CA1176694A - Imaging process - Google Patents
Imaging processInfo
- Publication number
- CA1176694A CA1176694A CA000400057A CA400057A CA1176694A CA 1176694 A CA1176694 A CA 1176694A CA 000400057 A CA000400057 A CA 000400057A CA 400057 A CA400057 A CA 400057A CA 1176694 A CA1176694 A CA 1176694A
- Authority
- CA
- Canada
- Prior art keywords
- photoreceptor
- layer
- photosensitive layer
- electrically insulating
- corotron
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
- G03G15/0291—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices corona discharge devices, e.g. wires, pointed electrodes, means for cleaning the corona discharge device
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/22—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20
- G03G15/226—Apparatus for electrographic processes using a charge pattern involving the combination of more than one step according to groups G03G13/02 - G03G13/20 where the image is formed on a dielectric layer covering the photoconductive layer
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- General Physics & Mathematics (AREA)
- Discharging, Photosensitive Material Shape In Electrophotography (AREA)
- Electrophotography Using Other Than Carlson'S Method (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
There is disclosed an imaging process utilizing a photoreceptor comprising a conductive substrate, a photosensitive layer and an electrically insulating layer over the photosensitive layer wherein said photoreceptor is charged by means of an AC corotron so as to provide an electrical field across the photosensitive layer only. The AC corotron drive the voltage across the electrically insulating layer to zero by means of a bias voltage applied to the corotron shield.
There is disclosed an imaging process utilizing a photoreceptor comprising a conductive substrate, a photosensitive layer and an electrically insulating layer over the photosensitive layer wherein said photoreceptor is charged by means of an AC corotron so as to provide an electrical field across the photosensitive layer only. The AC corotron drive the voltage across the electrically insulating layer to zero by means of a bias voltage applied to the corotron shield.
Description
g 4 IMAGING PROCESS
This invention relates to a xerographic imaging process and apparatus and, more particularly, to a process and apparatus for uniformly charging a photosensitive member which is overcoated with an electrically 5insulating layer.
For many years during the development of the xerographic process, the need for protecting the photosensitive layer has been appreciated. ~qany proposals have been made to protect the photosensitive layer by coating the layer with various materials. By coatin~ the photosensitive layer, the wear 10occasioned by repeated use is absorbed by a tough, polymeric surface rather than the more delicate, expensive photosensitive material itself. One example of such an attempt to protect the photosensitive layer in the xerographic process is described by Blakney et al. in U.S. Patent No. 3,041,167 wherein the problem of charge build-up in the photoreceptor was observed. An electrically 15insulating, protective overcoating on a photosensitive layer was utilized to support the electrostatic latent image in a process disclosed in U.S. Patent No.3,234,019 to Hall. In this process, as in the Blakney et al. process, an initialcharge of one polarity is provided on the photoreceptor followed by a second charge of opposite polarity in order to establish an electrical field across the20photoreceptor. While one may calculate voltages to be utilized in order to arrive at a condilion in the photoreceptor wherein the electrical field is entirely across the photoreceptor and none is across the bonded, electrically insulating protective coating, such condition is difficult to achieve in practice.
Actually, there is always a small imbalance of charges resulting in a small 25charge residing on the surface of the electrically insulating overcoating which charge may build up with repeated use of the photoreceptor and ultimately interfere with the quality of images provided by the process.
Other examples of photoreceptors having protective, electrically insulating coatings over the photosensitive layers include U.S. 3,895,943 and 30U.S. 3,904,409 to lIanada wherein the electrically insulating overcoating is utilized in conjunction with persistent internal polarization and contains the problem of charge build-up on the surface of the electrically insulating layer.
As a practical matter, it ls very difficult to operate a process wherein said layer is returned, at the beginning of each imaging cycle, to zero voltage.
35Small variations in the operation of the DC corotrons particularly utilized inthe prior art to provide the sequential charging steps make the condition of ~ 1~66~
zero voltage on the electrically insulating layer nearly impossible with ordinary equipment.
It is an object of an aspect of this invention to provide an imaging process utilizing a photoreceptor containing an electrically insulating protective layer over the photosensitive layer wherein charge build-up on the electrically insulating layer is prevented.
An object of an aspect of this invention is to simplify the operation of xerographic processes utilizing a photoconductive element containing an electrically insulating protective layer over the photosensitive layer.
An ob~ect of an aspect of this invention is to provide an apparatus having a reduced number of charging units required to establish an electric field across the photosensitive layer having bonded thereto an electrically insulating, protective coating.
In accordance with an aspect of this invention, there is provided an apparatus and process wherein an electric field is provided in a single charging step across the photosensitive layer of a photoconductive member having an electrically insulating protective layer over the photosensitive layer, which step eliminates or prevents the build-up of electrical charge on the surface of the electrically insulating layer. Briefly, the process of an aspect of this invention -comprises charging such a photoreceptor containlng a photoconductive layer on an electrically conductive substrate, which photosensitive layer is protected by an electrically insulating layer of sufficient thickness to support the electrostatic charges utilized in the imaging process, by means of an AC corotron having a bias voltage applied to the corotron shield. By adjusting the voltage applied to the corotron shield, a condition of zero voltage on the electrically insulating overcoating is achieved and an electrical field established across the photosensitive layer in a single charging step. As in any xerographic process, the charged photoreceptor is exposed to an r r ~
1 ~76694 imagewise pattern of electromagnetic radiation to which the photosensitive layer is sensitive to provide a latent electrostatic image entirely within the photosensitive layer. Typically, the latent image is developed by electroscopic materials applied to the electrically insulating overcoating, which image is then transferred to an image receiving sheet thereby allowing erasure of the electrostatic latent image by flood exposure of the photosensitive layer and reuse of the photoreceptor.
Other aspects of this invention are as follows:
An electrophotographic imaging process comprising providing a photoreceptor comprising a conductive substrate, a photosensitive layer, and an electrically insulating layer over said photosensitive layer;
charging said photoreceptor by means of an AC
corotron, said corotron having a shield bias voltage adjusted so as to provide substantially no voltage across said electrically insulating layer; and exposing said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photosensitive layer is sensitive whereby an electrostatic latent image is formed in said photosensitive layer.
In an electrophotographic imaging process comprising providing a photoreceptor comprising a conductive- substrate, photosensitive layer and an electrically insulating layer over said photosensitive layer and a) charging said photoreceptor by means of an AC
corotron, said corotron having an adjustable shield bias voltage;
b) exposing said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photoreceptor is sensitive, whereby an electrostatic latent image is formed in said photosensitive layer;
c) visibly developing said latent image on said photoreceptor;
,~
, . .
2b 1 1~6~
d) transferring said developed image from said photoreceptor to an image receiving substrate;
e) erasing said latent image by means of flood exposi.ng said photosensitive layer to electromagnetic radiation to which it is sensitive;
f) measuring the voltage remaining on said photoreceptor subsequent to said flood exposure;
g) utilizing said measured voltage to adjust said shield bias voltage so as to maintain zero voltage on the surface of said electrically insulating layer; and h) repeating steps (a) - (f) at least once.
An electrophotographic imaging apparatus comprising a photoreceptor comprising an electrically conductive substrate, a photosensitive layer and an electrically insulating layer over said photosensitive layer, an AC corotron charging device to provide an electrical field across the photosensitive layer of said photoreceptor, said corotron having means to apply a bias voltage to the shield thereof, means to expose said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photosensitive layer is sensitive, means to develop said image on said electrically insulating layer, means to transfer said image from said electrically insulating layer, means to erase said latent image subsequent to said transfer and to clean untransferred imaging material from said ;~ electrically insulating layer.
- Of fundamental significance in the present invention is the presence of a rectifying layer at the interface of.the photosensitive layer and the ~ ~L fi' ~ ~ 9 ~1 electrically conductive substrate. In the case of an amorphous ~e alloy, one typically chooses a rectifying contaet which injects positive charges into the photoconductive layer and blocks negative charges. If negative charges are deposited on the top of the photoreceptor, positive charges are injected from 5 the interface into the photoconducting layer. They travel through the photoconducting layer to the interface between the photoconducting layer and the insulating layer where they are trapped. If the surface charge on top of the photoreceptor is positive, the negative counter charge remains at the conductive substrate because of the blocking nature of the interface. If one 10 wants to operate the photoreceptor with negative surface charges, the interface would have to be injecting for electronics and blocking for positive charges. The preferred operating mode depends on the photoreceptor mate-rials used. For example, in the case of the utilization of a selenium alloy photosensitive layer, positive charges are injected into the photosensitive 15 layer during periods of negative charge on the surface of the electrically insulating layer. Because of the rectifying properties of the photosensitive layer, no negative charge is injected during those periods when the charge on the surface of the electrically insulating layer is positive. In such instance, a positive voltage is established across the photosensitive layer. With the proper20 adjustment of bias voltage on the shield of the AC corotron, the total current influx integrated over the time of exposure to charge can be made zero on the surface of the electrically insulating layer. Such condition also eliminates charge build-up due to the polarization of the overcoating since the net total charge deposited by the AC corotron is of such polarity to counteract the 25 overcoating polarization.
As noted above, there is thus provided, in a single charging step, an electrical field across the photoconductive layer by a single corotron in place of the two corotrons required in the prior art. Further, since the polarization or charge buil~up on the surface of the electrically insulating layer is 30 eliminated, there is no need for a corotron, typically an AC corotron, to level the charge subsequent to image development and transfer. In accordance with this invention, a single corotron replaces three corotrons required in the priorart in order to properly provide an electrical field across the photoreceptor only and to eliminate residual charge on the electrically insulating, protective35 overcoating on the photosensitive layer. Typically, the AC corotron is operated in the Irequency range of from about 50 Hz to about 1000 ~Iz in the ~ ~7~9~
process of this invention. Preferably, the frequency is in the range of from about50Hztoabout400Hz.
The invention will be more fully described with reference to the attached drawings wherein:
Figure 1 is a diagrammatic representation of a section of a xerographic photoreceptor utilized in the process of this invention.
Figure 2 is a diagrammatic representation of a section of a photoreceptor indicating an intermediate charging condition during the process of this invention.
Figure 3 is a diagrammatic representation of a section of a photoreceptor indicating the charged condition subsequent to the charging step in the process of this invention.
Figure 4 is a diagrammatic representation of a section of a photoreceptor indicating the creation of an electrostatic latent image upon light exposure in accordance with the process of this invention.
Figure 5 is a schematic representation of a xerographic printing apparatus incorporating the process of this invention.
In Figure 1, there is shown photoreceptor l comprising a conductive substrate 3 supporting a photosensitive layer 5. An electrically insulating layer 7 resides on photosensitive layer 5 to provide protection from wear and contamination due to the repeated toning, transferring and cleaning which occurs in each imaging cyele and retards crystallization in the event a Se alloyis used.
In Figure 2, there is shown the intermediate charge condition of the photoreceptor during the charging step in the process of this invention. In Figure 2, photoreceptor l is shown receiving, at the surface of the electricallyinsulating layer 7, both positive and negative charges, which are provided by an AC corotron. The charged designations indicating positive and negative charges contained within circles indicate a transitory condition or charges in motion while those charge designations, both positive and negative, without circles indicate stable charges which remain in the photoreceptor until further processing occurs. Thus, there is shown both positive and negative charges on the surface of electrically insulating layer 7 which are alternately supplied byan AC corotron. With a proper voltage bias on the corotron shield, these charges will equal each other thereby resulting in a net zero charge residing onthe surface of electrically insulating layer 7. However, during periods of ~:~ 7~g4 negative charge deposition on the surface of the electrically insulating layer 7, positive charges are presented to the photosensitive material at the interface of electrically conductive layer 3 and photosensitive layer 5. These positive charges are shown in a circle at the interface and, because of the negative charge, residing simultaneously on the surface of electrically insulating layer 7, the positive charges are drawn to the interface of photosensitive layer 5 andelectrically insulating layer 7 where they are trapped. During periods in which the AC corotron is depositing positive charges on the surface of electrically insulating layer 7, negative charges are presented a~ the interface between conductive layer 3 and photosensitive layer 5. These charges remain trapped at said interface because of the rectifying nature cf the photosensitive material in layer 5.
While Figure 2 indicates the segment of a photoreceptor, during the charging step, said segment is considered to be extremely small at any particular point in time during the charging step in the process of this invention. Figure 2 illustrates the condition for purposes of illustration only.In Figure 3, the photoreceptor is illustrated in its charged condition wherein there are stable negative charges residing at the interface of electrically conductive layer 3 and photosensitive layer 5 while equal charges of opposite polarity reside at the interface of photosensitive layer 5 and electrically insulating layer 7. These charges provide an electrical field across the photosensitive layer with no charge residing on the surface of electrically insulating layer 7.
The thus charged photosensitive layer is ready for imagewise light exposure to establish a latent image therein as is illustrated in Figure 4. Light rays 9 are shown impinging on the surface of electrically insulating layer 7 which is transparent to said electromagnetic radiation allowing charge carriers to be created in the photosensitive material thereby eliminating the equal amounts of charge residing at the interfaces of said layer. There are thus provided areas of charged and uncharged photoreceptor which can be detected at the surface of electrically insulating layer 7 in any suitable manner.
Obviously, subsequent to image formation, development and transfer, the remaining electrical field within the photoreceptor 1 is eliminated by flood exposure of the photoreceptor.
The photosensitive layer 5 may be exposed from either side as is known in the prior art when providing a transparent conductive substrate 3 or, `~ ~ 7~3~
more commonly, a transparent electrically insulating layer 7. Apparatus convenient for the purpose of the user is constructed utilizing the principals of the process of this invention in either case. In addition, intermediate layers may be placed between the conductive layer 3 and photosensitive layer 5 to 5 enhance the charge injecting nature of the interface. Such materials are well known in the prior art and are chosen with regard for the type of photo-sensitive material utilized in layer 5. In addition, adhesive layers may also beapplied to the surfaces of photosensitive layer 5 in order to adhere the electrically insulating protective layer thereto, as well as providing adhesion 10 of the photosensitive material to the conductive substrate as injection layer.
Typical electrically insulating layers include organic, as well as inorganic, materials. ~ particularly preferred m,aterial is polyethylene tere-phthalate available commercially under the~ f~omn~he E.I. du Pont de Nemours & Company, Inc.. Such material is preferred because of its 15 availability and ease of handling, as well as its electrical properties. Other materials which can be typically utilized as protective layers include polyester, polyvinylchloride, polypropylene, polyvinylidenechloride, polycar-bonate, polystyrene, polyamide, polyfluoroethylene, polyethylene, polyimide, polyvinylfluoride, polyvinylidene fluoride, polyvinylidenechloride, poly-20 urethane, etc..
Photosensitive materials utilized in the process of this inventionare typically those which provide a rectifying boundary at the conductive substrate. Typical photosensitive materials include selenium, selenium alloys such as selenium-tellurium alloys, selenium-arsenic alloys containing various 25 dopants, such as cadmium sulfide, cadmium selenide, cadmium sulfoselenide, zinc oxide, zinc sulfide and zinc selenide. Of course, said photosensitive materials may be dispersed in suitable binder materials as is well known in the art. Any suitable photosensitive material is included within the scope of this invention, such as a composite layer leaving fine photoconductive material in 30 contact with the electrically insulating layer and relatively coarse photocon-ductive particles contacting the base. Each portion of the composite layer is desirably dispersed in a suitable binder. Such a photoreceptor is more fully described in U.S. Ratent 3,801,317 to Tanada et al.. If desired, additional layers may be incorporated into the imaging member to aid in the various 35 desired properties. For example, materials can be utilized at the interface between the photosensitive layer and the electrically conductive layer which ~7~
promote charge injection Oe one polarity and suppress charge injection of another. Such materials include trigonal Se, gold, Te-alloys and carbon.
As mentioned above, the AC corotron utilized in the process of this invention is provided with a voltage bias on the shield thereof. The bias 5 voltage to the shield is adjusted so as to provide the desired zero voltage onthe surface of the electrically insulating layer. This voltage bias is typicallydetermined empirically as it is highly dependent upon numerous operational factors such as distance between the corotron and the surface being charged, the amount of voltage desired to be utilized on the corotron wire and the 10 nature of the surface being charged. As a typical example of the operation ofthe process of this invention, there is shown in Fig-ure 5 a schematic of a xerographic apparatus indicating the major operations of the xerographic process. In Figure 5, there is shown xerographic apparatus 11, comprising a photoreceptor 13 having the configuration of the photoreceptor illustrated in 15 Figure 1. In this instance, photoreceptor 13 is in the form of a typical xerographic rotary drum mounted upon a grounded support 15. In the cyclic process, corotron 17 is utilized to charge photoreceptor 13 through power supply 19, either directly coupled to the wire or to the wire via a capacitance.In addition, a variable power supply 21 is utilized to supply a bias voltage to 20 the shield of corotron 17 as indicated in Figure 5. Por testing purposes only, a probe 23 is inserted subsequent to the charging operation to monitor the amount of charge on the photoreceptor. The charged photoreceptor is then rotated past a typical slit scanning optical system 25 whereby the charged photoreceptor is exposed to a pattern of electromagnetic radiation to which 25 the photosensitive material is sensitive. The exposed photoreceptor is then rotated past the developing station whereby the electrostatic latent image in the photosensitive layer is developed. After development, the image is transferred as shown at transfer station 29 with the aid of transfer corotron 31. After transfer, the photoreceptor 13 is prepared for further use by erase 30 lamp 33 which collapses the remaining field in the photoreceptor followed by removal of residual toner material at cleaning station 35. Por testing purposes, a probe 37 is inserted in the cycle after the erase lamp 33 to determine the amount of charge remaining in the photoreceptor. Since the erase lamp collapses the field remaining across the photosensitive layer, any 35 voltage detected by probe 37 must represent charge residing on the electri-cally insulating layer. Power supply 21 is adjusted so as to provide a proper -8~ 9 ~
bias voltage to the shield of corotron 17 which results in a zero net charge on the insulating layer as indicated by probe 37. When the voltage indicated by probe 37 is positive, then the bias voltage to the shield is made more negative.Conversely, when the indicated voltage is negative, the bias voltage to the 5 shield is made more positive.
RXAMPLE I
In an apparatus as illustrated in Figure 5, there is provided a photoreceptor comprising an electrically conductive substrate having coated thereon a 3 micron thick trigonal selenium injecting layer over which is coated 10 a 60 micron thick selenium-arsenic alloy doped with chlorine. Over the photosensitive layer there is applied a 12 micron thick coating of an electri-cally insulating polyurethane layer. At a surface speed of about 51 cm./sec.
the photoreceptor is rotated past a double wire corotron 13.5 cm in length and operated at 60 Hz. The corotron shield is biased to a negative 30 volts, while 15 the corotron wire has 16,000 volts AC peak to peak applied thereto. A field condition of +80 volts was measured at probe 23 subsequent to charging. It was established that this voltage is completely across the photosensitive layer by the fact that no voltage was detected at probe 37 subsequent to the erase lamp. Any voltage detected by probe 37 would indicate a voltage across the 20 overcoating since there would be no field left in the photosensitive layer.
EXAMPLE II
The procedure of Example I is repeated with the exception that the photoreceptor is moved past a double wire corotron which is the same as that of Example I except that the length was 12 cm. A positive voltage of 350 volts 25 is measured at probe 23 while the shield voltage is held at +400 volts and the voltage applied to the corotron wires was 16,000 volts peak to peak. Again, there is no voltage measured at probe 37, indicating that the entire field of +350 volts existed across the photosensitive layer of the photoreceptor and no voltage was left residing on the surface of the electrically insulating poly-30 urethane layer.
EXAMPLE III
A single wire corotron 20 cm in length is utili~ed in the process of Example I to establish a field of 500 volts which is measured at probe 23 after exposure to the AC corotron having a shield bias of +520 volts and 16,000 volts 35 peak to peak applied to the wire. Again, no voltage was detected by probe 37 subsequent to exposure to the erase lamp.
6 g ~
_9_ Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure.
These are intended to be included within the scope of this invention. Of especial note is the fact that the procedures described herein are not limited 5 to structures with dimensions typical of Rxample I. The insulating protective layer may vary in thickness from a few microns to in excess of 20 m and the 60 m photosensitive layer may vary in thickness from approximately 5 m to 80 m so that operation with a large range of electroscopic image development materials may be accommodated.
This invention relates to a xerographic imaging process and apparatus and, more particularly, to a process and apparatus for uniformly charging a photosensitive member which is overcoated with an electrically 5insulating layer.
For many years during the development of the xerographic process, the need for protecting the photosensitive layer has been appreciated. ~qany proposals have been made to protect the photosensitive layer by coating the layer with various materials. By coatin~ the photosensitive layer, the wear 10occasioned by repeated use is absorbed by a tough, polymeric surface rather than the more delicate, expensive photosensitive material itself. One example of such an attempt to protect the photosensitive layer in the xerographic process is described by Blakney et al. in U.S. Patent No. 3,041,167 wherein the problem of charge build-up in the photoreceptor was observed. An electrically 15insulating, protective overcoating on a photosensitive layer was utilized to support the electrostatic latent image in a process disclosed in U.S. Patent No.3,234,019 to Hall. In this process, as in the Blakney et al. process, an initialcharge of one polarity is provided on the photoreceptor followed by a second charge of opposite polarity in order to establish an electrical field across the20photoreceptor. While one may calculate voltages to be utilized in order to arrive at a condilion in the photoreceptor wherein the electrical field is entirely across the photoreceptor and none is across the bonded, electrically insulating protective coating, such condition is difficult to achieve in practice.
Actually, there is always a small imbalance of charges resulting in a small 25charge residing on the surface of the electrically insulating overcoating which charge may build up with repeated use of the photoreceptor and ultimately interfere with the quality of images provided by the process.
Other examples of photoreceptors having protective, electrically insulating coatings over the photosensitive layers include U.S. 3,895,943 and 30U.S. 3,904,409 to lIanada wherein the electrically insulating overcoating is utilized in conjunction with persistent internal polarization and contains the problem of charge build-up on the surface of the electrically insulating layer.
As a practical matter, it ls very difficult to operate a process wherein said layer is returned, at the beginning of each imaging cycle, to zero voltage.
35Small variations in the operation of the DC corotrons particularly utilized inthe prior art to provide the sequential charging steps make the condition of ~ 1~66~
zero voltage on the electrically insulating layer nearly impossible with ordinary equipment.
It is an object of an aspect of this invention to provide an imaging process utilizing a photoreceptor containing an electrically insulating protective layer over the photosensitive layer wherein charge build-up on the electrically insulating layer is prevented.
An object of an aspect of this invention is to simplify the operation of xerographic processes utilizing a photoconductive element containing an electrically insulating protective layer over the photosensitive layer.
An ob~ect of an aspect of this invention is to provide an apparatus having a reduced number of charging units required to establish an electric field across the photosensitive layer having bonded thereto an electrically insulating, protective coating.
In accordance with an aspect of this invention, there is provided an apparatus and process wherein an electric field is provided in a single charging step across the photosensitive layer of a photoconductive member having an electrically insulating protective layer over the photosensitive layer, which step eliminates or prevents the build-up of electrical charge on the surface of the electrically insulating layer. Briefly, the process of an aspect of this invention -comprises charging such a photoreceptor containlng a photoconductive layer on an electrically conductive substrate, which photosensitive layer is protected by an electrically insulating layer of sufficient thickness to support the electrostatic charges utilized in the imaging process, by means of an AC corotron having a bias voltage applied to the corotron shield. By adjusting the voltage applied to the corotron shield, a condition of zero voltage on the electrically insulating overcoating is achieved and an electrical field established across the photosensitive layer in a single charging step. As in any xerographic process, the charged photoreceptor is exposed to an r r ~
1 ~76694 imagewise pattern of electromagnetic radiation to which the photosensitive layer is sensitive to provide a latent electrostatic image entirely within the photosensitive layer. Typically, the latent image is developed by electroscopic materials applied to the electrically insulating overcoating, which image is then transferred to an image receiving sheet thereby allowing erasure of the electrostatic latent image by flood exposure of the photosensitive layer and reuse of the photoreceptor.
Other aspects of this invention are as follows:
An electrophotographic imaging process comprising providing a photoreceptor comprising a conductive substrate, a photosensitive layer, and an electrically insulating layer over said photosensitive layer;
charging said photoreceptor by means of an AC
corotron, said corotron having a shield bias voltage adjusted so as to provide substantially no voltage across said electrically insulating layer; and exposing said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photosensitive layer is sensitive whereby an electrostatic latent image is formed in said photosensitive layer.
In an electrophotographic imaging process comprising providing a photoreceptor comprising a conductive- substrate, photosensitive layer and an electrically insulating layer over said photosensitive layer and a) charging said photoreceptor by means of an AC
corotron, said corotron having an adjustable shield bias voltage;
b) exposing said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photoreceptor is sensitive, whereby an electrostatic latent image is formed in said photosensitive layer;
c) visibly developing said latent image on said photoreceptor;
,~
, . .
2b 1 1~6~
d) transferring said developed image from said photoreceptor to an image receiving substrate;
e) erasing said latent image by means of flood exposi.ng said photosensitive layer to electromagnetic radiation to which it is sensitive;
f) measuring the voltage remaining on said photoreceptor subsequent to said flood exposure;
g) utilizing said measured voltage to adjust said shield bias voltage so as to maintain zero voltage on the surface of said electrically insulating layer; and h) repeating steps (a) - (f) at least once.
An electrophotographic imaging apparatus comprising a photoreceptor comprising an electrically conductive substrate, a photosensitive layer and an electrically insulating layer over said photosensitive layer, an AC corotron charging device to provide an electrical field across the photosensitive layer of said photoreceptor, said corotron having means to apply a bias voltage to the shield thereof, means to expose said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photosensitive layer is sensitive, means to develop said image on said electrically insulating layer, means to transfer said image from said electrically insulating layer, means to erase said latent image subsequent to said transfer and to clean untransferred imaging material from said ;~ electrically insulating layer.
- Of fundamental significance in the present invention is the presence of a rectifying layer at the interface of.the photosensitive layer and the ~ ~L fi' ~ ~ 9 ~1 electrically conductive substrate. In the case of an amorphous ~e alloy, one typically chooses a rectifying contaet which injects positive charges into the photoconductive layer and blocks negative charges. If negative charges are deposited on the top of the photoreceptor, positive charges are injected from 5 the interface into the photoconducting layer. They travel through the photoconducting layer to the interface between the photoconducting layer and the insulating layer where they are trapped. If the surface charge on top of the photoreceptor is positive, the negative counter charge remains at the conductive substrate because of the blocking nature of the interface. If one 10 wants to operate the photoreceptor with negative surface charges, the interface would have to be injecting for electronics and blocking for positive charges. The preferred operating mode depends on the photoreceptor mate-rials used. For example, in the case of the utilization of a selenium alloy photosensitive layer, positive charges are injected into the photosensitive 15 layer during periods of negative charge on the surface of the electrically insulating layer. Because of the rectifying properties of the photosensitive layer, no negative charge is injected during those periods when the charge on the surface of the electrically insulating layer is positive. In such instance, a positive voltage is established across the photosensitive layer. With the proper20 adjustment of bias voltage on the shield of the AC corotron, the total current influx integrated over the time of exposure to charge can be made zero on the surface of the electrically insulating layer. Such condition also eliminates charge build-up due to the polarization of the overcoating since the net total charge deposited by the AC corotron is of such polarity to counteract the 25 overcoating polarization.
As noted above, there is thus provided, in a single charging step, an electrical field across the photoconductive layer by a single corotron in place of the two corotrons required in the prior art. Further, since the polarization or charge buil~up on the surface of the electrically insulating layer is 30 eliminated, there is no need for a corotron, typically an AC corotron, to level the charge subsequent to image development and transfer. In accordance with this invention, a single corotron replaces three corotrons required in the priorart in order to properly provide an electrical field across the photoreceptor only and to eliminate residual charge on the electrically insulating, protective35 overcoating on the photosensitive layer. Typically, the AC corotron is operated in the Irequency range of from about 50 Hz to about 1000 ~Iz in the ~ ~7~9~
process of this invention. Preferably, the frequency is in the range of from about50Hztoabout400Hz.
The invention will be more fully described with reference to the attached drawings wherein:
Figure 1 is a diagrammatic representation of a section of a xerographic photoreceptor utilized in the process of this invention.
Figure 2 is a diagrammatic representation of a section of a photoreceptor indicating an intermediate charging condition during the process of this invention.
Figure 3 is a diagrammatic representation of a section of a photoreceptor indicating the charged condition subsequent to the charging step in the process of this invention.
Figure 4 is a diagrammatic representation of a section of a photoreceptor indicating the creation of an electrostatic latent image upon light exposure in accordance with the process of this invention.
Figure 5 is a schematic representation of a xerographic printing apparatus incorporating the process of this invention.
In Figure 1, there is shown photoreceptor l comprising a conductive substrate 3 supporting a photosensitive layer 5. An electrically insulating layer 7 resides on photosensitive layer 5 to provide protection from wear and contamination due to the repeated toning, transferring and cleaning which occurs in each imaging cyele and retards crystallization in the event a Se alloyis used.
In Figure 2, there is shown the intermediate charge condition of the photoreceptor during the charging step in the process of this invention. In Figure 2, photoreceptor l is shown receiving, at the surface of the electricallyinsulating layer 7, both positive and negative charges, which are provided by an AC corotron. The charged designations indicating positive and negative charges contained within circles indicate a transitory condition or charges in motion while those charge designations, both positive and negative, without circles indicate stable charges which remain in the photoreceptor until further processing occurs. Thus, there is shown both positive and negative charges on the surface of electrically insulating layer 7 which are alternately supplied byan AC corotron. With a proper voltage bias on the corotron shield, these charges will equal each other thereby resulting in a net zero charge residing onthe surface of electrically insulating layer 7. However, during periods of ~:~ 7~g4 negative charge deposition on the surface of the electrically insulating layer 7, positive charges are presented to the photosensitive material at the interface of electrically conductive layer 3 and photosensitive layer 5. These positive charges are shown in a circle at the interface and, because of the negative charge, residing simultaneously on the surface of electrically insulating layer 7, the positive charges are drawn to the interface of photosensitive layer 5 andelectrically insulating layer 7 where they are trapped. During periods in which the AC corotron is depositing positive charges on the surface of electrically insulating layer 7, negative charges are presented a~ the interface between conductive layer 3 and photosensitive layer 5. These charges remain trapped at said interface because of the rectifying nature cf the photosensitive material in layer 5.
While Figure 2 indicates the segment of a photoreceptor, during the charging step, said segment is considered to be extremely small at any particular point in time during the charging step in the process of this invention. Figure 2 illustrates the condition for purposes of illustration only.In Figure 3, the photoreceptor is illustrated in its charged condition wherein there are stable negative charges residing at the interface of electrically conductive layer 3 and photosensitive layer 5 while equal charges of opposite polarity reside at the interface of photosensitive layer 5 and electrically insulating layer 7. These charges provide an electrical field across the photosensitive layer with no charge residing on the surface of electrically insulating layer 7.
The thus charged photosensitive layer is ready for imagewise light exposure to establish a latent image therein as is illustrated in Figure 4. Light rays 9 are shown impinging on the surface of electrically insulating layer 7 which is transparent to said electromagnetic radiation allowing charge carriers to be created in the photosensitive material thereby eliminating the equal amounts of charge residing at the interfaces of said layer. There are thus provided areas of charged and uncharged photoreceptor which can be detected at the surface of electrically insulating layer 7 in any suitable manner.
Obviously, subsequent to image formation, development and transfer, the remaining electrical field within the photoreceptor 1 is eliminated by flood exposure of the photoreceptor.
The photosensitive layer 5 may be exposed from either side as is known in the prior art when providing a transparent conductive substrate 3 or, `~ ~ 7~3~
more commonly, a transparent electrically insulating layer 7. Apparatus convenient for the purpose of the user is constructed utilizing the principals of the process of this invention in either case. In addition, intermediate layers may be placed between the conductive layer 3 and photosensitive layer 5 to 5 enhance the charge injecting nature of the interface. Such materials are well known in the prior art and are chosen with regard for the type of photo-sensitive material utilized in layer 5. In addition, adhesive layers may also beapplied to the surfaces of photosensitive layer 5 in order to adhere the electrically insulating protective layer thereto, as well as providing adhesion 10 of the photosensitive material to the conductive substrate as injection layer.
Typical electrically insulating layers include organic, as well as inorganic, materials. ~ particularly preferred m,aterial is polyethylene tere-phthalate available commercially under the~ f~omn~he E.I. du Pont de Nemours & Company, Inc.. Such material is preferred because of its 15 availability and ease of handling, as well as its electrical properties. Other materials which can be typically utilized as protective layers include polyester, polyvinylchloride, polypropylene, polyvinylidenechloride, polycar-bonate, polystyrene, polyamide, polyfluoroethylene, polyethylene, polyimide, polyvinylfluoride, polyvinylidene fluoride, polyvinylidenechloride, poly-20 urethane, etc..
Photosensitive materials utilized in the process of this inventionare typically those which provide a rectifying boundary at the conductive substrate. Typical photosensitive materials include selenium, selenium alloys such as selenium-tellurium alloys, selenium-arsenic alloys containing various 25 dopants, such as cadmium sulfide, cadmium selenide, cadmium sulfoselenide, zinc oxide, zinc sulfide and zinc selenide. Of course, said photosensitive materials may be dispersed in suitable binder materials as is well known in the art. Any suitable photosensitive material is included within the scope of this invention, such as a composite layer leaving fine photoconductive material in 30 contact with the electrically insulating layer and relatively coarse photocon-ductive particles contacting the base. Each portion of the composite layer is desirably dispersed in a suitable binder. Such a photoreceptor is more fully described in U.S. Ratent 3,801,317 to Tanada et al.. If desired, additional layers may be incorporated into the imaging member to aid in the various 35 desired properties. For example, materials can be utilized at the interface between the photosensitive layer and the electrically conductive layer which ~7~
promote charge injection Oe one polarity and suppress charge injection of another. Such materials include trigonal Se, gold, Te-alloys and carbon.
As mentioned above, the AC corotron utilized in the process of this invention is provided with a voltage bias on the shield thereof. The bias 5 voltage to the shield is adjusted so as to provide the desired zero voltage onthe surface of the electrically insulating layer. This voltage bias is typicallydetermined empirically as it is highly dependent upon numerous operational factors such as distance between the corotron and the surface being charged, the amount of voltage desired to be utilized on the corotron wire and the 10 nature of the surface being charged. As a typical example of the operation ofthe process of this invention, there is shown in Fig-ure 5 a schematic of a xerographic apparatus indicating the major operations of the xerographic process. In Figure 5, there is shown xerographic apparatus 11, comprising a photoreceptor 13 having the configuration of the photoreceptor illustrated in 15 Figure 1. In this instance, photoreceptor 13 is in the form of a typical xerographic rotary drum mounted upon a grounded support 15. In the cyclic process, corotron 17 is utilized to charge photoreceptor 13 through power supply 19, either directly coupled to the wire or to the wire via a capacitance.In addition, a variable power supply 21 is utilized to supply a bias voltage to 20 the shield of corotron 17 as indicated in Figure 5. Por testing purposes only, a probe 23 is inserted subsequent to the charging operation to monitor the amount of charge on the photoreceptor. The charged photoreceptor is then rotated past a typical slit scanning optical system 25 whereby the charged photoreceptor is exposed to a pattern of electromagnetic radiation to which 25 the photosensitive material is sensitive. The exposed photoreceptor is then rotated past the developing station whereby the electrostatic latent image in the photosensitive layer is developed. After development, the image is transferred as shown at transfer station 29 with the aid of transfer corotron 31. After transfer, the photoreceptor 13 is prepared for further use by erase 30 lamp 33 which collapses the remaining field in the photoreceptor followed by removal of residual toner material at cleaning station 35. Por testing purposes, a probe 37 is inserted in the cycle after the erase lamp 33 to determine the amount of charge remaining in the photoreceptor. Since the erase lamp collapses the field remaining across the photosensitive layer, any 35 voltage detected by probe 37 must represent charge residing on the electri-cally insulating layer. Power supply 21 is adjusted so as to provide a proper -8~ 9 ~
bias voltage to the shield of corotron 17 which results in a zero net charge on the insulating layer as indicated by probe 37. When the voltage indicated by probe 37 is positive, then the bias voltage to the shield is made more negative.Conversely, when the indicated voltage is negative, the bias voltage to the 5 shield is made more positive.
RXAMPLE I
In an apparatus as illustrated in Figure 5, there is provided a photoreceptor comprising an electrically conductive substrate having coated thereon a 3 micron thick trigonal selenium injecting layer over which is coated 10 a 60 micron thick selenium-arsenic alloy doped with chlorine. Over the photosensitive layer there is applied a 12 micron thick coating of an electri-cally insulating polyurethane layer. At a surface speed of about 51 cm./sec.
the photoreceptor is rotated past a double wire corotron 13.5 cm in length and operated at 60 Hz. The corotron shield is biased to a negative 30 volts, while 15 the corotron wire has 16,000 volts AC peak to peak applied thereto. A field condition of +80 volts was measured at probe 23 subsequent to charging. It was established that this voltage is completely across the photosensitive layer by the fact that no voltage was detected at probe 37 subsequent to the erase lamp. Any voltage detected by probe 37 would indicate a voltage across the 20 overcoating since there would be no field left in the photosensitive layer.
EXAMPLE II
The procedure of Example I is repeated with the exception that the photoreceptor is moved past a double wire corotron which is the same as that of Example I except that the length was 12 cm. A positive voltage of 350 volts 25 is measured at probe 23 while the shield voltage is held at +400 volts and the voltage applied to the corotron wires was 16,000 volts peak to peak. Again, there is no voltage measured at probe 37, indicating that the entire field of +350 volts existed across the photosensitive layer of the photoreceptor and no voltage was left residing on the surface of the electrically insulating poly-30 urethane layer.
EXAMPLE III
A single wire corotron 20 cm in length is utili~ed in the process of Example I to establish a field of 500 volts which is measured at probe 23 after exposure to the AC corotron having a shield bias of +520 volts and 16,000 volts 35 peak to peak applied to the wire. Again, no voltage was detected by probe 37 subsequent to exposure to the erase lamp.
6 g ~
_9_ Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure.
These are intended to be included within the scope of this invention. Of especial note is the fact that the procedures described herein are not limited 5 to structures with dimensions typical of Rxample I. The insulating protective layer may vary in thickness from a few microns to in excess of 20 m and the 60 m photosensitive layer may vary in thickness from approximately 5 m to 80 m so that operation with a large range of electroscopic image development materials may be accommodated.
Claims (11)
1. An electrophotographic imaging process comprising providing a photoreceptor comprising a conductive substrate, a photosensitive layer, and an electrically insulating layer over said photosensitive layer;
charging said photoreceptor by means of an AC corotron, said corotron having a shield bias voltage adjusted so as to provide substantially novoltage across said electrically insulating layer; and exposing said photoreceptor to an imagewise pattern of electro-magnetic radiation to which said photosensitive layer is sensitive whereby an electrostatic latent image is formed in said photosensitive layer.
charging said photoreceptor by means of an AC corotron, said corotron having a shield bias voltage adjusted so as to provide substantially novoltage across said electrically insulating layer; and exposing said photoreceptor to an imagewise pattern of electro-magnetic radiation to which said photosensitive layer is sensitive whereby an electrostatic latent image is formed in said photosensitive layer.
2. The process of claim 1 further including the steps of developing said latent image on said photoreceptor and transferring said image from said photoreceptor.
3. The process of claim 1 wherein said corotron is operated in the range of from about 50 Hz to about 1,000 Hz.
4. In an electrophotographic imaging process comprising pro-viding a photoreceptor comprising a conductive substrate, photosensitive layer and an electrically insulating layer over said photosensitive layer and a) charging said photoreceptor by means of an AC corotron, said corotron having an adjustable shield bias voltage;
b) exposing said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photoreceptor is sensitive, whereby an electrostatic latent image is formed in said photosensitive layer;
c) visibly developing said latent image on said photoreceptor;
d) transferring said developed image from said photoreceptor to an image receiving substrate;
e) erasing said latent image by means of flood exposing said photosensitive layer to electromagnetic radiation to which it is sensitive;
f) measuring the voltage remaining on said photoreceptor subse-quent to said flood exposure, g) utilizing said measured voltage to adjust said shield bias voltage so as to maintain zero voltage on the surface of said electrically insulating layer, and h) repeating steps (a) - (f) at least once.
b) exposing said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photoreceptor is sensitive, whereby an electrostatic latent image is formed in said photosensitive layer;
c) visibly developing said latent image on said photoreceptor;
d) transferring said developed image from said photoreceptor to an image receiving substrate;
e) erasing said latent image by means of flood exposing said photosensitive layer to electromagnetic radiation to which it is sensitive;
f) measuring the voltage remaining on said photoreceptor subse-quent to said flood exposure, g) utilizing said measured voltage to adjust said shield bias voltage so as to maintain zero voltage on the surface of said electrically insulating layer, and h) repeating steps (a) - (f) at least once.
5. The process of claim 4 wherein there is also provided a charge injection layer situated at the interface between said electrically conductive substrate and said photosensitive layer.
6. The process of claim 1 wherein there is additionally provided a charge injection layer at the interface between said electrically conductive substrate and said photosensitive layer.
7. The process of claim 6 wherein said photosensitive layer is a selenium-arsenic alloy and said injection layer comprises trigonal selenium.
8. The process of claim 1 wherein said photosensitive layer is a composite photosensitive layer comprising one layer adjoining the electrically insulating layer containing fine particles of photoconductor adjacent said electrically insulating layer and another layer adjoining the electrically conductive substrate and containing relatively larger particles of photo-conductor.
9. The process of claim 1 wherein said electrically insulating layer is bonded to said photosensitive layer by means of an adhesive.
10. An electrophotographic imaging apparatus comprising a photoreceptor comprising an electrically conductive substrate, a photo-sensitive layer and an electrically insulating layer over said photosensitive layer, an AC corotron changing device to provide an electrical field across the photosensitive layer of said photoreceptor, said corotron having means to apply a bias voltage to the shield thereof, means to expose said photoreceptor to an imagewise pattern of electromagnetic radiation to which said photo-sensitive layer is sensitive, means to develop said image on said electrically insulating layer, means to transfer said image from said electrically insulatinglayer, means to erase said latent image subsequent to said transfer and to clean untransferred imaging material from said electrically insulating layer.
11. The apparatus of claim 10 further including means to detect the voltage on said photoreceptor subsequent to the latent image erasure and means to adjust said bais voltage on said corotron shield so as to maintain zerovoltage on said photoreceptor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US27016981A | 1981-06-03 | 1981-06-03 | |
| US270,169 | 1981-06-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176694A true CA1176694A (en) | 1984-10-23 |
Family
ID=23030198
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000400057A Expired CA1176694A (en) | 1981-06-03 | 1982-03-31 | Imaging process |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0067623B1 (en) |
| JP (1) | JPS57200060A (en) |
| CA (1) | CA1176694A (en) |
| DE (1) | DE3266508D1 (en) |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5030532A (en) * | 1973-07-04 | 1975-03-26 | ||
| JPS5264936A (en) * | 1975-11-25 | 1977-05-28 | Canon Inc | Apparatus for electronic photography |
| JPS6040024B2 (en) * | 1976-09-17 | 1985-09-09 | キヤノン株式会社 | Electrostatic latent image stabilization method |
| JPS607269B2 (en) * | 1979-04-03 | 1985-02-23 | キヤノン株式会社 | electrophotographic method |
| US4254199A (en) * | 1980-03-10 | 1981-03-03 | Xerox Corporation | Electrophotographic imaging method having a double charging sequence |
-
1982
- 1982-03-31 CA CA000400057A patent/CA1176694A/en not_active Expired
- 1982-05-26 JP JP8959582A patent/JPS57200060A/en active Pending
- 1982-06-02 EP EP19820302847 patent/EP0067623B1/en not_active Expired
- 1982-06-02 DE DE8282302847T patent/DE3266508D1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0067623A3 (en) | 1983-08-31 |
| EP0067623A2 (en) | 1982-12-22 |
| JPS57200060A (en) | 1982-12-08 |
| EP0067623B1 (en) | 1985-09-25 |
| DE3266508D1 (en) | 1985-10-31 |
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