Method for manufacturing wound magnetic core, and wound magnetic core

Abstract

The present invention provides a method for manufacturing a wound magnetic core and a wound magnetic core capable of improving the insulation between the thin strips of a wound magnetic core formed into a ring-shaped roll by winding a soft magnetic metal thin strip. A non-magnetic and insulating metal oxide powder is attached to the surface of a soft magnetic metal thin strip of an amorphous structure, and the thin strip is wound into a ring to form a roll with the metal oxide powder intercalated between the thin strips. After the roll is heat-treated in a non-oxidizing atmosphere, the roll is subjected to an oxidation film forming treatment in an oxidizing atmosphere adjusted to a temperature lower than that of the heat treatment, so that the surface of the soft magnetic metal thin strip is oxidized, and then a resin is impregnated between the thin strips of the roll and cured to bond the metal oxide powder.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a wound magnetic core and the wound magnetic core. Background Art

[0002] At present, coil parts such as inductors, transformers, and chokes are used in various applications such as home appliances, industrial equipment, and vehicles. Coil parts are composed of a coil laid on a magnetic core, and among these magnetic cores, wound magnetic cores, which are rolls of amorphous and crystalline soft magnetic metal thin strips with excellent magnetic properties, are widely used.

[0003] The winding magnetic core is formed into a ring-shaped coil in which a tension is applied to a soft magnetic metal strip, which is also commonly referred to as a strip or a belt, while being firmly wound around a support (reel), and the soft magnetic metal strip is overlapped in multiple layers in the winding diameter direction. The coil with the support removed is welded and fixed at the ends of the soft magnetic metal strip at the beginning and the end of the winding so that the soft magnetic metal strip will not spread out. Alternatively, the coil with the support is welded and fixed at the end of the soft magnetic metal strip at the end of the winding. Next, a heat treatment is implemented to relax the stress given when the coil is formed, or to nanocrystallize and embody the desired magnetic properties. The soft magnetic metal strip is impregnated with epoxy resin, etc. in a manner that does not spread out due to changes over time or external forces applied to the coil after heat treatment, and the winding state is maintained.

[0004] The thickness of the soft magnetic metal strip is very thin, usually 10 μm to several hundred μm thick, and has several μm of unevenness on the surface, but it is a smooth surface in macroscopic terms. The soft magnetic metal strip is a good conductor, so if the smooth surfaces are short-circuited to each other and the insulation between the strips is insufficient, eddy currents sometimes flow between the strips, causing large power losses in the winding core. In particular, this trend is significant in high-frequency applications exceeding 100 kHz, and if there is no proper electrical insulation between the strips, it is not suitable for use as a coil part at high frequencies.

[0005] At present, in order to obtain high insulation between thin strips, Patent Document 1 proposes to attach fine powder composed of non-magnetic insulating inorganic matter to the surface of a magnetic metal thin strip to form a wound magnetic core, and Patent Document 2 proposes to oxidize the magnetic metal thin strip to form an insulating layer containing iron oxide between the layers.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 1-259510

[0009] Patent Document 2: Japanese Patent Application No. 2003-500850 Summary of the invention

[0010] Problems to be solved by the invention

[0011] Depending on the environment of use, a high surge voltage may be applied to the coil parts due to lightning or the like. In such coil parts, it is sought that the voltage vibration caused by the surge voltage applied to the coil will not cause insulation breakdown. In order to confirm the insulation resistance of the coil parts, a pulse test is sometimes performed. In the pulse test, a narrow pulse voltage with a width of less than hundreds of ns is applied to both ends of the coil of the coil parts at a high voltage of kV level. If a pulse test is performed, it is found that magnetostrictive vibration occurs in the thin strips due to the rapid change of magnetic flux generated in the winding core. Even if the winding core is constructed in a manner to obtain high insulation between the thin strips as in Patent Documents 1 and 2, in the winding core after the pulse test, there is sometimes a short circuit between the thin strips, and the insulation between the thin strips is deteriorated. In the case of requiring resistance to surges, even if insulation breakdown does not occur, such coil parts are not suitable for use at high frequencies. If high insulation is obtained between the thin strips, it is also possible to attach a thicker fine powder composed of insulating inorganic substances, or to form a thick insulating layer containing iron oxide to expand the interval between the thin strips. However, the occupancy rate (also called filling factor) of the wound core is reduced, and sometimes the size specifications of the coil parts determined by the large-scale wound core cannot be met. In addition, even if the wound core is constructed with a specified size, the desired magnetic properties may not be obtained.

[0012] Therefore, an object of the present invention is to provide a method for manufacturing a wound magnetic core and a wound magnetic core capable of improving the insulation between the thin strips of a wound magnetic core formed by winding a soft magnetic metal thin strip into an annular roll.

[0013] Technical solutions to solve problems

[0014] According to one embodiment of the present invention, a method for manufacturing a wound magnetic core can be provided, which comprises: a first step of attaching non-magnetic and insulating metal oxide powder to the surface of a soft magnetic metal strip with an amorphous structure; a second step of, after the first step, winding the soft magnetic metal strip into a ring shape to obtain a roll with the metal oxide powder interspersed between the strips; 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 roll in an oxidizing atmosphere at a temperature lower than the heat treatment temperature of the third step to oxidize the surface of the soft magnetic metal strip; and a fifth step of, after the fourth step, impregnating resin between the strips of the roll and curing.

[0015] In addition, according to one embodiment of the present invention, preferably, the third step is a heat treatment A for precipitating nanocrystals in the soft magnetic metal strip having an amorphous structure, or a heat treatment B for relaxing stress on the soft magnetic metal strip having an amorphous structure.

[0016] According to one embodiment of the present invention, it is preferred that the amount of the metal oxide powder deposited in the first step be 0.1% to 1.2% by weight of the metal oxide obtained by the following formula (1).

[0017] Weight ratio of metal oxide (%) = weight of metal oxide attached to the soft magnetic metal strip / weight of the soft magnetic metal strip × 100 ... (1)

[0018] According to one embodiment of the present invention, it is preferred that the temperature of the heat treatment in the third step is set to 450° C. to 620° C. in the heat treatment A and to 250° C. to 400° C. in the heat treatment B.

[0019] According to one aspect 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.

[0020] According to another embodiment of the present invention, there is provided a wound magnetic core wound with a soft magnetic metal strip, wherein the soft magnetic metal strip has an amorphous structure or a nanocrystalline structure, and an oxide layer of Fe derived from metal constituting the soft magnetic metal strip is provided on the surface of the soft magnetic metal strip, and powder of non-magnetic and insulating metal oxide is intercalated between the soft magnetic metal strips and impregnated with resin, with an occupancy ratio of not less than 65% and not more than 75%.

[0021] According to another aspect of the present invention, it is preferred that the Fe oxide layer comprises hematite (Fe 2 O 3 ).

[0022] 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.

[0023] Impedance change rate (%) = (impedance before pulse test - impedance after pulse test) / impedance before pulse test × 100 ... (2)

[0024] Effects of the Invention

[0025] According to the present invention, a method for manufacturing a wound magnetic core and a wound magnetic core capable of improving the insulation between thin strips of a wound magnetic core formed by winding a soft magnetic metal thin strip into an annular roll can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a process for manufacturing a wound magnetic core according to one embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a powder coating device used for manufacturing a wound magnetic core according to an embodiment of the present invention.

[0028] Figure 3 (a) is a schematic cross-sectional view of a soft magnetic metal ribbon in a state where metal oxide powder is attached to the surface, and (b) is a schematic cross-sectional view of a soft magnetic metal ribbon showing another attachment state.

[0029] Figure 4 It is an enlarged schematic diagram of a cross section perpendicular to the winding axis showing the state between the thin strips of the roll.

[0030] Figure 5 This is a graph showing the relationship between the impedance change rate and the frequency obtained from the impedance before and after the pulse test of the wound magnetic core.

[0031] Figure 6 This is a graph showing the relationship between the amount of metal oxide powder adhered (MgO weight ratio) and the rate of change in impedance before and after the pulse test.

[0032] Figure 7 This is a circuit diagram used to illustrate the pulse test. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

[0034] Figure 1 FIG. 1 is a flow chart of the manufacturing process of the method for manufacturing a wound magnetic core of the present invention. Figure 1 As shown, in the first step, a soft magnetic metal strip with an amorphous structure is used as a material, and a non-magnetic and insulating metal oxide powder is attached to its surface (powder coating step S1). In the second step, the soft magnetic metal strip with an amorphous structure obtained in the first step is wound into a ring shape in a manner of a roll of a specified shape and size, and a roll with metal oxide powder interspersed between the strips is made (rolling step S2). In the third step, the roll is heat-treated in a non-oxidizing atmosphere, and nanocrystals are precipitated in the soft magnetic metal strip with an amorphous structure, or the soft magnetic metal strip with an amorphous structure is subjected to stress relaxation (heat treatment step S3). In the fourth step, a temperature lower than the heat treatment temperature of the heat treatment step S3 is adjusted, and an oxide film forming treatment is performed in an oxidizing atmosphere to oxidize the surface of the soft magnetic metal strip (oxide film forming step S4). In the fifth step, resin is impregnated between the strips of the obtained roll and cured, and the powder of the metal oxide is adhered to form a winding magnetic core (resin impregnation step S5).

[0035] The wound magnetic core of the present embodiment is a wound magnetic core wound with a soft magnetic metal strip. The soft magnetic metal strip has an amorphous structure or a nanocrystalline structure, an oxide layer of a metal derived from a metal constituting the soft magnetic metal strip is formed on the surface of the soft magnetic metal strip, and a non-magnetic and insulating metal oxide powder is adhered between the soft magnetic metal strips by resin. Hereinafter, each process is described in detail.

[0036] (1)Material

[0037] The soft magnetic metal strip of the amorphous structure that becomes the material in the present embodiment is preferably composed of a soft magnetic alloy with Fe as the main component. Usually, it is a soft magnetic alloy with an Fe content of more than 65 atomic %, and the composition of the soft magnetic alloy is not particularly limited except that Fe is the main component. It also depends on the balance with other non-ferrous metals, but because it affects magnetic properties such as saturation magnetization, it is preferably Fe that contains more than 77.5% in atomic %, and more preferably Fe that contains more than 78.0%. The soft magnetic metal strip of the amorphous structure that becomes the material can be made into a soft magnetic metal strip of nanocrystalline structure or a soft magnetic metal strip of amorphous structure by heat treatment.

[0038] The soft magnetic alloy ribbon constituting the wound magnetic core has an amorphous structure or a nanocrystalline structure. The distinction between the soft magnetic metal ribbon being an amorphous structure or a nanocrystalline structure can be easily determined by the X-ray diffraction spectrum of the X-ray diffraction method. For example, the X-ray diffraction spectrum of the ribbon with nanocrystalline structure has a diffraction peak in the portion representing the crystalline phase (near the diffraction angle 2θ=45°), and the X-ray diffraction spectrum of the ribbon with amorphous structure has a halo pattern representing the amorphous phase. The diffraction peak near the diffraction angle 2θ=45° is the (110) diffraction peak of Fe crystal or FeSi crystal of the bcc structure. The angle of the diffraction peak includes errors such as data changes relative to the JCPDS card due to the solid solution of elements, etc., and therefore, the angle (2θ) of the diffraction peak that is extremely close to each JCPDS card is set to "near".

[0039] Amorphous structure does not have crystalline structure.On the other hand, nanocrystalline structure has the crystal grain that common average grain size is below 100nm.Nanocrystalline structure is usually for being the starting point crystallization, average grain size for example be the Fe crystallization below 30nm or FeSi crystallization particle from amorphous phase with the cluster of Cu and other non-ferrous metals that become the core of crystallization, becomes the organization that nanocrystal is randomly oriented and dispersed in amorphous phase.Nanocrystalline structure is obtained by implementing heat treatment to the soft magnetic metal thin band of the amorphous structure that can be nanocrystallized.

[0040] As a soft magnetic metal strip of nanocrystalline structure, for example, it can be set to a soft magnetic alloy of Fe-Si-M1-B-Cu system and a soft magnetic alloy of Fe-M2-B system, or other soft magnetic alloys. M1 is preferably selected from one or more of the group consisting of Nb, Ti, Zr, Hf, V, Ta, and Mo. In addition, M2 is preferably selected from one or more of the group consisting of Nb, Cu, Zr, and Hf. As a soft magnetic alloy of Fe-Si-M1-B-Cu system, ファインメット (finemet, registered trademark) of Hitachi Metals, Ltd., VITROPERM (registered trademark) of VACUUMSCHMELZE GmbH&Co.KG. are known, and as a soft magnetic alloy of Fe-M2-B system, NANOPERM (registered trademark) of MAGNETEC Gesellschaft fur Magnettechnologie mbH is known, and these alloys can be used.

[0041] As the soft magnetic metal ribbon having an amorphous structure, for example, a soft magnetic alloy of Fe—Si—B system is used. METGLAS (registered trademark) 2605SA1 manufactured by METGLAS, Inc. is known, and this alloy can be used.

[0042] The soft magnetic metal strip is obtained by a liquid quenching method in which a molten alloy is rapidly cooled and solidified. 6 The soft magnetic metal strip can be continuously formed into a long strip by a known method of a single roll method or a double roll method with a cooling rate of about 100°C / second or more. The soft magnetic metal strip can use a metal strip of a width and thickness that is circulated on the market, or a metal strip of a width cut from a material of a width that is circulated on the market, for example, a metal strip of a width of about 2 to 300 mm can be used. In addition, the thickness is 10 μm or more and hundreds of μm or less, and the soft magnetic metal strip is preferably set to a thickness of 50 μm or less from the perspective of being able to form an amorphous material.

[0043] (2) Powder coating step S1

[0044] A soft magnetic metal strip adjusted to a predetermined width and length and a non-magnetic and insulating metal oxide powder are prepared. The metal oxide powder is preferably magnesium oxide (MgO), titanium oxide (TiO 2 ), or aluminum oxide (Al 2 O 3). The average particle size of the metal oxide powder measured by a laser diffraction scattering particle size distribution measuring device (median particle size d50 in the cumulative particle size distribution) is preferably 0.5 μm or more and 1.0 μm or less, so that the metal oxide powder is evenly attached to the surface of the soft magnetic metal strip, and the prescribed interval between the strips is obtained while obtaining the occupancy rate of the wound magnetic core. In addition, if the effect of stress on the strip is taken into consideration, it is not preferred that coarse powder is mixed between the strips, and the maximum particle size of the powder is preferably 7 μm or less. Here, the maximum particle size is the 95 volume % particle size (d95).

[0045] The powder of the metal oxide is dispersed in a solvent such as toluene, isopropanol, ethanol, etc. to prepare a suspension. The amount of metal oxide powder attached to the soft magnetic metal strip can be adjusted by the concentration of the suspension. Setting the occupancy rate of the wound magnetic core to 65% or more also depends on the tension applied to the soft magnetic metal strip when it is set as a roll, but if the metal oxide is magnesium oxide (MgO), MgO is preferably 30 to 200 g relative to 1 kg of the solvent. Prepare a suspension adjusted to a specified powder concentration and apply it to the surface of the soft magnetic metal strip. Figure 2 A schematic diagram of a powder coating device for illustrating the process of immersing a soft magnetic metal strip in a suspension and coating it with a powder of a metal oxide is shown. In the device shown in the figure, a soft magnetic metal strip 100 made into a roll shape is used, and its end is drawn out and immersed in a container 150 to which a suspension 120 is added, and then the soft magnetic metal strip is drawn out from the suspension, and a rod 145 for scraping off the remaining suspension on the roller surface (the surface in contact with the cooling roller when the soft magnetic metal strip is obtained by a single roller method) of the soft magnetic metal strip is passed through, and the suspension on the free surface (the surface not in contact with the cooling roller when the soft magnetic metal strip is obtained by a single roller method) of the soft magnetic metal strip is controlled through a rotating scraper 140, and then the suspension on the free surface (the surface not in contact with the cooling roller when the soft magnetic metal strip is obtained by a single roller method) of the soft magnetic metal strip is controlled, and then the suspension is continuously passed through a drying furnace 130 adjusted to a specified temperature, so that the soft magnetic metal strip with a specified amount of metal oxide powder coated on the surface is wound into a roll shape. In addition, the suspension can also be applied to the surface of the soft magnetic metal strip by a roller coater, or sprayed and coated.

[0046] Figure 3 A schematic cross-sectional view of a soft magnetic metal strip showing a state where metal oxide powder is attached to the surface. The soft magnetic metal strip may also have recesses and protrusions, but they are not shown. Figure 3 (a) After the soft magnetic metal strip passes through the rod 145, the metal oxide powder is substantially uniformly attached to the entire surface (free surface, upper surface in the figure), and most of the metal oxide powder is removed from the other surface (roller surface, lower surface in the figure). In addition, after the suspension on one side of the soft magnetic metal strip is controlled by the scraper (scraper, scraper) 140, as shown in Figure 3(b) On one surface (free surface, upper surface in the figure) of the soft magnetic metal strip 10, the amount of metal oxide powder 20 attached is reduced. The amount of metal oxide powder attached also depends on the metal oxide powder used, but the weight ratio of the metal oxide is preferably 0.1% or more and 1.2% or less. It is preferably 0.2% or more, and more preferably 0.3% or more. In addition, it is preferably 1.1% or less, and more preferably 1.0% or less. In the case of MgO, it is preferably 0.1×10 －3 kg / m 2 Above 1.5×10 －3 kg / m 2 the following.

[0047] The powder 20 of the metal oxide attached to the surface of the soft magnetic metal strip 10 is easy to fall off when gently rubbed with fingers. Therefore, by drying the soft magnetic metal strip in the handling mechanical device, the powder of the metal oxide is easy to adhere to and accumulate on the parts in contact with the soft magnetic metal strip, especially the parts such as the handling roller, sometimes causing the inconvenience of unstable handling. In addition, due to the falling off of the powder of the metal oxide, the amount of the powder of the metal oxide attached to the soft magnetic metal strip is different at the beginning and end of the powder coating, and it is sometimes difficult to make the powder of the metal oxide evenly attached. Therefore, it is preferred to reduce the attachment of the powder of the metal oxide on a surface (for example, the roller surface) of the soft magnetic metal strip on the side in contact with the parts of the mechanical device. In addition, it can also be set to a state where the powder of the metal oxide is not attached to one surface of the soft magnetic metal strip. In addition, after the powder of the metal oxide is attached, by removing the powder of the metal oxide on the surface of the soft magnetic metal strip, it is possible to form a state where the powder of the metal oxide is reduced in attachment or the powder of the metal oxide is not attached.

[0048] In addition, in the case of obtaining a soft magnetic metal strip by a single-roll method, it is known that the surface morphology of the soft magnetic metal strip is different on the side in contact with the cooling roll (roll surface) and the side not in contact with the cooling roll (free surface). On the roller surface, it is easy to produce depressions with a depth of several μm to tens of μm caused by defects of the cooling roll and the adhesion of foreign matter, or the entrapment of atmospheric gas during casting, and it is easy to produce protrusions with a height of less than ten μm on the free surface. The protrusions affect the short circuit between the strips, so if the surface morphology of the soft magnetic metal strip is considered, the metal oxide powder is preferably attached to at least the free surface of the soft magnetic metal strip.

[0049] (3) Rolling process S2

[0050] The reel-shaped soft magnetic metal strip with a powder of metal oxide attached to the surface is installed on a winding device, the end of the soft magnetic metal strip is drawn out, and tension is applied while it is strongly wound around the support (reel) to form a ring-shaped reel with multiple layers of soft magnetic metal strips overlapping in the winding diameter direction. The winding speed of the soft magnetic metal strip is preferably more than 10m / minute and less than 500m / minute. The size of the reel is varied, but for example, it is preferably set to an inner diameter of more than 5mm and less than 140mm, and an outer diameter of more than 20mm and less than 200mm. The support is removed from the reel, and the end of the start winding of the soft magnetic metal strip and the end of the winding end are spot welded and fixed to form a reel. Through the powder of metal oxide, the sliding and winding of the soft magnetic metal strip can be made into a good reel, the adjustment of the tension during winding is easy and the workability is excellent, and the deviation of the interval between the thin strips from the inner circumference to the outer circumference is small.

[0051] Figure 4 It is a schematic diagram of a cross section perpendicular to the winding axis showing the state between the thin strips of the winding body. An air layer 30 is formed in which the powder 20 of the metal oxide is interspersed between the soft magnetic metal thin strips 10. The powder of the metal oxide between the thin strips is not shown in the figure, but the particles with large particle size are sandwiched between the thin strips, but at most they are attached to one surface of the soft magnetic metal thin strip.

[0052] The spacing between the strips can be adjusted by the tension applied to the soft magnetic metal strip when the roll is formed, the uneven state of the surface of the soft magnetic metal strip, and the thickness of the metal oxide powder on the surface of the soft magnetic metal strip. However, the wider the spacing between the strips, the lower the occupancy rate of the wound magnetic core, and sometimes the desired magnetic properties cannot be obtained. In addition, if oxygen is supplied between the strips when an oxide film is formed on the surface of the soft magnetic metal strip described later, it is preferable to appropriately select the conditions for forming the metal oxide powder and the roll so that the occupancy rate of the wound magnetic core is 65% or more and 75% or less. In addition, even if the spacing between the strips is narrow, the occupancy rate is 0.2 μm or more.

[0053] (4) Heat treatment step S3

[0054] Next, the coil is heat treated at a predetermined temperature in a non-oxidizing atmosphere to relax the stress imparted during coil formation or to nanocrystallize the coil to achieve the desired magnetic properties. The non-oxidizing atmosphere is N with an oxygen concentration of 100 ppm or less. 2, Ar and other inert gas atmospheres. Although it also depends on the alloy composition, if the soft magnetic metal strip is an amorphous structure, it is preferably heat treated at a temperature above 250°C in a non-oxidizing atmosphere for stress relaxation. When the temperature is raised too much, crystallization begins. Therefore, it is preferably a temperature 10°C to 150°C lower than the crystallization temperature of the alloy, typically preferably below 400°C. For example, if it is METGLAS (registered trademark) 2605SA1, a heat treatment temperature of 340°C to 400°C is preferred. The heat treatment temperature is the highest temperature reached after heating, and it is also the holding temperature when the temperature is maintained for a specified time.

[0055] In addition, when nanocrystals are precipitated in the soft magnetic metal strip to form a soft magnetic metal strip having a nanocrystalline structure, it is preferred to perform heat treatment at a temperature above the crystallization temperature of the soft magnetic alloy constituting the soft magnetic metal strip. If the temperature is too high, the crystal magnetoanisotropy is high, and the soft magnetic properties are sometimes deteriorated. 2 B and other crystalline phases are precipitated, so the heat treatment temperature is above the crystallization temperature of the alloy, and it is expected to be above 500°C and below 620°C, preferably in the range of above 540°C and below 590°C. Nanocrystalline structure is a structure in which nanocrystalline particles of Fe crystal or FeSi crystal are randomly oriented and dispersed in an amorphous phase. The average grain size of the nanocrystalline particles is preferably below 30nm, more preferably below 20nm. The average grain size of the nanocrystalline particles is the size of the crystallites obtained by the Scherrer formula using the peak of the bccFe(Si)〔diffraction plane (110)〕in the X-ray diffraction spectrum. In addition, in the nanocrystalline structure, the nanocrystalline particles preferably occupy more than 30 volume %, more preferably more than 50 volume %. The volume fraction of the nanocrystalline particles of the nanocrystalline structure is calculated by the line segment method. In addition, it is known that when the soft magnetic metal strip of the amorphous structure is crystallized by heat treatment to make a nanocrystalline structure, a volume shrinkage of about 1% is generated in the soft magnetic metal strip. By intercalating the metal oxide powder between the thin strips, the soft magnetic metal thin strips are facilitated to slide in the circumferential direction of the winding, so that the winding of the roll body due to contraction can suppress the application of stress to the soft magnetic metal thin strips.

[0056] In the case of stress relaxation or nanocrystallization, the heat treatment time is expected to be more than 5 minutes and less than 14 hours. The heat treatment time is the time maintained at the highest reached temperature. If the furnace used in the heat treatment is a heating furnace that can be temperature-controlled to 620°C in a non-oxidizing atmosphere, even if it is an arbitrary heating furnace, it can be used without special problems, but if it is a heating furnace that can control oxygen concentration, it is more preferred to use the same heating furnace in the following oxide film forming operation S4, and continuously process.

[0057] (5) Oxide Film Formation Step S4

[0058] After the heat treatment step S3, the coil is subjected to an oxide film forming treatment in an oxidizing atmosphere, preferably in an atmosphere with an oxygen concentration of 1% to 50% and at a temperature of 240°C or more and lower than the heat treatment temperature (maximum reaching temperature) in the heat treatment step S3, to form an oxide film on the surface of the soft magnetic metal strip. The oxygen concentration in the atmosphere is preferably 50% by volume or less, and more preferably an air atmosphere. The coil has an air layer 30 formed by intercalating metal oxide powder 10 between the soft magnetic metal strips 10. By the oxide film forming treatment, oxygen is also supplied to the air layer 30, and the soft magnetic metal strips on the outer surface of the coil are formed with an oxide film on the surface of the wound soft magnetic metal strip. The thickness of the oxide film is a thickness that improves the insulation between the strips and is a thickness that suppresses the reduction of magnetic properties of the wound magnetic core, and is preferably a thickness that exceeds the thickness of the oxide film based on natural oxidation (about 10 to 10 nm), and is tens of nm 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), or by using a technique such as X-ray photoelectron spectroscopy (XPS).

[0059] The oxide film is an oxide layer derived from the metal constituting the soft magnetic metal strip, and is preferably hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ). It may also contain pyrite (FeO), but it has a lower resistance than hematite and magnetite, so it is desirable to use a small amount. The identification of the oxide can be performed by analytical techniques such as Raman spectroscopy. After the oxide film is formed, the powder of the metal oxide between the ribbons is still attached to the surface of the soft magnetic metal ribbon as when the coil is formed. If the soft magnetic metal ribbon is a nanocrystalline structure, it is desirable to set the oxide film formation temperature to a range of 240 to 350°C. In addition, if the soft magnetic metal ribbon is an amorphous structure, it is desirable to set the heat treatment temperature to a range of 240 to 300°C.

[0060] (6) Resin impregnation step S5

[0061] After the oxide film forming step S4, insulating resin is impregnated between the surface of the obtained coil and the thin strips of the soft magnetic metal strip, and cured to form a wound magnetic core. By bonding the thin strips with insulating resin, a structure in which the magnetic alloy thin strips are integrated is formed, which can prevent the soft magnetic metal strip in the coil state from loosening due to external force, etc., and maintain the wound state. In addition, the powder of the metal oxide is bonded between the thin strips, and it also contributes to the insulation between the thin strips. In addition, the insulating resin preferably covers the surface of the soft magnetic metal strip without spots, but between the thin strips of the coil, at least 3% of the surface of the soft magnetic metal strip is preferably covered with insulating resin.

[0062] As the insulating resin, epoxy-based and polyimide-based thermosetting resins are preferably used. As a method for impregnating the insulating resin between the thin strips of the roll, the roll can be immersed in a bath of the insulating resin and impregnated, or the insulating resin and its precursor can be applied to the side of the roll in the axial direction of the roll and impregnated. In addition, methods such as vacuum impregnation can be used to promote the impregnation of the resin between the thin strips of the roll. In order to cure the thermosetting resin or its precursor applied to the surface of the roll and between the thin strips, a curing treatment is performed at a prescribed temperature. The temperature of the curing treatment also depends on the resin used, but if it is an epoxy resin, it is preferably cured at a temperature of 20 to 180°C for 1 minute to 24 hours.

[0063] Example

[0064] (Example 1)

[0065] As the material, the soft magnetic metal strip is prepared as an amorphous soft magnetic metal strip composed of a soft magnetic alloy with Fe as the main component and containing Si, B and trace amounts of Cu and Nb, that is, FT-3 manufactured by Hitachi Metals Co., Ltd., which can be heat-treated to precipitate nanocrystals. The soft magnetic metal strip is a long strip with a thickness of 14 μm and a width of 20 mm. The density is 7.3×10 3 kg / m 3 The crystallization start temperature of the alloy was confirmed to be 470° C. by differential scanning calorimetry (DSC).

[0066] In the powder coating step S1, metal oxide powder is attached to the surface of the soft magnetic metal strip. As a non-magnetic and insulating metal oxide powder, magnesium oxide (MgO) powder having an average particle size (d50) of 0.7 μm is prepared. The density of magnesium oxide is 3.6×10 3 kg / m 3 Isopropyl alcohol was used as a solvent, and 100 g of magnesium oxide powder was dispersed in the solvent per 1 kg of the solvent to prepare a suspension. The suspension was transferred to Figure 2The container of the powder coating device shown in the figure is used to immerse the soft magnetic metal strip 100 in the suspension for 0.5 seconds while stirring the suspension to prevent the aggregation and precipitation of magnesium oxide in the suspension. The soft magnetic metal strip 100 is drawn out from the suspension, passes through a rod 145 for scraping off the remaining suspension on the roller surface side of the soft magnetic metal strip, passes through a rotating scraper 140 to make the remaining suspension on the surface of the soft magnetic metal strip fall, controls the suspension on the free surface side, and continues to pass through a drying furnace 130 adjusted to a temperature of 80° C., thereby obtaining a soft magnetic metal strip 100 with a predetermined amount of MgO powder coated on the surface.

[0067] The amount of MgO powder attached to the surface of the soft magnetic metal strip was calculated as the MgO weight ratio (weight ratio of metal oxide) by the following formula. The MgO weight ratio was 0.73%.

[0068] MgO weight ratio = MgO weight attached to the soft magnetic metal strip / weight of the soft magnetic metal strip × 100 (%)

[0069] In addition, the weight of the soft magnetic metal strip is the weight A of the soft magnetic metal strip per roll before the powder coating process, and the weight of MgO attached to the soft magnetic metal strip is the weight obtained by subtracting the above-mentioned weight A from the weight B of the soft magnetic metal strip per roll after the powder coating process.

[0070] The soft magnetic metal strip with the powder of metal oxide attached to the surface in the winding process S2 is set as a coil. The soft magnetic metal strip obtained in the powder coating process S1 is installed in a winding device, the end of the soft magnetic metal strip is drawn out, and it is strongly wound around the stainless steel support body, and multiple layers of soft magnetic metal strips are wound in the coil diameter direction. The support body is removed from the coil, and the ends of the soft magnetic metal strip at the start and end of the winding of the soft magnetic metal strip are spot welded and fixed to form a coil with an inner diameter of 33 mm and an outer diameter of 50 mm.

[0071] In the heat treatment step S3, the coil is heat treated to convert the amorphous structure of the soft magnetic metal strip into a nanocrystalline structure. The coil is heat treated in an electric furnace and a nitrogen atmosphere at a maximum temperature of 580° C. and a holding time of 20 minutes (temperature curve) to convert the amorphous soft magnetic metal strip into a nanocrystalline soft magnetic metal strip.

[0072] The sample obtained from the soft magnetic metal strip of nanocrystalline structure was observed by using a transmission electron microscope (TEM) at a magnification of 20,000 times. In the obtained photo, an arbitrary straight line of length Lt was drawn, and the total length Lc of the part where the straight line intersects with the nanocrystalline grains of a size that can be visually confirmed was calculated, and the ratio of the grains along the straight line was calculated as LL = Lc / Lt. This operation was repeated five times, and LL was averaged to obtain the volume fraction of the nanocrystalline grains. Here, the volume fraction VL = Vc / Vt (Vc is the sum of the volumes of the nanocrystalline grains, and Vt is the volume of the sample.) VL≒Lc is approximately considered. 3 / Lt 3 =LL 3 In the soft magnetic metal ribbon, the average grain size of the nanocrystal grains based on X-ray diffraction was 10 nm, and the volume fraction of the nanocrystal grains in the structure was 80 volume %.

[0073] In the oxide film forming step S4, the coil of the heat treatment step S3 is heat treated to form an oxide film on the surface of the soft magnetic metal strip. The coil that has completed the heat treatment for nanocrystallization is heat treated in an electric furnace and in the atmosphere at a maximum temperature of 280°C and a holding time of 2 hours (temperature curve), thereby forming an oxide film on the surface of the soft magnetic metal strip. A portion of the soft magnetic metal strip is peeled off from the periphery of the coil, and Raman spectroscopy analysis and transmission electron microscopy (TEM) cross-sectional observation are performed. As a result, the oxide film formed on the surface of the soft magnetic metal strip of the obtained coil is mainly hematite (Fe 2 O 3 ) In addition, an oxide film thicker than the surface of the soft magnetic metal strip before the metal oxide powder is attached is formed.

[0074] The wound body after the oxide film forming step S4 is immersed in resin. The wound body with the oxide film formed is immersed in an impregnation liquid in which the epoxy resin is diluted to a concentration of 5% to 30% in acetone for 1 minute, and then the epoxy resin is cured in a thermostatic bath adjusted to 150°C to obtain a wound magnetic core with an occupancy rate of 70%. In addition, the occupancy rate is calculated as follows.

[0075] Occupancy rate = (We / ρ) / {(OD 2 -ID 2 )×HT×π / 4}

[0076] Here,

[0077] We: Roll weight after oxide film formation (g)

[0078] ρ: Density of soft magnetic metal strip (g / cm 3 )

[0079] OD: The outer diameter of the roll after the oxide film is formed (cm)

[0080] ID: The inner diameter of the roll after the oxide film is formed (cm)

[0081] HT: Height of the coil after oxide film formation (cm)

[0082] exist Figure 7 In the circuit shown, a pulse test was performed on the wound magnetic core obtained through the resin impregnation step S5 under the conditions of 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 magnetic core was evaluated based on the change. In terms of impedance, a coil of one turn was passed through the inner diameter of the wound magnetic core, and the impedance was evaluated at a frequency of 1 kHz to 10 MHz using an impedance analyzer HP4194A, and the impedance change rate before and after the test was calculated using the following formula.

[0083] Impedance change rate = (impedance before pulse test - impedance after pulse test) / impedance before pulse test × 100 (%)

[0084] In addition, the wound core subjected to the pulse test was used to evaluate the DC resistance Rdc of the inner diameter side surface and the outer diameter side surface before and after the pulse test using a DC resistance meter HIOKI 3227. The DC resistance Rdc before the test was 161Ω, and the DC resistance Rdc after the test was 81Ω.

[0085] (Comparative Example 1)

[0086] The winding core was produced in the same order and under the same conditions as in Example 1, except that the metal oxide powder was not attached to the surface of the soft magnetic metal strip and the oxide film was not formed on the surface of the soft magnetic metal strip. The occupancy rate was 73.8%. The obtained winding core was subjected to a pulse test to evaluate the impedance change rate and the DC resistance Rdc before and after the test. The DC resistance Rdc before the test was 34Ω, and the DC resistance Rdc after the test was 1.7Ω.

[0087] (Comparative Example 2)

[0088] The winding core was made in the same order and under the same conditions as in Example 1, except that the metal oxide powder was not attached to the surface of the soft magnetic metal strip. The occupancy rate was 73.7%. In addition, a pulse test was performed on the obtained winding 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.

[0089] (Comparative Example 3)

[0090] The wound magnetic core was produced in the same order and under the same conditions as in Example 1 except that no oxide film was formed on the surface of the soft magnetic metal strip. The occupancy rate was 72.8%. In addition, a pulse 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.

[0091] Figure 5 The relationship between the impedance change rate calculated from the impedance before and after the pulse test and the frequency is shown. In the wound magnetic cores of Comparative Examples 1 to 3, the DC resistance Rdc before and after the test is high in the wound magnetic core of Example 1, and the change in impedance in the high frequency band is suppressed.

[0092] (Examples 2 to 6)

[0093] 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. The obtained wound magnetic core was subjected to a pulse test to evaluate the impedance change rate at a frequency of 1 MHz and the DC resistance Rdc before and after the test.

[0094] (Comparative Examples 4 to 8)

[0095] Except that the amount of metal oxide powder attached to the soft magnetic metal strip was adjusted by the concentration of the suspension, and no oxide film was formed on the surface of the soft magnetic metal strip, a wound magnetic core was produced in the same procedure and under the same conditions as in Example 1. A pulse 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.

[0096] Table 1 shows the occupancy rate of the wound magnetic cores of Examples 2 to 6 and Comparative Examples 4 to 6, the weight change rate before and after the oxide film formation, the DC resistance Rdc before and after the pulse test, and the impedance. Figure 6 The relationship between the amount of metal oxide powder adhered (MgO weight ratio) and the rate of change in impedance before and after the pulse test is shown.

[0097]

Table 1

[0098]

[0099] The impedance changes of the wound magnetic cores of Examples 2 to 6 before and after the pulse test were small, and the absolute value of the impedance change rate was less than 20%. In addition, the DC resistance Rdc after the pulse test was also maintained at a high level. Even if the metal oxide powder adheres less to the surface of the soft magnetic metal strip, excellent insulation performance can be obtained.

[0100] Explanation of symbols

[0101] 10, 100 soft magnetic metal strip

[0102] 20 Oxide powder

[0103] 30 air layers

[0104] 120 Suspension

[0105] 130 drying oven

[0106] 140 scraper (scraper)

[0107] 150 containers.

Claims

1. A method for manufacturing a wound magnetic core, comprising: In the first step, a non-magnetic and insulating metal oxide powder is attached to the surface of the soft magnetic metal thin strip having an amorphous structure; A second step, after the first step, winding the soft magnetic metal strip into a ring shape to obtain a roll body in which metal oxide powder is intercalated between the strips; The third step is to heat treat the roll in a non-oxidizing atmosphere; A fourth step, after the third step, performing an oxide film forming treatment on the coil 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 strip; and The fifth step is to impregnate resin between the thin strips of the roll and cure it after the fourth step. In the first step, the soft magnetic metal strip is immersed in a suspension containing the powder of the metal oxide, and then the suspension attached to one side surface of the soft magnetic metal strip drawn out from the suspension is removed, so that the attached amount of the powder of the metal oxide is set to 0.1% or more and 1.2% or less by weight ratio of the metal oxide obtained by the following formula (1), The formula (1) is: weight ratio of metal oxide (%) = weight of metal oxide attached to the soft magnetic metal strip / weight of the soft magnetic metal strip×100, The metal oxide is MgO, and the adhesion amount is 0.1×10 - 3kg / m 2 Above 1.5×10 - 3kg / m 2 the following, The average particle size of the metal oxide powder is 0.5 μm or more and 1.0 μm or less.

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 strip having an amorphous structure, or a heat treatment B for relaxing stress on the soft magnetic metal strip having an amorphous structure.

3. The method for manufacturing a wound magnetic core according to claim 2, wherein: The temperature of the heat treatment in the third step is set to 450° C. or higher and 620° C. or lower in the heat treatment A, and to 250° C. or higher and 400° C. or lower in the heat treatment B.

4. The method for manufacturing a wound magnetic core according to any one of claims 1 to 3, wherein: 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.

5. A wound magnetic core, wound with a soft magnetic metal strip, wherein: The soft magnetic metal strip has an amorphous structure or a nanocrystalline structure. The soft magnetic metal strip has an oxide layer derived from Fe, a metal constituting the soft magnetic metal strip, on its surface. Non-magnetic and insulating metal oxide powder is mixed between the soft magnetic metal strips and impregnated with resin. The plot ratio is between 65% and 75%. The amount of the metal oxide powder attached to one surface of the soft magnetic metal strip is smaller than the amount of the metal oxide powder attached to the other surface of the soft magnetic metal strip, and the amount of the metal oxide powder attached is set to 0.1% to 1.2% by weight of the metal oxide obtained by the following formula (1). The formula (1) is: weight ratio of metal oxide (%) = weight of metal oxide attached to the soft magnetic metal strip / weight of the soft magnetic metal strip×100, The metal oxide is MgO, and the adhesion amount is 0.1×10 - 3kg / m 2 Above 1.5×10 - 3kg / m 2 the following, The average particle size of the metal oxide powder is 0.5 μm or more and 1.0 μm or less.

6. The wound magnetic core according to claim 5, wherein: The Fe oxide layer includes hematite (Fe2O3).

7. The wound magnetic core according to claim 5 or 6, wherein: The absolute value of the impedance change rate at a frequency of 1 MHz obtained by the following formula (2) is less than 20%. The formula (2) is: impedance change rate (%) = (impedance before pulse test - impedance after pulse test) / impedance before pulse test × 100.

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