Small-diameter coaxial cable and multi-core cable

Abstract

The invention provides a small-diameter coaxial cable and a multi-core cable, which can suppress deterioration of appearance and electrical characteristics caused by shape deformation of an inner conductor. The small-diameter coaxial cable (1) is provided with an inner conductor (2) formed by twisting four metal wires (21), an insulator (3) covering the periphery of the inner conductor (2), a shielding layer (4) covering the periphery of the insulator (3), and an outer sleeve layer (5) covering the periphery of the shielding layer (4), and when the twisting pitch of the inner conductor (2) is set as P and the layer core diameter of the inner conductor (2) is set as Pd, P / Pd is less than 25.

Description

Technical Field

[0001] The present invention relates to a small-diameter coaxial cable and a multi-core cable. Background Art

[0002] In a multi-core cable used as a medical cable such as a probe cable for ultrasonic diagnosis, a very thin small-diameter coaxial cable with an outer diameter of 0.25 mm or less is used. In such a small-diameter coaxial cable, a stranded conductor formed by stranding metal wires is used as an inner conductor. Regarding the number of metal wires used for the inner conductor, it is necessary to determine as follows: When setting a desired cross-sectional area, considering the cable outer diameter, it is necessary to be able to sufficiently ensure the distance between the inner conductor and the shielding layer (outer conductor), and the cost does not become too high.

[0003] For example, when the number of metal wires is set to 3, the metal wires become thick, and sometimes the distance between the inner conductor and the shielding layer cannot be sufficiently ensured. In addition, for example, in the case of 7-strand stranding formed by stranding 6 metal wires around 1 metal wire, although the distance between the inner conductor and the shielding layer can be ensured, the outer diameter of the metal wire is too small and the cost is very high. And in the case of 5-strand stranding and 6-strand stranding, the stranding shape is difficult to stabilize. Therefore, in a small-diameter coaxial cable, considering the balance between performance and cost, there are times when it is desirable to set the number of metal wires to 4 (for example, refer to Patent Document 1).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 1-168918 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, when the number of metal wires is set to 4, there is a problem that the relative positions of the 4 metal wires in the cross-sectional view are likely to deviate. For example, 2 opposed metal wires enter between 2 opposed metal wires, etc., resulting in a possible deformation of the shape of the inner conductor. If the shape of the inner conductor is deformed, sometimes the appearance of the small-diameter coaxial cable becomes abnormal, or in a part in the circumferential direction, a thin part is generated in the insulator, the distance between the inner conductor and the shielding layer becomes small, and the electrical characteristics deteriorate.

[0009] Therefore, an object of the present invention is to provide a small-diameter coaxial cable and a multi-core cable that can suppress deterioration of appearance and electrical characteristics due to deformation of the shape of the inner conductor.

[0010] Means for Solving the Problems

[0011] For the purpose of solving the above problems, the present invention provides a small-diameter coaxial cable, which includes an inner conductor formed by stranding 4 metal wires, an insulator covering the periphery of the inner conductor, a shielding layer covering the periphery of the insulator, and a jacket layer covering the periphery of the shielding layer. When the stranding pitch of the inner conductor is set to P and the core diameter of the inner conductor is set to Pd, P / Pd is 25 or less.

[0012] In addition, for the purpose of solving the above problems, the present invention provides a multi-core cable, which includes a cable core and a sheath. The cable core has a plurality of the small-diameter coaxial cables, and the sheath covers the periphery of the cable core together.

[0013] Advantages of the Invention

[0014] According to the present invention, it is possible to provide a small-diameter coaxial cable and a multi-core cable that can suppress deterioration of appearance and electrical characteristics due to shape deformation of the inner conductor. Description of the Drawings

[0015] Figure 1 The figure shows a small-diameter coaxial cable according to an embodiment of the present invention. (a) is a cross-sectional view showing a cross-section perpendicular to the length direction, and (b) is a diagram for explaining the core diameter.

[0016] Figure 2 The figure is for explaining the shape deformation of the inner conductor.

[0017] Figure 3 The figure shows a multi-core cable according to an embodiment of the present invention. (a) is a cross-sectional view showing a cross-section perpendicular to the length direction, and (b) is a cross-sectional view showing a cross-section of the sub-strand perpendicular to the length direction.

[0018] Description of Reference Numerals

[0019] 1: Small-diameter coaxial cable, 2: Inner conductor, 21: Metal wire, 3: Insulator, 31: Foam layer, 32: Surface layer, 4: Shielding layer, 41: Metal wire, 5: Jacket layer, 10: Multi-core cable, 11: Sub-strand, 12: Cable core, 14: Binding tape, 15: Overall shielding layer, 16: Sheath. Detailed Embodiments

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0021] Figure 1 The figure shows a small-diameter coaxial cable 1 according to an embodiment of the present invention. Figure 1 (a) is a cross-sectional view showing a cross-section perpendicular to the length direction. Figure 1 (b) is a diagram for explaining the core diameter. As Figure 1(As shown in (a), the small-diameter coaxial cable 1 has an inner conductor 2, an insulator 3 covering the periphery of the inner conductor 2, a shielding layer 4 covering the periphery of the insulator 3, and an outer jacket layer 5 covering the periphery of the shielding layer 4.)

[0022] (Inner conductor 2)

[0023] The inner conductor 2 is formed by stranding four metal wires 21. By forming the inner conductor 2 from four metal wires 21, compared with the case where the inner conductor 2 is formed from three metal wires 21, when the inner conductor 2 has the same conductor cross-sectional area and the insulator 3 has the same outer diameter, the distance between the inner conductor 2 and the shielding layer 4 can be reduced, and good electrical characteristics can be maintained. In addition, by forming the inner conductor 2 from four metal wires 21, compared with the case where the inner conductor 2 is formed from seven metal wires 21 (the case where six metal wires 21 are stranded around one metal wire 21), the outer diameter of the metal wire 21 can be increased, and cost reduction can be achieved.)

[0024] The metal wire 21 is made of copper or a copper alloy. The metal wire 21 may also be plated on its surface with silver, tin, etc. In the present embodiment, in order to improve the conductivity and mechanical strength, a metal wire 21 made of a silver-plated copper alloy is used. From the viewpoint of cost, the outer diameter of the metal wire 21 is preferably 0.015 mm or more, and in order to prevent the insulator 3 from becoming locally too thin, it is preferably 0.20 mm or less. In the present embodiment, a metal wire 21 with an outer diameter of 0.018 m is used. The outer diameter when four metal wires 21 are stranded is 19.6 mm.)

[0025] In the small-diameter coaxial cable 1 according to the present embodiment, when the stranding pitch of the inner conductor 2 is P and the core diameter of the inner conductor 2 is Pd, P / Pd is 25 or less. The stranding pitch P of the inner conductor 2 refers to the interval along the length direction at positions where the circumferential positions of any metal wire 21 are the same. In addition, as Figure 1 (shown in (b), the core diameter Pd of the inner conductor 2 refers to the diameter of a circle passing through the centers of the four metal wires 21 in a cross-section perpendicular to the length direction. If the outer diameter of the entire inner conductor 2 is D and the outer diameter of the metal wire 21 is d, then Pd = (D - d).)

[0026] As Figure 2 shown, in the four-stranded inner conductor 2, a gap 2a is generated at the center during stranding, so some metal wires 21 enter this gap 2a, etc., resulting in the shape of the inner conductor 2 being prone to deformation. In particular, such a shape deformation is likely to occur, that is, a pair of opposed metal wires 21 (the left and right metal wires 21 in Figure 2 enter the gap 2a, and the other pair of opposed metal wires 21 (inFigure 2 The metal wire 21 in the up-and-down direction is extruded radially outward. Such shape deformation is likely to occur when the stranding pitch P of the inner conductor 2 is relatively large and the stranding is loose. As in the present embodiment, by setting P / Pd of the inner conductor 2 to 25 or less, it is possible to suppress the shape deformation of the inner conductor 2 caused by stranding relaxation.

[0027] As Figure 2 shown, when the shape of the inner conductor 2 is deformed, in the cross-sectional view (a cross-sectional view perpendicular to the length direction), the shape connecting the centers of the four metal wires 21 is no longer a square shape but becomes a substantially parallelogram shape, and its inner angle θ deviates from 90°. The greater the deviation of the inner angle θ from 90°, the greater the appearance defect and the degree of deterioration of the electrical characteristics. Therefore, the inner angle θ when connecting the centers of the four metal wires 21 preferably satisfies the following relationship:

[0028] |θ - 90°| ≤ 10°.

[0029] More preferably, it satisfies the following relationship:

[0030] |θ - 90°| ≤ 5°.

[0031] If the stranding pitch P of the inner conductor 2 is too small, breakage is likely to occur during stranding. Therefore, P / Pd of the inner conductor 2 is preferably 16 or more. That is, P / Pd of the inner conductor 2 is preferably 16 or more and 25 or less. In the present embodiment, the stranding pitch P of the inner conductor 2 is set to 0.5 m, and P / Pd of the inner conductor 2 is set to 19.6.

[0032] (Insulator 3)

[0033] The insulator 3 is formed so as to cover the periphery of the inner conductor 2. In the present embodiment, the insulator 3 has a foamed layer 31 made of foamed resin that covers the periphery of the inner conductor 2 and a non-foamed surface layer 32 that covers the periphery of the foamed layer 31. By having the foamed layer 31, it is possible to increase the dielectric constant of the insulator 3, and in particular, it is possible to improve the electrical characteristics when transmitting high-frequency signals. Since the foamed layer 31 has air bubbles, by covering its periphery with the non-foamed surface layer 32, insulation between the inner conductor 2 and the shield layer 4 is ensured.

[0034] In the present embodiment, as the foamed layer 31, a foamed layer made of foamed PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) is used. The thickness of the foamed layer 31 is set to 0.043 m, and the outer diameter is set to 0.129 mm. The foamed layer 31 is extrusion-molded around the inner conductor 2 by full extrusion.

[0035] The surface layer 32 is formed by winding a resin tape around the foam layer 31. In the present embodiment, as the resin tape, a resin tape having an adhesive layer made of a thermosetting resin provided on one surface of the resin layer is used. The adhesive layer is used as the inner side (foam layer 31 side), and it is wound in a spiral shape so that a part of the width direction of the resin tape overlaps. Then, after winding the resin tape, the adhesive layer is cured by heating to integrate the surface layer 32 and the foam layer 31.

[0036] As the resin tape used for the surface layer 32, PET (polyethylene terephthalate), PI (polyimide), PEEK (polyether ether ketone), PEI (polyetherimide), etc. can be used. In order to withstand heat during soldering etc., as the resin tape used for the surface layer 32, it is more preferable to use a resin tape with as high heat resistance as possible. More specifically, it is more preferable to use a resin tape made of a resin having a softening temperature higher than that of PET. As the resin tape used for the surface layer 32, it is more preferable to use a resin tape made of PI, PEEK, or PEI. Here, the thickness of the surface layer 32 is set to 0.005 mm.

[0037] (Shielding layer 4)

[0038] The shielding layer 4 is composed of a transverse winding shield formed by winding a plurality of metal wires 41 in a spiral shape around the insulator 3. The metal wire 41 is made of copper or a copper alloy. The metal wire 41 may also be plated on its surface using silver, tin, etc. In the present embodiment, similar to the metal wire 41 of the inner conductor 2, in order to improve the conductivity and mechanical strength, a metal wire 41 made of a silver-plated copper alloy is used. The outer diameter of the metal wire 41, that is, the thickness of the shielding layer 4 is set to 0.020 mm.

[0039] In order to make the small-diameter coaxial cable 1 easy to bend and improve the bending resistance, it is preferable that the stranding direction of the shielding layer 4 and the stranding direction of the inner conductor 2 are the same direction. It should be noted that the stranding direction of the shielding layer 4 or the inner conductor 2 refers to the direction in which the metal wires 21 and 41 rotate from one end to the other end when observing the small-diameter coaxial cable 1 from one end.

[0040] (Outer jacket layer 5)

[0041] The outer jacket layer 5 is arranged to surround the shielding layer 4. In this embodiment, the outer jacket layer 5 is formed by winding a resin tape. In this embodiment, the outer jacket layer 5 is of a two-layer structure. In the first layer, a non-adhesive resin tape is wound in a spiral manner with a part of the width direction overlapping. Then, in the second layer, an adhesive resin tape having an adhesive layer made of a thermosetting resin provided on one surface of the resin layer is wound in a spiral manner with the adhesive layer on the inner side and a part of the width direction overlapping. Then, heating is performed to cure the adhesive layer, forming the outer jacket layer 5. As the resin constituting the resin tape, PET (polyethylene terephthalate), PI (polyimide), PEEK (polyetheretherketone), PEI (polyetherimide), etc. can be used. The thickness of the outer jacket layer 5 is set to 0.015 mm. The outer diameter of the outer jacket layer 5, that is, the outer diameter of the small-diameter coaxial cable 1, is set to 0.250 mm or less, more preferably 0.220 mm or less. In this embodiment, the outer diameter of the outer jacket layer 5, that is, the outer diameter of the small-diameter coaxial cable 1, is set to 0.209 mm.

[0042] By setting the outer jacket layer 5 to a two-layer structure of a non-adhesive resin tape and an adhesive resin tape, it is possible to prevent the outer jacket layer 5 from adhering to the shielding layer 4, and improve the ease of bending and bending resistance. It should be noted that the winding direction of the non-adhesive resin tape forming the inner layer is preferably set to the same direction as that of the shielding layer 4 to prevent the stranding of the shielding layer 4 from being untied. Moreover, the winding direction of the adhesive resin tape forming the outer layer is preferably set to a direction different from that of the non-adhesive resin tape forming the inner layer. This is because if the winding directions of both the inner layer and the outer layer are set to the same direction, a bending tendency may be imparted to the small-diameter coaxial cable 1.

[0043] (Multi-core cable 10)

[0044] Next, the multi-core cable 10 using the small-diameter coaxial cable 1 will be described. Figure 3 is a diagram showing the multi-core cable 10 according to this embodiment, Figure 3 (a) is a cross-sectional view showing a cross-section perpendicular to the length direction, Figure 3 (b) is a cross-sectional view showing a cross-section perpendicular to the length direction of the sub-strand 11.

[0045] As shown in Figure 3 (a), Figure 3 (b), the multi-core cable 10 includes a cable core 12 having a plurality of small-diameter coaxial cables 1 and a sheath 16 that collectively covers the periphery of the cable core 12. In this embodiment, it is configured as follows: a bundling tape 14 is wound around the cable core 12, a general shielding layer 15 is arranged to cover the periphery of the bundling tape 14, and a sheath 16 is arranged to cover the periphery of the general shielding layer 15.

[0046] The cable core 12 is formed by stranding a plurality of sub-strands 11, each of which is formed by stranding a plurality of fine-diameter coaxial cables 1. In the illustrated example, 16 fine-diameter coaxial cables 1 are stranded to form a sub-strand 11, and 12 sub-strands 11 are stranded to form the cable core 12. A total of 192 fine-diameter coaxial cables 1 are used to form the cable core 12.

[0047] The sub-strand 11 is formed by stranding 5 fine-diameter coaxial cables 1 and stranding 11 fine-diameter coaxial cables 1 around them. The stranding direction in each layer of the sub-strand 11 is set to the same direction. Hereinafter, the stranding direction in each layer of the sub-strand 11 (the direction in which the fine-diameter coaxial cable 1 rotates from one end to the other end when viewed from one end of the sub-strand 11) is referred to as the stranding direction of the sub-strand 11.

[0048] The cable core 12 is formed by stranding 3 sub-strands 11 and stranding 9 sub-strands 11 around them. The stranding direction in each layer of the cable core 12 is set to the same direction. Hereinafter, the stranding direction in each layer of the cable core 12 (the direction in which the sub-strand 11 rotates from one end to the other end when viewed from one end of the cable core 12) is referred to as the stranding direction of the cable core 12.

[0049] The stranding direction of the cable core 12 is set to the same direction as the stranding direction of the sub-strand 11. Thereby, it is easy to bend the multi-core cable 10, and the bending resistance can also be improved. The outer diameter of the cable core 12 is set to 3.7 mm.

[0050] The binding tape 14 is spirally wound around the cable core 12 in such a manner that a part of its width direction overlaps. In order to make the fine-diameter coaxial cable 1 move easily within the binding tape 14 when the multi-core cable 10 is bent or the like, thereby improving the bending ease and bending resistance, it is preferable that the binding tape 14 is made of a material that is as easy to slide as possible. More specifically, as the binding tape 14, a binding tape made of a fluororesin such as PTFE (polytetrafluoroethylene) can be used. However, the tape made of PTFE is expensive, so it is more preferable to use a foamed tape made of foamed polypropylene, which has a lower cost and is easy to slide, as the binding tape 14. In particular, in the case of using the overall shielding layer 15 made of a braided shield as in the present embodiment, by using the binding tape 14 made of foamed polypropylene, the binding tape 14 functions as a buffer layer, alleviates the fastening of the overall shielding layer 15 to the cable core 12, and can further improve the bending resistance.

[0051] In addition, the winding direction of the binding tape 14 is set to a direction different from the stranding direction of the cable core 12. Thereby, the shape deformation of the cable core 12 can be suppressed, and a multi-core cable 10 with an outer shape closer to a circle can be obtained. It should be noted that the winding direction of the binding tape 14 refers to the direction in which the binding tape 14 rotates from one end to the other end when the multi-core cable 10 is viewed from one end.

[0052] The overall shielding layer 15 is composed of a braided shielding member formed by braiding a plurality of wires. In the present embodiment, as the wire material for the overall shielding layer 15, tinned copper foil wires are used. The tinned copper foil wire is formed by winding a copper foil with tin plating around the wire into a spiral shape. Here, as the central wire, a single wire with a diameter of 0.08 mm is used to make the wire material thin and light, thereby realizing the thinning and lightening of the multi-core cable 10.

[0053] The sheath 16 is provided so as to cover the periphery of the overall shielding layer 15. In the present embodiment, as the sheath 16, a sheath made of PVC (polyvinyl chloride) with a thickness of 0.6 mm is used. The sheath 16 is preferably formed by tube extrusion so that the resin constituting the sheath 16 does not enter between the wire materials of the overall shielding layer 15. The outer diameter of the sheath 16, that is, the outer diameter of the multi-core cable 10 is set to 5.4 mm.

[0054] (Function and effect of the embodiment)

[0055] As described above, in the thin-diameter coaxial cable 1 of the present embodiment, the P / Pd of the inner conductor 2 is set to 25 or less. Thereby, the shape deformation of the inner conductor 2 can be suppressed, and the deterioration of the appearance and electrical characteristics can be suppressed.

[0056] (Summary of the embodiment)

[0057] Next, the technical idea grasped from the above-described embodiment will be described by referring to the reference numerals in the embodiment. However, the symbols and the like in the following description do not limit the constituent elements in the claims to the members specifically shown in the embodiment.

[0058] [1] A thin-diameter coaxial cable (1), comprising an inner conductor (2) formed by stranding 4 metal wires (21), an insulator (3) covering the periphery of the inner conductor (2), a shielding layer (4) covering the periphery of the insulator (3), and an outer jacket layer (5) covering the periphery of the shielding layer (4). When the stranding pitch of the inner conductor (2) is set to P and the core diameter of the inner conductor (2) is set to Pd, P / Pd is 25 or less.

[0059] [2] The thin-diameter coaxial cable (1) according to [1], wherein the P / Pd of the inner conductor (2) is 16 or more and 25 or less.

[0060] [3] The thin-diameter coaxial cable (1) according to [1], wherein the outer diameter of the outer jacket layer (5) is 0.250 mm or less.

[0061] [4] The small-diameter coaxial cable (1) according to [1], wherein the insulator (3) has a foamed layer (31) made of foamed resin covering the periphery of the inner conductor (2) and a surface layer (32) formed by winding a resin tape around the foamed layer (31), and the resin tape is made of a resin having a softening temperature higher than that of PET.

[0062] [5] The small-diameter coaxial cable (1) according to [4], wherein the resin tape is made of polyimide, polyether ether ketone or polyetherimide.

[0063] [6] A multi-core cable (10) comprising a cable core (12) and a sheath (16), wherein the cable core (12) has a plurality of the small-diameter coaxial cables (1) described in any one of [1] to [5], and the sheath (16) covers the periphery of the cable core (12) together.

[0064] [7] The multi-core cable (10) according to [6], wherein the cable core (12) is formed by stranding a plurality of sub-strands (11) each formed by stranding a plurality of the small-diameter coaxial cables (1).

[0065] [8] The multi-core cable (10) according to [7], wherein the stranding direction of the sub-strand (11) is the same as the stranding direction of the cable core (12).

[0066] [9] The multi-core cable (10) according to [8], further comprising a bundling tape (14) wound around the cable core (12), and the winding direction of the bundling tape (14) is different from the stranding direction of the cable core (12).

[0067]

[10] The multi-core cable (10) according to [6], further comprising a bundling tape (14) wound around the cable core (12), a general shielding layer (15) covering the periphery of the bundling tape (14) and made of a braided shield, and the sheath (16) covering the periphery of the shielding layer (15), and the bundling tape (14) is made of foamed polypropylene.

[0068] (Supplementary Note)

[0069] The embodiments of the present invention have been described above, but the above-described embodiments do not limit the invention claimed in the claims. In addition, it should be noted that the combinations of the features described in the embodiments are not necessarily all essential for the method of solving the problems of the invention. In addition, the present invention can be implemented with appropriate modifications within the scope of its gist.

Claims

1. A narrow coaxial cable comprising an inner conductor formed by twisting four metal wires, an insulator covering the periphery of the inner conductor, a shielding layer covering the periphery of the insulator, and a sheathing layer covering the periphery of the shielding layer, When the twist pitch of the internal conductor is denoted as P and the layer core diameter of the internal conductor is denoted as Pd, P / Pd is 25 or less.

2. The narrow coaxial cable according to claim 1, wherein: The P / Pd of the inner conductor is 16 or more and 25 or less.

3. The narrow coaxial cable according to claim 1, wherein: The outer diameter of the outer jacket layer is less than 0.250 mm.

4. The narrow coaxial cable according to claim 1, wherein: The insulator includes a foam layer made of a foamed resin covering the periphery of the inner conductor and a surface layer formed by winding a resin tape around the foam layer. The resin tape is made of a resin having a higher softening temperature than PET.

5. The narrow coaxial cable according to claim 4, wherein: The resin belt is made of polyimide, polyetheretherketone or polyetherimide.

6. A multi-core cable comprising: A cable core comprising a plurality of thin-diameter coaxial cables according to any one of claims 1 to 5, and A sheath also covers the periphery of the cable core.

7. The multi-core cable according to claim 6, wherein: The cable core is formed by twisting a plurality of sub-stranded wires formed by twisting a plurality of the narrow-diameter coaxial cables.

8. The multi-core cable according to claim 7, wherein: The twisting direction of the sub-twisted wires is the same as the twisting direction of the cable core. 9 . The multi-core cable according to claim 8 , further comprising a binding tape wound around the cable core, wherein a winding direction of the binding tape is different from a twisting direction of the cable core.

10. The multi-core cable according to claim 6, comprising: a strapping tape wrapped around the cable core, an overall shielding layer covering the periphery of the strapping tape and consisting of a braided shield, and The sheath covers the periphery of the shielding layer; The strapping tape is made of foamed polypropylene.

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