Powder magnetic core and manufacturing method thereof

Abstract

To provide a powder magnetic core that uses a magnetic alloy powder and has excellent radial crushing strength and moldability, and a method for manufacturing the same.SOLUTION: A powder magnetic core according to the present invention is made of granulated powder obtained by adding 2.0 mass% or more and 4 mass% or less of a binder whose main component is acrylic resin to a magnetic alloy powder. The pH (hydrogen ion exponent) of the binder is preferably 6 or more and 8 or less. The glass transition point of the binder is preferably -5°C or more and less than 25°C. The magnetic alloy powder is preferably any one of sendust powder, amorphous alloy powder, and nanocrystalline alloy powder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a powder magnetic core for miniaturizing and improving the efficiency of magnetic devices, and to a method for manufacturing the same. [Background technology]

[0002] When a magnetic device is constructed using a powder magnetic core, it can be made smaller and more efficient by using magnetic powder with a high magnetic flux density. Known magnetic alloy powders capable of achieving high magnetic flux density include sendust powder, metallic amorphous alloy powder, and nanocrystalline material powder. However, these magnetic alloy powders all have high hardness, making it difficult to achieve high density when used to make powder magnetic cores. Furthermore, when these magnetic alloy powders are compacted, the powder particles do not intertwine well, making it difficult to ensure the strength of the compact and to give it a complex shape.

[0003] The dust core using the magnetic alloy powder described above has low hysteresis loss, and the use of fine particles also reduces eddy current loss. However, reducing the particle size of magnetic alloy powders reduces flowability, and the powder may get into the clearance of the mold during compaction, causing problems such as galling. Furthermore, because these magnetic alloy powders are hard and do not easily intertwine with each other during compression compaction, attempts have been made to granulate them by adding a resin binder such as PVA, as described in the following patent documents, in order to avoid the problem of reduced strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-180154 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-120678 [Patent Document 3] Patent No. 7049752 [Patent Document 4] Patent No. 7096220 Summary of the Invention [Problem to be solved by the invention]

[0005] When a magnetic alloy powder is used for a powder magnetic core, it is difficult for the magnetic alloy powder particles to intertwine with each other due to its hardness and resistance to plastic deformation. This means that the compact is brittle and prone to chipping and cracking, making compaction more difficult as the shape becomes more complex. Although fine-grained magnetic alloy powder can be used to reduce eddy current loss, powder with a particle size that is too small can get into the die clearance and cause galling. Also, when press-molding, if the powder has poor fluidity and poor filling ability into the die, the density of the compact will vary from part to part, which can also cause cracks.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a powder magnetic core that can achieve a high magnetic flux density, has excellent flowability even when using a magnetic powder with high hardness, and can also achieve high strength when formed into a compact, and a method for manufacturing the same. [Means for solving the problem]

[0007] (1) In order to solve the above-mentioned problems, the dust core of the present invention is characterized by comprising a granulated powder in which 2.0 mass % to 4 mass % of a binder mainly composed of an acrylic resin is added to a magnetic alloy powder. (2) In the dust core according to the present invention described in (1), the pH (hydrogen ion exponent) of the binder is preferably 6 or more and 8 or less.

[0008] (3) In the dust core according to the present invention described in (1) or (2), the glass transition point of the binder is preferably not less than -5°C and less than 25°C. (4) In the dust core according to any one of (1) to (3) of the present invention, the magnetic alloy powder is preferably any one of sendust powder, amorphous alloy powder, and nanocrystalline alloy powder.

[0009] (5) The method for producing a powder magnetic core according to the present invention is characterized in that a granulated powder to which a binder having a glass transition temperature of −5° C. or more and less than 25° C. and containing an acrylic resin as a main component is added in an amount of 2.0 mass % to 4 mass % is compacted at a mold temperature of 80° C. or less during mold press molding. (6) In the method for producing a powder magnetic core according to the present invention described in (5), a binder is preferably added to the magnetic alloy powder having an insulating coating in a wet state, and the resulting granulated powder is vacuum dried. A lubricant powder is then added to the granulated powder in a dry state, mixed, and sintered to form a powder magnetic core.

[0010] (7) In the method for producing a powder magnetic core according to the present invention as set forth in (5) or (6), it is preferable to use a binder having a pH of 6 or more and 8 or less. (8) In the method for producing a dust core according to any one of (5) to (7) of the present invention, it is preferable that the magnetic alloy powder is any one of sendust powder, amorphous alloy powder, and nanocrystalline alloy powder. [Effects of the Invention]

[0011] According to the dust core of the present invention, it is possible to provide a dust core having a structure with high radial crushing strength in which the binder containing an acrylic resin as a main component is sufficiently spread to every corner of the gaps between the magnetic alloy powder particles. This powder magnetic core can use FeSiAl alloy powder (Sendust powder), amorphous alloy powder, nanocrystalline alloy powder, amorphous metal powder, and other powders with excellent soft magnetic properties, resulting in high magnetic permeability and high saturation magnetic flux density, making it possible to provide a magnetic core that contributes to the miniaturization of magnetic devices.In addition, the use of these magnetic alloy powders makes it possible to provide a magnetic core that can reduce hysteresis loss and eddy current loss.

[0012] According to the method for producing a powder magnetic core of the present invention, the frictional heat generated during warm compaction causes the binder, which is the glass transition point of −5° C. or more but less than 25° C., to soften at a temperature moderately above the glass transition point, and the binder, which is primarily composed of acrylic resin, softens at a temperature moderately above the glass transition point. Since the magnetic alloy powder is compacted while the acrylic resin is in a softened state, the soft magnetic alloy powder coated with the acrylic resin is more densely bound, thereby providing a powder magnetic core with improved radial crushing strength. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view showing a first example of a magnetic core formed from a powder magnetic core according to the present invention. [Figure 2] FIG. 3 is a perspective view showing a second example of a magnetic core formed from a powder magnetic core according to the present invention. [Figure 3] FIG. 10 is a perspective view showing a third example of a magnetic core formed from a powder magnetic core according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 shows a first embodiment of an inductor made of a powder magnetic core according to the present invention, in which the inductor 1 is formed in a ring shape with a uniform thickness and height all around. This inductor 1 is a powder magnetic core obtained by placing an insulating coating powder (described below) together with a binder into a mold for forming the desired shape, warm compacting at 80°C or less, and then firing (annealing) after compaction. The insulating coating powder is formed by forming an insulating coating layer on magnetic alloy powder using an insulating material such as resin.

[0015] The magnetic alloy powder is a soft magnetic alloy powder whose main component is Fe, and can be one or a mixture of two or more of FeSi alloy powder, FeNi alloy powder, FeSiAl alloy powder (Sendust powder), amorphous alloy powder, nanocrystalline alloy powder, and amorphous metal powder. All of these magnetic alloy powders are highly hard and hardly deform, so even if they are annealed as magnetic alloy powder or sintered (annealed) as insulating powder covered with an insulating film, a molded body with the required strength cannot be obtained. For example, the sendust powder may be sendust powder having a composition of Fe-9.5%Si-5.5%Al by mass. For example, the amorphous metal powder may be Fe-Cr-Si-BC amorphous alloy powder. For example, the Fe-Si-Al alloy powder may contain 7-11% by mass of Si and 3-11% by mass of Al. For example, the Fe-Si alloy powder may contain 4.5% by mass or more and 7% by mass or less of Si. In addition, FeSi alloy powder, FeNi alloy powder, FeSiAl alloy powder (Sendust powder), amorphous alloy powder, nanocrystalline alloy powder, and amorphous metal powder are known to have various compositions, and therefore, the powders are not limited to those having the aforementioned compositions, and any known compositions may be used.

[0016] Silicone resin can be used for the insulating coating. Silicone resin is a resin with a siloxane bond (Si-O-Si) as its main skeleton. Methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified, alkyd resin-modified, polyester resin-modified, rubber-based, etc. can be used as the silicone resin. Among these, it is preferable to use silicone resin composed of methyl groups and phenyl groups. These silicone resins can be mixed with a solvent. The amount of silicone resin added can be, for example, about 1% by mass relative to the magnetic alloy powder.

[0017] The inductor 1 of this embodiment is obtained by wet-adding 2.0% to 4.0% by mass of an acrylic resin binder to the insulating coating powder on which the insulating coating is formed, granulating the powder, and then placing the granulated powder in a mold together with a lubricant powder and warm-molding (powder compaction) it in a temperature range of 40 to 80°C to obtain a shape close to the desired shape, followed by firing (annealing) it at a high temperature that does not destroy the insulating coating. The mold temperature during mold press molding is preferably in the above-mentioned range.

[0018] When a silicone resin insulating coating is used on magnetic alloy powder, the silicone resin is water-repellent. Here, with a water-repellent binder that is compatible with water, such as an anionic or cationic binder, its affinity with water increases during granulation in the process of forming liquid bridges that bind the powder together, making it less compatible with the powder. For this reason, a nonionic binder, such as a nonionic binder, is desirable. Therefore, the binder used for granulation is preferably one primarily composed of acrylic resin, a nonionic binder with a pH (hydrogen ion exponent) of 6 to 8.

[0019] For example, the glass transition temperature of a binder primarily composed of acrylic resin is preferably −5° C. or higher and lower than 25° C. The glass transition temperature of the binder is more preferably −5° C. or higher and 20° C. or lower. The amount of the binder primarily composed of acrylic resin added is preferably 2.0% by mass or higher and 4.0% by mass or lower. By using a binder whose main component is an acrylic resin with a low glass transition temperature, the magnetic alloy powder coated with the acrylic resin is more tightly bound during molding, improving shape retention. If the binder has a glass transition temperature higher than the aforementioned range (-5°C or higher but lower than 25°C), the strength of the molded body after warm molding will not improve. If the glass transition temperature is too low below the aforementioned range (-5°C or higher but lower than 25°C), the binder will soften due to frictional heat generated during molding, and the molded body may deform when held immediately after molding.

[0020] By warm molding using the aforementioned acrylic resin binder having a glass transition point, the compact is further compacted and the binder spreads between the particles of the magnetic alloy powder, resulting in an improved strength of the compact. When using a binder having the aforementioned glass transition point, the fluidity of the powder decreases if the warm molding temperature exceeds 80° C. Therefore, the warm molding temperature is preferably in the range of room temperature to 80° C., and more preferably 40° C. or higher and 80° C. or lower.

[0021] The frictional heat generated during warm molding causes the acrylic resin to soften at a temperature that is moderately above its glass transition point (Tg).Since the acrylic resin is in a softened state when pressure molding is performed, the soft magnetic alloy powder coated on the acrylic resin is more densely bound, improving shape retention. Furthermore, when the mold is heated to 40°C to 80°C, the binder is reliably softened and the materials are bound more tightly, improving the strength of the bound body after warm molding.

[0022] The inductor 1 produced by the above-mentioned warm compaction can use FeSiAl alloy powder (Sendust powder), amorphous alloy powder, nanocrystalline alloy powder, amorphous metal powder, and the like, which have excellent soft magnetic properties, and therefore has high magnetic permeability and can exhibit high saturation magnetic flux density, thereby providing a magnetic core that contributes to the miniaturization of magnetic devices. Furthermore, since these magnetic alloy powders can be used, it is possible to provide a magnetic core that has low hysteresis loss and reduced eddy current loss.

[0023] (Manufacturing method) The manufacturing method of the inductor 1 includes (1) a resin coating step for forming an insulating film, (2) a granulating step, (3) a lubricant adding step, (4) a press molding step, and (5) an annealing step. In the resin coating process, silicone resin is dissolved in an organic solvent, and this organic solvent is sprayed onto the magnetic alloy powder to a required thickness. The organic solvent is then evaporated by a drying process such as vacuum drying to form an insulating coating. By vacuum drying, it is possible to obtain magnetic alloy powder with an insulating coating, the surface of which is covered with an insulating coating layer (resin coating layer) of the required thickness.

[0024] In the granulation process, the acrylic resin solvent can be dissolved in pure water and used for granulation. A known granulation method, such as agitation granulation, can be used as the granulation method. The required amount of binder (mainly acrylic resin) is gradually added dropwise to the powder mixture mixed by agitation granulation. After the binder is added, it is preferable to dry the mixture in a vacuum. The amount of acrylic resin added can be 2.0% by mass or more and 4.0% by mass or less. By granulation, the average particle size (D 50 It is possible to obtain granulated powder with particle sizes of about 50 μm to 200 μm. The dried powder is then dry-added with the required amount of lubricant (lubricating powder, for example, 1% by mass or less), and then placed in the cavity of a die. A green compact can be obtained by warm compacting at room temperature to 80°C. The compacting pressure is 10 to 16 ton / cm. 2 You can choose the degree. The resulting compact is subjected to a heat treatment to remove distortion by firing (annealing) at a high temperature (650 to 750°C for Sendust, or -50°C to 0°C below the glass transition temperature for amorphous alloys) that does not destroy the insulating coating layer. Through the above manufacturing process, a powder magnetic core can be obtained in which magnetic alloy powder with an insulating coating is bound and compacted with an acrylic resin binder.

[0025] The binder used for granulation is a nonionic (pH 6-8) binder mainly composed of acrylic resin.Since acrylic resin has good compatibility with magnetic alloy powder, it easily spreads into the gaps between the magnetic alloy powder during warm compaction, resulting in a compact with high strength and excellent shape retention.

[0026] In the above embodiment, the case where the ring-shaped inductor 1 is manufactured has been described, but the shape of the inductor is not limited to a ring shape. For example, the inductor may be an inductor 2 made of an E-shaped core as shown in FIG. 2, or an inductor 3 made of an EER core as shown in FIG. In the case of an inductor 2 made of an E-shaped core, a transformer can be made by combining two inductors 2 of the same shape and winding them together. A transformer can also be made by combining an inductor 2 made of an E-shaped core with an I-shaped core and winding it together. In addition, in the case of the inductor 3 that constitutes the EER core, a transformer can be formed by combining and winding two inductors 3 of the same shape. In addition, there are various types of core shapes, and the powder magnetic core of this embodiment may be configured with any core of a conventionally known shape. [Example]

[0027] The present invention will be described in more detail below by showing examples, but the present invention is not limited to these examples. As the magnetic alloy powder, sendust powder (particle size D50=50 μm) and amorphous alloy powder (composition: (Fe, Cr, Mn)-Si-PBCS, particle size D50=10 μm) were used. Xylene was mixed into the silicone resin solvent and sprayed to form an insulating film with an additive amount of 1 mass %.

[0028] Binders A to E having the pH and glass transition temperature shown in Table 1 below were added to magnetic alloy powder having an insulating coating in the amounts shown in Table 2, and this mixture was added with 1 mass% or less of a lubricant, and then placed in a mold and warm-molded at room temperature or 40 to 80°C as shown in Table 2, to obtain a ring-shaped compact with an inner diameter of 25 mm, an outer diameter of 35 mm, and a height of 5 mm, as shown in Figure 1. The ring-shaped compact was heated to 700°C in an inert gas atmosphere for 0.5 hours, and then slowly cooled to obtain a sintered body. The sample using amorphous alloy powder was annealed at 470°C.

[0029] [Table 1]

[0030] The resulting ring-shaped fired samples were measured for radial crushing strength, Rattler value, and fluidity by the following methods. 〇Radial crushing strength The radial crushing strength of the compact was measured by measuring the breaking load with a universal testing machine using a ring-shaped test piece of ψ35 (outer diameter) × ψ25 (inner diameter) × 5H (height). The radial crushing strength was calculated from the dimensions of the compact (ring dimensions) according to the following relational expression. K = (F × (De)) / (L × e 2 ) K = radial crushing strength (MPa), F = maximum load at break (N), D = outer diameter of specimen (mm), e = wall thickness of specimen (mm), L = length and thickness of specimen (mm)

[0031] Rattler value A test piece of ψ20 × 10 was prepared in the same manner as above, and placed in a mesh box at 87 rpm for a total rotation speed of 1000, and the reduction rate after insertion was measured. The Rattler value can be calculated by the formula: Rattler value=1-(weight before charging / weight after charging), and the smaller the value, the better the moldability. Flow test The test sample was placed in the funnel of a Kasa specific gravity measuring instrument based on JIS K6720, with the mechanical shutter closed and properly sealed. The shutter was opened, and a timer was started as the powder fell. The timer was stopped the moment the last powder left the orifice, and the passage time was measured. The passage time was measured and recorded to the nearest 0.1 second. The above results are summarized in Table 2 below.

[0032] [Table 2]

[0033] As shown in Table 2, the samples of Examples 1 to 9 were produced by warm molding at room temperature or at 40°C, 60°C, or 80°C using an acrylic resin binder with a pH of 6 to 8 (6.5 to 6.9) and a glass transition point of -5°C to less than 25°C (-5°C to 20°C), with the binder addition amount in the range of 2.0% by mass or more and 4.0% by mass. In Table 2, the standard for excellent fluidity is an FR of 13 seconds or less, which is judged as passing (◯), and an FR of more than 13 seconds is judged as insufficient fluidity (×). Regarding the radial crushing strength, if it was 1 MPa or more, it was judged to have high strength. Regarding the Rattler value, if it was 10% or less, it was judged to have good formability.

[0034] The samples of Examples 1 to 7, which used sendust powder as a raw material, had excellent fluidity, high radial crushing strength, small Rattler values, and excellent moldability. Excellent fluidity means that a material flows smoothly into the molding cavity of a mold when it is placed in the mold, and is therefore a criterion for judging excellent moldability. In particular, the samples of Examples 5 to 7 were warm-molded products in which the mold was heated to 40° C. to 80° C. during molding. It is believed that the strength of these samples as powder magnetic cores was significantly improved as a result of the softening of the acrylic resin binder, which has a glass transition point of −5° C. to less than 25° C., allowing the binder to spread sufficiently among the magnetic alloy powder. In Examples 8 and 9, the raw material was changed to amorphous alloy powder, but like the sample using Sendust powder, they had excellent fluidity, high radial crushing strength, small Rattler value, and excellent moldability. In Examples 8 and 9, too, it is believed that the strength as a powder magnetic core was improved by softening the binder.

[0035] The sample of Comparative Example 1 was a sample using a binder with a low pH and a high glass transition point, but the radial crushing strength was low and the Rattler value was also large. The sample of Comparative Example 2 used a binder with a high pH, ​​and therefore had a low radial crushing strength and a large rattler value. The sample of Comparative Example 3 had a high pH and used a binder with a glass transition temperature of 25°C, so the radial crushing strength was low and the Rattler value was also large. The sample of Comparative Example 4 used a binder that was desirable in terms of pH and glass transition point, but the amount of binder added was too small, resulting in poor fluidity and a large rattler value. The sample of Comparative Example 5 used a binder with desirable pH and glass transition temperature, but the amount of binder added was too high. This sample had high radial crushing strength and a low Rattler value, but cracks occurred in the sample after firing due to the effects of gas generated during the firing process.

[0036] From the above test results, it was found that by warm compacting and annealing granulated powder to which 2.0 mass% or more and 4 mass% or less of an acrylic resin binder has been added to magnetic alloy powder, a powder magnetic core with high radial crushing strength and excellent formability can be obtained. Furthermore, it was found that when manufacturing a powder magnetic core with high radial crushing strength and excellent formability, if a hard magnetic alloy powder is used, an acrylic resin binder with a pH of 6 to 8 and a glass transition point of -5°C or higher but lower than 25°C can be used, and the powder magnetic core is compressed into the desired shape by warm molding, followed by annealing, thereby manufacturing a powder magnetic core with high radial crushing strength and excellent formability. [Explanation of symbols]

[0037] 1, 2, 3... inductor.

Claims

1. A dust core made of granulated powder in which 2.0% by mass or more and 4% by mass or less of a binder whose main component is acrylic resin is added to a magnetic alloy powder.

2. 2. The powder magnetic core according to claim 1, wherein the binder has a pH (hydrogen ion exponent) of 6 or more and 8 or less.

3. 3. The powder magnetic core according to claim 1, wherein the binder has a glass transition point of −5° C. or higher and lower than 25° C.

4. 3. The dust core according to claim 1, wherein the magnetic alloy powder is any one of sendust powder, amorphous alloy powder, and nanocrystalline alloy powder.

5. A method for producing a powder magnetic core, comprising the steps of: adding 2.0% by mass or more and 4% by mass or less of a binder having a glass transition point of −5°C or more and less than 25°C and containing an acrylic resin as a main component to a magnetic alloy powder; and compacting the resulting granulated powder at a mold temperature of 80°C or less during mold press molding.

6. A method for producing a powder magnetic core, comprising: adding a binder to magnetic alloy powder having an insulating coating in a wet state; vacuum drying the resulting granulated powder; adding a lubricant powder in a dry state; mixing the resulting granulated powder; and firing the resulting powder to form a powder magnetic core.

7. 7. The method for producing a powder magnetic core according to claim 5, wherein a binder having a pH of 6 or more and 8 or less is used.

8. 7. The method for producing a dust core according to claim 5, wherein the magnetic alloy powder is any one of sendust powder, amorphous alloy powder, and nanocrystalline alloy powder.

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