JP2006160584A - Ni-Zn based ferrite composition and antenna coil - Google Patents

Abstract

PROBLEM TO BE SOLVED To stabilize frequency characteristics and current values in a characteristic range used when an antenna coil is configured.
When an evaluation core having a closed magnetic circuit configuration is used as an evaluation condition, including iron oxide (Fe ₂ O ₃ ), nickel oxide (NiO), copper oxide (CuO), and zinc oxide (ZnO). Amplitude specific permeability represented by the equation Δμ _a / μ _a = (1−μ _a0 / μ _a1 ) × 100 (where μ _a0 is the amplitude relative permeability at 20 ° C., μ _a1 is the amplitude relative permeability at a predetermined temperature). A Ni—Zn ferrite composition having a temperature change rate of magnetic susceptibility in a range of −6 to + 6% under a temperature environment of −30 to 85 ° C.
[Selection] Figure 2

Description

  The present invention relates to a Ni—Zn ferrite composition excellent in frequency characteristics and current value stability, and an antenna coil made of the composition.

For example, one of the characteristics regarded as important in the core material used in the conventional antenna coil for a keyless entry system as shown in Patent Document 1 is that the temperature change rate of the initial permeability (μi) is small. . However, on the other hand, the keyless entry system is required to have good transmission / reception sensitivity and to improve the distance of radio waves. For this reason, it is necessary to design the antenna coil so as to generate a magnetic flux and a magnetic field that are larger than those in the current situation.
JP 2000-203846 (Claims, Abstract, etc.)

  However, when the magnetic flux and magnetic field applied to the antenna coil are increased, the conventional ferrite is outside the range of the desired characteristic region, and there is a problem that the frequency characteristic and the characteristic stable to the applied current cannot be obtained.

In view of this problem, an object of the present invention is to stabilize frequency characteristics and current values in a characteristic range used when an antenna coil is configured. Generally, when evaluating the magnetic properties peculiar to a ferrite composition, a core having a closed magnetic circuit configuration represented by a toroidal shape is used. If the core shape of the open magnetic circuit structure, properties by the leakage magnetic flux will be averaged, because determination of quality is difficult even for the temperature change rate and the like of the mu _a. An object of the present invention is to provide a core member having excellent desired characteristics when used as a core material for an antenna coil, regardless of whether the core material is used in a closed magnetic circuit configuration or an open magnetic circuit configuration. I have to.

In order to achieve the above object, the present invention includes iron oxide (Fe ₂ O ₃ ), nickel oxide (NiO), copper oxide (CuO), and zinc oxide (ZnO). When the core is used, the temperature change rate of the amplitude relative permeability represented by the formula Δμ _a / μ _a = (1−μ _a0 / μ _a1 ) × 100 is −6 to The Ni—Zn ferrite composition is characterized by being in the range of + 6%. Here, the evaluation core having a closed magnetic circuit configuration means a core material represented by a toroidal shape. Δμ _a / μ _a is the temperature change rate of the amplitude relative permeability (μ _a ), μ _a0 is the value of μ _a at room temperature (20 ° C.), μ _a1 is the value of μ _a at _a predetermined temperature, respectively. Show.

Further, the present invention relates to iron oxide (Fe ₂ O ₃ ) 48.2 to 48.8 mol%, and a mixture of nickel oxide (NiO) and copper oxide (CuO) 26.7 to 27.3 mol% (including, Copper oxide substitution rate 30.0%), zinc oxide (ZnO) as the balance, and 300 to 1800 ppm of bismuth oxide (Bi ₂ O ₃ ) based on the total weight of the above components, a Ni—Zn ferrite composition It is a thing.

In addition, another invention of the present invention is a Ni—Zn ferrite composition in which the content of bismuth oxide (Bi ₂ O ₃ ) is in the range of 700 to 1300 ppm in both the above inventions.

  In another aspect of the present invention, an antenna coil using any of the above-described Ni—Zn ferrite compositions is used.

_Here, Fe ₂ O 3, NiO, each molar ratio of CuO and ZnO _is a numerical value when the Fe ₂ O 3, NiO, the total amount of CuO and ZnO and 100 mol%. The content of _Bi 2 _{O 3} is, _Fe 2 _O 3 of the ferrite composition, NiO, are shown in weight percentage relative to the total weight of CuO and ZnO.

When the molar ratio of Fe ₂ O ₃ is smaller than 48.2 mol%, the core loss is increased, which is not preferable. On the other hand, when the molar ratio of Fe ₂ O ₃ is larger than 48.8 mol%, the specific resistance is lowered and the temperature characteristics are deteriorated. Therefore, the content of Fe ₂ O ₃ is preferably in the range of 48.2 to 48.8 mol%.

  If the lower limit of the mixture of NiO + CuO is 26.7 mol%, assuming that the copper oxide substitution rate is 30.00%, NiO is 18.69 mol% and CuO is 8.01 mol%.

  When the upper limit of the mixture of NiO + CuO is 27.3 mol%, assuming that the copper oxide substitution rate is 30.00%, NiO is 19.11 mol% and CuO is 8.19 mol%.

  When the molar ratio of NiO is greater than 19.11 mol%, the balance between the saturation magnetic flux density and the initial magnetic permeability is lost. On the other hand, even if the molar ratio of NiO is smaller than 18.69 mol%, the balance between the saturation magnetic flux density and the initial magnetic permeability is similarly lost. For this reason, it is preferable that the molar ratio of NiO is in the range of 18.69 to 19.11 mol%.

  Further, when the molar ratio of CuO is larger than 8.19 mol%, the saturation magnetic flux density is lowered. On the other hand, when the molar ratio of CuO is smaller than 8.01 mol%, the firing temperature is increased. For this reason, it is preferable that the molar ratio of CuO exists in the range of 8.01-8.19 mol%. The molar ratio of the NiO + CuO mixture is preferably in the range of 26.7 to 27.3 mol%.

Further, when the content of Bi ₂ O ₃ is more than 1800 ppm, the strength is lowered. On the other hand, if the content of Bi ₂ O ₃ is less than 300 ppm, the characteristics are deteriorated. Therefore, the content of Bi ₂ O ₃ is preferably in the range of 300 to 1800 ppm. In particular, the preferable Bi ₂ O ₃ content is 700 to 1300 ppm.

  According to the present invention, it is possible to stabilize frequency characteristics and current values in a characteristic range used when an antenna coil is configured.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  The Ni—Zn based ferrite composition according to the embodiment of the present invention is suitable for the core material of the antenna coil. In this embodiment, an example in which a Ni—Zn ferrite composition is used as a core material of an antenna coil will be described.

  FIG. 1 is a flowchart showing a process for producing an evaluation core for a Ni—Zn based ferrite composition suitable for an antenna coil.

  As shown in FIG. 1, the evaluation core includes a raw material mixing step (step S1), a granulation step (step S2), a calcining step (step S3), a sieving step (step S4), and a crushing step (step S5). ), Granulation process (step S6), molding process (step S7), and baking process (step S8). The evaluation core is subjected to various evaluations after production in order to examine its performance. Hereinafter, each process for manufacturing the evaluation core will be described.

(Raw material mixing step: Step S1)
First, Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder are weighed, put into a ball mill mixer together with a predetermined amount of water and a dispersant, and the ball mill mixer is rotated.
(Granulation process: Step S2)
This step is a step performed to increase the molding density and the subsequent sintering density. After the mixing step, the slurry is transferred from the ball mill mixer to another container and mixed with a predetermined amount of binder using a stirrer. When foam comes out after adding the binder, add antifoaming agent. Moreover, when it is thought that a dispersing agent is insufficient, you may add a dispersing agent, stirring. Next, the slurry is put into a spray dryer and granulated.
(Calcination process: Step S3)
The granulated raw material is transferred from a spray dryer to a heat-resistant container and calcined at a temperature of about 800 ° C.
(Sieving process: Step S4)
Next, the raw material after calcination is passed through a 30 mesh (mesh size: about 500 microns) sieve to remove large particles.
(Crushing step: Step S5)
Next, the powder dropped from the sieve (adding Bi ₂ O ₃ fine powder as an additive depending on conditions) is put into a ball mill mixer together with a predetermined amount of water and a dispersant, and the ball mill mixer is rotated. Let The ball mill mixer contains iron balls, and the powder under the sieve (mixed powder with Bi ₂ O ₃ fine powder depending on conditions) is crushed in the ball mill mixer. During this process, periodically samples the slurry, at a 1.3 micron average particle size (D ₅₀ value), and terminates the crushing. The particle size distribution of the crushed particles is measured by a laser method.
(Granulation process: Step S6)
Since the next granulation process is the same as the process of step S2, the description thereof is omitted.
(Molding process: Step S7)
Next, the granulated powder is put into a molding die and molded into a toroidal shape.
(Baking process: Step S8)
Next, the molded body is taken out from the mold and fired at a temperature of about 1100 ° C. under normal pressure (normal pressure sintering).

  In addition, the manufacturing method which consists of said each process is only one form in manufacturing the core for evaluation, and can employ | adopt a process different from the above. In each step, a method different from the above can be adopted.

For example, the calcining process (step S3), the sieving process (step S4), the crushing process (step S5) and the granulating process (step S6) are omitted from the process consisting of the above-described steps S1 to S8. You may employ | adopt the manufacturing method which consists of a mixing process (step S1), a granulation process (step S2), a shaping | molding process (step S3), and a baking process (step S4). When the particle size of the raw material to be charged in step S1 is large, the raw material mixing step (step S1) may also serve as a raw material pulverization step. Further, the sieving step is performed before the raw material mixing step, and from the sieving step (step S1), the raw material mixing step (step S2), the granulation step (step S3), the molding step (step S4), and the firing step (step S5). The following manufacturing method may be adopted. Furthermore, you may employ | adopt the manufacturing method which consists of a raw material mixing process (step S1), a granulation process (step S2), a sieving process (step S3), a shaping | molding process (step S4), and a baking process (step S5). Further, an additive (Bi ₂ O ₃ ) may be added in the raw material mixing step (step S1).

A temperature lower or higher than 800 ° C. may be adopted as the temperature in the calcination step. However, even when a temperature higher than 800 ° C. is employed, the temperature is lower than the firing temperature in the firing step. Further, the sieve used in the sieving step is not limited to a 30-mesh net, and a finer mesh or a coarser net can be used. The sieve can be appropriately selected depending on the characteristics of the granulated powder, the particle size of the raw material used, and the like. Further, indication of the crushing ends in crushing step, the average particle diameter (D ₅₀ value) other than the guide, for example, a D ₉₀ value or D ₁₀ value when the maximum value of the particle size in particle size distribution was D ₁₀₀ It may be adopted. Further, even when employing a D ₅₀ value, it may be terminated disintegrated to measure a value other than 1.3 microns. This is because the degree of crushing can vary depending on the molding conditions and the density requirements of the sintered body. In the molding process, a method other than molding using a mold, for example, cold isostatic pressing (CIP) or the like may be employed. In the firing step, a method other than atmospheric pressure sintering, for example, a sintering method in which a pressure such as hot pressing or hot isostatic pressing (HIP) is applied may be employed. When such pressure sintering is employed, the sintering may be performed at a temperature lower than 1100 ° C. Further, the sintering temperature can be appropriately changed according to the pressure.

  Hereinafter, the evaluation method of the evaluation core will be described.

Items that can be evaluated are initial permeability (μi), quality factor (Q), relative loss factor (tan δ / μiac), saturation magnetic flux density (Bs), core loss (Pcv), amplitude relative permeability (μ _a ), Relative temperature coefficient (αμir) and specific resistance (ρv). By using a part of the above evaluation items, the temperature change rate (Δμ _a / μ _a ) of the amplitude relative permeability in the temperature range of −30 to 85 ° C. is obtained.

Here, the initial permeability (μi) refers to the limit value of the amplitude permeability of the magnetic core when the strength of the magnetic field is made as close to zero as possible. For this reason, the initial permeability (μi) indicates the response of the magnetic core to the external magnetic field. The quality factor (Q) is the reciprocal of the loss coefficient tan δ (the sum of hysteresis loss coefficient, eddy current loss coefficient, and residual loss coefficient). The relative loss coefficient (tan δ / μi) is a value obtained by dividing the loss coefficient (tan δ) by the AC initial permeability (μiac). The saturation magnetic flux density (Bs) refers to the maximum magnetic flux density possible in the magnetic material. Core loss (Pcv) refers to the energy consumed when moving in a magnetic hysteresis curve by an external magnetic field after a ferromagnetic material such as ferrite is magnetized. In general, the core loss (Pcv) is expressed as the sum of energy loss converted to heat and energy loss caused by eddy current. However, an insulator such as ferrite hardly generates eddy current. This is mainly equivalent to energy loss due to heat generation. Since the core loss is proportional to the area of the magnetic hysteresis curve, the smaller the area, the smaller the core loss. Amplitude relative permeability (μ _a ) is the magnetic flux density when a magnetic field that periodically changes with time and whose average strength is zero is applied to a magnetic core in a state where no magnetic field is applied. The relative magnetic permeability obtained from the maximum value of and the maximum value of the magnetic field strength. The relative temperature coefficient (αμir) refers to a coefficient represented by (μi2−μi1) / μi1 (T2−T1). Here, T1 and T2 indicate the temperature, and μi1 and μi2 indicate the initial permeability at the temperature T1 and the initial permeability at the temperature T2, respectively. Specific resistance (ρv) refers to the electrical resistance per unit volume of a substance.

  Hereinafter, each example of the present invention and each comparative example for comparison with these will be described. First, the manufacturing method and the evaluation method in each example and each comparative example will be described, and then the evaluation result will be described with reference to the tables and drawings.

1. Manufacturing method and evaluation method [Example 1]
(1) Raw material and mixing treatment As component ratios in the evaluation core, Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were 48.50 mol%, 18.90 mol% and 8.10 mol%, respectively. 24.50 mol%, and each raw material powder was weighed so that the total weight of the raw material was 3 kg. The CuO substitution rate at this time was 30.00%. Subsequently, each raw material powder after weighing was placed in an attritor together with 1,800 ml of pure water, about 20 cc of a dispersant made of special polycarboxylic acid ammonium salt and 17.5 kg of steel balls having a diameter of 4 mm. The slurry concentration at this time was 62.5% by weight. Thereafter, the attritor was rotated under the conditions of a rotation speed of 200 rpm and a mixing time of 30 minutes, and each raw material powder was wet mixed.

(2) Granulation After mixing raw materials using an attritor, the slurry in the attritor was transferred to a stainless steel container. Next, a diluted aqueous solution of a binder made of polyvinyl alcohol was put into the container, and mixed for 1 hour or more using a stirrer. The stirring speed of the stirrer was in the range of 100 to 150 rpm. The diluted aqueous solution of the binder was added so that the pure binder was 1% with respect to the total weight of the raw material powder. In this example, since the raw material powder was 3 kg and the concentration of the diluted aqueous solution of the binder was 10 wt% (the solid content of the binder was 10 wt% and the remaining 90 wt% was water), 300 g of the diluted binder aqueous solution was added. The slurry viscosity was adjusted to the range of 1000 to 2000 cps by the addition of the binder. Moreover, when foam | bubble came out after throwing in a binder, the antifoamer which consists of nonionic polyether was added suitably. Next, the slurry thus prepared was gradually supplied to a spray dryer to perform granulation. Granulation was performed using a spray dryer. The rotation speed of the spray dryer disk was 8000 rpm, and granulation was performed for about 1 hour.

(3) Calcination The granulated raw material was transferred from the spray dryer to an alumina container. Next, the alumina container containing the granulated raw material was placed in a batch firing furnace. The calcination was controlled by a program in which the temperature was raised from room temperature at 200 ° C./hr, held at 800 ° C. for 2 hours, and lowered to room temperature at 100 ° C./hr.

(4) Sieve After the inside of the furnace had cooled, the alumina container was taken out, and the raw material after calcination was passed through a 30-mesh sieve to remove coarse particles.

(5) Crushing Next, the powder under the sieve was put into an attritor together with a predetermined amount of water and a dispersing agent so that the slurry concentration was in the range of 63 to 65% by weight. The balls placed in the attritor were the same as in the first mixing and the same amount. Further, the rotation speed of the attritor was set to 200 rpm, and the pulverization was performed for about 1 hour. In the middle, the slurry was sampled to measure the particle size. When the average particle size was about 1.3 microns as a result of the particle size measurement, the attritor was stopped. A laser type particle size distribution measuring device was used for measuring the particle size.

(6) Granulation The conditions for granulation were the same as those described in (2). Here, duplicate explanation is avoided.

(7) Molding Next, the granulated powder was put into a die made of cemented carbide of φ30 mm × φ20 mm and shaped into a toroidal shape by applying a pressure of 9.5 t. The weight of the powder used for molding was 7.20 g. In addition, a 20t press was used for molding.

(8) Firing Next, the compact was removed from the mold, placed in a horizontal tubular atmosphere furnace, and fired. Firing is performed at room temperature from 1.6 ° C./min to 500 ° C., from 500 ° C. to 3.2 ° C./min to 1089 ° C., held at 1089 ° C. for 2 hours, and 5.0 ° C./min. It was carried out while controlling with a program that lowered the temperature to room temperature. The obtained core for evaluation was sample No. It was set to 1.

(9) Evaluation method Next, the characteristics of the evaluation core were evaluated. μi was determined using an impedance / gain phase analyzer. The measurement conditions were wire S1-UEW-0-30-NTL, number of turns 20T, f = 10 kHz, 0SC LV = 0.1V. Bs was obtained using a direct current magnetization characteristic automatic recording apparatus. The measurement conditions were wire S1-UEW-0-35-NTL (RED), the number of turns of 8T on the primary side and the secondary side, f = 130 kHz, Bm = 70 to 100 mT. Temperature change rate of mu _a were determined using a DC magnetization characteristic automatic recording apparatus and a thermostat. The measurement conditions in the direct current magnetization characteristic automatic recording apparatus were the wire S1-UEW-0-35-NTL (RED), the number of turns of 8T on the primary side and the secondary side, f = 130 kHz, and Bm = 70 to 100 mT. Moreover, the measurement conditions in a thermostat were -30, 20 and 85 degreeC. Temperature change rate of mu _a is a mu _a at 20 ° C. and mu _a0, a mu _a at -30 ° C. and 85 ° C. as mu _a1, wherein _{Δμ a / μ a = (1} -μ a0 / μ a1) × 100 (Unit:%)

[Example 2]
Manufactured under the same conditions as in Example 1 except that Bi ₂ O ₃ was changed to 600 ppm. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. 2.

[Example 3]
Except that the Bi ₂ O ₃ to 900ppm was prepared under the same conditions as in Example 1. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 3.

[Example 4]
Manufactured under the same conditions as in Example 1 except that Bi ₂ O ₃ was changed to 1200 ppm. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 4.

[Example 5]
Manufactured under the same conditions as in Example 1 except that Bi ₂ O ₃ was changed to 1500 ppm. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 5.

[Example 6]
Manufactured under the same conditions as in Example 1 except that Bi ₂ O ₃ was changed to 1800 ppm. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 6.

  Next, an example (comparative example) for comparison with the example of the present invention will be described.

[Comparative Example 1]
As component ratios in the evaluation core, Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were 48.00 mol%, 18.90 mol%, 8.10 mol% and 25.00 mol%, respectively. In addition, each raw material powder was weighed so that the total weight of the raw material was 3 kg. The CuO substitution rate at this time was 30.00%. Bi ₂ O ₃ fine powder was not added at all. Others were manufactured under the same conditions as in Example 1. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 7.

[Comparative Example 2]
The same as Comparative Example 1 except that the Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were changed to 48.50 mol%, 17.50 mol%, 7.50 mol% and 26.50 mol%, respectively. Manufactured under conditions. The CuO substitution rate at this time was 30.00%. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 8.

[Comparative Example 3]
The same as Comparative Example 1 except that the Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were changed to 48.50 mol%, 18.20 mol%, 7.80 mol% and 25.50 mol%, respectively. Manufactured under conditions. The CuO substitution rate at this time was 30.00%. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 9.

[Comparative Example 4]
Same as Comparative Example 1 except that Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were changed to 48.50 mol%, 18.90 mol%, 8.10 mol% and 24.50 mol%, respectively. Manufactured under conditions. The CuO substitution rate at this time was 30.00%. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 10.

[Comparative Example 5]
As component ratios in the evaluation core, Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were 49.00 mol%, 17.50 mol%, 7.50 mol% and 26.00 mol%, respectively. Except for the above, it was produced under the same conditions as in Comparative Example 1. The CuO substitution rate at this time was 30.00%. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 11.

[Comparative Example 6]
As component ratios in the evaluation core, Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were 49.00 mol%, 18.20 mol%, 7.80 mol% and 25.00 mol%, respectively. Except for the above, it was produced under the same conditions as in Comparative Example 1. The CuO substitution rate at this time was 30.00%. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 12.

[Comparative Example 7]
As component ratios in the evaluation core, Fe ₂ O ₃ fine powder, NiO fine powder, CuO fine powder and ZnO fine powder were 49.00 mol%, 18.90 mol%, 8.10 mol% and 24.00 mol%, respectively. Except for the above, it was produced under the same conditions as in Comparative Example 1. The CuO substitution rate at this time was 30.00%. The evaluation conditions were the same as those in Example 1. The obtained core for evaluation was sample No. It was set to 13.

2. Evaluation Results Table 1 shows the compositions of the evaluation cores obtained in the above Examples and Comparative Examples. Table 2 shows the characteristics of the evaluation cores obtained in the above examples and comparative examples. Further, FIGS. 2 to 9 show the relationship between the temperature change rate of μ _a (Δμ _a / μ _a ) and each composition constituting the evaluation core.

  Based on FIGS. 2 to 5, an appropriate main component composition of the Ni—Zn ferrite will be described.

First, based on FIGS. 2 and 3, looking at the relationship between the _{NiO + CuO = 27.00mol% Fe 2} O 3 content and mu _a rate of temperature change in the case of _{(Δμ a / μ a),} -30 ℃ Write (low temperature) in _Fe 2 _{O 3} content is low, tends temperature change rate of _{μ a (Δμ a / μ a} ) is smaller were observed. Further, at 85 ° C. (high temperature), a tendency that the temperature change rate of μ _a (Δμ _a / μ _a ) was small was observed when the Fe ₂ O ₃ content was around 48.5 mol%. Therefore, sample no. Among 7, 10, and 13, it was found that the evaluation core (sample No. 10) having the Fe ₂ O ₃ content of 48.5 mol% has the best characteristics.

Next, with reference to FIGS. 4 and _5, when viewing the relationship between the Fe ₂ O 3 = 48.5mol% of the time (NiO + CuO) content and mu rate of temperature change _{a (Δμ a / μ a)} , in the range -30 ° C. the (low) (NiO + CuO) content of 26.00~27.00mol%, rate of temperature change _{μ a (Δμ a / μ a} ) tends to decrease was observed. Also, the 85 ° C. (high temperature), (NiO + CuO) rate of temperature change mu _a content of at _{27.00mol% (Δμ a / μ a} ) tends to decrease was observed. Therefore, sample no. Among 8, 9, and 10, it was found that the evaluation core (sample No. 10) having a (NiO + CuO) content of 27.00 mol% has the best characteristics.

Next, based on FIGS. 6 and _7, looking at the relationship between the Fe ₂ O 3 = 49.00mol% of the time (NiO + CuO) content and mu rate of temperature change _{a (Δμ a / μ a)} , -30 ° C. tends in (low temperature) of (NiO + CuO) rate of temperature change as low content _{μ a (Δμ a / μ a} ) decreases were observed. Further, it tended at 85 ° C. (high temperature) of (NiO + CuO) rate of temperature change mu _a content of at _{25.00~26.00mol% (Δμ a / μ a} ) is reduced. However, among sample Nos. 11, 12, and 13, sample no. Temperature change rate also mu _a than 10 (Δμ _a / _{μ a)} becomes greater results.

From the above, as the main component composition of the evaluation core made of Ni—Zn-based ferrite, sample no. 10 compositions, that is, Fe ₂ O ₃ = 48.50 mol%, NiO + CuO = 27.00 mol%, and ZnO = 24.50 mol% were found to be the best.

Next, based on FIG. 8 and FIG. Content of _Bi 2 _{O 3} in the main component composition of 10 and mu rate of temperature change _a Looking at the relationship between ([Delta] [mu _a / mu _a), at -30 ° C. (low temperature), the content of _Bi 2 _{O 3} Yorazu, temperature change rate of _{μ a (Δμ a / μ a} ) low results. On the other hand, at 85 ° C. (high temperature), _Bi 2 _{O 3} than the rated core containing no (Sample No.10), evaluation core containing 300~1800ppm the _Bi 2 _{O 3} (Sample No.1~6 who) is the temperature change rate of _{μ a (Δμ a / μ a} ) low results. From this result, it was found that the characteristics of the evaluation core containing 300 to 1800 ppm of Bi ₂ O ₃ were the best at −30 to 85 ° C. In particular, Sample No. with a low temperature change rate (μμ _a / μ _a ) of μ _a at 90 mT. 2 and 3 (containing 600 ppm and 900 ppm Bi ₂ O ₃ respectively) are preferred.

  The Ni-Zn ferrite composition of the present invention can be used for an antenna coil for keyless entry. In particular, it is suitable as a core material for an antenna coil having good reception sensitivity in a three-dimensional direction. Here, depending on the operating frequency of the antenna coil, a core material having an open magnetic circuit configuration such as a rod shape, a cross shape, or a U shape can be used. It is also possible to use a core material having a path configuration.

  By using a ferrite composition in which the temperature change rate of the amplitude relative permeability at −30 to 85 ° C. is suppressed to a range of −6% to + 6% when an evaluation core having a closed magnetic circuit configuration is used as an evaluation condition, an antenna is obtained. The frequency change rate and current change rate at high and low temperatures required for characteristics can be made flat, and a high-performance keyless entry antenna can be obtained.

  INDUSTRIAL APPLICABILITY The present invention can be used in the industrial field where a core material for an antenna coil is manufactured or used.

It is a flowchart which shows the process which manufactures the Ni-Zn type ferrite composition which concerns on embodiment of this invention. In a comparative example to be compared with the present invention, the Fe ₂ O ₃ content and the temperature change rate of μ _a (Δμ _a / μ) when (NiO + CuO) content = 27.00 mol% under the condition of −30 ° C. (low temperature). It is a graph which shows the relationship with _a ). Comparative Example for comparing with the present invention, under conditions of 85 ° C. (high temperature), (NiO + CuO) content = 27.00mol% _Fe 2 _{O 3} content and mu temperature change rate of the _a when the ([Delta] [mu _a / mu _a ). In the comparative example to be compared with the present invention, the temperature change rate (Δμ _a / μ _a ) of (NiO + CuO) content and μ _a when Fe ₂ O ₃ = 48.50 mol% under the condition of −30 ° C. (low temperature) It is a graph which shows the relationship. Comparative Example for comparing with the present invention, under conditions of 85 ° C. (high _{temperature),} when the Fe ₂ O 3 = 48.50mol% and (NiO + CuO) content and temperature change rate of _{μ a (Δμ a / μ a} ) It is a graph which shows the relationship. In the comparative example compared with the present invention, the temperature change rate (Δμ _a / μ _a ) of (NiO + CuO) content and μ _a when Fe ₂ O ₃ = 49.00 mol% under the condition of −30 ° C. (low temperature). It is a graph which shows the relationship. Comparative Example for comparing with the present invention, under conditions of 85 ° C. (high _{temperature),} when the Fe ₂ O 3 = 49.00mol% and (NiO + CuO) content and temperature change rate of _{μ a (Δμ a / μ a} ) It is a graph which shows the relationship. In an embodiment of the present invention, under the conditions of -30 ° C. (low temperature) is a graph showing the relationship between the content and the mu rate of temperature change _a of _{Bi 2 O 3 (Δμ a /} μ a). For comparison, the temperature change rate (Δμ _a / μ _a ) of μ _a of the evaluation core (sample No. 10) obtained in Comparative Example 4 is also shown. In an embodiment of the present invention, under the conditions of 85 ° C. (high temperature), is a graph showing the relationship between the content and the mu rate of temperature change _a of _{Bi 2 O 3 (Δμ a /} μ a). For comparison, the temperature change rate (Δμ _a / μ _a ) of μ _a of the evaluation core (sample No. 10) obtained in Comparative Example 4 is also shown.

Claims (4)

When an evaluation core having a closed magnetic circuit configuration is used as an evaluation condition including iron oxide (Fe ₂ O ₃ ), nickel oxide (NiO), copper oxide (CuO), and zinc oxide (ZnO), the formula Δμ _a / Temperature change of amplitude relative permeability represented by μ _a = (1−μ _a0 / μ _a1 ) × 100 (where μ _a0 is the amplitude relative permeability at 20 ° C., μ _a1 is the amplitude relative permeability at a predetermined temperature) A Ni—Zn based ferrite composition characterized in that the rate is in the range of −6 to + 6% in a temperature environment of −30 to 85 ° C. Iron oxide (Fe ₂ O ₃ ) 48.2 to 48.8 mol%, nickel oxide (NiO) and copper oxide (CuO) mixture 26.7 to 27.3 mol% (including copper oxide substitution rate 30.0%) ), Zinc oxide (ZnO) as the balance, and 300 to 1800 ppm of bismuth oxide (Bi ₂ O ₃ ) with respect to the total weight of the above components, a Ni—Zn-based ferrite composition.   The Ni-Zn ferrite composition according to claim 2, wherein a content of the bismuth oxide is in a range of 700 to 1300 ppm.   An antenna coil using the Ni-Zn ferrite composition according to claim 1, 2 or 3.

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