JPH0259565B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cross-linked polyolefin insulated power cable, particularly a high voltage cable, in which a cross-linked polyolefin insulator and an external semi-conducting layer are in close contact with each other, and if necessary, an external semi-conducting layer can be easily peeled off. It is something. Conventionally, materials obtained by mixing polyethylene, ethylene/vinyl acetate copolymer, or ethylene/ethyl acrylate copolymer with a conductive filler have often been used as external semiconductive materials for crosslinked polyolefin insulated high voltage cables. However, these materials are in perfect contact with the adjacent cross-linked polyolefin insulation layer, making cable connections,
When carrying out terminal work, there is a problem in that it is very difficult to separate the two layers. As a solution to this problem, power cables have been proposed in which the outer semiconducting layer is made of vinyl chloride grafted ethylene/vinyl acetate copolymer, chlorinated polyethylene, or vinyl acetate/ethylene copolymer with a high vinyl acetate content (for example, Japanese Patent Publication No. 55-76508,
Special Publication No. 54-9714, Special Publication No. 51-53286, Special Publication No. 52-Sho.
41875). However, although these materials for the outer semiconducting layer have improved removability by increasing the content of vinyl acetate or chlorine that imparts polar groups, they have the disadvantage of poor cold resistance. Furthermore, if a crosslinked polyethylene cable with semiconducting layers made of these materials is crosslinked at a high temperature of 200°C or higher to improve productivity, the outer semiconducting layer made of such materials will be heated to 200°C or higher.
Even if there is no problem in terms of physical properties, heating at temperatures above 230° C. causes problems such as poor peelability and discoloration due to corrosion of the shielding copper tape on the external semiconducting layer. These phenomena are further accelerated when water vapor is used as a heating medium, so organic acids generated by thermal decomposition or hydrolysis,
It is presumed that this is due to the influence of decomposition products such as inorganic acids. Recently, not only has excellent peeling workability, etc.
There is a growing need for high performance power cables with external semiconducting layers that can withstand high temperature crosslinking, water vapor crosslinking, and do not cause corrosion of the copper tape. The present inventors have made various efforts to provide a power cable coated with a free strip type outer semiconductive layer that has excellent electrical properties, cold resistance, oil resistance, and extrusion processability, as well as good peelability and copper corrosion resistance. As a result of our investigation, we found that a modified vinyl acetate/ethylene copolymer obtained by polymerizing vinyl acetate/ethylene copolymer with an acrylic monomer under grafting conditions has a semiconducting material with a conductive filler, a crosslinking agent, etc. The inventors have discovered that the above-mentioned problems can be solved by using the composition for the outer semiconductive layer, leading to the present invention. That is, the present invention provides a power cable in which a semiconducting layer is formed on an insulator made of an olefinic polymer extrusion coated on a conductor, in which the semiconducting layer has a solubility coefficient (sp value) of 8.6 to 9.4, a Mooney Viscosity 10~
40. It is made by blending a conductive filler and a crosslinking agent with an acrylic grafted vinyl acetate/ethylene copolymer with a thermal decomposition onset temperature of 315℃ or higher. Crosslinking aids, anti-aging agents, processing aids, etc. are added as necessary. Provided is a crosslinked polyolefin insulated power cable made of a semiconductive composition suitably blended with additives. The composition forming the semiconductive layer of the power cable of the present invention has excellent electrical properties, cold resistance, oil resistance, extrusion processability, etc., and is also excellent in peelability from an insulator and copper corrosion resistance. Acrylic grafted vinyl acetate used in the present invention
Ethylene copolymers (hereinafter referred to as graft copolymers) have a high sp value in order to obtain good releasability from olefinic polymers, such as polyethylene and ethylene-propylene copolymers, which are constituent materials of insulators.
Must be between 8.6 and 9.4. This sp value is 8.6
If it is less than 9.4, the peelability from the insulator will be poor, and if it is more than 9.4, the cold resistance will be poor, which does not meet the object of the present invention. Note that the sp value of polyethylene is 7.9. The Mooney viscosity of the graft copolymer is required to be 10 to 40 from the viewpoint of peelability, copper corrosion resistance, and moldability. If the Mooney viscosity is less than 10, the peelability and copper corrosion resistance will be poor, and if it exceeds 40, the moldability will be poor. In addition, the thermal decomposition temperature of the above graft copolymer is 315
Must be above ℃. If it is less than 315℃
Copper corrosion occurs when cross-linked at high temperatures of 230℃ or higher or with water vapor. The vinyl acetate/ethylene copolymer, which is the main component of the graft copolymer, is manufactured by an emulsion polymerization method and has a vinyl acetate content of 50 to 80% by weight and a Mooney viscosity of 5 to 40.
A copolymer of is preferred. The graft component of the graft copolymer of the present invention is obtained by graft polymerizing an acrylic monomer,
Examples of such acrylic monomers include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and 2-(meth)acrylate.
Examples include ethylhexyl and acrylonitrile. Olefins such as ethylene and propylene, vinyl esters such as vinyl acetate and vinyl propionate, styrenes, etc. may also be used in combination as long as they do not impair the effects of the present invention, and these may be used alone or in combination of two or more. Good too. Vinyl chloride or styrene alone is not preferred from the viewpoint of copper corrosion. The amount of the graft component varies depending on the sp value of the monomer, but is preferably 5 to 50% of the graft copolymer. Further, rubbers or plastics such as chlorinated polyethylene, acrylic rubber, ethylene/propylene rubber, ethylene copolymer, and polystyrene may be used in combination with the graft copolymer to the extent that the effects of the present invention are not impaired. Acetylene black as a conductive filler,
Furnace black, butcher black, etc. are commonly used, and the amount added may be 20 to 100 parts by weight per 100 parts by weight of the graft copolymer. As a crosslinking agent, dicumyl peroxide, 1,
3-bis(t-butylperoxyisopropyl)benzene, 2,5-dimethyl(t-butyl-
Organic peroxides such as (peroxy)hexyne-3 are common. In addition to the addition of a crosslinking agent, the crosslinking means may also be crosslinking by irradiation with high energy radiation such as an electron beam. Further, the olefin polymer used in the insulating layer of the power cable of the present invention is composed of a polymer such as polyethylene or ethylene/propylene copolymer and a crosslinking agent. This insulating layer is usually crosslinked simultaneously with the crosslinking of the semiconducting composition coated thereon. In the high voltage cable of the present invention, for example, as shown in FIG. 1, an inner semiconducting layer 2 of polyethylene containing carbon, an insulator 3, and an outer semiconducting layer 4 are sequentially extruded and coated on a conductor 1. A shielding copper tape 5, a holding tape 6, and a sheath 7 are applied to the top. These semiconducting layers 2 and 4 need to be in sufficient contact with the insulator 3 without any gaps in order to prevent insulation deterioration due to corona discharge. Since the power cable of the present invention uses a specific material as the outer semiconducting layer, the adhesion between the semiconducting layer and the insulating layer is appropriate, and when the cables are connected to each other, the outer semiconducting layer is insulated. It is easy to peel off from the body layer. On the other hand, in power cables that have an outer semiconducting layer made of conventionally used materials, the outer semiconducting layer adheres moderately to the insulator and cannot be peeled off. After scraping, the surface of the insulator must be smoothed using sandpaper, etc., which requires a lot of time and skill. Next, in order to clarify the characteristics of the present invention, examples will be given to specifically explain the present invention. Note that all parts in Examples and Comparative Examples indicate parts by weight. Examples 1 to 3, Comparative Examples 1 to 4 33KV with an external semiconductive layer having the composition shown in Table 1
A cross-linked polyethylene insulated vinyl sheathed power cable (100 mm ³ × 1 core) was molded using an extruder and then prototyped by steam cross-linking. Table 1 shows the physical properties of the cables of Examples and Comparative Examples. The testing methods for various physical properties are shown below. Solubility coefficient (sp value) Encyclopedia of Polymer Science and
The polymer sp value according to Technology (published by Wiley Inter Science) was used. The sp value of the copolymer was calculated assuming additivity depending on the composition ratio. Peelability: According to IPCEA S-66-524, 12.7 mm (1/2 inch) is applied to the outer semiconducting layer of a 30 cm long sample cable.
A cut was made in the middle of the cable, and a peel test was performed at a speed of 750 mm/min using a tensile tester perpendicular to the cable axis. A peel strength of 0.5 to 2.5 kg was considered good. Volume resistivity Volume resistivity is based on IPCEA S-66-524.
Measurements were made using a sample cable with a length of 30 cm. Copper Tape Corrosion Test A 30cm sample cable from which the sheath layer had been removed was cut and placed in a hot air dryer adjusted to 105℃ for 30 days to perform an accelerated test. Visually observed. The evaluation criteria were as follows: compared to Comparative Example 2, a sample that was equal to or better than Comparative Example 2 was considered good, and a sample that was less than or equal to Comparative Example 2 was considered bad. Cold resistance Measurement was performed according to JIS K-6301 using a sheet obtained by press-crosslinking the composition shown in Table 1 at 200° C. for 15 minutes before extrusion into a cable. still,
-15°C or lower was considered acceptable. Extrusion processability Before being extruded into cables, the formulations shown in Table 1 were subjected to a Brabender Plaft graph at 160°C.
The torque was tracked under the conditions of ×60 rpm, and the time until it reached the maximum peak was measured as the vulcanization time. It was considered good if the vulcanization time was 15 minutes or more. Under these conditions, scorch will not occur even under practical extrusion molding conditions. Mooney viscosity Measured according to JIS K-6300. Thermal decomposition onset temperature Measured using a differential thermal balance under the following conditions. Furthermore, 1
The temperature at which the weight was reduced by % was defined as the thermal decomposition start temperature. Atmosphere Nitrogen gas 30ml/min Heating rate 20℃/min Sample amount 10±1mg

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【table】 [Brief explanation of drawings]

FIG. 1 is a partially exploded perspective view of the power cable of the present invention. DESCRIPTION OF SYMBOLS 1... Conductor, 2... Inner semiconducting layer, 3... Insulator, 4... Outer semiconducting layer, 5... Shielding copper tape,
6... Presser tape, 7... Sheath layer.

Claims (1)

[Claims] 1. A power cable in which an external semiconducting layer is formed on an insulating layer made of an olefin polymer, in which the semiconducting layer has a solubility coefficient of 8.6 to 9.4, a Mooney viscosity of 10 to 40, and a thermal decomposition onset temperature of 315°C or higher. A crosslinked polyolefin insulated power cable comprising a semiconductive composition comprising an acrylic grafted vinyl acetate/ethylene copolymer mixed with a conductive filler and a crosslinking agent.