CA1115334A - Electrographic element provided with electrical connection means - Google Patents

Abstract

ELECTROGRAPHIC ELEMENT PROVIDED WITH
ELECTRICAL CONNECTION MEANS

Abstract of the Disclosure An electrographic element comprising an electri-cally insulating support, an electrically conductive layer overlying the support, and an electrically insulating photo-conductive layer overlying the conductive layer, is provided with electrical connection means adapted to establish electri-cal connection between the conductive layer and a grounding or biasing member which engages a surface of the element while the element is in motion. The electrical connection means comprises a region of dispersed particulate electrically-conducting material within a non-recording portion of the element which extends from the surface of the element into contact with the conductive layer. This region defines on the surface of the element an elongated stripe which is longi-tudinally disposed in the direction of motion of the element and which encompasses an elongated longitudinally disposed groove. To form the region of dispersed particulate electri-cally-conducting material, an elongated groove extending from the surface of the element at least to a position proxi-mate to the conductive layer is formed in the element and an imbibable composition comprising the particulate material is then applied to the surface of the element as an elongated stripe which encompasses the groove. The groove serves to promote the imbibition of the particulate material into contact with the conductive layer so as to form an electrical path from the conductive layer to the stripe on the surface of the element and thus provide electrical connection with the grounding or biasing member which engages the stripe.

Description

~115334 ELECTROGI~APHIC EI.EMENT PROVIDED WITH
ELECTRICAL CONNECTION MEANS
BACKGROUND OF THE INV~r~TION
1. Field Of The Invention This invention relates in general to electro-photography and in particular to an electrographic element provided with novel electrical connection means~ to a method of forming such connection means, and to an electro-graphic copier utilizing such electrographic element. More 10 specifically, this invention relates to an electrographic element comprising an electrically insulating support, an electrically conductive layer overlying the support, and an electrically insulating photoconductive layer overlying the conductive layer, and to a method of providing electrical 15 connection means within such element, which means are adapted ; to establish electrical connection between the conduc-tive layer of the element and a grounding or biasing memDer which engages a~surface of the element during use of the element within the copier.
20 ? _ Description Of The Prior Art A common type of electrographic element is an element comprising an electrically insulating support, an electrically conductive layer overlying the support, and an electrically insulating photoconductive layer overlying the 25 electrically conductive layer. The photoconductive layer contains a normally insulating material whose electrical resistance varies with the amount of incident electromagnetic radiation it receives during an imagewise exposure. A wide variety of materials can be used as the support for such 30 elements, for example, the support can be composed of paper or of a polymeric sheet material. The electrically conduc-tive layer can be a separate layer or a part of the support layer and can be formed from a wide variety of materials, such as a thin metal foil, a vapor deposited metal layer, a dis-35 persion of a semiconductor in a resinous material, or anelectrically conducting salt. The electrographic element can be opaque or transparent, depending upon the intended mode of use.

- ~ i , ~' In use, the electrographic element is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of dif-5 ferentially reducing the potential of this surface chargein accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electro-graphic element is then made visible by contacting the surface 10 with a suitable electroscopic marking material. Such marking material,or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern, or the absence of charge pattern, as desired. Deposited marking material 15 can then be either permanently fixed to the surface of the - element by known means such as heat, pressure, solvent vapor, or the like, or transferred to a second element to which it can similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed-; 20 there.
The function of the electricall~ conducting layerin electrographic elements is to create a highly conducting reference plane which ideally is held at or near ground poten-tial. During charging of the photoconductive layer with a 25 corona charger, the potential of the conducting layer has a tendency to build up with respect to ground if it is not grounded. Typically, if the surface of the photoconductive layer is charged to 600 volts, the potential of an ungrounded conducting layer can vary from about 50 to about 450 volts or 30 more. Thus, the differential between the conducting layer and the photoconductive layer may range from about 150 volts to about 550 volts. In this situation, when the charging step is completed and the surface of the element is exposed to a pattern of actinic radiation, the photoconductive layer becomes 35 conducting in the light-struck regions and the potential of the surface of the photoconductive layer in these areas approaches that of the conducting layer. Because of the small difference in potentials which may exist between areas struck by light and those not struck, little or no latent image is produced.

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Similarly poor results are obtained when the conducting layer is inefficiently grounded. Conventional grounding methods, such as metal strips, rollers, etc.
placed in electrical contact with the element may be satis-5 factory in those systems where the element is charged whilestationary but are often ineffective when used in those systems wherein the element is charged while in motion.
Direct electrical contact with the conducting layer for gro~nding purposes is very difficult and inefficient when, 10 as is usually the case, it is extremely thin, e.g., a few hundred ~ngstroms, and creates wear problems if the element is contacted for grounding while in motion. Ideally, during charging of the photoconductive layer, the electrically con-ducting layer should be held at ground potential to insure 15 that the maximum charge be impressed and stored in the photo-conductive layer.
Conducting lacquers such as those described in U. S.
Patent 3,639,121, issued February 1, 1972 to W. C. York, can be used to aid in maintaining electrically conducting layers at ground potential. However, these materials should be applied directly to the electrically conducting layer, i.e., to an exposed portion of the layer. This is accomplished~by either applying it to the edge of the element or, if the conducting layer is set off so that a portion of its surface is exposed, by applying the lacquer to the exposed surface.
Thus, the modes of application are somewhat limited, particu-larly if the conducting layer is inaccessible.
An alternative approach to providing electrical connection means in electrographic elements is that described in U. S. Patent 3,684,503, issued August 15, 1972 to W. D.
Humphriss et al. In this method, a particulate electrically-conducting material is imbibed into the element to form a dis-persion extending from the surface of the element through the overlying layer or layers and into contact with the electri-cally conductive layer, thereby forming an electrical pathfrom the surface to tAe electrically conductive layer which can be utilized in grounding the element. The method of U. S.
Patent 3,684,503 is very effective with many electrographic elements but is limited in regard to the range of electro-graphic elements to which it is applicable. Thus, for example, 33~

if the photoconductive layer overlying the conductive layeris thick, or if there are several contiguous photoconductive layers, or if there are overcoat and/or subbing layers and/or interlayers in addition to one or more photoconductive layers, then the total thickness of material overlying the conductive layer can be so great as to prevent the electrically-conductive particulate material from being imbibed all the way from the surface of the element to the conductive layer and thereby render the method of U. S. Patent 3,684,503 inoperative.
Moreover, even though the total thickness of material over-lying the conductlve layer may not be so great as to preclude imbibition from the surface because of the depth of imbibition needed, if one or more of the layers overlying the conductive layer contains a tough polymeric binder which strongly resists imbibition, then the method may again be rendered inoperative.
Other ~rocedures for the formation of electrical connection means in electrographic elements are also known.
For example, British Patent No. 1,490,001, published October 26, 1977, describes a method in which electrical connection means is provided by forming a hole in a non-image area of the element extending from the outer surface to at least the electrically conductive layer and inserting in the hole an electrically-conductive composition comprising an adhesive and a pigment in an amount sufficient to completely fill the hole. Preferably, a piece of metallic foil is utilized to cover the exposed adhesive composition in the hole and provide a suitable surface for contact with an electrode. This patent also discloses that a channel can be formed in place of the hole and the electrically-conductive composition can be inserted into the channel. A similar disclosure is provided in U. S.
Patent 3,743,410, issued July 3, 1973 to R. I. Edelman et al, which describes an electrographic element adapted to be grounded while in motion which includes a channel in the photoconductive layer exposing the underlying conductive layer and an electrically-conductive material that has been inserted into the channel. In comparison with these procedures, the method of this invention is much better suited to use in production operations carried out on a commercial scale in view of its simplicity and adaptability to high speed manu-4 facturing operations.

SUMMA~Y OF 'l`~IE INVENT:[ON
The present inve~tion provides improved electrical connection means within an electrographic element, which means are adapted to establish electrical connection between a con-5 ductive layer of the element and a grounding or biasingmember which engages a surface of the element while the ele-- ment is in motion. The electrographic element is comprised of an electrically insulating support, an electrically con-duc~ive layer overlying the support, and an electrically 10 insulating photoconductive layer overlying the conductive layer and the electrical connection means comprises a region of dispersed particulate electrically-conducting material within a non-recording portion of the element which extends from the surface of the element into contact with the conductive 15 layer. This region defines on the surface of the element an elongated stripe which is longitudinally disposed in the direc-tion of motion of the element and which encompasses an elongated longitudinally disposed groove. To form the region of dispersed particulate electrically-conducting material, an elongated groove 20 extending from the surface of the element at least to a position proximate to the conductive layer is formed in the element and an imbibable composition comprising the particulate material is then applied to the surface of the element as an elongated stripe which encompasses the groove. The groove serves to promote the 25 imbibition of the particulate material into contact with the conductive layer so as to form an electrical path from the conductive layer to the stripe on the surface of the element and thus provide electrical connection with the grounding or biasing member which engages the stripe.
The electrographic element of this invention is adapted for use in an electrographic copier in which it is moved through a plurality of processing stations including an exposure station to form a visible image and in which the copier includes a grounding or biasing member for applying a 35 reference potential to the conductive layer o~ the element during movement of the element through the exposure station.
Means are provided within the copier for positioning the ele-ment during movement of an image area thereof through the exposure station to maintain effective contact between the 40 grounding or biasing member and the stripe on the surface Of I the element, thereby connecting the reference potential to the conductive layer.

. -5-~llS334 BRIEF` DL~SCRIPTION OF T~IE DRAWINGS
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FIG. 1 is a schematic representation of an electrographic copying apparatus employing the improved electrographic element of this invention.
FIG. 2 is a face view of a portion of an electro-graphic element having electrical connection means in accor-dance with this invention disposed along one edge thereof and a row of perforations disposed along the opposite edge.
FIG, 3 is a face view of a portion of an electro-graphic element having electrical connection means in accor-dance with this invention disposed along both edges thereof.
FIG. 4-a is a cross sectional view taken along the line 4-4 in FIG. 2 illustrating the electrical connection means.
FIG. 4-b is a cross sectional view of an alterna-tive embodiment of the electrical connection means.
FIG. 4-c is a cross sectional view of a further alternative embodiment of the electrical connection means.
FIG. 5 is a cross sectional view illustrating the electrical connection means of this invention in an alterna-tive embodiment of the electrographic element.
FIG. 6 is a cross sectional view illustrating the electrical connection means in contact with a grounding or biasing member of an electrographic apparatus.
FIG, 7 is a schematic illustration of the cutting of an elongated groove and formation of a conductive stripe in an electrographic element in accordance with this invention.
~IG. 8 is a schematic illustration of an alternative procedure for cutting the elongated groove in an electrographic element.
DESCRIPTION OF THE PREFERRED E~BODIMEMTS
The present invention is characterized by the usein combination of an imbibable composition containing particu-late electrically-conducting material and a groove which extends from a surface of the electrographic element at least into proximity with the conductive layer of the element. This combination provides very effective electrical connection means under a wide variety of circumstances. For example, the function ~l~S334 o~ the groove in promoting the imbibition of the particulate material into contact with the conductive layer renders the method effective with electrographic elements having one or more layers overlying the conductive layer which together are of such substantial thickness as to render it impossible to imbibe the particulate material all the way from the sur-face of the element to the conductive layer. Moreover, it also enables the method to be used with electrographic elements in which a photoconductive layer, or other layer that overlies the conductive layer, is comprised of a tough polymeric binder which is so resistant to imbibition of particulate material as to render it impossible to imbibe the particulate material all the way from the surface of the element to the conductive layer. The method of the present invention can be readily varied to render it especially suitable for the particular electrographic element involved. Thus, when the element is one which is moderately susceptible to penetration by ~mbibition, the groove can be relatively shallow as long as it is of sufficient depth to enable the particulate material to make good contact with the conductive layer. Under particular circumstances, it may be desirable to form the groove with a depth such that only a very slight thickness of mate~ial overlies the con-ductive layer, or to form the groove with such a depth that the conductive layer is exposed but not penetrated, i.e., all overlying material is removed, or to form the groove with such a depth that it extends into the conductive layer or through the conductive layer and into the underlying material.
Any of these techniques can be successfully utilized in carrying out the present invention.
Turning now to FIG. 1, there is schematically shown an electrographic copying apparatus 1 comprising an electrographic element 2 in the form of an endless belt configured for movement along an endless path past various operative stations of the apparatus. As shown in FIG. 4, the electrographic element 2 is a layered structure comprising an electrically insulating support 3, an electrically conductive layer 4 overlying support 3, and an electrically insulating photoconductive layer 5 overlying conductive layer 4. The conductive layer 4 is electrically connected to ground or other selected reference potential source by engagement of element 2 with metal bristle brush 6.

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Operati~e stations of the apparatus 1 include a primary charging station at which corona discharge device 7 applies an overall charge to the external surface of photoconductive layer 5. After receiving the primary charge, 5 an image se~ment of electrographic element 2 advances past the exposure station 8 where the segment is imagewise exposed to light patterns of a document to be copied by xenon lamps or other known imaging apparatus. Rollers 16 serve to con-vey electrographic element 2 past the operative stations and 10 properly position it during movement of the image segment through exposure station 8 to maintain effective contact between brush 6 and the surface of electrographic element 2.
The electrostatic image residing on the image segment after passage through exposure station 8 is next advanced over a 15 magnetic brush or other development station 9 where toner is attracted to the charge pattern corresponding to dark image areas of the document. The developed image is then advanced to a transfer station 10 where the toner image is transf`erred by the action of corona discharge device 12 to pap-er which is 20 fed from supply 11. The paper bearing the toner image is then transported through a fixing station 13, for example, a roller fusing device, to a bin 14. In the meantime, the segment from which the toner is transferred advances past a cleaning station 15 in preparation for another copy cycle.
Referring now to FIG. 2, electrographic element 2 is shown to include a row of perforations 17 adjacent to one side thereof and electrical connection means 18 adjacent to the opposite side thereof. Electrographic element 2, provided with perforations 17, is especially adapted for use in an 30 electrographic copying apparatus of the type described in U. S. Patent 3,914,047 issued October 21, 1975 to W.`E. Hunt, Jr, et al. The perforations 17 are utilized to generate control timing signals for synchronizing machine functions as described in detail in U. S. Patent 3,914,047. Electrical 35 connection means 18 comprises a region of dispersed particulate electrically-conducting material, within a non-recording ; portion of electrographic element 2, which extends from th_ surface of electrographic element 2 and, as shown in FIG. 4, reaches into contact with electrically conductive layer 4.
4 The dispersed particulate electrically-conducting material can be any suitable material such as, for example, carbon I
' 11~S334 black or graphite particles. The region of dispersed particu late electrically-conducting material defines on the surface of electro~raphic element 2 an elongated stripe 19 which is longitudinally disposed in the direction of motion of electro-5 graphic element 2 and which enco~passes an elongated longitu-dinally disposed groove 20.
In the alternative embodiment of electrographic element 2 which is shown in FIG. 3, there is provided a second electrical connection means 21 comprising a region of 10 dispersed particulate electrically-conducting material which extends into contact with electrically conductive layer 4 and which defines an elongated longitudinally disposed stripe 22 which encompasses an elongated longitudinally disposed groove 23. In electrical connection means 21, contact of the dispersed 15 particulate electrically-conducting material with conductive layer 4 is achieved both as a result of the presence of groove 23 and as a result of contact with the exposed edges of conduc-tive layer 4 within each of perforations 17.
Referring now to parts (a), (b) and (c) of FIG. 4, 20 there are shown alternative embodiments of electrical connec-tion means 18. In each of these embodiments groove 20 extends frcm the exterior surface of electrographic element 2 at least to a position proximate to conductive layer 4. In the embodi-ment of part (a), groove 20 terminates a short distance above 25 the upper surface of conductive layer 4 and the dispersed particulate electrically-conducting material has traveled by a process of imbibition from the bottom of groove 20 into contact with conductive layer 4. In the embodiment of part (b), groove 20 is of a depth such as to expose conductive 30 layer 4, that is, it terminates at the upper surface of con-ductive layer 4. Dispersed particulate electrically-conductive material is in contact with conductive layer 4 at the bottom of groove 20 and also as a result of its lateral movement into photoconductive layer 5 by a process of imbibition. In the 35 embodiment o~ part (c), groove 20 extends completely through conductive layer 4 and into support 3. Dispersed particulate electrically-conductive material is in contact with conductive layer 4 at its exposed edges 24 and 24' within groove 20 and also as a result of its lateral movement into photoconductive 40 layer 5 by a process of imbibition.

FIG. 5 shows an alternative embodiment of electro-graphic element 2 which includes a subbing layer 25 between electrically conductive layer 4 and photoconductive layer 5 and a protective overcoat layer 26 over photoconductive layer i 5. In this embodiment, groove 20 extends from the surface of electrographic element 2 through each of overcoat layer 26, photoconductive layer 5, subbing layer 25, and electrically-conductive layer 4,and into support 3. Dispersed particulate electrically-conductive material is in contact with conductive layer 4 at its exposed edges 24 and 24' within groove 20 and also as a result of its lateral movement into subbing layer 25 by a process of imbibition.
As illustrated in FIG. 6, grounded metal bristle brush 6 serves to engage stripe 19 as electrographic element

2 is conveyed past the operative stations of an electrographic copying apparatus. Since there is an electrical path from conductive layer 4 to the surface of electrographic element 2, provided by the dispersed particulate electrically-conducting material, this serves to ground conductive layer 4.
Electrographic elements provided with improved electrical connection means in accordance with this invention, can be formed using any of a wide variety of materials as the support. Typical supports include cellulose triacetate film, poly(vinyl acetal) film, polystyrene film, pol~(ethylene terephthalate) film, polycarbonate film, paper, polymer-coated paper, and the like. Most usually the support is a tough, flexible, transparent, electrically insulating material such as a poly(ethylene terephthalate) film.
The conductive layer in the electrographic elements of this invention is a thin layer which is sandwiched between the support and the photoconductive layer. It can be formed from many different materials, as is well known in the electro-graphic art. For example, it can be a thin sheet of a metal such as aluminum, copper, zinc or brass, or a metal foil such as an aluminum foil, or a vapor deposited metal layer of a metal such as silver, aluminum or nickel, or a layer which is a dispersion of a semi-conductor in a resin, as described for example in U. S. Patent 3,245,833, or a layerOf an electrically-conducting salt, as described for example in U. S. Patents

3,007,801 and 3,267,807. A further example of a useful con-ductive layer is a layer comprised of a dispersion Gf carbonblack or graphite in a polymeric binder.

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The electrical connection means of this invention is a region of dispersed particulate electrically-conducting material which defines an elongated conductive stripe on the . surface of the electrographic element. This stripe can be located along the edge of the electrographic element, as 5 illustrated herein, or it can be spaced inwardly from the edge at any desired location. Typically, it will be at the edge or close to the edge of the element. In certain instances it is desirable to provide two stripes, one adjacent each edge of the element, as also illustrated herein. In this case, the 10 electrographic copying apparatus is, of course, provided with means for engaging each of the stripes. Perforations can be located within the region of one of the stripes, as illustrated herein, or they can be located outside the stripe region. An advantage of locating them within a stripe is that it is then 15 possible for them to assist in providing electrical connection to the conductive layer. Whether one, or more than one stripe is used, each such stripe will be located in a non-recording portion of the electrographic element. To obtain the region of dispersed particulate electrically-conducting material within 20 the element an imbibable composition comprising the particulate material is applied to the surface of the element as an elongated stripe and, with the aid of the elongated groove, imbibed into contact with the conductive layer.The imbibable composition, as hereinafter described in greater detail, advantageously contalns 25 a polymeric binder which will aid in bonding the particulate material within the element and assist in providing a stripe which ls durable and abrasion resistant. Any suitable form of grounding or biasing member can be used to engage the conductive stripe, for example, the member can be a metal bristle brush, as 30 illustrated herein, or a metal strip, or a metal Y~lle.r.
It is to be understood that the term "ground" as used herein is relative and merely represents a relative potential to which other positive or negative potentials are referred.
For example, in referring to the surface of the photoconductive 35 layer as being charged to 600 volts, it is intended to mean 600 volts above a reference ground potential. For convenience, ground potential as used herein is arbitrarily assigned a value of zero volts.

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The dispersed par!iculate electrically-conductive material which forms the electrical connection means of this invention can be any finely-divided particulate material having good electrical conducting properties. Typical conducting materials include graphite, carbon black, nickel, silver, alumi-num, copper, tin, etc. and mixtures thereof, all of which are particulate and have good electrical conducting properties. The particle size of these conducting materials can vary depending on the particular material used but generally ranges from about 0.001~ to about 100~. Graphite has been found to be very satis-factory based on its property of being a good lubricant as well as a conductor. When graphite is used, less wear is encountered in those non-recording regions of the element which are in contact with the metal grounding devices.
In preparing the novel electrographic elements of this invention, a liquid dispersion of the particulate electrically conducting material in a solvent is applied to the surface of the electrographic element. The solvent should be one which is capable of impregnating (e.g., by swelling, cracking or dissolving) the polymeric binder contained in a photoconductive layer or other layer, such as a subbing layer, which is in direct contact with the electrically conductive layer, and preferably one which is capable of impregnating the binders in all layers overlying the electrically conductive layer. Suitable solvents having these characteristics include aliphatic alcohols having 1 to 8 carbon atams such as methanol, ethanol, isopropanol, etc., ketones having 3 to 10 carbon atoms such as acetone, methylethyl ketone, etc., and chlorinated alkanes having l to 8 carbon atoms such as methyl-ene chloride, propylene chloride, chloroform, etc. Mixtures of 3 these solvents may also be used. The particular solvent or mix-ture employéd is somewhat dependent upon the polymer to be im-pregnated and the selection of the optimum solvent to be used is - apparent to those skilled in the art. A particularly useful sol-vent which is capable of impregnating most of the more common hyd~ophobic film-forming resin binders employed in the various layers of electrographic elements, comprises a mixture of a ketone such as acetone or methyl ethyl ketone with a chlorinated hydro-carbon such as methylene chloride or propylene chloride.
The solvent and particulate electrically-conducting material are thoroughly mixed, e.g., with a ball mill or blender, so as to create a uniform dispersion of the conducting material in the solvent.

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Frequently, in order to obtain a uniform stable dispersion of solids in liquid, it is necessary to employ a small amount of a polymerlc binder. The added binder aids primarily in the creation of a more uniform dispersion. When such a binder is employed, 5 the ratio Or conducting material to binder ranges from 0.5 to 10 parts by weight and preferably 1.5 to 2.5 parts by weight of conducting materlal for each part by weight of binder. Enou~h solvent is added to bring the solids content to at least 5%
and hOt more than 90% of the liquid dispersion. The binder 10 used in the imbibable composition can be any of a wide variety Or polymeric materials. Suitable materials include styrene-butadiene copolymers; silicone resins; styrene-alkyd resins;
silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride);
poly(vinylidene chloride); Uinylidene chloride-acrylonitrile 15 copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals) such as poly(vinyl butyral);
polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly (n-butylmethacrylate), poly(isobutyl methacrylate), etc.;
polystyrene; nitrated polystyrene; polymethylstrene; polyesters 20 such as poly(ethylene terephthalate); phenolformaldehydè resins;
polyamides; polycarbonates, polythiocarbonates; poly(ethyleneglycol-`co-bishydroxyethoxyphenyl propane terephthalate); copolyme~s of vinyl haloarylates and vinyl acetate such as poly(vinyl-m-bromobenzoate-covinylacetate); polyolefins such as polyethylene, 25polypropylene, etc.
The electrographic elements of this invention can be composed of only three layers, namely, an electrically conductive layer sandwiched between a support and a photoconductive layer.
However, they may include two or more contiguously disposed 3 photoconductive layers, each of which exhibits different characteristics, and may include a variety of other layers such as barrier layers, subbing layers, overcoat layers, and so forth.
The various layers making up the element typically vary greatly in thickness. For example, the support may have a th~ckness of 35 about 100 microns and the photoconductive layer a thickness of about 20 microns while each of the electrically conductive layer, subbing layer and overcoat layer may have a thickness of less than one micron. The electrographic element is typically utilized in the form of a continuous belt but it may be employed in other

4 configurations such as for example in the form of a flat sheet or in cylindrical form.

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1~533~a .
The photoconductive layer in the electrographic element of th~s invention can be prepared from a wide variety of materials.
In general, this layer is prepared by dispersing a photoconductor in a resinous binder and coating the resultant dispersion on

5 the electrically conductive layer or on a subbing layer overlying the electrically conductive layer. Binders useful for this purpose include the same polymeric materials referred to above as being useful as binders in the imbibable composition. Photo-conductors suitable for use in the photoconductive layer include 10 inorganic, organic and organo-metallic materials. Typical photoconductors which are useful include zinc oxide, titanium di-oxide, organic derivatives of Group lVa and Va metals such as those having at least one amino-aryl group attached to the metal atom, aryl amines, polyarylalkaneshaving at least one amino 15 substituent~-and the like. The use of organic photoconductors is preferred. Illustrative examples of organic photoconductors are those described in U.S. patents 3,139,338; 3,139,339;
3,140,946; 3,141,770; 3,148,982; 3,155,503; 3,257,202; 3,257,203;
3,257,204; 3,265,496; 3,265,497; 3,274,000; and 3,615,414.
A sensiti7er for the photoconductor may optionally be included in the photoconductive layer to change the elect~o~hoto-sensitivity or spectral sensitivity of the element. Sensitizing compounds useful in the photoconductive layers described herein can be selected from a wide variety of materials, including such 25 materials as pyryliums, including thiapyrylium and selenapyrylium dye salts, disclosed in U.S. Patent 3,250,615; fluorenes such as 7,12-dioxo-13-dibenzo(a,h)fluorene, 5,10-dioxo-4a,11-diazabenzo(b)fluorene, 3,13 -dioxo- 7 - oxadibenzo(b,g)fluorene, and the like; aromatic nitro compounds of the kinds described 3 in U S. Patent 2,610,120; anthrones like those disclosed in U.S.
Patent 2,670,284; quinones, U.S. Patent 2,670,286; benzophenones U S Patent 2,670,2~7; thiazoles U.S. Patent 2,732,301; mineral acids; carboxylic acids, such as maleic acid, dichloroacetic acid, and salicylic acid; sulfonic and phosphoric acids; and 35various dyes, such as cyanine (including carbocyanine), mercocyanine diarylmethane, thiazine, azine, oxazine, xanthene, phthalei~, acridine, azo, anthraquinone dyes and the like and mixtures thereof. The sensitizing dyes preferred for use with this invention are selected from pyrylium, selenapyrylium and thia-4pyrylium salts, and cyanines, including carbocyanine dyes.
Where a sensitizing compound is employed with the binderand organic photoconductor to form a sensitized electrographic .

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element, it is suitable to mix an amount Or the sensitizing compound with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed in the coated element. Other methods of incorporating the sensitizer 5 or the effect of the sensitizer may, however, be employed consistent with the practice of this invention. In preparing the photoconductive layers, no sensitizing compound is required to give photoconductivity in the layers which contain the photo-conducting substances, therefore, no sensitizer is required in 10 a particular photoconductive layer. However, since relatively minor amounts of sensitizing compound give substantial improvement in speed in such layers, the sensitizer is preferred. The amount of sensitizer that can be added to the photoconductive layer to give effective increases in speed can vary widely. The 15 optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, : substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film-20 forming coating composition. Normally, a sensitizer is addedto the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.
Solvents useful for preparing the photoconductive 25coating compositions include a wide variety of organic solvents for the components of the coating composition. For example, benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbons suoh as methylene chloride, ethylene chloride, and the like;
ethers, such as tetrahydrofuran and the like, or mixtures of 3such solvents can advantageously be employed in the practice of this invention.
In preparing the coating compositions for the photo-conductive layer, useful results are obtained where the photo-conductive substance is present in an amount equal to at least 35about 1 weight percent of the coating composition. The upper limit on the amount of photoconductive material present can be widely varied in accordance with usual practice It is normally required that the photoconductive material be present in an amount ranging from about 1 weight percent of the coating 4composition to about 99 weight percent of the coating composition.
A preferred weight range for the photoconductive material in the coating composition is from about 10 weight percent to about 60 weight percent.
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.

33~a Coating thicknesses of the photoconductive composi-tion can vary widely. Norrnally, a wet coating thickness in the range of about 0.01 to 2 millimeters is useful in the practice of this invention. A preferred range of coating thickness is 5 from about 0.02 to 0.2 millimeters before drying, although such thicknesses can vary widely depending on the particular application desired for the electrographic element.
In the method of this invention an elongated longitudi-nally disposed groove is formed in a non-recording portion of 10 the electrographic element. This groove extends from an exterior surface of the elemént at least to a position proximate to the electrically conductive layer. It is formed with a depth and width adapted to promote the imbibition of the particulate electrically-conducting material into contact with the elec-15 trically conductive layer. The optimum depth and width willdepend upon numerous circumstances including the structure and-composition of the electrographic element and the imbibing characteristics of the composition containing the particulate electrically-conducting material. As explained hereinabove, the 20 groove may terminate a short distance above the electrically conductive layer, may terminate at the surface of the electrically conductive layer, or may extend into or through the electrically conductive layer. Typically~ a groove with a width of from about 0.2 millimeters to about 5 millimeters is suitable.
Imbibition of the composition containing the particulate electrically-conducting material causes it to spread laterally as well as to penetrate downwardly from the surface to which it is applied. Since the composition is applied as a stripe which encompasses the groove, it flows into the groove and spreads 3 laterally from the walls of the groove as well as penetrating downwardly from the bottom of the groove. Even though the distance it is capable of penetrating may be relatively small, since the groove extends to a position at least proximate to the conductive layer the resulting dispersion of particulate electrically-35 conducting material will easily extend into effective contactwith the conductive layer and thereby provide an electrically-conductive path from the conductive layer to the surface of the element.
The groove can be formed in the electrographic element in any suitable manner. One technique which is suitable for forming I the groove is the use of a revolving knife blade which is rotated at high speeds, such as speeds of several thousand revolutions .

33~ :
per minute. The blade is preferably made of a very durable and wear resistant material, such as a stainless steel blade or a steel blade with a diamond edge. An alternative technique is to carry out a localized pyrolysis in which the material is , 5, vaporized in a controlled manner along the desired path.' Methods of accomplishing this include the use of a laser beam or an electron beam.
In forming the groove by use of a laser, the action of the laser beam serves to vaporize the material on which the beam,is impinged and thereby generate a groove. Suitable lasers for this purpose are well known. Laser beams having wavelengths in theinfrared range are generally satisfactory. A C02 laser is preferred because of its high efficiency characteristics.
me wldth of the laser beam wlll be selected in accordance with the desired width of the groove. The laser beam can be moved relative to a stationary substrate to form the groove but it will usually be more convenient for the laser beam to be fixed in position and the substrate to be moved at an appropriate rate to form a groove of the desired depth.
' After the groove has been formed in the electrographic element, the imbibable composition containing the particulate electrically-conducting material is applied to the surface of the élement as an elongated stripe which encompasses the gr,oove.
The stripe may be of any suita~le width, with the width ordinarily 25 being commensurate with the size of the grounding or biasing member in the electrographic apparatus which is intended to engage the stripe. Typically the stripe will have a width of about 5 to about 25 millimeters and it will typically be about 5 to about 100 times as wide as the groove. The groove will 3 usually be located at or near the midpoint of the stripe but it may be at any position wlthin the stripe, as desired.
Application of the imbibable composition to the surface of the electrographic element can be carried out in any suitable manner. For example,'it can be carried out by spraying or by 35 the use of a coating hopper such as a hopper of the extrusion type. The imbibable composition flows into the groove and penetrates into the material surrounding the groove. If the groove dQes not extend all the way through the photoconductive layer, the composition will be imbibed through the material 4 which lies between the bottom of the groove and the electrically conductive layer. It will also spread laterally from the walls of the groove by the process of imbibitlon into the photoconductive -17- !

- ' , .

11~533~

layer and into any subbing layer overlying the electrically conductive layer. The imbibable composition is applied in an amount sufficient to provide effective contact of the particulate electrically~conducting material wlth the electrically conductive ;~
layer. The optimum amount to be used will depend on the characteristics of both the imbibable composition and the electrographic element as well as the method of application.
The amount used can be su~icient to completely fill the groove and provide a level surface thereover. However, lesser amounts can also be used. In any event, the result will be that the groove will be at least partially filled with the particulate electrically-conducting material.
The method of this invention is a simple, effective and reliable procedure which is well adapted to use in a high volume production operation. The steps of forming the groove and applying the imbibable composition can be carried out as independent operations or as sequential steps in a single continuous process. If carried out independently, they can, of course, be conducted at different speeds with the speed chosen for each step being optimum for that particular operation. When the groove-forming step and the step of applying the imbibable composition are carried out as sequential steps of a single continuous operation, the speed at which the web is advanced can be selected within a broad range, for example, a speed in the range of from about 5 to about 200 centimeters per second. The steps of forming the groove and applying the imbibable composition can also be carried out as part of a continuous process which involves other operations such as coating o~ the various layers on the support, forming 3 the perforations, slitting, and so forth. After application of the imbibable composition, it is pre~erred to impinge air or other gaseous medium on the element and/or to heat the element in order to drive off the solvent. Heating also serves to promote the penetrating action of the imbibable composition and thereby facilitate good contact with the electrically conduc-tive layer. As explained hereinabove, the imbibable composition preferably contains a polymeric binder. The binder promotes the bonding of the particulate material within the element and assists in forming a stripe which is durable and abrasion resistant .

111533"
and, accordingly, is able to resist being worn away by the frictional contact with the grounding or biasing member.
In view of the long-wearing characteristics of the conductive stripe, the electrographic element can be re-used a great many times while still maintaining excellent electrical contact with the grounding or biasing member.
Referring now to FIG. 7, there is shown a particular embodiment of the method of this invention in which the groove is formed in the electrographic element by the use of a laser beam. In this method, electrographic element 2 is unwound from supply roll 30 which is-mounted for rotation about its axis on a suitable framework (not shown) and passes around guide rollers 32 and 34, which maintain it under proper tension,and over bac~ing roll 36. A laser 38 positioned above electrographic element 2, opposite backing roll 36, impinges a laser beam 40 onto electrographic element 2 as it advances and thereby forms a groove 20. To assist in removing vapors produced by vaporization of the material on which laser beam 40 impinges, an exhaust duct 42 connected to a vacuum source (not shown) is positioned closely adjacent to the region of impingement. A spray nozzle 44 fed with the imbibable composition from a suitable supply source (not shown) directs a liquid spray 46 onto the surface of elect~o-graphic element 2 to form a stripe 19 which encompasses groove 20. After passing under spray nozzle 44, electro-graphic element 2 is advanced into a drying chamber (notshown) in which warm air or other gaseous medium is directed into contact with the stripe to remove solvent and promote imbibition.
FIG. 8 illustrates an alternative embodiment of 3 thè method of this invention in which the groove is formed in the electrographic elément by the use of a rotating knife blade. In this method, electrographic element 2 is unwound from supply roll 30 and passes around guide rollers 32 and 34 and over backing roll 36. A rotatable knife blade 48 driven by a suitable drive means 50, such as a variable-speed motor, engages the surface of electrographic elernent 2 as it passes over backing roll 36 and thereby forms a groove 20. To assist in the removal of dust formed by the cutting action of knife blade 48, exhaust duct 42 is positioned closely 4 ad~acent to the region where cutting takes place. After groove 20 has been cut, the advancing element passes under -19- :

33~
- spray nozzle 41~, which direc~s liquid spray 46 onto its surface and thereby forms stripe l9 encompassing groove 20, and then passes through the drying chamber in which warm air impinges on the stripe.
In either the embodiment of FIG. 7 or the embodiment of FIG. 8,the web can be wound onto a take-up roll after the stripe has been dried or it can be cut to appropriate lengths, each of which will serve to form an endless belt for use in an electrographic copying apparatus, or it can be subjected to additional operations such as slitting.
In forming the groove in the electrographic element, it is ordinarily desirable that it be made as narrow as possible since this will involve the minimum removal of material and therefor the minimum formation of vapors or dust. It must, of course, be made wide enough to enable the imbibable composition to enter the groove The most appropriate width for the groove may be determined, at least in part, by the choice of method used to form the groove, for example, it may be determined by the minimum practical thickness for knife blades used in forming the groove by a cutting process. As previously indicated, there is a wide degree of choice in regard to the depth of the groove. The groove can be readily cut to a desired depth by, for example, varying the pressure applied to a rotating knife blade or varying the power output from a laser. It is a particular advantage of the method of this invention that the groove does not have to be cut to an exact predetermined depth and does not have to be of exactly the same depth at all points along its longitudinal extent. Since the imbibable composition is capable of penetrating a gubstantial distance into the photo-3 conductive layer, or other layer of the electrographic element,it is pnly necessary that the groove extend to a position at least proximate to the electrically-conductive layer, that is, to a position that is not so far away that the imbibable compo-sition will not be able to reach the electrically-conductive layer. It should be noted that while mechanical methods of cutting the groove, such as a rotating knife blade, result in the generation of dust, the use of a laser beam brings about a vaporization of the solid materials. This vaporization is, of course, accompanied by the generation of considerable heat and 4 the solid material is rendered molten and flowable. The groove will usually be somewhat jagged and irregular in appearance, and considerable flow of the molten material will take place.
For simplicity~ no attempt has been made to illustrate this in the drawings herein. With some polymeric binders, the fused material formed by the laser beam may, upon subsequent 5 cooling, be converted to a crystalline state in which it is quite resistant to penetration by imbibable compositions.
Under these circumstances, it may be necessary to control the laser such that it cuts a groove which reaches or at least very nearly reaches the electrically conductive layer or 10 which extends into the electrically conductive layer or completely through it. Thus, if the electrically conductive layer is exposed by removing all overlying material this provides for contact between the particulate electrically-conducting material and the electrically conductive layer at 15 the bottom of the groove. If the groove cuts into or through the electrically conductive layer, there is opportunity for contact between the particulate electrically-conducting material and the edges of the electrically conductive layer within the groove. In either instance, contact between the 20 particulate electrically-conducting material and the electrically conductive layer is also provided as a result of the lateral spreading of the imbibabLe composition. The lateral spreading action which occurs is an important feature of the present invention since it provides much more effective contact with 25 the electrically conductive layer than is achieved merely as a result of contact at the bottom of a groove which exposes the electrically conductive layer. Use of an eLectrically conductive composition which is not capable of imbibition would, of course, not provide the lateral spreading action and 30 thereby would give much less effective contact.
The combined use of a groove and an imbibable composi-tion in accordance with this invention is useful with electro-graphic elements of many different structural variations.
Thus, the method of this invention is applicable in any situation 35 where thereiS an inaccessible electrically conductive layer sandwiched between other layers of an electrographic element.
It is particularly advantageous where the electrically conductive layer is very thin and the overlying layers are very resistant to imbibition.
Electrographic elements containing the novel electrical connection means of this invention are useful in the xerographic process. In this process, the electrographic element, while held in the dark, is given a blanket electrostatic charge by placing it under a corona discharge to give a uniform charge 45 to the surface of the photoconductive layer. During this charg-ing step, the electricall" conducting layer is maintained at ground potential by ~lcci rically connecting the conductive stripe on the electrograpnic element to ground. In the absence of grounding in this manner, the difference in potential 5 between the photoconductive layer and the conducting layer is not large enough to produce a suitable latent image.
The charge is retained on the surface of the photoconductive layer because of the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark.
10 When using an element,containing electrical connection means as described herein,that is charged while in motion, the potential of the conducting layer is maintained at grounu potential as efficiently as with an element that is charged while stationary. In other words ? the electrical connection 15 means permits exceptionally good contact to be made between the conducting layer and the grounding means while the element is in motion. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the la~er by imagewise exposure to light 20 by means of a conventional exposure operation such as for example, by a contact-printing technique, or by lens projection of an image, or by reflex techniques and the like, to thereby form a latent image in the photoconductive layer.
Exposing the surface in this manner forms a pattern of electro- ;
static charge by virtue of the fact that light energy striking the photconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the i~lumination in a particular area.
The charge pattern produced by exposure is then de-30 veloped or transferred to another surface and developed there, i.e., either the charge or uncharged areas are rendered visible, by treatment with a medium comprising electrostatically respon-sive particles having optical density. The developing electro-statically responsive particles can be in the form of a dust 35 or powder and generally comprise a pigment in a resinous carrier called a toner. A preferred method of applying such a toner to a latent electrostatic image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following 40 U. S. Patents 2,786,439; 2,786,440; 2,786,441; 2,811,465j 2,874, o63; 2, 984,163; 3, 040,704; 3,117,884; and reissue Re.
25,779. Liquid development of the latent electrostatic image may also be used. In liquid development the developing parti-cles are carried to the image-bearing surface in an electrically ~1~5334 ~l~S33~
insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent' literature, for example, in U. S. Patent 2,297,691 and in Australian Patent 212,315. In dry developing processes the most widely used method of obtaining a permanent record is 5 achieved by selecting a developing particle which has as one of its components a low-melting resin. Heating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. In other cases, a - ' 10 transfer of the charge image or powder image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after developing and fusing or fusing respectively. Techniques of the type indicated are well known in the art and have been described in 15 a number of U. S. and foreign patents, such as U. S. Patents 2,297,691 and 2,551,5~2 and in "RCA Review", vol 15. It is f'requently necessary during development to maintain the elec-trically-conducting layer at a given potential in order to obtain a clean background. The electrical connection means 20 provided in the elements of this invention enables one to easily maintain the potential of the electrically-conducting layer at a preselected level.
In a typical example of the practice of this invention, an electrographic element comprised of a poly(ethylene tere-25 phthalate) support with a thickness of 100 microns, a nickellayer with a thickness of less than 1 micron overlying the support, and a photoconductive layer, comprised of an organic photoconductor dispersed in a polycarbonate binder and having a thickness of approximately 20 microns, overlying the nickel 30 layer, is grooved by the use of a rotating knife blade and then spray coated to form the desired conductive stripe. The groove is formed with a width of approximately 1 millimeter and a depth of approximately 15 microns and is cut by a rotating stainless steel knife blade driven by a motor at a speed of 6000 revolu-35 tions per minute while the electrographic element is advancedat a speed of 30 centimeters per second. After the groove is formed, a stripe with a width of 10 millimeters, which encom-passes the groove, is applied by spraying the following imbibable composition onto the surface of the element:

11~S334 Component Weight %
Polyvinylbutyral resin 3.3 Carbon black 6.5 Propylene chloride 41.2 5 Acetone 49.0 After formation of the stripe by the spray coating operation, the solvent is removed by contacting the element with warm air at a temperature of about 165F.
In a further typical example of the practice of 10 this invention, the electrographic element described above is grooved by the use of a laser beam and then coated with an imbibable composition to form the desired conductive stripe. A suitable laser for this purpose is a 50-watt C2 laser equipped with a 2.5 inch focal length lens. The 15 groove can be formed along only one edge of the element or, by equipping the laser with two lenses and a beam splitter, grooves can be simultaneously formed along both edges. The element can be advanced at any suitable speed during the step of forming the grooves with a laser beam, such as a speed of 20 30 centimeters pèr second. Preferably, the power output from the laser is regulated so that the groove is cut completely through the nickel layer of the element described above and into the poly(ethylene terephthalate) support. Following formation of the groove, an imbibable composition,as described 25 above,is applied in the form of a stripe which encompasses~the groove by a suitable method of application such as spraying or hopper coating.
The invention has been described in detail with particular reference to preferred ernbodiments thereof, but 3 it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

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Claims (31)

WE CLAIM:

1. A method of providing electrical connection means within an electrographic element, said element comprising an electrically insulating support, an electrically conductive layer overlying said support, and an electrically insulating photoconductive layer overlying said conductive layer, said means defining a conductive electrical path connecting an exterior surface of said element to said conductive layer, said method comprising the steps of (1) forming within a non-recording portion of said element an elongated groove which extends from said surface at least to a position proximate to said conductive layer, and (2) applying to said surface an imbibable composition comprising particulate electrically-conducting material to imbibe said particulate material into said element and form a region of dispersed particulate material extending from said surface into contact with said conductive layer, said composition being applied to said surface as an elongated stripe which encompasses said groove, said groove being of width and depth adapted to promote the imbibition of said particulate material into contact with said conductive layer and thereby form said conductive electrical path.

2. The method as claimed in Claim 1 wherein said groove is formed by a process of localized pyrolysis.

.

3. The method as claimed in Claim 1 wherein said groove is formed by the action of a laser beam.

4. The method as claimed in Claim 1 wherein said groove is formed by the action of a rotating knife blade.

5. The method as claimed in Claim 3 wherein said groove extends through said electrically conductive layer into said support.

6. The method as claimed in Claim 1 wherein said imbibable composition is applied by spray coating.

7. The method as claimed in Claim 1 wherein said imbibable composition is applied by extrusion hopper coating.

8. The method as claimed in Claim 1 wherein said imbibable composition comprises a dispersion of said particulate electrically-conducting material in a solvent solution of a polymeric binder.

9. The method as claimed in Claim 8 wherein said element is heated after application of said imbibable composition to facilitate the removal of said solvent.

10. The method as claimed in Claim 1 wherein said support is a poly(ethylene terephthalate) film, said electrically conductive layer is a nickel layer, said photoconductive layer is a dispersion of an organic photoconductor in a polymeric binder, and said particulate electrically-conducting material is carbon black.

11. The method as claimed in Claim 1 wherein said electrographic element additionally comprises a subbing layer between said electrically conductive layer and said photoconductive layer,

12. The method as claimed in Claim 1 wherein said electrographic element additionally comprises an overcoat layer overlying said photoconductive layer.

13. A method of providing electrical connection means within an electrographic element, said element comprising an electrically insulating support, an electrically conductive layer overlying said support, and an electrically insulating photoconductive layer overlying said conductive layer, said means being adapted to establish electrical connection between said conductive layer and a grounding or biasing member which engages a surface of said element while said element is in motion, said method comprising the steps of (1) forming within a non-recording portion of said element an elongated groove which is longitudinally disposed in the direction of motion of said element, said groove extending from said surface at least to a position proximate to said conductive layer, and (2) applying to said surface an imbibable composition comprising particulate electrically-conducting material to imbibe said particulate material into said element and form a region of dispersed particulate material extending from said surface into contact with said conductive layer, said composition being applied to said surface as an elongated stripe which is longitudinally disposed in the direction of motion of said element and which encompasses said groove, said groove being of width and depth adapted to promote the imbibition of said particulate material into contact with said conductive layer, said stripe being adapted for engagement with said grounding or biasing member to thereby provide electrical connection between said member and said conductive layer.

14. In an electrographic element comprising an electrically insulating support, an electrically conductive layer overlying said support, and an electrically insulating photoconductive layer overlying said conductive layer; the improvement comprising a conductive electrical path connecting an exterior surface of said element to said conductive layer, said path comprising a region of dispersed particulate electri-cally-conducting material within a non-recording portion of said element, said region extending from said surface into contact with said conductive layer and defining on said surface an elongated stripe which encompasses an elongated groove, said groove extending from said surface at least to a position proxi-mate to said conductive layer and being at least partially filled with said particulate electrically-conducting material.

15. An electrographic element as claimed in Claim 14 which is in the form of a continuous belt.

16. An electrographic element as claimed in Claim 14 wherein said region of dispersed particulate electrically-conducting material is adjacent to an edge of said element.

17. An electrographic element as claimed in Claim 16 additionally comprising a second similar region of dispersed particulate electrically-conducting material adjacent to a second edge of said element.

18. An electrographic element as claimed in Claim 17 additionally comprising a row of perforations within said second region.

19. An electrographic element as claimed in Claim 14 wherein said groove extends to a position within said photoconductive layer that is closely adjacent to said elec-trically conductive layer.

20. An electrographic element as claimed in Claim 14 wherein said groove is of a depth such that it exposes but does not penetrate said electrically conductive layer.

21. An electrographic element as claimed in Claim 14 wherein said groove extends through said electrically conductive layer into said support.

22. An electrographic element as claimed in Claim 14 wherein said support is a poly(ethylene terephthalate) film, said electrically conductive layer is a nickel layer, said photoconductive layer is a dispersion of an organic photocon-ductor in a polymeric binder, and said particulate electrically-conducting material is carbon black.

23. An electrographic element as claimed in Claim 14 wherein said region of dispersed particulate electrically-conducting material has been formed by imbibition of a dis-persion of said particulate electrically-conducting material in a solvent solution of a polymeric binder.

24. An electrographic element as claimed in Claim 14 which additionally comprises a subbing layer between said electrically conductive layer and said photoconductive layer.

25. An electrographic element as claimed in Claim 14 which additionally comprises an overcoat layer overlying said photoconductive layer.

26. In an electrographic element comprising an electrically insulating support, an electrically conductive layer overlying said support, and an electrically insulating photoconductive layer overlying said conductive layer; the improvement comprising means for establishing electrical con-nection between said conductive layer and a grounding or biasing member which engages a surface of said element while said element is in motion, said means comprising a region of dispersed particulate electrically-conducting material within a non-recording portion of said element, said region extending from said surface into contact with said conductive layer and defining on said surface an elongated stripe which is longitu-dinally disposed in the direction of motion of said element and which encompasses an elongated longitu-dinally disposed groove, said groove extending from said surface at least to a position proximate to said conductive layer and being at least partially filled with said particulate electrically-conducting material, said stripe being adapted for engagement with said grounding or biasing member to thereby provide electrical connection between said member and said conductive layer.

27. In a copier having (1) an electrographic element comprising an electrically insulating support, an electrically conductive layer overlying said support, and an electrically insulating photoconductive layer overlying said conductive layer, said element having at least one image area which is moved through a plurality of processing stations, including an exposure station, within said copier to form a visible image, and (2) means for applying a reference potential to said conductive layer during movement of said image area through said exposure station, the improvement comprising:
(a) electrical connection means adjacent said image area comprising a region of dispersed particulate electrically-conducting material within a non-recording portion of said element, said region extending from an exterior surface of said element into contact with said conductive layer to form a conductive path therebetween and defining on said surface an elongated stripe which is longitudinally disposed in the direction of motion of said element and which encompasses an elongated longitudinally disposed groove, said groove extending from said surface at least to a position proximate to said conductive layer and being at least partially filled with said particulate electrically-conducting material, and (b) means positioning said element during movement of said image area through said exposure station to make contact between said applying means and said path, thereby connecting said reference potential to said conductive layer.

28. A copier as claimed in Claim 27 wherein said electrographic element is in the form of a continuous belt.

29. A copier as claimed in Claim 27 wherein said electrographic element comprises a region of dispersed particulate electrically conducting material adjacent to each edge of said element, each of which regions forms a conductive path between an exterior surface of said element and said conductive layer, each said conductive path making contact with said applying means.

30. A copier as claimed in Claim 27 wherein said means for applying a reference potential comprises a metal bristle brush adapted to engage with said elongated stripe.

31. A copier as claimed in Claim 27 wherein said support is a poly(ethylene terephthalate) film, said electrically conductive layer is a nickel layer, said photoconductive layer is a dispersion of an organic photoconductor in a polymeric binder, and said particu-late electrically-conducting material is carbon black.