JP2005197272A - Ferrite core, its production process and electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength ferrite core exhibiting excellent adhesion to other ferrite core. <P>SOLUTION: In the ferrite core 2 having a bonding face 6 to other ferrite core, maximum height Ry of the bonding face 6 measured by a method conforming to JIS-B0601 is 10-46 μm (46 μm is excluded), and the width of a grain boundary clearance 44 appearing between two adjacent ferrite particles is 5-31 μm (31 μm is excluded) for ferrite particles 4 exposed to the bonding face 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ferrite core composed of a ferrite sintered body, a manufacturing method thereof, and an electronic component.

  Ferrite cores composed of soft magnetic ferrite are widely used as core materials for various electronic components. In recent years, electronic components have become smaller, thinner, and lighter, and with this trend, core materials used in electronic components are also becoming increasingly smaller, thinner, and lighter.

  As an example of an electronic component, a surface mount self-inductive inductance element is known. As this surface mount self-inductive inductance element, for example, as shown in FIGS. 3A and 3B, a drum type ferrite core 104 is inserted into a hollow portion 102 of a cylindrical ferrite core 100 to form a closed magnetic circuit. A common mode filter 106, a configuration in which an external electrode is provided on a resin sheath, and a winding wound around a ferrite core is connected to the external electrode, are known.

  In recent years, there has been a demand for further reduction in size, thickness, and weight of this type of surface-mount self-inductive inductance element. In the former configuration, the size of the cylindrical ferrite core 100 is reduced. In the latter configuration, the size of the resin sheath is limited, and it is difficult to reduce the size significantly.

  Therefore, as shown in FIG. 4, a technique has been proposed in which a flat ferrite core 200 instead of a cylindrical ferrite core is bonded to a drum type ferrite core 204 via an adhesive 202 such as a thermosetting type or an ultraviolet curing type. (See Patent Document 1).

  However, even when ordinary ferrite cores are bonded to each other, the bonding strength is weak, and problems such as bonding displacement and peeling occur, resulting in a high defect rate.

  In addition, when the ferrite cores are bonded to each other, it is necessary to have strength that does not cause chipping or breakage.

Patent Document 2 discloses a technique for bonding a piezoelectric ceramic plate and another substrate via an adhesive layer, which is a member used for a piezoelectric element such as an actuator, a diaphragm, or a buzzer. In this technology, the tensile stress generated by the polarization treatment is uniformly generated over the entire surface, and the surface roughness of the surface opposite to the bonded surface is arithmetically averaged in order to reduce the occurrence of warpage with waviness. This is a technique for controlling the roughness (Ra) to 1 μm or less, and does not relate to the magnitude of the adhesive strength.
JP 2000-133522 A JP 2003-46158 A

  An object of the present invention is to provide a high-strength ferrite core excellent in adhesiveness to other members (for example, a ferrite core), a manufacturing method thereof, and an electronic component having the ferrite core.

  The present inventor properly controls the surface state of the ferrite core composed of an aggregate of ferrite particles and the surface state of the joint surface with the other member, thereby reducing the strength of the ferrite core itself. The present inventors have found that the adhesiveness can be improved and completed the present invention.

According to a first aspect of the invention,
A ferrite core having a joint surface with another member and composed of an aggregate of ferrite particles,
A ferrite core having a maximum height Ry measured by a method according to JIS-B0601 of the joint surface of 10 to 46 μm (excluding 46 μm) is provided.

According to the second aspect,
A ferrite core having a joint surface with another member and composed of an aggregate of ferrite particles,
The maximum height Ry measured by a method based on JIS-B0601 of the joint surface is 10 to 46 μm (excluding 46 μm),
With respect to the ferrite particles exposed on the joint surface, a ferrite core is provided in which the width of a grain boundary gap formed between two adjacent ferrite particles is 5 to 31 μm (excluding 31 μm).

  Preferably, the depth of the grain boundary gap is 10 to 46 μm (excluding 46 μm).

  Preferably, a ferrite core obtained by firing a compact obtained by applying pressure to ferrite granules, wherein the ferrite granules are granulated by a spray drying method and have an average particle size of 40 to 150 μm It is.

  Preferably, a ferrite core obtained by firing a compact obtained by applying pressure to ferrite granules, wherein the ferrite granules are granulated by an oscillating extrusion method and have an average particle size of 80 to 500 μm. Is.

  Preferably, the content of coarse granules having an average particle diameter of 200 μm or more of the ferrite granules (including both spray-drying granulation method and oscillating extrusion granulation method) is 5% by mass or less, and 20 μm or less. The content of fine granules having an average particle size is 5% by mass or less.

  Preferably, the average grain size of the ferrite particles constituting the ferrite core is 15 μm or less.

  According to the present invention, any one of the above ferrite cores is produced by using a slurry containing polyvinyl alcohol having an average saponification degree of 88 to 98 mol% and an average degree of polymerization of 500 to 2500. A method for producing a ferrite core using ferrite granules is provided.

  Preferably, the said polyvinyl alcohol is contained in the said slurry in the ratio of 0.6-2.0 mass parts with respect to 100 mass parts of ferrite powders.

  Preferably, a compact formed by applying a pressure of 50 to 400 MPa to the ferrite granules is fired.

  According to the present invention, an electronic component having any one of the above ferrite cores is provided.

  In the present invention, the ferrite core is a core material composed of a ferrite sintered body, and is used in a concept including a part of the core.

  In the present invention, examples of the “other members” include ferrite cores, ceramics, resin compositions (molded products), plastics, and the like, but the technology of the present invention is particularly suitable for bonding with ferrite cores. To do.

  In the present specification, “to” means that numerical values described before and after that are included as a lower limit value and an upper limit value unless otherwise specified.

  As used herein, “low-pressure crushability” means the ease of crushing of granules at a low pressure (typically 29 to 147 MPa) when a ferrite granule is molded. And “low pressure crushability is good” means that the ferrite granule is crushed uniformly. “Disintegration resistance” means resistance to the collapse of ferrite granules caused by rolling and mutual collision during storage, transportation or filling into a mold. “Sticking resistance” means the adhesion resistance of fine particles in ferrite granules to the surface of a mold or the like.

  The present inventor, among the ferrite particles constituting the ferrite core, the “depth” and the “width” of the intergranular gap generated between two adjacent ferrite particles with respect to the ferrite particles exposed on the joint surface with other members. The experiment was conducted on the premise that the strength of the ferrite core itself and the adhesiveness to other members may change depending on the size of "." As a result, by controlling the maximum height Ry which is the “maximum value of the depth” to a specific range, the adhesiveness with other members can be improved without reducing the strength of the ferrite core itself. I got the knowledge. When the maximum value of the intergranular gap depth is in a specific range, the ferrite core itself will not cause a drop in strength such as chipping or breaking, and the adhesive will enter the gap efficiently, Adhesive strength with other members is improved.

  By controlling the “width” of the grain boundary gap within a specific range in addition to the “maximum depth” of the grain boundary gap, the efficiency of adhesive flow into the grain boundary gap is further improved, and as a result, the adhesive strength is increased. While improving dramatically, the intensity | strength of the ferrite core itself does not fall.

  By using a specific ferrite granule having a uniform particle diameter and having an average particle diameter in a predetermined range, and by firing a molded body obtained by applying pressure thereto, the ferrite particles constituting the resulting ferrite core The average crystal grain size is finely controlled to 1 to 15 μm. The present inventors considered that such refinement of the average grain size of ferrite particles contributed to the improvement of adhesion. The depth and width of the grain boundary gap at the joint surface of the obtained ferrite core are controlled within a predetermined range, and the strength of the ferrite core is maintained at a relatively high value.

  Note that the ferrite particles constituting the ferrite core are constituted by gathering primary particles of ferrite crystals after calcining and pulverization. Even in one ferrite particle, a gap may be formed between individual ferrite crystals. The “granular boundary gap” as used in the present invention is not limited to those between the ferrite particles exposed on the joint surface of the ferrite core, and may be generated between the ferrite crystals existing in the individual ferrite particles. Including.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, FIG. 1 is a cross-sectional view showing the vicinity of the joint surface of a ferrite core according to an embodiment of the present invention, FIG. 2 is a plan view when FIG. 1 is viewed from the II direction, and FIGS. ) Is a divided view and a completed perspective view of a common mode filter which is an example of a surface mount self-inductive inductance element as an example of an electronic component, and FIG. 4 is an example of a surface mount self-inductive inductance element as an example of an electronic component. FIG. 5 is an SEM photograph of the vicinity of the joint of the sample 4 corresponding to the embodiment of the present invention, FIG. 6 is an SEM photograph of the vicinity of the joint of the sample 7 corresponding to the comparative example of the present invention, It is.

  As shown in FIG. 1, the ferrite core 2 according to an embodiment of the present invention is composed of an aggregate of a plurality of ferrite particles 4. Each ferrite particle 4 is composed of an aggregate of a plurality of ferrite crystals. The specific shape of the ferrite core 2 is not particularly limited, and may be various shapes depending on applications and purposes.

  The ferrite core 2 has a joint surface 6 with other members. In this embodiment, a ferrite core is illustrated as another member. A plurality of ferrite particles 4 are exposed on the joint surface 6. The joint surface 6 includes a flat portion 42 in which individual ferrite particles 4 are crushed by pressure, and a grain boundary gap 44 generated between two adjacent ferrite particles 4 and 4. The flat part 42 is a part joined to another ferrite core.

In the present embodiment, the maximum height Ry of the joint surface 6 measured by a method in accordance with JIS-B0601 (reference length l: 2.5 mm, evaluation length l _n : 12.5 mm) is in a specific range. Is controlled. The maximum height Ry means the maximum value of the depth D of the grain boundary gap 44 generated between the two adjacent ferrite particles 4, 4 with respect to the ferrite particles 4 exposed on the joint surface 6 of the ferrite core 2. The depth D here means a vertical distance from a flat portion 42 of one ferrite particle 4 to a portion where the ferrite particle 4 contacts the adjacent ferrite particle 4 as shown in FIG. In the present invention, the maximum height Ry of the joining surface 6 is 10 to 46 μm (however, excluding 46 μm), preferably 12 to 35 μm. The depth D of the grain boundary gap 44 is preferably 10 to 46 μm (excluding 46 μm), and more preferably 12 to 35 μm.

  In the present embodiment, the width W of the grain boundary gap 44 is preferably controlled to 5 to 31 μm (however, excluding 31 μm), more preferably 5 to 25 μm, and even more preferably 8 to 20 μm. In the joint surface 6, the joint strength can be further improved by controlling the width W of the grain boundary gap 44 in addition to Ry (maximum value of the grain boundary gap depth) to a specific range. The width W here is such that the curvature of the adjacent ferrite particle 4 starts from the finite value from the portion where the curvature starts to change toward the finite value from the flat portion 42 (the curvature is infinite (∽)) of one ferrite particle 4. It means the distance to the part that becomes infinity (∽).

  In the present embodiment, the average grain size of the ferrite particles 4 is reduced to 15 μm or less, more preferably 5 μm or less. The lower limit is preferably 1 μm. Since the average crystal grain size is refined, the adhesion is improved. The reason is not necessarily clear, but it is considered that the wettability of the ferrite core surface is changed. The average crystal grain size of the ferrite particles is adjusted by arbitrarily changing the firing temperature when firing a ferrite compact to be described later.

  In addition, as shown in FIG. 2, the ferrite particle 4 exposed on the joint surface 6 has a plurality of tears 46 formed therein. The crevice 46 is generated when the ferrite granule is crushed by applying pressure to the ferrite granule during the production of the molded product after granulation. This tear 46 can also be a factor that improves the adhesion of the ferrite core 2.

  Next, an example of a method for manufacturing a ferrite core will be described.

  First, various ferrite raw material powders (starting raw materials) appropriately selected according to the intended use of the finally obtained ferrite core are weighed and mixed so as to have a predetermined composition ratio to obtain a raw material mixture. Examples of the mixing method include wet mixing using a ball mill and dry mixing using a dry mixer. It is preferable to use a ferrite raw material powder having an average particle size of 0.1 to 3 μm.

For example, in order to produce Ni—Zn-based ferrite or Ni—Zn—Cu-based ferrite, the raw material mixture includes, for example, Fe ₂ O ₃ , NiO, CuO, MnO, MgO, and ZnO as main component raw materials. And contains auxiliary component raw materials. This raw material may contain metal oxides such as Co, W, Bi, Si, B, and Zr as inevitable impurities.

  Next, the raw material mixture is calcined to obtain a calcined material. Calcining causes thermal decomposition of raw materials, homogenization of ingredients, formation of ferrite, disappearance of ultrafine powder due to sintering and grain growth to an appropriate particle size, and converts the raw material mixture into a form suitable for the subsequent process. Done for. Such calcination is preferably performed at a temperature of 800 to 1100 ° C. for about 1 to 3 hours. The calcination may be performed in the atmosphere (air) or may be performed in an atmosphere having a higher oxygen partial pressure than in the atmosphere. In addition, when a subcomponent is included in ferrite, the main component raw material and the subcomponent raw material may be mixed before calcination or after calcination.

  Next, the calcined material is pulverized so as to have a predetermined average particle size and particle size distribution to obtain a pulverized material. The pulverization is performed in order to produce a powder having appropriate sinterability by destroying the aggregation of the calcined material. The calcination material can be pulverized by a conventionally known means such as a ball mill, an attritor, or a wet media agitation pulverizer. The pulverization method may be either a wet pulverization method or a dry pulverization method. When the calcined material forms a large lump, it is preferable to perform wet pulverization using a ball mill or an attritor after coarse pulverization. The wet pulverization is performed until the average particle size of the calcined material is preferably about 0.5 to 2 μm.

  Next, the pulverized material (ferrite powder) is granulated (granule) to obtain a granulated product (ferrite granule). The granulation is performed in order to convert the pulverized material into aggregated particles having an appropriate size and convert it into a form suitable for molding. Examples of the granulation method include a spray drying granulation method and an oscillating extrusion granulation method. Specifically, by preparing a slurry in which pulverized material, binder, and various additives as required are dispersed in water, and spray-drying the prepared slurry with a spray dryer (spray dryer) or the like, or The granulated powder is prepared by mixing and granulating the pulverized material, binder, and various additives as desired with a stirring granulator, and this granulated powder is repeatedly extruded and granulated and dried by an oscillating granulator. By applying, ferrite granules are produced. These granulation methods can be appropriately selected depending on the granulation amount of the ferrite granules, the properties of the target ferrite compact, and the like. The oscillating extrusion granulation method is, for example, a process in which particles granulated to a particle size of about several millimeters are crushed on a net and dropped into fine particles, and the steps are made by successively finely knitting the stitches. This is a method for obtaining particles having a predetermined particle size or less.

  The average particle diameter of the granulated ferrite granule can be appropriately selected depending on the granulation method, the shape of the target molded product, and the like. Usually, if the average particle size is too small, the flowability of the ferrite granules and the filling property into the mold are deteriorated, and the size of the obtained molded product and the mass of the molded product may vary greatly. In addition, fine powder adhesion (sticking) tends to occur on the mold. On the other hand, if the average particle size is too large, a large number of grain boundaries are left in the molded product, and molding failure may occur, or the size and single mass variation of the molded product may increase. Therefore, the ferrite core obtained by firing this molded body has fewer defects due to the grain boundary, and the sintered body strength is relatively high.

  In the present invention, particularly when the granulation is performed by a spray drying method in order to meet the demands for further miniaturization, thinning, and weight reduction of electronic components, the average particle diameter of the ferrite granules is preferably 250 μm. Hereinafter, the granulation conditions and the like are adjusted so as to be more preferably 200 μm or less, and further preferably 150 μm or less. The lower limit of the average particle size is preferably about 40 μm, more preferably about 60 μm, and still more preferably about 80 μm.

  In the present invention, when granulated by the oscillating extrusion method, the average particle size of the ferrite granule is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. Adjust. The lower limit of the average particle size is preferably about 80 μm, more preferably about 100 μm, and still more preferably about 125 μm.

  In the present invention, when granulated by the spray drying method or the oscillating extrusion method, the content of coarse granules having an average particle diameter of 200 μm or more is 5% by mass or less and the average is 20 μm or less. The content of fine granules having a particle size is preferably 5% by mass or less. By doing so, it is possible to obtain a ferrite granule having a uniform average particle size, and there is an advantage that the filling property of the granule into the mold is stable and high dimensional accuracy is obtained.

  In this embodiment, the depth D and / or the width W of the intergranular gap 44 of the ferrite particle 4 after firing is predetermined by using ferrite granules having an average particle diameter in a predetermined range in which such particle diameters are uniform. It is possible to control within the range, and it is easy to maintain the strength at a relatively high value.

  The shape of the ferrite granule is preferably a spherical shape in consideration of fluidity and the like.

  The binder used for the granulation of the ferrite granule can be appropriately selected from binders conventionally used for granulating the ferrite granule according to the purpose of use. Typically, for example, polyvinyl alcohol (PVA), polyvinyl acetal, polyacrylic resin, cellulose resin, acrylamide resin, and the like can be given. These binders can be used alone or as a mixture of two or more.

  In the present invention, it is particularly preferable to use a specific PVA as the binder. By using a specific PVA as a binder, the density and bending strength of the sintered body can be improved by reducing defects due to the grain boundary and maintaining a high molded body density and strength. Moreover, the expansion phenomenon after mold release called a spring back can be suppressed, generation | occurrence | production of the crack of a molded object can be suppressed, and the burden to a metal mold | die can also be reduced.

  PVA as a binder functions as a binder for primary particles, that is, a binder between ferrite powders, and affects the low-pressure crushability, collapse resistance, and compact strength of ferrite granules. In particular, the average saponification degree of PVA affects the moldability of the molded body.

  The average saponification degree of PVA suitably used in the present invention is preferably 88 mol% or more as a whole PVA. PVA having a saponification degree in such a range is referred to as intermediate saponified PVA.

  In the so-called partially saponified PVA having an overall average saponification degree of less than 88 mol%, the collapse resistance and sticking resistance are deteriorated although the low-pressure crushability of the ferrite granule is good. PVA having an average saponification degree of less than 88 mol% is suitable for spray granulation because of its good solubility in water and easy slurry preparation. However, when granulating by the oscillating extrusion method, Since the material adheres to it, continuous granulation becomes difficult.

  In contrast, so-called completely saponified PVA, in which the average degree of saponification of PVA is too high, has good collapse resistance, but the granulated ferrite granules are relatively hard, so that the low-pressure crushing property may be poor. Furthermore, the solubility in water becomes worse, and slurry adjustment may be difficult.

  For this reason, the average saponification degree of PVA becomes like this. More preferably, it is 88-98 mol%, More preferably, it is 93-97 mol%. PVA having a single average saponification degree (88 mol% or more) is preferably used as the water-soluble resin. However, PVA having different saponification degrees is blended so that the average saponification degree is 88 mol% or more as a whole. It is also possible to use it.

  Moreover, the average degree of polymerization of PVA becomes like this. Preferably it is 500-2500, More preferably, it is 500-1700, More preferably, it is 800-1500. If the average degree of polymerization is less than 500, the granulated ferrite granule has good low-pressure crushing property, but the collapse resistance is poor, and the bending strength of the molded product obtained from this ferrite granule tends to be low. On the other hand, when the average degree of polymerization exceeds 2500, although the granulated ferrite granules have relatively good collapse resistance and the resulting molded article has a good bending strength, the ferrite granules become too hard and the low-pressure crushing property deteriorates. In addition, defects due to the grain boundary tend to occur easily.

  PVA is not particularly limited as long as it has the above-mentioned predetermined average saponification degree and polymerization degree, and even if it is unmodified, for example, alkyl vinyl ether, hydroxy vinyl ether, allyl acetate, amide, vinyl silane, It may be modified with ethylene or the like.

  The content of PVA as a binder is preferably 0.6 to 2.0 parts by mass, more preferably 0.8 to 1.5 parts by mass with respect to 100 parts by mass of the pulverized material (ferrite powder). If the PVA content is too small, the pulverized material (ferrite powder) may not be granulated. At 0.4 to 0.6 parts by mass, granulation is possible, but the ferrite granules are soft, the strength of the molded product is low, there is a problem in handling properties, chipping and breaking etc. occur before firing. It tends to be easy. On the other hand, if the content is too large, the ferrite granules become too hard and the crushing becomes worse, so that many granule boundaries are left and molding defects may occur. Similarly, capacity deficiencies tend to increase.

  In granulating the ferrite granule, in addition to the pulverized material (ferrite powder) and the binder, conventionally known various additives can be contained as long as the purpose and effect of the present invention are not impaired. Examples of such additives include dispersants such as polycarboxylates, condensed naphthalene sulfonic acids, plasticizers such as glycerin, glycols and triols, waxes, lubricants such as stearic acid (salts), polyethers, Examples thereof include organic polymer flocculants such as urethane-modified polyether-based, polyacrylic acid-based, and modified acrylic acid-based polymers, and inorganic flocculants such as aluminum sulfate, aluminum chloride, and aluminum nitrate.

  The ferrite granule may be a mixture of different granules.

  Next, the granulated product (ferrite granule) is molded into a predetermined shape by various compression molding methods such as a single-press method, a double-press method, a floating die method, a withdrawal method, and the like to obtain a compact. Examples of the molding of the granulated product include dry molding, wet molding, and extrusion molding. The dry molding method is a molding method in which a granulated product is filled in a mold and compressed and pressed (pressed). The press machine is appropriately selected depending on the size, shape, and quantity such as a mechanical press, a hydraulic press, and a servo press.

  The molding pressure for forming the molded body is preferably 50 to 400 MPa, more preferably 100 to 300 MPa. If the molding pressure is too small, the width W or the depth D of the intergranular gap 44 of the ferrite particles 4 after firing becomes larger than the range of the present invention, and the strength thereof tends to be low, and chipping and breakage tend to occur. is there. On the other hand, if the molding pressure is too large, the width W or the depth D of the intergranular gap 44 of the sintered ferrite particle 4 becomes smaller than the range of the present invention, and the adhesive strength tends to be lowered. Further, the obtained molded body also has a large spring back (molded body expansion) after being discharged from the mold, and tends to cause lamination cracks.

  The shape of the molded body is not particularly limited, and may be appropriately determined according to the application.

  Next, the compact is fired to obtain a sintered body (the ferrite core 2 of the present embodiment, or a part of the ferrite core 2 (which is combined to become the ferrite core 2). This is performed to obtain a dense sintered body by causing sintering in which the powder adheres at a temperature below the melting point between the powder particles of the molded body containing voids. Examples thereof include a batch type, a pusher type, a cart type, etc. The firing temperature is preferably 1000 to 1300 ° C., more preferably 1000 to 1200 ° C. The firing time is preferably about 1 to 5 hours. The average crystal of the ferrite particles 4 constituting the ferrite core 2 to be obtained can be adjusted by adjusting the firing temperature. Particle size It can be changed. Contribute to adhesion improvement thereby.

  The sintered body (ferrite core) thus obtained can be used for electronic devices based on information terminals such as laptop computers, PDAs, mobile phones, mobile phones such as PHS, and peripheral devices such as these, It is also used as a core material for various electronic components for relatively large household appliances such as televisions and stereos.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, in the range which does not deviate from the summary of this invention, it can implement in various aspects. .

  Next, the present invention will be described in more detail with reference to examples that further embody the embodiment of the present invention. However, the present invention is not limited to only these examples.

Example 1
Preparation of core sample First, Fe ₂ O ₃ , NiO, CuO and ZnO ferrite raw material powders (starting materials) were prepared using Fe ₂ O ₃ : 49 mol%, NiO: 17 mol%, CuO: 6 mol%, and ZnO. : Weighed so as to have a ratio of 28 mol%, and then wet mixed for 4 hours using a wet media stirring type pulverizer to obtain a raw material mixture. In this wet mixing, pure water was used as a dispersion medium.

Next, after drying the obtained raw material mixture with a spray dryer, it was calcined in air at 900 ° C. for 2 hours to obtain a calcined material of Ni—Cu—Zn ferrite, and this calcined material was wet The mixture was pulverized with a media stirring type pulverizer for 8 hours to obtain a pulverized material (ferrite powder) having a BET value of 2.5 m ² / g.

  Next, after drying this pulverized material, 1.0 part by mass of PVA having an average saponification degree of 93 mol% and an average polymerization degree of 1200 as a binder is added to 100 parts by mass of the pulverized material, and sprayed with a spray dryer. By granulating and drying, Ni—Cu—Zn ferrite granules (granulated material) were obtained. The average particle size of the ferrite granules was calculated by the same code method as the method shown below. As a result, the average particle size was 100 μm. Further, when the content of coarse granules having an average particle size of 200 μm or more and the content of fine granules having an average particle size of 20 μm or less were measured, both were 5% by mass or less.

  Next, the obtained ferrite granules are filled into a mold, and the molding pressure is changed as shown in Table 1 to perform press molding, thereby having a compact density shown in Table 1, length 14 mm × width 14 mm. X A rectangular parallelepiped block-shaped molded body having a height of 2 mm was produced. The molded body density was measured by cutting the molded body and using a mercury porosimeter.

  Next, the obtained compact is fired in air at 1060 ° C. for 2 hours, and a ferrite core sample having a joint surface with another ferrite core, which is composed of a Ni—Cu—Zn ferrite sintered body (Sample 1) was obtained.

Evaluation of Sample 1 The sintered density of Sample 1 obtained, the maximum height Ry of the joint surface of Sample 1 and the width W of the grain boundary gap, the shear strength of the joint surface, and the bending strength of Sample 1 were as follows. ,It was measured. Moreover, the average crystal grain size of the ferrite particles constituting Sample 1 was measured.

The sintered density was determined by measuring the size and mass of Sample 1 and calculating the mass W / volume V (unit: g / cm ³ ). The sintering density was set to be 4.94 g / cm ³ or more.

  The maximum height Ry and the width W of the grain boundary gap were measured by a method in accordance with JIS-B0601 using the “ultra-deep shape measurement microscope” manufactured by KEYENCE Corp. and the sample 1 bonding surface (surface).

The shear strength of the joint surface was measured as follows. First, in the same manner as the above-mentioned “Preparation of core sample”, the sintered density is 5.01 g / cm ³ , the maximum height Ry is 18 μm, the width W of the grain boundary gap is 15 μm, and the length is 1 mm × width. A core sample (sample 2) for evaluation of adhesive strength in a rectangular parallelepiped block shape of 2 mm × 5 mm in height was prepared. Next, the tip of the sample 2 (the portion having an area of 10 mm ² between the width portion and the height portion) is approximately with respect to the bonding surface of the sample 1 with a one-component heat curing type epoxy resin as an adhesive interposed therebetween. The two were adhered by contacting them so as to be 90 degrees, and then performing heat treatment at 120 ° C. for 90 minutes (adhesion surface 1 mm × 2 mm). Next, a force was applied to sample 2 and the force when peeled off from the joint surface of sample 1 was determined as the shear strength. A shear strength of 46 kg / cm ² or more was considered good.

The bending strength was measured with respect to Sample 1 by using a load tester (manufactured by Aiko Engineering Co., Ltd.) according to a method based on JIS-R1601. The bending strength was good at 4.9 kg / mm ² or more.

  The average crystal grain size of the ferrite particles in Sample 1 was calculated as follows. The size of each ferrite crystal of an SEM image having a visual field of 43 μm × 64 μm (magnification 2000 times) was measured and obtained by arithmetic average.

表１に示すように、最大高さＲｙが本発明内の試料２〜６では、剪断強度及び抗折強度ともに良好な値が得られている。これに対し、Ｒｙが本発明の上限値超の試料１では、剪断強度及び抗折強度のいずれも不十分であることが確認された。また、Ｒｙが本発明の下限値未満の試料７では、抗折強度は十分であるが、剪断強度が不十分であることが確認できた。 The results are shown in Table 1.

As shown in Table 1, in the samples 2 to 6 in which the maximum height Ry is within the present invention, good values are obtained for both the shear strength and the bending strength. On the other hand, it was confirmed that in the sample 1 with Ry exceeding the upper limit of the present invention, both the shear strength and the bending strength are insufficient. Moreover, it was confirmed that Sample 7 having Ry less than the lower limit of the present invention has sufficient bending strength but insufficient shear strength.

  In addition, the SEM photograph of the sample 4 and the sample 7 is shown in FIG. 5 and FIG. 6 (both figures are viewed from the same direction as FIG. 2).

表２に示すように、最大高さＲｙが本発明内の試料９〜１３では、剪断強度及び抗折強度ともに良好な値が得られている。これに対し、Ｒｙが本発明の上限値を超える試料１４では、剪断強度は十分であるが、抗折強度が不十分であることが確認された。また、Ｒｙが本発明の下限値未満の試料８では、抗折強度は十分であるが、剪断強度が不十分であることが確認できた。 Example 2
Sample 1 was prepared in the same manner as Sample 4 in Example 1 except that the amount of PVA added as a binder was changed as shown in Table 2, and the same evaluation as in Example 1 was performed. The results are shown in Table 2.

As shown in Table 2, in the samples 9 to 13 having the maximum height Ry in the present invention, good values are obtained for both the shear strength and the bending strength. On the other hand, it was confirmed that in the sample 14 in which Ry exceeds the upper limit of the present invention, the shear strength is sufficient, but the bending strength is insufficient. Further, it was confirmed that Sample 8 having Ry less than the lower limit of the present invention has sufficient bending strength but insufficient shear strength.

表３に示すように、最大高さＲｙが本発明内の試料１６〜１９では、剪断強度及び抗折強度ともに良好な値が得られている。これに対し、Ｒｙが本発明の下限値未満の試料１５では、抗折強度は十分であるが、剪断強度が不十分であることが確認できた。 Example 3
Sample 1 was prepared in the same manner as Sample 4 in Example 1 except that the saponification degree of PVA as a binder was changed as shown in Table 3, and the same evaluation as in Example 1 was performed. The results are shown in Table 3.

As shown in Table 3, in the samples 16 to 19 having the maximum height Ry in the present invention, good values are obtained for both the shear strength and the bending strength. On the other hand, it was confirmed that Sample 15 having Ry less than the lower limit of the present invention has sufficient bending strength but insufficient shear strength.

表４に示すように、最大高さＲｙが本発明内の試料２１〜２５では、剪断強度及び抗折強度ともに良好な値が得られている。これに対し、Ｒｙが本発明の下限値未満の試料２０では、抗折強度は十分であるが、剪断強度が不十分であることが確認できた。 Example 4
Sample 1 was prepared in the same manner as Sample 4 in Example 1 except that the degree of polymerization of PVA as a binder was changed as shown in Table 4, and the same evaluation as in Example 1 was performed. The results are shown in Table 4.

As shown in Table 4, the samples 21 to 25 having the maximum height Ry within the present invention have good values for both the shear strength and the bending strength. On the other hand, it was confirmed that the sample 20 having Ry less than the lower limit of the present invention has sufficient bending strength but insufficient shear strength.

表５に示すように、成形体密度が同一である場合に、焼成温度が高くなるにつれて、剪断強度が低下していく傾向があることが確認された。また、抗折強度については、成形体密度が同一である場合に、焼成温度が比較的低い領域では、高くなるにつれて抗折強度が上昇するが（試料４２〜４４）、それ以上では、逆に抗折強度が低下していく傾向にあることが確認できた。 Example 5
Sample 1 was prepared in the same manner as Sample 4 of Example 1 except that the firing temperature of the molded body was changed as shown in Table 5, and the same evaluation as in Example 1 was performed. The results are shown in Table 5.

As shown in Table 5, it was confirmed that when the compact density was the same, the shear strength tended to decrease as the firing temperature increased. As for the bending strength, when the density of the molded body is the same, the bending strength increases as the firing temperature increases in the region where the firing temperature is relatively low (samples 42 to 44). It was confirmed that the bending strength tends to decrease.

FIG. 1 is a cross-sectional view showing the vicinity of a joint surface of a ferrite core according to an embodiment of the present invention. FIG. 2 is a plan view of FIG. 1 viewed from the II direction. 3A and 3B are a divided view and a completed perspective view of a common mode filter which is an example of a surface mount self-inductive inductance element as an example of an electronic component. FIG. 4 is a completed front view of a common mode filter which is an example of a surface mount self-inductive inductance element as an example of an electronic component. FIG. 5 is an SEM photograph of the vicinity of the joint of Sample 4 corresponding to the example of the present invention. FIG. 6 is an SEM photograph of the vicinity of the joint of Sample 7 corresponding to the comparative example of the present invention.

Explanation of symbols

2 ... Ferrite core 4 ... Ferrite particle 42 ... Flat part 44 ... Intergranular gap 46 ... Rip 6 ... Joint surface

Claims (11)

A ferrite core having a joint surface with another member and composed of an aggregate of ferrite particles,
The ferrite core whose maximum height Ry measured by the method based on JIS-B0601 of the said joint surface is 10-46 micrometers (however, except 46 micrometers). A ferrite core having a joint surface with another member and composed of an aggregate of ferrite particles,
The maximum height Ry measured by a method based on JIS-B0601 of the joint surface is 10 to 46 μm (excluding 46 μm),
A ferrite core in which the width of a grain boundary gap formed between two adjacent ferrite particles is 5 to 31 μm (excluding 31 μm) with respect to the ferrite particles exposed on the joint surface. The ferrite core according to claim 2, wherein the grain boundary gap has a depth of 10 to 46 μm (excluding 46 μm). A ferrite core obtained by firing a molded body obtained by applying pressure to a ferrite granule,
The ferrite core according to any one of claims 1 to 3, wherein the ferrite granule is granulated by a spray drying method and has an average particle diameter of 40 to 150 µm. A ferrite core obtained by firing a molded body obtained by applying pressure to a ferrite granule,
The ferrite core according to any one of claims 1 to 3, wherein the ferrite granule is granulated by an oscillating extrusion method and has an average particle diameter of 80 to 500 µm. The content of coarse granules having an average particle size of 200 μm or more in the ferrite granules is 5% by mass or less, and the content of fine granules having an average particle size of 20 μm or less is 5% by mass or less. Or the ferrite core of 5. The ferrite core according to any one of claims 1 to 6, wherein an average crystal grain size of the ferrite particles constituting the ferrite core is 15 µm or less. A method for producing a ferrite core according to claim 1,
The manufacturing method of a ferrite core using the ferrite granule manufactured using the slurry containing the polyvinyl alcohol which has the average saponification degree of 88-98 mol% and the average polymerization degree of 500-2500. The manufacturing method of the ferrite core of Claim 8 which makes the said polyvinyl alcohol contain in the said slurry in the ratio of 0.6-2.0 mass parts with respect to 100 mass parts of ferrite powders. The manufacturing method of the ferrite core of Claim 8 or 9 which bakes the molded object shape | molded by applying the pressure of 50-400 Mpa to the said ferrite granule. The electronic component which has a ferrite core in any one of Claims 1-7.

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