JP3042929B2 - Magnet roll and method of forming the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roll used in a developing mechanism using a one-component or two-component magnetic toner in an electrophotographic apparatus such as a copying machine or a laser beam printer, or supplies toner to the developing roll. Toner supply roll,
Alternatively, the present invention relates to a magnet roll used as a cleaning roll for cleaning toner adhered to a photoreceptor, and a molding method thereof.

[0002]

2. Description of the Related Art In a conventional general magnet roll, a metal supporting portion is projected from both ends of a metal magnet body which is a magnetic material. The support portion is supported by a bearing provided on a flange of a sleeve body having a non-magnetic cylindrical shape such as aluminum or stainless steel. In order to control the potential of the sleeve body, the flange and the support are formed from a conductive metal material. As an improvement, it was considered that the metal shaft was covered with a cylindrical resin magnet. However, since these materials used a metal material, there was a problem of an increase in weight and an increase in cost due to cutting of the shaft. Therefore, recently, a resin molded integrally with the shaft portion has been developed, and the magnet body and the support portion are also molded with the resin to reduce the weight and cost.

[0003]

A magnet roll integrally formed of resin has a magnet body having a diameter of 9 to 50 mm.
, Which is extremely thick compared to general injection molded products. For this reason, there is a disadvantage that the cooling time is prolonged and sink occurs, resulting in a large variation in dimensions and magnetic characteristics. There is also a disadvantage that fine bubbles are generated inside the magnet main body, and the variation in magnetic force characteristics in the axial direction becomes large. Further, even if the motor is integrally formed of resin, it is required to further reduce the weight and to reduce the driving torque to reduce the weight of the motor.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnet roll having a further reduced weight, a shorter molding time, reduced sink marks and bubbles, stable magnetic properties, and a method of manufacturing the same.

[0005]

In order to achieve the above-mentioned object, the present invention provides a magnet body formed of a molded resin magnet, and a support formed by injection molding at least one end of the magnet body integrally with the magnet body. And a hollow portion formed in the magnet main body. Further, a resin material mixed with magnetic powder is injected into an injection mold having a magnet body and a cavity for molding a support portion provided at least on one end side of the magnet body. The hollow resin is formed by injecting the active gas and expanding the injected resin by gas pressure.

[0006]

According to the present invention, the weight is reduced by the presence of the hollow portion, and the formation of such a hollow portion suppresses the occurrence of sink marks and bubbles and exhibits stable magnetic force characteristics.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

The magnet roll shown in FIG. 1 has a magnet main body 1 formed of a molded resin magnet, and a support portion 2 integrally molded with the magnet main body 1 at both ends of the magnet main body 1. A hollow portion 3 is formed therein. A gate mark 4 at the time of injection molding remains at a predetermined portion of one support portion 2. FIG. 2 shows a distribution of magnetic force when the magnetic powder is uniformly mixed in the magnet roll shown in FIG.

FIG. 3 shows that the gate mark 4 is formed at the center of the end face of the shaft.

In the magnet roll shown in FIG. 4, a support portion 2 is injection-molded integrally with the magnet main body 1 only on one end side of the magnet main body 1, and an opening of the hollow portion 3 is exposed on the other end side. This shows an example in which the support portion 2 'is attached later.

The magnet roll shown in FIG.
Is formed into a concave shape. In addition, in addition to making the both ends of the support portion concave in this way, only one side is made concave,
It is also possible to make the opposite side convex, and the shape of the support portion may be formed in accordance with the form of support of the developing device that supports the magnet roll. FIG. 6 shows an example in which the diameter of the end of the roll body is reduced. In this way, the thickness of the roll body becomes substantially constant, and the magnetic force is made uniform over the entire length of the roll as shown in FIG.

As shown in FIG. 8, for any of the above-described magnet rolls, an injection mold 7 having a magnet body 1 and cavities 5 and 6 for molding the support 2 is prepared. A resin material mixed with magnetic powder is injected from the nozzle 8 and an inert gas is injected from a gas nozzle 9 into the cavity 5 for molding the magnet main body at the time of injection of the resin material, and the injected resin is expanded by gas pressure to form a hollow. The part 3 is formed. In the mold shown in FIG. 8, a magnet roll as shown in FIG. 3 is formed. The nozzle tip of the gas nozzle 9 remains as the gate mark 4. In addition, the magnet roll as shown in FIG. 4 can also be formed by general injection molding without using the gas injection molding method as shown in FIG. The gas injection molding method has a process of injecting an inert gas into molten resin injected into a mold by injection molding. One of them is a full shot method applied to housings and chassis, etc., in which gas channels are designed in the molded product, and the pressure holding process of injection molding is performed by the gas pressure of inert gas. The molded product has a hollow structure. Part and a thin solid part. Another method is to spread the short-shot resin to an unfilled portion by gas pressure to form a continuous hollow portion inside to obtain a pipe-shaped hollow article such as blow molding. The magnet roll of the present invention can be suitably formed by the short shot method. Generally, nitrogen gas is used as the inert gas. By injecting and injecting the inert gas, the gas pressure acts on the resin in the peripheral portion from the gas channel to press the resin against the mold surface, thereby preventing sink marks. In addition, the gas pressure can be more uniformly applied to the gas channel formed up to the flow front end portion, and since the pressure-holding step of the injection molding is usually performed at this gas pressure, it is possible to form the gas at a low pressure. When the resin is sufficiently cooled, the internal gas is released into the atmosphere to release the pressure, and the molded product is taken out, whereby the magnet roll shown in FIGS. 1 to 6 can be formed.

FIG. 9 shows an example of a molding method for injecting a gas from a runner, and FIG. 10 shows an example of a molding method for injecting a gas directly into a mold cavity.

[0014]

As described above, according to the magnet roll of the present invention, since the hollow portion is provided inside the magnet main body, the weight can be reduced and the driving torque can be reduced.
A small and lightweight motor can be used. Further, according to the molding method of the present invention, generation of sink marks and bubbles is suppressed, and a magnet roll having stable magnetic force characteristics can be manufactured. In addition, the amount of resin material used is reduced, the cooling time is shortened, the production can be performed efficiently, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a magnet roll according to the present invention.

FIG. 2 is a magnetic force distribution diagram of the first embodiment.

FIG. 3 is a sectional view showing a second embodiment.

FIG. 4 is a sectional view showing a third embodiment.

FIG. 5 is a sectional view showing a fourth embodiment.

FIG. 6 is a sectional view showing a fifth embodiment.

FIG. 7 is a magnetic force distribution diagram of the fifth embodiment.

FIG. 8 is a sectional view for explaining an example of a molding method for injecting a gas from a nozzle.

FIG. 9 is a sectional view for explaining an example of a molding method for injecting a gas from a runner.

FIG. 10 is a cross-sectional view for explaining an example of a molding method for directly injecting a gas into a mold cavity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet main body 2 Support part 3 Hollow part 5, 6 Cavity 7 Injection molding die 8 Injection molding machine 9 Gas nozzle

Claims (2)

(57) [Claims] 1. A magnet body formed of a molded resin magnet, a support portion formed by injection molding integrally with at least one end of the magnet body, and a hollow portion formed in the magnet body. A magnet roll characterized by the following. 2. Injecting a resin material containing magnetic powder into an injection mold having a magnet body and a cavity for molding a support portion provided at least on one end side of the magnet body, and forming a cavity for molding the magnet body at the time of injection. A method of forming a magnet roll, characterized by injecting an inert gas into the inside of the resin and expanding the injected resin by gas pressure to form a hollow portion.