JPS606048B2 - How to make 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, a method for producing plastic insulated wire that does not generate 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 generally used as a secondary column.

In this extruder, 1 is the screw, 2 is the cylinder, 3 is the breaker plate, 4 is the fed plastic, 5 is the passageway, 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.
If the extruder is operated continuously for more than 0 feeding time, scorch will occur in the extruder, and the surface of the extrudate will become rough or have large lumps attached.

It also leads to a decrease in the amount of extrusion. 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 neck of the cylinder 2, and also accumulates at the center 81 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, which also causes plastic waste to accumulate. 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 breaker mark (molecules passing through the breaker plate). It is assumed that this is due to the orientation.

This invention (Taru Kansho 54-70
Based on the discovery of 803), this also leads to a reduction in the accumulation of plastic near the screw tip and cylinder wall, and at the same time structurally eliminates the dead zone of the breaker plate itself, allowing continuous operation for more than 100 hours. Method for manufacturing plastic insulated wire with almost no scorch generation (Tsubaki Gansho 55-134130
), but as we continued our research, we discovered that there are still areas that need improvement. The present invention has been made from the above viewpoint, and its gist 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 breaker plate At the same time, the porosity of the inlet and outlet sides for the entire breaker plate is set within a predetermined range, and at the same time, the center hole of the breaker plate, or the center hole and the outermost hole, are formed larger than the surrounding holes to further prevent plastic from accumulating. The point is that this prevents the occurrence of scorch.

Next, the present invention will be explained in detail 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 part 15a due to the flow of plastic, but other shapes such as rounded (R) are preferred.
), or even formed at right angles. At this time, on the inlet and outlet sides of the breaker plate 13, as shown in FIG. , entrance side separability rate (%
) is a2×number of holes (n)X,.

○ Table C2 Separation rate (%) on exit side Baldness x number of holes ○
It is expressed as 2×C2100.

In the present invention, the porosity on the inlet side is set to 10 to 30.
%, and the porosity on the outlet side is preferably in the range of 40 to 65%. Here, each of these porosity ratios indicates the front surface of the breaker plate, in other words, the ratio of all the holes to the total amount of plastic extruded by the screw on this surface, and the value is smaller on the inlet side. ,
A large value on the outlet side means that the flow velocity of the plastic flowing through the plastic passage is far from the inlet side and slow at the outlet side. When the porosity is set to 10 to 30%, the porosity of conventional breaker plates (Fig. 1) is generally about 35 to 40%, but it is quite small, and this causes the play force to decrease. This is because the flow velocity of plastic passing through the inlet side is considerably farther (approximately twice) compared to the conventional one, and the accumulation of plastic on the inlet side is effectively removed. When the fluid flows smoothly, the breaker plate as a whole is less likely to accumulate,
This is because the occurrence of scorch can be prevented. However, if the porosity is too small (less than 10%), the pressure (back pressure) of the molten plastic inside the cylinder will become too high, which is undesirable, and if it exceeds 30%, it will become almost the same as the conventional one. This is because it is not desirable. Well, the reason why the porosity on the outlet side was increased to 40-65% compared to the conventional one (both the inlet and outlet sides are the same, about 35-40% as mentioned above) is because of the breaker. This is to prevent the flow resistance of the entire plate from becoming too large. Another reason is that by increasing the pore size on the exit side, the dead zone consisting of the wall surface between the holes is made smaller and scorch does not occur there. If the porosity is less than 40%, the flow resistance will become too large due to the relationship with the porosity on the inlet side.On the other hand, if it exceeds 65%, the flow velocity on the outlet side will become extremely low, and the breaker This is because it causes problems during plate processing and mechanical strength problems, which is undesirable.In the above-mentioned breaker plate 13, in the present invention, the plastic passage 15' in the center hole is formed larger than the surrounding plastic passage 15. That is, the flea a' on the inlet side and the flap on the outlet side are respectively enlarged to be the same as the expansion ratio (b2/a2) of the surrounding plastic passage 15.In this way, the center hole The reason why the plastic passage 15' is made large is to further reduce the flow resistance in the center of the breaker plate.This makes it possible to avoid the accumulation of especially large plastic near the tip of the screw by making the entire hole the same size. Retention can be removed more effectively than in the case of
The occurrence of scorch can be prevented. FIG. 3 is a schematic diagram showing another example of the breaker plate used in the present invention. In this breaker plate 13, in addition to the plastic passage 15' in the center hole, the plastic passage 15'' in the outermost hole also has an inner plastic passage. It is formed larger than 15.

In this case as well, the diameter a'' on the inlet side and the diameter b'' on the outlet side are respectively increased to be the same as the expansion ratio (z/a2) of the inner plastic passage 15. Depending on the type of extruder or manufacturing conditions, plastic may accumulate considerably near the pipe wall of the cylinder, but this reduces flow resistance and eliminates the accumulation more completely. The occurrence of scorch can be prevented. Incidentally, since the retention near the cylinder wall is not as great as near the tip of the screw, it is generally advisable to form the outermost hole smaller in size than the center hole.

When a plastic insulated wire was 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 high, and the flow resistance at the center hole or the outermost hole was small. Furthermore, since there is almost no dead zone on the outlet side of the breaker plate, there is no accumulation of plastic before and after the breaker plate, and no scorch occurs before or after the breaker plate even after continuous operation for more than 10 hours. was confirmed.

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 the occurrence of scorch have almost disappeared. Also,
In FIG. 2 or 3, the length distribution of hole diameters a, a', a'' and b, b', b'' and the number of holes (n
) must be determined in consideration of the geometrical resistance of the entire breaker plate, that is, the resin pressure just before 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. Furthermore, various plastic materials can be used, such as polyolefins such as polyethylene, polyvinyl chloride, and crosslinked synthetic rubbers such as ethylene-propylene rubber (EPR, EPDM) and butyl rubber.

In either case, it is best to select the open area ratio on the inlet side in the range of 10 to 30% and the closed area ratio on the outlet side in the range of 40 to 65%. Since it is sufficient for the passage to be expanded at least once on the outlet side, various shapes can be used in addition to providing one step in the plastic passage in the breaker plate as shown in FIG. For example, a two-stage structure in which the plastic passage in the breaker plate is expanded twice is possible.

Next, an example will be described.

Example 1 Using the breaker plate shown in Fig. 2, a-4.2 side, b-6.6 side, c-150 side, d-10 rib, e
-28 side, e'-6 ribs (however, the center hole is a'-6.3 ribs, b'-9. Monoho◇, c, d, e, e'' are the same),
Nominal cross-sectional area 40 ribs 2 under the condition of number of holes (n) - 271
A 6-board V-crosslinked polyethylene insulated wire was manufactured by extrusion coating polyethylene containing an inferior diaphragm on the conductor, and then gas crosslinking.

At this time, the pore size on the inlet side was 21.3%, and the pore size on the outlet side was 52.7%. 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 side, number of holes (n) 391, other conditions being the same). . The continuous operation time is 10 field hours in each case. In these wires,
Table 1 shows the results of examining the densities of amber (a foreign substance that has scorched and turned into a lees-like color) and black (a foreign substance that has further changed color and turned black) in the insulator.

Table 1: Density of Foreign Matter (Individuals) Table 1 shows that when the breaker plate according to the present invention is used, the amount of foreign matter that has changed color to white or black due to scorch is significantly less than that of the conventional breaker plate.

Example 2 Using the breaker plate shown in Fig. 2, a-4.2 side, b-6.6 side, c-15 rear, d-10 side, e-
28 pieces, e'-6 side (however, the center hole is a'-6.3 ribs, b'-9.9 ribs, d-5 side, e-33 ribs, c, e'
are the same), the nominal cross section is 40 under the condition of number of holes (n) - 271.
A 6-thigh V crosslinked polyethylene insulated wire was manufactured by extrusion coating polyethylene containing a crosslinking agent onto the conductor of Enfan 2, and then by gas crosslinking.

At this time, the pore rate on the inlet side was 21.3%, and the pore rate on the outlet side was 52.7%. The continuous operation time is 10 calm hours. Table 2 shows the results of examining the densities of amber and black in the insulator for this wire. Table 2 Density of foreign substances (individuals) According to the present invention, if the pore size on the inlet side and the outlet side are the same, the same effect can be obtained even if the internal structure of the center hole is slightly different. Recognize.

In each of the above examples, the same screen mesh was used in each case.

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 porosity of the breaker plate and the porosity of the outlet side within a predetermined range, and by making the center hole, or the center hole and the outermost hole larger than the others, the retention of plastic in front and behind the breaker plate is more effective. Because it is removed by
There is almost no scotch generation before and after the breaker plate, which allows continuous operation time to be longer than before, and problems such as a decrease in extrusion amount and roughness of the surface can be significantly reduced.

[Brief Description of the Drawings] Figure 1 is a schematic diagram of a conventional screw, cylinder, conventional breaker plate, and crosshead, and Figures 2 and 3 are schematic diagrams of each breaker plate used in the method of the present invention. be. 13, 13'...Breaker plate, 14...Plastic, 15, 15', 15''...Plastic passage. Fig. 1 Fig. 2 Fig. 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 Opening ratio of 10 to 30%, exit side opening ratio of 40%
~65% and further uses an extruder in which the center hole or the center hole and the outermost hole are larger than the other holes, thereby preventing scorch of a compound containing a crosslinking agent. Method of manufacturing electric wire.