JP2020057792A - Bond magnet - Google Patents

Abstract

To improve the water resistance of a bond magnet without complicating a process.SOLUTION: In a bond magnet including a magnetic powder and resin, non-magnetic powder is added such that the ratio of the average particle size of magnetic powder to non-magnetic powder is magnetic powder: non-magnetic powder=1:0.03-1.00. The amount of non-magnetic powder added is 2 vol% or more and 8 vol% or less with respect to the entire bond magnet. The magnetic powder is anisotropic Sm-Fe-N, and the resin is polyamide 12.SELECTED DRAWING: None

Description

  The present disclosure relates to a bonded magnet.

Permanent magnets can be broadly classified into sintered magnets and bonded magnets. The sintered magnet is made of only magnetic powder, while the bonded magnet is made by mixing magnetic powder and resin to form a molded product. Bonded magnets can be molded by injection molding, compression molding, extrusion molding, etc. in the same way as resin, so they can be molded in a shape close to the shape of the final product, with a high degree of freedom in shape and high dimensional accuracy. It has the characteristic of being expensive.
However, the bonded magnet has a problem of water absorption because it has a resin component.

JP 2011-134995 A Japanese Patent No. 2940571

Patent Literature 1 aims to improve water resistance by adding a nonmagnetic powder to the surface of a bonded magnet and coating the surface with a resin. However, it is necessary to perform coating after forming the bonded magnet, which complicates the process.
On the other hand, Patent Document 2 discloses that a nonmagnetic powder is added to a bonded magnet. However, since it does not solve the problem relating to water resistance, no means for increasing the water resistance is disclosed.

  The present disclosure has been made in view of such circumstances, and has as its object to improve the water resistance of a bonded magnet without complicating the process.

  In the bonded magnet of the present disclosure, in a bonded magnet composed of a magnetic powder and a resin, the ratio of the average particle diameter of the magnetic powder to the nonmagnetic powder is 1: 0.03 to 1.00, ie, magnetic powder: nonmagnetic powder. Thus, a nonmagnetic powder is added.

  According to the present disclosure, it is possible to improve the water resistance of a bonded magnet without complicating the process.

  Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as appropriate. However, the bond magnet described below is for embodying the technical idea of the present disclosure, and the present disclosure is not limited to the following unless otherwise specified. Further, what is described in one embodiment or example can be applied to other embodiments or examples.

  The inventors of the present invention have conducted intensive studies and have found that by adding a predetermined size and a predetermined amount of non-magnetic powder to a bonded magnet, the water resistance of the bonded magnet is improved without sacrificing moldability and magnetic properties. I found out.

Bonded magnets have higher water absorption than sintered magnets. This is because the water absorption of the resin in the bonded magnet is high. Resin absorbs water by holding water between molecules.
When the bonded magnet is immersed in warm water, the resin starts to absorb water. Then, water is taken into the resin up to the saturated water content of the resin. The magnetic powder is in a steamed state. Then, the magnetic powder is oxidized by water, and the magnetic properties are reduced. Moisture in the resin consumed by the oxidation of the magnetic powder is replenished to the resin from warm water around the bonded magnet. Further, a cycle of water consumption occurs in which the magnetic powder consumes water, and the magnetic properties of the bonded magnet deteriorate and the weight increases at an accelerated rate.

In a bonded magnet, reducing the amount of resin has two main disadvantages. One is a decrease in moldability, and the other is a decrease in orientation.
Examples of the method for forming the bonded magnet include injection molding, extrusion molding, and compression molding. In each case, the resin in the bonded magnet composition is melted in a mold to form a bonded magnet molded product. In order to improve the moldability, the larger the amount of the resin, the better.

  In the case of an anisotropic magnetic powder having magnetic anisotropy, the magnetic properties are improved by performing an operation of applying a magnetic field from the outside to align the orientation of the magnetic powder by a magnetic field orientation. Since the magnetic powder needs to move in the resin, the amount of the resin must be increased as compared with a bonded magnet using an isotropic magnetic powder.

As described above, the moldability and the orientation of the bonded magnet are improved as the amount of the resin increases. However, when the amount of the resin increases, the amount of water absorption increases, and the magnetic powder deteriorates due to oxidation, thereby deteriorating the water resistance of the bonded magnet.
As described above, the bond magnets originally had a trade-off relationship between the moldability and orientation and the water resistance. The present embodiment breaks this trade-off relationship.

In the present embodiment, the non-magnetic powder is added such that the ratio of the average particle diameter between the magnetic powder and the non-magnetic powder is magnetic powder: non-magnetic powder = 1: 0.03 to 1.00.
By setting the particle diameters of the magnetic powder and the non-magnetic powder in this way, the non-magnetic powder enters the resin that has entered the gap between the adjacent magnetic powders without disturbing the arrangement of the adjacent magnetic powders. The non-magnetic powder is dispersed in the resin. This nonmagnetic powder prevents smooth diffusion of water into the resin due to the so-called maze effect. The diffusion rate of water is reduced, and consequently the oxidative degradation of the magnetic powder is also slowed. Since non-magnetic powder is added without disturbing the arrangement of adjacent magnetic powders, it does not disturb the movement of the magnetic powder at the time of molding or orientation, so there is no decrease in moldability and orientation. . In other words, the resin and the non-magnetic powder act as a new resin material. In the present embodiment, it is possible to realize improvement of the moldability and orientation and the water resistance in this way.

  The nonmagnetic powder added to the bonded magnet of the present invention preferably has an average particle size of 0.1 μm or more and 3 μm or less. When the average particle size is smaller than 0.1 μm, the fluidity of the resin is extremely deteriorated. When the average particle size is larger than 3 μm, the effect of improving the water resistance of the bonded magnet decreases.

  In the present specification, the value of the average particle size is determined by the air permeation method or F.I. S. S. S. No. (Fisher-SubSieve-Sizers-No.).

  Further, the addition amount of the nonmagnetic powder to the whole bonded magnet is preferably 2 vol% or more and 8 vol% or less. When the addition amount is less than 2 vol%, the effect of improving the water resistance of the bonded magnet decreases. If it is more than 8 vol%, the fluidity of the bonded magnet composition will be reduced and molding will not be possible.

  Examples of the non-magnetic powder that can be used in the present embodiment include calcium carbonate, silica, alumina, glass, talc, mica, and the like, and magnetic powder: non-magnetic powder = 1: 0.03 to 1.00. There is no particular limitation on the non-magnetic powder having such a particle diameter.

  As the magnetic powder, any powder such as a ferrite-based powder and a rare-earth-based powder may be used. It is preferable to use a rare earth-based material such as NdFeB-based, SmFeN-based, or SmCo-based to improve magnetic characteristics. It is further preferable to use anisotropic magnetic powder for improving the magnetic properties of the bonded magnet. Anisotropic SmFeN magnetic powder is most preferred. This is because the average particle size is about 3 μm and the particle size distribution is sharper than other rare earth magnetic powders, so that the particle size of the nonmagnetic powder can be set accurately, and the effect of improving the water resistance is remarkably exhibited.

  The rare earth magnetic powder applicable to the present embodiment is preferably subjected to a surface treatment for the purpose of improving oxidation resistance, water resistance, improving wettability with a resin, and improving chemical resistance as described below. These processes can be used in combination as needed. The surface treatment method is basically performed by a wet method, a dry method such as a mixer, plating, or vapor deposition as necessary. Examples of the chemical conversion treating agent include a phosphorus compound having a PO bond.

  Examples of the phosphating agent include phosphates such as orthophosphoric acid, sodium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, zinc phosphate, and calcium phosphate; Inorganic phosphoric acid and organic phosphoric acid such as phosphoric acid, hypophosphite, pyrophosphoric acid, and polyphosphoric acid can be used.

  These phosphoric acid sources are dissolved in water or an organic solvent such as IPN, and if necessary, the magnetic powder is introduced into a phosphoric acid bath to which a reaction accelerator such as nitrate ion is added, and the P-O bond is formed on the powder surface. Is formed. In addition, using wet or dry methods, silica, alumina, titania film and other inorganic oxide films using submicron, nano-order particles, surface-adsorbed to magnetic powder to form a film, or organic metal The sol-gel method used and the inorganic oxide treatment film forming treatment for forming a film on the surface of the magnetic powder can be applied. In the present invention, a treatment method for forming a silica film on the surface of the magnetic powder by hydrolysis of ethyl silicate is preferably used.

  Next, the coating treatment of the magnetic powder with the coupling agent will be described. The coupling agent treatment is performed using γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane. Silane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyl Triethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethylenedisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyl [3- (trimethoxyallyl) propyl Ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, vinyltrichlorosilane, vinyltris (βmethoxyethoxy) silane, vinyltriethoxysilane, β- ( 3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxy Silane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, oleidopropyltriethoxysilane, γ-isocyanatopropyltriethoxy Silane, polyethoxydimethylsiloxane, polyethoxymethylsiloxane, bis (trimethoxysilylpropyl) amine, bis (3-triethoxysilylpropyl) tetrasulfane, γ-isocyanatopropyltrimethoxysilane, vinylmethyldimethoxysilane, 1,3 , 5-N-tris (3-trimethoxysilylpropyl) isocyanurate, t-butylcarbamate trialkoxysilane, N- (1,3-dimethylbutylidene) -3- (triethoxysilyl) -1-propanamine and the like Silane coupling agent, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl (N-aminoethyl-aminoethyl) titanate, isopropyl tris (dioctyl pyrophore) Fate) titanate, tetraisopropyl bis (dioctyl phosphite) titanate, tetraisopropyl titanate, tetraoctyl bis (trioctyl phosphite) titanate, isopropyl trioctyl titanate, isopropyl tri (dioctyl phosphate), isopropyl dimethacrylate isostearyl titanate, tetraoctyl Bis (ditridecyl phosphite) titanate, tetra (2,2-diallyloxymethyl-1-butyl) bis (di-tridecyl phosphite) titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, isopropyl isostearyl diacryl titanate , Bis (dioctylpyrophosphate) ethylene titanate and other titanate coupling agents; Aluminum coupling agents such as lucoxyaluminum diisopropylate can be used.

  Amino, methacrylic, vinyl, epoxy silane coupling agent, titanate coupling agent, aluminum coupling agent, coupling agent treatment using fluorine coupling agent, organic such as methacrylic resin A method of forming a protective film, a method of forming a metal protective film of zinc, nickel, or the like by vacuum deposition, electrolytic plating, or electroless plating can be applied. In the present invention, a coupling agent having an amino group that is familiar with a nylon resin described below is preferably used.

  In the present embodiment, the magnetic powder suitably used is composed of fine particles having a relatively small average particle size of about 3 μm, and a resin binder is introduced by introducing a hydrophilic group which is familiar with the resin to the surface by surface treatment. Can be stocked on the surface, and can be used effectively as a protective film or an insulating film between particles for separating particles. Therefore, as a result, a bonded magnet exhibiting excellent corrosion resistance is obtained. In order to obtain such a bonded magnet, the weight of the amino group derived from the coupling agent per unit surface area of the magnetic powder is more preferably 0.5 to 5 mg / m 2. If the amount is less than 0.5 mg / m 2, the above-mentioned insulation between the particles is insufficient. If the amount exceeds 5 mg / m 2, the affinity of the particles of the magnetic powder becomes too high, and the particles agglomerate. , Corrosion resistance and mechanical strength are all undesirably reduced.

  The resin used in the present embodiment is not particularly limited, for example, thermoplastic resins such as polypropylene, polyethylene, polyvinyl chloride, polyester, polyamide, polycarbonate, polyphenylene sulfide, and acrylic resin, ester-based, polyamide-based, and the like. Or a thermosetting resin such as an epoxy resin, a phenol resin, an unsaturated polyester resin, a urea resin, a melamine resin, a polyimide resin, an allyl resin, and a silicone resin.

  In particular, it is preferable to use polyamide 12 among polyamides. This is because polyamide has a high polarity and can be filled with a large amount of magnetic powder. Among them, polyamide 12 has a small water absorption, so that a bonded magnet having high magnetic properties and a small water absorption can be produced.

  Although the mixing ratio of the magnetic material and the resin depends on the type of the resin, it is desirable that the ratio of the magnetic material to the entire bonded magnet composition be 45 to 65 vol%. Further, an antioxidant can be added to the resin component for the purpose of improving the heat stability. Specific examples include triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate]. A lubricant may be used to improve kneading and injection moldability. Specifically, examples of the lubricant include waxes such as paraffin wax and polyethylene wax, fatty acids such as stearic acid and salts thereof, metal soap, fatty acid amide, urea compound, fatty acid ester, polyether, silicone oil, silicone grease, and the like. Polysiloxanes, fluorine-based oils, fluorine-based greases, fluorine resin powders, and the like. Further, in addition to these, a plasticizer, a flame retardant, an antistatic agent and the like may be added. Further, an antioxidant, a lubricant and the like can be further mixed.

  As a molding method, for a bonded magnet using a thermoplastic resin, injection molding, extrusion molding and the like can be mentioned. When a thermosetting resin is used, compression molding and the like can be mentioned. When using an anisotropic magnetic powder, it is preferable to perform magnetic field orientation. According to the present embodiment, even if the amount of the resin is increased to perform the magnetic field orientation, the deterioration due to water absorption can be suppressed.

Hereinafter, examples will be described, but the present invention is not limited thereto.
The value of the average particle size in this example is a value obtained by measurement using a Fischer sub-sieve sizer model 95 (trade name, manufactured by Fischer).
<Example 1>
(Preparation of magnetic material)
The magnetic material is an anisotropic Sm—Fe—N-based magnetic material (average particle diameter 3 μm).
(Preparation of bonded magnet composition)
First, the Sm-Fe-N-based magnetic material is surface-treated with ethyl silicate and a silane coupling agent. The surface treatment was performed Sm-Fe-N based magnetic material (density 7.66 g / cm ³⁾ to 908 g, polyamide 12 (density 1.02 g / cm ³⁾ of 71 g, the non-magnetic powder as the silica (density 2.2 g / cm ³ ) is mixed with a mixer in an amount of 22 g. The obtained mixed powder is kneaded at 220 ° C. using a biaxial kneader, cooled, and cut into a suitable size to obtain a bonded magnet composition.

(injection molding)
The barrel of the injection molding machine is set at 230 ° C., and the mold is set at 90 ° C. Injection molding is performed at an injection speed of 100 mm / s and an injection time of 1 s. At this time, a magnetic field of 9 kOe is applied to the cavity to orient the SmFeN powder. The shape of the molded product is a column having a diameter of 10 mm and a height of 7 mm, and the orientation direction of the SmFeN powder is the height direction.

<Examples 2 to 9>
Table 1 shows the difference in the composition of the bonded magnet composition from that of Example 1. The density of the calcium carbonate and alumina was used as the non-magnetic powder in Example 8 and 9, respectively 2.7 g / cm ³ and 4.0 g / cm ^3, determined the formulation of bonded magnet composition using this did. Except for this, a bonded magnet molded product was produced in the same manner as in Example 1 as Examples 2 to 9.

<Comparative Example 1 to Comparative Example 8>
Table 1 shows the difference in the composition of the bonded magnet composition from that of Example 1. Except for that, the bonded magnet molded products of Comparative Examples 1 to 8 were produced in the same manner as in Example 1.

<Evaluation>
(Injection pressure)
This is the injection pressure during the injection molding process. Table 1 shows the results.

(PCT)
A pressure cooker test (PCT) is performed on the bonded magnet obtained in the injection molding process. The conditions were 120 ° C.-2 atm-200 hr. The magnetic flux before and after the test was measured with a flux meter, and the flux change rate was evaluated. The weight before and after the test was measured with an electronic balance, and the rate of weight change was evaluated. Table 1 shows the results.

(Effect of non-magnetic powder particle size)
It can be seen that when the average particle diameter of the nonmagnetic powder is 3 μm or less, the flux change rate is small and the weight change rate is also small. From these results, it can be seen that a substance having a large amount of water absorption and a large weight change rate has a large decrease in flux. It can be seen that when the nonmagnetic powder is smaller than 0.03 μm, the injection pressure increases. Taking these results into consideration, the average particle diameter of the nonmagnetic powder is preferably 0.1 to 3 μm.

(Effect of non-magnetic powder filling amount)
It can be seen that when the filling amount of the nonmagnetic powder is 2 vol% or more, the flux change rate is small and the weight change rate is also small. It can be seen that when the amount of the nonmagnetic powder is 10 vol% or more, the injection pressure becomes extremely large. On the basis of these results, the non-magnetic powder filling amount is preferably 2 to 8 vol%.

(Type of non-magnetic powder)
From the comparison between Example 3, Example 8, and Example 9, the weight change rate and the flux change rate are almost the same regardless of the type of the non-magnetic powder, as long as the particle diameter of the non-magnetic powder is the same. I understand.

  For example, it is possible to apply a rare-earth bonded magnet to a motor such as an electric water pump or a water heater in which a magnet is used by being immersed in water.

Claims (4)

In a bonded magnet composed of magnetic powder and resin,
A bonded magnet, wherein the nonmagnetic powder is added so that the ratio of the average particle diameter between the magnetic powder and the nonmagnetic powder is magnetic powder: nonmagnetic powder = 1: 0.03 to 1.00.   2. The bonded magnet according to claim 1, wherein an addition amount of the nonmagnetic powder is 2 vol% or more and 8 vol% or less with respect to the whole of the bonded magnet.   The bonded magnet according to claim 1, wherein the magnetic powder is anisotropic Sm—Fe—N.   The bonded magnet according to any one of claims 1 to 3, wherein the resin is polyamide 12.