to the side thereof facing the recordiny paper so as to form the secondary electro~tatic latent image. Upon formation of the 20 secondary electrostatic latent image on the recording paper, it i~ developed by a liquid developer to obtain a clear positive image of the original. When the retention copying i~ conducted for 100 times using this secondary electrostatic latent image on the recording paper, the decrease in the image density in the 100th sheet is recognized to be less than 10%
with re~pect to the image density in the initial sheet~ the reproduced i~age of which is found serviceable for practical use7 This third e~bodiment of the electrophoto~raphic ~ 55 -: . . . .

3~06~L35~
process according to the present inven~ion comprises the primary voltage application to uniformly charge the above-mentioned screen, and the image irradiation process to be conducted simultaneously with the primary voltage application.
In the explanations of the electrophotographic process in this embodiment, the screen to be referred ~o is the same as tha~
shown in Figure 36 above in its construction and in its electrical characteristics.
Referring to Figures 45 to 47 inclusive, the numeral 139 designates a conductive member of a screen 138, the numeral 140 designates a photoconductive member, the numeral 141 designates a surface insulating member and the nume~al 142.
d~signates a conductive member provided at one sur~ace side o the screen 138. Figure 45 indicate~ the simultaneous image irradiation and the primary voltage application, wherein khe surface insulating member 141 is charged, for example, in positive polarity by means of a corona wire 143. In the figure, the reference numeral 1~4 designates an original image to be reproduced, having therein a dark image portion D and a bright image portion L, the numeral 145 designates a light for exposure in the arrow direction, and the numeral 146 repre-sents a power source for the corona wire. The electric charging of the screen in the above-mentioned process steps i~ identical with that explained with re~erence to Figura 36:
hence a repeated explanation is dispsnsed with.
Figure 46 indica~es a result of conducting uniform exposure ~ver the ent re surface of the screen 138 by means of the expvsure light 147 in the arrow direction, whereby the photoconductive member 140 achieves a low resistance value and ~ ~061399 . ; :
is drawn by the static charge on the insulating member 141 with the result that the electrostatic contrast of the screen : :
increases, thereby to form the primary electrostatic latent image.
Figure 47 indicates the secondary electrostatic latent :
image ~orming process, in which the same principle of ion flow modulation as mentionëd earlier applies. In the illustration of Figure 470 the reference numeral 149 clesignates the power ~ource for a corona wire 148, the numeral 150 designates a recordi~g member, the numeral 151 refers to a conductive support member, the numeral 152 represents a power source for applying the bia~ field between the conductive members 139 and 142 and the numeral 153 represents a power source for applying the bias ~ield between the screen 138 and the conductive support me~ber 151. Further, the reference letter ~ designates the inhibiting field of the ion flow shown by dotted lines, and designates the accelerating field.
Figure 48 shows surface potential curves on the sur~ace of the screen 138 according to the afore-described electrophotographic proces Fourth Embodime~t .....
On one surface of a conductive member as the base ~or a screen which i~ made o~ stainle~s steel wire of 30 microns in diameter in the form of a metal wire net of 200 m~sh size, ~here is deposited ~elenium (Se) containing therein 5% o~
tellurium (Te) as the photoconductive member by vac~um-~vaporation ~o a thickness at the thickest portion thereo~
of approximately 40 micxons. Thereafter, "Parylene" ~produced by Union carbide Corporation) is coated on the photoconductive _ 1061399 , and conductive members to a thickness of approximately lQ
microns. Subsequentl~; aluminum is deposited by evaporation to a thickness of 2,000 angstroms onto the surface side of the screen opposite to that where selenium is coated by evaporation, whereb~ the screen for use in the electropho~o-graphic process according to the presen~ invention is fabricated.
The image exposure is conducted rom the surface side of the screen coated with selenium with the amount o~ ~he exposure liyht at the bright image portion being about 6 lu~/sec.
accompanied by a -~imultaneous prima~y voltage application at ~6 ~V~ Followi~g this simultaneous image irradiation and pr~mary voltage applicatian, the overall surface of the ~creen is expo~ed to form thereon a primary electrostatic latent image ha~ing a ~urace potentia~ o approximately -~200 V at the dark image portion and approximately ~450 V at the bright image portion. Then, an electrostatic recording paper is disposed ... ..
~... .
facing the primary electrostatic latent image surface of the screen at a space interval therebetween of 3mm. The stainless steel wire as the conductive member of the screen is earthed, ;,. .
the aluminum layer deposited on the screen i~ impressed by a voltage of ~400 V, while the recording paper i~ im~ressed by .
a voltage of -3 kV, and a corona discharge of -~7 kV ~s applied ~rom ~he side o~ the aluminum layer on the screen ~o as to form a seeondary electrostatic latent image on the re-cording paperO ~pon formation of the secondary electrostatic latent image on the recording paper, it is developed by a liquid .~..
developing agent to obtain a clear positive image o~ the ori~-inal. When the re~en~ion copying i5 conducted for 10~ times using this secQndary electrostatic latent image on the recor-din~ paper, the decrease in the image density in the hundredth , .

.- ~ ~ 10~L3~9 sheet is recognized to be less than 10% with respect to the image density in the initial sheet, the reproduced imaga of which is found serviceable for practical use.
The fourth embodiment of the electropnotographic process according to the pre~ent invention comprises the .
primary voltage application to uniformly charge the screen, the subsequent secondary voltage application, the image ir-radiation following the second voltage application, ancl the :~
third voltage applicatio~. In the explanation~ of ~he electro-photographic process in this embodiment, the screen to be referred to is one that uses an ~-type photoconductive body having a rectifying property, i.e., having elec~rons as the prinaipal carrier.
Referring to Figures 49 to 66 inclu~ive which indicate the electrophotographic process in the fourth embodiment, khe construction o~ the screen 154 is the æame as that shown in .;:
Figure 36 and con#ists of a conductive member 155 which pro-vides the basic element for the screen 154, a photoconducti~e .
member 156, a surface in.~ulating member 157, and another con- :~
ductive member 158 provided at one surface side of the screen 154. . ;
Figure 49 indicates the primar.y voltage application pracess, wherein the surface insulating member 157 is po~
tively charged by a corona wire 159. By this primary voltage application, electrons are injected into the photoconductive me~ber 156 from the conductive member 155, whereby a negati~e charge layer is ormed in the photoconductive member 156 at a - position contiguous to the insulating member 157 having a -~
positive charge~ Where the photoconductive me~ber 156 is made _ 59 _ ,, ~ Cl 6~399 of a substance that does not have the property o~ rectifying the disposition of ~he electric charge as shown in Figure 49 can be obtained by performing the uniform exposure to the photoconductive member at the time of the primary voltage application.
Figure 50 shows a result of performing the secondary voltage application to the screen 154 in the dark with a ..
voltage having a polarity opposite to that o~ the primary voltage application hy means of a corona wire 160 and a power source l91 there~or. . . ~ ~
Figure Sl indicates the image irradiation of an .;:
origi~al image 161 onto the screen 154 with a light 162 for .: .
the exposure in the arrow directio.n whereby, at the bright image portion, there takes place injection o the holes.in the bright portion of the conductive member 155, or release o~ the ...
electrons which have been.trapped ~ithin the photoconductive mem~er 156, into the conductive member 155 as a result of their .
being.energized by light rays, although no change takes place at the dark image portion of the photoconductiYe member. As a result of this image irradiation, there is formed an electric charge couple at both sides of the insulating member 157 in the bright image portion o~ the screen 154~
Figure 52 indica~es the tertiary voltage application by means of a corona wire 163, wherein a voltage is applied having the same polarity as in the above-menkioned secondary vo~tage application. By the application of a negative voltage, the surface potential of the screen 154 at the dark image port.ion varies little,. while the surface potential at the bright image portion again takes a negative polarity. The above-~ 60 - ..

6~39~
, .
mentioned image irradiation and the tertiary voltage applica-tion can be performe~ almost at the same time.
Figure 53 indicates the total surface irradiation of the screen 154 by an exposure light 164 in the arrow direction, whereby the bright image portion o~ the scr~en 154 is nega-tively charged at its surface, and the dark image por~ion is positively charged, whereby a primary elec-trostatic latent image of high electrostatic contrast i~ formed. This primary electrostatic latent image is not eliminated in the bxight image portion.
Figure 54 indicates the secondary electrostatic latent image ~orming process, in which the same principle of ion 10w modulation as explained previously applie~. In the drawin~, ;
the reerence numeral 165 designates a corana wire, to which a voltage o~ opposite polarity to that o~ the surface potential o~ the dark image portion is applied, the numeral 167 de~ignates a recording member held on a conductive support me~ber 168, the numeral 169 refers to a power source for applying a bias field between the conductive support member 168 and the screen 154, and dotted lines denote the flow of corona ions from khe corona wire 165. Where the primary electrostatic latent image is formed by surface potentials o mutually opposite polarity be~ween the bright and dark image portions, no bias field is required to be applied between ~he conductiva members 155 and 158; hence suficient secondar~ electrostatic latent image can be ~ormed even with the screen as shown in ~igure 1 which has no part corresponding to the conductive member 158 as in this embodiment. Variations in the electric potential on the screen 154 at every stage o the electrophokographic :

106~3~t processes according to this embodiment are shown by the sur-face potential curves in Figure 66.
Referring now to Figures 55 to 60 inclusive~ another type of electrophotographic proces~ will be explained herein- ;
below. In this particular process, the secondary voltage applicakion shown in Figure 56 and the tertiary voltage application shown in Figure 58 are carried out b~ an A.C.
power source~
Figure 55 indicates the prim~ry voltage application, wherein the screen 154 is charged in a positive polarity by a corona wire 170.
Figure 56 show~ a result of performing the secondar~
voltage application to the screen 154 by a corona wire 171 and an A.C. power source 195 there~or. The use of the A.C.
power source, however, is inferior in the power to remove the electric charge on the insulating member 157 to the case applying the secondary voltage as in Figure 50, with the conse~
quence that the disposition of the electric charge as shown in the drawing i~ obtained.
Figure 57 indicates the image irradiakion to the screen 154, wherein an original image 172 to be reproduced is irradia-ked by an exposure light 173.
Figure 58 shows a result o~ performing the tertiary voltage application by means of a corona wire 17~ and an A.C.
power source 196 therefor~ Inciden~ally, when the primary voltage application is carried out in a positive polarity, use o~ the above-mentioned A.C. power source, on which a negative curxent has been superposed, also is e~ectiveO
Figure 59 shows khe total surface irradiation of the screen 1S4, by which the-~econdary elec~rostat:ic lakent image 1399 ,-due to the electrostatic contrast of the same polarity is formed on a screen 174. Arrow marks 175 ,in the drawing desig-nate light rays.
Figure 60 indicates the secondary electrostatic latent image forming process onto a recording me~er 17~ held on a conduc~ive support member 179, in which the ion flows as shown '' by dotted lines are modulated under satisactory conditions by impressing the vol*age onto the conductive members 155 and 158 thro~gh a corona wire 177 and a power source 176 in view, `-of the ~act that the primary electrostatic latent image formed in the above-mentioned manner has the same polarity in both ',the dark and the,bright image portions thereo. The same principle of ion flow modulation as has been explained with re~erence to Figure 5 i8 applicable. Variations in the surface potential on the screen 174 at every stage o~ the ele¢trophoto-graphic process according to this embodiment are shown by the ,~
surace potential curves in Figure 67. ,;
Re~erring further to Figures 61 to 65 inclu~ive, still another type of electrophotographic process will be explained hereinbelow. In this particular process, the image irradiation ~hown i~ Fi~ure 51 and the tertiary voltage application shown in Figure 52 are carried out simultaneously, and the ~ertiary -voltage application is performed by the A.C. power source.' ,'~ Fi~ure 61 shows the primary voltage application, in which the screen 154 is positively charged by a corona wire 180~
Figure 62 shows the secondary voltage application, in which the screen 154 is charged in the opposite polarity to that in the primary voltage application by a corona wire, 181.

.
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` . 1.06~.39~
Figure 63 indicates a result of performing the tertiary voltage application onto the screen 154 by a coxona wire 184 and an A.C. power source 200, while the image irradiation is being performed simultaneously by way of an original ima~e 182 to be reproduced and an exposure light 18:3.
Figure 64 indicates a result of performing the total surface irradiation to the above-mentioned screen 154, ~hereby :~
the primary ele~trostatic latent image due to the electro~tatic contrast, in which the dark image portion having the same ~
polarity as that of the primary voltage application and the :~ ;
bright imag~ portion having almost zero surface potential, is formed on the scxeen 154. Arrow marks 185 in this dxawing designate light rays.
Figure ~5 shows the secondary electrostatic latent image foxmin~ process onto a recording member 187 held on a co~ductive support member 188 by means of a corona wire 186. In this secondary electrostatic latent image forming process, even i ;. .
~he ~urface potential on one surface side of the screen 154 where the primary electrostatic latent image is formed is zero, .20 it is possible to modulate the ion flow as shown b~ dotted lines .:
in a ~tate of being free fro~ fog through application.o~ bias fiela between the conductive ~embers 155 and 158 as illustrated. .~.
The sa~e principle of modulating the ion flo~ as has been described previously with reference to Figure 5 is applica~le ~.:
to this embodiment. variations in the surface potential on the screen 154 at every stag~ o the electrophotographic process according to this embodiment are shown ~y the surf~ce p~tential curves in Figure 68~
~he Table in Figure 69 shows one example of pol~rity . .
,, 6~ :

6~3~9 characteristic in the primary, secondary, and tertiary voltage applications in the electrophotographic process shown in Figures 49 to 54 inclusive, in which the primary voltage appli-cation is carried out in a positive polarity. In the Table, the symbol "AC" includes both alternating current and alter-nating current superposed by direct current.
In Figures 49 through 65, the reference numerals 190 and 201 respectively de~ignate a power source for a corona wire and ~he reference numeral 202 in Figure 60 and the n~mer~l 203 in Figure 66 refer to a power source to form the bias field between the screen and the conduc~ive support member.
In the foregoing ~xplanations of the electrophotographic process according to the present invention, the construction of the screen has been diagrammatically shown for ease of understanding and explanation, and hence the screen is not limited to any particular configuration. Also, the character-istics of the photoconductive sub~tance are not limited to those exemplified. Furthermore, the direction for the voltage application in the pximary electrostatic latent image formation as well as the direction for ~he image irradiation have been described in connection with those which can only achieve the ~aximwm effect, although they are not limiked to the~e examples alone. In addition, in each process that has been exemplified, the secondary electrostatic la~ent image i~
formed on the recording member without e~cepkion. It goes without saying that this recording member may be not only the electrostatic re~ording paper, but also may be any type of conventionally known electrostatic latent image formillg member.
The photos~nsitive screen sho~n in Figure 1 gives the best .
, .: . .

6~399 results in the electrophotographic process according to the:~
invention.
While the invention has been illustrated and described ~:
by way of preferred em~odiments thereof, it is to be understood that such are merely illustrative and not restrictive, and that variations and modifications may be made therein without departing from th~ spirit and scope of the invention as set forth in the appended claims.

Ridout & May~ee 101 Richmond St. West .
Toronto 1, Canada :
Patent Agents of the Applicant .: .
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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 An electrophotographic photosensitive perforate screen comprising a base member of conductive material, a photo-conductive layer covering the base member, an insulating layer which covers the photoconductive layer and is capable of supporting electrostatic charge and a conductive member exposed at one side of the screen, the insulating member having first portions forming the surface of the opposite side of said screen.

2. A screen according to Claim 1, wherein said conduc-tive member exposed at one side of said screen is a portion of said base member of said screen.

3. A screen according to Claim 1, wherein said conduc-tive member exposed at one side of said screen is separate from said base member and is attached to said insulating member at said one side of the screen.

4. A screen according to Claim 1, wherein alternate por-tions of said base member are exposed at said one side of said screen to constitute said conductive member, the portions of said base member between said alternate portions being covered by said insulating member.

5. A screen according to Claim 1, including an insulat-ing layer between said base member and said photoconductive layer.

6. A screen according to Claim 1, wherein a major por-tion of said photoconductive layer is at one side of said base member.

7. A screen according to Claim 2, 4, or 5, wherein said conductive member is used for a member to be applied with a voltage for maintaining, upon formation of an electrostatic latent image on the screen, the screen at a predetermined potential, and for maintaining, upon modulation of a flow of ions, the screen at a predetermined potential.

8. A screen according to Claim 2, 4 or 5, wherein said conductive member absorbs excess ions, upon modulation of the flow of ions.

9. A screen according to Claim 3, wherein said conduc-tive member is used for a member to be applied with a voltage for maintaining, upon formation of an electrostatic latent image on the screen, the screen at a predetermined potential, and said at-tached conductive member is used for a member to be applied with a voltage for maintaining, upon modulation of a flow of ions, the screen at a predetermined potential.

10. A screen according to Claim 3, wherein said attached conductive member absorbs excess corona ions, upon modulation of the flow of ions.

11. A screen according to Claim 1, wherein the thick-ness of the insulating and photoconductive layer are both at a maxiumum at said opposite side of said screen and decrease progres-sively towards said one side of said screen.