JPH0367416A - Manufacture of foamed insulator electric wire - Google Patents

Abstract

PURPOSE:To manufacture a foam electric wire with excellent electric and mechanical characteristics at a low cost by coating two layers of insulators with different contents of foaming materials on a conductor within the temperature region that the foaming materials are not decomposed, radiating and bridging them with an electron beam, then heat-treating them. CONSTITUTION:ADCA 3% as a foaming material and silica 0.5% as a nucleus material are added to low-density polyethylene 90% and polypropylene 10% for an inner layer insulator 2. High-density polyethylene with a coloring material is used for an outer layer insulator 2'. Insulators are fed to a head from two extruding machines to cover a conductor 1 with the diameter 0.2mm in the unfoamed state so that the thickness of the inner and outer layers becomes 0.2mm and 0.07mm respectively. An electron beam 15Mrad is radiated to bridge insulators of both layers 2 and 2', heat treatment is applied, then the insulator of the inner layer 2 is foamed at the foaming ratio 70-75%, the insulator of the outer layer 2' contains no foaming material, thus it is made solid, and the surface can be smoothly finished.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a method of manufacturing a foamed electric wire used particularly for high-speed transmission lines for computer signal transmission.

(Prior Art) Foamed wires used in computer signal transmission lines are generally required to have a short signal propagation delay time, excellent terminal processability, and excellent mechanical properties. For this reason, it is necessary for the foamed wire to have a high foaming rate of the insulator and a smooth outer surface. The foamed wires that are currently in practical use are made by crosslinking the inner layer with a crosslinked polyolefin foam and the outer layer with a skin layer after foaming, or by crosslinking the molded wire after foaming, or by using polytetrafluoroethylene-perfluoroalkoxy copolymer (PFA). It can be made by foaming Teflon (foamed Teflon) or porous tetrafluoroethylene (
It was made by wrapping EPTFE tape around it.

(The problem that the invention tries to solve is 1ft) However! I! Electric wire made of Tachibana polyethylene foam is 1
Since it is in a molten state when foaming, it is not possible to increase the foaming rate by more than 70%, and electric wires made of 1-foam Teflon also have a 70% expansion rate.
It is difficult to foam the above, the thickness is limited to 0.4 mm, and it is not possible to make it thinner than that, and the foaming rate of the tape itself is as high as 85 to 90% for electric wires formed by wrapping EPTFE tape. However, it has the disadvantage that the foaming rate decreases during wrapping and it is expensive.

An object of the present invention is to provide a method for manufacturing a foamed electric wire that avoids the above-mentioned drawbacks, has a high foaming rate, has good mechanical properties, and can be manufactured at low cost.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides that, of the two layers of insulation, the foaming agent in the outer insulation layer is smaller than the foaming agent in the inner insulation layer. The insulators of these inner and outer layers are extruded and coated onto the conductor at a temperature range that does not decompose with a foaming agent, and the conductor coated with these insulators is crosslinked by electron beam irradiation, and then the foam is formed. The present invention provides a method for manufacturing a foamed electric wire, which is characterized by carrying out a heat treatment at a temperature higher than the decomposition temperature of the agent.

[Effect]

In order to obtain a highly foamed polyolefin material as a foamed insulator, for example, it is necessary to have appropriate viscoelasticity during foaming, but it is said that such appropriate viscoelasticity exists during the melting process of the material; Although it is difficult to obtain a very stable state, the present invention makes it possible to obtain viscoelasticity suitable for foaming by appropriately crosslinking the material. After coating the insulator and before foaming, the insulator is cross-linked by irradiating it with an electron beam, and then heat-treated to the decomposition temperature of the foaming agent, so foaming is performed with appropriate viscoelasticity, and the insulation The content of the foaming agent in the two layers inside and outside the body is made smaller in the outer layer than in the inner layer to reduce or eliminate foaming in the outer layer during heat treatment, thereby eliminating unevenness on the surface of the wire.

(Example) Next, a method of manufacturing a foamed electric wire according to the present invention will be described with reference to the drawings. FIG. 1 schematically shows the method of the present invention,
Two layers of insulation 2, 2 inside and outside are applied to the conductor l by the extrusion device 10.
' (see Figure 2), two layers of insulation 2, inside and outside 2'.The foaming agent in the outer insulation layer 2' is smaller than the foaming agent in the inner insulation layer 2. or zero, and the inner layer insulator 2 contains a sufficient amount of foaming agent necessary to obtain a predetermined high foaming rate. The extrusion coating of these insulators 2.2'' is carried out at a temperature range that does not cause the blowing agent to decompose.

As an insulator, low-density or high-density polyethylene or a mixture of both, a mixture of polyethylene and 20% or less of polypropylene, vinyl acetate-ethynelene copolymer, vinyl acrylate-ethynelene copolymer, or ethylene-propylene-diene rubber Alternatively, an inexpensive polyolefin material such as a mixture of polyethylene and ethylene/propylene/diene rubber may be used. The two inner and outer layers of insulators 2 and 2' may be made of the same material, or may be made of different materials.

Azo dicarbonamide (ADCA) is used as a blowing agent.
) or p, p'-oxybisbenzenesulfonyl hydrazide (OBSH) can be used. When ADCA is used as the blowing agent, the amount added in the inner layer is 1.

0~15.0Phr, and O~lO,0Ph in the outer layer
When 0BSH is used as a blowing agent, the amount added is 1.0 to 20.0 Phr for the inner layer, and 0 to 15.0 Phr for the outer layer.

Incidentally, talc, silica, etc. can be added as a nucleating agent to either the inner or outer insulators 2.2'.

After the conductor l is coated with two layers of insulator 2.2° on the inside and outside in this way, the conductor l coated with this insulator 2.2° is
is passed through an electron beam irradiation device 12 and irradiated with an electron beam to crosslink the insulator 2.2''. This crosslinking is performed to impart appropriate viscoelasticity to the insulator 2.2°.

Finally, the material is passed through a heating furnace 14 and heated at a temperature higher than the decomposition temperature of the foaming agent to foam the insulator 2.2°. As already mentioned, before the first foaming, the insulator 2.2" is cross-linked by irradiating it with an electron beam, so the first foaming is carried out well with appropriate viscoelasticity, and the outer layer of the insulator 2" has little or no blowing agent, resulting in main foaming or a low foaming rate, while the inner layer insulator 2 can be foamed with a high foaming rate.

FIG. 3 shows the foamed electric wire 20 obtained in this way,
The inner layer insulator 22 is a foam having a predetermined foaming rate, and the outer layer insulator 22 is not foamed or has only a slight amount of foam, indicating that the outer surface is smooth. has been done.

Next, specific examples of the present invention will be described below along with comparative examples.

(Specific example) A mixture of 90% low density polyethylene and 10% polypropylene is used as the inner layer insulator, and AD is used as the blowing agent.
Added 3.0% CA and also added 0.5% silica as a nucleating agent.
% added. On the other hand, high-density polyethylene was used as the outer layer insulator, and a color masterbatch was mixed as a colorant at a ratio of 30:1. The inner layer insulator had a thickness of 0.2 mm, and the outer layer insulator had a thickness of 0.07 mm. These two inner and outer layers of insulators are supplied from two extruders to one head and coated on a conductor with a diameter of 0.2 mm in an unfoamed state, and a voltage of t & 500 kv is applied to l 5 M r
Electron beam irradiation 12 to irradiate the electron beam of a d? The two layers of insulation, the inner and outer layers, were cross-linked by passing the material through them, and immediately after that, the insulation was heat-treated by passing it through a heating furnace. As a result, the inner layer insulator was foamed at a foaming rate of 70 to 75%. Further, since the outer insulating layer did not contain a foaming agent, a solid outer insulating layer was obtained as shown in FIG. 3, and its outer surface was smooth.

(Comparative example) A conductor with a diameter of 0.2 mm was extruded and coated with one layer of insulator made of exactly the same material as the inner layer insulator of the above specific example, and electron beam irradiation and heat treatment were performed in exactly the same procedure as in the specific example. . The foaming rate of the insulator in this case was 75 to 80%, but the outer surface was uneven.

(Effects of the Invention) According to the present invention, as described above, after coating the two layers of insulators, the inner and outer layers, the insulators are crosslinked by irradiating electron beams before foaming.
After that, heat treatment is carried out to the decomposition temperature of the blowing agent, so that foaming is carried out with appropriate viscoelasticity and a high foaming rate can be obtained.Also, the amount of blowing agent added to the two layers of the insulator, the outer layer, is higher than that of the outer layer. Since foaming in the outer layer is reduced or eliminated during heat treatment by reducing the foaming content to less than that of the inner layer, there is no unevenness on the surface of the wire, so the mechanical strength does not decrease, thus improving the electrical and mechanical properties. There is a practical benefit of being able to obtain high-quality foamed wires at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram schematically showing the method of the present invention;
The figure is a cross-sectional view of a conductor coated with an insulator before foaming.
The figure is a cross-sectional view of a foamed electric wire manufactured according to the present invention. 1-----One conductor, 2.2' and 22.22゜----
Insulator with one and two outer layers. Figure 1 Figure 2 Figure 3 ra

Claims (1)

[Claims] Of the two layers of insulation, the outer layer of the insulation, the foaming agent in the outer layer of insulation is smaller than the foaming agent in the inner layer of insulation, or zero;
The insulators of the inner and outer layers are extruded and coated onto the conductor at a temperature range where the foaming agent does not decompose, and the conductor coated with these insulators is crosslinked by electron beam irradiation, and then the temperature is increased to a temperature higher than the decomposition temperature of the foaming agent. A method for producing a foamed electric wire, the method comprising heating at a temperature of .