JP3144088B2 - Manufacturing method of ferrite magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing a ferrite magnet in which a slurry containing a powder for a ferrite magnet is formed in a magnetic field and then sintered.

[0002]

2. Description of the Related Art Ferrite magnets are used in various applications including rotating devices such as motors and generators. As one of the methods for producing this ferrite magnet, a so-called wet method is known in which a slurry containing a ferrite magnet powder having a particle size of about 1 μm is wet-formed in a magnetic field, and the obtained formed body is sintered ( For example, Japanese Patent Publication Nos. 55-6041 and 59-8
No. 047). Recently, the required characteristics for ferrite magnets have become strict. For example, residual magnetic flux density (Br)
In some cases, magnetic properties such as 00 G or more and a coercive force (iHc) of 4000 Oe or more are required. In order to obtain a ferrite magnet having such high magnetic properties, CaO, SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ ,
An element such as Cr ₂ O ₃ is added (for example, see JP-A-2-98106).

In order to enhance the magnetic properties of ferrite magnets, studies on materials such as particle size and molar ratio, and manufacturing conditions such as slurry temperature and sintering temperature have been made in addition to the above.

[0004]

However, it is difficult to improve both the residual magnetic flux density and the coercive force. In other words, it is effective to increase the degree of orientation and to increase the sintering density in order to increase the residual magnetic flux density. For this purpose, it is desirable to increase the sintering temperature to increase the crystal structure to some extent. On the other hand, from the point of coercive force, it is desirable to refine the crystal structure. Therefore, conventionally, the amount and timing of addition of various additives and the sintering temperature have been devised in order to increase the residual magnetic flux density and the coercive force.
It has been difficult to satisfy in together. Accordingly, an object of the present invention is to provide a manufacturing method capable of obtaining a ferrite magnet having a high residual magnetic flux density and a high coercive force.

[0005]

Method of manufacturing a ferrite magnet of the present invention which achieves the above object In order to achieve the above, powder for ferrite magnet
Ammonium bicarbonate salt in advance to the slurry containing the powder,
Add ammonium sulfate or ammonium sulfonate
And then add the polycarboxylic dispersant, then
It is characterized by being molded and sintered in a magnetic field. MO · nFe ₂ O ₃ (M is Ba, Sr,
At least one of Pb, and n = 5 to 6)
Those having the basic composition of are preferred.

In order to obtain a ferrite magnet having high magnetic properties, ferrite whose composition and physical properties are appropriately controlled is required.
In addition to preparing magnet powder, this ferrite magnet
It is important that the stone powder does not agglomerate in the slurry.
Therefore the inventors have found that the powder <br/> particles ferrite magnet made various studies to create a state that may be present independently in the slurry, by adding a specific dispersing agent in the slurry, ferrite magnets It has been found that the powder particles are sufficiently oriented in the direction of the magnetic field, thereby improving the magnetic properties.

Surfactants, higher fatty acids, higher fatty acid soaps, higher fatty acid esters and the like are known as dispersants for magnetic powder, but polycarboxylic acid dispersants, which are a kind of anionic surfactant, are used. By doing ferrite
It was found that the dispersibility of the magnet powder particles in the slurry was improved, and aggregation could be effectively prevented. Although there are various types of polycarboxylic acid-based dispersants, ammonium polycarboxylate represented by the general formula : [ Formula 1 ] has been found to be particularly effective in improving the dispersibility of powder particles for ferrite magnets .

[0008]

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The ammonium polycarboxylate desirably has a weight average molecular weight in the range of 10,000 to 80,000. The amount of the dispersant added is a powder for ferrite magnets.
The amount is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.0 part by weight, per 100 parts by weight.

[0010] as a function of a polycarboxylic acid ammonium salt, for strong ferrite magnet aggregation tendency as shown in FIG. 1
Preparative to form a sterically hindered 2 adsorbed on the surface of the powder particle 1
Also, aggregation state of powder for ferrite magnet fine particles each other is reduced or alleviated by the negative electrification electrical repulsion Karuboniru group, Ru can improve orientation.

[0011] alkaline earth metal ions constituting the powder for ferrite magnet in the feed slurry that continue to elute, generates another salt and these eluted metal ion and such as ammonium polycarboxylic acid is reacted, It electrically neutralizes the negative charge of the carbonyl group and significantly reduces the dispersing action. As a countermeasure for this, most of the metal ions added eluted before the ammonium polycarboxylate in advance Totaba purposes, ammonium bicarbonate, ammonium sulfate or <br/> after added pressure to the sulfonic acid ammonium salt to the raw material slurry, It is advantageous to add the ammonium polycarboxylate and then carry out a suitable milling and mixing.

In order to produce a ferrite magnet using a slurry containing a polycarboxylic acid-based dispersant, the following steps and conditions may be used, for example. First, by heating with Fe ₂ O ₃ , MO (M is at least one of Ba, Sr and Pb)
A compound having a predetermined molar ratio n (n = 5 to 5).
6) and then calcined at 1200-1300 ° C, and the resulting calcined product is roughly pulverized . Next, wet pulverization is performed to a predetermined particle size using water as a pulverizing medium. It is desirable to add at least one additive such as SiO ₂ , CaO, and Cr ₂ O ₃ according to the magnetic properties required here. It was added ammonium bicarbonate salts in the start and end of wet milling, followed by the addition of further polycarboxylic acid dispersant to the slurry, thoroughly stirred. Ferrite in slurry
The concentration of the magnet powder is suitably from 40 to 70% by weight. next,
A molded body is obtained by molding the slurry in a magnetic field of several KOe or more in a magnetic field. Molding pressure is 400 ~ 1000kg /
A range of cm ² is appropriate. Next, the obtained molded body was 1200
By sintering at 11300 ° C., a ferrite magnet is obtained.

[0013]

According to the method for producing a ferrite magnet of the present invention, the slurry containing the powder for the ferrite magnet is prepared in advance.
Ammonium bicarbonate, ammonium sulfate or sulfite
Addition of ammonium phonate and then addition of a polycarboxylic acid-based dispersant make it possible to efficiently suppress aggregation of the powder particles for ferrite magnets , so that the powder particles for ferrite magnets are sufficiently oriented in the magnetic field direction in the molding process. And a ferrite magnet having high magnetic properties can be obtained.

[0014]

EXAMPLE SrCO ₃ and Fe ₂ O ₃ were replaced with SrO and Fe ₂ O
1 at ₃ and a molar ratio were mixed so that 5.9, then 12
Calcination was performed at 00 ° C. for 2 hours . Subsequently , dry grinding was performed with a vibration mill to obtain coarsely ground powder. SiO ₂ was added to this coarsely pulverized powder in an amount of 0.
4% by weight, 0.4% by weight of CaCO ₃ and 1.5% by weight of Cr ₂ O ₃ were added, and water was further added to form a slurry having a solid content of 40%, and wet-milled to an average particle size of 0.8 μm. Before comminution
Ammonium bicarbonate 0.2% by weight, it was added ammonium bicarbonate 0.1% by weight on exit. Next , a dispersant [ammonium polycarboxylate: SN Dipper Santo 5468 manufactured by San Nopco Co., Ltd.] was added to 100 parts by weight of the obtained slurry.
Into the attritor with 0 to 2 parts by weight of
Stir for 10 minutes and then with a mixer. Stir and get
Each of the obtained slurries was compression-molded at a pressure of 400 kg / cm ^{2 in} a magnetic field of 5 KOe . Then , sintering at a temperature of 1220 ° C.
An r ferrite magnet was obtained. Table 1 shows the results of measuring the magnetic properties and the degree of orientation of each of the obtained ferrite magnets.

[0015]

[Table 1]

[0016] From Table 1, by adding a distributed agent to the slurry, the residual magnetic flux density (Br), it can be seen that the improved coercive force (iHc) and distribution <br/> Mukodo. Also, from Table 1, it can be seen that when the amount of the dispersant added increases, iHc increases but Br decreases, so that an appropriate amount of addition is 0.5 to 1.0 part by weight.

[0017]

As described above, according to the method of the present invention, the dispersibility of the powder for a ferrite magnet in a slurry is improved, so that a ferrite magnet having high magnetic properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the action of a dispersant in the present invention.

[Explanation of symbols]

 1 Ferrite fine particles,  2 Three-dimensional barrier.

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01F 1/00 C04B 35/622 H01F 41/02

Claims (1)

(57) [Claims] 1. A slurry containing ferrite magnet powder.
Ammonium bicarbonate, ammonium sulfate
Or ammonium sulfonate is added and then polycarbonate
Add rubonic acid-based dispersant, then mold in a magnetic field and sinter
A method for producing a ferrite magnet.