JP2001358003A - Rare-earth permanent magnet with insulating coat and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare-earth permanent magnet together with its manufacturing method which is appropriate for an electric car motor and a household appliance motor and comprises, on its surface, a thin coat excellent in insulation and corrosion-proof, for an integral magnet body with excellent insulation and effective volume ratio. SOLUTION: The rare-earth permanent magnet is featured in that its surface has the filer mainly composed of a compound chrome oxide of chrome and bivalent metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin film, which is useful for obtaining an integrated magnet body having excellent insulation and an effective volume ratio, which is suitably used for a motor for electric vehicles and a motor for home appliances. The present invention relates to a rare earth permanent magnet having on its surface a coating exhibiting excellent insulation and corrosion resistance, and a method for producing the same.

[0002]

2. Description of the Related Art As a motor for an electric vehicle (EV: Electric Vehicle or HEV: Hybrid Electric Vehicle) and a motor for home electric appliances, for example, a rare-earth permanent magnet represented by an R-Fe-B permanent magnet is made of silicon steel plate. So-called IP used embedded in the rotor formed by
M (Interior Permanent Magnet Motor: embedded magnet type motor) and SPM (Surface Permanent Magnet Moto
r: surface magnet type motor) has been developed. In recent years, materials for rare-earth permanent magnets have been improved, and the performance of motors has been improved accordingly. However, since rare-earth permanent magnets have conductivity, when an AC magnetic field is applied to the magnets, eddy currents are generated in the magnets and motor efficiency decreases as eddy current loss, and motor characteristics deteriorate due to thermal demagnetization of the magnets Or inconvenience such as dropping. As a method of reducing the eddy current generated in the magnet, there is a method of dividing the magnet, stacking a plurality of magnet pieces in a state of being electrically insulated from each other, and using an integrated magnet body (for example,
See JP-A-4-79741). Conventionally, when this method is adopted, for example, an adhesive having an insulating property is applied to the magnet pieces, and the magnet pieces are bonded and fixed.

[0003]

However, the above-mentioned insulating adhesive is applied to the surface of the magnet piece,
In the method of bonding and fixing, in order to secure a predetermined bonding strength, the film thickness of the adhesive formed between the magnet pieces must be increased to 100 μm or more. Accordingly, in the integrated magnet body of a predetermined size, even if sufficient insulation is obtained between the magnet pieces, the volume ratio of the magnet pieces constituting the integrated magnet body by the thickness of the adhesive ( Hereinafter, the effective volume ratio) will decrease. As a result, the effective magnetic flux density is reduced, and the motor characteristics are reduced, and the motor efficiency is reduced. Further, in this method, the thickness of the adhesive affects the dimensional accuracy, and it has not been possible to obtain an integrated magnet having high dimensional accuracy. In order to solve such a problem, it is necessary to form a coating having excellent insulation and corrosion resistance even on a thin film on the surface of each magnet piece. Therefore, the present invention is useful for obtaining an integrated magnet body having an excellent insulating property and an effective volume ratio, which is preferably used for a motor for an electric vehicle and a motor for a home appliance, and has excellent insulating properties and corrosion resistance even in a thin film. It is an object of the present invention to provide a rare-earth permanent magnet having a coating exhibiting the effect on the surface and a method for producing the same.

[0004]

In the course of conducting various studies in view of the above points, the present inventors have found that chromium oxide (Cr) containing trivalent chromium (Cr) having excellent insulation and corrosion resistance is provided.
Attention was paid to forming a coating mainly composed of ₂ O ₃ ) on the magnet surface. However, in the case of the R-Fe-B permanent magnet, the structure near the surface is composed of an R-rich phase, a B-rich phase, and the like in addition to the main phase of tetragonal, and the electrochemical corrosion potentials are different from each other. In addition, it is difficult to uniformly form a dense film with excellent adhesion to the magnet surface, and the surface is porous. There are technical issues such as the need to infiltrate the environment, and these issues need to be solved. Therefore, as a result of further study, when a processing solution obtained by adding a divalent metal oxide or the like to a solution containing chromic anhydride or the like is used, the processing solution instantaneously penetrates into the pores of the magnet surface, By the heat treatment, a uniform coating mainly composed of a composite chromium oxide with a divalent metal containing trivalent chromium is formed under strong adhesion to the magnet surface. It was found that the coating exhibited excellent insulation properties and corrosion resistance even in a thin film.

The present invention has been made based on the above findings, and the rare earth permanent magnet according to the present invention comprises a composite chromium oxide of chromium and a divalent metal as a main component. Characterized by having a coating on the surface. The rare earth permanent magnet according to the second aspect is the rare earth permanent magnet according to the first aspect, wherein the film thickness of the coating is 0.005.
μm to 50 μm. The rare earth permanent magnet according to claim 3 is the rare earth permanent magnet according to claim 1 or 2, wherein the divalent metal is Mg, Ca,
It is characterized by being at least one selected from Zr, Zn, and Mn. A rare earth permanent magnet according to a fourth aspect is characterized in that, in the rare earth permanent magnet according to any one of the first to third aspects, the rare earth permanent magnet is an R—Fe—B permanent magnet. . Further, the method of the present invention for producing a rare earth permanent magnet having on its surface a coating mainly composed of a composite chromium oxide of chromium and a divalent metal is claimed.
As described, a treatment solution obtained by adding at least one selected from divalent metal oxides, hydroxides, and carbonates to a solution containing at least one selected from chromic anhydride and dichromate is magnetized. It is characterized in that it is heat-treated after being applied to the surface. A manufacturing method according to a sixth aspect is characterized in that, in the manufacturing method according to the fifth aspect, a processing liquid obtained by adding an emulsion type organic resin and / or a water-soluble type organic resin to the processing liquid is used. . A manufacturing method according to a seventh aspect is characterized in that, in the manufacturing method according to the fifth or sixth aspect, the pH of the treatment liquid is 4 to 7. The manufacturing method according to claim 8 is characterized in that, in the manufacturing method according to any one of claims 5 to 7, the heat treatment is performed at 150 ° C to 400 ° C.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The rare earth permanent magnet of the present invention is characterized in that its surface has a coating mainly composed of a composite chromium oxide of chromium and a divalent metal.

Here, as the divalent metal, for example, M
g, Ca, Zr, Sr, Ba, Ni, Co, Zn, M
n, Sn, Pb, and Cu. The coating mainly composed of a composite chromium oxide of chromium and these metals is a coating that is uniform, dense, and excellent in adhesion. Among them, a composite chromium of chromium and Mg, Ca, Zr, Zn, or Mn is particularly preferred. Oxide-based coatings are particularly good.

The rare earth permanent magnet of the present invention having on its surface a coating mainly composed of a composite chromium oxide of chromium and a divalent metal is, for example, at least one kind selected from chromic anhydride and dichromate. At least one selected from divalent metal oxides, hydroxides and carbonates in a solution containing
It is manufactured by applying a treatment liquid to which a seed has been added to the surface of the magnet and then performing a heat treatment. By using such a treatment liquid, a film containing chromium oxide (Cr ₂ O ₃ ) having excellent insulating properties and corrosion resistance can be formed more easily.

The dichromate includes, for example, K, Na, Mg, Ca, and Zn salts of dichromic acid.

The divalent metal oxide includes, for example, the above-mentioned divalent metal oxides, that is, MgO, CaO, Zr
O _{2 and the} like.

As the hydroxide of the divalent metal, for example,
The above-mentioned hydroxide of the divalent metal, that is, Mg (OH) ₂ ,
Ca (OH) ₂ , Zr (OH) _{4 and the} like.

As the divalent metal carbonate, for example, the above-mentioned divalent metal carbonate, that is, MgCO ₃ , CaCO _3
3 , Zr (CO ₃ ) _{2 and the} like.

The content ratio of chromium and divalent metal (divalent metal / chromium) in the treatment liquid is 0.01 to 10 (w
(t / wt). By using the treatment liquid adjusted in this way, it is possible to obtain a film having excellent insulation and corrosion resistance.

An organic resin of an emulsion type and / or an organic resin of a water-soluble type is added to the above-mentioned processing solution,
It may be a coating containing an organic resin. By forming a coating using a processing solution to which an organic resin is added, the adhesion of the coating to a magnet is improved, the coating is prevented from cracking at the time of film formation,
Improvement of heat resistance of coating, improvement of adhesiveness of coating with adhesive,
It is possible to improve the wettability between the treatment liquid and the magnet surface. Examples of the organic resin include an acrylic resin, a urethane resin, a vinyl acetate resin, an epoxy resin, and a copolymer of these organic resins. The organic resin may have been subjected to various modification treatments. Addition of a urethane-modified acrylic resin is effective in improving the heat resistance of the coating. The addition of an acrylic-modified epoxy resin or a silica-modified acrylic resin has the effect of improving the adhesion of the coating to the adhesive. Further, in order to improve the wettability between the treatment liquid and the magnet surface and the treatment property, a nonionic surfactant may be added to the treatment liquid as needed.

When an organic resin is added to the treatment liquid, the content ratio of chromium to the organic resin in the treatment liquid (organic resin / chromium) may be adjusted to be 0.1 to 50 (wt / wt). desirable. By using the treatment liquid adjusted in this way, the above-described effect of forming a film using the treatment liquid to which the organic resin is added can be easily obtained.

Further, in order to promote the reduction of hexavalent chromium to trivalent chromium to facilitate formation of a coating containing chromium oxide (Cr ₂ O ₃ ), A reducing agent may be added to the treatment liquid in order to easily obtain a film having the following. Examples of the reducing agent include alcohols such as methyl alcohol, polyhydric alcohols such as ethylene glycol, and saccharides such as glucose, lactose, and starch.

Further, boric acid may be added to the treatment liquid to improve the heat resistance of the film, or a powdered oxide such as alumina, silica or titania may be added. Further, by adding phosphoric acid or the like to the treatment liquid, the corrosion resistance of the film can be further improved.

It is desirable that the pH of the treatment liquid is adjusted to 3 to 10. The present inventors have confirmed that when the pH is in this range, a film having excellent insulating properties can be obtained. This result is presumed to be due to the fact that the R-rich phase of the magnet is preferentially dissolved when the pH is lower than 3, and a uniform and dense coating cannot be formed on the magnet surface. . A more desirable pH of the processing solution is 4 to
7 By adjusting the pH of the processing solution to this range,
Further, a stable and desired coating film having excellent insulating properties based on excellent adhesion can be formed on the magnet surface. Usually, a solution containing at least one selected from chromic anhydride and dichromate is added to a solution containing at least one selected from divalent metal oxides, hydroxides, and carbonates.
By adding seeds, the pH of the resulting processing solution can be adjusted to the above range, but if necessary, the pH may be adjusted using an acid or an alkali.

As a method of applying the treatment liquid prepared by the above method to the magnet surface, for example, a dipping method (immersion method), a dip-spin method (immersion-shake-off method), spray coating, and roller coating are employed. You. Before applying the treatment liquid, the magnet surface is degreased with an organic solvent, phosphoric acid, acetic acid, or the like for removing a surface altered layer that can be formed in a manufacturing process (for example, a processing process or a polishing process). A pretreatment such as weak pickling using an aqueous solution of oxalic acid or the like may be performed.

The heat treatment performed after the treatment liquid is applied to the magnet surface is preferably performed at 150 ° C. to 400 ° C.
It is more desirable to carry out at a temperature of from 00C to 350C. If the treatment temperature is lower than 150 ° C., the reduction of hexavalent chromium to trivalent chromium does not proceed sufficiently, and it may be difficult to form a coating containing chromium oxide (Cr ₂ O ₃ ).
If the temperature is higher than ℃, the coating may be broken at the time of film formation or the magnetic properties of the magnet may be deteriorated.

Since the film formed by the above method is firmly adhered to the magnet surface, if a film thickness appropriate for the surface roughness of the magnet is secured, excellent insulation and corrosion resistance are exhibited. I do. For example, for a magnet manufactured by a general method, if the film thickness is 0.005 μm or more, excellent insulating properties and corrosion resistance are exhibited. Although the upper limit of the film thickness is not limited, it is preferably 50 μm or less from the viewpoint of reducing the motor efficiency due to a request based on miniaturization of the magnet itself and a reduction in cost and effective volume ratio.
m or less is more desirable.

If necessary, the application of the treatment liquid to the magnet surface under the above conditions and the subsequent heat treatment may be repeated a plurality of times.

The coating of the present invention mainly composed of a composite chromium oxide of chromium and a divalent metal has excellent insulating properties. However, when the coating is formed on the surface of the rare earth permanent magnet itself, In addition to high insulation properties, high adhesion to the magnet surface can be obtained. Further, another coating (for example, A) formed on the surface of the magnet itself for the purpose of imparting corrosion resistance or the like.
1 film or Ni film).
Further, another film may be laminated on the surface of the film of the present invention. By adopting such a configuration, the characteristics of the coating of the present invention can be enhanced or supplemented, and further functionality can be imparted.

The magnet of the present invention having on its surface a coating mainly composed of a composite chromium oxide of chromium and a divalent metal may be prepared, for example, by previously converting a plurality of such magnets to an unsaturated polyester or epoxy resin. It is laminated in an outer frame made of an organic resin, fixed by surrounding and integrating by applying pressure and heating from the outside, and incorporated into the IPM as a unitary magnet body by a method as shown in FIG. That is, IPM3 is the core 4
And a rotor 5 disposed inside the rotor 5, and integrated magnet bodies 2 formed by using a plurality of magnets 1 of the present invention as rotor magnets 6 are embedded in six locations of the rotor 5. The motor obtained in this manner is a motor having high efficiency because the integrated magnet body has excellent insulating properties and an effective volume ratio. The magnet of the present invention having a coating mainly composed of a composite chromium oxide of chromium and a divalent metal on its surface is not limited to the configuration in which a plurality of the magnets are used as an integrated magnet body as described above. Without chrome and 2
Utilizing the excellent insulating properties and corrosion resistance of the coating mainly composed of a complex chromium oxide with a valent metal, it can also be adopted in a configuration in which it is disposed alone in various magnetic circuits.

Examples of the rare earth permanent magnet applied to the present invention include known rare earth permanent magnets such as R—Co permanent magnet, R—Fe—B permanent magnet, and R—Fe—N permanent magnet. Is mentioned. Above all, R-Fe-B-based permanent magnets are desirable from the viewpoints of high magnetic properties, excellent mass productivity and economic efficiency, and excellent adhesion to the coating. The rare earth element (R) in these rare earth permanent magnets is at least one of Nd, Pr, Dy, Ho, Tb, and Sm, or further, La, Ce, G
Desirably, at least one of d, Er, Eu, Tm, Yb, Lu, and Y is included. Also, usually one of R
Although seeds are sufficient, a mixture of two or more kinds (such as misch metal or dymium) can be used for practical reasons for convenience in obtaining. Further, Al, Ti,
V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb,
By adding at least one of Ge, Sn, Zr, Ni, Si, Zn, Hf, and Ga, the coercive force and the squareness of the demagnetization curve, the productivity, and the price are reduced. Can be.

[0026]

EXAMPLES The present invention will be described in detail with reference to examples. In addition,
Although the following examples use a sintered magnet, the present invention can be applied not only to a sintered magnet but also to a bonded magnet. Examples 1 to 6: For Examples 1 to 5,
26 wt% Nd of 10 mm long x 50 mm wide x 5 mm high
-72 wt% Fe-1 wt% B-1 wt% Co composition N
The following experiment was performed using d-Fe-B permanent magnets (sintered magnets). In order to make the size of the magnet having the coating obtained by the following method substantially the same, in Example 6, except that the height was 4.85 mm,
The following experiment was performed using the same magnet as that used in Example 5. The above magnet (hereinafter, referred to as a magnet piece) was degreased with an organic solvent and then weakly pickled with a phosphoric acid aqueous solution. An undiluted treatment solution containing 350 g / l of chromic acid, 150 g / l of magnesium hydroxide, 50 g / l of an acrylic resin emulsion, 5 g / l of ethylene glycol as a reducing agent, and 20 g / l of boric acid was prepared (Mg / Cr was 0 g / l). .35 (wt /
wt), resin / Cr is 0.29 (wt / wt), pH =
5). This treatment liquid stock solution was diluted with water to prepare treatment liquids of various concentrations, and this treatment liquid was applied to the entire surface of the magnet piece by a dipping method, and was heated at 280 ° C.
As a result, a composite chromium oxide of chromium and magnesium is used as a main component, the film thickness is 0.05 μm (Example 1),
0.5 μm (Example 2), 2.5 μm (Example 3), 5
μm (Example 4), 10 μm (Example 5), 100 μm
The coating of Example 6 was formed on the entire surface of the magnet piece.

FIG. 1 shows the insulating properties of the magnet pieces obtained in Example 3.
The evaluation was performed according to the method shown in FIG. That is, a magnet piece having a film thickness of 2.5 μm is sandwiched between two Al plates having a thickness of 2 mm as a sample, and the resistance value (Ω) when a load is applied is measured using a commercially available simple tester. Was evaluated. The results are shown in FIG. As is clear from FIG. 2, the measured values were within the range indicated by oblique lines, and the magnet pieces obtained in Example 3 exhibited excellent insulation properties.

The magnet pieces obtained in Examples 1 to 6 were
30 under high temperature and high humidity conditions of temperature 80 ° C x relative humidity 90%
After leaving for 0 hour, a corrosion resistance test was performed. Table 1 shows the results. As is clear from Table 1, the magnet pieces obtained in all the examples exhibited excellent corrosion resistance.

The magnet pieces obtained in Examples 1 to 6 were
Eight layers are stacked in the height direction in the outer frame formed of the unsaturated polyester prepared in advance, and are fixed by being surrounded and integrated by applying pressure and heating from the outside to obtain an integrated magnet body Was. This integrated magnet body is connected to an IPM (4-pole, 15 kW:
Pulse width modulation method), and rotation speed 5400 rpm
, The motor efficiency (output power / input power) was evaluated.
Table 1 shows the results. As is clear from Table 1, the integrated magnet bodies using the magnet pieces obtained in all the examples exhibited excellent insulating properties, and the IPM incorporating them exhibited a motor efficiency of 85% or more.

[0030]

[Table 1]

Example 7: 26% by weight Nd-72% by weight Fe-1% by weight B of 10 mm long × 50 mm wide × 5 mm high
The following experiment was performed using an Nd-Fe-B permanent magnet (sintered magnet) having a -1 wt% Co composition. The above magnet (hereinafter, referred to as a magnet piece) was degreased with an organic solvent and then weakly pickled with a phosphoric acid aqueous solution. Sodium dichromate 200g /
l, calcium hydroxide 100 g / l, urethane-modified acrylic resin 300 g / l, nonionic surfactant 1 g /
1 was prepared (a Ca / Cr content of 0.1%).
77 (wt / wt), resin / Cr 4.3 (wt / w)
t), pH = 6). A treatment liquid obtained by diluting this treatment liquid stock solution with water is applied to the entire surface of the magnet piece by dipping, and is then applied to the magnet.
C. to form a coating having a thickness of 1 .mu.m and composed mainly of a composite chromium oxide of chromium and calcium on the entire surface of the magnet piece. When a corrosion resistance test was performed on the obtained magnet pieces under the same conditions as in the above example, there was no rust,
It showed excellent corrosion resistance. Also, using the obtained magnet pieces,
An integrated magnet was produced in the same manner as in the above example. The motor efficiency of the IPM incorporating this integrated magnet body is 9
3%.

[0032]

The rare earth permanent magnet according to the present invention, which has a coating mainly composed of a composite chromium oxide of chromium and a divalent metal on its surface, has a uniform coating with excellent adhesion. Since it is formed on the magnet surface, it exhibits excellent insulation properties and corrosion resistance even in a thin film. Therefore, a magnet having this coating on the surface is useful for obtaining an integrated magnet body having excellent insulating properties and an effective volume ratio, which is suitably used for electric vehicle motors and home appliance motors. .
In addition, this coating mainly contains a composite chromium oxide of a chromium oxide containing trivalent chromium (Cr ₂ O ₃ ) and a divalent metal. Therefore, it does not contain hexavalent chromium and is environmentally friendly.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for evaluating the insulating properties of a magnet piece having a coating according to the present invention.

FIG. 2 is a view showing the insulating properties of a magnet piece obtained in Example 3.

FIG. 3 is a diagram showing a configuration example of an IPM.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rare earth permanent magnet having the coating of the present invention 2 Integrated magnet body 3 IPM 4 Core 5 Rotor 6 Rotor magnet (Integrated magnet body)

Claims (8)

[Claims] 1. A rare-earth permanent magnet having on its surface a coating mainly composed of a composite chromium oxide of chromium and a divalent metal. 2. A film having a thickness of 0.005 μm to 50 μm.
The rare earth permanent magnet according to claim 1, wherein: 3. The divalent metal is Mg, Ca, Zr, Zn,
The rare-earth permanent magnet according to claim 1, wherein the rare-earth permanent magnet is at least one selected from Mn. 4. The rare earth permanent magnet according to claim 1, wherein the rare earth permanent magnet is an R—Fe—B permanent magnet. 5. A treatment solution obtained by adding at least one selected from divalent metal oxides, hydroxides and carbonates to a solution containing at least one selected from chromic anhydride and dichromate. A method for producing a rare-earth permanent magnet having on its surface a coating mainly composed of a composite chromium oxide of chromium and a divalent metal, which is heat-treated after being applied to the magnet surface. 6. The method according to claim 5, wherein a processing liquid obtained by adding an emulsion type organic resin and / or a water-soluble type organic resin to the processing liquid is used. 7. The method according to claim 5, wherein the pH of the treatment liquid is 4 to 7. 8. The method according to claim 5, wherein the heat treatment is performed at 150 ° C. to 400 ° C.