JPH0520928A - Insulated wire and manufacturing method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an insulated wire having a low dielectric constant and a small diameter, and a method for manufacturing the same. [Structure] Expandable particles made of a thermoplastic resin in which a foaming agent is encapsulated are mixed in a dispersion of a crosslinkable thermoplastic resin, and the mixed dispersion is applied to the outer circumference of a conductor to form the expandable particles in a heating furnace. The dispersion of the thermoplastic resin is melted and integrated at a temperature at which foaming does not occur. Then, the thermoplastic resin layer is cross-linked by gamma rays or the like, and then foamed in a heating furnace heated to a temperature at which the expandable particles are foamed or more to obtain a foamed insulator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulated wire which has a low dielectric constant and can be reduced in diameter, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, in advanced fields such as computers and diagnostic equipment, there has been a great demand for insulated wires having a small diameter and a low dielectric constant as the performance of equipment has improved. For this type of application, it is difficult to respond to this with an insulated wire using a normal insulating material, so a foam insulated wire with improved electrical characteristics is used by foaming an insulator.

As a conventional technique for such an insulated wire, for example, a thermoplastic resin mixed with a pyrolytic foaming agent such as azodicarbonamide is extruded on the outer circumference of the conductor, or freon or hydrocarbon is gaseous or liquid. A method of injecting the molten resin into a molten resin in an extruder and foaming the resin has been widely used (Japanese Patent Laid-Open Nos. 1-117210 and 3-97746).

Another method different from this is Japanese Patent Publication No.
Japanese Patent Publication No. 6-43564 discloses a method of melt extrusion of a micro hollow sphere made of an inorganic material such as glass and alumina coated with a thermoplastic resin, and Japanese Patent Publication No. 57-39006 discloses a method. A method for forming a multi-foamed insulator layer by mixing the fine hollow spheres in a solution of a resin such as polyvinyl chloride, which is soluble in a solvent, and applying the dispersion to the outer circumference of the conductor and drying. Is proposed.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 2-242536, a composition comprising an unfoamed sphere containing a foaming agent and an energy ray curable resin is coated on the outer circumference of a conductor, and this coating layer is cured before or after curing. A method for manufacturing an insulated wire in which the foaming agent is foamed by heating is disclosed.

[0006]

Among these conventional foaming methods, in the case of extrusion molding, it is difficult to obtain a foam having a high foaming rate in which the cells are fine and have a uniform diameter.
Moreover, there is a drawback that a thin foam cannot be obtained. In addition, Japanese Patent Publication No. 56-43564 and Japanese Patent Publication 57-
Although the method described in Japanese Patent No. 39006 can easily control the foaming rate, it has a drawback that a highly foamed insulator containing a large amount of fine hollow spheres cannot be obtained due to the mechanical strength of the foamed insulator. . Further, the method described in JP-A-2-242536 is to expand a swellable sphere before or after curing a resin using a curable resin, and when expanding before curing, Since the uncured resin is applied, it is difficult to maintain its shape, and the outer diameter of the coating layer tends to vary. Further, in the case of expanding after curing, since the resin is hardened and its softness hardly changes even when heated, expansion of the expandable sphere is suppressed to some extent. Therefore, in this case, there remains a problem to be solved in any of the methods, such as that a highly foamed product cannot be obtained.

Therefore, in view of these problems of the prior art, an object of the present invention is to provide an insulated wire which has an insulator which can be reduced in diameter and has uniform bubbles and high foaming, and a manufacturing method.

[0008]

In order to achieve the above object, according to the present invention, in an insulated wire in which a foam insulation is provided on the outer periphery of a conductor, the foam insulation is hollow and the shell wall is made of a thermoplastic resin. It is characterized by being formed from a crosslinked thermoplastic resin composition containing spheres.

Further, in order to manufacture such an insulated wire, a mixture of expandable particles made of a thermoplastic resin in which a foaming agent is encapsulated is mixed with a crosslinkable thermoplastic resin, and then the mixture is crosslinked at a temperature not higher than the foaming temperature of the foaming agent. The thermoplastic resin alone is melted to coat the outer circumference of the conductor, and then this coating layer is crosslinked at a temperature not higher than the foaming temperature of the foaming agent, and then heated to a temperature above the foaming agent's foaming temperature, whereby the coating layer becomes a foamed insulator. Can be

In the present invention, the crosslinked thermoplastic resin which holds the hollow spheres dispersedly to form the foamed insulating material is, for example, polyethylene, polypropylene, polystyrene, polyacrylate, polyacrylamide, polyvinyl chloride, polyurethane, polybutene, or chlorinated. It is a crosslinked thermoplastic resin capable of intermolecular crosslinking such as polyethylene, polyamide, polyester, and ethylene-tetrafluoroethylene copolymer resin. Crosslinking of these crosslinkable thermoplastic resins can be carried out by chemical crosslinking with an organic peroxide or the like, or radiation crosslinking with gamma rays, X rays, electron beams or the like. In this case, a cross-linking aid may be added in order to efficiently carry out the cross-linking reaction, and various fillers, flame retardants, antioxidants, etc. may be appropriately mixed for the purpose of improving the properties of the foamed insulation. can do. The cross-linkable thermoplastic resin may have various properties such as powder, pellets and dispersion when mixed with the expandable particles described later. Then, as a method of coating the mixture on the outer week of the conductor, for example, melt extrusion at a temperature at which the expandable particles do not foam, the dispersion phase of the expandable particles or a dispersion of the expandable particles and a cross-linking thermoplastic resin It is possible to coat, etc., especially to obtain a thin insulated wire by thinning the thickness of the foam insulation
Coating is preferred.

The expandable particles mixed in the above-mentioned crosslinkable thermoplastic resin are unexpanded particles containing a low boiling point liquid or a chemical foaming agent which generates a gas by thermal decomposition therein.
The shell wall portion is made of a thermoplastic resin, and the foaming agent inside is vaporized and expanded by heating to form a hollow sphere. The amount of the expandable particles to be blended is appropriately selected depending on the required characteristics of the insulated wire, the presence or absence of other additives, etc., but is not particularly limited, but normally, in the mixture before foaming, the crosslinkable thermoplastic resin 10 is used. It is used in the range of 0.1 to 90 parts by weight with respect to parts by weight. Also, the particle size is not limited in the same manner, and a particle having a spherical diameter after expansion of about 1 to 70 μm is suitably used according to the coating thickness of the insulator.

Specific examples of the low boiling point liquid enclosed in the expandable particles include hydrocarbons such as petroleum ether, isobutane, heptane and hexane, monochlorotrifluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, Examples thereof include low-boiling halogenated hydrocarbons such as dichlorotetrafluoroethane, and methylsilane. Further, as the chemical foaming agent, as an azo foaming agent, azobisisobutyronitrile, azodicarbonamide,
Diethyl azodicarboxylate, diazoaminobenzene, azocyclohexyl nitrile, etc. as hydrazide type benzene sulfonyl hydrazide, p-toluene sulfonyl hydrazide, p, p-oxybisbenzene sulfonyl hydrazide etc., semicarbazide blowing agent p, p- Oxybisbenzenesulfonyl semicarbazide, p-toluenesulfonyl semicarbazide, etc., as a nitroso-based foaming agent, a pyrolytic organic foaming agent such as N, N-dinitrosopentamethylenetetramine, or an inorganic such as ammonium carbonate, sodium bicarbonate, ammonium nitrite, etc. The use of foaming agents is possible.

Examples of the thermoplastic resin containing these foaming agents include polyethylene, polypropylene,
Polystyrene, polyvinylidene chloride, polyacrylonitrile, polyacrylic acid ester, a homopolymer or copolymer such as a heat-meltable fluororesin can be used,
The material is not limited to this and can be appropriately selected as long as it softens by heating and does not hinder the vaporization of the foaming agent. These thermoplastic resins that form the shell walls of hollow spheres expand and become thin, so even if the dielectric constant is a little high, it can be used with little effect, but the low dielectric constant of the material itself, polyethylene, heat melting Fluororesin is particularly preferable.

[0014]

[Function] A mixture of expandable particles and a cross-linking type thermoplastic resin,
The outer circumference of the conductor is coated by a method such as extrusion or coating at a temperature below the temperature at which the foaming agent foams. Then, the coating layer is irradiated with gamma rays or the like to crosslink the crosslinkable thermoplastic resin in the admixture in a state where the expandable particles are not expanded. By this cross-linking reaction, the resin takes a three-dimensional network structure to improve its thermal and electrical properties, and at the same time, its mechanical properties are improved and viscoelasticity suitable for foaming is imparted. Then, by heating the coating layer thus modified into a crosslinked thermoplastic resin to a temperature at which the foaming agent foams or higher to foam the foaming agent in the foamable particles, the foamable particles become hollow spheres. To form innumerable bubbles in the coating layer. In this case, the crosslinked thermoplastic resin that surrounds the expandable particles, although the heat fluidity is lost due to crosslinking, allows the expansion of the expandable particles by appropriately softening when heated, so that unexpanded. Unlike the conventional example in which the expandable particles are dispersed in the cured thermosetting resin, the expandable particles are not pressed from the outside to prevent their expansion, and a foam having a high expansion rate is obtained.

Further, since the unfoamed foaming agent contained in the expandable particles is covered with the thermoplastic resin, it does not aggregate as in the case where the foaming agent is directly mixed with the resin. Moreover, by appropriately selecting the thickness of the shell wall of the expandable particles and the filling amount of the foaming agent, it is possible to control the spherical diameter of the hollow spheres after expansion, so that the foam having a uniform and fine cell diameter can be obtained. Is obtained.

[0016]

FIG. 1 is a sectional view showing an embodiment of an insulated wire according to the present invention. In the illustrated insulated wire 1, a hollow sphere 3 having a shell wall made of a thermoplastic resin is provided around an outer periphery of a conductor 2. And a foamed insulation 5 made of a composition of the crosslinked thermoplastic resin 4.

Next, a method of manufacturing the insulated wire 1 will be described with reference to FIG. The conductor 2 sent from the conductor supply device 10 is coated with a dispersion of expandable particles and a crosslinkable thermoplastic resin on the outer periphery of the conductor with a die 11, and the dispersion layer is heated to a temperature below the temperature at which the expandable particles do not foam. In the heated heating furnace 12, only the cross-linking type thermoplastic resin melts to form a coating layer. Then, this coating layer is irradiated with energy rays such as gamma rays by the irradiation cross-linking device 13,
The crosslinked thermoplastic resin in the coating layer is crosslinked to form the crosslinked thermoplastic resin 4. Further, when the crosslinked coating layer passes through the heating furnace 14 which is maintained at a temperature at which the expandable particles are foamed or higher, the expandable particles are expanded into hollow spheres 3, and the hollow spheres 3 and the crosslinked thermoplastic resin are crosslinked. The foamed insulator 5 is composed of 4 and 4. The insulated electric wire 1 thus covered with the foamed insulation 5 is sent to the winding device 15.

Hereinafter, the insulated wire of the present invention will be described with reference to specific examples, but the present invention is not limited to the embodiments, and modifications can be made within the technical idea of the present invention.

Example 1 70 parts by weight of modified polyethylene (Chemipearl A-100, manufactured by Mitsui Petrochemical Co., Ltd.) in the form of dispersion, and unfoamed expandable particles of acrylonitrile resin in which liquid isobutane was encapsulated (Japan Phillite: Expancel DU-051, average particle size 5 microns,
30 parts by weight of the average particle size after expansion (20 μm) was added and stirred to prepare a mixed dispersion for coating. Then, this mixed dispersion liquid is applied to the outer circumference of a silver-plated annealed copper wire having an outer diameter of 0.19 mm using a die, and this is applied at 60 to 80 ° C.
In the heating furnace described above, only polyethylene was melted to form a 0.05 mm thick coating layer made of a polyethylene composition containing unexpandable expandable particles on the outer circumference of the conductor. Then, the coating layer was irradiated with 20 Mrad gamma rays to crosslink polyethylene, and then the crosslinked polyethylene coating layer was mixed with 9
The expandable particles were foamed by heating again in a heating furnace at 0 to 130 ° C. This makes the coating layer a foam,
Its thickness is increased from 0.05mm to 0.2mm, the outer diameter is 0.
A 59 mm insulated wire according to the invention was obtained.

Next, a semi-rigid coaxial cable in which a copper pipe was provided as an outer conductor on the outer circumference of the insulated wire and its propagation delay time was measured.
It was m. From this fact, the foamed insulator of the insulated wire according to the present invention has a relative dielectric constant of 1.10, which is an electric wire having an extremely low dielectric constant. Further, the tensile strength of the foamed insulator was 100 gf / square millimeter, which was a mechanical strength sufficient for practical use.

Example 2 Low-density polyethylene in the form of fine powder (Sumitomo Seika: MG)
101-N) was dispersed in ion-exchanged water using a surfactant, and the expandable particles used in Example 1 were mixed with this dispersion at a weight ratio of 3: 7 with respect to low-density polyethylene to prepare a coating solution. A mixed dispersion of was prepared. Then, this mixed dispersion was applied to the outer periphery of the conductor, and cross-linking and foaming were performed under the same conditions as in Example 1 to obtain an insulated electric wire. The foamed insulator of this insulated wire has a relative permittivity of 1.10, which is an electric wire having a low permittivity similar to that of Example 1, but compared with that of Example 1 using modified polyethylene, It was somewhat less flexible.

Example 3 A fine powder of polypropylene (manufactured by Sanyo Kasei Co., Ltd .: Viscole) was dispersed in ion-exchanged water using a surfactant, and this dispersion was foamed more than the expandable particles used in both of the above Examples. Effervescent particles with a high temperature (Matsumoto Yushi-Seiyaku Co., Ltd .: Matsumoto Microspheres 85G) were mixed with polypropylene at a weight ratio of 3: 7 to prepare a mixed dispersion liquid for coating. Then, this mixed dispersion liquid is applied to the outer periphery of the conductor,
The insulated wire of the present invention was obtained by melting polypropylene in a heating furnace at 0 to 150 ° C., crosslinking the polypropylene, and then foaming the expandable particles in a heating furnace at 150 to 180 ° C. The foamed insulator of this insulated wire had a relative permittivity of 1.15 and its mechanical characteristics had no problem in practical use.

[0023]

As described above, according to the present invention, an insulated wire having a low dielectric constant and a small diameter can be stably obtained, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an insulated wire according to the present invention.

FIG. 2 is a schematic explanatory view showing an example of a method of manufacturing an insulated wire according to the present invention.

[Explanation of symbols]

1 insulated wire 2 conductors 3 hollow spheres 4 Cross-linked thermoplastic resin 5 foam insulation 11 dice 12 heating furnace 13 Cross-linking device 14 heating furnace

Claims (2)

[Claims] 1. An insulated wire in which a foam insulation is provided on the outer periphery of a conductor, wherein the foam insulation is formed of a crosslinked thermoplastic resin composition containing hollow spheres whose shell walls are made of a thermoplastic resin. Insulated wire characterized by. 2. An admixture in which expandable particles made of a thermoplastic resin in which a foaming agent is enclosed are mixed with a crosslinkable thermoplastic resin,
To melt only the crosslinkable thermoplastic resin below the foaming temperature of the foaming agent to coat the outer circumference of the conductor, then to crosslink this coating layer below the foaming temperature of the foaming agent, and then to heat above the foaming temperature of the foaming agent. According to the method for producing an insulated wire, the covering layer is a foamed insulator.