JP2023040640A - Resin composition for bonded magnet, method for producing bonded magnet, and bonded magnet - Google Patents

Abstract

To provide a resin composition for a bonded magnet from which the bonded magnet excellent in kneadability and heat resistance can be obtained while suppressing water absorption, a bonded magnet using the bonded magnet resin composition, and a method for producing the same.SOLUTION: A resin composition for a bonded magnet includes an aliphatic polyamide (A) and an amorphous resin (B), and the total amount of terminal amino groups and terminal carboxyl groups in the resin composition for the bonded magnets is 140.0. less than mmol/kg. A method for producing the bonded magnet includes the steps of melting the resin composition for the bonded magnet in an amount of 5% by mass or more and 10% by mass or less and magnetic powder in an amount of 90% by mass or more and 95% by mass or less with respect to the total mass of the bonded magnet, and kneading and injection-molding them to obtain a bonded magnet. The bonded magnet includes an injection-molded article containing 5% by mass or more and 10% by mass or less of the resin composition for the bonded magnet and 90% by mass or more and 95% by mass or less of the magnetic powder with respect to the total mass of the bonded magnet.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a resin composition for bonded magnets, a method for producing bonded magnets, and bonded magnets.

Rare earth magnets exhibit high magnetic properties, and are therefore used in various devices such as electric appliances and automobiles for which energy saving and weight reduction are desired. Rare earth magnets include dense magnets made of sintered or hot compacts of rare earth magnet powder (hereinafter simply referred to as "magnet powder"), and magnet powders made of resin (binder resin) by injection molding, compression molding, extrusion molding, or the like. ) and bonded magnets. Recently, there is a tendency to use bonded magnets, which have a high degree of freedom in molding and are suitable for manufacturing light and thin parts.

When a bonded magnet is used, not only is it intended to improve its magnetic properties, heat resistance, and low water absorption, but it is also possible to heat and knead magnet powder and binder resin to obtain a magnet raw material, such as a compound that can be kneaded and its binder. It is also important to ensure moldability when the resin is melted for injection molding or the like. Polyamide (PA) and polyphenylene sulfide (PPS) are known as binder resins (see, for example, Patent Documents 1 to 3).

JP-A-9-162019 JP 2019-067957 A Japanese Patent No. 5234207

In Patent Document 1, polyamide 12 (PA12) is used as a binder resin, which is excellent in kneadability and moldability, but poor in heat resistance and limited in application.
In Patent Document 2, polyamide 66 (PA66) is used as a binder resin to adjust the amount of terminal groups of amino groups and carboxy groups, and an attempt is made to improve heat resistance while maintaining kneadability and moldability. There is room for improvement in terms of properties and water absorbency.
In Patent Document 3, a combination of PPS and a small amount of PA is used as a binder resin to try to improve kneadability and moldability while maintaining the heat resistance and low water absorbency of PPS, but there is room for improvement.

The present invention has been made in view of the above circumstances, and provides a resin composition for a bonded magnet that can provide a bonded magnet that is excellent in kneadability and heat resistance while suppressing water absorption, and the resin composition for a bonded magnet. A bond magnet using a material and a method for manufacturing the same are provided.

That is, the present invention includes the following aspects.
(1) A resin composition for a bonded magnet, comprising an aliphatic polyamide (A) and an amorphous resin (B),
A resin composition for a bond magnet, wherein the total amount of amino group terminals and carboxy group terminals in the resin composition for a bond magnet is 140.0 mmol/kg or less.
(2) The resin composition for a bonded magnet according to (1), wherein the amorphous resin (B) contains polyphenylene ether (PPE).
(3) The resin composition for a bonded magnet according to (1) or (2), wherein the repeating unit of the aliphatic polyamide (A) has 12 or more carbon atoms.
(4) The resin composition for a bonded magnet according to any one of (1) to (3), wherein the aliphatic polyamide (A) contains polyamide 612.
(5) The bonded magnet according to any one of (1) to (4), wherein the total amount of terminal amino groups and terminal carboxy groups in the resin composition for bonded magnets is 115.0 mmol/kg or less. resin composition for
(6) The resin composition for a bonded magnet according to any one of (1) to (5), which is 5% by mass or more and 10% by mass or less relative to the total mass of the bonded magnet, and 90% by mass or more and 95% by mass. % or less of magnetic powder, followed by injection molding to obtain a bonded magnet.
(7) The resin composition for a bonded magnet according to any one of (1) to (5), which is 5% by mass or more and 10% by mass or less relative to the total mass of the bonded magnet, and 90% by mass or more and 95% by mass. % or less of magnetic powder, and a bonded magnet comprising an injection molded body.

According to the resin composition for a bonded magnet of the above aspect, it is possible to provide a resin composition for a bonded magnet that provides a bonded magnet that is excellent in kneadability and heat resistance while suppressing water absorption. The bonded magnet and the method for producing a bonded magnet according to the above aspect use the resin composition for a bonded magnet, and a bonded magnet having excellent kneadability and heat resistance can be obtained while suppressing the amount of water absorption.

EMBODIMENT OF THE INVENTION Hereinafter, the form (henceforth "this embodiment") for implementing this invention is demonstrated in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. Various modifications are possible for the present invention without departing from the gist thereof.

As used herein, the term "polyamide" means a polymer having an amide bond (--NHCO--) in its main chain.
Further, in this specification, "mmol/kg" means the molar amount (mmol) of terminal groups present in 1 kg of resin.

<<Resin composition for bond magnet>>
The resin composition for a bonded magnet of this embodiment comprises an aliphatic polyamide (A) and an amorphous resin (B).

The total amount of amino group terminals and carboxy group terminals in the resin composition for a bond magnet of the present embodiment is 140.0 mmol/kg or less, preferably 115.0 mmol/kg or less.

When a polyamide whose terminals are not adjusted is used in a resin composition for a bond magnet, the amino group terminal ( _NH2 group) and the carboxy group terminal (COOH group) are nearly equimolar, and when kneading with magnetic powder, _NH2 Groups and COOH groups or _NH2 groups tend to react with each other to increase the molecular weight and thicken (the total amount of terminal groups, which is the sum of _NH2 groups and COOH groups, tends to decrease).

On the other hand, in the bonded magnet resin composition of the present embodiment, the balance between the NH ₂ groups and the COOH groups of the polyamide is adjusted (to keep them away from equimolar amounts), and the total amount of the amino group terminal amount and the carboxy group terminal amount is reduced. It is presumed that the thickening phenomenon peculiar to polyamide was eliminated, and the kneadability and moldability were improved.

The amount of terminal amino groups and the amount of terminal carboxy groups in the resin composition for bond magnets can be measured, for example, using the following methods.
The amount of amino group terminals bonded to the polymer terminals of the resin composition for bonded magnets is measured by neutralization titration as follows.
3.0 g of the bond magnet resin composition is dissolved in 100 mL of a 90% by mass phenol aqueous solution, and the resulting solution is titrated with 0.025N hydrochloric acid to determine the amount of terminal amino groups (mmol/kg). The end point is determined from the reading of the pH meter.

The amount of carboxy group terminals bonded to the polymer terminals of the resin composition for bond magnets is measured by neutralization titration as follows.
4.0 g of the bond magnet resin composition is dissolved in 50 mL of benzyl alcohol, and the obtained solution is titrated with 0.1N NaOH to determine the amount of terminal carboxy groups (mmol/kg). The endpoint is determined from the color change of the phenolphthalein indicator.

By adding the terminal amino group amount and the terminal carboxy group amount measured by the above method, the total amount of the terminal amino group amount and the terminal amount of the carboxy group in the resin composition for a bond magnet can be obtained.

With the resin composition for a bonded magnet of the present embodiment having the above structure, it is possible to obtain a bonded magnet excellent in kneadability and heat resistance while suppressing the amount of water absorption.

Next, each constituent component of the resin composition for a bonded magnet according to the present embodiment will be described in detail below.

<Aliphatic Polyamide (A)>
The aliphatic polyamide (A) may be a polyamide consisting of an aliphatic dicarboxylic acid unit (Aa) and an aliphatic diamine unit (Ab), a lactam unit (Ac) or an aminocarboxylic acid unit (Ad ) may be used.
Aliphatic polyamide (A) may be used alone or in combination of two or more.

[Aliphatic dicarboxylic acid unit (Aa)]
The aliphatic dicarboxylic acid constituting the aliphatic dicarboxylic acid unit is not limited to the following, but examples include malonic acid, dimethylmalonic acid, succinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethyl Glutaric acid, 2,2-diethylsuccinic acid, 2,3-diethylglutaric acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaine acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, eicosanedioic acid, diglycolic acid, etc. mentioned.
The aliphatic dicarboxylic acids constituting the aliphatic dicarboxylic acid unit may be used alone or in combination of two or more.

[Aliphatic diamine unit (Ab)]
Aliphatic diamines constituting the aliphatic diamine unit are not limited to the following, but examples include ethylenediamine, propylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, Linear saturated aliphatic diamines having 2 to 20 carbon atoms such as nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, tridecamethylenediamine; 2-methylpentamethylenediamine (2-methyl-1, 5-diaminopentane), 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 2-methyl-1,8-octanediamine (also called 2-methyloctamethylenediamine ) and branched saturated aliphatic diamines having 3 to 20 carbon atoms such as 2,4-dimethyloctamethylenediamine.
The aliphatic diamines constituting the aliphatic diamine unit may be used alone or in combination of two or more.

[Lactam unit (Ac)]
Examples of the lactam constituting the lactam unit include, but are not limited to, butyrolactam, pivalolactam, ε-caprolactam, caprylolactam, enantholactam, undecanolactam, laurolactam (dodecanolactam), and the like. be done.
The lactams constituting the lactam unit may be used alone or in combination of two or more.

[Aminocarboxylic acid unit (Ad)]
Examples of the aminocarboxylic acid constituting the aminocarboxylic acid unit include, but are not limited to, ω-aminocarboxylic acids and α,ω-amino acids, which are lactam ring-opened compounds.
The aminocarboxylic acids constituting the aminocarboxylic acid unit may be used alone or in combination of two or more.

Among them, the aliphatic polyamide (A) preferably contains an aliphatic polyamide having a repeating unit of 12 or more carbon atoms, and preferably contains polyamide 612 (PA612), from the viewpoint of suppressing water absorption.

[Terminal blocking agent]
Terminal adjustment of the polyamide is performed, for example, by adding a dicarboxylic acid or a diamine or terminal blocking with a known terminal blocking agent. Terminal blockers may be used alone or in combination of two or more.

The dicarboxylic acid and diamine added for terminal adjustment are the same as those exemplified in the above "aliphatic dicarboxylic acid unit (Aa)" and "aliphatic diamine unit (Ab)". mentioned.

Examples of terminal blocking agents include, but are not limited to, monocarboxylic acids, monoamines, acid anhydrides, monoisocyanates, monoacid halides, monoesters, and monoalcohols. Examples of acid anhydrides include phthalic anhydride and the like.
Among them, a monocarboxylic acid or a monoamine is preferable as the terminal blocking agent. By blocking the ends of the polyamide with a terminal blocking agent, the polyamide tends to be more excellent in thermal stability.
Terminal blockers may be used alone or in combination of two or more.

The monocarboxylic acid that can be used as a terminal blocker may have reactivity with an amino group that may be present at the terminal of the polyamide, and is not limited to the following, for example, aliphatic monocarboxylic acid acids, alicyclic monocarboxylic acids, aromatic monocarboxylic acids, and the like. Examples of aliphatic monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, lauric acid, tridecylic acid, myristic acid, palmitic acid, stearic acid, pivalic acid, and isobutyric acid. mentioned. Alicyclic monocarboxylic acids include, for example, cyclohexanecarboxylic acid. Examples of aromatic monocarboxylic acids include benzoic acid, toluic acid, α-naphthalenecarboxylic acid, β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid, and phenylacetic acid.
Monocarboxylic acids may be used alone or in combination of two or more.

The monoamine that can be used as a terminal blocking agent is not limited to the following, as long as it has reactivity with a carboxyl group that may be present at the terminal of the polyamide. For example, aliphatic monoamine, alicyclic monoamines, aromatic monoamines, and the like. Examples of aliphatic monoamino include methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, decylamine, stearylamine, dimethylamine, diethylamine, dipropylamine and dibutylamine. Alicyclic monoamines include, for example, cyclohexylamine and dicyclohexylamine. Examples of aromatic monoamines include aniline, toluidine, diphenylamine, naphthylamine and the like.
Monoamines may be used alone or in combination of two or more.

[Method for producing aliphatic polyamide (A)]
When producing the aliphatic polyamide (A), the amount of dicarboxylic acid added and the amount of diamine added are preferably about the same molar amount. Considering the amount of diamine that escapes to the outside of the reaction system during the polymerization reaction, the molar ratio of the total diamine to the total molar amount of the dicarboxylic acid is preferably 0.9 or more and 1.2 or less. , is more preferably 0.95 or more and 1.1 or less, and more preferably 0.98 or more and 1.05 or less.

The method for producing the aliphatic polyamide (A) includes, but is not limited to, the following polymerization step (1) or (2).
(1) A step of polymerizing one or more selected from the group consisting of lactams constituting lactam units and aminocarboxylic acids constituting aminocarboxylic acid units to obtain a polymer.
(2) A step of polymerizing a combination of a dicarboxylic acid constituting a dicarboxylic acid unit and a diamine constituting a diamine unit to obtain a polymer.

Moreover, it is preferable that the method for producing the aliphatic polyamide (A) further includes an increasing step for increasing the degree of polymerization of the polyamide after the polymerization step. Further, if necessary, a blocking step of blocking terminals of the obtained polymer with a terminal blocking agent may be included after the polymerization step and the rising step.

Specific methods for producing the aliphatic polyamide (A) include, for example, various methods exemplified in 1) to 4) below.
1) A lactam and one or more aqueous solutions or aqueous suspensions selected from the group consisting of aminocarboxylic acids, dicarboxylic acid-diamine salts, and mixtures of dicarboxylic acids and diamines are heated to polymerize while maintaining the molten state. method (hereinafter sometimes referred to as “thermal melt polymerization method”).
2) A method of increasing the degree of polymerization of a polyamide obtained by a hot melt polymerization method while maintaining a solid state at a temperature below the melting point (hereinafter sometimes referred to as "hot melt polymerization/solid phase polymerization method").
3) A method of polymerizing one or more selected from the group consisting of dicarboxylic acid-diamine salts, mixtures of dicarboxylic acids and diamines, lactams, and/or aminocarboxylic acids while maintaining a solid state (hereinafter referred to as "solid phase may be referred to as "polymerization method").
4) A method of polymerizing using a dicarboxylic acid halide component equivalent to the dicarboxylic acid and a diamine component (hereinafter sometimes referred to as "solution method").

Among them, as a specific method for producing the aliphatic polyamide (A), a production method including a hot melt polymerization method is preferable. Moreover, when producing a polyamide by a hot melt polymerization method, it is preferable to maintain a molten state until the polymerization is completed. In order to maintain the molten state, it is necessary to produce the polyamide composition under suitable polymerization conditions. Polymerization conditions include, for example, the conditions shown below. First, the polymerization pressure in the hot melt polymerization method is controlled to 14 kg/cm ² or more and 25 kg/cm ² or less (gauge pressure), and heating is continued. Then, the pressure in the tank is lowered over 30 minutes or more until it reaches the atmospheric pressure (gauge pressure is 0 kg/cm ² ).

In the method for producing the aliphatic polyamide (A), the form of polymerization is not particularly limited, and may be a batch system or a continuous system.
A polymerization apparatus used for producing the aliphatic polyamide (A) is not particularly limited, and a known apparatus can be used. Specific examples of the polymerization apparatus include an autoclave reactor, a tumbler reactor, and an extruder reactor (kneader, etc.).

As a method for producing the aliphatic polyamide (A), a method for producing a polyamide by a batch-type hot-melt polymerization method will be specifically described below, but the method for producing a polyamide is not limited to this.
First, an aqueous solution containing about 40% by mass or more and 60% by mass or less of raw material components for the aliphatic polyamide (A) (one or more selected from the group consisting of lactams and aminocarboxylic acids, dicarboxylic acids, and diamines) is prepared. Then, the aqueous solution is heated to a temperature of 110° C. or higher and 180° C. or lower, and In a concentration tank operated at a pressure of about 0.035 MPa or more and 0.6 MPa or less (gauge pressure), the solution is concentrated to about 65 mass % or more and 90 mass % or less to obtain a concentrated solution.
The resulting concentrated solution is then transferred to an autoclave and heating is continued until the pressure in the autoclave is about 1.2 MPa to 2.2 MPa (gauge pressure).
Then, in an autoclave, the pressure is maintained at about 1.2 MPa or more and 2.2 MPa or less (gauge pressure) while removing at least one of water and gas components. Next, when the temperature reaches approximately 220° C. or higher and 260° C. or lower, the pressure is lowered to atmospheric pressure (gauge pressure is 0 MPa). By reducing the pressure in the autoclave to atmospheric pressure and then reducing the pressure as necessary, water produced as a by-product can be effectively removed.
The autoclave is then pressurized with an inert gas such as nitrogen and the polyamide melt is extruded from the autoclave as a strand. The extruded strand is cooled and cut to obtain pellets of the aliphatic polyamide (A).

<Amorphous Resin (B)>
The amorphous resin (B) is a resin that does not crystallize in an irregular arrangement and becomes a solid, and has a crystallization enthalpy δH of 15 J/g or less. The enthalpy of crystallization δH is measured, for example, according to JIS-K7121 using Diamond-DSC manufactured by PERKIN-ELMER. Specifically, it can be measured using the method described in the examples below.

Examples of the amorphous resin (B) include, but are not limited to, polyamide 6I (PA6I), polyamide 6I/6T (PA6I/6T), and polyphenylene ether (PPE). It is preferable to contain PPE because it has excellent heat resistance while suppressing water absorption.
These amorphous resins (B) may be used alone, or two or more of them may be used in combination.

<Mass ratio of aliphatic polyamide (A) to amorphous resin (B)>
From the balance of kneadability, moldability, suppression of water absorption, and heat resistance, the mass ratio (A)/(B) of the aliphatic polyamide (A) and the amorphous resin (B) is 70/30 or more and 80/ It is preferably 20 or less.

<Method for producing resin composition for bonded magnet>
A resin composition for a bonded magnet can be obtained by melt-kneading the aliphatic polyamide (A) and the amorphous resin (B).

Examples of the method for mixing the components (A) to (B) include the following method (1) or (2).
(1) A method of mixing the components (A) to (B) using a Henschel mixer or the like, supplying the mixture to a melt-kneader, and kneading the mixture.
(2) Using a single-screw or twin-screw extruder, the components (A) to (B) are mixed in advance using a Henschel mixer or the like to prepare a mixture containing the components (A) to (B). and then supplying the mixture to a melt kneader and kneading it.

The method of supplying the components constituting the resin composition for a bonded magnet to the melt kneader may be to supply all the components to the same supply port at once, or to supply the components from different supply ports. good.

The melt-kneading temperature is preferably about 1° C. to 100° C. higher than the melting point of the aliphatic polyamide (A), more preferably about 10° C. to 60° C. higher than the melting point of the aliphatic polyamide (A).

The shear rate in the kneader is preferably about 100 sec ^-1 or more. Also, the average residence time during kneading is preferably about 0.5 minutes or more and 5 minutes or less.

As a melt-kneading device, a known device may be used, and for example, a single-screw or twin-screw extruder, a Banbury mixer, a melt-kneader (mixing roll, etc.), etc. are preferably used.

The blending amounts of the above components (A) and (B) when producing the resin composition for a bonded magnet of the present embodiment are It is preferable to use an amount that satisfies the mass ratio of the components.

≪Bond magnet≫
The bonded magnet of the present embodiment contains 5% by mass or more and 10% by mass or less of the resin composition for a bonded magnet and 90% by mass or more and 95% by mass or less of the magnetic powder with respect to the total mass of the bonded magnet. It consists of an injection molded body containing

The bonded magnet of the present embodiment contains the above resin composition for a bonded magnet in the above compounding ratio, so that the amount of water absorption is suppressed and the kneadability and heat resistance are excellent.

<Magnetic powder>
Examples of magnetic powder include, but are not limited to, ferrite magnetic powder, Sm (samarium)-Co (cobalt) magnetic powder, Sm (samarium)-Fe (iron)-N ( nitrogen)-based magnetic powder, Nd (neodymium)--Fe (iron)--B (boron)-based magnetic powder, and mixtures of these magnetic powders.

The content of the magnetic powder with respect to the total mass of the bonded magnet can be 70% by mass or more and 95% by mass or less, preferably 80% by mass or more and 95% by mass or less, and 90% by mass or more and 95% by mass. % or less. When the content of the magnetic powder is equal to or higher than the above lower limit, it is possible to prevent the residual magnetic flux density of the obtained magnet from being lowered, and to secure the practicality as a permanent magnet. On the other hand, when the content of the magnetic powder is equal to or less than the above upper limit, the amount of the magnetic powder per unit volume of the obtained magnet does not become too large, and deterioration in magnetic field orientation can be prevented. In addition, the residual magnetic flux density can be improved while the content of the binder resin component is moderately reduced, and moldability and fluidity can be improved. Therefore, it is possible to effectively prevent troubles such as insufficient filling in the kneading process of compounding and the like and the molding process.

<Application>
Since the bonded magnet of the present embodiment has excellent heat resistance, it is suitable not only for electromagnetic equipment used in a normal temperature range, but also for electromagnetic equipment used in a high temperature range, electromagnetic equipment that becomes hot during use, and the like.

<<Manufacturing method of bonded magnet>>
The method for producing a bonded magnet according to the present embodiment comprises the resin composition for a bonded magnet in an amount of 5% by mass or more and 10% by mass or less and the magnetic powder in an amount of 90% by mass or more and 95% by mass or less with respect to the total mass of the bonded magnet. and are melted and kneaded, followed by injection molding to obtain a bonded magnet.

As a method for melting and kneading the resin composition for a bonded magnet and the magnetic powder, the same methods as those exemplified in the above "Method for producing a resin composition for a bonded magnet" can be employed.

A bond magnet can be obtained by filling the resulting melt-kneaded product into a mold of an injection molding machine and molding it by a known injection molding method. Various conditions for injection molding can be appropriately set by those skilled in the art according to the type of resin used.

Hereinafter, the present embodiment will be described in more detail by showing specific examples and comparative examples, but the present embodiment is not limited by the following examples and comparative examples as long as the gist thereof is not exceeded. .

<raw materials>
[Aliphatic polyamide (A)]
A-1: Polyamide 612 (PA612) (manufactured by Asahi Kasei, trade name “Leona ^TM 4100-001”)
A-2: Polyamide 66 (PA66) (manufactured by Asahi Kasei, trade name “Leona ^TM 1300-301”)
A-3: Polyamide 12 (PA12) (manufactured by Ube Industries, trade name “P3012U”)

[Amorphous resin (B)]
B-1: PPE (manufactured by Asahi Kasei, trade name “Zylon ^TM S203A”, crystallization enthalpy 0 J/g)
B-2: Polyamide 6I (PA6I) (synthesized by hot melt polymerization method, number average molecular weight 10000, weight average molecular weight 20000, crystallization enthalpy 0 J/g)
B-3: Polyamide 6T (PA6T) (manufactured by Mitsui Chemicals, trade name “Arlen A3000”, crystallization enthalpy 0 J/g)
B-4: PPS (manufactured by DIC, trade name “FZ-2100”, crystallization enthalpy 0 J/g)

[Magnetic powder]
Commercially available Nd-Fe-B anisotropic magnet powder (manufactured by Aichi Steel Co., Ltd., trade name "MF18P")

<Method for measuring physical properties>
[Physical properties 1]
(Total amount of terminal amino group (NH ₂ ) and terminal carboxy group (COOH))
The amount of amino group terminals bonded to the polymer terminals of the resin composition for bond magnets was measured by neutralization titration as follows.
3.0 g of the bond magnet resin composition was dissolved in 100 mL of a 90% by mass phenol aqueous solution, and the obtained solution was titrated with 0.025N hydrochloric acid to determine the amount of terminal amino groups (mmol/kg). The endpoint was determined from the pH meter reading.

The amount of carboxy group terminal bound to the polymer terminal of the resin composition for bond magnet was measured by neutralization titration as follows.
4.0 g of the bond magnet resin composition was dissolved in 50 mL of benzyl alcohol, and the obtained solution was titrated with 0.1N NaOH to determine the amount of terminal carboxy groups (mmol/kg). The endpoint was determined from the color change of the phenolphthalein indicator.

The total amount of terminal amino groups (NH ₂ ) and terminal amounts of carboxy groups (COOH) was calculated by adding the amounts of terminal amino groups (NH ₂ ) and terminal amounts of carboxy groups (COOH) obtained by the above method.

[Physical properties 2]
(Method for measuring enthalpy of crystallization δH)
It was measured using a Diamond-DSC manufactured by PERKIN-ELMER in accordance with JIS-K7121. Specifically, it was measured as follows.
First, in a nitrogen atmosphere, about 10 mg of a sample was heated from room temperature to 300° C. or more and 350° C. or less depending on the melting point of the sample at a temperature elevation rate of 20° C./min. The highest peak temperature of the endothermic peak (melting peak) appearing at this time was defined as Tm1 (°C). The temperature was then held at the maximum temperature of the ramp for 2 minutes. At this maximum temperature the polyamide was in the molten state. After that, the temperature is lowered to 30° C. at a temperature lowering rate of 20° C./min. The exothermic peak that appears at this time is defined as the crystallization peak, the crystallization peak temperature is Tc, the crystallization extrapolation start temperature is _Tic , the crystallization extrapolation end temperature is _Tec , and the crystallization peak area is the crystallization enthalpy δH (J / g).

<Evaluation method>
[Manufacturing of bonded magnet]
10 parts by mass of each resin composition for bonded magnets and 90 parts by mass of magnetic powder were mixed while being heated to 280° C. or higher and 320° C. or lower using a twin-screw extruder (ZSK-26MC, manufactured by Coperion GmbH (Germany)). tempered The kneaded material thus obtained was cut by a pelletizer to obtain pellets of the magnetic powder-containing bonded magnet resin composition.

The obtained pellets of the magnetic powder-containing bonded magnet resin composition are put into a hopper of an injection molding machine (EC-100 manufactured by Toshiba Machine Co., Ltd.), heated, and filled into a mold cavity. A bonded magnet of length 127 mm×width 12 mm×thickness 3 mm was obtained. The injection molding was performed at a mold temperature of 120°C and a nozzle temperature of 280°C while applying an oriented magnetic field to the mold cavity.
It should be noted that the resin compositions for bonded magnets of Comparative Examples 1 and 4 could not be made into strands and pelletized (although the evaluation of "kneadability", which will be described later, was x). The die head was opened, stranding was abandoned, and extrusion continued in chunk form to relieve torque, and the chunk was later crushed and molded to produce bonded magnets and ASTM D1822 TYPE L specimens. . Using these, the water absorption rate and the tan δ peak temperature Tg, which will be described later, were evaluated.

[Evaluation 1]
(Kneadability)
When kneading the resin composition for a bonded magnet and the magnetic powder in the above "Production of a bonded magnet", those that were kneaded were evaluated as "○", and the torque of the extruder reached the upper limit and kneading was not possible. was evaluated as "x".

[Evaluation 2]
(water absorption rate)
The bond magnet was dried as mold, and the pre-test mass (mass before water absorption) was measured. It was immersed in pure water at 80° C. for 24 hours. After that, the test piece was taken out of the water, the moisture adhering to the surface was wiped off, and after standing for 30 minutes in a constant temperature and humidity (23°C, 50 RH%) atmosphere, the weight after the test (mass after water absorption) was measured. The increase in the mass after water absorption to the mass before water absorption (mass after water absorption - mass before water absorption) is defined as the amount of water absorption, and the ratio of the amount of water absorption to the mass before water absorption is obtained with the number of trials n = 3, and the average value is the water absorption rate (mass %).

[Production of test piece for measuring tan δ peak temperature Tg]
Using 10 parts by mass of each resin composition for bonded magnets and 90 parts by mass of magnetic powder, ASTM D1822 TYPE L test pieces were produced.

[Evaluation 3]
(tan δ peak temperature Tg)
The temperature dispersion spectrum of the dynamic viscoelasticity of the test piece obtained by cutting the parallel part of the ASTM D1822 TYPE L test piece obtained above into strips using a viscoelasticity measurement analyzer (manufactured by Rheology: DVE-V4) is shown below. was measured under the conditions of The dimensions of the test piece were 3.1 mm (width) x 2.9 mm (thickness) x 15 mm (length: distance between grips). The measurement conditions were as follows.

(Measurement condition)
Measurement mode: Tensile Waveform: Sine wave Frequency: 3.5Hz
Temperature range: 0°C to 180°C Temperature rising step: 2°C/min
Static load: 400g
Displacement amplitude: 0.75 μm

The ratio (E2/E1) of the loss modulus E2 to the storage modulus E1 was defined as tan δ, and the highest temperature was defined as the tan δ peak temperature.

<Production of resin composition for bonded magnet>
[Examples 1-2 and Comparative Examples 1-4]
After dry blending the aliphatic polyamide (A) and the amorphous resin (B) so as to have the types and ratios shown in Table 1, the mixture was supplied from the upstream supply port of the twin-screw extruder and extruded from the die head. The melt-kneaded product was cooled in the form of strands and pelletized to obtain resin compositions for bonded magnets (containing no magnetic powder).
A twin-screw extruder (ZSK-26MC, manufactured by Coperion GmbH (Germany)) was used as a manufacturing apparatus.
The twin-screw extruder has an upstream feed port on the first barrel from the upstream side of the extruder, a downstream first feed port on the sixth barrel, and a downstream second feed port on the ninth barrel. had Also, in the twin-screw extruder, the L/D was 48 and the number of barrels was 12. Also, in the twin-screw extruder, the L/D was 48 and the number of barrels was 12. In the twin-screw extruder, the temperature from the upstream supply port to the die was set to 280° C. or higher and 320° C. or lower, the screw rotation speed was set to 300 rpm, and the discharge rate was set to 25 kg/hour.

Using each of the obtained resin compositions for bonded magnets, physical properties were measured, bonded magnets were produced by the above-described methods, and various evaluations were performed. The results are shown in Table 1 below.

Resin compositions for bonded magnets of Examples 1 and 2, comprising an aliphatic polyamide (A) and an amorphous resin (B), and having a total amount of terminal amino groups and terminal carboxy groups within a specific range. Thus, a bonded magnet having excellent kneadability and heat resistance was obtained while suppressing the water absorption to 0.25% by mass or less.
On the other hand, it consists of an aliphatic polyamide (A) and an amorphous resin (B), and the total amount of the amino group terminal amount and the carboxy group terminal amount is more than 140.0 mmol / kg, or the aliphatic polyamide ( Bonded magnet resin compositions of Comparative Examples 1 to 4, which consisted only of A) or amorphous resin (B), did not yield bonded magnets excellent in all of water absorption, kneadability and heat resistance.

According to the resin composition for a bonded magnet of the present embodiment, it is possible to provide a resin composition for a bonded magnet that can obtain a bonded magnet that is excellent in kneadability and heat resistance while suppressing water absorption. The bonded magnet of the present embodiment contains the resin composition for a bonded magnet, and is suitable for use in electromagnetic equipment that is used at high temperatures or that becomes hot during use.

Claims (7)

A resin composition for a bonded magnet, comprising an aliphatic polyamide (A) and an amorphous resin (B),
A resin composition for a bond magnet, wherein the total amount of amino group terminals and carboxy group terminals in the resin composition for a bond magnet is 140.0 mmol/kg or less. 2. The resin composition for a bonded magnet according to claim 1, wherein said amorphous resin (B) contains polyphenylene ether (PPE). 3. The resin composition for a bonded magnet according to claim 1, wherein the repeating unit of said aliphatic polyamide (A) has 12 or more carbon atoms. The resin composition for a bonded magnet according to any one of claims 1 to 3, wherein the aliphatic polyamide (A) contains polyamide 612. 5. The resin composition for a bonded magnet according to claim 1, wherein the total amount of terminal amino groups and terminal carboxy groups in said resin composition for bonded magnets is 115.0 mmol/kg or less. 5% by mass or more and 10% by mass or less of the resin composition for a bonded magnet according to any one of claims 1 to 5, and 90% by mass or more and 95% by mass or less of the magnetic powder, relative to the total mass of the bonded magnet. A method for producing a bonded magnet, comprising a step of melt-kneading a body and then injection molding to obtain a bonded magnet. 5% by mass or more and 10% by mass or less of the resin composition for a bonded magnet according to any one of claims 1 to 5, and 90% by mass or more and 95% by mass or less of the magnetic powder, relative to the total mass of the bonded magnet. A bonded magnet comprising an injection molded body comprising: