JP7387456B2 - Iron-based powder for powder magnetic core - Google Patents

Description

The present invention relates to iron-based powder for powder magnetic cores.

Iron-based powder for powder magnetic cores is made into a powder compact by compression molding using a metal mold, and is used in magnetic cores for motors, reactors for power supply circuits, and the like.

As such iron-based powder for powder magnetic core, iron powder having an insulating coating on the surface for the purpose of improving magnetic properties is known (see Japanese Patent Application Laid-Open No. 2013-149661).

This iron-based powder for powder magnetic cores with improved magnetic properties is molded into a high-density magnetic core by using a mold lubrication molding method in which a lubricant is applied to the mold surface and molded. I'm trying. However, since it is necessary to apply lubricant to the surface of the mold every time molding is performed, manufacturing efficiency decreases and productivity is hindered. For this reason, there is a need for an iron-based powder for powder magnetic cores that can be easily taken out of the mold after compression molding without applying a lubricant to the surface of the mold.

Japanese Patent Application Publication No. 2013-149661

The present invention has been made based on the above-mentioned circumstances, and uses iron powder having an insulating coating on the surface, but it can be easily removed from the mold after compression molding without applying lubricant to the surface of the mold. The purpose of the present invention is to provide iron-based powder for dust cores that can be taken out.

The iron-based powder for powder magnetic core according to one aspect of the present invention includes iron powder having an insulating coating on the surface, a lubricant, and a fluidity improver, and the content of the lubricant with respect to 100 parts by mass of the iron powder. The sum of the amount and the content of the fluidity improver is 0.7 parts by mass or less, and the ratio of the content of the lubricant to the content of the fluidity improver is in accordance with JIS-Z2502 (2012). This is the ratio that is not considered illiquid when measuring liquidity.

Since the iron-based powder for powder magnetic core includes a lubricant, it can be easily taken out from the mold after compression molding without applying a lubricant to the surface of the mold. Further, the iron-based powder for powder magnetic core includes a fluidity improver, and the ratio between the content of the lubricant and the content of the fluidity improver is determined by fluidity measurement in accordance with JIS-Z2502 (2012). This is the ratio that is not considered illiquid. In the iron-based powder for powder magnetic core, the decrease in fluidity caused by adding a lubricant is suppressed by containing this fluidity improver, and the iron-based powder for powder magnetic core can be easily poured uniformly into a mold. can do. Furthermore, since the iron-based powder for powder magnetic core has a sum of the content of the lubricant and the content of the fluidity improver below the above upper limit, the iron-based powder for powder magnetic core can be molded. It is possible to prevent the magnetic properties of the molded body from deteriorating due to the lubricant and fluidity improver.

It is preferable that the content of the lubricant and the content of the fluidity improver satisfy the following formula (1). In this way, by setting the content of the lubricant and the content of the fluidity improver at a ratio that satisfies the following formula (1), the fluidity of the iron-based powder for powder magnetic core can be easily ensured. Can be done.
Content of fluidity improver [parts by mass] ≧ 0.7 × content of lubricant [parts by mass] (1)

It is preferable that the lubricant is a fatty acid amide and the fluidity improver is zinc oxide. In this way, by using fatty acid amide as the lubricant and zinc oxide as the fluidity improver, the fluidity of the iron-based powder for powder magnetic core can be ensured and the ease of taking it out from the mold after molding can be improved. It can be made easier to achieve both.

The content of the lubricant relative to 100 parts by mass of the iron powder is preferably 0.2 parts by mass or more. By setting the content of the lubricant to the above lower limit or more in this way, it is possible to make it easier to take out the molded body obtained by molding the iron-based powder for powder magnetic core from the mold.

The ratio of the average particle size of the fluidity improver to the average particle size of the iron powder is preferably 1/200 or more and 1/30 or less. By setting the average particle size of the fluidity improver to the average particle size of the iron powder within the above range, the density of the molded product obtained by molding the iron-based powder for powder magnetic core can be maintained, and The fluidity of iron-based powder for powder magnetic cores can be improved.

Here, "considered to have no fluidity" means a fluidity measurement based on JIS-Z2502 (2012), and if the powder does not flow out even after opening the orifice, tap the funnel once to make it flow. This applies when the flow does not flow even after the test is completed, or when the flow stops during measurement. Note that, based on JIS-Z2502 (2012), fluidity is measured from the time it takes for 50 g of powder to pass through a predetermined funnel orifice.

"Average particle size of iron powder" refers to the opening (D50) of the sieve through which 50% by mass of iron powder passes when iron powder is sieved, and "average particle size of fluidity improver" refers to Refers to particle size measured by transmission method.

As explained above, the iron-based powder for powder magnetic core of the present invention uses iron powder having an insulating coating on the surface and can be easily removed from the mold after compression molding without applying lubricant to the surface of the mold. It can be taken out.

FIG. 1 is a plot diagram showing the measurement results of fluidity in an example in which the lubricant is stearamide. FIG. 2 is a plot diagram showing the measurement results of fluidity in an example in which the lubricant is lauric acid amide.

Hereinafter, an iron-based powder for powder magnetic core according to one embodiment of the present invention will be described.

The iron-based powder for powder magnetic core includes iron powder, a lubricant, and a fluidity improver.

<Iron powder>
The iron powder of the iron-based powder for powder magnetic core has an insulating coating on the surface. Since the iron powder has an insulating coating on its surface, even if the iron powders come into contact with each other when molding the iron-based powder for powder magnetic core, the iron particles can be kept separated by the insulating coating. By setting it as such a state, the magnetic properties of the molded body obtained by molding the iron-based powder for powder magnetic core can be improved.

As the above-mentioned insulating coating, an oxide or resin having insulating properties can be used, but among them, the first insulating layer is mainly composed of iron phosphate glass and is laminated on the surface of the iron particles, and the first insulating layer is mainly composed of silicone resin. A two-layer insulating coating having a second insulating layer and a second insulating layer laminated on the outer surface of the first insulating layer is preferable. By using such a two-layer insulating coating, heat resistance can be improved while maintaining high insulation properties. Here, "main component" means the component with the highest content, for example, the component with the content of 50% by mass or more.

The above-mentioned two-layer insulating coating can be produced, for example, by the following procedure. First, iron particles are immersed in an aqueous phosphate solution and then dried to form an insulating coating of iron phosphate glass on the surface of the iron particles. Next, the iron particles coated with the iron phosphate glass insulating film are mixed into a solution of silicone diluted with toluene and dried. In this way, a two-layer insulating coating can be formed on the surface of the iron particles.

The lower limit of the average particle size of the iron powder is preferably 30 μm, more preferably 40 μm. On the other hand, the upper limit of the average particle size of the iron powder is preferably 70 μm, more preferably 60 μm. If the average particle size of the iron powder is less than the lower limit, the proportion of the insulating coating becomes larger than the iron particles, so it may be difficult to secure the magnetic force of the iron powder. Conversely, if the average particle size of the iron powder exceeds the upper limit, eddy currents within the iron particles may increase, leading to increased loss.

<Lubricant>
The lubricant is added to make it easier to take out the molded body obtained by molding the iron-based powder for powder magnetic core from the mold. By adding a lubricant, it is possible to reduce the ejection pressure when taking out the molded body from the mold, and to prevent cracking of the molded body and damage to the mold.

Examples of the lubricant include metal soaps such as lithium stearate, calcium stearate, and zinc stearate, fatty acid amides, amide waxes, hydrocarbon waxes, and crosslinked (meth)acrylic acid alkyl ester resins.

Among these, fatty acid amides are preferred because they can easily reduce the segregation of the iron powder. Examples of the fatty acid amide include primary amides such as lauric acid amide, stearic acid amide, and oleic acid amide, secondary amides such as stearyl stearic acid amide, and bisamides such as ethylene bis stearic acid amide.

The lower limit of the content of the lubricant relative to 100 parts by mass of the iron powder is preferably 0.2 parts by mass, more preferably 0.4 parts by mass. On the other hand, the upper limit of the content of the lubricant is preferably 0.6 parts by mass, more preferably 0.5 parts by mass. If the content of the lubricant is less than the lower limit, there is a risk that the effect of making it easier to take out from the mold after molding may not be sufficiently achieved. Conversely, if the content of the lubricant exceeds the upper limit, it may be difficult to suppress the decrease in fluidity caused by adding the lubricant by including a fluidity improver, which will be described later.

The lower limit of the average particle size of the lubricant is preferably 10 μm, more preferably 20 μm. On the other hand, the upper limit of the average particle size of the lubricant is preferably 60 μm, more preferably 50 μm. If the average particle size of the lubricant is less than the above lower limit, it cannot be said to be sufficiently large compared to the average particle size of the fluidity improver, which will be described later, and the fluidity improver is likely to be prevented from entering between the iron powder. Therefore, there is a possibility that the fluidity of the iron-based powder for powder magnetic core may decrease. On the other hand, if the average particle size of the lubricant exceeds the upper limit, voids are likely to be formed between the lubricants or between the lubricant and the iron powder, and the iron-based powder for powder magnetic cores cannot be obtained by molding the iron-based powder. There is a risk that the density of the molded product will decrease. Note that the "average particle size of lubricant" refers to the median system (D50) measured by laser diffraction/scattering method.

<Fluidity improver>
The fluidity improver is added in order to ensure the fluidity of the iron-based powder for powder magnetic core and to make it easier to uniformly pour the iron-based powder for powder magnetic core into a mold.

Examples of the fluidity improver include metal oxides such as alumina, titania, and zinc oxide, and silicon oxide. Among them, zinc oxide is preferred. The present inventors conjecture that zinc oxide improves the fluidity of the iron-based powder for powder magnetic core and also improves the lubricity. Further, it is more preferable that the lubricant is a fatty acid amide and the fluidity improver is zinc oxide. In this way, by using fatty acid amide as the lubricant and zinc oxide as the fluidity improver, the fluidity of the iron-based powder for powder magnetic core can be ensured and the ease of taking it out from the mold after molding can be improved. It can be made easier to achieve both.

The lower limit of the content of the fluidity improver relative to 100 parts by mass of the iron powder is preferably 0.1 parts by mass, more preferably 0.2 parts by mass. On the other hand, the upper limit of the content of the fluidity improver is preferably 0.5 parts by mass, more preferably 0.3 parts by mass. If the content of the fluidity improver is less than the lower limit, the effect of suppressing the decrease in fluidity caused by adding a lubricant may be insufficient. On the other hand, if the content of the fluidity improver exceeds the upper limit, the total content with the lubricant added to make it easier to take out from the mold after molding becomes too large, and the iron-based powder for powder magnetic core There is a risk that the magnetic properties of the molded product obtained by molding the product may deteriorate.

The lower limit of the average particle size of the fluidity improver is preferably 0.3 μm, more preferably 0.5 μm. On the other hand, the upper limit of the average particle size of the fluidity improver is preferably 1 μm, more preferably 0.8 μm. The fluidity improver penetrates between the iron powders and keeps them separated from each other, thereby reducing the attractive force between the iron powders. However, since the fluidity improver itself has poor fluidity, if a large amount of the fluidity improver enters between the iron powder, the fluidity of the iron-based powder for powder magnetic core will decrease. In other words, if the average particle size of the fluidity improver is less than the lower limit, a large amount of the fluidity improver will easily enter between the iron powder, which may reduce the fluidity of the iron-based powder for powder magnetic core. be. On the other hand, if the average particle size of the fluidity improver exceeds the above upper limit, it becomes difficult for the fluidity improver to penetrate between the iron powders, making it easier for the iron powders to stick to each other, causing the iron-based powder for powder magnetic core to Liquidity may decrease.

The upper limit of the sum of the content of the lubricant and the content of the fluidity improver with respect to 100 parts by mass of the iron powder is 0.7 parts by mass, more preferably 0.6 parts by mass, and 0.5 parts by mass. Part is more preferable. If the above sum exceeds the above upper limit, the density and magnetic properties of a molded product obtained by molding the iron-based powder for powder magnetic core may be reduced by the lubricant and fluidity improver. On the other hand, the lower limit of the above sum is not particularly limited, but may be, for example, 0.25 parts by mass. By setting the above-mentioned sum to the above-mentioned lower limit or more, it is possible to easily ensure the lubricity and fluidity of the iron-based powder for powder magnetic core.

Further, the ratio between the content of the lubricant and the content of the fluidity improver is such that it is not considered to have no fluidity in fluidity measurement based on JIS-Z2502 (2012). More specifically, the content of the lubricant and the content of the fluidity improver may be in a ratio that satisfies the following formula (1). In this way, by setting the content of the lubricant and the content of the fluidity improver at a ratio that satisfies the following formula (1), the fluidity of the iron-based powder for powder magnetic core can be easily ensured. Can be done.
Content of fluidity improver [parts by mass] ≧ 0.7 × content of lubricant [parts by mass] (1)

The lower limit of the ratio of the average particle size of the fluidity improver to the average particle size of the iron powder is preferably 1/200, more preferably 1/100. On the other hand, the upper limit of the above ratio is preferably 1/30, more preferably 1/50. If the above ratio is less than the above lower limit, a large amount of the fluidity improver tends to enter between the iron powders, and there is a possibility that the fluidity of the iron-based powder for powder magnetic cores may be inhibited on the contrary. On the other hand, if the ratio exceeds the upper limit, the density of the molded body obtained by molding the iron-based powder for powder magnetic core may decrease.

<Advantages>
Since the iron-based powder for powder magnetic core includes a lubricant, it can be easily taken out from the mold after compression molding without applying a lubricant to the surface of the mold. Further, the iron-based powder for powder magnetic core includes a fluidity improver, and the ratio between the content of the lubricant and the content of the fluidity improver is determined by fluidity measurement in accordance with JIS-Z2502 (2012). This is the ratio that is not considered illiquid. In the iron-based powder for powder magnetic core, the decrease in fluidity caused by adding a lubricant is suppressed by containing this fluidity improver, and the iron-based powder for powder magnetic core can be easily poured uniformly into a mold. can do. Furthermore, since the iron-based powder for powder magnetic core has a sum of the content of the lubricant and the content of the fluidity improver below the above upper limit, the iron-based powder for powder magnetic core can be molded. It is possible to prevent the magnetic properties of the molded body from deteriorating due to the lubricant and fluidity improver.

[Other embodiments]
The above embodiments do not limit the configuration of the present invention. Therefore, in the above embodiment, it is possible to omit, replace, or add components of each part of the above embodiment based on the description of this specification and common general technical knowledge, and all of these are interpreted as falling within the scope of the present invention. Should.

For example, the iron-based powder for powder magnetic core may contain optional components such as a binder within a range that does not impede magnetic properties, lubricity, and fluidity.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Liquidity evaluation]
Iron powder with an insulating coating on the surface ("MH23D" manufactured by Kobe Steel, average particle size 50 μm), stearic acid amide (average particle size 41 μm) as a lubricant, and zinc oxide powder (JIS) as a fluidity improver. - K1460 (2006) equivalent to type 1, average particle size 0.75 μm) were mixed at the mass ratio shown in Table 1, and No. 1~No. No. 18 iron-based powder for powder magnetic core was obtained.

In addition, lauric acid amide (average particle size 20 μm) was used as a lubricant instead of the above-mentioned stearic acid amide, and iron powder, a lubricant, and a fluidity improver were mixed in the mass proportions shown in Table 2. 19~No. No. 26 iron-based powder for powder magnetic core was obtained.

No. 1~No. The fluidity of 26 iron-based powders for powder magnetic cores was measured in accordance with JIS-Z2502 (2012). The results are shown in Tables 1 and 2. In addition, "NF" in Tables 1 and 2 means that it was considered to have no fluidity.

Moreover, the presence or absence of fluidity is shown as a plot diagram in FIGS. 1 and 2. In FIGS. 1 and 2, the samples whose fluidity could be measured are plotted as black circles, and the samples that were considered to have no fluidity are plotted as white triangles.

From the plot diagrams in Figures 1 and 2, it is clear that the iron-based powder for powder magnetic core exhibits fluidity when the content of the lubricant and the content of the fluidity improver are in a ratio that satisfies the following formula (1). I understand.
Content of fluidity improver [parts by mass] ≧ 0.7 × content of lubricant [parts by mass] (1)

[Magnetic property evaluation]
No. of Table 1 4.No. 11 and no. A ring test piece was prepared using No. 18 iron-based powder for powder magnetic core, and its magnetic properties were evaluated.

For the ring test piece, a mold with an outer diameter of 45 mm and an inner diameter of 33 mm was used, and the mold was filled with iron-based powder for powder magnetic core so as to obtain a molded body with a height of 5 mm, and molded at a molding pressure of 980 MPa. Further, the obtained molded body was heat treated at 600° C. for 30 minutes in a nitrogen atmosphere to obtain a ring test piece. Table 3 shows the density of this ring test piece. In addition, No. 11 and no. Since the iron-based powder for powder magnetic core No. 18 contained a lubricant and a fluidity improver, it could be easily taken out from the mold after compression molding without applying a lubricant to the surface of the mold. On the other hand, No. The iron-based powder for powder magnetic cores in No. 4 contains a lubricant, so it can be easily taken out from the mold, but it has no fluidity, so it is difficult to fully fill the mold. It was necessary to poke and fill the base powder.

The density of the ring test piece was calculated by measuring the outer diameter (diameter) D1, inner diameter D2, thickness T, and mass W of the ring, and using the following formula.
Density=W/{(D1×D1−D2×D2)×π/4×T} (2)

The above ring test piece was wound with 25 turns of primary winding and 400 turns of secondary winding, and the BH curve was measured at a maximum excitation magnetic field of 10,000 A/m using a BH curve measuring device manufactured by Metron Giken. did. From this BH curve, magnetic flux density (B10 kA/m), coercive force (Hc), and maximum relative permeability (μ) were determined. The results are shown in Table 3.

In addition, another above-mentioned ring test piece was wound with 25 turns of primary winding and 25 turns of secondary winding, and the excitation magnetic flux density was 0.1 T using BH Analyzer SY-8218 manufactured by Iwasaki Tsushinki. Iron loss (W1/10k) at a frequency of 10kHz was measured. The results are shown in Table 3.

From Table 3, the above magnetic properties are. No. 1 containing zinc oxide, a fluidity improver. 11 and no. Also in No. 18, zinc oxide was not used. The magnetic properties were maintained at the same level as No. 4, and no decrease in magnetic properties was observed due to the addition of zinc oxide.

As explained above, the iron-based powder for powder magnetic core of the present invention uses iron powder having an insulating coating on the surface and can be easily removed from the mold after compression molding without applying lubricant to the surface of the mold. It can be taken out.

Claims (3)

Iron powder with an insulating coating on the surface,
lubricant and
Equipped with a fluidity improver and
The average particle size of the iron powder is 30 μm or more and 70 μm or less,
The content of the lubricant is 0.2 parts by mass or more with respect to 100 parts by mass of the iron powder,
The sum of the content of the lubricant and the content of the fluidity improver with respect to 100 parts by mass of the iron powder is 0.7 parts by mass or less,
An iron-based powder for powder magnetic core, wherein the content of the lubricant and the content of the fluidity improver satisfy the following formula (1) .
Content of fluidity improver [parts by mass] ≧ 0.7 × content of lubricant [parts by mass] (1) The iron-based powder for powder magnetic core according to claim 1 , wherein the lubricant is a fatty acid amide and the fluidity improver is zinc oxide. The iron-based powder for powder magnetic core according to claim 1 or 2, wherein the ratio of the average particle size of the fluidity improver to the average particle size of the iron powder is 1/200 or more and 1/30 or less.

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