JP2006210493A - Antenna coil and transponder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle-mounted antenna coil that is compatible with miniaturization. <P>SOLUTION: The antenna coil 10 comprises a magnetic core member 1 and a conductor 2 wound to the magnetic core member 1. In the magnetic core member 1, Fe<SB>2</SB>O<SB>3</SB>is set to be 54 to 55 mol% and ZnO to be not more than 14 mol% (O is not included). MnO is set to be a main component in terms of remaining substance. 60 to 800 ppm of Si in SiO<SB>2</SB>conversion, 600 to 4,000 ppm of Ca in CaCO<SB>3</SB>conversion and not more than 1,200 ppm of Co<SB>3</SB>O<SB>4</SB>are included as a subsidiary component. Thus, the coil is superior in a characteristic and has high reliability. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antenna coil and a transponder that are suitably used for in-vehicle use.

As shown in FIG. 1, an antenna coil 10 having a magnetic core member 1 and a conductor 2 wound around the magnetic core member 1 is known. Although the antenna coil 10 is used in various applications, the in-vehicle antenna coil 10 is required to have a small change in inductance in a wide temperature range, that is, a low temperature dependency of the initial permeability μi. . In particular, the stability of the initial permeability μi is required in a very wide temperature range of −40 ° C. to 125 ° C.
For the in-vehicle antenna coil 10 used under such severe conditions, the magnetic core member 1 made of Ni-based ferrite having excellent temperature characteristics has been conventionally used.

JP-A-11-3813 (Claims, Examples) JP 2000-286119 A (Claims, Examples)

In-vehicle antenna coils are required to have a characteristic that the temperature dependence of the initial permeability μi is small and that the loss factor (tan δ) is small, that is, the Q value (Q = 1 / tan δ) is large. . However, since the Ni-based ferrite cannot increase the inductance and the Q value so much, the quality improvement of the antenna coil using the Ni-based ferrite has almost reached the limit. As for the inductance, a high value can be obtained even when Ni-based ferrite is used by increasing the number of turns of the conducting wire. However, miniaturization is also required for the vehicle-mounted antenna coil, and the number of turns cannot be increased.
The present invention has been made based on such a technical problem, and an object of the present invention is to provide an in-vehicle antenna coil that can be reduced in size.

Ferrite materials containing Mn and further Zn are known as ferrite materials. Since this ferrite material has an advantage of high saturation magnetic flux density, it is mainly used for transformers for large currents (see, for example, Patent Documents 1 and 2). However, a ferrite material containing Mn and further Zn has a large temperature dependency and has not been used for a vehicle-mounted antenna coil used under severe conditions.
The inventor conducted various studies paying attention to the fact that ferrite materials containing Mn and Zn can have higher inductance and Q value than Ni-based ferrite. As a result, the ferrite material containing Mn or the like also has an appropriate content of the main component and the subcomponent and the content of the subcomponent, so that the temperature dependency of the initial permeability μi is improved and the in-vehicle antenna coil is obtained. It was found that it can be applied sufficiently. That is, in an antenna coil including a ferrite sintered body and a conductor wound around the ferrite sintered body, the composition of the ferrite sintered body is Fe ₂ O ₃ : 54.1 to 57.5 mol%, ZnO: 10. 5 mol% or less (however, not including 0), the balance being substantially composed of MnO as the main component, Si as an auxiliary component in the range of 60 to 800 ppm in terms of SiO ₂ , Ca in the range of 600 to 4000 ppm in terms of CaCO ₃ , and Co ₃ O ₄ It has been found that excellent characteristics can be obtained by containing 1000 to 3800 ppm.

Based on such knowledge, the present inventors continued further studies on the premise of mass production of antenna coils. As a result, there was a demand for further increasing the initial permeability μi. This is because when the conductor wire is wound around the magnetic core member in the manufacturing process of the antenna coil, if the initial permeability μi of the magnetic core member is high, the number of turns of the conductor wire can be reduced to obtain equivalent magnetic characteristics. This is because the time required for the winding process can be shortened to increase the throughput, and the mass productivity can be improved.
Moreover, it is required to further improve the reliability. In the case of mass production, it may be required to satisfy the conditions such as the characteristics do not fluctuate greatly due to temperature changes and the characteristics do not fluctuate greatly even when used in adverse environments such as high temperatures. It is.

As a result of repeated studies by the present inventors to satisfy such requirements, the following knowledge has been obtained. That is, an antenna coil including a ferrite sintered body and a conductor wound around the ferrite sintered body, and the composition of the ferrite sintered body is Fe ₂ O ₃ : 54 to 55 mol%, ZnO: 14 mol% or less. (However, 0 is not included) The balance is substantially composed of MnO as a main component, and as subcomponents, Si is 60 to 800 ppm in terms of SiO ₂ , Ca is 600 to 4000 ppm in terms of CaCO ₃ , and Co ₃ O ₄ It has been found that by including 1200 ppm or less (however, not including 0), the reliability can be particularly improved.
For example, the change in the initial permeability when this ferrite sintered body is placed in an environment at 175 ° C. for 48 hours (hereinafter referred to as a change with time in the initial permeability as appropriate) can be 10% or less. . Further, assuming that Co ₃ O ₄ as an accessory component is contained in an amount of 1000 ppm or less (excluding 0), for example, the time-dependent change in initial permeability when placed in an environment of 175 ° C. for 48 hours is 5 % Or less, and the reliability can be further improved.

If the ferrite sintered body contains Co ₃ O ₄ as an auxiliary component in an amount of 300 ppm or more, the change in the initial permeability in the range of −40 ° C. to 125 ° C. with reference to the initial permeability at 20 ° C. An excellent characteristic that the absolute value of the ratio (hereinafter referred to as the temperature change rate of the initial permeability) is 20% or less can be exhibited.
In addition, with the above composition, the antenna coil of the present invention can have an initial permeability of 1400 or more at 20 ° C.

Furthermore, the content of Co ₃ O ₄ can be reduced by including TiO ₂ . By controlling the amount of TiO ₂ , the minimum value of Q (Q = 1 / tan δ, where tan δ is a dielectric loss tangent) in the range of −40 ° C. to 125 ° C. can be increased. For example, the minimum value of Q can be made 120 or more by including TiO ₂ or less (but not including 0) TiO _2, and by including 1000 to 6000 ppm of TiO ₂ , The minimum value can be 150 or more.

  ZnO as a main component is effective for improving stability against temperature change, and by making ZnO 7 to 14 mol%, the absolute value of the rate of change of initial permeability in the range of −40 ° C. to 125 ° C. can be obtained. Excellent characteristics of 20% or less can be obtained. Furthermore, by making ZnO in the range of 9.5 to 11.5 mol%, the absolute value of the rate of change of the initial permeability in the range of −40 ° C. to 125 ° C. can be made 5% or less, The initial permeability can be as high as 1600 or more.

Furthermore, the ferrite sintered body constituting the antenna coil of the present invention may contain at least one or more of Ta ₂ O ₅ of 3000 ppm or less, Nb ₂ O ₅ of 500 ppm or less, and ZrO ₂ of 500 ppm or less. Inclusion of Ta ₂ O ₅ , Nb ₂ O ₅ , ZrO ₂ is optional, but by containing these, the absolute value of the rate of change of initial permeability in the range of −40 ° C. to 125 ° C. is 15% or less, Furthermore, it becomes possible to make it 10% or less.

Although the antenna coil of the present invention can be applied to various uses, a typical example is a transponder. That is, the present invention is a transponder including an antenna coil and a signal processing circuit electrically connected to the antenna coil. The antenna coil includes a ferrite sintered body and a conductor wound around the ferrite sintered body. And the composition of the ferrite sintered body is Fe ₂ O ₃ : 54 to 55 mol%, ZnO: 14 mol% or less (however, not including 0), and the balance is essentially composed of MnO as a main component. And Si containing 60 to 800 ppm in terms of SiO ₂ , Ca in the range of 600 to 4000 ppm in terms of CaCO ₃ , and Co ₃ O ₄ of 1200 ppm or less (however, not including 0). A transponder including a recording unit for recording individual identification information and a control circuit for signal transmission / reception is provided. The signal processing circuit includes a capacitor that forms a parallel resonance circuit together with an antenna coil, a recording unit that records individual identification information and the like, and a main processing unit that includes a control circuit for signal transmission and reception in one chip. When the parallel resonance circuit of the antenna coil and the capacitor receives the command radio wave, the main processing unit transmits, for example, individual identification information from the antenna coil using the command radio wave as power.
In such a transponder, in order to obtain a ferrite sintered body that is stable against temperature changes and high temperature environments, a particularly preferred composition is that 7 to 14 mol% of ZnO as a main component and Co ₃ O ₄ as an auxiliary component. It contains 300-1200 ppm.

  According to the present invention, the initial permeability is stable in a very wide temperature range of −40 ° C. to 125 ° C., and the Q value (Q = 1 / tan δ, tan δ is a loss coefficient) is high. It is possible to obtain an antenna coil or the like that has little fluctuation with respect to a temperature change and has high reliability. Moreover, since the initial permeability can be further increased and the number of turns of the conductor can be suppressed, the throughput in the manufacturing process can be increased and the mass productivity can be improved.

The antenna coil in the present invention has the basic configuration shown in FIG. 1, but the present invention is characterized in that a ferrite sintered body having the following composition is used as the magnetic core member (ferrite sintered body) 1.
Hereinafter, the reasons for limiting the composition of the ferrite sintered body will be described.

First, the reasons for limiting the main components constituting the ferrite sintered body will be described.
Fe ₂ O ₃ is 54 to 55 mol%. When Fe ₂ O ₃ is less than 54 mol%, the temperature change rate Δμt of the initial permeability μi increases. On the other hand, when Fe ₂ O ₃ exceeds 55 mol%, the initial permeability μi decreases, and the change rate of the initial permeability μi in a high temperature environment increases. Therefore, the desirable amount of Fe ₂ O ₃ is 54 to 55 mol%.

  ZnO is 14 mol% or less (however, 0 is not included). When ZnO exceeds 14 mol%, the temperature change rate Δμt of the initial permeability μi tends to increase, and when ZnO is less than 7 mol%, the temperature change rate Δμt of the initial permeability μi increases, and the initial permeability μi decreases. Get smaller. Therefore, the desirable amount of ZnO is 7 to 14 mol%. Further, when ZnO exceeds 11.5 mol%, the initial permeability μi is rapidly reduced. Therefore, the desirable amount of ZnO for satisfying both the temperature change rate Δμt and the initial permeability μi is 9.5 to 11.5 mol%.

  In addition to the above, the sintered ferrite body of the present invention contains MnO as a substantial remainder.

Next, the reason for limiting the subcomponent will be described.
The ferrite sintered body of the present invention contains Si as a first subcomponent in a range of 60 to 800 ppm in terms of SiO ₂ and Ca in a range of 600 to 4000 ppm in terms of CaCO ₃ .
Si and Ca are segregated at the grain boundaries to form a high resistance layer and contribute to low loss, and have the effect of improving the sintering density as a sintering aid. However, when Si exceeds 800 ppm in terms of SiO ₂ or Ca exceeds 4000 ppm in terms of CaCO ₃ , loss deterioration due to discontinuous abnormal grain growth is large. Therefore, in the present invention, Si is set to 800 ppm or less in terms of SiO ₂ and Ca is set to 4000 ppm or less in terms of CaCO ₃ . On the other hand, if Si is less than 60 ppm in terms of SiO ₂ or Ca is less than 600 ppm in terms of CaCO ₃ , the above effect cannot be obtained sufficiently, so Si is 60 ppm or more in terms of SiO ₂ and Ca is 600 ppm or more in terms of CaCO _3. To do.
The desirable Si content is 70 to 600 ppm in terms of SiO ₂ , and the more desirable Si content is 100 to 500 ppm in terms of SiO ₂ .
The desirable Ca content is 600 to 3500 ppm in terms of CaCO ₃ , and the more desirable Ca content is 1200 to 3500 ppm in terms of CaCO ₃ .

The ferrite sintered body of the present invention contains a predetermined amount of Co ₃ O ₄ as the second subcomponent. Co ₃ O ₄ is effective in reducing the change rate of the initial permeability μi and making the change rate of the initial permeability μi flat and effective in improving the Q value. This is effective for suppressing the change rate with time Δμr and the change rate with temperature Δμt.
When Co ₃ O ₄ exceeds 1200 ppm, the change rate Δμr of the initial permeability μi with time increases, so that it may be contained at 1200 ppm or less (however, not including 0). Further, when Co ₃ O ₄ is made smaller than 300 ppm, the temperature change rate Δμt of the initial permeability μi increases. Therefore, the desirable amount of Co ₃ O ₄ is 300 to 1200 ppm, and the more desirable amount of Co ₃ O ₄ is 500 to 1000 ppm.

Furthermore, the ferrite sintered body of the present invention can contain TiO ₂ as a third subcomponent. TiO ₂ has an effect of suppressing the fluctuation of the initial permeability μi with respect to the temperature change, thereby making it possible to suppress the amount of Co ₃ O ₄ .
Ti exists in the crystal grains and at the crystal grain boundaries, and has an effect of reducing loss. However, when the amount of TiO ₂ exceeds 8000 ppm, the Q value is lowered. Therefore, in the present invention, the amount of TiO ₂ is preferably 8000 ppm or less.
On the other hand, in order to fully enjoy the effect of loss reduction, it is desirable to contain 500 ppm or more of TiO ₂ as the third subcomponent.
The ferrite sintered body of the present invention can also contain SnO ₂ as the third subcomponent. SnO _2, there are TiO ₂ similar effect can be added in the form of replacing composite addition with TiO _2, or a TiO _2. The addition amount of SnO ₂ is preferably equivalent to the above-mentioned TiO ₂ in mol amount. That is, the upper limit of SnO ₂ addition is 16000 ppm.

  When the third subcomponent is contained in combination, the total content is 20000 ppm or less, preferably 7000 to 12000 ppm.

The ferrite sintered body of the present invention includes, as the fourth subcomponent, Ta ₂ O ₅ of 3000 ppm or less (including 0), Nb ₂ O ₅ of 500 ppm or less (including 0), and ZrO ₂ of 500 ppm. At least one or more of the following (including 0) can be included. By including these fourth subcomponents, it is possible to obtain the effect of reducing the μi change rate and / or reducing the loss. In order to fully enjoy the effect, it is desirable to contain 50 ppm or more of Ta ₂ O ₅ , Nb ₂ O ₅ , and ZrO ₂ .
A desirable amount of Ta ₂ O ₅ is 0 to 2500 ppm, and a more desirable amount of Ta ₂ O ₅ is 500 to 2000 ppm.
A desirable Nb ₂ O ₅ content is 0 to 400 ppm, and a more desirable Nb ₂ O ₅ content is 50 to 350 ppm.
A desirable amount of ZrO ₂ is 0 to 400 ppm, and a more desirable amount of ZrO ₂ is 50 to 350 ppm.
When the fourth subcomponent is contained in combination, the total content is 3000 ppm or less, preferably 300 to 2000 ppm.

The ferrite sintered body of the present invention exhibits a characteristic that the maximum value of the μi change rate at −40 ° C. to 125 ° C. is 20% or less, desirably 15% or less in absolute value. In particular, by selecting a desired composition, the maximum value of the μi change rate at −40 ° C. to 125 ° C. can be made 15% or less, further 10% or less in absolute value.
The ferrite sintered body of the present invention can have a change rate Δμr with time of initial permeability μi of 10% or less when placed in an environment of 175 ° C. for 48 hours. Further, in particular, by selecting a desirable composition, it is possible to reduce the change rate Δμr with time of the initial permeability μi when it is placed in an environment of 175 ° C. for 48 hours to 5% or less.
As described above, the ferrite sintered body of the present invention is suitable as a material for in-vehicle parts such as an antenna coil and a transponder because it can obtain high reliability that could not be obtained with MnZn ferrite. .
Moreover, the ferrite sintered body of the present invention has a high characteristic that the initial permeability μi at 20 ° C. is 1400 or more. As a result, the number of turns of the conductive wire can be reduced when configuring the antenna coil, the manufacturing efficiency can be increased and the throughput can be improved, and the antenna coil can be downsized.

Next, the manufacturing method suitable for the ferrite sintered body according to the present invention will be described.
As the raw material of the main component, an oxide or a powder of a compound that becomes an oxide by heating is used. Specifically, Fe ₂ O ₃ powder, Mn ₃ O ₄ powder, ZnO powder, or the like can be used. In addition, what is necessary is just to select suitably the average particle diameter of each raw material powder in the range of 0.1-5.0 micrometers.
The raw material powder of the main component is wet mixed and then calcined. The calcining temperature may be a predetermined temperature within a range of 650 to 1000 ° C., and the atmosphere may be N ₂ or air. What is necessary is just to select the stable time of calcination suitably in the range of 0.5 to 5.0 hours. After the calcination, the calcined body is pulverized, for example, to an average particle size of about 0.5 to 2.0 μm. In the present invention, not only the above-mentioned main component materials, but also a composite oxide powder containing two or more metals may be used as the main component materials. For example, a complex oxide powder containing Fe and Mn can be obtained by oxidizing and roasting an aqueous solution containing iron chloride and manganese chloride. This powder and ZnO powder may be mixed and used as a main component material. In such a case, calcining is unnecessary.

Similarly, an oxide or a powder of a compound that becomes an oxide by heating can also be used as a raw material for the accessory component. Specifically, SiO ₂ , CaCO ₃ , Co ₃ O ₄ , TiO ₂ , SnO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , ZrO ₂ or the like can be used.
The raw material powders of these subcomponents are mixed with the main component powder pulverized after calcining. However, after mixing with the raw material powder of the main component, it can be subjected to calcining together with the main component.

  The mixed powder composed of the main component and the subcomponent is granulated into a granule in order to smoothly execute the subsequent molding process. Granulation can be performed using, for example, a spray dryer. A small amount of a suitable binder such as polyvinyl alcohol (PVA) is added to the mixed powder, and this is sprayed and dried with a spray dryer. The particle size of the obtained granules is preferably about 40 to 400 μm.

The obtained granule is formed into a desired shape using, for example, a press having a mold having a predetermined shape, and this formed body is subjected to a firing step.
In the firing step, it is necessary to control the firing temperature and firing atmosphere. The firing temperature can be appropriately selected from the range of 1050 to 1250 ° C., but it is desirable to fire in the range of 1100 to 1200 ° C. in order to sufficiently bring out the effect of the ferrite material of the present invention.

  The ferrite sintered body in the present invention can be obtained through the above steps. Such a ferrite sintered body is suitable as a material for an antenna coil, particularly an in-vehicle antenna coil used in a severe situation.

Next, the antenna coil of the present invention will be described. The antenna coil 10 of the present invention includes a magnetic core member 1 and a conductor 2 wound around the magnetic core member 1 in the same manner as the conventional example shown in FIG. In the present invention, a ferrite sintered body having the above-described composition is used for the magnetic core member 1.
There is no restriction | limiting in particular in the shape and dimension of the magnetic core member 1, According to the use of the antenna coil 10, it can set suitably. As a rectangular parallelepiped shape, many are in the range of (5-20) × (2-10) × (2-10) mm.
For example, a copper wire can be used for the conductor 2. The pitch and number of turns of the winding pattern can also be set as appropriate according to the application.

Next, the transponder of the present invention will be described. FIG. 2A is a schematic sectional view of the transponder. As shown in FIG. 2A, the transponder 200 includes a magnetic core member (ferrite sintered body) 1a, an antenna coil 20 including a conductor 2a wound around the magnetic core member 1a, a signal processing circuit 30, and an antenna. A case C for housing the coil 20 and the signal processing circuit 30 is provided. In the present invention, a ferrite sintered body having the above-described composition is used for the magnetic core member 1 a constituting the antenna coil 20.
There is no restriction | limiting in particular in the dimension of the magnetic core member 1a, According to the use of the transponder 200, it can set suitably. For example, a copper wire can be used for the conductor 2a, but the pitch and the number of turns of the winding pattern can be appropriately set according to the application.
Case C can be made of glass or resin, for example.

The signal processing circuit 30 to which the terminal of the conductor 2a of the antenna coil 20 is connected is mounted on a substrate 40 made of phenol resin or ceramics.
As shown in FIG. 2B, the signal processing circuit 30 on the substrate 40 includes a capacitor 31 that forms a parallel resonant circuit together with the antenna coil 20, a recording unit in which individual identification information and the like are recorded, and transmission / reception of signals. And a main processing unit 32 in which a control circuit and the like are integrated into one chip. When the parallel resonance circuit of the antenna coil 20 and the capacitor 31 receives the command radio wave, the main processing unit 32 transmits, for example, individual identification information from the antenna coil 20 using the command radio wave as power.

Now, the transponder 200 of the present invention is suitably used for an immobilizer. Here, the mechanism of the immobilizer will be described with reference to FIG.
FIG. 3 shows an outline of the configuration of an immobilizer in which the transponder 200 of the present invention is embedded in a grip portion of an ignition key K of an automobile. The ignition key K in which the transponder 200 is embedded is inserted into the key cylinder S on the automobile side. Then, a unique ID code recorded in advance in the recording unit of the transponder 200 is transmitted to the coil 50 wound on the key cylinder S side and read. The data read by the coil 50 is transmitted to a vehicle-side controller, that is, an ECU (Electronic Control Unit) 60 via the amplifier A, and electronically collated with an ID code recorded in the ECU 60 in advance. Only when the collated ID codes match, engine ignition and fuel injection are possible. When the ID codes do not match, engine ignition and fuel injection are prohibited and the engine cannot be started.

  The antenna coil 10 (20) of the present invention can have higher inductance than a conventional Ni-based antenna coil. For this reason, the number of turns of the conductor 2 (2a) can be reduced as compared with the conventional Ni-based antenna coil, and the antenna coil can be downsized.

Hereinafter, the present invention will be described based on specific examples.
First, an example of study on the composition of the ferrite core as the base of the present invention will be shown.
(First basic study example)
Ferrite cores having the compositions shown in Table 1 were produced.
Fe ₂ O ₃ powder, MnO powder and ZnO powder were used as raw materials for the main component, and these were wet mixed and then calcined at 850 ° C. for 3 hours.
Next, the calcined product of the main component material and the subcomponent material were mixed. SiO ₂ powder, CaCO ₃ powder, Ta ₂ O ₅ powder, Co ₃ O ₄ powder, and TiO ₂ powder were used as the raw materials for the accessory components. The auxiliary component raw material was added to the calcined material of the main component raw material and mixed while being pulverized. The pulverization was performed until the average particle size of the calcined product was about 1.0 μm. A binder was added to the resulting mixture, granulated, and then molded to obtain a toroidal shaped molded body.

The obtained molded body was fired at a temperature of 1150 ° C. (stable part 5 hours, stable part oxygen partial pressure 0.5%) under oxygen partial pressure control to obtain a ferrite core. Using this ferrite core, the Q value in the temperature range of −40 ° C. to 130 ° C. was measured. The toroidal was measured with an outer diameter of 20 mm, an inner diameter of 10 mm, and a thickness of 5 mm, a winding number of 20 turns, and an excitation voltage of 250 mV. Table 1 shows the minimum Q value in the range of −40 ° C. to 130 ° C. as Qmin. Moreover, the initial permeability μi (measurement frequency: 100 kHz) in the range of −40 ° C. to 130 ° C. was measured. Based on the initial permeability μi at 20 ° C., the absolute value of the change rate of the initial permeability μi in the range of −40 ° C. to 130 ° C. is shown as “Δμi” in Table 1. Table 1 also shows the minimum value μi _min of the initial permeability μi in the range of −40 ° C. to 130 ° C. The change rate of the initial permeability μi was calculated based on the following formula.

Change rate of initial permeability μi = (μi _T −μi ₂₀ ) / μi ₂₀ × 100 (%)
μi _T : Initial permeability μi at temperature T ° C
μi ₂₀ : Initial permeability μi at a temperature of 20 ° C.

Sample No. 1-7, Fe ₂ O ₃ is increased in this order. Among them, the Q value is low and Δμi is large when Fe ₂ O ₃ is as low as 54.0 mol% and as large as 58.0 mol%.
Next, sample No. As for 8-13, ZnO is increasing in this order. Among them, when ZnO is as high as 11.0 mol%, the Q value is low and Δμi is large.

(Second basic study example)
In the second basic study example, changes in Qmin and Δμi accompanying changes in the Co content are confirmed.
A ferrite core having the composition shown in Table 2 was prepared in the same procedure as in the first basic study example, and Qmin, Δμi, and μi _min were obtained under the same conditions as in the first basic study example. The results are shown in Table 2.

Sample No. 14 to 18, Co ₃ O ₄ is increased in this order. Among them, the Q value is low and Δμi is large when Co ₃ O ₄ is as low as 500 ppm and as large as 4000 ppm.
Next, Sample No. with an Fe ₂ O ₃ content of 55.5 mol% was used. 19 to 21 and the sample No. having an amount of Fe ₂ O ₃ of 56.5 mol%. When focusing on Nos. 22 to 25, sample Nos. In which the amount of Co ₃ O ₄ is in the range of 1000 to 3800 ppm. 22 to 25 all have a Q value of 200 or more. At the same time, sample no. 22 to 25 show the characteristic that Δμi is 20% or less in absolute value.

(Example of third basic study)
In the third basic study example, the Q value and the variation of Δμi accompanying the variation of the Si and Ca contents are confirmed.
A ferrite core having the composition shown in Table 3 was prepared in the same procedure as in the first basic study example, and Qmin, Δμi, and μi _min were obtained under the same conditions as in the first basic study example. The results are shown in Table 3.

Sample No. 26 to 30, SiO ₂ is increased in this order. Among them, when SiO ₂ is as low as 50 ppm, Δμi shows a good value, but Qmin is as low as 180. On the other hand, when SiO ₂ is as high as 1000 ppm, Qmin decreases to 85.

Sample No. 31 to 34, CaCO ₃ is increasing in this order. Among them, when CaCO ₃ is as low as 500 ppm and when CaCO ₃ is as high as 5000 ppm, Qmin is low.

(Fourth basic study example)
In the fourth basic study example, changes in the Q value and Δμi accompanying the inclusion of Ti and Sn are confirmed.
A ferrite core having the composition shown in Table 4 was prepared in the same procedure as in the first basic study example, and Qmin, Δμi, and μi _min were obtained under the same conditions as in the first basic study example. The results are shown in Table 4.

Sample No. 35 to 38, TiO ₂ has increased in this order. Sample No. 35 (without TiO ₂ content) and sample no. From the comparison of 36 (TiO ₂ : 2000 ppm), it can be seen that Δμi is reduced by containing TiO ₂ . However, when the content of TiO ₂ becomes 7000 ppm (sample No. 38), Δμi becomes larger than that without TiO ₂ (sample No. 35), and Qmin also decreases. Therefore, in this basic study example, the amount of TiO ₂ is set to 0 to 5000 ppm. Desirable amount of TiO ₂ is 500～4000Ppm, more preferably TiO ₂ amount is 500～3000Ppm.
The samples shown in the first to third basic examination examples described above all contained TiO ₂ . From 35, even if it does not contain TiO _{2, by} setting the other components within the range recommended by the present basic study example, it is possible to combine Qmin of 200 or more and Δμi of 20% or less in absolute value. Therefore, in this basic study example, the inclusion of TiO ₂ is not essential and is optional.

Sample No. 35,39～41 is, SnO ₂ has increased in this order. First, sample no. 35 (no SnO ₂ content) and sample no. Comparison of 39 (SnO ₂ : 2000 ppm) shows that Δμi is reduced by containing SnO ₂ . However, when the content of SnO ₂ reaches 7000 ppm (sample No. 41), Qmin decreases. Therefore, in this basic study example, the SnO ₂ amount is set to 0 to 5000 ppm. Preferably SnO ₂ weight 500～4000Ppm, more preferably the amount of SnO ₂ is 500～3000Ppm.
Sample No. 35, even when SnO ₂ is not contained, by setting the other components within the range recommended by the present basic study example, it is possible to combine Qmin of 200 or more and Δμi of 20% or less in absolute value. Therefore, the inclusion of SnO ₂ is not essential in this basic study example, but is optional.

(Fifth basic study example)
In the fifth basic study example, the variation of the Q value and Δμi accompanying the contents of Ta, Nb and Zr is confirmed.
A ferrite core having the composition shown in Table 5 was prepared in the same procedure as in the first basic study example, and Qmin, Δμi, and μi _min were obtained under the same conditions as in the first basic study example. The results are shown in Table 5.

Sample No. In 42 to 45, Ta ₂ O ₅ increases in this order. Sample No. 42 (without Ta ₂ O ₅ content) and sample no. From the comparison of 43 (Ta ₂ O ₅ : 1000 ppm), it can be seen that the inclusion of Ta ₂ O ₅ also improves Qmin. However, when the content of Ta ₂ O ₅ is 4000 ppm (sample No. 45), Δμi becomes larger than that when no Ta ₂ O _{5 is} contained (sample No. 42), and Qmin is significantly reduced. . Therefore, in this basic study example, the amount of Ta ₂ O ₅ is set to 0 to 3000 ppm. A desirable amount of Ta ₂ O ₅ is 0 to 2500 ppm, and a more desirable amount of Ta ₂ O ₅ is 500 to 2000 ppm.

Sample No. In 42, 46, and 47, Nb ₂ O ₅ increases in this order. First, sample no. 42 (Nb ₂ O _{5 not} contained) and Sample No. Comparison of 46 (Nb ₂ O ₅ : 300 ppm) shows that Qmin is improved while maintaining a smaller Δμi by containing Nb ₂ O ₅ . However, when the content of Nb ₂ O ₅ is 700 ppm (sample No. 47), the effect of improving Qmin while suppressing the deterioration of Δμi cannot be enjoyed. Therefore, in this basic study example, the amount of Nb ₂ O ₅ is set to 0 to 500 ppm. A desirable amount of Nb ₂ O ₅ is 0 to 400 ppm, and a more desirable amount of Nb ₂ O ₅ is 50 to 350 ppm.

Sample No. In 42, 48 and 49, ZrO ₂ increases in this order. First, sample no. 42 (without ZrO ₂ content) and sample no. Comparison of 48 (ZrO ₂ : 300 ppm) shows that Qmin is improved while maintaining a smaller Δμi by containing ZrO ₂ . However, when the content of ZrO ₂ is 700 ppm (sample No. 49), Qmin is significantly reduced. Therefore, in this basic study example, the amount of ZrO ₂ is set to 0 to 500 ppm. A desirable amount of ZrO ₂ is 0 to 400 ppm, and a more desirable amount of ZrO ₂ is 50 to 350 ppm.

Based on the tendency obtained by the first to fifth basic examples as described above, the amounts of Co ₃ O ₄ , Fe ₂ O ₃ , ZnO and TiO ₂ are set as follows in order to further improve the reliability and characteristics. Reviewed.
(First embodiment)
In the first example, changes with time and temperature of the initial permeability μi accompanying the content of Co ₃ O ₄ are confirmed.
A ferrite core having the composition shown in Table 6 was prepared in the same procedure as in the first basic study example, and the time-dependent change rate Δμr of initial permeability μi when placed in an environment of 175 ° C. for 48 hours, −40 ° C. to 125 ° C. The temperature change rate Δμt of the initial permeability μi in the range was obtained.
The change rate with time Δμr and the change rate with temperature Δμt were obtained by the following equations.
Δμr = (μ ₂ −μ ₁ ) / (μ ₂ + μ ₁ ) × 100
Δμt = (μ _max −μ _min ) / (μ _max + μ _min ) × 100
Here, μ ₁ is the value of initial permeability μi at 20 ° C. before the test, μ ₂ is the value of initial permeability μi at 20 ° C. after the test, and μ _max is the initial permeability in the range of −40 ° C. to 125 ° C. The maximum value of μi, μ _min is the minimum value of the initial permeability μi in the range of −40 ° C. to 125 ° C.
The results are shown in Table 6 and FIGS.

Sample No. In 101 to 107, Co ₃ O ₄ decreases in this order. As shown in Table 6 and FIG. 4, it can be seen that the rate of change with time Δμr is increased by containing Co ₃ O ₄ . In particular, when the content of Co ₃ O ₄ exceeds 1500 ppm (sample No. 101), the temporal change rate Δμr increases to 10% or more.

Further, as shown in Table 6 and FIG. 5, it can be seen that the temperature change rate Δμt is reduced by containing Co ₃ O ₄ . In particular, when the content of Co ₃ O ₄ exceeds 300 ppm (sample No. 105), the temperature change rate Δμt decreases to 20% or less.
Thus, in the present invention, the amount of Co ₃ O ₄ is 1200 ppm or less, the more desirable range of Co ₃ O ₄ is 300 to 1200 ppm, and the more desirable range is 300 to 1000 ppm.

(Second embodiment)
In the second example, a change with time and a change in temperature of the initial permeability μi accompanying the content of Fe ₂ O ₃ are confirmed.
Ferrite cores having the compositions shown in Table 7 were prepared in the same procedure as in the first basic study example, and the time change rate Δμr was obtained. The results are shown in Table 7, FIG. 6, FIG. 7, and FIG.

Sample No. In 110 to 115 and 116 to 121, Fe ₂ O ₃ increases in this order. Sample No. 110-115 and sample no. In 116-121, the addition amount of ZnO differs.
As shown in Table 7 and FIG. 6, it can be seen that the rate of change with time Δμr increases as the content of Fe ₂ O ₃ increases. Sample No. From the comparison of 110 to 115 and 116 to 121, it can be seen that the same tendency is shown regardless of the added amount of ZnO. The content of Fe ₂ O ₃ is the equal to or less than 55 mol%, aging rate Δμr becomes 10% or less, further below the 54.5Mol% with time rate of change Δμr of 5% or less. Therefore, the content of Fe ₂ O ₃ is preferably 55 mol% or less, and more preferably 54.5 mol% or less.

Further, the temperature change rate Δμt and the initial permeability μi were determined for the ferrite core.
Sample No. In 110 to 115, 116 to 121, and 122 to 126, Fe ₂ O ₃ increases in this order. Sample No. 110-115 and sample no. 116-121, Sample No. In 122-126, the addition amount of ZnO differs.
As shown in Table 7 and FIG. 7, it can be seen that the temperature change rate Δμt tends to decrease as the content of Fe ₂ O ₃ increases. Sample No. 110-115, 116-121, 122-126, regardless of the amount of ZnO added, these generally show the same tendency as described above, but the more the ZnO added, the smaller the temperature change rate Δμt, Thus, it can be seen that the amount of Fe ₂ O ₃ can be reduced if an equivalent temperature change rate Δμt is obtained.
Further, as described above, the content of Fe ₂ O ₃ is preferably 55 mol% or less in terms of the rate of change with time Δμr. Within this range, when ZnO is 4.5 mol%, the temperature change rate Δμt exceeds 20% when the content of Fe ₂ O ₃ is 54.7 mol% or less, and when ZnO is 7 mol%, Fe ₂ O ₃ When the content of is 54.3 mol% or less, the temperature change rate Δμt exceeds 20%. Even if ZnO is 9.5 mol%, the temperature change rate Δμt tends to exceed 20% when the content of Fe ₂ O ₃ is 54 mol% or less. Therefore, the content of Fe ₂ O ₃ is preferably 54 mol% or more, and a more preferable range varies depending on the composition, but is 54.5 mol% or more, and a particularly preferable range is 54.7 mol% or more.

As shown in Table 7 and FIG. 8, when the ZnO content is 4.5 mol%, the initial permeability μi is 1400 or more when the Fe ₂ O ₃ content is 54.3 to 55.3 mol%. When the ZnO content is 7 mol%, the initial permeability μi is 1500 or more when the Fe ₂ O ₃ content is 54 to 55.2 mol%, and the ZnO content is 9.5 mol. %, The initial permeability μi is as high as 1600 or more when the content of Fe ₂ O ₃ is 54.2 to 54.7 mol%.
Thus, if in the range of ZnO 7～14Mol%, it may preferably be 54～55Mol% content of Fe ₂ O _3, further particularly preferably in the above range depending on the composition I understand.

(Third embodiment)
In the third example, the initial permeability μi and the temperature change of the initial permeability μi accompanying the ZnO content are confirmed.
A ferrite core having the composition shown in Table 8 was prepared in the same procedure as in the first basic study example, and the initial permeability μi and the temperature change rate Δμt were obtained. The results are shown in Table 8 and FIGS.

Sample No. As for 130-136, ZnO is increasing in this order.
As shown in Table 8 and FIG. 9, the temperature change rate Δμt can be made 10% or less by setting the added amount of ZnO to 8 to 13.5 mol%, and the added amount of ZnO is about 11 mol%. It can be seen that the temperature change rate Δμt can be made 5% or less.
Further, as shown in FIG. 10, by setting the added amount of ZnO to 6.5 to 11.8 mol%, the initial permeability μi can be set to 1600 or more, and the added amount of ZnO is set to 9. It can be seen that the initial permeability μi can be set to a high value of 1700 or more by setting the content to 5 to 11.0 mol%.
Thus, in this invention, the preferable addition amount of ZnO is 8-13.5 mol%, the range of more desirable addition amount is 9.5-11.5 mol%, and the more desirable range is 9.5-11.0 mol%. %.

(Fourth embodiment)
In the fourth example, changes in temperature change rate Δμt and Qmin accompanying the content of TiO ₂ are confirmed.
A ferrite core having the composition shown in Table 9 was prepared in the same procedure as in the first basic study example, and the initial permeability μi and Qmin were determined. The results are shown in Table 9 and FIGS.

Sample No. In 140 to 144, 145 to 149, and 150 to 154, TiO ₂ increases in this order. Sample No. 140-144 and sample no. 145-149, Sample No. In 150 to 154, the amount of Co ₃ O ₄ added is different.
As shown in Table 9 and FIG. Comparison of 140 to 144, 145 to 149, and 150 to 154 shows that the addition amount of Co ₃ O ₄ can be reduced if the equivalent temperature change rate Δμt is obtained by adding TiO ₂ .
In addition, as shown in FIG. 12, Qmin may tend to decrease with the addition amount of TiO ₂ peaking around 4000 ppm. Therefore, the addition amount of TiO ₂ is preferably 8000 ppm or less, and it can be seen that the Qmin can be 150 or more by further setting the addition amount of TiO ₂ to 1000 to 7000 ppm.

(5th Example)
In the fifth example, the variation of the Q value and Δμi accompanying the variation of the Si and Ca contents is confirmed.
A ferrite core having the composition shown in Table 9 was prepared in the same procedure as in the first basic study example, and Qmin and temperature change rate Δμt were obtained under the same conditions as in the first basic study example. The results are shown in Table 10.

Sample No. 160-166 is, SiO ₂ has increased in this order. Temperature change rate Δμt is 10% or less in both, in which, if SiO ₂ is small and 50 ppm, when SiO ₂ is large and 1000ppm, the temperature change rate Δμt is more than 7%. Therefore, it is preferable to the SiO ₂ and 60～800Ppm. Further, when the SiO ₂ is in the range of 70 to 500 ppm, the temperature change rate Δμt is 5% or less. In addition, when the SiO ₂ is in the range of 100 to 600 ppm, the Qmin is 140 or more. Accordingly, SiO ₂ is preferably 60 to 800 ppm, more preferably 70 to 500 ppm, and particularly preferably 60 to 800 ppm.

Sample No. 167-175 is, CaCO ₃ is increasing in this order. Among them, when CaCO ₃ is small and 500 ppm, when CaCO ₃ is large and 5000ppm is, Qmin is particularly low. Therefore, it is preferable to the CaCO ₃ and 600～4000Ppm. Moreover, in the range of 1000 to 2500 ppm of CaCO ₃ , Qmin is 150 or more, and the temperature change rate Δμt is about 5% or less. Further, when CaCO ₃ is in the range of 1500 to 2000 ppm, Qmin is 180 or more, and the temperature change rate Δμt is about 5%. Therefore, CaCO ₃ is preferably 600 to 4000 ppm, more preferably 1000 to 2500 ppm, and particularly preferably 1500 to 2000 ppm.

(Sixth embodiment)
In the sixth embodiment, fluctuations in the Q value and Δμi accompanying the contents of Ta, Nb, and Zr are confirmed.
A ferrite core having the composition shown in Table 11 was prepared in the same procedure as in the first basic study example, and Qmin and temperature change rate Δμt were obtained under the same conditions as in the first basic study example. The results are shown in Table 11.

Sample No. 180-183 is, Ta ₂ O ₅ is increasing in this order. Sample No. 180 (without Ta ₂ O ₅ content) and sample no. From the comparison of 181 (Ta ₂ O ₅ : 1000 ppm), it can be seen that the temperature change rate Δμt is decreased by containing Ta ₂ O ₅ . However, when the content of Ta ₂ O ₅ is 4000 ppm (sample No. 183), the temperature change rate Δμt becomes larger than that when no Ta ₂ O _{5 is} contained (sample No. 180), and the Qmin is greatly increased. To drop. Therefore, in this embodiment, the amount of Ta ₂ O ₅ is set to 0 to 3000 ppm. A desirable amount of Ta ₂ O ₅ is 0 to 2500 ppm, and a more desirable amount of Ta ₂ O ₅ is 500 to 2000 ppm.

Sample No. In 184, 185, and 186, Nb ₂ O ₅ increases in this order. First, sample no. 184 (Nb ₂ O _{5 not} contained) and Sample No. From the comparison of 185 (Nb ₂ O ₅ : 300 ppm), it can be seen that the temperature change rate Δμt is reduced by containing Nb ₂ O ₅ . However, when the content of Nb ₂ O ₅ is 700 ppm (sample No. 186), the temperature change rate Δμt becomes larger than that when Nb ₂ O _{5 is not} contained (sample No. 184), and the Qmin is greatly increased. To drop. Therefore, in this embodiment, the amount of Nb ₂ O ₅ is set to 0 to 500 ppm. A desirable amount of Nb ₂ O ₅ is 0 to 400 ppm, and a more desirable amount of Nb ₂ O ₅ is 50 to 350 ppm.

Sample No. In 187, 188, and 189, ZrO ₂ increases in this order. When the content of ZrO ₂ is 700 ppm (sample No. 189), Qmin is significantly reduced. Therefore, in this embodiment, the amount of ZrO ₂ is set to 0 to 500 ppm. A desirable amount of ZrO ₂ is 0 to 400 ppm, and a more desirable amount of ZrO ₂ is 50 to 350 ppm.

The desirable composition of the ferrite sintered body has been described in detail above. The ferrite sintered body having the composition recommended by the present invention has a small temperature dependency of the initial permeability μi, a large Q value, and high reliability even in a high temperature environment.
Further, the ferrite sintered body having the composition recommended by the present invention can increase the inductance. For this reason, according to the antenna coil using the ferrite sintered body of the present invention, the number of turns of the conductor can be reduced, the throughput can be increased, and the mass productivity can be improved. In addition, since the antenna coil can be reduced in size, the transponder incorporating the antenna coil can also be reduced in size.

It is a figure for demonstrating the basic composition of an antenna coil. It is a figure for demonstrating the basic composition of a transponder. It is a figure for demonstrating the structure outline | summary of an immobilizer. Is a diagram showing the amount and time change rate Δμr relationship Co ₃ O _4. Is a diagram showing the amount and temperature change rate Δμt relationship Co ₃ O _4. Is a diagram showing the relationship between the addition amount and time change rate Δμr of Fe ₂ O _3. It is a diagram showing the relationship between the addition amount and the temperature change rate Δμt of Fe ₂ O _3. It is a diagram showing the relationship between the added amount and the initial permeability μi of Fe ₂ O _3. It is a figure which shows the relationship between the addition amount of ZnO, and temperature change rate (DELTA) microt. It is a figure which shows the relationship between the addition amount of ZnO, and initial permeability (mu) i. Is a diagram showing the relationship between the addition amount of TiO ₂ with time rate of change Derutamyuaru. Is a diagram showing the relationship between the addition amount and the Q value of the TiO _2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1a ... Magnetic core member (ferrite sintered body), 2, 2a ... Conductor 10, 20 ... Antenna coil, 200 ... Transponder, 30 ... Signal processing circuit, C ... Case

Claims (11)

A ferrite sintered body,
An antenna coil including a conductor wound around the ferrite sintered body,
The ferrite sintered body is
Fe ₂ O ₃ : 54 to 55 mol%, ZnO: 14 mol% or less (however, not including 0), the balance being substantially composed of MnO as the main component, and subcomponents, Si of 60 to 800 ppm in terms of SiO ₂ , and Ca An antenna coil comprising 600 to 4000 ppm in terms of CaCO ₃ and 1200 ppm or less of Co ₃ O ₄ (excluding 0).   2. The antenna coil according to claim 1, wherein a change in magnetic permeability is 10% or less when left in an environment at 175 ° C. for 48 hours. The antenna coil according to claim 1 or 2, wherein the ferrite sintered body contains 300 ppm or more of Co ₃ O ₄ as a subcomponent.   The antenna coil according to any one of claims 1 to 3, wherein the ferrite sintered body contains 7 mol% or more of ZnO as a main component.   5. The absolute value of the rate of change of the initial permeability in the range of −40 ° C. to 125 ° C. is 20% or less with reference to the initial permeability at 20 ° C. 5. Antenna coil.   The antenna coil according to any one of claims 1 to 5, wherein an initial permeability at 20 ° C is 1400 or more. The TiO ₂ 8000 ppm or less (not inclusive of 0) antenna coil according to any one of claims 1 to 6, characterized in that it comprises.   8. The antenna coil according to claim 1, wherein a minimum value of Q (Q = 1 / tan δ, where tan δ is a dielectric loss tangent) in a range of −40 ° C. to 125 ° C. is 150 or more. 9. The antenna coil according to claim 1, comprising at least one of Ta ₂ O ₅ of 3000 ppm or less, Nb ₂ O ₅ of 500 ppm or less, and ZrO ₂ of 500 ppm or less. A transponder including an antenna coil and a signal processing circuit electrically connected to the antenna coil,
The antenna coil is
Including a ferrite sintered body, and a conductor wound around the ferrite sintered body, and
The ferrite sintered body is
Fe ₂ O ₃ : 54 to 55 mol%, ZnO: 14 mol% or less (however, not including 0), the balance being substantially composed of MnO as the main component, and subcomponents, Si of 60 to 800 ppm in terms of SiO ₂ , and Ca While containing 600 to 4000 ppm in terms of CaCO ₃ and 1200 ppm or less (excluding 0) of Co ₃ O ₄ ,
The signal processing circuit includes:
A transponder comprising: a recording unit for recording individual identification information; and a control circuit for transmitting and receiving signals. The ferrite sintered body is
11. The transponder according to claim 10, comprising 7 to 14 mol% of ZnO as a main component and 300 to 1200 ppm of Co ₃ O ₄ as a subcomponent.

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