JPS596011B2 - 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 by continuously extrusion coating a cross-linked piercing compound over a long period of time.

More specifically, it is a method for manufacturing a plastic insulated wire that does not cause scorch (early vulcanization) even after long-term continuous operation. When extruding plastics, an extruder equipped with a breaker plate as shown in FIG. 1 is used. That is,
FIG. 1 is a schematic diagram of a screw, a cylinder, a conventional breaker plate and a crosshead, where 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. It is the head. The plastic passage of the conventional breaker plate was straight as shown in FIG.
Normally, when manufacturing cross-linked polyethylene insulated wires using the breaker plate shown in Figure 1, if the extruder is operated continuously for more than 100 hours, scorch will occur in the extruder, making the surface of the extrudate rough and causing large fluoresces. It may stick. It also leads to a decrease in the amount of extrusion. Therefore, about 100 hours after starting, the extruder had to be stopped for cleaning and then restarted, resulting in poor workability. Furthermore, as mentioned above, when the extrusion rate decreased, there was also a manufacturing problem in that the thickness of the insulator became thinner from the middle. As a result of various investigations, it has been found that the cause of these problems is that the cross-linked penetration compound accumulates significantly near the tip 7 of the screw 1 in FIG. 1, causing scorch.

Therefore, we investigated a manufacturing method that would prevent the compound from accumulating near the tip of the screw. As a result, it has been found that by enlarging the plastic passage in the breaker plate at least once along the plastic flow, compound retention near the screw tip can be significantly reduced. It was also confirmed that when manufactured in this way, almost no scorch occurred even after continuous operation for over 100 hours. The present invention was developed through the above process, and is characterized by the use of a breaker plate of an extruder configured such that the plastic passage in the breaker plate expands at least once on the outlet side. It's about doing. Next, the present invention will be explained in detail. Second
The figure 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.
According to the invention, the passages 5' of the plastic 1 in the individual holes of the breaker plate 3' are enlarged midway. That is, a stepped portion 5'a is formed. Scorch can be completely prevented or reduced by appropriately selecting the value of the enlarged portion and the length distribution of the different diameter holes depending on the type of plastic and extrusion conditions. The value of the enlargement of the plastic passage 5' is determined as follows:
The value is preferably in the range of 1.5 to 7.0.

The reason why a favorable phenomenon occurs in such a range is that when the plastic passage 5' suddenly expands, molecular entanglement occurs due to stress relaxation in the plastic, and the viscosity distribution of the plastic changes. it is conceivable that. In other words, in the case of the conventional breaker plate (Fig. 1), the flow of plastic is poor in the inner layer (corresponding to the vicinity of the tip of the screw) and the outer layer (corresponding to the vicinity of the cylinder) of the breaker plate, and assemblage occurs, causing the breaker plate to In the middle layer, the flow was good and stagnation was unlikely to occur. In other words, the plastic near the middle layer was under greater shear stress, so its viscosity was lower than that of the inner and outer layers. However, in the breaker plate shown in FIG. 2, it was found from color change extrusion experiments that the inner and outer layers flow better.
This is thought to be because molecular entanglement occurs where the plastic channel suddenly expands, causing the viscosity distribution to reverse and the viscosity of the inner and outer layers to be lower than the viscosity of the middle layer. Now, as shown in Fig. 2, the value of the enlarged portion mentioned above is calculated as follows:
It is defined by expressing it as 2/A2. It was confirmed that when a plastic insulated wire was manufactured using the breaker plate constructed as described above, scorch did not occur even after continuous operation for over 100 hours.

The continuous operation time is now approximately three times longer than before. In addition, problems such as a decrease in extrusion amount and roughness of the surface due to scorch generation have almost disappeared. Further, in FIG. 2, the length distribution of the hole diameters a and b and the number of holes need to be determined in consideration of the geometrical resistance of the entire breaker plate, that is, the resin field force immediately in front of the breaker plate.

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 to perform steam crosslinking, silicone oil crosslinking, gas crosslinking, silane crosslinking, and the like. Various plastic materials can be used, including crosslinked polyolefins such as polyethylene, polyvinyl chloride, and crosslinked 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 7.0
It is better to choose. In addition, in the present invention, it is sufficient that the plastic passage in the breaker plate of the extruder is expanded at least once on the exit side. In addition to the configuration in which the plastic passage is provided with one step, various shapes can be considered.For example, a two-stage structure in which the plastic passage in the breaker plate is expanded twice, and the plastic passage is A structure that expands in a tapered shape from the middle may be used.

Next, an example will be described.

(Example 1) Using the breaker plate shown in Figure 2, a-3.5mm
φ, b-6.0m7! lφ, c-150mmφ, d-1
A conductor with a nominal cross-sectional area of 22 m1 was extruded and coated with polyethylene containing a crosslinking agent under the conditions of 0.0 min, e-27 mm, 5 holes, and 391 holes, and then a 600 cross-linked polyethylene insulated wire was manufactured by steam cross-linking.

At this time, B2/A2 is 2.9. For comparison, a similar crosslinked polyethylene insulated wire was produced using the breaker plate shown in FIG. 1 (hole diameter: 5φ, hole length: 37 mm, other conditions being the same). In these wires,
Table 1 shows the results of investigating the continuous operation time until scorch occurs and trouble occurs in the insulator.

It can be seen from Table 1 that when the breaker plate according to the present invention is used, the continuous operation time is tripled.

(Example 2) Using the same breaker plate as in Example 1, a cross-linked polyethylene insulated wire similar to that in Example 1 was manufactured while press-fitting a cross-linking agent from the cylinder, and the continuous operation time was investigated. It was hot.

(Example 3) Using the same breaker plate as in Example 1, a 600V insulated wire was prepared by extrusion coating with silane compound, and the continuous operation time was investigated.
It took 260 hours.

(Examples 4 to 6) Using the breaker plate shown in Table 2 below, polyethylene containing a crosslinking agent was extruded and coated, and then the crosslinking treatment shown in the same table was applied to produce 6.6K and 0.6K crosslinked polyethylene electric wires. The results of manufacturing and investigating the continuous operation time are shown in the third section below.
Shown in the table.

From the above examples, it can be seen that when plastic insulated wires are manufactured using the breaker plate according to the present invention, continuous operation can be approximately three times longer than conventional wires.

As is clear from the above detailed description, the method of manufacturing a plastic insulated wire according to the present invention is characterized in that the passage of the plastic in each hole of the breaker plate is expanded at least once on the exit side. Scorch can be reduced near the tip of the cylinder) and near the cylinder, thereby extending the continuous operation time and significantly reducing problems such as a decrease in the amount of extrusion and roughness of the surface.

[Brief explanation of drawings]

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, 3t.
・Breaker plate, 4,4'...Blastic,
5,5t...Plastic passage, 6...Crosshead.

Claims (1)

[Claims] 1. When producing an insulated wire by extruding and coating a conductor with plastic using an extruder, by using an extruder in which the passage of the plastic in the breaker plate of the extruder is expanded at least once on the exit side thereof. A method for producing a plastic insulated wire characterized by preventing scorch of a compound containing a crosslinking agent.