JPH0257572B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a crosslinked molded body suitable as an insulator for electric wires and cables. Currently, cross-linked polyethylene, which has excellent insulation properties and heat resistance, is most commonly used as an insulator for power cables. However, it has been recognized that cables made of cross-linked polyethylene as an insulator are subject to treeing and electrical deterioration when energized while submerged in water. Various studies have already been conducted on this problem in various fields, and although some effects of polymer blends and additives have been recognized, none of them has led to a fundamental solution. In the future, power cables will continue to be used in flooded environments, such as by being buried underground, so controlling water trees will become an important issue. The present invention has been made based on the above, and provides a method for producing a crosslinked molded article that can significantly suppress the occurrence of water tree. That is, the present invention is obtained by reacting an A-B-A block copolymer (A is polystyrene, B is a polymer obtained by adding hydrogen to polybutadiene or polyisoprene to destroy unsaturated parts) with a silane compound and a radical generator. Silane grafting A-
A B-A block copolymer is mixed with a silanol condensation catalyst and extruded while undergoing a heating reaction, and the resulting extruded product is crosslinked in the presence of moisture. A-B-A block copolymer is a styrene-based thermoplastic elastomer that has excellent electrical insulation, is strong, and has a high heat softening temperature of 160°C or higher.
Furthermore, it has excellent heat deterioration resistance. The inventors mixed a silanol condensation catalyst into a silane-grafted A-B-A block copolymer and extruded it while reacting with heat, and crosslinked the resulting molded product in the presence of moisture, resulting in extremely excellent water resistance. It was discovered that this material has tree properties, and the present invention was developed based on this discovery. As a silane compound, a hydrolyzable organic group,
Compounds containing alkoxy groups, such as methoxy, ethoxy, butoxy groups, and having aliphatically unsaturated hydrocarbon or hydrocarbonoxy groups that are reactive with free radical sites generated in organic polymers. are preferred, and typical examples include vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacetoxysilane. As a radical generator, dicumyl peroxide, benzoyl peroxide, 2,5-dimethyl-
Examples include organic peroxides such as 2,5-di(tert-butyl-peroxy)hexyne-3, and azo compounds such as azobisisobutyronitrile and dimethylazoisobutyrate. To obtain a silane-grafted A-B-A block copolymer, a silane compound and a radical generator are added to the A-B-A block copolymer, and the mixture is heated to about 200°C using equipment such as an extruder, Banbury mixer, or roll mill. to react by heating. The silane grafted A- thus obtained
A crosslinked molded product is obtained by adding and mixing a silanol condensation catalyst to a B-A block copolymer, extruding the mixture, and bringing the extruded product into contact with moisture. Examples of the silanol condensation catalyst include dibutyltin dilauret, dibutyltin diacetate, and cobalt naphthenate. In the present invention, it is also possible to blend polyethylene, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, ethylene/α-olefin copolymer, etc. within a range that does not reduce water tree resistance. In addition, an antioxidant, a lubricant, etc. may be added as appropriate, and the antioxidant is 4,4'-thiobis(6
-tertiarybutyl-3-methylphenol),
Examples include 4,4'-thiobis(6-tertiarybutyl-ortho-cresol), dilauryl thiodipropionate, and lubricants include fatty acids or fatty acid metal salts such as zinc stearate. Examples of the present invention will be described below. 0.1 part by weight of dicumyl peroxide and 2.5 parts by weight of vinyltrimethoxysilane were mixed and reacted with 100 parts by weight of A-B-A block copolymer (Krayton G1650 manufactured by Schiel Chemical Co., Ltd.), and 0.1 part by weight of dibutyltin dilaurate. Add parts by weight,
A polyethylene semiconductive layer with a thickness of 0.5 mm was extruded on the outer periphery of a copper conductor with an outer diameter of 3 mm so that the insulator thickness was 2 mm while undergoing a heating reaction.
Thereafter, it was left in water at 80°C for 24 hours to obtain a crosslinked insulated wire. For comparison, 100 parts by weight of low-density polyethylene with a density of 0.290 and a melt index of 1 and 2.5 parts by weight of dicumyl peroxide were extruded onto the outer periphery of the semiconductive layer to a thickness of 2 mm as in the example. A crosslinked insulated wire was obtained by heating in high pressure steam at 200°C. The results of observing the occurrence of water trees in the crosslinked insulated wire thus obtained are shown in the following table.

[Table] The observations were made as follows. An insulated wire was immersed in distilled water, and a 3 Kv, 50 Hz AC voltage was applied between the copper conductor and the water at room temperature for 18 months. After the electrification was completed, the insulator was cut into thin slices, boiled and stained with a methylene blue aqueous solution, and the number of water trees generated was observed using an optical microscope. As is clear from the above description, according to the present invention, a crosslinked molded article having an excellent water tree suppression effect can be obtained, and particularly contributes significantly to improving the reliability of crosslinked electric wires and cables.

Claims (1)

[Claims] 1 A silane obtained by reacting an A-B-A block copolymer (A is polystyrene and B is a polymer obtained by adding hydrogen to polybutadiene or polyisoprene to crush unsaturated parts) with a silane compound and a radical generator. A method for producing a crosslinked molded article, which comprises mixing a grafted A-B-A block copolymer with a silanol condensation catalyst, extruding the mixture while causing a heating reaction, and crosslinking the obtained extruded molded article in the presence of moisture. .