JP2009043778A - Metal magnetic material powder for composite magnetic body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce μ" with respect to μ' of 13.56 MHz in a metal magnetic material powder used for a composite magnetic body having function of converging the magnetic flux in a magnetic field to improve the sensitivity of an antenna element, compared to a flat powder of a metal magnetic material such as Sendust (R) used for a conventional composite magnetic body for suppressing an electromagnetic noise, in an RFID (radio frequency identification) tag for performing radio communication with an electromagnetic wave having frequency 13.56 MHz. <P>SOLUTION: The metal magnetic material powder for a composite magnetic body employs powder of a metal magnetic material having a volume intrinsic resistivity value ρ larger than that of the Sendust (R) and having ductility, and comprises flat powder containing a large number of particles having a large particle size and having wide particle size distribution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal used for a composite magnetic body that has a function of converging a magnetic flux in a magnetic field in order to improve the sensitivity of an antenna element in an RFID (Radio Frequency Identification) tag that performs radio communication with an electromagnetic wave having a frequency of 13.56 MHz. The present invention relates to a powder of magnetic material.

  In recent years, RFID using mobile terminals or the like that has been rapidly spread has been put to practical use mainly in the 13.56 MHz band for wireless communication at a short distance of about 1 m.

  Wireless data communication is more convenient for data transmission / reception as the communication distance becomes longer, and it is desired that data can be transmitted / received within a possible distance even in close-range wireless communication within 1 m. The communication distance is affected not only by the antenna sensitivity, but also by the environment around the antenna. Especially when a metal member is present near the antenna, the magnetic flux forming the electromagnetic wave signal passes through the metal member and is made of metal. An eddy current loss occurs in the member and is converted into thermal energy. As a result, the electromagnetic wave signal is attenuated and wireless communication cannot be performed satisfactorily.

  Such a problem can be solved by placing a magnetic body having a high complex relative permeability μ between the antenna element and the metal member. As the magnetic body, a magnetic body made of a composite magnetic powder obtained by mixing a flat powder of a metal magnetic material having a high initial permeability μi and a binder is used. Examples of magnetic materials made of such composite magnetic powder are shown in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and the like.

  As described in Patent Document 2, Patent Document 3, and Patent Document 4, many of such composite magnetic bodies are intended to suppress electromagnetic noise, and the complex relative permeability μ is improved. Although the complex relative permeability μ has a real part μ ′ and an imaginary part μ ″, the higher the real part μ ′ of the complex relative permeability μ, the more the magnetic flux in a weak magnetic field converges. The higher the shielding property and the higher the imaginary part μ ”, the energy of the magnetic field is converted into heat energy and absorbed. 2 has been improved by using flat powders of high magnetic permeability magnetic materials such as Sendust (registered trademark) 2 and Permalloy in Patent Document 3 and Patent Document 4, and so on. It was.

  However, in a composite magnetic material that is placed between an RFID tag antenna element and a metal member and is intended to increase the communication distance for wireless data transmission and reception, the higher μ ′ is the weaker magnetic flux in the magnetic field. However, if the magnetic loss term μ ″ is high, the energy of the magnetic field is lost. Therefore, it is difficult to increase the communication distance of the RFID, and it is preferable that μ ″ is low. As described above, since the purpose has been to suppress electromagnetic wave noise, improvement of μ ″, which is a magnetic loss term, and wide-area dispersion have been studied, but no attempt has been made to reduce μ ″. It was.

  Patent Document 1 discloses an example of a composite magnetic body for an RFID tag. However, the material and form of the magnetic material are not particularly studied, and the magnetic material used for the above-described composite magnetic body for the purpose of suppressing electromagnetic noise. Is the same as the one that is supported. As described above, the imaginary part μ ″ of the complex relative permeability μ having a frequency of 13.56 MHz is preferably as low as possible and the real part μ ′ is as high as possible to extend the wireless communication distance of the RFID. In Example 1, μ ′ at 13.56 MHz is as high as 61, but μ ″ is as high as 3, and μ ″ reaches about 5% of μ ′. Also, Example 2 and Example 3 of Patent Document 1. Is due to Sendust (registered trademark), but μ ″ at 13.56 MHz is low, but μ ′ at 13.56 MHz is also low.

  FIG. 1 is a plot of these data and the data of Sendust (registered trademark) composite magnetic material. In the metal magnetic material powder used for the conventional composite magnetic body for the purpose of suppressing electromagnetic noise, 13.56 MHz is a frequency at which μ ″ which is a magnetic loss term starts to increase. As shown in FIG. Since 56 ′ μ ′ and μ ″ have a positive correlation, it can be seen that it is difficult to reduce μ ″ with respect to 13.56 MHz μ ′.

  Further, in a composite magnetic body made of a metal magnetic material having a lower volume resistivity value than Sendust (registered trademark) such as Permalloy, μ ″ increases from a low frequency of 13.56 MHz or lower, so 13.56 MHz. Μ ”is higher than μ ′, and for a composite magnetic body having a function of converging magnetic flux in a magnetic field in order to improve the sensitivity of an antenna element in an RFID tag that performs radio communication with an electromagnetic wave having a frequency of 13.56 MHz. It is not preferable as a metal magnetic material.

Japanese Patent No. 3647446 Japanese Patent Laid-Open No. 2005-281783 JP 2005-264317 A Japanese Patent Laid-Open No. 2006-60008

  Therefore, the object of the present invention is to converge the magnetic flux in the magnetic field in order to improve the sensitivity of the antenna element in the RFID tag that performs wireless communication with the electromagnetic wave having a frequency of 13.56 MHz, which is difficult with the conventional technology as described above. An object of the present invention is to provide a metal magnetic material powder for a composite magnetic body that can reduce μ ″ with respect to 13.56 MHz μ ′ used in a composite magnetic body having the function of:

  The present invention provides a composite magnetic material characterized by having a volume resistivity value ρ of 0.9 μΩm or more, a saturation magnetic flux density Bs of 1.2 T or more, an initial permeability μi of 1000 or more, and ductility. Metal magnetic material powder for use.

  Further, the present invention is a composite characterized in that the shape of the metal magnetic material powder for a composite magnetic material is thin and flattened, and the particle size at which the particle size distribution becomes 90% of the integrated particle size distribution is 120 μm or more. It is a metal magnetic material powder for magnetic bodies.

  Further, the present invention provides the composite characterized in that the ratio of the particle size at which the particle size distribution of the metal magnetic material powder for composite magnetic material is 10% to 90% in the integrated particle size distribution is 8 times or more. It is a metal magnetic material powder for magnetic bodies.

  The present invention also provides the metal magnetic material powder for composite magnetic material, wherein the metal magnetic material powder for composite magnetic material is dispersed in a shape anisotropically oriented state in the composite magnetic material. is there.

  In the present invention, the real part μ ′ of the complex relative permeability μ at a frequency of 13.56 MHz of the metal magnetic material powder for composite magnetic material is 35 or more, and the imaginary part μ of the complex relative permeability μ of the frequency 13.56 MHz. "Is 2% or less of the real part μ 'of the complex relative permeability μ having a frequency of 13.56 MHz, which is a metal magnetic material powder for composite magnetic materials.

  In general, high permeability magnetic materials such as pure iron, silicon steel, and permalloy have a low volume resistivity ρ and a low frequency at which eddy current loss increases. Therefore, the real part μ of the complex relative permeability μ at high frequencies 'Is not expensive. The volume specific resistance value ρ is a specific value depending on the composition of the metal material, and it is difficult to increase the volume specific resistance without changing the magnetic characteristics. In addition, the magnetic material having a low saturation magnetic flux density Bs has a smaller capacity for converging the magnetic flux on the magnetic body and is more likely to leak the magnetic flux than the magnetic body. Therefore, it is necessary to increase the thickness of the magnetic body. It is not preferable for related communication devices.

  Sendust (registered trademark) is a metal magnetic material having excellent magnetic properties such as a high volume resistivity ρ of 0.8 μΩm, a saturation magnetic flux density Bs of 1 T, and an initial permeability μi of 30,000. Moreover, the magnetostriction constant λ≈0 is not easily affected by stress, and is a metal magnetic material most suitable for a composite magnetic body, and has been used for a composite magnetic body having a high complex relative permeability μ. However, because of the magnetic material having excellent permeability, the imaginary part μ ″ of the complex relative permeability μ is also high, and it is difficult to reduce μ ″ with respect to μ ′ having a frequency of 13.56 MHz.

  The inventor of the present invention pays attention to a metal magnetic material having a volume resistivity value ρ and a saturation magnetic flux density Bs larger than Sendust (registered trademark) and having ductility, and in a composite magnetic body, has a frequency of 13.56 MHz than Sendust (registered trademark). Have been found to be a metal magnetic material powder capable of suppressing the μ ″.

  The powder of the metal magnetic material used for the composite magnetic body has a flat shape in which the powder shape is thinly crushed in order to suppress eddy current loss and reduce the demagnetizing field. The eddy current loss is suppressed in the case of a thin powder having a small particle size, but if the particle size of the flat powder is small, the demagnetizing factor is small, so that a high μ ′ cannot be obtained. In order to improve μ ′ of the flat powder, there are means such as using a magnetic material with high magnetic permeability or increasing the flatness of the flat powder to increase the demagnetizing factor. However, such as Sendust (registered trademark) With a hard and brittle material, it is difficult to obtain a flat powder having a large particle size, and the particle size distribution of the flat powder is not wide. Therefore, if the particle size of the flat powder is reduced to suppress eddy current loss, the overall particle size of the powder is also reduced, and μ ′ is reduced due to the influence of the demagnetizing field.

  On the other hand, since the powder of the metal magnetic material rich in ductility is easy to extend, it is possible to obtain a thin powder having a thin and large particle size and a high aspect ratio, and a flat powder having a wide particle size distribution can be obtained. Even with a magnetic material having a low initial permeability μi, if the particle size of the flat powder can be increased and the demagnetizing factor can be increased, the magnetic permeability can be increased. It is possible to increase the magnetic susceptibility.

  The metal magnetic material powder of the present invention is an imaginary number having a complex relative permeability μ having a frequency of 13.56 MHz, compared to a metal magnetic material powder such as Sendust (registered trademark) used in a composite magnetic material for the purpose of suppressing electromagnetic wave noise. The part μ ″ can be kept lower than the real part μ ′. According to the present invention, the composite magnetism for improving the sensitivity of the antenna element of the RFID tag that performs radio communication with an electromagnetic wave having a frequency of 13.56 MHz. It is possible to provide a powder of a metal magnetic material that can keep μ ″ low compared to μ ′ of 13.56 MHz required for the body.

  The specific configuration of the present invention will be described below.

(Material property)
The metal magnetic material powder for composite magnetic material of the present invention has the characteristics that the volume resistivity ρ is 0.9 μΩm or more, the saturation magnetic flux density Bs is 1.2 T or more, the initial permeability μi is 1000 or more, and has ductility. It has a metal magnetic material. The larger the volume resistivity ρ is 0.9 μΩm or more, the higher the effect of suppressing eddy current loss at high frequencies, and the frequency at which the imaginary part of the complex relative permeability μ increases can be increased.

  However, as the volume resistivity increases, there is a tendency that good characteristics cannot be obtained as a soft magnetic material. In particular, in a material having a remarkably low initial permeability μi, the real part μ ′ of the complex relative permeability μ becomes low. Therefore, the metal magnetic material needs to have an initial permeability μi of 1000 or more.

  Furthermore, the material having a higher saturation magnetic flux density Bs is less likely to saturate the magnetic flux converged on the magnetic material, and can suppress the leakage magnetic flux from the magnetic material and reduce the thickness of the magnetic material. Those having 2T or more are preferable.

  If it is less than 1.2T, the saturation magnetic flux density Bs is low, so it is necessary to increase the thickness of the magnetic material, which is not preferable as an RFID-related product that is required to be light and thin. In addition, the metal material must have ductility that allows roll rolling. By having ductility, the metal powder easily extends, and a flat powder having a thin and large particle size can be produced in a short time. Moreover, since the powder with a small particle size is also crushed thinly, the difference of the crushing condition between powders is small.

(Particle size of flat powder)
The metal magnetic material powder for composite magnetic material of the present invention is a flat powder in which the shape of the metal magnetic material is thinly crushed, and the particle size distribution (D90) of 90% in the integrated particle size distribution is 120 μm or more, In the particle size distribution, the ratio of the particle size (D10) that becomes 10% and the particle size (D90) that becomes 90% in the cumulative particle size distribution is 8 times or more, and is a metal magnetic material powder for composite magnetic materials. A flat powder containing a large amount of flat powder having a wide particle size distribution and a large particle size can increase the demagnetizing factor, so that the μ ′ of the powder can be increased comprehensively.

  The particle size distribution in the present invention was measured with a laser diffraction particle size distribution measuring device (manufactured by Nippon Laser Co., Ltd.).

(Powder flattening method)
The method for flattening the metal magnetic material powder for composite magnetic material of the present invention is not particularly limited. Any technique may be used as long as the desired flat powder state can be obtained, and it is preferable to use an efficient technique. Examples of such a method include a medium agitation mill and a ball mill, and among these, a medium agitation mill such as a pin mill is preferably used.

(Heat treatment)
The metal magnetic material powder for composite magnetic material of the present invention is preferably subjected to heat treatment after flattening. The heat treatment conditions vary depending on the material, but the heat treatment temperature is selected from 300 ° C or higher at which the stress relaxation effect of the flat powder begins to 900 ° C or lower at which the flat powder does not sinter, and optimal magnetic properties. It is preferable to do.

  The holding time at that temperature is preferably the time for the entire flat powder to reach that temperature, and varies depending on the capacity and structure of the furnace, and is preferably held for about 10 minutes to 10 hours.

  The heat treatment atmosphere is preferably performed in an atmosphere containing as little oxygen as possible, and is preferably performed in a vacuum or an inert gas atmosphere such as argon or nitrogen.

  Super sendust or 6.5 wt% is a metallic magnetic material having a volume resistivity value ρ of 0.9 μΩm or more, a saturation magnetic flux density Bs of 1.2 T or more, an initial permeability μi of 1000 or more, and a ductility. An Fe—Si—Cr alloy in which Cr is mixed with an Si—Fe alloy is preferable.

  Samples 1 to 3 of the present invention are super sendust water atomized powder composed of 10 wt% Si, 4 wt% Al, 3 wt% Ni, and the balance Fe, and 6.5 wt% Si—Fe alloy with 2 wt% and 5 wt% Cr. % Mixed Fe-Si-Cr alloy water atomized powder was obtained, and then the powder was flattened by a medium stirring mill. For comparison, each metal magnetism of Sendust (6Si-4Al-Fe), Permalloy (6Mo-13Fe-Ni), 6.5 wt% Si-Fe alloy, Alpalm (16Al-Fe alloy) and 15Si-2Cr-Fe alloy Comparative samples 4 to 8 using the materials were obtained by the same treatment as the sample of the present invention.

  FIG. 2 is an example of the cumulative particle size distribution of the produced flat powder. Since these powders extend more softly than Sendust (registered trademark), it was possible to obtain flat powder having a particle size larger than that of Sendust (registered trademark) and having a wide particle size distribution. The flat powder of the magnetic metal material thus obtained was heat-treated at 400 ° C. for 2 hours in a nitrogen atmosphere.

  The composite magnetic material was produced by orienting the metal magnetic material powder for composite magnetic material thus prepared in a binder made of chlorinated polyethylene in a shape anisotropic manner. Table 1 shows the results of the comparison metal magnetic material prepared by the same method for the real part μ ′ and the imaginary part μ ”of the complex relative permeability μ of frequency 13.56 MHz after being formed into such a composite magnetic body. It shows with the measurement result of the composite magnetic body of a flat powder.

  According to Table 1, the flat powder of the metal magnetic material of the present invention is suppressed to 2% or less of μ ″ at 13.56 MHz with respect to μ ′, compared with the flat powder of the metal magnetic material of the comparative example. Is confirmed.

  FIGS. 3 and 4 show a metallic magnetic material having a ductility and a volume resistivity value ρ of 0.9 μΩm or more, a saturation magnetic flux density Bs of 1.2 T or more, and an initial permeability μi of 1000 or more. This is a comparison of μ′-f and μ ″ -f of a composite magnetic body made of flat powder and a composite magnetic body made of Sendust (registered trademark) flat powder, and has a higher volume resistivity than Sendust (registered trademark). It is confirmed that the super sendust or the like has a higher frequency at which μ ″ starts increasing and a lower μ ″ at a frequency of 13.56 MHz.

  FIG. 5 is a plot of the composite magnetic material data of Super Sendust flat powder on the data of the composite powder of Sendust (registered trademark) flat powder of FIG. It is confirmed that the flat powder of super sendust has a tendency to suppress μ ″ with respect to μ ′ of 13.56 MHz than the magnetic material such as sendust (registered trademark) in FIG.

The figure which shows the data in the Example of patent document 1 and 13.56-MHz (micro | micron | mu) 'and (mu) "of the composite magnetic body by Sendust (trademark) flat powder. The figure which shows the particle size distribution of the sample 1, the sample 2, and the sample 4 in the Example of this invention. The figure which shows the μ'-f characteristic at the time of making sample 1, sample 2, and sample 4 into a composite magnetic body in the example of the present invention. The figure which shows the μ ''-f characteristic at the time of making sample 1, sample 2, and sample 4 into a composite magnetic body in the example of the present invention. The figure which shows (mu) 'and (micro | micron | mu) "of 13.56 MHz when the sample 1 and the sample 4 in the Example of this invention are made into a composite magnetic body.

Claims (5)

  In a metal magnetic material powder for composite magnetic material forming a composite magnetic material containing a metal magnetic material powder and a binder, the volume resistivity ρ is 0.9 μΩm or more, the saturation magnetic flux density Bs is 1.2 T or more, and the initial permeability. A metal magnetic material powder for composite magnetic materials, wherein μi has a characteristic of 1000 or more and has ductility.   2. The metal for composite magnetic material according to claim 1, wherein the shape of the metal magnetic material powder for composite magnetic material is a flattened shape that is thinly crushed, and a particle size of 90% in an integrated particle size distribution is 120 μm or more. Magnetic material powder.   3. The composite magnetic body according to claim 1, wherein a ratio of a particle size of 10% to a particle size of 90% in the cumulative particle size distribution of the metal magnetic material powder for composite magnetic material is 8 times or more. Metal magnetic material powder for use.   The metal magnetic material powder for composite magnetic bodies according to claim 1, wherein the metal magnetic material powder for composite magnetic bodies is dispersed in a state oriented in a certain direction in the composite magnetic body.   The real part μ ′ of the complex relative permeability μ at a frequency of 13.56 MHz is 35 or more, and the imaginary part μ ″ of the complex relative permeability μ at a frequency of 13.56 MHz is 13.56 MHz. 5. The metal magnetic material powder for composite magnetic bodies according to claim 1, which is 2% or less of the real part μ ′ of the complex relative permeability μ.

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