US3833364A

US3833364A - Method of developing electrostatic image charge

Info

Publication number: US3833364A
Application number: US00064032A
Authority: US
Inventors: M Sato; I Takahasi; H Satoru
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1968-11-18
Filing date: 1970-07-21
Publication date: 1974-09-03
Anticipated expiration: 1991-09-03

Abstract

A novel development system is disclosed to be used in conjunction with an electrophotographic imaging process. A developer composition comprising a toner, carrier and an electrodeforming material is used with a development electrode in order to enhance the development phase of the electrophotographic imaging process.

Description

United States Patent 1 [111 3,833,364 Sato et a1. Sept. 3, 1974 [54] METHOD OF DEVELOPING 2,919,247 12/1959 Allen 252/621 ELECTROSTATIC IMAGE CHARGE 2,965,573 12/1960 Gundlach 117/17.5

3,011,473 12/1961 Gundlach 117/17.5

[ Inventorsl Masamichisaw; IsojiTakahashi; 3,380,437 4/1968 Swyler ..117/17.s

Honjo Satoru, all of Asaka, Japan 3,390,664 7/1968 Donalies 117/17.5

. 3,393,663 7/1968 Donalies 1l7/17.5

[73] Asslgneel Xemx Corlmamm, Chester, 3,542,579 11/1970 Gundlach 117/17.5 22 Filed; J l 21 1970 3,607,342 9/1971 Sato et al 117/17.5

[21] Appl' No; 64o32 Primary Examiner-Michael Sofocleous Related US. Application Data [63] Cont' t'on f Se. N 776,835, N 18, 1968,

@112; ABSTRACT A novel development system is disclosed to be used in [52] 1.8. CI. 96/1 SD, 117/ 17.5 Conjunction with an electrophotographic i i [51] Int. Cl G03g 13/08 cess A developer Composition Comprising a toner, [58] Field of Search l17/17.5; 118/637; Carrier and an electrodeforming material is used with 96/1 SD; 252/621 a development electrode in order to enhance the development phase of the electrophotographic imaging [5 6] References Cited process.

6 Claims, 6 Drawing Figures PATENIEDSEP 14 3.833.364

SHEU 1M 2 FIG. 3

INVENTORS MASAMICHI SATO BY ISOJI TAKAHASHI ATTORNEY METHOD OF DEVELOPING ELECTROSTATIC IMAGE CHARGE BACKGROUND OF THE INVENTION The subject matter of this patent application relates to a method of developing an electrostatic charge pattern and in particular to an improved cascade development system.

In the electrophotographic process as described in US. Pat. No. 2,297,691 an electrophotographic plate comprising a conductive base material having a photoconductive insulating layer on the surface thereof is electrostatically charged uniformly in the dark. The charged plate is then exposed to a light image. The charges leak off to the base plate in proportion to the intensity of the light to which any given area is exposed. An image of electrostatic charge is thus formed on the surface of the photoconductive layer. The resulting electrostatic latent image is contacted with electroscopic marking particles thereby forming a visible image corresponding to the charge pattern. The developed image may then be fixed in situ to the photoconductive plate or, in instances when it is desirable to reuse a photoconductive plate, the developer particles may be transferred to a secondary substrate to which they are subsequently fixed.

Numerous techniques are known whereby an electrostatic charge pattern is made visible by development with the above mentioned marking particles. One such technique, known as cascade development, involves the use of developing materials consisting of a combination of finely divided pigmented electroscopic powder particles otherwise called toner with a coarser carrier material. The carrier material is triboelectrically charged to a polarity opposite to that of the electroscopic powder upon frictional engagement therewith and acts to retain the electroscopic powder which is attracted to and surrounds the carrier particles. The carrier particles transport and bring the toner particles into contact with the surface of the photosensitive member and the electrostatic latent image. The charge relationship is such that the charge of the image areas has a greater attractive force for the electroscopic powder particles than has the charge on the carrier material, the electroscopic powder particles thereby being attracted to the electrostatic latent image causing the latent image to be made visible.

According to the above process satisfactory results may be obtained when adapting the process to line copy imaging of black images on a white background or, in the case where a half toned image is employed as the original, simulated solid area coverage may be obtained. However, in the case where the original document is a continuous tone or of a uniform image density or where the line copy to be reproduced consists of large areas, due to the nature of the unevenness in the electrostatic fields, it has been substantially impossible to reproduce and develop uniformly electrostatic charge images of the nature described. Generally, when attempting to develop large continuous toned images, edge-only effects are realized which lack solid area reproduction thereby resulting in the reproduction of only the outline areas of the particular image. Recently, in an attempt to solve the above described deficiency, the use of a development electrode has been introduced into the system, the electrode being placed in close proximity to the surface of the electrostatic image-bearing surface so as to leave a very narrow gap between the development electrode and the imagebearing surface. However, when such a configuration is used in conjunction with a continuous imaging process there often results a noticeable impediment to the flow of the developer thereby lowering substantially the process speed as well as increasing down time of the apparatus as a result of conglomerating and clogging of the developer.

In order to overcome this disadvantage a method has been proposed whereby a screen pattern is introduced into the conventional xerographic process thereby decomposing the continuous tone or image of large area into a half tone pattern. Though this method eliminates the need for a development electrode the resulting image produced shows a significant reduction in image density.

Therefore, it is an object of this invention to provide an imaging system which will overcome the above noted disadvantages.

It is a further object of this invention to provide a novel electrophotographic imaging apparatus.

Another object of this invention'is to provide an imaging process capable of reproducing images having large areas and uniformly high densities in a manner which does not significantly effect the overall operating efficiency of the system.

Still a further object of this invention is to provide an imaging system capable of reproducing continuous tone images.

Yet, still another object of this invention is to provide an imaging system capable of reproducing high density image areas by means of cascade development.

Yet, still a further object of this invention is to provide a novel electrophotographic imaging system.

SUMMARY OF THE INVENTION- The foregoing objects and others are accomplished in accordance with the present invention by providing a novel development system to be used in conjunction with the generally accepted electrophotographic process steps. An image pattern is formed on the surface of an electrophotographic plate comprising a photoconductive insulating material and the resulting electrostatic latent image developed according to the above described cascade process wherein a developing electrode in the shape of a lattice network is utilized. The developer composition comprising the electroscopic marking particlesor toner and the granular carrier. ma-

terial is cascaded across the image bearing surface of the photoconductive plate. The toner particles are electrostatically attracted and held to the surface of the photoconductive plate in areas corresponding to the existing electrostatic charge pattern. In addition to the standard carrier-toner components of the developer there is present an electrode forming material which when used as a part of the developer composition in conjunction with the development electrode of the present invention substantially effects the resulting development process herein applied when used in conjunction with a cascade mode of image development.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in the accompanying drawings in which:

FIG. 1 represents a sectional view of the apparatus implementing the process of the present invention;

FIG. 2 is a top view of the developing electrode used in conjunction with the present invention;

FIG. 3 is a sectional view along the line AA of the developing electrode illustrated in FIG. 2 superimposed on an electrophotographic plate;

FIG. 4 is a sectional view representing an alternate embodiment of the configuration of the developing electrode of the present invention; and

FIGS. 5 and 6 represent a magnified sectional view of the configuration of the present invention as it appears during the development process herein described.

Referring now to FIG. 1 there is seen an exemplary drawing generally demonstrating the process of the present invention in which an electrophotographic plate generally designated 10 comprising a photoconductive insulating material 11 coated on the surface of a conductive substrate or support material 12. An electrostatic latent image is formed on the surface of the photoconductive material by any suitable technique such as by applying electrostatic charge to the surface of the photoconductive plate through a stencil or by the more conventional xerographic steps which entail uniformly charging the surface of the photoconductive plate and selectively discharging the charged plate so as to form an electrostatic charge pattern. A developer composition 14 comprising an electrode forming material in conjunction with a toner-carrier composition is cascaded across the surface of the image-bearing substrate from container 13. There is employed during the development phase of the process a development electrode consisting of a member of conductive wires 16 fixed to frame 17.

Any suitable photoconductive material may be used to prepare the electrophotographic plate of the present invention. Typical photoconductor materials include selenium, sulphur, anthracene, inorganic photoconductive pigments, such as zinc oxide or cadmium sulfide dispersedin inertbinder resins, organic photoconductivepigmentssuchas phthalocyanine dispersed in an inert bind'r r'esin and homogeneous photoconductive organic materials. Any suitable backing material for the photoconductive layer may be used. Generally it is preferred that the backing material have an electrical resistance less than the photoconductive layer such that it will act as a ground when the electrostatically charged coating is exposed to light. Typical such materials include aluminum, brass, conductive glass, steel, nickel and conductive paper.

In FIG. 2 there is seen a development electrode characteristic of the present invention generally designated 20 which consists of a series of metallic wires 21 stretched through frame 22 in a manner such that the wires form one continuous electrical circuit. The interval at which the metallic wires are stretched is generally set such that they are greater than the size of the electrode forming material which is more completely described hereafter so as not to impede the developer flow during the development phase of the present invention. It is preferred that the interval be kept as small as possible within the working parameters of the invention and practically it is effective to select the interval within a range from a value slightly larger than the size of the electrode forming material.

FIG. 3 represents a sectional view of the development electrode of FIG. 2 seen along the line AA, wherein the electrode wires 21 within the frame 22 are superimposed upon the surface of a photoconductive plate 25 comprising a conductive substrate 26 and photoconductive layer 27. The space between the development electrode wires 21 and the surface of a photoconductive layer 27 carrying the electrostatic latent image should be such that the developer composition including the carrier and toner particles may freely pass.

FIG. 4 represents an alternate configuration of the developing electrode of the present invention seen in a cross sectional view wherein the development electrode 30 constitutes frame 31 and two rows of upper and lower metallic wires each centrally located with respect to the other. The nearest distance between the lower wire 32 and the upper wire 33 corresponds to the interval between wires is discussed in FIG. 2 and should satisfy the conditions with respect to this interval. That is, the interval should be such so as not to obstruct the movement of carrier and electrode forming material during development.

FIG. 5 represents the implementation of the electrode forming material of the present invention in conjunction with the development electrode of FIG. 3. In FIG. 5 there is seen a magnified sectional view of a photoconductive plate 35 comprising a photoconductive insulating material 36 superimposed upon the conductive substrate 37. Represented on the surface of the photoconductive plate is the carrier-toner developer composition 38 and the electrode forming material 39. The wires of the development electrode 40 are strategically placed above the image-bearing surface of the photoconductive member 35. The electrode forming material 39 is illustrated for convenience of simplicity in a globular form but the material may be employed in any desired shape as will be further discussed hereinafter. As in FIG. 1 if a development electrode is placed a little apart from the surface bearing the electrostatic latent image, the surface is slightly tilted with respect to the horizontal and developer as well as electrode forming material is cascaded from above the development electrode as illustrated so the carrier being heavier and smaller than the electrode forming material sinks while the electrode forming material is refloated. If vibration is applied either in the lateral or longitudinal direction relative movement is produced between the developer and the electrode forming material thereby promoting the separation of carrier from electrode forming material. The carrier material with attached toner lies below and separate from the electrode forming material and contacts the latent image with toner while the electrode forming material remains above and is separate from the developer. The electrode forming material being electrically connected in the lateral and longitudinal directions acts similar to a segment of development electrode. Inasmuch as the electrode forming material also touches the metallic wires, mutual electrical contact is insured in a more perfect manner. If the particles making up the electrode forming material are electrically shorted in perfect mutual contact they will display the effectof a piece of development electrode and therefore the metallic wires may be excluded from the system. However, the electrode forming material is generally relatively light and therefore mutual contact is not always assured. Electrical contact is enhanced by the more frequent introduction of lateral or longitudinal motion to the materials of the system especially in those instances when the metallic wires are eliminated from the operation. It is preferred however that the metallic wires be included in conjunction with the electrode forming material for optimum results.

FIG. 6 represents the utilization of the electrode forming material of the present invention in conjunction with the development electrode of FIG. 4. Inasmuch as the metallic wires are placed alternately in upper and lower rows more opportunities are given for contact with the electrode forming material thus enhancing mutual electrical connection.

The electrode forming material of the present invention generally will have an apparent specific gravity at least less than that of the carrier component of the developer composition. In addition, at least the surface of the electrode forming material should be conductive in nature so as to satisfy the necessary surface properties which provides for adequate conductivity. A globular or similar shape is preferred, however, cylindrical, columnar, ring, coil or bulky shape material have also been found suitable and acceptable. The minimum diameter of the electrode forming material should be at least equal to or larger than that of the carrier and the apparent specific gravity of the electrode forming material should be at least less than the specific gravity of the carrier. It is further desirable although not necessary that the order of frictional charging of the electrode forming material be in the neighborhood of that of the particular toner utilized.

Any suitable material may be used as the electrode forming material of the present invention such that it satisfies the above requirements. For example, cylindrical or globular shaped plastic or foam plastic pellets processed with chemical plating may be utilized, hollow metallic globes, hollow metal tubing, hollow glass globes or tubing processed with chemical plating and other like materials either alone or as mixtures may be utilized. Any other material meeting the conditions and requirements set forth above may be used in the course of the present invention.

The expression apparent specific gravity refers to the specific gravity of the electrode forming material itself in cases where the composition of the material is homogeneous throughout its interior. If heterogeneous components are existing in the interior then the expression apparent specific gravity refers to the total weight as divided by the total volume occupied by the electrode forming material. For example, if a globular body is considered for convenience of explanation and in the case where the entire globe is made of homogeneous glass, its specific weight is the specific weight of glass. However, if the globe is hollow or contains many air bubbles the weight of the globe per unit volume becomes smaller. Accordingly, even if the electrode forming material is larger in specific gravity than the carrier, its apparent specific gravity can be made smaller than the carrier by properly selecting its shape.

The surface of the electrode forming material should be conductive and preferably should possess metallic conductivity. The condition can be satisfied completely if the electrode forming material is made of metal or a semi-conductor similar to metal but if the material is an insulating substance then conductive treatment can be applied to its surface. A typical method of such a treatment consists in the formation of a conductive film over the surface of the specific insulating material by applying chemical plating or by vacuum evaporation or by applying a conductive paint to the surface.

Though the application of metallic wire as the development electrode as described above is preferred, similar results may be obtained by employing a plastic wire processed with a conductive treatment such as chemical plating, metal stripping or similar procedures. Also, although in the present illustrations the electrode forming materials are illustrated as if they are generally uniform in size this need not be the case and both large and small particles may be utilized and the electrode forming material may thus exist in a mixed condition. Depending upon the case, mixture of especially large particles of electrode forming material may improve mutual electrical connection. As for the structure of the development electrode although the present illustration represents the metallic wires as being laid in parallel any other similar configuration may be utilized such that it is in accordance with the requirements of the present invention. For example, it has been experimentally established that wires arranged in the form of a gauze have been found to be quite suitable so long as they do not impede the movement and flow of the developer composition and electrode forming material.

The developer composition and electrode forming material may be mixed and then cascaded across the image bearing member or they may be cascaded separately without being mixed. Thus development may be carried out either independently, simultaneously, or in a stepwise manner. For example, if the electrode forming material is in a globular form and quite light, it has good separability and therefore satisfactory results can be obtained when the developer composition and electrode forming material are mixed prior todevelopment. If, however, the separability between the developer material and the electrode forming material is not suitable then it is preferred to cascade each separately or one after the other. For example, if the electrode forming material is cylindrical in shape and is relatively heavy its separability will not be as good and therefore the developer composition is first cascaded to form a layer and then the electrode forming material is cascaded onto the first layer with simple separation being the result. If the electrode forming materials are used for an extended period, toners will stick to their surface and thus deteriorate mutual electrical connection. As a result it is desirable to periodically remove the toner particles from the electrode forming material. Such may be accomplished by washing the toner particles from the electrode forming material by the application of an organic solvent. In addition, the developer composition and electrode forming material may be separated simply by means of simple sieve.

PREFERRED EMBODIMENTS To further define the specifics of the present invention the following examples are intended to illustrate but not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated.

EXAMPLE I Foam polystyrene formed to a globular shape of about 2 mm. in diameter the surface of which is covered with a silver film by means of chemical plating is employed as the electrode forming material. The weight of electrode forming material is about 3 mg. per piece. The developer composition comprises carriers made up of glass globes about 0.86 mm. in diameter, covered with a thin layer, about 0.5 micron, of nitrocellulose, and toner made up of polystyrene and carbon black kneaded, mixed and prepared in powder form. The carrier and toner are mixed and subjected to revolving motion and friction resulting in the carrier material being charged negatively and the toner material charged positively with the latter adhering uniformly to the surface of the carrier.

Zinc oxide paper prepared by applying a kneaded mixture of photoconductive zinc oxide and a resin to a paper substrate processed with a conductive treatment is employed. The paper is uniformly charged negatively in the dark and exposed to a positive transparency to produce an electrostatic latent image. The photoconductive paper is placed on a metal plate with the surface bearing the latent image facing up and a development electrode placed above it. The development electrode has a structure similar to that disclosed in FIG. 2 and employs stainless steel wire 0.3 mm. in diameter as the metallic wire element, with each wire being stretched at intervals of about mm. and at a distance of about 2 mm. from the surface bearing the latent image. The frame supporting the metallic wires is made of polyvinylchloride plates. A mixture of the developer composition and electrode forming material is cascaded from above across the electrostatic latent image bearing plate by tilting the structure at an angle of about 10. Total concentration of the developer and electrode forming material consists of 43 parts carrier, 2 parts toner and 8 parts of the electrode forming material. The cascaded developer composition and the electrode forming material is rolled across the surface carrying the latent image. Under these conditions the developer composition settles and the electrode forming material is refloated both, therefore, having nearly completely separated. Some of the electrode forming material remains in the lower part in an unseparated condition. Complete separation is realized by shaking the structure a few times in the horizontal direction. Next, the entire structure is tilted upside down. After rocking the structure in its tilted position several times the developer and electrode forming material are removed. A developed image is observed which is not at all effected by edge effects. The image is fixed, after removal of the development electrode, by infrared radiation, to the surface of the photoconductive paper. A high quality image is produced.

EXAMPLE ll The process of Example I is repeated with the exception that the polystyrene foam material has a diameter of about 1.5 mm. and a weight of about 8 mg. per piece. The remaining steps and aspects of the example are the same.High quality images are obtained.

EXAMPLE Ill The process of Example I is repeated with the exception that the electrode forming material has a diameter of about 3 mm. and a weight of about 1 mg. per piece. Satisfactory results are obtained.

' EXAMPLE IV Under the conditions of Example I globular pellets about 3 mm. in diameter of polymethyl methylacrylate, the surface of which is made conductive by chemical plating with copper, are employed as the electrode forming material. The concentration of the developer composition and electrode forming material consists of parts carrier, 2 parts toner and 40 parts electrode forming material. The remaining steps and aspects of the process being the same, similar results are obtained.

EXAMPLE V Under the conditions of Example I aluminum pipes 25 mm. in outer diameter, 0.2mm. in wall thickness and cut to a length of about 4 mm. are employed as the electrode forming material. The concentration of the combined electrode forming material and developer composition consists of 30 parts electrode forming material, 40 parts carrier and 1.5 parts toner. Satisfactory results are obtained while following the remainder of the procedure of Example I.

EXAMPLE VI Utilizing spherical nitrocellulose shells about 1.5 cm. in diameter and 0.4 mm. in wall thickness with a silver plated surface as the electrode forming material, satisfactory results are obtained with the developer and latent image forming material being the same as that in Example I. The electrode forming material, carrier and toner are applied at the ratio of 3025022 parts respectively.

EXAMPLE Vll EXAMPLE Vlll A mixture of 40 parts of silver plated polystyrene globes about 3 mm. in diameter and 25 parts of silver plated cylindrical polystyrene pellets having a diameter of about 1 mm. and a length of about 2 cm. is employed as the electrode forming material. Using the same developer, development electrode and latent image forming material as in Example I good results are obtained.

EXAMPLE lX Under the conditions of Example I the development electrode is replaced by the following and satisfactory results are obtained. Employing 0.4 mm. copper wire as the metallic wire the development electrode consists of two rows of stretched wires as illustrated in FIG. 4. Copper wires in the lower row are stretched at intervals of about 10 mm. and at the height of about 4 mm. from the bottom of the frame. The copper wires in the upper row are stretched at the height of about 6 mm. from the bottom of the frame and at intervals of about 10 mm. in such alternate manner that the wires in the upper row are situated in between the wires in the lower row.

Employing this development electrode in the manner described in Example I good results are obtained.

EXAMPLE X The steps of Example I are repeated with the exception that instead of the metallic wire being utilized as the development electrode, an electrode consisting of aluminum strips, mm. in width and 1 mm. in thickness, stretched at intervals of mm. and at a height of 4 mm. from the surface of the latent image is employed with satisfactory results being obtained.

EXAMPLE XI Cylindrical pellets of phenoxy resin PKDA 8080, commercially available from Union Carbide Company, about 2 mm. in external diameter and 3 mm. in length and covered with silver by chemical plating are employed as the electrode forming material. The developer composition comprises carriers made up of glass balles about 0.8 in diameter and covered with a thin layer of ethyl cellulose and toner made up of polystyrene in carbon powder kneaded and prepared in the form of powder. Carrier and toner are mixed and subjected to revolving motion and friction as a result of which the carrier is charged positively and the toner is charged negatively with the latter being attracted to the carrier.

An aluminum plate on which selenium is vacuum evaporated is employed as the photoconductive plate. The selenium flat plate is exposed to and uniformly electrostatically charged. The charged plate is exposed to an image in a manner which produces an electrostatic positive latent image corresponding to the original. With the electrostatic latent image facing up a development electrode is placed above the latent image side. A development electrode similar to that used in Example I is utilized. Developer is cascaded across the surface bearing the latent image by tilting the resulting structure about with respect to the horizontal level. The developer contacts the entire surface of the image bearing member. Next, the electrode forming material is poured onto the developer. Under this condition the entire structure is rocked several times in the horizontal direction and then the latent image surface tilted upside down. The entire structure is further rocked several times and then the device tilted to remove the developer and electrode forming material. As a result an image completely free of edge effects is obtained. After removal of the development electrode a sheet of white paper is placed on the developed image and the positively charged toner image electrostatically transferred and heat fixed to the paper. An excellent image is produced. The ratio in terms of weight of developer to electrode forming material employed in this example is 45 parts of developer (43.5 parts carrier and 1.5 parts toner) as against 40 parts of electrode forming material. In this example the developer and electrode forming material are supplied in an unmixed condition, one after the other to the latent image bearing surface. The

advantage realized utilizing this procedure is that the developer and electrode forming material remain separated from the beginning and as a result the development is accomplished at higher speeds and the quantity of toner adhering to the electrode forming material is substantially reduced.

Although the present examples were specific in terms of conditions and materials used any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention other steps or modifications may be used if desirable. In addition other materials may be incorporated in the electrode forming material and other aspects of the invention which will enhance, synergize or otherwise desirably effect the properties of the materials for the present use.

Anyone skilled in the art will have other modifications occur to them based on the teachings of the present invention. These modifications are intended to be encompassed within the scope of this invention.

We claim:

1. An electrophotographic imaging process comprising forming an electrostatic latent image on the surface of a photoconductive member, providing a development electrode spacially positioned opposite the image bearing surface of said photoconductive member and cascading a developer composition comprising an electrode-forming material, a carrier component and toner across the surface of said image bearing photoconductive member, said spacial positioning of said development electrode being such that the developer composition freely passes between said electrode and said photoconductive member, and said electrode forming material of said developer composition maintaining continuous contact with said development electrode during the development phase of said imaging process.

2. The process as disclosed in claim 1 wherein said development electrode comprises a latticed network of conductive wires, the interval between said wires being generally greater than the size of the electrode-forming material.

3. The process as disclosed in claim 1 wherein the specific gravity of said electrode-forming material is generally less than the specific gravity of the carrier component of said developer composition and at least the surface of said electrode-forming material is conductive.

4. The process as disclosed in claim 3 wherein the minimum diameter of the electrode-forming material is at least equal to that of the carrier component of the developer composition.

5. The process as disclosed in claim 1 wherein said development electrode is spaced about 4 mm. from the surface of said photoconductive member.

6. The process as disclosed in claim 1 wherein vibration is applied during the development phase of said process.

Claims

2. The process as disclosed in claim 1 wherein said development electrode comprises a latticed network of conductive wires, the interval between said wires being generally greater than the size of the electrode-forming material.
3. The process as disclosed in claim 1 wherein the specific gravity of said electrode-forming material is generally less than the specific gravity of the carrier component of said developer composition and at least the surface of said electrode-forming material is conductive.
4. The process as disclosed in claim 3 wherein the minimum diameter of the electrode-forming material is at least equal to that of the carrier component of the developer composition.
5. The process as disclosed in claim 1 wherein said development electrode is spaced about 4 mm. from the surface of said photoconductive member.
6. The process as disclosed in claim 1 wherein vibration is applied during the development phase of said process.