JPS604531B2 - Method for manufacturing cross-linked highly foamed insulated wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a foam insulated wire with excellent adhesive properties between a conductor and an insulator and excellent appearance properties.

High-speed information circuits for computers, telephone communications, and the like require low-permittivity, low-capacity wires, and foamed polyethylene insulated wires are often used for this purpose.

However, with the conventional manufacturing method of adding a chemical foaming agent to polyethylene and simultaneously foaming it during extrusion coating, even if an attempt is made to achieve high foaming of 50% or more, each pore explodes, resulting in coarse pores and gas loss. Currently, only about 50% or less foam can be obtained.

・Individual pores that should originally be independent pores become coarse pores,
The cause of gas dissipation is that the strength of polyethylene during melt extrusion is extremely weak against gas pressure, resulting in destruction of the coating.

In this way, foamed polyethylene must have two characteristics: a viscosity that allows it to expand under the pressure of the foaming gas near the decomposition temperature of the added blowing agent, and a strength that should prevent further expansion. It won't happen. As a countermeasure, polyethylene containing a foaming agent is coated on the conductor at a low temperature below the decomposition temperature of the foaming agent, crosslinked appropriately by radiation irradiation, and then heated to a high temperature above the foaming temperature. Experiments have confirmed that a highly foamed material with fine pores can be obtained by doing so. However, when this method was applied to insulated wires, it had the following drawbacks and could not be applied as is. In other words, there is no adhesion between the polyethylene and the conductor, so a gap is created between them, and the insulation expands not only in the radial direction of the wire, but also in the length direction, resulting in a meandering shape in the insulator. It is.
The present invention has been made with the aim of solving the drawbacks of the prior art described above and providing an excellent highly foamed insulated wire. An adhesive layer having adhesive properties is extruded and coated at a temperature higher than the coupling reaction temperature, and then an insulator containing a high concentration of foaming agent is coated on the outer periphery of the adhesive layer at a temperature that allows it to bond to the adhesive layer and in a non-foaming state. The method of manufacturing a cross-linked highly foamed insulated wire is characterized in that the wire is press-coated, then cross-linked by radiation irradiation, and then foamed by heating to a temperature higher than the decomposition temperature of the foaming agent. Polyethylene, which is inert to conductors and does not have adhesive properties to conductors, is bonded and integrated by providing an adhesive layer, thereby obtaining an excellent highly foamed insulation that overcomes the drawbacks of the conventional method.

In the above, suitable adhesive layers that have adhesive properties to both metals and insulators include polyolefins mixed with vinylsilane capable of performing a coupling reaction or an appropriate amount of organic titanates. .

Next, one embodiment of the manufacturing method of the present invention will be further described with reference to the accompanying drawings.

1 is a conductor, and 2 is an adhesive layer press-coated on its outer periphery.

Adhesive layer 2 is a mixture of 100 parts of ethylene-vinyl acetate copolymer, 2 parts of vinyltrimethoxysilane, 0.2 parts of dicumyl peroxide, and 0.2 parts of an antioxidant. 20 on conductor 1 heated to 20,000
Pressure coating was carried out at a temperature of 0°C.

As a result, ``complete adhesion between the conductor and adhesive layer 2 was achieved.
Furthermore, polyethylene mixed with a foaming agent was extrusion coated onto this wire, which was also heated to 200 qo, at a high temperature such that the foaming agent did not decompose. Next, radiation was applied to give the required gel content, and the desired highly foamed insulator 3 was obtained by heating to a temperature higher than the decomposition temperature of the foaming agent.

In this case, since the highly foamed insulator 3 is in a state of strong adhesion to the adhesive layer 2, volume expansion due to foaming cannot occur in the length direction, and all expansion occurs in the radial direction.

Therefore, the conventional drawbacks are solved, and it becomes possible to provide a highly foamed insulated wire with a uniform cross section.

As explained above, according to the present invention, it has become possible to provide a cross-linked highly foamed insulated wire with excellent adhesive properties between a conductor and an insulator, and a uniform cross section with excellent appearance characteristics, and its industrial use. There is great value.

[Brief explanation of drawings]

The accompanying drawing is an explanatory cross-sectional view showing an example of a highly foamed insulated wire manufactured by the method of the present invention. 1: Conductor, 2: Adhesive layer, 3: Highly foamed insulator.

Claims (1)

[Claims] 1 An adhesive layer that has adhesive properties for both metal and insulator is extruded on the outer periphery of the conductor at a temperature higher than the coupling reaction temperature, and then an insulator containing a high concentration of foaming agent is bonded around the outer periphery of the conductor. Production of a crosslinked highly foamed insulated wire characterized by extrusion coating at a temperature at which the layer is bonded and in a non-foamed state, then crosslinked by irradiation with radiation, and then foamed by heating above the decomposition temperature of the foaming agent. Method.