Soft magnetic metal powder

Abstract

To provide soft magnetic metal powder that is soft magnetic metal powder made of fine particles capable of manufacturing a green compact high in molding density, capable of preparing a dust core excellent in magnetic property because of low content of boron that deteriorates saturation magnetization, and capable of forming a thin layer excellent in surface flatness because of an aggregate of fine particles having a narrow particle size distribution.SOLUTION: Soft magnetic metal powder having an average particle size of 0.05 μm or more and 1.5 μm or less, the coefficient of variation represented by the following (formula) of 0.25 or less, and the boron content of less than 5.0 wt.% (however, 0 is not included). (Formula) Standard deviation of particle size / Average particle size.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a soft magnetic metal powder. More specifically, the soft magnetic metal powder is composed of fine particles, which allows for the production of powder compacts with high compaction density, and contains a low amount of boron, which reduces saturation magnetization, which allows for the production of powder cores with excellent magnetic properties. Furthermore, the soft magnetic metal powder is an aggregate of fine particles with a narrow particle size distribution, which allows for the formation of thin layers with excellent surface smoothness. [Background technology]

[0002] As various electrical devices become more sophisticated and smaller and thinner, the inductors and transformers built into these devices are required to have thinner layers as well as improved magnetic properties.

[0003] To improve the magnetic properties of inductors and the like, powder magnetic cores are required to have a high molding density.

[0004] If the soft magnetic metal powder is an aggregate of fine particles, it is possible to expect an improvement in the compact density of the powder magnetic core.

[0005] As a method for producing fine particle soft magnetic metal powder, there is a liquid phase reduction method as described in Patent Document 1, in which a reducing solution containing a boron (B)-based reducing agent is dropped into an aqueous metal salt solution.

[0006] However, because B reduces saturation magnetization, there is a problem that dust cores made from soft magnetic metal powders that contain a large amount of B have reduced saturation magnetization.

[0007] Furthermore, by using soft magnetic metal powder with a wide particle size distribution and filling the gaps between large particles with medium and small particles, the compact density of the powder magnetic core can also be improved.

[0008] Soft magnetic metal powder with a wide particle size distribution can be produced by a common method such as water atomization, gas atomization, or spray pyrolysis.

[0009] However, soft magnetic metal powders with a wide particle size distribution have the problem that it is difficult to obtain a good surface smoothness when they are made into a thin layer.

[0010] Therefore, there is a need for the development of a soft magnetic metal powder consisting of fine particles that can be used to produce powder magnetic cores with high molding density, low B content, and excellent magnetic properties, and that can form thin layers with a narrow particle size distribution and excellent surface smoothness. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2010-261065 Summary of the Invention [Problem to be solved by the invention]

[0012] Patent Document 1 describes a method for producing soft magnetic metal powder with a smaller particle size than conventional methods by a liquid-phase reduction method in which a reducing liquid containing a B-based reducing agent is added dropwise to an aqueous iron salt solution containing an iron salt, a complexing agent, a dispersant, a pH adjuster, and a P-based reducing agent.

[0013] However, the soft magnetic metal powder described in Patent Document 1 contains a large amount of B, which causes a problem of reduced saturation magnetization.

[0014] The inventors set out to solve the above-mentioned problems as a technical task, and as a result of numerous trial and error prototypes and experiments, they succeeded in producing a soft magnetic metal powder having a narrow particle size distribution, in which the average particle size is 0.05 μm or more and 1.5 μm or less, and the coefficient of variation, expressed as the standard deviation of particle size / average particle size, is 0.25 or less, without adding a large amount of B-based reducing agent, thereby solving the above-mentioned technical task.

[0015] The soft magnetic metal powder according to the present invention can be used to produce powder compacts with high molding density, making it possible to produce powder cores with improved magnetic properties due to the increased density.Furthermore, since the content of B, which reduces saturation magnetization, is low, this soft magnetic metal powder can be used to produce powder cores with even better magnetic properties, and it can also form thin layers with excellent surface smoothness. [Means for solving the problem]

[0016] The above technical problems can be solved by the present invention as follows.

[0017] The present invention provides a soft magnetic metal powder having an average particle size of 0.05 μm or more and 1.5 μm or less, a coefficient of variation represented by the following formula of 0.25 or less, and a boron (B) content of less than 5.0% by weight (excluding 0). (Formula) Standard deviation of particle size / average particle size (σ / D)

[0018] The present invention also relates to the soft magnetic metal powder, wherein the iron (Fe) content is 90% by weight or more.

[0019] The present invention also provides The coated soft magnetic metal powder is obtained by coating a soft magnetic metal powder with one or more metal oxides.

[0020] The present invention also relates to the soft magnetic metal powder, wherein the metal element of the metal oxide is aluminum (Al), silicon (Si), zirconium (Zr), titanium (Ti), yttrium (Y) or phosphorus (P).

[0021] The present invention also provides a method for producing the soft magnetic metal powder by a liquid-phase reduction method in which a reducing liquid containing a B-based reducing agent is dropped into an aqueous metal salt solution containing a metal salt, a complexing agent, a pH adjuster, and a P-based reducing agent. [Effects of the Invention]

[0022] The present invention uses soft magnetic metal powder with an average particle size of 0.05 μm to 1.5 μm, which is an aggregate of fine particles, and therefore can achieve a high compaction density, making it possible to produce a dust core with excellent magnetic properties.

[0023] Furthermore, since the soft magnetic metal powder is made of fine particles with a narrow particle size distribution, where the coefficient of variation expressed as "standard deviation of particle size / average particle size" is 0.25 or less, it is possible to form a thin layer with excellent surface smoothness.

[0024] Furthermore, since the content of B, which reduces saturation magnetization, is less than 5.0% by weight, a dust core with even more excellent magnetic properties can be produced.

[0025] Furthermore, if the iron (Fe) content is 90% by weight or more, a powder magnetic core with high saturation magnetization can be produced.

[0026] Furthermore, if the soft magnetic metal powder is coated with a metal oxide, electrical insulation between the particles can be ensured, thereby suppressing energy loss. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is an SEM photograph (10,000 times) of a soft magnetic metal powder (σ / D=0.180) according to the present invention. [Figure 2] 1 is an SEM photograph (10,000 times) of a soft magnetic metal powder (σ / D=0.167) according to the present invention. [Figure 3] 1 is an SEM photograph (10,000 times) of a soft magnetic metal powder (σ / D=0.113) according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The soft magnetic metal powder of the present invention is an aggregate of fine particles and has a narrow particle size distribution, so that a green compact with a high compacting density can be produced and a thin layer with excellent surface smoothness can be formed.

[0029] The average particle size of the soft magnetic metal powder is preferably 0.05 μm to 1.5 μm, and more preferably 0.07 μm to 1.0 μm.

[0030] If the average particle size is less than 0.05 μm, the proportion of oxide film on the particle surface will be high, resulting in a decrease in saturation magnetization, and if it exceeds 1.5 μm, the maximum surface height (Rmax) will increase when the layer is thinned, which may result in a decrease in the surface smoothness of the thin layer.

[0031] To prevent a decrease in saturation magnetization due to the oxide film, the oxygen (O) content in the soft magnetic metal powder is preferably less than 8.0% by weight, and more preferably 5.0% by weight or less.

[0032] The coefficient of variation of the soft magnetic metal powder particles, expressed as "standard deviation of particle diameter / average particle diameter", is preferably 0.25 or less, and more preferably 0.22 or less.

[0033] If the coefficient of variation exceeds 0.25, the value of Rmax will increase when the layer is thinned, and the surface smoothness of the thin layer may decrease.

[0034] According to the present invention, even with a thin layer of 10 to 30 μm, Rmax can be made less than 3.5 μm.

[0035] The particle size of the soft magnetic metal powder can be measured using image analysis software after taking an image at a magnification of 2000 to 10000 times using a scanning electron microscope (SEM).

[0036] The content of B in the soft magnetic metal powder of the present invention is less than 5.0% by weight, but not 0% by weight.

[0037] Since B reduces saturation magnetization, it is preferable to have a small amount of B. However, if a B-based reducing agent is not used, there is a risk that the number of non-spherical fine particles will increase and the molding density will decrease.

[0038] The soft magnetic metal powder in the present invention is coated with a metal oxide. Even if This is good because it is expected to improve the insulation effect.

[0039] Examples of the metal element contained in the metal oxide include Al, Si, Zr, Ti, Y, and P.

[0040] The content of the metal element in the metal oxide is preferably 0.1% by weight to 3.0% by weight, because if it is contained in excess of 3.0% by weight, the saturation magnetization may decrease.

[0041] To produce a dust core with sufficient magnetic properties, it is preferable that the saturation magnetization of the soft magnetic metal powder be 150 Wb·m / kg or more and the coercive force be 10 kA / m or less.

[0042] The present invention can be produced by a liquid phase reduction method in which an aqueous solution of a metal salt is reduced with a B-type reducing agent.

[0043] The metal salt is not limited, but iron salts are preferred.

[0044] Examples of iron salts include iron(II) sulfate, iron(II) chloride, iron(II) acetate, iron(II) oxalate, iron(III) chloride, and iron(III) sulfate.

[0045] A complexing agent or a reducing agent may be added to the aqueous metal salt solution.

[0046] The complexing agent is not particularly limited, but examples thereof include glycine, alanine, ammonium sulfate, ammonium chloride, and sodium citrate III.

[0047] The reducing agent is not particularly limited, but it is preferable to use a P-based reducing agent.

[0048] Examples of P-based reducing agents include sodium hypophosphite and calcium hypophosphite.

[0049] The pH of the aqueous metal salt solution is preferably adjusted to 6.5 to 11.0.

[0050] The pH adjuster is not particularly limited, but examples thereof include sodium hydroxide, aqueous ammonia, and sodium bicarbonate.

[0051] A dispersant, a catalyst, and an antifoaming agent may be added to the aqueous metal salt solution as needed.

[0052] The reducing agent used to reduce the aqueous metal salt solution is a B-type reducing agent.

[0053] Examples of the B-type reducing agent include sodium borohydride, potassium borohydride, and dimethylaminoborane.

[0054] Hydrazine containing no B may be used in combination with the B-based reducing agent.

[0055] The reduction temperature is preferably 10°C to 95°C. [Example]

[0056] Examples of the present invention will be described below, but the present invention is not limited to these.

[0057] Example 1 Iron (II) sulfate heptahydrate 0.2 mol / L, glycine 0.08 mol / L, and sodium hypophosphite 0.1 mol / L were placed in a glass beaker together with 1500 ml of distilled water, and an aqueous metal salt solution with a pH of 7.0 to 8.5 was prepared using sodium hydroxide while stirring at room temperature at a rotation speed of 100 rpm to 300 rpm.

[0058] The prepared metal salt aqueous solution was heated to 45°C while stirring at a rotation speed of 100 rpm to 300 rpm in an inert atmosphere created in the beaker with nitrogen gas.

[0059] Sodium borohydride was mixed with 300 ml of distilled water to a concentration of 0.25 mol / L, and dissolved by stirring at 100 rpm to 300 rpm at room temperature to prepare a B-type reducing solution.

[0060] The metal salt aqueous solution was stirred at 45° C. in a nitrogen atmosphere at a rotation speed of 100 rpm to 300 rpm, and the prepared B-based reducing agent was gradually added dropwise. The point at which no more bubbles were generated from the aqueous metal salt solution was taken as the end point of the reduction reaction.

[0061] After the reduction reaction was completed, the mixture was washed with distilled water, substituted with alcohol, and then dried in an inert atmosphere of nitrogen gas, thereby obtaining the soft magnetic metal powder of Example 1.

[0062] (Examples 2 to 5 and Comparative Examples 1 to 3) Examples 2 to 5 and Comparative Examples 1 to 3 were produced under the same conditions as Example 1, except that the raw materials were as shown in Table 1.

[0063] Example 6 The soft magnetic metal powder obtained in Example 1 was weighed to a concentration of 0.30 mol / L, tetraethoxysilane (TEOS) 0.04 mol / L, and ammonia water 0.20 mol / L, and these were placed in a glass beaker together with 150 ml of isopropyl alcohol. The mixture was stirred at room temperature for 1 hour at a rotation speed of 100 rpm to 300 rpm to hydrolyze the TEOS, thereby coating the surfaces of the fine particles of the soft magnetic metal powder with silica.

[0064] After washing with isopropyl alcohol, the powder was dried in an inert atmosphere of nitrogen gas to obtain silica-coated soft magnetic metal powder.

[0065] Comparative Example 4 Iron (II) chloride hydrate 1.0 mol / L, ammonium chloride 1.5 mol / L, trisodium citrate hydrate 0.8 mol / L, sodium hypophosphite hydrate 1.5 mol / L, and polyvinylpyrrolidone as a dispersant 0.004 mol / L were weighed out and placed in a glass container together with 200 ml of distilled water. The solution was stirred at room temperature at a rotation speed of 160 rpm to 300 rpm for 60 to 120 minutes to prepare an aqueous metal salt solution.

[0066] The prepared metal salt aqueous solution was adjusted to pH 10 by adding an aqueous sodium hydroxide solution dropwise while stirring at a rotation speed of 160 rpm to 300 rpm at room temperature.

[0067] The same B-based reducing liquid as in Example 1 was gradually added dropwise to an aqueous metal salt solution being stirred at a rotation speed of 160 rpm to 300 rpm. After confirming that bubbles had ceased to form on the surface of the aqueous metal salt solution, the precipitated powder was separated from the liquid. The obtained powder was washed with water and alcohol, and then dried in an inert atmosphere of nitrogen gas to obtain an amorphous soft magnetic alloy powder.

[0068] (Comparative Example 5) Fe particles were synthesized using the polyol method. 100 ml of ethylene glycol was placed in a glass vessel equipped with a reflux condenser, nitrogen gas was blown in at a flow rate of 300 ml / min, and the liquid was stirred at a rotation speed of 100 rpm with a Teflon (registered trademark) stirring blade.

[0069] Ferrous chloride tetrahydrate (FeCl2·4H2O) was added to the stirred liquid to a concentration of 0.1 mol / L.

[0070] Next, [OH] relative to [Fe] - ] concentration ratio [OH - NaOH was added so that the ratio of [Fe] / [Fe] was 40.

[0071] Furthermore, hexachloroplatinic acid (IV) was used as a platinum precursor for nucleation at 2.0 × 10 -8 mol / L was added.

[0072] After the addition, cooling water was passed through the reflux condenser, and the mixture was heated while continuing to blow in nitrogen gas and mechanically stir, and the mixture was held at 170°C for 20 minutes under reflux to carry out the reduction reaction.

[0073] The precipitated particles were allowed to cool to room temperature, then transferred into ethanol, washed repeatedly by centrifugation, and dried in a nitrogen atmosphere to obtain Fe particle powder.

[0074] (Comparative Example 6) Carbonyl iron powder (product name: HQ manufactured by BASF) was used.

[0075] (particle shape) The specimens were visually observed using a scanning electron microscope (SEM) (S-4800 FE-SEM / Hitachi High-Tech Corporation) photograph (10,000x magnification).

[0076] The ratio (a / b) of the longest diameter a to the shortest diameter b of the particle was calculated, and the shape was evaluated as shown below.

[0077] Spherical: a / b≦1.7 and 1.0≦a / b≦1.2 ratio is 90% or more Spherical / granular: the ratio of a / b≦1.7 and 1.0≦a / b≦1.2 is 50% or more and less than 90% Granular: a / b≦1.7 and 1.0≦a / b≦1.2 ratio is less than 50% Acicular: a / b>1.7

[0078] (average particle size, standard deviation and coefficient of variation) Images were taken using a scanning electron microscope at magnifications of 2000 to 10000 times, and the longest diameter of all particles within the field of view was measured using image analysis software A-zo-kun (manufactured by Asahi Kasei Engineering Co., Ltd.) to calculate the average particle size, and the standard deviation was also calculated. The coefficient of variation was also calculated from these values.

[0079] (crystal structure) Measurements were performed using an X-ray diffractometer (D8 ADVANCE, manufactured by Bruker Japan Co., Ltd.), and the crystalline phases in the samples were identified by Rietveld analysis.

[0080] (composition analysis) <Fe、P、Si> Measurements were carried out using a fluorescent X-ray diffractometer (ZSX Primus II, manufactured by Rigaku Corporation) in accordance with JIS K0119 "General rules for fluorescent X-ray analysis."

[0081] Measurements were carried out using an inductively coupled plasma (ICP) optical emission spectrometer (iCAP6500, manufactured by Thermo Fisher Scientific Co., Ltd.).

[0082] <o> Measurements were carried out using an oxygen, nitrogen, and hydrogen analyzer (EMGA-930 / Horiba, Ltd.).

[0083] (magnetic properties) The saturation magnetization (σs) and coercive force (Hc) were measured using a vibrating sample magnetometer (VSM) (Model TM-VSM2130MRHL / manufactured by Tamagawa Seisakusho Co., Ltd.) at an applied magnetic field of 797.7 kA / m.

[0084] (Thin layer characteristics) To 5.0 g of the soft magnetic metal powder of Example 1, 0.5 ml of castor oil and 4.5 g of nitrocellulose clear lacquer (P-use clear (standard sample) 151-009 / manufactured by Kansai Paint Co., Ltd.) were added, and the mixture was stirred at a rotation-revolution mixer (Awatori Rentaro ARE-310 / manufactured by Thinky Corporation) at a rotation speed of 1500 rpm for 3 minutes to prepare a paste.

[0085] The prepared paste was applied to a PET film using a 3-mill applicator and dried at room temperature to prepare a thin layer of approximately 20 μm.

[0086] The maximum height (Rmax) of the thin layer was measured using a non-contact surface roughness meter (NewView600, manufactured by Canon Marketing Japan Inc.).

[0087] [Table 1]

[0088] [Table 2]

[0089] Tables 1 and 2 demonstrate that the soft magnetic metal powder of the present invention has high saturation magnetization and coercive force, and can form a thin layer with excellent surface smoothness. [Industrial Applicability]

[0090] The soft magnetic metal powder of the present invention is made up of fine particles, so that a powder compact with a high compaction density can be produced, and the low B content allows the production of a powder magnetic core with excellent magnetic properties. Furthermore, since it is an aggregate of fine particles with a narrow particle size distribution, it is possible to prepare a thin layer with excellent surface smoothness. Therefore, the present invention has high industrial applicability.< / o>

Claims

1. A soft magnetic metal powder having an average particle size of 0.05 μm or more and 1.5 μm or less, a coefficient of variation represented by the following formula of 0.25 or less, a boron content of less than 5.0 wt % (but not including 0), and an iron content of 90 wt % or more. (Formula) Standard deviation of particle size / average particle size

2. A coated soft magnetic metal powder obtained by coating the soft magnetic metal powder according to claim 1 with one or more metal oxides.

3. 3. The coated soft magnetic metal powder according to claim 2, wherein the metal element of said metal oxide is aluminum, silicon, zirconium, titanium, yttrium or phosphorus.

4. 2. The method for producing soft magnetic metal powder according to claim 1, wherein the powder is produced by a liquid phase reduction method in which a reducing solution containing a boron-based reducing agent is added dropwise to an aqueous metal salt solution containing a metal salt, a complexing agent, a pH adjuster, and a phosphorus-based reducing agent.

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