Patent Application
20110074531
1. Field of the Invention
The present invention relates to a rare earth-iron based resin bonded magnet, and more particularly to an anisotropic rare earth-iron based resin bonded magnet with high magnetic properties that will satisfy the following conditions: when coercivity HcJ at a room temperature is approximately 1 MA/m, a squareness at a room temperature is Hk/HcJRT, and a squareness at a temperature of 100° C. is Hk/HcJ100, Expression Hk/HcJRT<k/HcJ100 is obtainable. In this anisotropic rare earth-iron based resin bonded magnet, squareness deterioration based on a demagnetization curve at a high temperature can be avoided, and the maximum energy product (BH)max can be 170 kJ/m3 or more.
2. Description of the Related Art
Material types for rare earth-iron based magnet such as Nd2Fe14B base, αFe/Nd2Fe14B base and Fe3B/Nd2Fe14B base that are obtainable through rapid solidification, for example, a melt spinning method, are limited to a thin strip such as a ribbon, or powder obtained by milling the thin strip. Accordingly, for obtaining a bulked magnet applicable to a compact rotary machine, there will be necessary to conduct material transformation, that is, solidifying the thin strip or the powder into specific bulks with some measures. A primary measures to solidify the powder by means of powder metallurgy is pressureless sintering. However, it is not easy to apply the pressureless sintering to magnetic materials while maintaining their magnetic properties in a metastable condition. Based on the above, the thin strip or the powder has been solidified into specific bulks through binding materials such as epoxy resin, being able to obtain so-called resin bonded magnets.
For example, in 1985, R. W. Lee et al. reported that an isotropic Nd2Fe14B based bonded magnet with a (BH)max of 72 kJ/m3 is obtainable in such a manner that a thin strip with a (BH)max of 111 kJ/m3 is solidified with resin (see Non-Patent Document 1).
In 1986, the present inventors have proved through the Non-Patent Document 1 that an annular isotropic Nd2Fe14B magnet with a (BH)max of up to 72 kJ/m3 where the thin strip is solidified with epoxy resin is practicable to compact rotary machines. Further, for example, in 1990, G. X. Huang et al. have proved practicability of an isotropic resin bonded magnet to compact rotary machines (see Non-Patent Document 2), and in the 1990's such a isotropic resin bonded magnet has been widely become known as an annular magnet for a high-performance compact rotor machine applicable to an electromagnetic driving device in electric and electronic equipment such as OA (office automation), AV (audio and visual), PC (personal computer), PC peripheral devices, and telecommunication equipment.
On the other hand, starting from the 1980's, extensive researches on magnetic materials in a melt spinning method have been conducted. Accordingly, Nd2Fe14B based materials, Sm2Fe17N3 based materials, or nanocomposite materials through exchange coupling with αFe based or Fe3B based materials based on the forenamed materials (Nd2Fe14B based and Sm2Fe17N3 based materials) have become publicly known. Further, in addition to diversified alloy compositions or materials where the structure of the alloy compositions is subjected to fine-control, magnetic materials in different shapes obtainable by a rapid solidification method other than the melt spinning method became also known in recent (see for example, Non-Patent Documents 3 and 4). Also, Davies et al. reported magnetic materials where a (BH)max is reachable up to 220 kJ/m3 even though the magnetic materials are isotropic (see Non-Patent Document 5). However, it is speculated that the (BH)max of industrial applicable strips through the rapid solidification method is up to 134 kJ/m3, and the (BH)max of an isotropic resin bonded magnet where the stripes are solidified with resin at 0.8 to 1.0 GPa can be estimated approximately up to 80 kJ/m3.
Regardless of the above, considering electromagnetic driving devices such as relatively compact rotary machines to which the present invention relates, along with the high performability of electrical and electric equipments, demands for further miniaturization, high-output and high efficiency have never been ceased. Thus, it is obvious that just improving the magnetic properties of magnetically isotropic strips through the rapid solidification method is no longer enough for catching up with the enhancing performance of electric and electronic equipment. Accordingly, necessity has been further focused on a magnet generating static magnetic fields in which to fit the most preferable magnetic circuits for the iron core of the rotary machines (preferably, magnets that generate further strong static magnetic fields per unit volume).
Here, considering Sm—Co based magnetic materials applied for a rare-earth magnet, it is possible to obtain high coercivity (HcJ) even though ingots have been milled. However, the application of Co has problems in its stable supply due to a fragile resource balance and so on. It would be thus not suitable to apply Co as general-purpose industrial materials. On the other hand, rare earth-iron based magnetic materials that are mostly based on Fe as well as rare-earth elements such as Nd, Pr and Sm are advantageous in stable resource supplies of a resource balance. However, only a limited HcJ is obtainable even if the ingots of Nd2Fe14B based alloy or sintering magnets are milled. Accordingly, for producing anisotropic Nd2Fe14B based magnetic materials, researches where melt spinning materials are applied as starting materials were advanced.
In 1989, Tokunaga obtained an anisotropic magnet with a (BH)max of 127 kJ/m3 in such a manner as that a bulk where Nd14Fe80-XB6GaX (X=0.4 to 0.5) is subjected to hot upsetting (die-upset) is milled so as to form anisotropic Nd2Fe14B based magnetic materials where HcJ=1.52 MA/m, and the magnetic materials are then solidified with resin (see Non-Patent Document 6). Also, in 1991, H. Sakamoto et al. obtained anisotropic Nd2Fe14B based magnetic materials where HcJ=1.30 MA/m in such a manner as that Nd14Fe79.8B5.2Cu1 is subjected to hot rolling (see Non-Patent Document 7). Accordingly, high HcJ (coercive) magnetic materials become publicly available while hot processing treatments are improved with addition of Ga and Cu, and the refinement of an Nd2Fe14B crystal particle size is further advanced.
In 1991, V. Panchanathan et al. obtained a resin bonded magnet with a (BH)max of 150 kJ/m3 through a hot mill method, specifically as that the invasion of hydrogen is made from a grain boundary so as to make a bulk collapsed as Nd2Fe14BHX, and then HD (hydrogen decrepitation)—Nd2Fe14B magnetic materials that have been dehydrogenated by vacuum heating are extracted. Finally, the magnetic materials are solidified by resin (see Non-Patent Document 8). In 2001, through the same method, Iriyama obtained a modified anisotropic magnet with a (BH)max of 177 kJ/m3 by making Nd0.137Fe0.735CO0.067B0055Ga0.006 into magnetic materials and then solidified with resin (see Non-Patent Document 9).
Then, in 1999, a resin bonded magnet with a (BH)max of 193 kJ/m3 is obtained in such a manner that an Nd—Fe(Co)—B ingot is heat-treated in hydrogen atmosphere such that: Nd2(Fe, Co)14B phase is hydrogenated (hydrogenation, Nd2(Fe, Co)14BHX); the phase is decomposed at 650 to 1000° C. (decomposition, NdH2+Fe+Fe2B); hydrogen is desorbed (desorption); and recombination is performed (recombination). Finally, HDDR Nd2Fe14B based magnetic materials are solidified with resin at 1 GPa (see Non-Patent Document 10).
In 2001, Mishima et al. reported Co-free d-HDDR Nd2Fe14B based magnetic materials (see Non-Patent Document 11), and N. Hamada et al. obtained a cubic anisotropic magnet (7 mm×7 mm×7 mm) with a density of 6.51 Mg/m3 and a (BH)max of 213 kJ/m3 in such a manner that d-HDDR Nd2Fe14B based magnetic materials with a (BH)max of 358 kJ/m3 are compressed together with resin at 0.9 GPa and at temperature of 150° C. in orientation magnetic field of 2.5 T (see Non-Patent Document 12).
Considering resin bonded magnets where the above descried anisotropic rare earth-iron based magnetic materials are solidified with resin at 0.9 GPa, for example, it is possible to gain the magnetic property of a (BH)max that is more than as twice as an isotropic resin bonded magnet with 80 kJ/m3. However, for adapting the anisotropic resin bonded magnets to rotary machines, it would be necessary to satisfy magnetic stability such as demagnetizing strength against irreversible demagnetization or demagnetizing fields.
Here, compared to the grain size 15-20 nm of an isotropic Nd2Fe14B based magnetic material obtained through a rapid-solidified thin strip (for example, see Non-Patent Document 13), an anisotropic Nd2Fe14B based magnetic material obtained through either the milling of hot-worked bulks or HDDR treatments has the grain size of 200 to 500 nm which is the texture of a Nd2Fe14B crystal that is one digit larger than the isotropic Nd2Fe14B based magnetic materials.
In case that the grain size of Nd2Fe14B is, for example, 15 to 20 nm, magnetic properties (including magnetic stability), such as remanence Mrp based on remanence enhancement effects or temperature coefficient βp%/° C. of coercivity HcJp, are improved. In addition, the magnetic properties such as HcJp or (BH)maxp of the magnetic materials would be not prominently deteriorated even if the particle size becomes lessened approximately to, for example, 40 μm.
That is, in case that the grain size of Nd2Fe14B is, for example, 15 to 20 nm, at the stage where the materials are compressed with resin, for example, at 0.8 to 1.0 GPa so as to obtain resin bonded magnets in a specific form, it would be inevitable that the surface of the magnetic material are damaged or fractured. However, the magnetic property deterioration of the magnetic materials is within a range that can be actually ignored.
Here, when considering Nd2Fe14B based magnetic materials where hot-worked bulks with a Nd2Fe14B grain size of 200 to 500 nm are milled, or anisotropic resin bonded magnets where HDDR-Nd2Fe14B based magnetic materials are solidified with resin at 0.8 to 1.0 GPa, occurrence of newly created surfaces or microcracks would be inevitable due to the damage or breakage of the surface of magnetic materials through densification. Accordingly, Nd2Fe14B crystals formed on the most outer surface of the magnetic materials are oxidized so as to cause texture evolution, whereby magnetic properties based on HcJp, (BH)maxp, etc. may be deteriorated. The treatment deterioration of the magnetic properties of the anisotropic Nd2Fe14B based magnetic materials is obvious compared to the isotropic Nd2Fe14B based magnetic materials. Thus, in order to suppress the deterioration of the magnetic properties occurring when the anisotropic Nd2Fe14B based magnetic materials are densified, it would be necessary to reduce or modify pressures toward the magnetic materials through the densification.
On the other hand, considering magnetic materials that have a nucleation-typed coercive generation mechanism which is typical in SmCoS base or Sm2Fe17N3 base, they generally need a particle size of 10 μm or less. As to resin bonded magnets where these magnetic materials with such a small particle size are compressed with resin, it would be difficult to make their densities to be 5 Mg/m3 or more (relative density: 65%). Accordingly, these resin bonded magnets are generally used as an injection-molded resin bonded magnet. Therefore, compared to an isotropic Nd2Fe14B based resin bonded magnet with a (BH)max of approximately 80 kJ/m3 where an isotropic Nd2Fe14B based magnetic materials are milled and solidified with resin at 0.8 to 1 GPa, the advantage of (BH)max is far behind, largely lowered than the (BH)max of an anisotropic Nd2Fe14B based resin bonded magnet.
It can be therefore said that these technical problems discussed hereinabove could be one of the factors which hampers an anisotropic rare earth-iron based resin bonded magnet from being applied to electromagnetic driving devices such as rotary machines although the anisotropic rare earth-iron based resin bonded magnet is regarded as the next generation type of the isotropic Nd2Fe14B based resin bonded magnet with a (BH)max of 80 kJ/m3.
The present invention has been made in view of the circumstances described above, and it is an object of the present invention to provide an anisotropic rare earth-iron based resin bonded magnet that can be a next generation type for isotropic Nd2Fe14B based resin bonded magnets with (BH)max of 80 kJ/m3, contributing to miniaturization and a high mechanical output power of rotary machines.
In order to achieve the object described above, according to an aspect of the present invention, there is provided an anisotropic rare earth-iron based resin bonded magnet comprising:
[1] a continuous phase including: (1) a spherical Sm2Fe17N3 based magnetic material where its average particle size is 1 to 10 μm, its average aspect ratio ARave is 0.8 or more in a condition that AR is b/a when the maximum diameter of a particulate picture is “a” while the maximum diameter perpendicular to the “a” is “b”, and mechanical mining is not applied after an Sm—Fe alloy is nitrided, the spherical Sm2Fe17N3 based magnetic material being covered with solid epoxy oligomer at a room temperature; (2) a linear polymer that has an active hydrogen group in which to react to the oligomer; and (3) an additive to be added in when necessary; and
[2] a discontinuous phase being defined by an Nd2Fe14B based magnetic material where its average particle size is 50 to 150 μm, and its average aspect ratio ARave is 0.65 or more, the Nd2Fe4B based magnetic material being covered with solid epoxy oligomer at a room temperature, the anisotropic rare earth-iron based resin bonded magnet further satisfying the following:
[3] an air-gap ratio of a granular compound on the continuous and discontinuous phases is 5% or less; and
[4] a composition where a crosslinking agent having an average particle size of 10 μm or less is adhered on a surface of the granular compound is formed into a predetermined shape through a magnetic field press at 50 MPa or less.
In an anisotropic rare earth-iron based resin bonded magnet according to the present invention, for improving magnetic stability such as irreversible demagnetization or demagnetizing proof stress against reverse magnetic fields at a high temperature, and magnetic properties typically defined by a (BH)max, the following conditions should be established. When the coercivity of Sm2Fe17N3 based magnetic materials is set to HcJpS, the coercivity of Nd2Fe14B based magnetic materials at a room temperature is set to HcJpN, and a ratio between HcJpS and HcJpN (HcJpS/HcJpN) is set to α, HcJpN is 1 to 1.25 MA/m, and HcJpS is equal to or less than HcJpN (HcJpS<HcJpN). Further, a should be 0.75 or less, or more preferably 0.65 or less.
Based on the above, according to the present invention, when the remanence of the anisotropic rare earth-iron based resin bonded magnet is set to Mrm, the remanence of a mixing body defined by spherical Sm2Fe17N3 based magnetic materials and Nd2Fe14B based magnetic materials is set to Mrp, and the volume fraction of the whole magnetic materials accounting for the resin bonded magnet is set to Vfp, it is possible that the orientation degree MrM/(Mrp×Vfp) of the magnetic materials can be set to 0.96 or more, and a (BH)max can be set to 170 kJ/m3 or more in a condition that α is 0.75 or less, and Vfp is equal to or greater than 80 vol. % (Vfp≧80 vol. %). Further, in a condition that α is 0.65 or less, and Vfp is equal to or greater than 80 vol. % (Vfp≧80 vol. %), the orientation degree MrM/(Mrp×Vfp) can be set to 0.98 or more, and a (BH)max can be set to 180 kJ/m3 or more.
Moreover, in case that the squareness of a demagnetization curve of the anisotropic rare earth-iron based resin bonded magnet at a room temperature according to the present invention is set to Hk/HcJRT, and squareness at 100° C. is set to Hk/HcJ100, it is preferable to establish that Hk/HcJRT is less than Hk/HcJ100 (Hk/HcJRT<Hk/HcJ100).
In the anisotropic rare earth-iron based resin bonded magnet according to the present invention, when considering the structure of rotary machines that can effectively secure magnetic stability and can employ air-gap magnetic flux density between a magnet and an iron core (that is, a magnetic circuit structure between the iron core and the magnet), it is preferable to establish that permeance coefficient Pc is 3 or more.
As discussed hereinabove, the anisotropic rare earth-iron based resin bonded magnet according to the present invention can be structured as that the squareness of the demagnetization curve at a high temperature based on Hk/HcJRT<Hk/HcJ100 is not deteriorated. Further, since the anisotropic rare earth-iron based resin bonded magnet according to the present invention also has high magnetic properties where the maximum energy product (BH)max is 170, or more than 180 kJ/m3, it would be applicable as the next generation type of an isotropic Nd2Fe14B based resin bonded magnet with a (BH)max of 80 kJ/m3, contributing to make the rotary machines to be further miniaturized and to have higher mechanical output.
A resin bonded magnet satisfying the following conditions is going to be considered:
<1> A continuous phase is composed of: (1) a spherical Sm2Fe17N3 based magnetic material that has an average aspect ratio ARave of 0.80 or more and is covered with epoxy oligomer; (2) a linear polymer having an active hydrogen reactive group that can react to the oligomer; and (3) an additive to be properly added when necessary;
<2> a discontinuous phase is Nd2Fe14B based magnetic materials that are covered with epoxy oligomer;
<3> the air-gap ratio of a granular compound existed in the continuous and discontinuous phases is set to 5% or less; and
<4> a composition, in which crosslinking agents made of impalpable powder are adhered on the surface of the granular compound, is produced through a magnetic field pressing at 50 MPa or less.
In the above conditions, when the coercivity of Sm2Fe17N3 based components is set to HcJpS, the coercivity of Nd2Fe14B based components is set to HcJpN, and their ratio (HcJpS/HcJpN) is set to α, HcJpN can be set to 1 to 1.25 MA/m while HcJpS can be equal to or less than HcJpN (HcJpS≦HcJpN). Further, in case that the remanence of resin bonded magnets is set to MrM, the remanence of magnetic materials is set to Mrp, and the volume fraction of the magnetic materials is set to Vfp, the following is established: Vfp is equal to or greater than 80 vol. % (Vfp≧80 vol. %), MrM/(Mrp×Vfp) is 0.96 or more where α is 0.75 or less, and a (BH)max is 170 kJ/m3 or more. Still further, when Vfp is equal to or greater than 80 vol. % (Vfp≧80 vol. %), and α is 0.65 or less, the following is established: MrM/(Mrp×Vfp) is 0.98 or more, and a (BH)max is 180 kJ/m3 or more. In addition, when the squareness of the resin bonded magnets at a room temperature is set to Hk/HcJRT, and the squareness at a temperature of 100° C. is set to Hk/HcJ100, it is possible to establish that Hk/HcJRT is less than Hk/HcJ100(Hk/HcJRT<Hk/HcJ100).
As discussed hereinabove, in an anisotropic rare earth-iron based resin bonded magnet according to the present invention, when the coercivity HcJ at a room temperature is approximately 1 MA/m or more, the squareness at a room temperature is Hk/HcJRT, and the squareness at a temperature of 100° C. is Hk/HcJ100, Hk/HcJRT will be less than Hk/HcJ100 (Hk/HcJRT<Hk/HcJ100). Accordingly, the squareness of demagnetization curve will not be deteriorated at a high temperature, magnetic stability can be well secured, and the maximum energy product (BH)max can be 170 kJ/m3 or more. Here, when considering rotary machines (meaning a magnetic circuit structure between an iron core and a magnet) that can effectively secure the magnetic stability and can employ the air-gap magnetic flux density of the anisotropic rare earth-iron based resin bonded magnet according to the present invention, it is preferable that permeance coefficient Pc is 3 or more.
First, in terms of a continuous phase according to the present invention, spherical Sm2Fe17N3 based magnetic materials will be explained hereinafter. The spherical Sm2Fe17N3 based magnetic materials satisfy the following condition as that: its average particle size is 1 to 10 μm, its average aspect ratio ARave is 0.80 or more; and mechanical milling is not conducted following the nitriding of Sm—Fe alloy. Further, the above spherical Sm2Fe17N3 based magnetic materials are covered with solid epoxy oligomer at a room temperature.
The Sm2Fe17N3 based magnetic materials may be formed with the following method: a melt casting method disclosed by Japanese Patent Application Laid-Open No Hei 2-57663, or a reduction/diffusion method disclosed by Japanese Patent No. 17025441 or Japanese Patent Application Laid-Open No. Hei 9-157803. These methods are performed as that: an Sm—Fe based alloy or an Sm—(Fe, Co) based alloy is produced; and the alloy is nitrided and then mechanically milled so as to be reduced into a particle size.
Considering the spherical Sm2Fe17N3 based magnetic material where its average particle size is 1 to 10 μm, and its average aspect ratio ARave is 0.80 or more, after an Sm2Fe17 alloy is nitrided, mechanical milling means such as jet mill, vibration ball mill or rotation ball mill are not conducted. This is due to a reason that micronized powder, which is inevitably produced through mechanical milling, will never exist.
As to a specific method that can produce the Sm2Fe17N3 based magnetic materials where the mechanical milling means is not applied following the nitriding of the Sm2Fe17 alloy, the following method can be introduced: impalpable powder such as an Sm—Fe based alloy or an Sm—(Fe, Co) based alloy is produced based on a molten alloy through a gas-atomized method, and then the impalpable powder is nitrided. Accordingly, without conducting the mechanical milling following nitriding, it is possible to obtain the Sm2Fe17N3 based magnetic materials according to the present invention.
Further, as shown in Japanese Patent Application Laid-Open No. Hei 6-1151127, it is possible to obtain the Sm2Fe17N3 based magnetic material according to the present invention which is not necessary for mechanical milling following nitriding in such a manner that carbonyl iron is applied, and the temperature of the reduction/diffusion method used for the reduction of an rare-earth element is set within 650 to 880° C.
Still further, in Japanese Patent Application Laid-Open No. Hei 11-335702, for example, Sm2O3 with an average particle size of 35 μm and Fe2O3 with an average particle size of 1.3 μm are mixed with Sm (11% at atomic percent) and Fe (89.0% at atomic percent), and then milled and blended through wet milling to obtain dried, blended powder. The blended powder is then preheated at 600° C. in hydrogen flow for 4 hours so as to reduce the iron oxide into metals with an average particle size of 2 to 3 μm. The reduced blended powder is then mixed with Ca particles and heated at 1000° C. in an Ar atmosphere for one hour. After conducting the diffusion/reduction treatments, nitriding at 450° C. for 2 hours is performed. Lastly, rinsing and dehydrated drying are performed. Accordingly, the Sm2Fe17N3 based magnetic material can be obtained without conducting mechanical milling following nitriding.
In addition, Japanese Patent Application Laid-Open No. 2004-115921 discloses a sol-gel method enabling to obtain the Sm2Fe17N3 based magnetic material without conducting mechanical milling. In the sol-gel method, Sm and Fe are dissolved in acid, and materials generating salt that is insoluble in Sm ion and Fe ion are precipitated through solution reaction. The precipitated materials are then calcined so as to obtain metallic oxide.
Still further, Japanese Patent Application Laid-Open No. 2004-115921 also discloses the sol-gel method. In the method, Sm and Fe, are dissolved in acid, and materials that produce salt insoluble in Sm ion and Fe ion are precipitated through a solution reaction. The precipitated materials are then calcined producing metallic oxide. For example, from Sm ion or Fe ion solution, materials that produce salt insoluble in the metallic ion will be supplied. Oxalic acid may be supplied as a material that provides hydroxide ion. In these organic solvents of metal alkoxide, addition of water can separate out metal hydroxide, the metal hydroxide being precipitated. The metallic oxide obtained as discussed above is then reduced so as to obtain fine Sm2Fe17 alloy powder which is then nitrided. Based on the above, it is possible to obtain the Sm2Fe17N3 based magnetic materials without conducting mechanical milling.
Accordingly, the present invention can provide the spherical Sm2Fe17N3 based magnetic material where, among the Sm2Fe17N3 based magnetic materials that are produced without mechanical milling after nitriding Sm—Fe alloy, its average particle size is 1 to 10 μm, and its average aspect ratio ARave is 0.80 or more. With the spherical Sm2Fe17N3 based magnetic materials, it would be possible to eliminate micronized powder that is inevitably produced by mechanical milling.
Here, in the present invention, the micronized powder means a particle size less than 1 μm (exclusive). As disclosed in Japanese Patent Application Laid-Open No. 2000-12316, the micronized powder of this size will negatively influence the magnetic properties of the Sm2Fe17N3 based magnetic material. However, by applying a temperature history of 50° C. or more that will be necessary for resin bonded magnets to be a specific form, the micronized powder with a particle size less than 1 μm (exclusive) will be disappeared. Accordingly, only the Sm2Fe17N3 based magnetic material with a particle size of 1 μm or more (providing no negative influence) will exist and satisfactorily deal with the determined magnetic properties of the resin bonded magnet.
In the spherical Sm2Fe17N3 based magnetic material according to the present invention, it would be possible to have multiple surface treatments (more than one time). Specifically, the surface formation of a de-oxidation film is disclosed by Japanese Patent Publication Laid-Open No. Sho 52-54998, Japanese Patent Publication Laid-Open No. Sho 59-170201, Japanese Patent Publication Laid-Open No. Sho 60-128202, Japanese Patent Publication Laid-Open No. Hei 3-211203, Japanese Patent Publication Laid-Open No. Sho 46-7153, Japanese Patent Publication Laid-Open No. Sho 56-55503, Japanese Patent Publication Laid-Open No. Sho 61-154112, Japanese Patent Publication Laid-Open No, Hei 3-126801, etc. Further, the surface formation of a metallic film is disclosed by Japanese Patent Publication Laid-Open No. Hei 5-230501, Japanese Patent Publication Laid-Open No. Hei 5-234729, Japanese Patent Publication Laid-Open No. Hei 8-143913, Japanese Patent Publication Laid-Open No. Hei 7-268632, etc. Still further, the surface formation of an inorganic film is disclosed by Examined Patent Publication No. Hei 6-17015, Japanese Patent Publication Laid-Open No. Hei 1-234502, Japanese Patent Publication Laid-Open No. Hei 4-217024, Japanese Patent Publication Laid-Open No. Hei 5-213601, Japanese Patent Publication Laid-Open No. Hei 7-326508, Japanese Patent Publication Laid-Open No. Her 8-153613, Japanese Patent Publication Laid-Open No. Hei 8-183601, etc.
Here, in the spherical Sm2Fe17N3 based magnetic material according to the present invention where no mechanical milling means is applied following nitriding, it would be necessary to have a solid epoxy oligomer layer on the most outer surface thereof at a room temperature. As to the preferable example of the epoxy oligomer, an o-cresol novolac epoxy oligomer can be, for example, named where epoxy equivalent is 205 to 220 g/eq, a melting point is 70 to 76° C., and the suitable thickness of the layer is 30 to 100 nm. Here, if the thickness of the layer is less than 30 nm (exclusive), the fixing strength of the spherical Sm2Fe17N3 based magnetic material will be decreased. On the other hand, if 100 nm or more, a (BH)max will be decreased along with the increase of the volume fraction of non-magnetic materials.
Next, a continuous phase according to the present invention that is composed of: a linear polymer having active hydrogen groups that may react to a sold epoxy oligomer coated on the spherical Sm2Fe17N3 based magnetic material at a room temperature; and an additive which is added in when necessary will be hereinafter explained.
Considering the linear polymer constructing the continuous phase of the present invention, for example, a polyamide-12 where a number-average molecular weight Mn is 4000 to 12000 or its copolymer can be named. Further, as to the additive which is properly added in when necessary, the following are preferably named as internal lubricant: a hydrophilic functional group that accelerates external elusion from a molten linear polymer when the magnetic materials are densified; and organic compounds where at least one long-chain alkyl group for producing internal lubricating effects is included per molecule and a melting point is approximately 50° C. or more. Specifically, one hydroxyl group (—OH) per molecule, or organic compounds with 3 heptadecyl groups (—(CH2)16—CH3) of carbon number 17 may be exemplified.
Next, an Nd2Fe14B based magnetic material where its discontinuous phase is coated with a solid epoxy oligomer at a room temperature, its average particle size is 50 to 150 μM, and its average aspect ratio ARave 0.65 or more will be explained. Further, the reason that the air-gap ratio of a granular compound on the continuous and discontinuous phases is set to 5% or less will be also explained.
The Nd2Fe14B based magnetic material according to the present invention where its average particle size 50 to 150 μm while its average aspect ratio ARave is 0.65 or more may suitably be a so-called Hydrogenation, Disproportionation, De-sorption, and Re-combination HDDR-N2Fe14B based magnetic materials or Co-free d-HDDR-R2Fe14B based magnetic materials, these magnetic materials being disclosed by Japanese Patent No. 3092672, Japanese Patent No. 2881409, Japanese Patent No. 3250551, Japanese Patent No. 3410171, Japanese Patent No. 3463911, Japanese Patent No. 3522207, Japanese Patent No. 3595064, etc. The HDDR discussed hereinabove is performed as that: R2(Fe, Co)14B based alloy (R is Nd, Pr) is hydrogenated (Hydrogenation, R2(Fe, Co)14B Hx), a phase decomposition is performed at a temperature of 650 to 1000° C. (Decomposition, RH2+Fe+Fe2B), dehydrogenation is performed (Desorption), and recombination is finally performed (Recombination). Here, as disclosed by Japanese Patent Publication Laid-Open No, 2004-266093, Japanese Patent Publication Laid-Open No. 2005-26663, Japanese Patent Publication Laid-Open No, 2006-100560, etc., it could be alternated by the magnetic materials that have predetermined surface treatments.
Considering the Nd2Fe14B based magnetic materials where hot-working bulks are milled by means of a mechanical means, an anisotropic Nd2Fe14B grain is flat, and the materials that are mechanically milled can be structured in many cases that its thickness direction is correspondent with a C axial direction. That is, the magnetic material will have a shape magnetic anisotropy that is perpendicular to the C axis whereby it would be difficult to obtain the average particle size of 50 to 150 μm, and the average aspect ratio Alave of 0.65 or more.
As discussed, the Nd2Fe14B based magnetic material according to the present invention where its average particle size is 50 to 150 μm, and its average aspect ratio ARave is 0.65 or more will need to have a solid epoxy oligomer at a room temperature that is coated on the most outer surface thereof. Here, it would be preferable that the coated layer is approximately 30 to 100 nm. Here, if the thickness of the coated layer is less than 30 nm (exclusive), the fixing strength of the spherical Sm2Fe17N3 based magnetic material will be decreased. On the other hand, if 100 nm or more, magnetization and a (BH)max will be decreased along with increase of the volume fraction of non-magnetic materials.
As discussed, in the present invention,
<1> a continuous phase includes: (1) a spherical Sm2Fe17N3 based magnetic material where its average particle size is 1 to 10 μm, its average aspect ratio ARave is 0.8 or more, and mechanical milling is not applied after an Sm—Fe alloy is nitrided, the spherical Sm2Fe17N3 based magnetic material being covered with epoxy oligomer that is solid at a room temperature; (2) a linear polymer that has an active hydrogen group in which to react to the oligomer; and (3) an additive to be added in when necessary;
<2> a discontinuous phase includes an Nd2Fe14B based magnetic material where its average particle size is 50 to 150 μm, and its average aspect ratio ARave is 0.65 or more, the Nd2Fe14B based magnetic material being covered with epoxy oligomer that is solid at a room temperature:
<3> the air-gap ratio of a granular compound on the continuous and discontinuous phases is 5% or less;
<4> the particle size of the compound is 1 mm or less; and
<5> a composition where the crosslinking agent of an impalpable powder is physically adhered on the surface of the granular compound is formed into a predetermined shape through a magnetic field press at 50 MPa or less.
The following methods can be considered as a specific means that the air-gap ratio for the granular compound on the continuous and discontinuous phases can be 5% or less. That is, the mixtures of the continuous and discontinuous phases are mixed by means of a mixing roll at least in a molten linear polymer. The mixed materials that have been cooled down to a room temperature are then shredded so as to obtain granular compound with a particle size of at least 1 mm or less. Aim to make the mixed materials to have the particle size of 1 mm or less is to provide powder flowability. Here, if the particle size is 1 mm or less, there is no obstruction of making magnetic materials to be arranged in the magnetic fields in a melting condition of the linear polymer. Note that if the particle size becomes greater than 1 mm (exclusive), a crosslinking reaction between the granular compound and crosslinking agents of impalpable powder that have been physically adhered on the surface of the granular compound will become heterogeneity. Accordingly, that causes mechanical deficiencies of the resin bonded magnet along with strength deterioration.
By performing the above described mixing in a molten linear polymer, it is possible to set the air-gap ratio of the granular compound to be 5% or less. Here, it should be emphasized that it is possible to obtain the anisotropic rare earth-iron based resin bonded magnet according to the present invention with the air-gap ratio of 5% or less at an extremely low temperature of 50 MPa or less.
As a crosslinking agent according to the present invention, a so-called latent crosslinking agent can be suitably exemplified, the latent crosslinking agent being, for example, an imidazole adduct (2-phenyl-4,5-dihydroxymethylimidazole) with a thermal decomposition temperature of 230° C. where its average particle size is approximately 5 μm.
Next, in the present invention, in order to obtain the magnetic stability of the anisotropic rare earth-iron based resin bonded magnet, the following conditions should be established. That is, when the coercivity of Sm2Fe17N3 based magnetic material at a room temperature is HcJpS, the coercivity of Nd2Fe14B based magnetic material is HcJpN, and a ratio between HcJpS and HcJpN (HcJpS/HcJpN) is α, HcJpN will be 1 to 1.25 MA/m. Further details are explained hereinbelow.
A relation between the coercivity of Nd2Fe14B based magnetic material (for example, an alloy composition Nd12.3-7 6Dy0.3-50Fe64.6CO12.3B6.0Ga0.6Zr0.1) at a room temperature and its (BH)maxPN can be defined to have a certain tendency as shown in
Further, in the anisotropic rare earth-iron based resin bonded magnet according to the present invention, for improving irreversible demagnetization, demagnetization proof stress against reverse magnetic fields at a high temperature, or magnetic performance typically defined by a (BH)max, when the coercivity of Sm2Fe17N3 based magnetic material is HcJpS, the coercivity of Nd2Fe14B based magnetic material at a room temperature is HcJpN, and a ratio between HcJpS and HcJpN (HcJpS/HcJpN) is α, the following can be determined: HcJpN is 1 to 1.25 MA/m while HcJpS is equal to or less than HcJpN (HcJpS≦HcJpN). Further, α should be 0.75 or less, or more preferably 0.65 or less.
In the anisotropic rare earth-iron based resin bonded magnet according to the present invention, when its remanence is MrM, the remanence of a mixture between a spherical Sm2Fe17N3 based magnetic material (real density: 7.67 Mg/m3) and an Nd2Fe14B based magnetic material (real density: 7.55 Mg/m3) is Mrp, and the volume fraction of the whole magnetic material accounting for the resin bonded magnet is Vfp, the following can be established. That is, by setting that Vfp is equal to or greater than 80 vol. % (Vfp≧80 vol. %) and α is 0.75 or less, the orientation degree of the magnetic material MrM/(Mrp×Vfp) can be 0.96 or more while its (BH)max is 170 kJ/m3 or more. Further, by setting that Vfp is equal to or greater than 80 vol. % (Vfp≧80 vol. %) and α is 0.65 or less, the orientation of the magnetic material MrM/(Mrp×Vfp) can be 0.98 or more while its (BH)max is 180 kJ/m3 or more.
Further, in the anisotropic rare earth-iron based resin bonded magnet according to the present invention, in case that the squareness of a demagnetization curve at a room temperature is Hk/HcJRT, and the squareness at 100° C. is Hk/HcJ100, it would be preferable that Hk/HcJRT<Hk/HcJ100.
Here, considering a rotary machine that can effectively secure the magnetic stability and can employ the air-gap magnetic flux density of the anisotropic rare earth-iron based resin bonded magnet according to the present invention (that is, a magnetic circuit structure between an iron core and the magnet according to the present invention), it would be preferable that air-gap permeance coefficient Pc is 3 or more.
As discussed hereinabove, in the anisotropic rare earth-iron based resin bonded magnet according to the present invention, it is possible to obtain the following structure that coercivity HcJ at a room temperature is approximately 1 MA/m or more while the squareness of the demagnetization at a high temperature which satisfies Hk/HcJRT<HcJ100 will not be deteriorated. Further, since a high magnetic property where the maximum energy product (BH)max is 170 or 180 kJ/m3 or more is also provided, it can be regarded as the next generation type of the isotropic Nd2Fe14B based resin bonded magnet with (BH)max of 80 kJ/m3 contributing to the miniaturization and the high mechanical output of the rotary machine.
Hereinafter, the present invention will be explained in further details based on embodiments. The present invention is not however limited to the embodiments.
As disclosed by Japanese Patent Application Laid-Open No. 2000-12316, the micronized powder discussed hereinabove will negatively influence magnetic properties such as coercivity HcJS of Sm2Fe17N3 based magnetic materials. However, by being subjected to a temperature history of 50° C. or more that is inevitable when resin bonded magnets are formed into a specific shape, the micronized powder having a particle size of less than 1 μm (exclusive) will be disappeared. Accordingly, as to the final magnetic property of the resin bonded magnets, Sm2Fe17N3 based magnetic materials having a particle size of 1 μm or more where their magnetic properties have not been impaired are going to take over. More specifically, the micronized powder having a particle size of less than 1 μm (exclusive) that can be observed at the fragmentary Sm2Fe17N3 based magnetic materials as shown in
As discussed hereinabove, the Sm2Fe17N3 based magnetic material that is applied to the anisotropic rare earth-iron based resin bonded magnet according to the present invention should be satisfied with the following condition: 1) the magnetic material should be a sphere produced without mechanical milling after the Sm—Fe alloy of
Here, as shown in
Considering the above magnetic material, it would be difficult to adjust to be that its average particle size is set to 50 to 150 μm while its average aspect ratio ARave is set to 0.65 or more. On the other hand, the crystal of a so-called HDDR-Nd2Fe14B based magnetic material where hydrogen decomposition/recombination is performed as shown in
Next, through application of the Sm2Fe17N3 based magnetic materials and the Nd2Fe14B based magnetic materials according to the present invention,
[1] a continuous phase is formed by comprising: (1) an Sm2Fe17N3 based magnetic material that is coated with 4.5 vol. % of an o-cresol novolac epoxy oligomer where an epoxy equivalent is 205 to 220 g/eq, and a melting point is 70 to 76° C.; (2) 9.1 vol. % of a linear polymer that has an average molecular weight Mn of 4000 to 12000 and has a molecular chain amino active hydrogen making a crosslinking reaction with the oxazolidone ring of the oligomer; (3) 1.8 vol. % of a partial esterification material including pentaerythritol and higher fatty acid as internal lubricant,
[2] a discontinuous phase is coated with 2.0 vol. % of o-cresol novolac epoxy oligomer where an epoxy equivalent is 205 to 220 g/eq, and a melting point is 70 to 76° C., and
[3] the continuous phase is melted and mixed by means of an 8-inch mixing roll mill (a rotational speed: 12 rpm and a temperature: 140° C.). Further, the discontinuous phase will be added thereinto so as to produce melted/mixed materials comprising the continuous and discontinuous phases.
As discussed hereinabove, considering chemical stabilities of the melted/mixed treatments, it would be preferable that the spherical Sm2Fe17N3 based magnetic materials according to the present invention as shown in
Next, the melted/mixed materials are cooled off up to a room temperature, and then shredded and classified with a general method so as to obtain a granular compound having a particle size of 1 mm or less. Further, as the crosslinking agent of the micronized powder, 1.8 vol. % of imidazole adduct (2-phenyl-4,5-dihydroxymethylimidazole) with an average particle size of 4 μm and thermal decomposition temperature of 230° C. is adhered on the surface of the granular compound through a dry-mixing process with a V-blender. With these processes, a composition according to the present invention can be obtained. Here, the volume fraction of the whole magnetic materials accounting for the composition will be 80.7 vol. %. Further, when removing internal lubricant that is eluted from the continuous phase to the system during magnetic field formation, the volume fraction of the whole magnetic materials accounting for the resin bonded magnet will be 82.7 vol. %. Note that this value will be a level in which to exceed the volume fraction 80 vol. % of the magnetic material of an isotropic Nd2Fe14B based resin bonded magnet with a density of 6 Mg/m3.
Through the application of a curelastmeter,
Next, the compositions according to the present invention are formed into 7×7 mm cube through the magnetic field press in a condition that a temperature is 160° C., an orthogonal magnetic field is 1.4 MA/m or more, and a pressure is less than 50 MPa (inclusive). Accordingly, anisotropic rare earth-iron based resin bonded magnets according to the present invention and comparative examples are obtained. Here, the composition according to the present invention is precedently adjusted to have the density of 6 Mg/m3 or more in a melted/mixed condition. By rearranging magnetic materials by means of external magnetic fields in a condition that a linear polymer is melted in a molding cavity, it would be possible to re-obtain the density of 6 Mg/m3 or more even with a lower pressure of 50 MPa.
Next,
Based on
As discussed hereinabove, in the present invention, when the coercivity of the Nd2Fe14B based magnetic material at a room temperature is HcJpN, and the coercivity of the spherical Sm2Fe17N3 based magnetic material is HcJpS, it would be necessary to satisfy that HcJpN is equal to or greater than HcJpS. In addition, more preferably, when a ratio between HcJpS and HcJpN (HcJpS/HcJpN) is α, α is set to 0.75 or 0.65. Accordingly, when the remanence of the resin bonded magnet is MrM, the remanence of a compound including the spherical Sm2Fe17N3 based magnetic material and the Nd2Fe14B based magnetic material is Mrp, and the volume fraction of the whole magnetic material accounting for the resin bonded magnet is Vfp, Vfp is equal to or greater than 80 vol. %, and when α is 0.75 or 0.65, the orientation degree of the whole magnetic material MrM/(Mrp×Vfp) becomes 0.96 or 0.98, respectively. Accordingly, the present invention can provide the anisotropic rare earth-iron based resin bonded magnet where the magnetic material is highly oriented.
In
In
As discussed hereinabove, in the anisotropic rare earth-iron based resin bonded magnet according to the present invention, it is possible that its coercivity HcJ at a room temperature is approximately 1 MA/m, and that the squareness of a high-temperature demagnetization curve (Hk/HcJRT<Hk/HcJ100) is not deteriorated. Moreover, since high magnetic properties are obtainable (the maximum energy product (BH)max is 170, 180 kJ/m3 or more), it can be the next generation type of isotropic Nd2Fe14B based resin bonded magnets with (BH)max of 80 kJ/m3 thereby contributing to miniaturization and a high mechanical output of the rotary machines.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-223908 | Sep 2009 | JP | national |
