Magnetic sheet and inductor

Abstract

To provide a magnetic sheet and an inductor that can achieve both excellent adhesion of the first main surface and excellent adhesion of the second main surface. [Solution] The magnetic sheet 1 has a first main surface 2 and a second main surface 3 facing each other in the thickness direction. The magnetic sheet 1 contains magnetic particles and resin. The total amount ratio of carbon and oxygen on either the first main surface 2 or the second main surface 3 is 10% by mass or more and 60% by mass or less.

Description

Technical Field

[0001] The present invention relates to a magnetic sheet and an inductor.

Background Art

[0002] A magnetic sheet containing magnetic particles and a resin is known (see, for example, Patent Document 1 below). In Patent Document 1, magnetic particles and a resin are dispersed in an organic solvent to prepare a magnetic composition solution (varnish), which is applied to a separator and heated after drying to obtain a magnetic sheet. The magnetic sheets are laminated and adhered to each other, adhered to a substrate, or coated on wiring and adhered to the wiring.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the method of Patent Document 1, during drying, the particles sink, so the proportion of resin on the surface may become excessively high. Then, the adhesion of the surface of the magnetic sheet increases.

[0005] On the other hand, if the proportion of resin on the back surface becomes excessively low, the adhesion of the back surface decreases. However, for the magnetic sheet, both excellent adhesion on the surface and excellent adhesion on the back surface (excellent balance) are required.

[0006] The present invention provides a magnetic sheet and an inductor capable of achieving both excellent adhesion on the first main surface and excellent adhesion on the second main surface.

Means for Solving the Problems

[0007] The present invention (1) includes a magnetic sheet having a first main surface and a second main surface facing each other in the thickness direction, containing magnetic particles and resin, wherein the total amount ratio of carbon and oxygen on either the first main surface or the second main surface is 10% by mass or more and 60% by mass or less.

[0008] The present invention (2) includes the magnetic sheet described in (1), wherein the total amount ratio in the first main surface and the second main surface, respectively, is 10% by mass or more and 50% by mass or less.

[0009] The present invention (3) includes a magnetic sheet according to (1) or (2), wherein the total amount ratio on the first main surface and the total amount ratio on the second main surface are the same, or the total amount ratio on one of the first and second main surfaces is lower than the total amount ratio on the other remaining surface, and the ratio of the total amount ratio on the one surface to the total amount ratio on the other surface is 0.3 or more and less than 1.0.

[0010] The present invention (4) includes a magnetic sheet according to any one of (1) to (3), wherein the total amount ratio on either the first main surface or the second main surface is the same as the total amount ratio in the center in the thickness direction, or the total amount ratio on the one surface is lower than the total amount ratio in the center, and the ratio of the total amount ratio on the one surface to the total amount ratio in the center is 0.3 or more and less than 1.

[0011] The present invention (5) includes an inductor comprising wiring and a magnetic sheet described in any one of (1) to (4) for covering the wiring. [Effects of the Invention]

[0012] In the magnetic sheet of the present invention, the total amount ratio of carbon and oxygen on either the first main surface or the second main surface is 10% by mass or more and 60% by mass or less, so that an excessive decrease in the resin ratio on the first main surface and the second main surface can be suppressed.

[0013] Therefore, the magnetic sheet and the inductor can achieve both excellent adhesion on the first main surface and excellent adhesion on the second main surface. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a cross-sectional view of one embodiment of the magnetic sheet of the present invention. [Figure 2] Figures 2A and 2B are process diagrams for obtaining a magnetic sheet by the first manufacturing method. Figure 2A shows the process of preparing the coating film. Figure 2B shows the process of drying the coating film in the first dryer. [Figure 3] Figure 3 is a schematic diagram showing the drying of the coating film in a second dryer using the second manufacturing method. [Figure 4] Figures 4A and 4B are manufacturing process diagrams for laminated magnetic sheets. Figure 4A shows the process of arranging multiple magnetic sheets. Figure 4B shows the process of obtaining a laminated magnetic sheet. [Figure 5] Figure 5 is a cross-sectional view of the inductor. [Figure 6] Figures 6A and 6B are side views of the adhesion force measurement in the embodiment. Figure 6A is Test A. Figure 6B is Test B. [Modes for carrying out the invention]

[0015] <An embodiment of a magnetic sheet> One embodiment of the magnetic sheet of the present invention will be described with reference to Figure 1.

[0016] As shown in Figure 1, the magnetic sheet 1 has a first main surface 2 and a second main surface 3. The first main surface 2 and the second main surface 3 face each other in the thickness direction. The magnetic sheet 1 extends in a direction perpendicular to the thickness direction. The magnetic sheet 1 also contains magnetic particles and resin. The magnetic particles and resin will be explained in detail later.

[0017] <Total percentage of carbon and oxygen on the first and second main surfaces> The total proportion of carbon and oxygen on either the first major surface 2 or the second major surface 3 is 10% by mass or more and 60% by mass or less. When the total proportion of carbon and oxygen on either the first major surface 2 or the second major surface 3 is below the above-mentioned lower limit (10% by mass), the proportion of the resin on the first major surface 2 and the second major surface 3 becomes excessively low. When the total proportion of carbon and oxygen on either the first major surface 2 or the second major surface 3 exceeds the above-mentioned upper limit (60% by mass), the proportion of the resin on the first major surface 2 and the second major surface 3 becomes excessively high. In either case, it is impossible to achieve both the excellent adhesion of the first major surface 2 and the excellent adhesion of the second major surface 3.

[0018] The total proportion of carbon and oxygen on either the first major surface 2 or the second major surface 3 is preferably 13% by mass or more, more preferably 15% by mass or more, and even more preferably 17% by mass or more. Also, the total proportion of carbon and oxygen on either the first major surface 2 or the second major surface 3 is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 25% by mass or less. If the total proportion of carbon and oxygen on either the first major surface 2 or the second major surface 3 is above the above-mentioned lower limit or below the above-mentioned upper limit, it is possible to further achieve both the excellent adhesion of the first major surface 2 and the excellent adhesion of the second major surface 3.

[0019] Furthermore, the total proportion of carbon and oxygen on each of the first major surface 2 and the second major surface 3 is, for example, 10% by mass or more, preferably 15% by mass or more, and also, for example, 50% by mass or less. In this case, in either the first major surface 2 or the second major surface 3, excessive segregation of particles can be suppressed, the resin can exist in an appropriate proportion, and the balance of the adhesion of the first major surface 2 and the second major surface 3 can be achieved.

[0020] The total proportion of carbon and oxygen on each of the first major surface 2 and the second major surface 3 is determined by energy dispersive X-ray spectroscopy (EDX).

[0021] The total proportion of carbon and oxygen refers to the relative proportion of carbon and oxygen to the total elements constituting the magnetic sheet 1, and is an indicator of the proportion of organic components, i.e., resin (organic components), in the magnetic sheet 1. As described later, EDX analysis can be used to analyze the elements constituting the magnetic sheet 1.

[0022] For example, if magnetic sheet 1 contains Fe-Si magnetic particles (described later) and resin, the constituent elements in magnetic sheet 1 are C, O, Si, and Fe. Therefore, in this case, the total proportion of carbon and oxygen is the relative proportion of the total amount of C and O to the total amount of C, O, Si, and Fe; in other words, it represents the proportion (percentage) of C and O when C, O, Si, and Fe are set to 100%. Note that in EDX analysis, elements such as Pt are sometimes used in the sample preparation process, but such elements are excluded.

[0023] In EDX analysis, the analysis field is, for example, in the range of width 300 to 2,500 μm and height 200 to 2,500 μm, more preferably in the range of width 500 to 700 μm and height 300 to 500 μm. The analysis points may be in one field or multiple fields. Preferably, in order to understand the trend of the entire main surface, there are multiple analysis points (e.g., 2 to 4 analysis points), and specifically, the average value of the multiple analysis points is obtained.

[0024] The magnification ratio in EDX analysis is, for example, 50 times or more, preferably 100 times or more, and also, for example, 400 times or less, preferably 300 times or less from the viewpoint of understanding the overall trend of the main surface.

[0025] Furthermore, during EDX (Electron Diatomography) of the first main surface 2 and the second main surface 3, surface SEM (Scanning Emission Microscope) observations of the first main surface 2 and the second main surface 3 are performed simultaneously.

[0026] Furthermore, the total proportion of carbon and oxygen on the first main surface 2 and the total proportion of carbon and oxygen on the second main surface 3 are preferably the same (Requirement [1]).

[0027] In this application, "identical" in the comparison of the proportions of the two includes a relationship where multiplying one by a value of 0.95 or more or 1.04 or less results in the other being equal (so-called "approximately identical").

[0028] Alternatively, if the total amount of carbon and oxygen on one of the first main surface 2 and the second main surface 3 is lower than the total amount of carbon and oxygen on the other surface, the ratio R1 of the total amount of carbon and oxygen on one surface to the total amount of carbon and oxygen on the other surface is preferably 0.3 or greater, and for example, less than 1.0 (Requirement [2]). Ratio R1 may hereafter be referred to as the first ratio R1.

[0029] If requirement [1] or requirement [2] is met, an excessive decrease in the total proportion of carbon and oxygen on one surface can be avoided, thereby further enhancing the excellent adhesion of the first main surface 2 and the excellent adhesion of the second main surface 3.

[0030] The requirements [1] and [2] are more preferably satisfied by requirement [2]. Satisfying requirement [2] makes it possible to more reliably achieve both the excellent adhesion of the first main surface 2 and the excellent adhesion of the second main surface 3.

[0031] The first ratio R1 is preferably 0.4 or higher, more preferably 0.5 or higher, and even more preferably 0.6 or higher.

[0032] The entire area of ​​the first main surface 2 and the second main surface 3 satisfies the above-described total amount ratio, or a portion of the area satisfies it. The portion is, for example, an area of ​​50% or more of the entire area, preferably an area of ​​70% or more of the entire area, and more preferably an area of ​​90% or more of the entire area.

[0033] <Total percentage of carbon and oxygen in the center of the thickness direction> The total amount of carbon and oxygen in the central portion 4 of the magnetic sheet 1 in the thickness direction is, for example, 10% by mass or more, preferably 20% by mass or more, and also, for example, 60% by mass or less, preferably 50% by mass or less. The central portion 4 is the part between the first main surface 2 and the second main surface 3. Specifically, the central portion 4 is the part that extends inward from the first main surface 2 or the second main surface 3 in the thickness direction by half the thickness.

[0034] Preferably, the total proportion of carbon and oxygen in the one surface described above and the total proportion of carbon and oxygen in the central part 4 are the same (Requirement [3]).

[0035] Alternatively, if the total amount of carbon and oxygen on one surface is lower than the total amount of carbon and oxygen in the central part 4, the ratio R2 of the total amount of carbon and oxygen on one surface to the total amount of carbon and oxygen in the central part 4 is preferably 0.3 or more and less than 1 (Requirement [4]). Ratio R2 may hereafter be referred to as the second ratio R2.

[0036] If requirements [3] or [4] are met, an excessive decrease in the total proportion of carbon and oxygen on one surface can be avoided, thereby improving adhesion.

[0037] The requirements [3] and [4] are more preferably satisfied by requirement [4]. Satisfying requirement [4] improves the adhesion force of one surface and further improves the cohesive force of the magnetic sheet 1.

[0038] The second ratio R2 is preferably 0.4 or higher, more preferably 0.5 or higher, and even more preferably 0.6 or higher. Furthermore, the second ratio R2 is preferably 0.9 or lower, and more preferably 0.8 or lower.

[0039] The total proportion of carbon and oxygen in the central region 4 is determined by energy-dispersive X-ray spectroscopy (EDX). Specifically, first, the magnetic sheet 1 is cut along its thickness to expose the cross-section, and then EDX analysis is performed on the central region 4 in the cross-section.

[0040] Specifically, first, the magnetic sheet 1 is cut along its thickness to expose the cross-section, and then EDX analysis is performed on the central part 4 of the cross-section.

[0041] In this application, the term "central region" refers to the central region in the thickness direction when the magnetic sheet 1 is cut along the thickness direction and the cross-section is exposed. If the thickness direction is divided into three parts, the central region refers to the area of ​​1 / 3 of the thickness direction, and if it is divided into five parts, the central region refers to the area of ​​20% of the thickness. Depending on the number of divisions, an area of ​​10-30% in the thickness direction relative to the center can be observed as the central region.

[0042] When performing EDX analysis, it is necessary to specify the width in addition to the height as part of the measurement area. In this case, the measurement area should be a rectangular region with a width 5 to 10 times the height. For example, this area might be about 5 times the height.

[0043] In addition, cross-sectional SEM observation will be performed simultaneously with the EDX examination of the central section 4.

[0044] The thickness of the magnetic sheet 1 is not particularly limited. For example, the thickness of the magnetic sheet 1 may be 1 μm or more, and 1 mm or less.

[0045] Next, a method for manufacturing the magnetic sheet 1 will be described. The manufacturing method is not particularly limited. The manufacturing method includes, for example, a first manufacturing method and a second manufacturing method.

[0046] <First manufacturing method> First, the first manufacturing method will be explained with reference to Figures 2A and 2B.

[0047] In the first manufacturing method, a magnetic composition is first prepared. The magnetic composition contains magnetic particles and a resin. Magnetic compositions are disclosed, for example, in Japanese Patent Publication Nos. 2020-150057, 2020-150060, 2020-150063, and 2020-150066. Examples of magnetic particles include particles made of soft magnetic material, preferably flattened Fe-Si alloy magnetic particles, flattened Fe-Si-Al alloy, and spherical carbonyl iron powder. The proportion of particles in the magnetic composition is, for example, 90% by volume or less, preferably 80% by volume or less, and also, for example, 10% by volume or more, preferably 20% by volume or more. Examples of resins include thermoplastic resins and thermosetting resins, preferably acrylic resins and epoxy resin compositions. The proportion of resin in the magnetic composition is, for example, 90% by volume or less, preferably 80% by volume or less, and also, for example, 10% by volume or more, preferably 20% by volume or more.

[0048] Preferably, a varnish (magnetic composition solution) is prepared by further blending an organic solvent with the magnetic composition. Specifically, the varnish contains magnetic particles, a resin, and a solvent. Examples of solvents include organic solvents and aqueous solvents. Examples of organic solvents include ketone compounds, ester compounds, ether compounds, and amide compounds. Examples of ketone compounds include acetone and methyl ethyl ketone. Examples of ester compounds include ethyl acetate. Examples of ether compounds include propylene glycol monomethyl ether. For example, an example of an amide compound is N,N-dimethylformamide. Examples of aqueous solvents include water and alcohols. Examples of alcohols include methanol, ethanol, propanol, and isopropanol. From the viewpoint of being removable in a short time, organic solvents are preferred as the solvent. The proportion of solvent in the varnish is, for example, 5% by mass or more, and for example, 90% by mass or less. The solid content concentration in the varnish is, for example, 10% by mass or more, and for example, 95% by mass or less.

[0049] Next, a varnish is applied. As shown in Figure 2A, for example, the varnish is applied to the release sheet 5. The release sheet 5 extends in the planar direction. The release sheet 5 has a third main surface 6 and a fourth main surface 7 that are opposite each other in the thickness direction. At least the third main surface 6 is peeled. The release sheet 5 includes, for example, a resin sheet and a metal sheet. Examples of resins include polyester and polyolefin. Examples of polyester include polyethylene terephthalate. Examples of polyolefins include polyethylene and polypropylene. The thickness of the release sheet 5 is, for example, 1 μm or more, and also, for example, 500 μm or less.

[0050] Varnish is applied to the third main surface 6 of the release sheet 5. For example, an applicator, bar coating, or brush application can be used. Preferably, an applicator is used. The varnish is applied by machine or by hand. Preferably, the varnish is applied by hand.

[0051] This forms a coating film 8 on the third main surface 6. Immediately after application, the coating film 8 still contains solvent. If the resin includes a thermosetting resin, the thermosetting resin is in stage A. The thickness of the coating film 8 is set so that its thickness after drying is equal to the thickness of the magnetic sheet 1.

[0052] Next, the coating film 8 is left at room temperature. Specifically, room temperature is 20°C or higher and 30°C or lower. The standing time is, for example, 3 minutes or more, preferably 5 minutes or more. There is no upper limit to the standing time. The normal pressure is atmospheric pressure, which is about 0.1 MPa.

[0053] During the standing period of the coating film 8, wind is present around the coating film 8, and the generation of parallel flow and impinging flow (both described later) is permitted. The upper limit of the wind speed for parallel flow is, for example, 0.5 m / sec, preferably 0.25 m / sec. The upper limit of the wind speed for impinging flow is, for example, 1 m / sec, preferably 0.5 m / sec. The wind speed is measured by a thermal anemometer, Anemomaster.

[0054] Subsequently, the coating film 8 is dried by heating. As shown in Figure 2B, for example, a first dryer 9 is used for drying by heating. Examples of the first dryer 9 include a hot air dryer 10, a hot plate, and an infrared lamp. Preferably, the first dryer 9 is a hot air dryer 10. On the other hand, a hand dryer is unsuitable as the first dryer 9 because the coating film 8 is heated by contact with the impinging flow (described later).

[0055] As a preferred example of the first dryer 9, a tabletop hot air dryer 10 will be described. The hot air dryer 10 comprises a housing 11, a shelf 12, a heat source (not shown), and a blower (not shown). The housing 11 has a box shape. The shelf 12 extends horizontally. The shelf 12 is provided with a plurality of holes 13. The plurality of holes 13 penetrate the shelf 12 vertically. Hot air can pass through the plurality of holes 13. However, each of the plurality of holes 13 is smaller than the release sheet 5. The heat source (not shown) is located inside the housing 11. The blower is close to the heat source. The air blown from the blower comes into contact with the heat source and becomes hot air. The hot air flows along the shelf 12 (horizontally). On the upper side of the shelf 12, the hot air that reaches the downstream end in the direction of flow passes through the holes 13 and reaches the lower side of the shelf 12. At the lower side of the shelf 12, the hot air that reaches the downstream end in the direction of airflow passes through the hole 13 and reaches the upper side of the shelf 12. In this way, the hot air circulates inside the housing 11 in the hot air dryer 10.

[0056] The coating film 8 and the release sheet 5 are placed in the hot air dryer 10. Specifically, the release sheet 5 is placed on the top surface of the shelf board 12.

[0057] In the hot air dryer 10, the impact flow of hot air hitting the coating film 8 from above is suppressed as much as possible. However, in the hot air dryer 10, the coating film 8 is heated to a predetermined temperature by a parallel flow parallel to the surface direction. This heats the coating film 8. Specifically, the coating film 8 is heated gently.

[0058] The wind speed of the parallel flow is, for example, 0.5 m / sec or more, preferably 1 m / sec or more, and also, for example, 5 m / sec or less, preferably 3.0 m / sec or less, and more preferably 2.5 m / sec or less. The wind speeds of the parallel flow and the impinging flow are measured by a thermal anemometer, Anemomaster.

[0059] The heating time is, for example, 1 minute or more, preferably 2 minutes or more, and also, for example, 15 minutes or less, preferably 10 minutes or less.

[0060] The internal temperature of the hot air dryer 10 is, for example, 50°C or higher, and also, for example, 130°C or lower.

[0061] By drying the coating film 8 using the first dryer 9, the solvent is removed from the coating film 8, and the magnetic sheet 1 is formed. If the resin contains a thermosetting resin, the thermosetting resin is in stage B.

[0062] As shown in Figure 2A, the first main surface 2 of the magnetic sheet 1 obtained by the first manufacturing method is the top surface (front surface) and is the surface opposite to the release sheet 5. The second main surface 3 of the magnetic sheet 1 is the bottom surface (back surface) and is the contact surface that comes into contact with the release sheet 5.

[0063] The magnetic sheet 1 obtained by the first manufacturing method satisfies requirement [2], for example (see Example 1 in Table 2). In this case, for example, the total proportion of carbon and oxygen on the first main surface 2 is lower than the total proportion of carbon and oxygen on the second main surface 3. Therefore, the first ratio R1 is the total proportion of carbon and oxygen on the first main surface 2 relative to the total proportion of carbon and oxygen on the second main surface 3. In the first manufacturing method, the sinking of magnetic particles downward is suppressed. Therefore, the proportion of resin on the first main surface 2 is moderately lower than the proportion of resin on the third main surface 6. That is, the resin is moderately segregated on the second main surface 3. Therefore, it is possible to achieve both excellent adhesion of the first main surface 2 and excellent adhesion of the second main surface 3.

[0064] Furthermore, the magnetic sheet 1 obtained by the first manufacturing method satisfies requirement [4] (see Example 1 in Table 2). In this case, for example, the total amount ratio of carbon and oxygen on the first main surface 2 is lower than the total amount ratio of carbon and oxygen on the central part 4, and the second ratio R2 of the total amount ratio of carbon and oxygen on the first main surface 2 to the total amount ratio of carbon and oxygen on the central part 4 is 0.3 or more and less than 1. In the first manufacturing method, the sinking of magnetic particles downward is suppressed. Therefore, the proportion of resin on the first main surface 2 is moderately lower than the proportion of resin on the central part 4. The first main surface 2 can suppress a decrease in adhesion.

[0065] <Second manufacturing method> In the second manufacturing method, a magnetic composition (varnish) is prepared. The preparation method is the same as that of the first manufacturing method. Subsequently, the varnish is applied. In the second manufacturing method, the application method is not particularly limited. Examples of application methods include blade coating, gravure coating, fountain coating, cast coating, spin coating, comma coating, die coating, and roll coating. The application is carried out, for example, in a continuous manner or in a single-wafer manner. The application is carried out, for example, by machine or by hand, and preferably by machine from the viewpoint of manufacturing efficiency. To carry out the application by machine, a coating machine 25 for carrying out the above-described application method is arranged as shown in Figure 3. Specifically, the coating machine 25 is placed between two rolls 33. The two rolls 33 are a feed roll and a take-up roll, respectively. The feed roll feeds out the release sheet 5. The take-up roll takes up the laminated sheet 34 comprising the release sheet 5 and the magnetic sheet 1. The release sheet 5 is unfurled from the feed roll, and the varnish is continuously applied to the release sheet 5 using the coating machine 25.

[0066] In the second manufacturing method, for example, the coating film 8 is dried by heating using a second dryer 30. The second dryer 30 may be, for example, a continuous dryer 14.

[0067] The continuous dryer 14 is positioned downstream of the coating machine 25 in the conveying direction. The continuous dryer 14 is equipped with multiple drying chambers 15, 16, 17, and 18.

[0068] The multiple drying chambers 15, 16, 17, and 18 are arranged in order toward the downstream side in the transport direction of the release sheet 5, with the first drying chamber 15, the second drying chamber 16, the third drying chamber 17, and the fourth drying chamber 18. Adjacent drying chambers are separated by partition walls 21. An opening 22 is formed at the bottom of the partition wall 21 through which the release sheet 5 and the coating film 8 pass. Furthermore, the first drying chamber 15, the second drying chamber 16, and the third drying chamber 17 are configured such that the internal temperature increases as you move toward the downstream side in the transport direction. Each of the multiple drying chambers 15, 16, 17, and 18 is equipped with a heat source (not shown), a blower 27, and an outlet 19.

[0069] The outlet 19 is positioned downstream of the blower 27 in the direction of airflow. The outlet 19 faces the paint film 8 being conveyed. The opening cross-sectional area of ​​the outlet 19 decreases as it moves towards the paint film 8.

[0070] The first drying chamber 15, the second drying chamber 16, and the third drying chamber 17 are equipped with shielding members 20. However, the fourth drying chamber 18 is not equipped with a shielding member 20. Each of the multiple shielding members 20 covers the outlet of the air outlet 19. Examples of shielding members 20 include pressure-sensitive adhesive tape (adhesive tape). The shielding member 20 also serves as a sealing tape. Due to the shielding member 20, the hot air generated by the heat source (not shown) and the operation of the blower 27 does not pass through the outlet of the air outlet 19, but leaks to the side of the inlet of the air outlet 19. As a result, in the first drying chamber 15, the second drying chamber 16, and the third drying chamber 17, a collision flow of hot air from above onto the coating film 8 does not substantially occur, or the collision flow is slow. On the other hand, a collision flow occurs in the fourth drying chamber 18.

[0071] In addition, the first drying chamber 15, the second drying chamber 16, and the third drying chamber 17 are set to a predetermined internal temperature by the warm air leaking laterally from the outlet 19 described above. In the fourth drying chamber 18, the predetermined internal temperature is set by the impinging flow described above. The temperatures of the multiple drying chambers 15, 16, 17, and 18 are, for example, 50°C or higher and, for example, 130°C or lower. Specifically, the temperature of the first drying chamber 15 is, for example, 50°C or higher and, and less than 70°C. The temperature of the second drying chamber 16 is, for example, 70°C or higher and, and less than 90°C. The temperatures of the third drying chamber 17 and the fourth drying chamber 18 are, for example, 90°C or higher and, for example, 130°C or lower.

[0072] As the coating film 8 passes through multiple drying chambers 15, 16, 17, and 18 of the second dryer 30, the solvent is removed and the magnetic sheet 1 is formed on the upper surface of the release sheet 5. If the resin contains a thermosetting resin, the thermosetting resin enters the B stage. The magnetic sheet 1, together with the release sheet 5, forms a laminated sheet 34. The laminated sheet 34 is wound up on a winding roll.

[0073] In the magnetic sheet 1 obtained by the second manufacturing method, the first main surface 2 is the top surface (front surface) and is the surface opposite to the release sheet 5. The second main surface 3 of the magnetic sheet 1 is the bottom surface (back surface) and is the contact surface that comes into contact with the release sheet 5.

[0074] The magnetic sheet 1 obtained by the second manufacturing method satisfies requirement [1], for example (see Example 2 in Table 2). In this case, for example, the total proportion of carbon and oxygen on the first main surface 2 is the same as the total proportion of carbon and oxygen on the second main surface 3. Therefore, the proportion of resin on the first main surface 2 is the same as the proportion of resin on the third main surface 6. As a result, there is an excellent balance between the excellent adhesion of the first main surface 2 and the excellent adhesion of the second main surface 3.

[0075] The magnetic sheet 1 obtained by the second manufacturing method satisfies requirement [4], for example (see Example 2 in Table 2). In this case, for example, the total amount ratio of carbon and oxygen on the second main surface 3 is lower than the total amount ratio of carbon and oxygen on the central part 4, and the second ratio R2 of the total amount ratio of carbon and oxygen on the second main surface 3 to the total amount ratio of carbon and oxygen on the central part 4 is 0.3 or more and less than 1. In the second manufacturing method, the proportion of resin on the second main surface 3 is moderately lower than the proportion of resin on the central part 4. Therefore, the second main surface 3 has excellent adhesion.

[0076] <Variation of the second manufacturing method> In the following modifications, the same reference numerals are used for components and processes as in the second embodiment described above, and their detailed descriptions are omitted. Furthermore, the modifications can achieve the same effects and advantages as the second embodiment, unless otherwise noted. In addition, the second embodiment and its modifications can be combined as appropriate.

[0077] Although not shown in the diagram, the second dryer 30 (continuous dryer 14) does not need to be equipped with a shielding member 20. In this case, a collision flow occurs in each of the multiple drying chambers 15, 16, 17, and 18. Therefore, in the modified drying method, the collision flow hits the coating film 8 for a longer time compared to the drying method of the second manufacturing method. As a result, the surface of the coating film 8 (the surface corresponding to the first main surface 2 of the magnetic sheet 1) dries and solidifies quickly, making it difficult for the interior of the coating film 8 (the part corresponding to the central part 4 in the thickness direction of the magnetic sheet 1) to dry, and the magnetic particles settle. As a result, in the magnetic sheet 1, the proportion of resin on the first main surface 2 is moderately higher than the proportion of resin on the second main surface 3.

[0078] In other words, the magnetic sheet 1 obtained by this modification preferably satisfies requirement [2] (see Example 3 in Table 2). In this case, for example, the total proportion of carbon and oxygen on the second main surface 3 is lower than the total proportion of carbon and oxygen on the first main surface 2. Therefore, the first ratio R1 is the total proportion of carbon and oxygen on the second main surface 3 relative to the total proportion of carbon and oxygen on the first main surface 2. In the second manufacturing method, although there is some sinking of magnetic particles downward, the degree of this is suppressed as much as possible. Therefore, the proportion of resin on the second main surface 3 is moderately lower than the proportion of resin on the first main surface 2. That is, the resin is moderately segregated on the first main surface 2. Therefore, it is possible to achieve both excellent adhesion of the second main surface 3 and excellent adhesion of the first main surface 2.

[0079] Furthermore, the magnetic sheet 1 obtained by the second manufacturing method also satisfies requirement [3] (see Example 3 in Table 2). In this case, for example, the total proportion of carbon and oxygen on the second main surface 3 is the same as the total proportion of carbon and oxygen on the central part 4. Therefore, the proportion of resin on the second main surface 3 is the same as the proportion of resin on the central part 4. As a result, the second main surface 3 has excellent adhesion, and the cohesive force of the magnetic sheet 1 can be further improved.

[0080] Of the first manufacturing method, the second manufacturing method, and the modified version of the second manufacturing method described above, the first manufacturing method and the second manufacturing method are preferred from the viewpoint of ensuring an excellent balance of adhesion between the first main surface 2 and the second main surface 3. More preferably, the first manufacturing method is preferred from the viewpoint of satisfying requirements [2] and [4] and ensuring an even better balance of adhesion.

[0081] In addition to the method described above, a method may be appropriately employed to produce a magnetic sheet 1 in which the total amount of carbon and oxygen on either the first main surface 2 or the second main surface 3 is 10% by mass or more and 60% by mass or less.

[0082] <Other variations> The number of drying chambers in the second dryer 30 is not limited. The number of drying chambers may be 1 to 3, or 5 or more.

[0083] A shielding member 20 may be provided at all outlets 19.

[0084] <Laminated magnetic sheet> As shown in Figure 4A, a laminated magnetic sheet 41 can also be obtained by laminating multiple magnetic sheets 1. The laminated magnetic sheet 41 is also an example of a magnetic sheet of the present invention. For example, multiple magnetic sheets 1 are arranged adjacent to each other in the thickness direction and then heated and pressed. The heating and pressing conditions are disclosed, for example, in Japanese Patent Publication Nos. 2020-150057, 2020-150060, 2020-150063, and 2020-150066. In the lamination of multiple magnetic sheets 1, as shown in Figure 4A, the first main surface 2 of one magnetic sheet 1 and the second main surface 3 of another magnetic sheet 1 adjacent to the first magnetic sheet 1 in the thickness direction are in contact. Alternatively, as referred to by the parenthetical reference numerals in Figure 1A, the first main surface 2 of one magnetic sheet 1 and the first main surface 2 of another magnetic sheet 1 are in contact. Furthermore, the second main surface 3 of one magnetic sheet 1 may be in contact with the second main surface 3 of the other magnetic sheet 1.

[0085] As shown in Figure 4B, the laminated magnetic sheet 41 has a first main surface 2 and a second main surface 3. The first main surface 2 and the second main surface 3 in the laminated magnetic sheet 41 are the same as those in the magnetic sheet 1. In other words, the total amount of carbon and oxygen on either the first main surface 2 or the second main surface 3 in the laminated magnetic sheet 41 is 10% by mass or more and 60% by mass or less.

[0086] Furthermore, the laminated magnetic sheet 41 satisfies requirement [1] or requirement [2] and also satisfies requirement [3] or requirement [4].

[0087] <Inductor> Next, an inductor 50 comprising a laminated magnetic sheet 41 will be described with reference to Figure 5. The inductor 50 has a sheet shape. The inductor 50 comprises a plurality of wirings 45 and a laminated magnetic sheet 41. The plurality of wirings 45 are adjacent to each other with spacing in the width direction. The width direction is perpendicular to the direction in which the plurality of wirings 45 extend and to the thickness direction of the inductor 50. The plurality of wirings 45 are parallel to each other. The wirings 45 are disclosed in Japanese Patent Publication No. 2020-150057, Japanese Patent Publication No. 2020-150060, Japanese Patent Publication No. 2020-150063, and Japanese Patent Publication No. 2020-150066.

[0088] The laminated magnetic sheet 41 has the same shape as the inductor 50 in a plan view. The laminated magnetic sheet 41 has multiple wirings 45 embedded in its cross-section along the width and thickness directions. The laminated magnetic sheet 41 is formed, for example, from multiple magnetic sheets 1 as shown in Figure 4A.

[0089] <Effects and Effects> In magnetic sheet 1 and laminated magnetic sheet 41, the total amount of carbon and oxygen on either the first main surface 2 or the second main surface 3 is 10% by mass or more and 60% by mass or less. Therefore, an excessive decrease in the resin content on the first main surface 2 and the second main surface 3 can be suppressed.

[0090] Therefore, the magnetic sheet 1, the laminated magnetic sheet 41, and the inductor 50 can achieve both excellent adhesion on the first main surface 2 and excellent adhesion on the second main surface 3. In other words, there is an excellent balance of adhesion between the first main surface 2 and the second main surface 3.

[0091] Furthermore, if the total amount of carbon and oxygen on the first main surface 2 and the second main surface 3 is 10% by mass or more and 50% by mass or less, then excessive segregation of particles can be suppressed on both the first main surface 2 and the second main surface 3, and the adhesion force on both sides can be balanced.

[0092] Furthermore, if requirement [1] or requirement [2] is satisfied in the magnetic sheet 1 and the laminated magnetic sheet 41, an excessive decrease in the total amount ratio of carbon and oxygen on one surface can be avoided, thereby further enhancing the excellent adhesion of the first main surface 2 and the excellent adhesion of the second main surface 3.

[0093] Furthermore, if requirement [3] or requirement [4] is satisfied in the magnetic sheet 1 and the laminated magnetic sheet 41, an excessive decrease in the total proportion of carbon and oxygen on one surface can be avoided, thereby improving adhesion. [Examples]

[0094] The present invention will be further described below with reference to examples and comparative examples. However, the present invention is not limited in any way to the examples and comparative examples. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than or equal to") of the blending ratios (content ratios), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0095] [Example 1] <First manufacturing method> A varnish was prepared by mixing 55 parts by volume of flattened Fe-Si alloy magnetic particles, 11.0 parts by volume of cresol novolac type epoxy resin (main component), 11.0 parts by volume of phenol resin (curing agent), 0.4 parts by volume of imidazole compound (curing accelerator), 21.2 parts by volume of thermoplastic resin (carboxyl group-containing acrylic ester copolymer), 0.4 parts by volume of dispersant (phosphate ester compound), 0.4 parts by volume of thixotropic agent (urea-modified polyamide compound), and methyl ethyl ketone (organic solvent) in such a way that the volume ratio of solids was 11.5% by volume, and then stirring the mixture.

[0096] The varnish was applied to the release sheet 5 using an applicator. This formed a coating film 8.

[0097] Subsequently, the coating 8 was left in an atmospheric environment at 25°C for 3 minutes. The impingement flow relative to the coating 8 was 0.12 [m / sec], and the parallel flow was 0.33 [m / sec].

[0098] As shown in Figure 2B, a hot air dryer 10 was prepared as the first dryer 9. The heat source and blower of the hot air dryer 10 were started to raise the internal temperature to 110°C. Next, the release sheet 5 and the coating film 8 were placed in the hot air dryer 10 and left for 2 minutes. The parallel flow of hot air in the hot air dryer 10 was 2.9 [m / sec].

[0099] Subsequently, the release sheet 5 was removed from the hot air dryer 10. Methyl ethyl ketone was removed from the coating film 8. The thermosetting resin was in stage B. This produced a magnetic sheet 1 with a thickness of 85 μm. The magnetic sheet 1 has a first main surface 2 which is the side opposite to the release sheet 5, and a second main surface 3 which is in contact with the release sheet 5.

[0100] [Example 2] <Second manufacturing method> A varnish was prepared in the same manner as in Example 1.

[0101] As shown in Figure 3, a continuous dryer 14 was prepared as the second dryer 30. The internal temperature of the first drying chamber 15 was 60°C. The internal temperature of the second drying chamber 16 was 80°C. The internal temperature of the third drying chamber 17 was 110°C. The internal temperature of the fourth drying chamber 18 was 110°C. The outlets of the air outlets 19 in each of the first to third drying chambers 15 to 17 were covered with shielding members 20 made of sealing tape. On the other hand, the outlet of the air outlet 19 in the fourth drying chamber 18 was left open.

[0102] A release sheet 5 similar to that in Example 1 was stretched across two rolls 33. The release sheet 5 was long and passed through the coating machine 25 and the continuous dryer 14.

[0103] Varnish was placed in the coating machine 25, and the varnish was applied to the release sheet 5 using comma coating. This formed a coating film 8 on the third main surface 6 of the release sheet 5.

[0104] Next, the coating film 8 was dried using a continuous dryer 14. In Example 2, the coating film 8 was not left to stand at 25°C as in Example 1. The impingement flow of hot air in the first drying chamber 15 to the third drying chamber 17 of the continuous dryer 14 was 0.02 [m / sec]. On the other hand, the impingement flow of warm air in the fourth drying chamber 18 was 2.0 [m / sec].

[0105] This resulted in the production of a magnetic sheet 1 with a thickness of 85 μm.

[0106] [Example 3] <Variation of the second manufacturing method> A magnetic sheet 1 with a thickness of 85 μm was manufactured in the same manner as in Example 2. However, the shielding member 20 was not provided in the hot air dryer 10. The impingement flow of hot air in the first drying chamber 15 to the fourth drying chamber 18 of the continuous dryer 14 was 2.0 [m / sec].

[0107] [Comparative Example 1] A magnetic sheet 1 with a thickness of 85 μm was manufactured in the same manner as in Example 1. However, instead of leaving the coating film 8 at 25°C, the coating film 8 was subjected to a colliding flow of hot air using a hand dryer before being placed in the first dryer 9. The colliding flow of the hand dryer was 11.2 [m / sec].

[0108] The following items were measured for magnetic sheet 1 in each example and comparative example. The results are shown in Table 2.

[0109] <Total percentage of carbon and oxygen in the first main surface 2, the second main surface 3, and the central part 4> Energy-dispersive X-ray spectroscopy (EDX) was used to determine the total proportions of carbon and oxygen in the first main surface 2, the second main surface 3, and the central portion 4 of the magnetic sheet 1. The measurement equipment and conditions are described below.

[0110] EDX device: HORIBA EMAX Evolution EX-470 X-MAX150 Acceleration voltage for the first main surface 2 and the second main surface 3: 10kV Acceleration voltage for central section 4: 5kV Number of repetitions: 3

[0111] In addition, the calculation of the total carbon and oxygen proportions in EDX described above excludes elements derived from pretreatment.

[0112] In addition, surface SEM observation and cross-sectional SEM observation of magnetic sheet 1 were performed simultaneously with EDX. The measurement equipment and conditions are described below.

[0113] FE-SEM equipment: Hitachi, SU8020 Observed image: Backscattered electron image

[0114] <Surface SEM> Acceleration voltage: 10kV Magnification: 200x Analysis field of view: 600 μm wide x 400 μm high

[0115] <Cross-sectional SEM> Acceleration voltage: 5kV Magnification: 2,000x Analysis field of view: width 50μm x height 10μm

[0116] <Adhesion> <Exam A> Two magnetic sheets 1, each measuring 5 mm in length and 10 mm in width, were prepared. As shown in Figure 6A, one magnetic sheet 1 was placed on the edge of a copper plate 70 measuring 40 mm in length and 10 mm in width, via an adhesive layer 65 of the same size as the other magnetic sheet 1. The other magnetic sheet 1 was placed on the edge of a long copper plate 70, via an adhesive layer 65 of the same size as the other magnetic sheet 1. Next, the two magnetic sheets 1 were bonded together. At this time, the first main surface 2 of one magnetic sheet 1 came into contact with the first main surface 2 of the other magnetic sheet 1. The bonding was carried out by the following two presses.

[0117] The adhesive layer 65 was prepared by mixing 61.5 parts by volume of magnetic particles consisting of spherical carbonyl iron powder, 9.6 parts by volume of cresol novolac type epoxy resin (main component), 9.6 parts by volume of phenol resin (curing agent), 0.3 parts by volume of imidazole compound (curing accelerator), 18.5 parts by volume of thermoplastic resin (carboxyl group-containing acrylic ester copolymer), 0.5 parts by volume of dispersant (phosphate ester type), and methyl ethyl ketone (organic solvent) so that the solid content concentration was 30% by volume, and stirring these together to prepare a varnish. The adhesive layer 65 was prepared by applying and drying this varnish using the method shown in Example 1.

[0118] [First press release] Pressing equipment: Parallel plate press Temperature: 110℃ Pressure: 0.9 MPa Time: 1 minute [Second press release] Pressing equipment: Dry laminator (manufactured by Nikkiso Co., Ltd.) Temperature: 170℃ Pressure: 9 MPa

[0119] This resulted in the creation of a test sample 80 in which a copper plate 70, an adhesive layer 65, two magnetic sheets 1, another adhesive layer 65, and another copper plate 70 were arranged sequentially in the thickness direction. One end of one copper plate 70 in the longitudinal direction protrudes from the adhesive layer 65 and the magnetic sheet 1. The other end of the other copper plate 70 in the longitudinal direction protrudes from the adhesive layer 65 and the magnetic sheet 1.

[0120] One end of one copper plate 70 and the other end of the other copper plate 70 were pulled in the longitudinal direction, applying a shear force to the two magnetic sheets 1 (180-degree peeling). The peeling speed was 300 mm / min. The shear force at the time of peeling was obtained as the adhesion force of the magnetic sheets 1. Five measurements were taken, and the average value was obtained.

[0121] <Exam B> The adhesion force between the two magnetic sheets 1 was measured in the same manner as in Test A. However, as shown in Figure 6B, when the two magnetic sheets 1 were bonded together, the first main surface 2 of one magnetic sheet 1 and the second main surface 3 of the other magnetic sheet 1 came into contact.

[0122] <Evaluation of adhesion> The adhesion strength of Test A and Test B was evaluated according to the following criteria. ◎: 0.8 ≤ [Adhesion strength of Test A] / [Adhesion strength of Test B] < 1.2 ○: 0.7 ≤ [Adhesion strength of Test A] / [Adhesion strength of Test B] < 0.8, or, 1.2 ≤ [Adhesion strength of Test A] / [Adhesion strength of Test B] < 1.5 △: 0.5 ≤ [Adhesion strength of Test A] / [Adhesion strength of Test B] < 0.7, or, 1.5 ≤ [Adhesion strength of Test A] / [Adhesion strength of Test B] < 2 ×: [Adhesion strength of Test A] / [Adhesion strength of Test B] < 0.5, or [Adhesion strength of Test A] / [Adhesion strength of Test B] ≥ 2

[0123] [Table 1]

[0124] [Table 2]

[0125] The above invention is provided as an illustrative embodiment of the present invention, but this is merely illustrative and should not be interpreted restrictively. Modifications of the present invention that are obvious to those skilled in the art are included in the claims below. [Industrial applicability]

[0126] Magnetic sheets are used for magnetic applications. [Explanation of Symbols]

[0127] 1 Magnetic sheet 2. First main surface 3. Second main surface 41. Laminated magnetic sheet 4. Center in the thickness direction 41. Laminated magnetic sheet 45 Wiring 50 Inductors

Claims

1. It has a first main surface and a second main surface facing each other in the thickness direction, It contains magnetic particles and resin, A magnetic sheet in which the total amount of carbon and oxygen on either the first main surface or the second main surface is 10% by mass or more and 60% by mass or less.

2. The magnetic sheet according to claim 1, wherein the total amount ratio in each of the first main surface and the second main surface is 10% by mass or more and 50% by mass or less.

3. The total amount ratio on the first main surface and the total amount ratio on the second main surface are the same, or The magnetic sheet according to claim 1 or 2, wherein the total amount ratio on one of the first main surface and the second main surface is lower than the total amount ratio on the other remaining surface, and the ratio of the total amount ratio on the one surface to the total amount ratio on the other surface is 0.3 or more and less than 1.

0.

4. The total amount ratio on either the first main surface or the second main surface is the same as the total amount ratio in the center of the thickness direction, or The magnetic sheet according to any one of claims 1 to 3, wherein the total amount ratio on one surface is lower than the total amount ratio in the central part, and the ratio of the total amount ratio on one surface to the total amount ratio in the central part is 0.3 or more and less than 1.

5. Wiring and, A magnetic sheet covering the wiring as described in any one of claims 1 to 4 An inductor equipped with the following features.

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