JPS6040647B2 - Manufacturing method of plastic insulated wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a plastic insulated wire with improved electrical insulation properties and conductor protrusion caused by shrinkage of the plastic insulator.

More specifically, it is a method for manufacturing a plastic insulated wire having an insulator with stable physical properties such as low distortion and no density deviation. Conventionally, when coating a conductor with plastic, a weighing machine having a die and a nipple as shown in FIG. 1 has been used.

That is, FIG. 1 is a schematic diagram of the die and nipple parts of a conventional extruder, in which 1 is a conductor of an electric wire cable, 2 is a nipple, 3 is a die, 4 is a plastic to be extrusion coated, and 6 is a schematic diagram of a die and nipple portion of a conventional extruder.
is that passage. In this way, the conventional plastic passage 5 is configured to become gradually narrower near the plastic outlet (extrusion outlet) due to the die 3 and nipple 2. The present inventors have conducted various studies on the physical properties of plastic insulators coated with such an extruder, especially the variations in strain and density of the insulators, and have found that they can be manufactured using the conventional extruder shown in Figure 1. It was found that the strain and density of the insulators were quite locally uneven. We thought that such distortion and density deviations might affect the electrical properties, so we investigated a method of manufacturing an insulator that does not have such distortion or density fluctuations. As a result, it has been found that by enlarging the die of a conventional extruder to a certain size on the exit side of the plastic insulator, the above-mentioned fluctuations in strain and density can be made extremely small. It has been confirmed that the electrical properties, especially dielectric breakdown properties, of the insulator manufactured in this manner are significantly improved compared to insulators produced by conventional methods. Furthermore, in plastic insulated wires manufactured using conventional extruders,
When the wire was cut after being manufactured, a phenomenon was observed in which the conductor protruded from the cut end.

This is due to shrinkage of the insulator, but it was also confirmed that this phenomenon hardly occurs in the plastic insulated wire manufactured by the method of the present invention.
The present invention was developed through the above process, and its feature, as mentioned above, is that the plastic passage of the extruder is configured to be narrowed once and then expanded. cross-sectional area and
The ratio to the cross-sectional area of the narrowed plastic passage is 1.
5 to 4.5 is used.

Next, the present invention will be explained in detail. FIG. 2 is a schematic diagram of a die and nipple portion showing an example of the present invention.

In the present invention, the plastic passage 5' formed by the nipple 2' and the die 3' is formed so as to become narrower as it approaches its outlet end. The passage 5' is configured to be enlarged. By setting the value of this enlarged portion to a certain specific value, it is possible to minimize the internal strain and density fluctuations and deviations of the extruded plastic insulator. The value is selected depending on manufacturing conditions such as the type of plastic and the thickness of the insulator or sheath. That is, from various experimental results, it is 1.5 to 5.0 for polyethylene and crosslinked polyethylene, 1.3 to 4.5 for polyvinyl chloride, and 1 for ethylene propylene copolymers (EPR, EPDM), butyl rubber, etc. .5~5.
It turns out that it is better to set it to 0. Therefore, its value is preferably in the range of 1.5 to 4.5 for various materials. The reason why a favorable phenomenon is exhibited in such a range is considered to be because the strain becomes uniform due to stress relaxation in the portion where the inner diameter of the die 3' is suddenly expanded. Now, as shown in Fig. 2, the above-mentioned values are as follows: a is the inner diameter of the die at the outlet end 6 of the plastic passage, b is the minimum inner diameter of the die, and c is the outer diameter of the tip of the nipple 2'.
It is determined by expressing (a2 - d2)/(1 c2), where d is the outer diameter of the conductor 1' of the electric wire or cable.

However, d is applied not only to the outer diameter of the conductor, but also when an inner semiconductive layer is provided, or when an insulator, outer semiconductive layer, tape, etc. are further provided.

When a plastic insulated wire is manufactured using the die and nipple configured as described above and the strain and density of the insulator are measured, it is found that the insulator manufactured in this way has a The heating shrinkage rate in the center direction is concentrated at a certain value.

Similar results were also obtained regarding density. On the other hand, with conventional equipment, both the heat shrinkage rate and the density show a wide range of values. Furthermore, regarding the dielectric breakdown voltage, an improvement of 10% or more in breakdown value was observed compared to conventional insulators. It is predicted that such results will also improve water resistance, electrical resistance, and chemical resistance. Above, we mainly explained the case of insulators.
According to this device, it can be used in the same way for forming the outer sheath and the inner and outer semiconducting layers.

Furthermore, it can be used in conjunction with a crosslinking device, allowing steam crosslinking,
Silicone oil crosslinking, gas crosslinking, silane crosslinking, etc. can be performed. In addition, plastic materials include polyolefins such as polyethylene, polyvinyl chloride, crosslinked products thereof, and ethylene-propylene rubber (ERR, EPDM).
), butyl rubber, and other synthetic rubbers can be used.

The length of the enlarged portion may be determined depending on the line speed and the thickness of the extruded coating.

That is, the longer the linear velocity or the thicker the thickness, the longer the length of the enlarged portion may be. Note that the die and nipple portion of the extruder in the present invention only need to be such that the plastic passage is once narrowed and then expanded, so the inner diameter of the die is adjusted as shown in FIG. In addition to enlarging the nipple, various shapes can be considered. For example, as shown in Fig. 3, the tip of the nipple may be cut off, or the inner diameter of the die may be enlarged. A similar effect can be obtained.

In this case, it may be applied as a=b in the equation (a2-d2)/(zarc2). Next, an example will be described.

Example 1 Using the extruder shown in Fig. 2, a = 23.60 side? ,b=
21.06 side, c = 18.6 side, the diameter is 16.
6. Extrusion coating polyethylene containing a cross-linking agent on the conductor d on the 70 side to a thickness of 3 sides, followed by steam cross-linking. A V-shaped crosslinked polyethylene insulated wire was manufactured.

At this time, (a2-d2)/(the-c2) is 2.9. For comparison, a similar crosslinked polyethylene insulated wire was produced using the extruder shown in FIG. 1 (inner diameter of die tip = 23.6 Makuramisaki J). Next, take a length of 1 from these insulators.
A ring-shaped sample on the 5th side was prepared, and the heat shrinkage rate in the length direction and center direction of the electric wire was measured for the purpose of measuring strain. The results are as shown in Fig. 4, Fig. 5 (comparative example using the extruder shown in Fig. 1), Fig. 6, and Fig. 7 (the present invention using the extruder shown in Fig. 2). . As is clear from this figure, the wire insulator manufactured by the conventional method using the die shown in Figure 1 has a wide range of heat shrinkage rates in both the length direction and the center direction of the wire. It can be seen that it is distributed. This indicates that the strain of the insulator varies and is biased over a wide range. On the other hand, as shown in FIGS. 6 and 7, in the case of the insulator of the present invention manufactured using the die shown in FIG. concentrated at a certain value.

This indicates that the strain is uniform throughout the insulator. Next, the above-mentioned sample was
(1.5 ribs thick) and measured the density of the inner and outer parts.

The results are shown in FIGS. 8, 9, 10, and 11. 8th
9 shows the density distribution when manufactured using the die shown in FIG. 1, and it can be seen that the density is distributed over a wide range both on the inside and outside. In contrast, it can be seen that the insulator of the wire manufactured by the die shown in FIG. 2 of the present invention is concentrated at a certain density value, as shown in FIGS. 10 and 11. As described above, according to the present invention, the density distribution of the insulator of electric wires and cables can be made uniform. This is thought to be due to the fact that the strain is uniform. In addition, as is clear from Table 1, which shows the results of measuring the positive polarity impact breakdown voltage and AC long-term breakdown voltage of the above-mentioned crosslinked polyethylene insulated wire, it is clear that the electric wire manufactured according to the present invention In all cases, an improvement of 20% or more can be seen compared to the conventional method.

This is considered to be an effect of uniformizing the strain and density of the insulator. The strain measurement described above was performed on a sample heated at 18,000 for 9 hours in a nitrogen gas atmosphere. Example 2 Using the extruder used in Example 1, 6. Samples for Example 2 and Comparative Example 2 were made by extrusion coating polyvinyl chloride as a sheath to a thickness of 3 sides on the cross-linked polyethylene insulated wire 4 (outside diameter 16.70 skin) of the gunwale V, and The amount of extension of the conductor was measured.

The results are shown in Table 2. In addition, the test was carried out after cutting into three ridge lengths. Table 2 Example 3 Insulation thickness 3 side 6. Regarding the ball V polyethylene insulated wire, the amount of extension of the conductor was measured using an extruder in which the value of (a2 -)/(b2 - c2) was varied.

For comparison, the extruder shown in Figure 1 and the Tokkotsu 8296
A method using an extruder shown in FIG. 1 of No. 5 was also described. The results are shown in Table 3. As is clear from the results, the (a2-c2)/(b2-d2) value is 1.5 to 4.5.
Electric wires manufactured using the extruder included in the invention have less distortion in the polyethylene insulating layer, so the shrinkage is small and the amount of conductor extension can be reduced to about 1/3 of that of conventional wires. It should be noted that if the value is too large (greatly exceeding 5.0), another problem will arise in relation to the swelling ratio of the plastic, which is not preferable. The test method is 3
Measurements were taken after a wire cut to 0 arc length was left in a 70 oo oven for 4 hours. Table 3 Note (1) Examples 3-1, 3-2, 3-3, 3-4 and 3-5 were produced using the extruder shown in FIG. 2 of the present invention.

Note (2) Examples 3-6 are based on the extruder shown in FIG. 3 of the present invention.

note. (3) Comparative Example 3-1 was produced using the extruder shown in FIG. 1 of the present invention. Note (4) Comparative Example 3-2 was made using the extruder shown in FIG. 1 of JP-A-52-82965. Examples 4 to 16 Using an extruder under the conditions shown in Table 4, a coating was extruded onto the conductor under the conditions shown in Table 4, and then crosslinked as shown in the same table to give a 0. Salmon V, 6.
Manufactured insulated wires for Kyu-V and 6-ro V. Table 5 shows the results of measuring the positive polarity impact breakdown voltage and AC long-time breakdown voltage of these insulated wires. Note that all breakdown voltages are expressed as average breakdown voltage (Emean/kV/side). Fourth
Table note 1. Examples 4 to 15 were carried out using the extruder shown in FIG. 2 of the present invention Note 2. Example 16 was obtained using the extruder shown in FIG. 3 of the present invention.

Note 3. Comparative Example 4 was produced using the extruder shown in FIG. 1 of the present invention. Note 4. Comparative Example 5 was produced using an extruder shown in FIG. 1 of JP-A No. 52-82965. Table 5 As is clear from Table 5, the method of the present invention has excellent dielectric breakdown voltage (improved by more than 10% compared to the comparative example).

). As is clear from the above explanation,
In the method for manufacturing a plastic insulated wire of the present invention, the plastic passage in the vicinity of the extrusion port of the extruder is narrowed once by 4 times and then expanded, and the expansion ratio is expressed by the formula (a2-d2)/
(ge-c2)=i. Since it uses an extruder in the range of 5 to 4.5, it is possible to equalize the strain and density of the plastic insulator and sheath, thereby producing insulated wires with significantly improved breakdown voltage of the insulator. Obtainable.

In addition, according to the method of the present invention, as described above, since strain is removed based on stress relaxation at the die and nipple portions, almost no heating shrinkage occurs, so there is an effect that almost no stretching of the conductor occurs. be.

Further, according to the method of the present invention, even when manufacturing low-voltage electric wires using scrap materials, insulated electric wires with excellent surface properties and no irregularities can be obtained.

In addition, according to the method of the present invention, improvements in water resistance, electrical resistance, chemical resistance, etc. are expected, and furthermore, it is possible to obtain plastic insulated wires that are less discolored by heating in high-temperature air. can.

[Brief explanation of the drawing]

FIG. 1 is an enlarged schematic cross-sectional view of the extruder die and vicinity of the nipple in the conventional method, and FIGS. 2 and 3 are enlarged schematic cross-sectional views of the extruder die and nipple vicinity used in the method of the present invention. FIGS. 4 to 7 are graphs showing the distribution of heat shrinkage rates, and FIGS. 8 to 11 are graphs showing the distribution of density. 1', 1''...Conductor, 2', 2''...Nipple, 3',
3″…Die, 5′, 5″…Plastic passage. 1st
Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (1)

[Scope of Claims] 1. When manufacturing an insulated wire by extruding and coating a conductor with plastic using an extruder, a passage for the plastic near the extrusion outlet of the extruder is composed of a die and a nipple, and this passage is A method for manufacturing a rustic insulated wire, characterized by using an extruder that narrows the wire to a small size and then expands it toward the extrusion port, and satisfies the following relationship. (a^2-d^2)/(b^2-c^2)=1.5~4
．． 5 (where a is the inner diameter of the die at the exit end of the plastic passage, b is the minimum inner diameter of the die, c is the outer diameter of the tip of the nipple, and d is the outer diameter of the conductor.) 2 of the die. 2. A method for manufacturing a plastic insulated wire according to claim 1, characterized in that an extruder is used in which the inner diameter is narrowed at least once toward the extrusion port and then expanded. 3. The method of manufacturing a plastic insulated wire according to claim 1, characterized in that an extruder is used in which the outer diameter of at least the nipple is rapidly reduced near the extrusion port.