MXPA00004578A - Cable semiconducting shield - Google Patents

Abstract

A cable comprising one or more electrical conductors or communications media or a core of two or more electrical conductors or communications media, each electrical conductor, communications medium, or core being surrounded by a layer comprising:(a) polyethylene;polypropylene;or mixtures thereof;(b) carbon nanotubes;(c) optionally, a conductive carbon black other than carbon nanotubes;and (d) optionally, a copolymer of acrylonitrile and butadiene wherein the acrylonitrile is present in an amount of about 30 to about 60 percent by weight based on the weight of the copolymer or a silicone rubber.

Description

SEMICONDUCTOR COVER FOR CABLES TECHNICAL FIELD This invention relates mainly to an electrical power cable that has a semiconductor cover. BACKGROUND OF THE INVENTION A typical electric power cable generally comprises one or more conductors in a cable core surrounded by several layers of polymeric materials including a first semiconductor cover (conductor or braid cover), an insulating cover, a second semiconductor cover ( insulating cover), a wire or metal tape cover, and a protective cover. The outer semiconductive cover can be attached to the insulation cover or it can be removable and most applications employ removable covers. Additional covers within this construction such as, for example, covers made of materials that do not allow moisture penetration are incorporated frequently. Semiconductor polymeric roofs have been used in the construction of multi-roof electrical power cables for many decades. Generally, they are used to manufacture solid dielectric energy cables especially for voltages greater than 1 kilovolt (kV). These covers are used to provide layers of intermediate conductivity between the high potential conductor and the primary insulation, and between the primary insulation and the neutral potential or ground. The volume resistivity of these semiconductor materials are typically within the range of 10"1 to 108 ohm-cm when measured in a finished electrical power cable construction using the methods described in ICEA S-66-524, section 6.12, or IEC 60502-2 (1997), Annex C. Typical release cover compositions contain a polyolefin such as, for example, ethylene / vinyl acetate copolymer with a high content of vinyl acetate, conductive carbon black, a crosslinking agent of organic peroxide, and other conventional additives such as, for example, nitrile rubber, which function as a release strength reduction aid, processing aids, and antioxidants.These compositions are usually prepared in the form of pellets or pellets. polyolefins of this type are presented in U.S. Patent No. 4,286,023 and in European Patent Application 420,271. Erta is typically introduced into an extruder wherein said composition is co-extruded around an electrical conductor at a temperature lower than the decomposition temperature of the organic peroxide to form a cable. The cable is then exposed to higher temperatures at which the organic peroxide decomposes in order to provide free radicals, which crosslinks the polymer. In order to offer a semiconductor cover, it is necessary to incorporate conductive particles in the composition. These conductive particles have been generally provided by particulate carbon black. Useful smoke blacks can have a surface area of about 50 to about 1000 square meters per gram. The surface area is determined in accordance with ASTM D 4820-93a (Multipoint B.E.T. Nitrogen Adsorption) 10 (Absorption of nitrogen B.E.T. of multiple points). The carbon blacks have been employed in the semiconductor coating composition in the amount of about 20 to about 60% by weight based on the weight of the composition, and are preferably used in an amount of about 25 to about 45%. in weigh. Both standard conductivity black smoke and high conductivity are used, with standard conductivity blacks being preferred. Examples of conductive carbon black are the grades described by ASTM N550, N472, N531, NllO, black Ketjen, and acetylene blacks. The industry is constantly trying to select carbon blacks that, at moderate cost, improve cable resistance and provide more efficient conductivity. 25 - * t < - ** ,, i¿mt * -t? , -tnt? T - i * r r n - ,, - _ ^,. - -. ... .. ~ x ~ a. -% ** * - .üa¿ * ...

PRESENTATION OF THE INVENTION An object of the present invention is therefore to provide a cable having an improved semiconductor sheath in terms of structure and conductivity. Other objects and advantages will be apparent below. In accordance with the invention, said cable has been discovered. The cable comprises one or more electrical conductors or means of communication of a core of two or more electrical conductors or communication means, each electrical conductor, communication medium or core is surrounded by a layer comprising: (a) polyethylene; Polypropylene; or mixtures thereof; (b) carbon nanotubes; (c) optionally, a conductive carbon black other than carbon nanotubes; and (d) optionally, an acrylonitrile-butadiene copolymer wherein the acrylonitrile is present in an amount of about 30 to about 60% by weight based on the weight of the copolymer or a silicone rubber. DESCRIPTION OF THE PREFERRED EMBODIMENT (S) (S) The polyethylene according to this term is an ethylene homopolymer or a copolymer of ethylene and a minor proportion of one or more alpha-olefins having 3 or more. at 12 carbon atoms, and preferably from 4 to 8 carbon atoms, and, optionally, a diene, or a The mixture of such homopolymers and copolymers is described. The mixture may be a mechanical mixture or an in situ mixture of two or more polymers. Examples of the alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene. The polyethylene can also be a copolymer of ethylene and an unsaturated ester such as, for example, vinyl ester, such as, for example, vinyl acetate or an ester of acrylic or methacrylic acid, which are preferably used in semiconductor shells. The polyethylene can be homogeneous or heterogeneous. The homogeneous polyethylenes typically have a polydispersity (Mw / Mn) within a range of about 1.5 to about 3.5 and an essentially uniform comonomer distribution, and are characterized by unique and relatively low DSC melting points. The heterogeneous polyethylenes, on the other hand, have a polydispersity (Mw / Mn) greater than 3.5 and do not have a uniform distribution of comonomers. Mw is defined as the average weight of molecular weight and Mn is defined as the average number of molecular weight. The polyethylenes can have a density in the range of 0.860 to 0.950 per cubic centimeter and preferably have a density within the range of 0.870 about 0.930 grams per cubic centimeter. They may also have a melt index within the range of about 0.1 to about 50 grams per 10. - ^ f-frfit - 1? ftÉWA minutes. Polyethylenes can be produced by low pressure or high pressure processes. They are preferably produced in the gas phase, but can also be produced in the liquid phase in solutions or pastes by conventional techniques. Low pressure processes are typically handled at pressures below 1000 psi (pounds per square inch) while high pressure processes are typically handled at pressures above 15,000 psi. Typical catalyst systems that can be used to prepare these polyethylenes, are magnesium / titanium based catalyst systems, which can be exemplified by the catalyst system described in US Patent no. 4,302,565 (heterogeneous polyethylenes); vanadium-based catalyst systems such as those described in U.S. Patents 4,508,842 (heterogeneous polyethylenes) and 5,332,793; 5,342.907; Y ,410,003 (homogeneous polyethylenes); a chromium-based catalyst system in accordance with that described in U.S. Patent 4,101,445; a metallocene catalyst system such as those described in U.S. Patents 4,937,299, 5,272,236, 5,278,272 and 5,317,036 (homogeneous polyethylenes); or other transition metal catalyst systems. Many of these catalyst systems are often referred to as Ziegler-Natta catalyst systems or Phillips catalyst systems. Catalyst systems, which employ chromium or molybdenum oxides on silica-alumina support, can be included there. Typical processes for preparing the 5 polyethylenes are also described in the aforementioned patents. Typical polyethylene mixtures in situ and catalyst system processes to provide the same are described in U.S. Patents 5,371,145 and 5,045,901. the various polyethylenes can include 10 low density ethylene homopolymers made by high pressure process (HP-LDPEs), linear low density polyethylenes (LLDPEs) very low density polyethylenes (VLDPEs), medium density polyethylenes (MDPEs), polyethylene High density (HDPE) that has a density greater than 15 0.940 grams per cubic centimeters and copolymers of metalóceno with densities less than 0.900 grams per cubic centimeter. The last five polyethylenes are preferably processed by low pressure processes. A conventional high pressure process is described in Introduction to 20 Polymer Chemistry, Stille, Wiley and Sons, New York, 1962 page 149-151. High pressure processes are typically polymerizations initiated by free radicals that are carried out in a tubular reactor or in a stirred autoclave. In the agitated autoclave, the pressure is - • "- -" - *. -J ~, - * ~ * ~ ^ * ¿> it is within the range of about 10,000 to 30,000 psi, and the temperature is within the range of about 175 to about 250 degrees C and in the tubular reactor, the pressure is within the range of about 25,000 to about 45, 00 psi and the temperature is within the range of about 200 to about 350 degrees C. HP-LDPE and ethylene copolymers and unsaturated esters are usually made through these high pressure processes. Mixtures of high pressure polyethylene and resins of metalóceno can also be used, the first component due to its excellent processing capacity and the second component due to its flexibility. As indicated, the copolymers formed of ethylene and Unsaturated esters can be prepared through the conventional high-pressure techniques described above and are preferred for semiconductor casings The unsaturated esters can be alkyl acrylates, alkyl methacrylates, and vinyl carboxylates. having from one to eight carbon atoms and preferably having from 1 to 4 carbon atoms. The carboxylate group can have from 2 to 8 carbon atoms and preferably has from 2 to 5 carbon atoms. In semiconductor covers the portion of the copolymer attributed to the ester comonomer may be within the range of about 20 to ».« «W -,. - -,. ... , ",". . , £ $ á¿íííÁáAJ > k about 55% by weight based on the weight of the copolymer, and preferably lies within the range of about 35 to about 55% by weight. The ester can have from about 4 to about 20 carbon atoms, and preferably has from about 4 to about 7 carbon atoms. Examples of vinyl esters (or carboxylates) are vinyl acetate, vinyl butyrate, vinyl pivalate, vinyl neononanoate, vinyl neodecanoate, and vinyl 2-ethylhexanoate. Vinyl acetate is preferred. Examples of esters of acrylic and methacrylic acid are lauryl methacrylate; myristyl methacrylate; palmityl methacrylate; stearyl methacrylate; 3-methacryloxypropyltrimethoxysilane; 3- methacryloxypropyltriethoxysilane; cyclohexyl methacrylate; n-hexylmethacrylate; isodecyl methacrylate; 2-methoxyethyl methacrylate; tetrahydrofurfuryl methacrylate; octyl methacrylate; 2-phenoxyethyl methacrylate; isobornyl methacrylate; isooctyl ethacrylate; octyl methacrylate; isooctyl methacrylate; oleyl methacrylate; ethyl acrylate; methyl acrylate; t-butyl acrylate; n-butyl acrylate; and 2-ethylhexyl acrylate. Methyl acrylate, ethyl acrylate, and n- or t-butyl acrylate are preferred. The alkyl group may be substituted with an oxyalkyltrialkoxysilane, for example. The polymers can have a density in the range of 0.900 to 0.990 grams per cubic centimeter and preferably have a density in the range 0.920 to 0.970 degrees per cubic centimeter. The copolymers can also have a melt index in the range of about 0.1 to about 100 grams per ten minutes, and preferably have a melt index within the range of about 1 to about 50 grams per ten minutes. A process for the preparation of a copolymer of ethylene and an unsaturated ester is described in U.S. Patent 3,334,081. The VLDPE can be a copolymer of ethylene and one or more alpha olefins having from 3 to 12 carbon atoms and preferably 3 to 8 carbon atoms. The density of VLDPE can be in the range of about 0.870 to about 0.915 grams per cubic centimeter. It can be produced, as for example, in the presence of (i) a catalyst containing chromium and titanium, (ii) a catalyst containing magnesium, titanium, a halogen, and an electron donor; or (iii) a vanadium containing catalyst, an electron donor, an alkyl aluminum halide modifier and a halocarbon promoter. Catalysts and processes for preparing VLDPE are described, respectively, in U.S. Pat. 4,101,445; 4,302,565; and 4,508,842. The VLDPE melt index can be in the range of about 0.1 to about 100 grams per 10 minutes and preferably lies within the range of about 1 to about 50 grams per 10 minutes. The portion of the VLDPE attributed to the comonomer (s), other than ethylene, may be within the range of about 1 to about 49% by weight based on the weight of the copolymer and is preferably within the range from about 15 to about 40% by weight. A third comonomer may be included, for example, another alpha-olefin or a diene such as ethylidene norbornene, butadiene, 1,4-hexadiene, or a dicyclopentadiene. Ethylene / propylene copolymers and ethylene / propylene / diene terpolymers are generally known as EPRS and the terpolymer are generally known as an EPDM. The third comonomer may be present in an amount of about 1 to 15% by weight based on the weight of the copolymer and is preferably present in an amount of about 1 to about 10% by weight. It is preferred that the copolymer contains 2 or 3 comonomers including ethylene. LLDPE may include VLDPE and MDPE, which are also linear, but generally have a density within the range of 0.916 to 0.925 grams per cubic centimeter. It can be a copolymer of ethylene and one or more alpha-olefins having from 3 to 12 carbon atoms, and preferably from 3 to 8 carbon atoms. The melt index may be within the range of about 0.1 to about 100 grams per 10 minutes, and preferably within the range of about 1 to about 50 grams per 10 minutes. The alpha-olefins may be the same as those mentioned above, and the catalysts and processes may also be the same subject to variations necessary to obtain the desired densities and the desired melt indexes. As previously indicated, ethylene homopolymers produced by a conventional high pressure process are included in the definition of polyethylene. The homopolymer preferably has a density in the range of 0.910 to 0.930 grams per cubic centimeter. The homopolymer can also have a melt index within the range of about 1 to about 5 grams per 10 minutes, and preferably has a melt index in the range of about 0.75 to about 3 grams per 10 minutes. The melt index is determined in accordance with ASTM-D-1238, condition E, measured at a temperature of 190 degrees C. Polyethylenes can be prepared to be moisture curable by making the resin hydrolysable, which is achieved by the addition of hydrolysable groups such as -Si (OR) 3, wherein R is a hydrocarbyl radical to the resin structure through copolymerization or grafting. Suitable crosslinking agents are organic peroxides such as dicumyl peroxide; 2,5-dimethyl-2,5-di (t-butylperoxy) hexane; t-butylcumyl peroxide; and 2,5-dimethyl-2, 5di (t-butylperoxy) hexane-3. dicumyl peroxide is preferred. Hydrolyzable groups can be added as for example, by copolymerization of ethylene with an ethylenically unsaturated compound having one or several groups - Si (OR) 3 such as vinyltrimethoxysilane, vinyltriethoxysilane, and gamma-methacryloxypropyltrimethoxysilane, or by grafting these compounds of silane to the resin in the presence of the aforementioned organic peroxides. The hydrolysable resins are then crosslinked by moisture in the presence of a silanol condensation catalyst such as dibutyltin dilaurate., dioctyltin maleate, dioctyltin diacetate, stannous acetate, lead naphthenate and zinc caprylate. Dibutyltin dilaurate is preferred. Examples of hydrolysable copolymers and hydrolysable graft copolymers are ethylene / vinyltrimethoxysilane copolymers, ethylene / gamma-methacryloxypropyltrimethoxy silane copolymer, vinyltrimethoxysilane / ethyl acrylate grafted ethylene copolymer, vinyltrimethoxy / 1-butene grafted linear low density ethylene copolymer and Low density polyethylene grafted with vinyltrimethoxy silane. In applications where a moisture cured insulation is employed, it is desired to provide a removable semiconductive cover cured with moisture to protect the insulation. The cover composition would then be prepared in the same manner as the moisture cured insulation as indicated above. With respect to polypropylene: Homopolymers and copolymers of propylene and one or more other olefins can be used in themselves or in mixtures with polyethylene where the propylene-based copolymer portion is at least about 60% by weight based on weight of the copolymer. The polypropylene can be prepared by conventional processes such as, for example, through the process described in U.S. Pat. 4,414,132. Alpha-olefins In the copolymer are preferably alpha olefins having from 2 or 4 to 12 carbon atoms. Component (b) consists essentially of carbon nanotubes. The carbon nanotubes are made with carbon and are particles of fibrils of smaller size than the miera of high resistance that have a morphological structure and graphical configuration (a tangled three-dimensional network). They have been known as carbon fibrils and graphite fibrils and can be prepared in accordance with that described in U.S. Pat. 5,707,916. A typical carbon nanotube can be described as a tube consisting of eight layers of rolled graphite sheets having a hollow core of 0.005 microns in diameter and an external diameter of 0.01 miera (100 Angstroms). The length of the tube is from 1 to 10 microns. Each of the graphite layers consists of carbon atoms. The tube is not straight 5 but can be acicular or serpentine. They usually appear as several interwoven or tangled fibers; they have a high resistance; and they have a high level of electrical conductivity. Graphite fibrils are graphene carbon nanotubes that grow in steam. They are produced as agglomerates in a manner relatively similar to steel wool cushions, evidently on a much smaller scale. The carbon nanotubes have a black color and their composition is essentially pure carbon with a trace of residual metal oxide catalyst, which means that can be considered clean with a low concentration of metal ions. Due to their porous structure, they have a very low mass density, that is, approximately 0.10 grams per cubic centimeter or 6.24 pounds per cubic foot; The BET surface area is approximately 250 square meters per grams; and the DBP absorption is 450 cubic centimeters per 100 grams. When carbon nanotubes are essentially the only carbon in the semiconductor layer composition, they can be used in amounts of about 1 to about 35 parts by weight per 100 parts by weight of Mt ^ h ^ a £ ^ component (a), and are preferably used in amounts of 2 to about 20 parts by weight. When used together with another conductive carbon black the weight ratio between the carbon nanotubes and the conductive carbon black can be from about 0.1: 1 to about 10: 1, and the total carbon nanotubes and other conductive carbon black it may be in the range of about 5 to about 80 parts by weight per 100 parts by weight of component (a). Component (c) is optional and can be a conventional conductive carbon black used in semiconductor jacket. These blacks of smoke are described above. Taking into account the weight ratios mentioned above and the parts by weight, the conductive carbon black other than carbon nanotubes can be employed in amounts of about 13 to about 100 parts by weight per 100 parts by weight of component (a). The component (d) is also optimal. It may be a copolymer of acrylonitrile and butadiene wherein the acrylonitrile is present in the amount of from about 30 to about 60 weight percent based on the weight of the copolymer, and is preferably present in the amount of about 50 to about 50 weight percent. % in weigh. This copolymer is also known as nitrile rubber or an acrylonitrile / butadiene copolymer rubber. The tüS-i. density can be, for example, 0.98 grams per cubic centimeter and the Mooney viscosity can be (ML 1 + 4) 50. The component (d) can also be a rubber, silicone. The components are commonly used in semiconductor covers. For each 100 parts by weight of component (a) ie polyethylene, polypropylene, or mixtures thereof, the other components may be present in approximately the following values (in parts by weight): range component wide range preferred (b) carbon nanotubes from 1 to 35 from 2 to 20 (c) carbon blacks from 13 to 100 from 15 to 80 conductor (optional (d) nitrile rubber * or from 10 to 60 from 15 to 45 well silicone rubber from 1 to 10 from 3 to 8 (optional) weight ratio between 0.1: 1 to 10: 1 from 0.2: 1 to 3: 1 (b) and (c) * nitrile rubber is a copolymer of acrylonitrile and butadiene. Component (a) can be crosslinked This is achieved in conventional manner with an organic peroxide or through irradiation, with the first form being preferred The amount of organic peroxide that is employed can be within a range of about 0.15 to about 0.8 part by weight of organic peroxide for each 100 parts by weight of component (a), and preferably within the range of about 0.3 to about 0.6 part by weight.The organic peroxide crosslinking temperatures may be within the range of about 30 to about 250 degrees C and of preferential a is within the range of about 140 to about 210 degrees C. Examples of useful organic peroxides for crosslinking 10 are dicumyl peroxide; t-butylcumyl peroxide; lauryl peroxide; benzoyl peroxide; tertiary butyl perbenzoate; di (butyl-tertiary) peroxide; cumene hydroperoxide; 2,5-dimethyl-2,5-di (t-butyl-peroxy) hexin-3; 2,5-dimethyl-2,5- (t-butyl-peroxy) hexane; 15 tertiary butyl hydroperoxide; isopropyl percarbonate; and alpha, alpha 'bis (tertiary butylperoxy) diisopropylbenzene. Another form of crosslinking is by irradiation, typically through an electron beam. The composition in the form of pellets is subjected to an electronic beam at a given dose rate or is exposed to a source of gamma rays of a specific force for a given period of time to provide a specific dose rate of radiation. Conventional additives, which can be introduced into the composition, are exemplified by antioxidants, _ ^ - ^ É? -É¿4 > ÍÍÉ __ & ÉS_1 ^ ~ ^ - ^ - d ^ _ ^ - > Ull k > - ^ -, coupling agents, ultraviolet light absorbers or stabilizers, antistatic agents, pigments, dyes, nucleating agents, reinforcing fillers or polymeric additives, slip agents, plasticizers, processing aids, lubricants, control agents of the viscosity, tackifiers, antiblocking agent, surfactants, extension oils, metal deactivators, voltage stabilizers, flame retardant fillers as well as additives, crosslinking agents, enhancers and catalysts and smoke suppressors. Additives and fillers may be added in amounts that fall within a range of less than about 0.1 to more than about 50% by weight, based on the weight of the composition. Examples of antioxidants are: hindered phenols such as tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane, bis [(beta- (3,5-ditert-butyl-4-hydroxybenzyl) -methylcarboxyethyl) )] sulfide, 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4-4'-thiobis (2-tert-butyl-5-methylphenol), 2,2'-thiobis (4-methyl) -6-tert-butylphenol), and thiodiethylene bis (3, 5-di-tert-butyl-4-hydroxy) hydroxynamate; phosphites and phosphonites such as tris (2,4-di-tert-butylphenyl) phosphite and di-tert-butylphenylphosphonite; thio compounds such as dilaurylthiodipropyanate, dimyristyldiodipropyanate, and distearylthiodipropyanate; several siloxanes; and various amines such as polymerized 2,2, 4-trimethyl-1,2-dihydroquinoline, 4, '-bis (alpha, alpha-dimethylbenzyl) diphenylamine, and alkylated diphenylamine. The antioxidants can be used in amounts of about 0.1 to about 5% by weight based on the total weight of the composition. The compounding can be carried out in a conventional melt / mixer or in a conventional extruder, and these terms are used interchangeably in this specification. In general terms, the conductive coating composition is prepared in a melter / mixer and then pellets are formed by the use of a pelletizing device or an extruder adapted to form pellets. Both the melter / mixer, as its name implies, and the extruder, in fact have melting and mixing zones even though the various sections of each of the devices are known by those skilled in the art through different names . The semiconductor coating composition of the present invention can be prepared in various types of dye melters / mixers and extruders for example a Brabender® mixer, a Banbury® mixer, a roll mill, a Buss® co-mixer, a biaxial screw kneader extruder, as well as single screw or double screw extruders. A description of the conventional extruder can be found in U.S. Patent 4,857,600. In addition to the melting / mixing, the extruder can coat a cable or a cable core. An example of co-extrusion and an extruder for this purpose can be found in U.S. Pat. 5,575,965. A typical extruder has a hopper at its upstream end and a die at its downstream end. The hopper feeds into a barrel containing a screw. At the downstream end, between the end of the screw and the die, there is a screen and a break plate. The screw portion of the extruder is considered divided into 3 sections, the feeding section, the compression section, and the introduction section, and two zones, the rear heat zone and the front heat zone, the sections and the areas located from upstream to downstream. In the alternative, there may be numerous heating zones (more than two) along the axis from current to downstream. If there is more than one barrel, the barrels are connected in series. The relationship between length and diameter of each barrel is within the range of approximately 15: to approximately 30: 1. In wire coating, when the material is crosslinked after exclusion, the crosshead die feeds directly into a heating zone and this zone can be maintained at a temperature within a range of about 120 ° C to about 260 ° C and from * 6s • * ~ **? ? ' preference within the range of about 140 ° C to about 220 ° C. The advantages of the present invention are the following: where the carbon is essentially carbon nanotubes, the interfacial roughness between the insulation and the semiconductor cover is eliminated and the cleaning of the semiconductor cover improves. Where a combination of carbon nanotubes and other conductive carbon black is used, a lower total cost is observed; a cleaner composition; smaller filler loads; higher production speeds; easier coating and formation of end-use compounds; and better mechanical and electrical properties. The basis of the advantages of the combination is that one part by weight of carbon nanotubes provides a conductivity approximately equal to about 7.5 parts by weight of conductive carbon black. In addition there may be a synergistic effect between carbon nanotubes and conductive carbon blacks in terms of electrical properties, particularly conductivity, which changes less over time than systems containing only conductive carbon blacks and it seems that the nanotube mixtures of coal are more stable. There is also a benefit in terms of rheological properties in terms of a lower cutting viscosity, which may require a smaller amount of energy to form compounds; improve the ^^ g ^^ tgtíms ^ processability; and decrease the extrusion temperature which results in better thermal stability. In the mixed system, the volume resistivity is adequate at lower viscosity levels, and shows very little change with temperature which is helpful for a lower dissipation factor. It is expected that carbon nanotubes will present a better disposition than black Ketjen. The carbon nanotubes can also be employed in the insulating layer in amounts of about 0.01 to about 1 part by weight per 100 parts by weight of the component (a), ie, polyethylene, polypropylene, or mixture thereof, and is used for Preference in the insulating layer in amounts of about 0.05 to about 0.3 parts by weight. The advantages of using carbon nanotubes in the insulating layer are the reduction or prevention of arborescence of water and the increase in the resistance to decomposition by dissipating electrical energy or reducing electrical voltage. The term "surrounded" when applied to a substrate surrounded by an insulating composition, jacket material, semiconductor cover, or other cable layer is considered to include extrusion around the substrate; the substrate coating; or the wrap around the substrate as known to those skilled in the art. The substrate may include, for example, a core including a conductor or a set of conductors, or several layers of underlying cables in accordance with the above. The conductors can be electrical, such as copper or a means of communication, such as fiber optic made of fiberglass. All molecular weights mentioned in this specification are average molecular weight weights unless otherwise indicated. The patents mentioned in this specification are incorporated herein by reference. The invention is illustrated through the following examples: Examples 1 to 4 Suitable products are prepared for a semiconductor jacket and electrical power cables in various proportions between the conductive carbon black and carbon nanotubes. The viscosity and electrical properties of these compositions are then measured. Example 1 is a material that is known in the art to be useful for creating semiconductor sheath of electric power cables. This material is made up of 60% by weight based on the weight of the ethylene / ethyl acrylate composition which is a copolymer of ethylene and ethyl acrylate having a content of 18% by weight of ethylene acrylate and a melt index of 20 grams per 10 minutes. Example 1 also contains 38% by weight of conductive carbon black commercially available, Denka Granules which is an acetylene black having a surface area of 60 square meters per gram in accordance with that determined according to ASTM D 4820-93 (Multipoint B.E.T. Nitrogen Adsorption) (nitrogen absorption B.E.T. of multiple points). The polymerized 2, 2, 4-trimethyl-1,2-dihydroquinoline is an added antioxidant at a rate of 1% by weight, and the processing additive, polyethylene glycol, is also added in a proportion of 1% by weight. The composition of Example 1 appears in Table 1. Example 2 is a commercially available mixture of carbon nanotubes with polyethylene. The composition contains 78% by weight, in terms of weight of the composition, of linear low density polyethylene (LLDPE) having a density of 0.92 grams per cubic centimeter and a melt index of 20 grams per 10 minutes. Example 2 also contains 20% by weight of carbon nanotubes. This composition also contains about 1% by weight of antioxidant. The composition of Example 2 is shown in Table 1. Examples 3 and 4 are prepared by mixing the compositions of Examples 1 and 2 with a 30 millimeter laboratory scale double screw mixing device. Example 3 is a mixture of examples 1 and 2 in a ratio of 72:25. Example 4 is a mixture of examples 1 and 2 in a ratio of 50:50. The compositions of examples 3 and 4 are shown in table 1. The apparent cutting viscosities of examples 1 to 4 are measured with a piston-driven capillary rheometer, Góttfert Rheograph® model 2001. The capillary die has a diameter of 5 mm and 20 mm long. The test temperature is 125 ° C, which is similar to the temperature at which commercial cross-linkable semiconductor materials are extruded to form electric power cable covers. The piston speed varies to obtain an apparent cutting speed of 90 to 900 sec "1, ie a representative range for commercial extrusion processes used for semiconductor cover products.The drop in pressure in the capillary die is measured with a single pressure transducer The viscosity is calculated from the 15 die dimensions, the piston cross section, the piston speed, and the pressure drop in the die The results of these measurements are shown in table 1. TABLE 1 Example number 1 2 3 4 20 Composition, weight percentage Ethylene / ethyl acrylate 60.0 0.0 45.0 30.0 LLDPE 0.0 79.0 19.8 39.5 Black smoke 38.0 0.0 28.5 19.0 Carbon nanotubes 0.0 20.0 5.0 10.0 25 Antioxidant 1.0 1.0 1.0 1.0 ,. ***** .. 1 *. ,,, * ^ -w. ». . . .... ** * "* fa" * - ^ -'- *. * .. *.

Process assistant 1.0 0.0 0.8 0.5 Total 100.0 100.0 100.0 100.0 Viscosity, Pascal * seconds at the cutting speed of 90 sec "1 3470 4480 1770 2520 at the cutting speed of 180 sec" 1 2360 2940 1170 1560 at the cutting speed of 360 sec "1 1570 1810 840 1000 at the cutting speed of 900 sec "1 858 875 506 557 The viscosity of Example 1 at a cutting speed of 360 sec "1, 1570 Pascal seconds, is very typical of commercial products useful as a semiconductor cover for electric power cables.This viscosity is dictated by the double requirement of a high molecular weight. to maintain adequate mechanical properties, and a sufficient amount of carbon black to ensure a suitably low volume resistivity The viscosities of example and example 4 are significantly lower than the viscosity of example 1, which is advantageous for the manufacture of cable Isolated Electric Energy EXAMPLES 5 TO 8 Examples 5 to 8 are prepared by the addition of 1.1% by weight, based on the weight of the dicumyl peroxide composition.The materials are then compression molded into tiles with an applied pressure of 170 megapascals, and then the materials are cured for 15 minutes at a temperature of 175 ° C. The tiles mold das are cut into rectangular samples with dimensions of approximately 3 mm in thickness, 25 mm in width and 70 mm in length. A conductive silver paint (DuPont® grade 4817N) is used to apply electrodes in these samples across the width and thickness, separated by a distance of 50 millimeters. After curing, electrical conductors are connected to the silver electrodes with staples. The resistance of the samples is measured with a two-wire resistance meter. The volume resistivity is calculated from the measured resistance, the length between the electrodes (50 mm), and the cross-sectional area of the sample (75 mm2). The resistance to high temperatures is measured by placing the sample inside a laboratory oven. The volume resistivity of Examples 5 to 8 is measured at room temperature, and at 90 and 130 ° C after exposure in the oven for 1 and 15 days. After 15 days, the samples are removed from the oven and allowed to cool for one day at room temperature, at this time the resistance is measured again. The results of these measurements in Examples 5 to 8 are shown in Table 2. The coefficient of variation (ie, standard deviation divided by the average result) for this test method is approximately 10%. The relative difference less than 20% is not significant. TABLE 2 Example number 5 6 7 8 Composition, percentage by weight Example 1 98.9 Example 2 98.9 Example 3 98.9 Example 4 98.9 Dicumyl peroxide 1.1 1.1 1.1 1.1 Total 100.0 100.0 100.0 100.0 Volumetric resistivity (ohm centimeters) at 23 ° C 13 4.0 67 14 at 90 ° C, 1 day exposure 50 4.2 150 19 at 90 ° C, 15 day exposure 47 150 20 at 23 ° C, after 15 days at 90 ° C 13 82 17 at 130 ° C 1 day exposure 260 5.6 220 18 at 130 ° C 15 day exposure 250 200 18 at 23 ° C, after 15 days at 130 ° C 28 110 17 The volume resistivity of the roof Semiconductor in insulated electrical power cable should be the lowest possible. The dielectric loss factor of the cable, when used for transmission of AC electrical power at voltages greater than 5 kV, is related to the volume resistivity of the roof layers. As the resistivity increases, the dissipation factor also rises. It is desirable to minimize the dielectric loss of the electrical power cable and therefore it is desirable to minimize the volume resistivity. Example 5 shows the volume resistivity for materials that are used commercially to cover electric power cables. The volume resistivity of the cross-linked semiconductor material rises with temperature, and remains stable after exposure to high temperatures for an extended period of time. After exposure to 130 ° C and cooling to room temperature, this material shows a significant increase in volume resistivity, which is undesirable. Example 7 exhibits a similar behavior to Example 5 except that there is a smaller relative increase in volumetric resistivity with temperature, and a smaller relative permanent increase in volume resistivity at room temperature after the temperature cycle. Even though the absolute value of the volume resistivity for Example 7 is greater than for Example 5, the stability of the volume resistivity with the temperature and time cycle is very desirable. Example 8 has superior characteristics of volume resistivity compared to example 5. This semiconductor composition has very little dependence on temperature in terms of volume resistivity, and essentially no change in volume resistivity is observed after a temperature cycle. The lower absolute volume resistivity and the improved thermal stability of the volume resistivity of Example 8 is a highly desirable and unexpected behavior, especially taking into account the lowest viscosity measured in this composition in Example 4.

Claims (1)

1. CLAIMS A cable comprising one or several electrical conductors or means of communication or a core of two or more electrical conductors or means of communication, each electrical conductor, means of communication, or core is surrounded by a layer comprising: (a) polyethylene; Polypropylene; or mixtures thereof; (b) carbon nanotubes; (c) optionally, a conductive carbon black other than carbon nanotubes; and (d) optionally an acrylonitrile-butadiene copolymer wherein the acrylonitrile is present in an amount of about 30 to about 60% by weight, based on the weight of the copolymer or a silicone rubber. The cable according to that defined in claim 1, wherein the component (a) is a copolymer of ethylene and an unsaturated ester. The cable according to the one defined in claim 2, wherein the copolymer is selected from the group consisting of vinyl esters, acrylic acid esters, and methacrylic acid esters, wherein the ester is present in the copolymer in an amount of about 20 to about 55% by weight.