JPH0673329B2 - Manufacturing method of composite magnet - Google Patents

Description

The present invention relates to a method for producing a composite magnet having excellent magnetic properties. More specifically, in the method for producing a composite magnet in which magnetic powder is kneaded and molded with a resin, the magnetic powder is previously kept in intimate contact with a radically polymerizable monomer, and the polymerization reaction is performed in the presence of acidic sulfite ion. The present invention relates to a method for producing a composite magnet, characterized in that the surface of magnetic powder is modified by coating the powder with a polymer.

[Conventional technology]

It is well known that a composite magnet is manufactured by mixing and kneading a magnetic powder and a binder and performing extrusion molding, compression molding, or injection molding. Since composite magnets have features such as less cracking and cracking, no need for secondary processing, suitable for complicated shapes and thin shapes, and products with radial anisotropy, etc. For example, their use in small motors, sensors, relays and office automation equipment is increasing.

[Problems to be solved by the invention]

On the other hand, a drawback of composite magnets is that nonmagnetic binders and additives are mixed as components, and the magnetic properties are reduced by the volume. As a method of improving this drawback, it is necessary to increase the filling amount of the magnetic powder and increase the degree of orientation of the magnetic powder. However, in general, if the amount of magnetic powder mixed in is increased, the flow becomes worse during molding,
Moldability deteriorates or the product cannot be obtained. Further, even if the shape is barely formed, the degree of orientation of the magnetic powder is lowered and satisfactory magnetic characteristics cannot be obtained.

As one of the methods for improving such a problem, there has been proposed a method for improving the filling rate and the mechanical strength by surface-treating magnetic powder with various coupling agents. This method has the effect of changing the surface of the magnetic powder from hydrophilic to lipophilic and improving the compatibility with the binder, and therefore the packing ratio, orientation and mechanical strength can be improved. With such a method, the magnetic characteristics can be particularly improved as compared with the conventional method, but especially for magnets for motors for OA equipment, etc., there is a strong tendency toward lightness, thinness, miniaturization, and further improvement in magnetic characteristics is desired. ing.

The present invention has been made in view of these circumstances, and an object thereof is to provide a manufacturing method for further improving the magnetic characteristics.

[Means for solving problems]

That is, the present invention is a method for producing a composite magnet in which magnetic powder is kneaded and molded with a resin, in which the magnetic powder is kept in close contact with a radical-polymerizable monomer in advance and polymerized in the presence of acidic sulfite ion. It is characterized in that surface modification is carried out by reacting and coating with the powdered polymer, and a remarkable effect can be obtained by kneading this magnetic powder with a polyamide resin to form a composite. The inventors have found what is recognized and have completed the present invention.

According to the present invention, the magnetic powder has the general formula MO.6Fe ₂ O ₃ (where M
Is a divalent metal ion such as Ca ⁺⁺ , Ba ⁺⁺ , Sr ⁺⁺ , and Pb ⁺⁺ ), and a ferrite powder having a magnetoplumbite type crystal is used.

Further, the resin is preferably a thermoplastic resin as described below, which has a good compatibility with the above-mentioned polymer in the kneading step, and specifically, a polyolefin resin such as polyethylene or polypropylene, nylon-6, nylon-12, nylon. 610,
Polyamide resins such as nylon 11 and nylon 66, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, polyphenylene sulfide, polyether ether ketone,
Polyether sulfone and modified types of these resins are preferable, but polyamide-based resins can remarkably exert the effect of the surface treatment according to the present invention.

When the ferrite powder is coated with a polymer in the present invention, the radical-polymerizable or radical-copolymerizable monomers used include acrylic acid, methacrylic acid and methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, etc. Acrylic esters, methacrylic esters, vinyl acetate, aliphatic vinyl esters such as vinyl propionate, styrene, α-
Mention may be made of aromatic vinyl compounds such as methylstyrene, dienes such as butadiene, isoprene and chloroprene, and acrylonitrile.

In the method of the present invention, one or more monomers selected from the above-mentioned radically polymerizable or radically copolymerizable monomers are used.

If the amount of the monomer used in the present invention is too large, the mechanical strength and heat resistance are deteriorated, and if it is too small, the ferrite powder cannot be completely covered and the surface treatment effect cannot be exerted, and the weight of the ferrite powder is too small. 0.1 ~ 10
%, Preferably 0.5% to 7%.

Further, as the substance that provides the acidic sulfite ion used in the present invention, aqueous sulfite, sulfurous acid gas, an aqueous solution of sulfite, an aqueous solution of acidic sulfite and the like are used. The amount of the sulfite ion is in the range of 0.1 to 50 parts by weight, preferably 0.5 to 30 parts by weight, based on 100 parts by weight of the monomer in terms of sulfurous acid.

The coating treatment conditions of the present invention can be performed as follows. After suspending 1 part by weight of ferrite powder in 1-10 parts by weight of water and adjusting the liquidity to neutral (pH 6-8), a monomer and a polymerization initiator that donates sulfite ion are added and the temperature is 10 ° C-100
The coating treatment is performed at a temperature in the range of 20 to 70 ° C. The treatment time is 1 to 4 hours, and the monomer is converted to almost 100% of the polymer. Next, the obtained suspension of the coated powder is neutralized, dehydrated and dried.

The magnetic powder treated according to the present invention is then mixed and kneaded with a resin and then pelletized. The kneading can be performed by a heating kneader or a single-screw or twin-screw extruder. Of course, the surface-treated magnetic powder may be subjected to compression molding.

〔Example〕

Examples of the present invention will be described in more detail below.
Of course, the invention is not limited to these examples.

Example 1 5 kg of strontium ferrite powder (average particle size 1 μ) and 50 l of water were added to a reaction vessel equipped with a stirrer and a thermometer, and the mixture was vigorously stirred at 50 ° C. for 30 minutes. The pH at this time was 11. This liquid
After adjusting to pH 3 with 1N hydrochloric acid, methyl acrylate monomer 200
g and 52 g of sodium hydrogen sulfite were added and the reaction was carried out at 50 ° C. for 2 hours with stirring. After completion of the reaction, the reaction solution was cooled and adjusted to pH 7.5 with a 1N aqueous solution of sodium hydroxide. Dehydrating and drying this one,
When the coating amount was measured, it was 125 g.

The coated ferrite powder thus obtained
543 g of nylon-6 powder was mixed with 5 kg, kneaded with a twin-screw extruder, and then pelletized to obtain a molding compound. This product was injection molded under a magnetic field of 15 KOe. The results are shown in Table-1.

Comparative Example-1 The same procedure as in Example-1 was carried out except that the ferrite powder was used without being surface-treated in Example-1. The results are shown in Table-1.

Comparative Example-2 5 kg of strontium ferrite (average particle size 1 µ) was put into a super mixer and heated to 120 ° C, and then a silane coupling agent (-aminopropyltriethoxysilane)
50 g was added, and the surface treatment was further performed by continuing stirring at 120 ° C for 30 minutes. This ferrite powder was pelletized by the same method as in Example-1 and subjected to injection molding. The results are shown in Table-1
It was shown to.

Examples 2 to 6 Using the resins shown in Table-2, the volume ratio of ferrite powder was
The same procedure as in Example 1 was carried out except that the amount was 60%. The results are shown in Table-2.

Examples 7 to 10 The same procedure as in Example-1 was carried out except that the monomers and catalysts shown in Table 3 were used. The results are shown in Table-3.

FIG. 1 shows the relationship between the ferrite powder content and the magnetic properties in the composite magnets when the surface treatment according to the present invention was performed (however, in the case of Example-1), the silane coupling method and the untreated case. Indicated.

〔The invention's effect〕

As described above, according to the present invention, by discovering a very effective surface treatment method, not only was it possible to obtain a composite magnet with greatly improved magnetic characteristics, but also it was characterized by excellent formability. I was able to do it. Therefore, its industrial value is great.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the ferrite powder content and the magnetic properties of the composite magnet when the surface treatment according to the present invention is performed, the silane coupling method, and the untreated case.

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A 61-106629 (JP, A) JP-A 57-82196 (JP, A) JP-A 48-88496 (JP, A) JP-A 51- 7092 (JP, A)

Claims (3)

[Claims] 1. A method for producing a composite magnet comprising kneading and molding magnetic powder with a resin, wherein the magnetic powder is kept in intimate contact with a radically polymerizable monomer in advance in the presence of acidic sulfite ion. A magnetic powder surface modification step of modifying the surface of the magnetic powder in a state where the surface of the magnetic powder is covered with a polymer by a polymerization reaction, and the magnetic powder having the surface modified, A composite characterized by having a kneading step of kneading a kneaded material with a thermoplastic resin having a good compatibility with the polymer selected as a resin, and a molding step of molding the kneaded material to obtain the composite magnet. Magnet manufacturing method. 2. The magnetic powder has the general formula MO.6Fe ₂ O ₃ (where M
Is a divalent metal ion such as Ca ⁺⁺ , Ba ⁺⁺ , Sr ⁺⁺ , and Pb ⁺⁺ ), and is a ferrite powder having a magnetoplumbite-type crystal structure. A method for manufacturing a composite magnet according to claim 1. 3. The method for producing a composite magnet according to claim 1, wherein the thermoplastic resin having a good affinity with the polymer is a polyamide resin.