JP3239684B2 - Foam insulated wire and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed insulated wire for high-speed signal transmission, which is lightweight and has excellent mechanical strength, especially bending resistance even when it is thinned.

[0002]

2. Description of the Related Art Foam insulation which secures the overall mechanical strength by covering the outer periphery of a conductor with a foam and further forming a non-foamed solid layer on the outer periphery to form an insulating layer having a two-layer composite structure. Electric wires are widely used for various communication cables and coaxial cables. For example, as described in Japanese Utility Model Publication No. 60-10026, an insulated coaxial cable in which a composite insulating layer with a solid plastic layer is provided on a polyethylene layer having a foaming degree of 65% or more is disclosed in Japanese Utility Model Publication No. 6-38119. As described in, a double-layer insulated wire in which a composite insulating layer of a foamed polyethylene layer and a non-foamed polyethylene layer is formed on a stranded wire conductor, and as described in JP-A-5-2938, A foamed insulated wire and the like are known in which a foamed layer made of a mixture of an ethylene-based polymer and polypropylene is simultaneously coated with a polypropylene containing no foaming agent.

[0003]

A communication cable for a mobile object and a cable for wiring a computer peripheral device are required to be thinner in order to reduce the signal processing time and to reduce the weight and size. In order to shorten the signal processing time, it is necessary to increase the foaming. However, when the foaming is increased, the strength of the electric wire is weakened. Furthermore, when this is made thinner, a very high strength wire structure is required. In particular, in order to maintain the bending resistance in the state of a cable with a highly foamed and thinned cable, simply using a hard material for the foamed wire will cause the wire to buckle due to bending. There was a problem that the characteristics deteriorated.

[0004]

As a result of various studies on the above problems, the present inventor has found that a conductor is coated with a composite insulating layer of a crosslinked polyethylene-based foam layer and an uncrosslinked, unfoamed polypropylene-based coating layer. The present inventors have found that a foamed insulated wire which is lightweight and excellent in electrical characteristics and bending characteristics can be obtained even if the wire is thinned, and the present invention has been completed. That is,
The present invention is: foamed on a conductor to a foaming degree of 35% or more and a gel fraction of 40%
Provided is a foamed insulated wire in which a crosslinked polyethylene-based foam layer crosslinked as described above is coated, and an upper layer thereof is further coated with an uncrosslinked, unfoamed polypropylene coating layer. Also,

Another characteristic is that the polyethylene constituting the crosslinked polyethylene foam layer contains 50% or more of high-density polyethylene having a melting point of 120 ° C. or more. In addition, the foamed insulated wire described above includes at least one core of a foamed insulated wire in which a shield layer made of a metal layer is applied, and another insulated wire or a foamed insulated wire is combined to form a multicore foamed insulated wire covered with a sheath. provide. In addition, after forming a polyethylene foam layer having a foaming degree of 35% or more on the conductor and crosslinking by irradiation to a gel fraction of 40% or more,
Provided is a method for producing a foamed insulated electric wire in which an uncrosslinked, unfoamed polypropylene covering layer is formed as an upper layer.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing the basic structure of the foamed insulated wire of the present invention. The structure of the foam insulated wire of the present invention will be described with reference to FIG. The foamed insulated wire of the present invention basically foams on the conductor 1 to a degree of foaming of 35% or more and has a gel fraction of 40%.
It has a structure in which the crosslinked polyethylene-based foamed insulating layer 2 crosslinked as described above is covered, and a non-crosslinked, unfoamed polypropylene covering layer 3 is further coated thereon.

The polyethylene constituting the crosslinked polyethylene foam layer is not particularly limited, and examples thereof include low-density polyethylene, ultra-low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and ethylene-α-olefin copolymer. Base polymers as the main component can be exemplified. Of course, a polymer, such as polypropylene, ethylene-ethyl acrylate-based copolymer, ethylene-vinyl acetate-based copolymer, which does not significantly reduce the electrical properties, is blended with the above base polymer constituting the crosslinked polyethylene foam layer in an amount of 10% or less. May be.

The crosslinked polyethylene foam layer has a foaming degree of 35%.
Or more, preferably 40% to 80%, more preferably 50% to 80%.
% To 70%. Foaming degree is 35%
If it is smaller, the capacitance increases, and the electrical characteristics deteriorate. Although the foaming method is not particularly limited, for example, a chemical foaming method using azodicarbonamide, dinitropendamethylenetetramine, oxybisbenzenesulfonyl hydrazide, or the like, or a gas foaming method using nitrogen gas, chlorofluorocarbon or the like may be used.

In the case of the present invention, the polyethylene foam layer must be crosslinked to a gel fraction of 40% or more, preferably 50% to 90%, more preferably 60% to 80%. The gel fraction referred to here means a value determined by immersing in xylene at 120 ° C. for 8 hours and measuring the weight of the fraction insoluble in xylene. If the gel fraction is lower than 40%, there arises a problem that the polyethylene-based layer shrinks at the time of soldering at the end processing, or the polyethylene-based foamed layer is melted and bubbles are crushed.

Irradiation such as electron beam irradiation can be preferably used to crosslink the polyethylene foam layer to a predetermined gel fraction. Of course, a peroxide crosslinker is preliminarily blended with the polyethylene material to prepare a conductor. It may be thermally crosslinked after extrusion coating. The acceleration voltage and irradiation amount of the radiation irradiation are not particularly limited as long as a predetermined gel fraction can be obtained, but the electron beam acceleration voltage is usually about 0.5 to 3 MV, and the irradiation amount is preferably about 50 kGy to 500 kGy.

When the polyethylene-based foam layer contains 50% or more of high-density polyethylene having a melting point of 120 ° C. or more, it is less crushed when formed into an electric wire and has excellent electric characteristics. For the polypropylene coating layer coated on the polyethylene foam layer, a propylene-ethylene block copolymer or a propylene-ethylene random copolymer may be used in addition to the propylene homopolymer. This polypropylene coating layer must be uncrosslinked and unfoamed. When crosslinked and foamed, the elongation of the polypropylene is lost, and the bending characteristics are deteriorated. If necessary, additives such as a lubricant, an antioxidant, a light stabilizer, a filler, a flame retardant, and a pigment may be added to the polymer material constituting the foamed layer and the coating layer.

[0012] In order to produce the foamed insulated wire of the present invention, there is no particular limitation as long as a wire having a predetermined composition and structure can be obtained. A preferred production method is a polyethylene foam having a foaming degree of 35% or more on the conductor. The layer is formed by molding means such as extrusion, and after crosslinking with an electron beam or the like to a gel fraction of 40% or more, an uncrosslinked, unfoamed polypropylene coating layer is formed on the upper layer by molding means such as extrusion. good.
Since the polypropylene coating layer must be uncrosslinked,
When cross-linking the foamed polyethylene-based layer with an electron beam or the like,
After extruding the polyethylene layer, electron beam crosslinking is performed, and then the polypropylene layer is extruded. For this reason,
It is desirable that extrusion of the polyethylene layer and extrusion of the polypropylene layer be performed separately.

FIG. 3 is a schematic view showing a cross-sectional structure of a coaxial electric wire in which a copper tape winding layer and an insulating sheath layer are provided on a foamed insulated electric wire of the present invention, and a sheath layer is provided on a plurality of cores.
That is, in order to enhance the signal transmission characteristics, the foamed insulated wire of the present invention is provided with an insulating sheath layer 9 on the foamed insulated wire provided with the shield layers 7 and 8 comprising a copper tape and a horizontally wound shield, The above may be combined into a multi-core foamed insulated wire that is collectively covered with the sheath layer 10.

FIG. 4 is a schematic diagram showing a cross-sectional structure of a coaxial electric wire in which a plurality of insulated electric wires are arranged around the coaxial electric wire of FIG. 3 and a sheath layer for integrating them is provided. That is, the sheath insulating layer 11 around the conductor 1 around the coaxial electric wire of FIG.
A plurality of insulated wires covered with a wire may be arranged as signal wires, and a heat multi-core foamed insulated wire may be collectively covered with the sheath 10.

[0015]

The present invention will be illustrated by the following examples, which do not limit the scope of the present invention. (Example 1) As a conductor, a tin-plated annealed copper wire with seven strands having a diameter of 0.2 mm was used. MI
= 0.9, high-density polyethylene having a density of 0.95, and a foaming compound obtained by adding 1 wt% of azodicarbonamide as a foaming agent were extruded with an extruder to obtain an outer diameter of 1.2 mmφ.
A foam insulated wire having a foaming degree of 50% was prepared. The electric wire was irradiated with an electron beam having an accelerating voltage of 1 MV at 200 kGy to crosslink. The gel fraction was 62%. Further, a propylene-ethylene block copolymer having MI = 2 was coated on the foamed polyethylene wire with a thickness of 0.2 mm to prepare a crosslinked / foamed insulated wire having the structure shown in FIG.

This wire was subjected to a 180-degree bending test according to the bending test method shown in FIG. In this case, the number of bends was measured until the insulation was cracked by the bending and the conductor and the supporting metal became conductive. Result 1
There were more than ten thousand bends. Also, in order to check whether the insulation shrinks due to the heat of soldering when the wire is processed at the end, place a 200 mm long wire in a 200 ° C thermostat.
After heating for one minute and measuring the shrinkage length of the insulation, the shrinkage of the insulation was 0.25 mm.

(Examples 2 to 5) In the same manner as in Example 1,
An electric wire was prepared using the foam layer and the coating layer shown in Table 1. In all cases, the number of bending was 10,000 or more. (Example 6) On the electric wire obtained in Example 4, a thickness of 25 μm was applied.
m copper tape is wound thereon, a PVC sheath is applied to an electric wire which is horizontally wound with a tin-plated annealed copper wire, two electric wires are twisted, and a PVC sheath is further coated thereon as shown in FIG. A two-stranded coaxial electric wire was prepared. Using the same bending test apparatus as in Example 1, this electric wire was measured for the number of bending times until a crack occurred in the foam layer and the center conductor was electrically connected to the copper tape layer. As a result, the number of bending was 23,586.

(Embodiment 7) The shielded electric wire was the same as in Embodiment 6, four insulated electric wires were arranged as signal lines around it, and a sheathed coaxial electric wire was prepared. The number of times of bending was 21,879 times.

(Comparative Examples 1-2) As shown in Table 1, PP
Irradiates the bending characteristic to 10,000 times or less. Even if high-density polyethylene (HDPE) is used instead of polypropylene (PP) as the coating layer, the bending characteristics are poor. (Comparative Example 3) An electric wire having the same structure as that of Comparative Example 1 and not irradiating the foam layer and the coating layer was prepared.

[0020]

[Table 1]

(Note) Foaming degree 40% Conductor 0.20mmφ Tin-plated soft copper wire 7 strands Foaming layer outer diameter 1.2mmφ Coating layer outer diameter 1.6mmφ Bending test 180 degree bending, load 500g, speed 30 times / min Heat shrinkage 200 ° C 1 minute, 1 = 150mm 1) MI = 2.0 at 190 ° C, low density polyethylene 0.92 specific gravity 2) MI = 230 at 230 ° C, 0.90 propylene-ethylene block copolymer 3) MI = 230 at 230 ° C Propylene-ethylene random copolymer, specific gravity 0.90 4) MI at 190 ° C = 5.0, specific gravity 0.95 high density polyethylene 5) MI at 190 ° C = 1.0, specific gravity 0.89 ultra-low density polyethylene

[0022]

As described above, the foamed insulated wire of the present invention is a foamed insulated wire which is lightweight and has excellent bending resistance even when the diameter is reduced, and is particularly suitable for high-speed signal transmission.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a basic structure of a foamed insulated wire of the present invention.

FIG. 2 is a schematic view illustrating a method for testing a bending resistance of a foamed insulated wire according to the present invention.

FIG. 3 is a schematic diagram showing a cross-sectional structure of a coaxial electric wire in which a copper tape winding layer and an insulating sheath layer are provided on a foamed insulated electric wire of the present invention, and a sheath layer is provided on a plurality of cores.

FIG. 4 is a schematic diagram showing a cross-sectional structure of a coaxial cable in which a plurality of (foamed) insulated cables are arranged around the coaxial cable of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductor 2 Crosslinked polyethylene foam layer 3 Polypropylene coating layer 4 Foamed insulated electric wire of the present invention 5 Load 6 Support metal rod 7 Copper tape winding layer 8 Tin-plated soft copper wire horizontal winding shield layer 9 Sheath layer 1 10 Sheath layer 2 11 Insulation layer

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01B13 / 14 H01B13 / 14B (56) References JP-A-5-28838 (JP, A) JP-A-5-2938 ( JP, A) JP-A-63-216218 (JP, A) JP-A-3-67416 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 7/02 H01B 13/14

Claims (4)

(57) [Claims] 1. A conductor is coated with a cross-linked polyethylene foamed layer foamed to a foaming degree of 35% or more and crosslinked to a gel fraction of 40% or more, and further coated with an uncrosslinked and unfoamed polypropylene covering layer. A foam insulated wire. 2. The foam insulated wire according to claim 1, wherein the polyethylene constituting the crosslinked polyethylene foam layer contains at least 50% of high-density polyethylene having a melting point of 120 ° C. or higher. 3. The foamed insulated wire according to claim 1, including at least one core of a foamed insulated wire provided with a shield layer made of a metal layer, another insulated wire or a foamed insulated wire being compounded and covered with a sheath. A multi-core foam insulated wire, characterized in that: 4. Forming a polyethylene-based foamed layer having a foaming degree of 35% or more on a conductor, irradiation-crosslinking to a gel fraction of 40% or more, and then forming an uncrosslinked, unfoamed polypropylene coating layer on the upper layer. A method for producing a foamed insulated wire.