Method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, and bonded magnets

Abstract

This invention provides a method for producing anisotropic magnetic powder having excellent heat and water resistance, and a bonded magnet. [Solution] The present invention relates to a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, comprising a phosphate treatment step of adding an inorganic acid to a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphate compound to adjust the pH of the slurry to 1 or more and 4.5 or less to obtain SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface, and an oxidation step of heat-treating the phosphate-coated SmFeN-based anisotropic magnetic powder in an oxygen-containing atmosphere at 200°C or more and 330°C or less.

Description

[Technical Field]

[0001] This invention relates to a method for producing phosphate-coated SmFeN-based anisotropic magnetic powder, and to bonded magnets. [Background technology]

[0002] Bonded magnets using SmFeN-based anisotropic magnetic powder are known as composite components used in motors that operate in humid environments, such as water pumps. In particular, for automotive applications, bonded magnets are required that have excellent not only water resistance and corrosion resistance (oxidation resistance) but also resistance to hot water. For example, Patent Document 1 discloses that the resistance to hot water can be improved by surface-treating SmFeN-based anisotropic magnetic powder with a plasma-treated gas and then forming a coating layer.

[0003] On the other hand, it is known that the coercivity of SmFeN-based anisotropic magnetic powder can be improved by forming a phosphate coating on its surface. For example, Patent Document 2 discloses a method for forming a phosphate coating on the surface of SmFeN-based anisotropic magnetic powder by adding a pH-adjusted phosphate treatment solution containing orthophosphoric acid to a slurry containing SmFeN-based anisotropic magnetic powder with water as the solvent.

[0004] Patent Document 3 discloses a method in which a pH-adjusted phosphoric acid treatment solution is added to a slurry containing large-particle SmFeN-based anisotropic magnetic powder in an organic solvent, and then the SmFeN-based anisotropic magnetic powder is pulverized to reduce its particle size, while also forming a phosphate coating on the surface of the SmFeN-based anisotropic magnetic powder.

[0005] Patent Document 4 discloses that the coercivity of magnetic powder is increased by subjecting a phosphate-coated SmFeN-based anisotropic magnetic powder to a slow oxidation treatment. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-050904 [Patent Document 2] Japanese Patent Publication No. 2020-056101 [Patent Document 3] Japanese Patent Publication No. 2017-210662 [Patent Document 4] Japanese Patent Publication No. 2014-160794 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a method for producing anisotropic magnetic powder having excellent heat and water resistance, and a bonded magnet. [Means for solving the problem]

[0008] A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to one aspect of the present invention includes a phosphate treatment step in which an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphate compound to adjust the pH of the slurry to 1 or more and 4.5 or less in order to obtain SmFeN-based anisotropic magnetic powder with a phosphate coating on its surface, and an oxidation step in which the phosphate-coated SmFeN-based anisotropic magnetic powder is heat-treated at 200°C or more and 330°C or less in an oxygen-containing atmosphere.

[0009] Furthermore, a bonded magnet according to one aspect of the present invention comprises a phosphate-coated SmFeN-based anisotropic magnetic powder having a phosphate content greater than 0.5% by mass, and polypropylene, and the retention rate of the total flux after being held for 1000 hours under immersion conditions in hot water at 120°C is 95% or more of the value before the test.

[0010] Furthermore, a magnetic powder according to one aspect of the present invention is a phosphate-coated SmFeN-based anisotropic magnetic powder having a phosphate content greater than 0.5% by mass, wherein the phosphate coating present on the surface of the SmFeN-based anisotropic magnetic powder has a first region and a second region, the Sm atom concentration of the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, the Sm atom concentration of the first region is 0.5 times or more and 4 times or less the Fe atom concentration of the first region, and the second region is located on the first region, the Sm atom concentration of the second region is 1 / 3 times or less the Fe atom concentration of the second region. [Effects of the Invention]

[0011] According to the above embodiment, a method for producing anisotropic magnetic powder having excellent heat and water resistance and a bonded magnet can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This shows the relationship between immersion time and irreversible demagnetization rate under hot water immersion conditions for bonded magnets. [Figure 2] The STEM-EDX mapping analysis results for the magnetic powders of Example 1 and Comparative Example 2 are shown. [Figure 3] The results of the EDX line analysis of the magnetic powder from Example 1 are shown. [Figure 4] The results of the EDX line analysis of the magnetic powder in Comparative Example 2 are shown. [Figure 5] A schematic diagram of one aspect of the phosphate coating is shown. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments shown below are examples for embodying the technical idea of the present invention, and the present invention is not limited to the following. In this specification, the term "step" includes not only an independent step but also a step in which the intended purpose of the step is achieved even if it cannot be clearly distinguished from other steps. Also, the numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively.

[0014] <Method for Producing Phosphate-Coated SmFeN-Based Anisotropic Magnetic Powder> The method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to this embodiment is By adding an inorganic acid to a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphate compound, and adjusting the pH of the slurry to 1 or more and 4.5 or less, a phosphate-treated step of obtaining SmFeN-based anisotropic magnetic powder coated with phosphate on the surface, and It is characterized by including an oxidation step of heat-treating the phosphate-coated SmFeN-based anisotropic magnetic powder at 200°C or higher and 330°C or lower in an oxygen-containing atmosphere.

[0015] In the phosphate treatment step, an inorganic acid is added to a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphate compound to adjust the pH of the slurry to between 1 and 4.5, thereby obtaining SmFeN-based anisotropic magnetic powder coated with phosphate on its surface. The phosphate-coated SmFeN-based anisotropic magnetic powder is formed when metal components (e.g., iron or samarium) contained in the SmFeN-based anisotropic magnetic powder react with phosphate components contained in the phosphate compound, causing phosphates (e.g., iron phosphate, samarium phosphate) to precipitate on the surface of the SmFeN-based anisotropic magnetic powder. According to this embodiment, by adding an inorganic acid to adjust the pH of the slurry to between 1 and 4.5, the amount of phosphate precipitated can be increased compared to when no inorganic acid is added, resulting in phosphate-coated SmFeN-based anisotropic magnetic powder with a thicker coating. Furthermore, according to this embodiment, by using water as the solvent, smaller particle sizes of phosphate precipitates compared to when an organic solvent is used, resulting in phosphate-coated SmFeN-based anisotropic magnetic powder with a denser coating.

[0016] Next, in the oxidation process, the obtained phosphate-coated SmFeN-based anisotropic magnetic powder is heat-treated at a high temperature of 200°C to 330°C in an oxygen-containing atmosphere. As a result, the surface of the phosphate-coated SmFeN-based anisotropic magnetic powder base material is oxidized, forming a thick iron oxide layer, which is expected to improve the water resistance of the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0017] [Phosphating treatment process] The method for preparing a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphate compound is not particularly limited, but for example, it can be obtained by mixing SmFeN-based anisotropic magnetic powder and an aqueous phosphoric acid solution containing a phosphate compound with water as the solvent. The content of SmFeN-based anisotropic magnetic powder in the slurry is, for example, 1% by mass or more and 50% by mass or less, and is preferably 5% by mass or more and 20% by mass or less from the viewpoint of productivity. The content of the phosphate component (PO4) in the slurry is, for example, 0.01% by mass or more and 10% by mass or less in terms of PO4 equivalent, and is preferably 0.05% by mass or more and 5% by mass or less from the viewpoint of the reactivity of the phosphate component and productivity.

[0018] A phosphoric acid aqueous solution is obtained by mixing a phosphoric acid compound with water. Examples of phosphoric acid compounds include phosphates such as orthophosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, zinc phosphate, and calcium phosphate, as well as inorganic phosphoric acids such as hypophosphorous acid, hypophosphite, pyrophosphoric acid, and polyphosphoric acid, and organic phosphoric acids. One of these may be used alone, or two or more may be used in combination. Furthermore, to improve water resistance, corrosion resistance, and the magnetic properties of magnetic powders through coating, oxo salts such as molybdate, tungstate, vanadate, and chromate, oxidizing agents such as sodium nitrate and sodium nitrite, and chelating agents such as EDTA may be added.

[0019] The concentration of phosphoric acid (in PO4 equivalent) in the aqueous phosphoric acid solution is, for example, 5% by mass or more and 50% by mass or less, and is preferably 10% by mass or more and 30% by mass or less from the viewpoint of solubility of phosphoric acid compounds, storage stability, and ease of chemical treatment. The pH of the aqueous phosphoric acid solution is, for example, 1 or more and 4.5 or less, and is preferably 1.5 or more and 4 or less from the viewpoint of being able to easily control the precipitation rate of phosphates. The pH can be adjusted with dilute hydrochloric acid, dilute sulfuric acid, etc.

[0020] In the phosphoric acid treatment process, the pH of the slurry is adjusted to between 1 and 4.5 by adding an inorganic acid, preferably between 1.6 and 3.9, and more preferably between 2 and 3. Below pH 1, the phosphate-coated SmFeN-based anisotropic magnetic powders tend to aggregate, starting from locally precipitated phosphates, and the coercivity tends to decrease. Above pH 4.5, the amount of phosphate precipitated decreases, resulting in insufficient coating and a tendency for the coercivity to decrease. Examples of inorganic acids to be added include hydrochloric acid, nitric acid, sulfuric acid, boric acid, and hydrofluoric acid. During the phosphoric acid treatment process, inorganic acids are added as needed to maintain the pH within the above range. Inorganic acids are used from the viewpoint of wastewater treatment, but organic acids can be used in combination depending on the purpose. Examples of organic acids include acetic acid, formic acid, and tartaric acid. A mixture of inorganic and organic acids may also be used.

[0021] The phosphoric acid treatment step may be carried out such that the lower limit of the phosphate content in the resulting phosphate-coated SmFeN-based anisotropic magnetic powder is greater than 0.5% by mass. The lower limit of the phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder obtained in the phosphoric acid treatment step is preferably 0.55% by mass or more, and particularly preferably 0.75% by mass or more. The upper limit of the phosphate content is preferably 4.5% by mass or less, preferably 2.5% by mass or less, and particularly preferably 2% by mass or less. When the phosphate content is 0.5% by mass or less, the effect of coating with phosphate tends to be small, and when it exceeds 4.5% by mass, the phosphate-coated SmFeN-based anisotropic magnetic powders tend to aggregate and the coercivity decreases. The phosphate content of the magnetic powder is expressed in terms of PO4 molecules, measured using ICP emission spectrometry (ICP-AES).

[0022] The adjustment of a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphate compound to a pH range of 1 to 4.5 can be carried out for 10 minutes or more, and is preferably carried out for 30 minutes or more to reduce the area where the coating is thin. Initially, the pH rises rapidly, so the interval between adding the inorganic acid for pH control is short, but as the coating progresses, the pH fluctuations gradually slow down, and the interval between adding the inorganic acid lengthens, allowing the reaction endpoint to be determined.

[0023] [Oxidation process after phosphoric acid treatment] In the oxidation process following the phosphoric acid treatment, the SmFeN-based anisotropic magnetic powder coated with the phosphate obtained in the phosphoric acid treatment process is subjected to oxidation by heat treatment at a temperature of 200°C to 330°C in an oxygen-containing atmosphere. By heat-treating the phosphate-coated SmFeN-based anisotropic magnetic powder at a high temperature of 200°C to 330°C in an oxygen-containing atmosphere, the surface of the phosphate-coated base material SmFeN-based anisotropic magnetic powder is oxidized, forming a thick iron oxide layer, and improving the hot water resistance of the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0024] The oxidation step after phosphoric acid treatment is carried out by heat treatment of the phosphate-coated SmFeN-based anisotropic magnetic powder in an oxygen-containing atmosphere. The reaction atmosphere preferably contains oxygen in an inert gas such as nitrogen or argon. The oxygen concentration is preferably 3% to 21%, and more preferably 3.5% to 10%. During the oxidation reaction, it is preferable to exchange the gas at a flow rate of 2 L / min to 10 L / min per kg of magnetic powder.

[0025] The heat treatment temperature in the oxidation step after phosphoric acid treatment is 200°C to 330°C, preferably 200°C to 250°C, and more preferably 210°C to 230°C. Below 200°C, the formation of the iron oxide layer is insufficient, and the resistance to hot water tends to decrease. Above 330°C, the iron oxide layer is formed excessively, and the coercivity tends to decrease. The heat treatment time is preferably 3 hours to 10 hours.

[0026] The oxidation step after phosphoric acid treatment is preferably carried out such that the phosphate coating on the surface of the SmFeN-based anisotropic magnetic powder has a first region, the Sm atom concentration in the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, and the Sm atom concentration in the first region is 0.5 times or more and 4 times or less than the Fe atom concentration in the first region. The Sm atom concentration in the first region can be 1.02 times or more than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.2 times or more. The Sm atom concentration in the first region can be 3 times or less than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder. The Sm atom concentration in the first region is preferably 0.6 times or more and 3.5 times or less than the Fe atom concentration in the first region, and more preferably 0.7 times or more and 3 times or less. The atomic concentrations (atm%) of the SmFeN-based anisotropic magnetic powder and the first region are determined by averaging the atomic concentrations (atm%) in each region obtained from STEM-EDX line analysis.

[0027] <Phosphate-coated SmFeN-based anisotropic magnetic powder> The phosphate-coated SmFeN-based anisotropic magnetic powder of this embodiment is characterized by having a phosphate content greater than 0.5% by mass. The phosphate-coated SmFeN-based anisotropic magnetic powder is obtained by the method described above.

[0028] The phosphate-coated SmFeN-based anisotropic magnetic powder preferably has an exothermic start temperature of 170°C or higher in DSC, more preferably 200°C or higher, and particularly preferably 260°C or higher. The exothermic start temperature in DSC is a comprehensive evaluation of the density, thickness, and oxidation resistance of the phosphate coating, and high coercivity is obtained when it is 170°C or higher. The exothermic start temperature in DSC can be measured under the conditions described in the examples.

[0029] In the XRD diffraction pattern, the phosphate-coated SmFeN-based anisotropic magnetic powder has a ratio (I) / (II) of 2.0 × 10⁻¹⁰ of the diffraction peak intensity (I) of the (110) plane of αFe to the peak intensity (II) of the (300) plane of the SmFeN-based magnetic powder.-2 Preferably, it is 1.0 × 10 -2 The following is more preferable: The diffraction peak intensity (I) of the (110) plane of αFe represents the amount of αFe present as an impurity, and the aforementioned ratio (I) / (II) is 2.0 × 10⁻⁶. -2 High coercivity can be obtained when the following conditions are met. The diffraction peak intensity in the XRD diffraction pattern was measured using a powder X-ray crystal diffractometer (Rigaku, X-ray wavelength: CuKa1), and the diffraction peak intensity of the (110) plane of αFe was taken as Sm2Fe. 17 The αFe peak height ratio can be obtained by dividing the peak intensity of the N3 (300) plane by 10,000 and then multiplying by 10,000. A low αFe peak height ratio means that the content of αFe, an impurity, is low.

[0030] The phosphate-coated SmFeN-based anisotropic magnetic powder preferably has a carbon content of 1000 ppm or less, and more preferably 800 ppm or less. The carbon content indicates the amount of organic impurities in the phosphate. If the carbon content exceeds 1000 ppm, the organic impurities decompose when the phosphate-coated SmFeN-based anisotropic magnetic powder is exposed to high temperatures during the process of manufacturing bonded magnets, causing defects in the coating and a tendency for the coercivity to decrease. The carbon content can be measured by the TOC method.

[0031] The thickness of the phosphate coating in phosphate-coated SmFeN-based anisotropic magnetic powder is preferably between 10 nm and 200 nm, from the viewpoint of the coercivity of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the phosphate coating can be measured by performing compositional analysis by line analysis using EDX in a cross-section of the phosphate-coated SmFeN-based anisotropic magnetic powder.

[0032] Preferably, the phosphate coating on the surface of the SmFeN-based anisotropic magnetic powder has a first region, the Sm atom concentration in the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, and the Sm atom concentration in the first region is 0.5 times or more and 4 times or less than the Fe atom concentration in the first region.

[0033] The Sm atom concentration in the first region can be 1.02 times or more the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.2 times or more. The Sm atom concentration in the first region can be 3 times or less the Sm atom concentration in the SmFeN-based anisotropic magnetic powder. The Sm atom concentration in the first region is preferably 0.6 times or more and 3.5 times or less the Fe atom concentration in the first region, and more preferably 0.7 times or more and 3 times or less. When the relationship between the Sm atom concentration and Fe atom concentration in the first region is within the above range, the Fe atom concentration near the surface of the SmFeN-based anisotropic magnetic powder becomes lower, and the content of samarium phosphate, which has low solubility in water, increases, which tends to further improve water resistance.

[0034] Here, the first region is the region encompassing the layer showing the maximum peak of P (phosphorus) in the STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the first region can be 1 nm to 200 nm, and preferably 3 nm to 100 nm. The atomic concentrations (atm%) of each element in the first region, the second region (described later), and the high-concentration Mo layer are determined by averaging the atomic concentrations (atm%) in each region in the STEM-EDX line analysis.

[0035] The phosphate coating has a second region on top of the first region, and it is preferable that the Sm atom concentration in the second region is 1 / 3 or less of the Fe atom concentration in the second region. More preferably, the Sm atom concentration in the second region is 1 / 5 or less of the Fe atom concentration in the second region, and even more preferably 1 / 10 or less. The Sm atom concentration in the second region can be 0 or more of the Fe atom concentration in the second region. Here, the second region is the region that encompasses the layer showing the maximum Fe (iron) peak in the phosphate coating in the STEM-EDX line pro analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the second region can be 1 nm to 200 nm, and is preferably 5 nm to 100 nm. As described above, when the second region is on top of the first region, by including an iron-containing region in addition to the phosphate coating, even if there are areas where the thickness of the phosphate coating is relatively thin, it is reinforced by the iron-containing region, and the water resistance tends to be further improved.

[0036] The Fe atom concentration in the second region is preferably at least twice the Fe atom concentration in the first region, and more preferably at least three times. The Fe atom concentration in the second region is preferably 10 times or less the Fe atom concentration in the first region. Furthermore, the Fe atom concentration in the second region is preferably 0.25 to 1 times the Fe atom concentration in the base material, SmFeN-based anisotropic magnetic powder, and more preferably 0.5 to 0.8 times. It is also preferable that the P (phosphorus) atom concentration in the second region is lower than the P atom concentration in the first region. The P atom concentration in the second region is preferably 1 / 5 or less the P atom concentration in the first region, and more preferably 1 / 10 or less. By setting the P atom concentration in the second region as described above, water resistance tends to improve further.

[0037] When molybdate is added to the reaction slurry during the phosphate treatment process, the phosphate coating may have a high-concentration Mo layer within the first and second regions. It is preferable that three high-concentration Mo layers exist in the phosphate coating, i.e., it is preferable that three Mo (molybdenum) peaks are present in the STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. Furthermore, the high-concentration Mo layer can also be confirmed in STEM-EDX mapping analysis. Figure 5 shows a schematic diagram of the phosphate coating when the high-concentration Mo layer exists on the outermost surface, within the first region, and on the outermost surface of the second region of the phosphate-coated SmFeN-based anisotropic magnetic powder, which is the base material. The high-concentration Mo layer is a region encompassing the layer showing the Mo (molybdenum) peak in the STEM-EDX line analysis of the phosphate-coated SmFeN-based anisotropic magnetic powder. The thickness of the high-concentration Mo layer is preferably 1 nm to 40 nm. As mentioned above, when there are three high-concentration Mo layers, the phosphate coating has a more layered structure, which tends to improve water resistance.

[0038] The Mo atom concentration in the high-Mo concentration layer is preferably 1.1 to 40 times, and more preferably 2 to 20 times, the Mo atom concentration in the first region other than the high-Mo concentration layer. Furthermore, the Mo atom concentration in the high-Mo concentration layer is preferably 1.1 to 20 times, and more preferably 2 to 10 times, the Mo atom concentration in the second region other than the high-Mo concentration layer. The Sm atom concentration, Fe atom concentration, and Mo atom concentration can be measured by compositional analysis using EDX line analysis on phosphate-coated SmFeN-based anisotropic magnetic powder.

[0039] [Silica treatment process] The SmFeN-based anisotropic magnetic powder after phosphoric acid treatment may be subjected to silica treatment as needed. The oxidation resistance can be improved by forming a silica thin film on the magnetic powder. The silica thin film can be formed, for example, by mixing an alkyl silicate, a phosphate-coated SmFeN-based anisotropic magnetic powder, and an alkaline solution.

[0040] [Silane coupling treatment process]The magnetic powder after silica treatment may be further treated with a silane coupling agent. By treating the magnetic powder on which a silica thin film has been formed with silane coupling, a coupling agent film is formed on the silica thin film, improving the magnetic properties of the magnetic powder, as well as improving its wettability with the resin and the strength of the magnet.Silane coupling agents are not particularly limited and should be selected according to the type of resin, but examples include 3-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, and γ-methyl Captopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethylenedisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyl[3-(trimethoxysilyl)propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, vinyl Trichlorosilane, vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, oleidopropyltriethoxysilane, γ-isocyanatetopropyltriethoxy Silane coupling agents include silane, polyethoxydimethylsiloxane, polyethoxymethylsiloxane, bis(trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)tetrasulfan, γ-isocyanatetopropyltrimethoxysilane, vinylmethyldimethoxysilane, 1,3,5-N-tris(3-trimethoxysilylpropyl)isocyanurate, t-butylcarbamatetrialkoxysilane, and N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine.These silane coupling agents may be used alone or in combination of two or more. The addition amount of the silane coupling agent is preferably 0.2 parts by weight or more and 0.8 parts by weight or less, more preferably 0.25 parts by weight or more and 0.6 parts by weight or less, based on 100 parts by weight of the magnetic powder. If it is less than 0.2 parts by weight, the effect of the silane coupling agent is small, and if it exceeds 0.8 parts by weight, the magnetic properties of the magnetic powder and the magnet tend to deteriorate due to aggregation of the magnetic powder.

[0041] After the phosphoric acid treatment step, after the oxidation step, after the silica treatment, or after the silane coupling treatment, the SmFeN-based anisotropic magnetic powder can be filtered, dehydrated, and dried by a conventional method.

[0042] <Method for producing SmFeN-based anisotropic magnetic powder> The SmFeN-based anisotropic magnetic powder used in the phosphoric acid treatment step is not particularly limited. For example, a step of mixing a solution containing Sm and Fe with a precipitating agent to obtain a precipitate containing Sm and Fe (precipitation step), a step of firing the precipitate to obtain an oxide containing Sm and Fe (oxidation step), a step of heat-treating the oxide in an atmosphere containing a reducing gas to obtain a partial oxide (pretreatment step), a step of reducing the partial oxide (reduction step), and a step of nitriding the alloy particles obtained in the reduction step (nitriding step) can be preferably used those produced by a method including the above steps.

[0043] [Precipitation step] In the precipitation step, a Sm raw material and an Fe raw material are dissolved in a strongly acidic solution to prepare a solution containing Sm and Fe. When obtaining Sm2Fe 17 N3 as the main phase, the molar ratio of Sm and Fe (Sm:Fe) is preferably 1.5:17 to 3.0:17, more preferably 2.0:17 to 2.5:17. Raw materials such as La, W, Co, Ti, Sc, Y, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Tm, Lu may be added to the above-mentioned solution.

[0044] The Sm and Fe raw materials are not limited as long as they can dissolve in a strongly acidic solution. For example, in terms of availability, samarium oxide can be used as the Sm raw material and FeSO4 as the Fe raw material. The concentration of the solution containing Sm and Fe can be adjusted as appropriate within the range in which the Sm and Fe raw materials are substantially soluble in the acidic solution. In terms of solubility, sulfuric acid can be used as the acidic solution.

[0045] An insoluble precipitate containing Sm and Fe is obtained by reacting a solution containing Sm and Fe with a precipitating agent. Here, the solution containing Sm and Fe only needs to be a solution containing Sm and Fe when reacted with the precipitating agent. For example, the raw materials containing Sm and Fe may be prepared as separate solutions, and each solution may be added dropwise to react with the precipitating agent. Even when preparing the raw materials as separate solutions, they should be adjusted appropriately so that each raw material is substantially soluble in the acidic solution. The precipitating agent is not limited as long as it is an alkaline solution that reacts with a solution containing Sm and Fe to produce a precipitate, and examples include aqueous ammonia and caustic soda, with caustic soda being preferred.

[0046] For the precipitation reaction, a method is preferred in which a solution containing Sm and Fe and a precipitant are added dropwise to a solvent such as water, as this allows for easy adjustment of the particle properties of the precipitate. By appropriately controlling the supply rate of the solution containing Sm and Fe and the precipitant, the reaction temperature, the concentration of the reaction solution, and the pH during the reaction, a precipitate with a homogeneous distribution of constituent elements, a sharp particle size distribution, and a well-formed powder shape can be obtained. Using such a precipitate improves the magnetic properties of the final magnetic powder product. The reaction temperature can be 0 to 50°C, and is preferably 35 to 45°C. The concentration of the reaction solution is preferably 0.65 mol / L to 0.85 mol / L as the total concentration of metal ions, and more preferably 0.7 mol / L to 0.84 mol / L. The reaction pH is preferably 5 to 9, and more preferably 6.5 to 8.

[0047] The anisotropic magnetic powder particles obtained in the precipitation process roughly determine the particle size, shape, and particle size distribution of the final magnetic powder. When the particle size of the obtained particles is measured using a laser diffraction wet particle size analyzer, it is preferable that the size and distribution of the entire powder fall approximately within the range of 0.05 to 20 μm, preferably 0.1 to 10 μm. Furthermore, the average particle size of the anisotropic magnetic powder particles is measured as the particle size corresponding to 50% of the volume cumulative from the small particle size side in the particle size distribution, and it is preferable that it falls within the range of 0.1 to 10 μm.

[0048] After separating the precipitate, it is preferable to desolvent the separated material to prevent the precipitate from redissolving in the remaining solvent during the subsequent oxidation heat treatment, which can lead to aggregation of the precipitate, changes in particle size distribution, powder particle size, etc., as the solvent evaporates. Specifically, a method for desolvation is to dry the material in an oven at 70-200°C for 5-12 hours, for example, when water is used as the solvent.

[0049] The process may include a step of separating and washing the precipitate after the precipitation step. The washing step is performed when the conductivity of the supernatant solution is 5 mS / m 2 Continue as needed until the following is achieved. For example, to separate the precipitate, a solvent (preferably water) can be added to the obtained precipitate and mixed, after which filtration, decantation, or the like can be used.

[0050] [Oxidation process] The oxidation process involves calcining the precipitate formed in the precipitation process to obtain an oxide containing Sm and Fe. For example, the precipitate can be converted into an oxide by heat treatment. When heat treating the precipitate, it must be done in the presence of oxygen, for example, in an atmospheric environment. Furthermore, because it must be done in the presence of oxygen, it is preferable that the nonmetallic portion of the precipitate contains oxygen atoms.

[0051] The heat treatment temperature in the oxidation process (hereinafter referred to as the oxidation temperature) is not particularly limited, but is preferably 700 to 1300°C, and more preferably 900 to 1200°C. Below 700°C, oxidation is insufficient, and above 1300°C, the desired shape, average particle size, and particle size distribution of the magnetic powder tend not to be obtained. The heat treatment time is also not particularly limited, but is preferably 1 to 3 hours.

[0052] The resulting oxides exhibit sufficient microscopic mixing of Sm and Fe within the oxide particles, and the shape and particle size distribution of the precipitate are reflected in the oxide particles.

[0053] [Pre-treatment process] The pretreatment step is a process in which an oxide containing Sm and Fe is heat-treated in a reducing gas atmosphere to obtain a partial oxide in which a portion of the oxide has been reduced.

[0054] Here, a partially oxide refers to an oxide in which a portion of the oxide has been reduced. The oxygen concentration of the oxide is not particularly limited, but it is preferably 10% by mass or less, and more preferably 8% by mass or less. If it exceeds 10% by mass, the exothermic reaction with Ca during the reduction process increases, and the firing temperature rises, which tends to result in particles with abnormal particle growth. The oxygen concentration of the partially oxide can be measured by non-dispersive infrared absorption spectroscopy (ND-IR).

[0055] The reducing gas can be appropriately selected from hydrocarbon gases such as hydrogen (H2), carbon monoxide (CO), and methane (CH4), but hydrogen gas is preferred in terms of cost, and the gas flow rate is appropriately adjusted within a range where oxides do not scatter. The heat treatment temperature in the pretreatment step (hereinafter referred to as the pretreatment temperature) is in the range of 300°C to 950°C, preferably 400°C or higher, more preferably 750°C or higher, and preferably less than 900°C. When the pretreatment temperature is 300°C or higher, the reduction of oxides containing Sm and Fe proceeds efficiently. When the temperature is 950°C or lower, particle growth and segregation of oxide particles are suppressed, and the desired particle size can be maintained. Furthermore, when hydrogen is used as the reducing gas, it is preferable to adjust the thickness of the oxide layer used to 20 mm or less, and to adjust the dew point in the reaction furnace to -10°C or lower.

[0056] [Reduction Process] The reduction process is a process of obtaining alloy particles by heat-treating the partial oxide in the presence of a reducing agent at a temperature of 920°C to 1200°C. For example, reduction is carried out by contacting the partial oxide with a calcium melt or calcium vapor. The heat treatment temperature is preferably 950°C to 1150°C, and more preferably 980°C to 1100°C, from the viewpoint of magnetic properties. The heat treatment time is preferably less than 120 minutes, more preferably less than 90 minutes, from the viewpoint of carrying out the reduction reaction more uniformly, and the lower limit of the heat treatment time is preferably 10 minutes or more, and more preferably 30 minutes or more.

[0057] Metallic calcium is used in granular or powder form, but its particle size is preferably 10 mm or less. This allows for more effective suppression of aggregation during the reduction reaction. Furthermore, metallic calcium can be added in an amount of 1.1 to 3.0 times the reaction equivalent (the stoichiometric amount required to reduce Sm oxide, and including the amount required to reduce Fe if it is in oxide form), with 1.5 to 2.0 times being preferable.

[0058] In the reduction process, a disintegration accelerator can be used as needed together with metallic calcium as a reducing agent. This disintegration accelerator is appropriately used to promote the disintegration and granulation of the product during the subsequent water washing process. Examples thereof include alkaline earth metal salts such as calcium chloride and alkaline earth metal oxides such as calcium oxide. These disintegration accelerators are used at a ratio of 1 to 30% by mass, preferably 5 to 28% by mass, based on the Sm oxide used as the Sm source.

[0059] [Nitriding process] The nitriding process is a process of obtaining anisotropic magnetic particles by subjecting the alloy particles obtained in the reduction process to a nitriding treatment. Since the particulate precipitate obtained in the above-described precipitation process is used, porous massive alloy particles are obtained in the reduction process. As a result, heat treatment can be immediately performed in a nitrogen atmosphere for nitriding without performing a pulverization treatment, so that nitriding can be performed uniformly.

[0060] The heat treatment temperature (hereinafter referred to as the nitriding temperature) in the nitriding treatment of the alloy particles is preferably 300 to 600°C, particularly preferably 400 to 550°C, and this is performed by replacing the atmosphere with a nitrogen atmosphere within this temperature range. The heat treatment time may be set to such an extent that the nitriding of the alloy particles is sufficiently uniform.

[0061] The product obtained after the nitriding process contains, in addition to the magnetic particles, by-produced CaO, unreacted metallic calcium, etc., and in some cases, these are in a sintered massive state in which they are combined. Therefore, in that case, this product can be put into cooling water to separate CaO and metallic calcium from the magnetic particles as a calcium hydroxide (Ca(OH)2) suspension. Further, the remaining calcium hydroxide may be sufficiently removed by washing the magnetic particles with acetic acid or the like.

[0062] The SmFeN-based anisotropic magnetic powder has a 17 crystal structure of the Th2Zn x type, and the general formula is Sm 100-x-y Fe yThis nitride is composed of the rare earth metal samarium (Sm), iron (Fe), and nitrogen (N), represented by the formula shown. Here, it is preferable that x is between 8.1 atomic% and 10 atomic%, y is between 13.5 atomic% and 13.9 atomic%, and the remainder is mainly Fe.

[0063] The average particle size of the SmFeN-based anisotropic magnetic powder is between 2 μm and 5 μm, preferably between 2.5 μm and 4.8 μm. Below 2 μm, the amount of magnetic powder filling the bonded magnet decreases, resulting in reduced magnetization. Above 5 μm, the coercivity of the bonded magnet tends to decrease. Here, the average particle size is the particle size measured under dry conditions using a laser diffraction particle size distribution analyzer.

[0064] The particle size D10 of the SmFeN-based anisotropic magnetic powder is between 1 μm and 3 μm, and preferably between 1.5 μm and 2.5 μm. If the particle size is less than 1 μm, the amount of magnetic powder filling the bonded magnet becomes small, resulting in a decrease in magnetization. On the other hand, if the particle size exceeds 3 μm, the coercivity of the bonded magnet tends to decrease. Here, D10 is the particle size that corresponds to 10% of the cumulative value of the volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0065] The particle size D50 of the SmFeN-based anisotropic magnetic powder is between 2.5 μm and 5 μm, and preferably between 2.7 μm and 4.8 μm. Below 2.5 μm, the amount of magnetic powder filling the bonded magnet decreases, resulting in reduced magnetization, and above 5 μm, the coercivity of the bonded magnet tends to decrease. Here, D50 refers to the particle size corresponding to 50% of the cumulative value of the volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0066] The particle size D90 of the SmFeN-based anisotropic magnetic powder is between 3 μm and 7 μm, with a preference of 4 μm and 6 μm. Below 3 μm, the amount of magnetic powder filling the bonded magnet becomes small, resulting in decreased magnetization, and above 7 μm, the coercivity of the bonded magnet tends to decrease. Here, D90 refers to the particle size corresponding to 90% of the cumulative value of the volume-based particle size distribution of the SmFeN-based anisotropic magnetic powder.

[0067] The span defined below for SmFeN-based anisotropic magnetic powders: Span = (D90 - D10) / D50 From the viewpoint of coercivity, it should be 2 or less, and preferably 1.5 or less.

[0068] The circularity of SmFeN-based anisotropic magnetic powder is not particularly limited, but is preferably 0.5 or higher, and more preferably 0.6 or higher. Below 0.5, the fluidity deteriorates, causing stress between particles during molding and reducing magnetic properties. Here, the circularity is measured by binarizing SEM images taken at 3000x magnification using image processing, and determining the circularity for each particle. The circularity defined in this invention refers to the average value of the circularity obtained by measuring approximately 1000 to 10000 particles. Generally, the circularity increases as there are more particles with smaller particle sizes, so the circularity is measured for particles of 1 μm or larger. The definition formula for measuring circularity is: Circularity = (4πS / L 2 ) is used, where S is the two-dimensional projected area of ​​the particle and L is the two-dimensional projected perimeter.

[0069] <Method for manufacturing compound for bonded magnets> The manufacturing method for the bonded magnet compound of this embodiment is characterized by including the steps of obtaining a phosphate-coated SmFeN-based anisotropic magnetic powder and kneading the magnetic powder with polypropylene, and by using polypropylene, the resistance to hot water is improved. Of these, the phosphate-coated SmFeN-based anisotropic magnetic powder is obtained by the method described above.

[0070] [Mixing process] In the process of kneading phosphate-coated SmFeN-based anisotropic magnetic powder with polypropylene, the mixture of phosphate-coated SmFeN-based anisotropic magnetic powder and polypropylene is kneaded at 180-300°C using a kneader such as a single-screw kneader or twin-screw kneader. For example, after mixing the magnetic powder and resin powder in a mixer, the strand is extruded with a twin-screw extruder, air-cooled, and then cut into pieces of several millimeters in size with a pelletizer to obtain a compound for bonded magnets in pellet form.

[0071] The weight-average molecular weight of the polypropylene used is preferably in the range of 20,000 to 200,000. If the weight-average molecular weight is less than 20,000, the mechanical strength of the bonded magnet after molding decreases, and if it is greater than 200,000, the viscosity of the compound for the bonded magnet tends to increase. Furthermore, in order to improve the bonding with the coupling-treated magnetic powder, it is preferable that the polypropylene is acid-modified, for example, polypropylene acid-modified with maleic anhydride is preferably used. The acid modification rate of the polypropylene is preferably 0.1% by weight or more and 10% by weight or less. If it is less than 0.1% by weight, the adhesion with the magnetic powder will be insufficient, and the mechanical strength and water resistance of the bonded magnet will decrease. If it exceeds 10% by weight, the water absorption rate of the resin will increase, and the water resistance of the bonded magnet will decrease.

[0072] The content of phosphate-coated SmFeN-based anisotropic magnetic powder in the compound for bonded magnets is preferably 80% to 95% by mass, and more preferably 90% to 95% by mass from the viewpoint of obtaining high magnetic properties. On the other hand, the content of polypropylene in the compound for bonded magnets is preferably 3% to 20% by mass, and more preferably 5% to 15% by mass from the viewpoint of ensuring fluidity.

[0073] In addition to phosphate-coated SmFeN-based anisotropic magnetic powder and polypropylene, a thermoplastic elastomer and an antioxidant such as a phosphorus-based antioxidant can be kneaded together. When a thermoplastic elastomer is included, the mass ratio of polypropylene to thermoplastic elastomer is preferably in the range of 90:10 to 50:50, and more preferably in the range of 89:11 to 70:30 from the viewpoint of impact resistance. Furthermore, when a phosphorus-based antioxidant is included, the content of the phosphorus-based antioxidant in the compound for bonded magnets is preferably 0.1% by mass or more and 2% by mass or less.

[0074] In addition to the aforementioned polypropylene (PP), other crystalline resins with low water absorption rates, such as polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), polyamide (PA), and polyethylene (PE), can be used as resins in compounds for water-resistant bonded magnets.

[0075] To improve the resistance to hot water, mixtures or polymer alloys can be used that are obtained by mixing the aforementioned crystalline resin with amorphous resins having a glass transition temperature (Tg) of 100°C or higher, such as modified polyphenylene ether (m-PPE), cycloolefin polymer (COP), or cycloolefin copolymer (COC). In the present invention, for example, a polymer alloy of modified polyphenylene ether (m-PPE) and polypropylene can be suitably used.

[0076] <Compound for adhesive magnets> The compound for bonded magnets of this embodiment is characterized by containing phosphate-coated SmFeN-based anisotropic magnetic powder and polypropylene. By including phosphate-coated SmFeN-based anisotropic magnetic powder and polypropylene, the heat and water resistance of bonded magnets made using these compounds for bonded magnets is improved. The compound for bonded magnets is obtained by the method described above.

[0077] [Method for manufacturing bonded magnets] Bonded magnets can be manufactured using a compound for bonded magnets and a suitable molding machine. Specifically, for example, a bonded magnet can be obtained by injecting a molten compound for bonded magnets in a mold with a magnetic field applied, aligning the easy magnetization axis (orientation step), cooling and solidifying it, and then magnetizing it with an air-core coil or magnetizing yoke (magnetization step).

[0078] The barrel temperature is selected according to the type of resin used, ranging from 160°C to 320°C, and similarly, the mold temperature can be, for example, 30°C to 150°C. The orientation magnetic field in the orientation process is generated using electromagnets or permanent magnets, with a magnetic field magnitude of 4 kOe or more, and more preferably 6 kOe or more. Furthermore, the magnetic field magnitude in the magnetization process is preferably 20 kOe or more, and more preferably 30 kOe or more.

[0079] [Bonded Magnets] The bonded magnet of this embodiment contains a phosphate-coated SmFeN-based anisotropic magnetic powder with a phosphate content greater than 0.5% by mass, and polypropylene, and is characterized in that the retention rate of the total flux after being held for 1000 hours under immersion conditions in hot water at 120°C is 95% or more of the amount before the test. The fact that the total flux of the bonded magnet after a hot water resistance test, held for 1000 hours under immersion conditions in hot water at 120°C, is 95% or more of the amount before the test means that it has high resistance to hot water, with 96% or more being preferable and 97% or more being more preferable. The retention rate of the total flux can be measured under the conditions described in the examples. The bonded magnet can be obtained by the method described above.

[0080] Since the bonded magnet of this embodiment is resistant to hot water, it can be suitably used as a drive source for fuel pumps and water pumps in automobiles, motorcycles, and the like. [Examples]

[0081] (Example 1) 5.0 kg of FeSO4·7H2O was mixed and dissolved in 2.0 kg of pure water. Then, 0.49 kg of Sm2O and 0.74 kg of 70% sulfuric acid were added and the mixture was thoroughly stirred until completely dissolved. Next, pure water was added to the resulting solution to adjust the final concentration to 0.726 mol / L for Fe and 0.112 mol / L for Sm, thus obtaining the SmFe sulfuric acid solution.

[0082] [Precipitation process] The entirety of the prepared SmFe sulfuric acid solution was added dropwise to 20 kg of pure water maintained at 40°C, while stirring for 70 minutes from the start of the reaction. Simultaneously, 15% ammonia solution was added dropwise to adjust the pH to 7-8. This yielded a slurry containing SmFe hydroxide. The obtained slurry was washed with pure water by decantation, and then the hydroxide was separated into solid and liquid phases. The separated hydroxide was dried in an oven at 100°C for 10 hours.

[0083] [Oxidation process] The hydroxide obtained in the precipitation process was calcined in air at 1000°C for 1 hour. After cooling, red SmFe oxide was obtained as the raw material powder. [Pre-treatment process] 100 g of SmFe oxide was placed in a steel container to a thickness of 10 mm. The container was placed in a furnace, the pressure was reduced to 100 Pa, and then the temperature was raised to the pretreatment temperature of 850°C while introducing hydrogen gas, and it was held at that temperature for 15 hours. The oxygen concentration was measured by non-dispersive infrared absorption spectroscopy (ND-IR) (EMGA-820, Horiba, Ltd.) and found to be 5 mass%. This indicates that the oxygen bonded to Sm was not reduced, while 95% of the oxygen bonded to Fe was reduced, resulting in a black partial oxide.

[0084] [Reduction Process] 60 g of partial oxide obtained in the pretreatment process and 19.2 g of metallic calcium with an average particle size of approximately 6 mm were mixed and placed in the furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. The temperature was raised to 1045°C and held for 45 minutes to obtain Fe-Sm alloy particles.

[0085] [Nitriding process] Subsequently, the furnace temperature was cooled to 100°C, then the chamber was evacuated, and the temperature was raised to 450°C while introducing nitrogen gas. This temperature was maintained for 23 hours to obtain a massive product containing magnetic particles.

[0086] [Washing process] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decanting was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was added and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decanting was repeated twice, followed by dehydration and drying, and then mechanical crushing to obtain SmFeN-based anisotropic magnetic powder (average particle size 3 μm).

[0087] [Phosphating treatment process] As the phosphoric acid treatment solution, a mixture of 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a weight ratio of 1:6:1 was prepared, and the pH was adjusted to 2 and the PO4 concentration to 20% by mass using pure water and dilute hydrochloric acid. Dilute hydrochloric acid of hydrogen chloride:70g was added to the slurry containing 1000g of SmFeN-based anisotropic magnetic powder obtained in the water washing step and stirred for 1 minute to remove surface oxide film and contaminants. Then, the draining and adding of water was repeated until the conductivity of the supernatant liquid was 100 μS / cm or less, to obtain a slurry containing 10% by mass of SmFeN-based anisotropic magnetic powder. While stirring the obtained slurry, 100g of the prepared phosphoric acid treatment solution was added entirely to the treatment tank, and the pH of the phosphoric acid treatment reaction slurry was controlled within the range of 2.5 ± 0.1 by adding 6% by weight hydrochloric acid as needed and maintained for 30 minutes. Subsequently, suction filtration, dehydration, and vacuum drying were performed to obtain phosphate-coated SmFeN-based anisotropic magnetic powder.

[0088] [Oxidation treatment process after phosphoric acid treatment] 1000 g of phosphate-coated SmFeN-based anisotropic magnetic powder was subjected to a heat treatment in an atmosphere of nitrogen and air mixed gas (oxygen concentration 4%, 5 L / min), gradually increasing the temperature from room temperature until it reached a maximum temperature of 230°C for 8 hours, thereby obtaining oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0089] (Example 2) Except for changing the heat treatment temperature in the oxidation process from 230°C to 200°C, the oxidized phosphate-coated SmFeN-based anisotropic magnetic powder was obtained by the same procedure as in Example 1.

[0090] (Comparative Example 1) The procedure was carried out in the same manner as in Example 1, except that the heat treatment temperature in the oxidation process was changed from 230°C to 170°C, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0091] (Comparative Example 2) In Example 1, the phosphate-coated SmFeN-based anisotropic magnetic powder was used, and no oxidation treatment was performed after the phosphoric acid treatment step.

[0092] (Comparative Example 3) [Phosphating treatment process] Magnetic powder was obtained by carrying out the water washing step in the same manner as in Example 1. As the phosphoric acid treatment solution, a mixture of 85% orthophosphoric acid, sodium dihydrogen phosphate, and sodium molybdate dihydrate in a weight ratio of 1:6:1 was prepared, and the pH was adjusted to 2.5 and the PO4 concentration to 20% by mass with pure water and dilute hydrochloric acid. Dilute hydrochloric acid of hydrogen chloride:70g was added to the slurry containing 1000g of the SmFeN-based anisotropic magnetic powder obtained in the water washing step and stirred for 1 minute to remove surface oxide film and contaminants. Then, the draining and adding of water was repeated until the conductivity of the supernatant liquid was 100 μS / cm or less, to obtain a slurry containing 10% by mass of SmFeN-based anisotropic magnetic powder. While stirring the obtained slurry, 100g of the prepared phosphoric acid treatment solution was added entirely to the treatment tank. The pH of the reaction slurry rose from 2.5 to 6 over 5 minutes. After stirring for 15 minutes, the material was filtered by suction, dehydrated, and vacuum dried to obtain a phosphate-coated SmFeN-based anisotropic magnetic powder.

[0093] [Oxidation treatment process after phosphoric acid treatment] 1000 g of phosphoric acid-treated SmFeN-based anisotropic magnetic powder was subjected to a heat treatment in an atmosphere of nitrogen and air mixed gas (oxygen concentration 4%, 5 L / min), gradually increasing the temperature from room temperature until it reached a maximum temperature of 230°C for 8 hours, thereby obtaining oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0094] (Comparative Example 4) Except for changing the heat treatment temperature in the oxidation process from 230°C to 200°C, the oxidized phosphate-coated SmFeN-based anisotropic magnetic powder was obtained in the same manner as in Comparative Example 3.

[0095] (Comparative Example 5) Except for changing the heat treatment temperature in the oxidation process from 230°C to 170°C, the oxidized phosphate-coated SmFeN-based anisotropic magnetic powder was obtained in the same manner as in Comparative Example 3.

[0096] (Comparative Example 6) In Comparative Example 3, a phosphate-coated SmFeN-based anisotropic magnetic powder was used, and no oxidation treatment was performed after the phosphoric acid treatment step.

[0097] (Comparative Example 7) [Reduction Process 2] A crucible filled with a mixed powder of 52.5 g of iron powder with an average particle size (D50) of approximately 50 μm, 21.3 g of samarium oxide powder with an average particle size (D50) of 3 μm, and 10.5 g of metallic calcium was placed in a furnace. After evacuating the furnace, argon gas (Ar gas) was introduced. Fe-Sm alloy particles were obtained by raising the temperature to 1150°C and holding it for 5 hours.

[0098] [Nitriding Process 2] Next, the Fe-Sm alloy particles were heat-treated in an ammonia-hydrogen mixed gas at 420°C for 23 hours to obtain a massive product containing magnetic particles.

[0099] [Water washing process 2] The lumpy product obtained in the nitriding process was added to 3 kg of pure water and stirred for 30 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated 10 times. Next, 2.5 g of 99.9% acetic acid was added and stirred for 15 minutes. After standing, the supernatant was drained by decantation. The process of adding to pure water, stirring, and decantation was repeated twice. Subsequently, dehydration and drying treatment were performed to obtain SmFeN-based anisotropic magnetic powder (average particle size 30 μm).

[0100] [Phosphating treatment process 2] 15 g of the obtained magnetic powder was placed in a glass bottle with 0.44 g of 85% orthophosphoric acid aqueous solution, 100 ml of isopropanol (IPA), and 200 g of 10 mm diameter alumina beads, and the mixture was ground in a vibrating ball mill for 120 minutes. After filtering the slurry, it was vacuum-dried at 100°C to obtain phosphate-coated SmFeN-based anisotropic magnetic powder (average particle size 1.5 μm).

[0101] [Oxidation treatment step 2 after phosphoric acid treatment step] 15 g of phosphoric acid-treated SmFeN-based anisotropic magnetic powder was subjected to a heat treatment in a nitrogen-air mixed gas atmosphere (oxygen concentration 4%, 5 L / min) by gradually raising the temperature from room temperature, and reaching a maximum temperature of 150°C for 8 hours to obtain oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0102] (Comparative Example 8) The procedure was carried out in the same manner as in Comparative Example 7, except that the heat treatment temperature in the oxidation process was changed from 150°C to 200°C, to obtain an oxidized phosphate-coated SmFeN-based anisotropic magnetic powder.

[0103] [Magnetic powder evaluation] (magnetic powder Br, iHc) The magnetic properties (remanent magnetization σr, intrinsic coercivity iHc) of the magnetic powders obtained in Examples 1 to 2 and Comparative Examples 1 to 8 were measured using a VSM (Vibrating Sample Magnetometer, RIKEN Electronics; Model: BHV-55). Furthermore, the remanent magnetization σr (unit: emu / g) was calculated using the formula (Br = 4 × π × ρ × σr, ρ: density = 7.66 g / cm³). 3 The residual magnetic flux density Br (unit: kG) was calculated using ). The results are shown in Table 1.

[0104] (PO4 adhesion amount) The phosphorus concentration in each magnetic powder obtained in Examples 1 to 2 and Comparative Examples 1 to 8 was measured using ICP emission spectroscopy (ICP-AES) and converted to PO4 molecular weight. The results are shown in Table 1.

[0105] (DCS heat generation start temperature) 20 mg of each magnetic powder obtained in Examples 1 to 2 and Comparative Examples 1 to 8 was weighed out, and DSC analysis was performed using a high-temperature differential scanning thermal analyzer (DSC6300, Hitachi High-Tech Science Corporation) under the following conditions: air atmosphere (200 mL / min), room temperature to 400°C (heating rate: 20°C / min), and reference: alumina (20 mg). The exothermic onset temperature was measured. The DSC results are shown in Table 1. A high exothermic onset temperature indicates that heat generation due to oxidation is less likely to occur, meaning that the phosphoric acid coating is more densely formed.

[0106] (STEM-EDX mapping) The magnetic powders obtained in Example 1 and Comparative Example 2 were dispersed in epoxy resin and solidified. Cross-sections were then prepared using a cross-section polisher to obtain cross-sectional samples for measurement. STEM images (acceleration voltage 200kV) were measured on the obtained samples using a scanning transmission electron microscope (STEM; JEOL) and an energy-dispersive X-ray spectrometer (EDX; JEOL). Figure 2 shows the STEM-EDX mapping analysis results (elements: O, P, Fe, Sm, Mo). In Figure 2, it can be seen that Example 1, which underwent oxidation treatment, has multiple layers after oxidation treatment, compared to Comparative Example 2, which did not undergo oxidation treatment. Specifically, in Example 1, five regions can be observed from the outermost surface of the SmFeN-based anisotropic magnetic powder, outward from the phosphate coating: (1) an oxide layer concentrated with Mo, (2) a phosphate coating concentrated with Sm, (3) a phosphate layer concentrated with Mo and Fe, (4) an oxide layer concentrated with Fe, and (5) an oxide layer concentrated with Mo and Fe. On the other hand, in Comparative Example 2, a layer corresponding to (2) can be confirmed on the outermost surface of the SmFeN-based anisotropic magnetic powder, which is the base material, but the majority is a phosphate coating containing Fe, Sm, and Mo, and no significant layer changes corresponding to (1) and (3) to (5) of Example 1 can be confirmed.

[0107] (STEM-EDX line analysis) Figures 3 and 4 show the EDX line analysis corresponding to the arrows at the phosphate coating / SmFeN-based anisotropic magnetic powder interface in Example 1 and Comparative Example 2, respectively. In Example 1 in Figure 3, three split Mo peaks (at approximately 21 nm, 13 nm, and 7 nm) and peaks containing high concentrations of Sm and Fe are observed, which is consistent with the results in Figure 2. On the other hand, in Comparative Example 2 in Figure 4, Mo has a peak at around 65 nm, which is the outermost surface of the SmFeN-based anisotropic magnetic powder, and shows a characteristic trend of gradually increasing toward the outside of the phosphate coating, but it is presumed that the majority is a composite phosphate mainly composed of samarium phosphate.

[0108] From the above, it is considered that by oxidizing the phosphate coating of Comparative Example 2 at a high temperature of 200°C or higher, each metal element (Fe, Sm, Mo) mutually diffused with oxygen, transforming into multiple thermodynamically more stable layers, resulting in the formation of the coating of Example 1. Magnetic powder having such an oxidized coating has superior water resistance as a bonded magnet.

[0109] [Silica treatment process] The magnetic powders obtained in Examples 1 to 2 and Comparative Examples 1 to 8, ethyl silicate 40, and 12.5% ​​by weight of aqueous ammonia were mixed in a mixer in a weight ratio of 97.8:1.8:0.4, respectively. The mixture was heated in a vacuum at 200°C to obtain SmFeN-based anisotropic magnetic powder in which a thin silica film was formed on the particle surface.

[0110] [Silane coupling treatment] The SmFeN-based anisotropic magnetic powder on which the silica thin film was formed as described above was mixed with 12.5% ​​by weight of aqueous ammonia in a mixer, and then mixed with a 50% by weight ethanol solution of 3-aminopropyltriethoxysilane in the mixer. The weight ratio of the SmFeN-based anisotropic magnetic powder on which the silica thin film was formed to the 12.5% ​​by weight aqueous ammonia and ethanol solution of 3-aminopropyltriethoxysilane was 99:0.2:0.8, respectively. The mixture was dried at 100°C under a nitrogen atmosphere for 10 hours to obtain silane-coupled SmFeN-based anisotropic magnetic powder.

[0111] [Mixing and molding process] Silane-coupled SmFeN magnetic powder, polypropylene (maleic anhydride modification rate: 1% by weight, weight-average molecular weight: 90,000), and an antioxidant were mixed in a weight ratio of 91.5:8:0.5, and kneaded in a twin-screw extruder to obtain a compound for bonded magnets. The kneading temperature at this time was 210°C. [Molding process]

[0112] This compound was heated to 240°C in the barrel of an injection molding machine, and the molten compound was injection molded into a mold heated to 90°C while applying a magnetic field of 9 kOe, to obtain a cylindrical bonded magnet molded product with a diameter (Φ) of 10 mm and a height (t) of 7 mm for water resistance evaluation.

[0113] [Magnet evaluation] (Magnet iHc) Bonded magnet molded products for water resistance evaluation were placed inside an air-core coil and magnetized with a magnetization magnetic field of 60 kOe. After magnetization, the magnetic properties (intrinsic coercivity iHc of the molded magnet) were measured using a BH tracer. The results are shown in Table 1.

[0114] (Heat and water resistance of magnets) Bonded magnet molded products for water resistance evaluation were magnetized using an air-core coil with a magnetic field of 60 kOe, and then any dirt or oil on the magnet surface was wiped off. Afterward, the magnets were placed in a pressure vessel with a sufficient amount of water to completely immerse them, and held in a 120°C oven for a predetermined time. The irreversible demagnetization rate was determined based on the change in the total flux of the magnets before and after the test after 1000 hours. The total flux was measured using a flux meter (manufactured by Nippon Denji Sokki; model: NFX-1000) by pulling the bonded magnet molded product, which was placed inside the search coil, out of the search coil to measure the change in magnetic flux. The irreversible demagnetization rate was calculated using the following formula. Irreversible demagnetization rate (%) = (Total flux (value at 0 hr) - Total flux (value after a specified time)) / Total flux (value at 0 hr) × 100 Table 1 shows the time it took for the irreversible demagnetization rate to reach 5%, and Figure 1 shows the relationship between processing time and irreversible demagnetization rate.

[0115] [Table 1]

[0116] Table 1 shows that the magnetic powders obtained in Examples 1 to 2 had a higher DSC exothermic onset temperature than Comparative Examples 1 to 8, and demonstrated superior density, thickness, and oxidation resistance of the phosphate coating. Furthermore, Table 1 and Figure 1 show that the bonded magnets of Examples 1 to 2 maintained an irreversible demagnetization rate of 5% or less even after immersion in hot water for 1000 hours, demonstrating excellent resistance to hot water.

Claims

1. A phosphoric acid treatment step to obtain SmFeN-based anisotropic magnetic powder coated with phosphate on its surface by adding an inorganic acid to a slurry containing SmFeN-based anisotropic magnetic powder, water, and a phosphoric acid compound to adjust the pH of the slurry to 1 or more and 4.5 or less, and The process includes an oxidation step in which a phosphate-coated SmFeN-based anisotropic magnetic powder is heat-treated in an oxygen-containing atmosphere at a temperature of 200°C to 330°C. A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder.

2. In the oxidation step, heat treatment is performed at a temperature of 200°C or higher and 250°C or lower. A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1.

3. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 1 or 2, wherein the phosphate content in the phosphate-coated SmFeN-based anisotropic magnetic powder is greater than 0.5% by mass.

4. The phosphate coating present on the surface of the SmFeN-based anisotropic magnetic powder has a first region. The Sm atom concentration in the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder, and The Sm atom concentration in the first region is 0.5 times or more and 4 times or less than the Fe atom concentration in the first region. A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 3.

5. The phosphate coating portion further has a second region on top of the first region, The Sm atom concentration in the second region is 1 / 3 or less of the Fe atom concentration in the second region. A method for producing phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 4.

6. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 5, comprising performing the adjustment for 10 minutes or more in the phosphate treatment step.

7. A method for producing a phosphate-coated SmFeN-based anisotropic magnetic powder according to any one of claims 1 to 6, wherein the pH is adjusted to 1.6 or more and 3.9 or less in the phosphate treatment step.

8. A method for producing a compound for bonded magnets, comprising the step of kneading a phosphate-coated SmFeN-based anisotropic magnetic powder obtained by the manufacturing method described in any one of claims 1 to 7 with polypropylene.

9. A bonded magnet comprising a phosphate-coated SmFeN-based anisotropic magnetic powder with a phosphate content greater than 0.5% by mass, and polypropylene, wherein the retention rate of the total flux after 1000 hours of immersion in hot water at 120°C is 95% or more of the pre-test value.

10. The bonded magnet according to claim 9, wherein the exothermic start temperature in the DSC of the phosphate-coated SmFeN-based anisotropic magnetic powder is 170°C or higher.

11. A phosphate-coated SmFeN-based anisotropic magnetic powder, The phosphate content is greater than 0.5% by mass. The phosphate coating present on the surface of the SmFeN-based anisotropic magnetic powder has a first region and a second region, wherein the Sm atom concentration in the first region is higher than the Sm atom concentration in the SmFeN-based anisotropic magnetic powder. The Sm atom concentration in the first region is 0.5 times or more and 4 times or less than the Fe atom concentration in the first region, The second region is located on the first region, and the Sm atom concentration in the second region is 1 / 3 or less of the Fe atom concentration in the second region. Phosphate-coated SmFeN-based anisotropic magnetic powder.

12. The phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 11, wherein the exothermic onset temperature in DSC is 170°C or higher.

13. Obtained by the manufacturing method described in any one of claims 1 to 7, The phosphate-coated SmFeN-based anisotropic magnetic powder according to claim 11 or 12.

14. A bonded magnet comprising the phosphate-coated SmFeN-based anisotropic magnetic powder described in any one of claims 11 to 13.

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