JP5488649B2 - Shielded cable - Google Patents

Description

  The present invention relates to a flexible shielded cable suitable for use in portable AV equipment, information equipment, electronic equipment, and the like.

  In recent years, the development of small electronic devices has been remarkable, and in the field of industrial equipment, there is the use of control devices having many movable parts, as represented by various robots. These devices are increasingly required to have high performance, and in addition, light weight and downsizing are required. For this reason, a braided shield is applied to an extremely fine wiring cable to prevent external noise emission and external noise intrusion. In the field of consumer equipment, there are AV equipment and the like typified by portable sound reproduction equipment, and the sound of this equipment is also listened to with an earphone (including a headphone) using a coaxial cable. Recently, a portable television receiver has been developed, and the sound is listened to by an earphone, and a cable for the earphone is formed by a shielded cable, which is also used for transmission of a high-frequency signal such as a receiving antenna.

  A common problem with shielded cables used in these devices is that they are repeatedly bent or twisted, so that the stored conductors are easily disconnected. In contrast, various shielded cables (or coaxial cables) have been proposed so far. For example, Patent Document 1 has a configuration in which a rigid metal wire is mixed for reinforcement in a strand of a horizontally wound shield to suppress kink breakage. Further, in Patent Document 2, it is said that the flexibility and twistability can be improved by using a silver alloy copper alloy wire for the braided shield wire. Further, Japanese Patent Laid-Open No. 2004-228561 has a structure in which a part of the braided shield wire is replaced with a plastic yarn, and is fused with the heat of the sheath at the time of extrusion molding of the insulating sheath to provide watertightness and airtightness.

JP-A-10-334750 JP 2003-132745 A Japanese Utility Model Publication No. 56-143732

  As a shielded cable used for the above-described application, it is desired that the cable be as thin and flexible as possible, have a low bending resistance, have a smooth flexibility, and have a sufficient tensile strength. Furthermore, it has a shielding effect against low frequencies, and as a coaxial line for transmitting high frequency signals, it has a characteristic impedance of 75Ω or 50Ω with low resistance and little attenuation, and has a function as an antenna. It needs to be inexpensive to manufacture.

  The shielded cable disclosed in Patent Document 1 has a configuration in which a part of a shield or a metal wire mainly of electrical characteristics is replaced with a metal wire mainly of reinforcement, but the metal wire of reinforcement mainly includes a stainless steel wire or a piano. A wire or other highly rigid material is used. For this reason, even if the occurrence of kinks can be suppressed, the flexibility and flexibility of the cable are reduced by the amount of increased rigidity. In addition, since the configuration is a horizontal winding shield, a gap is more likely to occur during bending than a braided shield, and sufficient shield characteristics cannot be obtained.

Moreover, since the shielded cable disclosed in Patent Document 2 uses a special wire such as a silver-containing copper alloy wire for the outer conductor, the cost is high. In Patent Document 3, a part of the strand of the braided shield is replaced with a plastic thread, but even if watertightness and airtightness can be obtained by fusion with the insulating sheath, it is not possible to improve the tensile strength of the shielded cable. Can not.
The present invention has been made in view of the above-described circumstances, and can be manufactured at low cost without using a special material for the conductor material of the shielded cable, and breakage occurs by increasing the tensile strength without lowering the flexibility. It is an object of the present invention to provide a shielded cable that can reduce power consumption and obtain predetermined electrical characteristics.

The shielded cable according to the present invention is a shielded cable in which an inner conductor, an insulator, and an outer conductor are arranged coaxially and the outer periphery is covered with an insulating sheath, and the inner conductor is formed by twisting a plurality of strands, and The outer conductor is formed of a braided shield formed by braiding a plurality of conductive wires and a wire body, and the wire body is formed from a strand. It is a linear body made of a material having high tensile strength characteristics, and the dielectric constant of the insulator is adjusted so that the characteristic impedance by the coaxial structure of the inner conductor and the outer conductor becomes a predetermined value.

  According to the present invention, a normal annealed copper wire can be used as the main conductor of the shielded cable, and a general-purpose wire can be used as the reinforcing wire body, which can be manufactured at low cost. In addition, by using a material with low rigidity but high tensile strength for the reinforcing wire of the shielded cable, it is possible to increase the tensile strength and prevent the occurrence of disconnection without lowering the flexibility and flexibility. Predetermined electrical characteristics can be secured.

It is a figure explaining the outline of the present invention. It is a figure explaining other embodiment of this invention. It is a figure explaining other embodiment of this invention. It is a figure which shows the test method of the bending characteristic of the shielded cable by this invention.

  An outline of an embodiment of the present invention will be described with reference to FIG. In the figure, 1 is a shielded cable, 2 is an inner conductor, 2a is a reinforcing fiber, 2b is a conductor, 3 is an insulator, 4 is an outer conductor (braided shield), 5 is an insulating sheath, 6 is a strand, 7 is a filament Showing the body.

  The shielded cable 1 according to the present invention is configured such that an inner conductor 2 is insulated by an insulator 3, an outer conductor 4 is coaxially arranged on the outer periphery of the insulator 3, and the entire outer periphery is covered with an insulating sheath 5. The internal conductor 2 (also referred to as a central conductor) is formed of one conductive wire made of annealed copper or tin-plated annealed copper, or a twisted wire in which a plurality of conductive wires made of annealed copper or tin-plated annealed copper are twisted together. It is formed. Further, as shown in FIG. 1, for example, a plurality of conductive wires 2b such as annealed copper can be twisted around the reinforcing fiber 2a.

  The insulator 3 is made of a thermoplastic resin such as vinyl chloride, polyethylene, or polypropylene, and is preferably a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) having excellent electrical characteristics and heat resistance, or a dielectric. It is preferable to use a crosslinked foamed polyethylene having a low rate and dielectric loss. The outer conductor 4 is wound around the outer periphery of the insulator 3, and the dielectric constant of the insulator 3 is adjusted so that the characteristic impedance by the coaxial structure of the inner conductor 2 and the outer conductor 4 is 75Ω or 50Ω.

  In the present invention, the outer conductor 4 has a shield structure using a braided shield. Hereinafter, the outer conductor 4 is referred to as a braided shield. The braided shield is known as an electrostatic shield method that has less flexibility in bending even when bent, and has adequate flexibility, bending strength, and mechanical strength, compared to a horizontal shield. is there. The braided shield 4 usually has several strands 6 as one set, and this number of sets is referred to as a “strike” number, and the number of strands per stroke is displayed as a “hold” number. “Number of possessions” × “Number of strokes”. In the braided shield of an extra-fine shielded cable, the number of possessions is usually 2 to 10 and the number of strikes is 10 to 30. In the present invention, a part of the strand 6 of the braided shield having such a configuration is formed by the filament 7 made of a material having higher tensile strength characteristics.

  The filament 7 has the same outer diameter or thickness as the strand 6 constituting the braided shield 4, and is knitted into the braided shield 4 in the same manner as the braid 6. In this case, for example, if the number is 4 as shown in FIG. 1, one of the strands 6 is replaced with a filament 7, and a quarter of the entire braided shield 4 is defined as a filament 7. . In addition, as long as it is the linear body 7 of the material which has a tensile strength characteristic higher than the strand 6 which comprises the braided shield 4, any of a metal wire and a nonmetallic wire may be sufficient.

  Note that, for example, when an alloy wire is used for the wire body 7, a metal wire may be plated with good conductivity to ensure shielding characteristics. Further, when a non-metallic material such as a high-strength fiber is used for the filament 7, for example, a metallized fiber in which the surface of the high-tensile fiber is coated with copper or the like, or a high-strength fiber thread with a rectangular wire shape is used. You may use a linear body known as a copper foil thread which wrapped the copper foil tape. In addition, when the insulating sheath 5 is formed by molding with an extruder, it is accompanied by heating, so that the wire body 7 is heat resistant. The insulating sheath 5 (sometimes referred to as a jacket or a jacket) is formed, for example, by molding a resin such as a styrene-based elastomer with an extruder.

  FIG. 2 is a diagram for explaining another embodiment, and FIG. 2A is a diagram showing an example in which the filament 7 made of a material having high tensile strength is used in units of “strike” of the braided shield 4. As in this example, instead of replacing one of the “strikes” of the braided shield 4 shown in FIG. The effect can be expected. That is, the braided shield 4 is braided with a mixture of “striking” consisting only of the strands 6 and “striking” consisting only of the filaments 7. The mixing ratio of the strand 6 and the filament 7 can be made to have the same high tensile strength by making it the same as the example of FIG. Moreover, the combination of the strand 6 and the filament 7 becomes simple in terms of manufacturing, and work errors can be reduced.

  FIG. 2 (B) is obtained by knitting the linear body 7 replaced with the “striking” unit in the modified example of FIG. 2 (A) into a tape-shaped linear body 7 ′. Further, the tape-like linear body 7 'can also be formed of metal or nonmetal. In the case of metal, a flat wire-like metal band can be knitted into the braid, and when non-metallic high-tensile fibers are used, a tape knitted in advance can be knitted into the braid.

In any case of FIGS. 1 to 2, aramid fibers excellent in high tensile properties and heat resistance can be used as the filaments 7 and 7 ′. This aramid fiber can also be used as a reinforcing fiber for the internal conductor 2 and can be used in common. For example, commercially available aramid fibers such as Kevlar (DuPont registered trademark) and Twaron (Teijin registered trademark) can be used.

  FIG. 3 is a view showing another embodiment, and is a shielded cable 1 ′ in which an auxiliary conductive wire 8 is wound around the outer periphery of the braided shield 4 described in FIGS. The conductive wire 8 is directly wound around the surface of the braided shield 4 at a spiral pitch smaller than the spiral pitch of the strands constituting the braided shield 4 using, for example, a bare copper wire or a copper alloy wire. By winding the conductive wire 8, it is possible to reduce the occurrence of a gap due to the movement of the braided shield strand or wire when the shield cable 1 ′ is bent. Moreover, even if a gap occurs, the conductive wire 8 itself can cover the gap portion to prevent shield leakage.

  As an example of the above-described shielded cable 1, 1 ′ according to the present invention, the inner conductor 2 is wound around eight reinforcing wires 2b made of bare soft copper having an outer diameter of 0.06 mm around a reinforcing fiber 2a made of aramid fiber or the like. The outer diameter was 0.21 mm. The insulator 3 is made of PFA and has an outer diameter of 0.5 mm. The braided shield 4 is made of an annealed copper wire with an outer diameter of 0.08 mm, the number of strikes per strike is 3, and the total number of strikes is 16 (right-winding 8 strokes, left-winding 8 strokes). Was formed of 100 denier aramid fibers. That is, as the whole braided shield, a total of 36 strands of annealed copper wire and a total of 12 aramid fiber tensile strength wires are used. In this case, the wound outer diameter of the braided shield 4 is about 0.9 mm. The insulating sheath 5 was molded with an extruder using a styrene diameter elastomer so that the outer diameter was 1.3 mm.

  Further, as a comparative example of the above embodiment, the inner conductor 2, the insulator 3, and the insulating sheath 5 are formed in the same manner as the embodiment, and all the strands 6 constituting the braided shield 4 are made of annealed copper wire. did. In other words, the braided shield 4 was formed of a conventional soft copper wire without any high tensile strength for reinforcing the strength.

  The shielded cable produced as described above was evaluated using the test method shown in FIG. In this test method, a tensile load of 100 g is applied to the suspended shielded cables 1 and 1 ′, and round bars 9 having an outer diameter of 8 mm are arranged on both sides and bent to 90 degrees to the left and right. Bending is performed at a bending speed of 30 times / minute, with the left and right bending reciprocation (bending of 360 degrees in total) as one time. Each lead wire of the inner conductor and each strand of the braided shield were connected in series, and the number of bendings until continuity was lost was measured.

  As a result, the shielded cable of the example was able to satisfy the standard without bending because of the bending characteristic of 3000 times or more of the acceptable standard. Also, the tensile strength could withstand a standard load of 980 N or more. On the other hand, the shielded cable of the comparative example was disconnected 200 to 1500 times and could not clear the standard. Also, the tensile strength was broken at 490N to 590N, and the standard could not be cleared.

1, 1 'Shield cable 2 Inner conductor 2a Reinforcing fiber 2b Conductor 3 Insulator 4 Outer conductor (braided shield)
5 Insulating sheath 6 Wires 7, 7 'Wire body 8 Conductive wire 9 Round bar.

Claims (7)

A shielded cable in which an inner conductor, an insulator, and an outer conductor are arranged coaxially and the outer periphery is covered with an insulating sheath,
The inner conductor is formed by twisting a plurality of strands and including a reinforcing fiber having higher tensile properties than the strands,
The outer conductor is formed by a braided shield obtained by braiding a plurality of strands having conductivity and a filament .
The striated body is a striated body made of a material having higher tensile properties than the strands,
A shielded cable, wherein a dielectric constant of the insulator is adjusted so that a characteristic impedance by a coaxial structure between the inner conductor and the outer conductor becomes a predetermined value.   The shielded cable according to claim 1, wherein the predetermined value is a value at which the shielded cable functions as an antenna.   The shielded cable according to claim 2, wherein the predetermined value is a value with respect to a frequency of a high-frequency signal received as the antenna, and has a shielding effect for a low-frequency signal.   The shielded cable according to claim 2 or 3, wherein the predetermined value is 75Ω or 50Ω. The shielded cable according to claim 2 , wherein the filament is used in units of “striking” constituting the braided shield. The shield cable according to claim 5 , wherein the linear body is formed in a tape shape. The shielded cable according to any one of claims 1 to 6 , wherein a conductive wire is wound on the braided shield at a spiral pitch smaller than a spiral pitch of the braided shield.

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