US3676313A - Removing undesired potential from the blocking electrode in a photoelectrophoretic imaging system - Google Patents

Removing undesired potential from the blocking electrode in a photoelectrophoretic imaging system Download PDF

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US3676313A
US3676313A US60675A US3676313DA US3676313A US 3676313 A US3676313 A US 3676313A US 60675 A US60675 A US 60675A US 3676313D A US3676313D A US 3676313DA US 3676313 A US3676313 A US 3676313A
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blocking electrode
charge
electrode
imaging
blocking
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US60675A
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Roger N Ciccarelli
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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
    • G03G17/00—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process
    • G03G17/04—Electrographic processes using patterns other than charge patterns, e.g. an electric conductivity pattern; Processes involving a migration, e.g. photoelectrophoresis, photoelectrosolography; Processes involving a selective transfer, e.g. electrophoto-adhesive processes; Apparatus essentially involving a single such process using photoelectrophoresis

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  • the undesired charge build-up on a surface of the blocking electrode may be eliminated or neutralized in several different ways.
  • the surface of the blocking electrode may be brushed with a conductive brush between successive imaging cycles or the electrode surface may be treated with an opposite polarity potential sufficient to neutralize the surface charge between successive imaging cycles.
  • Any suitable method may be used to apply a neutralizing charge to the blocking electrode surface to eliminate undesired charge thereon. Typical methods include AC or DC corona discharge as taught by Carlson in U.S. Pat. No. 2,588,699 and Walkup in U.S. Pat. No. 2,777,957; triboelectric charging as taught by Carlson in U.S. Pat. No.
  • FIG. 1 shows a schematic representation of a single electrophoretic imaging system
  • FIG. 2 shows a blocking electrode immediately after image formation
  • FIG. 3 shows an embodiment in which the blocking electrode surface is grounded between imaging steps
  • FIG. 4 shows an alternative embodiment for eliminating charge build-up on the blocking electrode.
  • a transparent electrode generally designated 1 which in this exemplary instance, is made up of a layer of optically transparent glass 2 overcoated with a thin optically transparent layer 3 of tin oxide, commercially available under the name NESA glass.
  • This electrode will hereafter be referred to as the injecting" electrode.
  • Coated on the surface of injecting electrode 1 is a thin layer 4 of finely divided photosensitive particles dispersed in an insulating liquid carrier.
  • Photosensitive for the purposes of this application, refers to the properties of a particle which, once attracted to the injecting electrode, will migrate away from it under the influence of an applied electric field when it is exposed to actinic electromagnetic radiation.
  • a second electrode 5 Adjacent to the liquid suspension 4 is a second electrode 5, hereinafter called the blocking electrode" which is connected to one side of the potential source 6 through a switch 7.
  • the opposite side of potential source 6 is connected to the injecting electrode 1 so that when switch 7 is closed, an electric field is applied across the liquid suspension 4 between electrodes l and 5.
  • An image projector made up of a light source 8, a transparency 9, and a lens is provided to expose the dispersion 4 to a light image of the original transparency 9 to be reproduced.
  • Electrode 5 is made in the form of a roller having a conductive central core 11 connected to the potential source 6.
  • the core is covered with a layer of a blocking electrode material 12, which may be any suitable insulating material as further discussed below.
  • the particle suspension is exposed to the image to be reproduced while a potential is applied across blocking and injecting electrodes by closing switch 7.
  • Roller 5 is caused to roll across the top surface of injecting electrode 1 with switch 7 closed during the period of image exposure.
  • This light exposure causes exposed pigment particles originally attracted to electrode 1 to migrate through the liquid and adhere to the surface of transferred blocking electrode, leaving behind a particulate image on the injecting electrode surdace which is a duplicate of the original transparency 9.
  • the relatively volatile carrier liquid evaporates off, leaving behind the particulate image.
  • This particulate image may then be fixed in place, as for example, by placing a lamination over its top surface or by virtue of a dissolved binder material in the carrier liquid such as paraffin wax or other suitable binder that comes out of the solution as the carrier liquid evaporates.
  • the particulate image remaining on the injecting electrode may be transferring to another surface and fixed thereon.
  • This system can produce either monochromatic or polychromatic images depending upon the type and number of pigments suspended in the carrier liquid and the color of light to which this suspension is exposed in the process.
  • FIG. 2 shows the blocking electrode after imaging where the blocking electrode surface 12 consists of a highly insulating material. In this instance, a negative potential was maintained on the blocking electrode core 11 during imaging.
  • FIG. 2 shows the blocking electrode immediately after imaging. As the roller moved across the injecting electrode an apparent positive charge was built up on the surface of blocking electrode material 12. Thus, even after the switch 7 is opened, a potential remains across the blocking electrode material 12.
  • the blocking electrode material is at least slightly conductive
  • charge can gradually migrate through the blocking electrode material 12 neutralizing the surface charge. Once the charge has thus been neutralized an acceptable image may again be produced.
  • most materials having desirable physical properties for use as the surface of a blocking electrode are not sufficiently conductive to allow the built-up charge to leak off within a reasonable time.
  • FIG. 3 One embodiment of a system for removing undesired surface charge from a blocking electrode is shown in FIG. 3.
  • a conductive brush 13 is brought into contact with the blocking electrode surface and the blocking electrode roller is rotated thereagainst.
  • brush 13 may perform the dual functions of removing undesired surface charge and may also be used to clean unwanted particles from the blocking electrode surface thus readying the blocking electrode roller for successive imaging operations.
  • the conductive brush 13 it is preferred to have the brush l3 maintained at a potential level that can compete with the voltage level coupled to the core of the blocking electrode roller.
  • the brush 13 should be coupled to substantially the same or a more negative voltage (more positive if opposite polarities are being used) than the voltage coupled to the blocking electrode.
  • the shorting wire 20 coupled to brush l3 and to the core of roller 5 maintains the brush at substantially the same voltage level as the blocking electrode 5.
  • the conductive brush may be maintained at any suitable potential so as to leave a slight surface charge on the blocking electrode roller after cleaning.
  • a suitable potential may be a potential that increases rather than decreases the electric field between the electrodes.
  • FIG. 4 shows an alternative embodiment of the means for eliminating surface charge on the blocking electrode surface after imaging.
  • the surface charge remaining on the blocking electrode surface 12 may be neutralized after imaging by rotating the roller 5 adjacent a DC corona discharge unit 14 with power supply 15 held at a polarity opposite to that of the undesired charge on the blocking electrode surface 12.
  • an AC corona unit may be used which will reduce the potential on the blocking electrode to substantially zero potential.
  • Any suitable corona discharge unit may be used, such as those described in US. Pat. No. 2,588,699 to Carlson and US. Pat. No. 2,777,957 to Walkup.
  • the surface charge on blocking electrode 12 may be, alternatively, neutralized by charge applied by other conventional methods.
  • a charge of a potential opposite to the undesired surface charge may be applied triboelectrically by rubbing the blocking electrode surface with suitable material as taught by Carlson in US. Pat, No. 2,297,691.
  • the opposite potential may be applied by contacting the blocking electrode surface with a conductive roller or conductive liquid held at the desired potential as taught by Tregay et al. in US. Pat. No 2,980,834 and Walkup in U.S. Pat. No. 2,987,660.
  • the blocking electrode material may include dopants or additives to modify resistivity or other physical properties for particular uses.
  • resistivity may be modified by the addition of carbon black, conductive pigments and dyes, powdered metals, inorganic salts, etc.
  • organic donor-acceptor (Lewis acid-Lewis base) charge transfer complexes made up of donors such as phenolaldehyde resins, phenoxides, epoxies, polycarbonates, urethanes, styrene or the like complexed with electron acceptors such as 2,4,7-trinitro-9-fluorenone; 2,4,5,7-tetranitro-9-fluorenone; picric acid; 1,3,5-trinitro benzene; chloranil; 2,5-dichloro-benzoquinone; anthraquinone-2-carboxylic acid, Bromal, 4-nitro-phenol; maleic anhydride; metal halides of the metals and metalloids of groups 1-3 and lI-Vlll of the periodic table including, for example, aluminum chloride, zinc chloride, ferric chloride, magnesium chloride, calcium iodide, strontium bromide, chromic bromide, arsenic triiodide, magnesium
  • charge transfer complexes In addition to the charge transfer complexes it is to be noted that many additional ones of the above materials may be further sensitized by the charge transfer complexing technique and that many of these materials may be dye-sensitized to narrow, broaden or heighten their spectral response curves.
  • the particles When one or more of the particles are caused to migrate from the injecting electrode towards the blocking electrode, they leave behind particles which produce a color equivalent to the color of the impinging light.
  • red light exposure causes the cyan colored particles to migrate, leaving behind the magenta and yellow particles which combine to produce red in the final image.
  • blue and green colors are reproduced by the removal of yellow and magenta respectively.
  • white light impinges upon the mix all particles migrate, leaving behind the color of the white or transparent substrate. No exposure leaves behind all pigments which combine to produce a black image.
  • All pigments which have a relatively large particle size as received commercial or is made are ground in a ball mill for about 48 hours to reduce their size in order to provide a more stable dispersion and improve the resolution of the final images.
  • measurements of resistivity of insulating materials are made according to ASTM D257-6l methods.
  • TheLexan film blocking electrode surface is then replaced with a fresh piece of Lexan film.
  • Eight images are successively produced as described above, except in this instance after each cleaning step the blocking electrode is rotated slowly for about 30 seconds in contact with a metal brush coupled to the same potential as the blocking electrode of the sort shown in FIG. 3. The eight images produced are then compared. All eight images are of substantially uniform high quality with excellent color balance.
  • Example III A blocking electrode and a pigment tri-mix are prepared as in Example I.
  • the imaging tests of Example I are repeated except that after each cleaning step, the blocking electrode is rotated slowly for about 1 minute adjacent a DC corona discharge unit.
  • the DC discharge wire is held about onefourth inch from the blocking electrode surface and is maintained at a negative potential of about 5,000 volts.
  • the surface of the blocking electrode is continuously electrometered and DC corona discharge is stopped when the charge on the blocking electrode surface is substantially eliminated or is slightly negative.
  • the eight images produced by successive imaging operations utilizing the DC corona discharge after each image is formed are then compared. They are found to be of uniform high color quality and excellent color balance.
  • EXAMPLE IV The experiments of Examples l and II are repeated using a blocking electrode which consists of a metal core having a diameter of about 2 V1 inches which has on the surface thereof a 2 mil Mylar (polyethylene terephthalate available from E.I. duPont de Nemours & Company) film.
  • the eight images produced as in Example I, with no treatment of the blocking electrode surface other than cleaning between image operations show a gradual definite decrease in image quality with successive images. A loss in density in blue image areas is immediately noticeable. With further images an overall density loss and shift towards the magenta is observed.
  • the images produced as in Example I with charge elimination from the blocking electrode surface after each cleaning step by means of the conductive brush, the images produced are of substantially uniform high quality with consistently good color balance and image density.
  • a blocking electrode in roller configuration is prepared consisting of a metal core surrounded by carbon black filled rubber having a volume resistivity of about ohm-centimeters and having on the surface a 2 mil Tedlar (a polyvinyl fluoride material from El. duPont de Nemours & Company) film as the blocking electrode surface.
  • a tri-mix is prepared as in Example I and coated onto the NESA injecting electrode to a thickness of about 3 mils.
  • a negative potential of about 3,000 volts is imposed on the core of the blocking electrode roller and the roller is rolled across the injecting electrode surface while the suspension is exposed to an image from a conventional Kodachrome transparency. When the blocking electrode roller has passed beyond the injecting electrode surface, potential application and image exposure are stopped.
  • the blocking electrode surface is then cleaned.
  • the image produced on the injecting electrode is observed to be of excellent quality and good color balance.
  • the image is transferred to a receiving sheet and the coating, imaging, cleaning and transfer steps are repeated seven additional times.
  • the average time between the imaging steps is about 20 seconds.
  • the images produced by the successive imaging steps are then compared. A gradual loss in color density is observed with succeeding images.
  • the Tedlar film blocking electrode surface is then replaced with a fresh piece of Tedlar film. Eight images are successively produced as described above, except in this instance, there is a delay of about 10 minutes between imaging operations.
  • the eight images produced are then compared. All images are of good quality. Since Tedlar has a volume resistivity of about 10 ohm-cm., it is apparent that substantially all of the charge built-up on the blocking electrode surface during the imaging operation is able to leak away during the 10 minute delay between the imaging operations.
  • EXAMPLE VI The experiments of Examples l and II are repeated except that in this instance a monochromatic imaging suspension is used and the image is exposed to a black-and-white image.
  • the uni-mix consists of about 7 parts 2,4,6-tris(N-ethyl-N- hydroxyethyl-p-amino-phenylazo) phluoroglucinol prepared as described in copending application Ser. No. 473,607, filed July 21, 1965, dispersed in about parts lsopar-G.
  • This suspension is then imaged as described in Examples 1 and ll. With no treatment to eliminate charge build-up between imaging steps, image quality steadily decreases with succeeding images. Principally, a drastic fall off in image density is observed. Where the build-up of undesired charge is eliminated either by use of the conductive brush as in Example I or by the corona discharge as in Examples II and III, the images produced are of consistently high quality with little or no loss of image density in succeeding images.
  • EXAMPLE Vll The experiments of Examples l and ll are repeated except that here a different tri-mix is used.
  • a mixture of photosensitive pigments is prepared by mixing equal parts of a cyan pigment, Methyl Violet, C.l. No. 42535, a phosphotungstomolybdic acid lake of 4(N,N',N-trimethyl anilino)-methylene-N", N"-dimethyl anilinium chloride, available from Collway Colors; magenta pigment, Naphtho Red B, C.l. No.
  • EXAMPLE Vlll A blocking electrode in roller configuration is prepared as in Example 1, except that the surface layer consists of Teflon FEP (a fiuorinated ethylene-propylene copolymer available from E. I. duPont de Nemours & Company), film having a thickness of about 3 mils.
  • a tri-mix is prepared as in Example I, but is coated to a thickness of about 3 mils onto the blocking electrode surface instead of onto the NESA electrode. Twenty-four images are produced, using this configuration, as described in Examples I and II. Where there is no treatment of the blocking electrode to eliminate charge build-up there is a gradual, definite loss of image quality with succeeding images. Where charge build-up is eliminated by grounding an A.C. corona treatment of the blocking electrode between imaging operations, image quality remains high through each set of 8 succeeding images.
  • the photosensitive particles may be dye sensitized or electrically sensitized if desired, or be mixed with any other photosensitive materials both organic and inorganic.
  • said photosensitive particles comprise cyan colored particles primarily responsive to red light, magenta colored particles primarily sensitive to green light and yellow colored particles primarily responsive to blue light and said image formed is a subtractive polychromatic images.
  • said blocking electrode has a resistivity of from about 10 to l0 ohm-centimeters.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
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  • General Physics & Mathematics (AREA)
  • Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)
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  • Wet Developing In Electrophotography (AREA)
US60675A 1967-03-28 1970-08-03 Removing undesired potential from the blocking electrode in a photoelectrophoretic imaging system Expired - Lifetime US3676313A (en)

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US62691767A 1967-03-28 1967-03-28
US6067570A 1970-08-03 1970-08-03

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AT (1) AT293167B (enrdf_load_stackoverflow)
BE (1) BE712785A (enrdf_load_stackoverflow)
CH (1) CH489042A (enrdf_load_stackoverflow)
FR (1) FR1558168A (enrdf_load_stackoverflow)
GB (1) GB1225369A (enrdf_load_stackoverflow)
LU (1) LU55754A1 (enrdf_load_stackoverflow)
NL (1) NL6804232A (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3776628A (en) * 1969-06-02 1973-12-04 Xerox Corp Photoelectrophoretic imaging system
US3961949A (en) * 1972-01-03 1976-06-08 Xerox Corporation Photoelectrophoretic imaging method producing a desired image border
US3967960A (en) * 1974-10-21 1976-07-06 Xerox Corporation Photoelectrophoretic imaging process employing dark charge injecting element
US3967961A (en) * 1974-12-04 1976-07-06 Xerox Corporation Photoelectrophoretic imaging process employing a dark charge injecting agent - alkyd resin coating
US3972717A (en) * 1973-03-21 1976-08-03 Hoechst Aktiengesellschaft Electrophotographic recording material
US3980477A (en) * 1974-11-26 1976-09-14 Xerox Corporation Photoelectrophoresis with dark charge injecting element

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2945434A (en) * 1959-07-02 1960-07-19 Haloid Xerox Inc Sheet feed mechanism
US3013878A (en) * 1955-12-29 1961-12-19 Xerox Corp Method and apparatus for transferring and fixing xerographic images
US3384565A (en) * 1964-07-23 1968-05-21 Xerox Corp Process of photoelectrophoretic color imaging
US3449568A (en) * 1966-12-27 1969-06-10 Xerox Corp Corona discharge apparatus for creating an electrostatic charge pattern on a xerographic surface
US3532494A (en) * 1969-09-08 1970-10-06 Gopal C Bhagat Solid area development in xerography employing an insulating screen in the charging step

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3013878A (en) * 1955-12-29 1961-12-19 Xerox Corp Method and apparatus for transferring and fixing xerographic images
US2945434A (en) * 1959-07-02 1960-07-19 Haloid Xerox Inc Sheet feed mechanism
US3384565A (en) * 1964-07-23 1968-05-21 Xerox Corp Process of photoelectrophoretic color imaging
US3449568A (en) * 1966-12-27 1969-06-10 Xerox Corp Corona discharge apparatus for creating an electrostatic charge pattern on a xerographic surface
US3532494A (en) * 1969-09-08 1970-10-06 Gopal C Bhagat Solid area development in xerography employing an insulating screen in the charging step

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3776628A (en) * 1969-06-02 1973-12-04 Xerox Corp Photoelectrophoretic imaging system
US3961949A (en) * 1972-01-03 1976-06-08 Xerox Corporation Photoelectrophoretic imaging method producing a desired image border
US3972717A (en) * 1973-03-21 1976-08-03 Hoechst Aktiengesellschaft Electrophotographic recording material
US3967960A (en) * 1974-10-21 1976-07-06 Xerox Corporation Photoelectrophoretic imaging process employing dark charge injecting element
US3980477A (en) * 1974-11-26 1976-09-14 Xerox Corporation Photoelectrophoresis with dark charge injecting element
US3967961A (en) * 1974-12-04 1976-07-06 Xerox Corporation Photoelectrophoretic imaging process employing a dark charge injecting agent - alkyd resin coating

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DE1772060B2 (de) 1975-08-07
LU55754A1 (enrdf_load_stackoverflow) 1968-11-29
BE712785A (enrdf_load_stackoverflow) 1968-09-26
DE1772060A1 (de) 1971-01-21
FR1558168A (enrdf_load_stackoverflow) 1969-02-21
NL6804232A (enrdf_load_stackoverflow) 1968-09-30
CH489042A (de) 1970-04-15
AT293167B (de) 1971-09-27
GB1225369A (enrdf_load_stackoverflow) 1971-03-17

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