JPH01272101A - Surface-modified magnetic powder and bond magnet composition containing same - Google Patents

Abstract

PURPOSE:To form a bond magnet whose magnetic force is high, whose maximum energy product is large and whose performance is not lowered with the passage of time by a method wherein the surface of a magnetic powder composed of an alloy containing a rare-earth metal and iron is treated with a treating agent which is composed mainly of an alkali silicate. CONSTITUTION:An alloy which can give a high magnetic force and contains a rare-earth element and iron is used as a raw material for a magnetic powder. An alloy expressed by a composition formula of RxTyBz is particularly suitable; in this formula, R represents at least one kind selected from neodymium, praseodymium and a rare-earth metal composed of a misch metal, T represents iron or an iron group element and B represents boron; x, y and z represent individual atomic percentages of R, T and B; a relationship among x, y and z is as follows: 8<=x<=30, 2<=z<=20 and y=10. Water glass (composed mainly of Na2O and SiO2), potassium silicate, lithium silicate or the like can be enumerated as an alkali silicate as a main component of a treating agent which is used to treat the surface of the magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface-modified magnetic powder with excellent oxidation resistance and moisture resistance, and a bonded magnet composition containing the same.

(Conventional technology) Due to rapid technological innovation in the field of electronics, home appliances, electronic devices, office automation equipment, etc. are becoming smaller, lighter, and thinner in order to save energy and resources. ing. In order to miniaturize these home appliances and electronic devices, it is necessary to miniaturize the various components used therein. For example, there is a demand for small, high-performance permanent magnets that are needed in tape recorder motors and the like.

Sintered magnets and cast magnets, which have traditionally been used as permanent magnets, have poor mechanical properties such as impact resistance and tensile strength, and are extremely difficult to process.

This is insufficient as a magnet for the above-mentioned applications, which require complex shapes and highly accurate dimensions. In contrast, a bonded magnet (also called a plastic magnet) obtained by adhesively molding magnetic powder with a resin binder has been developed. Bonded magnets are easy to mold.

Moreover, by selecting the type of magnetic powder, a small permanent magnet having high magnetic force can be obtained. Filling Technique 1 Dispersion Technique for Preparing Bonded Magnets.

Due to advances in molding machines and molding materials, the scope and amount of use of bonded magnets is expanding.

Ferrite-based or alnico-based magnetic materials have been used as magnetic materials for bonded magnets.

However, recently, in order to obtain the above-mentioned compact and high-performance bonded magnets, magnetic materials with a very large maximum energy product (
For example, samarium-cobalt alloys) have been developed and put into practical use.

However, the samarium-cobalt-based magnetic material is highly susceptible to oxidation, and there is a risk of explosion unless proper treatment is performed during molding. moreover.

Sumari, one of its constituents, is contained in only a small amount among the rare earth metals in the ore.

Therefore, the supply of samarium depends on the demand for other light rare earth metals, which are contained in large quantities in ores. moreover,
Purification and separation of samarium requires a large amount of money, making it extremely expensive.

On the other hand, cobalt is not only expensive, but also has problems with stable supply because it is a dual strategic material.

Under these circumstances, efforts have recently been made to develop high-performance and inexpensive magnetic materials to replace samarium-cobalt magnetic materials. For example, JP-A-59-211549 discloses a neodymium-iron-boron based magnetic material. This magnetic material has extremely high magnetic force and is mainly composed of commonly used iron, so it can be supplied stably at low cost.

However, this magnetic material is also easily oxidized, unlike the samarium-cobalt based magnetic material.

Furthermore, since it is mainly composed of iron, it will rust if moisture is present. For example, when a bonded magnet is prepared by molding this magnetic material into powder and using a binder, the magnetic material is contained in the binder. Alternatively, moisture and oxygen mixed in during molding may oxidize the iron and cause rust. In other words, the composition of the magnetic material changes, and as a result, the magnetic force of the bonded magnet decreases significantly over time. It is also possible to treat the surface of this magnetic powder with phosphoric acid, chromic acid, etc. (known as rust preventive agents for iron). However, since iron reacts with phosphoric acid or chromic acid over a certain thickness from the surface of the powder, in other words, the composition of the magnetic powder changes, so a high-performance bonded magnet cannot be obtained.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional drawbacks, and its purpose is to achieve a high magnetic force, a large maximum energy product, and a device that does not deteriorate in performance over time. An object of the present invention is to provide magnetic powder that can form a bonded magnet. Another object of the present invention is to provide oxidation resistance and moisture resistance by treating the surface of neodymium-iron-boron based magnetic powder by appropriate means, and to make it stable during and after molding into a bonded magnet. An object of the present invention is to provide surface-modified magnetic powder for bonded magnets that does not deteriorate.

Still another object of the present invention is to provide a magnetic powder containing the above-mentioned magnetic powder, which has excellent oxidation resistance, moisture resistance, and stability over time.

An object of the present invention is to provide a bonded magnet composition from which a high-performance and inexpensive bonded magnet can be prepared.

(Means for Solving the Problems) The surface-modified magnetic powder of the present invention is obtained by surface-treating magnetic powder containing a rare earth metal and iron with a treatment agent containing an alkali silicate as a main component, This achieves the above objective.

The bonded magnet composition of the present invention contains the above surface-modified magnetic powder and a binder, thereby achieving the above object.

As the material for the surface-modified magnetic powder of the present invention, an alloy containing rare earth and iron that can impart high magnetic force is used. Among these, an alloy represented by the compositional formula RxTyBz is suitable. In the above formula, R is at least one selected from the group of rare earth metals consisting of neodymium, petittheodymium, and mitsch metal, T is iron, or iron and an iron group element, and B is boron.

X+V and 2 represent the atomic percentages of R, T and B, respectively, and the following formula holds between X+V and 20:
8≦x≦30, 2≦2≦20. y=100-X-)
'a In the above formula, "Mitsuhmetal" refers to a mixture mainly of cerium group rare earth elements obtained in a smelting process. As T, iron alone can be used, or iron can be used as the main component, and cobalt, nickel, etc., which are iron group metals, can be used in combination. In particular, adding a small amount of cobalt or nickel can improve the Curie point of the magnetic powder.

Furthermore, in order to increase the coercive force of the magnetic powder, it is also possible to add one or more of dysprosium (Dy), terbium (Tb), zirconium (Zr), hafnium (Hf), and the like. X+V and 2
If it is out of the above range, the magnetic force tends to decrease somewhat.

The alkali silicate which is the main component of the treatment agent for surface treating the magnetic powder is water glass (Na, 0 and Si).
O□ is the main component), potassium silicate.

Examples include lithium silicate. like this.

Alkali silicates have the property of forming a film on the surface of magnetic powder that has functions such as oxidation resistance, heat resistance, ultraviolet resistance, radiation resistance, abrasion resistance, oil resistance, and organic solvent resistance. The processing agent further preferably contains a curing agent. This curing agent is
It has the function of increasing the water resistance of the alkali silicate film and firmly adhering the film to the surface of the magnetic powder. Examples of such curing agents include silica, hydrochloric acid, and phosphoric acid.

Inorganic acids such as sulfuric acid, nitric acid, and boric acid; Metal oxides such as zinc oxide, magnesium oxide, and calcium oxide; Metal hydroxides such as calcium hydroxide, magnesium hydroxide, and zinc hydroxide; Sodium fluorosilicide.

Silicides such as potassium fluorosilicate and calcium silicate; inorganic salts such as sodium aluminate, sodium bisulfate, magnesium sulfate, and sodium bicarbonate.

Examples include borates such as potassium borate and calcium borate; ethylene carbonate; gamma-butyrolactone, glyoxal; and ethylene glycol diacetate. As the above-mentioned treatment agent, for example, ultrafine particulate silica or colloidal silica is added to an aqueous alkali silicic acid solution and dissolved by heating.

The amount of alkali silicate used is 0.01 to 10% by weight as a solid content based on the magnetic powder, preferably 0.0%.
5 to 1 % natoru. If it is less than 0.01% by weight, no oxidation prevention effect or rust generation prevention effect can be obtained. Even if it exceeds 10% by weight, the above effects proportional to the content cannot be obtained.

Due to the thick coating of alkali silicate on the magnetic powder, the preparation of bonded magnets using the obtained surface-modified magnetic powder results in a low relative content of magnetic material in the bonded magnet, resulting in high magnetic force. is not obtained. The above alkali silicates may be used alone or in combination of two or more.

The binder contained in the bonded magnet composition of the present invention is 2
For example, it is a thermosetting or thermoplastic resin. Examples of thermosetting resins include phenol resins, epoxy resins, and silicone resins. Thermoplastic resins include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyamide.

Polyacecool, polyphenylene sulfide.

Examples include polysulfone, polyether sulfone, polyethylene terephthalate, polybutylene terephthalate, and polycarbonate. Liquid crystal polymers and the like may also be used.

The amount of these resins is 1% in 2 compositions, for example, 2 to 10% by weight in the case of thermosetting resins.

Preferably around 3% by weight, in the case of thermoplastic resins 5-2%
It is contained in an amount of 0% by weight, preferably around 10% by weight. If it is too small, the moldability will be poor, and if it is too large, the resulting bonded magnet will have poor magnetic force.

The magnetic powder of the present invention can be prepared by a conventional method using a desired metal. For example, first, an ingot is prepared by melting a composition containing metals such as neodymium, iron, boron, and optionally cobalt nickel in desired proportions. Next, this is remelted in a quartz tube and formed into a ribbon shape by melt spinning. That is, the molten metal in the quartz tube is injected onto the surface of a rotating quenching drum under the pressure of argon gas, and the metal is rapidly cooled and formed into a ribbon shape. This ribbon is ground into magnetic powder in an argon atmosphere. What is the particle size of magnetic powder?

It is usually 20 to 200 μm. If the particle size is too small, magnetic force will not be maintained, and if the particle size is too large, molding will be difficult.

The surface-modified magnetic powder of the present invention can be obtained by mixing the magnetic powder with a processing agent solution containing the alkali silicate as a main component, and then drying the mixture at a temperature of about room temperature to 250°C. There are no restrictions on the mixing method, and in some cases,
The magnetic powder ribbon may be pulverized in the aqueous alkali silicate solution and then dried. The obtained magnetic powder may be further treated with a silane coupling agent or a titanium coupling agent in order to improve contact with a resin binder during molding as described below.

A bonded magnet is prepared using the composition of the present invention containing the magnetic powder thus obtained and the binder described above. This composition is prepared by two conventional compression molding methods.

It is molded into a desired shape by transfer molding, extrusion molding, injection molding, etc.

(Function) According to the present invention, a surface-modified magnetic powder is obtained in which the surface of the magnetic powder is treated and modified with a treatment agent containing an alkali silicate as a main component. In this powder, unlike when the magnetic powder surface is treated with phosphoric acid or chromic acid, there is no major change in its composition. Therefore, the original properties of the magnetic material do not change (high magnetic force is maintained).If the iron contained in the magnetic powder comes into contact with moisture due to condensation during or after molding, ferrous hydroxide is formed. To,
The alkali silicate that makes up the film has the function of passivating it without dissolving it in water. Therefore, ferrous hydroxide is prevented from being further oxidized to become ferric hydroxide (which is the main body of rust and causes corrosion). In other words, the alkali silicate film prevents the magnetic powder from being oxidized by oxygen and moisture and causing rust. Furthermore, this film
Heat resistant.

It imparts various properties to magnetic powder, such as resistance to ultraviolet rays, radiation, abrasion, oil, and organic solvents. Such surface-modified magnetic powders do not require expensive inert gases, which are normally used to prevent oxidation during storage. When molding and processing bonded magnets using this powder, even if it comes into contact with air at high temperatures, ignition due to oxidation does not occur, and there is no danger in handling it. Furthermore, the material remaining in the sprue portion and runner portion during injection molding etc. does not deteriorate due to oxidation and can be reused. The resulting bonded magnet has excellent stability over time and has a long product life.

(Example) The invention will be explained below with reference to examples.

Preparation of surface-modified magnetic powder: 100 mj! 50 g of Magnequench (manufactured by General Motors; NdzFe+ 7B) was collected into five beakers.

10 of processing agents (A-E) containing the components separately shown in Table 1
A wt% aqueous solution was prepared. However, for processing agent B-E, each component was added to water, and the mixture was heated to 90 to 100°C for 1 hour to dissolve. In Table 1.

As colloidal silica, Snowtex 0 (manufactured by Nissan Chemical Co., Ltd.) is used, and as ultrafine powder silica.

1.5 g of the processing agent solution was added to each of the five beakers using Nipple Seal E-200 (Nihon Shiri, manufactured by Kanigyo Co., Ltd.) and stirred so that the whole was uniform. This was placed in a hot air oven and heated at 120°C for 10 minutes.

Table 1 (B) Evaluation of surface-modified magnetic powder (1): Magnequench (sample 1-1) used in section (A), and (A
Surface-modified magnetic powder obtained in section ) (Samples 1-2 to 1-6)
; Corresponding to processing agents A to H, respectively)
The following tests were conducted: ■ Raising the temperature in air at a rate of 5°C/min.

Measure the weight increase rate (%) at 400°C (thermogravimetric analysis); ■ In a hot air oven, 250'C, 30
Examine the weight increase rate of the sample when heated for 30 minutes at each temperature of 0°C and 350"C; and ■ immerse the sample in 20 times the volume of tap water and leave it at room temperature for 2 and 24 hours to prevent rust. Examine the occurrence situation. Table 2 shows the results of each test.
Shown below. In Table 2, the amount of treatment agent is.

It shows the solid content weight % based on the magnetic powder. The same applies to Tables 3 to 6.

(The following is a blank space) As shown in Table 2, in the case of the untreated sample (1-1), the weight increase rate due to oxidation at high temperatures was large, and the occurrence of rust was significant. On the other hand, those treated with a treatment agent containing an alkali silicate have a very small weight increase rate at high temperatures. Furthermore, it does not rust at all even when immersed in water.

It can thus be seen that the alkali silicate film provides oxidation resistance and rust prevention performance.

(C) Evaluation of surface-modified magnetic powder (2): Magnequench used in section (A) (sample 1-1) and surface-modified magnetic powder obtained in section (A) (sample 1-2 to 1) -6) were left in an atmosphere of 60° C. and 90% relative humidity for 7 days. Maximum energy product before and after leaving (B
H) max was measured and compared. Table 3 shows the results.
Shown below.

(Margins below) As shown in Table 3, in the case of the untreated sample (1-1), the magnetic force decreased sharply under high humidity, whereas the treated samples (samples 1-2 to 1-6) ), it can be seen that there is almost no change and it is stable.

Rare earth magnetic powder Magnequench Nd2Fe+J (manufactured by General Motors) was stirred at low speed in a Henschel mixer. A processing agent similar to that prepared in Example 1 (A) was added to the magnetic powder so that the solid content was 0.3% by weight. After stirring for 10 minutes, the temperature was 120°C.
It was dried for 60 minutes. The obtained surface-modified magnetic powder was left in a constant temperature and humidity chamber at a temperature of 60° C. and a humidity of 90% for 7 days. Add 5% by weight of 2-ethyl-4-methyl-imidazole as a curing agent to bisphenol A epoxy resin.
The mixture was added at a ratio of 2% by weight to the magnetic powder and kneaded. This was compression molded and heated to 80°C for 2 hours.

First, it was cured at 150°C for 1 hour and magnetized in a magnetic field of 40KOe. The residual magnetic flux density, coercive force and maximum energy product of these magnets were measured. A similar test was also conducted on powder that was not treated with the treatment agent. The results are shown in Table 4.

(The following is a blank space) As shown in Table 4, in the case of untreated samples, the magnetic powder deteriorated significantly under high humidity, and the magnetic properties when made into bonded magnets were poor. On the contrary.

It can be seen that there is no deterioration in the surface-treated bonded magnets, and the magnetic properties of the bonded magnets are good.

The head of the custodian A bonded magnet was created in the same manner as in Example 2.

The obtained bonded magnets were left in a constant temperature and humidity chamber at a temperature of 60° C. and a humidity of 90% for 500 hours, and then their performances were similarly compared. The results are shown in Table 5.

(Left below) As shown in Table 5, in the case of bonded magnets using untreated magnetic powder, the deterioration is large when stored for long periods of time under high humidity, whereas the bonded magnets using surface-modified magnetic powder 1. Bonded magnets show almost no deterioration.

Magnequench NdzFe+J (manufactured by General Motors), a rare earth magnetic powder, was stirred at low speed in a Henschel mixer. This was added to the treatment agent B (1) prepared in Example 1 (A).
0% by weight aqueous solution) as a solid content of the magnetic powder.
．． It was added at a concentration of 3% by weight.

After stirring uniformly, heat at 120"C for 5 minutes and then 20 minutes.
Heated at 0°C for 5 minutes. Obtained surface modified magnetic powder 9
0 parts and 1210 parts of nylon were heated and kneaded at 270'C.

Pelleted. This was molded using the injection molding method, and 40KO
A magnetic field of e was applied to form a bonded magnet. moreover.

The material remaining in the mold was collected and molded in the same manner to prepare a bonded magnet. The materials remaining in the mold were collected and recycled 10 times, and the performance of the resulting magnets was compared. The results are shown in Table 6.

As shown in Table 6, in the case of bonded magnets using untreated magnetic powder, the molding material is reused.

At high temperatures, oxidation deterioration is severe and magnetic properties are significantly degraded.

On the other hand, bonded magnets using surface-modified magnetic powder have an extremely low degree of deterioration.

(Effects of the Invention) According to the present invention, there is provided a surface-modified magnetic powder that can form a bonded magnet with high magnetic force and a large maximum energy product (and whose performance does not deteriorate over time).

And a bonded magnet composition using the same is obtained.

Since this magnetic powder is mainly composed of an alloy mainly composed of rare earth elements and iron, it can be provided at a lower cost than conventional samarium-cobalt magnetic powders.

that's all

Claims (7)

[Claims] 1. A surface-modified magnetic powder obtained by surface-treating magnetic powder made of an alloy containing rare earth metals and iron with a treatment agent containing an alkali silicate as a main component. 2. The surface-modified magnetic powder according to claim 1, wherein the magnetic powder is mainly composed of an alloy represented by the composition formula R_xT_yB_z: where R is from the group of rare earth metals consisting of neodymium, praseodymium, and misch metal. at least one selected from the group, T is iron or iron and an iron group element, and B is boron; x, y, and z each represent the atomic percentage of R, T, and B; The following formula holds: 8≦x≦30, 2≦z≦20, y=100−x−y. 3. The surface-modified magnetic powder according to claim 1 or 2, wherein the treatment agent contains water glass and silica. 4. A bonded magnet composition containing a surface-modified magnetic powder obtained by surface-treating a magnetic powder made of an alloy containing a rare earth metal and iron with a treatment agent containing an alkali silicate as a main component, and a binder. 5. The composition according to claim 4, wherein the magnetic powder is mainly composed of an alloy represented by the composition formula R_xT_yB_z: where R is at least one selected from the group of rare earth metals consisting of neodymium, praseodymium, and misch metal. 1, T is iron or iron and iron group elements, and B is boron, x, y, and z represent the atomic percentages of R, T, and B, respectively, and the following formula is between x, y, and z: Holds: 8≦x≦30, 2≦z≦20, y=100−x−y. 6. The composition according to claim 4 or 5, wherein the treatment agent contains water glass and silica. 7. 7. The composition according to claim 4, 5 or 6, wherein the binder is a resin.