JP3023881B2 - R-Fe-BC bonded magnet with excellent oxidation resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a rare earth (R) -iron (Fe)-
The present invention relates to a bonded magnet having excellent oxidation resistance and comprising a magnetic alloy powder composed of boron (B) -carbon (C) and a resin component.

[0002]

2. Description of the Related Art In recent years, many reports have been made since R-Fe-B magnets were disclosed by Sagawa et al. As next-generation permanent magnets exceeding the magnetic force of Sm-Co magnets. However, although the magnet is superior in magnetic force to the Sm-Co based magnet, its magnetism is significantly inferior in oxidation resistance. For example, the permanent magnet material disclosed in Japanese Patent Application Laid-Open No. 59-46008 is substantially resistant to oxidation. It is difficult to get.

[0003] Further, since the magnet alloy is usually manufactured by a sintering method, processing such as grinding and cutting is required in order to produce a product, and the cost is high. A method that does not require this processing is disclosed in, for example,
The bonding method can be used as disclosed in JP-294808-A.

[0004] However, no drastic solution has been made regarding the oxidation resistance, and the oxidation resistance is remarkably inferior as in the case of the above-mentioned sintered magnet, so that it is difficult to practically endure as a permanent magnet material.

[0005]

As described above, the conventional R
In -fe-B Keibo command magnet not yet to obtain a drastic improvement in the oxidation resistance, at a practical level has a problem in oxidation resistance.

[0006] In general R-Fe-B system magnets, in order to impart oxidation resistance, but the formation of strong oxidation resistant protective film on the surface is essential, if the magnetic alloy powder, firmly on its surface There is a problem that it is necessary to establish a manufacturing method that forms an oxidation-resistant protective film and prevents the formed film from being removed. The present invention is shall be trying to solve this problem, is intended to provide an excellent bonded magnet oxidation resistance with excellent oxidation resistance magnetic alloy powder was granted.

[0007]

In order to solve these problems, the present inventors have developed a microscopic concept, rather than the conventional macroscopic concept of coating the magnet surface with an oxidation-resistant protective film. As a result of intensive studies on drastic improvement of oxidation resistance by
With the conventional technology of coating each of the magnetic crystal grains in the magnetic alloy powder with an oxidation-resistant protective film, a new technology was found that was difficult even with the conventional technology, and furthermore, the conventional technology no longer provides high magnetic properties. B content 2 outside the practical range
By newly finding that good magnetic properties that can withstand practical use can be imparted even in the region of less than atomic%, it has become possible to provide a novel bonded magnet with an epoch-makingly improved oxidation resistance.

That is, the present invention relates to an R—Fe—BC alloy powder (where R is at least one of rare earth elements including Y).
Seed) and each of the magnetic crystal grains in the alloy powder is 16
50% by volume of magnetic alloy powder covered with an oxidation-resistant protective film containing C in an amount of not more than 0% by weight (not including 0% by weight)
An object of the present invention is to provide an R-Fe-BC bonded magnet comprising the following resin components. Here, the magnetic crystal grains preferably have a grain size in the range of 0.3 to 50 μm, and the thickness of the grain boundary phase covering each crystal grain of this grain size is in the range of 0.001 to 30 μm. The preferred composition of the magnetic alloy powder (the total composition of the magnetic crystal grains and the oxidation-resistant protective film) in the bonded magnet of the present invention is, as an atomic percentage, R: 10 to 30%, B: 7% or less, preferably 2% or less. % (Excluding 0 atomic%), C: 0.1-20
%, The balance consists of Fe and impurities inevitable in production. Even if B is 2% or more, the effect of oxidation resistance is sufficiently exhibited, but especially when B is less than 2%, the magnetic properties are also low. The oxidation resistance is remarkably improved while being sufficiently shown.

[Action] Such oxidation resistance is obtained by covering the periphery of each magnetic crystal grain in the magnetic powder constituting the bonded magnet of the present invention with a nonmagnetic film having an appropriate C content. It was done. That is, the present inventors include the above-mentioned predetermined amount of C (carbon) in the grain boundary phase which is a non-magnetic phase, specifically, so that 16% by weight or less of the film becomes C, preferably, It has been found that by containing C in the range of 0.05 to 16% by weight, a remarkable oxidation resistance function can be imparted to this nonmagnetic phase.
By coating each magnetic crystal grain with this non-magnetic film having an oxidation resistance function, a sufficient oxidation resistance effect can be exhibited even with the same B content as in the past, and the formation of the C-containing protective film can be achieved by using a B film. This makes it possible to reduce the amount, and even if it is less than 2 atomic%, the magnetic properties of the bonded magnet consisting of this magnetic alloy powder and the resin component are more than the same level as before, and the oxidation resistance is dramatically improved. Was found.

[Detailed Description of the Invention] The bonded magnet of the present invention is C
The use of (carbon) has significant characteristics, so we will first explain from this point. In the R-Fe-B magnet, C has conventionally been regarded as a passive element with respect to magnetic properties and oxidation resistance, and has not been regarded as an essential additive element.

[0011] The present inventors have proposed the addition of C to a nonmagnetic phase (grain boundary) surrounding magnetic crystal grains of the alloy, instead of including C as a mere substitution element for B. In this way, contrary to conventional wisdom, it has been found that C can greatly contribute to the oxidation resistance of the magnetic alloy powder, and it has also been clarified that this can improve the magnetic properties. . That is, due to the inclusion of C in the non-magnetic phase in such a magnetic alloy powder, even if the B content is within a known ordinary range, the oxidation resistance is improved as compared with the conventional case, and in particular, the B content is less than 2 atomic%. The effect was found to be even more pronounced in the case of the amount.
For example, conventionally, if the B content is less than 2 atomic%, iHc is 1K
According to the present invention, iHc is 4 KOe or more even if the amount of B is less than 2 atomic%. Such a novel effect according to the present invention is brought about by the formation of the C-containing oxidation-resistant protective film surrounding each of the magnetic crystal grains. From this, it is completely different from the conventional magnet using C as the depolarizing element, which has caused the deterioration of the oxidation resistance and the deterioration of the magnetic properties. did it.

In this case, C surrounding each of the magnetic crystal grains
The contained oxidation-resistant protective film contains substantially all of the alloying elements constituting the magnetic crystal grains other than C. Such a C-containing oxidation-resistant protective film can be formed by allowing C to be contained in the grain boundary layer existing between the magnetic crystal grains in the magnetic alloy powder. The reason is presumed as follows.

That is, since the protective film contains substantially all of the alloying elements constituting the magnetic crystal grains, particularly,
It is thought to be largely due to the formation of -Fe-C intermetallic compound. It is generally said that rare earth elements are easily rusted and carbides of rare earth elements are easily hydrolyzed. However, it is presumed that a non-stoichiometric R-Fe-C-based intermetallic compound is generated in the protective film according to the present invention, which is considered to suppress the above-mentioned disadvantages.

As described above, the present inventors remarkably improve the oxidation resistance by coating each magnetic crystal grain in the magnetic alloy powder with the C-containing oxidation-resistant protective film, and further reduce the B content. They have found that the effect is even more remarkable, and have invented a good bonded magnet which has been difficult with known techniques.

The C-containing oxidation-resistant protective film contains substantially all of the elements constituting the magnetic crystal grains as described above, and the C content is 16% by weight in the protective film composition. (Not including 0% by weight). That is, since C in the protective film not only imparts oxidation resistance to the magnet but also has the effect of suppressing the decrease in iHc due to the decrease in B, its content is preferably 0.05 to 0.05% in the composition of the protective film. 16% by weight, more preferably 0.1 to 12% by weight is essential. If the content of C is less than 0.05% by weight, oxidation resistance cannot be imparted, and iHc is less than 4KOe. On the other hand, if the C content in the protective film exceeds 16% by weight,
The decrease of r is remarkable, and it is no longer practical.

In the bonded magnet of the present invention, the composition of the protective film in the magnetic alloy powder is not limited to C, and may be composed of magnetic crystal grains even if the amount ratio differs from that of the magnetic crystal grains. Contains substantially all of the alloying elements present. Oxidation resistance is substantially maintained irrespective of the thickness of the protective film as long as it covers the individual magnetic crystal grains uniformly, but iHc decreases when the film thickness is less than 0.001 μm. Noticeably,
On the other hand, if it exceeds 30 μm, Br no longer satisfies the value intended in the present invention. Therefore, the range is preferably 0.001 μm to 30 μm, more preferably 0.005 μm to 15 μm. In addition,
The thickness of the protective film includes the grain boundary triple point. The thickness of this protective film can be measured using a TEM.

On the other hand, each magnetic crystal grain itself surrounded by the oxidation-resistant protective film may have the same composition as a well-known R-Fe-B- (C) -based permanent magnet. However, even when the amount of B is low, the bonded magnet of the present invention can exhibit good magnetic properties. The composition of the magnetic alloy powder (the entire composition including the magnetic crystal grains and the oxidation-resistant protective film) in the bonded magnet of the present invention is preferably R: 10 to 30%, B: 7% or less, preferably 2% or less in atomic percentage. % (Excluding 0%), C: 0.1-20%,
The balance: Fe and impurities unavoidable in production. A resin component having a volume ratio of 50% or less is used to obtain a bonded magnet formed into a required shape from the magnetic alloy powder.

The total C content in the magnetic alloy powder of the bonded magnet of the present invention is preferably 0.1 to 20 atomic%. When the total C content exceeds 20 atomic%, the decrease of Br is remarkable,
If it is less than 0.1 atomic%, it is no longer possible to impart oxidation resistance. As described above, the total C content in the magnetic alloy powder is preferably 0.1 to 20 atomic%, but C in the above-described oxidation-resistant protective film not only imparts oxidation resistance,
Since it has the effect of suppressing the decrease in iHc due to the decrease in B, its content is 16% by weight in the composition of the protective film.
The following (excluding 0%), preferably 0.05 to 16% by weight, more preferably 0.1 to 12% by weight is essential. The C of the raw material can be used carbon black, high purity carbon emissions.

R is a rare earth element, Y, La, Ce, Nd,
Pr, Tb, Dy, Ho, Er, Sm, Gd, Eu, Pm, Tm, Yb and Lu
One or more of them are used. Incidentally, a mixture of two or more kinds, such as misch metal and dymium, can also be used. Here, the reason why R is preferably set to 10 to 30 atomic% is that Br is extremely excellent in practical use within this range.

As B, pure boron or ferroboron can be used, and its content exceeds the known range of 2 at.% Or up to about 7 at. Is remarkably improved, and the above object of the present invention is achieved. However, it is preferable that B is less than 2 atomic%, more preferably 1.8 atomic% or less. On the other hand, when B is not added, the oxidation resistance is good, but iHc is extremely reduced, and the object of the present invention cannot be achieved. As the ferroboron, those containing impurities such as Al and Si can also be used.

As described above, in the bonded magnet of the present invention, each magnetic crystal grain in the magnetic alloy powder preferably has a thickness.
It is covered with a C-containing oxidation-resistant protective film in the range of 0.001 to 30 μm, more preferably 0.005 to 15 μm, and the magnetic crystal grains preferably have a particle size of 0.3 to 50 μm, more preferably 1 to 30 μm. In the range. The size of the magnetic crystal grains
If less than 0.3μm, iHc becomes less than 4KOe, and 50μm
When i exceeds 3, the decrease in iHc becomes remarkable, and the characteristics of the magnet of the present invention are impaired. The grain size can be accurately measured by SEM, and the composition analysis can be accurately performed by EPMA.

Further, the bonded magnet of the present invention is obtained by molding the magnetic alloy powder into a required shape with a resin component, and the resin component has a volume ratio of 50% or less, preferably 5 to 40%.
If the resin component is less than 5%, molding becomes difficult, and if it exceeds 50%, good magnetic properties cannot be exhibited.

As the resin component, either a thermoplastic resin or a thermosetting resin can be used. For example, phenolic resin, furan resin, polyester resin, epoxy resin, polyurethane resin, silicon resin, fluororesin, polyimide resin, polyamide resin, diallyl phthalate resin, polyphenyl oxide resin are resins having excellent mechanical and thermal properties and other properties. Is appropriately selected. Also,
Magnetic alloy powder enhances adhesiveness with resin and improves mechanical and thermal properties. Silane coupling agent, titanate coupling agent, aluminum coupling agent, zircoaluminate coupling agent, functional monomer Surface treatment with various treatment agents can be used together. Plasticity, lubricants, etc. are used as needed. Representative examples of these plasticizers are dibutyl phthalate (DBP), dioctyl phthalate (DOP), and dioctyl adipate.
(DOA) can be used. Representative examples of lubricants include fatty acid esters and metal soaps.

As a method of producing the magnetic powder of the bonded magnet of the present invention, when pulverizing from a sintered body, melting, casting, pulverizing, molding, sintering, pulverizing or melting, casting, pulverizing, molding, firing, etc. Although it can be produced by a conventional method comprising a series of steps of sintering, pulverization and heat treatment, preferably, in the above-mentioned production process, a step of heat-treating the cast alloy after casting or introducing C The production can be advantageously performed by introducing a step of secondary addition of a part or all of the raw material, or by introducing these two steps in combination. When pulverizing from a cast alloy, a good magnetic alloy powder exhibiting the above-described effects can be obtained by pulverizing or pulverizing and heat-treating using a hot plastic working method. In addition, a good magnetic alloy powder exhibiting the above-mentioned effects can be obtained even if the molten metal is formed into a powder by a spraying method or the powder is heat-treated.

A bonded magnet molded product can be manufactured by mixing, molding, and solidifying the magnetic alloy powder and a resin component.
By using compression molding, injection molding, extrusion molding, hydrostatic molding, or the like, the bonded magnet of the present invention exhibiting the above-described effects can be produced.

Since the bonded magnet according to the present invention is remarkably improved in oxidation resistance as compared with the conventional material, the outermost surface of the bonded magnet is coated with an oxidation-resistant protective film as in the prior art. Even without coating, the magnet itself has extremely excellent oxidation resistance, so that the protective coating on the outermost surface may be unnecessary in some cases.

As described above, according to the present invention, the oxidation resistance is remarkably improved as compared with the conventional material, and the magnetic material has good magnetic properties, so that it can be suitably used for various magnet applied products. Examples of the magnet application products include the following products. Various motors such as DC brushless motors and servo motors; various actuators such as drive actuators and F / T actuators for optical big-up; various audio equipment such as speakers, headphones and earphones; various sensors such as rotation sensors and magnetic sensors; Electromagnet replacement products such as; Reed relays, polarized relays and other various relays; Brake, clutches and other magnetic couplings;
Various vibration oscillators such as buzzers and chimes; Various suction devices such as magnet separators and magnet chucks; Various opening and closing control devices such as electromagnetic switches, micro switches, rodless air cylinders; Various micro devices such as optical isolators, klystrons, and magnetrons Wave equipment; magnet generator; health equipment, toys, etc. In addition, such a magnet application product is an example, and is not limited to these.

The characteristics of the bonded magnet according to the present invention are as follows.
Even when used at high environmental temperature, it does not easily rust, and its characteristics are less deteriorated than conventional materials.High magnetic characteristics can be achieved without forming an oxidation-resistant protective coating on the outermost exposed surface of the magnet product unlike conventional materials. Since the magnet itself has excellent oxidation resistance while being held, not only is the separate protective coating unnecessary, but even if a protective coating is needed for special environments, Since there is no rust from the surface, the adhesion is good when the protective film is formed, and the problem of dimensional accuracy due to peeling of the film and fluctuation of the film thickness is eliminated. From this aspect as well, it is possible to provide an optimal bonded magnet for applications requiring oxidation resistance. Examples will be described below.

[0029]

Example 1 As raw materials, electrolytic iron having a purity of 99.9%, ferroboron alloy having a boron content of 19.32%, and neodymium metal having a purity of 98.5% (containing other rare earth metals as impurities) were used as composition ratios (atomic ratios). It was weighed and blended to 20Nd-72Fe-1B, melted in a high-frequency induction furnace in a vacuum, and cast into a water-cooled copper mold to obtain an alloy ingot. The obtained alloy mass in this way is 10-15 mm with a jaw crusher
And then kept at 700 ° C. for 5 hours, then cooled at a rate of 50 ° C./min. Furthermore, this alloy ingot was crushed to -100 mesh using a stamp mill in argon gas.
Carbon black having a purity of 99.5% was further added to the crushed powder so that the (atomic ratio) became 20Nd-72Fe-1B-7C, and then ground using a vibrating mill to an average particle diameter of 5 μm.
The alloy powder obtained in this way is put in a magnetic field of 10 KOe for 1 ton.
After forming at a pressure of / cm ² , it was kept at 1100 ° C. for 2 hours in an argon gas, and then rapidly cooled to obtain a sintered body. The sintered body thus obtained was roughly crushed to −100 mesh using a stamp mill in an argon gas to obtain a magnetic alloy powder. The carbon content of the oxidation-resistant protective film in this magnetic alloy powder is
The thickness of the protective film was 0.012 to 6.3 μm, and the magnetic crystal grain size was 1.3 to 29 μm.

An epoxy resin having a volume ratio of 12% was added to the magnetic alloy powder thus obtained in argon gas,
The mixture is kneaded with a kneader, and the kneaded material is 4 ton / cm ^{2 in a} 20KOe magnetic field.
After heating at 130 ° C. for 1 hour, a bonded magnet was obtained. As Comparative Example 1, the raw materials were the same as in Example 1 except for carbon black, and the composition ratio (atomic ratio)
Was measured and blended so as to be 20Nd-74Fe-6B, and dissolved as in Example 1 (but no carbon black was added).
After obtaining a magnetic alloy powder obtained by crushing, pulverizing, magnetic forming sintering, quenching, and pulverizing, this magnetic alloy powder was kneaded, magnetically formed, and heat-cured in the same manner as in Example 1 to obtain a bonded magnet. The evaluation of the oxidation resistance (weather resistance test) of the bonded magnet obtained in this way was conducted at a constant temperature and humidity of 80 ° C and 90% humidity.
Table 1 shows the demagnetization rates of Br and iHc when left for 96 hours.
It was shown to.

As can be seen from Table 1, the demagnetization rate of the bonded magnet of Example 1 (prepared from the magnetic alloy powder obtained by coating each magnetic crystal grain with the C-containing protective film) according to the present invention after 96 hours. Is extremely small, Br; -1.6%, iHc; -14.1%, and it is recognized that the oxidation resistance is remarkably improved. No rust was observed by microscopic surface observation.

On the other hand, in the bonded magnet of Comparative Example 1 made from the magnetic alloy powder having no C-containing protective film, the rust was so severe that the sample shape was not retained even after leaving for only 96 hours. .

Table 1 also shows the values of Br, iHc and (BH) max measured using a VSM as magnetic properties. It can be seen that the bonded magnet according to the present invention has significantly better oxidation resistance than that of Comparative Example 1, but at the same time has the same or better magnet properties.

[0034]

Examples 2 to 3 Bonded magnets were obtained in the same manner as in Example 1 except that the magnetic alloy powder and the epoxy resin used in Example 1 were mixed so as to have the volume ratio shown in Table 1. The oxidation resistance and magnetic properties of the bond magnet thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

As is clear from Table 1, the bonded magnet according to the present invention has remarkably excellent oxidation resistance as compared with that of Comparative Example 1, and has the same or better magnet properties.

[0036]

Example 4 Electrolytic iron having a purity of 99.9%, ferroboron alloy having a boron content of 19.32%, carbon black having a purity of 99.5%, and neodymium metal having a purity of 98.5% (containing other rare earth metals as impurities) were used as raw materials. The alloy powder was weighed and blended to have a composition ratio (atomic ratio) of 20Nd-72Fe-1B-7C, melted in a high-frequency induction furnace in a vacuum, and adjusted to -100 mesh by an atomizing method to obtain an alloy powder. The alloy powder thus obtained was kept in an argon gas at 700 ° C. for 5 hours, and then cooled at a cooling rate of 50 ° C./min to obtain a magnetic alloy powder. The carbon content of the magnetic powder in the oxidation-resistant protective film is 3.9% by weight. 0.010 protective film thickness
6.56.5 μm, and the magnetic grains were 1.2-32 μm.

The magnetic crystal powder thus obtained was mixed with an epoxy resin having a volume ratio of 12% in argon gas and kneaded with a kneading machine. The kneaded product was formed at 4 ton / cm ² , and then kneaded. It was cured by heating at ℃ 1 hour to obtain a bonded magnet. In Comparative Example 2, the raw materials were the same as in Example 1 except for carbon black, and the composition ratio (atomic ratio) was 20.
After weighing and blending to obtain Nd-74Fe-6B, melting and obtaining a magnetic alloy powder by an atomizing method, the magnetic alloy powder is kneaded, molded and heat-cured in the same manner as in Example 4. A bonded magnet was obtained. The oxidation resistance and magnetic properties of the thus obtained bonded magnet were evaluated in the same manner as in Example 1, and the results are shown in Table 1. As is clear from Table 1, the bonded magnet according to the present invention has remarkably excellent oxidation resistance as compared with that of the comparative example, and has the same or better magnet properties.

[0038]

[Table 1]

Continuing from the front page (72) Inventor Mikio Minato 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Toshio Ueda 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. In-company (72) Inventor Seiichi Kuno 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (56) References JP-A-2-208902 (JP, A) JP-A-2-250303 (JP) , A) JP-A-4-119605 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 1/08 C22C 33/02 H01F 1/053

Claims (3)

(57) [Claims] 1. An atomic percentage of R: 10 to 30% and B: 7% or less.
Bottom (not including 0 atomic%), C: 0.1-20%, balance Fe
And R-Fe-BC composed of unavoidable impurities in production
Alloy powder (where R is at least one of rare earth elements including Y) and the magnetic crystal grains in the alloy powder are
A magnetic alloy powder having a diameter of 1 to 50 μm , each of whose magnetic crystal grains is covered with an oxidation-resistant protective film containing C of 16% by weight or less (not including 0% by weight), and 50% by volume An R-Fe-BC bonded magnet excellent in oxidation resistance comprising the following resin components. Wherein oxidation resistance protective film has a thickness 0.001~30μ
The bonded magnet according to claim 1, which is in a range of m. 3. An oxidation-resistant protective film comprising 0.05 to 16% by weight of C
The bonded magnet according to claim 1 or 2, wherein