JPS6041203A - Bonding magnet having excellent magnetic characteristic and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a bonding magnet which assures grain orientation being convenient for magnetization pattern of multipole magnetization. CONSTITUTION:About 90wt% of strontium ferrite magnetic powder with average longer diameter of 1-10mum (desirably 2-4mum) and a thickness to longer diameter ratio of about 0.25-0.9 and about 10wt% of EVA resin are kneaded under a temperature of about 150 deg.C. This kneaded material is cracked into pellet. The material is then heated up to about 150 deg.C with an extruder with auger diameter of about 50mm.. Thereby the material is molded into a round bar in diameter of about 10.5mm.. Owing to this manufacturing method, anisotropic characteristic can be enhanced at the area near the surface of molded material but weakened at the center thereof and moreover the magnetic characteristic can also be improved.

Description

[Detailed Description of the Invention] The present invention provides a bonded magnet with excellent magnetic properties, a method for manufacturing the same,
More specifically, the present invention relates to a bonded magnet manufactured by extrusion using Hard Ferrite 1 magnet powder and a method for manufacturing the same.

Bonded magnets are made by bonding magnetic powder with a binder such as rubber or plastic. Although the magnetic properties deteriorate due to the amount of binder included, they have good dimensional accuracy and workability, so they are small and thin.

It has the advantage of being suitable for complex-shaped products, and its demand has been increasing in recent years. In the case of bonded magnets, the magnetic properties of the product directly reflect the properties of the magnetic powder used therein, so the magnetic powder itself must have excellent permanent magnetic properties.

It should be noted that in normal manufacturing methods, for example, when taking a ferrite magnet, the final magnet is produced by pressing magnet powder and then sintering it to grow crystal grains. It is not necessarily necessary to exhibit excellent permanent magnetic properties in the original state. Therefore, it is necessary to prepare ferrite magnet powder suitable for bonded magnets.

On the other hand, in molding a bonded magnet, it is known to mechanically orient Ferray I particles by rolling or extruding a resin mixture to obtain an anisotropic bonded magnet. In this case, the more tabular the ferrite particles are, the more aligned the particles are from the surface of the molded article to the deeper part, and the more anisotropic it becomes. An example of this is shown in FIG. 1(a), taking the case of anisotropy caused by extrusion processing as an example. The direction of the arrow is the direction of easy magnetization. Note that when the material is anisotropic, the magnetic properties in the direction perpendicular thereto, that is, the direction in which magnetization is difficult, are of course inferior to those in the case of isotropy.

Furthermore, if the tabularity of the grains is not very strong, the region where the grains become uniform and anisotropic is limited to only the portion near the surface.

An example of this is shown in FIG. 1(b).

Now, in practical bonded magnets, for example, a typical case is seen in a magnet roll for a copying machine, in which multi-pole magnetization is performed along two circumferential directions on the surface of the magnet. There are many.

At this time, the flow of magnetostriction inside the magnet is as shown in FIG. 1(C). As is clear from Fig. 1(C), near the surface the magnetic flux is oriented in the radial direction;
) Coincides with the easy magnetization direction in (b). However, as it goes inside, the flow of magnetic flux changes in the circumferential direction, as shown in Figure 1 (a
), the flow of magnetic flux no longer coincides with the easy magnetization direction, but with the hard magnetization axis. Therefore, the magnetic path is cut off at this point, which is extremely disadvantageous in terms of the magnetic circuit. On the other hand, in the case of FIG. 1(b), inside,
Although the direction of magnetic flux flow is not along the axis of easy magnetization, it is not along the axis of hard magnetization, which is more advantageous than the case shown in FIG. 1(a).

(In Fig. 1(b), this part is drawn as if it is isotropic, but as described later, according to the experimental results, the axial direction of the molded body, that is, the direction perpendicular to the plane of the paper in Fig. 1(b) Since it was found that the direction of magnetization is difficult, in a sense, both the radial direction and the circumferential direction are easy directions in this part, which is more advantageous than isotropy in terms of the magnetic circuit.) According to experimental results, in order to achieve such anisotropy,
The ratio of thickness/major axis (hereinafter -3- is abbreviated as t/'d) of the ferrite particles exceeds 0.25 and 0.
It has been found that good results are obtained in processing over a wide range of extrusion ratios when the extrusion ratio is 9 or less. If t/d is Q, 5 or less, the anisotropy will occur even to the inside of the molded body, which is not preferable, especially when the extrusion ratio is large (80%) or more. When t/d is 0.25 or less, the interior becomes anisotropic even when the extrusion ratio is 50%. On the other hand, [/'d
On the contrary, as the value becomes larger, the anisotropy becomes weaker. t/d
Although a creditability effect can be obtained in the surface portion even when the value is about 0.95, the degree of the effect is usually insufficient. In order to obtain a significant anisotropic effect in the surface area, it is desirable to select a powder with a t/d of 0.9 or less.

Now, the strength of the magnetic force is proportional to the magnetic powder filling ratio, that is, the amount of magnetic powder occupying the total volume of the bonded magnet, so in order to obtain a bonded magnet with excellent magnetic properties, the magnetic powder filling ratio must be as high as possible. .

As a result of experiments on this matter, it was found that the filling rate could not be increased if the particle size of the magnetic powder was too fine. The reason for this is that when the particle size is fine, the surface area of the powder becomes relatively larger than that of coarse-grained powder, even for the same weight of powder. This is thought to be because more binder is required for coating. For this purpose, it is desirable that the average major axis of the magnetic particles be at least 1 μ or more, preferably 2 μ or more. On the other hand, if the particle size is not balanced, the value of coercive force 11c, which is one of the important magnetic properties, decreases and the surface texture as a bonded magnet deteriorates. If the average major axis is 10 μm or more, the surface texture becomes extremely poor, so it is usually not preferred as a bonded magnet. From this point of view, it is more desirable to select magnetic particles with a diameter of 4 μm or less.

Furthermore, it was found that even if the particle size is the same, the flatter the shape of the magnetic powder, that is, the smaller the t/d of the front), the more difficult it is to increase the filling rate. The reason for this is similar to (previously), when t/d is small, the powder surface area becomes relatively larger compared to powder with large t/d even if the powder has the same particle size, so it takes more to mix thoroughly. This is thought to be because a binder is required. In particular, from this point of view, it is desirable to select magnetic particles whose t/d value exceeds 0.25, preferably, whose value is 0.5 or more.

In the case of magnetic powder with t /d = 0.1 and an average major axis of -1.7μ, complete kneading was possible only at a magnetic powder filling rate of 55va1% or less, but with t /d = 0.3 and an average major axis - 2.3μ magnetic powder up to 61vo1%, and t/d″
, 0.6 and an average major axis of 2.7μ, it was possible to knead up to 69vol%. Furthermore, it was possible to knead up to 72% of magnetic powder with a t/d-0.8 and an average major axis of 4.5μ.

To summarize what has been explained in detail below, in order to obtain an excellent bonded magnet suitable for practical use by extrusion molding a mixed material consisting of ferrite magnetic powder and a binder, it is necessary to Considering both the filling rate and the magnetic powder, the average major axis is 1 to 10 μ, preferably more than 2 μ.
It is understood that ferrite particles should be selected whose thickness/major axis ratio is greater than 0.25 and less than 0.95, preferably greater than 0.5 and less than 0.9.

This will be explained below using examples.

Example 1 Strontium ferrite with an average major axis of 2.7μ and a thickness/major axis ratio of approximately 0.4.
10% by weight of VA resin was cross-wired at 150°C. This is 61vo1% of ferrite magnetic powder when converted to volume%.
However, as a result of SEM observation, it was confirmed that the mixture was completely kneaded. After pulverizing this mixed material into pellets, an extruder with an auger diameter of 50 mm+ (heating temperature 150 ° C.
) was extruded into a round bar with a diameter of 10.5 mm.

This round bar 10011IIIl was cut out and magnetized into four axially symmetrical poles using a pulse magnetizer, and the surface magnetic flux density BO was measured and found to be 830G. In addition, cubic samples approximately 2 mm square were sequentially cut out from the surface of this round bar toward the center, and the magnetic properties of each of these three samples were measured in the radial direction (R), circumferential direction (φ), and axial direction. Measurements were made in three directions (Z) using a VSM (sample vibrating magnetometer). The results are shown in Figure 2 (a). Figure 2 (b
) is a diagram illustrating the position of the sample and the measurement direction. In Figure 2 (a), γ is the old value expressed as 100% of γ=(Br(E)−“101)・−1−/′.However, Br(L) and is the direction in question (R, φ.

The value of 3r measured in either Z direction), Sr is 3
The average value of the 13r measurements in the direction, i.e. 13r= (
Br(12)+Br"+Br")/3.

Since Br is considered to represent the amount of magnetization in which that direction is the easy direction, a positive γ value indicates the amount of magnetization that has changed from that direction to the other two directions. It can be said that a negative γ value is a measure of the amount of magnetization that has changed from that direction to the other two directions.

As is clear from Fig. 2(a), in the surface part (a), φ,
The magnetization is directed from the Z direction to the R direction, and the R direction is the easy direction.

In the intermediate part (b) between the surface and the center, the magnetization in the Z direction changes to the R direction, increasing Br in the R direction than in the isotropic case. It is natural that the characteristics in the R1φ direction are the same in the center (c), but it can be said that the magnetization from these seven directions has changed, and B' has increased compared to the case of complete isotropy. .

・ -8- In this way, the surface part has anisotropy only in the R direction, and the characteristics are improved, but as you go inside, the direction of easy magnetization gradually becomes dispersed in the φ direction, and the It can be seen that the grain orientation is very convenient for the magnetization pattern of multipolar magnetization as described (FIG. 1(C)).

Moreover, internally, as shown in this example, the 7 directions that are not used at all in the magnetization pattern are difficult to magnetize directions, and the magnetic properties in the R1φ direction are improved by that amount, which is also a good point. It is.

Comparative Example 1 90% by weight of Sr ferrite having an average major axis of 1.7 μm and a thickness/diameter ratio of approximately 0.1] magnetic powder and 10% by weight of EVA resin were kneaded at 150°C. However, this may be because the magnetic powder has a large particle surface area, but it was not possible to achieve satisfactory crosstalk with this amount of resin, so more resin was added. The maximum amount of magnetic particles that could be crossed was 87.5% by weight. This kneaded material was extruded in the same manner as in Example 1, and the diameter was 10.5111 mm.
Eleven round bars were obtained. However, when this round bar was measured in the same manner as in Example 1, the Bo value was only 710G. Further, as in Example 1, the results of measuring changes in magnetic properties depending on the position from the surface are shown in FIG.

In Figure 3, the surface part (a) has anisotropy in the R direction, which is the same as in Example 1, but the middle part (b) also has strong anisotropy in the R direction. This point is significantly different from Example 1. Because of this, the φ direction becomes a direction in which magnetization is rather difficult in this part, which is disadvantageous for the @magnetic pattern as shown in FIG. 1(C). This means that although the R direction Br at the surface portion of Example 1 and Comparative Example 1 is almost the same, Comparative Example 1 cannot obtain a low value of the surface magnetic flux density BO, which is of practical value. This is considered to be the reason.

Comparative Example 2 90% by weight of granular 3R ferrite magnetic powder with an average particle size of 2.15μ and a thickness/diameter ratio of approximately 1.0 and EVA resin 1
0% by weight was thoroughly kneaded at 150°C. This kneaded product was extruded in the same manner as in Example 1 to obtain a round bar with a diameter of 1105Il1. This round bar was measured in the same manner as in Example 1.
The value of O was only 730G.

Further, as in Example 1, the results of measuring changes in magnetic properties depending on the position from the surface are shown in FIG.

Also in FIG. 4, it can be seen that the surface portion (A) has anisotropy in the R direction. The reason for this is that although it appears almost granular from photographic observation, that is, the thickness/diameter ratio is approximately 1.0, it is still the original (0001
) It is thought that this is because the particles have plane cleavage properties, and the particles are oriented to some extent on the surface due to extrusion processing. However, looking at the degree of anisotropy, Example 1 has γ=44% and Comparative Example 1 has γ=50%, whereas γ=21%, which is a low value. Therefore, the Br value at the surface portion (A) is also low. However, although the j-direction of the surface magnetic flux density BO is far lower than that of Example 1, it is rather larger than that of Comparative Example 1, which indicates that the internal anisotropy is different from the magnetization pattern. This is thought to be because he is right-handed. From these examples, it can be understood that in practical terms, imparting anisotropy along the magnetization pattern is extremely important.

[Brief explanation of drawings]

Figure 1 (a) is a diagram explaining how anisotropy is created when ferrite particles with strong tabularity are extruded.
b) is a diagram explaining how to obtain anisotropy when extruding ferrite particles with low flatness, and Figure 1 (0) is a diagram explaining the flow of magnetic flux inside the magnet during magnetization of a magnet roll. 2 to 4 are diagrams showing the results of measuring the dependence of the magnetic properties of extruded bonded magnets in the depth direction from the surface.・ -・12- (a) rb) (C) Figure l (屹V 1 (xhorn (5th 4g (outside) (middle) (core) Figure 3 Figure 4 Procedure revised 1988 Month 18 Date 1'1 Indication 1982 Patent Application No. 88963 Title of the invention Bonded magnet with excellent magnetic properties and its manufacturing method Case related to the case Patent applicant address Marunouchi 2, Chiyo 81-ku, Tokyo Chome 1-2 name (
508) "Detailed description of the invention" column of Hitachi Metals, Ltd. specification. Contents of amendment 1: The statement in the "Detailed description of the invention" column of Akiyama is corrected as follows. (1) "Magnetostriction" at the end of page 3 of the specification is corrected to "magnetic flux." (2) In the same book, page 5, lines 4 to 5, "(80% or more)" is corrected to "(more than 80%)." (3) Correct rBr J on page 9, line 3 of the same book to "B". (4) Correct r13r J on the 4th line of the same page to r[3r J. (5) In line 8 of the same page of the same book, ``toward 12 directions'' was changed to ``from 2 directions.''
Correct. (6) The word “magnetization” in line 19 of the same page of the same book is deleted (7)
) In the same book, page 11, line 13, ``the value that is 1 lower is corrected'' to ``only the value that is 1 lower.'' (8) Lines 19 to 20 of the same page [105mm]
Correct J to "10.5ml1". (9) “Kore” in line 12, line 19 of the same book. Delete. -L・-1- Procedural amendment 59, 9.17' Mr. Commissioner of the Japan Patent Office "fl@l 'f-II +1 shot Jl
cn name f4 magnetic, characteristic, excellent. Eh, 21.12~. . , Wow. Patent applicant for amendments to the manufacturing process and method Iyu Nisumi 1-2 Marunouchi-bun-chome, 111-ku, Chiyo, Tokyo Name 4* (5081 Hitachi Metals Co., Ltd. Substitute Norio Kono Managing Director Subject of amendment August 1982) Summary of “Contents of amendment” of the written amendment for submission procedures dated 18th

Claims (1)

[Claims] 1. The average major axis is 1 to 10μ, and the thickness/major axis ratio is 0.
．． Magneto over 25 and under 0.9] - Plan By (
・A composition consisting of 50 to 12% by volume of tabular grains of rontium ferrite or barium ferrite, the remainder being a binder, is extruded into a molded product having a desired cross-sectional shape. As a result, the easy magnetization axis direction of the ferrite grains is mechanically oriented in the part near the surface of the molded product to be stronger than the core valve of the molded product so that it coincides with the surface direction of the molded product. A patented bonded magnet and manufacturing method. 2. A bonded magnet with excellent magnetic properties and a method for manufacturing the same, as set forth in claim 1, characterized in that the average major axis is more than 2μ and less than 4μ.