JP2612494B2 - Manufacturing method of plastic magnet - Google Patents

Description

The present invention relates to a method for producing a bonded magnet, and more particularly, to a method for producing a plastic magnet having excellent rust prevention performance.

"Prior art and problems" Alloy magnets containing rare earth metals and transition metals as main components (hereinafter referred to as rare earth magnets) have superior magnetic properties compared to conventional ferrite-based and alnico-based magnets. ,
Although it has been used in various fields in recent years, it has a disadvantage that it is easily oxidized, and the tendency is particularly remarkable in Nd—Fe—B magnets. A plastic magnet in which such a rare earth magnetic powder is fixed with a synthetic resin binder has a problem that when used in a highly humid atmosphere, magnetic properties deteriorate with time due to oxidation.

In order to overcome such a problem, a method of forming a resin coating or a metal coating on the surface is considered. However, even when a resin coating or a metal coating is formed, the resin coating or the metal coating may be defective at corners of the plastic magnet during handling, transportation, and during the assembly process. It is extremely difficult to obtain a plastic magnet having excellent rust prevention performance.

The causes of coating defects are (1) in the case of a resin coating, the thickness of the resin coating at the corners of the plastic magnet is significantly thinner than other portions, and (2) the plastic magnets and the plastic magnet and the packaging material This is because corners of the plastic magnet are intensively damaged by collision and contact between the plastic magnet and other assembled parts.

To solve such a problem, for example,
62-206806 proposes an alloy magnet in which a chamfered surface is coated with a fluorine-based polyamideimide resin. Japanese Patent Publication No. 43-8338 proposes a Mn-Bi magnetic material having rounded corners and a metal layer provided by polishing.

However, although the above-mentioned sintered magnet has excellent magnetic force, it is processed into a small and thin ring shape required for mounting on small precision motors used for information equipment represented by, for example, HDDs and FDDs. Requires a cutting process after sintering, which involves not only a complicated process but also a brittle material, which is not practical.

In the case of coating with a resin as disclosed in Japanese Patent Application Laid-Open No. 62-206806, as described above, the paint or the coating film moves to other parts due to surface tension or gravity, so that the coating film in that part becomes thinner and satisfactory. Rust prevention performance cannot be imparted.

"Means for Solving the Problems" The present inventors have conducted intensive studies to solve the above problems, and as a result, by removing the corners of the plastic magnet, the contact area at the time of collision or contact was increased, and the damage was reduced. By forming a metal coating by electrolytic plating, it avoids the flow of paint and other coatings that occur in the case of resin coating to other parts of the coating, resulting in easy manufacturing and excellent rust prevention performance. It has been found that a small and thin ring-shaped plastic magnet which can be mounted on a small precision motor can be obtained, and the present invention has been completed.

That is, the present invention relates to a magnetic powder represented by R-T-B (R is Nd or a part thereof substituted with a rare earth element, T is Fe or a part thereof substituted with a transition metal). A plastic magnet characterized by forming a metal film by electrolytic plating on the surface of a molded article after removing part or all of the corners of the molded article mainly comprising a synthetic resin as a binder. The manufacturing method is described as a content.

The magnetic powder used in the present invention is RTB (R is Nd
Or a part of which is replaced by a rare earth element, but T is an alloy or an unavoidable impurity represented by Fe or a part of which is replaced by a transition metal), and the particle size is mostly 1 to 500.
Those having a range of μm are preferred. If it is less than 1 μm, it will easily ignite during the manufacturing process or its magnetic properties will be easily degraded by oxidation, while if it exceeds 500 μm, the filling rate will be reduced and it will be difficult to obtain sufficient magnetic properties.

The synthetic resin as the binder used in the present invention is appropriately selected and used from widely used thermoplastic resins, thermosetting resins or rubbers in consideration of a molding method. Examples of the thermosetting resin of the binder used in the present invention include phenol resins, epoxy resins, and melamine resins. Examples of the thermoplastic resins include polyamides such as nylon 6 and nylon 12, polyolefins such as polyethylene and polypropylene, and polyolefins such as polypropylene. Examples thereof include vinyl chloride, polyester, and polyphenylene sulfide.

The molding method of the magnetic powder and the resin binder compound used in the present invention can be exemplified by compression molding, injection molding, extrusion molding, calendar molding and the like.

The corner removal method used in the present invention includes (1)
A method in which a large number of plastic magnets are placed in a container and a vibration is applied thereto, and a method in which an abrasive is added at the same time; (2) A method in which a large number of plastic magnets are charged in a container and a rotation is applied; Examples of the method include a method of removing corners by cutting, and (4) a method of removing corners by polishing.

Further, as the shape after removing the corners, a curved surface, a flat surface, etc. can be exemplified, but a curved surface is preferable, and the radius of curvature thereof is 100.
Most preferably, it is not less than μm.

Ni, Cr, Zn, Cu, as components of the metal coating in the present invention
Examples thereof include Fe, Cd, Sn, Pb, Al, Au, Ag, Pd, Pt, and Rh, and one or more of these.

In the metal film forming method used in the present invention, electrolytic plating is suitable in terms of rust prevention performance and cost.

The electrolytic plating bath used in the present invention can be appropriately selected depending on the type of metal to be plated, and includes a copper cyanide bath, a copper pyrophosphate bath,
Copper sulfate bath, matte Ni bath, watt bath, sulfamic acid bath,
Wood strike bath, Immersion Ni bath, Hexavalent Cr surge bath, Hexavalent Cr low concentration bath, Hexavalent Cr fluoride containing bath, High cyanide alkali Zn plating bath, Medium cyanide alkali
Zn plating bath, low cyanide alkali Zn plating bath, zincate bath, Cyanide cyanide plating bath, borofluoride Cd plating bath, sulfuric acid Sn plating bath, borofluoric acid Sn plating bath, borofluoric acid Pb plating bath, sulfamic acid Pb plating bath, methanesulfonic acid Pb plating bath, borofluoric acid solder plating bath, phenolsulfonic acid solder plating bath, alkanolsulfonic acid solder plating bath, chloride Fe plating bath, sulfate Fe plating bath, borofluoride Fe
Plating bath, sulfamate Fe plating bath, Sn-Co alloy stannate bath, Sn-Co alloy pyrophosphate bath, Sn-Co alloy fluoride bath, Sn-Ni alloy pyrophosphate bath, Sn-Ni alloy fluoride bath, etc. For example, additives such as a brightener, a leveler, a pit inhibitor, a satin forming agent, an anode dissolving agent, a PH buffer, and a stabilizer can be added.

The electrolytic plating step in the present invention may include a pre-treatment step and a post-treatment step. Examples of the pre-treatment step include immersion degreasing, electrolytic degreasing, solvent degreasing, acid treatment, alkali treatment, palladium treatment, and water washing. Examples of the post-treatment process include chromate treatment and water washing.

A barrel plating method is also suitable for the electrolytic plating method performed in the present invention, in addition to a method using a hooking jig which is usually performed, and further, a pulse plating method and a strike base plating method can be adopted.

The thickness of the metal coating is preferably 4 to 50 μm. 4
If it is less than μm, sufficient corrosion resistance cannot be obtained, and if it exceeds 50 μm, the distance from the magnet surface becomes large, so that the magnetic force that can be used effectively decreases and sufficient magnetic characteristics cannot be obtained.

〔Example〕

Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Comparative Example 1 An Nd-Fe-B-based magnetic powder (manufactured by General Motors) was blended at a ratio of 80% by volume and a resol-type phenol resin at a ratio of 20% by volume, and the mixture was stirred at room temperature under a pressure of 5 ton / cm ² . After molding, the synthetic resin is cured at a temperature of 190 ° C for 2 hours, and a ring-shaped molded product A having an outer diameter of 8 mm, an inner diameter of 6 mm, and a height of 4 mm
I got

Comparative Example 2 An epoxy resin was applied to the surface of the molded body obtained in Comparative Example 1 by a dipping method (film thickness: 40 μm) to obtain a molded body B.

Comparative Example 3 Electrodeposition coating (film thickness 40 μm) on the molded article obtained in Comparative Example 1 above
To obtain a molded body C. Table 1 shows the electrodeposition coating conditions.

Comparative Example 4 The compact obtained in Comparative Example 1 was subjected to electrolytic Cu plating, and then subjected to electrolytic Ni plating (film thickness: 40 μm) to obtain a compact D. Table 2 shows the electrolytic Cu plating conditions and Table 3 shows the electrolytic Ni plating conditions.

Comparative Example 5 After removing the corners of the molded body obtained in Comparative Example 1, the surface of the molded body was coated with an epoxy resin by a dipping method under the same conditions as in Comparative Example 2 to obtain a molded body E. The corners were removed by putting 1000 molded bodies in a wire mesh basket and vibrating the wire mesh basket for 10 minutes at a frequency of once per second and an amplitude of 15 cm. The shape after the corner removal had a radius of curvature of 100 μm or more.

Comparative Example 6 After removing the corners of the molded article obtained in Comparative Example 1 in the same manner as in Comparative Example 5, electrodeposition coating was performed under the same conditions as in Comparative Example 3 to obtain a molded article F. Table 1 shows the electrodeposition coating conditions.

Comparative Example 7 After removing the corners of the molded article obtained in Comparative Example 1 in the same manner as in Comparative Example 5, the molded article G was obtained by electroless Ni plating (6 μm in thickness). Table 4 shows the electroless Ni plating conditions.

Example 1 After removing the corners of the molded body obtained in Comparative Example 1 in the same manner as in Comparative Example 5, electrolytic Cu plating was performed under the same conditions as in Comparative Example 4, followed by electrolytic Ni plating to obtain a molded body H. Was. Table 2 shows the electrolytic Cu plating conditions, and Table 3 shows the electrolytic Ni plating.

Evaluation Test Rust prevention performance of the molded articles A to H obtained by the above operation and 1000 molded articles B to H were respectively put in a wire netting basket, and once.
After a wire mesh basket was vibrated for 10 minutes at a frequency of / 1 second and an amplitude of 15 cm to simulate damage to plastic magnets, their rust prevention performance was evaluated by the following method.

The above-described operation of causing damage was performed for the purpose of simulating the damage to the plastic magnet during the process, transportation, and assembly. The samples subjected to the above-described operation of giving the damage to the molded bodies of BG are referred to as B ′ to G ′ below.
It is written.

 The rust prevention performance was evaluated by the following environmental test.

Environmental test Using a high-temperature and high-humidity tester, the molded body was allowed to stand in an atmosphere of 80 ° C and 95% RH, and the appearance was observed every 24 hours.

The evaluation criteria in Table 5 are as follows: [Actions and Effects] As described above, according to the present invention, excellent rust prevention performance, HD
Resin-bonded permanent magnets useful for small precision motors represented by D and FDD can be provided, and their usefulness is extremely large.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-206806 (JP, A) JP-A-61-130453 (JP, A) JP-A-2-46710 (JP, A) JP-B-43 8338 (JP, B1)

Claims (1)

(57) [Claims] 1. A magnetic powder represented by RTB (R is Nd or a part thereof substituted with a rare earth element, T is a part of Fe or a part thereof substituted with a transition metal), After removing a part or all of the corners of the molded body mainly composed of a synthetic resin as a binder, a plastic magnet characterized by forming a metal coating on the surface of the molded body by electrolytic plating. Production method.