JP4752849B2 - Manufacturing method of sintered ferrite - Google Patents

Description

  The present invention relates to a ferrite fired body that is used to ensure a good communication function and is mounted on a portable terminal having a reader / writer exchange spiral antenna, and a method for manufacturing the same.

  A 13.56 MHz band RFID system (IC tag, wireless communication using an IC card) consisting of a reader / writer communication spiral antenna is applied to a convenience store specification electronic money card as a structure in which an IC tag is incorporated into a thin resin card. ing. As a next development, efforts to mount a 13.56 MHz band RFID system on mobile terminals that have become explosively popular in recent years have become full-scale.

  The 13.56 MHz band RFID system performs power supply and communication by electromagnetic induction generated between spiral antennas provided in both the reader / writer and the wireless tag.

  However, various studies have been made to mount the 13.56 MHz band RFID system on a mobile terminal, but unlike a case where it is incorporated into a thin resin card, a housing located near the communication spiral antenna of the mobile terminal. The communication function was significantly impaired by the metal surface of the body cell. That is, when the magnetic flux generated in the spiral antenna penetrates the metal surface, eddy current centering on the magnetic flux flows through the metal surface according to Faraday's law, but the direction of rotation flows in the direction opposite to the direction of the current flowing through the spiral antenna. . That is, since the magnetic flux generated in the spiral antenna is canceled by the magnetic flux in the opposite direction due to the eddy current generated on the metal surface, the communication function of the RFID system is greatly attenuated. Therefore, in order to prevent such a situation, a magnetic material having permeability such as ferrite is applied. That is, by inserting a magnetic material having a magnetic permeability between the spiral antenna and the metal surface of the housing cell, the magnetic material focuses the magnetic flux before the magnetic flux generated in the spiral antenna penetrates the metal surface. This suppresses the generation of eddy currents on the metal surface.

  For example, Patent Document 1 discloses a specific contact type IC card reader / writer in which a flexible magnetic material is disposed between a reader / writer and a metal surface. According to this, in order to suppress the above problems caused by the metal surface, a flexible magnetic material is applied to ensure stable reading and writing of the IC card reader / writer.

(Patent Document 2) discloses a ferrite powder containing SiO2 in a Ni-Zn ferrite powder composed of Fe2O3, NiO, and ZnO, and firing the ferrite powder at 1100 to 1300 ° C. An example of applying the body to an inductance element is described.
JP 2002-298095 A JP 2007-145703 A

  However, in the RFID system using the above-described conventional magnetic material, the communication function greatly fluctuates depending on the manufacturing conditions of the magnetic material, its structure, and the fine structure.

  For example, a flexible sheet-like magnetic body disclosed in (Patent Document 1) is a ferrite composite in which a soft magnetic powder is kneaded with an organic binder to form a sheet. Since the magnetic structure becomes a fine structure in which soft magnetic powder is dispersed in the matrix, high magnetic permeability cannot be obtained. When the flexible sheet-like magnetic material is applied to an RFID system for a mobile terminal, the magnetic flux generated in the spiral antenna is reduced. There was a concern that the focusing effect was not sufficient and a good communication function could not be obtained.

Moreover, the ferrite fired body disclosed in (Patent Document 2) is obtained by converting a Ni—Zn-based ferrite powder composed of Fe ₂ O ₃ , NiO, and ZnO into SiO ₂ and then forming a green sheet. It is fired at ˜1300 ° C. and becomes a high magnetic permeability fired body having a fine microstructure in which the sintering progresses with the addition of SiO ₂ and a high firing temperature and the crystal grains grow greatly. When applied to the RFID system for terminals, high magnetic permeability is obtained due to the dense microstructure due to excessively grown crystal particles, but the conductivity increases in the high frequency band of 13.56 MHz, and the magnetic flux generated in the spiral antenna. As a result, there is a possibility that a sufficient communication function cannot be obtained.

  As described above, in the conventional technology, when the ferrite sintered body and the ferrite composite are applied to the RFID system for the portable terminal, the relationship between the fine structure of the sintered body and the composite, the manufacturing conditions, and the communication function has not been grasped in detail. . That is, in an RFID system configured by inserting a ferrite sintered body between the spiral antenna and the metal surface of the mobile terminal housing cell, the microstructure of the ferrite sintered body that exhibits the maximum communication function and the manufacturing conditions thereof It was not established.

  Then, this invention solves the above subjects, In the RFID system for portable terminals which inserted the ferrite sintered body between the reader / writer exchange spiral antenna and the metal surface of the portable terminal housing cell, An object of the present invention is to provide a ferrite fired body that exhibits a good communication function and a method for producing the same.

In order to achieve this object, the method for producing a sintered body of ferrite according to the present invention comprises 46.0 to 50.0 mol% Fe2O3 , 18.0 to 22.0 mol% produced at a synthesis temperature of 880 degrees. A Ni-Zn ferrite powder containing NiO, 18.0 to 22.0 mol% ZnO and 8.0 to 12.0 mol% CuO is mixed with a resin, a plasticizer and an organic solvent to produce a slurry. A step of coating the slurry on a film to produce a raw sheet, a step of laminating the raw sheet to produce a laminate, and the laminate was cut into predetermined dimensions. Thereafter, a step of firing at a firing temperature of 890 ° C. to 930 ° C. to produce a ferrite sintered body is sequentially performed.

  As described above, according to the present invention, a ferrite fired body having a high magnetic flux focusing effect and a method for manufacturing the same are provided. The ferrite fired body is used as a metal for a reader / writer communication spiral antenna and a mobile terminal housing cell. An RFID system for a portable terminal having a good communication function can be realized by inserting it between the two surfaces.

According to invention of Claim 1, 46.0-50.0 mol% Fe2O3, 18.0-22.0 mol% NiO, 18.0-22. Mixing a Ni—Zn ferrite powder containing 0 mol% ZnO and 8.0 to 12.0 mol% CuO together with a resin, a plasticizer and an organic solvent to produce a slurry; A process for producing a raw sheet by coating on the surface, a process for producing a laminate by laminating the raw sheets, and a firing temperature of 890 to 930 degrees after the laminate is cut to a predetermined size The RFID system for portable terminals having a good communication function can be realized by sequentially performing the process of firing the ferrite and producing the sintered ferrite body.

Further, since the synthesis temperature is 880 ° C., an RFID system for portable terminals having a good communication function can be realized.

Further, in a portable terminal having a reader / writer communication spiral antenna, a ferrite fired body inserted between the reader / writer communication spiral antenna and the metal surface of the portable terminal housing cell, the Ni— By having a fine structure in which Zn-based ferrite crystal particles are three-dimensionally connected via a neck portion, an RFID system for a portable terminal having a good communication function can be realized.

Example 1
Hereinafter, embodiments of the present invention will be described with reference to the drawings with specific examples.

  FIG. 1 is a microstructure diagram of a sintered ferrite body with respect to the firing temperature. In addition, the ferrite powder used for manufacture of the ferrite sintered body of a present Example is the Ni-Zn type ferrite powder synthesize | combined at the temperature of 880 degreeC. In FIG. 1, the microstructure of the sintered ferrite body of the present invention is fired at a firing temperature of 890 to 930 ° C., and 1 to 5 μm Ni—Zn-based ferrite crystal particles are three-dimensionally arranged through the neck portion. It had a connected microstructure. On the other hand, the sintered ferrite body fired at 880 ° C. whose firing temperature is less than 890 ° C. has a fine structure in which neck formation and grain growth are not observed between the ferrite crystal particles, and sintering is hardly progressed. It was. The sintered ferrite body having this microstructure has a low magnetic permeability and a low mechanical strength. Therefore, a sufficient communication function cannot be obtained in the RF-ID system, and defects such as cracks and chipping occur in the sintered ferrite body in the manufacturing assembly process. On the other hand, when the firing temperature is 940 ° C. or more, as is apparent from the microstructure of FIG. 1, it has a microstructure in which the growth of the ferrite crystal particle neck and ferrite crystal particles proceeds simultaneously with the generation of the liquid phase, Abnormal grain growth was observed in the fired body fired at 1000 ° C. Although the ferrite sintered body having such a fine structure has high permeability, the conductivity in the high frequency band is increased, so that a sufficient magnetic flux focusing effect cannot be obtained, and the communication function in the RF-ID system is defective. Predicted to do. That is, the fine structure that can obtain the best communication function in the RF-ID system is a sintered body of 890 to 930 ° C. in FIG.

  FIG. 2 is a schematic diagram of the microstructure of the sintered ferrite body of the present invention. As shown in FIG. 2, Ni—Zn ferrite crystal particles 21 having a particle diameter average particle diameter of 1 to 5 μm are connected via a neck portion 22.

FIG. 3 is a manufacturing process diagram of a sintered ferrite body. A Ni—Zn ferrite powder synthesized by heating a composition composed of Fe ₂ O ₃ , NiO, ZnO and CuO at a predetermined synthesis temperature T1 is used as a resin, plastic Mixing with an agent and an organic solvent to produce a slurry, forming the slurry on a PET film to produce a green sheet, laminating the green sheet to produce a laminate, The laminated body is cut into predetermined dimensions and then fired at a predetermined firing temperature T2 to sequentially produce a ferrite fired body. The fine structure of the sintered ferrite body of the present invention is obtained by satisfying the relationship of T1 <T2 and 10 ≦ | T2−T1 | ≦ 50 in the relationship between T1 and T2.

  Next, a specific method for producing the sintered ferrite body of the present invention will be described.

46.0 to 50.0 mol% of Fe ₂ O _3, 18.0~22.0 mol% of NiO, from 18.0 to 22.0 mol% of CuO of ZnO and 8.0 to 12.0 mol% The composition was heat-treated with a rotary kiln at a temperature of 880 ° C., and then pulverized with a dry rod mill and a wet attraction mill to synthesize a Ni—Zn ferrite powder having an average particle size of 0.5 to 1.5 μm. . As a powder characteristic of the synthesized Ni—Zn-based ferrite powder, a specific surface area value measured by a nitrogen gas adsorption method was found to be 3.000 to 5.500 m ² / g.

  In the next slurry preparation step, a slurry suitable for the average particle diameter and specific surface area value of the Ni-Zn ferrite powder was prepared. That is, 4.0 to 6.5 parts by weight of polyvinyl butyral resin, 3.5 to 6.0 parts by weight of phthalate ester plasticizer, and organic solvent with respect to 100 parts by weight of Ni—Zn ferrite powder. Was mixed at a ratio of 40 to 60 parts by weight, and then mixed with a dedicated mill to prepare a slurry containing Ni-Zn ferrite powder. The viscosity of the produced slurry was 1500 to 2000 Pa · sec at 20 ° C., and had an appropriate viscosity for sheet molding.

  In the next green sheet production process, the slurry was formed on a PET film to produce a green sheet containing Ni-Zn ferrite powder having a predetermined thickness. That is, while supplying the slurry with adjusted viscosity to the coating machine, the gap and line speed were adjusted to form a film on a PET film, dried, and then rolled up to produce a green sheet. The thickness of the produced green sheet was controlled within a range of 50 to 200 μm. Moreover, the drying temperature which affects the lamination | stacking adhesiveness of a green sheet was adjusted to 70-90 degreeC. The line speed needs to be adjusted according to the thickness of the green sheet to be produced, and was controlled within the range of 0.5 to 2.0 m / min.

  In the next laminate manufacturing step, green sheets containing Ni—Zn ferrite were laminated in a predetermined number of layers using a laminator. That is, the green sheet formed on the PET film was laminated in 2 to 6 layers by heating roller pressure bonding of a laminating machine to produce a laminate having a predetermined thickness. The surface temperature of the heating roller was controlled to 100 to 120 ° C., which is higher than the glass transition temperature of the polyvinyl butyral resin, to ensure good lamination adhesion.

  In the next cutting step, the stacked green sheets were cut into a predetermined shape. That is, a green body having a predetermined shape and thickness was produced by punching and cutting the laminated green sheets using a special mold designed to obtain a predetermined shape suitable for the communication spiral antenna. Since the green sheet has good lamination adhesion, problems such as delamination did not occur in this process.

  In the next degreasing and firing step, the compact was filled with a sheath and then degreased and fired to produce a sintered ferrite body. That is, after compacting a molded body having a predetermined thickness and shape onto an alumina thin plate, before burning the Ni-Zn ferrite powder, the polyvinyl butyral resin and the phthalate ester plasticizer are burned. Degreasing was performed. The degreasing conditions were 350 to 500 ° C., and the degreasing conditions were performed using a tunnel-type firing furnace, a belt-type firing furnace, and a box-type firing furnace. And after degreasing, it baked within the range of 890-930 degreeC with the baking furnace, and produced the ferrite sintered compact. The fracture surface of the obtained ferrite fired body was observed with a scanning electron microscope at a magnification of 5000 times to photograph the fine structure. As a result, the ferrite fired body of the present invention was fired at a firing temperature range of 890 to 930 ° C. shown in FIG. 1, and the fine structure had an average particle diameter as shown in the schematic diagram of FIG. 1 to 5 μm Ni—Zn ferrite crystal grains 21 had a fine structure in which they were three-dimensionally connected via the neck portion 22.

  The ferrite fired body described above is mainly applied to obtain a good communication function of a mobile terminal, and FIG. 4 is a cross-sectional perspective view of the mobile terminal to which the ferrite fired body is applied. According to this, the ferrite sintered body 44 is inserted between the portable terminal housing cell 42 and the communication spiral antenna 43.

  FIG. 5 is a schematic diagram of an RF-ID system, and FIG. 6 is a schematic diagram of an RF-ID system equipped with a sintered ferrite body. The RF-ID system of FIG. 5 includes a mobile terminal housing cell 51 and a communication spiral antenna 52. In the RF-ID system of FIG. The communication function is greatly attenuated by being canceled by the magnetic flux 54 in the opposite direction due to the eddy current generated on the metal surface 51. On the other hand, in the RF-ID system of FIG. 6, a sintered ferrite body 64 is inserted between the reader / writer communication spiral antenna 62 and the metal surface of the mobile terminal housing cell 61. As a result, the magnetic flux 63 entering the communication spiral antenna 62 is focused by the ferrite fired body 64, and the eddy current on the metal surface of the mobile terminal housing cell 61 is suppressed. The RF-ID system for a portable terminal of the present invention is obtained by changing the fine structure of the sintered ferrite body 64 to the fine structure of the sintered body of 890 to 930 ° C. in FIG. Are three-dimensionally connected via a neck portion. Thereby, the best communication function can be obtained. On the other hand, when the ferrite sintered body 64 has a fine structure of the sintered body at 880 ° C. and the sintered body at 940 ° C. or higher in FIG. 1, the communication function is deteriorated.

  Next, measurement of the communication function with a configuration similar to that of FIG. 4 will be described. That is, the communication function of the RF-ID system for mobile terminals in which the sintered ferrite body was inserted between the reader / writer communication spiral antenna 62 shown in FIG. 6 and the metal surface of the mobile terminal housing cell 61 was measured. Here, as a measurement item as a communication function, a communication distance between the tag and the reader / writer is set.

  Based on the method described in Example 1, starting from Ni—Zn-based ferrite powder synthesized at a temperature of 880 ° C., each ferrite fired body fired at a firing temperature of 880 to 1000 ° C. was produced. A tape was affixed to both sides of each of the produced ferrite fired bodies to prepare a sample for measuring communication functions. The sample dimensions were 30 mm × 25 mm and the thickness was 120 μm. A ferrite sintered body sample inserted between a copper plate of the same size as the measurement sample and a spiral antenna was set as a tag, and the communication distance with the reader / writer at a resonance frequency of 13.56 MHz was measured.

  FIG. 7 is a communication distance diagram of an RF-ID system equipped with a sintered ferrite body. According to this, in the fired body fired at 890 to 930 ° C. in which the microstructure of the present invention is obtained, the communication distance at the resonance frequency of 13.56 MHz was the best. On the other hand, the communication distance decreased in the fired body fired at 880 ° C. and the fired body fired at 940 ° C. or higher. This can be considered as follows.

  That is, the fired body fired at 880 ° C. is in a state where the individual crystal particles are isolated without being connected because sufficient sintering has not progressed. Accordingly, it can be considered that the communication distance is deteriorated because sufficient magnetic permeability as a magnetic material cannot be obtained and the focusing effect of the magnetic flux entering from the reader / writer side is not sufficient. Further, in the fine structure of the fired body fired at 940 ° C. or higher, the growth of the neck portion between the crystal grains and the abnormal growth of the crystal grains occurred simultaneously with the generation of the liquid phase. Accordingly, although the magnetic permeability is increased, it is considered that the communication distance is deteriorated because the conductivity of the surface of the fired body in the high frequency band of 13.56 MHz is increased and the focusing effect of the magnetic flux is reduced. On the other hand, the fired body fired at 890 to 930 ° C. has a fine structure in which 1 to 5 μm Ni—Zn ferrite crystal particles are three-dimensionally connected via the neck portion, at 880 ° C. The best communication distance was obtained because there was no decrease in magnetic permeability as in the fired fired body, and there was no decrease in the magnetic flux focusing effect due to the increase in conductivity as in the fired body fired at 940 ° C or higher. it is conceivable that.

  As described above, the RF-ID system for a portable terminal of this example has a fine structure in which 1 to 5 μm Ni—Zn ferrite crystal particles are three-dimensionally connected via a neck portion. By applying, a good communication function is acquired.

  As described above, the ferrite fired body of the present invention has a relationship of T1 <T2 and 10 ≦ | in the relationship between the synthesis temperature T1 of the Ni—Zn ferrite powder and the firing temperature T2 of the compact containing the Ni—Zn ferrite powder. Since it is produced by a manufacturing method characterized by T2-T1 | ≦ 50, it has a fine structure in which 1 to 5 μm ferrite crystal particles are three-dimensionally connected via a neck portion. It is. Thereby, the RFID system for mobile terminals having excellent communication characteristics can be realized by inserting the sintered ferrite body of the present invention between the reader / writer communication spiral antenna and the metal surface of the mobile terminal housing cell.

  The ferrite sintered body and the method for manufacturing the same of the present invention can be used for communication terminals having a reader / writer communication spiral antenna, particularly portable terminals, because a good communication distance can be secured.

Fine structure diagram of ferrite sintered body with respect to firing temperature Schematic diagram of microstructure of sintered ferrite body of the present invention Manufacturing process diagram of sintered ferrite Cross-sectional perspective view of a portable terminal to which a ferrite sintered body is applied Schematic diagram of RF-ID system Schematic diagram of an RF-ID system with a sintered ferrite body Communication distance diagram of RF-ID system equipped with sintered ferrite

Explanation of symbols

21 Ni-Zn ferrite crystal particles 22 Neck portion 41 Mobile terminal 42 Mobile terminal housing cell 43 Communication spiral antenna 44, 64 Ferrite sintered body 51, 61 Mobile terminal housing cell 52 Communication spiral antenna 53, 63 Communication spiral Magnetic flux entering antenna 54 Magnetic flux in opposite direction due to eddy current 62 Reader / writer exchange spiral antenna

Claims (1)

46.0-50.0 mol% Fe2O3, 18.0-22.0 mol% NiO, 18.0-22.0 mol% ZnO and 8.0 produced at a synthesis temperature of 880 degrees A step of preparing a slurry by mixing Ni-Zn ferrite powder containing 12.0 mol% CuO together with a resin, a plasticizer and an organic solvent, and coating the slurry on a film to prepare a raw sheet A step of producing a laminate by laminating the raw sheets, and firing the laminate at a firing temperature of 890 to 930 degrees to produce a ferrite fired body. And a step of sequentially performing the steps.