Ferrite powder and method for producing the same

Abstract

Provided are a ferrite powder that suppresses decreases in saturation magnetization and decreases in filler filling rate and also suppresses inhibition of resin curing, and a method for producing the same. A ferrite powder composed of spherical ferrite particles, wherein the ferrite powder contains iron (Fe) 54.0-70.0 mass% and manganese (Mn) 3.5-18.5 mass%, has an average volume particle size of 2.0-20.0 μm, and has a carbon content of 0.100 mass% or lower.

Description

Ferrite powder and its manufacturing method

[0001] The present invention relates to a ferrite powder and a method for producing the same.

[0002] Ferrite-resin composite materials (resin compositions) composed of ferrite powder and resin are widely used in a variety of applications, including electromagnetic wave shielding materials. Composite materials are produced by kneading ferrite powder as a filler with resin, and then molding the composite into a shape such as a sheet to form a compact (composite). When the particles constituting the ferrite powder are nearly spherical, the fluidity during molding increases, resulting in a high filling rate of the ferrite powder in the composite. This improves moldability and can improve properties such as electromagnetic wave shielding performance. From this perspective, ferrite powders composed of spherical particles have attracted attention, and it has been proposed to produce such spherical particles by a thermal spraying method.

[0003] For example, Patent Document 1 (WO 2017 / 212997) discloses ferrite particles that are single crystals with an average particle size of 1 to 2000 nm and have a spherical particle shape, the ferrite particles being substantially free of Zn and containing 3 to 25 wt % Mn and 43 to 65 wt % Fe, and the real part μ′ of complex permeability measured using a molded product made of the ferrite particles and a binder resin has a maximum value in a frequency band of 100 MHz to 1 GHz. The ferrite particles are produced by thermally spraying a granulated product made of a ferrite raw material in the atmosphere to form ferrite, followed by rapid solidification and recovery of only particles with particle sizes within a predetermined range. The ferrite particles are also disclosed to be capable of stably shielding electromagnetic waves in a wide frequency band that require shielding, regardless of frequency, when used as an electromagnetic wave shielding material for electronic devices (claim 1,

[0039] and

[0078] of Patent Document 1).

[0004] Patent Document 2 (WO 2017 / 169316) describes Mn-based ferrite particles that are single crystals with an average particle size of 1 to 2000 nm and have a spherical particle shape, and have a saturation magnetization of 45 to 95 Am ２ / kg, and describes that the ferrite particles are produced by thermally spraying a ferrite raw material containing Mn and Fe in the atmosphere to form ferrite, followed by rapid solidification, and then recovering only particles having particle sizes within a predetermined range, and that the ferrite particles can have high saturation magnetization and excellent dispersibility in resins, solvents, or resin compositions (claim 1,

[0033] and

[0089] of Patent Document 2).

[0005] Patent Document 3 (JP 2016-060682 A) discloses a spherical ferrite powder characterized by containing 15 to 30 wt % of ferrite particles having a particle size of less than 11 μm and having a volume average particle size of 10 to 50 μm. It also describes that the prepared granulated material is thermally sprayed in the atmosphere to form ferrite, and that the spherical ferrite powder has good filling properties and moldability when used as a filler, has excellent handleability, and has high resistance. Therefore, the spherical ferrite powder is combined with a resin to form a resin composition, and the resulting molded product can be used for various applications, including an IC sealant for absorbing electromagnetic waves (claim 1,

[0058] and

[0093] of Patent Document 3).

[0006] Patent Document 4 (Japanese Patent Laid-Open Publication No. 2005-015303) discloses a method for producing spherical powder, which comprises: a surface treatment step in which a raw material powder and a treating agent comprising at least one of a higher fatty acid or a derivative thereof, a higher hydrocarbon, and a higher alcohol are heated to a predetermined temperature and then stirred to surface treat the raw material powder; and a spherical powder production step in which the surface-treated raw material powder is introduced into a combustion flame generated by a burner to melt and thereby spheroidize, and the raw material powder is then moved out of the combustion flame and solidified to obtain a spherical powder (Claim 1 of Patent Document 4).

[0007] International Publication No. 2017 / 212997 International Publication No. 2017 / 169316 JP 2016-060682 A JP 2005-015303 A

[0008] However, the inventors have found through their investigations that even when ferrite powder is produced by a thermal spraying method, the ferrite powder may contain many irregularly shaped particles in addition to spherical particles. Ferrite powder containing such irregularly shaped particles has problems in that it has poor magnetic properties, particularly low saturation magnetization, and does not have a high filler loading when used in a resin composition.

[0009] As a result of further investigations, the present inventors have discovered that a ferrite powder containing a carbon-hydrogen-oxygen (C-H-O)-containing compound and consisting of spherical particles with a carbon content limited within a specific range can suppress the inclusion of irregularly shaped particles, thereby suppressing a decrease in saturation magnetization and a decrease in filler loading. They have also discovered that when this ferrite powder is applied to a resin composition, the resin has excellent curing performance.

[0010] The present invention was completed based on such findings, and an object of the present invention is to provide a ferrite powder that prevents a decrease in saturation magnetization and a decrease in filler loading rate and has excellent resin curing performance, and a method for producing the same.

[0011] The present invention includes the following aspects (1) to (5). In this specification, the expression "to" includes the numerical values ​​at both ends. In other words, "X to Y" is synonymous with "at least X and at most Y."

[0012] (1) A ferrite powder composed of spherical ferrite particles, the ferrite powder containing 54.0 to 70.0 mass% of iron (Fe) and 3.5 to 18.5 mass% of manganese (Mn), having an average volume particle size of 2.0 to 20.0 μm, and having a carbon content of 0.100 mass% or less.

[0013] (2) The ferrite powder according to (1) above, wherein the ferrite powder has an average shape factor SF-1 of 100 to 110.

[0014] (3) A method for producing the ferrite powder of (1) or (2) above, comprising the following steps: mixing ferrite raw materials to prepare a raw material mixture; pre-granulating the raw material mixture to prepare a pre-granulated product; pre-firing the pre-granulated product to prepare a pre-fired product; pulverizing the pre-fired product to prepare a pre-fired powder; adding 0.5 to 13.0 mass % of a lubricant to and mixing the pre-fired powder to prepare a thermal spray raw material; and spraying the thermal spray raw material to prepare a thermal sprayed product.

[0015] (4) The lubricant is a compound represented by the general formula: CH ３ ・(CH ２ ) ｍ The method according to (3) above, wherein the compound is a compound represented by COOH (where m is an integer of 10 or more and 16 or less).

[0016] (5) The method according to (3) or (4) above, wherein the thermal spray raw material is a granule or an aggregate, and the volume average particle size of the granule or aggregate is larger than the primary particle size of the calcined powder.

[0017] According to the present invention, there are provided ferrite powders which prevent a decrease in saturation magnetization and a decrease in filler loading rate and which have excellent resin curing performance, and a method for producing the same.

[0018] A specific embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0019] Ferrite Powder The ferrite powder of this embodiment is composed of spherical ferrite particles. That is, the ferrite powder includes a plurality of spherical ferrite particles. This ferrite powder contains 54.0 to 70.0 mass% iron (Fe) and 3.5 to 18.5 mass% manganese (Mn), and has an average volume particle size of 2.0 to 20.0 μm. Furthermore, this ferrite powder has a carbon content of 0.100 mass% or less.

[0020] By using spherical ferrite particles as the ferrite powder, excellent moldability and packing properties can be achieved when the ferrite powder is used as a filler in a resin composition (ferrite-resin composite material). In other words, spherical particles smoothly avoid contact with other particles during molding. This improves fluidity during molding and allows for dense packing. In contrast, particles with an anisotropic (irregular) shape, such as a plate or needle shape, have poor moldability and packing properties. In this specification, the term "irregularly shaped particles" encompasses anisotropically shaped particles and is used in contrast to particles with regular shapes, such as spherical shapes.

[0021] The ferrite powder of this embodiment contains 54.0 to 70.0 mass% iron (Fe) and 3.5 to 18.5 mass% manganese (Mn). The remainder is primarily oxygen (O) and unavoidable impurities, although this is not a limitation. This ferrite powder has the composition of manganese (Mn) ferrite. Here, manganese (Mn) ferrite does not contain zinc (Zn) in an amount exceeding the unavoidable impurity level. Therefore, it is distinguished from manganese (Mn)-zinc (Zn) ferrite, to which zinc (Zn) is actively added. Note that unavoidable impurities refer to components that are inevitably mixed in during the manufacturing process and whose content is 5000 ppm or less. Examples of unavoidable impurities include silicon (Si), aluminum (Al), calcium (Ca), chlorine (Cl), boron (B), zirconium (Zr), and chromium (Cr).

[0022] When the iron content of manganese (Mn) ferrite is excessively low or when the manganese content is excessively high, the imaginary part of magnetic permeability (μ'') and tan δ at 100 MHz become high. Therefore, when the ferrite powder is applied to a resin composition, there is a risk that the saturation magnetic flux density will decrease or the magnetic loss will increase. Therefore, in this embodiment, the iron (Fe) content is limited to 54.0 mass% or more, and the manganese (Mn) content is limited to 18.5 mass% or less. The iron content is preferably 58.0 mass% or more, and more preferably 60.0 mass% or more. The manganese content is preferably 10.0 mass% or less, and more preferably 9.0 mass% or less. On the other hand, when the iron content is excessively high or the manganese content is excessively low, the ferrite composition becomes similar to magnetite, which is easily oxidized, and there is a risk of a decrease in saturation magnetization due to oxidation. In addition, the real part of magnetic permeability (μ') at 100 MHz becomes small. Therefore, in this embodiment, the iron (Fe) content is limited to 70.0 mass% or less, and the manganese (Mn) content is limited to 3.5 mass% or more. The iron content is preferably 69.0 mass% or less, and more preferably 67.0 mass% or less. The manganese content is preferably 6.0 mass% or more, and more preferably 7.0 mass% or more. The total of iron and manganese does not exceed 73.5 mass%.

[0023] The ferrite powder of this embodiment has an average volume particle size (D50) of 2.0 to 20.0 μm. If the volume average particle size is less than 2.0 μm, when the ferrite powder is applied as a filler to a resin composition, the viscosity of the ferrite powder alone will be too high. This may make it impossible to increase the filler filling rate. The volume average particle size is preferably 2.5 μm or more, more preferably 3.0 μm or more. On the other hand, if the volume average particle size exceeds 20.0 μm, the magnetic loss (tan δ) may become too large, making it impossible to use the resin composition at high frequencies. The volume average particle size is preferably 15.0 μm or less, more preferably 10.0 μm or less, even more preferably 7.0 μm or less, and particularly preferably 5.0 μm or less.

[0024] The ferrite powder of this embodiment has a carbon content of 0.100% by mass or less. This carbon is a component derived from the carbon-hydrogen-oxygen-containing compound. Furthermore, the carbon-hydrogen-oxygen-containing compound is a component derived primarily from the lubricant added during the production of the ferrite powder. If the ferrite powder contains an excessive amount of the carbon-hydrogen-oxygen-containing compound, when the ferrite powder is used as a filler in a resin composition, the viscosity of the resin composition before curing may increase or the curing of the resin may be inhibited. While the detailed mechanism is unknown, since the carbon-hydrogen-oxygen-containing compound derived from the lubricant is a linear compound without functional groups, it does not directly react with the resin. However, it is believed that the carbon-hydrogen-oxygen-containing compound may mix with the resin molecules, increasing the viscosity or adversely affecting the curing process. The carbon content is preferably 0.080% by mass or less, and more preferably 0.060% by mass or less. On the other hand, there is no particular lower limit for the carbon content. However, if the amount of lubricant is too low, irregularly shaped particles may easily become mixed into the ferrite powder. These irregularly shaped particles cause deterioration of magnetic properties and packing properties. Therefore, the carbon content is preferably 0.010% by mass or more, more preferably 0.015% by mass or more, and even more preferably 0.030% by mass or more. Note that carbon less than 0.010% by mass is a component derived from substances other than the lubricant that adhere to the ferrite particles.

[0025] The ferrite powder preferably contains ferrite particles containing a carbon-hydrogen-oxygen (C-H-O)-containing compound. This compound mainly contains carbon (C), hydrogen (H), and oxygen (O), and may be composed only of carbon, hydrogen, and oxygen. If a lubricant is not added during the production of the ferrite powder, the supply of raw material in the thermal spraying process becomes unstable. As a result, a large amount of raw material passes through the thermal spray flame, which prevents sufficient spheroidization and results in irregularly shaped particles being mixed into the ferrite powder. As a result, the magnetic properties of the ferrite powder and the filling ability of the resin composition deteriorate. Furthermore, saturation magnetization decreases due to insufficient firing by thermal spraying and an increase in the oxygen concentration in the thermal spray flame. The carbon-hydrogen-oxygen-containing compound has the formula: CH ３ ・(CH ２ )ｎ ・COOCH ３ (where n is an integer of 6 or more and 9 or less) is preferred, and among them, methyl decanoate (CH ３ ・(CH ２ ) ８ ・COOCH ３ It is believed that by using lauric acid as a lubricant, the ferrite powder obtained after thermal spraying contains methyl decanoate.

[0026] The ferrite powder preferably has an average shape factor SF-1 of 100 to 110. SF-1 is an index of the sphericity of the particles (powder), with a perfect sphere being 100 and increasing as the particle becomes less spherical. By setting SF-1 to 110 or less, the fluidity of the powder is improved, resulting in better moldability and packability. SF-1 is more preferably 108 or less, even more preferably 105 or less, and particularly preferably 103 or less.

[0027] The average shape factor SF-1 of the ferrite powder can be determined by determining the shape factor SF-1 of each particle for a plurality of ferrite particles and calculating the average value. The SF-1 of a ferrite particle is calculated by the horizontal Feret diameter R (unit: μm), projected perimeter L (unit: μm), and projected area S (unit: μm ２ ) can be measured and calculated according to the following formula (1).

[0028]

[0029] The ferrite powder preferably has a content of particles (irregularly shaped particles) with an SF-1 greater than 103.6 of 15.0% by number or less, more preferably 10.0% by number or less, even more preferably 7.0% by number or less, particularly preferably 6.0% by number or less, and most preferably 5.0% by number or less. By reducing the content of particles with large SF-1 (irregularly shaped particles) in this way, when the ferrite powder is used as a filler in a resin composition (ferrite resin composite material), the moldability and filling properties become better. The lower limit of the content of irregularly shaped particles is not particularly limited, but is typically 1.0% by number or more, more typically 3.0% by number or more.

[0030] 2. Method for Producing Ferrite Powder The method for producing ferrite powder of this embodiment includes the following steps: a step of mixing ferrite raw materials to prepare a raw material mixture (raw material mixing step), a step of pre-granulating the raw material mixture to prepare a pre-granulated product (pre-granulation step), a step of pre-firing the pre-granulated product to prepare a pre-fired product (pre-firing step), a step of pulverizing the pre-fired product to prepare a calcined powder (pulverization step), a step of adding 0.5 to 13.0 mass % of a lubricant to and mixing the calcined powder to prepare a thermal spray raw material (pretreatment step), and a step of thermally spraying the thermal spray raw material to prepare a thermal spray product (thermal spraying step). Each step is described in detail below.

[0031] <Raw Material Mixing Step> First, ferrite raw materials are mixed to prepare a raw material mixture. As the ferrite raw material, known ferrite raw materials such as oxides, carbonates, hydroxides and / or chlorides may be used. For example, iron oxide (Fe ２ O ３ ), trimanganese tetroxide (Mn ３ O ４ ), manganese dioxide (MnO ２ ) and / or manganese carbonate (MnCO ３ The mixing ratio of the raw materials may be determined so as to obtain a ferrite powder of a desired composition. The raw materials may be mixed using a known mixer, and may be mixed by either a dry method or a wet method, or both.

[0032] <Pre-granulation step> The obtained raw material mixture is pre-granulated to produce a pre-granulated product. By providing a pre-granulation step, raw materials can be added stably and continuously in the pre-firing step described below. This is because the pre-granulated product is larger in size than the raw materials and has excellent fluidity. In the pre-granulation step, the slurried raw material mixture may be granulated using a wet granulator such as a spray dryer, or the granular raw material mixture may be granulated using a dry granulation device such as a rotor compactor. This allows for the production of pre-granulated products with high sphericity and excellent fluidity.

[0033] <Pre-firing step> The obtained pre-granulated material is pre-fired to produce a pre-firing product. This promotes ferritization of the raw material mixture. The pre-firing temperature can be set to 600 to 1300°C. The oxygen concentration in the atmosphere may be adjusted to between 0 and 21% by volume to promote ferritization. Pre-firing can be carried out using a furnace such as a stationary electric furnace or a rotary kiln.

[0034] <Pulverization Step> The obtained calcined product is pulverized to produce calcined powder. The pulverization can be performed using a known pulverizer, and can be performed using either a dry method or a wet method, or both. A media mill such as a bead mill or a rod mill can be used for the pulverization. Furthermore, media such as stainless steel, alumina, zirconia, and / or steel balls can be used. The media size can be selected depending on whether coarse or fine pulverization is performed to obtain the desired pulverized particle size.

[0035] <Main Granulation Step> If necessary, a step of granulating the calcined powder (main granulation step) may be performed. This results in a granulated product of the calcined powder. In the main granulation step, the obtained calcined powder is dispersed in water to form a slurry, and the slurry is then granulated using a spray dryer. The size of the granulated product is larger than the primary particle size of the calcined powder and has excellent fluidity. This allows for improved supply stability of raw materials during the thermal spraying step described below.

[0036] <Pretreatment Step> Next, a thermal spray feedstock is prepared by adding and mixing a lubricant in an amount of 0.5 to 13.0 mass% to the obtained calcined powder or its granules. Adding a predetermined amount of lubricant improves the fluidity of the thermal spray feedstock. Adding an excessively large amount of lubricant does not provide any benefit in terms of improving fluidity. In fact, when ferrite powder is used as a filler in a resin composition, the problem of resin curing being inhibited is likely to occur. This is because the carbon content of the ferrite powder becomes excessively high. The amount of lubricant added is preferably 10.0 mass% or less, and more preferably 5.0 mass% or less. On the other hand, if no lubricant is added or if the amount of lubricant added is too small, the fluidity of the thermal spray feedstock deteriorates. Therefore, in the thermal spraying step described below, the thermal spray feedstock (calcined powder) is fed into the equipment in a time-varying state. As a result, excessive supply of lubricant is likely to result in non-spherical particles. These non-spherical particles have irregular shapes and the ferritization reaction does not progress sufficiently to their interiors. Therefore, the obtained ferrite powder contains a large amount of irregularly shaped particles and has low magnetic properties, particularly low saturation magnetization.The amount of lubricant added is preferably 1.0 mass % or more, and more preferably 1.5 mass %.

[0037] The calcined powder or its granules may be mixed with the lubricant using a known mixer, for example, a Henschel mixer. ３ ・(CH ２ ) ｍ COOH (where m is an integer of 10 or more and 16 or less), and among them, lauric acid (CH ３ ・(CH ２ ) １０ .COOH) and / or stearic acid (CH ３ ・(CH ２ ) １６・COOH) is more preferable. This is because such compounds are excellent in improving the fluidity of the thermal spray feedstock, and are inexpensive and easily available. When the main granulation step is performed, the thermal spray feedstock is a calcined powder granule containing a lubricant, while when the main granulation step is not performed, the thermal spray feedstock is a calcined powder agglomerate containing a lubricant. The volume average particle size of the thermal spray feedstock (granules and agglomerates) is larger than the primary particle size of the calcined powder. Therefore, the fluidity of the thermal spray feedstock is high in the subsequent thermal spraying step.

[0038] <Thermal Spraying Process> Next, the thermal spray material is thermally sprayed to produce a thermal sprayed product. In thermal spraying, a mixture of combustion gas and oxygen (total oxygen) can be used as a combustible gas combustion flame source. The volume ratio of combustion gas to oxygen (total oxygen) is preferably 1:3.5 to 1:10.0, more preferably 1:5 to 1:8.0. This allows for the formation of particles with high sphericity to proceed favorably. Examples of the combustion gas include combustible gases such as propane gas, propylene gas, and acetylene gas, with propane gas being particularly preferred. The supply rate of the thermal spray material is preferably 3.5 to 20 kg / hour, more preferably 4.5 to 9 kg / hour. If the supply rate is excessively high, the thermal spray material is likely to adhere to itself and it becomes difficult to sufficiently advance the ferritization reaction to the interior of the particles. On the other hand, if the supply rate is excessively low, this increases production costs.

[0039] The oxygen used in thermal spraying is also used to transport the feedstock to the thermal spray flame. Therefore, it is divided into combustion oxygen, which is used directly in the flame, and feedstock supply oxygen, which is burned after transporting the feedstock to the center of the thermal spray source. The carbon content of the ferrite powder after thermal spraying can be controlled by the volume ratio of oxygen to feedstock supply oxygen. Total oxygen = combustion oxygen + feedstock supply oxygen, and the volume ratio of combustion oxygen to feedstock supply oxygen is preferably 95:5 to 80:20. If the combustion oxygen ratio is greater than the above (approaching 100), the feedstock supply capacity decreases and the feedstock may clog the feedstock supply pipe. If the combustion oxygen ratio is smaller than the above (below 80), the feedstock is supplied to areas away from the center of the flame, where the highest temperature occurs, which makes the carbon compounds (lubricants) carried with the feedstock more likely to burn incompletely, potentially increasing the carbon content of the ferrite powder after thermal spraying. From the viewpoint of reducing the carbon content, the combustion oxygen:feedstock supply oxygen ratio is more preferably 95:5 to 85:15, even more preferably 95:5 to 87:13, and most preferably 95:5 to 89:11.

[0040] Furthermore, the combustion oxygen is preferably at least 0.85 times the volume required for complete combustion of the combustion gas. For example, when propane gas is used as the combustion gas, the combustion oxygen volume is preferably at least 4.25 times the volume of the propane gas. By doing so, even if oxygen in excess of the oxygen required for complete combustion of the combustion gas is supplied, it is possible to minimize the temperature drop in the thermal spray flame and prevent incomplete combustion of carbon compounds (lubricants) brought in together with the raw material (calcined powder).

[0041] The combustion gas amount ratio is preferably 1.05 or more and 2.00 or less. Here, the combustion gas amount ratio is the amount of combustion gas (Nm ３ / time) and is calculated according to the following formula (2).

[0042]

[0043] Net combustion gas volume (Nm ３ / time) can be calculated according to the following formula (3) or (4).

[0044]

[0045] Nitrogen, oxygen, air, etc. can be used as a carrier gas for transporting the thermal spray raw material into the combustible gas. The flow rate of the transported thermal spray raw material is preferably 20 to 60 m / sec. Thermal spraying is preferably carried out at a temperature of 1000 to 3500°C, more preferably 2000 to 3500°C. The particles ferritized by thermal spraying are rapidly cooled and solidified in an air atmosphere and recovered using a cyclone or a filter to obtain the thermal spray material.

[0046] <Classification step> If necessary, the obtained thermal sprayed material may be classified. In classification, the particle size may be adjusted to the desired particle size using a known method such as air classification (air flow classification), mesh classification, or sieve classification. It is also possible to separate and recover particles with larger particle sizes in a single process using air flow classification such as a cyclone. In this way, a ferrite powder with reduced content of irregularly shaped particles can be obtained.

[0047] According to the present embodiment, a ferrite powder that prevents a decrease in saturation magnetization and a decrease in filler filling rate and has excellent resin curing performance, and a method for producing the same are provided. This ferrite powder has a low content of irregularly shaped particles, which prevents the problems of a decrease in saturation magnetization and a decrease in filler filling rate. Furthermore, this ferrite powder has a carbon content limited to a specific range, which has the effect of excellent resin curing performance.

[0048] To the best of the inventors' knowledge, such ferrite powder has not been known in the past. Patent Documents 1 to 3 disclose spherical ferrite particles produced by thermal spraying, but do not disclose the carbon content. Patent Document 4 discloses a manufacturing method in which raw material powder is treated with a surface treatment agent such as a higher fatty acid, but does not mention the carbon content of the resulting powder, nor does it recognize the curing performance of the resin. Furthermore, the manufacturing method of Patent Document 4 does not involve granulation of the raw material powder, and it is thought that such powder has poor flowability during manufacturing.

[0049] Ferrite Resin Composite Material The ferrite powder of this embodiment can be applied to a ferrite resin composite material (resin composition). The ferrite resin composite material contains ferrite powder and a resin. By using the ferrite powder of this embodiment, a composite material can be obtained that has a high filler filling rate, excellent magnetic properties (saturation magnetic flux density, magnetic loss, etc.), and excellent resin curing performance.

[0050] Examples of resins constituting the composite material include epoxy resins, urethane resins, acrylic resins, silicone resins, polyamide resins, polyimide resins, polyamideimide resins, fluororesins, and combinations thereof. Here, the silicone resin may be a modified silicone resin modified with acrylic, urethane, epoxy, and / or fluorine.

[0051] The ratio of the ferrite powder to the total solid content in the composite material is preferably 50 to 95 mass%, more preferably 80 to 95 mass%. The ratio of the resin to the total solid content in the composite material is preferably 5 to 50 mass%, more preferably 5 to 20 mass%. By setting the ratios of the ferrite powder and resin within the above ranges, the dispersion stability of the ferrite powder in the composite material, as well as the storage stability and moldability of the composite material, are excellent, and the composite (molded product) obtained by molding the composite material has excellent properties such as mechanical strength and electromagnetic wave shielding performance.

[0052] The composite material may contain components other than the ferrite powder and resin, such as solvents, fillers (organic fillers, inorganic fillers), plasticizers, antioxidants, dispersants, colorants such as pigments, and thermally conductive particles.

[0053] Such a ferrite resin composite material can be used as an electromagnetic wave shielding material, electronic material, or electronic component. The electromagnetic wave shielding material, electronic material, or electronic component can be produced by molding the composite material using a known method. The molding method is not particularly limited, and examples include compression molding, extrusion molding, injection molding, blow molding, and calendar molding. Alternatively, a coating film of the composite material can be formed on a substrate.

[0054] The present invention will be explained in more detail by the following examples, but the present invention is not limited to these examples.

[0055] (1) Preparation of ferrite powder [Example 1] <Raw material mixing step and preliminary granulation step> Iron oxide (Fe ２ O ３ ) and trimanganese tetroxide (Mn ３ O ４ The raw materials were weighed and mixed so that the molar ratio of iron (Fe) to manganese (Mn) was Fe:Mn = 8:1. Water was added to the resulting mixture, which was then pulverized using a wet bead mill to produce a slurry with a solid content of 50% by mass. The slurry was then granulated using a spray dryer to produce a pre-granulated product.

[0056] <Pre-firing step and pulverization step> The obtained pre-granulated material was pre-fired to produce a pre-firing product. Pre-firing was performed using a rotary kiln under conditions of a pre-firing temperature of 780°C and an air atmosphere. Next, the obtained pre-firing product was pulverized using a dry bead mill to produce a pre-firing powder. The obtained pre-firing powder had a particle size (primary particle size) of 4.2 μm.

[0057] <Main Granulation Step> Water was added to the obtained calcined powder and pulverized using a wet bead mill to prepare a slurry with a solid content of 50% by mass. The particle size (primary particle size) of the pulverized powder in the slurry was 4.2 μm. The slurry was then granulated using a spray dryer. The average particle size of the obtained granules (calcined powder granules) was 50 μm.

[0058] <Pretreatment Step> Lauric acid was added as a lubricant to the obtained granules, and the mixture was mixed using a Henschel mixer. At this time, the amount of lubricant (lauric acid) added was 15.0 parts by mass (15.0 mass%) per 100.0 parts by mass of the granules. This produced a thermal spray raw material.

[0059] <Thermal spraying process> The lubricant-added granules (thermal spray raw material) were thermally sprayed and quenched in a combustible gas combustion flame. During thermal spraying, the ratio of propane gas flow rate to total oxygen flow rate was 1:5.42, and the raw material supply rate was 1.13 in terms of combustion gas volume ratio. The cooled particles were then collected using a cyclone installed downstream of the airflow to obtain a thermal spray material. At this time, the combustion oxygen:raw material supply oxygen ratio was 89.5:10.5.

[0060] <Classification step> Coarse powder was removed from the obtained thermal sprayed material using a sieve, and fine powder was further removed by air classification to obtain ferrite powder composed of ferrite particles. The production conditions for the ferrite powder are also shown in Table 1.

[0061] Example 2 Ferrite powder was prepared in the same manner as in Example 1, except that in the pretreatment step, the amount of lubricant (lauric acid) added was 5.0 parts by mass (5.0 mass%) per 100.0 parts by mass of the granules.

[0062] Example 3 Ferrite powder was prepared in the same manner as in Example 1, except that in the pretreatment step, the amount of lubricant (lauric acid) added was 3.0 parts by mass (3.0 mass%) per 100.0 parts by mass of the granules.

[0063] Example 4 Ferrite powder was prepared in the same manner as in Example 1, except that in the pretreatment step, the amount of lubricant (lauric acid) added was 1.5 parts by mass (1.5% by mass) per 100.0 parts by mass of the granules.

[0064] Example 5 Ferrite powder was prepared in the same manner as in Example 1, except that no lubricant (lauric acid) was added to the granules.

[0065] [Example 6] Ferrite powder was produced in the same manner as in Example 4, except that in the mixing and grinding step, iron (Fe) and manganese (Mn) were weighed and mixed so that the molar ratio of Fe:Mn was Fe:Mn = 3:1. In this granulation step, the particle size (primary particle size) of the ground powder in the slurry was 4.7 µm.

[0066] [Example 7] Ferrite powder was produced in the same manner as in Example 4, except that in the mixing and grinding step, iron (Fe) and manganese (Mn) were weighed and mixed so that the molar ratio of Fe:Mn was Fe:Mn = 14:1. In this granulation step, the particle size (primary particle size) of the ground powder in the slurry was 3.9 µm.

[0067] [Example 8] Except for changing the classification conditions in the classification step, ferrite powder was produced in the same manner as in Example 4. In this granulation step, the particle size (primary particle size) of the pulverized powder in the slurry was 4.2 µm.

[0068] [Example 9] Except for changing the classification conditions in the classification step, ferrite powder was produced in the same manner as in Example 4. In this granulation step, the particle size (primary particle size) of the pulverized powder in the slurry was 4.2 µm.

[0069] (2) Evaluation of Ferrite Powder The ferrite powders of Examples 1 to 9 were evaluated as follows.

[0070] <Chemical Analysis (ICP)> The metal component content of the ferrite powder was measured as follows. First, 0.2 g of a sample (ferrite powder) was weighed, and 60 ml of pure water, 20 ml of 1 N hydrochloric acid, and 20 ml of 1 N nitric acid were added to the weighed sample, followed by heating to prepare an aqueous solution in which the sample was completely dissolved. The resulting aqueous solution was placed in an ICP analyzer (Shimadzu Corporation, ICPS-10001V), and the metal component content was measured.

[0071] <Carbon Content> The carbon content of the ferrite powder was measured by infrared absorption. Specifically, 1 g of ferrite powder was burned in an oxygen stream to convert the carbon contained in the ferrite powder into carbon dioxide. The amount of infrared absorption of carbon dioxide was measured using an infrared absorption detector (LECO Japan, LLC, carbon sulfur analyzer CS200 model), and the carbon content was calculated.

[0072] <Analysis of Associated Carbon-Containing Compounds (GC-MS)> The associated carbon-containing compounds of the ferrite powder were analyzed using a high-resolution mass spectrometer GC / MS. 5 g of ferrite powder was weighed and placed in a beaker with an internal volume of 200 ml, to which 500 ml of methyl ethyl ketone (MEK) was added, followed by ultrasonic treatment for 5 minutes to extract organic components associated with the ferrite powder. The extracted MEK solution was filtered, and the obtained filtrate was used as the test solution. The analytical conditions for the high-resolution mass spectrometer GC / MS are shown below.

[0073] - Gas chromatography: Agilent Technologies, 6890N - Mass spectrometer: Agilent Technologies, 5973N - Column: Agilent Technologies, DB.5MS (film thickness 0.25 μm) - Heating device: Parkin-Elmer, TurboMatrix 650ATD - Temperature conditions: 50°C (2 min) → 280°C (18 min) - Heating rate: 20°C / min - Carrier gas flow rate: Helium 1 ml / min - Injection method: Splitless 0.5 min - Injection port temperature: 280°C - Interface: 280°C - Measurement mass range: m / z 29 to 600 - Injection volume: 1 μl

[0074] The carbon-containing compounds were identified as follows: Using an analyzer (Agilent Technologies, 5973N), the peaks detected on the TIC chromatogram due to the analyzer and MEK were eliminated, and a library search was performed on each of the remaining peaks. The compound with the highest library match rate in the mass spectral pattern was identified as the carbon-containing compound associated with the ferrite powder.

[0075] <Particle Size Distribution> The particle size distribution of the ferrite powder was measured. First, 10 g of sample and 80 ml of water were placed in a 100 ml beaker, and two drops of sodium hexametaphosphate were added as a dispersant. Next, dispersion was performed using an ultrasonic homogenizer (SMT Corporation, UH-150 model). At this time, the output level of the ultrasonic homogenizer was set to 4, and dispersion was performed for 20 seconds. After that, bubbles formed on the peaker surface were removed, and the sample was introduced into a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7500nano) and measured. From this measurement, the 10% diameter (D10), 50% diameter (volume average particle size, D50), and 90% diameter (D90) in the volume particle size distribution were determined. Here, the measurement conditions were a pump speed of 7, an internal ultrasonic irradiation time of 30, and a refractive index of 1.70-050i.

[0076] <BET Specific Surface Area> The BET specific surface area of ​​the ferrite powder was measured using a specific surface area measurement device (Mountec Co., Ltd., Macsorb HM model-1208). First, approximately 10 g of the obtained ferrite powder was placed on a medicine wrapping paper and degassed in a vacuum dryer to confirm that the degree of vacuum was -0.1 MPa or less. Then, the moisture adhering to the particle surface was removed by heating at 200°C for 2 hours. Approximately 0.5 to 4 g of the ferrite powder from which the moisture had been removed was placed in a standard sample cell dedicated to the measurement device and accurately weighed using a precision balance. Next, the weighed ferrite particles were placed in the measurement port of the measurement device and measurement was performed. The measurement was performed using the single-point method. The measurement atmosphere was a temperature of 10 to 30°C and a relative humidity of 20 to 80% (no condensation).

[0077] <Tap Density> The tap density of the ferrite powder was measured using a USP tap density measuring device (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation) in accordance with JIS Z 2512-2012.

[0078] <Shape Factor (SF-1)> The average shape factor (SF-1) of the ferrite powder was determined as follows. The ferrite powder was analyzed using a particle image analyzer (Malvern Panalytical, Morphologi G3). During the analysis, image analysis was performed on each of 30,000 particles in the powder, and the maximum length (horizontal Feret diameter) R (unit: μm), projected perimeter L (unit: μm), and projected area S (unit: μm ２ ) was automatically measured. Then, SF-1 for each particle was calculated according to the following formula (1), and the average value was taken as SF-1 for the ferrite powder.

[0079]

[0080] Furthermore, the number of particles (irregularly shaped particles) having an SF-1 of more than 103.6 was counted, and the proportion of irregularly shaped particles was calculated according to the following formula (5).

[0081]

[0082] <Magnetic Properties (Saturation Magnetization, Remanent Magnetization, and Coercive Force)> The magnetic properties (saturation magnetization, remanent magnetization, and coercive force) of the ferrite powder were measured as follows. First, a sample was packed into a cell with an inner diameter of 5 mm and a height of 2 mm, and set in a vibrating sample magnetometer (Toei Industry Co., Ltd., VSM-C7-10A). A magnetic field was applied and swept up to 5 kOe, and then the applied magnetic field was reduced to draw a hysteresis curve. From the data of the obtained curve, the saturation magnetization σs, remanent magnetization σr, and coercive force Hc of the sample were determined.

[0083] <Magnetic Permeability> The magnetic permeability of the ferrite powder was measured using an RF impedance / material analyzer (Agilent Technologies, Inc., E4991A) and a magnetic material measurement electrode (16454A). First, 9 g of ferrite powder and 1 g of binder resin (Kynar 301F: polyvinylidene fluoride) were placed in a polyethylene container (100 ml capacity) and stirred and mixed using a ball mill at a rotation speed of 100 rpm. Approximately 0.6 g of the resulting mixture was filled into a die (inner diameter 4.5 mm, outer diameter 13 mm) and pressed at a pressure of 40 MPa for 1 minute using a press to form a molded body. The resulting molded body was heat-cured at 140°C for 2 hours using a hot air dryer to form a measurement sample. The resulting measurement sample was placed in the RF impedance / material analyzer, and the outer diameter, inner diameter, and height of the measurement sample, which had been measured in advance, were entered. The measurement was performed with an amplitude of 100 mV, and the measurement frequency range was swept on a logarithmic scale from 1 MHz to 3 GHz. The real part μ′ and imaginary part μ″ of the complex permeability at a frequency of 100 MHz were determined, and the loss factor tanδ was calculated according to the following formula (6).

[0084]

[0085] <Resin curing performance> The ferrite powder was applied to a resin composition to evaluate the resin curing performance. First, 80 parts by mass of the ferrite powder, 18 parts by mass of an epoxy resin, and 2 parts by weight of a curing agent were dispersed and mixed using a planetary mixer to prepare a resin composition. The resulting resin composition was dried at 120°C for 5 minutes. The dried resin composition was heated at 180°C to promote curing, and the curing time required for the resin to reach a degree of cure of 95% or more was determined. Based on the obtained curing time, the composition was rated as follows:

[0086] A: Curing time is Std x 1.00 or more and less than Std x 2.00 B: Curing time is Std x 2.00 or more and less than Std x 3.00 C: Curing time is Std x 3.00 or more

[0087] Here, the resin curing degree indicates the degree of progress (reaction rate) of the resin curing reaction. The resin curing degree of the unreacted material is 0%, and the resin curing degree of the reacted material is 100%. The resin curing degree was determined using an FT-IR (Fourier transform infrared spectroscopy) device. Specifically, the resin was irradiated with infrared light and transmitted or dispersed to obtain an FT-IR spectrum, which was used to analyze the progress of the resin curing reaction. The spectra of the unreacted material, the 100% reacted material, and the resin being measured were then compared, and the resin curing degree was determined by comparing the peak intensities of each sample in the region where the greatest difference was observed. The curing time of each sample was then calculated using the curing time of Example 4 as the standard (Std).

[0088] The drying conditions for the resin composition are not limited to those described above, and the resin composition should preferably be dried so that the organic solvent content is 10% by mass or less, more preferably 5% by mass or less. Suitable drying conditions can be determined appropriately through simple experiments. While this varies depending on the amount of organic solvent in the varnish (resin composition), for example, a varnish containing 30 to 60% by mass of organic solvent can be dried at 50 to 150°C for approximately 3 to 10 minutes. Furthermore, the measurement of the resin curing degree is not limited to that using FT-IR, and a dispersive infrared spectrophotometer or the like may also be used.

[0089] (3) Results The evaluation results obtained for Examples 1 to 9 are shown in Tables 1 and 2. As shown in Tables 1 and 2, in Examples 1 to 9, ferrite powders having a volume average particle size (D50) of 2.6 to 7.5 μm and a manganese ferrite composition were obtained. This ferrite powder contained spherical particles.

[0090] The samples of Examples 2 to 4 and Examples 6 to 9, in which the amount of lubricant (lauric acid) added was 1.5 to 5.0 mass%, contained the carbon-hydrogen-oxygen-containing compound methyl decanoate and had a carbon content of 0.012 to 0.080 mass%. These samples had a low percentage of irregularly shaped particles (the percentage of particles with an SF-1 greater than 103.6) of 6.2% or less by number, and presented no problems in terms of magnetic properties and magnetic permeability. Furthermore, there were no problems with resin curing performance when applied to resin compositions. In particular, the samples of Examples 3, 4, 6, 7, and 9, which had carbon contents of 0.012 to 0.060 mass%, exhibited superior resin curing performance. Furthermore, the sample of Example 5, in which no lubricant was added, also exhibited excellent resin curing performance. Although no lubricant was added during production, the sample of Example 5 contained a small amount of carbon (0.002 mass%). It is speculated that this carbon originated from soot generated during thermal spraying, but the details are unknown.

[0091] In contrast, the sample of Example 1, in which the amount of lubricant added was 15.0 mass %, had a high carbon content (0.200 mass %). This sample had a long resin curing time when applied to a resin composition, and was problematic in terms of resin curing performance.

[0092]

[0093]

Claims

1. A ferrite powder composed of true spherical ferrite particles, wherein the ferrite powder contains 54.0 to 70.0% by mass of iron (Fe) and 3.5 to 18.5% by mass of manganese (Mn), has an average volume particle diameter of 2.0 to 20.0 μm, and a carbon content of 0.100% by mass or less.

2. The ferrite powder according to claim 1, wherein the average shape factor SF-1 of the ferrite powder is 100 to 110.

3. A method for producing the ferrite powder according to claim 1 or 2, comprising the following steps: a step of mixing ferrite raw materials to produce a raw material mixture; a step of pre-granulating the raw material mixture to produce a pre-granulated product; a step of pre-firing the pre-granulated product to produce a pre-fired product; a step of pulverizing the pre-fired product to produce pre-fired powder; a step of adding and mixing 0.5 to 13.0% by mass of a lubricant to the pre-fired powder to produce a thermal spraying raw material; and a step of thermal spraying the thermal spraying raw material to produce a thermal sprayed product.

4. The lubricant is a compound represented by the general formula: CH ３ ・(CH ２ ) ｍ ・COOH (where m is an integer of 10 or more and 16 or less).

5. The method according to claim 3 or 4, wherein the thermal spraying raw material is a granulated product or an aggregate, and the volume average particle diameter of the granulated product or the aggregate is larger than the primary particle diameter of the pre-fired powder.