JPS6022485B2 - Composition for magnets - Google Patents

Description

[Detailed description of the invention] The olefin content is 20 to 50 mol%.

The present invention provides a permanent magnet which is made of an olefin-pinyl alcohol copolymer and ferrite in an amount of 1 to 5 times the weight of the copolymer, and is rich in oil resistance and has excellent heat resistance, mechanical strength, and workability. Or it relates to a composition for electromagnets. Rubber magnet or plastic magnet compositions in which ferrite powder is mixed with rubber or plastic are known in order to improve the processability and flexibility of late-setting ferrite magnets.

However, since these compositions use natural rubber, synthetic rubber, or general-purpose plastics (eg, polyvinyl chloride), there are problems in using them in fields where oil resistance is necessarily required. Furthermore, rubber has poor heat resistance, e.g.
qo or higher, it is unsuitable for regular use, and its mechanical strength is inherently inferior to that of plastics. On the other hand, when so-called engineering plastics such as polyester resin and nylon resin, which have relatively good heat resistance and excellent mechanical strength, are mixed with ferrite,
The resin deteriorates significantly, making it impossible to obtain a composition with high strength. In order to improve these drawbacks, it has been proposed to mix glass fiber with ferrite into a thermosetting resin as a matrix (Tokukan Sho 47-12422).
No. 5), there is a problem that the use of thermosetting resin generally lengthens the molding cycle. An object of the present invention is to provide a composition for permanent magnets or electromagnets that is rich in oil resistance and has excellent heat resistance, mechanical strength, and workability. is 20
It has been found that this can be achieved by a composition consisting of an olefin-vinyl alcohol copolymer in an amount of ~50 mol % and ferrite in an amount of 1 to 5 times the weight of the copolymer.
The magnet composition of the present invention has much better oil resistance than other resin-based compositions, and has a 160 qo
Can withstand continuous use.

Furthermore, the major features of the magnet composition obtained by the present invention are:
It has high mechanical strength. For example, the bending strength of compositions obtained by blending ferrite with polypropylene resin and nylon resin is approximately 200 to 250, respectively.
X9/mass and 550 to 600k9/mass, whereas in the case of the vinyl alcohol-ethylene copolymer-ferrite composition, a strength of 900k9/mass or more can be obtained.
In the present invention, the olefin-vinyl alcohol copolymer is a completely saponified copolymer resin of various vinyl esters such as vinyl formate and vinyl acetate and monoolefins having up to 4 carbon atoms, or 90% or more of the ester groups. includes partially saponified products.

The olefin content in the copolymer ranges from 20 to 5, depending on the performance such as strength required depending on the use of the composition of the present invention.
It may be appropriately selected from the range of 0 mol%. The ferrite that can be used in the present invention is a solid melt of Fe203 and a metal oxide, and includes both so-called hard ferrite and soft ferrite.

The metal of the metal oxide is Pb, Ba or Sr in the case of hard ferrite, and one or more combinations selected from Mn, Fe, Nj, Cu, Mg or Zn in the case of soft ferrite. used. The mixing ratio of ferrite to vinyl alcohol-olefin copolymer is preferably as high as possible from the viewpoint of practicality as a magnet.

If the amount of ferrite added to the matrix is less than 1 times by weight, a composition with practical magnetic properties cannot be obtained. On the other hand, if it exceeds 5 times the weight, the viscosity during melt-kneading and molding becomes high, making molding difficult. There is no particular restriction on the blending method, and various melt-filling methods including the known dry blending method can be employed. Furthermore, the vinyl alcohol-olefin copolymer may be dissolved in an alcohol-water temperature mixed solvent or a solvent such as dimethyl sulfoxide, mixed with Nada-Azusashita ferrite, and dried. The magnet composition of the present invention can be molded into any desired shape by supplying it to a conventional injection molding machine, extrusion molding, compression molding machine, or calender molding machine. In particular, the time and economic advantages of the injection molding process are industrially useful. The magnet composition obtained according to the present invention is preferably used in fields where oil resistance, heat resistance and mechanical strength are simultaneously required.

For example, when hard ferrite is used, centering magnets for television cathode ray tubes and magnets for various micromotors can be used, and when soft ferrite is used, examples include magnet 0 for electromagnets. The present invention will be explained below with reference to Examples, but these Examples are not intended to limit the present invention in any way.

Examples 1 to 5 Powder of a copolymer consisting of 70 mol percent of vinyl alcohol and 30 mol percent of ethylene (ethylene-vinyl alcohol copolymer may be abbreviated as EVA hereinafter) and Mn-Zn ferrite [(Mn○ )0.235
(Zn○)0.235(Fe203)0.53] in Table 1
The mixture was charged into an extrusion molding machine at a mixing ratio shown in , and melted and kneaded into pellets at a predetermined cylinder temperature.

The pellet is then heated to a predetermined cylinder temperature and mold temperature of 6.
Injection molded at 0x0, injection pressure 1200k9/base, length 12
Plate-shaped test specimens of Gonu, 5mm wide, and 3mm thick were obtained, and all had good moldability. Table 1 shows the molding conditions, bending strength and magnetic properties of the composition. The heat distortion temperature of the molded product obtained in Example 5 measured under the load of 6 groups of Si was 137°C.
The Bitskart softening point was 170oo.

No change in shape was observed even when the molded product was left in a hot air dryer adjusted to 150°C for 1 hour, and in order to measure thermal deterioration, it was left in air at 130 pm for 10 days and then brought to room temperature. The bending strength of the cooled sample was measured, and the bending strength retention rate was 91%, indicating good heat deterioration resistance. Cut the molded product into 3 pieces vertically and horizontally,
After being immersed in machine oil kept at 40℃ for one month, it was cooled to room temperature, and the oil absorption rate, bending strength retention rate, bending elastic modulus,
The retention rate was measured. The oil absorption rate is less than 0.00%, and the bending strength retention rate, bending elastic modulus, and retention rate are 1.
It was 00%. From the above results, it was clear that the composition had extremely excellent heat resistance and oil resistance. Table 1 Example 6 EVA2 cough isopropyl alcohol-water = 5.5:4
．． 5 in a mixed solvent of 100% and 8000%, and then 100g of barium ferrite [Boat○・(Fe
03)6] was mixed under the fly Azusa.

After 30 minutes, the mixture was poured into the water at high speed to obtain a coagulated crumb.

After drying the crumb at 100°C under reduced pressure, the cylinder temperature was 250°C, the mold temperature was 6000°C, and the injection pressure was 1000k9/cm.
Injection molded. The bending strength of the resulting composition was 930
k9/uniformity, (B・H)max was 0.50×ho・戊. Comparative Examples 1 and 2 Injection molded products of polypropylene or nylon 12-MnZn ferrite compositions were obtained in the same manner as in Examples 1 to 5.

The results are shown in Table 2. Table 2 *1 Extrusion molding machine and injection molding machine cylinder temperature The above molded product was left in a hot air dryer kept at 150:00 for 1 hour, but no significant change in shape was observed.

Next, these molded products were placed in a 130 oo hot air dryer for 1 hour.
After allowing it to stand for 0 days, it was cooled to room temperature and the bending strength retention rate was measured. The strength retention rates of the polypropylene-based composition and nylon-12-based composition were 7 cents and 45 cents, respectively, indicating that they had good resistance to heat deterioration. was significantly poorer than the ethylene-vinyl alcohol copolymer composition. Further, the above-mentioned molded product was cut vertically and horizontally into 3 pieces, and immersed in machine oil maintained at 4 and 0 for one month, cooled to room temperature, and oil absorption and bending strength retention were measured. The oil absorption rate is 2.9 for polypropylene compositions.
In the case of the nylon-12 composition, the oil absorption rate was 1.05%, which was higher than that of the ethylene-vinyl alcohol composition. The flexural strength retention was 82% for the polypropylene-based composition and 75% for the nylon-12-based composition. From the above results, it was clear that these compositions were inferior in heat resistance and oil resistance compared to vinyl alcohol olefin copolymer-ferrite compositions. Comparative Examples 3 and 4 EVA consisting of 96 mol% vinyl alcohol and 4 mol% ethylene and the Mn-Zn ferrite used in Examples 1 to 5 were mixed at a weight ratio of ferrite/EVA=7/3, and the mixture An attempt was made to melt and knead the product using an extruder at 250q0, but the melt viscosity was extremely high, making melt kneading and pelletizing impossible.

When the extruder cylinder temperature is raised to 260qo, E
Significant gas generation was observed due to thermal decomposition of the VA resin (Comparative Example 3). Also, using EVA consisting of 10 mol% vinyl alcohol and 90 mol% ethylene, ferrite/
Experiments were conducted in the same manner as in Examples 1 to 5, with the weight ratio of EVA being 3.

Claims (1)

[Claims] 1. A magnet composition comprising an olefin-vinyl alcohol copolymer having an olefin content of 20 to 50 mol% and ferrite in an amount of 1 to 5 times the weight of the copolymer.