JP2005272925A - R-t-n based magnetic powder and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide high-performance R-T-N based magnetic powder which has high thermal stability and excellent weather resistance and can be oriented to a higher degree than heretofore and also to provide its manufacturing method. <P>SOLUTION: The method for manufacturing the R-T-N based magnetic powder comprises the following steps: a step of mixing R-T-N based coarse powder (wherein, R is one or more kinds among rare earth elements including Y and necessarily contains Sm; and T is Fe or Fe and Co and contains inevitable impurities) into an organic solvent; a step of pulverizing the R-T-N based coarse powder; and a step of drying the resultant pulverized powder. The pulverization of the R-T-N based coarse powder is carried out by adding a surfactant to the organic solvent, and, in this pulverizing step, phosphoric acid is added in a stage midway through the progress of the pulverization of the R-T-N based coarse powder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is in the field of applied magnet products, for example, various types of rotating machines, magnet rolls used in electrostatic development type printers and copiers, various actuators represented by voice coil motors and linear motors, acoustic speakers, buzzers, The present invention relates to a method for producing an R-TN-based magnetic powder used for a magnet applied to a sensor, an adsorption or magnetic field generator, and the R-TN-based magnetic powder.

  Bonded magnets obtained by combining hard magnetic powder and resin have characteristics of higher shape flexibility and higher dimensional accuracy and superior productivity than sintered magnets manufactured by a powder metallurgical method. For example, an R-TN bond magnet composed of a rare earth element (R), a transition metal (T) and nitrogen (N) or an R-T-B bond magnet composed of a rare earth element, a transition metal and boron (B) Compared to ferrite sintered magnets, it has a higher degree of freedom in shape, is excellent in workability, and has high magnetic properties. Therefore, its application to various magnet application fields has been studied. In particular, RTN-based magnetic powder represented by the 2-17 type crystal structure has a higher anisotropic magnetic field than other magnet materials and has a high potential for its magnetic properties. Development is underway.

  However, R-TN magnetic powders that are finely pulverized to develop a coercive force are mainly composed of chemically active rare earth elements and easily oxidized Fe. It deteriorated and did not fully demonstrate the magnetic properties that it originally had. In addition, bond magnets using R-TN magnetic particles have the problem that rust is likely to occur for the same reason, and development of means for improving magnet performance such as anisotropy is insufficient. For this reason, the magnetic properties were not at the expected level. In order to solve the problem that the magnetic powder is easily oxidized, as a conventional method for producing an R-TN magnet, for example, Patent Document 1 discloses that rare earth elements are added by adding phosphoric acid when pulverizing magnet alloy powder. A method for improving the weather resistance of iron-based magnet alloy powders containing iron is disclosed.

In addition, regarding the improvement of magnetic properties, in particular, in extrusion molding, which is the main molding method for anisotropic sheet-shaped RTN magnets, the viscosity of the elastomer component used as a binder is high, so that the particle size is several μm. In the R-T-N fine powder, the magnetic powder is aggregated and the orientation during molding is insufficient, and there is a problem that a magnet having a high BH _max cannot be obtained. As a means for avoiding this, as disclosed in Patent Document 2, for example, a surfactant is added during the kneading of the magnetic powder and the elastomer component in order to enhance the orientation. In Patent Document 3, a predetermined amount of a surfactant is added, pulverized and dried, the average particle size is 1.5 to 3.5 μm, and the surface of the magnetic powder is C: 0.5 to 1. It is disclosed that magnetic powder with high orientation can be obtained by a method for producing magnetic powder having a surface active agent of 5% and H: 0.1 to 0.5%.
JP 2002-124406 A ((0032) to (0034), Table 1) JP 2001-115044 ((0035) to (0036)) JP 2003-293002 A ((0020), Table 1)

  The above-mentioned Patent Document 1 discloses a method for producing a highly weather-resistant magnet powder, and Patent Documents 2 and 3 disclose a method for producing a magnet or the like with improved orientation, both of which have high weather resistance, high thermal stability and high performance. It has not yet provided a method for realizing the orientation simultaneously. Since R-TN magnetic powder has a fundamental problem of being easily oxidized, it has both high weatherability and high thermal stability that should solve this problem, and also has higher orientation and magnetic properties. However, it is required for an R-TN-based magnetic powder as a magnet material. That is, the problem to be solved by the present invention is to provide a high-performance RTN-based magnetic powder having high thermal stability, excellent weather resistance, and at the same time capable of higher orientation than before, and a method for producing the same. It is.

The present invention that has solved the above problems is an R-TN-based coarse powder in an organic solvent (where R is one or more of rare earth elements including Y and an element that always contains Sm, and T is Fe. R—T—N comprising a step of mixing Fe and Co (including inevitable impurities), a step of finely pulverizing the RTN-based coarse powder, and a step of drying the finely pulverized powder. A method for producing a magnetic powder comprising adding a surfactant in the organic solvent to finely pulverize the RTN fine powder, and in the fine pulverization step, the RTN fine powder The phosphoric acid is added at a stage in the middle of the pulverization.
With this manufacturing method, 0.5 to 1.5% by mass of C to 0.5% by mass with respect to the magnetic powder mass of the R-TN magnetic powder while being an anisotropic magnetic powder with an average particle diameter of 1.0 to 3.5 μm. , And 0.1 to 0.5 mass% of H is present on the surface of the magnetic powder, Br is 1.3 T or more, and the magnetic powder is kept at 24 hours in an atmosphere of 90% humidity and 80 ° C. It has become possible to provide an R-T-N type magnetic powder having both high weather resistance, high heat resistance and high orientation with a magnetic force reduction rate of 50% or less.

  Further, in the method for producing the R-TN magnetic powder, an R-T-N magnetic powder having higher orientation is obtained by adding a surfactant again to the organic solvent after the finely pulverized powder is added and stirring. Can be provided.

  In addition, by using a medium stirring mill for pulverization, phosphoric acid can be easily added at a stage in the course of pulverization in the fine pulverization step. By using such a medium stirring mill, phosphoric acid can be added as needed, and phosphoric acid and a surfactant can be reliably acted on the magnetic powder.

  According to the present invention, a magnetic powder containing a surfactant is finely pulverized by a medium agitating mill, a predetermined amount of phosphoric acid is added during the fine pulverization, and after pulverizing to a predetermined particle size, drying is achieved. It is possible to provide a magnetic powder having both heat resistance and good high orientation, and a high-performance bonded magnet formed by blending it.

  As an example of the manufacturing method of the present invention, FIG. As shown in FIG. 1, in the present invention, when pulverizing R-TN system coarse powder in an organic solvent, a predetermined amount of a surfactant is added in advance in the organic solvent and pulverized. A predetermined amount of phosphoric acid is added at a stage in the course of pulverization in the fine pulverization step, and the resulting slurry is dried. Here, the addition of phosphoric acid in the middle of the pulverization may be performed intermittently or continuously during the fine pulverization process. Moreover, intermittent means that it is added in one or two or more times. Thus, by adding the surfactant to the magnetic powder first, and then adding phosphoric acid during pulverization, the surface of the magnetic powder can be coated with the surfactant at the same time as the phosphate. Magnetic powder comprising an aggregate of single crystal grains such as a 2-17 type hard magnetic phase excellent in heat resistance and orientation can be obtained.

  The surfactant is uniformly adhered to the surface of the magnetic powder by adding the R-TN system coarse powder before being finely pulverized in an organic solvent, and as a result, contributes to improving the orientation of the magnetic powder. Further, the surfactant can be added not only before the magnetic powder pulverization, but also post-added to the slurry after addition of phosphoric acid and pulverization, and the post-addition can further improve the orientation of the magnetic powder. However, in the case where the surfactant is not added at the beginning of the pulverization but only after the addition, the adhesion of the surfactant to the surface of the magnetic powder becomes non-uniform, resulting in low orientation and a decrease in (BH) max. .

  On the other hand, it is desirable to add phosphoric acid intermittently or continuously after the average particle size of the R-TN magnetic powder is pulverized to 10 μm or less during pulverization. That is, it is important to add phosphoric acid during pulverization. Thereby, a phosphate film can be uniformly formed on the surface of the magnetic powder, and the weather resistance is improved. If phosphoric acid is added before pulverization, phosphoric acid reacts excessively with the magnetic powder while the particle size is coarse, and the phosphoric acid concentration decreases as pulverization proceeds. The phosphoric acid reaction becomes insufficient, and finally a uniform phosphate film cannot be formed, and the weather resistance is lowered. When phosphoric acid addition is performed after the pulverization is completed, the magnetic particles are reattached and reaggregated, the orientation is deteriorated, and (BH) max is lowered. Moreover, it is more preferable to add phosphoric acid in several steps in the latter half of the pulverization. Furthermore, it is desirable to neutralize by adding an ethanol solution or the like in which 0.02 to 0.10 mol / kg NaOH is dissolved after adding phosphoric acid. The neutralizing agent is not particularly limited as long as it exhibits alkalinity when dissolved in alcohol, but is preferably one that does not form a large amount of precipitates that lower the magnetization by a neutralization reaction. The final particle size of the R-TN magnetic powder is 1.0 to 3.5 μm. Therefore, it is preferable to add phosphoric acid when the average particle size exceeds 3.5 μm. More preferably, it is preferably added when the average particle size is 5 μm or more, more preferably 7 μm or more.

  Thus, the order and timing of adding the surfactant and phosphoric acid are important in the present invention, and magnetic powder having both high weather resistance and high orientation cannot be obtained by methods other than those described above. In other words, considering the function of improving the weather resistance, etc., achieved by the film formation performed by phosphoric acid and the function of improving the orientation achieved by the surfactant, it is considered that it is seemingly preferable to add the surfactant after the film formation by phosphoric acid is completed. However, with such a configuration, high weather resistance and high orientation cannot be realized at the same time. In other words, the present invention simultaneously achieves high weather resistance / heat resistance and high orientation of magnetic powder with a configuration unthinkable by conventional common sense.

Examples of the surfactant used in the present invention include lauric acid, myristic acid, palmitic acid and stearic acid represented by the chemical formula CH ₃ (CH ₂ ) _x COOH. In addition, oleic acid, isostearic acid, and the like can be used as appropriate.
Further, the addition amount of the surfactant is preferably 1.0 to 5.0 mass% with respect to the mass of the R-TN magnetic powder. At this time, the carbon content present on the surface of the magnetic powder is 0.5 to 1.5 mass%. This amount of carbon can be specified using a high-frequency heating infrared absorption method. If the surfactant is less than 1.0% by mass, the surfactant cannot uniformly adhere to the surface of the RTN powder, and the orientation is not sufficient. When the surfactant is more than 5.0% by mass, the volume ratio of the R—T—N phase having hard magnetism decreases and Br becomes small. Further, the bonding with the binder is weakened, and the strength of the molded product is weakened. When the surfactant is added in an amount of 1.0 to 5.0% by mass with respect to the mass of the R—T—N system magnetic powder, the Br of the R—T—N system magnetic powder is 1.3 T or more. Hereinafter, what is simply described as% means mass percentage.

  The amount of phosphoric acid added is preferably 0.1 to 0.3 mol / kg with respect to the weight of the R-TN magnetic powder. If it is less than 0.1 mol / kg, it becomes difficult to form a phosphate film over the entire surface of the magnetic powder, and the weather resistance decreases. On the other hand, if it exceeds 0.3 mol / kg, the corrosion of the magnetic powder becomes prominent and Hcj decreases. By performing this phosphoric acid addition, even if a high-temperature and high-humidity test (measurement of the decrease in coercivity when held in the atmosphere of 90% humidity and 80 ° C. for 24:00), the decrease in coercivity is 50%. Hereinafter, it can be further suppressed to 30% or less, and further to 10% or less.

  In the present invention, the coating phase containing phosphate and a surfactant on the surface of the magnetic powder is present on the surface of the R-TN magnetic powder in a thickness of 5 to 500 nm so as to wrap the R-TN magnetic powder. It is.

  After the nitriding treatment, the average particle size of the magnetic powder is 10 μm or more, and Hcj is small as a practical magnet as it is. In order to increase Hcj, it is necessary to reduce the particle size of the magnetic powder by pulverization. Moreover, in this invention, it is preferable to use a medium stirring mill as a grinder. The advantage of using this pulverizer is that it is easy to arbitrarily add phosphoric acid or the like during pulverization. In addition, a phosphate and surfactant film can be reliably formed on the surface of the magnetic powder. That is, by using a ball mill, jet mill, vibration mill, attritor or the like as another pulverizing means, the average particle size can be reduced to 3.5 μm or less, but phosphoric acid is added during pulverization and uniformly. From the viewpoint of reaction, wet grinding using a medium stirring mill is desirable. Here, the medium agitation mill is a medium to be pulverized (alloy coarse powder for R-TN system magnet) and a medium (for example, pulverizing spheres such as zirconia) in a solvent such as an organic solvent. , A mill that pulverizes the object to be pulverized by forcibly stirring only the solvent, pulverized powder, and medium inside without moving the storage container by the rotational power of a motor or the like. The thing of 3-2 mm was used. A more preferable diameter of the medium is 0.5 to 1.5 mm. In the medium agitating mill, the magnetic powder is easily dispersed during pulverization, and uniform pulverization is realized, so that the particle size distribution becomes sharp. As a result, an R-TN-based magnetic powder having a sharp particle size distribution in which the average particle size after pulverization is 1.5 to 3.5 [mu] m and 0.9 to 6.0 [mu] m is 80% or more is obtained. Can do. As the particle size distribution becomes sharp, coarse powder having a low intrinsic coercive force Hcj is reduced, so that magnetic powder having a higher coercive force and good demagnetization curve squareness can be obtained.

  The average particle size after fine pulverization of the R—T—N magnetic powder of the present invention is preferably 1.0 to 3.5 μm. When the average particle size is less than 1.0 μm, the increase in the specific surface area, or when an anisotropic magnet is produced by applying a magnetic field, the orientation deteriorates, so that Br decreases. When the diameter exceeds 3.5 μm, the intrinsic coercive force Hcj is remarkably reduced. The average particle size is more preferably 1.3 to 2.8 μm, particularly preferably 1.5 to 2.5 μm.

  By molding using the R—T—N system magnetic powder obtained by the production method of the present invention, a magnet having good weather resistance and higher BHmax than the conventional one can be produced. This magnet includes, for example, magnetic powder composed of an aggregate of single crystal grains of 2-17 type hard magnetic phase, and a binder. The magnetic powder is dispersed in the binder. An anisotropic magnet having a high BHmax can be manufactured by rotating the magnetic powder so that the easy magnetization axis (c-axis) is highly oriented.

  Next, the manufacturing method of the magnetic powder used for the grinding | pulverization of this invention is demonstrated. R is one or more of rare earth elements including Y, and Sm is necessarily included. The R content is preferably 20 to 30%, more preferably 22 to 28%. If the R content is less than 20%, the Hcj at room temperature is less than 397.9 kA / m (5 kOe), and if it exceeds 30%, (BH) max is greatly reduced. Furthermore, in order to obtain Hcj ≧ 397.9 kA / m (5 kOe) at room temperature, the ratio of Sm to R is preferably 50% or more, and more preferably 95% or more. R can contain La and unavoidable R components in addition to Sm. If the La content exceeds 5%, the decrease in (BH) max becomes significant, so the La content is preferably 5% or less, and more preferably 3% or less. Note that at least one selected from the group of Y, Ce, Pr, Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu corresponds to the inevitable R component. An inexpensive mixed rare earth alloy such as Sm misch metal can also be used as a raw material alloy for R.

  Replacing part of Fe with Co improves the Curie point, magnetization and oxidation resistance. The Co content is preferably less than 20%, and more preferably less than 10%. If it exceeds 20%, the decrease in magnetization becomes large, which is not preferable. Further, a small part of Fe is selected from the group of Ga, Al, Zn, Sn, Cr, Ni, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Pd, C, Cu, Si, and Ge. Is also preferable because it can improve magnetic properties and corrosion resistance by substituting with one element. The total content of these elements is preferably less than 10%. If it exceeds 10%, the decrease in magnetization becomes remarkable. Further, the anisotropic magnetic powder of the present invention contains a total of 5% or less of at least one unavoidable impurity element selected from the group of F, Na, Mg, Ca and Li, which is inevitably mixed in production. It is acceptable.

  Further, the nitrogen (N) content in the magnetic powder is preferably 2.5 to 4.0%. If the nitrogen content is less than 2.5% or more than 4.0%, Hcj and (BH) max are greatly reduced, making it difficult to obtain useful magnetic properties.

  The RT mother master alloy used for nitriding can be produced by, for example, a high frequency melting method, an arc melting method, a strip casting method, or a reduction / diffusion method (RD method).

R-Fe based master alloy prepared by melting method such as high frequency melting method, arc melting method or strip casting method is homogeneously heated at 1010 to 1280 ° C for 1 to 40 hours in an inert gas (excluding nitrogen) atmosphere A segregation phase such as αFe or SmFe ₃ can be reduced by performing a heat treatment and then cooling to room temperature. If the condition of the homogenization heat treatment is less than 1010 ° C. and less than 1 hour, the diffusion is not sufficient, so αFe, SmFe _3, etc. remain. The composition shift due to becomes remarkable.

Preferred production conditions for producing an RT master alloy by the reduction / diffusion method will be described below. First, an R oxide powder and an Fe powder having an average particle size of about 50 μm are blended into the main component composition of an RT master alloy corresponding to the magnetic powder of the present invention, and further the R oxide in the blend Is added to the above mixture in an amount corresponding to 0.5 to 2 times the amount (100% required for stoichiometry) to be reduced 100% in the chemical reaction formula, and mixed. Next, the mixture is heated in an inert gas atmosphere at 1000 to 1300 ° C. for 1 to 20 hours to reduce the R oxide, and then the reduced R and Fe are sufficiently interdiffused and then cooled to room temperature. If the amount of the reducing agent added is less than 0.5 times the stoichiometrically required amount, a reduction reaction beneficial for industrial production cannot be realized, and if it exceeds 2 times, the amount of Ca remaining in the finally obtained magnetic powder increases and magnetism is increased. Degradation of characteristics is caused. When the heating condition is less than 1000 ° C. and less than 1 hour, the reduction / diffusion reaction beneficial for industrial production does not proceed, and when it exceeds 1300 ° C. and more than 20 hours, the reduction / diffusion reactor deteriorates significantly. The obtained reaction product is put into a cleaning liquid, and reaction by-products such as CaO are washed away, followed by dehydration and heat drying in a vacuum to obtain an RT-based master alloy by a reduction / diffusion method.
A predetermined amount of Ca is inevitably mixed in the RT master alloy. The Ca content is usually 0.4% or less, and can be 0.2% or less, particularly 0.1% or less, by appropriately selecting the washing and drying conditions. The oxygen content in the coarse powder before pulverization after RD washing (average particle size of 10 μm or more) is usually 0.8% or less, and should be 0.4% or less by appropriately selecting the washing and drying conditions. In particular, it can be made 0.2% or less.

The nitriding will be described. In an atmosphere of a mixed gas of 1 to 95% by volume of hydrogen and the balance of nitrogen (hydrogen + nitrogen), or a mixed gas of 10% to 90% of the volume of NH ₃ and a balance of hydrogen (NH ₃ + hydrogen) It is preferable to employ gas nitriding which is heated at 300 to 650 ° C. for 0.1 to 30 hours. When the temperature is less than 300 ° C. and less than 0.1 hour, nitriding is practically not performed. When the temperature exceeds 650 ° C. and more than 30 hours, RN phase, αFe, and amorphous phase are generated, and the magnetic properties are remarkably deteriorated. The heating conditions for gas nitriding are more preferably 400 to 550 ° C. × 0.5 to 20 hours. The pressure of the nitriding gas is preferably 0.2 × 10 ^{5 to} 1.0 × 10 ⁶ Pa (0.2 to 9.87 atm), and 0.5 × 10 ^{5 to} 0.5 × 10 ⁶ Pa (0.49 to 4.94 atm) is more preferable. If it is less than 0.2 × 10 ⁵ Pa (0.2 atm), the nitriding reaction is very slow, and if it exceeds 1.0 × 10 ⁶ Pa (9.87 atm), the cost of the high-pressure gas equipment increases.

  After nitriding, residual magnetic flux density, Hcj and (BH) max can be increased by performing heat treatment at 300 to 600 ° C. for 0.5 to 50 hours in a vacuum atmosphere or an inert gas atmosphere (excluding nitrogen gas). .

The main phase of the RTN magnetic powder of the present invention is preferably a hard magnetic phase having a 2-17 type crystal structure, and unavoidable αFe and / or impurity phases (oxides, etc.), RTN It is preferable to consist only of a hard magnetic phase having a 2-17 type crystal structure other than the phase containing phosphate and surfactant generated on the surface of the system magnetic powder.
In order to obtain Hcj ≧ 716.4 kA / m (9 kOe) at room temperature, the ratio of αFe present in the anisotropic magnetic powder of the present invention needs to be 5% or less in terms of average area ratio, and 3% or less. Of these, 1% or less is particularly preferable.
The identification of hard magnetic phases and unavoidable αFe, and the calculation of the area ratio of each phase were performed using a cross-sectional structure photograph of an anisotropic magnetic powder photographed by an electron microscope or an optical microscope, an electron diffraction result, and an X-ray. Obtained in consideration of diffraction results. For example, it can be obtained by matching a transmission electron micrograph of the cross-sectional structure of the target anisotropic magnetic powder particles and the identification result of the cross-sectional structure.

  The magnet using the magnetic powder of the present invention uses as a molding material a magnetized elastomer composition in which an elastomer component such as acrylic rubber is mixed with a binder containing a surfactant as required. For example, the present invention is rolled by a calender roll while heating to form a sheet, and a method of applying a magnetic field in the thickness direction of the sheet to align and magnetize the magnetic powder, a method of extruding in a magnetic field, etc. It is possible to obtain a bonded magnet having high weather resistance, high thermal stability, and high characteristics utilizing the characteristics of magnetic powder.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
A mother alloy melt of Sm _24.4 Fe _75.6 (mass%) was prepared by high frequency melting, and casted in a mold. The obtained ingot was heated in an argon gas atmosphere at 1100 ° C. for 10 hours, and then subjected to a homogenization heat treatment for cooling to room temperature. The alloy having the Sm ₂ F ₁₇ phase as the main phase is pulverized (coarsely pulverized) to 125 μm or less in an N ₂ atmosphere, classified, and then mixed in a mixed gas of NH ₃ having a partial pressure of 35 kPa and H ₂ having a partial pressure of 65 kPa. Nitriding was performed at 430 ° C. for 10 hours to obtain a powder having a composition (Sm _24.4 Fe _75.6 ) _96.6 N _3.4 (mass%) containing Sm ₂ F ₁₇ N ₃ as a main phase. The average particle size at this time was 24 μm (manufactured by Sympatec, measured by HELOS · RODOS). This magnetic powder is composed of a hard magnetic phase having a Th ₂ Zn ₁₇ type crystal structure. Next, 2 wt% of stearic acid as a surfactant was mixed with this powder with respect to the SmFeN powder, and wet pulverized with a medium stirring mill. The solvent was IPA, and the medium was zirconia (ZrO ₂ ) having a diameter of 0.8 mm. The peripheral speed of the mill was 10 m / sec and pulverized for 60 minutes. At this time, a mixed solution of phosphoric acid aqueous solution and IPA (0.15 mol / kg) was added in 6 portions every 5 minutes 30 minutes after the start of grinding. Subsequently, a solution obtained by dissolving NaOH granules (0.04 mol / kg) in ethanol was added for neutralization. The slurry thus obtained was dried in vacuum at 150 ° C. for 2 hours. Table 1 shows the addition conditions of stearic acid and phosphoric acid. Next, a predetermined amount of finely pulverized magnetic powder and paraffin wax were filled in a VSM copper container and sealed. Thereafter, the copper container was heated to 80 ° C. while applying a parallel magnetic field of 1.59 MA / m (20 kOe) to dissolve the paraffin wax, orient the magnetic powder, and cooled to room temperature to fix the magnetic powder. Next, room temperature magnetic properties of the magnetic powder were measured using a VSM with a maximum applied magnetic field of 1.59 MA / m (20 kOe). Table 2 shows the results obtained by converting the measured values into 100% magnetic powder only (theoretical density is 7.65 Mg / m ³ ) together with other characteristics of the magnetic powder. The 0.9 to 6.0 μm magnetic powder ratio in the table indicates the ratio of the magnetic powder having a particle diameter of 0.9 μm or more and 6.0 μm or less to the whole in the particle size distribution measurement. This ratio and average particle diameter were measured by HELOS · RODOS. Moreover, the Hcj reduction rate in Table 1 indicates the Hcj reduction rate after the obtained magnetic powder was held at 80 ° C. and a humidity of 90% for 24 hours as an evaluation of weather resistance.

(Example 2, Comparative Examples 1-6)
Further, Table 1 and Table 2 show the addition conditions and results in the case where 1 mass% of stearic acid was further added after completion of fine grinding in Example 1 (Example 2), respectively. For comparison, when both stearic acid and phosphoric acid are not added in Example 1 (Comparative Example 1), when only stearic acid is added (Comparative Example 2), when only phosphoric acid is added (Comparative Example 3), When only stearic acid is added after grinding (Comparative Example 4), phosphoric acid is added during grinding, and when stearic acid is added after grinding (Comparative Example 5), phosphoric acid is added to IPA before grinding at once. Table 1 and Table 2 together show the addition conditions and results when the magnetic powder was added and pulverized (Comparative Example 6).

  Subsequently, the sheet-like magnet was shape | molded using the RTN type magnetic powder of Examples 1 and 2, and Comparative Examples 1-6. In forming the sheet-like magnet, 7.2 parts by mass of an alkyl acrylate acrylic resin was added to 92.0 parts by mass of the magnetic powder. As a stabilizer, 0.2 parts by mass of an aromatic amine-based antioxidant was used. Further, 0.6 part by mass of a silane coupling agent was added as a surface treatment material. These were kneaded while being heated in a kneader. The kneaded product was cooled and then pulverized to a particle size of 5 mm or less to obtain a compound for forming a sheet. This compound was stretched by a calender roll whose temperature was adjusted to 50 to 150 ° C. to obtain a sheet-like magnet molded body having a thickness of 1.2 mm. This molded body is cut into a size of 100 mm × 100 mm, and then placed in a magnetic field application device capable of pressing flat surfaces, and both surfaces are heated at a temperature of about 15 to 50 ° C. in a pressure of 1 kPa. An orientation magnetic field of 59 MA / m (20 kOe) was applied in the thickness direction of the sheet. Further, a magnetic field was applied in the opposite direction to that described above under the same conditions. This was repeated and a magnetic field was applied 5 times in the thickness direction. Table 3 shows the values of the magnetic properties of the molded body measured with a BH tracer. Further, Table 3 shows the irreversible demagnetization rate after being kept in the atmosphere at 120 ° C. for 24 hours as the thermal stability of the magnet. Compared to the case where neither surfactant nor phosphoric acid is added (Comparative Example 1), the magnetic properties, thermal stability, and weather resistance are greatly improved in the case of the steps of Examples 1 and 2 of the present invention. It was confirmed that magnetic properties, high thermal stability and high weather resistance were realized at the same time. Conversely, when only one of surfactant or phosphoric acid is added, or even when both are added, the comparative example in which the addition time is different from the present invention, high magnetic properties and high heat No one that could achieve stability and the like at the same time was obtained.

  In the process of Example 1, when lauric acid, myristic acid, palmitic acid, oleic acid, and isostearic acid are used instead of stearic acid (Examples 3 to 7), the evaluation results of the magnetic powder and the evaluation results of the sheet magnet are respectively shown. Tables 4 and 5 show. It can be seen that these surfactants also achieve high magnetic properties, high thermal stability and high weather resistance at the same time as stearic acid.

It is the flowchart figure which showed the outline of an example of the magnetic powder manufacturing method of this invention.

Claims (6)

R-TN-based coarse powder in an organic solvent (where R is one or more of rare earth elements including Y and must contain Sm, T is Fe or Fe and Co, unavoidable impurities) A process for mixing the R-TN system coarse powder, a process for finely pulverizing the R-TN system coarse powder, and a process for drying the fine pulverized powder, A surfactant is added to the organic solvent to finely pulverize the RTN-based coarse powder, and at the stage where the pulverization of the RTN-based coarse powder proceeds in the fine pulverization step. A method for producing an R-TN magnetic powder comprising adding phosphoric acid. The method for producing an R-TN magnetic powder according to claim 1, wherein the phosphoric acid is added at a stage where the particle size of the R-TN coarse powder is pulverized to 10 µm or less. The manufacturing method of the R-T-N type magnetic powder characterized by these. The method for producing an R-TN magnetic powder according to claim 1, wherein a surfactant is added again to the organic solvent after the pulverization is completed, and the resultant is stirred together with the R-TN magnetic powder. Manufacturing method of RTN magnetic powder. The method for producing an R-TN magnetic powder according to claim 1 or 2, wherein a medium stirring mill is used as a pulverizing means. 0.5 to 1.5 mass% of C and 0.1 to 0.5 mass% of H are present on the surface of the magnetic powder with respect to the magnetic powder mass of the R-TN magnetic powder, and Br is 1. An R-TN magnetic powder having a coercive force decrease rate of 3T or more and a magnetic powder held in an atmosphere of 90% humidity and 80 ° C for 24 hours is 50% or less. 6. The RTN-based magnetic powder according to claim 5, wherein the RTN-based magnetic powder is an anisotropic magnetic powder having an average particle size of 1.0 to 3.5 μm. -N-based magnetic powder.

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