JP2001189214A - Bonded rare earth magnet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high anticorrosion, without deteriorating the magnetic characteristics and improve mechanical strength. SOLUTION: In a bonded rare earth magnet, the surface of a magnet material is covered with a nonmagnetic amorphous metal plated layer which is formed by electrolytic plating. The magnet material is constituted of a molded body of a mixed material, where e.g. rare earth magnet powder such as neodymium- iron-boron(Nd-Fe-B), samarium-iron-nitrogen(Sm-Fe-N) and samarium-cobalt(Sm- Co) and a resin binder of nylon 12, nylon 6, nylon 66, polyphenyl sulfide(PPS), epoxy resin, etc., are mixed at a specified ratio. As the amorphous metal plated layer, a nickel-phosphorus plated layer is suitable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth bonded magnet in which an amorphous metal plating layer is formed by electrolytic plating on the surface of a magnet material obtained by mixing a rare earth magnet powder and a resin binder in a required ratio, and its production. It is about the method.

[0002]

2. Description of the Related Art Rare earth bonded magnets obtained by injection molding or compression molding of a mixture of a rare earth magnet powder and a resin binder in a required ratio are suitably used for, for example, a rotor in a spindle motor for a hard disk. I have. However, since rare-earth bonded magnets contain raw material components that are easily oxidized, rust easily occurs over time if the surface is unmodified, and if used as is for motor parts, the durability and failure may be reduced. Will be invited.
Therefore, measures are generally taken to coat the surface of the rare-earth bonded magnet with a resin film by a spray coating method, an electrodeposition coating method, a dip coating method or the like to prevent rust.

However, a product using a rare-earth bonded magnet coated on the surface with a resin film has a low mechanical strength, so that the resin film is easily damaged when the resin film is damaged during the assembling process or accidentally dropped during transportation. Problems such as breakage are pointed out. Therefore, in order to improve the mechanical strength, it has been proposed to cover the surface of the rare earth bonded magnet with a metal plating layer such as nickel (Ni) instead of the resin film.

[0004]

As described above, the mechanical strength of a rare earth bonded magnet can be improved by coating the surface of the rare earth bonded magnet with a nickel plating layer. It has been reported that the properties deteriorate. This is considered to be because the magnet was covered with the magnetic film because ferromagnetic nickel was used as the metal for plating. However, when the thickness of the plating layer is reduced, the mechanical strength and the corrosion resistance are reduced, which causes a problem that the magnet cannot be sufficiently protected.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks inherent in the prior art, and has been proposed in order to solve the problem suitably.
It is an object of the present invention to provide a novel rare earth bonded magnet capable of obtaining high corrosion resistance and improving mechanical strength, and a method for manufacturing the same.

[0006]

In order to overcome the above-mentioned problems and achieve the intended object, a rare-earth bonded magnet according to the present invention is formed by molding a mixture in which a rare-earth magnet powder and a resin binder are mixed at a required ratio. A non-magnetic amorphous metal plating layer is electrolytically plated on a surface of a magnet material made of a body.

In order to overcome the above problems and achieve the intended object, a method for manufacturing a rare earth bonded magnet according to another invention of the present application is to form a mixture in which a rare earth magnet powder and a resin binder are mixed at a required ratio. On the surface of the body magnet material,
A nonmagnetic amorphous metal plating layer is formed by electrolytic plating.

[0008]

Next, a rare earth bonded magnet and a method of manufacturing the same according to the present invention will be described below. The rare earth bonded magnet according to the example is, for example, neodymium-iron-
Boron (Nd-Fe-B), samarium-iron-nitrogen (Sm
-Fe-N), a rare earth magnet powder such as samarium-cobalt (Sm-Co) and a resin binder such as nylon 12, nylon 6, nylon 66, polyphenyl sulfide (PPS), epoxy, etc. in a required ratio. A non-magnetic amorphous metal plating layer is electrolytically plated on the surface of a magnet material made of a molded body of the mixture thus obtained. As this amorphous metal plating layer, a nickel-phosphorus plating layer is preferable. This is because the crystal structure of the nickel-phosphorus plating layer can be made amorphous by adding phosphorus to nickel. In this case, the phosphorus content may be 4 wt% or more.
9 to 11 wt% is more preferable because amorphous can be obtained stably.

In the rare earth bonded magnet according to the embodiment constructed as described above, since the nickel-phosphorus plating layer is non-magnetic, the magnetic properties of the magnet are not deteriorated even if the thickness of the nickel-phosphorus plating layer is increased. The mechanical strength can be improved by forming a sufficient film thickness. In addition, the amorphous nickel-phosphorous plating layer is harder than the conventional nickel plating layer and is excellent in corrosion resistance.

The non-magnetic amorphous metal plating layer includes a nickel-phosphorus plating layer and a nickel-phosphorus plating layer.
A boron plating layer (Ni-B) or a nickel-copper-phosphorus plating layer (Si-Cu-P) can be employed.

As a method for forming a nickel-phosphorus plating layer on the surface of the magnet material, electroless plating and electrolytic plating can be considered. In electroless plating, a plating layer is formed by chemically depositing particles on the surface of a magnetic material to be plated by activating a reducing agent contained in a plating solution. However, in this electroless plating, it is difficult to control the composition of the plating solution, it is difficult to control the composition of the metal deposited on the surface of the magnet material, and nickel-phosphorus plating is performed on the surface of the magnet material in an amorphous state. It is not suitable for forming a layer stably. That is, as a method of forming a non-magnetic, amorphous nickel-phosphorus plating layer on the surface of a magnet material,
Electroplating, in which the composition of the metal to be deposited can be easily controlled by current density, plating time, and the like, is suitable.

The specific method of this electrolytic plating is as follows.
The magnet material held by the hanging tool was immersed in a plating solution (Brenner bath) composed of, for example, nickel sulfate, nickel chloride, orthophosphoric acid, and phosphorous acid stored in a plating tank, and immersed in the plating solution. A plating method is preferable in which an electric current is applied to a nickel anode and a magnet via a hanging tool. In addition, instead of the nickel anode,
A nickel-phosphorous anode can be used. In addition, a barrel tank charged with a magnet material is placed in a plating tank in which the plating solution is stored, and the tank is rotated, and between the magnet and the anode via an electrode disposed in the barrel tank. It is also possible to use a barrel method or the like in which plating is performed by flowing an electric current.

[0013]

[Test Examples] Neodymium-iron-boron (Nb-F
An annular magnet material having an outer diameter of 22 mm, an inner diameter of 20 mm, and a shaft length of 10 mm was molded using a mixture obtained by mixing and compression molding EB) with an epoxy resin. The magnet material was electroplated using a plating solution (Brenner bath) having the composition shown in Table 1 below (electrolytic Ni-P), and the electroless plated comparative example (electroless Ni-P). , And a conventional example (electrolytic Ni) electrolytically plated using a Watts bath,
Table 2 shows the measured values of the Vickers hardness in the as-plated state and in the state after the heat treatment. The electroplating conditions of the invention example and the conventional example are as follows: plating solution temperature: 50 to 95 ° C.
(Electrolytic Ni-P: 75-95 ° C, electroless Ni-P: 85-9
5 ° C, electrolytic Ni: 50-60 ° C), current density: 1-40A
/ Dm ² , plating time: 5 to 30 minutes.

[0014]

[0015]

That is, from the results of this test, the hardness (mechanical strength) of the rare earth bonded magnet of the invention in which the nickel-phosphorous plating layer is electrolytically plated on the surface of the magnet material is improved as compared with the conventional rare earth bonded magnet. It became clear to do. Further, in the plated-up state, it was confirmed that the hardness of the rare earth bonded magnet of the invention was superior to that of the comparative example.

Next, the invention example in which the nickel-phosphorus plating layer, which is a nonmagnetic amorphous metal plating layer, and the conventional example, in which a nickel plating layer, which is a ferromagnetic crystal metal plating layer, were formed, FIG. 1 shows the result of measuring the relationship between the layer thickness and the flux or (BH) max.
And FIG.

From this measurement result, in the conventional example, the flux and (BH) m
It is clear that the flux and (BH) max can be maintained at high values regardless of the thickness of the plating layer in the invention examples, while any of the values of ax decrease. That is,
It was confirmed that by forming a non-magnetic nickel-phosphorus plating layer having an amorphous crystal structure on the surface of the magnet material, the mechanical strength could be improved without lowering the magnetic properties of the magnet.

[0019]

As described above, according to the rare earth bonded magnet and the method of manufacturing the same according to the present invention, high corrosion resistance can be obtained and mechanical strength can be improved without deteriorating the magnetic properties of the rare earth bonded magnet. be able to. Also, by plating by electrolytic plating, an amorphous metal plating layer can be formed stably, and a high quality product can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the thickness of a plating layer and the flux in a test example of the invention and the conventional example in a test example.

FIG. 2 is a graph showing the relationship between the thickness of a plated layer and (BH) max of the invention and the conventional example in a test example.

Claims (3)

[Claims] 1. A rare earth element, wherein a nonmagnetic amorphous metal plating layer is electrolytically plated on a surface of a magnet material formed of a mixture of a rare earth magnet powder and a resin binder in a required ratio. Bond magnet. 2. A non-magnetic amorphous metal plating layer is formed by electrolytic plating on a surface of a magnet material formed of a mixture of a rare earth magnet powder and a resin binder in a required ratio. Production method of a rare earth bonded magnet. 3. The method according to claim 2, wherein the amorphous metal plating layer is a nickel-phosphorus plating layer.