Magnetic sheet, coil module including the magnetic sheet, and non-contact power supply device

Abstract

To provide a magnetic sheet that can be stably manufactured and has excellent magnetic properties, and a coil module and a non-contact power supply device having the magnetic sheet.SOLUTION: A magnetic sheet 2 according to the present invention contains Mn-Zn ferrite as a main component and is composed of a sheet-shaped sintered body. In the thickness direction of the cross section of the magnetic sheet 2, when the maximum value of the Zn content converted into oxides is ZMAX, and the minimum value of the Zn content converted into oxides is ZMin, the ratio of ZMin to ZMAX (ZMin / ZMAX×100) is 90% or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a magnetic sheet composed of an Mn-Zn ferrite, a coil module including the magnetic sheet, and a non-contact power supply device.

Background Art

[0002] Conventionally, in the fields of short-range wireless communication, wireless power transmission, electromagnetic wave protection, etc., magnetic sheets containing ferrite have been used for the purpose of electromagnetic wave shielding, electromagnetic wave absorption, or magnetic flux convergence.

[0003] Such a magnetic sheet is manufactured by firing a green sheet containing ferrite powder on a setter made of ceramics. However, since the ferrite sheet obtained as a sintered body is highly brittle, physical damage such as cracks is likely to occur. Also, when the thickness of the ferrite sheet is thin, deformation is likely to occur after firing, and it is difficult to manufacture stably. If cracks or deformation occur in the magnetic sheet, it leads to a decrease in mechanical strength and magnetic properties.

[0004] In response to the above problems, Patent Document 1 realizes stable manufacturing by preparing a composition and a grain growth inhibitor in a magnetic sheet composed of a Ni-Zn ferrite. However, the invention disclosed in Patent Document 1 is only a technology applied to Ni-Zn ferrites, and even if it is applied to the case of Mn-Zn ferrites, the occurrence of cracks and deformation cannot be suppressed.

[0005] Although Mn-Zn ferrites have superior magnetic properties compared to Ni-Zn ferrites, precise atmosphere control is required during firing, and manufacturing is extremely difficult. In particular, when the thickness of the magnetic sheet is thin, the difficulty of manufacturing increases, and defects such as cracks and deformation are more likely to occur after firing.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In view of such circumstances, the present invention has been made, and an object thereof is to provide a magnetic sheet that can be stably manufactured and has excellent magnetic properties, a coil module having the magnetic sheet, and a non-contact power supply device.

Means for Solving the Problems

[0008] To achieve the above object, the magnetic sheet according to the present invention is composed of a sheet-shaped sintered body, the sintered body contains Mn-Zn ferrite as a main component, in the thickness direction of the cross section of the sintered body, the maximum value of the Zn content in terms of oxide is Z MAX and the minimum value of the Zn content in terms of oxide is Z MIN then, Z MAX the ratio of Z MIN to Z MIN / Z MAX ×100) is 90% or more.

[0009] As a result of intensive studies, the present inventors have found that the magnetic sheet of the present invention having the above characteristics can be stably manufactured industrially. Further, the magnetic sheet according to the present invention has excellent magnetic properties (initial permeability and magnetic loss).

[0010] In particular, the magnetic sheet according to the present invention can be stably manufactured industrially even when thinned, and the average thickness of the sintered body can be 2500 μm or less.

[0011] Also, preferably, in the thickness direction of the cross section of the sintered body, the standard deviation of the Zn content in terms of oxide is 0.3 mol% or less.

[0012] The magnetic sheet according to the present invention can be produced, for example, by the production method shown below. That is, the production method of the magnetic sheet according to the present invention has a firing step of mounting a green sheet containing ferrite powder on a setter and firing it. And the setter used in the above firing step has a porosity of preferably less than 30%, more preferably 4% to 27.5%. Further, the arithmetic mean roughness (Ra) of the surface of the setter is preferably 2.0 μm or less, more preferably 1.5 μm or less.

[0013] Also, in the above firing step, the maximum oxygen concentration in the furnace atmosphere is preferably controlled to be 6.0 vol% or less, more preferably in the range of 0.5 vol% to 6.0 vol%. In particular, the maximum oxygen concentration is preferably controlled within the above oxygen concentration range not only during the temperature holding process but also during the heating process from 900 °C to the holding temperature of the object temperature and during the cooling process from the holding temperature to 900 °C of the object temperature.

[0014] The magnetic sheet according to the present invention can be used in fields such as short-range wireless communication, wireless power transmission, and electromagnetic wave protection. In particular, it can be suitably used as a component of a coil module in a non-contact power supply device.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

[0017] First Embodiment In the first embodiment, based on FIGS. 1 to 3, a magnetic sheet 2 according to an embodiment of the present invention will be described. The magnetic sheet 2 of the present embodiment is composed of a sheet-shaped ferrite sintered body.

[0018] The planar shape of the magnetic sheet 2 is not particularly limited. For example, it can be circular, elliptical, square, polygonal, etc., and is appropriately determined according to the use of the magnetic sheet 2. And the planar dimensions of the magnetic sheet 2 are not particularly limited either, but the area of the front surface 2a or the back surface 2b can be 2000 mm 2 or more, preferably 5000 mm 2 ~10000 mm 2 or the like.

[0019] On the other hand, the average thickness T0 of the magnetic sheet 2 shown in FIG. 1 can be 2500 μm or less, preferably 50 μm to 2500 μm, more preferably 100 μm to 2000 μm, and still more preferably 100 μm to 1000 μm. The thickness T0 of the magnetic sheet 2 is obtained by image analysis of a cross section as shown in FIG. 1, and it is preferable to measure at least five or more points and calculate the average value thereof.

[0020] Note that since the magnetic sheet 2 can have the dimensions as described above, the ratio (area / volume) of the area (mm 3 ) of the front surface 2a or the back surface 2b to the volume (mm 2 ) of the magnetic sheet 2 can be 0.4 mm -1 or more, preferably 0.5 mm -1 or more, more preferably 1 mm -1 or more.

[0021] The magnetic sheet 2 of this embodiment contains Mn-Zn ferrite as the main component. This Mn-Zn ferrite preferably contains 51 to 58 mol% of iron oxide in terms of Fe 2 O 3 , 3 to 18 mol% of zinc oxide in terms of ZnO, and the balance is composed of manganese oxide (MnO). Since the main component, Mn-Zn ferrite, is configured with the above composition, the magnetic sheet 2 of this embodiment has excellent magnetic properties.

[0022] In addition to the above main components, the magnetic sheet 2 can contain sub-components. Examples of sub-components include zirconium oxide (ZrO 2 ), silicon oxide (SiO 2 ), calcium oxide (CaO), niobium oxide (Nb 2 O 5 ), vanadium oxide (V 2 O 5 ), tantalum oxide (Ta 2 O 5 ), nickel oxide (NiO), titanium oxide (TiO 2 ), tin oxide (SnO 2 ), and cobalt oxide (CoO), etc. One or a combination of multiple types selected from the above oxides can be included.

[0023] In the above, the content of each sub-component is preferably within the following range with respect to 100 parts by weight of the main component. That is, zirconium oxide is 0.005 to 0.04 parts by weight in terms of ZrO 2 , silicon oxide is 0.005 to 0.02 parts by weight in terms of SiO 2 , calcium oxide is 0.02 to 0.2 parts by weight in terms of CaO, niobium oxide is 0.005 to 0.075 parts by weight in terms of Nb 2 O 5 , vanadium oxide is 0.005 to 0.05 parts by weight in terms of V 2 O 5 , tantalum oxide is 0.005 to 0.15 parts by weight in terms of Ta 2 O 5 , nickel oxide is 0.05 to 1 part by weight in terms of NiO, and titanium oxide is TiO 2In terms of conversion, it is 0.01 to 0.6 parts by weight, and tin oxide is SnO 2 In terms of conversion, it is 0.05 to 0.8 parts by weight, and cobalt oxide is 0.02 to 0.4 parts by weight in terms of CoO. By including the above-mentioned sub-components within such a range, the magnetic properties can be further improved.

[0024] In addition to the above-mentioned oxide-based sub-components, the magnetic sheet 2 may also contain a metal component or a compound component containing typical elements and transition metal elements as shown below. Examples of the above-mentioned typical elements include boron (B), carbon (C), phosphorus (P), sulfur (S), chlorine (Cl), arsenic (As), selenium (Se), bromine (Br), tellurium (Te), iodine (I), lithium (Li), sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), gallium (Ga), germanium (Ge), strontium (Sr), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), barium (Ba), lead (Pb), bismuth (Bi), etc. On the other hand, examples of the transition metal elements include scandium (Sc), titanium (Ti), chromium (Cr), nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), molybdenum (Mo), palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), etc. The content of the metal component or the compound component is not particularly limited, but it is preferably in the range of about 0.0001 to 0.1 parts by weight with respect to 100 parts by weight of the main component. The sub-components of the metal component or the compound component may be intentionally added, but may also be included as inevitable impurities in the raw materials.

[0025] The contents of the main components and sub-components of the magnetic body sheet 2 described above can be measured by various analysis methods, including component analysis by an electron probe microanalyzer (EPMA), composition analysis by X-ray diffraction (XRD) or electron diffraction (ED), and various ICP analyses including laser irradiation type inductively coupled plasma mass spectrometry (LA-ICP-MS), and the analysis method is not particularly limited. Preferably, the content ratio of the oxides (iron oxide, zinc oxide, and manganese oxide) constituting the main component is analyzed by EPMA.

[0026] As described above, since the magnetic sheet 2 of the present embodiment is a sheet-shaped sintered body, the resin component is not substantially contained inside the magnetic sheet 2. "Not substantially contained" in the resin component means that the resin component is 40 weight ppm or less with respect to 100% by weight of the main component. Note that a magnetic sheet containing resin has flexibility compared to a sintered body sheet, but tends to have inferior magnetic properties such as magnetic permeability.

[0027] Specifically, as a characteristic of the magnetic sheet 2 which is a sintered body, the initial magnetic permeability μi is preferably 1800 or more, more preferably 2000 or more, and even more preferably 2200 or more. Further, the magnetic sheet 2 has a magnetic loss (core loss) of 1000 kW / m 3 or less, preferably 800 kW / m 3 or less, more preferably 600 kW / m 3 or less.

[0028] In the magnetic sheet 2 of the present embodiment, in any cross section as shown in FIG. 1, the variation of the Zn component in the thickness direction is controlled within a predetermined range. Specifically, in any cross section of the magnetic sheet 2, the maximum value of the Zn content in the thickness direction is Z MAX and the minimum value of the Zn content in the thickness direction is Z MIN . Then, the ratio of Z MAX to Z MIN (Z MIN / Z MAX ×100) is 90% or more.

[0029] In the above, any cross section of the magnetic sheet 2 is not particularly limited as long as it is a cross section where the thickness direction (Z-axis direction) of the magnetic sheet 2 is exposed. However, preferably, the cross section for component analysis is an X-Z cross section or a Y-Z cross section at substantially the center of the X-Y plane of the magnetic sheet 2.

[0030] Further, in the above, the Zn content is obtained by continuously performing component analysis along the thickness direction in any cross-section of the magnetic sheet 2, and the ratio of the Zn component in 100 mol% of the main component is expressed in terms of ZnO conversion (oxide conversion) (unit: mol%). In the present embodiment, the continuous component analysis is performed by observing the cross-section of the magnetic sheet 2 with a scanning electron microscope (SEM) or the like and performing line analysis by EPMA at that time.

[0031] Figure 2 is a graph showing an example of the line analysis result by EPMA. Specifically, in the line analysis, component analysis is performed at regular intervals of about 1 to 20 μm on the measurement line 4 (Figure 1) along the thickness direction to obtain continuous data. For example, in the graph of Figure 2, the Zn content in terms of ZnO conversion is taken on the Y-axis and continuous data is plotted, showing the variation of the Zn component in the thickness direction. And in the continuous data as shown in Figure 2, the maximum value is Z MAX and the minimum value is Z MIN is set as.

[0032] As shown by the solid line (ex1) in Figure 2, in the magnetic sheet 2 of the present embodiment, the variation of the Zn component in the thickness direction is kept within a small range. Specifically, the standard deviation of the Zn content in the thickness direction is preferably 0.3 mol% or less. Also, taking the target value of the Zn content calculated from the charged amount of the raw material powder as Z T and the average value of the continuous data obtained by line analysis as Z A , then the ratio of Z T to Z A (Z A / Z T ) is preferably about 0.94 to 1.02.

[0033] In addition, in the line analysis by EPMA, it is difficult to perform accurate component analysis at the edge on the surface 2a side and the edge on the back surface 2b side, which are the edge portions of the measurement sample. Therefore, each data (Z MAX , Z MIN , Z AAs continuous data used for the analysis of [[ID=]], out of the entire data range obtained by line analysis, a range of about 3 to 5 μm from the edges of the front surface 2a and the back surface 2b is removed (ignored). For example, when the thickness of the magnetic sheet 2 is 100 μm, first, component analysis is performed at intervals of 1 μm on the measurement line 4 to obtain continuous data. Then, as shown in FIG. 2, from the continuous data, data in the range from the edge of the front surface 2a to 5 μm (range where distance is 0 to 5 μm), and data in the range from the edge of the back surface 2b to 5 μm (range where distance is 95 to 100 μm) are removed, and data analysis is carried out.

[0034] Next, an example will be shown and explained for the manufacturing method of the magnetic sheet 2 shown in FIG. 1.

[0035] First, prepare the ferrite raw materials that make up the magnetic sheet 2. Specifically, weigh the starting materials of the main component and the starting materials of the sub-components so as to have the above-mentioned predetermined composition ratio, and then mix them to obtain a raw material mixture. Examples of the mixing method include wet mixing using a ball mill and dry mixing using a dry mixer, and there is no particular limitation. Note that the average particle size of each starting material is preferably about 0.1 to 3 μm.

[0036] As the starting material of the main component, iron oxide (α-Fe 2 O 3 ), zinc oxide (ZnO), manganese oxide (Mn 3 O 4 ), or these composite oxides can be used. In addition, various compounds such as those that become the above-mentioned oxides or composite oxides by firing can also be used. Examples of the compounds that become the above-mentioned oxides by firing include simple metals, carbonates, oxalates, nitrates, hydroxides, halides, organometallic compounds, etc. Note that the content of manganese oxide in the main component is converted in terms of MnO, but as the starting material, Mn 3 O 4 is preferably used.

[0037] In addition, as starting materials for the secondary components, not only oxides but also complex oxides and compounds that become oxides after firing can be used, similar to the case of the main components. The starting materials for the secondary components can be added in the first mixing step as described above, but they may also be added after the calcination step described later.

[0038] Next, the raw material mixture obtained in the above mixing step is calcined to obtain a calcined material. As the conditions for this calcination, it is preferable that the holding temperature is 800 to 1100°C and the holding time is 1 to 3 hours. Also, the processing atmosphere during calcination may be an air atmosphere or an atmosphere with a higher oxygen partial pressure than in air.

[0039] After the calcination step, the calcined material is pulverized to obtain a pulverized material. Pulverization is performed to break up the aggregation of the calcined material and obtain a powder having appropriate sinterability. When the calcined material forms large lumps, it is preferable to perform coarse pulverization first and then perform wet pulverization using a ball mill or an attritor, etc. Also, the average particle size of the pulverized material is preferably about 0.1 to 2 μm.

[0040] Next, using the pulverized material obtained in the previous step, a sheet-shaped molded body (green sheet) is produced. As a method for obtaining the green sheet, various molding methods such as the doctor blade method, extrusion molding, and powder compression molding can be adopted, and there is no particular limitation. For example, when the average thickness T0 of the magnetic sheet 2 is 300 μm or less, it is preferable to mold by the doctor blade method, and when the average thickness T0 is 300 μm or more, it is preferable to perform extrusion molding.

[0041] When obtaining a green sheet by the doctor blade method, first, the pulverized material is kneaded together with a binder, a solvent, a dispersant, etc. to obtain a ferrite paste. The types and contents of the binder, solvent, etc. in the ferrite paste are arbitrary, and known specifications can be adopted. Then, the ferrite paste is applied onto a carrier tape and sheeted to obtain a green sheet.

[0042] On one hand, when obtaining a green sheet by extrusion molding, first, a ferrite clay is obtained by kneading a pulverized material together with a binder. The type and content of the binder used at this time are arbitrary, and known specifications can be adopted. Then, this ferrite clay is introduced into the die of an extruder, and pressure is applied while appropriately heating to extrude it from a gap having a predetermined cross-sectional shape, thereby obtaining a green sheet.

[0043] The magnetic sheet 2 is obtained by firing the green sheet obtained in the above process after appropriately performing treatments such as drying and punching to obtain the product dimensions. In the firing process, as shown in FIG. 3, after mounting the green sheet 3 on the setter 6, this setter 6 is put into a firing furnace, and heat treatment is performed while controlling the furnace atmosphere and the furnace temperature to sinter the green sheet 3. In the production of the magnetic sheet 2 according to the present embodiment, this firing is a crucial process. In particular, the variation in the Zn component in the cross-section of the magnetic sheet 2 is controlled by adjusting various conditions such as the holding temperature and holding time during firing, the oxygen partial pressure in the atmosphere, and the characteristics of the setter used. Hereinafter, the preferable firing conditions will be described.

[0044] First, as the setter 6, ceramic materials such as alumina (Al 2 O 3 ), zirconia (ZrO 2 ), and mullite (3Al 2 O 3 ·2SiO 2 ~2Al 2 O 3 ·SiO 2 ) can be used, but it is preferable to use high-purity alumina with a purity of 99% or more. In addition, the setter 6 is preferably denser and smoother. Specifically, the porosity of the setter 6 is preferably less than 30%, more preferably 4% - 27.5%. In addition, the surface roughness of the setter 6 is preferably 2.0 μm or less, more preferably 1.5 μm or less, in terms of the arithmetic mean roughness Ra. By using such a dense and smooth setter 6 with a smooth surface 6a, it is possible to particularly suppress the decrease in the Zn component in the vicinity of the back surface 2b of the magnetic sheet 2.

[0045] Further, as the firing furnace, any furnace capable of controlling the atmosphere inside the furnace may be used, and a batch-type firing furnace or a continuous-type firing furnace can be used. The holding temperature during firing is preferably 1150°C to 1300°C, and the holding time is preferably 0.5 to 3 hours. Note that, in the above, the holding temperature means the temperature at which the object temperature (the temperature of the sheet itself) is stable at the highest reaching point.

[0046] Furthermore, regarding the oxygen partial pressure, the maximum oxygen concentration in the furnace atmosphere is preferably controlled to be 6.0 vol% or less, more preferably in the range of 0.5 vol% to 6.0 vol%. In particular, in this embodiment, the oxygen partial pressure is controlled within the above oxygen concentration range not only during the temperature holding process but also during the heating process from 900°C to the holding temperature of the object temperature and during the cooling process from the holding temperature to 900°C of the object temperature. By controlling the temperature and atmosphere during firing as described above, it is possible to suppress the decrease of the Zn component particularly in the vicinity of the surface 2a of the magnetic sheet 2.

[0047] Note that, during firing, in addition to the above-described conditions, a treatment for increasing the vapor pressure of zinc in the atmosphere may be performed. Examples of such a treatment include a treatment of installing a zinc oxide block on the setter 6, a treatment of covering the surface 3a of the green sheet 3 with zinc oxide powder, and a treatment of covering the green sheet 3 to be a product with a ferrite box and firing.

[0048] Also, in FIG. 3, one green sheet 3 is mounted on one setter 6, but a plurality of green sheets 3 may be mounted simultaneously. However, in that case, it is preferable that the plurality of green sheets 3 are arranged side by side on the X-Y plane instead of being stacked on top of each other on the Z axis. This is because when a plurality of green sheets of Mn-Zn ferrite are stacked and fired, there is a risk of fusing with each other.

[0049] Furthermore, after the fired magnetic sheet 2 is removed from the setter 6, a protective layer may be formed on its front surface 2a and / or back surface 2b (the back surface 2b is the surface that was in contact with the setter 6). However, it is preferable that the fired front surface 2a and the fired back surface 2b be the surfaces as they are after firing without being subjected to machining such as blasting, polishing, or cutting.

[0050] The above is the manufacturing method of the magnetic sheet 2 in this embodiment. In the manufacture of the magnetic sheet 2, in addition to the above-described steps, processing as described below may be performed. For example, the magnetic sheet 2 may be divided into a number of small pieces in order to improve its impact resistance. In this case, the green sheet 3 before firing is subjected to pre-cut processing to form lattice-shaped grooves. After firing this green sheet 3, a resin film such as polyethylene terephthalate (PET) is laminated and attached to the front surface 2a and the back surface 2b of the obtained magnetic sheet 2. Then, by applying a roller to the magnetic sheet 2 to which the film is attached, the magnetic sheet 2 is divided into regular small pieces while being sandwiched between the films.

[0051] (Summary of the First Embodiment) The magnetic sheet 2 of this embodiment is composed of a sheet-shaped sintered body and contains Mn-Zn ferrite as a main component. In the cross-section of this magnetic sheet 2, the ratio (Z MAX ) of the maximum value (Z MIN ) to the minimum value (Z MIN / Z MAX ) of the Zn content in the thickness direction is 90% or more.

[0052] Conventionally, Mn-Zn ferrites have been put into practical use as massive ferrite cores such as drum type, E type, and I type, but it has been extremely difficult to put them into practical use in a sheet shape. In the case of a sheet shape, various defects occur in the manufacturing process, making it difficult to manufacture with the prior art. The reasons are considered as follows.

[0053] For example, in the case of a sheet-shaped ferrite sintered body, the ratio of the flat surface (the area of ​​the front surface 2a and the back surface 2b of the magnetic sheet 2) to the volume is large, so that deformation such as warping or undulation and internal cracks are likely to occur after firing. Also, in the case of a Mn-Zn ferrite sheet, fusion failure in which the green sheet 3 sticks to the setter 6 is likely to occur during the firing process.

[0054] In particular, poor fusion rarely occurs with Ni-Zn ferrites, and is a failure mode specific to Mn-Zn ferrites. Ni-Zn ferrites can be sintered in the air, but Mn-Zn ferrites must be sintered under low oxygen partial pressure to ensure their magnetic properties. In the case of a lump-shaped ferrite core, even if abnormalities such as deformations and cracks are formed on the surface of the core, the abnormalities can be removed by polishing or other methods. However, in the case of a sheet-shaped ferrite sheet, the thickness is so thin that the abnormalities cannot be removed by polishing or other methods. This is because the sheet would be damaged if machined.

[0055] As a result of thorough investigation into the above-mentioned problems, the inventors have found that the variation in the Zn component in the cross section of the magnetic sheet 2 is related to the occurrence of various defects such as deformation defects, crack defects, and fusion defects. Based on this, the inventors have found that the degree of variation in the Zn component in the thickness direction of the magnetic sheet 2 can be controlled by the firing conditions and the characteristics of the setter 6 used during firing. Furthermore, the inventors have found that the Zn content ratio (Z MIN / Z MAX × 100) is 90% or more, the above-mentioned deformation defects, crack defects, fusion defects, and the like can be suppressed during the manufacturing process, and it has been found that the magnetic sheet 2 has good mass productivity.

[0056] The reason why mass productivity is good is not necessarily clear, but it is thought that the dezincification phenomenon on the front surface 3a and the back surface 3b of the green sheet 3 is related to it.

[0057] For example, on the surface 3a of the green sheet 3, it is considered that zinc oxide contained in the green sheet 3 is reduced to metallic zinc. Since this metallic zinc has a lower sublimation temperature than zinc oxide, on the surface 3a of the green sheet 3, the generated metallic zinc is likely to volatilize easily (zinc removal phenomenon on the surface 3a), which may cause the occurrence of cracks and deterioration of magnetic properties. In the present embodiment, not only during the temperature holding process but also during the heating process and the cooling process, by controlling the oxygen concentration in the atmosphere within a predetermined range, the volatilization of the zinc component on the surface 3a is suppressed. As a result, on the surface 2a of the obtained magnetic sheet 2, it is considered that the generation of cracks and the deterioration of magnetic properties are suppressed without a decrease in the Zn component.

[0058] On the other hand, on the back surface 3b of the green sheet 3, during firing, it is considered that the zinc component on the green sheet 3 side diffuses into the setter 6 and reacts with the ceramic component of the setter 6 (zinc removal phenomenon on the back surface 3b). When this zinc removal phenomenon occurs on the back surface 3b, it is considered that the obtained magnetic sheet 2 and the setter 6 are fused together, leading to defects such as deformation, cracks, and breakage.

[0059] Generally, as the setter 6, in order to reduce the contact area between the green sheet and the setter, it has been considered preferable to use a material with a rough surface and a high porosity (30% or more). However, according to the experiments by the present inventors, it has been clarified that when a setter with a high porosity and a rough surface is used, the Zn component is likely to decrease on the back surface 3b side. On the other hand, when a highly dense and smooth setter 6 as in the present embodiment is used, the Zn component hardly decreases on the back surface 3b side. When the porosity of the setter is high and the surface is rough, it is considered that the zinc component is likely to diffuse deep into the setter, promoting the zinc removal phenomenon on the back surface 3b. On the other hand, when the setter 6 is highly dense and smooth, it is considered that the diffusion of the zinc component is limited to the minimum necessary range on the outermost surface of the setter 6.

[0060] In the magnetic sheet 2 of the present embodiment, in the manufacturing process, since the dezincification phenomenon on the front surface 3a and the back surface 3b is suppressed by the above principle, it is considered that mass productivity is good (that is, it can be stably manufactured industrially).

[0061] As a method for suppressing the dezincification phenomenon on the front surface 2a, a treatment of firing a dummy member such as an individual or powder of zinc oxide or a box of ferrite together with the green sheet 3 to increase the vapor pressure of zinc in the atmosphere is also conceivable. In this method, zinc preferentially volatilizes from the dummy member, so that the volatilization of the Zn component from the green sheet 3 side can be suppressed to some extent. However, in this method, it is difficult to keep the vapor pressure of zinc constant, and it is not suitable for mass production. On the other hand, the oxygen partial pressure can be controlled by adjusting the gas components introduced into the furnace, and it is easier to control than the vapor pressure control of zinc. Therefore, in the case of the method for controlling the oxygen partial pressure of the present embodiment, the dezincification phenomenon on the front surface 3a can be preferably suppressed without co-firing the dummy member.

[0062] Further, conventionally, as a measure for preventing poor fusion to the setter 6, a treatment of coating zinc oxide or zirconium oxide as a release agent on the front surface 6a of the setter 6, or a treatment of previously containing zinc oxide or zirconium oxide inside the setter 6 itself is also known. However, in the manufacture of a sheet-shaped ferrite sintered body such as the magnetic sheet 2, the above-described conventional measures are insufficient. This is because in the case of a sheet shape, the ratio of the area of the back surface 3b to the volume of the green sheet 3 is large, and the dezincification phenomenon on the back surface 3b is activated. In addition, when zinc oxide or zirconium oxide is interposed between the magnetic sheet 2 and the front surface 6a of the setter 6, deformation or defects occur in the magnetic sheet 2. Therefore, in the case of a thin magnetic sheet, reduction of poor fusion cannot be achieved by the above-described conventional techniques, but can be preferably realized by the manufacturing method of the present embodiment.

[0063] In addition, in the magnetic sheet 2 of the present embodiment, as described above, as a result of suppressing various defects, deterioration of magnetic properties does not occur. Therefore, the initial permeability is improved and the magnetic loss is reduced. In particular, when the average thickness T0 of the magnetic sheet 2 is made as thin as 2500 μm or less, or when the sheet area is widened to 2000 mm 2 or more, good mass productivity can be achieved and excellent magnetic properties can be obtained. In other words, the magnetic sheet 2 of the present embodiment can be made thinner and wider.

[0064] The magnetic sheet 2 of the present embodiment can be mounted on a smartphone, a tablet, a non-contact IC card, etc. for the purpose of electromagnetic wave shielding and used. It can also be used as a noise filter or an electromagnetic wave absorber, and furthermore, it can be incorporated into a coil module and suitably used as a component of a non-contact power supply device.

[0065] Second Embodiment In the second embodiment, as an example of the use of the magnetic sheet 2 described in the first embodiment, a coil module 10 (FIG. 4) and a non-contact power supply device 100 (FIG. 5) having the magnetic sheet 2 will be described. Regarding the configuration common to the first embodiment in the second embodiment, the description will be omitted and the same reference numerals will be used.

[0066] FIG. 4 is a schematic perspective view showing a coil module 10 according to the second embodiment. As shown in FIG. 4, the coil module 10 has a magnetic sheet 2 and a coil 12.

[0067] The coil 12 is a flat spiral coil. In FIG. 4, the outer edge shape of the coil 12 in plan view is a rounded rectangular shape, but the outer edge shape of the coil 12 is not limited to this and may be a circular shape, an elliptical shape, a polygonal shape, etc.

[0068] Further, the coil 12 is formed by winding a conductive wire such as an insulated copper wire or aluminum wire in a planar and spiral manner. The cross-sectional shape of the conductive wire to be used is not particularly limited, and can be circular, elliptical, triangular, quadrangular, or the like. Note that the method of forming the coil 12 is not limited to the above method, and it may be formed by a thin film method. The thin film method means a method of forming a coil by, for example, metal foil, conductive paste, plating transfer, sputtering, vapor deposition, or screen printing.

[0069] Also, as shown in FIG. 4, a pair of lead terminals 13 are electrically connected to the coil 12. The lead terminals 13 are formed by pulling out the front end and the rear end of the conductive wire constituting the coil 12 to the outside of the coil 12. Note that the extraction position of the lead terminals 13 is not particularly limited.

[0070] In the second embodiment, the above-described coil 12 is formed on the magnetic sheet 2 described in the first embodiment via an adhesive layer (not shown) such as an adhesive or a double-sided tape. The thickness of the adhesive layer is not particularly limited, and can be, for example, 10 μm to 100 μm. Note that resin films (not shown) may be formed on the front surface 2a and the back surface 2b of the magnetic sheet 2 as protective layers.

[0071] Further, in addition to the above-described components, the coil module 10 may have an alignment magnet. The alignment magnet is disposed, for example, at the center of the coil 12. Furthermore, FIG. 4 illustrates the configuration when the coil module 10 has a single coil 12, but the coil module 10 may be a coil array type module configured by combining a plurality of coils 12.

[0072] The coil module 10 having the magnetic sheet 2 is preferably used in a non-contact power feeding device 100 as shown in FIG. 5. Hereinafter, the non-contact power feeding device 100 according to the second embodiment will be described.

[0073] The non-contact power supply device 100 mainly includes a power transmission side coil module 10a and a power reception side coil module 10b. The power transmission side coil module 10a and the power reception side coil module 10b each have coils 12a and 12b and a magnetic sheet 2, corresponding to the coil module 10 shown in FIG. 4. In this embodiment, the magnetic sheet 2 can be mounted on both the power transmission side and the power reception side as described above, but it may be mounted on only one of the power transmission side and the power reception side. However, the magnetic sheet 2 is particularly preferably used for the power transmission side coil module 10b.

[0074] FIG. 5 shows a state in which the power transmission side coil module 10a and the power reception side coil module 10b are positioned for non-contact power supply. As shown in FIG. 5, during non-contact power supply, the power transmission side coil 12a and the power reception side coil 12b are arranged to face each other at a predetermined interval. Then, the magnetic sheet 2 is arranged so as to cover the back surfaces of the coils 12a and 12b.

[0075] The power transmission side coil module 10a is incorporated on the charger side. A power transmission side internal circuit 20a including an AC / DC converter, an LC resonance circuit, etc. is connected to the power transmission side coil 12a via a lead terminal 13 (not shown). Further, a power supply 22 is connected to the power transmission side internal circuit 20a. By having the above configuration, an AC voltage having a predetermined frequency is supplied to the power transmission side coil 12a during power supply. When an AC voltage is supplied to the power transmission side coil 12a, a magnetic field is generated around the coil 12a.

[0076] On one hand, the power receiving coil module 10b is incorporated into a device to be charged such as a mobile terminal or a PC. Similar to the power transmitting side, for the power receiving coil module 10b, a power receiving internal circuit 20b including a converter, a resonance circuit, etc. is connected to the power receiving coil 12b via a lead terminal 13 (not shown). And a secondary battery 24 is connected to the power receiving internal circuit 20b. When the power receiving coil 12b is brought close to the magnetic field generated on the power transmitting side, an alternating current is generated in the power receiving coil 12b by electromagnetic induction. The alternating current generated on the power receiving side is converted into a direct current via the power receiving internal circuit 20b and used for charging the secondary battery 24.

[0077] In the non-contact power supply device 100 as described above, the magnetic sheet 2 is mainly arranged for the purpose of preventing magnetic flux leakage and forming a magnetic path. As also described in the first embodiment, since the magnetic sheet 2 according to the present invention has excellent permeability characteristics, in the non-contact power supply device 100 having the magnetic sheet 2, magnetic flux can be efficiently converged, and the power transmission efficiency is improved.

[0078] Also, in the non-contact power supply device 100 as shown in FIG. 5, in recent years, higher output and smaller size have been required. To meet these requirements, in particular, the heat generation during power supply is a problem. As also described in the first embodiment, since the magnetic sheet 2 according to the present invention has little magnetic loss, the heat generation of the non-contact power supply device 100 can be reduced.

[0079] As described above, in the non-contact power supply device 100 according to the present embodiment, since it has the magnetic sheet 2 having excellent magnetic characteristics, improvement in power transmission efficiency and reduction in size and thickness can be achieved.

[0080] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments and can be variously modified within the scope of the present invention. For example, the non-contact power supply device 100 may have, in addition to the above-described components, a sensor for detecting the position of the device to be charged (i.e., the power receiving coil 12b), a driving device for moving the power transmitting coil 12a to the position of the power receiving coil 12b, etc.

Example

[0081] Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

[0082] Experiment 1 In Experiment 1, the firing conditions and the like were adjusted so that the ratio of the Zn content in the cross-section (Z MIN / Z MAX ×100) was 90% or more, and the magnetic sheet according to Example 1 was produced. 500 magnetic sheets according to Example 1 were produced each, and the product yield, the initial magnetic permeability μi, and the magnetic loss Pcv in Example 1 were evaluated. Hereinafter, the detailed experimental conditions will be described.

[0083] (Example 1) First, the starting materials of the main component and the starting materials of the sub-components were weighed and mixed at a predetermined mixing ratio, and then calcined at 900 °C for 2 hours in an air atmosphere. At this time, as the starting materials of the main component, powders with an average particle size of 0.1 to 3.0 μm were used respectively, and the final main component composition was Fe 2 O 3 : 53.5 mol%, ZnO: 10.5 mol%, and the balance was weighed so as to be MnO. As the sub-components, SiO 2 , CaCO 3 , Nb 2 O 5 , and V 2 O 5 were added, and the content of each final sub-component was 0.01 part by weight of SiO 2 , 0.08 part by weight of CaO, 0.02 part by weight of Nb 2 O 5 , and 0.01 part by weight of V 2 O 5 with respect to 100 parts by weight of the main component. The raw materials were formulated.

[0084] Next, the calcined material obtained in the previous step was ground in a ball mill for 14 hours to obtain a ground material with an average particle size of 1.0 - 2.0 μm. Then, this ground material was kneaded together with a binder, a solvent, etc. to obtain a ferrite paste. And this ferrite paste was applied onto a carrier tape and sheeted to obtain a green sheet. In this forming step, the coating amount of the paste was controlled so that the thickness of the magnetic sheet after firing would be 100 μm.

[0085] Next, the green sheet obtained in the above step was placed on the surface of a setter and put into a continuous firing furnace for firing. At this time, in Example 1, firing was carried out under the improvement conditions shown in Table 1. Specifically, in Example 1, the holding temperature during firing was set to 1200 - 1250 °C, and the holding time was set to 1 - 2 hours. Also, in the temperature rising process from 900 °C to the holding temperature, the temperature holding process at 1200 - 1250 °C, and the temperature decreasing process from the holding temperature to 900 °C, the maximum oxygen concentration in the atmosphere was controlled in the range of 0.01 vol% - 4.0 vol%. Furthermore, as the setter, a high-purity alumina substrate with a porosity of 12 - 15%, a surface roughness Ra of 1.1 - 1.4 μm, and a purity of 99.5% or more was used.

[0086] By firing under the above conditions, the magnetic sheet according to Example 1 was obtained. The produced magnetic sheet was in a plate shape with dimensions of 100 mm × 50 mm in plan view. Also, the following evaluations were carried out on the obtained magnetic sheet.

[0087] Line Analysis by EPMA First, line analysis by EPMA was performed during SEM observation to evaluate the degree of variation of the Zn component in the thickness direction of the magnetic sheet. Specifically, as shown in Fig. 1, in the cross-section of the magnetic sheet, a measurement line 4 (the line length was approximately the same as the thickness T0 of the magnetic sheet) substantially parallel to the thickness direction was drawn, and component analysis was performed at intervals of 1 μm in the point width on the measurement line 4 to obtain continuous data. At this time, the acceleration voltage was 15 kV and the irradiation current was 50 nA. In addition, the sample for measurement was obtained by cutting the magnetic sheet at a substantially central position in the X-Y plane, embedding it in resin, and mirror-polishing the cross-section. The results of the line analysis in Experiment 1 are shown in Fig. 2. Further, the continuous data obtained by the line analysis was analyzed, and the minimum value Z MIN , the maximum value Z MAX , the average value Z A , the standard deviation σ, Z MIN / Z MAX , and Z A / Z T were calculated. The results are shown in Table 2.

[0088] Calculation of Product Yield To evaluate the mass productivity of the magnetic sheet according to Example 1, the product yield was calculated. In Example 1, 500 magnetic sheets were produced. For each of the 500 magnetic sheets, an appearance inspection was performed to evaluate the presence or absence of various defects such as deformation defects, crack defects, and fusion defects. Then, based on the results of the appearance inspection, the ratio of the number of non-defective products to the number of produced sheets, that is, the product yield, was calculated. When the product yield is 97% or more, it is judged as qualified and the mass productivity is good. The calculated product yield is shown in Table 2.

[0089] Evaluation of Magnetic Properties As a preliminary step for evaluating the magnetic properties, first, the magnetic sheets of Examples 1 to 3 were cut into a toroidal shape with an outer diameter of 20 mm and an inner diameter of 10 mm by laser processing. Then, a wire with a wire diameter of 0.35 mm was wound around this evaluation sample for 10 turns, and the initial permeability μi (dimensionless quantity) and the magnetic loss Pcv (unit: kW / m 3 ) were measured.

[0090] The initial permeability μi was measured using an LCR meter (Keysight Technologies: E4980A). The measurement conditions were a measurement temperature of room temperature (25 °C) and a measurement frequency of 100 kHz. Also, the measurement of the initial permeability μi was carried out 4 times, and the average value was calculated. The initial permeability μi is based on 1800, and values of 2000 or more are considered good, and values of 2200 or more are considered even better.

[0091] The magnetic loss Pcv was measured using a BH analyzer (Iwaki Communications Co., Ltd.: SY-8218). The measurement conditions were a measurement temperature of room temperature (25 °C), a measurement frequency of 100 kHz, and an excitation magnetic flux density of 200 mT. For the magnetic loss Pcv, 8 measurements were made, and the average value was calculated. The magnetic loss Pcv is based on 1000 kW / m 3 with values of 800 kW / m or less being considered good, and 3 values of 600 kW / m or less being considered even better. 3

[0092] In the evaluation of magnetic properties, among the 500 magnetic sheets produced in each example and each comparative example, a plurality of magnetic sheets obtained as good products were selected as evaluation samples. The evaluation results of the magnetic properties are shown in Table 2.

[0093] (Comparative Example 1) In Comparative Example 1, unlike Example 1, firing was carried out under the conventional conditions 1 shown in Table 1 to produce a magnetic sheet according to Comparative Example 1. Specifically, in Comparative Example 1, the holding temperature during firing was 1300 - 1350 °C, and the holding time was 3 - 5 hours. Also, the control of the oxygen partial pressure in the firing atmosphere was carried out only during the temperature holding process and the cooling process, and the maximum oxygen concentration at that time was 0.03 vol% - 3.0 vol%. Also, as the setter, an alumina substrate with a porosity of 30 - 32%, a surface roughness Ra of 2.1 - 2.6 μm, and a purity of about 95% was used. The experimental conditions other than the above in Comparative Example 1 were the same as those in Example 1, and the same evaluation as in Example 1 was carried out.

[0094] (Comparative Example 2) In Comparative Example 2, firing was performed using a dummy member (conventional condition 2) to produce a magnetic sheet according to Comparative Example 2. Specifically, in Comparative Example 2, a zinc oxide block was placed as a dummy member around the green sheet and fired. The firing conditions (holding temperature, holding time, oxygen concentration, properties of the setter, etc.) other than those described above in Comparative Example 2 were the same as those in Comparative Example 1.

[0095]

Table 1

[0096]

Table 2

[0097] Evaluation 1 In FIG. 2, the solid line ex1 is the line analysis result of Example 1, the dotted line ce1 is the line analysis result of Comparative Example 1, and the alternate long and short dash line ce2 is the line analysis result of Comparative Example 2. In Comparative Example 1, on both the surface side and the setter side, the Zn content decreased significantly from the target value (10.5 mol%). For Comparative Example 2, although the decrease in the Zn content is somewhat suppressed by the dummy member on the surface side, the Zn content decreased significantly on the setter side. Thus, in Comparative Examples 1 and 2, the variation in the Zn component in the thickness direction was large, and Z MIN / Z MAX was less than 90%.

[0098] In contrast, in Example 1, the decrease in the Zn content was suppressed not only on the surface side but also on the setter side, and a magnetic sheet with Z MIN / Z MAX of 90% or more was obtained. In this Example 1, almost no defects (such as deformation defects, crack defects, and fusion defects) occurred after firing, and it was confirmed that the product yield was much improved compared to Comparative Examples 1 and 2. From this result, it was proven that a magnetic sheet with Z MIN / Z MAX of 90% or more can be industrially stably manufactured.

[0099] Also, as shown in Table 2, in Example 1, the magnetic properties are far superior to those of Comparative Examples 1 and 2, and the reference values of the initial permeability μi and the magnetic loss Pcv are satisfied. That is, Z MIN / Z MAX It was proven that in a magnetic sheet where is 90% or more, mass productivity is excellent and high magnetic properties can be obtained.

[0100] Experiment 2 (Examples 11 to 16) In Experiment 2, by changing the average thickness T0 of the magnetic sheet, magnetic sheets according to Examples 11 to 16 were produced. In particular, in Examples 11 to 12, a green sheet was formed by the doctor blade method in the same manner as in Experiment 1, and the thickness of the obtained magnetic sheet was adjusted by changing the coating amount of the ferrite paste at that time. On the other hand, in Examples 13 to 16, a green sheet was formed by the extrusion molding method, and the thickness of the obtained magnetic sheet was adjusted by changing the diameter of the mold (extrusion diameter) used at that time. The average thickness T0 in each of Examples 11 to 16 is shown in Table 3. In addition, the experimental conditions other than the above in Experiment 2 are common to Experiment 1, and the same evaluation as in Experiment 1 was carried out.

[0101] (Comparative Examples 11 to 15) In Comparative Examples 11 to 15, magnetic sheets with different average thicknesses T0 were produced by changing the molding conditions. The average thickness T0 in Comparative Examples 11 to 15 is shown in Table 3. In addition, the experimental conditions other than the above in Comparative Examples 11 to 15 are common to Comparative Example 1 of Experiment 1.

[0102] Evaluation 2 The evaluation results of Examples 11 to 16 and Comparative Examples 11 to 15 in Experiment 2 are shown in Table 3.

[0103]

Table 3

[0104] Comparing the experimental data of Comparative Examples 11 to 15, especially in Comparative Examples 11 and 12 where the thickness T0 is thin, the product yield deteriorates and the magnetic properties also decrease. From this result, it can be confirmed that the thinner the thickness of the magnetic sheet, the easier it is for deformation, cracks, and defects due to fusion to occur after firing. Also, in Comparative Example 13, although the magnetic properties are ensured for the samples obtained as good products, the product yield is 97% or less, and the mass productivity is poor. When the thickness of the sheet is 2.0 mm or more as in Comparative Example 13, by optimizing the firing temperature etc., the magnetic properties of the sheet obtained as a good product can be ensured to a certain extent. However, an improvement in mass productivity cannot be achieved.

[0105] In contrast, in Examples 11 to 16 of the present invention, not only when T0 is in the range of 1.0 mm to 2.5 mm (Examples 14 to 16), but also when T0 is as thin as 50 μm to 1.0 mm or less (Examples 11 to 13), since Z MIN / Z MAX is 90% or more, the product yield is high and stable production is possible. Also, in Examples 11 and 12, the initial permeability μi is higher and the magnetic loss Pcv is less than in Comparative Examples 11 and 12. From this result, it was confirmed that in a magnetic sheet where Z MIN / Z MAX is 90% or more, even if the thickness is reduced, mass productivity can be ensured and high magnetic properties can be obtained.

[0106] Supplementary remarks are made regarding the results of Comparative Examples 14 and 15. In Comparative Examples 14 and 15, although Z MIN / Z MAX is less than 90%, the product yield is high and the magnetic properties are also high. When the thickness T0 exceeds 2.5 mm and is thick, it becomes more like a lump than a sheet, and the ratio of the plane to the volume decreases. Therefore, even if Z MIN / Z MAX is less than 90%, it is considered that mass productivity can be maintained.

[0107] Experiment 3 In Experiment 3, magnetic sheets according to Examples 21 to 23 were produced by changing the composition ratio of the main components. Table 4 shows the composition of the main components in each of Examples 21 to 23. The experimental conditions other than those described above in Experiment 3 were common to Experiment 1, and the same evaluation as in Experiment 1 was carried out.

[0108] Evaluation 3 Table 4 shows the evaluation results of Examples 21 to 23 in Experiment 3.

[0109]

Table 4

[0110] As shown in Table 4, even when the ratio of the main components was changed, it was confirmed that stable production was possible as long as Z MIN / Z MAX was controlled within a predetermined range. Comparing Examples 21 to 22, it was confirmed that when the blending ratio of ZnO increased, although the initial permeability μi improved, the magnetic loss Pcv increased. Also, when the blending ratio of ZnO decreased, although the magnetic loss Pcv could be reduced, on the contrary, the initial permeability μi decreased. As the composition of the Mn-Zn ferrite, when Fe 2 O 3 is 51 to 58 mol% and ZnO is in the range of 3 to 18 mol%, stable production is possible and excellent magnetic properties can be obtained.

Explanation of Symbols

[0111] 2... Magnetic sheet 2a... Surface 2b... Back surface 3... Green sheet 4... Measurement line 6... Setter 6a... Setter surface 10... Coil module 12... Coil 13... Lead terminal 100... Non-contact power supply device 10a … Power transmission side coil module 10b … Power reception side coil module 20a … Power transmission side internal circuit 20b … Power reception side internal circuit 22 … Power supply 24 … Secondary battery

Claims

1. A magnetic sheet composed of a sheet-shaped sintered body, The sintered body contains Mn-Zn ferrite as a main component, The average thickness of the sintered body is 100 μm or more and 2500 μm or less, In the thickness direction of the cross section of the sintered body, the maximum Zn content calculated as an oxide is Z MAX The minimum oxide-equivalent Zn content is Z Min Then, Z MAX Z for MIN The ratio (Z MIN / Z MAX × 100) is 90.6% or more and 93.7% or less, The Mn-Zn ferrite is made of iron oxide. 2 O 3 The magnetic sheet contains 53.5 to 58.0 mol % of zinc oxide calculated as ZnO.

2. 2. The magnetic sheet according to claim 1, wherein the standard deviation of the Zn content calculated as an oxide in the thickness direction of a cross section of the sintered body is 0.3 mol % or less.

3. A coil module comprising the magnetic sheet according to claim 1 or 2.

4. A contactless power supply device comprising the coil module according to claim 3.

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