JPH0570288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multipolar plastic magnet, particularly a multipolar plastic magnet suitable for magnet rolls used in electronic copying machines and the like.

The magnet for the magnet roll has a diameter of 15 to 30 mm and a length of 200 to 400 mm (a long cylindrical steel rotating shaft with a length of approximately 7 times the diameter or more). This magnet is located inside a sleeve made of non-magnetic material such as aluminum or stainless steel plate, and the developer attracted onto the sleeve is moved by the magnet itself or by rotating the sleeve. It is used for purposes such as conveying the image, or creating a magnetic brush to rub and develop the electrostatic latent image formed on the photoreceptor.

The magnet used in such a magnet roll has a cylindrical outer peripheral surface with magnetic poles extending in the axial direction, and a plurality of such magnetic poles are arranged in the rotation direction.

When manufacturing these magnets, a steel shaft is usually installed in the center of a cylindrical cavity in a plastic mold, and then plasticized plastic magnet material is filled and molded. . Furthermore, in order to improve the magnetic properties, a magnetic circuit is provided in the mold so that magnetic poles are formed at locations in the mold corresponding to the locations where the magnetic poles of the magnets are to be attached. When a magnetic field is applied to the plastic magnet material from the magnetic pole of the molding die during injection molding of the plastic magnet material, the magnetic powder in the plastic magnet material, such as barium ferrite powder, rare earth cobalt powder of Sm ₂ Co ₁₇ system, changes its axis of easy magnetization. are aligned in the direction of the applied magnetic field.
When solidified in this state, it becomes a plastic magnet with magnetic anisotropy and a strong magnetic force.

However, although there is no problem if the magnetic field applied to the molding die is symmetrical with respect to the axis of the cylindrical magnet, it is often not necessarily symmetrical. When an asymmetric magnetic field is applied to the axis, the steel shaft 2 placed in the molding die 1 is attracted to the side with the strong magnetic pole 3, as shown in Figure 1, and It is bent as shown by the two-dot broken line 2a. If the plastic magnet material 4 is injection molded in this state, the material will cool and solidify inside.
The plastic magnet taken out from the cavity is bent by the restoring force of the shaft 2 as shown by the two-dot broken line 4a in the figure. Therefore, the outer periphery must be machined to achieve straightness, but this machining process is extremely troublesome, and because it removes the strongly anisotropic surface area, it inevitably reduces the magnetic force. .

In order to eliminate the above-mentioned disadvantages, it has been proposed to use non-magnetic metal materials such as austenitic stainless steel, aluminum, or copper alloys as shaft materials, but these materials are all expensive, and plastic magnets In addition to the drawback of increasing the price, the specific gravity was large and went against the need for weight reduction.

The present invention solves the above-mentioned problems, and is characterized by having a plurality of magnetic poles asymmetrically arranged on the surface, which is obtained by injection molding in a magnetic field using a shaft made of a polymeric organic material. It is a long cylindrical multipolar plastic magnet with

The polymeric organic material suitable for this shaft may be either a thermoplastic resin or a thermosetting resin. Preferably, the material has the hardness and rigidity necessary for the shaft, and has a hardening temperature that does not soften at the temperature at which plastic magnet materials are injection molded. Thermoplastic resins such as polycarbonate and tetrafluoroethylene can be used, and thermosetting resins such as phenol resins and epoxy resins are good.If higher hardness and rigidity are required, glass can be used in addition to these resins. A mixture of inorganic materials such as fibers and carbon fibers may be used.

When using a shaft made of such a polymeric organic material, it can be made by injection molding or extrusion molding into the dimensions and shape required for the shaft. Additionally, grooves and keyways for inserting snap springs can be easily made by cutting and grinding. The shaft of the polymeric organic material made in this way was placed in the shaft groove 12 of a mold similar to that shown in Fig. 1, and the plastic was inserted while applying a magnetic field from around the cavity of the mold. The shaft is cast by injecting the magnetic material. After the plastic magnet material has solidified, the plastic magnet is removed from the mold. This plastic magnet is subjected to machining such as chamfering if necessary, but it is sometimes used without machining.
This magnet can also be re-magnetized before use.

Since the multipolar plastic magnet of the present invention uses a polymeric organic material for its shaft, the shaft will not bend when molded in a magnetic field. Additionally, it has a low specific gravity of 1.5 to 2.5, which is less than 1/3 of the specific gravity of metal materials, such as 7.8 for steel and 8.9 for copper, contributing to weight reduction. Furthermore, polymeric organic materials are generally easier to machine than metal materials. Further, it is possible to manufacture shafts in desired dimensions in large quantities at high speed by injection molding or extrusion molding, which is economically advantageous.

Embodiment Figure 2 shows a cross section of the mold used to make the multipolar plastic magnet of the present invention. In the figure, 5 is the mold part, inside of which was a cylindrical cavity with an inner diameter of 23 mm and a length of 270 mm. 51, and the cavity 51
around magnetic poles N ₁ , S ₁ , N ₂ , with surface magnetic flux densities of 870 Gauss, 650 Gauss, 760 Gauss, and 670 Gauss, respectively.
S ₂ is located. A shaft 2 made of polycarbonate having a diameter of 8 mm and a length of 300 mm was placed in the center of the cavity 51, and a Ba ferrite plastic magnet material was injected and filled into the cavity. The shaft of the plastic magnet roll thus obtained was free from bending, the central axis of the shaft with respect to the outer periphery of the plastic magnet roll coincided with the shaft, and the magnet had perfect straightness in the longitudinal direction. Additionally, the weight was reduced by 32% compared to when the shaft was made of steel.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a conventional mold for molding a magnet, and FIG. 2 is a cross-sectional view of a mold for molding a magnet of the present invention. Explanation of symbols, 2...Shaft.

Claims (1)

[Claims] 1 A shaft made of a polymeric organic material and a shaft that is integrally formed on the outer periphery of this shaft by injection molding in a magnetic field, has multiple magnetic poles arranged asymmetrically on the surface, and has a length approximately 7 times the diameter. A multipolar plastic magnet characterized by comprising the above cylindrical plastic magnet.