Ferrite powder and resin composition containing the same

Abstract

The spherical ferrite powder of the present invention has a median diameter D of 10 μm to 200 μm. 50 The ferrite powder has the following characteristics: on the particle surface of the ferrite powder, the maximum height Rz is 1.5 μm or less, and the Heywood diameter of the crystal grains is in the range of 2.0 μm to 8.0 μm. A 1 mm thick plate obtained by kneading 60 vol% of the ferrite powder with a resin and curing it has a dielectric constant of 1 to 20 measured at 50 MHz.

Description

[Technical Field]

[0001] This invention relates to ferrite powder and resin compositions containing the same. [Background technology]

[0002] Molded bodies containing resin and ferrite powder, which is a filler dispersed within the resin, are used for electronic components such as inductors, magnetic cores, and magnetic heads, as well as magnetic materials such as magnetic shielding materials. These molded bodies have a sheet-like shape and are obtained by kneading the resin and ferrite powder and molding them into a desired shape. When the shape of the particles constituting the ferrite powder is close to spherical, the fluidity during molding increases, resulting in good moldability, and the filling rate of the ferrite powder within the resin increases, resulting in good magnetic properties. Therefore, several techniques have been proposed for forming ferrite powder into spherical shapes. For example, Patent Document 1 describes a method of thermal spraying granules obtained by calcining and granulating a mixture of ferrite raw materials by passing it through a combustion flame. The thermal spraying causes a ferritization reaction, and a portion of the granules melts to form perfectly spherical ferrite particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-66648 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present inventors have found that while the technology described in Patent Document 1 can produce ferrite powder with high sphericity, it has the problem that the dielectric constant of the ferrite powder becomes high, causing the resonance frequency to appear in the low-frequency range. Furthermore, they have found that this problem arises because, during thermal spraying, the granulated material is passed through a high-temperature combustion flame of approximately 2000°C, causing the ferrite structure to collapse and some of the metal elements to separate and precipitate from the ferrite structure.

[0005] An object of the present invention is to provide a ferrite powder or the like that has high fluidity when kneaded with a resin and can keep the dielectric constant low.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention provides the following technology. [1] Spherical ferrite powder having a median diameter D of 10 μm to 200 μm , , [Figure 2] , , , 3 , , [Figure 1] , ,

[0008] , , ,

[0007] , , 50 , , , , , , , , which is At the particle surface of the ferrite powder, the maximum height Rz is 1.5 μm or less, and the Heywood diameter of the crystal grains is in the range of 2.0 μm to 8.0 μm, For a plate obtained by kneading and curing 60 vol% of the ferrite powder and a resin, the dielectric constant measured at 50 MHz is less than 20, the ferrite powder. [2] In the ferrite powder, the ferrite is represented by the composition formula of AFe2O4, and A is at least one element selected from the group consisting of Mg, Mn, Co, Ni, Cu, and Zn, the ferrite powder according to [1] above. [3] The true density is 5.10 g / cm 3 or more, the ferrite powder according to [1] above. [4] The pore volume is 0.025 mL / g or less, the ferrite powder according to [1] above. [5] A resin composition containing the ferrite powder according to [1] above.

Advantages of the Invention

[0007] According to the present invention, when kneaded with a resin, it has high fluidity and can keep the dielectric constant low.

Brief Description of the Drawings

[0008] [Figure 1] SEM photograph at 1,000 times of the ferrite powder of Example 2. [Figure 2] SEM photograph at 5,000 times of the ferrite powder of Example 2. [Figure 3] SEM photograph at 1,000 times magnification of the ferrite powder of Comparative Example 1. [Figure 4] SEM photograph at 5,000 times magnification of the ferrite powder of Comparative Example 1. [Figure 5] SEM photograph at 1,000 times magnification of the ferrite powder of Comparative Example 2. [Figure 6] SEM photograph at 5,000 times magnification of the ferrite powder of Comparative Example 2. [Figure 7] SEM photograph at 1,000 times magnification of the ferrite powder of Comparative Example 3. [Figure 8] SEM photograph at 5,000 times magnification of the ferrite powder of Comparative Example 3. [Figure 9] SEM photograph at 1,000 times magnification of the ferrite powder of Comparative Example 4. [Figure 10] SEM photograph at 5,000 times magnification of the ferrite powder of Comparative Example 4. [Figure 11] SEM photograph at 1,000 times magnification of the ferrite powder of Comparative Example 5. [Figure 12] SEM photograph at 5,000 times magnification of the ferrite powder of Comparative Example 5. [Figure 13] It is a drawing schematically showing crystal grains on the particle surface in the ferrite powder.

Mode for Carrying Out the Invention

[0009] <Ferrite powder> As shown in FIG. 13, the ferrite powder 1 of the present embodiment includes spherical ferrite particles 2 (hereinafter sometimes simply referred to as "particles"). "Spherical" means that the two-dimensional projection image of the particles observable with a microscope or the like is a shape close to a circle. For example, the roundness coefficient of the particles 2 is preferably 0.8 or more or 0.9 or more. The roundness coefficient is a value calculated based on the two-dimensional projection image of the particles 2, and is (4π × area inside the outer periphery of the particle) / (perimeter of the outer periphery of the particle) 2 and is. The roundness coefficient is calculated as the average value of the values obtained for 50 particles 2 in the ferrite powder 1.

[0010] The median diameter D of the ferrite powder 1 50 is 10 μm to 200 μm. The ferrite powder 1 having the median diameter D within the above range 50 can be uniformly dispersed when kneaded with a resin or the like, and a resin composition with a high filling of the ferrite powder 1 can be obtained. Specifically, when the median diameter D 50 is 10 μm or more, the particles 2 are more likely to be dispersed in the resin. The ferrite powder with the median diameter D 50 of 50 μm or less is suitable for applications such as small electronic components. Also, when the median diameter D 50 is 200 μm or less, it is suitable for sheet shapes such as magnetic shielding materials. The median diameter D 50 is preferably 10 μm to 150 μm, more preferably 20 μm to 110 μm. The particle size distribution is measured dry by a laser particle size distribution analyzer, and more specifically, by injection-type dry measurement. Note that the particle size distribution is based on volume.

[0011] The maximum height Rz on the surface of the particle 2 is 1..5 μm or less. The maximum height Rz is calculated by the following procedure. Photograph the particle surface with a microscope and determine the roughness curve by analyzing the obtained image. Sample this roughness curve within the range of the reference length, and the sum of the highest part (maximum peak height) and the deepest part (maximum valley depth) within this range is the maximum height Rz. The maximum height Rz is preferably 0.05 μm to 1.0 μm, more preferably 0.1 μm to 0.5 μm.

[0012] Each of the particles constituting the ferrite powder 1 is formed by a plurality of crystal grains (grains) 3 gathering together (Fig. 13). There is a boundary called a grain boundary 4 between the crystal grains 3 and the crystal grains 3. The Heywood diameter (equivalent diameter of the projected area circle) of the crystal grains 3 on the surface of the particle 2 is 2.0 μm to 8.0 μm. The Heywood diameter is determined from the SEM image of the particle 2 surface using image analysis software and calculated as the average value of 50 crystal grains 3. The Heywood diameter of the crystal grains 3 is preferably 2.2 μm to 6.0 μm, more preferably 2.5 to 5.0 μm.

[0013] If the maximum height Rz on the surface of particle 2 and the Heywood diameter of the crystal grain 3 are within the above range, then the surface of particle 2 can be said to be smooth. When ferrite powder 1 containing spherical particles 2 with such a smooth surface is used, the viscosity of the mixture obtained by kneading the resin with the dispersed ferrite powder 1 is low and the fluidity is high, so high moldability can be obtained when forming a molded body with this mixture. Furthermore, the ferrite powder 1 is easily dispersed uniformly in the resin and easily packed at high density.

[0014] Furthermore, a 1 mm thick plate obtained by kneading 60 vol% ferrite powder 1 with resin and curing it has a dielectric constant of less than 20 when measured at 50 MHz. Having a dielectric constant within this range allows ferrite powder 1 to exhibit properties such as electromagnetic shielding performance across a wide frequency band. Moreover, having a dielectric constant within this range means that ferrite powder 1 has a well-structured ferrite structure, and the metal elements constituting ferrite powder 1 are contained within this structure.

[0015] A mixture of 30 vol% of the ferrite powder 1 and an epoxy resin having a viscosity of 1820 mPa·s was subjected to testing at 25°C and a shear rate of 200 S. -1 The viscosity measured by the E-type viscometer is preferably 7000 mPa·s or less. The viscosity of the epoxy resin alone is measured under the same conditions as the viscosity measurement of the mixture with ferrite powder.

[0016] The ferrite in ferrite powder 1 is preferably spinel ferrite. Spinel ferrite is represented by the compositional formula AFe2O4, where A is exemplified by at least one element selected from the group consisting of Mg, Mn, Co, Ni, Cu, and Zn. More specifically, Ni-Zn-Cu ferrite and Mn-Zn ferrite are examples. Ni-Zn-Cu ferrite has a lower dielectric constant than Mn-Zn ferrite and is therefore often used in electronic components for high-frequency applications.

[0017] The true density of ferrite powder 1 is 5.10 g / cm³. 3 The above is preferable. The true density is measured by dry density measurement (gas displacement method). The true density is 5.10 g / cm³. 3 This result in higher magnetic permeability, improving the performance of the ferrite powder as an electronic component or magnetic shielding material. Furthermore, having a true density within this range means that there are few voids in the particles constituting the ferrite powder 1. The true density of the ferrite powder 1 is more preferably 5.15 g / cm³. 3 That concludes the explanation. Theoretically, the upper limit of true density is 5.50 g / cm³. 3 That is the case.

[0018] The pore volume of ferrite powder 1 is preferably 0.025 mL / g or less. The pore volume is measured by the mercury intrusion method. A pore volume of 0.025 mL / g or less suppresses the increase in viscosity of the mixture when ferrite powder is kneaded with resin. The pore volume of ferrite powder 1 is more preferably 0.001 mL / g to 0.020 mL / g, and more preferably 0.002 mL / g to 0.010 mL / g.

[0019] <Resin composition> The resin composition of this embodiment comprises a resin and the ferrite powder 1 described above dispersed in the resin.

[0020] Examples of resins include epoxy resins, urethane resins, acrylic resins, silicone resins, various modified silicone resins (acrylic modified, urethane modified, epoxy modified, fluorine), polyamide resins, polyimide resins, polyamide-imide resins, polyvinyl chloride, polyvinyl acetate, phenolic resins, melamine resins, water-soluble polyesters, and fluororesins. One or more of these can be selected and used in combination.

[0021] The resin composition is obtained by kneading (or mixing) the resin and ferrite powder 1. The resin composition is then molded into a shape suitable for its intended use and cured as needed to form a molded article.

[0022] The content of ferrite powder 1 in the resin composition can be changed depending on the intended use, target properties, shape of the molded product, etc. For example, the content of ferrite powder 1 is 50% by mass or more and 95% by mass or less.

[0023] <Method for producing ferrite powder> The ferrite powder 1 mentioned above is produced by the following process; (a) A process of obtaining a mixed powder by mixing raw materials in amounts corresponding to the desired composition. (b) A process to obtain primary calcined powder by primary calcining the mixed powder obtained in (a) above at 700°C to 850°C. (c) A step of obtaining spherical granules from the primary calcined powder obtained in (b) above by spray drying, (d) A process of secondary calcination of the granules obtained in (c) above at 900°C to 1000°C. It can be manufactured by a method that includes [a specific feature / method].

[0024] The mixing of the raw materials in step (a) above may be done either dry or wet. If the step includes obtaining a slurry by wet mixing, step (a) may further include filtering the slurry and drying it.

[0025] The temperature during the primary firing in step (b) above is preferably 800°C or lower.

[0026] A step of grinding the primary calcined powder to refine and homogenize it may be included between step (b) and step (c) described above.

[0027] Furthermore, step (c) above may include the step of preparing a slurry by adding a solvent to the primary calcined powder, and the step of obtaining spherical granules from this slurry by spray drying. Water is preferred as the solvent. In addition to the raw materials, binders, dispersants, etc. may be added to the solvent as needed. For example, polyvinyl alcohol can be preferably used as a binder. The amount of binder added should preferably be about 0.1% to 2% by mass in the slurry. For example, ammonium polycarboxylate-based dispersants and methacrylic acid-based polymers can be preferably used as dispersants. The amount of dispersant added should preferably be about 0.1% to 2% by mass in the slurry. Other substances such as pH adjusters such as ammonia, lubricants, and sintering accelerators may also be added. The solid content concentration of the slurry is preferably in the range of 60% to 90% by mass. If it is 60% by mass or more, there will be fewer pores in the granules, and insufficient sintering during calcination can be prevented.

[0028] The spray dryer used in spray drying may be of the nozzle type or the disc type. The ambient temperature during spray drying is preferably in the range of 100°C to 300°C. If the ambient temperature during spray drying is in the range of 100°C to 300°C, there will be fewer pores in the granules, which will prevent insufficient sintering during firing.

[0029] By setting the secondary firing temperature in step (d) above to 1000°C or lower, a ferrite powder with a low dielectric constant is obtained. This is because, due to the low firing temperature, the ferrite structure is maintained even after firing. By maintaining the ferrite structure, some of the metal elements, such as Fe3O4, α-Fe2O3, or metal oxides, are retained within the ferrite structure without precipitating.

[0030] Furthermore, by performing secondary sintering at temperatures below 1000°C, spherical ferrite powder with high surface smoothness can be obtained. Specifically, by performing secondary sintering at low temperatures, the growth rate of the ferrite structure is reduced, and the crystal grains grow slowly and uniformly. As a result, it is possible to grow crystal grains to a size that satisfies the aforementioned Heywood diameter range while keeping the maximum height Rz on the particle surface small.

[0031] Furthermore, the reason why smooth-surfaced, high-density spherical ferrite powder can be obtained even by such low-temperature secondary firing is that the primary firing powder mentioned above is fired at 700°C to 850°C and is sufficiently ferriteized, making it a powder that can be sintered even at the low secondary firing temperature of 1000°C or less. A powder that can be sintered at low temperatures is, for example, a powder made by mixing 15g of primary firing powder with 1.5mL of a 6.5% diluted PVA aqueous solution, placing the mixture into a mold with an outer diameter of 20mmφ and an inner diameter of 10mmφ, and firing it in a press machine at a rate of 1 ton / cm². 2 When a compressed molded body is fired at 900°C in air for 2 hours, the sintered density is 5.00 g / cm³. 3 The above is the powder.

[0032] Furthermore, a secondary firing temperature of 900°C or higher can increase the density of the granulated material.

[0033] Furthermore, the secondary firing time should be set within the range in which sintering progresses to produce ferrite powder with the desired true density, but for example, holding it for about 1 to 10 hours is sufficient.

[0034] The method for producing ferrite powder may further include a step of crushing the calcined material after step (d). The crushing is sufficient if it can disperse the aggregated particles. [Examples]

[0035] <Manufacturing of ferrite powder> [Example 1] According to the composition shown in Table 1, oxides of Fe, Ni, Zn, and Cu were weighed and wet-mixed to obtain a slurry. The slurry was filtered and dried to obtain a mixed powder of the raw materials. This mixed powder was primary calcined at 760°C for 3 hours. The resulting calcined material was pulverized in a vibratory mill to obtain primary calcined Ni-Zn-Cu ferrite powder. 15 g of the obtained primary calcined powder and 1.5 mL of a 6.5% diluted PVA aqueous solution were mixed and placed into a mold with an outer diameter of 20 mmφ and an inner diameter of 10 mmφ, and pressed at a rate of 1 ton / cm². 2 The sintered body obtained by firing a compressed molded body at 900°C in air for 2 hours has a sinter density of 5.21 g / cm³. 3 It was a powder that could be sintered at low temperatures.

[0036] A polyammonium carboxylate-based dispersant was used at a concentration of 1.0% by mass relative to the primary calcined powder, and 25% by mass aqueous ammonia was used as a pH adjuster at a concentration of 0.5% by mass relative to the primary calcined powder. The primary calcined powder was added to the water containing the polyammonium carboxylate-based dispersant and aqueous ammonia, stirred, and wet-milled to prepare a slurry with a concentration of 67% by mass. The obtained slurry was sprayed into 145°C hot air using a spray dryer to obtain spherical granules.

[0037] The obtained granules were placed in an electric furnace and calcined by holding at 950°C for 3 hours. The resulting calcined material was crushed. The resulting powder was used as the ferrite powder of Example 1.

[0038] [Example 2] The ferrite powder of Example 2 was prepared in the same manner as in Example 1, except that the particle size of the dried granules in the spray drying process was changed.

[0039] [Example 3] The ferrite powder of Example 3 was prepared in the same manner as in Example 1, except that the particle size of the dried granules in the spray drying process was changed.

[0040] [Example 4] The ferrite powder of Example 4 was prepared in the same manner as in Example 1, except that it was sprayed into hot air at 150°C using a spray dryer, and the particle size of the dried granules was changed during the spray drying process.

[0041] [Example 5] The ferrite powder of Example 5 was prepared in the same manner as in Example 1, except that it was sprayed into hot air at 150°C using a spray dryer, and the particle size of the dried granules was changed during the spray drying process.

[0042] [Comparative Example 1] The ferrite powder of Comparative Example 1 was prepared in the same manner as in Example 2, except that the electric furnace temperature in the secondary firing process was changed to 1200°C.

[0043] [Comparative Example 2] According to the composition shown in Table 1, oxides of Fe, Ni, Zn, and Cu were weighed and wet-mixed to obtain a slurry. The slurry was filtered and dried to obtain a mixed powder of the raw materials. This mixed powder was subjected to primary calcination at 1300°C for 3 hours. The resulting calcined material was pulverized in a vibratory mill to obtain primary calcined Ni-Zn-Cu ferrite powder. Comparative Example 2's ferrite powder was prepared in the same manner as in Example 2, except that the primary calcined powder used as the raw material was changed and the amount of polycarboxylate ammonium dispersant was changed to 1.5% by mass.

[0044] [Comparative Example 3] According to the composition in Table 1, oxides of Fe, Ni, Zn, and Cu were weighed and wet-mixed to obtain a slurry. The slurry was filtered and dried. This was crushed in a hammer mill and used for spray drying without primary calcination. Comparative Example 3 ferrite powder was obtained in the same manner as in Example 2, except that the raw materials used were changed.

[0045] [Comparative Example 4] The ferrite powder obtained in Example 5 was subjected to LP gas (flow rate 10 m³). 3 ( / hr) and oxygen (flow rate 45m³) 3 The material was supplied at a rate of 6 kg / hr into a flame formed from gas. The sample after processing was collected to obtain the magnetic powder of Comparative Example 4.

[0046] [Comparative Example 5] According to the composition shown in Table 1, oxides of Fe, Ni, Zn, and Cu were weighed and wet-mixed to obtain a slurry. The slurry was filtered and dried to obtain a mixed powder of the raw materials. This mixed powder was subjected to primary calcination at 1300°C for 3 hours. The resulting calcined material was ground in a vibratory mill to obtain primary calcined powder. The primary calcined flour is subjected to LP gas (flow rate 10 m³). 3 ( / hr) and oxygen (flow rate 45m³) 3 The powder was supplied at a rate of 6 kg / hr into a flame formed from gas. The powder after flame treatment was used as the ferrite powder for Comparative Example 5.

[0047] <Rating> [Particle size distribution] The particle size distribution was measured by dispersing ferrite powder at a pressure of 4 bar using the dry dispersion unit of the LMS-3000 particle size distribution analyzer (manufactured by Seishin Corporation).

[0048] [Particle circularity coefficient] The circularity coefficient was measured by image analysis using Mac-View Ver.4 (Mountec Co., Ltd.) after acquiring SEM images with a scanning electron microscope S-4800 (Hitachi High-Technologies Corporation).

[0049] The circularity coefficient is (4π × area) / (perimeter) 2 The circularity coefficient was calculated using the following formula. Here, "area" refers to the area inside the outer shape (perimeter) when the particles constituting the ferrite powder are viewed from a predetermined direction, and "perimeter" refers to the perimeter (length of the outer edge) of that outer shape. Specifically, the "area" in the formula for calculating the circularity coefficient was calculated from the area inside the outer perimeter obtained from the coordinates of the pixels that form the outer perimeter of the particle, and the "perimeter" was calculated from the sum of the distances between pixels obtained from the coordinates of the pixels that form the outer perimeter of the particle. The particles used in the analysis were 50 particles randomly selected from SEM images, and the average of the measured values ​​of the circularity coefficient obtained from them is shown as the result.

[0050] [Maximum height Rz] The median diameter D of ferrite powder 1 as measured by laser microscope. 50 0.8D 50 ~1.2D 50 Particles with an acicularity ratio of less than 1.5 were extracted, their 3D shapes were captured, and Rz was determined. Here, the acicularity ratio is a parameter calculated from the ratio of the particle's maximum length to its diagonal width, and the diagonal width represents the shortest distance between two lines parallel to the maximum length when the particle is sandwiched between them. A super-depth color 3D shape measuring microscope ("VK-X3000" manufactured by Keyence Corporation) was used for the laser microscope. Measurements were performed using a 100x objective lens with high-speed RPD scan pitch and the RPD algorithm for the Z axis set to RPDI for surface observation and capturing the 3D shape. Rz was measured using particle roughness inspection software ("WinROOF2023" manufactured by Mitani Corporation). From the obtained 3D shapes, 21 roughness curves were obtained by drawing parallel lines over a 15 μm × 15 μm region of the particle surface. Subsequently, surface correction was performed, a low-pass filter was applied with an intensity of 1.5 μm, and the cutoff value λ was set to 80 μm. However, the median diameter D of ferrite powder 1 50 If the particle size was less than 25 μm, the Rz value was calculated using a 5 μm × 5 μm region on the particle surface.

[0051] Rz was calculated as the sum of the height of the highest peak and the depth of the deepest valley in the roughness curve. For the calculation of Rz, the average value of 30 or more particles was used as the average value of each parameter. The Rz measurements described above were performed in accordance with JIS B0601 (2001 edition).

[0052] [Heywood diameter] The Heywood diameter of the crystal grains was calculated from SEM images of the particle surface using the image analysis software Mac-View (manufactured by Mountec Co., Ltd.), and the average value for 50 crystal grains was obtained.

[0053] [True density] The true density was measured using a dry-type automatic densimeter, Accupic II 1340 (manufactured by Shimadzu Corporation).

[0054] [Pore volume] The evaluation device used was the POREMASTER-60GT manufactured by Quantachrome. The specific measurement conditions were as follows: Cell Stem Volume: 0.5cm 3 Head pressure: 20PSIA Surface tension of mercury: 485.00 erg / cm² 2 Contact angle of mercury: 130.00 degrees High-voltage measurement mode: Fixed Rate Motor Speed: 1 High-voltage measurement range: 20.00~10000.00 PSI Then, weigh 1,500g of the sample and measure 0.5cm. 3 The sample was filled into a cell and measured. Also, the volume B (cm³) at 10,000 PSI 3 Volume A (cm³) at 60 PSI from g / g 3 The value obtained by subtracting ( / g) was defined as the pore volume.

[0055] [Specific surface area (BET)] The specific surface area was measured using the BET method with Macsorb HM Model-1201 (manufactured by Mountec). The pretreatment conditions involved heating at 120°C for 20 minutes while passing nitrogen gas through, followed by degassing. The results are shown in Table 2.

[0056] [viscosity] The ferrite powder was mixed with epoxy resin (WE-2025, manufactured by Pernox Co., Ltd.) to a content of 30 vol%, and then stirred at 2000 rpm for 1 minute using a rotating and revolving mixer "Awatori Rentaro ARE-310" (manufactured by Thinky Co., Ltd.).

[0057] Using an E-type viscometer (TVE-35H, manufactured by Toki Sangyo Co., Ltd., 3°×R9.7 cone rotor (measurement sample 0.2 mL)), at room temperature (25°C), the rotation speed was 100 rpm (shear rate 200 s). -1The viscosity of the paste after stirring was measured. The viscosity of the epoxy resin used alone, measured under the same conditions, was 1820 mPa·s.

[0058] [Magnetic permeability] The ferrite powder was mixed with epoxy resin (Pernox WE-1264 / HV-127) to a content of 60 vol%, and stirred at 2000 rpm for 1 minute in a rotating / revolving mixer "Awatori Rentaro" ARE-310 (Sinky Co., Ltd.). The resulting resin composition was sandwiched between glass plates to a thickness of 1 mm and cured at 120°C for 1 hour. The resulting plates were processed by laser cutting into a toroidal ring with an outer diameter of 20 mmφ and an inner diameter of 9 mmφ, and used as a measurement sample.

[0059] The magnetic permeability μ' and μ'' were measured using an impedance / material analyzer E4991A (manufactured by Agilent Technologies).

[0060] [dielectric constant] Under the same conditions as for measuring magnetic permeability, epoxy resin and ferrite powder were mixed and cured to obtain a 1 mm thick plate. The obtained plate was then laser-processed into a 20 mm diameter disc. The dielectric constants ε' and ε'' of this disc were measured using an impedance / material analyzer E4991A (manufactured by Agilent Technologies). Table 3 shows the measurement results for viscosity, magnetic permeability, and dielectric constant.

[0061] [Observation using a scanning electron microscope (SEM)] The ferrite powders of Example 2 and Comparative Examples 1-5 were observed at 1000x and 5000x magnification using a SEM S-4800 (manufactured by Hitachi High-Technologies Corporation). The results are shown in Figures 1-12.

[0062] <Result> As shown in Table 2, the ferrite powders of Examples 1 to 5 had a true density of 5.1 g / cm³. 3 The above results show that it exhibited high magnetic permeability.

[0063] Furthermore, in Examples 1-5, the specific surface area was 0.05 m². 2 The specific surface area was less than 0.05 m². This means the surface was extremely smooth. In contrast, the specific surface area of ​​the comparative example was 0.05 m². 2 It was above / g.

[0064] Furthermore, when the ferrite powders were kneaded with resins for viscosity measurement, the ferrite powders of Examples 1-5 showed lower viscosity compared to the ferrite powders of Comparative Examples 1-5. This indicates that the powders had high fluidity in the resin. Comparative Examples 2 and 3, in particular, which had large pore volumes, showed especially high viscosity.

[0065] In the measurement of permeability and dielectric constant, Comparative Examples 1-3 had too high a viscosity to be mixed with the resin. Examples 1-5 and Comparative Examples 4 and 5 could be mixed with the resin and molded into plates, but Examples 1-5 showed high permeability and low dielectric constant, while Comparative Examples 4 and 5 showed low permeability and high dielectric constant.

[0066] Observation using SEM revealed that the particles in Example 2 had a high circularity coefficient, as shown in Figure 1, and a smooth surface, as shown in Figure 2.

[0067] Comparative Example 1 was granulated by spray drying and then fired at a high temperature, resulting in the observation of many irregularly shaped particles and numerous irregularities on the particle surface (Figures 3 and 4).

[0068] Comparative Example 2 was subjected to primary firing at a high temperature, resulting in a high circularity coefficient, but numerous small pores (irregularities) were observed on the particle surface (Figures 5 and 6).

[0069] Comparative Example 3 was fired at a relatively low temperature after granulation without primary firing. Although it had a high circularity coefficient, the grain size was small, and numerous pores (irregularities) were observed on the particle surface (Figures 7 and 8).

[0070] Comparative Example 4 is obtained by further exposing the powder from Example 5 to high temperatures using the flame method. Although the circularity coefficient was high, fine irregularities were observed on the surface, and precipitation of metallic elements was also observed (Figures 9 and 10).

[0071] Comparative Example 5 is a powder that was first calcined at high temperature, then pulverized (not spray-dried), and subsequently exposed to high temperature using the flame method. Although Comparative Example 5 had a high circularity coefficient (Figure 11), fine irregularities were observed on the surface, as well as the precipitation of metallic elements (white particles in Figure 12).

[0072] Furthermore, in Comparative Examples 4 and 5, the boundaries between crystal grains (grain boundaries) could not be identified, and therefore the Heywood diameter could not be measured. This is thought to be because, when secondary firing is performed using the flame method, the surface of the particles melts before solidifying.

[0073] As described above, in Examples 1 to 5, by performing primary firing at a relatively low temperature followed by spray drying, and then secondary firing at a relatively low temperature, it was possible to obtain particles with a high circularity coefficient, a small maximum surface height Rz, and a Heywood diameter within a favorable range, resulting in favorable fluidity for molding. Furthermore, the molded articles obtained from the ferrite powder and resin in Examples 1 to 5 showed a low dielectric constant.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3] [Industrial applicability]

[0077] The ferrite powder of the present invention can be used in electronic components such as inductors, magnetic cores, and magnetic heads, as well as magnetic materials such as magnetic shielding materials. [Explanation of Symbols]

[0078] 1. Ferrite powder 2 particles 3 crystal grains 4. Grain boundaries

Claims

1. Median diameter D of 10 μm to 200 μm ５０ A spherical ferrite powder having, On the particle surface of the ferrite powder, the maximum height Rz is 1.5 μm or less, and the Heywood diameter of the crystal grains is in the range of 2.0 μm to 8.0 μm. A plate obtained by kneading 60 vol% of the ferrite powder with a resin and curing it has a dielectric constant of less than 20 as measured at 50 MHz. Ferrite powder.

2. In the ferrite powder, the ferrite is AFe ２ O ４ It is represented by the following empirical formula, where A is at least one element selected from the group consisting of Mg, Mn, Co, Ni, Cu, and Zn. The ferrite powder according to claim 1.

3. True density is 5.10 g / cm³ ３ That's all. The ferrite powder according to claim 1.

4. Pore ​​volume is 0.025 mL / g or less. The ferrite powder according to claim 1.

5. A resin composition containing the ferrite powder described in any one of claims 1 to 4.

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