JPS637564B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked polyolefin composition that can improve crosslinking efficiency during crosslinking treatment. The crosslinked polyolefin composition is composed of a polyolefin 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. Crosslinked polyolefin insulated electrical cables are manufactured by extruding a mixture of polyolefin resin, added with an antioxidant and a crosslinking agent, onto the circumference of the conductor using an extruder, and then subjecting the conductor to crosslinking treatment. In recent years, as extruders with superior kneading effects have been adopted due to improved extruders, methods of injecting a crosslinking agent into the extruder (crosslinking agent injection method) and extrusion of a solution containing an antioxidant dissolved in the crosslinking agent have been introduced. A method of injecting into a machine (simultaneous injection method) has been proposed. These manufacturing methods are methods that lead to improved cable characteristics by omitting the kneading step and reducing the amount of foreign matter mixed in during kneading, compared to conventional methods. From the viewpoint of productivity, the crosslinking agents used in this method are di-tertiary butyl peroxide, tertiary-butyl cumyl peroxide, and 2,5-dimethyl-2,5-di-
(tertiary butyl peroxin) Crosslinking agents such as hexine-3 or solid dicumyl
It is used in combination with peroxide, 1,3-bis-(tertiarybutylperoxyisopropyl)benzene, etc. However, the liquid cross-linking agent suitable for this production method, in other words, the cross-linking agent containing tertiary butyl, has a long half-life at the decomposition temperature, which is an indicator of the cross-linking rate, so the cross-linking efficiency is poor, and the cross-linking agent is not added in excess. However, these methods have drawbacks such as adversely affecting the characteristics of the cable, and are economically disadvantageous. An object of the present invention is to provide a novel crosslinked polyolefin composition that can eliminate the drawbacks of the prior art described above and improve crosslinking efficiency. The gist of the present invention is to use a combination antioxidant of 4,4'-thiobis(6-tert-butyl-m-cresol) and a hindered phenol derivative in the combination of a crosslinking agent, a crosslinking accelerator, and an antioxidant. It is at the point where it was. First, since the crosslinking agent containing tertiary butyl has poor crosslinking efficiency as described above, we considered adding a crosslinking accelerator to increase the crosslinking efficiency. However, although crosslinking accelerators are effective for increasing crosslinking efficiency, in the system of crosslinking agents and crosslinking accelerators, polymerization reaction of the crosslinking accelerator produces polymers, and the effects of the crosslinking agent and crosslinking accelerator, respectively. This defeats the purpose and creates other problems, such as blocking the injection port due to the formation of cloudy substances. Addition of hydroquinoline or the like as a polymerization inhibitor for this crosslinking accelerator is known, but it requires a large amount of addition to obtain the desired polymerization prevention effect.
It is easy to cause various harmful effects. After various studies, we found that a combination antioxidant of 4,4'-thiobis(6-tert-butyl-m-cresol) and a hindered phenol derivative can be used as a combination antioxidant without the need for large amounts of addition. It was discovered that the mixed solution of the crosslinking agent, crosslinking accelerator and antioxidant can be stored for a long time without producing cloudy substances (precipitates). The present invention has been made based on this knowledge. As the crosslinking accelerator used in the present invention, ordinary reactive monomers can be used, and 0.1 to 2 parts by weight of mono- to trifunctional methacrylates and acrylates can be added to 100 parts by weight of the base polyolefin resin. can. The base resin is low density polyethylene,
medium density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer,
This applies to polyolefins containing a majority of ethylene, such as ethylene-propylene copolymers. One type or a combination of two or more types of these may be used. There is no problem in adding other lubricants, colorants, fillers, etc. as necessary. As the antioxidant for the hindered phenol derivative used in the present invention, bis[2-methyl-4-
{3-n-alkyl ( _C12 or _C14 )}], 2,2-thio[diethyl-bis-3(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate, and the like. Next, examples of the present invention will be described together with comparative examples. Example 1 2.0 parts by weight of tertiary butyl cumyl peroxide as a crosslinking agent, 0.2 parts by weight of trimethacrylate as a reactive monomer as a crosslinking accelerator,
4,4′-thiobis-(6-tert-butyl-m-cresol) and bis[2-methyl-4-{3-n-alkyl (C ₁₂ or
A mixed solution in which 0.25 parts by weight of the combination antioxidant C ₁₄ )] was dissolved was left for 30 days. The crosslinking properties of polyethylene (melt index MI=
A pellet obtained by adding and impregnating 100 parts by weight of the above solution (density d=0.920) was molded into a sheet by hot pressing and crosslinked. Example 2 In addition to the same crosslinking agent and crosslinking accelerator as in Example 1, 4,4'-thiobis-(6-tertiary-butyl-m-cresol) and 2,2-thio[diethyl-bis-3] were added as polymerization inhibitors. (3,5-Di-tert-butyl-4-hydroxyphenyl) A mixed solution containing a total of 0.25 parts by weight of a combined antioxidant of propionate was allowed to stand. The crosslinking properties were measured in the same manner as in Example 1. Comparative Example From Examples 1 and 2, bis[2-methyl-4
-{3-n-alkyl (C ₁₂ or C ₁₄ )}], 2.2-
Excluding thio[diethyl-bis-3(3,5-tertiarybutyl-4-hydroxyphenyl)]propionate, only 4,4'-thiobis-(6-tertiarybutyl-m-cresol) was added at 0.25% by weight. The partially dissolved mixed solution was left to stand. The crosslinking properties were measured in the same manner as in Examples 1 and 2. Table 1 shows the storage stability and crosslinking properties of the mixtures according to each example.

【table】

[Table] As is clear from the above explanation, the combined oxidation of 4,4'-thiobis(6-tertiary-butyl-m-cresol) and hindered phenol derivatives in a solution of a crosslinking agent and a crosslinking accelerator. The composition of the present invention to which an inhibitor is added inhibits the polymerization reaction of the crosslinking accelerator, and can improve the long-term storage stability of a mixed solution of the crosslinking agent, crosslinking accelerator, and antioxidant. Therefore, the crosslinking efficiency can be improved without causing the disadvantage of formation of a polymer due to the addition of a crosslinking promoter. Furthermore, since an antioxidant that inhibits crosslinking is used, the crosslinking properties are also good.

Claims (1)

[Claims] 1 Di-tersiary butyl peroxide, Tertiary butyl cumyl peroxide, 1.
4,4′-Thiobis(6-tert-butylperoxy isopropyl) as a polymerization inhibitor for the cross-linking promoter is added to a polyolefin containing a cross-linking agent containing tert-butyl such as 3-bis-(tert-butylperoxy isopropyl)benzene and a cross-linking accelerator. -butyl-m-cresol) and a hindered phenol derivative as a combined antioxidant.