JPH0341703A - Sintered magnet of rare-earth-iron based alloy having p-xylylene polymer film and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve corrosion resistance by forming a protective film comprising a vapor-phase plated layer and the polymer film of vapor-phase p-xylylene or p-xylylene chloride which is continued from the plated film on the surface of the sintered body of rare-earth-element (including Y)-boron-iron based alloy having the porous surface. CONSTITUTION:Them main components of rare-earth-iron based alloy to be protected are 8-30 atomic% rare earth element, 2-28 atomic% boron and 42-90 atomic% iron in general. The alloy is obtained by sintering. A protective film has a double-layer structure. The first layer comprises a vapor-phase plated layer. The second layer comprises the polymer film of vapor-phase p-xylylene or p-xylylene chloride. The first layer of the protective film is the vapor-phase plated layer which is directly formed on the surface of the rare-earth-iron based sintered alloy that is a porous material. The second layer of the protecting film is formed on the surface of the first layer of the protective film. The second layer is the polymer film of the p-xylylene and the polymer film of the p-xylylene chlorided.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a technique for improving the corrosion resistance of rare earth iron-based magnets that are prone to corrosion, and in particular to a technique for improving the corrosion resistance of rare earth-boron-iron magnets.
The present invention relates to a corrosion-resistant magnet formed with a xylylene polymer film or a chlorinated p-xylylene polymer film, and a method for manufacturing the same.

According to the present invention, the bonding force between the protective coating and the magnet is large.

(Prior art and its problems) Conventional high energy product magnets include Sm-C.

However, rare earth iron magnets have recently attracted attention due to their advantages in terms of cost, machinability, and higher energy product. ), 2-28% atomic B, and the balance Fe
(42 to 90 atom %) and unavoidable impurities have been found to be effective.

However, rare earth iron magnets are inferior to Sm--Co magnets in terms of corrosion resistance, and various surface protection treatments are being considered.

Rare earth iron magnets are manufactured using sintering and rapid cooling methods. Since this type of magnet contains a large amount of Nd%Fe, which is easily oxidized, it has poor chemical resistance, especially against acids and alkalis.In surface treatments such as wet plating, the surface may be attacked during pre-treatment with acids, alkalis, etc. or during the plating process. Even if plating is possible, internal corrosion may occur due to the influence of chemicals that have entered the interior, and magnetic properties may deteriorate due to erosion between crystal grains.

Various methods have been proposed to solve this problem.

The basic method is to apply it to the surface of a rare earth iron-based sintered magnet.

The protective layer is formed by plating corrosion-resistant Ni, Ti, oxidized or carbide Ti, or other metals or compounds by a vapor phase plating method such as ion blasting or ion sputtering. Depending on the case, methods such as further chromate treatment to improve corrosion resistance or
No. 1, JP-A-61-166116, JP-A-63-99
No. 08.

JP-A No. 63-110706), there is also a method of diffusing a vapor phase plating layer into the magnet to increase the bonding force with the base magnet (JP-A No. 62-120002). Because it is porous with gaps, even if a vapor phase plating layer is formed, pores still exist on the magnet surface, and acid,
Alkali, moisture, etc. are trapped in the pores, causing erosion. To avoid this problem, after vapor phase plating, the surface is mechanically bombarded with a metal ball (shot peening).
It has been proposed to perform chromate treatment after that (Japanese Patent Application Laid-Open No. 63-9919, JP-A No. 63-120003). However, even with this method, sufficient sealing treatment cannot be achieved, so further synthetic resin treatment is proposed. It has been proposed that the remaining pores be closed by applying a paint of
However, in addition to sealing, this method requires drying, curing, etc., which not only makes the process even more complicated, but also allows water contained in the resin paint to enter the pores. It is not possible to avoid deterioration of the magnet over time due to corrosion because the magnet remains trapped in the magnet.Also, when applying paint, the rust prevention effect will not be achieved unless the thickness of the coating is thick, resulting in poor dimensional accuracy. There are some serious drawbacks.

Furthermore, it is known that this type of magnet, especially this type of sintered magnet, is provided with a plasma polymerized coating (Japanese Patent Application Laid-Open No. 1983-1999-1).
6811), it was difficult to obtain a sufficient degree of polymerization with conventional multi-element coatings. For example, in the case of acrylic acid, active oxygen is present during plasma polymerization, and plasma etching occurs simultaneously with plasma polymerization. Therefore, the hardness and density of the protective polymer film are insufficient, and the degree of polymerization is also low. Therefore, it cannot function satisfactorily as a corrosion-resistant protective film, such as not being able to provide sufficient gas barrier properties.

Additionally, a polymer resin film has been formed on the surface of rare earth sintered metal magnets as a protective coating (Japanese Unexamined Patent Publication No. 6
No. 1-198221, No. 56-81908,
No. 60-63901, etc.), polymer resin films have high moisture permeability and oxygen permeability, and have low affinity with rare earth sintered metal magnets, so they cannot ensure sufficient adhesion. There are various types of materials, including those that require high-temperature baking, which leads to oxidation of the magnet, and those that have poor corrosion resistance, such as epoxy resin, but no film has been provided that has both adhesion and corrosion resistance.

Furthermore, it has been proposed to form a film of xylene resin by vacuum deposition, but the degree of polymerization is low and there are problems with corrosion resistance (Japanese Patent Laid-Open No. 55-103714).

(Object of the Invention) Therefore, the object of the present invention is to provide a rare earth sintered metal magnet with good corrosion resistance, and to provide a manufacturing method thereof.

(Summary of the Invention) The present invention provides a vapor phase plating layer on the surface of a rare earth element (including Y)-boron-iron alloy sintered body, followed by a vapor phase p-xylylene polymer film or a chlorinated p- Provided is a corrosion-resistant permanent magnet characterized by forming a protective coating of xylylene polymer film.

The present invention also includes forming a plating phase by bringing the metal above into contact with the surface of the rare earth element-boron-iron alloy sintered body, and then forming a plating phase.
- thermally decomposing a xylylene polymer film or a chlorinated p-xylylene dimer to form p-xylylene or chlorinated p-xylylene radicals, and polymerizing these radicals on the surface of the plating layer to form a protective coating. The above-mentioned corrosion-resistant permanent magnet is manufactured by the above method.

Although vapor-phase p-xylylene polymer films or chlorinated p-xylylene polymer films have excellent corrosion resistance, they are known to have extremely poor adhesion to substrates. However, according to the present invention, a vapor-phase p-xylylene polymerized film or a chlorinated p-
A rare earth iron-based sintered alloy magnet with high corrosion resistance can be provided by making use of the extremely high corrosion resistance due to the inherent properties of the protective coating of the xylylene polymer film while compensating for poor adhesion.

Furthermore, according to the present invention, since the protective coating is polymerized in a gas phase, the radicals penetrate into the pores and polymerize, resulting in increased bonding properties to the base sintered alloy, making it difficult to peel off. As a result, the corrosion resistance and durability of the permanent magnet are further improved.

(Detailed Description of the Invention) 2. Soil A The rare earth iron-based sintered alloy protected by the present invention generally contains 8 to 30 at.% of rare earth elements, 2 to 28 at.% of boron, and 42 at.% of iron.
It is obtained by sintering using a known method with a main component of ~90 atomic %. Examples of rare earth elements include JP-A-62-1
Nd%Pr, Dy, as shown in No. 23004
At least one of Ho, Tb and La, Ce, Sm, C
It consists of at least one of d, Er, Eu, Tm, Yb, Lu, and Y. Although magnets with this composition have extremely excellent magnetic properties, it is known that the crystals develop into columnar shapes and gaps are formed between the crystal grains. Since the present invention physically seals the pores with a p-xylylene polymer film or a chlorinated p-xylylene polymer film of a rare earth iron-based sintered alloy having a porous surface, the composition of the sintered alloy is is not directly dependent on
Note that it depends on the surface condition of the alloy.

In the present invention, the protective film has a two-layer structure, the first layer is a vapor phase plating layer, and the second layer is a vapor phase p-xylylene polymer film or a chlorinated p-layer.
- Consists of xylylene polymer film.

Gas-phase polymerized p-xylylene polymer membranes or chlorinated p-xylylene polymer membranes have extremely good barrier properties against moisture and oxygen, and are therefore known as materials with extremely excellent corrosion resistance. No previous attempt has been made to use it to protect ferrous magnets. Therefore, the present inventor attempted to form these polymer films directly on the surface of rare earth iron-based sintered alloys, but found that the adhesive properties were extremely poor and they were easily peeled off.

The inventor tried various pre-treatments before applying a vapor phase p-xylylene polymer film and a chlorinated p-xylylene polymer film, and found that a metal compound layer or a metal layer was formed in advance by vapor phase plating. It has been found that the adhesiveness of the polymer is significantly improved. This result was surprising. Even if the vapor phase plating layer has a surface that is active to some extent, vapor phase polymerization p-
This is because the xylylene polymer film and the chlorinated p-xylylene polymer film do not normally have sufficient bonding strength. This is p
- When xylylene radicals attach to the surface of the first layer,
It penetrates into the pores of the base sintered alloy, where most of the pores are preserved, and polymerizes within the pores, completely filling the pores, resulting in an anchoring effect. This assumption was confirmed by observing the cross section of the magnet using an SEM photograph. From this, it can be understood that the corrosion resistance of the magnet is perfect and that the second layer of the protective film, p-xylylene or chlorine or p-xylylene polymer film, has good adhesion. The first and second layers of the protective film reinforce each other's defects to form a complete protective film.

The first layer of the protective film is a vapor phase plating layer formed directly on the surface of the porous rare earth iron-based sintered alloy. The vapor phase plating layer can be formed by various known vapor phase plating methods, such as those described in JP-A-61-150201. This method includes vacuum evaporation method, ion sputtering method, ion blating method, ion vapor deposition method (IVD),
There are plasma vapor deposition methods (CVD), etc., and vacuum vapor deposition methods heat and evaporate raw materials using methods such as resistance heating, electron beam heating, and RF induction heating to create atomic or molecular vapor.
This is a method of attaching this to the surface of a sintered alloy. In the ion sputtering method, an inert gas such as Ar is introduced into a vacuum container, ionized by a discharge, and accelerated by an electric field to impact the raw material target to form raw material ions, which are sintered and bonded. This is a method of attaching it to the surface of gold. In the ion blating method, the raw material is heated and evaporated using methods such as resistance heating, electron beam heating, and RF induction heating to create steam, which is bombarded with thermal electrons to create an ion flow of molecules or atoms of the raw material, which is then applied to an electric field. This is a method of accelerating and depositing a film on the surface of a magnet. The ion vapor deposition method uses an electron gun,
This is a method in which raw material evaporated by arc discharge or the like and ions from a raw material ion source are simultaneously deposited on the magnet surface in a certain proportion. The plasma deposition method is a method in which a reducing gas is introduced into a vacuum chamber, the gas is turned into plasma by electric discharge, etc., and a film is formed on the surface of a magnet.

The metal or metal compound for the first layer that can be used in the present invention includes:
AI% Metals such as Ni, Cr, Cu, and Co, and metal compounds such as silica, alumina, chromia, titanium carbide, titanium nitride, and aluminum nitride are included. The above-mentioned metal compound can be prepared by directly evaporating the metal compound or by evaporating the metal and introducing a gas such as nitrogen, methane, oxygen, etc. to cause a reaction.

A second layer of the protective film is formed on the surface of the first layer of the protective film. The second layer is a p-xylylene polymer film and a chlorinated p-xylylene polymer film. Such coatings include, for example, Parylene N (poly p-xylylene), Parylene C (polymonochlorochloro p-xylylene), and Parylene D (polydichloro p-xylylene) manufactured by Union Carbide Corporation in the United States, but they have poor gas permeability. Parylene C is particularly preferred because it is low.

Films such as polyp-xylylene are obtained by thermally decomposing dimer gas under reduced pressure. Film thickness is 0.5μm
Above, preferably 1 to 20 um.

In addition, if necessary, a p-xylylene polymer film and a chlorinated p-
When a highly corrosion-resistant magnet coated with a xylylene polymer film is fixed to a part of an electrical or electronic device using an epoxy resin or other adhesive, the polymer film has a high contact angle of 90 degrees and is water repellent, making it compatible with the adhesive. The adhesive strength is poor and sufficient adhesion cannot be obtained, which is an obstacle to practical application. Therefore, if adhesion to other parts is required, the surface of the polymer film may be subjected to plasma treatment (Japanese Patent Application No. 67521) or (or additionally) coated with a plasma polymer film (Japanese Patent Application No. 67521). No. 63-109063), it is possible to improve the bonding strength between a p-xylylene polymer film or a chlorinated p-xylylene polymer film and a synthetic resin adhesive.

Plasma treatment uses rare gases such as Ar, He, Ne, Hz, N
x, Ox, Co, Cot, Hz OlNow,
This is carried out by introducing gas such as Now, NHs, etc. into a vacuum chamber, turning it into plasma, and bringing it into contact with the polymer film.

The following conditions are usually used for plasma treatment. Direct current or alternating current can be used as a power source at a gas pressure of 0.01 to 10 Torr, and the frequency of alternating current can be used from 50 Hz to 5 GHz. Processing conditions vary depending on the shape and amount of sample, but power consumption is 10W-10KW and processing time is 0.5 seconds or more.
It can be set to 10 minutes. The contact angle of the surface after treatment is preferably 30° or less. Plasma treatment activates the surface of p-xylylene polymer film and chlorinated p-xylylene polymer film, and depending on the type of gas used, various active radicals,
Functional groups such as OH groups are generated, which improves the reactivity and wettability of the subsequently formed plasma polymerized film or synthetic resin film, allowing the adhesive to fully penetrate into the substrate (anchor effect), significantly improving adhesion. Furthermore, the surface hardness is significantly improved.

The plasma polymerized membrane can use any conventionally known monomer gas. For example, in addition to hydrocarbon monomers such as methane, ethane, propane, butane, pentane, ethylene, propylene, butene, butadiene, acetylene, and methylacetylene, silicon monomers such as tetramethoxysilane, and hydrogen fluoride monomers such as tetrafluoroethylene. , methyl methacrylate and the like.

In particular, plasma-polymerized films consisting essentially only of carbon and hydrogen form a film that is dense and hard without pinholes, has good corrosion resistance, and has magnetic properties with excellent long-term stability. Among these, H/C is preferably 1.5 or less in terms of the ratio of the number of atoms (atomic composition ratio), which is a plasma polymerized film with good three-dimensionally crosslinked properties. can be formed. In this case, sufficient corrosion resistance can be obtained with a film thickness of 0.2 μm or less. Such a plasma polymerized protective film can be produced by reducing the amount of hydrocarbon monomer gas, lowering the reaction pressure, and increasing the applied power. That is, by lowering the reaction pressure and increasing the applied power, the decomposition energy per unit amount of monomer increases, the decomposition progresses, and a crosslinked plasma polymerized protective film can be formed. The energy density W suitable for carrying out the present invention is 10'J/kg or more. Other gases such as hydrogen and inert gas can be used as carrier gases. However, more than a trace amount of oxygen, which comes as an unavoidable impurity, must not be used. In this way, when the material consists essentially only of carbon and hydrogen, excluding unavoidable impurity gases, it exhibits high corrosion resistance and good adhesion. Furthermore, when forming a plasma polymerized film, the effect can be further improved by raising the temperature of the magnet.

If necessary, the synthetic resin applied on the highly corrosion-resistant magnet having the p-xylylene polymer film or chlorinated p-xylylene polymer film may be epoxy resin, acrylic resin, melamine resin, etc. Ganpei No. 1-103344).

(Explanation of Examples) The alloy composition of the raw material powder is N d +sF e tA B8
The ingot was weighed, melted under high frequency, and cooled to produce a zero-order ingot, which was coarsely pulverized with a stamp mill and further finely pulverized with a ball mill.

This powder was compression molded into a rectangular parallelepiped shape using a mold. The obtained molded body was sintered at 1100°C for 1 hour in an Ar atmosphere.
When the surface roughness was measured, it was found to be JIS surface roughness Ra2.1.
Met. After reducing the vacuum level to 5X 10-'Torr or less, Ar gas was introduced and the pressure was reduced to IXI O-'Torr.
It was then discharged at 500V for 15 minutes to remove dirt such as oxides on the surface. This sintered alloy was used in the following examples.

Immediately on the surface of the above-mentioned cleaned sintered alloy, a thin film of AI was deposited to a thickness of about 5 μm by an ion-blating method (Comparative Example 1). Next, Parylene C was polymerized in a gas phase until the thickness became 5 μm. When the characteristics were measured, the results shown in Table 1 were obtained.

In addition, corrosion resistance, magnetic deterioration, and dimensional stability were evaluated based on the following criteria.

Corrosion resistance: Spray 5% saline solution at 35℃ onto the sample,
The time required for rust to occur was measured.

Dimensional stability: The dimensions of the sample are measured at 20 locations, and the variations are shown.

Decrease in magnetism: shows the rate of decrease in magnetism after being kept at 90°C and 90% high temperature and high humidity for 90 days.

Migosho 1 A thin film of Cu was deposited on the surface of the sintered alloy to a thickness of about 5 μm by ionization vapor deposition (Comparative Example 2), and then parylene C was vapor-phase polymerized to a thickness of 10 LLm.

Comparative Examples 1.2 and 1.2 are the same as Example 1.2 in which the Parylene C film is not formed.

Construction 3 After the treatment in Comparative Example 1, a sealing treatment by shot peening was performed, and then a chromate treatment was performed.

Hiyoshi Kita 4 After the treatment in Comparative Example 2, an epoxy resin was applied and cured by heating.

Furthermore, when sections were prepared for Example 1 and Comparative Example 4 and the cross sections were observed, it was found that there were no air bubbles in Example 1 and the pores were completely filled. In Comparative Example 4, a thin layer was formed on the pores, but there were scattered areas where the resin and magnet were not in close contact.

(Effects) From the Examples and Comparative Examples, it can be seen that the gas-phase polymerized film of p-paraxylylene or the like of the present invention has extremely excellent corrosion resistance and dimensional stability when a vapor-deposited film is interposed therebetween. On the other hand, using vapor-deposited metal alone has poor corrosion resistance. Even when sealed, corrosion resistance is not sufficient. On the other hand, when it has a resin coating, a decrease in magnetism is observed, probably due to internal moisture.
There was also a problem with dimensional accuracy.

Claims (1)

[Claims] 1) A vapor phase plating layer on the surface of a rare earth element (including Y)-boron-iron alloy sintered body having a porous surface, followed by a vapor phase polymerized p-xylylene polymer film or A corrosion-resistant permanent magnet characterized by forming a protective coating of a chlorinated p-xylylene polymer film. 2) The alloy is the first alloy whose main components are 8 to 30 at% of rare elements, 2 to 28 at% of boron, and 42 to 90 at% of iron.
Corrosion-resistant permanent magnet as described in section. 3) A plating phase is formed by bringing the metal above into contact with the surface of a rare earth element-boron-iron alloy sintered body having a porous surface, and then a p-xylylene dimer or a chlorinated p-xylylene dimer is formed. A method for producing a corrosion-resistant permanent magnet, which comprises thermally decomposing p-xylylene or chlorinated p-xylylene radicals, and polymerizing the radicals on the surface of the plating layer to form a protective coating. 4) The alloy is the third alloy whose main components are 8 to 30 at% of rare earth elements, 2 to 28 at% of boron, and 42 to 90 at% of iron.
A method for producing a corrosion-resistant permanent magnet as described in .