JP2017190491A - Flat powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat powder capable of contributing to reduction of magnetic loss of a magnetic member in a high frequency region.SOLUTION: The flat composite powder is aggregation of many flat composite particles 8. The composite particle 8 has a metal 10 and a coating film 12 laminated on the metal 10. Material of the metal 10 is an alloy which contains 0.01 mass% to 3.0 mass% of C and 0.1 mass% to 5.0 mass% of Si and Cr and/or Mo and the balance Fe with inevitable impurities. Total amount of Cr and Mo in the alloy is 10 mass% to 30 mass%. A value A calculated by the following mathematical formula (I) of the alloy is -600 to 800. A=50 Cr%+80 Mo%-3 AR (I). Material of the coating film 12 is a polymer obtained from a mixture containing titanium alkoxides and silicon alkoxides.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a powder composed of many flat particles. Specifically, the present invention relates to a flat metal powder and a flat composite powder.

  Portable electronic devices such as mobile phones, notebook personal computers, and tablet personal computers are widespread. In recent years, miniaturization and high performance of this electronic device have been advanced. Along with this, there is an increasing demand for miniaturization and high performance of magnetic members used in the circuit of this electronic device.

  As the magnetic member in the circuit board, a base in which wiring is printed on a sheet made of ferrite is used. Ferrite is an oxide and a magnetic material. Examples of the use of ferrite include multilayer inductors and multilayer capacitors. Ferrite has a small loss when it receives current and converts it into magnetic force in a high frequency range of 10 MHz to 10 GHz. However, ferrite has a drawback of low magnetic permeability.

  In order to compensate for the defect of ferrite having low magnetic permeability, a molded body in which soft magnetic metal particles having high magnetic permeability are dispersed in an insulator such as resin and rubber is used as a magnetic member. Particles in which an insulator is coated on the metal particles are also used for the molded body. These molded bodies can be used as magnetic sheets. However, soft magnetic metal particles having a high magnetic permeability have a drawback that magnetic loss occurs in a low frequency region. If magnetic loss occurs in the low frequency region, a further significant magnetic loss occurs in the high frequency region where the frequency is 10 MHz to 10 GHz.

Various investigations have been made on powders used in magnetic sheets. Japanese Unexamined Patent Application Publication No. 2014-204051 includes 84.0% to 96.0% Fe, 3.0% to 8.5% Si, and 1.0% to 13.0% Al. A soft magnetic flat powder is disclosed. The aspect ratio of this powder is 15 or more. This powder satisfies the following mathematical formula.
2 · Si%-Al% ≤ 15.0

  Japanese Patent Application Laid-Open No. 2014-077551 discloses a soft magnetic flat powder made of an Fe—Si—Cr alloy. The aspect ratio of this powder is 100-150. The average thickness of this powder is 1 μm or less.

  Japanese Patent Application Laid-Open No. 2007-266031 discloses a magnetic core member made of an Fe—Si—Cr alloy. This member has a large figure of merit (μ ′ × Q).

  Japanese Patent Application Laid-Open No. 2015-0500361 discloses an Fe—Si—Al-based flat powder and an Fe—Si-based flat powder. In these powders, the particles have an insulating film. Magnetic members using these powders have little magnetic loss due to eddy currents. A similar powder is also disclosed in JP-A-2015-050360.

JP, 2014-204051, A JP2014-077551A JP 2007-266031 A JP-A-2015-050361 JP2015-050360A

  In the powder disclosed in Japanese Patent Application Laid-Open No. 2014-204051, no study has been made on magnetic loss in a high frequency region, specifically in a region where the frequency is 10 MHz to 10 GHz. According to the knowledge of the present inventor, this powder has a tendency to have a high magnetic loss in a region where the frequency is less than 10 MHz. Therefore, this powder causes a further significant magnetic loss in the high frequency region.

  In the magnetic body using the flat soft magnetic powder described in the above Japanese Patent Application Laid-Open No. 2014-077551, no investigation has been made regarding the magnetic loss in the high frequency region. According to the knowledge of the present inventor, this powder has a tendency to have a high magnetic loss in a region where the frequency is less than 13.56 MHz. Therefore, in this powder, a further significant magnetic loss occurs in a high frequency region where the frequency is from 13.56 MHz to 10 GHz.

  In the magnetic body using the flat soft magnetic powder described in the above-mentioned Japanese Patent Application Laid-Open No. 2007-266031, no study has been made regarding the magnetic loss in the high frequency region. According to the knowledge of the present inventor, this magnetic material has a tendency to have a high magnetic loss in a frequency region of less than 13.56 MHz. Therefore, in this powder, a further significant magnetic loss occurs in a high frequency region where the frequency is from 13.56 MHz to 10 GHz.

  In the powder disclosed in the above Japanese Patent Application Laid-Open No. 2015-0500361, a detailed examination on the component of the insulating film has not been made. In the magnetic member using this powder, the magnetic loss in the high frequency region may be increased. Furthermore, in this magnetic member, there is a possibility that the frequency range where the effect can be obtained becomes narrow. A similar problem exists in the powder disclosed in JP-A-2015-050360.

  An object of the present invention is to provide a flat powder that can contribute to a reduction in magnetic loss of a magnetic member in a high frequency region having a frequency of 10 MHz to 10 GHz.

The flat metal powder according to the present invention comprises a large number of flat metal particles. The material of the flat metal particles includes 0.01 mass% or more and 3.0 mass% or less of C, 0.1 mass% or more of 5.0 mass% or less of Si, and Cr and / or Mo, and It is an alloy with the balance being Fe and inevitable impurities. The total amount of Cr and Mo in this alloy is 10% by mass or more and 30% by mass or less. The value A derived from the following mathematical formula (I) of this alloy is −600 or more and 800 or less.
A = 50 · Cr% + 80 · Mo%-3 · AR (I)
In this mathematical formula (I), Cr% represents the mass content of Cr in the alloy, Mo% represents the mass content of Mo in the alloy, and AR represents the aspect ratio of this powder.

The alloy may further include one or more metal elements MB having a body-centered cubic lattice other than Fe, Cr, and Mo. Preferably, the content of the metal element MB in the alloy is 1.0% by mass or more and 7.0% by mass or less. The value B derived from the following formula (II) of this alloy is −600 or more and 3500 or less.
B = 50 · Cr% + 80 · Mo% + 170 · MB%-3 · AR (II)
In this mathematical formula (II), MB% represents the mass content of the metal element MB in the alloy.

  Preferably, the ratio R1 of the bulk density to the tap density of the flat metal powder is 0.5 or more and 1.0 or less.

  Preferably, the average particle diameter of the flat metal powder is 20 μm or more and 150 μm or less.

According to another aspect, the flat composite powder for a magnetic member according to the present invention comprises a large number of flat composite particles. Each flat composite particle has a metal and a film covering the metal. This metal material contains 0.01 mass% or more and 3.0 mass% or less of C, 0.1 mass% or more and 5.0 mass% or less of Si, and Cr and / or Mo, and the balance is Fe and alloys that are inevitable impurities. The total amount of Cr and Mo in this alloy is 10% by mass or more and 30% by mass or less. The value A derived from the following mathematical formula (I) of this alloy is −600 or more and 800 or less. The material of the film is a polymer obtained from a mixture containing titanium alkoxides and silicon alkoxides.
A = 50 · Cr% + 80 · Mo%-3 · AR (I)
In this mathematical formula (I), Cr% represents the mass content of Cr in the alloy, Mo% represents the mass content of Mo in the alloy, and AR represents the aspect ratio of this powder.

The metal portion of the flat composite particles may further include one or more metal elements MB having a body-centered cubic lattice other than Fe, Cr, and Mo as an alloy component. Preferably, the content of the metal element MB in the alloy is 1.0% by mass or more and 7.0% by mass or less. The value B derived from the following formula (II) of this alloy is −600 or more and 3500 or less.
B = 50 · Cr% + 80 · Mo% + 170 · MB%-3 · AR (II)
In this mathematical formula (II), MB% represents the mass content of the metal element MB in the alloy.

  Preferably, the ratio R2 of the true density of the flat composite particles to the true density of only the metal portion of the flat composite particles is 0.70 or more and 0.95 or less.

  The magnetic member using the flat powder according to the present invention has a small magnetic loss in a high frequency region having a frequency of 10 MHz to 10 GHz.

FIG. 1 is a cross-sectional view showing particles of a flat metal powder according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a part of a magnetic sheet including the particles of FIG. FIG. 3 is a cross-sectional view showing particles of a flat composite powder according to an embodiment of the present invention.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[First embodiment]
[Flat metal powder]
The flat metal powder according to the present invention is an assembly of a large number of flat metal particles. In the present invention, the flat metal particle means a particle having a flat shape and made of a single metal or an alloy. FIG. 1 shows the flat metal particles 2. FIG. 2 shows a magnetic sheet 4 containing this flat metal powder.

  The material of the flat metal particles 2 is an alloy. This alloy contains 0.01 mass% or more and 3.0 mass% or less of C, 0.1 mass% or more and 5.0 mass% or less of Si, and Cr and / or Mo. Preferably, the balance of the alloy is Fe and inevitable impurities. The total amount of Cr and Mo in this alloy is 10% by mass or more and 30% by mass or less. This alloy is a soft magnetic material.

As indices representing the performance of the magnetic member, there are magnetic permeability μ, real part magnetic permeability μ ′ and imaginary part magnetic permeability μ ”. Real part magnetic permeability μ ′ represents superiority or inferiority of electromagnetic wave shielding characteristics. "" Indicates superiority or inferiority of electromagnetic wave absorption characteristics. The magnetic permeability μ is derived by the following mathematical formula.
μ = μ '+ jμ ”
In this equation, j represents an imaginary number. The square of j is -1. Each of the magnetic permeability μ, the real part magnetic permeability μ ′, and the imaginary part magnetic permeability μ ″ represents a relative magnetic permeability that is a ratio to the vacuum magnetic permeability. A magnetic loss tan δ at a high frequency is derived by the following equation.
tanδ = μ ”/ μ '
As is clear from this equation, when μ ′ is small and μ ″ is large, the magnetic loss tan δ is large. Due to eddy current loss and magnetic resonance, μ ′ can be lowered and μ ″ can be raised.

  Metallic magnetic materials have a higher saturation magnetic flux density and superior magnetic properties than ferrite. In the metal particles 2 made thinner than the skin depth (a measure of the depth at which the generated eddy current can flow) by flattening, eddy current loss is suppressed. The sheet 4 including the metal particles 2 is excellent in magnetic characteristics in a high frequency region.

  Metal magnetic resonance occurs on the lower frequency side than ferrite. From this point of view, metals are not suitable for loss reduction in a high frequency region. The inventor has found that the metal particles 2 made of the aforementioned alloy are suitable for the magnetic sheet 4. The inventor obtained a magnetic sheet 4 in which magnetic loss is suppressed in a high frequency region.

  In this alloy, the C content is 0.01% by mass or more and 3.0% by mass or less. In the sheet 4 containing the powder whose content is in this range, the magnetic loss in the high frequency region is small. In this respect, the content is more preferably equal to or greater than 0.1% by weight, and particularly preferably equal to or greater than 0.3% by weight. The content is more preferably 2.5% by mass or less, and particularly preferably 2.2% by mass or less.

  In this alloy, the Si content is 0.1% by mass or more and 5.0% by mass or less. In the sheet 4 containing the powder whose content is in this range, the magnetic loss in the high frequency region is small. In this respect, the content is more preferably equal to or greater than 0.5% by mass, and particularly preferably equal to or greater than 1.0% by mass. This content is more preferably 4.5% by mass or less, and particularly preferably 4.0% by mass or less.

  The crystal structure of Fe is a body-centered cubic lattice. In an alloy containing Fe with C and Si, one of the three axes of the crystal lattice is longer than the other two axes. This crystal has magnetic anisotropy. This crystal shifts the magnetic resonance of the sheet 4 to the high frequency region. In the sheet 4 containing Fe, the magnetic loss in the high frequency region is small.

  The crystal structure of Cr is a body-centered cubic lattice. In an alloy containing Cr together with C and Si, one of the three axes of the crystal lattice is longer than the other two axes. This crystal has magnetic anisotropy. This crystal shifts the magnetic resonance of the sheet 4 to the high frequency region. In the sheet 4 containing Cr, the magnetic loss in the high frequency region is small.

  The crystal structure of Mo is a body-centered cubic lattice. In an alloy containing Mo together with C and Si, one of the three axes of the crystal lattice is longer than the other two axes. This crystal has magnetic anisotropy. This crystal shifts the magnetic resonance of the sheet 4 to the high frequency region. In the sheet 4 containing Mo, the magnetic loss in the high frequency region is small.

  From the viewpoint of suppressing loss in the high frequency region, the total amount of Cr and Mo in the alloy is preferably 10% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more. The total amount is preferably 30% by mass or less, more preferably 27% by mass or less, and particularly preferably 25% by mass or less. The Cr content is preferably 2% by mass or more and 25% by mass or less. The content of Mo is preferably 2% by mass or more and 25% by mass or less. The alloy preferably contains both Cr and Mo.

The value A derived from the following mathematical formula (I) of this alloy is −600 or more.
A = 50 · Cr% + 80 · Mo%-3 · AR (I)
In this mathematical formula (I), Cr% represents the mass content of Cr in the alloy, Mo% represents the mass content of Mo in the alloy, and AR represents the aspect ratio of the powder. The sheet 4 containing the powder having a value A of −600 or more has a small magnetic loss in a high frequency region having a frequency of 10 MHz to 10 GHz. The value A is more preferably −500 or more, and particularly preferably −400 or more. The value A is preferably 800 or less.

  The alloy may further include one or more metal elements MB having a body-centered cubic lattice other than Fe, Cr, and Mo. The sheet 4 including the metal particles 2 made of this alloy has extremely small magnetic loss in the high frequency region. The content of the metal element MB in the alloy is preferably 1.0% by mass or more and 7.0% by mass or less. The content is more preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more. This content is more preferably 4.5% by mass or less, and particularly preferably 4.0% by mass or less. Specific examples of the metal element MB include V, Mn, Nb, Ta, and W.

When the alloy contains the metal element MB, the value B derived by the following mathematical formula (II) is preferably −600 or more and 3500 or less.
B = 50 · Cr% + 80 · Mo% + 170 · MB%-3 · AR (II)
In this mathematical formula (II), MB% represents the mass content of the metal element MB in the alloy. The sheet 4 containing powder having a value B of −600 or more and 3500 or less has a small magnetic loss in the high frequency region. The value B is more preferably −500 or more, and particularly preferably −400 or more. The value B is more preferably 3000 or less, and particularly preferably 2500 or less.

  The aspect ratio AR of the flat metal powder is preferably 10 or more and 300 or less. The sheet 4 containing a metal powder having an aspect ratio AR of 10 or more has a large real part magnetic permeability μ ′ in a high frequency region. In this respect, the aspect ratio AR is more preferably 30 or more, and particularly preferably 50 or more. In the sheet 4 containing metal powder having an aspect ratio AR of 300 or less, the flat metal particles 2 are unlikely to come into contact with each other, and therefore magnetic loss due to eddy current is unlikely to occur. From this viewpoint, the aspect ratio is more preferably 250 or less, and particularly preferably 200 or less.

  In the calculation of the aspect ratio AR, the flat metal particles 2 are observed with a scanning electron microscope (SEM), and the length L of the longest line segment that can be drawn in the outline in plan view is obtained. The length L is obtained for 50 metal particles 2 extracted at random, and the arithmetic average value Lav is calculated. Next, the metal particles 2 are embedded in the resin and polished, and the polished surface is observed with an optical microscope. The thickness direction of the metal particle 2 is specified, and the maximum thickness tm and the minimum thickness tn are measured. An average value ((tm + tn) / 2) of the maximum thickness tm and the minimum thickness tn is calculated. Based on the average value ((tm + tn) / 2) of 50 metal particles 2 extracted at random, these arithmetic average values tav are calculated. By dividing the average value Lav by the average value tav, the aspect ratio AR of the flat metal particles 2 is obtained.

  The ratio R1 of the bulk density to the tap density of the flat metal powder is preferably 0.5 or more. A powder having a ratio R1 of 0.5 or more is excellent in kneadability with a resin or the like. In the sheet 4 containing this powder, overcurrent caused by contact between the metal particles 2 is suppressed. The magnetic loss of this sheet 4 is small. In this respect, the ratio R1 is more preferably equal to or greater than 0.6, and particularly preferably equal to or greater than 0.7. The ideal ratio R1 is 1.0. The tap density is measured in accordance with the rules of “JIS Z 2512”. The bulk density is measured in accordance with the provisions of “JIS Z 2504”.

  The average particle size of the flat metal powder is preferably 20 μm or more and 150 μm or less. A powder having an average particle size within this range is excellent in kneadability with a resin or the like. In the sheet 4 containing this powder, overcurrent caused by contact between the metal particles 2 is suppressed. The magnetic loss of this sheet 4 is small. In this respect, the average particle diameter ratio R1 is more preferably 40 μm or more, and particularly preferably 50 μm or more. The average particle size is more preferably 130 μm or less, and particularly preferably 110 μm or less. The average particle diameter is the particle diameter at which the cumulative curve becomes 50% when the cumulative curve is obtained with the total volume of the powder as 100%. The particle diameter is measured by a Nikkiso Co., Ltd. laser diffraction / scattering particle size distribution measuring apparatus “Microtrack MT3000”. The powder is poured into the cell of this apparatus together with pure water, and the average particle diameter is detected based on the light scattering information of the particles.

  In the production of flat metal powder, a mother powder is first obtained. The mother powder can be obtained by gas atomization, water atomization, mechanical grinding, chemical process or the like. Gas atomization and water atomization are preferred. This mother powder is put into a media stirring mill (attritor) and pulverized. During this pulverization, the particles become flat and a flat metal powder is obtained. The flattened particles may be subjected to strain relief annealing.

  This flat metal powder is mixed with resin or rubber by a mixer. By mixing, a composition is obtained. The composition may contain processing aids such as a lubricant and a binder. The magnetic sheet 4 is formed from this composition by a known forming method such as extrusion. As shown in FIG. 2, in this sheet 4, many flat metal particles 2 are dispersed in a resin or rubber matrix 6. These metal particles 2 are oriented in the longitudinal direction (extrusion direction) of the sheet 4.

  The magnetic member containing the flat metal powder according to the present invention is not limited to the sheet 4. The magnetic member can have various shapes such as a ring, a cube, a rectangular parallelepiped, and a cylinder.

[Second Embodiment]
[Flat composite powder]
The flat composite powder according to the present invention is an assembly of a large number of flat composite particles. In the present invention, the flat composite particle means a particle in which an insulating film is formed on the surface of the flat metal particle. FIG. 3 shows one flat composite particle 8. The composite particle 8 includes a metal 10 (flat metal particle) and a coating 12 laminated on the metal 10. The film 12 is bonded to the metal 10. The film 12 covers the entire metal 10. The film 12 may partially cover the metal 10. The composite particle 8 may have another film between the metal 10 and the film 12. The composite particle 8 may have another film covering the film 12.

  The flat composite powder is used for a magnetic member such as a sheet, similarly to the flat metal powder of the first embodiment. In this magnetic member, flat composite particles 8 are dispersed in a matrix 6 (see FIG. 2) such as resin or rubber.

  The metal 10 is made of an alloy. The material of the metal 10 is the same as the material of the flat metal particles 2 of the first embodiment. The properties of the powder made of a large number of metals 10 are the same as the properties of the flat metal powder of the first embodiment.

  The film 12 is made of an organic material. This film 12 is more insulative than the metal 10. The film 12 prevents the metals 10 from contacting each other in the magnetic member. With this magnetic member, overcurrent is unlikely to occur. In this magnetic member, an increase in the real part permeability μ ″ is suppressed.

  A typical material of the film 12 is a polymer obtained from a mixture containing titanium alkoxides and silicon alkoxides. Titanium alkoxides are compounds in which at least one alkoxide group is bonded to a titanium atom in one molecule. Silicon alkoxides are compounds in which at least one alkoxide group is bonded to a silicon atom in one molecule. In the present invention, an alkoxide group is a compound in which an organic group is bonded to oxygen having a negative charge. An organic group is a group made of an organic compound. The concept of titanium alkoxides includes a titanium alkoxide monomer, an oligomer formed by polymerizing a plurality of such monomers, and a compound at a stage before titanium alkoxide is produced (hereinafter also referred to as a precursor). . The concept of silicon alkoxides includes a monomer of silicon alkoxide, an oligomer formed by polymerizing a plurality of such monomers, and a compound at a stage before silicon alkoxide is formed (hereinafter also referred to as a precursor). . The film 12 may be formed from a polymer mixture of a mixture containing further components in addition to the titanium alkoxides and silicon alkoxides.

  Specific examples of the titanium alkoxide include titanium tetramethoxide, titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, titanium tetra-2-ethylhexoxide, and isopropyltridodecylbenzenesulfonyl titanate.

  Specific examples of silicon alkoxide include tetraethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraisopropoxysilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane and N- (β-aminoethyl) -γ-amino. And propylmethyldimethoxysilane.

  The film 12 can be produced by various coating methods. Examples of the coating method include a mixing method, a sol-gel method, a spray dryer method, and a rolling fluidized bed method.

  Titanium alkoxides and silicon alkoxides can be used after diluted with a solvent. Various solvents that can dissolve or disperse titanium alkoxides or silicon alkoxides can be used. Specific examples of the solvent include acetone, methyl ethyl ketone, acetonitrile, methanol, ethanol, isopropyl alcohol, n-butanol, benzene, toluene, hexane, heptane, cyclohexane, chloroform, chlorobenzene, dichlorobenzene, ethyl acetate, ethyl propionate and tetrahydrofuran. It is done.

  The mixture of titanium alkoxides and silicon alkoxides polymerizes on the surface of the metal 10 at an appropriate reaction rate as compared with alkoxides such as titanium alkoxides, silicon alkoxides, aluminum alkoxides, and zirconium alkoxides alone. In the film 12 formed from this mixture, there are few cracks. Moreover, the coating 12 is thin. This coating 12 can contribute to the improvement of the electromagnetic wave shielding characteristics and electromagnetic wave absorption characteristics of the magnetic member.

  Preferred titanium alkoxides are oligomers of titanium alkoxide. This oligomer causes a polymerization reaction at an appropriate rate as compared with the monomer of titanium alkoxide. Therefore, the occurrence of cracks is further suppressed in this film 12, and a thinner film 12 can be obtained. This coating 12 can contribute to the improvement of the electromagnetic wave shielding characteristics and electromagnetic wave absorption characteristics of the magnetic member.

  Titanium alkoxide oligomers may be formed from titanium alkoxide monomers. This oligomer is obtained by polymerization of a plurality of monomers. The number of monomers constituting the oligomer affects the reaction rate of the mixture when the coating 12 is formed. From the viewpoint of an appropriate reaction rate, the number of monomers is preferably 4 or more, and preferably 50 or less.

  This film 12 contains titanium oxide and silicon oxide. Silicon contributes to electromagnetic wave shielding characteristics and electromagnetic wave absorption characteristics. This silicon enhances the adhesion between the metal particles 2 and the coating 12. Accordingly, when the flat composite powder is mixed with resin, rubber or the like to obtain a composition, or when a magnetic member is molded from this composition, peeling of the coating 12 from the metal particles 2 is prevented.

  The ratio of the mass of titanium to the mass of silicon contained in the film 12 is preferably 2.0 or more and 6.0 or less. The coating 12 having this ratio within the above range is excellent in adhesion with the metal 10. This film 12 is difficult to peel from the metal 10. Accordingly, a decrease in insulation resistance due to peeling is unlikely to occur. The composite particles 8 having this film 12 are excellent in electromagnetic wave shielding characteristics and electromagnetic wave absorption characteristics. From the viewpoint of adhesion, this ratio is particularly preferably 3.5 or more. From the viewpoint of adhesion, this ratio is particularly preferably 5.5 or less.

  The coverage of the metal 10 by the film 12 is preferably 20% or more. The composite particles 8 having a coverage of 20% or more are excellent in electromagnetic wave shielding characteristics and electromagnetic wave absorption characteristics. From this viewpoint, the coverage is more preferably 30% or more, and particularly preferably 50% or more. Ideally, the coverage is 100%. In the composite particle 8 shown in FIG. 3, the coverage is 100%.

  For the calculation of the coverage, a cross-sectional image of the composite particle 8 taken with a transmission electron microscope (TEM) is used. Specifically, an image of a state in which the boundary between the metal 10 and the coating 12 can be confirmed is taken from among a large number of composite particles 8 observed with a TEM. In this image, the length of the metal 10 covered with the coating 12 (hereinafter also referred to as the coating length) and the surface length of the composite particle 8 are measured. The coating length is divided by the surface length of the composite particle 8 to calculate the coverage. The coverage is calculated for 10 randomly extracted images, and an average value is obtained.

  In FIG. 3, what is indicated by a double arrow T is the thickness of the film 12. The thickness T affects the electromagnetic field absorption characteristics and electromagnetic wave shielding characteristics of the magnetic member. The thickness T is preferably 1 nm or more and 200 nm or less. The magnetic member including the composite particles 8 having a thickness T of 1 nm or more has a large insulation resistance. In this magnetic member, the real part permeability μ ′ is large and the imaginary part permeability μ ″ in the high frequency region is also large. From this viewpoint, the thickness T is particularly preferably 5 nm or more. The thickness T is 200 nm or less. The magnetic member containing the flat composite powder can contain a large amount of the metal 10. In this magnetic member, the real part permeability μ ′ is large and the imaginary part permeability μ ″ in the high frequency region is also large. In this respect, the thickness T is particularly preferably equal to or less than 180 nm.

  The thickness T is measured in an image obtained by photographing a cross section of the composite particle 8 with a transmission electron microscope (TEM). At the time of imaging, the composite particles 8 are processed by focused ion beam (FIB) processing. The thickness of 10 randomly extracted composite particles 8 is measured and averaged.

  The ratio R2 of the true density of the flat composite powder to the true density of only a large number of metal 10 powders is preferably 0.70 or more and 0.95 or less. The magnetic member including the flat composite powder having the ratio R2 of 0.70 or more can contain a large amount of the metal 10. In this magnetic member, the real part permeability μ ′ is large and the imaginary part permeability μ ″ in the high frequency region is also large. From this viewpoint, the ratio R2 is particularly preferably 0.75 or more. The ratio R2 is 0.95 or less. A magnetic member containing a certain flat composite powder has a high insulation resistance, and this magnetic member has a large real part permeability μ ′ and a high frequency part imaginary part permeability μ ″. In this respect, the ratio R2 is particularly preferably equal to or less than 0.90.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Experiment 1]
A mother powder having the components shown in Table 1 was prepared. This mother powder (10 kg) was put into an attritor, pulverized and flattened to obtain a flat metal powder. Table 1 below shows the aspect ratio AR of the flat metal powder, the value A derived from the formula (I), the bulk density, the tap density, the ratio R1 of the bulk density to the tap density, and the average particle diameter.

  This flat metal powder was kneaded with an epoxy resin at a temperature of 100 ° C. using a small mixer to obtain a resin composition in which the powder was uniformly dispersed. The volume ratio of the epoxy resin to the flat metal powder was 5 to 2. This resin composition was hot-pressed for 5 minutes under the conditions of a pressure of 4 MPa and a temperature of 200 ° C. to obtain a magnetic sheet having a thickness of 0.1 mm.

  With respect to the produced magnetic sheet, a loss coefficient tanδ, which is an index of magnetic loss, was measured at a temperature of 25 ° C. for each frequency, and a frequency FR at which tanδ = 0.1 was investigated. The results are shown in Table 1 below. For measurement of tan δ, a product name “Vector Network Analyzer N5245A” manufactured by Agilent Technologies was used.

  In Table 1, the overall evaluation of each powder is ranked as one of S2, S1, A, B, and F.

[Experiment 2]
The elements shown in Table 3 were added to the ingredients shown in Table 2 to prepare mother powder. This mother powder (10 kg) was put into an attritor, pulverized and flattened to obtain a flat metal powder. The aspect ratio AR of this flat metal powder, the value A derived from the formula (I), the value B derived from the formula (II), the bulk density, the tap density, the ratio R1 of the bulk density to the tap density, and the average particle size Are shown in Table 3 below.

  This flat metal powder was kneaded with an epoxy resin at a temperature of 100 ° C. using a small mixer to obtain a resin composition in which the powder was uniformly dispersed. The volume ratio of the epoxy resin to the flat metal powder was 5 to 2. This resin composition was hot-pressed for 5 minutes under the conditions of a pressure of 4 MPa and a temperature of 200 ° C. to obtain a magnetic sheet having a thickness of 0.1 mm.

  With respect to the produced magnetic sheet, a loss coefficient tanδ, which is an index of magnetic loss, was measured at a temperature of 25 ° C. for each frequency, and a frequency FR at which tanδ = 0.1 was investigated. The results are shown in Table 3 below. For measurement of tan δ, a product name “Vector Network Analyzer N5245A” manufactured by Agilent Technologies was used.

  In Table 3, the overall evaluation of each powder is ranked as one of S2, S1, A, B, and F.

[Experiment 3]
A mother powder having the components shown in Table 4 was prepared. This mother powder (10 kg) was put into an attritor, pulverized and flattened to obtain a flat metal powder. Table 4 below shows the aspect ratio AR of the flat metal powder, the value A derived from the formula (I), and the value B derived from the formula (II).

  A film having the composition shown in Table 5 was formed on the surface of the particles of the flat metal powder to obtain a flat composite powder. Table 6 below shows the value B, the bulk density, the tap density, the ratio of the bulk density to the tap density R1, the average particle diameter, and the density ratio R2 of this flat composite powder. .

  This flat composite powder was kneaded with an epoxy resin at a temperature of 100 ° C. using a small mixer to obtain a resin composition in which the powder was uniformly dispersed. The volume ratio of the epoxy resin to the flat metal powder was 5 to 2. This resin composition was hot-pressed for 5 minutes under the conditions of a pressure of 4 MPa and a temperature of 200 ° C. to obtain a magnetic sheet having a thickness of 0.1 mm.

  With respect to the produced magnetic sheet, a loss coefficient tanδ, which is an index of magnetic loss, was measured at a temperature of 25 ° C. for each frequency, and a frequency FR at which tanδ = 0.1 was investigated. The results are shown in Table 3 below. For measurement of tan δ, a product name “Vector Network Analyzer N5245A” manufactured by Agilent Technologies was used.

  In Table 6, the overall evaluation of each powder is ranked as one of S2, S1, A, B, and F.

  From the results of Experiment 1-3, the superiority of the present invention is clear.

  The flat powder according to the present invention can be applied to various magnetic members.

2 ... Flat metal particles 4 ... Magnetic sheet 6 ... Matrix 8 ... Flat composite particles 10 ... Metal 12 ... Film

Claims (7)

Consisting of many flat metal particles,
The material of the flat metal particles includes 0.01 mass% or more and 3.0 mass% or less of C, 0.1 mass% or more and 5.0 mass% or less of Si, and Cr and / or Mo, and The balance is Fe and inevitable impurities alloy,
The total amount of Cr and Mo in the alloy is 10% by mass or more and 30% by mass or less,
The flat metal powder whose value A derived | led-out by following numerical formula (I) of the said alloy is -600 or more and 800 or less.
A = 50 · Cr% + 80 · Mo%-3 · AR (I)
(In this formula (I), Cr% represents the mass content of Cr in the alloy, Mo% represents the mass content of Mo in the alloy, and AR represents the aspect ratio of the powder.) The alloy further includes one or more metal elements MB having a body-centered cubic lattice other than Fe, Cr, and Mo;
The content of the metal element MB in the alloy is 1.0 mass% or more and 7.0 mass% or less,
The flat metal powder according to claim 1, wherein a value B derived from the following mathematical formula (II) of the alloy is −600 or more and 3500 or less.
B = 50 · Cr% + 80 · Mo% + 170 · MB%-3 · AR (II)
(In this formula (II), MB% represents the mass content of the metal element MB in the alloy.)   The flat metal powder according to claim 1 or 2, wherein the ratio R1 of the bulk density to the tap density is 0.5 or more and 1.0 or less.   The flat metal powder according to any one of claims 1 to 3, wherein the average particle size is 20 µm or more and 150 µm or less. Consisting of many flat composite particles,
Each flat composite particle has a metal and a film covering the metal,
The metal material contains 0.01 mass% or more and 3.0 mass% or less of C, 0.1 mass% or more and 5.0 mass% or less of Si, and Cr and / or Mo, and the balance is An alloy that is Fe and inevitable impurities;
The total amount of Cr and Mo in the alloy is 10% by mass or more and 30% by mass or less,
The value A derived from the following mathematical formula (I) of the alloy is −600 or more and 800 or less,
A flat composite powder for a magnetic member, wherein the material of the film is a polymer obtained from a mixture containing titanium alkoxides and silicon alkoxides.
A = 50 · Cr% + 80 · Mo%-3 · AR (I)
(In this formula (I), Cr% represents the mass content of Cr in the alloy, Mo% represents the mass content of Mo in the alloy, and AR represents the aspect ratio of the powder.) The alloy further includes one or more metal elements MB having a body-centered cubic lattice other than Fe, Cr, and Mo;
The content of the metal element MB in the alloy is 1.0 mass% or more and 7.0 mass% or less,
The flat composite powder according to claim 5, wherein a value B derived from the following mathematical formula (II) of the alloy is −600 or more and 3500 or less.
B = 50 · Cr% + 80 · Mo% + 170 · MB%-3 · AR (II)
(In this formula (II), MB% represents the mass content of the metal element MB in the alloy.)   The flat composite according to claim 5 or 6, wherein the ratio R2 of the true density of the flat composite powder to the true density of a large number of metal powders that are raw materials of the flat composite powder is 0.70 or more and 0.95 or less. Powder.

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