JP3325642B2 - Manufacturing method of foam insulated wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foamed insulated electric wire, and more particularly to a method for producing a polyolefin-based foamed insulated electric wire capable of controlling the degree of foaming of a foamed insulating coating to a high degree and precisely.

[0002]

2. Description of the Related Art Polyolefin foamed insulated wires are widely used because of their characteristics such as low transmission loss and high high-frequency transmission speed. Conventionally, in order to manufacture a polyolefin foam insulated wire, a resin mixture is prepared by adding a chemical foaming agent and a crosslinking agent such as an organic peroxide to a polyolefin resin, and extruding it onto a core wire with an extruder. After coating, a method is used in which the resin is sent to a foaming and crosslinking furnace heated to 200 to 250 ° C. to form and crosslink at the same time as foaming. Further, as a more efficient production method, instead of using a foaming and crosslinking furnace, a method of heating a die portion of an extruder to a foaming and crosslinking temperature or higher and extruding and simultaneously performing foaming and crosslinking is also performed. When foaming and cross-linking are performed at the same time, the bubbles generated in the foam nuclei expand and the cell walls thicken, and are fixed as closed cells when they have grown to a certain cell diameter.

[0003]

However, in such a conventional method for producing a foamed insulated wire, the growth of the bubbles and the thickening of the cell walls due to the cross-linking proceed simultaneously, and the foaming and the thickening of the bubbles occur. And so on proceed uniformly in the thickness direction of the foam, so that in the vicinity of the surface layer in which the viscosity has not yet been sufficiently increased, a part of the generated gas breaks the cell wall and is diffused to the outside. Therefore, this method could not improve the degree of foaming to a certain degree or more. In addition, since the reaction rates of both foaming and crosslinking are adjusted only depending on the temperature, it is extremely difficult to adjust these balances optimally and constantly. Therefore, not only the foaming degree cannot be increased by the conventional method, but also it is difficult to precisely control the foaming degree. The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a method for producing a polyolefin foam insulated wire in which the degree of foaming of a foamed insulation coating on a foamed insulated wire is high and can be precisely adjusted. Is to provide.

[0004]

The object of the present invention is to extrude a resin mixture obtained by adding a chemical blowing agent to a polyolefin resin onto a conductor, and then heat the resin mixture to a temperature equal to or higher than the decomposition temperature of the chemical blowing agent to cause foaming. After that, the problem can be solved by a method for producing a foamed insulated wire characterized by immediately irradiating an electron beam to crosslink. Further , it is preferable that the irradiation of the electron beam is performed from at least two directions on the side of the electric wire. here,
The polyolefin-based resin is a thermoplastic resin such as polyethylene and EP rubber that can be used as an insulating coating material for electric wires and can be cross-linked by an electron beam. The polyolefin-based resin may include a crosslinking aid, a filler, a coloring agent, and the like for increasing the efficiency of electron beam crosslinking.

[0005]

According to the process of the present invention, a resin mixture containing a chemical foaming agent is extruded onto a conductor, and then the resin mixture is heated to a temperature not lower than the decomposition temperature of the chemical foaming agent to cause foaming. At this time, since the foaming reaction proceeds uniformly in the thickness direction of the foam, bubbles are generated and expanded simultaneously near the conductor and also near the outer periphery of the coating. Then, the foam is irradiated with an electron beam to perform crosslinking. The electron beam has high permeability, and even if bubbles are present, it penetrates into the inside of the coating and induces a crosslinking reaction. At this time, since the cross-linking reaction by the electron beam proceeds from the surface layer part to the inner part, the foam starts to be cross-linked from the surface part by the electron beam to form a gas-impermeable skin layer, and then the inner part. The crosslinking reaction proceeds gradually. Therefore, the generated air bubbles are surrounded by the formed outer wall and are not radiated to the outside, and gas escape is prevented. As a result, high foaming becomes possible. Further, the foaming rate can be adjusted by the heating temperature and the crosslinking reaction can be adjusted by the amount of electron beam irradiation, so that the foaming degree of the coating layer can be precisely adjusted. Since electron beams have high linearity, irradiation from one direction may cause insufficient cross-linking on the back side of the electric wire. Therefore, the irradiation is preferably performed from at least two directions on the side of the electric wire. Equal angle 3
Irradiation from the direction allows the crosslinking reaction to proceed uniformly around the entire circumference.

[0006]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the steps of an embodiment for producing a foamed insulated wire. In this step, first, the conductor core wire A is sent out from the wire feeder 1, straightened by the wire straightening machine 2, straightened by the preheater 3 to remove adhering moisture and the like, and connected to the extruder tip portion 4. Into the crosshead die 5. Separately, from an extruder (not shown), a molten resin mixture P containing a chemical foaming agent is introduced into a crosshead die 5 through an extruder tip 4, where a core wire A is connected to the resin mixture P. Covered. The coated wire B drawn out from the crosshead die 5 is introduced into a heating cylinder 6 and heated and foamed, and then immediately introduced into an electron beam irradiation device 7, where the electron beam is irradiated. Next, the coated wire B is sent to the cooling water tank 8 where it is cooled, a tension for winding is provided in the capstan 9, and the wound wire is wound on a bobbin in the winder 10.

In the process of this embodiment, an AWG25 copper conductor was used as the conductor core wire A. As the resin mixture P, a mixture of 100 parts by weight of low-density polyethylene and 20 parts by weight of azodicarbonamide (chemical blowing agent) was put into an extruder, kneaded and extruded at 120 to 140 ° C., and used. This resin mixture P was coated on the core wire A in the crosshead die 5 so as to have a thickness of 1 mm. The covered wire B pulled out from the crosshead die 5 was heated to 250 ° C. in the heating cylinder 6 to foam. Next, the covering wire B immediately after passing through the heating cylinder 6 is applied to the covering wire B from three equal-angle directions.
The dynamitron electron beam irradiation device 7 was used to irradiate an electron beam while changing the dose in the following three stages to crosslink and cure the resin mixture to obtain foamed insulated wires of Examples 1 to 3. (Example 1) Electron beam irradiation condition: 1 MeV5 mA. (Example 2) Electron beam irradiation conditions: 1 MeV7 mA. (Example 3) Electron beam irradiation conditions: 1 MeV10 mA.

Comparative Example In the step of FIG. 1, as a resin mixture P, 100 parts by weight of low density polyethylene, 20 parts by weight of azodicarbonamide (chemical blowing agent) and 5 parts by weight of dicumyl peroxide (crosslinking agent) were mixed. This resin mixture was put into an extruder, kneaded and extruded at 120 to 140 ° C., and this resin mixture was extruded on a copper conductor A of AWG25 at a thickness of 1 mm in the same manner as in the example, and then heated. 6
To form a foamed insulated wire of a comparative example at 250 ° C. simultaneously with foaming.

(Test) With respect to each of Examples and Comparative Examples, the degree of foaming of the coating layer of the obtained foamed insulated wire was measured. Table 1 shows the results.

[0010]

[Table 1]

From the above test results, it can be seen that the foamed insulated wire obtained by irradiating with an electron beam according to the method of the embodiment and crosslinked by heating using a foaming agent and a crosslinking agent is a comparative example. In comparison, it is clear that it has a high degree of foaming.

[0012]

According to the method of manufacturing the foamed insulated wire of the present invention, a resin mixture obtained by adding a chemical foaming agent to a polyolefin resin is extruded onto a conductor, and then the resin mixture is heated to a temperature not lower than the decomposition temperature of the chemical foaming agent. After then, since immediately those which crosslink by electron beam irradiation, and can separately adjust the reaction conditions of the foaming and crosslinking, together with allowing precise adjustment of the degree of foaming, coating by irradiation of an electron beam Since the cross-linking proceeds from the surface layer of, the generated gas is not released,
A foamed insulated wire having a coating with a high foaming degree can be manufactured.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a foam insulated wire showing one embodiment of the present invention.

[Explanation of symbols]

A: conductor core wire, B: covered wire, P: resin mixture, 5: crosshead die, 6: heating cylinder, 7: electron beam irradiation device.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01B 13/14

Claims (1)

(57) [Claims] 1. A resin mixture comprising a polyolefin resin and a chemical foaming agent added thereto is extruded onto a conductor, and then the resin mixture is foamed by heating it to a temperature not lower than the decomposition temperature of the chemical foaming agent .
In addition, a method for producing a foamed insulated wire characterized by irradiating an electron beam immediately to crosslink.