JPS606046B2 - 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 excellent electrical insulation properties.

Plastic electric wires in which the outer periphery of a conductor is coated with plastic such as polyethylene or polyvinyl chloride as an insulator are generally manufactured using an extruder 2 having a crosshead 1 as shown in Figs. 1 and 2. It is being done.

In other words, conductor 3 is closed. The conductor 3 is inserted into a through hole in the center of the mandrel 4 of the head 1, and the conductor 3 is coated with molten plastic 6 discharged from a die 5. By the way, in the case where a cross-linked plastic such as cross-linked polyethylene is used as an insulator, the conductor 3 is coated with the plastic 6 mixed with a cross-linking agent in the extruder 2, and then the plastic is However, so-called scorch occurs near the tip 7a of the screw 7 of the extruder 2 and the breaker plate 8, and this scorch causes the dielectric strength of the insulated wire to decrease or Inconveniences such as the formation of scorch on the surface of the plastic and the necessity of dismantling the extruder 2 and cleaning the barrel 9 and screw 7 occur when scorch generation is significant. This scorch occurs when the flow of molten plastic between the screw tip 7a and the breaker plate 8 stagnates and is partially heated, and the crosslinking reaction of the molten plastic in the stagnation portion gradually progresses, causing the molten plastic to decompose. It is a phenomenon that occurs as a brownish or now black carbonized foreign material.

In an insulated wire coated with a crosslinked plastic containing scorch, foreign matter caused by the scorch becomes a starting point for dielectric breakdown, resulting in a decrease in the dielectric strength of the wire and foreign matter being exposed on the coated surface, resulting in defects in appearance. This invention was made in view of the above circumstances, and aims to provide a method for manufacturing a plastic insulated wire that can prevent the occurrence of scorch and form a plastic insulator with high electrical insulation properties. An extruder in which the molten plastic inlet side of the breaker plate of the machine has a porosity of 10 to 30%, the outlet side has a porosity of 40 to 65%, and the distance between the breaker plate and the screw tip is 5 skins or less. It is characterized in that the plastic insulator is formed using

Hereinafter, the present invention will be explained in detail with reference to the drawings.

3 and 4 show an example of an extruder suitable for carrying out the method of manufacturing a plastic insulated wire of the present invention, and the same components as in FIGS. 1 and 2 are given the same reference numerals. The explanation will be omitted.

Arrow Z in FIG. 3 indicates the direction of flow of molten plastic. In the breaker plate of the extruder 2 used in this invention, the inlet side porosity of the holes 10a through which the molten plastic flows is set to 10 to 30%, the outlet side porosity is set to 40 to 65%, and the inlet side porosity is set to 10 to 30%. is smaller than the outlet side porosity. Here, the porosity of the breaker plate 10 is given by the following equation. Inlet side porosity (%) = a2 x number of holes XI
.

〇C2 outlet side open area ratio (%) = # x number of holes XIOOC2 a is the entrance diameter of the hole 10a shown in FIG. 3, b is the exit diameter, and C is the effective diameter of the breaker plate 10.

Therefore, the hole 10a of this breaker plate 10 is a hole of different diameters in which the inlet diameter is 4 mm larger than the outlet diameter, and in addition to the hole 10a which is tapered toward the outlet as shown in FIG. It may be expanded with a step at a right angle or expanded in a curved shape. The opening ratio on the inlet side is 1
If it is less than 0%, the pressure (spinal pressure) of the molten plastic in the barrel 9 of the extruder 2 will become too high, which is undesirable.
If it exceeds 30%, the flow rate of the molten plastic at the breaker plate 10 will decrease, causing problems. Furthermore, the reason why the pore size on the outlet side is increased is to prevent the flow resistance of the entire breaker plate from becoming too large. Furthermore, in the extruder according to the present invention, the breaker plate 10 is provided, and the distance between the tip 7a of the screw 7 and the inlet face of the breaker plate 10 (indicated by the sleeve in FIG. 4) is set to 5 ribs or less. be.

If this distance exceeds the 5th side, molten plastic will accumulate between the screw tip 7a and the breaker plate, which is not preferable. In the extruder configured as described above, by setting the distance between the screw tip 7a and the breaker plate 10 to 5 ribs or less, the effect of kneading the molten plastic in the gap between the screw 7 and the breaker plate 10 is increased. , a flow of molten plastic also occurs near the screw tip 7a.

In addition, the porosity on the inlet side of the breaker plate should be set to 10 to 30.
%, and by setting the outlet side porosity to 40 to 65% and making the inlet side porosity smaller than the outlet side porosity, the flow velocity of molten plastic passing through the holes 10a of the breaker plate 10 is increased at the inlet side. The molten plastic becomes larger in size, making it difficult for molten plastic to stagnate on the inlet side, improving the flow of molten plastic as a whole in the breaker plate 10, and reducing stagnation.The combination of the above effects prevents molten plastic from stagnation near the screw tip 7a. This eliminates the accumulation of plastic, and therefore almost no scorch occurs when cross-linked plastic is coated by extrusion.Plastic insulated wires coated with cross-linked plastic by this extruder have high dielectric strength and a beautiful appearance. The explanation above has mainly been given to the case of insulators for plastic insulated wires, but the extruder with the above configuration can also obtain favorable results in the formation of sheaths of electric cables and internal and external semiconductive layers. .

Further, the plastic material is not limited to crosslinked plastics such as crosslinked polyethylene, but also non-crosslinked plastics such as polyvinyl chloride, or synthetic rubbers such as ethylene propylene rubber and butyl rubber. EXAMPLES The present invention will be specifically described below with reference to Examples.

[Example] Let the distance between the tip 7a of the screw and the breaker plate 10 be the 2nd side, and a=4.2nd side and b=shown in FIG.
6.6 ribs ◇, c = 150 side ◇, d = 10 willow, e 28 ribs, f = 6 willow, the number of holes 10a is 271, and the inlet side porosity is 2
Using an extruder 2 equipped with a breaker plate 10 having a porosity of 1.2% and an exit side porosity of 52.4%, polyethylene containing a crosslinking agent was extruded and coated onto a conductor having a nominal cross-sectional area of 40 mm. Crosslinking was performed by gas crosslinking to produce a 6-arc V crosslinked polyethylene insulated wire.

For comparison, the distance between the screw tip 7a and the breaker plate 8 is set to 1 ratio, as shown in Fig. 2, the hole diameter is on the 5th side, the hole length (d + e) is 391, and the number of holes is 391. A similar crosslinked polyethylene insulated wire was manufactured using an extruder 2 equipped with breaker plates 8. The operating time was 10 consecutive hours in all cases. The number of foreign substances due to scorch in the insulator of the obtained electric wire was investigated, and the results are shown in the table.

In the table, ``amber'' refers to a foreign substance that has scorched to a competitive lees color, and ``black'' refers to a foreign substance that has further changed color to black. As explained above, the method for manufacturing a plastic insulated wire of the present invention is to increase the porosity of the molten plastic inlet side of the breaker plate of the extruder from 10 to 10.
30%, and the porosity on the exit side is 40 to 65%, and the distance between the breaker plate of the breaker plate and the screw tip is 5 ribs or less, so the plastic is coated using an extruder. This eliminates the accumulation of molten plastic, and therefore almost eliminates the occurrence of scorch, which was conventionally seen during extrusion coating of cross-linked plastics.
The generation of foreign matter due to scorch is reduced, and the resulting plastic insulated wire has a high dielectric strength voltage and a beautiful appearance.In addition, because the generation of scorch is reduced, the time required to dismantle and clean the extruder is reduced, making manufacturing easier. This has advantages such as improved efficiency.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of a crosshead extruder for manufacturing plastic insulated wires, Figure 2 is an enlarged view of the main parts of the extruder shown in Figure 1, and Figure 3 is the playing force used in this invention. FIG. 4 is a schematic diagram showing an example of a plate, and FIG. 4 is a schematic diagram of an extruder screw and a flaker plate used in the present invention. 2... Extruder, 3... Conductor, 6... Molten plastic, 7...
・Screw, 7a...screw tip, 10...breaker plate, 10a...hole. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. When producing an insulated wire by extruding plastic onto a conductor using an extruder, the breaker plate has a porosity of 10 to 10 on the inlet side of the molten plastic given by the following formula.
30%, the outlet side opening rate is 40 to 65%, and the distance between the screw tip and the breaker plate is 5 mm.
A method for producing a plastic insulated wire, characterized by using the following extruder. Inlet side open area ratio (%) = ((Inlet side hole diameter) ^ 2 x (number of holes)) / ((Effective diameter of breaker plate) ^ 2) x
100 Outlet side pore opening rate (%) = ((Exit side hole diameter) ^2
×(Number of holes))/((Effective diameter of breaker plate)^
2)×100