US3730709A - Method for electrophotography - Google Patents

Method for electrophotography Download PDF

Info

Publication number
US3730709A
US3730709A US00108733A US3730709DA US3730709A US 3730709 A US3730709 A US 3730709A US 00108733 A US00108733 A US 00108733A US 3730709D A US3730709D A US 3730709DA US 3730709 A US3730709 A US 3730709A
Authority
US
United States
Prior art keywords
charge
layer
electric field
highly insulative
photoconductive layer
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 - Lifetime
Application number
US00108733A
Other languages
English (en)
Inventor
K Kinoshita
M Watanabe
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Katsuragawa Electric Co Ltd
Original Assignee
Katsuragawa Electric Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Katsuragawa Electric Co Ltd filed Critical Katsuragawa Electric Co Ltd
Application granted granted Critical
Publication of US3730709A publication Critical patent/US3730709A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

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
    • G03G15/056—Apparatus for electrographic processes using a charge pattern using internal polarisation

Definitions

  • This invention relates to a method and apparatus for electrophotography.
  • an improved method of electrophotography has recently been developed wherein an electrostatic latent image is formed by using a photosensitive element including a photoconductive layer having a property of trapping electric charges or manifesting persisting internal polarization and a highly insulative layer integrally bonded to one surface of the photoconductive layer, and wherein, in the first step, an electric field is applied by means of a corona discharge unit across the photosensitive element for depositing a charge of the same polarity as the minority carriers of the photoconductive layer on the surface of the highly insulative layer, and, in the second step, another charge of the same polarity as the majority carriers of the photoconductive element is then applied on the surface of the highly insulative layer concurrently with the projection of a light image whereby an electrostatic latent image corresponding to the light image is formed on the surface of the highly insulative layer.
  • the latent image is characterized by not being erased by later irradiation of light, can be developed by any conventional developing method into a visible powder image and the powder image can be readily transfer printed on a recording medium, ordinarily a paper. After cleaning the surface the photosensitive element can be used repeatedly.
  • the highly insulative layer acts also as a protective layer for the underlying photoconductive layer, the quality of the reproduced visible images gradually deteriorates due to the spoilage of the highly insulative layer caused by the toner and scratches caused by the magnetic carrier for the toner.
  • an electric insulative recording medium is brought close to the latent image formed on a photoconductive element with a small air gap between the latent image and the recording medium and a charge is deposited on the rear surface of the recording medium by means of a corona discharge unit so as to electrostatically transfer the latent image from the photoconductive element to the recording medium.
  • a recording paper is superimposed upon the powder image formed on a photosensitive element and a roller supplied with a suitable voltage is rolled along the rear surface of the recording paper.
  • a powder image formed by the method of the patents described above is transfer printed on a recording paper by this method, if the roller is operated in the absence of the recording paper, the roller would be brought into direct contact with the photosensitive element thus causing the breakdown of the highly insulative layer on the photosensitive element by the voltage impressed upon the roller.
  • the latent image formed by the improved method of electrophotography utilizing two electric fields of the opposite polarities is not erased by later light irradiation the light image can be developed in bright light or under room light. For this reason, it is not necessary to perform the transfer step and the developing step in the dark or in a light tight compartment as in the conventional electrophotographic machines, so that when the latent image or the developed powder image is transfer printed onto a recording paper by utilizing a roller applied with a substantially high potential as above described, the roller is exposed and there is a danger of electric shock for the operator. Accordingly, the following method of transferring the latent image is suitable.
  • an electric insulative recording paper is firmly pressed by means of a roller applied with a high potential against a latent image formed on a photoconductive element including a backing electrode while the potential difference between the recording paper and the photoconductive element is reduced to zero by short circuiting the transfer roller and the backing electrode of the element.
  • Another object of this invention is to provide an improved method and apparatus for electrophotography which can reproduce copies of high contrast or intermediate tone at high speed.
  • a latent image is formed by the steps of applying a first electric field across a photosensitive element including a photoconductive layer manifesting persistent internal polarization and a highly insulative layer integrally bonded to one side of the photoconductive layer for depositing a charge of one polarity on the surface of the highly insulative layer, and applying a second field across the photosensitive element for depositing a charge of the opposite polarity on the surface of the highly insulative layer concurrently with the projection of a light image upon the photoconductive layer, a third step is added wherein a third electric field is applied across the photosensitive element for depositing a charge of the same polarity as the charge deposited by the second electric field on the surface of the highly insulative layer.
  • the charge deposited by the third field is effective to increase the contrast of the latent image or the potential difference between portions of the latent image corresponding to bright portions of the light image and portions of the latent image corresponding to dark portions of the light image.
  • the latent image formed in this manner can be developed on the photosensitive element and then transfer printed onto a recording paper, or transfer printed onto an electric insulative receptor material and then developed, all in the conventional manner, except that the latent image can be processed in bright light as above described.
  • the purpose of the second electric field which is impressed concurrently with the light image is to selectively release the charge that has been trapped in the charge trapping levels in the photoconductive layer during the first step.
  • the releasing speed of the trapped charge in the second step is relatively low so that extremely high speed operation is not possible.
  • it is advantageous to project uniform light upon the latent image to accelerate the release of the trapped charge this technique being known in the art as the post exposure.
  • the first, second and third electric fields are applied by means f cor a disch ge units, p ra ly dis osed about a rotary cylinder carrying a photosensitive element.
  • the light image is projected through the second corona discharge unit.
  • the polarities of the charges deposited by the second and third corona discharge units should be the same but the intensity of the third electric field may be the same or higher than that of the second electric field.
  • FIG. 1 is a graph to show the variation of the surface potential at the time of forming a latent image according to a prior art method
  • FIG. 2 is a similar graph showing the variation of the surface potential at the time of forming a latent image in accordance with the method of this invention
  • FIG. 3 shows a sectional view of corona discharge units employed in the method of electrophotography shown in FIG. 2;
  • FIG. 4 shows a graph showing the variation of the surface potential at the time of forming a latent image according to a modified embodiment of this invention
  • FIG. 5 shows a sectional view of corona discharge units suitable for use in the modified embodiment shown in FIG. 4;
  • FIG. 6 shows a perspective view of electrophotographic apparatus embodying the invention.
  • FIG. 7 shows an end view of the rotary drum and the photosensitive element utilized in the apparatus shown in FIG. 6.
  • FIG. 1 is a graph to show the variation of the surface potential of the highly insulative layer wherein an electrostatic latent image is formed thereon by the step of applying a first electric field across a photosensitive element including a photoconductive layer having a plurality of charge trapping levels, that is manifesting persistent internal polarization, and a highly insulative layer integrally bonded to one surface of the photoconductive layer for depositing a charge of one polarity on the surface of the highly insulative layer, and applying a second electric field across the photosensitive element to deposit a charge of the opposite polarity on the surface of the highly insulative layer concurrently with the projection of a light image upon the photoconductive layer.
  • Curves depicted in FIGS. 1, 2 and 3 represent the case where the photoconductive layer comprises SeTe. However, when the photoconductive layer is made of photoconductors of different conductivity type the polarity of the surface potential is reversed, but the configurations of the curves are generally identical to those illustrated in the drawing.
  • solid line curves A and B represent the potential variations with time at bright portions and dark portions of the light image where the highly insulative layer is relatively thin (or having a large capacitance) whereas dotted line curves a and b represent corresponding potential variations where the highly insulative layer is relatively thick (or having a small capacitance).
  • a charge of the same polarity as the minority carriers in the photoconductive layer is deposited on the surface of the highly insulative layer by means of a corona discharge unit, not shown.
  • the surface potential of the highly insulative layer builds 'up gradually as shown by curve A.
  • the polarity of the charge deposited by the corona discharge unit is reversed while at the same time the light image is projected upon the photoconductive layer, preferably through the highly insulative layer.
  • the intensity of the charge deposited in the second step is selected to such a value that the deposited charge can be retained at portions corresponding to the bright portions of the light image by the charge that has been trapped in the first step.
  • the surface potential rapidly builds down because the charge that has been trapped in the first step is preserved and the photoconductive layer manifests an extremely high resistance at these dark portions. Accordingly, the polarity of the surface charge is rapidly reversed by a small quantity of charge deposited in the second step.
  • the surface potential varies along a characteristic curve determined by the characteristics of the photoconductive layer and the corona discharge until a definite value is reached in a relatively short time.
  • the surface potentials at bright and dark portions build down at different rates.
  • the surface potentials at the bright and dark portions vary according to curves A and B included in interval t .
  • the charge trapped in the photoconductive layer in the first step increases to cancel the charge deposited on the surface of the highly insulative layer in the second step so that the eifect of the charge deposited in the second step is decreased with the time elapsed as shown in FIG. 1.
  • the surface charge deposited in the second charging step is preserved substantially unchanged.
  • the build down speed of the surface potential at the bright portions can be increased during the second step and the potential of the latent image formed will be substanially equal to that of the majority carriers in the photoconductive layer. Accordingly, if it were possible to share a substantial potential across the photoconductive layer during interval t for trapping a sufficiently large charge in the photoconductive layer, it will be possible to increase the contrast as shown by dotted line curves a and b shown in FIG. 1.
  • the capacitance of the highly insulative layer is decreased, it is impossible to carry out the method with a high speed machine utilizing a corona discharge unit of the conventional design.
  • it is possible to improve the contrast of the latent image or the image reproduced therefrom it is not possible to reproduce at a high fidelity an original of the intermediate tone. In other words, it is not possible to reproduce well defined patterns.
  • FIG. 2 shows a graph representing the variation in the surface potential according to the novel method of electrophotography of improved sensitivity.
  • a third step t' is added in which the charge of the same polarity as the charge deposited in the second step is deposited.
  • the variations of the surface potentials at portions of the highly insulative layer corresponding to the bright and dark portions of the light image are shown by curves A and -B, respectively.
  • FIG. 3 diagrammatically shows a construction of a corona discharge unit suitable for this purpose.
  • the corona discharge unit comprises discharge electrodes in the form of fine metal wires 20 and a grounded inverted cup shaped counter electrode 21.
  • Section S1 of the corona discharge unit is utilized to perform the second step whereas section S2 is utilized to perform the third step.
  • a window 22 is formed through the top wall of the counter electrode 21 for projecting the light image upon the photosensitive element 23 through this window as shown by an arrow.
  • FIG. 4 is a graph showing the variations in the surface potentials appearing in a modified method of electrophotography wherein a modified corona discharge unit shown in FIG. 5 is employed. As shown by curves A" and B", 'by the end of the second interval t the surface potentials at bright and dark portions vary in the same manner as in the interval t shown in FIG. 2.
  • electrodes 20 are used to apply the second electric field across the photosensitive element concurrently with the projection of the light image through these electrodes as shown by an arrow in FIG.
  • electrodes 20 surrounded by grounded inverted cup shaped counter electrode 21 are used to apply an electric field of the same polarity but higher than the second electric field during interval t" or the third step, thus increasing the charge deposited on the surface of the highly insulative layer.
  • the surface potential at bright portions is substantially the same as that at dark portions so that after interruption of the application of the field by electrodes 20,,, that is during interval t" the surface potential at the bright portions does not vary as shown by curve A" in FIG. 4, thus maintaining the increased level.
  • the second electric field concurrently with the projection of the light image and then applying in the dark the third field of the same polarity as the second electric field and having the same or higher potential, it is possible to increase the potential difference between dark and bright portions, thus increasing the contrast and sensitivity.
  • This makes it possible to transfer the latent image onto a recording paper by using a transfer roller which is short circuited with the photosensitive element as above described.
  • the latent image transferred onto the recording paper can be developed by any conventional developing method to obtain a copy of excellent quality.
  • the polarity of the charge deposited in the first step should be the same polarity as that of the majority carriers in the photoconductive layer and the polarity of the charge deposited in the second step should be the same polarity as the minority carriers.
  • the object of this invention can be accomplished by continuing the application of the second field after interruption of the projection of the light image or by reapplying the electric field of the same polarity as the minority carriers a short interval after interruption of the light image.
  • FIGS. 6 and 7 illustrate a preferred embodiment of the electrophotographic apparatus embodying the invention.
  • a photoconductive layer 2 is wrapped about an electroconductive rotary drum 1.
  • the photoconductive layer 2 comprises a first layer of SeTe containing about 16 mol percent of Te and vapour deposited to a thickness of 30 microns and a second layer of 1 micron thick which is formed 'by simultaneously vapour depositing a powder of SeTe containing about 16 mol percent of Te and a powder of SeTe containing 40 mol percent of Te, upon the first layer.
  • the second layer contains a plurality of charge trapping levels thus manifesting intense persistent internal polarization.
  • polycarbonate is applied on the second layer to a thickness of 10 microns to form a highly insulative layer 3.
  • the assembly of drum 1, photoconductive layer 2 and insulative layer 3 is termed a photosensitive drum 4.
  • the potential of the portions of the highly insulative layer corresponding to dark portions of the light image becomes v.
  • the potential of the bright portions becomes +200 v.
  • a positive charge is deposited on the surface of the highly insulative layer by means of a third corona discharge unit 9 to deposit a charge of +300 v. at dark portions and a charge of +700 v. at bright portions.
  • a lamp L for post exposure may be provided to the rear of the third corona discharge unit 9 for increasing the contrast and the operating speed.
  • the latent image formed in this manner may be developed on the photosensitive drum and then transfer printed onto a recording paper.
  • the feeding of the receptor medium may he made either by the transfer printing roller, or a feed roller 11 in front of the transfer printing station or a tension roller 12 to the rear thereof. After erasing the latent image remaining on the photosensitive drum by means of an AC electric field, the photosensitive drum can be used repeatedly.
  • the latent image transfer printed onto the receptor medium 13 is then developed by any conventional developing device comprising for example a supply of developer 14 containing a developer admixed with about 2%, by weight, of a negatively charged toner and a rotating brush 15 and the developed image is then fixed by means of a heater 16 to obtain a permanent copy.
  • any conventional developing device comprising for example a supply of developer 14 containing a developer admixed with about 2%, by weight, of a negatively charged toner and a rotating brush 15 and the developed image is then fixed by means of a heater 16 to obtain a permanent copy.
  • the potential difference of the latent image between portions corresponding to dark and bright portions of the light image can be increased so that it is possible to increase the contrast and sensitivity thus producing at a high speed copies of improved quality.
  • the novel electrophotographic apparatus it is not only possible to increase the useful life of the photosensitive element but also decrease the physical dimensions of the apparatus because the latent image is not developed on the photosensitive element so that it is not necessary to use any means for cleaning the developer remaining on the photosensitive element after transfer printing. Further, as the drum 1 and transfer printing roller 10 are grounded by a conductor 19 and since it is not necessary to apply any transfer potential there is no danger of electric shock.
  • a method of electrophotography comprising the steps of providing a photosensitive element including a photoconductive layer manifesting persistent internal polarization, a highly insulative layer integrally bonded to one side of said photoconductive layer and a transparent electrode layer on the side of said photoconductive layer opposite to said highly insulative layer, applying a first electric field across said photosensitive element to deposit a charge of one polarity on the surface of said highly insulative layer, said first electric field having the same polarity as the majority carriers in said photoconductive layer, applying a second electric field across said photosensitive element to deposit a charge of the opposite polarity on the surface of said highly insulative layer, said second electric field having the same polarity as the minority carriers in said photoconductive layer, projecting a light image upon said photoconductive layer through said transparent electrode layer concurrently with the application of said second field, and applying a third electric field across said photosensitive element to deposit a charge of the same polarity as the charge deposited by said second electric field on the surface of said highly insulative layer.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrophotography Using Other Than Carlson'S Method (AREA)
  • Photoreceptors In Electrophotography (AREA)
US00108733A 1970-01-24 1971-01-22 Method for electrophotography Expired - Lifetime US3730709A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP45006603A JPS4910056B1 (enrdf_load_stackoverflow) 1970-01-24 1970-01-24

Publications (1)

Publication Number Publication Date
US3730709A true US3730709A (en) 1973-05-01

Family

ID=11642903

Family Applications (1)

Application Number Title Priority Date Filing Date
US00108733A Expired - Lifetime US3730709A (en) 1970-01-24 1971-01-22 Method for electrophotography

Country Status (2)

Country Link
US (1) US3730709A (enrdf_load_stackoverflow)
JP (1) JPS4910056B1 (enrdf_load_stackoverflow)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3883349A (en) * 1973-02-22 1975-05-13 Rank Xerox Ltd Electrophotographic charging method
US3970452A (en) * 1974-08-30 1976-07-20 Addressograph Multigraph Corporation Charged particle modulator device and imaging methods
US3997259A (en) * 1973-11-08 1976-12-14 Xerox Corporation Apparatus for reducing image background in electrostatic reproduction machines
US4038943A (en) * 1974-06-05 1977-08-02 Xerox Corporation Signal amplification by charging and illuminating a partially developed latent electrostatic image
US4052206A (en) * 1974-11-07 1977-10-04 Hitachi, Ltd. Electrophotography
US4087168A (en) * 1976-01-19 1978-05-02 Xerox Corporation Charging system for electrostatic reproduction machine
US4126388A (en) * 1976-03-15 1978-11-21 Minolta Camera Kabushiki Kaisha Electrophotocopying machine of electrostatic latent image transfer type
US4329413A (en) * 1979-02-23 1982-05-11 Canon Kabushiki Kaisha Electrophotographic process capable of forming overlaid images and apparatus for carrying out the same
US4378418A (en) * 1979-09-04 1983-03-29 Xerox Corporation Hole injecting contact for overcoated photoreceptors

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3883349A (en) * 1973-02-22 1975-05-13 Rank Xerox Ltd Electrophotographic charging method
US3997259A (en) * 1973-11-08 1976-12-14 Xerox Corporation Apparatus for reducing image background in electrostatic reproduction machines
US4038943A (en) * 1974-06-05 1977-08-02 Xerox Corporation Signal amplification by charging and illuminating a partially developed latent electrostatic image
US3970452A (en) * 1974-08-30 1976-07-20 Addressograph Multigraph Corporation Charged particle modulator device and imaging methods
US4052206A (en) * 1974-11-07 1977-10-04 Hitachi, Ltd. Electrophotography
US4087168A (en) * 1976-01-19 1978-05-02 Xerox Corporation Charging system for electrostatic reproduction machine
US4126388A (en) * 1976-03-15 1978-11-21 Minolta Camera Kabushiki Kaisha Electrophotocopying machine of electrostatic latent image transfer type
US4329413A (en) * 1979-02-23 1982-05-11 Canon Kabushiki Kaisha Electrophotographic process capable of forming overlaid images and apparatus for carrying out the same
US4378418A (en) * 1979-09-04 1983-03-29 Xerox Corporation Hole injecting contact for overcoated photoreceptors

Also Published As

Publication number Publication date
JPS4910056B1 (enrdf_load_stackoverflow) 1974-03-08

Similar Documents

Publication Publication Date Title
US3684364A (en) Lift off electrode
US2901374A (en) Development of electrostatic image and apparatus therefor
US4021586A (en) Method of and means for the development of electrostatic images
US3551146A (en) Induction imaging system
US3937572A (en) Apparatus for inductive electrophotography
US3776627A (en) Electrophotographic apparatus using photosensitive member with electrically high insulating layer
US3752572A (en) Apparatus for making electrographs
US3778841A (en) Induction imaging system
US3653890A (en) Screen electrophotographic charge induction process
US3216844A (en) Method of developing electrostatic image with photoconductive donor member
US3332396A (en) Xerographic developing apparatus with controlled corona means
US3166418A (en) Image development
US3719481A (en) Electrostatographic imaging process
US3722992A (en) Apparatus for creating an electrostatic latent image by charge modulation
US3730709A (en) Method for electrophotography
US3703376A (en) Induction imaging system
US4021106A (en) Apparatus for electrostatic reproduction using plural charges
US3609031A (en) Method of forming electrostatic latent images
US4210448A (en) Process for electrophotographic image formation and transfer
US3464818A (en) Method of photoelectric copying
US3834809A (en) Electrophotographic system
US3888664A (en) Electrophotographic printing
US3598580A (en) Photoelectrostatic copying process employing organic photoconductors
US3666364A (en) Electrophotographic apparatus
US4255507A (en) Electrophotographic screen process