JPS6031083B2 - High magnetic force permanent magnet - Google Patents

Description

[Detailed description of the invention] The present invention relates to permanent magnets.

Conventionally, rubber magnets or plastic magnets in which ferrite powder is mixed into a rubber or plastic matrix are known in order to improve the workability and maneuverability of sintered ferrite magnets.

Generally, these magnets are made by kneading ferrite powder and solid polymer, and then extruding or calendering the mixture. child. Magnets formed in this way are superior to sintered ferrite in terms of workability and, in some cases, maneuverability and elasticity, and are used in a variety of applications, but their magnetic force is weak and high magnetic force is required. It cannot be used for any purpose. The magnetic force of a magnet depends on 1) the ferrite loading and D) the degree of orientation of the ferrite particles in the matrix. Normally, when blending ferrite powder into a polymer, there is an upper limit to the amount of ferrite filled. For example, when natural rubber is used as the polymer, it is not possible to blend ferrite in an amount exceeding 9 times the weight of natural rubber. Can not. On the other hand, although not all of the factors that regulate the degree of orientation of ferrite particles in the matrix have been clarified, it has been empirically shown that as the viscosity of the matrix increases during mud mixing, the degree of blending decreases. known to. The inventors of the present invention have fully taken into account the above points and as a result of intensive research, have developed a liquid rubber with the general formula M○, medium e203 (where M in the formula represents mother, Sr, and Pb.
One or more selected from the group of, n is 4.5 to 6.
It has been discovered that by blending hard magnetic ferrite powder represented by the number 2) in an amount exceeding 9 times the weight of the liquid rubber, a permanent magnet with superior magnetic force than conventional products can be obtained. .

Conventionally, ferrite is blended into natural rubber using a mixing roll, but if the blending amount of ferrite exceeds 9 times the weight of natural rubber, the mixed composition will peel off from the roll and the ferrite will not be mixed. becomes impossible. On the other hand, when using liquid rubber, it is possible to mix ferrite with a screw-type kneading machine, and filling with ferrite is possible until the load on the kneading machine exceeds the allowable amount. A large amount of ferrite can be blended. Furthermore, since the viscosity of the mixed composition during kneading is significantly lower than when a solid polymer is used, the orientation of the ferrite particles is improved, and the magnetic force is increased even at the same mixing ratio of ferrite. It is presumed that the high magnetic force of the present invention is achieved for the reasons mentioned above. Another feature of the magnet according to the invention is that it has good heat resistance.

If natural rubber is used as a matrix, it cannot be used economically at temperatures above 100 qo, whereas the magnet of the present invention, which uses liquid polybutadiene as a matrix and is molded and cured by an appropriate means, can be used at 300°C. However, it has a rigidity of 1 pid skin e/c tiger, and from the measurement results of its bending strength retention rate, it has been found that it can sufficiently withstand continuous use at 12,000 yen. The liquid rubber used in the present invention is a rubber that is liquid at room temperature in the absence of a solvent, and includes liquid polybutadiene, liquid polyisoprene, liquid polyisobutylene, and liquid copolymers thereof, as well as hydroxyl groups and carboxyl groups in these polymers. A wide range of derivatives can be used, including derivatives into which a group, a maleic anhydride group, an isocyanate group, etc. have been introduced.

The moldability of the magnet of the present invention is affected by the viscosity of the liquid rubber used.

For example, in rubbers with excessively low viscosity, in other words with low molecular weight, the chain length is too short for the liquid rubber to serve as a binder or matrix for the ferrite. On the other hand, if the molecular weight is excessively high, the viscosity of the composition becomes too high, making it difficult to mold it using normal molding means. Therefore, the liquid rubber used depends on the type of ferrite or the molding method used.
It goes without saying that one with an appropriate molecular weight must be used based on preliminary experiments and the like. For example, in the case of liquid polybutadiene rubber, those having an average molecular weight of 1,000 to 10,000 are preferably used. The higher the mixing ratio of ferrite to liquid rubber, the more desirable it is from the viewpoint of magnetic properties.

The ferrite powder used in the present invention is a high-magnetic oxide having a hexagonal crystal structure, such as Mari 0 and Bai E203.
, Sr○・bait e203, Pb○・carp e203, and the like are preferably used.

The ferrite powder is required to be easily kneaded with liquid rubber, and plate-shaped ferrite powder having an average particle size of 1 to 3A is particularly preferred. Mixing of ferrite powder and liquid rubber can be carried out by a normal kneading method.

This can be said to be a significant advantage in terms of processing compared to the case where ferrite is blended into solid rubber such as natural rubber, which is limited to roll kneading. Next, the bran-blended composition is molded into an arbitrary shape by supplying it to an injection molding machine, a compression molding machine, a calender molding machine, or the like. It can be easily cured by adding a crosslinking agent or a vulcanizing agent during drilling, and if necessary, by selecting an appropriate curing agent, a flexible crosslinked composition can be formed. It is also possible to obtain magnets. The magnet obtained by the present invention can be used for various purposes by changing the blending ratio of ferrite and liquid rubber.

For example, it can be used as a substitute for scale magnets for micro motors, etc., for which it was previously considered impossible to use rubber magnets due to their weak magnetic force. EXAMPLES The present invention will be specifically explained below with reference to Examples, but these Examples are not intended to limit the present invention in any way.

Example 1 Liquid polybutadiene with an average molecular weight of 4000 (butadiene homopolymer 1 manufactured by Nippon Soda Co., Ltd., NISSOPB-4000)
), iron oxide, and barium carbonate were mixed so that the molar ratio of Fe203/mother ○ was 5.75, and after firing at a temperature of 1150 qC, 1. A predetermined weight of the barium ferrite powder obtained by grinding to a fine level was pulverized at room temperature using a Brabender Plastograph at a rotor speed of 20 rpm.
The mixture was heated for 5 minutes under conditions of 5 minutes.

The mixture was press-molded for 3 minutes at room temperature under a pressure of 50k9' and a magnetic field of 500e to obtain a plate-shaped sample. The (BH)max of the obtained sample and the Br/ferrite/ground (Br value shown by ferrite in a unit volume composition) indicating the degree of orientation of ferrite particles are shown together with the data of the conventional product using a natural rubber matrix. Shown in 1. Table I Reference Example During kneading, 2 parts by weight of dicumyl peroxide was added per 10 parts by weight of rubber, and press molding was performed at 150 qo for 3
A magnet was obtained from the cured composition in exactly the same manner as in Experiment No. 5 except that the experiment was carried out for a longer time.

As shown in Fig. 1, this magnet maintains a sufficient rigidity even at 30,000 yen, and as shown in Table 2, even after being left in air for 4 weeks at 1g 0, the magnet maintains a rigidity of 72.8%. The flexural elasticity retention rate was shown. 2 Example 2 A magnet obtained in exactly the same manner as in the reference example except for using the composition of experiment number 6 had a rigidity of 30,000 and a stiffness of 1 in air.
Both flexural elasticity retention after being left at 20°C for 4 weeks was excellent.

Example 3 Liquid polybutadiene with an average molecular weight of 3000 into which terminal hydroxyl groups were introduced (manufactured by Nippon Soda Co., Ltd., hydroxyl group-introduced polybutadiene,
Example 1 except that NISSOP8G-3000) was used.
A magnet made of a ferrite composition was obtained using the same machine.

Table 3 shows the magnetic properties of the obtained magnet. Table 3 Example 4 Liquid polyptadiene with an average molecular weight of 6200 (Nippon Zeon Co., Ltd. butadiene homopolymer 1, Polyoil 160)
12g, same barium ferrite powder as Example 1 120
g and 0.2 dicumyl peroxide at room temperature.
The mixture was kneaded using a plastograph under the condition of 0 revolutions/min.

Next, the slurry was press-molded for 5 hours under a pressure of 150 qo and 50 k9/c while applying a magnetic field of 500 e to obtain a magnet made of a flexible crosslinked composition.
The (B・H)max of the magnet was 0.86×1 pi○・Cji. Example 5 The following mixture was kneaded in a blastograph at room temperature and at 20 revolutions/min.

Polyoil160
12 g barium ferrite (same ferrite powder as in Example 1) 12 female sulfur
0.96g activated zinc leather
0.60g stearic acid
0.1 g Noxela-DM (vulcanization accelerator) 0.12 g Noxela 1 day (vulcanization accelerator) 0.0 g Noxela NS#6 (anti-aging agent) 0.12 g Then, the above mixture was heated at 150oC.
A vulcanizate was obtained by press molding under a pressure of 50k9/c for 5 hours while applying a magnetic field of 500e.

The (B.H)max of the vulcanizate was 0.89×1 piG・Chi. Example 6 The liquid polybutadiene, iron oxide, and strontium carbonate used in Example 1 were mixed with Fe20
Mix so that the molar ratio of 3/Sro is 5.75, and
After firing at a temperature of 200 qo, 1. A predetermined amount of strontium ferrite powder obtained by crushing to a certain degree is
Concentration molding was carried out under exactly the same conditions as in Example 1, except that a magnetic field of 1000 e was applied to the product.

Table 4 shows the magnetic properties of the molded product obtained. Table 4 *Natural rubber matrix

[Brief explanation of drawings]

The curve shown in FIG. 1 represents the relationship between temperature and rigidity of a magnet obtained by blending barium ferrite with liquid polybutadiene (ferrite/matrix = 9 weight ratio) and crosslinking. Ticket/■

Claims (1)

[Claims] 1 Liquid rubber has a compound represented by the general formula MO・nFe_2O_3 (where M is one or more selected from the group of Ba, Sr and Pb, and n is a number from 4.5 to 6.2). A high magnetic force permanent magnet formed by blending hard magnetic ferrite powder in an amount exceeding 9 times the weight of the liquid rubber and molding the mixture.