JPH09306768A - Manufacture of cylindrical resin magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable providing a cylindrical resin magnet having a high magnetic force, by applying to a mixture a first magnetic field acting substantially in the direction of the diameter of a mold, and then applying a second magnetic field having the same direction as the magnetization pattern while performing extrusion molding. SOLUTION: A material fused by heating is passed through a parallel magnetic field (that is, a magnetic field formed substantially in the direction of the diameter of a mold) generated by a first magnetic field generation member 8, so that ferromagnetic particles in the material are oriented. Then, this material is passed through a magnetic field (that is, a polar anisotropy magnetic field) generated by a second magnetic field generation member 9, so that the ferromagnetic particles are oriented. In this anisotropic process, the intensity of the first magnetic field is made higher than the intensity of the second magnetic field. The content of the ferromagnetic particles in the material is set to 90-94% by weight. The compact which is caused to be anisotropic is extruded from a metal mold, then cut under the condition of L/D>=5 or greater (where L represents the length and D represents the outer diameter), and then cooled, solidified and demagnetized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a cylindrical resin magnet which constitutes a magnet roll used as a developing roll in electrophotography, electrostatic recording and the like.

[0002]

2. Description of the Related Art In electrophotography, electrostatic recording, etc., a magnetic developer (one-component magnetic toner or toner and magnetic carrier) that forms an electrostatic charge image on the surface of an image carrier (photoreceptor or dielectric) and contains toner. A two-component developer, etc.) to a developing area by a developing roll to develop an electrostatic image, transfer the resulting toner image to a transfer member (plain paper, etc.), and then heat and / or pressurize. The image is formed by fixing with.

As the developing roll, for example, a magnet roll having a structure shown in FIG. 5 is often used. In FIG. 5, reference numeral 1 denotes a permanent magnet member, which has a cylindrical permanent magnet 11 having a plurality of magnetic poles extending in the axial direction on the surface, and a shaft 12 coaxially fixed to the central portion thereof. The permanent magnet member 1 is housed inside a sleeve 2 formed in a cylindrical shape, and is supported by flanges 3 a and 3 b on both ends of the shaft 12 via bearings 4 and 4. The sleeve 2 and the flanges 3a and 3b fixed to both ends thereof are formed of a non-magnetic material such as an aluminum alloy or austenitic stainless steel. Reference numeral 5 is a seal member (oil seal).
With the above-described structure, the relative rotation between the permanent magnet member 1 and the sleeve 2 (for example, the permanent magnet member 1 is fixed and the flange 3a is rotated), the magnetic developer is adsorbed on the surface of the sleeve 2 and developed. The electrostatic charge image is visualized by transporting it to a region (a region where the image carrier and the sleeve face each other).

[0004]

The cylindrical permanent magnet constituting the above magnet roll usually has an outer diameter (D) of 10 to 10.
60mm, length (L) is 200 ~ 350mm, L / D ≧ 5
Such a long and narrow object is formed of, for example, a resin magnet containing ferromagnetic particles and a resin as main components. This resin magnet is produced, for example, by heating and kneading a raw material mixture, extruding the mixture in a magnetic field, and then magnetizing the mixture in a predetermined magnetizing pattern. According to this method, there are advantages such as high dimensional accuracy and high efficiency of production (for example, Japanese Patent Publication No. Sho 60-3).
No. 5806, JP-A-63-182803).

However, in the conventional magnetic field extrusion molding method, a magnetic field (such that the easy axis of magnetization of the ferromagnetic particles is oriented in the same direction as the predetermined magnetization pattern until the raw material mixture is melted and solidified). Although a direct-current magnetic field is applied, there is a problem that it cannot be applied when a specific magnetic pole (for example, a developing magnetic pole) needs to have a high magnetic force (for example, 1600 G on the magnet surface). Therefore, it is possible to increase the magnetic field strength in order to increase the degree of orientation.
The magnetic field generating means (magnetic field coil or permanent magnet) becomes large,
If the number of magnetic poles is large, another problem is that it cannot be dealt with. Furthermore, even if the magnetic field strength is increased unnecessarily, the degree of orientation becomes supersaturated, and there is a problem that further improvement of the degree of orientation cannot be expected.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems existing in the prior art and to provide a manufacturing method capable of obtaining a cylindrical resin magnet having a high magnetic force.

[0007]

In order to achieve the above object, in the present invention, a raw material mixture containing ferromagnetic particles and a thermoplastic resin is extruded in a magnetic field to form a cylindrical compact, Then, in the method for producing a cylindrical resin magnet, in which a predetermined magnetizing pattern is formed by magnetizing a plurality of magnetic poles on the surface of the cylindrical molded body, the first resin which acts on the mixture in a substantially diametrical direction of the molded body. A technical means of applying a magnetic field and then extruding while applying a second magnetic field having the same method as the magnetization pattern was adopted. In the present invention, the cylindrical molded body preferably has a ratio (L / D) of the length (L) to the outer diameter (D) of 5 or more. In the present invention, the cylindrical molded body has 9 ferromagnetic particles.
It is desirable to contain 0 to 94% by weight. In the present invention, the strength of the first magnetic field is preferably higher than the strength of the second magnetic field.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a raw material for molding is first prepared. That is, at least the ferromagnetic particles and the thermoplastic resin are dry-mixed by, for example, a mixer, the mixture is kneaded by heating, and then pulverized to a few mm or less and then granulated to obtain a raw material. The above-mentioned kneading and granulation can be carried out at a temperature of 100 to 200 ° C. by a twin-screw kneading extruder, for example.

As the ferromagnetic particles, for example, barium ferrite and / or strontium ferrite, or magnetic particles having a large magnetic anisotropy constant such as R-Co or R-Fe-B-based rare earth magnet powders are used. It is possible to use, and it is preferable to use particles having an average particle size of 0.5 to 3 μm in terms of magnetic properties, moldability, and productivity. In order to improve the wettability with the resin material, the surface of the ferromagnetic particles may be treated with, for example, an organic silicon compound (silane coupling agent) or an organic titanate compound (titanium coupling agent). From the viewpoint of magnetic properties, these ferromagnetic particles account for 88% by weight or more (more preferably 90% by weight) based on the total weight of the raw material.
Above) It is preferable to contain. However, when the content of the magnetic particles increases, the resin content becomes insufficient, the mechanical strength becomes insufficient, and molding becomes difficult. Therefore, 94% by weight or less is preferable.

As the resin component, polyethylene, vinyl chloride, ethylene-ethyl acrylate copolymer (EE
Thermoplastic resins such as A), ethylene-vinyl acetate copolymer (EVA), polyacetal (Delrin), and ABS resin can be used. Among these, EEA is preferable in consideration of extruding a long and thin product.

In addition to the above essential components, a magnetic powder dispersant, a lubricant, a plasticizer and the like can be added to the raw material. The total addition amount of these is preferably 3% by weight or less, and more preferably 1 to 2% by weight. As the dispersant, a phenol type, an amine type or the like can be used. As the lubricant, waxes (paraffin wax, microlisterin wax, etc.), fatty acids (stearic acid, oleic acid, etc.), fatty acid salts (calcium stearate, zinc stearate, etc.), etc. can be used. Examples of the plasticizer include di2-phthalate.
Ethylhexyl (DOP), dibutyl phthalate (DB
Phthalates such as P) may be used.

The above raw material mixture is put into a molding apparatus,
It is anisotropic when it passes through an alignment mold provided at the tip. The obtained cylindrical molded body is cooled, demagnetized, and then cut into a predetermined length. After the shaft is fixed to the center of the cylindrical molded body, a plurality of magnetic poles (usually 3 to 8 poles) are magnetized on the surface to obtain the permanent magnet member shown in FIG. Here, the configuration of the above-described molding apparatus will be described with reference to FIGS. 1 is a vertical cross-sectional view showing the main part of the molding apparatus, FIG.
1 is a sectional view taken along the line AA in FIG. 1, and FIG. 3 is a sectional view taken along the line BB (but enlarged). In FIG. 1, 6 is a twin-screw kneading type extruder, which has a hopper 61 at one end and is divided into a plurality of barrels 62 and two screws 63 (in the figure, 1). (Only a book is shown) and an adapter 64 installed at the tip of the barrel 62. The orientation mold 7 is connected to the ejection port of the adapter 64. This mold 7 has a cylindrical molding space 73 formed between it and the mandrel 72, and
The first magnetic field generating member 8 arranged around the molding space 73
And a second magnetic field generating member 9.

The first magnetic field generating member 8 includes an upper block 81 and a lower block 82 made of a ferromagnetic material such as iron and steel, and a spacer 83 made of a non-magnetic material such as austenitic stainless steel mounted between them. And a DC magnetic field coil (not shown). A plurality of second magnetic field generating members 9 are arranged inside a cylindrical yoke 91 made of a ferromagnetic material so as to surround a molding space 73 formed inside a ring-shaped spacer 96 made of a non-magnetic material. Magnet unit 9
2 is provided. Each magnet unit includes a spacer 93 made of a ferromagnetic material, a permanent magnet 94 magnetized in the radial direction, and a pole piece 95 made of a ferromagnetic material.

According to the above molding apparatus, an anisotropic resin magnet having a high degree of orientation can be obtained as follows. Hopper 6
The raw material charged into the barrel 62 via 1 is conveyed to the orienting die 7 while being heated and melted at a temperature of 150 to 230 ° C. while a shearing force is applied by the rotation of the pair of screws 63, and a magnetic field is applied there. While receiving, it is narrowed down to a predetermined cross-sectional area and passes through the molding space.

Since the heated and melted raw material first passes through the parallel magnetic field generated by the first magnetic field generating member 8 (the magnetic field formed in the substantially diametrical direction of the compact), the ferromagnetic particles in the raw material are shown in FIG.
It is oriented as shown in (a). That is, since the magnetic force lines generated by the first magnetic field generating member 8 are directed from the N ₁ pole to the S ₂ pole (however, the magnetic field lines are spread at the S ₂ pole), the ferromagnetic particles are oriented along the magnetic force lines, so that the magnetic force lines are concentrated. Done N ₁
The poles are strongly anisotropy. Next, since the raw material passes through the magnetic field (polar anisotropic magnetic field) generated by the second magnetic field generating member 9, the ferromagnetic particles in the raw material are oriented as shown in FIG. 4 (b). In the molded body 10 thus obtained, the specific magnetic pole portion (N ₁ pole in FIG. 1) is made more anisotropic than the other magnetic pole portions, so that the surface magnetic flux density of that portion is changed to other portions. Can be higher than. In the above anisotropy step, it is desired that the intensity (H ₁ ) of the first magnetic field is higher than the intensity (H ₂ ) of the second magnetic field, and more preferably H ₁ is 1.5 times that of H ₂ . ~ 2 times. This is because the content of the ferromagnetic particles in the raw material is large in the present invention (90% by weight or more),
This is because it is possible to improve the magnetic flux density of the specific pole by first orienting only a specific portion with a high magnetic field strength and then orienting another portion with a lower magnetic field strength.

The anisotropy molded body is extruded from the mold, cut into a predetermined length (L / D ≧ 5 or more), and cooled.
It is solidified and demagnetized. Next, this molded body is fixed to a shaft to obtain the permanent magnet member 1 shown in FIG. As concrete magnetic field strength, H ₁ is 50 to 100 KOe and H ₂ is 30 to 5
It may be 0KOe. If H ₁ and H ₂ are too low, a sufficient degree of orientation cannot be obtained, and if H ₁ and H ₂ are too high, they do not contribute to the improvement of the degree of orientation (saturate).

[0017]

EXAMPLES Next, the present invention will be described more specifically by the following examples and comparative examples. First, 93 parts by weight of Sr ferrite particles having an average particle diameter of 1 μm, 5 parts by weight of ethylene-ethyl acrylate copolymer (MB-870 manufactured by Nippon Unicar Co., Ltd.), and 1 part by weight of a dispersant (DH-37 manufactured by ADEKA ARGUS CORPORATION). , 0.5 part by weight of a lubricant (Sripax E manufactured by Nippon Kasei Co., Ltd.) were mixed in a mixer, and the resulting mixture was heated and kneaded at 150 ° C., cooled and solidified, and then pulverized into particles having a diameter of 5 mm or less. 5 parts by weight (KF9 manufactured by Shin-Etsu Chemical Co., Ltd.
After adding 68), granulate at a temperature of 150 ° C. The kneading and granulation were performed by a twin-screw kneading extruder. The raw material adjusted in this way is charged into the molding apparatus shown in FIG.
The mixture is extruded from a mold while being kneaded at a temperature of 0 ° C., cut into a predetermined length, fixed with a shaft at the center, and then asymmetrically magnetized with 5 poles to obtain a permanent magnet member shown in FIG. This permanent magnet member is a cylindrical permanent magnet having an outer diameter of 16.5 mm and a length of 220 mm, and a shaft (SUM material) having an outer diameter of 5 mm is fixed to the central portion thereof. At the time of the extrusion molding, by applying a parallel magnetic field of 70 KOe by the first magnetic field generating means and then applying a magnetic field having a polar anisotropy of 40 KOe by the second magnetic field generating means, the N ₁ pole of the permanent magnet is Surface magnetic flux density is 16
And the surface magnetic flux density of other magnetic poles was 1400G. On the other hand, when the anisotropy treatment is performed only by the second magnetic field generating means, the surface magnetic flux density of the N ₁ pole is 1400G.
Met.

[0018]

As described above, according to the present invention, since the extruded product in which the ferromagnetic particles are dispersed in the resin is subjected to the specific anisotropy treatment, the orientation degree of the ferromagnetic particles is improved. Therefore, a cylindrical resin magnet having a high magnetic force can be obtained.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a main part of a molding apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a sectional view taken along line BB in FIG.

FIG. 4 is a diagram for explaining the orientation state of the molded body obtained by the present invention, which is a state after the first magnetic field is applied (a) and after the second magnetic field is applied (b).

FIG. 5 is a vertical sectional view (a) and a horizontal sectional view of a magnet roll including a cylindrical resin magnet obtained according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Permanent magnet member, 11 Cylindrical permanent magnet, 6 Extruder, 7 Orientation metallic mold, 8 1st magnetic field generation member 9
Second magnetic field generating member

Claims (4)

[Claims] 1. A cylindrical molded body is produced by extruding a raw material mixture containing ferromagnetic particles and a thermoplastic resin in a magnetic field, and then a plurality of magnetic poles are magnetized on the surface of the cylindrical molded body. In the method for producing a cylindrical resin magnet for forming a predetermined magnetizing pattern according to, a first magnetic field acting in a substantially diametrical direction of a molded body is applied to the mixture, and then a second magnetic field having the same direction as the magnetizing pattern is applied. A method for producing a cylindrical resin magnet, which comprises extruding while applying a magnetic field. 2. The ratio (L / L) of the length (L) and the outer diameter (D).
The method for producing a cylindrical resin magnet according to claim 1, wherein a cylindrical molded body having D) of 5 or more is prepared. 3. The cylindrical molded body contains ferromagnetic particles in an amount of 90 to 9
The method for producing a cylindrical resin magnet according to claim 1, wherein the content is 4% by weight. 4. The method for manufacturing a cylindrical resin magnet according to claim 1, wherein the strength of the first magnetic field is higher than the strength of the second magnetic field.