JPS61119017A - Manufacture of anisotropic composite magnet - Google Patents

Abstract

PURPOSE:To enable to manufacture the anisotropic cylindrical composite magnet having few warpages and cracks and excellent characteristics in a highly efficient manner by a method wherein the temperature of a metal mold is adjusted by controlling the difference between the flow-in temperature and the flow-out temperature of a metal mold temperature adjusting medium. CONSTITUTION:The temperature T1 deg.C at the flow-in part X of a metal mold temperature adjusting medium and the temperature T2 deg.C at the flow-out part Y of the medium are controlled in such a manner that they are brought to T1-T2>=20 deg.C. As a result, the generation of a weld mark can be prevented, and the warpage and cracks of a molded body can also be effectively prevented. To be more precise, when the difference between the flow-in temperature and the flow-out temperature is smaller than 20 deg.C, a weld mark is generated at the tip part of the molded body, and it is necessary that the difference of temperature is brought to 20 deg.C or more, because the degree of orientation of magnetic powder decreases by the magnetic field. Also, when the difference of temperature is smaller than 20 deg.C, a large distortion is generated in the center part of the molded body because of the long size of the molded body and a warpage and cracks are also generated on the molded body.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an anisotropic permanent magnet, which includes a step of injection molding a kneaded material containing ferromagnetic powder and a polymer compound in a magnetic field.

[Conventional technology]

In image reproducing devices (dry type) such as electrophotographic copying machines, facsimile machines, and printers, a means for transporting magnetic developer (two-component developer that is a mixed powder of magnetic carrier and toner, or one-component magnetic toner, etc.) A permanent magnet member having a plurality of magnetic poles is installed inside a non-magnetic sleeve as a developing roll or cleaning roll, etc.
A magnetic roll configured to rotate the two relative to each other is generally used.

The above magnetic rolls also have various structures,
For example, as described in Japanese Utility Model Publication No. 57-97913, a permanent magnet is formed by fixing a long anisotropic block magnet obtained by press-forming ferrite powder in a magnetic field and then sintering it around a shaft. Those using a magnetic member, or those using a permanent magnet member formed by fixing a cylindrical permanent magnet made of hard ferrite to a shaft (for example,
Publication No. 6907, Special Publication No. 53-47043 (Tani Teru)
There are many business activities. However, in the former case, there are problems such as increased assembly man-hours and low-temperature demagnetization, while in the case of the contact type, magnetic material is also used in the part between the magnetic poles and the density of the sintered body is about 5 g. /cm3, so there is a problem that the weight is large. In addition, ferrite magnets generally have the problem of poor yields because the material itself is brittle and tends to crack or crack during or after sintering.

On the other hand, ferromagnetic powder (generally ferrite powder is used) and polymer compounds (
A magnetic sail using a so-called composite magnet, which is made by integrally molding a kneaded material (generally made of rubber or plastic material) into a cylindrical shape by extrusion molding or injection molding, and then magnetizing it after cooling and solidifying it. has been proposed and its practical application is being considered. (For example, JP-A-56-10
No. 8207 No. 57-130407, No. 57-164
(Refer to various publications such as No. 509) Injection molding is advantageous from the viewpoint of productivity.

When manufacturing this cylindrical composite magnet, since composite magnets have a lower density than sintered magnets, in order to obtain magnetic properties equivalent to ferrite magnets, it is necessary to easily magnetize the ferromagnetic powder before cooling and solidifying. Align the axis with the direction of the lines of magnetic force inside the magnet after magnetization. It is well known that a so-called anisotropy process is necessary.

[Problem to be solved by the invention]

By the way, in the manufacturing process of the above-mentioned anisotropic cylindrical composite magnet, a heating or cooling medium (usually water or oil is used around the circular mold) to solidify the molded object after injection molding. ) is being carried out. However, since the cylindrical composite magnet used in magnet rolls is generally long with a length/diameter of 5 or more, the initially injected molten material begins to solidify by the time filling is completed and the tip of the molded object There were problems in that weld marks were generated in the magnetic field, the degree of orientation of the magnetic particles due to the magnetic field was reduced, and warping and cracking were more likely to occur.

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a method for manufacturing an anisotropic composite magnet that can improve production efficiency.

Another object of the present invention is to provide a method for manufacturing an anisotropic composite magnet that can prevent dimensional defects and appearance defects including warpage, bending, etc.

[Means for solving problems]

The method for producing an anisotropic composite magnet of the present invention includes the steps of injection molding a kneaded material mainly consisting of ferromagnetic powder and a polymer compound in a mold having a cylindrical molding space in the presence of a magnetic field; In a method for manufacturing an anisotropic composite magnet, which includes a step of solidifying a molded body by passing a medium for controlling the mold temperature around the mold, the difference between the inlet temperature of the mold temperature adjusting medium and the outflow temperature thereof The mold temperature is controlled by controlling the temperature to 20°C or higher.

The details of the present invention will be explained below according to the manufacturing process.

First, in the present invention, the raw material kneaded material is prepared using the following materials used in ordinary composite magnets.

Examples of the ferromagnetic powder include ferrite powder having a magnetic brambite-type structure such as T3ay elite or 9r ferrite, AJ-Ni-Co magnet powder, Fe
Known magnet powders such as -Cr-Co magnet powder and rare earth cobalt magnet powder can be used.

As the polymer compound, various thermoplastic resins such as polyamide resin, polyethylene, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, polypropylene, etc. can be used. In addition to this, a small amount of lubricant such as calcium stearate (
Furthermore, in order to improve the wettability of the ferromagnetic powder, the surface of the ferromagnetic powder may be previously treated with an organosilicon compound, an organotitanate compound, or the like.

The blending amount of the ferromagnetic powder is ferromagnetic powder: W fat = 80 to 94
: It is preferable that the weight ratio is 20 to 6. This is because if the amount of ferromagnetic powder blended is less than the above range, the magnetic properties will deteriorate, and if the blend amount is greater than the above range, molding will become substantially difficult.

Next, the raw material kneaded material is injected into a predetermined mold, molded while applying a magnetic field, solidified, and then the molded product is taken out. Although the injection molding may be carried out in a magnetic field by an electromagnet, it is preferred to carry out the injection molding in a magnetic field by a permanent magnet in order to downsize and simplify the equipment (for example, Japanese Patent Application No. 58-1021
27, No. 58-117857) or in a magnetic field using a pulsed magnetic field (for example, Japanese Patent Application No. 58-14).
5441) or by using a combination of a pulsed magnetic field and a magnetic field generated by a permanent magnet (for example, Japanese Patent Application No. 11786/1986).
(see No. 2) is preferred.

This process will be described below using an injection mold as described in Japanese Patent Application No. 58-117857.

FIG. 1 is a cross-sectional view showing an example of an injection mold used in the present invention, and FIG. 2 is a cross-sectional view taken along line AA in FIG.

First, in FIG. 1, a mold has a cylindrical molding space 1 in which a core 2 is provided concentrically. Molding space 1
Permanent magnets 31 to 3. are surrounded by radially magnetized permanent magnets 31 to 3. , permanent magnets 41 to 44 magnetized in the circumferential direction, and a nonmagnetic spacer 5 are installed.

Further, the outer periphery of these is surrounded by a yoke 6 made of a soft magnetic material, and permanent magnets 31 to 3. The yokes 71 to 7. are also made of soft magnetic material inside the yokes 71 to 7. is provided.

Further, a cylindrical cover 8 is attached to the outer periphery of the yoke 6, and a cylindrical cover 18 is also attached to the outside of the cylindrical cover 8. A flow path 9 for a mold temperature regulating medium is formed in the inner wall of the cylindrical cover 8, and a flow path 17 for a cooling medium is formed in a spiral shape in the inner wall of the cylindrical cover 18. In addition,
The cooling medium flow path 17 is formed only on the mold injection side.

Next, in FIG. 2, 10 is a protruding pin, and an extrusion sleeve 11 is fixed to the tip thereof.A template 12 and a template 13 are provided on the opposite side of the extrusion sleeve 11. 13 is provided with a spool 14, and the II plate 12 is provided with a runner 15 and a nozzle 16 that communicate with the spool 14, and one end of the nozzle 16 communicates with the molding space 1 via a gate (not shown).

When injection molding is performed in the mold, the raw material mixture injected into the mold heated to a predetermined temperature is filled into the molding space 1 through the spool 14, runner 15 and nozzle 16, and is filled with the magnetic field described above. Oriented by Then flow path 9
Mold temperature #l! After solidifying the object to be molded by passing the fI medium through the cooling medium through the flow path 17 and exchanging heat, the mold plate 12 and the mold plate 13 are separated to separate the molded object from the molded piece on the spool or the like, Further, the protruding bottle 10 is protruded and the molded body is taken out from the mold.

As a result of various studies conducted by the present inventors regarding this solidification process,
The temperature at the inlet of the mold temperature control medium (shown as X in Figure 2) (hereinafter referred to as inflow temperature, shown at 71°C) and the temperature at the outlet of the medium (shown as Y in Figure 2) It was discovered that weld marks can be prevented by controlling the outflow temperature (71°C) below T, -T, 220°C, and warping and cracking of the molded product can be effectively prevented. .

In other words, if the difference between the inflow temperature and the outflow temperature is less than 20°C, weld marks will occur at the tip of the compact, and the degree of orientation of the magnetic particles due to the magnetic field will decrease.
It is necessary to do more than that. Further, if the temperature difference is smaller than 20° C., since the molded product is long, a large strain will occur in the center of the molded product, causing warpage or cracking in the molded product. However, if the above-mentioned temperature difference is 20° C. or more, the molded body is uniformly cooled, so that distortion can be reduced and warping and cracking of the molded body can be prevented. Note that the inflow temperature may be set depending on the type of resin. In order to make the difference between the inflow temperature and the outflow temperature 20° C. or more, the flow rates and temperatures of the mold temperature adjusting medium and the cooling medium may be adjusted. For example, using water heated to a predetermined temperature as a mold temperature adjustment medium and using water at a predetermined temperature as a cooling medium, T, -T,
The flow rate of each medium may be appropriately set so that the temperature becomes 220°C. However, from the viewpoint of ease of mold temperature control, it is desirable to set the flow rate of each medium so that the Raynozzle number (Re) is aooo or more, and it is preferable to select the temperature of each medium so that T+Tt≧20℃. Good. The Reynolds number (Re) is defined by the diameter of the pipe through which the medium flows, d, the flow velocity of the medium, V,
If the density of the medium is ρ and the viscosity of the medium is μ, then Re=dv·ρ/μ.

The outer diameter of the thus obtained compact is machined to a predetermined size as required, and after the shaft is fixed, it is magnetized in the same direction as the anisotropy direction, as shown in Fig. 3. You can get a magnetic roll. In FIG. 3, 19 is a cylindrical composite magnet, and 2a is a shaft. However, the shaft 20 may be molded integrally with the cylindrical composite magnet 19 by insert molding.

EXAMPLES The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Examples and comparative examples]

135 kg of polyamide resin (nylon 6: trade name) was added to 7.65 kg of Ba ferrite powder having an average particle size of 1 μm, and the mixture was kneaded at 250° C. using a kneader. This kneaded material was put into an experimental injection molding machine equipped with the mold shown in FIGS. 1 and 2, and was injected into the mold at a temperature of 270° C. and a pressure of 900 kU/cd and solidified. Here, the permanent magnet of the mold has a Br of 9. oooG, IHC is 1o, ooooo
A rare earth cobalt magnet (H-22A manufactured by Hitachi Metals) was used, and the magnetic flux density distribution in the molding space was as shown in No. 4 @.

The obtained molded body (outer diameter sowxf4.inner diameter 12.11
, length 260B), and then magnetized to obtain a magnet roll as shown in FIG. When we measured the magnetic flux density distribution of this magnetic roller, we found that
The waveform shown in the figure was obtained.

In the above molding process, the flow rates of the mold temperature adjustment medium and cooling medium are each set so that b = sooo, and the temperature of the cooling water is adjusted using 120°C water as the mold temperature adjustment medium. The presence or absence of weld marks, dimensions, and appearance were measured and evaluated by varying the outflow temperature. The results are shown in Table 1.

Table 1 (Note) The measured values are the average values for 10 samples.As is clear from Table 1, according to experimental graves 5 to 7, where the temperature difference was within the range of the present invention, weld marks, warping, and cracks were observed. It can be seen that better results than Experimental Grave 1.2 can be obtained for all of the above.

〔Effect of the invention〕

As described above, according to the present invention, an anisotropic cylindrical composite magnet with less warpage and cracking and excellent magnetic properties can be manufactured with high efficiency.

[Brief explanation of drawings]

Figure 911 is a cross-sectional view showing an example of a mold used in the present invention, Figure 2 is a sectional view taken along line A-A in Figure 1, Figure 3 is a perspective view of the magnet roll, and Figure 4 is Figure 1. FIG. 5 is a diagram showing the magnetic flux density distribution on the inner surface of the mold, and FIG. 5 is a diagram showing the magnetic flux density distribution of the magnet roll obtained by the present invention. 1: molding space, 2: core, 3.4=permanent layer, 9 two channels.

Claims (1)

[Claims] 1. A step of injection molding a kneaded material mainly consisting of ferromagnetic powder and a polymer compound in a mold having a cylindrical molding space in the presence of a magnetic field, and a mold temperature adjusting medium is provided around the mold. In the method for producing an anisotropic composite magnet, which includes a step of solidifying the molded body by passing the medium through the mold, the mold temperature is controlled by controlling the difference between the inflow temperature and the outflow temperature of the mold temperature adjusting medium to 20°C or more. 1. A method for manufacturing an anisotropic composite magnet, the method comprising adjusting: