US3476935A - Control of xerographic images by charging the photoconductor with only an outer band of a corona discharge - Google Patents

Control of xerographic images by charging the photoconductor with only an outer band of a corona discharge Download PDF

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Publication number
US3476935A
US3476935A US576091A US3476935DA US3476935A US 3476935 A US3476935 A US 3476935A US 576091 A US576091 A US 576091A US 3476935D A US3476935D A US 3476935DA US 3476935 A US3476935 A US 3476935A
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United States
Prior art keywords
charging
zone
charge
corona
outer band
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Expired - Lifetime
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US576091A
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English (en)
Inventor
Kenneth A Metcalfe
Frank C Gillespie
Ian E Smith
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Australian Government
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Australian Government
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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
    • G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
    • G03G15/0291—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices corona discharge devices, e.g. wires, pointed electrodes, means for cleaning the corona discharge device

Definitions

  • This invention relates to an improved control of xerographic images and in particular it relates to a method of and means whereby firstly a better image can be produced and secondly wherein the tone or hue of the image comes under closer control.
  • the present invention relates to those processes where charging forms a part during some stage of the process, be it for the purpose of achieving intensification of an image due to the charging of the surface and the bleeding away of unwanted charge in an imagewise manner or whether the charging is merely for the purposes of producing a bias on the surface which will then control deposition of developer in accordance with this bias, the latter part of the process probably being the more important one in that it has been found that by its use very exact control of charge levels is possible without the introduction of artifacts so that in, for instance, colour reproduction, it is possible to vary the hues which are being applied by means of a succession of developers by controlling the charge characteristic on the surface rather than the colour value of the toners themselves.
  • the invention can be applied to practically all cases where xerographic images are being produced and developed the present invention will be described more in reference to tone control with any of the processes known heretofore, such as the usual process in which the photoconductor is first charged and then image-modified by light or the like or where a chargeless process is used in which the surface is itself simply modified by light or other electro-magnetic waves and independently of whether dry or wet development processes are used.
  • the principle of our invention is to utilise a corona discharge to apply a bias on a surface which is to have a latent electrostatic image developed thereon or on which a latent electrostatic image has already been produced, the corona being however so controlled that only a certain portion of the corona acts on the surface, which portion of the corona is selected by an appropriate positioning of the corona discharge means and the control of the field generally at such discharge means.
  • a charging electrode and a base electrode are so spaced and directioned, one in relation to the other, that a series of bands are produced outwardly of a core which is substantially medial to the discharge direction from the electrode, and utilising only an outer band for charging purposes.
  • FIG. 1 is a perspective view showing the experiment carried out to demonstrate the effects of a corona dis charge on a photoconductive surface, using a combination of red and black developers of opposite polarity in an insulating liquid,
  • FIG. 2 shows an inner core or zone and an outer band or zone, is simplified form, the inner zone having been found to produce interior results, but the outer zone giving improved results,
  • FIG. 3 is a simplified version of the inner and outer zone which can be deduced from the experiments undertaken
  • FIGS. 4 and 5 respectively show graphs of charging time against the diameter of the inner zone, and point to plane distance in relation to the outer zone, and
  • FIG. 6 shows a form of device which can conveniently be used to charge xerographic papers, the points being used successiveively.
  • the photoconductive sheet 1 formed the lower electrode of a corona discharge system by placing this sheet on to a metal backing to which the voltage was applied, the electrode 2 being positioned approximately one inch above the sheet 1 and at an angle of about sixty degrees to the vertical, numerous experiments of course having been carried out with different angles and different spacings.
  • the potential was applied from a suitable generator 3 which produced approximately three to seven kv.
  • a secondary area 8 Surrounding the area 7 of positive charge is a secondary area 8, or an outer zone, which takes a very light hue of red, showing that here there is a negative charge of much lesser intensity, which negative charge in the experiments carried out invariably had a soft and uniform nature and obviously thus was free of the streaming or similar effects which gave mottling in the other areas, so that this particular area produced a relatively weak but uniform charge which we have found is ideal for applying a biasing voltage of negative characteristic to a surface which is subsequently to be developed.
  • an inner zone 5 is formed which is of inferior characteristic for charging purposes, and it can be assumed that in all the previous work utilising coronas to charge photoconductors it is this area which'has been effective in applying a chargebeing readily available and offast chargingcharacteristics.
  • the outer zone 8 is however of highly desirable characteristic and it is this zone which is used according to our invention.
  • the charge pattern produced by a single point corona comprises a number of zones which may however be divided into two main concentric zones, the central zone 5 and the larger outer zone 8.
  • the boundary of zone 8 is established early in the charging cycle and remains fixed in diameter regardless of charging time;
  • the diameter of zone 8 increases with increasing point to plane distanceas shown in FIG. 1.
  • the diameter of zone 5 increases with charging time as shown in FIG. 4.
  • the charge zone 8 is characterised by superior electro-' photographic speed and exceptional continuous-tone image quality as compared with the zone 5, the developed density varying radially across Zone 8 being of greatest value in the vicinity of zone 5.
  • the portion of the charge pattern giving optimum speed and contrast is in the form of a ring surrounding zone 5 in the case of a point corona and comprises :a parallel band displaced on each side of the wire electrode for a wire corona charging device.
  • the width of this zone may be increased by increasing the inter-electrode distance, this arrangement requires increased charging periods. For example the width of the optimum zone is not greater than 8" for a point to plane distance of 12" :at 15 kv. requiring a charging time of 1 /2 minutes.
  • the graph of FIG. 4 shows charging time in seconds against the diameters of zones 5 and 8 produced and this suggests that shorter times reduce the central zone 5.
  • the graph of FIG. 5 shows how the distance from the point varies the diameter of the zone 8.
  • One method of producing a large area of the optimum charge consists of using a plurality of corona points as shown in FIG. 6 arranged so that the outer charge zone 8 produced independently by each corona overlaps adjacent patterns, resulting in a charge area which produces uniform developed density. Unlike conventional multicorona charging devices this new method is dependent on each corona point acting consecutively. This allows each charge pattern to be superimposed on the other. Simultaneous multiple-corona action does not produce charge overlap due to mutual repulsion of adjacent plasmaenvelopes which also reduce the size of the outer, charge zone 8 without effecting zone 5.
  • FIG. 6 shows a typical arrangement using two point electrodes. A greater charge uniformity is achieved by using a greater number of points.
  • a convenient method of. supplying consecutive high voltage pulses to the points is the use of a system similar to the automotive high tension ignition system.
  • Another method of achieving the optimum charge is to use the overlapping charges from two spaced parallel wire corona discharges each supplied by consecutivevolt': age pulses.
  • the method of charging a surface to produce a latent charge thereon which consists in applying a direct current corona-producing voltage between at least a charging electrode and a base electrode, spacing and directing the charging electrode to produce a central zone with an outer band surrounding the same and inserting a work-piece into the outer band of the corona whereby the surface of the work-piece is charged only by the said outer band and is not subjected to the central zone.
  • Apparatus for charging a surface comprising a charging electrode shaped to emit a corona, a base electrode spaced from the charging electrode, direct current voltage supply means connected between the charging electrode and the base electrode to produce a corona discharge having a central zone and an outer band surrounding said central zone and a work-piece holder positioned to allow the surface of the work-piece to be positioned in the outer band only of the corona.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Physics & Mathematics (AREA)
  • Treatments Of Macromolecular Shaped Articles (AREA)
  • Electrostatic Charge, Transfer And Separation In Electrography (AREA)
US576091A 1965-08-30 1966-08-30 Control of xerographic images by charging the photoconductor with only an outer band of a corona discharge Expired - Lifetime US3476935A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AU63375/65A AU412769B2 (en) 1965-08-30 1965-08-30 Improved control of xerographic images

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US3476935A true US3476935A (en) 1969-11-04

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US (1) US3476935A (enExample)
JP (1) JPS5017856B1 (enExample)
AU (1) AU412769B2 (enExample)
GB (1) GB1156178A (enExample)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3603851A (en) * 1968-11-11 1971-09-07 Commw Of Australia Method of contour charging
US3729649A (en) * 1972-05-25 1973-04-24 Eastman Kodak Co Corona charging apparatus
US4507373A (en) * 1983-10-03 1985-03-26 Eastman Kodak Company Method and apparatus for uniformly charging a surface
EP0144236A3 (en) * 1983-12-08 1985-07-10 Xerox Corporation Corona generating device
WO1987004018A1 (en) * 1985-12-23 1987-07-02 Eastman Kodak Company Corona generating apparatus

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3169886A (en) * 1959-11-18 1965-02-16 Bayer Ag Apparatus for the electrophotographic production of images
US3178281A (en) * 1956-07-16 1965-04-13 Eastman Kodak Co Electrostatic color printing
US3307034A (en) * 1963-12-09 1967-02-28 Xerox Corp Two-wire corona discharge system for single-step electrostatic image formation

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3178281A (en) * 1956-07-16 1965-04-13 Eastman Kodak Co Electrostatic color printing
US3169886A (en) * 1959-11-18 1965-02-16 Bayer Ag Apparatus for the electrophotographic production of images
US3307034A (en) * 1963-12-09 1967-02-28 Xerox Corp Two-wire corona discharge system for single-step electrostatic image formation

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3603851A (en) * 1968-11-11 1971-09-07 Commw Of Australia Method of contour charging
US3729649A (en) * 1972-05-25 1973-04-24 Eastman Kodak Co Corona charging apparatus
US4507373A (en) * 1983-10-03 1985-03-26 Eastman Kodak Company Method and apparatus for uniformly charging a surface
EP0144236A3 (en) * 1983-12-08 1985-07-10 Xerox Corporation Corona generating device
US4549244A (en) * 1983-12-08 1985-10-22 Xerox Corporation Corona generating device
WO1987004018A1 (en) * 1985-12-23 1987-07-02 Eastman Kodak Company Corona generating apparatus

Also Published As

Publication number Publication date
AU412769B2 (en) 1971-04-28
GB1156178A (en) 1969-06-25
AU6337565A (en) 1968-02-29
JPS5017856B1 (enExample) 1975-06-24

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