Patent Publication Number: US-3876917-A

Title: Electrostatic charging apparatus

Description:
United States Patent [191 Gaynor et al.  
 [5 1 ELECTROSTATIC cnARgiNG APPARATUS [75] Inventors: Joseph Gaynor, Cleveland. Ohio;  
 Walter Hines, Sierra Madre, Calif.  
 [73] Assignee: Bell &amp; Howell Company, Chicago,  
 Ill.  
  22 Filed: Mar. 26, 1973 211 Appl.No.:345,035  
 [&#39;52] US. CL 317/262 511 I t. Cl G03g 15/02 [58] Field of Search 317/2, 3, 4, 262 A [56] References Cited UNITED STATES PATENTS 3.546.545 l2/l97l Sato et al 317/262 A i 1 Apr. 8, 1975 3,626,260 12/197] Kirnljra et al. 3l7/262 A Primary E.\&#39;aminerL. llik Attorney, Agent, or Firm-Robert A. Walsh 7] ABSTRACT 9 Claims, 2 Drawing Figures PATENTEUAPR 8 ms ELECTROSTATIC CHARGING APPARATUS The present invention relates to an apparatus for applying an electrostatic charge to a photoconductive member as usually found in electrostatic image transfer and reproduction systems. More specifically, it relates to an apparatus for charging or polarizing a photoconductive member by supplying sufficient contact area between the member and a properly electrically conductive surface. I  
  In the electrophotographic arts, it is customary to form electrostatic images on photoconductive members by first imposing an electrostatic charge pattern on the surface of the photoconductive member and then exposing the precharged surface to a pattern of activated radiation, corresponding to a desired image, to selectively dissipate the charge in a manner consistent with the image transferred.  
  A variety of photoconductive members have become widely accepted for use in electrophotographic processes. It is known, for example, that suitable photoconductive members can be constructed from a&#39;web of foil or paper containing a lacquer coating of a photoconductive pigmentfsuch as zinc oxidedispersed in a resin binder. I  
  In any case however, during the elec trophotographic process, an electrostatic charge is imposed on the surface of the photoconductive member before the member is exposed to a radiation image. Consequently, to reduce production costs and to increase product efficiency, it is highly desirable that the photoconductive member] which carries the electrostatic charge be charged in as short a time as possible, while ensuring that complete polarization is effected.  
  previous methods and apparatus for pre-charging a photoconductive member such as zinc oxide paper have included imposing approximately a 5K volt charge across-a sandwich&#34; consisting of zinc oxide paper surrounded by polycarbonate. or polyethylene terephthalate based polyesters in roll or magazine form. ln this arrangement, the zinc oxide paper &#39;was observed to acquire a substantial charge after only rather short polarization times. However, this sandwich construction has provedto&#39;be rather cumbersome, since&#39;they must be partially disassembled in order to feed a sheet of zinc oxide paper. In addition, the amount of current needed for polarization was in the milli-amp range, which amounts to a relatively substantial power drain.  
  It is an object of the presentinvention. to provide an apparatus for applying an electrostatic charge to a photoconductive member in a relatively shorter period of time than is possibleusing known devices.  
 &#39; It is an additional object of the present invention to provide an apparatus for applying an electrostatic charge to a photoconductive member with a minimum electrical power drain.  
 Still another object of the present invention is to provide an apparatus for providing sufficient surface contact area between a photoconductive member, an insulating material, and an electrical conductive element while applying an electrostatic charge to the photoconductive member.  
  Yet a further object of the present invention is to provide a sandwich type electrostatic charging device wherein only one outer element of the sandwich construction includes an insulating material.  
  In a first embodiment of the invention, a photoconductive member, such as a zinc oxide coated sheet, is passed between adjacent runs of a pair of endless conveyor belts providing a contact area at least as large as the photoconductive member itself. One of the belts is coated with an insulating material which is in full contact with the zinc oxide layer on the photoconductive member. An electric charge is applied across the conveyor belts, which is transferred to the photoconductive member.  
  In a second embodiment, a substantial portion of the periphery of a rotative dru m having a conductive outer surface and covered with an insulating material comes into adjacent contact with a flexible conductive belt. The photoconductive element is adopted to pass between the belt and the insulating material on the drum, with the contact area between belt and drum being at least equal in area to that of the photoconductive element. With the element so located, an electric power source is connected between the drum and the conductive belt, and an electric charge is imposed on the photoconductive element.  
  Additional objectives and advantages of the present invention will become apparent from the following description of the embodiments of the invention, and with reference to the accompanying drawings in which:  
  FIG. 1 is a schematic-mechanical diagram of the two conductive conveyor belts and photoconductive element comprising the first embodiment of the invention; and  
  FIG. 2 is a schematic-mechanical diagram of the drum and belt configuration comprising the second em bodiment of the present invention.  
  Referring first to FIG. 1, there is shown a first electrically conductive movable surface comprising conveyor belt 10, and a second electrically conductive movable surface comprising conveyoi belt 12. In the preferred configuration of this embodiment, the outer surface of belt 10 is coated with a layer of insulating material 14 which may be either a polycarbonate or polyethylene I terephthalate based polyester, known in the trade as Mylar.&#34; If desirable, the outer surface of belt 12 may also be coated with a layer of insulating material 14, although that configuration is not illustrated.  
  The conveyor belt 10 passes endlessly around a set of rollers l6, 18 which are composed of an electrically conductive material. Likewise, conveyor belt 12 passes endlessly around a set of electrically conductive rollers 20,22. Suitable mechanical. power means are connected to one or more of the rollers to drive the belts l0, 12 in the direction shown by arrows 24 in FIG. 1. Also, a source of electrical voltage 26 is applied across one of the rollers 18, which supports conveyor belt 10,  
 and roller 22, which supports conveyor belt 12. hasmuch as the rollers 18 and 22, and belts 10 and 12 are electrically conductive, an&#39;electrical circuit is formed between the adjacent runs 28, 30 of belts 10,12, re-  
  spectively, which runs are in intimate contact with each the present inventive concept, the width of conveyor belts l0, 12 is at least equal to the width of web member 32 to provide sufficient contact area between conveyor belts l0, l2, and web member 32.  
  To further insure proper electrical contact between conveyor belt and insulating material 14, an additional conductive coating 38 such as a film of evaporated aluminum is placed between the belt and the insulating material.  
  In operation, mechanical power is applied to one of rollers l6, l8 and to one of rollers 20, 22 to drive conveyor belts in the direction indicated by arrows 24. As shown in FIG. 1, the lower run 28 of belt 10 and the upper run 30 of belt 12 are in intimate contact with each other throughout their length and width. The layer of insulating material 14 covering belt 10 comes into direct contact with upper run 30 of belt 12.  
 &#39; In the present invention, a sufficient contact area is provided between belts 10 and 12, enabling the dyna&#39;micpolarization (electrostatic charging) of web material 32, which is coated with a photoconductive material such as zinc oxide, without the need for a complex roll or magazine sandwich structure. The web material 32 is fed into the nip created between rollers 16 and 20, and is carried between conveyor belts 10 and 12 until it passes completely between rollers 18, 22. Belts l0 and 12 have a mutual contacting area at least equal to the length of web material 32, and the width of the contacting area is also at least equal to the width of the web material.  
  As the web material 32 passes between belts l0 and 12, an electrical voltage in the range of 4-5K volt is applied across the belts through rollers 18, 22 and source 26. As the web 32 passes between belts I0, 12 an electrostatic charge is deposited on the photoconductive 1 layer 36 of the web.  
  Two methods of applying a charge to the web material32may be utilized in conjunction with the disclosed first embodiment of the invention. First, the sheet of web material 32 could already be in the charging apparatusbe&#39;tween runs 28 and 30 of conveyor belts l0 and 12, respectively, so that when the apparatus and the electrical&#39;voltage were turned on, the web material would be charged as it moved through the apparatus.  
 &#34;&#39;For subsequent copies, additional sheets of web material 32 are fed into the nip formed by rollers 16 and 18 as required. In this way, a piece of web material 32 would always be left in the apparatus. By using this method, voltages measured on the surface of web material 32 are well within the range required to produce eminently satisfactory electrophotographic images and agree substantially with preconceived dynamic meastion with the first method of use were also found to be evident when the second method of operation was employed.  
  The second embodiment of the present invention is disclosed in FIG. 2, and includes a rotatable drum 40 composed of an electrically conductive material. The  
 drum is circumferentially covered with a layer of insulating material 42 which may be either a polycarbonate or polyethylene terephthalate based polyester, known in the trade as Mylar. Between drum and insulating layer 42, an additional coating of conductive material such as a film of evaporated aluminum is applied to enhance the electrical conductivity of the system.  
  An endless conductive flexible belt 46 passes over rollers 48, 50, 52, and 54, with a portion 56 of the belt in intimate contact with a substantial portion of the layer of insulating material 42 surrounding drum 40. Belt 46 may or may not be insulated. The linear peripheral distance covered by the portion 56 of belt 46 is at least as long as the photoconductive web material 32 which is intended to be charged by the apparatus, and width of the drum 40 and belt 46 is sufficient to cover the entire width of web material 32. Therefore, the area of contact between portion 56 of belt 46, and drum 40 covers the entire surface area of sheet material 32.  
  A source of electrical voltage 26 is applied between drum 40 and belt 46. As web material 32 is fed between the nip formed between roller 48 and insulating layer 42, it is held firmly between drum 40 and portion 56 of belt 46. The potential difference between belt 46 and drum 40 causes an electrostatic charge to be applied to the surface of web material 32 in the manner described in connection with the operation of the embodiment disclosed in FIG. 1. Sufficient contact is afforded between drum 40, belt 46, and web material 32 to perfect charging (or polarization) of the web material with a current drain in the microamp range.  
  Various other modifications and variations may be made to the disclosed apparatus without departing from the spirit and scope of the present invention. Therefore, the invention disclosed is not to be limited to the illustrated embodiments, except as defined by the appended claims:  
 What is claimed is:  
  1. An apparatus for electrostatically charging a photoconductive member having a photoconductive layer and a substrate carrying said layer including:  
 a first movable electrically conductive surface, a  
 layer of insulating material applied to said first surface,  
 a second movable electrically conductive surface in intimate contact with a substantial portion of said layer of insulating material on said first movable surface, said first surface and said layer of insulating material on said second surface contacting each other over a specified area, said member being of a size substantially approximating the size of said area and adapted to pass between said layer of insulating material and said second movable surface in intimate contact therewith, whereby the whole of said member unitarily passes between said substantial portion of said insulating layer and said second movable surface, and a source of electrical voltage connected across said first and second movable surfaces whereby the entire area of said member is electrostatically charged simultaneously as it passes between said movable surfaces. 2. The apparatus of claim I wherein said photoconductive layer on said member is zinc oxide.  
  3. The apparatus of claim I wherein said insulating material is selected from the group consisting of polycarbonate and polyethylene terephthalate based polyesters.  
 4. The apparatus of claim 3 wherein said second movable surface has a layer of insulating material applied thereto;  
  5. The apparatus of claim 4 wherein said insulating material applied to said second movable surface is selected from the group consisting of polycarbonate and polyethylene terephthalate based polyesters.  
  6. The apparatus of claim 1 wherein a conductive coating is disposed between said first movable surface and said layer of insulating material to assure satisfactory electrical contact between said first movable surface and said layer of insulating material.  
  7. The apparatus of claim 6 wherein said conductive coating is an evaporated aluminum film.  
  8. An apparatus for electrostatically charging a photoconductive member having a photoconductive layer and a substrate carrying said layer including:  
 a first conveyor belt having the property of electrical conductivity rotatively disposed around a first pair of rollers having at least one substantially linear run,  
 a layer of insulating material applied to said first conveyor belt having the property of electrical conductivity rotatively disposed around a second pair of rollers having at least one substantially linear run,  
 said substantially linear run of said first belt and said insulating material disposed in adjacent contact with said substantially linear run of said second belt over a specified area,  
 said photoconductive member being of a size substantially approximating the size of said area and adapted to pass between said substantially linez run of said insulating material and said second cor veyor belt in intimate contact therewith, a source of electrical voltage connected across sai 5 first and second conveyor belts whereby the entii area of said member is electrostatically charged s multaneously as it passes between said conveyc belts. 9. An apparatus for electrostatically charging a phi toconductive member having a photoconductive layc and a substrate carrying said layer including:  
 rotatable drum means having an electrically COlldUt tive outer surface, a layer of insulating material applied to said out:  
  surface of said drum, endless belt means having a portion thereof in int mate contact with a substantial portion of sai layer of insulating material on said drum over specified area, said member being of a size substantially approxima ing the size of said area and adapted to pass b1 tween said insulating material and said belt meat in intimate contact therewith whereby the entii area of said member unitarily passes between sai substantial portion of contact between said insula ing material and said belt means, and a source of electrical voltage connected across sai drum means whereby the entire area of said men her is electrostatically charged simultaneously as passes between said drum means and said be means.