Wound core

Abstract

To provide a wound core excellent in magnetic characteristics.SOLUTION: A wound core is formed by winding a surface-oxidized thin strip made of a nanocrystalline material in a plurality of layers, and in the nanocrystalline material thin strip 10, an oxidation degree of a F2 part 11 in a width-direction center part of the nanocrystalline material thin strip is different from oxidation degrees of an end part 12 and an end part 13 located on both width-direction sides of the center part in the nanocrystalline material thin strip.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wound core. [Background technology]

[0002] Wound cores formed by winding a thin strip (hereinafter referred to as a thin strip) made of a soft magnetic material in multiple layers are used as the cores of magnetic devices such as power conversion transformers. For example, power conversion transformers require high conversion efficiency and also high saturation magnetic flux density to achieve compactness. Therefore, the soft magnetic material that constitutes the wound cores of power conversion transformers and the like is particularly required to have low iron loss (core loss) and high saturation magnetic flux density.

[0003] Traditionally, crystalline alloys such as silicon steel and amorphous alloys such as iron-based amorphous alloys have been used as soft magnetic materials for wound cores. However, silicon steel cores have high saturation magnetic flux density but low conversion efficiency due to high core loss. Iron-based amorphous alloy cores have low core loss and therefore good conversion efficiency, but low saturation magnetic flux density. In light of these issues, nanocrystalline materials with high saturation magnetic flux density have been considered in recent years as soft magnetic materials for wound cores.

[0004] Nanocrystalline material is produced in the form of a thin ribbon by a known method such as a liquid quenching method. This thin ribbon of nanocrystalline material (hereinafter referred to as nanocrystalline material ribbon) has an amorphous structure in the initial state, and can be transformed into a nanocrystalline structure by appropriate heat treatment. Iron cores made of such nanocrystalline material ribbon are characterized by having a high saturation magnetic flux density of, for example, 1.7 T or more, while also having low iron loss. For this reason, nanocrystalline material ribbon is suitable as a soft magnetic material used in wound cores of power conversion transformers, etc.

[0005] As a conventional technique for nanocrystallizing a nanocrystalline ribbon by heat treatment, for example, a method is known in which a sample taken from an amorphous ribbon that can be nanocrystallized is subjected to heat treatment for nanocrystallization, and then the amorphous ribbon is wound into multiple layers to form a wound body, which is then subjected to heat treatment for nanocrystallization (see Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-9921 Summary of the Invention [Problem to be solved by the invention]

[0007] In general, nanocrystalline ribbons are materials that undergo self-heating during nanocrystallization by heat treatment. Therefore, when nanocrystallizing a nanocrystalline ribbon, it is important to appropriately control the heat treatment temperature of the nanocrystalline ribbon. Conventionally, nanocrystallization of such nanocrystalline ribbons has been performed by winding the nanocrystalline ribbon to form a wound core having multiple layers, and then heat-treating the wound core. In this case, self-heating occurs in each of the multiple layers of nanocrystalline ribbons that make up the wound core, and the influence of this self-heating makes it difficult to appropriately control the temperature of the heat treatment. Therefore, the heat treatment is preferably performed on a single (single-layer) nanocrystalline ribbon that is in a state prior to being formed into a wound core.

[0008] However, in the heat treatment of a single (single layer) nanocrystalline ribbon, the contact area between the nanocrystalline ribbon and the atmosphere (air) is increased compared to the heat treatment of the above-mentioned wound core, so the surface of the nanocrystalline ribbon is easily oxidized and an oxide film is easily formed. If the oxide film on the surface of the nanocrystalline ribbon becomes excessively thick, a problem occurs in that the magnetic properties of the wound core made of the nanocrystalline ribbon, such as the saturation magnetic flux density and conversion efficiency, decrease.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a wound core with excellent magnetic properties. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, the wound core of the present invention is a wound core formed by winding a thin ribbon made of a nanocrystalline material and having an oxidized surface in multiple layers, and is characterized in that the oxidation degree of the central portion of the thin ribbon in the width direction is different from the oxidation degree of the end portions of the thin ribbon located on both sides of the central portion in the width direction.

[0011] In addition, in the wound core according to the present invention, in the above invention, the degree of oxidation of the ribbon is higher at the end portions than at the center portion.

[0012] Furthermore, in the wound core according to the present invention, in the above invention, the oxide film thickness on both surfaces of the ribbon in the thickness direction is 5 nm or more and 350 nm or less, and a representative value of the oxide film thickness at the center and a representative value of the oxide film thickness at the end portions are different on the surfaces on the same side in the thickness direction of the ribbon.

[0013] Furthermore, in the wound core according to the present invention, in the above invention, the color of the central portion and the color of the end portions of each of the two surfaces in the thickness direction of the ribbon are different.

[0014] Furthermore, in the above invention, the wound core according to the present invention is characterized in that a representative value of the oxide film thickness in each of the outermost and innermost ribbons among the plurality of layers of ribbons is larger than a representative value of the oxide film thickness in an intermediate ribbon sandwiched between the outermost and innermost ribbons. [Effects of the Invention]

[0015] The present invention has the effect of providing a wound core with excellent magnetic properties. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a wound core according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a structural example of the wound core shown in FIG. 1 taken along line AA. [Figure 3] FIG. 3 is a schematic diagram showing an example of the configuration of a nanocrystalline ribbon according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing a structural example of the nanocrystalline ribbon taken along the line BB shown in FIG. [Figure 5] FIG. 5 is a schematic diagram showing an example of a main configuration of a heat treatment device for performing a primary heat treatment on a nanocrystalline ribbon according to an embodiment of the present invention. [Figure 6] FIG. 6 is a top view of the heat treatment apparatus shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing a structural example of the heat treatment apparatus shown in FIG. 6 taken along the line CC. [Figure 8] FIG. 8 is a flow diagram showing an example of a method for manufacturing a wound core according to an embodiment of the present invention. [Figure 9] FIG. 9 is a schematic diagram showing the measurement area of ​​the oxide film thickness of the ribbon sample in the example. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of a wound core according to the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to these embodiments. It should be noted that the drawings are schematic, and the dimensional relationships and ratios of elements may differ from those in reality. The drawings may also include parts whose dimensional relationships and ratios differ from one another. In addition, the same components are designated by the same reference numerals in the various drawings.

[0018] (wound core) First, a wound core according to an embodiment of the present invention will be described in detail. Fig. 1 is a schematic diagram showing an example of the configuration of a wound core according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing an example of the configuration of the wound core shown in Fig. 1 along line AA. Wound core 1 according to an embodiment of the present invention is, for example, a wound core for a power conversion transformer, and as shown in Fig. 1, has a pair of legs 2, 3 that face each other.

[0019] 1 and 2, the wound core 1 is an annular structure formed by winding nanocrystalline material ribbons 10 in multiple layers and having a laminated structure made up of these multiple layers of nanocrystalline material ribbons 10. For example, in the plan view shown in FIG. 1, the wound core 1 has a rounded rectangular ring shape having an inner circumferential surface 1a and an outer circumferential surface 1b. The thickness of such wound core 1 corresponds to the distance between the inner circumferential surface 1a and the outer circumferential surface 1b shown in FIG. 1, i.e., the thickness of the laminated structure made up of multiple layers of nanocrystalline material ribbons 10 shown in FIG. 2. The width of the wound core 1 corresponds to the width of the nanocrystalline material ribbons 10.

[0020] As shown in Fig. 1, a pair of legs 2, 3 of the wound core 1 are formed to face each other in the thickness direction. Of the pair of legs 2, 3, one leg 2 is provided with an input winding 4, and the other leg 3 is provided with an output winding 5. When an AC current flows through the input winding 4, the wound core 1 generates an alternating magnetic field (variable magnetic field). This alternating magnetic field is converted back into a current by the output winding 5, and this current is output from the winding 5.

[0021] As shown in FIG. 2 , the nanocrystalline material ribbons 10 constituting the wound core 1 are classified into an outermost ribbon 20, an innermost ribbon 30, and intermediate ribbons 40. The outermost ribbon 20 is the nanocrystalline material ribbon 10 located on the outermost side of the wound core 1. That is, of both surfaces in the thickness direction of the outermost ribbon 20, the outermost surface is the surface exposed to the outer periphery of the wound core 1, and becomes the outer periphery surface 1b of the wound core 1 (see FIGS. 1 and 2). The innermost ribbon 30 is the nanocrystalline material ribbon 10 located on the innermost side of the wound core 1. That is, of both surfaces in the thickness direction of the innermost ribbon 30, the innermost surface is the surface exposed to the inner periphery of the wound core 1, and becomes the inner periphery surface 1a of the wound core 1 (see FIGS. 1 and 2). The intermediate ribbon 40 is the nanocrystalline material ribbon 10 sandwiched between the outermost ribbon 20 and the innermost ribbon 30. For example, as shown in Fig. 2, a plurality of layers of intermediate ribbons 40 are present between the outermost ribbon 20 and the innermost ribbon 30. For the above reasons, in this specification, when the outermost ribbon 20, the innermost ribbon 30, and the plurality of layers of intermediate ribbons 40 are described without distinction, they will be referred to as nanocrystalline ribbons 10.

[0022] Although not particularly shown, the stacked structure of the nanocrystalline ribbons 10 may have an overlap structure in which both longitudinal end portions of the nanocrystalline ribbons 10 overlap each other in the stacking direction (thickness direction), or a step-lap structure in which the both end portions face each other with a predetermined gap therebetween. Alternatively, the stacked structure of the nanocrystalline ribbons 10 may have a structure that combines the overlap structure and the step-lap structure.

[0023] (nanocrystalline ribbon) Next, the nanocrystalline material ribbon 10 constituting the wound iron core 1 according to the embodiment of the present invention will be described in detail. Fig. 3 is a schematic diagram showing one configuration example of a nanocrystalline material ribbon in the embodiment of the present invention. Fig. 3 shows a schematic plan view of a main surface of the nanocrystalline material ribbon 10. Fig. 4 is a schematic cross-sectional view showing one configuration example of the nanocrystalline material ribbon shown in Fig. 3 along line BB.

[0024] 3 and 4, for convenience of explanation of nanocrystalline ribbon 10, a longitudinal direction F1, a width direction F2, and a thickness direction F3 are set. Longitudinal direction F1 is the longitudinal direction of nanocrystalline ribbon 10, width direction F2 is the width direction (short direction) of nanocrystalline ribbon 10, and thickness direction F3 is the thickness direction of nanocrystalline ribbon 10. These three directions are perpendicular to each other. Note that these three directions do not limit the present invention, and the same applies to ribbons other than nanocrystalline ribbon 10.

[0025] The nanocrystalline ribbon 10 according to the embodiment of the present invention is a ribbon made of a nanocrystalline material and having an oxidized surface. The nanocrystalline material is a soft magnetic material that can be fabricated into a ribbon shape by a known method such as a liquid quenching method, and contains an amorphous structure that can be nanocrystallized by heat treatment. That is, the nanocrystalline ribbon 10 contains an amorphous structure in its initial state before heat treatment for nanocrystallization is performed, and contains an amorphous structure and a nanocrystalline structure after the heat treatment.

[0026] Specifically, as shown in FIGS. 3 and 4 , the nanocrystalline ribbon 10 contains an internal structure 17 in which an amorphous structure and a nanocrystalline structure are mixed, and the surface is in an oxidized state after heat treatment for nanocrystallization. The nanocrystalline structure contained in the internal structure 17 is obtained by nanocrystallizing an amorphous structure through heat treatment. In such a nanocrystalline ribbon 10, the oxidation degree of the central portion 11 in the width direction F2 is different from the oxidation degrees of the end portions 12 and 13 on both sides in the width direction F2. In this specification, the oxidation degree means the degree of oxidation of the surface of the nanocrystalline ribbon. For example, the thickness of the oxide film (oxide film thickness) on the surface of the nanocrystalline ribbon, color, etc., can be used as an indicator of the oxidation degree.

[0027] As shown in FIG. 3 , the central portion 11 in the width direction F2 of the nanocrystalline material ribbon 10 is a region having a width W2 centered on a central axis 10L parallel to the longitudinal direction F1 of the nanocrystalline material ribbon 10, the width W2 having a ratio of less than 1 to the width W1 of the nanocrystalline material ribbon 10. As shown in FIG. 4 , the nanocrystalline material ribbon 10 has a first strip surface 14 and a second strip surface 15 as main surfaces on both sides in the thickness direction F3. As shown in FIG. 4 , the nanocrystalline material ribbon 10 has, as the central portion 11, a central portion 11A in the width direction F2 of the first strip surface 14 and a central portion 11B in the width direction F2 of the second strip surface 15. For example, the width W2 of the central portion 11 differs between the central portion 11A of the first strip surface 14 on one side and the central portion 11B of the second strip surface 15 on the other side in the thickness direction F3 of the nanocrystalline material ribbon 10.

[0028] As shown in FIG. 3 , the end portions 12 and 13 on both sides of the nanocrystalline ribbon 10 in the width direction F2 are regions located on both sides of the central portion 11 in the width direction F2. These end portions 12 and 13 include the edge portions on both sides of the nanocrystalline ribbon 10 in the width direction F2. Of these end portions 12 and 13, one end portion 12 has a width W3, and the other end portion 13 has a width W4. The width W3 of one end portion 12 is approximately the same as the width W4 of the other end portion 13. For example, as shown in FIG. 3 , the width W1 of the nanocrystalline ribbon 10 is the sum of the width W2 of the central portion 11 and the widths W3 and W4 of the end portions 12 and 13. As shown in FIG. 4, the nanocrystalline ribbon 10 has such ends 12, 13 as ends 12A, 13A on both sides of the first strip surface 14 in the width direction F2 and ends 12B, 13B on both sides of the second strip surface 15 in the width direction F2.

[0029] 4, the nanocrystalline ribbon 10 has side surfaces 16a and 16b as end surfaces on both sides in the width direction F2 in addition to the first strip surface 14 and the second strip surface 15. In the nanocrystalline ribbon 10, for example, the first strip surface 14 is a free surface of the nanocrystalline ribbon 10, and the second strip surface 15 is a roll surface of the nanocrystalline ribbon 10.

[0030] The roll surface is the surface in the thickness direction of a ribbon that is produced by spraying molten metal onto a rotating casting roll (chill roll) in the production of ribbon by a liquid quenching method or the like, that comes into contact with the casting roll. The free surface is the surface opposite the roll surface, i.e., the surface that does not come into contact with the casting roll. When ribbon production by a liquid quenching method or the like is performed in the atmosphere (under an air atmosphere), the free surface of the produced ribbon comes into contact with the atmosphere. For this reason, the nanocrystalline ribbon 10 produced by the liquid quenching method tends to have a higher oxidation degree on the free surface than on the roll surface at the stage of production. Note that the distribution of oxidation degrees in the nanocrystalline ribbon 10 is not determined by the roll surface and free surface described above, and depending on the heat treatment method for nanocrystallization, the oxidation degrees of the roll surface and the free surface may be reversed.

[0031] The nanocrystalline ribbon 10 having the rolled surface and the free surface described above has its first strip surface 14, second strip surface 15, and side surfaces 16a, 16b oxidized during the ribbon manufacturing process using a liquid quenching method or the like, or heat treatment for nanocrystallization. As a result, an oxide film 18 is formed on the nanocrystalline ribbon 10 over the entire first strip surface 14, second strip surface 15, and side surfaces 16a, 16b, as shown in FIG. 4 . The oxide film 18 grows from the surface toward the inside of the nanocrystalline ribbon 10. That is, as the oxide film 18 grows, the volume of at least one of the amorphous structure and the nanocrystalline structure in the internal structure 17 of the nanocrystalline ribbon 10 decreases. The thickness of the oxide film 18 (hereinafter referred to as the oxide film thickness) corresponds to the dimension (depth) from the surface toward the inside of the nanocrystalline ribbon 10, and tends to be larger in regions of the nanocrystalline ribbon 10 with a high degree of oxidation and smaller in regions of the nanocrystalline ribbon 10 with a low degree of oxidation.

[0032] In the embodiment of the present invention, the degree of oxidation of the nanocrystalline ribbon 10 differs between the central portion 11 and the two end portions 12 and 13 in the width direction F2. Therefore, the representative value of the oxide film thickness of the nanocrystalline ribbon 10 differs between the central portion 11 and the two end portions 12 and 13. For example, the degree of oxidation of the nanocrystalline ribbon 10 at the two end portions 12 and 13 in the width direction F2 is higher than that of the central portion 11. In this nanocrystalline ribbon 10, the representative value of the oxide film thickness at the two end portions 12 and 13 is higher than that of the central portion 11. The representative value of the oxide film thickness is the oxide film thickness of a representative portion in each of the central portion 11 and the two end portions 12 and 13 in the width direction F2 of the nanocrystalline ribbon 10. For example, the representative portion is a portion that is aligned in the stacking direction (thickness direction F3) among multiple layers of the nanocrystalline ribbon 10 (see FIG. 2 ).

[0033] 4, the oxide film 18 on the first strip surface 14 of the nanocrystalline material ribbon 10 has an oxide film thickness D1 in the center portion 11A in the width direction F2 and an oxide film thickness D2 at the end portions 12A and 13A in the width direction F2. The oxide film 18 on the second strip surface 15 of the nanocrystalline material ribbon 10 has an oxide film thickness D3 in the center portion 11B in the width direction F2 and an oxide film thickness D4 at the end portions 12B and 13B in the width direction F2. The oxide film thickness D1 is a representative value of the oxide film thickness in the center portion 11A in the width direction F2, and the oxide film thickness D2 is a representative value of the oxide film thickness at the end portions 12A and 13A in the width direction F2. The oxide film thickness D3 is a representative value of the oxide film thickness in the center portion 11B in the width direction F2, and the oxide film thickness D4 is a representative value of the oxide film thickness at the end portions 12B and 13B in the width direction F2.

[0034] 4, the oxide film 18 is illustrated as having oxide film thicknesses D1 to D4 at various portions each having a constant representative value. However, in reality, the thickness of the oxide film 18 is not necessarily uniform at the center portions 11A and 11B and at the opposite end portions 12A, 12B, 13A, and 13B in the width direction F2 of the nanocrystalline ribbon 10.

[0035] 4, on a first strip surface 14 of the nanocrystalline ribbon 10, an oxide film thickness D1 at a center portion 11A in the width direction F2 is different from an oxide film thickness D2 at both end portions 12A and 13A in the width direction F2. On a second strip surface 15 of the nanocrystalline ribbon 10, an oxide film thickness D3 at a center portion 11B in the width direction F2 is different from an oxide film thickness D4 at both end portions 12B and 13B in the width direction F2. For example, on the first strip surface 14 of the nanocrystalline ribbon 10, the oxide film thickness D2 at the both end portions 12A and 13A is larger than the oxide film thickness D1 at the center portion 11A. On the second strip surface 15 of the nanocrystalline ribbon 10, the oxide film thickness D4 at the both end portions 12B and 13B is larger than the oxide film thickness D3 at the center portion 11B.

[0036] When the oxidation degree of the first strip surface 14 of the nanocrystalline ribbon 10 is higher than that of the second strip surface 15, as shown in Fig. 4, the oxide film thickness D1 of the central portion 11A on the first strip surface 14 is larger than the oxide film thickness D3 of the central portion 11B on the second strip surface 15. In addition, the oxide film thickness D2 of the opposite end portions 12A and 13A on the first strip surface 14 is larger than the oxide film thickness D4 of the opposite end portions 12B and 13B on the second strip surface 15. Also, as shown in Fig. 4, the distance L1 between the oxide film 18 of one end portion 12A and the oxide film 18 of the other end portion 13A on the first strip surface 14 is narrower than the distance L2 between the oxide film 18 of one end portion 12B and the oxide film 18 of the other end portion 13B on the second strip surface 15.

[0037] The oxide film 18 preferably has a thickness within a predetermined upper and lower limit range. For example, the oxide film thickness on both sides (first strip surface 14 and second strip surface 15) of the nanocrystalline material ribbon 10 in the thickness direction F3 is preferably 5 nm to 350 nm, more preferably 65 nm to 315 nm. This prevents the magnetic properties, such as core loss and saturation magnetic flux density, of the wound core 1 made of the nanocrystalline material ribbon 10 from being reduced due to an excessive increase in the thickness of the oxide film 18 on the nanocrystalline material ribbon 10. Furthermore, by setting the oxide film thickness within the range of 5 nm to 350 nm, the wound core 1 can have a high saturation magnetic flux density, for example, of 1.7 T or more.

[0038] Furthermore, in the wound core 1 (see FIG. 1) according to an embodiment of the present invention, the representative oxide film thickness of each of the outermost ribbon 20 and the innermost ribbon 30 (see FIG. 2) among the multiple layers of nanocrystalline ribbons 10 is larger than the representative oxide film thickness of the intermediate ribbon 40. In particular, the outermost ribbon surface (e.g., first ribbon surface 14) of the outermost ribbon 20 corresponds to the outer peripheral surface 1b of the wound core 1, and the innermost ribbon surface (e.g., second ribbon surface 15) of the innermost ribbon 30 corresponds to the inner peripheral surface 1a of the wound core 1. The representative oxide film thicknesses of each of the outermost ribbon surface of the outermost ribbon 20 and the innermost ribbon surface of the innermost ribbon 30 are larger than the representative oxide film thicknesses on both surfaces of the intermediate ribbon 40 in the thickness direction F3. The difference between these representative oxide film thicknesses is preferably large enough to improve the weather resistance of the wound core 1 while maintaining the excellent magnetic properties of the wound core 1.

[0039] Furthermore, in each of the multiple-layer intermediate ribbons 40, it is preferable that the representative value of the oxide film thickness on the inner band surface (e.g., the second band surface 15) of both surfaces in the thickness direction F3 is smaller than the representative value of the oxide film thickness on the outer band surface (e.g., the first band surface 14).

[0040] With the wound core 1 having the above-described configuration, it is possible to reduce core loss to a target value or less. This target core loss is the core loss per unit mass when excited with a maximum magnetic flux density of 1.6 T at a frequency of 50 Hz, and specifically, is 1.0 W / kg or less. More preferably, the core loss is less than 0.5 W / kg. Furthermore, the oxide films on the outer band surface of the outermost ribbon 20 and the inner band surface of the innermost ribbon 30 described above can protect the inner circumferential surface 1a and the outer circumferential surface 1b of the wound core 1, thereby improving the weather resistance of the wound core 1 while maintaining its excellent magnetic properties.

[0041] Meanwhile, color may be used as an index representing the degree of oxidation of nanocrystalline ribbon 10. Specifically, on both sides of nanocrystalline ribbon 10 in thickness direction F3, the color of center portion 11 in width direction F2 is different from the color of both end portions 12, 13.

[0042] Specifically, in the first strip surface 14 in the thickness direction F3 of the nanocrystalline ribbon 10 shown in FIG. 4, the color of the central portion 11A in the width direction F2 is different from the color of the end portions 12A and 13A on both sides. More specifically, since the degree of oxidation of the central portion 11A is lower than the degree of oxidation of the end portions 12A and 13A, the color of the central portion 11A is closer to the metallic luster of the nanocrystalline ribbon 10 before oxidation than the color of the end portions 12A and 13A. Conversely, the color of the end portions 12A and 13A is farther from the metallic luster of the nanocrystalline ribbon 10 before oxidation than the color of the central portion 11A, and is closer to purple or blue, for example. In the first strip surface 14, a striped pattern due to the difference in color extends along the longitudinal direction F1 of the nanocrystalline ribbon 10 (see FIG. 3).

[0043] 4, the color of the central portion 11B in the width direction F2 is different from the color of the end portions 12B and 13B on both sides. The difference in color between the central portion 11B and the end portions 12B and 13B is the same as that of the first strip surface 14, except that the width of the color is different. Although not shown, a striped pattern due to the difference in color also extends along the longitudinal direction F1 of the nanocrystalline ribbon 10 on the second strip surface 15.

[0044] In the wound core 1 according to the embodiment of the present invention, the color, which is an index showing the degree of oxidation of such nanocrystalline ribbons 10, differs between the respective ribbon surfaces of the outermost and innermost ribbons 20 and 30 and the respective ribbon surfaces of the intermediate ribbons 40.

[0045] The soft magnetic material constituting the nanocrystalline ribbon 10 may be, for example, an iron-based nanocrystalline material containing iron (Fe) as a main component. The iron-based nanocrystalline material may contain an α-Fe crystal structure with a bcc structure in order to improve magnetic properties such as increasing the saturation magnetic flux density. The nanocrystalline ribbon 10 typically has a thickness of, for example, 25 μm.

[0046] (Heat treatment) Next, the heat treatment for nanocrystallizing the nanocrystalline ribbon 10 in the embodiment of the present invention will be described in detail. The nanocrystalline ribbon 10 is subjected to a first heat treatment in a single layer state before being wound in multiple layers to form the wound core 1, and a second heat treatment in a multiple-layer state forming the wound core 1. The first heat treatment is a heat treatment for nanocrystallizing the nanocrystalline ribbon 10. After nanocrystallization, the internal structure 17 (see FIG. 4 ) of the nanocrystalline ribbon 10 has a structure in which a nanocrystalline structure and an amorphous structure are mixed. After the first heat treatment, the nanocrystallization of the nanocrystalline ribbon 10 is mostly completed. The second heat treatment is a heat treatment for promoting the remaining nanocrystallization of the nanocrystalline ribbon 10 and for relieving stress in the multiple layers of the nanocrystalline ribbon 10 in the wound core 1 state. The first heat treatment of the nanocrystalline ribbon 10 will be described in detail below.

[0047] FIG. 5 is a schematic diagram showing an example of the main configuration of a heat treatment apparatus for performing a primary heat treatment on a nanocrystalline ribbon according to an embodiment of the present invention. FIG. 5 is a schematic side view of the main configuration of this heat treatment apparatus 50. FIG. 6 is a top view of the heat treatment apparatus shown in FIG. 5. FIG. 7 is a schematic cross-sectional view showing an example of the configuration of the heat treatment apparatus shown in FIG. 6 along line CC. In FIGS. 6 and 7, the longitudinal direction F1, width direction F2, and thickness direction F3 respectively indicate the longitudinal direction, width direction, and thickness direction of the nanocrystalline ribbon 9 located on the heating surface 51a of the heater 51 in the heat treatment apparatus 50.

[0048] The heat treatment apparatus 50 according to the embodiment of the present invention is an apparatus that performs the primary heat treatment on the nanocrystalline ribbon 9, which is a target of the primary heat treatment, while transporting the nanocrystalline ribbon 9 by a roll-to-roll method. The nanocrystalline ribbon 9 is a thin ribbon of soft magnetic material manufactured by a known method such as a liquid quenching method, and becomes the nanocrystalline ribbon 10 in a nanocrystallized state by the primary heat treatment. That is, the nanocrystalline ribbon 9 is the nanocrystalline ribbon 10 in a state (initial state) before the primary heat treatment is performed, and its internal structure is mainly an amorphous structure, and is the same as the nanocrystalline ribbon 10 except for the proportion of the nanocrystalline structure in the internal structure and the degree of oxidation of the surface.

[0049] 5 and 6 , the heat treatment apparatus 50 includes a heater 51, a fixed sheet 52, and a movable sheet 53. The heat treatment apparatus 50 also includes guide rolls 54 and 55 on the inlet and outlet sides of the heater 51, respectively. Although not shown, the heat treatment apparatus 50 also includes, upstream of the guide roll 54 on the inlet side of the heater 51, an unwinding roll that unwinds the nanocrystalline material ribbon 9, a plurality of guide rolls that guide the unwound nanocrystalline material ribbon 9 toward the heater 51 while reducing its winding tendency, a tension applying unit that applies a tensile force to the nanocrystalline material ribbon 9, and the like. The heat treatment apparatus 50 also includes, downstream of the guide roll 55 on the outlet side of the heater 51, a take-up roll that winds the nanocrystalline material ribbon 10 after the primary heat treatment, and a plurality of guide rolls that guide the nanocrystalline material ribbon 10 from the heater 51 side toward the take-up roll, and the like.

[0050] As shown in Figures 5 and 6, the heater 51 has a heating surface 51a on a predetermined surface (for example, the upper surface) facing the transport path of the nanocrystalline ribbon 9, and generates heat required for the primary heat treatment from this heating surface 51a. As shown in Figures 5 to 7, a fixing sheet 52 is disposed on the heating surface 51a of the heater 51. The fixing sheet 52 is in close contact with the heating surface 51a of the heater 51. In this state, the fixing sheet 52 is in sliding contact with the second ribbon surface 15 of the nanocrystalline ribbon 9 that is transported successively.

[0051] The movable sheet 53 is a movable sheet having a drive unit and the like (not shown), and is disposed opposite the fixed sheet 52 on the heating surface 51a across the transport path of the nanocrystalline material ribbon 9, as shown in FIGS. 5 to 7 . As shown in FIG. 7 , the movable sheet 53 can move toward the fixed sheet 52. As a result, the movable sheet 53 presses the fixed sheet 52 and the nanocrystalline material ribbon 9 against the heating surface 51a of the heater 51, and sandwiches the nanocrystalline material ribbon 9 between the movable sheet 53 and the fixed sheet 52. Furthermore, both ends in the width direction of the movable sheet 53 are in close contact with the fixed sheet 52, thereby covering the nanocrystalline material ribbon 9 between the movable sheet 53 and the fixed sheet 52. The width directions of the fixed sheet 52 and the movable sheet 53 are the same as the width direction F2 of the nanocrystalline material ribbon 9 located on the heating surface 51a of the heater 51. In this state, the movable sheet 53 comes into sliding contact with the first ribbon surface 14 of the nanocrystalline material ribbon 9 that is transported sequentially. 5 to 7, the movable sheet 53 is preferably sandwiched between the fixed sheet 52 and the movable sheet 53 so as to cover the nanocrystalline ribbon 9 over the entire area in the longitudinal direction F1 of the nanocrystalline ribbon 9 located on the heating surface 51a of the heater 51. On the other hand, the movable sheet 53 can also move in a direction away from the fixed sheet 52. This causes the movable sheet 53 to release the nanocrystalline ribbon 9 from being sandwiched between the movable sheet 53 and the fixed sheet 52.

[0052] The fixed sheet 52 and the movable sheet 53 are each made of a material having higher thermal conductivity and reducibility than the nanocrystalline ribbon 9. Examples of such materials include titanium-based materials containing titanium, aluminum-based materials containing aluminum, and carbon-based materials containing carbon.

[0053] 5 and 6, the guide rolls 54 and 55 are arranged on the inlet and outlet sides of the heater 51, respectively, to guide the nanocrystalline ribbons 9 and 10 in directions inclined relative to the heating surface 51a of the heater 51. For example, the inlet guide roll 54 guides the nanocrystalline ribbon 9 so that the nanocrystalline ribbon 9 ascends obliquely from the heater 51 side and enters the contact surface with the fixed sheet 52. The outlet guide roll 55 guides the nanocrystalline ribbon 10 after the primary heat treatment so that the nanocrystalline ribbon 10 runs obliquely downward from the contact surface with the fixed sheet 52.

[0054] In the heat treatment apparatus 50 having the above-described configuration, the nanocrystalline ribbon 9 to be treated is unwound from a winding roll (not shown) and then sequentially transported between a fixed sheet 52 and a movable sheet 53 on a heater 51 via an inlet guide roll 54 or the like. The nanocrystalline ribbon 9 is sandwiched and covered in the thickness direction F3 between the fixed sheet 52 and the movable sheet 53 and transported along the heating surface 51a of the heater 51. During this transport, a tensile force is applied to the nanocrystalline ribbon 9 in the longitudinal direction F1, and a pressing force is applied by the movable sheet 53. Due to these tensile and pressing forces, the second ribbon surface 15 of the nanocrystalline ribbon 9 is pressed against the fixed sheet 52, which is in close contact with the heating surface 51a of the heater 51, while the nanocrystalline ribbon 9 is transported over the heater 51.

[0055] As described above, the nanocrystalline ribbon 9 is transported on the heating surface 51a while being sandwiched and covered between the fixed sheet 52 and the movable sheet 53, and is subjected to primary heat treatment at a desired temperature by heating from the heater 51 via the fixed sheet 52.

[0056] 7, the heat of the heater 51 is transferred sequentially to the nanocrystalline ribbon 9 during transportation via the fixed sheet 52, which has a higher thermal conductivity than the nanocrystalline ribbon 9. In addition, the heat of the heater 51 is transferred from the fixed sheet 52 to the movable sheet 53, which has a higher thermal conductivity than the nanocrystalline ribbon 9, and then transferred sequentially to the nanocrystalline ribbon 9 during transportation via the movable sheet 53. This allows the nanocrystalline ribbon 9 to be heated from both sides (first strip surface 14 and second strip surface 15) in the thickness direction F3.

[0057] In addition to the above, in the heat treatment device 50, the nanocrystalline ribbon 9 on the heating surface 51a of the heater 51 is sandwiched between the fixed sheet 52 and the movable sheet 53 so as to cover both sides in the thickness direction F3. This reduces the contact area between the nanocrystalline ribbon 9 and the atmosphere, thereby suppressing direct heat radiation from the nanocrystalline ribbon 9 to the atmosphere.

[0058] The heating effect from both the first strip surface 14 and the second strip surface 15 of the nanocrystalline material ribbon 9 and the suppression of direct heat dissipation to the atmosphere reduce the temperature distribution inside the nanocrystalline material ribbon 9, so that the temperature rise rate of the nanocrystalline material ribbon 9 by the primary heat treatment can be increased to, for example, 300°C / min or more. As a result, the crystal grain size of the nanocrystalline material ribbon 10 after the primary heat treatment can be set to the target crystal grain size of the nanocrystalline structure (for example, 30 nm or less, preferably 20 nm or less), and therefore good magnetic properties can be obtained for the wound core 1 made of the nanocrystalline material ribbon 10.

[0059] Furthermore, as described above, the fixed sheet 52 and the movable sheet 53 sandwiching the nanocrystalline ribbon 9 have reducing properties, which can suppress oxidation of the nanocrystalline ribbon 9 during the first heat treatment. This can prevent an excessively thick oxide film from forming on the nanocrystalline ribbon 10 after the first heat treatment. Furthermore, because the fixed sheet 52 and the movable sheet 53 sandwich the nanocrystalline ribbon 9 so as to cover it from both sides in the thickness direction F3, the amount of air that enters from the width direction F2 onto each of the second strip surface 15 (heater-side surface) and the first strip surface 14 (air-side surface) that face the heating surface 51a of the heater 51 can be reduced. This can further narrow the region with a thick oxide film on each of the first strip surface 14 and the second strip surface 15 of the nanocrystalline ribbon 10 after the first heat treatment. Because the thickness and width of the oxide film on the nanocrystalline ribbon 10 can be reduced as described above, deterioration of the magnetic properties of the wound core 1 made of the nanocrystalline ribbon 10 can be suppressed.

[0060] After the above-described primary heat treatment is performed on the nanocrystalline ribbon 9, the nanocrystalline ribbon 10 after the primary heat treatment is carried out from the heater 51 in the heat treatment device 50. The nanocrystalline ribbon 10 is transported via an outlet guide roll 55 or the like, cooled to room temperature by air cooling or the like, and then sequentially wound into a roll by a winding roll (not shown).

[0061] (Manufacturing method of wound core) Next, a method for manufacturing a wound core 1 according to an embodiment of the present invention will be described in detail. Figure 8 is a flow chart showing an example of a method for manufacturing a wound core according to an embodiment of the present invention. This wound core 1 (see Figures 1 and 2) is manufactured by sequentially performing the steps shown in Figure 8.

[0062] In detail, as shown in FIG. 8, in the method for manufacturing the wound core 1, first, a primary heat treatment step is carried out to nanocrystallize the nanocrystalline ribbon 10 that is the material for the wound core 1 (step S101).

[0063] In the primary heat treatment step of step S101, a roll of nanocrystalline ribbon 9 (nanocrystalline ribbon 10 in an initial state) is prepared in advance by a known method such as a liquid quenching method, and the roll is set in a heat treatment device 50 (see FIGS. 5 to 7) for the primary heat treatment. Then, the nanocrystalline ribbon 9 is subjected to the primary heat treatment as described above while being transported by the heat treatment device 50 in a roll-to-roll manner. As a result, nanocrystalline ribbon 10 is obtained in a state in which nanocrystallization of the nanocrystalline ribbon 9 has progressed to a target value (e.g., a nanocrystallization degree of 95%). The obtained nanocrystalline ribbons 10 are sequentially carried out from the heater 51, cooled to room temperature by air cooling, etc., and then wound into a roll.

[0064] The temperature of the heater 51 when the nanocrystalline ribbon 9 is subjected to the first heat treatment is adjusted taking into consideration the heat treatment temperature of the nanocrystalline ribbon 9, the conveying speed, and the like. For example, the heat treatment temperature of the nanocrystalline ribbon 9 is set within a range of −50° C. above the reference temperature, which is the first crystallization temperature at which α-Fe crystals precipitate inside the nanocrystalline ribbon 9, and a temperature of +150° C. above the reference temperature. The temperature of the heater 51 is adjusted so that the nanocrystalline ribbon 9 can be heated to the heat treatment temperature during conveyance.

[0065] After the primary heat treatment step of step S101, a cutting step of cutting the nanocrystalline ribbon 10 is performed (step S102). In the cutting step of step S102, a roll of the nanocrystalline ribbon 10 is set in a predetermined cutting device, and the nanocrystalline ribbons 10 are sequentially dispensed from the roll. The dispensed nanocrystalline ribbons 10 are then sequentially cut to a length required to form the desired wound core 1 (hereinafter referred to as the target length). This results in multiple layers of nanocrystalline ribbons 10 of the desired length. Note that examples of methods for cutting the nanocrystalline ribbon 10 include laser cutting.

[0066] After the cutting step of step S102, a lamination step is performed in which the nanocrystalline ribbons 10 are laminated into multiple layers (step S103). In the lamination step of step S103, the nanocrystalline ribbons 10 cut to a target length are laminated to form multiple layers in the thickness direction F3. For example, the nanocrystalline ribbons 10 are laminated into multiple layers so that, of both surfaces of the nanocrystalline ribbon 10 in the thickness direction F3 (see FIG. 4), a first strip surface 14 (free surface) faces the outer periphery of the wound core 1 and a second strip surface 15 (roll surface) faces the inner periphery of the wound core 1.

[0067] After the lamination step of step S103, a winding step is performed in which multiple layers of nanocrystalline ribbons 10 are wound (step S104). In the winding step of step S104, multiple layers of nanocrystalline ribbons 10 are wound one turn in sequence from the inside to the outside, and both ends of these nanocrystalline ribbons 10 in the longitudinal direction F1 are overlapped. As a result, the wound core 1 having the desired annular structure is formed. The layered structure of the multiple layers of nanocrystalline ribbons 10 that form this wound core 1 may have an overlap structure, a step-lap structure, or a combination of the overlap structure and the step-lap structure.

[0068] After the winding step of step S104, a secondary heat treatment step is performed (step S105) to nanocrystallize and stress-relieve the multiple layers of nanocrystalline material ribbon 10 that form wound core 1. In the secondary heat treatment step of step S105, the multiple layers of nanocrystalline material ribbon 10 are set in a heating furnace such as an elevating high-temperature furnace while in the state of wound core 1. Then, while a magnetic field is applied to wound core 1 in the heating furnace, the multiple layers of nanocrystalline material ribbon 10 in wound core 1 are subjected to the secondary heat treatment. This further advances and completes the nanocrystallization in each of the multiple layers of nanocrystalline material ribbon 10 from the state after the above-mentioned primary heat treatment, and also relieves stress that has occurred in each of the multiple layers of nanocrystalline material ribbon 10 during, for example, the formation of wound core 1. The multiple layers of nanocrystalline material ribbon 10 that have undergone the secondary heat treatment are cooled to room temperature while in the state of wound core 1 and then removed from the heating furnace. In this manner, the manufacture of wound core 1 is completed. Even after the above-described secondary heat treatment, in each of the multiple-layer nanocrystalline ribbons 10, the oxidation degree of the central portion 11 in the width direction F2 illustrated in Fig. 3 is different from the oxidation degree of the end portions 12, 13 on both sides. Accordingly, the central portion 11 and the end portions 12, 13 maintain different oxide film thicknesses (representative values) and colors.

[0069] The heat treatment temperature of the multi-layered nanocrystalline ribbon 10 during the secondary heat treatment is set to the same as that of the above-described primary heat treatment, but the temperature rise rate of the multi-layered nanocrystalline ribbon 10 may be set to be lower than the temperature rise rate during the above-described primary heat treatment.

[0070] As described above, in an embodiment of the present invention, a wound core 1 is formed by winding nanocrystalline ribbons 10 made of nanocrystalline material and having an oxidized surface in multiple layers, and in each of the multiple layers of nanocrystalline ribbons 10 forming this wound core 1, the degree of oxidation of central portion 11 in width direction F2 of nanocrystalline ribbon 10 is made different from the degree of oxidation of end portions 12, 13 located on both sides of central portion 11 in width direction F2 of nanocrystalline ribbon 10.

[0071] Therefore, even if it is difficult to uniformly suppress the degree of oxidation of the surface (e.g., first strip surface 14 and second strip surface 15) of nanocrystalline ribbon 10 when heat treatment (particularly the above-described primary heat treatment) required for nanocrystallization of nanocrystalline ribbon 10 is performed in air, the degree of oxidation of nanocrystalline ribbon 10 can be controlled so that the degree of oxidation of one of center portion 11 and end portions 12, 13 in width direction F2 of nanocrystalline ribbon 10 is lower than the degree of oxidation of the other portion. This control of the degree of oxidation can prevent oxide film 18 on the surface of nanocrystalline ribbon 10 from becoming excessively thick, thereby ensuring a sufficient volume of the nanocrystalline structure in internal structure 17 of nanocrystalline ribbon 10. By winding such nanocrystalline ribbon 10 in multiple layers to form wound core 1, wound core 1 with both low core loss and high saturation magnetic flux density and excellent magnetic properties can be realized.

[0072] By applying the wound core 1 according to the embodiment of the present invention as the core of a magnetic device such as a power conversion transformer, it is possible to realize a magnetic device with excellent magnetic properties, such as high conversion efficiency. Furthermore, the high saturation magnetic flux density of the wound core 1 can facilitate miniaturization of the magnetic device. Furthermore, since the heat treatment required for nanocrystallization of the nanocrystalline ribbon 10 does not need to be performed in a special gas atmosphere such as nitrogen gas or an inert gas, equipment for heat treating the nanocrystalline ribbon 10 in the special gas atmosphere is not required. As a result, the cost required for heat treatment (nanocrystallization) of the nanocrystalline ribbon 10 can be reduced, and therefore the manufacturing cost of the wound core 1 can be reduced.

[0073] Furthermore, in the embodiment of the present invention, the oxidation degree of the end portions 12, 13 in the width direction F2 of the nanocrystalline ribbon 10 is set higher than the oxidation degree of the central portion 11. Therefore, by performing heat treatment on the nanocrystalline ribbon 10 in the air while focusing on the oxidation degree of the end portions 12, 13, it is possible to easily control the oxidation degree of the nanocrystalline ribbon 10 so that the oxidation degree of the end portions 12, 13 and the oxidation degree of the central portion 11 become lower. This makes it easy to prevent the oxide film 18 on the surface of the nanocrystalline ribbon 10 from becoming excessively thick, and therefore makes it easy to realize a wound core 1 with excellent magnetic properties using the nanocrystalline ribbon 10.

[0074] In addition, in the embodiment of the present invention, the oxide film thickness on both sides of the nanocrystalline material ribbon 10 in the thickness direction F3 is 5 nm or more and 350 nm or less, and the representative value of the oxide film thickness in the central portion 11 is different from the representative value of the oxide film thickness at the ends 12, 13 on the same side of the nanocrystalline material ribbon 10 in the thickness direction F3. This makes it possible to control the oxidation degree of the nanocrystalline material ribbon 10 so that the oxide film thickness at one of the central portion 11 and the ends 12, 13 of the nanocrystalline material ribbon 10 is smaller than the oxide film thickness at the other portion, and also makes it possible to suppress the upper limit of the oxide film thickness at both of these portions to 350 nm or less. This makes it possible to reduce the core loss of the wound core 1 to a low value of 1.0 W / kg or less when excited with a magnetic flux density of a maximum value of 1.6 T at a frequency of 50 Hz. As a result, excellent magnetic properties can be easily obtained from the wound core 1.

[0075] Furthermore, in the embodiment of the present invention, the representative oxide film thickness of each of the outermost ribbon 20 and the innermost ribbon 30 of the multiple layers of nanocrystalline material ribbons 10 is set to be larger than the representative oxide film thickness of the intermediate ribbon 40 sandwiched between the outermost ribbon 20 and the innermost ribbon 30. As a result, thick oxide films can be formed on the inner circumferential surface 1a and outer circumferential surface 1b exposed to the atmosphere in the wound core 1 formed by winding multiple layers of nanocrystalline material ribbons 10, within a range that allows the wound core 1 to obtain the target magnetic properties. As a result, the inner circumferential surface 1a and outer circumferential surface 1b of the wound core 1 can be protected by the oxide film, and as a result, the weather resistance of the wound core 1 can be improved.

[0076] In the above-described embodiment, a wound core for a power conversion transformer is illustrated, but the present invention is not limited to this. For example, the wound core may be a wound core applied to a magnetic device other than a power conversion transformer, such as a choke coil.

[0077] In the above-described embodiment, the nanocrystalline ribbon has a low oxidation degree in the central portion in the width direction and a high oxidation degree in the end portions, but the present invention is not limited thereto. For example, the nanocrystalline ribbon may have a high oxidation degree in the central portion in the width direction and a low oxidation degree in the end portions.

[0078] In addition, in the above-described embodiment, an example was given of a wound core that has an annular shape with rounded corners in a plan view, but the present invention is not limited to this. For example, the wound core may have an annular shape other than a rounded rectangle, such as a circle, an ellipse, or an oval, in a plan view.

[0079] In the above-described embodiment, the primary heat treatment of the nanocrystalline ribbon is performed by placing the roll surface of the nanocrystalline ribbon facing the heating surface of the heater, but the present invention is not limited to this. For example, in the primary heat treatment of the nanocrystalline ribbon, the free surface may be placed facing the heating surface of the heater. [Example]

[0080] The present invention will be described in more detail below with reference to examples. Note that the present invention is not limited to the following examples. Furthermore, unless otherwise specified, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower and upper limits.

[0081] (Example) In the example, a plurality of samples of wound core 1 (hereinafter referred to as wound core samples) were produced using the manufacturing method of wound core 1 according to the embodiment of the present invention. The nanocrystalline material ribbon constituting the wound core sample underwent a primary heat treatment while sandwiching and covering the nanocrystalline material ribbon in the thickness direction F3 between the fixed sheet 52 and the movable sheet 53. The secondary heat treatment of the nanocrystalline material ribbon was performed in a wound core state in a magnetic field. The heat treatment temperatures of the nanocrystalline material ribbon in the primary and secondary heat treatments were within a range of −50 to +150°C from the first crystallization temperature at which α-Fe crystals precipitate, similar to the manufacturing method of wound core 1 described above. Specifically, the heat treatment temperature of the nanocrystalline material ribbon in the primary heat treatment was 465°C, and the heat treatment time was 8 seconds. The heat treatment temperature of the nanocrystalline material ribbon in the secondary heat treatment was 450°C, and the heat treatment time was 10 minutes.

[0082] For each of the wound core samples prepared as described above, the core loss per unit mass (W / kg) was measured when excited with a maximum magnetic flux density of 1.6 T at a frequency of 50 Hz. Furthermore, nanocrystalline ribbon samples (hereinafter referred to as ribbon samples) were collected from each of the wound core samples. For each of the collected ribbon samples, the oxide film thickness was measured at the center and end portions in the width direction F2 on the roll surface, and at the center and end portions in the width direction F2 on the free surface. FIG. 9 is a schematic diagram showing the measurement area for the oxide film thickness of a ribbon sample in the example. As shown in FIG. 9, for ribbon sample 100 of the example, the central region in a center portion 111 in the width direction F2 was designated as a representative portion R1 to be measured, and the oxide film thickness of the representative portion R1 of this center portion 111 was measured. In addition, in the ribbon sample 100 of the example, of the end portions 112, 113 on both sides in the width direction F2, the central region of one end portion 112 was set as the representative portion R2 to be measured, and the oxide film thickness of the representative portion R2 of this end portion 112 was measured.

[0083] The measurement results of core loss and oxide film thickness in the examples are shown in Table 1 below, along with the heat treatment conditions for the primary heat treatment and the secondary heat treatment. In Table 1, "core loss of wound core" is the core loss measured for the wound core sample, and "oxide film thickness" is the oxide film thickness measured for the ribbon sample. Also, "center" is the center in the width direction of the ribbon sample, and "end" is the end in the width direction of the ribbon sample.

[0084] As shown in Table 1, in the example, the core loss was measured for each of a plurality of wound core samples, and a low core loss of less than 0.5 W / kg (specifically, 0.40 to 0.46 W / kg) was obtained.

[0085] In the examples, the oxide film thickness was measured for each of a plurality of ribbon samples, and the oxide film thickness at the center of the roll surface of the ribbon sample was 65 to 193 nm, and the oxide film thickness at the end of the roll surface was 122 to 223 nm. The oxide film thickness at the center of the free surface of the ribbon sample was 83 to 132 nm, and the oxide film thickness at the end of the free surface was 106 to 207 nm.

[0086] Here, when comparing the oxide film thicknesses measured in the examples by dividing them into the center and the end portions, the lower limit of the oxide film thickness at the end portions is the lower limit of the oxide film thickness at the end portions on the free surface (=106 nm), and the lower limit of the oxide film thickness at the center portions is the lower limit of the oxide film thickness at the center portions on the roll surface (=65 nm). Therefore, the lower limit of the oxide film thickness at the end portions is larger than the lower limit of the oxide film thickness at the center portions. Furthermore, the upper limit of the oxide film thickness at the center portions is the upper limit of the oxide film thickness at the center portions on the roll surface (=193 nm), and the upper limit of the oxide film thickness at the end portions is the upper limit of the oxide film thickness at the end portions on the roll surface (=223 nm). Therefore, the upper limit of the oxide film thickness at the center portions is smaller than the upper limit of the oxide film thickness at the end portions.

[0087] Therefore, the median (center value) of the oxide film thickness at the end is larger than the median of the oxide film thickness at the center on both the roll surface and the free surface. Specifically, the median oxide film thickness at the end on the roll surface is 172.5 nm, and the median oxide film thickness at the end on the free surface is 156.5 nm. The median oxide film thickness at the center on the roll surface is 129 nm, and the median oxide film thickness at the center on the free surface is 107.5 nm. From the above, it can be seen that in the example, the oxide film thickness at the end is thicker than the oxide film thickness at the center.

[0088] In addition, in the examples, an outermost ribbon sample, an innermost ribbon sample, and an intermediate ribbon sample were taken from each of a plurality of wound core samples, and the oxide film thickness of a representative portion of each of these samples was measured. As a result, the oxide film thickness of the outermost ribbon was 223 nm, the oxide film thickness of the innermost ribbon was 153 nm, and the oxide film thickness of the intermediate ribbon was 114 nm. Comparing these oxide film thicknesses, it was found that the oxide film thickness of the intermediate ribbon was thinner than both the oxide film thickness of the outermost ribbon and the oxide film thickness of the innermost ribbon.

[0089] Furthermore, when focusing on the core loss and oxide film thickness in the examples, it was found that the upper limit of the oxide film thickness was 350 nm or less (specifically, 315 nm or less), and at this time, the core loss of the wound core (measurement conditions: frequency = 50 Hz, maximum magnetic flux density = 1.6 T) was 1.0 W / kg or less (specifically, less than 0.5 W / kg).

[0090] (Comparative Example) Next, a comparative example of the present invention will be described. In the comparative example, the fixed sheet 52 and the movable sheet 53 described above were not used, and the nanocrystalline ribbon was heated from one side in the thickness direction F3 by the heater 51, thereby performing a primary heat treatment on the nanocrystalline ribbon. A plurality of wound core samples of the comparative example were produced by the same manufacturing method as in the example, except for the method of the primary heat treatment. The heat treatment conditions for the primary heat treatment and the secondary heat treatment in the comparative example were the same as in the example.

[0091] In the comparative example, the core loss (W / kg) was measured for each of the wound core samples prepared as described above under the same measurement conditions as in the example. Then, for each of the ribbon samples taken from each of the wound core samples, the oxide film thickness was measured at the center and end portions in the width direction F2 on the roll surface and the oxide film thickness at the center and end portions in the width direction F2 on the free surface, in the same manner as in the example.

[0092] The measurement results of the core loss and oxide film thickness in the comparative example are shown in Table 1, along with the heat treatment conditions for the primary heat treatment and the secondary heat treatment. In the comparative example, as shown in Table 1, the core loss measured for each of the multiple wound core samples was 3.8 to 4.2 W / kg, which was extremely high compared to the examples. Furthermore, in the comparative example, the oxide film thickness on the roll surface and the oxide film thickness on the free surface of the ribbon sample did not differ between the center and the end in the width direction F2, being approximately 800 nm and 900 nm, respectively. That is, the oxide film thickness of the ribbon sample in the comparative example was thicker than the examples, exceeding 350 nm. Furthermore, it was found that the core loss of the wound core in the comparative example (measurement conditions: frequency = 50 Hz, maximum magnetic flux density = 1.6 T) was a high value exceeding 1.0 W / kg.

[0093] [Table 1]

[0094] The present invention is not limited to the above-described embodiments and examples, and also includes configurations in which the above-described components are appropriately combined. In addition, other embodiments, examples, and operational techniques made by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention. Industrial Applicability

[0095] As described above, the wound core according to the present invention is suitable for use as a wound core with excellent magnetic properties. [Explanation of symbols]

[0096] 1 wound core 1a Inner surface 1b Outer surface 2, 3 legs 4, 5 windings 9, 10 Nanocrystalline ribbon 10L center axis 11, 11A, 11B center part 12, 12A, 12B, 13, 13A, 13B End 14 First Belt 15 Second Belt 16a, 16b side 17 Internal organization 18 Oxide film 20 Outermost thin ribbon 30 Innermost thin ribbon 40 Medium thin ribbon 50 Heat treatment equipment 51 Heater 51a Heating surface 52 Fixed seat 53 Movable seat 54, 55 Guide roll 100 thin ribbon samples 111 Central part 112, 113 End F1 Longitudinal F2 width direction F3 thickness direction R1, R2 representative parts

Claims

1. A wound core formed by winding a thin ribbon made of a nanocrystalline material and having an oxidized surface in multiple layers, The thin ribbon is the oxidation degree of the central portion of the ribbon in the width direction is different from the oxidation degree of the end portions of the ribbon located on both sides of the central portion in the width direction; A wound core characterized by:

2. The oxidation degree of the end portion of the ribbon is higher than the oxidation degree of the central portion.

2. The wound core according to claim 1 .

3. the oxide film thickness on both surfaces of the ribbon in the thickness direction is 5 nm or more and 350 nm or less; a representative value of the oxide film thickness at the central portion is different from a representative value of the oxide film thickness at the end portion on the same surface in the thickness direction of the ribbon; 3. A wound core according to claim 1 or 2.

4. On each of the two surfaces of the ribbon in the thickness direction, the color of the central portion is different from the color of the end portion.

4. A wound core according to claim 1.

5. a representative value of the oxide film thickness in each of the outermost and innermost ribbons among the plurality of layers of the ribbons is larger than a representative value of the oxide film thickness in an intermediate ribbon sandwiched between the outermost and innermost ribbons; 5. A wound core according to claim 1.

Images