JPH05275220A - Rare earth-ferrous bond magnet - Google Patents

Abstract

PURPOSE:To cause powder to hardly drop by forming a specific film. CONSTITUTION:A title magnet contains a polymer at least a kind selected out of a group consisting of styrene, acrylate ester, methacrylate ester, and an oligomer made of their monomer as A components and at least a kind of butadiene, butyrene, and isoprene as B components. A film forming material mixture where the content of B components is 3-30wt% of A components is applied to form a film. This process improves corrosion resistance of a bond magnet without decreasing magnetic characteristics, thereby causing powder to hardly drop.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-iron-based bonded magnet which has excellent corrosion resistance and less powder loss.

[0002]

2. Description of the Related Art Bonded magnets are widely used as electronic equipment parts because they have good dimensional accuracy and can be formed into a complicated shape or integrally molded. Among them, rare earth-
Iron-based bonded magnets are particularly noteworthy because they are inexpensive and have high magnetic properties. However, rare earth-
Iron-based bonded magnets have the disadvantage that they are extremely rusty, inferior in corrosion resistance, and easily fallen into powder, so that their magnetic properties gradually deteriorate. Therefore, in order to improve the corrosion resistance of the bond magnet and reduce powder loss, for example, a metal plating film of Al, Ni, Cr, AlCr or the like is formed on the bond magnet, or an epoxy resin-based organic film is formed. The process of doing is performed.

However, the bonded magnet which has been subjected to the above-mentioned treatment has a drawback in that the metal plating film formed is thick and magnetic properties are deteriorated thereby. Furthermore, since the adhesion between the bond magnet and the metal plating film is poor, the metal plating is easily peeled off, and it is difficult to obtain sufficient corrosion resistance.
On the other hand, as a method of treating the bond magnet, generally, a spray method and an electrodeposition method can be mentioned. However, when it is attempted to sufficiently enhance the corrosion resistance and reduce the powder drop, the resin film becomes thick and It is unavoidable that the magnetic properties of the magnet deteriorate, and if the amount of resin is reduced to prevent this, it is difficult to reduce powder drop.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a rare earth-iron based bonded magnet which has improved corrosion resistance and reduced powder loss while maintaining excellent magnetic properties.

[0005]

In order to solve the above-mentioned problems, the present invention provides a rare earth-iron-based bonded magnet comprising (A) styrene, an acrylic ester and a methacrylic ester and at least one of these monomers. Which comprises at least one selected from the group consisting of the following oligomers and (B) a polymer comprising at least one of butadiene, butylene and isoprene, wherein the content of the (B) component is 3 of the (A) component. The present invention provides a highly corrosion-resistant rare earth-iron-based bonded magnet obtained by applying a coating material mixture of about 30% by weight to form a coating film. The bonded magnet of the present invention will be described in detail below.

The bonded magnet of the present invention is characterized in that the above-mentioned specific coating is formed. By forming such a film, it is possible to improve the corrosion resistance of the bonded magnet and reduce the powder drop without deteriorating the magnetic characteristics of the bonded magnet.

Bonded magnet In the present invention, the rare earth-iron based bonded magnet on which the above-mentioned coating film is to be formed is a rare earth-iron based alloy formed by a liquid quenching method into a ribbon-like material having a thickness of several tens of microns. Is pulverized to a size of 36 mesh (JIS) or less, and the obtained powder is mixed with a resin binder and molded. The rare earth-iron-based alloy used here has a composition known per se such that it is based on iron and contains rare earth elements such as neodymium and boron. Among these, especially as a magnetic material, Nd-Fe-Co-B system, Nd-Dy-Fe-B system, Sm-Fe
-Ti series, Sm-Fe-Co series, Nd-Fe-B series, etc. are suitable,
Among them, a rare earth-iron-boron ternary alloy is preferably used.

The ribbon-like material is formed by the liquid quenching method, for example, by melting the alloy having the above-mentioned composition by means of high frequency induction or the like, and then rapidly cooling the molten metal by spraying it on a high-speed rotating copper or aluminum roll. It is done by The ribbon-shaped material can be pulverized by dry or wet pulverization using a stamp mill, a ball mill or the like. Further, it is desirable to heat-treat this ribbon prior to crushing, and this heat-treatment suppresses the growth of crystal grains, for example, the average crystal grain size becomes 3000 Å or less.

Examples of the resin binder mixed with the alloy powder obtained above include polyamide resin such as nylon and polyester resin such as polybutylene terephthalate when an injection molding method is adopted as a subsequent molding method. When the thermoplastic resin is used and the compression molding method is adopted, a thermosetting resin such as an epoxy resin or a phenol resin is preferably used. Such a resin binder is generally 5 to 10% by weight in the case of a thermoplastic resin, and 0.5 to 4.0 in the case of a thermosetting resin, based on the alloy powder.
It is desirable to use it in a weight percentage. If it is used in a larger amount than this range, the magnetic properties of the obtained bond magnet will be unsatisfactory, and if it is less than the above range, the strength of the bond magnet will tend to be unsatisfactory.

[0010] (A) component contained in the coating material a mixture of the coating material mixture component (A) the present invention include styrene, from the group consisting of oligomers consisting of at least one acrylic acid ester and methacrylic acid esters and these monomers It is at least one selected. This component (A) is inexpensive, and also has hydrophobicity by itself, and when attached to the surface of the bond magnet and / or impregnated inside the bond magnet and thermally polymerized, it becomes a polymer having high water repellency, It is possible to form a dense and thin coating on a bonded magnet. Therefore, it is possible to prevent the intrusion of water, which is a cause of rust generation, into the inside of the bonded magnet, so that the corrosion resistance of the bonded magnet can be improved. That is,
Since the bond magnet is formed by solidifying powder, pores at a maximum of about 10% by volume are present inside the bond magnet, which makes it easy to retain water. By filling the pores with the above-mentioned component (A), the corrosion resistance can be improved rather than rust prevention only on the surface. Other than the polymer obtained by polymerizing the component (A), there are those having water repellency, but it is difficult to form a solution to form a film, or a film having an appropriate thickness can be formed. It is difficult to use, and it is also disadvantageous in terms of price, so it cannot be practically used. When the inside of the bonded magnet is impregnated with the component (A) and heat-polymerized to form a coating, the degree of polymerization thereof is preferably 20 or more, and more preferably 50 or more. If the degree of polymerization is too low, the polymer is easily decomposed and the water repellency is poor, so that sufficient corrosion resistance cannot be obtained.

Examples of the monomer include the above-mentioned styrene, acrylic acid ester and methacrylic acid ester. Among them, methyl acrylate is preferable as the acrylic ester, and as the methacrylic ester,
Methyl methacrylate is preferred. An oligomer is a homo-oligomer consisting of only one of the above monomers,
It may be a co-oligomer obtained by copolymerizing the above monomers. The degree of polymerization of the oligomer is preferably 2-20. If the degree of polymerization is too high, the solidification tends to be strong, and the film formed when forming a film on the bonded magnet becomes thick, resulting in deterioration of magnetic properties. The above monomers and oligomers can be used alone or as a mixture of two or more kinds.

Component (B) The component (B) contained in the coating material mixture of the present invention is a polymer obtained by polymerizing at least one of butadiene, butylene and isoprene. These polymers can not only improve the corrosion resistance of the bond magnet, but also improve the film strength such as impact resistance (elasticity) and scratch resistance, and reduce the powder loss of the bond magnet. be able to. Although there are those other than these polymers that improve the strength, they are easily water-absorbing,
Since it is poorly compatible with the polymer (A), there is a problem that the corrosion resistance is lowered, and it cannot be practically used.

The component (B) may be a homopolymer consisting of only one of butadiene, butylene and isoprene, or a copolymer obtained by copolymerizing two or more of these monomers. Moreover, these polymers can be used individually or as a mixture of 2 or more types.
The degree of polymerization of the component (B) is preferably 20 or more, and more preferably 50 or more. If the degree of polymerization is too low, it is difficult to improve the strength, and it is not possible to reduce powder drop. The content of the component (B) is 3 to 30% by weight of the polymer (A), preferably 5 to 25% by weight. When the amount of the polymer (B) is too small, it is difficult to reduce the powder drop of the bonded magnet, and when the amount of the polymer (B) is too large, the water absorption is high and the corrosion resistance is low.

The coating material mixture used in the present invention is prepared by mixing the above-mentioned component (A) with the component (B) or, if necessary, dissolving the component (B) in a suitable solvent. ) It may be mixed with the component. Examples of the solvent that dissolves the component (B) include organic solvents such as toluene, xylene, benzene, and tetrahydrofuran, and they can be used for viscosity adjustment as necessary. The coating material mixture preferably has a viscosity at 20 ° C of 500 cP or less, and further 300 cP.
The following is preferable. If the viscosity of the coating material mixture is too high, the thickness of the coating formed may increase, resulting in a decrease in magnetic properties. In addition, it may be difficult to sufficiently fill the inside of the pores. Sex deteriorates. Further, if the viscosity is too high, unevenness is likely to occur when a coating film is formed on the bonded magnet, resulting in poor dimensional accuracy.

Formation of a coating After the above coating material mixture is prepared, the above-mentioned bonded magnet is immersed in the mixture, or the above-mentioned bonded magnet is sprayed with the mixture, and then heated at an appropriate temperature for thermal polymerization. By doing so, a film is formed. If a polymerization initiator such as benzoyl peroxide or azobisisobutyronitrile is added to the coating material mixture in advance, a denser coating can be formed.

When the bond magnet is dipped in the above coating material mixture, it is preferably carried out by a vacuum impregnation method. This vacuum impregnation method is performed, for example, by holding the bonded magnet in a vacuum of 1 × 10 ^-2 torr or less for about 10 to 30 minutes and immersing the bonded magnet in the mixture while maintaining the vacuum degree. Be seen. Immersion is usually performed for a time such that foaming subsides. According to this vacuum impregnation method, the mixture penetrates not only into the surface of the bonded magnet but also into the pores (usually 10% by volume maximum) formed inside the magnet, and as a result, the void The holes are filled with the coating material, and the generation of rust from the holes is effectively suppressed.

The coating formed on the bonded magnet contains a polymer of the component (A) and a polymer of the component (B), and
The component (A) and the component (B) may be copolymerized. The thickness of the coating film formed is preferably 5 to 20 μm, and the thickness of the coating film can be set within the above range by adjusting the viscosity of the coating material mixture and the concentration of the solution used.

[0018]

[Examples] Preparation of bonded magnets: Ingot of Nd-Fe-Co-B alloy was melted by high frequency, and pressure was applied to the surface of a copper roll rotating at a peripheral speed of 40 m / sec.
Sprayed at 0.5kg / cm ² and cooled rapidly, width 2mm, thickness 20μm
Got a ribbon. This ribbon was heated in vacuum at 750 ° C. for 10 minutes, cooled to room temperature, and then ground to 36 mesh (JIS) or less. The composition of this powder, in atomic%, is Nd 12.5
%, Co 5.5%, B 5.0%, and the balance Fe. 100 g of the magnetic powder obtained above was mixed with 2 g of a binder composed of an epoxy resin and a curing agent, and compression molded at a surface pressure of 5 t / cm ² ,
By heating at 130 ℃ for 1 hour, width 5mm, length 10m
A cured product with m and a height of 6 mm was obtained. Next, this cured product is treated with 50 kOe
The magnet was magnetized in a magnetic field to obtain a bond magnet (bond magnet I). Further, 100 g of the magnet powder obtained above was mixed with 7.5% by weight of polyamide resin (PA-12). 2 this mixture
After kneading at 50 ° C for 15 minutes, injection molding was performed at 240 ° C in a magnetic field of 18kOe. The obtained molded body was magnetized in a magnetic field of 50 kOe to obtain a bond magnet (bond magnet II).

Example 1 Experiment Nos. 101 to 155 In each experiment, the monomers and polymers shown in Tables 1 to 4 were mixed at the compounding ratios shown in Tables 1 to 4 to prepare coating material mixtures. In addition, (A) in Tables 1 to 4 is a liquid at room temperature. Table 1 shows the results of measuring the viscosity of the mixture using a B-type rotational viscometer calibrated with a calibration solution (JIS Z 8809).
4 shows. The bond magnet I left for 30 minutes in a vacuum of 1 × 10 ⁻³ Torr was immersed in the mixture. After the foaming stopped, the bonded magnet was heated in an oven at 80 ° C. for 30 minutes to obtain a bonded magnet on which a polymer film was formed. However, Experiment Nos. 108 to 116, 122 to 129, 137 marked with *
˜155 are comparative examples using coating material mixtures that do not meet the conditions of the invention. The obtained polymer-coated bonded magnet was subjected to a corrosion resistance test, a powder drop test, and a magnetic property test by the following methods. The results are shown in Tables 1 to 4.

Corrosion resistance test After immersing the polymer-coated bonded magnet in a sodium chloride aqueous solution having a concentration of 1% by weight at room temperature for 10 minutes, the temperature is 80 ° C and the relative humidity is 90%
An exposure test was carried out in a constant temperature and humidity chamber to visually check the rusting state of the polymer film-formed bonded magnet. The evaluation criteria are as follows. ○: No rusting over 100 hours △: Rusting over 100 hours within 100 hours ×: Rusting within 50 hours Powder falling test Micro type electromagnetic vibrating sieve M-2 type (Tsutsui Science Kiki Co., Ltd.
(Manufactured by Sieve: 100 mesh, diameter 7.5 cm), five polymer coated bond magnets were vibrated on a scale 5 for 1 hour. After the vibration was completed, the weight of the magnet powder that had fallen off from the polymer-coated bonded magnet was measured to determine the ratio with respect to the initial polymer-coated bonded magnet. This ratio was evaluated according to the following criteria. ◯: 0.3% by weight or less Δ: 0.3 to 0.5% by weight ×: 0.5% by weight or more Magnetic characteristics The maximum energy product BH _max was measured with a Thiophy type self-recording magnetometer (VSM).

Experiment No. 156 Bonded magnet I left in a vacuum of 1 × 10 ^-3 Torr for 30 minutes
To, NiSO ₄ · 6H ₂ O, the NiCl ₂ and _{H 3 BO 4 10: 1:} 1
This is a comparative example in which a Ni coating is formed by electrolytic plating in a plating bath composed of an electrolytic solution mixed in a (weight ratio) ratio. Regarding the obtained Ni-coated bonded magnet, Experiment No. 101-
Similarly to 155, a corrosion resistance test, a powder drop test and a magnetic property test were performed. The results are shown in Table 4.

Experiment No. 157 A surface of the bond magnet I left in a vacuum of 1 × 10 ^-3 Torr for 30 minutes was sprayed with a methyl ethyl ketone solution of a bisphenol A type epoxy resin (viscosity at 20 ° C. was 120 cP). , 80 this bond magnet in the oven
This is a comparative example in which a film was formed by heating at 130 ° C for 30 minutes and then at 130 ° C for 30 minutes. The obtained epoxy resin-coated bonded magnet was subjected to a corrosion resistance test, a powder drop test and a magnetic property test in the same manner as in Experiment Nos. 101 to 155. The results are shown in Table 4.

Experiment No. 158 Experiment Nos. 101 to 155 except that a methyl ethyl ketone solution of a bisphenol A type epoxy resin (viscosity at 20 ° C. was 120 cP) was used in place of the coating material mixture used in Experiments No. 101 to 155. This is a comparative example in which a film is formed on the bond magnet I in the same manner as in. The obtained epoxy resin-coated bonded magnet was subjected to a corrosion resistance test, a powder drop test and a magnetic property test in the same manner as in Experiment Nos. 101 to 155. The results are shown in Table 4.

Experiment No. 159 Bonded magnet I left in a vacuum of 1 × 10 ^-3 Torr for 30 minutes
Is a comparative example in which is treated with rust preventive oil specified in JIS K 2246. Experiment N was performed on the obtained anti-rust oil treated bonded magnet.
Similarly to o.101 to 155, a corrosion resistance test, a powder drop test and a magnetic property test were performed. The results are shown in Table 4.

Example 2 Experiment Nos. 201 to 216 In each experiment, the polymers shown in Table 5 were mixed at the compounding ratio shown in Table 5, and 100 g of the polymer was dissolved in 500 ml of xylene to prepare a coating material mixture. For the mixture, a calibration solution
Table 5 shows the results of viscosity measurement using a B-type rotational viscometer calibrated with (JIS Z 8809). 1 × 10 ⁻³ To the mixture
The bonded magnet II left for 30 minutes was immersed in a vacuum of rr.
After the foaming stopped, the bonded magnet was heated in an oven at 80 ° C. for 30 minutes to obtain a bonded magnet on which a polymer film was formed. However, Experiment Nos. 207 to 216 marked with * are comparative examples using coating material mixtures that do not satisfy the conditions of the present invention. The obtained polymer-coated bonded magnet was subjected to a corrosion resistance test, a powder drop test and a magnetic property test in the same manner as in Example 1. The results are shown in Table 5.

Experiment No. 217 Experiment No. 156 was performed in the same manner as Experiment No. 156 except that Bond Magnet II was used instead of Bond Magnet I. The results are shown in Table 6. Experiment No. 218 Experiment No. 157 was carried out in the same manner as Experiment No. 157 except that Bond Magnet II was used instead of Bond Magnet I. The results are shown in Table 6. Experiment No. 219 Experiment No. 158 was performed in the same manner as Experiment No. 158, except that Bond Magnet II was used instead of Bond Magnet I. The results are shown in Table 6. Experiment No. 220 Experiment No. 159 was performed in the same manner as Experiment No. 159 except that Bond Magnet II was used instead of Bond Magnet I. The results are shown in Table 6.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

[Table 6]

[0033]

EFFECT OF THE INVENTION The rare earth-iron based bonded magnet on which the specific film of the present invention is formed has not only good magnetic properties but also excellent corrosion resistance and less powder falling.

Claims (1)

[Claims] 1. A rare earth-iron-based bonded magnet having at least one selected from the group consisting of (A) styrene, an acrylic acid ester and a methacrylic acid ester, and an oligomer comprising at least one of these monomers,
And (B) a polymer comprising at least one of butadiene, butylene and isoprene, and (B)
A highly anticorrosive rare earth-iron based bonded magnet obtained by applying a film-forming material mixture having a content of 3 to 30% by weight of the component (A) to form a film.