JPS5953645B2 - Manufacturing method for cross-linked polyolefin coated wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a crosslinked polyolefin coated electric wire.

FIG. 1 is a cross-sectional view showing an example of a crosslinked or uncrosslinked polyolefin-covered electric wire, in which 1 is an electric conductor, 21 is a semiconductive conductive shielding layer formed on this conductor 1, and 3
1 is an insulating layer made of crosslinked (or uncrosslinked) polyolefin provided so as to surround the conductor shielding layer 21;
41 is an insulating shielding layer having semiconductivity provided on this insulating layer 31.

Conventionally, there has been an apparatus shown in FIG. 2 as an apparatus for producing a crosslinked polyolefin-coated wire as shown in FIG.

In the figure, 2 is an extruder for extruding an uncrosslinked semiconductive compound onto the conductor 1 as the wire core wire to form a conductor shielding layer 21, and 3 is an extruder for extruding, for example, uncrosslinked polyethylene onto the conductor shielding layer 21 to form an insulating layer 31. 4 is an extruder for extruding the uncrosslinked semiconductive compound onto the insulating layer 31 to form an insulating shielding layer 41; 11 is an extruder for forming the insulating shielding layer 41;
1 and 41 are uncrosslinked polyethylene-coated wires; 5 is a heating device for heating the uncrosslinked polyethylene-covered wire 11 from the outside to crosslink the three coating layers 21, 31, and 41; and 6 is a heating crosslinking device. This is a cooling device for cooling the coated layer. Next, the operation of the conventional device configured as described above will be explained with respect to θ.

Conductor shielding layer 2 formed by extruders 2, 3 and 4
The uncrosslinked polyethylene-coated wire 11 covered with the L insulation layer 31 and the insulation shielding layer 41 is heated while passing through the heating device 5 until the entire coating layer reaches the crosslinking temperature. The polyethylene-coated electric wire heat-crosslinked in this way is cooled while passing through the cooling device 6 and becomes a cross-linked polyethylene-coated electric wire 10. Here, the heating device 5 is a heating device that heats from the external surface using high pressure steam, electric heater, etc.
Heat conduction must wait until the innermost uncrosslinked coating layer 21 reaches the crosslinking temperature. Figure 3 shows an example of the temperature rise characteristics when a conductor 1 has a diameter of 26 mm and a covered wire 11 has an outer diameter of 44 mm, that is, a wire with a coating thickness of 9 mm is heated while maintaining the temperature of the outer surface of the coating at 270°C. . In this figure, the horizontal axis is the distance from the center of the wire, and the vertical axis is the temperature, 1, 21, 31
and 41 indicate the same parts as shown in FIG. Also, e
is the initial temperature of the conductor], and f is the initial temperature of each coating layer 21, 31 and 41.
indicates the initial temperature of The electric wire at these temperatures is heated while passing through the heating device 5, but here we will talk about a device that heats the wire while maintaining the temperature of the outer surface of the coating at about 270°C.
It shows the temperature distribution within the wire at each elapsed time after the start of heating. Curves G, h, i, and j are respectively 100% after the start of heating.
These are temperature distributions at seconds, 200 seconds, 300 seconds, and 400 seconds. As can be seen from this figure, the innermost part of the coating layer reaches the crosslinking temperature (approx.
00 seconds. Therefore, the uncrosslinked polyethylene coated wire must pass through the heating device for 300 to 400 seconds. Therefore, if the wire manufacturing speed is 10 cm per second, the length of the heating device 5 shown in FIG. 1 will be 30 to 40 m. Further, instead of a heating device that directly maintains the temperature of the outer surface of the coating at a high temperature as in this example, a heating device that heats the coating through a heating medium such as high-pressure steam takes more heating time and requires a longer device. As mentioned above, in devices using conventional methods, heating is conducted from the outer surface of the sheath through polyolefin, which is a poor conductor of heat, so it takes a long time for thickly sheathed wires to reach the crosslinking temperature at the innermost part. This has the disadvantage that the equipment is long and the building that houses the equipment is also long or tall. moreover,
A method of using a high-frequency heating device as a heating device has been considered, but in the case of an electric wire provided with an insulating shielding layer 4 as shown in FIG.
Since it absorbs and generates heat, there is little heat generated internally, and the drawbacks of conventional coatings caused by heating from the surface cannot be greatly improved.
This invention was made in order to eliminate the drawbacks of the conventional method as described above. Before forming the insulating shielding layer 41, the inside of the coating is preheated by heating the conductive shielding layer 21 using high frequency. The objective is to provide a method in which the crosslinking time can be shortened by subsequently forming the insulating shielding layer 41 and heating it again to bring the entire coating layer to the crosslinking temperature in a short time.

An embodiment of an apparatus to which the method of the present invention is applied will be described below with reference to the drawings.

In FIG. 4, 5a and 5b are a high frequency power source 7,
High frequency power from 8 is connected to uncrosslinked polyethylene coated wire 12
, 13 for heating. Other than this, the configuration is the same as the conventional device. Next, the operation of this device will be explained.

Similarly to the conventional method, a conductor shielding layer 21 made of an uncrosslinked semiconductive compound and an insulating layer 31 made of uncrosslinked polyethylene are formed on the conductor 1 using extruders 2 and 3, respectively, to obtain an uncrosslinked polyethylene covered wire 12. . While this uncrosslinked polyethylene coated wire 12 then passes through the high frequency heating device 5a, the conductor shielding layer 21 of the two coating layers 21 and 31 absorbs the high frequency power from the high frequency power source 7 and generates heat. , part of the heat is also transferred to the insulating layer 31. Further, a semiconductive compound is extruded by an extruder 4 onto the uncrosslinked polyethylene coated T-wire which has passed through the high frequency heating device 5a and the inside of the coating layer is heated, to form an insulating shielding layer 41, and the uncrosslinked polyethylene coated electric wire 1
Get 3. After that, while the uncrosslinked polyethylene coated electric wire 13 passes through the high frequency heating device 5b, the high frequency power from the high frequency power source 8 is mainly absorbed by the insulating shielding layer 41 of the three coating layers 2], 31 and 4], generating heat. do. The electric wire, in which the entire coating layer reaches the crosslinking temperature in this way and is sufficiently crosslinked, is cooled by the cooling device 6 and becomes a crosslinked polyethylene covered electric wire 10. Next, heating by this method will be explained using figures.

In FIG. 5, e and f respectively indicate the initial temperature of the conductor 1 and the coating layer, that is, the temperature distribution immediately before entering the high frequency heating device 5a. Further, curve k shows the temperature distribution immediately after leaving the high-frequency heating device 5a, l shows the temperature distribution just before entering the high-frequency heating device 5b, m shows the temperature distribution immediately after leaving the high-frequency heating device 5b, and n shows the temperature distribution just before entering the cooling device 6. Furthermore, if the elapsed time for each curve is shown after the start of heating, that is, after entering the high-frequency heating device 5a, k is after 10 seconds, l is after 20 seconds, m is after 40 seconds, and n is after 70 seconds. The entire coating layer therefore reaches the crosslinking temperature (about 180° C.) in about 70 seconds, as shown by curve n. Therefore, the wire manufacturing speed was reduced to 10 c/sec.
m, the entire heating device can be constructed with a length of 7 m, which is less than a fraction of that of conventional devices. Furthermore, if the length of the device is the same as that of the conventional device, the manufacturing speed can be increased and the manufacturing cost per unit length of electric wire can be reduced. In the above embodiment, a high-frequency heating device was also used as a heating device after forming the insulating shielding layer 41, but this part may be heated by a heating device 5 that heats from the outside of the base. Since the inside of the coating layer is heated by the high-frequency heating device 5a, the heating time can be sufficiently shortened, and the entire heating device can be made shorter than the conventional device.

Although the above explanation mainly concerns the production of cross-linked polyethylene-coated wires, other polyolefins such as polypropylene may also be used, and copolymers of these polyolefins may also be used. Known compounding materials such as colorants may be appropriately added to the olefin resin as desired.

As described above, according to the present invention, since the conductive shielding layer is heated by the high-frequency heating device before forming the insulating shielding layer, the crosslinking time can be significantly shortened.

In addition, when the method of the present invention is used to obtain an apparatus for manufacturing a crosslinked polyolefin-coated electric wire, the entire apparatus can be shortened, and the building housing the apparatus can also be made small, which has the effect of greatly reducing equipment costs. Alternatively, if the size of the device is the same as that of the conventional device, the manufacturing speed can be increased and the manufacturing cost per unit length of electric wire can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a polyethylene-coated electric wire, Fig. 2 is a schematic configuration diagram showing a conventional cross-linked polyethylene-coated electric wire manufacturing apparatus, Fig. 3 is an example of heating characteristics by the conventional apparatus, and Fig. 4 is a diagram of the present invention. FIG. 5, which is a schematic configuration diagram showing an apparatus for manufacturing a crosslinked polyethylene coated electric wire according to an embodiment, shows an example of heating characteristics by the apparatus of the present invention. 1... Conductor, 2, 3 and 4... Extruder, 5a, 5b... High frequency heating device, 10.
...Cross-linked polyethylene coated wire, 2]...
・Conductor shielding layer, 31...Insulating layer, 41...
...Insulating shielding layer.

Claims (1)

[Claims] 1. After providing a conductor shielding layer having semiconductivity on a conductor and an insulating layer made of uncrosslinked polyolefin so as to surround this conductor shielding layer, the conductor shielding layer is exposed to high frequency. After that, an insulating shielding layer having semiconductivity is provided so as to surround the insulating layer, and then the insulating layer is heated to at least a temperature necessary for crosslinking the polyolefin. A method for producing crosslinked polyolefin coated wire. 2. The method for producing a crosslinked polyolefin-coated electric wire according to claim 1, wherein the polyolefin is polyethylene.