JPH0113167B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to power cable insulation layers with improved water resistance. Conventionally, in plastic insulated power cables such as polyethylene insulated cables, trace amounts of water mixed in during manufacturing or use have formed a deterioration called water tree in the insulator due to interaction with the electric field.
It is known that if there is a supply of moisture, this will progress and the insulation performance will be significantly reduced. The present inventors have previously studied in detail the mechanism by which this water tree occurs, and it is believed that microscopic stress cracks occur when microscopic water droplets are excited by electric field energy and exert stress on the insulator. I discovered that this is a phenomenon. i.e. water tree
The phenomenon is an electrical stress cracking phenomenon, similar to the well-known environmental stress cracking, thermal stress cracking, solvent cracking, etc., and is closely related to the molecular structure and crystal structure of polyethylene. It has been found that this phenomenon is difficult to occur in polyethylene, which has a highly entangled molecular chain and a crosslinked structure. The present invention was made based on this knowledge, and aims to provide a power cable insulating composition with less water tree formation by adding polybutene-1 to polyethylene to increase pseudo-crosslinking points. . That is, in the present invention, 100 parts by weight of polyethylene,
The present invention relates to a power cable insulator layer characterized by using a composition containing 1 to 50 parts by weight of polybutene-1. Polybutene-1 used in the present invention is butene-1
A crystalline thermoplastic polymer obtained by regular polymerization of one monomer under low pressure.It is known to have excellent environmental stress cracking resistance due to its high molecular weight, but it has poor water resistance and tree-like properties. There have never been any cases where it has been blended with polyethylene to improve Polybutene-1 with an MI of 0.4 to 20 is commercially available, and all of them are effective, but in particular, polybutene-1 with an MI of 0.8 to 4 is preferred in consideration of compatibility with polyethylene and processability. The appropriate amount of addition is 1 to 50 parts by weight per 100 parts by weight of polyethylene; if it is less than this, there is no effect, and if it is more than this, it is not preferred because it will adversely affect the extrusion processability of the mixture. The composition of the present invention does not lose its effectiveness even if it is crosslinked by an appropriate method such as organic peroxide such as dicumyl peroxide, electron beam irradiation, or a silane coupling agent; Tree performance is further improved. Further, if necessary, antioxidants, carbon black for improving weather resistance, inorganic fillers, crosslinking aids, vulcanization accelerators, voltage stabilizers, etc. can be added. These components are kneaded by a conventional method and coated on a conductor directly or via a shielding layer to form an insulating layer of a power cable. Next, an example will be described. [Example] Each component shown in Table 1 was kneaded with an electric heated roll,
A 1 mm thick sheet was produced using an electric press at 130°C. Those containing a crosslinking agent were crosslinked by pressurizing at 170°C for 15 minutes. The surface of the obtained sheet was scratched with 150 ml side paper, and the sheet was
After applying an AC voltage of 2KV (3000Hz) for 7 days in the presence of 2N saline, the area to which the electric field was applied was sliced to examine tree generation from the surface. The results are shown in Table 1, with no water trees occurring at all, and cases with even a small amount of water tree occurring. Ease of processing was also judged as good or bad.

[Table] *2 Product name manufactured by Mitsui Petrochemical Co., Ltd. *3 Witron manufactured by Witoko Chemical Co., Ltd.
As is clear from the above examples, the insulating layer of the present invention has good water resistance and no deterioration in processability, making it extremely useful.

Claims (1)

[Claims] 1. A power cable insulator layer characterized by using a composition in which 1 to 50 parts by weight of polybutene-1 is added to 100 parts by weight of polyethylene.