JPH04273413A - Manufacture of rare-earth bonded magnet - Google Patents

Abstract

PURPOSE:To enhance the weatherproofness and the corrosion resistance of the title magnet by a method wherein a rare-earth bonded-magnet molded product is impregnated with the low-viscosity solution of a thermoset resin or a thermoplastic resin under a reduced pressure or under a pressurized state after reducing a pressure, the solution is dried and hardened and the inner surface and the outer surface of the molded product are covered with resin films. CONSTITUTION:A rare-earth bonded-magnet molded product is housed in a lower-part vacuum container; the pressure of the container is reduced down to about 10<-2> to 10<-3>mmHg; the air is evacuated. A resin solvent solution whose viscosity has been adjusted to be low is housed separately in an upper-part vacuum container connected, via a valve, to the upper part of the lower-part vacuum container; the air existing in the solution and the air existing in the space at the upper part of the solution are removed sufficiently under a reduced pressure. Then, gaps in the molded product are impregnated with the degassed solution until the molded product is buried. An impregnation operation is performed at room temperature for 3 to 30 minutes; after that, an inert gas such as nitrogen gas or the like is introduced; a vacuum is broken; the molded product is taken out and dried at a comparatively low temperature at the boiling point or lower of a solvent; after that, the resin is hardened at an optimum thermal hardening treatment temperature.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a new rare earth bonded magnet, and more particularly, to a rare earth bonded magnet that is extremely resistant to corrosion even in a harsh environment of high humidity, has excellent mechanical strength, and has stable magnetic properties. be.

0002

[Prior Art] In recent years, rare earth bonded magnets have sufficiently retained the magnetic properties of conventional anisotropic sintered ferrite magnets, and also have good formability, high impact strength, and light weight.
Due to these advantages, it is attracting attention as a highly functional material, and is expected to be used in motors, timers, switches, relays, communication equipment, audio equipment, electric/electronic equipment, automobiles, medical fields, etc. ing. Such rare earth bonded magnets are usually made by compressing a composition made by filling a thermoplastic resin or thermosetting resin with rare earth magnetic powder with a particle size of about 0.1 to 500 μm and homogeneously dispersing or kneading it. It is manufactured by molding into a desired shape using methods such as molding, injection molding, and extrusion molding. Rare earth bonded magnets using this rare earth magnetic powder are currently attracting attention because they have excellent magnetic properties.

[0003] However, since the rare earth magnetic powder is extremely susceptible to corrosion in a high-humidity environment, deterioration of magnetic properties is inevitable, and even after it is kneaded with resin, made into a bonded magnet, and made into a molded product, It also has the disadvantage that it tends to do so. In addition, for bonded magnet molded products,
Many voids are open. There are various types of voids, such as a closed-cell structure in which the voids inside the molded product are independent, and an open-cell structure in which the voids are continuous from the surface to the inside of the molded product. Since the voids in the bonded magnet molded product are in the latter state, moisture easily enters the interior under high humidity, which is a factor that promotes poor corrosion resistance of the rare earth bonded magnet.

[0004] Therefore, in order to improve these drawbacks, rare earth magnetic powders are subjected to surface treatment (as disclosed in Japanese Patent Laid-Open No. 1-2).
97806, JP-A-1-161803), coating the surface of rare earth bonded magnet molded products (
JP-A-1-245504, JP-A-1-16651
(see Publication No. 9), or both. However, these methods have insufficient surface treatment effects on rare earth magnetic powder, are unable to coat the inside of the voids even if the surface is coated, and are not effective enough, and processing equipment is expensive, making it difficult to manufacture products. This poses problems such as increasing costs and increasing the number of steps. For example, in the method disclosed in JP-A-1-166519, only the outer surface of the molded product is coated, leaving voids inside the molded product, resulting in a so-called closed cell structure. This is because oxygen and moisture are trapped inside the molded product, and while the molded product is exposed to various environments, corrosion gradually begins from that part.
It has not yet achieved sufficient results. Furthermore, since the impregnation is carried out under normal pressure, it takes a long time to sufficiently impregnate the internal voids, which poses a problem in terms of production efficiency.

[0005]

[Problems to be Solved by the Invention] The present invention aims to solve these various problems, and aims to be resistant to corrosion even in harsh high-humidity environments, to have stable magnetic properties, and to have mechanical properties. The aim is to provide a rare earth bonded magnet with improved strength.

[0006]

[Means for Solving the Problem] As a result of intensive research aimed at developing rare earth bonded magnets having the above-mentioned preferable properties, the present inventors found that it is not possible to form a film on the outer surface of a rare earth bonded magnet molded product. Of course, by impregnating and curing the voids of the open cell structure that extends from the outer surface of the rare earth bonded magnet molded product into the inside of the molded product in a network-like manner, and coating the molded product to the inner surface, the resin can be cured. We have found that the object can be achieved, and based on this knowledge, we have completed the present invention. The present invention applies a low-viscosity solvent solution of a thermosetting resin or thermoplastic resin to a rare earth bonded magnet molded product mainly consisting of rare earth magnetic powder and a thermosetting resin or thermoplastic resin as an organic binder under or after reduced pressure. A method for producing a rare earth bonded magnet, characterized by impregnating the magnet under pressure, drying and curing, and coating the inner and outer surfaces of the molded product with the resin coating, in which the thermosetting resin for impregnation is an epoxy resin. The main points are as follows.

The present invention will be explained in detail below. The rare earth magnetic powder that is the raw material for the rare earth bonded magnet molded product of the present invention is SmCo5-based, Sm2Co17-based, Nd2Fe1.
There are no particular limitations as long as it is used in rare earth bonded magnets such as 4B type magnets. The particle size is Sm-Co
1 to 50 μm for Nd2Fe14B system, 5 to 50 μm for Nd2Fe14B system
It is preferable to use particles with a particle size range of 200 μm. This is because if rare earth magnetic powder is made too fine, it will react violently in the presence of oxygen or moisture, leading to oxidation or ignition, and if it is too large, it will be difficult to fill it with high filling, making it difficult to make molded products with excellent magnetic properties. This is because you will no longer be able to obtain it. The particle size of the Nd2Fe14B type is larger than that of the Sm-Co type because the Nd2Fe14B type is more easily oxidized, and if it is too finely pulverized, the magnetic properties of the magnetic powder itself will be deteriorated. In addition, surface treatment of these rare earth magnetic powders is optional, and in order to improve adhesion with organic binders and impregnating resins, they may be treated with silane coupling agents, titanate coupling agents, silicone varnish, etc. There is a way.

There are no particular restrictions on the thermosetting resin or thermoplastic resin used as the organic binder in the present invention, and those conventionally used in bonded magnets may be used. Examples include thermosetting resins such as epoxy resins and polyurethane, and thermoplastic resins such as polyethylene, polyvinyl chloride, and polyamide, and one type or a combination of two or more types selected from these may be used. The ratio of the rare earth magnetic powder to the organic binder varies depending on the molding method, but is usually selected in a weight ratio of 99:1 to 90:10. Rare earth magnetic powder 9
If it is less than 0% by weight, the magnetic properties will not be sufficiently exhibited and the advantage of using expensive rare earth magnetic powder as a material will not be obtained.If it exceeds 99% by weight, the characteristics of bonded magnets such as impact resistance and bending strength will be deteriorated. This is not preferred because the mechanical properties deteriorate. In addition, various additives such as lubricants, colorants, heat stabilizers, antioxidants, plasticizers, etc. may optionally be added to this rare earth bonded magnet as necessary.

[0009] Here, the bonded magnet composition can be prepared by melting and kneading these rare earth magnetic powders, an organic binder, and various additives used as desired in predetermined proportions. There are no particular restrictions on the kneading device, and for example, a Henschel mixer, a super mixer, a single-screw or twin-screw extruder, a Banbury mixer, a roll, a universal stirrer, etc. are used. The rare earth bonded magnet composition thus prepared is molded into a desired shape by, for example, compression molding, injection molding, extrusion molding, etc. to obtain a rare earth bonded magnet molded product.

This rare earth bonded magnet molded product has voids with an open cell structure extending from the outer surface of the molded product into the interior of the molded product. This void ratio is 5 to 5 in compression molded products.
12%, and about 1 to 5% for injection molded products. In addition, the ratio of this void is (1-d/D) x 10, where D is the density of the rare earth bonded magnet molded product when it is 100% filled, and d is the density of the actual rare earth bonded magnet molded product.
It is calculated from the formula 0.

The greatest feature of the present invention is that the voids in the open cell structure of such rare earth bonded magnet molded products are filled with a thermosetting resin and/or thermoplastic resin, and the outer surface is coated with a coating of these resins. The aim is to improve weather resistance and corrosion resistance, and the manufacturing process will be described below.

First, a rare earth bonded magnet molded product (hereinafter referred to as molded product) is placed in a lower vacuum container, and the pressure is reduced to about 10-2 to 10-3 mmHg using a vacuum pump, diffusion pump, etc., and the voids in the molded product are sufficiently removed. Eliminate the air present in the Separately, a resin solvent solution adjusted to have a low viscosity is charged into an upper vacuum container connected to the upper part of the lower vacuum container via a valve, and the air dissolved in the solution and the air present in the upper space of the solution are sufficiently removed under reduced pressure. Eliminate it. Next, this degassed solution is sufficiently charged into the lower vacuum container through a valve until the molded product is buried, and is impregnated into the voids of the molded product. After performing the impregnation operation for 3 to 30 minutes at room temperature, introduce an inert gas such as nitrogen gas to break the vacuum, take out the molded product, and soak at a relatively low temperature below the boiling point of the solvent to prevent bubbles from forming due to the solvent gas. After drying to ensure that the resin is dry, it is cured at the optimum heat curing temperature for the resin. Through the above steps, the inner surface of the internal void of the molded product can be coated with a resin film or the void can be filled with resin, and the outer surface of the molded product can also be coated with the resin film. Furthermore, as a finishing process, a resin coating is coated on the outer surface of the molded product using an atmospheric pressure dipping method, a spray method, etc.
A resin film having a thickness of 1 to 10 μm may be formed by drying and curing.

[0013] In the vacuum impregnation method described above, the molded article and the low-viscosity resin solution may be simultaneously charged in a vacuum container, and then the pressure is reduced to about the room temperature vapor pressure of the solvent, and the impregnation may be carried out while excluding air. In addition, after the vacuum impregnation operation is completed, inert gas is introduced into the space above the resin solution using a gas compressor, and 5 to 10 atm of inert gas is introduced into the space above the resin solution.
By applying a certain amount of pressure, the effect of impregnating the voids of the molded product with the resin solution can be further enhanced.

[0014] Examples of the resin used to coat the inner surface of this molded article include silicone resin, epoxy resin, acrylic resin, phenol resin, urethane resin, vinyl chloride resin, vinyl acetate resin, fluororesin, etc. These can be used alone or in a mixture of two or more, but since the adhesiveness between the surface of the molded product and the resin to be impregnated must be good, the organic binder used in the rare earth bonded magnet molded product must be It is preferable to select the organic binder while considering the adhesion of the organic binder and the adhesion with the rare earth magnetic material used. A method using a resin or a combination of both methods may be used.

The viscosity of the impregnating resin solution is preferably 0.1 to 10 cP at room temperature. If the viscosity is higher than 10 cP, it will take time to impregnate the resin into the voids of the magnet molded product, resulting in poor production efficiency, and if the viscosity is higher than 0.
This is because if it is smaller than 1 cP, the coating formed on the inner and outer surfaces of the magnet molded product will be too thin, pinholes will occur, and the sufficient effect will not be exhibited, requiring multiple impregnation treatments. . In the present invention, sufficient anticorrosion effects can be achieved even if the impregnated and hardened state is stored in a high humidity environment of 60°C and 95% RH. For example, better anticorrosion effects can be obtained. Furthermore, since the impregnated resin has the effect of reinforcing the strength of the magnet molded product, it also has the effect of improving the mechanical strength.

[0016]

[Examples] Hereinafter, embodiments of the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples in any way. (Example 1) Nd-Fe-B magnetic powder MQP-B (
GM (product name, particle size: 40 mesh or more, 0.1% by weight or less, 325 mesh or less, 15% by weight or less) and epoxy resin EPX-6136 (product name, Yuka Shell Co., Ltd.) in a volume ratio of 85: 15 (weight ratio 97.3:2.
7) and compression molded at a pressure of 8T/cm2 into a cylindrical shape with a diameter of 15mm and a height of 10mm, which was then cured at 150°C for 2 hours under normal pressure to produce a bonded magnet molded product. . Next, this magnet molded product was placed in acetone containing a mixture of bisphenol A type epoxy resin (resin content 10% by weight) and vinyl chloride/vinyl acetate copolymer (resin content 40% by weight) in a weight ratio of 87:13. After being immersed and co-immersed in a solution (viscosity: 0.35 cP) under a reduced pressure of 1 mmHg for 10 minutes, it was pulled out and dried and cured. 60℃, 95% of this resin-impregnated/coated magnet molded product
We investigated the occurrence of rust in an RH atmosphere over time,
The results are shown in Table 1. In addition, bending strength (based on JIS K 7203) was measured as mechanical strength, and the results are also listed in Table 1.

[0017]

[Table 1]

(Example 2) Same as Example 1 Nd-Fe
- 100 parts of B-based magnetic powder, silicone resin KR-2
The surface was treated with 0.83 parts of 55 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.). Compression molded products were produced in the same manner as in Example 1, except that this surface-treated powder was used, resin impregnation treatment was performed under reduced pressure, and the rusting status and bending strength were measured and are also listed in Table 1.

(Comparative Example 1) Immersion and impregnation conditions were 1 under normal pressure.
A compression molded product was produced in the same manner as in Example 1 except that the time was 0 minutes, and the properties were measured after impregnation treatment and are also listed in Table 1.

(Comparative Example 2) Compression molded products were produced in the same manner as in Example 1, and coated with a fluororesin by the immersion method under normal pressure.The properties were measured and are also listed in Table 1.

Table 1 shows that the rare earth bonded magnet of the present invention is extremely rust-resistant and has excellent mechanical strength.

[0022]

Effects of the Invention According to the present invention, not only the outer surface of a rare earth bonded magnet molded product but also the voids extending from the outer surface to the inside of the molded product can be coated with a resin film or filled with resin. It becomes possible to provide a rare earth bonded magnet that is resistant to corrosion even in a humid environment, has excellent mechanical strength, and has stable magnetic properties, and has extremely high industrial value.

Claims (2)

[Claims] Claim 1: For a rare earth bonded magnet molded product mainly consisting of rare earth magnetic powder and a thermosetting resin or thermoplastic resin as an organic binder, the thermosetting resin or thermoplastic resin is applied under reduced pressure or after reduced pressure and under increased pressure. A method for producing a bonded rare earth magnet, which comprises impregnating the molded product with a viscous solution, drying and curing the molded product, and coating the inner and outer surfaces of the molded product with the resin film. 2. The method for manufacturing a rare earth bonded magnet according to claim 1, wherein the thermosetting resin for impregnation is an epoxy resin.