JPH0864045A - Highly foamed body covered electric wire and its manufacture - Google Patents

Abstract

PURPOSE: To provide the highly foamed body covered electric wire which has a highly foamed body kept at its center with respect to a conductor core, prevents moisture from being mixed with the highly foamed body to the utmost, and is excellent in dielectric characteristics suitable for a coaxial cable for high frequency signal transmission and the like. CONSTITUTION: A thermal plastic resin composition (resin in an ethylene system + chemical foaming agent/gas foaming agent) capable of foaming is extruded into a filament over a conductor core as a foamed body for covering a conductor, and a foamed body covered conductor core wire is gradually cooled down thereafter while being moved in olgano polysiloxane oil at the temperature of 100 to 20 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-foam covered electric wire and a method for manufacturing the same, and more particularly to a high-frequency signal of high quality in which the covered foam layer is concentric with the inner conductor without being eccentric. The present invention relates to a highly foamed thermoplastic resin-coated electric wire having excellent dielectric properties, which is used for a transmission coaxial cable and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, in coaxial cables and the like used for high frequency signal transmission, the dielectric constant and tan δ have been reduced by increasing the foaming degree of the insulator covering the conductor core wire (making it a high foaming rate). By doing so, the leakage attenuation of the cable is reduced, the image and sound are made clear, and the number of repeaters is reduced. As a method of manufacturing such an insulated wire having a high foaming rate, there are a so-called chemical foaming method and a gas foaming method. In the chemical foaming method, a resin composition is blended with a chemical foaming agent at a temperature not higher than its decomposition temperature, which is supplied to an extruder, extrusion-coated on a conductor at a temperature higher than the decomposition temperature, and then foamed in air. Since it is a method of cooling and solidifying after that, since the equipment cost is lower and the operation is easier than the gas foaming method, the upper limit of foaming degree is about 70%, which is lower than 90% of gas foaming. Instead, it has gained a certain share.
In the gas foaming method, halogenated hydrocarbons, hydrocarbons, nitrogen gas, etc. are injected as high pressure into the molten resin from the middle part of the extruder barrel as a foaming agent without using a pyrolytic chemical foaming agent. It is a method of extrusion coating on a conductor, then foaming this in the air, then cooling and solidifying, but the equipment cost is high,
This method also gains a certain market share because it has high foaming and there is no problem of decomposition residue of chemical foaming agent.

[0003]

In both the chemical foaming method and the gas foaming method, the foam on the conductor core wire extruded in the atmosphere must be cooled and solidified. Conventionally, solidification by cooling is
This is done by passing the foam insulated wire through the cooling water tank, but in general, in order to obtain a foam with a uniform cell structure while balancing foaming and solidification, from the upstream side to the downstream side A cooling water tank is divided into zones in which the water temperature gradually decreases, and the most downstream zone is set to room temperature, and a foam insulated wire is run in the water vessel from the upstream side to the downstream side. However, in this conventional method, the conductor is not covered with the foam in a concentric pattern, which often causes eccentricity. This may be due to the temperature setting of the cooling water tank, but the biggest reason is that when the foam passes through the cooling water, the specific gravity of the foam is about 1/3 to 1/4 of the specific gravity of water. Therefore, while the conductor core wire remains at a fixed position, the foam floats in water and a force acts to deviate from a concentric circle centered on the conductor core wire. Further, when the foam runs through the cooling water, water may enter between the foam particles, which causes a problem that the attenuation rate of the cable deteriorates.

The present invention has been made in order to solve the above-mentioned problems of the prior art, in which the foam is not eccentric with respect to the conductor core wire, and the mixing of water into the foam is suppressed as much as possible. An object of the present invention is to provide a high-quality high-foam covered electric wire and a manufacturing method thereof.

[0005]

The present inventors have found that the eccentricity of the high foam layer and the conductor is such that the specific gravity of the high foam and the specific gravity of water are different, and the buoyancy of the high foam becomes too large. Focusing on the fact that the water remaining in the foam is a cause of deteriorating the characteristics of the high-foam covered electric wire, its specific gravity is smaller than water, and it does not adversely affect the manufacturing environment and manufacturing conditions of the high-foam covered electric wire. When a cooling medium that does not adversely affect the characteristics of the produced high-foam covered electric wire was sought, experiments were conducted using a large number of compounds, and it was found that a specific silicone compound gives good results. The present invention has been completed through studies.

That is, in the present invention, a foamable thermoplastic resin composition is coated on a conductor core wire as a foam from an extruder, and then the foam-covered conductor core wire is dipped in an organopolysiloxane oil. The present invention relates to a method for producing a high-foam covered electric wire, which is characterized by slow cooling. In the present specification, the high foamed material means that the foaming degree is 60% or more. Further, in the present invention, it is preferable to use a high foam having a foaming degree of 70% or more in order to improve the quality of the covered electric wire. Further, in the present invention, as the conductor core wire, any conductor wire can be used, and examples thereof include those made of copper or aluminum.

The thermoplastic resin composition capable of being foamed in the present invention means that 100 parts by weight of the thermoplastic resin contains 0.5 parts of a foaming agent.
˜12 parts by weight is added, and a high foam coating layer can be formed on the conductor core wire by extrusion-coating on the conductor core wire by a known method and then cooling in organopolysiloxane as a cooling medium. It is a thing. In addition, other additives such as an antioxidant and a flame retardant may be added to the thermoplastic resin composition within a range not impairing the object of the present invention.

The thermoplastic resin used in the present invention is, for example, high-pressure low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, density 0.
It is selected from the group consisting of a linear ethylene-α-olefin copolymer of 910 g / ml or more, a linear ultra-low density ethylene-α-olefin copolymer of a density of 0.910 g / ml or less, and a fluororesin. At least one kind.

The foaming agents used in the present invention include so-called chemical foaming agents and gas foaming agents. The chemical foaming agent thermally decomposes to generate an inert gas such as NH ₃ , N ₂ or CO ₂ to foam the plastic, and examples thereof include azodicarbonamide and 4,4′-oxybisbenzenesulfonyl. Examples thereof include hydrazide, N, N'-dinitrosopentamethylenetetramine and azobisisobutyronitrile. Gas blowing agents include halogenated hydrocarbons such as methylene chloride, trichlorofluoromethane, dichlorofluoromethane, chlorodifluoromethane, chlorotrifluoromethane, dichlorodifluoromethane, 1,1-difluoroethane, 1-chloro-1,
Hydrocarbons such as 1-difluoroethane, 1,2-dichlorotetrafluoroethane or chloropentafluoroethane, such as propane, butane, pentane, penrane,
Hexane, hexene, heptene, octane and the like, and inert gases such as nitrogen, argon, helium, carbon dioxide and the like can be mentioned. These chemical foaming agents and gas foaming agents can be used alone or as a chemical foaming agent or a mixture of gas foaming agents or a mixture of a chemical foaming agent and a gas foaming agent.

When a chemical foaming agent is used, a foaming aid of this chemical foaming agent may be used in combination, which includes salicylic acid, stearic acid, phthalic acid, zinc stearate, lead stearate, magnesium stearate, calcium stearate. , Ethylene glycol, glycerin, ethanolamine, urea, urea derivatives, melamine, dibasic lead phosphite, tribasic lead sulfate, zinc oxide, etc. are used, and 0.0003 is added to 1 part by weight of the chemical foaming agent. ~ 0.6 parts by weight of V
Type blender, ribbon mixer, Henschel mixer,
20 ~ 120 ℃ with a mixer such as a tumbler, desirably 3
A chemical foaming agent is obtained by performing a mixing treatment at 0 to 80 ° C.

The organopolysiloxane oil used in the present invention is not particularly limited as long as it is an oily organopolysiloxane and can be represented by the general formula

Embedded image (In the formula, R's each independently represent a monovalent hydrocarbon group,
And m is 2 to 500, n is 0 to 25, and n / m ≦.
It represents an integer in the range of 0.05).
Examples of the group R include a methyl group, an ethyl group, a propyl group,
A butyl group, an octyl group, a decyl group and the like, which may be the same or different in the same molecule. The most desirable example is dimethylpolysiloxane in which all the groups R are methyl groups, because it has the lowest density, and when this is used as a cooling medium, the eccentricity of the foam layer is small. The presence of phenyl groups in the organopolysiloxane molecule has advantages such as heat resistance and low vapor pressure, but slightly increases the density. Therefore, it is preferable to use the organopolysiloxane oil depending on the foaming temperature of the resin composition used. In the present invention, the organopolysiloxane oil may be used alone or in combination with various organopolysiloxane oils.

The m representing the number of diorganopolysiloxane units is from 2 to 500. If it is less than 2, vapor pressure rises, which is not desirable because it causes a loss due to evaporation and the working environment deteriorates. Is too high, the handleability is not good, and removal from the surface of the foam layer is troublesome, which is not desirable. N representing the number of phenylsiloxane units is 0 to 25, and if it exceeds 25, the density increases and the eccentricity of the foam layer increases, which is not desirable. Further, the ratio of n / m is 0.05 or less, and if it exceeds 0.05, the density increases and the eccentricity of the foam layer increases, which is not desirable.

In the present invention, after the foamable thermoplastic resin composition is extrusion-coated on the conductor core wire as a foam,
The foam-coated conductor core, especially the surface of the foam, is gradually cooled by being immersed in an organopolysiloxane oil as a cooling medium. This gradual cooling operation is usually carried out by sequentially passing through an organopolysiloxane oil set so that the temperature gradually decreases from about 100 ° C. to about 20 ° C., but it is not stepwise. It goes without saying that it may be passed through a cooling medium whose temperature continuously decreases. In a preferred embodiment of the present invention, the slow cooling operation is performed by moving the foam-coated conductor core wire in organopolysiloxane oil at 100 to 20 ° C. Further, after cooling to near room temperature in the organopolysiloxane oil, cooling may be performed by air drying.

In the present invention, the apparatus for producing the foam-covered electric wire may be a known apparatus, one example of which is shown in FIG. On the conductor core wire 1 which is wound through the inside of the extruder 3,
After extrusion-coating a thermoplastic resin as a foam 2 from the extruder 3, the foam-coated conductor core wire is sent to a cooling tank 4 filled with an organopolysiloxane oil 5. The organopolysiloxane oil 5 in the cooling tank 4 is divided by partitions 6 into six cooling zones S _{1 to} S ₆ (first section to sixth section) from the upstream (extruder side) to the downstream, The temperature is set to gradually decrease from the first section to the sixth section, and the foam-coated conductor core wire is gradually cooled by sequentially passing through the cooling zones S _{1 to} S ₆ .

[0015]

EXAMPLES The following examples illustrate the effects of the present invention, but the present invention is not limited to these examples.

Example 1 Melt index 2.0 g / 10 minutes, density 0.917
Melt index of 3. with respect to 100 parts by weight of high-pressure low-density polyethylene with g / ml and swelling ratio of 60%.
0 g / 10 min, density 0.960 g / ml, swelling ratio 45%, high-density polyethylene 30 parts by weight with a melting point of 135 ° C., and butylated hydroxytoluene 0.2 parts by weight are blended for 10 minutes with a Banbury mixer. The mixture was kneaded at 140 ° C to obtain a kneaded product having a melting point of 124 ° C. This kneaded product 100
1.3 parts by weight of p, p′-oxybisbenzenesulfonyl hydrazide was added to parts by weight, and the mixture was kneaded at 127 ° C. for 10 minutes using a Banbury mixer to prepare a sheet with a prefoaming degree of 4% and cut with a sheet cutter. Then, a pellet having a thickness of 3 mm, a length of 5 mm and a width of 4 mm was obtained.

Next, a 50 mmφ extruder (L / D = 2
4) supplying the pellets, the cylinder temperature in the supply zone is 130 ° C, the cylinder temperature in the compression zone is 140 ° C,
Cylinder temperature in the measuring area was 147 ° C, and the wire winding speed was 20m / on a copper core wire of 1.8mmφ preheated to 50 ° C.
Extrusion coating in minutes, cooling medium dimethylpolysiloxane (m = 35, n = 0, R are all methyl groups, density 90
0.91 g / cm ³ at ℃, 0.92 g / c at 80 ℃
m ³ , 70 ° C., 0.928 g / cm ³ , 60 ° C., 0.933 g / cm ³ , 50 ° C., 0.94 g / c
m ^3, 0 at 0.95g / cm ^3, 30 ℃ at 40 ° C..
96 g / cm ³ , 0.97 g / cm ³ at 20 ° C) in a cooling tank (first section 3 m long, cooling medium temperature 90 ° C, second section 5 m long, cooling medium temperature 75
℃, the third section is 5m long, the cooling medium temperature is 60 ℃,
The fourth section has a length of 5 m, the cooling medium temperature is 40 ° C, the fifth section has a length of 5 m, the cooling medium temperature is 23 ° C, the sixth section has a length of 2 m, and the cooling medium temperature is 23 ° C. After passing through, a high-foaming polyethylene-coated coaxial cable core having an outer diameter of φ7.3 mm was obtained.

The obtained foam had a foaming degree of 71.0%, a cell diameter of 100 to 150 μm, and a cylindrical test piece of a coaxial cable core having a length of 20 mm was radially compressed at a speed of 10 mm / min. Then, the compressive strength was measured with Young's modulus calculated from the amount of compression (strain) and the force, and it was 0.87 kg / mm ² . The foam layer of this coaxial cable is concentric with the conductor core wire and has an impedance of 75Ω,
Capacitance is 50-51nF / km, attenuation rate is 220MH
57 dB / km at z and 115 dB / k at 770 MHz
m was good at 150 dB / km at 1300 MHz.

Example 2 Instead of the dimethylpolysiloxane used in Example 1, dimethylphenylpolysiloxane (m = 490,
n = 23, n / m = 0.047, all R are methyl groups, the density is 0.965 g / cm ³ at 90 ° C., and the density is 0.8 at 80 ° C.
0.96g / cm ³ at ^{956g / cm 3, 70 ℃,} 6
0.968 g / cm ³ at 0 ° C, 0.971 at 50 ° C
g / cm ^3, 40 ℃ at 0.987g / cm ^3, 30 ℃
0.996 g / cm ³ at 20 ° C. 1.02 g / c
A similar experiment was conducted except that m ³ ) was used.

The eccentricity was slightly larger than that of the coated electric wire obtained in Example 1, but the impedance was 74 Ω, the electrostatic capacitance was 51 to 52 nF / km, and the attenuation rate was 220 MHz.
6 dB / km, 113 dB / km at 770 MHz, 13
It was 147 dB / km at 00 MHz, which was sufficiently practical.

Comparative Example A similar experiment was conducted except that warm water was used as the cooling medium instead of dimethylpolysiloxane which was the cooling medium in Example 1. The eccentricity is much larger than that of the coated electric wire obtained in Example 1, the impedance is 72Ω, the capacitance is 53 to 54 nF / km, and the attenuation rate is 59 at 220 MHz.
121 dB / km, 130 at 770 MHz, dB / km
It was 168 dB / km at 0 MHz, and the characteristics of the coaxial cable were worse than in Example 1.

[0022]

As described above in detail, in the method for producing a high-foam covered electric wire of the present invention, the organopolysiloxane oil is used as the cooling medium instead of the conventional water, so that the conductor core wire It enables the high foam to be coated concentrically without causing eccentricity around the periphery, and the water repellency of the organopolysiloxane oil prevents water from penetrating into the high foam. Also, 100
By cooling in an organopolysiloxane oil at -20 ° C, it is possible to obtain a higher quality, higher foam covered electric wire. Therefore, the present invention provides a method for producing a very high quality high-foam covered electric wire, which makes it possible to provide a coaxial cable for high frequency signals and the like having higher performance than conventional products.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an apparatus for producing a high-foam covered electric wire of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Conductor core wire 2 Foam 3 Extruder 4 Cooling tank 5 Organopolysiloxane oil 6 Partition S _{1 to} S ₆ Cooling zone

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01B 11/18 D // B29K 83:00

Claims (5)

[Claims] 1. A foamable thermoplastic resin composition is coated on a conductor core wire as a foam from an extruder, and then the foam-covered conductor core wire is immersed in an organopolysiloxane oil and gradually cooled. A method for producing a high-foam covered electric wire, comprising: 2. The method for producing a high-foam covered electric wire according to claim 1, wherein the slow cooling is performed by moving the foam-covered conductor core wire in an organopolysiloxane oil at 100 to 20 ° C. 3. The high-pressure process low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, linear ethylene-α-olefin copolymer having a density of 0.910 g / ml or more, density 0.910 g. / M
The method for producing a high-foam covered electric wire according to claim 1 or 2, which is at least one selected from the group consisting of a linear ultra-low density ethylene-α-olefin copolymer having 1 or less and a fluororesin. 4. The organopolysiloxane oil has the general formula: (In the formula, R's each independently represent a monovalent hydrocarbon group,
And m is 2 to 500, n is 0 to 25, and n / m ≦.
The method for producing a high-foam covered electric wire according to any one of claims 1 to 3, which is a compound represented by (expressing an integer in the range of 0.05). 5. A high-foam covered electric wire produced by the method according to any one of claims 1 to 4.