CA1060943A

CA1060943A - Electrophotographic process

Info

Publication number: CA1060943A
Application number: CA315,606A
Authority: CA
Inventors: Katsunobu Ohara; Keiji Tanaka; Yujiro Ando; Inao Moriyama
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1973-06-19
Filing date: 1978-10-31
Publication date: 1979-08-21

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 of the conductive member to be exposed.

Description

BACKGROUND OF THE INVENTIO~
-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 been 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 zinc oxide.
This direct method, however, has a drawback in that as the image formed 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 conve~tional paper, and hence a particular feeding means which is different from that for ordinary paper should be employed.
According to the indirect process, an image of high con-trast and good quality can be obtained by using ordinary paper asthe image 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 surface of the photosensiti~e member for removal of the residual toner thereon with the consequence that the photosensitive member is impaired at every time the transfer and cleaning operations are carried out. As a result of this, life of the expensive photosensitive member becomes shortened, which unavoidably results in a high cost in the image reproduction.
In order therefore to remove such drawbacks inherent 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 August 1, 1972 to Eastman ~odak 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. ~atent 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 of 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 cha-rge 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-

2 --~io~s whe~e the corona ions pass, if 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 No. 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 theconductive grid and the control grid so as to modulate the flow of the corona ions for forming an image on the recording member. In - this patented process, however, it is quite difficult to hold the control grid and the conductive grid to form an electrostatic latent image over a large area with finely spaced intervals therebetween.
Moreover, the control grid absorbs the corona ions to be imparted to the recording member with the result that the image recording efficiency becomes lowered. In the case of forming a positive image, the flow of the corona ions having a polarity apposite 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 No. 3,645,614, the screen comprises an insulating material overlaid with a conductive material, and the in-sulating material comprises a photoconductive material. An electric field to prevent the ion flow from passing through the screen is formed 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 . . . . .
:' ' ' ~ . .

106~9'~3 formed on the recording member is the image rever~al 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 i on the screen, since the image is in a single polarity. By this application 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 positiv~ image, although the - process has two major disadvantages in that two layers of the conductive su~stance must be provided on the thinly formed screen, which entails complexity in the manufacture of such ~- scree~, 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 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 bright 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 i 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 of which the desired electrostatic latent image can hardly be obtained on the screen with satis-factory contrast in the tones of image.
SUMMARY OF T~E INVENTION
In view of the foregoing discussion of 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 irherent in the known processes.

~ ,:

106094~
It is a secondary object of the present in~ention to provide an improved electrophotographic process which enables a reproduced image ~o 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 object of the present invention to provide an improv~d electrophotographic process, by which is obtained a complete reproduced image of sufficient contrast in the to~es 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 major objects and other objects, as well as the construction and function of the present invention will become more readily understanda~le 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 of 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 1060~43 explain the forming processes o.f 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 for the present invention;
Figures 18 to 20 inclusive are respectively schematic diagrams to explain the formation of the primary electrostatic latent image on the modified screen shown in Figure 14 above;
Figure 21 is a schematic diagram to explain ths 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 prvcess of the secondary electrostatic latent image by the same ~:
screen as shown in Figure 16; ~ ;
Figures 26 to 28 are respectively schematic diagrams to expiain the forming processes of the primary electrostatic latent :;; image by the modified screen shown in Figure 17;
Figure 29 is a schematic diagram to explain the forming 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 .:

10609~3 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 forming 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 electrostatic latent image by the same screen;
Figure 44 which precedes Figure 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 explain 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 process of the secondary electrostatic latent image by the same screen;
Figures 55 to 59 inclusive are respectively schematic dia-~rams to explain the forminc3 ~rocesses of the primary electrostatic 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 ; 10 process of the secondary electrostatic latent image by the same screen;
Figure 66 is a graphical representation showing the surface :
. potential curve of the screen in the latent image forming steps :. ~hown in Figures 49 to 53;
. Figure 67 is a graphical representation showing the surface , . . .
potential curve 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 sh~wn in Figures 61 to 64;
Figure 69 is a table showing the polarity of voltage for ;' use at the time of applying the primary, secondary, and tertiary . voltages in the electrophotographic processes according to the present invention;
Figures 70 to 73 inclusive are respectively schematic dia-grams to explain the form.ing processes of the primary electrostatic : latent image on the screen;
Figure 74 is a schematic diagram to explain the forming process of the secondary electrostatic latent image by the same _ 9 _ `:

~060943 screen; and Figure 75 is a graphical representation showing the surface potential curve of the screen in the image forming steps shown in 1 .
Figures 70 to 73.
DETAILED DESCRIPTION OF THE INVENTION
At the outset, the electrophotographic reproduction process according to the present invention will be outlined in the following.
; The photosensitive screen to be used for the electrophoto-. . .
graphic reproduction process is provided therein with a multitude of small openings. Its basic construction is composed of a conductive ~,' .
` member as the base, on which a photoconductive member and a surface nsulating member are laminated. One surface part of this screen is rendered 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 performed, 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 fxom 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 term "primary electrostatic latent image" means an electrostatic latent image formed on the photosensitive screen in conformity to the original image through the process steps as described above, and the term . . .
..~. .: ~:
. .

1060~43 "seco~dary electrostatic latent image" means one formed on the electrically char~eable member by the flow of corona ions which has been modulated with the above-mentioned primary electro-static latent image on the screen in the course of its passage therethrough.
The above-outlined 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 surface of a screen in a uniform manner so as to form a primary electrostatic latent image thereoni 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 multitude 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-. .

10~iO943 plating or it is made of 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 the 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 conductive member 2 by vacuum evaporation of an alloy or of an inter-metallic compound containing S, Se, PbO, and S, Se, Te, As, Sb, Pb, etc.. Also, according to the sputtering method, a high melting point photoconductive substance such aSZnOi-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 - substances and Lewis acid, and a mixture of these semiconductors and an insulative binder. For this spray method, a mixture of 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

3~ to be described hereinafter may properly be used.
.

; - 12 -~O~iO943 The thickness of ~he photoconductive member 3 to be deposited on the conductive member 2 ~y 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 o~ these monomeric substances ~:, in solvent type, thermal polymerization type and pho~opoly-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 insulatLve 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-1060~43 lating member 4 are formed on the conductive member 2, as in the above-described screen construction, each of theæ substances 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 adhesion 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 necessary 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 surface of the photosensitive screen 1, -, the effect of which will be as follows. By forming the primary electrostatic latent image on the insulating member 4, attenua- ' tion of the latent image becomes remarkably low 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 thephotoconductive 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 ; - 14 -10~iO943 reproduced images from one and the same prirnary electrostatic latent image, becomes feasible.
The process steps for forming the primary and the secon-dary electrostatic latent image by the electrophotographic process according to the present invention using 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 electrostatlc latent image formed on the screen by the preceding process steps. The explanations hereinbelow of the electrophotography will 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 of the voltage impression. Of these known expedients, the corona ~: .......................... . .
discharger is particularly preferable; hence the explanations ; which follow will be made with reference to the conona discharger.

-- In the primary voltage application step as shown in ,. . .
Figure 1, the screen 1 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 member 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 ,' ' .:

10~0943 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 s~ep as described above, it is preferable that the electric voltage be applied to the screen from the surface thereof where the insulating member !, ` 4 exists (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 "surface B"), because the corona ions flow into the conductive member 2.
Figure 3 indicates a result of the simultaneous image irradiation and secondary voltage impression onto the screen l which has undergone the abo~e-mentioned first voltage impression.
The reference numeral 7 designates a corona wire 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 voltage, the numberal 10 is an original image, of which the reference :
letter D indicates a dark image portion and the letter L
indicates a bright image portion, and the arrows ll designate "

light from a light source (not shown).

, 106D9~3 In the embodiment shown in ~igure 3, electric 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 substantially .zero due to alternate discharge of positive and negative polarities. However, in the actual . 10 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 voltage 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 . . .
surface 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 positive, the substance constituting the photoconductive member 3 becomes conductive at the bright image portion L due to the image irradiation, 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 layer present in the photoconducl:ive member 3 to the side of the insulating member 4.
The relationship bet~een 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-taneously, contrary to the foregoing explanation, but may be done sequentially. Furthermore, the direction for the image irradiation may preferably be from the surface A oE 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.
; 30 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.
.

. . .
, ?

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

C C ~ C Va ~ . .,,, ~1 ) i p where Ci is the electrostatic capacitance of the insulating member 4, and Cp is the electrostatic cap~itance of the photoconductive member 3.
When a photosensitive body of a three-layer structure con-sisting of a conductive base plate, a photoconductive layer, and a surface insulating layer is used, it is desirable that the electro-static capacitance ratio between Ci (insulating layer) and C (photo-conductive layer) be l 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 effective result can be obtained if the electrostatic capacitance ratio between Ci and Cp is set at 2 to 1 or so. Also, the coating thickness of the photoconductive member 3 surrounding the conductive member 2 becomes consecutively thinner from the sur-face A toward the surface B. On account of this, as the charge layer in the photoconductive member 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 from the surface B toward the surface A of the screen 1. Incidentally, the ~060943 above-described overall irradiation step is not always necessary.
However, by conductin~ this process step, it becomes possible to quickly form the primary electros~atic latent image on the screen 1 where the electrostatic contrast should be kept high.
Figure 5 indicates the secondary electrostatic latent image forming process, wherein a positive electrostatic latent image in conformity to the original image is formed on the recording mem~er by the primary electrostat.ic 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 ths reference numeral 15 designates a recording 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 of the record-; ing member 15 is disposed facing toward the surface A of the screen 1 at an appropriate space interval therebetween o~ from 1 mm to 10 ; mm or so. .
:.
When the secondary electrostatic latent image is to be formed on the recording member 15, the ~low of corona ions is direc-ted to the recordi~g member 15 from the corona wire 8. At this time, the bright image portion of the screen 1 is constantly changing its potential-difference from the surface A to the surface B, thereby creating an electric field as indicated by solid lines a in Figure 5, whexeby the passage of the corona ions through the opeoings of the screen 1 is inhibited to result in flowing of the corona ion3 . 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 member 3, the screen is charged in the polarity of the corona ions ' ~ ' : , .

10609~43 from the corona wire 14, and the passage of the corona ions throughthe openings of the screen is accelerated by the charged potential.
n other words, as the corona ions pass through even the bright image portion, fog 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 lines ~ is created, and the corona ions, in spite of their being of an opposite polarity to that of the electrostatic latent image on the insulating member 4, reach the recording member 15 in an effective manner in a state of causing the latent image to be extinguished to a lesser degree.
Inversely, when the original image is to be 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 reference numeral 16 in Figure 5 designates a power source for the corona wire 14, and the numeral 17 designates another power source to the conductiva 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 latent image can be obtained and, if a voltage of the positive polarity is impressed, a negative electrostatic latent image can be obtained. The dot-ted lines 18 in the drawing designate the flow of the corona ions from the corona wire 14.
For the recording member lS, 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 member as mentioned above, however, the insulating member must be sufficiently closely adhered onto theconductive supporting member 13; otherwise, irregularities in the secondary electrostatic latent image formed on the recording member will ocGur. As 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 supporting member 13 is effective.
The reason for such favorable results when the screen 1 of the afore-described construction is used, particularly for retention copying, is considered to be the fact that the primary electrostatic latent image having a smooth potential change is formed on the in-sulating member 4 at the opening part of the screen 1. Furthermore, such effect is presumed to be derivea fro~ the function such that the surplus flow of the corona ions from the corona wire is absorbed : - by the conductive member exposed to the side of the surface B of the screen l.
Moreover, in carrying out the retention copying, there sometimes occurs a situation in which the quantity of flowing corona ions passing through the scree~ 1 is rather small at the time of forming the secondary electrostatic latent image on the recording member 15 and, more particularly, at the time of modulating the , ion flow at the initial stage. If the latent image formed on the recording member under such electric conditions is developed, a reproduction image of varying clensity results. The cause for this undesirable phenomenon is thouyht 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 prevented ~y 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 screen 1 from its surface B a separate corona discharge having the same polarity as that of the corona discharge for the secondary i ~ electrostatic image formation, the corona discharge of which is ' different 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 presence of the conductive supporting member 13 which functions as the opposite electrode to the corona wire 14 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.

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~060943~
oltage application is used Eor forming the secondary electrostatic latent image as mentioned above, 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 Eogging 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 dischar~e electrode for the flow of the corona ions that is applied onto the recording member, 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 of 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 curre~t 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 parts are designated by the same reference numerals as are used in Figure 5.
In the drawin~s, reference numeral 19 designates a variable capacitor, :`
numeral 20 designates a rectifier, numeral 21 designates a trans-former, and numerai 22 refers to an A~C. power source. The construc-tion of the screen and the electrostatic latent image forming process for ion modulation are not limited to those mentioned above, but it is only sufficient if the primary electrostatic latent image on the - 2~ -106094~
screen 1 is almost symmetrical from the standpoint of electriccharginy in the bright and dark image portions of the original image. The recording mem~er, too, is not limited to recording paper, but any chargeable member m~y satisfy the requirements.
Moreover, as in the basic device 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 resistor 19 and the rectifier 20, and the other being connected to the conductive supporting member 13. In this circuit construction, the variable resistor 19 and the rectifier 20 function to adjust the intensity of the polarity (positive and negative) of 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 that 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 between the corona wire 14 and the conductive supporting member 13 over substantially the entire period of the ion flow modulating step. For this reason, the use of the transformer 21 is nothing ' 1C~609'~3 but an example of the ion flow modulatinq method. This tran~former can be replaced by various methods such as, for example, control-ling by means of a relay two direct current power sources having mutually opposite polarities. By using such method~ the conduc-tive support member 13 is maintained in a negative polarity, so long as the corona wire 14 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 recording member 15. On the other hand, while the corona 10 wir~ 14 is in a negative polarity, the conductive support member 13 is Xept in a positive polarity, whereby the negative ions pass through only the portion where the screen 1 is maintained in the positive polarity and adhere onto the recording member 15.
As a result of such processing, there is formed a secondary electrostatic latent image on the recording member, wherein the dark image portion is in the negative polarity and the bright image portion is in the positive polarity. When this secondary electrostatic latent image is developed by the use of colouring particles such as toner having a positive polarity, a reproduc-... .. .
, 20 tion of the original image free from the fogging can easily be obtained. Also, harmony i~ the reproduced image can be ad~usted~
.~ -appropriately by the variable resistor 19. Needless to say, prod~ction of a negative image is also possible when a toner of negative polarity is used.

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106~)94,3 DESCRIPTION OF T~IF` PREFERRED EM~3ODIME~TS
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In order to enable per~ons akilled in the art ~o reduce to practice the present invention, the following preferred em-bodiments of the electrophotographic method are presented. It should be noted however that changes and modifications may be made to the extent that they do not depart from the spirit and scope of the invention as recited in the appended claim~.
First Embodiment _ In the production of a photosensitive screen for use in the electrophotographic method according to the inven-~ion, selenium (Se) is deposited by vacuum-evaporation onto a conductive member of 200 mesh made of stainless steel w~re 40 microns in diameter in such a manner that the openings of the conductive mem~er are not closed by the evaporated metal. At this time, deposition of the vacuum-evapoxated selenium is con-ducted 50 as to bring the thickness of the deposited layer on the conductive member at its thickest portion to approximately 50 microns Subse~uently, parylene as the insulative substance is adhered onto the selenium photoconductive member thu~ obtained to a thicknes~ of about 10 microns. Since parylene i5 coated on the entire s~rface of the photoconductive member, the surface opposite to that where selenium as a screen for the conductive member is deposited at its maximum thickness i5 ground by an abrasive agent so as to expose a part of the con-ductive member to the external atmosphere. For the surface in-sulating member, a thinner solution of polystyrene can be spray-coated on the photoconductive member in place of the above-mentioned parylene .' . lo~v~4~
The screen produce~ in theiabove process step~ 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 with an exposure light of 30 lux per second and, at almost same time, corona discharge is im-parted to an electric current in the negative direction by means of an A.C. current through a resistance component of 10 Mn . After this, when the overall surface of the screen is irradiated, a primary electrostatic image is formed on the surface insulating member of the screen, the surface potential at the bright image portion being ~150 V, while that at the dark image portion being -200 V. An electrostatic recording - paper is then placed facing the thus formed primary electro-static latent image at a space interval therebetween of 3 mm, and a positive corona discharge is carried out onto the recor-ding paper through the primary electrostatic latent image formed on the surface insulating member of the screen, while ::.
;~ maintaining the potential of the recording paper at -2 KV with respect to the conductive member, whereby the flow of corona ions is modulated by the primary electrostatic latent image, and the secondary electrostatic latent image is formed on the recording paper.
The recording paper bearing the secondary electrostatic latent image foxmed by the afore-described processes is then subjected to development by the use of negatively charged colour developing particles in a liquid developer, The result is a reproduced image having high resolution and capable of reproducing even intermediate colour tones in the original at high fidelity.
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10~ 9~3 When retention copying is done for 50 consecutive times using one and the same primary electrostatic latent imag~
formed on the screen, 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 viewpoint.
- In forming the secondary electrostatic latent image, if it is assumed that the screen is stationary, the corona discharger for the ion flow modulat~on can be moved at velocities of 30 cm/sec. 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 use in the electrophotographic process according to the present inven-tion, a solution of CdS powder used as a photosensitive body in ordinary electrophotography and 20% by weight of solvent ~ type epoxy resin as a binder is spray-coated from one direction r onto a metal net of 200 mesh made of stainless 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 photocon~uctive member. After dr~ing and polymerizing the ~oated 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 openings of the conductive member, thereby forming the surface insulating member.
In forming the primary electr~static latent image, the electric voltage to be applied to the corona discharge in the primary voltage application step is made an opposite polarity to the case of the first embodiment, and the corona discharge .

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is conducted.
The image irradiation step is carried out by irradiating the image with an exposure light of 8 lux/Recond. As a result, there is formed on the screen a primary electrostatic latent image having a surface potential of -100 V at the bright image portion and +200 V at the dark image portion.
In forming the secondary electrostatic latent image, a negative corona discharge is carried out, and the secondary electrostatic latent image formed on th~ electrostatic recor-ding member is developed by positively charged colouringparticles in the dry development method. The reproduced image obtained thereby has a high image resolution as in the fore-going first embodiment, and is capable of reproducing with high fidelity the intermediate colour tones of the original image, - Also, in the same manner as in the first embodiment, the ;;
retention copying is carried out by use of a photosensitive screen bearing the electrostatic latent image formed by the afore-described process steps. The result is such that a good quality 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 electrophotographic reproduction machine, in which the afore-descri~ed photosen~itive screen 1 is applicable.
In the present invention, the corona discharge for forming the primary electrostatic latent image is carried out from the surface A, and the other corona discharge for the image irradiation and the secondary electrostatic latent image ,.............. ~ , .
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10609~3 formation is carried out from the surface ~. Accordingly, when the screen l is flat and stationary, the recording member 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 comprises a fixed table 24 on which may be placed an original image 2S to be reproduced, a lamp 26 to illuminate the original image 25, a movable optical system 27 consisting of a reflection mean~ and a lens, a corona d-ischarger 28 to carry out the primary voltage application to.the flat, stationary type photosensitive screen l, another corona discharger 29, a lamp 30 for overall surface irradiation, and a container 31 to hold the corona discharger~ 28 and 29 and the lamp 30, which container is 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 belt 35 provided with a Saxon conveying mechanism 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 fixing means 38, and a tray 39 to receive and hold the recording paper 33, on which the original image has been reproduced The electrophotographic device o the above-described cons.truction is operated in the following fashion. Referring to Figure 7, the original image 25 on the fixed table 24 is illuminated by the lamp 26, and its image is irradiated on the ;'~ .

4;~
screen 1 through the optical system 27. At the time of illum-inating the above-mentioned original image, the lamp 26 , the optical system 27, and the contai.ner 31 move in parallel with and in the vicinity of the fixed photosensitive screen at the same speed and in the same direction, whereby the primary electrostatic image is formed on the screen 1. The conveyor belt 35 beneath the screen 1 is coloured in a low brightness such as black so as to prevent light which has passed through the openings of the screen 1 from scattering to other parts of the device. The recording paper 33 is forwarded sheet by sheet by the paper feeding roller 34 onto the conveyor belt 35, and i5 positioned by the conveyor belt 35 facing the scrnen 1 at the stage of the primary electrostatic latent image having been formed on the screen-l. Then, the flow of corona ion~
from 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 the recording paper 33. Thereafter, the secondary electrostatic latent image is 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 i~ received and held in the tray 39 outside the :~ reproduction device. The corona discharger 36 i~ capable o ; increasing its moving ~peed higher than 30 cm/sec.; hence it can be operated.at a very high speed at the time of the reten-tion copying. ;
For the purpose of the retention copying, the lamp 26, the optical system 27, and thn container 31 are in a stationary state, only the corona discharger 36 moving above the screen 1.
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_ 32 ~

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:^` 10~0943 The operations of the discharger 36 and of the recording paper 33 at this time are as follows. The recording paper stop~ at its de~ignated 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-~tatic latent image on the recording paper 33, it is shifted toward the developing means 37 and the fixing means 38, and the next succeeding recording paper is fed to the position beneath the screen 1. In this case, before the paper comes to the de~ignated position and stops, the corona discharger 36 .
returns to it~ starting position. In other words, at the time of the retention copying, only the corona discharger 36 moves among ~arious means for the electrostatic latent image forma-tion, and hence the device is able to operate at high speed .: and with a small load imposed thereon.
The el.ectrophotographic reproduction device 40 shown in Figure 9 is the same in ~asic 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 so a~ to narrow the space interval between the ~creen 1 and the recording paper 33 as shown in Figure 10, whereby the flow of the corona ions from the coro~a discharger 36 ~or the secondary electrostatic latent image formation is 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 formation of the ~econdary electro3tatic latent image, the screen 1 is maintained in a state of its having shifted in close proximity 1~60943 to the recording paper 33 as shown in Figure lO, in the course of which the recording paper 33 is fed and brought to the designated position. As soon as the paper stops at the destin-ation, the above-mentioned corona discharger 36 begins to shift.
As stated previously, displacement of the photosensitive screen l in close proximity to the recoraing paper 33 ma~e~
it possible to reduce the electric voltage to be impre~ed on the corona di~charger 36 ~o form the secondary electro~tati~
latent image lower than that in th0 device shown in Figure 7.
For example, when the distance between the screen l and the recording paper 33 is 20 mm, a voltage o 6 to 20 kV or so is necessary. However, when the distance therebetween is 3 mm, voltage application of 2 to 3 kV or so would be sufficient to form the secondary electrostatic latent image.
The electrophotographic reproauction device 41 shown -in Figure ll is different ~rom the device shown in Figure 9 in that, upon formation of the primary electrostatic latent , . . . . .
~ ~ image, the conveyor belt 42 move~ upward to the fixed screen 1 ~
,.. .
and stops immediately ~elow it as shown in Figure 12. By thus narrowing the space interval between the screen l and the re- ~
cording paper 33, the same effect as explained in connection ~ -with the device o~ Figure 9 can be attained. In Figure 11, the developing vessel 43 is of a wet type, 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 the conveyor belt 42. The separ-ating pawl 45 and the guide members provided therearound move simultaneously with the conveyor belt 42. It will be convenient ., .

~` 10609143 that the po~itional relation~hip of tha 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 members. ~n ~he state as shown in Figure 11, the tip end of the separating pawl 45 does not contact the conveyor belt 42, and the other end of the guide member is dis-posed at a position di~tant from the developing vessel 43.
When the primary electrostatic latent image formation is complete and the conveyor belt 42 moves up to the position immediately below the screen 1, the separating pawl 45 also move~ 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 conveyor belt 42 thererom, while the other end of the separating pawl 45 exhibits its function to guide the recording paper 33 to the - developing ve~sel 43.
Incidentally, in Figures 7 to 12 inclusive, component members in the devices having the same functions are de~ignated by like reference numerals.
The reproduction device 46 shown in Figure 13 forms the photosensitive screen 1 in a cylindrical shape. In this figure, an original image 47 placed on the fixed plate is il-luminated by a lamp 48 and exposed on the cylindrical sc~een 1 by mean~ o~ an optical system comprising mirrors 49, S0 and Sl and an optical lenQ 52. The screen 1 rotates in a cloc~-wise direction as shown by an arrow, and has its conductive member inwardly expo~ed. The primary electrostatic latent image is formed on this cyiindrical screen in such a way that, upon its passage through a corona discharger 53 for the primary voltage application and su~sequently through a corona di~charger . .

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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. ~ secondary electrostatic late~t image is formed on the recording paper held on a conductive suppor-ting member 58 by modulating the flow of corona ions from a corona di~charger 57 by the primary electrostatic latent image formed on the screen. After the secondary electrostatic 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 flxed, and the original image is thereby reproduced on the recording paper.
When multiple reproductions are desired to be obtained from the single original image, the forming process of the secondary electrostatic latent image alone is carried out, while synchro-nizing the rotation of the screen 1 and the paper feed. It is also possible to re-use the screen 1 after the primary electro-static latent image which has become unnecessary i~ removed by a corona di~charger 61 for removing the electric charge, and a lamp 62.
In the following, the construction of a screen capable ~ o~ forming primary and secondary electrostatic Iatent images - by the electrostatic latent image for~ing process will be ex-plained with reference to Figures 14 to 17 inclusive which indicate enlarged cross-sections of photosensitive screens ~onstructed according to the present invention. The screen 63 in Figure 14 is of 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 portion substantially to one side .: , .

' , 1060'943 ther~of, a surface insulating mernber 66 is further coated on the partially exposed conductive member 64 and the photo-conductive memher 65 so as to wrap both parts, and a separate .
; conductive member 67 which is di;~ferent from the above-mentioned conductive member is provided on one part of the surface in-sulating member 66. The conductive member 67 is deposited on the insulating member 66 by the vacuum-evaporation of metals such as aluminum, copper, gold, indium and nickel, or by spray-coating of a mixture of a resin as a binder and a conductive resin containing therein quaternary ammonium salt, carbon powder, or a fine powder of metals such as silver and copper.
The screen 68 shown in Figure 15 is substantially the same as the screen 63 in Figure 14 with the exception that a photocon-ductive membex 70 is provided around a conductive member 69 so as to surround it completely. In the screan 73 of Figure 16, a photoconductive member 75 is provided around a conductive member 74 to be the base or the screen 73 in such a manner that .~ :
a part o the conductive member 74 may be exposed, and also a ~urface insulating member 76 is provided on the photoconduc-tive member 75 in such a manner that a part of the lattermember may bee*posed to the opening of the ~creen 73. Further, the screen 77 shown in Figure 17 is so con~tructed that an insulating member 79, a photoconductive member 80, and a : surface in3ulating member 81 are provided one after the other in such a manner that a conductive member 78 to be the base for the screen 77 may be exposed as is the case with each of the aore-described screens of different structures. The materiala and the method to be used for fabricating the afore-described screens may be the same as those used in fabricating ~ 1060943 the screen 1 of Figure 1.
The latent image forming processes using each of the above-explained screens will be de~cribed hereinbelow. ~ow-ever, as the processes are not much different from the case of the screen 1 shown in Figure 1, only an outline of each step 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 15 i8 dispensed with in view of the explanation of the screen 63 10 - in Figure 14.
Figures 18 to 22 indicate the state of the electric charge in the screen 63 of Figure 14 due to the electrophoto-graphic method according to the present invention, of which Figure 18 show~ the primary voltage application proces~ to ; the screen 63 and hence it indicates a state o~ the surface insulating member 66, for example, being uniformly charged in negative polarity by a corona discharger. Owing to this electric charging, the surface of the surface insulating member 4 is negatively charged, whereby a positively charged layer which is the opposite po~arity to that of the insulating member 4 is formed in the photoconductive member 65 at a position contiguous to the vicinity of the insulating me~ber 4 of the conductive member 64. ~igure 19 shows a result of - simultaneou~ image irradiation and the secondary ~oltage application processes having been carried out on the screen 63 which has undergone the above-mentioned voltage application process. The reference numeral 82 designates an original image to be reproduced, wherein the part D is a dark image portion and the part L is a bright image portion In Figure 20 _ 38 --` ~ 1060~43 the surface insulating member 66 is shown to be di~charged by the corona discharger with an A. C. voltage as a power source, on which a voltage o~ positive polarity has been ~uper-posed, in such a manner that the surface potential of the in-sulating member 66 may be made in substantially a positive polarity. When the surface potential of the insulating member 66 is thus made in the opposite polarity to that at the time of the primary voltage application process, the surface 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 of conducting a uniform exposure on the centre surface of the screen 63 which has unaergone the above--mentioned pxocess steps. By this overall exposure, the dark image portion D of the screen 63 changes it~ potential in proportion to the charged quantity ~- on the surface of the insulating member 66. As a conseguence, there is formed on the screen 63 the primary electrostatic latent image in con~ormity to the original image to be repro-duced.
Figure 21 show~ a state of the ~econdary electrostatic ~, .
~ latent image being formed on the xecording member by way of l the primary electrostatic latent image on the screen 63. ~he ' reexence numeral 84 in th;s figure designates a corona wire, , .
the numeral 85 designates a recording member held on a con-ductive support member 86 which also function~ as the ~pposi~e ~` electrode to the corona wire 84. The corona wire 84 is im-pressed by a voltage of positive polarity, and the conductive .

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- ~: 1060'943 support member 86 is maintained at zero p~tential. The dotted lines in this figure show the ion flow from the coro~a wire 84. The principle of modulating the ion flow is as de-scribed in the foregoing with regard to the formation of the econdary electrostatic latent image shown in Figure 5. Also as mentioned previously, the image irraaiation and the secon-dary voltage application may be carried out in sequence de-pending on characteristics of the photoconductive substance constituting the screen. This holds good for other proce~es of the present invention as will be described hereinafter.
Throughout the processes as de~cribed above, the conductive members 64 and 67 are electrically continuous, and they are able to adjust khe passion ion flow at the tLme of modulating the corona ion flow by impressing a bias voltage.
Figures 70 to 74 inclusive indicate respectively the charged states in the screen which, unlike that explainea with reference to Figure l, does not cause the carrier injection at the time of the primary voltage application. Figure 75 is a graphical representation showing variations in the surface potential of the screen in each proces~ step in Figures 70 to 74. A screen 204 in Figure 70 has a conductive member 208 provided at only one surface side of a conductive me~ber 205 to be the basic element for the screen 20~, a photoconduc-tive member 206, an insulating member 207 and the screen 204 per se. This figure show# the primary voltage application process-to the above-mentioned screen 204 by way of a corona wire 209 and a power source 210. In the illustrated example, the screen 204 is in a state of being charged in a positive polarity at the dark image portion D. In the above-described -- ~0 --^~
1060~43 process step, a positive electrostatic charge is adhered onto the insulating mem~er 207. ~owever, as the photoconductive member 206 exhi~its a highly insulative property, no negative charge layer corresponding to the positive electrostatic charge can be formed.
Figure 72 indicates the image irradiation process, wherein an original image 211 is irradiated by a light 212 for the exposure. By this image irradiation process, the photo-conductive member 206 at the bright image portion of the screen 204 lowers its resistance value wi$h the consequent formation of a negative charge layer corresponding to the above-mentioned positive static charge in the neighborhood of the insulating member 207 contiguous to the photoconductive member 206. Figure 72 shows a resu~t of applying onto the dark image portion of . the æcreen 204 a secondary voltage having a polarity opposite .: to that o~ the primary voltage by means of a corona wire 213 ~ and a power source 214. For the purpose of the latent image -- formation, the secondary voltage may either be of the same-polarity as that of the primary voltage, or it may be an alter-nate current, By this secondary voltage application process, the electrical potential at the dark ~mage portion on the screen 204 become.~ zero while, at the bright image portion, the posi-tive charge on the surface of the screen is.eliminated to some .` extent.
Figure 73 shows a result of the overall sur~ace exposureof the screen.204 whereby the primary electrostatic latent image having a high electrostatic contrast is formed on the screen 204. The reference numeral 215 designates an exposure light.

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Figure 74 shows the secondary electrostatic latent image forming process by way of the screen 204. In this figure the reference numeral 216 designates a corona wire, the numeral 217 designates a conductive support member, the numeral 218 designates recording member, the numeral 219 designates a power ;~
source ~or the corona wire, and the numeral 220 designates a power source for forming a bias field between the screen 204 and the recording member 218. When the fiow of the corona ions as indicated by dotted lines in the drawing and having the same polarity as that of the surace charge at the bright image portion of the screen 204 is directed to the recording member 218, the ion flow is modulated by the primary electrostatic latent image on the screen 204, and the secondary electrostatic latent image is formed on the recording member 218. In order ... . . . .
for the ion flow to be sati-~factorily modulated, formation of a bias field by an electrode 221 between the conductive members ~05 and 208 may be efective. In this secondary electrostatic latent image forming process, the image irxadiation aDd the secondary voltage application cannot be performed simultaneously.
Turning back now to the previous figures of the drawings Figure 22 to 25 indicate respectively a state of the electric charge on the screen 63 of Figure 16 for use in the electro-photographic proceæs according to the present invention.
Pigure 22 shows the primary voltage application proce~s to the screen 73, wherein the surface insulating member 76 is indi-cated to be charged in negative polarity by the corona dis-charger. By the above-mentioned charging, an electric charge layer of positive polarity which is opposite to the charge polarity on the insulating member 76 i~ formed on the photo-` -``'` 1060C~43 conductive member 75 at a position contiguous to the insulating member 76. Figure 23 indicates a result of performing the simultaneous image irradiation and the secondary voltage appli-cation onto the screen 73, wherein the reference numeral 87 designates the original image to be reproduced, the reference letter D designates a dark image portion, the letter L a bright image portion, and the numeral 88 the light for expo~ure.
Figure 23 indicates a result of discharging the screen 73 by the corona di~charger using an A.C. power source, on which a voltage of po~itive polarity has been superposed, in such a manner that the surface potential of the screen 73 may take substantially the positive polarity. As a consequence o thi~
corona discharge, the surface potential of the insulating member 76 can be made in the opposite polarity to the previous process step, although the surface potential of the insulating member 76 at the dark image portion D remains in the negative polarity. Also, the photoconductive me~ber 75 exposed to the openings of the screen 73 on some occasion has an electric charge adhered on its surface due to the secondary voltage application in case insufficient light reaches the photoconduc-tive member 75. Figure 24 indicates a result of carrying out sufficlent exposure to the overall surface of the screen 73 which has undergone the afore-mentioned process steps. By this light exposure, the dark image portion D of the screen 73 changes its electric potential in prop~rtion to the charge quantity on the surface of the insulating member 76, as a result of which the primary electrostatic latent image is formed on the screen 73 in conformity to the original image to be re-produced. Figure 25 indicates formation of the secondary ` ~` ` 106C~943 electrostatic lat~nt image on a recording member, wherein the recording me~ber 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 ~low shown by dotted lines is in respect of the secondary electrostatic latent image forming process of Figure 5.
~ Figures 26 to 2g inclusive respectively indicate a - state of electric charge on the screen 77 in FigUre 17 by the electrophotographic process according to the present invention.
As illu~trated in FiguLe 26, the primary voltage application charges the surface insulating member 81 in negative polarity.
By the above-mentioned electric charging, the carrier existing in the interior of the photoconductive member 80 moves, or the carrier formed by the overall exposure of the screen to be carried out simultaneously with the electric charging moves toward the surace insulating member 81 and the above-mentioned carrier of positive charge is captured at the interface ~e-tween the photoconductive member 80 and the insulating mem~er - 81. As a consequence, the charge layer is formed in the in-terior of the screen 77. Figure 27 indicate~ a result of con-ducting the simultaneous image irradiation and the secondary voltage application on the screen 77 which has undergone the above-mentioned primary voltage application process, wherein the original image 93 having the dark image _ ~4 --` 10~;0943 portion D and the bright image portion L is irradiated by exposure light 92 represented by arrows, A~ has been mentioned previously, Figure 26 also indicates a res~lt of discharging the screen 77 by the use of a corona discharge with an A.C.
voltage, on which a voltage of positive polarity has been super-posed, as the power source in such a way that the surface po-tential of the insulating member 81 may become substantially of positive polarity. As ae~cribed abo~e, at the time of the secondary voltage application, the surface potential of the in-sulating member 81 takes an oppo~ite polarity to that of thepximary voltage application although, at the dar~ image portion D of the insulating member 81, there still remains the negative charge on the surface thereof. Figure 28 shows a result of conducting a uniform, overall exposure to the-screen 77. By this overall exposure 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 con~equence of which the primary electrostatic laten~ image is formed on the screen 77 in conformity to the original image to be reproduced. Figure 29 indicates the secondary electrostatic latent image being formed on the sur-face of the recording member 95 which is held on the conductive ; support member 96 which also serves as the opposite electrode ;~
to the corona wire 94. The corona wire 94 is impressed by a voltage of positive polarity. The principle of the ion flow modulati~n as indicated by the dotted lines is as already described in the secondary electrostatic latent image forming process of Figure 5, Figure 30 shows the potential curves on the surface o~

the insulating member at each process ~tep of forming the electrostatic latent image as described in the foregoing, As will be seen from this graphical representation, when the surface of the insulating member o~ the 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 indicate the characteristic as represented by the curve Vp. Next, when the image irradiation and the re-charging with A.C. corona discharge biassed in positive polarity to some extent are carried out, the negative charge in the bright image portion of the image is entirely discharged to be char~ed in substantially the positive polarity as represented by the characteristic curve VL.. Also, in the dark image portion, .
the negativa charge formed on the surface of 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 surace potential in the dark image portion is as shown by the characteristic curve VD. Thus, when the overall surface exposure of the screen is conducted after the image irradia-tion and the secondary voltage impression to form the electro- .
static latent image on the surface of the insulating member, no remarkable change takes place in the above-mentioned bright image portion o the photoconductive member, so that the surface potential becomes as ~hown by the curve VLL. In contradistinction, in the above-mentioned dark image portion, the resistance value of the photoconductive member lowers abruptly to become conductive, as a result of which the electric charge within the photoconductive member remains to be slightly 10~;0943 captured by the neg~tive charge field on the surface of the insulating member, and the surface potential thereof ahruptly reduces as represented by the characteristic curve VDL.
Through the foregoing process steps, the primary electrostatic latent image i~ formed on the screen.
In ~igure~ 21, 25 and 29, the reference numerals 97 to 102 de~ignate a power source ~or the corona wire, a screen, and a conductive support member. Also, in the formation of the primary electrostatic latent image on the screens 63, ~8, 73 and 77, the voltage used for the secondary voltage applica-tion process may be one having the opposite polarity to that uæed for the primary voltage application, besides the A.C.
voltage, on which a D~C. voltage is superposed as mentioned above. Further, ~s to the direction of the image irradiation, . .
it can be done rom the side where the conductive member is exposed, besides 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 the surface insulating - 20 member, it is necessary that the conductive member also be made of a transparent material. It goes without saying that the retention copying is feasible even in the case of using such screen.
The screen as mentioned with reference to Figure 31 differs from the screens that have been described hereinbefore in that it shows the insulative property at its one surface side due to the surface 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 :

.

i 1060943 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 screen 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 photoconducti~e mem~ex 105, and then by grinding only one side of the screen 103 by an appropriate grinding means. More particularly, when the conductive member 104 has ups and downs in its cross-section as in the case of a metal net, if one side of the screen 103 is ground uniormly the higher portion thereo 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 mentioned in the foregoing, the outline o~ which will be given hereinbelow.
Figures 31 to 35 respectively indicate the state of the electric charge in the screen 103 of Figure 31 by processes su~tantially the same as the afore-described electrophoto-; 20 graphic processes. Figure 31 indicates the primary voltage application to the screen 103, in which the surface insulating member 106 is shown to have been charged uniformly in negative polarity, for example, by the corona discharger. By the above-mentioned electric charging, the surface o~ the insulating membex 106 i9 charged in negative polarity, whereby a charge layer having a positive polarity which is opposite to that o the electric charge on the insulating member 106 is formed in the photoconductive me~ber 105 at the position in the vicinity of the insulating member 106. Figure 32 shows a result o ~' ' .
1~60943 conducting the simultaneo~s image irradiation and the 8econ-dary voltage application onto the screen 103 which has under-gone the primary voltage application, wherein the reference numeral 107 designates an original image having a dark image - portion D and a bright image portion L, and the numeral 108 (arrows) designates 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 polarity is superposed, or a power source o a voltage having the opposite p~larity to that used in the primary voltage ap-plication. The discharge is carried out in such a manner th~t the surface potential of the insulating member 106 may become substantially positive in polarity. In this case, as the photoconductive member 105 in the dark image portion D has a high resistance, the surface charge o the insulating member 106 remains negative due to the above-mentioned charge layer.
Figure 33 shows a result of conducting the uniform e~posure - 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 portion D o the screen 103 varies in accordance with the electric charge quantity on the surface of the insulating member 106. A~ a result of this, the pri-mary electrostatic latent image is formed on the screen 103 in conformity to the original image.
Figure 34 5hows the process for removing unnecessary electric charge on the insulating member 106 existing on the exposed surface side of the conductive member of the above-mentioned screen. This process can be dispensed with. l'hs reference numeral 108 in this figure designates a corona wire _ 49 -, ;

an~ the numeral 109 represents a power source for the corona wire 108. The polarity of the voltage to be applied onto the corona wire 108 may be selected from A.C. voltage and D.C. voltage which are capable oE eliminating the above-mentioned unnecessary electric charge. Incidentally, this unnecessary charge is considered to be formed at the time of the primary and secondary 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 ima~e is formed on the recording member 102 held on the conductive support member 103 by way of the corona wire.
The conductive support member 103 also ~erves as the opposing electrode to the corana wire 101. This corona wire i8 impres-sed by a voltage of positive polarity, and the electric potential on the conductive support member 103 is maintained at zero. The principle o~ modulating the ion flow as indica-ted by dotted lines is the same as is already explained with regard to the secondary electrostatic laten~ image forming process of Figure 5. In the drawing, the reference numerals 104 and 105 designate the power source to the corona wire 101 and to the screen 103, respectively.
~ he electrophotographi~ process according to this second embodiment comprises the primary voltage application process to uniformly charge the screen according to the present invention for the purpose of the primary electrostatic latent image formation, the image irradiation proce~s, and the second voltage application process to be conducted thereafter ~,, ~`` iO60'~43 to vary the s~rface potential of the screen in accordance with the dark and bright patternC; due to the above-mentioned imaye irradiation. The screen to be used in this ~lectrophoto-graphic process is the same as that mentioned in the first embodiment. Here, the electrophotographic process will be explained with reference to Figures 36 to 3~ using the screen 14 of the construction shown in Figure 14. The screen 106 to be used in this embodiment consists of a conductive member 107 to be the base for the screen, a photoconductive member 108, a surface in~ulating member 109, and a conductive member 110 provided only at one surface side of the screen 106. The substance to be used for the photoc~nductive member 108 i~
either those that do not cause the carrier injection by the primary voltage application, or those that do not form the electric charge layer in the photoconductive member 108 at a position in the vicinity of the insulating material depending on the kind of charge.
Figure 36 indicates the simultaneous image irradiation and the primary voltage application processes, wherein the surface insulating member 109 i~ charge~, for example, in positive polarity by the corona wire 111 through a power source 114, and an original image 112 having a dark image po~tion D and a bright image portion L is irradiated by an exposure - light 113 in the arrow direction. By this electric charging, the positive charge is accumulated on the surface of the insulating member 109 and, particularly, a negative charge layer is formed 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 .

-" 10609~43 proportion to th~ capacity of the photoconductive member loa, as it is insulative.
Figure 37 indicates the secondary voltage 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 to be applied is either an A.C. voltage, or a voltage having the opposite polarity to that in the primary voltage application. As a re~ult of this, both bright and dark image portions of the screen 106 ta~e the same surface potential.
Figure 38 indicates a result of conducting a uniform exposure with a light 118 in the arrow direction over the en-tire ourface of the screen 106. By this total exposure, the electric charge within the screen 106 moves again, and the electrostatic contrast increases, whereby the primary electro-static latent image is formed 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 with re~pect of Figures 5 and 21: hence detailed explanations are dispensed with. In Figure 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 numeral 123 represents a power source for ~orming 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 member~ 107 and 110. A~ mentioned ~ . , ~ ~
1060~43 above, when the bright and the dark image portions are not in mutually opposite polarities as in the screen 106 and the primary electrostatic latent im~ge can be formed in the same polarity, it is e~fective to intensify the accelerating and inhibiting fields by forming the bias field ~etween the con-ductive members 107 and 110 in the screen 106 of the above-described construction.
Figures 40 to 43 inclu~ive indicate the application of a secondary voltage having the same p~larity as that of the - 10 primary voltage application to the ~creen 106. On account of this application of a vol~age having the same polarity, the primary electrostatic latent image as formed become~ high in contrast. However, by adjusting the bia~ voltage to be ap-plied between the conductive members 107 and 110, a secondary - electrostatic latent image having less fog can be obtained.
In Figure 40, the primary voltage application is carried out onto the screen 106 by means of a ~orona wire 128, a power source 127, and an exposure light 126 in the arrow - direction to illuminate an original image 125 having a dark image portion D and a bright image portion 1. By this primary volta~e application, if the screen 106 is charged, for example, in positive polarity, it i~ again impressed by a voltage of the same positive polarity in the subsequent secondary voltage application aY s~own in Figure 41.
In Figure 41, the reference numeral 129 designates a power source for a corona wire 130. Figure 42 indicates a re~ult of conducting a uniform exposure over the entire sur~ace of ~he akove-mentioned screen 106 by an expo~ure light 131 in the arrow direction, whereby the primary electrostatic -` 1060943 latent image i~ formed on the screen 10~. Figure 43 indi-cates the secondary e~ectro~t~tic latent image forming process, wherein the reference numeral 132 de~ignates a corona wire, the numeral 133 designates a power source for the wire, the numeral 134 designates a recording member, the numeral 135 designates a conductive support member, the numeral 136 desig-nates a power source for forming the bias field between the conductive member 107 and the conductive support member 135, and the numeral 137 represents a power source for forming the bias field between the conductive members 107 and 110.
F~gure 44 shows surface potential curves which vary on the screen surace in each process step as shown in Figures 36 to 38 inclusive.
~hird Embodiment The photoconductive member is formed on one surface of a conductive member as the base for a screen which is made of stainless steel wire of 30 microns in diameter in the form of a metal wire net of 200 mesh size, by vacuum-evaporation of selenium (Se) containing therein 5% o~ tellurium (Te) to a 2~ thickness at the thickest portion thereo of approximately 50 microns. Subsequently, from both surfaces of the screen, a -~olution of a copolymer of vinyl chloride and vinyl acetate in methyl isobutyl ketone is spray-coated to a thic~ness of approximately 15 microns to form an insulating member on the photoconductive member. Thereafter, aluminum is deposited by evaporation to a thickness of 2,000 angstroms onto the surface side of the ~creen opposite to that where selenium is coated by evaporation, whereby the screen for use in the electrophoto-graphic process according to the present invention is fabricated.

- 1060'943 The image exposure is conducted from the surface side of the screen co~ted with selenillm with the amount of the exposure light at the bright image portion beiny about 6 lux/sec.
accompanied 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 surace exposure, a primary electrostatic latent image is formed having a surface potential of approximately 0 V at the dark image portion and approximately ~250 V at the bright image portion. Then an electrostatic recording paper is dis-posed facing the primary electrostatic latent image surface of the screen at a space interval of 3mm between them. The ætainless steel wire as the conductive mem~er of the screen is earthed, the aluminum layer deposited on the screen is im-pressed by a voltage of ~180 V, while the recording paper is impressed by a voltage of -3kV, and the corona discharge of ~7 kV is applied from the side of the screen opposite to the side thereof facing the recording paper so as to form the secondary electrostatic latent image. upon formation of the ~econdary electrostatic latent image on the recording paper, it is developed by a liquid developex to obtain a clear positive image of the original. When the retention copying i~ conducted for 100 time5 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 lO
with respect to the image density in the initial sheet, the reproduced image of which is found serviceable for practica}
u~e.
This third embodiment oE the electrophotographic . .

. .: ' .
, ' - . 1060943 process according to the pre~ent inve~tion compri~e~ the primary voltage application to uniformly charge the ahove-mentioned screen, and the image irradiation process to be conducted simultaneou~ly with the primary voltage application.
In the explanations of the electrophotographic process in this embodiment, the screen to be referred to is the same as that 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 de~ignates a photoconductive member, the numeral 141 designates a surface insulating member and the numeral 142.
designates a conductive member provided at one surface side of the screen 138. Figure 45 indicates the simultaneous image irradiation and the primary voltage application, wherein the surface insulating member 141 is charged, for example, in positive polarity by means of a corona wire 143. In the figure, the reference numeral 144 designate~ 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 proce~s steps .
i5. identical with that explained with reference to Figure 36;
hence a repeated explanation is dispensed with. -Figure 46 indicates a result of conducting uniformexposure over the entire surface of the screen 138 by means of the exposure liyht 147 in the arrow direction, whereby the - photoconductive member 140 achieves a low resistance value and 1060'~43 is drawn by the static charge on the insulatiny member 141 with the result th~t the electro~tatic contra~t of the screen increases, thereby to form the primary electrostatic latent image.
Figure 47 indicates the secondary electrostatic latent image forming process, in which the same principle of ion flow modulation a~ mentioned earlier applies. In the illu~tration of Figure 47, the reference numeral 149 designates the power ~ource for a corona wire 148, the numeral 150 designates a recording member, the numeral 151 refer~ to a conductive support member, the numeral 152 represent~ a power source for applying $he bias field between the conductive members 139 and 142 and the numeral 153 represents a power source for applying the bias field between the screen 138 and the conductive support member 151. ~urther, the reference letter ~ de~ignates the .
inhibiting field of the ion flow ~hown by dotted lines, and designates the accelerating field.
Figure 48 shows surface potential curves on the surface of the screen 138 according to the afore-described electrophotographic process.
Fourth Embodiment On one surface of a conductive member as the base for a screen which is made of stainless steel wire of 30 microns in diameter in khe form of a metal wire net of 200 mesh size, there is depo~ited selenium (Se) containing therein 5~ of tellurium (Te) as the photoconductive member by vacuum-evaporation to a thickness at the thickest portion thereof - of approximately 40 microns. Thereafter, "Parylene" (produced by Union Carbide Corporation) is coated on the photoconductive .,' ,. ~ - ~ .

~060~43 and conductive members to a thickness of approximately 10 microns S~b~equently, aluminum is deposited by evaporation to a thickne3s of 2,000 angstroms onto the ~urface side of the screen opposite to that where selenium is coated by evaporation, whereby the screen for use in the electrophoto-graphic process according to the present invention is fa~ricated.
The image exposure is conducted from the surface side of the screen coated with selenium with the amount of the exposure light at the bright image portion being about 6 lux/sec.
accompanied by a simultaneous primary voltage application at ~6 kV. Following this simultaneous image irradiation and pr~mary voltage application, the overall surface of the screen is exposed to form thereon a primary electrostatic latent image having a surface potential of approximately ~00 V at the dark , image portion and approximately +450 V at the bright image portion. Then, an electrostatic recording paper is disposed facing ~he 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 i9 impressed by a voltage of ~400 V, while the recording paper iq impressed by a vo~tage of -3 kV, ana a corona discharge of ~7 kV i~
applied from the side of the aluminum layer on the screen so as to form a secondary electrostatic latent image on the re-cording paper. Upon formation of the secondary electrostatic latent image on the recording paper, it i5 developed by a li~uid developing agent to obtain a clear positive image of the orig-inal When the retention copying is conducted for lOO times using this secondary electrostatic latent image on the recor-ding paper, the decrease in the imRge density in the hundredth sheet is recognized to be less than lOx with respect to the image density in the initial sheet, the reproduced image of which is found serviceable for practical use.
The fourth embodiment of the electrophotographic process according to ~he present invention comprises the pri~axy voltage application to uniormly charge the screen, the sub~equent secondary voltage application, the image ir-radiation following the second voltage application, and the third voltage application. In the explanations of the electro-photographic process in this embodiment, the screen to be referred to is one that u~es an N-type photoconductive body having a rectifying property, i.e., having electrons as the principal carrier~
Referring to Figures 49 to 66 inclu~ive which indicate the electrophotographic process in the fourth embodiment, the construction of the screen 154 is the same as that shown in Figure 36 and consists of a conductive member 155 which pro-vides the basic element for the screen 154, a photoconductive member 156, a surface insulating member 157, and another con-ductive member 158 provided at one surface side of the screen 154, Figure 49 indicates the primary voltage applicatiQn process, wherein the surface insulating member 157 i~ po~
tively charged by a corona wire 159. By this primary voltage application, electrons are injected into the photoconductive member 156 from the conductive member 155, whereby a negative charge layer is formed in the photoconductive member 156 at a position contiguous to the insulating member 157 having a - positive charge. Where the photoconductive member 156 is made _ 59 _ ' ~06~943 of a sub~tance that doe~ n~t h~ve the property of rectifying the dispo~ition of the 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 oppo~ite to that of the primary voltage application by means of a corona wire 160 and a po~er source 191 therefor.
Figure 51 indicates the image irradiation ~f an original image 161 onto the screen 154 with a light 162 for the exposure in the arrow direction whereby, at the bright image portion, there takes place injection of the holes in the bright portion of the conductive member 155, or release of the electrons which have been trapped ~ithin the photoconductive member 156, into the conductive member 155 as a result of their being energized by ligh~ rays, although no change takes place at the dark image portion of the photoconductive 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 of the screen 154.
Figure 52 indicates the tertiary volta~e application by mean~ of a corona wire 163, wherein a voltage is applied having the same polarity as in the above-mentioned secondary vo~tage application. By the application of a negative voltage, the surface potential of the screen 154 at the dark image portion varies little, while the surface potential at the bright image portion again takes a negative polarity. The above-_ 60 -- 106~)~43 mentioned image irradiation and the tertiary voltage applica-tion can be performed 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 of the screen 154 is nega-tively charged at its surface, and the dark image portion is positively charged, whereby a primary electrostatic latent image of high electrostatic contrast is formed. This primary electrostatic latent image is not eliminated in the bright i ~ :
image portion.
Figure 54 indicates the secondary electrostatic latent image forming process, in which the same principle of ion flow modulation as explained previously applies. In the drawingr the reference numeral 165 designates a corona wire, to which a voltage of opposite polarity to that of the surface potential of the dark image portion is applied, the numeral 167 designates a recoxding member held on a conductive support member 168, the numeral 169 refer~ 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 the corona wire 165. Where the primary electrostatic latent ; image is formed by surface potentials of mutually oppo~ite polarity between the bright and dark image portions, no bias field is required to be applied between the conductive members ; 155 and 158; hence sufficient secondary electrostatic latent image can be formed even with the screen as shown in Figure 1 which has no part corresponding to the conductive member 158 as in this embodiment. Variations in the electric poten~ial on the screen 154 at every stage of the electrophotographic ,~, ' .

' 106~943 processeq 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 process will be explained herein-below. In this particular process, the secondary voltage application shown in Figure 56 and the tèrtiary voltage ;; application shown in Figure 58 are carried out by an A.C.
power source.
Figure S5 indicates the primary 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 secondary voltage application to the screen 154 by a corona wire 171 and an A.C. power æource 195 therefor. 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 of applying the secondary voltage as in Figure 50, with the conse-quence that the disposition of the electric charge as shown in the drawing is obtained.
Figure 57 indicates the image irradiation to the screen 154, wherein an original image 172 to be reproduced is irradia-ted by an exposure light 173.
Figure 58 shows a result of performing the tertiary voltage application by means of a corona wire 174 and an A.C.
power source 196 therefor. Incidentally~ when the primary voltage ap~lication is carried out in a positive polarity, use of the above-mentioned A.C. power source, on which a negative current has been superposed, also is effective.
Figure 59 shows the total surface irradiation of the screen 154, by which the secondary electrostatic latent image 1061Dg43 due to the electrostatic contra3~ of the same polarity i~
formed on a screen 174. Arrow marks 175 in the drawing de~ig-nate light rays.
Figure 60 indicat~s the seconclary electrostatic latent image forming process onto a recording mem~er 178 held on a conductive support member 179, in which the ion flows a~ shown by dotted lines are modulated under satisfactory conditions by impre~sing the voltage onto the conductive members 155 and 158 through 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 darX and the bright i~age portions thereof. The same principle of ion flow modulation as has been explained with reference to Figure 5 is applicable. Variations in the surface potential on the screen 174 at every stage of the electrophoto-graphic process according to this embodiment are shown by the surface potential curves in Figure 67.
Referring further to Figures 61 to 65 inclusive, still `` another type of electrophotographic process will be explained hereinbelow. In this particular process, the image irradiation shown i~ Figure 51 and the tertiary voltage application shown in Figure 52 are carried out simultaneously, and the tertiary - voltage application is performed by the A.C. power source.
Figure 61 shows the primary voltage application, in which the screen 1S4 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.

_ 63 -Figure 63 indicate~ a result of performing the tertiary voltage application onto the scr~en 154 by a corona wire 184 and an A.c. power source 200, whi.le the image irradiation is being performed simultaneously by way of an original image 182 to be reproduced and an exposure light 183.
Figure 64 indicates a result of performing the total surface irradiation to the above-mentioned screen 154, whereby the primary electrostatic latent image due to the electrostatic contrast, in which the dark image portion having the same polarity as that of the primary voltage application and the bright image portion having almost zero surface potential, is formed on the screen 154. Arrow marks 185 in this drawing designate light rays~
Figure 65 show~ the ~econdary electrostatic latent image forming process onto a recording member 187 held on a conductive support member 188 by means of a corona wire 186. In this secondary electro~tatic latent image forming process, even if the surface potential on one ~urface side of the screen 154 where ~he primary electrostatic latent image is formed i5 zero, it is possible to modulate the ion flow as shown by dotted lines in a state of being free from fog through application of bias ~ield between the conductive members 155 and 158 as illu~trated.
The same principle of modulating the ion flow as has been ; described previously with reference to Figure 5 is applicable to this embodiment. VariationS in the surface potential on the screen 154 at every ~tage of the electrophotographic process according to this e~bodiment are shown by the surface potential curves in Figure 68.
The Table in Figure 69 sh~ws one example of polarity ~,0943 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 su~erposed by direct current.
In Figures 49 through 65, the reference numerals 19 and 201 respectively designate a power source for a corona wire and the reference numeral 202 in Figure 60 and the numeral 203 in Figure 66 refer to a power source to form the bias field between the screen and the conductive support member.
In the foregoing axplanation~ 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-istic~ of the photoconductive substance are not limited to - those exemplified. Furthermore, the direction for the voltage application in the primary electrostatic latent image formation ;~
as well as the direction for the image irradiation have been described in connection with those which can only achieve the maximum effect, although they are not limited to these - examples alone. In addition, in each process that has been exemplified, the secondary electrostatic latent image is ,:
formed on the recording member without exception. It goes without saying that this recording member may be not only the electrostatic recording paper, but also may be any type of conventionally known electrostatic latent image forming member.
The photosensit~ve screen shown in Figure 1 gives the best 101~094;~
results in the electrophotographic process according to the invention.
While the invention has been illustrated ~nd described by way of preferred embodiments 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 the spirit and scope of the invention as set forth in the appended claims.

Ri dout ~ I~A ~
101 R,cllmoncl St. ~N~st Toronto 1, Canada Patent Agents of the A~plicant .

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Claims

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

1. An electrophotographic process wherein an electro-static latent image is formed on a screen, and a flow of ions is applied to a chargeable member through said screen to control the flow of ions to form another electrostatic latent image on said chargeable member, the improvement residing in that said screen comprises a conductive screen having a num-ber of fine openings, a photoconductive layer on said conductive screen and an insulating layer on said photoconductive layer;
when the flow of ions is applied and modulated by said screen bearing the latent image, there are (1) an electric field, adjacent to the openings of the screen, formed by the electrostatic latent image having charges of opposite polarities sandwiching the insulating layer; (2) an electric field formed between the screen and a corona discharge electrode for producing the flow of ions to be modulated to direct the flow of ions from the corona discharge electrode toward the screen; and (3) an electric field formed between said screen and said chargeable member to direct the flow of ions modulated by said screen toward the chargeable member.

2. An electrophotographic process according to Claim 1, wherein the electric field adjacent to the openings and the elec-tric field between the corona discharge electrode and the charge-able member are directed in the same direction.

3. An electrophotographic process according to Claim 1, wherein the electric field adjacent to the openings and the electric field between the corona discharge electrode and the chargeable member are directed oppositely to each other.

4. An electrophotographic process according to Claim 1, wherein the electric field formed on said screen corresponds to dark area of an original image.

5. An electrophotographic process according to Claim 1, wherein the electric field formed on said screen corresponds to light area of an original image.

6. An electrophotographic process according to Claim 1, wherein the electric field formed adjacent to the openings at an area corresponding to a dark area of an original, is directed in the same direction as that of the electric field between the corona discharge electrode and the chargeable member, so that a positive latent image of an original is formed on the chargeable member.

7. An electrophotographic process according to Claim 1, wherein the electric field formed adjacent to the openings at an area corresponding to a light area of an original, is directed in the same direction as that of the electric field between the corona discharge electrode and the chargeable member, so that a negative latent image of an original is formed on the chargeable member.

8. An electrophotographic process according to Claim 1, wherein the electric field adjacent to the openings at an area corresponding to a light area and the electric field adjacent to the openings at an area corresponding to a dark area, are directed oppositely to each other.

9. An electrophotographic process according to Claim 8, wherein a direction of the electric field between the corona dis-charge electrode and the chargeable member is selectively changed, to pass through the screen the flow of ions having a selected po-larity, thereby providing selectively a negative or positive image on the chargeable member.

10. An electrophotographic process according to Claim 9, wherein the corona discharge electrode is supplied with a power of a polarity and a power of an opposite polarity alternately, and in synchronism therewith a direction of the electric field between the corona discharge electrode and the chargeable member is altered to form on the chargeable member said another electrostatic latent image which has a charge of a polarity at an area corresponding to a dark area of an original and a charge of a polarity opposite to that of the area corresponding to the dark area of the original at an area corresponding to a light area of the original.