JP2003142310A - Dust core having high electrical resistance and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dust core, which is made of soft magnetic metallic powder and in which strains are fully eliminated from the inside of the metallic powder through high-temperature annealing and the deterioration of permeability does not become an issue, even in a high frequency region due to significantly increased electrical resistance of the core. SOLUTION: On the surface of the soft magnetic metallic powder, having average Si content of at least 0.5 wt.% in its portion from the surface to a depth of 0.2 μm, an insulating coating film is formed by treating the surface of the powder with a phosphoric acid, boric acid, Na, K, Ca, Mg, Al, Si, Mn, or Zn phosphate or borate solution, or silicone resin. The dust core is obtained by molding the powder into the shape of the core by compression molding and performing stress relief annealing on the molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core having high electric resistance and a method for producing the dust core, and also includes an intermediate product for producing the dust core. INDUSTRIAL APPLICABILITY The dust core of the present invention is useful as a core having a small core loss, especially when used in a high frequency range.

[0002]

2. Description of the Related Art Soft magnetic metal powders such as Fe-3%
In many cases, a choke or a transformer in which powder of silicon steel typified by Si is compacted into a ring shape and a coil is wound around the powder is used in a wide technical field. For example, D
It is a C-DC converter, a noise filter, an injector, or the like. The powder magnetic core is used to increase the electric resistance inside the magnetic core, and it is desirable to suppress power loss due to eddy currents and heat generation of circuit components to be low.
It requires that there be sufficient insulation between the powders.

In order to manufacture this dust core, a soft magnetic metal is compressed by an appropriate method, for example, a powder obtained by spraying a molten metal with water is filled in a mold together with a binder and pressure is applied. To do. An epoxy resin, an imide resin, a phenol resin, or a silicone resin is used as the binder.

However, since a high pressure (10 tons / cm ² or more) is applied in order to achieve a high powder packing density, distortion remains in the soft magnetic metal powder, and this distortion lowers the magnetic characteristics. There is. Specifically, coercive force increases, core loss increases and magnetic permeability decreases. Therefore, the molded product is usually used as a magnetic core after strain relief annealing.

Annealing is performed at 500 ° C. in the case of silicon steel.
As mentioned above, it is desirable to carry out at a temperature of 600 ° C or higher,
When an organic synthetic resin is used as the binder, the resin decomposes at too high a temperature and does not serve as a binder, so only an annealing temperature up to 400 ° C. can be adopted. Therefore, even if it takes a long time to anneal, the strain applied to the soft magnetic metal powder in the molded product is not completely removed, that is, the original performance of the soft magnetic metal cannot be sufficiently exhibited. , Must be used as a magnetic core.

On the other hand, the meaning of increasing the electric resistance increases as the frequency at which the dust core is used increases. If the resistance of the dust core is high, the magnetic permeability can be kept substantially constant even if the frequency is increased, but if the resistance is low, the magnetic permeability is drastically reduced in the high frequency region.

As one means for increasing the electric resistance, it has been devised and practiced to subject the soft magnetic metal powder to a phosphate treatment to form a phosphate insulating coating. This technology prepares a metal salt of phosphoric acid such as magnesium, calcium, or zinc as an aqueous solution or an aqueous dispersion, and optionally adds boric acid to the surface of the powder to form a phosphate coating. To form. Although the insulating property is enhanced, the phosphate itself has a low function as a powder binder, so the above-mentioned synthetic resin binder is added if necessary.

If an organic binder is used, the limit of the annealing temperature which can be applied to the molded article made of the phosphate-treated soft magnetic metal powder is determined by it.
If it is not used, there is no problem of decomposition of organic substances, but it was experienced that when the annealing was performed at 500 ° C or higher, the electric resistance was remarkably reduced. It was found that the film is an inorganic substance and has no problem of decomposition, but it is crystallized at high temperature, resulting in low electric resistance. After all, it is the current situation that annealing exceeding 500 ° C cannot be performed.

In the process of searching for a technique for more effectively performing insulation treatment with a solution of phosphoric acid or a salt thereof, the inventors have noted that the effect of insulation treatment differs depending on the alloy composition of the soft magnetic metal. As a result of the research, if Si is present near the surface of the soft magnetic metal powder at a certain concentration or more,
It was found that the treatment with the solution of phosphoric acid or its salt was highly effective. Furthermore, it has been found that this effect can be similarly obtained when the insulating treatment is performed using a solution of boric acid or a salt thereof and when the insulating treatment is performed using a silicone resin.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to make use of the above new findings of the inventors, and
Strain inside the soft magnetic metal powder is sufficiently eliminated by annealing at a high temperature, and the electric resistance is remarkably improved, so that the magnetic permeability hardly decreases even in the high frequency region, or slightly. And to provide a method for manufacturing such a dust core. It is also included in the object of the present invention to provide an intermediate product used for producing the dust core as described above.

[0011]

The powder magnetic core having a high electric resistance according to the present invention is a soft magnetic material having an average Si content of at least 0.5% by weight from the surface of the powder to a depth of 0.2 μm. On the surface of metal powder, phosphoric acid, boric acid, or phosphoric acid or boric acid such as Na, K, Ca, Mg, Al,
The one with a coating film of a salt of Si, Mn or Zn is
The powder magnetic core is formed by compression molding into a magnetic core shape and subjected to strain relief annealing.

According to the method of the present invention for producing the powder magnetic core having high electric resistance, the average Si content in the portion from the surface of the powder to the depth of 0.2 μm is increased by spraying the soft magnetic metal containing Si. A powder of at least 0.5% by weight is produced, which powder is treated with phosphoric acid, boric acid or phosphoric acid or boric acid Na, K, Ca, Mg, Al, Si, Mn.
Alternatively, it is formed by treating with a Zn salt solution to form an insulating coating on the powder surface, followed by compression molding to form a magnetic core, and annealing the molded product at a temperature of 500 to 1000 ° C.

The intermediate product of the present invention for producing the above-mentioned dust core having a high electric resistance has an average Si content of at least 0.5% by weight in a portion from the surface of the powder to a depth of 0.2 μm. The soft magnetic metal powder is subjected to the above-mentioned treatment.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, powder of any soft magnetic metal can be used as the material of the dust core as long as it contains a certain amount of Si. , Especially water spray powder. -Si: Fe-Si alloy containing 1 to 11 wt% -Si: Fe-Si-Al alloy containing 1 to 11 wt% and Al: 7 wt% or less-Si: 0.1 to 5 wt% And Co: Fe-Si-Co alloy containing 10 to 60% by weight.

As will be seen in the examples described below, the insulating treatment with phosphoric acid, boric acid, salts thereof, or silicone resin was performed so that the average Si content in the portion from the surface of the soft magnetic metal powder to a depth of 0.2 μm was measured. Is at least 0.5% by weight, the effect is high. The condition of the Si content is naturally satisfied if the soft magnetic metal contains 0.5% by weight or more of Si as a whole, but even if the Si content does not reach 0.5% by weight, When the value is close to that, it is often recognized that the Si concentration increases near the surface (the reason is not clear), and therefore, it can be expected that the effect of the insulating treatment is high. This phenomenon is useful when one does not want to add too much Si to the soft magnetic metal.

[0016]

Examples [Examples 1 to 3 and Comparative Example 1] The molten Fe-Si alloy having the Si content shown in Table 1 was sprayed with water to give -1.
A powder of 00 mesh was prepared. The average amount of Si in the portion from the surface to the depth of 0.2 μm of each powder was measured and listed in Table 1. The average Si amount is a value obtained by measuring and averaging the Si concentration distribution from the surface of the powder in the depth direction by Auger spectroscopy. Each powder was treated with the treatment liquid shown in Table 1, dried, and then subjected to a pressure of 15 ton / cm ² at room temperature to produce a test piece. 7 in an argon gas atmosphere
The strain was removed by a heat treatment of holding at 00 ° C for 2 hours.

The following tests were carried out using these test pieces. The results are also shown in Table 1. [Electrical resistivity] Test piece: 5 mm length x 5 mm width x 30 mm length DC four-terminal method or DC two-terminal method [core loss] Test piece: Outer diameter 28 mm x inner diameter 20 mm x height 5 mm Core loss tester, frequency 20 KHz, magnetic flux Density 0.1T

Table 1 Alloy components Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (% by weight) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 1 Si: 0.5 0.80 Phosphoric acid 0.2% 2.5 × 10 ³ 8.5 × 10 ³ Example 2 Si: 3.1 4.50 Phosphoric acid (80) + 4.5 × 10 ³ 7.9 × 10 ³ Boric acid (20) 0.2% Example 3 Si: 6.6 9.30 Zn phosphate 0.5% 6.5 × 10 ⁵ 3.3 × 10 ² Comparative Example 1 Si: 0.05 0.20 Phosphoric acid 0.2% 2.5 × 10 ³ 4.9 × 10 ⁴

[Example 4] Fe-Si as a soft magnetic alloy
A powder magnetic core was manufactured in the same manner as in Example 1, except that the Al treatment was used and the insulating treatment agent was changed. The results are shown in Table 2. Table 2 Alloy components Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (wt%) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 4 Si: 9.6, 15.90 Al phosphate 0.5% 7.5 × 10 ⁵ 2.0 × 10 ² Al: 5.4

[Example 5 and Comparative Example 2] A Fe-Ni-Mo-Si alloy was used as the soft magnetic alloy, and the insulating treatment agent was changed to carry out the same operation as in Example 1 to produce a dust core. The results are shown in Table 3 together with the comparative example. Table 3 Alloy composition Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (wt%) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 5 Ni: 80, Mo: 2, 2.60 Mn0 phosphate .5% 3.3 × 10 ⁴ 1.9 × 10 ² Si: 1 Comparative Example 2 Ni: 80, Mo: 2, 0.20 Mn phosphate 0.5% 5.4 × 10 ³ 3.1 × 10 ³ Si: 0.1

[Example 6 and Comparative Example 3] A Fe-Co (-Si) alloy was used as the soft magnetic alloy, and a dust core was manufactured in the same manner as in Example 1. The results are shown in Table 4 together with the comparative example. Silicone resin liquid "SR2400" (manufactured by Toray Dow Corning) was used as an insulation treatment agent. Table 4 Alloy components Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (wt%) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 6 Co: 49, Si: 2 5.60 Silicone 1.0% 1.6 × 10 ⁴ 8.6 × 10 ² Comparative Example 3 Co: 49 0 Silicone 1.0% 2.5 × 10 ² 8.5 × 10 ⁴

[Example 7 and Comparative Example 4] An Fe-Co-V (-Si) alloy was used as the soft magnetic alloy, and Example 1 was used.
A powder magnetic core was manufactured by the same operation as. The results are shown in Table 5 together with the comparative examples. Table 5 Alloy components Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (wt%) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 7 Co: 25, V: 1, 1.60 Phosphoric acid 0.2 % 5.6 × 10 ⁴ 5.5 × 10 ³ Si: 0.5 Comparative Example 4 Co: 25, V: 1 0 Phosphoric acid 0.2% 8.0 × 10 ¹ 6.9 × 10 ⁵

[Example 8 and Comparative Example 5] A powder magnetic core was manufactured in the same manner as in Example 1, except that an Fe-Co-Ti (-Si) alloy was used as the soft magnetic alloy and the insulating treatment agent was changed. did. The results are shown in Table 6 together with the comparative examples. Table 6 Alloy component Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (wt%) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 8 Co: 35, Ti: 0.5, 2.90 MgO phosphate .5% 8.6 × 10 ³ 4.6 × 10 ³ Si: 1 Comparative Example 5 Co: 35, Ti: 0.5 0 Mg phosphate 0.5% 1.3 × 10 ² 5.3 × 10 ⁴

[Examples 9 and 10 and Comparative Example 6] A Fe-Cr-Si alloy was used as the soft magnetic alloy, the insulating treatment agent was changed, and the powder magnetic core was manufactured in the same manner as in Example 1. The results are shown in Table 7 together with the comparative examples. Table 7 Alloy components Surface 0.2 Insulation treatment agent Electrical resistivity Core loss (% by weight) μm Si (concentration) ρ (μΩcm) (kW / m ³ ) Example 9 Cr: 13, Si: 1.0 1.90 Boric acid 1.0% 3.8 × 10 ³ 4.3 × 10 ³ Example 10 Cr: 13, Si: 1.0 1.90 Na borate 1.0% 2.9 × 10 ³ 3.9 × 10 ³ Comparative Example 6 Cr: 13, Si: 0.05 0.15 Boric acid 1.0% 2.5 × 10 ² 6.1 x 10 ⁴

[0025]

Industrial Applicability The dust core of the present invention contains 0.5% by weight or more of phosphoric acid, boric acid, a salt thereof, or a silicone resin applied as an insulating treatment agent on the surface of a soft magnetic metal powder. A strong insulating film is formed by the action of Si existing in a concentration, and its insulating effect does not decrease even when annealed at a high temperature, and therefore the insulating performance does not decrease. Holds a high electrical resistance. Since the annealing can be performed at a temperature of 500 ° C. or higher, for example 700 ° C., at which a sufficient effect can be obtained, the problem of the conventional pressure-dividing magnetic core that the residual strain cannot be removed due to the limitation of the annealing temperature is solved. did.

As a result of sufficient annealing, the coercive force of the dust core is kept low, and the permeability does not decrease even in the high frequency range. Therefore, the dust core of the present invention can well cope with the tendency of various electric and electronic devices to be used in a higher frequency region.

The surface-treated soft magnetic metal powder, which is an intermediate product of the present invention, is molded into a magnetic core shape by ordinary compression molding and annealed at an appropriate temperature to produce a high-performance dust core. It is a material that can.

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Claims (6)

[Claims] 1. A soft magnetic metal powder having an average Si content of at least 0.5% by weight from the surface of the powder to a depth of 0.2 μm is treated with phosphoric acid, boric acid, or phosphoric acid or boric acid. Na, K, Ca, Mg, Al, Si, Mn
Alternatively, a powder magnetic core having a high electric resistance obtained by compression-molding a product obtained by performing insulation treatment with a Zn salt solution and performing strain relief annealing. 2. A soft magnetic metal powder having an average Si content of at least 0.5% by weight from the surface of the powder to a depth of 0.2 μm, the surface of which is insulated with a silicone resin is compressed. A dust core having a high electric resistance, which is formed by molding into a magnetic core shape and subjected to strain relief annealing. 3. A soft magnetic metal powder is a Fe—Si alloy containing Si: 1 to 11 wt%, or Si: 1 to 11.
Fe-Si containing 1 wt% and Al: 7 wt% or less
The powder magnetic core according to claim 1 or 2, which is a powder of an Al alloy. 4. The soft magnetic metal powder contains Si: 0.1 to 5
Fe-containing wt% and Co: 10-60 wt%
The powder magnetic core according to claim 1 or 2, which is a powder of a Si-Co alloy. 5. An average S of a portion from the surface of the powder to a depth of 0.2 μm by water spraying a soft magnetic metal containing Si.
A powder having an i content of at least 0.5% by weight is produced, and the powder is mixed with phosphoric acid, boric acid, or phosphoric acid or boric acid such as Na, K, Ca, Mg, Al, Si, Mn, or Zn. After treatment with a salt solution or with a silicone resin to form an insulating coating on the surface of the powder, compression molding is performed to form a magnetic core, and the molded product is made to have a thickness of 500 to 100.
A method for producing a dust core having a high electric resistance, which comprises annealing at a temperature of 0 ° C. 6. A soft magnetic metal powder having an average Si content of at least 0.5% by weight from the surface of the powder to a depth of 0.2 μm is subjected to the treatment described in claim 5. , An intermediate product for producing a dust core having high electric resistance.