JPH03280402A - Permanent magnet of excellent corrosion-resisting property - Google Patents

Abstract

PURPOSE:To improve the corrosion-preventing property of a permanent magnet effectively without incurring deterioration of characteristics by a method wherein a metal coating, on which inorganic fine particles are dispersed, is provided on the surface. CONSTITUTION:Not only corrosion-resisting metal, but also sacrificial rust- resisting metal and the like is suitable as a coating metal material. Also, the wet method such as electroplating or non-electrolytic plating and the like is suitable as a coating method. Oxide particles and pigment fine particles are suitable as the inorganic fine particles to be dispersed into metal coating. It is considered suitable that one or two or more kinds of the above-mentioned particles are added to the plating solution, they are suspended and dispersed into the coating layer by performing a plating treatment. Moreover, the improvement in corrosion-resisting property can be achieved by conducting a treatment on the metal-coated surface using one kind or two or more kinds of coupling agents.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to permanent magnets with excellent corrosion resistance, and in particular aims to improve the corrosion resistance of permanent magnets that are easily corroded as they are, such as rare earth magnets. be.

(Prior Art) Permanent magnetic materials are one of the most important electronic equipment materials used in a wide variety of applications, from large plasma devices for nuclear fusion and computer peripherals to home appliances. When selecting permanent magnet materials, one of the most important evaluation items is energy product, and as electronic devices have become more sophisticated and smaller in recent years, permanent magnet materials are also required to have even higher performance. There is.

As such high-performance permanent magnets, permanent magnet materials made of intermetallic compounds or alloys mainly composed of rare earth metals and transition metals are attracting attention because they have a high energy product. Among them, rare earth-iron-boron permanent magnet materials This is particularly promising due to its high energy output and low raw material costs.

However, while rare earth-iron-boron permanent magnet materials have the advantage of high energy product, they also contain oxidation and
Because it contains large amounts of rare earth elements and iron, which are easily corroded,
It has not been widely used because there is a risk of deterioration of magnet performance due to surface oxidation and corrosion, as well as equipment contamination and failure due to oxidized and corrosive substances peeled off from the surface.

Therefore, in order to improve the drawbacks of such rare earth-iron-poron permanent magnet materials, oxidation resistance was imparted by adding a fourth element (Japanese Patent Application Laid-Open No. 63-217549), and plating with oxidation-resistant metal (Japanese Patent Application Laid-Open No. 63-217549) was carried out. 1986-54406), vapor deposition of metals and inorganic compounds (JP-A-61-163266),
Base metal diffusion coating (JP-A-62-18591C1), silica glass coating (JP-A-63-9103), resin coating (JP-A-60-63902), and surface forced oxidation (JP-A-63-9102). Various methods have been proposed, such as Japanese Patent Publication No. 1-84701, etc.).

In addition, casting and sintering have traditionally been the main methods used to mold permanent magnets, but recently molding has become easier and more complex shapes can be molded, and anisotropy is also easier. Applications of the resin-bonded type with its features are expanding. In this molding method, permanent magnet raw material magnetic powder is mixed with a resin and processed and molded into a desired shape using a pressure molding method such as injection molding, extrusion molding, or compression molding.

However, when a rare earth-iron-boron permanent magnet material is applied to this resin-bonded boss magnet, oxidation and corrosion of the magnetic particles causes oxidation and corrosion particles to fall off from the magnet molding, resulting in problems with oxidation resistance and corrosion resistance. becomes even more serious.

(Problems to be Solved by the Invention) As described above, there is an urgent need to improve the oxidation resistance and corrosion resistance of rare earth-iron-boron permanent magnets. However, with conventional methods, the coating and surface treatment are incomplete, resulting in: (1) insufficient oxidation and corrosion resistance; (2) changes in the microstructure due to the coating and surface treatment, resulting in poor magnetic properties; (3) Coating and surface treatment reduce the volume fraction of the magnet, resulting in a decrease in energy product. (4) Coating and surface treatment processes are complex and inefficient. (5)
) Problems such as insufficient durability of coating and surface treatment remained. In particular, metal coating has the highest productivity,
Although it is a practical coating method, the chemical stability of the coating layer itself is not sufficient, and the necessary oxidation resistance and corrosion resistance are difficult to obtain.

The present invention advantageously solves the above-mentioned problems, and aims to propose a permanent magnet that effectively improves corrosion resistance without causing deterioration of characteristics.

(Means for Solving the Problems) That is, the present invention is a permanent magnet (first invention) having excellent corrosion resistance and having a metal coating on the surface in which fine inorganic particles are dispersed.

This invention also provides a permanent magnet with excellent corrosion resistance, which has a metal coating on the surface of which fine inorganic particles are dispersed, and the surface of the metal coating has been treated with a coupling agent (second invention). be.

In this invention, as the coating metal material, not only corrosion-resistant metals such as chromium and nickel, but also sacrificial rust-preventing metals such as zinc are suitable from the viewpoint of ease of coating and corrosion resistance.

In addition, the coating method may be a wet method such as electroplating or electroless plating, or the inorganic particles may be suspended in the plating solution so that the inorganic particles can be dispersed in the coating at the same time as the plating process. suit advantageously. The thickness of the metal coating layer is 0.5 μm to 500 l1m.
It is preferable that That means the coating thickness is 0.5 μm.
If the thickness is less than 500 μm, it is difficult to expect sufficient corrosion resistance.
This is because if it exceeds this, there is a risk of deterioration of magnetic properties.

Next, as the inorganic fine particles to be dispersed in the metal coating,
Oxide particles such as silica, alumina and titania, as well as fine pigment particles such as red lead, zinc oxide, lead cyanamide, zinc white and iron oxide are advantageously suitable. The particle size of the inorganic fine particles here is desirably equal to or less than the thickness of the coating layer. If the particle size exceeds 10 μm, it will be difficult to suspend it in the plating solution or to precipitate it simultaneously with coating, so the upper limit of the particle size is preferably about 10 μm. In addition, the amount of dispersion in the metal coating is 1 to 20 vo
It is preferable to set it to about 1%. This is for distributed quantity power~
□If it is less than 1%, the reduction of the exposed area of the metal coating, which has lower chemical stability than inorganic fine particles, will not be sufficient.
Furthermore, the processing effect of the coupling agent is also insufficient. on the other hand,
This is because if it exceeds 20 vol 96, the bond between the metal matrix of the coating layer will be weakened, and there is a strong possibility that the strength will actually decrease.

As mentioned above, it is important to know whether it is appropriate to add one or more of these particles to the plating solution, suspend them, and disperse them into the coating layer by plating, and the amount of inorganic fine particles added in the plating solution. If the amount is less than 1 wt%, the necessary amount of inorganic fine particles cannot be dispersed in the coating layer, and on the other hand, if the amount of inorganic fine particles added exceeds 40 wt%, the coating itself becomes difficult. be.

Furthermore, corrosion resistance can be further improved by treating the metal coating surface with one or more coupling agents such as a silane coupling agent, a titanate coupling agent, and an aluminum coupling agent. can. At this time, if a coupling agent having the same metal element as that of the inorganic fine particles dispersed in the metal coating is used, the strongest water resistance can be provided. Further, the coupling agent treatment can be carried out using a general method. In other words, by immersing a magnet in a treatment solution made by adding a coupling agent and water for hydrolysis to a solvent such as alcohol, and heating it after drying, a film with hydrophobic groups can be formed on the surface. can.

In this invention, any magnet to be coated may be suitable as long as it has poor corrosion resistance as it is.
It is particularly suitable for application to sintered magnets or resin-bonded magnets using magnetic powder made of intermetallic compounds or alloys containing rare earth metals and transition metals as main components.

(Function) According to this invention, since the inorganic fine particles are dispersed in the metal coating coated on the magnet surface, the chemical stability of the metal coating is lower than that of the inorganic fine particles, and the area exposed to the outside air is reduced. This improves oxidation resistance and corrosion resistance.

In addition, even if oxidation or corrosion occurs on the surface of the metal coating, the inorganic fine particles dispersed inside the coating will prevent gases, water, acids, alkalis, and other liquids that cause oxidation and corrosion from entering the coating layer. However, since the progress of oxidation and corrosion is stopped on the surface of the coating layer, and substances that cause oxidation and corrosion do not reach the magnet inside the coating, there is no further deterioration of oxidation resistance and corrosion resistance.

In addition, when oxidation or corrosion occurs on the metal coating surface, the high-strength inorganic fine particles dispersed inside the coating prevent the occurrence and growth of cracks due to expansion due to oxidation and corrosion, which causes the coating to lose its effectiveness. Therefore, deterioration in oxidation resistance and corrosion resistance is kept to a minimum.

In this invention, if one or more of chemically stable oxides such as silica, alumina, and titania are used as inorganic fine particles to be dispersed in the metal coating, the above effects can be more effectively achieved. can be done.

Furthermore, by treating the metal-coated surface in which the inorganic fine particles of the present invention are dispersed with one or more coupling agents selected from a silane coupling agent, a titanate coupling agent, and an aluminum coupling agent,
Since the inorganic fine particles exposed on the coating surface and the coupling agent are strongly bonded, strong water resistance is exhibited, and it is possible to further improve oxidation resistance and corrosion resistance.

The silane coupling agent, titanate coupling agent, and aluminum coupling agent are Si,
Hydrophobic group and hydrophilic group are bonded to Ti and AI, and the hydrophilic group is hydrolyzed and bonded to the metal atom on the surface of the inorganic fine particle exposed on the coated surface, while the hydrophobic group is oriented outward. Second, it exhibits the above-mentioned water resistance.

(Example) The magnets used in each example and comparative example described below are:
It was manufactured by the following method using magnetic powder obtained by melting a metal having a composition represented by Nd2Fe+J2 (neodymium-iron-boron system), rapidly solidifying it, and then pulverizing it.

The sintered magnet was obtained by press-molding the above-mentioned magnetic powder to 4 tb and dry press-molding it, and then sintering it in a vacuum at 1100° C. for 12 hours.

In addition, the resin-bonded magnet is made by dry press-molding a raw material prepared by mixing 49 parts by weight (hereinafter simply referred to as "parts") of the above magnetic powder and 1 part of epoxy resin powder with a press pressure of 6 ton/cm 2 . It was obtained by curing the epoxy resin in a nitrogen atmosphere at 170°C for 1 hour.

Example 1 A resin-bonded magnet with an outer diameter of 10 mm, an inner diameter of 8 mm, and a height of 10 mm was degreased with ethanol, and then 3 parts of nickel chloride, 1 part of sodium hypophosphite, and 5 parts of ammonium chloride were added. It was immersed in an electroless plating bath (90°C) in which 5 parts of silica dissolved in 100 parts of water and having an average particle size of 20 parts m was suspended. This was held for a minute to form a coating with a thickness of 10 μm in which fine silica particles were dispersed in the nickel coating. At this time, the amount of silica fine particles dispersed in the coating was 3%.

Example 2 After degreasing a sintered magnet with diameter: 8-1 height:] Omm with trichlene, 50 parts of chromic anhydride and 1 part of sulfuric acid were added to water =
5 parts of alumina having an average particle size of 15 parts m dissolved in 250 parts was suspended in a plating bath kept at 45°C without stirring, and plated for 5 minutes at a current density of 20 A/dm2. The treatment was carried out to form a coating with a thickness of 1 μm in which fine alumina particles were dispersed in the chromium coating. At this time, the amount of alumina fine particles dispersed in the coating was 4%.

Example 3 A sintered magnet with a diameter of 8 mm and a height of 1 mm was degreased with trichlene, then zinc oxide: 3 parts, sodium cyanide, 8 parts
5 parts of sodium hydroxide were dissolved in 67 parts of water, and 10 parts of titania with an average particle size of 25 parts were suspended in a tempering bath and immersed in a solution maintained at 50'C without stirring. Then, plating was performed for 40 minutes at a current density of 8 A/dm2 to form a coating with a thickness of 10 μm in which fine titania particles were dispersed in the zinc coating. At this time, the amount of titania fine particles dispersed in the coating was 6%.

Example 4 A resin-bonded magnet with an outer diameter of 10 plates, an inner diameter of 8, and a height of 10 mm was degreased with ethanol, and then dichloride ink: 3 was degreased with ethanol.
part, sodium hypophosphite, 1 part, ammonium chloride,
5 parts of silica with an average particle size of 20 parts m were suspended in an electroless plating bath in which 5 parts were dissolved in 100 parts of water, stirred, and immersed for 50 minutes in a solution maintained at 90°C. A coating having a thickness of 10 μm was formed by dispersing fine silica particles in a nickel coating. At this time, the amount of silica fine particles dispersed in the coating was 3%.

Thereafter, it was further immersed for 15 minutes in a solution containing 1 part gammapropyltriethoxysilane, 1 part water, and 30 parts methanol, and then subjected to a coupling agent treatment by drying at 110°C for 1 hour.

Example 5 A sintered magnet with a diameter of 8 mm and a height of 10 mm was degreased with trichlene, and then alumina with an average particle size of 15 nm was placed in a plating bath in which 50 parts of chromic anhydride and 1 part of sulfuric acid were dissolved in 250 parts of water. - 5 parts were suspended and immersed in a solution kept at 45°C without stirring, and plated for 5 minutes at a current density of 2OA/dm2 to form a 1μm thick alumina coating with fine alumina particles dispersed in the chromium coating. A coating was applied. At this time, the amount of alumina fine particles dispersed in the coating was 496.

After that, it was further immersed for 15 minutes in a solution containing 1 part of acetalkoxyaluminum diisopropylate, 1 part of water, and 30 parts of methanol, and heated to 120°C.
Coupling agent treatment was performed by drying for 1 hour.

Example 6 A sintered magnet with a diameter of 8 mm and a height of 10 mu+ was degreased with trichlene and then plated with 3 parts of zinc oxide, 6 parts of sodium cyanide, and 5 parts of sodium hydroxide dissolved in 67 parts of water. Average particle size in bath: 25 parts m titania = 10
The zinc coating was suspended and immersed in a solution maintained at 50°C with stirring, and then plated for 10 minutes at a current density of 8 A/dm2, resulting in fine titania particles dispersed in the zinc coating to a thickness of 10 μm.
A coating of m was applied. At this time, the amount of alumina fine particles dispersed in the coating was 6%.

Thereafter, the sample was further treated with a coupling agent by immersing it in a solution containing 1 part of isopropyl triisostearoyl titanate, 1 part of water, and 30 parts of methanol for 15 minutes, and drying at 120°C for 1 hour.

Comparative Example 1 A resin-bonded magnet with an outer diameter of 10 mm, an inner diameter of 8 mm, and a height of 10 mm was degreased with ethanol, and then 3 parts of nickel chloride, 1 part of sodium hypophosphite, and 5 parts of ammonium chloride were added. Water: Electroless plating bath (9 parts) dissolved in 100 parts
0°C) for 5 minutes, and electroless nickel plating (thickness: 13 μm) was applied.

Comparative Example 2 Sintered magnets with a diameter of 28 mm and a height of 10 mm were degreased with trichlene and then placed in a plating bath (45°C) in which 50 parts of chromic anhydride and 1 part of sulfuric acid were dissolved in 250 parts of water. chromium plating (thickness: 1 μm) was applied at a current density of 20 A/dm for 5 minutes.

Comparative Example 3 A sintered magnet with a diameter of 8 mm and a height of 10 mm was degreased with trichlene, and then 3 parts of zinc oxide, 6 parts of sodium cyanide, and 5 parts of sodium hydroxide were dissolved in 67 parts of water. Immersed in a plating bath (50°C) at a current density of 8 A/
Zinc plating (thickness: 12 μm) was applied at dm2 for 10 minutes.

The magnets of Examples 1 to 6 and Comparative Examples 1 to 3 above were each 10
0 in a constant temperature and humidity chamber at 80°C and 195% RH.
When exposed for 0 hours and investigated its corrosion resistance,
None of the magnets in the examples had any rust that could be confirmed with a 10x magnifying glass, whereas there were 8 rust spots in Comparative Example 1, 10 spots in Comparative Example 2, and 7 spots in Comparative Example 3. Rust was observed in each case. In addition, when 100 magnets each of Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to a 5% salt spray test at 35°C, all of the magnets of Comparative Examples showed visual rust after 30 hours. On the other hand, there was no rust that could be confirmed with a 10x magnifying glass in any of the magnets of the examples. After a further 100 hours, rust was observed on almost the entire surface of the magnet of the comparative example. On the other hand, in the example magnets, Example 1 had 2 magnets, Example 2 had 5 magnets, and Example 3 had 3 magnets.
Although spots of rust were observed using a magnifying glass for a total of 10 magnets, no rust was observed in the magnets of Examples 4 to 6.

In the above-mentioned examples, gammapropyltriethoxysilane was used as the silane coupling agent, isopropyltriisostearoyl titanate was used as the titanate coupling agent, and acetalkoxyaluminum diisopropylate was used as the aluminum coupling agent.
Electroless nickel plating and chromium and zinc electroplating are used as metal coating treatments, and silica and chromium are used as inorganic fine particles.
Although examples in which titania and alumina are combined are mainly shown, the present invention is not limited to the above cases.
In addition to the above combinations, combinations of various coupling agents, metal coating methods, and inorganic fine particles are naturally included within the scope of the present invention.

(Effects of the Invention) Thus, according to the present invention, in the metal coating on the surface of a magnet for the purpose of imparting oxidation resistance and corrosion resistance, inorganic fine particles are dispersed inside the coating layer, and the surface of the coating layer is coated with a coupling agent. By processing, oxidation resistance and corrosion resistance can be significantly improved compared to conventional methods.

Claims (2)

[Claims] 1. A permanent magnet with excellent corrosion resistance that has a metal coating on its surface with fine inorganic particles dispersed in it. 2. A permanent magnet having excellent corrosion resistance, the surface of which is provided with a metal coating in which fine inorganic particles are dispersed, the surface of which is coated with a coupling agent.