JP7528599B2 - Resin composition for bonded magnets and method for producing the resin composition for bonded magnets - Google Patents

Description

The present invention relates to a resin composition for bonded magnets and a method for producing the resin composition for bonded magnets.

Bonded magnets are obtained by pressure molding a resin composition for bonded magnets, which is a mixture of magnetic powder made of rare earth magnet alloy and resin, using methods such as compression molding. Bonded magnets have a high degree of freedom in terms of shape and are easy to process, so they are widely used in fields such as motors for automobiles and motors for electronic devices.

Patent Document 1 discloses a resin composition for bonded magnets that contains rare earth bonded magnet powder, epoxy resin, a phenolic resin curing agent, and a curing accelerator.

JP 2015-153778 A

Among rare earth magnet alloys, Sm-Fe-N rare earth magnet alloys have the characteristic of being more heat resistant and less prone to loss of magnetic force than neodymium magnets such as Nd-Fe-B rare earth magnet alloys and Nd-Fe-N rare earth magnet alloys. However, if polyphenylene sulfide resin, for example, is used as the resin that constitutes the resin composition for bonded magnets, the magnetic force of the Sm-Fe-N rare earth magnet alloy will decrease due to oxidation in the molding temperature range (approximately 300°C). For this reason, the epoxy resin described in the above-mentioned Patent Document 1 is an example of a resin that can be molded at a lower temperature.

The inventors of the present invention have conducted research into further improving the durability of a resin composition for bonded magnets that contains a magnetic powder made of a Sm-Fe-N rare earth magnet alloy and an epoxy resin, and have discovered that combining it with a specific resin is effective.

The present invention aims to provide a resin composition for bonded magnets that can improve the durability of bonded magnets.

According to the present invention, there is provided a magnetic material comprising an Sm-Fe-N magnetic powder, a phenolic resin (excluding aralkyl-modified novolac-type phenolic resin), and at least one of an aralkyl-modified novolac-type phenolic resin and a polyvinyl butyral resin,
A resin composition for bonded magnets comprising:
The resin composition for bonded magnets has a content of the Sm-Fe-N magnetic powder of 88 mass % or more relative to the entire resin composition for bonded magnets.

The present invention also provides a method for producing a resin composition for bonded magnets that contains Sm-Fe-N magnetic powder and phenolic resin, the method including a kneading step in which the Sm-Fe-N magnetic powder and the phenolic resin are kneaded using a pair of rolls with grooves on their surfaces.

The present invention provides a resin composition for bonded magnets that can improve the durability of bonded magnets.

Fig. 1(a) is a side view showing a schematic of a roller device, and Fig. 1(b) is a schematic view showing the surface shape of a roll used in the roller device.

The following is a detailed description of an embodiment of the present invention. In this specification, the notation "a to b" in the description of a numerical range means that the range is from a to b, unless otherwise specified.

(Resin composition for bonded magnets)
The resin composition for bonded magnets according to the embodiment includes Sm-Fe-N magnetic powder (component A), a phenolic resin (excluding aralkyl-modified novolac-type phenolic resin) (component B), and at least one of an aralkyl-modified novolac-type phenolic resin and a polyvinyl butyral resin (component C). Each component included in the resin composition for bonded magnets will be described in detail below.

(Component A: Sm-Fe-N magnetic powder)
The magnetic powder contained in the resin composition for bonded magnets of this embodiment is an Sm - Fe - N type, generally represented as Sm ₂ Fe ₁₇ N ₃ .

The lower limit of the average particle size of the Sm-Fe-N magnetic powder is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more. The upper limit of the average particle size of the Sm-Fe-N magnetic powder is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 5 μm or less.
By setting the average particle size of the Sm-Fe-N magnetic powder within the above range, it is possible to avoid an increase in pulverization costs while improving dispersibility when kneaded with the phenolic resin described below, and to improve the strength of the bonded magnet obtained from the resin composition for bonded magnets.
The average particle size is determined by measuring the particle size using a laser diffraction particle size distribution analyzer, and the particle size value at which the cumulative frequency is 50% is defined as the average particle size.

The lower limit of the content of Sm-Fe-N magnetic powder in the entire resin composition for bonded magnets of this embodiment is 88% by mass or more, more preferably 89% by mass or more, and even more preferably 90% by mass or more. The upper limit of the content of Sm-Fe-N magnetic powder in the entire resin composition for bonded magnets of this embodiment is preferably 98% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less, and even more preferably 92% by mass or less.

By making the content of Sm-Fe-N magnetic powder 88% by mass or more, the magnetic flux density of the bonded magnet obtained from the resin composition for bonded magnets can be increased. In addition, when the content of Sm-Fe-N magnetic powder is 88% by mass or more, for example, in a resin composition for bonded magnets using polyphenylene sulfide resin, the flowability is reduced, which causes deterioration of moldability. However, in the resin composition for bonded magnets of this embodiment using phenolic resin (excluding aralkyl-modified novolac-type phenolic resin) and at least one of aralkyl-modified novolac-type phenolic resin and polyvinyl butyral resin, good moldability can be maintained. In the resin composition for bonded magnets of this embodiment, by making the content of Sm-Fe-N magnetic powder 98% by mass or less, the binding property of the phenolic resin and the compatibility with the phenolic resin described later can be improved.

(Component B: Phenolic resin)
The phenolic resin of the present embodiment does not include aralkyl-modified novolac-type phenolic resin, and may be a conventionally known phenolic resin. The phenolic resin is not particularly limited, but may be, for example, a novolac-type phenolic resin, a resol-type phenolic resin, or an aryl alkylene-type phenolic resin. As the phenolic resin, one of these may be used alone, or two or more types having different weight average molecular weights may be used in combination, or one or more types may be used in combination with their prepolymers. Among these, novolac-type phenolic resins are preferably used from the viewpoint of heat resistance.

The novolac type phenolic resin can be appropriately selected according to the application, so long as it is a resin obtained by reacting a phenol with an aldehyde in the absence of a catalyst or in the presence of an acid catalyst. For example, a random novolac type or a high ortho novolac type phenolic resin can also be used.
The novolac type phenolic resin can usually be obtained by controlling the molar ratio of aldehydes to phenols (aldehydes/phenols) to 0.5 to 1.0 and then carrying out the reaction.

Specific examples of phenols that can be used to prepare this novolac phenolic resin include phenol, o-cresol, m-cresol, p-cresol, xylenol, alkylphenols, catechol, resorcin, etc. These phenols may be used alone or in combination of two or more.

Aldehydes used in preparing the novolac phenolic resin include, for example, aldehyde compounds such as formaldehyde, paraformaldehyde, and benzaldehyde, as well as sources of these aldehyde compounds, and solutions of these aldehyde compounds. These aldehydes may be used alone or in combination of two or more.

The lower limit of the molecular weight of the phenolic resin is, for example, preferably 300 or more in weight average molecular weight (Mw), more preferably 1000 or more, even more preferably 2000 or more, and especially preferably 3000 or more. On the other hand, the upper limit of the molecular weight of the phenolic resin is, for example, preferably 20000 or less in weight average molecular weight (Mw), more preferably 18000 or less, and even more preferably 15000 or less.

By setting the weight average molecular weight (Mw) of the phenolic resin within the above range, the workability when producing the resin composition for bonded magnets can be improved, and the moldability when obtaining a bonded magnet from the resin composition for bonded magnets can be improved. In addition, the mechanical strength and heat resistance of the obtained bonded magnet can be improved.
The weight average molecular weight can be calculated based on a calibration curve prepared by gel permeation chromatography (GPC) using a polystyrene standard substance.

The lower limit of the content of the phenolic resin in the entire resin composition for bonded magnets of this embodiment is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more. The upper limit of the content of the phenolic resin in the entire resin composition for bonded magnets of this embodiment is preferably 20 mass% or less, more preferably 15 mass% or less, and even more preferably 10 mass% or less.

By making the phenolic resin content 1% by mass or more, the binding properties of the phenolic resin can be increased. Also, by making the phenolic resin content 10% by mass or less, the amount of non-magnetic components can be suppressed, and the magnetic flux density can be maintained at a sufficiently high level.

(Component C)
The resin composition for bonded magnets of this embodiment further contains at least one of an aralkyl-modified novolac type phenolic resin or a polyvinyl butyral resin, and both may be used in combination.
The lower limit of the content of the aralkyl-modified novolac-type phenolic resin in the entire resin composition for bonded magnets of this embodiment is preferably 0.5 mass% or more, more preferably 1.5 mass% or more, and even more preferably 2.5 mass% or more. The upper limit of the content of the aralkyl-modified novolac-type phenolic resin in the entire resin composition for bonded magnets of this embodiment is preferably 10 mass% or less, more preferably 8 mass% or less, and even more preferably 6 mass% or less.
By making the content of the aralkyl-modified novolac type phenolic resin equal to or more than the lower limit, the binding property of the phenolic resin can be improved, while by making the content of the aralkyl-modified novolac type phenolic resin equal to or less than the upper limit, the amount of non-magnetic components can be suppressed, and the magnetic flux density can be maintained at a sufficiently high level.
The weight average molecular weight (Mw) of the aralkyl-modified novolak-type phenolic resin may be the same as that of the above-mentioned phenolic resin.

Polyvinyl butyral resin is a type of polyvinyl acetal that is produced by reacting polyvinyl alcohol with butyraldehyde under acidic conditions.
The lower limit of the content of the polyvinyl butyral resin in the entire resin composition for bonded magnets of this embodiment is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 1.0 mass% or more. The upper limit of the content of the polyvinyl butyral resin in the entire resin composition for bonded magnets of this embodiment is preferably 8 mass% or less, more preferably 5 mass% or less, and even more preferably 3 mass% or less.
By making the content of the polyvinyl butyral resin equal to or higher than the lower limit, the binding property of the phenol resin can be improved, while by making the content of the polyvinyl butyral resin equal to or lower than the upper limit, the amount of non-magnetic components can be suppressed, and the magnetic flux density can be maintained at a sufficiently high level.

(Other ingredients)
In addition to the components described above, the resin composition and photosensitive resin composition of the present embodiment can contain various other components depending on the application.
For example, additives such as a curing agent, a silane coupling agent, a filler, a release agent, and an organic solvent may be added as necessary.
Examples of the curing agent include hexamethylenetetramine, hexamethoxymethylolmelamine, and isocyanate resin. The lower limit of the content of the curing agent in the entire resin composition for bonded magnets is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. The upper limit of the content of the curing agent in the entire resin composition for bonded magnets is preferably 1% by mass or less, more preferably 0.9% by mass or less, and even more preferably 0.8% by mass or less. By setting the content of the curing agent in the above range, it is possible to fully exert the curing promotion effect while improving durability.
Examples of the silane coupling agent include epoxy silane, mercapto silane, amino silane, alkyl silane, ureido silane, and vinyl silane.
Examples of the filler include silica, calcium carbonate, titanium oxide, barium sulfate, zinc oxide, aluminum hydroxide, magnesium hydroxide, talc, and mica.
The organic solvent includes acetone, methyl ethyl ketone, benzene, toluene, xylene, and the like.

(Rate of change in tensile strength)
When the resin composition for bonded magnets of this embodiment is subjected to the treatment under the following conditions, where the initial tensile strength before the treatment is X1 and the tensile strength after the treatment is X2, the tensile strength change rate Δ=(X2-X1)/X1×100 is -15% or more, preferably -10% or more, and more preferably -5% or more.
(Processing details)
The resin composition for bonded magnets is used to mold a test piece in the shape of a square prism, 4 mm square and 60 mm long, under compression molding conditions of 175°C, 3 minutes, and 500 MPa. The test piece is sintered at 150°C for 4 hours, and then sintered at 180°C for another 4 hours. The sintered test piece is treated at 85°C, 85 RH%, and 500 hours. A tensile test is performed on the test pieces before and after treatment. The tensile test is performed with a chuck distance of 20 mm and a test speed of 5 mm/min.

The resin composition for bonded magnets of this embodiment can improve the durability of the bonded magnet obtained from the resin composition for bonded magnets by making the above-mentioned tensile strength change rate Δ -15% or more. There is no particular upper limit to the tensile strength change rate Δ, but it is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less. By making the upper limit of the tensile strength change rate Δ 40% or less, it is possible to suppress the occurrence of cracks in the bonded magnet obtained from the resin composition for bonded magnets.

The resin composition for bonded magnets described above contains Sm-Fe-N magnetic powder, which improves heat resistance and makes it difficult for magnetic force to decrease. In addition, the phenolic resin allows the molding temperature to be lowered, making the Sm-Fe-N magnetic powder less susceptible to oxidation. Furthermore, the durability of the bonded magnets obtained from the resin composition for bonded magnets can be improved by the synergistic effect of combining at least one of an aralkyl-modified novolac-type phenolic resin or a polyvinyl butyral resin.

(Method of manufacturing resin composition for bonded magnets)
The resin composition for bonded magnets according to the embodiment is obtained by kneading at least one of the above-mentioned Sm-Fe-N magnetic powder, phenolic resin, aralkyl-modified novolac-type phenolic resin, and polyvinyl butyral resin, and any additives. The kneading method is not particularly limited, but a known open roll method using two rolls or a roll method using a special roll device shown below can be used.
In the case of a known open roll method, the temperatures of the pair of rolls (front roll and rear roll) are not particularly limited, but for example, the temperature of the front roll may be set in the range of 70° C. to 130° C., and the temperature of the rear roll may be set in the range of 20° C. to 50° C. The rotation speed of the front roll may be the same as the rotation speed of the rear roll, but there may be a difference between the rotation speeds of the front roll and the rear roll, and for example, the rotation ratio of the front and rear rolls (rotation speed of the front roll:rotation speed of the rear roll) may be set in the range of 2:1 to 1:0.9.

Next, a roll method using a special roll device will be described.
Fig. 1(a) is a side view showing an outline of a roll device 10. Fig. 1(b) is a schematic diagram showing the surface shape of a roll used in the roll device 10.
As shown in Fig. 1(a), the roll device 10 includes a pair of rolls (front roll 20, rear roll 30) and a material returning mechanism 40. Also, as shown in Fig. 1(b), a plurality of grooves 22 are formed on the surface of the front roll 20 so as to extend in the circumferential direction at predetermined intervals. Also, a plurality of grooves (not shown) are formed on the surface of the rear roll 30 so as to extend in the circumferential direction at predetermined intervals, similar to the grooves 22.

As shown in FIG. 1(a), when the roll device 10 is viewed from the side, the material return mechanism 40 is a belt conveyor mechanism that is installed in an arc from below the gap between the front roll 20 and the rear roll 30 to above the front roll 20 at a predetermined distance from the surface of the front roll 20. Material that falls between the rolls 20 and 30 and from the roll 20 is transported above the roll 20 by the material return mechanism 40 and returned to the top of the roll 20.

The temperature of the front roll 20 and the rear roll 30 and the rotation ratio of the front roll 20 and the rear roll 30 can be in the same range as in the known open roll method described above.

As in the roll device 10 described above, by using the front roll 20 and rear roll 30 with grooves on the surface and returning the spilled material to the front roll 20 and rear roll 30 by the material return mechanism 40, the compatibility between the Sm-Fe-N magnetic powder and at least one of the phenolic resin and the aralkyl-modified novolac-type phenolic resin or polyvinyl butyral resin is improved, and the initial strength and durability can be improved.

In addition, in this embodiment, by appropriately adjusting the types and mixing ratios of each component contained in the resin composition for bonded magnets, and the manufacturing method for the resin composition for bonded magnets, it is possible to obtain a resin composition for bonded magnets that satisfies the parameters related to the rate of change in tensile strength described above.
More specifically, for example, the resin composition for bonded magnets of this embodiment can be obtained by appropriately selecting the content and average particle size of the Sm-Fe-N magnetic powder. Also, the resin composition for bonded magnets of this embodiment can be obtained by appropriately selecting the type, content, and weight average molecular weight (Mw) of the phenolic resin. Furthermore, the resin composition for bonded magnets of this embodiment can be obtained by kneading the Sm-Fe-N magnetic powder and the phenolic resin using a special roll device as shown in FIG. 1. The resin composition for bonded magnets of this embodiment can be obtained by adjusting these factors comprehensively.

(bonded magnet)
The resin composition for bonded magnets according to the embodiment can be heated and melted at a temperature equal to or higher than the melting point of the phenolic resin, for example, in the range of 130 to 230° C., and then a molded bonded magnet can be obtained using injection molding, extrusion molding, compression molding, etc. For example, the resin composition for bonded magnets can be compression molded using a compression molding machine under conditions of 130 to 230° C., 1 to 5 minutes, and 200 to 600 MPa to obtain a bonded magnet.
The resin composition for bonded magnets during molding or the resulting bonded magnet may be magnetized with a magnetic field strength appropriate for the intended use.

The bonded magnets molded using the resin composition for bonded magnets according to the embodiment have excellent magnetic properties and mechanical strength such as rigidity. The bonded magnets can be suitably used in motors for automobiles and motors for electronic devices.

Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can also be adopted.
Below, examples of reference forms are given.
1. Sm—Fe—N magnetic powder;
Phenol resin (excluding aralkyl-modified novolac type phenol resin),
At least one of an aralkyl-modified novolac type phenolic resin and a polyvinyl butyral resin,
A resin composition for bonded magnets comprising:
A resin composition for bonded magnets, in which the content of the Sm-Fe-N magnetic powder in the entire resin composition for bonded magnets is 88 mass % or more.
2. The resin composition for bonded magnets according to 1., wherein the content of the Sm-Fe-N magnetic powder in the entire resin composition for bonded magnets is 98 mass % or less.
3. A resin composition for bonded magnets according to 1. or 2., wherein the content of the phenol resin in the entire resin composition for bonded magnets is 1% by mass or more and 20% by mass or less.
4. A method for producing a resin composition for bonded magnets, comprising Sm-Fe-N magnetic powder, a phenolic resin (excluding aralkyl-modified novolac-type phenolic resin), and at least one of an aralkyl-modified novolac-type phenolic resin and a polyvinyl butyral resin,
The method for producing a resin composition for bonded magnets comprises a kneading step of kneading the Sm-Fe-N magnetic powder and the phenol resin using a pair of rolls having grooves on their surfaces.
5. The method for producing a resin composition for bonded magnets according to 4., wherein the kneading step is carried out while the Sm-Fe-N magnetic powder and the phenolic resin that have fallen from the rolls are returned to the kneading step by the pair of rolls.

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

Each of the resin compositions for bonded magnets in Examples 1 to 4 and Comparative Examples 1 to 4 was prepared so as to have the components and content ratios shown in Table 1. Details of the components shown in Table 1 are as follows.
Sm-Fe-N magnetic powder: SFN-C, manufactured by Sumitomo Metal Mining Co., Ltd.
Novolac phenolic resin: PR-HF-3, manufactured by Sumitomo Bakelite Co., Ltd.
Aralkyl-modified novolac-type phenolic resin: XLC-4L, manufactured by Mitsui Chemicals, Inc.
Polyvinyl butyral resin: BX-5, manufactured by Sekisui Chemical Co., Ltd.
Trisphenylmethane type epoxy resin: 1032H60, manufactured by Mitsubishi Chemical Corporation
Hardener: Hexamethylenetetramine Secondary aminosilane Coupling agent: Shin-Etsu Chemical Co., Ltd., KBM-573
Release agent 1: Ca-St (calcium stearate)
Release agent 2: Carnauba wax-based hardening catalyst: TPP, manufactured by Hokko Chemical Industry Co., Ltd.

<Kneading method>
Mixtures of the components and formulations shown in Table 1 were kneaded using either of two methods: an open roll method using two general rolls (hereinafter referred to as "normal rolls"), or an open roll method equipped with a grooved roll and a material return mechanism as shown in Figure 1 (hereinafter referred to as "special rolls"). The kneading conditions are described below.
Normal roll conditions: Pre-roll temperature: 110°C
Rear roll temperature: 25°C
Front and rear roll rotation ratio: 0.7
Special roll conditions: Pre-roll temperature: 110°C
Rear roll temperature: 25°C
Front and rear roll rotation ratio: 0.7

(durability)
The resin composition for bonded magnets was used to mold a test piece in the shape of a square pillar having a size of 4 mm on each side and a length of 60 mm under the following molding conditions.
Temperature: 175°C
Time: 3 minutes Pressure: 500 MPa
Molding machine: 37t compression molding machine The obtained test pieces were sintered at 150°C for 4 hours, and then sintered at 180°C for 4 hours. The tensile strength test was carried out on these test pieces. Note that magnetization was omitted because it was thought that the magnetic properties did not affect the tensile strength of the test pieces.
The test pieces after baking were subjected to a treatment at 85° C. and 85% RH for 500 hours. A tensile strength test was performed on the test pieces after the treatment.
Tensile strength tests before and after the treatment were carried out using a Tensilon universal testing machine (manufactured by Shimadzu Corporation). The test conditions were a chuck distance of 20 mm and a test speed of 5 mm/min.
The initial tensile strength before the treatment was designated as X1, the tensile strength after the treatment was designated as X2, and the rate of change in tensile strength Δ was calculated from the following formula 1. The results are shown in Table 1.
Tensile strength change rate Δ=(X2−X1)/X1×100 (Formula 1)

(Method of evaluating density)
The resin composition for bonded magnets was used to mold cylindrical test pieces having a diameter of 16 mm and a height of 5 mm under the following molding conditions.
Temperature: 175°C
Time: 3 minutes Pressure: 500 MPa
Molding machine: 37t compression molding machine The specific gravity of this test piece was measured by the underwater displacement method. The obtained value was designated as Y1, the specific gravity of the resin was designated as Y2 (specific gravity of phenol resin: 1.25, specific gravity of epoxy resin: 1.30), and the specific gravity of the Sm-Fe-N magnetic powder was designated as Y3 (7.47), and the density (volume %) was calculated from the following formula 2. The results obtained for the density are shown in Table 1.
Density (volume%)=(Y1-Y2)/(Y3-Y2)×100 (Formula 2)

As shown in Table 1, the tensile strength change rate Δ of each of the bonded magnet resin compositions of Examples 1 to 4 was suppressed to -15% or more, and the durability of the bonded magnets obtained from the bonded magnet resin compositions of each Example was improved. On the other hand, the tensile strength change rate Δ of each of the bonded magnet resin compositions of Comparative Examples 1 to 4 was lower than -15%, confirming that the bonded magnets obtained from the bonded magnet resin compositions of each Comparative Example had insufficient durability.

10 Roll device 20 Front roll 30 Rear roll 40 Material return mechanism

Claims (5)

Sm—Fe—N based magnetic powder;
Phenol resin (excluding aralkyl-modified novolac type phenol resin),
At least one of an aralkyl-modified novolac type phenolic resin and a polyvinyl butyral resin,
A resin composition for bonded magnets comprising:
The content of the Sm-Fe-N magnetic powder in the entire resin composition for bonded magnets is 88% by mass or more and 98% by mass or less ,
The content of the phenol resin in the entire resin composition for bonded magnets is 1% by mass or more and 20% by mass or less,
A resin composition for bonded magnets, wherein the content of the aralkyl-modified novolac-type phenolic resin relative to the entire resin composition for bonded magnets is at least 0.5% by mass or more and 10% by mass or less, or the content of the polyvinyl butyral resin relative to the entire resin composition for bonded magnets is at least 0.1% by mass or more and 8% by mass or less . The resin composition for bonded magnets according to claim 1, wherein the particle diameter at which the cumulative frequency of 50% in particle size measurement of the Sm-Fe-N magnetic powder is 0.5 μm or more and 10 μm or less. 3. A resin composition for bonded magnets according to claim 1 or 2, wherein the phenolic resin (excluding aralkyl-modified novolac-type phenolic resin) is one or more selected from novolac-type phenolic resins, resol-type phenolic resins, and aryl alkylene-type phenolic resins. A method for producing a resin composition for bonded magnets, comprising Sm-Fe-N magnetic powder, a phenolic resin (excluding aralkyl-modified novolac-type phenolic resin), and at least one of an aralkyl-modified novolac-type phenolic resin and a polyvinyl butyral resin,
The resin composition for bonded magnets is
The content of the Sm-Fe-N magnetic powder in the entire resin composition for bonded magnets is 88% by mass or more and 98% by mass or less,
The content of the phenol resin in the entire resin composition for bonded magnets is 1% by mass or more and 20% by mass or less,
At least one of the following: the content of the aralkyl-modified novolac-type phenolic resin is 0.5% by mass or more and 10% by mass or less with respect to the entire resin composition for the bonded magnet; or the content of the polyvinyl butyral resin is 0.1% by mass or more and 8% by mass or less with respect to the entire resin composition for the bonded magnet;
The method for producing a resin composition for bonded magnets comprises a kneading step of kneading the Sm-Fe-N magnetic powder and the phenol resin using a pair of rolls having grooves on their surfaces. The method for producing a resin composition for bonded magnets according to claim 4, in which the kneading process is carried out while the Sm-Fe-N magnetic powder and the phenolic resin that have fallen from the rolls are returned to the pair of rolls for kneading.

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