JPH038219A - Manufacturing method of foamed plastic electric wire - Google Patents

Abstract

PURPOSE:To improve the electric characteristic and mechanical characteristic of a conductor by coating the conductor with plastics having no foaming agent contained therein, subsequently coating the resultant conductor with another plastics having a foaming agent contained therein, and then foaming this coated plastics having its foaming agent contained therein. CONSTITUTION:A conductor 4 is coated with plastics having no foaming agent contained therein by means of a crosshead 2a constructed in such a manner that the surface of the plastics having no foaming agent contained therein may be coated with another plastics having its foaming agent contained therein, and the coated plastics having its foaming agent contained therein is foamed subsequently. On this account, a foam insulator may be equally formed in the circumferential direction of the conductor so as to manufacture a foam plastics cable capable of improving the electric characteristic and mechanical characteristic thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a foamed plastic electric wire.

[Prior Art] FIG. 2 shows a conventional example of an extrusion device used for manufacturing conventional foamed plastic electric wires.

As shown in the figure, the extrusion apparatus includes a crosshead 2 in which a plastic extruder 1a that does not contain a foaming agent and a plastic extruder 1b that contains a foaming agent are connected. In extrusion using the Cross-Head Lad 2 configured in this way, the inner layer of plastic not containing a foaming agent and the outer layer of plastic containing a foaming agent are placed at the nipple 3.
There are two layers near the tips of wires a and 3b, and after extrusion coating is applied around the core wire (conductor) 4 while maintaining this two layer state,
It is foaming. As described above, conventional foamed plastic electric wires have been manufactured by two-layer coextrusion. In addition, in the figure, 5 is a die.

[Problems to be Solved by the Invention] According to the studies of the present inventors, in the above-mentioned conventional technology, it is difficult to uniformly form the foamed insulator serving as the outer layer in the circumferential direction. As described above, unless the foamed insulator is formed uniformly in the circumferential direction, a foamed plastic electric wire with good electrical properties cannot be obtained.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a foamed plastic electric wire that enables improved electrical properties and mechanical properties.

[Means for Solving the Problems] The above object is a crosshead configured so that a plastic containing a foaming agent is coated on a plastic not containing a foaming agent, and the plastic not containing a foaming agent is coated on a conductor. This is achieved by coating the plastic containing the blowing agent and foaming the coated plastic containing the blowing agent.

[Operations] Since the above means is provided, the foamed insulator is formed uniformly in the circumferential direction, and the electrical and mechanical properties are improved.

[Example〕 The present invention will be described below based on the illustrated embodiment ρ1.

FIG. 1 shows an extrusion device according to one embodiment of the invention. In this embodiment, a crosshead 2a is configured such that a plastic containing a foaming agent is coated on a plastic that does not contain a foaming agent, and after coating a conductor 4 with a plastic that does not contain a foaming agent, The plastic was coated and the coated plastic containing the foaming agent was allowed to foam. By doing so, the foamed insulator can be formed uniformly in the circumferential direction, and a method for manufacturing a foamed plastic electric wire that can improve the electrical properties and mechanical properties can be obtained.

That is, the cross head 2a is the nipple 3a.

In steps 3b and 3c, the extruder 1a is extruded and coated with the foaming agent-free plastic from the extruder 1a as the inner layer and the foaming agent-containing plastic as the outer layer. After the blowing agent-free plastic from is coated around the conductor, the extruder 1
The plastic containing the foaming agent from b is covered once as an outer layer and exits to the outside through the die 5, thereby foaming to form a foamed plastic.

In this way, according to this embodiment, by separately coating the inner layer with a plastic that does not contain a foaming agent and the outer layer with a plastic that contains a foaming agent within the same crosshead, it is possible to improve the mechanical and electrical properties in the circumferential direction. Uniformity can be achieved.

In addition, the plastics used for the inner layer in the present invention include low density polyethylene, medium density polyethylene, high density polyethylene, polypropylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer, and copolymer of ethylene and acrylic monomer. Examples include polymers and bolybdenum. Also, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP).

Ethylene-tetrabutylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECT
FE), vinylidene fluoride (p V d F
) and other fluororesins can also be mentioned.

The plastic used for the outer foam layer is preferably of the same type as the filler plastic, but may be of a different type.

These foamable plastics include chemical blowing agents such as azodicarbonamide and 4,4'-oxybisbenzenesulfonyl hydrazide, inert gases such as nitrogen, argon, and carbon dioxide, and methane, propane, butane, and pentane. Hydrocarbons, fluorocarbons such as monofluorotrichloromethane, difluorodichloromethane, trifluorotrichloroethane, and tetrafluorodichloroethane are uniformly incorporated as blowing agents. Further, if necessary, an inorganic fine powder such as boron nitride is used as a nucleating agent.

[Effects of the Invention] As mentioned above, the present invention is a crosshead configured such that plastic containing a foaming agent is coated on a plastic containing no foaming agent, and the plastic not containing a foaming agent is coated on a conductor. After that, the plastic containing the foaming agent was coated, and the coated plastic containing the foaming agent was foamed, so that the foamed insulation was formed uniformly in the circumferential direction, and the electrical and mechanical properties were improved. It is possible to improve the

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view of an extrusion apparatus according to the method of manufacturing a foamed plastic electric wire of the present invention, and FIG. 2 is a longitudinal sectional side view of an extrusion apparatus according to a conventional method of manufacturing a foamed plastic electric wire. 1a: Plastic extruder without foaming agent; 1b: Plastic extruder containing foaming agent; 2a: Crosshead; 4: Conductor.

Claims (1)

[Claims] 1. A foamed plastic electric wire that is equipped with a crosshead in which a plastic extruder that does not contain a foaming agent and an extruder that contains a foaming agent are connected, and that these extruders and crosshead extrude and form a foamed plastic insulator around the outer periphery of the conductor. In the manufacturing method, after coating the conductor with the foaming agent-free plastic using the crosshead configured to coat the foaming agent-containing plastic on the foaming agent-free plastic, the 1. A method for producing a foamed plastic electric wire, comprising the steps of: coating a plastic containing a foaming agent; and foaming the covered plastic containing a foaming agent.