JP4654782B2 - Shielded cable - Google Patents

Description

  The present invention relates to a shielded cable in which a conductive wire is wound around the outer periphery of a plurality of insulating cores whose conductors are insulated with an electrical insulator, and the outside is covered with a jacket.

  In recent years, in addition to the high performance and multi-functionality of electronic devices, the amount of information has been increased, the speed of transmission signals has been increased, and digitalization has progressed, and the density of internal wiring has been increased. In addition, in order to reduce the influence of external noise and the like and to reduce electromagnetic waves radiated to the outside from a high-frequency current, the use of shielded cables in which the outer periphery of the signal line insulator is covered with a conductor is increasing. FIG. 3 is a diagram showing an outline of a general shielded cable as disclosed in, for example, Patent Document 1, in which 1 is a two-core parallel shielded cable, 2 is an insulated wire, 3a and 3b are shield layers, 4 shows a jacket.

The shielded cable shown in FIG. 3 is an example of a two-core parallel shielded cable having two signal lines. The main body of an information device such as a notebook personal computer, a mobile phone, and a video camera, and a portion involving twisting of a liquid crystal display. It is an example of the shielded cable used for wiring etc. Two signal lines 2 in the flat rows state, the shield layer 3a by winding a conductor on the outer periphery thereof, and 3b, a configuration in which covering the outside with jacket 4.

  The shield layers 3a and 3b are formed by winding a conductive wire such as a tin-plated copper alloy wire by horizontal winding, and the shield layers 3a and 3b are wound in opposite directions. With this configuration, when the cable is bent or twisted, a gap is generated between the conductors, so that the shielding effect is insufficient and the occurrence of the wire habit is reduced. Further, a metal foil tape is wound around the outside of the shield layers 3a and 3b to form a third shield layer.

The insulated wire 2 is a single wire or a stranded wire made of a good electrical conductor such as copper, and the electrical insulator is an electrical insulating material such as fluororesin or polyethylene. Shield layer 3a, 3b are typically formed of wire made of the same electrical conductor as that used in the central guide body or braid shape laterally wound, covering the outer periphery outside the 4. The outer jacket 4 is sometimes referred to as a sheath or a jacket, and is formed of a resin such as polyolefin or vinyl chloride.

  In recent years, these shielded cables used for wiring inside or between electronic devices are also required to be flame retardant so that the fire does not spread through the cables in the event of a device fire. For flame retardancy related to equipment wiring materials, for example, evaluation by a vertical combustion test called a VW-1 test in the US UL standard (Underwriters Laboratories) is often used as one standard.

  FIG. 4 is a diagram for explaining the UL standard VW-1 vertical combustion test method. In this combustion test method, a sample 5 (a cable under test) having a length of about 60 cm is vertically held by a pair of holding portions 6 arranged on the upper and lower positions of the shielding wall 10. The flame 8 of the gas burner 7 is adjusted so that the outer red outer flame 8a is 127 mm and the inner blue inner flame 8b is 38 mm, and the tip of the flame 8 is applied to the sample 5 at an angle of 20 °. A flag 9 is attached at a position 25 cm above the position where the tip of the flame 8 is applied. The marker flag 9 is attached by wrapping around the sample 5 once using kraft paper having a length of 2 cm, a width of 1.25 cm, and a thickness of 0.013 cm. The flame 8 is ignited for 15 seconds and extinguished for 15 seconds. After repeating this for 5 cycles, the flame 8 is turned off within 60 seconds after being ignited, and the flag 9 does not burn more than 25% is accepted.

  Conventionally, in order to comply with this standard, the sheath 4 of the shielded cable in the above-mentioned field includes a flame retardant polymer such as polyvinyl chloride (PVC), a polyolefin resin such as polyethylene, and a chlorine or bromine flame retardant. Incombustible products have been used. However, in recent years, environmentally friendly products have been developed and recycled in various fields from the viewpoint of global environmental protection. In the field of electric wires and cables, the generation of highly corrosive halogen gas during incineration has caused global environmental pollution. It has come to be regarded as a problem.

For this reason, the use of halogen compounds is extremely effective in increasing the flame retardancy of electric wires and cables. However, for example, as disclosed in Patent Document 2, halogen compounds are not included for global environmental conservation (generally, Development of flame retardant shielded cables (also called non-halogen and halogen-free) is underway.
JP 2004-63418 A JP 2001-52537 A

  In Patent Document 2, it is premised that flame retardancy is realized in a state where the outer conductor 3 and the jacket 4 of the shielded electric wire are removed. For this reason, a low dielectric constant is secured for the insulator 2 so as not to impair the signal transmission characteristics, and a non-halogen flame-retardant shielded electric wire is obtained. However, since a special material is used, the cost increases. In general, in order to increase the signal transmission speed and reduce transmission loss, the insulator 2 is made of polyethylene, foamed polyethylene, or the like with low dielectric loss, and the flame resistance of the shielded wire as a whole is ensured by the jacket 4. May be sufficient. In this case, it is desired to use a non-halogen and inexpensive inexpensive flame retardant polyolefin for the jacket 4, but it is inferior in flame retardancy compared to a halogen-based jacket such as polyvinyl chloride, and VW It was difficult to clear the combustion test of -1.

  The present invention has been made in view of the above-described circumstances, and is a commercially available low-cost general material that achieves flame retardancy without impairing electrical characteristics with a low-cost configuration in production. The objective is to provide a shielded cable that can be used.

Shielded cable according to the present invention, the shield conductor by winding a conductive wire outer periphery of the electrical conductor on the outer periphery of the plurality of insulated core insulated with an electrical insulator, a shielded cable covering the outer periphery in the jacket, the insulating core Are twisted together, the winding pitch of the shield conductor is 70% to 100% of the twist pitch of the insulating core , the metal tape is overlapped between the shield conductor and the jacket, and the width is 1/3 to 3/3 of the tape width. Installing wound helically 4, the envelope formed by the flame-retardant polyolefin. Further, the drain wire may be arranged in the gap between the plurality of insulating cores and the shield conductor .

  According to the shielded cable of the present invention, the metal foil itself of the metal tape is flame retardant and is tightly wound on the shield conductor. For this reason, it can suppress that an electrical insulator spreads by suppressing oxygen supply to an internal insulator at the time of combustion. The shielded cable can be made of a general and inexpensive material, and the shield conductor can be formed by an inexpensive manufacturing method in a horizontal winding form. Furthermore, the metal tape can be brought into close contact with the outer cover, and when forming the terminal, it can be easily peeled off together with the removal of the outer cover, and the workability is not deteriorated.

  Embodiments of the present invention will be described with reference to the drawings. 1A is a diagram for explaining the outline of a shielded cable according to the present invention, FIG. 1B is a diagram for explaining an example of another shielded cable, and FIGS. 2A and 2B are used in the present invention. The figure explaining the example of a metal foil tape, FIG.2 (C) is a figure explaining the example of winding of a metal foil tape. In the figure, 11 is a shielded cable, 12 is an insulating core, 13 is an electrical conductor, 14 is an electrical insulator, 15 is a shield conductor, 16 is a metal tape, 16a is a metal foil, 16b is a tape substrate, 17 is a jacket, Reference numeral 18 denotes a drain wire.

Shielded cable according to the present invention, the basic structure, as shown in FIG. 1 (A), combined Ri twisting a plurality of insulated core 12 insulates the outer periphery of the electrical conductor 13 with an electrical insulator 14, the A shield conductor 15 is formed on the outer periphery by horizontal winding of a conductive wire and covered with an outer jacket 17. As the electric conductor 13 of the insulating core 12, a single electric wire or a stranded wire made of a good electric conductor made of copper, aluminum, a copper alloy wire, various plated copper wires or the like is used. For example, the outer diameter is about 0.08 to 0.16 mm. A tin-plated annealed copper wire of which seven are twisted is used.

  The electrical insulator 14 is made of a non-halogen electrical insulation material such as polyethylene or foamed polyethylene, and when the dielectric constant needs to be adjusted, it is adjusted by changing the thickness of the insulator or the degree of foaming. The use of a flame-retardant non-halogen foamed insulator as disclosed in Patent Document 2 as the electrical insulator 14 does not exclude the present invention.

  The shield conductor 15 is usually formed by laterally winding a conductor of a good electric conductor having the same thickness as that used for the electric conductor 13. In the present invention, a metal tape 16 is spirally wound around the shield conductor 15 and the outside thereof, and the outer periphery thereof is covered with a jacket 17. In addition, as shown in FIG. 1B, the drain wire 18 may be interposed in a gap portion formed between the shield conductor 15 and the plurality of insulating cores 12. The drain wire 18 is in electrical contact with a large number of conductors forming the shield conductor 15 to facilitate ground connection at the terminal portion.

  As shown in FIG. 2 (A), the metal tape 16 may be used as a shape with increased strength by attaching a metal foil 16a to a resin tape base 16b. Further, as shown in FIG. 2 (B), a tape base material 16b with a metal foil 16a attached to both sides may be used. As the tape substrate 16b, for example, a polyester tape such as polyethylene terephthalate (PET) can be used.

  The metal foil 16a is desirably made of a metal material that is easy to wind around the outer periphery of the shield conductor 15 and that does not melt and disappear at this temperature if the temperature during combustion is about 1000 ° C. For this, for example, it is preferable to use a soft copper foil having a melting point of 1000 ° C. or higher. Further, the metal foil 16a needs to have a certain thickness in order to effectively maintain strength and shield oxygen, and is formed with a thickness of at least 5 μm (preferably 8 μm to 20 μm). Is desirable.

  As shown in FIG. 2C, when the tape width is T, the overlapping width W of the tape is “1/3 to 3/4” times the tape width T, as shown in FIG. It is desirable that By spirally winding the metal tape 16 with a relatively large overlap width, the supply of oxygen from the outside to the inside during combustion is suppressed. Thereby, when combustion occurs in the electrical insulator 14 inside the shield conductor 15, the spread of fire can be suppressed. The metal tape 16 may be any of various thin metals such as copper, iron, aluminum, and other stainless steel that can be wound around the shield conductor 15.

  A jacket 17 is applied to the outside of the metal tape 16. As the jacket 17, it is desirable to use polyolefin called non-halogen plastic as a material to replace vinyl chloride. However, this polyolefin is more flammable than vinyl chloride. Even if the metal tape 16 is used to make the internal electrical insulator 14 flame-retardant as described above, the jacket 17 itself has flame retardancy. Is preferred. For this reason, it is preferable to use a non-halogen flame-retardant polyolefin or a cross-linked flame-retardant polyolefin for the jacket 17. As non-halogen flame retardant polyolefins, for example, polyolefin resins containing magnesium hydroxide and aluminum hydroxide as flame retardants are known.

  According to the configuration described above, it is possible to obtain a flame-retardant shielded cable that can clear the VW-1 combustion test as shown in FIG. That is, the metal tape 16 itself is flame retardant, and the supply of oxygen necessary for combustion of the electrical insulator 14 can be cut off by covering the inner insulating core 12 relatively densely. For this reason, it is possible to suppress the spread of fire without using the electrical insulator 14 as a flame retardant. In the conventional structure of FIG. 3 (Patent Document 1), it is said that a metal tape may be wound between the shield layer and the jacket, but this is intended to supplement the shield effect and is intended to be flame retardant. It is not a thing. For this reason, it is unclear what the winding state is, and flame retardancy cannot be expected.

  Moreover, even if it is the structure which winds the metal tape 16 between the insulation core 12 and the shield conductor 15, it is possible to give a flame-retardant effect, but compared with removing the metal tape 16 at the time of terminal formation. Will require labor. By providing the metal tape 16 on the side in contact with the outer cover 17, the metal tape 16 can be peeled off together with the outer cover 17 at the time of forming the terminal, so that workability can be improved. Further, the shield conductor 15 may be formed by braiding, but the winding mechanism is larger than that of the horizontal winding, the production line speed is slowed down, the productivity is lowered, and the production cost is increased.

  Further, in the present invention, since a plurality of insulating cores 12 are used, a void is easily generated between the insulating core 12 and the shield conductor 15 wound around the outer periphery, and a void containing oxygen necessary for combustion is easily formed. For this reason, by interposing the drain wire, the volume of the gap portion can be reduced, and electrical grounding can be facilitated.

  Moreover, when it was set as the structure which twists the several insulation core 12, when the twist relationship of the insulation core 12, winding of the shield conductor 15, and the winding relationship of the metal tape 16 were investigated, the winding direction and winding pitch of the metal tape 16 itself and There was no particular influence on the combustion characteristics due to the twisted state of the insulating core 12 and the state of the shield conductor 15 being wound. However, when the winding pitch of the shield conductor 15 exceeds the twist pitch of the insulating core 12, a shield failure is likely to occur. Therefore, it is desirable that the winding pitch of the shield conductor 15 is equal to or less than the twist pitch of the insulating core 12.

When the twist pitch of the insulating core 12 is 16 mm and the winding pitch of the shield conductor 15 is 10 mm, the VW-1 combustion test may not be cleared. However, the twist pitch of the insulating core 12 is 16 mm, When the winding pitch of 15 was set to 15 mm, the VW-1 combustion test was reliably cleared. Therefore, it is preferable that the winding pitch of the shield conductor 15 is 70% or more of the twist pitch of the insulating core 12 in terms of improving flame retardancy. That is, the winding pitch of the shield conductor 15 is 70% or more and 100% or less of the twist pitch of the insulating core 12.

  As a specific example, the outer periphery of an electric conductor 13 made of a copper stranded wire was insulated with an insulator 14 made of foamed polyethylene, and a shield conductor 15 was formed on the outer periphery by lateral winding. On the outer periphery of the shield conductor 15, a metal tape 16 obtained by attaching a 9 μm thick copper foil to a 12 μm thick polyester tape base material is 15 mm so that the overlapping width W becomes 1/2 of the tape width T. Wound spirally at the pitch. The outer periphery of the wound metal tape 15 was coated with a flame retardant polyolefin resin so as to have a coating thickness of about 0.25 mm to 0.45 mm to form a jacket 17, and a non-halogen flame retardant shielded cable was produced. .

  When the above-mentioned shielded cable was tested by the VW-1 vertical combustion test method shown in FIG. 4, this combustion test could be cleared. In addition, the shielded cable which used aluminum foil for the metal foil of the metal tape 16 and made the overlap width W 1/4 of the tape width T was not able to clear the VW-1 vertical combustion test. Further, from the combustion state of the vertical combustion test, it is considered that if the overlap width W is 1/3 or more of the tape width T, the VW-1 vertical combustion test can be cleared. The larger the overlap width W is, the easier it is to clear the combustion test. However, if the overlap width W is too large, the production line speed is lowered and the productivity is lowered. Therefore, the overlap width W should be 3/4 or less of the tape width T. Desirable from a manufacturing standpoint.

It is a figure explaining embodiment of this invention. It is a figure explaining the metal tape example used by this invention, and a winding state. It is a figure explaining a prior art. It is a figure explaining the vertical combustion test method of VW-1 of UL specification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Shield cable, 12 ... Insulation core, 13 ... Electric conductor, 14 ... Electric insulator, 15 ... Shield conductor, 16 ... Metal tape, 16a ... Metal foil, 16b ... Tape base material, 17 ... Outer cover, 18 ... Drain Wire.

Claims (2)

A shield cable in which a conductor is wound around the outer periphery of a plurality of insulating cores, the outer periphery of which is insulated with an electrical insulator, and the outer periphery is covered with a jacket,
The insulating core is twisted, the winding pitch of the shield conductor is 70% to 100% of the twist pitch of the insulating core, and a metal tape is overlapped between the shield conductor and the jacket, and the width is the tape width 1 / 3-3 / 4 in Installing wound helically, shielded cables, characterized in that the envelope formed by the flame-retardant polyolefin.   The shielded cable according to claim 1, wherein a drain wire is disposed in a gap between the plurality of insulating cores and the shield conductor.

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