JP6501148B2 - Magnetic sheet material using green compact and method of manufacturing the same - Google Patents

Description

  The present invention relates to a magnetic sheet material suitable for use in a noncontact power feeding apparatus utilizing an electromagnetic induction system and a method of manufacturing the same.

  In recent years, the performance and functionality of small information communication devices and electronic devices have been promoted, and in particular, a new power supply method called contactless power supply has attracted attention in order to expand the convenience of mobile phones, smartphones, etc. ing. In these small portable devices, secondary batteries such as lithium ion batteries are used as a power source. In this charging method of the secondary battery, a contact charging method in which charging is performed by bringing the power receiving side electrode and the power feeding side electrode into direct contact with each other, transmission coils are provided on both the power feeding side and the power receiving side, and electromagnetic induction is used. There is a non-contact charging method of charging by power transmission.

  In order to obtain high power transmission efficiency, a magnetic sheet is installed on the transmission coil on the side opposite to the contact surface of the power feeding device and the power receiving device. When leakage flux is generated between coils during charging of the non-contact charging device, these parts generate heat due to eddy currents generated inside the secondary battery or in parts such as a metal member used as a case. The magnetic sheet plays a role of suppressing this heat generation as a magnetic shield material. The magnetic sheet also has a function as a yoke member that increases the magnetic flux generated in the coil during charging, and enhances the magnetic force (inductance) generated from the coil.

  In the noncontact charging method, the magnetic flux generated in the primary transmission coil is fed by generating an electromotive force in the secondary transmission coil via the power feeding device and the power receiving device. Therefore, in order to obtain high power transfer efficiency in the non-contact charging system, it is necessary to match the central axes of the primary coil and the secondary coil. For example, in Patent Documents 1 to 3, in order to provide a contactless charging device having a simple structure while suppressing a decrease in power transmission efficiency, the magnetic attraction means is disposed inside the transmission coil to form a primary coil and a secondary coil. A configuration is disclosed that causes the central axes of the two to coincide.

JP 2005-340759 A Unexamined-Japanese-Patent No. 2006-42519 WO 2011/096569

  When a thin plate-like compacted body as in the present invention is used for a magnetic sheet, the compacted body is required to have high mechanical strength as well as excellent magnetic properties. The green compact is required to have high mechanical strength so as not to have cracks or cracks at the time of manufacture, and when modularized as an antenna material, it needs to have "handling property" enough to withstand the incorporating process.

  Furthermore, since the magnetic sheet is used in a high frequency region of several hundreds kHz, it is also assumed to use magnetic powder such as Fe-Si powder, Fe-Al-Si powder, amorphous powder, etc. with a small high frequency loss. Since these magnetic powders are all hard powders, when a green compact is produced, the density, shape retention, and strength are significantly impaired.

  As one of the methods for improving the strength of a green compact, a method of mixing magnetic powder and resin and performing molding / high temperature heat treatment has been widely studied. The strength of the green compact can be greatly improved by the resin binding between the magnetic powder and the resin filling the voids in the green compact, but the magnetic property (inductance) is reduced by the decrease in density. Will also drop significantly. In addition, the flowability of the powder is deteriorated as the amount of resin increases also in the manufacturing aspect, which causes the defective filling of the powder and the dispersion of the product size.

  On the other hand, when high-pressure molding is performed using only pure iron powder which has an insulating coating of phosphate on the surface and is excellent in moldability, sliding flaws called galling easily occur on the sliding surface of the product against the mold. The term "scratching" refers to a sliding scratch that occurs when metal slides against each other when the product is pushed out of a mold or the like, and when this scuffing occurs, it locally occurs on the surface of pure iron powder. Plastic deformation occurs, and the insulating coating is broken. When such a thin green compact is used in a high frequency region, the AC resistance significantly increases and the loss increases. Therefore, when using pure iron powder, in order to suppress galling, a large amount of internal lubricant must be added, and a decrease in the magnetic force (inductance) due to the reduction in density and a decrease in the strength of the molded body are avoided. I can not do it.

  The magnetic sheet is strongly required to have an ultra-thin shape of 1.0 mm or less, preferably 0.5 mm or less, from the needs for downsizing and thinning of the terminal as well as excellent magnetic properties. The present invention provides a magnetic sheet of a high density powder compact having a density ratio of more than 90% even with a thickness of 1.0 mm or less using powder metallurgy technology based on the material index of high density and high inductance. The purpose is that.

The present invention has been made in view of the above problems, and has been made by finding a combination of a combination having a high mechanical strength even with a hard magnetic powder while using a very small amount of resin addition, and a powder shape. That is, the magnetic sheet material for non-contact power feeding of the present invention (hereinafter, abbreviated as "magnetic sheet material") is a thin plate-like compact having a thickness of 1.0 mm or less containing soft magnetic powder and resin. Of soft magnetic powder A having a Vickers hardness of 300 to 500 HV and a soft magnetic powder B having a Vickers hardness of 70 to 150 HV, and the ratio of the soft magnetic powder A is 30 to 50 70% by mass , the soft magnetic powder A is Fe-Si powder containing 5.0 to 7.0% by mass of Si, the soft magnetic powder B is pure iron powder, and the soft magnetic powder It is characterized in that the average particle diameter (equivalent circle diameter) of A and the soft magnetic powder B satisfies the following expression 1 .

  In the present invention, when compared to a green compact comprising only a single magnetic powder, mechanical strength can be improved before and after heat treatment, so that the occurrence of cracks and cracks can be suppressed. Is possible. In addition, the loss (AC resistance) can be effectively reduced even in the several hundreds kHz region by containing the magnetic powder which is excellent in high frequency characteristics even in view of the magnetic characteristic surface, and the density is higher than the method of adding the resin. As a result, it is possible to maintain high magnetic flux (inductance).

  Further, in the present invention, soft magnetic powders different in particle diameter and powder hardness are mixed and strongly entangled, so that it is possible to make it difficult to produce galling on the sliding surface even with a small amount of lubricant. As described above, since the flowability of the excellent powder is maintained by reducing the content of the lubricant and the resin powder, the dimensional system of the product can be stabilized.

In the present invention, the resin content is desirably 1.0% by mass or less .

Next, the present invention is a manufacturing method of the following non-contact power supply for magnetic sheet thickness 1.0 mm, a mixing step of obtaining a mixed powder by mixing a plurality of soft magnetic powder and resin and internal lubricant, The method includes a forming step of filling the mixed powder in a mold and forming the step, and a step of heat treating the thin plate-like compact obtained in the forming step, and the soft magnetic powder has an aspect ratio of 1.5 to 2 .5 soft magnetic powder A having a Vickers hardness of 300 to 500 HV and soft magnetic powder B having a Vickers hardness of 70 to 150 HV, wherein the ratio of the soft magnetic powder A is 30 to 70 mass%, The soft magnetic powder A is an Fe-Si powder containing 5.0 to 7.0% by mass of Si, the soft magnetic powder B is a pure iron powder, and the amount of the resin added is 0.1 to 0.1. It is characterized in that it is 0.5% by mass .

  By adapting the magnetic sheet material of the present invention to a small electronic device such as a smartphone equipped with a non-contact power feeding function, it is possible to make the product thinner, smaller and more efficient. Furthermore, by maintaining high mechanical strength, an effect such as suitably acting on improvement of long-term reliability of product characteristics as an antenna material can be obtained.

It is a graph which shows the influence of the aspect ratio of Fe-6.5Si powder and the particle size on the bending strength. 5 is an optical microscope image of the cross-section of Example 1 after polishing. It is an optical microscope image after cross-sectional grinding | polishing of the comparative example 1. FIG. It is an optical microscope image after cross-sectional grinding | polishing of the comparative example 2. FIG. It is a graph which shows the influence on the die strength at the time of changing the ratio of Fe-6.5Si powder and a pure iron powder. It is a graph which shows the relationship between resin addition amount and bending strength. It is a graph which shows the magnetic characteristic at the time of changing pure iron powder / Fe-6.5Si powder ratio.

(Function of magnetic sheet)
The magnetic sheet functions as a magnetic shield material, and prevents leakage flux generated during charging of the non-contact charging device from flowing to parts such as a metal member used as an inside of a secondary battery or a case, and those parts Suppress the heat of In addition, the magnetic sheet functions as a yoke member that circulates the magnetic flux generated in the coil during charging, and enhances the magnetic force (inductance) generated from the coil.

(Existing ferrite sheet)
Conventionally, as a magnetic sheet material in non-contact power feeding, ferrite excellent in high frequency characteristics has been used. However, ferrite, which is iron oxide, tends to produce magnetic saturation (a state in which the magnetization no longer changes regardless of how much the magnetic field applied to the magnetic material is strengthened) because the saturation magnetic flux density is small and the sheet thickness is reduced. Have the problem of This causes heat generation due to a significant reduction in inductance and an increase in eddy current loss around the battery pack. Such a phenomenon becomes remarkable especially when using a permanent magnet for alignment between coils, and in order to prevent the sheet material from being magnetically saturated, the thickness of the sheet material must be increased. It was not. In general, since the high frequency characteristics and the height of the saturation magnetic flux density in the soft magnetic material are in a trade-off relationship, it is difficult to achieve both the required characteristics and the thin terminal in the magnetic sheet using ferrite. .

(Magnetic sheet material of the present invention)
On the other hand, since the magnetic sheet material of the present invention is a high density, high permeability powder compact, it has a feature that it has high inductance when compared with an existing ferrite sheet with the same thickness. As a result, the number of coil turns can be reduced, leakage flux can be suppressed, and magnetic saturation under magnetic field interference can be avoided, thus enabling highly efficient power supply.

(Problems of thin plate compacts)
However, the magnetic sheet of the present invention uses a fine magnetic component to reduce high frequency loss, and is an extremely thin powder compact, so that the mechanical strength is low and the major problem on the product is Become. The mechanical strength referred to in the present invention has two meanings, one being "strength required in the manufacturing process". Since the green compact before heat treatment has a lower strength than the green compact after heat treatment, cracks and cracks are likely to occur, and such a green compact remains in workability and handleability. Second, when considered as a product, high strength is required to prevent breakage when modularized with a coil as a magnetic sheet material and to maintain long-term reliability of the product. .

  The magnetic sheet material using the ultrathin compacted powder compact according to the present invention is made of a soft magnetic material, and is manufactured using a resin, a lubricant or the like in order to improve various characteristics described later. Hereinafter, each component will be described in order. In the following description, “%” means “mass%”.

  The role of Si has the effect of reducing the magnetic anisotropy and the magnetostriction constant, and the effect of increasing the electrical resistance and reducing the eddy current loss. If the amount of Si added is less than 1%, the effect of improving the soft magnetic characteristics is poor. If the amount of Si added is more than 10 wt%, the drop in saturation magnetization is large and the DC bias characteristics are degraded. Therefore, 3 to 8% or less of Si is more preferable, More preferably, 5.0 to 7.0% is good.

[Particle size]
The soft magnetic powder used in the present invention is characterized in that two or more different soft magnetic powders are used in combination.
One soft magnetic powder is a hard soft magnetic powder containing Si, and the other soft magnetic powder is softer in powder than the hard soft magnetic powder containing Si described above, and pure iron is excellent in compressibility and formability. It is powder. The role of the particles is different, so that suitable particle diameters are also different. As the pure iron powder having excellent compressibility, particles having relatively large particle diameters are preferable, and specifically, the average particle diameter is preferably 20 to 100 μm, Preferably, 30 to 75 μm is good.

  On the other hand, as hard soft magnetic powder containing Si, when it is larger than pure iron powder or fine powder of less than 10 μm, the strength of the molded body is significantly reduced, which is not preferable. In particular, when soft magnetic powder having a particle size of less than 10 μm is used, mass density decreases and strength decreases due to an increase in pores, and powder flowability and filling properties are poor. But not preferable. Specifically, the particle size of the hard soft magnetic powder containing Si is preferably 10 to 50 μm, and more preferably 20 to 40 μm. By setting the soft magnetic powder constituting the green compact to the particle diameter as described above, eddy current loss can be suppressed even in a frequency range of 120 kHz.

[Powder shape]
The aspect ratio of the soft magnetic powder containing Si used in the present invention is preferably 1.5 to 2.5. Although the details will be described later in the examples, by setting the aspect ratio to such a range, the entanglement between the magnetic powders is improved, whereby the mechanical strength of the green compact can be remarkably improved. It is possible to form magnetic powder with an aspect ratio of less than 1.5 or more than 2.5, but it is expected that it is expected that voids will be easily formed and that the entanglement between powders will be significantly reduced. Strength improvement effect can not be obtained.

[Surface insulation coating]
The soft magnetic powder used in the present invention may have an insulating film on the surface of the magnetic powder as necessary in order to reduce loss (AC resistance) in a high frequency region. Any insulating coating can be used as long as the eddy current loss can be reduced by improving the surface electrical resistance. Specifically, it may be an inorganic film such as a phosphate-based insulating film, or an organic film using a silicone resin, an epoxy resin, a polyimide resin or the like.

[resin]
The resin used in the present invention is uniformly disposed near the surface of the soft magnetic powder at the time of molding by being mixed with the soft magnetic powder. In addition to the addition of the insulating property, the addition of the resin strongly couples the soft magnetic powders together through the heat treatment step after molding to strongly contribute to the increase in the strength of the green compact. The resin in the present invention may not be completely cured in the green compact. Also, part of the structure may be pyrolyzed to go through the high temperature heat treatment process.

As the resin used in the present invention, any of a thermosetting resin and a thermoplastic resin can be used. Specifically, a phenol resin, an epoxy resin, a polyimide resin, a silicone resin etc. can be mentioned. Among these resins, polyimide resins and silicone resins, which are excellent in heat resistance, are particularly preferable for the convenience of performing high-temperature heat treatment for strain removal. The polyimide resin used in the present invention is preferably one having a small weight loss even under heat treatment conditions of 500 ° C. or higher under N ₂ atmosphere in consideration of high temperature heat treatment (those remaining as carbides in the system).

  Specifically, the weight loss after heat treatment is preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less. The weight average molecular weight Mw of the resin is preferably 5,000 g / mol or more, more preferably 10,000 g / mol or more, and still more preferably 500,000 g / mol or more. Considering the process of powder metallurgy (net shape molding and high temperature heat treatment), a solid resin with a fine particle diameter is suitable for the process, but the resin is dissolved in a suitable solvent such as acetone or toluene, coated, dried Then, the magnetic powder surface may be coated with a resin.

  The amount of resin added in the present invention is preferably 0.001 to 5.0%, more preferably 0.01 to 2.0, and still more preferably 0.1 to 0.5%. By increasing the amount of resin, the strength of the green compact can be enhanced, and resistance (AC resistance) can be reduced also as a magnetic characteristic described later. When the resin is not contained, the strength of the green compact tends to be insufficient. On the other hand, when the resin amount is too large, sufficient density and inductance can not be obtained, which is not preferable for practical use.

[lubricant]
As the lubricant used in the present invention, any lubricant can be used as long as it is a lubricant used in powder metallurgy. Specifically, metal soaps such as zinc stearate, magnesium stearate, lithium stearate, calcium stearate and the like, wax-based lubricants such as long chain hydrocarbon, EBS (ethylene bis-stearic acid amide) and polyethylene may be used. it can. The lubricant may be dispersed in a suitable dispersion medium to form a dispersion, which may be applied to the inner wall of the die (the wall in contact with the punch), dried and used.

[Proportion, composition ratio]
The magnetic sheet material of the present invention is a composite magnetic material containing soft magnetic powder and a resin, and optionally containing a lubricant. Since higher density is required from the viewpoint of high inductance, the ratio of soft magnetic powder is preferably 95% or more, more preferably 99% or more, still more preferably 99.5% or more. Good. The magnetic properties, mechanical strength and mechanical strength can be adjusted by adjusting the amount of resin to a level that does not impair the entanglement between soft magnetic powders, including a lubricant that can maintain the flowability of powder in the manufacturing process and mold releasability. It becomes a well-balanced powder composition having mass productivity.

[Compounding ratio of soft magnetic powder]
The compounding ratio of the soft magnetic powder containing Si is 30 to 70%. By setting it as this compounding ratio, it is possible to obtain a magnetic sheet material having high bending strength, high inductance (index of strength of magnetic force) and low resistance (AC resistance). Such effects will be described in detail in the examples.

[Density ratio]
The thin green compact suitable as the magnetic sheet material of the present invention can be evaluated using the density ratio. The density ratio is represented by the ratio (ρ / ρ ₀ :%) of the bulk density (ρ) of the green compact to the true density (ρ ₀ ) of the soft magnetic powder. For example, in the case of a composite material consisting of component A, component B and component C, the following equation 2 holds. In Equation 2, X is the content (mass ratio), W is the weight, and ρ is the density.

Here, since X _A [%] + X _B [%] + X _C [%] = 100 [%], the true density 全体 of the entire material can be expressed by the following formula 3.

  The density ratio of the thin green compact in the present invention is preferably 91% or more, more preferably 95% or more. With a green compact of less than 91%, the strength and the handling property are inferior, and application as a magnetic sheet material becomes difficult. The inductance (an indicator of the strength of the magnetic force) can be increased by using such a high-density compact. In addition, when mounted as a magnetic sheet material in a portable terminal, the number of winding of the coil can be reduced, and magnetic alignment does not occur even when alignment is performed using a magnet, and a high inductance can be obtained. be able to.

[Manufacturing process]
The magnetic sheet material of the present invention can be manufactured by filling a powder in a mold and subjecting it to high-pressure molding, and subjecting the obtained thin-plate shaped compacted body to high-temperature heat treatment. This manufacturing process includes a mixing process of mixing soft magnetic powder and a trace amount of resin and a lubricant, a forming process of filling the mixed powder in a forming mold and pressing and forming, and compacting of the obtained thin plate shape. It is roughly divided into the heat treatment process of subjecting the body to high temperature heat treatment.

[Mixing process]
When manufacturing the magnetic sheet of the present invention, it is preferable to uniformly mix and disperse soft magnetic powder, resin, and lubricant in order to reduce variations in properties and dimensions of the magnetic sheet material to be obtained. This mixing process can use any apparatus. Specifically, since the soft magnetic powder has a high specific gravity, it is preferable to mix using a V-type or W-type mixer or the like. Although depending on the processing amount, as preferable mixing conditions, the soft magnetic powder and the resin or the lubricant can be uniformly dispersed by mixing and stirring for 30 minutes to 2 hours at a rotation speed of 20 to 60 rpm.

[Molding process]
The forming step in producing the thin green compact of the present invention can be performed by a general forming method by powder metallurgy regardless of whether it is cold or warm. Further, from the viewpoint of improving the magnetic properties and mechanical strength by increasing the density, it is also possible to employ a mold lubrication method in which a lubricant is applied to the mold. As a result, even if the molding pressure is increased, it is possible to suppress the occurrence of nicks or excessive extraction pressure between the inner surface of the molding die and the coated metal powder, and the mold life is extended. The higher the molding pressure is, the higher the density of the powder magnetic core is obtained, but as the density of the molded body approaches the true density, further densification can not substantially be expected even at a molding pressure of a certain value or more. In consideration of mold life and productivity, the molding pressure is preferably set to 600 to 1200 MPa.

[Shaped shape]
The magnetic sheet using the powder compact in the present invention is characterized in that the thickness is 0.1 mm or more and 1.0 mm or less. The dimensions depend on the mold used at the time of molding, and the green compact may have asperities if necessary.

[Heat treatment process]
In general, when high-pressure molding of soft magnetic powder is performed, residual stress or residual strain occurs in the inside thereof. In order to remove the forming strain generated during the high-pressure forming, it is preferable to subject the obtained green compact to a high-temperature heat treatment. Hysteresis loss can be reduced by relieving the molding strain, and the obtained green compact becomes a high permeability material. Therefore, in the present invention, "compacted compact" means a compact after heat treatment.

  Residual strain and the like are more effectively removed as the heat treatment temperature is higher. However, even a heat resistant resin may cause partial destruction. By setting the heat treatment temperature to 500 ° C. to 1000 ° C., it is possible to achieve both the removal of the residual strain and the excellent insulation of the film. The heating time is preferably 1 to 120 minutes, more preferably 10 to 60 minutes, in consideration of the effects and the economy.

The atmosphere for heat treatment is preferably a vacuum atmosphere or an inert gas (N ₂ ) atmosphere. By performing the heat treatment step in a non-oxidizing atmosphere, it is possible to suppress that the magnetic powder constituting the magnetic sheet material is oxidized to deteriorate the magnetic characteristics and the electrical characteristics.

[Strength of green compact]
Due to its shape, it is difficult to measure the strength of the thin-plate-like compacted body as in the present invention with high precision. Therefore, in order to obtain an index of strength, a three-point bending test in accordance with JIS-Z-2248 is performed to perform relative evaluation of strength. Although the details of the bending test are described in the examples, small-sized bending test pieces (12 mm × 34 mm × 5 mm thick) are produced and a three-point bending test is performed to obtain an indicator of strength. As a result of the present inventors' investigation, it is preferable when producing a thin-plate shaped green compact by making the flexural strength 40 MPa or more in the bending test according to the present test. If the pressure is less than 40 MPa, cracks and chips are likely to occur, and the workability and handling are also inadequate. From the viewpoint of practical use of the product, the pressure is preferably 60 MPa or more, and more preferably 80 MPa or more.

[Evaluation method]
As an evaluation method of the soft magnetic material, an inductance indicating the strength of the magnetic force and a resistance (AC resistance) serving as an index of loss can be mentioned. In general, measurement of inductance and resistance is performed using an LCR meter or the like. As will be described in detail in the examples, a ring-shaped test piece is produced, and a coil is wound around the ring-shaped test piece to cause an alternating current to flow to form a magnetic flux. The magnetic sheet material is required to be a high inductance and low resistance material.

  The invention will be explained in more detail with reference to the examples. The present invention is not limited to the following examples.

As soft magnetic powder having a Vickers hardness of 300 to 500 HV, a plurality of types of Fe-6.5Si powder different in particle diameter and shape were prepared (Examples 1 to 8 and Comparative Examples 1 to 6). In addition, as the soft magnetic powder having a Vickers hardness of 70 to 150 HV, an insulation-coated iron powder (product name: Somaloy 110i 1 P, average particle diameter D ₅₀ = 46.9 μm) manufactured by Heganez Co., Ltd. was used. The details of these soft magnetic powders are shown in Table 1. Hereinafter, the manufacturing method and evaluation method of the compacting body of this invention are described in order.

  First, each Fe-Si powder and pure iron powder were mixed in a mass ratio of 1: 1. Next, to a mixed powder of Fe-6.5Si powder and pure iron powder, 0.15% by mass of powdered polyimide resin (AULUM PD450 manufactured by Mitsui Chemicals, Inc.) and 0.2% of zinc stearate as an internal lubricant %, And mixed and stirred for about 1.0 hour using a 1-kg volume V-type mixer.

Next, the mixed powder containing soft magnetic powder, resin and lubricant is filled in a molding die of 12 mm wide and 34 mm long, and pressurized using a 2000 kN Amsler universal tester to a thickness of 5.0 mm, Anti-folding test pieces were produced. The molding pressure was constant at 1176 MPa (12 ton / cm ² ). Heat treatment for 30 minutes is performed at 530 ° C in an inert gas (N ₂ ) atmosphere to remove processing strain generated during high-pressure molding, and the bending test pieces are measured for weight and dimension changes before and after heat treatment. The density of each specimen was measured.

  The three-point bending test based on JIS-Z-2248 was implemented with respect to the obtained bending test piece in order to obtain the parameter | index of strength. All bending tests are performed using a precision universal testing machine (autograph), the distance between the fulcrum is 25.4 mm, and the bending strength is measured from the maximum test force under the condition of pressing speed 0.5 mm / min. Calculated. These results are shown in Table 1 and FIG.

  In FIG. 1, the “Fe-6.5 Si powder / pure iron powder particle size ratio” in Table 1 is taken along the horizontal axis, and the “major axis / short axis ratio (aspect ratio) of the Fe-6.5 Si powder” is taken along the vertical axis. The subscripts of the plot indicate the bending strength. In addition, the pure iron powder used as a reference | standard was shown by "(circle)" in the figure. It can be seen from FIG. 1 that the bending strength largely varies from 11.2 MPa to 68.8 MPa depending on the circle equivalent average particle diameter and the aspect ratio of Fe-6.5Si powder blended with pure iron powder. When Fe--Si powder having a particle diameter larger than that of pure iron powder is used, that is, when the horizontal axis is larger than 1.0, the bending strength tends to decrease. Also, when the particle diameter ratio of Fe-6.5Si powder / pure iron powder is less than 0.4, the bending strength is greatly reduced. From this, the Fe-6.5Si powder mixed with pure iron powder has a suitable particle size, and 0.4 ≦ “Fe-6.5Si powder / pure iron powder particle size ratio” ≦ 1.0 preferable. Further, as shown in FIG. 1, by setting the aspect ratio (long axis / short axis ratio) to 1.5 to 2.5, high bending strength can be maintained.

  Next, the surface image after cross-sectional grinding | polishing of Example 1 and Comparative example 1 and Comparative example 2 is shown to FIGS. In Example 1 having the highest bending strength, it was confirmed that the pure iron powder excellent in the compressibility and the formability was largely plastically deformed, and the Fe-6.5Si powder and the powder were strongly intertwined. On the other hand, in Comparative Examples 1 and 2, it is assumed that many voids exist and the entanglement between the powders is weak.

(Evaluation of the effect of the compounding ratio of Fe-6.5Si powder)
Next, using pure iron powder and Fe-6.5Si powder used in Example 1, the ratio of pure iron powder to Fe-6.5Si powder was changed to evaluate the influence on magnetic properties and folding strength. did. The bending test pieces were produced under the same conditions as described above, and the bending strength was measured by a three-point bending test. The ring-shaped test piece was filled with a mixed powder in a mold having an outer diameter of 30 mm and an inner diameter of 20 mm, and was pressurized using a 2000 kN Amsler universal tester to a height of 5 mm. The molding pressure at that time was set to 1176 MPa (12 ton / cm ² ) as in the preparation of the bending test piece.

The obtained ring-shaped test pieces and bending test pieces were subjected to heat treatment at 530 ° C. for 30 minutes in an inert gas (N ₂ ) atmosphere, and the changes in weight and size before and after heat treatment were measured to perform each test. The density of the pieces was measured. Magnetic characteristics of each ring-shaped test piece were evaluated using an LCR meter (KC-605, manufactured by Kuniyo Denki Co., Ltd.), inductance (L, index of magnetic force strength) and resistance (R, AC resistance) at a frequency of 120 KHz Was measured. The number of windings at the time of measurement was 20 turns, and the voltage was measured as 1.0 V (constant). The powder compounding ratio used for the test is shown below.

(Comparative example 7)
The bending test piece and the ring-shaped test piece were produced only with pure iron powder without adding Fe-6.5Si powder. The other steps were the same as in Example 1.

(Comparative example 8)
The bending test piece and the ring-shaped test piece were produced by setting the ratio of pure iron powder to Fe-6.5Si powder to 20%: 80%. The other steps were the same as in Example 1.

(Example 9)
Bending test pieces and ring-shaped test pieces were prepared with the mass ratio of pure iron powder to Fe-6.5Si powder being 30%: 70%. The other steps were the same as in Example 1.

(Example 10)
Bending test pieces and ring-shaped test pieces were prepared with the ratio of pure iron powder to Fe-6.5Si powder being 50%: 50%. The other steps were the same as in Example 1.

(Example 11)
Bending test pieces and ring-shaped test pieces were prepared with the ratio of pure iron powder to Fe-6.5Si powder being 70%: 30%. The other steps were the same as in Example 1.

(Example 12)
The bending test piece and the ring-shaped test piece were manufactured by setting the ratio of pure iron powder to Fe-6.5Si powder to 80%: 20%. The other steps were the same as in Example 1.

(Comparative example 9)
The bending test piece and the ring-shaped test piece were produced only with Fe-6.5Si powder without adding pure iron powder. The other steps were the same as in Example 1.

[Strength strength evaluation result]
The bending strength evaluation result of a compacting body (without heat treatment) and a heat treatment body is shown in FIG. According to FIG. 5, the strength of the heat-treated body gradually increases as the ratio of the pure iron powder increases, but the strength of the green compact is higher than that of the pure iron powder alone or the Fe-6.5Si powder alone. It was found that the case was higher. Comparing the bending strength after the heat treatment, the bending strength is greatly reduced when the ratio of Fe-6.5Si powder increases from 70% to 80%. Therefore, when mixing Fe-6.5Si powder | flour, it is preferable to set it as 70% or less.

  Next, the amount of resin was changed to evaluate the bending strength. The evaluation results are shown in FIG. In the case of Fe-6.5Si powder alone, the bending strength tends to increase with the increase of the resin amount, but in order to increase the strength, a large amount of resin addition is required. On the other hand, when Fe-6.5Si powder and pure iron powder were mixed at 50:50, it was confirmed that the maximum value of the bending strength was obtained when the resin amount was 0.3%. Overall, a uniformly higher bending strength is obtained as compared to the result of Fe-6.5Si powder alone. It was found that the resin addition amount is preferably 0.1% to 1.0%, and most preferably 0.3%.

  Next, FIG. 7 shows the evaluation results of the magnetic characteristics of the ring-shaped test piece. As shown in FIG. 7, as the proportion of Fe-6.5Si powder increases, the inductance tends to gradually decrease up to 70%. On the other hand, resistance (AC resistance) tends to decrease as the proportion of Fe-6.5Si powder increases, but resistance increases significantly when the proportion of Fe-6.5Si powder increases from 20% to 30%. It has fallen. Therefore, the proportion of Fe-6.5Si powder needs to be 30% or more on the magnetic properties. In FIG. 7, L is preferably high (magnetic force is high) and R is preferably low (loss is small).

  From the above results, the proportion of Fe-6.5Si powder in the mixed powder is required to be 30 to 70% from the viewpoint of balancing the magnetic characteristics and the bending strength.

  By adapting the magnetic sheet material of the present invention to a small electronic device such as a smartphone, a tablet terminal, a wearable device or the like equipped with the non-contact power feeding function, the product can be thinner, smaller and more efficient. Further, the magnetic sheet material of the present invention can maintain high mechanical strength even when containing a large amount of hard soft magnetic powder, thereby contributing to the improvement of the long-term reliability of product characteristics as an antenna material.

Claims (2)

Soft magnetic powder A with a thickness of 1.0 mm or less containing soft magnetic powder and a resin, an aspect ratio of 1.5 to 2.5, and a Vickers hardness of 300 to 500 HV, and a Vickers hardness And 70 to 150 HV, and the ratio of the soft magnetic powder A is 30 to 70% by mass .
The soft magnetic powder A is an Fe-Si powder containing 5.0 to 7.0% by mass of Si,
The soft magnetic powder B is pure iron powder,
A magnetic sheet material for non-contact electric power feeding, wherein an average particle diameter (equivalent circle diameter) of the soft magnetic powder A and the soft magnetic powder B satisfies the following expression 1 .

A mixing step of mixing a plurality of soft magnetic powders, a resin and an internal lubricant to obtain a mixed powder;
A forming step of filling the mixed powder in a mold and forming it;
Heat treating the thin plate-like compact obtained in the forming step ;
The soft magnetic powder includes soft magnetic powder A having an aspect ratio of 1.5 to 2.5 and Vickers hardness of 300 to 500 HV, and soft magnetic powder B having a Vickers hardness of 70 to 150 HV, The proportion of powder A is 30 to 70% by mass,
The soft magnetic powder A is an Fe-Si powder containing 5.0 to 7.0% by mass of Si,
The soft magnetic powder B is pure iron powder,
The method for producing a non-contact power feeding magnetic sheet material having a thickness of 1.0 mm or less, wherein the addition amount of the resin is 0.1 to 0.5 mass% .

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