JPH0161202B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to semiconducting compositions. More specifically, the present invention relates to a semiconductive composition suitable for use as a material for forming an external semiconductive layer of an insulated power cable on crosslinked polyethylene for high voltage use. Conventionally, in high-voltage cross-linked polyethylene insulated power cables, in order to prevent deterioration due to corona discharge that occurs in the gaps between the center conductor and the cross-linked polyethylene insulation layer and between the cross-linked polyethylene insulation layer and the shielding layer, Inner and outer semiconductive layers are provided on the inner and outer layers of the crosslinked polyethylene insulating layer, respectively. Due to the purpose of its installation, this semiconducting layer is
It is necessary to have good adhesion to the cross-linked polyethylene insulating layer and excellent surface smoothness.For this reason, recently, this layer and the polyethylene insulating layer are extruded at the same time, a so-called multilayer coextrusion method. This is becoming a trend. Among the outer semiconducting layers formed in this way, the outer semiconducting layer is peeled off from the crosslinked polyethylene insulating layer during cable connection and terminal processing, but at this time, the adhesion between both layers is strong. If this makes the peeling operation difficult, or if the peeling is performed forcefully, the crosslinked polyethylene insulating layer may be damaged during the peeling process, which is undesirable. Conventionally, compositions in which conductive carbon black is blended with ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, etc. have been used as materials for forming this type of semiconductive layer. Resin-based compositions generally adhere strongly to crosslinked polyethylene insulating layers, making it extremely difficult to peel the semiconducting layer from the insulating layer and causing significant problems in cable termination operations. there was. In order to avoid these drawbacks, various semiconducting layer forming materials have been proposed. For example, ethylene-vinyl acetate copolymer containing 80% by weight or more of vinyl acetate, ethylene-vinyl acetate copolymer blended with styrene polymer, nitrile rubber, styrene rubber, polyvinyl chloride, chlorinated polyethylene, etc. The use of chlorinated ethylene-vinyl acetate copolymers, or graft copolymerized styrene has been proposed, but these all have poor flexibility and are brittle at low temperatures. Alternatively, they have other problems such as being easy to decompose during the crosslinking process. In particular, recently there has been a tendency to adopt polyethylene dry crosslinking to prevent insulation deterioration due to water trees, etc. However, since this dry crosslinking method requires a high crosslinking temperature, some of the above-mentioned forming materials cannot be crosslinked. Gases such as halogen and cyanogen are generated during the process,
This causes problems such as deterioration of cable performance. The present inventors have developed a semiconducting layer-forming material that has excellent flexibility, low-temperature non-embrittlement, thermal stability, and extrudability, and also allows for easy peeling from a crosslinked polyethylene insulating layer when necessary. As a result of various studies, we have previously discovered that a random copolymer of propylene and an α-olefin with _C4 or more, or a blend of it with an ethylene-vinyl ester copolymer, is extremely effective (especially Hope
No. 57-126029 (see Japanese Unexamined Patent Publication No. 59-16206)). As a result of further investigation, the inventors found that
By blending a mixture of these ethylene-based copolymers, each with a specific melt flow rate, with a specific conductive carbon black, a semiconducting material that can provide optimal peelability, flexibility, and extrudability. It has been found that a composition can be obtained. Accordingly, the present invention relates to a semiconducting composition, which composition has (A) a melt flow rate of about 1 to
Ethylene-vinyl ester copolymer with vinyl ester content of 16 mol% or more at 10 dg/min approximately 60-80
Part by weight and (B) melt flow rate is approximately 10~
(C) Acetylene black is added to an olefinic copolymer mixture consisting of about 40 to 20 parts by weight of a random copolymer of propylene with a propylene content of 50 to 87 mol% and an α-olefin of _C4 or more at 50 dg/min. about 30
~50 parts by weight and (D) Furnace Black approx. 20-40
% by weight of conductive carbon black. As an ethylene-vinyl ester copolymer,
A copolymer obtained by copolymerizing ethylene and a vinyl ester such as vinyl acetate or vinyl propionate by generally known methods, such as radical polymerization under high pressure, solution or emulsion polymerization under medium to normal pressure, etc. Melt flow rate (JIS K-
7210 Table 1, Condition 4) is approximately 1 to 10 dg/min,
Preferably about 2 to 5 dg/min and a vinyl ester content of 16 mol% or more (about 7% by weight for vinyl acetate)
(above) are used. Random copolymers of propylene and α-olefin with C4 or _more include propylene and 1-butene, 4-methyl-1-bentene, 1-hexene,
It is a copolymer with 1-octene or the like or a copolymer containing a small amount of ethylene, and has a melt flow rate (JIS K-7210 Table 1, According to condition 4) is about 10 to 50 dg/min and the propylene content is 50 to 87 mol%. Such copolymers can be prepared by copolymerizing propylene and α-olefin using stereoregular catalysts known per se, preferably those used for the production of isotactic polypropylene. can be manufactured. A preferred copolymer is a propylene-1-butene random copolymer, which is described, for example, in Japanese Patent Publication No. 57
-11322 Publication, JP-A-50-128781, JP-A No. 55
-Described in Publication No. 748, etc. The melting point (Tm) of the propylene-α-olefin random copolymer used is generally about 75 to 140.
within the range of ℃. Propylene content is 87 mol%
If it exceeds this range, the melting point will become higher than this, which will cause problems when compounding conductive carbon black, especially when compounding using a crosslinking agent, or when extruding the composition. On the other hand, when the propylene content is less than 50 mol% and the melting point is lower than this, the tensile strength decreases and the tensile strength value approaches the peel strength value, which not only makes peeling work difficult, but also makes the composition This is not desirable because the product itself becomes sticky. From this point of view, the most preferred copolymer has a propylene content of 60 to 85 mol%. Regarding crystallinity, if it is too high, kneading and blending and extrusion molding become difficult, while if it is too low, the tensile strength of the composition decreases and it becomes sticky, making it unusable. Therefore, it is desirable that the degree of crystallinity expressed as the heat of crystal fusion is within the range of about 10 to 80 Joule/g. The ethylene-vinyl ester copolymer and the propylene-α-olefin random copolymer are about 60 to 80 parts by weight, preferably about 65 to 75 parts by weight of the former, and about 40 to 20 parts by weight, preferably about 20 parts by weight of the latter. It is used in a proportion of 35 to 25 parts by weight. When these ethylene copolymers are used in such a mixing ratio, optimum peelability and extrusion moldability for the crosslinked polyethylene layer are provided. Here, optimal extrusion moldability means that the melting torque during kneading with the Brabender Plastograph is
It means 3.5Kg/m or less, preferably 3.0Kg/m or less. Extrusion molding is possible even if the melting torque value is higher than this, but in that case, it becomes necessary to take measures such as selecting a crosslinking agent with a high decomposition temperature. This olefinic copolymer mixture contains a mixture of
A conductive carbon black consisting of about 30 to 50 parts by weight of acetylene black and about 20 to 40 parts by weight of furnace black is incorporated per 100 parts by weight.
If the proportion of furnace black used is about 20 parts by weight or more, the melt viscosity of the composition will not increase and the extrusion moldability will also be good. On the other hand, if it is used in a proportion of about 40% by weight or more, the appearance of the extrudate will be impaired. The semiconductive composition of the present invention comprising each of these components can be crosslinked and used by appropriately blending a crosslinking agent such as an organic peroxide. As a crosslinking agent, dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexyne-3,1,3-bis(tert-butylperoxyisopropyl)benzene, etc. are used. be able to. Furthermore, in order to increase the strength of molded articles obtained from this composition, it is desirable to incorporate a crosslinking aid into the composition. As the crosslinking aid, well-known polyfunctional monomers such as triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, and polyfunctional polymers such as polybutadiene are used. In addition to this, the composition may contain stabilizers,
Processing aids and the like can be added. Examples of the stabilizer include 4,4-thiobis(6-tert-butylmetacresol), which is well known as a stabilizer for polyolefins, and polymeric phenolic stabilizers such as octadecyl-3-(3,5-di-tert-butyl-4). A combination of -hydroxyphenyl)propionate and an aliphatic carboxylic acid thioester, such as dilauryl dipropionate, is effective, and is particularly preferred since this combination does not adversely affect the degree of crosslinking.
Further, as processing aids, for example, low molecular weight substances such as polyethylene wax, paraffin wax, and carboxylic acid wax are used, and these are effectively used as viscosity regulators and dispersants of the composition. The composition can be prepared by adding these components simultaneously or sequentially using a batch kneader such as a mixing roll, a Banbury mixer, a Brabender blastograph, or a pressure kneader, or a single-screw or twin-screw extruder. This is done by melt blending. In the case of sequential blending, a propylene-α-olefin random copolymer is dry blended with a melt blend of an ethylene-vinyl ester copolymer and a conductive carbon black, and then extruded. , a semiconducting layer of the final composition can also be formed. Although the semiconductive composition according to the present invention is also used for surface heating elements, it is mainly used for forming an external semiconductive layer of high-voltage crosslinked polyethylene insulated power cables, and in this case, it is used for forming internal semiconductive layers. It is processed by co-extrusion molding with the layer composition and the insulation layer composition onto the center conductor, or by co-extrusion molding with the insulation layer composition onto the center conductor via an internal semiconducting layer. Ru. Next, the present invention will be explained with reference to examples. Examples (Composition components) Ethylene-vinyl acetate copolymer:

【table】 Propylene-1-butene copolymer:

[Table] Acetylene black: Electrochemical products Denka black Furnace black: Nippon Steel Chemicals Niteron 10 Dicumyl peroxide: Mitsui Petrochemicals Mitsui
DCP Yoshinox SR: Stabilizer, Yoshitomi Pharmaceutical product Irganox 1076: Stabilizer, Nippon Ciba Geigy product DLTDP: Dilauryl thiodipropionate TAIC: Triallyl isocyanurate (Preparation of composition) The formulation shown in the table below was heated at the surface temperature. 120℃
The mixture was kneaded on a 6-inch mixing roll adjusted to give a semiconductive composition. (Property measurement or evaluation method) Melting torque test: 55 g of the blend sample was kneaded at 130° C. and 30 rpm using a Brabender blastograph, and the melting torque was determined and used as an index of extrudability. Gel fraction: The semiconductive composition was press-molded under the conditions of 170° C., 100 Kg/cm ² and 10 minutes to prepare a sample with a thickness of 2 mm. Add 0.7g of this sample to 100ml of xylene at 110℃.
After soaking for 24 hours, the proportion of undissolved matter was determined. Appearance of extrudate: The semiconductive composition was extruded using a 30 mm diameter extruder,
It was extruded into a tape shape with a width of 25 mm at ℃, and the appearance of the tape was visually judged, and those with a smooth surface were judged as good, and those with rough surfaces were judged as bad. Peeling force: Low density polyethylene (Mitsui Polychemical product Mirason 9, density 0.921g/cm ³ , melt fluorate
1.5dg/min) 100 parts by weight, 2 parts by weight of dicumyl peroxide and 0.2 parts by weight of stabilizer (Yoshinox SR)
Parts by weight were added and kneaded using a 6-inch roll to prepare a composition for an insulating layer. This insulating layer composition and the semiconductive composition were each molded at 120°C using a press molding machine to obtain a press sheet with a thickness of 1 mm, and these sheets were stacked and preheated at 120°C for 3 minutes. After, 30Kg/cm ²
Pressing was carried out for 3 minutes under the pressure of This temporary adhesive sheet was press-molded under conditions of 170° C., 30 kg/cm ² , and 10 minutes to produce a crosslinked bonded sample. This sample was cut to a width of 25 mm, and the insulating layer and semiconducting layer were peeled off at a rate of 100 mm/min using a tensile testing machine, and the force required for this was determined. The results for each of the above properties are shown in Tables 1 and 2 below. As can be seen from this result, the layer formed from the semiconductive composition according to the present invention can be easily peeled from the crosslinked polyethylene insulating layer, and has good extrusion moldability and extrudate appearance, so it is suitable for high voltage applications. It has excellent properties as a material for forming the outer semiconducting layer of cross-linked polyethylene insulated power cables. Considering the results shown in the table in more detail, when using the composition according to the present invention, good extrudability, peelability and appearance of the extrudates are obtained. On the other hand, when an ethylene-vinyl ester copolymer and a propylene-α-olefin copolymer with low melt flow rates are used, the melting torque becomes too large and becomes unsuitable for extrusion molding (Comparative Example 1). ). Furthermore, when one of these copolymers has a high melt flow rate, the melting torque is reduced, but the peeling force becomes too large, which is not preferable (Comparative Examples 2 and 3). Generally, a value of about 8 to 20 N/25 mm width is appropriate for the peeling force; if the peeling force is less than this, the semiconductive layer may naturally peel off from the crosslinked polyethylene layer over time, and conversely, if the peeling force is greater than this, , a large force is required for peeling, and peeling may be difficult. Furthermore, when the vinyl ester content in the ethylene-vinyl ester copolymer is less than 16 mol%, the peeling force increases (Comparative Example 3). Further, when the amount of the propylene-α-olefin copolymer blended is small, the peeling force is too large (Comparative Example 4), and when it is too large, the peeling force is too small (Comparative Example 5). From the relationship with the gel fraction, it is desirable that it is 60% or more, preferably 70% or more,
If it is less than that, the heat resistance and strength of the semiconductive layer will not be satisfied (Comparative Example 5). When only acetylene black is used as the carbon black, the melting torque tends to increase, and the peeling force is not sufficient (Comparative Example 7).
Furthermore, if only the furnace black or the mixing ratio of the furnace black is increased, the appearance of the extrudate becomes rough, which is not preferable (Comparative Example 8).
~9).

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Claims (1)

[Scope of Claims] 1 (A) about 60 to 80 parts by weight of an ethylene-vinyl ester copolymer having a melt flow rate of about 1 to 10 dg/min and a vinyl ester content of 16 mol% or more;
(B) Propylene and C ₄ with a melt flow rate of approximately 10 to 50 dg/min and a propylene content of 50 to 87 mol%
Random copolymer with more than 40 α-olefins
About 30 to 50 parts by weight of (C) acetylene black and
(D) A semiconductive composition containing conductive carbon black comprising about 20 to 40 parts by weight of furnace black. 2. The semiconductive composition according to claim 1, wherein the ethylene-vinyl ester copolymer is an ethylene-vinyl acetate copolymer. 3. The semiconductive composition according to claim 1, wherein the propylene-α-olefin random copolymer is a propylene-1-butene random copolymer. 4. The semiconductive composition according to claim 1, which is used as an outer semiconductive layer forming material of a high voltage crosslinked polyethylene insulated power cable.