JPS606050B2 - 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 extrusion, 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 it is continuously operated for more than 10 feeds, scorch will occur in the extruder and the surface of the extrudate will become rough. or large particles may stick to it.

It also leads to a decrease in the amount of extrusion. For this reason, the extruder had to be stopped, cleaned, and restarted about 10 hours after the start, 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 at the outlet side wall part 8 of the breaker plate, which also causes plastic to accumulate. It was found that this was due to scorch occurring due to the presence of water.

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 eliminating breaker marks (due to the orientation of molecules passing through the breaker plate). The opaque ring-like striped pattern, which is presumed to be a plastic insulated wire, can be significantly reduced. ), this also leads to a reduction in the accumulation of plastic near the screw tip and near the cylinder pipe wall, and at the same time, the dead zone of the breaker plate itself has been eliminated structurally, allowing continuous operation for more than 100 hours. The company also provides a method for manufacturing plastic insulated wires with little scorch generation (Tokuiso Sho 55-134130).
As we continued our research, we discovered areas for further improvement.

That is, in the above-mentioned conventional extruder, the tip tapered portion 9 of the screw that faces the front side of the breaker plate 3 is usually formed symmetrically, but it is necessary to create a flow of plastic at the tip of the screw. , they discovered that the left and right taper portions are configured asymmetrically.

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 expanded at least once. At the same time, we set the porosity of the inlet and outlet sides to a predetermined range, and at the same time made the tapered tip of the screw facing the front of the breaker plate asymmetrical to create a smooth flow of plastic near the tip. 1. Playing force - The retention of plastic at the front and rear of the plate is more effectively eliminated to prevent the generation 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 enlarged midway. That is, a tapered rigid portion 15a is formed in the middle. Note that this stepped portion 15a is formed due to the flow of plastic.
Although this tapered shape is preferable, other shapes such as a shape with a radius (R) or a shape formed at a right angle may also be used. At this time, on the inlet and outlet sides of the breaker plate 13, as shown in FIG. , the porosity (%) on the inlet side is a2×number of pores (n)XI.

Table C2 with 〇, separability rate (%) on the exit side baldness x number of pores (
n) It is expressed and defined as XC2100.

In the present invention, the porosity on the entrance 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. ,
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 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 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, resulting in plastic retention 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 will be less likely to accumulate on the breaker plate as a whole.
This is because the occurrence of scorch can be prevented. However, if the porosity is less than 10% and too high, 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. In addition, we have increased the exit ratio on the exit side to 40 to 65% compared to the conventional one (approximately 35 to 40% as mentioned above, both the entrance and exit sides are the same) because the entire breaker plate is made of plastic. Another reason is to adjust the flow resistance so that it does not become too large. Another reason is that by increasing the aperture ratio on the exit side, the dead zone consisting of the wall area between the holes can be reduced. This is to prevent scorch from occurring there.However, 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, This is because if the extruder is exceeded, the flow velocity on the outlet side becomes extremely small, which also causes problems during processing of the breaker plate and mechanical strength problems, which is undesirable. The tip tapered portions 19 of the opposing screws 11 are formed asymmetrically.

In making the left and right sides asymmetrical in this way, the ratio of the left and right lengths, 〆'2:〆', is 1. It is best to use it as a finishing touch. That is, if this ratio is less than 1.2, a sufficient plastic flow cannot be created due to asymmetry. Also, the projecting angle Q' of the tapered portion 19 is 15o.
The above is desirable. That is, it is thought that if this angle Q' is less than 15 degrees and is too small, the scouring effect at the tip of the screw will be small and no effect of causing flow to the plastic that is going to stay there can be expected. By configuring like this,
Conventionally, plastic did not move much near the tip of the screw and tended to accumulate, but the plastic that attempts to accumulate hits the asymmetrical tip and is forced to flow, preventing the plastic from accumulating. effectively removed. Therefore, scorch can be prevented. Although the taper portion 19 is shown as a curved taper, it is not limited to this, and may be straight or wave-shaped to increase the rope cascading effect.

When plastic insulated wires were manufactured using the breaker plate configured as described above, as mentioned above, the plastic was well coated near the tip of the screw, causing a smooth flow of the plastic, and the plastic was flowing smoothly at the entrance side of the breaker plate. Because the flow velocity is far and there is almost no dead zone on the exit side, there is no accumulation of plastic before and after the breaker plate, and there is no scorch before or after the breaker plate even after continuous operation for over 100 hours. It has been confirmed that this does not occur.

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, the length distribution and the number of holes (n) in the portions with hole diameters a and b need to be determined by taking into account the geometrical resistance of the entire breaker plate, that is, the resin pressure just before the breaker plate. be.

Although the above description has mainly been given to the case of insulators, this apparatus can be similarly used for forming 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 polyolefins such as polyethylene, polyvinyl chloride materials, and synthetic rubber materials such as ethylene-propylene rubber (EPR, EPDM) and butylene rubber.

In either case, it is best to select a porosity ratio of 10 to 30% on the inlet side and a closure ratio of 40 to 65% on the outlet side. 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.

Using the extruder shown in Figure 2, the breaker plate is a
-4.2 side◇, b-6.6 side◇, c-150 rib 0, d-
10 leg side, e-28 side, e'-6 female, number of holes (n) -27
1 piece, the screw configuration is so', 72.1 rib, Z'2
A conductor with a nominal cross-sectional area of 40 ratios was extruded and coated with polyethylene containing a crosslinking agent under the conditions of -108.2 ribs and Q'-33.70, and then gas crosslinking was performed to produce a 6-round V crosslinked polyethylene insulated wire. .

At this time, the porosity on the inlet side was 21.2%, and the porosity on the outlet side was 52.5%. For comparison, the breaker plate of the extruder shown in Figure 1 (pore diameter: 5 squares, hole length on the paper side, number of holes (n): 391, other conditions being the same) and the screw (1, 2 -88.4 side, Q -42.70
) was used to fabricate a similar crosslinked polyethylene insulated wire.

Incidentally, the continuous operation time is 10 lifetimes in each case. Table 1 shows the results of examining the densities of amber (foreign matter that has scorched and changed to a lees color) and black (foreign matter that has further changed color to black) in the insulators of these wires. Table 1 Density of foreign matter (pieces/clumps) From Table 1, when using the screw and breaker plate of the present invention, it is almost impossible to detect foreign matter that has changed color to white or black due to scorch compared to conventional ones. I understand that.

The same screen mesh was used in all cases.

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 aperture ratio of the breaker plate and the aperture ratio of the outlet side within a predetermined range, and by forming part of the tip taper of the screw that diverges on the front side of the breaker plate asymmetrically, the plastic can be smoothed near the screw tip. This creates a flow that effectively removes plastic buildup before and after the breaker plate, so there is almost no scorch occurring before or after the breaker plate.
As a result, continuous operation time can be extended further than before, and problems such as reduction in extrusion amount 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 cous head of an extruder used in the conventional method, and FIG. 2 is a schematic diagram of the extruder used in the method of the present invention. 11...screw, 13...breaker plate, 1
4...Plastic 15...Plastic aisle, 1
9... Part of the taper of the screw. Figure 1 Figure 2

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, the plastic insulated wire is characterized in that scorching of the crosslinking agent-containing compound is prevented by using an extruder in which the tip tapered portion of the screw facing the front surface of the breaker plate is formed asymmetrically. manufacturing method.