Magnetic shielding sheet and communication cable equipped with the same

Abstract

To provide a magnetic shield sheet having sufficient flexibility and a high shielding characteristic.SOLUTION: A magnetic shield sheet 1 includes a copper foil 10 having flexibility and permalloy layers 21 and 22 formed on both surfaces of the copper foil, and total thickness T21+T22 of the permalloy layers 21 and 22 is thinner than thickness T10 of the copper foil 10. Like this, since the magnetic shield sheet has a configuration in which both surfaces of the copper foil 10 are covered with the permalloy layers 21 and 22, electromagnetic wave noise is absorbed by the permalloy layers 21 and 22, a component that has not been absorbed can be reflected by the copper foil 10, and a high shielding characteristic can be obtained. Moreover, since the thickness of the hard permalloy layers 21 and 22 is thinner than that of the copper foil 10, sufficient flexibility can be secured as a whole.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetic shielding sheet, and more particularly to a flexible magnetic shielding sheet. The present invention also relates to a communication cable around which such a magnetic shielding sheet is wound.

Background Art

[0002] Patent Document 1 discloses a magnetic shielding sheet for shielding electromagnetic wave noise by winding it around a communication cable. The magnetic shielding sheet described in Patent Document 1 is composed of a main body made of permalloy with a thickness of about 10 μm and copper plating formed on both sides thereof. By combining permalloy and copper in this way, it becomes possible to shield electromagnetic wave noise in a wide frequency band.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the outermost layer of the magnetic shielding sheet described in Patent Document 1 is composed of copper plating, most of the electromagnetic waves are reflected by the copper plating, and there is a problem that the electromagnetic waves reaching the permalloy layer are reduced.

[0005] Therefore, an object of the present invention is to provide an improved magnetic shielding sheet composed of a combination of copper and permalloy and a communication cable provided with the same.

Means for Solving the Problems

[0006] The magnetic shielding sheet according to the present invention includes a flexible copper foil and permalloy layers formed on both sides of the copper foil, and is characterized in that the total thickness of the permalloy layers is thinner than that of the copper foil.

[0007] According to the present invention, since both sides of the copper foil are covered with permalloy layers, it is possible to absorb electromagnetic wave noise by the permalloy layers and reflect the components that have not been absorbed by the copper foil, thereby obtaining high shielding characteristics. Moreover, since the thickness of the hard permalloy layer is thinner than that of the copper foil, it is possible to ensure sufficient flexibility as a whole.

[0008] In the present invention, the thickness of the copper foil may be more than 25 μm and less than 100 μm. According to this, it is possible to enhance the shielding characteristics particularly in the high-frequency region while ensuring sufficient flexibility.

[0009] In the present invention, the total thickness of the permalloy layers may be more than 8 μm and less than 25 μm, or may be more than 10 μm and less than 20 μm. If the thickness of the permalloy layer is set within this range, it is possible to enhance the shielding characteristics particularly in the low-frequency region while ensuring sufficient flexibility. In this case, the thickness of the copper foil may be 2 times or more and 3 times or less the total thickness of the permalloy layers. According to this, it is possible to optimally balance the shielding characteristics, flexibility, and overall thickness.

[0010] In the present invention, the entire outer periphery of a predetermined cross-section of the copper foil may be covered with a permalloy layer. According to this, since the exposed surface of the copper foil is reduced, it is possible to further enhance the shielding characteristics.

[0011] The magnetic shielding sheet according to the present invention may further include an adhesive layer covering the permalloy layer and a release film covering the adhesive layer. According to this, the work of attaching or winding around an object becomes easy.

[0012] The magnetic shield sheet according to the present invention may have flexibility that allows it to be wound around a communication cable main body with an outer diameter of 10 mm or less. According to this, by winding it around a communication cable main body with an outer diameter of 10 mm or less, it becomes possible to provide a communication cable shielded from electromagnetic waves.

Effects of the Invention

[0013] Thus, according to the present invention, it becomes possible to provide a magnetic shield sheet having sufficient flexibility and high shielding characteristics, and a communication cable provided with the same.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

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Figure 6

Figure 7

Modes for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0016] FIG. 1 is a schematic cross-sectional view for explaining the configuration of a magnetic shield sheet 1 according to the first embodiment of the present invention.

[0017] As shown in Fig. 1, the magnetic shield sheet 1 according to this embodiment includes a flexible copper foil 10, a permalloy layer 21 formed on one main surface 11 of the copper foil 10, and a permalloy layer 22 formed on the other main surface 12 of the copper foil 10. The surfaces of the permalloy layers 21 and 22 may be subjected to rust prevention treatment. The thickness of the copper foil 10 is T10, and the thicknesses of the permalloy layers 21 and 22 are T21 and T22 respectively. Although not particularly limited, the thickness T21 of the permalloy layer 21 and the thickness T22 of the permalloy layer 22 are the same.

[0018] The copper foil 10 is a support for ensuring the mechanical strength of the magnetic shield sheet 1, and mainly serves to reflect the high-frequency components of electromagnetic wave noise. Although the specific thickness T10 of the copper foil 10 is not particularly limited, it is necessary to have a thickness that can sufficiently ensure the shielding characteristics in the high-frequency region and a thinness that can ensure flexibility for pasting along a curved surface. Specifically, it is preferably more than 25 μm and less than 100 μm. This is because when the thickness T10 of the copper foil 10 is 25 μm or less, the shielding characteristics in the high-frequency region may be insufficient, while when the thickness T10 of the copper foil 10 is 100 μm or more, it becomes difficult to paste along a surface with a large curvature (small radius of curvature).

[0019] The permalloy layers 21 and 22 are made of a NiFe alloy having a composition with a permeability μ of 1000 or more, for example, PC permalloy with a Ni content of about 76%. Other metal elements such as Mo, Co, Cu, and Cr may be added to the permalloy layers 21 and 22. The permalloy layers 21 and 22 convert electromagnetic wave noise into heat by collecting magnetic flux, and mainly serve to absorb the low-frequency components of electromagnetic wave noise.

[0020] Although the specific thicknesses T21 and T22 of the permalloy layers 21 and 22 are not particularly limited, at least the total thickness needs to be thinner than the thickness T10 of the copper foil 10. That is, T10>T21+T22 ···(1) It is necessary to satisfy this. Specifically, the total thickness T21 + T22 of the permalloy layers 21 and 22 is preferably more than 8 μm and less than 25 μm, and more preferably more than 10 μm and less than 20 μm. This is because when the total thickness T21 + T22 is 8 μm or less, the shielding characteristics in the low-frequency region may be insufficient, and by setting the total thickness T21 + T22 to more than 10 μm, high shielding characteristics can be obtained in the low-frequency region. Also, since permalloy is harder than Cu (Vickers hardness of Cu HV = 50, Vickers hardness of permalloy HV = 200), when the total thickness T21 + T22 is 25 μm or more, there is a risk of insufficient flexibility, and by setting the total thickness T21 + T22 to less than 20 μm, high flexibility can be obtained. In addition, since the material cost of permalloy is about 10 times that of Cu, when the total thickness T21 + T22 of the permalloy layers 21 and 22 is 25 μm or more, the material cost increases and the corrosion resistance also decreases.

[0021] As described above, the relationship between the thickness T10 of the copper foil 10 and the total thickness T21 + T22 of the permalloy layers 21 and 22 is not particularly limited as long as the formula (1) is satisfied, but the thickness T10 of the copper foil 10 is preferably 2 times or more and 3 times or less the total thickness T21 + T22 of the permalloy layers 21 and 22. According to this, it becomes possible to obtain high shielding characteristics in a wide frequency band while ensuring sufficient flexibility. Moreover, since the overall thickness does not become too thick, for example, when used by winding around a communication cable, it becomes possible to minimize the increase in the outer diameter of the communication cable. As an example, if T10 is about 35 μm and T21 + T22 is about 15 μm, it becomes possible to optimally balance the shielding characteristics, flexibility, and overall thickness.

[0022] The permalloy layers 21 and 22 can be formed by electrodepositing permalloy on both sides of the copper foil 10 by the roll-to-roll method. FIG. 2 shows a first configuration example of the magnetic shield sheet 1, and shows an example in which the permalloy layers 21 and 22 are formed only on the main surfaces of the copper foil 10 constituting the xy plane. No permalloy layer is formed on the yz plane or xz plane of the copper foil 10. The magnetic shield sheet 1 having such a configuration can be manufactured by electrodepositing permalloy on both sides of the copper foil 10 and then cutting it to a predetermined size. FIG. 3 shows a second configuration example of the magnetic shield sheet 1, and shows an example in which a permalloy layer 23 is also formed on the side surface of the copper foil 10 constituting the yz plane. No permalloy layer is formed on the xz plane of the copper foil 10. The magnetic shield sheet 1 having such a configuration can be manufactured by electrodepositing permalloy on both sides of the copper foil 10 with the y direction as the longitudinal direction and then cutting it so that the length in the y direction becomes a predetermined length. According to the example shown in FIG. 3, since the entire outer periphery of the xz cross section of the copper foil 10 is covered with the permalloy layers 21 to 23, higher shielding characteristics can be obtained. FIG. 4 shows a third configuration example of the magnetic shield sheet 1, and shows an example in which a permalloy layer 24 is also formed on the side surface of the copper foil 10 constituting the xz plane. According to the example shown in FIG. 4, since the entire outer periphery of an arbitrary cross section of the copper foil 10 is covered with the permalloy layers 21 to 24, even higher shielding characteristics can be obtained.

[0023] FIG. 5 is a schematic cross-sectional view for explaining the configuration of the magnetic shield sheet 2 according to the second embodiment of the present invention.

[0024] As shown in FIG. 5, the magnetic shield sheet 2 according to the present embodiment is different from the magnetic shield sheet 1 according to the first embodiment in that it further includes an adhesive layer 30 that covers the permalloy layer 22 and a release film 40 that covers the adhesive layer 30. Since the other basic configurations are the same as those of the magnetic shield sheet 1 according to the first embodiment, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0025] The adhesive layer 30 has an inner surface 31 adhered to the permalloy layer 22 and an outer surface 32 covered with the release film 40. Both the inner surface 31 and the outer surface 32 have adhesiveness, but since the adhesive force to the release film 40 is weak, the release film 40 can be peeled off. Thereby, after peeling the release film 40 from the adhesive layer 30, it becomes possible to attach the magnetic shield sheet 2 to the surface of the object through the adhesive layer 30.

[0026] FIG. 6 is a schematic diagram of the communication cable 3 configured by winding the magnetic shield sheet 2 around the communication cable body 50. The communication cable body 50 includes a core material 51 and an insulating coating 52 that covers the periphery of the core material 51. The magnetic shield sheet 2 is spirally attached to the outer periphery of the insulating coating 52, thereby shielding electromagnetic wave noise. When the magnetic shield sheet 2 is wound around the communication cable body 50, if the outer diameter φ of the communication cable body 50 is, for example, 10 mm or less, the curvature of the wound magnetic shield sheet becomes very large. However, since the magnetic shield sheet 2 according to the present embodiment has sufficient flexibility, even when the outer diameter φ of the communication cable body 50 is 10 mm or less, the workability does not decrease in the winding operation, and cracks do not occur in the permalloy layers 21 and 22.

[0027] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and it goes without saying that those are also included in the scope of the present invention.

Example

[0028] A plurality of samples A1 to A6 and B1, B2 having the cross-section shown in FIG. 1 and different combinations of the thickness T10 of the copper foil 10 and the total thickness T21 + T22 of the permalloy layers 21 and 22 were actually produced, and the flexibility and shielding characteristics were evaluated. The evaluation results are shown in Table 1. Table 1 also shows evaluations regarding material cost and corrosion resistance.

[0029]

Table 1

[0030] As shown in Table 1, Samples A1 to A6, in which the total thickness T21+T22 of the permalloy layers 21 and 22 is thinner than the thickness T10 of the copper foil 10, had high flexibility that enabled them to be wound around the communication cable body, and showed high shielding characteristics in the frequency band of 100 kHz to 1 MHz. On the other hand, Sample B1, in which the thickness T10 of the copper foil 10 and the total thickness T21+T22 of the permalloy layers 21 and 22 were the same, and Sample B2, in which the total thickness T21+T22 of the permalloy layers 21 and 22 was thicker than the thickness T10 of the copper foil 10, lacked flexibility and were difficult to wind around a communication cable body with an outer diameter of 10 mm or less. In addition, these Samples B1 and B2 had high costs because of the large amount of expensive Ni used, and also had low corrosion resistance.

[0031] Furthermore, Samples A3 to A6 showed high shielding characteristics in a wide frequency band from 10 kHz to 1 MHz. Among them, Sample A4 showed excellent results in all items of flexibility, shielding characteristics, cost, and corrosion resistance.

[0032] FIG. 7 is a graph showing the relationship between the thickness T10 of the copper foil 10, the total thickness T21+T22 of the permalloy layers 21 and 22, and the shielding characteristics. As shown in FIG. 7, it was confirmed that by setting the thickness T10 of the copper foil 10 to 35 μm and the total thickness T21+T22 of the permalloy layers 21 and 22 to 15 μm, shielding characteristics equivalent to those of an aluminum plate with a thickness of 1 mm can be obtained.

Explanation of Signs

[0033] 1, 2 Magnetic shielding sheet 3 Communication cable 10 Copper foil 11, 12 Main surfaces of the copper foil 21 to 24 Permalloy layers 30 Adhesive layer 31 Inner surface of the adhesive layer Outer surface of the adhesive layer 40 Release film 50 Communication cable body 51 Core material 52 Insulating coating

Claims

1. A magnetic shielding sheet having flexibility and capable of being wound around a communication cable body with an outer diameter of 10 mm or less, comprising a flexible copper foil and permalloy layers formed on both surfaces of the copper foil, wherein the thickness of the copper foil is more than 25 μm and less than 100 μm, the total thickness of the permalloy layers is more than 10 μm and less than 20 μm, and the thickness of the copper foil is 2 times or more and 3 times or less the total thickness of the permalloy layers. A magnetic shielding sheet characterized by this.

2. The magnetic shielding sheet according to claim 1, wherein the permalloy layer is made of a NiFe alloy having a composition with a magnetic permeability μ of 1000 or more.

3. The magnetic shielding sheet according to claim 1 or 2, wherein the permalloy layer is formed by electrodepositing on both surfaces of the copper foil.

4. The magnetic shielding sheet according to any one of claims 1 to 3, wherein the cross-section perpendicular to the longitudinal direction of the copper foil has the entire outer periphery covered with the permalloy layer.

5. The magnetic shielding sheet according to any one of claims 1 to 4, further comprising an adhesive layer covering the permalloy layer and a release film covering the adhesive layer.

6. A communication cable comprising the communication cable body and the magnetic shielding sheet according to claim 1 wound around the communication cable body.

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