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Home | Alpha Telephone | Domain Names | Web Hosting | Get Traffic | xrEvidence | xrSoccer United States Patent
Magnetic brush roll having resilient polymeric surface A magnetic brush roll of an electrostatic reproduction machine is formed of a non-magnetic core with a resilient polymeric material such as polyurethane, for example, on its surface. The polyurethane surface is textured to provide a desired roughness, is non-abrasive, and is abrasion resistant. Carbon is added to the polyurethane to render it conductive.
Primary Examiner: Stein; Mervin Assistant Examiner: Salser; Douglas A. Attorney, Agent or Firm: What is claimed is: 1. In an electrophotographic development apparatus of the magnetic brush type having: a surface on which a latent image is formed; a rotatably mounted hollow roll including a core of non-magnetic material and a resilient polymeric material secured to said core to form the surface of said roll; said resilient polymeric material having at least its surface electrically conductive; said resilient polymeric material having its surface non-abrasive, abrasion resistant, and rough; magnetic means disposed within said core for creating a magnetic field in the path of the periphery of said roll; and means to bring a developer material into contact with the surface of said resilient polymeric material of said roll, said roll being disposed adjacent said surface on which the latent image is formed so that said roll can transport the developer material in a brush-like configuration to the surface on which the latent image is formed. 2. The apparatus according to claim 1 in which said resilient polymeric material of said roll is electrically conductive throughout its entirety. 3. The apparatus according to claim 2 in which said resilient polymeric material comprises a single homogeneous layer on said core. 4. The apparatus according to claim 3 in which said resilient polymeric material has a hardness no greater than 95 on a Shore A durometer. 5. The apparatus according to claim 4 in which said layer of resilient polymeric material is at least 0.010 inch thick. 6. The apparatus according to claim 5 in which said layer of resilient polymeric material is polyurethane having an electrically conductive material dispersed throughout. 7. The apparatus according to claim 2 in which said resilient polymeric material comprises: a first homogeneous layer secured to said core; and a second layer secured to said first layer, said second layer being electrically conductive. 8. The apparatus according to claim 7 in which: said resilient polymeric material is polyurethane; and said second layer includes an electrically conductive material in said polyurethane. 9. The apparatus according to claim 8 in which said resilient polymeric material has a hardness no greater than 95 on a Shore A durometer. 10. The apparatus according to claim 1 in which said resilient polymeric material is polyurethane. In well-known electrostatic printing processes, a surface bearing a latent electrostatic image is developed by applying a developer material comprising toner and a carrier material to the surface. The small toner particles are held onto the surfaces of the relatively large carrier particles by electrostatic forces, which develop from the contact between the toner and carrier particles producing triboelectric charging of the toner and carrier to opposite polarities. A portion of the applied triboelectrically charged toner is selectively attracted to the image areas of the surface, and the remainder of the developer material is removed and allowed to recirculate to form subsequent images. In order to assure clear, sharp images, it is necessary that the toner obtain a high triboelectric charge prior to development. This has generally been effected in prior devices by selecting toner and carrier materials which are widely separated in the triboelectric series and by causing agitation and stirring of the developer material prior to development. Further, the ratio of toner to carrier in the developer material or mix is closely controlled. However, even when the most optimum materials and mixing devices are utilized, the triboelectric charge of the toner for a given toner-carrier ratio is often insufficient to provide uniform high quality copy output. Various prior art developing mechanisms incorporate a magnetic brush comprising a cylindrical member or roll rotatably mounted relative to a fixed magnetic field generating means onto which multicomponent magnetic developer material is delivered. The magnetic field generating means creates a magnetic field causing the magnetic developer to form in bristle-like arrays over the surface of the cylindrical member or roll as it is rotated into contact with an electrostatic latent image-bearing surface. For the surface of a magnetic brush roll to transport the magnetic developer to an electrostatic latent image-bearing surface, it has previously been suggested in U.S. Pat. No. 3,040,704 to Bliss to form the roll with a roughened external surface. However, attempts to roughen the surface of the roll, which is formed of a non-magnetic material such as aluminum, brass, or other soft alloy, by cutting grooves, serrations, or knurls therein have resulted in the surface being rapidly worn down by the abrasive action of the developer material. It also has been previously suggested in U.S. Pat. No. 3,219,014 to Mott et al to sandblast the surface of a magnetic brush roll to roughen the surface in a uniform pattern. However, sandblasting does not make the surface rough enough. Furthermore, the wear of the sandblasted surface results in polished high spots to reduce the transport capability for the developer material by the sandblasted surface. Instead of forming the roughened surface directly in the magnetic brush roll by grooves, serrations, knurls, or sandblasting, it has previously been suggested in U.S. Pat. No. 3,246,629 to Shelffo to bond a layer of irregular shaped particles to the surface of the magnetic brush roll. This provides a random roughened surface. In transporting the developer material to the electrostatic latent image-bearing surface, the developer material is moved either uphill or downhill depending on how the entire machine is arranged. When the developer material is moved uphill, the surface of the magnetic brush roll must be rough enough to enable the carrier particles to not slide relative thereto while being advanced uphill by the magnetic brush roll. While the magnetic brush roll of the aforesaid Shelffo patent provides a roughened surface, this surface lacks the desired properties of being non-abrasive and resilient. The abrasive surface of the magnetic brush roll of the aforesaid Shelffo patent causes wear on the carrier particles of the developer material, particularly in the slight clearance area between the magnetic brush roll and the electrostatic latent image-bearing surface since the abrasive surface causes the carrier particles to rub against each other and against the surface of the magnetic brush roll. Lack of resiliency in the surface of the magnetic brush roll of the aforesaid Shelffo patent prevents the surface of the magnetic brush roll from giving to a slight degree when a plurality of the carrier particles are disposed in engagement with each other between the magnetic brush roll and the electrostatic latent image-bearing surface with a slightly greater overall distance than the clearance. The present invention satisfactorily solves the foregoing problems by providing a roughened surface which is both resilient and non-abrasive as well as being abrasion resistant. The resilient and non-abrasive surface of the magnetic brush roll of the present invention increases the life of the carrier particles by reducing wear of the carrier particles. Thus, wear on the carrier particles is reduced not only by the non-abrasive surface of the magnetic brush roll of the present invention, but its resiliency prevents wear when the carrier particles are within the clearance area in which they tend to have the greatest rubbing relation with the magnetic brush roll and with each other. Even though the surface of the magnetic brush roll of the present invention is both resilient and non-abrasive, it still is rough. As a result, it provides the desired surface to enable the magnetic brush roll to advance the developer material or mix in an uphill direction so that the carrier particles, which have the toner particles thereon, are advanced to the clearance area between the magnetic brush roll and the electrostatic latent image-bearing surface. The present invention provides the improved magnetic brush roll through having a resilient polymeric material secured to a non-magnetic core. Because it is necessary to have a bias on the magnetic brush roll, at least the surface of the resilient polymeric material must be conductive. In its preferred form, the resilient polymeric material of the magnetic brush roll of the present invention is homogeneous and conductive throughout. An object of this invention is to provide a magnetic brush roll having a non-abrasive and resilient surface that is rough or textured. Another object of this invention is to provide a magnetic brush roll having a resilient polymeric material as its surface. The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawing. In the drawing: FIG. 1 is a schematic sectional view of a portion of an electrostatic reproduction machine having the magnetic brush roll of the present invention. FIG. 2 is a fragmentary perspective view of a portion of one form of the magnetic brush roll of the present invention. FIG. 3 is a fragmentary sectional view of another form of the magnetic brush roll of the present invention. Referring to the drawing and particularly FIG. 1, there is shown a portion of an electrostatic reproduction machine 10 having a photoconductor drum 11, which functions as the electrostatic latent image-bearing surface. The photoconductor drum 11 is rotated clockwise by being driven from a main power source. The developer material, which comprises a mix of carrier particles and toner particles, is stored in a sump portion 14 of a magnetic brush developer station 15. The toner particles are supplied to the sump portion 14 from a toner cartridge (not shown) by a metering cylinder (not shown) of a replenisher (not shown), which has an agitator (not shown), through an opening 16 in the magnetic brush developer station 15 to the sump portion 14 of the magnetic brush developer station 15. Counter rotating augers 17 and 18 stir the freshly added toner with the developer material in the sump portion 14 to assure complete mixing thereof as well as to enhance the triboelectric charging of the developer material. The developer material is metered from the sump portion 14 to a transport portion 19 of the magnetic brush developer station 15 by a metering gate 20. The transport portion 19 of the magnetic brush developer station 15 has a transport roll 21 disposed therein beneath a magnetic brush roll 22. The transport roll 21, which rotates at a speed less than the rotational speed of the magnetic brush roll 22 to provide a surface velocity of the transport roll 21 no greater than the surface velocity of the magnetic brush roll 22, rotates clockwise while the magnetic brush roll 22 rotates counterclockwise. The transport roll 21 surrounds a fixed drum 23 which has magnets 24 on a portion of the surface thereof to aid in holding the developer material on the transport roll 21 until the developer material is advanced to a position adjacent the oppositely rotating magnetic brush roll 22. As the developer material is advanced by the transport roll 21 to the magnetic brush roll 22, the developer material is attracted to the magnetic brush roll 22 by magnets 25, which are fixed and disposed within the magnetic brush roll 22. The magnets 25 may be of any suitable type as long as they cause the developer material to adhere to the magnetic brush roll 22 and have a bristle-like array adjacent the photoconductor 11. As shown in FIG. 2, the magnetic brush roll 22 includes a core 26 of a non-magnetic material such as aluminum, for example. The core 26 is closed at its ends by plates 27. A shaft 28 extends from the plate 27 at one end of the core 26 and is driven from a main power source by a chain passing around a sprocket on the shaft 28. The transport roll 21 is driven in unison with the magnetic brush roll 22 through the same chain cooperating with a shaft 29 of the transport roll 21. The other plate 27 is rotatably supported by a bearing on a fixed shaft 30 (see FIG. 1) on which the magnets 25 are supported. The core 26 of the magnetic brush roll has a sleeve 31 of a resilient polymeric material secured thereto. The sleeve 31 has its surface textured so as to be roughened to a desired extent. The roughness pattern in the sleeve 31 can be uniform or non-uniform. One suitable example of the resilient polymeric material of the sleeve 31 is polyurethane. The sleeve 31 is homogeneous and is conductive so that a desired bias can be applied to the magnetic brush roll 22. While polyurethane is not conductive, carbon is added thereto to insure that the sleeve 31 is conductive. One means of forming the sleeve 31 is to use Norton Company's AH299 grinding tube as a mold. The tube is machined to an outer diameter of 2.4 inches and then grit blasted to produce a random, textured surface on the tube as the mold. Then, DuPont 958-202 steel blue Teflon release coat is applied to the surface of the mold. The mold is then dip coated twelve times within a conductive polyurethane solution with the mold being inverted after each of the dips. The conductive polyurethane solution is prepared by adding one hundred parts by weight of Hughson Chemical Company's TS-1525-37 urethane lacquer resin, 8.3 parts by weight of Cabot Corporation's Vulcan XC-72 conductive carbon black, 100 parts by weight of toluene, and 100 parts by weight of isopropyl alcohol within an attritor and running the attritor at full speed for 1 hour. After each coating of the conductive polyurethane solution is formed on the mold, it is air dryed for at least 15 minutes before an additional coat is applied by dipping. After every fourth dip and after air drying, the mold is placed in an air circulating oven and allowed to dry for at least 15 minutes at 150.degree. F to remove any residual solvent. This forms the sleeve 31, which is removed from the mold. After turning the sleeve 31 inside out, the sleeve 31 is deposited over the core 26, which has been adhesive coated by spray coating with EC2290 modified epoxy adhesive of 3M and completely dried. The sleeve 31 is expanded by air to be able to fit over the core 26. After the sleeve 31 has been disposed over the core 26, it is cured for one hour at 300.degree. F. Tests have indicated that the tensile strength of the sleeve 31 is 4,000 p.s.i. with an ultimate elongation in excess of 800 per cent. The tear strength of the sleeve 31 is 330 pounds per inch thickness, and it has a hardness of 65 on a shore A durometer. Its volume resistivity is 10.sup.4 ohm-cm. Accordingly, the magnetic brush roll 22 has a surface, which is rough or textured, non-abrasive, and abrasion resistant. At the same time, the sleeve 31 is resilient and is conductive throughout. This permits the required bias to be applied to the magnetic brush roll 22. As the magnetic brush roll 22 advances the developer material toward the photoconductor drum 11, it passes a bead control device 32. The bead control device 32 limits the thickness of the developer material on the magnetic brush roll 22 prior to being advanced into the position adjacent the photoconductor drum 11. The magnetic brush developer station 15 supports a pile fabric seal 33, which is made of a material such as Kodel, for example. The purpose of the seal 33, which engages the photoconductor drum 11, is to prevent a toner cloud from escaping from the magnetic brush developer station 15. After the magnetic brush roll 22 has advanced the developer material past the photoconductor drum 11, the developer material remaining on the magnetic brush roll 22 is released after passing the last of the magnets 25 and returned to the sump portion 14 of the magnetic brush developer station 15. The magnetic brush developer station 15 also supports a blade scraper 34, which is conductive coated Mylar, adjacent the photoconductor drum 11 and spaced slightly therefrom. The purpose of the blade scraper 34 is to keep the toner and carrier particles from escaping from the magnetic brush developer station 15. A seal 35, which is spaced slightly from the photoconductor drum 11, also is supported by the magnetic brush developer station 15 and is passed by the photoconductor drum 11 after the photoconductor drum 11 moves past the scraper 34. The seal 35, which also is conductive coated Mylar, likewise functions to keep the toner and carrier particles from escaping from the magnetic brush developer station 15. Instead of the magnetic brush roll 22 having the sleeve 31, which is homogeneous polyurethane with carbon, a magnetic brush roll 37 (see FIG. 3) could be employed in which the core 26 would again be used. The core 26 would have a layer 38 of polyurethane without carbon thereon so that the layer 38 would not be conductive. Then, a layer 39 of polyurethane with carbon could be applied to the layer 38 by being painted thereon. The layer 39 would need to be only about 0.001 inch thick. Thus, the magnetic brush roll 37 would be conductive only along its surface. However, this is sufficient to provide the desired bias thereon. The sleeve 31 of the magnetic brush roll 22 or the layer 38 of the magnetic brush roll 37 must be at least 0.010 inch thick and is preferably at least 0.015 inch thick. While the sleeve 31 of the magnetic brush roll 22 or the layer 39 of the magnetic brush roll 37 has a hardness of 65 on a Shore A durometer, it should be understood that either could have a hardness up to 95 on a Shore A durometer and still have sufficient resiliency. While the resilient polymeric material has been described as being polyurethane, it should be understood that any other resilient polymeric material having the desired properties could be employed. This includes the capability of having a conductive material such as carbon, for example, added without the material losing its other desired properties of being resilient, non-abrasive, and abrasion resistant. Thus, any synthetic rubber having the properties of being resilient, non-abrasive, and abrasion resistant could be utilized, for example. The rubber could be dip-coated on a textured core of a non-magnetic material, for example, to have the desired roughness. It is necessary that any resilient polymeric material be non-abrasive and abrasion resistant as well as having a sufficient roughness to permit the developer material to have a foothold on the magnetic brush roll. While the roughness of the material can be within varying ranges, it is preferred that the roughness be no greater than that produced by a molding from a 50 grit sandpaper. The roughness preferably is no less than that produced by ninety grit sandpaper. While the sleeve 31 has been described as being formed through a dipping process on a mold and then removing the sleeve 31 for application on the core 26, it should be understood that any other suitable process could be employed. For example, the material could be injection molded around a core or a sleeve could be extruded with the material having to be thermoplastic in nature to allow the desired roughness to be embossed in its surface. While the present invention has been shown and described as having the developer material moved uphill by the magnetic brush roll, it should be understood that the magnetic brush roll of the present invention could be utilized where the developer material is moved downhill. This would be particularly useful in a relatively high speed machine. An advantage of this invention is that it reduces the wear of the developer material. Another advantage of this invention is that it is particularly useful in moving a material uphill to an electrostatic latent image-bearing surface. While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention. For U.S. patent law, rules, and procedures see MPEP. Disclaimer. Information presented on this page while believed to be reliable, is provided "as is" with no warranties of its accuracy or timeliness. For legal advice seek help of a licensed professional. |