Strip-shaped ferrite sheet, cable using the same and manufacturing method for antenna device using the same

Abstract

This invention provides a strip-shaped ferrite sheet, a cable using the same, and a method for manufacturing an antenna device using the same. The strip-shaped ferrite sheet prevents the deterioration of appearance and the decrease in magnetic properties caused by the overlap and gaps between ferrite sintered plates when they are bonded to a substrate. The ferrite sheet 1 includes a substrate 10 and a ferrite sintered plate 20 disposed on the surface of the substrate 10. The ferrite sintered plate 20 extends continuously along the length direction of the substrate 10, and the ferrite sheet 1 has a length of 0.3 m or more in the length direction.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a strip-shaped ferrite sheet, a cable using the same, and an antenna device using the same. Prior Technology

[0002] Previously, IC tags, which include an IC chip and an antenna device electrically connected to the IC chip, were known. These tags utilize electromagnetic waves to non-contactly receive power from a reader / writer and transmit and receive signals with the reader / writer. In recent years, IC tags have been integrated into magnetic cards for use as IC cards in transportation tickets, credit cards, and other similar applications. The antenna device embedded in the IC tag is typically manufactured by winding a wire around a substrate to form a coil, or by printing a coil pattern onto the substrate surface.

[0003] When an antenna device is placed near metal materials such as metal cards, magnetic flux is converted into eddy currents in the metal, which can lead to problems such as shortened communication distance or inability to communicate. Therefore, to prevent such adverse effects, a method of stacking soft magnetic sheets between a conductive loop coil and the metal material is widely used. By stacking soft magnetic sheets, a path can be formed through which magnetic flux can pass, thus improving communication characteristics.

[0004] As a material for the soft magnetic sheet as described above, ferrite can be used, for example (see Patent Documents 1 and 2, etc.). Ferrite sheets used as soft magnetic sheets are usually distributed in the form of rectangular sheets laminated from ferrite sintered plates of about 100 mm × 100 mm. However, from the point of view of ease of operation for users, it is also necessary to form ferrite sheets in the shape of strips (e.g., see Patent Document 3, etc.). Existing technical documents Patent documents

[0005] Patent document: Japanese Patent Application Publication No. 2008-124197 Patent document: Japanese Patent Application Publication No. 2009-113370 Patent document: Japanese Patent Application Publication No. 2009-123771 Summary of the Invention

[0006] -The problem the invention aims to solve-

[0007] From a storage and transportation perspective, it is conceivable to roll elongated ferrite sheets into rolls before use. However, since ferrite sheets are composed of sintered ferrite bodies, they are prone to breakage. Furthermore, the length of the ferrite sheets is limited to approximately less than 300 mm due to the dimensions of the fixtures and firing furnaces used to produce flat ferrite sintered bodies. Therefore, it is difficult to form elongated ferrite sheets and roll them into rolls. As an alternative, it is considered to form elongated ferrite sheets by arranging multiple rectangular ferrite sintered plates of approximately 100 mm × 100 mm along the length of the elongated substrate.

[0008] However, if multiple ferrite sintered sheets overlap, the appearance of the overlapping portion deteriorates, which in turn alters the magnetic properties. To address this issue, gaps are sometimes placed between the multiple ferrite sintered sheets, taking into account fit tolerances. However, when such elongated ferrite sheets are used, for example, in antenna devices or wound in coils on cables, the presence of these gaps leads to deterioration of the ferrite sheet's appearance and may also adversely affect the magnetic properties.

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a strip-shaped ferrite sheet, wherein the ferrite sintered plates do not overlap each other and there are no gaps between the ferrite sintered plates when the ferrite sheet is attached to the substrate. -Solutions for solving the problem-

[0010] To achieve the above objectives, in this invention, the elongated ferrite sheet is not a structure in which multiple ferrite sintered plates are bonded to the surface of a substrate, but rather a structure in which ferrite sintered plates extend continuously along the length direction.

[0011] Specifically, the elongated ferrite sheet of the present invention includes an elongated substrate and a ferrite sintered plate disposed on the surface of the substrate, characterized in that the ferrite sintered plate extends continuously along the length direction of the substrate, and the elongated ferrite sheet has a length of 0.3m or more in the length direction.

[0012] The elongated ferrite sheet of this invention is not formed by bonding multiple ferrite sintered plates together at predetermined intervals as in conventional methods. Instead, it is formed on the surface of a substrate, creating a ferrite sintered plate that extends continuously along the length of the substrate, resulting in a ferrite sheet with a length of 0.3 m or more. Therefore, even with an elongated ferrite sheet, the continuity of the ferrite sintered plate is not compromised, thereby preventing deterioration of the ferrite sheet's appearance and magnetic properties.

[0013] The elongated ferrite sheet of the present invention can be formed as a rolled ferrite sheet. As described above, the elongated ferrite sheet of the present invention has a ferrite sintered plate that extends continuously along the length direction of the substrate. Therefore, even if it is rolled into a roll, the continuity of the ferrite sintered plate will not be damaged, thereby preventing the deterioration of magnetic properties.

[0014] Another object of the present invention is a cable with a noise filter wound around its outer periphery, characterized in that the noise filter comprises any of the above-mentioned elongated ferrite sheets.

[0015] The cable described in this invention uses the aforementioned elongated ferrite sheet as a noise filter, and therefore can be manufactured by directly and continuously winding the ferrite sheet, which makes it easy to manufacture and is preferred.

[0016] The method for manufacturing the antenna device of the present invention is characterized by comprising: a step of arranging a plurality of antenna substrates having a ring coil made of conductive material disposed on the surface of any of the elongated ferrite sheets described in the present invention along the length direction of the elongated ferrite sheet; a step of attaching the plurality of antenna substrates to the elongated ferrite sheet; and a step of cutting the elongated ferrite sheet with the plurality of antenna substrates attached to it to a desired length.

[0017] According to the antenna device manufacturing method of the present invention, since the elongated ferrite sheet described above is used, the antenna device can be manufactured by directly cutting the ferrite sheet with multiple antenna substrates attached, thereby enabling easy and continuous production of the antenna device. -The Effects of the Invention-

[0018] According to the present invention, a strip-shaped ferrite sheet can be obtained in which the ferrite sintered plates do not overlap each other and there are no gaps between the ferrite sintered plates when they are bonded to a substrate. Therefore, it is possible to prevent the deterioration of the appearance and magnetic properties of the ferrite sheet caused by such overlap and gaps. Simple Explanation of the Diagram

[0019] Figure 1 is a top view showing an elongated ferrite sheet according to an embodiment of the present invention. Figure 2 is a side view showing a strip-shaped ferrite sheet wound into a roll according to an embodiment of the present invention, and an enlarged view showing the stacked structure of the ferrite sheet. Implementation

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following description of preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its applicable methods, or its uses.

[0021] First, referring to Figures 1 and 2, an embodiment of the elongated ferrite sheet according to the present invention will be described. As shown in Figures 1 and 2, the ferrite sheet 1 according to an embodiment of the present invention is composed of a substrate 10 and a ferrite sintered plate 20 disposed on the surface of the substrate 10. Adhesive materials 21 and 22, such as double-sided tape, are disposed on the upper and lower surfaces of the ferrite sintered plate 20. The ferrite sintered plate 20 is bonded to the substrate 10 by the adhesive material 21.

[0022] The material of the substrate 10 is not particularly limited; for example, resin materials such as polyethylene terephthalate (PET) and metal materials such as aluminum foil can be used. It should be noted that in Figure 1, the substrate 10 is only disposed on the lower surface, but it can also be disposed on the upper surface and bonded to the adhesive material 22.

[0023] Ferrite sintered plate 20 is obtained by forming a ferrite sintered body into a plate shape. The type of ferrite used is not particularly limited as long as it has magnetic properties. For example, Ni-Zn ferrite, Mn-Zn ferrite, etc. can be used.

[0024] In the ferrite sheet 1 of this embodiment, as described above, a ferrite sintered plate 20 is formed on the surface of the substrate 10. Specifically, the ferrite sintered plate 20 is formed to extend continuously along the length direction of the substrate 10. Therefore, unlike conventional methods, it is not necessary to bond multiple ferrite sintered plates 20 to the substrate 10 with gaps between them, thus preventing damage to the continuity of the ferrite sintered plates 20 and preventing deterioration of the appearance and magnetic properties of the ferrite sheet 1 caused by gaps. Furthermore, the ferrite sheet 1 is elongated and has a length of 0.3 m or more. Conventionally, the dimensions of the fixtures and sintering furnaces used for sintering the ferrite sintered plates 20 make it difficult to manufacture ferrite sintered plates 20 with a length of 0.3 m or more. However, the manufacturing method described later allows for the manufacture of ferrite sintered plates 20 that are continuous without gaps and have a length of 0.3 m or more. Thus, a long strip-shaped ferrite sheet 1 can be obtained, such that when the ferrite sintered plate 20 is attached to the substrate, the ferrite sintered plates 20 do not overlap each other and there are no gaps between them. Here, since the ferrite sheet 1 is a long strip-shaped sheet, it has a shape in both the length and width directions. As long as the length is 0.3m or more, the size is not particularly limited, for example, the length is 0.3m to 100m, and the width is 20mm to 50mm. In addition, the thickness of the ferrite sheet 1 is not particularly limited, but it is preferably 60μm to 300μm.

[0025] In the ferrite sheet 1 of this embodiment, the ferrite sintered plate 20 may have cracks 20a to improve the flexibility of the ferrite sheet 1. Figure 1 shows a plurality of grid-like cracks 20a extending along the longitudinal and transverse directions, but this is not limited to this; irregular cracks may also be present. When the grid-like cracks 20a shown in Figure 1 are provided, for example, a grid-like groove can be pre-formed on at least one of the front and back surfaces of the ferrite sintered plate 20, and then the ferrite sintered plate 20 can be divided with the groove as the starting point to form the cracks 20a. Alternatively, the ferrite sintered plate 20 may be divided into a plurality of small pieces 20b by pressing with rollers or the like without forming grooves. When grooves are formed, the width of the groove opening is generally preferably 250 μm or less, more preferably 1 to 150 μm. If the width of the opening is greater than 250 μm, the change in magnetic permeability of the ferrite sintered plate 20 increases, which is undesirable. Furthermore, the depth of the groove is typically 1 / 20 to 3 / 5 of the thickness of the ferrite sintered plate 20. It should be noted that, in the case of a thin ferrite sintered plate 20 with a thickness of 0.1 mm to 0.2 mm, the depth of the groove is preferably 1 / 20 to 1 / 4, and more preferably 1 / 20 to 1 / 6, of the thickness of the ferrite sintered plate 20. Adjacent ferrite sintered plate pieces 20b are at least partially in contact with each other, separated by cracks 20a.

[0026] In the ferrite sheet 1 of this embodiment, as described above, the ferrite sintered plate 20 is formed to extend continuously along the length direction of the substrate 10. Here, "continuous" means that the ferrite sintered plate 20 extends seamlessly except for the aforementioned crack 20a. That is, the ferrite sintered plate 20 does not include intentionally provided gaps. It should be noted that a gap refers to a gap provided between multiple ferrite sintered plates 20 to prevent the multiple ferrite sintered plates 20 from overlapping, and the width of the gap is greater than 0.1 mm.

[0027] As described above, the ferrite sheet 1 according to this embodiment is characterized in that a ferrite sintered plate 20 extending continuously along the length direction of the substrate 10 is formed on the surface of the substrate 10, and the ferrite sheet 1 has a length of 0.3m or more, so that a long strip ferrite sheet 1 can be obtained without compromising the continuity of the ferrite sintered plate 20.

[0028] The ferrite sheet 1 involved in this embodiment is relatively long, so it can be freely cut to the required length for use. Therefore, unlike rectangular sheets, unnecessary parts are not discarded, and multiple sheets are not joined together due to insufficient length, which would lead to deterioration in appearance or magnetic properties.

[0029] In other embodiments of the present invention, the ferrite sheet 1 is formed as a roll. This allows for the sequential arrangement of multiple antenna substrates followed by individual cutting into antenna devices, facilitating continuous production and enabling easy winding onto cables or similar objects. Furthermore, this is preferable from the viewpoint of storage and transportation.

[0030] Furthermore, the ferrite sheet 1 described in this embodiment can be applied to noise filters wound around the outer periphery of a cable. Conventionally, ferrite sheets are known to be used as noise filters to suppress electromagnetic noise generated by cables. In this embodiment, by winding the elongated ferrite sheet 1 around the outer periphery of the cable, electromagnetic noise generated by the cable can be suppressed. The method of winding the ferrite sheet 1 around the outer periphery of the cable is not particularly limited; from an operational point of view, it is preferable to continuously wind the ferrite sheet 1 in a spiral shape along the axial direction of the cable.

[0031] Furthermore, the ferrite sheet 1 according to this embodiment can be used to manufacture an antenna device. The method for manufacturing the antenna device according to this embodiment is characterized by including: a step of arranging a plurality of antenna substrates, each having a ring coil made of conductive material disposed on its surface along the length direction of the elongated ferrite sheet having the above-described features; a step of attaching the plurality of antenna substrates to the elongated ferrite sheet; and a step of cutting the elongated ferrite sheet with the attached plurality of antenna substrates to a desired length. The method for manufacturing the antenna device according to this embodiment uses an elongated ferrite sheet having the above-described features; therefore, the antenna device can be manufactured by directly cutting the ferrite sheet with the attached plurality of antenna substrates, thereby enabling easy and continuous production of the antenna device.

[0032] Next, the manufacturing method of the ferrite sheet 1 according to this embodiment will be described.

[0033] First, a coating is prepared by mixing 70-120 parts by weight of polyvinyl alcohol resin, 15-25 parts by weight of butyl phthalate (as a plasticizer), and 400-600 parts by weight of solvent, relative to 1000 parts by weight of ferrite powder. As a solvent, ethylene glycol ethers or methyl ethyl ketone (MEK), toluene, methanol, ethanol, n-butanol, etc., can be used. Considering the dispersibility, mixing operability, and drying properties of the ferrite powder, the optimal formulation range for the coating is: relative to 1000 parts by weight of ferrite, 80-110 parts by weight of polyvinyl butyral resin, 18-22 parts by weight of dibutyl phthalate, and 450-550 parts by weight of solvent.

[0034] The coating can be manufactured using, for example, a ball mill, but is not limited to. First, the solvent and ferrite are filled and mixed, then the resin and plasticizer are added and mixed again to obtain a homogeneous coating. During the coating and drying process, it is important to thoroughly depressurize and defoam in a vacuum chamber to prevent cracking of the coating film.

[0035] There are no particular limitations on the coating method for ferrite dispersion coatings; roller coaters and blade coaters can be used. However, blade coaters are preferred for achieving the desired film thickness accuracy and coating stability. Applying the desired thickness to a plastic film using a blade coater and drying at 80–130°C for 30–60 minutes yields a green sheet.

[0036] There are no particular limitations on the plastic film used for coating ferrite dispersion coatings; various films such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and polyimide can be used, preferably obtained through sandblasting. Considering the processability of the film surface and its thermal stability during coating and drying, polyethylene terephthalate (PET) film is more suitable. By using sandblasted plastic film, the texture of the plastic film can be transferred onto the green sheet, thereby obtaining a green sheet with the desired surface roughness.

[0037] Next, the obtained green sheet is fired to obtain a ferrite sintered plate 20. The green sheet peeled from the plastic film is wound into a roll and fired. It should be noted that the size of the rolled green sheet is not particularly limited as long as it can be accommodated in the firing furnace. In the firing conditions, it is important to set up a process for removing resin components and growing ferrite particles using an electric furnace or the like. Resin removal is carried out at 150°C to 550°C for 5 to 80 hours, and ferrite particle growth is carried out at 850°C to 1200°C for 1 to 5 hours. To prevent the sheet from deforming and cracking due to heating, it is best to remove the resin components by raising the temperature at about 10 to 20°C / hour from room temperature and then maintaining a certain temperature. Then, it is best to raise the temperature at 30 to 60°C / hour and maintain a certain temperature for thorough sintering, allowing the ferrite particles to grow, and then slowly cooling. The ferrite sintered plate 20 is obtained through the above process. Using the above method, it is possible to obtain long strip ferrite sintered plates 20 with a length of 0.3m or more without being limited by the size of the fixtures and sintering furnaces used to make the ferrite sintered plates 20.

[0038] Then, the ferrite sintered plate 20, which has been sintered in a roll, is stretched into a long strip and bonded to the substrate 10 by an adhesive material 21 to obtain a long strip ferrite sheet 1. It should be noted that the substrate 10 can also be disposed on the upper surface and bonded to the adhesive material 22. In addition, the obtained long strip ferrite sheet 1 can be further processed into a roll.

[0039] It should be noted that, as described above, the ferrite sintered plate 20 can be divided into small pieces. To divide the ferrite sintered body into small pieces, for example, stress can be applied to the ferrite sheets made from the ferrite sintered plate supported by the substrate using rollers to divide the ferrite sintered body. Additionally, predetermined grooves can be formed during the green sheet stage. The grooves can be continuous or discontinuous, or multiple tiny recesses can be formed instead of grooves. The sintered body is divided into triangles, quadrilaterals, polygons, or combinations thereof of arbitrary sizes by the pre-formed grooves. Alternatively, grooves can be omitted, and the pieces can be divided into irregular shapes.

[0040] Therefore, in the manufacturing method of the elongated ferrite sheet according to this embodiment, since the green sheet containing ferrite material is wound into a roll and then fired, instead of bonding multiple ferrite sintered plates with a specified gap to form an elongated shape as in the past, a ferrite sintered plate that extends continuously along the length direction of the substrate can be formed on the surface of the substrate, resulting in an elongated ferrite sheet with a length of 0.3 m or more.

[0041] As described above, the elongated ferrite sheet according to the present invention can obtain an elongated ferrite sheet in which the ferrite sintered plates do not overlap each other and there are no gaps between the ferrite sintered plates when they are bonded to a substrate. It can be used in antenna devices, cables, etc. without reducing their characteristics, and is extremely useful.

[0042] 1: Ferrite sheet 10: Substrate 20: Ferrite sintered plate 20a: Crack 20b: Small film 21, 22: Adhesive materials

Claims

1. A strip-shaped ferrite sheet, comprising a strip-shaped substrate and a ferrite sintered plate disposed on the surface of the substrate, characterized in that: the ferrite sintered plate extends continuously along the length direction of the substrate and is divided into a plurality of small pieces; adjacent small pieces are sandwiched with cracks and at least partially in contact with each other; the strip-shaped ferrite sheet has a length of 0.3 m or more in the length direction.

2. As in request item 1, the elongated ferrite sheet, wherein, The long strip of ferrite sheet is formed into a roll.

3. A cable having a noise filter wound around its outer periphery, characterized in that the noise filter comprises an elongated ferrite sheet as claimed in claim 1 or 2.

4. A method for manufacturing an antenna device, characterized in that the method comprises: The steps include: arranging multiple antenna substrates with a ring coil made of conductive material on the surface of the long strip ferrite sheet along the length direction of the long strip ferrite sheet; attaching the multiple antenna substrates to the long strip ferrite sheet; and cutting the long strip ferrite sheet with the attached multiple antenna substrates to the required length.

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