Manufacturing method of wound magnetic core and wound magnetic core

Abstract

To provide a manufacturing method of a wound magnetic core capable of improving the insulation between thin bands of a wound magnetic core formed as an annular wound body by winding a soft magnetic metal thin band, and a wound magnetic core.SOLUTION: A non-magnetic and insulating metal oxide powder is adhered to the surface of a soft magnetic metal thin band of an amorphous structure, and is wound in a ring shape to form a winding body in which a metal oxide powder is interposed between the thin bands, and after the winding body is heat-treated in a non-oxidizing atmosphere, the winding body is subjected to oxide film forming treatment in an oxidizing atmosphere adjusted to a temperature lower than that of the heat treatment, the surface of the soft magnetic metal thin band is oxidized, and a resin is impregnated between the thin bands of the winding body and cured, and the metal oxide powder is fixed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a wound core, and to a wound core. [Background technology]

[0002] Coil components such as inductors, transformers, and chokes have been used in a wide variety of applications, including home appliances, industrial equipment, and vehicles. Coil components are composed of a coil laid around a magnetic core, and wound magnetic cores, which are wound bodies of amorphous or crystalline soft magnetic metal ribbons with excellent magnetic properties, are widely used for such magnetic cores.

[0003] The wound core is formed as a ring-shaped winding in which soft magnetic metal ribbons, also called strips or ribbons, are stacked in multiple layers in the radial direction by tightly winding the soft magnetic metal ribbon around a support (spool) while applying tension. In order to prevent the soft magnetic metal ribbon from unwinding from the winding, the ends of the soft magnetic metal ribbon at the beginning and end of the winding are welded and fixed to the winding from which the support has been removed. Alternatively, the ends of the soft magnetic metal ribbon at the end of the winding are welded and fixed to the winding from which the support remains attached. Next, a heat treatment is performed to relieve the stress applied during winding formation or to nano-crystallize the soft magnetic metal ribbon to develop the desired magnetic properties. After the heat treatment, the soft magnetic metal ribbon is treated to maintain the wound state by impregnating it with epoxy resin so that it does not unwind due to changes over time or external forces applied to the winding.

[0004] The thickness of the soft magnetic metal ribbon is very thin, typically 10 μm to several hundred μm. The soft magnetic metal ribbon has a surface with a few μm of unevenness, but is a smooth surface macroscopically. Since the soft magnetic metal ribbon is a good conductor, if the smooth surfaces are shorted and the insulation between the ribbons is insufficient, eddy currents flowing between the ribbons may occur, causing a large power loss in the wound magnetic core. This tendency is particularly noticeable in high frequency applications of over 100 kHz. If the ribbons are not electrically insulated appropriately, the wound magnetic core will not be suitable for use at high frequencies as a coil component.

[0005] Conventionally, in order to obtain high insulation between ribbons, Patent Document 1 proposes forming a wound magnetic core by adhering fine powder made of a nonmagnetic insulating inorganic material to the surface of a magnetic metal ribbon. Patent Document 2 proposes oxidizing the magnetic metal ribbon to form an insulating layer containing iron oxide between 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 Summary of the Invention [Problem to be solved by the invention]

[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. Such coil components are required to ensure that insulation does not break down due to voltage oscillations caused by the surge voltage applied to the coil. Impulse tests are sometimes performed to check the insulation strength of coil components. In impulse tests, a high voltage of the order of kV and a narrow pulse voltage that rises in less than several hundred nanoseconds is applied to both ends of the coil of the coil component.

[0008] When an impulse test is performed, magnetostrictive vibration occurs in the ribbon due to the rapid change in magnetic flux occurring in the wound core. Even if the wound core is configured as in Patent Document 1 and Patent Document 2 to obtain high insulation between the ribbons, it has been found that the insulation between the ribbons may deteriorate, such as causing a short circuit between the ribbons, in the wound core after the impulse test. When surge voltage resistance is required for the coil component, such a coil component is not suitable for use at high frequencies, even if it does not lead to insulation breakdown.

[0009] To obtain high insulation between the ribbons, a thicker layer of fine powder made of insulating inorganic material may be attached to the ribbon, or a thicker insulating layer containing iron oxide may be formed on the ribbon to widen the gap between the ribbons. However, this may result in a decrease in the space factor (also called packing factor) of the wound core, leading to an increase in the size of the wound core and thus making it impossible to satisfy the dimensional standards of the coil component. In addition, even if a wound core is constructed to the specified dimensions, there are cases in which the desired magnetic properties cannot be obtained.

[0010] Therefore, an object of the present invention is to provide a manufacturing method for a wound core that can improve insulation between thin ribbons in a wound core formed by winding a soft magnetic metal thin ribbon into an annular winding, and to provide a wound core. [Means for solving the problem]

[0011] According to one embodiment of the present invention, it is possible to provide a method for manufacturing a wound magnetic core, comprising: a first step of adhering nonmagnetic and insulating metal oxide powder to a surface of a soft magnetic metal ribbon having an amorphous structure; after the first step, a second step of winding the soft magnetic metal ribbon into a ring shape to obtain a winding having metal oxide powder between the ribbons; a third step of heat treating the winding in a non-oxidizing atmosphere; after the third step, a fourth step of performing an oxide film formation treatment on the winding 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 ribbon; and after the fourth step, a fifth step of impregnating resin between the ribbons of the winding and hardening it.

[0012] According to one embodiment of the present invention, the third step is preferably a heat treatment A for precipitating nanocrystals in the soft magnetic metal ribbon having an amorphous structure, or a heat treatment B for stress-relaxing the soft magnetic metal ribbon having an amorphous structure.

[0013] According to one aspect of the present invention, the temperature of the heat treatment in the third step is preferably 450° C. or more and 620° C. or less in the heat treatment A, and 250° C. or more and 400° C. or less in the heat treatment B.

[0014] According to one embodiment of the present invention, the amount of the metal oxide powder adhered in the first step is preferably 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 attached to soft magnetic metal ribbon / weight of soft magnetic metal ribbon) × 100 (1)

[0015] According to one aspect of the present invention, the oxide film forming treatment in the fourth step is preferably 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 aspect of the present invention, it is possible to provide a wound core in which a soft magnetic metal ribbon is wound, the soft magnetic metal ribbon having an amorphous structure or a nanocrystalline structure, a surface of the soft magnetic metal ribbon having an Fe oxide layer derived from a metal constituting the soft magnetic metal ribbon, nonmagnetic and insulating metal oxide powder being interposed between the soft magnetic metal ribbons, and impregnated with resin, and the wound core having a space factor of 65% or more and 75% or less.

[0017] According to another aspect of the present invention, the Fe oxide layer preferably includes hematite (Fe2O3).

[0018] According to another aspect 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 20% or less. Impedance change rate (%) = {(impedance before impulse test – impedance after impulse test) / impedance before impulse test} × 100 (2) Effect of the Invention

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

[0020] [Figure 1]4 is a flowchart of a manufacturing process for a wound core according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a powder coating apparatus used to manufacture a wound core according to one embodiment of the present invention. [Figure 3a] 1 is a schematic cross-sectional view of a soft magnetic metal ribbon having metal oxide powder attached to its surface. [Figure 3b] 10 is a schematic cross-sectional view of a soft magnetic metal ribbon showing another adhesion state of metal oxide powder. FIG. [Figure 4] FIG. 2 is an enlarged schematic view of a cross section perpendicular to the winding axis, showing the state between the thin ribbons of the winding body. [Diagram 5] FIG. 13 is a diagram showing the relationship between the impedance change rate obtained from the impedance before and after an impulse test of a wound magnetic core and frequency. [Figure 6] FIG. 1 is a graph showing the relationship between the amount of metal oxide powder attached (MgO weight ratio) and the rate of change in impedance before and after an impulse test. [Figure 7] FIG. 1 is a circuit diagram for explaining an impulse test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

[0022] FIG. 1 is a flow chart of the manufacturing process of the wound magnetic core manufacturing method of the present invention. As shown in FIG. 1, in the first step, a soft magnetic metal ribbon with an amorphous structure is used as a material, and a powder of a nonmagnetic and insulating metal oxide is attached to the surface of the material (powder application step S1). In the second step, the soft magnetic metal ribbon with an amorphous structure obtained in the first step is wound into a ring shape to obtain a wound body of a predetermined shape and size, with the powder of the metal oxide being interposed between the ribbons (winding step S2). In the third step, the wound body is heat-treated in a non-oxidizing atmosphere to precipitate nanocrystals in the soft magnetic metal ribbon with an amorphous structure, or to relax the stress of the soft magnetic metal ribbon with an amorphous structure (heat treatment step S3). In the fourth step, an oxide film formation process is performed in an oxidizing atmosphere adjusted to a temperature lower than the heat treatment temperature in the heat treatment step S3, and the surface of the soft magnetic metal ribbon is oxidized (oxide film formation step S4). In the fifth step, resin is impregnated between the thin ribbons of the obtained wound body, and the resin is hardened to fix the metal oxide powder and form a wound magnetic core (resin impregnation step S5).

[0023] The wound core of this embodiment is a wound core in which a soft magnetic metal ribbon is wound. The soft magnetic metal ribbon has an amorphous structure or a nanocrystalline structure. A metal oxide layer derived from the metal constituting the soft magnetic metal ribbon is formed on the surface of the soft magnetic metal ribbon. Nonmagnetic and insulating metal oxide powder is fixed between the soft magnetic metal ribbons with a resin. Each process will be described in detail below.

[0024] (1) Material The amorphous soft magnetic metal ribbon used as the material in this embodiment is preferably made of a soft magnetic alloy mainly composed of Fe. Typically, the soft magnetic alloy contains 65 atomic % or more of Fe, and the composition of the soft magnetic alloy is not particularly limited except that Fe is the main component. Although it depends on the balance with other non-ferrous metals, it is preferable that the soft magnetic alloy contains 77.5 atomic % or more of Fe, more preferably 78.0 atomic % or more, because it affects magnetic properties such as saturation magnetization. As the amorphous soft magnetic metal ribbon used as the material, an amorphous soft magnetic metal ribbon that can be formed into a nanocrystalline soft magnetic metal ribbon by heat treatment can be used.

[0025] The soft magnetic alloy ribbons that make up the wound magnetic core have an amorphous structure or a nanocrystalline structure. Whether the soft magnetic metal ribbon has an amorphous structure or a nanocrystalline structure can be easily identified by the X-ray diffraction spectrum by the X-ray diffraction method. For example, the X-ray diffraction spectrum of a ribbon with a nanocrystalline structure has a diffraction peak in the part indicating the crystalline phase (near the diffraction angle 2θ = 45°), and the X-ray diffraction spectrum of a ribbon with an amorphous structure has a halo pattern indicating the amorphous phase. The diffraction peak near the diffraction angle 2θ = 45° is the (110) diffraction peak of Fe crystal or FeSi crystal with a bcc structure. The diffraction peak angle includes an error, such as fluctuating from the data of the JCPDS card due to solid solution of elements. Therefore, the diffraction peak angle (2θ) that is very close to that of each JCPDS card is considered to be "near".

[0026] Amorphous structures do not have a crystal structure. On the other hand, nanocrystalline structures generally have crystal grains with an average crystal grain size of 100 nm or less. Nanocrystalline structures are structures that are typically crystallized from amorphous phases starting from clusters of Cu or other nonferrous metals that act as nuclei for crystallization. Nanocrystalline structures are Fe crystals or FeSi crystal grains with an average crystal grain size of, for example, 30 nm or less, and are structures in which nanocrystals are randomly oriented and dispersed in the amorphous phase. Nanocrystalline structures are obtained by applying heat treatment to soft magnetic metal ribbons with an amorphous structure that can be nanocrystallized.

[0027] As the soft magnetic metal ribbon having a nanocrystalline structure, for example, a Fe-Si-M1-B-Cu based soft magnetic alloy or a Fe-M2-B based soft magnetic alloy 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 the Fe-Si-M1-B-Cu based soft magnetic alloy, FINEMET (registered trademark) of Hitachi Metals, Ltd. and VITROPERM (registered trademark) of VACUUMSCHMELZE GmbH & Co.KG. are known, and these can be used. As the Fe-M2-B based soft magnetic alloy, NANOPERM (registered trademark) of MAGNETEC Gesellschaft fur Magnettechnologie mbH is known, and this can be used.

[0028] As the soft magnetic metal ribbon having an amorphous structure, for example, a Fe-Si-B based soft magnetic alloy can be used. As an Fe-Si-B based soft magnetic alloy, METGLAS (registered trademark) 2605SA1 by METGLAS, Inc. is known, and this can be used.

[0029] Soft magnetic metal ribbons are obtained by the liquid quenching method, in which the molten alloy is rapidly cooled and solidified. 6 The soft magnetic metal ribbon can be obtained by a known liquid quenching method called a single roll method or a twin roll method, which can obtain a cooling rate of about ° C. / sec or more. By these methods, the soft magnetic metal ribbon can be continuously formed into a long length.

[0030] The soft magnetic metal ribbon may have a width and thickness that are distributed on the market. A soft magnetic metal ribbon having a width slit from a soft magnetic metal ribbon having a width that is distributed on the market may be used. The soft magnetic metal ribbon may have a width of, for example, about 2 to 300 mm. The thickness of the soft magnetic metal ribbon is preferably 10 μm or more and several hundred μm or less, and from the viewpoint of the amorphous forming ability, the soft magnetic metal ribbon is more preferably 50 μm or less.

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

[0032] Metal oxide powder is uniformly applied to the surface of the soft magnetic metal ribbon. In order to obtain a predetermined interval between the ribbons while obtaining the space 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 value of the metal oxide powder is a value measured by a laser diffraction scattering type particle size distribution measuring device. Also, considering the effect of stress on the ribbons, it is not preferable for coarse powder to be present between the ribbons. The maximum particle size of the powder is preferably 7 μm or less. Here, the maximum particle size refers to 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. The amount of metal oxide powder attached to the soft magnetic metal ribbon can be adjusted by adjusting the concentration of the suspension. When the metal oxide is magnesium oxide (MgO), the amount of MgO is preferably 30 to 200 g per kg of solvent in order to achieve a space factor of 65% or more in the wound magnetic core, although the specific value varies depending on the tension applied to the soft magnetic metal ribbon when wound. A suspension adjusted to a predetermined powder concentration is prepared and applied to the surface of the soft magnetic metal ribbon.

[0034] FIG. 2 shows a schematic diagram of a powder coating device that immerses a soft magnetic metal ribbon in a suspension and coats it with metal oxide powder. In the illustrated device, a reel-shaped soft magnetic metal ribbon 100 is used. Then, an end of the soft magnetic metal ribbon 100 is pulled out and immersed in a container 150 containing a suspension 120. After that, the soft magnetic metal ribbon 100 is pulled out from the suspension 120. Then, the soft magnetic metal ribbon 100 is passed through a rod 145 that scrapes off excess suspension 120 on the roll surface side of the soft magnetic metal ribbon 100 (the surface that contacts a cooling roll when the soft magnetic metal ribbon 100 is obtained by a 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 ribbon 100 (the surface that does not contact a cooling roll when the soft magnetic metal ribbon is obtained by a single roll method). Then, the soft magnetic metal ribbon 100 is passed through a drying furnace 130 adjusted to a predetermined temperature. Thereafter, the soft magnetic metal ribbon 100 having a surface coated with a predetermined amount of metal oxide powder is wound up in a reel shape. In addition to immersing the suspension 120, the suspension 120 may be applied to the surface of the soft magnetic metal ribbon 100 by a roll coater or by spraying.

[0035] 3a and 3b are schematic cross-sectional views of a soft magnetic metal ribbon with metal oxide powder attached to its surface. The soft magnetic metal ribbon may have depressions or protrusions, but these are not shown in FIGS. 3a and 3b. As shown in FIG. 3a, the soft magnetic metal ribbon 10 after the rod 145 has passed has metal oxide powder 20 attached almost uniformly to the entire one surface (free surface, upper surface in the figure), and most of the metal oxide powder 20 has been removed from the other surface (roll surface, lower surface in the figure).

[0036] After the suspension 120 on one side of the soft magnetic metal ribbon 10 is controlled by the scraper 140, as shown in FIG. 3b, the amount of metal oxide powder 20 attached to one surface (free surface, upper surface in the figure) of the soft magnetic metal ribbon 10 is reduced. Although it depends on the metal oxide powder used, the amount of metal oxide powder 20 attached is preferably 0.1% or more and 1.2% or less in terms of the weight ratio of the metal oxide. The amount of metal oxide powder 20 attached is preferably 0.2% or more, and more preferably 0.3% or more. The amount of metal oxide powder 20 attached 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 attached is 0.1×10 per unit area. -3 kg / m 2 More than 1.5 x 10 -3 kg / m 2 It is also preferable to have the following:

[0037] The metal oxide powder 20 attached to the surface of the soft magnetic metal ribbon 10 easily falls off when lightly rubbed with a finger. Therefore, when the soft magnetic metal ribbon 10 is dried and transported in a machine device, the metal oxide powder 20 is likely to adhere to or accumulate on parts that come into contact with the soft magnetic metal ribbon 10, particularly parts such as transport rollers. As a result, problems such as unstable transport may occur. In addition, due to the falling off of the metal oxide powder 20, the amount of the metal oxide powder 20 attached to the soft magnetic metal ribbon 10 differs between the start and end of powder application. As a result, it may be difficult to uniformly attach the metal oxide powder 20.

[0038] Therefore, it is preferable to reduce the amount of the metal oxide powder 20 attached to one surface (e.g., roll surface) of the soft magnetic metal ribbon 10 that comes into contact with a mechanical device component. Also, the one surface of the soft magnetic metal ribbon 10 may be in a state where no metal oxide powder 20 is attached.

[0039] After the metal oxide powder 20 is adhered, the metal oxide powder 20 can be removed from one surface of the soft magnetic metal ribbon 10, thereby reducing the amount of adhesion of the metal oxide powder 20 or making it possible to achieve a state in which no metal oxide powder 20 is adhered.

[0040] In addition, when a soft magnetic metal ribbon is obtained by a single roll method, it is known that the surface morphology of the soft magnetic metal ribbon differs between the surface that comes into contact with the chill roll (roll surface) and the surface that does not come into contact with the chill roll (free surface). The roll surface is prone to depressions with a depth of several μm to tens of μm due to scratches on the chill roll, adhesion of foreign matter, or entrapment of atmospheric gas during casting. The free surface is prone to protrusions with a height of tens of μm or less. Since the protrusions affect short circuits between ribbons, it is preferable to adhere the metal oxide powder 20 to at least the free surface of the soft magnetic metal ribbon in consideration of the surface morphology of the soft magnetic metal ribbon.

[0041] (3) Rolling process S2 A reel-shaped soft magnetic metal ribbon with metal oxide powder attached to its surface is attached to a rewinding device, and the end of the soft magnetic metal ribbon is pulled out and tightly wound around a support (spool) while applying tension to form a ring-shaped roll in which the soft magnetic metal ribbon is layered in multiple layers in the radial direction. The winding speed of the soft magnetic metal ribbon is preferably 10 m / min to 500 m / min. The dimensions of the roll vary, but it is preferable that the inner diameter is 5 mm to 140 mm, and the outer diameter is 20 mm to 200 mm, for example.

[0042] The support was removed from the roll, and the start and end of the soft magnetic metal ribbon were spot welded to secure them in place, forming the final roll. The soft magnetic metal ribbon slips due to the metal oxide powder, improving the tightness of the roll and making it easy to adjust the tension when winding, resulting in excellent workability. As a result, a roll with little variation in the spacing between the ribbons from the inner circumference to the outer circumference can be formed.

[0043] Fig. 4 is a schematic diagram of a cross section perpendicular to the winding axis, showing the state between the ribbons of the winding body. Metal oxide powder 20 is interposed between the soft magnetic metal ribbons 10 to form an air layer 30. Although not shown in Fig. 4, among the metal oxide powder 20 between the ribbons, large grain particles are sandwiched between the ribbons, and many particles remain attached to one surface of the soft magnetic metal ribbon 10.

[0044] The interval between the ribbons can be adjusted by the tension applied to the soft magnetic metal ribbon 10 when wound, the uneven state of the surface of the soft magnetic metal ribbon 10, or the thickness of the metal oxide powder 20 on the surface of the soft magnetic metal ribbon 10. However, as the interval between the ribbons increases, the space factor of the wound magnetic core decreases, and the desired magnetic properties may not be obtained. In addition, taking into consideration the supply of oxygen between the ribbons when forming an oxide film on the surface of the soft magnetic metal ribbon described later, it is preferable to appropriately select the metal oxide powder 20 and the conditions for forming the winding so that the space factor of the wound magnetic core is 65% or more and 75% or less, or so that the interval between the ribbons is 0.2 μm or more at the narrowest part.

[0045] (4) Heat treatment process S3 The wound body is then heat-treated at a predetermined temperature in a non-oxidizing atmosphere to relieve the stress applied during winding or to nano-crystallize the material to develop the desired magnetic properties. The non-oxidizing atmosphere may be an inert gas atmosphere such as N2 or Ar with an oxygen concentration of 100 ppm or less.

[0046] Although it depends on the alloy composition, when the soft magnetic metal ribbon has an amorphous structure, it is preferable to perform stress relaxation by heat treatment at a temperature of 250°C or higher in a non-oxidizing atmosphere. If the temperature of the soft magnetic metal ribbon is raised too high, crystallization will begin, so the heat treatment temperature is preferably set to a temperature 10°C to 150°C lower than the crystallization temperature of the alloy, and typically is preferably 400°C or lower. For example, when METGLAS (registered trademark) 2605SA1 is used, the heat treatment temperature is preferably 340°C to 400°C. The heat treatment temperature is the maximum temperature reached by heating. When this temperature is held for a predetermined time, the heat treatment temperature is also the holding temperature.

[0047] In addition, when nanocrystals are precipitated in a soft magnetic metal ribbon to form a soft magnetic metal ribbon having a nanocrystalline structure, it is preferable to perform heat treatment at a temperature equal to or higher than the crystallization temperature of the soft magnetic alloy constituting the soft magnetic metal ribbon. If the temperature is raised too high, a crystalline phase such as Fe2B, which has high crystalline anisotropy and deteriorates soft magnetic properties, may precipitate. Therefore, it is preferable that the heat treatment temperature is equal to or higher than the crystallization temperature of the alloy and is in the range of 500°C to 620°C, 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 the amorphous phase. The average crystal grain size of the nanocrystalline grains is preferably 30 nm or less, and more preferably 20 nm or less. The average crystal grain size of the nanocrystalline grains is the crystallite size calculated by the Scherrer formula using the difference from the peak width of bccFe(Si) [diffraction plane (110)] in the X-ray diffraction spectrum.

[0049] In addition, the nanocrystalline structure preferably contains nanocrystalline grains at 30% by volume or more, and more preferably 50% by volume or more. The volume fraction of the nanocrystalline grains in the nanocrystalline structure is calculated by the line segment method. It is known that when an amorphous soft magnetic metal ribbon is crystallized by heat treatment to form a nanocrystalline structure, the soft magnetic metal ribbon undergoes volumetric shrinkage of about 1%. The presence of metal oxide powder between the ribbons makes the soft magnetic metal ribbon more slippery in the circumferential direction of the winding, so that it is possible to suppress the application of stress to the soft magnetic metal ribbon due to the tightening of the winding body caused by shrinkage.

[0050] The heat treatment time is preferably 5 minutes to 14 hours, regardless of whether stress relaxation or nanocrystallization is performed. The heat treatment time is the time during which the maximum temperature is maintained. Any furnace can be used for the heat treatment without any problem, so long as it can control the temperature up to about 620°C in a non-oxidizing atmosphere. If the furnace can control the oxygen concentration, it is even more preferable to use the same furnace in the next oxide film formation step S4, so that the treatment can be performed continuously.

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

[0052] The winding body has an air layer 30 formed by interposing metal oxide powder 20 between the soft magnetic metal ribbons 10. This oxide film forming process supplies oxygen to the air layer 30. As a result, not only is an oxide film formed on the surface of the soft magnetic metal ribbon that appears on the outer surface of the winding body, but an oxide film is also formed on the surface of the wound soft magnetic metal ribbon.

[0053] The thickness of the oxide film is preferably several tens to several hundreds of nm, which is thick enough to improve the insulation between the ribbons and prevent the deterioration of the magnetic properties as a wound magnetic core, and exceeds the thickness of the oxide film due to natural oxidation (up to about 10 nm). The thickness of the oxide film can be quantified by observing with a transmission electron microscope (TEM) at 50k to 200k magnification. The thickness of the oxide film may also be quantified using a method such as X-ray photoelectron spectroscopy (XPS).

[0054] The oxide coating is a metal oxide layer derived from the metal constituting the soft magnetic metal ribbon, and is preferably hematite (Fe2O3) or magnetite (Fe3O4). The oxide coating may contain wustite (FeO). However, since wustite has a lower resistance than hematite or magnetite, the content of wustite is preferably small.

[0055] The oxides can be identified by analytical methods such as Raman spectroscopy. After the oxide film is formed, the metal oxide powder between the ribbons remains attached to the surface of the soft magnetic metal ribbon, just as when the roll is formed. If the soft magnetic metal ribbon has a nanocrystalline structure, the oxide film formation temperature is preferably set to a range of 240°C to 350°C. If the soft magnetic metal ribbon has an amorphous structure, the heat treatment temperature is preferably set to a range of 240°C to 300°C.

[0056] (6) Resin impregnation process S5 After the oxide film forming step S4, insulating resin is impregnated between the surface of the obtained winding and the thin strips of the soft magnetic metal ribbon, and the insulating resin is hardened to form a wound magnetic core. By bonding the thin strips with insulating resin, the magnetic alloy ribbon is integrated, and the wound soft magnetic metal ribbon is prevented from being unwound by external force or the like. This makes it possible to maintain the wound state. In addition, bonding the thin strips with insulating resin not only fixes the metal oxide powder between the strips, but also contributes to insulation between the strips. Note that the surface of the soft magnetic metal ribbon is preferably evenly covered with insulating resin. Between the thin strips of the winding, at least 3% or more of the surface of the soft magnetic metal ribbon is preferably covered with insulating resin.

[0057] As the insulating resin, it is preferable to use an epoxy-based or polyimide-based thermosetting resin. As a method for impregnating the insulating resin between the thin strips of the roll, the roll may be immersed in a bath of insulating resin, or the insulating resin or its precursor may be applied to the side of the roll that appears in the winding axis direction. In addition, a method such as vacuum impregnation may be adopted to promote the impregnation of the resin between the thin strips of the roll. In order to harden the thermosetting resin or its precursor applied to the surface of the roll and between the thin strips, a curing process is performed at a predetermined temperature. The temperature of the curing process depends on the resin used, but in the case of an epoxy-based resin, it is preferable to harden it at a temperature of 20 to 180°C for 1 minute to 24 hours. EXAMPLES

[0058] Example 1 As the soft magnetic metal ribbon, a soft magnetic metal ribbon having an amorphous structure composed of a soft magnetic alloy containing Fe as the main component and Si, B and trace amounts of Cu and Nb, and capable of precipitating nanocrystals by heat treatment, Finemet (registered trademark) FT-3 manufactured by Hitachi Metals, Ltd., was prepared. The soft magnetic metal ribbon used was long, with a thickness of 14 μm and a width of 20 mm. The density of the soft magnetic metal ribbon was 7.3 × 10 3 kg / m 3 The crystallization onset temperature of this alloy was confirmed to be 470°C by differential scanning calorimetry (DSC).

[0059] In the powder coating process S1, a metal oxide powder was applied to the surface of the soft magnetic metal ribbon. As the non-magnetic and insulating metal oxide powder, magnesium oxide (MgO) powder with an average particle size (d50) of 0.7 μm was prepared. The density of magnesium oxide was 3.6 × 10 3 kg / m 3 The suspension 120 was prepared by dispersing 100 g of magnesium oxide powder per 1 kg of solvent using isopropyl alcohol as a solvent. The suspension 120 was transferred to a container 150 of a powder coating device shown in FIG. 2, and the soft magnetic metal ribbon 100 was immersed in the suspension for 0.5 seconds while stirring the suspension 120 to prevent aggregation and precipitation of magnesium oxide in the suspension 120. The soft magnetic metal ribbon 100 was lifted from the suspension 120, passed through a rod 145 that scrapes off excess suspension 120 on the roll surface side of the soft magnetic metal ribbon, and passed through a rotating scraper 140 to drop the excess suspension 120 on the surface of the soft magnetic metal ribbon, thereby controlling the suspension 120 on the free surface side. Thereafter, 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 attached to its surface. The amount of MgO powder attached 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 attached to the soft magnetic metal ribbon / weight of the soft magnetic metal ribbon) x 100 (%) The weight of the soft magnetic metal ribbon is weight A of one reel of the soft magnetic metal ribbon before the powder coating process S1, and the weight of MgO attached to the soft magnetic metal ribbon is weight B of one reel of the soft magnetic metal ribbon after the powder coating process S1 minus weight A.

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

[0061] In the heat treatment process S3, the roll was heat treated to nano-crystallize the amorphous structure of the soft magnetic metal ribbon into a nano-crystalline structure. The roll was heat treated in an electric furnace in a nitrogen atmosphere at a maximum temperature of 580°C and a holding time of 20 minutes (temperature profile), to convert the amorphous soft magnetic metal ribbon into a nano-crystalline soft magnetic metal ribbon.

[0062] A sample obtained from a soft magnetic metal ribbon with a nanocrystalline structure was subjected to structural observation at a magnification of 20,000 times using a transmission electron microscope (TEM). An arbitrary straight line of length Lt was drawn on the photograph obtained using the transmission electron microscope, and the total length Lc of the parts where the line intersects with nanocrystalline grains of a size that can be seen with the naked eye was obtained, and the proportion of crystal grains along the line was calculated as LL = Lc / Lt. This operation was repeated five times, and the volume fraction VL of nanocrystalline grains was obtained by averaging LL. Here, the volume fraction VL = Vc / Vt (Vc is the total volume of the nanocrystalline grains, and Vt is the volume of the sample) is expressed as VL ≒ Lc 3 / Lt 3 =LL 3 In the soft magnetic metal ribbon, the average crystal grain size of the nanocrystal grains measured by X-ray diffraction was 10 nm, and the volume fraction VL of the nanocrystal grains in the nanocrystal structure was 80 volume %.

[0063] In the oxide film forming step S4, the roll from the heat treatment step S3 was subjected to heat treatment to form an oxide film on the surface of the soft magnetic metal ribbon. The roll after the nanocrystallization heat treatment was heat treated in an electric furnace in the atmosphere at a maximum temperature of 280°C and a holding time of 2 hours (temperature profile), forming an oxide film on the surface of the soft magnetic metal ribbon. A part of the soft magnetic metal ribbon was peeled off from the outer periphery of the roll and subjected to Raman spectroscopy and cross-sectional observation using a transmission electron microscope (TEM). As a result, it was found that the oxide film formed on the surface of the soft magnetic metal ribbon of the obtained roll was mainly hematite (Fe2O3). It was also found that a thicker oxide film was formed than on the surface of the soft magnetic metal ribbon before the metal oxide powder was attached.

[0064] The wound body after the oxide film forming step S4 was impregnated with resin. The wound body on which the oxide film was formed was immersed for 1 minute in an impregnation liquid in which epoxy resin was diluted with acetone to a concentration of 5% to 30%, and then the epoxy resin was cured in a thermostatic bath adjusted to 150°C to obtain a wound core with a space factor of 70%. The space factor was calculated as follows. Occupancy factor=[(We / ρ) / {(OD 2 -ID 2 )×HT×π / 4}]×100(%) Where: We: Roll weight after oxide film formation (g) ρ: Density of the soft magnetic metal ribbon (g / cm 3 ) OD: Outer diameter of the roll after oxide film formation (cm) ID: Inside diameter of roll after oxide film formation (cm) HT: Height of the roll after the oxide film is formed (cm).

[0065] An impulse test was carried out on the wound core obtained through the resin impregnation step S5 using the circuit shown in Figure 7, with a peak voltage of 1.6 kV and a voltage application width of 200 nsec. The impedance was measured before and after the test, and the insulation of the wound core was evaluated based on the change in impedance. The impedance was evaluated at frequencies of 1 kHz to 10 MHz using an impedance analyzer HP4194A, with a one-turn coil passed around the inner diameter of the wound core, and the impedance change rate 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} x 100 (%)

[0066] In addition, the DC resistance Rdc of the inner diameter side surface and the outer diameter side surface of the wound core subjected to the impulse test was evaluated before and after the impulse test using a DC resistance meter HIOKI 3227. The DC resistance Rdc before the test was 161 Ω, and the DC resistance Rdc after the test was 81 Ω.

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

[0068] Comparative Example 2 A wound core was produced under 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 ribbon. The space factor was 73.7%. An impulse test was also performed on the obtained wound 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 core was produced under the same procedure and conditions as in Example 1, except that no oxide film was formed on the surface of the soft magnetic metal ribbon. The space factor was 72.8%. An impulse test was also performed on the obtained wound 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] The relationship between the impedance change rate calculated from the impedance before and after the impulse test and frequency is shown in Figure 5. Compared to the wound cores of Comparative Examples 1 to 3, the wound core of Example 1 had a high DC resistance Rdc before and after the test, and the change in impedance in the high frequency band was suppressed.

[0071] (Examples 2 to 6) A wound magnetic core was produced in the same manner as in Example 1, except that the amount of metal oxide powder attached to the soft magnetic metal ribbon was adjusted by adjusting the concentration of the 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 to 8) Except for adjusting the concentration of the suspension 120 to adjust the amount of metal oxide powder attached to the soft magnetic metal ribbon and not forming an oxide film on the surface of the soft magnetic metal ribbon, a wound core was produced under the same procedures and conditions as in Example 1. An impulse test was performed on the obtained wound core to evaluate the impedance change rate and DC resistance Rdc before and after the test.

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

[0074] [Table 1]

[0075] In the wound cores of Examples 2 to 6, the change in impedance before and after the impulse test was small, and the absolute value of the impedance change rate was 20% or less. In addition, the DC resistance Rdc after the impulse test was also maintained high. Even if the adhesion of metal oxide powder to the surface of the soft magnetic metal ribbon was small, excellent insulation performance was obtained. [Explanation of symbols]

[0076] 10,100 Soft magnetic metal ribbon 20 Metal oxide powder 30 Air Layer 120 Suspension 130 Drying oven 140 Scraper 150 containers

Claims

1. A method for manufacturing a wound magnetic core, in which a soft magnetic metal ribbon is wound to form a winding body in which multiple layers are stacked in the winding diameter direction, A first step of adhering a powder of a non-magnetic, insulating metal oxide to a surface of an amorphous soft magnetic metal ribbon; a second step of winding the soft magnetic metal ribbon into a circular shape after the first step to obtain a winding body in which the metal oxide powder is interposed between the ribbons; a third step of heat treating the roll in a non-oxidizing atmosphere; a fourth step of, after the third step, performing an oxide film forming 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 a surface of the soft magnetic metal ribbon; a fifth step of impregnating a resin between the thin ribbons of the wound body and curing the resin after the fourth step, In the first step, the soft magnetic metal ribbon is immersed in a suspension containing the metal oxide powder, and the suspension adhering to one surface of the soft magnetic metal ribbon is removed after the ribbon is pulled out of the suspension, so that the amount of the metal oxide powder adhering thereto is 0.1% or more and 1.2% or less in terms of a weight ratio of the metal oxide obtained by the following formula (1): Weight ratio of metal oxide (%)=(weight of metal oxide attached to soft magnetic metal ribbon / weight of soft magnetic metal ribbon)×100 (1) The metal oxide is MgO, and the amount of the metal oxide powder attached is 0.1×10 －３ kg / m ２ That's it, 1.5 x 10 －３ kg / m ２ The following is a method for manufacturing a wound magnetic core.

2. 2. The method for manufacturing a wound magnetic core according to claim 1, wherein the third step is a heat treatment A for precipitating nanocrystals in the soft magnetic metal ribbon with an amorphous structure, or a heat treatment B for stress relaxation of the soft magnetic metal ribbon with an amorphous structure.

3. A wound magnetic core in which a soft magnetic metal ribbon is wound, The winding body is made up of multiple layers stacked in the radial direction. the soft magnetic metal ribbon has an amorphous structure or a nanocrystalline structure, a surface of the soft magnetic metal ribbon having an oxide layer of Fe derived from a metal constituting the soft magnetic metal ribbon; a non-magnetic, insulating metal oxide powder is interposed between the soft magnetic metal ribbons; an adhesion amount of the metal oxide powder on one surface of the soft magnetic metal ribbon being smaller than an adhesion amount of the metal oxide powder on the other surface of the soft magnetic metal ribbon, and the adhesion amount of the metal oxide powder being 0.1% or more and 1.2% or less in terms of a weight ratio of the metal oxide obtained by the following formula (1): Weight ratio of metal oxide (%)=(weight of metal oxide attached to soft magnetic metal ribbon / weight of soft magnetic metal ribbon)×100 (1) The metal oxide is MgO, and the amount of the metal oxide powder attached is 0.1×10 －３ kg / m ２ That's it, 1.5 x 10 －３ kg / m ２ Below is the Wound magnetic core.

4. The soft magnetic metal ribbons are interposed with powder of the metal oxide and impregnated with resin, and the space factor is 65% or more and 75% or less, The space factor is calculated by the following formula (2): Occupancy rate = [(We / ρ) / {(OD ２ -ID ２ )×HT×π / 4}]×100(%) ・・・(2) where: We: Weight of the roll after the oxide layer is formed (g) ρ: density of the soft magnetic metal ribbon (g / cm ３ ) OD: outer diameter of the roll after the oxide layer is formed (cm) ID: inner diameter of roll after oxide layer formation (cm) HT: Height of the roll after the oxide layer is formed (cm) 4. The wound magnetic core of claim 3, wherein:

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