US3444369A - Method and apparatus for selective corona treatment of toner particles - Google Patents

Method and apparatus for selective corona treatment of toner particles Download PDF

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US3444369A
US3444369A US585825A US3444369DA US3444369A US 3444369 A US3444369 A US 3444369A US 585825 A US585825 A US 585825A US 3444369D A US3444369D A US 3444369DA US 3444369 A US3444369 A US 3444369A
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Prior art keywords
toner
image
image areas
charge
xerographic
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US585825A
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English (en)
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Paul J Malinaric
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Xerox Corp
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Xerox Corp
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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
    • G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
    • G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
    • G03G15/169—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer with means for preconditioning the toner image before the transfer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
    • Y10S430/001—Electric or magnetic imagery, e.g., xerography, electrography, magnetography, etc. Process, composition, or product
    • Y10S430/102—Electrically charging radiation-conductive surface

Definitions

  • a developed toner image on a photoconductive surface is subjected to a low level corona discharge of a polarity opposite the charge on the toner particles overlying the image areas.
  • the corona discharge adjacent the image areas will be repelled by the like but higher charge pattern in the image areas of the photoconductive surface to thereby render image area toner uneifected.
  • the corona discharge adjacent the non-image areas of the photoconductive surface will not be repelled and will thus convert the charge on the toner overlying the non-image areas to a polarity opposite that on the image area toner particles. This will permit the electrostatic transfer of either the image area toner or the nonimage area toner to a backing sheet.
  • This invention relates in general to xerography and in particular to a method and apparatus for preventing the transfer of toner powder to non-image areas of Xerographic copy.
  • a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support electrostatic images.
  • the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer.
  • the undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.
  • the latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as a resinous powder.
  • a finely divided electrostatically attractable material such as a resinous powder.
  • the powder is held in image areas by the electrostatic charges on the layer. Where the charge is greatest, the greatest amount of material is deposited; and where the charge is least, little or no material is deposited.
  • a powder image is produced in conformity with the light image of the copy being reproduced.
  • the powder is subsequently transferred to a sheet of paper or other surface and suitably aflixed to thereby form a permanent print.
  • the electrostatically attractable developing material commonly used in xerography consists of a pigmented resinous powder referred to herein as toner.
  • toner In order for the toner to attach itself to the electrostatic charge corresponding to the image areas, it is first necessary to charge the toner particles to a polarity opposite from the charge on the image areas.
  • the toner In the most common form of development, generally called cascade, the toner is mixed with a coarse granular material called carrier.
  • the carrier is usually a glass or sand bead coated with a material removed in the triboelectric series from the toner so that a triboelectric charge is generated between the powder and the granular carrier upon mutual interaction. Such charge causes the toner powder to adhere to the carrier.
  • the toner ladened carrier is moved into contact with a latent elec- 3,444,369 Patented May 13, 1969 trostatic image, the charge of the image areas attracts the toner from the carrier to the image areas to thus render the latent electrostatic image visible.
  • toner powder In the practice of xerography, toner powder often becomes deposited on portions of the xerographic surface corresponding to non-image areas. The principal causes of such unintended deposition are uncontrolled toner clouds and incomplete scavenging.
  • Scavenging occurs when carrier granules move across a toner bearing surface after depositing their previously associated toner powder onto image areas. As the granules continue their movement across the surface, they contact and attract those toner particles which are held to the photoconductive surface by weak electrostatic forces.
  • toner deposition on non-image areas may also be caused by toner particles becoming charged to a polarity opposite from that intended. When this happens these particles are repelled from image areas to non-image areas. Toner powder may also assume a neutral polarity in which case it may also settle on non-image areas.
  • the present invention is directed to reducing the deleterious effects of toner particles deposited in non-image areas of a developed image, regardless of their polarity, the manner by which they were deposited or the method of development employed.
  • the developed image-bearing photoconductive surface is exposed to a low corona current immediately after development.
  • the toner powder in non-image areas can all be charged to a polarity opposite from that of the toner particles corresponding to the image areas. This is achieveable with no degrading of the charges on the image area toner.
  • the resulting polarity difference between the toner powder in the image and non-image areas makes possible, with the aid of a transfer corotron, the transfer of only image area toner and, consequently, a background free area toner particles from the developed photoconductive surface to thereby leave a background free image on the photoconductive surface.
  • the first alternative is readily adaptable for incorporation into existing xerographic machines adapted for continous and automatic operation.
  • the second alternative is of special interest when considering xeroprinting, xerographic master making and lithography.
  • a further object of the present invention is to eliminate the transferral of toner powder from non-image areas of xerographic copy.
  • a further object of this invention is to effectuate the charging of all non-image area toner powder to a polarity opposite from all image area toner powder in a developed xerographic surface to thereby allow the transfer of only like-polarity toner powder from the developed imagebearing surface.
  • a further object of the invention is to remove unwanted background toner powder from xeroprinting masters.
  • FIGS. 1-3 are diagrammatic front cross sectional views of a xerographic surface being processed in accordance with the invention
  • FIGS. 4-7 are diagrammatic front cross sectional views of a xerographic surface being processed in accordance with a second embodiment of the invention.
  • FIG. 8 is a diagrammatic side cross sectional view of a xerographic machine adapted for continuous and automatic operation adapted to carry out the process of the instant invention.
  • the principle upon which this invention is founded is that when a corona emitting device, such as a corotron described for example in US. Patent No. 2,836,725, is positioned over a photoconductive surface, it will tend to charge the photoconductive surface therebeneath up to an equilibrium voltage with the corotron.
  • the equilibrium voltage for any system is determined by such variables as the corotron diameter, the medium and distance between the corotron and photoconductive surface as well as the potential difference therebetween. The equilibrium voltage must fall between these potentials.
  • the photoconductive surface, or any part thereof is of a lesser than equilibrium voltage, then the photoconductive surface will accept the corona emissions. By accepting the emissions, the corotron will thus raise those portions of the surface with a lesser than equilibrium voltage up to the equilibrium voltage.
  • the equilibrium voltage equals or is lower than the voltage already on the photoconductive surface beneath the corotron, no charge, can be accepted by the surface and the surface in such areas will remain electrically unchanged. This is because the potential difference between the photoconductive surface and corotron is insufficient to support a flow of emissions to the photoconductive surface. Emissions continue to flow from the corotron under such conditions but are repelled by the higher like-potential fields adjacent the photoconductive surface and are directed to the corotron shield. If no shield were employed, the corona emitting wire would raise the surface up to the equilibrium voltage and then cease emitting so long as the potential difference remained less than that required to produce emissions.
  • This tendency of a photoconductive surface adjacent a corotron to reach an equilibrium voltage is a one way process.
  • the emitted corona will have no effect on photoconductive surface portions with potentials equal to or greater than the equilibrium voltage. It will, however, tend to raise the lesser than equilibrium voltage portions of the photoconductive surface up to the equilibrium voltage and then cease having an effect on those areas.
  • the corona ceases to have an effect on such areas since they are no longer below the equilibrium voltage. In this sense, the equilibrium voltage may be considered a corona cut off voltage. It has also been determined that the portions of the photoconductive surface wherein the voltage beneath the equilibrium voltage is farthest therefrom, Will start becoming charged first and fastest.
  • the xerographic surface 10 is composed of a conductive substrate 12, coated with a photoconductive layer 14, selenium for example, upon which latent electrostatic images may be formed.
  • the photoconductive surface may be of the conventional types usable in the field of Xerography capable of retaining latent electrostatic images thereon.
  • FIG. 1 represents schematically, a cross sectional view of a photoconductive surface after development.
  • the positive signs within the photoconductive layer represent undischarged portion 16 of the image photoconductive surface corresponding to image areas of the copy being reproduced.
  • the portions of the photoconductive layer without such positive signs represent discharged portion 18 of the imaged photoconductive surface which correspond to non-image areas of the copy being reproduced.
  • the negative marked circles adjacent the image areas represent negative toner particles desirably held in image areas by the electrostatic attraction between the dissimilar polarities and are properly oriented on the photoconductive surface for image reproduction.
  • Also located on the photoconductive surface are a variety of toner particles of positive negative and neutral (0) polarity located in positions representing non-image areas. If these particles were to be transferred and fused to a final backing material they would manifest themselves as unwanted background.
  • the developed image is first subjected to a background clean-up step. This is accomplished by merely moving the corona-emitting corotron 20 relative to the photoconductive surface, in close proximity thereto, as shown in FIG. 2.
  • the corotron must be at a very low current and of the opposite polarity as the toner overlying the image areas of the photoconductive surface. This would be positive in the illustrated embodiment.
  • the corotron and photoconductive surface move relative to each other, the emitted corona will begin to raise those portions of the photoconductive surface representing non-image areas up to the equilibrium potential. Due to the fact that toner particles of varying charge and consequently varying potential, both positive and negative, overlie these non-image areas, the sprayed nonimage areas will become charged in accordance with the emission charge concurrently with their overlying toner particles. A potential opposite from that found in the toner of the image areas can thus be imparted to all nonimage area toner regardless of their original charge.
  • corona suppression it is meant that positive emissions from the corotron will be repelled from the photoconductive surface by the higher like-potential field representing the image areas. Consequently, the corona has no effect on image areas and their overlying toner particles. This repelling action is most pronounced over extended image areas.
  • This suppression of corona is illustrated by the absence of emission lines over the extended image area of FIG. 2. In smaller image areas, corona suppression exhibits itself as a bending of the corona emissions around the highly positive image areas to thereby reach adjacent non-image areas. Note the bent emission lines around the small image area and at the edges of the extended image area of FIG. 2.
  • the polarities of the toner particles after being subjected to the corona emissions can be seen in FIG. 2. Note these toner polarities as compared with FIG. 1.
  • This background clean up step is usually done in the dark according to conventional practices so as the charge of the image areas of the photoconductive surface are not dissipated by light striking these areas.
  • the image area toner may then be transferred to the final backing sheet 24 in the conventional manner for subsequent fusing.
  • the use of a positive transfer corotron 22, as shown in FIG. 3, will facilitate transfer of only the image area toner to the backing sheet.
  • the non im-age area toner, having been charged to a polarity opposite from the image area toner, will be repelled from the backing sheet due to its like polarity to the transfer corotron.
  • the instant invention should be considered in its broadest sense as being directed to a clean up corotron polarity opposite from that of the toner overlying those areas desired to be developed.
  • the clean up corotron polarity need not always be the same as the original surface charging polarity.
  • the invention herein is applicable independent of the development method employed. This is because the toner polarity reversal is basically a function of the photoconductor charge distribution. The other element of the system, beyond the proper polarity used, merely involves the retention of the original photoconductor charge distribution up to the time of the low level clean up charging.
  • FIGURES 4-7 relate to an embodiment quite similar to the first mentioned embodiment but difiering therefrom in the transfer procedure.
  • FIGURES 4 and 5 of this embodiment are identical with FIGURES 1 and 2 of the first embodiment.
  • the two embodiments are identical in the development and precleaning steps, that is, the resulting developed surfaces with dissimilar toner polarities in the image and non- .image areas are the same.
  • a preliminary transfer corotron 26 is employed with a polarity opposite from the conventional transfer corotron 22 of the first embodiment. Note FIG. 6. This preliminary transfer corotron would thus be of the same polarity as the image area toner charge.
  • This particular embodiment of the invention is especially adapted for xeroprinting wherein a toner image is formed and fused onto a conductive substrate coated with a photoconductive layer.
  • This process will produce a xeroprinting master.
  • fiat plate operations as is the first embodiment.
  • this embodiment could be employed in continuous and automatic xerographic machinery but would require the use of a preliminary clean-up backing sheet to be fed through the machine under the influence of a reverse polarity preliminary transfer electrode prior to the conventional transfer.
  • This preliminary sheet could take the form of an endless web positioned between the clean-up electrode and conventional transfer station.
  • the first embodiment would not require such a preliminary clean-up step prior to transfer. In this respect, the first embodiment would be more suitable for incorporation into continuous and automatic xerographic machinery of the present commercial variety.
  • the preliminary transfer paper or background clean-up web may be of any dielectric material or conductorbacked dielectric.
  • a conductive material contacting the photoconductive surface would short out the fields on the photoconductive layer and thus remove the change orientations previously placed on the photoconductive surface and the toner.
  • paper is a suitable dielectric for removing the non-image area toner
  • smooth surfaces such as Mylar or Teflon achieve a more complete removal of this background toner.
  • the smooth surface for toner removal is desirable since it presents a surface which more completely covers and contacts all areas of the photoconductive surface.
  • a nonimage area toner particle will not readily transfer to a rough surface if complete contact is not made therebetween.
  • a rough preliminary transfer sheet is undesirable since it is likely to abrade and remove toner depositions from image areas. In either event, the smooth surface is preferred.
  • FIG. 8 there is illustrated a machine constructed for continuous and automatic operation. All of the processing stations referred to by letters are conventional in the xerographic art. For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the xerographic surface may be described as follows:
  • a charging station A at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;
  • An exposure station B at which the light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the copy to be reproduced;
  • a development station C at which a xerographic developing material including toner powder having an electrostatic charge opposite to that of the latent electrostatic image, are moved into contact with the drum surface, whereby the toner particles adhere to the latent electrostatic image to form a xerographic powdered image in the configuration of the copy being reproduced;
  • a transfer station D at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or a support surface;
  • a drum cleaning and discharging station E at which the drum surface is brushed to remove residual toner particles remaining thereon after image transfer, 'and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.
  • the corotron device 34 operates in the same manner as that described with respect to FIGURES 1-3 and 4-7. As the developed image passes beyond the development station, the developed image passes beneath the clean up corotron 34. The corotron must have the opposite polarity as the charge on the toner on image areas. The corona emissions being of a low current will then render all of the non-image toner particles to a polarity opposite from all of the image area toners. The developed image will then pass through the transfer station for transferring only image area toner particles to a backing sheet for subsequent fusing. The transfer is made under the influence of a conventional transfer corotron 36. The drum will then continue its rotation past the cleanup station for the removal of all of the untransferred toner particles including all non-image area toner. This portion of the photoconductive surface of the drum is now ready for subsequent charging, imaging and development in a continuing cycle for operation.
  • one set of illustrative parameters in which the invention is operable includes an original photoconductive plate charging of 800 volts with an imaging to bring image areas down to 650 volts and non-image areas down to 40 volts.
  • a cleanup corotron, /2 inch from the drum, may be employed at 0.20 microamps per inch. This would be approximately two microamps when a 10 inch corotron is used. It should be understood that these operating conditions are by way of example only since wide ranges of operating conditions may be employed.
  • xerographic processing apparatus having a charging station to deposit an electrostatic charge on a photoconductive surface, an exposure station adapted to dissipate the charge in a patterned configuration of image and non-image areas corresponding to the image to be reproduced, a development station at which a xerographic developing material is adapted to be moved into contact with the photoconductive surface to thereby deposit charged toner powder on the photoconductive surface in a configuration corresponding to the image to be reproduced and a transfer station adapted to transfer toner adhering to the photoconductive surface to a backing material, the improvement comprising,
  • the transfer station includes electrostatic means biased to facilitate the electrostatic transfer of the image area toner from the xerographic surface to a backing material.
  • the transfer station includes electrostatic means biased to facilitate the electrostatic transfer of the non-image area toner from the xerographic surface to a backing material.
  • the method of producing powdered xerographic images which includes the steps of charging a photoconductive surface with an electrostatic charge, exposing the charged photoconductive surface to discharge portions of the charge in a configuration of image and non-image areas corresponding to the copy to be reproduced, developing the photoconductive surface with charged toner particles and transferring toner particles from the photconductive surface to a backing material, the improvement comprising,
  • corona emissions having a polarity opposite that on image area toner particles and sufficient in magnitude to convert the toner overlying the non-image areas to a polarity opposite that on the toner overlying the image areas, the corona emissions being of insufiicient magnitude to change the polarity of toner overlying the image areas and electrostatically transferring like polarity toner from the photoconductive surface.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
  • Printing Methods (AREA)
  • Fixing For Electrophotography (AREA)
  • Cleaning In Electrography (AREA)
  • Developing Agents For Electrophotography (AREA)
US585825A 1966-10-11 1966-10-11 Method and apparatus for selective corona treatment of toner particles Expired - Lifetime US3444369A (en)

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AT (1) AT288863B (da)
BE (1) BE704919A (da)
CH (1) CH487438A (da)
DE (1) DE1597884B2 (da)
DK (1) DK119094B (da)
ES (1) ES345918A1 (da)
GB (1) GB1203811A (da)
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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3628950A (en) * 1969-12-10 1971-12-21 Xerox Corp Improved method of removing the residual toner particles from a photoconductive surface
DE2250062A1 (de) * 1971-12-23 1973-07-05 Xerox Corp Elektrofotografisches kopierverfahren und kopiergeraet
US3779749A (en) * 1971-09-10 1973-12-18 Fuji Photo Film Co Ltd Method of charging in electrophotography
US3804659A (en) * 1970-12-10 1974-04-16 Fuji Photo Film Co Ltd Electrophotographic reversal development process for enhancing the quality of the developed image
US3972611A (en) * 1970-03-18 1976-08-03 Canon Kabushiki Kaisha Apparatus for transferring images produced by liquid developer
US3984182A (en) * 1974-02-07 1976-10-05 Xerox Corporation Pretransfer conditioning for electrostatic printing
DE2929548A1 (de) * 1978-07-21 1980-03-13 Hitachi Koki Kk Elektrophotographierverfahren
DE3036731A1 (de) 1979-09-29 1981-04-16 Canon K.K., Tokyo Elektrophotographische einrichtung
US4265998A (en) * 1979-11-13 1981-05-05 International Business Machines Corporation Electrophotographic photoreceptive background areas cleaned by backcharge process
US5038177A (en) * 1988-12-15 1991-08-06 Xerox Corporation Selective pre-transfer corona transfer with light treatment for tri-level xerography
US5351113A (en) * 1994-01-10 1994-09-27 Xerox Corporation Pre-pretransfer treatment to increase transfer latitude in tri-level xerography
US5480751A (en) * 1994-06-30 1996-01-02 Xerox Corporation Tri-level background suppression scheme using an AC scorotron with front erase

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3628950A (en) * 1969-12-10 1971-12-21 Xerox Corp Improved method of removing the residual toner particles from a photoconductive surface
US3972611A (en) * 1970-03-18 1976-08-03 Canon Kabushiki Kaisha Apparatus for transferring images produced by liquid developer
US3804659A (en) * 1970-12-10 1974-04-16 Fuji Photo Film Co Ltd Electrophotographic reversal development process for enhancing the quality of the developed image
US3779749A (en) * 1971-09-10 1973-12-18 Fuji Photo Film Co Ltd Method of charging in electrophotography
DE2250062A1 (de) * 1971-12-23 1973-07-05 Xerox Corp Elektrofotografisches kopierverfahren und kopiergeraet
US3984182A (en) * 1974-02-07 1976-10-05 Xerox Corporation Pretransfer conditioning for electrostatic printing
DE2929548A1 (de) * 1978-07-21 1980-03-13 Hitachi Koki Kk Elektrophotographierverfahren
DE3036731A1 (de) 1979-09-29 1981-04-16 Canon K.K., Tokyo Elektrophotographische einrichtung
US4265998A (en) * 1979-11-13 1981-05-05 International Business Machines Corporation Electrophotographic photoreceptive background areas cleaned by backcharge process
US5038177A (en) * 1988-12-15 1991-08-06 Xerox Corporation Selective pre-transfer corona transfer with light treatment for tri-level xerography
US5351113A (en) * 1994-01-10 1994-09-27 Xerox Corporation Pre-pretransfer treatment to increase transfer latitude in tri-level xerography
US5480751A (en) * 1994-06-30 1996-01-02 Xerox Corporation Tri-level background suppression scheme using an AC scorotron with front erase

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Publication number Publication date
BE704919A (da) 1968-02-15
AT288863B (de) 1971-03-25
SE337986B (da) 1971-08-23
CH487438A (de) 1970-03-15
DE1597884B2 (de) 1976-11-04
GB1203811A (en) 1970-09-03
DE1597884A1 (de) 1970-10-01
NL152375B (nl) 1977-02-15
DK119094B (da) 1970-11-09
ES345918A1 (es) 1968-12-01
NL6713356A (da) 1968-04-16

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