METHOD FOR PROVIDING ELECTRICAL CONNECTION MEANS IN AN ELECTROGRAPHIC ELEMENT

Abstract: An electrographic element comprising an electrically insulating support (3), an electrically conductive layer (4) overlying the support, and an electrically insulating photoconductive layer (5) overlying the conductive layer, is provided with electrical connection means (18) adapted to establish electrical connection between the conductive layer and a grounding or biasing member (6) which engages a surface of the element while the element is in motion. The electrical connection means (18) comprises a region of dispersed electrically conductive particles within a non-recording portion of the element which extends from the surface of the element into contact with the conductive layer (4). This region defines on the surface of the element an elongated stripe (19) which is longitudinally disposed in the direction of motion of the element and which encompasses an elongated longitudinally disposed groove (20). To form the region of dispersed electrically conductive particles, an elongated groove 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 suspension (46) comprising the particles and a solvent 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 particles 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: METHOD FOR PROVIDING ELECTRICAL CONNECTION MEANS -IN AN ELECTROGRAPHIC ELEMENT 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 electrically conductive layer. The photoconductive layer contains a normally insulating material whose electrical resistance varies with the amount of incident electromagnetic radiation it re¬ ceives during an imagewise exposure. The electrically conductive layer can be a separate layer or a part of the support layer and can be formed from a wide variety of materials. The electrographic element can be opaque or transparent, depending upon the intended mode of use. - The function of the electrically conducting layer in electrographic elements is to create a highly conducting reference plane which ideally is held at or near ground potential. During charging of the photoconductive layer with a 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 un¬ grounded conducting layer can vary from about 5Q to about 450 volts or more. Thus, the differential be¬ tween 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 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 O PI which may exist between areas struck by light and those not struck when the conducting layer is not grounded, little or no latent image is produced. Ideally, during charging of the photoconductive layer, the electrically conducting layer should be -held at ground potential to insure that the maximum charge be impressed and stored in the photoconductive layer. Similarly poor results are obtained when the conducting layer is inefficiently grounded. Direct electrical contact with the conducting layer for grounding purposes is very difficult and inef¬ ficient when, as is usually the case, it is ex¬ tremely thin, e.g., a few hundred angstroms, and creates wear problems if the element is contacted for grounding while in motion. An approach to providing electrical con¬ nection means in electrographic elements is de¬ scribed in U.S. Patent 3,684,503, issued August 15, 1972 to . D. Humphriss et . al. In this method, electrically-conducting particles are imbibed into the element to form a dispersion extending from the surface of the element through the overlying layer or layers and into contact with the electrically con¬ ductive layer, thereby forming an electrical path from the ' surface to the 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 electrographic elements to which it is applicable. Thus, for example, if the photoconductive layer overlying the conductive layer is 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 particles from being imbibed - O P all the way from the surfa.ce of th-e elemen to th.e conductive l yer and thereby* render the mettiod of U.S. Patent 3,6.84,503 inoperative. Moreover, even though the tot^,l thickness of material over- lying the conductive layer may not be very great, if one or more of the layers overlying the conductive layer contains a tough polymeric binder which strongly resists imbibition, then the method of U.S. Patent 3,684,503 may be rendered inoperative. Other procedures 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 pro- vided 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 com¬ prising an adhesive and a pigment in an amount suf- ficient to completely .fill the hole. Preferably, a piece of metallic foil is utilized to cover the ex¬ posed 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 chan¬ nel. In U.S. Patent 3,743,410, issued July 3, 1973 to R. I. Edelman et al, there is described an electro¬ graphic 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 in¬ serted 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 manufacturing operations. Tha present invention provides improved electrical connection means within an electrographic element, which means are adapted to establish electrical connection between a conductive layer of the element and a grounding or biasing member which engages a surface of the element while the element is in motion. The electrographic element is com¬ prised of an electrically insulating support, an electrically conductive layer overlying the support, and an electrically insulating.photoconductive layer overlying the conductive layer. The electrical con¬ nection means comprises a region of dispersed elec¬ trically-conducting particles 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 longitudinally disposed in the direction of motion of the element and which encompasses an elongated longitudinally disposed groove. To form the region of dispersed electrically-conducting particles, an elongated groove 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 sur¬ face of the element as an elongated stripe which en¬ compasses the groove. The groove serves to promote the imbibition of the particulate material into con¬ tact 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 in- vention 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 reference potential to the conductive layer of the element during movement of the element through the exposure station. Means are provided within the copier for positioning the element during movement of an image area thereof through the exposure station to maintain effective contact between the grounding .or biasing member and the stripe on the surface of the element, thereby connecting the reference potential to the conductive layer. FIG. 1 is a schematic representation of an electrographic copying apparatus employing the im¬ proved electrographic element of this invention. FIG. 2 is a face view of a portion of an electrographic element having electrical connection means in accordance 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 electrographic element having electrical connection means in accordance 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 alternative 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 alternative embodiment of the electrographic element. O PI FIG. 6 is a cross sectional view illustrating the electrical connection means in contact with a grounding, or biasing member of an electrographic ap¬ paratus. PIG. 7 is a schematic illustration of the cutting of an elongated groove and formation of a conductive stripe in an electrographic element in ac¬ cordance with this invention. FIG. 8 is a schematic illustration of an alternative procedure for cutting the elongated groove in an electrographic element. The present invention is characterized in its manufacture by the use, in combination, of an imbibable composition containing electrically,--. conductive particles 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 of the groove in promoting the imbibition of the particulate material into con¬ tact with the conductive layer renders the method ef¬ fective with electrographic elements having one or more layers overlying the conductive layer which to- gether are of such substantial thickness as to render it impossible to imbibe the particulate material all the way from the surface of the element to the con¬ ductive 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 poly¬ meric binder which is so resistant to imbibition of electrically conductive particles as to render it im¬ possible to imbibe the particles 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 O electrographic element involved. Thus, when the element is one which is moderately susceptible to penetration by imbibition, the groove can be relatively shallow as long as it is of sufficient depth to enable the electrically conductive particles 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 material overlies the conductive 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 schematical¬ ly shown an electrographic copying apparatus 1 com- prising 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 elec- trically insulating support 3, an electrically con¬ ductive layer 4 overlying support 3, and an elec¬ trically insulating photoconductive layer 5 over¬ lying 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. Operative 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, an image seg¬ ment of electrographic element 2 advances past the exposure' station 8 wh.ere the segment is image- wise exposed by Xenon lamps or other known imaging apparatus to light patterns of a document to be copied. Rollers 16 serve to convey electrographic element 2 past the operative stations and properly position it during movement of the image segment through exposure station 8 to maintain effective contact between brush 6 and the surface of electro¬ graphic element 2. The electrostatic image residing on the image segment after passage through exposure station 8 is next advanced over a 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 transferred by the action of corona discharge device 12 to paper which is 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 con¬ nection means 18 adjacent to the opposite side there¬ of. Electrographic element 2, provided with per¬ forations 17, is especially adapted for use in an electrographic copying apparatus of the type de¬ scribed in U.S. Patent 3,914,047 issued October 21, 1975 to . 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 con¬ nection means 18 comprises a region of dispersed electrically conductive particles, within a non- recording portion of electrographic element 2, which extends from the surface of electrographic element 2 and, as shown in FIG. 4, reaches into contact with electrically conductive layer 4. The dispersed electrically conductive particles can be of any suitable conducting material such as, for example, carbon black or graphite. The region of dis¬ persed electrically conductive particles defines on the surface of electrographic element 2 an elongated stripe 19 which is longitudinally disposed in the direction of motion of electrographic element 2 and which encompasses an elongated longitudinally dis¬ posed groove 20. In the alternative embodiment of electro¬ graphic element 2 which is shown in FIG. 3, there is provided a second electrical connection means 21 comprising a region of dispersed electrically conductive particles 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 electrically conductive particles 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 con¬ ductive layer 4 within each of perforations 17. Referring now to parts (a), (b) and (c) of FIG. 4, there are shown alternative embodiments of electrical connection means 18. In each of these embodiments groove 20 extends from the exterior surface of electrographic element 2 at least to a position proximate to conductive layer 4. In the embodiment of part ( . a), groove 20 terminates a short distance above the upper surface of conductive layer 4 and the dispersed electrically conductive OMPI -ια- particles have 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 layer 4, that is, it terminates at the upper surface of conductive layer 4. Dispersed electrically conductive particles are in contact with conductive layer 4 at the bottom of groove 20 and also as a result of their lateral movement into photoconductive layer 5 by a process of imbibition. In the embodi¬ ment of part (.c), groove 20 extends completely through conductive layer 4 and into support 3 - Dispersed electrically conductive particles are in contact with conductive layer 4 at its exposed edges 24 and 24' within groove 20 and also as a result of their lateral movement into photoconductive layer 5 by a process of imbibition. FIG. 5 shows an alternative embodiment of electrographic element 2 which includes a subbing layer 25 between electrically conductive layer 4 and photoconductive layer 5 and a protective over¬ coat layer 26 over photoconductive layer 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 electrically conductive particles are in contact with conductive layer 4 at * its exposed edges 24 and 24' within groove 20 and also as a result of their 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 electrically conductive particles), this serves to ground _ O 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, poly(ethylene terephthalate) film, polycarbonate film, paper, polymer-coated paper, and the like. Most usually the support is a tough, flexible, transparent, elec¬ trically insulating material such as a polyCethylene 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 photo- conductors, as is well known in the electrographic 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 de¬ posited 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 layer of an electrically conductive salt, as described for ex¬ ample in U.S. Patents 3,007,801 and 3,267,807. A further example of a useful conductive layer is a layer comprised of a dispersion of carbon black or graphite in a polymeric binder. The electrical connection means of this invention is a region of dispersed electrically conductive particles, which region 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 illustrated herein, or it can be spaced inwardly from the edge at any desired location. Typically, O PI it will be at the edge or close to the edge of th.e 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 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 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 electrically conductive particles with¬ in the element an imbibable suspension comprising the electrically conductive particles and at least one organic solvent 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 suspension, as hereinafter described in greater detail, advantage¬ ously contains a polymeric binder which will aid in bonding the conductive particles within the element and assist in providing a stripe which is 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 illustrated herein, or a metal strip, or a metal roller. 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 layer as being charged to 6QQ volts, it is intended to mean 6QQ volts above a reference ground potential. For convenience, ground potential as used herein is arbitrarily assigned a value of zero volts. The electrically conductive particles which form the electrical connection means of this invention can be any finely-divided particles having good electrical conducting properties. Typical conductive particles include particles of graphite, carbon black, nickel, silver, aluminum, copper, tin, etc. and mixtures thereof. The size of these conductive particles can vary depending on ' the particular material used but generally ranges from about O.OOlμ to about 100μ. Graphite has been found to be very satisfactory based on its property of being a good lubricant as well as 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 electrically conductive particles 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 dis¬ solving) the polymeric binder contained in a photo¬ conductive layer or other layer, such as a subbing layer, which is in direct contact with the elec- trically 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 atoms such as methanol, ethanol, isopropanol, etc. ketones having 3 to 1Q earbon atoms such as acetone, methyl- ethyl ketone, etc., and chlorinated alkanes having *-gtJREX^ OMPI 1 to 8 carbon-atoms such as methylene chloride, propylene chloride, chloroform, etc. Mixtures of these solvents may also be used. The particular solvent or mixture employed is somewhat dependent upon the polymer to be impregnated and the selection of the optimum solvent to be used is apparent to those skilled in the art. A particularly useful solvent which is capable of impregnating most of the more common hydrophobic film-forming resin binders employed in the various layers of electrographic elements, com¬ prises a mixture of a ketone such as acetone or methyl ethyl ketone with a chlorinated hydrocarbon such as methylene chloride or propylene chloride. The solvent and electrically conductive particles are thoroughly mixed, e.g., with a ball mill or blender, so as to create a uniform dispersion of the conductive particles in ' the solvent. Frequently, in order to obtain a uniform stable dispersion of solids in liquid, it is necessary to employ a small amount of a polymeric binder. The added binder aids primarily in the creation of a more uniform dispersion. When such a binder is employed, the weight ratio of conductive particles to binder ranges from 0.5 to 10 parts and preferably 1.5 to 2.5 parts of conductive particles for each part of binder. Enough solvent is added to bring the solids content to at least 5% and not more than 90% of the liquid dispersion. The binder used in the imbibable suspension can be any of a wide variety of polymers. Suitable polymers include styrene-butadiene copolymers; silicone resins; styrene- alkyd resins; silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly (vinyl acetals) such as pol (vinyl butyral); poly- acrylic and methacrylic esters, such as polyCmethyl- methacrylate), poly (n-butylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; polyesters such " as pol (ethylene - U terephthalate.); phenolfor aldehyde resins; polya ides; polycarbonates; polythiocarbonates; polyCethylene- glycol-co-bishydroxyethoxyphenyl propane terephthalate1; copolymers of vinyl haloarylates and vinyl acetate 5 such as poly(vin 1-m-bromobenzoate-covinylacetate1; polyolefins such as polyethylene, polypropylene, etc. The electrographic elements of this invention can be composed of only three layers, namely, an electrically conductive layer sandwiched between a Q support and a photoconductive layer. However, they may include two or more contiguously disposed photo¬ conductive layers, each of which exhibits different characteristics , and may include a variety of other layers such as barrier layers, subbing layers, over- 5 coat layers, and so forth. The various layers making up the element typically vary greatly in thickness. For example, the support may have a thickness of 100 microns and the photoconductive layer a thickness of 20 microns while each of the electrically conductive Q 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 con¬ tinuous belt but it may be employed in other con¬ figurations such as for example in the form of a flat 5 sheet or in cylindrical form. The photoconductive layer in the electro¬ graphic element of this invention can be prepared from a wide variety of materials. In general, this layer is prepared by dispersing a photoconductor in 0 a resinous binder and coating the resultant dispersion on the electrically conductive layer or on a subbing layer overlying the electrically conductive layer. Binders useful for this purpose include the same polymers referred to above as being useful as binders 5 in the imbibable suspension. Photoconductors suitable for use in the photoconductive layer include inorganic, organic and organo-metallic photoconductors. Typical photoconductors which are useful include zinc oxide, " EX " ^ OMPI titanium dioxi.de, organic derivatives of Group lΥa and Va metals such, as those having at .least one amino-aryl group ' attached to the metal atom, aryl amines, polyarylalkanes having at least one a ino 5 substituent, and the like. The use of organic photo¬ conductors 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; 10 3,265,496; 3,265,497; 3,274,000; and 3,6l5,4l4. A sensitizer for the photoconductor may • optionally be included in the photoconductive layer to change the electrophotosensitivity or spectral sensitivity of the element. Sensitizing compounds use- 15 ful in the photoconductive layers described herein can be selected from a wide variety of materials, in¬ cluding such materials as pyryliums, including thiapyrylium and selenapyryliu dye salts, disclosed in U.S. Patent 3,250,615; fluorenes such as 7,12- 20 dioxo-13-dibenzo(a,h)fluorene, 5,10-dioxo-4a,ll- diazabenzo(b)fluorene, 3,13 -dioxo- 7 -oxadibenzo- (b,g)fluorene, ' and the like; aromatic nitro compounds of the kinds described in U.S. Patent 2,610,120; anthrones like those disclosed in U.S. Patent 25 2,670,284; quinones, U.S. Patent 2,670,286; benzo- phenones U.S. Patent 2,670,287; 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 various dyes, 30. such as cyanine (including carbocyanine), mercocyanine diarylmethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, azo, anthraquinone dyes and the like and mixtures thereof. The sensitizing dyes preferred for use with this invention are selected 35 from pyrylium, selenapyrylium and thiapyrylium salts, and cyanines, including carbocyanine dyes. OMP Where a sensitizer is employed with the binder and organic pho o.conduc or to form a sensitized electrographic layer, it is suitable to mix an amount of the sensitizer with the coating composition so that, after thorough, mixing, the sensitizer is uniformly distributed in the coated layer. Other methods of incorporating the sensitizer 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 photoconductors, therefore, no sensitizer is required in a particular photoconductive layer. However, since relatively minor amounts of sensitizer give substantial improvement in speed in such layers, use of a sensitizer is preferred. The amount of sensitizer that can be added to the photo¬ conductive layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photo- conductor and sensitizing compound used. In general, substantial speed gains can be obtained where an ap¬ propriate sensitizer is added in a concentration range from 0.0001 to 30 percent oy weignt based on the weight of the film-forming coating com¬ position. Normally, a sensitizer. is added to the coating composition in an amount by weight from 0.005 to .0 percent, by weight of the total coating composition. Solvents useful for preparing the photo¬ conductive coating compositions include a wide variety of organic solvents for the components of the coating composition. For example, benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, and the like; ethers, such as tetrahydrofuran and the like, or mixtures of such solvents can advantageously be employed in the practice of this invention. In preparing the coating compositions for the photoconductive layer, useful results re obtained where the photoconductive substance is present in an amount equal to at least about 1 weight percent of 5 the coating composition. The upper limit on the amount of photoconductor present can be widely varied in accordance with usual practice. It is normally required that the photoconductor be present in an amount ranging from about 1 weight 10. percent of the coating composition to about 99 weight percent of the coating composition. A preferred weight -range for the photoconductor in the coating composition is from about 10 weight percent to about 60 weight percent. - j c Coating thicknesses of the photoconductive layer(s) can vary widely. Normally, a wet coating thickness in the range of 0.01 to 2 millimeters is useful in the practice of this invention. A prefer¬ red range of coating thickness is from 0.02 to 0.2 20 millimeters before drying, although such thicknesses can vary widely depending on the particular ap¬ plication desired for the electrographic element. In the method of manufacturing this in¬ vention an elongated longitudinally disposed groove 5 is formed in a non-recording portion of the electro¬ graphic element. This groove extends from an ex¬ terior surface of the element at least to a position proximate to the electrically conductive layer. It is formed with a depth and width adapted to promote 0 the imbibition of the suspension of electrically- conducting particles into contact with the elec¬ trically conductive layer. The optimum depth and width will depend upon numerous circumstances in¬ cluding the structure and composition of the electro- 5 graphic element and the imbibing characteristics of the suspension containing the electrically conductive particles. As explained hereinabove, the groove O ay 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, but may not penetrate through, the electrographic element. Typically, a groove with a width of from 0.2 mil¬ limeters to 5 millimeters is suitable. Imbibition of the suspension containing the electrically conductive particles causes it to spread laterally as well as to penetrate downwardly from the surface to which it is applied. Since the suspension is applied as a stripe which encompasses the groove, it flows into the groove and spreads 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 region of imbibed electrically conductive particles will easily extend into ef¬ fective contact with the conductive layer and there¬ by provide an electrically conductive path from the conductive layer to the surface of the element. The groove can be formed in the electro- graphic -element in any suitable manner. One technique which is suitable for forming the groove is the use of a revolving knife blade which is rotated at high speeds, such as speeds of several thousand revolutions per minute. The blade is pre- ferably made of a very durable and wear resistant material, such as stainless steel. It may be a steel blade with a diamond edge. An alternative technique is to carry out a localized pyrolysis in which part of the electrographic element is vaporized in a controlled manner along the desired path. Methods of accomplishing this include the use of a laser beam or an electron beam. -2Q- 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 the infrared range are generally satisfactory. A C0 2 laser is preferred because of its high efficiency characteristics. The width of the laser beam will be selected in accordance with the desired width of the groove. The laser beam can be moved relative to a stationary sub¬ strate to form the groove but it will usually be more convenient for the laser beam to be fixed in position and the substrate 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 dispersion containing the electrically conductive particles is applied to the surface of the element as an elongated stripe which encompasses the groove. The stripe may be of any suitable width,.with the width ordinarily 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 usually be located at or near the mid¬ point of the stripe but it may be at any position within the stripe, as desired. Application of the imbibable dispersion 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 the use of a coating hopper such as a hopper of the extrusion type. The imbibable dispersion flows into the groove and penetrates into the material surrounding OM the grooye. If the groove does not extend all the way through, the photoconductive layer, the .com- * - position will be imbibed through the.material which lies between the bottom of the groove and the elec- trically conductive layer. It will also spread laterally from the walls of the groove by the process of imbibition into the photoconductive layer and into any subbing layer overlying the electrically conductive layer. The Imbibable suspension is applied in an amount sufficient to provide effective contact of the electrically conductive particles with the electrically conductive layer. The optimum amount to be used will depend on the characteristics of both the imbibable suspension and the electro- graphic element, as well as the method of application of the suspension. The amount used can be sufficient 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 electrically conductive particles. 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 suspension 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 op¬ eration. When the groove-forming step and the step of applying the imbibable suspension 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 5 to 200 centimeters per second. The steps of forming the groove and and applying the imbibable suspension can also be carried out as part of a continuous process which involves other operations such as coating of the various layers on the support, forming the per- forations, slitting, and so forth. After application of the imbibable suspension, it is preferred to im¬ pinge 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 suspension and thereby facilitate good contact with the electrically conductive layer. As explained hereinabove, the imbibable suspension preferably contains a polymeric binder. The binder promotes the bonding of the electrically conductive particles within the element and assists in forming a stripe which is durable and abrasion resistant. 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 char- acteristics of the conductive stripe, the electro¬ graphic 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 in¬ vention in which the groove is formed in the electro¬ graphic 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 backing 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 2Q. To assist in removing vapors produced by vaporization of the material on -^f O which laser beam 4Q impinges, an exhaust duct 42 con¬ nected to a vacuum source (hot shown1 is positioned closely adjacent to. the region of impingement. A spray nozzle 44 fed with the imbibable suspension from a suitable supply source Cnot shown) directs a liquid spray 46 onto the surface of electrographic element 2 to form a stripe 19 which encompasses groove 20. After passing under spray nozzle 44, electrographic element 2 is advanced into a drying chamber (not shown) 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 em¬ bodiment of the method of this invention in which the groove is formed in the electrographic element 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 element 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 posi¬ tioned closely adjacent to the region where cutting takes place. After groove 20 has been cut, the advancing element passes under spray nozzle 44, which directs liquid spray 46 onto its surface and there- by forms stripe 19 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 eiectrographic 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 suspension 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 pre- viously 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 ex¬ ample, 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 sus- pension is capable of penetrating a substantial distance into the photoconductive layer, or other layer of the electrographic element, it is only 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 suspension 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. O This vaporization is, of course, accompanied by the " generation of considerable heat and the solid material is rendered molten and flow.ab.le, 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 here¬ in. With some polymeric binders, the fused material formed .by the laser beam may, upon subsequent cooling, be converted to a crystalline state in which it is quite resistant to penetration by imbibable suspen¬ sions. 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 electrical- 5 ly conductive layer or which extends into the elec¬ trically 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 electrically conductive particles 0and the electrically conductive layer at the bottom of the groove. If the groove cuts into or through the electrically conductive layer, there is opportunity for contact between the electrically conductive par¬ ticles and the edges of the electrically conductive 5layer within the groove. In either instance, contact between the electrically conductive particles and the electrically conductive layer is also provided as a result of the lateral spreading of the imbibable suspension. The lateral spreading action which oc- 0curs is an important feature of the present invention since it provides much more effective contact with 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 5of an electrically conductive composition which is not capable of imbibition would, of course, not provide the lateral spreading action and thereby would give much less effective contact. - REXCΓ OMPI . WWIIPPOO The combined use of a grooye and an imbibable suspension in accordance with this invention is -use¬ ful with electrographic elements of many * different structural variations. Thus, the method.of this in- vention is applicable in any situation where there is an inaccessible electrically conductive layer sand¬ wiched 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 to the surface of the photoconductive layer. During this charging step, the electrically conducting layer is maintained at ground potential by electrically con- necting the conductive stripe on the electrographic element to ground. In the absence of grounding in this manner, the difference in potential 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 photocon¬ ductive layer because of the substantial dark in¬ sulating property of the layer, i.e., the low con¬ ductivity of the layer in the dark. 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 ground potential as efficiently as with an element that is charged while stationary. In other words, the electrical connection 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 O photoconductiye layer is then selectively dissipated from the surface of the layer by imagewise exposure to light 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 photoconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area. The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charged or uncharged areas are rendered visible, by treatment with a medium comprising electrostatically responsible particles having optical density. Liquid development of the latent electrostatic image may also be used. It is frequently necessary during development to maintain the electrically-conducting layer at a given potential in order to obtain a clean background. The electrical connection means 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 terephthalate) support with a thickness of 100 microns, a nickel layer with a thickness of less than 1 micron overlying the support, and a photo¬ conductive layer, comprised of an organic photocon¬ ductor dispersed in a polycarbonate binde and having a thickness of approximately 20 microns, overlying the nickel 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 b a rotating stainless steel knife blade driven by a motor at a speed of 6000 revolutions per minute while the electro¬ graphic element is advanced at a speed of 30 centi¬ meters 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 fol¬ lowing imbibable suspension onto the surface of the element: Component Weight % Polyvinylbutyral resin 3-3 Carbon black 6.5 Propylene chloride 41.2 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 165°F. In a further typical example of the practice of this invention, the electrographic element described above is grooved by the use of a laser beam and then coated with an imbibable suspension to form the de¬ sired conductive stripe. A suitable laser for this purpose is a 50-watt C0 2 laser equipped with a 2.5 inch focal length lens. The 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 30 centimeters per second. Pre¬ ferably, 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 polyCethylene terephthalate) support. Following formation of the groove, an imbibable suspension, as described above, is applied in the form of a stripe O which encompasses the groove by a suitable method of application such as spraying or hopper coating . OMPI Λ> WIPO .

Claims: We claim: 1. A method for providing electrical con¬ nection means within an electrographic element, said element comprising an electrically insulating support, an electrically conductive layer overlying said support, and an electrically insulating photo¬ conductive layer overlying said conductive layer, said means defining a conductive electrical path connecting an exterior surface of said element to said conductive layer, characterized in that said method comprises 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, (2) applying to said surface an imbibable suspension comprising electrically conductive particles, and (3) imbibing said particles into said element to form a region of dispersed elec¬ trically conductive particles extending from said surface into contact with said conductive layer, said suspension 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 particles into contact with said- conductive layer and thereby form said conductive electrical path. 2. The method as claimed in Claim 1 where¬ in 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 where¬ in said imbibable suspension is applied by spray -^J O - W coating. 7. The method as claimed in Claim 1 wherein said imbibable .suspension comprises a dispersion of said electrically conductive particles in a solution containing a polymeric binder. 8. The method as claimed in Claim 7 wherein said element is heated after application of said imbibable suspension to facilitate the removal of said solvent. 9- The method as claimed in Claim 1 where¬ in said support is a poly(ethylene terephthalate) film, said electrically conductive layer is nickel, said photoconductive layer comprises an organic photocon¬ ductor in a polymeric binder, and said electrically- conducting particles are particles of carbon black. 10. A method of providing electrical con¬ nection means within an electrographic element, said element comprising an electrically insulating support, an electrically conductive layer overlying said sup- port, and an electrically insulating photoconductive layer overlying said conductive layer, said means being adapted to establish electrical connection be¬ tween said conductive layer and a grounding or biasing member which engages a surface of said element while said element is in motion, characterized in that said method comprises the steps of (1) forming within a non-recording portion of said element an elongated groove which is longitudinally disposed in the direction of intended motion of .said element, said groove extending from said surface at least to a position proximate to said conductive layer, (2) ap- plying to said surface an imbibable suspension com¬ prising electrically conductive particles, and (3) imbibing said particles into said element and form in said element a region of dispersed electrically conductive particles extending from said surface into contact with said conductive layer, said suspension OMPI being applied to said surface as an elongated stripe which is longitudinally disposed in the intended direction of motion of said element and which en¬ compasses said groove, said groove being of width and depth, adapted to promote the imbibition of said particles Into contact with said conductive layer, said stripe being adapted for engagement with said grounding or biasing member to thereby provide elec¬ trical connection between said member and said con- ductive layer.

Inventors: MCCROSSEN D, MYLROIE V
Applicants: EASTMAN KODAK CO
Application year: 1979
Main classification: G03G5
IPC codes: G03G5, G03G15, G03G21