JP2008277663A - Magnet, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnet which does not require an elevated temperature at the time of forming and has excellent magnetic property, and a manufacturing method thereof. <P>SOLUTION: A magnet 10 comprises a magnetic particulate 11 the surface of which is covered with a film 12 formed of a film compound having a reactive functional group at one end of a molecule, and a cross-linking agent 13 having a plurality of cross-link reaction groups which react with the functional group and form a connection. The covered magnetic particulate 11 is formed and cured via the connection formed by reaction between the functional group and the cross-link reaction group. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a magnet and a manufacturing method thereof. More specifically, the present invention relates to a magnet produced using magnetic fine particles having a reactive functional group introduced on the surface and a crosslinking agent having a crosslinking reactive group, and a production method thereof.

Conventionally, sintered magnets (ceramic magnets) obtained by sintering rare earth-based (Sm-Co-based, Nd-Fe-B-based, etc.) and ferrite-based magnetic particles, and magnetic particles in plastics, rubbers, and other resins. There are many known bonded magnets (see, for example, Patent Document 1) in which the above is dispersed and molded and solidified.

JP-A-8-264360

However, sintered magnets have problems that a large amount of heat energy is required to sinter at a high temperature of 1000 ° C. or higher, and that magnetic properties of magnetic particles deteriorate and it is difficult to obtain a high-performance magnet. is doing.
In addition, the bonded magnet has advantages such as being easy to mold and having flexibility because it uses a resin as a binder, but has a problem that it is difficult to obtain a magnet with excellent magnetization strength.

This invention is made | formed in view of this subject, and it aims at providing the magnet which does not require high temperature at the time of shaping | molding, and has the outstanding magnetic characteristic, and its manufacturing method.

The magnet according to the first invention in accordance with the above object forms a bond by reacting the functional group with magnetic fine particles whose surface is coated with a film formed by a film compound having a reactive functional group at one end of the molecule. The coated magnetic fine particles are molded and cured via a bond formed by a reaction between the reactive functional group and the crosslinking reactive group. .

In the magnet according to the first invention, the film compound may be covalently bonded to the surface of the magnetic fine particle via Si.

In the magnet according to the first invention, the coating is preferably a monomolecular film.

In the magnet according to the first aspect of the present invention, it is preferable that the reactive functional group and the cross-linking reactive group are either a thermal reactive group or an ion reactive functional group.

In the magnet according to the first invention, N—CH ₂ in which a bond formed by a crosslinking reaction between the reactive functional group and the crosslinking reactive group is formed by a reaction between an amino group or an imino group and an epoxy group. It may be a CH (OH) bond.

In the magnet according to the first invention, the bond formed by the crosslinking reaction between the reactive functional group and the crosslinking reaction group is an NH—CONH bond formed by the reaction of an amino group or imino group and an isocyanate group. It may be.

According to a second aspect of the present invention, there is provided a magnet manufacturing method, wherein a film compound having a reactive functional group and a binding group at both ends of a molecule is brought into contact with magnetic fine particles, and a bond is formed between the binding group and the surface of the fine particles Step A for producing reactive magnetic fine particles whose surfaces are covered with a film formed by the film compound, and a plurality of cross-linking reactive groups that react with the functional magnetic groups to form bonds by reacting with the functional groups. And a step B in which the cross-linking agent is mixed and placed in a template, and a bond is formed in the template by a reaction between the reactive functional group and the cross-linking reactive group.

In the magnet manufacturing method according to the second invention, it is preferable that the film formed by the film compound is a monomolecular film.

In the method for producing a magnet according to the second invention, the bond formed by the cross-linking reaction between the reactive functional group and the cross-linking reactive group is formed by a reaction between an amino group or imino group and an epoxy group. It may be a —CH ₂ CH (OH) bond.

In the magnet manufacturing method according to the second aspect of the present invention, the bond formed by the crosslinking reaction between the reactive functional group and the crosslinking reactive group is formed by the reaction of an amino group or imino group with an isocyanate group. It may be a -CONH bond.

In the method for manufacturing a magnet according to the second invention, it is preferable that the step B is performed in a magnetic field.
Moreover, it is more preferable to perform the said process B, applying an ultrasonic wave.

In the magnet of Claims 1-6 and the manufacturing method of the magnet of Claims 7-12, the functional group of the film | membrane which the film compound formed in the surface of a magnetic fine particle forms, and the crosslinking reaction group which a crosslinking agent has The magnetic fine particles are shaped and hardened through the bonds formed by the reaction with. Therefore, it can be formed into an arbitrary shape.
In addition, since the temperature necessary for forming the bond is lower than the sintering temperature and the Curie temperature of the magnetic fine particles, it is possible to reduce the energy cost required for production and to suppress the disappearance of spontaneous magnetization due to heating during molding. .
Furthermore, since a binder such as a resin is not required, a magnet having a higher energy density can be provided.

In the magnet according to claim 2, since the film compound is covalently bonded to the surface of the magnetic fine particle through Si, the film compound is hardly peeled off from the surface of the magnetic fine particle, and the durability of the magnet can be improved.

In the magnet according to claim 3 and the magnet manufacturing method according to claim 8, since the film formed by the film compound is a monomolecular film, the content of the film compound in the magnet is minimized, Performance can be improved.

In the magnet according to claim 4, since the reactive functional group is either a thermal reactive group or an ion reactive functional group, no special manufacturing equipment is required, and the reaction is performed in a normal molding die. It is possible to cause a reaction between the functional group and the crosslinking reactive group.

The magnet according to claim 5 and the method for producing a magnet according to claim 9, wherein the bond formed by a crosslinking reaction between a reactive functional group and a crosslinking reactive group is a reaction between an amino group or imino group and an epoxy group. Since the N—CH ₂ CH (OH) bond is formed and has high strength, a magnet having high mechanical strength and high durability can be provided.

In the magnet according to claim 6 and the method for producing a magnet according to claim 10, a bond formed by a crosslinking reaction between the reactive functional group and the crosslinking reactive group is an amino group or an imino group and an isocyanate group. Since the NH—CONH bond is formed and formed by the above reaction and has high strength, a magnet having high mechanical strength and high durability can be provided.

In the magnet manufacturing method according to claim 11, the step B of forming the bond formed by the reaction of the reactive functional group and the cross-linking reactive group by mixing the reactive magnetic fine particles and the cross-linking agent and putting them in the template. Since it is performed in a magnetic field, a magnet having excellent magnetic anisotropy can be produced.
In the magnet manufacturing method according to the twelfth aspect, since the process B is performed while applying an ultrasonic wave in a magnetic field, a magnet having further excellent magnetic anisotropy can be manufactured.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is an explanatory view schematically showing a cross-sectional structure of a magnet according to an embodiment of the present invention, and FIG. 2 is a view for explaining a process of manufacturing epoxidized magnetite fine particles in the magnet manufacturing method. FIG. 2 is a schematic diagram enlarged to a molecular level, where (a) shows a cross-sectional structure of magnetite fine particles before reaction, and (b) shows a cross-sectional structure of epoxidized magnetite fine particles on which a monomolecular film containing an epoxy group is formed.

As shown in FIG. 1, a magnet 10 according to an embodiment of the present invention is a single unit in which an alkoxysilane compound (an example of a film compound) having an epoxy group (an example of a reactive functional group) at one end of a molecule is formed. Epoxidized magnetite fine particles 11 (an example of a magnetic fine particle whose surface is coated with a film formed by a film compound) 11 and 2-methylimidazole 13 (an example of a crosslinking agent) The epoxidized magnetite fine particles 11 are molded and cured via a bond formed by a reaction between an epoxy group, an amino group of 2-methylimidazole 13 and an imino group (an example of a cross-linking reactive group). .

The magnet 10 is made by bringing a film compound having an epoxy group and an alkoxysilyl group (an example of a bonding group) at both ends of a molecule into contact with a magnetite fine particle (an example of a magnetic fine particle) 21 so that the alkoxysilyl group and the hydroxyl group on the surface of the magnetite fine particle 22, a process A for producing epoxidized magnetite fine particles 11, epoxidized magnetite fine particles 11, and 2-methylimidazole 13 are mixed and placed in a mold, heated in the mold, and epoxy And a step B in which a bond is formed by the reaction of an amino group and an amino group of 2-methylimidazole 13 and an imino group (an example of a crosslinking reactive group).

Hereinafter, steps A and B will be described in more detail.
In step A, epoxidized magnetite fine particles 11 whose surface is covered with a monomolecular film 12 of a film compound having an epoxy group are produced.
The diameter of the magnetite fine particles 21 used for the production of the epoxidized magnetite fine particles 11 is not particularly limited, but is preferably 100 μm or less. When the diameter is larger than 100 μm, the gap between the epoxidized fine particles 11 is increased, so that the magnetic properties of the magnet 10 are lowered and the ratio of the mass to the surface area is increased, and the mass cannot be supported by the crosslinking reaction. The mechanical strength is reduced.
Considering various factors such as availability in the market, manufacturing cost, and handling due to secondary aggregation, the diameter of the magnetite fine particles 21 is preferably 10 to 500 nm.
The magnetite fine particles 21 used may have a single particle size, or may be used by mixing magnetite fine particles having two or more different particle sizes.

The reaction liquid used for the production of the epoxidized magnetite fine particles 11 includes an alkoxysilane compound containing an epoxy group, a condensation catalyst for accelerating the condensation reaction between the alkoxysilyl group and the hydroxyl group 22 on the surface of the magnetite fine particle 21, and a non-aqueous system. It is prepared by mixing with an organic solvent.

The alkoxysilane compound containing an epoxy group has a functional group containing an epoxy group (oxirane ring) and an alkoxysilyl group at both ends of the linear alkylene group, and is represented by the following general formula (Formula 1). An alkoxysilane compound is preferable.

In the above formula, E represents a functional group containing an epoxy group, m represents an integer of 3 to 20, and R represents an alkyl group having 1 to 4 carbon atoms.

As an example of the alkoxysilane compound which has an epoxy group which can be used in process A, the compound shown to following (1)-(12) is mentioned.

(1) (CH ₂ OCH) CH ₂ O (CH ₂ ) ₃ Si (OCH ₃ ) _{3
(2) (CH 2 OCH)} CH 2 O (CH 2) 7 Si (OCH 3) 3
(3) (CH ₂ OCH) CH ₂ O (CH ₂ ) ₁₁ Si (OCH ₃ ) _{3
(4) (CH 2 CHOCH (} CH 2) 2) CH (CH 2) 2 Si (OCH 3) 3
_{(5) (CH 2 CHOCH (} CH 2) 2) CH (CH 2) 4 Si (OCH 3) 3
(6) (CH ₂ CHOCH (CH ₂ ) ₂ ) CH (CH ₂ ) ₆ Si (OCH ₃ ) _{3
(7) (CH 2 OCH)} CH 2 O (CH 2) 3 Si (OC 2 H 5) 3
_{(8) (CH 2 OCH)} CH 2 O (CH 2) 7 Si (OC 2 H 5) 3
(9) (CH ₂ OCH) CH ₂ O (CH ₂ ) ₁₁ Si (OC ₂ H ₅ ) ₃
(10) (CH ₂ CHOCH (CH ₂ ) ₂ ) CH (CH ₂ ) ₂ Si (OC ₂ H ₅ ) _{3
(11) (CH 2 CHOCH (} CH 2) 2) CH (CH 2) 4 Si (OC 2 H 5) 3
(12) (CH ₂ CHOCH (CH ₂ ) ₂ ) CH (CH ₂ ) ₆ Si (OC ₂ H ₅ ) ₃

Here, the (CH ₂ OCH) CH ₂ O— group represents a functional group (glycidyloxy group) represented by Chemical Formula ₂ , and the (CH ₂ CHOCH (CH ₂ ) ₂ ) CH— group is represented by Chemical Formula 3. Represents a functional group (3,4-epoxycyclohexyl group).

As the condensation catalyst, metal salts such as carboxylic acid metal salts, carboxylic acid ester metal salts, carboxylic acid metal salt polymers, carboxylic acid metal salt chelates, titanate esters and titanate ester chelates can be used.
The addition amount of the condensation catalyst is preferably 0.2 to 5% by mass of the alkoxysilane compound, and more preferably 0.5 to 1% by mass.

Specific examples of carboxylic acid metal salts include stannous acetate, dibutyltin dilaurate, dibutyltin dioctate, dibutyltin diacetate, dioctyltin dilaurate, dioctyltin dioctate, dioctyltin diacetate, stannous dioctanoate, naphthenic acid Lead, cobalt naphthenate, and iron 2-ethylhexenoate.

Specific examples of the carboxylic acid ester metal salt include dioctyltin bisoctylthioglycolate ester salt and dioctyltin maleate ester salt.
Specific examples of the carboxylic acid metal salt polymer include dibutyltin maleate polymer and dimethyltin mercaptopropionate polymer.
Specific examples of the carboxylic acid metal salt chelate include dibutyltin bisacetylacetate and dioctyltin bisacetyllaurate.

Specific examples of the titanate ester include tetrabutyl titanate and tetranonyl titanate.
Specific examples of titanate chelates include bis (acetylacetonyl) dipropyl titanate.

When the reaction solution is applied to the surface of the magnetite fine particles 21 and reacted in air at room temperature, the alkoxysilyl group and the hydroxyl groups 22 on the surface of the magnetite fine particles 21 cause a condensation reaction, as shown in the following chemical formula 4. A monomolecular film 12 of a film compound having an epoxy group having a structure is generated. The three single bonds extending from the oxygen atom are bonded to the surface of the magnetite fine particle 21 or the silicon (Si) atom of the adjacent silane compound, and at least one of them is bonded to the silicon atom on the surface of the magnetite fine particle 21. is doing.

Since the alkoxysilyl group decomposes in the presence of moisture, the reaction is preferably performed in air with a relative humidity of 45% or less. The condensation reaction is hindered by oils and fats and moisture adhering to the surface of the magnetite fine particles 21. Therefore, it is preferable to remove these impurities in advance by thoroughly washing and drying the magnetite fine particles 21.
When any of the above metal salts is used as the condensation catalyst, the time required for completion of the condensation reaction is about 2 hours.

When one or more compounds selected from the group consisting of ketimine compounds, organic acids, aldimine compounds, enamine compounds, oxazolidine compounds, and aminoalkylalkoxysilane compounds are used as the condensation catalyst instead of the above metal salts, Time can be shortened to about 1/2 to 2/3.

Alternatively, when these compounds are used as a co-catalyst and mixed with the above-described metal salt (mass ratio 1: 9 to 9: 1 can be used, preferably around 1: 1), the reaction time is further shortened. it can.

For example, when H3 from Japan Epoxy Resin Co., Ltd., which is a ketimine compound, is used as the condensation catalyst instead of dibutyltin oxide, and the other conditions are the same, the quality of the epoxidized magnetite fine particles 11 is improved. The reaction time can be shortened to about 1 hour without loss.

Furthermore, when a mixture of H3 and dibutyltin bisacetylacetonate of Japan Epoxy Resin Co., Ltd. (mixing ratio is 1: 1) is used as the condensation catalyst, and the other conditions are the same, the epoxidized magnetite fine particles 11 are produced. The reaction time can be shortened to about 20 minutes.

The ketimine compound that can be used here is not particularly limited, and examples thereof include 2,5,8-triaza-1,8-nonadiene, 3,11-dimethyl-4,7,10-triaza- 3,10-tridecadiene, 2,10-dimethyl-3,6,9-triaza-2,9-undecadiene, 2,4,12,14-tetramethyl-5,8,11-triaza-4,11-penta Decadiene, 2,4,15,17-tetramethyl-5,8,11,14-tetraaza-4,14-octadecadiene, 2,4,20,22-tetramethyl-5,12,19-triaza -4,19-trieicosadiene and the like.

Moreover, although it does not specifically limit as an organic acid which can be used, For example, a formic acid, an acetic acid, propionic acid, a butyric acid, malonic acid etc. are mentioned.

For the preparation of the reaction solution, an organic chlorine solvent, a hydrocarbon solvent, a fluorocarbon solvent, a silicone solvent, and a mixed solvent thereof can be used. In order to prevent hydrolysis of the alkoxysilane compound, it is preferable to remove water from the desiccant or the solvent used by distillation. Moreover, it is preferable that the boiling point of a solvent is 50-250 degreeC.

Specific usable solvents include non-aqueous petroleum naphtha, solvent naphtha, petroleum ether, petroleum benzine, isoparaffin, normal paraffin, decalin, industrial gasoline, nonane, decane, kerosene, dimethyl silicone, phenyl silicone, and alkyl-modified silicone. , Polyether silicone, dimethylformamide and the like.
Furthermore, alcohol solvents such as methanol, ethanol, propanol, or a mixture thereof can also be used.

Fluorocarbon solvents that can be used include fluorocarbon solvents, Fluorinert (manufactured by 3M, USA), Afludo (manufactured by Asahi Glass Co., Ltd.), and the like. In addition, these may be used individually by 1 type and may mix 2 or more types as long as it mixes well. Furthermore, an organic chlorine solvent such as dichloromethane or chloroform may be added.

The preferable density | concentration of the alkoxysilane compound in a reaction liquid is 0.5-3 mass%.

After the reaction, washing with a solvent to remove excess alkoxysilane compound and condensation catalyst remaining on the surface as unreacted substances yields epoxidized magnetite fine particles 11 whose surface is covered with a monomolecular film 12 of a film compound.
Either continuous processing or batch processing may be used for cleaning. Separation of the washing solvent and the epoxidized magnetite fine particles can be performed using any known method such as filtration, decantation, and centrifugation.
A schematic diagram of the cross-sectional structure of the epoxidized magnetite fine particles 11 produced in this way is shown in FIG.

As the cleaning solvent, any solvent that can dissolve the alkoxysilane compound can be used, but dichloromethane, chloroform, N-methylpyrrolidone, etc. that are inexpensive, have high solubility, and can be easily removed by air drying are preferable. .

After the reaction, when the produced epoxidized magnetite fine particles 11 are left in the air without being washed with a solvent, a part of the alkoxysilane compound remaining on the surface is hydrolyzed by moisture in the air, and the produced silanol group is converted to alkoxy. Causes a condensation reaction with a silyl group. As a result, an ultrathin polymer film made of polysiloxane is formed on the surface of the epoxidized magnetite fine particles 11. Although this polymer film is not fixed to the surface of the epoxidized magnetite fine particles 11 by a covalent bond, it contains an epoxy group, and therefore has the same reactivity with respect to 2-methylimidazole as the monomolecular film 12 of the film compound. Have. Therefore, there is no particular hindrance to the subsequent manufacturing process of the magnet 10 even without cleaning.

In the present embodiment, an alkoxysilane compound having an epoxy group is used, but an amino group and an alkoxysilyl group are respectively present at both ends of the linear alkylene group, and represented by the following general formula (Formula 5). An alkoxysilane compound can be used.

In the above formula, m represents an integer of 3 to 20, and R represents an alkyl group having 1 to 4 carbon atoms. The epoxy group may be protected by a protecting group in order to avoid side reactions with the alkoxysilyl group. The protecting group is preferably one that can be easily removed by hydrolysis or the like, and examples thereof include a ketimine derivative produced by the reaction between a ketone and an amino group.
The amino group may be a secondary amine other than the primary amine shown in Chemical Formula 5, and an alkoxysilane compound containing a functional group having an imino group such as a pyrrole group or an imidazole group may be used instead of the amino group. Can do.
In this case, examples of the alkoxysilane compound having an amino group that can be used include the compounds shown in the following (21) to (28).

(21) H ₂ N (CH ₂ ) ₃ Si (OCH ₃ ) ₃
(22) H ₂ N (CH ₂ ) ₅ Si (OCH ₃ ) ₃
(23) H ₂ N (CH ₂ ) ₇ Si (OCH ₃ ) ₃
(24) H ₂ N (CH ₂ ) ₉ Si (OCH ₃ ) ₃
(25) H ₂ N (CH ₂ ) ₅ Si (OC ₂ H ₅ ) ₃
(26) H ₂ N (CH ₂ ) ₅ Si (OC ₂ H ₅ ) ₃
(27) H ₂ N (CH ₂ ) ₇ Si (OC ₂ H ₅ ) ₃
(28) H ₂ N (CH ₂ ) ₉ Si (OC ₂ H ₅ ) ₃

Among condensation catalysts, a compound containing a tin (Sn) salt reacts with an amino group contained in an alkoxysilane derivative to generate a precipitate, and thus cannot be used as a condensation catalyst.
Therefore, when using an alkoxysilane compound having an amino group, except for a carboxylic acid tin salt, a carboxylic acid ester tin salt, a carboxylic acid tin salt polymer, and a carboxylic acid tin salt chelate, a compound similar to the reaction solution alone or Two or more types can be mixed and used as a condensation catalyst.
The types of cocatalysts that can be used and combinations thereof, the types of solvents, the concentration of alkoxysilane compounds, condensation catalysts, and cocatalysts, the reaction conditions, and the reaction time are the same as when using alkoxysilane compounds having an epoxy group. Since there is, description is abbreviate | omitted.

In the present embodiment, magnetite fine particles are used as the magnetic fine particles, but any magnetic fine particles used in the manufacture of magnets can also be used.
Specific examples of magnetic fine particles include iron, cobalt, and nickel fine particles, martensitic steel-cobalt, iron-chromium-cobalt, alloy-based magnetic fine particles such as iron-platinum, alnico, and metal oxides such as ferrite and chromium oxide. Fine particles, rare earth magnetic fine particles such as Sm ₂ Co ₇ , Nd ₂ Fe ₁₄ B, and the like.
The particle size of magnetic fine particles that can be used is difficult to determine unambiguously, and has different optimum ranges depending on various factors such as individual material characteristics, market availability, and manufacturing costs. Have. For example, in the case of spherical iron powder, the particle size must be 10 to 100 nm in order to ensure sufficient holding power.
(End of process A)

In step B, the epoxidized magnetite fine particles 11 and 2-methylimidazole 13 are mixed and placed in a mold, heated in the mold, and reacted with the epoxy group and the amino group and imino group of 2-methylimidazole 13. A bond is formed to produce the magnet 10 (FIG. 1).
2-methylimidazole has an amino group (> NH) and an imino group (= N-) which react with an epoxy group at the 1-position and 3-position, respectively, and a crosslinking reaction as shown in the following chemical formula 6 To form a bond.

The addition amount of 2-methylimidazole 13 is preferably 5 to 15% by weight of the epoxidized magnetite fine particles 11. When the addition amount of 2-methylimidazole 13 is less than 5 wt% of the epoxidized magnetite fine particles 11, the mechanical strength of the magnet 10 to be produced is low, and when it exceeds 15 wt%, the presence of the epoxidized magnetite fine particles 11 is present. Since the ratio is lowered, the magnetic properties of the obtained magnet 10 are deteriorated.

Epoxidized magnetite fine particles 11 and 2-methylimidazole 13 may be mixed in a solid state, but a solution containing 2-methylimidazole 13 is added while mixing epoxidized magnetite fine particles 11, and epoxidized magnetite fine particles. 11 may be prepared by uniformly attaching 2-methylimidazole 13 to the surface of 11.
Or you may increase the addition amount of a solvent and may prepare a paste-form or slurry-form mixture.

For the preparation of the solution of 2-methylimidazole 13, any solvent in which 2-methylimidazole 13 is soluble can be used. However, considering the price, volatility at room temperature, toxicity, etc., isopropyl alcohol, ethanol A lower alcohol solvent such as

The amount of the solvent used for the preparation of the paste-like or slurry-like mixture is determined appropriately depending on the direct system of the epoxidized magnetite fine particles 11 and the like, and thus it is difficult to determine uniquely, but the epoxidized magnetite fine particles 11 and 2-methyl 10 to 50% by weight of imidazole 13.
Specifically, an amount necessary for coating the surface of the epoxidized magnetite fine particles 11 with a monomolecular film of 2-methylimidazole 13 may be set.
Mixing of the epoxidized magnetite fine particles 11, the 2-methylimidazole 13, and the solvent can be performed by any means such as a stirring spring or a hand mixer.

A mixture of the epoxidized magnetite fine particles 11 thus obtained and 2-methylimidazole 13 is filled in a mold, heated while being pressurized, and the epoxy groups on the surface of the epoxidized magnetite fine particles 11 and 2- A cross-linking reaction is formed with the nitrogen functional group of methylimidazole 13. The pressurization and heating of the mold can be performed using any known means.
Although the heating temperature depends on various factors such as the particle size of the epoxidized magnetite fine particles and the size and shape of the magnet 10 to be produced, it is difficult to determine uniquely, but 50 to 300 ° C. is preferable. . When the heating temperature is less than 50 ° C., the crosslinking reaction does not proceed sufficiently and the solvent cannot be completely removed. When the heating temperature exceeds 300 ° C., thermal decomposition of the monomolecular film 12 of the film compound having an epoxy group and 2-methylimidazole 13 occurs.
The heating time depends on the heating temperature in addition to the particle size of the epoxidized magnetite fine particles, the size and shape of the magnet 10 to be manufactured, and is appropriately determined in consideration of these factors.

By performing filling into the mold and pressurization and heating of the mold in a magnetic field (magnetic field orientation treatment), the orientation of the epoxidized magnetite fine particles 11 can be improved, and a stronger magnet 10 can be obtained. Any of a permanent magnet, an electromagnet, and a superconducting magnet may be used for applying the magnetic field. The intensity and direction of the magnetic field to be applied are appropriately determined according to the shape, application, etc. of the magnet 10 to be manufactured.

Further, it is preferable to further apply ultrasonic waves in a magnetic field when filling the mold. By ultrasonic waves, the orientation of the epoxidized magnetite fine particles 11 is promoted, and a stronger magnet 10 can be obtained.
Any known means can also be used for application of ultrasonic waves.

In the present embodiment, 2-methylimidazole is used as a crosslinking agent, but any imidazole derivative represented by the following chemical formula 7 can be used. Alternatively, an imidazole-metal complex may be used.

Specific examples of the imidazole derivative represented by Chemical Formula 7 include those shown in the following (31) to (38).
(31) 2-Methylimidazole (R ₂ = Me, R ₄ = R ₅ = H)
(32) 2-Undecylimidazole (R ₂ = C ₁₁ H ₂₃ , R ₄ = R ₅ = H)
(33) 2-Pentadecylimidazole (R ₂ = C ₁₅ H ₃₁ , R ₄ = R ₅ = H)
(34) 2-methyl-4-ethylimidazole _{(R 2 = Me, R 4} = Et, R 5 = H)
(35) 2-Phenylimidazole (R ₂ = Ph, R ₄ = R ₅ = H)
(36) 2-phenyl-4-ethylimidazole _{(R 2 = Ph, R 4} = Et, R 5 = H)
(37) 2-phenyl-4-methyl-5-hydroxymethylimidazole _{(R 2 = Ph, R 4} = Me, R 5 = CH 2 OH)
(38) 2-Phenyl-4,5-bis (hydroxymethyl) imidazole (R ₂ = Ph, R ₄ = R ₅ = CH ₂ OH)
Me, Et, and Ph represent a methyl group, an ethyl group, and a phenyl group, respectively.

In addition, compounds such as acid anhydrides such as phthalic anhydride and maleic anhydride, and phenol derivatives such as dicyandiamide and novolak, which are used as curing agents for epoxy resins, may be used as a crosslinking agent. In this case, an imidazole derivative may be used as a catalyst in order to accelerate the crosslinking reaction.

In this embodiment, the case where a film compound having an epoxy group is used is described. However, in the case where a film compound having an amino group or an imino group is used in Step A, 2 or A coupling agent having 3 or more epoxy groups or 2 or 3 or more isocyanate groups is used. Specific examples of the compound having an isocyanate group include hexamethylene-1,6-diisocyanate, toluene-2,6-diisocyanate, and toluene-2,4-diisocyanate.
The addition amount of these diisocyanate compounds is preferably 5 to 15% by weight of the epoxidized silica fine particles as in the case of 2-methylimidazole. In this case, examples of the solvent that can be used for the production of the film precursor include aromatic organic solvents such as xylene.
Moreover, as a crosslinking agent, the compound which has 2 or 3 or more epoxy groups, such as ethylene glycol diglycidyl ether, can also be used.
(End of process B)

Hereinafter, although the detail of this invention is demonstrated using an Example, this invention is not limited at all by these Examples.
In this example, a case where magnetite fine particles are used as magnetic fine particles will be described.

Example 1: Manufacture of magnet [1]
(1) Production of epoxidized magnetite fine particles Dry magnetite fine particles having a particle diameter of about 100 nm were prepared and dried well.
0.99 parts by weight of 3-glycidyloxypropyltrimethoxysilane (Chemical Formula 8) and 0.01 parts by weight of dibutyltin bisacetylacetonate (condensation catalyst) are weighed and dissolved in 100 parts by weight of hexamethyldisiloxane solvent. The reaction solution was prepared.

Magnetite fine particles were mixed in the reaction solution thus obtained, and reacted in the air (relative humidity 45%) for about 2 hours while stirring.
Thereafter, the resultant was washed with trichlene to remove excess alkoxysilane compound and dibutyltin bisacetylacetonate.

(2) Molding and curing of epoxidized magnetite fine particles 5% by weight of 2-methylimidazole was added to 100 parts by weight of the epoxidized magnetite fine particles prepared in (1) and sufficiently mixed, and filled into a mold. When pressure is applied while irradiating with ultrasonic waves in a magnetic field and further heated to about 50 to 100 ° C., it cures through a covalent bond formed by a cross-linking reaction between an epoxy group and a nitrogen functional group of an imidazole group. A magnet with sufficient strength could be manufactured.

Example 2: Manufacture of magnet [2]
(1) Production of aminated magnetite fine particles Dry magnetite fine particles having a particle diameter of about 100 nm were prepared and dried well.
0.99 parts by weight of 3-aminopropyltrimethoxysilane (Chemical 9; manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.01 part by weight of acetic acid (condensation catalyst) were weighed and added to 100 parts by weight of a hexamethyldisiloxane solvent. To prepare a reaction solution.

Magnetite fine particles were mixed in the reaction solution thus obtained, and reacted in the air (relative humidity 45%) for about 2 hours while stirring.
Thereafter, the resultant was washed with trichlene to remove excess alkoxysilane compound and dibutyltin bisacetylacetonate.

(2) Molding and curing of aminated magnetite fine particles 5 parts by weight of hexamethylene-1,6-diisocyanate was added to 100 parts by weight of the aminated magnetite fine particles prepared in (1), and the mixture was sufficiently mixed and filled into a mold. When pressure is applied while irradiating with ultrasonic waves in a magnetic field, and further heated to about 50 to 100 ° C., it cures through a covalent bond formed by a crosslinking reaction between an amino group and a nitrogen functional group of an isocyanate group, and sufficient machinery A magnet with sufficient strength could be manufactured.

It is explanatory drawing which represented typically the cross-section of the magnet which concerns on one embodiment of this invention. It is the schematic diagram expanded to the molecular level in order to demonstrate the process of manufacturing the epoxidized magnetite fine particle in the manufacturing method of the magnet, (a) is the cross-sectional structure of the magnetite fine particle before reaction, (b) is an epoxy group. Each represents a cross-sectional structure of an epoxidized magnetite fine particle on which a monomolecular film is formed.

Explanation of symbols

10: magnet, 11: epoxidized magnetite fine particle, 12: monomolecular film formed by alkoxysilane compound having epoxy group, 13: 2-methylimidazole, 21: magnetite fine particle, 22: hydroxyl group

Claims (12)

A magnetic fine particle whose surface is coated with a film formed by a film compound having a reactive functional group at one end of the molecule, and a cross-linking agent having a plurality of cross-linking reactive groups that react with the functional group to form a bond. The magnet is characterized in that the coated magnetic fine particles are molded and cured through a bond formed by a reaction between the reactive functional group and the crosslinking reactive group. The magnet according to claim 1, wherein the film compound is covalently bonded to the surface of the magnetic fine particle through Si. The magnet according to any one of claims 1 and 2, wherein the coating is a monomolecular film. The magnet according to any one of claims 1 to 3, wherein the reactive functional group and the crosslinking reactive group are any one of a thermally reactive and an ion reactive functional group. . The magnet according to any one of claims 1 to 4, wherein a bond formed by a crosslinking reaction between the reactive functional group and the crosslinking reactive group is caused by a reaction between an amino group or an imino group and an epoxy group. magnets, characterized in that formed is a _N-CH 2 CH (OH) bond. The magnet according to any one of claims 1 to 4, wherein a bond formed by a crosslinking reaction between the reactive functional group and the crosslinking reactive group is caused by a reaction between an amino group or imino group and an isocyanate group. A magnet characterized by being formed NH-CONH bonds. A film compound having a reactive functional group and a bonding group at both ends of the molecule is brought into contact with the magnetic fine particles, and a bond is formed between the bonding group and the surface of the fine particles. Step A for producing the coated reactive magnetic fine particles,
The reactive magnetic fine particles and a cross-linking agent having a plurality of cross-linking reactive groups that react with the functional group to form a bond are mixed and placed in a template, and the reactive functional group and the cross-linking reactive group in the template And a step B of forming a bond by the reaction of the method. 8. The method for manufacturing a magnet according to claim 7, wherein the film formed by the film compound is a monomolecular film. 9. The magnet manufacturing method according to claim 7, wherein a bond formed by a crosslinking reaction between the reactive functional group and the crosslinking reactive group is an amino group or an imino group and an epoxy group. A method for producing a magnet, which is an N—CH ₂ CH (OH) bond formed by the reaction of 9. The magnet manufacturing method according to claim 7, wherein a bond formed by a crosslinking reaction between the reactive functional group and the crosslinking reactive group is an amino group or an imino group and an isocyanate group. A method for producing a magnet, which is an NH—CONH bond formed by the reaction of The method for producing a magnet according to any one of claims 7 to 10, wherein the step B is performed in a magnetic field. 12. The method of manufacturing a magnet according to claim 11, wherein the step B is performed while applying an ultrasonic wave.

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