JPH07176416A - Bonded magnet - Google Patents

Abstract

PURPOSE:To enhance heat resistance and magnetic characteristics of a bonded magnet by using organic bonding material as a bonding material for bonding magnetic powder, molding it and burning and carbonizing the material. CONSTITUTION:As organic bonding material for magnetic powder obtained by regulating pulverizing particle size of a magnetic material, at least one of phenol resin, furan resin, resol resin and epoxy resin for forming three- dimensional mesh structure by curing reaction is used, kneaded, covered with magnetic powder, molded in a predetermined shape by a molding method such as an extrusion compression molding, etc., and the material is cured to form the structure. Thereafter, volatile thermally decomposable product and contained moisture contained in the material is scattered by burning, formed in a desired size, and magnetized to form a bonded magnet. Thus, since the material is of the burned organic bonding material, its thermal stability is high. Further, the material is shrinked by burning the material, and the magnetic powder is approached to improve magnetic characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bonded magnet obtained by firing and carbonizing an organic binder which is a binder for binding magnetic powder.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a bonded magnet is made by miniaturizing a magnetic material and kneading it with an organic resin material such as an epoxy resin or a polyamide resin as a binder, coating the fine magnetic material, and extruding. It is molded into a predetermined shape by a molding method such as compression / injection. If the binder is thermosetting, it goes through a curing step, and if the binder is thermoplastic, it is magnetized after molding to form a bond magnet. Has been.

However, in the above-mentioned conventional example, although the state of finished molding or curing is close to the shape of the product used as a magnet (Near Net Shape), there is an advantage that almost no additional machining is required, but the binder is epoxy. In a thermosetting resin such as a resin or a phenol resin or a thermoplastic resin such as a polyamide resin, the Tg (glass transition temperature) of the binder is about 100 ° C.,
It has a drawback in heat resistance that the bonded magnet cannot be continuously used at a temperature higher than that.

Further, the volume ratio of the binder in the bond magnet is as high as ten and several percent even in the compression molded product having the smallest binder, and the maximum energy product (BHmax) when the sintered magnet is 100 is 100%. However, the number of stable products was as low as 50.

Therefore, with respect to heat resistance, selection of a binder having higher heat resistance, for example, a low melting point metal binder such as Zn, Sn, Al, or Pb has been proposed, but sufficient bonding force can be obtained in compression molding. Therefore, it is necessary to further increase the amount of the binding material rather than the organic binding material, and the BHmax value is lowered in exchange for the increase in heat resistance.

Further, for low BHmax values, isotropic magnet materials of ferrite type, SmCo ₅ type, Nd ₂ Fe ₁₄ B type, and further Sm ₂ Co ₁₇ type, Nd ₂ Fe ₁₄ B type.
Materials having higher magnetic properties such as Sm ₂ Fe ₁₇ N ₃ system anisotropic materials have been used, but the present situation is that they are not used because of the above-mentioned reasons. .

[0007]

The problems to be solved are the lack of thermal stability of the bonded magnet and the small value of the maximum energy product.

[0008]

SUMMARY OF THE INVENTION The present invention is characterized in that, in a bonded magnet formed by binding magnetic powder with a binder, the binder is an organic binder that has been fired.

The bonded magnet according to the present invention has a high thermal stability because the binder is an organic binder which is fired, and the binder shrinks due to the firing treatment of the organic binder.
The magnetic powder can approach and the magnetic properties can be improved.

The organic binder used as the binder of the present invention is an organic binder having a three-dimensional network structure by a curing reaction, and the volatile thermal decomposition product from the organic binder is obtained by firing after softening. It is also preferable that the water content is scattered.

When a three-dimensional network structure is formed in association with the curing reaction, a curing shrinkage stress is generated, and the binding that covers the magnetic powder is accompanied by the scattering of the volatile thermal decomposition products and the built-in moisture due to the firing. By contracting the material, it became possible for the magnetic powder to approach and enhance the magnetic performance. Further, the three-dimensional network structure is maintained even during the firing, and by setting the molding shape in consideration of the shrinkage, it is possible to maintain the Near Net Shape, which is an advantage of the bonded magnet, even after the firing.

FIG. 1 is a process drawing of a bonded magnet according to the present invention. The magnetic material is used as a binder for the magnetic powder whose grain size is adjusted, and at least one of phenol resin, furan resin, resole resin, epoxy resin, etc. is used as an organic binder for forming a three-dimensional network structure by a softening reaction, and kneading / The magnetic powder is coated, molded into a predetermined shape by a molding method such as extrusion compression injection, the binder is hardened to form a three-dimensional network structure, and then the volatile pyrolysis products contained in the binder and built-in by firing. Water is dispersed and magnetized to a desired size to form a bonded magnet. The weight reduction rate due to firing based on the completion of softening of the binder is 2% or more, particularly 5% from the viewpoint of improving thermal stability and magnetic properties.
% Or more, preferably 90% or more, and particularly preferably 60% or less from the viewpoint of Near Net Shape and mechanical strength.

[0013]

【Example】

Example 1 As a magnetic material, an isotropic Nd ₂ —Fe ₁₄ —B magnet (trade name: MQP-B, manufactured by Delco Demi) was pulverized and adjusted to 250 μm or less, and a phenol resin (trade name: as a binder).
HP-500R, manufactured by Hitachi Chemical Co., Ltd., was added to the magnetic powder at a volume ratio of 12% to cover the magnetic powder. Using this coated magnetic powder, 5ton / cm ² in a compression molding device
With a pressure of 10 × 10 × 10 mm, a rectangular granular molded product was obtained.

After curing these at 150 ° C. for 3 hours, they were divided into two groups, one group was used to measure the magnet performance after magnetization, and the other group was used as an example to measure the dimensions in three directions. As firing conditions, 240 ° C. for 10 hours, nitrogen flow rate 100 ml /
Pre-baking was carried out under cm ² , further baking was carried out under a nitrogen flow rate of 150 ml / cm ^{2 for} 280 ° C./20 hours, and the temperature was returned to room temperature to measure the dimensions in the following three directions and obtain the magnet performance after magnetization. The heat resistance was determined by a DSC (differential scanning calorimeter) after curing with a phenol resin alone and the difference before and after the firing. Those results are

[0015]

[Table 1]

It was also confirmed that the dimensional changes in the three directions in this example were also caused by firing, and the shrinkage ratio was 98.8% as compared with that before firing, and the shrinkage was isotropic in all three directions.

The weight reduction rate of the binder due to this firing was 7.5% with respect to the completion of curing.

Example 2 Sm ₂ -Co ₁₇ type anisotropic magnetic powder (trade name: as magnetic powder)
R30, manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared, adjusted to 250 μm or less, and 10% by volume of phenol resin (HP-500R) was added to the magnetic powder to coat the magnetic powder.

5 tons of this magnetic powder was applied in a transverse magnetic field type compression device.
Molding was performed in a magnetic field while applying a pressure of / cm ² to obtain a 10 × 10 × 10 mm square granular molded product as in Example 1.

After curing these at 150 ° C. for 3 hours, they were divided into two groups, one group was used as a comparative example to evaluate the magnet performance after magnetization, and the other group was used as an example to measure the dimensions in three directions and then fired. As conditions, 240 ° C./10 hours, N ₂ flowing air 100 ml /
cm subjected to preliminary calcination at ² under, 280 ° C. / 20 hours, N
₂ Nagareki 150 ml / cm ² performs calcination under further 4
Firing was carried out at 00 ° C. for 20 hours under a N ₂ stream of 150 ml / cm ² . After returning to room temperature, the magnet performance after three-dimensional dimension measurement and magnetization, and also as in Example 1, the phenol resin alone cured product was baked under the above conditions, and its heat resistance was evaluated by DSC. Where I did

[0021]

[Table 2]

Further, the dimensional changes in the three directions in this example also contracted isotropically by firing, which was 97.7%, which was less than that before firing. If you make it big, the desired Near Net
A Shape bond magnet is obtained.

The weight reduction rate of the binder due to this firing was 15.0% compared to when the curing was completed.

The structural changes of the phenolic resins used in Examples 1 and 2 due to firing were observed by FT-IR (Fourier transform infrared spectrophotometer). The results are shown in FIGS.

FIG. 3 shows the FT- after the curing treatment (150 ° C.).
It is an IR absorption curve.

FIG. 4 is an absorption curve of FT-IR when baked at 240 ° C. (5 hr) after the curing treatment.

FIG. 5 is an absorption curve of FT-IR when baked at 280 ° C. (5 hr) after the softening treatment.

FIG. 6 is an absorption curve of FT-IR when baked at 400 ° C. (5 hr) after the softening treatment.

FIG. 7 is an absorption curve of FT-IR when baked at 700 ° C. (5 hr) after the softening treatment.

OH associated with the benzene ring shown in FIG.
The peaks of the base are shown in Fig. 4 (240 ° C firing) and Fig. 5 (280 ° C).
(Firing) and FIG. 6 (firing at 400 ° C.), and FIG.
It is recognized that the carbon is changed in the baking at 00 ° C.

[Other Examples] Organic binders applicable to the present invention have a three-dimensional network structure due to reaction, and the network structure is not broken during high temperature firing.
It is preferable that the volatile thermal decomposition product and the built-in moisture are scattered, and the material is not limited to the material of the above-mentioned embodiment. Further, as the firing conditions, the temperature is at least
180 ℃ or above, especially 200 ℃ considering the scattering efficiency
The above is preferable, and the shrinkage due to the scattering of the binder progresses as the temperature increases, so an upper limit is allowed up to 1200 ° C, but some magnetic materials may cause deterioration of magnet performance due to oxidation or phase transformation. A lower temperature is selected, and the processing time and size / shape are taken into consideration.

As for the firing atmosphere, only nitrogen flow is described in the embodiment, but other inert gas, reducing atmosphere, vacuum, etc. are also applicable.

After firing according to the present invention, coating for the purpose of rust prevention or resin impregnation for the purpose of increasing the bond strength of the bonded magnet may be carried out.

Further, although the compression molding is described in the present embodiment, it can be applied to other extrusion molding and injection molding.

Regarding the volume ratio of the binder in the bonded magnet, the two examples of 12% and 10% are described in the examples, but it is a volume ratio for further increasing BHmax in compression molding. The volume ratio is generally selected in the range of 2% to 90% depending on the type and the molding method, and it is recognized that it changes.

[0036]

As described above, the organic bonding material is used as the binding material for binding the magnetic powder, and the binding material is calcined and carbonized after molding and curing.
While maintaining r Net Shape, it was possible to greatly improve the poor heat resistance and poor magnet performance, which were the disadvantages of conventional bonded magnets.

[Brief description of drawings]

FIG. 1 is a process drawing for carrying out the present invention.

FIG. 2 is a process drawing showing a conventional example.

FIG. 3 F after phenolic resin curing treatment (150 ° C.)
It is an absorption curve of T-IR.

FIG. 4 is an absorption curve of FT-IR when baked at 240 ° C. after curing treatment of a phenol resin.

FIG. 5 is an absorption curve of FT-IR when baked at 280 ° C. after curing treatment of a phenol resin.

FIG. 6 is an absorption curve of FT-IR when baked at 400 ° C. after curing treatment of a phenol resin.

FIG. 7 is an absorption curve of FT-IR when baked at 700 ° C. after curing treatment of a phenol resin.

Claims (3)

[Claims] 1. A bond magnet obtained by binding magnetic powder with a binder, wherein the binder is a fired organic binder. 2. The bonded magnet according to claim 1, wherein the organic binder is selected from a phenol resin, a furan resin, a resole resin and an epoxy resin. 3. The bonded magnet according to claim 1, wherein the weight loss rate of the fired organic binder is 2 to 90%.