JP6393737B2 - Rare earth bonded magnet - Google Patents

Description

  The present invention relates to a rare earth bonded magnet.

  In recent years, rare earth permanent magnets have excellent magnetic properties, and thus have been applied in a wide range of fields such as rotating devices such as motors, general home appliances, acoustic devices, medical devices, and general industrial devices. In particular, rare earth bonded magnets, which are a combination of powdered rare earth magnet materials and a resin (binding resin) that binds the powder, take advantage of the high degree of freedom in shape, and can be used to reduce the size and performance of the above equipment. Contributing.

  Further, rare earth bonded magnets are remarkable for use in the field of vehicles typified by automobiles (hereinafter simply referred to as “vehicles”). In conventional in-vehicle permanent magnets, ferrite permanent magnets have been used. This is because ferrite permanent magnets have excellent heat resistance and the like. However, since the ferrite permanent magnet has a relatively weak spontaneous magnetization or magnetic force, there is a problem that the magnet volume becomes large in order to obtain a necessary magnetic flux. In view of the demand for higher output and smaller size, the use of rare earth magnets with high spontaneous magnetization is increasing year by year instead of ferrite permanent magnets.

Japanese Patent Laying-Open No. 2015-8232

  Such a vehicle-mounted permanent magnet is required to have sufficient magnetic characteristics over a wide range of temperature environments because a vehicle such as an automobile is driven in various environments. That is, in-vehicle permanent magnets are required to have low demagnetization characteristics and physical heat resistance against temperature changes. Here, in this specification, the physical heat resistance means heat resistance related to mechanical strength. In general, rare earth permanent magnets have a large demagnetization characteristic at high temperatures, so-called thermal demagnetization. Against this background, attempts have been made to produce rare earth magnets and rare earth magnets whose magnetic properties do not easily deteriorate even at high temperatures (see, for example, Patent Document 1).

  The present invention has been made in view of the above, and an object of the present invention is to provide a rare-earth bonded magnet having a small demagnetization characteristic with respect to a temperature change and a high physical heat resistance.

In order to solve the above-described problems and achieve the object, a rare earth bonded magnet according to one aspect of the present invention includes a rare earth-iron-based magnet powder and a thermosetting resin composition, and the thermosetting The resin composition comprises, as a main component, a dicyclopentadiene-type epoxy resin represented by the following chemical formula (1) and having a structure in which the average value of the repeating unit n is 1 to 3, and dicyandiamide as a curing agent. It is characterized by becoming.

  The rare earth bonded magnet according to an aspect of the present invention is a dicyclopentadiene type epoxy resin having the above structure in which the repeating unit n is 1 among the dicyclopentadiene type epoxy resins blended in the thermosetting resin composition. % Or more.

  The rare earth bonded magnet which concerns on 1 aspect of this invention is characterized by including 1-3 mass% of the said thermosetting resin compositions.

  In the rare earth bonded magnet according to an aspect of the present invention, the magnet powder is mainly composed of neodymium, iron, and boron.

  According to the present invention, it is possible to realize a rare-earth bonded magnet having a small demagnetization characteristic against temperature change and high physical heat resistance.

FIG. 1 is a diagram showing thermal demagnetization rates of rare-earth bonded magnets of Examples and Comparative Examples. FIG. 2 is a diagram showing the rate of change in dimensions when a thermomechanical analysis is performed on the rare-earth bonded magnets of Examples and Comparative Examples. FIG. 3 is a diagram showing the relationship between the thermal expansion coefficient, the thermal demagnetization factor, and the crushing strength of the rare-earth bonded magnets of Examples and Comparative Examples.

  Embodiments of a rare earth bonded magnet according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

(Embodiment)
The present inventors have scrutinized the cause of the occurrence of thermal demagnetization in rare earth bonded magnets. As a result, the dimensional change with respect to temperature change is large, that is, the rare earth bonded magnet with a high coefficient of thermal expansion has large thermal demagnetization. I found The reason is considered to be that rare earth bonded magnets with a high coefficient of thermal expansion generate voids inside when the temperature rises, and the magnet powder that comes into contact with the air present in the voids is oxidized and deteriorated.
Therefore, when a thermosetting composition having a low coefficient of thermal expansion is used as a binder for bonding magnet powders, it is considered that the thermal demagnetization factor is reduced. It has also been discovered that when a resin composition is used, practically sufficient crushing strength cannot be obtained, and physical heat resistance may be low. Therefore, the present inventors have intensively studied to realize a low demagnetization property against temperature change and high physical heat resistance, and have found a thermosetting resin composition capable of realizing this.

That is, a rare earth bonded magnet according to an embodiment of the present invention includes a rare earth-iron-based magnet powder and a thermosetting resin composition, and the thermosetting resin composition has the following chemical formula (1) as a main agent. The dicyclopentadiene type epoxy resin containing the structure where the average value of the repeating unit n is 1-3, and the dicyandiamide which is a hardening | curing agent are mix | blended.

Dicyandiamide is represented by the following chemical formula (2).

熱硬化性樹脂組成物の主剤として、分子量が比較的小さく、繰り返し単位ｎの平均値が１〜３の上記構造を含むジシクロペンタジエン型エポキシ樹脂を用いることにより、これをバインダーとして用いた希土類ボンド磁石の熱膨張率を好適に小さくすることができる。さらに、この主剤に対してジシアンジアミドを硬化剤として使用することで、実用上十分高い圧環強度を持ち、高い物理的耐熱性を有する希土類ボンド磁石を実現することができる。なお、ジシアンジアミドを硬化剤として使用することで高い圧環強度が得られる理由は、ジシクロペンタジエン型エポキシ樹脂との反応性が良好であり、高い圧環強度を得るために好適なためであると考えられる。 In addition, as a dicyclopentadiene type | mold epoxy resin represented by Chemical formula (1) and including the structure whose average value of the repeating unit n is 1-3, in the following Chemical formula (3), the repeating unit m is 0-2. There is something that is.

A rare earth bond using a dicyclopentadiene type epoxy resin containing the above structure having a relatively low molecular weight and an average value of 1 to 3 as the main component of the thermosetting resin composition, and using this as a binder The coefficient of thermal expansion of the magnet can be suitably reduced. Furthermore, by using dicyandiamide as a curing agent for this main material, a rare earth bonded magnet having practically sufficiently high crushing strength and high physical heat resistance can be realized. The reason why a high crushing strength can be obtained by using dicyandiamide as a curing agent is considered to be because the reactivity with the dicyclopentadiene type epoxy resin is good and suitable for obtaining a high crushing strength. .

  The repeating unit n of the above structure contained in the dicyclopentadiene type epoxy resin blended in the thermosetting resin composition has an average value in the range of 1 to 3, preferably in the range of 1 to 2, and the repeating unit n May contain a dicyclopentadiene type epoxy resin containing a structure larger than 1. Moreover, it is preferable that the ratio of the dicyclopentadiene type epoxy resin of the said structure whose repeating unit n is 1 among the dicyclopentadiene type epoxy resins mix | blended with a thermosetting resin composition is 70% or more. It is most preferable that the repeating unit n of all dicyclopentadiene type epoxy resins blended in the thermosetting resin composition is 1.

  The rare earth-iron-based magnet powder is not particularly limited, but Nd-Fe-B-based magnet powder mainly composed of neodymium (Nd), iron (Fe), and boron (B) is used. preferable. The mass ratio between the magnet powder and the thermosetting resin composition is preferably about 100: 1 to 100: 3 (that is, the rare earth bonded magnet contains 1 to 3 mass% of the thermosetting resin composition). .

The rare earth bonded magnet according to the present embodiment can be manufactured as follows, for example.
First, the rare earth-iron magnet powder is pulverized. Here, the particle size range of the rare earth-iron-based magnet powder is preferably 30 μm to 500 μm, and more preferably 50 μm to 250 μm. If the particle size of the magnet powder is 30 μm or more, the specific surface area of the magnet powder becomes small, so that the probability that the magnet powder itself is oxidized becomes low. A magnet powder having a particle size smaller than 500 μm is also suitable when compression molding a ring magnet having a thickness of less than 1 mm. In addition, in order to obtain good formability at the time of molding, which is a subsequent process, it is desirable that the width of the particle size distribution of the rare earth magnet powder is narrow.

  Subsequently, the rare earth-iron-based magnet powder and the thermosetting resin composition solution are kneaded. The solution of the thermosetting resin composition is obtained by mixing a dicyclopentadiene type epoxy resin as a main agent and dicyandiamide as a curing agent in a predetermined mass ratio and dissolving them in a solvent. The kneaded material generated by the kneading is called a compound.

  Next, dry the compound. This drying process is for volatilizing the solvent contained in the solution of the thermosetting resin composition.

  Subsequently, the dried compound is crushed and the particle size of the compound is classified. The particle size range of the compound is desirably about 30 to 500 μm, for example, in consideration of the filling property into a mold cavity such as a mold in the subsequent process.

  Next, mix the lubricant with the compound. This lubricant is for facilitating filling of a mold cavity such as a mold during molding, which is a subsequent process, and reducing friction with the mold cavity when pressure is applied.

  Subsequently, the compound is filled into the mold cavity, and compression molding is performed by applying pressure. The applied pressure is a pressure equal to or higher than the yield stress of the thermosetting resin composition, and is preferably about 0.1 GPa to 1.5 GPa, for example. Moreover, it is preferable that the molded object after compression molding shall be 6 volume% or more and 12 volume% or less of the volume fraction of the residual space | gap which occupies for the said molded object.

  Finally, the compact after compression molding is heated and cured. In the case of this embodiment, for example, thermosetting is performed at a temperature of 150 ° C. to 190 ° C. for about 10 minutes to 100 minutes. The heat-cured magnetized body is separately subjected to a coating treatment as a rust prevention treatment. Thereafter, a rare earth bonded magnet is completed by performing a separate magnetizing process.

(Examples and comparative examples)
Next, examples of the present invention and comparative examples will be described. As an example of the present invention, Nd-Fe-B magnet powder (chemical formula: Nd ₂ Fe ₁₄ B) is used as the magnet powder, and dicyclopentadiene type epoxy resin (reacted with a curing agent) as the main component of the thermosetting resin composition. Tg after curing: about 160 ° C.), using dicyandiamide as a curing agent and 2-butanone as a solvent, in the production method exemplified above, two hollow cylindrical shaped rare earth bonded magnets (changing thermosetting conditions) Sample 1-1 and sample 1-2) were prepared. Here, the blending amount of each material was adjusted so that the mass ratio of the magnet powder and the thermosetting resin composition was 100: 2.5. In Sample 1-1, the thermosetting step was performed by heating the molded body from room temperature to 190 ° C. over 1 hour and holding at 190 ° C. for 30 minutes. In Sample 1-2, the molded body was directly put into an oven at 190 ° C., and the oven temperature was maintained at 190 ° C. for 30 minutes.

  In addition, when it analyzed using a gel permeation chromatograph (GPC), the used dicyclopentadiene type | mold epoxy resin is the dicyclopentadiene type | mold epoxy resin whose repeating unit n is 1 in chemical formula (1), and repeating unit n is 2. The dicyclopentadiene type epoxy resin contained about 76% and about 24%, respectively, and the average repeating unit n was about 1.24.

Moreover, as a comparative example, Nd-Fe-B magnet powder (chemical formula: Nd ₂ Fe ₁₄ B) is used as the magnet powder, and a naphthol type epoxy resin represented by the following chemical formula (4) is used as the main component of the thermosetting resin composition ( Tg after being cured by reacting with a curing agent: 200 ° C. or higher), a phenolic curing agent represented by the following chemical formula (5) as a curing agent, and 2-butanone as a solvent, and the production method exemplified above A hollow cylindrical rare earth bonded magnet was produced (referred to as Sample 2-1). On the other hand, in the manufacturing method exemplified above, a hollow-cylindrical rare earth bonded magnet having an unreacted (uncured) state remained in the thermosetting step (referred to as Sample 2-2). Here, the blending amount of each material was adjusted so that the mass ratio of the magnet powder and the thermosetting resin composition was 100: 2.5. Moreover, the thermosetting at the time of preparation of Sample 2-1 was performed at 190 ° C. for 30 minutes.

  Next, the magnetic flux generated by the rare earth bonded magnet was measured while exposing the manufactured rare earth bonded magnets of Examples and Comparative Examples to a temperature of 180 ° C. for 1000 hours. FIG. 1 is a diagram showing the thermal demagnetization rate (magnetic flux reduction rate) of the rare-earth bonded magnets of the example (sample 1-1) and the comparative example (sample 2-1). The vertical axis indicates the thermal demagnetization factor, and the horizontal axis indicates the heat exposure time in logarithm. As shown in FIG. 1, the demagnetization factor of the rare-earth bonded magnet of the example is smaller in absolute value than the demagnetizing factor of the rare-earth bonded magnet of the comparative example, and the difference between the two thermal demagnetization factors increases as the heat exposure time becomes longer. It was confirmed that it would grow.

  Next, the results of experiments in which the rare earth bonded magnets of the example (sample 1-1) and the comparative example (sample 2-1) were verified by thermomechanical analysis (TMA) will be described. Thermomechanical analysis is a technique for measuring deformation (the rate of change in dimensions in this experiment) with respect to the temperature of the object while changing the temperature of the object according to a certain program.

  FIG. 2 is a diagram showing the rate of change in dimensions when TMA is performed on the rare-earth bonded magnets of Examples and Comparative Examples. The left vertical axis represents the temperature of the rare earth bonded magnet, the right vertical axis represents the rate of change in the dimensions of the rare earth bonded magnet, and the horizontal axis represents time. Moreover, the broken line has shown the change of temperature, and the thick solid line and the thin solid line have shown the change of the change rate of the dimension of an Example and a comparative example, respectively.

  As shown in FIG. 2, the rare earth bonded magnet of the comparative example has a history of temperature change accumulated as the test time becomes longer, and the dimensional change rate of the rare earth bonded magnet tends to increase. On the other hand, it was confirmed that the rare earth bonded magnet of the example had a relatively small dimensional change rate. This result is considered that the rare earth bonded magnet of an Example has a small coefficient of thermal expansion and high physical heat resistance.

  Next, the crushing strength of the rare earth bonded magnets of the examples and comparative examples was measured. Here, the crushing strength is the strength against the radial load of the rare-earth bonded magnet formed in the hollow cylinder, and is specifically measured according to the method described in JIS Z 2507. As a result, the crushing strength of the rare earth bonded magnet of the example (sample 1-1) was 72 MPa, and the crushing strength of the rare earth bonded magnet of the comparative example (sample 2-1) was 63 MPa. As described above, it was confirmed that the rare earth bonded magnet of the example had higher crushing strength than the bonded magnet of the comparative example.

FIG. 3 is a diagram showing the relationship between the thermal expansion coefficient, the thermal demagnetization factor, and the crushing strength of the rare-earth bonded magnets of Examples and Comparative Examples. The left vertical axis indicates the thermal demagnetization rate, the right vertical axis indicates the crushing strength, and the horizontal axis indicates the thermal expansion coefficient of the rare-earth bonded magnet at 180 ° C. obtained from the TMA result. Table 1 shows specific numerical values of the dimensional change rate (maximum value), the crushing strength, and the thermal demagnetization factor measured for the example (sample 1-1) and the comparative example (sample 2-1). It is.

  As shown in FIG. 3, the thermal expansion coefficient and the thermal demagnetization factor are substantially proportional to each other regardless of the difference in the thermosetting resin composition between the rare earth bonded magnet of the example and the rare earth bonded magnet of the comparative example. It was confirmed that the smaller the expansion coefficient, the smaller the absolute value of the thermal demagnetization factor. In addition, it was confirmed that the crumbling strength and the thermal demagnetization factor are in a trade-off relationship for both the rare earth bonded magnet of the example and the rare earth bonded magnet of the comparative example. Then, it was confirmed that the rare earth bonded magnet of the example can increase the crushing strength while suppressing the thermal demagnetization rate as compared with the rare earth bonded magnet of the comparative example. The crushing strength is preferably about 50 MPa or more in practice.

  By the way, as mentioned above, Tg of the naphthol type epoxy resin used as the main component of the thermosetting resin composition of the comparative example is 200 ° C. or more, and dicyclo used as the main component of the thermosetting resin composition of the example. It is higher than Tg (160 ° C.) of the pentadiene type epoxy resin. However, as the above experimental results show, the rare earth bonded magnets of the examples have less demagnetization characteristics and higher physical heat resistance against temperature changes. Thus, in order to realize a low demagnetization characteristic with respect to a temperature change and a high physical heat resistance, not only a main agent having a high Tg but also a dicyclopentadiene type epoxy resin used in the examples is used. Thus, it is important to use a main agent in consideration of the molecular weight and a curing agent suitable for it.

  The present invention is not limited to the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

Claims (4)

Rare earth-iron magnet powder,
A thermosetting resin composition;
Including
The thermosetting resin composition is represented by the following chemical formula (1) as a main agent, and includes a dicyclopentadiene type epoxy resin having a structure in which the average value of repeating units n is 1 to 3, and dicyandiamide as a curing agent; A rare earth bonded magnet characterized by comprising:

  2. The dicyclopentadiene-type epoxy resin having the above-mentioned structure in which the repeating unit n is 1 among the dicyclopentadiene-type epoxy resins blended in the thermosetting resin composition is 70% or more. The rare earth bonded magnet described in 1.   3. The rare earth bonded magnet according to claim 1, comprising 1 to 3% by mass of the thermosetting resin composition.   The rare earth bonded magnet according to any one of claims 1 to 3, wherein the magnet powder contains neodymium, iron, and boron as main components.

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