JP2012234760A - Shield wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shield wire of which flame retardancy is improved based on the relationship between the extent of forming of an insulating body and a pull-out force of a cover.SOLUTION: In the shield wire, a central conductor 1 is covered with an insulating body 2, and a shield conductor 3 is arranged on its outer periphery, with a cover 4 covering the periphery. The central conductor 1 has a diameter equivalent to AWG24 or less. The insulating body 2 is made from a foamed polyolefin resin. The shield conductor 3 is formed by winding a plurality of conductive wires around it in spiral. The cover 4 is made from a halogen-free flame-retardant resin. The pulling-out force of the cover is 1.0-7.0 (N) when the capacitance of the insulating body is 70-80 (pF/m). The pulling-out force of the cover is 1.0-4.0 (N) when the capacitance of the insulating body is more than 80 (pF/m) and equal to 90 (pF/m) or less.

Description

  The present invention relates to a shielded electric wire in which a central conductor is covered with an insulator, a shield conductor is disposed on the outer periphery thereof, and the periphery thereof is covered with an outer jacket.

  As shown in FIG. 1, a shielded electric wire (also referred to as a shielded cable) used for signal transmission within and between communication devices is such that a central conductor 1 is covered with an insulator 2 and a shield conductor 3 is arranged on the outer periphery thereof. The outer periphery of the outer cover 4 is formed in a coaxial shape with a small diameter (equivalent to AWG24 or less) (see, for example, Patent Document 1). This shielded wire is used, for example, in wiring that forms a signal transmission path in electronic equipment, and reduces the influence of external noise and the like, and reduces electromagnetic waves radiated to the outside. Sometimes it says.

  In recent years, even for shielded electric wires with a small diameter as described above used for wiring in electronic devices, it is required to be flame retardant so that the fire does not spread through the electric wires in the event of a fire in the device. . In order to give flame resistance to the shielded wire, as disclosed in the above-mentioned Patent Document 1, the outer sheath of the wire is made of polyvinyl chloride (PVC), polyolefin resin such as polyethylene, chlorine or bromine. Those made flame retardant by adding a flame retardant are considered effective. In addition, about the flame retardance regarding an apparatus wiring material, the evaluation by the vertical combustion test called the VW-1 test in US UL (Underwriters Laboratories), for example is often made into one standard.

JP 2002-298663 A

In order to increase the flame retardancy of shielded wires, it is effective to use a halogen compound for the jacket, but generation of highly corrosive halogen gas during incineration is regarded as a problem as one of the global environmental pollution. Therefore, there is a demand for the development of shielded wires that do not contain halogen compounds (halogen-free).
The present invention has been made in view of the above-described actual situation, and an object thereof is to provide a shielded electric wire having a halogen-free insulator and a jacket and having improved flame retardancy.

A shielded electric wire according to the present invention is a shielded electric wire in which a central conductor is covered with an insulator, a shield conductor is disposed on the outer periphery thereof, and the periphery thereof is covered with an outer sheath. The body is made of a foamed polyolefin resin, the shield conductor is formed by spirally winding a plurality of conductors, and the jacket is made of a halogen-free flame-retardant resin. When the electrostatic capacity of the insulator is 70 (pF / m) or more and 80 (pF / m) or less, the pulling force of the outer jacket is 1.0 to 7.0 (N), and the insulator When the electric capacity is more than 80 (pF / m) and not more than 90 (pF / m), the drawing force of the outer jacket is set to 1.0 to 4.0 (N).
Moreover, it is preferable that the winding pitch of a shield conductor is 8 to 12 times the winding diameter of a shield conductor.

  According to the present invention, a shielded electric wire can be obtained by changing the pulling force of the outer sheath when the capacitance of the insulator is small (the degree of foaming is large) and when the capacitance is large (the degree of foaming is small). As a flame retardant, it can be improved.

It is a figure explaining the shielded electric wire made into the object of this invention. It is a figure explaining the measuring method of the pulling-out force of the jacket in this invention. It is a figure which shows the VW-1 test method which determines the flame retardance of an electric wire. It is a figure which shows the test result of the shielded electric wire by this invention.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a shielded electric wire targeted by the present invention. In the figure, 1 is a central conductor, 2 is an insulator, 3 is a shield conductor, and 4 is a jacket.
As shown in the figure, the shielded electric wire according to the present invention covers, for example, a central conductor 1 made of stranded wire with an insulator 2, a shield conductor 3 is arranged on the outer periphery of the insulator 2, and the outer side is covered with a jacket 4. It is a coated coaxial wire.

The center conductor 1 is made of, for example, tin-plated annealed copper wire, and seven wires are twisted together to make it thinner than AWG # 24 (conductor cross-sectional area is 0.23 mm ² or less, conductor outer diameter 0.55 mm or less) Is used. For example, a conductor having a conductor outer diameter of 0.38 mm (corresponding to a conductor cross-sectional area of 0.089 mm ² AWG28) is used by twisting seven strands having an outer diameter of 0.127 mm.

  For the insulator 2, a foamed polyolefin resin such as foamed polyethylene is used. For example, the insulator 2 is formed with an insulator thickness of about 0.35 mm and an insulator outer diameter of about 1.07 mm. The capacitance obtained by this insulator is 80 ± 10 (pF / m), that is, 70 (pF / m) to 90 (pF / m), and the capacitance varies depending on the degree of foaming. When the foaming degree is larger than the target value, the capacitance becomes small, and when the foaming degree is smaller than the target value, the capacitance becomes large.

  The shield conductor 3 is made of a tinned annealed copper wire similar to the center conductor 1, and a plurality of conductive wires that are the same as or slightly thinner than the strands of the center conductor are spirally wound around the outer periphery of the insulator 2. It is formed. As this conductor, for example, when the size of the central conductor is equivalent to AWG # 28 and the outer diameter is 0.1 mm, the outer diameter of the shield conductor 3 when wound is about 1.3 mm. Further, the winding pitch of the conducting wire is preferably about 8 to 12 times the winding diameter of the shield conductor 3. If the shield conductor diameter is about 1.3 mm, the winding pitch is about 10 mm to 16 mm. However, if the winding pitch is too small, the winding of the conductive wire will rise, and if the winding pitch is too large, the winding will be easily broken. It becomes difficult.

  For the jacket 4 covering the periphery of the shield conductor 3, a halogen-free flame-retardant resin is used instead of the halogen-based resin. As the flame retardant resin, for example, a flame retardant resin composition in which magnesium hydroxide is added to a resin containing a thermoplastic polyurethane elastomer and an ethylene vinyl acetate copolymer as disclosed in Japanese Patent No. 4412407. Can be used. This flame-retardant resin is formed by extrusion molding so that, for example, the thickness is about 0.35 mm and the outer diameter is about 2.0 mm.

  In the above-described shielded electric wire, the fact that the capacitances of the insulators are different with the same insulator material and the same size and shape means that the foaming degree of the insulator is different. And if the foaming degree of an insulator differs, a flame retardance will differ. In this case, it is clear from various test results that the flame retardance is better when the foaming degree is larger than the one with a smaller foaming degree, and further, the flame retardancy changes depending on the degree of adhesion of the jacket with respect to the foaming degree of the insulator. did.

  The present invention is characterized in that in a shielded electric wire using a foamed insulator, flame retardancy is improved in relation to the degree of foaming of the insulator and the degree of adhesion of the jacket. Note that the capacitance value (pF / m) is used as an index indicating the foaming degree of the insulator, and the pulling force (N) of the jacket is used as the index of the foaming degree.

The pulling force of the jacket in the present invention is measured by the method shown in FIG.
(1) Strip the shield conductor 3 by removing the outer cover 4 of the shield wire by a length of 50 mm. Next, the shielded wire is cut at a position 100 mm from the tip of the shield conductor 3 and the outer cover 4 is left for a length of 50 mm for measurement.
(2) A die 10 having a hole with an inner diameter larger than the outer diameter of the shield conductor 3 and smaller than the outer diameter of the jacket 4 is prepared, and the shield conductor 3 of the shield wire is inserted into the hole of the die 10.

  Next, the exposed end of the shield conductor 3 is gripped by the clamp member 11, the die 10 is gripped by the clamp member 12, and the die 10 is fixed so as not to move. Then, the shield conductor 3 is pulled at a speed of 200 mm / min so that the shield conductor 3 is pulled out from the jacket 4 having a length of 50 mm. The force (N) required to pull out the shield conductor 3 at this time is defined as the degree of adhesion.

  Also, the UL standard VW-1 vertical combustion test is performed by the method shown in FIG. In this combustion test method, a sample 14 (test electric wire) having a length of about 60 cm is vertically held by a pair of holding portions 15 arranged at the upper and lower positions of the shielding wall 19. The flame 17 of the gas burner 16 is adjusted so that the outer red outer flame 17a is 127 mm and the inner blue inner flame 17b is 38 mm, and the tip of the flame 17 is applied to the sample 14 at an angle of 20 °. A flag 18 is attached at a position 25 cm above the position where the tip of the flame 17 is applied. The flag 18 is attached by wrapping around the sample 14 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 17 is ignited for 15 seconds and extinguished for 15 seconds. After repeating this for 5 cycles, the flame 17 is extinguished within 60 seconds after being ignited, and the flag 18 does not burn more than 25% is accepted.

  FIG. 4 is a diagram showing the result of testing the combustion characteristics by the electrostatic capacity of the shielded wire (foaming degree of the insulator) and the drawing force (adhesion degree) of the jacket. As a shielded wire sample used for the test, a conductor equivalent to AWG28 in which seven strands having an outer diameter of 0.127 mm were twisted to the center conductor was used. For the insulator, radiation-crosslinked foamed polyethylene is used, the thickness is 0.35 mm, the outer diameter is 1.07 m, and the capacitance is different in the range of 70 to 90 (pF / m). I made several things. For the shield conductor 3, a plurality of conductor wires having an outer diameter of 0.1 mm were horizontally wound so that the shield conductor diameter was 1.3 mm.

  The jacket is made of a flame retardant resin containing 50 parts by weight of thermoplastic polyurethane elastomer, 50 parts by weight of ethylene vinyl acetate copolymer, and 120 parts by weight of magnesium hydroxide, so that the pulling force on the shield conductor is different. Samples 1 to 11 were prepared. The pulling force was varied by changing the distance between the die and the point when extruding the jacket. With respect to the various shielded wires of Samples 1 to 11, the capacitance and the pulling force of the jacket were measured, and the flame retardancy test described in FIG. 3 was performed. As a result of the flame retardancy test, a case where the passing rate in the combustion test was 70% or more was rated as ◯, and a case where the passing rate was less than that was marked as x.

  From the test results, in the range where the capacitance of samples 1 to 7 is in the range of 70.5 to 80.0 (pF / m), that is, in the range where the foaming degree of the insulator is (medium to large), the outer casing is drawn. The flame retardancy was good in the range where the strength is 1.2 to 6.0 (N) and the degree of adhesion is (small to medium). On the other hand, in the range where the capacitances of the samples 8 to 11 are in the range of 81.3 to 88.1 (pF / m), that is, in the range in which the foaming degree of the insulator is (small to medium), the extraction force of the jacket is The flame retardancy was good in the range where the adhesion degree of 1.0 to 3.6 (N) was (small to medium).

  From the above, roughly, in the range of the capacitance of 70 to 80 (pF / m), the extraction force of the jacket is set to 1.0 to 7.0 (N), and the capacitance is 80 to 90 ( In the range of pF / m), it can be said that the flame retardancy can be improved by setting the pulling force of the outer jacket to 1.0 to 4.0 (N).

  In the present invention, the degree of freedom of the shielded electric wire can be increased by combining the foaming degree of the insulator (expressed by electrostatic capacity) and the drawing force of the jacket. If the pulling force of the jacket is too small, workability is poor at the time of terminal processing, and there is a problem that the position is shifted after the connector is attached. It has been found that increasing the pulling force of the jacket is disadvantageous in terms of flame retardancy, but if the foaming degree of the insulator is increased (capacitance decreases), flame retardancy can be ensured. I understood.

DESCRIPTION OF SYMBOLS 1 ... Center conductor, 2 ... Insulator, 3 ... Shield conductor, 4 ... Outer jacket.

Claims (2)

A shielded electric wire covering the center conductor with an insulator, arranging a shield conductor on the outer periphery, and covering the periphery with a jacket,
The central conductor has a small diameter equivalent to or smaller than AWG24, the insulator is made of foamed polyolefin resin, the shield conductor is formed by winding a plurality of conductors in a spiral shape, and the jacket is a halogen-free flame-retardant resin Consists of
When the electrostatic capacity of the insulator is not less than 70 (pF / m) and not more than 80 (pF / m), the pulling-out force of the jacket is 1.0 to 7.0 (N), and the insulator When the electrostatic capacity is more than 80 (pF / m) and not more than 90 (pF / m), the shield wire is characterized in that the extraction force of the jacket is 1.0 to 4.0 (N).   The shielded wire according to claim 1, wherein a winding pitch of the shield conductor is 8 to 12 times a winding diameter of the shield conductor.

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