JP2813487B2 - Silane cross-linked semiconductive resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a silane-crosslinked semiconductive resin composition, and more particularly, to a method for extruding and coating the resin composition on a conductor to obtain a power cable.
It can form a semiconductive layer having a smooth surface and excellent electrical characteristics.

[0002]

2. Description of the Related Art In a conventional method for producing a low-voltage power cable from a silane-crosslinked polyethylene composition, an insulating layer is formed by adding an organic silane compound and an organic peroxide to a polyolefin resin based on a low-density polyethylene material. Is added to form a silane-grafted polyolefin by a graft reaction, which is coated on a conductor by extrusion molding in the presence of a silanol condensation catalyst, and then exposed to an atmosphere in which water is present for crosslinking. is there.

The above-mentioned silanol condensation catalyst is used either by a method of adding after polysilane silane grafting or a method of mixing simultaneously with silane grafting. The method is generally performed.

However, recently, there has been active development of high-voltage power cables having a two-layer or three-layer structure of an insulating layer made of the silane-crosslinkable polyethylene composition and a silane-crosslinked semiconductive layer made of the silane-crosslinked semiconductive resin composition. Although it is being advanced, a predetermined amount of conductive carbon black is mixed with an ethylene-propylene copolymer or an ethylene-vinyl acetate copolymer as a silane-crosslinked semiconductive resin composition used at this time. A versatile semiconductive material for power cables was used, and an organic silane compound, an organic peroxide and a silanol condensation catalyst were added thereto, respectively, to perform silane crosslinking.

However, when this conventional silane-crosslinked semiconductive resin composition is extruded and coated on a conductor to form a semiconductive layer, projections, bumps, undulations, etc. are remarkably generated on the surface of the semiconductive layer, This has had a great effect on the electrical characteristics of the resulting power cable.

In order to obtain a high-voltage power cable comprising a silane-crosslinked semiconductive layer and a silane-crosslinked insulating layer as described above,
The following methods are used, but all of these methods have problems in workability and characteristics. That is

(1) As shown in FIG. 1, a silane-crosslinked semiconductive resin composition 2 is extruded and coated on a conductor 1, and an inner semiconductive layer is provided. The silane cross-linked polyethylene composition 4 is extrusion-coated to provide an insulating layer, which is wound up by a winder 5 and supplied again.
Further, a method of obtaining a power cable by extrusion-coating a silane-crosslinked semiconductive resin composition 6 on the outside thereof to provide an external semiconductive layer.

(2) As shown in FIG. 2, an extruder for an inner semiconductive layer, an extruder for an insulating layer, and an extruder for an outer semiconductive layer are sequentially arranged side by side on one extrusion line, and silane is formed on a conductor by these extruders. A method for obtaining a power cable by extrusion-coating a crosslinked inner semiconductive layer, a silane crosslinked polyethylene insulating layer, and a silane crosslinked outer semiconductive layer.

(3) As shown in FIG. 3, one extruder is provided with three internal semiconductive layer extruders, a green layer extruder, and an external semiconductive layer extruder. Head), and simultaneously extruding and coating a silane-crosslinked inner semiconductive layer, a silane-crosslinked polyethylene insulating layer and a silane-crosslinked outer semiconductive layer on a conductor at a time to obtain a power cable.

However, in the method (1), since the extrusion step is performed separately, the productivity is significantly reduced and the cost is increased. In the method (2), after providing the silane-crosslinked internal semiconductive layer, the semiconductive layer is not sufficiently cooled and the process immediately proceeds to the step of forming the silane-crosslinked polyethylene insulating layer. If it comes into contact with a die to perform, it will easily damage the surface of the semiconductive layer, which will cause the characteristics of the power cable to deteriorate. In the case of the method (3), as shown in FIG. 4, the mutual interface between the silane-crosslinked polyethylene insulating layer 7 and the silane-crosslinked inner semiconductive layer 8 or the silane-crosslinked outer semiconductive layer (not shown) or the silane-crosslinked Voids 9, 9 ', 9''inside each layer
And thereby degrade the electric characteristics of the power cable.

[0011]

SUMMARY OF THE INVENTION In view of the present situation, the present invention has made intensive studies. As a result, when a silane-crosslinked semiconductive layer is formed by extrusion coating on a conductor, it has excellent smoothness.
Moreover, even when the silane-crosslinked semiconductive layer and the insulating layer are commonly co-extrusion coated on the conductor as described above, it is possible to obtain a power cable having excellent electrical characteristics without generating any voids at the interface between the two. A silane-crosslinked semiconductive resin composition has been developed.

[0012]

The semiconductive resin composition of the present invention comprises 60 to 95% by weight of polyethylene and ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer. , One or more ethylene copolymers selected from the group consisting of ethylene-methyl acrylate copolymer and ethylene-acrylic acid copolymer 5
To 100 parts by weight of a resin component consisting of 100 to 40 parts by weight and 15 to 80 parts by weight of conductive carbon, and 0.5 to 10.0 parts by weight of an organic silane compound and 0.05 to 5 parts by weight of an organic peroxide.
0 part by weight and a silane grafting reaction, wherein 0.01 to 3.0 parts by weight of a silanol condensation catalyst is added to the mixture before the silane grafting reaction or the silane grafting reaction. It is characterized in that it is added to the resin composition after the silane grafting reaction at some time or is kneaded.

In the silane-crosslinked semiconductive resin composition of the present invention, a resin blended with 60 to 95% by weight of polyethylene and 5 to 40% by weight of an ethylene copolymer is used. In the present invention, polyethylene means polyethylene or a known low density having a density of 0.88 to 0.97 g / cc obtained by copolymerization of polyethylene or ethylene with an α-olefin such as butene-1, hexene-1, or octene-1. Indicates high density polyethylene,
In particular, a direct-mirror low-density polyethylene (referred to as L-LDPE) having a density of 0.88 to 0.93 obtained by producing ethylene and an α-olefin by a medium to low pressure method is preferable. The reason for this is that in obtaining a silane crosslinked semiconductive resin calendar, the appearance is made smooth and the mechanical properties (elongation) are excellent.

The ethylene copolymer to be mixed with the above-mentioned polyethylene includes ethylene-vinyl acetate copolymer (hereinafter referred to as EVA), ethylene-propylene copolymer (hereinafter referred to as EPR), ethylene-acrylic acid. Ethylene copolymer selected from the group consisting of an ethyl copolymer copolymer (hereinafter referred to as EEA), an ethylene-acrylic methyl copolymer copolymer (hereinafter referred to as EMA), and an ethylene-acrylic acid copolymer (hereinafter referred to as EAA). The reason for limiting the blending amount in the resin component to 5 to 40% by weight is that when the ethylene copolymer is less than 5% by weight, the obtained silane-crosslinked semiconductive layer This is because the mechanical properties, especially the elongation properties, are reduced. If the content exceeds 40% by weight, protrusions and undulations are liable to be formed on the surface of the silane cross-linked semiconductive layer, and the same as in the common. Extrusion interface electrical characteristics of the power cable bubbles is obtained occurred when performing coating semiconductive layer and the insulating layer is lowered.

The conductive carbon black to be added to the silane-crosslinked semiconductive resin composition of the present invention may be any of commercially available carbon blacks such as acetylene, ketchene, and balkan. On the other hand, the reason for limiting to 15 to 80 parts by weight is that if the amount is less than 15 parts by weight, sufficient conductivity cannot be obtained in providing the silane cross-linked semiconductive layer, and the amount exceeds 80 parts by weight. This is because the mechanical properties, particularly the elongation properties, of the silane-crosslinked conductive layer obtained when blended are reduced.

The organic silane compound in the present invention is a silane compound having an unsaturated bond, such as vinyltrimethoxysilane, vinyltriethoxysilane, etc., which is used when silane-crosslinking a polyolefin resin. is there. The amount was limited to 0.5 to 10.0 parts by weight based on 100 parts by weight of the resin component. The reason for this is that if the amount is less than 0.5 part by weight, the degree of crosslinking in the silane crosslinked semiconductive layer is low, Further, even if it is added in a large amount exceeding 10.0 parts by weight, the improvement in the degree of crosslinking does not appear remarkably, and this is because wasteful expensive silane compounds are wasted. In this case, voids due to gasification of the unreacted silane compound are likely to be generated at the interface between the semiconductive layer and the insulating layer, and the electrical characteristics of the obtained power cable are degraded.

The organic peroxide in the present invention may be any organic peroxide capable of forming a free radical site in a polyolefin resin under silane graft reaction conditions. Examples of the organic peroxide include benzoyl peroxide, dichlorobenzoyl peroxide, and dichlorobenzoyl peroxide. Mil peroxide, etc.

As the silanol condensation catalyst, organotin compounds such as dibutyltin dilaurate and dibutyltin diacetate are preferred, and carboxylate salts such as cobalt naphthenate or organic bases such as ethylamine have a function as silanol condensation catalyst. The compound having is used.

The amounts of the organic peroxide and the silanol condensation catalyst may be small, respectively.
Usually, 0.05 parts of organic peroxide per 100 parts by weight of resin.
To 5.0 parts by weight, silanol condensation catalyst 0.01 to 3.0 parts by weight
Parts by weight are preferred. The silane-crosslinked semiconductive resin composition of the present invention can be obtained by the following two methods.

(A) (i) A polyethylene resin, an ethylene copolymer and conductive carbon black are kneaded in a Banbury, and then pelletized by an extruder to prepare a semiconductive polyethylene resin admixture. (Ii) an organic silane compound in the semiconductive resin mixture,
The organic peroxide is uniformly added and mixed with a tumbler and a Henschel mixer, and then charged into an extruder. (Iii) A silane graft semiconductive pellet is prepared by designating the silane grafting reaction time with the screw rotation speed and the reaction temperature with the extruder set temperature in the extruder.

(Iv) The above semiconductive pellets and a catalyst masterbatch to which a silanol condensation catalyst has been added are mixed with a tumbler, Henschel mixer or the like to obtain the resin composition of the present invention. This method is called a two-stage molding method.

(B) (i) After kneading a polyethylene resin, an ethylene copolymer, a conductive carbon black and a silanol condensation catalyst in a Banbury, pelletize with an extruder to prepare a semiconductive polyethylene resin admixture. I do. (Ii) an organic silane compound in the semiconductive resin mixture,
The organic peroxide is uniformly added and mixed by a tumbler and a Henschel mixer, and then charged into an extruder. (Iii) The silane graft reaction time was determined by the number of screw rotations in the extruder. The resin composition of the present invention is obtained by specifying the reaction temperature at the set temperature of the extruder. This method is called a one-step molding method.

At this time, the mixing of the polyethylene resin, the ethylene copolymer, the conductive carbon black and, if necessary, the silanol condensation catalyst, the addition of an organic silane compound and an organic peroxide, and the silane grafting reaction are carried out. In order to achieve economical performance, a compounding step (A), a silane grafting step (B), and a step of extrusion coating on a conductor (FIG. 5) using a high kneading degree extruder such as a twin-screw extruder. And C) can be performed all at once.
In the figure, 10 is a resin inlet, 11 is carbon,
A silanol condensation catalyst inlet, 12 is a vent hole, 13 is an organic silane compound, an organic peroxide injection tank, and 14 is an extrusion die.

[0024]

The silane-crosslinked semiconductive resin composition of the present invention has two major properties as described below. The reason cannot be clearly explained,
It is assumed as follows. (1) When a semiconductive layer is formed by extrusion coating on a conductor, there are no bumps, protrusions, and undulations in the semiconductive layer. (2) When the conductive layer is formed by common coextrusion coating with the silane cross-linked insulating layer, no void is generated at the interface between the conductive layer and the insulating layer.

That is, a gas component such as an unreacted silane compound and methanol generated during the condensation reaction is placed under high temperature and high pressure in a container of an extruder for silane grafting the silane crosslinked semiconductive resin composition of the present invention. However, when the resin composition is discharged from the extrusion die and reaches a state where the resin composition is extruded and coated on the conductor, the gas component is extruded with the release of the resin pressure and the decrease in the resin temperature. It evaporates sequentially from the surface of the coating layer.

As described above, a silane-crosslinked semiconductive resin composition in which a silane crosslinking agent is blended with a conventional general-purpose semiconductive material for power cables, and a low-density polyethylene resin having a density of 0.90 to 0.94 are prepared as described above. And a common co-extrusion of a semiconductive layer of the above silane crosslinked semiconductive resin composition and an insulating layer of the silane crosslinked polyethylene resin composition on a conductor using a polyethylene resin composition containing the same amount of a silane crosslinker as above. When coated and formed, the slight difference in gas permeability and crystallization rate between the semiconductive layer and the insulating layer causes the insulating property before all the gas components evaporate from the silane-grafted semiconductive layer and the insulating layer. Solidification occurs on the surface of the layer and on the semiconductive layer, and gas components that easily volatilize do not escape and remain at the interface between the semiconductive layer and the insulating layer to form voids. In addition, this phenomenon is a cause of the above-mentioned void generation when the interface state between the semiconductive layer and the insulating layer, that is, the surface of the semiconductive layer is not smooth due to projections, bumps, undulations, and the like.

On the other hand, when a semiconductive layer is formed from the silane-crosslinked semiconductive resin composition of the present invention, the gas permeability is increased, the crystallization rate is made as close as possible to the insulating layer, and the insulating layer is formed. This is to obtain a close surface condition. That is, as the base resin of the resin composition of the present invention, a polyethylene resin which is a polyolefin resin of the same type as the insulating layer is selected, and a small amount of an ethylene copolymer is used to satisfy the required performance as the semiconductive layer. By mixing, the surface of the semiconductive layer can be smoothed by the silane cross-linked semiconductive resin composition, and a common coextrusion coating with the insulating layer is performed, but voids are generated at the interface between the two layers. It was possible to find a silane-crosslinked semiconductive composition that does not need to be used.

[0028]

EXAMPLES [Examples (1) to (7)] The silane-crosslinked semiconductive resin composition of the present invention as shown in Table 1 was extruded on a stranded conductor having a diameter of 5.7 mm by an extruder (D = 45 φL /
D = 28), and a semiconductive layer was provided by extrusion coating to a coating thickness of 1.0 mm under the extrusion conditions shown in Table 2. The obtained cable core was immersed in warm water of 80 ° C. for 24 hours to perform a crosslinking treatment. The appearance, degree of crosslinking and tensile properties of the semiconductive layer thus formed were measured. The results obtained are shown in Table 1.

[0029]

[Table 1]

[0030]

[Table 2]

[Comparative Examples (1) to (6)] A silane-crosslinked semiconductive composition as shown in Table 3 (Comparative Examples 1 to 3 correspond to conventional examples) was applied on a stranded conductor having a diameter of 5.7 mm. Extrusion coating was performed in the same manner as in Example (1) to obtain a comparative example cable core made of a conventional silane-crosslinked semiconductive composition. The characteristics of the thus obtained comparative example cable core were measured in the same manner as in Example (1). The results are as shown in Table 3.

[0032]

[Table 3]

The abbreviations for the polyolefin resins in Tables 1 and 3 are the following resins. (1) L-LDPE is a direct mirror low density polyethylene (2) EAA is an ethylene acrylic acid copolymer (3) LDPE is a low density polyethylene (4) EPR is an ethylene propylene copolymer (5) HDPE is a high density polyethylene (6) EVA is an ethylene-vinyl acetate copolymer. (7) EEA is an ethylene-ethyl acrylate copolymer. (8) EMA is an ethylene-methyl acrylate copolymer. The gel fraction in the table is 12
It is the result of extracting with xylene at 0 degreeC for 24 hours. Irganox 1010 in the table is an anti-aging agent.

Examples (8) to (14) Table 6 was obtained by a two-layer extrusion molding method on a stranded conductor having a diameter of 5.7 mm.
The same silane-crosslinked semiconductive resin composition as used in Examples (1) to (7) shown in (1) was extrusion-coated with the same extruder as in Example (1) to provide a semiconductive layer and common co-extrusion. The silane cross-linked polyethylene composition shown in Table 4 was extruded on the outside thereof with an extruder (D: 60φ, L / D = 30) to a coating thickness of 3.5 mm under the extrusion conditions shown in Table 5 to insulate. The layers were provided to produce a power cable core. The interface state (void generation state) between the semiconductive layer and the insulating layer was observed for the manufactured cable core. The results are shown in Table 6.

[0035]

[Table 4]

[0036]

[Table 5]

[0037]

[Table 6]

[Comparative Examples (8) to (13)] Comparative Examples (1) to (13) shown in Table 7 on a stranded conductor having a diameter of 5.7 mm.
Except that the same silane-crosslinked semiconductive resin composition as used in (6) was used, a semiconductive layer and an insulating layer were provided on a conductor in the same manner as in Example (8), and a comparative example power cable core was prepared. I got it. With respect to the thus manufactured comparative example power cable core, the presence or absence of voids was measured for the interface state between the semiconductive layer and the insulating layer. As a result, many voids were observed as shown in FIG. 4 and Table 7.

[0039]

[Table 7]

Table 8 shows the overall evaluation results determined from the characteristics of the cable cores according to Examples (1) to (14) and the cable cores according to Comparative Examples (1) to (13).

[0041]

[Table 8]

[0042]

Industrial Applicability The silane-crosslinked semiconductive resin composition of the present invention is used to produce a power cable in which the semiconductive layer is extruded on a conductor and the semiconductive layer or the semiconductive layer and the insulating layer are co-extrusion coated. When applied to a high-voltage power cable, it is possible to obtain a high-voltage power cable having excellent electrical characteristics without causing a surface to be smooth and generating a void at the interface between the semiconductive layer and the insulating layer.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of a process line of a silane cross-linked power cable.

FIG. 2 is a schematic explanatory view showing another example of the process line of the silane cross-linked power cable.

FIG. 3 is a schematic explanatory view showing another example of the process line of the silane cross-linked power cable.

FIG. 4 is a side sectional view showing an example of a power cable core manufactured using a silane-crosslinked semiconductive resin composition.

FIG. 5 is a schematic explanatory view showing a continuous production process of a silane crosslinked resin composition.

[Explanation of symbols]

1: extruder for conductor, 2: extruder for silane-crosslinked resin composition for internal semiconductive layer, 4: extruder for insulating layer, 6: extruder for external semiconductive layer,
3, 5: winding machine, 7: insulating layer, 8: internal semiconductive layer, 9,
9 ', 9'': void.

Continuation of the front page (51) Int.Cl. ⁶ identification code FI H01B1 / 24 H01B1 / 24Z (58) Investigated field (Int.Cl. ⁶ , DB name) C08L 23/00-23/36 H01B 1 /twenty four

Claims (1)

(57) [Claims] An ethylene-vinyl acetate copolymer, an ethylene-propylene copolymer, an ethylene-ethyl acrylate copolymer, and an ethylene-vinyl acetate copolymer.
100 parts by weight of a resin component comprising 5 to 40% by weight of one or more ethylene copolymers selected from the group consisting of methyl acrylate copolymer and ethylene-acrylic acid copolymer, and conductive carbon 15 to 80 To 0.5 parts by weight of an organic silane compound and 0.05 parts by weight of an organic peroxide.
To 5.0 parts by weight and a silane grafting reaction, wherein 0.01 to 3.0 parts by weight of a silanol condensation catalyst is added to the mixture before the silane grafting reaction, or A silane-crosslinked semiconductive resin composition which is added to and kneaded with the resin composition during the silane graft reaction or after the silane graft reaction.