WO2015122271A1

WO2015122271A1 - Rare-earth-based magnetic powder and method for producing same, resin composition for bonded magnets, and bonded magnet

Info

Publication number: WO2015122271A1
Application number: PCT/JP2015/052188
Authority: WO
Inventors: 晴美永尾; 山辺　秀敏; 石川　尚
Original assignee: 住友金属鉱山株式会社
Priority date: 2014-02-13
Filing date: 2015-01-27
Publication date: 2015-08-20
Also published as: JPWO2015122271A1

Abstract

Provided are a Nd-Fe-B-based magnetic powder and a Sm-Fe-N-based magnetic powder, each of which can improve an anti-corrosive property and heat resistance of a bonded magnet without deteriorating magnetic properties of the bonded magnet. A rare-earth-based magnetic powder according to the present invention comprises a magnetic powder selected from a Nd-Fe-B-based magnetic powder and a Sm-Fe-N-based magnetic powder, wherein the whole areas of the surfaces of particles of the magnetic powder are coated with at least one cyclic siloxane compound selected from the group consisting of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane and 1,3,5,7-tetramethylcyclotetrasiloxane, and wherein the coating amount of the cyclic siloxane compound is 0.1 to 20 parts by mass relative to 1000 parts by mass of the rare-earth-based magnetic powder.

Description

Rare earth magnetic powder and method for producing the same, resin composition for bonded magnet, bonded magnet

The present invention relates to rare earth-based magnetic powders, and more particularly, Nd—Fe—B or Sm—Fe used for bonded magnets and imparting excellent rust resistance and heat resistance without deteriorating magnetic properties. The present invention relates to an N-based rare earth magnetic powder, a method for producing the same, a resin composition for a bonded magnet containing the rare earth magnet powder, and a bonded magnet.

Since bonded magnets have advantages such as shape flexibility and high dimensional accuracy, they have been widely used in various applications such as electrical products and automobile parts. For example, for the use of spindle motors for CDs, DVDs, HDDs, vibration motors for mobile phones, actuators for digital cameras, etc., as well as high bond magnets used to reduce the weight, save energy, and increase the functionality of automobile parts. High corrosion resistance that can withstand performance and harsh environments is strongly required.

In addition, bond magnets are usually manufactured by kneading a binder resin such as rubber or plastic material and magnetic powder and then molding them. That is, there is a strong demand for magnetic powder having a large residual magnetic flux density (Br) and a high coercive force (iHc) and, as a result, a large maximum magnetic energy product (BH) max.

In general, magnetoplumbite type ferrite such as barium ferrite and strontium ferrite, Nd—Fe—B based magnetic powder and Sm—Fe—N based magnetic powder are known as magnetic powder. Nd-Fe-B-based magnetic powders are widely deployed in high-efficiency motors because of their high saturation magnetization and anisotropic magnetic field, and sintered magnets include mobile phones and various home appliances, as well as magnetic medical diagnostics. Widely used in large magnetic circuits such as devices (MRI) and synchrotron radiation generators.

In addition, Sm—Fe—N based magnetic powder has recently attracted attention because it has both a high saturation magnetization value and an anisotropic magnetic field, as well as a high Curie temperature, like Nd—Fe—B based magnetic powder. In particular, since it has higher rust prevention than Nd—Fe—B magnetic powder, it is expected to be used in harsh environments where bond magnets using Nd—Fe—B magnetic powder cannot be used. Yes.

By the way, in order to obtain Nd—Fe—B based magnetic powder, for example, an alloy lump made of neodymium, iron and boron is treated at a high temperature in a hydrogen atmosphere to form a rare earth hydride, Fe, Fe and B compound. It can be obtained by performing hydrogenation and disproportionation treatment (HD treatment) once decomposed, then removing hydrogen, and refining fine compound crystals (DR treatment) again. It needs to be moderately sized. Therefore, it is necessary to perform the minimum necessary pulverization. However, when pulverization is performed, an active surface is exposed, and oxidation proceeds due to the surface. In particular, in a humid air, it is easily oxidized in a short time and causes a decrease in magnetic properties. Furthermore, in each step of kneading and molding with a resin, the magnetic properties are reduced by an oxidizing or reducing atmosphere and heat. Furthermore, the Nd—Fe—B based magnetic powder is very susceptible to rust because it contains Fe, and even if it is used as a bonded magnet in a corrosive environment such as a coast, it uses a resin with low water absorption. Even when a bonded magnet is used, rust is generated.

On the other hand, Sm—Fe—N based magnetic powder can be obtained by occluding nitrogen in an alloy of samarium and iron. Limited grinding is necessary. However, even in this Sm—Fe—N magnetic powder, an active surface is exposed when pulverized, and oxidation proceeds due to the surface, especially in humid air for a short time. It easily oxidizes and causes a decrease in magnetic properties. Furthermore, also in each process of kneading | mixing and shaping | molding with resin, it causes a fall of a magnetic characteristic with oxidizing or reducing atmosphere and heat. Furthermore, although Sm—Fe—N based magnetic powder is less rusting than Nd—Fe—B based magnetic powder, it decomposes at high temperatures. It can be used only with a melting point resin, and rust is gradually generated by absorbing water. For example, rust is easily generated when used in a corrosive environment such as a coast. In addition, super engineering plastics that are difficult to absorb water have a high melting point. Therefore, when kneaded, the coercive force of the Sm—Fe—N magnetic powder is greatly reduced, and the target magnetic properties of the bonded magnet cannot be obtained.

That is, in the Nd—Fe—B magnetic powder and the Sm—Fe—N magnetic powder, the oxidizing or reducing atmosphere received in each step of drying, surface treatment, kneading and molding, and deterioration of magnetic properties due to heat are caused. There are few, and it is strongly demanded that it is hard to rust in a corrosive environment even after making a bonded magnet.

In addition, the formability, which is an important practical characteristic of bonded magnets, depends on the fluidity in a mixed state with the resin under high temperature and high pressure. It is important that it be a powder.

Under such circumstances, for example, Patent Document 1 discloses a method of coating with a phosphoric acid compound as a surface treatment method for improving the oxidation resistance of Nd—Fe—B magnetic powder. Patent Document 2 discloses forming a SiO ₂ protective film on Nd—Fe—B based magnetic powder.

Further, as a surface treatment method for improving the oxidation resistance of the Sm—Fe—N magnetic powder, a method of coating with a phosphoric acid compound is disclosed in Patent Document 3. Patent Documents 4 to 6 disclose forming a silica film as a surface treatment method for improving the oxidation resistance of the Sm—Fe—N based magnetic powder. Further, Patent Documents 7 and 8 disclose that a silica coating is formed on a Sm—Fe—N magnetic powder after coating with a phosphoric acid compound.

JP 2006-49863 A JP-A-8-111306 JP 2000-260616 A JP 2000-160205 A JP 2000-309802 A JP 2010-202974 A JP 2009-246294 A JP 2010-202974 A

Specifically, Patent Document 1 includes at least one flaky fine powder selected from Al, Mg, Ca, Zn, Si, Mn, and alloys thereof and silane and / or a partial hydrolyzate of silane. It is described that the corrosion resistance is improved by forming a treatment film with a treatment liquid that is included. However, under severe conditions after forming a bonded magnet, for example, in a severe condition such as immersing in a salt solution having a NaCl concentration of 5%, which is almost equal to the salinity concentration in the sea, or a solution containing SO ₄ ^2- Rust is generated and the magnetic properties deteriorate. In the method described in Patent Document 1, a processing liquid is processed on a molded permanent magnet with a spray gun so that the film thickness of the heating composite coating becomes 10 μm, and further, 300 in a hot air drying furnace. Since it is heat-treated at a high temperature of ℃, it is difficult to say that it is practical in terms of capital investment and production efficiency.

Patent Document 2 describes a method of forming a protective film of silicon dioxide on the surface of an Nd—Fe—B based magnetic powder by plasma chemical vapor deposition, and the temperature is maintained at 80 ° C. and 95 RH by forming an SiO ₂ film. Even after holding in a constant temperature and humidity chamber for 500 hours, the rusting state was not observed, and the decrease rate of open flux was also small. However, when a bonded magnet is produced using the treated magnetic powder, the corrosion resistance evaluation in a constant temperature and humidity chamber maintained at 80 ° C. and 95% RH described in Patent Document 2 shows a certain effect. Under more severe conditions, for example, under severe conditions such as immersion in salt water having a NaCl concentration of 5%, rust is generated and the magnetic properties are deteriorated.

Also, Patent Document 3 states that the rate of decrease of open flux in the bonded magnet can be suppressed by coating with a phosphoric acid compound, but rust is not specified. Further, Patent Document 4 states that the degree of deterioration of magnetic properties after accelerated deterioration is greatly improved by forming a fine particle silica film, but this Patent Document 4 also does not specify rust. Further, in Patent Document 5, when a bonded magnet is produced using a magnetic powder having a silica film formed on the particle surface, the magnetic powder having a silica film is formed when the flux is measured after heating at 100 ° C. for a predetermined time. It is said that the rate of decrease in flux of bonded magnets using copper is suppressed and the stability over time is extremely high, but rust is not specified.

In Patent Document 6, the surface of magnetic particles is coated with a first layer made of a phosphoric acid compound, and the surface of the first layer is made of a second layer made of a composite film containing a silicon compound and a phosphoric acid compound. Rust prevention is given by covering. However, since the magnetic particles for the permanent magnet are magnetically aggregated with each other, it is difficult to form a uniform film on the aggregated surface of the magnetically agglomerated magnetic particles by wet processing, and the part where the film is not formed If the film thickness becomes uneven, such as the occurrence of a thick film, and a thick film portion is formed, the magnetic characteristics may be deteriorated. Since the coating is formed so as to wrap the outside of the aggregated particles, even if it exhibits good corrosion resistance and the like as a powder, the agglomerated surface is exposed when it is kneaded by applying a shearing force together with a resin binder to form a bonded magnet. Since it becomes a trap, the improvement of corrosion resistance becomes incomplete.

In Patent Documents 7 and 8, the surface of magnetic particles is coated with a first layer made of a phosphoric acid compound, and the surface of the first layer is covered with a second layer made of a silicon compound containing silica as a main component. By giving it, rust prevention is given. However, as described above, since the magnetic particles for the permanent magnet are magnetically aggregated with each other, even in the techniques of these Patent Documents 7 and 8, even in wet processing, the magnetic particles that are magnetically agglomerated are uniformly formed on the aggregation surface. It is difficult to form a thick film, resulting in unevenness in the film thickness such as a part where the film is not formed. If a thick film part is formed, the magnetic characteristics may be deteriorated. And, as described above, since the coating is formed so as to wrap the outside of the aggregated particles, even if it shows good corrosion resistance etc. as a powder, it is kneaded by applying a shearing force together with a resin binder and a bonded magnet. Then, since the aggregated surface is exposed, the improvement in corrosion resistance is incomplete.

As described above, there are various technical problems in these prior arts, and these technical problems cannot be completely solved by any method. For example, if rust is generated when using a bonded magnet using Nd-Fe-B magnetic powder or Sm-Fe-N magnetic powder in a motor, the magnetic characteristics deteriorate and the performance decreases. , May cause motor lock and heat loss. There is also a problem that the generated rust contaminates the periphery of the equipment.

The present invention has been proposed in view of such circumstances, and an Nd—Fe—B based magnetic powder capable of enhancing the rust prevention and heat resistance of a bonded magnet without deteriorating magnetic properties and It is an object of the present invention to provide Sm—Fe—N-based magnetic powder and a method for obtaining these magnetic powders by a simple treatment.

In order to solve the above-mentioned problems, the present inventors have a coating having an action of suppressing the elution of the main component Fe on the particle surfaces of the Nd—Fe—B based magnetic powder and the Sm—Fe—N based magnetic powder. We have intensively studied to improve the anticorrosive property without deteriorating the magnetic properties by covering the entire surface with a coating film very thinly. As a result, certain cyclic siloxanes are volatilized in a vacuum vessel, and the entire surface of the magnetic powder, including the agglomerated surface of the magnetic powder that has been magnetically agglomerated, is completely covered, thereby further improving rust prevention and heat resistance. As a result, the present invention has been completed. That is, the present invention is as follows.

(1) A first invention of the present invention is composed of magnetic powder selected from Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, and includes hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane. The entire surface of the magnetic powder particles is coated with one or more cyclic siloxane compounds selected from the group consisting of 1,3,5,7-tetramethylcyclotetrasiloxane, and the coating amount of the cyclic siloxane compound is The rare earth based magnetic powder is characterized in that it is 0.1 to 20 parts by mass per 1000 parts by mass of the rare earth based magnetic powder.

(2) A second invention of the present invention is a rare earth-based magnetic powder according to the first invention, wherein the cyclic siloxane compound is coated on the magnetic powder previously treated with a phosphoric acid compound. is there.

(3) The third invention of the present invention is the first or second invention, wherein the residual magnetic flux density is 1.2 T (12 kG) or more as magnetic characteristics in the invention of (1) or (2) above. 3. The rare earth-based magnetic powder according to claim 1, wherein the squareness is 398 kA / m (5.0 kOe) or more and the coercive force is 800 kA / m (10 kOe) or more.

(4) According to a fourth aspect of the present invention, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, a magnetic powder selected from Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, The entire surface of the magnetic powder particles is coated with a gas containing one or more cyclic siloxane compounds selected from the group consisting of 1,3,5,7-tetramethylcyclotetrasiloxane. In this step, the cyclic siloxane compound is placed together with the magnetic powder in a vacuum vessel, and held for 1 to 48 hours under the conditions of a vacuum pressure of −0.1 MPa or less and a temperature of 40 to 100 ° C. Is a method for producing a rare earth-based magnetic powder.

(5) According to a fifth aspect of the present invention, in the fourth aspect of the present invention, only the magnetic powder obtained by coating the surface of the particles with the cyclic siloxane compound is vacuum pressure of −0.1 MPa or less and a temperature of 80 to 110 in a vacuum vessel. It is a method for producing a rare earth-based magnetic powder characterized by being held for 1 to 12 hours under the condition of ° C.

(6) According to a sixth aspect of the present invention, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, a magnetic powder selected from Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, The entire surface of the magnetic powder particles is coated with a gas containing one or more cyclic siloxane compounds selected from the group consisting of 1,3,5,7-tetramethylcyclotetrasiloxane. In the step, the cyclic siloxane compound is placed together with the magnetic powder in a container, and nitrogen and / or argon gas is allowed to flow under atmospheric pressure and at a temperature of 80 to 110 ° C. A method for producing a rare earth-based magnetic powder characterized by holding for ˜24 hours.

(7) According to a seventh aspect of the present invention, in the sixth aspect, only the magnetic powder having the particle surface coated with the cyclic siloxane compound is heated at a temperature of 80 while nitrogen and / or argon gas is circulated in the container. It is a method for producing a rare earth-based magnetic powder characterized by holding for 1 to 12 hours under a condition of ˜110 ° C.

(8) According to an eighth aspect of the present invention, in any one of the fourth to seventh aspects, prior to coating the surface of the particles of the magnetic powder with the cyclic siloxane, a phosphoric acid compound is added to the magnetic powder. It is a manufacturing method of the rare earth type magnetic powder characterized by processing.

(9) A ninth invention of the present invention is a bonded magnet resin composition comprising the rare earth-based magnetic powder according to any one of the first to third inventions and a resin.

(10) A tenth aspect of the present invention is a bonded magnet including the rare earth-based magnetic powder according to any one of the first to third aspects.

According to the present invention, an extremely thin coating film of a cyclic siloxane compound is formed on the particle surface of the Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, thereby reducing the magnetic properties. In addition, the rust prevention and heat resistance of the bonded magnet can be improved.

In addition, according to such rare earth-based magnetic powder, it can be used without generating rust even in a harsh environment that could not be used in the past due to increased rust prevention. In addition, since this rare earth-based magnetic powder has excellent heat resistance, it can maintain its magnetic properties even in the process of forming a bond magnet using a high melting point poniphenylene sulfide resin, which is more severe than ever. Can also be used.

FIG. 5 is a schematic diagram showing the configuration of a processing apparatus used for surface treatment of magnetic powder in Examples 11 to 13.

Hereinafter, specific embodiments of the present invention (hereinafter referred to as “present embodiments”) will be described in detail in the following order. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention.
1. 1. Rare earth magnetic powder 2. Manufacturing method of rare earth magnetic powder 3. Resin composition for bonded magnet Bond magnet

<< 1. Rare earth magnetic powder >>
The rare earth based magnetic powder according to the present embodiment is composed of a magnetic powder selected from Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder. It is characterized by being coated with a coating film of a specific cyclic siloxane compound.

Thus, by covering the entire surface of the particle with the coating film, elution of iron (Fe), which is the main component of the magnetic powder, can be suppressed, and deterioration of the magnetic properties of the magnetic powder can be prevented. it can. And, in this rare earth-based magnetic powder, a specific cyclic siloxane compound is coated very thinly as its coating film, thereby effectively improving rust prevention and heat resistance without deteriorating magnetic properties. Can do.

<1-1. Starting material>
In the rare earth based magnetic powder according to the present embodiment, the rare earth based magnetic powder used as a starting material is either Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder.

As the Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, known ones can be used. Among them, the phosphoric acid compound is treated in advance, and the particle surface is made of a phosphoric acid compound. It is preferred to use a magnetic powder that is coated.

<1-2. Rare earth-based magnetic powder with a cyclic siloxane compound coating film>
(About coating film)
As described above, the rare earth-based magnetic powder according to the present embodiment has a specific cyclic siloxane formed on the entire surface of the Nd—Fe—B-based magnetic powder or Sm—Fe—N-based magnetic powder as the starting material powder. A coating film of the compound is formed.

Specifically, the cyclic siloxane compound to be coated is one or more cyclic groups selected from hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, and decamethylcyclopentasiloxane. It is a siloxane compound. In addition, other volatile cyclic siloxane compounds can also be used.

As will be described in detail later, in this rare earth magnetic powder, the cyclic siloxane compound having volatility as described above is volatilized in an evacuated container or under an atmospheric pressure while circulating an inert gas, and the gas and A coating film of a cyclic siloxane compound is formed on the entire surface of the particle by a so-called gas phase method in which the starting raw material powder is Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder. . According to this vapor phase method, a nano-level ultra-thin coating film layer can be uniformly formed on the particle surface, and extremely excellent rust prevention (corrosion resistance), etc. without deteriorating the magnetic properties of the magnetic powder. Can be demonstrated.

It is important that the amount of the cyclic siloxane compound coated by the above-described vapor phase method is 0.1 to 20 parts by mass per 1000 parts by mass of the rare earth magnetic powder. Further, it is more preferably 1 to 10 parts by mass per 1000 parts by mass of the rare earth magnetic powder.

When the coating amount of the cyclic siloxane compound is less than 0.1 parts by mass, the coating film of the cyclic siloxane compound cannot always cover the entire surface of the magnetic powder particles, or the film thickness is sufficient even when the entire surface is coated. Therefore, it reacts with moisture in the environment and elution of Fe, which is the main component of the magnetic powder, makes it easy to generate rust. Also, sufficient heat resistance cannot be obtained. On the other hand, if the coating amount of the cyclic siloxane compound exceeds 20 parts by mass, the coating film becomes thick and the magnetic properties are deteriorated, which is not preferable.

(About compression density)
The rare earth-based magnetic powder in which the coating film of the cyclic siloxane compound is formed is not particularly limited as the compression density (CD), but is preferably 4.1 g / ml or more. When the compression density is less than 4.1 g / ml, the density per volume at the time of injection molding at the time of molding the bonded magnet is lowered, and the magnetic properties may be lowered.

(About BET specific surface area)
The BET specific surface area of the rare earth-based magnetic powder in which the coating film of the cyclic siloxane compound is formed is not particularly limited, but in the case of the Nd—Fe—B based magnetic powder, 0.01 to 3.5 m ² / g It is preferable that it is the range of these. In the Nd—Fe—B based magnetic powder with the coating film formed, if the BET specific surface area is out of the above range, it means that proper pulverization has not been performed, and high magnetic properties cannot be obtained. The BET specific surface area is more preferably in the range of 0.01 to 2.5 m ² / g.

Further, the BET specific surface area in the case of the Sm—Fe—N based magnetic powder is not particularly limited, but is preferably 0.35 to 2.6 m ² / g. In the Sm—Fe—N-based magnetic powder with the coating film formed, if the BET specific surface area is outside the above range, it means that proper pulverization has not been performed, and high magnetic properties cannot be obtained. The BET specific surface area is more preferably in the range of 0.35 to 2.0 m ² / g.

(About the average particle size of powder particles)
The average particle size of the rare earth-based magnetic powder in which the coating film of the cyclic siloxane compound is formed is not particularly limited, but in the case of the Nd—Fe—B based magnetic powder, it may be 10 to 200 μm. The thickness is preferably 40 to 130 μm.

The average particle size of the powder particles in the case of the Sm—Fe—N magnetic powder is not particularly limited, but is preferably 1.0 to 5.0 μm, and preferably 1.0 to 4.0 μm. Is more preferable.

(About the structure of magnetic powder)
The powder structure of the rare earth based magnetic powder on which the coating film of the cyclic siloxane compound is formed is not particularly limited, but the Nd—Fe—B based magnetic powder has a structure of Nd ₂ Fe ₁₄ B type. Is preferred.

The powder structure in the case of the Sm—Fe—N based magnetic powder is not particularly limited, but preferably has a Th ₂ Zn ₁₇ type, TbCu ₇ type, or Th ₂ Ni ₁₇ type structure.

(Magnetic properties of magnetic powder)
As described above, the rare earth-based magnetic powder according to the present embodiment has a coating film of a cyclic siloxane compound that is formed extremely thin, so that it is effectively rust-proof without deteriorating magnetic properties. And heat resistance can be improved. Specifically, as for the magnetic characteristics, when Nd—Fe—B based magnetic powder is used, as a result of measuring the magnetic powder after being oriented in a magnetic field, for example, the coercive force is 478 to 1989 kA / m (6 ˜25 kOe), the residual magnetic flux density is 1.1 to 1.5 T (11 to 15 kG), and the maximum magnetic energy product is 199.1 to 358 kJ / m ³ (25 to 45 MGOe).

Further, when the Sm—Fe—N based magnetic powder is used, the magnetic properties thereof are measured by, for example, aligning the magnetic powder in a magnetic field, and have a coercive force of 398.1 to 1592 kA / m (5 to 20 kOe). ), The residual magnetic flux density is 1.0 to 1.5 T (10 to 15 kG), and the maximum magnetic energy product is 158.8 to 358.1 kJ / m ³ (20 to 45 MGOe).

≪2. Method for producing rare earth magnetic powder with a cyclic siloxane compound coating film >>
Next, regarding a method for producing a rare earth-based magnetic powder according to the present embodiment, that is, a rare earth-based magnetic powder in which a coating film of a cyclic siloxane compound is formed, the case of Nd—Fe—B based magnetic powder and Sm—Fe Each will be described separately for the case of -N-based magnetic powder.

<2-1. Preparation of starting material powder>
(Nd-Fe-B magnetic powder)
First, the case of Nd—Fe—B based magnetic powder will be described. The Nd—Fe—B magnetic powder used as a starting material is a starting alloy using any of known alloy manufacturing methods such as a book mold method, a centrifugal casting method, a strip casting method, an atomizing method, and a reduction diffusion method. An Nd—Fe—B ingot is produced.

Next, the produced Nd—Fe—B ingot is subjected to a homogenization treatment for the purpose of coarsening crystal grains and reducing the α-Fe phase. In this homogenization treatment, for example, heat treatment is performed for 1 to 48 hours in an inert gas other than a nitrogen atmosphere under a temperature condition of 1000 to 1200 ° C. By performing the homogenization process in this way, the main component elements in the Nd—Fe—B ingot are diffused, and each component can be homogenized.

Here, the Nd—Fe—B ingot is composed of the main phases Nd ₂ Fe ₁₄ B phase, Nd rich phase, and B rich phase, but in addition to the Nd ₂ Fe ₁₄ B phase, α- Ferromagnetic phases such as Fe phase and Nd ₂ Fe ₁₇ phase are often present. Therefore, by performing the above-described homogenization treatment, a structure composed of only the Nd ₂ Fe ₁₄ B phase can be obtained. In addition, by performing such a homogenization treatment, the crystal grain size can be coarsened to about 100 μm or more. The coarsening of the average particle diameter is preferable because it has magnetic anisotropy.

Regarding the conditions for the homogenization treatment, when nitrogen is used as the inert gas atmosphere, the nitrogen reacts with the Nd—Fe—B ingot, which is not preferable. Further, if the heat treatment temperature for the homogenization treatment is less than 1000 ° C., it is not preferable because it takes time to diffuse the main component elements and increases the manufacturing cost. On the other hand, if the heat treatment temperature for the homogenization treatment exceeds 1200 ° C., the Nd—Fe—B ingot is melted, which is not preferable.

Next, the homogenized Nd—Fe—B ingot is pulverized by a known pulverization method such as mechanical pulverization using a jaw crusher, hydrogen storage pulverization, pulverization using a disk mill, or the like. Apply processing.

After the grinding treatment, the HDDr treatment can be performed on the Nd—Fe—B based magnetic powder. The HDDR process is divided into a hydrogenation / disproportionation process (HD process) and a dehydrogenation / recombination process (DR). First, the pulverized Nd—Fe—B powder is put into a vacuum heat treatment furnace, and hydrogenation / disproportionation treatment (HD treatment) is carried out at a temperature range of 800 ° C. to 900 ° C. for 1 to 5 hours while circulating hydrogen gas. )I do. Thereafter, dehydrogenation and recombination processing (DR processing) is performed in vacuum at the same temperature as HD processing. By performing the HDDR process in this way, it is possible to obtain an Nd—Fe—B based magnetic powder which is a starting material powder having excellent magnetic anisotropy.

(Sm-Fe-N magnetic powder)
Next, the case of Sm—Fe—N based magnetic powder will be described. The Sm—Fe—N based magnetic powder as a starting material can be produced by introducing nitrogen into, for example, an Sm ₂ Fe ₁₇ alloy powder having a Th ₂ Zn ₁₇ type structure. The Sm ₂ Fe ₁₇ alloy powder can be produced using any of known alloy production methods such as a book mold method, a centrifugal casting method, a strip casting method, an atomizing method, and a reduction diffusion method. It is preferable to use a diffusion method.

Here, in the reduction diffusion method, for example, iron powder and samarium oxide powder are used as raw materials, and metal calcium particles are added to and mixed with these, and heat treatment (reduction diffusion treatment) is performed in a non-oxidizing atmosphere such as Ar gas. Apply. In this heat treatment, samarium oxide is reduced by metallic calcium, and the reduced samarium is alloyed by diffusing into the iron powder. The calcium oxide contained in the reaction product after the heat treatment can be removed by washing by adding the reaction product into water after cooling to form calcium hydroxide and repeating decantation.

Sm ₂ Fe ₁₇ introduction of nitrogen to the alloy powder (nitride) is to dry the Sm ₂ Fe ₁₇ alloy powder recovered after removing the calcium component, it is subjected to heat treatment in an atmosphere containing nitrogen gas, the nitrogen, such as ammonia gas Is done by. The powder obtained after the nitriding heat treatment thus obtained has a composition of Sm ₂ Fe ₁₇ N ₃ . Note that nitriding may be performed on the reaction product after the reduction diffusion, and then a cleaning process for removing the calcium component may be performed.

Then, by adjusting the particle size of the obtained powder after nitriding by pulverization, pulverization, classification, etc. so that the average particle size becomes 1.0 to 5.0 μm, for example, Sm—Fe as a starting material powder is obtained. -N-based magnetic powder can be obtained.

<2-2. Phosphate compound treatment for starting raw material powder>
In the method for producing a rare earth based magnetic powder according to the present embodiment, a coating film of a cyclic siloxane compound is formed on the starting raw material powder obtained as described above. Prior to the formation of the coating film, it is preferable to perform a treatment (phosphate compound treatment) for attaching (coating) a phosphate compound to the particle surface of the starting material powder.

Thus, by subjecting the starting raw material powder to the phosphoric acid compound treatment, the durability of the raw magnetic powder can be improved and the rust prevention property and the like can be further enhanced.

With respect to the phosphoric acid compound treatment, the phosphoric acid compound used for coating the Nd—Fe—B magnetic powder or Sm—Fe—N magnetic powder is not particularly limited. For example, orthophosphoric acid, disodium hydrogen phosphate, Pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate, aluminum phosphate and the like can be suitably used. Among these, orthophosphoric acid is particularly preferable as the phosphoric acid compound to be adhered to the particle surface.

In addition, in the phosphoric acid compound treatment, in order to uniformly coat the surface of the magnetic powder with the phosphoric acid compound, for example, isopropyl alcohol (IPA) is mixed as a diluted solution with the phosphoric acid compound described above, and a stirrer is used. It is preferable to stir and mix while heating at a temperature of 50 to 175 ° C. for 1 to 3 hours. More preferably, wet pulverization, pulverization, classification, and the like are performed when the particle size is adjusted by pulverization, pulverization, classification, etc. so that the average particle diameter becomes 1.0 to 5.0 μm. The phosphoric acid compound described above is added to the treatment solvent. Thereafter, the magnetic powder slurry whose particle size has been adjusted is stirred and dried in a non-oxidizing atmosphere at 50 to 175 ° C. while heating for 1 to 3 hours. By doing in this way, a phosphoric acid compound coat can be formed also on the particle surface which is carrying out magnetic aggregation.

The addition amount (adhesion amount, coating amount) of the phosphoric acid compound is not particularly limited, but is 0.1 to 5 with respect to 100 parts by mass of the Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder. About 0.0 part by mass is preferable.

<2-3. Formation of coating film on cyclic siloxane compound>
Next, a process of forming a coating film of a cyclic siloxane compound on the starting material powder (magnetic powder) prepared as described above will be described.

In forming the coating film, first, the prepared magnetic powder is put in a heatable vacuum vessel, and another vessel containing a volatile cyclic siloxane compound is placed in the vacuum vessel. Then, after the inside of the vacuum vessel is deaerated to −0.1 MPa or less by a vacuum pressure, the whole vacuum vessel is heated to 40 to 100 ° C. and heat treatment is performed for 1 to 48 hours. In other words, in the formation of the coating film, the agglomerated surface is magnetically agglomerated by volatilizing the cyclic siloxane compound in a separate container and bringing the volatilized cyclic siloxane compound into contact with the magnetic powder surface in the gas phase. A coating film is appropriately formed on the entire surface of the magnetic powder including (formation of a coating film by a vapor phase method).

As a temperature condition for forming the coating film, if the temperature of the entire vacuum vessel is less than 40 ° C., the volatilization of the cyclic siloxane compound is not sufficient, and it is difficult to coat the entire surface of the magnetic powder particles. On the other hand, when the temperature is higher than 100 ° C., the cyclic siloxane compound may be altered. Therefore, as a temperature condition, the entire vacuum vessel is heated to 40 to 100 ° C., more preferably 50 to 80 ° C. as described above.

Also, regarding the processing time, if the processing time is too short, the coating film is not sufficiently formed. On the other hand, even if the processing time is increased, the coating is not performed beyond a certain coating amount. Therefore, the processing time is 1 to 48 hours as described above, and more preferably 12 to 24 hours.

As the conditions for forming the coating film based on the vapor phase method, the above-described temperature conditions and processing time conditions are used, so that the magnetic powder and the volatile cyclic siloxane compound are simply installed in the vacuum vessel. Then, the volatilized cyclic siloxane compound comes into contact with the surface of the magnetic powder, and a coating film can be efficiently formed over the entire surface and details of the surface of the magnetic powder. In order to coat the entire surface of the magnetic powder particles with the cyclic siloxane compound more efficiently and reliably, it is preferable to incorporate a mixing device such as a stirrer inside the vacuum vessel.

In forming the coating film, the magnetic powder is brought into vapor phase contact with the cyclic siloxane compound by maintaining the magnetic powder at 80 to 110 ° C. for 1 to 24 hours while flowing an inert gas under atmospheric pressure. It may be. The gas species to be circulated is preferably an inert gas such as nitrogen gas or argon gas from the viewpoint of concern about the deterioration of magnetic properties due to heating in an oxygen atmosphere. In addition, when the gas phase contact is performed in the atmosphere, it is preferable to carry out the stirring of the magnetic powder in order to positively bring the cyclic siloxane compound into contact with the surface of the magnetic powder.

Here, as described above, after forming a coating film on the entire surface of the magnetic powder, it is preferable to stabilize the cyclic siloxane compound adhering to the surface. Specifically, the process of stabilizing the cyclic siloxane compound coated by contacting in a vapor phase in a vacuum vessel is to take out only the magnetic powder that has been subjected to the coating treatment from the vessel used for the vapor phase treatment and put it in another vacuum vessel. When using the same vacuum vessel that has been transferred or vapor-phase treated, take out the vessel containing the cyclic siloxane compound, replace the gas inside with the atmosphere, and then again under vacuum at a vacuum pressure of -0.1 MPa or less. Then, a drying process (heat treatment) is performed for 1 to 12 hours at a temperature of 80 to 110 ° C.

In addition, in the case where the cyclic siloxane compound is coated by vapor phase contact with an inert gas flowing in the atmosphere, an inert nitrogen gas, argon gas, or the like is placed in the vessel used for the vapor phase treatment or in another vessel. For example, heat treatment is performed for 1 to 12 hours under a temperature condition of 80 to 110 ° C. while circulating the active gas. Even when the cyclic siloxane compound is coated in a vacuum container as described above, only the magnetic powder subjected to the coating treatment is transferred to another container, and an inert gas is circulated in the container under the atmosphere. In this state, heat treatment may be performed under similar processing conditions.

In this way, the coating film can be stabilized and the excess adsorbed component can be removed by performing the heat treatment after coating the cyclic siloxane compound by vapor phase contact. In addition, regarding the temperature conditions of heat processing, when it is less than 80 degreeC, the cyclic siloxane compound adhering to magnetic powder cannot fully be stabilized, On the other hand, when it exceeds 110 degreeC, the rare earth type magnetic powder obtained This is not preferable because it may affect the magnetic characteristics. Therefore, it is preferably carried out under a temperature condition of 80 to 110 ° C., more preferably under a temperature condition of 80 to 90 ° C.

In the method for producing a rare earth-based magnetic powder according to the present embodiment, as described above, the gas containing the vaporized cyclic siloxane compound is brought into contact with the surface of the magnetic powder in the gas phase using the vapor phase method, and the coating film To form. Such a vapor phase method is different from a liquid phase method (wet method) in which a coating layer is formed on the surface particle surface in a liquid, for example, a nano level having a thickness of about 0.5 to 20 nm, preferably about 1 to 5 nm. The uniform coating film layer can be formed on the entire surface of the magnetic powder particles.

In this way, an extremely thin uniform coating film layer can be formed on the particle surface of the magnetic powder, so that it has excellent rust prevention (corrosion resistance) and heat resistance without deteriorating the magnetic properties of the magnetic powder. Can be granted. Further, after the coating film is formed by the vapor phase method, the attached cyclic siloxane compound can be made denser and stabilized by performing the heat treatment again.

≪3. Bonded Magnet Resin Composition >>
Next, the resin composition for bonded magnets using the rare earth based magnetic powder according to the present embodiment will be described.

The resin composition for bonded magnets is obtained by dispersing magnetic powder in a binder resin. In the bonded magnet resin composition according to the present embodiment, as described above, the magnetic powder is composed of Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, and a specific cyclic siloxane compound. Thus, the entire surface of the particle is covered.

The resin composition for bonded magnets contains the above-mentioned surface-treated Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder in a proportion of, for example, 85 to 99 mass%, with the balance being a binder resin. In addition, it is comprised with the additive added as needed.

Here, the binder resin is not particularly limited and can be variously selected depending on a molding method. For example, a thermoplastic resin can be used in the case of injection molding, extrusion molding, and calendar molding, and a thermosetting resin can be used in the case of compression molding. Examples of thermoplastic resins include nylon (PA), polypropylene (PP), ethylene vinyl acetate (EVA), polyphenylene sulfide (PPS), liquid crystal resin (LCP), elastomer, and rubber. Can be used. In addition, as the thermosetting resin, for example, an epoxy resin, a phenol resin, a silicone resin, or the like can be used.

Further, when producing a resin composition for bonded magnets, in order to improve the fluidity, moldability, etc., and sufficiently draw out the magnetic properties of the Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder, If necessary, known additives such as plasticizers, lubricants, coupling agents and the like can be used. Moreover, you may mix other types of magnet powders, such as a ferrite magnet powder.

The resin composition for bonded magnets can be obtained by mixing and kneading the surface-treated Nd—Fe—B magnetic powder or Sm—Fe—N magnetic powder with a binder resin at a predetermined ratio. The mixing can be performed using a mixer such as a Henschel mixer, a V-shaped mixer, or a nauter. The kneading is performed using a uniaxial kneader, a biaxial kneader, a mortar-type kneader, an extrusion kneader, or the like. It can be carried out.

<< 4. Bond magnet >>
The bonded magnet can be obtained using the above-described resin composition for bonded magnet. Specifically, the above-described resin composition for bonded magnet is molded by a known molding method such as injection molding, extrusion molding, compression molding, calender molding, and then subjected to electromagnetization or pulse magnetization according to a known method. Thus, a bonded magnet can be obtained.

The rare earth magnetic powder according to the present embodiment is obtained by coating the entire particle surface of the Nd—Fe—B magnetic powder or Sm—Fe—N magnetic powder with a cyclic siloxane compound. In addition, the surface condition is remarkably changed. The coating film made of a cyclic siloxane compound on the particle surface of the magnetic powder is very thin, hardly affecting the magnetic properties, and suppressing the deterioration of the magnetic powder due to heat. Therefore, compared with the magnetic powder that is not surface-coated, i.e., does not form a coating film of a cyclic siloxane compound, the magnetic properties are not deteriorated, while it is extremely excellent in rust prevention and heat resistance. Yes. Moreover, the rust prevention property and heat resistance which such a magnetic powder has give the rust prevention property outstanding with respect to the bond magnet, even when it is a case where it shape | molds to the bond magnet using the magnetic powder.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

<Preparation of rare earth magnetic powder>
[Example 1]
50 g of anisotropic Nd—Fe—B magnetic powder (manufactured by Aichi Steel Co., Ltd., MF-18P) was placed in the lower stage of the vacuum desiccator, and 5 g of a cyclic siloxane compound (hexamethylcyclotrisiloxane) was placed on the upper stage. After reducing the pressure to −0.1 MPa or less, the mixture was placed in a constant temperature bath at 80 ° C. for 24 hours. Thereby, the volatilized cyclic siloxane compound and the magnetic powder were brought into contact with each other in a gas phase, and the surface treatment was performed on the magnetic powder. After the treatment, the magnetic powder was taken out and dried in a vacuum dryer at 90 ° C. for 6 hours to obtain an Nd—Fe—B based magnetic powder coated with a cyclic siloxane compound.

The treated Nd—Fe—B magnetic powder was coated with 0.3 g of a cyclic siloxane compound (hexamethylcyclotrisiloxane). That is, the coating amount of the cyclic siloxane compound was 6 parts by mass with respect to 1000 parts by mass of the magnet powder.

[Examples 2 to 3]
In Example 2, octamethylcyclotetrasiloxane was used as the cyclic siloxane compound. In Example 3, 1,3,5,7-tetramethylcyclotetrasiloxane was used as the cyclic siloxane compound. Thus, a surface-treated Nd—Fe—B based magnetic powder was obtained.

In the treated Nd—Fe—B magnetic powder, a cyclic siloxane compound (Example 2: Octamethylcyclotetrasiloxane, Example 3: 1,3,5,7-tetramethylcyclotetrasiloxane) is Example 2. 3 was coated with 0.2 g. That is, the coating amount of the cyclic siloxane compound was 4 parts by mass with respect to 1000 parts by mass of the magnet powder.

[Examples 4 to 6]
50 g of Sm—Fe—N based magnetic powder (manufactured by Sumitomo Metal Mining Co., Ltd., SFN-C, phosphoric acid compound treated product) is placed in the lower stage of the vacuum desiccator, and the cyclic siloxane compound (hexamethylcyclotrisiloxane) is placed in the upper stage. 5 g was placed, and after reducing the pressure to −0.1 MPa or less, each was put in a thermostat set at 50 ° C. in Example 4, 60 ° C. in Example 5, and 80 ° C. in Example 6 for 24 hours. Thereby, the volatilized cyclic siloxane compound and the magnetic powder were brought into contact with each other in a gas phase, and the surface treatment was performed on the magnetic powder. After the treatment, the magnetic powder was taken out and dried in a vacuum dryer at 90 ° C. for 6 hours to obtain an Sm—Fe—N based magnetic powder coated with a cyclic siloxane compound.

In the Sm—Fe—N-based magnetic powder after the treatment, cyclic siloxane compounds (hexamethylcyclotrisiloxane) were 0.15 g (Example 4), 0.25 g (Example 5), and 0.35 g (Example 5), respectively. Example 6) It was coated. That is, the coating amount of the cyclic siloxane compound with respect to 1000 parts by mass of the magnet powder was 3 parts by mass (Example 4), 5 parts by mass (Example 5), and 7 parts by mass (Example 6), respectively.

[Examples 7 and 8]
Example 8 is the same as Example 4 except that octamethylcyclotetrasiloxane was used as the cyclic siloxane compound and was put in a thermostatic bath at 40 ° C. in Example 7 and 80 ° C. in Example 8 for 24 hours. Thus, a surface-treated Sm—Fe—N magnetic powder was obtained.

The treated Sm—Fe—N magnetic powder was coated with 0.025 g (Example 7) and 0.05 g (Example 8) of a cyclic siloxane compound (octamethylcyclotetrasiloxane), respectively. That is, the coating amount of the cyclic siloxane compound was 0.5 parts by mass (Example 7) and 1 part by mass (Example 8) with respect to 1000 parts by mass of the magnet powder.

[Examples 9 and 10]
1,3,5,7-tetramethylcyclotetrasiloxane was used as the cyclic siloxane compound, except that it was brought into contact with a gas phase for 24 hours in a constant temperature bath at 40 ° C. in Example 9 and 80 ° C. in Example 10. Obtained surface-treated Sm—Fe—N-based magnetic powders in the same manner as in Example 4.

In the Sm—Fe—N-based magnetic powder after the treatment, cyclic siloxane compounds (1,3,5,7-tetramethylcyclotetrasiloxane) were 0.15 g (Example 9) and 0.2 g (Example), respectively. Example 10) It was coated. That is, the coating amount of the cyclic siloxane compound was 3 parts by mass (Example 9) and 4 parts by mass (Example 10) with respect to 1000 parts by mass of the magnet powder.

[Example 11]
In Example 11, the magnetic powder was subjected to a surface treatment by bringing the magnetic powder into vapor phase contact with a cyclic siloxane compound while flowing an inert gas under atmospheric pressure using the apparatus shown in FIG.

That is, first, 50 g of Sm—Fe—N-based magnetic powder was put into a mixing tank (mixing vessel) 11 in the apparatus shown in FIG. 1 and heated to 80 ° C. with stirring. On the other hand, the cyclic siloxane compound (hexamethylcyclotrisiloxane) 20 was accommodated in the storage tank 12 and heated to maintain the temperature at 50 ° C. Nitrogen (N ₂ ) gas 30a is introduced into the storage tank 12 at 500 sccm, and then N ₂ gas 30b is sent in an amount of 150 sccm to introduce a gas containing a cyclic siloxane compound into the mixing tank 11 for 24 hours. did. Thus, the volatilized cyclic siloxane compound and the magnetic powder were brought into vapor phase contact under atmospheric pressure in the mixed layer 11, and surface treatment was performed on the magnetic powder.

After the surface treatment, the magnetic powder was taken out and dried in a vacuum dryer at 90 ° C. for 6 hours to obtain an Sm—Fe—N magnetic powder coated with a cyclic siloxane compound. The treated Sm—Fe—N based magnetic powder was coated with 0.25 g of a cyclic siloxane compound (hexamethylcyclotrisiloxane). That is, the coating amount of the cyclic siloxane compound was 5 parts by mass with respect to 1000 parts by mass of the magnet powder.

[Examples 12 and 13]
In Example 12, Example 11 was used except that octamethylcyclotetrasiloxane was used as the cyclic siloxane compound, and in Example 13, 1,3,5,7-tetramethylcyclotetrasiloxane was used as the cyclic siloxane compound. Surface treatment was performed in the same manner as described above to obtain an Sm—Fe—N based magnetic powder coated with a cyclic siloxane compound.

In the Sm—Fe—N-based magnetic powder after the treatment, a cyclic siloxane compound (Example 12: Octamethylcyclotetrasiloxane, Example 13: 1,3,5,7-tetramethylcyclotetrasiloxane) 0.04 g (Example 12) and 0.2 g (Example 13) were coated. That is, the coating amount of the cyclic siloxane compound was 0.8 parts by mass (Example 12) and 4 parts by mass (Example 13) with respect to 1000 parts by mass of the magnet powder.

[Comparative Examples 1 and 2]
The Nd—Fe—B based magnetic powder (Comparative Example 1) and Sm—Fe—N based magnetic powder (Comparative Example 2) used in the above-described examples were used without surface treatment, and are shown below. Thus, it evaluated similarly to the Example.

<Production of bonded magnet>
Using the magnetic powders prepared in Examples 1 to 10 and Comparative Examples 1 and 2, 88.81 parts by mass of magnetic powder and 8.91 parts by mass of polyphenylene sulfide resin were mixed using a Henschel mixer, and biaxial. The mixture was kneaded (kneading temperature 300 ° C.) with an extrusion kneader to produce an injection molded product of 20 mmφ × 13 mm while applying an orientation magnetic field of 1592 kA / m (20 kOe).

<Evaluation, results>
(Evaluation of magnetic properties)
Regarding the magnetic characteristics, a bonded magnet molded in an orientation magnetic field was measured with a BH tracer (manufactured by Toei Kogyo Co., Ltd.), and the residual magnetic flux density (kG), squareness (kOe), and coercive force (kOe) were evaluated. Table 1 shows the results.

(Water repellency test)
5 g of magnetic powder was placed on a stainless steel plate, one drop of water was dropped, and water repellency was observed. The case where water droplets were held round on the magnetic powder was evaluated as “◯”, the case where the water droplets became elliptical was evaluated as “Δ”, and the case where water droplets were absorbed was evaluated as “×”. Table 1 shows the results.

(Corrosion resistance test)
A corrosion resistance test using artificial sweat (disodium hydrogen phosphate 0.32 mass%, sodium chloride 0.8 mass%, acetic acid 0.5 mass% aqueous solution) was performed on 5 g of the magnetic powder and the bonded magnet molded body. Specifically, 10 ml of artificial sweat was put in a sealed container, magnetic powders or bonded magnet molded bodies were arranged, and the sealed container was left in a constant temperature bath heated to 30 ° C. for 24 hours. As a result of being left as it was, the case where red rust was observed was evaluated as “×”, and the case where no discoloration was observed was evaluated as “◯”. Table 1 shows the results.

(Heat resistance test)
5 g of the magnetic powder was heat-treated for 10 minutes in the air at a predetermined temperature (150 to 270 ° C.), and the subsequent color change was confirmed. Table 2 shows the results.

As shown in the results of Table 1, the Nd—Fe—B magnetic powder or Sm—Fe—N magnetic powder in Examples 1 to 13 was obtained by coating a specific cyclic siloxane compound with a predetermined coating amount. It can be seen that the obtained magnetic powder has the same magnetic characteristics as the magnetic powder not subjected to the surface treatment of Comparative Example 1 or Comparative Example 2, and the magnetic characteristics are not deteriorated. On the other hand, the magnetic powders of Examples 1 to 13 have improved water repellency, and the magnetic powder and the bonded magnet formed from the magnetic powder do not generate rust and have excellent corrosion resistance. I understood.

In addition, from the results of Table 2, regarding heat resistance, the Nd—Fe—B based magnetic powder (Comparative Example 1) not subjected to surface treatment is discolored at a relatively low temperature of about 150 ° C., and Sm—Fe Even in the -N-based magnetic powder (Comparative Example 2), the color changed at a temperature of about 210 ° C. In contrast, in the magnetic powders in Examples 1 to 13, there was no discoloration after the heat treatment up to 270 ° C. regardless of the type of the coated cyclic siloxane compound, so even in a very high temperature environment. It was found that there was an effect of suppressing the deterioration of the magnetic powder, and it had excellent heat resistance.

The rare earth-based magnetic powder according to the present invention is obtained by coating a particle surface of a Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder with a heat-resistant cyclic siloxane compound at a predetermined coating amount. Yes, the rust prevention and heat resistance of the bonded magnet can be improved without deteriorating the magnetic properties. Such rare earth based magnetic powder can be suitably used as Nd—Fe—B based magnetic powder and Sm—Fe—N based magnetic powder for bonded magnets. Moreover, according to this rare earth-based magnetic powder, it is possible to use it in a severe, inferior and corrosive environment that has been difficult until now.

11 Mixing tank (mixing container)
12 Containment tank 20 Cyclic siloxane compound

Claims

Composed of magnetic powder selected from Nd—Fe—B based magnetic powder or Sm—Fe—N based magnetic powder;
The entire surface of the magnetic powder particles is coated with one or more cyclic siloxane compounds selected from the group consisting of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and 1,3,5,7-tetramethylcyclotetrasiloxane. And
The amount of the cyclic siloxane compound covered is from 0.1 to 20 parts by mass per 1000 parts by mass of the rare earth magnetic powder.
2. The rare earth magnetic powder according to claim 1, wherein the cyclic siloxane compound is coated on the magnetic powder previously treated with a phosphoric acid compound.
The magnetic characteristics include a residual magnetic flux density of 1.2 T (12 kG) or more, a squareness of 398 kA / m (5.0 kOe) or more, and a coercive force of 800 kA / m (10 kOe) or more. 3. The rare earth based magnetic powder according to 1 or 2.
Hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, 1,3,5,7-tetramethylcyclotetra can be used for magnetic powder selected from Nd-Fe-B magnetic powder or Sm-Fe-N magnetic powder. A step of coating the cyclic siloxane compound on the entire surface of the particles of the magnetic powder by contacting with a gas containing one or more cyclic siloxane compounds selected from the group consisting of siloxanes;
In the step, the cyclic siloxane compound is placed together with the magnetic powder in a vacuum vessel, and is maintained for 1 to 48 hours under a vacuum pressure of −0.1 MPa or less and a temperature of 40 to 100 ° C. Manufacturing method of magnetic powder.
The magnetic powder having the particle surface coated with the cyclic siloxane compound alone is held in a vacuum vessel for 1 to 12 hours under the conditions of a vacuum pressure of -0.1 MPa or less and a temperature of 80 to 110 ° C. 4. A method for producing a rare earth-based magnetic powder according to 4.
Hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, 1,3,5,7-tetramethylcyclotetra can be used for magnetic powder selected from Nd-Fe-B magnetic powder or Sm-Fe-N magnetic powder. A step of coating the cyclic siloxane compound on the entire surface of the particles of the magnetic powder by contacting with a gas containing one or more cyclic siloxane compounds selected from the group consisting of siloxanes;
In the step, the cyclic siloxane compound is placed together with the magnetic powder in a container, and maintained at a temperature of 80 to 110 ° C. for 1 to 24 hours while flowing nitrogen and / or argon gas under atmospheric pressure. A method for producing a rare earth-based magnetic powder.
Only the magnetic powder having the particle surface coated with the cyclic siloxane compound is held in a container at a temperature of 80 to 110 ° C. for 1 to 12 hours while flowing nitrogen and / or argon gas. The method for producing a rare earth-based magnetic powder according to claim 6.
The rare earth magnetism according to any one of claims 4 to 7, wherein the magnetic powder is treated with a phosphoric acid compound prior to coating the surface of the particles of the magnetic powder with the cyclic siloxane. Powder manufacturing method.
A resin composition for bonded magnets, comprising the rare earth-based magnetic powder according to claim 1 and a resin.
A bonded magnet comprising the rare earth-based magnetic powder according to claim 1.