JPS637408B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to power cables. A conventional crosslinked polyethylene cable is comprised of a conductor 1, an inner semiconducting layer 2, a crosslinked polyethylene layer 3, and an outer semiconducting layer 4 in order from the inside to the outside as shown in FIG. Cross-linked polyethylene cables are sometimes used underwater or in humid environments, but it is well known that if they are installed in such conditions and are energized for a long time, they will suffer from so-called water tree deterioration. There are two types of water trees: so-called bow tie trees that occur in the insulator, and normal water trees that occur from the inner semiconducting layer or the outer semiconducting layer. In particular, a practical problem is water trees generated from the semiconducting layer, which gradually develop over time and eventually lead to dielectric breakdown. On the other hand, the bow tree that forms in the center of the insulator has a slow growth rate and poses relatively little practical trouble compared to the water tree that forms from the semiconducting layer. Therefore, various methods have been proposed as methods for preventing water trees. For example, a method of incorporating additives and a method of employing an extruded semiconductive layer have been proposed, but each has advantages and disadvantages, and these methods are not particularly preferable. In view of the above circumstances, the present inventors investigated the occurrence of water tree in the case of various polymer materials in order to find a power cable that can more reliably prevent water tree. It has the following properties: ethylene, α-olefin, and polyene, α-olefin is C ₃ to C ₁₀ , polyene is non-conjugated diene,
The molar ratio of ethylene and α-olefin is 50/50 to 95/
5, and the molecular weight is 1 at the intrinsic viscosity (135℃, decalin).
~6, iodine value is 5-50, melt index is
It was found that water trees do not occur in ethylene-α-olefin-polyene copolymers having a molecular weight of 0.1 to 20. More preferably, the residual ash content is at its maximum value.
0.1% by weight, with a maximum volatile content of 0.6% by weight. Furthermore, when a power cable having an insulator having a laminated structure of a crosslinked rubber layer and a crosslinked polyethylene layer having the above properties was made, it was found that water trees did not occur from the inner semiconducting layer or the outer semiconducting layer. Based on these findings, we manufactured various power cables and investigated their characteristics. As a result, we found that power cables with an insulating layer consisting of a cross-linked polyethylene layer and a cross-linked rubber layer have extremely excellent water resistance and have a long service life. It was found that the cable was extremely long and had a breakdown voltage equivalent to that of a cross-linked polyethylene cable. The present invention was completed based on these findings. The present invention will be described in detail below with reference to FIGS. 2 and 3. FIG. 2 shows a power cable according to one embodiment of the invention. In Fig. 2, numeral 10 is a power cable, and this power cable 10 has conductors 1 in order from the inside to the outside.
1, an inner semiconductive layer 12, a crosslinked rubber layer 13, a crosslinked polyethylene layer 14, and an outer semiconductive layer 15. The crosslinked rubber layer 13 consists of ethylene and α
- Consists of olefin and polyene, α-olefin has C ₃ to C ₁₀ , polyene is non-conjugated diene, and the molar ratio of ethylene and α-olefin is 50/50 to 95/5.
Molecular weight is 1 to 6 in intrinsic viscosity (135℃, Decalin),
Iodine value is 5~50, melt index is 0.1~
20, preferably the residual ash is 0.1% by weight or less,
It is composed of a crosslinked ethylene-α-olefin-polyene copolymer with a volatile content of 0.6% by weight or less. In this copolymer, the α-olefin is preferably propylene, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-octene, etc., and the polyene is dicyclopentadiene, 1,4-hexadiene, etc. etc. are preferable. Furthermore, if the molar ratio of ethylene and α-olefin is outside the above range, a crosslinked rubber layer with the desired characteristics cannot be obtained, and if the intrinsic viscosity, which indicates the molecular weight, is less than 1 and the melt index is less than 0.1, the molecular weight is excessive, resulting in poor extrusion processability and moldability.
When the intrinsic viscosity exceeds 6 and the melt index exceeds 20, physical properties such as elongation deteriorate. If the amount of polyene is less than 5 in terms of iodine value, crosslinking will be insufficient when using a free radical generator other than organic peroxide, and if it exceeds 50, crosslinking will proceed too much, causing elongation and failure. Lack of flexibility. The residual ash content and volatile content are determined from the electrical characteristics of the insulator layer when used as a power cable, and the residual ash content is 0.1% by weight.
If the content exceeds 0.6% by weight, the amount of inorganic content such as polymerization catalyst increases, and if the volatile content exceeds 0.6% by weight, water content and low molecular weight increase, resulting in a decrease in electrical properties, which is disadvantageous. In the power cable of this embodiment, the inner semiconducting layer 1
A cross-linked rubber layer 13 is provided directly above the cross-linked rubber layer 2, and a cross-linked polyethylene layer 14 is provided thereon, and the cross-linked polyethylene layer 14 and the cross-linked rubber layer 13 are characterized as insulating layers. .
By the way, a shielding tape layer (not shown) or a polyvinyl chloride sheath layer (not shown) can be provided on the outside of the external semiconductive layer 15, if necessary. Next, an example of a method for manufacturing the power cable shown in FIG. 2 will be described. After forming the internal semiconductive layer 12 by wrapping carbon paper or the like around the conductor 11, it is sequentially coated with an ethylene-α-olefin-polyene copolymer and polyethylene, and then coated with a continuous crosslinking device. The insulator layer is then crosslinked at a predetermined vapor pressure and temperature to form an insulating layer consisting of a crosslinked rubber layer 13 and a crosslinked polyethylene layer 14. The outer semiconducting layer 15 is then applied by winding or other means. If necessary, a predetermined layer such as a shielding tape layer or a sheath layer is then provided. Although the power cable 10 is manufactured through the above-mentioned steps, the method for manufacturing the power cable is not limited to the above-described method, and it goes without saying that other methods can also be used. Next, a power cable according to another embodiment will be described with reference to FIG. Reference numeral 20 in FIG. 3 is a power cable, and this power cable 20 has a conductor 21, an internal semiconductive layer 22, and crosslinked rubber layers 23a, 23b, 23 arranged alternately from the inside to the outside.
c, 23d and crosslinked polyethylene layers 24a, 24
b, 24c, 24d, and a crosslinked rubber layer 23e provided outside the outermost crosslinked polyethylene layer 24d.
and an outer semiconducting layer 25. The crosslinked rubber layer in the power cable of this example is made of the above-mentioned ethylene-α-olefin-polyene copolymer, and the feature of this example is that the crosslinked rubber layer and the crosslinked polyethylene layer are alternately provided. It is in the fact that it is being given. The other configurations and manufacturing methods are the same as those of the previous embodiments, so their explanations will be omitted. Note that the power cable of the present invention is not limited to the two embodiments described above, and can be modified in various ways. For example, not only the number of layers can be changed, but also the structure, shape, etc. can be changed. As explained above, in the power cable of the present invention, the crosslinked polyethylene layer and the specific ethylene α-
An insulating layer composed of a crosslinked rubber layer made of an olefin-polyene copolymer is provided. Therefore, according to the present invention, even if the device is used for a long period of time under submerged electricity, no deterioration or destruction will occur due to water trees. In the case of a structure in which a semiconductive layer and a crosslinked rubber layer of an ethylene-α-olefin-polyene copolymer are closely attached, water trees from the interface between the two do not occur. In addition, in the case of a structure in which a semiconductive layer and a crosslinked polyethylene layer are brought into close contact with each other and a crosslinked rubber layer of ethylene-α-olefin-polyene copolymer is provided, water generated from the interface between the semiconductive layer and the crosslinked polyethylene layer The tree progresses into the crosslinked polyethylene layer, but does not progress into the crosslinked rubber layer, so the progress stops. Therefore, the power cable of the present invention has excellent water resistance, does not cause dielectric breakdown, has dielectric breakdown strength equivalent to that of conventional cross-linked polyethylene cable, and has a long life. Further, it has a relatively simple structure and has practical effects such as being able to be manufactured with good mass productivity. Hereinafter, the present invention will be specifically explained with reference to Examples. Example The power cable shown in Figure 2 was made by wrapping carbon paper around 100 mm ² soft conductive strands to provide an internal semiconductive layer, and then sequentially applying ethylene-α-olefin-polyene copolymer and polyethylene. The coating is alternately coated in 0.2 mm increments to give a thickness of 4 mm, and then crosslinked using a continuous vulcanizer at a vapor pressure of 6 kg/cm ² and a temperature of 160°C to form an insulator layer consisting of a crosslinked rubber layer and a crosslinked polyethylene layer. and then wrapping the outer semiconducting layer tape. Thereafter, a shielding layer and a polyvinyl chloride sheath layer were sequentially provided. A power cable shown in FIG. 3 was also produced in the same manner. Here, as the ethylene-α-olefin-polyene copolymer, the α-olefin is 1-butene, the polyene is dicyclopentadiene, and the molar ratio of ethylene and 1-butene is 85/15 and 80/20.
Two types of polyenes were used with an iodine value of 10.2 and 15.1, a molecular weight of intrinsic viscosity of 5.2 and 9.8, a melt index of 5.0 and 10.3, a residual ash content of 0.07 and 0.08% by weight, and a volatile content of 0.3 and 0.5% by weight. . The power cables shown in Figures 2 and 3 manufactured as described above were immersed in water, and the applied voltage was
Electricity was applied at 10 KV and a frequency of 1 KHz, and the tree occurrence status and dielectric breakdown voltage were measured after 3 months. The results obtained are shown in the table below. For comparison,
Similar measurements were made on the conventional power cable shown in FIG. 1, and the results are also listed in the following table.

[Table] As is clear from the above table, the power cable of the present invention having an insulating layer composed of a crosslinked polyethylene layer and a crosslinked rubber layer of a specific ethylene-olefin-polyene copolymer is different from the conventional polyethylene It has much better cable properties than one with a single insulation layer. Comparative Example A power cable having the structure shown in FIG. 3 was manufactured in the same manner as in the example. At that time, ethylene-α-
Three types of power cables were obtained using the following three types of olefin-polyene copolymers: A, B, and C. A: α-olefin is 1-octene, polyene is dicyclopentadiene, molar ratio of ethylene and 1-octene is 35/65, iodine number is 11.3, intrinsic viscosity is 3.5, melt index is 5.5, residual ash is 0.05. % by weight, with a volatile content of 0.4% by weight. B: The α-olefin is 1-dodecene, the polyene is dicyclopentadiene, the molar ratio of ethylene and 1-dodecene is 85/15, the iodine value is 10.0, the intrinsic viscosity is 4.3, the melt index is 9.5, and the residual ash content is 0.06. % by weight, with a volatile content of 0.3% by weight. C: α-olefin is 1-octene, polyene is dicyclopentadiene, molar ratio of ethylene and 1-octene is 98/2, iodine value is 14.3, intrinsic viscosity is 2.3, melt index is 4.5, residual ash content is 0.05% by weight, volatile content 0.4% by weight. These three types of power cables were immersed in water, and an applied power of 10 KV and a frequency of 1 KHz was applied, and three months later, tree generation status and dielectric breakdown voltage were measured. The results are shown in the table below.

[Table] From this result, when the molar ratio of ethylene to α-olefin in the ethylene-α-olefin-polyene copolymer is smaller than 50/50 (A),
Although there is no tree formation, the withstand voltage is low, and α
- In the case of olefins other than C ₃ to C ₁₀ (B), tree formation occurs and a decrease in voltage resistance is observed.
Furthermore, when the molar ratio of ethylene to α-olefin is greater than 95/5 (C), tree generation also occurs, and a decrease in voltage resistance is observed.

[Brief explanation of the drawing]

FIG. 1 is a front view of a conventional power cable, FIG. 2 is a front view of a power cable according to an embodiment of the present invention, and FIG. 3 is a front view of a power cable according to another embodiment of the present invention. 10,20...Power cable, 11,21...
Conductor, 12, 22... Internal semiconducting layer, 13, 23
a, 23b, 23c, 23d, 23e...Crosslinked ethylene-α-olefin-polyene rubber layer, 1
4, 24a, 24b, 24c, 24d...Crosslinked polyethylene layer, 15, 25...Outer semiconductive layer.

Claims (1)

[Claims] 1 Cross-linked polyethylene layer, molecular weight is 1 to 6 in intrinsic viscosity (135℃ decalin), iodine value is 5 to 50,
Melt index is 0.1~20g/min, α-
A crosslinked layer of an ethylene/α-olefin/polyene copolymer in which the olefin is C ₃ to C ₁₀ , the polyene is a non-conjugated diene, and the molar ratio of ethylene to α-olefin is 50/50 to 95/5. A power cable characterized by being provided with an insulator layer consisting of.