JP2017130650A - Rare earth bond magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare earth bond magnet having a small demagnetization property with respect to a temperature change and a high physical heat resistance.SOLUTION: A rare earth bond magnet comprises: rare earth-iron based magnet powder; and a thermosetting resin composition. The thermosetting resin composition includes: a main agent containing a first epoxy resin which is a multifunction epoxy resin and has a glass transition point of 200°C or higher after curing as a result of a reaction with a hardening agent, and a second epoxy resin which is a straight-chain epoxy resin and has a glass transition point of 120°C or lower after curing as a result of a reaction with the hardening agent; and the hardening agent. The proportion of the first epoxy resin and the second epoxy resin blended in the main agent is set so that the thermosetting resin composition has a glass transition point of 150°C or higher and an elastic modulus of 65 GPa or smaller.SELECTED DRAWING: None

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 resin (binding resin) that is responsible for bonding rare earth magnet materials, take advantage of their high degree of freedom in shape, making the devices smaller and more sophisticated. Contributing to

  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 is a polyfunctional epoxy resin, a first epoxy resin having a glass transition point of 200 ° C. or higher after being cured by reacting with a curing agent, and a linear epoxy resin, which is cured. A main agent containing a second epoxy resin having a glass transition point of 120 ° C. or lower after being cured by reacting with the agent and a curing agent are blended, and the first epoxy resin and the second epoxy resin in the main agent are blended. Is set such that the glass transition point of the thermosetting resin composition is 150 ° C. or higher and the elastic modulus is 65 GPa or lower.

  In the rare earth bonded magnet according to an aspect of the present invention, the first epoxy resin is made of a cresol novolac type epoxy oligomer, the second epoxy resin is made of a bisphenol A type epoxy oligomer, and the blending ratio is 80: 20-60. : 40.

  The rare earth bonded magnet according to one aspect of the present invention is characterized in that the curing agent is a phenol novolac resin.

  The rare earth bonded magnet according to one aspect of the present invention is characterized in that the magnet powder contains neodymium, iron, and boron as main components.

  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 the relationship between the bisphenol A type compounding ratio and the glass transition point Tg. FIG. 2 is a graph showing the relationship between the bisphenol A type blending ratio and the tensile elastic modulus. FIG. 3 is a diagram showing the thermal demagnetization rate of the manufactured rare-earth bonded magnet.

  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. 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.
More specifically, at the time of cooling after thermosetting the thermosetting resin composition as a binder for bonding the magnet powders, or when cooling and heating the bonded magnet repeatedly, the magnet powder and the heat Due to the difference in coefficient of linear expansion from the curable resin composition, internal stress is generated in the rare-earth bonded magnet, causing the resin to break or peel from the magnet powder, which is one of the causes of void generation. it is conceivable that. Therefore, it is considered that the thermal demagnetization rate can be reduced by reducing the internal stress generated in the rare earth bonded magnet.

式（１）において、Ｅｒは熱硬化性樹脂の弾性率、αｒは熱硬化性樹脂の線膨張係数、αｓは磁石粉末の線膨張係数である。 Here, the internal stress σ is expressed by the following formula (1).

In the formula (1), Er is the elastic modulus of the thermosetting resin, αr is the linear expansion coefficient of the thermosetting resin, and αs is the linear expansion coefficient of the magnet powder.

  According to Equation (1), in order to reduce internal stress, the elastic modulus or linear expansion coefficient of the thermosetting resin may be reduced. However, a thermosetting resin having a low elastic modulus generally has a low glass transition point Tg. Therefore, in a rare earth bonded magnet using this, the internal thermosetting resin softens in a temperature environment higher than the glass transition point Tg. Since the mechanical strength is reduced, the physical heat resistance is considered to be lowered. 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, the rare earth bonded magnet according to the embodiment of the present invention includes a rare earth-iron-based magnet powder and a thermosetting resin composition. The thermosetting resin composition is a polyfunctional epoxy resin, a first epoxy resin having a glass transition point Tg of 200 ° C. or higher after being cured by reacting with a curing agent, and a linear epoxy resin The glass transition point Tg after being cured by reacting with a curing agent is blended with a main agent containing a second epoxy resin having a temperature of 120 ° C. or less and a curing agent. Furthermore, the compounding ratio of the first epoxy resin and the second epoxy resin is set so that the glass transition point Tg of the thermosetting resin composition is 150 ° C. or more and the elastic modulus is 65 GPa or less.

  In general, when a polyfunctional epoxy resin is used, the thermosetting resin composition has a high glass transition point Tg and can be set to 200 ° C. or higher, but has a high elastic modulus. On the other hand, when a linear epoxy resin is used, the thermosetting resin composition has a low elastic modulus but has a low glass transition point Tg and may be 120 ° C. or lower.

  Therefore, the present inventors realized a thermosetting resin composition having both an appropriate glass transition point and an elastic modulus by blending these epoxy resins having different properties at an appropriate blending ratio. We have come up with the realization of rare earth bonded magnets with low demagnetization characteristics against temperature changes and high physical heat resistance.

  The polyfunctional first epoxy resin is not particularly limited as long as it has a glass transition point Tg of 200 ° C. or higher. For example, a polyfunctional first epoxy resin made of a cresol novolac type epoxy oligomer can be used. When an epoxy resin composed of a cresol novolac type epoxy oligomer is used alone as a main agent and a phenol novolac type resin is used as a curing agent, the glass transition point Tg of the thermosetting resin composition is about 225 ° C., and the tensile modulus of elasticity. Is about 67 GPa.

  The linear second epoxy resin is not particularly limited as long as it has a glass transition point Tg of 120 ° C. or higher. For example, a linear second epoxy resin made of a bisphenol A type epoxy oligomer can be used. When the epoxy resin composed of bisphenol A type epoxy oligomer is used alone as a main agent and a phenol novolak type resin is used as a curing agent, the glass transition point Tg of the thermosetting resin composition is about 120 ° C., and the tensile modulus of elasticity. Is about 22 GPa.

  As shown in the experimental examples later, the glass transition point is obtained by using, as a main ingredient, a mixture of an epoxy resin composed of these cresol novolac type epoxy oligomers and an epoxy resin composed of bisphenol A type epoxy oligomers in a predetermined range. A thermosetting resin composition having a Tg of 150 ° C. or more and a tensile modulus of 65 GPa or less can be realized.

  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 of the magnet powder to the thermosetting resin composition is preferably about 99: 1 to 97: 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 for compression molding of a ring magnet having a wall 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 a mixture of a cresol novolac type epoxy resin as a main agent and a phenol novolac type resin as a curing agent in a predetermined mass ratio and dissolved 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. Therefore, it is desirable to crush and classify the compound so that crushing and classification fall within the range.

  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 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.

(Experimental example 1)
Below, in order to confirm the characteristic of thermosetting resin composition itself, the epoxy resin which consists of a cresol novolak-type epoxy oligomer with the compounding ratio (shown in percentage in Table 1) shown in following Table 1 (in Table 1, cresol). Novolak type) and an epoxy resin composed of bisphenol A type epoxy oligomer (described in Table 1 as bisphenol A type) as a main agent, and a phenol novolac type resin as a curing agent. Samples 1 to 7 of the thermosetting resin composition were prepared, and their glass transition point Tg and tensile modulus were measured. The glass transition point Tg is a value measured by the DSC method. The tensile modulus is a value measured by the method disclosed in JIS-K7161-1. In addition, as shown in Table 1, the sample 1 is composed of a 100% cresol novolac type as a main ingredient. In Samples 2, 3, 4, 5, and 6, the blending ratio of bisphenol A type in the main agent is 10%, 20%, 30%, 40%, and 50%, respectively. Sample 7 consists of 100% bisphenol A as the main ingredient.

  FIG. 1 is a diagram showing the relationship between the bisphenol A type compounding ratio in the main agent and the glass transition point Tg. As shown in FIG. 1, the glass transition point Tg of Sample 1 whose main agent is a 100% cresol novolak type was about 225 ° C. On the other hand, the glass transition point Tg of Sample 7 whose main agent is 100% bisphenol A type was about 120 ° C. About samples 2-6, the glass transition point fell, so that the compounding rate of the bisphenol A type | mold became high, and the glass transition point Tg became 150 degreeC or more in the samples 1-5 whose compounding rate is 40% or less.

  FIG. 2 is a view showing the relationship between the bisphenol A type compounding ratio and the tensile elastic modulus in the main agent. As shown in FIG. 2, the tensile modulus of the sample 1 whose main agent is 100% cresol novolak type was about 67 GPa. On the other hand, the tensile modulus of the sample 7 whose main agent is 100% bisphenol A type was about 22 GPa. For Samples 2-6, the tensile modulus decreased as the blending ratio of bisphenol A type increased, and in Samples 3-7, where the blending ratio was 20% or more, the tensile modulus was 65 GPa or less.

(Experimental example 2)
Next, as Experimental Example 2 of the present invention, Nd—Fe—B based magnet powder (chemical formula: Nd ₂ Fe ₁₄ B) is used as the magnet powder, and samples 1 to 1 in Table 1 are used as the main agent and curing agent of the thermosetting resin composition. Seven, seven columnar rare earth bonded magnets having a diameter of 10 mm and a height of 7 mm were produced by the above-described production method using methyl ethyl ketone as a solvent. Here, the compounding amount of each material was adjusted so that the mass ratio of the magnet powder and the thermosetting resin composition in the compound was 100: 2.5. Further, a pressure of 0.8 GPa was applied during compression molding. The thermosetting process was performed at 190 ° C. for 30 minutes. In addition, about the magnetization process, the magnetic field of magnetic flux density 5T (T: Tesla) was applied to the axial direction of a cylinder.

  Next, the magnetic flux generated by the rare earth bonded magnet was measured while exposing each rare earth bonded magnet of Experimental Example 2 to a temperature of 180 ° C. for 1000 hours. FIG. 3 is a diagram showing the thermal demagnetization rate (magnetic flux reduction rate) of the manufactured rare-earth bonded magnet. The vertical axis indicates the thermal demagnetization factor, and the horizontal axis indicates the heat exposure time in logarithm. In the legend, for example, Sample 1: 0% indicates a rare-earth bonded magnet using the main agent and curing agent of Sample 1 in which the mixing ratio of the bisphenol A type shown in Table 1 is 0%.

  As shown in FIG. 3, the demagnetization rate was -10% or less in Sample 1 where the blending ratio of bisphenol A type was 0%, but 1000% in Samples 2-7 where the blending ratio of bisphenol A type was 20% or more. It was confirmed that the thermal demagnetization factor after exposure to time heat could be within -5%. The thermal demagnetization rate was not greatly improved even when the blending ratio of bisphenol A type was increased from 20%.

  As shown in the results shown in FIGS. 1 to 3, if the blending ratio of bisphenol A type is 20% to 40% (that is, the blending ratio of cresol novolac type to bisphenol A type is 80:20 to 60:40). The glass transition point Tg of the thermosetting resin composition is 150 ° C. or more and the elastic modulus is 65 GPa or less, which is suitable for use at a high temperature of 150 ° C. A rare earth bonded magnet having high physical heat resistance can be realized.

  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 a polyfunctional epoxy resin, a first epoxy resin having a glass transition point of 200 ° C. or higher after being reacted with a curing agent and cured, and a linear epoxy resin The glass transition point after being cured by reacting with a curing agent is a main component containing a second epoxy resin having a temperature of 120 ° C. or less, and a curing agent,
The mixing ratio of the first epoxy resin and the second epoxy resin in the main agent is set so that the glass transition point of the thermosetting resin composition is 150 ° C. or more and the elastic modulus is 65 GPa or less. A rare earth bonded magnet characterized by having   The first epoxy resin is made of a cresol novolac type epoxy oligomer, the second epoxy resin is made of a bisphenol A type epoxy oligomer, and the blending ratio is 80:20 to 60:40. The rare earth bonded magnet described in 1.   The rare earth bonded magnet according to claim 2, wherein the curing agent is a phenol novolac resin.   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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