JPH09157401A - Production of cross-linked molding product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the cross-linked molding product suitable for producing an insulator for power cables by extruding a composition containing a polyolefin-based resin, etc., at a prescribed temperature, heating the resultant extrudate, reducing the moisture content and increasing the cross-linking degree. SOLUTION: A composition comprising (A) 100 pts.wt. polyolefin-based resin, (B) 0.5-3.0 pts.wt. unsaturated silane compound and (C) 1.0-3.0 pts.wt. organic peroxide (preferably dicumyl peroxide) is extruded at 100-150 deg.C and the resultant extrudate is then heated at 160-240 deg.C. Furthermore, (D) an antioxidant, e.g. 4,4'-thiobis(6-t-butyl-3-methylphenol) is preferably used. For example, a low- density polyethylene is preferably used as the component (A) and vinyltrimethoxysilane, etc., are preferably used as the component (B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked molded article that can obtain a molded article with a reduced water content and a high degree of crosslinking, and is particularly suitable for producing an insulator for a power cable. The present invention relates to a method for producing a crosslinked molded article.

[0002]

2. Description of the Related Art
A cross-linked molded body of a polyolefin resin is used for various purposes, for example, an insulator for various cables, a plastic pipe and the like.

Hitherto, as a method for crosslinking a polyolefin resin, a silane crosslinking method or an organic peroxide crosslinking method has been known. The cross-linking reaction by silane cross-linking is to thermally decompose an organic peroxide, graft an unsaturated silane compound to a polyolefin-based resin by radicals generated at that time, and then cross-link by an moisture.
More specifically, the following procedure is performed. First, a composition comprising a polyolefin resin, an unsaturated silane compound, and an organic peroxide is heated at a high temperature not lower than the decomposition temperature of the organic peroxide, for example, about 220 ° C. for dicumyl peroxide, thereby heating A radical is generated by decomposing mill peroxide, and an unsaturated silane compound is grafted on the polyolefin resin by the action of the radical to obtain a silane-grafted polyolefin resin composition. If the temperature at this time is too low, the unsaturated silane compound will not be grafted to the polyolefin resin, so that the molded article will not be crosslinked. If the temperature is too high, burnt may occur in the polyolefin resin. Then, the silane-grafted polyolefin resin composition is molded into a desired shape,
Then, the molded body is immersed in hot water, hot water, or the like, exposed to a steam atmosphere, or left to stand to be crosslinked by water in the air to obtain a crosslinked molded body.

[0004] On the other hand, the crosslinking reaction by an organic peroxide is to thermally decompose the organic peroxide and to crosslink the polyolefin resin by radicals generated at that time.
More specifically, the following procedure is performed. First, a composition comprising a polyolefin-based resin and an organic peroxide is formed into a desired shape at a temperature not lower than the melting point of the polyolefin and lower than the decomposition temperature of the organic peroxide, for example, about 130 ° C. for dicumyl peroxide. Extrusion molding. If the temperature at this time is too low, molding becomes difficult because the fluidity of the polyolefin resin decreases, and if the temperature is too high, the organic peroxide is decomposed and the polyolefin resin is crosslinked at an early stage, and the molding is performed. Becomes difficult. Next, crosslinking is performed by heating the molded body at a temperature higher than the decomposition temperature of the organic peroxide, or about 220 ° C. or higher for dicumyl peroxide, to obtain a cross-linked molded body having a desired shape.

However, in the silane cross-linking, since the cross-linking is carried out using water, an excessive amount of water may enter and remain inside the cross-linked molded article. Water may be generated as a side reaction from the decomposition residue of the organic peroxide remaining inside the molded body. In particular, when an insulator of a power cable is used as the above-mentioned cross-linked molded body, there is a problem that the insulation performance of the power cable deteriorates due to the moisture inside the cross-linked molded body.
Also, in silane crosslinking, the degree of crosslinking of the molded body is 7 at maximum.
Although it is about 0%, development of a molded product having a higher degree of crosslinking is desired from the viewpoint of heat resistance.

An object of the present invention is to provide a method for producing a crosslinked molded article which can obtain a molded article with a reduced water content and a high degree of crosslinking, and is particularly suitable for producing an insulator for a power cable. It is intended to provide a method for producing a crosslinked molded article.

[0007]

According to the present invention, a composition comprising a polyolefin resin, an unsaturated silane compound, and an organic peroxide is extruded at 100 to 150 ° C. and then 160
The above object is achieved by a method for producing a crosslinked molded article, which comprises heating at ˜240 ° C. In addition, the above composition is obtained by blending 0.5 to 3.0 parts by weight of an unsaturated silane compound and 1.0 to 3.0 parts by weight of an organic peroxide with respect to 100 parts by weight of a polyolefin resin. Further, the water content of the molded body can be reduced and the degree of crosslinking can be increased. Further, the use of dicumyl peroxide as the organic peroxide facilitates the production of a crosslinked molded article. Further, by further adding an antioxidant to the composition, the heat resistance of the molded product can be further enhanced. Further, by using the above method for manufacturing an insulator for a power cable, a power cable having high reliability in terms of insulation and heat resistance can be obtained. The present invention also provides a method for producing a crosslinked molded article, which comprises heating a composition comprising a silane-grafted polyolefin and / or a silane-ethylene copolymer and an organic peroxide at 160 to 240 ° C. It achieves the above object. Further, the present invention is characterized in that a composition comprising a silane-grafted polyolefin and / or a silane-ethylene copolymer, a polyolefin resin, and an organic peroxide is heated at 160 to 240 ° C. for crosslinking molding. The above object is achieved by a method for producing a body.

That is, the present invention achieves the above object by using two kinds of crosslinking methods, namely, silane crosslinking and crosslinking with an organic peroxide. That is, a composition comprising a polyolefin resin, an unsaturated silane compound, and an organic peroxide is extruded and molded at 100 to 150 ° C., and then heated at 160 to 240 ° C. to thermally decompose the organic peroxide. Then, radicals are generated, and the unsaturated silane compound is grafted onto the polyolefin resin by the action of the radicals, and at the same time, the polyolefin resin is cross-linked by the radicals not used for the silane grafting. Further, since water is generated as a side reaction from the decomposition residue of the organic peroxide, the water causes the polyolefin resin grafted with the unsaturated silane compound to undergo silane crosslinking. By cross-linking the polyolefin resin by using two types of cross-linking methods, that is, silane cross-linking and cross-linking with organic peroxide, water generated as a side reaction from the decomposition residue of the organic peroxide is cross-linked by silane cross-linking. Since it is consumed, the water content of the molded product can be reduced and the degree of crosslinking can be increased.

The method for producing the crosslinked molded article of the present invention will be described in detail below. First, a composition including a polyolefin resin, an unsaturated silane compound, and an organic peroxide is extruded within a temperature range of 100 to 150 ° C. At this time,
The extrusion temperature is preferably about the melting point of the polyolefin resin and below the decomposition temperature of the organic peroxide so that the composition has sufficient fluidity for extrusion. Therefore, the extrusion temperature is preferably adjusted to 100 to 150 ° C, and particularly preferably 115 to 135 ° C from the viewpoint of preventing early crosslinking. If the extrusion temperature is less than 100 ° C., the fluidity of the composition will be poor, and if it exceeds 150 ° C., the organic peroxide will be decomposed and the polyolefin resin will be cross-linked at an early stage, resulting in poor fluidity.

Next, the above composition is heated to 160 to 240 ° C. to decompose the organic peroxide, thereby grafting the unsaturated silane compound to the polyolefin resin and crosslinking the polyolefin resin with the organic peroxide. Also at the same time. The heating method is not particularly limited as long as it is a commonly used method, and examples thereof include electric heating, steam heating, and far-infrared heating. At this time, since the heating temperature is preferably about the decomposition temperature of the organic peroxide, the heating temperature is adjusted to 160 to 240 ° C. It is particularly preferable to adjust the temperature to 190 to 230 ° C from the viewpoint of graft efficiency. When the heating temperature is lower than 160 ° C., a long time is required for a graft reaction between the polyolefin resin and the unsaturated silane compound and for crosslinking of the polyolefin resin,
Exceeding ° C is not preferred because the crosslinking efficiency is reduced. Further, since water is generated as a side reaction from the decomposition residue of the organic peroxide, the water causes the polyolefin-based resin on which the unsaturated silane compound is grafted to undergo silane crosslinking.

When a silane-grafted polyolefin and / or a silane-ethylene copolymer is used in the method for producing a crosslinked molded article of the present invention, a silane-grafted polyolefin and / or a silane-ethylene copolymer, 1 composition containing an organic peroxide or a composition containing a polyolefin resin
By heating at 60 to 240 ° C., crosslinking with an organic peroxide is performed. At this time, the heating temperature is preferably about the decomposition temperature of the organic peroxide, so that the heating temperature is 16
Adjust to 0-240 ° C. 180 from the viewpoint of crosslinking efficiency
It is preferable to adjust the temperature to 220 ° C. Heating temperature is 160
If it is less than ℃, it will take a long time to crosslink, and 240 ℃
If it exceeds, cross-linking efficiency is lowered, which is not preferable. Then, since water is generated as a side reaction from the decomposition residue of the organic peroxide, the silane-grafted polyolefin and / or the silane-ethylene copolymer is silane-crosslinked with this water.

The materials used in the method for producing a crosslinked molded article of the present invention will be described in detail below. Examples of the polyolefin resin used in the present invention include high-density polyethylene, medium-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, linear ultra-low-density polyethylene, polypropylene, ethylene-propylene copolymer, or
Homopolymers of α-olefins such as 1-butene, 1-hexene and 1-octene, copolymers of these α-olefins with ethylene, or copolymers of vinyl acrylate, methyl acrylate, ethyl acrylate with ethylene. Examples thereof include polymers, and low density polyethylene is particularly preferable from the viewpoint of the degree of crosslinking. As the low-density polyethylene, the melt flow rate measured at 190 ° C. according to JIS K6760 is 0.5 to 4.0 g / 10 minutes, and the density measured according to JIS K6760 is 0.910 to 0.930 g / cm ³ is suitably used.

The unsaturated silane compound used in the present invention is represented by the chemical formula SiXY ₂ Z, where X is an organic group containing a vinyl group, Y is an alkoxy group having 1 to 3 carbon atoms, and Z is Each represents a methoxy group. As the unsaturated silane compound represented by the above chemical formula, for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ
-Methacryloxypropyltrimethoxysilane, gamma methacryloxypropyltriethoxysilane and the like can be mentioned, and vinyltrimethoxysilane is particularly preferable from the viewpoint of grafting efficiency. The amount of the unsaturated silane compound is preferably 0.5 to 3.0 parts by weight based on 100 parts by weight of the polyolefin resin, and is 1.0 to 2.0 parts by weight in view of the water content and the degree of crosslinking. Parts are more preferred.
If the blending amount of the unsaturated silane compound is less than 0.5, the water content reducing effect tends to decrease, and if it exceeds 3.0, the amount of unreacted unsaturated silane compound tends to increase.

The silane-grafted polyolefin used in the present invention is obtained by grafting an unsaturated silane compound to a polyolefin. As the polyolefin, high density polyethylene, medium density polyethylene, low density polyethylene, ultra low density polyethylene, linear ultra low density polyethylene, polypropylene, ethylene-propylene copolymer, or 1-butene, 1-hexene, 1
-Homopolymers of α-olefins such as octene, copolymers of these α-olefins with ethylene, or copolymers of vinyl acrylate, methyl acrylate, ethyl acrylate and the like with ethylene, and the like. From the viewpoint of, low density polyethylene is particularly preferable. The unsaturated silane compound is represented by the chemical formula SiXY ₂ Z, where X is an organic group containing a vinyl group, Y
Represents an alkoxy group having 1 to 3 carbon atoms, and Z represents a methoxy group. Examples of the unsaturated silane compound represented by the above chemical formula include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, gammamethacryloxypropyltriethoxysilane, and the like. Particularly, vinyltrimethoxysilane is preferable from the viewpoint. In the silane-grafted polyolefin used in the present invention, a graft ratio of the above unsaturated silane compound to the polyolefin is preferably 0.1 to 5.0% from the viewpoint of the degree of cross-linking. Rate is 0.5
It is more preferable that the content is up to 3.0%.

In the present invention, a silane-ethylene copolymer may be used together with or instead of the silane-grafted polyolefin. The silane-ethylene copolymer is composed of ethylene and the chemical formula SiXY ₂
A copolymer with an unsaturated silane compound represented by Z, wherein X is an organic group containing a vinyl group, and Y is a group having 1 to 3 carbon atoms.
And Z represents a methoxy group, respectively. Examples of the unsaturated silane compound represented by the above chemical formula include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, gammamethacryloxypropyltriethoxysilane, and the like. Particularly, vinyltrimethoxysilane is preferable from the viewpoint. In the present invention, those in which the unsaturated silane compound is contained in the silane-ethylene copolymer in a proportion of 0.1 to 5.0% are preferably used. Among them, the unsaturated silane compound is particularly preferable. What is contained at a rate of 0.5 to 3.0% is more preferably used. In the present invention, the above-mentioned silane-grafted polyolefin and silane-ethylene copolymer may be used alone or as a mixture, and further, silane-grafted polyolefin and / or silane-ethylene copolymer and polyolefin-based resin may be used. You may mix and use it. When mixed and used, the mixing ratio of the silane-grafted polyolefin and / or the silane-ethylene copolymer and the polyolefin resin is 1: 0.5 to
The ratio is preferably about 1:10, and the ratio of the unsaturated silane compound in the mixture is preferably about 0.009 to 3.3%.

The organic peroxide used in the present invention is preferably one which produces water as a side reaction from its decomposition residue. Specifically, dicumyl peroxide,
1,3-bis (t-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 and the like can be mentioned, and in view of decomposition temperature, dicumyl is particularly preferable. Peroxide is preferred. The compounding amount of such an organic peroxide may be a polyolefin resin, a silane-grafted polyolefin and / or a silane-
1.0 to 3.0 parts by weight is preferable with respect to 100 parts by weight of the ethylene copolymer and the mixture thereof, and 1.5 to 2.0 parts by weight is particularly preferable from the viewpoint of the degree of crosslinking. If the compounding amount of the organic peroxide is less than 1.0, the degree of crosslinking tends to decrease, and if it exceeds 3.0, the effect of reducing the water content tends to decrease.

From the viewpoint of heat resistance, it is preferable to further add an antioxidant to the composition used in the present invention.
As the antioxidant, for example, various hindered phenol-based, aminophenone-based, quinone-based, phosphorus-based, etc. antioxidants can be used, but particularly hindered phenol-based antioxidants from the viewpoint of improving the heat resistance of the molded product. A suitable agent is, specifically, 4,4-thiobis (6-t-butyl-
3-methylphenol), 2,2'-methylenebis (4
-Ethyl-6-t-butylphenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t. -Butyl-4-methylphenol,
2,5-di-t-butylhydroxynone and the like, among which 4,4-thiobis (6-t-butyl-3-methylphenol) and 2,2'-methylenebis (4-ethyl- 6-t-butylphenol), 2,2
'-Methylenebis (4-methyl-6-t-butylphenol) is preferred. The amount of such an antioxidant compounded is usually 0.1 to 100 parts by weight of the polyolefin resin.
2.0 parts by weight and 0.15 to 1.5 parts by weight are particularly preferable from the viewpoint of heat resistance. If the compounding amount of the antioxidant is less than 0.1, the heat resistance improving effect tends to decrease, and if it exceeds 2.0, the water content decreasing effect tends to decrease.

In addition, the composition used in the present invention may further include, if necessary, a silane crosslinking accelerator such as dibutyl-tin-dilaurate, a crosslinking aid, a stabilizer such as stearic acid, and an ultraviolet absorber such as a benzophenone derivative. Further, a plasticizer such as phthalic acid ester, other processing aids, reinforcing fillers, flame retardants and the like may be appropriately added.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a crosslinked molded article according to the present invention can be applied to the production of various crosslinked molded articles, for example, the production of insulators for various cables, plastic pipes, etc. It is useful for manufacturing an insulator of a power cable because it is required to have an excellent heat resistance and an excellent insulating property.

[0020]

【Example】

(Example 1) A composition comprising the components shown in Table 1 was added to 110
After extruding at ℃, it was cross-linked and molded by a compression molding machine at 180 ° C. for 15 minutes to prepare a sample. (Example 2) Extrusion temperature is 120 ° C, crosslinking temperature is 200 ° C
The same as Example 1 except for the above. (Example 3) Extrusion temperature is 140 ° C, crosslinking temperature is 230 ° C
The same as Example 1 except for the above. (Example 4) A composition comprising each component shown in Table 1 was crosslinked and molded by a compression molding machine at 180 ° C for 15 minutes to prepare a sample. (Example 5) Example 4 except that the crosslinking temperature was 200 ° C.
Is the same as (Example 6) Example 5 except that the crosslinking temperature was 230 ° C.
Is the same as (Comparative Example 1) A composition containing the components shown in Table 2 was used as 120
After extruding at 0 ° C, a sample was prepared by crosslinking and molding under a condition of 200 ° C for 15 minutes by a compression molding machine. (Comparative Example 2) Comparative Example 1 except that the crosslinking temperature was 150 ° C.
A sample was prepared under the same conditions as above. (Comparative Example 3) A composition comprising each of the components shown in Table 2 was crosslinked and molded by a compression molding machine at 150 ° C for 15 minutes to prepare a sample.

Tables 1 and 2 show the composition ratios and evaluation results of Examples and Comparative Examples. The evaluation method is as follows. <Degree of crosslinking> ASTM D2765 using each of the above samples
The degree of crosslinking was evaluated by measuring the gel fraction in accordance with the above. The case where the gel fraction was 80% or more was evaluated as ○, and the case where it was less than 80% was evaluated as ×. <Moisture Content> The moisture content of each sample was measured using a Karl Fischer moisture meter. Water content is 200pp
When it was m or less, it was evaluated as ◯, and when it exceeded 200 ppm, it was evaluated as x.

[0022]

[Table 1]

[0023]

The method for producing a crosslinked molded article according to the present invention comprises the steps of extruding a composition comprising a polyolefin resin, an unsaturated silane compound, and an organic peroxide at 100 to 150 ° C and then heating at 160 to 240 ° C. By doing,
By using two types of cross-linking methods, silane cross-linking and organic peroxide cross-linking, the water generated from the decomposition residue of the organic peroxide is consumed by the silane cross-linking, so that the water content of the molded product can be reduced and the cross-linking can be performed. You can increase the degree. Also,
The composition further comprises 0.5 to 3.0 parts by weight of an unsaturated silane compound and 1.0 to 3.0 parts by weight of an organic peroxide with respect to 100 parts by weight of a polyolefin resin. The water content of the molded body can be reduced and the degree of crosslinking can be increased. Further, the use of dicumyl peroxide as the organic peroxide facilitates the production of a crosslinked molded article. The heat resistance of the molded product can be improved by adding an antioxidant to the composition. In addition, when the insulation of a power cable is molded using the method for producing a crosslinked molded article of the present invention, the amount of water in the insulation can be reduced and the degree of crosslinking of the insulation can be increased. It is possible to obtain a power cable with high reliability in terms of insulation. Further, the method for producing a crosslinked molded article of the present invention comprises heating a composition comprising a silane-grafted polyolefin and / or a silane-ethylene copolymer and an organic peroxide at 160 to 240 ° C, that is, 2 called silane crosslinking and organic peroxide crosslinking
Since water generated from the decomposition residue of the organic peroxide is consumed by the silane cross-linking in combination with various kinds of cross-linking methods, the water content of the molded product can be reduced and the degree of cross-linking can be increased. In addition, the composition can be further reduced in the water content of the molded article by adding 1.0 to 3.0 parts by weight of the organic peroxide to 100 parts by weight of the resin component, and the degree of crosslinking can be increased. Can be higher. Further, the method for producing a crosslinked molded article of the present invention comprises a composition comprising a silane-grafted polyolefin and / or a silane-ethylene copolymer, a polyolefin resin and an organic peroxide.
By heating at 60 to 240 ° C, the water content of the molded product can be reduced and the degree of crosslinking can be increased.

[Table 2]

Claims (15)

[Claims] 1. A composition comprising a polyolefin resin, an unsaturated silane compound, and an organic peroxide is 100 to 1 in composition.
A method for producing a crosslinked molded article, which comprises extruding at 50 ° C and then heating at 160 to 240 ° C. 2. The composition comprises a polyolefin resin 10
The unsaturated silane compound is added in an amount of 0.5 to 3.0 to 0 part by weight.
The method for producing a crosslinked molded article according to claim 1, wherein 1.0 part by weight to 3.0 parts by weight of an organic peroxide are mixed. 3. The method for producing a crosslinked molded article according to claim 1, wherein the organic peroxide is dicumyl peroxide. 4. The method for producing a crosslinked molded article according to claim 1, which further comprises an antioxidant added to the composition. 5. The method for producing a crosslinked molded article according to claim 1, which is used for an insulator of a power cable. 6. A method for producing a crosslinked molded article, which comprises heating a composition comprising a silane-grafted polyolefin and / or a silane-ethylene copolymer and an organic peroxide at 160 to 240 ° C. 7. The composition comprises a silane-grafted polyolefin and / or a silane-ethylene copolymer 10.
The method for producing a crosslinked molded article according to claim 6, wherein 1.0 to 3.0 parts by weight of an organic peroxide is mixed with 0 part by weight. 8. The method for producing a crosslinked molded article according to claim 6, wherein the organic peroxide is dicumyl peroxide. 9. The method for producing a crosslinked molded article according to claim 6, wherein the composition is further blended with an antioxidant. 10. The method for producing a crosslinked molded article according to claim 6, which is used for an insulator of a power cable. 11. A composition comprising a silane-grafted polyolefin and / or a silane-ethylene copolymer, a polyolefin resin and an organic peroxide is contained in an amount of from 160 to 160.
A method for producing a crosslinked molded article, which comprises heating at 240 ° C. 12. The composition comprises 100 parts by weight of a total amount of silane-grafted polyolefin and / or silane-ethylene copolymer and polyolefin resin.
The method for producing a crosslinked molded article according to claim 11, which comprises 1.0 to 3.0 parts by weight of an organic peroxide. 13. The method for producing a crosslinked molded article according to claim 11 or 12, wherein the organic peroxide is dicumyl peroxide. 14. The method for producing a crosslinked molded article according to claim 11, which further comprises an antioxidant added to the composition. 15. The method for producing a crosslinked molded article according to claim 11, which is used for an insulator of a power cable.