WO2021200746A1

WO2021200746A1 - Ferrite powder, ferrite resin composition, resin molded body, electronic component, electronic equipment, or electronic equipment housing

Info

Publication number: WO2021200746A1
Application number: PCT/JP2021/013107
Authority: WO
Inventors: 康二安賀; 小島　隆志; 忠志續; 曉美近野; 翔桑原; 隆男杉浦
Original assignee: パウダーテック株式会社
Priority date: 2020-03-31
Filing date: 2021-03-26
Publication date: 2021-10-07

Abstract

Provided is a zinc ferrite powder that has exceptional magnetic properties despite not containing manganese and has excellent moldability, fluidity, and filling properties. A ferrite powder: is constituted from spherical or polyhedral ferrite particles; has a composition that contains 5.0-10.0 mass% of zinc (Zn) and 55.0-65.0 mass% of iron (Fe), the balance being oxygen (O) and unavoidable impurities; has a crystallite diameter in the range of 8.0-15.0 Å; and has a divalent iron ion (Fe2+) content of 0.5-10.0 mass%.

Description

Ferrite powder, ferrite resin composition, resin molded body, electronic component, electronic device or electronic device housing

The present invention relates to a ferrite powder, a ferrite resin composition, a resin molded body, an electronic component, an electronic device, or an electronic device housing.

Ferrite resin compositions (composite materials) composed of ferrite powder and resin are widely used in various applications such as electromagnetic wave shielding materials. The resin composition is produced by kneading the ferrite powder as a filler with the resin, and is molded into a shape such as a sheet to form a molded body (complex). At this time, if the shape of the particles constituting the ferrite powder is close to a sphere, the fluidity at the time of molding becomes high, and the filling rate of the ferrite powder in the resin composition becomes high. Therefore, the moldability is improved and the characteristics such as electromagnetic wave shielding performance are excellent. From this point of view, ferrite powder composed of spherical particles has attracted attention, and it has been proposed to prepare such spherical particles by a thermal spraying method.

For example, Patent Document 1 (International Publication No. 2017/212997) contains substantially no Zn, 3 to 25% by weight of Mn, and 43 to 65% by weight of Fe, and has an average particle size of 1. A ferrite particle which is a single crystal having a diameter of about 2000 nm and has a spherical particle shape is disclosed (claim 1 of Patent Document 1). Further, Patent Document 1 states that a granulated product made of a ferrite raw material is sprayed in the air to be ferrite, and then rapidly cooled and solidified, and then only particles having a particle size within a predetermined range are recovered for production. It is described that when used as an electromagnetic wave shielding material for an apparatus, electromagnetic waves in a wide frequency band can be stably shielded regardless of the frequency (Patent Documents 1 [0039] and [0078]).

According to Patent Document 2 (International Publication No. 2016/043051), ferrite obtained by adjusting a predetermined ratio of ferrite composition with respect to Mn-Mg-based ferrite particles having an average particle size of 1 to 2000 nm and being spherical. It is described that the raw material is sprayed in the air to be ferrite, and then rapidly cooled and solidified to be produced, and that it is particularly preferably used as a filler or a magnetic fluid for a resin composition for electromagnetic wave shielding (Patent Document 2 []. 0036] and [0077]).

By the way, the ferrites proposed in Patent Documents 1 and 2 are manganese (Mn) -based ferrites containing manganese (Mn) as a main component and having a spinel-type structure. Manganese-based ferrite has excellent magnetic properties such as magnetic permeability, and is used in various applications. On the other hand, as spinel type ferrite, various ferrites other than manganese-based ferrite are known, and among them, zinc ferrite having zinc (Zn) as a main component is included. Zinc ferrite shows antiferromagnetism in stoichiometric composition and has no magnetism when viewed macroscopically. However, zinc ferrite becomes ferromagnetic when an excessive amount of iron (Fe) is added to it, and the magnetization and magnetic permeability become high.

Patent Documents 3 to 5 are examples of documents that disclose ferromagnetic zinc ferrite and a method for producing the same. In Patent Document 3 (Japanese Unexamined Patent Publication No. 55-65406), _{99.9 to 51 mol% of iron oxide is converted into Fe 2} O ₃ and 0.1 is converted into MO (M is Zn, etc.). A ferrite powder for electrophotographic magnetic toner having a spinel-type structure composed of up to 49 mol% of zinc oxide or the like is disclosed (Patent Document 3, claim 1). Further, in Patent Document 3, in Example 2, _{after blending Fe 2} O ₃ to 80 mol% and Zn O to 20 mol%, granulation and firing were performed, and the obtained fired body was crushed, dried and baked. To obtain a ferrite powder by crushing, the average particle size of the obtained powder is 0.45 μm, the specific surface area is 17.2 m ² / g, and the σm (maximum magnetization force) under an external magnetic field of 1000 Oe is It is described that 65 emu / g and Hc (coercive force) are 185 Oe (upper left column on page 7 of Patent Document 3).

Patent Document 4 (Japanese Unexamined Patent Publication No. 8-34616) describes a method for producing zinc ferrite powder, which is a solid solution of magnetite and zinc ferrite, and describes a mixed material containing metal chloride and metal oxide and composed of zinc and iron. It is described that the roasting step is performed in an atmosphere in which steam is present as a starting material (Patent Document 4, claim 1). Further, Patent Document 4 states that the saturation magnetization is 85 to 96 emu / g, the coercive force is 90 to 210 Oe, and the specific surface area is 1 to 5 m ² / g when the applied magnetic field is 5000 Oe. It is described that it can be preferably used for magnetic toner and the like (Patent Document 4, claim 5 and [0023]).

Patent Document 5 (Japanese Unexamined Patent Publication No. 6-310318) proposes to produce granular magnetite particle powder coated with zinc ferrite by wet synthesis. Specifically, 0 for a granular magnetite particles the particle surface is coated with a _{_{_{Zn x Fe 2 + y O z}}} , the _Zn x _{Fe 2} + y _O _Zn amount in _z is the total Fe in the granular magnetite particles Granular magnetite particle powder having a content of 5.5 to 4.0 mol% is disclosed, and a ferrous salt aqueous solution and an alkali hydroxide aqueous solution are added and mixed in an aqueous dispersion containing the granular magnetite particle powder. after adjusting the OH group concentration and, by passing an oxygen-containing gas, (claims 1 and 2 of Patent Document 5) the granular magnetite particles surface Zn x _Fe 2 + _y that the coating with O _z is described.

International Publication No. 2017/212997 International Publication No. 2016/043051 JP-A-55-65406 Japanese Unexamined Patent Publication No. 8-34616 Japanese Unexamined Patent Publication No. 6-310318

Although the spherical particles made of manganese-based ferrite proposed in Patent Documents 1 and 2 have excellent magnetic properties and are useful for applications such as electromagnetic wave shielding materials, there is room for improvement. That is, manganese-based ferrite contains manganese as a main component, but it has been reported that inhalation of a large amount of manganese by inhalation exposure causes health hazards to the nervous system. Therefore, manganese and its compounds are classified as substances subject to the Industrial Safety and Health Act Specified Chemical Substance Hazard Prevention Regulations (Control Class 2 substances). For this reason, dustproof treatment for preventing the scattering of manganese raw materials is indispensable during the production of manganese-based ferrite, which has been a cause of an increase in production cost.

On the other hand, although zinc ferrite powders are proposed in Patent Documents 3 to 5, these powders do not consist of spherical particles. Therefore, when applied to a filler of a resin composition, there are problems in terms of moldability, fluidity and filling property. Further, although Patent Documents 3 to 5 show static magnetic field characteristics such as saturation magnetization and coercive force with respect to the characteristics of zinc ferrite powder, there is no description regarding high frequency characteristics, and there is no description of specific uses other than electrophotographic toner. .. Therefore, it is unclear whether these zinc ferrite powders are applied to high frequency applications such as electromagnetic wave shielding materials.

The present inventors have conducted diligent studies in view of such problems. As a result, the specific zinc ferrite powder composed of spherical or polyhedral particles is excellent in magnetic properties, especially magnetic permeability in the high frequency region, even though it does not contain manganese, and further, moldability, fluidity and It was found that the filling property is good.

The present invention has been completed based on such findings, and an object of the present invention is to provide a zinc ferrite powder which is excellent in magnetic properties even though it does not contain manganese and has good moldability, fluidity and filling property. do. Another object of the present invention is to provide a ferrite resin composition containing such zinc ferrite powder, a resin molded body, an electronic component, an electronic device, or an electronic device housing.

The present invention includes the following aspects (1) to (8). In addition, in this specification, the expression "-" includes the numerical values at both ends thereof. That is, "X to Y" is synonymous with "X or more and Y or less".

(1) Ferrite powder composed of spherical or polyhedral ferrite particles.
The ferrite powder contains 5.0 to 10.0% by mass of zinc (Zn) and 55.0 to 65.0% by mass of iron (Fe), has a composition of residual oxygen (O) and unavoidable impurities, and is crystalline. A ferrite powder having a child diameter in the range of 8.0 to 15.0 Å and a divalent iron ion (Fe ²⁺ ) content of 0.5 to 10.0% by mass.

(2) The ferrite powder according to (1) above, wherein the ferrite powder has a crystallite diameter of 9.0 to 13.0 Å.

(3) The ferrite powder according to (1) or (2) above, which has a divalent iron ion content of 1.0 to 7.6% by mass.

(4) The ferrite powder according to any one of (1) to (3) above, wherein the ferrite powder has an average shape coefficient SF-1 of 100 to 105.

(5) The ferrite powder according to any one of (1) to (4) above, wherein the volume average particle diameter (D50) of the ferrite powder is 0.1 to 10.0 μm.

(6) A ferrite resin composition containing the ferrite powder according to any one of (1) to (5) above and a resin.

(7) A ferrite resin molded body made of the ferrite resin composition of the above (6).

(8) An electronic component, an electronic device, or an electronic device housing provided with the ferrite resin molded body according to (7) above.

According to the present invention, there is provided a zinc ferrite powder which is excellent in magnetic properties even though it does not contain manganese and has good moldability, fluidity and filling property. Further, a ferrite resin composition containing such zinc ferrite powder, a resin molded body, an electronic component, an electronic device, or an electronic device housing is provided.

An example of the SEM image of the ferrite powder produced by the thermal spraying method is shown. An example of the SEM image of the ferrite powder produced by the thermal spraying method is shown. An example of the SEM image of the ferrite powder produced by the electric furnace firing method is shown. An example of the SEM image of the ferrite powder produced by the electric furnace firing method is shown.

A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described. The present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.

<< 1. Ferrite powder >>
The ferrite powder of this embodiment is composed of spherical or polyhedral ferrite particles. Further, this ferrite powder contains 5.0 to 10.0% by mass of zinc (Zn) and 55.0 to 65.0% by mass of iron (Fe), and has a composition of residual oxygen (O) and unavoidable impurities. Further, the crystallite diameter is in the range of 8.0 to 15.0 Å, and ^{the content of divalent iron ion (Fe 2+} ) is 0.5 to 10.0% by mass.

The ferrite powder of this embodiment is composed of spherical or polyhedral ferrite particles. That is, the ferrite powder contains a large number of spherical or polyhedral ferrite particles. By being composed of such ferrite particles, the ferrite powder becomes excellent in moldability and filling property when it is applied to a resin composition (ferrite resin composite material) as a filler. Spherical or polyhedral particles smoothly avoid contact with other particles during molding. Therefore, the fluidity at the time of molding is improved and the mixture is densely packed. On the other hand, particles having an anisotropic shape (indefinite shape) such as a plate shape or a needle shape are inferior in moldability and filling property. In the present specification, the amorphous particle includes an anisotropic particle and is used in comparison with a spherical particle or the like.

The shape of the particles constituting the ferrite powder may be spherical or polyhedral. However, the ferrite powder of the present embodiment contains zinc (Zn) having a high saturated vapor pressure, and the particles tend to be polyhedral. This is a high-temperature heating (spraying) process during the production of ferrite powder, in which components with high saturated vapor pressure move from the inside to the outside of the particles and function as flux, which causes the particles to grow into a polyhedron that reflects the crystal structure. It is thought to be easier.

Polyhedral particles basically have a shape in which a plurality of polygons are three-dimensionally combined. The polygons that make up a polyhedron typically consist of triangles, quadrilaterals, hexagons, octagons, decagons, or combinations thereof. Examples of such a polyhedron include a truncated cuboctahedron composed of a combination of a quadrangle, a hexagon, and an octagon. A polyhedron is closer to a sphere as the number of faces increases. Therefore, the polyhedral particles preferably have a shape of a tetradecahedron or more, more preferably a dodecahedron or more, and even more preferably a tetradecahedron or more. The polyhedral particles typically have a shape of 100 faces or less, more typically 72 faces or less, and more typically 24 faces or less.

The ferrite powder contains 5.0 to 10.0% by mass of zinc (Zn) and 55.0 to 65.0% by mass of iron (Fe), and has a composition of residual oxygen (O) and unavoidable impurities. This ferrite powder has a zinc ferrite composition and does not contain metal components other than zinc (Zn) and iron (Fe) in excess of the amount of unavoidable impurities. Here, the unavoidable impurity is a component that is inevitably mixed in during the manufacturing process, and refers to a component having a content of 5000 ppm or less. Inevitable impurities typically include silicon (Si), aluminum (Al), calcium (Ca), chlorine (Cl), boron (B), zirconium (Zr) and chromium (Cr).

Zinc ferrite is a type of spinel ferrite. Spinel ferrite is _{an oxide represented by the molecular formula of MO · Fe 2} O ₃ (M is a divalent metal such as Mn, Ni, Zn), and most of them exhibit ferromagnetism. Spinel ferrite has an ^{A site that occupies a tetrahedral position surrounded by four oxygen ions (O 2-} ) in the crystal structure and a B site that occupies an octahedral position surrounded by six oxygen ions. Have. Zinc ferrite belongs to positive spinel in the chemical composition, divalent zinc ion (Zn ²⁺ ) which is a non-magnetic ion occupies A site, and trivalent iron ion (Fe ³⁺ ) which is a magnetic ion occupies B site. Occupy. Half of the iron ions (Fe ³⁺ ) that occupy the B site have an upward magnetic moment (spin), and the other half have a downward magnetic moment. Since the magnetic moment of iron ions cancels out at temperatures below the nail point, zinc ferrite (ZnO · Fe ₂ O ₃ ) having a chemical composition is an antiferromagnetic material and does not exhibit magnetism. The stoichiometric composition of zinc ferrite has a zinc content of 27.1% by mass and an iron content of 46.3% by mass.

On the other hand, zinc ferrite containing an excess amount of iron (Fe) is a ferromagnet. That is, the surplus iron becomes divalent and trivalent iron ions (Fe ²⁺ , Fe ³⁺ ), which occupy the A and B sites in the spinel structure. Specifically, occupy A site trivalent iron ions ^{(Fe 3+)} together with divalent zinc ions ^{(Zn 2+),} divalent iron ions ^{(Fe 2+)} together with trivalent iron ions ^{(Fe 2+)} Occupies B site. Zinc ferrite containing an excess amount of iron can be regarded as a solid solution _{of zinc ferrite (ZnO · Fe 2} O ₃ ) and magnetite (FeO · Fe ₂ O _{3) having a stoichiometric composition.} The molecular formula of this ferrite is represented by (Zn ²⁺ , Fe ³⁺ ) O · [Fe ³⁺ , Fe ²⁺ ] ₂ O ₃ . Here, the ions in parentheses () are A-site ions, and the ions in square brackets [] are B-site ions. In this way, the trivalent iron ion (Fe ³⁺ ) enters the A site and the divalent iron ion (Fe ²⁺ ) enters the B site, so that the zinc ferrite exhibits ferromagnetism as a whole.

The ferrite powder of this embodiment has a composition of zinc ferrite containing excess iron and exhibits ferromagnetism. Therefore, the saturation magnetization (σs) is large. Further, this ferrite powder has a soft magnetic property, has a small coercive force (Hc) and a small remanent magnetization (σr), and has a high magnetic permeability (μ). Therefore, this ferrite powder is suitable for applications that require soft magnetic properties, such as inductors, transformers, electromagnetic wave shielding materials, and filters. In particular, the ferrite powder of the present embodiment has a high magnetic permeability (μ) at high frequencies and exhibits excellent moldability and filling property when applied to a ferrite resin composition as a filler. Therefore, when applied to an electromagnetic wave shielding material, it is possible to obtain excellent electromagnetic wave shielding performance.

When the zinc content is less than 5.0% by mass and / or the iron content is more than 65.0% by mass, the composition of the ferrite powder _{becomes close to magnetite (FeO / Fe 2} O ₃ ), which is not preferable. Magnetite tends to destabilize its saturation magnetization (σs) due to oxidation. In addition, the coercive force (Hc) is high and the magnetic permeability is relatively small. For these reasons, the zinc content is limited to 5.0% by mass or more and the iron content is limited to 65.0% by mass or less. The zinc content may be 6.0% by mass or more, 7.0% by mass or more, and 8.0% by mass or more. The iron content may be 64.0% by mass or less, 63.0% by mass or less, 62.0% by mass or less, or 61.0% by mass or less. On the other hand, when the zinc content is more than 10.0% by mass and / or the iron content is less than 55.0% by mass, the composition of the ferrite powder becomes close to that of zinc ferrite having a stoichiometric composition. Therefore, the saturation magnetization (σs) and the magnetic permeability (μ) may decrease, which is not preferable. For this reason, the zinc content is limited to 10.0% by mass or less and the iron content is limited to 55.0% by mass or more. The zinc content may be 9.0% by mass or less, 8.0% by mass or less, or 7.0% by mass or less. The iron content may be 58.0% by mass or more, 59.0% by mass or more, 60.0% by mass or more, 61.0% by mass or more, 62. It may be 0.0% by mass or more, and may be 63.0% by mass or more.

The ferrite powder of this embodiment has a crystallite diameter of 8.0 to 15.0 Å. Crystallets are the largest collection of single crystals that make up the particles in a powder, and each particle is generally made up of a plurality of single crystals. By limiting the crystallite diameter within the above numerical range, the magnetic permeability in the high frequency range becomes high. The detailed reason for this is not certain, but as described above, the correlation (length) of the magnetic moment inside the ferrite particles is moderately suppressed by having an appropriately sized crystallite diameter, so that the magnetic moment is appropriately suppressed with respect to the externally applied magnetic field. As a result of creating a state in which the magnetic moment is easy to move, it is estimated that the frequency characteristics of the real magnetic permeability (μ') are maintained up to the high frequency side. Further, it is considered that the contribution of rotational magnetization in the magnetization mechanism increases as the crystallite diameter becomes smaller to some extent, which affects the magnetic permeability. On the other hand, if the crystallite diameter is excessively large, the eddy current loss becomes large, and if the crystallite diameter is excessively small, the deterioration of magnetic characteristics due to the development of superparamagnetism cannot be ignored. The crystallite diameter is preferably 9.0 to 13.0 Å.

The crystallite diameter can be determined by the X-ray diffraction method. Specifically, an X-ray profile of the ferrite powder is obtained by an X-ray diffraction method. Focusing on a specific diffraction peak in the profile, the full width at half maximum (FWHM) β is obtained. From the obtained full width at half maximum β, the crystallite diameter D is obtained according to Scherrer's equation shown in the following equation (1). In the following equation (1), K is the Scheller constant, λ is the wavelength of the X-ray used, and θ is the Bragg angle of the diffraction peak. Further, in order to correct the error of the measuring device, it is preferable to use the corrected value for the half width β.

The ferrite powder of this embodiment has a divalent iron ion (Fe ²⁺ ) content of 0.5 to 10.0% by mass. By keeping the amount of divalent iron ions within the above range, it is possible to maintain the saturated magnetization and the magnetic permeability real part (μ') in the high frequency range at a high level even if the particle size is small. If the amount of ferrous ions is excessively small, the zinc ferrite constituting the powder does not exhibit ferromagnetism. Further, it is not preferable because the amount of non-magnetic hematite increases. The amount of ferrous ion may be 1.0% by mass or more, 2.0% by mass or more, 3.0% by mass or more, 4.0% by mass or more, and may be 4.0% by mass or more. It may be 5.0% by mass or more. On the other hand, if the amount of divalent iron ions is excessively large, the particles constituting the ferrite powder may be oxidized when the ferrite powder mixed with the resin is heat-cured or when treated with a chemical solution such as acid or alkali. There is. Oxidation of such particles is not preferable because the magnetic properties are impaired. Further, if the amount of divalent iron ions is excessively large, the amount of the non-magnetic wustite phase (FeO) increases, which may lead to deterioration of magnetic characteristics. The amount of divalent iron ion may be 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, and may be 5.0% by mass or less. It may be 4.0% by mass or less, and may be 3.0% by mass or less. The amount of divalent iron ions can be determined, for example, by redox titration.

Ferrite powder mainly contains a spinel phase. The content ratio of the spinel phase is preferably 90.0% by mass or more. Since the spinel phase exhibits ferromagnetism, the higher the content ratio, the higher the saturation magnetization (σs) and magnetic permeability (μ). The content ratio of the spinel phase may be 95.0% by mass or more, 99.0% by mass or more, or 99.5% by mass or more. On the other hand, the ferrite powder may contain phases other than the spinel phase and unavoidable impurities. Examples of other phases include excess zinc oxide (ZnO) and iron oxides other than spinel (α-Fe ₂ O ₃ , FeO, etc.). However, from the viewpoint of effectively utilizing the high magnetic properties based on the spinel phase, it is preferable that the content ratio of the other phases is small. The content ratio of the other phase may be 10.0% by mass or less, 5.0% by mass or less, 1.0% by mass or less, and 0.5% by mass or less. .. The ferrite powder does not have to contain other phases. Further, the unavoidable impurities are components having a content of 5000 ppm or less as described above.

_{The ferrite powder may contain hematite (α-Fe 2} O ₃ ) as long as the magnetic properties are not excessively deteriorated. By containing hematite, when the ferrite powder is mixed with the resin and further heat-cured, the oxidation of the particles constituting the powder is suppressed. Therefore, it is expected that the deterioration of the magnetic properties of the ferrite powder after heat curing is suppressed. The content of hematite may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 3.0% by mass or more. On the other hand, if an excessively large amount of hematite is contained, the saturation magnetization and magnetic permeability of the ferrite powder may decrease. The content of hematite may be 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.0% by mass or less, and 3. It may be 0% by mass or less.

The saturation magnetization (σs) of the ferrite powder is preferably 80.0 emu / g or more. By increasing the saturation magnetization, the real magnetic permeability (μ') can be increased, and the magnetic characteristics such as electromagnetic wave shielding performance can be improved. The saturation magnetization may be 82.0 emu / g or more, 84.0 emu / g or more, or 86.0 emu / g or more. The upper limit of saturation magnetization is limited by the composition of the ferrite powder and is typically 96.0 emu / g or less.

The residual magnetization (σr) of the ferrite powder is preferably 5.0 emu / g or less. By reducing the remanent magnetization, the real magnetic permeability (μ') can be increased, and magnetic characteristics such as electromagnetic wave shielding performance can be improved. Further, by lowering the residual magnetization, magnetic aggregation can be prevented. Therefore, the moldability, filling property and dispersibility of the ferrite powder applied to the filler can be made more excellent. The remanent magnetization may be 4.0 emu / g or less, 3.5 emu / g or less, or 3.0 emu / g or less. The lower limit of the remanent magnetization is not particularly limited. However, it is typically 0.5 emu / g or higher.

The coercive force (Hc) of the ferrite powder is preferably 100 Oe or less. By reducing the coercive force, the real magnetic permeability (μ') can be increased, and magnetic characteristics such as electromagnetic wave shielding performance can be improved. Further, by lowering the coercive force, magnetic aggregation can be prevented, and as a result, moldability, filling property and dispersibility can be improved. The coercive force may be 80 Oe or less, 60 Oe or less, 50 Oe or less, and 40 Oe or less. The lower limit of the coercive force is not particularly limited. However, it is typically 10 Oe or more.

The ferrite powder has a magnetic permeability real part (μ') at 100 MHz measured in the state of the ferrite resin molded body, preferably 6.00 or more. Here, the ferrite resin molded product is a molded product obtained by molding a ferrite resin composition containing a ferrite powder and a resin as described later. By increasing the actual magnetic permeability in this way, magnetic characteristics such as electromagnetic wave shielding performance become excellent. The actual magnetic permeability portion may be 6.50 or more, 7.00 or more, 7.50 or more, or 8.00 or more. The upper limit of the actual magnetic permeability portion is not particularly limited. However, it is typically 12.00 or less, and more typically 10.00 or less.

The ferrite powder has a loss coefficient (tan δ) at 100 MHz measured in the state of the ferrite resin molded body, preferably 0.15 or less. This makes it possible to suppress loss. The loss coefficient may be 0.12 or less, 0.10 or less, 0.08 or less, 0.06 or less, or 0.04 or less. The loss coefficient (tan δ) can be calculated from the real part (μ ″) and the imaginary part (μ ″) of the complex magnetic permeability at a frequency of 100 MHz according to the following equation (2).

The ferrite powder has a relative density ratio (μ'/ d) of the actual magnetic permeability portion at 100 MHz, preferably 2.00 or more. ^{Here, the relative density ratio of the actual magnetic permeability is the density (d, unit: g / cm 3} ) of the sample for measurement, which is the actual magnetic permeability (μ') measured in the state of the ferrite resin molded body (measurement sample). It is a value divided by) and is calculated according to the following equation (3).

When the measurement sample is made of a uniform material, the magnetic permeability is calculated in consideration of the influence of the sample shape (thickness, inner diameter, outer diameter). Therefore, the influence of the sample shape is excluded from the calculated magnetic permeability. On the other hand, when the sample is made of a composite material (ferrite resin molded body) composed of a filler (ferrite powder) and a resin, the calculated magnetic permeability includes the influence of the dispersion / filling state of the filler in the sample and the voids. .. In evaluating the magnetic permeability of the ferrite powder alone, it is desirable to eliminate the influence of the filler dispersion / filling state and voids. This effect can be minimized by finding the relative density ratio of the real magnetic permeability part. Therefore, it can be said that the relative density ratio of the actual magnetic permeability portion represents the actual magnetic permeability portion of the ferrite powder alone, excluding the influence of the filler dispersion / filling state and the like. The relative density ratio of the real part of the magnetic permeability may be 2.20 or more, 2.40 or more, or 2.60 or more.

Permeability The shape of the sample for measurement is not limited as long as the magnetic permeability can be measured in determining the relative density ratio of the real part. An example is the toroidal shape. When the measurement sample is a toroidal having an outer diameter φo (unit: cm), an inner diameter φi (unit: cm), a thickness t (unit: cm), and a mass m (unit: g), the measurement sample density d (unit: g / cm ³ ) is obtained according to the following equation (4).

The average shape coefficient SF-1 of the ferrite powder is preferably 100 to 105. Here, the average shape coefficient SF-1 of the powder is an average value of the shape coefficients of individual particles. Further, the shape coefficient SF-1 of the particle is an index of the sphericity of the particle, and is 100 for a perfect sphere, and increases as the distance from the sphere increases. By setting the average shape coefficient SF-1 to 105 or less, the fluidity of the powder becomes high, and the moldability and the filling property become more excellent. SF-1 may be 103 or less, and may be 101 or less.

The average shape coefficient SF-1 of the ferrite powder is obtained by obtaining the shape coefficient SF-1 of each particle for a plurality of ferrite particles and calculating the average value thereof. The ferrite particle SF-1 measures the horizontal ferret diameter R (unit: μm), projected peripheral length L (unit: μm), and projected area S (unit: μm ² ) of the particle, and uses the following equation (5). Therefore, it can be obtained.

The volume average particle size (D50) of the ferrite powder is preferably 0.1 to 10.0 μm. Here, the volume average particle diameter is a 50% cumulative diameter in the volume particle size distribution of the ferrite powder. By increasing the volume average particle size to some extent, it is possible to suppress an increase in the viscosity of the resin composition and increase the filler filling rate. The volume average particle diameter may be 0.2 μm or more, and may be 0.4 μm or more. On the other hand, the loss coefficient (tan δ) can be made smaller by setting the volume average particle size to 10.0 μm or less. The volume average particle size may be 7.5 μm or less, and may be 5.0 μm or less. The particle size distribution may have two or more peaks. Here, having two or more peaks means that when the volume particle size distribution is viewed as a function of the logarithmic particle size, the derivative (differential coefficient) of the function or the value of the derivative twice or more becomes 0. It means that there are two or more points (maximum points, inflection points, saddle points, etc.).

The particle size distribution ratio ((D90-D10) / D50) of the ferrite powder is preferably 0.1 to 30.0. The particle size distribution ratio is an index of particle size variation, and the higher the particle size distribution ratio, the larger the particle size variation. By appropriately increasing the particle size variation, when the ferrite powder is applied to the resin composition as a filler, the filling property of the ferrite powder in the composition can be improved. The particle size distribution ratio may be 1.0 or more, 6.0 or more, or 10.0 or more. On the other hand, if the particle size distribution ratio is excessively high, the proportion of fine particles and coarse particles increases, which may reduce the fluidity and moldability of the ferrite powder. The particle size distribution ratio may be 20.0 or less, 10.0 or less, or 5.0 or less. The particle size distribution ratio can be determined according to the following equation (6) using the 10% cumulative diameter (D10), 50% cumulative diameter (D50), and 90% cumulative diameter (D90) in the volumetric particle size distribution of the ferrite powder. can.

The BET specific surface area of the ferrite powder is preferably 0.1 to 10.0 m ² / g. By setting the BET specific surface area to 0.1 m ² / g or more, the generation of interparticle voids can be suppressed, and the filling property becomes more excellent. BET specific surface area may be at 0.2 m ² / g or more, may be 0.4 m ² / g or more. On the other hand, by setting the BET specific surface area to 10.0 m ² / g or less, the aggregation of the ferrite powder can be suppressed, and the moldability and the filling property become more excellent. Further, by setting the BET specific surface area within the above range, the adhesion to the resin becomes better when the ferrite powder is applied to a composite material or a composite. BET specific surface area may be less than or equal 8.5 m ² / g, may be not more than 6.5m ² / g.

The true specific gravity (true density) of the ferrite powder is preferably 5.00 g / cm ³ or more. As a result, the saturation magnetization and magnetic permeability of the ferrite powder become even higher. True specific gravity may be at 5.10 g / cm ³ or more, may be at 5.20 g / cm ³ or more, may be at 5.30 g / cm ³ or more, even 5.40 g / cm ³ or more good. The upper limit of the true specific density is not particularly limited. However, it is difficult to make the true specific density of ferrite ^{more than 6.00 g / cm 3.} Therefore, the true specific density is typically 6.00 g / cm ³ or less.

The tap density of the ferrite powder is preferably 0.01 to 3.50 g / cm ³ . The tap density can be increased by mixing the small particle size particles and the large particle size particles, and as a result, the filling property of the ferrite powder when applied to the resin composition becomes better as a whole. The tap density may be at 0.10 g / cm ³ or more, may be 1.00 g / cm ³ or more.

The tap density ratio of the ferrite powder is preferably 0.15 to 0.60. As a result, the filling property of the ferrite powder when applied to the resin composition is improved. The tap density ratio may be 0.20 to 0.59. The tap density ratio is the ratio of the tap density to the true specific gravity, and can be obtained according to the following equation (7).

The lattice constant of the ferrite powder is preferably 8.350 to 8.402 Å. By keeping the lattice constant within the above range, the true specific gravity of the ferrite powder becomes high, and as a result, the relative density ratio (μ'/ d) of the real magnetic permeability part representing the real magnetic permeability part of the ferrite powder alone becomes high. Become.

<< 2. Ferrite powder manufacturing method >>
The method for producing the ferrite powder of the present embodiment is not particularly limited. However, it is preferably produced by the thermal spraying method. The production method of a preferred embodiment is as follows: a step of mixing a zinc (Zn) raw material and an iron (Fe) raw material to form a raw material mixture (raw material mixing step), and a calcined product by calcining the obtained raw material mixture. (Temporary firing process), crushing and granulating the obtained temporary baked product to make a granulated product (granulation process), and spraying the obtained granulated product into a molten product. Has (spraying process). In the step of making a thermal spray (spraying step), the raw material supply rate is set to 3 to 20 kg / hour, the combustion gas flow rate is set to 3 to 15 m ³ / hour, and the oxygen flow rate is set to 15 to 120 m ³ / hour. Details of each step will be described below.

<Ingredient mixing process>
In the raw material mixing step, a zinc (Zn) raw material and an iron (Fe) raw material are mixed to form a raw material mixture. As the zinc raw material and the iron raw material, known ferrite raw materials such as oxides, carbonates, hydroxides and / or chlorides may be used. For example, zinc oxide (ZnO), zinc carbonate (ZnCO ₃ ), and zinc hydroxide (Zn (OH) ₂ ) can be used as the zinc raw material. Further, as iron raw materials, iron oxide (Fe ₂ O ₃ , FeO, Fe ₃ O ₄ ), iron carbonate (FeCO ₃ ), iron hydroxide (Fe (OH) ₂ , Fe (OH) ₃ ), iron oxide hydroxide ( FeO (OH)) can be used. The mixing ratio of the raw materials may be adjusted so that a ferrite powder having a desired composition can be obtained. The raw materials may be mixed using a known mixer such as a Henschel mixer, and either dry or wet may be used. Further, the raw material mixture may be granulated (temporarily granulated) using a granulation device such as a roller compactor.

<Temporary firing process>
In the calcining step, the obtained raw material mixture is calcined to obtain a calcined product. Temporary firing may be performed by a known method. For example, a furnace such as a rotary kiln, a continuous furnace, or a batch furnace may be used. The tentative firing conditions may also be known conditions. For example, a condition of holding at 700 to 1300 ° C. for 0.5 to 12 hours in an atmosphere such as air can be mentioned.

<Granulation process>
In the granulation step, the obtained calcined product is crushed and granulated (main granulation) to obtain a granulated product (main granulated product). The crushing method is not particularly limited. For example, a known crusher such as a vibration mill, a ball mill or a bead mill may be used, and either the dry type or the wet type or both may be performed. The granulation method may be a known method. For example, water and, if necessary, an additive such as a binder resin such as polyvinyl alcohol (PVA), a dispersant and / or an antifoaming agent are added to the pulverized temporary baked product to adjust the viscosity, and then the viscosity is adjusted. Granulation may be performed using a granulator such as a spray dryer.

<Spraying process>
In the thermal spraying process, the granulated material is sprayed into a thermal spray. In thermal spraying, a mixed gas of combustion gas and oxygen is used as a flammable gas combustion flame source. Granulated products, which are the raw materials for thermal spraying, pass through a high-temperature combustion flame. At that time, a ferrite reaction occurs, and a part of the granulated product melts into spherical ferrite particles. As the combustion gas, flammable gas such as propane gas, propylene gas, and acetylene gas can be used, and among them, propane gas is preferably used.

At the time of thermal spraying, set the raw material supply rate to 3 to 20 kg / hour. If the supply rate is excessively high, the granulated products tend to adhere to each other, and it becomes difficult to sufficiently proceed the ferrite formation reaction to the inside of the particles. Therefore, there is a possibility that it is difficult to obtain particles having a high sphericity, or problems such as not being able to obtain desired magnetic characteristics may occur. On the other hand, if the supply rate is excessively low, it causes an increase in manufacturing cost. From these viewpoints, the present embodiment defines the supply rate of the thermal spraying raw material. By setting the supply rate within the above range, it becomes possible to efficiently obtain a ferrite powder having a high sphericity and excellent magnetic properties. The feeding rate may be 4-10 kg / hour.

At the time of thermal spraying, the combustion gas flow rate is set to 3 to 15 m ³ / hour and the oxygen flow rate is set to 15 to 120 m ³ / hour. By defining the combustion gas flow rate and the oxygen flow rate within the above ranges, it becomes possible to efficiently obtain a ferrite powder having a high sphericity and excellent magnetic characteristics.

Oxygen used in thermal spraying also has the function of transporting the raw material to the thermal spray flame. Depending on the function, it is possible to consider the oxygen as the combustion oxygen directly used for the flame and the raw material supply oxygen that is burned after the raw material is transported to the central part of the thermal spray source. Therefore, total oxygen can be represented by combustion oxygen + raw material supply oxygen. Further, the amount of carbon contained in the ferrite powder after thermal spraying can be controlled by the ratio of the volumes of combustion oxygen and raw material supply oxygen. The ratio of combustion oxygen to raw material supply oxygen is a volume ratio, and combustion oxygen: raw material supply oxygen = 95: 5 to 80:20 is preferable. If the ratio of combustion oxygen becomes larger than 95 (approaches 100), the raw material supply capacity may decrease and the raw material may be blocked in the raw material supply pipe. On the other hand, when the ratio of combustion oxygen is smaller than 80 (less than 80), the raw material is spread and supplied to a portion outside the central portion of the flame, which has the highest temperature. Therefore, the ferrite formation reaction cannot be sufficiently advanced to the inside of the particles, and as a result, the _{amount of α-Fe 2} O ₃ contained in the ferrite powder after thermal spraying may increase. From the viewpoint of not increasing the amount of α-Fe ₂ O ₃ more than necessary, combustion oxygen: raw material supply oxygen = 92.5: 7.5 to 81.5: 18.5 is more preferable, and combustion oxygen: raw material supply. Oxygen = 91: 9 to 81.5: 18.5 is more preferable, and combustion oxygen: raw material supply oxygen = 91: 9 to 84:16 is particularly preferable.

Further, the amount of combustion oxygen is preferably 0.85 times or more the capacity (equivalent) required for complete combustion of the combustion gas. For example, when propane gas is used as the combustion gas, the capacity of combustion oxygen is preferably 4.25 times or more that of propane gas. By doing so, even if excess oxygen is supplied than the amount (equivalent) required for complete combustion of the combustion gas, the temperature drop of the thermal spray flame is minimized, and α-Fe ₂ O _{The occurrence of 3} can be prevented more than necessary.

The combustion gas amount ratio is preferably 1.05 or more and 2.00 or less. Here, the combustion gas amount ratio is the ratio of the combustion gas amount (Nm ³ / hour) used for net combustion to the raw material supply amount (kg / hour), and is calculated according to the following equation (8).

The amount of combustion gas (Nm ³ / hour) used for net combustion is calculated according to the following equation (9) or the following equation (10).

Particles ferriteified by thermal spraying are rapidly cooled and solidified in an atmospheric atmosphere, and these are recovered by a cyclone or a filter to obtain a thermal spray. When the sprayed material is recovered by a cyclone, it is preferable to introduce a diluting gas to quench the sprayed material (particles) and recover the sprayed material (particles) that has been rapidly cooled by the cyclone. As a result, ferrite particles (powder) with minimal composition deviation can be obtained. That is, zinc (Zn) has a high saturated vapor pressure and easily volatilizes in a high-temperature sprayed flame. Therefore, when zinc-containing ferrite is produced by a conventional thermal spraying method, the obtained particles may have a large composition deviation from the raw material and the characteristics may deteriorate. On the other hand, by introducing a diluting gas to quench the particles, it becomes possible to minimize the composition deviation. The gas is not particularly limited as long as it can rapidly cool the particles as the dilution gas. One example is air.

<Classification process>
If necessary, the obtained sprayed material may be classified. In the classification, the particle size may be adjusted to a desired particle size by using a known method such as wind power classification (air flow classification), mesh classification, or sieve (sieve) classification. It is also possible to separate and recover particles having a large particle size and particles having a small particle size in one step by airflow classification such as a cyclone. In this way, the ferrite powder can be obtained.

The ferrite powder of the present embodiment thus obtained has good moldability, fluidity and filling property because the particles constituting the ferrite powder have the shape of a sphere or a polyhedron. Further, this ferrite powder is excellent in magnetic properties even though it does not contain manganese. In particular, this ferrite powder maintains high magnetic permeability even at a high frequency of 100 MHz. Further, since this ferrite powder is composed of zinc ferrite containing no manganese, dustproof treatment for preventing scattering of the manganese raw material becomes unnecessary at the time of its production, and it becomes possible to reduce the production cost.

As far as the present inventors know, such a ferrite powder and a method for producing the same are not known conventionally. For example, the spherical particles made of manganese-based ferrite proposed in Patent Documents 1 and 2 have excellent magnetic properties and are useful for applications such as electromagnetic wave shielding materials, but manganese is an essential component. Therefore, dustproof treatment is required to prevent the scattering of manganese raw materials during manufacturing. Further, although true spherical manganese (Mn) ferrite is disclosed in Patent Document 1, since manganese is used, the true specific gravity does not increase. Zinc has a larger atomic weight and a larger ionic radius than manganese. Therefore, the ferrite powder containing zinc does not always have a high true specific gravity. The zinc ferrite powder of the present embodiment can have a higher true specific gravity by making the lattice constant smaller than that of manganese ferrite and by containing a certain amount of zinc. Further, the zinc ferrite powder of the present embodiment has a high true specific gravity, and the resin molded body produced by using the zinc ferrite powder has an increased amount of magnetic material per unit volume, so that the magnetic characteristics are improved.

A technique for producing zinc ferrite powder by firing and crushing a raw material has also been conventionally known, but the calcined zinc ferrite powder has a large crystallite diameter and is a pair of a magnetic permeability real part (μ') and a magnetic permeability real part. The density ratio (μ'/ d) is inferior. Further, the zinc ferrite powder crushed after firing has a further inferior density ratio between the actual magnetic permeability portion and the actual magnetic permeability portion due to the pulverization stress. Therefore, the conventional zinc ferrite powder produced by the firing method is inferior to the zinc ferrite powder of the present embodiment.

The zinc ferrite powders proposed in Patent Documents 3 and 4 do not consist of spherical particles, and have problems in terms of moldability, fluidity, and filling property. Further, Patent Documents 3 and 4 only show static magnetic field characteristics such as saturation magnetization and coercive force with respect to the characteristics of zinc ferrite powder, and there is no description regarding specific uses other than electrophotographic toner. Therefore, it is unclear whether these zinc ferrite powders can be applied to high frequency applications such as electromagnetic wave shielding materials. In fact, the zinc ferrite powder (ferrite B) of Patent Document 3 has a high holding power (coercive force) Hc of 185 Oe, and the zinc ferrite powder of Patent Document 4 has the lowest coercive force Hc of 92 Oe (Patent Document 3). Table 1 and Table 2) of Patent Document 4. It is presumed that the ferrite powder having such a high coercive force is inferior in magnetic permeability. In Patent Document 4, the thermal decomposition reaction and the solid phase reaction of the raw material mixture are simultaneously performed in the roasting step (claim 1 of Patent Document 4), but this roasting step is different from the spraying step of the present embodiment. .. That is, in Patent Document 4, roasting is performed at 750 ° C. in Examples, but the raw material does not melt at such a low temperature.

Patent Document 5 _{proposes a granular magnetite particle powder coated with Zn x} Fe _{2 +} _yOz (zinc ferrite), but the component composition of this powder is different from that of the ferrite powder of the present embodiment. That is, the powder of Patent Document 5 has a Zn amount of 0.5 to 4.0 mol% with respect to the total Fe (claim 1 of Patent Document 5), and the mass ratio of Zn with respect to Fe is 0.047 or less in terms of this. be. On the other hand, in the ferrite powder of the present embodiment in which the amount of Zn is 5.0% by mass or more and the amount of Fe is 65.0% by mass or less, the mass ratio of Zn to Fe is 0.077 or more. Therefore, it can be said that the powder of Patent Document 5 has a smaller amount of zinc (Zn) than the ferrite powder of the present embodiment. Moreover, it is unclear whether the powder of Patent Document 5 can be applied to high frequency applications such as electromagnetic wave shielding materials. In fact, the powder of the example of Patent Document 5 has an Fe ²⁺ content of 20.1 wt% or more, a residual magnetization of 4.8 emu / g or more, and a coercive force of 58 Oe or more (Table 3 of Patent Document 5). It is considered that the powder containing a large amount of ferrous iron (Fe ²⁺ ) and having high residual magnetization and coercive force is inferior in magnetic permeability.

<< 3. Ferrite resin composition >>
The ferrite powder of this embodiment can be applied to a ferrite resin composition (composite material) as a filler. The ferrite resin composition contains a ferrite powder and a resin. By using the ferrite powder of the present embodiment as a filler, a composition having excellent magnetic properties can be obtained even if the filler filling rate is high.

Examples of the resin constituting the resin composition include epoxy resin, urethane resin, acrylic resin, silicone resin, polyamide resin, polyimide resin, polyamideimide resin, fluororesin and / or a combination thereof. Here, the silicone resin may be a modified silicone resin modified with acrylic, urethane, epoxy and / or fluorine or the like.

The ratio of the ferrite powder to the total solid content in the resin composition is preferably 50 to 95% by mass, more preferably 80 to 95% by mass. The ratio of the resin to the total solid content in the resin composition is preferably 5 to 50% by mass, more preferably 5 to 20% by mass. By setting the ratio of the ferrite powder or the resin within the above range, the dispersion stability of the ferrite powder in the resin composition, the storage stability and moldability of the composition are excellent, and the molding obtained by molding the composition is excellent. The mechanical strength of the body and the electromagnetic wave shielding performance will be more excellent.

The resin composition may contain a ferrite powder and other components other than the resin. Examples of such components include solvents, fillers (organic fillers, inorganic fillers), plasticizers, antioxidants, dispersants, colorants such as content, and thermally conductive particles.

<< 4. Ferrite resin molded body >>
The ferrite resin molded body of the present embodiment is made of a ferrite resin composition. That is, a ferrite resin molded product can be obtained by molding the resin composition. The molding method is not particularly limited. For example, compression molding, extrusion molding, injection molding, blow molding or calendar molding can be mentioned. Further, a method of forming a coating film of the resin composition on the substrate may be used. Further, heat curing treatment may be performed after molding.

The ferrite resin molded body has a magnetic permeability real part (μ') at 100 MHz, preferably 6.00 or more. As a result, magnetic characteristics such as electromagnetic wave shielding performance become excellent. The actual magnetic permeability portion may be 6.50 or more, 7.00 or more, 7.50 or more, or 8.00 or more. The upper limit of the actual magnetic permeability portion is not particularly limited. However, it is typically 12.00 or less, and more typically 10.00 or less.

The ferrite resin molded body has a loss coefficient (tan δ) at 100 MHz, preferably 0.15 or less. This makes it possible to suppress loss. The loss coefficient may be 0.12 or less, 0.10 or less, 0.08 or less, 0.06 or less, or 0.04 or less.

<< 5. Electronic components, electronic devices or electronic device housings >>
The electronic component, electronic device, or electronic device housing of the present embodiment includes a ferrite resin molded body. Here, the electronic component is a component provided with a ferrite resin molded body as an inductor, a transformer, an electromagnetic wave shielding material, or a filter. For example, by incorporating a conductive coil in a ferrite resin molded body, it becomes an inductor. The electronic component may include this inductor. Further, a ferrite resin molded body that acts as an electromagnetic wave shielding material may be provided on an element provided with a passive component such as a capacitor or an active component such as an IC. As a result, it is possible to block the radiation of electromagnetic waves generated from the element to the outside, and it is possible to suppress the invasion of electromagnetic waves in the external environment into the element. As long as the electronic component includes a ferrite resin molded body, its mode is not limited.

Electronic devices are devices equipped with electronic components. For example, a mobile phone equipped with an inductor, a computer, and the like can be mentioned. The electronic device housing is a housing used for electronic devices. By applying the ferrite resin molded body to the housing, it is possible to suppress the radiation of electromagnetic waves from the inside to the outside or the invasion from the outside to the inside. The mode in which the ferrite resin molded body is applied to the housing is not particularly limited. For example, the molded body may be attached to the housing body, or the ferrite resin composition may be applied and cured on the housing body to form a molded body.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples.

(1) Preparation of Ferrite Powder [Example 1]
In Example 1, a zinc (Zn) ferrite powder was prepared by a thermal spraying method. The specific production procedure is as shown below.

<Ingredient mixing and temporary granulation process>
Using iron oxide (Fe ₂ O ₃ ) and zinc oxide (ZnO) as raw materials, weigh the raw materials so that the molar ratio of iron (Fe) to zinc (Zn) is Fe: Zn = 11.95: 1. Mixing was performed. A Henschel mixer was used for mixing. The obtained mixture was tentatively granulated using a roller compactor to obtain a tentative granulation product.

<Calcination process>
The temporarily granulated raw material mixture (temporarily granulated product) was calcined to obtain a calcined product. The calcining was carried out using a rotary kiln under the conditions of 900 ° C. for 1 hour in the air.

<Main granulation process>
The obtained calcined product was crushed and granulated to obtain a granulated product (main granulated product). First, the obtained calcined product is roughly pulverized using a dry bead mill (3/16 inch φ steel ball beads), then water is added, and finely pulverized using a wet bead mill (0.65 mmφ zirconia beads). bottom. The obtained slurry had a solid content concentration of 50% by mass. Then, the obtained slurry was supplied to a spray dryer for granulation.

<Thermal spraying and classification process>
The obtained granulated product was sprayed and rapidly cooled in a flammable gas combustion flame. During spraying, the propane gas flow rate 7m ³ / time, the oxygen flow rate set to 38m ³ / time, the raw material supply rate was 5 kg / time for propane gas 7m ³ / time. Subsequently, the cooled particles were recovered by a cyclone provided on the downstream side of the air flow to obtain a thermal spray. When recovering the particles, air was introduced as a dilution (quenching) gas immediately after the thermal spraying to quench the particles. Further, the obtained sprayed material was subjected to a rating treatment for removing coarse powder using a mesh (sieve). As a result, a ferrite powder was produced. At the time of thermal spraying, the volume ratio was set to combustion oxygen: raw material supply oxygen = 85.5: 14.5.

[Example 2]
In the thermal spraying step, the cooled particles were recovered using a bag filter. In addition, no classification treatment was performed after thermal spraying. A ferrite powder was prepared in the same manner as in Example 1 except for the above.

[Example 3]
In the raw material mixing step, the raw materials were weighed and mixed so that the molar ratio of iron (Fe) and zinc (Zn) was Fe: Zn = 10: 1. A ferrite powder was prepared in the same manner as in Example 1 except for the above. As in Example 1, immediately after the thermal spraying, air was introduced as a dilution (quenching) gas to quench the particles.

[Example 4]
In the thermal spraying step, the cooled particles were recovered using a bag filter. In addition, no classification treatment was performed after thermal spraying. A ferrite powder was prepared in the same manner as in Example 3 except for the above.

[Comparative Example 1]
In Comparative Example 1, zinc (Zn) ferrite powder was prepared by an electric furnace firing method. The specific production procedure is as shown below.

<Ingredient mixing and temporary granulation process>
Using iron oxide (Fe ₂ O ₃ ) and zinc oxide (ZnO) as raw materials, weigh the raw materials so that the molar ratio of iron (Fe) and zinc (Zn) is Fe: Zn = 8.36: 1. Mixing was performed. A Henschel mixer was used for mixing. The obtained mixture was tentatively granulated using a roller compactor to obtain a tentative granulation product.

<Calcination process>
The temporarily granulated raw material mixture (temporarily granulated product) was calcined to obtain a calcined product. The calcining was carried out using a rotary kiln under the condition of 800 ° C. for 1 hour in the air.

<De-binder and main firing process>
The obtained granulated product was debindered and further fired. The debinder treatment was carried out under the condition of 800 ° C. for 2 hours in an atmosphere having an oxygen concentration of 0 vol%. The main firing was carried out in an atmosphere of 0 vol% oxygen concentration using an electric furnace under the condition of 1300 ° C. × 4 hours.

<Grinding and drying process>
The obtained fired product was finely pulverized using a wet bead mill (zirconia beads having a diameter of 0.65 mm). The obtained slurry was solid-liquid separated using a filter paper to obtain a pulverized product, and then dried at 120 ° C. using a dryer (Airbus). The dried pulverized product was pulverized with a sample mill to obtain a ferrite powder.

[Comparative Example 2]
In the raw material mixing step, the raw materials were weighed and mixed so that the molar ratio of iron (Fe) and zinc (Zn) was Fe: Zn = 11.99: 1. A ferrite powder was prepared in the same manner as in Comparative Example 1 except for the above.

[Comparative Example 3]
After the main firing, crushing and drying were not performed, but instead crushing treatment and classification were performed. The crushing treatment was carried out by crushing the fired product after the main firing using an impact type crushing device. The classification was performed by classifying the obtained crushed product using an air flow classifier. A ferrite powder was prepared in the same manner as in Comparative Example 1 except for the above.

[Comparative Example 4]
The classification conditions for crushed material were changed. A ferrite powder was prepared in the same manner as in Comparative Example 3 except for the above.

[Comparative Example 5]
In Comparative Example 5, a manganese (Mn) ferrite powder was prepared by a thermal spraying method. The specific production procedure is as shown below.

<Ingredient mixing process>
_{Iron oxide (Fe 2} O ₃ ) and trimanganese tetraoxide (Mn ₃ O ₄ ) are used as raw materials, and the molar ratio of iron (Fe) to manganese (Mn) is set to Fe: Mn = 7.8: 1. Weighed so as to be, and mixed using a Henschel mixer.

<Temporary firing process>
The resulting mixture was calcined using a rotary kiln. The calcination was carried out by holding the mixture in the air at 900 ° C. for 4 hours.

<Main granulation process>
The obtained calcined product was crushed and granulated to obtain a granulated product (main granulated product). First, the obtained calcined product is roughly pulverized using a dry bead mill (3/16 inch steel ball beads), then water is added and finely pulverized using a wet bead mill (0.65 mm zirconia beads). bottom. The particle size of the pulverized powder was 2.26 μm. Next, polyvinyl alcohol (PVA, 10% aqueous solution) as a binder was added to the obtained slurry in an amount of 0.017% by mass in terms of solid content. Then, the slurry to which the binder was added was granulated using a spray dryer.

<Thermal spraying and classification process>
The obtained granulated product was sprayed and rapidly cooled in a flammable gas combustion flame. Thermal spraying was carried out under the conditions of a propane gas flow rate of 7 m ³ / hour, an oxygen flow rate of 38 m ³ / hour, and a raw material supply rate of 6.5 kg / hour. Subsequently, the cooled particles were recovered by a cyclone provided on the downstream side of the air flow to obtain a thermal spray. Coarse powder was removed from the obtained sprayed product using a sieve, and fine powder was further removed by air flow classification to obtain manganese ferrite powder.

(2) Evaluation of Ferrite Powder The ferrite powders obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were evaluated as shown below.

<Component analysis-Amount of metal component>
The metal component content of the ferrite powder was determined by chemical analysis (ICP). First, 0.2 g of a sample (ferrite powder) was weighed, 60 ml of pure water, 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid were added thereto, and then heated to prepare an aqueous solution in which the sample was completely dissolved. The obtained aqueous solution was set in an ICP analyzer (Shimadzu Corporation, ICPS-10001V), and the metal component content was measured.

<Component analysis-Fe ²⁺ amount>
The amount of ferrous ion (Fe ²⁺ ) in the ferrite powder was measured. Specifically, the ferrite powder was dissolved in sulfuric acid, and the measurement was carried out by redox titration using a potassium permanganate standard solution.

<Crystal structure analysis>
The ferrite powder was analyzed by an X-ray diffraction method to analyze the crystal phase and crystal structure. Specifically, the analysis was performed under the following conditions.

-X-ray diffractometer: PANalytical X'pert MPD (including high-speed detector)
-Radioactive source: Co-Kα
-Tube voltage: 45kV
-Tube current: 40mA
-Scan speed: 0.002 ° / sec (continuous scan)
-Scan range (2θ): 15-90 °

Next, the analysis results were analyzed to determine the proportions of the spinel phase, hematite phase (α-Fe ₂ O ₃ ) and wustite phase (FeO) among the crystal phases of the ferrite powder. The analysis was performed as follows. That is, after removing the background and peaks of Co-Kβ rays using analysis software (PANalytical, HighScorePlus3.0), the peak of the profile was automatically detected. The full width at half maximum and the position of each detected peak were optimized (refined) by Rietveld analysis, and the ratio of each phase and the lattice constant of each phase were obtained based on the obtained results. The ratio of each phase and the lattice constant were obtained by automatic calculation of analysis software.

Further, the above analysis result was analyzed to determine the crystallite diameter of ferrite. Specifically, focusing on the (311) diffraction peak in the X-ray profile, the full width at half maximum (FWHM) β of this diffraction peak was determined. From the obtained full width at half maximum β, the crystallite diameter D was determined according to Scherrer's equation shown in the following equation (1). In the following equation (1), K is the Scheller constant (0.9), λ is the wavelength of the X-ray used (1.78901 Å), and θ is the Bragg angle (about 41.3 °) of the (311) diffraction peak. ..

<Particle shape-SEM observation>
The shape of the particles in the ferrite powder was evaluated by observing with a scanning electron microscope (SEM). The observation was carried out using a scanning electron microscope (Hitachi High-Technologies Corporation, SU-8020) under the conditions of a magnification of 1000 to 100,000 times.

<Particle shape-SF-1>
The measurement of the average shape coefficient (SF-1) of the ferrite powder was carried out separately for the case where the volume average particle diameter (D50) of the ferrite powder was 1 μm or more and the case where it was less than 1 μm.

For ferrite powder with D50 of 1 μm or more, SF-1 was determined as follows. Ferrite powder was analyzed using a particle image analyzer (Malvern Panasonic, Moforogi G3). At the time of analysis, image analysis for each particle of 30,000 particles in the powder was performed with the magnification of the objective lens set to 50 times, and the maximum length R (horizontal ferret diameter, unit: μm) and projection peripheral length L (unit: μm). And the projected area S (unit: μm ² ) was automatically measured. Next, SF-1 was calculated for each particle according to the following equation (5), and the average value was taken as SF-1 of the ferrite powder.

For ferrite powders with a D50 of less than 1 μm, SF-1 was determined as follows. A resin molded body was produced in the same manner as the resin molded body for measuring magnetic permeability, which will be described later, and cross-section processing was performed with an ion milling device. Then, the particle cross section was photographed in a plurality of fields with a field emission scanning electron microscope (FE-SEM; Hitachi High-Tech Technologies Corporation, SU-8020). The shooting was performed at a magnification of 50,000 times. In the obtained SEM image, the ferrite powder was analyzed using image analysis software (Media Cybernetics, ImageProPlus). At the time of analysis, image analysis is performed for each of 300 particles in the powder, and the maximum length R (horizontal ferret diameter, unit: μm), projection circumference length L (unit: μm), and projection area S (unit: μm ^{2) are performed.} ) Was calculated. Next, SF-1 was calculated for each particle according to the above equation (5), and the average value thereof was taken as SF-1 of the ferrite powder.

<Particle size distribution>
The particle size distribution of the ferrite powder was measured. First, 10 g of a sample and 80 ml of water were placed in a 100 ml beaker, and 2 drops of sodium hexametaphosphate was added as a dispersant. Then, dispersion was performed using an ultrasonic homogenizer (SMT Co., Ltd., UH-150 type). At this time, the output level of the ultrasonic homogenizer was set to 4, and dispersion was performed for 20 seconds. Then, the bubbles formed on the surface of the peaker were removed and introduced into a laser diffraction type particle size distribution measuring device (Shimadzu Corporation, SALD-7500 nano) for measurement. By this measurement, 10% diameter (D10), 50% diameter (volume average particle diameter, D50), 90% diameter (D90) and maximum diameter (Dmax) in the volume particle size distribution were determined. The measurement conditions were a pump speed of 7, a built-in ultrasonic irradiation time of 30, and a refractive index of 1.70-050i.

<BET specific surface area>
The BET specific surface area ( _SBET ) of the ferrite powder was measured using a specific surface area measuring device (Mountech Co., Ltd., Macsorb HM model-1208). First, about 10 g of the obtained ferrite powder was placed on a medicine wrapping paper and degassed with a vacuum dryer to confirm that the degree of vacuum was −0.1 MPa or less. Then, by heating at 200 ° C. for 2 hours, the water adhering to the particle surface was removed. Approximately 0.5 to 4 g of the water-removed ferrite powder was placed in a standard sample cell dedicated to the measuring device and weighed accurately with a precision balance. Next, the weighed ferrite particles were set in the measuring port of the measuring device and measured. The measurement was performed by the one-point method. The measurement atmosphere was a temperature of 10 to 30 ° C. and a relative humidity of 20 to 80% (no condensation).

<True Relative Density>
The true specific gravity of the ferrite powder was measured using the gas replacement method according to JIS Z8807: 2012. Specifically, the measurement was performed using a fully automatic true density measuring device (Mountech Co., Ltd., Macpycno).

<Tap density>
The tap density of the ferrite powder was measured according to JIS Z 2512-2012 using a USP tap density measuring device (Hosokawa Micron Co., Ltd., Powder Tester PT-X). In addition, the tap density ratio (tap density / true specific gravity) was determined using the values of tap density and true specific gravity.

<Magnetic properties-saturation magnetization, residual magnetization and coercive force>
The magnetic properties (saturation magnetization, residual magnetization and coercive force) of the ferrite powder were measured as follows. First, the sample was packed in a cell having an inner diameter of 5 mm and a height of 2 mm, and set in a vibration sample type magnetic measuring device (Toei Kogyo Co., Ltd., VSM-C7-10A). An applied magnetic field was applied and swept to 5 kOe, then the applied magnetic field was reduced to draw a hysteresis curve. From the obtained curve data, the saturation magnetization (σs), residual magnetization (σr) and coercive force (Hc) of the sample were determined.

<Magnetic characteristics-Permeability>
The magnetic permeability of the ferrite powder was measured using an RF impedance / material analyzer (Agilent Technologies, Inc., E4991A) and a magnetic material measuring electrode (16454A). First, 9 g of ferrite powder and 1 g of binder resin (Kynar301F: polyvinylidene fluoride) were placed in a polyethylene container (content volume 100 ml), and the mixture was stirred and mixed under the condition of a rotation speed of 100 rpm using a ball mill. About 0.6 g of the obtained mixture was filled in a die (inner diameter 4.5 mm, outer diameter 13 mm) and pressed with a press machine at a pressure of 40 MPa for 1 minute to obtain a molded product. The obtained molded product was heat-cured at 140 ° C. for 2 hours using a hot air dryer to prepare a sample for measurement. The obtained measurement sample was set in the RF impedance / material analyzer, and the outer diameter, inner diameter and height of the measurement sample measured in advance were input. The measurement was performed by sweeping a range of an amplitude of 100 mV and a measurement frequency of 1 MHz to 3 GHz on a logarithmic scale. The real part μ'and the imaginary part μ'' of the complex magnetic permeability at a frequency of 100 MHz were obtained, and the loss coefficient (tan δ) was calculated according to the following equation (2).

Furthermore, the density (d) of the sample is calculated from the outer diameter (φo), inner diameter (φi), thickness (t), and mass (m) of the measurement sample, and this is used to calculate the density ratio of the actual magnetic permeability part. (Μ'/ d) was determined.

(3) Results SEM images of the ferrite powders obtained in Examples 1 and 2 are shown in FIGS. 1 and 2, respectively. The SEM images of the ferrite powders obtained in Comparative Examples 3 and 4 are shown in FIGS. 3 and 4, respectively. Note that FIGS. 1, 3 and 4 are SEM images taken at a magnification of 1000 times, and FIG. 2 is an SEM image taken at a magnification of 100,000 times. In the ferrite powders of Examples 1 and 2 produced by the thermal spraying method, the particles had a spherical or polyhedral shape. On the other hand, in the ferrite powders of Comparative Examples 3 and 4 produced by the electric furnace firing method, the shape of the particles was granular.

The evaluation results obtained for Examples 1 to 4 and Comparative Examples 1 to 5 are shown in Tables 1-1 to 1-3. The ferrite powders of Comparative Examples 1 to 4 produced by the electric furnace firing method had a large average shape coefficient SF-1 of 106 or more. These powders are considered to be inferior in fluidity, moldability and filling property.

Looking at the magnetic properties, the ferrite powders of Comparative Examples 1 and 2 had large residual magnetization (σr) and coercive force (Hc) despite their low saturation magnetization (σs). In addition, the actual magnetic permeability (μ') at 100 MHz when formed into a molded body was small. Therefore, it was found that the magnetic characteristics were inferior. These ferrite powders are obtained by pulverizing the fired product after the main firing in order to adjust the particle size. It is considered that the surface of the particles is oxidized during crushing and the crystal strain increases due to the impact force applied during crushing, resulting in deterioration of magnetic properties (σs, σr, Hc, μ'). In addition to this, in Comparative Example 2, as a result of the amount of zinc (Zn) being too small, a large amount of non-magnetic hematite phase (α-Fe ₂ O ₃ ) and wustite phase (FeO) were generated, which are the magnetic characteristics. It is also considered to have caused deterioration.

The ferrite powders of Comparative Examples 3 and 4 had a large crystallite diameter, and the actual magnetic permeability (μ') at 100 MHz when formed into a molded product was small. These ferrite powders are obtained by performing crushing and classification treatment instead of crushing to adjust the particle size. It is speculated that the crystallite diameter becomes excessive as the crushing stress decreases, which leads to a decrease in magnetic permeability. Further, in Comparative Examples 3 and 4, a non-magnetic wustite phase (FeO) was generated, which is considered to have caused deterioration of magnetic characteristics.

The ferrite powder of Comparative Example 5 is made of manganese ferrite. This ferrite powder was spherical, and SF-1 was as small as 101. Furthermore, the saturation magnetization (σs) was relatively high, and the residual magnetization (σr) and coercive force (Hc) were small. The magnetic permeability real part (μ') was also high as compared with the examples, and the result was good. However, the relative density ratio (μ'/ d) of the actual magnetic permeability portion is inferior, and there is a possibility that the magnetic permeability will not be sufficiently high when actually used as a filler for a resin molded body. Further, Comparative Example 5 contains manganese, which is considered to have a health hazard, as a main component, and can be said to be less preferable than zinc ferrite from the viewpoint of manufacturing cost.

On the other hand, the ferrite powders of Examples 1 to 4 were made of zinc ferrite and had a spherical or polyhedral shape close to a spherical shape. Moreover, these ferrite powders were excellent in magnetic properties.

Claims

Ferrite powder composed of spherical or polyhedral ferrite particles.
The ferrite powder contains 5.0 to 10.0% by mass of zinc (Zn) and 55.0 to 65.0% by mass of iron (Fe), has a composition of residual oxygen (O) and unavoidable impurities, and is crystalline. A ferrite powder having a child diameter in the range of 8.0 to 15.0 Å and a divalent iron ion (Fe 2+ ) content of 0.5 to 10.0% by mass.
The ferrite powder according to claim 1, wherein the ferrite powder has a crystallite diameter of 9.0 to 13.0 Å.
The ferrite powder according to claim 1 or 2, wherein the content of divalent iron ions is 1.0 to 7.6% by mass.
The ferrite powder according to any one of claims 1 to 3, wherein the ferrite powder has an average shape coefficient SF-1 of 100 to 105.
The ferrite powder according to any one of claims 1 to 4, wherein the ferrite powder has a volume average particle diameter (D50) of 0.1 to 10.0 μm.
A ferrite resin composition containing the ferrite powder according to any one of claims 1 to 5 and a resin.
A ferrite resin molded body made of the ferrite resin composition according to claim 6.
An electronic component, an electronic device, or an electronic device housing provided with the ferrite resin molded body according to claim 7.