JP5071722B2 - Powder magnetic core and method for manufacturing the powder magnetic core - Google Patents

Description

  The present invention relates to a composite soft magnetic material, a dust core, and a method for producing a composite soft magnetic material. In particular, the present invention relates to a composite soft magnetic material that can prevent defects during production or use of the dust core when used in a dust core material and can maintain the performance of the dust core over a long period of time.

  Conventionally, as a magnetic core (core) of an electronic component such as a reactor, a transformer, or a choke coil, a powder magnetic core obtained by press-molding and firing a composite soft magnetic material in which soft magnetic powder and an insulating binder are mixed is used. ing. The dust core has a structure in which soft magnetic powders are bonded together via an insulating binder, and insulation between the soft magnetic powders is ensured by the insulating binder. The dust core has magnetic properties such that the iron loss is relatively small and the magnetic flux density is relatively large even when used in a high frequency range (see Patent Document 1).

  As the insulating binder of the dust core, an organic binder such as an epoxy resin or a fluororesin or an inorganic binder such as water glass is employed.

Patent Document 2 discloses an amorphous powder using a raw material powder in which an amorphous soft magnetic alloy powder and a glass having a low softening point (specifically, PbO.B ₂ O ₃ .SiO ₂ glass) are mixed. A soft magnetic alloy powder compact is described. Amorphous soft magnetic alloys are superior to crystalline ones in terms of strength, magnetic permeability, etc., but in order to maintain an amorphous state in this powder forming process, The heating temperature must be lower than the crystallization temperature. Therefore, a glass whose softening point is lower than the crystallization temperature of the amorphous soft magnetic alloy is used.

JP-A-6-132109 JP 2001-73062 A

  In the dust core, heat treatment is performed for the purpose of removing strain introduced into the soft magnetic powder during pressure molding, and the heat treatment temperature is preferably 500 to 700 ° C. This heat treatment may be performed simultaneously with the firing, for example, by setting the heating temperature during firing to 500 ° C. or higher. By performing the heat treatment at such a high temperature, the strain is removed, the magnetic properties of the dust core are improved, and the core loss when used in the core of various electronic components can be reduced.

  However, the above-described organic resin and water glass have a low heat-resistant temperature, and when used as an insulating binder, heat treatment must be performed at a temperature that does not cause destruction by heat. Therefore, there is a possibility that the distortion of the soft magnetic powder introduced at the time of pressure molding cannot be sufficiently removed. In addition, water glass is excellent in insulating properties compared to organic resins, but it cannot be said to have sufficient insulating properties because it contains a large amount of alkali metal as a component and has high ionic conductivity.

  The amorphous soft magnetic alloy described in Patent Document 2 requires a special process for production, and when used as a material for a dust core, the cost increases. Further, the low softening point glass is not preferable from the environmental viewpoint because it contains Pb which is an environmental pollutant.

  Furthermore, in the prior art, no consideration is given to the thermal expansion coefficient of the insulating binder.

  For example, when glass is used as the insulating binder, it is necessary to heat the powder magnetic core at least to the extent that the glass softens when firing the powder magnetic core. If the difference in expansion coefficient is large, cracks will occur in the glass existing between the soft magnetic powders after cooling, resulting in a decrease in mechanical strength and magnetic properties, such as a decrease in the strength of the dust core and an increase in iron loss. Concerned. In addition, when using a dust core, that is, when used for a core of various electronic components, depending on the driving conditions, a temperature change is repeatedly given to the core. It is thought that a decrease in magnetic properties can occur. In particular, in a reactor used in a booster circuit of a hybrid vehicle or an electric vehicle, it has been studied to drive with a high frequency of several tens kHz or more and a large current, and such a problem is likely to occur.

  The present invention has been made in view of the above circumstances, and one of its purposes is to prevent defects that occur during the production or use of a dust core when used as a dust core material. An object of the present invention is to provide a composite soft magnetic material capable of maintaining the performance of a dust core over a long period of time.

  The inventors have conducted various studies on lead-free glass that is suitable for an insulating binder of a powder magnetic core and that has high insulating properties and an appropriate thermal expansion coefficient. As a result, the present invention is completed. It came.

(Composite soft magnetic material, dust core)
The composite soft magnetic material of the present invention is formed by mixing soft magnetic powder and an insulating binder, and the insulating binder contains 30 to 40% of B ₂ O ₃ and P ₂ O ₅ in mol%. A lead-free glass having a composition containing 25 to 40% and a total of 20 to 35% of two or more kinds of alkali metal oxides.

The dust core of the present invention is formed by pressure-molding a mixture of soft magnetic powder and an insulating binder, and then subjected to a heat treatment, and the insulating binder contains 30% of B ₂ O ₃ in mol%. 40%, characterized in that the P ₂ O ₅ 25 to 40%, and lead-free glass consisting of two or more alkali metal oxides from compositions containing 20 to 35% in total.

Here, as the soft magnetic powder in the present invention, powder of pure iron or iron alloy can be employed. Examples of iron alloys include Fe-Si alloys (silicon steel), Fe-Si-Al alloys (Sendust), Fe-Ni alloys (Permalloy), and the like. For example, the thermal expansion coefficient of pure iron is 12.1 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of commonly used silicon steel is 12 × 10 ⁻⁶ to 15 × 10 ⁻⁶ / ° C.

The glass having the above specific composition has a thermal expansion coefficient close to that of the soft magnetic powder, and can prevent defects generated during the production or use of the dust core, that is, cracks in the glass. In addition, this glass has a volume resistivity of 2 × 10 ¹² Ω · cm or more and excellent insulation, and a softening point of 450 ° C. or more. Hereinafter, the reason which specified the composition of the glass used as an insulating binder in this invention is demonstrated.

SiO ₂ , P ₂ O ₅ , B ₂ O _{3 and the} like are known as glass-forming oxides that can form glass alone, but in the present invention, P ₂ O ₅ and B ₂ O ₃ are used in combination. By using a combination of P ₂ O ₅ and B ₂ O ₃ , the softening point of the glass can be adjusted, and the heat treatment temperature of the dust core can be 500 ° C. or higher. The softening point of glass referred to here is the temperature obtained by thermomechanical analysis (TMA). The mixing ratio of P ₂ O ₅ and B ₂ O ₃ is preferably 1: 1 to 1: 1.6 in terms of molar ratio.

  Generally, glass softens when it exceeds the softening point, that is, starts to have a viscosity, but at a higher temperature, the viscosity decreases, and the fluidity (here, soft enough that the shape of the dust core cannot be maintained). Will have a state). Therefore, as a result of the examination by the present inventors, it is important that the softening point of the glass is at least 50 ° C. lower than the heat treatment temperature of the dust core, and the heat treatment temperature of the dust core is 500 ° C. or more. In this case, it was found that it is effective to set the temperature to 450 ° C. or higher.

Further, in the present invention, for the purpose of improving the properties of the glass, specifically, increasing the thermal expansion coefficient, the glass forming oxide is oxidized with an alkali metal such as Li ₂ O, K ₂ O, Na ₂ O. Mix two or more things. Alkali metal oxides are incorporated into glass, thereby cutting the glass network and contributing to high thermal expansion. The mixing ratio of the glass-forming oxide (here P ₂ O ₅ and B ₂ O ₃ ) and the alkali metal oxide (total of two or more) is preferably 1: 0.25 to 1: 0.6 in molar ratio. . In addition, by using two or more kinds of alkali metal oxides, an alkali mixing effect can be expected, and the insulation can be improved as compared with the case of using one kind of alkali metal oxide. When two kinds of alkali metal oxides are used, it is preferable to select Li ₂ O and K ₂ O, and the mixing ratio is preferably the same in terms of molar ratio.

In addition, the present invention allows impurities that are inevitably mixed in to be included. Such impurities may be mixed from a crucible or the like used when melting a glass raw material during glass production. Examples of the impurities include Al ₂ O ₃ and SiO ₂ .

The glass having the specific composition described above can satisfy a thermal expansion coefficient of 8 × 10 ⁻⁶ to 23 × 10 ⁻⁶ / ° C. More preferably, the glass has a thermal expansion coefficient of 10 × 10 ^{−6 to} 17 × 10 ⁻⁶ / ° C.

  The compounding amount of the glass in the composite soft magnetic material is preferably 0.2 to 2.5% by mass%.

  When the powder magnetic core is used, if the blending amount of the glass is 0.2% by mass or more, the soft magnetic powders can be sufficiently joined together and insulation between the soft magnetic powders can be sufficiently secured. Moreover, if the compounding quantity of glass is 2.5 mass% or less, the ratio which a soft magnetic powder occupies does not become small too much, and it is easy to ensure sufficient magnetic characteristics. A more preferable glass blending amount is 0.5% by mass or more.

The glass preferably contains Al ₂ O ₃ and the content thereof is more than 0 and not more than 10% in terms of mol%.

As described above, Al ₂ O ₃ is inevitably mixed into the glass as an impurity, but may be actively mixed into the glass. P ₂ O ₅ that is a glass-forming oxide is known to have low water resistance, but water resistance can be improved by mixing Al ₂ O ₃ .

The glass contains SiO ₂ and the content thereof is preferably more than 0 and less than 10% in terms of mol%.

Similarly to Al ₂ O ₃ , SiO ₂ may inevitably be mixed into the glass as an impurity, but may be actively mixed into the glass. By mixing SiO ₂ , the softening point of the glass can be increased. For example, the heat treatment temperature of the dust core can be 600 ° C. or higher. In the case of containing both of Al ₂ O ₃ and SiO _2, it is preferable that the total content of both the glass is 10 mol% or less.

  Any one of silicone resin and stearate may be further added to the composite soft magnetic material.

  Silicone resin and stearate can improve the lubricity of the soft magnetic powder during pressure molding, and can improve the dispersibility of the soft magnetic powder in the material and the releasability from the mold. Silicone resin has high heat resistance to some extent, and also functions as an insulating binder. Examples of the stearate include sodium stearate, magnesium stearate, calcium stearate, strontium stearate, barium stearate and zinc stearate. Moreover, when using such an additive, it is preferable that the total compounding quantity which combined the glass and additive in a composite soft magnetic material is 2.5 mass% or less.

(Production method of composite soft magnetic material)
The composite soft magnetic material of the present invention can be obtained by a production method including the following steps.
Raw materials for preparing glass raw materials adjusted to contain 30 to 40% by mole of B ₂ O ₃ , 25 to 40% of P ₂ O ₅ , and a total of 20 to 35% of two or more alkali metal oxides Process Glass making process for producing glass by melting and cooling the raw material Grinding process for grinding glass to obtain glass powder Mixing process for mixing soft magnetic powder and glass powder

As the raw material of the glass raw material, B ₂ O ₃ , P ₂ O ₅ , and two or more of the alkali metal oxides listed above can be selected and used. It is also possible to use such starting materials. Such starting materials include lithium metaphosphate (Li ₂ PO ₃ ), potassium metaphosphate (K ₂ PO ₃ ), sodium metaphosphate (Na ₂ PO ₃ ), barium metaphosphate (Ba (PO ₃ ) ₂ ), In addition to zinc metaphosphate (Zn (PO ₃ ) ₂ ) and aluminum metaphosphate (Al (PO ₃ )), lithium carbonate (LiCO ₃ ) and the like can be given. For example, Li ₂ PO ₃ , K ₂ PO _3, or Na ₂ PO ₃ can be a starting material for the alkali metal oxides Li ₂ O, K ₂ O, or Na ₂ O, and can also be used as a starting material for P ₂ O ₅ . Can be a raw material.

In the raw material process, Al ₂ O ₃ or SiO ₂ may be mixed with the glass raw material, and in the mixing process, the above-described additives may be further blended.

  When the composite soft magnetic material of the present invention is used as a dust core material, it can prevent defects that occur during the production or use of the dust core, and can maintain the performance of the dust core for a long period of time. Moreover, since the glass used as the insulating binder does not contain Pb, it is excellent in terms of environment.

  The dust core of the present invention can be heat-treated at a temperature of 500 ° C. or higher, and can remove the strain introduced into the soft magnetic powder during pressure molding to improve the magnetic properties. Further, since the insulation between the soft magnetic powders is ensured by highly insulating glass, the iron loss in the high frequency range is small and the magnetic characteristics are excellent. Furthermore, mechanical strength is high by using glass for the insulating binder.

  Embodiments of the present invention will be described below.

<Production of glass>
First, a method for producing glass used for the composite soft magnetic material will be described.

The composition of the glass is, in mol%, B ₂ O ₃ : 30 to 40%, P ₂ O ₅ : 25 to 40%, and two alkali metal oxides (R ′ ₂ O + R ″ ₂ O, R ′, R ″) Is an alkali metal): A glass raw material adjusted to 20 to 35% was prepared. Here, commercially available boron oxide (B ₂ O ₃ ) powder and two kinds of alkali metaphosphate powder as starting materials for P ₂ O _5, R ′ ₂ O, and R ″ ₂ O are used as glass raw materials. Specifically, Li ₂ PO ₃ and K ₂ PO ₃ were selected as the alkali metaphosphate, and the mixing ratio was B ₂ O ₃ : P ₂ O ₅ : Li ₂ O: K ₂ O = 1 ( 33.3): 1 (33.3): 0.5 (16.7): 0.5 (16.7) The amount of each raw material powder was calculated and weighed so that 50 g of glass was produced from this raw material 1. Table 1 shows the blending amount of each raw material.

Moreover, the raw materials 2-4 which each changed the mixing ratio of each raw material with respect to the raw material 1 were prepared. As for the raw material 2 and 4 were mixed with Al ₂ O _3, with LiCO ₃ in place of the starting material 3, Li ₂ PO _3, using the combination of the raw material 4 in the Li ₂ PO ₃ and LiCO _3. The specific mixing ratio (molar ratio) of each raw material is shown below.
(Raw material 2) B ₂ O ₃ : P ₂ O ₅ : Li ₂ O: K ₂ O: Al ₂ O ₃ = 30: 30: 15: 15: 10
(Raw material 3) B ₂ O ₃ : P ₂ O ₅ : Li ₂ O: K ₂ O = 25: 25: 25: 25
(Raw material 4) B ₂ O ₃ : P ₂ O ₅ : Li ₂ O: K ₂ O: Al ₂ O ₃ = 25: 25: 20: 20: 10
Table 1 shows the blending amount of each raw material when producing 50 g of glass from these raw materials 2 to 4.

  A raw material 1 was sufficiently mixed in a mortar to prepare a glass batch, and this batch was put in a high-purity alumina crucible and melted in an electric furnace in an air atmosphere for 0.5 to 1 hour. The set temperature of the electric furnace was 1100-1300 ° C. Next, the glass melt was taken out from the electric furnace, cast into a stainless steel mold or a graphite plate, and slowly cooled to obtain glass. This glass was designated as Sample 1. It is also possible to use a quartz crucible or a graphite crucible instead of the alumina crucible.

  Moreover, it carried out similarly to the raw material 1, and produced the glass also about the raw materials 2-4, and made the obtained glass the samples 2-4.

<Characteristics and evaluation of glass>
(composition)
Table 2 shows the results of analyzing the glass compositions of Samples 1 to 4 using an ICP emission spectroscopic analyzer.

As shown in Table 2, the glass of Sample 1 contains Al ₂ O ₃ that is not mixed with the glass raw material. This is presumed to be mixed from the alumina crucible used at the time of glass production.

(Glass transition point and crystallization start temperature)
For samples 1 to 4, the sample was pulverized and passed through a 50 μm and 40 μm mesh sieve to obtain glass powder of a specific size. Set each glass powder on a differential thermal balance (TG-DTA-8120 manufactured by Rigaku), raise the temperature from room temperature to 800 ° C at a rate of 10 ° C / min, and perform differential thermal analysis (DTA) curves for each sample. Was measured. Table 3 shows the results of obtaining the glass transition point and the crystallization start temperature from this DTA curve.

(Glass softening point and thermal expansion coefficient)
For samples 1 to 4, the sample is processed to the same size as the standard sample (eg, 4 mm x 4 mm x 12 mm) and set in a thermomechanical analyzer (TMA-8310 manufactured by Rigaku). The sample was heated at a rate of 10 ° C./min until it shifted from plus to minus, and the thermal expansion curve of each sample was measured. Table 3 shows the results of obtaining the glass softening point and the thermal expansion coefficient from this thermal expansion curve. The thermal expansion coefficient was determined in the range from room temperature to the glass transition point.

(Insulation evaluation)
About the samples 1-4, the glass covering copper wire which coated the sample on the copper round wire (diameter 1mm (phi)) was produced. A tin foil is wound over 10 cm in the longitudinal direction of each coated copper wire, a voltage is applied between the copper wire and the tin foil, and the volume resistivity (volume resistivity) and withstand voltage when the applied voltage is 10 V And the insulation of each sample was evaluated. The glass coating thickness of the glass-coated copper wire was 128 μm. Table 3 shows the volume resistivity and withstand voltage of each sample obtained.

From the results in Table 3, the glass of Samples 1 and 2 has a softening point of 450 ° C or higher, and when used as an insulating binder for a powder magnetic core, the heat treatment temperature of the powder magnetic core should be 500 ° C or higher. Is possible. On the other hand, the glass of Samples 3 and 4 has a softening point of less than 450 ° C., specifically 430 ° C. or less, and when the heat treatment temperature of the dust core is 500 ° C. or more, the degree of softening proceeds excessively, It is difficult to set the temperature to 500 ° C. or higher. Samples 1 and 2 have a thermal expansion coefficient of 8 × 10 ⁻⁶ to 23 × 10 ⁻⁶ / ° C., which is close to the thermal expansion coefficient of the soft magnetic powder used for the dust core, Defects that occur during manufacture or use can be prevented. Furthermore, the samples 1 and 2 have a volume resistivity of 2 × 10 ¹² Ω · cm or more, and it is found that the insulation evaluation using the glass-coated copper wire has high insulation.

<Production of composite soft magnetic material>
A composite soft magnetic material using the glass of Sample 1 described above as an insulating binder was produced. Specifically, the sample 1 was pulverized and mixed by mixing a glass powder having an average particle diameter of 1.7 μm and a soft magnetic powder separately prepared at a predetermined mixing ratio. Here, pure iron powder was prepared as the soft magnetic powder, and a silicone resin (additive) was further added to the composite soft magnetic material. This pure iron powder is a water atomized powder having an average particle size of 30 to 100 μm. Further, the compounding amounts of the glass powder and the silicone resin in the composite soft magnetic material were 0.5% by mass and 1.0% by mass, respectively. This composite soft magnetic material is designated as material 1.

<Production of dust core>
Next, the material 1 was filled in a mold and subjected to pressure molding at a surface pressure of 1270 MPa. Then, the molded body was taken out, and the molded body was fired to produce a dust core. The molded body was in the form of a ring with an inner diameter of 20 mm, an outer diameter of 34 mm, and a height of 5 mm, and was heat treated at 500 ° C. for 1 hour in a nitrogen stream atmosphere for the purpose of removing distortion during firing. This dust core is referred to as Example 1.

  As a comparison, a composite soft magnetic material in which the compounding amount of the silicone resin in the composite soft magnetic material was 1.5% by mass without glass powder was prepared, and a dust core was prepared in the same manner as in Example 1. This dust core is referred to as Comparative Example 1.

<Evaluation of dust core>
First, when the composition of the glass component of the dust core of Example 1 was analyzed using an ICP emission spectroscopic analyzer, the composition was slightly changed from the glass composition of Sample 1, but it was almost close to that. there were.

Next, for Example 1 and Comparative Example 1, the density (g / cm ³ ), iron loss W1 / 10k (W / kg), and crushing strength (MPa) were measured. Here, the iron loss W1 / 10k was measured using a BH curve tracer (BHS-40S manufactured by Riken Denshi Co., Ltd.), the excitation magnetic flux density at the time of measurement was 0.1 T, and the measurement frequency was 10 kHz. The crushing strength is determined by crushing strength test method (JIS Z
2507). Table 4 shows the measurement results.

  From the results of Table 4, it can be seen that the dust core of Example 1 has a small iron loss value in a high frequency region such as 10 kHz, is excellent in magnetic characteristics, and has a high crushing strength. Therefore, the dust core of the present invention is suitable for a core of a reactor for a booster circuit of an automobile used in a high frequency range, for example.

  Moreover, when the cross section of the dust core of Example 1 after measuring the magnetic properties was observed with a scanning electron microscope (SEM), there was a gap between the soft magnetic powder and the glass, or there was a crack in the glass. It was not allowed to do. Therefore, it is estimated that the performance of the dust core of the present invention is maintained over a long period of time.

  Note that the present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the gist of the present invention. For example, the composition of the glass used as the insulating binder can be changed as appropriate, or the blending amount of the glass in the composite soft magnetic material can be changed as appropriate.

  The composite soft magnetic material of the present invention can be suitably used as a core material for a transformer or a choke coil in addition to a booster circuit for a hybrid vehicle, a reactor used in power generation / transforming equipment, and the like.

Claims (5)

A powder magnetic core obtained by press-molding a mixture of soft magnetic powder and insulating binder, and then heat-treated,
The average particle size of the particles constituting the soft magnetic powder is 30 to 100 μm,
The insulating binder has a composition containing 30 to 40% of B ₂ O ₃ by mol%, 25 to 40% of P ₂ O ₅ , and a total of 20 to 35% of two or more kinds of alkali metal oxides. lead-free glass der made is,
The powder magnetic core according to claim 1, wherein an amount of the lead-free glass in the whole is 0.2 to 2.5% by mass . 2. The dust core according to claim 1, wherein an amount of the lead-free glass in the whole is 0.5% or more by mass%. The powder magnetic core according to claim 1 or 2, wherein the composite soft magnetic material contains any one of a silicone resin and a stearate as an additive.   4. The dust core according to claim 3, wherein a total blending amount of the additive and the lead-free glass in the whole is 2.5% or less by mass%. _B 2 _{O 3} is _30-40% by _mole%, the raw material P 2 _{O 5} is to prepare a 25% to 40%, and a glass material alkali metal oxides of two or more was adjusted to contain 20 to 35% in total Process,
A glass production process for producing glass by melting and cooling the raw material;
Crushing step of crushing the glass to obtain glass powder;
A mixing step of mixing the soft magnetic powder composed of particles having an average particle diameter of 30 to 100 μm and the glass powder so that the blending ratio of the glass powder in the whole is 0.2 to 2.5% by mass%. When,
A molding step of pressure-molding the mixed powder obtained in the mixing step;
A firing step of firing the molded body obtained in the molding step at 500 ° C. or higher;
A method for producing a powder magnetic core comprising the steps of: