JPS629137B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the water resistance of crosslinked polyethylene insulators, particularly to a composition capable of suppressing bow tree. The crosslinked polyethylene composition is composed of polyethylene or an ethylene copolymer blended with an antioxidant and a crosslinking agent. In addition, if necessary, a lubricant or a weather resistance imparting agent may be added to improve processability, and a coloring agent may be added for the purpose of core identification. In recent years, the occurrence of water trees and bow tree trees has become a growing problem with cross-linked polyethylene insulated cables. Considering that underground burying will continue to progress in the future, it is important to suppress deterioration due to electrical charging in flooded conditions, that is, water tree and bow tree. By the way, the antioxidant 4,4'-thiobis(6-tertiarybutyl-) is currently most commonly used.
Although the limit of compatibility with polyethylene (3-methylphenol) is as low as about 0.1 parts by weight, it is usually used in amounts of 0.2 parts by weight or more in order to maintain the heat resistance of crosslinked polyethylene cables. Therefore, there is a concern that something that exceeds the compatibility limit will bloom and become the nucleus of bow tite tree. Therefore, we believe that if we can develop a composition that has excellent heat aging properties and also significantly reduces the occurrence of bow tie tree, it will make a significant contribution to improving the reliability of high voltage cross-linked polyethylene cables. An object of the present invention is to provide a crosslinked polyethylene composition for high-voltage insulators that can eliminate the drawbacks of the prior art described above and has excellent heat aging characteristics and significantly improved bow tie resistance. . As a result of various research and experiments, the inventors of the present application have found that 4,4'-thiobis(6
It has been found that it is effective to use tetrakis{methylene (dodecylthiopropionate)}methane in combination with tertiarybutyl-3-methylphenol). As a result, not only is the heat aging property superior to that of 4,4'-thiobis-(6-tertiarybutyl-3-methylphenol) alone, but the bowtery resistance is also significantly improved. It was confirmed. Note that it is difficult to impart heat aging properties with tetrakis{methylene (dodecylthiopropionate)}methane alone, and when added in a large amount, crosslinking is inhibited. The base resin is low density polyethylene,
This applies to polyolefins containing a majority of ethylene, such as medium-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate, and ethylene-propylene copolymer. One type or a combination of two or more types of these may be used. Commonly used crosslinking agents include dicumyl peroxide, 1,3-bis-(t-butyl peroxy-isopropal)benzene, and 2,5-dimethyl-2,5-di-(t-butyl peroxy). -Hexine-3 etc. Other lubricants, colorants, fillers, if necessary,
There is no problem in adding a crosslinking accelerator or the like. Examples of the present invention will be described below along with comparative examples. Example 1 Polyethylene (melting index MI=1.0, density d=
0.92) 100 parts by weight, 0.1 part by weight of 4′,4′-thiobis-(6-tertiarybutyl-3-methylphenol) as an antioxidant, and tetrakis {methylene-
(Dodecylthiopropionate)} 0.2 parts by weight of methane and 2.5 parts by weight of dicumyl peroxide as a crosslinking agent were kneaded with a heated roll at 120°C. This was extruded and coated onto a copper conductor having an outer diameter of 3 mm to an insulation thickness of 3 mm. This was crosslinked with water vapor at 15 kg/cm ² for 10 minutes and cooled under pressure. Immerse this wire in heat cycle water at room temperature to 90℃, and apply 300 AC5KV between the conductor and the water.
time was applied. This was sliced thinly and boiled and stained with a methylene blue aqueous solution. The presence or absence of bow tit tree development was observed using an optical microscope. Example 2 Ethylene-vinyl acetate copolymer (vinyl acetate amount 1.8
%, MI=2), 0.2 parts by weight of 4,4′-thiobis(6-tertiarybutyl-3-methylphenol), 0.2 parts by weight of tetrakis {methylene-(dodecylthiopropionate)}methane, Experiments were conducted in the same manner as in Example 1 using a composition consisting of 2.5 parts by weight of dicumyl peroxide. Example 3 To 100 parts by weight of polyethylene (MI=3, d=950), 4',4'-thiobis(6-tertiarybutyl-
3-methylphenol) 0.1 part by weight, tetrakis {methylene-(dodecylthiopropionate)}methane 0.3 parts by weight, 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexyne-31.5 parts by weight Experiments were conducted using the same method as in Example 1. Comparative Example 1 100 parts by weight of polyethylene (MI=1.0, d=0.92) was added with 4,4′-thiobis(6-tertiarybutyl).
Example 1: A composition consisting of 0.25 parts by weight of 3-methylphenol) and 2.5 parts by weight of dicumyl peroxide.
An experiment was conducted using the same method as . Comparative Example 2 A composition consisting of 100 parts by weight of polyethylene (MI=1.0, d=0.92), 0.4 parts by weight of tetrakis {methylene-(dodecylthiopropionate)}methane, and 2.5 parts by weight of dicumyl peroxide was used as in Example 1. Experiments were conducted in a similar manner. Comparative Example 3 To 100 parts by weight of polyethylene (MI=1.0, d=0.92), 4,4'-thiobis(6-tertiarybutyl-
3-methylphenol) 0.1 part by weight, n-octadecyl-3-(4'-hydroxy-3',5'-di-t
An experiment was conducted in the same manner as in Example 1 using a composition consisting of 0.3 parts by weight of -butyl phenyl) propionate and 2.5 parts by weight of dicumyl peroxide. Comparative Example 4 100 parts by weight of polyethylene (MI=1.0, d=0.92), 0.2 parts by weight of tetrakis {methylene-(dodecylthiopropionate)}methane, tetrakis-
{methylene-3-(3',5'-t-butyl-4'-hydroxyphenyl)propionate} A composition consisting of 0.1 parts by weight of methane and 2.5 parts by weight of dicumyl peroxide was tested in the same manner as in Example 1. did. Comparative Example 5 4′,4′-thiobis(6-tertiarybutyl-3) was added to 100 parts by weight of polyethylene (MI=1.0, d=0.92).
- Methylphenol) 0.2 parts by weight, dilauryl
Experiments were conducted in the same manner as in Example 1 using a composition consisting of 0.2 parts by weight of thiodipropionate and 2.5 parts by weight of dicumyl peroxide. Table 1 shows the number of bow tie occurrences and heat aging properties of the model cables according to each example.

【table】

[Table] As is clear from the above explanation, the antioxidant system of the present invention was able to significantly improve both heat aging resistance and bow tie resistance compared to the case of conventional thiobisalkylphenol alone. . The reason for this is that tetrakis{methylene-(dodecylthiopropionate)}methane has an excellent affinity with polyethylene, which improves wetting with the polymer and makes it difficult to generate bowtery. It seems to be. Note that in the case of tetrakis{methylene-(dodecylthiopropionate)}methane alone, the heat aging properties are insufficient, and even if the amount is increased, crosslinking will be inhibited, making it difficult to put it into practical use. It is important to use both together.

Claims (1)

[Claims] 1 Add 4,4'-thiobis- as an antioxidant to polyethylene or ethylene copolymer containing a crosslinking agent.
A crosslinked polyethylene composition characterized in that it is formed by using a combination of (6-tertiarybutyl-3-methylphenol) and tetrakis{methylene-(dodecylthiopropionate)}methane.