JPS6325622B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to materials suitable for improved outer semiconducting layers of polyethylene insulated cables, particularly for use under high voltages. Specifically, the present invention provides a semiconducting material suitable for obtaining an insulated cable in which an insulating layer and an outer semiconducting layer are in good adhesion, and the outer semiconducting layer can be peeled off very easily if necessary. This invention relates to a resin composition. In high-voltage cables, semiconducting layers are formed on the inner and outer layers of the insulating layer for the purpose of alleviating the electric field, but these semiconducting layers are in close contact with the insulating layer without any gaps to prevent corona discharge. It is necessary that it is glued. However, excessive contact between the outer semiconducting layer and the insulating layer is not preferable. In other words, for example, when connecting cables to each other, it is extremely difficult to peel off the external semiconducting layer from the insulating layer, and it takes a long time to peel off, the insulating layer is easily damaged, and the terminal processing requires a lot of time and effort. Or skill is required. Conventionally, the best semiconducting layer of this type is one that uses ethylene-vinyl ester copolymer as the base resin. Because it has an extremely strong adhesion property, it has almost no peelability from the insulating layer, making cable terminal processing extremely difficult. Therefore, the insulating layer and the external semiconductive layer are in good contact with each other, and the external semiconductive layer can be peeled off very easily if necessary, and the peeled pieces can be easily cut during the peeling operation. It would be of great benefit if a semiconductive resin composition could be obtained that has excellent mechanical strength to avoid such problems. Prior Art The following materials are known as semiconducting layer materials. (1) Ethylene-unsaturated ester copolymers such as ethylene-vinyl acetate copolymers (high vinyl acetate content, e.g. exceeding 35% by weight; hereinafter referred to as high-vinyl acetate EVA) and ethylene-ethyl acrylate copolymers Added carbon black to the combination. (2) Single or mixtures of halogen-containing resins such as chlorinated polyethylene, chlorosulfonated polyethylene, EVA-vinyl chloride graft copolymer, chlorinated polyethylene-vinyl chloride graft copolymer, polyvinyl chloride, chloroprene, etc. Carbon black is added to a blend of this and olefin polymer. (3) Carbon black is added to a blend of polystyrene, styrene copolymer, butadiene-acrylonitrile copolymer, polyester, etc. and olefin polymer. However, as described above, (1) is unsuitable due to poor peelability from the insulating layer. (2) was proposed for the purpose of improving the peelability from the insulating layer, and although its effect is recognized, it has the following problems. In other words, in the case of polyethylene cross-linked insulated cables, the cross-linking system tends to be changed from wet cross-linking to dry cross-linking in order to suppress the dielectric breakdown phenomenon caused by water trees, etc. Generally, the crosslinking temperature becomes high, so the material for the outer semiconducting layer is required to have greater thermal stability during processing.
EVA and the like generate corrosive gases through thermal decomposition at high temperatures, which promotes corrosion of equipment and corrodes cable shielding copper tape, deteriorating cable performance. Similar to (2), (3) is intended to improve the peelability from the insulating layer, but both have poor compatibility with the olefin polymer, and it is necessary to increase the blending amount to improve the peelability. Therefore, the outer semiconducting layer becomes quite fragile, and the peeling pieces break during the peeling process, which poses a practical problem. [] Summary of the Invention The present invention aims to solve the above-mentioned problems, and uses a blend of a specific modified ethylene polymer and an acrylonitrile-butadiene copolymer as a base resin in which carbon black is blended. The aim is to achieve this purpose by using Therefore, the semiconductive resin composition according to the present invention is
It is characterized by containing each of the following components (A) to (C). (A) (a) 40 to 95% by weight of ethylene polymer particles; (b) 60 to 60% modified vinyl monomer selected from the group consisting of an aromatic vinyl monomer and a mixture of an aromatic vinyl monomer and an α,β-unsaturated nitrile. 5% by weight
and (c) 0.01 to 5 parts by weight of a radical polymerization initiator having a decomposition temperature of 50 to 130°C to obtain a half-life of 10 hours per 100 parts by weight of the modified vinyl monomer.
Parts by weight of an aqueous suspension containing 80% by weight or more of the modified vinyl monomer are impregnated into the ethylene polymer particles under conditions where decomposition of the radical polymerization initiator does not substantially occur. 97 to 40 parts by weight of a modified ethylene polymer obtained by raising the temperature of this aqueous suspension to 50 to 130°C to complete the polymerization of the modified vinyl monomer; (B) acrylonitrile-butadiene copolymer; Combine 3~
60 parts by weight, (C) Carbon black 100% of the above (A) and (B) components
3 to 150 parts by weight. Effects The resin composition according to the present invention has the following effects. 1 The resulting semiconducting layer adheres well to the insulating layer. 2. The semiconducting layer can be easily peeled off from the insulating layer if necessary. 3. Has excellent mechanical strength (flexibility and elongation properties). 4. Carbon black has good dispersibility. 5. Excellent processability and extrusion processability when blending with carbon black. 6. Excellent thermal stability and little generation of corrosive thermal decomposition gas. The present inventors have already discovered a semiconductive resin composition consisting of this modified ethylene polymer, a reinforcing rubber (especially preferred is ethylene-propylene rubber or styrene-conjugated diolefin block copolymer rubber), and carbon black. I proposed something (Special application 1984-
139492), the present invention has discovered that by using an acrylonitrile-butadiene copolymer as such a reinforcing and modified rubber, it has sufficient electrical conductivity and further improves the balance of releasability/material strength with cross-linked polyethylene. It was made by As mentioned above, unmodified ethylene polymers and acrylonitrile-butadiene copolymers generally have poor compatibility, and blends of the two do not exhibit sufficient material strength because the dispersion state of each is poor. This tendency is especially strong when the latter has a high nitrile content. However, in the combination of modified ethylene polymer and acrylonitrile-butadiene copolymer, the compatibility is significantly improved, and because the acrylonitrile-butadiene copolymer is homogeneously dispersed in the modified ethylene polymer, this rubber has improved material strength. Fully demonstrate the purpose of reinforcement. [] Detailed Description of the Invention The semiconductive resin composition according to the present invention contains a modified ethylene polymer (A), an acrylonitrile-butadiene copolymer (B), and carbon black (C). 1 Modified ethylene polymer (A) A modified ethylene polymer is obtained by subjecting an ethylene polymer and a specific modified vinyl monomer to graft polymerization conditions. (1) Ethylene polymer Ethylene polymer refers to an aliphatic mono- or diolefin polymer. One group of such polymers is a homopolymer of aliphatic mono- or diolefins, and the other group is a copolymer of these olefins with each other or with a copolymerizable monomer. Preferred specific examples include high-pressure, medium-pressure, or low-pressure polyethylene, ethylene-propylene copolymer, ethylene-propylene-butene-1 random copolymer, ethylene-(meth)acrylic acid copolymer ( Meta)
"acrylic acid" shall mean both acrylic acid and methacrylic acid), ethylene-(meth)acrylic acid ester copolymer,
Representative examples include unsaturated carboxylic acid-modified polyethylene. Among them, high-pressure polyethylene and ethylene-vinyl acetate copolymer (EVA content of about 35 to 1% by weight)
is more preferable. (2) Modified vinyl monomer Modified vinyl monomer consists of (1) aromatic vinyl monomer and (2) aromatic vinyl monomer and α,
selected from the group consisting of mixtures of β-unsaturated nitriles. The aromatic vinyl monomer is represented by the following formula. In the formula, R ¹ is a hydrogen atom or a carbon number of 1 to 4
alkyl group, R ² to ^{R 6} are each a hydrogen atom,
Indicates a chlorine atom or an alkyl group having 1 to 4 carbon atoms. Specifically, for example, styrene, methylstyrene (vinyltoluene), chlorostyrene,
Examples include α-methylstyrene. Typical α,β-unsaturated nitriles include acrylonitrile and methacrylonitrile. In the case of a mixture of both monomers, the usage ratio is:
(1):(2)=about 95:5 to 60:40 (weight). (3) Modified graft polymerization treatment The modification of the ethylene polymer with the modified vinyl monomer in the present invention is as follows. That is, (1) 40 to 95% by weight of ethylene polymer particles (generally 1 to 7 mm diameter, preferably 2 to 5 mm diameter) and (2) 60% by weight of modified vinyl monomer.
~5% by weight and (3) a radical polymerization initiator (preferably dissolved in the modified vinyl monomer) with a decomposition temperature of 50 to 130°C to obtain a half-life of 10 hours; monomer
0.01 to 5.0 parts by weight per 100 parts by weight) of a suspending agent used in aqueous suspension polymerization, such as polyvinyl alcohol, polyvinylpyrrolidone,
In the presence of methylcellulose or other poorly soluble inorganic substances such as calcium phosphate, magnesium oxide, etc., in an aqueous medium at any concentration that facilitates stirring of the system (generally ethylene polymers and modified vinyl per 100 parts by weight of water). 5 to 100 parts by weight of monomer) and stir to disperse. This aqueous suspension is then heated within a range that does not substantially cause decomposition of the polymerization initiator used to impregnate the modified vinyl monomer into the ethylene polymer particles. In impregnation treatment, a higher heating temperature is better from the point of view of promoting impregnation, but from the viewpoint of preventing the modified vinyl monomer before impregnation from polymerizing alone due to premature decomposition of the polymerization initiator, the heating temperature is higher. The lower the better. Preferred temperatures range from room temperature to
The temperature is around 50℃. Under such temperature conditions, at least 80% by weight, preferably at least 90% by weight, of the modified vinyl monomer is impregnated or deposited into the ethylene polymer particles, i.e. until the free modified vinyl monomer droplets reach 20% by weight. %, preferably less than 10% by weight, the aqueous suspension is preferably left under stirring for about 1 to 5 hours. Unimpregnated modified vinyl monomer
If the amount is 20% by weight or more, independent vinyl polymer particles may precipitate, and the vinyl polymer in the ethylene polymer particles will be non-uniformly dispersed. In addition, in the next polymerization step, the free modified vinyl monomer is impregnated into the ethylene polymer particles or attached to the surface of the ethylene polymer particles and polymerized. In fact, it is not recognized that it exists independently of particles. Modified ethylene polymer particles are obtained by further heating the aqueous suspension prepared in this way to a high temperature to complete polymerization of the modified vinyl monomer. At this time, the heating temperature should be such that the polymerization initiator used is sufficiently decomposed. However, it is necessary that the temperature does not exceed 130℃. If the temperature exceeds 130°C, gel-like substances tend to form in the resulting modified ethylene polymer, so a temperature of 50 to 130°C is generally appropriate. As the polymerization initiator, an oil-soluble one is used since this graft polymerization process follows the technique of aqueous suspension polymerization. This polymerization initiator is
The decomposition temperature is ~50 to obtain a half-life of 10 hours.
Although the temperature is 130°C, it is particularly preferably within the range of 55 to 110°C. This decomposition temperature is 50
If the temperature is less than 0.degree. C., polymerization of the modified vinyl monomer will occur during the impregnation process, and a homogeneous product will not be obtained. If the temperature exceeds 130°C, a gel will form in the product, which is unfavorable in terms of physical properties. This is thought to be because an intermolecular crosslinking reaction of the ethylene polymer occurs as a result of excessively raising the temperature. Specific examples of initiators include octanoyl peroxide,
Benzoyl peroxide, cyclohexanone peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-dibenzoyl peroxyhexane, di-tert-butyl-
Di-peroxyphthalate, lauroyl peroxide, tert-butyl peroxypivalate, 3,5,5-trimethylhexanoyl peroxide, and the like. (4) Modified ethylene polymer The vinyl monomer-modified ethylene polymer thus obtained is a mixture of three components: ethylene polymer, modified vinyl monomer-grafted ethylene polymer, and modified vinyl polymer. Ori,
The presence of the graft component improves the compatibility between the ethylene polymer and the modified vinyl polymer, so that the modified vinyl polymer is homogeneously and finely dispersed in the ethylene polymer matrix. Therefore, even if the number of modified vinyl monomer units is increased, its homogeneity is not impaired, and the molded product exhibits excellent appearance and physical properties. A simple blend of ethylene polymer and modified vinyl polymer has poor compatibility between the two, resulting in poor dispersion.
It is not practical because the appearance deteriorates due to the occurrence of delamination during the molding process and the physical properties of the material (especially elongation properties and impact resistance) are significantly reduced. 2 Acrylonitrile-butadiene copolymer (B) As the acrylonitrile-butadiene copolymer which is the other essential component of the resin component of the composition of the present invention, copolymers with various copolymerization ratios of acrylonitrile and butadiene may be used. Can be done. Specifically, when the amount of bound acrylonitrile is within the range of 15 to 50% by weight, the Mooney viscosity is
20 to 140 are used. The "acrylonitrile-butadiene copolymer" referred to in the present invention is
Modified acrylonitrile-butadiene, such as carboxylated nitrile rubber made by copolymerizing a small amount of acrylic acid or methacrylic acid in addition to these two essential monomers, and vinylpyridine terpolymer made by copolymerizing 2-methyl-5-vinylpyridine. It also includes copolymers. These acrylonitrile-butadiene copolymers are mixed with the modified ethylene polymer.
3 to 60 parts by weight, preferably 5 to 100 parts by weight
Used in a proportion of 30 parts by weight. Acrylonitrile-butadiene copolymer is
When there are many modified vinyl monomer units in the modified ethylene polymer (generally about 40 parts by weight or more),
In other words, when the releasability is to be further strengthened, or when the carbon black filling amount is large (generally
20 parts by weight or more), i.e. higher conductivity levels, are particularly useful for reinforcing the material strength of the composition, which may otherwise be poor. 3 Carbon Black Carbon blacks used in the composition of the present invention include furnace black, acetylene black, channel black, butthorn black, and the like. The mixing ratio thereof is in the range of 3 to 150 parts by weight, preferably 3 to 80 parts by weight, based on a total of 100 parts by weight of the modified ethylene polymer and the acrylonitrile-butadiene copolymer. 4 Auxiliary Components Depending on the required level of peelability from the insulating layer, the composition of the present invention may be mixed with an ethylene polymer to reduce the amount of modified vinyl monomer units in the modified ethylene polymer, or Conversely, polymers of modified vinyl monomers (eg polystyrene) can be mixed. Even in these mixed systems, the dispersibility of the resin layer is extremely good. Furthermore, processing aids such as crosslinking agents, stabilizers, antioxidants, plasticizers, lubricants, etc. can be added to the composition of the present invention in appropriate amounts depending on the conditions of use. 5 Preparation of Composition The composition of the present invention can be easily obtained using a continuous extruder such as a single-screw extruder or a twin-screw extruder in addition to a batch-type kneader such as a Banbury, Roll, or Prabender Plastograph. be able to. The order of blending is not particularly limited, and in addition to mixing and kneading each component at once, it is also possible to first mix the components with a modified ethylene polymer or acrylonitrile-butadiene copolymer in a batch or continuous extruder. It is also possible to knead carbon black and then knead the kneaded product with the modified ethylene polymer or/and the acrylonitrile-butadiene copolymer. 6 Experimental Examples Reference examples, working examples, and comparative examples are shown below. Physical property measurement method (1) The peel test method used in this experimental example is as follows. Sheet of semiconductive resin composition and density
0.920g/cc, MI1.0 low density polyethylene
For insulation, 100 parts by weight is mixed with 2 parts by weight of a crosslinking agent (dicumyl peroxide) and 0.3 parts by weight of an anti-aging agent (4,4'-butylidene-bis(3-methyl-6-tert-butylphenol)). In order to make polyethylene sheets, each sheet with a thickness of 1 mm, a length of 200 mm, and a width of 200 mm was obtained using a compression molding machine under molding conditions of 120° C., 100 kg/cm ² , and 9 minutes. Next, the above-mentioned two sheets were overlapped and heated and pressed at 180° C. and 50 kg/cm ² for 30 minutes using a compression molding machine to produce a laminated sheet. From the obtained laminated sheet, a width of 0.5 inch,
A test piece with a length of 150 mm was punched out and a peel test was performed using a tensile tester. The peel test was conducted at 23℃ and 65%RH.
A sheet of semiconductive layered resin composition is applied to a sheet of insulating polyethylene at a speed of 50 mm/min.
The film was peeled off at a 90° angle, and the resistance force at that time was defined as the peel strength (Kg/0.5 inch). (2) Volume resistivity was measured using a Wheatstone bridge type measuring device manufactured by Yokogawa Electric Corporation in accordance with the Japan Rubber Association standard "Volume resistivity test method for conductive rubber and plastics" 2301-1969. . (3) Tensile strength and elongation were measured according to JIS K-7113. (4) Molding processability is 3 mm in diameter using a 40 mm diameter extruder.
A circular strand was extrusion molded, and the surface condition of the molded product (surface irregularities and presence or absence of delamination) was measured. Reference example 1 20 liters of pure water in an autoclave with a capacity of 50 liters
Kg and tricalcium phosphate as suspending agent 600
g and sodium dodecylbenzenesulfonate 0.6
g to form an aqueous medium, and EVA (density
0.95, MI 15.0, vinyl acetate content 28% by weight) 6 kg of 3 mm diameter particles were suspended by stirring. Separately, add 8 g of benzoyl peroxide and 4 g of tert-butyl peroxybenzoate as a polymerization initiator to 6 kg of styrene.
(100 parts by weight for 100 parts by weight of EVA),
This was put into the suspension system, the temperature inside the autoclave was raised to 45°C, and the temperature was maintained for 3 hours to impregnate the styrene containing the polymerization initiator into the EVA particles. This aqueous suspension was heated to 80℃ and maintained at that temperature for 5 minutes.
The polymerization was completed by holding at 125° C. for 5 hours. It was confirmed that the obtained modified resin particles contained 100 parts by weight of a styrene polymer component based on 100 parts by weight of EVA. Reference Example 2 In Reference Example 1, EVA with a density of 0.943, MI of 12.0, and vinyl acetate content of 20% by weight was used as the ethylene polymer to be modified, and 75 parts by weight of styrene was added to 100 parts by weight of the EVA instead of parts by weight of styrene. and 25 parts by weight of acrylonitrile to complete the polymerization, resulting in styrene-acrylonitrile modification.
EVA (the styrene/acrylonitrile copolymer component was contained in an amount of 100 parts by weight based on 100 parts by weight of EVA) was obtained. Example 1 (1) Modified EVA of Reference Example 1...80 parts by weight [Styrene polymer component content 100 parts by weight] (2) Acrylonitrile-butadiene copolymer...20 parts by weight [JSR NBR N230S (bonded nitrile Amount = 35% by weight)] 100 parts by weight (3) Carbon black [Denka Acetylene Black] ...40 parts by weight (4) Anti-aging agent [Tetrakis [Methylene (3,5
-di-tert-butyl-4-hydroxy-hydrocinnamate) methane] ...0.1 part by weight Example 2 (1) Modified EVA of Reference Example 1 ...48 parts by weight (2) EVA used in Reference Example 1 [Vinyl acetate content 28%] ...32 parts by weight (3) Acrylonitrile-butadiene copolymer ...20 parts by weight [same as Example 1] 100 parts by weight (4) Carbon black [same as Example 1]
40 parts by weight (5) Anti-aging agent [Same as Example 1]
...0.1 part by weight Example 3 (1) Modified EVA of Reference Example 1 ...97 and 40 parts by weight (2) Acrylonitrile-butadiene copolymer...3 and 60 parts by weight [Same as Example 1] 100 parts by weight Part (3) Carbon black [Same as Example 1]
40 parts by weight (4) Anti-aging agent [same as Example 1] 0.1 part by weight Comparative Example 1 (1) EVA used in Reference Example 1...80 parts by weight (2) Acrylonitrile-butadiene copolymer...20 Parts by weight [same as Example 1] 100 parts by weight (3) Carbon black [Same as Example 1]
...40 parts by weight (4) Anti-aging agent [Same as Example 1]
...0.1 part by weight Comparative Example 2 (1) EVA used in Reference Example 1 ...40 parts by weight (2) GP-polystyrene ...40 parts by weight [Dialex HF-77 manufactured by Mitsubishi Monsanto] (3) Acrylonitrile-butadiene copolymer...20 parts by weight [same as Example 1] 100 parts by weight (4) Carbon black [same as Example 1]
...40 parts by weight (5) Anti-aging agent [Same as Example 1]
...0.1 part by weight Example 4 (1) Modified EVA of Reference Example 2 ...90 and 80 parts by weight (2) Acrylonitrile-butadiene copolymer...10 and 20 parts by weight [JSR NBR N220S (bonded nitrile amount = 40% by weight] 100 parts by weight (3) Carbon black [Same as Example 1]
...40 parts by weight (4) Anti-aging agent [Same as Example 1]
...0.1 parts by weight Example 5 (1) Modified EVA of Reference Example 2 ...80 parts by weight (2) Acrylonitrile-butadiene copolymer ...20 parts by weight [same as Example 4] 100 parts by weight (3 ) Carbon black [Same as Example 1]
...40 parts by weight (4) Crosslinking agent [dicumyl peroxide]
...1 part by weight (5) Anti-aging agent [Same as Example 1]
...0.5 parts by weight Comparative Example 3 (1) EVA used in Reference Example 2 ...40 parts by weight (2) Acrylonitrile-styrene copolymer ...40 parts by weight ["Sanrex SAN-C" manufactured by Mitsubishi Monsanto] (3) Acrylonitrile-butadiene copolymer...20 parts by weight [same as Example 4] 100 parts by weight (4) Carbon black [same as Example 1]
...40 parts by weight (5) Anti-aging agent [Same as Example 1]
...0.1 parts by weight Comparative Example 4 (1) Modified EVA of Reference Example 2 ...100 parts by weight (2) Carbon black [same as Example 1]
...40 parts by weight (3) Anti-aging agent [Same as Example 1]
...0.1 part by weight Example 6 The Mooney viscosity of the composition of Example 1 at 150°C was measured. The viscosity test was conducted in accordance with JIS K-6300 "Physical test method for uncross-cured rubber" using an L-shaped rotor and pre-kneading 1.
The viscosity (ML ₁₊₄ ) after 4 minutes was determined. Comparative Example 5 In the composition of Example 1, 150
The Mooney viscosity in °C was measured. Measurement Results of Physical Properties The results of the peel test etc. performed on the compositions obtained in the above Examples and Comparative Examples are shown in the table below. In the table, NBR refers to acrylonitrile-butadiene copolymer.

【table】

【table】

[Table] *2 Surface deterioration of extruded product due to delamination.

[Table] Analysis of results (1) As is clear from Tables 1 and 2, the composition of the present invention has excellent peelability from the insulating polyethylene layer, material strength, moldability, and electrical conductivity. It has well-balanced properties that fully satisfy the requirements as a conductive layer material. In addition, especially when EVA with a low vinyl acetate content is used as the base resin, it can provide an industrially effective outer semiconducting layer because of its excellent thermal stability during molding. (2) In Table 1, blending of acrylonitrile-butadiene copolymer with modified EVA has a very large effect on improving the toughness (tensile strength and elongation) of carbon-filled systems, and also has peel strength. is also slightly improved. Moreover, it does not inhibit the excellent conductivity and moldability of this copolymer. Comparative examples of blend systems of EVA and acrylonitrile-butadiene copolymer, and blend systems of EVA, polystyrene, and acrylonitrile-butadiene copolymer had poor blend compatibility, and as shown in Table 1, material strength and molding process were affected by poor dispersion. The properties of the product deteriorate, making it unsuitable for practical use. (3) In Table 2, the blend of acrylonitrile-butadiene copolymer into modified EVA is shown in Table 2.
Similar to 1, it greatly improves the toughness of carbon black-filled modified EVA. This is modified EVA
This is thought to be due to the good compatibility between the vinyl monomer units in the copolymer and the copolymer. Also,
When a crosslinking agent is used in combination with the composition of the present invention, the quoted strength and elongation are greatly improved, and the material has sufficient strength as an outer semiconductive layer. (4) Furthermore, compared to other rubber filling systems, the composition of the present invention exhibits a small increase in viscosity as shown in Table 3, probably because it has good dispersibility, which is advantageous in terms of processing during cable extrusion. .

Claims (1)

[Scope of Claims] 1. A semiconductive resin composition characterized by containing each of the following components (A) to (C). (A) (a) 40 to 95% by weight of ethylene polymer particles; (b) 60 to 60% modified vinyl monomer selected from the group consisting of an aromatic vinyl monomer and a mixture of an aromatic vinyl monomer and an α,β-unsaturated nitrile. 5% by weight
and (c) 0.01 to 5 parts by weight of a radical polymerization initiator having a decomposition temperature of 50 to 130°C to obtain a half-life of 10 hours per 100 parts by weight of the modified vinyl monomer.
Parts by weight of an aqueous suspension containing 80% by weight or more of the modified vinyl monomer are impregnated into the ethylene polymer particles under conditions where decomposition of the radical polymerization initiator does not substantially occur. 97 to 40 parts by weight of a modified ethylene polymer obtained by raising the temperature of this aqueous suspension to 50 to 130°C to complete the polymerization of the modified vinyl monomer; (B) acrylonitrile-butadiene copolymer; Combine 3~
60 parts by weight, (C) Carbon black 100% of the above (A) and (B) components
3 to 150 parts by weight.