Winding core

Abstract

To provide a wound magnetic core that can improve insulation between thin bands. [Solution] A wound magnetic core in which a soft magnetic metal ribbon is wound, wherein the soft magnetic metal ribbon has a nanocrystalline structure, the surface of the soft magnetic metal ribbon has an oxide layer derived from the metal constituting the soft magnetic metal ribbon, a non-magnetic and insulating metal oxide powder is interposed between the soft magnetic metal ribbons, and the core is impregnated with resin, with a packing density of 65% to 75%, the amount of powder adhering to one surface of the soft magnetic metal ribbon is less than the amount of powder adhering to the other surface of the soft magnetic metal ribbon, and the amount of powder adhering is 0.1% to 1.2% by weight ratio of the metal oxide obtained by the following formula (1), in a wound magnetic core. Weight ratio of metal oxide (%) = (Weight of metal oxide attached to soft magnetic metal strip / Weight of soft magnetic metal strip) × 100 ... (1)

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a coiled magnetic core, and to a coiled magnetic core. [Background technology]

[0002] Coil components such as inductors, transformers, and chokes have traditionally been used in a wide variety of applications, including home appliances, industrial equipment, and vehicles. Coil components consist of coils laid on a magnetic core, and wound magnetic cores, which are windings of amorphous or crystalline soft magnetic metal thin strips with excellent magnetic properties, are widely used for such magnetic cores.

[0003] A wound magnetic core is formed by tightly winding thin strips of soft magnetic metal, generally also called strips or ribbons, around a support (spool) while applying tension, resulting in an annular winding in which the soft magnetic metal strips are layered in multiple layers in the winding direction. To prevent the soft magnetic metal strips from unraveling from the winding, the ends of the soft magnetic metal strips at the beginning and end of the winding are welded to the winding body after the support has been removed. Alternatively, the end of the soft magnetic metal strip at the end of the winding is welded to the winding body while the support is still attached. Next, heat treatment is applied to relieve the stress applied during winding or to induce nanocrystallization and exhibit the desired magnetic properties. After heat treatment, the winding state is maintained by impregnating with epoxy resin or other methods to prevent the soft magnetic metal strips from unraveling due to changes over time or external forces applied to the winding body.

[0004] Soft magnetic metal strips are extremely thin, typically ranging from 10 μm to several hundred μm in thickness. While their surfaces have surface irregularities of a few micrometers, they are macroscopically smooth. Because soft magnetic metal strips are good conductors, short circuits can occur between smooth surfaces, and insufficient insulation between strips can generate eddy currents, potentially causing significant power loss in the winding core. This tendency is particularly pronounced in high-frequency applications exceeding 100 kHz. If the strips are not properly electrically insulated, the winding core becomes unsuitable for use as a coil component at high frequencies.

[0005] Conventionally, in order to obtain high insulation between thin strips, Patent Document 1 proposes forming a wound magnetic core by attaching fine powder made of non-magnetic insulating inorganic material to the surface of a magnetic metal thin strip. Patent Document 2 proposes oxidizing a magnetic metal thin strip to form an insulating layer containing iron oxide between the layers. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 1-259510 [Patent Document 2] Special Publication No. 2003-500850 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Depending on the environment in which they are used, coil components may be subjected to high surge voltages, such as those caused by lightning. In such coil components, it is required that dielectric breakdown does not occur due to voltage fluctuations caused by the surge voltage applied to the coil. Impulse testing is sometimes performed to confirm the dielectric strength of the coil component. In impulse testing, a narrow pulse voltage with a rise time of several hundred nanoseconds or less and a high voltage on the order of kV is applied to both ends of the coil component.

[0008] When an impulse test is performed, magnetostrictive vibrations occur in the thin band due to the rapid change in magnetic flux that occurs in the wound core. Even if the wound core is configured to obtain high insulation between the thin bands, as in Patent Documents 1 and 2, it has been found that the insulation between the thin bands may deteriorate, such as short circuits occurring between them, in the wound core after the impulse test. When resistance to surge voltage is required for coil components, such coil components are unsuitable for use at high frequencies, even if they do not lead to dielectric breakdown.

[0009] To achieve high insulation between thin bands, one can either apply a thicker layer of fine powder made of insulating inorganic material to the thin bands, or form a thicker insulating layer containing iron oxide on the thin bands to widen the gaps between them. However, this can reduce the packing factor of the winding core, increase its size, and make it impossible to satisfy the specified dimensional specifications for the coil components. Furthermore, even when the winding core is constructed to the specified dimensions, the desired magnetic properties may not be obtained.

[0010] Therefore, the present invention aims to provide a method for manufacturing a wound magnetic core and a wound magnetic core that can improve the insulation between thin strips of soft magnetic metal, which is formed by winding thin strips of soft magnetic metal to form an annular winding body. [Means for solving the problem]

[0011] According to one embodiment of the present invention, a method for manufacturing a wound magnetic core is provided, comprising: a first step of attaching a non-magnetic and insulating metal oxide powder to the surface of an amorphous soft magnetic metal strip; a second step of winding the soft magnetic metal strip in a ring shape after the first step to obtain a wound body in which the metal oxide powder is interposed between the strips; a third step of heat-treating the wound body in a non-oxidizing atmosphere; a fourth step of performing an oxide film formation treatment on the wound body at a temperature lower than the heat treatment temperature of the third step and in an oxidizing atmosphere to oxidize the surface of the soft magnetic metal strips; and a fifth step of impregnating the spaces between the strips of the wound body with resin and curing it after the fourth step.

[0012] According to one embodiment of the present invention, the third step is preferably a heat treatment A that precipitates nanocrystals on the amorphous soft magnetic metal thin strip, or a heat treatment B that relieves stress on the amorphous soft magnetic metal thin strip.

[0013] According to one embodiment of the present invention, it is preferable that the temperature of the heat treatment in the third step be 450°C to 620°C for heat treatment A, and 250°C to 400°C for heat treatment B.

[0014] According to one embodiment of the present invention, it is preferable that the amount of the metal oxide powder adhered in the first step is 0.1% or more and 1.2% or less in terms of the weight ratio of the metal oxide obtained by the following formula (1). Weight ratio of metal oxide (%) = (weight of metal oxide adhered to soft magnetic metal ribbon / weight of soft magnetic metal ribbon) × 100 ··· (1)

[0015] According to one embodiment of the present invention, it is preferable that the oxide film forming treatment in the fourth step is performed in an oxidizing atmosphere at a temperature of 240°C or higher and lower than the heat treatment temperature in the third step.

[0016] According to another embodiment of the present invention, there is provided a wound magnetic core in which a soft magnetic metal ribbon is wound, the soft magnetic metal ribbon has an amorphous structure or a nanocrystalline structure, the surface of the soft magnetic metal ribbon has an Fe oxide layer derived from the metal constituting the soft magnetic metal ribbon, a powder of a non-magnetic and insulating metal oxide is interposed between the soft magnetic metal ribbons, and the wound magnetic core is impregnated with a resin and has an occupancy rate of 65% or more and 75% or less.

[0017] According to another embodiment of the present invention, it is preferable that the Fe oxide layer contains hematite (Fe2O3).

[0018] According to another embodiment of the present invention, it is preferable that the absolute value of the impedance change rate at a frequency of 1 MHz obtained by the following formula (2) is 2% or less. Impedance change rate (%) = {(impedance before impulse test - impedance after impulse test) / impedance before impulse test} × 100 ··· (2)

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a method for manufacturing a wound magnetic core and a wound magnetic core that can improve the insulation between the ribbons of a wound magnetic core formed by winding a soft magnetic metal ribbon into an annular wound body.

Brief Description of the Drawings

[0020] [Figure 1]This is a flowchart of the manufacturing process for a wound magnetic core according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of a powder coating apparatus used in the manufacture of a wound magnetic core according to one embodiment of the present invention. [Figure 3a] This is a schematic cross-sectional view of a soft magnetic metal strip with metal oxide powder adhering to its surface. [Figure 3b] This is a schematic cross-sectional view of a soft magnetic metal strip showing other deposition states of metal oxide powder. [Figure 4] This is an enlarged schematic diagram of a cross-section perpendicular to the winding axis, showing the state between the thin bands of the rolled material. [Figure 5] This figure shows the relationship between the impedance change rate and frequency, obtained from the impedance of a wound magnetic core before and after an impulse test. [Figure 6] This figure shows the relationship between the amount of metal oxide powder attached (MgO weight ratio) and the rate of change in impedance before and after the impulse test. [Figure 7] This is a circuit diagram used to explain impulse testing. [Modes for carrying out the invention]

[0021] The following describes specific embodiments of the present invention, but the present invention is not limited thereto.

[0022] Figure 1 is a flowchart of the manufacturing process in the method for manufacturing a wound magnetic core of the present invention. As shown in Figure 1, in the first step, a soft magnetic metal thin strip with an amorphous structure is used as the material, and a non-magnetic, insulating metal oxide powder is attached to the surface of the material (powder coating step S1). In the second step, the soft magnetic metal thin strip with an amorphous structure obtained in the first step is wound in a ring shape to form a wound body of a predetermined shape and size, so that the metal oxide powder is interposed between the thin strips (winding step S2). In the third step, the wound body is heat-treated in a non-oxidizing atmosphere to precipitate nanocrystals on the soft magnetic metal thin strip with an amorphous structure, or to relieve stress on the soft magnetic metal thin strip with an amorphous structure (heat treatment step S3). In the fourth step, an oxide film formation treatment is performed in an oxidizing atmosphere adjusted to a temperature lower than the heat treatment temperature in the heat treatment step S3, oxidizing the surface of the soft magnetic metal thin strip (oxide film formation step S4). In the fifth step, resin is impregnated between the thin strips of the resulting winding, and the resin is cured to fix the metal oxide powder and form a winding magnetic core (resin impregnation step S5).

[0023] The winding core of this embodiment is a winding core in which a thin strip of soft magnetic metal is wound. The thin strip of soft magnetic metal has an amorphous or nanocrystalline structure. A metal oxide layer derived from the metal constituting the thin strip of soft magnetic metal is formed on the surface of the thin strip of soft magnetic metal. A non-magnetic, insulating metal oxide powder is fixed between the thin strips of soft magnetic metal with resin. Each step will be described in detail below.

[0024] (1) Materials In this embodiment, the amorphous soft magnetic metal thin strip used as the material is preferably made of a soft magnetic alloy mainly composed of Fe. Typically, it is a soft magnetic alloy with an Fe content of 65 atomic percent or more, and there are no particular restrictions on the composition of the soft magnetic alloy other than that Fe is the main component. Depending on the balance with other non-ferrous metals, it is preferable to contain 77.5% or more Fe in atomic percent, and more preferably 78.0% or more, as this affects magnetic properties such as saturation magnetization. As the amorphous soft magnetic metal thin strip used as the material, an amorphous soft magnetic metal thin strip that can form a nanocrystalline soft magnetic metal thin strip by heat treatment can be used.

[0025] The soft magnetic alloy strips that constitute the coiled magnetic core have either an amorphous or nanocrystalline structure. Distinguishing between an amorphous or nanocrystalline structure of a soft magnetic metal strip can be easily determined by X-ray diffraction, specifically by observing the X-ray diffraction spectrum. For example, the X-ray diffraction spectrum of a nanocrystalline strip shows a diffraction peak in the crystalline phase (around diffraction angle 2θ = 45°), while the X-ray diffraction spectrum of an amorphous strip shows a halo pattern indicating the amorphous phase. The diffraction peak around diffraction angle 2θ = 45° is the (110) diffraction peak of a bcc structure Fe crystal or FeSi crystal. The diffraction peak angle contains errors, such as variations in elemental solid solution relative to the JCPDS card data. Therefore, a diffraction peak angle (2θ) that is very close to that of each JCPDS card is considered "nearby."

[0026] Amorphous structures lack a crystalline structure. Nanocrystalline structures, on the other hand, generally have crystal grains with an average grain size of 100 nm or less. Nanocrystalline structures are typically structures that crystallize from an amorphous phase, starting from clusters of Cu or other non-ferrous metals that act as crystallization nuclei. Nanocrystalline structures consist of Fe crystals or FeSi crystals with an average grain size of, for example, 30 nm or less, and the nanocrystals are randomly oriented and dispersed within the amorphous phase. Nanocrystalline structures can be obtained by heat-treating a soft magnetic metal thin strip with an amorphous structure that is capable of nanocrystallization.

[0027] As the soft magnetic metal thin strip with a nanocrystalline structure, for example, Fe-Si-M1-B-Cu soft magnetic alloys or Fe-M2-B soft magnetic alloys can be used, and other soft magnetic alloys may also be used. M1 is preferably one or more selected from the group consisting of Nb, Ti, Zr, Hf, V, Ta, and Mo. Also, M2 is preferably one or more selected from the group consisting of Nb, Cu, Zr, and Hf. As Fe-Si-M1-B-Cu soft magnetic alloys, Finemet (registered trademark) from Hitachi Metals, Ltd. and VITROPERM (registered trademark) from VACUUMSCHMELZE GmbH & Co.KG. are known and can be used. As an Fe-M2-B soft magnetic alloy, NANOPERM (registered trademark) from MAGNETEC Gesellschaft fur Magnettechnologie mbH is known and can be used.

[0028] As an amorphous soft magnetic metal thin strip, for example, an Fe-Si-B type soft magnetic alloy can be used. METGLAS® 2605SA1 from METGLAS, Inc. is a known Fe-Si-B type soft magnetic alloy that can be used.

[0029] Soft magnetic metal strips are obtained by a liquid quenching method, which involves rapidly cooling and solidifying the molten alloy. Generally, 10 6 The soft magnetic metal strips are obtained by known liquid quenching methods, such as the single-roll method or the double-roll method, which achieve cooling rates of approximately °C / second or higher. These methods allow for the formation of long, continuous strips of soft magnetic metal.

[0030] Soft magnetic metal strips of a width and thickness commonly available on the market can be used. Alternatively, soft magnetic metal strips of a width obtained by slitting from soft magnetic metal strips of a width commonly available on the market may be used. Soft magnetic metal strips of a width of, for example, 200 to 300 mm can be used. Furthermore, the thickness of the soft magnetic metal strip is 10 μm or more, preferably several hundred μm or less, and from the viewpoint of amorphous formation ability, a thickness of 50 μm or less is more preferable.

[0031] (2) Powder coating process S1 A thin strip of soft magnetic metal adjusted to a predetermined width and length, and a powder of a non-magnetic, insulating metal oxide are prepared. The metal oxide powder is preferably magnesium oxide (MgO), titanium oxide (TiO2), or aluminum oxide (Al2O3).

[0032] A metal oxide powder is uniformly attached to the surface of a soft magnetic metal strip. To obtain a predetermined spacing between strips while obtaining the packing factor of the wound magnetic core, the average particle size of the metal oxide powder (median diameter d50 in the cumulative particle size distribution) is preferably 0.5 μm or more and 1.0 μm or less. Here, the metal oxide powder is a value measured by a laser diffraction scattering particle size distribution analyzer. Furthermore, considering the effect of stress on the strips, it is undesirable for coarse powder to be interposed between the strips. The maximum particle size of the powder is preferably 7 μm or less. Here, the maximum particle size represents the 95 volume% particle size (d95).

[0033] A suspension is formed by dispersing metal oxide powder in a solvent such as toluene, isopropyl alcohol, or ethanol. By adjusting the concentration of the suspension, the amount of metal oxide powder adhering to the soft magnetic metal strip can be adjusted. The specific values ​​will vary depending on the tension applied to the soft magnetic metal strip when it is wound, but if the metal oxide is magnesium oxide (MgO), it is preferable to contain 30 to 200 g of MgO per 1 kg of solvent in order to achieve a core packing coefficient of 65% or more. A suspension adjusted to the predetermined powder concentration is prepared and applied to the surface of the soft magnetic metal strip.

[0034] Figure 2 shows a schematic diagram of a powder coating apparatus for coating a metal oxide powder by immersing a soft magnetic metal strip in a suspension. The illustrated apparatus uses a reel-shaped soft magnetic metal strip 100. The end of the soft magnetic metal strip 100 is pulled out and immersed in a container 150 containing a suspension 120. Then the soft magnetic metal strip 100 is pulled out of the suspension 120. The soft magnetic metal strip 100 is then passed through a rod 145 that scrapes off excess suspension 120 from the roll surface side of the soft magnetic metal strip 100 (the surface that contacts the cooling roll when obtaining the soft magnetic metal strip 100 using the single-roll method), and then through a rotating scraper 140. This controls the suspension 120 on the free surface side of the soft magnetic metal strip 100 (the surface that does not contact the cooling roll when obtaining the soft magnetic metal strip 100 using the single-roll method). After that, the soft magnetic metal strip 100 is passed through a drying oven 130 adjusted to a predetermined temperature. Subsequently, the soft magnetic metal strip 100, on which a predetermined amount of metal oxide powder has been coated on its surface, is wound into a reel. In addition to immersing it in the suspension 120, the suspension 120 may also be applied to the surface of the soft magnetic metal strip 100 using a roll coater or by spraying it.

[0035] Figures 3a and 3b show schematic cross-sectional diagrams of a soft magnetic metal strip with metal oxide powder adhering to its surface. The soft magnetic metal strip may have depressions or protrusions, but these are not shown in Figures 3a and 3b. As shown in Figure 3a, after passing through the rod 145, the soft magnetic metal strip 10 has metal oxide powder 20 almost uniformly adhering to the entire surface of one surface (free surface, upper surface in the figure), while most of the metal oxide powder 20 has been removed from the other surface (rolled surface, lower surface in the figure).

[0036] Furthermore, after controlling the suspension 120 on one side of the soft magnetic metal strip 10 with the scraper 140, as shown in Figure 3b, the adhesion of metal oxide powder 20 to one surface (free surface, top surface in the figure) of the soft magnetic metal strip 10 decreases. Depending on the metal oxide powder used, the amount of metal oxide powder 20 adhering is preferably 0.1% to 1.2% by weight ratio of the metal oxide. The amount of metal oxide powder 20 adhering is preferably 0.2% or more, and more preferably 0.3% or more. Also, the amount of metal oxide powder 20 adhering is preferably 1.1% or less, and more preferably 1.0% or less. If the metal oxide is MgO, the amount of metal oxide powder 20 adhering is 0.1 × 10⁻⁶ per unit area. -3 kg / m 2 The above 1.5 × 10 -3 kg / m 2 The following is also preferable.

[0037] The metal oxide powder 20 adhering to the surface of the soft magnetic metal strip 10 easily falls off with just a light rub of a finger. Therefore, during the transport of the soft magnetic metal strip 10 after drying within the machinery, the metal oxide powder 20 tends to adhere to or accumulate on parts that come into contact with the soft magnetic metal strip 10, particularly parts such as transport rollers. As a result, problems such as unstable transport may occur. In addition, due to the detachment of the metal oxide powder 20, the amount of metal oxide powder 20 adhering to the soft magnetic metal strip 10 differs between the beginning and end of powder application. As a result, it may be difficult to uniformly adhere the metal oxide powder 20.

[0038] Therefore, it is preferable to minimize the adhesion of metal oxide powder 20 to one surface (for example, the roll surface) of the soft magnetic metal strip 10 that comes into contact with the machine's components. Alternatively, one surface of the soft magnetic metal strip 10 may be free of metal oxide powder 20.

[0039] Furthermore, after applying the metal oxide powder 20, removing the metal oxide powder 20 from one surface of the soft magnetic metal strip 10 can reduce the amount of metal oxide powder 20 adhering to it, or it can be made possible to have no metal oxide powder 20 adhering to it at all.

[0040] Furthermore, when obtaining soft magnetic metal strips using the single-roll method, it is known that the surface morphology of the soft magnetic metal strip differs between the side in contact with the cooling roll (roll surface) and the side not in contact with the cooling roll (free surface). On the roll surface, depressions of several μm to tens of μm in depth are likely to occur due to scratches on the cooling roll, adhesion of foreign matter, or entrapment of atmospheric gas during casting. On the free surface, protrusions with a height of 10 μm or less are likely to occur. Since these protrusions affect short circuits between strips, considering the surface morphology of the soft magnetic metal strip, it is preferable to adhere the metal oxide powder 20 to at least the free surface of the soft magnetic metal strip.

[0041] (3) Rolling process S2 A reel-shaped soft magnetic metal strip with metal oxide powder attached to its surface is attached to a rewinding device. The end of the soft magnetic metal strip is pulled out and tightly wound around a support (spool) while tension is applied, forming an annular winding body in which multiple layers of soft magnetic metal strips are stacked in the winding diameter direction. The winding speed of the soft magnetic metal strip is preferably 10 m / min to 500 m / min. The dimensions of the winding body vary, but for example, an inner diameter of 5 mm to 140 mm and an outer diameter of 20 mm to 200 mm are preferred.

[0042] The support was removed from the winding body, and the beginning and ending ends of the soft magnetic metal strip were spot-welded to secure them, forming the final winding body. The metal oxide powder makes the soft magnetic metal strip slippery, resulting in better winding tightness and easier adjustment of tension during winding, thus improving workability. As a result, it is possible to form a winding body with small variations in the spacing between the strips from the inner circumference to the outer circumference.

[0043] Figure 4 is a schematic diagram of a cross-section perpendicular to the winding axis, showing the state between the thin strips of the winding. An air layer 30 with metal oxide powder 20 interposed between the soft magnetic metal thin strips 10 is formed. Although not shown in Figure 4, of the metal oxide powder 20 between the thin strips, the larger particles are sandwiched between the strips, while many particles remain attached to one surface of the soft magnetic metal thin strips 10.

[0044] The spacing between the thin strips can be adjusted by the tension applied to the soft magnetic metal strip 10 when it is wound, the surface irregularities of the soft magnetic metal strip 10, or the thickness of the metal oxide powder 20 on the surface of the soft magnetic metal strip 10. However, as the spacing between the thin strips widens, the packing density of the wound magnetic core decreases, and the desired magnetic properties may not be obtained. Furthermore, considering the supply of oxygen to the spaces between the thin strips when forming an oxide film on the surface of the soft magnetic metal strip, as described later, it is preferable to appropriately select the conditions for forming the metal oxide powder 20 and the wound body so that the packing density of the wound magnetic core is between 65% and 75%, or so that the spacing between the thin strips is at least 0.2 μm even in the narrowest areas.

[0045] (4) Heat treatment process S3 Next, the coil is heat-treated at a predetermined temperature in a non-oxidizing atmosphere to relieve the stress applied during coil formation or to induce nanocrystallization and exhibit the desired magnetic properties. The non-oxidizing atmosphere can be any inert gas atmosphere such as N2 or Ar with an oxygen concentration of 100 ppm or less.

[0046] Depending on the alloy composition, if the soft magnetic metal strip has an amorphous structure, it is preferable to relieve stress by heat treatment at a temperature of 250°C or higher in a non-oxidizing atmosphere. Since crystallization will begin if the temperature of the soft magnetic metal strip is raised too high, it is preferable that the heat treatment temperature be 10°C to 150°C lower than the crystallization temperature of the alloy, and typically 400°C or lower. For example, when using METGLAS® 2605SA1, a heat treatment temperature of 340°C to 400°C is preferable. The heat treatment temperature is the highest temperature reached by heating. The heat treatment temperature is also the holding temperature if this temperature is held for a predetermined time.

[0047] Furthermore, when forming a soft magnetic metal thin strip having a nanocrystalline structure by depositing nanocrystals onto it, it is preferable to perform heat treatment at a temperature above the crystallization temperature of the soft magnetic alloy constituting the soft magnetic metal thin strip. If the temperature is raised too high, crystalline phases such as Fe2B, which have high crystalline magnetic anisotropy and degrade the soft magnetic properties, may precipitate. Therefore, the heat treatment temperature should be above the crystallization temperature of the alloy and preferably in the range of 500°C to 620°C, more preferably 540°C to 590°C.

[0048] The nanocrystalline structure is a structure in which nanocrystalline grains of Fe crystals or FeSi crystals are randomly oriented and dispersed in an amorphous phase. The average grain size of the nanocrystalline grains is preferably 30 nm or less, and more preferably 20 nm or less. The average grain size of the nanocrystalline grains is the size of the crystallite determined by Scherrer's formula using the difference from the peak width of bccFe(Si) [diffraction plane (110)] in the X-ray diffraction spectrum.

[0049] Furthermore, it is preferable that nanocrystalline grains occupy 30% or more by volume in the nanocrystalline structure, and more preferably 50% or more by volume. The volume fraction of nanocrystalline grains in the nanocrystalline structure is calculated by the line segment method. It is known that when an amorphous soft magnetic metal thin strip is crystallized by heat treatment to form a nanocrystalline structure, a volume shrinkage of about 1% occurs in the soft magnetic metal thin strip. Because metal oxide powder is interposed between the thin strips, the soft magnetic metal thin strip is more likely to slip in the circumferential direction of winding, thus suppressing the stress applied to the soft magnetic metal thin strip due to the tightening of the winding due to shrinkage.

[0050] The heat treatment time is preferably between 5 minutes and 14 hours, regardless of whether stress relaxation or nanocrystallization is performed. The heat treatment time is the time the material is held at the highest temperature reached. Any heating furnace capable of controlling the temperature up to approximately 620°C in a non-oxidizing atmosphere can be used without any particular problems. A heating furnace capable of controlling the oxygen concentration is even more preferable, as it allows the same heating furnace to be used in the subsequent oxide film formation step S4, enabling continuous processing.

[0051] (5) Oxide film formation step S4 After the heat treatment step S3, the rolled material is subjected to an oxide film formation treatment in an oxidizing atmosphere, preferably with an oxygen concentration of 1% to 50%, at a temperature of 240°C or higher but lower than the heat treatment temperature (maximum temperature reached) in the heat treatment step S3, thereby forming an oxide film on the surface of the soft magnetic metal thin strip. The oxygen concentration in the atmosphere is preferably 50% by volume or less, and the oxidizing atmosphere is more preferably an atmospheric atmosphere.

[0052] The rolled material includes an air layer 30 formed by interposing metal oxide powder 20 between soft magnetic metal strips 10. This oxide film formation treatment supplies oxygen to the air layer 30. As a result, an oxide film is formed not only on the surface of the soft magnetic metal strips that appear on the outer surface of the rolled material, but also on the surface of the rolled soft magnetic metal strips.

[0053] The thickness of the oxide film is preferably such that it improves insulation between thin bands and suppresses the deterioration of magnetic properties as a wound core, exceeding the thickness of the oxide film due to natural oxidation (approximately 10-20 nm) and being tens to hundreds of nm. The thickness of the oxide film can be quantified by observation at 50k to 200k magnification using a transmission electron microscope (TEM). Alternatively, the thickness of the oxide film may be quantified using methods such as X-ray photoelectron spectroscopy (XPS).

[0054] Furthermore, the oxide film is a metal oxide layer derived from the metal constituting the soft magnetic metal thin strip, and is preferably hematite (Fe2O3) or magnetite (Fe3O4). The oxide film may also contain wustite (FeO). However, since wustite has lower resistance compared to hematite and magnetite, it is preferable that the wustite content be small.

[0055] The oxides can be identified using analytical techniques such as Raman spectroscopy. After the oxide film is formed, the metal oxide powder between the thin strips remains attached to the surface of the soft magnetic metal strip, similar to the process during winding. If the soft magnetic metal strip has a nanocrystalline structure, it is preferable to set the oxide film formation temperature in the range of 240°C to 350°C. If the soft magnetic metal strip has an amorphous structure, it is preferable to set the heat treatment temperature in the range of 240°C to 300°C.

[0056] (6) Resin impregnation process S5 After the oxide film formation step S4, an insulating resin is impregnated between the surface of the obtained winding and the thin strips of the soft magnetic metal, and the insulating resin is cured to form a winding magnetic core. By bonding the thin strips with the insulating resin, the magnetic alloy thin strips become an integrated structure, preventing the winding of the soft magnetic metal thin strips from unraveling due to external forces, etc. This allows the winding state to be maintained. In addition, bonding the thin strips with the insulating resin also fixes the metal oxide powder between the thin strips and contributes to insulation between the thin strips. It is preferable that the surface of the soft magnetic metal thin strips be covered evenly with the insulating resin. In the spaces between the thin strips of the winding, it is preferable that at least 3% or more of the surface of the soft magnetic metal thin strips is covered with the insulating resin.

[0057] As the insulating resin, it is preferable to use an epoxy-based or polyimide-based thermosetting resin. Methods for impregnating the thin bands of the winding with the insulating resin include immersing the winding in a bath of insulating resin, or applying the insulating resin or its precursor to the sides of the winding that are visible in the direction of the winding axis. Furthermore, methods such as vacuum impregnation may be used to promote the impregnation of the resin between the thin bands of the winding. To cure the thermosetting resin or its precursor applied to the surface of the winding and between the thin bands, a curing treatment is performed at a predetermined temperature. The curing temperature depends on the resin used, but for epoxy resins, a temperature of 20 to 180°C for 1 minute to 24 hours is preferable. [Examples]

[0058] (Example 1) As the soft magnetic metal ribbon of the material, a soft magnetic metal ribbon having an amorphous structure composed of a soft magnetic alloy mainly composed of Fe and containing Si, B, and trace amounts of Cu and Nb, and capable of precipitating nanocrystals by heat treatment, Hitachi Metals, Ltd.'s Finemet (registered trademark) FT-3 was prepared. The soft magnetic metal ribbon was long, and the thickness was 14 μm and the width was 20 mm were used. The density of the soft magnetic metal ribbon is 7.3×10 3 kg / m 3 . By measurement with a differential scanning calorimeter (DSC), it was confirmed that the crystallization start temperature of this alloy was 470°C.

[0059] In the powder coating step S1, a powder of metal oxide was adhered to the surface of the soft magnetic metal ribbon. As the powder of metal oxide that is non-magnetic and insulating, a powder of magnesium oxide (MgO) with an average particle size (d50) of 0.7 μm was prepared. The density of magnesium oxide is 3.6×10 3 kg / m 3 . Using isopropyl alcohol as a solvent, 100 g of magnesium oxide powder was dispersed in 1 kg of the solvent to prepare a suspension 120. The suspension 120 was transferred to the container of the powder coating apparatus shown in Fig. 2, and while stirring the suspension 120 to prevent aggregation and precipitation of magnesium oxide in the suspension 120, the soft magnetic metal ribbon 100 was immersed in the suspension for 0.5 seconds. The soft magnetic metal ribbon 100 was pulled up from the suspension 120, passed through a rod 145 for scraping off the excess suspension 120 on the roll surface side of the soft magnetic metal ribbon, and through a rotating scraper 140 to drop the excess suspension 120 on the surface of the soft magnetic metal ribbon and control the suspension 120 on the free surface side, After that, the soft magnetic metal ribbon with the suspension 120 was passed through a drying furnace 130 adjusted to a temperature of 80°C to obtain a soft magnetic metal ribbon 100 with a predetermined amount of MgO powder adhered to the surface. The adhesion amount of MgO powder to the surface of the soft magnetic metal ribbon was calculated as the MgO weight ratio (weight ratio of metal oxide) by the following formula. The MgO weight ratio was 0.73%. MgO weight ratio = (weight of MgO adhered to the soft magnetic metal ribbon / weight of the soft magnetic metal ribbon) × 100 (%) The weight of the soft magnetic metal strip is the weight A of one reel of soft magnetic metal strip before the powder coating process S1, and the weight of MgO attached to the soft magnetic metal strip is the weight B of one reel of soft magnetic metal strip after the powder coating process S1, minus the aforementioned weight A.

[0060] In the winding process S2, a winding of a soft magnetic metal strip with metal oxide powder attached to its surface was formed. The soft magnetic metal strip obtained in the powder coating process S1 was attached to a rewinding device, the end of the soft magnetic metal strip was pulled out and tightly wound around a stainless steel support, winding the soft magnetic metal strip in multiple layers in the winding diameter direction. The support was removed from the winding body, and the beginning and end ends of the soft magnetic metal strip were spot welded to fix them, forming a winding body with an inner diameter of 33 mm and an outer diameter of 50 mm.

[0061] In heat treatment step S3, the rolled material was heat-treated to perform nanocrystallization, transforming the amorphous structure of the soft magnetic metal thin strip into a nanocrystalline structure. The rolled material was heat-treated in an electric furnace under nitrogen atmosphere conditions (temperature profile) of a maximum temperature of 580°C and a holding time of 20 minutes, transforming the amorphous structure of the soft magnetic metal thin strip into a nanocrystalline structure.

[0062] Samples obtained from soft magnetic metal thin strips with nanocrystalline structures were observed using a transmission electron microscope (TEM) at a magnification of 20,000x. An arbitrary straight line of length Lt was drawn on the image obtained with the transmission electron microscope. The total length Lc of the portion where the line intersects with nanocrystalline grains of a size observable by the naked eye was calculated, and the proportion of crystal grains along the line, LL = Lc / Lt, was calculated. This operation was repeated five times, and the volume fraction VL of the nanocrystalline grains was obtained by averaging LL. Here, the volume fraction VL = Vc / Vt (where Vc is the sum of the volumes of the nanocrystalline grains and Vt is the volume of the sample) is approximately VL ≈ Lc 3 / Lt 3 =LL 3 This was treated as an approximation. The soft magnetic metal thin strip had an average grain size of 10 nm as determined by X-ray diffraction of nanocrystalline grains, and the volume fraction VL of nanocrystalline grains in the nanocrystalline structure was 80 volume%.

[0063] In the oxide film formation step S4, the rolled material from the heat treatment step S3 was heat-treated to form an oxide film on the surface of the soft magnetic metal strip. The rolled material, after the nanocrystallization heat treatment was completed, was heat-treated in an electric furnace in air at a maximum temperature of 280°C and a holding time of 2 hours (temperature profile) to form an oxide film on the surface of the soft magnetic metal strip. A portion of the soft magnetic metal strip was peeled off from the outer circumference of the rolled material and observed in cross-section using Raman spectroscopy and transmission electron microscopy (TEM). The results showed that the oxide film formed on the surface of the obtained rolled material was mainly hematite (Fe2O3). Furthermore, it was found that a thicker oxide film had been formed than the one on the surface of the soft magnetic metal strip before the metal oxide powder was attached.

[0064] The coiled core, after the oxide film formation process S4, was impregnated with resin. The coiled core with the oxide film formed was immersed for 1 minute in an impregnation solution prepared by diluting epoxy resin with acetone to a concentration of 5% to 30%, and then cured in a constant temperature bath adjusted to 150°C to obtain a coiled magnetic core with a packing ratio of 70%. The packing ratio was calculated as follows. Occupancy factor=[(We / ρ) / {(OD 2 -ID 2 ) × HT × π / 4}] × 100 (%) Here, We: Roll weight after oxide film formation (g) ρ: Density of soft magnetic metal thin strip (g / cm³) 3 ) OD: Outer diameter of the roll after oxide film formation (cm) ID: Inner diameter of the roll after oxide film formation (cm) HT: This is the height (cm) of the rolled material after the oxide film has formed.

[0065] An impulse test was performed on the wound magnetic core obtained after the resin impregnation process S5 using the circuit shown in Figure 7, under the conditions of a peak voltage of 1.6kV and a voltage application width of 200nsec. The impedance was measured before and after the test, and the insulation properties of the wound magnetic core were evaluated based on the change in impedance. The impedance was measured by passing a one-turn coil through the inner diameter of the wound magnetic core and evaluating the impedance at frequencies from 1kHz to 10MHz using an impedance analyzer HP4194A, and the rate of change in impedance before and after the test was calculated using the following formula. Impedance change rate = {(Impedance before impulse test - Impedance after impulse test) / Impedance before impulse test} × 100 (%)

[0066] Furthermore, the DC resistance Rdc of the inner and outer diameter surfaces of the winding core used in the impulse test was evaluated before and after the impulse test using a HIOKI 3227 DC resistance meter. The DC resistance Rdc before the test was 161Ω, and the DC resistance Rdc after the test was 81Ω.

[0067] (Comparative Example 1) A wound magnetic core was fabricated using the same procedure and conditions as in Example 1, except that no metal oxide powder was attached to the surface of the soft magnetic metal strip, and no oxide film was formed on the surface of the soft magnetic metal strip. The packing factor was 73.8%. An impulse test was performed on the obtained wound magnetic core, and the impedance change rate and DC resistance Rdc before and after the test were evaluated. The DC resistance Rdc before the test was 34Ω, and the DC resistance Rdc after the test was 1.7Ω.

[0068] (Comparative Example 2) A wound magnetic core was fabricated using the same procedure and conditions as in Example 1, except that metal oxide powder was not attached to the surface of the soft magnetic metal strip. The packing factor was 73.7%. An impulse test was also performed on the obtained wound magnetic core to evaluate the impedance change rate and DC resistance Rdc before and after the test. The DC resistance Rdc before the test was 92Ω, and the DC resistance Rdc after the test was 2.1Ω.

[0069] (Comparative Example 3) A wound magnetic core was fabricated using the same procedure and conditions as in Example 1, except that no oxide film was formed on the surface of the soft magnetic metal strip. The packing factor was 72.8%. An impulse test was performed on the obtained wound magnetic core to evaluate the impedance change rate and DC resistance Rdc before and after the test. The DC resistance Rdc before the test was 105Ω, and the DC resistance Rdc after the test was 4.4Ω.

[0070] Figure 5 shows the relationship between the impedance change rate calculated from the impedance before and after the impulse test and the frequency. Compared to the wound cores of Comparative Examples 1 to 3, the wound core of Example 1 had a higher DC resistance Rdc before and after the test, and the change in impedance in the high-frequency range was suppressed.

[0071] (Examples 2-6) A wound magnetic core was fabricated in the same manner as in Example 1, except that the amount of metal oxide powder adhering to the soft magnetic metal strip was adjusted by adjusting the concentration of suspension 120. An impulse test was performed on the obtained wound magnetic core, and the impedance change rate and DC resistance Rdc at a frequency of 1 MHz before and after the test were evaluated.

[0072] (Comparative Examples 4-8) A wound magnetic core was fabricated using the same procedure and conditions as in Example 1, except that the amount of metal oxide powder adhering to the soft magnetic metal strip was adjusted by adjusting the concentration of suspension 120, and no oxide film was formed on the surface of the soft magnetic metal strip. An impulse test was performed on the obtained wound magnetic core, and the impedance change rate and DC resistance Rdc before and after the test were evaluated.

[0073] Table 1 shows the packing factor, weight change rate before and after oxide film formation, DC resistance Rdc before and after the impulse test, and impedance of the wound magnetic cores for Examples 2-6 and Comparative Examples 4-6. Figure 6 shows the relationship between the amount of metal oxide powder attached (MgO weight ratio) and the change rate of impedance before and after the impulse test.

[0074] [Table 1]

[0075] In all of the wound magnetic cores in Examples 2-6, the change in impedance before and after the impulse test was small, with the absolute value of the impedance change rate being 20% ​​or less. Furthermore, the DC resistance Rdc after the impulse test was also maintained at a high level. Excellent insulation performance can be obtained even with minimal adhesion of metal oxide powder to the surface of the soft magnetic metal thin strip. [Explanation of symbols]

[0076] 10,100 Soft magnetic metal ribbon 20 Metal oxide powders 30 Air layer 120 suspension 130 Drying oven 140 Scrapers 150 containers

Claims

1. A wound magnetic core in which a thin strip of soft magnetic metal is wound, The aforementioned soft magnetic metal thin strip has a nanocrystalline structure, The surface of the soft magnetic metal thin strip has an oxide layer derived from the metal constituting the soft magnetic metal thin strip. Between the thin strips of soft magnetic metal, a non-magnetic and insulating metal oxide powder is interposed, and the strips are impregnated with resin. The occupancy rate is between 65% and 75%. The amount of powder adhering to one surface of the soft magnetic metal strip is less than the amount of powder adhering to the other surface of the soft magnetic metal strip, and the amount of powder adhering is set to be 0.1% or more and 1.2% or less by weight ratio of the metal oxide obtained by the following formula (1). Winding magnetic core. Weight ratio of metal oxide (%) = (Weight of metal oxide attached to soft magnetic metal strip / Weight of soft magnetic metal strip) × 100 ... (1)

2. A wound magnetic core according to claim 1, The amount of adhesion is 0.1 × 10 －３ kg / m ２ The above is 1.5 x 10 －３ kg / m ２ The following is: Winding magnetic core.

3. A wound magnetic core according to claim 1 or 2, The said oxide layer includes an oxide layer of Fe, Winding magnetic core.

4. A wound magnetic core according to claim 1 or 2, The absolute value of the impedance change rate at a frequency of 1 MHz obtained by the following equation (2) is 20% or less. Winding magnetic core. Impedance change rate (%) = {(Impedance before impulse test - Impedance after impulse test) / Impedance before impulse test} × 100 ... (2)

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