JPS6236061B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked polyethylene composition, and particularly to a crosslinked polyethylene composition with excellent heat resistance used as an insulator for electric wires and cables. Since cross-linked polyethylene has excellent electrical insulation and heat resistance, demand for it as an insulating material for electric wires and cables has been increasing in recent years. However, for applications such as motor lead wires and internal panel wiring, insulating materials with far superior heat resistance are now required. The present invention has been made in view of the above, and its object is to provide a crosslinked polyethylene composition that has particularly excellent heat resistance. The feature of the present invention is that 0.2 to 0.8 parts by weight of 4,4'-thiobis(3-methyl-6-t-butylphenol) and bis{2-
A crosslinked polyethylene composition obtained by adding methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl}sulfide in combination with 0.5 to 3 parts by weight and crosslinking with an organic peroxide. It is in. The heat resistance of crosslinked polyethylene depends on the type and amount of antioxidant used. In order to improve heat resistance, a large amount of antioxidant is required, so compatibility with polyethylene is an absolute requirement. In contrast, 4,4'-thiobis(3
-Methyl-6-t-butylphenol) has poor compatibility with polyethylene, and the upper limit of its addition amount is very small at 0.1 parts by weight. Therefore, this antioxidant alone cannot improve heat resistance. Therefore, in the present invention, 4,4'-thiobis(3-
methyl-6-t-butylphenol) to bis[2
-Methyl-4-{3-n-alkyl ( _C12 or
C ₁₄ )thiopropionyloxy}-5-t-butylphenyl] sulfide was added in combination, which has extremely good compatibility with polyethylene and also has high antioxidant ability. It also has extremely excellent properties such as low volatility at high temperatures and little inhibition of crosslinking. What is also noteworthy is that the antioxidant effect is even higher when each antioxidant is used in combination than when used alone; The addition of t-butylphenyl}sulfide increases the compatibility limit of 4,4'thiobis(3-methyl-6-t-butylphenol). In addition, 4,4'-thiobis(3-methyl-6-t
- butylphenol) was limited to 0.2 to 0.8 parts by weight because if it is less than 0.2 parts by weight, bis[2
-Methyl-4-{3-n-alkyl ( _C14 or
Even when used in combination with _C14 ) thiopropionyloxy}-5-t-butylphenyl] sulfide, the contribution to improving heat resistance is small, and if it exceeds 0.8 parts by weight, there is a lack of compatibility even when used in combination, and crosslinking inhibition increases. It's for a reason. Also, bis[2-methyl-4-{3-n-alkyl (C ₁₂ or C ₁₄ ) thiopropionyloxy}-
5-t-butylphenyl] sulfide from 0.5 to 3
Parts by weight are limited to less than 0.5 parts by weight.
This is because the compatibility limit of 4,4'-thiobis(3-methyl-6-t-butylphenol) cannot be improved, and if it exceeds 3 parts by weight, it exceeds its own compatibility limit. Organic peroxides for crosslinking low-density polyethylene added with these antioxidants include:
Dicumyl peroxide is the most desirable for processing, but 1,3-bis-(t-butylperoxy-isopropyl)benzene, 2-5-dimethyl-2,
5-di(t-butylperoxy)-hexyne-3
It is also possible to use . The amount of crosslinking agent added is determined by the amount of antioxidant used.
It is necessary to increase it more than before. Other lubricants, colorants, and crosslinking accelerators may be added as necessary. Next, examples and comparative examples of the present invention will be described. Table 1 shows examples of the present invention, and Table 2 shows the formulations and amounts of comparative examples.
Eight comparative examples are shown, and the blending amounts are expressed in parts by weight.

[Table] Next, the method for preparing the sample will be explained. diameter
Using a 150mm mixing roll, temperature 110-120
Antioxidants and crosslinking agents were added to polyethylene at ℃, and after uniformly kneading, the pressure was 100Kg/cm ² and the temperature was 180℃.
Press crosslink at ℃ for 10 minutes and form into a 3 mm thick sheet. Next, the test method will be explained. For the heat resistance test, the test temperature was set at 170℃, and JIS-C-300 ⁵

This was done in accordance with [Table]. Heat resistance is evaluated by the number of days until the elongation decreases to 50%. Less than 20 days is F, 20 to 29 days is E, 30 to 39 days is D, 40 to 39 days.
C for up to 49 days, B for 50 to 59 days, A for 60 days or more
It was evaluated on a five-point scale. Compatibility was evaluated as follows. The roll-kneaded sheet was pelletized using a pelletizer and left at room temperature for 20 days, and then the sample surface was visually observed using a stereomicroscope to check for bloom and bleed. Crosslinking inhibition was judged from the scorch time at 150°C. In this case, a Mooney viscometer was used as a testing machine, an L rotor was used, and the preheating time was 1 minute. Scorch time is 5 from the minimum viscosity
It is the time until points increase, from 11 to
13 minutes was evaluated as the best scorch time for processing.
Table 3 shows the test results of the samples of the examples shown in Table 1,
Table 4 shows the test results for the comparative sample shown in FIG.

【table】

[Table] As can be seen from Tables 1 to 4, compared to the conventional thiobisalkylphenol alone, the antioxidant system shown in the examples of the present invention has improved heat resistance and polyethylene It has excellent compatibility with The reason for this is that bis[2-methyl-4
-{3-n-alkyl (C ₁₂ or C ₁₄ ) thiopropionyloxy}-5-t-butylphenyl] sulfide is also used, so it is added to 4,4'-thiobis(3-methyl-6 -t-butylphenol) dissolves and tends to remain inside the polyethylene. The reason why the antioxidant effect is greater when a combination of both antioxidants is added than when each antioxidant is used alone is mainly due to 4.
The phenolic OH group in 4'thiobis(3-methyl-6-t-butylphenol) and bis[2-methyl-4-{3-n-alkyl (C ₁₂ or C ₁₄ ) thiopropinioloxy}- This is believed to be due to the synergistic action of the sulfur atoms in the 5-t-butylphenyl sulfide. As a result of the above, a crosslinked polyethylene composition with excellent heat resistance can be obtained and can be used at high temperatures.Furthermore, when used under conventional conditions, its lifespan can be significantly extended, especially for electric wires and cables. It is suitable as an insulator for
It has very high industrial value. As explained above, according to the present invention, it is possible to provide a crosslinked polyethylene composition having particularly excellent heat resistance.

Claims (1)

[Claims] 1 4.4'thiobis(3-methyl-6-t-butylphenol) in 100 parts by weight of low-density polyethylene
and 0.2 to 0.8 parts by weight of bis{2-methyl-4-(3
-n-alkylthiopropionyloxy)-5-
1. A crosslinked polyethylene composition, characterized in that it is made by adding 0.5 to 3 parts by weight of t-butylphenyl}sulfide in combination and crosslinking with an organic peroxide.