INSERT MOLDED END PIN SHAFTS FOR MAGNET ROLL DEVELOPER

Abstract: A developer magnet roll (1) with insert molded end pin shafts (2) on both ends. The end pin shafts are insert molded within a ferrite and binder magnet roll to provide improved strength, straightness, and processing at reduced costs.

Description: INSERT MOLDED END PIN SHAFTS FOR MAGNET ROLL DEVELOPER BACKGROUND OF THE INVENTION The invention relates to electrophotography and more particularly to developer magnet rolls for electrophotography. Developer magnet rolls are typically made of strontium ferrite in a nylon binder and are formed into cylindrical shapes that function within a surrounding cylindrical developing sleeve. The magnetic pole pattern which is contained within the core of the magnet, is typically comprised of four or more alternating North-South poles formed longitudinally along the cylinder, resembling a "four leaf clover pattern" when viewed from the end. The core is supported within the developing sleeve framework via end shafts that are integral to the developer magnet roll. The developer magnet roll, which is usually composed of a ferrite and a binder, is formed by the following methods. If the binder is a soft, flexible thermoplastic such as extruded polyvinyl chloride (PVC), the magnets are typically assembled onto a cold rolled steel shaft for strength and magnetized longitudinally during the extrusion process and formed into a hollow cylinder, then demagnetized and finally, remagnetized into a final pole configuration using electromagnets after assembly. This method is inherently expensive due to the multi-step process of extruding the magnetic compound, gluing the soft, flexible magnet onto a shaft and magnetizing the developer magnet into a final desired pattern. Alternatively, a strong metallic shaft is insert molded within a ferrite and soft, flexible thermoplastic such as ethylene vinyl acetate (EVA) binder to form the developer magnet roll with magnetization accomplished with permanent magnets within the mold or with electromagnets. If the binder is nylon, a hard thermoplastic, the magnets are typically 100% molded to include the small diameter end mounting means. The roll magnets using a nylon binder are either magnetized during molding with the use of permanent l magnets or by using electromagnetic coils within the mold to partially magnetize the roll with final magnetization occurring after molding. The nylon binder magnets have acceptable performance and are inexpensive, but if the ratio of weight to length and/or magnet diameter to mounting diameter is large, the end shafts are fragile and can break easily. If the end shaft diameters are increased for added strength, then acceptable strength is obtained. However, the mounting diameter size is limited in many applications, due to the surrounding geometry and the necessity for adequate clearance by adjoining elements, such as the inside diameter of the developer sleeve end plugs, through which the end shafts protrude. Completed magnet rolls must be straight with a minimum circular run out to have acceptable magnetic performance. Many patents have been issued relating to magnet design and manufacture. The following patents relate to unique shaft designs. U.S. Patent 4,557,582, describes the planar attachment of magnetic strips to a non-circular cross sectioned, asymmetrical polygon shaped supporting shaft which has at least the end portions shaped this way to attach it to a cartridge. Adhesive bonds magnetic strips to the central shaft. The magnetic strips when made separately are difficult to assemble together in a long cylindrical shaped envelope and the shaft provides the mechanical mounting method. U.S. Patent 4,580,121, describes ferrite magnets with a rubber binder held on an aluminum extruded shaft that has a plurality of ribs and is bound together using heat shrink tubing. The nonmagnetic aluminum extruded shaft provides the vehicle to mount the strip magnets. U.S. Patent 4,604,042, describes an insert-molding method that places a central shaft within a bonded (nylon) ferrite magnet to compensate for large length to diameter: ratios greater than 5 where rare earth permanent magnets within the mold magnetize the final cylindrical magnet roll. U.S. Patent 4,872,418, describes a ferrite magnet with nylon binder that includes a cross sectioned flat drive or longitudinal end polygon protrusion at each end. U.S. Patent 4,954,800, describes the use of electromagnetic magnetization of roll magnets during molding to establish longitudinal poles. The 2 resultant roll magnet typically has only two poles, is then demagnetized and then re- magnetized with four poles in a final configuration. This shows an alternative way to perform the final magnetization. The shafts are again an integral part of the roll magnet. U.S. Patent 5,319,337, describes an insert-molded shaft within a magnet roll that also serves as the sleeve. The metallic magnetic shaft is preheated and thermally fused with thermoplastic resin using a thin layer of adhesive. There are a plurality of 50 poles on the surface and the magnetic shaft helps to provide a key magnetic path when forming the surface poles. U.S. Patent 5,682,587, describes a universal hollow magnet with metal filled resin bearings of different configurations which have unique end shaft shapes like D's or squares. These support bearings are described as conical end support members that can also perform the electrical contact with the bias voltage of the cartridge. The end shafts perform multiple purposes including support, an accurate bearing surface and an electrical contact point. U.S. Patent 3,149,403, pertains to stub shafts inserted or insert-molded into a non-magnetic core or body, to which magnetic modules are subsequently attached. In summary, the magnet body is a composite structure of magnetic and nonmagnetic elements. U.S. Patent 4,142,218, relates to a magnetic roll created as a composite structure consisting of a non-magnetic body and/with end hubs to which longitudinal magnet inserts are added, and to which end shafts are inserted post molding of the body/hubs. U.S. Patent 5,583,473, discloses one shaft end integrally molded as a part of the magnet roll body, and the second end shaft being press-fit past the molding of the body/first-end. It is an object of the present invention to provide a developer roll magnet having improved strength versus a one piece molded magnet with integral end shafts. It is a further object of the present invention to provide a developer magnet roll having improved straightness. 3 It is a further object of the present invention to provide a developer roll magnet with a lower cost alternative versus magnets employing a through shaft. It is a further object of the present invention to provide an improved developer magnet roll having insert molded end pin shafts for processing benefits for 5 certain manufacturing methods. It is a further object of the present invention to provide an improved developer magnet roll having insert molded non-magnetic end pin shafts for processing benefits for certain manufacturing methods. i o SUMMARY OF THE INVENTION In accordance with the present invention, an improved developer magnet roll for use in a developer sleeve for electrophotography is provided. Manufacturing of developer magnet rolls and especially those with a large ratio of overall magnet diameter to support shaft diameter is accomplished is through a process wherein roll strength, straightness, processing and cost is much improved. BRIEF DESCRIPTION OF THE DRAWINGS 20 Figure 1 is a longitudinal cross-sectional view showing a magnet roll according to the invention. DETAILED DESCRIPTION OF THE INVENTION The present invention is described in detail with reference to the 25 attached figure. In manufacturing a developer magnet roll 5, see figure 1, there is provided a magnet body roll 1, comprised of a particulate ferrite material, such as strontium ferrite and a binder, and end pin shafts 2, attached thereto. The end pin shafts are made of a material such as metal, ceramic or plastic. The end pin shafts 2, 30 are inserted into a mold and the magnet body roll 2 is formed during a standard injection molding process (i.e., by injecting melted binder with the ferrite particles 4 thoroughly mixed in the binder). A typical binder for the ferrite is a rigid thermoplastic such as nylon 6 or nylon 12. The injection molded developer magnet roll exhibits improved strength, improved straightness, improved processing and cost savings through the incorporation of the insert molded end shafts, especially in situations with a large ratio of overall magnet diameter to support shaft diameter. A preferred embodiment of this invention utilizes a non-magnetic material for the end shafts, such as non-magnetic grades of stainless steel. This embodiment is preferable when used with injection molding equipment containing permanent magnets to produce said magnetic rollers. The embedded portions of shaft 2 are textured (roughened) to assure physical locking. More extreme locking surfaces, such as a machined recess, are alternatives. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as they may come within the purposes of the improvements or the scope of the following claims.

Claims: What is claimed is: 1. A developer magnet roll comprising end pin shafts that are insert molded during roll formation. 2. A developer magnet roll with end pin shafts as claimed in claim 1, wherein said magnetic body roll is comprised of magnetizable ferrite particles in a binder of nylon. 3. A developer magnet roll with end pin shafts as claimed in claim 1, wherein said end pin shafts are metal, ceramic or plastic material. 4. A method of manufacturing a developer magnetic roll with end pin shafts as claimed in claim 1, wherein said end pin shafts are insert molded on both said ends. 5. A method of manufacturing a developer magnetic roll with end pin shafts as claimed in claim 1, wherein said end pin shafts are non-magnetic and insert molded in an injection mold that contains permanent magnets.

Inventors: FOSTER MARK DUANE, HACKETT ROBERT EDWARD, ZUTT MARTIN J JR, FOSTER, MARK, DUANE, HACKETT, ROBERT, EDWARD, ZUTT, MARTIN, J., JR.
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL INC.
Application year: 1999
Main classification: B29C45
IPC codes: B29C45, G03G15, H01F7