JPS597171B2 - Manufacturing method of plastic insulated wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a plastic insulated wire with improved electrical insulation properties.

More specifically, it is a method for manufacturing a plastic insulated wire that has improved dielectric breakdown characteristics by creating a homogeneous insulator with stable physical properties and no striped pattern. When extruding plastic, an extruder equipped with a breaker plate as shown in Figure 1 is used. That is, Fig. 1 shows the screw,
1 is a schematic diagram of a cylinder, a conventional breaker plate and a crosshead, 1 is a screw, 2 is a cylinder, 3 is a conventional breaker plate, 4 is plastic, 5 is its passage, and 6 is a crosshead. The plastic passage of the conventional breaker plate was straight as shown in FIG. As a result of slicing and observing plastic insulators, the present inventors found that many opaque ring-shaped striped patterns were observed in the insulators manufactured using the conventional breaker plate shown in Figure 1. There was found. Since this striped pattern is presumed to be due to the orientation of molecules passing through the breaker plate, this will be referred to hereinafter as a breaker mark. On the other hand, as a result of conducting an impulse breakdown test on plastic insulated wires and examining the vicinity of breakdown, we found that breakdown occurred preferentially in areas where there were many of the above-mentioned breaker marks. In other words, it was found that the breaker mark was a weak point in terms of electrical insulation breakdown. Therefore, we investigated a method of manufacturing insulators without breaker marks. As a result, it has been found that breaker marks can be significantly reduced by enlarging the plastic passage in the breaker plate at least once along the flow of the plastic. It has been confirmed that the insulator manufactured in this manner has improved electrical properties, particularly dielectric breakdown properties, as compared to insulators manufactured by conventional methods. The present invention was developed through this process, and is characterized by the use of a breaker plate configured such that the plastic passage in the breaker plate of the extruder expands at least once on the outlet side. There is a particular thing.

Next, the present invention will be explained in detail. FIG. 2 is a schematic diagram of a breaker plate showing an example of the present invention.

The direction of the arrow in FIG. 2 indicates the direction of plastic flow.
In the present invention, the passages 5' of the plastic 4' in the individual holes of the breaker plate 3' are enlarged midway. That is, a stepped portion 5'a is formed. At this time, if the value of the enlarged portion and the length distribution of the different diameter holes are appropriately selected depending on the type of plastic and extrusion conditions, the breaker mark can be completely eliminated or reduced. The value of the enlargement of the passage 5/ of the plastic stick is determined as follows, and is preferably in the range of 1.5 to 8.0.

In such a range, a favorable phenomenon occurs where the plastic passage 5' suddenly expands, and due to stress relaxation in the plastic, the strong molecular orientation that had occurred near the entrance of the breaker plate is relaxed and disordered. It is thought that this was due to an accident. Now, the value of the expansion part mentioned above is
As shown in Fig. 2, the inlet diameter of the plastic passage 5/ is a
, is determined by expressing it as B2/A2, where b is the outlet diameter.

When plastic insulated wires are manufactured using the breaker plate configured as described above, and the insulator is sliced thinly and observed with the naked eye or polarized light, the number of breaker marks and the number of individual It was confirmed that the opacity of the breaker mark decreased or the breaker mark completely disappeared.

In addition, the dielectric breakdown voltage is 20% higher than that of conventional insulators.
% improvement in the fracture value was observed. From these results, it is predicted that the water resistance, electrical resistance and chemical resistance will also be improved. In addition, the larger the value of the enlarged part, the more preferable results can usually be obtained, but if the value of the enlarged part is too large, that is, in FIG.
Since there is a limit to how much a can be made, a must be made quite small, resulting in a considerable increase in the resin pressure just before the breaker plate, which may lead to an unfavorable situation in terms of erasing the breaker mark.

Further, in FIG. 2, the length distribution of the hole diameters a and b and the number of holes need to be determined by taking into consideration the geometrical resistance of the entire breaker plate, that is, the breaker pressure and the immediately preceding resin pressure.

Although the above description has mainly been given to the case of an insulator, this apparatus can be similarly used in the formation of an outer sheath and inner and outer semiconducting layers.

Furthermore, it can be used in conjunction with a crosslinking device, steam crosslinking, ・1
- - VL44 gate 4 υ-4shi 1 grade 6)
), 21-no-ka-n-nan-ryoku-jit) da;' can be done.

Various plastic materials can be used, including polyolefins such as polyethylene, polyvinyl chloride, and crosslinked products thereof, and synthetic rubbers such as ethylene-propylene rubber (EPR, EPDM) and butyl rubber.

In either case, the value of B2/A2 mentioned above is 1.5 to 8.0
It is better to choose. In addition, in the present invention, since it is sufficient that the plastic passage in the breaker plate of the extruder is expanded at least once on the exit side, as shown in FIG. In addition to the configuration with one step, various shapes can be considered. For example, a two-step structure in which the plastic passage in the breaker plate expands twice, or a structure in which the plastic passage is tapered from the middle. It is also possible to have a structure that expands to .

In addition to being used in ordinary plastic extruders, the breaker plate of the present invention can also be used to remove breaker marks, which was previously filed by the present applicant. It is even more effective when used in conjunction with an extruder in which the passage is narrowed toward the extrusion port and then expanded.

Next, an example will be described. (Example 1) Using the breaker plate shown in Fig. 2, a-3.5r
mφ, b-6.0wrmφ, c-150mφ, d-25
TW1. A 6.6K crosslinked polyethylene insulated wire was manufactured by extrusion coating polyethylene containing a crosslinking agent onto a conductor having a nominal cross-sectional area of 150m7M under the conditions of e-12wrm and 391 holes, and then steam crosslinking.

B2/A2 at this time is 2.9. For comparison, the breaker plate shown in Figure 1 (hole diameter is 5Wf1φ
, The length of the hole is 37w1! A similar cross-linked polyethylene insulated wire was produced using the same conditions. Next, cut out slices with a thickness of 1w1n from these insulators,
The breaker mark was observed with the naked eye.

Table 1 shows the number of breaker marks visible to the naked eye. From Table 1, it can be seen that when the breaker plate according to the present invention is used, the breaker mark is significantly reduced compared to the conventional method.

Table 2 shows the results of measuring the AC long-time breakdown voltage and positive polarity impact breakdown voltage of these wires.

All breakdown voltages are average breakdown voltage (EmeanKV/7
m). As is clear from Table 2, all of the electric wires manufactured according to the present invention show an improvement of about 20% compared to those of the conventional method.

This is thought to be due to the disappearance of the breaker mark, which indicates inhomogeneity in the insulator. (Examples 2 to 4) A 6.6KV, 66K crosslinked polyethylene electric wire was produced by extrusion coating polyethylene containing a crosslinking agent using the breaker plate shown in Table 3 below, and then performing the crosslinking treatment shown in the same table. .

Table 4 below shows the results of slicing the insulators of these wires to a thickness of 1Tn1n and examining the number of breaker marks visible to the naked eye. From Table 4, it can be seen that when a plastic insulated wire is manufactured using the breaker plate according to the present invention,
It can be seen that a homogeneous insulator with very few or no breaker marks is obtained.

As is clear from the above detailed description, the method of manufacturing a plastic insulated wire of the present invention is characterized in that the plastic passage in each hole of the breaker plate is expanded at least once on the outlet side. The breaker mark in the insulator can be erased, thereby making it possible to obtain an insulated wire in which the breakdown voltage of the insulator is greatly improved.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of a conventional screw, cylinder, conventional breaker plate and crosshead, and FIG. 2 shows a schematic diagram of a breaker plate used in the method of the present invention. 1... Screw 1 2... Cylinder, 3, 3'... Breaker plate, 4, 4'
...Plastic, 5,5'...Plastic passage, 6...Crosshead.

Claims (1)

[Claims] 1. When producing an insulated wire by extruding and coating a conductor with plastic using an extruder, the extruder is characterized in that the passage of the plastic in the breaker plate of the extruder is expanded at least once on the exit side thereof. A method of manufacturing plastic insulated wire.