Magnetic particle-containing sheet, inductor, and electronic circuit

Abstract

Provided are: a magnetic particle-containing sheet satisfying (1), (2), and (3); an inductor including the magnetic particle-containing sheet; and an electronic circuit including the inductor. (1) The arithmetic average of the median value of the major axis diameter of magnetic particles obtained in each of five images acquired by SEM observation of five arbitrary measurement regions on a surface of the magnetic particle-containing sheet is 1.20 μm or less, (2) the arithmetic average of the number of magnetic particles having a major axis diameter of 5.00 μm or more obtained in each of the five images is 6 or more, and (3) the maximum value of the arithmetic average of magnetic particle intervals obtained in each of 12 images acquired by SEM observation of one arbitrary measurement region on the surface of the magnetic particle-containing sheet at each of measurement angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° is 1.20 μm or less.

Description

Magnetic particle-containing sheet, inductor and electronic circuit

[0001] The present invention relates to a magnetic particle-containing sheet, an inductor, and an electronic circuit.

[0002] An inductor is a passive electronic element included in various electronic circuits. A known inductor includes a magnetic particle-containing sheet and a coil (see, for example, paragraph 0035 of Patent Document 1).

[0003] JP 2014-127624 A

[0004] Inductance, which is the main performance of an inductor, is proportional to the magnetic permeability of the magnetic particle-containing sheet. Therefore, to realize an inductor with high inductance or a small inductor, a magnetic particle-containing sheet with high magnetic permeability is desirable. However, the magnetic permeability of a magnetic particle-containing sheet can vary depending on the angle in the sheet plane. Therefore, if multiple magnetic particle-containing sheets are cut from the same magnetic particle-containing sheet roll at different angle positions, inductors incorporating these multiple magnetic particle-containing sheets may exhibit variations in inductance. Therefore, from the perspective of stable inductor performance, a magnetic particle-containing sheet that exhibits high magnetic permeability at various angles is desirable.

[0005] In view of the above, an object of one aspect of the present invention is to provide a magnetic particle-containing sheet that can exhibit high magnetic permeability at various angles.

[0006] One aspect of the present invention is as follows: [1] A magnetic particle-containing sheet that satisfies the following (1), (2), and (3): (1) the arithmetic mean of the median major axis diameters of the magnetic particles obtained in each of five images obtained by observing five arbitrary measurement areas on the surface of the magnetic particle-containing sheet with a scanning electron microscope is 1.20 μm or less, the size of each of the five measurement areas is 63 μm × 47 μm, and the magnification of the scanning electron microscope is 3000 times, (2) the arithmetic mean of the number of magnetic particles having a major axis diameter of 5.00 μm or more obtained in each of the five images is 6 or more, (3) One arbitrary measurement area on the surface of the magnetic particle-containing sheet is observed with a scanning electron microscope at measurement angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165°, with an arbitrary measurement angle being 0°. The maximum arithmetic mean of the magnetic particle spacing determined in each of 12 images is 1.20 μm or less, the size of one measurement area is 63 μm × 47 μm, and the observation magnification of the scanning electron microscope is 3000x. [2] The magnetic particle-containing sheet according to [1], wherein the maximum arithmetic mean of the magnetic particle spacing of (3) above is 1.00 μm or less. [3] The magnetic particle-containing sheet according to [1] or [2], wherein ΔGAP, calculated by the following formula: ΔGAP=(GAPH-GAPL) / (GAPH+GAPL), where GAPH is the maximum value of the arithmetic mean of the magnetic particle intervals in (3) above and GAPL is the minimum value, is 0.13 or less. [4] The magnetic particle-containing sheet according to [3], wherein ΔGAP is 0.05 or more and 0.13 or less. [5] The magnetic particle-containing sheet according to any of [1] to [4], wherein the arithmetic mean of the median major axis diameters in (1) above is 0.80 μm or more and 1.20 μm or less. [6] The magnetic particle-containing sheet according to any of [1] to [5], wherein the arithmetic mean of the number in (2) above is 6 or more and 20 or less. [7] The magnetic particle-containing sheet according to any of [1] to [6], wherein the arithmetic mean of the magnetic particle intervals in (3) above is 0.80 μm or more and 1.20 μm or less. [8] The magnetic particle-containing sheet according to any one of [1] to [7], further comprising a resin.[9] The magnetic particle-containing sheet according to any of [1] to [8], wherein the maximum arithmetic mean of the magnetic particle spacings in (3) above is 1.00 μm or less, and ΔGAP calculated by the following formula: ΔGAP=(GAPH-GAPL) / (GAPH+GAPL), where GAPH is the maximum value of the arithmetic mean of the magnetic particle spacings in (3) above and GAPL is the minimum value, is 0.13 or less.

[10] The magnetic particle-containing sheet according to [9], wherein the ΔGAP is 0.05 or more and 0.13 or less, the arithmetic mean of the median major axis diameters in (1) above is 0.80 μm or more and 1.20 μm or less, the arithmetic mean of the number of particles in (2) above is 6 or more and 20 or less, the maximum arithmetic mean of the magnetic particle spacings in (3) above is 0.80 μm or more and 1.00 μm or less, and the magnetic particle-containing sheet further contains a resin.

[11] An inductor comprising the magnetic particle-containing sheet according to any one of [1] to

[10] .

[12] An electronic circuit comprising the inductor according to

[11] .

[0007] According to one aspect of the present invention, it is possible to provide a magnetic particle-containing sheet that can exhibit high magnetic permeability at various angles, an inductor including the magnetic particle-containing sheet that can exhibit high magnetic permeability at various angles, and an electronic circuit including such an inductor.

[0008] [Magnetic Particle-Containing Sheet] One aspect of the present invention relates to a magnetic particle-containing sheet that satisfies the above-mentioned (1), (2), and (3).

[0009] In the present invention and this specification, the term "magnetic" means ferromagnetic property. Also, in the present invention and this specification, the term "sheet" is used synonymously with the term "film."

[0010] The above-described (1), (2), and (3) are determined by the following measurement method. In the present invention and this specification, "any measurement area" means a randomly selected measurement area, "any measurement angle" means a randomly selected measurement angle, and "any position" means a randomly selected position. The measurement sample is either the magnetic particle-containing sheet to be measured, or a sheet piece cut out from any position of the magnetic particle-containing sheet to be measured. The size of the measurement sample may be a size that can be introduced into a scanning electron microscope (SEM) and that allows SEM observation of the multiple measurement areas described below. In SEM observation, the size of one measurement area is 63 μm × 47 μm, and the observation magnification is 3000x. The image obtained by SEM is a backscattered electron image. Regarding the surface to be measured, the surface with the larger arithmetic mean roughness Ra of both surfaces of the measurement sample is the surface to be measured. As described below, in a magnetic particle-containing sheet produced by applying a composition for forming a magnetic particle-containing sheet to a support, the surface opposite the support at the time of application will have a significantly higher Ra than the surface facing the support at the time of application. Therefore, for such a surface, the surface may be used as the surface to be measured without measuring Ra. When measuring Ra to determine the surface to be measured, an optical interferometer is used to measure Ra. In this case, the surface to be measured is determined based on the Ra value obtained by measuring a 140 μm × 105 μm area of ​​each surface. The following measurement conditions can be given as an example of the measurement conditions for the optical interferometer. An optical interferometer (NewView 7300 manufactured by Zygo) is used to measure a 140 μm × 105 μm area of ​​the surface to be measured for Ra. The resolution is 640 pixels × 480 pixels. For the obtained three-dimensional roughness profile, an auxiliary measurement line is drawn from end to end of the measurement area in the longitudinal direction of the measurement area, i.e., the horizontal direction of the screen, to calculate Ra. This measurement is made five times by changing the position in the shorter direction of the measurement area, i.e., the vertical direction of the screen. The arithmetic mean of the five measured values ​​thus obtained is taken as the Ra of the surface to be measured.The SEM used has a scan rotation function that allows images to be acquired at different measurement angles for the same observation area. The scan rotation function rotates the image on the screen by changing the scanning direction of the electron probe. For example, a tabletop microscope TM-1000 manufactured by Hitachi High-Technologies Corporation can be used as such an SEM. In the measurements described in the Examples section below, a tabletop microscope TM-1000 manufactured by Hitachi High-Technologies Corporation was used as the SEM. For (1) and (2) above, five different locations randomly selected on the surface of the object to be measured are used as measurement areas, and SEM observation is performed on each of the five measurement areas to acquire a total of five images. For (3) above, one area different from the five measurement areas is randomly selected as the measurement area. For this measurement area, an arbitrary measurement angle is set to 0°, and SEM observation is performed at each measurement angle of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° to acquire images. The measurement angle can be set in the SEM. For example, with a Hitachi High-Technologies Corporation tabletop microscope TM-1000, SEM observation is performed at measurement angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° by setting the rotation button to 0° and clicking the rotation button + to change the angle, thereby acquiring a total of 12 images.

[0011] Each of the above images is binarized using the following method. The acquired image is read in grayscale using the cv2.imread() function of the image processing library OpenCV4 (manufactured by Intel) with the second argument set to 0. The scale bar portion is truncated from the image with a size of 1280 pixels x 1040 pixels, and the image size is adjusted to 1280 pixels x 957 pixels. The adjusted image is then used with the cv2.threshold() function with the fourth argument set to cv2.THRESH_OTSU to obtain a binarized image. The white areas in this binarized image are considered to be magnetic particles, and the black areas are considered to be the areas between the magnetic particles.

[0012] Regarding (1) above, the major axis diameters of all magnetic particles (white areas) contained in each binary image are determined. However, for particles in which the binary image contains only a portion of the particle shape and not the entire particle, the major axis diameter is not determined. The "major axis diameter" is determined as the diameter of a circumscribing circle of the outline of the white areas, which is drawn using image processing software. Such circumscribing circles can be drawn using known image processing software. After determining the major axis diameters of all magnetic particles for each image in this way, the median of these major axis diameter values ​​is determined. If the total number of measured values ​​is an odd number, the median is the middle measured value when the measured values ​​are sorted in ascending order. If the total number of measured values ​​is an even number, the median is the arithmetic mean of the two values ​​closest to the middle when the measured values ​​are sorted in ascending order. The arithmetic mean of the five median major axis diameters of the magnetic particles determined in this way for the five images is used as the arithmetic mean of the median major axis diameters in (1) above.

[0013] Regarding (2) above, for each of the five images, the number of magnetic particles whose major axis diameter is determined as described above and whose major axis diameter is 5.00 μm or more is determined. The arithmetic mean of the five numbers thus determined for the five images is used as the arithmetic mean of the numbers in (2) above.

[0014] Regarding (3) above, the brightness of pixels at coordinates X = 0 to 1279 is read at each Y coordinate of Y = 100, 200, 300, 400, 500, 600, 700, 800, and 900 of the binarized image obtained as described above, the number of consecutive pixels with a brightness of 0 is counted, and multiplied by 67 μm / 1280 pixels to determine the particle spacing [μm]. That is, if the number of consecutive pixels with a brightness of 0 is N, the particle spacing [μm] is calculated as "N × 67 / 1280". For each of 12 images acquired at different measurement angles, the arithmetic mean of the particle spacing values ​​obtained in that image is used as the arithmetic mean of the magnetic particle spacing for that image. The maximum value among the 12 arithmetic mean values ​​of the magnetic particle spacing calculated for the 12 images is used as the maximum arithmetic mean of the magnetic particle spacing in (3) above.

[0015] Specific examples of the above measurement methods (1) to (3) include the measurement methods described in the Examples section below.

[0016] The present inventors believe that the magnetic particles that primarily contribute to the high magnetic permeability of magnetic particle-containing sheets are those with large particle sizes. The present inventors believe that magnetic particle-containing sheets with an arithmetic mean of 6 or more of the number of magnetic particles (2) above contain many such large magnetic particles. Furthermore, in order to prevent a decrease in the high magnetic permeability provided by magnetic particles with large particle sizes, it is desirable to have few non-magnetic portions between magnetic particles with large particle sizes. In this regard, the present inventors believe that in magnetic particle-containing sheets with an arithmetic mean of the median major axis diameter (1) above of 1.20 μm or less, many magnetic particles with small particle sizes exist between magnetic particles with large particle sizes. In other words, the present inventors believe that the decrease in the high magnetic permeability provided by magnetic particles with large particle sizes can be prevented. Furthermore, the narrow spacing between magnetic particles is also believed to contribute to increasing the magnetic permeability of magnetic particle-containing sheets. In this regard, the fact that the maximum arithmetic mean of the magnetic particle spacing in (3) is 1.20 μm or less means that the arithmetic mean of the magnetic particle spacing is 1.20 μm or less in all of the 12 images. Therefore, the inventor believes that a magnetic particle-containing sheet in (3) having a maximum arithmetic mean of the magnetic particle spacing of 1.20 μm or less can be said to be a magnetic particle-containing sheet in which the spacing between magnetic particles is narrow when observed at various angles. The inventor speculates that the above points are the reason why the magnetic particle-containing sheet in (1) having an arithmetic mean of the median major axis diameter of 1.20 μm or less, (2) having an arithmetic mean of the number of particles of 6 or more, and (3) having a maximum arithmetic mean of the magnetic particle spacing of 1.20 μm or less can exhibit high magnetic permeability at various angles. However, the present invention is not limited to the speculation described in this specification. Furthermore, the fact that a material has high magnetic permeability at various angles can be confirmed by, for example, the magnetic permeability measured at various angles being high on average (for example, the arithmetic mean value being large).

[0017] The magnetic particle-containing sheet will now be described in more detail.

[0018] <Arithmetic mean of the median major axis diameters of (1) above> The arithmetic mean of the median major axis diameters of the magnetic particles of (1) above is the arithmetic mean (arithmetic mean of five values) obtained by observing five arbitrary measurement areas on the surface of the magnetic particle-containing sheet using an SEM. The arithmetic mean of the median major axis diameters of the magnetic particles of (1) above is 1.20 μm or less. This can contribute to the magnetic particle-containing sheet being able to exhibit high magnetic permeability at various angles. From this perspective, the arithmetic mean of the median major axis diameters of the magnetic particle-containing sheet of (1) above is preferably 1.18 μm or less, more preferably 1.16 μm or less, 1.14 μm or less, 1.12 μm or less, 1.10 μm or less, and 1.00 μm or less in that order. The arithmetic mean of the median major axis diameter of the magnetic particle-containing sheet (1) above can be, for example, 0.50 μm or more, 0.60 μm or more, 0.70 μm or more, 0.80 μm or more, or 0.90 μm or more. However, from the viewpoint of increasing the magnetic permeability of the magnetic particle-containing sheet, it is preferable that the arithmetic mean of the median major axis diameter of the magnetic particle-containing sheet (1) above is small. Therefore, the arithmetic mean of the median major axis diameter of the magnetic particle-containing sheet (1) above may be lower than the value exemplified here.

[0019] <Arithmetic mean of the number of (2)> The arithmetic mean of the number of (2) is the arithmetic mean (arithmetic mean of five values) of magnetic particles having a major axis diameter of 5.00 μm or more obtained in each of the five images. The arithmetic mean of the number of (2) in the magnetic particle-containing sheet is 6 or more. This can also contribute to the magnetic particle-containing sheet being able to exhibit high magnetic permeability at various angles. From this perspective, the arithmetic mean of the number of (2) in the magnetic particle-containing sheet is preferably 7 or more, with 8 or more, 9 or more, and 10 or more being more preferred in this order. The arithmetic mean of the number of (2) in the magnetic particle-containing sheet can be, for example, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, or 14 or less. However, from the viewpoint of increasing the magnetic permeability of the magnetic particle-containing sheet, it is preferable that the arithmetic mean of the number of (2) is large. Therefore, the arithmetic mean of the number of particles (2) in the magnetic particle-containing sheet may exceed the value exemplified here.

[0020] <Maximum arithmetic mean of magnetic particle spacing in (3)> The maximum arithmetic mean of the magnetic particle spacing in (3) above is the maximum arithmetic mean of the magnetic particle spacing (the maximum of the 12 values) obtained in each of 12 images obtained by observing one arbitrary measurement area on the surface of the magnetic particle-containing sheet with a scanning electron microscope at measurement angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165°, with an arbitrary measurement angle being 0°. The maximum arithmetic mean of the magnetic particle spacing in (3) above for the magnetic particle-containing sheet is 1.20 μm or less. This can also contribute to the magnetic particle-containing sheet being able to exhibit high magnetic permeability at various angles. From this viewpoint, the maximum value of the arithmetic mean of the magnetic particle spacing (3) above is preferably 1.18 μm or less, and more preferably 1.16 μm or less, 1.14 μm or less, 1.12 μm or less, 1.10 μm or less, and 1.00 μm or less in that order. The maximum value of the arithmetic mean of the magnetic particle spacing (3) above of the magnetic particle-containing sheet can be, for example, 0.50 μm or more, 0.60 μm or more, 0.70 μm or more, 0.80 μm or more, or 0.90 μm or more. However, from the viewpoint of increasing the magnetic permeability of the magnetic particle-containing sheet, it is preferable that the maximum value of the arithmetic mean of the magnetic particle spacing (3) above is small. Therefore, the maximum value of the arithmetic mean of the magnetic particle spacing (3) above of the magnetic particle-containing sheet may be below the values ​​exemplified here.

[0021] <ΔGAP> With regard to inductors, for example, when multiple magnetic particle-containing sheets are cut from different angular positions of the same raw magnetic particle-containing sheet, inductors incorporating these multiple magnetic particle-containing sheets may exhibit large variations in inductance. From the viewpoint of suppressing the occurrence of this phenomenon or reducing the extent of the phenomenon, it is desirable that the angle dependency of the magnetic permeability of the magnetic particle-containing sheet is small, that is, that the anisotropy of the magnetic permeability is small. As a result of the inventor's investigation into this point, it has become clear that magnetic particle-containing sheets with small ΔGAP, calculated by the following formula, where GAPH is the maximum value and GAPL is the minimum value among the arithmetic means of the magnetic particle spacings of the 12 images obtained in (3) above, have small anisotropy of the magnetic permeability. Here, "GAP" is an abbreviation for "gap between magnetic particles," the "H" in "GAPH" being an abbreviation for "Highest," and the "L" in "GAPL" being an abbreviation for "Lowest." A small ΔGAP value means that there is little variation in the arithmetic mean of the magnetic particle spacing at various measurement angles. The ΔGAP of the magnetic particle-containing sheet can be, for example, 0.24 or less, 0.23 or less, or 0.22 or less. From the viewpoint of reducing the anisotropy of the magnetic permeability of the magnetic particle-containing sheet, it is preferably 0.13 or less, with 0.12 or less, 0.11 or less, and 0.10 or less being more preferred in that order. The ΔGAP of the magnetic particle-containing sheet can be, for example, 0.01 or more, 0.05 or more, or 0.10 or more. However, from the viewpoint of reducing the anisotropy of the magnetic permeability of the magnetic particle-containing sheet, a small ΔGAP is preferable, and therefore the ΔGAP of the magnetic particle-containing sheet may be less than the values ​​exemplified here.

[0022] One method for controlling the various values ​​of (1) to (3) above is to use multiple types of magnetic particles with different particle sizes as the magnetic particles used to prepare the magnetic particle-containing sheet, and to control their particle sizes and mixing ratios. Furthermore, one method for controlling the arithmetic mean of the magnetic particle spacing in (3) above is to adjust the amount of resin, which will be described later. Regarding ΔGAP, one method is to adjust the liquid viscosity of the composition used to prepare the magnetic particle-containing sheet.

[0023] The magnetic particle-containing sheet will now be described in more detail.

[0024] <Magnetic Particles> The magnetic particles contained in the magnetic particle-containing sheet may be one selected from the group consisting of magnetic particles generally called soft magnetic particles, such as metal particles and ferrite particles, or a combination of two or more types. In the present invention and this specification, the term "particle" is used to mean a single particle or a collection of particles. In a collection of magnetic particles, the magnetic particles may be in direct contact with each other at least on a part of the particle surface, or other components (for example, a resin as described below, other components as described below, etc.) may be present between the magnetic particles.

[0025] In the present invention and this specification, the term "metal particles" includes both pure metal particles consisting of a single metal element and alloy particles of one or more metal elements with one or more other metal elements and / or non-metal elements. Metal particles may or may not be crystalline. That is, metal particles may be crystalline or amorphous. For example, magnetic particles commercially available as nanocrystalline alloys or magnetic particles commercially available as iron-based amorphous particles can be used as metal particles. "Iron-based" means containing iron as a constituent element. Examples of metal or non-metal elements contained in metal particles include Ni, Fe, Co, Mo, Cr, Si, B, P, etc. Metal particles may or may not contain components other than the constituent elements of the metal (including alloys). In addition to the constituent elements of the metal (including alloys), metal particles may contain elements contained in optional additives and / or elements contained in impurities that may be unintentionally mixed in during the manufacturing process of the metal particles, at any content. In the metal particles, the content of the constituent elements of the metal (including alloys) is preferably 90.0% by mass or more, more preferably 95.0% by mass or more, and may also be 100% by mass, less than 100% by mass, 99.9% by mass or less, or 99.0% by mass or less.

[0026] An example of an index of the particle size of magnetic particles is "d50," which is the cumulative 50% diameter in a number-based particle size distribution measured by a laser diffraction scattering method. d50 can be measured, for example, by the following method. The d50 described in the Examples section below is a value measured by the following method. 10 mg of magnetic particles are diluted with 500 mL of cyclohexanone, and then stirred for 30 seconds using a shaker, and the resulting liquid is used as a sample for particle size distribution measurement. Next, the particle size distribution is measured by a laser diffraction scattering method using the sample for particle size distribution measurement. A laser diffraction / scattering particle size distribution analyzer is used as the measuring device. A specific example of a laser diffraction / scattering particle size distribution analyzer is the Partica LA-960 manufactured by Horiba, Ltd. The d50 described in the Examples section below is a value measured using a Partica LA-960 manufactured by Horiba, Ltd. as the laser diffraction / scattering particle size distribution analyzer. The d50 of the magnetic particles contained in the magnetic particle-containing sheet can be confirmed, for example, by the following method. The magnetic particle-containing sheet is finely chopped and then ultrasonically dispersed in a solvent (e.g., acetone). A magnet is used to separate the components that are attracted to the magnet, i.e., the magnetic particles, from the resulting dispersion, and this is used as a sample to measure using a laser diffraction scattering method. In this way, the d50 of the magnetic particles can be confirmed.

[0027] The d50 of the magnetic particles contained in the magnetic particle-containing sheet can be, for example, 1.0 μm or more. The d50 of the magnetic particles can be, for example, 50.0 μm or less. For example, magnetic particles having a d50 of 1.0 μm or more and 10.0 μm or less, or 1.0 μm or more and 5.0 μm or less (hereinafter also referred to as "small-size particles") can be combined with magnetic particles having a d50 of more than 10.0 μm and 50.0 μm or less, or 15.0 μm or more and 30.0 μm or less (hereinafter also referred to as "large-size particles"). Only one type of small-size particle may be used, or two or more types with different d50s may be used. Only one type of large-size particle may be used, or two or more types with different d50s may be used. Using smaller magnetic particles as small-size particles can contribute to reducing the arithmetic mean of the median major axis diameter (1) above and / or reducing the maximum arithmetic mean of the magnetic particle spacing (3) above. Decreasing the proportion of large-sized particles can contribute to decreasing the arithmetic mean of the median major axis diameter (1) above, and increasing the proportion of large-sized particles can contribute to increasing the arithmetic mean of the number (2) above.

[0028] The content of magnetic particles in the magnetic particle-containing sheet can be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, relative to the total mass of the sheet, and can also be, for example, less than 100% by mass, 99% by mass or less, or 98% by mass or less.

[0029] <Resin> The magnetic particle-containing sheet contains at least magnetic particles and may further contain a resin. In the present invention and this specification, "resin" refers to a polymer, and polymers include homopolymers and copolymers. As the resin, a thermosetting or photocurable resin is preferred, and a thermosetting resin is more preferred. Examples of thermosetting resins include various thermosetting resins such as epoxy resin, phenolic resin, acrylic resin, silicone resin, urethane resin, urea resin, and melamine resin, and from the viewpoint of the durability of the sheet, epoxy resin is preferred.

[0030] Examples of epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol S epoxy resins, bisphenol AF epoxy resins, dicyclopentadiene epoxy resins, trisphenol epoxy resins, naphthol novolac epoxy resins, phenol novolac epoxy resins, tert-butyl-catechol epoxy resins, naphthalene epoxy resins, naphthol epoxy resins, anthracene epoxy resins, glycidylamine epoxy resins, glycidyl ester epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexanedimethanol epoxy resins, naphthylene ether epoxy resins, and trimethylol epoxy resins. These epoxy resins may be used alone or in combination of two or more in any proportion. The composition containing an epoxy resin can be cured by heating the epoxy groups contained in the epoxy resin to open the rings and form crosslinked structures. In a sheet formed by curing the composition containing an epoxy resin, some or all of the epoxy groups contained in the epoxy resin may be contained in a state in which they have opened the rings and formed crosslinked structures.

[0031] The resin content of the magnetic particle-containing sheet is preferably in the range of 1.00 to 20.00 parts by mass per 100.00 parts by mass of magnetic particles. Furthermore, when the magnetic particle-containing sheet contains two or more types of resin, the resin content is the total content of these two or more types of resin. This also applies to the contents and percentages of other components. According to the inventors' studies, the arithmetic mean of the magnetic particle spacing (3) above tends to decrease as the resin amount decreases.

[0032] <Other Components> The magnetic particle-containing sheet can be produced using a composition (hereinafter also referred to as a "sheet-forming composition") that contains at least magnetic particles and optionally a resin. The sheet-forming composition can contain any amount of known additives. Examples of additives include components that can function as curing catalysts for thermosetting resins, components that can function as dispersants for magnetic particles, coupling agents, surfactants, thixotropic agents, etc. Such components are known, and examples include phenolic compounds, amine compounds, imidazole compounds, acid anhydrides, polymeric dispersants, etc.

[0033] The magnetic particle-containing sheet may also contain an additive (dispersant) that can contribute to improving the dispersibility of the magnetic particles. Examples of such dispersants include compounds containing polyalkyleneimine chains and polyester chains. In such compounds, the proportion of polyalkyleneimine chains in the compound (hereinafter also referred to as the "polyalkyleneimine chain ratio") is preferably less than 5.0% by mass, and the number-average molecular weight of the polyalkyleneimine chains contained in the compound is preferably in the range of 300 to 3,000. Here, the number-average molecular weight of the polyalkyleneimine chain refers to the number-average molecular weight described in paragraph 0027 of JP 2015-28830 A. For a method for measuring such number-average molecular weight, see paragraphs 0100 to 0101 of JP 2015-28830 A. The number-average molecular weight of the polyalkyleneimine chain is more preferably 500 or more and more preferably 2,000 or less. On the other hand, the proportion of polyalkyleneimine chains in the above compound (polyalkyleneimine chain ratio) is determined according to the description in paragraph 0030 of JP 2015-28830 A. The polyalkyleneimine chain ratio is preferably 4.9% by mass or less, more preferably 4.8% by mass or less, even more preferably 4.5% by mass or less, even more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less. Furthermore, the polyalkyleneimine chain ratio is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0034] The polyalkyleneimine chain possessed by the above-mentioned compound can be a polymer structure containing two or more alkyleneimine chains represented by Formula A described in paragraph

[0032] of JP 2015-28830 A and / or Formula B described in paragraph

[0034] of the same publication. In one embodiment, the polyalkyleneimine chain can be a polyethyleneimine chain. Meanwhile, the polyester chain possessed by the above-mentioned compound can be a polyester chain represented by Formula 1 described in paragraph

[0044] of JP 2015-28830 A and a polyester chain represented by Formula 2 described in paragraph

[0046] of the same publication. For details of the above-mentioned compounds, reference can be made to paragraphs

[0026] to

[0070] of JP 2015-28830 A and the Examples therein. The magnetic particle-containing sheet can contain 0.10 to 10.00 parts by mass of a dispersant per 100.00 parts by mass of magnetic particles. In one embodiment, the magnetic particle-containing sheet can contain 0.10 to 10.00 parts by mass of a compound containing a polyalkyleneimine chain and a polyester chain (preferably a compound in which the polyalkyleneimine chain ratio is less than 5.0% by mass, and more preferably a compound in which the number average molecular weight of the polyalkyleneimine chain is in the range of 300 to 3,000) per 100.00 parts by mass of magnetic particles.

[0035] The sheet-forming composition may be a solvent-free composition, or may contain one or more solvents, for example, to improve coatability. Examples of solvents include various organic solvents, such as ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone; acetate-based solvents such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; carbitols such as cellosolve and butyl carbitol; aromatic hydrocarbon-based solvents such as toluene and xylene; and amide-based solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. The solvent can be selected, for example, taking into consideration the solubility of the components used in preparing the sheet-forming composition. The solvent can be a single solvent or a mixture of two or more solvents in any ratio. When the sheet-forming composition contains a solvent, the solvent can be used in any amount, taking into consideration the coatability of the composition.

[0036] The sheet-forming composition can be prepared by sequentially or simultaneously mixing the various components in any order. If necessary, the components can be dispersed using a known dispersing machine such as a ball mill, bead mill, sand mill, or roll mill, and / or stirred using a known stirrer such as a vibration stirrer.

[0037] The ΔGAP described above can be controlled by the liquid viscosity of the sheet-forming composition. The higher the liquid viscosity, the smaller the ΔGAP tends to be in the magnetic particle-containing sheet that is formed. The liquid viscosity can be adjusted by the liquid concentration (solid mass / total mass) of the sheet-forming composition. For compositions that contain a solvent, the "solid mass" refers to the components excluding the solvent. A high magnetic particle concentration (magnetic particle mass / solid mass) in the solid content of the sheet-forming composition can lead to a high magnetic particle content in the magnetic particle-containing sheet that is formed. This can contribute to reducing the arithmetic mean of the magnetic particle spacing in (3) above.

[0038] The sheet-forming composition can be applied onto a support, for example. The application can be performed using a known application device such as a blade coater or a die coater. The application can be performed by a so-called roll-to-roll method or a batch method.

[0039] Examples of substrates onto which the sheet-forming composition is applied include films of various resins, such as polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylics such as polycarbonate (PC) and polymethyl methacrylate (PMMA), cyclic polyolefins, triacetyl cellulose (TAC), polyether sulfide (PES), polyether ketone, and polyimide. For details of these resin films, see paragraphs 0081 to 0086 of JP 2015-187260 A. As the substrate, a substrate whose surface (the surface to be coated) onto which the sheet-forming composition is applied has been subjected to a release treatment by a known method can be used. One form of release treatment is the formation of a release layer. For details of the release layer, see paragraph 0084 of JP 2015-187260 A. Alternatively, commercially available release-treated resin films can be used as the substrate. By using a substrate whose surface to be coated has been subjected to a release treatment, the magnetic particle-containing sheet and the substrate can be easily separated after film formation.

[0040] When the sheet-forming composition is a curable composition, the applied composition can be subjected to a curing treatment such as heat treatment or light irradiation depending on the type of components contained in the composition, thereby forming a magnetic particle-containing sheet as a cured layer formed by curing the curable composition. The curing treatment conditions can be determined depending on the type of components contained in the composition. In this invention and this specification, the term "cured layer" includes a cured layer in which the curing reaction of the curable components contained in the curable composition has progressed to saturation or nearly saturation, and a partially cured layer in which only a portion of the curing reaction has progressed. For example, the magnetic particle-containing sheet can be a partially cured layer before being used to manufacture an inductor. In this case, curing can further progress when heated and pressurized, for example, as described below.

[0041] The magnetic particle-containing sheet can be, for example, a single-layer sheet. The thickness of the magnetic particle-containing sheet can be, for example, in the range of 5 μm to 2000 μm. However, the thickness of the magnetic particle-containing sheet can be determined depending on the application of the inductor, and is not limited to the above range. The thickness of the sheet can be measured using a known contact or non-contact film thickness measuring means. For example, the thickness value can be the arithmetic average of thicknesses measured at 20 randomly selected locations. Alternatively, the sheet thickness can be determined as the design thickness calculated from the manufacturing conditions.

[0042] The magnetic particle-containing sheet can exhibit high magnetic permeability at various angles, making it suitable as a component of an inductor.

[0043] [Inductor] One aspect of the present invention relates to an inductor including the magnetic particle-containing sheet.

[0044] The inductor includes one or more of the magnetic particle-containing sheets and may further include a coil. The configuration of an inductor including a magnetic sheet (e.g., a magnetic particle-containing sheet) and a coil is publicly known, and publicly known techniques can be applied to the inductor. For example, the inductor may be an inductor obtained by heating and pressurizing a laminate in which a coil is disposed between two magnetic sheets, thereby sealing the coil by pressing the sheets together. In such an inductor, one or both of the two magnetic sheets may be the magnetic particle-containing sheet. When both magnetic sheets are the magnetic particle-containing sheets, the thickness and / or composition of the two sheets may be the same or different. The coil may be a wound coil typically used in inductors.

[0045] [Electronic Circuit] One aspect of the present invention relates to an electronic circuit including the inductor described above.

[0046] An example of an electronic circuit including an inductor is a DC (Direct Current) / DC (Direct Current) converter. For details of the DC / DC converter, see paragraphs 0009 to 0017 and FIG. 1 of Japanese Patent Application Laid-Open No. 2023-54823. Furthermore, various types of electronic devices can be manufactured using such an electronic circuit. Examples of electronic devices including such an electronic circuit include mobile information terminals such as mobile phones, automotive computers, flat panel displays, game consoles, and personal computers.

[0047] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the embodiments shown in the examples.

[0048] Details of the various components described below are as follows:

[0049] Large particle: nanocrystalline alloy magnetic particle KUAMET NC1 053C03A (manufactured by Epson Atmix Corporation, d50: 23.9 μm) Small particle 1: iron-based amorphous magnetic particle SAP-2D (manufactured by Shinto Kogyo Co., Ltd., d50: 2.4 μm) Small particle 2: iron-based amorphous magnetic material AW2-08 PF-3F (manufactured by Epson Atmix Corporation, d50: 3.2 μm) Epoxy resin 1: bisphenol A-type epoxy resin EXA-4816 (manufactured by DIC Corporation) Epoxy resin 2: bisphenol A-type epoxy resin jER827 (manufactured by Mitsubishi Chemical Corporation) Dispersant: polyalkyleneimine derivative J-2 of Synthesis Example 22 of JP 2015-28830 A (polyalkyleneimine chain ratio: 2.3 mass%, number average molecular weight of polyalkyleneimine chain: 600) Curing catalyst: Imidazole-type curing catalyst jER Cure IBMI12 (manufactured by Mitsubishi Chemical Corporation) MEK: Methyl ethyl ketone

[0050] Example 1 Preparation of sheet-forming composition (magnetic particle dispersion) The following were added to a plastic bottle and mixed for 30 minutes with a shaking mixer: Large size particles: 68.40 parts by mass Small size particles 1: 31.60 parts by mass Dispersant: 0.24 parts by mass Epoxy resin 1: 2.37 parts by mass Curing catalyst: 0.09 parts by mass MEK (solvent): 3.49 parts by mass A magnetic particle dispersion was prepared.

[0051] <Measurement of Liquid Viscosity> The liquid temperature of the prepared magnetic particle dispersion was adjusted to 25° C., and the liquid viscosity was measured using a viscometer (VM-10A-MH manufactured by Sekonic Corporation).

[0052] <Preparation of magnetic particle-containing sheet> A magnetic particle dispersion was applied to the release surface of a release-treated PET film (PET75TR manufactured by Nippa Corporation) using a blade coater with a coating gap of 200 μm, and then dried for 1 hour in a drying device with an internal atmosphere temperature of 80° C. to prepare a magnetic particle-containing sheet.

[0053] <Measurement of magnetic permeability at various measurement angles> The magnetic particle-containing sheet on the PET film was peeled from the PET film, and a measurement sample measuring 28 mm x 10 mm was cut out with an arbitrary direction of the magnetic particle-containing sheet as the reference direction and the long side parallel to the reference direction (0°). Similarly, the angles between the reference direction and the long side were set to 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165°, and measurement samples measuring 28 mm x 10 mm were cut out. The 12 rectangular measurement samples obtained by cutting out from different angle positions were placed in an oven with an internal atmosphere temperature of 150°C for 2 hours and cured. The magnetic permeability of each of the 12 cured measurement samples at a frequency of 1 MHz was measured using a magnetic permeability measuring device PER01 (manufactured by Keycom Co., Ltd.). When the complex relative permeability is measured using the above-mentioned magnetic permeability measuring device, the real part μ' and the imaginary part μ" are displayed. The above-mentioned magnetic permeability refers to the real part μ'. The maximum magnetic permeability, minimum magnetic permeability and arithmetic mean magnetic permeability were determined from the magnetic permeabilities of the 12 measurement samples. From the values ​​thus determined, "Δ magnetic permeability = (maximum magnetic permeability - minimum magnetic permeability) / (maximum magnetic permeability + minimum magnetic permeability)" shown in Table 1 below was calculated. The arithmetic mean magnetic permeability can be used as an indicator that the magnetic permeability measured at various angles is high on average. A magnetic particle-containing sheet with an arithmetic mean magnetic permeability of 40.0 or more is preferred because the magnetic permeability measured at various angles is high on average. A magnetic particle-containing sheet with an arithmetic mean magnetic permeability of 45.0 or more is even more preferred. The Δ magnetic permeability can be used as an indicator of the anisotropy of magnetic permeability. A magnetic particle-containing sheet having a Δ magnetic permeability of 0.100 or less is preferred because it has small anisotropy of magnetic permeability.

[0054] <SEM Observation and Measurement of Various Values> A 5 ​​mm x 5 mm sample for SEM observation was cut from an arbitrary angular position of the magnetic particle-containing sheet peeled from the PET film. This SEM sample was placed in an oven with an internal atmosphere temperature of 150°C for 2 hours to cure, and then SEM observation was performed using the following method. A 10 mm-long piece of double-sided carbon tape for SEM (7311 manufactured by Nissin EM Co., Ltd.) was attached to a metal sample stage for a Hitachi High-Technologies Corporation tabletop microscope TM-1000. The SEM sample was attached to this carbon double-sided tape, with the PET film side at the time of application facing the carbon double-sided tape. The sample stage on which the SEM sample was placed was inserted into a Hitachi High-Technologies Corporation tabletop microscope TM-1000, and SEM observation was performed under conditions of 3000x magnification and an observation area of ​​63 μm x 47 μm, with the surface opposite the PET film side at the time of application being the surface to be measured. Brightness and contrast were adjusted using the auto-brightness function, and focus was adjusted using the auto-focus function. Images were obtained by SEM observation of five randomly selected locations using the XY knobs on the sample stage. Furthermore, at randomly selected locations, without changing the observation position, SEM observation was performed at angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150°, and 165° by setting the rotation button to 0° and clicking the + button. A total of 12 images were obtained by SEM observation at 3000x magnification and an observation area of ​​63 μm × 47 μm. The various images thus obtained were binarized using the method described above to obtain binarized images. Using the obtained binarized images, the arithmetic mean of the median major axis diameter (1), the arithmetic mean of the number (2), the maximum magnetic particle spacing (3), and ΔGAP were calculated using the method described above.

[0055] Examples 2 to 6, Comparative Examples 1 to 4 Magnetic particle-containing sheets were produced and various evaluations were carried out in the same manner as described for Example 1, except that the items shown in Table 1 were changed as shown in Table 1.

[0056] The results are shown in Table 1.

[0057]

[0058] One aspect of the present invention is useful in the technical fields of various electronic circuits.

Claims

1. A magnetic particle-containing sheet that satisfies the following (1), (2), and (3); (1) the arithmetic mean of the median major axis diameters of the magnetic particles obtained in each of five images obtained by observing five arbitrary measurement areas on the surface of the magnetic particle-containing sheet with a scanning electron microscope is 1.20 μm or less, the size of each of the five measurement areas is 63 μm × 47 μm, and the observation magnification of the scanning electron microscope is 3000 times, (2) the arithmetic mean of the number of magnetic particles having a major axis diameter of 5.00 μm or more obtained in each of the five images is 6 or more, (3) An arbitrary measurement angle is set to 0°, and one arbitrary measurement area on the surface of the magnetic particle-containing sheet is observed with a scanning electron microscope at each of the measurement angles of 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 120°, 135°, 150° and 165°, and the maximum arithmetic mean of the magnetic particle spacing obtained in each of the 12 images is 1.20 μm or less, the size of the one measurement area is 63 μm × 47 μm, and the observation magnification of the scanning electron microscope is 3000 times.

2. The magnetic particle-containing sheet according to claim 1, wherein the maximum arithmetic mean of the magnetic particle intervals in (3) is 1.00 μm or less.

3. A magnetic particle-containing sheet according to claim 1, wherein ΔGAP calculated by the following formula: ΔGAP=(GAPH-GAPL) / (GAPH+GAPL) where GAPH is the maximum value of the arithmetic mean of the magnetic particle intervals in (3) and GAPL is the minimum value, is 0.13 or less.

4. The magnetic particle-containing sheet according to claim 3, wherein the ΔGAP is 0.05 or more and 0.13 or less.

5. A magnetic particle-containing sheet according to claim 1, wherein the arithmetic mean of the median major axis diameter of (1) is 0.80 μm or more and 1.20 μm or less.

6. The magnetic particle-containing sheet according to claim 1, wherein the arithmetic average of the number of particles in (2) is 6 or more and 20 or less.

7. The magnetic particle-containing sheet according to claim 1, wherein the maximum arithmetic mean of the magnetic particle intervals in (3) is 0.80 μm or more and 1.20 μm or less.

8. The magnetic particle-containing sheet according to claim 1, further comprising a resin.

9. A magnetic particle-containing sheet according to claim 1, wherein the maximum arithmetic mean of the magnetic particle spacing in (3) is 1.00 μm or less, and ΔGAP calculated by the following formula: ΔGAP=(GAPH-GAPL) / (GAPH+GAPL), where GAPH is the maximum value of the arithmetic mean of the magnetic particle spacing in (3) and GAPL is the minimum value, is 0.13 or less.

10. A magnetic particle-containing sheet according to claim 9, wherein the ΔGAP is 0.05 or more and 0.13 or less, the arithmetic mean of the median major axis diameter of (1) is 0.80 μm or more and 1.20 μm or less, the arithmetic mean of the number of (2) is 6 or more and 20 or less, the maximum arithmetic mean of the magnetic particle spacing of (3) is 0.80 μm or more and 1.00 μm or less, and the magnetic particle-containing sheet further contains a resin.

11. An inductor comprising the magnetic particle-containing sheet according to any one of claims 1 to 10.

12. An electronic circuit comprising the inductor of claim 11.

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