JP7633825B2 - Soft magnetic powder and dust cores - Google Patents

Description

The present invention relates to soft magnetic powder using pure iron powder and a dust core containing this soft magnetic powder.

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. Powder magnetic cores are often used for this core.

Powder cores contain soft magnetic powder and an insulating layer formed around the soft magnetic powder, and are formed by pressurizing the soft magnetic powder with this insulating layer formed. The pressure during pressurization is fairly high, ranging from several tons to several tens of tons, to compress 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 minimize energy loss when the magnetic flux density changes. The magnetic property related to energy loss is specifically iron loss (Pcv). Iron loss (Pcv) is expressed as the sum of hysteresis loss (Ph) and eddy current loss (Pe).

Patent No. 5929819

Research into reducing hysteresis loss has been ongoing for some time. For example, as shown in Patent Document 1, research has been conducted into the fact that low hysteresis loss can be obtained when the crystal grains are coarse. However, in recent years, the applications of coil components have become more diverse, and there is a demand for further reduction in hysteresis loss.

The present invention has been made to solve the above problems, and its purpose is to provide a soft magnetic powder and a dust core that can reduce hysteresis loss.

The soft magnetic powder of the present invention comprises pure iron powder, and is characterized in that the ratio of the peaks of all planes in an X-ray diffraction pattern to the peak with plane index 110 is 0.430 or less.

A dust core containing the above soft magnetic powder is also an aspect of the present invention.

According to the present invention, it is possible to obtain soft magnetic powder and dust cores that can reduce hysteresis loss.

1 is a graph showing the relationship between the ratio of the peak of all directional faces to the peak of the face index 110 and non-uniform strain. 1 is a graph showing the relationship between non-uniform strain and hysteresis loss. 1 is a graph showing the relationship between the ratio of the peak of all directional planes to the peak of the plane index 110 and the hysteresis loss.

(Embodiment)
The soft magnetic powder in this embodiment will be described below. Note that the present invention is not limited to the embodiment described below.

Soft magnetic powder is used as a material for dust cores, which are the magnetic bodies in coil components installed in office equipment, solar power generation systems, automobiles, etc. Dust cores are made by compacting soft magnetic powder surrounded by an insulating layer to form a compact, and then annealing this compact.

As the soft magnetic powder, pure iron powder is used. Pure iron powder contains 99% or more Fe. It is preferable to use water atomized powder or gas atomized powder as the pure iron powder.

In X-ray diffraction, the pure iron powder has a ratio of the peaks of all planes in all directions to the peak with plane index 110 of 0.430 or less. This peak ratio is calculated by X-ray diffraction using the Lieveld analysis method. By keeping the peak ratio at 0.430 or less, it is possible to reduce hysteresis loss.

The peak here refers to the peak height (value on the vertical axis, number of counts) in a graph obtained by X-ray diffraction, with the horizontal axis being the diffraction angle 2θ (unit: deg) and the vertical axis being X-ray intensity (unit: CPS = counts/second). In this X-ray diffraction, the peak heights of six faces, (110), (112), (113), (200), (211), and (220), are detected. In other words, the peak with face index 110 refers to the peak height at face index 110 out of these six faces. Also, the peak of faces in all directions refers to the sum of the peak height values of these six faces.

One way to make the peak ratio below 0.430 is to manufacture pure iron powder using the gas atomization method. In other words, gas is sprayed onto pure iron powder that has been melted at high temperature, and then it is cooled. The peak ratio can be changed by adjusting the cooling speed.

Another method for reducing the peak ratio to 0.430 or less is to perform two heat treatments as follows. First, the pure iron melted by atomization is powdered, and then the first heat treatment process is performed. The heat treatment temperature is about 800°C to 900°C. After the first heat treatment, the heat-treated pure iron powder is crushed, and then a second heat treatment is performed at a higher temperature than the first heat treatment, for example, about 900°C to 1000°C. This method can also reduce the peak ratio to 0.430 or less. When heat treating the pure iron powder, inorganic insulating powder such as alumina powder may be added.

In addition, non-uniform strain is formed in the crystal structure of pure iron powder. Uniform strain refers to the variation in strain when observing an aggregate of tens of thousands of powder particles and looking at each crystal lattice plane. Non-uniform strain is calculated from the following formula (1) by performing X-ray diffraction on the crystal structure of the soft magnetic powder. The value of this non-uniform strain calculated by formula (1) is preferably 0.0030% or less. By keeping it in this range, it is possible to reduce hysteresis loss.

数式（１）のうち、βは積分幅、Ｄは結晶子の大きさ（ｎｍ）、θは回析角（ｒａｄ）、λはＸ線の波長（ｎｍ）、ηは不均一歪（％）、を表す。なお、積分幅とは、Ｘ線回析で得られたピーク波形の面積をピーク高さで割った比である。

In formula (1), β is the integral width, D is the crystallite size (nm), θ is the diffraction angle (rad), λ is the wavelength of X-rays (nm), and η is the non-uniform strain (%). The integral width is the ratio of the area of the peak waveform obtained by X-ray diffraction divided by the peak height.

An insulating layer is formed around the pure iron powder, which is a soft magnetic powder. The insulating layer is made of an insulating material, and this insulating material is attached to the periphery of the pure iron powder. As long as the insulating layer is interposed around the pure iron powder, the manner in which the insulating material is attached does not matter. That is, the insulating material may be attached so as to completely cover the periphery of the pure iron powder, or it may be attached so as to cover a portion of the pure iron powder, with a portion of the surface of the pure iron powder being exposed. The insulating material may also be attached to the surface of each particle of the pure iron powder, or it may be attached to the surface of the aggregates of the pure iron powder, or it may be attached in a mixture of these manners.

As the insulating material, a silane coupling agent, a silicone oligomer, a silicone resin, or a mixture of these can be used. That is, the silane coupling agent, the silicone oligomer, and the silicone resin can each be used alone, or, for example, a mixture of a silane coupling agent and a silicone oligomer, or a mixture of a silane coupling agent and a silicone resin can be used.

The insulating layer may be a single layer or multiple layers. For example, the insulating layer may be composed of multiple layers, each of which is divided into layers for each type, or may be composed of a single layer of insulating material that is a mixture of one type or two or more types. The insulating material may also contain moisture. In this embodiment, an insulating layer containing a silane coupling agent and silicone resin is formed around the pure iron powder. Note that the moisture evaporates during the molded body heat treatment process described below, so no moisture remains as an insulating layer.

Silane coupling agents that can be used include aminosilane, epoxysilane, and isocyanurate silane coupling agents, with 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and tris-(3-trimethoxysilylpropyl)isocyanurate being particularly preferred.

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.

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.

Examples of moisture include water and ethanol. Moisture is added after the soft magnetic powder is mixed with a silane coupling agent, silicone resin, etc., or at the initial stage of drying the silane coupling agent, silicone resin, etc. Moisture is added by dispersing it in a mist or spray form, or by dripping it as fine droplets. Adding moisture improves the hydrolysis and condensation reactions required for silane coupling agents, etc., and improves the strength of the core.

A lubricant is added to the pure iron powder with an insulating layer formed around it, and the powder core is produced through a pressure molding process and a compact heat treatment process. Examples of lubricants include stearic acid and its metal salts, as well as ethylene bis stearamide, ethylene bis stearamide, and ethylene bis stearate amide.

The pressure molding process is a process for producing a powder compact by pressure molding the pure iron powder on which the insulating layer has been formed. First, the pure iron powder is filled into a die, and then the powder compact is obtained by applying a pressure of 10 to 20 ton/ ^cm2 during molding.

In the compact heat treatment process, heat treatment is performed in a non-oxidizing atmosphere such as nitrogen gas, a mixture of nitrogen and hydrogen gas, or a low-oxygen atmosphere such as 0.01%, at a temperature of 600°C or higher and lower than the temperature at which the insulating layer formed around the pure iron powder is destroyed (e.g., 850°C).

(effect)
As described above, the soft magnetic powder of the present embodiment includes pure iron powder, and the pure iron powder has an X-ray diffraction ratio of the peaks of all directional planes to the peak with plane index 110 of 0.430 or less. This makes it possible to reduce hysteresis loss.

The pure iron powder is water atomized powder or gas atomized powder. Water atomized powder has an irregular shape, while gas atomized powder has a shape close to a sphere. In other words, the shape is different from that of flat powder. In the case of flat powder, it is common to give it orientation because the magnetic properties are improved by flowing magnetic flux in the long side direction. Therefore, there is a tendency to promote the growth of only specific faces out of the six faces detected by X-ray diffraction. However, unlike flat powder, water atomized powder or gas atomized powder is preferable for the magnetic flux to flow to the same extent regardless of the direction from which it flows, so that there is no anisotropy. The present invention suppresses the peak of the face index 100 to promote the growth of other faces and grow overall. In other words, it does not promote the growth of only specific faces. Therefore, it is particularly effective in the case of water atomized powder or gas atomized powder that is not flat powder.

(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.

Soft magnetic powders of Examples 1 to 4 and Comparative Examples 1 to 10 and dust cores using these soft magnetic powders were produced. In Examples 1 to 4 and Comparative Examples 1 to 10, pure iron powder was used as the soft magnetic powder having different peak ratios of all directional planes to the peak with plane index 110 in X-ray diffraction. The peak ratios in Examples 1 to 4 and Comparative Examples 1 to 10 are as shown in Table 1 below. The pure iron powder was sieved with the mesh sizes shown in Table 1.

Here, the crystal structure of the sieved pure iron powder was observed. Specifically, the ratio of the peaks of all directional planes to the peak with a plane index of 110 and the non-uniform distortion were measured by X-ray diffraction. A fully automatic X-ray diffractometer (BRUKER D2 PHASER: Cu tube, X-ray wavelength λ = 0.154 nm) was used as the X-ray diffractometer. As shown in Table 1, soft magnetic powders were produced in Examples 1 to 4 and Comparative Examples 1 to 10, which have different ratios of the peaks of all directional planes to the peak with a plane index of 110. The process for producing the powder magnetic cores shown below is common to Examples 1 to 4 and Comparative Examples 1 to 10.

Next, 0.5 wt% of a silane coupling agent, 2.2 wt% of a methylphenyl silicone resin, and 0.5 wt% of water as moisture were added and mixed into the sieved pure iron powder, and then dried at a temperature of 150°C for 2 hours. As a result, an insulating layer containing the silane coupling agent and the methylphenyl silicone resin was formed around the pure iron powder.

Then, for the purpose of crushing, the powder was passed through a sieve with an opening of 500 μm, and 0.5 wt% zinc stearate was added as a lubricant. The lubricated pure iron powder was then filled into a container with an outer diameter of 20.85 mm, an inner diameter of 12.4 mm, and a height of 5.0 mm, and pressed at a molding pressure of 10.5 ton/ ^cm2 to produce a powder compact. Finally, the powder compact was heat-treated at a temperature of 620° C. for 2 hours in a hydrogen atmosphere with a hydrogen concentration of 5%, to produce a powder magnetic core.

A primary winding of 30 turns and a secondary winding of 30 turns were wound with φ0.5 mm copper wire around the powder magnetic cores of Examples 1 to 4 and Comparative Examples 1 to 10 produced as described above, and the hysteresis loss was measured. The measurement conditions were a frequency of 20 kHz and a maximum magnetic flux density Bm = 200 mT. The magnetic measuring device used was a BH analyzer (Iwatsu Measurement Co., Ltd.: SY-8219). The hysteresis loss coefficient was calculated using the least squares method using the following equations (1) to (3), and the hysteresis loss was finally calculated.

Pcv =Kh×f+Ke×f ² ...(1)
Ph = Kh×f...(2)
Pe = Ke×f ² ...(3)
Pcv: Iron loss Kh: Hysteresis loss coefficient Ke: Eddy current loss coefficient f: Frequency Ph: Hysteresis loss Pe: Eddy current loss

The above measurement results are shown in Table 1 and Figures 1 to 3. Figure 1 is a graph showing the relationship between the ratio of the peak of all directional faces to the peak of the face index 110 and non-uniform strain. Figure 2 is a graph showing the relationship between non-uniform strain and hysteresis loss. Figure 3 is a graph showing the relationship between the ratio of the peak of all directional faces to the peak of the face index 110 and hysteresis loss.

As shown in Table 1 and Figure 1, in Examples 1 to 4, in which the ratio of the peak of the faces in all directions to the peak of the face index 110 is 0.430 or less, the value of non-uniform strain is 0.0030 or less, and it was confirmed that the non-uniform strain is significantly reduced compared to Comparative Examples 1 to 10. In particular, it was confirmed that when the peak ratio is made smaller than 0.400, the value of non-uniform strain is smaller than 0.0010.

In addition, the hysteresis loss in Examples 1 to 4 in which the non-uniform strain was greatly reduced was smaller than 1070 (kW/m ³ ), and it was confirmed that the hysteresis loss was reduced more than that in Comparative Examples 1 to 10. In particular, when comparing Example 4 and Comparative Example 1, the peak ratio differs only by 0.003, but the non-uniform strain value is significantly different, and it was confirmed that Example 4 can reduce the hysteresis loss by 100 (kW/m ³ ) or more than Comparative Example 1. Furthermore, the hysteresis loss in Examples 1 and 2 in which the non-uniform strain is smaller than 0.0010 was smaller than 1060 (kW/m ³ ), and it was confirmed that the hysteresis loss was further reduced. As described above, it was confirmed that Examples 1 to 4 in which the ratio of the peak of the face in all directions to the peak of the face index 110 is 0.430 or less have reduced hysteresis 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 (3)

Equipped with pure iron powder,
The pure iron powder has an X-ray diffraction ratio of the peaks of all planes in all directions to the peak of plane index 110 of 0.430 or less;
A soft magnetic powder characterized by: The pure iron powder is a water atomized powder or a gas atomized powder;
The soft magnetic powder according to claim 1 , Contains the soft magnetic powder according to claim 1 or 2;
A powder magnetic core characterized by:

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