JPH059884B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing a crosslinked polyolefin insulated cable in which an electron trap layer having a constant concentration gradient is formed at the interface between a semiconducting layer and a crosslinked polyolefin insulating layer. [Technical background of the invention and its problems] Conventionally, with the demand for higher voltage of cross-linked polyolefin insulated cables, as a method to improve the dielectric strength, a substance having a voltage stabilizing effect is dispersed in an insulating layer. A method of trapping electrons injected from the cathode to improve withstand voltage is known. However, although this method is effective in improving AC breakdown voltage, its effect on impulse breakdown voltage is not necessarily clear, and it also has the disadvantage that substances that have a voltage stabilizing effect bleed or act as impurities. [Purpose of the Invention] As a method to overcome these difficulties, a substance that reacts with the polyolefin of the insulator layer is selected as a substance having a voltage stabilizing effect, and this is blended into the polyolefin of the insulator forming material to form the insulator. It is conceivable to fix the layer by grafting after forming the layer to create a more structurally stable state. As a result of intensive research from this perspective, the present inventors discovered that an aromatic vinyl monomer that is reactive with polyolefin and has a voltage stabilizing effect is added to the semiconductive composition that forms the semiconductive layer. This monomer is diffused and transferred from the semiconductive layer to the insulating layer during the extrusion and crosslinking process, and grafted with the polyolefin in the insulating layer, thereby improving both the AC withstand voltage and the impulse withstand voltage. It has been found that a crosslinked polyolefin insulated cable having chemically and physically stable properties can be obtained. The present invention was made based on such knowledge, and an object of the present invention is to provide a method for manufacturing a chemically and physically stable crosslinked polyolefin insulated cable with improved AC withstand voltage and impulse withstand voltage. [Summary of the Invention] That is, the method for manufacturing a crosslinked polyolefin cable of the present invention includes the steps of manufacturing a crosslinked polyolefin insulated cable in which an internal semiconducting layer, a crosslinked polyolefin insulating layer, and an external semiconducting layer are sequentially formed on a conductor. The inner semiconductive layer and/or the outer semiconductive layer are extrusion coated in advance with a semiconductive composition containing an aromatic vinyl monomer, and the aromatic vinyl monomer is converted into an insulating layer by heating in the extrusion and crosslinking steps. It is characterized by being diffused and grafted with the polyolefin of the insulating layer. The drawing is a sectional view showing a crosslinked polyolefin cable obtained according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a conductor, and on this conductor 1, an inner semiconducting layer 2, a crosslinked polyolefin insulating layer 3, and an outer semiconducting layer 4 are formed in this order.
Therefore, an electron trap layer 5 is formed at the interface between the inner semiconducting layer 2 and the crosslinked polyolefin insulating layer 3 and/or the interface between the crosslinked polyolefin insulating layer 3 and the outer semiconducting layer 4 of the crosslinked polyolefin cable.
is formed. This electron trap layer 5 is formed by extruding an aromatic vinyl monomer blended into the inner semiconducting layer 2 and/or the outer semiconducting layer 4 in advance and forming a concentration gradient in the insulating layer during the crosslinking process, as will be described in Examples below. It is formed by diffusing and migrating with the insulating layer and grafting reaction with the polyolefin of the insulating layer. The aromatic vinyl monomer used in the present invention has a voltage stabilizing effect and an electric field relaxing effect, and undergoes a grafting reaction with polyolefin when heated at high temperature in the presence of a crosslinking agent. Examples of such aromatic vinyl monomers include styrene, methylstyrene, vinylpyridine, and vinylnaphthalene. Note that the more aromatic rings there are, the greater the electron trap function. In addition, the blending amount is the semiconductive composition that forms the semiconductive layer.
0.3 to 8 parts by weight per 100 parts by weight is suitable.
If it is less than 0.3 parts by weight, the voltage stabilizing effect cannot be expected to be so great, and if it exceeds 8 parts by weight, crosslinking of the insulating layer will be inhibited, so both are not preferred. In addition, this aromatic vinyl monomer may be added to either the inner semiconducting layer or the outer semiconducting layer, but
More preferably, it is added to both or at least the internal semiconducting layer. The semiconductive composition for forming a semiconductive layer used in the present invention includes ethylene-based polymers such as ethylene/vinyl acetate copolymer (abbreviated as EVA), ethylene/ethyl acrylate copolymer, and low-density polyethylene. A mixture of conductive carbon black and, if necessary, a crosslinking agent and an antioxidant is used. The polyolefin composition for forming an insulator used in the present invention is preferably one based on relatively high density polyethylene with a density of 0.930 to 0.950 and a melt index of 0.1 to 2, and a low melt index. . [Embodiments of the Invention] Next, embodiments of the present invention will be described. Examples 1 to 4 On a 250 mm ² conductor, 100 parts by weight of EVA, 60 parts by weight of conductive carbon, 1 part by weight of a crosslinking agent, 0.3 parts by weight of an antioxidant and the following were added as a semiconductive composition for forming an internal semiconductive layer. A composition consisting of 2 parts by weight of the aromatic vinyl monomer shown in the table, a crosslinkable polyethylene composition containing a crosslinking agent as a composition for forming an insulator, and a semiconducting composition for forming an outer semiconducting layer.
A composition containing 100 parts by weight of EVA, 60 parts by weight of conductive carbon, 1 part by weight of a crosslinking agent, 0.3 parts by weight of an antioxidant, and 2 parts by weight of styrene for Example 2 was prepared with a thickness of 1 mm and 2 mm, respectively. ,1
A 66 KV crosslinked polyolefin insulated cable was manufactured by sequentially extruding and crosslinking the cables to a diameter of 1.5 mm and heating and crosslinking them by a conventional method, and then sequentially providing a copper tape shielding layer and a sheath thereon. In addition, in addition to this, as a semiconductive composition for forming a semiconductive layer, a composition containing no aromatic vinyl monomer at all, or a composition containing a conventionally known voltage stabilizer instead of the aromatic vinyl monomer is used. Crosslinked polyolefin insulated cables of Comparative Examples 1 to 5 were produced in the same manner as in the Examples. of the obtained cross-linked polyolefin insulated cable
The AC withstand voltage and impulse withstand voltage were as shown in the same table.

[Table] As is clear from the above table, the cross-linked polyethylene cable obtained by the present invention has AC withstand voltage,
Both impulse withstand voltage has been improved. [Effects of the Invention] As explained above, since the crosslinked polyolefin insulated cable obtained by the present invention has an electron trap layer formed thereon, it is highly effective against destruction by electron avalanches, and has improved AC withstand voltage and impulse withstand voltage. ing. In addition, since a material that has a voltage stabilizing effect is grafted onto the base polyolefin, it will not bleed outside the insulator.
Physically and chemically stable.

[Brief explanation of the drawing]

The drawing is a sectional view showing an example of a crosslinked polyolefin cable obtained according to the present invention. DESCRIPTION OF SYMBOLS 1... Conductor, 2... Inner semiconducting layer, 3... Crosslinked polyolefin insulator layer, 4... Outer semiconducting layer,
5...Electron trap layer.

Claims (1)

[Claims] 1. When manufacturing a cross-linked polyolefin insulated cable in which an inner semi-conducting layer, a cross-linked polyolefin insulating layer, and an outer semi-conducting layer are sequentially formed on a conductor, the inner semi-conducting layer and/or the outer semi-conducting layer are scented in advance. The aromatic vinyl monomer is coated by extrusion with a semiconductive composition containing a group vinyl monomer, and the aromatic vinyl monomer is diffused into the insulating layer by heating in the extrusion and crosslinking steps, and grafted with the polyolefin of the insulating layer. A method for manufacturing a cross-linked polyolefin insulated cable.