JPS6153803B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulated core wire used in place of pairs or couples in communication cables.

As shown in FIGS. 1 and 2, pairs or joints generally used in communication cables are insulated wires 3 made by extruding a plastic insulator 2 on a conductor 1.
Two (Fig. 1) or four (Fig. 2) strands are twisted together. The insulator 2 of each wire 3 is usually made of solid polyethylene, foamed polyethylene, or the like.

Between the solid type and the foamed type, the latter has better transmission characteristics, but foamed plastic insulators contain many air bubbles, so if you reduce the thickness beyond a certain level, pinholes will occur and cause crosstalk. , not only is it more likely to cause breakdown voltage defects, etc.
The mechanical strength decreases, making it susceptible to damage due to friction and the like when twisted into pairs or joints. Also,
Solid plastic insulators do not have the problem of pinholes or a decrease in mechanical strength, but if the thickness is reduced beyond a certain point, the capacitance between each conductor in a pair or corner increases and the transmission characteristics deteriorate. do.

Conventionally, it has been difficult to reduce the outer diameter of a pair or a joint because it is not possible to reduce the thickness of the insulator of each wire composing a pair or a joint to a certain level. It has been almost impossible to increase the number of communication cables that can be accommodated (when the outer diameter of the cable is constant) or to reduce the outer diameter of the communication cable (when the number of cables that can be accommodated is constant).

In addition, in conventional pairs or joints, the insulated wires that make up the pair must be manufactured separately.
This requires a lot of manufacturing man-hours, making it difficult to reduce costs. To improve this point,
Conventionally, as shown in FIGS. 3 and 4, a common plastic insulator 4 is extruded and coated on two or four conductors 1, and the conductors 1 are twisted to give a predetermined twist to each other. Insulated core wires for cables have been proposed. With this structure, two or four conductors 1 can be extruded and coated with the plastic insulator 4 at the same time, making it possible to reduce costs compared to the ones in Figures 1 and 2. It is. However, even in such an insulated core wire, the thickness t of the plastic insulator 4 existing on the outside of each conductor 1 must be the same as the thickness t of the plastic insulator 2 of the conventional pair or cut. The outer diameter will be the same as that of a conventional pair or cup. Therefore, even if this type of insulated core wire is used, it is not possible to increase the number of pairs or couples accommodated in the communication cable or to reduce the outer diameter of the communication cable.

SUMMARY OF THE INVENTION An object of the present invention is to provide an insulated core wire for communication cables that eliminates the problems of the prior art as described above, has a smaller outer diameter, and has transmission characteristics equal to or better than those of the prior art.

The insulated core wire for communication cables of the present invention has two or four conductors arranged near the circumferential surface of a foamed plastic insulator having a circular cross section and twisted at equal intervals in the circumferential direction and at a predetermined length in the longitudinal direction. , and its outer periphery is covered with a solid plastic insulator.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 5 and 6.

In the embodiment shown in FIG. 5, two conductors 1 are arranged axially symmetrically so as to be almost inscribed in the peripheral surface of a foamed plastic insulator 5 having a circular cross section, and the outer periphery of the conductor 1 is covered with a solid plastic insulator 6. It is. The two conductors 1 are twisted together at a predetermined pitch in the longitudinal direction.

In the embodiment shown in FIG. 6, four conductors 1 are arranged at equal intervals in the circumferential direction so as to be almost inscribed in the peripheral surface of a foamed plastic insulator 5 having a circular cross section, and a solid plastic insulator 6 is arranged around the outer periphery. It is coated.
The four conductors 1 are twisted together at a predetermined pitch in the longitudinal direction.

In both embodiments, the foamed plastic insulation 5
Foamed polyethylene can be used as the material for the solid plastic insulator 6, and polyethylene or polypropylene can be used as the material for the solid plastic insulator 6.

In the above-mentioned insulated core wire, most of the electric lines of force generated by the signal voltage applied between the conductors pass through the foamed plastic insulator 5, as shown in FIGS. 7 and 8. (Figure 8 shows an example in which a voltage is applied between the upper and lower conductors). Since the foamed plastic insulator 5 has a small dielectric constant, transmission loss can be kept sufficiently small. In particular, in the above-mentioned insulated core wire, since the solid plastic insulator 6 is present on the outer periphery, the foamed plastic insulator 5 is used to increase the foaming rate without considering mechanical strength such as friction resistance. Is possible. The higher the foaming rate of the foamed plastic insulator, the lower the transmission loss.

If the foaming rate of the foamed plastic insulator 5 is too high, its ability to hold the conductors at regular intervals will be reduced. Furthermore, the electric lines of force are concentrated between the conductors, ie, in the center of the foamed plastic insulator 5. Taking these two points into consideration, the foamed plastic insulator 5 in FIGS. 5 and 6 has a high foaming rate near its center to reduce transmission loss.
The function of maintaining conductor spacing is ensured by lowering the foaming rate near the peripheral surface and increasing the strength.

The solid plastic insulator 6 has higher voltage resistance characteristics than the foamed plastic insulator, and
Since it has high mechanical strength, its thickness can be made sufficiently thin. Therefore, the insulated core wires of both embodiments can have smaller outer diameters than the conventional ones.

To manufacture an insulated core wire like the above example,
When extruding the foamed plastic insulator 5, two or four conductors are supplied around it at predetermined intervals, and at the same time, a solid plastic insulator 6 is extruded and coated, and after this is cooled. , the conductors may be twisted so that the desired pitch of twist is applied to each other.

As explained above, the insulated core wire for communication cables of the present invention has a structure in which a foamed plastic insulator is filled between two or four conductors with a foaming rate higher in the center than in the periphery. , transmission loss is small, and the outside of each conductor is coated with a common solid plastic insulator, so
The outer diameter can be made smaller. Therefore, by using this insulated core wire, it is possible to construct a communication cable with low transmission loss, a small outer diameter, or a large number of conductors, and its practical effects are extremely large.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of a conventional pair and a joint, respectively, and FIGS. 3 and 4 are cross-sectional views of conventionally proposed insulated core wires for communication cables, respectively.
5 and 6 are cross-sectional views of insulated core wires for communication cables according to embodiments of the present invention, and FIGS. 7 and 8 are electric force lines in the insulated core wires of FIGS. 5 and 6, respectively. FIG. 2 is an explanatory diagram showing the distribution of 1... Conductor, 5... Foamed plastic insulator,
6... Full plastic insulator.

Claims (1)

[Claims] 1 Two or four conductors are arranged at regular intervals in the circumferential direction and in the longitudinal direction so as to be almost inscribed in the circumferential surface of a foamed plastic insulator having a circular cross section with a higher foaming rate in the center than in the peripheral area. An insulated core wire for a communication cable, characterized in that the core wire is arranged in a twisted state, and the outer periphery of the insulated core wire is coated with a solid plastic insulator.