CA1105981A - Electrostatic imaging method - Google Patents
Electrostatic imaging methodInfo
- Publication number
- CA1105981A CA1105981A CA256,637A CA256637A CA1105981A CA 1105981 A CA1105981 A CA 1105981A CA 256637 A CA256637 A CA 256637A CA 1105981 A CA1105981 A CA 1105981A
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- Prior art keywords
- potential
- layer
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- plate
- polarity
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- 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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- General Physics & Mathematics (AREA)
- Photoreceptors In Electrophotography (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed is a novel high speed method for the formation of an electrostatic image in a photosensitive plate comprising a grounded conductive substrate having on its surface a layer of photoconductive material overcoated with a layer of an insulating resin. The process involves the consecutive steps of:
a) applying an initial electrostatic charge of one polarity to the surface of the plate to provide an initial potential which is solely across the insulating layer;
b) applying an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial charge to drive the initial potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential;
c) exposing the plate to imagewise activating radiation thereby forming an imagewise potential distribution across the layer of photoconductive material;
d) applying to the surface of the plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial charge to drive the imagewise potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential; and e) forming an imagewise potential distribution across the insulating layer by uniformly exposing the plate to activating radiation or allowing the inherent dark decay of the photoconductor to establish the imagewise potential distribution.
Disclosed is a novel high speed method for the formation of an electrostatic image in a photosensitive plate comprising a grounded conductive substrate having on its surface a layer of photoconductive material overcoated with a layer of an insulating resin. The process involves the consecutive steps of:
a) applying an initial electrostatic charge of one polarity to the surface of the plate to provide an initial potential which is solely across the insulating layer;
b) applying an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial charge to drive the initial potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential;
c) exposing the plate to imagewise activating radiation thereby forming an imagewise potential distribution across the layer of photoconductive material;
d) applying to the surface of the plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial charge to drive the imagewise potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential; and e) forming an imagewise potential distribution across the insulating layer by uniformly exposing the plate to activating radiation or allowing the inherent dark decay of the photoconductor to establish the imagewise potential distribution.
Description
BACXGROUND OF THE INVENTION
This invention relates to xerographic copying and more particularly to a novel method of imaging a particular type of electrostatographic photoreceptor. The art of xerography, as originally disclosed in U.S. Patent 2,297,691 by C. F. Carlson, involves the formation of an electrostatic latent image on the surface of a photosensitive plate normally - referred to as a photoreceptor. The photoreceptor comprises a conductive substrate having on its surface a layer of a photoconductive insulating material. Normally, there is a - - 25 thin barrier layer between the substrate and the photoconductive layer to prevent charge injection from the substrate into the layer upon charging of the plate's surface.
In operation, the plate is charged in the dark, such as by exposing it to a cloud of corona ions, and imaged by exposing it to a light shadow image to selectively discharge
This invention relates to xerographic copying and more particularly to a novel method of imaging a particular type of electrostatographic photoreceptor. The art of xerography, as originally disclosed in U.S. Patent 2,297,691 by C. F. Carlson, involves the formation of an electrostatic latent image on the surface of a photosensitive plate normally - referred to as a photoreceptor. The photoreceptor comprises a conductive substrate having on its surface a layer of a photoconductive insulating material. Normally, there is a - - 25 thin barrier layer between the substrate and the photoconductive layer to prevent charge injection from the substrate into the layer upon charging of the plate's surface.
In operation, the plate is charged in the dark, such as by exposing it to a cloud of corona ions, and imaged by exposing it to a light shadow image to selectively discharge
-2-~'` ' - ', ' ' ' ' ' ':
- . . . ..
98~
the photoreceptor and leave a latent image corresponding to the shadow areas. The latent electrostatic image is developed by contacting the plate's surface with an electroscopic marking material known as toner which will adhere to the latent image due to electrostatic attraction. Transfer of the toner image to a transfer member such as paper with subsequent fusing of the toner into the paper provides a permanent copy.
One type of electrostatographic photoreceptor comprises a conductive substrate having a layer of photo-conductive material on its surface which is overcoated with a layer of an insulating organic resin. Various methods of imaging this type of photoreceptor are disclosed by Mark in his article appearing in Photogra~hic Science and Engineering, Vol. 18, No. 3, May/June 1974. The processes referred to by Mark as the Katsuragawa and Canon processes can basically be divided into four steps. The first is to charge the insulating overcoating. This is normally accomplished by exposing it to d.c. corona of a polarity opposite to that of the majority charge carrier. When applying a positive charge to the surface of the insulating layer, as in the case where an n-type photoconductor is employed, a negative charge is induced in the conductive substrate, injected into the photo-! conductor and transported to and trapped at the insulating layer - photoconductive layer interface resulting in an initial potential being solely across the insulating layer. The charged plate is then exposed to a light and shadow pattern while simultaneously applying to its surface an electronic field of either alternating current (Canon) or direct current of polarity opposite that of the initial electrostatic charge ~1~5~1 (Katsuragawa). This step is carried out until the plate's surface potential is driven to zero (Canon) or to a chosen potential opposite in sign to that of the original surface potential (Katsuragawa). The plate is then uniformly exposed to activating radiation to produce a developable image with potential across the insulating overcoating and simultaneously reduce the potential across the photoconductive layer to zeros.
As is stated in the Mark article "during exposure to the optical image, the processes here described [Canon, Xatsuragawa, etc.] require the simultaneous application of a corona discharge to hold the front surface of the receptor at a constant potential." The process of the present invention is carried out in such a manner that the simultaneous application of corona discharge and exposure to the imagewise pattern of activating radiation is avoided.
Simultaneous a.c. shunting and imagewise exposure involves the disadvantage of the corotron wires being placed in the light path, thereby introducing the possibility of image distortion. In addition, this technique is not particularly adaptable to imaging in the full frame flash exposure mode because corona efficiency is such that the requisite discharge cannot readily be achieved in the 5 to 50 microsecond duration of the flash.
It would be desirable, and it is an object of the present invention, to provide a novel method for imaging an electrostatographic photoreceptor comprising a conductive substrate having on its surface a photoconductive insulating layer which is in turn overcoated with a layer of an insulating organic resin.
A further object is to provide such a method which is capable of much greater imaging speed than are conventional methods of imaging the type of photoreceptor described.
An additional object is to provide such a method S in which the increased speed is obtained by the use of exposure in the full frame flash exposure mode.
A further object is to provide such a method in which simultaneous exposure and a.c. shunting of the photo-receptor is eliminated.
O SUMMARY OF THE INVENTION
The present invention is a novel method for forming an electrostatic image in a photosensitive plate comprising a grounded conductive substrate having on its surface a layer of photoconductive material and an insulating resin layer overlaying the layer of photoconductive material. The !
process comprises the consecutive steps of:
a) applying an initial electrostatic charge of one polarity to the surface of said photosensitive plate to provide an initial potential which is solely across the insulating layer;
b) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial electro-static charge for a time sufficient to drive the initial ; potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential;
c) exposing said plate to imagewise activating radiation in the full frame flash exposure mode thereby forming an imagewise potential distribution ~5~81 across the layer of photoconductive material;
d) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial electrostatic charge for a time sufficient to drive the imagewise potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential; and e) forming an imagewise potential distribution across the insulating layer by uniformly exposing the plate to activating radiation or allowing the inherent dark decay of the photoconductor to establish the imagewise potential distribution.
DETAILED DESCRIPTION AND PREFERRED EM~30DIMENTS
Figure 1 is a cross-sectional schematic view of a photoreceptor utilized in the process of this invention indicating a three layered plate.
Figure 2 is a schematic view of an apparatus designed to utilize the process of this invention.
Figure 3(a)-(e) is a diagramatic representation of the location of the various electrical charges in and on the photoreceptor during the separate process steps of this invention.
Figure 4 is a schematic view of another apparatus utilizing the process described in the specification.
Figure 5 is a graphical representation of the photodischarge rate of a photoreceptor utilized in the process of this invention.
~ -6-3S~81 The method by which the present invention is carried out is further illustrated by the drawings. Figure 1 is a cross-section of one type of photoreceptor which is used in the method. The photoreceptor, generally designated as 10, comprises typically a conductive base 11, which is for example, a metal, a metallized plastic film or a tin oxide coated glass plate. Next, optionally, is a thin blocking layer 12 such as an insulating metal oxide or dielectric plastic film. The blocking layer is provided for the purpose of blocking injection of the minority carrier from the substrate. In cases where the mobility of the minority carrier i8 sufficiently low, a blocking layer is not needed. Above the blocking layer is a photoconducting layer 13, comprising photoconductive charge carrier generating pigment particles 14, dispersed in a matrix 15 of an electrically insulating -6a-i' 5~81 organic material. The charge generating layer 13 is depicted in Fi~ure 1 as being highly loaded with pigment particles 14 to insure particle to particle contact. Alternatively, the geometry controlled concept in which a smaller volume of pigment particles can be employed by causing them to form continuous chains through the photoconductive layer may be used. This concept is more fully disclosed by R. N. Jones in U.S. Patent 3,787,208. The photoconducting layer 13 is overcoated with a layer of an organic insulating overcoating 16 which may optionally comprise the same material as the matrix 15.
The full frame flash exposure method of imaging the photoreceptor, which method is conveniently employed in carrying out the present invention, is illustrated by Figure 2. In this drawing, the photoreceptor is depicted as being in the form of an endless, flexible belt 20 mounted on tri-rollers 22 a, b and c. The belt rotates around the tri-roller setup in a clockwise direction as indicated by the arrows.
In operation, the photoreceptor is charged to the desired initial voltage (VO) to provide an initial potential across the layer of insulating material at the charging corotron 24. Flood illumination may be used at this point to eliminate the fiald in the photoconductor thereby placing the field solely across the insulating layer. As the charged portion of the photoreceptor rotates past the pre-exposure shunt corotron 26, the initial potential is driven to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential. The belt continues its movement until the shunted _ 7_ ll~S981 portion of the full desired document size is under flash lamp 28 whereupon a light and shadow image is flash exposed onto the photoreceptor to partially create an imagewise potential distribution across the layer of photoconductive material. The photoreceptor continues to rotate around the tri-rollers and the imaged portion passes the post shunt corotron 30 where the creation of the imagewise potential is completed by driving the photoreceptor surface to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential. The exposed portion continues to move until it passes light housing 32 where it is uniformly exposed to activating radiation to reduce the voltage across the photo-conductive layer to its residual voltage, and therefore form an imagewise potential distribution across the insulating layer.
Alternatively, the inherent dark decay of certain photoconductors can be used in lieu of flood exposure.
At this point, the imagewise potential distribution (latent image) can be developed in the conventional manner which is accomplished at developer station 34. After development, the image is transferred to a receiving member at the transfer station (now shown) whereupon the imaged portion of the photoreceptor moves onto the pre-clean corotron 36 where it is subjected to an a.c. field or a field of polarity opposite - to that provided by the charging corotron 24. The photoreceptor then moves to the cleaning station 38 where any residual toner from the development process is removed by conventional cleaning means. The last step in the cycle involves erasing any residual surface potential by exposing the photoreceptor S~81 uniformly to activating radiation and the output of an a.c.
corotron or other device such as a contact discharging device at erasure station 40. After this step, the photoreceptor is ready to begin the next cycle by being charged at charging corotron 24.
The mechanism by which the imaging method of the present invention operates is illustrated by Figures 3a - 3~.
In these figures, there is depicted the photosensitive plate in which the electrostatic latent image is formed. Only the layer of photoconductive material and the insulating over-coating layer is depicted in Figure 3. Thus, the plate is depicted in less detail than in Figure 1, but the schematic representation of Figures 3a - 3~ is adequate for this discussion.
In Figure 3a, a positive electrostatic charge has been applied to the surface of the plate by a corotron device (not shown) and a negative charge is induced in the conductive substrate, injected, transported and trapped near the insulating layer's interface with the layer of photoconductive material thereby for~ing negative and positive charge pairs resulting in a surface potential across the layer of insulating material.
In Figure 3b, the plate is depicted as having been shunted by the pre-exposure corotron (shown in Figure 2 as 26) to zero surface potential.
In Figure 3c, the plate is depicted as having been exposed to activating radiation on the left side whereas the right side was not exposed. Upon exposure, which will normally be on the order of 50 microseconds in duration when full frame flash exposure is employed, an imagewise potential distribution is formed across the layer of photo-5~81 conductive material.
Figure 3d depicts the plate after it has been exposed to the post exposure a.c. corotron. It should be kept in mind that the pre-expose and post-expose corotrons can form a d.c. field of sign opposite to that of the initial electrostatic charge although a.c. is preferred since a.c.
corotron current is less sensitive to ambient conditions and therefore more uniform. Additionally, the use of a.c.
corotron permits one to draw carriers of either sign in the event that the PIDC ranges across the zero potential level.
It has been determined that simultaneous imagewise exposure and corotron shunting is not necessary because the charge carriers generated during the process steps have finite lifetimes which permit one to carry out the process in a consecutive mode of operation.
The final step of the process may be uniform exposure of the imaged plate to activating radiation. In this step, depicted in Figure 3e, the voltage across the layer of photo-conductive material is reduced to its residual voltage thereby forming an imagewise potential distribution across the layer of insulating material. As previously mentioned, the inherent dark decay of the photoconductor may be used to achieve this result.
Upon formation of the latent image by the technique outlined above, it is developed and transferred and the photoreceptor prepared for another cycle as previously described.
The conductive substrate upon which the layer of photoconductive material is deposited can be made up of any suitable conductive material. It may be rigid as in the case 598~
where a flat plate or drum configuration is employed, but must, of course, be flexible for use in the endless belt configuration depicted in Figure 2. In this regard, a continuous, flexible, nickel belt or a web or belt of an aluminized polymer such as mylar can be conveniently used.
If the substrate is not naturally injecting, a suitable interface should be provided to cause injection of the majority carrier from the substrate to the layer of photoconducting material to cause the initial potential to reside solely across the overcoating. In the case of an ambipolar photoconductor, a suitable interface should be provided to block injection of the carrier of the sign of the initial surface potential.
The layer of photoconductive material may be either n-type or p-type, organic or inorganic and is selected from those materials recognized in the art of xerography as being useful in photoreceptors. Exemplary of useful photoconductive materials are CdS, CdSe, CdSxSel x' ZnO, TiO2, and selenium and selenium alloys such as Se/Te and Se/As. Typically, these materials are dispersed in an insulating resin as binder such as the configuration disclosed in U.S. Patent
- . . . ..
98~
the photoreceptor and leave a latent image corresponding to the shadow areas. The latent electrostatic image is developed by contacting the plate's surface with an electroscopic marking material known as toner which will adhere to the latent image due to electrostatic attraction. Transfer of the toner image to a transfer member such as paper with subsequent fusing of the toner into the paper provides a permanent copy.
One type of electrostatographic photoreceptor comprises a conductive substrate having a layer of photo-conductive material on its surface which is overcoated with a layer of an insulating organic resin. Various methods of imaging this type of photoreceptor are disclosed by Mark in his article appearing in Photogra~hic Science and Engineering, Vol. 18, No. 3, May/June 1974. The processes referred to by Mark as the Katsuragawa and Canon processes can basically be divided into four steps. The first is to charge the insulating overcoating. This is normally accomplished by exposing it to d.c. corona of a polarity opposite to that of the majority charge carrier. When applying a positive charge to the surface of the insulating layer, as in the case where an n-type photoconductor is employed, a negative charge is induced in the conductive substrate, injected into the photo-! conductor and transported to and trapped at the insulating layer - photoconductive layer interface resulting in an initial potential being solely across the insulating layer. The charged plate is then exposed to a light and shadow pattern while simultaneously applying to its surface an electronic field of either alternating current (Canon) or direct current of polarity opposite that of the initial electrostatic charge ~1~5~1 (Katsuragawa). This step is carried out until the plate's surface potential is driven to zero (Canon) or to a chosen potential opposite in sign to that of the original surface potential (Katsuragawa). The plate is then uniformly exposed to activating radiation to produce a developable image with potential across the insulating overcoating and simultaneously reduce the potential across the photoconductive layer to zeros.
As is stated in the Mark article "during exposure to the optical image, the processes here described [Canon, Xatsuragawa, etc.] require the simultaneous application of a corona discharge to hold the front surface of the receptor at a constant potential." The process of the present invention is carried out in such a manner that the simultaneous application of corona discharge and exposure to the imagewise pattern of activating radiation is avoided.
Simultaneous a.c. shunting and imagewise exposure involves the disadvantage of the corotron wires being placed in the light path, thereby introducing the possibility of image distortion. In addition, this technique is not particularly adaptable to imaging in the full frame flash exposure mode because corona efficiency is such that the requisite discharge cannot readily be achieved in the 5 to 50 microsecond duration of the flash.
It would be desirable, and it is an object of the present invention, to provide a novel method for imaging an electrostatographic photoreceptor comprising a conductive substrate having on its surface a photoconductive insulating layer which is in turn overcoated with a layer of an insulating organic resin.
A further object is to provide such a method which is capable of much greater imaging speed than are conventional methods of imaging the type of photoreceptor described.
An additional object is to provide such a method S in which the increased speed is obtained by the use of exposure in the full frame flash exposure mode.
A further object is to provide such a method in which simultaneous exposure and a.c. shunting of the photo-receptor is eliminated.
O SUMMARY OF THE INVENTION
The present invention is a novel method for forming an electrostatic image in a photosensitive plate comprising a grounded conductive substrate having on its surface a layer of photoconductive material and an insulating resin layer overlaying the layer of photoconductive material. The !
process comprises the consecutive steps of:
a) applying an initial electrostatic charge of one polarity to the surface of said photosensitive plate to provide an initial potential which is solely across the insulating layer;
b) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial electro-static charge for a time sufficient to drive the initial ; potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential;
c) exposing said plate to imagewise activating radiation in the full frame flash exposure mode thereby forming an imagewise potential distribution ~5~81 across the layer of photoconductive material;
d) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial electrostatic charge for a time sufficient to drive the imagewise potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential; and e) forming an imagewise potential distribution across the insulating layer by uniformly exposing the plate to activating radiation or allowing the inherent dark decay of the photoconductor to establish the imagewise potential distribution.
DETAILED DESCRIPTION AND PREFERRED EM~30DIMENTS
Figure 1 is a cross-sectional schematic view of a photoreceptor utilized in the process of this invention indicating a three layered plate.
Figure 2 is a schematic view of an apparatus designed to utilize the process of this invention.
Figure 3(a)-(e) is a diagramatic representation of the location of the various electrical charges in and on the photoreceptor during the separate process steps of this invention.
Figure 4 is a schematic view of another apparatus utilizing the process described in the specification.
Figure 5 is a graphical representation of the photodischarge rate of a photoreceptor utilized in the process of this invention.
~ -6-3S~81 The method by which the present invention is carried out is further illustrated by the drawings. Figure 1 is a cross-section of one type of photoreceptor which is used in the method. The photoreceptor, generally designated as 10, comprises typically a conductive base 11, which is for example, a metal, a metallized plastic film or a tin oxide coated glass plate. Next, optionally, is a thin blocking layer 12 such as an insulating metal oxide or dielectric plastic film. The blocking layer is provided for the purpose of blocking injection of the minority carrier from the substrate. In cases where the mobility of the minority carrier i8 sufficiently low, a blocking layer is not needed. Above the blocking layer is a photoconducting layer 13, comprising photoconductive charge carrier generating pigment particles 14, dispersed in a matrix 15 of an electrically insulating -6a-i' 5~81 organic material. The charge generating layer 13 is depicted in Fi~ure 1 as being highly loaded with pigment particles 14 to insure particle to particle contact. Alternatively, the geometry controlled concept in which a smaller volume of pigment particles can be employed by causing them to form continuous chains through the photoconductive layer may be used. This concept is more fully disclosed by R. N. Jones in U.S. Patent 3,787,208. The photoconducting layer 13 is overcoated with a layer of an organic insulating overcoating 16 which may optionally comprise the same material as the matrix 15.
The full frame flash exposure method of imaging the photoreceptor, which method is conveniently employed in carrying out the present invention, is illustrated by Figure 2. In this drawing, the photoreceptor is depicted as being in the form of an endless, flexible belt 20 mounted on tri-rollers 22 a, b and c. The belt rotates around the tri-roller setup in a clockwise direction as indicated by the arrows.
In operation, the photoreceptor is charged to the desired initial voltage (VO) to provide an initial potential across the layer of insulating material at the charging corotron 24. Flood illumination may be used at this point to eliminate the fiald in the photoconductor thereby placing the field solely across the insulating layer. As the charged portion of the photoreceptor rotates past the pre-exposure shunt corotron 26, the initial potential is driven to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential. The belt continues its movement until the shunted _ 7_ ll~S981 portion of the full desired document size is under flash lamp 28 whereupon a light and shadow image is flash exposed onto the photoreceptor to partially create an imagewise potential distribution across the layer of photoconductive material. The photoreceptor continues to rotate around the tri-rollers and the imaged portion passes the post shunt corotron 30 where the creation of the imagewise potential is completed by driving the photoreceptor surface to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential. The exposed portion continues to move until it passes light housing 32 where it is uniformly exposed to activating radiation to reduce the voltage across the photo-conductive layer to its residual voltage, and therefore form an imagewise potential distribution across the insulating layer.
Alternatively, the inherent dark decay of certain photoconductors can be used in lieu of flood exposure.
At this point, the imagewise potential distribution (latent image) can be developed in the conventional manner which is accomplished at developer station 34. After development, the image is transferred to a receiving member at the transfer station (now shown) whereupon the imaged portion of the photoreceptor moves onto the pre-clean corotron 36 where it is subjected to an a.c. field or a field of polarity opposite - to that provided by the charging corotron 24. The photoreceptor then moves to the cleaning station 38 where any residual toner from the development process is removed by conventional cleaning means. The last step in the cycle involves erasing any residual surface potential by exposing the photoreceptor S~81 uniformly to activating radiation and the output of an a.c.
corotron or other device such as a contact discharging device at erasure station 40. After this step, the photoreceptor is ready to begin the next cycle by being charged at charging corotron 24.
The mechanism by which the imaging method of the present invention operates is illustrated by Figures 3a - 3~.
In these figures, there is depicted the photosensitive plate in which the electrostatic latent image is formed. Only the layer of photoconductive material and the insulating over-coating layer is depicted in Figure 3. Thus, the plate is depicted in less detail than in Figure 1, but the schematic representation of Figures 3a - 3~ is adequate for this discussion.
In Figure 3a, a positive electrostatic charge has been applied to the surface of the plate by a corotron device (not shown) and a negative charge is induced in the conductive substrate, injected, transported and trapped near the insulating layer's interface with the layer of photoconductive material thereby for~ing negative and positive charge pairs resulting in a surface potential across the layer of insulating material.
In Figure 3b, the plate is depicted as having been shunted by the pre-exposure corotron (shown in Figure 2 as 26) to zero surface potential.
In Figure 3c, the plate is depicted as having been exposed to activating radiation on the left side whereas the right side was not exposed. Upon exposure, which will normally be on the order of 50 microseconds in duration when full frame flash exposure is employed, an imagewise potential distribution is formed across the layer of photo-5~81 conductive material.
Figure 3d depicts the plate after it has been exposed to the post exposure a.c. corotron. It should be kept in mind that the pre-expose and post-expose corotrons can form a d.c. field of sign opposite to that of the initial electrostatic charge although a.c. is preferred since a.c.
corotron current is less sensitive to ambient conditions and therefore more uniform. Additionally, the use of a.c.
corotron permits one to draw carriers of either sign in the event that the PIDC ranges across the zero potential level.
It has been determined that simultaneous imagewise exposure and corotron shunting is not necessary because the charge carriers generated during the process steps have finite lifetimes which permit one to carry out the process in a consecutive mode of operation.
The final step of the process may be uniform exposure of the imaged plate to activating radiation. In this step, depicted in Figure 3e, the voltage across the layer of photo-conductive material is reduced to its residual voltage thereby forming an imagewise potential distribution across the layer of insulating material. As previously mentioned, the inherent dark decay of the photoconductor may be used to achieve this result.
Upon formation of the latent image by the technique outlined above, it is developed and transferred and the photoreceptor prepared for another cycle as previously described.
The conductive substrate upon which the layer of photoconductive material is deposited can be made up of any suitable conductive material. It may be rigid as in the case 598~
where a flat plate or drum configuration is employed, but must, of course, be flexible for use in the endless belt configuration depicted in Figure 2. In this regard, a continuous, flexible, nickel belt or a web or belt of an aluminized polymer such as mylar can be conveniently used.
If the substrate is not naturally injecting, a suitable interface should be provided to cause injection of the majority carrier from the substrate to the layer of photoconducting material to cause the initial potential to reside solely across the overcoating. In the case of an ambipolar photoconductor, a suitable interface should be provided to block injection of the carrier of the sign of the initial surface potential.
The layer of photoconductive material may be either n-type or p-type, organic or inorganic and is selected from those materials recognized in the art of xerography as being useful in photoreceptors. Exemplary of useful photoconductive materials are CdS, CdSe, CdSxSel x' ZnO, TiO2, and selenium and selenium alloys such as Se/Te and Se/As. Typically, these materials are dispersed in an insulating resin as binder such as the configuration disclosed in U.S. Patent
3,121,0Q6 or the previously mentioned geometry controlled configuration disclosed in U.S. Patent 3,787,208.
The insulating resin which constitutes the top layer of the photoreceptor can be any material which has high resistance against wear, high resistivity and the capability of binding electrostatic charge, and translucency or transparency to activating radiation. Examples of resins which may be used are polystyrene, butadiene polymers and copolymers, acrylic and methacrylic polymers, vinyl resins, alkyd resins, polycarbonate resins, polyethylene resins and polyester resins.
The method by which the present invention is carried out is further illustrated by the following examples.
EXAMPLE I
A photosensitive imaging device of the type contemplated for use in the instant invention has the following construction:
To a 9.6 inch diameter aluminum drum is taped a
The insulating resin which constitutes the top layer of the photoreceptor can be any material which has high resistance against wear, high resistivity and the capability of binding electrostatic charge, and translucency or transparency to activating radiation. Examples of resins which may be used are polystyrene, butadiene polymers and copolymers, acrylic and methacrylic polymers, vinyl resins, alkyd resins, polycarbonate resins, polyethylene resins and polyester resins.
The method by which the present invention is carried out is further illustrated by the following examples.
EXAMPLE I
A photosensitive imaging device of the type contemplated for use in the instant invention has the following construction:
To a 9.6 inch diameter aluminum drum is taped a
4 x 6 inch piece of a photoreceptor made up of an aluminum substrate having a thin blocking layer on its surface to prevent charge injection in the dark which is uniformly coated with a 35~u thick layer of 40 volume percent CdS
doped with 103 ppm chlorine dispersed in a polyester copolymer.
This photoconductive layer is, in turn, overcoated with a 25,u thick layer of Myla ~ polyester insulating resin. These layers are bonded together with a 1 to 2 ~ thick layer of adhesive.
The device is put through the process steps of the present invention as illustrated by Figure 4. In Figure 4, drum 42 is rotated at a rate of 20 RPM corresponding to a linear velocity of 10 inches per second. The drum's surface is charged to an initial potential of 2,500 V at charging corotron 44 which is a positive d.c. corotron. The ch~arged portion of the drum then rotates past the pre-shunt corotron 46 which is a negative d.c. corotron adjusted to provide zero surface potential. The drum next rotates past exposure slit 48 where it is exposed to a Xenon arc source of activating radiation having a relatively flat spectral content from 4,000 A to 7,000 A obtained using the appropriate cutoff filters. The exposed portion of the drum next rotates
doped with 103 ppm chlorine dispersed in a polyester copolymer.
This photoconductive layer is, in turn, overcoated with a 25,u thick layer of Myla ~ polyester insulating resin. These layers are bonded together with a 1 to 2 ~ thick layer of adhesive.
The device is put through the process steps of the present invention as illustrated by Figure 4. In Figure 4, drum 42 is rotated at a rate of 20 RPM corresponding to a linear velocity of 10 inches per second. The drum's surface is charged to an initial potential of 2,500 V at charging corotron 44 which is a positive d.c. corotron. The ch~arged portion of the drum then rotates past the pre-shunt corotron 46 which is a negative d.c. corotron adjusted to provide zero surface potential. The drum next rotates past exposure slit 48 where it is exposed to a Xenon arc source of activating radiation having a relatively flat spectral content from 4,000 A to 7,000 A obtained using the appropriate cutoff filters. The exposed portion of the drum next rotates
5~81 past post shunt corotron 50 which is an a.c. corotron employing a frequency of approximately 1 KHz. A positive d.c. bias of approximately 1,000 volts is provided to again shunt the surface potential to zero. As the exposed portion of the drum rotates past fluorescent lamp 52, it is flood illuminated, and after flood illumination, the post-exposure potential is measured by use of probe 54. The data generated by use of probe 54 is used to plot a photoinduced discharge curve which is reproduced as Figure 5 in which surface potential in volts is plotted against exposure in ergs/cm2. From this curve, it can be determined that approximately 9 ergs/cm2 is required for 600 volts of discharge. In the last step of the cycle, the drum rotates past the charge/flood erase station 56 where a 60 Hz a.c. corotron is used to remove any residual surface potential. No illumination is required to erase the drum in this experiment.
EXAMPLE II
The photosensitive imaging device described in Example I is charged and exposed as before except that the exposure is carried out in imagewise configuration, i.e.
the charged device is exposed to a light and shadow image.
A negative contrast potential is formed as the exposed portion of the drum rotates past post shunt corotron 50 which is intensified and reversed to form a positive contrast potential by flood illumination. The drum bearing this latent image is then developed in the ordinary xerographic mode by the application of toner. Transfer of the toner to a receiving member with subsequent removal of residual toner and erasure results in the drum being ready to begin another cycle.
598~
EXAMPLE III
A photosensitive imaging device of the type con-templated for use in the instant invention has the following construction:
A carbon black particle coating is applied to an aluminum substrate and a 39~u thick photoconductive layer comprised of 35 volume percent CdS 35Se 65 pigment which has been solvent coated in a polyester copolymer to form a photoconductive binder layer overlays the carbon black 0 layer. A 25 ~ thick layer of Mylar polyester overcoats the photoconductive layer. The majority charge carriers for this photoconductive material are electrons; the carbon black interface is selected because it injects the majority carrier telectrons).
The device, which is 4 x 6 inches, is taped to a 30 inch circumference aluminum drum and cycled as described in Figure 4.
The process steps are as described in Example I
except that the surface speed of the drum is 30 inches/sec.
0 Step 1 provides an initial charging potential of +2700 volts.
After flood, the dark potential obtained is +900 volts corresponding to a voltage return of 33%. A discharge curve is prepared from which it is determined that approximately 3.2 ergs/cm2 of exposure are required for 600 volts discharge.
Acceptably stable cycling characteristics are found to exist over 103 cycles. .
EXAMPLE IV
A photosensitive imaging device of the type contemplated for use in the instant invention is prepared 0 as in Example III except that the photoconductive layer is a 35~u thick layer of 20 volume percent trigonal selenium solvent coated onto the Myla ~ layer in a polyester copolymer. The devices of Examples III and IV are both prepared by coating the photoconductive layer directly onto the overcoating layer thereby eliminating the need for an adhesive layer. The trigonal selenium photoconducting layer photogenerates holes as the majority carrier.
The sample is measured as in Example III except that Step 1 provides an initial charging potential of -1900 volts. After flood, the dark potential obtained is -880 volts corresponding to a voltage return of 46%. From the photoinduced discharge curve obtained using this sample, it is determined that approximately 3.3 ergs/cm2 of exposure energy are required for 600 volts of discharge.
EXAMPLE V
The-photosensitive imaging device described in Example I is cut into 14 inch strips and these strips are taped to a 65 inch long endless, nickel belt. The belt is mounted on a tri-roller set-up similar to that depicted in Figure 2. Referring to Figure 2, the photosensitive strips are charged positively to approximately 2800 volts at charging corotron 24. The surface of the corotron device is driven to -350 volts at the pre-shunting station 26 which is a negative d.c. corotron (alternatively a negatively biased a.c. corotron). The purpose of this pre-exposure shunting is to place a field in the photoconductor prior to exposure, thereby increasing the recombination lifetime of light generated charges created during exposure. This pre-exposure shunting is necessary to obtain uniform lead to trail edge discharge.
~l~S98~
.
Next, the photosensitive device is exposed in the full frame flash exposure mode at exposure station 28. The exposure source consists of 4 Xenon flash lamps providing up to 50 ergs/cm2 in exposure energy. The device is then shunted to 0 volts by post-exposure corotron 30 which is an a.c. corotron adjusted to deposit no net d.c. current to ground. The post-exposure shunting not only completes the discharge of the background areas but also recharges the image areas, which have been driven to -350 volts, by pre-shunting to 0 volts.
The photoreceptor is then exposed to uniform activating radiation provided by a fluorescent lamp thereby eliminating the field in the photoconductor.
Dark development potentials and discharge levels are measured and the device is erased to 0 volts with a.c.
corona (and optionally uniform exposure to light) in preparation for recharging. Measurement of dark development potentials reveals a uniform lead to trail edge discharge. Measurement of discharge levels indicates contrast potentials in excess of 600 volts,
EXAMPLE II
The photosensitive imaging device described in Example I is charged and exposed as before except that the exposure is carried out in imagewise configuration, i.e.
the charged device is exposed to a light and shadow image.
A negative contrast potential is formed as the exposed portion of the drum rotates past post shunt corotron 50 which is intensified and reversed to form a positive contrast potential by flood illumination. The drum bearing this latent image is then developed in the ordinary xerographic mode by the application of toner. Transfer of the toner to a receiving member with subsequent removal of residual toner and erasure results in the drum being ready to begin another cycle.
598~
EXAMPLE III
A photosensitive imaging device of the type con-templated for use in the instant invention has the following construction:
A carbon black particle coating is applied to an aluminum substrate and a 39~u thick photoconductive layer comprised of 35 volume percent CdS 35Se 65 pigment which has been solvent coated in a polyester copolymer to form a photoconductive binder layer overlays the carbon black 0 layer. A 25 ~ thick layer of Mylar polyester overcoats the photoconductive layer. The majority charge carriers for this photoconductive material are electrons; the carbon black interface is selected because it injects the majority carrier telectrons).
The device, which is 4 x 6 inches, is taped to a 30 inch circumference aluminum drum and cycled as described in Figure 4.
The process steps are as described in Example I
except that the surface speed of the drum is 30 inches/sec.
0 Step 1 provides an initial charging potential of +2700 volts.
After flood, the dark potential obtained is +900 volts corresponding to a voltage return of 33%. A discharge curve is prepared from which it is determined that approximately 3.2 ergs/cm2 of exposure are required for 600 volts discharge.
Acceptably stable cycling characteristics are found to exist over 103 cycles. .
EXAMPLE IV
A photosensitive imaging device of the type contemplated for use in the instant invention is prepared 0 as in Example III except that the photoconductive layer is a 35~u thick layer of 20 volume percent trigonal selenium solvent coated onto the Myla ~ layer in a polyester copolymer. The devices of Examples III and IV are both prepared by coating the photoconductive layer directly onto the overcoating layer thereby eliminating the need for an adhesive layer. The trigonal selenium photoconducting layer photogenerates holes as the majority carrier.
The sample is measured as in Example III except that Step 1 provides an initial charging potential of -1900 volts. After flood, the dark potential obtained is -880 volts corresponding to a voltage return of 46%. From the photoinduced discharge curve obtained using this sample, it is determined that approximately 3.3 ergs/cm2 of exposure energy are required for 600 volts of discharge.
EXAMPLE V
The-photosensitive imaging device described in Example I is cut into 14 inch strips and these strips are taped to a 65 inch long endless, nickel belt. The belt is mounted on a tri-roller set-up similar to that depicted in Figure 2. Referring to Figure 2, the photosensitive strips are charged positively to approximately 2800 volts at charging corotron 24. The surface of the corotron device is driven to -350 volts at the pre-shunting station 26 which is a negative d.c. corotron (alternatively a negatively biased a.c. corotron). The purpose of this pre-exposure shunting is to place a field in the photoconductor prior to exposure, thereby increasing the recombination lifetime of light generated charges created during exposure. This pre-exposure shunting is necessary to obtain uniform lead to trail edge discharge.
~l~S98~
.
Next, the photosensitive device is exposed in the full frame flash exposure mode at exposure station 28. The exposure source consists of 4 Xenon flash lamps providing up to 50 ergs/cm2 in exposure energy. The device is then shunted to 0 volts by post-exposure corotron 30 which is an a.c. corotron adjusted to deposit no net d.c. current to ground. The post-exposure shunting not only completes the discharge of the background areas but also recharges the image areas, which have been driven to -350 volts, by pre-shunting to 0 volts.
The photoreceptor is then exposed to uniform activating radiation provided by a fluorescent lamp thereby eliminating the field in the photoconductor.
Dark development potentials and discharge levels are measured and the device is erased to 0 volts with a.c.
corona (and optionally uniform exposure to light) in preparation for recharging. Measurement of dark development potentials reveals a uniform lead to trail edge discharge. Measurement of discharge levels indicates contrast potentials in excess of 600 volts,
Claims (10)
1. A method for forming an electrostatic image in a photosensitive plate comprising a grounded conductive substrate having on its surface a layer of photoconductive material and an insulating organic resin layer overlaying the layer of photocon-ductive material, said method comprising the consecutive steps of:
a) applying an initial electrostatic charge of one polarity to the surface of said photosensitive plate to provide an initial potential which is solely across the insulating layer;
b) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial electrostatic charge for a time sufficient to drive the initial potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential;
c) exposing said plate to imagewise activating radiation in the full frame flash exposure mode thereby forming an imagewise potential distribution across the layer of photoconductive material;
d) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial charge to drive the imagewise potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential; and e) forming an imagewise potential distribution across the insulating layer by uniformly exposing the plate to activating radiation or allowing the inherent dark decay of the photoconductor to establish the imagewise potential distribution.
a) applying an initial electrostatic charge of one polarity to the surface of said photosensitive plate to provide an initial potential which is solely across the insulating layer;
b) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial electrostatic charge for a time sufficient to drive the initial potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential;
c) exposing said plate to imagewise activating radiation in the full frame flash exposure mode thereby forming an imagewise potential distribution across the layer of photoconductive material;
d) applying to the surface of said plate an electronic field of either alternating current or direct current of polarity opposite that of the polarity of the initial charge to drive the imagewise potential to a potential included in the range extending from a potential less than the initial potential through zero to a chosen potential opposite in sign to the polarity of the initial potential; and e) forming an imagewise potential distribution across the insulating layer by uniformly exposing the plate to activating radiation or allowing the inherent dark decay of the photoconductor to establish the imagewise potential distribution.
2. The method of Claim 1 wherein the photosensitive plate has a blocking layer between the conductive substrate and the layer of photoconductive material to prevent injection of the minority carrier from the substrate.
3. The method of Claim 1 wherein the layer of photoconducting material comprises photoconductive charge carrier generating pigment particles dispersed in a matrix of an electrically insulating organic resin.
4. The method of Claim 1 wherein the plate is exposed to imagewise radiation in the full frame flash exposure mode.
5. The method of Claim 1 wherein the photosensitive plate is in the form of an endless, flexible belt.
6. The method of Claim 1 wherein the photosensitive plate is exposed to uniform activating radiation after formation of the initial potential across the insulating layer.
7. The method of Claim 1 wherein the electronic field of steps b and d is generated by an a.c. corotron.
8. The method of Claim 1 wherein the layer of photoconductive material comprises CdS, CdSe, CdSxSel-x' ZnO, TiO2, and selenium or a selenium alloy selected from the group of Se/Te or Se/As.
9. The method of Claim 1 wherein the insulating organic resin is polystyrene, a butadiene polymer, an acrylic or methacrylic polymer, a vinyl resin, an alkyd resin, a polycarbonate resin, a polyethylene resin or a polyester resin.
10. The method of Claim 1 wherein the photoconductive material photogenerates holes as the majority carrier and the plate is charged negatively in step a.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60669475A | 1975-08-21 | 1975-08-21 | |
| US606,694 | 1975-08-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105981A true CA1105981A (en) | 1981-07-28 |
Family
ID=24429062
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA256,637A Expired CA1105981A (en) | 1975-08-21 | 1976-07-09 | Electrostatic imaging method |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1105981A (en) |
| GB (1) | GB1547218A (en) |
-
1976
- 1976-07-09 CA CA256,637A patent/CA1105981A/en not_active Expired
- 1976-08-18 GB GB3439376A patent/GB1547218A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1547218A (en) | 1979-06-06 |
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