JPS606051B2 - 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 compound containing a crosslinking agent 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 has conventionally been used. In this extruder, 1 is a screw;
2 is the cylinder, 3 is the breaker plate, 4 is the supplied plastic, 5 is its passage, and 6 is the crosshead. The plastic passage 5 of this conventional breaker plate 3 had approximately the same diameter on the inlet and outlet sides and was straight. Normally, when manufacturing cross-linked polyethylene insulated wire using the breaker plate shown in Fig. 1, if continuous operation is continued for more than 10 hours, scorch will occur in the extruder and the surface of the extrudate may become rough. , or a large lump may be attached.

It also leads to a decrease in the number of bases pushed out. For this reason, about 100 hours after starting, the extruder had to be stopped, cleaned, and then restarted, resulting in poor workability. Furthermore, as mentioned above, when the extrusion rate decreases, there is also a manufacturing problem in that the thickness of the insulator becomes thinner from the middle. After various investigations into the causes of such conventional problems, we found that in Fig. 1, the retention of the crosslinking agent-containing compound, that is, the plastic, was particularly significant near the tip 7 of the screw 1, and that depending on the type of extruder or manufacturing conditions, ,
It also accumulates near the pipe wall of the cylinder 2, furthermore, it accumulates in the center hole of the breaker plate 3 and before and after it, and a dead zone occurs in the wall section 8 on the outlet side of the breaker plate. It was found that this was due to scorch occurring due to stagnation.

Therefore, the present inventors have already solved this problem by enlarging the plastic passage in the breaker plate at least once along the plastic flow, thereby reducing the maker mark (molecules passing through the breaker plate). This invention (Japanese Patent Application No. 70803/1983) can significantly reduce the opaque ring-like cotton pattern, which is presumed to be caused by orientation, and is expected to significantly improve the electrical properties, especially the dielectric breakdown properties, of plastic insulated wires. ), this also leads to a reduction in the accumulation of plastic near the screw tip and cylinder pipe wall, and at the same time, the dead zone of the breaker plate itself is eliminated structurally, allowing continuous operation for more than 100 hours. He has presented a method for manufacturing plastic insulated wires that do not cause scorch even when the wires are scorch-free (Tokunosho 55-34130).
As we continued our research, we identified areas for further improvement.

The present invention has been made from the above viewpoints, and
The gist of this is that the breaker plate of an extruder has a structure in which the plastic passage is expanded at least once on the outlet side, and that the porosity on the inlet and outlet sides of the entire breaker plate is kept within a predetermined range. At the same time, an annular V-groove is formed on the outlet side of the breaker plate to connect the holes in each row arranged in the same circular pattern, further eliminating the accumulation of plastic and preventing the occurrence of scorch. It is in.

Next, the present invention will be explained with reference to the drawings. FIG. 2 is a schematic diagram showing an example of a breaker plate used in the present invention, and plastic flows in the direction of the arrow in the figure. The passages 15 of the plastic 14 in the individual holes of this breaker plate 13 are enlarged midway. That is, a tapered step portion 15a is formed in the middle.
Note that this tapered shape is preferable for the step portion 15a due to the flow of plastic, but other shapes such as rounded (R)
) and may also be formed at right angles.In this case, the diameter of the breaker plate 13 on the inlet and outlet sides of the breaker plate 13 should be c, as shown in FIG. Assuming that the diameter of the inlet side of the plastic passage 15 is a, and the diameter of the outlet side is b, the porosity of the inlet side (%
) is a2 × number of holes (n)
It is expressed in 100.

In the present invention, the porosity on the entrance side is set to 10 to 30.
%, and the opening ratio on the outlet side is preferably in the range of 40 to 65%. Here, each of these porosity ratios indicates the ratio of each hole to the total amount of plastic extruded from the front surface of the breaker plate by the screw, and the value is smaller on the inlet side. ,
Larger on the outlet side means that the flow velocity of the plastic flowing in the plastic passage is farther on the inlet side and slower on the outlet side. The reason why the value is set in the above range is that when the porosity on the inlet side is set to 10 to 30%, the porosity of the conventional breaker plate (Fig. 1) is generally about 35 to 40%. %, but it is quite small.As a result, the flow velocity of plastic passing through the breaker plate is considerably farther (approximately twice) on the inlet side compared to the conventional one, and the plastic stagnates on the inlet side. This is because it is effectively removed. In other words, if the plastic flows smoothly on the inlet side of the breaker plate, it is less likely to accumulate on the breaker plate as a whole, and scorch can be prevented from occurring. however,
If the porosity is too small (less than 100), the pressure (back pressure) of the molten plastic in the cylinder will become too high, which is undesirable, and if it exceeds 30%, it will become undesirable because it will become almost the same as the conventional one. In addition, the breaker plate has a higher porosity rate on the outlet side of 40 to 65% compared to the conventional one (both the inlet and outlet sides are the same, about 35 to 40% as mentioned above). This is to adjust the flow resistance to the entire plastic so that it does not become too large.Another reason is that by increasing the porosity on the exit side, the dead zone consisting of the hole and the wall of the hole can be made smaller. This is to prevent scorch from occurring there.However, if the porosity is less than 40%,
Due to the relationship with the porosity on the inlet side, if the flow resistance becomes too large and exceeds 65%, the flow velocity on the outlet side will become extremely low, which may also cause problems when processing the breaker plate and mechanical strength problems. This is because it causes problems and is not desirable. In the above breaker plate 13, in the present invention,
As shown in FIGS. 2 and 3, a V-groove 19 is formed in an annular shape on the exit side to connect the holes in each row arranged in the same D-circular shape.

That is, they are formed from the second row to the outermost row excluding the center 31. Although the V-grooves 19 in each row may be configured with some spacing between them, it is preferable that the top portions 19a of the grooves 19 coincide with each other. Further, the angle Q of the groove 19 opening from the bottom portion 19b is not particularly limited, but it varies depending on the type of extruder, the extrusion conditions of the breaker plate, etc., and is preferably set to 900, for example. Note that there is a tapered portion 2 on the exit side of the center hole corresponding to the second row of grooves 19.
It is preferable to form 0. By configuring like this,
There are no flat parts on both sides of the outlet side wall of the breaker plate, and together with the above-mentioned large opening ratio on the outlet side, the retention of plastic at the rear of the breaker plate is made more effective. Can be removed. Therefore, generation of scorch can be prevented. The shape of the V-groove 19 includes not only a linear shape but also a somewhat curved shape, for example, a shape close to a U-shape.

In addition to the case where the V-groove 19 has its bottom 19b passing through the center between each hole, it may also be slightly offset from the center, and furthermore, the bottom 19b can pass through the boundary between each row and the top 19b can pass between each hole. It may be configured so that it passes through the center of. In other words, any configuration may be used as long as the outlet side wall surface portion of the breaker plate does not have a flat portion that causes the generation of a dead zone. When plastic insulated wires were manufactured using the breaker plate configured as described above, as mentioned above, the flow velocity of the plastic at the inlet side of the breaker plate was far and there was no flat dead zone at the outlet side. It was confirmed that there was no accumulation of plastic before and after the plate, and that no scorch occurred before or after the breaker plate even after continuous operation for more than 10 field hours.

The continuous operation time is now approximately three times longer than before. In addition, problems such as a decrease in extrusion amount due to the occurrence of scorch and problems such as roughness of the surface have almost disappeared.
In FIG. 2, the length distribution of the peacocks a and b and the number of holes (n) need to be determined in consideration of the geometrical resistance of the entire breaker plate, that is, the resin pressure 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 combination with a crosslinking device to carry out steam crosslinking, silicone oil crosslinking, gas crosslinking, silane crosslinking, and the like. Also, various plastic materials can be used, such as polyolefins such as polyethylene, stretched ropes of polyvinyl chloride, and crosslinked products of synthetic rubbers such as ethylene-propylene rubber (EPR, EPDM) and butyl rubber.

In either case, the porosity on the inlet side should be selected in the range of 10 to 30%, and the porosity on the outlet side to be in the range of 40 to 65%. Since it is sufficient that the passage of the breaker plate is enlarged at least once on the outlet side, various methods can be used in addition to providing one step in the plastic passage in the breaker plate as shown in Fig. 2. Various shapes are possible, for example a two-stage structure in which the plastic passage in the breaker plate is expanded twice.

Next, an example will be described.

Using the breaker plate shown in Figures 2 and 3,
a-4.2 side, b-6.6 side, c-150 Yanagi Shao, d
Polyethylene containing a cross-linking agent is extruded and coated on a conductor with a nominal cross-sectional area of 40 x 2 under the conditions of 110 ribs, e-128 skin, e'-6 willow, Q-900, and number of holes (n) -271. Subsequently, a 6-view V crosslinked polyethylene insulated wire was manufactured by gas crosslinking.

At this time, the porosity on the inlet side was 21.2%, and the porosity on the outlet side was 52.5%. For comparison, a similar cross-linked polyethylene insulated wire was fabricated using the breaker plate shown in Figure 1 (hole diameter 5 side ◇, hole length 38, number of holes (n) 391, other conditions being the same). . Incidentally, the continuous operation time is 10 cycles in each case. In these wires,
Table 1 shows the results of examining the densities of amber (foreign matter that has scorched and changed to a lumpy color) and black (foreign matter that has further changed color to black) in the insulator.

Table 1: Density of Foreign Matter (Pieces/Number) Table 1 shows that when the breaker plate according to the present invention is used, there are significantly fewer foreign matters that have changed color to lees color or black due to scorch, compared to the conventional breaker plate.

As is clear from the above detailed description, in the method for manufacturing a plastic insulated wire of the present invention, the plastic passage in each hole of the breaker plate is expanded at least once on the outlet side, and By keeping the pore area ratio of the breaker plate and the pore area ratio of the outlet side within a predetermined range, and by forming an annular V groove connecting the holes in each row arranged in the same circular shape on the outlet side of the breaker plate, the breaker plate plastic retention before and after
In particular, the flat dead zone at the rear is eliminated and the removal is more effective, so there is almost no scorch occurring before and after the breaker plate, which allows for longer continuous operation times and lower throughput. Problems such as reduction and surface roughness can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the screw, cylinder, subordinate breaker plate and crosshead according to the conventional method, Fig. 2 is a schematic sectional view of the breaker plate used in the method of the present invention, and Fig. 3 is a view from behind. It is a schematic rear view. 13...Breaker plate, 14...Plastic, 15
...Plastic passage, 19...V groove. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. When manufacturing an insulated wire by extruding and coating a conductor with plastic using an extruder, the plastic passage in each hole of the breaker plate of the extruder is expanded at least once on the exit side, and The porosity on the outlet side is 10 to 30%, and the porosity on the exit side is 40%.
~65%, and furthermore, by using an extruder in which an annular V groove connecting holes in each row arranged in the same circular shape is formed on the exit side of the breaker plate, scorch of the compound containing a crosslinking agent is prevented. A method of manufacturing a plastic insulated wire, characterized by the following.