US3664857A

US3664857A - Xerographic development apparatus and process

Info

Publication number: US3664857A
Application number: US9225A
Authority: US
Inventors: Howard A Miller
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1970-02-06
Filing date: 1970-02-06
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23
Also published as: FR2080483A5; CA934233A; AU2512171A; GB1342911A; BE762379A

Abstract

Electroscopic toner material is applied to electrostatic charge patterns with at least one metallized fur brush having individual flexible filaments coated with a thin layer of an electrically conductive metal. The apparatus contains two metallized fur brushes, one having a low electrical conductivity and one having a high conductivity.

Description

United States Patent Miller [54] XEROGRAPHIC DEVELOPMENT APPARATUS AND PROCESS [72] Inventor: Howard A. Miller, Rochester, NY.

[73] Assignee: Eastman Kodak Company, Rochester,

[22] Filed: Feb. 6, 1970 [21] Appl No.: 9,225

[52] US. Cl. ..ll7/17.5, 118/637, 117/111 C [51] Int. Cl. t ..G03g 13/08, 603g 15/08 [58] Field ofSearch ..117/17.5, 111 C; 118/637 [56] References Cited UNITED STATES PATENTS 3,542,579 1 1/1970 Gundlach ..118/637 X 2,927,554 3/1960 Oldenboom. ..118/637 3,375,806 4/1968 Nost ..118/637 [15] 3,664,857 [451 May 23, 19 72 3,251,706 5/1966 Walkup ..1l7/17.5 3,492,151 1/1970 Cescon ..117/160X 3,097,962 7/1963 Whitacre ..117/160 X 3,420,151 l/l969 Levine et a]. ..355/4 2,902,974 9/1959 Greaves ..l l7/l7.5 X 3,357,402 12/1967 Bhaget ..1 l7/l7.5 X

Primary ExaminerWilliam D. Martin Assistant ExaminerM. Sofocleous Attorney-W. H. .l. Kline, J. R. Frederick and T. Hiatt [57] ABSTRACT Electroscopic toner material is applied to electrostatic charge patterns with at least one metallized fur brush having individual flexible filaments coated with a thin layer of an electrically conductive metal. The apparatus contains two metallized fur brushes, one having a low electrical conductivity and one having a high conductivity.

10 Claims, 2 Drawing Figures PATENTEDmza I972 3, 664, 857

FIG.

HOWARD A. MILLER INVENTOR.

'TTS ATTORNEY XEROGRAPHIC DEVELOPMENT APPARATUS AND PROCESS This invention relates to electrography, and more particularly, to the development of electrostatic latent images.

Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature, for example, U. S. Pat. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809; 2,551,582; 2,825,814; 2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing a normally insulating photoconductive element which is prepared to respond to image-wise exposure with electromagnetic radiation by forming a latent electrostatic charge image. The electrostatic latent image is then rendered visible by a development step in which the charged surface of the photoconductive element is brought into contact with a suitable developer mix.

One method of accomplishing development has been to cascade across the image-bearing surface a two-component developer mix as described in U. S. Pat. No. 2,618,551. This cascade development system is useful for ordinary line copies; however, it has limited application where solid area development is required. Consequently, workers in the art devised systems for magnetic brush development which provide improved solid area development.

In a magnetic brush system, a developer mix typically comprised of iron carrier particles and colored resin toner particles is applied to an apparatus of the type described in U. S. Pat. No. 3,003,462. In such an apparatus, the iron particles are held by a magnet in a bristle-like formation resembling a brush with the toner particles adhering by electrostatic attraction. These bristles of iron particles are electrically conductive which provides the effect of a development electrode having a very close spacing to the element being developed.

The development electrode effect obtained in magnetic brush development is advantageous where it is desired to copy images having large solid areas. However, there are several disadvantages associated with magnetic brush development. The bristles formed in a magnetic brush are relatively stiff and cause gradual wear on reusable charge-bearing elements. Also the stiff bristles often form streaks in the developed images. A further disadvantage arises from the particulate nature of the magnetic carrier. Loose carrier particles are often thrown off the magnetic brush and result in unwanted background density in the resultant images.

An alternative method of dry development has been proposed which involves the use of a fur brush. The fur brush method of development has an important advantage over the more common cascade and magnetic brush modes of development in that the carrier is an integral unit which can be fully controlled. However, for the most part, the use of the fur brush carrier is limited to so-called fringing development.

Furthermore, although convenient and relatively simple, fur brush development has been seriously restricted because of difficulty in grounding and electrically biasing the brush. These difficulties arise because of local differences in the electrical characteristics across the brush surface. This problem is magnified by the humidity dependent electrical characteristics of previous brushes.

When used at low relative humidity, previous brushes accumulate static charge which tend to bind the toner particles more tightly to the brush which results in less toner being applied to the charge pattern. Accordingly, the image density is considerably reduced. On the other hand, at high relative humidity the reverse is true in that excessive background density is produced which in some cases completely obliterates the developed image. Most prior art references to fur brush development contain specific warnings as to the problem associated with excessive conductivity.

Accordingly, there is a need in the art for a fur brush system of developing which eliminates the problems of humidity dependent conductivity, unwanted charge buildup, and grounding and biasing difficulties. In addition, there is a need for a system which permits the operator to select either a continuous tone or a fringing development mode from a single apparatus by the use of a simple mechanical switching.

It is, therefore, an object of this invention to provide an improved dry system for developing electrostatic charge patterns, which system is capable of producing solid area and/or fringing development.

It is another object of this invention to provide dry development apparatus utilizing fur brush toner applicators.

It is still another object of this invention to provide means for dry development of electrostatic charge patterns in a manner which provides reproducible characteristics that are independent of relative humidity.

These and other objects of the invention are achieved by the use of an apparatus for the dry development of electrostatic charge patterns which apparatus contains two toner applicators in the form of humidity insensitive, fur brush units. One of these brush units has a high electrical conductivity and the other has a low electrical conductivity. The fur brushes of this invention are in the form of a metallized fur material comprising soft flexible metallized bristles or filaments supported on a conducting support such as a core or web. This support provides an electrical connection between the individual electrically conducting metallized filaments. Such a brush can take the conventional form of a plurality of filaments held firmly by and projecting radially from a rigid spirally twisted wire support forming the longitudinal axis. The brush can also comprise a pile or coat of filaments each firmly attached at one or both ends to an underlying backing web. Such metallized fur brushes, including synthetic fur or pile fabrics and similarly constituted natural furs can be used in a fur brush development in the form of a covering over a rotating cylinder, as an endless belt running over a plurality of rollers and the like.

The invention will be described in more detail with reference to the figures in which:

FIG. 1 is a schematic cross section of a brush of this invention, and v FIG. 2 is a schematic cross section of an embodiment of the apparatus of this invention.

Referring now to FIG. 1, it is seen that the metallized fur brush 11 is typically comprised of a pile formed of a multitude of individual metallized fibers or filaments 12 carried on su port 13. This support 13 can be a woven substrate as in the case of a synthetic fur material or it can be a natural material as in the case ofanimal furs. Support 13 is also typically metal lized such that it is conducting. Additionally, support 13 can be in physical and electrical contact with an electrically conducting backing member 14 in order to provide suitable mechanical strength, etc. The actual form of this metallized fur brush can be varied to suit individual need. For example, the brush can be in the form of a flat platen. a cylindrical roller, a continuous belt, etc. In addition, the brush can also take the form of a test tube brush in which case support 13 would be in the form of twisted wire or other stiff material.

The brushes of this invention can be prepared from a variety of natural and synthetic fur materials. Suitable natural or animal furs would include rabbit, fox, beaver, skunk, and raccoon furs,and the like. Useful materials for preparing the synthetic fur brushes in accordance with this invention would include poly-a-olefins such as polyethylene, polypropylene, and others prepared from olefins containing from two to 10 carbon atoms; polyesters such as poly(ethylene terephthalate), polyesters of 1,4-cyclohexanedimethanol and terephthalic acid as described in U. S. Pat. No. 2,901,466; polyamides such as various nylons, for example, poly(hexamethylene adipamide), polycaprolactam, poly(hexamethylene sebacamide), etc; fiber-forming resins comprising 'copolymers of vinylidene chloride and acrylonitrile as dislimited only by the amount ofa flexibility desired. In general, the filaments have a useful range of thickness from about 0.002 to about 1 mm. with a preferred thickness in the range of about 0.0025 to about 0.75 mm. Of course, thicker filaments can be used advantageously in certain applications and particularly when the outermost end of the filament is flattened or split to provide soft, flexible contact with a photoconductive element. Smaller diameter filaments can also be used where desired with the smallest thickness theoretically being limited only b the capabilities of filament forming techniques. In addition, the length of the individual filaments, as measured from the support to the outermost portion of the filament, can vary over a wide range. Useful results are obtained with filaments ranging in in length from about /2 to about 4 cm., with preferred materials having a length of about 1 to about 3% cm. The lower limit offilament length is limited by the flexibility desired.

The natural or synthetic fur materials in accordance with this invention are given a coating of an electrically conducting metal. The metal is deposited as a thin, continuously conducting, adherent layer on each individual filament forming the brush. This metal film renders the individual filaments electrically conductive independentlv of the relative humidity. Such was not the case with many previous fur brushes, as witnessed by the apparatus necessary for maintaining a given relative humidity in the fur brush development assembly described in U. S. Pat. No. 2,902,974. In conventional fur brush development (fringing development) some leakage path must be provided to prevent accumulation of excessive charge. This is done by treating bristles or fur with antistatic compound which requires some moisture in the ambient air to insure conductivity; hence, relative humidity is important in using such brushes. However, one should not equate such humidity dependent conductivity with the humidity independent conductivity of the brushes of this invention.

Others have attempted to prepare brushes made of solid metal fibers; however, such attempts have not been entirely successful because of the relative stiffness of the resultant brush. I have found that a starting fur-like material can be chosen for its mechanical properties, i.e., softness and flexibility, and be metallized in accordance with this invention without substantial deterioration of the desired mechanical properties. In addition, suitable starting furs can be chosen without regard for their triboelectric properties in that the metallization technique described herein imparts triboelectric properties independent of the inherent properties of the starting material.

The fur materials useful in this invention are coated with a tightly adherent layer of an electrically conductive metal. Useful materials for forming these electrically conductive coatings include those metals in groups VIa, VIII, Ib and IIb of the Periodic Table (Cotton and Wilkinson, Advanced Inorganic Chemistry, l962, page 30) and aluminum. Particularly useful metals are aluminum, cadmium, chromium, cobalt, copper, gold, iron, nickel, silver, zinc, and the platinum group elements which include ruthenium, rhodium, palladium, osmium, iridium, and platinum as well as mixtures or alloys of any of these.

The metallization of any of the useful fur materials can be accomplished by various means such as vacuum evaporation, electroplating, electroless deposition, etc. In addition, combinations of the various procedures can be used. In the case of synthetic furs, the finished fur material can be metallized or the synthetic material could be metallized during manufacture of the filaments, e.g., immediatelv after extrusion, and then formed into a pile fabric, etc. The thickness of the metal coating can vary considerably provided that the coating does not become so thick as to make the filaments too stiff. In addition, sufficient metal should be deposited so as to provide a continuously conducting layer. Generally, the thickness of the metal will range from about 0.01 to about 1 micron, with a preferred range of from about 0.02 to about 0.2 micron. Useful metallized fur materials are described further in copending U. S. Application Ser. No. 9457, filed Feb. 6, 1970, entitled METALLIZED FUR MATERIALS, in the names of Miller and Ville.

A particularly useful method for metallizing the fur materials is the process of electroless deposition. In accordance with this process, the fur is sensitized, for example, by successive treatments in dilute stannous chloride and dilute palladium chloride to form a thin coating of palladium. The thin coating acts as a catalyst for the subsequent deposition of, for example, nickel from an alkaline electroless nickel plating solution typically comprising nickel chloride, sodium citrate, ammonium chloride, sodium hvpophosphite and ammonia. Such an electroless deposition technique can also be used to deposit copper, cobalt, palladium, etc.

In addition, a suitably adherent, continuously conducting layer of metal can readily be applied by vacuum evaporation. A convenient way of accomplishing this technique is to comb the filaments or fibers in one direction and subject the fur to vacuum deposition of, for example, aluminum. The fur is then combed in another direction and subjected again to vacuum deposition of aluminum. This process can be repeated as many times as necessary to provide sufficient conductivity.

In accordance with this invention, the apparatus contains two such metallized fur brushes which can be used as a carrier for dry particulate toner material. FIG. 2 shows an arrangement suitable for applying toner 22to metallized fur brushes 23 and 24 in the form of cylindrical rollers. Toner 22 is contained in a reservoir at the bottom of housing 21. The toner is applied to the rotating brushes by means of a toner applicator means 25 which is comprised of a stiff bristle brush which rotates at about 1 /2 to 3 times the peripheral speed of the fur brushes thereby applying a uniform coating of toner 22 to the pile of the brushes. Fur brushes 23 and 24 are comprised of a plurality of filaments l2 and 12' carried on a suitable support. The supports are underlaid by electrically conductive backings l4 and 14. The electrically conductive backings are supporting

cylinders

14 and 14 which are electrically insulated from one another and from ground. Cylinders l4 and 14 can be provided with conducting leads 26 and 27 which can be selectively connected to ground or to suitable circuitry (not shown) to provide or control electrical biasing. The fur brushes 23 and 24 are rotatably mounted and are driven by drive means not shown.

A charge-bearing element 20 is conveyed by

means

28, 29 and 30 shown for simplicity as being movable roller guides. In the particular embodiment shown guide means 29 is rotatably mounted in a stationary position whereas guide means 28 and 30 are mounted so as to be selectively movable. With guide means 28 in a lower position and guide means 30 in the upper position, element 20 will be brought in contact with brush 24 which has a higher electrical resistivity than brush 23. This results in a fringe developed image. When guide means 28 is in the upper position and guide means 30 in the lower position, element 20 will be brought in contact with brush 23 which has a lower electrical resistivity. This results in a solid area developed image. In the third mode of operation guide means 28 and 30 are both maintained in the lower position which results in element 20 being placed sequentially in contact with brush 24 and brush 23. In this mode, the electrostatic charge pattern is subjected to both fringing and solid area development.

The metallized fur brushes can be electrically connected to a conductive backing on element 20. By electrically connecting, for example, the high conductivity fur brush 23 to element 20, the brush acts as a closely spaced development electrode. This development electrode results in an intensification of the electric field of the electrostatic charge pattern on element 20. This alteration of the electric field during the development step results in the formation ofa high quality, continuous-tone or solid-area developed image. The development electrode can also be used to compensate for incorrect exposure or to alter toning characteristics, etc, by applying positive or negative potential to the electrode during development.

The metallized fur brush apparatus of the present invention has several advantages over any previous brush arrangement. In accordance with this invention, a fur material can be selected for its intrinsic softness or flexibility without regard for its conductivity or triboelectric characteristics. A flexible fur material can then be made suitably conductive by metallizing techniques as described below. Equally important is the fact that the conductivity of the resultant flexible metallized fur is entirely independent of the relative humidity. Additionally, the conductivity is independent of the amount of toner on the brush. This is not so in the case of conductive magnetic brush arrangement. In such an arrangement, the toner material tends to coat the individual magnetic particles.

This coating results in poor electrical contact between adjacent conductive carrier particles. Consequently, the conductivity of such a magnetic brush arrangement tends to decrease with increased use and increased amounts of toner present. However, the unitary structure of each conductive filament of the present metallized fur brushes avoid this problem found in magnetic brush apparatus.

The present apparatus has another distinct advantage over other fur brush and magnetic brush development apparatus in that both solid area and fringing development can be readily obtained by a simple mechanical switching mechanism. This is accomplished without the need for two separate toner hoppers and/or two distinct toner compositions. On the contrary, the instant invention allows for the production of both solid-area and/or fringe developed images from the same toner composition.

For continuous-tone or solid-area development, one of the metallized fur brushes must have a sufficiently high, humidityindependent level of conductivity to permit the brush to function effectively as a development electrode. The resistivity of such a brush is preferably in the range of about 0.01 ohm/square to about 10,000 ohms/square. The electrical resistivity is typically measured on the pile surface of the brush using two 1 inch by 1/16 inch electrodes which are placed parallel to one another spaced apart about 1 inch while held against the pile surface with approximately 5 pounds hand pressure. Resistivity values even higher than 104 ohms/square can be used to give good solid area development under appropriate development conditions. However, resistivity values of 100 ohms/square or lower require less critical developing conditions and are preferred in that this facilitates development at higher transit speed and prolongs the useful life of the brush between cleaning periods. Electrical resistance between the developing surface of the brush and the backside of the pile for support should be of about the same order as that referred to above. This resistance value can be checked by applying electrodes to the front and back of the fur material under about 5 pounds pressure such that the distance separating the electrodes is approximately equal to the greatest length of the electrode. If the front to back conductivity is not sufficiently high, electrical contact can be made directly with the developing or filamentary surface or pile of the brush using an electrode in the form of a comb, roller, platen and the like.

For use in fringing, edge, or outline development, a metallized fur brush is required which has a low level of conductivity which is uniform and humidity independent. A low conductivity is required to substantially reduce or eliminate the backing or development electrode effect. At the same time, however, the conductivity must be high enough to avoid excessive buildup of electrostatic charges which produce a selfbiasing effect. The preferred range of resistivity of thisbrush is from about and 10 ohms/square. An optimum value of resistivity can readily be determined experimentally to suit various parameters of the system, such as the circumference of the brush, the length of a fur belt, the relative transit speed against the charge-bearing surface, the bias voltage, resistance to ground, etc. The range of 10" to 10 ohms permits a selection of the degree of fringing development. Thus, semi-outline development is obtained at 10 to 10 ohms/square and is accompanied by a greater exposure latitude, improvement in fine-line reproduction and highlight detail and a cleaner background than solid area development will give. In addition, good, high density fill-in of solid areas of up to three-sixteenths inch width can be obtained. At brush resistivity of 10 to 10 ohms/square, the development becomes progressively more fringing with an accompanying increase in exposure latitude.

Typically, the separate brush units can be cylindrical comprising, for example, long fibers extended radially from a small diameter axial core. The fur brush unit can also be in the form of a fur material fitted around a cylinder arranged to rotate on its longitudinal axis, or disposed as an endless flexible belt moving in a designated path around two or more rollers or arranged in a flat or curved plane or other form suited to make effective developing contact with the electrostatic image to be developed. During use, the pile of the fur brush is saturated with toner powder and run in light contact with the surface of the element bearing the electrostatic charge pattern.

For good solid area development, the charge-bearing element passes over the brush at a rate of about 5 to 40 inches per second while the brush is moved or rotated at a peripheral speed of about 5 to 20 inches per second. Similar operating conditions are suitable for outline development using the low conductivity brush.

As is typical in electrography, charge-bearing element 20 can be an electrophotographic element comprised of a conductive support carrying a layer of a photoconductive electrically insulating composition. An electrostatic charge pattern is produced on such an element b uniformly charging the photoconductive layer in the dark and exposing the layer to a pattern of activating radiation which causes selective dissipation of the charge in the light-exposed areas. In addition, the charge-bearing element 20 can be comprised simply of a sheet of an electrically insulating material such as poly( ethylene terephthalate) in which case an electrostatic charge pattern can be applied thereto by, for example, charge transfer from an electrophotographic element of the type referred to above. The electrostatic charge pattern formed on element 20 is ultimately developed bv contacting element 20 with at least one of the toner-carrying

brushes

23 or 24. The element 20 bearing the charge pattern is shown for convenience as a continuous web. However, the element can be in the form of a roller or a flat plate.

The toner material used with the present metallized fur brush carrier can be selected from a wide variety of colored or colorless powders. Typical toners are comprised of a colorant such as a dye or pigment in a thermoplastic resin binder. Suitable toners can be prepared b any of the well known means such as melt blending or spray drying to produce colored particles having an average diameter from about 15p. to about 25p" These toner particles are given a positive or negative charge by frictional electrification. The particular polarity charge to be given to the toner will, of course, be dependent upon the type of image to be developed. When toner is applied to the metallized fur brush, the particles cling to the fibers of the bmsh by triboelectric attraction. The toner is then held by the brush until carried to the point of contact with the imagebearing element. At this point, electrostatic attraction overcomes the triboelectric attraction and the toner particles become deposited on the image-bearing element.

The fur brushes used in one embodiment of the invention are comprised of metal rollers covered with a synthetic fur having a dense pile of Type 505 Verel modified acrylic fibers having a free length of about seven-tenths inch. These brushes are metallized by the technique described in Example 3 of copending Miller and Ville application Ser. No. 9457, filled Feb. 6, 1970, and entitled METALLIZED FUR MATERI- ALS. The brushes are first catalyzed for electroless nickel deposition by first degreasing in an aqueous solution of potassium laurate, rinsing, immersing in a 0.25 percent palladous chloride solution for 2 minutes, followed by immersion in a 0.4 percent hydrazine solution and a water rinse. The fur material is then placed in a nickel plating bath containing the following ingredients:

Nickel chloride 45 gm/l. (NiCI,-6H O) Sodium Citrate 100 gm/l. (Na C H,0,-%H O) Ammonium Chloride 5O gm/l. Sodium Hypophosphitc l0 gm/l. (Nu H,PO,-H O) 28% Ammonia Sol. 90 gm/l.

The plating bath is maintained about 120 and 200 F and a pH of about to 11. The low conductivity or high resistivity brush is removed from the bath before a thick metal coating is deposited. This brush has an electrical resistivity of about 6 X 10 ohms/square. The highly conductive brush is left in the bath for a time sufiicient to deposit a thicker nickel coating. This latter brush has an electrical resistivity of about ohms/square.

The reservoir in housing 21 is filled with a toner 22 comprised of electroscopic particles having an average diameter of about 8 microns. The toner particles are composed of carbon black, nigrosine, and a polystyrene resin. This toner charges positively on the nickeled fur brushes. Next, a charge-bearing element 20, comprised ofa conducting support having coating thereon a photoconductive layer containing a polymeric binder and an organic photoconductor is subjected to a negative corona source. The resultant negatively charged element is then given an imagewise exposure to actinic radiation. This results in the formation ofa negative electrostatic charge pattern. Charge-bearing element 20 is then moved into contact with grounded brush 24 having a high resistivity. The brush is rotated at a peripheral speed of about 10 inches/second and element 20 is moved at a rate of passage over the brush of about 20 inches per second. Toner is transferred from brush 24 to element 20 in relation to the charge pattern. A good fringe developed image results.

The above procedure is repeated only with guide means 28 in the upper position and guide means 30 in the lower position. With the guide means so located, element 20 is brought into contact with highly conductive brush 23 which is biased to ISO volts with respect to the conductive backing of element 20. A direct positive image results which has a high maximum density with very little unwanted background density.

FIG. 2 shows an embodiment in which movable guide means 28 and 30 function to bring element 20 into contact with

brushes

23 and 24. Of course, element 20 can move in one plane with

brushes

23 and 24 being moved up into contact with the element. It is preferred, however, that brushes be substantially contained within housing 21 for purposes of cleanliness.

The present invention can also utilize a single brush in the form of a roller or continuous belt which has a high conductivity portion and a low conductivity portion. In accordance with this embodiment, the movement of element 20 would be synchronized or controlled such that element 20 is moved into contact with the desired portion or portions of the brush.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. Apparatus for applying electroscopic toner material to an element bearing an electrostatic charge pattern, said apparatus comprising first and second fur brushes capable of containing said element, each having individual flexible filaments, coated with an adherent, thin layer of an electrically conductive metal, said first brush having a low electrical conat a temperature between ductivity so as to produce fringing development and said second brush having a high electrical conductivity so as to produce solid area development, means for applying toner to said brushes, means for moving said element into proximity of said brushes and means for selectively contacting at least one of said brushes with said element while maintaining relative movement between said element and said brush, whereby said toner material is transferred onto areas of said elements in relation to said electrostatic charge pattern.

2. Apparatus as described in claim 1 wherein said first brush has an electrical resistivity of greater than said about 10* ohms/square and wherein said second brush has an electrical resistivity of less than about 10* ohms/square.

3. Apparatus as described in claim 1 wherein said first and second brushes are comprised of synthetic or natural furs hav ing coated thereon a metal selected from the group consisting ofa Group VIa metal, a group VIII metal, a Group Ib metal, a Group IIb metal, aluminum and mixtures thereof.

4. Apparatus as described in claim 1 wherein at least one of said brushes is in the form of a cylinder.

5. Apparatus as described in claim 1 wherein at least one of said brushes is in the form of a continuous belt.

6. Apparatus as described in claim 1 wherein said means for alternately contacting one of said brushes comprises selectively movable guide means for guiding said element into contact with at least one of said brushes.

7. Apparatus for applying electroscopic toner material to an element bearing an electrostatic charge pattern, said apparatus comprising first and second movable fur brushes capable of contacting said element, means for applying toner to said brushes, means for selectively conveying said element into contact with at least one of said brushes whereby said toner is attracted from said brush to the element in accordance with the charge pattern, said brushes comprising synthetic or natural furs having coated on the individual filaments thereof a thin layer of an electrically conductive metal imparting to said brushes a humidity independent electrical conductivity, said first brush having an electrical resistivity of greater than about 10" ohms/square and said second brush having an electrical resistivity of less than about 10 ohms/square.

8. Apparatus as described in claim 7 including means for sequentially guiding said element into contact with both of said brushes whereby toner is attracted to said element from both brushes.

9. A process for developing electrostatic charge patterns comprising the steps of:

a. forming an electrostatic charge pattern on an element,

b. applying electroscopic toner material to first and second movable fur brushes each comprised ofa support bearing individual flexible filaments which are coated with a thin layer of an electrically conductive metal, one of said brushes having an electrical resistivity of greater than 10 ohms per square and the other having an electrical resistivity of less than about 104 ohms per square, and

c. sequentially contacting said charge pattern with said first and second brushes whereby said toner is deposited in accordance with said charge pattern to give both fringing and solid area development.

10. A process as described in claim 9 wherein the fur brushes are comprised of synthetic or natural furs having coated on the individual filaments thereof a metal selected from the group consisting ofa Group VIa metal, a Group VIII metal, a Group Ib metal, a Group IIb metal, aluminum and combinations thereof.

Claims

2. Apparatus as described in claim 1 wherein said first brush has an electrical resistivity of greater than said about 108 ohms/square and wherein said second brush has an electrical resistivity of less than about 104 ohms/square.
3. Apparatus as described in claim 1 wherein said first and second brushes are comprised of synthetic or natural furs having coated thereon a metal selected from the group consisting of a Group VIa metal, a group VIII metal, a Group Ib metal, a Group IIb metal, aluminum and mixtures thereof.
4. Apparatus as described in claim 1 wherein at least one of said brushes is in the form of a cylinder.
5. Apparatus as described in claim 1 wherein at least one of said brushes is in the form of a continuous belt.
6. Apparatus as described in claim 1 wherein said means for alternately contacting one of said brushes comprises selectively movable guide means for guiding said element into contact with at least one of said brushes.
7. Apparatus for applying electroscopic toner material to an element bearing an electrostatic charge pattern, said apparatus comprising first and second movable fur brushes capable of contacting said element, means for applying toner to said brushes, means for selectively conveying said element into contact with at least one of said brushes whereby said toner is attracted from said brush to the element in accordance with the charge pattern, said brushes comprising synthetic or natural furs having coated on the individual filaments thereof a thin layer of an electrically conductive metal imparting to said brushes a humidity independent electrical conductivity, said first brush having an electrical resistivity of greater than about 108 ohms/square and said second brush having an electrical resistivity of less than about 104 ohms/square.
8. Apparatus as described in claim 7 including means for sequentially guiding said element into contact with both of said brushes whereby toner is attracted to said element from both brushes.
9. A process for developing electrostatic charge patterns comprising the steps of: a. forming an electrostatic charge pattern on an element, b. applying electroscopic toner material to first and second movable fur brushes each comprised of a support bearing individual flexible filaments which are coated with a thin layer of an electrically conductive metal, one of said brushes having an electrical resistivity of greater than 108 ohms per square and the other having an electrical resistivity of less than about 104 ohms per square, and c. sequentially contacting said charge pattern with said first and second brushes whereby said toner is deposited in accordance with said charge pattern to give both fringing and solid area development.
10. A process as described in claim 9 wherein the fur brushes are comprised of synthetic or natural furs having coated on the individual filaments thereof a metal selected from the group consisting of a Group VIa metal, a Group VIII metal, a Group Ib metal, a Group IIb metal, aluminum and combinations thereof.