JPS6114617B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing plastic insulated wires by continuously extrusion coating a compound containing a crosslinking agent over a long period of time. More specifically, it is a method of 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 the screw, 2 is the cylinder, 3 is the breaker plate, 4 is the supplied plastic, 5 is its passage, and 6 is the crosshead. And the plastic passage 5 of this conventional breaker plate 3
The inlet and outlet sides had approximately the same diameter and were straight. Normally, when manufacturing cross-linked polyethylene insulated wire using the breaker plate shown in Fig. 1, if it is continuously operated for more than 100 hours, scorch will occur in the extruder, and the surface of the extrudate may become rough. Or there may be large particles 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 decreased, there was a manufacturing problem in that the thickness of the insulator became 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 it was also caused by the type of extruder or manufacturing conditions. As a result, it accumulates near the pipe wall of the cylinder 2, and 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 surface portion 8 on the outlet side of the breaker plate. It was found that the scorch was caused by the accumulation of plastic. Therefore, the present invention has already solved this problem by enlarging the plastic passage in the breaker plate at least once along the flow of plastic, thereby eliminating the breaker mark (molecules passing through the breaker plate). This invention (Patent Application No. 70803/1986) can significantly reduce the opaque ring-shaped striped pattern that is presumed to be caused by orientation, and can thereby be expected to significantly improve the electrical properties, especially the dielectric breakdown properties, of plastic insulated wires. ), this also leads to a reduction in plastic buildup near the screw tip and cylinder wall, while structurally eliminating the dead zone of the breaker plate itself.
Method for manufacturing plastic insulated wire that hardly generates scorch even when operated continuously for hours
-34130), but as we continued our research, we discovered points that needed further improvement. That is, in the above conventional extruder, a screen 9 is placed in front of the breaker plate 3,
Usually multiple meshes, for example, one 40 mesh,
The screen is configured with three 250 meshes, one 40 mesh, etc., and it was discovered that in such a screen, the flow resistance of the screen part corresponding to the area where the plastic is largely accumulated can be configured to be small. It is. The present invention has been made from this point of view, and its gist is that in the breaker plate of an extruder, the plastic passage is expanded at least once on the outlet side, and the breaker plate is At the same time, at the same time, among the multiple screens inserted in the front of the breaker plate, at least one screen has holes in the area where the plastic accumulates most, for example, in the center. The annular screen is designed to reduce plastic flow resistance and more effectively eliminate plastic accumulation before and after the breaker plate, thereby preventing 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 an extruder used in the present invention, in which plastic flows in the direction of the arrow in the figure. The passages 15 of the plastic 14 in the individual holes of the breaker plate 13 of this extruder are widened midway. That is, a tapered step portion 15a is formed in the middle. Note that, from the viewpoint of the flow of the plastic, the stepped portion 15a preferably has a tapered shape, but may have other shapes such as a radiused shape or a right-angled shape. At this time, on the inlet side and outlet side of the breaker plate 13, as shown in FIG. 2, the diameter of the breaker plate 13 is c, the diameter on the inlet side of the plastic passage 15 is a, and the diameter on the outlet side is b.
The opening rate (%) on the inlet side is a ² × number of holes (n) / c ² × 10
0, and the opening rate (%) on the exit side is b ² × number of holes (n)/c
It is expressed as ² × 100. In the present invention, it is preferable that the pore area ratio on the inlet side is in the range of 10 to 30%, and the pore area ratio on the outlet side is 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 pushed out by the screw on this surface, and the value is smaller on the inlet side. , larger on the outlet side means that the flow velocity of the plastic flowing through the plastic passage is faster 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 is set at 10 to 30% on the inlet side, the porosity of the conventional breaker plate (Fig. 1) is generally about 35%.
~40%, whereas it is considerably smaller, and as a result, the flow velocity of plastic through the breaker plate is considerably faster (about twice) than that of the conventional one on the inlet side, resulting in plastic retention on the inlet side. This is because it is effectively removed. That is, if the plastic flows smoothly on the inlet side of the breaker plate, it becomes difficult for the plastic to stagnate on the breaker plate as a whole, thereby preventing the occurrence of scorch. 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 almost the same as conventional products, which is not desirable. That's because there isn't. In addition, the opening ratio on the exit side is 40 to 65%, compared to the conventional one (both the entrance and exit sides are the same, and as shown above, it is about 35% to 65%).
The reason why it is made larger than 40% is to prevent the flow resistance of the entire breaker plate against the plastic from becoming too large. Another reason is that by increasing the aperture ratio on the exit side, the dead zone consisting of the wall surface portion between the holes is made smaller, thereby preventing scorch from occurring there. However, the porosity
If it is less than 40%, the flow resistance will become too large due to the relationship with the porosity on the inlet side, and if it exceeds 65%, the flow velocity on the outlet side will be extremely low, and it will be difficult to process the breaker plate. This is because problems such as 1 and 2 and mechanical strength problems occur, which is undesirable. In the above extruder, in the present invention, a plurality of screens 19 ₁ are provided in front of the breaker plate 13.
_~6 is included. As shown in Fig. 3, the structure consists of, for example, six screens, which can be roughly divided into circular screens and annular screens.From the screw side, there are 40 mesh circular screens 19 1 , 40 mesh circular screens 19 ₁ ,
The circular screen ₁₉₂ of 250 meshes, the circular screen ₁₉₃ of 250 meshes, the circular screen ₁₉₄ of 250 meshes, the circular screen ₁₉₅ of 250 meshes, and the circular screen ₁₉₆ of 40 meshes are installed in this order. and annular screen 19
₃ , 19 The approximately central hole 19a of ₅ is relatively large;
For example, the center hole of the breaker plate 13 and the next 2
Each hole in the row is exposed. That is, it covers from each hole in the third row to each hole in the outermost row. By configuring like this,
Compared to the conventional screen configuration, the flow resistance to the center hole and each hole in the second row is smaller,
Conversely, the flow resistance for each hole from the third row to the outermost row becomes relatively large. Therefore, the flow of plastic 14 is more directed toward the center than before. Therefore, in the tip portion 17 of the screw 11 where the plastic buildup is particularly large, the plastic buildup is more effectively removed and scorch generation is prevented. The construction of the screens _191-6 is not limited to the above-mentioned combinations and mesh sizes, as long as the flow resistance is small at least in the portions corresponding to the portions where plastic is largely retained. Also, depending on the type of extruder or manufacturing conditions, plastic may accumulate considerably not only near the tip of the screw but also near the pipe wall of the cylinder. It is also possible to fix the screen to the front and rear circular screens. When plastic insulated wire was manufactured using the extruder configured as described above, the plastic could easily flow into the central part of the screen as described above, and the flow rate of the plastic at the inlet was high and the plastic insulated at the outlet. Because there is almost no dead zone on the sides, there is no accumulation of plastic before and after the breaker plate, and it was confirmed that no scorch occurred before or after the breaker plate 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 rate and roughness of the surface due to the occurrence of scorch have almost disappeared. In addition, in FIG. 2 or 3, the hole diameter a,
The length distribution of the portions 2 and b and the number n of holes 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. Various plastic materials can be used, such as crosslinked polyolefins such as polyethylene, polyvinyl chloride, or crosslinked synthetic rubbers such as ethylene-propylene rubber (EPR, EPDM) and butyl rubber. In either case, the opening ratio on the inlet side is
It is best to choose a pore size in the range of 10 to 30%, and the opening rate on the exit side to be in the range of 40 to 65%. 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, so as shown in FIG. In addition to the configuration with one step, various shapes are possible, such as a two-step structure in which the plastic passage in the breaker plate is expanded twice. Next, an example will be described. Using the extruder shown in Figure 2, the breaker plates were a-4.2mmφ, b-66mmφ, c-150mmφ,
d-10mm, e-28mm, e'-6mm, number of holes (n)-
271 pieces, screen configuration: 1 40 mesh circular screen, 2 250 mesh circular screens
Nominal cross-sectional area ^400mm 2 with two 250-mesh annular screens and one 40-mesh circular screen.
A 66 KV cross-linked polyethylene insulated wire was manufactured by extrusion coating polyethylene containing a cross-linking agent onto the conductor, followed by gas cross-linking. At this time, the aperture ratio on the inlet side was 21.2% and the aperture ratio on the outlet side was 52.5%. For comparison, the breaker plate of the extruder shown in Figure 1 (hole diameter 5 mmφ, hole length 38 mm, number of holes (n) 391, other conditions the same), one 40 mesh, three 250 mesh, A similar cross-linked polyethylene insulated wire was made using a circular screen consisting of one 40-mesh mesh. The continuous operation time is 100 hours in both cases. Table 1 shows the results of examining the densities of amber (foreign matter that has scorched to an amber color) and black (foreign matter that has further changed color to black) in the insulators of these wires.

[Table] It can be seen from Table 1 that when the extruder according to the present invention was used, there were significantly fewer foreign substances that turned amber or black due to scorch than when using the conventional extruder. 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 open pore ratio of the breaker plate and the pore ratio of the outlet side within a predetermined range, and by making at least one of the multiple screens inserted in the front of the breaker plate an annular screen with a hole in the center. , the flow resistance to the plastic is reduced and the accumulation of plastic before and after the breaker plate is more effectively removed, so there is almost no scorch occurring before and after the breaker plate.
As a result, the continuous operation time can be extended further than before, and problems such as a decrease in the amount of extrusion and roughness of the surface can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the screw, cylinder, breaker plate, and crosshead of an extruder used in the conventional method, Fig. 2 is a schematic diagram of the extruder used in the method of the present invention, and Fig. 3 is a schematic diagram of the screen used in the method of the present invention. FIG. 13...Breaker plate, 14...Plastic, 15...Plastic passage, 19 _1-6 ...Screen.

Claims (1)

[Claims] 1. When producing 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 outlet side, and Open area ratio of 10~
30%, and the opening ratio on the exit side is set to 40 to 65%, and among the plurality of screens inserted in the front of the breaker plate, at least one is an annular screen having a hole in the center of the extruder. 1. A method for producing a plastic insulated wire, characterized in that scorching of a compound containing a crosslinking agent is prevented by using.