JP7623327B2 - Manufacturing method of powder for dust core - Google Patents

Description

The present invention relates to a method for producing powder for dust cores.

Coil components such as reactors are used in a variety of applications, including office equipment, solar power generation systems, and automobiles. Coil components have a coil attached to a core. This core is made of a powder magnetic core.

Powder cores are made by compressing powder for powder cores, which contains soft magnetic powder, under high pressure of several tons to several tens of tons to produce a powder compact. This powder compact is then subjected to a heat treatment known as annealing to produce a powder core. Examples of soft magnetic powder include FeSiAl alloys, which are made by adding Si and Al to Fe, and an insulating layer made of insulating resin is formed around the soft magnetic powder.

Due to requirements for improved energy exchange efficiency and low heat generation, powder magnetic cores are required to have magnetic properties that allow a large magnetic flux density to be obtained with a small applied magnetic field, and that reduce energy loss when the magnetic flux density changes. An example of a magnetic property related to magnetic flux density is magnetic permeability. An example of a magnetic property related to energy loss is iron loss (Pcv), also known as core loss. Iron loss (Pcv) is expressed as the sum of hysteresis loss (Ph) and eddy current loss (Pe).

JP 2000-030925 A

In recent years, there has been an increasing demand for smaller, more powerful electronic devices, and measures to combat global environmental issues are becoming an urgent priority. As a result, there is an increasing demand for high magnetic permeability and low core loss in the powder cores and powders for powder cores that make up coil components.

The present invention was made to solve the above problems, and its purpose is to provide a method for producing powder for dust cores that can achieve both high magnetic permeability and low core loss.

（式２）

In order to achieve the above object, the method for producing a powder for dust cores of the present invention includes an insulating layer forming step of adding a lubricant and an insulating resin to a soft magnetic powder to form an insulating layer around the soft magnetic powder, the insulating layer forming step includes a lubricant adding step of adding the lubricant to the soft magnetic powder, and a coating step of adding an insulating resin to the soft magnetic powder that has been subjected to the lubricant adding step, drying the resin, and forming an insulating layer around the soft magnetic powder, and The lubricant satisfies the following formulas (1) and (2), where the absolute temperature at which the solution begins is Td (K), the absolute temperature of the upper limit of the drying temperature of the insulating resin in the insulating layer formation process is Th (K), and the absolute temperature of the lower limit of the drying temperature of the insulating resin in the insulating layer formation process is Tl (K), and the lubricant satisfies the following formulas (1) and (2), the upper limit absolute temperature Th of the drying temperature of the insulating resin and the lower limit absolute temperature Tl of the drying temperature of the insulating resin have a magnetic permeability of 142 or more and a hysteresis loss of 190 (kW/m3 ⁾ or less, and the drying temperature in the insulating layer formation process is equal to or greater than the lower limit value of Tl (K) and equal to or less than the upper limit value of Th (K), which are calculated from the following formulas (1) and (2).
(Equation 1)

(Equation 2)

The insulating layer forming process may include a lubricant adding process in which the lubricant is added to the soft magnetic powder, and a coating process in which an insulating resin is added to the soft magnetic powder that has been subjected to the lubricant adding process, the soft magnetic powder is dried, and an insulating layer is formed around the soft magnetic powder.

The present invention makes it possible to achieve both high magnetic permeability and low core loss.

1 is a graph showing the ranges of the relationships (1) and (2).

(Embodiment)
The powder for dust core and the dust core according to the present embodiment will be described in detail below. Note that the present invention is not limited to the embodiment described below.

Powder cores are magnetic materials used in the cores of coil components installed in office equipment, solar power generation systems, automobiles, etc. Powder cores are made by compressing powder for powder cores and annealing it. Powder for powder cores includes soft magnetic powder. A lubricant is added to the soft magnetic powder, and an insulating layer made of an insulating material is formed. The soft magnetic powder coated with this insulating layer is pressure-molded to make a powder compact, and the powder compact is annealed to make a powder core.

The soft magnetic powder is mainly composed of iron. Examples of the soft magnetic powder include permalloy (Fe-Ni alloy) which is mainly composed of iron, Si-containing iron alloy (Fe-Si alloy), sendust alloy (Fe-Si-Al alloy), or a mixture of two or more of these powders. The soft magnetic powder may be an amorphous alloy or a nanocrystalline alloy powder.

When using permalloy (Fe-Ni alloy), the ratio of Fe to Ni is preferably 50:50 or 25:75, but other ratios are also acceptable. For example, Fe-80Ni or Fe-36Ni may be used. In addition to Fe and Ni, it may contain Si, Cr, Mo, Cu, Nb, Ta, etc. Si-containing iron alloys may also contain Co, Al, Cr, or Mn.

Examples of Fe-Si alloy powder include Fe-3.5%Si alloy powder and Fe-5.5%Si alloy powder, but the ratio of Si to Fe may be other than 3.5% or 5.5%. Fe-Si-Al alloy is a ternary alloy made of iron, silicon, and aluminum, and contains, for example, about 6 wt% to 10 wt% Si and about 4 wt% to 5 wt% Al relative to Fe, but may also contain about 1 wt% to 3 wt% Ni relative to Fe, and may further contain Co, Cr, or Mn.

This soft magnetic powder may be produced by a pulverization method or an atomization method. In the pulverization method, lumps of soft magnetic powder are mechanically pulverized. If the lumps of soft magnetic powder are large, they are pulverized using a jaw crusher, hammer mill, stamp mill, etc., and if the lumps of soft magnetic powder are small, they are pulverized using a ball mill, vibration mill, etc. In addition, the atomization method may be any of water atomization, gas atomization, and water gas atomization. For example, in the gas atomization method, gas is blown onto soft magnetic powder melted at high temperature to pulverize it, and then it is cooled and solidified.

The soft magnetic powder may be subjected to a powder heat treatment process. The powder heat treatment process is a process for heat treating the soft magnetic powder. In the powder heat treatment process, the powder is heated in a non-oxidizing atmosphere for 1 to 6 hours. The non-oxidizing atmosphere includes a low oxygen atmosphere such as 0.01% in the atmosphere or an inert gas atmosphere. Examples of the inert gas include _H2 and _N2 . The heat treatment temperature is 400°C or higher and 800°C or lower.

Next, a first lubricant addition process is performed. The first lubricant addition process is a process in which a first lubricant is added to the soft magnetic powder. This first lubricant addition process corresponds to the lubricant addition process described in claim 1.

（関係式（２））

As the first lubricant, one that satisfies the following relations (1) and (2) can be used.
(Relationship (1))

(Relationship formula (2))

In the above relational expressions (1) and (2), Td(K) is the absolute temperature at which decomposition of the lubricant begins in a thermogravimetric differential thermal analysis (hereinafter also referred to as the "decomposition onset temperature"); Th(K) is the upper absolute temperature for the drying temperature of the insulating resin in the coating process described below (hereinafter also referred to as the "upper drying temperature"); and Tl(K) is the lower absolute temperature for the drying temperature of the insulating resin in the coating process (hereinafter also referred to as the "lower drying temperature").

The decomposition start temperature of a lubricant is, for example, the temperature at which the lubricant starts to thermally decompose in a thermogravimetric differential thermal analyzer. The upper drying limit temperature refers to the critical point of the upper limit temperature of the drying temperature of the insulating resin, and the lower drying limit temperature refers to the critical point of the lower limit temperature of the drying temperature of the insulating resin. The characteristics shown in Table 2 of the examples described below were obtained, and the critical points were derived from the obtained results.

After the first lubricant addition process, the soft magnetic powder undergoes a coating process. In the coating process, an insulating resin is added to the soft magnetic powder that has undergone the first lubricant addition process, and an insulating layer is formed around the soft magnetic powder. In other words, an insulating layer made of insulating resin is formed around the soft magnetic powder. As long as the insulating layer is formed around the soft magnetic powder, the manner in which the insulating resin is attached does not matter. In other words, the insulating resin may be attached so as to cover the entire periphery of the soft magnetic powder, or it may be attached so as to cover a part of it, with a part of the surface of the soft magnetic powder being exposed. In addition, the insulating resin may be attached to the surface of each particle of the soft magnetic powder, or it may be attached to the surface of the aggregate of the soft magnetic powder, or it may be attached so that these attachment modes are mixed.

The insulating resin may be a silane compound, a silicone resin, a silicone oligomer, or a mixture of these. The insulating layer may be a single layer or multiple layers. For example, the insulating layer may be composed of multiple layers divided by type, or may be a single layer of one type or a mixture of two or more types of insulating material.

The silane compounds include silane compounds without functional groups and silane coupling agents. As the silane compounds without functional groups, for example, alkoxysilanes such as ethoxy and methoxy types can be used, with tetraethoxysilane being particularly preferred. As the silane coupling agents, aminosilane, epoxysilane, and isocyanurate type silane coupling agents can be used, with 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate being particularly preferred.

The amount of silane compound added is preferably 0.05 wt% or more and 1.0 wt% or less of the soft magnetic powder. By adding the amount of silane compound within this range, the fluidity of the soft magnetic powder can be improved, and the density, magnetic properties, and strength properties of the molded powder core can be improved.

Silicone resin is a resin that has a siloxane bond (Si-O-Si) in its main skeleton. By using silicone resin, it is possible to form a coating with excellent flexibility. Silicone resins that can be used include methyl-based, methylphenyl-based, propylphenyl-based, epoxy resin-modified, alkyd resin-modified, polyester resin-modified, and rubber-based silicone resins. Among these, when using methylphenyl-based silicone resins in particular, it is possible to form an insulating layer with little loss on heating and excellent heat resistance.

The amount of silicone resin added is preferably 0.6 wt% or more and 2.5 wt% or less relative to the soft magnetic powder. If the amount added is less than 0.6 wt%, it will not function as an insulating layer, and eddy current loss will increase, resulting in reduced magnetic properties. If the amount added is more than 2.5 wt%, it will result in a reduction in the density of the powder core.

Silicone oligomers that can be used include methyl-based and methylphenyl-based ones that have an alkoxysilyl group but no reactive functional group, epoxy-based, epoxymethyl-based, mercapto-based, mercaptomethyl-based, acrylic methyl-based, methacrylic methyl-based, and vinylphenyl-based ones that have an alkoxysilyl group and a reactive functional group, and alicyclic epoxy-based ones that have a reactive functional group instead of an alkoxysilyl group. In particular, by using methyl-based or methylphenyl-based silicone oligomers, a thick and hard insulating layer can be formed. In addition, methyl-based and methylphenyl-based ones, which have a relatively low viscosity, may be used in consideration of the ease of forming the insulating layer.

The amount of silicone oligomer added is preferably 0.1 wt% or more and 2.0 wt% or less of the soft magnetic powder. If the amount added is less than 0.1 wt%, it will not function as an insulating layer, and eddy current loss will increase, resulting in reduced magnetic properties. If the amount added is more than 2.0 wt%, it will result in a decrease in the density of the powder core.

In this coating process, insulating resin is added to the soft magnetic powder, mixed, and then heated and dried. By heating and drying the insulating resin, an insulating layer is formed on the surface of the soft magnetic powder. The temperature for heating and drying is equal to or higher than the lower limit of Tl (K) and equal to or lower than the upper limit of Th (K) calculated from the relational expressions (1) and (2). By keeping the heating temperature within this range, it is possible to improve the magnetic permeability and reduce hysteresis loss.

This is speculation and we are not limited to this mechanism, but we surmise that by using a lubricant that satisfies the above relational expressions (1) and (2) and drying the insulating resin at a drying temperature equal to or higher than the lower limit of Tl (K) and equal to or lower than the upper limit of Th (K), the lubricating action of the lubricant is more effective, the movement of the soft magnetic powder becomes smoother, the particles are closer together, and the density is improved, resulting in the realization of both high magnetic permeability and low hysteresis loss.

In this embodiment, the lubricant addition process is performed to add the first lubricant, followed by the coating process to add the insulating resin, but the timing of adding the first lubricant and the insulating resin is not limited to this. In other words, the first lubricant addition process and the coating process may be combined into one insulating layer formation process, and the first lubricant and the insulating resin may be added simultaneously. Alternatively, the insulating resin may be added first, and then the first lubricant may be added, followed by heating and drying.

After the coating process, the second lubricant addition process is performed. The second lubricant addition process is a process in which a second lubricant is added to the soft magnetic powder on which the insulating layer has been formed. The second lubricant may be the same type as the first lubricant, but it is not necessary to use the same lubricant. In other words, the second lubricant may be a different type from the first lubricant. Also, the second lubricant may be a type that does not satisfy the relational expressions (1) and (2). The amount of the second lubricant added is preferably 0.2 wt% or more and 0.7 wt% or less with respect to the soft magnetic powder.

After the second lubricant addition process, the press forming process is performed. The press forming process is a process for producing a powder compact by press forming the soft magnetic powder on which the insulating layer has been formed. First, the soft magnetic powder is filled into a die, and then it is pressed at 10 to 20 ton/ ^cm2 . In this manner, the powder compact is produced.

After the pressure molding process, an annealing process is performed. The annealing process is a process in which the powder compact produced through the pressure molding process is annealed to remove distortion within the soft magnetic powder. In the annealing process, the powder compact is heat-treated in a non-oxidizing atmosphere such as nitrogen gas, hydrogen gas, a mixture of nitrogen and hydrogen gas, or a low-oxygen atmosphere of about 0.01%, at a temperature of 650°C or higher and lower than the temperature at which the insulating layer formed around the soft magnetic powder is destroyed (for example, 900°C). By undergoing this annealing process, a powder magnetic core is produced.

(Example)
The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

Powders for powder cores in Examples 1 to 12 and Comparative Examples 1 to 19 were prepared as follows, and powder cores were produced using these powders for powder cores. Examples 1 to 12 and Comparative Examples 1 to 19 differ only in the type of first lubricant and the drying temperature in the coating process; the other manufacturing processes and conditions are the same.

First, Fe-Si-Al alloy powder was used as the soft magnetic powder. The Fe-Si-Al alloy powder was heat-treated. The heat treatment conditions were heating at 650°C for 2 hours in a nitrogen atmosphere. 0.3 wt% of the first lubricant of the type in the table below was added to and mixed with the heat-treated Fe-Si-Al alloy powder.

As the first lubricant, five types were prepared: lauric acid, stearic acid, fatty acid derivative, zinc stearate, and ethylene bisstearamide, as shown in Table 1. The decomposition start temperature, upper limit drying temperature, and lower limit drying temperature of each lubricant are as shown in Table 1. The decomposition start temperature was measured using a thermogravimetric differential thermal analyzer STA7200RV (Hitachi High-Tech Science Corporation) by placing 3 to 7 mg of the lubricant to be measured in a cylindrical container with a diameter of 5.2 mm and a height of 2.5 mm in a nitrogen atmosphere at an atmospheric temperature rise rate of 10°C/min.

The upper and lower drying temperatures of the insulating resin were also calculated. The upper drying temperature is the upper critical point of the drying temperature derived from the results of changing the drying temperature of the insulating resin for each lubricant. The lower drying temperature is the lower critical point of the drying temperature derived from the results of changing the drying temperature of the insulating resin for each lubricant. Specifically, from the results of Table 2 described later, the lower critical point in the range where the permeability is 142 or more and the hysteresis loss is reduced was set as the lower limit of the drying temperature, and the upper critical point was set as the upper limit of the drying temperature. The upper and lower limits of the drying temperature, which are Celsius temperatures, are converted into absolute temperatures to become the upper drying temperature Th (K) and the lower drying temperature Tl (K) in Table 1.

For example, in the case of lauric acid, the magnetic permeability is as high as 142 or more in the drying temperature range of 50° C. to 150° C., and the hysteresis loss is reduced to 190 (kW/m ³ ) or less, with the lower limit drying temperature being 50° C. and the upper limit drying temperature being 150° C. When these Celsius temperatures of 50° C. and 150° C. are converted to absolute temperatures, the upper limit drying temperature Th shown in Table 1 below is 423.15 (K), and the lower limit drying temperature is 323.15 (K). For other lubricants, the upper limit drying temperature Th, which is the upper critical point, and the lower limit drying temperature Tl, which is the lower critical point, were calculated in the same manner from the magnetic permeability and hysteresis loss.

After adding the first lubricant, 0.3 wt% of a silane coupling agent and 1.2 wt% of silicone resin were added as insulating resins to the Fe-Si-Al alloy powder, mixed, and dried for 2 hours. The drying temperature for each sample is as shown in Table 2. As a result, an insulating layer of a mixture of the silane coupling agent and silicone resin was formed around the Fe-Si-Al alloy powder.

After drying, the powder was passed through a sieve with 850 μm mesh to eliminate agglomerations, and a second lubricant was added and mixed. The second lubricant used was the same type as the first lubricant for each sample. The second lubricant was added at 0.2 wt% to the Fe-Si-Al alloy powder.

The Fe-Si-Al alloy powder to which the second lubricant was added was filled into a die and pressed at 15 tons/ ^cm2 to produce a toroidal powder compact having an outer diameter of 16.5 mm, an inner diameter of 11.0 mm, and a height of 5.0 mm. This powder compact was then annealed at a temperature of 700°C in a nitrogen atmosphere for 2 hours to produce each powder core.

Then, the initial permeability at 0 A/m, hysteresis loss (kW/m ³ ), eddy current loss (kW/m ³ ), and core loss (kW/m ³ ) of each of the produced powder magnetic cores were measured.

When measuring each magnetic permeability, a φ0.5 mm copper wire was wound 30 turns around the powder magnetic core as the primary winding. Then, using an LCR meter (Agilent Technology: 4284A), the initial magnetic permeability was calculated from the inductance of the magnetic field strength at 100 kHz and 1.0 V.

In addition, when measuring the iron loss, a copper wire having a diameter of 0.5 mm was wound around the powder magnetic core as a primary winding with 15 turns, and as a secondary winding with 15 turns. Then, using a magnetic measuring device, a BH analyzer (Iwatsu Measuring Corporation: SY-8219), the iron loss Pcv (kW/m ³ ) was measured under the measurement conditions of a frequency of 100 kHz and a maximum magnetic flux density Bm of 100 mT. From the measurement results of the iron loss Pcv, the hysteresis loss Ph (kW/m ³ ) and the eddy current loss Pe (kW/m ³ ) were calculated. The hysteresis loss Ph (kW/m ³ ) and the eddy current loss Pe (kW/m ³ ) were calculated by calculating the hysteresis loss coefficient (Kh) and the eddy current loss coefficient (Ke) from the frequency curve of the iron loss Pcv using the following formulas (3) to (5) by the least squares method.

Pcv =Kh×f+Ke×f ² ...(3)
Ph = Kh×f...(4)
Pe = Ke×f ² ...(5)
Pcv: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

The measured results are shown in Table 2. Table 3 also shows the slope and intercept of the approximation line for the value obtained by subtracting the upper drying limit temperature from the decomposition onset temperature, and the slope and intercept of the approximation line for the value obtained by subtracting the lower drying limit temperature from the decomposition onset temperature.

（関係式（２））

As a result of intensive research, the inventors have focused on the relationship between the decomposition start temperature of the lubricant added before the coating process and the drying temperature of the insulating resin in the coating process. In particular, they have focused on the relationship between the decomposition start temperature of the lubricant and the upper and lower drying temperatures of the insulating resin. Specifically, for four types of lubricants excluding ethylene bisstearamide, which has a low initial permeability, they calculated approximation equations of "decomposition start temperature - upper drying temperature" and "decomposition start temperature - lower drying temperature" (solid lines in FIG. 1). Furthermore, as a result of intensive research, they have found that the initial permeability is improved and the hysteresis loss is reduced by using a lubricant that satisfies the following relational expressions (1) and (2), in which the intercepts of each approximation equation are ±20K (the two-dot chain line in FIG. 1 indicates the range of relational expression (1), and the one-dot chain line in FIG. 1 indicates the range of relational expression (2).
(Relationship (1))

(Relationship formula (2))

Looking specifically at the relational expressions (1) and (2), among the five types of lauric acid, stearic acid, fatty acid derivatives, zinc stearate, and ethylene bisstearamide, only ethylene bisstearamide does not satisfy the relational expression. Specifically, the value of ethylene bisstearamide calculated based on the expressions (1) and (2) is as follows:
417.864<Th<457.864
346.755<Tl<386.755
The upper limit drying temperature of ethylene bisstearamide shown in Table 1 is 473.15 (K) and the lower limit drying temperature is 453.15 (K), which does not satisfy the above relational formula.

And looking at ethylene bisstearamide (Comparative Examples 13 to 19), some of them have hysteresis loss and iron loss at the same level as other lubricants, but the initial permeability is low at a maximum of about 125. Therefore, it was confirmed that if a lubricant that does not satisfy the relationship formulas (1) and (2) is used, it is not possible to achieve both high permeability and low hysteresis loss, and therefore low iron loss.

It was also confirmed that even if a lubricant satisfies the above relational expressions (1) and (2), it is not possible to achieve both high magnetic permeability and low hysteresis loss, and therefore low iron loss, due to the relationship with the drying temperature in the coating process. Specifically, it was confirmed that the drying temperature in the coating process needs to be equal to or higher than the lower limit of Tl (K) and equal to or lower than the upper limit of Th (K) calculated from the relational expressions (1) and (2).

In Examples 1 to 12, in which the drying temperature in the coating process is equal to or higher than the lower limit of Tl(K) and equal to or lower than the upper limit of Th(K) calculated from the relational expressions (1) and (2), hysteresis loss is reduced and low iron loss is maintained compared to the comparative examples in which the same type of lubricant is used. Of particular note is the magnetic permeability of the Examples, which exceeds 140. In other words, it was confirmed that by setting the drying temperature in the coating process to equal to or higher than the lower limit of Tl(K) and equal to or lower than the upper limit of Th(K) calculated from the relational expressions (1) and (2), it is possible to achieve both high magnetic permeability and low iron loss.

Other Embodiments
In this specification, an embodiment of the present invention has been described, but this embodiment is presented as an example and is not intended to limit the scope of the invention. The above-mentioned embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. The embodiment and its modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and gist of the invention.

Claims (1)

and an insulating layer forming step of adding a lubricant and an insulating resin to the soft magnetic powder to form an insulating layer around the soft magnetic powder,
The insulating layer forming step includes:
a lubricant adding step of adding the lubricant to the soft magnetic powder;
a coating process in which an insulating resin is added to the soft magnetic powder that has been subjected to the lubricant adding process, the insulating resin is dried, and an insulating layer is formed around the soft magnetic powder;
Including,
When the absolute temperature at which decomposition of the lubricant begins in a thermogravimetric differential thermal analysis is Td (K), the absolute temperature of the upper limit of the drying temperature of the insulating resin in the insulating layer forming process is Th (K), and the absolute temperature of the lower limit of the drying temperature of the insulating resin in the insulating layer forming process is Tl (K),
The lubricant satisfies the following formulas (1) and (2):
The upper limit absolute temperature Th of the drying temperature of the insulating resin and the lower limit absolute temperature Tl of the drying temperature of the insulating resin satisfy the conditions that the magnetic permeability is 142 or more and the hysteresis loss is 190 (kW/m ³ ) or less,
The drying temperature in the insulating layer forming step is equal to or higher than the lower limit of Tl (K) and equal to or lower than the upper limit of Th (K), which are calculated from the following formulas (1) and (2):
A method for producing a powder for a dust core, characterized by the following formula (1):

(Equation 2)

Images