JP2005302620A - Shield cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shield cable formed by using a conventional cheap material, capable of realizing a fire retardant property without damaging electric properties. <P>SOLUTION: The shield cable is formed by insulating an outer periphery of a center conductor 11 by an insulator 12 made of foamed resin, and arranging an external conductor 13 by winding a conductive wire on the periphery of the insulator, and covering it by an outer cover 14. A metal tape 15 is spirally wound between the external conductor 13 and the outer cover 14, and the outer cover 14 is formed by fire retardant polyolefin or cross-linked fire retardant polyolefin. A tape base material 15b made of resin, to which a metal foil 15a is adhered, can be used as the metal tape 15, and a width of an overlapped part W of the wound metal tape 15 is made 1/3 to 1/4 of the width of the tape T. It is preferable to use a copper foil with a thickness of 5 μm or thicker as the metal foil 15a of the metal tape 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a shielded electric wire used for signal transmission or the like in an electronic device by arranging an insulator, an outer conductor, and a jacket coaxially on the outer periphery of a central conductor.

  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 wires in which the outer periphery of the signal line insulator is covered with a conductor is increasing. FIG. 2 is a diagram showing an outline of a general shielded electric wire as disclosed in, for example, Patent Document 1, in which 1 is a central conductor, 2 is an insulator, 3 is an external conductor, and 4 is a jacket. Show.

  As shown in FIG. 2, the shielded electric wire (or shielded cable) is configured by sequentially arranging an insulator, an outer conductor, and a jacket on the outer periphery of the center conductor 1 in a coaxial manner. The same configuration may be referred to as a coaxial cable or a coaxial cable. A single wire or a stranded wire made of a good electrical conductor such as copper is used for the center conductor 1, and an electrical insulating material such as polyethylene or foamed polyethylene is used for the insulator 2. The outer conductor 3 is usually formed by winding a conductive wire made of a good electric conductor similar to that used for the center conductor 1 or in a braided shape, and the outer periphery thereof is covered with a jacket 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 wires used for wiring in electronic devices are also required to be flame retardant so that the fire does not spread along the wires in the event of a fire in the device. For flame retardancy related to equipment wiring materials, for example, evaluation by a vertical combustion test called VW-1 test in the UL standard (Underwriters Laboratories) in the United States is often used as one standard.

  FIG. 3 is a diagram for explaining the UL standard VW-1 vertical combustion test method. In this combustion test method, a sample 5 (electric wire to be tested) having a length of about 60 cm is vertically held by a pair of holding portions 6 disposed 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 meet this standard, the outer sheath 4 of the shielded electric wire 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 conservation. Even in the electric wire field, the generation of highly corrosive halogen gas during incineration is one of the causes of global environmental pollution. As a matter of fact, it is becoming a problem.

For this reason, the use of a halogen compound is extremely effective in increasing the flame retardancy of an electric wire, but for example, as disclosed in Patent Document 2, it does not contain a halogen compound for the preservation of the global environment (generally, non-halogen, Development of flame retardant shielded wires (also called halogen-free) is underway.
JP 2003-208823 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, the insulator 2 has a low dielectric constant so as not to impair the signal transmission characteristics and obtains a non-halogen flame-retardant shielded electric wire. However, the use of a special material increases the cost. 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 shielded electric wire that can achieve flame retardancy without impairing electrical characteristics, using commercially available inexpensive and common materials. Offering is an issue.

  The shielded electric wire according to the present invention is a shielded electric wire in which the outer periphery of the central conductor is insulated with a foamed resin insulator, and the outer conductor is wound around the outer periphery by covering the outer conductor and the outer sheath. A metal tape is spirally wound between the two and a jacket is formed of a flame retardant polyolefin or a crosslinked flame retardant polyolefin. As the metal tape, a resin tape base material bonded with a metal foil can be used, and the overlapping width of the winding of the metal tape is 1/3 to 3/4 of the tape width. Moreover, it is preferable to use copper foil as the metal foil of the metal tape, and the thickness is desirably 5 μm or more.

  According to the shielded electric wire of the present invention, the metal foil itself of the metal tape is flame retardant, and is wound tightly on the external conductor with a relatively large overlapping width. For this reason, it is possible to suppress the supply of oxygen to the internal insulator during combustion and to prevent the insulator from spreading. Further, the shielded electric wire can be formed using a general and inexpensive material, and can be formed at a low cost by ordinary manufacturing.

  An embodiment of the present invention will be described with reference to FIG. FIG. 1A is a diagram for explaining an outline of a shielded electric wire according to the present invention, FIG. 1B is a diagram for explaining a winding form of a metal tape, and FIG. 1C is a diagram showing an example of a metal tape. . In the figure, 11 is a central conductor, 12 is an insulator, 13 is an external conductor, 14 is a jacket, 15 is a metal tape, 15a is a metal foil, and 15b is a tape substrate.

  A shielded wire (including a coaxial wire) according to the present invention has a basic configuration in which an insulator 12, an outer conductor 13, and a jacket 14 are sequentially arranged coaxially on the outer periphery of a central conductor 11 as in the conventional case. Is done. The center conductor 11 is made of a good electrical conductor made of copper, aluminum, a copper alloy wire, various plated copper wires, or the like, which is a single wire or a stranded wire. A wire which is a twist of 7 wires is used.

  The insulator 12 is made of a non-halogen electric insulating material such as polyethylene or foamed polyethylene. When the dielectric constant needs to be adjusted, the insulator 12 is adjusted by changing the thickness, the degree of foaming, or the like. Note that the use of a flame-retardant non-halogen foamed insulator as disclosed in Patent Document 2 as the insulator 12 does not exclude the present invention.

  The external conductor 13 is usually formed as a shield conductor by horizontally winding or braiding a conductor of a good electric conductor having the same thickness as that used for the central conductor 11. In the present invention, as shown in FIG. 1 (B), a metal tape 15 is spirally wound between the outer conductor 13 and the outer jacket 14 covered on the outer side, and the outer periphery thereof is covered with the outer jacket 14. To do. As for the spiral winding shape of the metal tape 15, it is desirable that the overlapping width W of the tape is “1/3 to 3/4” times the tape width T when the tape width is T.

  In other words, the metal tape 15 is spirally wound with a relatively large overlap width so as to suppress oxygen supply from the outside to the inside during combustion. Thereby, when combustion occurs in the insulator 12 between the center conductor 11 and the outer conductor 13, it is possible to suppress the spread of fire. The metal tape 15 may be any thin metal such as copper, iron, aluminum, or other stainless steel that can be wound around the external conductor 13. Further, as shown in FIG. 1C, a metal foil 15a may be attached to a resin tape base material 15b to be used as a shape with increased strength. For example, a polyester tape can be used as the tape base material 15b.

  In addition, the metal foil 15a is desirably a metal material that is easy to wind around the outer conductor 13 and that does not melt and disappear at this temperature if the temperature at the time of 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. In addition, this metal foil 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). desirable.

  An outer cover 14 is provided on the outer side of the metal tape 15. As the jacket 14, 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 15 is used to make the inner insulator 12 flame retardant as described above, the outer jacket 14 itself has flame retardancy. preferable. For this reason, it is preferable to use a non-halogen flame retardant polyolefin or a cross-linked flame retardant polyolefin for the jacket 14. As non-halogen flame retardant polyolefins, for example, polyolefin resins containing magnesium hydroxide and aluminum hydroxide as flame retardants are known.

  As a specific example, the outer periphery of the central conductor 11 made of a copper stranded wire was insulated with an insulator 12 made of foamed polyethylene, and the outer conductor 13 was formed on the outer periphery by lateral winding. On the outer periphery of the outer conductor 13, a metal tape 15 formed by attaching a 9 μm thick copper foil to a 12 μm thick polyester tape base material is spirally formed so that the overlapping width W becomes 1/2 of the tape width T. Wrapped around. 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 14, and a non-halogen flame retardant shielded electric wire was produced. .

  When the above-described shielded wire was tested by the VW-1 vertical combustion test method shown in FIG. 3, the combustion test was cleared. In addition, the shield electric wire which used aluminum foil for the metal foil of the metal tape 15, 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 background art. It is a figure explaining the vertical combustion test method of VW-1 of UL specification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Center conductor, 12 ... Insulator, 13 ... Outer conductor, 14 ... Outer coating, 15 ... Metal tape, 15a ... Metal foil, 15b ... Tape base material.

Claims (5)

  A shielded electric wire in which an outer periphery of a central conductor is insulated with a foamed resin insulator, and an outer conductor is wound around the outer periphery and covered with an outer sheath, and is covered with an outer sheath, and a metal between the outer conductor and the outer sheath A shielded electric wire characterized in that a tape is spirally wound and the jacket is formed of a flame retardant polyolefin or a crosslinked flame retardant polyolefin.   The shielded electric wire according to claim 1, wherein the metal tape is obtained by bonding a metal foil to a resin tape base material.   The shielded electric wire according to claim 1 or 2, wherein the overlapping width of the winding of the metal tape is 1/3 to 3/4 of the tape width.   The shielded electric wire according to any one of claims 1 to 3, wherein the metal of the metal tape is a copper foil.   The shielded electric wire according to claim 4, wherein the copper foil has a thickness of 5 μm or more.

Images