JPS6012765B2 - Manufacturing method of high coercive force and high surface magnetic flux density plastic composite magnet - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing a plastic composite magnet.

More specifically, the present invention relates to a method for producing a plastic composite magnet obtained by mixing a novel hexagonal ferrite powder and various thermoplastic resins. Typically, plastic composite magnets are
Manufactured by mixing various thermoplastic resins and ferrite powder.

Most of the ferrite powders used for this purpose are manufactured by a dry method that utilizes interphase reactions. However, ferrite powder obtained by the conventional dry method has various drawbacks as described below due to its manufacturing method. That is, in the case of the conventional dry method, the firing temperature for promoting the ferritization reaction during the manufacturing process is 1.
Since the temperature is as high as 0.000 to 130.000 C, not only the necessary reactions proceed, but also the sintering of the ferrite particles themselves, making it necessary to carry out fairly intense mechanical crushing in the subsequent process. As a result, impact strain occurs in the powder particles, and the coercive force, which is important in plastic composite magnets, does not reach a sufficiently large value. Furthermore, since mechanical pulverization is used, there is a tendency for the particle size distribution of the powder to become broader.
As a result of intensive research to solve these problems, the present inventors have developed an extremely superior plastic composite by using a new ferrite powder that performs the pre-ferrite reaction in a wet process, that is, in a liquid phase. I succeeded in making it with a magnet. In other words, by mixing the ferrite powder obtained by the above method with various thermoplastic resins to make a plastic composite magnet, it is possible to obtain a plastic composite magnet that has extremely superior properties compared to conventional plastic composite magnets. Ta. The ferrite powder obtained by the method developed by the inventors described above has good shape, excellent particle uniformity, and has an appropriate particle size. Furthermore, since the firing process that follows the wet process can be performed at a much lower temperature than the firing temperature used in the conventional dry process, plastic composite magnets are free from the drawbacks caused by high-temperature processes as described above. can be obtained. It was confirmed that the plastic composite magnet of the present invention has improved coercive force and magnetic flux density compared to conventional magnets. When manufacturing a composite magnet from hexagonal ferrite powder and various plastic materials, the factors that have the greatest influence on its magnetic properties are the magnetic properties of the hard ferrite powder itself, which is the raw material, and the mixing ratio of ferrite powder to the plastic material. It is.

In existing plastic composite magnets, the mixing ratio of ferrite powder is said to be limited to 85 to 90%. Therefore, the magnetic properties of plastic composite magnets are coercive force (IHc) of 25
The limit values are 00 to 300 pida and a surface magnetic flux density of 700 to 85. The present inventors have conducted research with the aim of breaking through these limitations and developing a plastic composite magnet with further improved characteristic values. On the other hand, various studies were conducted from the viewpoint of developing raw materials that can be mixed at an improved mixing ratio. As mentioned above, ferrite powder obtained by the conventional dry method is mechanically crushed to a particle size of several microns, which causes significant impact strain on the particles, which significantly reduces the magnetic value, especially the coercive force, of the product. This is one of the reasons for the decline.

For this reason, post-processing such as annealing is required, and since mechanical pulverization is performed, irregularities in particles are an unavoidable drawback. On the other hand, a wet method is also known as a known method, and the products obtained in the liquid phase by this method do not have the above-mentioned drawbacks, and the particle orientation, which is a problem when mixed with plastic materials, is not obtained by the dry method. However, it is said that the ferrite powder obtained by the conventional green method has particles that are too fine, so it has poor miscibility with plastic materials compared to that obtained by the dry method. There are drawbacks.

In response, the present inventors have invented a new method for manufacturing composite magnets using ferrite powder made by combining the conventional wet method and dry method, but the plastic composite magnet obtained by this method is It has been found that the plastic composite magnet has particularly excellent coercive force and good mixability of plastic material and ferrite powder.

The method for producing the ferrite powder itself is described in detail in the specification of the invention entitled "Hexagonal Ferrite Powder and Method for Producing the Same" (Samurai Seki 51-103357), which was patented at the same time as the present invention. A detailed explanation is omitted in this book. The present invention provides a method for manufacturing a novel plastic composite magnet having improved magnetic properties by mixing the new high-performance hexagonal ferrite powder obtained by the above-mentioned novel method with a plastic material. .
The ferrite powder employed in the practice of the present invention is generally Fe(OH)2 and MC03 (M is Ba
, representing Sr, Pb or Ca) at pH 9~
12, preferably pH 9-10, liquid temperature 50-80oo,
Preferably, it is maintained at 50 to 70q0, and a certain amount (
A first step in which a co-pillar material is obtained under a liquid phase by allowing the reaction to proceed while blowing air in the form of fine bubbles (e.g., 4.0 to 5.0 so/min); A second step of firing the conjoint product at a temperature of 400 to 900 qo, preferably 400 to 600 qo, more preferably 500 to 550°C.
It is manufactured by a method consisting of steps.

In the following description and claims, the term "coprecipitate obtained in a liquid phase" refers to the coprecipitate obtained in the first step, unless otherwise specified. The hexagonal ferrite powder obtained through the first and second steps described above is further heated to 700 to 900 q0 in a heat treatment furnace.
When the hexagonal ferrite powder is fired for 1 to 3 hours at a temperature of
A suitable ferrite powder with a narrow particle size distribution can be obtained. The material obtained in this manner showed almost perfect magnetoplumbite diffraction lines in X-ray diffraction identification, and it was confirmed that ferrite formation had progressed sufficiently. The powder thus obtained is loosened into single particles by simple crushing and used as a ferrite raw material. In carrying out the present invention, the plastic material used to mix with the ferrite raw material to make the plastic composite magnet is a known thermoplastic resin and is molded by at least one of compression molding, extrusion molding, and injection molding. Any applicable law may be used.

The mixing ratio of ferrite powder and plastic material can be arbitrarily selected depending on the purpose, but as mentioned above, the mixing ratio of 85 to 90% was the limit for ferrite powder obtained by conventional methods, whereas this method The novel ferrite powder used in the invention is characterized in that a high mixing ratio of 92 to 95% can be obtained.

This is the meaning of the limitations on the mixing ratio in the claims, and it is of course possible to set the mixing ratio lower if necessary. The ferrite powder and the plastic material can be kneaded using any known mixer.

A mixed molded product of plastic and ferrite powder has good fluidity, and therefore, for example, in the case of extrusion molding, the molding machine may be either a plunger type or a screw type. The molding conditions can be conveniently carried out, for example, at a cylinder temperature of 150 to 250 qo and an extrusion pressure of 500 to 1500 k9/m. As an example, the case of manufacturing a composite magnet of barium ferrite powder and methacrylic resin will be described as follows.

First, as a ferrite raw material powder, a coprecipitate for hexagonal ferrite is generated in the liquid phase as described above, and the resulting co-precipitate is used in a dry method using a conventional solid phase reaction. Hexagonal ferrite powder obtained by firing at a temperature of 400 to 600°C, which is much lower than the heat treatment temperature, or further fired in a heat treatment furnace at a temperature of 700 to 900°C for 1 to 3 hours to obtain an average particle size of the powder. The ferrite powder is grown to have a particle size of 1.0 to 7.0 degrees and has good mixability, and is then loosened into single particles by simple crushing. On the other hand, as a plastic material, methyl methacrylate is added with 0.1 to 0.5% of a sulfurous acid catalyst, and heated and polymerized to produce a paper-like syrup-like polymer with a polymerization rate of about 10 to 30%. 92% by weight or more of ferrite powder is mixed with this syrup and thoroughly kneaded using a known kneading machine. An example of the characteristics of the plastic composite magnet obtained in this way is that the mixing ratio of ferrite powder is 92 to 95%;
Coercive force (IHc) 3200-380 piX, surface magnetic flux density 850-120, saturation magnetization (oS) 50-65 emu
/It was evening. On the other hand, an example of a composite magnet obtained by the conventional method shows that the mixing ratio of ferrite powder is at the upper limit of 90%.
The coercive force (I
Hc) is 2800, the surface magnetic flux density is 750-80, and the saturation magnetization (〇s) is 45-5 m2, which clearly shows that the plastic composite magnet obtained by the present invention is substantially superior. The magnetic properties of the new ferrite powder obtained through the first and second steps are as follows: coercive force (mc): 4800-5300 Oersted (0e), saturation magnetization (〇s): 50.0-65. It has an extremely high value of 1/2 that could not be achieved with the conventional method.

Such a plastic composite magnet containing at least 9% by weight of ferrite powder is an extremely excellent plastic composite magnet that could not have existed before. This will be explained below using examples.

Example 1 A co-precipitate for hexagonal ferrite was produced by liquid phase formation, and the resulting co-precipitate was fired at 450°C for 2 hours to produce the "obtained Bao-
The feed e2Q powder was further calcined at 80,000 for 1 hour to produce ferrite powder with good miscibility with plastic materials.

After loosening this by simple crushing, it was mixed with a syrup-like polymer produced by adding 0.4% sulfite catalyst to methyl methacrylate prepared separately and polymerizing it by heating. The mixture was molded into a plastic composite magnet plate with a thickness of 15 m' using a screw extruder. The mixing ratio of ferrite powder to plastic material was 93%. The magnetic value obtained by measuring the sample cut from the plastic plate is the coercive force (IH
c) 350 e, surface magnetic flux density lo5 eaves, saturation magnetization (O
S)55. It was Mr. Mu'Yu. Example 2 S-nucleus was manufactured by a method similar to Example 1.

Bait e203 powder was kneaded with the same methacrylic resin as in Example 1 to produce a plastic composite magnet plate with a thickness of 15 mm.

The mixing ratio of ferrite powder to plastic material is 92
%Met. The magnetic properties cut out from a plastic plate and measured were: coercive force (5c) e of 410, surface magnetic flux density 1
00, saturation magnetization (〇s) 53. It was Danmu/Yu.
Example 3 B obtained by a method similar to Example 1 was also obtained. Prefecture/Sro. 250
- Bait e203 powder was kneaded with the same methacrylic resin as in Example 1 to produce a plastic composite magnet plate with a thickness of 15 mm.

The mixing ratio of ferrite powder to plastic material is 93
%Met. The magnetic measurement values extracted from this were that the coercive force (IHc) was ×460, the surface magnetic flux density was 111, and the saturation magnetization (〇s) was 56.1 emu/night. Example 4
B et al. obtained by a method according to Example 1. 45S [o. Machi PbMo0/bait e203 powder was kneaded in the same methacrylic resin to produce a plastic composite magnet plate similar to the above example.

Claims (1)

[Claims] 1 (a) Fe(OH)_2 and MCO_3 produced in a liquid with an alkali using ferrous salt as a reaction starting material.
(M represents Ba, Sr, Pb or Ca) was maintained at pH 9-12 and liquid temperature 50-80°C, and a certain amount of air was blown into it in the form of fine bubbles to produce Fe (
By oxidizing a part of OH)_2 to Fe(OH)_3, all or most of the Fe(OH)_2 precipitate is changed to a Fe_3O_4 precipitate, which provides good filterability and eliminates alkali and other coexisting ions. The first step of obtaining a coprecipitate with less entrainment and a narrow particle size distribution; (b)
The coprecipitate obtained in the first step was fired at a temperature of 400 to 600°C to obtain a coercive force (IHc) of 4800 to 5300 oersteds (Oe) and a saturation magnetization (σ_s) of 50.0 to 6.
A second step of forming a hexagonal ferrite powder of 5.0 emu/g; and (c) 92 to 95 parts by weight of the hexagonal ferrite powder obtained in the second step is added to 8 to 5 parts by weight of a thermoplastic resin.
A method for manufacturing a plastic composite magnet with high coercive force and high surface magnetic flux density, comprising: a third step of forming a composite magnet through an operation of simply kneading parts by weight. 2 Fe(OH)_2 and MCO_ in the first step
3. A method for producing a plastic composite magnet according to claim 1, characterized in that the coprecipitation with No. 3 is carried out at a pH of 9 to 10. 3 Fe(OH)_2 and MCO_ in the first step
3. A method for producing a plastic composite magnet according to claim 1 or 2, characterized in that the coprecipitation with 3 is carried out at a liquid temperature of 50 to 70°C. 4 The firing treatment in the second step is performed using oxygen gas of 0.2 to
A method for manufacturing a plastic composite magnet according to any one of claims 1 to 3, characterized in that the process is carried out while aerating at 0.5 l/min. 5 The firing treatment in the second step is performed at 500 to 550°C.
A method for manufacturing a plastic composite magnet according to any one of claims 1 to 4, characterized in that the manufacturing method is carried out at a temperature of 30 minutes to 3.0 hours. 6 The hexagonal ferrite powder obtained by the above firing was further fired in a heat treatment furnace at a temperature of 700 to 900°C for 1 to 3 hours to grow particles until the average particle size was 1.0 to 7.0μ. A method for manufacturing a plastic composite magnet according to any one of claims 1 to 5, characterized in that the hexagonal ferrite powder is prepared into a hexagonal ferrite powder having powder physical properties with a narrow particle size distribution, and then thoroughly kneaded with a thermoplastic resin. .