JP2008153406A - Rare earth bond magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method which is performed by a simple processing without kneading, granulation and grading of magnetic powder and thermoplastic and manufactures a rare earth bond magnet having high magnetic performance where [BH]max reaches 11MGOe in manufacture of the rare earth bond magnet by compression molding, in which rare earth magnetic powder is bonded with thermoplastic. <P>SOLUTION: Powdered mixture in which powder of thermoplastic adheres to a surface of rare earth magnet powder is formed by using coupling agent. A warmed press die is filled with powder mixture, a magnet shape is given by warm compression molding and it is cooled in a pressurized state. Thus, the rare earth bond magnet is manufactured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for manufacturing a rare earth bonded magnet, and also relates to a rare earth bonded magnet manufactured by the method.

A rare earth bonded magnet in which a rare earth magnet powder is bonded with a resin to form a magnet is manufactured by an injection molding, compression molding, or extrusion technique. In injection molding, a coupling agent is applied to a rare earth magnet powder pulverized to an appropriate size, combined with a thermoplastic resin, kneaded with a powerful kneading device such as a twin-screw kneader, and once pelletized, injected. It is carried out by supplying to a molding machine and injection molding into a mold. Although it is possible to directly form a magnet having a complicated shape, the ratio of the magnet powder in the product magnet cannot be increased due to the limitations due to the manufacturing method described above, and it is not possible to expect a very high magnetic property of the product.

Another problem with injection molding is that gate marks inevitably remain on the molded product. The gate mark often has to be finished smoothly by chamfering, and the magnet powder is exposed and easily rusted, and the rust is peeled off and causes various problems. In order to prevent this, it is necessary to coat the entire molded product or at least the gate portion. Extrusion molding is common with injection molding in that it is easy to produce magnet products with irregular cross-sections, but there is a common problem, and the cut surface of the extrusion product must be coated. Don't be. Due to manufacturing restrictions similar to injection molding, the magnetic powder occupies a limit of about 70% by volume, so the magnetic properties are also low. For example, the maximum magnetic energy product [BH] max value is only 6 MGOe. .

On the other hand, in compression molding, a thermosetting resin, typically an epoxy resin, is used, and usually a compound obtained by mixing a magnetic powder treated with a coupling agent and dried with a liquid resin. This is manufactured according to the process of pressing it with a mold to obtain a molded product, taking it out and heating it by infrared heating or the like to cure the resin. Although the molding cycle is slightly longer, there is a manufacturing method in which a molded product is cooled while it is placed in a mold to obtain a product. Compression molding can only produce products with simple shapes such as rings, but since the proportion of magnet powder in the product magnet can be increased to about 95% by mass, high magnetic properties such as [BH] max of 11 MGOe are achieved. More can be produced. However, bond magnets manufactured by compression molding have poor corrosion resistance, and eventually have to be subjected to anticorrosion coating.

In the production of bonded magnets by compression molding, a proposal has been made to use a thermoplastic resin as a binding resin instead of a conventional thermosetting resin (Patent Document 1). In this technique, the composition of the magnet powder and the thermoplastic resin is pressure-molded at a first temperature at which the thermoplastic resin is in a molten state, and the second temperature lower than the melting temperature of the thermoplastic resin in the pressurized state. It cools to the temperature of this, and the cooling is performed by water cooling. In the press molding, the mold is heated, and the material temperature at the time of molding is set to a temperature at which the thermoplastic resin is in a molten state, which is called “warm molding”. The thermoplastic resin used as the binder resin is preferably polyamide from the viewpoint of excellent moldability and high mechanical strength, liquid crystal polymer and polyphenylene sulfide from the viewpoint of heat resistance, and polyolefin from the viewpoint of ease of molding and cost. ing.

In manufacturing a bonded magnet using this thermoplastic resin as a binding resin, in practice, in order to obtain a composition to be supplied to compression molding, the magnet powder and the thermoplastic resin are heated at a temperature equal to or higher than the thermal deformation temperature of the thermoplastic resin. A step of kneading, granulating or sizing is necessary. Specifically, a magnetic powder and a thermoplastic resin are mixed using a mixer such as a Henschel mixer, and the heat distortion temperature of the thermoplastic resin is determined using a twin-screw extrusion kneader, a roll kneader, a kneader or the like. The kneading is preferably performed at a temperature equal to or higher than the melting point. The kneaded product is granulated by an extrusion granulator, or pulverized by using a ball mill, a vibration mill, a crusher, a jet mill, a pin mill, etc. The size is adjusted to 2 mm, preferably 0.02 to 2 mm, more preferably 0.05 to 2 mm.
Japanese Patent No. 36553852

The bonded magnet using the thermoplastic resin as a binding resin can obtain a compression molded product having a porosity of 4% or less, and therefore, a bonded magnet having [BH] max of 11 MGOe can be obtained. However, the work of kneading, granulating or sizing the magnet powder and the thermoplastic resin takes time, and it cannot be denied that this increases the cost of the product magnet.

An object of the present invention is to produce a bonded magnet in which rare earth magnet powder is bonded with a thermoplastic resin, and requires kneading and granulation or sizing of the magnet powder and the thermoplastic resin, which are necessary for a known production method. It is an object of the present invention to provide a manufacturing method capable of manufacturing a bonded magnet that can be compression-molded by a simple process and has a magnetic performance equivalent to or higher than that of a magnet product by a known method.

The method for producing a rare earth bonded magnet according to the present invention is a method for producing a rare earth bonded magnet in which rare earth magnet powder is bonded with a thermoplastic resin, in which a thermoplastic resin powder is adhered to the surface of the rare earth magnet powder by a coupling agent. A method for producing a rare earth bonded magnet is characterized in that a mixture is formed, the powdery mixture is filled into a heated press mold, a magnet shape is given by warm compression molding, and cooling is performed in a pressurized state.

According to the present invention, in manufacturing a rare earth bonded magnet in which rare earth magnet powder is bonded with a thermoplastic resin, the work of kneading and granulating or sizing the magnet powder and the thermoplastic resin is no longer necessary. The process has become very simple and the factors that have pushed up manufacturing costs have been eliminated. Further, the method of the present invention improves the familiarity between the magnet powder and the thermoplastic resin in the production process by using a coupling agent, so that the porosity is further lowered, the occupied volume ratio of the magnet powder is higher, and A magnet product with reduced oxidation of the magnet powder can be obtained. In comparison with injection molding, it goes without saying that a higher molding pressure can be applied and the porosity can be reduced. Therefore, the manufacturing method of the present invention has made it possible to provide a bonded magnet having a magnetic performance equal to or higher than that of a magnet product by a known method at a reduced cost.

As the rare earth magnet powder, a powder obtained by powdering a molten alloy of an Nd—Fe—B or Sm—Fe—N magnet alloy by a super rapid cooling method is preferable. The shape of the powder is preferably a flat flake shape, and the size is suitably 1 to 50 μm in thickness, 10 to 500 μm in major axis, 2 to 100 μm in minor axis, and 25 to 300 μm in average particle size.

As the coupling agent, a silane, titanate, or zirconate coupling agent used in the production of rare earth bonded magnets can be used as it is or diluted with water or an appropriate solvent. The amount used is suitably 0.1 to 1% by mass with respect to the magnet powder. If the amount is insufficient, the effect of the coupling agent to allow the resin powder to blend with the magnet powder is not sufficiently obtained. If the amount is too large, the ratio of the magnet powder in the product magnet will be reduced to obtain high magnetic properties. Contrary to the intention.

As the thermoplastic resin powder, any thermoplastic synthetic resin can be used as long as it is obtained in a powder state. However, among them, polyamide (PA), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF) or liquid crystal polymer is useful in that it gives high heat resistance and mechanical strength to the product magnet. In the production method of the present invention, it is important to use the thermoplastic resin in the form of a fine powder having a particle diameter of 1 to 50 μm. Due to such a fine powder, the thermoplastic resin powder is closely attached to the surface of the powder magnet by forming one or several layers through a coupling agent, and a small amount of binding resin. The intention of binding as much magnet powder as possible can be achieved. In order to obtain the fine powder of the thermoplastic resin as described above, a simple mechanical pulverization means is usually insufficient, and it is recommended to use freeze pulverization.

The production method of the present invention is to compress and mold a mixture of magnet powder and thermoplastic resin powder.
It is carried out as warm forming in which the temperature of the press die is raised and pressed. At this time, the temperature of the mold is preferably selected in the range of −10 to + 20 ° C. with respect to the melting temperature of the thermoplastic resin. If the melting temperature of the resin is significantly lower than the melting temperature of the resin, the effect of warm molding cannot be sufficiently obtained. The press die can be raised and lowered by any means, but the combined use of electric heating and cooling water is practical.

The higher the pressure during warm compression molding, the lower the porosity, and thus the higher the volume ratio of the magnet powder, which is advantageous. Should be decided. Usually, it is preferable that the pressure during warm compression molding is in the range of 10 to ²⁰ t / cm ² , and the subsequent cooling pressure is kept equal to or higher than the pressure during molding.

By the production method of the present invention, a rare earth bonded magnet made of a rare earth magnet powder, a coupling agent applied to the surface thereof, and a thermoplastic resin that binds the rare earth magnet powder can be produced. Since this product magnet has a magnet powder content of 80% by mass or more and a porosity of 1% or less, [BH] max is 11 MGOe which is the same as a compression-molded bond magnet using a thermosetting resin. It is a bond magnet that easily exceeds.

As the rare earth magnet powder, MQI-B2 powder according to the manufacture and sale of MQI was used. This is done by crushing a quenched ribbon of an Nd—Fe—B based magnet alloy, pulverizing a material that has been heat-treated once to improve its magnetic properties, and having an average particle size of 250 μm (thickness 1-50 μm, major axis 10 500 μm, minor axis 2 to 100 μm). PPS (“M3910” manufactured by Toray Industries Inc., melting temperature 282 ° C., specific gravity 1.35) was selected as the thermoplastic resin to be the binder resin, and freeze-pulverized to obtain a fine powder having a particle size of 10 μm or less. As a coupling agent, a solution prepared by diluting 19 g of a silane coupling agent with a mixed solvent of 500 g of ethanol and 6 g of on-exchanged water was prepared.

19,188 g of the above MQI-B2 powder and 754 g of PPS fine powder were put in a universal mixer and stirred and mixed at a rotation speed of 100 rpm for 10 minutes. Subsequently, the coupling agent solution prepared above was added to the mixture, and stirring and mixing were repeated for 10 minutes at a rotational speed of 100 rpm. To the mixture in a slurry state, 280 g of lithium stearate was added as a lubricant, and the mixture was stirred for 30 minutes at a rotation speed of 100 rpm while being heated to 130 ° C. to obtain a powdery mixture.

3 g of the mixture in the above powder state is put into a press die composed of a die having an inner diameter of 10 mm equipped with a heating means by electric heating and a flow path of cooling water, and upper and lower punches entering and exiting the die, and a surface pressure of 12 kgf by the punch. The pressure of / cm ² was maintained and the die temperature was raised to 300 ° C. After confirming that the target temperature was reached, the temperature was maintained for 10 seconds, and the die was cooled to a temperature of 280 ° C. After confirming the temperature drop, the molded product was extracted from the die and finished into a test piece having a height of 7 mm by machining.

This disk-shaped test piece having a diameter of 10 mm and a height of 7 mm is magnetized in an air core coil having a diameter of 30 mm and a height of 100 mm under the conditions of a magnetization voltage of 1700 V and a capacitor capacity of 1600 μF (magnetomotive force of 25 kOe). The magnetic properties were measured using “BH Tracer” (manufactured by Riken Denshi Co., Ltd.). The measurement results are shown in the table below together with the magnet density. (For reference, typical data of magnets manufactured by conventional injection molding technology are listed in the table.)
Measurement item (unit) Measurement result Conventional product data
Br (kG) 7.21 5.7-6.5
bHc (kOe) 5.92 4.0-4.8
iHc (kOe) 9.58 6.5-8.0
[BH] max (MGOe) 11.2 6.5-8.0
Density (g / cm ³ ) 5.98 5.0 to 5.5

The test piece was held at 120 ° C. for 1000 hours, the thermal demagnetization rate was measured during that time, and the heat resistance was examined by drawing a thermal demagnetization curve. The measurement results were plotted to obtain the graph shown in FIG. The thermal demagnetization curve of the bonded magnet by injection molding and the bonded magnet by compression molding according to the prior art is also shown in FIG. The bonded magnet according to the present invention exhibits the best heat resistance.

The thermal demagnetization curve of the bond magnet manufactured in the Example of this invention.

Claims (8)

In a method of manufacturing a rare earth bonded magnet in which rare earth magnet powder is bonded with a thermoplastic resin, a powdery mixture in which the thermoplastic resin powder adheres to the surface of the rare earth magnet powder is formed by a coupling agent, and this powdery mixture is added. A method for producing a rare earth bonded magnet, which comprises filling a heated press die, giving a magnet shape by warm compression molding, and cooling in a pressurized state. The powder mixture is formed by mixing rare earth magnet powder and thermoplastic resin powder, adding a coupling agent and stirring to obtain a slurry mixture, and adding a lubricant to the slurry mixture. The manufacturing method of Claim 1 performed by stirring and heat-drying and setting it as the powdery mixture which adhered the thermoplastic resin powder to the surface of the rare earth magnet powder. As a coupling agent, a silane, titanate or zirconate coupling agent used in the production of rare earth bonded magnets is selected and used in an amount of 0.1 to 1% by mass based on the rare earth magnet powder. Item 3. The method according to Item 1 or 2. The production method according to any one of claims 1 to 3, wherein the thermoplastic resin powder is a polyamide, polyphenylene sulfide, polyvinylidene fluoride or liquid crystal polymer powder having a particle diameter of 1 to 50 µm. The manufacturing method according to any one of claims 1 to 4, wherein the heating of the press die is performed in a range of -10 to + 20 ° C with respect to the melting temperature of the thermoplastic resin. The pressure at the time of warm compression molding is set in the range of 10 to ²⁰ t / cm ² , and the pressure at the time of cooling is maintained to be equal to or higher than the pressure at the time of warm compression molding. Production method. A rare earth bonded magnet manufactured by the manufacturing method according to claim 1. The rare earth bonded magnet according to claim 7, wherein the content of the magnet powder is 80% by mass or more and the porosity is 1% or less.

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