Surface-treated rare earth-based magnetic particles, resin composition for bonded magnets comprising the earth-based magnetic particles and bonded magnet comprising the earth-based magnetic particles

Abstract

The present invention relates to surface-treated rare earth-based magnetic particles comprising rare-earth-based magnetic particles, a first coating layer comprising a phosphoric acid compound which is formed on a surface of the respective magnetic particles and a second coating layer in the form of a composite coating film comprising a silicon compound and a phosphoric acid compound which is formed on a surface of the first coating layer, wherein an amount of Fe eluted from the rare earth-based magnetic particles is not more than 10 mg/L; a resin composition for bonded magnets comprising the above surface-treated rare earth-based magnetic particles and a resin; and a bonded magnet comprising the above surface-treated rare earth-based magnetic particles.

Claims

1. Surface-treated rare earth-based magnetic particles comprising rare-earth-based magnetic particles, a first coating layer comprising a phosphoric acid compound which is formed on a surface of the respective rare-earth-based magnetic particles, and a second coating layer in the form of a composite coating film comprising a silicon compound and a phosphoric acid compound, which is formed on a surface of the first coating layer, an amount of Fe eluted from the rare earth-based magnetic particles being not more than 5 mg/L.

2. Surface-treated rare earth-based magnetic particles according to claim 1, wherein the composite coating film comprising the silicon compound and the phosphoric acid compound which forms the second coating layer comprises a compound produced from the phosphoric acid compound selected from the group consisting of orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate and aluminum phosphate, an alkoxy oligomer whose molecular end is capped with an alkoxysilyl group, and a silane coupling agent.

3. Surface-treated rare earth-based magnetic particles according to claim 1, wherein a content of the phosphoric acid compounds in the surface-treated rare earth-based magnetic particles is 0.01 to 2.0% by weight.

4. Surface-treated rare earth-based magnetic particles according to claim 1 wherein a content of Si in the surface-treated rare earth-based magnetic particles is 0.01 to 2.0% by weight.

5. Surface-treated rare earth-based magnetic particles according to claim 1, wherein a content of carbon in the surface-treated rare earth-based magnetic particles is 0.01 to 2.0% by weight.

6. Surface-treated rare earth-based magnetic particles according to claim 1, wherein the rare earth-based magnetic particles are NdFeB-based magnetic particles.

7. Surface-treated rare earth-based magnetic particles according to claim 1, wherein the rare earth-based magnetic particles are SmFeN-based magnetic particles.

8. A resin composition for bonded magnets comprising the surface-treated rare earth-based magnetic particles as defined in claim 1, and a resin.

9. A bonded magnet comprising the surface-treated rare earth-based magnetic particles as defined in claim 1.

10. Surface-treated rare earth-based magnetic particles according to claim 1, wherein the amount of Fe eluted from the rare earth-based magnetic particles is not more than 2.5 mg/L.

11. Surface-treated rare earth-based magnetic particles according to claim 1, wherein the phosphoric acid compound forming the first coating layer is selected from the group consisting of orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate and aluminum phosphate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the results of a rust prevention test of a bonded magnet obtained in Example 13.

(2) FIG. 2 shows the results of a rust prevention test of a bonded magnet obtained in Comparative Example 11.

(3) FIG. 3 shows the results of measurement of an irreversible demagnetizing factor of each of the bonded magnets obtained in Example 13 and Comparative Example 11.

PREFERRED EMBODIMENTS OF THE INVENTION

(4) The construction of the present invention is described in more detail below.

(5) The surface-treated rare earth-based magnetic particles according to the present invention comprise NdFeB-based magnetic particles or SmFeN-based magnetic particles, a coating layer comprising a phosphoric acid compound which is formed on a surface of the respective NdFeB-based magnetic particles or SmFeN-based magnetic particles (first coating layer), and a coating layer in the form of a composite coating layer comprising a silicon compound and a phosphoric acid compound which is formed on a surface of the first coating layer (second coating layer). More preferably, the surface-treated rare earth-based magnetic particles comprise the NdFeB-based magnetic particles or SmFeN-based magnetic particles, the coating layer comprising a phosphoric acid compound which is formed on a surface of the respective NdFeB-based magnetic particles or SmFeN-based magnetic particles (first coating layer), the composite metal phosphoric acid salt coating layer comprising a silicon compound comprising silica derived from an alkoxy oligomer whose molecular end is capped with an alkoxysilyl group as a main component, and a phosphoric acid compound, which is formed on a surface of the first coating layer (second coating layer), and a surface-treating layer comprising a silane coupling agent which is formed on the composite metal phosphoric acid salt coating layer.

(6) The silicon compound used for treating the NdFeB-based magnetic particles or the SmFeN-based magnetic particles in the present invention is such a silicon compound comprising silica as a main component which is produced by subjecting an alkoxy oligomer whose molecular end is capped with an alkoxysilyl group and a silane coupling agent to hydrolysis reaction under predetermined conditions.

(7) The amount of Fe eluted from the surface-treated rare earth-based magnetic particles according to the present invention is not more than 10 mg/L (base on 1 L of water). When the amount of Fe eluted is more than 10 mg/L, there is a possibility that the phosphoric acid compound coating layer or the composite coating layer of the phosphoric acid and the silicon compound is insufficient in thickness or fails to be uniformly adhered, so that Fe tends to be eluted through these coating layers. The amount of Fe eluted from the surface-treated rare earth-based magnetic particles is preferably not more than 5.0 mg/L and more preferably not more than 2.5 mg/L. The lower limit of the amount of Fe eluted from the surface-treated rare earth-based magnetic particles is about 0.1 mg/L. Meanwhile, the method of measuring the amount of Fe eluted is described in the below-mentioned Examples.

(8) The content of Si in the surface-treated rare earth-based magnetic particles according to the present invention is preferably 0.01 to 2.0% by weight. When the Si content is less than 0.01% by weight, the thickness of the composite coating layer of the phosphoric acid and the silicon compound which is formed on the surface of the phosphoric acid compound-coated magnetic particles tends to be insufficient, so that rusts tend to be caused owing to elution of Fe therefrom. On the contrary, when the Si content is more than 2.0% by weight, in particular, the SmFeN-based magnetic particles tend to suffer from remarkable deterioration in magnetic properties owing to increase in content of non-magnetic components per unit weight thereof. The Si content in the surface-treated rare earth-based magnetic particles is more preferably 0.05 to 1.0% by weight and still more preferably 0.06 to 0.8% by weight.

(9) The total content of carbon in the surface-treated rare earth-based magnetic particles according to the present invention is preferably 0.01 to 2.0% by weight. When the total carbon content is less than 0.01% by weight, the amount of an organic functional group to be present on the surface of the respective magnetic particles when treated with the silane coupling agent tends to be extremely reduced, so that the magnetic particles tend to become poor in compatibility with resins, and the resulting resin composition tends to be deteriorated in flowability upon kneading and injection molding. In addition, since adhesion of the magnetic particles to resins tends to become low, the magnetic particles tend to have a resin-uncoated surface portion from which rusts are likely to be generated. The total carbon content in the surface-treated rare earth-based magnetic particles is more preferably 0.03 to 1.0% by weight and still more preferably 0.05 to 0.50% by weight.

(10) The compressed density (CD) of the surface-treated rare earth-based magnetic particles according to the present invention is preferably not less than 4.1 g/cc. When the compressed density (CD) of the surface-treated rare earth-based magnetic particles is less than the above-specified range, the density per unit volume of the resulting resin composition upon injection molding tends to be lowered, resulting in deteriorated magnetic properties of the resulting injection-molded product. The upper limit of the compressed density (CD) of the surface-treated rare earth-based magnetic particles which are produced using the NdFeB-based magnetic particles is about 5.5 g/cc, whereas the upper limit of the compressed density (CD) of the surface-treated rare earth-based magnetic particles which are produced using the SmFeN-based magnetic particles is about 4.5 g/cc.

(11) The BET specific surface area of the surface-treated rare earth-based magnetic particles according to the present invention which are produced using the NdFeB-based magnetic particles is preferably 0.01 to 3.5 m.sup.2/g. When the BET specific surface area of the surface-treated rare earth-based magnetic particles which are produced using the NdFeB-based magnetic particles is out of the above-specified range, the magnetic particles tend to be inadequately pulverized, thereby failing to exhibit high magnetic properties. The BET specific surface area of the surface-treated rare earth-based magnetic particles which are produced using the NdFeB-based magnetic particles is more preferably 0.01 to 2.5 m.sup.2/g.

(12) The BET specific surface area of the surface-treated rare earth-based magnetic particles according to the present invention which are produced using the SmFeN-based magnetic particles is preferably 0.35 to 2.6 m.sup.2/g. When the BET specific surface area of the surface-treated rare earth-based magnetic particles which are produced using the SmFeN-based magnetic particles is out of the above-specified range, the magnetic particles tend to be inadequately pulverized, thereby failing to exhibit high magnetic properties. The BET specific surface area of the surface-treated rare earth-based magnetic particles which are produced using the SmFeN-based magnetic particles is more preferably 0.35 to 2.0 m.sup.2/g.

(13) The rate of decrease in the BET specific surface area of the surface-treated rare earth-based magnetic particles according to the present invention (BET specific surface area after treated with the silane coupling agent/BET specific surface area before treated with the silane coupling agent) is preferably 5 to 80% as measured between before and after treated with the silane coupling agent. When the increase/decrease rate of the BET specific surface area is less than 5%, the thickness of the composite coating layer of the silicon compound and the phosphoric acid compound which is adhered onto the magnetic particles tends to be too small or non-uniform, so that Fe tends to be eluted from the resulting surface-treated magnetic particles. When the decrease rate of the BET specific surface area is more than 80%, the thickness of the coating layer of the silicon compound comprising silica as a main component which is adhered onto the magnetic particles tends to be too large, and the content of non-magnetic components per unit volume thereof tends to be lowered, so that it may be difficult to obtain desired properties of the resulting surface-treated magnetic particles. In particular, this phenomenon tends to be more remarkable in the case of using the SmFeN-based magnetic particles. The rate of decrease in the BET specific surface area of the surface-treated rare earth-based magnetic particles according to the present invention is more preferably 20 to 78%, still more preferably 35 to 75% and further still more preferably 40 to 70%.

(14) The average particle diameter of the surface-treated rare earth-based magnetic particles according to the present invention which are produced using the NdFeB-based magnetic particles is preferably 10 to 100 m and more preferably 40 to 80 m, whereas the average particle diameter of the surface-treated rare earth-based magnetic particles according to the present invention which are produced using the SmFeN-based magnetic particles is preferably 1.0 to 5.0 m and more preferably 1.0 to 4.0 m.

(15) The surface-treated rare earth-based magnetic particles according to the present invention which are produced using the NdFeB-based magnetic particles preferably have an Nd.sub.2Fe.sub.14B type structure. Also, the surface-treated rare earth-based magnetic particles according to the present invention which are produced using the SmFeN-based magnetic particles preferably have an Th.sub.2Zn.sub.17 type structure.

(16) The surface-treated rare earth-based magnetic particles according to the present invention which are produced using the NdFeB-based magnetic particles preferably have magnetic properties (as measured by orienting the particles in a magnetic field) including a coercive force of 478.6 to 2473 kA/m (6000 to 31000 Oe), a residual magnetic flux density of 1100 to 1500 mT (11 to 15 kG) and a maximum magnetic energy product of 199.1 to 557.4 kJ/m.sup.3 (25 to 70 MGOe).

(17) The surface-treated rare earth-based magnetic particles according to the present invention which are produced using the SmFeN-based magnetic particles preferably have magnetic properties (as measured by orienting the particles in a magnetic field) including a coercive force of 398.1 to 2387.3 kA/m (5000 to 30000 Oe), a residual magnetic flux density of 1000 to 1400 mT (10 to 14 kG) and a maximum magnetic energy product of 158.8 to 358.1 kJ/m.sup.3 (20 to 45 MGOe).

(18) Next, the process for producing the surface-treated rare earth-based magnetic particles according to the present invention is described.

(19) The surface-treated rare earth-based magnetic particles according to the present invention can be produced by coating the NdFeB-based magnetic particles or the SmFeN-based magnetic particles with a phosphoric acid compound, and then adding a mixed solution prepared by mixing at least one alkoxy oligomer whose molecular end is capped with an alkoxysilyl group, with at least one phosphoric acid-based compound selected from the group consisting of orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate and aluminum phosphate to the coated NdFeB-based magnetic particles or SmFeN-based magnetic particles, followed by heat-treating the resulting particles, and thereafter subjecting the thus treated particles to coating treatment with a silane coupling agent.

(20) The NdFeB-based magnetic particles to be surface-treated according to the present invention have a compressed density (CD) of not less than 4.1 g/cc, a BET specific surface area of 0.01 to 0.8 m.sup.2/g and an elution of Fe of 20 to 50 mg/L. Also, the SmFeN-based magnetic particles to be surface-treated according to the present invention have a BET specific surface area of 0.3 to 3 m.sup.2/g and an elution of Fe of 20 to 50 mg/L.

(21) The starting alloy used for producing the NdFeB-based magnetic particles in the present invention may be prepared by any of known alloy production methods such as a book mold method, a centrifugal cast method, a strip cast method, an atomizing method and a reducing diffusion method.

(22) The thus prepared NdFeB ingot may be subjected to homogenization treatment for the purposes of rendering crystal particles coarse and reducing an -Fe phase. The homogenization treatment may be carried out, for example, in an inert gas atmosphere other than a nitrogen atmosphere, at a temperature of 1000 to 1200 C. for 1 to 48 hr.

(23) When subjecting the NdFeB ingot to the homogenization treatment, elements in the NdFeB ingot are diffused, so that the respective components therein are homogenized. The NdFeB ingot comprises an Nd.sub.2Fe.sub.14B phase as a main phase, an Nd-rich phase and a B-rich phase. In many of the NdFeB ingot, a ferromagnetic phase such as an Nd.sub.2Fe.sub.17 phase tends to be present in addition to the Nd.sub.2Fe.sub.14 phase. However, the NdFeB ingot comprising only the Nd.sub.2Fe.sub.14B phase may be obtained by subjecting the ingot to heat treatment. When subjecting the NdFeB ingot to the homogenization treatment, the crystal particles thereof tend to become coarse so that the crystal particle size reaches about 100 m or more. The formation of the coarse crystal particles having a large average crystal particle size is preferred because they exhibit a magnetic anisotropy.

(24) The reason why nitrogen is not to be used as the inert gas atmosphere is that the NdFeB ingot tends to be undesirably reacted with nitrogen.

(25) In addition, when the heat treatment temperature is lower than 1000 C., the diffusion of elements in the ingot tends to take a longer period of time, resulting in undesirable increase in production costs. When the heat treatment temperature is higher than 1200 C., the ingot tends to be undesirably melted.

(26) After completion of the homogenization treatment, the NdFeB ingot may be pulverized by a known method including, for example, a mechanical pulverization method such as pulverization using a jaw crusher, a hydrogen absorbing pulverization method, or a pulverization method using a disk mill.

(27) The NdFeB-based magnetic particles used in the present invention may be subjected to HDDR treatment. The HDDR treatment may be divided into a hydrogenation/disproportionation treatment (HD treatment) and a dehydrogenation/re-coupling treatment (DR treatment). The resulting NdFeB-based magnetic particles are charged into a vacuum horizontal sintering furnace and then subjected therein to the hydrogenation/disproportionation treatment (HD treatment) in a temperature range of 800 to 900 C. for 1 to 5 hr while flowing a hydrogen gas therethrough. Thereafter, the thus treated magnetic particles are subjected to the dehydrogenation/re-coupling treatment (DR treatment) in vacuum at the same temperature as used in the HD treatment. The HDDR treatment enables production of the NdFeB-based magnetic particles having an excellent magnetic anisotropy.

(28) In the SmFeN-based magnetic particles to be surface-treated according to the present invention, it is preferred that the Sm/Fe atomic ratio near the surface of the respective magnetic particles is slightly larger than the Sm/Fe atomic ratio in a central portion of the respective magnetic particles. The SmFeN-based magnetic particles used in the present invention are produced by coating iron oxide particles with a hydrous samarium oxide such as samarium hydroxide, and then subjecting the thus coated particles to reducing reaction to reduce iron oxide into metallic iron. In this treatment, the samarium compound undergoes dehydration reaction and thereby transformed into samarium oxide. Thereafter, the samarium oxide is mixed with metallic calcium, and the resulting mixture is subjected to reducing diffusion reaction and then to nitridation reaction and further subjected to washing step to remove Ca therefrom and then dried, thereby obtaining the SmFeN-based magnetic particles which are slightly Sm-rich near the surface of the respective magnetic particles as compared to those having a composition of Sm.sub.2Fe.sub.17.

(29) First, the coating treatment of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles with the phosphoric acid compound is described.

(30) Examples of the phosphoric acid compound include orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate and aluminum phosphate. Among these phosphoric acid compounds, orthophosphoric acid is preferred as the phosphoric acid compound to be adhered to the surface of the magnetic particles. Upon addition of the phosphoric acid compound, in order to uniformly coat the surface of the magnetic particles therewith, the phosphoric acid compound is preferably added in the form of a dilute solution prepared by mixing the phosphoric acid compound with isopropyl alcohol (IPA).

(31) The phosphoric acid compound used in the present invention is preferably added in an amount of 0.1 to 5.0% by weight based on the weight of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles. When the amount of the phosphoric acid compound added is less than 0.1% by weight, the thickness of the resulting coating layer of the phosphoric acid compound on the surface of the magnetic particles tends to be too small, thereby failing to attain desired effects. In addition, the uniform coating layer of the phosphoric acid compound tends to be hardly formed on the surface of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles, so that Fe tends to be eluted therefrom. Further, even though the thickness of the composite coating layer of the silicon compound and the phosphoric acid compound which is subsequently surface-treated on the thus formed coating layer of the phosphoric acid compound is increased, adhesion between the magnetic particles and the composite coating layer of the silicon compound and the phosphoric acid compound tend to be deteriorated, so that Fe also tends to be eluted therefrom, resulting in promoted formation of rusts. On the contrary, when the amount of the phosphoric acid compound added is more than 5% by weight, the thickness of the coating layer of the phosphoric acid compound which is attached onto the surface of the magnetic particles tends to be too large, so that the content of the non-magnetic components therein per unit weight tends to be increased, so that the resulting particles tend to be undesirably deteriorated in magnetic properties. The deterioration of the magnetic properties owing to increase in content of the non-magnetic components tends to be caused more remarkably especially in the case of using the SmFeN-based magnetic particles. The amount of the phosphoric acid compound added is more preferably 0.1 to 4.0% by weight.

(32) In the present invention, the surface-treating agent may be charged in the form of a mixed solution of the phosphoric acid compound such as orthophosphoric acid and IPA after deaggregating or pulverizing the NdFeB-based magnetic particles or the SmFeN-based magnetic particles.

(33) The kinds of stirrers used in the above treatment is not particularly limited. However, there is preferably used a mixing type stirrer such as a universal stirrer. The heat treatment temperature is preferably 50 to 125 C. When the heat treatment temperature is lower than 50 C., the reaction tends to proceed too slowly, so that the formation of the phosphoric acid compound coating layer tends to take a long period of time, resulting in poor production efficiency. On the contrary, when the heat treatment temperature is higher than 120 C., the formation of the phosphoric acid compound coating layer tends to proceed excessively quickly, so that the uniform coating layer tends to be hardly formed. The heat treatment temperature is more preferably 80 to 125 C.

(34) The heat treatment time is preferably 1 to 3 hr. When the heat treatment time is shorter than 1 hr, the surface of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles tends to be hardly completely coated with the phosphoric acid compound. In addition, IPA tends to be insufficiently dried out. When the heat treatment time is longer than 3 hr, the reaction for formation of the phosphoric acid compound coating layer on the surface of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles as well as drying of the coating layer tend to be already completed. Therefore, such a long heat treatment tends to be meaningless.

(35) The atmosphere used upon the heat treatment in the present invention is preferably an inert gas atmosphere. However, the heat treatment may also be carried out in air.

(36) Next, the coating treatment with the composite coating layer comprising the silicon compound derived from an alkoxy oligomer whose molecular end is capped with an alkoxysilyl group, and the phosphoric acid compound (formation of a second coating layer) is described.

(37) In the present invention, there is used the alkoxy oligomer whose molecular end is capped with an alkoxysilyl group. Specific examples of the alkoxy group include an ethoxy group and a methoxy group. Among these alkoxy groups, preferred is an ethoxy group. The alkoxy oligomer is preferably added singly. However, the alkoxy oligomer may also be added in the form of a dilute solution prepared by diluting the oligomer with IPA, etc. Examples of the phosphoric acid compound include orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate and aluminum phosphate. Among these phosphoric acid compounds, preferred is orthophosphoric acid.

(38) The amount of the alkoxy oligomer added whose molecular end is capped with an alkoxysilyl group as used in the present invention is preferably 0.1 to 2.0% by weight based on the weight of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles. When the amount of the alkoxy oligomer added is less than 0.1% by weight, the thickness of the coating layer including the silicon compound comprising silica as a main component which is obtained after the surface treatment tends to be too small, so that even when subsequently treated with the silane coupling agent, the total thickness of the coating layers tends to be still insufficient, so that Fe tends to be eluted therefrom, resulting in formation of rusts. On the contrary, when the amount of the alkoxy oligomer added is more than 2.0% by weight, the thickness of the coating layer including the silicon compound comprising silica as a main component which is attached onto the surface of the magnetic particles tends to be too large, so that the content of the non-magnetic components per unit weight of the magnetic particles tends to be increased, resulting in undesirable deterioration in magnetic properties thereof. In particular, the SmFeN-based magnetic particles tend to more remarkably suffer from the deterioration in magnetic properties owing to the increased content of the non-magnetic components per unit weight of the magnetic particles. The amount of the alkoxy oligomer added is more preferably 0.2 to 1.8% by weight and still more preferably 0.4 to 1.5% by weight.

(39) The amount of the phosphoric acid compound added for forming the composite coating layer of the silicon compound and the phosphoric acid compound is preferably 0.01 to 3.0% by weight based on the weight of the NdFeB-based magnetic particles or the SmFeN-based magnetic particles. When the amount of the phosphoric acid compound added for formation of the composite coating layer is less than 0.01% by weight, the composite coating layer comprising the silicon compound and the phosphoric acid compound tends to be incompletely formed, so that Fe tends to be readily eluted out therefrom, resulting in promoted formation of rusts. On the contrary, when the amount of the phosphoric acid compound added for formation of the composite coating layer is more than 3.0% by weight, the thickness of the coating layer including the phosphoric acid compound which is attached onto the magnetic particles tends to be too large, so that the content of the non-magnetic components per unit weight of the magnetic particles tends to be increased, resulting in undesirable deterioration in magnetic properties thereof. In particular, the SmFeN-based magnetic particles tend to more remarkably suffer from the deterioration in magnetic properties owing to the increased content of the non-magnetic components per unit weight of the magnetic particles. Further, the pH value of the treating solution tends to be increased, so that the surface of the magnetic particles tends to be hardly uniformly treated, and Fe tends to be therefore eluted out. The amount of the phosphoric acid compound added for formation of the composite coating layer is more preferably 0.1 to 2.0% by weight.

(40) In the present invention, the time of preliminary mixing treatment to be conducted after adding the alkoxy oligomer whose molecular end is capped with an alkoxysilyl group, is 10 to 30 min.

(41) The atmosphere used upon the preliminary mixing treatment is preferably an inert gas atmosphere. However, the preliminary mixing treatment may also be carried out in air. The preliminary mixing treatment is conducted without heating. When the preliminary mixing treatment is conducted at an elevated temperature, the reaction for formation of the composite coating layer comprising the silicon compound and the phosphoric acid compound tends to proceed rapidly before the treating solution for forming the composite coating layer is fully diffused over the NdFeB-based magnetic particles or the SmFeN-based magnetic particles, so that the NdFeB-based magnetic particles or the SmFeN-based magnetic particles may fail to be uniformly coated with the composite coating layer comprising the silicon compound and the phosphoric acid compound, resulting in elution of Fe therefrom.

(42) The temperature used upon the above heat treatment is preferably 60 to 130 C. When the heat treatment temperature is lower than 60 C., the alkoxy oligomer tends to hardly undergo hydrolysis reaction, so that the composite coating layer comprising the silicon compound and the phosphoric acid compound tend to be hardly attached onto the magnetic particles. On the contrary, when the heat treatment temperature is higher than 130 C., the hydrolysis reaction tends to proceed too rapidly, so that the surface of the magnetic particles may fail to be uniformly coated with the composite coating layer comprising the silicon compound and the phosphoric acid compound, resulting in unevenness of the composite coating layer adhered. The heat treatment temperature is more preferably 80 to 130 C.

(43) The time required for the heat treatment is preferably 2 to 6 hr. When the heat treatment time is shorter than 2 hr, the reaction tends to proceed insufficiently, so that the composite coating layer comprising the silicon compound and the phosphoric acid compound may fail to be sufficiently adhered onto the surface of the magnetic particles. On the other hand, when the heat treatment time is longer than 6 hr, a sufficient amount of the composite coating layer comprising the silicon compound and the phosphoric acid compound is already adhered onto the surface of the magnetic particles, and therefore such a long heat treatment time tends to be meaningless.

(44) The amount of Fe eluted from the NdFeB-based magnetic particles or the SmFeN-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer comprising the silicon compound and the phosphoric acid compound according to the present invention is preferably not more than 15 mg/L. When the amount of Fe eluted is out of the above-specified range, even in the case where the treatment with the coupling agent is conducted after completion of the treatment with the composite coating layer, the elution of Fe tends to be hardly suppressed, thereby failing to sufficiently attain the aimed effects of the present invention. The amount of Fe eluted from the NdFeB-based magnetic particles or SmFeN-based magnetic particles which are coated with the composite coating layer is more preferably not more than 10 mg/L.

(45) The compressed density (CD) of the NdFeB-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer comprising the silicon compound and the phosphoric acid compound according to the present invention is preferably not less than 4.5 g/cc. When the compressed density (CD) is out of the above-specified range, the density of the magnetic particles in the resulting resin composition per unit volume thereof upon injection molding tends to be lowered, resulting in poor magnetic properties of the resulting molded product. The compressed density (CD) of the NdFeB-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer is more preferably 4.5 to 5.1 g/cc. Whereas, the compressed density (CD) of the SmFeN-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer comprising the silicon compound and the phosphoric acid compound according to the present invention is preferably not less than 4.2 g/cc. When the compressed density (CD) is out of the above-specified range, the density of the magnetic particles in the resulting resin composition per unit volume thereof upon injection molding tends to be lowered, resulting in poor magnetic properties of the resulting molded product. The compressed density (CD) of the SmFeN-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer is more preferably 4.2 to 4.8 g/cc.

(46) The BET specific surface area of the NdFeB-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer comprising the silicon compound and the phosphoric acid compound according to the present invention is preferably 0.1 to 5.0 m.sup.2/g. When the BET specific surface area is out of the above-specified range, no adequate coating treatment tends to be carried out, so that the resulting surface-treated magnetic particles may fail to exhibit the desired rust prevention property. The BET specific surface area of the NdFeB-based magnetic particles which are coated with the composite metal phosphoric acid salt coating layer is more preferably 0.15 to 4.5 m.sup.2/g.

(47) Next, the coating treatment with the silane coupling agent is described.

(48) In the present invention, after completion of the above surface treatment for forming the composite metal phosphoric acid salt coating layer comprising the silicon compound and the phosphoric acid compound, the resulting coated magnetic particles are further subjected to surface treatment with the silane coupling agent.

(49) Examples of the silane coupling agent used in the present invention include -(2-aminoethyl)aminopropyl trimethoxysilane, -(2-aminoethyl)aminopropylmethyl dimethoxysilane, -methacryloxypropyl trimethoxysilane, -methacryloxypropylmethyl dimethoxysilane, N--(N-vinylbenzylaminoethyl)--aminopropyl trimethoxysilane hydrochloride, -glycidoxypropyl trimethoxysilane, -mercaptopropyl trimethoxysilane, methyl trimethoxysilane, methyl triethoxysilane, vinyl triacetoxysilane, -chloropropyl trimethoxysilane, hexamethylene disilazane, -anilinopropyl trimethoxysilane, vinyl trimethoxysilane, octadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, -chloropropylmethyl dimethoxysilane, -mercaptopropylmethyl dimethoxysilane, methyl trichlorosilane, dimethyl dichlorosilane, trimethyl chlorosilane, vinyl trichlorosilane, vinyl tris(p-methoxyethoxy)silane, vinyl triethoxysilane, -(3,4-epoxycyclohexyl)ethyl trimethoxysilane, -glycidoxypropylmethyl dimethoxysilane, N--(aminoethyl) -aminopropyl trimethoxysilane, N--(aminoethyl) -aminopropylmethyl dimethoxysilane, -aminopropyl triethoxysilane, N-phenyl--aminopropyl trimethoxysilane, oleydpropyl triethoxysilane, -isocyanatopropyl triethoxysilane, polyethoxydimethyl siloxane, polyethoxymethyl siloxane, bis(trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)tetrasulfane, -isocyanatopropyl trimethoxysilane, vinylmethyl dimethoxysilane, 1,3,5-N-tris(3-trimethoxysilylpropyl)isocyanurate, t-butyl carbamate trialkoxysilane, -glycidoxypropyl triethoxysilane, -methacryloxypropylmethyl diethoxysilane, -methacryloxypropyl triethoxysilane, N--(aminoethyl) -aminopropyl triethoxysilane, and 3-acryloxypropyl trimethoxysilane N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propane amine.

(50) The silane coupling agent may also be used in the form of a dilute solution prepared by diluting the silane coupling agent with water, IPA, etc.

(51) The surface treatment with the silane coupling agent may be conducted by an ordinary method. In the present invention, the surface treatment is preferably carried out by mixing and stirring, and at the same time by heating.

(52) The atmosphere used upon the heat treatment is preferably an inert gas atmosphere such as a nitrogen gas or an argon gas. The heat treatment temperature is preferably 85 to 150 C. When the heat treatment temperature is lower than 85 C., IPA used for diluting the silane coupling agent tends to be hardly vaporized, and remain on the surface of the magnetic particles, so that the resulting magnetic particles tend to have a poor compatibility with resins upon kneading therewith. On the contrary, when the heat treatment temperature is higher than 150 C., the reaction of the silane coupling agent is already completed so that the silane compound comprising silica as a main component is fully attached onto the magnetic particles, and therefore the use of such a high heat treatment temperature is meaningless. In addition, under the high temperature condition, the organic functional group being present on the surface of the thus coated magnetic particles tends to be deteriorated by heat, so that the compatibility of the magnetic particles with resins tends to become poor, resulting in deterioration in strength of the resulting bonded magnet.

(53) Next, the resin composition for bonded magnets according to the present invention is described.

(54) The resin composition for bonded magnets according to the present invention comprises the surface-treated NdFeB-based magnetic particles or SmFeN-based magnetic particles and a binder resin in which the surface-treated magnetic particles are dispersed. Specifically, the resin composition for bonded magnets according to the present invention comprises the surface-treated NdFeB-based magnetic particles or SmFeN-based magnetic particles in an amount of 86 to 99% by weight, and the balance comprising the binder resin and other additives.

(55) The binder resin may be selected from various resins according to a molding method used. In the case of using an injection molding method, an extrusion molding method and a calendering method, thermoplastic resins may be suitably used as the binder resin. In the case of using a compression molding method, thermosetting resins may be suitably used as the binder resin. Examples of the thermoplastic resins usable in the present invention include nylon (PA)-based resins, polypropylene (PP)-based resins, ethylene vinyl acetate (EVA)-based resins, polyphenylene sulfide (PPS)-based resins, liquid crystal resins (LCP), elastomer-based resins, rubber-based resins, etc. Examples of the thermosetting resins usable in the present invention include epoxy-based resins and phenol-based resins.

(56) Meanwhile, upon production of the resin composition for bonded magnets, in order to improve a flowability and a moldability thereof and allow the NdFeB-based magnetic particles or SmFeN-based magnetic particles to sufficiently exhibit magnetic properties thereof, in addition to the binder resin, there may be used known additives such as a plasticizer, a lubricant and a coupling agent, if required. In addition, the other kinds of magnet particles such as ferrite magnet particles may also be mixed in the resin composition.

(57) These additives may be adequately selected according to the aimed applications and objects. As the plasticizer, there may be used commercially available products according to the respective resins used. The total content of the plasticizers used in the resin composition is about 0.01 to 5.0% by weight based on the weight of the binder resin.

(58) Examples of the lubricant usable in the present invention include stearic acid and derivatives thereof, inorganic lubricants, oil-based lubricants, etc. The lubricant may be used in an amount of 0.01 to 1.0% by weight based on the total weight of the bonded magnet.

(59) As the coupling agent, there may be used commercially available products according to the resins and fillers used. The coupling agent may be used in an amount of about 0.01 to 3.0% by weight based on the weight of the binder resin used.

(60) Examples of the other magnetic particles usable in the present invention include ferrite magnet particles, alnico-based magnet particles and rare earth-based magnet particles, etc.

(61) The flow property (MFR) of the resin composition for bonded magnets comprising the NdFeB-based magnetic particles or SmFeN-based magnetic particles is desirably about 10 to 500 g/10 min as measured by the below-mentioned evaluation method. When the flow property of the resin composition is less than 10 g/10 min, the resin composition tends to be considerably deteriorated in injection moldability and productivity.

(62) The resin composition for bonded magnets according to the present invention is obtained by mixing and kneading the NdFeB-based magnetic particles or SmFeN-based magnetic particles with the binder resin.

(63) The above mixing may be conducted using a mixer such as a Henschel mixer, a V-shaped mixer and a Nauter mixer, whereas the above kneading may be conducted using a single screw kneader, a twin screw kneader, a mill-type kneader, an extrusion kneader, etc.

(64) Next, the bonded magnet according to the present invention is described.

(65) The magnetic properties of the bonded magnet may vary according to the applications thereof as aimed. The bonded magnet preferably has a residual magnetic flux density of 350 to 850 mT (3.5 to 9.0 kG), a coercive force of 238.7 to 1428.5 kA/m (3000 to 18000 Oe) and a maximum energy product of 23.9 to 198.9 kJ/m.sup.3 (3 to 25 MGOe).

(66) The molded density of the bonded magnet is preferably 4.5 to 5.5 g/cm.sup.3.

(67) The bonded magnet of the present invention may be produced by subjecting the above resin composition for bonded magnets to a known molding method such as injection molding, extrusion molding, compression molding and calendaring, and then subjecting the resulting molded product to electromagnet magnetization or pulse magnetization by an ordinary method.

(68) <Function>

(69) The surface-treated NdFeB-based magnetic particles or SmFeN-based magnetic particles according to the present invention exhibit a less elution of Fe therefrom.

(70) The reason why the magnetic particles whose surface is coated with the phosphoric acid compound and then with the composite coating layer of the silicon compound and the phosphoric acid compound and further treated with the silane coupling agent are enhanced in rust prevention property as compared to those particles whose surface is coated with the phosphoric acid compound and then with the silicon compound solely and further treated with the silane coupling agent, is considered as follows, although not clearly determined. That is, it is considered that the composite coating layer comprising the silicon compound and the phosphoric acid compound exhibits a high adhesion property. In addition, it is considered that since the phosphoric acid is present during the reaction step for obtaining the silicon compound, the dense coating layer is formed around the phosphoric acid compound as a core, so that the barrier effect of the coating layer is enhanced synergistically and penetration of corrosive ions therethrough can be effectively suppressed.

(71) In the present invention, since the surface of the respective NdFeB-based magnetic particles or SmFeN-based magnetic particles is coated with the phosphoric acid compound and further the surface of the phosphoric acid compound coating layer is coated with both the silicon compound and the phosphoric acid compound, the resin composition using the magnetic particles can exhibit a high flowability, and the bonded magnet produced by molding the resin composition can exhibit an excellent rust prevention property.

EXAMPLES

(72) Next, the present invention is described in more detail by referring to Examples and Comparative Examples. However, these Examples are only illustrative and not intended to limit the present invention thereto.

(73) The average particle diameter of the NdFeB-based magnetic particles or SmFeN-based magnetic particles was measured using HELOS.

(74) The specific surface area of the NdFeB-based magnetic particles or SmFeN-based magnetic particles was measured by a BET method.

(75) The contents of P and Si were respectively calculated from the values as measured by X-F (fluorescent X-ray analysis) or compositional analysis by ICP.

(76) The compressed density of the particles was determined from the value as measured when compressing a sample by applying a pressure of 1 t/cm.sup.2 thereto.

(77) The carbon content was measured using a carbon and sulfur measuring apparatus EMIA-820W manufactured by Horiba Seisakusho Co., Ltd.

(78) The amount of iron eluted from the particles was measured as follows. That is, 1.0 g of a sample was dipped in 50 mL of pure water in which 0.05 g of catechol was dissolved, and the obtained mixture was allowed to stand at room temperature (30 C.) for 24 hr and then filtered to obtain a filtrate. The thus obtained filtrate was analyzed using an ICP emission spectroscopic apparatus. In the above measurement, catechol serves to stabilize Fe eluted from the sample by forming a complex of Fe therewith to thereby enable accurate measurement of the amount of Fe eluted from the sample.

(79) The magnetic properties of the NdFeB-based magnetic particles or SmFeN-based magnetic particles were measured as follow. That is, the magnetic particles to be measured were filled together with a wax in a capsule, and heated and cooled while applying an orientation magnetic field thereto. The magnetic properties of the thus magnetically oriented magnetic particles were expressed by the values measured using a vibration sample magnetometer VSM manufactured by Toei Kogyo Co., Ltd.

(80) The flow property (MFR) of the resin composition for bonded magnets was measured as follow. That is, as to the resin composition produced using the NdFeB-based magnetic particles, 88.81 parts by weight of the NdFeB-based magnetic particles and 8.91 parts by weight of polyphenylene sulfide were mixed with each other using a Henschel mixer, and then kneaded using a twin-screw extrusion kneader (kneading temperature: 300 C.). The flow property (MFR) of the obtained kneaded composition was measured at a heating temperature of 330 C. by applying a pressure of 5 kgf thereto using a semi-automatic melt indexer Model 2A manufactured by Toyo Seiki Co., Ltd. Also, as to the resin composition produced using the SmFeN-based magnetic particles, 91.64 parts by weight of the SmFeN-based magnetic particles, 7.3 parts by weight of 12 nylon, 0.5 part by weight of an antioxidant and 1.0 part by weight of a surface-treating agent were mixed with each other using a Henschel mixer, and then kneaded using a twin-screw extrusion kneader (kneading temperature: 190 C.). The flow property (MFR) of the obtained kneaded composition was measured at a heating temperature of 270 C. by applying a pressure of 10 kgf thereto using a semi-automatic melt indexer Model 2A manufactured by Toyo Seiki Co., Ltd.

(81) The magnetic properties of the bonded magnet which had been molded in an orientation magnetic field were measured using a BH tracer manufactured by Toei Kogyo Co., Ltd.

(82) The rust prevention property of the bonded magnet was measured as follows. That is, the obtained bonded magnet having a size of 107 mm was evaluated using a highly corrosive test solution as described in ASTM D1384. The degrees of formation of rusts on the bonded magnet as measured by dipping the bonded magnet in the test solution at 95 C. for 100 hr were compared, and evaluated according to the ratings (, , and X) as prescribed in Corrosion Test Method for Bonded Magnets in Guide Book of Testing Methods for Bonded Magnets published by The Japan Associate of Bonded Magnet Industries. In order to more clearly determine the degree of formation of rusts, the surface of the bonded magnet was filed before being dipped in the test solution to remove a skin layer on the surface of the bonded magnet for facilitating corrosion thereof.

(83) [Precursor 1]

(84) <Starting Alloy>

(85) The NdFeB ingot was prepared by a book mold method. The thus prepared ingot was pulverized into a lattice shape having a thickness of 20 mm and each side length of about 50 mm.

(86) <Homogenization Treatment>

(87) The NdFeB ingot thus prepared by a book mold method was subjected to soaking treatment for the purpose of forming coarse crystal particles and reducing an -Fe phase therein. The soaking treatment was carried out in an inert gas (argon gas) atmosphere at 1150 C. for 20 hr to obtain the aimed NdFeB ingot.

(88) <Pulverization>

(89) The NdFeB ingot after subjected to the soaking treatment was pulverized using a jaw crusher to obtain NdFeB particles.

(90) <HDDR Treatment>

(91) The thus obtained NdFeB-based magnetic particles were charged into a vacuum horizontal sintering furnace, and the temperature within the sintering furnace was changed stepwise in the range of 800 to 900 C. while flowing a hydrogen gas therethrough at a rate of 15 L/min to thereby subject the magnetic particles to hydrogenation/disproportionation treatment (HD treatment) for a period of about 5 hr in total. Thereafter, the magnetic particles were subjected to dehydrogenation/re-coupling treatment (DR treatment) in vacuum at the same temperature as used in the HD treatment, thereby obtaining NdFeB-based magnetic particles having an excellent magnetic anisotropy.

(92) As a result, it was confirmed that the thus obtained NdFeB-based magnetic particles had a BET specific surface area of 0.04 m.sup.2/g, a compressed density (CD) of 4.84 g/cc and an elution of Fe of 20.25 mg/L, and the magnetic properties of the NdFeB-based magnetic particles were a coercive force of 1135 kA/m (14230 Oe) and a maximum energy product of 251.87 kJ/m.sup.3 (31.63 MGOe) (the resulting NdFeB-based magnetic particles are hereinafter referred to sample A).

(93) <Surface Treatment>

(94) A universal stirrer was charged with 1500 g of the obtained NdFeB-based magnetic particles. Then, a mixed solution prepared from 3.75 g of orthophosphoric acid (0.25% by weight based on the magnetic particles) and 18.75 g of IPA (1.25% by weight based on the magnetic particles) was directly added to the NdFeB-based magnetic particles, and mixed therewith in air for 10 min. Thereafter, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining the NdFeB-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(95) [Precursor 2]

(96) The same treatment as defined in the above Precursor 1 was conducted except that a mixed solution prepared from 7.5 g of orthophosphoric acid (0.5% by weight based on the magnetic particles) and 37.5 g of IPA (2.5% by weight based on the magnetic particles) was used, thereby obtaining the NdFeB-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(97) [Precursor 3]

(98) The same treatment as defined in the above Precursor 1 was conducted except that a mixed solution prepared from 11.25 g of orthophosphoric acid (0.75% by weight based on the magnetic particles) and 57.0 g of IPA (3.8% by weight based on the magnetic particles) was used, thereby obtaining the NdFeB-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(99) [Precursor 4]

(100) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles as produced. Then, a mixed solution prepared from 7.5 g of orthophosphoric acid (0.5% by weight based on the magnetic particles) and 37.5 g of IPA (2.5% by weight based on the magnetic particles) was directly added to the NdFeB-based magnetic particles, and mixed therewith in air for 10 min. Thereafter, the obtained mixture was heat-treated at 80 C. for 1 hr in air under an atmospheric pressure while stirring, thereby obtaining the NdFeB-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(101) [Precursor 5]

(102) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles as produced. Then, a mixed solution prepared from 7.5 g of orthophosphoric acid (0.5% by weight based on the magnetic particles) and 37.5 g of IPA (2.5% by weight based on the magnetic particles) was directly added to the NdFeB-based magnetic particles, and mixed therewith in air for 10 min. Thereafter, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 100 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining the NdFeB-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(103) [Precursor 6]

(104) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles as produced. Then, a mixed solution prepared from 7.5 g of orthophosphoric acid (0.5% by weight based on the magnetic particles) and 37.5 g of IPA (2.5% by weight based on the magnetic particles) was directly added to the NdFeB-based magnetic particles, and mixed therewith in air for 10 min. Thereafter, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 150 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining the NdFeB-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(105) [Precursor 7]

(106) <Production of Samarium Compound-Coated Iron Oxide Particles>

(107) A reactor was charged with given amounts of water, sodium hydroxide and a ferrous sulfate solution, and the contents of the reactor were maintained at 90 C. and subjected to oxidation reaction while blowing air thereinto to thereby obtain magnetite particles. As a result, it was confirmed that the resulting magnetite particles had an average particle diameter of 0.70 m, a standard deviation of the particles diameters of 0.11 m and a particle size distribution of 15%.

(108) Into the resulting slurry comprising the magnetite particles was added a samarium chloride solution comprising a samarium atom in an amount of 11.76 mol %. Then, the pH value of the slurry was adjusted to 13 to subject the slurry to aging reaction for 2 hr while maintaining the temperature of the slurry at 90 C. Thereafter, the slurry was subjected to filtration and water-washing to remove soluble salts therefrom, and then dried, thereby obtaining samarium compound-coated magnetite particles.

(109) <Reducing Reaction and Stabilization Treatment>

(110) Next, the thus obtained samarium compound-coated magnetite particles were charged into a rotary heat treatment furnace, and heated at 800 C. over 7 hr while flowing a hydrogen gas having a purity of 99.99% therethrough at a rate of 40 L/min to thereby conduct a reducing reaction thereof. The product obtained after completion of the reducing reaction was in the form of a mixture of iron particles and samarium oxide particles. Then, the atmosphere in the rotary furnace was replaced with N.sub.2, and the temperature therein was dropped to 40 C. by cooling. After the temperature was stably held, the mixture was subjected to stabilization treatment while flowing N.sub.2 comprising about 2.0% by volume of oxygen therethrough to gradually oxidize the surface of the respective iron particles and thereby form an oxide coating layer thereon. The heat of reaction was monitored, and when generation of the heat of reaction was ceased, the whole reaction system was cooled to room temperature to withdraw the obtained mixture from the furnace into atmospheric air.

(111) <Reducing Diffusion Reaction>

(112) The thus obtained samarium oxide-coated iron particles and metallic Ca particles (in an amount of 3.0 mol per 1.0 mol of Sm in the samarium oxide-coated iron particles) were mixed with each other. The resulting mixture was placed on a pure iron tray, and inserted into an atmospheric furnace. After the inside of the furnace was evacuated, the atmosphere within the furnace was replaced with an argon atmosphere. Then, the inside temperature of the furnace was raised to 1050 C. while flowing an argon gas therethrough at which temperature the reaction system was maintained for 30 min to subject the contents of the furnace to reducing diffusion reaction. After completion of the reaction, the reaction system was cooled to 300 C.

(113) <Nitridation Reaction>

(114) After the furnace temperature was stabilized at 300 C., the inside of the furnace was once evacuated, and the atmosphere within the furnace was replaced with an N.sub.2 gas atmosphere. Next, the furnace temperature was raised to 420 C. under an N.sub.2 gas flow, and held at the same temperature for 8 hr to subject the contents of the furnace to nitridation reaction. After completion of the reaction, the reaction system was cooled to room temperature.

(115) The SmFeN-based magnetic particles before subjected to the below-mentioned phosphoric acid treatment used for production of the precursor 7 had an average particle diameter of 3.33 m, a BET specific surface area of 1.66 m.sup.2/g, a compressed density (CD) of 4.07 g/cc, an oil absorption of 13.4 g/cc and an elution of Fe of 35.2 mg/L, and the magnetic properties of the SmFeN-based magnetic particles were a coercive force of 1235 kA/m (15520 Oe), a residual magnetic flux density of 1120 mT (11.2 kG) and a maximum energy product of 223.3 kJ/m.sup.3 (28.074 MGOe) (the resulting SmFeN-based magnetic particles were hereinafter referred to a sample B).

(116) <Water-Washing and Pulverization>

(117) The particles obtained after the nitridation reaction were charged into water to prepare a slurry. At this time, the particles underwent spontaneous degradation to thereby begin separation of the particles into the SmFeN-based magnetic particles and the Ca component. After the SmFeN-based magnetic particles and the Ca component were fully separated from each other, the slurry was repeatedly subjected to decantation and water-washing to remove the Ca component therefrom. Next, the thus water-washed slurry was subjected to pulverization in the state comprising water as a solvent, and insoluble components generated upon the pulverization were removed by subjecting the slurry to decantation and water-washing.

(118) <Filtration, Surface Treatment and Drying>

(119) Next, the resulting slurry was subjected to filtration to remove water therefrom. The filtration was carried out such that a water content of the filtered product was 25% by weight, thereby obtaining a filter cake. The thus obtained filter cake was dried at 60 C. while stirring in a nitrogen flow under reduced pressure using a stirrer of an evacuating type.

(120) Thereafter, a universal stirrer was charged with 1500 g of the thus dried magnetic particles. Then, a mixed solution prepared from 7.5 g of orthophosphoric acid (0.5% by weight based on the magnetic particles) and 37.5 g of IPA (2.5% by weight based on the magnetic particles) was directly added to the SmFeN-based magnetic particles, and mixed therewith in air for 10 min. Thereafter, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in an inert gas atmosphere while stirring, thereby obtaining the SmFeN-based magnetic particles whose surface was coated with the phosphoric acid compound coating layer.

(121) The thus obtained SmFeN-based magnetic particles (precursor 7) had a total phosphorus content of about 0.15% by weight.

(122) [Precursor 8]

(123) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (treating agent 1) (0.7% by weight based on the NdFeB-based magnetic particles), 4.5 g of orthophosphoric acid (treating agent 2) (0.3% by weight based on the NdFeB-based magnetic particles) and 3.9 g of pure water (0.26% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 37.5 g of a diluting solution (2.5% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 60 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(124) [Precursor 9]

(125) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.7% by weight based on the NdFeB-based magnetic particles), 4.5 g of orthophosphoric acid (0.3% by weight based on the NdFeB-based magnetic particles) and 3.9 g of pure water (0.26% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 37.5 g of a diluting solution (2.5% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(126) [Precursor 10]

(127) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.7% by weight based on the NdFeB-based magnetic particles), 4.5 g of orthophosphoric acid (0.3% by weight based on the NdFeB-based magnetic particles) and 3.9 g of pure water (0.26% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 37.5 g of a diluting solution (2.5% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 180 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(128) [Precursor 11]

(129) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 5.25 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.35% by weight based on the NdFeB-based magnetic particles), 2.25 g of orthophosphoric acid (0.15% by weight based on the NdFeB-based magnetic particles) and 2.25 g of pure water (0.15% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 18.75 g of a diluting solution (1.25% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(130) [Precursor 12]

(131) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 15.75 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (1.05% by weight based on the NdFeB-based magnetic particles), 6.75 g of orthophosphoric acid (0.45% by weight based on the NdFeB-based magnetic particles) and 6.75 g of pure water (0.45% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 56.25 g of a diluting solution (3.75% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(132) [Precursor 13]

(133) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 31.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (2.1% by weight based on the NdFeB-based magnetic particles), 13.5 g of orthophosphoric acid (0.90% by weight based on the NdFeB-based magnetic particles) and 13.5 g of pure water (0.90% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 112.5 g of a diluting solution (7.50% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(134) [Precursor 14]

(135) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 46.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (3.1% by weight based on the NdFeB-based magnetic particles), 20.25 g of orthophosphoric acid (1.35% by weight based on the NdFeB-based magnetic particles) and 19.95 g of pure water (1.33% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 166.05 g of a diluting solution (11.07% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(136) [Precursor 15]

(137) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Manganese phosphate produced by Nihon Parkerizing Co., Ltd., was weighed (2.0% by weight based on the NdFeB-based magnetic particles), and mixed with 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.7% by weight based on the NdFeB-based magnetic particles) and 197.4 g of a diluting solution (13.16% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in nitrogen for 10 min. After completion of the addition, the obtained mixture was heat-treated at 90 C. for 10 min and then at 100 C. for 1 hr in nitrogen while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was adhered with a composite metal phosphoric acid salt coating layer comprising manganese and the phosphoric acid compound.

(138) [Precursor 16]

(139) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Zinc phosphate produced by Nihon Parkerizing Co., Ltd., was weighed (2.0% by weight based on the NdFeB-based magnetic particles), and mixed with 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.7% by weight based on the NdFeB-based magnetic particles) and 197.4 g of a diluting solution (13.16% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in nitrogen for 10 min. After completion of the addition, the obtained mixture was heat-treated at 90 C. for 10 min and then at 100 C. for 1 hr in nitrogen while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was adhered with a composite metal phosphoric acid salt coating layer comprising zinc and the phosphoric acid compound.

(140) [Precursor 17]

(141) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 5. Then, 1.92 g of aluminum isopropoxide (C.sub.9H.sub.2O.sub.3Al; 0.128% by weight based on the NdFeB-based magnetic particles), 10.5 g of orthophosphoric acid (0.7% by weight based on the NdFeB-based magnetic particles), 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.7% by weight based on the NdFeB-based magnetic particles), 8.4 g of pure water and 317.4 g of a diluting solution (21.16% by weight based on the NdFeB-based magnetic particles) were mixed with each other. Thereafter, the obtained mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in nitrogen for 10 min. After completion of the addition, the obtained mixture was heat-treated at 90 C. for 10 min and then at 100 C. for 1 hr in nitrogen while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was adhered with a composite coating layer comprising aluminum, the silicon compound and the phosphoric acid compound.

(142) [Precursor 18]

(143) A universal stirrer was charged with 1500 g of the SmFeN-based magnetic particles obtained in the above Precursor 7. Then, 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.70% by weight based on the SmFeN-based magnetic particles), 4.5 g of orthophosphoric acid (0.30% by weight based on the SmFeN-based magnetic particles) and 3.9 g of pure water (0.26% by weight based on the SmFeN-based magnetic particles) were respectively weighed and then mixed with 37.5 g of a diluting solution (2.50% by weight based on the SmFeN-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the SmFeN-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining SmFeN-based magnetic particles whose surface was coated with a composite coating layer comprising the silicon compound and the phosphoric acid compound.

(144) Various properties of the NdFeB-based magnetic particles and SmFeN-based magnetic particles treated with the phosphoric acid compound are shown in Table 1.

(145) Various properties of the NdFeB-based magnetic particles and SmFeN-based magnetic particles treated with the silicon compound and the phosphoric acid compound are shown in Table 2.

(146) TABLE-US-00001 TABLE 1 Amount of Magnetic phosphoric particles acid added Amount of IPA used (wt %) added (wt %) Precursor 1 Sample A 0.25 1.25 Precursor 2 Sample A 0.50 2.5 Precursor 3 Sample A 0.75 3.8 Precursor 4 Sample A 0.50 2.5 Precursor 5 Sample A 0.50 2.5 Precursor 6 Sample A 0.50 2.5 Precursor 7 Sample B 0.50 2.5 Phosphoric acid-treating Analyzed temperature value of P ( C.) (ppm) CD (g/cc) Precursor 1 80.fwdarw.120 340 4.88 Precursor 2 80.fwdarw.120 727 4.94 Precursor 3 80.fwdarw.120 1139 4.96 Precursor 4 80 734 4.94 Precursor 5 80.fwdarw.100 808 4.94 Precursor 6 80.fwdarw.150 728 4.94 Precursor 7 80.fwdarw.120 1592 4.19 Rate of change in BET specific specific surface area surface area Elution of Fe (m.sup.2/g) (%) (mg/L) Precursor 1 0.07 +175 14.45 Precursor 2 0.18 +450 8.20 Precursor 3 0.31 +775 8.40 Precursor 4 0.30 +750 10.25 Precursor 5 0.32 +800 10.1 Precursor 6 0.31 +775 10.00 Precursor 7 0.60 +55 21.55

(147) TABLE-US-00002 TABLE 2 Amount of Amount of treating treating Magnetic agent 1 agent 2 Diluting particles added added solution used (wt %) (wt %) (wt %) Precursor 8 Precursor 2 0.70 0.30 2.50 Precursor 9 Precursor 2 0.70 0.30 2.50 Precursor 10 Precursor 2 0.70 0.30 2.50 Precursor 11 Precursor 2 0.35 0.15 1.25 Precursor 12 Precursor 2 1.05 0.45 3.75 Precursor 13 Precursor 2 2.10 0.90 7.50 Precursor 14 Precursor 2 3.10 1.35 11.07 Precursor 15 Precursor 2 Mn: 2.0 0.70 13.16 Precursor 16 Precursor 2 Zn: 2.0 0.70 13.16 Precursor 17 Precursor 2 Al: 0.128 0.70 21.16 Precursor 18 Precursor 7 0.70 0.30 2.50 Analyzed Analyzed H.sub.2O Treating value of value of P (wt %) temp. ( C.) Si (ppm) (ppm) Precursor 8 0.26 60 1084 1838 Precursor 9 0.26 80.fwdarw.120 1043 1829 Precursor 10 0.26 80.fwdarw.180 1097 1874 Precursor 11 0.15 80.fwdarw.120 531 1379 Precursor 12 0.45 80.fwdarw.120 1538 2055 Precursor 13 0.90 80.fwdarw.120 3006 3370 Precursor 14 1.33 80.fwdarw.120 4585 4613 Precursor 15 0.26 90.fwdarw.100 1110 2250 Precursor 16 0.26 90.fwdarw.100 1125 1311 Precursor 17 0.56 90.fwdarw.100 1059 1871 Precursor 18 0.26 80.fwdarw.120 1347 2247 BET Other specific analyzed surface values CD area Elution of (ppm) (g/cc) (m.sup.2/g) Fe (mg/L) Precursor 8 4.85 1.49 8.18 Precursor 9 4.81 1.44 7.20 Precursor 10 4.87 1.61 7.30 Precursor 11 4.93 0.18 8.11 Precursor 12 4.84 2.72 7.45 Precursor 13 4.70 3.33 7.39 Precursor 14 4.57 4.01 7.34 Precursor Mn 4.93 0.19 7.35 15 (1372 ppm) Precursor Zn 4.93 0.10 8.00 16 (1288 ppm) Precursor Al 4.86 0.18 7.65 17 (3067 ppm) Precursor 4.31 0.31 7.12 18

(148) The NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in the above Precursor 1 to Precursor 7 were subjected to compositional analysis by ICP. The analyzed values of P of these magnetic particles are shown in Table 1. As a result, it was confirmed that the phosphoric acid compounds as desired were adhered on the respective magnetic particles.

(149) The NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in the above Precursor 1 to Precursor 7 were respectively subjected to measurement of a compressed density (CD) thereof. The measurement results are shown in Table 1. As a result, it was confirmed that the compressed density (CD) of the NdFeB-based magnetic particles was slightly increased by treating the magnetic particles with the phosphoric acid compound, whereas the compressed density (CD) of the SmFeN-based magnetic particles was slightly decreased by treating the magnetic particles with the phosphoric acid compound.

(150) The amounts of Fe eluted from the NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in the above Precursors 1 to Precursor 7 which were treated by varying the amounts of the respective components added and the heating temperature, were measured. As shown in Table 1, it was confirmed that the NdFeB-based magnetic particles obtained by treating the sample A with 0.5% by weight of orthophosphoric acid and 2.5% by weight of the diluting solution based on the sample A, followed by heat-treatments at temperatures of 80 C. and 120 C., exhibited the smallest elution of Fe.

(151) The NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in the above Precursor 8 to Precursor 14 and Precursor 18 were subjected to compositional analysis by ICP. The analyzed values of Si and P were those shown in Table 2. As a result, it was confirmed that the silicon compounds and phosphoric acid compounds as desired were adhered onto the magnetic particles.

(152) The NdFeB-based magnetic particles obtained in the above Precursor 15 to Precursor 17 were subjected to compositional analysis by ICP. The analyzed values of Mn, Zn, Al and P were those shown in Table 2. As a result, it was confirmed that the silicon compounds and phosphoric acid compounds as desired were adhered onto the magnetic particles.

(153) The NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in the above Precursor 8 to Precursor 17 were respectively subjected to measurement of a compressed density (CD) thereof. The measurement results are shown in Table 2. As a result, it was confirmed that the compressed density (CD) of the NdFeB-based magnetic particles was slightly decreased by treating the magnetic particles with the silicon compound and the phosphoric acid compound, whereas the compressed density (CD) of the SmFeN-based magnetic particles obtained in the above Precursor 18 was increased by the treatment.

(154) The NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in the above Precursor 8 to Precursor 18 were respectively subjected to measurement of a specific surface area thereof by a BET method. The measurement results are shown in Table 2. As a result, it was confirmed that the specific surface areas of these magnetic particles were increased as compared to those of the precursors 2 and 7, and therefore the change in surface condition of the magnetic particles was caused by forming the composite metal phosphoric acid salt coating layer comprising the silicon compound and the phosphoric acid compound thereon.

(155) The amounts of Fe eluted from the NdFeB-based magnetic particles obtained in the above Precursor 8 to Precursor 17 which were treated by varying the amounts of the respective components added and the heating temperature, were measured. As shown in Table 2, it was confirmed that the NdFeB-based magnetic particles obtained by treating the magnetic particles obtained in the above Precursor 2 with 0.7% by weight of the alkoxy oligomer, 0.3% by weight of orthophosphoric acid, 2.5% by weight of the diluting solution and 0.26% by weight of pure water based on the magnetic particles, followed by heat-treatments at temperatures of 80 C. and 120 C., exhibited the smallest elution of Fe.

Comparative Example 1

(156) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (treating agent 1) (0.7% by weight based on the NdFeB-based magnetic particles) and 3.9 g of pure water (0.26% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 37.5 g of a diluting solution (2.5% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with the silicon compound.

Comparative Example 2

(157) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 30.0 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (2.0% by weight based on the NdFeB-based magnetic particles) and 6.3 g of pure water (0.42% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 60 g of a diluting solution (4.0% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with the silicon compound.

Comparative Example 3

(158) A universal stirrer was charged with 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 2. Then, 30.0 g of an alkyl silicate represented by the formula: Si(OR).sub.4 wherein R is an alkyl group having 2 carbon atoms in which a molecular end of the alkyl silicate was capped with an alkoxysilyl group (2.0% by weight based on the NdFeB-based magnetic particles) and 6.3 g of pure water (0.42% by weight based on the NdFeB-based magnetic particles) were respectively weighed and then mixed with 60 g of a diluting solution (4.0% by weight based on the NdFeB-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the NdFeB-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining NdFeB-based magnetic particles whose surface was coated with the silicon compound.

Comparative Example 4

(159) A universal stirrer was charged with 1500 g of the SmFeN-based magnetic particles obtained in the above Precursor 7. Then, 10.5 g of an alkoxy oligomer whose molecular end was capped with an alkoxysilyl group (0.7% by weight based on the SmFeN-based magnetic particles) and 3.9 g of pure water (0.26% by weight based on the SmFeN-based magnetic particles) were respectively weighed and then mixed with 37.5 g of a diluting solution (2.5% by weight based on the SmFeN-based magnetic particles). Thereafter, the obtained treating agent mixture was directly added to the SmFeN-based magnetic particles, and then mixed therewith in air for 10 min. After completion of the addition, the obtained mixture was heat-treated at 80 C. for 1 hr and then at 120 C. for 2.5 hr in air under an atmospheric pressure while stirring, thereby obtaining SmFeN-based magnetic particles whose surface was coated with the silicon compound.

(160) Various properties of the thus obtained surface-treated SmFeN-based magnetic particles are shown in Table 3.

(161) TABLE-US-00003 TABLE 3 Amount of Amount of treating treating Magnetic agent 1 agent 2 particles Treating added added used agent used (wt %) (wt %) Comparative Precursor 2 Alkyl 0.70 Example 1 silicate oligomer Comparative Precursor 2 Alkyl 2.00 Example 2 silicate oligomer Comparative Sample A Alkyl 2.00 Example 3 silicate monomer Comparative Sample B Alkyl 0.70 Example 4 silicate oligomer Treating temp. of Diluting alkyl Analyzed solution H.sub.2O silicate value of (wt %) (wt %) ( C.) Si (ppm) Comparative 2.50 0.26 80.fwdarw.120 903.3 Example 1 Comparative 4.00 0.42 80.fwdarw.120 1870.9 Example 2 Comparative 4.00 0.42 80.fwdarw.120 267.0 Example 3 Comparative 2.50 0.26 80.fwdarw.120 1345 Example 4 BET Analyzed specific value surface Elution of P CD area T-C of Fe (ppm) (g/cc) (m.sup.2/g) (wt %) (mg/L) Comparative 726.0 4.87 2.13 0.04 8.00 Example 1 Comparative 734.0 4.72 3.71 0.70 8.03 Example 2 Comparative 748.0 4.80 0.04 0.020 7.98 Example 3 Comparative 1570 4.39 0.20 0.13 7.15 Example 4

Example 1

(162) To 1500 g of the NdFeB-based magnetic particles obtained in the above Precursor 8 was directly added a mixed solution comprising 7.5 g of a silane coupling agent (-aminopropyl triethoxysilane) (0.5% by weight based on the NdFeB-based magnetic particles), 35 g of IPA (2.5% by weight based on the NdFeB-based magnetic particles) and 4.5 g of pure water (0.3% by weight based on the NdFeB-based magnetic particles), and the resulting mixture was stirred in a nitrogen gas for 10 min using a universal stirrer. Thereafter, the mixture was heat-treated at 100 C. for 1 hr in a nitrogen atmosphere while stirring, and then cooled to withdraw the magnetic particles therefrom. Then, the resulting magnetic particles were heat-treated at 120 C. for 2.0 hr in an inert gas under an atmospheric pressure, thereby obtaining NdFeB-based magnetic particles whose surface was coated with a coating layer comprising the silicon compound and the phosphoric cid compound onto which Si of the silane coupling agent was further adhered.

Examples 2 to 10

(163) The same procedure as defined in Example 1 was conducted except that the kinds of precursors used were variously changed, thereby obtaining surface-treated NdFeB-based magnetic particles.

Example 11

(164) To 1500 g of the SmFeN-based magnetic particles obtained in the above Precursor 18 was directly added a mixed solution comprising 15.0 g of a silane coupling agent (-aminopropyl triethoxysilane) (0.5% by weight based on the NdFeB-based magnetic particles), 35 g of IPA (2.5% by weight based on the NdFeB-based magnetic particles) and 4.5 g of pure water (0.3% by weight based on the NdFeB-based magnetic particles), and the resulting mixture was stirred in a nitrogen gas for 10 min using a universal stirrer. Thereafter, the mixture was heat-treated at 100 C. for 1 hr in a nitrogen atmosphere while stirring, and then cooled to withdraw the magnetic particles therefrom. Then, the resulting magnetic particles were heat-treated at 120 C. for 2.0 hr in an inert gas under an atmospheric pressure, thereby obtaining SmFeN-based magnetic particles whose surface was coated with a coating layer comprising the silicon compound and the phosphoric cid compound onto which Si of the silane coupling agent was further adhered.

(165) Various properties of the thus treated SmFeN-based magnetic particles are shown in Table 4.

(166) TABLE-US-00004 TABLE 4 Amount of silane Magnetic coupling Diluting particles agent added solution used (wt %) (wt %) Example 1 Precursor 8 0.5 2.50 Example 2 Precursor 9 0.5 2.50 Example 3 Precursor 10 0.5 2.50 Example 4 Precursor 11 0.5 2.50 Example 5 Precursor 12 0.5 2.50 Example 6 Precursor 13 0.5 2.50 Example 7 Precursor 14 0.5 2.50 Example 8 Precursor 15 0.5 2.50 Example 9 Precursor 16 0.5 2.50 Example 10 Precursor 17 0.5 2.50 Example 11 Precursor 18 0.5 2.50 Analyzed Analyzed H.sub.2O value of value of P CD (wt %) Si (ppm) (ppm) (g/cc) Example 1 0.30 1282 1757 4.93 Example 2 0.30 1283 1713 4.89 Example 3 0.30 1289 1778 4.95 Example 4 0.30 649 1279 5.01 Example 5 0.30 1867 1975 4.92 Example 6 0.30 3009 3413 4.77 Example 7 0.30 5533 4469 4.64 Example 8 0.30 846 2960 5.00 Example 9 0.30 880 1229 5.00 Example 10 0.30 903 1729 4.91 Example 11 0.30 2637 2555 4.26 Rate of BET decrease specific in surface specific area surface T-C Elution of (m.sup.2/g) area (%) (wt %) Fe (mg/L) Example 1 0.77 51.7 0.10 1.21 Example 2 0.62 43.1 0.10 0.95 Example 3 0.72 44.7 0.10 0.96 Example 4 0.08 42.8 0.11 1.23 Example 5 1.33 48.9 0.09 0.99 Example 6 1.52 45.6 0.11 0.98 Example 7 1.72 43.0 0.10 0.96 Example 8 0.02 10.5 0.09 1.5 Example 9 0.05 50.0 0.10 1.35 Example 10 0.01 5.6 0.13 4.4 Example 11 0.41 * 0.10 0.92 Note *: Increased by 130.6%

(167) The NdFeB-based magnetic particles obtained in Examples 1 to 10 onto which the silicon compound was adhered, were subjected to compositional analysis by ICP. The analyzed values of Si are shown in Table 4. As a result, it was confirmed that the desired amount of Si was adhered onto the magnetic particles.

(168) The SmFeN-based magnetic particles obtained in Example 11 onto which the silicon compound was adhered, were subjected to compositional analysis by X-F. The analyzed values of Si are shown in Table 4. As a result, it was confirmed that the desired amount of Si was adhered onto the magnetic particles.

(169) The NdFeB-based magnetic particles obtained in Examples 1 to 10 onto which the silicon compound was adhered, were subjected to measurement of a specific surface area thereof by a BET method. The measurement results are shown in Table 4. As shown in Table 4, the rates of decrease in the specific surface area of the magnetic particles between after formation of the coating layer comprising the silicon compound and the phosphoric acid compound and after the treatment with the silane coupling agent (after the treatment with the silane coupling agent/before the treatment with the silane coupling agent) were in the range of 5% to 60%. Thus, it was confirmed that all of the NdFeB-based magnetic particles obtained in Examples 1 to 10 were decreased in BET specific surface area thereof. From the results, it was estimated that Si was uniformly adhered onto the surface of the respective NdFeB-based magnetic particles.

(170) The SmFeN-based magnetic particles obtained in Example 11 onto which the silicon compound was adhered, were subjected to measurement of a specific surface area thereof by a BET method. The measurement results are shown in Table 4. As shown in Table 4, the rate of change in the BET specific surface area of the magnetic particles between after formation of the coating layer comprising the silicon compound and the phosphoric acid compound and after the treatment with the silane coupling agent was +130.64% (increased). From this result, it was estimated that the silicon compound and the phosphoric acid compound were adhered onto the surface of the respective SmFeN-based magnetic particles.

(171) The NdFeB-based magnetic particles obtained in Examples 1 to 10 were subjected to measurement of elution of Fe therefrom. As shown in Table 4, it was confirmed that when treated with the silane coupling agent, elution of Fe from the magnetic particles could be further suppressed as compared to the magnetic particles before treated with the silane coupling agent.

(172) The SmFeN-based magnetic particles obtained in Example 11 were subjected to measurement of elution of Fe therefrom. As shown in Table 4, it was confirmed that when treated with the silane coupling agent, elution of Fe from the magnetic particles could be further suppressed as compared to the magnetic particles before treated with the silane coupling agent.

Comparative Examples 5 to 7

(173) In the same manner as defined in Example 1, 1500 g of the NdFeB-based magnetic particles obtained in Comparative Examples 1 to 3 were treated with the silane coupling agent, thereby obtaining NdFeB-based magnetic particles which were adhered with Si onto which Si of the silane coupling agent was further adhered.

Comparative Example 8

(174) In the same manner as defined in Example 11, 1500 g of the SmFeN-based magnetic particles obtained in Comparative Example 4 were treated with the silane coupling agent, thereby obtaining SmFeN-based magnetic particles which were adhered with Si onto which Si of the silane coupling agent was further adhered.

(175) The amounts of Fe eluted from the NdFeB-based magnetic particles and the SmFeN-based magnetic particles obtained in Comparative Examples 5 to 8 are shown in Table 5.

(176) TABLE-US-00005 TABLE 5 Amount of silane Magnetic coupling Diluting particles agent added solution used (wt %) (wt %) Comparative Comparative 0.5 2.50 Example 5 Example 1 Comparative Comparative 0.5 2.50 Example 6 Example 2 Comparative Comparative 0.5 2.50 Example 7 Example 3 Comparative Comparative 0.5 2.50 Example 8 Example 4 Analyzed Analyzed H.sub.2O value of value of (wt %) Si (ppm) P (ppm) CD (g/cc) Comparative 0.30 1268 719.0 4.95 Example 5 Comparative 0.30 2076 734.6 4.79 Example 6 Comparative 0.30 519 748.8 4.88 Example 7 Comparative 0.30 2213 1583.65 4.20 Example 8 Rate of BET decrease specific in surface specific Elution area surface T-C of Fe (m.sup.2/g) area (%) (wt %) (mg/L) Comparative 0.94 44.1 0.11 2.17 Example 5 Comparative 1.63 43.9 0.12 2.76 Example 6 Comparative 0.02 50.0 0.11 2.85 Example 7 Comparative 0.15 75.0 0.22 4.12 Example 8

Examples 12 to 21

(177) Using a Henschel mixer, 88.81 parts by weight of the NdFeB-based magnetic particles obtained in Examples 1 to 10 and 8.91 parts by weight of a polyphenylene sulfide resin were mixed with each other, and then the resulting mixture was kneaded (at a kneading temperature of 300 C.) using a twin-screw extrusion kneader to obtain pellets. The thus obtained pellets were injection-molded to produce respective bonded magnets.

Example 22

(178) Using a Henschel mixer, 91.64 parts by weight of the SmFeN-based magnetic particles obtained in Example 11, 7.34 parts by weight of 12 nylon, 0.51 part by weight of an antioxidant and 1.0 part by weight of the surface-treating agent 1 were mixed with each other, and then the resulting mixture was kneaded (at a kneading temperature of 190 C.) using a twin-screw extrusion kneader to obtain pellets. The thus obtained pellets were injection-molded to produce a bonded magnet.

(179) Various properties of the thus obtained bonded magnets are shown in Table 6.

Comparative Examples 9 to 11

(180) The bonded magnets were produced in the same manner as defined in Examples 12 to 21 except that the kinds of surface-treated NdFeB-based magnetic particles used were changed variously.

Comparative Example 12

(181) The bonded magnet was produced in the same manner as defined in Example 22 except that the kind of surface-treated SmFeB-based magnetic particles used was changed.

(182) TABLE-US-00006 TABLE 6 Magnetic Injection particles MI pressure (BH)max used g/10 min Kg/cm.sup.2 MGOe kJ/m.sup.3 Example 12 Example 1 20 1536 10.33 82.26 Example 13 Example 2 14 1601 10.34 82.33 Example 14 Example 3 15 1555 10.30 82.02 Example 15 Example 4 26 1543 10.34 82.34 Example 16 Example 5 29 1567 10.29 81.94 Example 17 Example 6 25 1512 10.19 81.14 Example 18 Example 7 25 1523 10.09 80.35 Example 19 Example 8 36 1611 10.4 82.82 Example 20 Example 9 20 1668 10.76 85.68 Example 21 Example 10 38 1555 10.57 84.17 Example 22 Example 11 477 1117 11.31 82.33 Comparative Comparative 16 1670 10.02 79.76 Example 9 Example 5 Comparative Comparative 19 1523 10.21 81.32 Example 10 Example 6 Comparative Comparative 18 1638 10.27 81.75 Example 11 Example 7 Comparative Comparative 484 1108 10.16 80.90 Example 12 Example 8 iHC bHc Oe kA/m Oe kA/m Example 12 13993 1113.5 5754 457.9 Example 13 13745 1096.0 5750 458.7 Example 14 13078 1040.7 5759 458.3 Example 15 13529 1076.6 5779 459.9 Example 16 13636 1085.1 5748 457.4 Example 17 13661 1087.1 5711 454.5 Example 18 13093 1041.9 5680 452.0 Example 19 12976 1035.0 5713 455.7 Example 20 13623 1087.0 5847 466.4 Example 21 13391 1068.0 5798 462.5 Example 22 8167 649.9 5566 442.9 Comparative 13924 1108.1 5748 457.4 Example 9 Comparative 13099 1042.3 5745 457.2 Example 10 Comparative 13226 1052.5 5779 459.9 Example 11 Comparative 8196 652.2 5641 448.9 Example 12 Rust Br prevention G T r/s (%) property Example 12 6866 686.6 91.23 Example 13 6873 687.3 91.80 Example 14 6871 687.1 91.07 Example 15 6869 686.9 91.32 Example 16 6799 679.9 91.10 Example 17 6780 678.0 92.11 Example 18 6750 675.0 91.10 Example 19 6921 692.1 91.90 Example 20 7007 700.7 92.21 Example 21 6952 695.2 92.00 Example 22 7068 707.2 96.26 Comparative 6962 696.6 91.39 Example 9 Comparative 6980 698.7 91.91 Example 10 Comparative 6869 687.2 91.09 Example 11 Comparative 7005 696.0 96.45 Example 12

(183) The bonded magnet molded products were evaluated for rust prevention property thereof. As shown in Table 6, it was confirmed that the bonded magnets obtained in Examples 12 to 21 which were produced using the surface-treated NdFeB-based magnetic particles all exhibited an excellent rust prevention property and a high coercive force .sub.iH.sub.c, in particular, a coercive force of not less than 716.2 kA/m (9000 Oe), as compared to those obtained in Comparative Examples 9 to 11. In Example 13, no formation rusts was recognized even after the elapse of 1000 hr, therefore the bonded magnet obtained in Example 13 was especially excellent in rust prevention property. In addition, it was confirmed that the bonded magnet obtained in Example 22 which was produced using the surface-treated SmFeN-based magnetic particles, was excellent in rust prevention property as compared to the bonded magnet obtained in Comparative Example 12. Meanwhile, MI indicating the flowability of the resin composition comprising the SmFeN-based magnetic particles was not less than 400 g/10 min. Therefore, it was confirmed that the resin composition comprising the SmFeN-based magnetic particles had a high flowability.

(184) The results of a rust prevention test of the bonded magnets obtained in Example 13 and Comparative Example 11 are shown in FIG. 1 and FIG. 2, respectively. As a result, it was confirmed that the bonded magnet obtained in Example 13 (FIG. 1) was substantially free from formation of rusts, whereas the bonded magnet obtained in Comparative Example 11 (FIG. 2) suffered from considerable formation of rusts.

(185) The measurement results of irreversible demagnetizing factors of the bonded magnets obtained in Example 13 and Comparative Example 9 as measured at a temperature of 100 C. for 100 hr are shown in FIG. 3. As shown in FIG. 3, it was confirmed that the bonded magnet obtained in Example 13 was improved in irreversible demagnetizing factor by about 2% as compared to the bonded magnet obtained in Comparative Example 11.

INDUSTRIAL APPLICABILITY

(186) In the surface-treated NdFeB-based magnetic particles and SmFeN-based magnetic particles according to the present invention, the silicon compound and the phosphoric acid compound are adhered on the surface of the magnetic particles, so that the bonded magnet produced using the magnetic particles can be enhanced in rust prevention property. Therefore, these surface-treated magnetic particles are suitable as NdFeB-based magnetic particles and SmFeN-based magnetic particles for bonded magnets. According to the present invention, the resulting bonded magnet can be used under more severe corrosive environmental conditions in which any conventional bonded magnets are not usable.