JP2023137392A - Composition for bonded magnet, method for manufacturing the same, and bonded magnet - Google Patents

Abstract

To provide a composition for a bonded magnet having excellent fluidity and fully exhibiting the effect of terminal treatment of a polyamide 12 resin, and also provide a method for manufacturing the composition for the bonded magnet, and the bonded magnet.SOLUTION: A composition for a bonded magnet includes a rare earth magnet powder and a polyamide 12 resin, and further includes an end treatment agent having a carbodiimide bond in an amount of 0.3 mass % or more, using a flow tester, the fluidity measured under the conditions of the capillary temperature of 250°C, the load of 588 N, the orifice diameter of 1 mm, the orifice diameter of 1 mm, and a preheating time of 300 seconds is 0.7 cm3/sec or more.SELECTED DRAWING: None

Description

The present invention relates to a composition for a bonded magnet, a method for producing the same, and a bonded magnet.

Bonded magnets are produced by heating and kneading a composition containing magnet powder, a binder component such as an organic resin, and additives such as a reinforcing agent, a plasticizer, and a lubricant using a kneading machine such as an extruder, and then forming it into a pellet or other shape. After being processed so that it becomes, it is manufactured by heat molding using methods such as injection molding, compression molding, or extrusion molding. Such bonded magnets have advantages over sintered magnets in that they have higher dimensional accuracy and are easier to obtain in complex shapes. It also has high uniformity in quality and performance, good yield, and good machinability. In particular, magnets that use thermoplastic resins such as polyamide resin or polyphenylene sulfide resin as the binder resin and are manufactured by injection molding have the advantage of reducing magnet manufacturing costs because they have high dimensional accuracy and do not require post-processing. There is. Further, a bonded magnet containing rare earth magnet powder has excellent magnetic properties (residual magnetic flux density Br, coercive force iHc, and maximum energy product (BH) max) and strong magnetic force. Therefore, it can be made smaller and have higher characteristics, and is useful for applications such as small motors and sensors.

In bonded magnet compositions, polyamide resins, particularly polyamide 12 resins, are often used as binder resins. Polyamide resin has an amide bond, which is a polar functional group, in its molecule, and is likely to adhere to the surface of the magnet powder through interaction. Therefore, it has a high affinity with the magnet powder, and can promote high dispersion and high filling of the magnet powder. Furthermore, polyamide resins, particularly polyamide 12 resins, have relatively low melting points. Therefore, the fluidity of the composition increases in the kneading process and molding process that involve heating, and as a result, it becomes possible to further improve the dispersibility and filling properties of the magnet powder. Furthermore, polyamide 12 resin has low water absorption and excellent cold and thermal shock resistance. Therefore, a bonded magnet with high mechanical strength and low water absorption can be obtained. For example, in Patent Document 1, regarding a bonded magnet made of magnetic powder and resin, it is stated that among polyamides, polyamide 12 is preferable as the resin, and that polyamide has high polarity, so it can be filled with a large amount of magnetic powder. It is stated that since polyamide 12 has a low water absorption rate, a bonded magnet with high magnetic properties and a low water absorption rate can be produced ([0027] of Patent Document 1).

By the way, in a composition for a bonded magnet, the fluidity of the composition may decrease during kneading or molding, making kneading or molding difficult. This is said to be due to the reaction between the functional groups of the binder resin and the components of the magnet powder, especially rare earth metals, due to heating during kneading or molding. That is, the magnet powder component acts as a catalyst and causes a reaction (condensation polymerization reaction, etc.) between the terminal functional groups (carboxyl group, amino group) of the binder resin. When a reaction occurs between the terminal functional groups, the resin becomes polymerized, thereby increasing the viscosity of the composition and reducing its fluidity.

In order to prevent the reaction of the terminal functional groups of the binder resin and the resulting increase in viscosity, the binder resin is treated with a terminal treatment agent in advance, and then the terminal-treated binder resin is kneaded with magnet powder and molded to form a bonded magnet. A manufacturing method has been proposed. It is said that because the functional groups of the binder resin are adjusted (sealed) by the terminal treatment, reaction with the magnet powder and thickening are suppressed, thereby improving the fluidity of the composition.

For example, in Patent Document 2, regarding a resin composition consisting of a polyamide resin and metal powder, the metal powder content can be reduced by using a specific terminal-modified polyamide resin whose terminals are modified with a monocarboxyl hydrocarbon compound. It has been taught that problems such as deterioration of flowability of the melt-kneaded product and increase in melt viscosity when increasing the amount can be solved ([0004] to [0008] of Patent Document 2). Patent Document 2 also describes, in Examples, that a composition consisting of 88 parts by weight of ferrite and 12 parts by weight of terminally modified polyamide resin is prepared, and that when a kneaded material is molded using an injection molding machine, metal It is described that the kneaded melt of powder and polyamide resin has high fluidity and therefore has good moldability even if it contains a large amount of metal powder ([0022] and [0029] of Patent Document 2).

Patent Document 3 discloses a composition used for manufacturing a bonded magnet, which is composed of rare earth magnet particles containing at least Nd-based magnet particles and a bonding resin, wherein the bonding resin has a terminal group consisting of a carboxyl group and an amine group. A bonded magnet composition comprising polyamide 66 (PA66) whose total amount is not more than a predetermined amount is disclosed (Claim 1 of Patent Document 3). Further, Patent Document 3 discloses that at least a part of the carboxyl group and/or amino group at the end of unmodified PA66 is substituted with an unreactive or low-reactivity end group, and as a result, It is stated that even when it comes into contact with rare earth magnet powder particles that act catalytically, it does not exhibit a rapid thickening phenomenon ([0037] of Patent Document 3).

JP2016-72406A Patent No. 3103149 Japanese Patent Application Publication No. 2019-67957

Although techniques for improving the fluidity of compositions by using end-treated binder resins have been proposed in the past, the inventor's research has revealed that there is room for improvement in the conventional techniques. I understand. That is, when attempting to manufacture a bonded magnet using rare earth magnet powder and polyamide 12 resin, even if polyamide 12 resin (binder resin) which has been terminally treated in advance is used, a thickening phenomenon occurs and the desired fluidity is not achieved. It was found that there were cases where molding was difficult.

As a result of further investigation, the present inventor found that it is effective to perform terminal treatment of polyamide 12 resin when kneading it with rare earth magnet powder, rather than using polyamide 12 resin that has been terminally treated in advance. Obtained. That is, by simultaneously kneading rare earth magnet powder, unterminated polyamide 12 resin, and an end treatment agent having a carbodiimide bond, the effect of end treatment of polyamide 12 resin can be fully exhibited, and as a result, the flowability The inventors have found that it is possible to obtain a composition for bonded magnets with excellent properties.

The present invention was completed based on such knowledge, and an object of the present invention is to provide a composition for a bonded magnet with excellent fluidity, in which the effect of terminal treatment of polyamide 12 resin is fully exhibited. Another object of the present invention is to provide a method for producing the composition for a bonded magnet, and a bonded magnet.

The present invention includes the following aspects (1) to (8). Note that in this specification, the expression "~" includes values at both ends thereof. That is, "X to Y" is synonymous with "more than or equal to X and less than or equal to Y."

(1) Contains rare earth magnet powder and polyamide 12 resin, and further contains a terminal treatment agent having a carbodiimide bond in an amount of 0.3% by mass or more,
A bonded magnet composition having a fluidity of 0.7 cm ³ /sec or more when measured using a flow tester under the conditions of capillary temperature of 250° C., load of 588 N, orifice diameter of 1 mm, orifice length of 1 mm, and preheating time of 300 seconds. .

(2) The bonded magnet composition according to (1) above, which contains the terminal treatment agent in an amount of 0.5% by mass or more and 0.9% or less.

(3) The composition for a bonded magnet according to (1) or (2) above, wherein the fluidity is 2.0 cm ³ /sec or more.

(4) The rare earth magnet powder is samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder with an average particle size of 1.8 μm or more and 2.8 μm or less, and The bonded magnet composition according to any one of (1) to (3) above, wherein the content of magnet powder is 88% by mass or more and 92% by mass or less.

(5) The bonded magnet composition according to any one of (1) to (4) above, which contains the rare earth magnet powder, the polyamide 12 resin, and the terminal treatment agent, and has a composition in which the remainder is unavoidable impurities.

(6) A method for producing a composition for a bonded magnet, comprising a step of simultaneously kneading rare earth magnet powder, polyamide 12 resin, and a terminal treatment agent having a carbodiimide bond,
A method, wherein the content of the terminal treatment agent in the bonded magnet composition is 0.3% by mass or more.

(7) The magnet powder is samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder with an average particle size of 1.8 μm or more and 2.8 μm or less, and the magnet in the bonded magnet composition The method according to (6) above, wherein the content of the powder is 88% by mass or more and 92% by mass or less.

(8) A bonded magnet that is a molded article of the bonded magnet composition according to any one of (1) to (5) above.

According to the present invention, a composition for a bonded magnet with excellent fluidity, in which the effect of terminal treatment of polyamide 12 resin is fully exhibited, is provided. Also provided are a method for producing the composition for a bonded magnet, and a bonded magnet.

A specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. Note that the present invention is not limited to the following embodiments, and various changes can be made without departing from the gist of the present invention.

<<1. Composition for bonded magnets >>
The bonded magnet composition (hereinafter sometimes simply referred to as "composition") of the present embodiment contains rare earth magnet powder and polyamide 12 resin, and further contains 0.3 mass of a terminal treatment agent having a carbodiimide bond. Contained in an amount of % or more. In addition, this bonded magnet composition has a fluidity of 0.7 cm ³ /sec when measured using a flow tester under the conditions of capillary temperature of 250° C., load of 588 N, orifice diameter of 1 mm, orifice length of 1 mm, and preheating time of 300 seconds. That's all.

The bonded magnet composition is a precursor of a bonded magnet (hereinafter sometimes simply referred to as a "bonded magnet"). That is, a bonded magnet is produced by molding the composition under heat using a technique such as injection molding or extrusion molding. Bonded magnets may be anisotropic or may be isotropic. An anisotropic magnet can be produced by applying a magnetic field to the composition during molding, and an isotropic magnet can be obtained by not applying a magnetic field.

[Magnet powder]
The bonded magnet composition of this embodiment includes rare earth magnet powder (hereinafter, sometimes simply referred to as "magnet powder"). Rare earth magnet powder is a powder that is made of a hard magnetic material and is the main component of the magnetic properties of a bonded magnet. The rare earth magnet powder is not particularly limited as long as it is made of rare earth hard magnetic material. For example, neodymium (Nd)-iron (Fe)-boron (B) based magnet powder whose basic composition _is Nd 2 Fe ₁₄ B, samarium (Sm)-iron (Fe) whose basic composition is Sm ₂ Fe ₁₇ N _x - Nitrogen (N)-based magnet powder, samarium (Sm)-cobalt (Co)-based magnet powder whose basic composition is SmCo ₅ or Sm ₂ Co ₁₇ . Further, some of the elements in these basic compositions may be replaced with other elements. For example, neodymium (Nd) or samarium (Sm) is partially replaced with lanthanum (La), cerium (Ce), praseodymium (Pr), terbium (Tb), and/or dysprosium (Dy), Good too. In addition, some of iron (Fe) and cobalt (Co) are cobalt (Co), iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), zirconium (Zr), and/or hafnium ( Hf) may be substituted.

The bonded magnet composition may contain only one type of magnet powder, or may contain a combination of multiple types of magnet powder. Further, the magnetic powder contained may be a magnetic powder alone, or may be a powder composited with other materials. For example, it may be a magnet powder whose surface is provided with a coating layer made of a treatment agent such as a phosphoric acid compound, a silica compound, and/or a triazinethiol derivative.

Preferably, the rare earth magnet powder is samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder. Samarium-iron-nitrogen magnets whose basic composition is Sm ₂ Fe ₁₇ N _x are known as high-performance and inexpensive magnets. Specifically, the samarium-iron-nitrogen magnet has a maximum saturation magnetization when x=3, that is, when the composition is Sm ₂ Fe ₁₇ N ₃ . Therefore, it is possible to increase the magnetic flux density of the obtained bonded magnet. It also has a high coercive force, about five times that of neodymium-iron-boron magnet powder.

Preferably, the average particle size of the rare earth magnet powder is 0.5 μm or more and 5.0 μm or less. Magnet powder with an excessively large particle size has a small coercive force. In addition, the fluidity of the composition may decrease, or the dimensional stability and surface properties of the resulting bonded magnet may deteriorate. On the other hand, if the particle size of the magnet powder is too small, the viscosity of the composition increases and fluidity deteriorates. In addition, rare earth magnet powder is oxidized and its characteristics deteriorate, and in some cases, there is a risk of ignition due to heat generated by oxidation. By appropriately increasing the particle size, it is possible to improve fluidity and avoid heat generation. The average particle size of the magnet powder is more preferably 1.0 μm or more and 3.0 μm or less, and even more preferably 1.8 μm or more and 2.8 μm or less.

Preferably, the content of magnet powder in the composition is 80% by mass or more and 95% by mass or less. If the amount of magnet powder, which is the main factor responsible for the development of magnetic properties, is too small, the magnetic properties of the bonded magnet, particularly the magnetic flux density, will be low. Furthermore, since the amount of binder resin increases, the linear expansion coefficient of the bonded magnet increases, and as a result, the adhesive force may become weak in applications where the bonded magnet is bonded to an iron yoke. On the other hand, if the amount of magnet powder is too large, the fluidity of the composition may decrease and molding may become difficult. The content of the magnet powder is more preferably 85% by mass or more and 93% by mass or less, and even more preferably 88% by mass or more and 92% by mass or less.

Particularly preferably, the magnet powder is samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder with an average particle size of 1.8 μm or more and 2.8 μm or less, and the magnet powder in the bonded magnet composition is The content is 88% by mass or more and 92% by mass or less. Since samarium-iron-nitrogen magnet powder has a nucleation-type coercive force generation mechanism, by limiting the average particle size to 2.8 μm or less, the coercive force can be further increased. Therefore, it is useful for applications such as motors, which are used in environments where a strong demagnetizing field is applied. In addition, by limiting the average particle size to 1.8 μm or more, it is possible to further improve the fluidity during molding of the composition, and to effectively prevent the problems of heat generation and ignition caused by oxidation of the magnet powder. becomes possible.

As methods for producing samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder, methods such as a dissolution method and a reduction diffusion method are known. In the melting method, metal powder containing iron and samarium is used as a raw material, and this raw material is heated and melted at a temperature of 1500° C. or higher using a furnace such as a high frequency furnace or an arc furnace. Next, the obtained product is pulverized and further heat-treated to make the composition uniform to produce an Sm--Fe master alloy. Thereafter, the obtained master alloy is nitrided to produce magnet powder. On the other hand, in the reduction diffusion method, a master alloy is obtained by heating a mixture of samarium oxide (Sm ₂ O ₃ ), iron raw materials (Fe, Fe ₂ O _3, etc.), and reducing agents (Ca, etc.). The master alloy is nitrided to produce magnet powder. Since samarium-iron-nitrogen magnet powder has a nucleation-type coercive force generation mechanism, it is desirable to make it fine in order to obtain a high coercive force. Therefore, methods are used in which the nitrided master alloy is finely pulverized or fine raw materials are used.

Preferably, the samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder produced by a reduction diffusion method is used. The reduction diffusion method using inexpensive oxide raw materials (such as Sm ₂ O ₃ ) has the characteristic of suppressing raw material costs. Furthermore, magnet powder with a smaller amount of impurities can be obtained compared to the melting method. On the other hand, the dissolution method requires extremely complicated steps. Furthermore, since the product is once exposed to the atmosphere between each step, there is a risk that impurities may be generated on the surface of the product due to oxidation. When the product surface is oxidized, nitriding does not proceed uniformly, and as a result, the properties of the obtained magnetic powder, especially the magnetic properties such as saturation magnetization, coercive force, and/or squareness, deteriorate, and the final result is This may reduce the maximum energy product of the bonded magnet.

In the reduction diffusion method, a samarium raw material (Sm ₂ O ₃ ), an iron raw material (such as Fe), and a reducing agent (such as Ca) are first subjected to a reduction treatment to obtain a reduction product containing an Sm--Fe alloy. Next, this reduction product is wet-treated to remove by-products (CaO, Ca(OH) ₂ , etc.) derived from the reducing agent contained in the reduction product, and then the obtained Sm-Fe alloy is , nitriding in a mixed stream containing ammonia and hydrogen. By crushing and drying the obtained nitride, samarium-iron-nitrogen magnet powder can be obtained.

When the samarium (Sm)-iron (Fe)-nitrogen (N) based magnet powder is composed of an Sm ₂ Fe ₁₇ N ₃ based alloy, it is desirable to crush the coarse powder. That is, since magnetic alloy coarse powder with an average particle size exceeding 20 μm has low magnetic properties, it is desirable to grind it in an organic solvent. During or after this pulverization, the magnet powder may be poured into a solution containing a surface treatment agent such as phosphoric acid and stirred to form a magnet powder with a coating such as a composite phosphate coating on the surface. For pulverization, a known pulverizer applicable to magnetic powder pulverization may be used. Among these, wet grinding devices such as a media agitation mill and a bead mill are particularly suitable because they are easy to obtain a uniform powder composition and particle size. Further, as the grinding solvent, organic solvents such as isopropyl alcohol, ethanol, toluene, methanol, and hexane are preferable. After pulverization, it may be filtered and dried using a filter with a predetermined mesh size. In this way, samarium-iron-nitrogen magnet powder can be obtained.

[Polyamide 12 resin]
The bonded magnet composition of this embodiment contains polyamide 12 resin as a binder resin. Polyamide 12 resin is a thermoplastic resin. Thermoplastic resin becomes plasticized by heating during molding and becomes fluid, and when cooled after molding, it solidifies and improves strength. Therefore, by using a thermoplastic resin and further performing molding involving heating such as injection molding or extrusion molding, it becomes possible to easily obtain a bonded magnet with high strength and a complex shape. In particular, since polyamide 12 resin has a low melting point, it is possible to further improve the dispersibility and filling properties of the magnet powder. This improves the moldability of the composition and makes it possible to produce a bonded magnet with excellent magnetic properties. Polyamide 12 resin also has a feature of low water absorption.

The shape of the binder resin (polyamide 12 resin) is not particularly limited. Various shapes such as powder, beads, and pellets can be used. Among these, a powdery binder resin that can be mixed uniformly with the magnet powder is particularly preferred.

Preferably, the content of the binder resin (polyamide 12 resin) in the bonded magnet composition is 7.1% by mass or more and 11.7% by mass or less. If the amount of binder resin is too small, the fluidity of the composition may decrease and molding may become difficult. On the other hand, if the amount of binder resin is too large, the proportion of magnet powder in the bonded magnet decreases, which may deteriorate the magnetic properties of the bonded magnet. Furthermore, since the linear expansion coefficient of the bonded magnet becomes large, cracks may occur during a thermal shock test. The content of the binder resin is more preferably 7.1% by mass or more and 11.5% by mass or less.

[Terminal treatment agent]
The bonded magnet composition of this embodiment contains a terminal treatment agent having a carbodiimide bond in an amount of 0.3% by mass or more. The terminal treatment agent has the effect of preventing thickening of the bonded magnet composition and improving fluidity. That is, the polyamide 12 resin contained in the bonded magnet composition has a carboxyl group or an amino group as a terminal functional group. In a composition that does not contain a terminal treatment agent, reactions between functional groups (degeneracy reaction, etc.) proceed due to the action of the rare earth magnet powder component contained therein, and the resin tends to polymerize. If the resin has a high molecular weight, the composition may increase in viscosity. On the other hand, when the terminal treatment agent is added in a highly dispersed state, the reaction between the resin and the rare earth magnet component and the reaction between the functional groups are suppressed, and as a result, the thickening of the composition is suppressed and the fluidity is improved. It becomes possible to improve the This is because the terminal treatment agent has the function of adjusting, sealing, and deactivating the terminal functional groups (carboxyl group, amino group) of the resin.

In order to fully exhibit the effect of the terminal treatment agent, it is important to uniformly disperse the terminal treatment agent in the composition. If the terminal treatment agent is not uniformly dispersed, the adjustment (sealing) of the terminal functional groups will be insufficient, making it difficult to suppress the reaction between the functional groups and thereby achieve the sufficient effect of improving fluidity. Become. In order to uniformly disperse the end treatment agent, it is effective to perform the end treatment of the polyamide 12 resin during the kneading stage with the rare earth magnet powder when producing the composition.

In this embodiment, a compound having a carbodiimide bond is used as the terminal treatment agent. Since a terminal treatment agent having a carbodiimide bond has high reactivity, terminal treatment is possible even at low temperatures. Since treatment at high temperatures is not required, damage to the magnet powder, specifically deterioration of magnetic properties, can be minimized. The type of carbodiimide compound serving as the terminal treatment agent is not particularly limited. For example, dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, bis(2,6-diisopropylphenyl)carbodiimide, di-t-butylcarbodiimide, and/or di-β -Naphthylcarbodiimide.

In this embodiment, the content of the terminal treatment agent in the composition is limited to 0.3% by mass or more. If the content is less than 0.3% by mass, the effect of terminal adjustment will be insufficient, and the effect of preventing thickening and improving fluidity of the composition will be insufficient. The content of the terminal treatment agent is preferably 0.5% by mass or more and 0.9% by mass or less.

[Liquidity]
The bonded magnet composition of this embodiment has good fluidity because the thickening phenomenon is suppressed. Specifically, the fluidity is 0.7 cm ³ /second or more when measured using a flow tester under the conditions of capillary temperature of 250° C., load of 588 N, orifice diameter of 1 mm, orifice length of 1 mm, and preheating time of 300 seconds. By increasing fluidity, moldability can be improved. Therefore, bonded magnets with a thin shape or a complicated shape can be easily obtained without any post-processing. Furthermore, the amount of magnet powder in the composition can be increased while maintaining a highly dispersed state, and even if the content remains the same, the orientation of the magnet powder can be improved. Furthermore, there is no need to perform molding at high temperatures to increase fluidity. Since low-temperature molding becomes possible, deterioration of the magnetic properties of the magnet powder can be suppressed. These factors act in combination, making it possible to manufacture bonded magnets, especially anisotropic bonded magnets, having excellent magnetic properties. The higher the fluidity, the more desirable it is, and preferably 2.0 cm ³ /g or more. On the other hand, compositions with excessively high fluidity are difficult to produce. The flowability is typically 4.0 cm ³ /sec or less.

[Amine value]
In the bonded magnet composition of this embodiment, the amino group as the terminal functional group of the polyamide 12 resin is effectively adjusted (sealed). Therefore, the amine value of the resin in the composition is relatively low. By reducing the amine value, reactions between functional groups and the resulting thickening can be more effectively prevented, and the fluidity of the composition can be increased. The amine value of the composition is preferably 1.0 or less, more preferably 0.4 or less.

[Other ingredients]
The bonded magnet composition of this embodiment may be composed only of the above-mentioned components (magnet powder, polyamide 12 resin, and terminal treatment agent). For example, it may contain a rare earth magnet powder, a polyamide 12 resin, and a terminal treatment agent, with the remainder being unavoidable impurities. Alternatively, components other than the above-mentioned components may be included as long as they have the desired fluidity. Such ingredients include, but are not limited to, toughening agents, stabilizers, and/or compatibilizers. Among these, the reinforcing agent is a reinforcing component such as carbon fiber, carbon flake, and/or glass fiber. By adding a reinforcing agent, the tensile strength of the bonded magnet can be effectively increased.

<<2. Manufacturing method of composition for bonded magnet >>
The method for producing a bonded magnet composition of the present embodiment includes a step of simultaneously kneading rare earth magnet powder, polyamide 12 resin, and a terminal treatment agent having a carbodiimide bond. The kneading is carried out under heating so that the polyamide 12 resin is melted. Further, the content of the terminal treatment agent in the bonded magnet composition is limited to 0.3% by mass or more.

Details of the rare earth magnet powder, polyamide 12 resin, and terminal treatment agent having a carbodiimide bond are as described above. In other words, the rare earth magnet powder is the powder that mainly causes the magnetic properties of the bonded magnet to be expressed. Further, by using polyamide 12 resin as the binder resin, it is possible to highly fill the magnet powder while maintaining a highly dispersed state. Furthermore, the terminal treatment agent has the effect of preventing thickening of the bonded magnet composition and improving fluidity.

In the manufacturing method of this embodiment, it is important to heat and knead the above-mentioned raw materials (rare earth magnet powder, polyamide 12 resin) and terminal treatment agent at the same time. This allows the terminal treatment agent to be uniformly dispersed in the composition, thereby making it possible to fully exhibit the effects of preventing thickening and improving fluidity of the composition. It is believed that this is because kneading with the magnet powder increases the kneading torque applied to the composition, and the end treatment agent is uniformly dispersed. On the other hand, a method can be considered in which the binder resin and the terminal treatment agent are kneaded in advance, the binder resin is terminally treated, and the obtained treated binder resin is kneaded with the magnet powder. In such a method, the end blocking agent cannot be uniformly dispersed, and there is a limit to the effect of improving the fluidity of the composition.

As the kneading device, a batch type kneader or a continuous extruder (continuous extruder) can be used. The kneading is performed in a kneading device while controlling the shear force applied to the composition. For example, when using a kneader, the amount of raw materials charged into the mixing tank, the temperature of the composition during kneading, the rotation speed of the kneading blade, and/or the kneading time are controlled. In addition, when using a continuous extruder, conditions such as feed rate of raw materials, temperature distribution, shape of screw segments, screw rotation speed, and/or die hole diameter are adjusted. Further, the kneading temperature may be any temperature as long as the polyamide 12 resin melts and does not decompose. The temperature is preferably 180°C or more and 270°C or less, more preferably 190°C or more and 240°C or less.

<<3. Bonded magnet >>
The bonded magnet of this embodiment (hereinafter sometimes simply referred to as "bond magnet") is a molded body of a bonded magnet composition. This bonded magnet is manufactured by injection molding or extrusion molding a bonded magnet composition under heating. That is, the bonded magnet is an injection molded product or an extrusion molded product. Specifically, a composition for a bonded magnet is heated and melted at a temperature higher than the melting point of the binder resin contained therein to form a molten product, and then the molten product is molded by injection molding or extrusion molding to form a molded product (bond magnet ) can be obtained. If a magnetic field is applied to the melt during molding, an anisotropic bonded magnet can be obtained, and if no magnetic field is applied, an isotropic bonded magnet can be obtained.

Preferably, the bonded magnet is an injection molded body. That is, a molded article is produced by injection molding the bonded magnet composition. By employing the injection molding method, it is possible to increase the degree of freedom in the shape of the bonded magnet, which is a molded product, and to improve the dimensional accuracy. Moreover, the bonded magnet has excellent surface properties and magnetic properties. Therefore, the molded body (bond magnet) after molding can be incorporated into an electronic component as it is without any post-processing. In particular, the bonded magnet composition of this embodiment has good fluidity. Therefore, the moldability during injection molding is excellent, and appearance defects such as welds can be effectively prevented from occurring.

Since the bonded magnet of this embodiment uses a composition with excellent fluidity and moldability as a precursor, it has excellent magnetic properties and can be made thinner and more complex in shape. Further, no post-processing is required, and insert molding is possible. Therefore, this bonded magnet is suitable for small, flat, complex-shaped parts, such as motor parts for electronic devices, for example.

Note that it is desirable to magnetize the bonded magnet before use. For magnetization, a magnetizing device such as an electromagnet that generates a static magnetic field or a capacitor magnetizer that generates a pulsed magnetic field is used. The strength of the magnetizing magnetic field varies depending on the type of magnet powder, so it cannot be determined unconditionally. For example, it may be 1200 kA/m (15 kOe) or more, or 2400 kA/m (30 kOe) or more.

The present invention will be explained in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples.

(1) Production of bonded magnet composition and bonded magnet [Example 1]
Samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder (manufactured by Sumitomo Metal Mining Co., Ltd.) with an average particle size of 2.3 μm was used as the rare earth magnet powder, and polyamide 12 resin (Ube Industries, Ltd.) was used as the binder resin. (P3012U, amine value: 3.6 mgKOH/g) were prepared. Next, a blended composition of 88.5% by mass of magnet powder (Sm-Fe-N-based magnet powder), 10.8% by mass of polyamide 12 resin, and 0.7% by mass of terminal regulator having a carbodiimide bond was obtained. The raw materials were blended so that the resulting mixture was simultaneously kneaded at 200° C. for 10 minutes using a batch kneader. In this way, a composition for bonded magnets was obtained.

Next, the obtained composition was injection molded using an injection molding machine and an injection mold, and a test piece (cylindrical shape with an outer diameter of 20 mm and a thickness of 13 mm) conforming to JIS K7139A was produced as a bonded magnet. At this time, the molding was performed so that the thickness direction of the test piece was in the orientation direction of the magnet powder.

[Example 2]
During the kneading, a continuous extruder was used instead of a batch kneader, and the kneading was carried out at a barrel temperature of 200°C. Other than that, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[Example 3]
A blending composition of magnet powder (Sm-Fe-N magnet powder): 91.5% by mass, polyamide 12 resin: 8.0% by mass, and terminal regulator having a carbodiimide bond: 0.5% by mass was obtained. It was blended into. Other than that, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[Comparative example 1]
In the composition of Example 1, the polyamide 12 resin and the end treatment agent were kneaded in advance at 200° C. for 10 minutes using a batch kneader, and the resulting kneaded product was pulverized. Thereafter, the obtained kneaded product and magnet powder were kneaded under the same conditions as in Example 1 to produce a bonded magnet composition. Other than that, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[Comparative example 2]
In the blended composition of Example 1, no terminal regulator was added, and the blended amount of polyamide 12 resin was increased by its mass (0.7% by mass). Other than that, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[Comparative example 3]
In the blending composition of Example 1, the blending amount of the terminal regulator was reduced by 0.5% by mass, and the blending amount of polyamide 12 resin was increased by the same mass (0.5% by mass). Other than that, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

[Comparative example 4]
In the blended composition of Example 3, no terminal regulator was added, and the blended amount of polyamide 12 resin was increased by its mass (0.5% by mass). Other than that, a bonded magnet composition and a bonded magnet were produced in the same manner as in Example 1.

(2) Evaluation Various properties of the bonded magnet compositions and bonded magnets obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated as follows.

<Magnetic properties>
The bonded magnet was magnetized using a pulse magnetizer with a magnetizing magnetic field of 3000 kA/m or more. The magnetic properties (residual magnetic flux density Br, coercive force iHc, and energy product (BH) max) of the bonded magnet after magnetization were measured using a BH tracer.

<Liquidity>
The fluidity of the bonded magnet composition was measured using a flow tester (Shimadzu Corporation, CFT-100D). The measurement was performed under the following conditions: capillary temperature of 250° C., load of 588 N, orifice diameter of 1 mm, orifice length of 1 mm, and preheating time of 300 seconds.

<Amine value>
The amine values of the polyamide 12 resin and the bonded magnet composition were measured according to the potentiometric titration method specified in JIS K7237. Specifically, a sample was dissolved in m-cresol and titrated with a perchloric acid methanol solution.

(3) Evaluation results The evaluation results are summarized in Tables 1 and 2.

In the bonded magnet composition of Comparative Example 1, it was not possible to obtain a composition with excellent fluidity. It is presumed that due to the pre-blending, the end treatment of the polyamide 12 resin was not sufficiently performed. Therefore, it is thought that a reaction occurred between the amide group at the end of the polyamide 12 resin and the rare earth magnet powder, and as a result, a thickening phenomenon occurred.

In the bonded magnet composition of Comparative Example 2, it was not possible to obtain a composition with excellent fluidity. It is considered that the thickening phenomenon occurred as a result of a reaction between the amide group at the end of polyamide 12 and the rare earth magnet powder because no end treatment agent was included.

In the bonded magnet composition of Comparative Example 3, it was not possible to obtain a composition with excellent fluidity. It is thought that because the amount of the end treatment agent was too small, a reaction between the amide group at the end of polyamide 12 and the rare earth magnet powder was caused, resulting in a thickening phenomenon.

The bonded magnet composition of Comparative Example 4 could not be kneaded and a composition with excellent filling properties could not be obtained. Moreover, molding could not be performed, and a bonded magnet could not be produced. It is thought that because no end treatment was performed, the reaction between the amide group at the end of polyamide 12 and the rare earth magnet powder progressed, resulting in a strong thickening phenomenon.

On the other hand, in Examples 1 to 3, bonded magnet compositions with high fluidity could be obtained. In particular, in Example 3, a composition with sufficient fluidity could be obtained despite the high proportion of magnet powder. Further, in Examples 1 and 2 in which the proportion of magnet powder was low, the fluidity was even better. In all Examples, the bonded magnets had sufficient magnetic properties.

The bonded magnet compositions of Examples 1 to 3 have amine values (0.22 to 0.28 mgKOH/g) that are significantly higher than those of Comparative Examples 1 to 3 (1.7 to 1.8 mgKOH/g). It was decreasing. It is considered that the terminal amino groups of the polyamide 12 resin were effectively adjusted (sealed) by kneading the terminal treatment agent with the magnet powder and the polyamide 12 resin at the same time.

Claims (8)

Contains rare earth magnet powder and polyamide 12 resin, and further contains a terminal treatment agent having a carbodiimide bond in an amount of 0.3% by mass or more,
A bonded magnet composition having a fluidity of 0.7 cm ³ /sec or more when measured using a flow tester under the conditions of capillary temperature of 250° C., load of 588 N, orifice diameter of 1 mm, orifice length of 1 mm, and preheating time of 300 seconds. . The bonded magnet composition according to claim 1, comprising the terminal treatment agent in an amount of 0.5% by mass or more and 0.9% by mass or less. The bonded magnet composition according to claim 1 or 2, wherein the fluidity is 2.0 cm ³ /sec or more. The rare earth magnet powder is samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder with an average particle size of 1.8 μm or more and 2.8 μm or less, and the magnet powder in the bonded magnet composition is The composition for a bonded magnet according to any one of claims 1 to 3, having a content of 88% by mass or more and 92% by mass or less. The composition for a bonded magnet according to any one of claims 1 to 4, comprising the rare earth magnet powder, the polyamide 12 resin, and the terminal treatment agent, with the remainder being unavoidable impurities. A method for producing a composition for a bonded magnet, comprising a step of simultaneously kneading rare earth magnet powder, polyamide 12 resin, and a terminal treatment agent having a carbodiimide bond,
A method, wherein the content of the terminal treatment agent in the bonded magnet composition is 0.3% by mass or more. The magnet powder is samarium (Sm)-iron (Fe)-nitrogen (N)-based magnet powder with an average particle size of 1.8 μm or more and 2.8 μm or less, and the magnet powder is contained in the bonded magnet composition. 7. The method according to claim 6, wherein the amount is 88% by weight or more and 92% by weight or less. A bonded magnet that is a molded article of the bonded magnet composition according to any one of claims 1 to 5.